JP2016188310A - Adhesive composition and adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive composition achieving both durability and suppression of a white spot.SOLUTION: There is provided an adhesive composition which comprises: a (meth)acrylic copolymer A containing 0.001 to 0.5 mass% of a structural unit derived from a monomer having a hydroxyl group based on the total structural unit; a (meth)acrylic copolymer B containing 0.1 to 4 mass% of a structural unit derived from a monomer having a hydroxyl group based on the total structural unit in which the content of the structural unit derived from a monomer having a hydroxyl group is higher than the content of the structural unit derived from a monomer having a hydroxyl group of the (meth)acrylic copolymer A; and 5 to 30 pts.mass of a tolylene diisocyanate-based compound based on total 100 pts.mass of the (meth)acrylic copolymer A and the (meth)acrylic copolymer B, wherein the content ratio (A/B) is in the range of 60/40 to 95/5 by mass basis and the total acid value is 2.5 mgKOH/g or less.SELECTED DRAWING: None

Description

  The present invention relates to a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet.

Many image display units such as mobile phones and portable terminals have a liquid crystal display device incorporated therein.
In general, a liquid crystal display device includes a liquid crystal cell and an optical film such as a polarizing plate, a retardation plate, and a brightness enhancement film. In recent years, the number of liquid crystal display devices further provided with a touch panel has increased. A liquid crystal cell and an optical film, optical films, or an optical film and a touch panel are bonded through the adhesive layer formed from an adhesive composition.

  An optical film such as a polarizing plate is usually constituted by laminating members having different shrinkage rates. Therefore, the optical film may be warped due to changes in temperature and humidity, and may float at the interface between the pressure-sensitive adhesive layer and the optical film, resulting in peeling or foaming. In addition, the stress generated when the optical film shrinks and expands due to changes in temperature and humidity cannot be relaxed by the adhesive layer, and the residual stress applied to the adhesive layer becomes uneven and light leakage occurs. So-called white spots may occur. Therefore, a pressure-sensitive adhesive composition capable of forming a pressure-sensitive adhesive layer capable of achieving both durability capable of suppressing floating and peeling and suppression of white spots is desired.

  In order to achieve both the durability of the pressure-sensitive adhesive layer and the suppression of white spots, a method has been proposed in which the cohesive force of the pressure-sensitive adhesive layer is increased and the dimensional change of the optical film is suppressed. For example, the carboxyl group-containing monomer 1 can be used as an adhesive that does not float or peel off at the adhesive interface between the adherend and the adhesive layer even if it is exposed to high temperature and high humidity for a long time after being attached to the adherend. A pressure-sensitive adhesive composition for a polarizing plate containing 100 parts by mass of an acrylic polymer obtained by copolymerizing 10% by mass and 4-20 parts by mass of a tolylene diisocyanate compound having an isocyanurate structure has been proposed. (For example, patent document 1).

  In addition, a method for imparting stress relaxation to an adhesive by combining two types of (meth) acrylic acid ester polymers has been proposed. For example, an acrylic copolymer (A) having a weight average molecular weight of 500,000 to 3,000,000 copolymerized with a carboxyl group-containing monomer and an aromatic ring-containing monomer, and a hydroxyl group-containing monomer and an aromatic ring-containing monomer are copolymerized. A pressure-sensitive adhesive composition containing an acrylic copolymer (B) having a weight average molecular weight of 8000 to 300,000 and a crosslinking agent (C) has been proposed (for example, Patent Document 2).

International Publication No. 2011/062127 JP 2012-214547 A

  In recent years, the capacitive type has become the mainstream input method for touch panels. In the capacitive method, an indium tin oxide (ITO) film that constitutes the touch panel is in contact with the adhesive layer. For this reason, it is requested | required that the adhesive composition used for a liquid crystal display device cannot corrode ITO easily.

  However, in the pressure-sensitive adhesive composition for polarizing plate described in Patent Document 1 and the pressure-sensitive adhesive composition described in Patent Document 2, the acrylic polymer has an acidic group derived from a carboxyl group-containing monomer. The problem of corrosion.

Generally, if there are few acidic groups contained in the pressure-sensitive adhesive composition, corrosion of ITO can be suppressed.
However, the conventional pressure-sensitive adhesive composition for polarizing plates is sufficiently soft when used as a pressure-sensitive adhesive layer, and is difficult to cause peeling. A copolymer is used. Here, when an acrylic copolymer with few acidic groups is used in the pressure-sensitive adhesive composition, it becomes too hard when used as a pressure-sensitive adhesive layer, and it tends to peel off due to changes in temperature and humidity, resulting in durability. Problems arise. For this reason, there is no known pressure-sensitive adhesive composition that uses an acrylic copolymer with few acidic groups and achieves both durability and suppression of white spots when used as a pressure-sensitive adhesive layer.

  The present invention has been made in view of the above problems, and provides a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet that achieve both durability and suppression of white spots while using an acrylic copolymer with few acidic groups. With the goal.

Means for solving the above problems include the following embodiments.
<1> A (meth) acrylic copolymer A having a hydroxyl group-containing monomer in a range of 0.001% by mass to 0.5% by mass with respect to all the structural units, and a hydroxyl group. The structural unit derived from the monomer is in the range of 0.1% by mass to 4% by mass with respect to all the structural units, and the content of the structural unit derived from the monomer having a hydroxyl group is the (meth) acrylic. (Meth) acrylic copolymer B, the (meth) acrylic copolymer A, and the (meth) acrylic are higher than the content of the structural unit derived from the monomer having a hydroxyl group of the acrylic copolymer A And a tolylene diisocyanate compound in the range of 5 to 30 parts by mass with respect to 100 parts by mass of the total amount of the copolymer B, and the (meth) acryl for the (meth) acrylic copolymer B The content ratio (A / B) of the copolymer A is The total acid value of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B is 2.5 mgKOH / g or less. A pressure-sensitive adhesive composition.
<2> In the (meth) acrylic copolymer A and the (meth) acrylic copolymer B, the content of the structural unit derived from the monomer having a hydroxyl group is the (meth) acrylic copolymer weight. <1> The pressure-sensitive adhesive composition according to <1>, which is in a range of 0.05% by mass to 1.5% by mass with respect to all structural units of the coalescence A and the (meth) acrylic copolymer B.
<3> Derived from the monomer having a hydroxyl group of the (meth) acrylic copolymer B with respect to the content rate a of the structural unit derived from the monomer having a hydroxyl group of the (meth) acrylic copolymer A The pressure-sensitive adhesive composition according to <1> or <2>, wherein the ratio (b / a) of the content rate b of the constituent units to be in the range of 5 to 500.
<4> An imidazole compound in a range of 0.01 to 1.5 parts by mass with respect to 100 parts by mass of the total amount of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B. Furthermore, the pressure-sensitive adhesive composition according to any one of <1> to <3>.
<5> A silane coupling agent in a range of 0.05 parts by mass to 1 part by mass with respect to 100 parts by mass of the total amount of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B. Furthermore, the pressure-sensitive adhesive composition according to any one of <1> to <4>.
<6> The pressure-sensitive adhesive composition according to any one of <1> to <5>, wherein the total acid value is 0 mgKOH / g.
<7> The pressure-sensitive adhesive composition according to any one of <1> to <6>, wherein the tolylene diisocyanate compound is an adduct of tolylene diisocyanate and a polyol.
<8> The glass transition temperature (TgA) of the (meth) acrylic copolymer A is in the range from −60 ° C. to −40 ° C., and the glass transition temperature (TgB) of the (meth) acrylic copolymer B. Is a range of −55 ° C. or higher and −25 ° C. or lower, and TgA is lower than TgB, according to any one of <1> to <7>.
<9> Any one of <1> to <8>, wherein the storage elastic modulus (G ′) at 30 ° C. after crosslinking is in the range of 2.0 × 10 ⁵ Pa to 1.0 × 10 ⁷ Pa. 2. The pressure-sensitive adhesive composition according to 1.

  <10> A pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer formed from the pressure-sensitive adhesive composition according to any one of <1> to <9>.

  According to the present invention, it is possible to provide a pressure-sensitive adhesive composition and a pressure-sensitive adhesive sheet that achieve both durability and suppression of white spots while using an acrylic copolymer with few acidic groups.

Embodiments that are examples of the present invention will be described below. In addition, the numerical value range shown using "to" in this specification shows the range which includes the numerical value described before and behind "to" as a minimum value and a maximum value, respectively. In addition, in the present specification, the amount of each component in the composition is such that when a plurality of substances corresponding to each component are used in the pressure-sensitive adhesive composition, a plurality of types corresponding to that component are used unless otherwise specified. It means the total amount of substance.
Furthermore, (meth) acryl means at least one of acryl and methacryl, and (meth) acrylate means at least one of acrylate and methacrylate.
Furthermore, the pressure-sensitive adhesive composition is a composition before the crosslinking reaction between the (meth) acrylic copolymer and the tolylene diisocyanate compound is completed. For example, a liquid, pasty or powdery composition is used. means.
The pressure-sensitive adhesive layer is a layer after the crosslinking reaction between the (meth) acrylic copolymer and the tolylene diisocyanate compound is completed, and means, for example, a solid or gel layer.

