JP7591371B2 - Adhesive composition - Google Patents

Description

The present invention relates to an adhesive composition.

Conventionally, in applications such as sheets and films, many attempts have been made to provide sufficient strength, improve processability, and reduce product costs by using compositions consisting of multiple components including polymeric substances as materials or by forming laminates.
In applications such as adhesives and asphalt modification, attempts have been made to improve strength by adding polymeric substances to tackifiers and asphalt.
In these applications, a combination of low viscosity and high mechanical strength is usually required.

In recent years, vinyl aromatic monomer-conjugated diene monomer block copolymers (e.g., SBS: styrene-butadiene-styrene block copolymer, SIS: styrene-isoprene-styrene block copolymer) have been widely used as base polymers for solution-type and hot-melt-type adhesives and pressure-sensitive adhesives.
For example, Patent Document 1 discloses a polymer composition for use as an adhesive or pressure sensitive adhesive, which uses SBS.
However, polymer compositions for adhesives or pressure-sensitive adhesives using SBS or SIS have an insufficient balance between processability and adhesive properties such as adhesive strength, and have the problem that when attempting to obtain high adhesive properties, the melt viscosity becomes high, resulting in poor processability.
As a method for improving such problems, Patent Document 2 discloses a polymer composition for adhesives containing a triblock copolymer and a diblock copolymer, and Patent Document 3 discloses a pressure-sensitive adhesive composition containing two or more types of block copolymer compositions.

Special Publication No. 61-278578 Japanese Unexamined Patent Publication No. 61-261310 JP 2000-309767 A

However, the polymer compositions and pressure-sensitive adhesive compositions disclosed in Patent Documents 1 to 3 are insufficient in improving the balance between processability (low viscosity) and adhesive properties, and further improvements are required.

In view of the problems of the conventional techniques described above, the present invention aims to provide a pressure-sensitive adhesive composition that has an excellent balance between processability (low viscosity) and adhesive properties.

Means for Solving the Problems of the Prior Art As a result of intensive research, the present inventors have found that the above problems can be effectively solved by blending a block copolymer composition having a specific structure with a softener having a specific component, and have thus completed the present invention.
That is, the present invention is as follows.

[1]
100 parts by weight of a block copolymer composition;
30 to 400 parts by mass of a tackifier;
10 to 200 parts by mass of a softener;
Contains
The block copolymer composition comprises:
A block copolymer (I-1) containing a polymer block (A) containing at least one vinyl aromatic monomer unit in an amount of 95% by mass or more and a polymer block (B) containing at least one conjugated diene monomer unit in an amount of 95% by mass or more , and having a weight average molecular weight of 70,000 or less;
The present invention comprises a block copolymer composition (I) which contains at least a polymer block (A) containing at least two vinyl aromatic monomer units in an amount of 95% by mass or more and a polymer block (B) containing at least one conjugated diene monomer unit in an amount of 95% by mass or more, and a block copolymer (I-2) having a weight average molecular weight of 1.5 times or more and 2.5 times or less that of the block copolymer (I-1),
the content of the block copolymer (I-1) is 50% by mass or more of the total amount of the block copolymer composition (I);
The content of vinyl aromatic monomer units in the block copolymer composition (I) is 40% by mass or more and 60% by mass or less,
The softener includes one having a naphthene content (% CN) of 30.0 or more as measured in accordance with ASTM D3238 or ASTM D2140;
Adhesive composition.
[2]
The pressure-sensitive adhesive composition according to [1] above, wherein the softener has a paraffin component content (% CP) of 70.0 or less, as measured in accordance with ASTM D3238 or ASTM D2140.
[3]
The pressure-sensitive adhesive composition according to [1] or [2] above, wherein the softener has an aroma component content (% CA) of 5.0 or less, as measured in accordance with ASTM D3238 or ASTM D2140.
[4]
The softener has a color of 0.5 or less as measured in accordance with ASTM D1500;
The pressure-sensitive adhesive composition according to any one of [1] to [3] above.
[5]
The pressure-sensitive adhesive composition according to any one of [1] to [4] above, wherein the tackifier is a hydrogenated aromatic modified alicyclic resin.
[6]
The block copolymer composition (I)
The pressure-sensitive adhesive composition according to any one of items [1] to [5 ] above, further comprising a block copolymer (I-3) which contains a polymer block (A) containing at least two vinyl aromatic monomer units at 95 mass% or more and a polymer block (B) containing at least one conjugated diene monomer unit at 95 mass% or more, and which has a vinyl aromatic monomer unit content of 40 mass% or more and 60 mass% or less and a weight average molecular weight of more than 2.5 times and 3.5 times or less that of the block copolymer (I-1).
[7]
The pressure-sensitive adhesive composition according to any one of [1] to [6] above, wherein the block copolymer composition (I) contains a block copolymer containing a carboxyl group in the main chain.
[8]
The block copolymer composition (I)
The block copolymer is represented by the following formula (a) and / or (b):
The pressure-sensitive adhesive composition according to any one of [1] to [7] above.
(a) (AB) _n -Y'
(b) (B-A-B) _n -Y'
(In the formulas (a) and (b), A represents the polymer block (A), B represents the polymer block (B), n represents an integer of 1 to 4, and Y' represents a coupling agent residue obtained when a block copolymer is coupled with a coupling agent that forms a structure represented by the following formula (Y1) or (Y2).)

(In general formulas (Y1) and (Y2), the curved portion is a saturated or unsaturated hydrocarbon group having 1 to 20 carbon atoms, which may be unsubstituted or substituted. Z is a functional group that can be eliminated by a coupling reaction. X is a Group 1 element.)

According to the present invention, a pressure-sensitive adhesive composition that has an excellent balance between processability (low viscosity) and adhesive properties can be obtained.

Hereinafter, an embodiment of the present invention (hereinafter, referred to as "the present embodiment") will be described in detail.
It should be noted that the following embodiment is merely an example for explaining the present invention, and is not intended to limit the present invention to the following content. The present invention can be implemented in various modifications within the scope of the gist thereof.

[Adhesive composition]
The pressure-sensitive adhesive composition of the present embodiment comprises
100 parts by weight of a block copolymer composition;
30 to 400 parts by mass of a tackifier;
10 to 200 parts by mass of a softener;
Contains.
The block copolymer composition comprises
The block copolymer composition (I) contains at least a block copolymer (I-1) which contains a polymer block (A) mainly composed of at least one vinyl aromatic monomer unit and a polymer block (B) mainly composed of at least one conjugated diene monomer unit and has a weight average molecular weight of 70,000 or less, and a block copolymer (I-2) which contains a polymer block (A) mainly composed of at least two vinyl aromatic monomer units and a polymer block (B) mainly composed of at least one conjugated diene monomer unit and has a weight average molecular weight of 1.5 to 2.5 times that of the block copolymer (I-1).
The content of the block copolymer (I-1) is 50% by mass or more of the entire block copolymer composition (I).
The content of vinyl aromatic monomer units in the block copolymer composition (I) is 40% by mass or more and 60% by mass or less,
The softener includes one having a naphthene component content (% CN) of 30.0 or more as measured in accordance with ASTM D3238 or ASTM D2140.
By having the above-mentioned constitution, it is possible to obtain a pressure-sensitive adhesive composition having an excellent balance between processability (low viscosity) and pressure-sensitive adhesive properties.

