Solvent-free hard coat resin composition and optical laminate comprising the same

Abstract

To provide a solvent-free hard coat resin composition having stable coating performance, excellent curing properties, and superior anti-blocking capability, and an optical laminate comprising a cured layer of the composition.SOLUTION: A solvent-free hard coat resin composition comprises a polyfunctional (meth)acrylate derived from pentaerythritol, a monofunctional (meth)acrylate containing a vinyl ether group, nanosilica, and a photopolymerization initiator, wherein the content of the nanosilica is 0.5 to 8.0 wt.% based on the total solid content.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a solvent-free hard coat resin composition that does not contain a diluent solvent, and an optical laminate using the same. [Background technology]

[0002] Acrylic photocurable resins are used in many fields to impart functionality to the surfaces of plastic films and plastic moldings. For example, hard coat (hereinafter referred to as HC) films, which are applied to PET (polyethylene terephthalate) films to impart high hardness, are used in large quantities as films for touch panels and molding films.

[0003] These HC resin compositions generally have high viscosity, and are often diluted with solvents to improve coatability. However, these solvent-containing compositions volatilize the solvent after application, placing a heavy burden on the environment and consuming a large amount of energy in the drying oven. Furthermore, compared to solvent-based compositions, solvent-free types have a lower penetration and swelling effect on the adhesive layer formed to promote adhesion, which tends to result in insufficient adhesion.

[0004] As a solventless curable composition for HC that addresses these issues, for example, a composition containing a urethane (meth)acrylate structure with a specific structure, a polyfunctional compound, a monofunctional compound, a silicone compound, and a photoradical initiator has been proposed (Patent Document 1). The use of such solventless HC agents has made it possible to solve the problems of environmental impact and energy loss during drying. However, there are advantages and disadvantages to the various properties required for HC resin compositions, such as storage stability, coatability, and curability, and for HC films, such as substrate adhesion and scratch resistance. There have been few compositions that can achieve a good balance of these physical properties. Furthermore, in recent years, anti-blocking properties have also become a requirement, and there is room for improvement in order to meet these performance requirements. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] WO2009 / 050957 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides an HC resin composition that is solvent-free yet has stable coatability, good curability, and excellent anti-blocking properties (hereinafter referred to as AB properties), and an optical laminate having a cured layer formed thereon. [Means for solving the problem]

[0007] In order to achieve the above object, the invention described in claim 1 provides a solventless hard coat resin composition comprising a polyfunctional (meth)acrylate (A) derived from pentaerythritol, a vinyl ether group-containing monofunctional (meth)acrylate (B), nanosilica (C), and a photopolymerization initiator (D), wherein the blending amount of (C) is 0.5 to 8.0 wt % based on the total solid content.

[0008] The invention according to claim 2 provides the solventless hard coat resin composition according to claim 1, characterized in that (D) contains an α-hydroxyacetophenone-based compound.

[0009] The invention of claim 3 provides the solventless hard coat resin composition of claim 1, characterized in that the average primary particle size of (C) is 50 to 500 nm.

[0010] The invention according to claim 4 provides an optical laminate in which a cured layer of the solventless hard coat resin composition according to any one of claims 1 to 3 is formed on at least one surface of a plastic substrate. [Effects of the Invention]

[0011] The resin composition of the present invention is solvent-free, yet has good coatability and stable appearance, and the cured product thereof has excellent AB properties, making it useful as a solvent-free HC resin composition for use in HC films, etc. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below.

[0013] The composition of the present invention comprises a polyfunctional (meth)acrylate (A) derived from pentaerythritol, a vinyl ether group-containing (meth)acrylate (B), nanosilica (C), and a photopolymerization initiator (D). In this specification, the term "(meth)acrylate" encompasses both acrylate and methacrylate. The term "solvent-free" refers to the absence of intentionally blending a solvent into the HC resin composition for the purpose of dilution, but does not refer to the absence of even trace amounts of volatile components contained in each component of the HC resin composition. The term "solvent-free" refers to a solvent content of 5% by weight or less, typically 1% by weight or less.

[0014] The polyfunctional (meth)acrylate (A) derived from pentaerythritol used in the present invention is a compound having a structure in which two or more OH groups of pentaerythritol are substituted with (meth)acryloyloxy groups, and is a monomer with very good curability. It may be modified with a (poly)alkylene oxide such as (poly)ethylene oxide or (poly)propylene oxide.

