WO2025205163A1 - Adhesive sheet - Google Patents

Abstract

The present invention provides an adhesive sheet having an adhesive layer that does not substantially contain ethyl acetate or toluene, and has good cuttability. The adhesive sheet has an adhesive layer that does not substantially contain ethyl acetate or toluene. The breaking strain of the adhesive layer is in the range of 210% to 1500% and tanδ at 80°C is in the range of 0.046 to 0.300.

Description

adhesive sheet

The present invention relates to a pressure-sensitive adhesive sheet.
This application claims priority based on Japanese Patent Application No. 2024-051945, filed on March 27, 2024, the entire contents of which are incorporated herein by reference.

Generally, adhesives (also known as pressure-sensitive adhesives; the same applies hereinafter) are soft solids (viscoelastic bodies) at temperatures near room temperature, and have the property of easily adhering to adherends when pressure is applied. Taking advantage of these properties, adhesives are widely used in the form of adhesive sheets for purposes such as joining parts and protecting surfaces. For example, adhesive sheets having an adhesive layer on one surface of a substrate are preferably used as surface protection sheets to prevent damage (scratches, stains, corrosion, etc.) to the surface of various items when they are processed or transported. For such applications, for example, acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, urethane adhesives, etc. are used. For example, Patent Documents 1 and 2 disclose prior art that disclose polyester adhesives.

Japanese Patent Application Publication No. 2011-236346 Japanese Patent Application Publication No. 2013-216875

In recent years, there has been a demand to reduce the amount of organic solvents used in light of environmental considerations and the need to eliminate the reliance on petroleum resources. This has led to the development of so-called solvent-free adhesives that do not use organic solvents added for dilution purposes (see, for example, Patent Document 1). Solvent-free adhesives generally have a high solids concentration and tend to have poor fluidity, so they must be designed to have good coatability, pot life, and curing properties, which places limitations on adhesive design compared to adhesives that use organic solvents. As a result, solvent-free adhesives can sometimes encounter problems that are not apparent with organic solvent-based adhesives. For example, solvent-free adhesives are prone to peeling off (glue residue) when cut to a specified shape or size, and tend to have poorer cutting properties compared to organic solvent-based adhesives.

The present invention was created in light of the above circumstances, and aims to provide an adhesive sheet that is substantially free of ethyl acetate and toluene and has an adhesive layer with good cutting properties.

This specification provides a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer that is substantially free of ethyl acetate and toluene. The pressure-sensitive adhesive layer has a breaking strain in the range of 210% to 1500% and a tan δ at 80°C in the range of 0.046 to 0.300. A pressure-sensitive adhesive layer that satisfies the above characteristics is substantially free of ethyl acetate and toluene, which are typical examples of organic solvents, and can achieve good cutting properties.

In some embodiments, the pressure-sensitive adhesive layer has a gel fraction of 70% or more. A pressure-sensitive adhesive layer having the above gel fraction has good cohesion, is less likely to leave adhesive residue, and also tends to have good releasability from the adherend. A pressure-sensitive adhesive sheet having the above pressure-sensitive adhesive layer can be preferably used, for example, as a pressure-sensitive adhesive sheet with good removability. The technology disclosed herein can preferably achieve both the above-mentioned high gel fraction and the effect of improving cuttability.

In some preferred embodiments, the adhesive layer has a breaking strain in the range of 400% to 1500% and a tan δ at 80°C in the range of 0.096 to 0.300. An adhesive layer that satisfies the above characteristics can achieve better cuttability.

In some embodiments, the pressure-sensitive adhesive layer contains at least one selected from polyesters and polyols. The technology disclosed herein is preferably implemented in a configuration including a pressure-sensitive adhesive layer containing at least one selected from polyesters and polyols.

In some embodiments, the pressure-sensitive adhesive layer preferably further contains an isocyanate-based crosslinking agent. The technology disclosed herein is preferably implemented in a configuration in which the pressure-sensitive adhesive layer contains an isocyanate-based crosslinking agent.

In some embodiments, a configuration containing a bifunctional isocyanate crosslinking agent is preferably used as the isocyanate crosslinking agent. In other embodiments, a configuration containing a bifunctional isocyanate crosslinking agent and a trifunctional isocyanate crosslinking agent may be used as the isocyanate crosslinking agent. A pressure-sensitive adhesive layer containing a bifunctional isocyanate crosslinking agent is more likely to achieve good cuttability.

In some embodiments, the pressure-sensitive adhesive layer preferably contains a polyol having a number average molecular weight in the range of 200 to 20,000. The technology disclosed herein is preferably implemented in embodiments using a polyol in the above molecular weight range.

The adhesive sheet disclosed herein is suitable, for example, as a surface protection film. The adhesive sheet disclosed herein reduces contamination such as glue residue when cut to fit the size and shape of the object to be protected, and after such a good cutting process, it can be preferably used for surface protection applications. The surface protection film is attached to the object to be protected, and after achieving its protective purpose, it is typically peeled off (removed) from the object to be protected. Adhesives used for such surface protection applications are typically required to have properties such as good wettability when attached to the object to be protected, easy peeling when peeled off from the object to be protected after achieving the surface protection purpose of the object to be protected (easy peelability), and low contamination, such as leaving no adhesive residue on the surface of the adherend after the adhesive sheet is peeled off (low contamination). The technology disclosed herein makes it possible to achieve an adhesive layer with good cuttability while satisfying the required properties for surface protection applications.

1 is a cross-sectional view schematically illustrating the configuration of a pressure-sensitive adhesive sheet according to one embodiment.

Preferred embodiments of the present invention will be described below. Matters necessary for carrying out the present invention other than those specifically mentioned in this specification can be understood by those skilled in the art based on the teachings on carrying out the invention described in this specification and the common general technical knowledge at the time of filing. The present invention can be carried out based on the contents disclosed in this specification and the common general technical knowledge in the relevant field.
In the following drawings, components and parts that perform the same function may be denoted by the same reference numerals, and duplicated explanations may be omitted or simplified. Furthermore, the embodiments shown in the drawings are schematic in order to clearly explain the present invention, and do not necessarily accurately represent the size or scale of the PSA sheet of the present invention that is actually provided as a product.

<Adhesive sheet configuration example>
The PSA sheet disclosed herein is configured to include a PSA layer. The PSA sheet may be a substrate-attached PSA sheet having the PSA layer on one or both sides of a non-releasable substrate (support substrate), or may be a substrate-less PSA sheet (i.e., a PSA sheet without a non-releasable substrate) having the PSA layer supported on a release liner.

The structure of an adhesive sheet according to one embodiment is shown schematically in Figure 1. This adhesive sheet 1 is configured as a substrate-attached single-sided adhesive sheet comprising a sheet-like support substrate (e.g., a resin film) 10 having a first side 10A and a second side 10B, and an adhesive layer 21 provided on the first side 10A. The adhesive layer 21 is fixedly provided on the first side 10A of the support substrate 10, i.e., without any intention to separate the adhesive layer 21 from the support substrate 10. While not particularly limited, such a single-sided adhesive sheet 1 is suitable as a surface protection film in which its adhesive surface is attached to the surface of an adherend (a target to be protected, for example, an optical component such as a polarizing plate). Before use, the adhesive sheet 1 can be a component of a release-liner-attached adhesive sheet 100, in which the surface (adhesive surface) 21A of the adhesive layer 21 is protected by a release liner 31, at least the side facing the adhesive layer 21 serving as a release surface, as shown in Figure 1. Alternatively, the release liner 31 may be omitted, and a support substrate 10 may be used in which the second surface 10B serves as the release surface, and the adhesive sheet 1 may be rolled up so that the adhesive surface 21A abuts against the second surface (back surface) 10B of the support substrate 10 and is protected (roll form).

The release liner (also referred to as a release film) mentioned above can be a release liner having a release layer on the surface of a liner substrate such as a resin film or paper, or a release liner made of a low-adhesion material such as a polyolefin resin (e.g., polyethylene or polypropylene) or a fluorine-based resin. The release layer can be formed by surface treating the liner substrate with a release treating agent such as a silicone-based, long-chain alkyl-based, fluorine-based, or molybdenum sulfide. As with the substrate of the PSA sheet described below, a liner substrate made from a biological material or a recycled material (recycled film, etc.) can be preferably used.

The concept of adhesive sheet here can include things called adhesive tape, adhesive labels, adhesive films, etc. The adhesive sheet may be in roll form or in sheet form. It may also be an adhesive sheet processed into various shapes.

<Adhesive layer>
<Characteristics>
(breaking strain)
One of the characteristics of the adhesive layer disclosed herein is that the breaking strain is within the range of 210% to 1500%. An adhesive layer that satisfies this breaking strain is likely to achieve good cuttability. As shown in the examples described below, the breaking strain is highly correlated with the evaluation results of cuttability. The reason for this is thought to be that adhesives with a breaking strain within the range of 210% to 1500% have good extensibility and moderate cohesive strength, making them less likely to become brittle and peel when cut. The technology disclosed herein is not limited to the above considerations. Furthermore, adhesives with a breaking strain of 1500% or less tend to have moderate cohesive strength and good releasability from the adherend. The breaking strain can be measured using the method described in the examples described below.

In some preferred embodiments, the breaking strain is 250% or more, more preferably 300% or more, even more preferably 350% or more, and particularly preferably 400% or more. It may be 500% or more, 600% or more, 700% or more, or 800% or more. The larger the breaking strain, the easier it is to achieve better cuttability. In some embodiments, the breaking strain is, for example, 1200% or less, preferably 1000% or less, more preferably 900% or less, or may be 800% or less, 700% or less, 600% or less, 500% or less, 400% or less, or 300% or less. The smaller the breaking strain, the better the cohesive strength, making it easier to achieve light peelability. By setting the breaking strain low within the specified range, it is possible to achieve a better balance between cuttability and cohesive strength.

(tan δ at 80°C)
One of the characteristics of the pressure-sensitive adhesive layer disclosed herein is that its tan δ at 80°C is in the range of 0.046 to 0.300. A pressure-sensitive adhesive layer satisfying the above characteristics is likely to achieve good cutting properties. As shown in the examples described below, tan δ at 80°C is highly correlated with the results of cutting properties evaluation. Furthermore, tan δ at 80°C is more highly correlated with the results of cutting properties evaluation than tan δ at other temperature ranges. This is thought to be because tan δ at 80°C effectively indicates the state of crosslinking in the bulk of the pressure-sensitive adhesive layer. Furthermore, pressure-sensitive adhesives having a tan δ at 80°C in the range of 0.046 to 0.300 are thought to have good followability to blade movement during cutting and are less likely to peel. The technology disclosed herein is not limited to the above considerations. Furthermore, pressure-sensitive adhesives having a tan δ of 0.300 or less at 80°C tend to have adequate cohesive strength and good releasability from adherends. The tan δ at 80°C can be measured using the method described in the examples described below.

In some preferred embodiments, the tan δ at 80°C is 0.050 or more, more preferably 0.055 or more, even more preferably 0.070 or more, even more preferably 0.085 or more, even more preferably 0.090 or more, and particularly preferably 0.096 or more. It may be 0.100 or more, 0.150 or more, or 0.200 or more. The higher the tan δ at 80°C, the more likely it is that excellent cutting properties will be achieved. In some embodiments, the tan δ at 80°C is, for example, 0.250 or less, preferably 0.200 or less, or 0.150 or less, 0.120 or less, or 0.100 or less. The smaller the tan δ at 80°C, the more likely it is that cohesive strength will be improved, making it easier to achieve light releasability. By setting the tan δ at 80°C low within the specified range, it is possible to achieve a better balance between cutting properties and cohesive strength.

The technology disclosed herein makes it possible to form an adhesive having a breaking strain and tan δ at 80°C within the above ranges using a composition that is substantially free of ethyl acetate and toluene. More specifically, the breaking strain and tan δ at 80°C can be adjusted by the design of the polymer contained in the adhesive layer (materials used, weight-average molecular weight, glass transition temperature (Tg), number of functional groups (e.g., number of hydroxyl groups), etc.), the crosslinking structure (e.g., type of crosslinking agent, number and amount of crosslinkable functional groups), and the use, type, amount, and number of functional groups (e.g., number of hydroxyl groups in the polyol, etc.) of additives (e.g., polyol, plasticizer, etc.).

(Gel fraction)
Although not particularly limited, in some embodiments, the gel fraction of the PSA layer may be approximately 60% or more, or may be 65% or more. In some preferred embodiments, the gel fraction is 70% or more. According to the technology disclosed herein, a high gel fraction of 70% or more and an improved cuttability can be advantageously achieved at the same time. A PSA layer having a gel fraction of 70% or more has good cohesion, is less likely to leave adhesive residue, and tends to have good releasability from an adherend. Therefore, a PSA sheet having a PSA layer with the above gel fraction can be preferably used, for example, as a PSA sheet with good removability. Furthermore, a PSA layer having a gel fraction of 70% or more is less likely to be deformed or damaged by dents or other external forces during production, and is less likely to experience changes in appearance, making it suitable for surface protection applications. From the viewpoints of easy releasability and low contamination, the gel fraction is more preferably 75% or more, even more preferably 80% or more, and may be 85% or more, or even 90% or more. The gel fraction may be 100%, but from the viewpoint of adhesion to an adherend, it may be, for example, less than 99% or less than 95%. The gel fraction is the gel fraction measured for the pressure-sensitive adhesive layer after formation (specifically, after drying and aging), and is specifically determined by the measurement method described in the Examples below.

(Glass transition temperature (Tg))
Although not particularly limited, the pressure-sensitive adhesive layer is preferably designed to have a low glass transition temperature (Tg). In embodiments in which organic solvents such as ethyl acetate and toluene are not substantially used, the viscosity of the pressure-sensitive adhesive composition can be reduced by using a material with a low Tg (e.g., polyester), thereby improving coatability. In some embodiments, the Tg of the pressure-sensitive adhesive layer may be 0°C or lower, -15°C or lower, or -25°C or lower. In some preferred embodiments, from the viewpoint of coatability of the pressure-sensitive adhesive composition, the Tg of the pressure-sensitive adhesive layer may be -30°C or lower, -45°C or lower, -50°C or lower, or -55°C or lower. Furthermore, from the viewpoint of cohesive strength, in some embodiments, the Tg of the pressure-sensitive adhesive layer is typically approximately -75°C or higher, or may be approximately -65°C or higher. The Tg of the pressure-sensitive adhesive layer can be determined by the measurement method described in the Examples below.

