JP4458515B2 - Acrylic adhesive composition and acrylic adhesive sheet - Google Patents

Description

  The present invention relates to an ultraviolet curable acrylic pressure-sensitive adhesive composition, a layer thereof, and an acrylic pressure-sensitive adhesive sheet. The acrylic adhesive sheet can be used for various purposes. In particular, it is useful when the adherend is a polycarbonate because it has excellent adhesion and foam resistance even after heat aging which is applied to a polycarbonate and placed in a heat and moisture resistant environment. Acrylic pressure-sensitive adhesive sheets are used as pressure-sensitive adhesive sheets in the form of a sheet or tape.

  Conventionally, a base polymer of an acrylic pressure-sensitive adhesive has been prepared by solution polymerization of an acrylic monomer mainly composed of (meth) acrylic acid alkyl ester in an organic solvent. In recent years, due to consideration for the global environment, restrictions on air pollution and environmental issues have become issues, so by manufacturing UV-polymerized acrylic monomers to produce pressure-sensitive adhesive sheets with a solvent-free adhesive layer Is particularly advantageous in terms of safety and environment.

  In recent years, polycarbonate (PC) is preferably used as an optical material as a transparent plastic. An adhesive sheet may be affixed on the PC for the purpose of protection or bonding. However, since gas is generated in the PC due to heat aging or the like, bubbles are generated in the pressure-sensitive adhesive layer, which may cause delamination between the pressure-sensitive adhesive layer and the PC, and further deteriorate the appearance. .

  Conventionally, as a pressure-sensitive adhesive satisfying such requirements, for example, a graft polymer formed by copolymerizing a macromonomer copolymerizable with (meth) acrylic acid ester as a main component by radiation curing is used. Has been proposed (see Patent Document 1). The pressure-sensitive adhesive can improve the foaming resistance against PC. However, since the macromonomer is an essential component in the pressure-sensitive adhesive, there is a problem associated with using the macromonomer. That is, such a macromonomer usually has poor copolymerizability, so that unreacted macromonomer remains after radiation curing, and the performance of the pressure-sensitive adhesive layer becomes unstable. Further, in order to increase the reaction rate of the macromonomer, it is necessary to lengthen the irradiation time, which may cause a problem in productivity.

  In addition, a carboxyl group-containing resin composition obtained by copolymerizing a (meth) acrylic acid alkyl ester and a carboxyl group-containing monomer, and a (meth) acrylic acid alkyl ester as a main component and further containing an amino group-containing monomer. A pressure-sensitive adhesive composition obtained by crosslinking a polymerized amino group-containing resin composition has been proposed (see Patent Document 2). The pressure-sensitive adhesive composition can prevent the bubbles from growing even if gas is generated, and has improved foam resistance. However, the method taught in US Pat. In addition, since the cross-linking between a carboxyl group and an amino group is used, there may be a problem in moisture resistance.

Further, as a pressure-sensitive adhesive composition having improved moisture resistance as described in Patent Document 2, a composition using a main component of a carboxyl group-containing resin composition and (meth) acrylic acid alkoxyalkyl ester has been proposed (see Patent Document 3). ). However, the pressure-sensitive adhesive composition is also solvent-based.
Japanese National Patent Publication No. 8-504229 JP-A-10-310754 JP 2002-327160 A

  An object of the present invention is to provide an ultraviolet-curable pressure-sensitive adhesive composition that does not substantially contain a solvent, and has an acrylic pressure-sensitive adhesive composition that has a high adhesion to PC even at high temperatures and high humidity.

  Moreover, an object of this invention is to provide the acrylic adhesive layer formed with the said acrylic adhesive composition. Furthermore, it aims at providing the acrylic adhesive sheet which has the said adhesive layer on the single side | surface or both surfaces of a base material.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above object can be achieved by the following acrylic pressure-sensitive adhesive composition, and have completed the present invention. That is, the present invention is as follows.

1. A photopolymerization initiator (b) with respect to 100 parts by weight of a vinyl monomer having an alkyl (meth) acrylate (a1) having an alkyl group having 2 to 14 carbon atoms as a main component or a partial polymer thereof (a) 0. 001-5 parts by weight, the softening temperature Ts is not less 40 ° C. or more and a weight average molecular weight of 1,000 to 30,000 (meth) acrylic acid ester oligomer (c) 5 to 40 parts by weight of the polyfunctional (meth) acrylate (d ) An acrylic pressure-sensitive adhesive composition containing 0.001 to 30 parts by weight , and the acrylic pressure-sensitive adhesive composition is adjusted to have a gel fraction of 45% or more when irradiated with ultraviolet rays. An acrylic pressure-sensitive adhesive composition characterized by the above.

2. An alkyl (meth) acrylate (c1) having a solubility parameter of 21.5 (MPa1 / 2) or less and a Tg of 15 ° C. or more when the (meth) acrylic acid ester oligomer (c) is a homopolymer. 2. The acrylic pressure-sensitive adhesive composition as described in 1 above, which is a polymer containing 50% by weight or more as a monomer unit.

3. 3. The acrylic pressure-sensitive adhesive composition according to the above 1 or 2 , which is used for a polycarbonate adherend.

4). An acrylic pressure-sensitive adhesive layer obtained by irradiating the acrylic pressure-sensitive adhesive composition according to any one of 1 to 3 with ultraviolet rays.

5. An acrylic pressure-sensitive adhesive sheet comprising the acrylic pressure-sensitive adhesive layer described in 4 above on one side or both sides of a substrate.