[0015] Regarding the number of functional groups in (A), it is preferable to substitute as many OH groups of pentaerythritol with (meth)acryloyloxy groups as possible, since this increases the melting point and facilitates crystallization due to intermolecular forces between carbon atoms as esterification proceeds. Specifically, trifunctional or more functional groups are preferred, and tetrafunctional groups are even more preferred. Examples include pentaerythritol triacrylate and pentaerythritol tetraacrylate.

[0016] The synthesis method of (A) can be esterification of pentaerythritol with acrylic acid. Strictly speaking, this results in a mixture of four compounds: pentaerythritol acrylate, pentaerythritol diacrylate, pentaerythritol triacrylate (hereinafter referred to as PET3A), and pentaerythritol tetraacrylate (hereinafter referred to as PET4A). However, most of the compounds are primarily composed of PET3A and PET4A. The applicant discovered that by selecting a (meth)acrylate derivative of pentaerythritol as the binder for the solventless HC resin composition, it is possible to ensure excellent AB properties as well as good coatability and curability.

[0017] The blending amount of (A) is preferably 40 to 65% by weight, more preferably 43 to 60% by weight, based on the total solid content. By making it 40% by weight or more, sufficient curability can be ensured, and by making it 65% by weight or less, sufficient storage stability can be ensured.

[0018] The vinyl ether group-containing (meth)acrylate (B) used in the present invention is blended as a reactive diluent for diluting (A). It is a monomer having both a cationically polymerizable vinyl ether group, which is free from polymerization inhibition by oxygen and has good dilution properties, and a (meth)acryloyl group, which has good compatibility and reactivity with (A), and can be represented, for example, by the following general formula (1): CH2=CR 1 -CO-(OCHR 2 CHR 3 )nO-CH=CHR 4 ···(1) (In the formula, R1 and R4 represent a hydrogen atom or a methyl group, R2 and R3 each independently represent a hydrogen atom or an organic residue, and n represents an integer of 2 or greater.)

[0019] Examples of (B) include 2-(2-vinyloxyethoxy)ethyl (meth)acrylate, 2-(2-vinyloxyisopropoxy)ethyl (meth)acrylate, 2-(2-vinyloxyethoxy)propyl (meth)acrylate, 2-(2-vinyloxyisopropoxy)propyl acrylate, and 2-(2-vinyloxyethoxyethoxy)ethyl (meth)acrylate, which can be used alone or in combination of two or more. Among these, 2-(2-vinyloxyethoxy)ethyl acrylate is preferred because of its particularly low viscosity, high dilution ability, and excellent curability.

[0020] The blending amount of (B) is preferably 25 to 50% by weight, more preferably 30 to 45% by weight, and particularly preferably 35 to 43% by weight, based on the total solid content. By making it 25% by weight or more, good coating properties and storage stability can be ensured, and by making it 50% by weight or less, sufficient curing properties can be ensured.

[0021] The nanosilica (C) used in the present invention is formulated for the purpose of imparting AB properties. (C) is preferably hydrophobic and organically surface-treated, as this provides good dispersibility. Organic surface treatment involves introducing organic groups onto the silica particle surface, such as treatment with a silane coupling agent. Examples of organic groups include dimethylsilyl, trimethylsilyl, dimethylpolysiloxane, dimethylsiloxane, aminoalkylsilyl, alkylsilyl, and methacrylsilyl groups.

[0022] The average primary particle size of (C) is preferably 50 to 500 nm, more preferably 80 to 300 nm, and particularly preferably 100 to 200 nm. Unlike solvent-diluted HC agents, the so-called lifting effect, in which silica rises to the surface as the solvent evaporates, cannot be expected when using a solvent-free agent. Therefore, selection of particle size is extremely important. A particle size of 50 nm or more can be expected to impart AB properties, while a particle size of 500 nm or less can ensure sufficient optical properties. The average primary particle size is the D50 value measured in IPA solvent using dynamic light scattering in accordance with ISO 22412:2017.

[0023] The blending amount of (C) is 0.5 to 8.0% by weight, preferably 0.8 to 7.0% by weight, and more preferably 1.0 to 6.0% by weight, based on the total solid content. If it is less than 0.5% by weight, sufficient AB properties may not be ensured, and if it exceeds 8.0% by weight, sufficient optical properties such as total light transmittance may not be ensured.

