JP2011195651A - Self-adhesive composition for optical use - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self-adhesive composition for optical use, where the self-adhesive composition is used for a touch panel, a plasma display panel and the like and does not induce whitening after being exposed to an environment under high temperature and high humidity conditions and then returned to the condition of room temperature even when the composition is thickly applied and dried.SOLUTION: The self-adhesive composition for optical use comprises: 100 parts by mass of an acrylic resin (A) which is a copolymer having a weight-average molecular weight of 300,000 to 2,000,000 and comprising 100 parts by mass of a 1-18C alkyl ester monomer (a) of a (meth)acrylic acid, 0.1 to 10 parts by mass of a copolymerizable monomer (b) having a hydroxy group and 5 to 30 parts by mass of a dialkyl-substituted acrylamide monomer (c); and 0.01 to 3.0 parts by mass of a crosslinking agent (B).

Description

  The present invention relates to a pressure-sensitive adhesive composition that can be applied to a thick film used for bonding optical members in a touch panel, a plasma display panel, and the like, and relates to an optical pressure-sensitive adhesive composition that is not affected by environmental changes.

  In recent years, liquid crystal display devices have been widely used due to the reduction in weight and thickness of displays for vehicles, outdoor instruments, displays such as personal computers, and televisions, and their demand is increasing. And especially recently, digital information devices such as ATMs of financial institutions such as banks, vending machines, mobile phones, personal digital assistants, digital audio players, portable game machines, electronic dictionaries, photocopiers, fax machines, car navigation systems, A touch panel using a liquid crystal display device is often used.

  The touch panel is an electronic component that combines a display device and a position input device, and displays the image information received from the outside on the liquid crystal display, and senses the touched screen position information and outputs it as an information signal to the outside. Have. There are mainly control methods such as a resistance film method, a capacitance method, an electromagnetic induction method, an optical method, and an acoustic method in the position input device of the touch panel. These common touch panels are arranged vertically with electrodes made of a transparent conductive layer such as an indium oxide (hereinafter referred to as ITO) film attached to a panel such as a film or glass, with a spacer in between. It has the structure. By touching this with a finger or a pen from the top of the panel, the upper and lower transparent conductive layers of the pressed portion are in electrical contact, and the touched portion can be detected.

  In the above capacitive touch panel, an optical adhesive is used when a transparent conductive layer is bonded to a panel such as a film or glass, or when a transparent conductive layer is bonded to a display device such as an LCD or a functional sheet. It is done. Moreover, it is used also for bonding of transparent conductive layers disposed on the upper and lower sides, and recently, an optical pressure-sensitive adhesive is used for bonding of transparent conductive layers even in the electrostatic capacity method. . Furthermore, there is an electroluminescence display as another optical member using a transparent conductive layer, and an optical pressure-sensitive adhesive is used for these applications.

  As described above, optical adhesives used for touch panel applications are used for bonding between transparent conductive layers and panels, bonding between transparent conductive layers, etc., so optical performance such as transparency and weather resistance Is required. In addition, the use environment of a touch panel using a liquid crystal display device has recently become very severe regardless of whether it is indoors or outdoors.

  In such a situation, in order to improve the impact resistance of the touch panel, in the above-mentioned capacitive touch panel, etc., an adhesive is used between the upper transparent conductive layer and the lower transparent conductive layer, which has been a space layer so far. It is required to be layered. For this reason, a pressure-sensitive adhesive layer having a thickness of 100 μm or more which is thicker than before has been required.

  On the other hand, according to the study by the present inventors, there are the following specific problems when the pressure-sensitive adhesive layer is 100 μm or more. That is, when a pressure-sensitive adhesive layer having a thickness of 100 μm or more is formed with a conventional optical pressure-sensitive adhesive, the pressure-sensitive adhesive film is whitened when it is returned to room temperature after being exposed to high-temperature and high-humidity conditions (for example, 60 ° C. and 90% RH). There was a problem of cloudiness. This whitening phenomenon is considered to be caused by dew condensation when moisture absorbed in the pressure-sensitive adhesive under wet heat returns to room temperature.