6). 5. The acrylic pressure-sensitive adhesive sheet according to 5 above , wherein the acrylic pressure-sensitive adhesive sheet is bonded to a polycarbonate plate and left to stand at 23 ° C. for 30 minutes or more (pulling speed 300 mm / second, peeling angle 180). )) After being allowed to stand at 70 ° C. for 72 hours and then measured at 23 ° C. (pulling speed 300 mm / second, peeling angle 180 °), and after standing at 60 ° C. and 95% RH for 72 hours, 23 An acrylic pressure-sensitive adhesive sheet characterized in that the adhesive strength (pulling speed 300 mm / second, peeling angle 180 °) measured at 0 ° C. is high.

7). 7. The acrylic pressure-sensitive adhesive sheet as described in 5 or 6 above , wherein the acrylic pressure-sensitive adhesive sheet is attached to a polycarbonate plate and allowed to stand at 70 ° C. for 72 hours and then at 60 ° C. and 95% RH for 72 hours. An acrylic pressure-sensitive adhesive sheet characterized in that foaming is not seen in the pasting portion after being placed.

  The acrylic pressure-sensitive adhesive composition of the present invention is an ultraviolet curable pressure-sensitive adhesive composition that does not substantially contain a solvent, and has high adhesive strength at high temperatures and high humidity. In particular, it has high adhesion to PC. For example, a pressure-sensitive adhesive sheet having a pressure-sensitive adhesive layer obtained by irradiating the acrylic pressure-sensitive adhesive composition with ultraviolet rays on one side or both sides of a base material is attached to a PC board, and then is 70 ° C. (high temperature) or 60 Adhesive strength when exposed to 95% RH (high humidity) for 72 hours is greater than the initial adhesive strength, and can suppress the foaming and swelling of the adhesive due to the gas generated from the adherend (PC). Adhesion can be maintained.

  The reason why the acrylic pressure-sensitive adhesive composition of the present invention exhibits excellent foaming resistance and blistering resistance against PC is not clear, but the softening temperature Ts is 40 ° C. or higher and the weight average molecular weight is 1000 to 1000. By including the (meth) acrylic acid ester oligomer (c) which is 30000, the intrusion of the gas generated from the PC into the pressure-sensitive adhesive is suppressed, and further, adhesion using the polyfunctional (meth) acrylate (d) is performed. This is probably because the gel fraction of the agent is cross-linked to 45% or more, so that the cohesive force is not easily lowered due to the wet heat deterioration of the pressure-sensitive adhesive.

  The acrylic pressure-sensitive adhesive composition of the present invention is a vinyl monomer having a main component of an alkyl (meth) acrylate (a1) having an alkyl group having 2 to 14 carbon atoms or a partial polymer (a) thereof, photopolymerization start The agent (b) contains a (meth) acrylate ester oligomer (c) and a polyfunctional (meth) acrylate (d) having a softening temperature Ts of 40 ° C. or more and a weight average molecular weight of 1000 to 30000.

  Examples of the alkyl (meth) acrylate (a1) having an alkyl group having 2 to 14 carbon atoms include ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, and n-butyl (meth). Acrylate, sec-butyl (meth) acrylate, t-butyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isononyl (meth) acrylate, dodecyl (meth) Examples include acrylates. One or more of these alkyl (meth) acrylates (a1) are used.

  The alkyl (meth) acrylate (a1) can be the total amount of the vinyl monomer (a), but for the vinyl monomer (a), a copolymerizable monomer (a2) is used together with the monomer (a1). Can do. Examples of the copolymerizable monomer (a2) include carboxyl group-containing monomers such as acrylic acid, methacrylic acid, carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleic acid, and crotonic acid; 2-hydroxyethyl (meth) acrylate, (Meth) acrylic acid 2-hydroxypropyl, (meth) acrylic acid 4-hydroxybutyl, (meth) acrylic acid 6-hydroxyhexyl, (meth) acrylic acid 8-hydroxyoctyl, (meth) acrylic acid 10-hydroxydecyl, Hydroxyl group-containing monomers such as (meth) acrylic acid 12-hydroxylauryl, (4-hydroxymethylcyclohexyl) -methyl acrylate; acid anhydride monomers such as maleic anhydride and itaconic anhydride; 2-acrylamido-2-methylpropanesulfuric acid Phosphate, sulfonic acid group-containing monomers such as sulfopropyl acrylate -; and 2-hydroxyethyl acryloyl phosphate, etc. phosphoric acid group-containing monomer. Further, amide monomers such as N-substituted (meth) acrylamide such as (meth) acrylamide and N-methylolacrylamide, N- (meth) acryloyloxymethylene succinimide, N- (meth) acryloyl-6-oxyhexamethylene succinimide, Succinimide monomers such as N- (meth) acryloyl-8-oxyoctamethylenesuccinimide are also exemplified as the copolymerizable monomer (a2). Furthermore, vinyl monomers such as vinyl acetate, N-vinyl pyrrolidone, N-vinyl carboxylic acid amides, styrene, N-vinyl caprolactam; cyanoacrylate monomers such as acrylonitrile and methacrylonitrile, glycidyl (meth) acrylate, Acrylic ester monomers such as tetrahydrofurfuryl (meth) acrylate, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, fluorine (meth) acrylate, silicone (meth) acrylate, 2-methoxyethyl acrylate; methyl ( Alkyl (meth) acrylates having an alkyl group different from alkyl (meth) acrylate (a1), which is the main component such as meth) acrylate and octadecyl (meth) acrylate, are also copolymerized. And the like as a monomer (a2). One or two or more copolymerizable monomers (a2) can be used.

