WO2024185366A1 - Adhesive, adhesive sheet, and optical film with adhesive layer - Google Patents

Abstract

This adhesive for optical applications contains a silane coupling agent having an acid anhydride group as an organic functional group, the adhesive having a loss elastic modulus G'' at 25°C of 0.012 MPa or more. The silane coupling agent is preferably a silane compound represented by general formula (I) (in the formula, R represents a hydrocarbon group having 1-6 carbon atoms, n is an integer of 2-8, m is an integer of 1-3, l is an integer of 1-3, k is an integer of 0-2, and k + l + m = 4). This adhesive demonstrates excellent durability even when formed into a thin layer.

Description

Adhesive, adhesive sheet, and optical film with adhesive layer

The present invention relates to adhesives and adhesive sheets for optical applications, as well as optical films with adhesive layers.

In recent years, image display devices such as liquid crystal displays have come to be used frequently as displays for various electronic devices, but recently there has been an increase in the use of organic electroluminescence (organic EL) displays (OLEDs).

Displays like the one above are manufactured by stacking various optical components. Examples of optical components include polarizing plates and retardation films, which are adhered and stacked using adhesives.

The above-mentioned adhesive may be used in the form of an adhesive layer of an adhesive sheet. An example of an adhesive sheet used for laminating optical components is disclosed in Patent Document 1.

JP 2022-021888 A

In recent years, as mobile electronic devices have become thinner, there has been a demand for thinner adhesive layers. In particular, there is a strong demand for thinner adhesive layers in organic EL displays. However, when the adhesive layer is made thinner, the adhesive strength tends to decrease, and durability becomes an issue.

The present invention was made in consideration of these circumstances, and aims to provide an adhesive, an adhesive sheet, and an optical film with an adhesive layer that have excellent durability even when the adhesive layer is made thin.

In order to achieve the above object, first, the present invention provides an adhesive for optical applications, which contains a silane coupling agent having an acid anhydride group as an organic functional group, and has a loss modulus G" of 0.012 MPa or more at 25°C (Invention 1).

The adhesive according to the above invention (Invention 1) has high viscosity due to the loss modulus G" being the above value, and due to this high viscosity and the inclusion of the above specific silane coupling agent, the adhesive layer has high adhesive strength and excellent durability even when made thin.

（式中、Ｒは炭素数１～６の炭化水素基を示し、ｎは２～８、ｍは１～３、ｌは１～３、ｋは０～２の整数であり、ｋ＋ｌ＋ｍ＝４である。）
で表されるシラン化合物であることが好ましい（発明２）。 In the above invention (Invention 1), the silane coupling agent is represented by the following general formula (I):

(In the formula, R represents a hydrocarbon group having 1 to 6 carbon atoms, n represents an integer of 2 to 8, m represents an integer of 1 to 3, l represents an integer of 1 to 3, k represents an integer of 0 to 2, and k+l+m=4.)
It is preferable that the silane compound is represented by the following formula (Invention 2).

In the above inventions (Inventions 1 and 2), it is preferable that the storage modulus G' at 25°C is 0.09 MPa or more and 2 MPa or less (Invention 3).

In the above inventions (Inventions 1 to 3), it is preferable that the loss tangent tan δ at 25°C is 0.14 or more (Invention 4).

In the above inventions (Inventions 1 to 4), it is preferable that the adhesive is an acrylic adhesive (Invention 5).

In the above inventions (Inventions 1 to 5), it is preferable that the adhesive base is a (meth)acrylic acid ester polymer or a crosslinked product thereof (Invention 6).

In the above inventions (Inventions 1 to 6), it is preferable that the (meth)acrylic acid ester polymer contains, as a monomer unit constituting the polymer, a hard monomer having a glass transition temperature (Tg) of 0°C or higher as a homopolymer (Invention 7).

The above inventions (Inventions 1 to 7) are preferably for use in organic EL displays (Invention 8).

Secondly, the present invention provides an adhesive sheet for optical applications having at least an adhesive layer, characterized in that the adhesive constituting the adhesive layer is the adhesive described above (Inventions 1 to 8) (Invention 9).

In the above invention (Invention 9), it is preferable that the thickness of the adhesive layer is 0.1 μm or more and 30 μm or less (Invention 10).

In the above inventions (Inventions 9 and 10), it is preferable that the adhesive strength to non-alkali glass is 10 N/25 mm or more (Invention 11).

In the above inventions (Inventions 9 to 11), it is preferable that two release sheets are provided, and the adhesive layer is sandwiched between the release sheets so as to contact the release surfaces of the two release sheets (Invention 12).

In the above inventions (Inventions 9 to 12), it is preferable that the release sheet comprises a substrate and a release layer (Invention 13).

In the above inventions (Inventions 9 to 13), the release sheet may comprise a substrate, a release layer, and an antistatic layer located between the substrate and the release layer (Invention 14).

Thirdly, the present invention provides an optical film with an adhesive layer, characterized in that it comprises an optical film and an adhesive layer of the adhesive sheet (Inventions 9 to 14) laminated on at least one side of the optical film (Invention 15).

In the above invention (Invention 15), it is preferable that the thickness of the optical film is 1 μm or more and 150 μm or less (Invention 16).

In the above inventions (Inventions 15 and 16), it is preferable that the optical film is a polarizing plate or a retardation film (Invention 17).

The adhesive, adhesive sheet, and optical film with an adhesive layer according to the present invention have excellent durability even when the adhesive layer is made thin.

1 is a cross-sectional view of a pressure-sensitive adhesive sheet according to one embodiment of the present invention. 1 is a cross-sectional view of a pressure-sensitive adhesive layer-attached optical film according to one embodiment of the present invention.

Hereinafter, an embodiment of the present invention will be described.
[Adhesive]
The adhesive according to one embodiment of the present invention is used for optical applications and contains a silane coupling agent (hereinafter sometimes referred to as "silane coupling agent S") having an acid anhydride group as an organic functional group. The loss modulus G" of the adhesive at 25°C is preferably 0.012 MPa or more. The loss modulus G" is a physical property that is an index of viscosity among viscoelasticity, and the above value makes the adhesive according to this embodiment highly viscous. The adhesive according to the embodiment has such high viscosity and contains the above specific silane coupling agent S, so that even when the adhesive layer is thinned, it has high adhesive strength and excellent durability. In particular, even when a polarizing plate, a retardation film, or the like is used as an adherend, it exhibits excellent durability.

Specifically, even when a laminate obtained by bonding a 60 μm-thick polarizing plate and an alkali-free glass plate via a 10 μm-thick adhesive layer made of the adhesive according to this embodiment is placed under each of the durability conditions (1) to (3) below for 500 hours, the occurrence of lifting, peeling, etc. is suppressed. Note that in this specification, "relative humidity α%" may be expressed as "α% RH"(RH; Relative humidity).
(1) 85℃ dry
(2) 60℃・95%RH
(3) Heat shock from -40℃ for 30 minutes to 85℃ for 30 minutes

In addition, polarizing plates and retardation films, especially thin polarizing plates and retardation films, are very susceptible to shrinking under the above-mentioned durability conditions. Due to the shrinkage stress generated at that time, the laminate described above is prone to floating and peeling, but by using the adhesive according to this embodiment, the occurrence of floating and peeling is suppressed even if the adhesive layer is a thin film.