(Block Copolymer Composition)
The block copolymer composition used in the pressure-sensitive adhesive composition of the present embodiment contains a block copolymer composition (I) including at least a block copolymer (I-1) which contains a polymer block (A) mainly composed of at least one vinyl aromatic monomer unit and a polymer block (B) mainly composed of at least one conjugated diene monomer unit and has a weight average molecular weight of 70,000 or less, and a block copolymer (I-2) which contains a polymer block (A) mainly composed of at least two vinyl aromatic monomer units and a polymer block (B) mainly composed of at least one conjugated diene monomer unit and has a weight average molecular weight of 1.5 times or more and 2.5 times or less that of the block copolymer (I-1).
The block copolymer composition containing the block copolymers (I-1) and (I-2) can be produced by carrying out a predetermined coupling reaction in a polymerization step.

In the block copolymer composition, if the content of the block copolymer (I-1) is large, the melt viscosity when made into a pressure-sensitive adhesive composition tends to decrease and the adhesive strength tends to increase. From this viewpoint, the content of the block copolymer (I-1) is 50 mass% or more, preferably 55 mass% or more, and more preferably 60 mass% or more of the entire block copolymer composition (I).
In addition, by suppressing the content of the block copolymer (I-1) so as not to be excessive, the holding power when made into a pressure-sensitive adhesive composition tends to be improved. Therefore, the content of the block copolymer (I-1) is preferably 90 mass % or less, more preferably 80 mass % or less, and even more preferably 70 mass % or less, based on the entire block copolymer composition (I).
The content of the block copolymer (I-1) can be measured by the method described in the examples below.
The content of the block copolymer (I-1) can be controlled within the above numerical range by controlling the amount of the coupling agent used in the polymerization step and the coupling time.

The content of the vinyl aromatic monomer unit in the block copolymer composition (I) is from 40% by mass to 60% by mass.
From the viewpoint of low viscosity, the content of the vinyl aromatic monomer unit in the block copolymer composition (I) is 60% by mass or less, preferably 50% by mass or less, and more preferably 45% by mass or less. Furthermore, from the viewpoint of high retention force, the content of the vinyl aromatic monomer unit in the block copolymer composition (I) is 40% by mass or more, preferably 41% by mass or more, and more preferably 42% by mass or more.
The content of the vinyl aromatic monomer unit in the block copolymer composition (I) can be measured by the method described in the examples below.
The content of the vinyl aromatic monomer unit in the block copolymer composition (I) can be controlled within the above numerical range by adjusting the amount of the vinyl aromatic monomer added during the polymerization step of the block copolymer composition (I).

In addition, it is preferable that the block copolymer composition (I) further contains a block copolymer (I-3) which contains at least two polymer blocks (A) mainly composed of vinyl aromatic monomer units and at least one polymer block (B) mainly composed of a conjugated diene monomer unit, has a vinyl aromatic monomer unit content of 40% by mass or more and 60% by mass or less, and has a weight average molecular weight of more than 2.5 times and 3.5 times or less that of the block copolymer (I-1).
This tends to provide an adhesive composition having an excellent balance between low viscosity and adhesive properties.
The block copolymer (I-3) can be contained in the block copolymer composition (I) by coupling the block copolymer (I-1) with a coupling agent having three or more reaction sites.

In addition, it is preferable that the block copolymer composition (I) further contains a block copolymer (I-4) which contains at least two polymer blocks (A) mainly composed of vinyl aromatic monomer units and at least one polymer block (B) mainly composed of a conjugated diene monomer unit and has a weight average molecular weight of more than 3.5 times and not more than 4.5 times that of the block copolymer (I-1).
This tends to provide an adhesive composition having an excellent balance between low viscosity and adhesive properties.
The block copolymer (I-4) can be contained in the block copolymer composition (I) by coupling the block copolymer (I-1) with a coupling agent having four or more reaction sites.

The weight average molecular weight of the block copolymer (I-1) is 70,000 or less, preferably 65,000 or less, more preferably 60,000 or less, and even more preferably 55,000 or less.
When the weight average molecular weight of the block copolymer (I-1) is within the above range, low viscosity tends to be improved.
On the other hand, if the weight average molecular weight of the block copolymer (I-1) is too low, the finishability during production of the block copolymer composition (I) tends to deteriorate, and the holding power during preparation of the adhesive composition of the present embodiment tends to decrease. More specifically, in order to reduce the viscosity of the adhesive composition of the present embodiment, it is effective to set the weight average molecular weight of the block copolymer (I-1) to a low value, but if the weight average molecular weight is too low, the block copolymer composition (I) tends to become sticky and difficult to mold into pellets. Therefore, the weight average molecular weight of the monobranched product is preferably 30,000 or more, more preferably 40,000 or more, and even more preferably 45,000 or more.
The weight average molecular weight of the block copolymer (I-1) can be controlled within the above numerical range by adjusting the polymerization conditions, such as the amount of monomer added, polymerization temperature, and polymerization time, during polymerization of the polymer.

The block copolymer composition (I) preferably contains a block copolymer containing a carboxyl group in the main chain. This tends to provide a pressure-sensitive adhesive composition with an excellent balance between low viscosity and adhesive properties. Furthermore, a pressure-sensitive adhesive composition containing such a block copolymer composition (I) tends to have improved adhesion to a substrate having a higher polarity. Specifically, the adhesion to a substrate containing cellulose as a raw material is improved, and as a result, the adhesion tends to be easily maintained even when wet.

The block copolymer composition (I) preferably contains a block copolymer represented by the following formula (a) and/or (b).
(a) (AB) _n -Y'
(b) (B-A-B) _n -Y'
(In the formulas (a) and (b), A represents the polymer block (A), B represents the polymer block (B), n represents an integer of 1 to 4, and Y' represents a coupling agent residue obtained when a block copolymer is coupled with a coupling agent that forms a structure represented by the following formula (Y1) or (Y2).)

(In general formulas (Y1) and (Y2), the curved portion is a saturated or unsaturated hydrocarbon group having 1 to 20 carbon atoms, which may be unsubstituted or substituted. Z is a functional group that can be eliminated by a coupling reaction. X is a Group 1 element.)

The general formula (Y1) is preferably represented by the following general formula (Y-I), and the general formula (Y2) is preferably represented by the following general formula (Y-II).

(In formulae (Y-I) and (Y-II), R ₁ and R ₂ are hydrogen or a saturated or unsaturated hydrocarbon group having 1 to 20 carbon atoms and having an unsubstituted or substituted group, and R ₁ and R ₂ may be independent of each other or may form a ring structure. Z is a functional group which can be eliminated by a coupling reaction. Also, X is a Group 1 element.)

By subjecting a block copolymer to a coupling reaction using a modifier (or coupling agent) having the structure of formula (Y1) or (Y2), a carboxyl group can be effectively incorporated into the main chain, which tends to result in a pressure-sensitive adhesive composition that is excellent in balance between low viscosity and adhesive properties. In addition, pressure-sensitive adhesive compositions containing such block copolymers tend to have improved adhesion to substrates with higher polarity. Specifically, the adhesion to substrates containing cellulose as a raw material is improved, and as a result, the adhesion tends to be easily maintained even when wet.

