Antireflection film

Abstract

To provide an antireflection film that, despite having a single-layer structure, exhibits low reflectance and has excellent visibility with minimal flickering and Newton rings.SOLUTION: Provided is an antireflection film in which a low refractive index layer is directly laminated on a transparent base film, wherein the low refractive index layer contains a polymerizable binder resin, hollow nano silica, solid silica, and a photopolymerization initiator, a blended amount of the hollow nano silica is 50 to 75 wt.% based on the total amount of solid content, and an average particle diameter of the solid silica is 0.8 to 4.0 μm.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an anti-reflection film having a single layer structure. [Background technology]

[0002] Anti-reflection films are widely used in image display devices such as liquid crystal displays and organic electroluminescence displays because they reduce reflection of external light sources such as fluorescent lights and provide good visibility. Anti-reflection films typically have a multi-layer structure, with a high refractive index layer on the surface of the film substrate and a low refractive index anti-reflection layer on top of that. However, this specification requires at least two coating processes, which is a major constraint in terms of low-cost production.

[0003] As a technology to address these issues, a single-layer antireflection film has been proposed in which a low refractive index layer is laminated via an easy-adhesion layer on a transparent substrate film (Patent Document 1). For example, a composition containing hollow silica and a polymerizable binder has been disclosed as the low refractive index layer used in this film, and the film is characterized by a single-layer structure that can be produced at low cost, as well as excellent adhesion to the substrate and scratch resistance.

[0004] However, in the case of high-definition displays with a significantly increased number of pixels, flickering (scintillation phenomenon) caused by diffuse reflection of image light is likely to occur, and when anti-reflection film is used inside a display, interference fringes (Newton rings) are likely to occur between overlapping films, significantly impairing image visibility. Therefore, there has been a demand for an anti-reflection film with a low reflectivity, a single-layer structure that can be reduced cost, and good visibility that is less prone to flicker and Newton rings. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2010-170089 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide an anti-reflection film that has a single layer structure but low reflectance, is less likely to cause flicker or Newton's rings, and has good visibility. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the invention of claim 1 provides an antireflection film in which a low refractive index layer is directly laminated on a transparent substrate film, wherein the low refractive index layer contains a polymerizable binder resin (A), hollow nanosilica (B), solid silica (C), and a photopolymerization initiator (D), the amount of (B) being 50 to 75 wt % of the total solid content of the low refractive index resin composition for forming the low refractive index layer, and the average particle size of (C) being 0.8 to 4.0 μm.

[0008] A second aspect of the present invention provides the anti-reflection film according to the first aspect, characterized in that the amount of (C) blended is 0.2 to 1.5% based on the total solid content of the low refractive index resin composition.

[0009] A third aspect of the present invention provides the anti-reflection film according to the first aspect, wherein the low refractive index resin composition further contains an amine-modified acrylate (E).

[0010] A fourth aspect of the present invention provides the anti-reflection film according to any one of the first to third aspects, characterized in that the low refractive index resin composition further contains a leveling agent (F). [Effects of the Invention]

[0011] The film of the present invention has a single-layer structure which is advantageous in terms of reducing costs, while having low reflection of external light sources, providing good visibility, and being less susceptible to flicker and Newton's rings, and is therefore useful as an anti-reflection film for use in image display devices and the like. BEST MODE FOR CARRYING OUT THE INVENTION

[0012] The anti-reflection hard coat film of the present invention has a configuration in which a low refractive index layer is directly laminated on a transparent substrate film. The low refractive index resin composition (hereinafter referred to as low refractive index resin composition) for forming the low refractive index layer is a composition containing a polymerizable binder resin (A), hollow nanosilica (B), solid silica (C), and a photopolymerization initiator (D). In this specification, (meth)acrylate includes both acrylate and methacrylate.

[0013] The polymerizable binder resin (A) used in the present invention disperses the hollow nanosilica (B) and solid silica (C) and is the main component that constitutes the coating. Examples of oligomers include acrylic resin binders such as urethane (meth)acrylate, epoxy (meth)acrylate, polyester (meth)acrylate, polycarbonate (meth)acrylate, acrylic (meth)acrylate, and diene (meth)acrylate, and these can be used alone or in combination of two or more.