From the viewpoint of adhesive strength and durability, the loss modulus G" of the adhesive according to this embodiment at 25°C is more preferably 0.014 MPa or more, particularly preferably 0.016 MPa or more, even more preferably 0.018 MPa or more, and of these, preferably 0.019 MPa or more. From the viewpoint of suppressing bleeding of the adhesive and from the viewpoint of handling, the upper limit of the loss modulus G" is preferably 1 MPa or less, more preferably 0.5 MPa or less, particularly preferably 0.1 MPa or less, even more preferably 0.05 MPa or less, and of these, preferably 0.025 MPa or less. Here, the loss modulus G" and storage modulus G' in this specification are values measured by a torsional shear method at a measurement frequency of 1 Hz in accordance with JIS K7244-6. Specifically, they are as shown in the test examples described later.

The storage modulus G' at 25°C of the adhesive according to this embodiment is preferably 0.09 to 2 MPa, more preferably 0.10 to 1.2 MPa, particularly preferably 0.11 to 0.6 MPa, and even more preferably 0.12 to 0.3 MPa. Having a storage modulus G' at 25°C within the above range results in superior adhesive strength and durability in a thin film.

The loss tangent tan δ of the adhesive according to this embodiment at 25°C is preferably 0.14 or more, more preferably 0.15 or more, and even more preferably 0.16 or more. This provides better adhesive strength and durability in a thin film. From the viewpoint of suppressing bleeding of the adhesive and from the viewpoint of ease of handling, the upper limit of the loss tangent tan δ is preferably 1 or less, more preferably 0.8 or less, especially preferably 0.5 or less, and even more preferably 0.25 or less. The loss tangent tan δ is a value calculated as the ratio of the loss modulus G" to the storage modulus G' (loss modulus G"/storage modulus G').

（式中、Ｒは炭素数１～６の炭化水素基を示し、ｎは２～８、ｍは１～３、ｌは１～３、ｋは０～２の整数であり、ｋ＋ｌ＋ｍ＝４である。）
で表されるシラン化合物であることが好ましい。 The silane coupling agent S in this embodiment is represented by the following general formula (I):

(In the formula, R represents a hydrocarbon group having 1 to 6 carbon atoms, n represents an integer of 2 to 8, m represents an integer of 1 to 3, l represents an integer of 1 to 3, k represents an integer of 0 to 2, and k+l+m=4.)
It is preferable that the silane compound is represented by the following formula:

The hydrocarbon group of R is preferably an alkyl group, a vinyl group, or an aryl group, and is particularly preferably an alkyl group. The number of carbon atoms in the hydrocarbon group of R is preferably 1 to 5, more preferably 1 to 4, particularly preferably 1 to 3, even more preferably 1 to 2, and most preferably 1. n is preferably 1 to 6, more preferably 2 to 5, particularly preferably 2 to 4, even more preferably 2 to 3, and most preferably 2. m is preferably 1 to 2, and most preferably 1. l is preferably 1 to 3, more preferably 2 to 3, and most preferably 3. k is preferably 0 to 2, more preferably 0 to 1, and most preferably 0.

A specific example of the silane coupling agent represented by the general formula (I) is 2-trimethoxysilylethyl succinate anhydride represented by the following formula (II).

The content of silane coupling agent S in the adhesive according to this embodiment is preferably 0.01 to 10 mass%, more preferably 0.05 to 8 mass%, particularly preferably 0.1 to 6 mass%, even more preferably 0.3 to 4 mass%, and of these, preferably 0.5 to 2 mass%. This makes it easier for the adhesive to exhibit high adhesive strength even in a thin film. In particular, in combination with the viscoelastic properties described above, it makes it easier for the adhesive to exhibit excellent durability.

The adhesive according to this embodiment may be any of an acrylic adhesive, a polyester adhesive, a polyurethane adhesive, a rubber adhesive, a silicone adhesive, etc. Furthermore, the adhesive may be any of an emulsion type, a solvent type, or a solventless type, and may be any of a cross-linked type or a non-cross-linked type. Among these, an acrylic adhesive is preferred, as it has excellent adhesive properties, optical properties, etc.

The acrylic adhesive may be active energy ray curable, non-active energy ray curable, crosslinkable, non-crosslinkable, or a combination of these. Among these, from the viewpoint of making effective use of the effects of the silane coupling agent S described above, non-active energy ray curable acrylic adhesives are preferred. As non-active energy ray curable acrylic adhesives, crosslinkable types are particularly preferred, and thermal crosslinkable types are even more preferred.

The adhesive constituting the adhesive layer according to this embodiment preferably contains a (meth)acrylic acid ester polymer or a crosslinked product thereof as the adhesive main agent, and more specifically, is preferably obtained by crosslinking an adhesive composition (hereinafter sometimes referred to as "adhesive composition P") containing a (meth)acrylic acid ester polymer (A), a crosslinking agent (B), and a silane coupling agent (C). In this specification, (meth)acrylic acid means both acrylic acid and methacrylic acid. The same applies to other similar terms. In addition, the concept of "copolymer" is also included in "polymer".

(1) Components (1-1) (Meth)acrylic acid ester polymer (A)
The (meth)acrylic acid ester polymer (A) preferably contains, as a monomer unit constituting the polymer, a hard monomer having a glass transition temperature (Tg) of 0° C. or higher as a homopolymer. When the (meth)acrylic acid ester polymer (A) contains a component derived from the hard monomer, the (meth)acrylic acid ester polymer (A) is more likely to satisfy the above-mentioned viscoelastic properties such as the loss modulus G", and the adhesive strength and durability of the thin film are more excellent.

From the viewpoint of adhesive strength and durability in a thin film, the glass transition temperature (Tg) of the homopolymer of the hard monomer is preferably 2 to 250°C, more preferably 4 to 200°C, particularly preferably 6 to 150°C, even more preferably 8 to 100°C, and of these, preferably 9 to 50°C. This makes it easier for the resulting adhesive to satisfy the above-mentioned viscoelastic properties, and in combination with the specific silane coupling agent S, it tends to have high adhesive strength and excellent durability even when the adhesive layer is made thin.

The hard monomer is preferably an alkyl (meth)acrylate ester. This allows good adhesion to be achieved. The hard monomer is more preferably an alkyl (meth)acrylate ester having an alkyl group with 1 to 20 carbon atoms, particularly preferably an alkyl (meth)acrylate ester having an alkyl group with 1 to 12 carbon atoms, and even more preferably an alkyl (meth)acrylate ester having an alkyl group with 1 to 6 carbon atoms. This makes it easier to satisfy the values of the loss modulus G", storage modulus G', and loss tangent tan δ described above.

The above hard monomers include, for example, methyl acrylate (Tg 10°C), methyl methacrylate (Tg 105°C), ethyl methacrylate (Tg 65°C), n-butyl methacrylate (Tg 20°C), isobutyl methacrylate (Tg 48°C), t-butyl methacrylate (Tg 107°C), n-stearyl acrylate (Tg 30°C), n-stearyl methacrylate (Tg 38°C), and cyclohexyl acrylate (Tg 15°C). , cyclohexyl methacrylate (Tg 66° C.), phenoxyethyl acrylate (Tg 5° C.), phenoxyethyl methacrylate (Tg 54° C.), benzyl methacrylate (Tg 54° C.), isobornyl acrylate (Tg 94° C.), isobornyl methacrylate (Tg 180° C.), acryloylmorpholine (Tg 145° C.), adamantyl acrylate (Tg 115° C.), adamantyl methacrylate (Tg 141° C.), etc. These may be used alone or in combination of two or more. Among the above hard monomers, methyl acrylate (Tg 10°C), methyl methacrylate (Tg 105°C), phenoxyethyl acrylate (Tg 5°C), phenoxyethyl methacrylate (Tg 54°C), isobornyl acrylate (Tg 94°C), or acryloylmorpholine (Tg 145°C) are preferred from the viewpoint of their tendency to exhibit high adhesive strength, methyl acrylate (Tg 10°C) or methyl methacrylate (Tg 105°C) are more preferred from the viewpoint of making it easier to satisfy the above-mentioned viscoelastic properties, and methyl acrylate (Tg 10°C) is particularly preferred from the viewpoint of adhesive strength and durability in a thin film.

