JP2016210909A - Photocurable resin composition and cured product - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photocurable resin composition that has sufficient adhesiveness and can maintain sufficient transparency under a high temperature environment.SOLUTION: A photocurable resin composition comprises a (meth) acrylic polymer, a crosslinking agent, a monomer, a photoinitiator and an antioxidant, and the (meth) acrylic polymer is a polymer obtained by polymerizing a (meth) acrylic monomer with a non-nitrile azo ester polymerization initiator.SELECTED DRAWING: None

Description

  The present invention relates to a photocurable resin composition and a cured product thereof, and more particularly to a photocurable resin composition used for bonding applications in which a cover glass or an LCD (liquid crystal) module is bonded to a touch sensor, and the cured product thereof.

  In recent years, touch panels such as smartphones, car navigation systems, and tablet terminals have spread in the market and are rapidly spreading. The current touch panel is composed of touch sensors, LCD (liquid crystal) modules, cover glasses, etc., and the air gap between the touch sensors and the modules is filled with optical transparent adhesive to improve visibility and absorb shock resistance. It is known to be excellent in performance. Examples of such an optically transparent pressure-sensitive adhesive include a pressure-sensitive adhesive composition described in Patent Document 1 below.

JP 2009-24098 A

  However, the pressure-sensitive adhesive composition described in Patent Document 1 is gradually colored with time in a severe high temperature environment. And for the conventional photo-curable resin composition used as an optical transparent adhesive, it is transparent without being colored like yellowing even when used for a long time in a high temperature environment while maintaining the adhesiveness. Sustained sex is required.

  An object of this invention is to provide the photocurable resin composition which has sufficient adhesiveness, and can maintain sufficient transparency in high temperature environment, and its hardened | cured material.

  As a result of the study by the present inventors, when a (meth) acrylic polymer obtained by polymerizing a (meth) acrylic monomer using a nitrile-based azo polymerization initiator as a constituent component of the resin composition is used It was found that radicals and colored substances (ketene imine and the like) generated from the residual polymerization initiator contained in the (meth) acrylic polymer promote the deterioration of the resin. And the present inventors discovered the following photocurable resin compositions and its hardened | cured material based on these knowledge.

  The photocurable resin composition according to the present invention contains a (meth) acrylic polymer, a crosslinking agent, a monomer, a photopolymerization initiator, and an antioxidant, and the (meth) acrylic polymer is a non-nitrile azoester polymerization. It is a polymer obtained by polymerizing a (meth) acrylic monomer using an initiator.

  According to the photocurable resin composition according to the present invention, sufficient transparency can be maintained in a high temperature environment while maintaining adhesiveness. In particular, the photocurable resin composition according to the present invention can maintain transparency and prevent yellowing even when used for a long time in a high temperature environment. Such a photocurable resin composition is excellent in adhesiveness, transparency, and weather resistance, and can be used as an optical transparent adhesive application.

  The photocurable resin composition according to the present invention contains the (meth) acrylic polymer with respect to 100 parts by mass of the total amount of the (meth) acrylic polymer, the crosslinking agent, the monomer, and the photoinitiator. The amount is 30 to 65 parts by mass, the content of the crosslinking agent is 1.0 to 5.0 parts by mass, the content of the monomer is 30 to 58 parts by mass, and the content of the photoinitiator The aspect which is 0.005-5.0 mass parts may be sufficient.

  The cured product according to the present invention is a cured product of the photocurable resin composition according to the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, while having sufficient adhesiveness, the photocurable resin composition which can maintain sufficient transparency in a high temperature environment, and its hardened | cured material can be provided. In the present invention, when the resin composition is held at 95 ° C. for 1000 hours, the YI value (coloring index) can be maintained at 1.0 or less, for example.

  Hereinafter, embodiments of the present invention will be described in detail. In the present specification, “(meth) acryl” means at least one of acryl and methacryl, “(meth) acrylic acid” means at least one of acrylic acid and methacrylic acid, and “( “Meth) acrylate” means at least one of acrylate and methacrylate. Further, the content of each component in the composition means the total amount of the plurality of substances present in the composition unless there is a specific notice when there are a plurality of substances corresponding to each component in the composition. .