  In the case of a general pressure-sensitive adhesive that crosslinks by drying at room temperature, it is possible to suppress the whitening phenomenon by making the pressure-sensitive adhesive highly hygroscopic, but a heat-crosslinking type like an optical pressure-sensitive adhesive In the case of an adhesive, whitening cannot be suppressed only by increasing the hygroscopicity of the adhesive.

  As a solution for solving the above problems, Patent Document 1 discloses an adhesive having a saturated moisture absorption rate of 0.7% by weight or more at 60 ° C. and 90% RH as an adhesive for directly attaching a filter for a plasma display. It has been proposed that the adhesive can avoid the above whitening problem. Moreover, what uses 20 or more parts of the copolymerizable monomer containing a hydroxyl group as a component of a copolymer is mentioned as an Example. However, in the case of a heat-crosslinking type pressure-sensitive adhesive using a crosslinking agent, if the amount of the hydroxyl group is large in the functional group of the copolymer, the pot life is shortened, which is not practical. Moreover, when it used for the touchscreen, there existed the new subject that the change rate of the surface resistance value after bonding on the surface of ITO became too large.

  Patent Document 2 proposes an optical filter containing ethylene vinyl acetate as an impact resistant layer, and the impact resistant layer has a haze value of the impact resistant layer after being exposed at 60 ° C. and 95% RH for 1000 hours, It is disclosed that it becomes 3.0 or less and can prevent clouding. However, although it is good as an optical filter having an impact resistant layer, it is difficult to apply the above technique to an adhesive layer.

JP 2004-263084 A JP 2006-47687 A

  Accordingly, the object of the present invention is to satisfy the characteristics required for optical applications applicable to touch panels, plasma display panels, etc., and even in the case of forming a thick coating applied and dried pressure-sensitive adhesive layer, in high temperature and high humidity conditions. It is to provide an optical pressure-sensitive adhesive composition that does not cause whitening when it is returned to room temperature after being exposed.

  The above object is achieved by the present invention described below. That is, the present invention comprises (meth) acrylic acid alkyl ester monomer having 1 to 18 carbon atoms (a) 100 parts by mass, copolymerizable monomer (b) 0.1 to 10 parts by mass containing a hydroxyl group, and The acrylic resin (A), which is a copolymer having a weight average molecular weight of 300,000 to 2,000,000, consisting of a monomer containing 5 to 30 parts by mass of a dialkyl-substituted acrylamide monomer (c), and a crosslinking agent (B) An optical pressure-sensitive adhesive composition comprising 0.01 to 3.0 parts by mass is provided.

  In the present invention, the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition has a haze value of 1.0 or less when the coating thickness is 175 μm; the pressure-sensitive adhesive layer is 60 ° C. and 90% RH for 200 hours. The haze value of the pressure-sensitive adhesive layer when taken out in a room temperature environment after being allowed to stand is preferably 4.0 or less; the moisture absorption rate of the pressure-sensitive adhesive layer is preferably 0.5% or more. The pressure-sensitive adhesive composition of the present invention is not particularly limited, but is particularly useful for touch panels.

  According to the present invention, in addition to satisfying the properties required for optical applications applicable to touch panels, plasma display panels, etc., even when an adhesive layer formed by thick coating and drying is formed, it is exposed to high temperature and high humidity conditions. Then, when the temperature is returned to room temperature, an optical pressure-sensitive adhesive composition that suppresses the occurrence of the whitening phenomenon can be provided.

  Next, the present invention will be described in more detail with reference to modes for carrying out the invention. In the specification and claims of the present invention, the term “(meth) acryl” means both “acryl” and “methacryl”, and the term “(meth) acrylate” ”And“ methacrylate ”.

