JP2019210343A - Optical adhesive sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pressure-sensitive adhesive sheet excellent in resistance to sebum and chemicals, less likely to cause foaming even under high temperature and high humidity, and excellent in optical characteristics. An optical pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing an acrylic copolymer, the pressure-sensitive adhesive layer having a swelling ratio after being immersed in oleic acid at 65 ° C. and a humidity of 90% for 24 hours. 100% by weight or more and 130% by weight or less, and the pressure-sensitive adhesive layer has a difference (A-) between the maximum value (A) and the minimum value (B) of the storage elastic modulus in the temperature range of 100 ° C or more and 140 ° C or less. An optical pressure-sensitive adhesive sheet having B) of 1.2 × 10 4 Pa or less. [Selection diagram] None

Description

The present invention relates to an optical pressure-sensitive adhesive sheet.

Conventionally, pressure-sensitive adhesive sheets have been widely used when fixing components in electronic devices. Specifically, for example, an adhesive sheet is used to bond a cover panel for protecting the surface of a portable electronic device to a touch panel module or a display panel module, or to bond a touch panel module and a display panel module. ing. An adhesive sheet is also used to fix the polarizing plate. Such adhesive sheets used for fixing electronic device parts are required to have functions such as heat resistance, thermal conductivity, and impact resistance in addition to high adhesiveness, depending on the environment of the part to be used (for example, Patent Documents 1 to 3).

Japanese Patent Laying-Open No. 2015-052050 Japanese Patent Laying-Open No. 2015-021067 JP, 2015-12076, A

In recent years, portable electronic devices such as mobile phones, smartphones, wearable terminals and the like that are always worn or placed at hand have become widespread. Portable electronic devices are frequently used, and since they are operated with bare hands using a touch panel, etc., sebum or chemicals adhering to the hands may enter the interior, causing the adhesive sheet to peel off or the adhesive sheet to swell. There is a problem that whitening occurs and visibility decreases. In recent years, so-called narrowing of the frame, which narrows the width of the outer frame (frame) of the display, has progressed, and the problem has become serious. Moreover, when an electronic device is exposed to high temperature and high humidity, there is a problem that outgas is generated from a component that easily absorbs moisture, such as a polarizing plate, and foaming occurs on the adhesive surface with the pressure-sensitive adhesive sheet. Such foaming also causes a decrease in the visibility of the display.

An object of the present invention is to provide an optical pressure-sensitive adhesive sheet which is excellent in resistance to sebum and chemicals, hardly foams even under high temperature and high humidity, and has excellent optical characteristics.

The present invention is an optical pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing an acrylic copolymer, and the pressure-sensitive adhesive layer has a swelling ratio after being immersed in oleic acid at 65 ° C. and a humidity of 90% for 24 hours. The pressure-sensitive adhesive layer has a difference between the maximum value (A) and the minimum value (B) of the storage elastic modulus in a temperature range of 100 ° C. or more and 140 ° C. or less (A−). B) is an optical pressure-sensitive adhesive sheet of 1.2 × 10 ⁴ Pa or less.
Hereinafter, the present invention will be described in detail.

In the optical pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing an acrylic copolymer, the swelling ratio of the pressure-sensitive adhesive layer after being immersed in oleic acid, which is the main component of sebum, for a certain time is within a specific range. It has been found that the resistance to sebum and chemicals can be improved by adjusting.
On the other hand, in order to suppress foaming that occurs under high temperature and high humidity, the storage elastic modulus of the pressure-sensitive adhesive layer, particularly the storage elastic modulus at a high temperature (about 80 to 100 ° C.) at which foaming occurs is adjusted to a relatively high range. It is possible. However, the storage elastic modulus in the temperature region where foaming occurs may not always correlate with the actual likelihood of foaming. This is presumably because the deformation speed of the pressure-sensitive adhesive layer when foaming occurs is very low. That is, from the temperature-speed conversion law, the foaming behavior at a low speed of the pressure-sensitive adhesive layer can be regarded as the foaming behavior in a higher temperature region than the temperature region in which foaming occurs, and the storage elastic modulus in such a high temperature region. If so, it is considered more correlated with the likelihood of actual foaming. However, there is a problem that accurate measurement cannot be performed in a temperature range higher than the temperature range in which foaming occurs due to decomposition of the pressure-sensitive adhesive.
On the other hand, the present inventors pay attention to the degree of change in the storage elastic modulus of the pressure-sensitive adhesive layer in a temperature range of 100 ° C. or more and 140 ° C. or less, and if the degree of change in the storage elastic modulus in this temperature range is small. Further, it was considered that the storage elastic modulus was kept high even in a higher temperature region. The inventors set the difference (A−B) between the maximum value (A) and the minimum value (B) of the storage elastic modulus of the pressure-sensitive adhesive layer in a temperature range of 100 ° C. or more and 140 ° C. or less to a specific value or less. By adjusting, it discovered that the foaming produced under high temperature and high humidity could be suppressed, and came to complete this invention.