<Thickness>
The thickness of the pressure-sensitive adhesive layer is not particularly limited and can be appropriately selected depending on the purpose. The thickness of the pressure-sensitive adhesive layer is, for example, approximately 1 μm or more, and may be approximately 10 μm or more. In some embodiments, from the viewpoint of adhesion to the adherend, the thickness of the pressure-sensitive adhesive layer may be 30 μm or more, 50 μm or more, for example, 70 μm or more. Furthermore, the thickness of the pressure-sensitive adhesive layer may be approximately 1000 μm or less, approximately 500 μm or less, or approximately 300 μm or less. In some embodiments, the thickness of the pressure-sensitive adhesive layer is, for example, approximately 150 μm or less, and may be 100 μm or less (e.g., less than 100 μm). A pressure-sensitive adhesive layer with a limited thickness facilitates the realization of a lighter, smaller, and thinner pressure-sensitive adhesive sheet. When the pressure-sensitive adhesive sheet disclosed herein is a double-sided pressure-sensitive adhesive sheet having pressure-sensitive adhesive layers on both sides of a substrate, the thicknesses of the pressure-sensitive adhesive layers may be the same or different.

<Amount of organic solvent>
The PSA layer disclosed herein is substantially free of ethyl acetate and toluene. The PSA layer disclosed herein is substantially free of ethyl acetate and toluene, which are used for dilution purposes to adjust the solid content concentration, viscosity, etc., and is coated with a good pot life and cured well after coating to form, thereby achieving both reduced organic solvent usage and high productivity. Here, "the PSA layer is substantially free of ethyl acetate and toluene" means that the amounts of ethyl acetate and toluene are less than 5 μg and less than 1 μg, respectively, per gram of PSA layer. This means that ethyl acetate and toluene are not intentionally added to the PSA layer, but does not exclude small amounts of ethyl acetate and toluene that are unavoidably present in the raw materials for the PSA layer or that are unintentionally mixed in during the preparation of the PSA composition or the production of the PSA sheet, remaining in the PSA layer.

Furthermore, in some embodiments, the PSA layer is substantially free of methyl ethyl ketone (MEK). Here, the technical meaning of "the PSA layer is substantially free of MEK" is basically the same as that explained for ethyl acetate and toluene, and specifically means that the amount of MEK is less than 1 μg per 1 g of the PSA layer.

The adhesive layer may also contain a compound having an acetylacetone skeleton (e.g., acetylacetone). While not particularly limited, in some embodiments, the adhesive layer may contain approximately 100 μg or less of the compound having an acetylacetone skeleton per gram of adhesive layer. In some preferred embodiments, the amount of the compound having an acetylacetone skeleton in the adhesive layer may be 50 μg or less, 45 μg or less, 40 μg or less, 35 μg or less, or 30 μg or less per gram of adhesive layer.

In this specification, the amounts of ethyl acetate, toluene, MEK and compounds having an acetylacetone skeleton in the PSA layer can be quantified by GC/MS. More specifically, they can be quantified by the method described in the quantification of residual volatile components below.
(Quantitative determination of residual volatile components)
A 10 ^cm2 sample (adhesive sheet) is collected and sealed in a 20 mL headspace vial. The vial containing the sample is heated at 150°C for 30 minutes using a headspace sampler (HSS: Shimadzu Corporation, HS-20), and 1 mL of the heated gas is injected into a GC/MS (Shimadzu Corporation, "QP-2020" instrument) for measurement. Using a calibration curve calculated for one appropriate volatile component (acetylacetone in the examples described below), the detected amount [μg/g] of each volatile component per 1 g of adhesive layer is determined from the peak area obtained for the residual volatile components (toluene, ethyl acetate, MEK, and acetylacetone) (in the examples described below, this is the acetylacetone equivalent value), and this is taken as the content per 1 g of adhesive layer. If the adhesive sheet includes a substrate, the weight of the substrate for the same area is subtracted to determine the amount of residual volatile components per 1 g of adhesive layer. It should be noted that it has been confirmed that the amount of residual volatile components is negligible for the substrate used in the examples described below. The specific measurement conditions for GC/MS are as shown in Table 1.

<Type of adhesive layer>
The adhesive constituting the adhesive layer can be one or more adhesives selected from various adhesives, such as acrylic adhesives, polyester adhesives, urethane adhesives, polyether adhesives, rubber adhesives, silicone adhesives, polyamide adhesives, and fluorine-based adhesives, and can be an adhesive that is substantially free of ethyl acetate and toluene and can satisfy the above-mentioned breaking strain characteristics and tan δ characteristics at 80°C. Specifically, for example, based on the following explanation, an adhesive composition that is substantially free of ethyl acetate and toluene and satisfies the above-mentioned breaking strain characteristics and tan δ characteristics at 80°C can be adopted. The composition of the adhesive layer, except for the volatile components, is as described below for the adhesive composition. Therefore, the details described for the adhesive composition can be applied to the adhesive layer, except for the details related to the volatile components.

<Polymer>
The pressure-sensitive adhesive composition for forming the pressure-sensitive adhesive layer may contain one or more of various polymers that can be used in the field of pressure-sensitive adhesives, such as acrylic polymers, polyester polymers (polyesters), urethane polymers, polyether polymers, rubber polymers (natural rubber, synthetic rubber, mixtures thereof, etc.), silicone polymers, polyamide polymers, and fluorine-based polymers. The above polymers are also referred to as base polymers, meaning structural polymers that form the pressure-sensitive adhesive. From the viewpoints of adhesive performance, cost, etc., pressure-sensitive adhesives containing polymers selected from acrylic polymers, polyester polymers, urethane polymers, polyether polymers, and rubber polymers are preferred, and among these, acrylic polymers, polyester polymers, urethane polymers, and polyether polymers are more preferred, and polyester polymers, urethane polymers, and polyether polymers are even more preferred.

The following description will primarily focus on adhesive compositions containing polyester and/or polyether, but it is not intended to limit the adhesive compositions and adhesive layers disclosed herein to those containing polyester and/or polyether.

<Polyester>
In some preferred embodiments, the PSA composition contains a polyester. In this specification, polyester refers to a polymer obtained by polycondensation of a dicarboxylic acid and a diol. PSA containing a polyester can achieve adhesive properties, properties required for surface protection applications such as wettability, easy peelability, and low contamination, and properties required for optical applications such as transparency, at levels equal to or better than those of other types of PSA. In addition, polyester has the advantage that it can be synthesized primarily from plant-derived materials, thereby reducing dependence on fossil resource-based materials, making it preferable.

(dicarboxylic acid)
The dicarboxylic acid used in the synthesis of the polyester may be any of aliphatic dicarboxylic acids, dimer acids, alicyclic dicarboxylic acids, unsaturated dicarboxylic acids, and aromatic dicarboxylic acids. Specific examples of the dicarboxylic acid include aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, dimethylglutaric acid, adipic acid, trimethyladipic acid, pimelic acid, suberic acid, azelaic acid, dodecanedioic acid, sebacic acid, thiodipropionic acid, and diglycolic acid; dimer acids obtained by dimerizing fatty acids such as oleic acid and erucic acid; 1,2-cyclopentanedicarboxylic acid, 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, and 4-methyl-1,2 Examples of suitable dicarboxylic acids include alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, norbornanedicarboxylic acid, and adamantanedicarboxylic acid; unsaturated dicarboxylic acids such as maleic acid, maleic anhydride, fumaric acid, itaconic acid, citraconic acid, and dodecenyl succinic anhydride; aromatic dicarboxylic acids such as isophthalic acid, terephthalic acid, orthophthalic acid, benzylmalonic acid, 2,2'-biphenyldicarboxylic acid, 4,4'-biphenyldicarboxylic acid, 4,4'-dicarboxydiphenyl ether, and naphthalenedicarboxylic acid; and derivatives thereof. Derivatives of the dicarboxylic acids include derivatives such as carboxylic acid salts, carboxylic acid anhydrides, carboxylic acid halides, and carboxylic acid esters. By appropriately selecting and using one or more of these dicarboxylic acids, a polyester exhibiting the desired adhesive properties can be obtained.

In some preferred embodiments, dimer acid is used as the dicarboxylic acid. Polyesters containing dimer acid units tend to have a low glass transition temperature and improved hydrolysis resistance. Furthermore, because dimer acid is less volatile, it can be preferably used in synthesis, for example, under high-temperature and highly reduced-pressure conditions. Dimer acids can be used alone or in combination. In embodiments where dimer acid is used as the dicarboxylic acid, the weight ratio of the dimer acid to the total amount (total weight) of dicarboxylic acids used in the synthesis of the polyester is not particularly limited, and is suitably approximately 1% by weight or more, and may be approximately 10% by weight or more, or approximately 30% by weight or more. In some preferred embodiments, the weight ratio of the dimer acid to the total amount of dicarboxylic acids is approximately 50% by weight or more, approximately 70% by weight or more, approximately 80% by weight or more, approximately 90% by weight or more, or approximately 95% by weight or more (e.g., 95-100% by weight). By using a specified amount or more of dimer acid, it is possible to design a polyester (for example, but not limited to, a polyester having a Mw within a specified range and a low Tg) based on the properties of the dimer acid.

In some preferred embodiments, it is preferable to use dicarboxylic acids derived from living organisms, in order to reduce dependence on fossil resource-based materials. Suitable examples of such dicarboxylic acids include sebacic acid derived from plants (e.g., castor oil), and dimer acids derived from fatty acids such as oleic acid and erucic acid. Biologically derived dicarboxylic acids can be used alone or in combination of two or more.

The molecular weight of the dicarboxylic acid used is not particularly limited, and is suitably 100 or more, and may be 150 or more, 250 or more, 350 or more, 450 or more, or 500 or more (for example, 550 or more). On the other hand, from the standpoint of monomer availability and ease of synthesis, the molecular weight of the dicarboxylic acid is suitably approximately 1000 or less, and may be, for example, 800 or less, 700 or less, or 600 or less. Suitable examples of dicarboxylic acids having the above molecular weights include dimer acids.

In this specification, the molecular weight of a dicarboxylic acid may be the molecular weight calculated from the chemical formula, or the manufacturer's nominal value (which may be the weight average molecular weight or number average molecular weight). In addition, in embodiments where two or more dicarboxylic acids are used, the molecular weight of the dicarboxylic acid is the sum (total value) of the products of the molecular weights and weight fractions of the individual dicarboxylic acids.

(diol)
As the diol used in the synthesis of the polyester, any of ethylene glycols, propylene glycols, polyether diols, aliphatic diols, dimer diols, alicyclic diols, aromatic diols, and unsaturated diols can be used. Specific examples of the diol include ethylene glycols such as ethylene glycol and diethylene glycol; propylene glycols such as propylene glycol and dipropylene glycol; polyether diols such as triethylene glycol, polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, polytetramethylene ether glycol, polytrimethylene ether glycol, a copolymer of 3-methyltetrahydrofuran and tetrahydrofuran, and a copolymer of neopentyl glycol and tetrahydrofuran; 1,3-propanediol, 2-methyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol (neopentyl glycol), 2-ethyl-2-butyl-1,3-propanediol, 2-ethyl-2-isobutyl-1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, and 3-methyl-1,5-pentanediol. aliphatic diols such as 2,4-diethyl-1,5-pentanediol, 1,6-hexanediol, 2-methyl-1,3-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; dimer diols (e.g., dimer diols derived from fatty acids such as oleic acid and erucic acid); 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, 1,5-cyclohexanediol, 1,6-hexanediol, 2-methyl-1,3-hexanediol, 2,2,4-trimethyl-1,6-hexanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; Examples include alicyclic diols such as methanol, spiroglycol, tricyclodecane dimethanol, adamantanediol, and 2,2,4,4-tetramethyl-1,3-cyclobutanediol; and aromatic diols such as 4,4'-thiodiphenol, 4,4'-methylenediphenol, 4,4'-dihydroxybiphenyl, o-, m-, and p-dihydroxybenzene, 2,5-naphthalenediol, p-xylenediol, and their ethylene oxide and propylene oxide adducts. By appropriately selecting and using one or more of these diols, a polyester capable of exhibiting desired adhesive properties can be obtained.

In some preferred embodiments, a polyether diol is used as the diol. Polyesters containing polyether diol units tend to achieve a low Tg, which can contribute to improving the fluidity and coatability of adhesive compositions that are substantially free of organic solvents. The use of polyether diols is also advantageous in terms of improving wettability and easy peelability. Preferred polyether diols include polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, and polytetramethylene ether glycol, with polyoxyethylene polyoxypropylene glycol being more preferred. Of these, polyether diols containing oxypropylene units are preferred. Polyesters synthesized using polyether diols containing oxypropylene units or polyoxypropylene structures have low viscosity due to their amorphous structure, and are advantageous in terms of handleability and coatability. Polyether diols containing oxypropylene units may further contain oxyethylene units or polyoxyethylene units. Preferred examples of such polyether diols include polypropylene glycols in which at least one end (preferably both ends) has been modified with (poly)oxyethylene, and polyoxyethylene-polyoxypropylene block copolymers or random copolymers having an oxyethylene unit or polyoxyethylene structure at at least one end (preferably both ends). Polyether diols with such structures allow for the oxypropylene unit to be incorporated into polyester with good reactivity. A suitable example of the polyoxyethylene-polyoxypropylene block copolymer is a polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer. One type of polyether diol can be used alone, or two or more types can be used in combination.

In embodiments in which a polyether diol is used as the diol, the weight percentage of the polyether diol relative to the total amount (total weight) of diols used in the synthesis of the polyester is not particularly limited, and is suitably approximately 1% by weight or more, and may be approximately 10% by weight or more, or approximately 30% by weight or more. In some preferred embodiments, the weight percentage of the polyether diol relative to the total amount of diols is approximately 50% by weight or more, may be approximately 70% by weight or more, may be approximately 80% by weight or more, may be approximately 90% by weight or more, or may be approximately 95% by weight or more (e.g., 95 to 100% by weight). By using a predetermined amount or more of polyether diol, it is possible to design a polyester (for example, but not limited to, a polyester having a Mw within a predetermined range and a low Tg) based on the properties of the polyether diol.

The molecular weight of the diol used is not particularly limited, and is suitably 100 or greater, and may be 150 or greater, 250 or greater, 350 or greater, 450 or greater, 550 or greater, 650 or greater, or 750 or greater. In some preferred embodiments, the molecular weight of the diol may be 1000 or greater, 1250 or greater, 1500 or greater, 1750 or greater, 2000 or greater, or 2250 or greater. Using a diol with a high molecular weight tends to make it easier to achieve good wettability and easy release properties. On the other hand, from the perspective of monomer availability and ease of synthesis, in some embodiments, the molecular weight of the diol is suitably approximately 6000 or less, preferably 5000 or less, more preferably 4500 or less, even more preferably 4000 or less, even more preferably 3000 or less, and particularly preferably 2800 or less. A suitable example of a diol having the above molecular weight is polyether diol.