From the viewpoint of easily satisfying the loss modulus G" described above, the (meth)acrylic acid ester polymer (A) preferably contains 1 to 40 mass % of the structural units derived from the hard monomer, more preferably 4 to 35 mass %, particularly preferably 8 to 30 mass %, even more preferably 12 to 25 mass %, and of these, preferably 16 to 22 mass %. This makes it easier for the resulting adhesive to satisfy the above-mentioned viscoelasticity properties, and in combination with the specific silane coupling agent S, it tends to have high adhesive strength even when the adhesive layer is made thin, and to have excellent durability.

The (meth)acrylic acid ester polymer (A) preferably contains a soft monomer having a glass transition temperature (Tg) of less than 0°C as a homopolymer as a monomer unit constituting the polymer. The (meth)acrylic acid ester polymer (A) is flexible due to the inclusion of a component derived from the soft monomer, and an adhesive obtained from the polymer can exhibit good viscoelasticity and adhesiveness. From this viewpoint, the glass transition temperature (Tg) of the soft monomer as a homopolymer is preferably -100 to -10°C, more preferably -80 to -20°C, particularly preferably -70 to -30°C, further preferably -65 to -40°C, and of these, preferably -60 to -50°C.

The soft monomer is preferably an alkyl (meth)acrylate ester, more preferably an alkyl (meth)acrylate ester having 1 to 20 carbon atoms in the alkyl group, particularly preferably an alkyl (meth)acrylate ester having 1 to 16 carbon atoms in the alkyl group, and even more preferably an alkyl (meth)acrylate ester having 1 to 12 carbon atoms in the alkyl group.

Examples of the soft monomers include ethyl acrylate (Tg-20°C), n-butyl acrylate (Tg-55°C), isobutyl acrylate (Tg-26°C), n-octyl acrylate (Tg-65°C), isooctyl acrylate (Tg-58°C), 2-ethylhexyl acrylate (Tg-70°C), 2-ethylhexyl methacrylate (Tg-10°C), isononyl acrylate (Tg-58°C), isodecyl acrylate (Tg-60°C), isodecyl methacrylate (Tg-41°C), n-lauryl acrylate (Tg-23°C), n-lauryl methacrylate (Tg-65°C), tridecyl acrylate (Tg-55°C), tridecyl methacrylate (-40°C), and isostearyl acrylate (Tg-18°C). These may be used alone or in combination of two or more. Among the above soft monomers, from the viewpoint of adhesion, n-butyl acrylate (Tg-55°C), n-octyl acrylate (Tg-65°C), or 2-ethylhexyl acrylate (Tg-70°C) are preferred, with n-butyl acrylate (Tg-55°C) being particularly preferred.

From the viewpoint of adhesion and the viewpoint of easily satisfying the loss modulus G" described above, the (meth)acrylic acid ester polymer (A) preferably contains 40 to 99 mass % of the structural units derived from the soft monomer, more preferably 50 to 90 mass %, particularly preferably 60 to 85 mass %, and even more preferably 70 to 80 mass %. This makes it easier for the resulting adhesive to satisfy the above-mentioned viscoelasticity properties, and in combination with the specific silane coupling agent S, the adhesive strength is increased even when the adhesive layer is made thin, and it is likely to have excellent durability.

The (meth)acrylic acid ester polymer (A) preferably contains a monomer having a reactive functional group in the molecule (reactive functional group-containing monomer) as a monomer unit constituting the polymer. This allows the reactive functional group derived from the reactive functional group-containing monomer to react with the crosslinking agent (B) to form a crosslinked structure (three-dimensional network structure), resulting in a pressure-sensitive adhesive with the desired cohesive strength.

Preferred reactive group-containing monomers include monomers having a hydroxyl group in the molecule (hydroxyl group-containing monomers), monomers having a carboxyl group in the molecule (carboxyl group-containing monomers), and monomers having an amino group in the molecule (amino group-containing monomers). Among these, hydroxyl group-containing monomers or carboxyl group-containing monomers that have excellent reactivity with the crosslinking agent (B) are preferred, and hydroxyl group-containing monomers that are less likely to adversely affect the adherend are particularly preferred.

Examples of hydroxyl group-containing monomers include hydroxyalkyl (meth)acrylate esters such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 3-hydroxybutyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Among these, 2-hydroxyethyl (meth)acrylate or 4-hydroxybutyl (meth)acrylate is preferred from the standpoint of reactivity with the crosslinking agent (B) and copolymerizability with other monomers. These may be used alone or in combination of two or more.

Carboxy group-containing monomers include, for example, ethylenically unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, itaconic acid, and citraconic acid. Among these, acrylic acid or methacrylic acid is preferred from the standpoint of reactivity with the crosslinking agent (B) and copolymerizability with other monomers, and acrylic acid is particularly preferred. These may be used alone or in combination of two or more.

The content of the structural units derived from the reactive functional group-containing monomer in the (meth)acrylic acid ester polymer (A) is preferably 0.1 to 30 mass %, more preferably 0.4 to 22 mass %, particularly preferably 0.8 to 14 mass %, even more preferably 1.2 to 6 mass %, and of these, preferably 1.6 to 3 mass % from the viewpoint of cohesive strength. This makes it easier for the resulting adhesive to satisfy the above-mentioned viscoelasticity properties, and in combination with the specific silane coupling agent S, it tends to have high adhesive strength even when the adhesive layer is made thin, and to have excellent durability.

It is also preferable that the (meth)acrylic acid ester polymer (A) does not contain a carboxyl group-containing monomer as a monomer unit constituting the polymer. Since the carboxyl group is an acid component, there is a concern that the resistance value change due to corrosion of the electrode with which the adhesive comes into contact may occur. However, by not containing a carboxyl group-containing monomer, corrosion of the electrode can be prevented and the resistance value change can be effectively prevented or suppressed. However, the above-mentioned "not containing a carboxyl group-containing monomer" means that the carboxyl group-containing monomer can be contained to an extent that the electrode with which the resulting adhesive comes into contact is not adversely affected. Specifically, it is acceptable for the (meth)acrylic acid ester polymer (A) to contain a carboxyl group-containing monomer as a monomer unit in an amount of 0.1 mass% or less, preferably 0.01 mass% or less, and more preferably 0.001 mass% or less.

The (meth)acrylic acid ester polymer (A) may contain other monomers as monomer units constituting the polymer, if desired. As the other monomers, monomers that do not contain reactive functional groups are preferred so as not to interfere with the action of the reactive group-containing monomer. Examples of such other monomers include (meth)acrylic acid alkoxyalkyl esters such as methoxyethyl (meth)acrylate and ethoxyethyl (meth)acrylate, vinyl acetate, and styrene. These may be used alone or in combination of two or more.

The (meth)acrylic acid ester polymer (A) may be a polymer obtained by solution polymerization, a polymer obtained without a solvent, or an emulsion polymerization. Among these, a solution polymer obtained by a solution polymerization method is preferable. By being a solution polymer, it is easy to obtain a high molecular weight polymer, and the aforementioned loss modulus G" is more easily satisfied in the resulting adhesive.