  The pressure-sensitive adhesive composition of the present invention comprises (meth) acrylic acid alkyl ester monomer (a) having 1 to 18 carbon atoms (hereinafter simply referred to as “monomer a”) and a copolymerizable monomer (b) containing a hydroxyl group. ) (Hereinafter simply referred to as “monomer b”) and a dialkyl-substituted acrylamide monomer (c) (hereinafter simply referred to as “monomer c”), which is a copolymer having a weight average molecular weight of 300,000 to 2,000,000. It is characterized by containing (A) and a crosslinking agent (B). Particularly, the acrylic resin (A) is characterized by containing a certain amount of monomer c.

  The monomer a is an alkyl ester monomer having 1 to 18 carbon atoms of (meth) acrylic acid, for example, methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, Examples include alkyl (meth) acrylates such as isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, and lauryl (meth) acrylate. These may be used alone or in combination.

  The monomer b is a copolymerizable monomer containing a hydroxyl group, such as 2-hydroxylethyl (meth) acrylate, 2-hydroxylpropyl (meth) acrylate, 4-hydroxylbutyl (meth) acrylate, 6-hydroxylhexyl. Hydroxyl groups such as (meth) acrylate, 8-hydroxyoctyl (meth) acrylate, 10-hydroxydecyl (meth) acrylate, 12-hydroxylauryl (meth) acrylate, N-hydroxy (meth) acrylamide, hydroxyethyl (meth) acrylamide, etc. And monomers. Preferred are 2-hydroxylethyl (meth) acrylate and 4-hydroxylbutyl (meth) acrylate, and these may be used alone or in combination.

  The usage-amount of the monomer b is 0.1-10 mass parts when the monomer a is 100 mass parts. When the proportion of the monomer b used is less than 0.1 parts by mass, when the acrylic resin (A) is crosslinked with the crosslinking agent (B), the gel fraction after crosslinking is low, and the durability of the pressure-sensitive adhesive layer However, the pressure-sensitive adhesive layer is peeled off, which is insufficient as an optical pressure-sensitive adhesive. On the other hand, when the proportion of the monomer b used exceeds 10 parts by mass, the gel fraction increases because the gelation of the acrylic resin (A) after the addition of the crosslinking agent is promoted, and in the durability test of the pressure-sensitive adhesive layer It becomes easy to peel off.

  The monomer c, which is a feature of the present invention, is a dialkyl-substituted acrylamide monomer, and improves the durability as an optical pressure-sensitive adhesive by copolymerization, and further suppresses the whitening of the film, which is the object of the present invention. An effect is obtained. Examples of the monomer c include N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, N-ethyl-N-methyl (meth) acrylamide, N, N-dibutyl (meth) acrylamide, N, N-dipropyl (meth) acrylamide, N, N-diisopropyl (meth) acrylamide, N-methyl-N-propylacrylamide, N-methyl-N-isopropylacrylamide and the like can be mentioned. N, N-dimethyl (meth) acrylamide, N, N-diethyl (meth) acrylamide, and N-ethyl-N-methyl (meth) acrylamide are preferable, and these may be used alone or in combination.

  The usage-amount of the monomer c is 5-30 mass parts when the monomer a is 100 mass parts. When the usage ratio of the monomer c is less than 5 parts by mass, a pressure-sensitive adhesive layer is formed, and after leaving for a certain period of time in a high temperature and high humidity condition, the coating film is whitened when taken out to room temperature. On the other hand, when the proportion of the monomer c used exceeds 30 parts by mass, the whitening of the film can be suppressed, but the cohesive force of the pressure-sensitive adhesive layer is excessively increased, resulting in poor impact resistance.

  The acrylic resin (A) used in the present invention may further contain an aromatic monomer unit. The aromatic monomer is a monomer containing an aromatic group in the structure, and examples thereof include phenoxyethyl (meth) acrylate, benzyl (meth) acrylate, styrene, and α-methylstyrene. By copolymerizing these aromatic monomers, the refractive index of the formed pressure-sensitive adhesive layer can be adjusted, the difference in refractive index between optical members can be reduced, total reflection can be reduced, and the transmittance can be improved. In particular, when used for an optical member, display performance can be improved. The amount of the aromatic monomer used in the case of using the aromatic monomer is preferably in the range of 5 to 30 parts by mass when the monomer a is 100 parts by mass.