In this specification, the molecular weight of a diol may be the molecular weight calculated from the chemical formula, or the manufacturer's nominal value (which may be the weight average molecular weight or number average molecular weight). In addition, in embodiments in which two or more diols are used, the molecular weight of the diol is the sum (total value) of the products of the molecular weights and weight fractions of the individual diols.

While the polyester may be substantially composed of the dicarboxylic acids and diols described above, other copolymerization components besides the dicarboxylic acids and diols may be copolymerized to the extent that the effects of the technology disclosed herein are not impaired, for purposes such as introducing desired functional groups or adjusting molecular weight. Examples of such other copolymerization components include polycarboxylic acids containing three or four or more carboxy groups (trivalent or higher polycarboxylic acids such as trimellitic acid, pyromellitic acid, adamantanetricarboxylic acid, trimesic acid, and trimer acid), polyols containing three or four or more hydroxyl groups per molecule (pentaerythritol, dipentaerythritol, tripentaerythritol, glycerin, trimethylolpropane, trimethylolethane, 1,3,6-hexanetriol, and adamantanetriol), monocarboxylic acids, monoalcohols, hydroxycarboxylic acids, and lactones. The above other copolymerization components may be used alone or in combination of two or more. The proportion of the other copolymerization components in the polyester is suitably, for example, less than 10% by weight, and may be less than 3% by weight, typically less than 1% by weight (or even less than 0.1% by weight). The technology disclosed herein can also be preferably implemented in an embodiment in which the polyester is substantially free of the other copolymerization components.

Although there are no particular limitations on the monomer components used in polyester synthesis, the total proportion of dicarboxylic acid and diol is suitably approximately 90% by weight or more, preferably approximately 95% by weight or more, more preferably approximately 98% by weight or more, and even more preferably approximately 99% by weight or more (e.g., 99 to 100% by weight). The technology disclosed herein is preferably implemented in an embodiment using a polyester synthesized substantially from dicarboxylic acid and diol.

In some preferred embodiments, the polyester uses a combination of a dimer acid as the dicarboxylic acid and a polyether diol as the diol. By using a combination of a dimer acid and a polyether diol, it is possible to preferably synthesize, for example, a polyester having a Mw within a specified range and a low Tg, although this is not particularly limited. From this perspective, in some embodiments, the total proportion of dimer acid and polyether diol in the total amount of monomer components of the polyester is suitably approximately 50% by weight or more, preferably approximately 60% by weight or more, more preferably approximately 70% by weight or more, and even more preferably approximately 80% by weight or more. It may also be approximately 90% by weight or more, or approximately 95% by weight or more (e.g., 99 to 100% by weight).

Although not particularly limited, in some embodiments, it is appropriate to combine more than 1 mole of diol per mole of dicarboxylic acid in the synthesis of the polyester, and the molar ratio of diol to dicarboxylic acid (diol/dicarboxylic acid) is preferably 1.2 or greater, more preferably 1.5 or greater. Increasing the proportion of diol makes it possible to obtain a polyester polyol having hydroxyl groups at its terminals (typically both terminals). This allows for favorable crosslinking with, for example, a crosslinking agent (e.g., an isocyanate-based crosslinking agent) described below. Furthermore, maintaining the molar ratio (diol/dicarboxylic acid) within the above range makes it easier to obtain a polyester with a Mw controlled within a predetermined range. The upper limit of the molar ratio of diol to dicarboxylic acid (diol/dicarboxylic acid) is not particularly limited, and in some embodiments, it may be 3.0 or less, 2.5 or less, 2.2 or less, or 2.0 or less, from the perspective of polymerization efficiency, etc.

There are no particular limitations on the method for obtaining the polyester, and any polymerization method known as a polyester synthesis technique can be used as appropriate. The polyester disclosed herein can be obtained by polycondensation of a dicarboxylic acid and a diol, similar to general polyesters. More specifically, polyester can be synthesized by proceeding with the reaction between a carboxy group of a dicarboxylic acid and a hydroxyl group of a diol, typically while removing water (produced water) produced by the reaction from the reaction system. Methods for removing the produced water from the reaction system include a method in which an inert gas is blown into the reaction system and the produced water is removed from the reaction system along with the inert gas; a method in which azeotropic dehydration is performed using a reaction water discharge solvent such as toluene or xylene; and a method in which the produced water is distilled from the reaction system under reduced pressure (decompression method).

The reaction temperature and reaction time during the above reaction (including esterification and polycondensation), as well as the degree of vacuum (pressure within the reaction system) when a vacuum method is used, can be appropriately set so as to efficiently obtain a polyester with the desired properties (e.g., molecular weight). While not particularly limited, a reaction temperature of approximately 150°C or higher (e.g., 180°C to 260°C) is typically appropriate. By maintaining a reaction temperature within this range, a good reaction rate can be achieved, productivity can be improved, and degradation of the resulting polyester can be easily prevented or suppressed. The reaction time is also not particularly limited and can be approximately 1 to 48 hours (e.g., 3 to 10 hours). When a vacuum method is used, although not particularly limited, a degree of vacuum of 10 kPa or less (typically 10 kPa to 0.1 kPa) is typically appropriate, e.g., 4 kPa to 0.1 kPa. Maintaining the pressure within the reaction system within this range allows the water produced by the reaction to be efficiently distilled out of the system, making it easier to maintain a good reaction rate. Furthermore, when the reaction temperature is relatively high, maintaining the pressure in the reaction system at or above the above lower limit makes it easier to prevent the distillation of the raw materials, dicarboxylic acid and diol, outside the system. From the perspective of maintaining a stable pressure in the reaction system, it is usually appropriate to maintain the pressure in the reaction system at or above 0.1 kPa.

In the above reaction, as with the synthesis of general polyesters, a known or conventional catalyst can be used in an appropriate amount for esterification and condensation. Examples of such catalysts include various metal compounds, such as titanium-based, germanium-based, antimony-based, tin-based, and zinc-based compounds; strong acids, such as p-toluenesulfonic acid and sulfuric acid; and the like. The amount of catalyst used can be appropriately determined depending on factors such as the reaction rate, so a detailed explanation will be omitted here.

In the above process of synthesizing a polyester by reacting a dicarboxylic acid with a diol, a solvent (typically an organic solvent) may or may not be used. The above synthesis can be carried out substantially without the use of an organic solvent (meaning, for example, that an organic solvent is intentionally used as a reaction solvent during the above reaction is excluded). Synthesizing a polyester substantially without the use of an organic solvent in this way, and preparing a pressure-sensitive adhesive using such a polyester, are preferable because they contribute to reducing the amount of organic solvent used.

Although not particularly limited, it is preferable that the polyester be designed to have a low glass transition temperature (Tg). In embodiments in which organic solvents such as ethyl acetate or toluene are not substantially used, using a polyester with a low Tg can reduce the viscosity of the pressure-sensitive adhesive composition and improve coatability. In some embodiments, the Tg of the polyester may be 0°C or lower, -15°C or lower, or -25°C or lower. In some preferred embodiments, from the viewpoint of coatability, the Tg of the polyester is -30°C or lower, -35°C or lower, -40°C or lower, -45°C or lower, -50°C or lower, -55°C or lower, -60°C or lower, or -65°C or lower. Furthermore, from the viewpoint of the cohesive strength of the pressure-sensitive adhesive layer, in some embodiments, the Tg of the polyester is typically approximately -85°C or higher, and may be approximately -75°C or higher, or approximately -70°C or higher.

In this specification, the Tg of a polyester can be determined by taking about 5 mg of a sample, subjecting it to DSC measurement (differential scanning calorimetry) under the following conditions, and calculating the midpoint Tg from the measurement results obtained.
(Measurement conditions)
Measuring device: TA Instruments, product name "Q-2000"
Temperature program: 50°C → -90°C → 50°C
Measurement speed: 10°C/min Atmospheric gas: _N2 (50 mL/min)
Measurement container: Aluminum airtight container

The molecular weight of the polyester is not particularly limited. A polyester with an appropriate molecular weight is used based on the intended use, etc. In some embodiments, the weight-average molecular weight (Mw) of the polyester may be, for example, 2,000 or more, 4,000 or more, 5,000 or more, or 6,000 or more. In some preferred embodiments, the Mw of the polyester is 8,000 or more, more preferably 10,000 or more (e.g., greater than 10,000), even more preferably 12,000 or more, even more preferably 14,000 or more, and particularly preferably 15,000 or more. Using a polyester with a high Mw increases the cohesive strength of the adhesive layer, making it easier to achieve better adhesive performance. In addition, in some embodiments, the weight-average molecular weight (Mw) of the polyester is approximately 50,000 or less, and may be 40,000 or less. In some preferred embodiments, the Mw of the polyester is 35,000 or less, may be 30,000 or less, 25,000 or less, or may be 23,000 or less. By using a polyester with a Mw limited to a specified value or less, the viscosity of the pressure-sensitive adhesive composition can be reduced, making it easier to achieve good coatability.

In this specification, the Mw of a polyester refers to a value calculated in terms of standard polystyrene obtained by GPC (gel permeation chromatography). As a GPC device, for example, a model "HLC-8320GPC" (column: TSKgel GMH-H(S), manufactured by Tosoh Corporation) can be used. More specifically, GPC measurement can be performed under the following conditions. Measurements are also performed in the examples described below using the same method.
[GPC measurement]
Column: TSKgel GMH-H(S)
Column temperature: 40°C
Eluent: THF (containing 0.1% by weight of amine components)
Flow rate: 0.5mL/min
Injection volume: 100μL
Detector: differential refractometer (RI)
Standard sample: polystyrene (PS)

In embodiments in which the adhesive composition contains a polyester, the polyester is used in an appropriate amount to function as an adhesive. In some embodiments, the content of polyester in the adhesive composition and adhesive layer can be approximately 25% by weight or more. By including a predetermined amount or more of polyester in a composition in which the amount of organic solvent used is sufficiently reduced, the effects of including the polyester can be preferably achieved. From this perspective, in some preferred embodiments, the content of polyester in the adhesive composition and adhesive layer is approximately 30% by weight or more, more preferably approximately 35% by weight or more, even more preferably approximately 40% by weight or more, particularly preferably approximately 45% by weight or more, and may be, for example, approximately 50% by weight or more (e.g., greater than 50% by weight). In other preferred embodiments, the content of polyester in the adhesive composition and adhesive layer may be approximately 55% by weight or more, approximately 60% by weight or more, approximately 65% by weight or more, approximately 70% by weight or more, or approximately 75% by weight or more. Furthermore, from the viewpoint of obtaining the effects of containing other components (e.g., the polyol and crosslinking agent described below), in some embodiments, the content of polyester in the PSA composition is suitably approximately 90% by weight or less, preferably approximately 80% by weight or less, and may be approximately 70% by weight or less, approximately 65% by weight or less, approximately 60% by weight or less, or approximately 55% by weight or less. The content of polyester in the PSA layer formed from the PSA composition is suitably approximately 95% by weight or less, and preferably approximately 85% by weight or less, and may be approximately 75% by weight or less, approximately 65% by weight or less, or approximately 60% by weight or less.

<Polyol>
In some embodiments, the PSA composition preferably contains a polyol. The polyol may be contained as a base polymer of the PSA (e.g., polyester-based, urethane-based, or polyether-based PSA), or may be contained as a different component that chemically bonds with the above-mentioned polyester or other polymer. The polyol can contribute to improved cuttability by being incorporated into the PSA in any of the above forms. The polyol may be used alone or in combination of two or more types.

As polyols, either bifunctional polyols (having two hydroxyl groups) or trifunctional or higher polyols (having three or more hydroxyl groups) can be used. Various polyols, such as polyether polyols, polyester polyols, and polycarbonate polyols, can also be used. While not particularly limited, polyether polyols such as polyalkylene glycols are preferred. Polyether polyols tend to provide good handling and coating properties, and are also advantageous in terms of improved wettability and easy release. Examples of such polyols include polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, polytetramethylene ether glycol, polytrimethylene ether glycol, copolymers of 3-methyltetrahydrofuran and tetrahydrofuran, and copolymers of neopentyl glycol and tetrahydrofuran. Among these, polyether polyols containing oxypropylene units are preferred. Polyether polyols containing oxypropylene units or polyoxypropylene structures have low viscosity due to their amorphous structure, making them advantageous in terms of handling and coating properties. Polyether polyols containing oxypropylene units may further contain oxyethylene units or polyoxyethylene units. From the standpoint of reactivity, for example, such polyols may include polypropylene glycols in which at least one end (preferably both ends) has been modified with (poly)oxyethylene, or polyoxyethylene-polyoxypropylene block copolymers or random copolymers having an oxyethylene unit or polyoxyethylene structure at at least one end (preferably both ends). An example of the polyoxyethylene-polyoxypropylene block copolymer is a polyoxyethylene-polyoxypropylene-polyoxyethylene block copolymer. These may be used alone or in combination of two or more.

The molecular weight of the polyol is not particularly limited, and for example, a polyol having a number average molecular weight in the range of 200 to 20,000 can be used. In some embodiments, the number average molecular weight of the polyol may be 300 or more, or 400 or more. In some preferred embodiments, the number average molecular weight of the polyol may be 1,000 or more, 2,000 or more, 3,000 or more, or 4,000 or more. Using a polyol with a high molecular weight tends to make it easier to achieve good wettability and easy releasability. In some embodiments, the number average molecular weight of the polyol may be 15,000 or less, or 13,000 or less. In some preferred embodiments, the number average molecular weight of the polyol may be less than 10,000, less than 8,000, 7,000 or less, or 5,000 or less. A pressure-sensitive adhesive composition containing a polyol having a number average molecular weight of a predetermined value or less is advantageous in terms of coatability, as it is easier to maintain a low viscosity.

In this specification, the number average molecular weight of a polyol (including tri- or higher functional polyols, as described below) can be determined by the manufacturer's nominal value. If the nominal value is unknown, the number average molecular weight (Mn) obtained by GPC measurement under conditions similar to those used for the Mw of the polyester can be used. In addition, in embodiments in which two or more polyols are used, the number average molecular weight of the polyol is the sum (total value) of the products of the number average molecular weights and weight fractions of the individual polyols. The same applies to embodiments in which two or more tri- or higher functional polyols are used.

