JP7630263B2 - Hard coat resin composition and hard coat film - Google Patents

Description

The present invention relates to a photocurable hard coat resin composition and a hard coat film using the same.

In recent years, touch panels that combine a display device and an input means have been used in a wide range of fields. In particular, touch panels that use a touch pen as an input means allow for more intuitive operation by directly inputting characters and complex figures, and are being widely adopted in a wide range of applications, including tablet PCs, pen tablets, smartphones, and portable game devices.

Touch panels have an exposed screen that is in direct contact with fingers, skin, pens, etc., and therefore have the problem of being susceptible to dirt and scratches caused by sebum and the like. To address these issues, technologies have been developed to make the surface of touch panels less susceptible to dirt, easier to clean, smooth, and less susceptible to scratches. For example, a hard coat film has been proposed in which a hard coat layer containing a hydrolyzable silyl group or silanol group, a radical polymerizable compound, and a polymerization initiator and a surface layer are laminated in that order (Patent Document 1).

The use of such hard coat films has made it possible to prevent dirt adhesion and scratches to a great extent, but abrasion resistance that can maintain surface functionality for a long period of time has also become a requirement, particularly when using a touch pen. However, there are not many hard coat films with sufficient abrasion resistance, and there are issues such as a large change in the water contact angle and a decrease in stain resistance when the film is rubbed with something that scrapes the film surface, such as an eraser, leaving room for improvement.

Patent No. 6519771

The objective of the present invention is to provide a photocurable resin composition that has excellent optical properties and abrasion resistance, and exhibits a very small rate of change in water contact angle even when rubbed with an eraser, and a hard coat (hereinafter referred to as HC) film having a cured resin layer of the composition.

In order to solve the above problems, the invention of claim 1 provides a hard coat film having a cured layer of a hard coat resin composition on a plastic film substrate, the hard coat resin composition being a composition comprising a binder (A) containing a polythiophene compound, a fluorine-based silicone compound (B) having a reactive functional group, and a photopolymerization initiator (C), the (A) containing a hexafunctional or higher (meth)acrylate, the ratio of the (B) being 0.3 to 12.0 parts by weight relative to 100 parts by weight of the photopolymerization component, the cured film having a water contact angle of 100° or more, and a decrease in water contact angle of less than 20% after 1000 reciprocating strokes with an eraser under a load of 1 kg, the hard coat film having a total light transmittance of 90% or more .

The invention of claim 2 provides the hard coat film according to claim 1, characterized in that it has a cured layer of a hard coat resin composition in which the content of the polythiophene-based compound contained in (A) is 0.8 to 5.0 wt % based on the total solid content .

A third aspect of the present invention provides the hard coat film according to the first aspect, characterized in that it has a cured layer of a hard coat resin composition, the cured film having a water contact angle of 110.1° or more .

A fourth aspect of the present invention provides the hard coat film according to any one of the first to third aspects, which has a haze of 1% or less .

The resin composition of the present invention has excellent optical properties and excellent abrasion resistance, with a very small change in water contact angle even when rubbed with an eraser, making it useful as an HC resin for use in HC films for touch panels.

The present invention will be explained in detail.

The HC resin composition of the present invention comprises a binder (A) containing a polythiophene-based compound, a fluorine-based compound (B), and a photopolymerization initiator (C). In this specification, (meth)acrylate includes both acrylate and methacrylate.

The binder (A) containing a polythiophene-based compound used in the present invention is the main component constituting the hard coat film, and contains a conductive polythiophene-based compound. Polythiophene is a polymer of thiophene, a sulfur-containing heterocyclic compound, and is a compound that becomes conductive when electrons are added to or removed from the conjugated n-orbital by doping. In particular, poly(3,4-ethylenedioxythiophene) (hereinafter PEDOT) is preferable in that it improves conductivity when combined with poly(4-styrenesulfonate) (hereinafter PSS), has high environmental stability, and has high light transmittance in a thin film. The inventors have found that water repellency can be stably maintained by combining this polythiophene-based compound with a specific binder.