[Adhesive composition]
The pressure-sensitive adhesive composition in the present invention is a (meth) acrylic copolymer having a structural unit derived from a monomer having a hydroxyl group in a range of 0.001% by mass to 0.5% by mass with respect to all the structural units. A and the content rate of the structural unit which has a structural unit derived from the monomer which has a hydroxyl group in the range of 0.1 mass%-4 mass% with respect to all the structural units, and originates in the monomer which has a hydroxyl group (Meth) acrylic copolymer B having a higher content of structural units derived from the monomer having a hydroxyl group of the (meth) acrylic copolymer A, and the (meth) acrylic copolymer A And a tolylene diisocyanate compound in a range of 5 to 30 parts by mass with respect to 100 parts by mass of the total amount of the (meth) acrylic copolymer B, and the (meth) acrylic copolymer B (Meth) acrylic copolymer for Content ratio (A / B) is in the range of 60/40 to 95/5 on a mass basis, and the acid value of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B is The total is 2.5 mgKOH / g or less.

  In the pressure-sensitive adhesive composition of the present invention, the total acid value of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B is as low as 2.5 mgKOH / g or less. When it is used for pasting touch panels, it is difficult to corrode ITO.

  Furthermore, the pressure-sensitive adhesive composition of the present invention achieves both durability and suppression of white spots when an optical film such as a polarizing plate or a touch panel is attached to an adherend such as a liquid crystal cell as a pressure-sensitive adhesive layer. The reason is presumed as follows.

In the pressure-sensitive adhesive composition of the present invention, a tolylene diisocyanate formed by reacting a cross-linked product obtained by chemically crosslinking a (meth) acrylic copolymer with a tolylene diisocyanate compound and a tolylene diisocyanate compound. The condensate is present.
Since the tolylene diisocyanate condensate is relatively hard, it is possible to suppress the generation of stress, and since the crosslinked product is relatively soft, adhesion to the adherend is considered to be good.
Therefore, it is thought that it is excellent in coexistence with durability and suppression of a white spot by making the hardness by a condensate and the partial softness by a crosslinked body into an appropriate range. More specifically, it is estimated as follows.

The pressure-sensitive adhesive composition in the present invention is a (meth) acrylic copolymer having a structural unit derived from a monomer having a hydroxyl group in a range of 0.001% by mass to 0.5% by mass with respect to all the structural units. A and the content rate of the structural unit which has a structural unit derived from the monomer which has a hydroxyl group in the range of 0.1 mass%-4 mass% with respect to all the structural units, and originates in the monomer which has a hydroxyl group (Meth) acrylic copolymer A and (meth) acrylic copolymer B higher than the content rate of the structural unit derived from the monomer which has a hydroxyl group of (meth) acrylic copolymer A. Further, the content ratio (A / B) of the (meth) acrylic copolymer A to the (meth) acrylic copolymer B is in the range of 60/40 to 95/5 on a mass basis. That is, the pressure-sensitive adhesive composition in the present invention contains two acrylic copolymers having different constituent unit contents derived from a monomer having a hydroxyl group at a predetermined ratio.
For this reason, a relatively hard portion and a relatively soft portion are also formed at a predetermined ratio in the soft portion of the pressure-sensitive adhesive layer due to the presence of the crosslinked body. Of these two parts, the relatively hard part suppresses the occurrence of stress to suppress white spots, and the relatively soft part increases the adhesion to an adherend such as a touch panel, an optical film, or a liquid crystal cell. It is difficult to peel off and has excellent durability. Since these two parts are contained in an appropriate ratio, the pressure-sensitive adhesive composition in the present invention can achieve both durability and suppression of white spots.

  In addition, unlike the pressure-sensitive adhesive composition in the present invention, it is difficult to achieve both durability and suppression of white spots with a pressure-sensitive adhesive composition using one kind of acrylic copolymer.

  Furthermore, when the pressure-sensitive adhesive composition in the present invention comprises a tolylene diisocyanate compound in the range of 5 to 30 parts by mass with respect to 100 parts by mass of the (meth) acrylic copolymer, a pressure-sensitive adhesive layer is formed. It becomes hard to suppress the generation of stress. More specifically, by including 5 parts by mass or more of tolylene diisocyanate compound as a crosslinking agent, it is excellent in durability (particularly heat resistance), can suppress foaming and peeling, and can also suppress white spots. it can. Moreover, by including 30 parts by mass or less of a tolylene diisocyanate compound as a crosslinking agent, it is possible to suppress whitening when used as a pressure-sensitive adhesive layer, and bonding of articles that require transparency such as touch panels and optical films. It is possible to use it suitably.

  In addition, since the pressure-sensitive adhesive composition of the present invention contains a tolylene diisocyanate compound as a crosslinking agent, it can be suitably used for laminating touch panels and optical films, and has both durability and suppression of white spots. it can. On the other hand, when the cross-linking agent is a xylene diisocyanate compound, the compatibility between the (meth) acrylic copolymer A and the (meth) acrylic copolymer B and the xylene diisocyanate compound is poor, and the pressure-sensitive adhesive layer is white. And cannot be used for bonding articles such as touch panels and optical films that require transparency. In addition, when the cross-linking agent is a hexamethylene diisocyanate compound, when the pressure-sensitive adhesive layer is used, hardness sufficient to suppress the generation of stress cannot be obtained, and white spots occur, and durability and white spots are suppressed. Cannot be compatible.

[(Meth) acrylic copolymer A and (meth) acrylic copolymer B]
The pressure-sensitive adhesive composition in the present invention is a (meth) acrylic copolymer having a structural unit derived from a monomer having a hydroxyl group in a range of 0.001% by mass to 0.5% by mass with respect to all the structural units. A and the content rate of the structural unit which has a structural unit derived from the monomer which has a hydroxyl group in the range of 0.1 mass%-4 mass% with respect to all the structural units, and originates in the monomer which has a hydroxyl group And (meth) acrylic copolymer B, which is higher than the content of the structural unit derived from the monomer having a hydroxyl group of (meth) acrylic copolymer A. Furthermore, the pressure-sensitive adhesive composition of the present invention has a content ratio (A / B) of (meth) acrylic copolymer A to (meth) acrylic copolymer B of 60/40 to 95/5 on a mass basis. The total acid value of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B is 2.5 mgKOH / g or less.

  The (meth) acrylic copolymer A and (meth) acrylic copolymer B used in the present invention are preferably copolymers mainly composed of alkyl (meth) acrylate, and have a carboxyl group as necessary. Monomers and other monomers may be used as copolymerization components. Here, the copolymer mainly composed of alkyl (meth) acrylate is a copolymer having 50 mass% or more of structural units derived from alkyl (meth) acrylate with respect to 100 mass% of structural units in the copolymer. It is a coalescence.

The content ratio (A / B) of (meth) acrylic copolymer A to (meth) acrylic copolymer B is in the range of 60/40 to 95/5 on a mass basis. When the content ratio (A / B) is smaller than 60/40, that is, when the content of the (meth) acrylic copolymer B is too large, the crosslinked part becomes excessively hard when the pressure-sensitive adhesive layer is formed and peels off. Tends to occur and is inferior in durability. If the content ratio is greater than 95/5, that is, if the content of the (meth) acrylic copolymer A is too large, the crosslinked body portion becomes excessively soft when used as an adhesive layer, and the suppression of white spots is inferior.
From the same viewpoint, the content ratio (A / B) is preferably in the range of 65/35 to 90/10, and more preferably in the range of 70/30 to 85/15.

  Since the total acid value of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B is 2.5 mgKOH / g or less, for example, when used for bonding a capacitive touch panel It is difficult to corrode ITO. From the viewpoint of more suitably suppressing the corrosion of ITO, the total acid value is preferably 2.0 mgKOH / g or less, more preferably 1.0 mgKOH / g or less, still more preferably 0.5 mgKOH / g or less, and 0 mgKOH / g. g is particularly preferred. The total acid value is a value calculated by the following calculation formula.

Acid value of (meth) acrylic copolymer A (mgKOH / g) = (A / B) × 56.1 × 10 × G
A = content (% by mass) of the monomer having a carboxyl group in all monomers used in the (meth) acrylic copolymer A
B = Molecular weight of the monomer having a carboxyl group used in the (meth) acrylic copolymer A G = Carbon group-containing monomer used in the (meth) acrylic copolymer A Number of carboxyl groups 56.1 is the molecular weight of KOH.

Acid value of (meth) acrylic copolymer B (mgKOH / g) = (C / D) × 56.1 × 10 × H
C = content of monomer having a carboxyl group in all monomers used for (meth) acrylic copolymer B (mass%)
D = Molecular weight of monomer having carboxyl group used in (meth) acrylic copolymer B H = Carbon group-containing monomer used in (meth) acrylic copolymer B Number of carboxyl groups 56.1 is the molecular weight of KOH.