In embodiments in which the pressure-sensitive adhesive composition contains a polyol, the polyol is used in an appropriate amount to function as a pressure-sensitive adhesive. In some embodiments, the content of polyol in the pressure-sensitive adhesive composition and the pressure-sensitive adhesive layer may be 0.1% by weight or more, or 1% by weight or more. In some preferred embodiments, the content of polyol in the pressure-sensitive adhesive composition and the pressure-sensitive adhesive layer is 2% by weight or more, 5% by weight or more, 10% by weight or more, 15% by weight or more, 20% by weight or more, 25% by weight or more, or 30% by weight or more. By using a predetermined amount or more of polyol, the effects of containing the polyol can be effectively exerted. In other embodiments, the content of polyol (e.g., bifunctional polyol) in the pressure-sensitive adhesive composition and the pressure-sensitive adhesive layer may be approximately 50% by weight or more (e.g., more than 50% by weight), approximately 70% by weight or more, approximately 80% by weight or more, or approximately 90% by weight or more. Furthermore, the content of polyol in the PSA composition and the PSA layer may be, for example, 99% by weight or less, or approximately 95% by weight or less. From the viewpoint of obtaining the effects of the inclusion of other components (e.g., crosslinking agents), in some embodiments, the content of polyol in the PSA composition and the PSA layer may be approximately 90% by weight or less, or approximately 70% by weight or less. In some preferred embodiments, the content of polyol in the PSA composition and the PSA layer is approximately 50% by weight or less (e.g., less than 50% by weight), approximately 40% by weight or less, approximately 30% by weight or less, approximately 20% by weight or less, or approximately 10% by weight or less.

(Tri- or higher functional polyol)
In some preferred embodiments, the pressure-sensitive adhesive composition contains a trifunctional or higher polyol. In a pressure-sensitive adhesive composition that is substantially free of ethyl acetate and toluene, the trifunctional or higher polyol can be used in combination with a suitable crosslinking agent, such as a bifunctional isocyanate-based crosslinking agent described below, to preferably achieve good cuttability. The reason for this is thought to be that by containing a polymer such as polyester or polyol, a predetermined amount of a trifunctional or higher polyol, and the crosslinking agent, a loose crosslinked structure with good extensibility is obtained, which has appropriate cohesive strength and prevents or suppresses the phenomenon of brittle peeling of the pressure-sensitive adhesive when cut. The technology disclosed herein is not limited to the above considerations. The trifunctional or higher polyol can be used alone or in combination of two or more.

The number of hydroxyl groups possessed by tri- or higher functional polyols is 3 or 4 or more, and although there is no particular upper limit, for example, 10 or less is preferred, 8 or less is more preferred, and 6 or less is even more preferred. When the number of hydroxyl groups in a tri- or higher functional polyol is within the specified range, it tends to be easier to obtain a good crosslinked structure with good cuttability.

It is preferable to use a tri- or higher functional polyol with a number average molecular weight in the range of 200 to 20,000. By using an appropriate amount of a tri- or higher functional polyol having such a number average molecular weight relative to a polymer such as a polyester or polyol, a favorable crosslinked structure with good cuttability can be obtained. Furthermore, a pressure-sensitive adhesive composition containing a tri- or higher functional polyol having a number average molecular weight of a predetermined value or less is more likely to maintain low viscosity and is advantageous in terms of coatability. From the viewpoint of cuttability, the number average molecular weight of the tri- or higher functional polyol is preferably 300 or more, more preferably 400 or more. In some embodiments, the number average molecular weight of the tri- or higher functional polyol may be 1,000 or more, 2,000 or more, 3,000 or more, 4,000 or more, 5,000 or more (e.g., greater than 5,000), or 6,000 or more. The number average molecular weight of the tri- or higher functional polyol is preferably 15,000 or less, more preferably 13,000 or less. By using a tri- or higher functional polyol with a relatively low molecular weight within a certain range, a crosslinked structure based on the tri- or higher functional polyol can be formed with a relatively small amount. This can help effectively develop adhesive properties based on polymers such as polyester. In some embodiments, the number average molecular weight of the tri- or higher functional polyol may be less than 10,000, less than 8,000, 7,000 or less, 5,000 or less, or 3,000 or less.

In some preferred embodiments, the tri- or higher functional polyol used has a number average molecular weight in the range of 8,000 or more and 20,000 or less. In such embodiments, the number average molecular weight of the tri- or higher functional polyol is preferably 15,000 or less, and more preferably 13,000 or less. In other preferred embodiments, the tri- or higher functional polyol used has a number average molecular weight in the range of 200 or more and less than 8,000. In such embodiments, the number average molecular weight of the tri- or higher functional polyol is preferably 7,000 or less, and may be 5,000 or less, 3,000 or less, 1,500 or less, or 1,000 or less (e.g., less than 1,000).

As the tri- or higher functional polyol, any polyol having three or more hydroxyl groups and a predetermined number-average molecular weight can be used without particular restrictions. For example, tri- or higher functional polyether polyols are preferred from the perspective of cuttability. The use of polyether polyols is also advantageous in terms of improving wettability and easy release properties. Examples of tri- or higher functional polyether polyols include polyethylene glycol, polypropylene glycol, polyoxyethylene polyoxypropylene glycol, polytetramethylene ether glycol, polytrimethylene ether glycol, a copolymer of 3-methyltetrahydrofuran and tetrahydrofuran, and a copolymer of neopentyl glycol and tetrahydrofuran. Such tri- or higher functional polyether polyols may contain units derived from glycerin, trimethylolpropane, or pentaerythritol (glycerin units, trimethylolpropane units, pentaerythritol units). Other examples of trifunctional polyols include dipentaerythritol and tripentaerythritol. These may be used alone or in combination of two or more.

As trifunctional or higher functional polyols, those containing oxypropylene units are preferably used. Trifunctional or higher functional polyols containing oxypropylene units or polyoxypropylene structures have low viscosity due to their amorphous structure, and are advantageous in terms of handleability and coatability. Trifunctional or higher functional polyols containing oxypropylene units may also contain oxyethylene units or polyoxyethylene units. From the standpoint of reactivity, for example, the trifunctional or higher functional polyol may be polypropylene glycol in which at least one end (e.g., both ends) has been modified with (poly)oxyethylene, or a polyoxyethylene-polyoxypropylene block copolymer or random copolymer having an oxyethylene unit or polyoxyethylene structure at at least one end (e.g., both ends).

In an embodiment in which the PSA composition comprises a polyester and a tri- or higher functional polyol, the content of the tri- or higher functional polyol in the PSA composition is preferably set so that the ratio (B _OH /A _OH ) of the amount of hydroxyl groups B _OH [mol] contained in the tri- or higher functional polyol to the amount of hydroxyl groups A _OH [mol] contained in the polyester is within the range of 0.5 to 5.5. When the ratio (B _OH /A _OH ) is within the range of 0.5 to 5.5, the PSA formed into a sheet with adequate cohesive strength preferably exhibits good cuttability. The amount of hydroxyl groups A _OH contained in the polyester is calculated from the formula: A _OH = polyester content (parts by weight) × number of hydroxyl groups per polyester molecule / weight-average molecular weight of polyester. The amount of hydroxyl groups B _OH contained in the tri- or higher functional polyol is calculated from the formula: B _OH = tri- or higher functional polyol content (parts by weight) × number of hydroxyl groups per tri- or higher functional polyol molecule / number-average molecular weight of the tri- or higher functional polyol. The ratio (B _OH /A _OH ) is preferably 4.5 or less, more preferably 4.0 or less, even more preferably 3.5 or less, and particularly preferably 3.0 or less (e.g., 2.5 or _{less). By using a trifunctional or higher polyol at a moderately limited ratio relative to the polyester, based on the amount of hydroxyl groups, within the above ratio (B OH /} A _OH ), excellent cutting properties tend to be easily obtained. Furthermore, the ratio (B _OH /A _OH ) is preferably 1.0 or more, more preferably 1.4 or more. By using a trifunctional or higher polyol in a predetermined amount or more relative to the polyester, based on the amount of hydroxyl groups, within the above ratio (B _OH /A OH ), the pressure-sensitive adhesive can preferably have a moderate cohesive force. Furthermore, a pressure-sensitive adhesive having the above ratio (B _OH /A _OH ) can preferably be obtained that has a gel fraction of a predetermined value or more and has good cutting properties.

The preferred range of the ratio (B _OH /A _OH ) may vary depending on the molecular weight of the tri- or higher functional polyol used. Specifically, in an embodiment using a tri- or higher functional polyol having a number average molecular weight in the range of 8,000 to 20,000, the ratio (B _OH /A _OH ) is preferably 4.5 or less, more preferably 4.0 or less, even more preferably 3.5 or less, and particularly preferably 3.0 or less (e.g., 2.5 or less). In an embodiment using a tri- or higher functional polyol having a number average molecular weight in the range of 200 to less than 8,000, the ratio (B _OH /A _OH ) may be 4.5 or less, 4.0 or less, or 3.5 or less. In either case of using a tri- or higher functional polyol having a number average molecular weight in the range of 8,000 or more and 20,000 or less, or a tri- or higher functional polyol having a number average molecular weight in the range of 200 or more and less than 8,000, the ratio (B _OH /A _OH ) is preferably 1.0 or more, and more preferably 1.4 or more.

In embodiments using a trifunctional or higher polyol, the amount of trifunctional or higher polyol used is not particularly limited. In some embodiments, the amount of trifunctional or higher polyol used is preferably, for example, an amount within a range satisfying the above ratio (B _OH /A _OH ). In some embodiments, the content of the trifunctional or higher polyol may be approximately 0.5 parts by weight or more, or approximately 1 part by weight or more, per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the pressure-sensitive adhesive composition. From the viewpoint of improving cohesive strength, in some preferred embodiments, the content of the trifunctional or higher polyol per 100 parts by weight of the polymer is 2 parts by weight or more, 5 parts by weight or more, 10 parts by weight or more, 15 parts by weight or more, or even 20 parts by weight or more. In embodiments using a predetermined amount or more of a trifunctional or higher polyol, good coatability tends to be easily obtained. In such embodiments, there is also the advantage that the Mw and Tg of the polymer, which tend to be limited due to coatability, can be more flexibly designed. In some embodiments, the content of the tri- or higher functional polyol may be approximately 200 parts by weight or less, or approximately 150 parts by weight or less, relative to 100 parts by weight of the polymer. By reducing the amount of the tri- or higher functional polyol within a predetermined range, the cutting ability can be improved. Furthermore, limiting the content of the tri- or higher functional polyol is also preferable from the viewpoint of reducing contamination of the adherend caused by the tri- or higher functional polyol. From the viewpoint of improving the cutting ability, in some preferred embodiments, the content of the tri- or higher functional polyol relative to 100 parts by weight of the polymer is 120 parts by weight or less, or may be 100 parts by weight or less, 80 parts by weight or less, 50 parts by weight or less, 30 parts by weight or less, or 20 parts by weight or less.

The amount of tri- or higher functional polyol used may vary depending on the molecular weight of the tri- or higher functional polyol used. Specifically, in an embodiment using a tri- or higher functional polyol having a number-average molecular weight in the range of 8,000 to 20,000, the content of the tri- or higher functional polyol is, for example, approximately 15 parts by weight or more, preferably approximately 20 parts by weight or more, more preferably approximately 30 parts by weight or more, even more preferably approximately 40 parts by weight or more, and particularly preferably approximately 50 parts by weight or more (e.g., more than 50 parts by weight) per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the adhesive composition. In such an embodiment, the content of the tri- or higher functional polyol may be approximately 200 parts by weight or less, and is suitably approximately 150 parts by weight or less, preferably 120 parts by weight or less, more preferably 100 parts by weight or less, and even more preferably 80 parts by weight or less, per 100 parts by weight of the polymer.

In addition, in embodiments using a tri- or higher functional polyol having a number average molecular weight in the range of 200 or more but less than 8,000, the content of the tri- or higher functional polyol is, for example, approximately 0.5 parts by weight or more, or may be approximately 1 part by weight or more, relative to 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the PSA composition. In some preferred embodiments, it is 1.5 parts by weight or more, more preferably 2 parts by weight or more, or may be 5 parts by weight or more, or may be 10 parts by weight or more, or may be 15 parts by weight or more, or may be 20 parts by weight or more, or may be 25 parts by weight or more. In such embodiments, the content of the tri- or higher functional polyol may be approximately 100 parts by weight or less, or suitably approximately 80 parts by weight or less, relative to 100 parts by weight of the polymer. In some preferred embodiments, it is 60 parts by weight or less, more preferably 50 parts by weight or less, even more preferably 40 parts by weight or less, or may be 30 parts by weight or less, or may be 20 parts by weight or less, or may be 10 parts by weight or less, or may be 5 parts by weight or less.

In an embodiment using a polyester and a tri- or higher functional polyol, the PSA composition may or may not contain a bifunctional polyol. In such an embodiment, the content of the bifunctional polyol in the PSA composition is, for example, less than 30 parts by weight, less than 10 parts by weight, less than 3 parts by weight, or less than 1 part by weight, per 100 parts by weight of the tri- or higher functional polyol. The technology disclosed herein can be preferably implemented in an embodiment in which the PSA composition contains a polyester and a tri- or higher functional polyol but is substantially free of the bi- or higher functional polyol. Furthermore, in an embodiment in which a bifunctional polyol and a tri- or higher functional polyol are used, the PSA composition may or may not contain a polyester. In such an embodiment, the content of the polyester in the PSA composition is, for example, less than 30 parts by weight, less than 10 parts by weight, less than 3 parts by weight, or less than 1 part by weight, per 100 parts by weight of the total amount of polyols. The technology disclosed herein can be implemented in an embodiment in which the PSA composition contains a polyol but is substantially free of a polyester.

<Crosslinking agent>
In some embodiments, the pressure-sensitive adhesive composition preferably contains a crosslinking agent. The crosslinking agent can be useful for increasing the cohesive strength of the pressure-sensitive adhesive. The crosslinking agent can be selected from various crosslinking agents known in the field of pressure-sensitive adhesives. Examples of such crosslinking agents include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, oxazoline-based crosslinking agents, aziridine-based crosslinking agents, melamine-based crosslinking agents, peroxide-based crosslinking agents, urea-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, carbodiimide-based crosslinking agents, hydrazine-based crosslinking agents, and amine-based crosslinking agents. The crosslinking agents can be used alone or in combination of two or more. The above-mentioned crosslinking agents are usually contained in the pressure-sensitive adhesive layer exclusively in the form after the crosslinking reaction. In addition, crosslinking agents used for crosslinking polyesters or polyols can also function as chain extenders.

