JP6116378B2 - Acrylic adhesive for optics - Google Patents

Description

  The present invention relates to an optical acrylic pressure-sensitive adhesive having an optical member as a fixed member.

  In the manufacture of image display devices and the like, acrylic pressure-sensitive adhesive sheets are used as fixing members for various optical members (see, for example, Non-Patent Document 1). Such a fixing member is required to have optical properties such as transparency.

  Further, when the above-described fixing member is bonded to the optical member, there may be a bonding failure such as contamination of foreign matter, positional deviation, and air contact. Since the optical member is relatively expensive, when a bonding failure occurs, the optical member is removed from the fixing member and reused, that is, reworked, at a predetermined timing immediately after bonding or after an autoclave process. There is a need. Therefore, the reworkability of the optical member is required for the fixing member described above.

  Furthermore, the fixing member described above is required to be excellent in fixing property of the optical member when the optical member is incorporated into a product such as an image display device and after it is incorporated. That is, in many cases, a plurality of optical members are bonded together by a fixing member and incorporated into a product in the state of a laminate. When the optical member in such a state is incorporated into a product, the fixing member is required to adhere to the optical member with sufficient strength and hardly cause peeling.

  In addition, the fixing member is required to maintain the adhesiveness at the beginning of bonding because it is difficult to be peeled off when an impact such as dropping is applied even after the laminated body of optical members is actually incorporated into a product. This requirement is conspicuous in mobile devices such as digital cameras, mobile phones, and portable game machines.

  Further, the laminated body of optical members may be exposed to a high-temperature and high-humidity environment depending on the environment in which the incorporated product is used, and may receive heat generated from the product itself. The fixing member is required to maintain a strong cohesive force and adhesive force even in such an environment and hardly cause peeling. Furthermore, even if the optical member is warped, the fixing member is required to have a strong assembly strength and thus hardly cause foaming or peeling.

"Highly transparent adhesive transfer tape", [online], 3M, [Search April 4, 2013], Internet <URL: http://www.mmm.co.jp/eas/oca/>

  An object of the present invention is to provide an optical acrylic pressure-sensitive adhesive that is excellent in optical properties, reworkability of optical members, and fixability.

As a result of intensive studies to solve the above-mentioned problems, the present inventors have found a solution means having the following constitution and have completed the present invention.
(1) Crosslinking a copolymer obtained by polymerizing (meth) acrylate having an ethylene glycol group, (meth) acrylate having a linear alkyl group having 16 to 22 carbon atoms, and a polar monomer. Acrylic pressure-sensitive adhesive for optical use formed by crosslinking with an agent.
(2) The (meth) acrylate having an ethylene glycol group includes 2-ethylhexyl-diglycol (meth) acrylate, methoxyethyl (meth) acrylate, methoxypolyethylene glycol mono (meth) acrylate, and ethoxy-diethylene glycol (meth) acrylate. The optical acrylic pressure-sensitive adhesive according to (1), which is at least one selected from the group consisting of:
(3) The acrylic acrylic pressure-sensitive adhesive according to (1) or (2), wherein the polar monomer is 2-hydroxyethyl (meth) acrylate.
(4) The optical acrylic system according to any one of (1) to (3), wherein the copolymer is obtained by further polymerizing a (meth) acrylate having an alkyl group having 1 to 12 carbon atoms. Adhesive.
(5) The optical acrylic pressure-sensitive adhesive according to (4), wherein the (meth) acrylate having an alkyl group having 1 to 12 carbon atoms is methyl (meth) acrylate.
(6) The copolymer is obtained by further polymerizing a high Tg monomer capable of forming a homopolymer having a glass transition temperature (Tg) of 90 ° C. or higher. The acrylic acrylic pressure-sensitive adhesive as described.
(7) The optical acrylic pressure-sensitive adhesive according to (6), wherein the high Tg monomer is isobornyl acrylate.
(8) The 180 ° peel strength with respect to glass is 20 N / 25 mm or more at an ambient temperature of 23 ° C. and 4 N / 25 mm or less at an ambient temperature of 90 ° C. The acrylic acrylic pressure-sensitive adhesive as described.
(9) An optical acrylic pressure-sensitive adhesive sheet comprising the optical acrylic pressure-sensitive adhesive according to any one of (1) to (8).
(10) The acrylic acrylic pressure-sensitive adhesive sheet according to (9), wherein a release film is laminated on one side or both sides.