<Photocurable resin composition>
The photocurable resin composition (photocurable (meth) acrylic resin composition) according to the present embodiment includes (A) (meth) acrylic polymer (sometimes referred to as “component (A)”), (B) cross-linking. Agent (sometimes referred to as “component (B)”), (C) monomer (sometimes referred to as “component (C)”), (D) photoinitiator (photopolymerization initiator, sometimes referred to as “component (D)”. )) And (E) an antioxidant (sometimes referred to as “component (E)”). The component (A) is a polymer obtained by polymerizing a (meth) acrylic monomer ((meth) acrylic monomer) using a non-nitrile azoester polymerization initiator. The photocurable resin composition according to this embodiment can be used as an optically transparent adhesive.

[(A) component: (meth) acrylic polymer]
The photocurable resin composition according to this embodiment contains a (meth) acrylic polymer. Conventional photo-curable resin compositions include rubber-based compositions and polyether-based compositions, but have high elastic modulus and cure shrinkage, which can cause liquid crystal display unevenness when applied to touch panels and the like. It has become a challenge. On the other hand, in this embodiment, by using a (meth) acrylic polymer that is flexible and has a low elastic modulus and low shrinkage, it has sufficient adhesive strength and can be used for a long time in a high temperature environment. It is possible to provide an optical pressure-sensitive adhesive and an optical pressure-sensitive cured product that can maintain transparency without being colored, such as a change.

  The (meth) acrylic polymer in this embodiment is a polymer obtained by polymerizing a (meth) acrylic monomer using a polymerization initiator, and has a structural unit derived from the (meth) acrylic monomer. (Meth) acrylic monomers include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, isobutyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, octyl (meth) (Meth) acrylic acid alkyl ester monomers such as acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate, lauryl (meth) acrylate; (meth) acrylate, maleic acid, maleic anhydride, itaconic acid, fumaric acid, fumaric anhydride Carboxy group-containing monomers such as acids and their anhydrides; 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, polyethylene glycol (medium ) Such as hydroxyl group-containing monomers such as acrylate. These monomers may be used individually by 1 type, and may use 2 or more types together.

  As the (meth) acrylic monomer, a (meth) acrylic acid alkyl ester monomer (such as 2-ethylhexyl acrylate) and a hydroxy group-containing monomer (such as 2-hydroxyethyl acrylate) are preferable. The ratio of the (meth) acrylic acid alkyl ester monomer is preferably 50 to 95% by mass, more preferably 55 to 90% by mass, based on the total amount of the (meth) acrylic acid alkyl ester monomer and the hydroxy group-containing monomer. -90 mass% is still more preferable. When the said ratio is 50 mass% or more, it is excellent in cohesion force, and when it is 95 mass% or less, it is further excellent in adhesive force and a weather resistance.

  As a polymerization initiator for obtaining a (meth) acrylic polymer, a non-nitrile azo ester polymerization initiator which is a non-nitrile structure polymerization initiator (a polymerization initiator not containing a nitrile structure) is used. Examples of the non-nitrile azo ester polymerization initiator include dimethyl 2,2′-azobis (2-methylpropionate), 2,2′-azobis (N-butyl-2-methylpropionamide), 2,2 ′. -Azobis [N- (2-propenyl) -2-methylpropionamide], 2,2'-azobis (2,4,4-trimethylpentane) and the like. The amount of the polymerization initiator is preferably selected as appropriate depending on the desired molecular weight and physical properties.

  Among non-nitrile azoester polymerization initiators, dimethyl 2,2′-azobis (2-methylpropionate), which is an azo polymerization initiator, has a stable molecular weight because of its excellent polymerization activity and low hydrogen abstraction ability. It is particularly preferable because it can be polymerized and can easily maintain transparency even in a high temperature environment for a long time.

  When polymerizing a (meth) acrylic monomer, for example, a solution polymerization method can be applied. Examples of the solvent used at that time include ethyl acetate, toluene, hexane, acetone, and methyl ethyl ketone. As specific examples of methods other than the solution polymerization method, polymerization may be performed by a bulk polymerization method, a suspension polymerization method, an emulsion polymerization method, or the like.