The number of crosslinkable functional groups in the crosslinking agent is not particularly limited, and typically 2 to 10, preferably 2 to 6, for example, 2 or 3 crosslinkable functional groups can be used. Therefore, bifunctional crosslinking agents with two crosslinkable functional groups, trifunctional crosslinking agents with three crosslinkable functional groups, and tetrafunctional or higher crosslinking agents with four or more crosslinkable functional groups can all be used. Furthermore, the crosslinking agent may be derived from biomass or non-biomass. From the perspective of producing adhesives that minimize dependence on fossil resource-based materials, it is preferable to use a biomass-derived crosslinking agent.

The amount of crosslinking agent used is not particularly limited. The amount of crosslinking agent used can be selected, for example, from the range of 0.1 to 50 parts by weight per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the adhesive composition. From the perspective of achieving a good balance between improved cohesive strength and adhesion to the substrate, the amount of crosslinking agent used per 100 parts by weight of the polymer is usually preferably 40 parts by weight or less, but may also be 30 parts by weight or less, or 25 parts by weight or less, and is suitably 1 part by weight or more, or may be 3 parts by weight or more. By using an appropriate amount of crosslinking agent within the appropriate range, it is possible to increase the cohesive strength of the adhesive, prevent adhesive residue on the substrate, and obtain adhesion to the substrate.

(Isocyanate-based crosslinking agent)
In some embodiments, the pressure-sensitive adhesive composition preferably contains an isocyanate-based crosslinking agent. The use of an isocyanate-based crosslinking agent allows the formation of a high-quality pressure-sensitive adhesive layer. The isocyanate-based crosslinking agents can be used alone or in combination of two or more.

As an isocyanate-based crosslinking agent, a polyisocyanate-based crosslinking agent having two or more isocyanate groups per molecule is preferably used. The number of isocyanate groups per molecule of the polyisocyanate-based crosslinking agent is preferably 2 to 10, for example, 2 to 4, and typically 2 or 3. Examples of the polyisocyanate-based crosslinking agent include aromatic polyisocyanates such as tolylene diisocyanate and xylene diisocyanate; alicyclic isocyanates such as isophorone diisocyanate; and aliphatic polyisocyanates such as hexamethylene diisocyanate. More specifically, for example, lower aliphatic polyisocyanates such as butylene diisocyanate, pentamethylene diisocyanate, and hexamethylene diisocyanate; alicyclic polyisocyanates such as cyclopentylene diisocyanate, cyclohexylene diisocyanate, and isophorone diisocyanate; aromatic diisocyanates such as 2,4-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, xylylene diisocyanate, and polymethylene polyphenyl diisocyanate; trimethylolpropane/tolylene diisocyanate trimer adduct, trimethylolpropane/hexamethylene diisocyanate trimer adduct (manufactured by Tosoh Corporation, trade name "Co Examples of suitable diisocyanates include isocyanate adducts such as derivatives of hexamethylene diisocyanate (manufactured by Asahi Kasei Corporation under the trade name "Duranate D101"), an isocyanurate of hexamethylene diisocyanate (manufactured by Tosoh Corporation under the trade name "Coronate HX"), and an isocyanurate of pentamethylene diisocyanate (manufactured by Mitsui Chemicals, Inc. under the trade name "STABIO D-370N"); polyisocyanates such as polyether polyisocyanate and polyester polyisocyanate; adducts of these polyisocyanates with polyols; and polyisocyanates obtained by multifunctionalizing these polyisocyanates with isocyanurate bonds, biuret bonds, allophanate bonds, etc. For example, in embodiments in which organic solvents are not substantially used, the use of aliphatic diisocyanates such as pentamethylene diisocyanate and hexamethylene diisocyanate, and isocyanurates of such aliphatic diisocyanates, is preferred from the viewpoint of coatability. The proportion of aliphatic polyisocyanates (aliphatic diisocyanates, isocyanurates of aliphatic diisocyanates, etc.) in the total amount of isocyanate-based crosslinking agent is preferably greater than 50% by weight, but may also be 70% by weight or greater, or 90% by weight or greater (e.g., 95 to 100% by weight).

In some preferred embodiments, the pressure-sensitive adhesive composition contains an isocyanate-based crosslinking agent (bifunctional isocyanate-based crosslinking agent) having two isocyanate groups. In pressure-sensitive adhesive compositions that are substantially free of ethyl acetate and toluene, the use of a bifunctional isocyanate-based crosslinking agent tends to improve cuttability. In pressure-sensitive adhesive compositions that do not use organic solvents for dilution, a relatively low-molecular-weight polymer (e.g., polyester) is used to achieve coatability. This tends to reduce cohesive strength, but a design is adopted in which a trifunctional or higher functional multifunctional crosslinking agent is used to ensure this. However, such a dense crosslinked structure tends to generate glue residue when the pressure-sensitive adhesive is cut, reducing cuttability. According to the technology disclosed herein, cuttability can be improved by using a bifunctional isocyanate-based crosslinking agent, rather than a trifunctional or higher functional crosslinking agent, as the crosslinking agent, to form a loose crosslinked structure with good extensibility. Although not particularly limited, for example, better cuttability can be achieved by combining a trifunctional or higher functional polyol with a bifunctional isocyanate-based crosslinking agent to form a loose crosslinked structure with good extensibility. As the bifunctional isocyanate crosslinking agent, any of the materials exemplified above as isocyanate crosslinking agents that are bifunctional (i.e., have two isocyanate groups) can be used. One type of bifunctional isocyanate crosslinking agent can be used alone, or two or more types can be used in combination.

In embodiments using a bifunctional isocyanate crosslinking agent, the amount of bifunctional isocyanate crosslinking agent used is not particularly limited and may be, for example, approximately 1 part by weight or more, or approximately 3 parts by weight or more, per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the adhesive composition. In some preferred embodiments, the amount of bifunctional isocyanate crosslinking agent used per 100 parts by weight of the polymer is approximately 5 parts by weight or more, more preferably approximately 10 parts by weight or more, even more preferably approximately 15 parts by weight or more, particularly preferably approximately 18 parts by weight or more, and may even be approximately 20 parts by weight or more. In some embodiments, the amount of bifunctional isocyanate crosslinking agent used per 100 parts by weight of the polymer is suitably approximately 50 parts by weight or less, and may be approximately 40 parts by weight or less. In some preferred embodiments, the amount of bifunctional isocyanate crosslinking agent used per 100 parts by weight of the polymer is approximately 30 parts by weight or less (e.g., less than 30 parts by weight), more preferably approximately 25 parts by weight or less, and even more preferably approximately 22 parts by weight or less. By keeping the amount of bifunctional isocyanate crosslinking agent used within the above range, it is possible to preferably achieve both appropriate cohesive strength and cuttability.

In addition, in embodiments in which the pressure-sensitive adhesive composition contains a polyester and a bifunctional isocyanate-based crosslinking agent, and preferably may further optionally contain a trifunctional or higher polyol, the amount of the bifunctional isocyanate-based crosslinking agent used is not particularly limited, and may be, for example, approximately 1 part by weight or more, or approximately 3 parts by weight or more, per 100 parts by weight of the polyester and the trifunctional or higher polyol combined. Increasing the amount of the bifunctional isocyanate-based crosslinking agent used makes it easier to obtain good curing properties and improve cohesive strength. In some preferred embodiments, the amount of the bifunctional isocyanate-based crosslinking agent used per 100 parts by weight of the polyester and the trifunctional or higher polyol combined is approximately 5 parts by weight or more, more preferably approximately 8 parts by weight or more, and may be approximately 10 parts by weight or more, approximately 12 parts by weight or more, or approximately 15 parts by weight or more. In some embodiments, the amount of the bifunctional isocyanate-based crosslinking agent used per 100 parts by weight of the polyester and the trifunctional or higher polyol combined is suitably approximately 50 parts by weight or less, and may be approximately 30 parts by weight or less. By limiting the amount of bifunctional isocyanate crosslinking agent used within a specified range, good cutting properties are likely to be obtained. In some preferred embodiments, the amount of bifunctional isocyanate crosslinking agent used per 100 parts by weight of the polyester and tri- or higher functional polyol combined is approximately 25 parts by weight or less, more preferably approximately 20 parts by weight or less, and may be approximately 18 parts by weight or less, approximately 16 parts by weight or less, or approximately 14 parts by weight or less. By limiting the amount of bifunctional isocyanate crosslinking agent used within the above range, it is possible to preferably achieve both appropriate cohesive strength and cutting properties.

In some embodiments, the pressure-sensitive adhesive composition may contain a trifunctional or higher isocyanate crosslinking agent. As the trifunctional or higher isocyanate crosslinking agent, any of the materials exemplified above as isocyanate crosslinking agents that are trifunctional or higher (i.e., have three or more isocyanate groups) can be used. One type of trifunctional or higher isocyanate crosslinking agent can be used alone, or two or more types can be used in combination.

Although not particularly limited, the adhesive composition may contain a bifunctional isocyanate crosslinking agent and a trifunctional or higher isocyanate crosslinking agent. By using a bifunctional isocyanate crosslinking agent in combination with a trifunctional or higher isocyanate crosslinking agent, it is possible to form a favorable crosslinked structure that achieves a good balance between cutting ability and cohesive strength based on the action of each isocyanate crosslinking agent.

In embodiments in which the pressure-sensitive adhesive composition contains an isocyanate-based crosslinking agent, the proportion of the bifunctional isocyanate-based crosslinking agent in the total isocyanate-based crosslinking agents contained in the pressure-sensitive adhesive composition may be 10% by weight or more, suitably 25% by weight or more, or may be 30% by weight or more, from the viewpoint of obtaining the effect of containing the bifunctional isocyanate-based crosslinking agent. In some preferred embodiments, the proportion of the bifunctional isocyanate-based crosslinking agent in the total isocyanate-based crosslinking agents is 50% by weight or more (e.g., more than 50% by weight), may be 70% by weight or more, may be 90% by weight or more, or may be 95% by weight or more (e.g., 99 to 100% by weight). The technology disclosed herein is preferably implemented in embodiments in which the pressure-sensitive adhesive composition uses only a bifunctional isocyanate-based crosslinking agent as the isocyanate-based crosslinking agent. Furthermore, in embodiments in which a bifunctional isocyanate crosslinking agent and a trifunctional or higher isocyanate crosslinking agent are used in combination, the proportion of the bifunctional isocyanate crosslinking agent in the total isocyanate crosslinking agents may be 90% by weight or less, 70% by weight or less, 50% by weight or less (e.g., less than 50% by weight), or 40% by weight or less.

In embodiments using an isocyanate-based crosslinking agent, the amount of isocyanate-based crosslinking agent used is not particularly limited. For example, it may be approximately 0.5 parts by weight or more, approximately 1 part by weight or more, or 3 parts by weight or more per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the adhesive composition. Increasing the amount of isocyanate-based crosslinking agent used makes it easier to achieve good curing properties and improve cohesive strength. In some embodiments, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of the polymer is suitably approximately 5 parts by weight or more, may be approximately 10 parts by weight or more, may be approximately 12 parts by weight or more, may be approximately 16 parts by weight or more, or may be approximately 18 parts by weight or more. In addition, in some embodiments, the amount of isocyanate-based crosslinking agent used per 100 parts by weight of the polymer is suitably approximately 50 parts by weight or less, may be approximately 40 parts by weight or less, or may be approximately 30 parts by weight or less. By using an isocyanate-based crosslinking agent in an amount within the above range, a suitably crosslinked structure is preferably formed within the adhesive layer, making it easier to obtain an adhesive with sufficient cohesive strength.

In embodiments using an isocyanate-based crosslinking agent, the pressure-sensitive adhesive composition may contain one or more crosslinking agents other than an isocyanate-based crosslinking agent (non-isocyanate-based crosslinking agent). Examples of such non-isocyanate-based crosslinking agents include the crosslinking agents exemplified above other than the isocyanate-based crosslinking agents. For example, from the perspective of obtaining the effects of using an isocyanate-based crosslinking agent, the proportion of the isocyanate-based crosslinking agent in the crosslinking agent contained in the pressure-sensitive adhesive composition may be 10% by weight or more, preferably 30% by weight or more, 50% by weight or more (e.g., more than 50% by weight), 70% by weight or more, 90% by weight or more, or 95% by weight or more (e.g., 99 to 100% by weight). The technology disclosed herein is preferably implemented in an embodiment using only an isocyanate-based crosslinking agent as the crosslinking agent.

Although not particularly limited, in an embodiment in which the pressure-sensitive adhesive composition contains at least one selected from polyesters and polyols and a crosslinking agent, the total content of the polyester, polyol, and crosslinking agent contained in the pressure-sensitive adhesive composition may be 80% by weight or more, 85% by weight or more, 90% by weight or more, or 95% by weight or more of the entire pressure-sensitive adhesive composition. According to the technology disclosed herein, the above configuration makes it possible to form a pressure-sensitive adhesive layer that can exhibit desired performance with good productivity while sufficiently reducing the amount of organic solvent used. The upper limit of the total content of the polyester, polyol, and crosslinking agent contained in the pressure-sensitive adhesive composition is, for example, less than 99% by weight, and may be 97% by weight or less.

<Metal catalyst>
In some embodiments, the pressure-sensitive adhesive composition preferably contains a metal catalyst. The use of a metal catalyst promotes the crosslinking reaction, efficiently curing the pressure-sensitive adhesive composition, and enables the pressure-sensitive adhesive layer to be formed with high productivity. The metal catalyst is also referred to as a crosslinking catalyst. Examples of metal catalysts include tin (Sn)-containing compounds (tin-based catalysts), zirconium (Zr)-containing compounds (zirconium-based catalysts), titanium (Ti)-containing compounds (titanium-based catalysts), hafnium (Hf)-containing compounds (hafnium-based catalysts), iron (Fe)-containing compounds (iron-based catalysts), aluminum (Al)-containing compounds (aluminum-based catalysts), zinc (Zn)-containing compounds (zinc-based catalysts), and bismuth (Bi)-containing compounds (bismuth-based catalysts). Organic compounds having a metal in the active center, i.e., organometallic catalysts, are preferably used as the metal catalyst. Metal catalysts can be used alone or in combination of two or more.