  When the monomer (a1) and the monomer (a2) are used, it is preferable that the monomer (a1) is 70 to 99.9% by weight and the monomer (a2) is 0.1 to 30% by weight. More preferably, the monomer (a1) is 80 to 99.9% by weight and the monomer (a2) is 0.1 to 20% by weight. More preferably, the monomer (a1) is 90 to 99% by weight and the monomer (a2) is 1 to 10% by weight.

  As the monomer (a2), a hydroxyl group-containing monomer and a carboxyl group-containing monomer are preferable, and acrylic acid is particularly preferable, and the use ratio is preferably 1 to 10% by weight. Adhesive force can be improved by using in the said range.

  Various kinds of photopolymerization initiators (b) can be used without particular limitation. For example, benzoin ethers such as benzoin methyl ether, benzoin isopropyl ether, 2,2-dimethoxy-1,2-diphenylethane-1-one; substituted benzoin ethers such as anisole methyl ether; 2,2-diethoxyacetophenone, 2, Substituted acetophenones such as 2-dimethoxy-2-phenylacetophenone, 1-hydroxy-cyclohexyl-phenylketone; substituted alpha-ketols such as 2-methyl-2-hydroxypropiophenone; aromatic sulfonyl chlorides such as 2-naphthalenesulfonyl chloride; And photoactive oximes such as 1-phenyl-1,1-propanedione-2- (o-ethoxycarbonyl) -oxime.

  These photopolymerization initiators (b) are preferably used in an amount of 0.01 to 5 parts by weight with respect to 100 parts by weight of the vinyl monomer (a). More preferably, it is used in a proportion of 0.1 to 3 parts by weight.

  The (meth) acrylic acid ester oligomer (c) has a softening temperature Ts of 40 ° C. or higher and a weight average molecular weight of 1000 to 30000. The softening temperature Ts of the (meth) acrylate oligomer (c) indicates the softening temperature Ts measured using a constant load capillary extrusion rheometer (Shimadzu Flow Tester CFT-500D), die: 1 mm × 1 mm, load: 4.9 N, temperature increase rate: Refers to a value measured at 5 ° C./min. The softening temperature Ts is preferably 45 ° C. or higher, and more preferably 55 ° C. or higher, because it exhibits excellent foam resistance and swelling resistance to PC. On the other hand, if the softening temperature Ts becomes too high, the Tg of the pressure-sensitive adhesive composition becomes high and the initial tack and the like are lowered. Therefore, the softening temperature Ts is preferably 200 ° C. or lower, more preferably 150 ° C. or lower.

  The (meth) acrylic acid ester oligomer (c) has a weight average molecular weight of 1000 to 30000. Preferably it is 2000-10000. If the weight average molecular weight is less than 1000, the effect of suppressing the occurrence of foaming is poor. On the other hand, when the weight average molecular weight exceeds 30000, the (meth) acrylic acid ester oligomer (c) is easily separated into layers, which may adversely affect the adhesive performance and appearance. The measurement of a weight average molecular weight is calculated | required in polystyrene conversion by GPC method. Specifically, TSKgelGMH-H (20) × 2 columns are used in HPLC 8020 manufactured by Tosoh Corporation, and the measurement is performed with a tetrahydrofuran solvent under a flow rate of 0.5 ml / min.

The (meth) acrylic acid ester forming the (meth) acrylic acid ester oligomer (c) has a solubility parameter of 21.5 (MPa ^{1 /} MPa) when the (meth) acrylic acid ester oligomer (c) is a homopolymer. ² ) A polymer containing 50% by weight or more of an alkyl (meth) acrylate (c1) having a Tg of 15 ° C. or more as a monomer unit can be preferably used.

Solubility parameter (SP value) T. T. It is calculated by the method described in Fedors, Polymer Engineering and Science, 14, 147 (1974). The solubility parameter is preferably 21.3 (MPa ^1/2 ) or less, more preferably 21.0 (MPa ^1/2 ), from the viewpoint of adhesion to an adherend having a nonpolar surface such as polypropylene or polyethylene. ) If the solubility parameter is too small, the main component of the acrylic pressure-sensitive adhesive composition is compatible with the vinyl monomer or its partially polymerized product (a), in particular, commonly used butyl acrylate or 2 -Since the compatibility with the copolymer of ethylhexyl acrylate and acrylic acid is lowered, the solubility parameter is 18.0 (MPa ^1/2 ) or more, more preferably 18.5 (MPa ^1/2 ) or more.

  Tg is determined from a numerical value described in POLYMER HANDBOOK FORTH EDITION. Tg is preferably 30 ° C. or higher, more preferably 50 ° C. or higher, from the viewpoint of cohesive strength and adhesive strength of the pressure-sensitive adhesive. In addition, when Tg becomes too high, it is not preferable in that the Tg of the pressure-sensitive adhesive composition is raised to reduce initial tack and the like, and therefore Tg is 200 ° C. or lower, more preferably 190 ° C. or lower.

