Photocurable resin composition and optical laminate using the same

Abstract

The present invention provides a photocurable resin composition that exhibits minimal curling, low haze, and good scratch resistance even when applied as a thick film to a relatively thin substrate, and an optical laminate coated therewith. [Solution] A photocurable resin composition comprising dipentaerythritol pentaacrylate with a hydroxyl value of 100-200 mg KOH / g, nanoalumina particles, and a photopolymerization initiator, wherein the nanoalumina particles include particles with an average particle diameter of 50-150 nm.

Description

Technical Field

[0001] The present invention relates to a photocurable resin composition that is cured by active energy rays such as ultraviolet rays and an optical laminate using the same.

Background Art

[0002] Acrylic-based photocurable resins are used in many fields to impart special performance to the surfaces of plastic films and plastic molded articles. For example, a hard coat film obtained by coating on a PET (polyethylene terephthalate) film to impart high hardness is widely used as a film for touch panels and a film for molding.

[0003] However, when a photocurable resin is applied to a film as a coating agent such as a hard coat, there is a problem that the film tends to curl due to the curing shrinkage of the coating film. Such a tendency becomes more prominent as the base film becomes thinner and as the thickness of the resin film to be applied becomes thicker.

[0004] Therefore, as a hard coating agent capable of preventing such curling, a urethane (meth)acrylic composition obtained by reacting a (meth)acrylic acid adduct of dipentaerythritol having a high hydroxyl value with a polyvalent isocyanate, and a composition containing silica in a specific ratio have been proposed (Patent Document 1). However, this composition cannot be said to have a sufficiently low curing shrinkage, and curling may increase under conditions such as coating a thick film on a substrate thickness of less than 100 μm (for example, 75 μm). Also, the optical properties and scratch resistance cannot be said to be sufficient, and there is room for improvement.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

[0006] The object of the present invention is to provide a photocurable resin composition that exhibits minimal curling, low haze, and good scratch resistance even when applied as a thick film to a relatively thin substrate, and an optical laminate coated therewith. [Means for solving the problem]

[0007] To achieve the above objectives, the invention of claim 1 provides a photocurable resin composition comprising dipentaerythritol pentaacrylate (A) having a hydroxyl value of 100 to 200 mg KOH / g, nanoalumina particles (B), and a photopolymerization initiator (C), wherein (B) comprises nanoalumina particles with an average particle diameter of 50 to 150 nm.

[0008] The invention of claim 2 provides the photocurable resin composition according to claim 1, characterized in that the amount of nanoalumina particles (B) blended is 1.0 to 8.0 parts by weight per 100 parts by weight of dipentaerythritol pentaacrylate (A).

[0009] The invention of claim 3 provides an optical laminate in which a cured layer of the photocurable resin composition described in claim 1 or 2 is disposed on at least one side of a light-transmitting substrate film. [Effects of the Invention]

[0010] The photocurable resin composition of the present invention exhibits minimal curling even when applied as a thick film to a thin substrate, and also has low haze and good scratch resistance, making it useful as a coating agent for optical laminates such as hard coat films (hereinafter referred to as HC films). [Best Mode for Carrying Out the Invention]

[0011] The photocurable resin composition of the present invention comprises a high hydroxyl value dipentaerythritol pentaacrylate (A), nanoalumina particles (B), and a photopolymerization initiator (C). In this specification, (meth)acrylate encompasses both acrylate and methacrylate.

[0012] The high hydroxyl value dipentaerythritol pentaacrylate (A) used in the present invention is the main binder constituting the resin composition and can be obtained by acrylate formation by dehydration condensation reaction of dipentaerythritol and acrylic acid in the presence of a dehydration condensation catalyst, such as an acid catalyst. The hydroxyl value is 100 to 200 mgKOH / g, preferably 110 to 180 mgKOH / g, and more preferably 120 to 150 mgKOH / g. Below 100 mgKOH / g, the amount of residual hexafunctional dipentaerythritol hexaacrylate increases, leading to greater curing shrinkage and a tendency for curling, while above 200 mgKOH / g, the control of the manufacturing process becomes more complex and costs tend to increase.

[0013] The amount of (A) added relative to the total solid content is preferably 45 to 96% by weight, more preferably 50 to 95% by weight, and particularly preferably 55 to 94% by weight. A concentration of 45% by weight or more ensures sufficient scratch resistance and optical properties, while a concentration of 96% by weight or less ensures sufficient pencil hardness.

[0014] The nanoalumina particles (B) used in this invention are formulated to improve scratch resistance and pencil hardness. It is preferable that the surface is modified to improve dispersibility in (A). Examples include treatment with silane coupling agents, titanate coupling agents, aluminate coupling agents, or reactive functional groups such as (meth)acryloyl groups, vinyl groups, and epoxy groups. Among these, coating with (meth)acryloyl groups is preferred because it can firmly bond with the acryloyl groups of the binder and suppress detachment from the coating surface, thereby improving surface hardness.

