WO2013183563A1

WO2013183563A1 - Adhesive composition for polarizing plates, polarizing plate with adhesive, and display device

Info

Publication number: WO2013183563A1
Application number: PCT/JP2013/065228
Authority: WO
Inventors: 太郎川口; 宏人中野; 直人安田; 雅樹西田
Original assignee: 日本カーバイド工業株式会社
Priority date: 2012-06-05
Filing date: 2013-05-31
Publication date: 2013-12-12
Also published as: KR20150016561A; KR102090220B1; CN104379694B; CN104379694A; JP6002220B2; TWI582189B; TW201406895A; JPWO2013183563A1

Abstract

The present invention provides an adhesive composition for polarizing plates, which contains: an acrylic copolymer (A) that has a weight average molecular weight of from 300,000 to 700,000 (inclusive) and contains a constituent unit derived from an alkyl (meth)acrylate and a constituent unit derived from a monomer having a carboxy group; an acrylic copolymer (B) that has a weight average molecular weight of from 1,000,000 to 2,000,000 (inclusive) and contains a constituent unit derived from an alkyl (meth)acrylate, a constituent unit derived from a monomer having a carboxy group and a constituent unit derived from a monomer having a hydroxyl group; and 20 parts by mass or less of an isocyanate-based crosslinking agent relative to 100 parts by mass of the total amount of the acrylic copolymer (A) and the acrylic copolymer (B). This adhesive composition for polarizing plates is configured such that the glass transition temperature of the acrylic copolymer (A) is not less than the glass transition temperature of the acrylic copolymer (B).

Description

Adhesive composition for polarizing plate, polarizing plate with adhesive, and display device

The present invention relates to a pressure-sensitive adhesive composition for a polarizing plate, a polarizing plate with a pressure-sensitive adhesive, and a display device.

In recent years, as a display device for displaying an image such as a liquid crystal display device or organic electroluminescence, devices of various display methods have been widely spread. Among these, a liquid crystal display device generally includes a liquid crystal cell in which a liquid crystal component oriented in a predetermined direction is sandwiched between two supporting substrates such as glass, and an optical film such as a polarizing plate, a retardation film, and a brightness enhancement film. Are bonded together. An adhesive is used when laminating optical films or sticking an optical film to a liquid crystal cell.

Liquid crystal display devices are widely used as display devices for personal computers, televisions, car navigation systems, etc. For example, various liquid crystal display devices such as harsh environmental conditions with a high amount of high temperature and high humidity and dry environmental conditions with low humidity. Used under environmental conditions. Therefore, even when used for a long period of time, the bonded part (that is, the interface between the pressure-sensitive adhesive layer and the liquid crystal cell or the polarizing film) peeled off or the pressure-sensitive adhesive layer is broken. It is required that the adhesive layer has a high durability performance such that bubbles are not easily generated.

The polarizing plate has a polarizing film (polarizer) using PVA or the like. When a stretched film is used for this polarizing film, for example, when exposed to a severe environment such as high temperature and high humidity, a dimensional change accompanying shrinkage or expansion is likely to occur, and stress is generated in the polarizing plate. When the stress accompanying the dimensional change is not relaxed by the adhesive disposed between the polarizing plate and the liquid crystal cell, the residual stress is generated unevenly in the polarizing plate. As a result, a phase shift occurs between the two polarizing plates arranged so that the extending axes of the polarizing film intersect each other between the front surface and the back surface of the display panel. For this reason, light leaks from the four surroundings of the display portion of the liquid crystal display device and becomes white, so-called “white spots” occur.

The occurrence of white spots described above varies depending on the size of the display panel. From such a viewpoint, generally, a soft soft type adhesive is used for a small display panel, and a relatively hard type adhesive is used for a large display panel. When this hard type adhesive is applied to a small display panel, the stress accompanying shrinkage or the like tends to concentrate on the edge, and the above-described white spots tend to appear remarkably around the panel. On the other hand, when a large-sized pressure-sensitive adhesive is produced for a large display panel application, the end portion of the original fabric cannot be used effectively, which is a cause of a decrease in yield. Moreover, since the soft type adhesive is soft, it tends to adhere to the processing blade and tends to be inferior in punching suitability.

In order to improve the above white spots, a pressure-sensitive adhesive that relaxes stress by adding a low molecular weight polymer to the pressure-sensitive adhesive composition has been proposed. For example, a pressure-sensitive adhesive composition for a polarizing plate comprising a high molecular weight acrylic copolymer, a low molecular weight acrylic copolymer having a weight average molecular weight of 30,000 or less, and a polyfunctional compound is disclosed. By having the characteristic of following the dimensional change that occurs in the polarizing plate, it is said that there is little color unevenness between the peripheral part and the central part (for example, see Patent Document 1).

Further, the (meth) acrylic copolymer (A) having a weight average molecular weight of 650,000 to 950,000 and the (meth) acrylic copolymer (B) having a weight average molecular weight of 1,05-1.35 million at a predetermined ratio. A pressure-sensitive adhesive composition for a polarizing plate containing an isocyanate compound is disclosed, which has durability under high temperature and high humidity and suppresses white spots (for example, see Patent Document 2).

Japanese Patent Laid-Open No. 10-279907 JP 2011-231189 A

However, a technique using a (meth) acrylic copolymer having a different weight average molecular weight in order to prevent the occurrence of color unevenness typified by white spots as in the above-described conventional technique is disclosed, By simply using a mixture of a plurality of different molecular weights, it is difficult to maintain good durability such as foaming, peeling and breaking, and at the same time, preventing white spots from occurring.

The pressure-sensitive adhesive has been conventionally adjusted according to the application and size. On the other hand, it can be applied to both large display panel applications and small display panel applications. Regardless of size, the occurrence of white spots is prevented and the adhesive has excellent durability and workability. The reality is that it has not yet been proposed.

The present invention has been made in view of the above. Under the circumstances described above, a pressure-sensitive adhesive composition for a polarizing plate and a pressure-sensitive adhesive with a pressure-sensitive adhesive that has high durability that hardly causes foaming or peeling, and that suppresses occurrence of color unevenness (particularly white spots) regardless of size. Is needed. Further, there is a need for a display device that displays an image with little color unevenness.

The present invention has been achieved based on the following findings. That is,
When two or more types of resins having different weight average molecular weights are blended and used, a resin having a low molecular weight out of two or more types of resins does not have a polar group such as a hydroxyl group but has a molecular weight higher than that of the resin having a polar group. When the reactivity with a crosslinking agent is small compared to a resin with a large size, the durability tends to decrease due to a decrease in molecular weight, but the reaction with an isocyanate-based crosslinking agent focuses on the glass transition temperature of the resin. It is the knowledge that the durability of the pressure-sensitive adhesive and the prevention of color unevenness can be achieved by adjusting the copolymerization component.

