Hard coat resin composition and hard coat film using the same

Abstract

To provide a hard coat resin composition and a film which have high pencil hardness and steel wool resistance, and can withstand bending with a small radius of curvature, regardless of whether a curable layer surface faces inward or outward.SOLUTION: A hard coat resin composition contains polyfunctional urethane (meth)acrylate, hydrophobic nano-silica, and a photopolymerization initiator, wherein the nano-silica contains two kinds of nano-silica having average particle diameters of 5-30 nm and 30-80 nm, and one thereof has a reactive functional group.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a hard coat resin composition having excellent flexural resistance and a hard coat film using the same.

Background Art

[0002] Image display devices such as smartphones equipped with touch panels often have a film having a hard coat (hereinafter referred to as HC) layer with high hardness and scratch resistance disposed on the display surface to prevent damage. In recent years, as various designs of smartphones have been commercialized, in addition to the conventional optical properties and pencil hardness of HC films, new properties such as flexibility have been required.

[0003] In response to these requirements, for example, a HC laminated film composed of a top coat containing polyfunctional (meth)acrylate, a water repellent, and a silane coupling agent and not containing inorganic fine particles, and a base coat containing polyfunctional (meth)acrylate and inorganic fine particles having a particle size of 1 to 300 nm has been proposed (Patent Document 1).

[0004] By using such HC films, even in smartphones having a curved surface structure, various design constraints have been relaxed. However, there is a difference in flexural resistance depending on the laminated surface of the HC layer. When the HC layer is oriented outward rather than inward, a load is more likely to be applied, and a difference in the curvature radius at which bending is possible is likely to occur. Therefore, there has been a demand for a HC film having flexural resistance that allows for a smaller diameter, regardless of whether the HC layer is oriented inward or outward.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention aims to provide an HC resin composition and an HC film using the same, which have high pencil hardness and resistance to steel wool (hereinafter referred to as SW resistance), and which can withstand bending with a small radius of curvature, regardless of whether the hardened layer surface is facing inward or outward. [Means for solving the problem]

[0007] To solve the above problems, a polyfunctional urethane (meth)acrylate (A), hydrophobic nanosilica (B), and a photopolymerization initiator (C) are provided, wherein (B) comprises hydrophobic silica (b1) with an average particle size of 5 to 30 nm and hydrophobic silica (b2) with an average particle size of 30 to 80 nm, and either (b1) or (b2) (meth)acrylic group It is silica having the following properties: The amount of (B) mentioned above is 60-75% by weight of the total solid content. The present invention provides a hard coat resin composition characterized in that the ratio of (b1) in (B) is 15 to 45% by weight in terms of solid content.

[0008] Furthermore, the invention of claim 2 is, The amount of (A) mentioned above is 20-45% by weight relative to the total solid content. The present invention provides a hard coat resin composition according to claim 1, characterized in that it is such.

[0009] Furthermore, the invention described in claim 3 provides the hard coat resin composition according to claim 1, characterized in that it further comprises a leveling agent (D).

[0010] Furthermore, the invention described in claim 4 provides a hard coat film in which a cured layer of the hard coat resin composition described in any one of claims 1 to 3 is formed on at least one side of a plastic substrate.

[0011] Furthermore, the invention described in claim 5 provides an article using a hard coat film on which a cured layer of the hard coat resin composition described in any one of claims 1 to 3 is formed. [Effects of the Invention]

[0012] The cured product of the resin composition of the present invention has high pencil hardness and SW resistance, and can follow small bending radii regardless of whether the cured layer surface is facing inward or outward. Therefore, it is useful as an HC resin for HC films that require flexibility. [Modes for carrying out the invention]

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

[0014] The HC resin composition of the present invention comprises a polyfunctional urethane (meth)acrylate (A), hydrophobic nanosilica (B), a photopolymerization initiator (C), and a leveling agent (D). In this specification, (meth)acrylate includes both acrylate and methacrylate.