[0015] The average particle size of (B) is 50 to 150 nm, preferably 60 to 130 nm, and more preferably 70 to 100 nm. If the average particle size is less than 50 nm, scratch resistance and pencil hardness may decrease, and if it exceeds 150 nm, the haze of the coating film tends to increase. The average particle size is defined as the median diameter (d=50) measured by dynamic light scattering (DLS). A commercially available example of (B) is OptisolLAA130C (product name: manufactured by SOOHYUN Hi-tech Materials, average particle size 80 nm, acrylic modified), etc.

[0016] The amount of (B) is 1.0 to 8.0 parts by weight per 100 parts by weight of (A), preferably 1.5 to 7.0 parts by weight, and more preferably 2.0 to 6.0 parts by weight. A minimum of 1.0 part by weight ensures sufficient scratch resistance and pencil hardness, while a minimum of 8.0 parts by weight ensures sufficiently low haze.

[0017] 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.

[0018] Among these, it is preferable to include an α-hydroxyacetophenone-based compound that is less prone to yellowing, and commercially available products include Omnirad 184 and 2959 (product name: manufactured by IGM Resins). The amount of compounding with respect to 100 parts by weight of the radical polymerizable component of (C) above is preferably 0.5 to 10 parts by weight, and more preferably 3 to 8 parts by weight.

[0019] The composition of the present invention may optionally contain a binder resin, reactive diluent, leveling agent, adhesion promoter, antioxidant, bluing agent, pigment, defoamer, thickener, precipitation inhibitor, antistatic agent, antifogging agent, slip agent, antibacterial agent, wax, matting agent, hydrophilic agent, water repellent agent, ultraviolet absorber, etc., to the extent that it does not impair performance.

[0020] As the binder resin mentioned above, (meth)acrylate compounds are preferred because they have good reactivity with (A). Examples include urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, polycarbonate (meth)acrylate, acrylic (meth)acrylate, diene (meth)acrylate, etc., which can be used alone or in combination of two or more.

[0021] When coating a substrate film with the composition of the present invention, the solid content is diluted to 10-70% with a solvent to improve the coatability to the substrate. Examples of solvents include alcohol-based solvents such as ethanol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol, and diacetone alcohol; ketone-based solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ester-based solvents such as ethyl acetate and butyl acetate; ether-based solvents such as propylene glycol monomethyl ether (hereinafter referred to as PGM), diethyl ether, and diisopropyl ether; and hydrocarbon-based solvents such as cyclohexane and methylcyclohexane. These can be used individually or in combination of two or more. Among these, PGM and MEK are preferred from the viewpoint of solubility and coatability.

[0022] Examples of the light-transmissive substrate film for applying the composition of the present invention include polyester films, triacetyl cellulose films, polycarbonate films, polysulfone films, nylon films, cycloolefin films, acrylic films, polyimide films, ABS films, polyolefin films, PVC films, PVA films, etc. Among them, a biaxially stretched polyester film is preferably used from the viewpoints of weather resistance, processability, dimensional stability, etc. The film thickness can be exemplified by 25 μm to 500 μm. However, since the composition of the present invention has a small curing shrinkage, it can exhibit its characteristics particularly in the case of a thin substrate with a film thickness of less than 100 μm.

[0023] For the purpose of improving the adhesion to the photocurable resin composition, the light-transmissive substrate film can be subjected to surface treatment such as primer treatment, sandblasting method, solvent treatment method for surface roughening, or surface oxidation treatment such as corona discharge treatment, chromic acid treatment, ozone-ultraviolet irradiation treatment, etc.

[0024] The method for applying the composition of the present invention is not particularly limited and can be formed by known coating methods such as spray coating, roll coating, die coating, air knife coating, blade coating, spin coating, reverse coating, gravure coating, wire bar, etc. or printing methods such as gravure printing, screen printing, offset printing, inkjet printing, etc. The coating film thickness can be exemplified by 1 μm to 30 μm when dried. However, since the composition of the present invention has a small curing shrinkage, it can exhibit its characteristics particularly when the coating thickness is 10 μm or more.

[0025] After applying the composition of the present invention, it is dried at 60-120°C and cured using an ultraviolet irradiation device. Suitable 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, LED lamps, and electrodeless ultraviolet lamps. The irradiation atmosphere may be air or an inert gas such as nitrogen or argon. Furthermore, heating the coating film with a back roll or an IR heater during ultraviolet irradiation can further improve curing properties. The irradiation conditions are set to an irradiation intensity of 500 mW / cm². 2 ~3000mW / cm 2 Exposure dose: 50-400 mJ / cm² 2 Examples are given, but this is not an exhaustive list.

[0026] The present invention will be described in detail below with reference to examples and comparative examples, but these are merely examples and the invention is not limited to them. Unless otherwise stated, measurements were taken under conditions of 25°C and 65% relative humidity. The amounts of ingredients are expressed in parts by weight on a solid content basis.

