JP2023057206A - Photocurable resin composition - Google Patents

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 The present invention relates to a solventless photocurable resin composition suitable for laminating an image display member such as a liquid crystal and a cover member.

Acrylic resins are used in a variety of applications, taking advantage of their characteristics of transparency and rapid curing. For example, in image display displays such as smartphones and touch panels, such transparent acrylic resin is filled between the image display member such as a liquid crystal display panel or organic EL display panel that displays images and the cover panel that protects it. A technique has been developed in which the air layer between the image display member and the cover panel is eliminated by bonding them together, thereby preventing deterioration in contrast and brightness. (Patent document 1).

Such applications are also called optical bonding, and can be roughly divided into OCR (Optical Clear Resin) using a liquid resin and OCA (Optical Clear Adhesive) pre-processed into a sheet shape. In particular, since OCA has already been processed into a sheet, it is possible to precisely control the film thickness, does not require special coating to curing equipment, and can be reworked (re-applied), making it widely used. .

As a resin composition that can be used for such OCA, the applicant has previously invented a pressure-sensitive adhesive composition containing an acrylic compound having a polypropylene glycol skeleton (Patent Document 2). However, as the performance of touch panels is improved, as typified by thinning and high definition, it is essential to reduce the dielectric constant of the optical adhesive layer in order to prevent malfunction and improve response speed and sensitivity. In addition to good optical properties, sufficient adhesive strength is required to absorb the difference in coefficient of thermal expansion that accompanies bonding of dissimilar materials. There was room for improvement in terms of compatibility.

Japanese Patent Application Laid-Open No. 2005-55641 Japanese Patent Application Laid-Open No. 2020-45416

An object of the present invention is to provide a photocurable resin composition having a low dielectric constant and high adhesive strength, which can be used for a tape-shaped adhesive (OCA) for optical adhesion.

In order to solve the above problems, the invention according to claim 1 provides a photocrosslinkable polymer (A) having a benzophenone skeleton, an alkyl (meth)acrylate (B) having an alkyl group having 10 to 24 carbon atoms, and an N- Alkyl acrylamide or/and N-vinylpyrrolidone (C) and a photopolymerization initiator (D) are included, and the amount of (B) is 30 to 70% by weight based on the total solid content of (C). is 3 to 18% by weight based on the total solid content of the photocurable resin composition.

The invention according to claim 2 provides the photocurable resin composition according to claim 1, wherein the (A) is a photocrosslinkable acrylic polymer.

Further, according to the invention of claim 3, the photocurable resin according to any one of claims 1 and 2, wherein (B) contains an alkyl (meth)acrylate having a branched alkyl group having 10 to 24 carbon atoms. A composition is provided.

Further, the invention according to claim 4 provides the photocurable resin composition according to any one of claims 1 to 3, wherein the cured product has a dielectric constant of 3.3 or less at a frequency of 1 MHz.

The invention according to claim 5 provides an image display device using the photocurable resin composition according to any one of claims 1 to 4.

The resin composition of the present invention is a photocurable resin composition that can be used for pressure-sensitive adhesive tapes that require good optical properties, has a low dielectric constant, and has sufficient adhesive strength. It is useful as a material for OCA, which is the application.

The present invention will be described in detail below.

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

The photocrosslinkable polymer (A) used in the present invention has a benzophenone skeleton in the polymer component, which is excited by light irradiation and capable of abstracting hydrogen radicals. Therefore, when irradiated with light, hydrogen radicals are extracted from the polymer molecules, and a crosslinked structure is formed by bonding between the generated radicals, making it possible to form a strong film with a high molecular weight and high crosslink density, resulting in a high elongation rate. Obtainable. When compared with polymers that are not photocrosslinkable, it also has the characteristics that unreacted crosslinkable components are less likely to bleed after curing, macroscopic phase separation is less likely to occur, and transparency is less likely to decrease.

(A) is preferably an acrylic photocrosslinkable polymer. As the monomer forming the acrylic copolymer, the alkyl group preferably has 2 to 10 carbon atoms for the purpose of imparting suitable viscoelasticity to the pressure-sensitive adhesive sheet and improving wettability to the adherend. , For example, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isodecyl (meth) acrylate, etc., alone or two or more Can be used in combination. Among these, 2-ethylhexyl acrylate (hereinafter referred to as 2-EHA) is preferable because it has a low glass transition point (hereinafter referred to as Tg), is excellent in wettability with an adherend, and has a branched structure and a large molar volume.