[0015] The polyfunctional urethane (meth)acrylate (A) used in the present invention is the main binder of the HC layer and has excellent SW resistance and flexural resistance due to the cohesive force of hydrogen bonds derived from the urethane bonds. The number of functional groups is preferably 2 to 8, and more preferably 2 to 4. By using 2 or more functional groups, sufficient curability and film cohesive force can be ensured, and by using 8 or fewer functional groups, curing shrinkage can be sufficiently suppressed, and a cured film with little warping can be formed.

[0016] The weight-average molecular weight (hereinafter referred to as Mw) of (A) above is preferably 500 to 10,000, more preferably 800 to 5,000, and particularly preferably 1,000 to 3,000. Setting it to 500 or higher ensures sufficient flexibility, while setting it to 10,000 or lower makes it easier to adjust the viscosity to one that offers excellent workability.

[0017] The amount of (A) is preferably 20 to 45% by weight, more preferably 22 to 35% by weight, and particularly preferably 24 to 30% by weight, relative to the total amount of solids. Sufficient SW resistance can be ensured by using 20% ​​by weight or more, and sufficient flexural resistance can be ensured by using 45% by weight or less.

[0018] The hydrophobic nanosilica (B) used in the present invention refers to silica whose surface is hydrophobized by a surface treatment agent such as a saturated fatty acid, an unsaturated fatty acid, a surfactant, a disiloxane compound, a disilazane compound, a silane coupling agent, a titanate coupling agent, etc. It is mainly blended for the purpose of improving the flexural resistance and SW resistance of the cured film, and ensuring adhesion when a sputtering layer is formed on the HC layer. (B) includes hydrophobic silica (b1) with an average particle size of 5 to 30 nm and hydrophobic silica (b2) with an average particle size of 30 to 80 nm, and is characterized in that either (b1) or (b2) has a reactive functional group. The average particle size is taken as the value calculated from the specific surface area (m 2 ) measured by the BET method.

[0019] The reactive functional group possessed by either (b1) or (b2) used in the present invention is, for example, a functional group capable of bonding to (A) by ultraviolet irradiation, etc. By chemical bonding with (A), the dropout of silica particles from the cured film can be suppressed. Specific reactive functional groups include (meth)acrylic group, epoxy group, isocyanate group, vinyl group, etc. Among these, silica having a methacrylic group, which has good reactivity with (A) and excellent availability, is preferable. When both (b1) and (b2) have reactive functional groups, the flexibility of the HC layer tends to decrease, especially when the HC layer is on the outside, the flexural property tends to decrease. Also, when neither (b1) nor (b2) has a reactive functional group, even if the flexural property is good, the SW resistance and pencil hardness tend to decrease.

[0020] The blending amount of the said (B) is preferably 50 to 75% by weight, more preferably 60 to 74% by weight, and particularly preferably 65 to 72% by weight with respect to the total solid content. By setting it at 50% by weight or more, sufficient SW resistance can be ensured, and by setting it at 75% by weight or less, sufficient optical properties and flexural resistance can be ensured.

[0021] The average particle diameter of the hydrophobic silica (b1) used in the present invention is 5 to 30 nm, preferably 8 to 20 nm, and more preferably 10 to 15 nm. If it is less than 5 nm, the pencil hardness may not be sufficient. If it exceeds 30 nm, the filling effect with (b2) decreases, and the SW resistance tends to decrease.

[0022] The blending ratio of the (b1) is 15 to 45% by weight, preferably 20 to 42% by weight, and more preferably 25 to 40% by weight, based on the total amount of the blending amount of (B). If it is less than 15% by weight, the filling effect with (b2) may not be sufficient and the pencil hardness may decrease. If it exceeds 45% by weight, sufficient SW resistance may not be ensured. Also, the blending amount based on the total amount of the solid content is preferably 10 to 35% by weight, and more preferably 15 to 30% by weight.

[0023] The average particle diameter of the hydrophobic silica (b2) used in the present invention is 30 to 80 nm, preferably 35 to 60 nm, and more preferably 40 to 50 nm. If it is less than 30 nm, the filling effect with (b2) decreases, and the SW resistance tends to decrease. If it exceeds 80 nm, it may affect optical properties such as total light transmittance and haze.