  According to the present invention, there is an effect that the optical characteristics, the reworkability of the optical member, and the fixing property are excellent.

  Hereinafter, an optical acrylic pressure-sensitive adhesive (hereinafter sometimes referred to as “pressure-sensitive adhesive”) according to an embodiment of the present invention will be described. The pressure-sensitive adhesive of this embodiment uses an optical member as a fixed member. Examples of the optical member include optical films such as polarizing films (polarizing plates) and retardation films used in image display devices such as liquid crystal display devices, organic electroluminescence devices, and plasma displays; glass plates of liquid crystal cells; touch panels and the like. However, it is not limited to these. That is, the pressure-sensitive adhesive of the present embodiment needs to be fixed continuously when it is normal, and can be suitably used for an optical member that requires rework when a defect is confirmed.

  Such an adhesive of this embodiment is obtained by polymerizing (meth) acrylate having an ethylene glycol group, (meth) acrylate having a linear alkyl group having 16 to 22 carbon atoms, and a polar monomer. The obtained copolymer is crosslinked with a crosslinking agent. According to such a composition, it is possible to exhibit excellent reworkability and fixability with respect to the optical member as well as excellent optical characteristics.

  Specifically, according to the composition described above, the 180 ° peel strength for glass can be 4 N / 25 mm or less at an atmospheric temperature of 90 ° C. Therefore, when the atmospheric temperature is set to 90 ° C. or higher, preferably 90 to 120 ° C. by a heating means such as a heater, the adhesive strength of the adhesive is sufficiently reduced, so that the optical member can be removed from the adhesive and reworked. Thus, manufacturing efficiency and cost can be improved.

  Moreover, according to the composition mentioned above, 180 degree peeling strength with respect to glass can be 20 N / 25mm or more in 23 degreeC atmospheric temperature. Therefore, when there is no need for reworking, the optical member can be kept fixed with a high fixing force, and thus both fixing property and reworking property can be achieved. Furthermore, according to the above-described composition, it is possible to suppress foaming, peeling of the optical member, whitening, and the like.

  Of the above-described monomers, (meth) acrylate having an ethylene glycol group is a monomer having a large degree of influence on the 180 ° peel strength value. That is, when (meth) acrylate having an ethylene glycol group is used as a monomer component, the 180 ° peel strength for glass tends to increase at an ambient temperature of 23 ° C. and decrease at an ambient temperature of 90 ° C.

In the (meth) acrylate having an ethylene glycol group, the ethylene glycol group means a group: —CH ₂ CH ₂ O—. In the (meth) acrylate having an ethylene glycol group, the number of ethylene glycol groups may be one or plural. Examples of the (meth) acrylate having an ethylene glycol group include 2-ethylhexyl-diglycol (meth) acrylate, methoxyethyl (meth) acrylate, methoxypolyethylene glycol mono (meth) acrylate, ethoxy-diethylene glycol (meth) acrylate, and methoxy- Examples thereof include triethylene glycol (meth) acrylate, and these may be used alone or in combination of two or more. The (meth) acrylate having an ethylene glycol group is at least selected from 2-ethylhexyl-diglycol (meth) acrylate, methoxyethyl (meth) acrylate, methoxypolyethylene glycol mono (meth) acrylate, and ethoxy-diethylene glycol (meth) acrylate. One type is preferred.

  Examples of the (meth) acrylate having a linear alkyl group having 16 to 22 carbon atoms include cetyl (meth) acrylate, stearyl (meth) acrylate, eicosyl (meth) acrylate, and behenyl (meth) acrylate. These may be used alone or in combination of two or more.

  The polar monomer is a crosslinking component, and specific examples include ethylenically unsaturated monomers having a carboxyl group such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid; 2-hydroxyethyl (meth) acrylate, Examples thereof include ethylenically unsaturated monomers having a hydroxyl group such as 2-hydroxypropyl (meth) acrylate and 2-hydroxyhexyl (meth) acrylate, and these may be used alone or in combination. Of these exemplified monomers, 2-hydroxyethyl (meth) acrylate is preferred. Since 2-hydroxyethyl (meth) acrylate functions as a component that imparts cohesive force to the pressure-sensitive adhesive, as in the case of methyl (meth) acrylate described above, it becomes easy to balance the fixability and reworkability.