Specific means for achieving the above-described problems are as follows.
1st this invention contains the structural unit derived from the monomer which has a carboxy group and the structural unit derived from the alkyl (meth) acrylate, and the weight average molecular weight is 300,000 or more and 700,000 or less A copolymer A, a structural unit derived from an alkyl (meth) acrylate, a structural unit derived from a monomer having a carboxy group, and a structural unit derived from a monomer having a hydroxyl group, and having a weight average molecular weight of 1 The amount of the acrylic copolymer B that is from 1,000,000 to 2,000,000 and the total amount of the acrylic copolymer A and the acrylic copolymer B of 100 parts by mass is 20 parts by mass or less. And an acrylic crosslinking agent having a glass transition temperature (TgA) of the acrylic copolymer A is a glass transition of the acrylic copolymer B. It is degrees (TgB) or a polarizing plate for a pressure-sensitive adhesive composition.

2nd this invention is a polarizing plate with an adhesive which has a polarizer and the adhesive layer formed on the said polarizer by provision of the adhesive composition for polarizing plates of said 1st invention.

According to the present invention, a pressure-sensitive adhesive composition for a polarizing plate and a polarizing plate with a pressure-sensitive adhesive, which have high durability in which foaming, peeling, etc. are unlikely to occur, and generation of color unevenness (particularly white spots) is suppressed regardless of size. Is provided. Also,
ADVANTAGE OF THE INVENTION According to this invention, the display apparatus with which an image with little color unevenness is displayed is provided.

Hereinafter, the pressure-sensitive adhesive composition for polarizing plates of the present invention, the polarizing plate with pressure-sensitive adhesive using the same, and the display device will be described in detail.

<Adhesive composition for polarizing plate>
The pressure-sensitive adhesive composition for polarizing plates of the present invention includes a structural unit derived from an alkyl (meth) acrylate and a structural unit derived from a monomer having a carboxy group, and has a weight average molecular weight of 300,000 or more and 700,000. Acrylic copolymer A and a structural unit derived from an alkyl (meth) acrylate, a structural unit derived from a monomer having a carboxy group, and a structural unit derived from a monomer having a hydroxyl group, The acrylic copolymer B having a weight average molecular weight of 1,000,000 or more and 2,000,000 or less and an isocyanate crosslinking agent are used. Furthermore, the pressure-sensitive adhesive composition for a polarizing plate of the present invention has an isocyanate cross-linking agent content of 20 parts by mass or less with respect to a total amount of 100 parts by mass of the acrylic copolymer A and the acrylic copolymer B. The glass transition temperature (TgA) of the acrylic copolymer A and the glass transition temperature (TgB) of the acrylic copolymer B satisfy the relationship of TgA ≧ TgB.

In addition to the acrylic copolymer A and the acrylic copolymer B, the pressure-sensitive adhesive composition for a polarizing plate of the present invention may further include a crosslinking agent, a silane coupling agent, other additives, etc. as necessary. Other components may be included.

Conventionally, a technique for forming a pressure-sensitive adhesive using a plurality of types of copolymers having different molecular weights is known. However, simply reducing the molecular weight of some of the copolymers can be expected to have an effect of stress relaxation against color unevenness such as white spots, but the durability is significantly reduced and the occurrence of foaming and peeling is suppressed. I can't. Therefore, in the present invention,
A relatively high-polarity isocyanate cross-linking agent is used in a predetermined ratio as a cross-linking agent, and at least a high molecular weight side acrylic copolymer B is provided with a hydroxyl group as a polar group so that a low molecular weight side acrylic copolymer A is present. The glass transition temperature (TgA) is set to be equal to or higher than the glass transition temperature (TgB) of the acrylic copolymer B. Thereby, reaction with the isocyanate type crosslinking agent of the acrylic copolymer A of the low molecular weight side is promoted. By reducing the molecular weight of the acrylic copolymer, stress relaxation is provided, and embrittlement associated with the lower molecular weight is prevented, and color unevenness (especially white spots) in the pressure-sensitive adhesive regardless of the size. Both prevention of occurrence and improvement of durability are achieved.

Since the pressure-sensitive adhesive composition for polarizing plates of the present invention is excellent in durability and color unevenness (particularly white spotting) prevention, it can be suitably used for large display panels of 19 inches or more (that is, large display devices). At the same time, it can be suitably used for a small display panel (that is, a small display device) of less than 19 inches (or even less than 10 inches). In other words, the pressure-sensitive adhesive composition for polarizing plates of the present invention can produce a large-sized display panel-use pressure-sensitive adhesive, and can produce a small-sized display panel-use pressure-sensitive adhesive from the edge of the original fabric, so the yield is high. improves. Therefore, it becomes possible to manufacture large and small pressure-sensitive adhesives according to the required amount, and there is an advantage that the necessity of inventory and storage is eliminated.

In addition, in this specification, (meth) acryl means acryl or methacryl, and (meth) acrylate means acrylate or methacrylate.

Each component is described in detail below.
-Acrylic copolymer A-
The pressure-sensitive adhesive composition for polarizing plates of the present invention includes a structural unit derived from an alkyl (meth) acrylate and a structural unit derived from a monomer having a carboxy group, and has a weight average molecular weight of 300,000 or more and 700,000. It contains at least one of the following acrylic copolymers A. This acrylic copolymer A is a copolymer obtained by copolymerizing at least an alkyl (meth) acrylate and a monomer having a carboxy group, and further derived from the monomer by copolymerization with another monomer. It may further have a structural unit.

Examples of the alkyl (meth) acrylate constituting the acrylic copolymer A include methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, and t-butyl. (Meth) acrylate, n-octyl (meth) acrylate, i-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-nonyl (meth) acrylate, i-nonyl (meth) acrylate, n-decyl (meth) ) Acrylate, n-dodecyl (meth) acrylate, stearyl (meth) acrylate, and the like. Of these, alkyl (meth) acrylates having 1 to 4 carbon atoms are preferable, alkyl acrylates having 1 to 4 carbon atoms are preferable, and n-butyl acrylate is particularly preferable in terms of easily adjusting the cohesive force and adhesive force of the pressure-sensitive adhesive. .

The ratio of the structural unit derived from the alkyl (meth) acrylate in the acrylic copolymer A is preferably 65.0 to 99.5% by mass, more preferably 65.0 to 94.5% by mass, and 75.%. 0 to 90.0% by mass is particularly preferable. Alkyl (meth) acrylate is contained as a main component constituting the copolymer, and when the content ratio is within the above range, it can be adjusted to an optimal elastic modulus, in terms of ensuring durability and tackiness. It is advantageous.

In addition to the alkyl (meth) acrylate contained as a main component, the acrylic copolymer A according to the present invention further includes the alkyl (meth) acrylate (preferably a monomer different from the alkyl (meth) acrylate). A monomer capable of forming a homopolymer having a glass transition temperature of which the absolute value of the difference from the glass transition temperature of a polymer obtained by homopolymerizing alkyl having 1 to 4 carbon atoms is 30 ° C. or more and 90 ° C. or less; A copolymerized embodiment is preferred. In such an embodiment, the glass transition temperature is increased, that is, the polarity of the resin is increased, the reactivity with the isocyanate-based crosslinking agent is increased, and the durability can be further improved.
Among these, methyl acrylate, t-butyl acrylate, phenoxyethyl acrylate, and n-butyl methacrylate are preferable as monomers capable of forming a homopolymer having a glass transition temperature having an absolute value of the difference in the above range. . Particularly preferred acrylic copolymer A is an embodiment in which n-butyl acrylate is copolymerized with methyl acrylate and / or t-butyl acrylate.