The content of the polythiophene compound contained in (A) is preferably 0.3 to 5.0% by weight, more preferably 0.5 to 3.0% by weight, and particularly preferably 0.8 to 2.0% by weight, based on the total solid content. By making it 0.3% by weight or more, it is possible to sufficiently suppress the decrease in the water contact angle after rubbing with an eraser, and by making it 5.0% by weight or less, the appearance of the HC layer can be maintained well. The amount of compounding can be determined based on the surface resistivity of the cured film, and specifically, it is preferably 1×10 ⁸ to 1×10 ¹² Ω/□ at the initial stage. The reason why the decrease in the water contact angle can be suppressed by improving the conductivity is not clear, but it is presumed that the damage to the film can be reduced by making it difficult to generate static electricity generated when rubbing with an eraser, and as a result, the decrease in the water contact angle can be suppressed.

The binder (A) contains a 6- or higher functional (meth)acrylate that forms a network-like crosslinked structure in the cured product. The upper limit is preferably 15 or less functional, and more preferably 12 or less functional. The binder used is not particularly limited as long as it is 6 or more functional, and examples of oligomers 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. Among these, urethane (meth)acrylate is preferred in terms of abrasion resistance and fast curing properties.

The urethane (meth)acrylate, which is the binder (A), may have a structure in which a polyfunctional (meth)acrylate having a hydroxyl group is reacted with a polyisocyanate. Examples of polyisocyanates include aliphatic polyisocyanates such as hexamethylene diisocyanate (hereinafter referred to as HDI), alicyclic polyisocyanates such as isophorone diisocyanate, and aromatic polyisocyanates such as diphenylmethane diisocyanate. Of these, HDI is preferred because of its excellent weather resistance and stretchability. Examples of (meth)acrylates having a hydroxyl group include pentaerythritol tri(meth)acrylate, dipentaerythritol tetra(meth)acrylate, and dipentaerythritol penta(meth)acrylate. Of these, pentaerythritol triacrylate is preferred.

An example of the low molecular weight binder (A) is dipentaerythritol hexa(meth)acrylate (hereinafter referred to as DPHA), which is hexafunctional. Binders with less than 6 functionalities, whether they are oligomers or low molecular weight monomers, are unsuitable because they result in a large decrease in the water contact angle after rubbing with an eraser. The reason why the water contact angle decreases due to a decrease in the number of functional groups is not clear, but it is speculated that the decrease in curability makes the coating surface more susceptible to fine scratches, and the charging inside makes it easier for water to penetrate, resulting in a decrease in the contact angle.

In addition to the (A) above, the composition may contain a (meth)acrylate monomer having less than 6 functionalities in order to adjust the viscosity of the composition and improve adhesion to the substrate. Examples of such monomers include butyl (meth)acrylate, isobornyl (meth)acrylate, hydroxyethyl (meth)acrylate, (poly)ethylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol tetra(meth)acrylate, diglycerin tetra(meth)acrylate, and dipentaerythritol penta(meth)acrylate. These monomers may be used alone or in combination of two or more.

The fluorine-based compound (B) used in the present invention is a leveling agent that imparts antifouling (antifingerprint) and water repellency. Since it has a reactive functional group that undergoes a polymerization reaction with (A), it does not fall off over time from the cured film, and the effect can be maintained for a long time. From the viewpoint of reducing the frictional force with the eraser, it is preferable to use a fluorine-based silicone compound. In particular, when photocuring is performed under nitrogen purging (deoxidation) conditions, the effect can be enhanced. Commercially available fluorine-based silicone compounds include X-71-1203M (product name: manufactured by Shin-Etsu Chemical Co., Ltd., solid content 20%), Megafac RS-851, RS-852 (product names: both manufactured by DIC Corporation), and Opstar TU2225 (product name: manufactured by JSR Corporation). Commercially available fluorine-based compounds include KY-1216 (product name: manufactured by Shin-Etsu Chemical Co., Ltd., solid content 20%).