[0014] A low molecular weight binder may be used as a component other than the oligomer. Examples include (meth)acrylates and acrylamide compounds having aliphatic, alicyclic, polyether skeleton, or functional groups such as hydroxyl groups, and these may be used alone or in combination of two or more. Regarding the number of functional groups, polyfunctionality is preferable in terms of reactivity. Examples include pentaerythritol triacrylate, pentaerythritol tetraacrylate, dipentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, dipentaerythritol hexaacrylate (hereinafter referred to as DPHA), and alkylene oxide-modified versions of these.

[0015] The amount of (A) is preferably 15 to 40% by weight, more preferably 18 to 38% by weight, and particularly preferably 20 to 35% by weight, based on the total solid content of the low refractive index resin composition. By making it 15% by weight or more, sufficient curability and abrasion resistance can be ensured, and by making it 40% by weight or less, sufficient low reflection characteristics can be ensured.

[0016] The hollow nanosilica (B) used in the present invention is blended for the purpose of lowering the refractive index of the low refractive index layer. (B) is a silica particle having internal cavities containing air with a refractive index of 1, which has the function of lowering the refractive index of the low refractive index layer while maintaining the coating strength of the layer. While the refractive index of solid silica particles is about 1.45, the refractive index of (B) decreases as the occupancy rate of the internal cavities increases, to about 1.15 to 1.40.

[0017] The average primary particle size of (B) is preferably 30 to 120 nm, more preferably 40 to 100 nm, and particularly preferably 50 to 90 nm. By setting it within this range, good dispersibility can be obtained without impairing the transparency of the low refractive index layer. In particular, a size of 50 to 90 nm can increase the void occupancy rate and lower the refractive index while ensuring a shell thickness that does not result in insufficient strength. The average particle size is the median diameter (d=50) measured by a laser diffraction / scattering method in accordance with JIS Z 8825-1.

[0018] The blending amount of (B) is 50 to 75 wt % of the total solid content of the low refractive index resin composition, preferably 55 to 72 wt %, and more preferably 57 to 70 wt %. If it is less than 50 wt %, the refractive index may not be sufficiently low, and if it exceeds 75 wt %, sufficient anti-Newton properties may not be ensured. An example of a commercially available product is Sururia 5320 (trade name: manufactured by JGC Catalysts and Chemicals, solid content 20.5%, average primary particle size 80 nm).

[0019] The solid silica (C) used in the present invention is blended for the purpose of forming irregularities on the coating surface to impart anti-Newtonian properties. The average particle size of (C) is 0.8 to 4.0 μm, preferably 1.0 to 3.5 μm, and more preferably 1.2 to 3.0 μm. If it is less than 0.8 μm, the height of the surface irregularities of the cured coating will be insufficient, and Newton rings will tend to occur more easily. If it exceeds 4.0 μm, the difference between the diameter of the surface irregularities and the size of the pixels will be small, and glare will tend to occur from this point. The average particle size was measured using a Coulter counter method.

[0020] The amount of (C) is preferably 0.2 to 1.5 wt. % of the total solids content of the low refractive index resin composition, more preferably 0.25 to 1.2 wt. %, and particularly preferably 0.3 to 1.0 wt. An amount of 0.2 wt. % or more can form surface irregularities in the cured coating, sufficiently suppressing Newton's rings, while an amount of 1.5 wt. % or less can suppress an increase in haze.

[0021] 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 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-diphenyl-phosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, and these can be used alone or in combination of two or more.

[0022] The (D) preferably contains an α-hydroxyacetophenone-based compound that is resistant to yellowing, and Omnirad127 (2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one) is particularly preferred because it is less susceptible to polymerization inhibition by oxygen. The amount of the photopolymerization initiator blended per 100 parts by weight of the radically polymerizable component in the low refractive index resin composition is preferably 5 to 20 parts by weight, more preferably 8 to 15 parts by weight.