In the case where the monomer (preferably methyl acrylate or t-butyl acrylate) other than the above-mentioned monomer (preferably methyl acrylate or t-butyl acrylate) is included in addition to the alkyl (meth) acrylate contained as the main component, The ratio in the copolymer A is preferably 5 to 30% by mass, more preferably 5 to 20% by mass. When the content ratio is within the above range, it is advantageous in that the reactivity with the isocyanate-based crosslinking agent is enhanced.

As the monomer having a carboxy group constituting the acrylic copolymer A, a (meth) acrylic monomer having a carboxy group is preferable. Examples of the monomer having a carboxy group include acrylic acid, methacrylic acid, and ω-carboxy-polycaprolactone mono (meth) acrylate. Among them, acrylic acid is preferable because it has high reactivity with other monomers during the copolymerization reaction and can reduce unreacted monomers.

The ratio of the structural unit derived from the monomer having a carboxy group in the acrylic copolymer A is preferably 0.5 to 5% by mass, more preferably 0.5 to 3% by mass. When the content ratio of the monomer having a carboxy group is within the above range, it is advantageous from the viewpoint of ensuring pot life and appropriately adjusting the degree of cross-linking of the resin.

The weight average molecular weight of the acrylic copolymer A is 300,000 or more and 700,000 or less. The weight average molecular weight being within the above range indicates that the acrylic copolymer A is a low molecular weight resin among a plurality of resins contained in the pressure-sensitive adhesive composition for polarizing plates. Further, if the weight average molecular weight of the acrylic copolymer A becomes too small, less than 300,000, peeling or the like is likely to occur, and durability (particularly durability when applied to a large size (for example, 19 inches or more)). Decreases. Conversely, when the weight average molecular weight of the acrylic copolymer A exceeds 700,000, the molecular size approaches that of the acrylic copolymer B, and the acrylic copolymer A is used in combination with the acrylic copolymer A. Stress relaxation is reduced, and color unevenness (particularly white spots) cannot be suppressed. This is particularly noticeable when applied to large size (for example, 19 inches or more) applications.

The glass transition temperature (TgA) of the acrylic copolymer A is preferably in the range of −50 ° C. to −30 ° C., more preferably in the range of −48 ° C. to −40 ° C. When the TgA is −50 ° C. or higher, the elastic modulus can be adjusted, and the durability and whiteout property are excellent. Moreover, when TgA is −30 ° C. or lower, the tackiness and the bonding suitability are excellent without extremely impairing the viscosity.

The content of the acrylic copolymer A in the pressure-sensitive adhesive composition for polarizing plate can be appropriately selected within the range satisfying the content ratio A / B described later. The range of 50 mass% or more and 74 mass% or less is preferable with respect to the minute, and the range of 54 mass% or more and 69 mass% or less is more preferable. When the content of the acrylic copolymer A is within the above range, flexibility is imparted to the pressure-sensitive adhesive, and color unevenness (particularly white spots) is suppressed due to stress relaxation.

-Acrylic copolymer B-
The pressure-sensitive adhesive composition for polarizing plates of the present invention comprises a structural unit derived from an alkyl (meth) acrylate, a structural unit derived from a monomer having a carboxy group, and a structural unit derived from a monomer having a hydroxyl group. And at least one acrylic copolymer B having a weight average molecular weight of 1,000,000 or more and 2,000,000 or less. The acrylic copolymer B is a copolymer obtained by copolymerizing at least an alkyl (meth) acrylate, a monomer having a carboxy group, and a monomer having a hydroxyl group. It may be copolymerized to further have a structural unit derived from the monomer.

Examples of the alkyl (meth) acrylate constituting the acrylic copolymer B include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, and t-butyl. (Meth) acrylate, n-octyl (meth) acrylate, i-octyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-nonyl (meth) acrylate, i-nonyl (meth) acrylate, n-decyl (meth) ) Acrylate, n-dodecyl (meth) acrylate, stearyl (meth) acrylate, and the like. Of these, alkyl (meth) acrylates having 1 to 8 carbon atoms are preferable, alkyl acrylates having 1 to 8 carbon atoms are preferable, and n-butyl acrylate, t -Butyl acrylate, methyl acrylate, 2-ethylhexyl acrylate are preferred.

The ratio of the structural unit derived from the alkyl (meth) acrylate in the acrylic copolymer B is preferably 93 to 99.4% by mass, and more preferably 96 to 99.4% by mass. Alkyl (meth) acrylate is contained as a main component constituting the copolymer, and if the content ratio is within the above range, it can be adjusted to an optimal elastic modulus, which is advantageous in terms of durability and adhesive properties. is there.

As the monomer having a carboxy group constituting the acrylic copolymer B, a (meth) acrylic monomer having a carboxy group is preferable. Examples of the monomer having a carboxy group include acrylic acid, methacrylic acid, and ω-carboxy-polycaprolactone mono (meth) acrylate. Among them, acrylic acid is preferable because it has high reactivity with other monomers during the copolymerization reaction and can reduce unreacted monomers.

The ratio of the structural unit derived from the monomer having a carboxy group in the acrylic copolymer B is preferably 0.5 to 5% by mass, and more preferably 0.5 to 3% by mass. When the content ratio of the monomer having a carboxy group is within the above range, it is advantageous in that the pot life property can be ensured and the resin crosslinking degree can be adjusted appropriately.

As the monomer having a hydroxyl group constituting the acrylic copolymer B, a (meth) acrylic monomer having a hydroxyl group is preferable, and a (meth) acrylic acid ester having a hydroxyl group is more preferable. Examples of monomers having a hydroxyl group include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, and 3-methyl. -3-hydroxybutyl (meth) acrylate, 1,3-dimethyl-3-hydroxybutyl (meth) acrylate, 2,2,4-trimethyl-3-hydroxypentyl (meth) acrylate, 2-ethyl-3-hydroxyhexyl Examples include (meth) acrylate, polypropylene glycol mono (meth) acrylate, polyethylene glycol mono (meth) acrylate, and poly (ethylene glycol-propylene glycol) mono (meth) acrylate.
Of these, hydroxyalkyl (meth) acrylates are preferred, and hydroxyalkyls having 1 to 4 carbon atoms in the alkyl moiety are preferred because of their high polymerization reactivity and excellent crosslinking reactivity when the resulting copolymer is included. (Meth) acrylate is more preferable, and 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 4-hydroxybutyl acrylate are more preferable.

The proportion of the structural unit derived from the monomer having a hydroxyl group in the acrylic copolymer B is preferably 0.1 to 2.0% by mass, more preferably 0.1 to 1.0% by mass. When the content ratio of the monomer having a hydroxyl group is within the above range, the reactivity with the isocyanate-based crosslinking agent can be ensured, which is advantageous for maintaining good durability.