As described above, the block copolymer constituting the block copolymer composition used in the adhesive composition of the present embodiment contains conjugated diene monomer units.
The "conjugated diene monomer unit" refers to a structure resulting from polymerization of one conjugated diene compound.
The conjugated diene compound is not particularly limited as long as it is a diolefin having a conjugated double bond, and examples thereof include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, and 1,3-hexadiene.
Among these, 1,3-butadiene and isoprene are preferred as the conjugated diene compound. Furthermore, the use of 1,3-butadiene is more preferred since it tends to result in a pressure-sensitive adhesive having excellent heat aging resistance and light resistance.
The conjugated diene compounds may be used alone or in combination of two or more kinds.

As described above, the block copolymer constituting the block copolymer composition used in the adhesive composition of the present embodiment contains a vinyl aromatic monomer unit.
The term "vinyl aromatic monomer unit" refers to a structure resulting from polymerization of one vinyl aromatic hydrocarbon compound. Examples of vinyl aromatic hydrocarbon compounds include, but are not limited to, alkylstyrenes such as styrene, α-methylstyrene, p-methylstyrene, and p-tert-butylstyrene; alkoxystyrenes such as p-methoxystyrene; vinylnaphthalene, and the like.
Among these, styrene is preferred as the vinyl aromatic hydrocarbon compound from the viewpoint of economy.
The vinyl aromatic hydrocarbon compounds may be used alone or in combination of two or more kinds.

Furthermore, the "polymer block (A) mainly composed of vinyl aromatic monomer units" constituting the block copolymers (I-1) and (I-2) refers to a polymer block in which the proportion of vinyl aromatic monomer units in the entire polymer block (A) is 50 mass % or more, preferably 70 mass % or more, more preferably 85 mass % or more, and even more preferably 95 mass % or more.
Further, the "polymer block (B) mainly composed of conjugated diene monomer units" constituting the block copolymers (I-1) and (I-2) refers to a polymer block in which the ratio of conjugated diene monomer units to the entire polymer block (B) exceeds 50% by mass, preferably 70% by mass or more, more preferably 85% by mass or more, and even more preferably 95% by mass or more.

The block copolymers (I-1) and (I-2) constituting the block copolymer composition contained in the pressure-sensitive adhesive composition of the present embodiment preferably have a vinyl aromatic hydrocarbon block ratio of 70 mass % or more, more preferably 80 mass % or more, and even more preferably 90 mass % or more, whereby an effect of further improving the holding power can be obtained.
The block ratio of vinyl aromatic hydrocarbon incorporated in a block copolymer can be determined from the following formula using a vinyl aromatic hydrocarbon polymer block component (excluding vinyl aromatic hydrocarbon polymer components having an average degree of polymerization of about 30 or less) obtained by a method of oxidatively decomposing a block copolymer with tert-butyl hydroperoxide using osmium tetroxide as a catalyst (the method described in I. M. KOLTHOFF, et al., J. Polym. Sci. 1, 429 (1946)).
Vinyl aromatic hydrocarbon block rate (mass%)
= (mass of vinyl aromatic hydrocarbon polymer block in block copolymer/mass of total vinyl aromatic hydrocarbon in block copolymer) x 100

[Tackifier]
The pressure-sensitive adhesive composition of the present embodiment contains a tackifier.
The tackifier can be selected from a wide variety of types depending on the application and required performance of the pressure-sensitive adhesive composition of the present embodiment.
Examples of tackifiers include, but are not limited to, natural rosin, modified rosin, hydrogenated rosin, glycerol ester of natural rosin, glycerol ester of modified rosin, pentaerythritol ester of natural rosin, pentaerythritol ester of modified rosin, pentaerythritol ester of hydrogenated rosin, copolymer of natural terpene, three-dimensional polymer of natural terpene, hydrogenated derivative of hydrogenated terpene copolymer, polyterpene resin, hydrogenated derivative of phenol-based modified terpene resin, aliphatic petroleum hydrocarbon resin, hydrogenated derivative of aliphatic petroleum hydrocarbon resin, aromatic petroleum hydrocarbon resin, hydrogenated derivative of aromatic petroleum hydrocarbon resin, cyclic aliphatic petroleum hydrocarbon resin, hydrogenated derivative of cyclic aliphatic petroleum hydrocarbon resin, and the like.
These tackifiers may be used alone or in combination of two or more.

As the tackifier, a liquid type tackifier resin can be used as long as it is colorless to pale yellow, substantially odorless, and has good thermal stability.
Tackifiers other than the various hydrogenated derivatives mentioned above are not limited to the following, but are preferably, for example, aliphatic resins, alicyclic resins, polyterpenes, natural and modified rosin esters, and mixtures thereof.
Specific examples include "Wingtack Extra" (trade name) manufactured by Sartomer, "Piccotac" (trade name) manufactured by Eastman Chemical Company, "Escorez" (trade name) manufactured by ExxonMobil Corporation, "Sylvagum" (trade name) and "Sylvalite" (trade name) manufactured by Arizona Chemical Company, and "Piccolyte" (trade name) manufactured by Ashland.

From the viewpoint of coloring resistance and low odor, the tackifier resin is preferably a hydrogenated derivative. Examples of such hydrogenated derivatives include, but are not limited to, Arkon P100 (trade name), Arkon M100 (trade name), and Arkon M115 (trade name) manufactured by Arakawa Chemical Co., Ltd., and Clearon P135 (trade name) manufactured by Yasuhara Chemical Co., Ltd.
Among the hydrogenated derivatives, hydrogenated dicyclopentadiene resins, hydrogenated alicyclic hydrocarbon resins, and hydrogenated aromatic modified alicyclic hydrocarbon resins are particularly preferred from the viewpoint of improving the balance between low viscosity and adhesive properties. Specific examples of these resins include Escorez 5400 (trade name) and Escorez 5600 (trade name) manufactured by Exxon Mobil Corporation, and Imave S-100 (trade name) and Imave P-140 (trade name) manufactured by Idemitsu Kosan Co., Ltd.

In addition, when the above-mentioned block copolymer composition contains a 1,3-butadiene monomer unit and is blended with the block copolymer composition, the tackifier is preferably a hydrogenated aromatic modified alicyclic resin from the viewpoint of compatibility.
The hydrogenated aromatic modified alicyclic resin means a resin obtained by partially or completely hydrogenating a copolymer of dicyclopentadiene and an aromatic compound.
Specific examples of these include Escorez 5600 (trade name) manufactured by Exxon Mobil Corporation, Imave S-100 (trade name) and Imave P-140 (trade name) manufactured by Idemitsu Kosan Co., Ltd.

In the pressure-sensitive adhesive composition of the present embodiment, when high adhesive property, resistance to change in adhesive strength over time, creep performance, or the like is to be imparted, it is more preferable to contain in the pressure-sensitive adhesive composition 20 to 75 mass % of a tackifier resin having affinity for a non-glassy phase block (usually a middle block) of the block copolymer, and 3 to 30 mass % of a tackifier having affinity for a glassy phase block (usually an outer block) of the block polymer.
As a tackifier having affinity for the glass phase block, a terminal block tackifier resin is preferred. The tackifier resin is a resin having a main aromatic structure, for example, a homopolymer or copolymer containing vinyltoluene, styrene, α-methylstyrene, coumarone or indene. Among these, Kristalex and Plastolyn (trade names, manufactured by Eastman Chemical Co.) having α-methylstyrene are preferred.