  The weight average molecular weight of the component (A) is preferably 10,000 to 500,000 from the viewpoint of excellent viscosity after blending, workability, toughness of the cured product, and elastic modulus. The weight average molecular weight can be measured by gel permeation chromatography (GPC).

  The content of the component (A) is preferably 30 to 65 parts by mass with respect to 100 parts by mass of the total amount of the components (A), (B), (C) and (D), and 35 to 60 parts by mass. Part is more preferable, and 40 to 55 parts by mass is still more preferable. (A) When content of a component is 30 mass parts or more, sclerosis | hardenability becomes favorable, and when it is 65 mass parts or less, hardening shrinkage can be suppressed.

[(B) component: cross-linking agent]
The photocurable resin composition according to this embodiment contains a crosslinking agent. The photocurable resin composition according to the present embodiment contains a (meth) acrylic polymer having a monomer-derived structural unit having a hydroxy group in order to enhance cohesion and impart heat resistance and the like. It is preferable to contain a crosslinking agent that reacts with a hydroxy group.

  Examples of the crosslinking agent include polyfunctional (meth) acrylate compounds, isocyanate compounds, epoxy compounds, oxazoline compounds, aziridine compounds, metal chelate compounds, and melamine compounds. Among these crosslinking agents, polyfunctional (meth) acrylate compounds and isocyanate compounds are preferable because the (meth) acrylic polymer can be easily crosslinked.

  Examples of polyfunctional (meth) acrylate compounds include trimethylolpropane tri (meth) acrylate, tetramethylolmethane tri (meth) acrylate, tetramethylolmethane tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, and dipentaerythritol hexa. The polyfunctional (meth) acrylate which has three or more (meth) acryloyl groups in a molecule | numerator, such as (meth) acrylate, is mentioned.

  Examples of the isocyanate compound include tolylene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

  Examples of the epoxy compound include N, N, N ′, N′-tetraglycidyl-m-xylenediamine (trade name: TETRAD-X, manufactured by Mitsubishi Gas Chemical Company) and 1,3-bis (N, N-diglycidylaminomethyl). ) Cyclohexane (trade name TETRAD-C, manufactured by Mitsubishi Gas Chemical Company, Inc.). As the oxazoline compound, trade name Epocros WS-700 (manufactured by Nippon Shokubai Co., Ltd.) and the like can be mentioned. Examples of the aziridine compound include trade names HDU, TAZM, TAZO (manufactured by Mutual Yakugyo Co., Ltd.) and the like. As a metal chelate compound, aluminum, iron, tin, titanium, nickel etc. are mentioned as a metal component, Acetylene, methyl acetoacetate, ethyl lactate etc. are mentioned as a chelate component. Examples of the melamine compound include hexamethylol melamine.

  The content of the component (B) is preferably selected as appropriate according to the desired pressure-sensitive physical properties. (B) As for content of a component, 1.0-5.0 mass parts is preferable with respect to 100 mass parts of total amounts of (A) component, (B) component, (C) component, and (D) component. When the content of the component (B) is 1.0 part by mass or more, a crosslinking structure can be easily formed by the crosslinking agent, and the cohesive force of the adhesive composition can be improved. In some cases, moderate fluidity can be maintained and coating properties can be improved.

[(C) component: monomer]
The photocurable resin composition according to the present embodiment contains a monomer (excluding a compound corresponding to the component (B) or the component (D)). The photocurable resin composition according to the present embodiment uses a diluted monomer and has a low viscosity from the viewpoint of suppressing a decrease in coating property due to a high elastic modulus only with a (meth) acrylic polymer and a crosslinking agent. Is preferable. Examples of the diluted monomer include 2-ethylhexyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, acroylmorpholine, and the like. The type of monomer is preferably selected as appropriate according to the desired adhesive properties such as compatibility with (meth) acrylic polymer, glass transition temperature (Tg), and cohesiveness.