The weight average molecular weight of the acrylic copolymer B is 1,000,000 or more and 2,000,000 or less. A weight average molecular weight within the above range indicates that acrylic copolymer B is a high molecular weight resin among a plurality of resins contained in the pressure-sensitive adhesive composition for polarizing plates. Further, when the weight average molecular weight of the acrylic copolymer B is reduced to less than 1,000,000, peeling or the like easily occurs, and durability (particularly durability when applied to a large size (for example, 19 inches or more)). Decreases. When the weight average molecular weight of the acrylic copolymer B exceeds 2,000,000, the stress relaxation effect due to the combined use of the acrylic copolymer A decreases. For this reason, it becomes difficult to follow the shrinkage, the adhesive is easily broken or peeled off, the durability is deteriorated, and color unevenness (especially white spots) occurs particularly when applied to a small size (for example, less than 10 inches). Can not be suppressed.

The glass transition temperature (TgB) of the acrylic copolymer B is preferably in the range of −50 ° C. to −40 ° C., and more preferably in the range of −50 ° C. to −45 ° C. When TgB is −50 ° C. or higher, the elastic modulus can be adjusted, and the durability and whiteout property are excellent. Further, when TgB is −40 ° C. or lower, the tackiness and the bonding suitability are excellent without extremely impairing the viscosity.

The content of the acrylic copolymer B in the pressure-sensitive adhesive composition for polarizing plates can be appropriately selected as long as the content ratio A / B described later is satisfied. The range of 17 mass% or more and 37 mass% or less is preferable with respect to the minute, and the range of 21 mass% or more and 32 mass% or less is more preferable. When the content of the acrylic copolymer B is within the above range, the ratio of the high molecular weight component in the pressure-sensitive adhesive is maintained, and the durability is improved.

In the acrylic copolymer A and the acrylic copolymer B in the present invention, the monomer having an alkyl (meth) acrylate and a carboxy group constituting each of them is an acrylic copolymer A and an acrylic copolymer B. And may be different from each other or the same.

In the present invention, the glass transition temperature (TgA; ° C) of the acrylic copolymer A and the glass transition temperature (TgB; ° C) of the acrylic copolymer B satisfy the relationship of TgA ≧ TgB. If TgA is less than TgB, the molecular weight is relatively small, and the reactivity with the isocyanate-based crosslinking agent is insufficient, so that failure such as foaming or peeling is likely to occur, resulting in poor durability. Among these, from the viewpoint of further improving the effect of preventing color unevenness (particularly white spots) and the durability, the difference between TgA and TgB (TgA-TgB; ° C) is preferably in the range of 1 ° C to 5 ° C. A range of not less than 3 ° C and not more than 3 ° C is more preferable.

In this specification, the glass transition temperature (Tg) of the acrylic copolymer is a molar average glass transition temperature determined by the following calculation. _Tg _1, Tg 2 of the following formulas, ... and Tg _n, the components 1, the glass transition temperature of the components 2, ... and component n respectively homopolymers, absolute temperature (° K). m ₁ , m ₂ ,... and _mn are the mole fractions of the respective components.

[Calculation formula of glass transition temperature (Tg)]

Incidentally, the “glass transition temperature (Tg) of the homopolymer” mentioned here includes L.P. E. The glass transition temperatures of the monomers described in Nielsen, Nojiharu Onoki, “Mechanical Properties of Polymers”, pp. 11-35, apply.

Moreover, the ratio (MwA / MwB) of the weight average molecular weight (MwA) of the acrylic copolymer A to the weight average molecular weight (MwB) of the acrylic copolymer B is preferably 0.5 or less. When MwA / MwB is 0.5 or less, the effect of preventing color unevenness (particularly white spots) can be further enhanced. Among these, MwA / MwB is more preferably 0.35 or less for the same reason as described above.

The content ratio (A / B) of the acrylic copolymer A to the acrylic copolymer B is preferably in the range of 60/40 to 80/20 on a mass basis. When the content ratio A / B is equal to or greater than the lower limit ratio, since the ratio of the acrylic copolymer A having a relatively small molecular weight is large, the effect of improving color unevenness (particularly white spots) due to stress relaxation is high, and the acrylic type Since the glass transition temperatures of the copolymers A and B satisfy the relationship of TgA ≧ TgB, there is little concern about a decrease in durability due to a large proportion of the acrylic copolymer A. Further, when the content ratio A / B is equal to or less than the upper limit ratio, the stress relaxation effect due to the lower molecular weight and the durability maintenance due to the relative amount of the acrylic copolymer B on the high molecular weight side being maintained. Can keep the balance.
In particular, the content ratio A / B is more preferably in the range of 65/35 to 75/25 for the same reason as described above.

Among the above, as the combination mode of the acrylic copolymer A and the acrylic copolymer B in the present invention, the following (1) first mode to (3) third mode are preferable. That is,
(1) As a first aspect,
Acrylic copolymer A is a structural unit derived from an alkyl (meth) acrylate having 1 to 4 carbon atoms, a structural unit derived from (meth) acrylic acid, and “the alkyl (meth) having 1 to 4 carbon atoms”. A structural unit derived from a `` monomer capable of forming a homopolymer having a glass transition temperature whose absolute value of the difference from the glass transition temperature of a polymer obtained by homopolymerizing acrylate is 30 ° C. or more and 90 ° C. or less; Including
Acrylic copolymer B is a structural unit derived from an alkyl (meth) acrylate having 1 to 8 carbon atoms, a structural unit derived from (meth) acrylic acid, a structural unit derived from hydroxyalkyl (meth) acrylate, (2) As a second aspect,
The acrylic copolymer A is derived from a structural unit derived from n-butyl acrylate, a structural unit derived from a (meth) acrylic monomer having a carboxy group, and derived from methyl acrylate and / or t-butyl acrylate. A structural unit, and
Acrylic copolymer B is a structural unit derived from n-butyl acrylate, a structural unit derived from a (meth) acrylic monomer having a carboxy group, and a structural unit derived from hydroxyalkyl (meth) acrylate. (3) As a third aspect,
Acrylic copolymer A includes a structural unit derived from n-butyl acrylate, a structural unit derived from (meth) acrylic acid, and methyl acrylate and / or t-butyl acrylate,
Embodiment in which acrylic copolymer B includes a structural unit derived from n-butyl acrylate, a structural unit derived from (meth) acrylic acid, and a structural unit derived from hydroxyalkyl (meth) acrylate

The polymerization method of the acrylic copolymer in the present invention is not particularly limited, and methods such as solution polymerization, emulsion polymerization and suspension polymerization can be applied. Solution polymerization is preferred because the treatment process is relatively simple and can be performed 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 under reflux of the organic solvent. Heat the reaction for several hours. The polymerization initiator is not particularly limited, and for example, an azo compound can be used.

The weight average molecular weight (Mw) of the acrylic copolymer can be adjusted to a desired molecular weight by adjusting the reaction temperature, time, amount of solvent, type and amount of catalyst.