  When the monomer having a carboxyl group used in the (meth) acrylic copolymer A or the (meth) acrylic copolymer B is two or more, the above formula is used for each monomer. Similarly, the acid value is obtained, and the obtained values are summed to obtain the acid value.

Total acid value (mgKOH / g) = [acid value of (meth) acrylic copolymer A × E / (E + F)] + [acid value of (meth) acrylic copolymer B × F / (E + F) ]
E = content of (meth) acrylic copolymer A (parts by mass)
F = content of (meth) acrylic copolymer B (parts by mass)

  The (meth) acrylic copolymer A and the (meth) acrylic copolymer B have structural units derived from a monomer having a hydroxyl group, and the hydroxyl group and the tolylene diisocyanate compound are Each undergoes a crosslinking reaction. Therefore, the cohesive force of the pressure-sensitive adhesive composition is increased, the pressure-sensitive adhesive force is excellent, and foaming can be suppressed in the durability test.

  Examples of the alkyl (meth) acrylate that is the main component of the (meth) acrylic copolymer A and (meth) acrylic copolymer B used in the present invention include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, sec-butyl (meth) acrylate, t-butyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) Acrylate, n-nonyl (meth) acrylate, isononyl (meth) acrylate, n-decyl (meth) acrylate, n-dodecyl (meth) acrylate, stearyl (meth) acrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate Raising It is. The alkyl group of the alkyl (meth) acrylate may be linear, branched or cyclic. 1-18 are preferable, as for carbon number of an alkyl group, 1-8 are more preferable, and 1-4 are still more preferable.

  In the (meth) acrylic copolymer A and the (meth) acrylic copolymer B, the content of the alkyl (meth) acrylate is preferably 80% by mass or more because it is easy to adjust the adhesive property and the viscoelastic property, 90 mass% or more is more preferable, and 95 mass% or more is still more preferable.

  Furthermore, as the alkyl (meth) acrylate which is the main component of the (meth) acrylic copolymer A, since it is easy to achieve both hardness and softness, at least any of methyl (meth) acrylate and n-butyl (meth) acrylate Are preferred, at least one of methyl acrylate and n-butyl acrylate is more preferred, and n-butyl acrylate is still more preferred.

  Further, as the alkyl (meth) acrylate which is the main component of the (meth) acrylic copolymer B, since both hardness and softness are easily achieved, methyl (meth) acrylate, n-butyl (meth) acrylate and t- At least one of butyl (meth) acrylate is preferable, at least one of n-butyl acrylate, t-butyl acrylate and methyl acrylate is more preferable, and a combination of n-butyl acrylate and t-butyl acrylate and n-butyl acrylate More preferred is at least one of a combination with methyl acrylate.

  Examples of the monomer having a hydroxyl group which is one component of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B used in the present invention include a (meth) acrylic monomer having a hydroxyl group, Saturated alcohol etc. are mentioned.

  Examples of the (meth) acrylic monomer having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth). Acrylate, 3-methyl-3-hydroxybutyl (meth) acrylate, 1,1-dimethyl-3-hydroxybutyl (meth) acrylate, 1,3-dimethyl-3-hydroxybutyl (meth) acrylate, 2,2,4 -Hydroxyalkyl (meth) acrylate represented by trimethyl-3-hydroxypentyl (meth) acrylate, 2-ethyl-3-hydroxyhexyl (meth) acrylate, glycerin mono (meth) acrylate, polypropylene glycol mono (meth) acrylate The Ethylene glycol mono (meth) acrylate, poly (ethylene glycol - propylene glycol) mono (meth) acrylate, N- methylolacrylamide.

  Among them, the (meth) acrylic monomer having a hydroxyl group has a carbon number from the viewpoint of good compatibility and copolymerization with other monomers and good crosslinking reaction with a crosslinking agent. A hydroxyalkyl (meth) acrylate having a hydroxyalkyl group of 1 to 5 is preferred, and a hydroxyalkyl (meth) acrylate having a hydroxyalkyl group having 2 to 4 carbon atoms is more preferred. Specifically, 2-hydroxyethyl (meth) acrylate and 4-hydroxybutyl (meth) acrylate are preferable, and 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate are more preferable.

  Examples of the unsaturated alcohol include allyl alcohol and methallyl alcohol.

The (meth) acrylic copolymer A has a structural unit derived from a monomer having a hydroxyl group in a range of 0.001% by mass to 0.5% by mass with respect to all the structural units.
Since the content of the structural unit derived from the monomer having a hydroxyl group of the (meth) acrylic copolymer A is 0.001% by mass or more, the pressure-sensitive adhesive layer does not become too soft, and the gas from the optical film Since generation (foaming) can be suppressed, durability can be enhanced. In addition, since the (meth) acrylic copolymer A has a content of 0.5% by mass or less, the pressure-sensitive adhesive layer does not become too hard and has excellent adhesion with the adherend. Peeling can be suppressed.
From the same viewpoint, the (meth) acrylic copolymer A has a structural unit derived from a monomer having a hydroxyl group in the range of 0.005% by mass to 0.1% by mass with respect to all the structural units. It is preferable to have it in the range of 0.005 mass% to 0.05 mass%.

Moreover, the (meth) acrylic-type copolymer B has the structural unit derived from the monomer which has a hydroxyl group in 0.1 mass%-4 mass% with respect to all the structural units.
Since the content of the structural unit derived from the monomer having a hydroxyl group of the (meth) acrylic copolymer B is 0.1% by mass or more, white spots are suppressed by suppressing the generation of stress. . In addition, since the content of the (meth) acrylic copolymer B is 4% by mass or less, the pressure-sensitive adhesive layer does not become too hard, has excellent adhesion to the adherend, and peels from the adherend. Can be suppressed.
From the same viewpoint, the (meth) acrylic copolymer B has a structural unit derived from a monomer having a hydroxyl group in a range of 0.5% by mass to 2% by mass with respect to all the structural units. It is preferable.

  Moreover, the content rate of the structural unit derived from the monomer which has a hydroxyl group of the (meth) acrylic-type copolymer B is the content rate of the structural unit derived from the monomer which has a hydroxyl group of the (meth) acrylic-type copolymer A. Greater than content. For this reason, the pressure-sensitive adhesive composition in the present invention contains two acrylic copolymers having different content of structural units derived from the monomer having a hydroxyl group, and the soft part of the pressure-sensitive adhesive layer, that is, acrylic A comparatively hard part and a comparatively soft part are also formed in the crosslinked part of the system copolymer. As a result, the adhesiveness with the adherend can be enhanced while suppressing the generation of stress, and therefore the pressure-sensitive adhesive composition in the present invention is superior in achieving both durability and suppression of white spots.

Moreover, the content rate of the structural unit derived from the monomer which has a hydroxyl group in (meth) acrylic-type copolymer A and (meth) acrylic-type copolymer B is (meth) acrylic-type copolymer A and ( The range of 0.05% by mass to 1.5% by mass with respect to all structural units of the (meth) acrylic copolymer B is preferred.
When the content is 0.05% by mass or more, the pressure-sensitive adhesive layer does not become too soft, and the generation (foaming) of gas from the optical film can be suppressed, so that durability can be enhanced. Further, when the content is 1.5% by mass or less, the pressure-sensitive adhesive layer does not become too hard, has excellent adhesion to the adherend, and can prevent peeling from the adherend.
From the same viewpoint, the content is preferably in the range of 0.1% by mass to 1.0% by mass.
In other words, in other words, in the pressure-sensitive adhesive composition with respect to all the structural units (mass basis) of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B in the pressure-sensitive adhesive composition. A structural unit derived from a monomer having a hydroxyl group contained in the (meth) acrylic copolymer A and a structural unit derived from a monomer having a hydroxyl group contained in the (meth) acrylic copolymer B It is the ratio of the total mass.

  Moreover, the structural unit derived from the monomer which has a hydroxyl group of the (meth) acrylic copolymer B with respect to the content rate a of the structural unit derived from the monomer having a hydroxyl group of the (meth) acrylic copolymer A The content ratio b (b / a) is preferably in the range of 5 to 500, more preferably in the range of 10 to 300, and in the range of 20 to 200, from the viewpoint of achieving both durability and suppression of white spots. Particularly preferred.

  In the range where the total acid value of (meth) acrylic copolymer A and (meth) acrylic copolymer B is 2.5 mgKOH / g or less, (meth) acrylic copolymer A and (meth) acrylic The copolymer B may have a monomer having a carboxyl group as a copolymerization component. Examples of the monomer having a carboxyl group include a (meth) acrylic monomer having a carboxyl group. Examples of the (meth) acrylic monomer having a carboxyl group include acrylic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, itaconic acid, citraconic acid, cinnamic acid, and monohydroxyethyl succinate. (Meth) acrylate, monohydroxyethyl maleate (meth) acrylate, monohydroxyethyl fumarate (meth) acrylate, monohydroxyethyl phthalate (meth) acrylate, 1,2-dicarboxycyclohexane monohydroxyethyl (meth) acrylate, (Meth) acrylic acid dimer, ω-carboxy-polycaprolactone mono (meth) acrylate.