  The content of component (C) is preferably selected as appropriate according to the desired pressure-sensitive physical properties. The content of the component (C) is preferably 30 to 58 parts by mass with respect to 100 parts by mass of the total amount of the components (A), (B), (C) and (D), and 35 to 55 parts by mass. Part is more preferable, and 40-50 mass parts is still more preferable. When content of (C) component is 30-58 mass parts, an elasticity modulus becomes a suitable range, and coatability can be improved. 40-58 mass parts may be sufficient with respect to 100 mass parts of total amounts of (A) component, (B) component, (C) component, and (D) component.

[(D) component: photoinitiator]
As photoinitiators, 4-phenoxydichloroacetophenone, 4-t-butyl-dichloroacetophenone, 4-t-butyl-trichloroacetophenone, diethoxyacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one 1- (4-Isopropylphenyl-2-hydroxy-2-methylpropan-1-one, 1- (4-dodecylphenyl) -2-hydroxy-2-methylpropan-1-one, 4- (2-hydroxy Acetophenone photoinitiation such as ethoxy) -phenyl- (2-hydroxy-2-propyl) ketone, 1-hydroxycyclohexyl phenylketone, 2-methyl-1- [4- (methylthio) phenyl] -2-morpholinopropane-1 Agents: benzoin, benzoin methyl ether, benzoin ethyl ether Benzoin photoinitiators such as benzoin isopropyl ether, benzoin isobutyl ether, benzyl dimethyl ketal; benzophenone, benzoylbenzoic acid, methyl benzoylbenzoate, 4-phenylbenzophenone, hydroxybenzophenone, 4-benzoyl-4'-methyldiphenyl sulfide Benzophenone photoinitiators such as 3,3′-dimethyl-4-methoxybenzophenone; thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2 Thioxanthone photoinitiators such as 1,4-dichlorothioxanthone, 2,4-diethylthioxanthone, and 2,4-diisopropylthioxanthone.

  The content of the component (D) varies depending on the extinction coefficient and the like, but is 0.005 to 100 parts by mass of the total amount of the components (A), (B), (C) and (D). 5.0 parts by mass is preferable, 0.1 to 3.0 parts by mass is more preferable, and 0.1 to 0.5 parts by mass is still more preferable. When content of (D) component is 0.005 mass part or more, the hardening reaction of a photocurable resin composition can fully be accelerated | stimulated, and hardened | cured material can be formed efficiently. When content of (D) component is 5.0 mass parts or less, it can suppress that a reaction rate falls in the thickness direction of a photocurable resin composition.

[(E) component: antioxidant]
As a method for suppressing deterioration phenomenon such as coloring, a method of adding various antioxidants to a synthetic resin is known. There is no restriction | limiting in particular in antioxidant used for this embodiment, A conventionally well-known compound can be employ | adopted suitably. Examples include primary antioxidants such as hindered phenolic antioxidants and amine antioxidants, and secondary antioxidants such as phosphorus antioxidants, thiol antioxidants, and thioether antioxidants. .

  The content of the antioxidant is preferably 0.05 to 2.0 parts by mass with respect to 100 parts by mass of the total amount of the components (A), (B), (C) and (D), and 0 0.1 to 1.5 parts by mass is more preferable, and 0.2 to 1.0 part by mass is still more preferable. When the content of the antioxidant is 0.05 parts by mass or more, yellowing of the resin composition can be easily suppressed, and when it is 2.0 parts by mass or less, a decrease in curability can be suppressed.

  In the photocurable resin composition according to the present embodiment, it is preferable to use a hindered phenol-based antioxidant, a thiol-based antioxidant, or the like, and 4,6-bis (octylthiomethyl) -o-cresol (BASF). Irganox-1520L, etc., manufactured by the company), distearyl thiodipropionate (IRG PS800FD, etc., manufactured by BASF) is more preferably used, and 4,6-bis (octylthiomethyl) -o-cresol is further used. preferable.

<Hardened product>
The cured product according to the present embodiment is a cured product of the photocurable resin composition according to the present embodiment, and ultraviolet (UV), electron beam, α-ray, β and the photocurable resin composition according to the present embodiment. It can be obtained by photocuring the photocurable resin composition by irradiating active energy rays such as rays and γ rays. The cured product of the photocurable resin composition is, for example, an optical adhesive cured product. The hardened | cured material which concerns on this embodiment is a sheet form, for example.