Specific examples of the alkyl (meth) acrylate (c1) having a solubility parameter of 21.5 (Mpa ^1/2 ) or less and a Tg of 15 ° C. or higher when a homopolymer is used include t-butyl acrylate (Tg: 43 ° C.). , SP value: 19.2 (Mpa ^1/2 )), 3,3,5-trimethylcyclohexyl acrylate (Tg: 15 ° C., SP value: 19.1 (MPa ^1/2 )), isobornyl acrylate (Tg : 94 ° C., SP value: 19.7 (MPa ^1/2 )), methyl methacrylate (Tg: 105 ° C., SP value: 20.3 (MPa ^1/2 )), ethyl methacrylate (Tg: 65 ° C., SP value) ; 19.9 (MPa ^1/2)), cyclohexyl methacrylate (Tg: 83 ℃, SP value: 20.1 (Mpa ^1/2)), isobutyl methacrylate (Tg: 53 ℃, SP value: 19.0 (M a ^1/2)), t- butyl methacrylate (Tg: 118 ℃, SP value: 18.6 (MPa ^1/2)) and the like.

The (meth) acrylic acid ester oligomer (c) is preferably a polymer containing 50% by weight or more of the alkyl (meth) acrylate (c1) as a monomer unit. The alkyl (meth) acrylate (c1) is used alone or in combination of two or more. When the content of the alkyl (meth) acrylate (c1) is less than 50% by weight, it is not preferable because humidification or foaming after humidification cannot be sufficiently suppressed in bonding to a PC adherend. The content of the alkyl (meth) acrylate (c1) is 50% by weight or more, and further 80% by weight or more. The (meth) acrylic acid ester oligomer (c) has a softening temperature Ts of 40 ° C. or higher and a weight average molecular weight of 1000 to 30000, in addition to the alkyl (meth) acrylate (c1), a solubility parameter. May be copolymerized with another monomer having a Tg of less than 15 ° C. and a Tg of more than 21.5 (MPa ^1/2 ).

  The amount of the (meth) acrylic acid ester oligomer (c) used is preferably 5 to 40 parts by weight with respect to 100 parts by weight of the vinyl monomer (a). More preferably, it is used in a proportion of 10 to 30 parts by weight. If it is less than 5 parts by weight, the effect of suppressing the occurrence of sufficient foaming is poor. When it exceeds 40 parts by weight, the (meth) acrylic acid ester oligomer (c) is likely to be separated into layers, which may adversely affect the adhesive performance and appearance.

  As the polyfunctional (meth) acrylate (d), a compound having at least two (meth) acryloyl groups can be used without particular limitation. For example, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, 1,2-ethylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,12-dodecanediol di Examples include (meth) acrylate.

  The amount of the polyfunctional (meth) acrylate (d) used is such that the gel fraction of the acrylic pressure-sensitive adhesive layer formed from the acrylic pressure-sensitive adhesive composition containing the components (a) to (d) is 45% by weight or more. It is preferable to blend so that. The gel fraction is more preferably 50% by weight or more. When the gel fraction is less than 45% by weight, the cohesive force of the pressure-sensitive adhesive layer is insufficient, and the effect of suppressing the occurrence of foaming is poor. On the other hand, if the gel fraction is too high, the tackiness of the pressure-sensitive adhesive layer is lowered, and the adhesive performance and appearance may be adversely affected. Therefore, the gel fraction is 99% by weight or less, and further 95% by weight or less. Preferably there is. .

  As for the gel fraction, about 1 g of the adhesive was precisely weighed, and this was immersed in about 40 g of ethyl acetate for 7 days. Thereafter, all insolubles in ethyl acetate were collected and dried at 130 ° C. for 2 hours. The weight was determined, and the obtained numerical value was substituted into the following formula. Solvent insoluble content (%) = (weight of insoluble content / weight of adhesive before immersion) × 100.

  Although the usage-amount of polyfunctional (meth) acrylate (d) changes with the molecular weight, the number of functional groups, etc., it is a ratio of 0.001-30 weight part normally with respect to 100 weight part of said vinylic monomers (a). Preferably there is. More preferably, it is used at a ratio of 0.05 to 20 parts by weight.

  The acrylic pressure-sensitive adhesive layer of the present invention is formed by photopolymerizing an acrylic pressure-sensitive adhesive composition containing the components (a) to (d). The acrylic pressure-sensitive adhesive composition is preferably adjusted to a viscosity suitable for coating (usually, 0.3 to 40 Pa · s at 25 ° C. in viscosity measurement with a B-type viscometer). Therefore, the monomer (a1) or the vinyl monomer (a) composed of the monomer (a1) and the monomer (a2) can be prepolymerized to be a partially polymerized product. The polymerization rate of the partially polymerized vinyl monomer (a) is preferably about 2 to 40% by weight, although it depends on the polymer molecular weight in the partially polymerized product. Furthermore, it is preferable to set it as 5 to 20 weight%. In partial polymerization, it is preferable to irradiate with ultraviolet rays while avoiding contact with oxygen. The polymerization rate of the partially polymerized product was determined by accurately weighing about 0.5 g of the partially polymerized product and then weighing the weight after drying it at 130 ° C. for 2 hours to determine the weight loss (volatile matter (unreacted monomer weight)). )), And the obtained numerical value was substituted into the following equation. Polymerization rate of partial polymer (%) = [1- (weight reduction) / (weight of partial polymer before drying)] × 100.

  The viscosity of the acrylic pressure-sensitive adhesive composition can also be adjusted by appropriately blending a thickening polymer. Examples of the thickening polymer include acrylic polymers obtained by copolymerizing acrylic acid, acrylamide, acrylonitrile, acryloylmorpholine, and the like (meth) acrylic acid alkyl ester (a1), styrene butadiene rubber (SBR), isoprene rubber, styrene. Butadiene block copolymer (SBS), ethylene-vinyl acetate copolymer, acrylic rubber, polyurethane, polyester and the like can be used. These thickening polymers are used in the acrylic pressure-sensitive adhesive composition in an amount of 40% by weight or less. When using the polymer for thickening, it is preferable to set it as 5 to 40 weight%.