[0024] 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-hydroxy-cyclohexyl-phenyl-ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, and 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one; α-aminoacetophenones include 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one; and acylphosphine oxides include 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, which can be used alone or in combination of two or more.

[0025] Among the (D) compounds, it is preferable to use an α-hydroxyacetophenone compound because of its excellent curing properties. Furthermore, among the α-hydroxyacetophenone compounds, it is even more preferable to use 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one (d1). Examples of commercially available products of (d1) include Omnirad 127 (trade name: manufactured by IGM Resins).

[0026] While most conventional photocleavage polymerization initiators have only one cleavage site per molecule, (d1) has two cleavage sites. Therefore, after cleavage by active energy ray irradiation, it can react with the polymerizable monomer at multiple sites, resulting in excellent reaction curing properties and a high molecular weight for the polymerization reaction product. As a result, unreacted monomers that reduce hard coat properties and plasticizer components such as dimers and trimers that have completed polymerization in a low molecular weight state are less likely to remain in the cured film, resulting in stable improvements in SW resistance, etc.

[0027] The amount of (D) is preferably 2 to 10 parts by weight, more preferably 3 to 8 parts by weight, per 100 parts by weight of the photopolymerizable component. By adding 2 parts by weight or more, sufficient curability can be ensured, and by adding 10 parts by weight or less, sufficient solubility can be ensured without excessive addition.

[0028] Furthermore, if necessary, the present composition may contain additives such as reactive diluents, surface conditioners, light stabilizers, polymerization inhibitors, wetting agents, antioxidants, curing aids, silane coupling agents, plasticizers, sensitizers, antifoaming agents, flame retardants, organic fine particles, colorants such as pigments, dyes and coloring agents, antibacterial agents and antiviral agents, within the scope of not impairing the performance.

[0029] Examples of substrate films onto which the HC resin composition of the present invention is applied include triacetyl cellulose films, PET films, polyimide films, polyethylene naphthalate films, polyvinyl chloride films, polystyrene films, acrylic films, polycarbonate films, cycloolefin (co)polymer films, polyolefin films, and composite films thereof. Among these, biaxially stretched PET films are preferred because of their good overall balance of price, processability, dimensional stability, etc.

[0030] The method for applying the HC resin composition of the present invention is not particularly limited, and for flat objects such as films and sheets, known coating methods such as spray coating, roll coating, die coating, air knife coating, blade coating, spin coating, reverse coating, gravure coating, and wire bar coating, or gravure printing, screen printing, offset printing, and inkjet printing can be used, while spray coating is useful for objects that are not flat but have an uneven surface such as molded products. This method is also excellent as a method that can coat a large area even on flat objects without requiring a large capital investment.

[0031] The viscosity of the HC resin composition of the present invention is preferably 10 to 100 mPs·s, more preferably 10 to 30 mPs·s. A viscosity of 10 mPs·s or more ensures sufficient coatability, while a viscosity of 100 mPs·s or less ensures good leveling properties.

[0032] The coating thickness of the HC resin composition of the present invention when dried can be, for example, 0.5 μm to 50 μm, but is not limited to this. However, when coating onto a film, the thickness is preferably 1 to 10 μm to prevent warping due to cure shrinkage.

[0033] After coating, the HC resin composition of the present invention is cured using an ultraviolet irradiator. Examples of light sources for ultraviolet irradiation include low-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, carbon arc lamps, xenon lamps, metal halide lamps, electrodeless ultraviolet lamps, and LED lamps. The curing conditions are 100 mW / cm. 2 ~3000mW / cm 2 The irradiation intensity is 50 to 2,000 mJ / cm as the cumulative light amount. 2 The irradiation atmosphere may be air or an inert gas such as nitrogen or argon, but curing in an inert gas is preferred to prevent curing inhibition due to oxygen.

[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 present invention. The blend amounts are in parts by weight, and unless otherwise specified, measurements were taken at room temperature of 25°C and a relative humidity of 65%.

[0035] Examples 1 to 4 The HC resin compositions of Examples 1 to 4 were prepared by using A-TMM-3L (product name: manufactured by Shin-Nakamura Chemical Co., Ltd., a mixture of PET3A and PET4A) as (A), VEEA (product name: manufactured by Nippon Shokubai Co., Ltd., 2-(2-vinyloxyethoxy)ethyl acrylate) as (B), Nanosilica A (average primary particle size 150 nm, hydrophobic, tripropylene glycol diacrylate dispersion, inorganic content 30% by weight) as (C), and Omnirad127 (product name: manufactured by IGM Resins, α-hydroxyacetophenone-based, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one) as (D) in the formulations shown in Table 1 and stirring until uniformly dissolved.