The polymerization form of the (meth)acrylic acid ester polymer (A) may be a random copolymer or a block copolymer.

The weight average molecular weight of the (meth)acrylic acid ester polymer (A) is preferably 400,000 to 4,000,000, more preferably 700,000 to 3,000,000, particularly preferably 900,000 to 2,400,000, even more preferably 1,100,000 to 2,000,000, and most preferably 1,300,000 to 1,800,000, and most preferably 1,400,000 to 1,700,000. This makes it easier for the resulting adhesive to satisfy the above-mentioned viscoelasticity properties, and in combination with the specific silane coupling agent S, the adhesive strength is increased even when the adhesive layer is made thin, and the adhesive tends to have excellent durability. The weight average molecular weight in this specification is a value measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

In the adhesive composition P, the (meth)acrylic acid ester polymer (A) may be used alone or in combination of two or more kinds.

The content of the (meth)acrylic acid ester polymer (A) in the adhesive composition P according to this embodiment is preferably 70.0 to 99.9% by mass, more preferably 75.0 to 99.7% by mass, particularly preferably 80.0 to 99.4% by mass, even more preferably 85.0 to 99.2% by mass, and of these, preferably 90.0 to 99.0% by mass. This makes it easier for the resulting adhesive to satisfy the above-mentioned viscoelasticity properties, and in combination with the specific silane coupling agent S, it is possible to obtain the desired adhesive strength and durability even when the adhesive layer is made thin.

(1-2) Crosslinking agent (B)
The crosslinking agent (B) crosslinks the (meth)acrylic acid ester polymer (A) by heating the adhesive composition P or the like, and can satisfactorily form a crosslinked structure of a three-dimensional network structure. This makes it possible to obtain an adhesive having a predetermined cohesive strength, and makes it easier to satisfy the viscoelastic properties such as the loss modulus G" described above. In particular, in combination with the action of the specific silane coupling agent S described above, it becomes easier to exhibit excellent adhesive strength, and the durability becomes even better.

The crosslinking agent (B) may be any that reacts with the reactive functional groups (hydroxyl groups, carboxyl groups, etc.) possessed by the (meth)acrylic acid ester polymer (A), and examples thereof include isocyanate-based crosslinking agents, epoxy-based crosslinking agents, amine-based crosslinking agents, melamine-based crosslinking agents, aziridine-based crosslinking agents, hydrazine-based crosslinking agents, aldehyde-based crosslinking agents, oxazoline-based crosslinking agents, metal alkoxide-based crosslinking agents, metal chelate-based crosslinking agents, metal salt-based crosslinking agents, and ammonium salt-based crosslinking agents. Here, when the (meth)acrylic acid ester polymer (A) contains a structural unit derived from a hydroxyl group-containing monomer, it is preferable to use an isocyanate-based crosslinking agent that has excellent reactivity with hydroxyl groups as the crosslinking agent (B). The crosslinking agent (B) may be used alone or in combination of two or more.

The isocyanate-based crosslinking agent contains at least a polyisocyanate compound. Examples of polyisocyanate compounds include aromatic polyisocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and xylylene diisocyanate, aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as isophorone diisocyanate and hydrogenated diphenylmethane diisocyanate, and their biurets, isocyanurates, and adducts which are reactants with low-molecular active hydrogen-containing compounds such as ethylene glycol, propylene glycol, neopentyl glycol, trimethylolpropane, and castor oil. Among these, trimethylolpropane-modified aromatic polyisocyanates, particularly trimethylolpropane-modified tolylene diisocyanate or trimethylolpropane-modified xylylene diisocyanate, are preferred from the viewpoint of reactivity with hydroxyl groups.

The content of the crosslinking agent (B) in the adhesive composition P is preferably 0.01 to 10 parts by mass, more preferably 0.04 to 5 parts by mass, particularly preferably 0.08 to 1 part by mass, even more preferably 0.1 to 0.5 parts by mass, even more preferably 0.12 to 0.3 parts by mass, and most preferably 0.15 to 0.22 parts by mass, relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A), from the viewpoint of cohesive strength. The resulting adhesive is more likely to satisfy the above-mentioned viscoelasticity properties, and, in combination with the specific silane coupling agent S, is able to obtain the desired adhesive strength and durability even when the adhesive layer is made thin.

(1-3) Silane coupling agent (C)
The silane coupling agent (C) used in the adhesive composition P is the silane coupling agent S described above, and its type and content (mass%) in the adhesive are as described above. The amount of the silane coupling agent (C) in the adhesive composition P relative to 100 parts by mass of the (meth)acrylic acid ester polymer (A) is preferably 0.01 to 10 parts by mass, more preferably 0.05 to 8 parts by mass, particularly preferably 0.1 to 6 parts by mass, further preferably 0.3 to 4 parts by mass, and of these, preferably 0.5 to 2 parts by mass. This, combined with the above-mentioned viscoelasticity, makes it easier to exert a large adhesive force and easier to obtain excellent durability.

(1-4) Various Additives The adhesive composition P may contain, if desired, various additives that are commonly used in acrylic adhesives, such as an ultraviolet absorber, an antistatic agent, a tackifier, a colorant, an infrared absorber, a rust inhibitor, an antioxidant, a light stabilizer, a softener, a filler, a refractive index adjuster, and the like.

In this embodiment, it is also preferable that the adhesive composition P contains an antistatic agent (D). This allows the resulting adhesive to exhibit good antistatic performance, and for example, can suppress peeling static electricity that occurs when peeling off a release sheet that is placed in contact with the adhesive.

The antistatic agent (D) may be any agent capable of exhibiting good antistatic properties, such as ionic compounds and nonionic compounds. Of these, ionic compounds are preferred, and it is particularly preferred that the agent does not inhibit the action of the silane coupling agent S. The ionic compound may be a liquid (ionic liquid) or a solid (ionic solid) at room temperature. In this specification, an ionic compound refers to a compound in which a cation and an anion are bonded together primarily by electrostatic attraction. The antistatic agent (D) may be used alone or in combination of two or more types.

As the ionic compound, nitrogen-containing onium salts, sulfur-containing onium salts, phosphorus-containing onium salts, alkali metal salts or alkaline earth metal salts are preferred, and from the viewpoint of durability, nitrogen-containing onium salts or alkali metal salts are particularly preferred. The nitrogen-containing onium salt is preferably an ionic compound composed of a nitrogen-containing heterocyclic cation and its counter anion.

The content of the antistatic agent (D) in the adhesive composition P is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 10 parts by mass, and even more preferably 0.8 to 5 parts by mass, per 100 parts by mass of the (meth)acrylic acid ester polymer (A). This provides better adhesive strength and durability, and also exhibits excellent antistatic properties.

(2) Production of adhesive composition The adhesive composition P can be produced by producing a (meth)acrylic acid ester polymer (A), mixing the obtained (meth)acrylic acid ester polymer (A) with a crosslinking agent (B) and a silane coupling agent (C), and adding additives, etc., as desired.

The (meth)acrylic acid ester polymer (A) can be produced by polymerizing a mixture of monomers constituting the polymer by a normal radical polymerization method. The polymerization of the (meth)acrylic acid ester polymer (A) is preferably carried out by a solution polymerization method using a polymerization initiator as desired. However, the present invention is not limited to this, and the polymerization may be carried out without a solvent. Examples of polymerization solvents include ethyl acetate, n-butyl acetate, isobutyl acetate, toluene, acetone, hexane, methyl ethyl ketone, etc., and two or more types may be used in combination. Examples of polymerization initiators include azo compounds, organic peroxides, etc., and two or more types may be used in combination. In addition, the weight average molecular weight of the obtained polymer can be adjusted by adding a chain transfer agent such as 2-mercaptoethanol in the above polymerization process.