  The weight average molecular weight (GPC measurement, standard polystyrene conversion) of the acrylic resin (A) obtained by copolymerizing the monomers a to c and other monomers is 300,000 to 2,000,000. When the weight average molecular weight of the acrylic resin is less than 300,000, durability of the formed pressure-sensitive adhesive layer becomes insufficient. On the other hand, when the weight average molecular weight of the acrylic resin exceeds 2 million, the viscosity increases, the amount of solvent for viscosity adjustment increases in the pressure-sensitive adhesive, and the evaporation residue of the pressure-sensitive adhesive inevitably decreases. It is easy to foam and is not suitable for thick coating.

  The acrylic resin (A) used in the present invention can be produced by either solution polymerization or emulsion polymerization, but solution polymerization is preferred. Examples of the polymerization method include, but are not limited to, radical copolymerization, ionic copolymerization, random copolymerization, alternating copolymerization, block copolymerization, and graft copolymerization.

  The crosslinking agent (B) used in the present invention can react with the reactive functional group of the monomer b constituting the acrylic resin (A) to form a crosslinked structure. For example, an isocyanate group in one molecule Polyisocyanate compound having 2 or more, 1 polyglycidyl compound having 2 or more glycidyl groups in one molecule, polyaziridine compound having 2 or more aziridinyl groups in one molecule, and 2 or more oxazoline groups in one molecule It is at least one selected from a polyoxazoline compound and a metal chelate compound.

  Specifically, adducts of hexamethylene diisocyanate, xylylene diisocyanate, tolylene diisocyanate, isophorone diisocyanate, etc. and trimethylolpropane, isocyanurate compounds, burette type compounds, bisphenol F type epoxy resins, N, N, N ′ , N′-tetraglycidyl-m-xylylenediamine, polyisocyanate compounds such as 1,3-bis (N, N-diglycidylaminomethyl) cyclohexane, N, N′-diphenylmethane-4,4′-bis (1 -Aziridinecarboxamide), N, N'-toluene-2,4-bis (1-aziridinecarboxamide), N, N'-hexamethylene-1,6-bis (1-aziridinecarboxamide), trimethylolpropane-tri- β-aziridinyl Pionate, polyglycidyl compounds such as tetramethylolmethane-tri-β-aziridinylpropionate, 2,2′-p-phenylene-bis- (1,3-oxazoline), 2,2′-tetramethylene-bis -(1,3-oxazoline), low molecular weight poly (1,3-oxazoline) compounds such as 2,2′-octamethylene-bis- (2-oxazoline), 2-isopropenyl-1,3-oxazoline, etc. A homopolymer of a 1,3-oxazoline group-containing vinyl monomer, or a copolymer of various vinyl monomers capable of copolymerizing the 1,3-oxazoline group-containing vinyl monomer, , 3-oxazoline group-containing vinyl polymer, aluminum chelate, zirconium chelate, metal chelate compounds such as titanium chelate, etc. A polyisocyanate compound, polyglycidyl compounds, metal chelate compound. These crosslinking agents can be used alone or in combination of two or more.

  It is preferable that the usage-amount of a crosslinking agent (B) is 0.01-3.0 mass parts with respect to 100 mass parts of acrylic resins (A). When the amount of the crosslinking agent (B) used is less than 0.01 parts by mass, the crosslinking density of the pressure-sensitive adhesive (resin) is lowered and the durability is inferior. Moreover, when the usage-amount of a crosslinking agent (B) exceeds 3.0 mass parts, the formed adhesive layer will peel off and durability will worsen.

  The pressure-sensitive adhesive composition of the present invention can further use a silane coupling agent, and any silane coupling agent known in the field of pressure-sensitive adhesives can be used.