  In the (meth) acrylic copolymer, the content of the structural unit derived from the monomer having a carboxyl group is 0. 0 with respect to all the structural units from the viewpoint of suppressing the corrosion of ITO by lowering the acid value. It is preferably 2% by mass or less, more preferably 0.05% by mass or less, and further preferably 0% by mass, that is, not including.

  The (meth) acrylic copolymer A and the (meth) acrylic copolymer B used in the present invention are other than the aforementioned alkyl (meth) acrylate, a monomer having a hydroxyl group, and a monomer having a carboxyl group. The monomer may be used as a copolymerization component. Examples of other monomers include (meth) acrylic monomers having an aromatic ring, (meth) acrylic monomers having a nitrogen atom, and other copolymerizable monomers.

  The (meth) acrylic copolymer A and (meth) acrylic copolymer B used in the present invention may contain a (meth) acrylic monomer having an aromatic ring as a copolymerization component. Thereby, the pressure-sensitive adhesive composition of the present invention can easily suppress white spots when used for adhesion of a polarizing plate.

  Examples of the (meth) acrylic monomer having an aromatic ring include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, phenoxydiethylene glycol (meth) acrylate, ethylene oxide (EO) -modified cresol (meth) acrylate, Examples include ethylene oxide (EO) -modified nonylphenol (meth) acrylate, hydroxyethylated β-naphthol acrylate, and biphenyl (meth) acrylate.

  The (meth) acrylic copolymer A and (meth) acrylic copolymer B used in the present invention may contain a (meth) acrylic monomer having a nitrogen atom as a copolymerization component. When a (meth) acrylic monomer having a nitrogen atom is included as a copolymer component, the curing time tends to be shortened.

  Examples of the (meth) acrylic monomer having a nitrogen atom include aminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, N, N-dimethyl (meth) acrylamide, N, N-diethylacrylamide, N-ethyl, N-methyl (meth) acrylamide, N-isopropyl (meth) acrylamide may be mentioned.

  The (meth) acrylic copolymer A and (meth) acrylic copolymer B used in the present invention may contain other copolymerizable monomers as a copolymerization component. Examples of such a monomer include aromatic monovinyl monomers represented by styrene, α-methylstyrene, t-butylstyrene, p-chlorostyrene, chloromethylstyrene, vinyltoluene, and vinylpyridine. , Vinyl cyanide monomers represented by acrylonitrile, methacrylonitrile, and vinyl carboxylates represented by, for example, vinyl formate, vinyl acetate, vinyl propionate, “vinyl versatate” (trade name, vinyl neodecanoate) Examples thereof include monomers and various derivatives thereof.

  The weight average molecular weight (Mw) of the (meth) acrylic copolymer A and (meth) acrylic copolymer B used in the present invention is not particularly limited, but is preferably in the range of 700,000 to 2,000,000. The range of 10,000 to 1,500,000 is preferable. The weight average molecular weight can be adjusted by the polymerization reaction temperature, time, the amount of organic solvent, and the like. When the weight average molecular weight is in the range of 700,000 to 2,000,000, the viscosity of the pressure-sensitive adhesive composition of the present invention is low, and coating properties are good, which is preferable.

The weight average molecular weights (Mw) of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B are values measured by the following methods, respectively.
(Measurement method of weight average molecular weight (Mw))
It measures according to following (1)-(3).
(1) A (meth) acrylic copolymer solution ((meth) acrylic copolymer A or a solution containing a (meth) acrylic copolymer) is applied to release paper and dried at 100 ° C. for 2 minutes, A film-like (meth) acrylic copolymer is obtained.
(2) The film-like (meth) acrylic copolymer obtained in (1) is dissolved in tetrahydrofuran so that the solid content is 0.2%.
(3) The weight average molecular weight (Mw) of the (meth) acrylic copolymer is measured as a standard polystyrene equivalent value using gel permeation chromatography (GPC) under the following conditions.
(conditions)
GPC: HLC-8220 GPC [manufactured by Tosoh Corporation]
Column: 4 TSK-GEL GMHXL used Mobile phase solvent: Tetrahydrofuran Flow rate: 0.6 ml / min
Column temperature: 40 ° C

  The glass transition temperature (TgA) of (meth) acrylic copolymer A used in the present invention and the glass transition temperature (TgB) of (meth) acrylic copolymer B give sufficient cohesive force to the pressure-sensitive adhesive composition. For the purpose of exhibiting sufficient durability, −80 ° C. or higher is preferable, and −60 ° C. or higher is more preferable. Moreover, TgA and TgB are preferably −25 ° C. or lower for the purpose of causing the adhesive composition to exhibit sufficient adhesion to the support substrate and exhibiting durability that does not cause peeling.

  More specifically, TgA is preferably in the range of −60 ° C. to −40 ° C., and TgB is preferably in the range of −55 ° C. to −25 ° C. When TgA is within the above numerical range, durability when used as an adhesive layer is higher, and white spots are further suppressed. When TgB is within the above numerical range, peeling from the adherend hardly occurs when the pressure-sensitive adhesive layer is formed, and durability is further increased.

Further, TgA is preferably in the range of −60 ° C. or more and −45 ° C. or less, and more preferably in the range of −60 ° C. or more and −50 ° C. or less from the viewpoint of further improving durability and further suppressing white spots.
From the same viewpoint, TgB is preferably in the range of −55 ° C. or higher and −30 ° C. or lower.

  Further, TgA and TgB are preferably 0 <TgB-TgA ≦ 30, and 0 <TgB-TgA ≦ 30 and −60 ≦ TgA ≦ −50 from the viewpoint of further improving durability and further suppressing white spots. More preferred.

  TgA and TgB are values obtained by converting the absolute temperature (K) obtained by calculation of the following formula into Celsius temperature (° C.) for each copolymer.

_Wherein, Tg _1, Tg 2, ..... and Tg _n is the monomer 1, monomer 2, a ..... and the monomer n each monomer was homopolymer It is a glass transition temperature expressed in absolute temperature (K). m ₁ , m ₂ ,..., and _mn are the mole fractions of the respective monomers.

  The “glass transition temperature represented by the absolute temperature (K) when used as a homopolymer” is represented by the absolute temperature (K) of a homopolymer produced by polymerizing the monomer alone. Refers to the glass transition temperature. The glass transition temperature of the homopolymer was measured using a differential scanning calorimeter (DSC) (manufactured by Seiko Instruments Inc., EXSTAR 6000), in a nitrogen stream, 10 mg of a measurement sample, and a heating rate of 10 ° C./min. Measurement is performed under the conditions, and the inflection point of the obtained DSC curve is defined as the glass transition temperature of the homopolymer.

The typical monomer “glass transition temperature expressed in Celsius temperature (° C.) of homopolymer” is 5 ° C. for methyl acrylate, −27 ° C. for ethyl acrylate, − 57 ° C, 2-ethylhexyl acrylate is -76 ° C, 2-hydroxyethyl acrylate is -15 ° C, 4-hydroxybutyl acrylate is -39 ° C, t-butyl acrylate is 41 ° C, Acrylic acid is 163 ° C. For example, the glass transition temperatures TgA and TgB described above can be appropriately adjusted by using these representative monomers.
The absolute temperature (K) can be converted into the Celsius temperature (° C.) by subtracting 273 from the absolute temperature (K), and the Celsius temperature (° C.) can be converted into the absolute temperature (° C.) by adding 273 to the Celsius temperature (° C.). K) can be converted.

  The production method of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B used in the present invention is not particularly limited, and may be a simple method such as solution polymerization, emulsion polymerization or suspension polymerization. It can be produced by polymerizing a monomer. In preparing the pressure-sensitive adhesive composition of the present invention after production, solution polymerization is preferred because the treatment process can be performed relatively easily and in a short time.

  In solution polymerization, a predetermined organic solvent, a monomer, a polymerization initiator, and a chain transfer agent used as needed are generally charged in a polymerization tank, and stirred in a nitrogen stream or at the reflux temperature of the organic solvent. However, a method such as heating reaction for several hours can be used. In addition, the weight average molecular weight of a (meth) acrylic-type copolymer can be made into a desired value by adjusting reaction temperature, time, the amount of solvents, and the kind and quantity of a catalyst.

  As an organic solvent for polymerization used in the production of (meth) acrylic copolymer A and (meth) acrylic copolymer B, aromatic hydrocarbon compounds, aliphatic or alicyclic hydrocarbon compounds, esters Examples include compounds, ketone compounds, glycol ether compounds, alcohol compounds, and the like. These organic solvents may be used alone or in combination of two or more. Moreover, as a polymerization initiator, the organic peroxide and azo compound which can be used with a normal polymerization method are mentioned, for example.

