Light-curing resin composition

Abstract

To provide a photocurable resin composition which can be used for a tape-shaped adhesive (OCA) for optical adhesive applications, has a low relative dielectric constant and has high adhesive strength.SOLUTION: There is provided a photocurable resin composition which comprises a photocrosslinkable polymer having a benzophenone skeleton, an alkyl (meth)acrylate having an alkyl group having 10 to 24 carbon atoms, an N-alkylacrylamide and / or a (meth)acrylate containing a hydroxyl group and a photopolymerization initiator, wherein the blending amount of the alkyl (meth)acrylate to the total solid content is 30 to 70 wt.% and the blending amount of the N-alkylacrylamide and / or N-vinylpyrrolidone to the total solid content is 3 to 18 wt.%.

Description

[Technical Field]

[0001] The present invention relates to a solvent-free photocurable resin composition suitable for bonding an image display member such as a liquid crystal display member to a cover member. [Background technology]

[0002] Acrylic resins are used in a variety of applications, taking advantage of their characteristics of transparency and fast curing. For example, in image display devices such as smartphones and touch panels, a technology has been developed in which such transparent acrylic resins are filled between the image display component, such as a liquid crystal display panel or organic EL display panel, and the cover panel that protects it, thereby eliminating the air gap between the image display component and the cover panel and preventing a decrease in contrast and brightness (Patent Document 1).

[0003] This type of application is also known as optical bonding, and can be broadly divided into OCR (Optical Clear Resin), which uses a liquid resin, and OCA (Optical Clear Adhesive), which is pre-processed into a sheet. OCA, in particular, is pre-processed into a sheet, so it is widely used because it allows precise control of film thickness, does not require special coating and curing equipment, and is also reworkable (re-adhesion).

[0004] The applicant previously invented a pressure-sensitive adhesive composition containing an acrylic compound with a polypropylene glycol skeleton as a resin composition that can be used in such OCAs (Patent Document 2). However, as touch panels become thinner and more highly detailed, a low dielectric constant for the optical adhesive layer is essential to prevent malfunctions and improve response speed and sensitivity. In addition to good optical properties, sufficient adhesive strength is required to absorb the difference in thermal expansion coefficients that occurs when different materials are bonded together. There was room for improvement in achieving both a low dielectric constant and high adhesive strength. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2005-55641 [Patent Document 2] Patent Publication No. 2020-45416 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a photocurable resin composition that has a low dielectric constant and high adhesive strength and can be used for tape-shaped pressure sensitive adhesives (OCA) for optical bonding applications. [Means for solving the problem]

[0007] In order to solve the above problems, the invention of claim 1 is a photo-crosslinkable compound having a benzophenone skeleton. Acrylic The composition comprises a polymer (A), an alkyl (meth)acrylate (B) having an alkyl group having 10 to 24 carbon atoms, an N-alkyl acrylamide and / or an N-vinyl pyrrolidone (C), and a photopolymerization initiator (D), The N-alkylacrylamide includes N,N-dimethylacrylamide or N,N-diethylacrylamide; The above (B) Photocurable resin composition The blending amount of (C) is 30 to 70% by weight based on the total solid content. Photocurable resin composition The photocurable resin composition is characterized in that the blending amount is 3 to 18% by weight based on the total solid content.

[0008] The invention of claim 2 is as follows: The (B) contains an alkyl (meth)acrylate having a branched alkyl group having 10 to 24 carbon atoms. The photocurable resin composition according to claim 1 is provided.

[0009] The invention of claim 3 is as follows: 3. The photocurable resin composition according to claim 1, wherein the cured product has a relative dielectric constant of 3.3 or less at a frequency of 1 MHz. to provide.

[0010] The invention of claim 4 is as follows: An image display device using the photocurable resin composition according to any one of claims 1 to 3. to provide. [Effects of the Invention]

[0012] The resin composition of the present invention can be used for adhesive tapes that require good optical properties. It is a photocurable resin composition that has a low dielectric constant and sufficient adhesive strength, and is useful as a material for OCA, which is used for optical bonding. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present invention will be described in detail below.