The blending amount of (A) with respect 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. When the content is 20% by weight or more, sufficient cohesion and elongation can be ensured, and when it is 60% by weight or less, the dielectric constant can be sufficiently lowered. Commercially available products include the acResin series (trade name: manufactured by BASF Japan, acrylic type).

The alkyl (meth)acrylate (B) having an alkyl group of 10 to 24 carbon atoms used in the present invention is a reactive diluent for (A), which has a high viscosity, and at the same time lowers the dielectric constant of the cured film. Formulated to In order to lower the dielectric constant, it is considered to reduce the molecular dipole moment and increase the molar volume. is preferable because it is bulky.

(B) includes, for example, isobornyl acrylate, decyl acrylate, lauryl acrylate, tridecyl acrylate, tetradecyl acrylate, isomystyryl (meth)acrylate, isostearyl (meth)acrylate, 2-propylheptyl (meth) Acrylate, isoundecyl (meth)acrylate, isododecyl (meth)acrylate, isohexadecyl (meth)acrylate and the like can be mentioned, and can be used alone or in combination of two or more. Among these, isostearyl acrylate (hereinafter referred to as ISTA) having a t-butyl group and a large molar volume is preferred.

The blending amount of (B) with respect 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. A content of 30% by weight or more can sufficiently lower the dielectric constant, and a content of 70% by weight or less can ensure sufficient cohesion and film elongation.

The N-alkylacrylamide or/and N-vinylpyrrolidone (hereinafter referred to as NVP) (C) used in the present invention is blended for the purpose of improving adhesion to adherends. Since the hydrophilic monomer can absorb water vapor, it is effective in suppressing whitening, especially when bonding 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, N-butyl(meth)acrylamide and the like can be mentioned, and 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.

The content of (C) in the total solid content is 3 to 18% by weight, preferably 4 to 15% by weight, more preferably 5 to 12% by weight. If it is less than 3% by weight, it may not be possible to ensure sufficient adhesion to the adherend and prevent whitening. may decrease.

The photopolymerization initiator (D) used in the present invention produces radicals when irradiated with ultraviolet rays, electron beams, or the like, and the radicals trigger a polymerization reaction. general-purpose photopolymerization initiators such as Curability can be imparted over a wide wavelength range from the ultraviolet region to the visible light region by arbitrarily selecting the light absorption wavelength of the polymerization initiator. Specifically, 2,2-dimethoxy-1,2-diphenylethan-1-one as a benzyl ketal system, and 1-hydroxy-cyclohexyl-phenyl-ketone and 1-[4-(2- hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one is 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropane-1 as α-aminoacetophenone -one is an acylphosphine oxide system such as 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, either alone or two or more can be used in combination. Among these, the α-hydroxyacetophenone type, which is resistant to yellowing, is preferred.

The content of (D) 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. When the amount is 0.05 parts by weight or more, sufficient curability can be ensured, and when the amount is 5 parts by weight or less, excessive addition can be avoided and a sufficient molecular weight can be ensured even after curing. Commercially available α-hydroxyacetophenone products include Omnirad 184 and Omnirad 2959 (trade name: manufactured by IGM Resins).

The photocurable resin composition of the present invention contains, as necessary, a tackifier, a plasticizer, a photosensitizer, an antioxidant, a flame retardant, a filler, a silane coupling agent, and a coloring agent, as long as the performance is not impaired. Additives such as agents, polymerization inhibitors, and organic fine particles can be added.

Since the tackifier is a non-reactive component, it can improve the peel strength without causing curing shrinkage. For example, there are (hydrogenated) rosin ester-based resins, terpene-based resins, petroleum resins, styrene-based resins, alkylphenol-based resins, etc., which can be used alone or in combination of two or more. hereinafter referred to as hydrogenation). Among these, hydrogenated petroleum resins and hydrogenated rosin ester resins, which are colorless and transparent and have excellent compatibility with (A), (B) and (C), are preferred.