[Tolylene diisocyanate compounds]
The pressure-sensitive adhesive composition according to the present invention is a tolylene diisocyanate in the range of 5 to 30 parts by mass with respect to a total of 100 parts by mass of (meth) acrylic copolymer A and (meth) acrylic copolymer B. Contains compounds.
The tolylene diisocyanate compound functions as a crosslinking agent.

  Tolylene diisocyanate compounds include tolylene diisocyanate, tolylene diisocyanate dimer, tolylene diisocyanate-polyol adduct, tolylene diisocyanate trimer or pentamer isocyanurate, tolylene diisocyanate Tolylene diisocyanate compounds derived from various tolylene diisocyanates such as burettes can be used. Among these, tolylene diisocyanate from the point that it is excellent in reactivity and can increase the crosslink density, and is excellent in compatibility with (meth) acrylic copolymer A and (meth) acrylic copolymer B. Adducts with polyols are preferred, and adducts with tolylene diisocyanate and trimethylolpropane are particularly preferred.

  The content of the tolylene diisocyanate compound in the pressure-sensitive adhesive composition is 5 parts by mass to 30 parts by mass with respect to 100 parts by mass in total of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B. Range. By containing 5 parts by mass or more of the tolylene diisocyanate compound, foaming and peeling can be suppressed, and durability (particularly heat resistance) is excellent. By containing 30 parts by mass or less of tolylene diisocyanate compound, it is possible to suppress whitening when used as an adhesive layer and to be suitably used for bonding articles such as touch panels and optical films that require transparency. Is possible.

  The content of the tolylene diisocyanate compound in the pressure-sensitive adhesive composition is 10 to 30 parts by mass with respect to a total of 100 parts by mass of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B. Is preferable, and the range of 12 to 30 parts by mass is more preferable. Thereby, it is excellent by coexistence with durability when it is set as an adhesive layer, and suppression of white spot.

  As the tolylene diisocyanate compound, a commercially available product may be used. In commercial products, as an adduct of tolylene diisocyanate and trimethylolpropane, “Coronate L” (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd. "Coronate 2030" etc. can be used conveniently.

[Other cross-linking agents]
The pressure-sensitive adhesive composition in the present invention may contain other crosslinking agents other than the tolylene diisocyanate compound within a range not impairing the object of the present invention. Other crosslinking agents are not particularly limited, and examples thereof include polyisocyanate compounds other than tolylene diisocyanate compounds, polyepoxy compounds, polyaziridine compounds, and metal chelate compounds. These other crosslinking agents can be used alone or in combination of two or more with a tolylene diisocyanate compound.

[Imidazole compound]
The pressure-sensitive adhesive composition in the present invention preferably contains an imidazole compound. The imidazole compound functions as, for example, a crosslinking catalyst in the pressure-sensitive adhesive composition. When the pressure-sensitive adhesive composition contains an imidazole compound, the curing time can be further shortened while maintaining excellent durability.
By including the imidazole compound, the curing time can be shortened without using a crosslinking catalyst containing a tin compound that is often used when the crosslinking point is a hydroxyl group and the crosslinking agent is an isocyanate compound.

  The imidazole compound is not particularly limited as long as it is a compound having at least one imidazole ring in the molecule, but an N-substituted imidazole compound is preferable from the viewpoint of shortening the curing time and increasing the pot life. The N-substituted imidazole compound is not particularly limited as long as it has at least one imidazole ring in the molecule and does not have a hydrogen atom on the nitrogen atom of the imidazole ring.

  Specific examples of the N-substituted imidazole compound include compounds represented by the following general formula (I).

In the general formula (I), in the formula (I), R ₁ , R ₂ and R ₄ each independently represent a hydrogen atom or a substituent, and R ₃ represents a substituent. Preferably, in general formula (I), R ₁ , R ₂ , and R ₄ each independently represent a hydrogen atom, an alkyl group, an aryl group, or an aralkyl group, and R ₃ represents an alkyl group, an aryl group, or an aralkyl group. Represents. R ₁ and R ₂ , or R ₃ and R ₄ may be connected to each other to form a cyclic structure.

The alkyl group (R _{1 to} R ₄ ) in the general formula (I) may be linear or branched. Moreover, as for carbon number of an alkyl group, 1-2 are preferable. The aryl group (R _{1 to} R ₄ ) in the general formula (I) preferably has 6 to 10 carbon atoms, and more preferably a phenyl group or a naphthyl group. The aralkyl group (R _{1 to} R ₄ ) in the general formula (I) is preferably composed of an alkylene group having 1 to 2 carbon atoms and an aryl group having 6 to 10 carbon atoms, and more preferably a benzyl group or a phenylethyl group. .

In the N-substituted imidazole compound represented by the general formula (I), R ₃ is an alkyl group or an aralkyl group from the viewpoint of shortening the curing time and prolonging the pot life, and R ₁ , R ₂ and R ₄ Are each independently preferably a hydrogen atom, an alkyl group or an aryl group. Among them, the N-substituted imidazole compound represented by the general formula (I) is at least one selected from the group consisting of 1,2-dimethylimidazole, 1-benzyl-2-methylimidazole and 1-benzyl-2-phenylimidazole. Is more preferable. Also preferred is an embodiment in which R ₃ and R ₄ are connected to each other to form a 5- or 6-membered saturated aliphatic ring, and R ₁ and R ₂ are connected to each other to form a 6-membered aromatic ring. From this viewpoint, 2,3-dihydro-1H-pyrrolo [1,2-a] benzimidazole is more preferable.

  The content of the imidazole compound in the pressure-sensitive adhesive composition is a total of 100 masses of (meth) acrylic copolymer A and (meth) acrylic copolymer B from the viewpoint of shortening the curing time and prolonging the pot life. The range of 0.01 parts by mass to 1.5 parts by mass is preferable, the range of 0.05 parts by mass to 1.2 parts by mass is more preferable, and the range of 0.1 parts by mass to 1.0 part by mass is preferable. A range is more preferred.

  Examples of the N-substituted imidazole compound used in the present invention include commercially available products such as “CUREZOL 1,2DMZ”, “CURESOL 1B2MZ”, “CURESOL 1B2PZ”, “CUREZOLE TBZ” manufactured by Shikoku Kasei Kogyo Co., Ltd. It is done.

  In addition, in order to increase the reaction rate and shorten the curing time, a tin compound may be used instead of the imidazole compound as a crosslinking catalyst, or an imidazole compound and a tin compound may be combined. The catalyst is preferably an imidazole compound. The preferable range of the content of the tin compound in the pressure-sensitive adhesive composition (the total amount when the imidazole compound and the tin compound are combined) is the same as the content of the imidazole compound described above.

[Silane coupling agent]
The pressure-sensitive adhesive composition in the present invention preferably further contains a silane coupling agent. When the pressure-sensitive adhesive composition contains a silane coupling agent, the pressure-sensitive adhesive layer exhibits better adhesion to glass, and the liquid crystal display device incorporating the polarizing plate is exposed to a high temperature environment or a high temperature and high humidity environment. Even if it is done, there exists a tendency for peeling to become difficult to generate | occur | produce between an adhesive layer and a polarizing plate or a liquid crystal cell.

  Examples of the silane coupling agent include a coupling agent having a mercapto group, a coupling agent having an epoxy group, a coupling agent having a carboxyl group, a coupling agent having an amino group, a coupling agent having a hydroxyl group, and an amide. Examples thereof include a coupling agent having a group, a coupling agent having an isocyanate group, and a coupling agent having an isocyanurate skeleton. These silane coupling agents may be used alone or in combination of two or more.

  As the silane coupling agent, a commercially available product may be used. Examples of commercially available products include “KBM-403”, “KBM-303”, “KBM-402”, “KBE-402”, and “KBE-403” (trade names) manufactured by Shin-Etsu Chemical Co., Ltd. A silane coupling agent having an epoxy group can be preferably used.

  When the pressure-sensitive adhesive composition in the present invention contains a silane coupling agent, the content of the silane coupling agent in the pressure-sensitive adhesive composition is (meth) acrylic copolymer A and (meth) acrylic copolymer B. Is preferably in the range of 0.05 parts by mass to 0.7 parts by mass, and more preferably in the range of 0.1 parts by mass to 0.5 parts by mass.

[solvent]
In the pressure-sensitive adhesive composition of the present invention, a solvent may be added to improve applicability to optical films such as polarizing plates, touch panels, liquid crystal cells, and the like.

  Examples of the solvent include hydrocarbons represented by hexane, heptane, octane, toluene, xylene, ethylbenzene, cyclohexane, and methylcyclohexane, halogenated hydrocarbons represented by dichloromethane, trichloroethane, trichloroethylene, tetrachloroethylene, and dichloropropane. Methanol, ethanol, propanol, isopropyl alcohol, butanol, isobutyl alcohol, alcohols represented by diacetone alcohol, diethyl ether, diisopropyl ether, dioxane, ethers represented by tetrahydrofuran, acetone, methyl ethyl ketone, methyl isobutyl ketone, isophorone, Ketones typified by cyclohexanone, methyl acetate, ethyl acetate, butyl acetate, isobutyl acetate Amyl acetate, esters typified by ethyl acetate, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, polyols represented by propylene glycol monomethyl ether acetate, and derivatives thereof.