  In addition, the pressure-sensitive adhesive composition of the present invention may further contain various additives in a range that does not impair the effects of the present invention, depending on necessary properties such as the purpose of adjusting the adhesive strength. For example, terpene, terpene-phenol, coumarone indene, styrene, rosin, xylene, phenol, or petroleum tackifier resins, antioxidants, UV absorbers, fillers, pigments, etc. can do. Moreover, the manufacturing method itself of the adhesive composition of this invention may be a well-known method, and is not specifically limited.

  The acrylic resin (A) of the present invention can be produced by ordinary solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization or the like, but is produced by solution polymerization in which the acrylic resin (A) is obtained as a solution. Is preferred. By obtaining the acrylic resin (A) as a solution, it can be used as it is for producing the pressure-sensitive adhesive composition of the present invention. Examples of the solvent used for the solution polymerization include organic solvents such as ethyl acetate, toluene, n-hexane, acetone, and methyl ethyl ketone.

  Examples of the polymerization initiator used in the polymerization include peroxides such as benzoyl peroxide and lauryl peroxide, azobis compounds such as azobisisobutyronitrile and azobisvaleronitrile, and polymer azo polymerization initiators. These can be used alone or in combination. Moreover, in the said superposition | polymerization, in order to adjust the molecular weight of an acrylic resin (A), a conventionally well-known chain transfer agent can be used.

  The pressure-sensitive adhesive composition of the present invention is a protective film such as a polyethylene terephthalate film (PET film) whose surface is coated with a release agent such as a silicone resin using a commonly used coating device such as a roll coating device. It is used to form a pressure-sensitive adhesive layer by coating on one or both sides and drying the coating layer. If necessary, the pressure-sensitive adhesive layer can be cured by heat crosslinking or light such as ultraviolet rays.

  The pressure-sensitive adhesive composition of the present invention has the following effects even when the coating amount is thickly applied so that the thickness of the pressure-sensitive adhesive layer after drying is 100 to 200 μm. That is, even when the thickness of the pressure-sensitive adhesive layer is within the above range, it is possible to form a pressure-sensitive adhesive layer without generating bubbles. Moreover, even if the adhesive composition of this invention is applied to the film thickness of 175 micrometers, the haze value of the adhesive layer is hold | maintained at 1.0 or less.

  In addition, the pressure-sensitive adhesive composition of the present invention has a coating layer when the pressure-sensitive adhesive layer having a coating thickness of 175 μm is left at 60 ° C. and 90% RH for 200 hours (hereinafter simply referred to as high temperature and high humidity conditions) and then taken out to room temperature. A haze value is maintained at 4.0 or less, and even when such thick coating is dried, the occurrence of whitening phenomenon is suppressed when the temperature returns to room temperature after exposure to high temperature and high humidity conditions. An effect is obtained.

In the pressure-sensitive adhesive composition of the present invention, the moisture absorption rate of the film of the pressure-sensitive adhesive layer having a coating thickness of 175 μm is preferably 0.5% or more. More preferably, it is 0.5% to 3.0%. If the moisture absorption rate of the film is at least 0.5% or more, the occurrence of the whitening phenomenon is suppressed. The reason for this is that since the film has an appropriate moisture absorption rate, the film absorbs moisture even when the film is allowed to stand at high temperature and high humidity and then returned to room temperature. We think that whitening can be suppressed without letting The “moisture absorption rate of the film” as used herein is a value calculated from the following equation 1 by measuring a mass of a sample piece of a certain size for 7 days under high-temperature and high-humidity conditions and before and after that.
[Formula 1]
Moisture absorption rate of film (%) = ((W2−W1) / W1) × 100
W1: Mass of the sample before leaving at high temperature and high humidity condition W2: Mass of the sample after leaving at high temperature and high humidity condition

  Further, “room temperature” means 20 ° C. ± 15 ° C., and “when taken out” means within 1 hour after taking out from high temperature and high humidity conditions. In the case of a conventional pressure-sensitive adhesive composition, the film has a high haze value when taken out at room temperature after being left under the above-described high temperature and high humidity condition, and the film is whitened, which is insufficient as an optical pressure-sensitive adhesive. The pressure-sensitive adhesive composition of the present invention solves the above problems. In particular, a pressure-sensitive adhesive layer that does not cause a whitening phenomenon is obtained by setting the haze value of the film when taken out to room temperature from the high temperature and high humidity conditions to 4.0 or less and the moisture absorption rate of the film to 0.5% or more. Can be provided.