  In addition, the acrylic pressure-sensitive adhesive composition may be appropriately mixed with various conventionally known additives such as plasticizers, softeners, fillers, pigments, dyes and the like within a range that does not impair photopolymerizability. it can.

The acrylic pressure-sensitive adhesive layer of the present invention can be obtained by applying the pressure-sensitive adhesive composition directly on an adherend, or by applying light to one or both sides of a support substrate. Usually, an acrylic pressure-sensitive adhesive layer is obtained by irradiating an ultraviolet ray having an illuminance of 1 to 200 mW / cm ² at a wavelength of 300 to 400 nm with a light amount of about 400 to 4000 mJ / cm ^{2 for} photopolymerization. The polymerization rate at this time is desirably 90% by weight or more. Unreacted monomers can also be removed by a normal drying process. The polymerization rate can be calculated by the same method as described above. Moreover, also when (meth) acrylic acid ester oligomer (c) etc. are included in an acrylic adhesive composition, it treats as a polymerization rate similarly to the above, and it is preferable that the said polymerization rate shall be 90% or more.

  The thickness of the acrylic pressure-sensitive adhesive layer is not particularly limited, but is usually 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more (usually up to 400 μm) in order to ensure good adhesive strength.

  The pressure-sensitive adhesive sheet of the present invention has an acrylic pressure-sensitive adhesive obtained from the acrylic pressure-sensitive adhesive composition on one side or both sides of a support substrate. As described above, the acrylic pressure-sensitive adhesive layer can be formed by coating the pressure-sensitive adhesive composition on one side or both sides of a support base material and photopolymerizing it. Moreover, an adhesive sheet can be formed also by the system etc. which transfer the acrylic adhesive layer formed on the separator to the single side | surface or both surfaces of a support base material. Furthermore, it can also be used as a double-sided pressure-sensitive adhesive sheet without using a separator as a supporting base material in practical use. The pressure-sensitive adhesive sheets are used in the form of a sheet or tape.

As the supporting base material in the pressure-sensitive adhesive sheet, such as paper, cloth, porous substrate comprising a nonwoven fabric, a plastic film or sheet, foam, thin material such as a metal foil, and the like. These support base materials are appropriately selected according to the use for which the pressure-sensitive adhesive sheet is used. The thickness of the supporting substrate is not particularly limited, and is appropriately determined depending on the application.

  The adherend to which the acrylic pressure-sensitive adhesive layer and the pressure-sensitive adhesive sheet of the present invention are applied is not particularly limited. As an adherend, polycarbonate, polypropylene, various resins such as polyester, polystyrene, phenol resin, epoxy resin, polyurethane, ABS, acrylic resin, and various metals such as iron, aluminum, copper, nickel, and alloys thereof It can be used similarly. Of these, application to polycarbonate is preferred as the adherend.

  Examples of the present invention will be described below in more detail, but the present invention is not limited to these examples. In the following, parts and% are based on weight.

Example 1
(Preparation of (meth) acrylic acid ester oligomer)
100 parts of toluene, 100 parts of cyclohexyl methacrylate, 0.3 part of azobisisobutyronitrile and 3 parts of 2-mercaptoethanol are charged into 4 flasks and reacted at 70 ° C. for 6 hours and at 80 ° C. for 1 hour in a nitrogen atmosphere. I let you. Thereafter, the reaction solution was added into methanol, the oligomer was precipitated and taken out, and further dried by a vacuum dryer. The resulting cyclohexyl methacrylate oligomer had a weight average molecular weight of 3800 and a softening temperature Ts of 97 ° C.

(Preparation of acrylic pressure-sensitive adhesive composition)
By placing 100 parts of butyl acrylate and 0.3 part of a photopolymerization initiator (Irgacure 2020, manufactured by Ciba Specialty Chemicals Co., Ltd.) into a four-necked flask and exposing it to ultraviolet rays in a nitrogen atmosphere, and partially photopolymerizing it, A partially polymerized product (monomer syrup) having a polymerization rate of 10% was obtained.

  After adding 20 parts of the cyclohexyl methacrylate oligomer obtained above and 2 parts of trimethylolpropane triacrylate to 100 parts of this partially polymerized product, these were uniformly mixed to prepare an acrylic pressure-sensitive adhesive composition.

(Production of acrylic adhesive sheet)
The acrylic pressure-sensitive adhesive composition was applied to a polyester film having a thickness of 25 μm so that the final thickness was 60 μm to form a coating layer. On top of this, a polyester film having a thickness of 38 μm having one surface peel-treated with silicone was coated so that the peel-treated surface was on the coating layer side and shielded from oxygen. The upper surface of this sheet was irradiated with ultraviolet rays having an illuminance of 4 mW / cm ² (measured with Topcon UVR-T1 having a maximum sensitivity of about 350 nm) for 180 seconds with a black light lamp (manufactured by Toshiba). Then, it heat-processed for 3 minutes with a 130 degreeC dryer, the monomer remaining in the amount was volatilized, and the acrylic adhesive sheet was obtained. The gel fraction of the pressure-sensitive adhesive of the obtained pressure-sensitive adhesive sheet was 81%.