The optical pressure-sensitive adhesive sheet of the present invention has a pressure-sensitive adhesive layer containing an acrylic copolymer, and the pressure-sensitive adhesive layer is swelled after being immersed in oleic acid at 65 ° C. and a humidity of 90% for 24 hours (“ The oleic acid swelling ratio ”is 100 wt% or more and 130 wt% or less.
If the oleic acid swelling rate is 100% by weight or more, it means that the adhesive component does not elute into oleic acid. When the oleic acid swelling ratio is 130% by weight or less, the pressure-sensitive adhesive layer has improved resistance to sebum and chemicals. A preferable upper limit of the oleic acid swelling rate is 120% by weight, and a more preferable upper limit is 115% by weight.
The swelling rate of oleic acid is a percentage of the weight of the pressure-sensitive adhesive layer after being dipped in oleic acid and dried with respect to the weight of the pressure-sensitive adhesive layer before being dipped in oleic acid as shown in the following formula (1). It is the value expressed by.
Oleic acid swelling ratio (% by weight) = 100 × (W ₃ −W ₁ ) / (W ₂ −W ₁ ) (1)
(W ₁ : Weight of base material, W ₂ : Weight before immersion of oleic acid in pressure-sensitive adhesive sheet, W ₃ : Weight of pressure-sensitive adhesive sheet after immersion in oleic acid)

Examples of a method for adjusting the oleic acid swelling ratio to the above range include a method for adjusting the monomer composition, weight average molecular weight, and the like of the acrylic copolymer.
More specifically, for example, as described later, (1) a method in which the acrylic copolymer contains a structural unit derived from fluoroalkyl (meth) acrylate, and (2) the acrylic copolymer has 2 or less carbon atoms. And a method of containing a structural unit derived from an alkyl (meth) acrylate having an alkyl group. The methods (1) and (2) may be used alone or in combination.

The pressure-sensitive adhesive layer has a difference (A−B) of 1.2 × 10 ⁴ Pa or less between the maximum value (A) and the minimum value (B) of the storage elastic modulus in a temperature range of 100 ° C. or more and 140 ° C. or less. is there.
If the difference (A-B) in the storage elastic modulus is 1.2 × 10 ⁴ Pa or less, the degree of change in the storage elastic modulus in the temperature region of 100 ° C. or higher and 140 ° C. or lower is small. Even in a high temperature region, the storage elastic modulus of the pressure-sensitive adhesive layer is kept high, and foaming generated under high temperature and high humidity can be suppressed. A preferable upper limit of the difference in storage elastic modulus (AB) is 0.8 × 10 ⁴ Pa, and a more preferable upper limit is 0.4 × 10 ⁴ Pa. The lower limit of the difference in storage elastic modulus (A-B) is not particularly limited and is preferably as small as possible. The substantial lower limit is about 0.01 × 10 ⁴ Pa.
The storage elastic modulus is measured in the range of −40 ° C. to 140 ° C. at a temperature rising rate of 5 ° C./min using a dynamic viscoelasticity measuring apparatus (for example, DVA-200 manufactured by IT Measurement Co., Ltd.). Can do.

Examples of a method for adjusting the difference in storage elastic modulus (AB) to the above range include a method for adjusting the monomer composition, weight average molecular weight, and the like of the acrylic copolymer. Further, by adjusting the type or amount of the monomer having a crosslinkable functional group in the acrylic copolymer and the type or amount of the crosslinking agent added to the pressure-sensitive adhesive layer, the gel fraction of the pressure-sensitive adhesive layer can be relatively reduced. The method of adjusting to a high range is also mentioned.

The acrylic copolymer preferably includes a structural unit derived from fluoroalkyl (meth) acrylate.
The fluoroalkyl (meth) acrylate is a fluorinated part or all of the hydrogen atoms of the alkyl group of the alkyl (meth) acrylate. When the acrylic copolymer contains a structural unit derived from the fluoroalkyl (meth) acrylate, the molecular chain of the acrylic copolymer is high due to high water and oil repellency of fluorine itself and dense packing of fluorine atoms. Infiltration of oleic acid into the inside is suppressed. As a result, the oleic acid swelling rate easily satisfies the above range, and the pressure-sensitive adhesive layer has improved resistance to sebum and chemicals.