  The photocurable resin composition and the cured product thereof according to the present embodiment are extremely effective for bonding with glass, polarizing plates, plastic films, composite sheets thereof and the like.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to these. “Part” and “%” mean “part by mass” and “% by mass”, respectively, unless otherwise specified.

<Production of adhesive sheet>
Example 1
[Polymerization process of acrylic polymer for adhesive]
Methyl ethyl ketone (MEK) as a solvent was added to a stainless steel pressure reactor equipped with a stirrer, a thermometer, a reflux condenser, a dropping device, and a nitrogen introduction tube, and stirred. Next, the temperature of the system was raised to 82 ° C. while blowing nitrogen into the charged solvent, and then polymerized with 75 parts of 2-ethylhexyl acrylate (AOEC) and 25 parts of 2-hydroxyethyl acrylate (AHEC), which were acrylic monomers. Equally mixed with 0.15 part of dimethyl 2,2′-azobis (2-methylpropionate) (trade name: V-601, manufactured by Wako Pure Chemical Industries, Ltd.) as an initiator over 2 hours. Was added in a small amount. And after dropping all the monomers and keeping the temperature for 1 hour, a mixed solution in which 0.2 part of the polymerization initiator V-601 was dissolved in MEK was added in an equal dropwise amount over 30 minutes. Thereafter, the mixture was kept warm for about 1 hour and then diluted with MEK. Next, as a polymerization initiator deactivation step, the temperature was raised to 128 ° C. under a 0.3 MPa pressure condition and kept for 2.5 hours to obtain an acrylic polymerization intermediate having a solid content of 50%.

[Demelting process of acrylic polymer for adhesive]
Since the acrylic polymer of this example was obtained by monomer substitution of the solvent in the acrylic polymerization intermediate polymerized above, the following steps were performed.

  Into a separable flask equipped with a stirrer, thermometer, air blowing tube and vacuum pump, an acrylic polymerization intermediate after deactivation (120 parts) and AOEC (35 parts) (solid content: AOEC = 65: 35) and 0.065 part of 3,5-di-tert-butyl-4-hydroxytoluene (BHT) were charged, and stirring and heating were started while bubbling Air. When the temperature was raised to 50 ° C., pressure reduction was started with a vacuum pump. The inside of the flask was depressurized while paying attention to foaming, and the temperature was raised until the liquid temperature reached 90 ° C. while distilling off the solvent. Depressurization was continued while maintaining the temperature at 90 ° C., and after 2 hours, it was confirmed by gas chromatography that the residual solvent amount in the system was 0.02% or less, and an acrylic polymer was obtained.

[Preparation of adhesive]
(B) 2.8 parts of (HGNR-003) which is a crosslinking agent and (C) 29.8 parts of 2-ethylhexyl acrylate (AOEC) which is a monomer with respect to 51 parts of the solid content of the acrylic polymer. -2.9 parts of hydroxybutyl acrylate (4-HBA) and 13.0 parts of acroylmorpholine (ACMO), (D) 1-hydroxycyclohexyl phenyl ketone (Irgacure 184 (I-184)) as a photopolymerization initiator A pressure-sensitive adhesive comprising 0.5 part and 0.3 part of (E) hindered phenol antioxidant 4,6-bis (octylthiomethyl) -o-cresol (IRG Irganox-1520L) (Photocurable resin composition, adhesive main agent).