Non-limiting examples of metal catalysts include dioctyltin dilaurate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin diacetylacetonate, tetra-n-butyltin, trimethyltin hydroxide, butyltin oxide, etc. (tin-based catalysts); zirconium tetraacetylacetonate, zirconium monoacetylacetonate, zirconium ethylacetoacetate, zirconium octylate compounds, etc. (zirconium-based catalysts); tetraisopropyl titanate, tetra-n-butyl titanate, nate, butyl titanate dimer, tetraoctyl titanate, titanium acetylacetonate, titanium tetraacetylacetonate, titanium ethylacetoacetate, etc. (titanium-based catalysts); hafnium tetraacetylacetonate, etc. (hafnium-based catalysts); nursem ferric, etc. (iron-based catalysts); aluminum sec-butoxide, aluminum trisacetylacetonate, aluminum bisethylacetoacetate, aluminum trisethylacetoacetate, etc. (aluminum-based catalysts); etc.

In some preferred embodiments, a compound containing a Group 4 element is used as the metal catalyst from the standpoint of catalytic activity and transparency. Preferred Group 4 element-containing compounds are zirconium-containing compounds (zirconium-based catalysts) and titanium-containing compounds (titanium-based catalysts). Group 4 element-containing compounds can be used alone or in combination of two or more.

In some preferred embodiments, from the standpoint of environmental impact and safety, the metal catalyst does not contain a tin-containing compound. By using a non-tin-based compound as the metal catalyst, the amount of tin-based compounds (typically organotin) used in the adhesive can be reduced. The adhesive composition disclosed herein can form a good crosslinked structure with high productivity without using a tin-based catalyst, which generally tends to have excellent reaction speeds. Furthermore, in some embodiments, the metal catalyst does not contain an iron-based catalyst. For example, in use embodiments where the adhesive requires transparency and optical properties, it is desirable to avoid the use of iron-based compounds, which may discolor the adhesive.

In embodiments using a metal catalyst, the amount of metal catalyst used is not particularly limited. In some embodiments, from the viewpoint of efficiently progressing the crosslinking reaction, the amount of metal catalyst used can be, for example, approximately 0.01 parts by weight or more, preferably approximately 0.10 parts by weight or more, and may be approximately 0.12 parts by weight or more (e.g., 0.15 parts by weight or more), per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the pressure-sensitive adhesive composition. Furthermore, the amount of metal catalyst used can be, for example, approximately 3 parts by weight or less, preferably approximately 1 part by weight or less, and may be approximately 0.3 parts by weight or less, per 100 parts by weight of the polymer.

<Organic solvent>
In some preferred embodiments, the PSA composition is substantially free of organic solvents. According to the technology disclosed herein, a PSA composition having a good pot life and excellent coatability can be obtained without using organic solvents that may be added for dilution purposes, such as to adjust the solid content or viscosity. This reduces the amount of organic solvent used in the preparation of the PSA composition, and ultimately in the formation of the PSA layer and the production of the PSA sheet. Here, "the PSA composition is substantially free of organic solvents" refers to the absence of intentional addition of organic solvents to the PSA composition. However, this does not exclude the possibility of small amounts of organic solvents inevitably present in the raw materials of the PSA composition or unintentionally mixed in during the preparation of the PSA composition remaining in the composition. Specifically, the term "the PSA composition is substantially free of organic solvents" can be defined as the content (total amount) of organic solvents in the PSA composition being less than 5 parts by weight per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the PSA composition. The content of the organic solvent is preferably less than 3 parts by weight, more preferably less than 1 part by weight, and even more preferably less than 0.3 parts by weight (e.g., less than 0.1 parts by weight). Note that the term "organic solvent" in this specification does not include compounds having an acetylacetone skeleton, which will be described later.

Typically, the PSA composition is substantially free of ethyl acetate and toluene. The technology disclosed herein is implemented without using ethyl acetate and toluene, which are typical organic solvents added for dilution purposes. By being substantially free of ethyl acetate and toluene, the amount of organic solvent used in preparing the PSA composition can be reduced. Here, the meaning of "the PSA composition is substantially free of ethyl acetate and toluene" is basically the same as that described above for organic solvents. Specifically, it is defined as the content (total content) of ethyl acetate and toluene in the PSA composition being less than 5 parts by weight per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the PSA composition. The content of ethyl acetate and toluene is preferably less than 3 parts by weight, more preferably less than 1 part by weight, and even more preferably less than 0.3 parts by weight (e.g., less than 0.1 part by weight).

Furthermore, the PSA composition may typically be substantially free of MEK. Here, the meaning of "the PSA composition is substantially free of MEK" is basically the same as that explained above for organic solvents, and specifically can be defined as the content of MEK in the PSA composition being less than 5 parts by weight per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the PSA composition. The MEK content is preferably less than 3 parts by weight, more preferably less than 1 part by weight, and even more preferably less than 0.3 parts by weight (e.g., less than 0.1 part by weight).

<Compounds having an acetylacetone skeleton>
In some embodiments, the PSA composition preferably contains a compound having an acetylacetone skeleton. Compounds having an acetylacetone skeleton exhibit keto-enol tautomerism, and their incorporation into the PSA composition effectively extends the pot life. Furthermore, they volatilize upon heating, such as drying, and thus allow the PSA layer to rapidly cure after heating. Furthermore, incorporating a compound having an acetylacetone skeleton can improve the coatability of the PSA composition. Using an appropriate amount of a compound having an acetylacetone skeleton can simultaneously reduce the amount of organic solvent used and improve productivity. Examples of compounds having an acetylacetone skeleton include acetylacetone and acetoacetic esters (e.g., methyl acetoacetate, ethyl acetoacetate, etc.). Among these, acetylacetone is preferred from the standpoints of coatability, PSA curability, etc.

Although not particularly limited, in some embodiments, from the viewpoint of obtaining sufficient pot life and coatability, the content of the compound having an acetylacetone skeleton in the pressure-sensitive adhesive composition is preferably more than 1 part by weight (specifically 1.0 part by weight) per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the pressure-sensitive adhesive composition, more preferably 3.0 parts by weight or more, even more preferably 5.0 parts by weight or more, even more preferably 7.0 parts by weight or more, and particularly preferably 9.0 parts by weight or more. Furthermore, in some embodiments, for example, from the viewpoint of exhibiting the catalytic action of the metal catalyst, the content of the compound having an acetylacetone skeleton is suitably approximately 15 parts by weight or less, and may be 12 parts by weight or less, per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the pressure-sensitive adhesive composition.

<Other additives>
In some embodiments, the PSA composition may contain a tackifier. The use of an appropriate amount of tackifier can improve adhesive strength. The tackifier may be one or more selected from various known tackifier resins, such as phenolic tackifier resins, terpene tackifier resins, modified terpene tackifier resins, rosin tackifier resins, hydrocarbon tackifier resins, epoxy tackifier resins, polyamide tackifier resins, elastomer tackifier resins, and ketone tackifier resins.

The amount of tackifier contained in the pressure-sensitive adhesive composition is not particularly limited. In some embodiments, the amount of tackifier contained in the pressure-sensitive adhesive composition is suitably about 1 to 120 parts by weight per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the pressure-sensitive adhesive composition, and may be 10 to 100 parts by weight or 20 to 80 parts by weight. In other embodiments, the amount of tackifier contained in the pressure-sensitive adhesive composition may be less than 10 parts by weight, less than 3 parts by weight, or less than 1 part by weight per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the pressure-sensitive adhesive composition, and the pressure-sensitive adhesive composition may be substantially free of tackifier. Such compositions are preferably applicable to applications that require removability, such as surface protection.

The adhesive composition disclosed herein may also contain a hydrolysis stabilizer (also called a hydrolysis inhibitor). By adding a hydrolysis stabilizer, hydrolysis reactions in the adhesive are suppressed, making it easier to achieve good durability. There are no particular limitations on the hydrolysis stabilizer, and known or commonly used hydrolysis stabilizers can be used. Examples include oxazoline group-containing compounds, epoxy group-containing compounds, and carbodiimide group-containing compounds. Of these, carbodiimide group-containing compounds are preferred. One hydrolysis stabilizer can be used alone, or two or more can be used in combination.

Carbodiimide group-containing compounds include dicyclohexylcarbodiimide, diisopropylcarbodiimide, dimethylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, di-t-butylcarbodiimide, di-β-naphthylcarbodiimide, polycarbodiimide, and cyclic carbodiimides. The polycarbodiimide is a compound in which two or more carbodiimide groups are bonded together via a linking group composed of an aliphatic group, an alicyclic group, an aromatic group, or a combination thereof. The cyclic carbodiimide is a compound in which one or more carbodiimide groups are bonded together via a linking group composed of an aliphatic group, an alicyclic group, an aromatic group, or a combination thereof to form a ring structure, with the first and second nitrogen atoms of the carbodiimide groups bonded together. The linking group may contain heteroatoms or substituents.

The amount of hydrolysis stabilizer (preferably a carbodiimide group-containing compound) used is not particularly limited, but to ensure that the effects of the hydrolysis stabilizer are favorably expressed, it is suitably approximately 0.05 parts by weight or more per 100 parts by weight of the polymer (e.g., polyester or bifunctional polyol) contained in the adhesive composition, and preferably approximately 0.1 parts by weight or more, and may be, for example, approximately 0.3 parts by weight or more. The upper limit of the amount of the hydrolysis stabilizer used is suitably approximately 5 parts by weight or less per 100 parts by weight of the polymer, and preferably approximately 3 parts by weight or less, and may be, for example, 1 part by weight or less.

In addition to the components described above, the adhesive composition may optionally contain various additives commonly used in the field of adhesives, such as leveling agents, fillers, plasticizers, softeners, colorants (pigments, dyes, etc.), antistatic agents, antioxidants, UV absorbers, antioxidants, and light stabilizers. As the various additives described above are conventionally known and can be used in the usual manner, they do not particularly characterize the present invention, and therefore detailed description will be omitted.

<Non-volatile component content>
Although not particularly limited, in some embodiments, the content of non-volatile components in the PSA composition is preferably approximately 90% by weight or more. Thus, a PSA composition with a low content of volatile components such as organic solvents has a sufficiently reduced amount of organic solvent used, and can be used as a substantially solvent-free PSA composition. The content of non-volatile components in the PSA composition may be 92% by weight or more, or even 94% by weight or more. The upper limit of the content of non-volatile components in the PSA composition may be, for example, less than 99% by weight or 97% by weight or less, since volatile organic solvents and the like may be contained due to the materials used. In this specification, the non-volatile components in the PSA composition refer to components present in the PSA layer after formation (after drying and aging), typically components present in the PSA layer as a solid (solid content) after formation.

<Formation of Pressure-Sensitive Adhesive Layer>
A pressure-sensitive adhesive layer can be formed from a pressure-sensitive adhesive composition by a conventionally known method. For example, in the case of a substrate-less double-sided pressure-sensitive adhesive sheet, a pressure-sensitive adhesive composition can be applied (typically coated) to a surface (release surface) having releasability, and then the pressure-sensitive adhesive composition is cured to form a pressure-sensitive adhesive layer on the surface, thereby forming a pressure-sensitive adhesive sheet. In the case of a pressure-sensitive adhesive sheet with a substrate, a method of directly applying a pressure-sensitive adhesive composition to the substrate and curing the composition to form a pressure-sensitive adhesive layer (direct method) can be preferably used. Alternatively, a method of applying a pressure-sensitive adhesive composition to a surface (release surface) having releasability and curing the composition to form a pressure-sensitive adhesive layer on the surface, and then transferring the pressure-sensitive adhesive layer to a substrate (transfer method) can also be used. The release surface can be the surface of a release liner, the back surface of a release-treated substrate, or the like. The pressure-sensitive adhesive composition can be cured by subjecting the pressure-sensitive adhesive composition to a curing treatment such as drying, crosslinking, polymerization, or cooling. Two or more curing treatments can be performed simultaneously or in stages. The pressure-sensitive adhesive layer disclosed herein is typically formed continuously, but is not limited to such a form, and may be a pressure-sensitive adhesive layer formed in a regular or random pattern such as a dotted or striped pattern.

The adhesive composition can be applied using a known or conventional coater, such as a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, die coater, comma coater, bar coater, knife coater, or spray coater. Alternatively, the adhesive composition may be applied by impregnation or curtain coating. The adhesive composition disclosed herein can be applied effectively without relying on heating (i.e., at a temperature roughly the same as the ambient temperature at which the application is performed, for example, about 10 to 40°C), and in a form that is substantially free of organic solvents (specifically, ethyl acetate and toluene) added for dilution purposes.

The pressure-sensitive adhesive composition is preferably dried under heating to promote the crosslinking reaction and improve manufacturing efficiency. In some embodiments, the drying temperature is suitably, for example, approximately 80°C or higher, typically approximately 100°C or higher, and may be 120°C or higher. The upper limit of the heating temperature is not particularly limited, but is suitably approximately 200°C or lower, preferably approximately 180°C or lower, and may be approximately 160°C or lower, approximately 150°C or lower, or approximately 130°C or lower. Setting the heating temperature within an appropriate range is preferable, for example, in embodiments in which the pressure-sensitive adhesive composition is dried on a substrate, as this can prevent thermal degradation of the substrate. After drying the pressure-sensitive adhesive composition, it is preferable to further perform aging for the purposes of adjusting component migration within the pressure-sensitive adhesive layer, promoting the crosslinking reaction, and alleviating distortion that may exist within the substrate or pressure-sensitive adhesive layer. The aging conditions are not particularly limited, and can be, for example, approximately 70°C or lower (typically approximately 20-70°C) for one day or more (e.g., three days or more).

≪Base material≫
The material of the support substrate used as the support of the pressure-sensitive adhesive sheet disclosed herein is not particularly limited, and for example, a resin film can be preferably used. The resin film can be formed by molding various resin materials into a film shape. The resin material is preferably one that can form a resin film excellent in one or more of the following properties: transparency, mechanical strength, thermal stability, moisture barrier properties, isotropy, etc. For example, a resin film composed of a resin material whose main component (i.e., a component contained in more than 50% by weight) is polyesters such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate; celluloses such as diacetyl cellulose and triacetyl cellulose; polycarbonates; acrylic polymers such as polymethyl methacrylate; etc. can be preferably used as the substrate. Other examples of resin materials constituting the resin film include those primarily composed of styrene-based polymers such as polystyrene and acrylonitrile-styrene copolymer; polyolefins such as polyethylene, polypropylene, polyolefins having a cyclic or norbornene structure, ethylene-propylene copolymer, etc.; polyvinyl chlorides; and polyamides such as nylon 6, nylon 6,6, and aromatic polyamides. Alternatively, a resin film composed of a resin material primarily composed of polyimides, polysulfones, polyethersulfones, polyetheretherketones, polyphenylene sulfides, fluorine-based resins, polyvinyl alcohols, polyvinyl acetates, polyvinylidene chlorides, polyvinyl butyrals, polyarylates, polyoxymethylenes, epoxy resins, etc. may be used as the substrate. The resin material constituting the resin film may be a blend of two or more of these.