[Other ingredients]
In addition to the (meth) acrylic copolymer A, the (meth) acrylic copolymer B, and the tolylene diisocyanate compound, the pressure-sensitive adhesive composition in the present invention includes the above-mentioned imidazole compound and silane cup as necessary. Ring agent, solvent and other crosslinking agents, weather resistance stabilizer, tackifier, plasticizer, softener, peeling aid, dye, pigment, inorganic filler, surfactant, antioxidant, metal corrosion inhibitor, You may contain suitably light stabilizers, such as a ultraviolet absorber and a hindered amine type compound.

The pressure-sensitive adhesive composition of the present invention has a storage elastic modulus (G ′) at 30 ° C. after crosslinking of 2.0 × 10 ⁵ Pa to 1.0 from the viewpoint of further enhancing durability and further suppressing white spots. The range of × 10 ⁷ Pa is preferable, the range of 2.0 × 10 ⁵ Pa to 5.0 × 10 ⁵ Pa is more preferable, and the range of 3.0 × 10 ⁵ Pa to 2.0 × 10 ⁶ Pa is more preferable. . In addition, the storage elastic modulus of an adhesive composition is a value measured by the method described in an Example.

[Adhesive sheet]
The adhesive sheet in this invention has the adhesive layer formed from the adhesive composition mentioned above. The pressure-sensitive adhesive sheet in the present invention may be a non-base material-type pressure-sensitive adhesive sheet having no base material, or may be a base material-type pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer on at least one surface of a base material such as an optical film. Even if the pressure-sensitive adhesive layer is exposed to a high-temperature environment or a high-temperature and high-humidity environment, the pressure-sensitive adhesive sheet of the present invention is excellent in durability because it is unlikely to float or peel off at the interface with the adherend.

  In the pressure-sensitive adhesive sheet of the present invention, the thickness of the pressure-sensitive adhesive layer is not particularly limited, and can be appropriately selected depending on the application and required performance. As a thickness of an adhesive layer, the range of 1-100 micrometers is mentioned, for example.

When using the adhesive sheet of this invention for an optical use, it is preferable that an adhesive layer has high transparency. Specifically, the total light transmittance of the pressure-sensitive adhesive layer in the visible light wavelength region measured according to JIS K 7361 (1997) is preferably 85% or more, and more preferably 90% or more.
Further, the haze of the pressure-sensitive adhesive layer measured in accordance with JIS K 7136 (2000) is preferably 2.5% or less, more preferably 2.0% or less, and further preferably 1.5% or less.

  The exposed adhesive layer of the adhesive sheet in the present invention may be protected by a release film. The release film is not particularly limited as long as it can be easily peeled off from the pressure-sensitive adhesive layer, and examples thereof include a resin film that has been subjected to easy release treatment on at least one side using a release treatment agent. As a resin film, the polyester film represented by the polyethylene terephthalate film is mentioned, for example. Examples of the release treatment agent include a fluorine-based resin, paraffin wax, silicone, and a long-chain alkyl group compound. The release film protects the surface of the pressure-sensitive adhesive layer until the pressure-sensitive adhesive sheet is practically used, and is peeled off during use.

  The pressure-sensitive adhesive sheet of the present invention can be produced, for example, by forming a pressure-sensitive adhesive layer by applying the pressure-sensitive adhesive composition of the present invention to a release film or a substrate and curing it for a certain period after drying. The curing conditions can be 1 to 10 days under an environment of 23 ° C. and 50% RH (relative humidity), for example. By curing the pressure-sensitive adhesive layer, the (meth) acrylic copolymer can be sufficiently crosslinked with the tolylene diisocyanate compound.

  The non-base type pressure-sensitive adhesive sheet is formed by, for example, applying a pressure-sensitive adhesive composition to the release-treated surface of a release film, drying it to form a layer of the pressure-sensitive adhesive composition, and contacting the release film of the obtained layer. It can be produced by a method in which another release film is stacked on the exposed surface so that the release treatment surface is in contact with the exposed surface, and is cured to form an adhesive layer.

  The substrate-type pressure-sensitive adhesive sheet may be produced by a method in which the pressure-sensitive adhesive composition is applied to a substrate such as an optical film, or may be produced by a method in which the pressure-sensitive adhesive composition is applied to a release film. As such a method, for example, the pressure-sensitive adhesive composition is applied to the release-treated surface of the release film and dried to form a layer of the pressure-sensitive adhesive composition, and the exposed layer that is not in contact with the release film is exposed. The method of bonding a base material to a surface and curing and forming an adhesive layer is mentioned.

  An example of the substrate of the substrate-type pressure-sensitive adhesive sheet is an optical film. Specific examples of the optical film include optical films used in liquid crystal display devices. More specifically, optical films such as a polarizing plate, a retardation plate, an antireflection film, a viewing angle widening film, a brightness enhancement film, and an ITO film are mentioned. Among these, as a base material of a base-material type adhesive sheet, an optical film is preferable and a polarizing plate is more preferable.

  The polarizing plate should just have a polarizer at least, for example, the polarizing plate which has a protective film on the single side | surface of a polarizer, and the polarizing plate which has a protective film on both surfaces of a polarizer can be used. As the polarizer of the polarizing plate, for example, a polyvinyl alcohol (PVA) film on which iodine is adsorbed and oriented is used, and as the protective film of the polarizer, for example, triacetyl cellulose (TAC) is used.

  When using a polarizing plate as a base material, an adhesive layer may be formed on a PVA film or may be formed on a TAC film.

  Examples of the method for applying the pressure-sensitive adhesive composition to the release film or substrate include known methods using a gravure roll coater, reverse roll coater, kiss roll coater, dip roll coater, bar coater, knife coater, spray coater, etc. It is done.

  The adhesive sheet in this invention can be used suitably for bonding of the optical film etc. of a liquid crystal display device. That is, the pressure-sensitive adhesive sheet according to the present invention includes a polarizing plate, a retardation plate, an antireflection film, a viewing angle widening film, a brightness enhancement film, bonding between optical films such as an ITO film, the optical film, a liquid crystal cell, and glass. It can use suitably for pasting with a substrate, a protection film, etc. Moreover, the adhesive sheet in this invention can be used suitably for bonding with a touch panel, a liquid crystal cell, a glass substrate, a protective film, etc.

  As an example of the pressure-sensitive adhesive sheet in the present invention, one of a base material-type pressure-sensitive adhesive sheet having a structure (peeling film / pressure-sensitive adhesive layer / peeling film) in which a release film is bonded to both surfaces of the pressure-sensitive adhesive layer, one of the pressure-sensitive adhesive layers An adhesive film of a base material type provided with a structure (optical film / adhesive layer / release film) in which an optical film is bonded to the other surface and a release film is bonded to the other surface.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

<Production of (meth) acrylic copolymer A>
(Production of resin A1)
In a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, 99.999 parts by mass of butyl acrylate (BA) as alkyl (meth) acrylate and 2-hydroxyethyl as a monomer having a hydroxyl group After mixing 0.001 part by mass of acrylate (2HEA) and 110 parts by mass of ethyl acetate as a solvent, the inside of the reactor was purged with nitrogen. Thereafter, the mixture in the reactor was heated to 70 ° C. while stirring, and 0.04 parts by mass of azobisdimethylvaleronitrile (ABVN) as a polymerization initiator and 40 parts by mass of ethyl acetate as a solvent were successively added. The polymerization reaction was carried out while maintaining the time. After completion of the polymerization reaction, it was diluted with ethyl acetate as a solvent to make the solid content 24.0% by mass. In this way, a solution of (meth) acrylic copolymer A (resin A1) was obtained.
Since this resin A1 has 0.001 mass% of structural units derived from 2HEA which is a monomer having a hydroxyl group, it is included in the (meth) acrylic copolymer A used in the present invention.

(Production of resins A2 to A11)
A solution of (meth) acrylic copolymer A (resins A2 to A11) was obtained in the same manner as in the above-mentioned “Production of Resin A1” except that the monomer composition shown in Table 1 was used. In Table 1, MA represents methyl acrylate and AA represents acrylic acid.
Since these resins A2 to A7 and A9 have a structural unit derived from 2HEA, which is a monomer having a hydroxyl group, in the range of 0.001% by mass to 0.5% by mass as described in Table 1, It is contained in the (meth) acrylic copolymer A used in the invention.

Table 1 shows the monomer composition (parts by mass), acid value, and TgA of resins A1 to A11. The acid value and TgA of the (meth) acrylic copolymer were calculated according to the procedure described above.
Specifically, the acid value of the resin A6 was calculated as follows.
(0.1 / 72.1) × 56.1 × 10 × 1 = 0.8 (mgKOH / g)
The molecular weight of AA is 72.1, and the number of carboxyl groups in AA1 molecule is 1.