[0023] In the present invention, it is preferable to further incorporate an amine-modified (meth)acrylate (E). (E) is a compound having at least one amino group and at least one acryloyl or methacryloyl group. It is incorporated to mitigate polymerization inhibition by oxygen during UV curing, increase the degree of cure, and improve abrasion resistance. A well-known method for avoiding curing inhibition by oxygen is exposure in an environment of inert gas such as nitrogen. However, in production processes involving high-speed transport, it is difficult to completely eliminate the effects of oxygen adhering to the exposed object. Therefore, combining this with (E) significantly improves curability. The amino group may be a primary, secondary, or tertiary amino group, but a tertiary amino group is preferred in terms of curing acceleration.

[0024] Examples of (E) include amino(meth)acrylate, amine-modified aliphatic (meth)acrylate, amine-modified polyether (meth)acrylate, amine-modified polyester (meth)acrylate, amine-modified epoxy (meth)acrylate, amine-modified urethane (meth)acrylate, etc., which can be used alone or in combination of two or more. Among these, amine-modified polyether (meth)acrylate is preferred because of its high reactivity.

[0025] The number of (meth)acryloyl groups in (E) is preferably 2 to 8, more preferably 2 to 6, and particularly preferably 2 to 4. By setting the number within this range, the surface hardness and abrasion resistance can be improved without increasing cure shrinkage.

[0026] The amount of (E) is preferably 0.1 to 3.0% by weight, more preferably 0.2 to 1.0% by weight, and particularly preferably 0.25 to 0.5% by weight, based on the total solid content of the low refractive index resin composition. By using an amount of 0.1% by weight or more, improvements in both curability and abrasion resistance can be expected, while by using an amount of 3.0% by weight or less, sufficient stain resistance can be ensured. An example of a commercially available product is EBECRYL 80 (trade name: Daicel Allnex Corporation, amine-modified polyether acrylate, solid content 100%, tetrafunctional tertiary amino group compound).

[0027] In the present invention, it is preferable to further incorporate a leveling agent (F). (F) is incorporated for the purposes of improving the slip properties of the low refractive index layer to improve abrasion resistance, as well as water and oil repellency to improve stain resistance. Examples include silicone-based, fluorine-based, and acrylic-based agents. Of these, silicone-based and fluorine-based agents are preferred because of their excellent stain resistance, and fluorine-based agents are particularly preferred because they tend to segregate on the coating surface after coating and drying due to their low surface free energy. Furthermore, it is preferable for the agent to have a reactive functional group capable of polymerizing with a binder resin to form a cured coating film, as this will not cause bleeding or other bleed-out effects from the cured coating over time and will maintain its effectiveness for a long period of time.

[0028] The blending amount of (F) is preferably 1 to 10% by weight or less, more preferably 2 to 8% by weight, and particularly preferably 3 to 6% by weight, based on the total solid content of the low refractive index resin composition. By making it 1% by weight or more, improved abrasion resistance and stain resistance can be expected, and by making it 10% by weight or less, sufficient curing properties can be ensured. An example of a commercially available product is Futergent 602A (trade name: manufactured by Neos Corporation, solid content 50%, fluorine-based compound having a reactive functional group).

[0029] To the low refractive index resin composition of the present invention, an antioxidant, an adhesion promoter, a bluing agent, a silane coupling agent, an antifoaming agent, a thickener, an anti-precipitation agent, an antistatic agent, an anti-fogging agent, an antibacterial agent, organic fine particles, etc. may be added as needed within a range that does not impair performance.

[0030] When applying the low refractive index resin composition, it may be diluted with a solvent to improve coating properties. Examples of dilution solvents include alcohol-based solvents such as ethanol, n-propyl alcohol, isopropyl alcohol (hereinafter referred to as IPA), n-butyl alcohol, isobutyl alcohol, and diacetone alcohol; ketone-based solvents such as acetone, methyl ethyl ketone (hereinafter referred to as MEK), methyl isobutyl ketone, and cyclohexanone; ester-based solvents such as ethyl acetate and butyl acetate; and ether-based solvents such as PGM, diethyl ether, and diisopropyl ether. These solvents can be used alone or in combination of two or more. The solid content when diluted is, for example, 1 to 70%, but is not particularly limited and can be appropriately set to obtain a viscosity that is easy to apply.