  Moreover, it is preferable that the copolymer mentioned above is obtained by further polymerizing the (meth) acrylate which has a C1-C12 alkyl group. Examples of the (meth) acrylate having an alkyl group having 1 to 12 carbon atoms include methyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and hexyl (meth). An acrylate etc. are mentioned, These may be used 1 type or in mixture of 2 or more types. Of these exemplified monomers, methyl (meth) acrylate is preferred. Since methyl (meth) acrylate functions as a component that imparts cohesive force to the pressure-sensitive adhesive, it becomes easy to balance the fixability and the reworkability.

  The above-mentioned copolymer is preferably obtained by further polymerizing a high Tg monomer capable of forming a homopolymer having a glass transition temperature (Tg) of 90 ° C. or higher, preferably 90 to 250 ° C. Thereby, Tg of the whole adhesive becomes high moderately, and it becomes easy to balance fixed property and rework property. Examples of the high Tg monomer include isobornyl acrylate (light acrylate IB-XA: Kyoeisha Chemical), isobornyl methacrylate (light ester IB-X: Kyoeisha Chemical), methyl methacrylate, tertiary butyl cyclohexyl methacrylate (TBCHMA: NOF). ), Dicyclopentanyl acrylate (FA513-AS: Hitachi Chemical), dicyclopentanyl methacrylate (FA513-M: Hitachi Chemical), 1-adamantyl acrylate (ADA: Osaka Organic Chemical), 1-adamantyl methacrylate (ADMA: Osaka) Of these high Tg monomers exemplified, isobornyl acrylate is preferred.

  Each of the above-described monomers is, for example, 10 to 50 parts by weight of (meth) acrylate having an ethylene glycol group, 1 to 10 parts by weight of (meth) acrylate having a linear alkyl group having 16 to 22 carbon atoms, and 1 carbon atom. It is preferable to polymerize at a ratio of 0 to 50 parts by weight of (meth) acrylate having ˜12 alkyl groups, 1 to 20 parts by weight of polar monomer, and 20 to 40 parts by weight of high Tg monomer.

  The polymerization method is not particularly limited, and for example, a solution polymerization method, a bulk polymerization method, a suspension polymerization method, an emulsion polymerization method and the like can be employed. When employing the solution polymerization method, the above-described monomers may be added to the solvent and stirred. The polymerization temperature is suitably about 40 to 90 ° C., and the polymerization time is suitably about 4 to 8 hours.

  The weight average molecular weight of the copolymer is preferably 400,000 to 2,000,000, more preferably 500,000 to 1,300,000, still more preferably 500,000 to 1,000,000, and 550,000 to 900,000. More preferably. The weight average molecular weight is a value obtained by measuring the copolymer by gel permeation chromatography (hereinafter referred to as “GPC”) and converting the obtained measurement value to polystyrene.

  As a crosslinking agent which bridge | crosslinks the copolymer mentioned above, an isocyanate compound, an aziridine compound, an epoxy compound, a metal chelate compound etc. are mentioned, for example, These may be used 1 type or in mixture of 2 or more types. When the optical member is easily corroded, it is preferable to employ an isocyanate compound as the crosslinking agent and an ethylenically unsaturated monomer having a hydroxyl group as the polar monomer. Thereby, corrosion of an optical member can be suppressed. Examples of the isocyanate compound include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, xylylene diisocyanate, diphenylmethane diisocyanate, tetramethylxylylene diisocyanate, naphthalene diisocyanate, triphenylmethane triisocyanate, and the like. In addition, adducts obtained by reacting polyols such as glycerol and trimethylolpropane with the exemplified isocyanate compounds, dimers and trimers of isocyanate compounds, and the like can also be employed.

  The addition amount of the cross-linking agent is preferably 0.1 to 5 parts by weight, more preferably 0.1 to 3 parts by weight in terms of solid content, with respect to 100 parts by weight of the copolymer. More preferably, it is 1-1 weight part.

  Crosslinking of the copolymer with a crosslinking agent can be performed by adding a crosslinking agent to the copolymer and then drying by heating. The heat drying conditions are not particularly limited as long as the conditions according to the crosslinking agent are adopted. When an isocyanate compound is employed, the temperature is about 40 ° C. and the time is about 2 weeks. In addition, when the solution polymerization method is employ | adopted in the polymerization method mentioned above, you may volatilize a solvent before bridge | crosslinking. As solvent volatilization conditions, the temperature is about 80 to 150 ° C., and the time is about 1 to 20 minutes.