[Softener]
The pressure-sensitive adhesive composition of the present embodiment contains a softener.
The softener includes one having a naphthene component content (% CN) of 30.0 or more as measured in accordance with ASTM D3238 or ASTM D2140.
By blending the softener with the above-mentioned block copolymer composition (I), it is possible to obtain a pressure-sensitive adhesive composition having properties that further reduce the viscosity at high temperatures in the vicinity of the coating temperature and further improve the adhesive properties at low temperatures at which the expression of adhesive properties is required.
Examples of such softening agents include, but are not limited to, Diana Process Oil NS-90S (trade name) and Diana Process Oil NS-100 (trade name) manufactured by Idemitsu Kosan Co., Ltd., Nyflex 222B, Nyflex 223, Nyflex 3095, Nyflex 801, and Nyflex 810 manufactured by Nynas Corporation, HyPrene Olympus L500 and HyPrene L500 manufactured by ERGON Corporation, and CALSOL NAPHTHENIC PROCESS OIL 815, Clight PRO, 5550, 810, and 806 manufactured by CALUMET Corporation.

From a similar viewpoint, the softener contained in the pressure-sensitive adhesive composition of the present embodiment preferably has a naphthene component content (% CN) measured in accordance with ASTM D3238 or ASTM D2140 of 33.0 or more, more preferably 38.0 or more, and even more preferably 40.0 or more.
The content of the naphthene component in the softener can be specified to be within the above numerical range by appropriately selecting the material used as the softener.

From the same viewpoint, the softener contained in the pressure-sensitive adhesive composition of the present embodiment preferably has a paraffin component content (% CP) measured in accordance with ASTM D3238 or ASTM D2140 of 70.0 or more, more preferably 68.0 or less, even more preferably 65.0 or less, and even more preferably 60.0 or less.
The content of the paraffin component in the softener can be specified to be within the above numerical range by appropriately selecting the material used as the softener.

From the same viewpoint, the softener contained in the pressure-sensitive adhesive composition of the present embodiment preferably has an aroma component content (% CA) of 5.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less, as measured in accordance with ASTM D3238 or ASTM D2140. In addition, when the aroma component content (% CA) is in the above range, the pressure-sensitive adhesive composition tends to be free of coloration and has a low odor, which is preferable.
The content of the aroma component in the softener can be specified to be within the above numerical range by appropriately selecting the material used as the softener.

[0081] From the viewpoint of obtaining a colorless and low odor pressure-sensitive adhesive composition, the softener contained in the pressure-sensitive adhesive composition of the present embodiment preferably has a color, measured in accordance with ASTM D1500, of 0.5 or less, more preferably less than 0.5.
The color of the softener can be specified within the above numerical range by appropriately selecting the material used as the softener.

From the viewpoint of low viscosity, the softener contained in the pressure-sensitive adhesive composition of the present embodiment preferably has a kinetic viscosity at 40° C. measured in accordance with ASTM D445 of 100.0 cSt or less, more preferably 90.0 cSt or less.
The kinetic viscosity of the softener can be specified to be within the above numerical range by appropriately selecting the material used as the softener.

From the same viewpoint, the softener contained in the pressure-sensitive adhesive composition of the present embodiment preferably has a pour point, as measured in accordance with ASTM D97, of −20.0° C. or lower, more preferably −30.0° C. or lower, and even more preferably −35.0° C. or lower.
The pour point of the softener can be specified to be within the above numerical range by appropriately selecting the material used as the softener.

The softener contained in the pressure-sensitive adhesive composition of the present embodiment may contain softeners other than those described above, depending on the application and required performance of the pressure-sensitive adhesive composition of the present embodiment.
As softeners other than those mentioned above, known paraffinic or naphthenic process oils and mixtures thereof can be used.
Examples of commercially available products include, but are not limited to, Diana Process Oil PW-90 (trade name) manufactured by Idemitsu Kosan Co., Ltd.

[Adhesive composition]
The pressure-sensitive adhesive composition of the present embodiment comprises
100 parts by weight of a block copolymer composition;
30 to 400 parts by mass of a tackifier;
10 to 200 parts by mass of a softener;
Contains.
In particular, when used in sanitary materials such as disposable diapers and sanitary napkins, from the viewpoint of enabling coating at lower temperatures and improving low odor properties, the tackifier is preferably contained in an amount of 100 to 400 parts by mass, more preferably 150 to 400 parts by mass, and even more preferably 200 to 400 parts by mass.
The softener is preferably used in an amount of 30 to 180 parts by mass, more preferably 40 to 150 parts by mass, and even more preferably 50 to 130 parts by mass.
When the contents of the block copolymer composition, tackifier and softener are within the above ranges, there is a tendency to obtain a pressure-sensitive adhesive composition that has an excellent balance between low viscosity and adhesive properties.

The block copolymer composition constituting the pressure-sensitive adhesive composition of the present embodiment contains the block copolymer composition (I) as described above.
The block copolymer composition (I) has an excellent balance between the adhesive properties and the melt viscosity and can therefore be preferably used as a material for adhesive compositions. In order to adjust the balance of the adhesive properties, the block copolymer composition can also be a composition to which a block copolymer other than the block copolymer composition (I) of the present embodiment is added.

The block copolymer other than the block copolymer composition (I) is not particularly limited, but for example, a styrene-butadiene block copolymer and a styrene-isoprene block copolymer are preferable.
In particular, when a block polymer having a high melt viscosity is contained, the adhesive composition using the block copolymer composition can be imparted with an effect of improving holding power in exchange for an increase in melt viscosity, which may be preferable depending on the application.
[0113] From the viewpoint of not inhibiting the performance exhibited by the combination of the block copolymer composition (I) and the softener, the content of the block copolymer other than the block copolymer composition (I) is preferably 50 mass% or less, more preferably 40 mass% or less, even more preferably 30 mass% or less, and even more preferably 20 mass% or less, based on the total block copolymer composition in the pressure-sensitive adhesive composition.

[Method for producing block copolymer composition]
The method for producing the block copolymer composition contained in the pressure-sensitive adhesive composition of the present embodiment is not particularly limited, and any known method can be used.
For example, methods described in JP-B-36-19286, JP-B-43-17979, JP-B-46-32415, JP-B-49-36957, JP-B-48-2423, JP-B-48-4106, JP-B-51-49567, JP-A-59-166518, and the like can be mentioned.
A modified polymer containing a functional group can be obtained by addition reaction of the living terminal of the polymer obtained by these methods with a modifying agent described below.