[0031] Examples of the transparent substrate film onto which the low refractive index resin composition is applied include polyester film, triacetyl cellulose film, polycarbonate film, polysulfone film, nylon film, cycloolefin film, acrylic film, polyimide film, ABS film, polyolefin film, PVC film, PVA film, etc. Among these, biaxially stretched polyester film (hereinafter referred to as PET film) is preferably used from the viewpoints of weather resistance, processability, dimensional stability, etc. The thickness of the film may be approximately 25 μm to 500 μm.

[0032] The method for applying the low refractive index resin composition is not particularly limited, and the composition can be formed by a known coating method such as spray coating, roll coating, die coating, air knife coating, blade coating, spin coating, reverse coating, gravure coating, or wire bar coating, or a printing method such as gravure printing, screen printing, offset printing, or inkjet printing.

[0033] The film thickness of the low refractive index resin composition in a dry state is preferably 50 to 200 nm, more preferably 80 to 150 nm. If the thickness of the low refractive index layer is in this range, it is possible to sufficiently reduce the reflectance.

[0034] Light sources for ultraviolet irradiation used to cure the low refractive index resin composition 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, but a nitrogen atmosphere is preferred in terms of improving curing properties. Furthermore, curing properties can be further improved by heating the back roll or the coating film with an IR heater during ultraviolet irradiation. The irradiation conditions are an irradiation intensity of 500 mW / cm. 2 ~3000mW / cm 2 , exposure dose 50-400mJ / cm 2 are exemplified, but are not limited to these.

[0035] The present invention will be described in detail below with reference to 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 room temperature of 25°C and a relative humidity of 65%. The blend amounts are in parts by weight. [Example]

[0036] Example 1 DPHA was used as (A), Sururia 5320 (trade name: manufactured by JGC Catalysts and Chemicals, solid content 20.5%, average primary particle size 80 nm) as (B), SS-50B (trade name: manufactured by Tosoh Silica Corporation, solid content 100%, average particle size 2 μm, hydrophobic) as (C), Omnirad 127 (trade name: manufactured by IGM Resins) as (D), EBECRYL 80 (trade name: manufactured by Daicel Allnex Corporation, amine-modified polyether acrylate, solid content 100%, tetrafunctional tertiary amino group compound) as (E), and Futergent 602A (trade name: manufactured by Neos Corporation, solid content 50%, fluorine-based) as (F) in the formulations shown in Table 1. The mixture was diluted with IPA and PGM (IPA:PGM=1:1) to a solid content of 3%, and stirred until uniformly dissolved and dispersed to obtain Example 1.

[0037] Examples 2 to 11 In addition to the materials used in Example 1, Sururia 4320 (trade name: manufactured by JGC Catalysts and Chemicals, solid content 20.5%, average primary particle size 60 nm) was used as (B), and SS-50F (trade name: manufactured by Tosoh Silica Corporation, solid content 100%, average particle size 1.2 μm, hydrophobic) and SS-50A (trade name: manufactured by Tosoh Silica Corporation, solid content 100%, average particle size 3 μm, hydrophobic) were used as (C) in the formulations shown in Tables 1 and 2. The mixture was diluted with IPA and PGM (IPA:PGM=1:1) to a solid content of 3%, and stirred until uniformly dissolved and dispersed, yielding Examples 2 to 11.

[0038] Comparative Examples 1 to 5 In addition to the materials used in the examples, SC2050-LNJ (trade name: manufactured by Admatechs Co., Ltd., solid content 70%, average particle size 0.5 μm, hydrophobic) and SS-70 (trade name: manufactured by Tosoh Silica Corporation, solid content 100%, average particle size 5 μm, hydrophobic) were used as (C) in the formulations shown in Table 2, diluted with IPA and PGM (IPA:PGM=1:1) to a solid content of 3%, and stirred until uniformly dissolved and dispersed to obtain Comparative Examples 1 to 5.

[0039] Table 1 JPEG2025175321000001.jpg122167

[0040] Table 2 JPEG2025175321000002.jpg121167

[0041] The evaluation method was as follows.