[0027] Examples 1-4 As (A), M-3545 (product name: manufactured by Toagosei Co., Ltd., dipentaerythritol pentaacrylate, hydroxyl value 120 mg KOH / g) was used, as (B), Optisol LAA130C (product name: manufactured by SOOHYUN Hi-tech Materials Co., Ltd., average particle size 80 nm, acryloyl group modified, solids content 30%) was used, as (C), Omnirad2959 (product name: manufactured by IGM Resins Co., Ltd., α-hydroxyacetophenone type) was used, and as the other binder resin, RUA-076MG-90PGM (product name: manufactured by Asia Industries Co., Ltd., hexafunctional urethane acrylate) was used. The mixtures were stirred until uniformly dissolved and dispersed according to the formulations shown in Table 1, and then PGM was added and the mixture was diluted and stirred until the solids content reached 40%, to obtain the photocurable resin compositions of Examples 1 to 4.

[0028] Comparative Examples 1-7 In addition to the materials used in the examples, KAYARAD DPHA (product name: manufactured by Nippon Kayaku Co., Ltd., a mixture of dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate, hydroxyl value 50 mg KOH / g), M-933 (product name: manufactured by Toagosei Co., Ltd., high hydroxyl value pentaerythritol triacrylate), and PET-30 (product name: manufactured by Nippon Kayaku Co., Ltd., a mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate) were used as binder resins, and ALM was used as nanoalumina. IBK30WT%-M47 (product name: manufactured by CIK Nanotech, average particle size 30 nm, acryloyl group modified, solid content 30%) and MEK-AC-5140Z (product name: manufactured by Nissan Chemical Industries, average particle size 85 nm, methacryloyl group modified, solid content 40%) as nanosilica were mixed in the formulations described in Tables 1 and 2 until uniformly dissolved and dispersed. Further dilution and mixing were performed by adding PGM to bring the solid content to 40% to obtain the photocurable resin compositions of Comparative Examples 1 to 7.

[0029] Table 1 JPEG2026054317000001.jpg94135

[0030] Table 2 JPEG2026054317000002.jpg106135

[0031] The evaluation method was as follows:

[0032] HC film creation The photocurable resin compositions prepared in the examples and comparative examples were applied to U403 (product name: Toray Industries, Inc., thickness 75 μm, PET) to a dry film thickness of 10 μm, dried at 80°C for 1 minute, and then irradiated with a FUSION electrodeless lamp (H bulb) at an intensity of 600 mW / cm². 2 , exposure amount 150mJ / cm 2 The film was cured under the condition of (365nm) to obtain an HC film.

[0033] Coatability: The surface appearance of the HC film was visually inspected. A score of ○ was given if there were no obvious defects such as repelling or uneven coating, even if some defects were present. A score of × was given if there were obvious defects such as repelling or uneven coating.

[0034] Haze: Measured using Haze-GARD2 manufactured by Toyo Seiki Seisakusho Co., Ltd., in accordance with JIS K7361-1. Less than 1.0% was marked with ○, and 1.0% or more was marked with ×.

[0035] Scratch resistance: Using an abrasion testing machine manufactured by Toyo Seiki Co., Ltd., a 1000g load was placed on steel wool #0000 with a contact area of ​​10mm square in diameter, and the machine was run 100 times back and forth at a reciprocating speed of 100 times / minute. Visual inspection determined that no scratches occurred (○), slight scratches occurred (△), and numerous scratches occurred (×).

[0036] 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 3H or higher was marked with ○, and a score of 2H or lower was marked with ×.

[0037] Curl: HC film was cut to 100mm x 100mm, the center was fixed to the mounting surface, and the height of the curl from the mounting surface at each vertex was measured. If the average of the four measured points was less than 4.0mm, it was marked as ○, and if it was 4.0mm or more, or if it was curled and could not be measured, it was marked as ×.

[0038] Evaluation results The evaluation results are shown in Tables 3 and 4.

[0039] Table 3 JPEG2026054317000003.jpg84135

[0040] Table 4 JPEG2026054317000004.jpg96135

[0041] The examples showed no problems in terms of coatability, haze, scratch resistance, pencil hardness, and curl, and were all good.

[0042] On the other hand, Comparative Example 1, which did not contain (B), Comparative Example 4, which used M-933 instead of (A), and Comparative Example 6, which used nanoalumina with a small average particle size instead of (B), exhibited inferior scratch resistance and pencil hardness. Comparative Example 2, which used urethane acrylate instead of (A), and Comparative Example 5, which used PET-30, exhibited high haze. Furthermore, Comparative Example 3, which used KAYARAD DPHA instead of (A), exhibited inferior haze and curl, and Comparative Example 7, which used nanosilica instead of (B), exhibited inferior scratch resistance. All of these were unsuitable for the present invention.

Claims

1. A photocurable resin composition comprising dipentaerythritol pentaacrylate (A) having a hydroxyl value of 100 to 200 mg KOH / g, nanoalumina particles (B), and a photopolymerization initiator (C), wherein (B) contains nanoalumina particles with an average particle size of 50 to 150 nm.

2. The photocurable resin composition according to claim 1, characterized in that the amount of nanoalumina particles (B) is 1.0 to 8.0 parts by weight per 100 parts by weight of dipentaerythritol pentaacrylate (A).

3. An optical laminate in which a cured layer of the photocurable resin composition according to claim 1 or 2 is disposed on at least one side of a light-transmitting substrate film.

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