  The use form of the pressure-sensitive adhesive of the present embodiment described above is not particularly limited. For example, a solvent is added to a copolymer to which a crosslinking agent is added, and the resultant is applied to an optical member and dried by heating. Good.

  Moreover, the adhesive of this embodiment can be used with the sheet-like form of a base material, for example. The sheet shape is not limited to a sheet shape, and is a concept including a sheet shape or a film shape as long as the effects of the present embodiment are not impaired. When using an adhesive in the form of an adhesive sheet, it is preferable that the thickness is 5-300 micrometers, and it is more preferable that it is 20-200 micrometers.

  It is preferable to laminate a release film on one or both sides of the pressure-sensitive adhesive sheet. Examples of the release film include those obtained by applying a release agent such as silicone to the surface of a film made of polyethylene terephthalate or the like.

  Moreover, the adhesive of this embodiment can also be used with the form of an adhesive tape. In the case where the pressure-sensitive adhesive is used in the form of a pressure-sensitive adhesive tape, a solvent may be added to the copolymer to which the cross-linking agent has been added, applied to one or both sides of the base film, and heated and dried. Thereby, the adhesive tape provided with the adhesive layer which consists of an adhesive of this embodiment on the single side | surface or both surfaces of a base film is obtained. As the substrate film, those having excellent optical properties are preferable.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited only to a following example.

[Examples 1-4 and Comparative Examples 1-2]
<Preparation of optical acrylic pressure-sensitive adhesive sheet>
First, the monomers shown in Table 1 were mixed in the proportions (parts by weight) shown in Table 1 to obtain a mixture. The monomers used are as follows.
EGA1: 2-ethylhexyl-diglycol acrylate “light acrylate EHDG-AT” manufactured by Kyoeisha Chemical Co., Ltd.
EGA2: Methoxyethyl acrylate “2-MTA” manufactured by Osaka Organic Chemical Industry Co., Ltd.
EGA3: Methoxypolyethylene glycol monomethacrylate “Blemmer PME-100” manufactured by NOF Corporation
EGA4: Ethoxy-diethylene glycol acrylate “Light acrylate EC-A” manufactured by Kyoeisha Chemical Co., Ltd.
BZA: benzyl acrylate “V160” manufactured by Osaka Organic Chemical Industry Co., Ltd.
C22MA: Behenyl methacrylate EHA: 2-ethylhexyl acrylate High Tg monomer: Isobornyl acrylate “light acrylate IB-XA” manufactured by Kyoeisha Chemical Co., Ltd. (homopolymer Tg: 94 ° C.)
C1A: Methyl acrylate HEA: 2-hydroxyethyl acrylate

  Next, the obtained mixture was added to 250 parts by weight of a mixed solvent of ethyl acetate: toluene = 8: 2 (weight ratio) together with 0.2 parts by weight of a polymerization initiator “Perbutyl ND” manufactured by NOF Corporation, and a liquid mixture Got. And each monomer was polymerized by stirring the obtained liquid mixture at 55 degreeC for 6 hours, and the copolymer was obtained.

  Next, a crosslinking agent was added at a ratio of 0.5 part by weight in terms of solid content to 100 parts by weight of the obtained copolymer. As the cross-linking agent, hexamethylene diisocyanate trimethylolpropane adduct “Coronate HL”, which is an isocyanate compound manufactured by Nippon Polyurethane Industry Co., Ltd., was used.

  Next, the copolymer to which the cross-linking agent was added was adjusted with ethyl acetate so that the solid content was 30% by weight to obtain a coating solution. And the obtained coating liquid was apply | coated on the release film, the solvent was volatilized by heating for 10 minutes at 100 degreeC, and the uncrosslinked adhesive sheet was obtained. Finally, the obtained uncrosslinked pressure-sensitive adhesive sheet was subjected to a crosslinking reaction by heating and drying at 40 ° C. for 2 weeks to obtain an optical acrylic pressure-sensitive adhesive sheet having a thickness of 160 μm. As the release film, a polyethylene terephthalate film having a thickness of 50 μm obtained by applying silicone was used.