In the present specification, the weight average molecular weight (Mw) of the acrylic copolymer is a value measured by the following method. That is, it is measured according to the following (1) to (3).
(1) An acrylic copolymer solution is coated on a release sheet (release sheet) and dried at 100 ° C. for 2 minutes to obtain a film-like acrylic copolymer.
(2) The film-like acrylic copolymer obtained in (1) is dissolved in tetrahydrofuran so that the solid content is 0.2% by mass.
(3) Under the following conditions, the weight average molecular weight (Mw) of the (meth) acrylic copolymer is measured using gel permeation chromatography (GPC).
<Condition>
・ GPC: HLC-8220 GPC [manufactured by Tosoh Corporation]
・ Column: TSK-GEL GMHXL (4 used)
-Mobile phase solvent: Tetrahydrofuran-Standard sample: Standard polystyrene-Flow rate: 0.6 ml / min
-Column temperature: 40 ° C

-Isocyanate-based crosslinking agent-
The pressure-sensitive adhesive composition for polarizing plates of the present invention contains at least one isocyanate-based crosslinking agent. This cross-linking agent is a polar compound, and in the case of a composition containing such a cross-linking agent, the effects of the present invention (prevention of color unevenness (particularly white spots) and improvement in durability) are further exhibited.

As the isocyanate-based cross-linking agent, a tolylene diisocyanate-based compound is preferably exemplified. As the tolylene diisocyanate compound, a tolylene diisocyanate compound derived from various isocyanates such as dimer or trimer of isocyanate or an adduct of isocyanate and trimethylolpropane polyol can be used.

As the tolylene diisocyanate compound, a commercially available product may be used, and “Coronate L” (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd. can be suitably used as an example of a commercially available product.

The content of the isocyanate-based crosslinking agent in the pressure-sensitive adhesive composition for polarizing plate is set to a range of 20 parts by mass or less with respect to 100 parts by mass of the total amount of the acrylic copolymer. When the content of the isocyanate cross-linking agent exceeds 20 parts by mass, the cohesive force becomes excessive, and when exposed to high temperature and high humidity, the polarizing plate (particularly cellulose triacetate (TAC), which is a protective sheet thereof) The adhesion between the two tends to deteriorate, and the occurrence of peeling cannot be suppressed. As content of an isocyanate type crosslinking agent, the range of 8 mass parts or more and 20 mass parts or less is preferable, and the range of 10 mass parts or more and 15 mass parts or less is more preferable. When the content of the isocyanate-based crosslinking agent is 8 parts by mass or more, good cohesive force is exhibited to suppress the shrinkage stress of the polarizing plate after the pressure-sensitive adhesive layer is adhered, and the occurrence of white spots is more effective. To be suppressed.

-Epoxy-based crosslinking agent-
The pressure-sensitive adhesive composition for polarizing plates of the present invention preferably contains an epoxy crosslinking agent together with the isocyanate crosslinking agent. When the polarizing plate pressure-sensitive adhesive composition contains an epoxy-based crosslinking agent, the cohesive force can be easily adjusted, and abnormal appearance can be suppressed even when exposed to high temperatures and high humidity.

Examples of the epoxy-based crosslinking agent include 1,3-bis (N, N-glycidylaminomethyl) cyclohexane, N, N, N ′, N′-tetraglycidyl-m-xylylenediamine and the like.
In addition, as the epoxy-based crosslinking agent, commercially available products may be used. As examples of commercially available products, “TETRAD-X”, “TETRAD-C” (trade name) manufactured by Mitsubishi Gas Chemical Co., Ltd. It can be preferably used.

As content in the adhesive composition for polarizing plates of an epoxy type crosslinking agent, 0.001 mass% or more and 0.1 mass% with respect to the total amount of acrylic copolymer A and acrylic copolymer B The following ranges are preferred. When the content of the epoxy crosslinking agent is within the above range, it is advantageous in that the cohesive force of the pressure-sensitive adhesive layer can be adjusted, and the occurrence of peeling due to durability (moisture and heat resistance) can be suppressed.

-Silane coupling agent-
It is preferable that the adhesive composition for polarizing plates of this invention contains a silane coupling agent. When the pressure-sensitive adhesive composition for polarizing plate contains a silane coupling agent, the pressure-sensitive adhesive layer and the polarizing plate or liquid crystal even when a display device (for example, a liquid crystal display device) incorporating the polarizing plate is exposed to a high temperature and high humidity environment. Peeling hardly occurs between cells. The pressure-sensitive adhesive composition for polarizing plates of the present invention is preferable in that it exhibits a good adhesive force on smooth glass.

Examples of the silane coupling agent include polymerizable unsaturated group-containing silane compounds such as vinyltrimethoxysilane, vinyltriethoxysilane, and 3-methacryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-mercapto. Mercapto group-containing silane compounds such as propyltriethoxysilane and 3-mercaptopropyldimethoxymethylsilane, and epoxies such as 3-glycidoxypropyltrimethoxysilane and 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane Silane compounds having a structure, 3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropyltrimethoxysilane, N- (2-aminoethyl) -3-aminopropylmethyldimethoxysilane, etc. Amino group-containing silane compound, and tris - (3-trimethoxysilylpropyl) isocyanurate. These may be used alone or in combination of two or more.

As the silane coupling agent, a commercially available product may be used, and “KBM-403” (trade name) manufactured by Shin-Etsu Chemical Co., Ltd. can be suitably used as an example of a commercially available product.

As content in the adhesive composition for polarizing plates of a silane coupling agent, 0.01 mass% or more with respect to 100 mass parts of total amounts of acrylic copolymer A and acrylic copolymer B 2. A range of 0% by mass or less is preferred. When the content of the silane coupling agent is within the above range, the adhesiveness of the pressure-sensitive adhesive layer can be further improved.

In addition to the above components, the pressure-sensitive adhesive composition for polarizing plates of the present invention may further contain various additives such as ultraviolet absorbers, solvents and the like.

<Polarizing plate with adhesive>
The polarizing plate with the pressure-sensitive adhesive of the present invention comprises at least a polarizer and a pressure-sensitive adhesive layer formed on the polarizer by the application of the pressure-sensitive adhesive composition for a polarizing plate of the present invention described above. Yes.

For example, a polyvinyl alcohol (PVA) film is generally used as the polarizer. The polarizer can be used as a polarizing plate having, for example, a three-layer structure (for example, TAC / polarizer / TAC) held between protective sheets such as triacetyl cellulose (TAC).

For example, by providing the pressure-sensitive adhesive composition for a polarizing plate of the present invention described above on at least one surface of a polarizing plate having a three-layer structure of TAC / polarizer / TAC, polarizing with pressure-sensitive adhesive A plate is made. In this case, the composition may be applied on the polarizing plate, but is preferably applied on a protective sheet (release sheet) that is peeled off during use. The application of the pressure-sensitive adhesive composition for a polarizing plate can be suitably performed by a coating method such as an immersion method, a coating method, or an ink jet method using the liquid pressure-sensitive adhesive composition for a polarizing plate. Among these, the application method is preferable.
Specifically, the pressure-sensitive adhesive composition for polarizing plate of the present invention is coated on a protective sheet (peeling sheet) and dried to form a pressure-sensitive adhesive layer on the protective sheet. A polarizing plate with an adhesive is produced by transferring and curing on the polarizing plate.