[0042] Preparation of anti-reflective films U403 (product name: manufactured by Toray Industries, Inc., thickness 50 μm, double-sided easy-adhesion layer PET) was used as a transparent substrate film, and the low refractive index resin compositions of Examples 1 to 11 and Comparative Examples 1 to 5 were applied to the film to a dry film thickness of 100 nm, and dried at 80°C for 1 minute. Then, a high-pressure mercury lamp was used to apply the coating with an output of 1300 mW / cm. 2 , cumulative light intensity 200mJ / cm 2 The film was irradiated with ultraviolet light in a nitrogen atmosphere so as to obtain an anti-reflection film.

[0043] Coating haze: The anti-reflection film was measured in accordance with JIS K7136 using Haze-GARD2 manufactured by Toyo Seiki Seisakusho Co., Ltd., with 2% or less being rated as ⊚, 2% to 4% being ◯, and 4% or more being x.

[0044] Minimum reflectance: Using the above anti-reflection film, the side opposite the coated side was scratched with sandpaper and filled in with a black pigment marker, and then a black PET film was attached to set the reflectance of the opposite side to 0%.Then, the reflectance of the HC side was measured with a spectrophotometer by plotting the reflectance in 1 nm increments in the range of 300 nm to 780 nm, and the minimum reflectance was measured. 0.5% or less was marked with ◎, over 0.5% to 1.0% was marked with 〇, and over 1.0% was marked with ×.

[0045] Anti-Newton ring properties (hereinafter referred to as AN properties): The anti-reflection film was placed on a black screen displayed on an iPad (registered trademark: manufactured by Apple Inc.) with the low refractive index layer side facing down, and the film was visually observed from above. If no Newton rings were visible, the film was marked with a circle, and if they were visible, the film was marked with an X.

[0046] High definition: A hard coat film was placed on a green screen displayed on an iPad (registered trademark: manufactured by Apple Inc.), and visually observed flickering was evaluated as ◯ if no flickering was observed, and x if present.

[0047] Scratch resistance: A load of 50 g / cm2 was placed on steel wool #0000 and moved back and forth 10 times. When visually observed, if no scratches were found, it was rated as ◎, if there were slight scratches, it was rated as ○, and if there were many scratches, it was rated as ×.

[0048] Evaluation results Table 3 JPEG2025175321000003.jpg79145

[0049] Evaluation results Table 4 JPEG2025175321000004.jpg79144

[0050] The Examples were satisfactory in all respects, including coating haze, minimum reflectance, AN property, high definition, and scratch resistance. However, Example 2, which did not contain (E), Example 3, which did not contain (F), and Example 7, which contained a large amount of (B), were slightly inferior in scratch resistance compared to the other Examples.

[0051] On the other hand, Comparative Example 1, in which the blending amount of (B) was small, had a high minimum reflectance, Comparative Example 2, in which the blending amount of (B) was large, had poor AN properties and scratch resistance, and Comparative Example 3, in which the average particle size of (C) was small, had poor AN properties. Furthermore, Comparative Example 4, in which the average particle size of (C) was large, had high haze and poor high definition, and Comparative Example 5, which did not contain (C), had poor AN properties, and none of these were suitable for the present invention.

Claims

1. An anti-reflection film in which a low refractive index layer is directly laminated on a transparent substrate film, An antireflection film characterized in that the low refractive index layer contains a polymerizable binder resin (A), hollow nanosilica (B), solid silica (C), and a photopolymerization initiator (D), the blending amount of (B) is 50 to 75 wt % with respect to the total amount of solids of the low refractive index resin composition for forming the low refractive index layer, and the average particle size of (C) is 0.8 to 4.0 μm.

2. 2. The anti-reflection film according to claim 1, wherein the amount of (C) is 0.2 to 1.5% based on the total solid content of the low refractive index resin composition.

3. 2. The anti-reflection film according to claim 1, wherein the low refractive index resin composition further contains an amine-modified acrylate (E).

4. 4. The anti-reflection film according to claim 1, wherein the low refractive index resin composition further contains a leveling agent (F).

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