The fluoroalkyl (meth) acrylate is not particularly limited. For example, 2,2,2-trifluoroethyl (meth) acrylate, 1H, 1H, 3H-tetrafluoropropyl (meth) acrylate, 2,2,3,3 , 3-pentafluoropropyl (meth) acrylate, 2- (perfluorohexyl) ethyl (meth) acrylate, 1H-1- (trifluoromethyl) trifluoroethyl (meth) acrylate, 1H, 1H, 3H-hexafluorobutyl (Meth) acrylate, 1,2,2,2-tetrafluoro-1- (trifluoromethyl) ethyl acrylate, 2- (perfluorobutyl) ethyl (meth) acrylate and the like. In addition, (meth) acrylate means that it may be an acrylate or a methacrylate. These fluoroalkyl (meth) acrylates may be used alone or in combination.
Among them, 2,2,2-trifluoroethyl (meth) acrylate, 2,2,3,3,3-pentafluoropropyl (meth) acrylate, 2- (perfluorobutyl) ethyl (meth) acrylate and 2- At least one selected from the group consisting of (perfluorohexyl) ethyl (meth) acrylate is preferred, and these acrylates are more preferred. 2- (perfluorohexyl) ethyl acrylate is particularly preferred because of its particularly high resistance to sebum and chemicals.

In the acrylic copolymer, the preferable lower limit of the content of the structural unit derived from the fluoroalkyl (meth) acrylate is 30% by weight, and the preferable upper limit is 80% by weight. When the content is 30% by weight or more, the penetration of oleic acid into the molecular chain of the acrylic copolymer is further suppressed, and the adhesive layer has improved resistance to sebum and chemicals. When the content is 80% by weight or less, the pressure-sensitive adhesive layer does not become too hard, and sufficient adhesive force can be exhibited. The more preferable lower limit of the content is 40% by weight, the more preferable upper limit is 70% by weight, the still more preferable lower limit is 45% by weight, and the still more preferable upper limit is 60% by weight.

The acrylic copolymer preferably includes a structural unit derived from an alkyl (meth) acrylate having an alkyl group having 2 or less carbon atoms.
When the acrylic copolymer contains a structural unit derived from an alkyl (meth) acrylate having an alkyl group having 2 or less carbon atoms, the cohesive force of the pressure-sensitive adhesive layer is increased. As a result, the oleic acid swelling rate easily satisfies the above range, and the pressure-sensitive adhesive layer has improved resistance to sebum and chemicals.

Examples of the alkyl (meth) acrylate having an alkyl group having 2 or less carbon atoms include methyl (meth) acrylate and ethyl (meth) acrylate. These alkyl (meth) acrylates having an alkyl group having 2 or less carbon atoms may be used alone or in combination. Of these, methyl acrylate is preferable because it exhibits high cohesive strength.

In the acrylic copolymer, the content of the structural unit derived from the alkyl (meth) acrylate having an alkyl group having 2 or less carbon atoms is not particularly limited.
When the acrylic copolymer includes both a structural unit derived from the fluoroalkyl (meth) acrylate and a structural unit derived from an alkyl (meth) acrylate having an alkyl group having 2 or less carbon atoms, the carbon The minimum with preferable content of the structural unit derived from the alkyl (meth) acrylate which has an alkyl group whose number is 2 or less is 10 weight%. If the said content is 10 weight% or more, the cohesion force of the said adhesive layer will become higher, and the tolerance to sebum and a chemical | medical agent will improve. Moreover, the preferable upper limit of the said content is 40 weight%. When the content is 40% by weight or less, the pressure-sensitive adhesive layer does not become too hard, and sufficient adhesive force can be exhibited. A more preferable lower limit of the content is 14% by weight, and a more preferable upper limit is 30% by weight.
On the other hand, when the acrylic copolymer does not include a structural unit derived from the fluoroalkyl (meth) acrylate and includes a structural unit derived from an alkyl (meth) acrylate having an alkyl group having 2 or less carbon atoms, The minimum with preferable content of the structural unit derived from the alkyl (meth) acrylate which has the said C2 or less alkyl group is 50 weight%. If the said content is 50 weight% or more, the cohesion force of the said adhesive layer will become higher, and the tolerance to sebum and a chemical | medical agent will improve. Moreover, the preferable upper limit of the said content is 99 weight%. When the content is 99% by weight or less, the pressure-sensitive adhesive layer does not become too hard, and sufficient adhesive force can be exhibited. The more preferable lower limit of the content is 70% by weight, and the more preferable upper limit is 95% by weight.

The acrylic copolymer preferably further includes a structural unit derived from a monomer having a crosslinkable functional group.
When the acrylic copolymer contains a structural unit derived from the monomer having the crosslinkable functional group, the chain of the acrylic copolymer is crosslinked when a crosslinking agent is used in combination. In that case, the gel fraction of the said adhesive layer can be adjusted by adjusting a crosslinking degree. In particular, by adjusting the gel fraction of the pressure-sensitive adhesive layer to a relatively high range, the difference in storage elastic modulus (AB) can be easily adjusted to the above range, and foaming that occurs under high temperature and high humidity can be further improved. Can be suppressed.