Hereinafter, an example of a method for producing a block copolymer composition containing a polymer including a polymer block (A) mainly composed of vinyl aromatic monomer units and a polymer block (B) mainly composed of conjugated diene monomer units will be described.
[0043] Examples of a method for producing a block copolymer composition contained in the pressure-sensitive adhesive composition of the present embodiment include a method having a polymerization step of copolymerizing a vinyl aromatic hydrocarbon compound such as styrene and a conjugated diene compound such as butadiene in an inert hydrocarbon solvent using an organolithium compound as a polymerization initiator to obtain a block copolymer, and a modification step (coupling step) of reacting the obtained block copolymer with a modifier (this compound is collectively referred to as a modifier when one or more polymers are bonded to the modifier, and is also referred to as a coupling agent when two or more polymers are bonded to the modifier).
In this case, as the coupling agent, for example, a compound having the structure of the above formula (Y1) or (Y2) can be preferably used.
The modification step (coupling step) gives the block copolymers (I-1) and (I-2).

The weight average molecular weight of the block copolymer (I-1) and the block copolymer (I-2) constituting the block copolymer composition can be adjusted by controlling the amount of a polymerization initiator such as an organolithium compound added.
After the polymerization reaction is completed, a coupling reaction is carried out, and water, an alcohol, an acid or the like is added to inactivate the active species. The polymerization solvent is separated, for example, by steam stripping, and then the mixture is dried to obtain a polymer composition.

The polymerization method for the block copolymer composition is not particularly limited, but examples thereof include polymerization methods such as coordination polymerization, anionic polymerization, and cationic polymerization. Among these, anionic polymerization is preferred from the viewpoint of ease of control of the structure. As a method for producing the block copolymer component by anionic polymerization, a known method can be used, and examples thereof include, but are not limited to, the methods described in JP-B-36-19286, JP-B-43-17979, JP-B-46-32415, JP-B-49-36975, JP-B-48-2423, JP-B-48-4106, JP-B-56-28925, JP-A-59-166518, and JP-A-60-186577.

The inert hydrocarbon solvent used in the polymerization process of the block copolymer composition is not particularly limited, but examples thereof include aliphatic hydrocarbons such as butane, pentane, hexane, isopentane, heptane, octane, and isooctane; alicyclic hydrocarbons such as cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, and ethylcyclohexane; and aromatic hydrocarbons such as benzene, toluene, ethylbenzene, and xylene. These may be used alone or in combination of two or more.

The organolithium compound used as a polymerization initiator in the polymerization step of the block copolymer composition is not particularly limited, and known compounds can be used, such as ethyllithium, propyllithium, n-butyllithium, sec-butyllithium, tert-butyllithium, phenyllithium, propenyllithium, hexyllithium, etc. In particular, n-butyllithium and sec-butyllithium are preferred.
The organolithium compound may be used alone or in combination of two or more kinds.

In the method for producing the block copolymer composition of this embodiment, a step of deashing metals derived from the polymerization initiator, etc. can be employed as necessary.

Furthermore, the method for producing the block copolymer composition of the present embodiment may further employ a step of adding an antioxidant, a neutralizing agent, a surfactant, and the like, as necessary.
The antioxidant is not limited to the following, but examples thereof include hindered phenol compounds, phosphorus compounds, and sulfur compounds similar to those described below.
Examples of the neutralizing agent include, but are not limited to, various metal stearates, hydrotalcite, benzoic acid, and the like.
Examples of surfactants include, but are not limited to, anionic surfactants, nonionic surfactants, cationic surfactants, etc. Examples of anionic surfactants include, but are not limited to, fatty acid salts, alkyl sulfate ester salts, alkylaryl sulfonates, etc. Examples of nonionic surfactants include, but are not limited to, polyoxyethylene alkyl ethers, polyoxyethylene alkylaryl ethers, etc. Examples of cationic surfactants include, but are not limited to, alkylamine salts, quaternary ammonium salts, etc.

After the block copolymer composition of the present embodiment is produced as described above, the block copolymer composition is isolated, that is, finished, by the method described below.
When the polymerization step of the block copolymer composition is carried out in an inert hydrocarbon solvent, the inert hydrocarbon solvent is removed to isolate the block copolymer composition. A specific method for removing the solvent includes steam stripping. A water-containing crumb is obtained by steam stripping, and the obtained water-containing crumb is dried to obtain the block copolymer composition.
In steam stripping, it is preferable to use a surfactant as a crumb forming agent. Examples of such surfactants include, but are not limited to, the same anionic surfactants, cationic surfactants, and nonionic surfactants as those mentioned above. These surfactants can generally be added to the water in the stripping zone in an amount of 0.1 to 3000 ppm. In addition to surfactants, water-soluble salts of metals such as Li, NA, Mg, CA, Al, and ZN can also be used as crumb dispersing aids.
The concentration of the crumb-like block copolymer composition dispersed in water obtained through the polymerization step of the block copolymer composition and the steam stripping is generally 0.1 to 20% by mass (ratio to the water in the stripping zone). Within this range, crumbs having good particle size can be obtained without causing operational problems. It is preferable to adjust the moisture content of the crumbs of the block copolymer composition to 1 to 30% by mass by dehydration, and then dry the crumbs until the moisture content is 1% by mass or less. In the dehydration step of the crumbs, dehydration may be performed using a compressed water squeezer such as a roll, a Banbury type dehydrator, or a screw extruder type squeezer dehydrator, or dehydration and drying may be performed simultaneously using a conveyor or a box-type hot air dryer.

[Method for producing pressure-sensitive adhesive composition]
[0133] The pressure-sensitive adhesive composition of the present embodiment can be produced by mixing the above-mentioned block copolymer composition, a tackifier, a softener, and, as necessary, other additives by a known method.
The mixing method is not particularly limited, but may be, for example, a method in which the block copolymer composition, the tackifier, and the softener are uniformly mixed while being heated in a mixer or kneader.
The temperature during mixing is preferably 100° C. to 210° C., more preferably 110° C. to 200° C., and even more preferably 120° C. to 190° C. When the temperature during mixing is 100° C. or higher, the block copolymer composition tends to be sufficiently melted and dispersed well. Furthermore, when the temperature during mixing is 210° C. or lower, evaporation of low molecular weight components of the crosslinking agent and tackifier and deterioration of adhesive properties tend to be prevented.
The mixing time is preferably 5 to 90 minutes, more preferably 10 to 80 minutes, and even more preferably 20 to 70 minutes. By setting the mixing time to 5 minutes or more, each component tends to be uniformly dispersed. By setting the mixing time to 90 minutes or less, evaporation of low molecular weight components of the crosslinking agent and tackifier, deterioration of the adhesive properties, and deterioration of the block copolymer composition tend to be prevented.

[Method of applying pressure-sensitive adhesive composition]
[0113] When the pressure-sensitive adhesive composition of the present embodiment is used by applying it to a predetermined substrate, the method is not particularly limited as long as the desired product can be obtained, and examples of the method include a method of dissolving the pressure-sensitive adhesive composition in a solvent and applying the solution, and a hot melt coating method of melting the pressure-sensitive adhesive composition and applying it.
Among these, the hot melt coating method is preferred from the viewpoints of preventing environmental pollution and ease of coating.
Hot melt coating methods are broadly classified into contact coating and non-contact coating. "Contact coating" refers to a coating method in which a sprayer is brought into contact with a member or a film when applying a hot melt adhesive. "Non-contact coating" refers to a coating method in which a sprayer is not brought into contact with a member or a film when applying a hot melt adhesive. Contact coating methods are not particularly limited, but examples thereof include die coater coating, slot coater coating, and roll coater coating. Non-contact coating methods are not particularly limited, but examples thereof include spiral coating, which can be applied in a spiral shape, omega coating and control seam coating, which can be applied in a wavy shape, slot spray coating and curtain spray coating, which can be applied in a planar shape, and dot coating, which can be applied in a dotted shape.