Example 2
(Preparation of acrylic pressure-sensitive adhesive composition)
95 parts of butyl acrylate, 5 parts of hydroxyethyl acrylate, and 0.3 part of a photopolymerization initiator (Irgacure 2020, manufactured by Ciba Specialty Chemicals) are put into a four-necked flask and partially exposed to ultraviolet rays in a nitrogen atmosphere. By photopolymerization, a partially polymerized product (monomer syrup) having a polymerization rate of 10% was obtained.

  To 100 parts of this partially polymerized product, 20 parts of the cyclohexyl methacrylate oligomer obtained in Example 1 and 0.2 part of trimethylolpropane triacrylate were added, and these were uniformly mixed to prepare an acrylic pressure-sensitive adhesive composition. did.

(Production of acrylic adhesive sheet)
In Example 1, an acrylic pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the acrylic pressure-sensitive adhesive composition obtained above was used. The gel fraction of the pressure-sensitive adhesive in the obtained pressure-sensitive adhesive sheet was 76%.

Example 3
(Preparation of acrylic pressure-sensitive adhesive composition)
95 parts of butyl acrylate, 5 parts of acrylic acid, and 0.3 part of a photopolymerization initiator (Irgacure 2020, manufactured by Ciba Specialty Chemicals) are put into a four-necked flask and exposed to ultraviolet rays in a nitrogen atmosphere to partially light. By polymerizing, a partial polymer (monomer syrup) having a polymerization rate of 10% was obtained.

  To 100 parts of this partially polymerized product, 20 parts of the cyclohexyl methacrylate oligomer obtained in Example 1 and 0.2 part of trimethylolpropane triacrylate were added, and these were uniformly mixed to prepare an acrylic pressure-sensitive adhesive composition. did.

(Production of acrylic adhesive sheet)
In Example 1, an acrylic pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the acrylic pressure-sensitive adhesive composition obtained above was used. The gel fraction of the pressure-sensitive adhesive in the obtained pressure-sensitive adhesive sheet was 65%.

Example 4
(Preparation of acrylic pressure-sensitive adhesive composition)
In the preparation of the acrylic pressure-sensitive adhesive composition of Example 3, prepared on to acrylic pressure-sensitive adhesive composition the same manner as in Example 3 except that the amount of cyclohexyl methacrylate oligomer obtained in Example 1 was 10 parts did.

(Production of acrylic adhesive sheet)
In Example 1, an acrylic pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the acrylic pressure-sensitive adhesive composition obtained above was used. The gel fraction of the pressure-sensitive adhesive in the obtained pressure-sensitive adhesive sheet was 71%.

Example 5
(Preparation of (meth) acrylic acid ester oligomer)
100 parts of toluene, 100 parts of isobornyl acrylate, 0.3 part of azobisisobutyronitrile, and 3 parts of 2-mercaptoethanol are charged into 4 flasks, and are placed at 70 ° C. for 6 hours under nitrogen atmosphere. Reacted for hours. Thereafter, the reaction solution was added into methanol, the oligomer was precipitated and taken out, and further dried by a vacuum dryer. The obtained isobornyl acrylate oligomer had a weight average molecular weight of 4000 and a softening temperature Ts of 75 ° C.

(Preparation of acrylic pressure-sensitive adhesive composition)
95 parts of butyl acrylate, 5 parts of acrylic acid, and 0.3 part of a photopolymerization initiator (Irgacure 2020, manufactured by Ciba Specialty Chemicals) are put into a four-necked flask and exposed to ultraviolet rays in a nitrogen atmosphere to partially light. By polymerizing, a partial polymer (monomer syrup) having a polymerization rate of 10% was obtained.

  To 100 parts of this partially polymerized product, 20 parts of the isobornyl acrylate oligomer obtained above and 0.2 part of trimethylolpropane triacrylate were added, and then mixed uniformly to prepare an acrylic pressure-sensitive adhesive composition. did.

(Production of acrylic adhesive sheet)
In Example 1, an acrylic pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the acrylic pressure-sensitive adhesive composition obtained above was used. The gel fraction of the pressure-sensitive adhesive in the obtained pressure-sensitive adhesive sheet was 68%.

Example 6
(Preparation of (meth) acrylic acid ester oligomer)
100 parts of toluene, 100 parts of t-butyl methacrylate, 0.3 part of azobisisobutyronitrile and 3 parts of 2-mercaptoethanol are charged into 4 flasks, and the mixture is heated at 70 ° C. for 6 hours and 1 at 80 ° C. in a nitrogen atmosphere. Reacted for hours. Thereafter, the reaction solution was added into methanol, the oligomer was precipitated and taken out, and further dried by a vacuum dryer. The obtained t-butyl methacrylate oligomer had a weight average molecular weight of 3500 and a softening temperature Ts of 107 ° C.

(Preparation of acrylic pressure-sensitive adhesive composition)
97 parts of butyl acrylate, 5 parts of acrylic acid, and 0.3 part of a photopolymerization initiator (Irgacure 2020, manufactured by Ciba Specialty Chemicals) are put into a four-necked flask and exposed to ultraviolet rays in a nitrogen atmosphere to partially light. By polymerizing, a partial polymer (monomer syrup) having a polymerization rate of 10% was obtained.

  After adding 20 parts of the t-butyl methacrylate oligomer obtained above and 2 parts of trimethylolpropane triacrylate to 100 parts of this partially polymerized product, these were uniformly mixed to prepare an acrylic pressure-sensitive adhesive composition.