In this specification, the term "resin film" refers to a resin film that has a non-porous structure and typically contains substantially no air bubbles (void-free). Therefore, the above-mentioned resin film is a concept that is distinct from foam films, nonwoven fabrics, and woven fabrics.

Other examples of substrates include foam sheets made from foams such as polyurethane foam, polyethylene foam, and polychloroprene foam; woven and nonwoven fabrics made from various fibrous materials (which can be natural fibers such as hemp and cotton, synthetic fibers such as polyester and vinylon, and semi-synthetic fibers such as acetate), either alone or in combination; papers such as Japanese paper, fine paper, kraft paper, and crepe paper; metal foils such as aluminum foil and copper foil; and glass. Substrates with a composite structure of these materials are also possible. Examples of substrates with such a composite structure include substrates in which metal foil and the above-mentioned plastic film are laminated together, and plastic sheets reinforced with inorganic fibers such as glass cloth.

The substrate may be formed from a biologically-derived material or a non-biologically-derived material. From the perspective of producing a PSA sheet that takes into consideration reducing dependence on fossil resource-derived materials, biologically-derived substrate materials (typically resin films) are preferably used.

The substrate may also be formed using recyclable or recycled materials (also referred to as recycled materials). Resin films are preferably used as such recycled materials. Resin films (for example, polyester films such as PET film) are recyclable, so regardless of whether they use biological materials or not, reusing used resin films allows for sustainable reproduction and reduces the environmental burden. Such recyclable or recycled resin films are also referred to as recycled films. The above-mentioned recycled materials (for example, recycled films) may be formed from biological or non-biological materials.

In some preferred embodiments, the substrate is a resin film (polyester resin film) formed from a resin (polyester resin) whose main component is polyester (a component contained in greater than 50% by weight). For example, a resin film in which the polyester is primarily PET (PET film) or a resin film in which the polyester is primarily PEN (PEN film) can be preferably used.

The substrate may have a single-layer structure or a multi-layer structure. Therefore, the resin film that can be used as the substrate may also have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure). A resin film with a single-layer structure is preferably used as the substrate.

The above-mentioned substrate (typically a resin film) may contain various additives, such as fillers, antioxidants, antioxidants, UV absorbers, antistatic components, plasticizers, colorants (pigments, dyes, etc.), etc., as needed.

The surface of the substrate facing the adhesive layer may be subjected to a surface treatment such as chromate treatment, ozone exposure, flame exposure, high-voltage shock exposure, or ionizing radiation treatment. Such surface treatments may be intended to enhance adhesion between the substrate and the adhesive layer. In some embodiments, the surface of the substrate facing the adhesive layer may be subjected to a primer treatment. In some embodiments, the back surface of the substrate may be subjected to a hard coat treatment. This improves the scratch resistance of the back surface of the substrate, and when the adhesive sheet is used as a protective sheet, it may exhibit superior protective performance. In other embodiments, the substrate may be subjected to an antistatic treatment in order to suppress the generation of static electricity. The substrate may also be subjected to various treatments such as antifouling, antifingerprint, antiglare, and antireflection.

The thickness of the substrate can be selected appropriately taking into consideration the application, purpose, and usage form of the pressure-sensitive adhesive sheet. Typically, the thickness of the substrate is selected from a range of approximately 1 to 1,000 μm. In some embodiments, from the perspective of workability such as strength and ease of handling, a substrate thickness of approximately 10 μm or more is appropriate, and this thickness is preferably approximately 30 μm or more, and may be approximately 50 μm or more (e.g., 70 μm or more). In some embodiments, from the perspective of cost, etc., the thickness of the substrate is appropriate to be approximately 500 μm or less, preferably approximately 300 μm or less, more preferably approximately 150 μm or less, and may be approximately 100 μm or less (e.g., less than 100 μm). Substrates having the above thicknesses are suitable, for example, as substrates for surface protection films.

<Total thickness>
The thickness (total thickness) of the PSA sheet disclosed herein (which includes a PSA layer, and in the case of a PSA sheet with a substrate, which further includes a substrate but does not include a release liner) is not particularly limited, and can be, for example, in the range of approximately 2 μm to 1000 μm. In some embodiments, the thickness of the PSA sheet is preferably about 5 μm to 500 μm (e.g., 10 μm to 300 μm, typically 15 μm to 200 μm), taking into consideration adhesive properties and the like. The lower limit of the thickness of the PSA sheet is not particularly limited, and may be, for example, approximately 30 μm or more, approximately 50 μm or more, or approximately 100 μm or more.

<Adhesive properties>
The pressure-sensitive adhesive sheet disclosed herein may have strong adhesive strength for bonding purposes, or may have relatively low adhesive strength so that it can be peeled (removed) from an adherend, such as for surface protection applications. Although not particularly limited, in some embodiments, the pressure-sensitive adhesive sheet preferably has a peel strength (glass peel strength) against a glass plate measured under conditions of a temperature of 23°C, a peel angle of 180°, and a tensile speed of 300 mm/min of 1.0 N/25 mm or less. A pressure-sensitive adhesive sheet that satisfies this characteristic exhibits a low peel strength when peeled from an adherend (e.g., an object to be protected), making it easy to peel. From the viewpoint of peeling workability, the glass peel strength is more preferably less than 1.0 N/25 mm, even more preferably 0.5 N/25 mm or less, and particularly preferably 0.1 N/25 mm or less (e.g., less than 0.1 N/25 mm). From the viewpoint of adhesion to the adherend and protection of the adherend, the glass peel strength is suitably 0.01 N/25 mm or more, and may be 0.03 N/25 mm or more, or may be 0.05 N/25 mm or more. Specifically, the glass peel strength is measured by the method described in the Examples below. When a pressure-sensitive adhesive sheet is produced and the glass peel strength is evaluated, the pressure-sensitive adhesive sheet is produced and then left to stand in an environment of 22°C and 50% RH for 3 days, and then the measurement is carried out.

≪Applications≫
The pressure-sensitive adhesive sheet disclosed herein can be used for various applications. For example, it is suitable as a surface protection film that is attached to an object to be protected and, after achieving its protective purpose, is peeled off (removed) from the object to be protected. The pressure-sensitive adhesive sheet disclosed herein can exhibit good cutting properties while satisfying the properties required of a surface protection film (wettability when attached to an adherend, easy peelability, low contamination). The pressure-sensitive adhesive sheet disclosed herein is preferably used as a surface protection film that is cut to fit the size and shape of the object to be protected. The object to be protected by the surface protection film is not particularly limited, and it can be used as a protective film for various products, parts, etc. For example, the surface protection film is particularly suitable as a surface protection film that protects the surface of optical components (e.g., optical components used as components of liquid crystal display panels, such as polarizing plates and wavelength plates) during processing and transportation of the optical components.

Furthermore, the pressure-sensitive adhesive sheet disclosed herein is transparent yet has good cutting properties, making it useful as a surface protection film for optical applications where transparency is required during inspection of adherends. More specifically, the surface protection film is suitable for protecting optical components used as components of liquid crystal display panels, plasma display panels (PDPs), organic electroluminescence (EL) displays, etc., during their manufacture, transportation, etc. In particular, it is useful as a surface protection film applied to optical components such as polarizing plates (polarizing films, e.g., reflective polarizing films) for liquid crystal display panels, wave plates, retardation plates, optical compensation films, brightness enhancement films, light diffusion sheets, and reflective sheets. Furthermore, the pressure-sensitive adhesive sheet can be attached to components that constitute products such as electronic devices, and can be used for purposes such as fixing, joining, and reinforcing components.

Furthermore, in some embodiments, the adhesive sheets disclosed herein can be formed from biologically derived materials, thereby contributing to reduced dependency on fossil resource-based materials. The adhesive sheets disclosed herein can typically be preferably used as adhesive sheets with reduced dependency on fossil resource-based materials.

The matters disclosed by this specification include the following:
[1] A pressure-sensitive adhesive layer that is substantially free of ethyl acetate and toluene,
The pressure-sensitive adhesive layer has a breaking strain in the range of 210% to 1500% and a tan δ at 80° C. in the range of 0.046 to 0.300.
[2] The pressure-sensitive adhesive sheet according to the above [1], wherein the pressure-sensitive adhesive layer has a gel fraction of 70% or more.
[3] The pressure-sensitive adhesive sheet according to [1] or [2] above, wherein the pressure-sensitive adhesive layer has a breaking strain in the range of 400% to 1500% and a tan δ at 80° C. in the range of 0.096 to 0.300.
[4] The pressure-sensitive adhesive sheet according to any one of [1] to [3] above, wherein the pressure-sensitive adhesive layer contains at least one selected from polyesters and polyols.
[5] The pressure-sensitive adhesive sheet according to any one of [1] to [4] above, wherein the pressure-sensitive adhesive layer further contains an isocyanate-based crosslinking agent.
[6] The pressure-sensitive adhesive sheet according to the above [5], wherein the isocyanate-based crosslinking agent includes a bifunctional isocyanate-based crosslinking agent.
[7] The pressure-sensitive adhesive sheet according to any one of [1] to [6] above, wherein the pressure-sensitive adhesive layer contains a polyol having a number average molecular weight in the range of 200 or more and 20,000 or less.
[8] The pressure-sensitive adhesive sheet according to any one of [1] to [7] above, which is used as a surface protection film.

Several examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples. In the following description, "parts" and "%" are by weight unless otherwise specified.

<Example 1>
A four-neck separable flask equipped with a stirrer, thermometer, and vacuum pump was charged with 28 g of dimer acid (trade name "PRIPOL 1009", manufactured by Cargill, weight average molecular weight 567, trimer acid content 1%) as the dicarboxylic acid, 233 g of polyether diol (trade name "SANNICS PL-2100", manufactured by Sanyo Chemical Industries, Ltd., number average molecular weight 2400) as the diol (molar ratio of the dicarboxylic acid to the diol: 1.00:1.80), and 0.25 g of tetra-normal-butyl titanate (trade name "ORGATIX TA21", manufactured by Matsumoto Fine Chemical Co., Ltd.) as the polymerization catalyst. The mixture was heated to 200°C while stirring in a reduced pressure atmosphere (0.002 MPa) and maintained at this temperature. The reaction was continued for approximately 4 hours to obtain Polyester A1. The weight average molecular weight (Mw) of this polyester A1 was 17,000, and the glass transition temperature (Tg) was -69°C.

100 parts of the resulting polyester were blended with 1.1 parts of polyether polyol (trade name "EXCENOL 430", manufactured by AGC, polypropylene glycol, number average molecular weight 400, functionality 3) as polyol B1, 12.3 parts of a bifunctional isocyanate compound (trade name "Duranate D101", manufactured by Asahi Kasei Corporation, a derivative of 1,6-hexamethylene diisocyanate) as crosslinking agent C1, 0.1 parts of zirconium tetraacetylacetonate (trade name "Orgatix ZC-150", manufactured by Matsumoto Fine Chemical Co., Ltd.) as a crosslinking catalyst, and 10 parts of acetylacetone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain a pressure-sensitive adhesive composition.

The above adhesive composition was applied to a polyethylene terephthalate (PET) film substrate (trade name "T100-75S", manufactured by Mitsubishi Chemical Corporation, thickness 75 μm) so that the dried thickness was 75 μm, and then dried at 130°C for 2 minutes. The release-treated surface of a release-treated PET film (trade name "Diafoil MRE38", manufactured by Mitsubishi Chemical Corporation) was then laminated onto the coated film. The adhesive sheet according to this example (a single-sided adhesive sheet having an adhesive layer on a substrate) was obtained by leaving the coated film at 22°C and 50% RH for 3 days.

<Examples 2 to 14>
In preparing the pressure-sensitive adhesive compositions, the pressure-sensitive adhesive compositions of each example were obtained in the same manner as in Example 1, except that the type and amount of polyol and the type and amount of crosslinking agent were changed as shown in Table 2, and the pressure-sensitive adhesive compositions were used to obtain pressure-sensitive adhesive sheets of each example.
The materials shown in Table 2 are as follows:
Polyol B2: Polyether polyol manufactured by AGC (trade name "EXCENOL 230", polypropylene glycol, number average molecular weight 3000, number of functional groups 3)
Polyol B3: Polyether polyol manufactured by AGC (trade name "EXCENOL 828", polypropylene glycol, number average molecular weight 5000, number of functional groups 3)
Polyol B4: Polyether polyol manufactured by AGC (trade name "PREMINOL7012", polypropylene glycol, number average molecular weight 10,000, number of functional groups 3)
Crosslinking agent C2: a trifunctional isocyanate compound manufactured by Mitsui Chemicals, Inc. (trade name "Stabio D-370N", a derivative of 1,5-pentamethylene diisocyanate)

<Example 15>
10.0 parts of a polyether polyol (trade name "EXCENOL 230", manufactured by AGC, number average molecular weight 3,000, number of functional groups 3) as polyol B2, 100.0 parts of a polyether polyol (trade name "PREMINOL 7012", manufactured by AGC, number average molecular weight 10,000, number of functional groups 3) as polyol B4, and 100.0 parts of a polyether polyol (trade name "PREMINOL 5005", manufactured by AGC) as polyol B5. A pressure-sensitive adhesive composition was obtained by blending 100.0 parts of a copolymer of 1,2-dimethylaminopropyl methyl acrylate (a copolymer of 1,2-dimethylaminopropyl methyl acrylate and 1,2-dimethylaminopropyl methyl acrylate) having a number average molecular weight of 4,000 and a functionality of 2, 18.0 parts of a bifunctional isocyanate compound (trade name "Duranate D101", manufactured by Asahi Kasei Corporation) as a crosslinking agent C1, 0.1 parts of zirconium tetraacetylacetonate (trade name "Orgatix ZC-150", manufactured by Matsumoto Fine Chemical Co., Ltd.) as a crosslinking catalyst, and 10 parts of acetylacetone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). A pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1, except that the pressure-sensitive adhesive composition obtained was used.