[0014] The composition of the present invention comprises a photocrosslinkable polymer (A), an alkyl(meth)acrylate (B) having an alkyl group with 10 to 24 carbon atoms, N-alkylacrylamide and / or N-vinylpyrrolidone (C), and a photopolymerization initiator (D). In this specification, (meth)acrylate includes both acrylate and methacrylate.

[0015] The photocrosslinkable polymer (A) used in the present invention has a benzophenone skeleton in the polymer component, which can be excited by light irradiation and extract hydrogen radicals. Therefore, when irradiated with light, hydrogen radicals are extracted from the polymer molecules, and a crosslinked structure is formed by the bonding of the generated radicals. This makes it possible to form a strong film with a high molecular weight and high crosslink density, and achieve high elongation. Compared to polymers that are not photocrosslinkable, this polymer is characterized by being less susceptible to bleeding of unreacted crosslinking components after curing, less susceptible to macroscopic phase separation, and less susceptible to a decrease in transparency.

[0016] The (A) is preferably an acrylic photocrosslinkable polymer. The monomer forming the acrylic copolymer preferably has an alkyl group with 2 to 10 carbon atoms, in order to impart suitable viscoelasticity to the pressure-sensitive adhesive sheet and improve wettability to the adherend. Examples include ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and isodecyl (meth)acrylate, and these can be used alone or in combination of two or more. Among these, 2-ethylhexyl acrylate (hereinafter referred to as 2-EHA) is preferred because it has a low glass transition temperature (hereinafter referred to as Tg), excellent wettability with the adherend, and a large molar volume due to its branched structure.

[0017] The blending amount of (A) relative to the total solid content is preferably 20 to 60% by weight, more preferably 25 to 55% by weight, and even more preferably 30 to 50% by weight. By making it 20% by weight or more, sufficient cohesive strength and elongation can be ensured, and by making it 60% by weight or less, the dielectric constant can be sufficiently low. Commercially available products include the acResin series (product name: acrylic, manufactured by BASF Japan Ltd.).

[0018] The alkyl (meth)acrylate (B) having an alkyl group with 10 to 24 carbon atoms used in the present invention functions as a reactive diluent for the highly viscous (A) compound, and is also incorporated to lower the dielectric constant of the cured coating. While it is thought that lowering the dielectric constant can be achieved by reducing the molecular dipole moment and increasing the molar volume, long-chain alkyl groups are preferred because they have low polarity, and branched alkyl groups or cyclic structures are bulky.

[0019] Examples of (B) include isobornyl acrylate, decyl acrylate, lauryl acrylate, tridecyl acrylate, tetradecyl acrylate, isomistyryl (meth)acrylate, isostearyl (meth)acrylate, 2-propylheptyl (meth)acrylate, isoundecyl (meth)acrylate, isododecyl (meth)acrylate, and isohexadecyl (meth)acrylate, and these may be used alone or in combination of two or more. Among these, isostearyl acrylate (hereinafter referred to as ISTA), which has a t-butyl group and a large molar volume, is preferred.

[0020] The blending amount of (B) relative to the total solid content is preferably 30 to 70% by weight, more preferably 35 to 65% by weight, and particularly preferably 40 to 60% by weight. By making it 30% by weight or more, the dielectric constant can be sufficiently low, and by making it 70% by weight or less, sufficient cohesive strength and film elongation can be ensured.

[0021] The N-alkylacrylamide and / or N-vinylpyrrolidone (hereinafter referred to as NVP) (C) used in the present invention is blended to improve adhesion to the adherend. Because it is a hydrophilic monomer capable of absorbing water vapor, it is also effective in preventing whitening, particularly when adhering to materials with low moisture permeability such as glass. Examples of N-alkylacrylamides include N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-isopropylacrylamide, and N-butyl(meth)acrylamide. These can be used alone or in combination of two or more. Among these, N,N-dimethylacrylamide (hereinafter referred to as DMAA) and N,N-diethylacrylamide (hereinafter referred to as DEAA) are preferred in terms of compatibility with other components.