The blending amount of the tackifier with respect to the total solid content is preferably 20% by weight or less, more preferably 15% by weight or less. Sufficient peel strength can be ensured by setting it as this range. Commercially available hydrogenated petroleum resins include the Alcon series (product name: manufactured by Arakawa Chemical Industries, Ltd.), and commercially available hydrogenated rosin ester resins include the Pine Crystal series (product name: manufactured by Arakawa Chemical Industries, Ltd.). be done.

The plasticizer permeates between polymer molecules to weaken the intermolecular force of the polymer and facilitate the movement of molecular chains, thereby lowering the glass transition point of the polymer and imparting flexibility to the polymer. For example, there are aliphatic esters, alicyclic esters, phthalates, aliphatic dibasic acid esters, polyalkylene polyols, phosphate esters, polyesters, paraffins, and the like, either alone or in combination of two or more. Can be used in combination. Among these, alicyclic esters are preferred from the viewpoint of compatibility with resins.

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

INDUSTRIAL APPLICABILITY The photocurable resin composition of the present invention can be used as an OCA material for laminating an image display body such as a touch panel or a flat panel display, such as a mobile device terminal, and a cover member for protecting it. When the photocurable resin composition of the present invention is used in an OCA, the dielectric constant is low, so malfunction is unlikely to occur, and the response speed and sensitivity are high. A specific example of tape production and usage will be described below, but the tape is not limited to this, and the order of applying the adhesive and the order of laminating the films can be selected as needed.

After applying the present resin composition to a peelable PET film, the resin composition is cured by UV irradiation to form an adhesive film. The coating method is not particularly limited, and known roll coating, die coating, air knife coating, blade coating, spin coating, reverse coating, gravure coating and the like can be used. The thickness of the coating is arbitrary, and for example, 50 to 400 μm can be exemplified.

Next, release PET films with different release strengths are laminated, and then cured by irradiation with ultraviolet rays to form an adhesive sheet with a three-layer structure. The ultraviolet light used for curing uses a known light source such as a high-pressure mercury lamp, a carbon arc lamp, a xenon lamp, a metal halide lamp, an LED lamp, an electrodeless lamp, etc., and the integrated light quantity is, for example, 50 to 10,000 mJ / cm. Curing the curable composition.

The cured product of the photocurable resin composition of the present invention preferably has a dielectric constant at a frequency of 1 MHz of 3.5 or less, more preferably 3.3 or less, particularly 3.0 or less. preferable. If the relative dielectric constant is 3.5 or less, it is possible to prevent malfunction, response speed, and sensitivity problems even when used as an OCA of a touch panel.

Hereinafter, the present invention will be described in detail based on Examples and Comparative Examples, but these are specific examples and are not particularly limited to these. Unless otherwise specified, measurements were made under the conditions of room temperature of 25° C. and relative humidity of 65%. In addition, a compounding quantity shows a weight part.

Example 1
(A) is acResin UV3532 (trade name: BASF Japan Co., Ltd., 2-EHA copolymer), (B) is ISTA (trade name: Osaka Organic Chemical Industry Co., Ltd., isostearyl acrylate), and (C). DMAA (trade name: KJ Chemicals Co., dimethylacrylamide) as (D) Omnirad 184 (trade name: IGM Resins Co.) as (D) was stirred until it was uniformly dissolved in the formulation shown in Table 1. A photocurable resin composition was prepared.

Examples 2-16
In addition to the materials used in Example 1, LA (trade name: Kyoeisha Chemical Co., Ltd., lauryl acrylate) and IB-XA (trade name: Kyoeisha Chemical Co., Ltd., isobornyl acrylate) were used as (B), and (C) DEAA (trade name: KJ Chemicals Co., Ltd., diethylacrylamide) and NVP (trade name: Nippon Shokubai Co., Ltd.) as an acrylic monomer, 2-EHA (trade name: Mitsubishi Chemical Co., Ltd., 2-ethylhexyl acrylate), adhesive KE-311 (trade name: hydrogenated rosin ester resin, manufactured by Arakawa Chemical Industries, Ltd.) and Alcon P-90 (trade name: hydrogenated petroleum resin, manufactured by Arakawa Chemical Industries, Ltd.) as a property imparting agent, and DINCH as a plasticizer. (trade name: 1.2-cyclohexanedicarboxylic acid diisononyl ester manufactured by BASF Japan) was stirred until it was uniformly dissolved in the formulations shown in Tables 1 and 2, and the photocurable resin compositions of Examples 2 to 16 were prepared. prepared.