  The pressure-sensitive adhesive composition of the present invention is effective for bonding various optical members, but is particularly useful for bonding various members in a touch panel. For example, in the case of the capacitance method, an adhesive is used for directly bonding the upper transparent conductive layer and the lower transparent conductive layer patterned with the conductive layer or for bonding the lower transparent conductive layer and the LCD panel. Layers may be used. These pressure-sensitive adhesive layers are required to have high optical performance, but by using the pressure-sensitive adhesive composition of the present invention, it is possible to satisfy the high optical performance as described above.

  Next, the present invention will be described more specifically with reference to examples and comparative examples. In the text, “part” or “%” is based on mass unless otherwise specified.

<Creation of copolymers 1-7>
Nitrogen gas was introduced into a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen introduction tube, and the air in the reaction apparatus was replaced with nitrogen gas. Thereafter, 100 parts of butyl acrylate, 1.0 part of 2-hydroxyethyl acrylate, 10 parts of N, N-diethylacrylamide and 60 parts of ethyl acetate were added to the reactor. Thereafter, 0.1 part of azobisisobutyronitrile was added as a polymerization initiator, and the mixture was allowed to react in a nitrogen gas stream at 65 ° C. for 5 hours while stirring, to obtain an acrylic copolymer having a weight average molecular weight of 800,000. A solution of 1 was obtained. Similarly, copolymers 2 to 7 were obtained using the monomer and solvent compositions shown in Table 1. Abbreviations in Table 1 are shown below.

BA: butyl acrylate 2EHA: 2-ethylhexyl acrylate MA: methyl acrylate EA: ethyl acrylate BZA: benzyl acrylate HEA: 2-hydroxyethyl acrylate 4HBA: 4-hydroxybutyl acrylate HEMA: 2-hydroxyethyl methacrylate DEAA: N, N- Diethylacrylamide DMAA: N, N-dimethylacrylamide EMAA: N-ethyl-N-methylacrylamide DMMA: N, N-dimethylmethacrylamide DBAA: N, N-dibutylacrylamide DEMA: N, N-diethylmethacrylamide

  The value of the weight average molecular weight (Mw) in Table 1 is a polystyrene-converted molecular weight measured by a GPC (GEL Permeation Chromatography) method. Specifically, the coating film obtained by drying the copolymer at room temperature was dissolved in tetrahydrofuran, and measured with a high performance liquid chromatograph (manufactured by Shimadzu Corporation, LC-10ADvp, column KF-G + KF-806 × 2). The weight average molecular weight (Mw) in terms of polystyrene was determined.

[Examples 1-5, Comparative Examples 1-2]
0.1 parts of Coronate L was mixed with 100 parts of the solid content of the copolymer 1 of Table 1 to obtain an adhesive composition of Example 1. The pressure-sensitive adhesive composition was applied on a PET film coated with a silicone resin, and then dried at 90 ° C. to remove the solvent, thereby obtaining a sheet having a pressure-sensitive adhesive layer thickness of 175 μm. In the same manner as in Example 1, the adhesive composition of Examples 1 to 5 and Comparative Examples 1 and 2, and a sheet on which an adhesive layer was formed by mixing and applying the components shown in Table 2 Got. Abbreviations in Table 2 are shown below.