[Method for producing adhesive sheet]
The pressure-sensitive adhesive adjusted to the prescribed composition is sandwiched between two types of release separators: heavy release separator: HTA-75 (film thickness: 75 μm) and light release separator: BD-50 (film thickness: 50 μm), and a 300 μm spacer is used. A pressure-sensitive adhesive sheet was prepared by coating and ultraviolet curing with a roller. The conditions for ultraviolet curing are as follows.
Ultraviolet irradiation device: GS YUASA LIGHTING Co., Ltd., UV SYSTEM CS60
Ultraviolet lamp: manufactured by GS YUASA LIGHTING Co., Ltd., metal halide lamp Exposure conditions: illuminance 200 mW / cm ² , integrated light quantity 3000 mJ / cm ² (500 mJ · cm ² × 4 times)

(Example 2)
In [Polymerization step of acrylic polymer for pressure-sensitive adhesive], a pressure-sensitive adhesive was obtained in the same manner as in Example 1 except that the acrylic monomer used was changed to 60 parts AOEC and 40 parts AHEC. And the adhesive sheet was obtained like Example 1 using this adhesive.

Example 3
In [Polymerization step of acrylic polymer for pressure-sensitive adhesive], a pressure-sensitive adhesive was obtained in the same manner as in Example 1 except that the acrylic monomer used was changed to 90 parts of AOEC and 10 parts of AHEC. And the adhesive sheet was obtained like Example 1 using this adhesive.

Example 4
In [Preparation of pressure-sensitive adhesive], a pressure-sensitive adhesive was obtained in the same manner as in Example 1 except that the amount of the antioxidant used was changed to 1.0 part of IRG1520L. And the adhesive sheet was obtained like Example 1 using this adhesive.

(Example 5)
In [Preparation of pressure-sensitive adhesive], the pressure-sensitive adhesive is the same as in Example 1 except that the antioxidant used is 1.0 part of distearyl thiodipropionate (IRG PS800FD) which is a thiol-based antioxidant. Got. And the adhesive sheet was obtained like Example 1 using this adhesive.

(Example 6)
A pressure-sensitive adhesive was obtained in the same manner as in Example 3 except that the monomer used in [Preparation of pressure-sensitive adhesive] was changed to 45.7 parts of AOEC. And the adhesive sheet was obtained like Example 1 using this adhesive.

(Comparative Example 1)
Implemented except that the polymerization initiator used in [Polymerization process of acrylic polymer for pressure-sensitive adhesive] was changed to AIBN (2,2′-azobis (2-methylpropionitrile)) and the addition of antioxidant was eliminated. A pressure-sensitive adhesive was obtained in the same manner as in Example 1. And the adhesive sheet was obtained like Example 1 using this adhesive.

(Comparative Example 2)
A pressure-sensitive adhesive was obtained in the same manner as in Example 1 except that the polymerization initiator used in [Acrylic polymer for pressure-sensitive adhesive] was changed to AIBN. And the adhesive sheet was obtained like Example 1 using this adhesive.

(Comparative Example 3)
A pressure-sensitive adhesive was obtained in the same manner as in Example 2 except that the polymerization initiator used in [Acrylic polymer for pressure-sensitive adhesive] was changed to AIBN and the addition of the antioxidant was eliminated. And the adhesive sheet was obtained like Example 1 using this adhesive.

(Comparative Example 4)
A pressure-sensitive adhesive was obtained in the same manner as in Example 3 except that the polymerization initiator used in [Acrylic polymer for pressure-sensitive adhesive] was changed to AIBN and the addition of the antioxidant was eliminated. And the adhesive sheet was obtained like Example 1 using this adhesive.

(Comparative Example 5)
A pressure-sensitive adhesive was obtained in the same manner as in Example 5 except that the polymerization initiator used in [Acrylic polymer for pressure-sensitive adhesive] was changed to AIBN. And the adhesive sheet was obtained like Example 1 using this adhesive.

(Comparative Example 6)
A pressure-sensitive adhesive was obtained in the same manner as in Example 6 except that the polymerization initiator used in [Polymerization step of acrylic polymer for pressure-sensitive adhesive] was changed to AIBN and the addition of the antioxidant was eliminated. And the adhesive sheet was obtained like Example 1 using this adhesive.

<Evaluation>
About the adhesive sheet of each Example and each comparative example, the coloring property (yellowishness) and the adhesive force with respect to glass were measured with the following method. The results are shown in Tables 1 and 2.