[0022] The blending amount of (C) relative to the total solid content is 3 to 18 wt %, preferably 4 to 15 wt %, and more preferably 5 to 12 wt %. If it is less than 3 wt %, it may not be possible to ensure sufficient adhesion to the adherend and to suppress whitening, while if it exceeds 18 wt %, it may not be possible to sufficiently lower the dielectric constant or the haze may increase, resulting in reduced optical properties.

[0023] The photopolymerization initiator (D) used in the present invention generates radicals upon irradiation with ultraviolet light or an electron beam, and these radicals trigger the polymerization reaction, and general-purpose photopolymerization initiators such as benzyl ketals, acetophenones, and phosphine oxides can be used. By arbitrarily selecting the light absorption wavelength of the polymerization initiator, it is possible to impart curability over a wide wavelength range from the ultraviolet region to the visible light region. Specifically, benzyl ketals include 2,2-dimethoxy-1,2-diphenylethan-1-one, α-hydroxyacetophenones include 1-hydroxycyclohexylphenylketone and 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one, α-aminoacetophenones include 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, and acylphosphine oxides include 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, which can be used alone or in combination. Among these, α-hydroxyacetophenones are preferred because they are less prone to yellowing.

[0024] The amount of (D) added per 100 parts by weight of the photopolymerizable component is preferably 0.05 to 5 parts by weight, more preferably 0.1 to 3 parts by weight. By adding 0.05 parts by weight or more, sufficient curability can be ensured, while by adding 5 parts by weight or less, an excessive amount can be avoided and a sufficient molecular weight can be ensured even after curing. Commercially available α-hydroxyacetophenone-based products include Omnirad 184 and Omnirad 2959 (trade names: manufactured by IGM Resins).

[0025] Additives such as tackifiers, plasticizers, photosensitizers, antioxidants, flame retardants, fillers, silane coupling agents, colorants, polymerization inhibitors, and organic fine particles can be added to the photocurable resin composition of the present invention as needed, within the range that does not impair performance.

[0026] The tackifier is a non-reactive component, and therefore can improve peel strength without causing shrinkage during cure. Examples include (hydrogenated) rosin ester resins, terpene resins, petroleum resins, styrene resins, and alkylphenol resins, which can be used alone or in combination of two or more. However, hydrogenated resins (hereinafter referred to as "hydrogenated") are preferred because of their excellent weather resistance. Among these, hydrogenated petroleum resins and hydrogenated rosin ester resins are preferred because they are colorless and transparent and have excellent compatibility with (A), (B), and (C).

[0027] The amount of the tackifier to be blended relative to the total solid content is preferably 20% by weight or less, more preferably 15% by weight or less. By adjusting the amount within this range, sufficient peel strength can be ensured. Examples of commercially available hydrogenated petroleum resins include the Alcon series (trade name: manufactured by Arakawa Chemical Industries, Ltd.), and examples of commercially available hydrogenated rosin ester resins include the Pine Crystal series (trade name: manufactured by Arakawa Chemical Industries, Ltd.).

[0028] The plasticizer penetrates between polymer molecules, weakening the intermolecular forces of the polymer and facilitating the movement of molecular chains, thereby lowering the glass transition temperature of the polymer and imparting flexibility to the polymer. Examples of the plasticizer include aliphatic esters, alicyclic esters, phthalates, aliphatic dibasic acid esters, polyalkylene polyols, phosphate esters, polyesters, and paraffins, which can be used alone or in combination of two or more. Among these, alicyclic esters are preferred in terms of compatibility with resins.

[0029] The amount of the plasticizer blended relative to the total solid content is preferably 20% by weight or less, and more preferably 15% by weight or less. By adjusting the blending amount to this range, the plasticity of the cured coating can be improved while maintaining a low dielectric constant. Commercially available alicyclic ester plasticizers include Hexamoll DINCH (product name: 1,2-cyclohexanedicarboxylic acid diisononyl ester, manufactured by BASF Japan Ltd.).

[0030] The photocurable resin composition of the present invention can be used as a material for an OCA, which bonds an image display such as a touch panel or flat panel display, for example, a mobile device terminal, to a cover member that protects it. When the photocurable resin composition of the present invention is used in an OCA, the low dielectric constant makes it less likely to malfunction, and the response speed and sensitivity are also high. Specific examples of tape production and usage methods are described below, but are not limited to these, and the order of applying the adhesive and the order of laminating the films can be selected as needed.