[0024] The blending amount of the (b2) is preferably 55 to 85% by weight, and more preferably 58 to 80% by weight, based on the total amount of the blending amount of (B). By setting it to 55% by weight or more, sufficient SW resistance can be ensured. By setting it to 85% by weight or less, sufficient optical properties can be ensured. Also, the blending amount based on the total amount of the solid content is preferably 30 to 65% by weight, and more preferably 40 to 60% by weight.

[0025] The photopolymerization initiator (C) used in this invention generates radicals upon irradiation with ultraviolet light or electron beams, and these radicals trigger the polymerization reaction. General-purpose photopolymerization initiators such as benzyl ketal, acetophenone, and phosphine oxide can be used. By arbitrarily selecting the light absorption wavelength of the polymerization initiator, curability can be imparted over a wide wavelength range from the ultraviolet region to the visible light region. Specifically, examples include 2,2-dimethoxy-1,2-diphenylethane-1-one as a benzyl ketal, 1-hydroxycyclohexyl-phenyl-ketone and 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane-1-one as α-hydroxyacetophenones, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropane-1-one as an α-aminoacetophenone, and 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide as acylphosphine oxides, which can be used individually or in combination of two or more.

[0026] Among these, it is preferable to include an α-hydroxyacetophenone-based compound that is less prone to yellowing, and commercially available examples include Omnirad 127, 184, and 2959 (product name: manufactured by IGM Resins). The amount of (C) added per 100 parts by weight of radical polymerizable component is preferably 0.5 to 10 parts by weight, and more preferably 3 to 8 parts by weight.

[0027] In the present invention, it is preferable to further incorporate a leveling agent (D). (D) is added for the purpose of stabilizing the coating appearance of the composition with a high density of nanosilica. A polysiloxane-based agent that can homogenize large surface tension differences on the coating surface is preferred, such as polyalkyl-modified siloxane, polyaryl-modified siloxane, polyalkylaryl-modified siloxane, and polyether-modified siloxane. It is also preferable that the agent has reactive functional groups that do not easily bleed from the cured film, and in particular, polydimethylsiloxane having (meth)acrylic groups that have good compatibility and reactivity with (A) is preferred.

[0028] The amount of (D) is preferably 0.05 to 3 parts by weight, and more preferably 0.1 to 1 part by weight, per 100 parts by weight of the radical polymerization component. Furthermore, relative to the total solid content, it is preferably 0.03 to 0.3% by weight, and more preferably 0.05 to 0.2% by weight. By keeping it within this range, excessive addition is avoided, wettability with the substrate is ensured, and a stable coating appearance can be secured.

[0029] Furthermore, the composition for forming the HC layer of the present invention may contain additives such as reactive diluents, antioxidants, ultraviolet absorbers, infrared absorbers, sensitizers, flame retardants, organic fine particles, dispersants, silane coupling agents, defoamers, antistatic agents, antibacterial agents, antiviral agents, polymerization inhibitors, colorants such as pigments, dyes, and dyes, and plasticizers, to the extent that they do not impair performance.

[0030] The resin composition forming the hard coat layer of the present invention may be diluted with a solvent to a solid content of 10-70% to improve its coatability on transparent substrate films. Examples of solvents include alcohol-based solvents such as ethanol, n-propyl alcohol, isopropyl alcohol (hereinafter IPA), n-butyl alcohol, isobutyl alcohol, and diacetone alcohol; ketone-based solvents such as acetone, methyl ethyl ketone (hereinafter MEK), methyl isobutyl ketone, and cyclohexanone; ester-based solvents such as methyl acetate, butyl acetate, and propylene glycol monomethyl ether acetate; and ether-based solvents such as propylene glycol monomethyl ether (hereinafter PGM), diethyl ether, and diisopropyl ether. These can be used individually or in combination of two or more. Among these, MEK and PGM, which have good compatibility with (A) and (D), are preferred.