(Production of acrylic adhesive sheet)
The acrylic pressure-sensitive adhesive composition was applied to a polyester film having a thickness of 25 μm so that the final thickness was 60 μm to form a coating layer. On top of this, a polyester film having a thickness of 38 μm having one surface peel-treated with silicone was coated so that the peel-treated surface was on the coating layer side and shielded from oxygen. The upper surface of this sheet was irradiated with ultraviolet rays having an illuminance of 4 mW / cm ² (measured with Topcon UVR-T1 having a maximum sensitivity of about 350 nm) for 180 seconds with a black light lamp (manufactured by Toshiba). Then, it heat-processed for 3 minutes with a 130 degreeC dryer, the monomer remaining in the amount was volatilized, and the acrylic adhesive sheet was obtained. The gel fraction of the pressure-sensitive adhesive in the obtained pressure-sensitive adhesive sheet was 89%.

Comparative Example 1
(Preparation of acrylic pressure-sensitive adhesive composition)
In the preparation of the acrylic pressure-sensitive adhesive composition of Example 3, except that no addition of cyclohexyl methacrylate oligomer obtained in Example 1 was prepared the same way acrylic pressure-sensitive adhesive composition as in Example 3.

(Production of acrylic adhesive sheet)
In Example 1, an acrylic pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the acrylic pressure-sensitive adhesive composition obtained above was used. The gel fraction of the pressure-sensitive adhesive in the obtained pressure-sensitive adhesive sheet was 77%.

Comparative Example 2
(Preparation of acrylic pressure-sensitive adhesive composition)
In the preparation of the acrylic pressure-sensitive adhesive composition of Example 3 to prepare an acrylic pressure-sensitive adhesive composition the amount of trimethylolpropane triacrylate except that the 0.1 parts in the same manner as in Example 3.

(Production of acrylic adhesive sheet)
In Example 1, an acrylic pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the acrylic pressure-sensitive adhesive composition obtained above was used. The gel fraction of the pressure-sensitive adhesive of the obtained pressure-sensitive adhesive sheet was 43%.

Comparative Example 3
(Preparation of (meth) acrylic acid ester oligomer)
100 parts of toluene, 100 parts of cyclohexyl methacrylate, 0.3 part of azobisisobutyronitrile and 6 parts of 2-mercaptoethanol are charged into 4 flasks and reacted at 70 ° C. for 6 hours and at 80 ° C. for 1 hour under a nitrogen atmosphere. I let you. Thereafter, the reaction solution was added into methanol, the oligomer was precipitated and taken out, and further dried by a vacuum dryer. The weight average molecular weight of the obtained cyclohexyl methacrylate oligomer was 2000, and the softening temperature Ts was 37 ° C.

(Preparation of acrylic pressure-sensitive adhesive composition)
95 parts of butyl acrylate, 5 parts of acrylic acid, and 0.3 part of a photopolymerization initiator (Irgacure 2020, manufactured by Ciba Specialty Chemicals) are put into a four-necked flask and exposed to ultraviolet rays in a nitrogen atmosphere to partially light. By polymerizing, a partial polymer (monomer syrup) having a polymerization rate of 10% was obtained.

  To 100 parts of this partially polymerized product, 20 parts of the cyclohexyl methacrylate oligomer (softening temperature Ts: 37 ° C.) obtained above and 0.2 part of trimethylolpropane triacrylate were added and then mixed uniformly to obtain an acrylic system. A pressure-sensitive adhesive composition was prepared.

(Production of acrylic adhesive sheet)
In Example 1, an acrylic pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the acrylic pressure-sensitive adhesive composition obtained above was used. The gel fraction of the pressure-sensitive adhesive of the obtained pressure-sensitive adhesive sheet was 64%.

Comparative Example 4
(Preparation of (meth) acrylic acid ester oligomer)
100 parts of toluene, 100 parts of isobutyl methacrylate, 0.3 part of azobisisobutyronitrile and 3 parts of 2-mercaptoethanol are charged into 4 flasks and reacted at 70 ° C. for 6 hours and at 80 ° C. for 1 hour in a nitrogen atmosphere. I let you. Thereafter, the reaction solution was added into cyclohexane, the oligomer was precipitated and taken out, and further dried by a vacuum dryer. The resulting isobutyl methacrylate oligomer had a weight average molecular weight of 4600 and a softening temperature Ts of 38 ° C.

(Preparation of acrylic pressure-sensitive adhesive composition)
95 parts of butyl acrylate, 5 parts of acrylic acid, and 0.3 part of a photopolymerization initiator (Irgacure 2020, manufactured by Ciba Specialty Chemicals) are put into a four-necked flask and exposed to ultraviolet rays in a nitrogen atmosphere to partially light. By polymerizing, a partial polymer (monomer syrup) having a polymerization rate of 10% was obtained.

  To 100 parts of this partially polymerized product, 20 parts of the isobutyl methacrylate oligomer (softening temperature Ts: 38 ° C.) obtained above and 0.2 part of trimethylolpropane triacrylate were added and then mixed uniformly to obtain an acrylic system. A pressure-sensitive adhesive composition was prepared.

(Production of acrylic adhesive sheet)
In Example 1, an acrylic pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the acrylic pressure-sensitive adhesive composition obtained above was used. The gel fraction of the pressure-sensitive adhesive of the obtained pressure-sensitive adhesive sheet was 64%.

Comparative Example 5
(Preparation of acrylic pressure-sensitive adhesive composition)
95 parts of butyl acrylate, 5 parts of acrylic acid, and 0.3 part of a photopolymerization initiator (Irgacure 2020, manufactured by Ciba Specialty Chemicals) are put into a four-necked flask and exposed to ultraviolet rays in a nitrogen atmosphere to partially light. By polymerizing, a partial polymer (monomer syrup) having a polymerization rate of 10% was obtained.