[0031] The resin composition is applied to a release PET film and then cured by ultraviolet irradiation to produce an adhesive film. The application method is not particularly limited, and known methods such as roll coating, die coating, air knife coating, blade coating, spin coating, reverse coating, and gravure coating can be used. The thickness of the coating is optional, and examples include 50 to 400 μm, but a thickness of 200 to 350 μm is preferred for curved glass cover panels.

[0032] Next, a release PET film with a different release strength is laminated, and then the laminate is cured by irradiating with ultraviolet light to create a three-layer adhesive sheet. The ultraviolet light used for curing is from a known light source such as a high-pressure mercury lamp, carbon arc lamp, xenon lamp, metal halide lamp, LED lamp, or electrodeless lamp, and the photocurable composition is cured by irradiating it with an integrated light dose of, for example, 50 to 10,000 mJ / cm2.

[0033] The photocurable resin composition cured product of the present invention preferably has a relative dielectric constant at a frequency of 1 MHz of 3.5 or less, more preferably 3.3 or less, and particularly preferably 3.0 or less. If the relative dielectric constant is 3.5 or less, malfunctions and problems in response speed and sensitivity can be prevented even when used as an OCA in a touch panel.

[0034] The present invention will be described in detail below based on examples and comparative examples, but these are intended to be specific examples and are not intended to limit the scope of the invention. Unless otherwise specified, measurements were taken at a room temperature of 25°C and a relative humidity of 65%. The blend amounts are in parts by weight.

[0035] Example 1 The photocurable resin composition of Example 1 was prepared by stirring (A) acResin UV3532 (trade name: 2-EHA copolymer manufactured by BASF Japan Ltd.), (B) ISTA (trade name: isostearyl acrylate manufactured by Osaka Organic Chemical Industry Co., Ltd.), (C) DMAA (trade name: dimethylacrylamide manufactured by KJ Chemicals Co., Ltd.), and (D) Omnirad184 (trade name: IGM Resins Co., Ltd.) in the formulation shown in Table 1 until uniformly dissolved.

[0036] Examples 2 to 16 In addition to the materials used in Example 1, LA (trade name: lauryl acrylate, manufactured by Kyoeisha Chemical Co., Ltd.) and IB-XA (trade name: isobornyl acrylate, manufactured by Kyoeisha Chemical Co., Ltd.) were used as (B), DEAA (trade name: diethylacrylamide, manufactured by KJ Chemicals Co., Ltd.) and NVP (trade name: Nippon Shokubai Co., Ltd.) were used as (C), 2-EHA (trade name: 2-ethylhexyl acrylate, manufactured by Mitsubishi Chemical Corporation) was used as an acrylic monomer, KE-311 (trade name: hydrogenated rosin ester resin, manufactured by Arakawa Chemical Industries Co., Ltd.) and Alcon P-90 (trade name: hydrogenated petroleum resin, manufactured by Arakawa Chemical Industries Co., Ltd.) were used as a tackifier, and DINCH (trade name: 1,2-cyclohexanedicarboxylic acid diisononyl ester, manufactured by BASF Japan Ltd.) was used as a plasticizer. These were mixed in the formulations shown in Tables 1 and 2 and stirred until uniformly dissolved, to prepare the photocurable resin compositions of Examples 2 to 16.

[0037] Comparative Examples 1 to 3 In addition to the materials used in the examples, ACMO (trade name: acryloylmorpholine, manufactured by KJ Chemicals) as another acrylic monomer was added and stirred until uniformly dissolved in the formulation shown in Table 2 to prepare photocurable resin compositions of Comparative Examples 1 to 3.