[0036] Comparative Examples 1 to 4 In addition to the materials used in the examples, SS50F (product name: manufactured by Tosoh Silica Corporation, average particle size 1.2 μm, hydrophobic) was used as silica, and the HC resin compositions of Comparative Examples 1 to 4 were prepared by stirring until uniformly dissolved in the formulation shown in Table 2.

[0037] Table 1 JPEG2025139008000001.jpg84156

[0038] Table 2 JPEG2025139008000002.jpg76141

[0039] The evaluation method was as follows.

[0040] Creation of HC film for evaluation The HC resin composition prepared above was applied to U403 (product name: PET film manufactured by Toray Industries, Inc., 50 μm thick) so that the dry film thickness was 5 μm, and then the coating was applied using an electrodeless UV lamp manufactured by FUSION Co., Ltd., with an H bulb output of 600 mW / cm. 2 , cumulative light intensity 150mJ / cm 2 (365 nm) to prepare an HC film for evaluation.

[0041] Viscosity: Using a Brookfield viscometer TVB-10 manufactured by Toki Sangyo, the viscosity was measured after 1 minute at 25±1°C with rotor No. M1 and a rotation speed of 60 rpm. Less than 30 mPa·s was rated as ◎, 30 to 50 mPa·s as 〇, and more than 50 mPa·s as ×.

[0042] Coating properties: When preparing the HC film for evaluation, the appearance was visually inspected, and a good result without any coating unevenness or coating streaks was rated as ◯, a result in which the leveling was incomplete and slight coating streaks or unevenness were observed was △, and a result in which obvious coating unevenness was observed was ×.

[0043] Curability: When preparing the HC film for evaluation, the tackiness of the coating film surface immediately after UV curing was checked, and a mark of "O" was given for a completely cured film with no tackiness, and a mark of "X" was given for a tacky film or a whitened film that was not cured.

[0044] Anti-blocking property: When two HC coating surfaces were placed on top of each other and rubbed together, if they slipped, they were marked as ◯, and if they did not slip, they were marked as ×.

[0045] Total light transmittance: Measured in accordance with JIS K7361-1 using a haze meter Haze-GARD2 manufactured by Toyo Seiki Seisakusho Co., Ltd. Evaluation was made as follows: 90% or more was rated as good, and less than 90% was rated as bad.

[0046] Haze: Measured in accordance with JIS K7136 using a haze meter Haze-GARD2 manufactured by Toyo Seiki Seisakusho, Ltd. The evaluation method was as follows: less than 1.0% was rated as good, and 1.0% or more was rated as bad.

[0047] Example evaluation results Table 3 JPEG2025139008000003.jpg138161

[0048] Comparative Example Evaluation Results Table 4 JPEG2025139008000004.jpg143167

[0049] Each of the formulations in the examples was satisfactory with no problems in all respects, including viscosity, coatability, curability, AB property, total light transmittance, and haze.

[0050] On the other hand, Comparative Example 1, which did not contain (C), and Comparative Example 2, which contained a small amount of (C), were inferior in AB properties, Comparative Example 3, which contained a large amount of (C), was inferior in curability and AB properties, and Comparative Example 4, which used silica other than nanosilica, was inferior in haze, and none of the formulations were suitable for the present invention.

Claims

1. A solventless hard coat resin composition comprising: a polyfunctional (meth)acrylate (A) derived from pentaerythritol; a vinyl ether group-containing monofunctional (meth)acrylate (B); nanosilica (C); and a photopolymerization initiator (D), wherein the blending amount of (C) is 0.5 to 8.0 wt % based on the total solid content.

2. 2. The solventless hard coat resin composition according to claim 1, wherein said (D) comprises an α-hydroxyacetophenone-based compound.

3. 2. The solventless hard coat resin composition according to claim 1, wherein the average primary particle size of said (C) is 50 to 500 nm.

4. An optical laminate comprising a plastic substrate and a cured layer of the solventless hard coat resin composition according to any one of claims 1 to 3 formed on at least one surface thereof.

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