Examples of the crosslinkable functional group include a hydroxyl group, a carboxyl group, a glycidyl group, an amino group, an amide group, and a nitrile group. Especially, since adjustment of the gel fraction of the said adhesive layer and the difference (AB) of the said storage elastic modulus is easy, a hydroxyl group or a carboxyl group is preferable and a hydroxyl group is more preferable.
Examples of the monomer having a hydroxyl group include (meth) acrylate having a hydroxyl group such as 4-hydroxybutyl (meth) acrylate and 2-hydroxyethyl (meth) acrylate. Examples of the monomer having a carboxyl group include (meth) acrylic acid. Examples of the monomer having a glycidyl group include glycidyl (meth) acrylate. Examples of the monomer having an amide group include hydroxyethyl acrylamide, isopropyl acrylamide, dimethylaminopropyl acrylamide and the like. Examples of the monomer having a nitrile group include acrylonitrile. These monomers having a crosslinkable functional group may be used alone or in combination.

In the acrylic copolymer, the content of the structural unit derived from the monomer having a crosslinkable functional group is not particularly limited, but a preferred lower limit is 0.05% by weight, a preferred upper limit is 10% by weight, and a more preferred lower limit. Is 1% by weight, and a more preferred upper limit is 5% by weight. It becomes easy to adjust the difference (AB) of the gel fraction of the said adhesive layer and the said storage elastic modulus because the said content exists in the said range.

The acrylic copolymer may further contain structural units derived from other monomers as long as the effects of the present invention are not impaired. The other monomers are not particularly limited. For example, propyl (meth) acrylate, butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, nonyl (meth) acrylate, Examples include isobornyl (meth) acrylate, benzyl (meth) acrylate, phenoxyethyl (meth) acrylate, and vinyl acetate.

Further, when the acrylic copolymer is prepared by an ultraviolet polymerization method, the acrylic copolymer further includes a structural unit derived from a polyfunctional monomer such as divinylbenzene or trimethylolpropane tri (meth) acrylate. It is preferable.

The weight average molecular weight of the acrylic copolymer is not particularly limited, but a preferable lower limit is 300,000. If the weight average molecular weight of the said acrylic copolymer is 300,000 or more, while the tolerance to the sebum of the said adhesive layer and a chemical | medical agent will improve, the foaming which arises under high temperature and high humidity can be suppressed more. The more preferable lower limit of the weight average molecular weight of the acrylic copolymer is 400,000, the more preferable lower limit is 500,000, and the particularly preferable lower limit is 1,000,000.
Although the upper limit of the weight average molecular weight of the acrylic copolymer is not particularly limited, the preferable upper limit is 2 million, and the more preferable upper limit is 1.8 million.
In addition, a weight average molecular weight is a polystyrene conversion molecular weight calculated | required by GPC measurement, and can be adjusted with polymerization conditions (For example, the kind or quantity of a polymerization initiator, polymerization temperature, a monomer concentration, etc.).

In order to synthesize the acrylic copolymer, the monomer derived from the structural unit may be radically reacted in the presence of a polymerization initiator.
The method of radical reaction is not particularly limited, and examples thereof include living radical polymerization and free radical polymerization. According to living radical polymerization, a copolymer having a more uniform molecular weight and composition can be obtained as compared with free radical polymerization, the production of low molecular weight components and the like can be suppressed, and the cohesive force of the pressure-sensitive adhesive layer is high. Become.
The polymerization method is not particularly limited, and a conventionally known method can be used. Examples include solution polymerization (boiling point polymerization or constant temperature polymerization), emulsion polymerization, suspension polymerization, bulk polymerization and the like. Of these, solution polymerization is preferred because synthesis is simple.

When solution polymerization is used as the polymerization method, examples of the reaction solvent include ethyl acetate, toluene, methyl ethyl ketone, methyl sulfoxide, ethanol, acetone, diethyl ether and the like. These reaction solvents may be used alone or in combination.

The said polymerization initiator is not specifically limited, For example, an organic peroxide, an azo compound, etc. are mentioned. Examples of the organic peroxide include 1,1-bis (t-hexylperoxy) -3,3,5-trimethylcyclohexane, t-hexylperoxypivalate, t-butylperoxypivalate, 2,5 -Dimethyl-2,5-bis (2-ethylhexanoylperoxy) hexane, t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butylperoxy Examples include isobutyrate, t-butylperoxy-3,5,5-trimethylhexanoate, and t-butylperoxylaurate. Examples of the azo compound include azobisisobutyronitrile and azobiscyclohexanecarbonitrile. These polymerization initiators may be used alone or in combination.
In the case of living radical polymerization, examples of the polymerization initiator include organic tellurium polymerization initiators. The organic tellurium polymerization initiator is not particularly limited as long as it is generally used for living radical polymerization, and examples thereof include organic tellurium compounds and organic telluride compounds. In living radical polymerization, in addition to the organic tellurium polymerization initiator, an azo compound may be used as the polymerization initiator for the purpose of accelerating the polymerization rate.