[0031] Examples of plastic substrates to which the hard coat resin of the present invention is applied include polyimide film, polyethylene terephthalate (PET) film, polyethylene naphthalate film, polyvinyl chloride film, polystyrene film, acrylic film, polycarbonate film, cycloolefin (co)polymer film, polyolefin film (PP, PE, etc.), and composite films thereof. Among these, polyimide film is preferred due to its good flexibility, and biaxially oriented PET film is preferred due to its good overall balance of price, processability, and dimensional stability.

[0032] The thickness of the aforementioned plastic substrate can be determined appropriately depending on the application. If it is too thin, the strength will be insufficient, and if it is too thick, the bending properties will deteriorate. Therefore, a thickness of 30 μm to 200 μm is exemplified, but there is no problem even if it is less than 30 μm or more than 200 μm.

[0033] The aforementioned plastic substrate can be subjected to surface treatments such as primer treatment, corona treatment, surface roughening treatment by sandblasting or solvent treatment, chromic acid treatment, or surface oxidation treatment by ozone or ultraviolet irradiation treatment, in order to improve adhesion with the HC resin.

[0034] Known methods such as the bar coater method, applicator method, curtain coater method, roll coater method, gravure coater method, reverse coater method, comma coater method, lip coater method, and die coater method can be applied to coat the HC resin composition of the present invention onto a plastic substrate.

[0035] After applying the HC resin composition of the present invention, the solvent is evaporated by drying at 60-120°C, and then cured using an ultraviolet irradiation device. The ultraviolet irradiation condition is 500 mW / cm². 2 ~3,000 mW / cm² 2 With this irradiation intensity, the integrated light dose is 100 mJ / cm². 2 ~2,000 mJ / cm 2Examples include the following. When the coating film thickness is less than 1 μm, it is preferable to purge with nitrogen to prevent curing inhibition by oxygen. As a light source, known light sources such as high-pressure mercury lamps, medium-pressure mercury lamps, low-pressure mercury lamps, metal halide lamps, xenon lamps, LED lamps, and electrodeless ultraviolet lamps can be used.

[0036] The present invention will be described in detail below based on examples and comparative examples, but these are merely examples and are not limiting. Unless otherwise stated, measurements were taken under conditions of 25°C and 65% relative humidity. The amounts of ingredients are shown in parts by weight on a solid content basis.

[0037] Examples 1-5 (A) is a trifunctional urethane acrylate (referred to as Ureac) (Mw1700), and (b1) is MEK-ST (product name: manufactured by Nissan Chemical Corporation, average particle size 10-15 nm, solids content 30%, MEK dispersion, hydrophobic silica without reactive functional groups) and PGM-AC-2140Y (product name: manufactured by Nissan Chemical Corporation, average particle size 10-15 nm nanosilica, solids content 40%, PGM dispersion, containing acryloyl groups). Hydrophobic silica was used as (b2) PGM-AC-4130Y (product name: manufactured by Nissan Chemical Corporation, average particle size 40-50 nm, solid content 32%, PGM dispersion, hydrophobic silica containing acryloyl groups) and MEK-ST-L (product name: manufactured by Nissan Chemical Corporation, average particle size 40-50 nm, solid content 30%, MEK dispersion, hydrophobic silica without reactive functional groups), as (C) Omnirad2959 (product name: manufactured by IGM Resins, α-hydroxyacetophenone type), and as (D) BYK-UV3576 (product name: manufactured by Bic Chemie, active ingredient 40%, polydimethylsiloxane-modified polyfunctional acrylate, diluted tripropylene glycol diacrylate), with PGM as the solvent. The mixture was stirred until uniformly dissolved and dispersed according to the formulations shown in Table 1 to prepare the HC resin compositions of Examples 1 to 5.

[0038] Comparative Examples 1-4 In addition to the materials used in the examples, tetrafunctional ethylene oxide-modified diglycerin acrylate (denoted as EO-modified DGTA) was used as a binder, and the mixture was stirred until it was uniformly dissolved and dispersed according to the formulations shown in the table to prepare the HC resin compositions of Comparative Examples 1 to 4.