  In 100 parts of this partially polymerized product, 20 parts of the cyclohexyl methacrylate oligomer obtained in Example 1 was dissolved and mixed. Furthermore, 0.5 parts of hydroxyethyl acrylate and 3 parts of Coronate L (manufactured by Nippon Polyurethane Industry Co., Ltd.) which is an isocyanate crosslinking agent are added and mixed in this, and mixed uniformly to obtain an acrylic pressure-sensitive adhesive composition. Prepared.

(Production of acrylic adhesive sheet)
In Example 1, an acrylic pressure-sensitive adhesive sheet was obtained in the same manner as in Example 1 except that the acrylic pressure-sensitive adhesive composition obtained above was used. The obtained pressure-sensitive adhesive sheet was further subjected to aging treatment at 50 ° C. for 3 days. The gel fraction of the pressure-sensitive adhesive in the obtained pressure-sensitive adhesive sheet was 57%.

  The following evaluation was performed about the adhesive sheet obtained by the above Example and comparative example. The results are shown in Table 1.

<Adhesive strength>
The prepared adhesive sheet was cut to a width of 20 mm, and a 2 kg roller was attached to a 2 mm-thick PC plate (Takiron Co., Ltd., product number 1600). The adhesive force was measured under the following conditions.

  Initial: After pasting, the sheet was allowed to stand at 23 ° C. for 30 minutes, and then the other end of the pressure-sensitive adhesive sheet was peeled off at a speed of 300 mm / min in a peeling direction of 180 °, and the resistance at that time was measured. The portion of 10 mm from the peeling start point was ignored, and the lowest resistance was defined as the adhesive strength (N / 20 mm).

  70 ° C .: After pasting, 72 hours were passed in an environment of 70 ° C., and then left for 30 minutes at 23 ° C. The adhesive strength was measured in the same manner as in the initial stage.

  60 ° C./95%: After pasting, 72 hours were passed in an environment of 60 ° C./95%, and then left for 30 minutes at 23 ° C. The adhesive strength was measured in the same manner as in the initial stage.

  When foaming occurs in the pasted part and partial peeling of the pressure-sensitive adhesive occurs, the adhesive strength of the foamed part is locally reduced. For this reason, the minimum value becomes significantly lower, and it is possible to confirm a decrease in adhesion due to foaming or the like.

<Foaming>
Adhering to the PC board by the same method as the measurement of adhesive strength, after 72 hours under the environment of 70 ° C. and 72 hours under the environment of 60 ° C./95%, the adhesive sheet is visually attached. The foaming state of the part was observed according to the following criteria.
○: No foaming was observed.
X: Many foams were observed, and large foams and blisters were observed.

Claims (7)

A photopolymerization initiator (b) with respect to 100 parts by weight of a vinyl monomer having an alkyl (meth) acrylate (a1) having an alkyl group having 2 to 14 carbon atoms as a main component or a partial polymer thereof (a) 0. 001-5 parts by weight, the softening temperature Ts is not less 40 ° C. or more and a weight average molecular weight of 1,000 to 30,000 (meth) acrylic acid ester oligomer (c) 5 to 40 parts by weight of the polyfunctional (meth) acrylate (d ) An acrylic pressure-sensitive adhesive composition containing 0.001 to 30 parts by weight , and the acrylic pressure-sensitive adhesive composition is adjusted to have a gel fraction of 45% or more when irradiated with ultraviolet rays. An acrylic pressure-sensitive adhesive composition characterized by the above. An alkyl (meth) acrylate (c1) having a solubility parameter of 21.5 (MPa ^1/2 ) or less and a Tg of 15 ° C. or more when the (meth) acrylic acid ester oligomer (c) is a homopolymer. the acrylic pressure-sensitive adhesive composition according to claim 1, characterized in that a polymer containing 50 wt% or more as a monomer unit. The acrylic pressure-sensitive adhesive composition according to claim 1 or 2 , which is used for a polycarbonate adherend. Acrylic pressure-sensitive adhesive layer, characterized in that is obtained by UV irradiation in the acrylic pressure-sensitive adhesive composition according to any one of claims 1-3. An acrylic pressure-sensitive adhesive sheet comprising the acrylic pressure-sensitive adhesive layer according to claim 4 on one side or both sides of a substrate. 6. The acrylic pressure-sensitive adhesive sheet according to claim 5 , wherein the acrylic pressure-sensitive adhesive sheet is attached to a polycarbonate plate and left to stand for 30 minutes or more at 23 ° C. (pulling speed 300 mm / second, peeling angle). 180 °), after 72 hours of standing at 70 ° C., after having been left for 72 hours at 60 ° C. and 95% RH, and the adhesive strength measured at 23 ° C. (pulling speed 300 mm / second, peeling angle 180 °). An acrylic pressure-sensitive adhesive sheet characterized in that the adhesive strength measured at 23 ° C. (pulling speed 300 mm / second, peel angle 180 °) is large. The acrylic pressure-sensitive adhesive sheet according to claim 5 or 6 , wherein the acrylic pressure-sensitive adhesive sheet is attached to a polycarbonate plate and left to stand at 70 ° C for 72 hours, and at 60 ° C and 95% RH for 72 hours. An acrylic pressure-sensitive adhesive sheet characterized in that foaming is not seen in the pasting portion after standing still.