The pressure-sensitive adhesive layer preferably contains a crosslinking agent in addition to the acrylic copolymer.
When the acrylic copolymer contains a structural unit derived from the monomer having the crosslinkable functional group, a crosslinked structure can be constructed between the chains of the acrylic copolymer by the crosslinking agent. In that case, the gel fraction of the said adhesive layer can be adjusted by adjusting a crosslinking degree. In particular, by adjusting the gel fraction of the pressure-sensitive adhesive layer to a relatively high range, the difference in storage elastic modulus (AB) can be easily adjusted to the above range, and foaming that occurs under high temperature and high humidity can be further improved. Can be suppressed.

The said crosslinking agent is not specifically limited, For example, an isocyanate type crosslinking agent, an aziridine type crosslinking agent, an epoxy-type crosslinking agent, a metal chelate type crosslinking agent etc. are mentioned. Of these, an isocyanate-based crosslinking agent and an epoxy-based crosslinking agent are preferable, and the isocyanate-based crosslinking agent is more preferable because the difference between the gel fraction of the pressure-sensitive adhesive layer and the difference in storage modulus (AB) is easy. preferable.
In the pressure-sensitive adhesive layer, the content of the crosslinking agent is not particularly limited, but a preferable lower limit with respect to 100 parts by weight of the acrylic copolymer is 0.01 part by weight, a preferable upper limit is 10 parts by weight, and a more preferable lower limit is 0. .1 part by weight, more preferably 5 parts by weight.

The pressure-sensitive adhesive layer preferably further contains a silane coupling agent.
When the pressure-sensitive adhesive layer contains the silane coupling agent, adhesion of the pressure-sensitive adhesive layer to the adherend is improved. As a result, the pressure-sensitive adhesive layer can be improved in resistance to sebum and chemicals, and foaming generated under high temperature and high humidity can be further suppressed.

The silane coupling agent is not particularly limited. For example, vinyltrimethoxysilane, vinyltriethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-glycidoxypropyltrimethoxysilane 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 3-glycidoxypropyltriethoxysilane, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, 3-amino Propyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethylmethoxysilane, N- (2-aminoethyl) 3-aminopropyltriethoxysilane, N- (2-aminoethyl) 3-aminopro Methyl dimethoxysilane, 3-mercaptopropyl trimethoxysilane, 3-mercaptopropyl triethoxy silane, mercaptopropyl butyl trimethoxy silane, 3-mercaptopropyl methyl dimethoxy silane, and the like. Of these, 3-glycidoxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, or a combination thereof is preferable.

In the pressure-sensitive adhesive layer, the content of the silane coupling agent is not particularly limited, but a preferable lower limit with respect to 100 parts by weight of the acrylic copolymer is 0.1 part by weight, and a preferable upper limit is 10 parts by weight. If the content of the silane coupling agent is 0.1 parts by weight or more, the adhesion of the pressure-sensitive adhesive layer to the adherend is improved, the resistance to sebum and chemicals is improved, and under high temperature and high humidity. The foaming which arises can be suppressed more. If content of the said silane coupling agent is 10 weight part or less, the adhesive residue at the time of peeling an optical adhesive sheet can be suppressed, and the rework property of an optical adhesive sheet improves. The minimum with more preferable content of the said silane coupling agent is 1 weight part, and a more preferable upper limit is 5 weight part.

The pressure-sensitive adhesive layer contains additives such as plasticizers, emulsifiers, softeners, fillers, pigments and dyes, tackifiers such as rosin resins and terpene resins, and other resins as necessary. It may be.

The gel fraction of the pressure-sensitive adhesive layer is preferably 70% by weight or more.
If the said gel fraction is 70 weight% or more, the said difference (AB) of the storage elastic modulus becomes easy to satisfy | fill the said range, and it can suppress more the foaming which arises under high temperature, high humidity. A more preferable lower limit of the gel fraction is 80% by weight. Although the upper limit of the said gel fraction is not specifically limited, A preferable upper limit is 99 weight%.
The gel fraction is a percentage of the weight of the pressure-sensitive adhesive layer after being dipped in ethyl acetate and dried with respect to the weight of the pressure-sensitive adhesive layer before being dipped in ethyl acetate as shown in the following formula (2). It is the expressed value.
Gel fraction (% by weight) = 100 × (W ₅ −W ₃ ) / (W ₄ −W ₃ ) (2)
(W ₃ : Weight of base material, W ₄ : Weight before soaking of ethyl acetate in pressure-sensitive adhesive sheet, W ₅ : Weight of pressure-sensitive adhesive sheet after soaking in ethyl acetate and drying)

Although the thickness of the said adhesive layer is not specifically limited, A preferable minimum is 5 micrometers and a preferable upper limit is 150 micrometers. If the thickness of the said adhesive layer is 5 micrometers or more, the adhesive force of the optical adhesive sheet will improve. If the thickness of the said adhesive layer is 150 micrometers or less, the workability of the optical adhesive sheet will improve.