Once the (meth)acrylic acid ester polymer (A) is obtained, the crosslinking agent (B), the silane coupling agent (C), and, if desired, additives, dilution solvent, etc. are added to the solution of the (meth)acrylic acid ester polymer (A) and thoroughly mixed to obtain a solvent-diluted adhesive composition P (coating solution). Note that, if any of the above components is in a solid state or if precipitation occurs when mixed with other components in an undiluted state, the component may be dissolved or diluted alone in a dilution solvent before mixing with the other components.

Dilution solvents that can be used include, for example, aliphatic hydrocarbons such as hexane, heptane, and cyclohexane; aromatic hydrocarbons such as toluene and xylene; halogenated hydrocarbons such as methylene chloride and ethylene chloride; alcohols such as methanol, ethanol, propanol, butanol, and 1-methoxy-2-propanol; ketones such as acetone, methyl ethyl ketone, 2-pentanone, isophorone, and cyclohexanone; esters such as ethyl acetate and butyl acetate; and cellosolve-based solvents such as ethyl cellosolve.

The concentration and viscosity of the coating solution prepared in this manner need only be within a range that allows coating, and are not particularly limited and can be appropriately selected depending on the situation. For example, the adhesive composition P is diluted so that its concentration is 10 to 60 mass %. Note that the addition of a dilution solvent or the like is not a necessary condition for obtaining the coating solution, and if the adhesive composition P has a viscosity that allows coating, it is not necessary to add a dilution solvent. In this case, the adhesive composition P becomes a coating solution in which the polymerization solvent for the (meth)acrylic acid ester polymer (A) itself serves as the dilution solvent.

(3) Production of Adhesive The above-described adhesive composition P is applied to a desired object and then crosslinked to obtain an adhesive (adhesive layer).

The crosslinking of the adhesive composition P can be carried out by a heat treatment. This heat treatment can also serve as a drying treatment after application of the adhesive composition P. The heating temperature for the heat treatment is preferably 50 to 150°C, and more preferably 70 to 120°C. The heating time is preferably 10 seconds to 10 minutes, and more preferably 50 seconds to 2 minutes.

After the heat treatment, a curing period of about 1 to 2 weeks may be provided at room temperature (e.g., 23°C, 50% RH) if necessary. If this curing period is required, the adhesive will be formed after the curing period has elapsed. If no curing period is required, the adhesive will be formed after the heat treatment has been completed.

The above heat treatment (and curing) allows the (meth)acrylic acid ester polymer (A) to be sufficiently crosslinked via the crosslinking agent (B).

(4) Physical Properties of the Pressure-Sensitive Adhesive The gel fraction of the pressure-sensitive adhesive according to this embodiment is preferably 40 to 99%, more preferably 50 to 98%, particularly preferably 60 to 97%, even more preferably 70 to 96%, and among these, preferably 80 to 95%, and most preferably 86 to 92%. This makes it easier to satisfy the viscoelastic properties such as the loss modulus G" described above. In particular, in combination with a specific silane coupling agent S, the desired adhesive strength and durability can be obtained even when the pressure-sensitive adhesive layer is made thin. The method for measuring the gel fraction is as shown in the test examples described later.

(5) Use of the Pressure-Sensitive Adhesive The pressure-sensitive adhesive according to the present embodiment is used for optical applications. Examples of optical applications include displays and solar cell modules, and displays are particularly preferred. Examples of types of displays include liquid crystal displays (LCDs), light-emitting diode (LED) displays, organic electroluminescence (organic EL) displays, and electronic paper. The display may be a touch panel. Among the above, organic EL displays, which are highly required to have a thinner pressure-sensitive adhesive layer, are particularly preferred.

The adhesive according to this embodiment is preferably used for bonding optical films, particularly polarizing plates and retardation films that are prone to thermal shrinkage, and is particularly preferably used for bonding polarizing plates and retardation films that are thinner than usual.

[Adhesive sheet]
The pressure-sensitive adhesive sheet according to one embodiment of the present invention has at least a pressure-sensitive adhesive layer and is used for optical applications. The pressure-sensitive adhesive layer is made of the pressure-sensitive adhesive according to the above-described embodiment.

FIG. 1 shows a specific configuration of an example of the pressure-sensitive adhesive sheet according to this embodiment.
As shown in Fig. 1, the adhesive sheet 1 is composed of two release sheets 12a and 12b, and an adhesive layer 11 sandwiched between the two release sheets 12a and 12b so as to be in contact with the release surfaces of the two release sheets 12a and 12b. In this specification, the release surface of the release sheet refers to the surface of the release sheet that has releasability, and includes both a surface that has been subjected to a release treatment and a surface that exhibits releasability even without being subjected to a release treatment.

1. Components (1) Adhesive Layer The adhesive constituting the adhesive layer 11 of the adhesive sheet 1 according to this embodiment is the adhesive according to the embodiment described above.

The thickness of the adhesive layer 11 in the adhesive sheet 1 according to this embodiment is preferably 30 μm or less, more preferably 26 μm or less, particularly preferably 22 μm or less, even more preferably 18 μm or less, and even more preferably 14 μm or less, most preferably 10 μm or less. This allows the adhesive layer 11 to be made thinner, and the resulting display body to be made thinner. Furthermore, in this embodiment, even if the thickness of the adhesive layer 11 is as thin as described above, the combination of the viscoelastic properties described above and the action of the specific silane coupling agent S results in high adhesive strength and excellent durability.

On the other hand, from the viewpoint of improving adhesive strength and durability, the thickness of the adhesive layer is preferably 0.1 μm or more, more preferably 1 μm or more, particularly preferably 3 μm or more, and even more preferably 5 μm or more.

(2) Release Sheet The release sheets 12a and 12b protect the adhesive layer 11 until the adhesive sheet 1 is used, and are peeled off when the adhesive sheet 1 (adhesive layer 11) is used. In the adhesive sheet 1 according to this embodiment, one or both of the release sheets 12a and 12b are not necessarily required.

The release sheets 12a and 12b may be made of, for example, polyethylene film, polypropylene film, polybutene film, polybutadiene film, polymethylpentene film, polyvinyl chloride film, vinyl chloride copolymer film, polyethylene terephthalate film, polyethylene naphthalate film, polybutylene terephthalate film, polyurethane film, ethylene vinyl acetate film, ionomer resin film, ethylene-(meth)acrylic acid copolymer film, ethylene-(meth)acrylic acid ester copolymer film, polystyrene film, polycarbonate film, polyimide film, or fluororesin film (as a substrate). Crosslinked films of these may also be used. Furthermore, laminated films of these may also be used. From the perspective of the SDGs, the material constituting the release sheets may be a material with a high biomass content, a material that can be recycled or reused, or a recycled or reused material.

The release surfaces of the release sheets 12a, 12b (particularly the surfaces in contact with the adhesive layer 11) are preferably subjected to a release treatment, and specifically, a release layer is preferably provided on the substrate. Examples of release agents used in the release treatment (release agents constituting the release layer) include alkyd-based, silicone-based, fluorine-based, unsaturated polyester-based, polyolefin-based, and wax-based release agents. It is preferable that one of the release sheets 12a, 12b is a heavy release type release sheet with a large release force, and the other is a light release type release sheet with a small release force.