[0039] Table 1 JPEG0007887311000001.jpg112162

[0040] Table 2 JPEG0007887311000002.jpg110136

[0041] Test film A PET film U403 (product name: manufactured by Toray Industries, Ltd., thickness 125 μm) was coated with an HC resin composition to a dry film thickness of 5 μm. After drying in a constant temperature oven at 80°C for 1 minute, it was heated with an electrodeless lamp at an output of 1,200 mW / cm². 2 The HC layer was formed by irradiating with ultraviolet light to achieve an integrated light intensity of 200 mJ, and test films for the examples and comparative examples were prepared.

[0042] The evaluation method was as follows:

[0043] Total light transmittance: Measured using a Haze-GARD2 haze meter manufactured by Toyo Seiki Seisakusho in accordance with JIS K7361-1, with ○ indicating 90% or higher and × indicating less than 90%.

[0044] Haze: Measured using a Haze-GARD2 haze meter manufactured by Toyo Seiki Seisakusho in accordance with JIS K7361-1. Less than 1.0% was marked with ◎, 1.0-1.2% with ○, and more than 1.2% with ×.

[0045] Pencil hardness: In accordance with JIS K5600-5-4 (1999 edition), the hardness was measured using a pencil scratch coating hardness tester (model P) manufactured by Toyo Seiki Seisakusho Co., Ltd. with a load of 750g. A score of 2H or higher was marked with ○, and a score of less than 2H was marked with ×.

[0046] SW resistance test: Using a flat abrasion tester manufactured by Toyo Seiki Co., Ltd., a 50g load was placed on a 10mm x 10mm steel wool #0000 sheet, and the sheet was run 10 times back and forth at a reciprocating speed of 30 times / minute. Visual inspection revealed that 5 or fewer scratches were marked with ◎, 5 to 10 scratches with ○, and 10 or more scratches with ×.

[0047] Flexural Test: Using a cylindrical mandrel tester PF-5710 manufactured by Vic Gardner, a 120mm x 30mm test film was bent 180°, and the diameter at which no cracks occurred was measured. The evaluation method was as follows: ○ if the radius diameter of the HC surface was 2mm on both the inner (inward fold) and outer (outward fold) sides, and × if either side exceeded 2mm.

[0048] Evaluation results Table 3 JPEG0007887311000003.jpg124146

[0049] Evaluation results Table 4 JPEG0007887311000004.jpg129129

[0050] Each HC film in the examples obtained good results in all evaluation items, including total light transmittance, haze, pencil hardness, SW test, and bending test.

[0051] On the other hand, Comparative Example 1, which had a high proportion of (b1), showed poor SW resistance in the SW test, and Comparative Example 2, in which neither (b1) nor (b2) had reactive functional groups, showed poor pencil hardness and SW resistance. Furthermore, Comparative Example 3, in which both (b1) and (b2) had reactive functional groups, and Comparative Example 4, which did not use urea, showed poor bending test results, and all of them were unsuitable for the present invention.

Claims

1. A hard coat resin composition comprising a polyfunctional urethane (meth)acrylate (A), hydrophobic nanosilica (B), and a photopolymerization initiator (C), wherein (B) comprises hydrophobic silica (b1) having an average particle size of 5 to 30 nm and hydrophobic silica (b2) having an average particle size of 30 to 80 nm, and either (b1) or (b2) is silica having a (meth)acrylic group, the amount of (B) blended is 60 to 75% by weight of the total solid content, and the ratio of (b1) in (B) is 15 to 45% by weight on a solid content basis.

2. The hard coat resin composition according to Claim 1, characterized in that the amount of (A) is 20 to 45% by weight with respect to the total amount of solids.

3. The hard coat resin composition according to claim 1, further characterized by containing a leveling agent (D).

4. A hard coat film having a cured layer of the hard coat resin composition according to any one of claims 1 to 3 formed on at least one side of a plastic substrate.

5. An article using a hard coat film on which a cured layer of the hard coat resin composition according to any one of claims 1 to 3 is formed.

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