[Evaluation method of colorability (yellowishness, heat-resistant coloring)]
The prepared pressure-sensitive adhesive sheet was cut into a size of 50 mm × 50 mm, and then the single-sided release separator was peeled off and bonded to glass to obtain a test piece. The peeling separator of this test piece was peeled off, and the initial YI value (initial sheet YI value) was measured with a color difference meter (Spectrophotometer SD6000 manufactured by Nippon Denshoku Industries Co., Ltd.). Then, after putting in 95 degreeC drying machine for 1000 hours, YI value (sheet YI value after a heat test) was measured similarly. Then, a change in YI value of 95 ° C. × 1000 hours (“95 ° C. × 1000 hours YI value” − “initial YI value”) was determined from the initial YI value. The higher the YI value, the stronger the yellowish color, and the greater the change, the more advanced the deterioration of the cured product.

[Measurement method of glass adhesive strength (shear stress, shear bond strength)]
After cutting out the produced adhesive sheet to 20 mm x 20 mm size, the peeling separator of both surfaces was peeled off and what was pinched | interposed with two glass was used as the test piece. The test piece is attached to a tensile tester (Autograph AG-X / R, manufactured by Shimadzu Corporation), measured at a peeling speed of 30 mm / min, and a measurement temperature of 85 ° C., and the strength when the test piece breaks is sheared. Adhesive strength.

  As is clear from Example 1 of Table 1, the thermal colorability was suppressed by using the non-nitrile polymerization initiator V-601 and adding the hindered phenol antioxidant IRG1520L. Further, from Examples 2 and 3, the same effect was confirmed even when the copolymerization ratio of the acrylic polymer was set to AOEC: AHEC = 60: 40 to 90:10. In addition, it is estimated that the larger the hydroxyl value by changing the copolymerization ratio, the stronger the interaction with glass and the greater the adhesive force. In Example 4 in which the amount of the antioxidant IRG1520L was increased, the coloration could be suppressed in the same manner as in Example 1, but the adhesive strength slightly decreased. In Example 5 using the thiol-based antioxidant IRG PS800FD as the antioxidant, the effect was lower than that of IRG1520L in Example 1, but thermal coloring was suppressed. In Example 6 in which the diluted monomer was only AOEC, thermal coloring was similarly suppressed.

  In contrast, in Comparative Example 1 in which AIBN having a nitrile structure was used as a polymerization initiator and no antioxidant was contained, coloring was large after 95 ° C. × 1000 hours. In Comparative Examples 2 and 5 to which an antioxidant is added, the thermal coloring property is suppressed as compared with Comparative Example 1, but the thermal coloring is less than when both the non-nitrile polymerization initiator and the antioxidant are formulated. It was big. Further, from Comparative Examples 3 and 4, even when the copolymerization ratio of the acrylic polymer was AOEC: AHEC = 60: 40 to 90:10, the thermal coloring was large when AIBN was used and the antioxidant was not used. Even in Comparative Example 6 in which the diluted monomer was only AOEC, thermal coloring was large when AIBN was used and no antioxidant was used.

  From these results, in the case of using a polymerization initiator having a nitrile structure, it is considered that radicals and colored substances (ketene imine, etc.) generated from the residual polymerization initiator are colored by promoting deterioration of the resin due to heat. Therefore, it is presumed that coloring was suppressed by the use of a polymerization initiator not containing a nitrile structure and radical scavenging by an antioxidant.

Claims (3)

Contains (meth) acrylic polymer, cross-linking agent, monomer, photoinitiator and antioxidant,
The photocurable resin composition, wherein the (meth) acrylic polymer is a polymer obtained by polymerizing a (meth) acrylic monomer using a non-nitrile azoester polymerization initiator.   The content of the (meth) acrylic polymer is 30 to 65 parts by mass with respect to 100 parts by mass of the total amount of the (meth) acrylic polymer, the crosslinking agent, the monomer, and the photoinitiator, and the crosslinking The content of the agent is 1.0 to 5.0 parts by mass, the content of the monomer is 30 to 58 parts by mass, and the content of the photoinitiator is 0.005 to 5.0 parts by mass. The photocurable resin composition according to claim 1.   Hardened | cured material of the photocurable resin composition of Claim 1 or 2.