It is also preferable that the release sheets 12a and 12b are provided with an antistatic layer. This makes it possible to suppress the peeling static electricity that occurs when the release sheet is peeled off. The antistatic layer can be provided on any part of the release sheet depending on the purpose, but it is particularly preferable to provide it between the base material and the release layer of the release sheet. The antistatic layer can be formed to a known thickness using a known antistatic agent.

In the adhesive sheet 1 according to this embodiment, it is preferable that the release surfaces of the release sheets 12a and 12b are not provided with an antistatic layer. This makes it difficult for the adhesive strength to decrease even if the adhesive sheet is stored for 7 days in a dry environment at 70°C, for example, and tends to maintain an adhesive strength equivalent to the initial adhesive strength, resulting in good durability. The reason for this is not entirely clear, but it is presumed that in a heated environment, the material derived from the antistatic layer in the release sheet reacts with the silane coupling agent S in the adhesive, causing a decrease in adhesive strength.

There are no particular limitations on the thickness of the release sheets 12a and 12b, but it is usually around 20 to 150 μm.

2. Manufacturing of adhesive sheet In one manufacturing example of the adhesive sheet 1, the coating solution of the adhesive composition P is applied to the release surface of one release sheet 12a (or 12b), heat treatment is performed to thermally crosslink the adhesive composition P, and a coating layer is formed, and then the release surface of the other release sheet 12b (or 12a) is superimposed on the coating layer. If a curing period is required, a curing period is provided, and if no curing period is required, the coating layer becomes the adhesive layer 11 as it is. The adhesive sheet 1 is obtained by the above steps. The conditions for the heat treatment and curing are as described above.

The coating solution of the adhesive composition P can be applied using methods such as bar coating, knife coating, roll coating, blade coating, die coating, and gravure coating.

3. Physical properties of the adhesive sheet (1) Initial adhesive strength The initial adhesive strength of the adhesive sheet 1 according to this embodiment to alkali-free glass is preferably 10 N/25 mm or more, more preferably 11 N/25 mm or more, and particularly preferably 12 N/25 mm or more. This makes it easier to exhibit higher durability when a polarizing plate, a retardation film, or the like is used as an adherend. The adhesive sheet 1 according to this embodiment can exhibit high adhesive strength as described above even if the adhesive layer 11 is thin, because the adhesive layer 11 is made of the above-mentioned adhesive.

On the other hand, the upper limit of the initial adhesive strength is not particularly limited, but taking into consideration reworkability, it is preferably 100N/25mm or less, more preferably 75N/25mm or less, particularly preferably 50N/25mm or less, even more preferably 30N/25mm or less, and of these, preferably 20N/25mm or less.

The initial adhesive strength mentioned above basically refers to the adhesive strength measured using the 180-degree peeling method in accordance with JIS Z0237:2009, and the specific test method is as shown in the test example described below.

(2) Adhesive strength after heat promotion The adhesive strength of the adhesive sheet 1 according to this embodiment to alkali-free glass after heat promotion is preferably 6N/25mm or more, more preferably 8N/25mm or more, particularly preferably 10N/25mm or more, and even more preferably 12N/25mm or more, and especially preferably 14N/25mm or more. The condition of the heat promotion is 70°C, in a dry environment for 7 days. This makes it easier to exhibit higher durability when a polarizing plate, a retardation film, or the like is used as an adherend. The adhesive sheet 1 according to this embodiment can exhibit high adhesive strength as described above even if the thickness of the adhesive layer 11 is thin, because the adhesive layer 11 is made of the above-mentioned adhesive.

On the other hand, the upper limit of the adhesive strength after the heat acceleration is not particularly limited, but taking into consideration reworkability, it is preferably 100N/25mm or less, more preferably 75N/25mm or less, particularly preferably 50N/25mm or less, even more preferably 30N/25mm or less, and of these, preferably 20N/25mm or less.

Here, the adhesive strength after heat acceleration basically refers to the adhesive strength measured using the 180-degree peel method in accordance with JIS Z0237:2009, and the specific test method is as shown in the test example described below.

(3) Haze value The haze value of the adhesive layer 11 of the adhesive sheet 1 according to this embodiment is preferably 10% or less, more preferably 5% or less, particularly preferably 2% or less, and even more preferably 1% or less. This provides very high transparency and is suitable for optical applications (displays). On the other hand, the lower limit of the haze value of the adhesive layer is not particularly restricted. The lower limit may be 0%, but is usually about 0.1% due to measurement accuracy and other factors. Here, the haze value in this specification is a value measured in accordance with JIS K7136:2000.

(4) Total Light Transmittance The total light transmittance of the pressure-sensitive adhesive layer 11 of the pressure-sensitive adhesive sheet 1 according to the present embodiment is preferably 70% or more as a lower limit, more preferably 80% or more, and particularly preferably 90% or more. This provides good visibility as an indicator. On the other hand, the upper limit of the total light transmittance of the pressure-sensitive adhesive layer is not particularly limited, but is usually 100% or less. Here, the total light transmittance in this specification is a value measured in accordance with JIS K7361-1:1997.

[Optical film with pressure-sensitive adhesive layer]
The pressure-sensitive adhesive layer-attached optical film according to one embodiment of the present invention includes an optical film and a pressure-sensitive adhesive layer laminated on at least one surface of the optical film. The pressure-sensitive adhesive layer is made of the pressure-sensitive adhesive according to the above-described embodiment.

The specific configuration of the optical laminate according to this embodiment is shown in FIG. 2. As shown in FIG. 2, the optical film 2 with an adhesive layer according to this embodiment is configured to include an optical film 21, an adhesive layer 11 laminated on one side of the optical film 21, and a release sheet 12b laminated on the side of the adhesive layer 11 opposite the optical film 21. This adhesive layer 11 is the adhesive layer 11 of the adhesive sheet 1 described above, and the release sheet 12b is the release sheet 12b of the adhesive sheet 1 described above.

Examples of the optical film 21 include a polarizing plate, a phase difference film, a brightness enhancement film, a viewing angle compensation film, a contrast enhancement film, a liquid crystal polymer film, a diffusion film, a semi-transparent reflective film, a transparent conductive film, and a shatterproof film. Among the above, a polarizing plate and a phase difference film are preferred from the viewpoint of durability.

Examples of polarizing plates include a polyvinyl alcohol (PVA) polarizer with triacetyl cellulose (TAC) film laminated on both sides as a protective film, a cycloolefin polymer film (COP polarizing plate) in which one of the TAC films is replaced with a cycloolefin polymer film, or a PVA polarizer with a TAC film laminated on one side as a protective film. The TAC film may or may not be saponified.

The thickness of the optical film 21 is preferably 1 to 150 μm, more preferably 5 to 120 μm, particularly preferably 10 to 100 μm, and even more preferably 30 to 80 μm. This allows the resulting display to be made thinner. Furthermore, in this embodiment, even if the thickness of the optical film 21 is as thin as described above, excellent durability is obtained because the adhesive layer 11 is made of the adhesive described above. In particular, when the polarizing plate or retardation film is as thin as described above, it is prone to thermal shrinkage under durability conditions (for example, the durability conditions (1) to (3) described above). However, in this embodiment, lifting or peeling is unlikely to occur under the durability conditions, and durability is excellent.

To manufacture the optical film 2 with the adhesive layer, as an example, one release sheet 12a of the adhesive sheet 1 described above is peeled off, and the exposed adhesive layer 11 of the adhesive sheet 1 is attached to one side of the optical film 21.