In addition, the pressure-sensitive adhesive composition of the present embodiment is suitable for spiral coating.
"Spiral coating" is a method of applying adhesive in a non-contact spiral fashion using air, either intermittently or continuously.
The ability to apply a hot melt adhesive over a wide width by spray coating is extremely useful for producing disposable products. Hot melt adhesives that can be applied over a wide width can be adjusted to a narrower coating width by adjusting the hot air pressure. Since it is difficult to apply a hot melt adhesive over a wide width, many spray nozzles are required to obtain a sufficient adhesive area, and the adhesive is unsuitable for producing relatively small disposable products such as urine absorbing liners and disposable products with complex shapes. Therefore, the adhesive composition of the present embodiment is suitable for disposable products because it can be spirally coated over a wide width.

[Characteristics of the adhesive composition]
The properties of the pressure-sensitive adhesive composition of this embodiment can be measured using a pressure-sensitive adhesive tape produced under the conditions shown in the examples described below, according to the measurement conditions shown in the examples.

The present invention will be described in more detail below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples and comparative examples.
In the examples and comparative examples, the physical properties of the polymers were measured and the characteristics were evaluated by the following methods.

[Measurement and evaluation methods]
(Physical properties of block copolymer)
<Vinyl aromatic monomer unit (styrene) content>
A certain amount of the block copolymer was dissolved in chloroform and measured with an ultraviolet spectrophotometer (Shimadzu Corporation, UV-2450). The content of the vinyl aromatic monomer unit (styrene) was calculated from the peak intensity at the absorption wavelength (262 Nm) due to the vinyl aromatic compound component (styrene) using a calibration curve.

<Weight average molecular weight>
The weight average molecular weights of the block copolymers (I-1), (I-2), (I-3), and (I-4) were determined based on the molecular weights of the peaks in the chromatograms using a calibration curve (prepared using the peak molecular weights of the standard polystyrene) determined from the measurement of commercially available standard polystyrene under the measurement conditions described below.
First, a single peak having the lowest peak top molecular weight in the molecular weight range of 20,000 or more and having an area ratio, calculated by peak division described below, of 0.1 or more to the total peak area of the block copolymer composition was designated as block copolymer (I-1), and peaks in a molecular weight range higher than this were designated as (I-2), (I-3), and (I-4) in order of decreasing molecular weight.
The weight average molecular weight of each of the block copolymers (I-1), (I-2), (I-3), and (I-4) was determined by vertical division to the baseline at the inflection point between each peak of the GPC curve using the system software described below.
Here, the inter-peak inflection points (inflection points) of block copolymers (I-1), (I-2), (I-3), and (I-4) were taken as the lowest point (valley peak) between adjacent peaks in the vertical direction. In addition, when the lowest points were consecutive, the midpoint was taken as the midpoint. Using the inflection points, vertical division was performed using the waveform separation function in the above-mentioned system software, and after division, each weight average molecular weight and area ratio was calculated.

[Conditions for measuring weight-average molecular weight]
GPC: ACQUITY APC system (manufactured by Nihon Waters K.K.)
System (measurement and analysis) software: EmpowEr3
Detector: RI
Refractive index unit full scale: 500 μRIU
Output full scale: 2000mV
Sampling rate: 10 points/sec
Column: ACQUITY APC XT125 (4.6 mm x 150 mm); 1 unit ACQUITY APC XT200 (4.6 mm x 150 mm); 1 unit ACQUITY APC XT900 (4.6 mm x 150 mm); 1 unit ACQUITY APC XT450 (4.6 mm x 150 mm); 1 unit Solvent: THF
Flow rate: 1.0mL/min Concentration: 0.1mg/mL
Column temperature: 40°C
Injection volume: 20 μL

<Contents of Block Copolymers (I-1), (I-2), (I-3), and (I-4)>
The ratio of the area of the block copolymers (I-1), (I-2), (I-3), and (I-4) to the total peak area of the elution curve measured above was defined as the content of the block copolymers (I-1), (I-2), (I-3), and (I-4).
The area ratio, weight average molecular weight, and weight average molecular weight ratio of the block copolymers (I-1), (I-2), (I-3), and (I-4) were determined by GPC measurement using the above-mentioned apparatus and conditions, followed by vertical division to the baseline at the inflection points between the peaks of the GPC curve using the above-mentioned system software.
Here, the inflection point between the peaks of each of the block copolymers (I-1), (I-2), (I-3), and (I-4) was the lowest point (valley peak) between adjacent peaks in the vertical direction. If the lowest points were consecutive, the midpoint was taken. Using the inflection points, vertical division was performed using the waveform separation function in the above-mentioned system software, and after division, each weight average molecular weight, each weight average molecular weight ratio, and area ratio were calculated.

[Measurement of physical properties of adhesive composition]
(Preparation of adhesive composition)
The block copolymer compositions (1 to 5), tackifiers (1 to 2), softeners (1 to 5), and stabilizer (2-t-butyl-6-(3-t-butyl-2-hydroxy-5-methylbenzyl)-4-methylphenyl acrylate) were mixed in the ratios shown in Tables 5 to 8 below, and melt-kneaded at 180° C., 50 rpm, and 30 minutes in a pressure kneader (model: DR0.5-3MB-E, Moriyama Corporation) to obtain a uniform hot melt type pressure-sensitive adhesive composition.
The physical properties of the tackifier and softener used are shown in Tables 3 and 4.

<Melt Viscosity of Pressure-Sensitive Adhesive Composition>
The melt viscosities (Pa·s) of the pressure-sensitive adhesive compositions of Examples 1 to 20 and Comparative Examples 1 to 18 were measured at temperatures of 100° C., 120° C., and 140° C. using a Brookfield viscometer (DV-III manufactured by Brookfield Corporation).

(Preparation of adhesive tape)
The molten adhesive composition was cooled to room temperature and dissolved in toluene to obtain a toluene solution.
The obtained toluene solution was coated on a polyester film with an applicator, and then the film was left at room temperature for 30 minutes and in an oven at 70° C. for 7 minutes to completely evaporate the toluene, thereby preparing an adhesive tape.
The coating thickness was 50 μm (substrate thickness: 50 μm).

<Adhesive properties of adhesive composition (1) (loop tack strength)>
Using the pressure-sensitive adhesive compositions of Examples 1 to 20 and Comparative Examples 1 to 18 described below, a loop-shaped pressure-sensitive adhesive tape having a length of 250 mm and a width of 15 mm was prepared as described above.
The loop-shaped adhesive tape was adhered to a SUS plate (SUS304) with a contact area of 15 mm×50 mm, a bonding time of 3 sec, and a bonding speed of 500 mm/min.
Thereafter, the adhesive tape was peeled off from the SUS plate at a peeling speed of 500 mm/min, and the peel strength (N/15 mm) was measured.