<Production of (meth) acrylic copolymer B>
(Production of resin B1)
In a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, 84 parts by mass of butyl acrylate (BA) as alkyl (meth) acrylate and t-butyl acrylate (t-) as alkyl (meth) acrylate (BA) 15 parts by mass, 1 part by mass of 2-hydroxyethyl acrylate (2HEA) as a monomer having a hydroxyl group and 110 parts by mass of ethyl acetate as a solvent were mixed, and the inside of the reactor was purged with nitrogen. Thereafter, the mixture in the reactor was heated to 70 ° C. while stirring, and then 0.04 parts by mass of azobisdimethylvaleronitrile (ABVN) as a polymerization initiator and 40 parts by mass of ethyl acetate as a solvent were sequentially added. The polymerization reaction was held for 6 hours. After completion of the polymerization reaction, the mixture was diluted with ethyl acetate as a solvent to make the solid content 19.0% by mass. In this way, a solution of (meth) acrylic copolymer B (resin B1) was obtained.
Since this resin B1 has 0.001 mass% of structural units derived from 2HEA which is a monomer having a hydroxyl group, it is included in the (meth) acrylic copolymer B used in the present invention.

(Production of resins B2 to B13)
A solution of (meth) acrylic copolymer B (resins B2 to B13) was obtained in the same manner as in the above-mentioned “Production of resin B1” except that the monomer composition shown in Table 2 below was used. In Table 2, MA represents methyl acrylate and AA represents acrylic acid.
Since these resins B2 to B8, B10, and B13 have a structural unit derived from 2HEA that is a monomer having a hydroxyl group in a range of 0.1% by mass to 4% by mass, as described in Table 2, It is contained in the (meth) acrylic copolymer B used in the invention.

Table 2 shows the monomer composition (parts by mass), acid value, and TgB of the resins B1 to B13. The acid value and TgB of the (meth) acrylic copolymer were calculated according to the procedure described above.
Specifically, the acid value of resin B7 was calculated as follows.
(0.1 / 72.1) × 56.1 × 10 × 1 = 0.8 (mgKOH / g)
The molecular weight of AA is 72.1, and the number of carboxyl groups in AA1 molecule is 1.

<Preparation of pressure-sensitive adhesive composition>
Example 1
As the (meth) acrylic copolymer A, 354.2 parts by mass of a resin A1 solution (85.0 parts by mass as a solid content) and as the (meth) acrylic copolymer B, 78.9 parts by mass of a resin B1 solution Parts (15.0 parts by mass as solid content) and 20.0 parts by mass of coronate L as a tolylene diisocyanate compound (manufactured by Nippon Polyurethane Industry Co., Ltd., adduct of tolylene diisocyanate and trimethylol propane, as an active ingredient) Is 15.0 parts by mass), and 0.5 parts by mass of Curazole TBZ as an imidazole compound (2,4-dihydro-1H-pyrrolo [1,2-a] benzimidazole manufactured by Shikoku Kasei Kogyo Co., Ltd.) Is 0.5 part by mass) and 0.4 part by mass of KBM-403 as a silane coupling agent (SC agent) (manufactured by Shin-Etsu Chemical Co., Ltd., 3-g A pressure-sensitive adhesive composition was obtained by sufficiently stirring and mixing lysidoxypropyltrimethoxysilane, 0.4 mass part as an active ingredient).
Table 3 shows the total acid value of the obtained pressure-sensitive adhesive composition, the content rate of monomers having a hydroxyl group (hydroxyl group-containing monomer content rate), and the ratio of hydroxyl groups (resin B / resin A).
In addition, Example 1 corresponds to the pressure-sensitive adhesive composition of the present invention.

(Examples 2 to 23)
In Examples 2 to 23, a pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the composition of the pressure-sensitive adhesive composition shown in Table 3 below was used.
Table 3 shows the total acid value, the content of the hydroxyl group-containing monomer, and the hydroxyl group ratio (resin B / resin A) of the obtained pressure-sensitive adhesive composition.
Specifically, the total acid value in Example 19 was calculated as follows.
0.8 × 80 / (80 + 20) + 0.8 × 20 / (80 + 20) = 0.8
In addition, Examples 2-23 correspond to the adhesive composition described in Claim 1.

(Comparative Examples 1-14)
In Comparative Examples 1 to 14, pressure-sensitive adhesive compositions were prepared in the same manner as in Example 1 except that the composition of the pressure-sensitive adhesive composition shown in Table 3 below was used.
Specifically, in Comparative Examples 1 and 2, the total acid value was more than 2.5 mgKOH / g.
In Comparative Example 3, the content of the structural unit having a hydroxyl group of the resin A is less than 0.001% by mass. In Comparative Example 4, the content of the structural unit having a hydroxyl group of the resin A is 0.5% by mass. It was super.
In Comparative Example 5, the content of the structural unit having a hydroxyl group of the resin B is less than 0.1% by mass. In Comparative Example 6, the content of the structural unit having a hydroxyl group of the resin B is more than 4% by mass. there were.
In Comparative Example 7, the content of the structural unit having a hydroxyl group of the resin A and the content of the structural unit having a hydroxyl group of the resin B were the same.
In Comparative Example 8, the content ratio (A / B) of resin A to resin B was smaller than 60/40 on a mass basis. That is, in Comparative Example 8, the content of the resin B was larger than those in Examples 1-23. In Comparative Example 9, the content ratio (A / B) was greater than 95/5 on a mass basis. That is, in Comparative Example 9, the content of the resin B was smaller than those in Examples 1-23. In Comparative Example 10, the resin B was not included.
In Comparative Example 11, the amount of the tolylene diisocyanate compound relative to 100 parts by mass of the total amount of Resin A and Resin B is less than 5 parts by mass. The amount of the range isocyanate compound was more than 30 parts by mass.
In Comparative Example 13, instead of the tolylene diisocyanate compound, Takenate D-110N (manufactured by Takeda Pharmaceutical Company Limited), which is a xylene diisocyanate compound, was used as a crosslinking agent. In Comparative Example 14, instead of the tolylene diisocyanate compound, Sumidur N-75 (manufactured by Sumika Bayer Urethane Co., Ltd.), which is a hexamethylene diisocyanate compound, was used as a crosslinking agent.

<Preparation of adhesive sheet sample>
Using the pressure-sensitive adhesive compositions of the Examples and Comparative Examples obtained above, pressure-sensitive adhesive sheet samples were prepared according to the following procedure. First, the pressure-sensitive adhesive composition was applied to the surface-treated surface of a release film (100E-0010NO23, manufactured by Fujimori Kogyo Co., Ltd.) surface-treated with a silicone release agent so that the coating amount after drying was 20 g / cm ^2. Applied. Subsequently, the release film after application of the adhesive composition was dried at 100 ° C. for 90 seconds using a hot-air circulating drier to form a layer of the adhesive composition on the release film. Subsequently, one surface of the polarizing plate of triacetyl cellulose (TAC) / polyvinyl alcohol (PVA) / TAC structure and the layer of the pressure-sensitive adhesive composition on the release film are laminated and bonded together, and pressed through a pressure nip roll. did. After pressure bonding, it is autoclaved (50 ° C, 5 kg / cm ² , 20 minutes), cured for 96 hours under conditions of 35 ° C and 45% RH, and has a laminate structure of release film / adhesive layer / polarizing plate A sheet sample was prepared.

  Table 3 below shows the compositions of the pressure-sensitive adhesive compositions obtained in Examples 1 to 23 and Comparative Examples 1 to 14, the measurement results of the pressure-sensitive adhesive compositions and the pressure-sensitive adhesive sheet samples, and the evaluation results.

The crosslinking agents a to c and crosslinking catalysts d to g shown in Table 3 are as follows.
Crosslinking agent a: Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd., adduct of tolylene diisocyanate and trimethylolpropane)
Crosslinking agent b: Takenate D-110N (manufactured by Takeda Pharmaceutical Company Limited, xylene diisocyanate compound)
Crosslinking agent c: Sumidur N-75 (manufactured by Sumika Bayer Urethane Co., Ltd., hexamethylene diisocyanate compound)
Cross-linking catalyst d: Curezol TBZ (2,3-dihydro-1H-pyrrolo [1,2-a] benzimidazole manufactured by Shikoku Kasei Kogyo Co., Ltd.)
Cross-linking catalyst e: Curesol 1B2MZ (Shikoku Chemicals Co., Ltd., 1-benzyl-2-methylimidazole)
Cross-linking catalyst f: Curesol 1B2PZ (Shikoku Kasei Kogyo Co., Ltd., 1-benzyl-2-phenylimidazole)
Cross-linking catalyst g: dibutyltin dilaurate SC agent: KBM-403 (manufactured by Shin-Etsu Chemical Co., Ltd., 3-glycidoxypropyltrimethoxysilane)

  In Table 3, “ND1” represents that evaluation was impossible due to peeling, and “ND2” represents that evaluation was impossible due to haze.