The optical pressure-sensitive adhesive sheet of the present invention may be a support type having a substrate or a non-support type having no substrate. In the case of the support type, the pressure-sensitive adhesive layer may be formed on one side of the substrate, or the pressure-sensitive adhesive layer may be formed on both sides.

The said base material is not specifically limited, For example, polyester-type resin films, such as polyolefin resin films, such as a polyethylene film and a polypropylene film, PET film, etc. are mentioned. Furthermore, polyolefin foam sheets, such as an ethylene-vinyl acetate copolymer film, a polyvinyl chloride resin film, a polyurethane resin film, a polyethylene foam sheet, and a polypropylene foam sheet, a polyurethane foam sheet, and the like. Of these, a PET film is preferable. From the viewpoint of impact resistance, a polyolefin foam sheet is preferred.
In addition, as the above-mentioned base material, a black-printed base material for preventing light transmission, a white-printed base material for improving light reflectivity, a metal-deposited base material, and the like can be used.

The optical pressure-sensitive adhesive sheet of the present invention is also excellent in optical properties.
The total light transmittance of the optical pressure-sensitive adhesive sheet of the present invention is not particularly limited, but a preferred lower limit is 90% and a more preferred lower limit is 95%. The haze of the optical pressure-sensitive adhesive sheet of the present invention is not particularly limited, but the preferable upper limit is 1%, and the more preferable upper limit is 0.5%. When the total light transmittance and haze are within the above ranges, the pressure-sensitive adhesive sheet is excellent in optical characteristics and suitable for optical applications.
In addition, the total light transmittance and haze are based on JIS K 7361 with respect to the measurement sample obtained by bonding an adhesive sheet to a glass plate having a thickness of 1 mm, and a haze meter (for example, manufactured by Nippon Denshoku Industries Co., Ltd.). Haze Meter NDH4000 etc.).

The color (tone) of the optical pressure-sensitive adhesive sheet of the present invention is not particularly limited, but the value of L ^* is preferably 98 or more. The value of a ^* is preferably −0.5 or more and 0.5 or less. Moreover, it is preferable that the value of b ^* is −0.5 or more and 0.5 or less. When the values of L ^* , a ^* and b ^* are within the above ranges, the pressure-sensitive adhesive sheet is excellent in optical characteristics and suitable for optical applications.
The values of L ^* , a ^*, and b ^* are based on a color sample (for example, Konica Minolta, Inc.) based on JIS Z 8730 with respect to a measurement sample obtained by bonding an adhesive sheet to a glass plate having a thickness of 1 mm. SPECTROPHOTOMETER CM-3700d, etc.)

The method for producing the optical pressure-sensitive adhesive sheet of the present invention is not particularly limited. For example, when the optical pressure-sensitive adhesive sheet of the present invention is a non-support type having no substrate, the following method can be mentioned.
First, a solvent is added to the acrylic copolymer and, if necessary, a crosslinking agent and a silane coupling agent to prepare a solution of the acrylic pressure-sensitive adhesive a. The obtained acrylic pressure-sensitive adhesive a solution is applied to the release-treated surface of the release film subjected to the silicone release treatment, and the solvent in the solution is completely removed by drying to form the pressure-sensitive adhesive layer a. Next, a release film different from the release film is overlaid on the formed pressure-sensitive adhesive layer a so that the release treatment surface faces the pressure-sensitive adhesive layer a. And the non-support type adhesive sheet which does not have a base material can be obtained by pressurizing the said laminated body with a rubber roller etc. FIG.

The application of the optical pressure-sensitive adhesive sheet of the present invention is not particularly limited, but can be preferably used for optical applications. In particular, the optical pressure-sensitive adhesive sheet of the present invention is excellent in resistance to sebum and chemicals, and therefore can be particularly preferably used for fixing parts of electronic devices that are frequently touched by human hands. Since foaming hardly occurs even underneath, it can be particularly preferably used for fixing components such as polarizing plates that easily absorb moisture and generate outgas.
Specifically, fixing of cover panels in portable electronic devices such as smartphones and tablet terminals, fixing of touch panels, fixing of polarizing plates, fixing of cover panels in in-vehicle electronic devices such as car navigation, fixing of display panels, The optical pressure-sensitive adhesive sheet of the present invention can be preferably used for fixing the polarizing plate or the like.

The shape of the optical pressure-sensitive adhesive sheet of the present invention is not particularly limited, and may be a rectangle or the like, a roll shape, or a sheet shape.