Coronate L: manufactured by Nippon Polyurethane Industry Co., Ltd. Polyisocyanate D-110N: manufactured by Mitsui Chemicals, Inc. Takenate D-110N xylylene diisocyanate compound D-120N: manufactured by Mitsui Chemicals, Inc. Takenate D-120N hydrogenated xylylene diisocyanate compound

<Test methods and evaluation criteria>
The sheet on which the pressure-sensitive adhesive layer in Examples and Comparative Examples was formed was aged in an atmosphere of 23 ° C. and 50% RH for 7 days, then an undercoat layer on one side of the PET film, an amorphous ITO layer on the opposite side, Attached to a hard coat layer of an ITO film with a total thickness of 125 μm provided with a hard coat layer, each cut to 200 mm × 300 mm, peeled off the film separator, pasted on a glass substrate, autoclaved, and evaluated A sample was made. About the obtained sample for evaluation, the test of the following item was performed, respectively.
[Haze value]
(1) At the time of coating The above-mentioned sample for evaluation was bonded on glass, and the haze value was measured by a method based on JIS K7136 with a NDH5000W haze meter manufactured by Nippon Denshoku Industries Co., Ltd.
(2) After moist heat After measuring the haze value at the time of coating, the sample was left at 60 ° C. and 90% RH for 200 hours, then taken out in a room temperature environment and used for 1 hour at a room temperature. The haze value was measured by a method based on JIS K7136 with an industrial NDH5000W haze meter.

[Hygroscopic rate]
The pressure-sensitive adhesive layers in Examples and Comparative Examples were formed, bonded to film separators having different peeling forces, and after aging was completed, the film was cut into 200 mm × 300 mm and the single-sided film separator was peeled off. After the sample was dried at 100 ° C. for 1 hour, the mass was accurately measured (W1). Thereafter, the sample was allowed to stand in an atmosphere of 60 ° C. and 90% RH (high temperature and high humidity conditions) for 7 days, and then the sample was taken out and the mass was measured again accurately (W2). Using the measured values obtained, the moisture absorption rate of the film was calculated from the following formula 1.
[Formula 1]
Moisture absorption rate of film (%) = ((W2−W1) / W1) × 100
W1: Mass of the sample before leaving at high temperature and high humidity condition W2: Mass of the sample after leaving at high temperature and high humidity condition

[Durability test]
(1) 80 ° C
The sample for evaluation was allowed to stand in an atmosphere of 80 ° C. (DRY) for 500 hours, and then visually confirmed for foaming and peeling. The evaluation criteria are as follows.
(2) 60 ° C 90% RH
The evaluation sample was allowed to stand in an atmosphere of 60 ° C. and 90% RH for 500 hours, and then visually confirmed for foaming and peeling. The evaluation criteria are as follows.

<Evaluation criteria>
○: No foaming or peeling is confirmed on the sheet.
Δ: Foaming and peeling were slightly confirmed on the sheet.
X: Foaming and peeling were confirmed on the sheet.

  According to the present invention, a pressure-sensitive adhesive composition used for a touch panel, a plasma display panel, etc., and even when it is thickly coated and dried, it is whitened when it is returned to room temperature after being exposed to high temperature and high humidity conditions. It is possible to provide an optical pressure-sensitive adhesive composition in which no occurrence occurs.

Claims (5)

  (Meth) acrylic acid alkyl ester monomer having 1 to 18 carbon atoms (a) 100 parts by mass, copolymerizable monomer (b) containing 0.1 to 10 parts by mass, and dialkyl-substituted acrylamide monomer (c) ) 100 parts by mass of acrylic resin (A), which is a copolymer having a weight average molecular weight of 300,000 to 2,000,000, and a crosslinking agent (B) of 0.01 to 3. An optical pressure-sensitive adhesive composition comprising 0 part by mass.   2. The optical pressure-sensitive adhesive composition according to claim 1, wherein the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition has a haze value of 1.0 or less when the coating thickness is 175 μm.   2. The haze value of the pressure-sensitive adhesive layer when the pressure-sensitive adhesive layer formed of the pressure-sensitive adhesive composition is left at 60 ° C. and 90% RH for 200 hours and then taken out in a room temperature environment is 4.0 or less. Or the optical adhesive composition of 2.   The optical pressure-sensitive adhesive composition according to claim 1, wherein a moisture absorption rate of the pressure-sensitive adhesive layer formed by the pressure-sensitive adhesive composition is 0.5% or more.   It is an object for touch panels, The optical adhesive composition of any one of Claims 1-4.