<Evaluation>
About the obtained adhesive sheet, the drop resistance by a weight average molecular weight, 180 degree peeling strength, room temperature fixing force, rework property, a reliability test, an optical characteristic, and a drop test was evaluated. Each evaluation method is shown below, and the results are also shown in Table 1.

(Weight average molecular weight)
The weight average molecular weight of the copolymer was measured by measuring the copolymer with GPC and converting the obtained measurement value into polystyrene. The results are shown in the column “MW” in Table 1.

(180 ° peel strength)
180 degree peel strength with respect to the glass plate in each atmospheric temperature of 23 degreeC and 90 degreeC was measured based on JISZ0237. Specifically, first, the atmospheric temperature was adjusted to 23 ° C. and 90 ° C., respectively. Next, at each atmospheric temperature, a polyethylene terephthalate film having a thickness of 25 μm was fixed to the glass plate via an adhesive sheet. As the glass plate, “EAGLE XG” manufactured by CORNING having a thickness of 1.1 mm was used.

  Then, the polyethylene terephthalate film was peeled 180 ° by pulling at a rate of 300 mm / min using a load cell. The result is shown in the column of “peel strength” in Table 1.

(Room temperature fixing force)
The room temperature fixing force was evaluated from the measurement result of the 180 ° peel strength at 23 ° C. (room temperature) described above. The evaluation criteria were set as follows.
○: 180 ° peel strength at 23 ° C. is 20 N / 25 mm or more.
X: 180 degree peeling strength in 23 degreeC is less than 20 N / 25mm.

(Reworkability)
First, an acrylic resin plate having a thickness of 1.0 mm was fixed to a glass plate through an adhesive sheet at an ambient temperature of 23 ° C. to obtain a laminate. The same glass plate as the 180 ° peel strength described above was used.

  Next, the laminate was molded into a size of 15 mm × 25 mm to obtain a test piece. The obtained test piece was set in an autoclave, and an autoclave process was performed for 20 minutes under conditions of a temperature of 50 ° C. and a pressure of 0.5 MPa.

After the autoclave process, the test piece was taken out from the autoclave, and the acrylic resin plate was removed from the glass plate. And the rework property was evaluated by visually observing the state of the removed acrylic resin board. The evaluation criteria were set as follows.
○: The acrylic resin plate was not damaged.
X: The acrylic resin plate was damaged.

(Reliability test)
First, at an ambient temperature of 23 ° C., a 250 μm thick polarizing plate whose surface was hard-coated was fixed to a glass plate via an adhesive sheet to obtain a test piece. Both the polarizing plate and the pressure-sensitive adhesive sheet were used after being molded to 15 mm × 25 mm. Further, the glass plate having the same 180 ° peel strength as described above was molded into 250 mm × 140 mm and used.

  Next, the obtained test piece was set in an autoclave, and an autoclave process was performed for 20 minutes under conditions of a temperature of 50 ° C. and a pressure of 0.5 MPa.

After the autoclave process, the test piece taken out from the autoclave was exposed to a high-temperature and high-humidity atmosphere at a temperature of 85 ° C. and a humidity of 85% RH for 24 hours. And reliability was evaluated by visually observing the test piece after 24 hours from the polarizing plate side. The evaluation criteria were set as follows.
○: No foaming, no peeling on the polarizing plate, and no whitening was observed on the entire test piece.
X: Foaming was observed, peeling was observed on the polarizing plate, or whitening was observed on the entire test piece.

(optical properties)
First, the cover glass was stuck on both surfaces of the adhesive sheet at an ambient temperature of 23 ° C. to obtain a test piece. As the cover glass, “MICRO COVER GLASS” manufactured by MATUNAMI having a thickness of 0.12 to 0.17 mm was used.

  Next, the obtained test piece was set in an autoclave, and an autoclave process was performed for 20 minutes under conditions of a temperature of 50 ° C. and a pressure of 0.5 MPa. And the optical characteristic of the test piece taken out from the autoclave was evaluated after the autoclave process.

  Specifically, transmittance and haze were measured according to ASTM D1003-95, and yellow index was measured according to ASTM D1925-70. As a measuring device, “SPECTRO PHOTOMETER CM-3600A” manufactured by KONICA MINOLTA was used. Each measurement was performed at an ambient temperature of 23 ° C.