[Evaluation of ITO corrosion prevention]
Silver paste (trade name Dotite FA-401CA is applied to both ends of the electrically conductive surface of an ITO film (trade name Tetrait TCF KB300N03-125-U3 / P, manufactured by Oike Kogyo Co., Ltd.) cut to a length of 30 mm and a width of 95 mm. , Manufactured by Fujikura Kasei Co., Ltd.) so as to have a width of 15 mm and fired at 140 ° C. for 15 minutes.
The adhesive sheet sample obtained using the adhesive composition of each Example and each comparative example was cut into 30 mm length x 75 mm width, the release film of the adhesive sheet sample was peeled off, and the adhesive layer was exposed.
After sticking the adhesive sheet sample on the surface of the ITO film subjected to the conductive treatment so that the exposed adhesive layer was filled between the silver paste and the silver paste, it was cut into a length of 20 mm and a width of 95 mm. After cutting, the sample was autoclaved under conditions of 0.5 MPa, 40 ° C., and 30 minutes to obtain a corrosion prevention test sample.
A lead wire of a tester was applied to the silver paste portions at both ends of the corrosion prevention test sample, and the resistance value before the test was measured. Next, the corrosion prevention test sample was subjected to a corrosion prevention test in which the sample was allowed to stand for 250 hours at 60 ° C. and 90% RH. After the test, the corrosion prevention test sample was taken out, and the resistance value after the test was measured by applying a tester lead bar to the silver paste portions at both ends of the corrosion prevention test sample in an environment of 23 ° C. and 50% RH. From the resistance value before the test and the resistance value after the test, the change rate of the resistance value was calculated by the following formula.
(Expression) Change rate of resistance value (%) = [(resistance value after test−resistance value before test) ÷ resistance value before test] × 100
In accordance with the change rate (%) of the resistance value calculated from the above formula and the following evaluation criteria, the ITO corrosion prevention property was evaluated. In addition, if an evaluation result is A or B, there is little corrosion of ITO and there is no problem practically.
Evaluation criteria A: Change rate of resistance value is less than 10%.
B: The change rate of the resistance value is 10% or more and less than 20%.
C: The change rate of the resistance value is 20% or more.

[Evaluation of durability (80 ° C., 60 ° C. × 90% RH)]
Prepare a 140 mm × 260 mm (long side) test piece obtained by cutting the pressure-sensitive adhesive sheet sample prepared as described above so that the long side is 45 ° with respect to the absorption axis, and peel off the release film of the test piece. The pressure-sensitive adhesive layer was exposed. Next, a sample for durability evaluation was prepared using a laminator so that the exposed surface of the pressure-sensitive adhesive layer was in contact with one side of a 0.7 mm Corning non-alkali glass plate “# 1737”. Next, this sample was subjected to autoclaving (50 ° C., 5 kg / cm ² , 20 minutes), and left for 24 hours at 23 ° C. and 50% RH. After that, it was left for 500 hours in a high temperature environment of 80 ° C. or a high temperature and high humidity environment of 60 ° C. × 90% RH, and the state of foaming, peeling and floating was visually observed, and the following evaluation criteria were used. evaluated. If the evaluation result is A or B, the durability is excellent and there is no practical problem.
Evaluation criteria A: Foaming and peeling are not seen at all.
B: Almost no foaming is observed, and there is no peeling at a position of 0.5 mm or more from the outer peripheral edge on the two sides.
C: Foaming is remarkably observed or peeling occurs at a position of 0.5 mm or more from the outer peripheral edge on two sides.

[Evaluation of white spots]
Prepare a 140 mm × 260 mm (long side) test piece obtained by cutting the pressure-sensitive adhesive sheet sample prepared as described above so that the long side is 45 ° with respect to the absorption axis, and peel off the release film of the test piece. The pressure-sensitive adhesive layer was exposed. Next, the pressure-sensitive adhesive sheet sample with the pressure-sensitive adhesive layer exposed was attached to both surfaces of a 0.7 mm Corning non-alkali glass plate “# 1737” using a laminator so that the polarizing axes of the polarizing plates were orthogonal to each other, An evaluation sample was produced. Next, this sample was subjected to autoclaving (50 ° C., 5 kg / cm ² , 20 minutes), and left for 24 hours at 23 ° C. and 50% RH. Thereafter, it was left under conditions of 85 ° C. and 0% RH for 500 hours. After standing, a uniform light source was used under the conditions of 23 ° C. and 50% RH, and the white spot state was visually observed and evaluated according to the following evaluation criteria. In addition, if an evaluation result is A or B, it is excellent in suppression of a white spot and there is no problem practically.
Evaluation criteria A: No white spots are observed.
B: Almost no white spots are observed.
C: Many white spots are recognized.

[Measurement of storage modulus (G ')]
The storage elastic modulus (G ′) of the pressure-sensitive adhesive composition of each example and each comparative example was measured by the following method.
The prepared pressure-sensitive adhesive composition was applied, dried and cured under the same conditions as in the preparation of the pressure-sensitive adhesive sheet sample described above to form a pressure-sensitive adhesive layer having a thickness of 20 μm. Adhesive layers were pasted together so that the formed adhesive layer had a thickness of 600 μm, and using a dynamic viscoelasticity measuring device (manufactured by Anton Paar, Physica MCR301), evaluation temperature: 30 ° C., cone used: 8 mmφ, measurement The storage elastic modulus (G ′) (Pa) was measured while applying a shear stress at a gap of 0.6 mm and a frequency of 1 Hz. The results are as shown in Table 3.

[result]
In Examples 1-23, in all of ITO corrosion prevention property, durability (each of 80 degreeC and 60 degreeC x 90RH), and white void, it turns out that it is more than evaluation B, and it turns out that there is no problem practically.
On the other hand, in Comparative Examples 1 to 14, the evaluation is C or measurement is impossible (cause of haze or peeling due to whitening) in any one of ITO corrosion prevention, durability (each of 80 ° C. and 60 ° C. × 90 RH) and white spots. There is a problem in practical use.

Claims (10)

A (meth) acrylic copolymer A having a structural unit derived from a monomer having a hydroxyl group in a range of 0.001% by mass to 0.5% by mass with respect to all the structural units;
The structural unit derived from the monomer having a hydroxyl group is in the range of 0.1% by mass to 4% by mass with respect to all the structural units, and the content of the structural unit derived from the monomer having a hydroxyl group is the above ( (Meth) acrylic copolymer B higher than the content of structural units derived from the monomer having a hydroxyl group of (meth) acrylic copolymer A;
And a tolylene diisocyanate compound in a range of 5 to 30 parts by mass with respect to 100 parts by mass of the total amount of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B,
The content ratio (A / B) of the (meth) acrylic copolymer A to the (meth) acrylic copolymer B is in the range of 60/40 to 95/5 on a mass basis,
The pressure-sensitive adhesive composition in which the total acid value of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B is 2.5 mgKOH / g or less.   In the (meth) acrylic copolymer A and the (meth) acrylic copolymer B, the content of the structural unit derived from the monomer having a hydroxyl group is the (meth) acrylic copolymer A and The pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive composition is in a range of 0.05% by mass to 1.5% by mass with respect to all the structural units of the (meth) acrylic copolymer B.   The structural unit derived from the monomer having a hydroxyl group of the (meth) acrylic copolymer B with respect to the content rate a of the structural unit derived from the monomer having a hydroxyl group of the (meth) acrylic copolymer A The pressure-sensitive adhesive composition according to claim 1 or 2, wherein a ratio (b / a) of the content rate b of the resin is in the range of 5 to 500.   The methacrylic copolymer A and the (meth) acrylic copolymer B further include an imidazole compound in a range of 0.01 to 1.5 parts by mass with respect to 100 parts by mass in total. The pressure-sensitive adhesive composition according to any one of claims 1 to 3.   The present invention further comprises a silane coupling agent in the range of 0.05 to 1 part by mass with respect to 100 parts by mass of the total amount of the (meth) acrylic copolymer A and the (meth) acrylic copolymer B. The pressure-sensitive adhesive composition according to any one of claims 1 to 4.   The pressure-sensitive adhesive composition according to any one of claims 1 to 5, wherein the total acid value is 0 mgKOH / g.   The pressure-sensitive adhesive composition according to any one of claims 1 to 6, wherein the tolylene diisocyanate compound is an adduct of tolylene diisocyanate and a polyol.   The glass transition temperature (TgA) of the (meth) acrylic copolymer A is in the range of −60 ° C. or higher and −40 ° C. or lower, and the glass transition temperature (TgB) of the (meth) acrylic copolymer B is − The pressure-sensitive adhesive composition according to any one of claims 1 to 7, wherein the pressure-sensitive adhesive composition is in a range of 55 ° C or higher and -25 ° C or lower, and TgA is lower than TgB. 9. The storage elastic modulus (G ′) at 30 ° C. after crosslinking is in the range of 2.0 × 10 ⁵ Pa to 1.0 × 10 ⁷ Pa. 9. Adhesive composition.   The adhesive sheet which has an adhesive layer formed from the adhesive composition of any one of Claims 1-9.