<Adhesive properties of adhesive composition (2) (adhesive strength)>
Using the pressure-sensitive adhesive compositions of Examples 1 to 20 and Comparative Examples 1 to 18 described below, pressure-sensitive adhesive tapes having a width of 25 mm were prepared as described above.
The prepared adhesive tape was attached to a SUS plate (SUS304), and the 180° peel strength (N/10 mm) was measured at a peel speed of 300 mm/min.

<Adhesive properties of adhesive composition (3) (holding strength at 40° C.)>
Using the pressure-sensitive adhesive compositions of Examples 1 to 20 and Comparative Examples 1 to 18 described below, pressure-sensitive adhesive tapes having a width of 15 mm were prepared as described above.
The prepared adhesive tape was attached to a SUS plate (SUS304) with a contact area of 15 mm×25 mm.
Thereafter, a load of 1 kg was applied to the adhesive tape in the vertical direction at 40° C., and the holding time (minutes) until the adhesive tape slipped off was measured, and this was taken as the 40° C. holding strength.

<Balance between adhesive properties and melt viscosity>
As an index for estimating the balance between adhesive properties and melt viscosity, a value was calculated by dividing the holding power (holding time) (minutes) at 40°C by the melt viscosity (Pa·s) at 100°C.
In the case of the composition ratios shown in Tables 5 and 6 below, if this value is 10.0 or more, it is judged to have excellent balanced performance in practical use, and if it is 30.0 or more, it is judged to have extremely excellent performance in practical use.
In the case of the composition ratios shown in Tables 7 and 8 below, if this value is 5.0 or more, it is judged to have excellent balanced performance in practical use, and if it is 15.0 or more, it is judged to have extremely excellent performance in practical use.

<Color of Pressure-Sensitive Adhesive Composition>
The colors of the pressure-sensitive adhesive compositions of Examples 1 to 20 and Comparative Examples 1 to 18 described below were visually observed.

[Preparation of Block Copolymer Composition]
(Block Copolymer Composition 1)
A 10 L stainless steel autoclave equipped with a stirrer and a jacket was washed, dried and purged with nitrogen, and then charged with 5094 g of cyclohexane and 503 g of previously prepared styrene. Hot water was passed through the jacket to heat the contents to 48°C.
Next, a cyclohexane solution containing 2.22 g of n-butyllithium was added to initiate the polymerization of styrene.
The liquid temperature increased due to the polymerization of styrene, and 5 minutes after the reaction temperature reached a maximum temperature of 53°C, a cyclohexane solution containing 697 g of 1,3-butadiene was added to continue the polymerization. 3 minutes after butadiene was almost completely polymerized and the reaction temperature reached a maximum temperature of 78°C, coupling agent 1 shown in Table 1 below was added as a coupling agent so that the molar ratio to the total mole number of n-butyllithium was 0.17, and the coupling reaction was carried out for 25 minutes. The average reaction temperature during this period was 78°C. 25 minutes after the addition of the coupling agent, 1.11 g of methanol was added to inactivate the reaction, and a block copolymer composition solution was obtained.
To the obtained block copolymer composition solution, 0.75 parts by mass of octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and 0.15 parts by mass of 2,4-bis(octylthiomethyl)-6-methylphenol were added relative to 100 parts by mass of the block copolymer composition, and the mixture was thoroughly mixed.
Thereafter, the solvent was removed by heating to obtain a block copolymer composition, Block Copolymer Composition 1.

(Block Copolymer Composition 2)
A 10 L stainless steel autoclave equipped with a stirrer and a jacket was washed, dried and purged with nitrogen, and then charged with 5094 g of cyclohexane and 518 g of previously prepared styrene. Hot water was passed through the jacket to heat the contents to 48°C.
Next, a cyclohexane solution containing 2.40 g of n-butyllithium was added to initiate the polymerization of styrene.
The liquid temperature rose due to the polymerization of styrene, and 5 minutes after the reaction temperature reached a maximum temperature of 53°C, a cyclohexane solution containing 682 g of 1,3-butadiene was added to continue the polymerization. 3 minutes after butadiene was almost completely polymerized and the reaction temperature reached a maximum temperature of 78°C, coupling agent 2 shown in Table 1 below was added as a coupling agent so that the molar ratio to the total mole number of n-butyllithium was 0.10, and the coupling reaction was carried out for 25 minutes. The average reaction temperature during this period was 78°C. 25 minutes after the addition of the coupling agent, 1.2 g of methanol was added to inactivate the reaction, and a block copolymer composition solution was obtained.
To the obtained block copolymer composition solution, 0.75 parts by mass of octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and 0.15 parts by mass of 2,4-bis(octylthiomethyl)-6-methylphenol were added relative to 100 parts by mass of the block copolymer composition, and the mixture was thoroughly mixed.
Thereafter, the solvent was removed by heating, to obtain a block copolymer composition 2.

(Block Copolymer Composition 3)
A 10 L stainless steel autoclave equipped with a stirrer and a jacket was washed, dried and purged with nitrogen, and then charged with 5094 g of cyclohexane and 518 g of previously prepared styrene. Hot water was passed through the jacket to heat the contents to 48°C.
Next, a cyclohexane solution containing 2.40 g of n-butyllithium was added to initiate the polymerization of styrene.
The liquid temperature rose due to the polymerization of styrene, and 5 minutes after the reaction temperature reached a maximum temperature of 53°C, a cyclohexane solution containing 682 g of 1,3-butadiene was added to continue the polymerization. 3 minutes after butadiene was almost completely polymerized and the reaction temperature reached a maximum temperature of 78°C, coupling agent 3 shown in Table 1 below was added as a coupling agent so that the molar ratio to the total mole number of n-butyllithium was 0.11, and the coupling reaction was carried out for 25 minutes. The average reaction temperature during this period was 78°C. 25 minutes after the addition of the coupling agent, 1.2 g of methanol was added to inactivate the reaction, and a block copolymer composition solution was obtained.
To the obtained block copolymer composition solution, 0.75 parts by mass of octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and 0.15 parts by mass of 2,4-bis(octylthiomethyl)-6-methylphenol were added relative to 100 parts by mass of the block copolymer composition, and the mixture was thoroughly mixed.
Thereafter, the solvent was removed by heating, to obtain a block copolymer composition 3.

(Block Copolymer Composition 4)
A 10 L stainless steel autoclave equipped with a stirrer and a jacket was washed, dried and purged with nitrogen, and then charged with 5094 g of cyclohexane and 457 g of previously prepared styrene. Hot water was passed through the jacket to heat the contents to 48°C.
Next, a cyclohexane solution containing 2.40 g of n-butyllithium was added to initiate the polymerization of styrene.
The liquid temperature rose due to the polymerization of styrene, and 5 minutes after the reaction temperature reached a maximum temperature of 53°C, a cyclohexane solution containing 743 g of 1,3-butadiene was added to continue the polymerization. 3 minutes after butadiene was almost completely polymerized and the reaction temperature reached a maximum temperature of 78°C, coupling agent 2 shown in Table 1 below was added as a coupling agent so that the molar ratio to the total mole number of n-butyllithium was 0.10, and the coupling reaction was carried out for 25 minutes. The average reaction temperature during this period was 78°C. 25 minutes after the addition of the coupling agent, 1.2 g of methanol was added to inactivate the reaction, and a block copolymer composition solution was obtained.
To the obtained block copolymer composition solution, 0.75 parts by mass of octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and 0.15 parts by mass of 2,4-bis(octylthiomethyl)-6-methylphenol were added relative to 100 parts by mass of the block copolymer composition, and the mixture was thoroughly mixed.
Thereafter, the solvent was removed by heating, to obtain a block copolymer composition 4.