According to the present invention, it is possible to provide an optical pressure-sensitive adhesive sheet which is excellent in resistance to sebum and chemicals, hardly foams even under high temperature and high humidity, and has excellent optical characteristics.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

(Example 1)
(1) Production of acrylic copolymer Ethyl acetate was added as a polymerization solvent in the reaction vessel, and after bubbling with nitrogen, the reaction vessel was heated while flowing nitrogen to start refluxing. Subsequently, a polymerization initiator solution in which 0.1 part by weight of azobisisobutyronitrile as a polymerization initiator was diluted 10 times with ethyl acetate was charged into the reaction vessel, and 67.5 parts by weight of butyl acrylate, 2, 2, 30 parts by weight of 2-trifluoroethyl acrylate, 0.5 part by weight of acrylic acid and 2 parts by weight of 2-hydroxyethyl acrylate were added dropwise over 2 hours. After completion of the dropwise addition, a polymerization initiator solution obtained by diluting 0.1 part by weight of azobisisobutyronitrile 10 times with ethyl acetate as a polymerization initiator was charged again into the reaction vessel, and the polymerization reaction was performed for 4 hours. A coalescence-containing solution was obtained.

(2) Measurement of weight average molecular weight The obtained acrylic copolymer was diluted 50-fold with tetrahydrofuran (THF), and the diluted solution was filtered with a filter (material: polytetrafluoroethylene, pore diameter: 0.2 μm). A measurement sample was prepared. This measurement sample was supplied to a gel permeation chromatograph (manufactured by Waters, 2690 Separations Model), GPC measurement was performed under the conditions of a sample flow rate of 1 ml / min and a column temperature of 40 ° C., and the polystyrene equivalent molecular weight of the acrylic copolymer Was measured to determine the weight average molecular weight. GPC LF-804 (manufactured by Showa Denko) was used as the column, and a differential refractometer was used as the detector.

(3) Production of pressure-sensitive adhesive sheet In the obtained acrylic copolymer-containing solution, 0.5 parts by weight of a crosslinking agent (isocyanate-based crosslinking agent, Coronate L-45, manufactured by Tosoh Corporation) with respect to 100 parts by weight of the acrylic copolymer 1 part by weight of a silane coupling agent (KBM-403, manufactured by Shin-Etsu Chemical Co., Ltd.) was added to prepare an adhesive solution. This pressure-sensitive adhesive solution was applied to a 75 μm-thick release PET film so that the thickness of the pressure-sensitive adhesive layer after drying was 15 μm, and then dried at 110 ° C. for 5 minutes. This pressure-sensitive adhesive layer was superimposed on a 75 μm-thickness-released PET film and cured at 40 ° C. for 48 hours to obtain a pressure-sensitive adhesive sheet (non-support type).

(4) Measurement of oleic acid swelling ratio The release film on one side of the obtained pressure-sensitive adhesive sheet was peeled off, bonded to a 50 μm thick PET film, and cut into a 20 mm × 40 mm flat rectangular shape. Further, the release film on the other surface of the pressure-sensitive adhesive sheet was peeled off to produce a test piece, and the weight was measured. After the test piece was immersed in oleic acid at 65 ° C. and 90% humidity for 24 hours, the test piece was taken out of oleic acid, washed with ethanol and then dried at 110 ° C. for 3 hours. The weight of the test piece after drying was measured, and the oleic acid swelling rate was calculated using the following formula (1).
Oleic acid swelling ratio (% by weight) = 100 × (W ₃ −W ₁ ) / (W ₂ −W ₁ ) (1)
(W ₁ : Weight of the PET film, W ₂ : Weight of test piece before immersion in oleic acid, W ₃ : Weight of test piece immersed in oleic acid, weight after drying)

(5) Measurement of gel fraction The release film on one side of the obtained pressure-sensitive adhesive sheet was peeled off, bonded to a PET film having a thickness of 50 μm, and cut into a flat rectangular shape of 20 mm × 40 mm. Further, the release film on the other surface of the pressure-sensitive adhesive sheet was peeled off to produce a test piece, and the weight was measured. After immersing the test piece in ethyl acetate at 23 ° C. for 24 hours, the test piece was taken out from ethyl acetate and dried at 110 ° C. for 1 hour. The weight of the test piece after drying was measured, and the gel fraction was calculated using the following formula (2).
Gel fraction (% by weight) = 100 × (W ₅ −W ₃ ) / (W ₄ −W ₃ ) (2)
(W ₃ : Weight of the PET film, W ₄ : Weight of test piece before immersion in ethyl acetate, W ₅ : Weight of test piece in ethyl acetate, weight after drying)

(6) Measurement of storage modulus Adhesion obtained using a dynamic viscoelasticity measuring device (DVA-200 manufactured by IT Measurement Co., Ltd.) at a temperature rising rate of 5 ° C / min and in a range of -40 ° C to 140 ° C. The storage elastic modulus of the adhesive layer of the sheet was measured. Calculates the maximum value (A), minimum value (B), and difference (AB) between the maximum value (A) and the minimum value (B) of the storage elastic modulus in the temperature range of 100 ° C. or more and 140 ° C. or less. did.

(Examples 2-14, Comparative Examples 1-8)
A pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the monomer composition or weight average molecular weight of the acrylic copolymer and the type or amount of the crosslinking agent were changed as shown in Table 1 or 2. The details of the materials shown in Table 1 or 2 are as follows.