The pressure-sensitive adhesive composition applied on the protective sheet (release sheet) is preferably dried at 70 to 120 ° C. for about 1 to 3 minutes using a hot air dryer or the like.

Furthermore, from the viewpoint of protecting the contact surface with the adherend, a protective sheet (peeling sheet) for protecting the exposed surface is provided in close contact with the exposed surface of the adhesive layer provided on the polarizing plate. It is preferable. As this protective sheet, a synthetic resin sheet such as polyester subjected to a release treatment with a release agent such as a fluororesin, paraffin wax, or silicone is suitable so that it can be easily peeled off from the adhesive layer. Used for. When affixing to a glass plate or the like of the display panel, the protective sheet is peeled off, and the exposed surface of the adhesive material layer is brought into close contact with the glass substrate or the like.
Moreover, you may further provide the surface protection sheet which protects the surface (exposed surface) of the side in which the adhesive layer of a polarizing plate is not provided. As the surface protective sheet, a protective film or the like that is adhesively processed on one side of a PET film is preferably used.

The layer thickness of the pressure-sensitive adhesive layer is not particularly limited, but is preferably 1 μm or more and 100 μm or less, more preferably 5 μm or more and 50 μm or less, and still more preferably 15 μm or more and 30 μm or less.

The polarizing plate with an adhesive of the present invention is applicable even when the size of the liquid crystal cell to be laminated is 19 inches wide (260 mm × 415 mm) or more. When the size of the liquid crystal cell is 19 inches wide (260 mm × 415 mm) or more, expansion and contraction due to the influence of heat and humidity of the polarizing plate are increased. Therefore, in the conventional polarizing plate with an adhesive, since the stress is not sufficiently suppressed when exposed to high temperature and high humidity, it occurs in the vicinity of the Bethel when the light source of a large display device (for example, a liquid crystal display device) is turned on. The occurrence of “white spots” cannot be suppressed. On the other hand, in the polarizing plate with the pressure-sensitive adhesive of the present invention, since the resin design of the copolymer and the type and amount of the crosslinking agent are appropriate, the stress is suppressed even when exposed to high temperature and high humidity. It is sufficient for a liquid crystal cell having a size of 19 inches wide (260 mm × 415 mm) or larger, and may be applied to a small display device (liquid crystal display device) of less than 19 inches (or less than 10 inches). The occurrence of white spots can be suppressed by moderate stress relaxation.

<Display device>
The display device of the present invention is configured by providing a display panel for displaying an image and the above-described pressure-sensitive adhesive polarizing plate of the present invention disposed on at least one surface of the display panel.
Examples of the display panel include a liquid crystal display panel in which a liquid crystal compound is sealed, an organic electroluminescence display panel, and the like.

As an example of the display device of the present invention, the polarizing plate with the pressure-sensitive adhesive of the present invention is arranged on both sides of the liquid crystal display panel so that the pressure-sensitive adhesive layer is in contact with the surface of the liquid crystal display panel (for example, the surface of the glass substrate). And a liquid crystal display device having a structure (polarizing plate / adhesive layer / liquid crystal display panel / adhesive layer / polarizing plate structure) in which polarizing plates are bonded to both surfaces of the liquid crystal display panel via an adhesive layer. Can do.

Hereinafter, it shows about the adhesive composition for polarizing plates of this invention, a polarizing plate with an adhesive, a display apparatus, and these preferable aspects.
<1> Acrylic copolymer A comprising a structural unit derived from an alkyl (meth) acrylate and a structural unit derived from a monomer having a carboxy group, and having a weight average molecular weight of 300,000 to 700,000. And a structural unit derived from an alkyl (meth) acrylate, a structural unit derived from a monomer having a carboxy group, and a structural unit derived from a monomer having a hydroxyl group, and the weight average molecular weight is 1,000,000. The content of acrylic copolymer B that is 2,000,000 or less, acrylic copolymer A, and acrylic copolymer B with respect to a total amount of 100 parts by mass is in the range of 20 parts by mass or less. An isocyanate-based crosslinking agent, and the glass transition temperature (TgA) of the acrylic copolymer A is the glass transition temperature (Tg) of the acrylic copolymer B. B) It is the adhesive composition for polarizing plates which is above.

<2> The pressure-sensitive adhesive composition for polarizing plate according to <1>, wherein the acrylic copolymer B has a glass transition temperature (TgB) of −50 ° C. or higher and −40 ° C. or lower.
<3> The ratio (MwA / MwB) of the weight average molecular weight (MwA) of the acrylic copolymer A to the weight average molecular weight (MwB) of the acrylic copolymer B is 0.5 or less <1 > Or <2> The pressure-sensitive adhesive composition for polarizing plates according to <2>.
<4> The content ratio (A / B) of the acrylic copolymer A to the acrylic copolymer B is 60/40 to 80/20 on a mass basis. It is an adhesive composition for polarizing plates as described in any one.

<5> The acrylic copolymer A includes a structural unit derived from an alkyl (meth) acrylate having 1 to 4 carbon atoms, a structural unit derived from (meth) acrylic acid, and the alkyl having 1 to 4 carbon atoms. A structural unit derived from a monomer capable of forming a homopolymer having a glass transition temperature of 30 ° C. or higher and 90 ° C. or lower in absolute value of the difference from the glass transition temperature of a polymer obtained by homopolymerizing (meth) acrylate. Including
The acrylic copolymer B includes a structural unit derived from an alkyl (meth) acrylate having 1 to 8 carbon atoms, a structural unit derived from (meth) acrylic acid, and a structural unit derived from hydroxyalkyl (meth) acrylate. The pressure-sensitive adhesive composition for a polarizing plate according to any one of <1> to <4>, comprising:

<6> A pressure-sensitive adhesive having a polarizer and a pressure-sensitive adhesive layer formed on the polarizer by application of the pressure-sensitive adhesive composition for a polarizing plate according to any one of <1> to <5>. It is an attached polarizing plate.
<7> A display device comprising: a display panel for displaying an image; and the polarizing plate with an adhesive according to <6>, which is disposed on at least one surface of the display panel.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Unless otherwise specified, “part” is based on mass.

(Production Example A1)
In a reactor equipped with a thermometer, a stirrer, a nitrogen inlet tube, and a reflux condenser, n-butyl acrylate (BA) 79.0 parts by mass, methyl acrylate (MA) 20.0 parts by mass, acrylic acid ( AA) 1.0 part by mass, 110 parts by mass of ethyl acetate (EAc), and 0.1 part by mass of azobisdimethylvaleronitrile (ABVN) were added and mixed, and then the inside of the reactor was purged with nitrogen. Thereafter, while stirring the obtained mixture, the mixture in the reactor was heated to 65 ° C. and held for 8 hours to carry out the polymerization reaction. After completion of the polymerization reaction, the reaction mixture was diluted with ethyl acetate to adjust the solid content to 37.0% by mass. In this way, a solution of BA / MA / AA copolymer A1 (acrylic copolymer A) was obtained.