The optical film 2 with the adhesive layer according to this embodiment can be used by peeling off the release sheet 12b and attaching the exposed adhesive layer 11 to a desired optical component.

Display bodies to which the pressure-sensitive adhesive layer-attached optical film 2 according to this embodiment can be applied include, for example, liquid crystal displays (LCDs), light-emitting diode (LED) displays, organic electroluminescence (organic EL) displays, electronic paper, etc. The display body may be a touch panel.

The above-described embodiments have been described to facilitate understanding of the present invention, and are not intended to limit the present invention. Therefore, each element disclosed in the above embodiments is intended to include all design modifications and equivalents that fall within the technical scope of the present invention.

For example, one of the release sheets 12a and 12b in the adhesive sheet 1 may be omitted. Also, the release sheet 12b in the adhesive layer-attached optical film 2 may be omitted.

In this specification, when it is written "X to Y" (X and Y are any numbers), it means "X or more and Y or less", and also means "preferably greater than X" or "preferably smaller than Y" unless otherwise specified. Furthermore, when it is written "X or more" (X is any number), it means "preferably greater than X" unless otherwise specified, and when it is written "Y or less" (Y is any number), it also means "preferably smaller than Y" unless otherwise specified.

The present invention will be explained in more detail below with reference to examples, but the scope of the present invention is not limited to these examples.

Example 1
1. Preparation of (meth)acrylic acid ester polymer 78 parts by mass of n-butyl acrylate, 20 parts by mass of methyl acrylate, and 2 parts by mass of 4-hydroxybutyl acrylate were copolymerized by a solution polymerization method to prepare a (meth)acrylic acid ester polymer (A). The molecular weight of this (meth)acrylic acid ester polymer (A) was measured by the following method, and the weight average molecular weight (Mw) was 1.5 million.

2. Preparation of adhesive composition 100 parts by mass (solid content equivalent; the same below) of the (meth)acrylic acid ester polymer (A) obtained in the above step 1, 0.2 parts by mass of trimethylolpropane-modified xylylene diisocyanate (B1; manufactured by Soken Chemical Industries, Ltd., product name "TD-75") as a crosslinking agent (B), and 0.2 parts by mass of 2-trimethoxysilylethyl succinate (C1) as a silane coupling agent (C) were mixed, thoroughly stirred, and diluted with methyl ethyl ketone to obtain a coating solution of adhesive composition P.

Here, the formulations (solid content equivalent) of the pressure-sensitive adhesive composition when the (meth)acrylic acid ester polymer (A) is taken as 100 parts by mass (solid content equivalent) are shown in Table 1. The details of the abbreviations and the like shown in Table 1 are as follows.
[(Meth)acrylic acid ester polymer (A)]
BA: n-butyl acrylate MA: methyl acrylate 4HBA: 4-hydroxybutyl acrylate 2EHA: 2-ethylhexyl acrylate HEA: 2-hydroxyethyl acrylate AA: acrylic acid
[Crosslinking agent (B)]
B1: Trimethylolpropane-modified xylylene diisocyanate (manufactured by Soken Chemical Industries, Ltd., product name "TD-75")
B2: 1,3-bis(N,N'-diglycidylaminomethyl)cyclohexane
[Silane coupling agent (C)]
C1: 2-trimethoxysilylethyl succinate C2: 3-glycidoxypropyltrimethoxysilane
[Antistatic agent (D)]
D1: 1-octyl-pyridinium bis(fluorosulfonyl)imide
[Light release type release sheet R2]
R2-1: A release film having an antistatic layer and a silicone-based release layer laminated in that order on one side of a polyethylene terephthalate film (manufactured by Fujimori Kogyo Co., Ltd., product name "Film Bina 38E-0010 BD AS")
R2-2: A release film having a silicone-based release layer laminated on one side of a polyethylene terephthalate film (manufactured by Fujimori Kogyo Co., Ltd., product name "Film Bina 38E-0010 BD")

3. Formation of adhesive layer The coating solution of the adhesive composition obtained in the above step 2 was applied by a coater to the release-treated surface of a heavy release type release sheet R1, which was obtained by treating one side of a polyethylene terephthalate film with a silicone-based release agent. Then, a coating layer was formed by heating at 90°C for 1 minute. Next, the coating layer on the release sheet R1 obtained above and a light release type release sheet R2 (R2-1; a release film manufactured by Fujimori Kogyo Co., Ltd., product name "Film Bina 38E-0010 BD AS") having a configuration in which an antistatic layer and a silicone-based release layer are laminated on one side of a polyethylene terephthalate film in this order were laminated so that the surface of the silicone-based release layer of the release sheet R2 was in contact with the coating layer, and the adhesive sheet was aged for 7 days under conditions of 23°C and 50% RH to produce an adhesive sheet having a thickness of 10 μm, that is, an adhesive sheet having a configuration of release sheet R1/adhesive layer (thickness: 10 μm)/release sheet R2.

The thickness of the adhesive layer was measured in accordance with JIS K7130 using a constant pressure thickness gauge (manufactured by Techclock, product name "PG-02"). It was also confirmed that the peel strength of release sheet R1 was greater than that of release sheet R2 in the resulting adhesive sheet.

[Examples 2 to 8, Comparative Examples 1 to 4]
Except for changing the composition of the (meth)acrylic acid ester polymer (A), the type and amount of the crosslinking agent (B), the type and amount of the silane coupling agent (C), the amount of the antistatic agent (D), and the type of the light release type release sheet R2 as shown in Table 1, a pressure-sensitive adhesive sheet was produced in the same manner as in Example 1.

The weight average molecular weight (Mw) mentioned above is a polystyrene-equivalent weight average molecular weight measured by gel permeation chromatography (GPC) under the following conditions (GPC measurement).
<Measurement conditions>
・GPC measurement device: Tosoh Corporation, HLC-8020
GPC column (passed in the following order): TSK guard column HXL-H manufactured by Tosoh Corporation
TSK gel GMHXL (x2)
TSK gel G2000HXL
Measurement solvent: tetrahydrofuran Measurement temperature: 40°C

[Test Example 1] (Measurement of gel fraction)
The pressure-sensitive adhesive sheets produced in the Examples and Comparative Examples were cut to a size of 80 mm x 80 mm, the pressure-sensitive adhesive layer was wrapped in a polyester mesh (mesh size 200), and the mass was measured using a precision balance. The mass of the mesh alone was subtracted to calculate the mass of the pressure-sensitive adhesive alone. This mass was designated M1.

Next, the adhesive wrapped in the polyester mesh was immersed in ethyl acetate at room temperature (23°C) for 24 hours. The adhesive was then removed and air-dried for 24 hours in an environment at 23°C and 50% RH, and then dried in an oven at 80°C for 12 hours. After drying, its mass was measured using a precision balance, and the mass of the adhesive alone was calculated by subtracting the mass of the mesh alone. This mass was designated M2. The gel fraction (%) was expressed as (M2/M1) x 100. The results are shown in Table 2.

[Test Example 2] (Measurement of Elastic Modulus)
The pressure-sensitive adhesive layers of the pressure-sensitive adhesive sheets produced in the Examples and Comparative Examples were laminated in multiple layers to a thickness of about 0.5 mm. A cylindrical body with a diameter of 8 mm (height of 0.5 mm) was punched out from the resulting pressure-sensitive adhesive layer laminate to prepare a sample.