(Block Copolymer Composition 5)
A 10 L stainless steel autoclave equipped with a stirrer and a jacket was washed, dried and purged with nitrogen, and then charged with 5094 g of cyclohexane and 442 g of previously prepared styrene. Hot water was passed through the jacket to heat the contents to 48°C.
Next, a cyclohexane solution containing 2.40 g of n-butyllithium was added to initiate the polymerization of styrene.
The liquid temperature increased due to the polymerization of styrene, and 5 minutes after the reaction temperature reached a maximum temperature of 53°C, a cyclohexane solution containing 758 g of 1,3-butadiene was added to continue the polymerization. 3 minutes after butadiene was almost completely polymerized and the reaction temperature reached a maximum temperature of 78°C, coupling agent 3 shown in Table 1 below was added as a coupling agent so that the molar ratio to the total mole number of n-butyllithium was 0.11, and the coupling reaction was carried out for 25 minutes. The average reaction temperature during this period was 78°C. 25 minutes after the addition of the coupling agent, 1.2 g of methanol was added to inactivate the reaction, and a block copolymer composition solution was obtained.
To the obtained block copolymer composition solution, 0.75 parts by mass of octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate and 0.15 parts by mass of 2,4-bis(octylthiomethyl)-6-methylphenol were added relative to 100 parts by mass of the block copolymer composition, and the mixture was thoroughly mixed.
Thereafter, the solvent was removed by heating to obtain Block Copolymer Composition 5, which is a block copolymer composition.

The coupling agents 1 to 3 used are shown in Table 1 below.
The physical properties of the resulting block copolymer composition are shown in Table 2 below.
The tackifiers used are shown in Table 3 below.
The softeners used are shown in Table 4 below.

[Examples 1 to 20], [Comparative Examples 1 to 18]
Using the block copolymer compositions 1 to 5 obtained as described above, pressure-sensitive adhesive compositions were prepared by the method described above, and evaluated by the method described above.
The evaluation results obtained are shown in Tables 5 to 8.

Comparisons between Example 4 and Comparative Example 1, Example 5 and Comparative Example 2, and Example 6 and Comparative Example 3 show that the combinations of the block copolymer composition and softener in Examples 4 to 6 exhibit outstanding performance from the results of the "balance between melt viscosity and adhesive performance" between formulations in which only the softener is replaced.

In addition, from comparisons between examples in which only the content of the vinyl aromatic monomer unit in the block copolymer composition is different, such as comparisons between Example 5 and Comparative Example 6, and comparisons between Example 6 and Comparative Example 7, it was found that the performance of the adhesive composition was significantly improved by including a block copolymer composition (I) having a vinyl aromatic monomer unit content of 40 mass% or more.

Furthermore, it was found from Examples 1 and 4 that the block copolymer composition exhibited sufficiently high performance by including block copolymer (I-2). It was also found from Examples 5 and 6 that the block copolymer composition exhibited even higher performance by including block copolymer (I-3).

Furthermore, a comparison between Example 5 and Example 6 revealed that the block copolymer composition (I) containing a carboxyl group in the main chain exhibited higher performance.

Furthermore, a comparison of Examples 9 and 19 with all other examples shows that a pressure-sensitive adhesive composition with good color can be obtained by using a softener with an aroma component content (% CA) of 5.0 or less as measured in accordance with ASTM D3238 or ASTM D2140.

The adhesive composition of the present invention has industrial applicability as a material for solution-type and hot-melt-type adhesives and pressure sensitive adhesives.

Claims (8)

100 parts by weight of a block copolymer composition;
30 to 400 parts by mass of a tackifier;
10 to 200 parts by mass of a softener;
Contains
The block copolymer composition comprises:
A block copolymer (I-1) containing a polymer block (A) containing at least one vinyl aromatic monomer unit in an amount of 95% by mass or more and a polymer block (B) containing at least one conjugated diene monomer unit in an amount of 95% by mass or more , and having a weight average molecular weight of 70,000 or less;
The present invention comprises a block copolymer composition (I) which contains at least a polymer block (A) containing at least two vinyl aromatic monomer units in an amount of 95% by mass or more and a polymer block (B) containing at least one conjugated diene monomer unit in an amount of 95% by mass or more, and a block copolymer (I-2) having a weight average molecular weight of 1.5 times or more and 2.5 times or less that of the block copolymer (I-1),
the content of the block copolymer (I-1) is 50% by mass or more of the total amount of the block copolymer composition (I);
The content of vinyl aromatic monomer units in the block copolymer composition (I) is 40% by mass or more and 60% by mass or less,
The softener includes one having a naphthene content (% CN) of 30.0 or more as measured in accordance with ASTM D3238 or ASTM D2140;
Adhesive composition. The softener has a paraffin content (% CP) of 70.0 or less, as measured in accordance with ASTM D3238 or ASTM D2140;
The adhesive composition according to claim 1 . The content (% CA) of aroma components of the softener, as measured in accordance with ASTM D3238 or ASTM D2140, is 5.0 or less;
The adhesive composition according to claim 1 or 2. The softener has a color of 0.5 or less as measured in accordance with ASTM D1500;
The pressure-sensitive adhesive composition according to claim 1 . The tackifier is a hydrogenated aromatic modified cycloaliphatic resin;
The pressure-sensitive adhesive composition according to claim 1 . The block copolymer composition (I)
the block copolymer (I-3) contains a polymer block (A) containing at least two vinyl aromatic monomer units at 95% by mass or more and a polymer block (B) containing at least one conjugated diene monomer unit at 95% by mass or more , the content of the vinyl aromatic monomer units being 40% by mass or more and 60% by mass or less, and the weight average molecular weight being more than 2.5 times and 3.5 times or less that of the block copolymer (I-1);
The pressure-sensitive adhesive composition according to claim 1 . The block copolymer composition (I)
A block copolymer containing a carboxyl group in the main chain.
The pressure-sensitive adhesive composition according to claim 1 . The block copolymer composition (I)
The block copolymer is represented by the following formula (a) and / or (b):
The pressure-sensitive adhesive composition according to claim 1 .
(a) (AB) _n -Y'
(b) (B-A-B) _n -Y'
(In the formulas (a) and (b), A represents the polymer block (A), B represents the polymer block (B), n represents an integer of 1 to 4, and Y' represents a coupling agent residue obtained when a block copolymer is coupled with a coupling agent that forms a structure represented by the following formula (Y1) or (Y2).)
(In general formulas (Y1) and (Y2), the curved portions are saturated or unsaturated hydrocarbon groups having 1 to 20 carbon atoms, which may be unsubstituted or substituted. Z is a functional group which can be eliminated by a coupling reaction. X is a Group 1 element.)