Comparative Examples 1-3
In addition to the materials used in the examples, ACMO (trade name: acryloyl morpholine manufactured by KJ Chemicals) as an acrylic monomer was stirred until it was uniformly dissolved in the formulation shown in Table 2, and photocured in Comparative Examples 1 to 3. A mold resin composition was prepared.

Preparation of sheet for evaluation On the release-treated surface of heavy release PET film E7002 (trade name: manufactured by Toyobo Co., Ltd., thickness 50 µm), a photocurable resin composition was applied to a film thickness of 200 µm, and then lightly applied. A release PET film E7006 (manufactured by Toyobo Co., Ltd., 75 μm) was laminated. Next, using a black light irradiation machine in which black lights FL15BL manufactured by NEC Corporation are arranged in parallel, irradiation is performed under the conditions of an output of 5 mW/cm ² and an integrated light amount of 300 mJ/cm ^{2 .} Using a GRANDAGE (high-pressure mercury lamp), irradiation was performed under the conditions of an output of 100 mW/cm ² and an integrated amount of light of 4000 mJ/cm ² to prepare an evaluation sheet.

Table 1

Table 2

The evaluation method was as follows.

Dielectric constant: The adhesive layer of the evaluation sheet is laminated to a thickness of 1 mm, and the relative dielectric constant at a frequency of 1 MHz is measured using an LCR meter 6440B manufactured by Wayne Kerr. A rating of up to 3.5 was rated as ◯, and a rating of greater than 3.5 was rated as x.

Peel strength: Peel off the light-peeling PET film of the evaluation sheet, attach it to easy-adhesive PET A4300 (trade name: manufactured by Toyobo Co., Ltd., 50 μm), then peel off the remaining peeling film, attach it to a white plate glass, and cut it into a width of 25 mm. Then, a test piece was prepared by autoclave treatment at 0.5 MPa and 50° C. for 30 minutes. Using a tensile tester TGI-1kN manufactured by Techno Graph, at a crosshead speed of 300mm/min, the peel strength at 180° to the white plate glass surface was measured, and less than 10N / 25mm ×, 10N to 20N / 25mm △. , more than 20 N to 30 N/25 mm was rated as ◯, and more than 30 N/25 mm was rated as ⊚.

Total light transmittance: Peel off the release PET film of the above evaluation sheet, attach white plate glass with a thickness of 1 mm to both sides of the sheet, and measure according to JISK7361-1 using a haze meter Haze-GARD2 manufactured by Toyo Seiki Seisakusho. In the evaluation, 90% or more was evaluated as ◯, and less than 90% as x.

Haze: Using the same sample as the total light transmittance, measured in accordance with JISK7361-1 using a haze meter Haze-GARD2 manufactured by Toyo Seiki Seisakusho Co., Ltd. Less than 1% was evaluated as ○, and 1% or more as x.

Evaluation results Table 3

Evaluation results Table 4

Each resin composition of Examples gave good results in all evaluations of dielectric constant, adhesive strength, total light transmittance and haze.

On the other hand, Comparative Example 1 using ACMO instead of (C) and Comparative Example 3 in which the amount of (C) exceeds the upper limit have poor optical properties, and Comparative Example 2 that does not contain (C) has adhesive strength. are low, and none of them are suitable for the present invention.

Claims (5)

A photocrosslinkable polymer (A) having a benzophenone skeleton, an alkyl (meth)acrylate (B) having an alkyl group having 10 to 24 carbon atoms, an N-alkylacrylamide or/and N-vinylpyrrolidone (C), and light and a polymerization initiator (D), wherein the amount of (B) is 30 to 70% by weight relative to the total solid content, and the amount of (C) is 3 to 18% by weight relative to the total solid content. A photocurable resin composition characterized by: 2. The photocurable resin composition according to claim 1, wherein (A) is a photocrosslinkable acrylic polymer. 3. The photocurable resin composition according to claim 1, wherein (B) contains an alkyl (meth)acrylate having a branched alkyl group with 10 to 24 carbon atoms. 4. The photocurable resin composition according to any one of claims 1 to 3, wherein the cured product has a dielectric constant of 3.3 or less at a frequency of 1 MHz. An image display device using the photocurable resin composition according to any one of claims 1 to 4.