About the obtained BA / MA / AA copolymer A1, the measurement of the weight average molecular weight (Mw) and the glass transition temperature (Tg) were computed by the method shown below. The results are shown in Table 1 below.
The weight average molecular weight was determined by gel permeation chromatography (GPC) using TSK-GEL GMHXL (styrene polymer filler made by Tosoh) as a column and converted to polystyrene according to the method described above.
Tg is a molar average glass transition temperature calculated using the above-described formula for calculating the glass transition temperature (Tg).

(Production Examples A2 to A11)
In Production Example A1, the ratio of n-butyl acrylate (BA), methyl acrylate (MA), and acrylic acid (AA) used for the synthesis of BA / MA / AA copolymer A1 is as shown in Table 1 below. In the same manner as in Production Example A1, except that the molecular weight was adjusted as shown in Table 1 below by adjusting the amount of the solvent and the amount of the catalyst, the solution of the BA / MA / AA copolymers A2 to A11 (acrylic) A copolymer A) was obtained.
Moreover, about each copolymer, it measured Mw and calculated Tg like copolymer A1 of manufacture example A1. The results are shown in Table 1 below.

(Production Examples A12 to A14)
In Production Example A1, n-butyl acrylate (BA), methyl acrylate (MA), and acrylic acid (AA) used for the synthesis were changed to the constituent monomers shown in Table 2 below, and synthesis was conducted. A solution of the copolymers A12 to A11 (acrylic copolymer A) was obtained by the same method.
Moreover, about each copolymer, it measured Mw and calculated Tg like copolymer A1 of manufacture example A1. The results are shown in Table 2 below.

(Production Example B1)
In a reactor equipped with a thermometer, a stirrer, a nitrogen introduction tube, and a reflux condenser, n-butyl acrylate (BA) 89.0 parts by mass, methyl acrylate (MA) 9.5 parts by mass, acrylic acid (AA) ) After adding 1.0 parts by weight, 0.5 parts by weight of 2-hydroxyethyl acrylate (2HEA), 90 parts by weight of ethyl acetate (EAc), and 0.03 parts by weight of azobisdimethylvaleronitrile (ABVN) The inside of the reactor was purged with nitrogen. Thereafter, while stirring the obtained mixture, the mixture in the reactor was heated to 65 ° C. and held for 8 hours to carry out the polymerization reaction. After completion of the polymerization reaction, the reaction mixture was diluted with ethyl acetate to adjust the solid content to 17.0% by mass. In this way, a solution of BA / MA / AA / 2HEA copolymer B1 (acrylic copolymer B) was obtained.
For copolymer B1, Mw was measured and Tg was calculated in the same manner as copolymer A1 in Production Example A1. The results are shown in Table 1 below.

(Production Examples B2 to B5, B7 to B9)
In Production Example B1, n-butyl acrylate (BA), methyl acrylate (MA), acrylic acid (AA), and 2-hydroxyethyl acrylate (2HEA) used for the synthesis of BA / MA / AA / 2HEA copolymer B1 In the same manner as in Production Example B1, except that the ratio was changed as shown in Table 1 below and the molecular weight was adjusted as shown in Table 1 below by adjusting the amount of solvent and catalyst, BA / MA / Solutions (acrylic copolymers B) of AA / 2HEA copolymers B2 to B5 and B7 to B9 were obtained.
Moreover, about each copolymer, it measured Mw and calculated Tg like copolymer B1 of manufacture example B1. The results are shown in Table 1 below.

(Production Example B6)
In Production Example B1, the ratios of n-butyl acrylate (BA), acrylic acid (AA), and 2-hydroxyethyl acrylate (2HEA) used for the synthesis of BA / MA / AA / 2HEA copolymer B1 are shown in Table 1 below. And 9.5 parts of methyl acrylate (MA) was replaced with 15 parts of 2-ethylhexyl acrylate (2EHA), and the molecular weight was adjusted as shown in Table 1 below by adjusting the amount of solvent and the amount of catalyst. Except for the above, a solution of BA / 2EHA / AA / 2HEA copolymer B6 (acrylic copolymer B) was obtained in the same manner as in Production Example B1.
Moreover, about each copolymer, it measured Mw and calculated Tg like copolymer B1 of manufacture example B1. The results are shown in Table 1 below.

(Production Examples B10 to B13)
In Production Example B1, n-butyl acrylate (BA), methyl acrylate (MA), acrylic acid (AA), and 2-hydroxyethyl acrylate (2HEA) used for the synthesis were changed to the constituent monomers shown in Table 2 below. Synthesis was carried out to obtain a solution of copolymers B10 to B13 (acrylic copolymer B) by the same method as in Production Example B1.
Moreover, about each copolymer, it measured Mw and calculated Tg like copolymer B1 of manufacture example B1. The results are shown in Table 2 below.

Example 1
-Preparation of adhesive composition-
As acrylic copolymer A, 189.2 parts by mass of the BA / MA / AA copolymer solution obtained in Production Example A1 (solid content of BA / MA / AA copolymer: 70.0 parts by mass) and As an acrylic copolymer B, 176.5 parts by mass of a solution of BA / MA / AA / 2HEA copolymer B1 obtained in Production Example B1 (solid content of BA / MA / AA / 2HEA copolymer: 30 0.0 part by weight), 20 parts by weight of Coronate L as an isocyanate compound (isocyanate compound produced by Nippon Polyurethane Industry Co., Ltd., active ingredient: 15 parts by weight), and 0.02 part by weight of TETRAD-X as an epoxy compound (manufactured by Mitsubishi Gas Chemical Co., Ltd.) Epoxy compound, active ingredient: 0.02 parts by mass), and silane compound (SC agent) as KBM-403 (a silane coupling agent manufactured by Shin-Etsu Chemical Co., Ltd., active ingredient: 0.1) The amount unit) and sufficiently stirred and mixed and 0.1 parts by weight to obtain an adhesive composition.
At this time, the weight average molecular weight (MwA) of BA / MA / AA copolymer A1 (acrylic copolymer A) and the weight average molecular weight of BA / MA / AA / 2HEA copolymer (acrylic copolymer B). The molecular weight ratio (MwA / MwB) to (MwB) is 0.33, and the acrylic copolymer A is higher than the acrylic copolymer B with respect to Tg.

-Production of optical film samples-
The pressure-sensitive adhesive composition was applied to the release agent-treated surface of the release film surface-treated with the silicone-based release agent so that the coating amount after drying was 25 g / cm ² . Next, this was dried at 100 ° C. for 90 seconds using a hot-air circulating dryer to form an adhesive layer on the release film. Subsequently, a polarizing base film (a laminated structure of TAC film / PVA film / TAC film by laminating cellulose triacetate (TAC) films on both sides of a polarizer mainly composed of polyvinyl alcohol (PVA) film; about 190 μm) The back surface of the adhesive layer and the surface of the pressure-sensitive adhesive layer were overlapped and bonded together, and pressed through a pressure nip roll. After pressure bonding, the film was cured for 10 days under an environmental condition of 23 ° C. and 65% RH, and a polarizing film having a laminate structure of release film / adhesive layer / polarizing base film was produced as an optical film sample.

-Evaluation-
The following evaluation was performed using the polarizing film produced above. The evaluation results are shown in Table 1 below.