・ Crosslinking agent (epoxy crosslinking agent, Tetrad C, manufactured by Mitsubishi Gas Chemical Company)

<Evaluation>
The following evaluation was performed about the adhesive sheet obtained by the Example and the comparative example. The results are shown in Table 1 or 2.

(1) One release film of the optical characteristic pressure-sensitive adhesive sheet was peeled off, bonded to a glass plate having a thickness of 1 mm, and the other release film was peeled off to prepare a measurement sample. The total light transmittance and haze were measured for this measurement sample using a haze meter (Haze Meter NDH4000 manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K 7361. Moreover, the value of L ^* , a ^*, and b ^* was measured with respect to this measurement sample using a color meter (SPECTROTOPOMETER CM-3700d manufactured by Konica Minolta Co., Ltd.) in accordance with JIS Z 8730.

(2) One release film of the adhesive sheet resistant to sebum and chemicals was peeled off, bonded to a 50 μm thick PET film, and cut into a 30 mm × 30 mm flat square shape. Further, the other release film of the pressure-sensitive adhesive sheet was peeled off and bonded to a glass plate having a thickness of 2 mm to prepare a test piece. After this test piece was immersed in oleic acid at 65 ° C. and 90% humidity for 24 hours, the test piece was taken out, washed with ethanol and then dried at 110 ° C. for 3 hours. The edge part of the taken-out test piece was observed at 100-times multiplication factor using the optical microscope, and the oleic acid penetration distance was measured.
The case where the oleic acid penetration distance was less than 1.0 mm was evaluated as ◎, the case where it was 1.0 mm or more and less than 1.5 mm was given as ◯, and the case where it was 1.5 mm or more was judged as ×.

(3) Inhibition of foaming under high temperature and high humidity (foaming resistance)
One release film of the pressure-sensitive adhesive sheet was peeled off, bonded to a COP film having a thickness of 50 μm, and cut into a 100 mm × 100 mm flat square. Further, the other release film of the pressure-sensitive adhesive sheet was peeled off and bonded to a glass plate (200 mm × 300 mm, thickness 1 mm), followed by pressure bonding in an autoclave at 40 ° C. and 0.4 MPa for 20 minutes to prepare a measurement sample. At this time, it was confirmed that there were no bubbles at the interface between the pressure-sensitive adhesive sheet and the COP film.
This measurement sample was placed in a humid heat oven at 85 ° C. and a humidity of 85% and heated for 240 hours. Thereafter, the measurement sample was taken out from the wet heat oven, and bubbles at the interface between the pressure-sensitive adhesive sheet and the COP film were observed at a magnification of 100 times using an optical microscope within 3 minutes after taking out the measurement sample.
The case where the number of bubbles having a major axis of 0.2 mm or more was 1 or less was evaluated as “◯”, and the case of having two or more bubbles whose major axis was 0.2 mm or more was determined as “X”.

According to the present invention, it is possible to provide an optical pressure-sensitive adhesive sheet which is excellent in resistance to sebum and chemicals, hardly foams even under high temperature and high humidity, and has excellent optical characteristics.

Claims (7)

An optical pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer containing an acrylic copolymer,
The pressure-sensitive adhesive layer has a swelling ratio of 100% by weight or more and 130% by weight or less after being immersed in oleic acid at 65 ° C. and a humidity of 90% for 24 hours,
The pressure-sensitive adhesive layer has a difference (A−B) of 1.2 × 10 ⁴ Pa or less between the maximum value (A) and the minimum value (B) of the storage elastic modulus in a temperature range of 100 ° C. or more and 140 ° C. or less. An optical pressure-sensitive adhesive sheet, comprising: The optical pressure-sensitive adhesive sheet according to claim 1, wherein the acrylic copolymer contains 30% by weight or more of a structural unit derived from fluoroalkyl (meth) acrylate. The acrylic copolymer further contains a structural unit derived from a (meth) acrylate having a hydroxyl group, and the pressure-sensitive adhesive layer has a gel fraction of 70% by weight or more. Optical adhesive sheet. The optical pressure-sensitive adhesive sheet according to claim 2, wherein the fluoroalkyl (meth) acrylate is 2- (perfluorohexyl) ethyl acrylate. The optical pressure-sensitive adhesive sheet according to claim 1, 2, 3, or 4, wherein the acrylic copolymer contains a structural unit derived from an alkyl (meth) acrylate having an alkyl group having 2 or less carbon atoms. The acrylic copolymer contains 50% by weight or more of a structural unit derived from an alkyl (meth) acrylate having an alkyl group having 2 or less carbon atoms, and the alkyl (meth) acrylate having an alkyl group having 2 or less carbon atoms is 6. The optical pressure-sensitive adhesive sheet according to claim 5, which is methyl acrylate. The optical pressure-sensitive adhesive sheet according to claim 1, wherein the pressure-sensitive adhesive layer contains a silane coupling agent.