And the optical characteristic was evaluated from each measurement result. The evaluation criteria were set as follows.
○: The conditions are such that the transmittance is 90% or more, the yellow index is smaller than 1.0, and the haze is smaller than 0.1.
X: The conditions that the transmittance is 90% or more, the yellow index is smaller than 1.0, and the haze is smaller than 0.1 are not satisfied.

(Drop test)
The drop test was performed according to JIS C60068-2-32. Specifically, first, an acrylic resin plate having a thickness of 25 mm × 40 mm and a thickness of 1.0 mm was attached to both surfaces of an adhesive sheet formed to 10 mm × 10 mm to obtain a laminate.

  Next, the laminate was fixed to a stainless steel plate with a double-sided tape at an ambient temperature of 23 ° C. to obtain a test piece. A stainless steel plate having a size of 40 mm × 40 mm and a weight of 80 g was used. As the double-sided tape, a commercially available acrylic double-sided tape molded to 25 mm × 40 mm was used.

  Next, the obtained test piece was set in an autoclave, and an autoclave process was performed for 20 minutes under conditions of a temperature of 50 ° C. and a pressure of 0.5 MPa. Then, after the autoclave process, the test piece taken out from the autoclave was dropped from a height of 200 cm onto a stainless steel test stand in an atmosphere temperature of 23 ° C. Specifically, SHINEEI TECHNOLOGY CO. Using a drop tester “DT-202” manufactured by LTD, the test piece was dropped so that the stainless steel plate was in contact with the test table among the test pieces.

After this process was repeated 5 times, drop resistance was evaluated by visually observing the state of the test piece. The evaluation criteria were set as follows.
A: The acrylic resin plate on the side of the test piece that is not fixed to the stainless steel plate was not detached.
X: The acrylic resin plate of the test piece which is not fixed to the stainless steel plate was detached.

  As is apparent from Table 1, all of Examples 1 to 7 are excellent in optical properties, reworkability and fixability (room temperature fixing force / reliability test / drop test). On the other hand, the comparative example 1 showed the result that the peeling strength in 90 degreeC atmospheric temperature is larger than 4 N / 25mm, and is inferior to rework property. Moreover, the comparative example 1 showed the result inferior also in the drop test. In both Comparative Example 2 and Comparative Example 3, the peel strength at an ambient temperature of 23 ° C. was smaller than 20 N / 25 mm, and the results were inferior to the room temperature fixing force and the reliability test.

Claims (9)

(Meth) acrylate having an ethylene glycol group;
(Meth) acrylate having a linear alkyl group having 16 to 22 carbon atoms;
A polar monomer;
The copolymer obtained by the polymerization, Ri Na crosslinked by a crosslinking agent,
180 degree peel strength against glass
At an ambient temperature of 23 ° C., it is 20 N / 25 mm or more,
Ru Der 4N / 25 mm or less at an ambient temperature of 90 ° C., acrylic pressure-sensitive adhesive for optical.   The (meth) acrylate having an ethylene glycol group is selected from 2-ethylhexyl-diglycol (meth) acrylate, methoxyethyl (meth) acrylate, methoxypolyethylene glycol mono (meth) acrylate, and ethoxy-diethylene glycol (meth) acrylate. The optical acrylic pressure-sensitive adhesive according to claim 1, which is at least one kind.   The optical acrylic pressure-sensitive adhesive according to claim 1 or 2, wherein the polar monomer is 2-hydroxyethyl (meth) acrylate.   The optical acrylic pressure-sensitive adhesive according to any one of claims 1 to 3, wherein the copolymer is obtained by further polymerizing a (meth) acrylate having an alkyl group having 1 to 12 carbon atoms.   The optical acrylic pressure-sensitive adhesive according to claim 4, wherein the (meth) acrylate having an alkyl group having 1 to 12 carbon atoms is methyl (meth) acrylate.   The optical acrylic system according to any one of claims 1 to 5, wherein the copolymer is obtained by further polymerizing a high Tg monomer capable of forming a homopolymer having a glass transition temperature (Tg) of 90 ° C or higher. Adhesive.   The optical acrylic pressure-sensitive adhesive according to claim 6, wherein the high Tg monomer is isobornyl acrylate. Consisting optical acrylic pressure-sensitive adhesive according to any one of claims 1 to 7 optical acrylic pressure-sensitive adhesive sheet. The optical acrylic pressure-sensitive adhesive sheet according to claim 8 , wherein a release film is laminated on one side or both sides.