(1) Tackiness The value of the tilted ball tack was measured by a method according to JIS Z 0237 (tilt plate angle = 30 °), and evaluated according to the following evaluation criteria using the stopped ball number.
<Evaluation criteria>
A: The ball number is 7 or more.
B: The ball number is 5-6.
C: The ball number is 3-4.
D: The ball number is less than 3.

(2) Durability (2-1) 4.3 inches (Dry, Wet)
Prepare a test piece (4.3 inches) of 54 mm × 96 mm (long side) obtained by cutting the polarizing film prepared in “Preparation of optical film sample” so that the long side is 45 ° with respect to the absorption axis. The release film was peeled from the test piece. By sticking the surface of the adhesive layer exposed by peeling to one side of a 0.7 mm non-alkali glass plate (# 1737, manufactured by Corning), the test piece is stacked on the glass plate and pasted using a laminator. To obtain a laminate. Next, this laminate was subjected to autoclave treatment (50 ° C., 5 kg / cm ² , 20 minutes), and allowed to stand at 23 ° C. and 65% RH for 24 hours. Then, it was left for 500 hours in a Dry environment (80 ° C., 0% RH) under high temperature and low humidity conditions and a WET environment (60 ° C., 90% RH) under high temperature and high humidity conditions. After the standing time had elapsed, the state of foaming and peeling was visually observed and evaluated according to the following evaluation criteria.
<Evaluation criteria>
A: Foaming and peeling were not observed at all.
B: Foaming and peeling were hardly observed.
C: Some foaming and peeling were observed.
D: Foaming and peeling were noticeable.

(2-2) 19 inches (Dry, Wet)
In “(2-1) 4.3 inches (Dry, Wet)”, except that the size of the test piece obtained by cutting the polarizing film was changed to 240 mm × 427 mm (19 inches), “(2) Durability (4.3 inches: Dry, Wet) "was evaluated by the same method.

(3) Color unevenness (3-1) White spot phenomenon (4.3 inches)
Two polarizing film test pieces cut to the same size as the “(2-1) 4.3 inch (Dry, Wet)” were prepared, and a 0.7 mm alkali-free glass plate (# 1737, Corning) The test samples were prepared by pasting them so that the polarization axes were orthogonal to each other. Next, this test sample was subjected to autoclaving (50 ° C., 5 kg / m ² , 20 minutes), and allowed to stand for 24 hours at 23 ° C. and 50% RH. Then, it was left for 500 hours in a dry environment (70 ° C., 0% RH). After standing, each was placed on the backlight of a liquid crystal monitor under the conditions of 23 ° C. and 50% RH, and the white spots were visually observed.
<Evaluation criteria>
A: No white spots were observed at all.
B: Almost no white spots were observed.
C: Some white spots were recognized.
D: Large white spots were recognized.

(3-2) White spot phenomenon (7 inches)
In the “(3-1) White spot phenomenon (4.3 inches)”, except that the size of the test piece obtained by cutting the polarizing film was changed to 88 mm × 156 mm (7.0 inches), “( Evaluation was made in the same manner as in “3-1) White spot phenomenon (4.3 inches)”.

(3-3) White spot phenomenon (19 inches)
In the “(3-1) White spot phenomenon (4.3 inches)”, except that the size of the test piece obtained by cutting the polarizing film was changed to 240 mm × 427 mm (19 inches), “(3- 1) Evaluation was made in the same manner as the “white spot phenomenon (4.3 inches)”.

(Examples 2 to 21, Comparative Examples 1 to 6)
In Example 1, the monomer composition and physical properties (Tg, Mw) of the acrylic copolymer, the weight average molecular weight, the content ratio of the acrylic copolymers A and B, and the amount of the crosslinking agent are shown in Tables 1 and 2 below. A pressure-sensitive adhesive composition was prepared in the same manner as in Example 1 except that the change was made, and a polarizing film was produced and evaluated.

As shown in Tables 1 and 2, in the examples, the occurrence of foaming and peeling was suppressed regardless of the DRY environment and the WET environment, and good durability was obtained. Moreover, the occurrence of white spots could be effectively suppressed regardless of the size. Moreover, there was no entrainment of the foam which is easy to occur at the time of bonding, and the favorable tack property was shown.

The disclosure of Japanese application 2012-128291 is incorporated herein by reference in its entirety.
All documents, patent applications, and technical standards mentioned in this specification are to the same extent as if each individual document, patent application, and technical standard were specifically and individually described to be incorporated by reference, Incorporated herein by reference.

Claims

An acrylic copolymer A comprising a structural unit derived from an alkyl (meth) acrylate and a structural unit derived from a monomer having a carboxy group, and having a weight average molecular weight of 300,000 to 700,000;
A structural unit derived from an alkyl (meth) acrylate, a structural unit derived from a monomer having a carboxy group, and a structural unit derived from a monomer having a hydroxyl group, and having a weight average molecular weight of 1,000,000 or more 2 Acrylic copolymer B which is less than 1,000,000,
An isocyanate crosslinking agent having a content of 20 parts by mass or less based on a total amount of 100 parts by mass of the acrylic copolymer A and the acrylic copolymer B;
A pressure-sensitive adhesive composition for a polarizing plate, wherein the glass transition temperature (TgA) of the acrylic copolymer A is not less than the glass transition temperature (TgB) of the acrylic copolymer B.
The pressure-sensitive adhesive composition for a polarizing plate according to claim 1, wherein the acrylic copolymer B has a glass transition temperature (TgB) of -50 ° C or higher and -40 ° C or lower.
The ratio (MwA / MwB) of the weight average molecular weight (MwA) of the acrylic copolymer A to the weight average molecular weight (MwB) of the acrylic copolymer B is 0.5 or less. 2. The pressure-sensitive adhesive composition for a polarizing plate according to 2.
The content ratio (A / B) of the acrylic copolymer A to the acrylic copolymer B is 60/40 to 80/20 on a mass basis. The adhesive composition for polarizing plates as described.
The acrylic copolymer A includes a structural unit derived from an alkyl (meth) acrylate having 1 to 4 carbon atoms, a structural unit derived from (meth) acrylic acid, and the alkyl (meth) having 1 to 4 carbon atoms. A structural unit derived from a monomer capable of forming a homopolymer having a glass transition temperature of 30 ° C. or more and 90 ° C. or less of an absolute value of a difference from a glass transition temperature of a polymer obtained by homopolymerizing an acrylate ,
The acrylic copolymer B includes a structural unit derived from an alkyl (meth) acrylate having 1 to 8 carbon atoms, a structural unit derived from (meth) acrylic acid, and a structural unit derived from hydroxyalkyl (meth) acrylate. The pressure-sensitive adhesive composition for a polarizing plate according to any one of claims 1 to 4, comprising:
A polarizing plate with a pressure-sensitive adhesive comprising a polarizer and a pressure-sensitive adhesive layer formed on the polarizer by applying the pressure-sensitive adhesive composition for a polarizing plate according to any one of claims 1 to 5.
A display device comprising: a display panel for displaying an image; and the polarizing plate with an adhesive according to claim 6 disposed on at least one surface of the display panel.