[0038] Preparation of evaluation sheets A photocurable resin composition was applied to a 200 μm thick film on the release-treated surface of a heavy-release PET film E7002 (product name: manufactured by Toyobo Co., Ltd., thickness: 50 μm), and a light-release PET film E7006 (manufactured by Toyobo Co., Ltd., 75 μm) was then laminated on top of the applied composition. Next, a black light irradiation device was used, in which NEC Corporation's black light FL15BL was arranged in parallel, and an output of 5 mW / cm was applied. 2 , cumulative light intensity 300mJ / cm 2 After irradiation under the conditions of , an EYE INVERTOR GRANDAGE (high pressure mercury lamp) UV irradiation device manufactured by Eye Graphics was used, and the output was 100 mW / cm 2 , cumulative light intensity 4000mJ / cm 2 The sheet for evaluation was prepared by irradiating under the conditions of:

[0039] Table 1 JPEG0007736513000001.jpg107135

[0040] Table 2 JPEG0007736513000002.jpg116135

[0041] The evaluation method was as follows.

[0042] Dielectric constant: The adhesive layers of the evaluation sheets were stacked to a thickness of 1 mm, and the relative dielectric constant at a frequency of 1 MHz was measured using an LCR meter 6440B manufactured by Wayne Kerr. A value of 3.0 or less was rated as ◎, a value of more than 3.0 to 3.5 was rated as ○, and a value of more than 3.5 was rated as ×.

[0043] Peel strength: The light-release PET film was peeled off from the evaluation sheet, and the sheet was attached to easy-adhesion PET A4300 (product name: Toyobo, 50 μm). The remaining release film was then peeled off and attached to a white glass plate. The sheet was cut to a width of 25 mm and autoclaved at 0.5 MPa and 50°C for 30 minutes to prepare a test specimen. The peel strength at 180° to the white glass plate was measured using a Techno Graph TGI-1kN tensile tester at a crosshead speed of 300 mm / min, with less than 10 N / 25 mm being evaluated as ×, 10 to 20 N / 25 mm as △, over 20 to 30 N / 25 mm as ○, and over 30 N / 25 mm as ◎.

[0044] Total light transmittance: The release PET film was peeled off from the evaluation sheet, and 1 mm thick white glass plates were attached to both sides of the sheet. The haze was measured in accordance with JIS K7361-1 using a haze meter Haze-GARD2 manufactured by Toyo Seiki Seisakusho, with a rating of ◯ for 90% or more and × for less than 90%.

[0045] Haze: Using the same sample as for the total light transmittance, the measurement was carried out in accordance with JIS K7361-1 using a haze meter Haze-GARD2 manufactured by Toyo Seiki Seisakusho Co., Ltd., with less than 1% being rated as ◯ and 1% or more being x.

[0046] Evaluation results Table 3 JPEG0007736513000003.jpg55135

[0047] Evaluation results Table 4 JPEG0007736513000004.jpg60135

[0048] Each of the resin compositions of the examples obtained good results in the evaluations of dielectric constant, adhesive strength, total light transmittance, and haze.

[0049] On the other hand, Comparative Example 1, in which ACMO was used instead of (C), and Comparative Example 3, in which the amount of (C) exceeded the upper limit, had poor optical properties, and Comparative Example 2, which did not contain (C), had low adhesive strength, and neither was suitable for the present invention.

Claims

1. A photocurable resin composition comprising (A) a photocrosslinkable acrylic polymer having a benzophenone skeleton, (B) an alkyl(meth)acrylate having an alkyl group of 10 to 24 carbon atoms, (C) an N-alkylacrylamide and / or N-vinylpyrrolidone, and (D) a photopolymerization initiator, wherein the N-alkylacrylamide comprises N,N-dimethylacrylamide or N,N-diethylacrylamide, and the blending amount of (B) relative to the total solid content of the photocurable resin composition is 30 to 70 wt %, and the blending amount of (C) relative to the total solid content of the photocurable resin composition is 3 to 18 wt %.

2. 2. The photocurable resin composition according to claim 1, wherein (B) contains an alkyl (meth)acrylate having a branched alkyl group having 10 to 24 carbon atoms.

3. 3. The photocurable resin composition according to claim 1, wherein the cured product has a relative dielectric constant of 3.3 or less at a frequency of 1 MHz.

4. An image display device using the photocurable resin composition according to any one of claims 1 to 3.

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