The dynamic viscoelasticity of the above sample was measured under the following conditions using a viscoelasticity measuring device (manufactured by Anton Paar, product name "MCR302") in accordance with JIS K7244-6, and the storage modulus G' (MPa) and loss modulus G" (MPa) at 25°C were observed. In addition, the loss tangent (tan δ) was calculated from the two obtained values (loss modulus (G")/storage modulus (G')). The results are shown in Table 2.
Measurement frequency: 1Hz
Measurement temperature range: 0 to 100°C
Heating rate: 4°C/min

[Test Example 3] (Measurement of haze value)
The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet produced in the Examples and Comparative Examples was attached to glass to prepare a measurement sample. After background measurement was performed on the glass, the haze value (%) of the measurement sample was measured in accordance with JIS K7136:2000 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH-5000"). The results are shown in Table 2.

[Test Example 4] (Measurement of total light transmittance)
The pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet produced in the Examples and Comparative Examples was attached to glass to prepare a measurement sample. After background measurement was performed on the glass, the total light transmittance (%) of the measurement sample was measured in accordance with JIS K7361-1:1997 using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name "NDH-5000"). The results are shown in Table 2.

[Test Example 5] (Measurement of initial adhesive strength)
The release sheet R2 was peeled off from the adhesive sheet produced in the Examples and Comparative Examples, and the exposed adhesive layer was attached to an easy-adhesion layer of a polyethylene terephthalate (PET) film (manufactured by Toyobo Co., Ltd., product name "Cosmoshine A4160", thickness: 100 μm) having an easy-adhesion layer, to obtain a release sheet R1/adhesive layer/PET film laminate. The obtained laminate was cut into a width of 25 mm and a length of 100 mm, which was used as a sample.

In an environment of 23°C and 50% RH, the release sheet R1 was peeled off from the above sample, and the exposed adhesive layer was attached to alkali-free glass (manufactured by Corning, product name "Eagle XG"), and then pressurized for 20 minutes at 0.5 MPa and 50°C in an autoclave manufactured by Kurihara Seisakusho. After leaving it for 24 hours under conditions of 23°C and 50% RH, the adhesive strength (N/25 mm) was measured using a tensile tester (manufactured by Orientec, product name "Tensilon") at a peel speed of 300 mm/min and a peel angle of 180 degrees, and this was taken as the initial adhesive strength. Measurements were performed under conditions other than those described here in accordance with JIS Z0237:2009. The results are shown in Table 2.

[Test Example 6] (Measurement of adhesive strength after accelerated heating)
The adhesive sheets produced in the examples and comparative examples were stored for 7 days under dry conditions at 70°C, and then left to stand for 24 hours under conditions of 23°C and 50% RH to obtain adhesive sheets after heat promotion. The adhesive strength (N/25mm) was measured under the same conditions as the initial adhesive strength described above, and this was taken as the adhesive strength after heat promotion. The results are shown in Table 2.

[Test Example 7] (Durability evaluation)
The release sheet R2 was peeled off from the pressure-sensitive adhesive sheet produced in the examples and comparative examples, and the exposed pressure-sensitive adhesive layer was attached to a polarizing plate (thickness 60 μm) having a saponified triacetyl cellulose (TAC) protective film, to obtain a polarizing plate with a pressure-sensitive adhesive layer. In addition, a polarizing plate with a pressure-sensitive adhesive layer was obtained in the same manner from the pressure-sensitive adhesive sheet after accelerated heating obtained in Test Example 6. Then, it was cut into a size of 140 mm x 90 mm.

Then, the release sheet R1 was peeled off from the polarizing plate with the adhesive layer, and the exposed adhesive layer was attached to alkali-free glass (manufactured by Corning Incorporated, product name "Eagle XG"), and then pressurized at 0.5 MPa and 50°C for 20 minutes in an autoclave manufactured by Kurihara Manufacturing Co., Ltd., to prepare an evaluation sample.

The above evaluation samples were placed in the following three types of durability conditions, and after 500 hours, the presence or absence of lifting or peeling was confirmed using a 10x magnifying glass. The evaluation criteria were as follows. The results are shown in Table 2.
⊚: No lifting or peeling was observed.
◯: Lifting or peeling of less than 0.5 mm was observed, but did not cause any practical problems.
×: Lifting or peeling of a size exceeding 0.5 mm was observed, and was problematic for practical use.
<Durability conditions>
・Heat resistance: 85℃ dry
・Moist heat: 60℃, 90%RH
- Heat shock (H.S.): Repeated cycle of -40℃ for 30 min and 85℃ for 30 min

As can be seen from Table 2, the adhesive sheets produced in the examples exhibited great adhesive strength even though the adhesive layer was thin, and also had excellent durability even when the adherend was a thin polarizing plate.

The adhesive sheet according to the present invention is suitable for use in bonding polarizing plates or retardation films to other optical components in organic EL displays, for example.

1... Adhesive sheet 11... Adhesive layer 12a, 12b... Release sheet 2... Optical film with adhesive layer 21... Optical film

Claims (17)

A pressure-sensitive adhesive for optical applications,
Contains a silane coupling agent having an acid anhydride group as an organic functional group,
A pressure-sensitive adhesive having a loss modulus G″ at 25° C. of 0.012 MPa or more. The silane coupling agent is represented by the following general formula (I):

(In the formula, R represents a hydrocarbon group having 1 to 6 carbon atoms, n represents an integer of 2 to 8, m represents an integer of 1 to 3, l represents an integer of 1 to 3, k represents an integer of 0 to 2, and k+l+m=4.)
The adhesive according to claim 1, characterized in that the adhesive is a silane compound represented by the formula: The adhesive according to claim 1, characterized in that the storage modulus G' at 25°C is 0.09 MPa or more and 2 MPa or less. The adhesive described in claim 1, characterized in that the loss tangent tanδ at 25°C is 0.14 or more. The adhesive according to claim 1, characterized in that it is an acrylic adhesive. The adhesive according to claim 1, characterized in that the adhesive base is a (meth)acrylic acid ester polymer or a crosslinked product thereof. The adhesive according to claim 6, characterized in that the (meth)acrylic acid ester polymer contains, as a monomer unit constituting the polymer, a hard monomer having a glass transition temperature (Tg) of 0°C or higher as a homopolymer. The adhesive according to claim 1, characterized in that it is for use in organic electroluminescence displays. A pressure-sensitive adhesive sheet for optical use having at least a pressure-sensitive adhesive layer,
A pressure-sensitive adhesive sheet, wherein the pressure-sensitive adhesive layer is formed of the pressure-sensitive adhesive according to any one of claims 1 to 8. The adhesive sheet according to claim 9, characterized in that the thickness of the adhesive layer is 0.1 μm or more and 30 μm or less. The adhesive sheet according to claim 9, characterized in that the adhesive strength to non-alkali glass is 10 N/25 mm or more. It has two release sheets,
10. The pressure-sensitive adhesive sheet according to claim 9, wherein the pressure-sensitive adhesive layer is sandwiched between the two release sheets so as to be in contact with the release surfaces of the release sheets. The adhesive sheet according to claim 12, characterized in that the release sheet comprises a substrate and a release layer. The adhesive sheet according to claim 12, characterized in that the release sheet comprises a substrate, a release layer, and an antistatic layer located between the substrate and the release layer. An optical film;
An optical film with a pressure-sensitive adhesive layer, comprising: a pressure-sensitive adhesive layer of the pressure-sensitive adhesive sheet according to claim 9 laminated on at least one surface of the optical film. The optical film with a pressure-sensitive adhesive layer according to claim 15, characterized in that the thickness of the optical film is 1 μm or more and 150 μm or less. The optical film with a pressure-sensitive adhesive layer according to claim 15, characterized in that the optical film is a polarizing plate or a retardation film.

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