<Example 16>
A four-neck separable flask was equipped with a stirrer, thermometer, and vacuum pump. 40 g of dimer acid (trade name "PRIPOL 1009", manufactured by Cargill, weight average molecular weight 567, trimer acid content 1%) as the dicarboxylic acid, 212 g of polyether diol (trade name "SANNICS PL-2100", manufactured by Sanyo Chemical Industries, Ltd., number average molecular weight 2400) as the diol (molar ratio of the dicarboxylic acid to the diol: 1.00:1.20), and 0.25 g of tetra-normal-butyl titanate (trade name "ORGATIX TA21", manufactured by Matsumoto Fine Chemical Co., Ltd.) as the polymerization catalyst were charged, and the mixture was heated to 200 ° C. while stirring in a reduced pressure atmosphere (0.002 MPa) and maintained at this temperature. The reaction was continued for approximately 4 hours, yielding polyester A2. The Mw of this polyester A2 was 30,000 and the Tg was -68 ° C.

A pressure-sensitive adhesive composition was obtained by blending 100 parts of the obtained polyester with 8.5 parts of a trifunctional isocyanate compound (product name "STABIO D-370N", manufactured by Mitsui Chemicals, Inc.) as crosslinking agent C2, 0.1 parts of zirconium tetraacetylacetonate (product name "ORGATIX ZC-150", manufactured by Matsumoto Fine Chemical Co., Ltd.) as a crosslinking catalyst, and 10 parts of acetylacetone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). A pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1, except for using the obtained pressure-sensitive adhesive composition.

<Example 17>
A four-neck separable flask was equipped with a stirrer, a thermometer, and a vacuum pump. 90 g of bis(hydroxyethyl) terephthalate (manufactured by Tokyo Chemical Industry Co., Ltd., molecular weight 254) as a dicarboxylic acid, 75 g of dimer diol (trade name "PRIPOL 2033", manufactured by Cargill, weight average molecular weight 152), 92 g of polyether glycol (trade name "BioPTMG650", manufactured by Mitsubishi Chemical Corporation, number average molecular weight 650) (molar ratio of the above dicarboxylic acid: dimer diol: polyether glycol: 1.00: 1.40: 0.40), and 0.26 g of tetra-normal butyl titanate (trade name "Orgatix TA21", manufactured by Matsumoto Fine Chemical Co., Ltd.) as a polymerization catalyst were charged, and the mixture was stirred in a reduced pressure atmosphere (0.002 MPa). The temperature was raised to 200 ° C. and maintained at this temperature. The reaction was continued for about 4 hours to obtain polyester A3. The Mw of this polyester A3 was 5,500 and the Tg was -45°C.

A pressure-sensitive adhesive composition was obtained by blending 100 parts of the obtained polyester with 14.0 parts of a bifunctional isocyanate compound (trade name "Duranate D101", manufactured by Asahi Kasei Corporation) as crosslinking agent C1, 11.0 parts of a trifunctional isocyanate compound (trade name "Stabio D-370N", manufactured by Mitsui Chemicals, Inc.) as crosslinking agent C2, 0.1 parts of zirconium tetraacetylacetonate (trade name "Orgatix ZC-150", manufactured by Matsumoto Fine Chemical Co., Ltd.) as a crosslinking catalyst, and 10 parts of acetylacetone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). A pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1, except for using the obtained pressure-sensitive adhesive composition.

<Example 18>
A four-neck separable flask equipped with a stirrer, thermometer, and vacuum pump was charged with 200 g of dimer acid (trade name "PRIPOL 1009" manufactured by Cargill, weight-average molecular weight 567, trimer acid content 1%) as a dicarboxylic acid, 40 g of 1,4-butanediol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., molecular weight 90) as a diol (molar ratio of the dicarboxylic acid to the diol: 1.00:1.25), and 0.24 g of tetra-n-butyl titanate (trade name "Orgatix TA21" manufactured by Matsumoto Fine Chemical Co., Ltd.) as a polymerization catalyst. The mixture was heated to 200°C with stirring under reduced pressure (0.002 MPa) and maintained at this temperature. The reaction was continued for approximately 4 hours to obtain Polyester A4. The Mw of this Polyester A4 was 24,000 and the Tg was -52°C.

100 parts of the resulting polyester were blended with 30.0 parts of polyether diol (trade name "Sannyx PL-2100", manufactured by Sanyo Chemical Industries, Ltd., number average molecular weight 2400, functionality 2) as polyol B6, 4.5 parts of a bifunctional isocyanate compound (trade name "Duranate D101", manufactured by Asahi Kasei Corporation) and 12.5 parts of a trifunctional isocyanate compound (trade name "Coronate HX", manufactured by Tosoh Corporation) as crosslinking agents C1 and C3, respectively, 0.1 parts of zirconium tetraacetylacetonate (trade name "Orgatix ZC-150", manufactured by Matsumoto Fine Chemical Co., Ltd.) as a crosslinking catalyst, and 10 parts of acetylacetone (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) to obtain a pressure-sensitive adhesive composition. A pressure-sensitive adhesive sheet according to this example was obtained in the same manner as in Example 1, except for using the resulting pressure-sensitive adhesive composition.

<Example 19>
In preparing the adhesive composition, 6.0 parts of polyether diol (trade name "Sannyx PP-400", manufactured by Sanyo Chemical Industries, Ltd., number average molecular weight 400, functionality 2) was used as polyol B7 instead of 30.0 parts of "Sannyx PL-2100", and the amounts of a bifunctional isocyanate compound (trade name "Duranate D101", manufactured by Asahi Kasei Corporation) and a trifunctional isocyanate compound (trade name "Coronate HX", manufactured by Tosoh Corporation) used were changed to 6.4 parts and 10.7 parts, respectively. Otherwise, the adhesive composition according to this example was obtained in the same manner as in Example 18, and an adhesive sheet according to this example was obtained using this adhesive composition.

<Evaluation>
(Gel fraction)
A 38 μm thick PET film (trade name "Diafoil MRF38", manufactured by Mitsubishi Chemical Corporation) with a release treatment on one side was prepared. The adhesive composition immediately after blending was applied to the release-treated surface and dried at 130 ° C for 2 minutes to form a 75 μm thick adhesive layer. The surface of the resulting adhesive layer was covered with a 38 μm thick PET film (trade name "Diafoil MRE38", manufactured by Mitsubishi Chemical Corporation) with a release treatment on one side, with the release-treated surface facing the adhesive layer, and the film was left standing at 22 ° C and 50% RH for 3 days. Next, 1 g of W was removed from the adhesive layer (the amount of adhesive layer was approximately 0.1 g) and wrapped in a porous PTFE (polytetrafluoroethylene) sheet to prepare a sample. The sample was placed in a glass bottle, immersed in toluene, and left standing at 23 ° C for 7 days, after which the sample was removed and dried at 130 ° C for 2 hours. The dried sample was weighed, and the weight of the porous PTFE sheet was subtracted therefrom to determine the weight of the PSA after drying, W2g. W1 and W2 were substituted into the following formula to calculate the gel fraction [%].
Gel fraction [%] = (W2/W1) x 100
As the porous PTFE sheet, a product under the trade name "TEMISH" manufactured by Nitto Denko Corporation or an equivalent product can be used.

(breaking strain)
A 38 μm thick PET film (trade name "Diafoil MRF38", manufactured by Mitsubishi Chemical Corporation) with a release treatment on one side was prepared, and the pressure-sensitive adhesive composition immediately after blending was applied to the release-treated surface. The composition was then dried at 130°C for 2 minutes to form a 75 μm thick pressure-sensitive adhesive layer. The surface of the resulting pressure-sensitive adhesive layer was then covered with a 38 μm thick PET film (trade name "Diafoil MRE38", manufactured by Mitsubishi Chemical Corporation) with a release treatment on one side, with the release-treated surface facing the pressure-sensitive adhesive layer. The film was then left to stand at 22°C and 50% RH for 3 days. The pressure-sensitive adhesive layer was then cut into 10 mm x 40 mm pieces, and the release-treated PET film was peeled off to prepare 40 mm long strip samples. The upper and lower 10 mm portions were fixed in the chuck of a tension and compression tester (product name "Autograph AGX-V2", manufactured by Shimadzu Corporation), and the sample was elongated until it broke under conditions of 22°C, 50% RH, a chuck distance of 20 mm, and a tension speed of 300 mm/min. The breaking strain was calculated from the measurement results.
Breaking strain [%] = (elongation at break / chuck distance 20 mm) x 100

(80°C tan δ and Tg)
A 38 μm thick PET film (trade name "Diafoil MRF38", manufactured by Mitsubishi Chemical Corporation) with a release treatment on one side was prepared, and the pressure-sensitive adhesive composition immediately after blending was applied to the release-treated surface. The composition was then dried at 130°C for 2 minutes to form a 75 μm thick pressure-sensitive adhesive layer. The surface of the resulting pressure-sensitive adhesive layer was then covered with a 38 μm thick PET film (trade name "Diafoil MRE38", manufactured by Mitsubishi Chemical Corporation) with a release treatment on one side, with the release-treated surface facing the pressure-sensitive adhesive layer. The film was then left to stand at 22°C and 50% RH for 3 days. The pressure-sensitive adhesive layer was then cut into 5 mm x 50 mm pieces, and the release-treated PET film was peeled off to prepare 50 mm long strip samples. Using a dynamic viscoelasticity measuring device (trade name "RSA-G2", manufactured by TA Instruments), the storage modulus E', loss modulus E" and loss tangent tanδ (loss modulus E"/storage modulus E') were measured under the following conditions, and tanδ at 80°C was determined. The temperature at the peak top of the loss tangent tanδ was taken as the glass transition temperature (Tg) [°C].
Load mode: tension Loading gap: 20 mm
- Temperature range: -80℃ to 100℃
Temperature increase rate: 5°C/min
Frequency: 1 Hz
Initial strain: 0.1%
The storage modulus E' corresponds to the portion stored as elastic energy when the material is deformed, and is an index representing the degree of hardness. The loss modulus E'' corresponds to the portion of energy lost that is dissipated due to internal friction, etc. when the material is deformed, and represents the degree of viscosity.

(peel strength against glass)
At an ambient temperature of 23°C, the release-treated PET film was peeled off from the surface of the adhesive layer of a pressure-sensitive adhesive sheet cut to a size of 25 mm wide x 140 mm long, and the sheet was attached to a glass plate (soda-lime glass, manufactured by Matsunami Glass Industry Co., Ltd.) as an adherend by rolling a 2 kg hand roller back and forth once to obtain an evaluation sample. After leaving the sample at the same ambient temperature for 30 minutes, the evaluation sample was placed in a tensile tester (manufactured by Kyowa Interface Science Co., Ltd., product name "VPA-H200") under the same environment, and the load when the pressure-sensitive adhesive sheet was peeled from the glass plate under conditions of a peel angle of 180° and a tensile speed of 300 mm/min was measured, and the average load was taken as the glass peel strength [N/25 mm].

(Cutting)
The release-treated PET film was peeled off from the surface of the adhesive layer of a 25 mm wide x 140 mm long adhesive sheet, and at room temperature (23°C), a cut was made in the center of the adhesive sheet at an angle of approximately 30 degrees, at a speed of approximately 3000 mm/min, and over a length of approximately 1 cm using a cutter knife (product name "Universal L-type 11B", manufactured by Olfa Corporation). The amount of glue residue generated was visually confirmed, and the cuttability was evaluated according to the following criteria.
⊚: No generation of glue residue was observed.
◯: A small amount of glue residue was generated, but it was at a level that did not cause any practical problems.
×: A large amount of glue residue was generated.

(cohesive force)
At an ambient temperature of 23°C, the adhesive surface of a measurement sample was exposed by cutting the pressure-sensitive adhesive sheet to a width of 25 mm and a length of 100 mm, and the sample was pressed against a glass plate (soda-lime glass, manufactured by Matsunami Glass Industry Co., Ltd.) using a 2 kg hand roller, with one reciprocating motion. The measurement sample thus pressed against the adherend was then left at the same ambient temperature for 30 minutes, and then the pressure-sensitive adhesive sheet was peeled from the adherend using a tensile tester (manufactured by Kyowa Interface Science Co., Ltd., product name "VPA-H200") at a peel angle of 180° and a tensile speed of 300 mm/min. At this time, it was visually confirmed whether the pressure-sensitive adhesive layer underwent cohesive failure, and the cohesive strength was evaluated according to the following criteria.
⊚: No cohesive failure was observed.
◯: Cohesive failure was observed, but at a level that does not pose a problem in practical use.

An overview of each example and the evaluation results are shown in Table 2.

As shown in Table 2, among Examples 1 to 19 of PSA sheets having a PSA layer substantially free of ethyl acetate and toluene, Examples 1 to 2, 4 to 5, 7, 9 to 11, and 13 to 15, in which the PSA layer had a breaking strain within the range of 210% to 1500% and a tan δ at 80°C within the range of 0.046 to 0.300, passed the cutability evaluation and also achieved acceptable levels of cohesion. Of these, Examples 2, 5, 10 to 11, and 13 to 15 had a high gel fraction of 70% or more, achieving a good balance between cutability and cohesion. On the other hand, Examples 3, 6, 8, 12, and 16 to 19 did not satisfy at least one of the conditions of a PSA layer breaking strain within the range of 210% to 1500% and a tan δ at 80°C within the range of 0.046 to 0.300, and all failed the cutability evaluation. These results show that in order to achieve good cuttability, it is important that the breaking strain of the adhesive layer is within the range of 210% to 1500% and that tanδ at 80°C is within the range of 0.046 to 0.300.

Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above.

1 Pressure-sensitive adhesive sheet 10 Supporting substrate 10A First surface 10B Second surface (rear surface)
21 adhesive layer 21A adhesive surface 31 release liner 100 adhesive sheet with release liner

Claims (8)

a pressure-sensitive adhesive layer that is substantially free of ethyl acetate and toluene,
The pressure-sensitive adhesive layer has a breaking strain in the range of 210% to 1500% and a tan δ at 80° C. in the range of 0.046 to 0.300. The adhesive sheet of claim 1, wherein the gel fraction of the adhesive layer is 70% or more. The adhesive sheet of claim 1 or 2, wherein the adhesive layer has a breaking strain in the range of 400% to 1500% and a tan δ at 80°C in the range of 0.096 to 0.300. The pressure-sensitive adhesive sheet according to claim 1 or 2, wherein the pressure-sensitive adhesive layer contains at least one selected from polyester and polyol. The adhesive sheet of claim 4, wherein the adhesive layer further contains an isocyanate-based crosslinking agent. The pressure-sensitive adhesive sheet according to claim 5, wherein the isocyanate-based crosslinking agent includes a bifunctional isocyanate-based crosslinking agent. The adhesive sheet according to claim 1 or 2, wherein the adhesive layer contains a polyol having a number average molecular weight in the range of 200 or more and 20,000 or less. The pressure-sensitive adhesive sheet according to claim 1 or 2, which is used as a surface protection film.