The amount of (B) to be blended per 100 parts by weight of the photocurable component is 0.3 to 12.0 parts by weight, preferably 0.35 to 11.0 parts by weight. If it is less than 0.3 parts by weight, the degree of decrease in the water contact angle when rubbed with an eraser will be large, and if it exceeds 12.0 parts by weight, there will be a lot of repelling when made into a film, which will tend to deteriorate the appearance and increase the haze, so this is not acceptable.

The photopolymerization initiator (C) used in the present invention generates radicals when irradiated with ultraviolet light or an electron beam, and these radicals trigger the polymerization reaction. General-purpose photopolymerization initiators such as benzyl ketal, acetophenone, and phosphine oxide types 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, which may be used alone or in combination of two or more. Among these, it is preferable to use α-hydroxyacetophenones that are less prone to yellowing, and commercially available products include Irgacure 184 and 2959 (trade names: manufactured by BASF Japan, α-hydroxyacetophenones).

The ratio of (C) to 100 parts by weight of the photocurable resin component is preferably 0.5 to 10 parts by weight, and more preferably 3 to 8 parts by weight. By adding 0.5 parts by weight or more, sufficient curing properties are achieved, and by adding 10 parts by weight or less, excessive addition is avoided, and yellowing of the coating film and deterioration of storage stability can be prevented.

If necessary, the HC resin composition of the present invention may contain ultraviolet absorbers, antioxidants, colorants, defoamers, thickeners, anti-precipitation agents, antistatic agents, anti-fogging agents, slip agents, antibacterial agents, antiviral agents, organic fine particles, inorganic fillers, etc.

The HC resin composition of the present invention is diluted with a solvent to a solid content of 10 to 70% in order to improve the coatability onto organic plastic films. Examples of the solvent 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 (hereinafter MEK), methyl isobutyl ketone, and cyclohexanone; ester-based solvents such as methyl acetate and butyl acetate; and ether-based solvents such as PGM, diethyl ether, and diisopropyl ether. These can be used alone or in combination of two or more kinds.

Examples of plastic film substrates onto which the HC resin of the present invention is applied include polyester film, polyethylene film, polypropylene film, diacetyl cellulose film, triacetyl cellulose film, acetyl cellulose butyrate film, polyvinyl chloride film, polyvinylidene chloride film, polyvinyl alcohol film, ethylene vinyl alcohol film, polystyrene film, polycarbonate film, polymethylpentene film, polysulfone film, polyether ether ketone film, polyether sulfone film, polyether imide film, polyimide film, fluororesin film, nylon film, acrylic film, cycloolefin (co)polymer film, etc.

Among these, biaxially oriented polyester films are preferred in terms of price, workability, and dimensional stability, and acrylic and polycarbonate films are preferred in terms of weather resistance. The film thickness should be approximately 23 μm to 250 μm.

There are no particular limitations on the method for applying the HC resin composition of the present invention, and 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, as well as gravure printing, screen printing, offset printing, and inkjet printing can be used. The dry film thickness is preferably 0.5 μm to 20 μm.

After the HC resin composition of the present invention is applied, it is dried at 60 to 120°C and cured using an ultraviolet irradiator. Examples of light sources for irradiating ultraviolet rays include low pressure mercury lamps, high pressure mercury lamps, extra-high pressure mercury lamps, carbon arc lamps, xenon lamps, metal halide lamps, electrodeless ultraviolet lamps, and LED lamps, and examples of curing conditions include an irradiation intensity of 500 mW/ ^cm2 to 3000 mW/ ^cm2 and an integrated light quantity of 50 to 2,000 mJ/ ^cm2 . The irradiation atmosphere may be air, but is preferably in an inert gas such as nitrogen or argon.

The reduction in water contact angle of an HC film having a cured layer of the HC resin composition of the present invention after 1,000 reciprocating strokes with an eraser at a load of 1 kgf is less than 20%. If the reduction rate is less than 20%, it is considered that most of the antifouling components remain without being scraped off by the eraser test, and therefore it can be judged that the film has excellent antifouling properties as well as excellent abrasion resistance.

The reason for using an eraser above is that the abrasion caused by an eraser is similar to that caused by a touch pen, and this evaluation allows for an approximate assessment of abrasion resistance to a touch pen. The abrasion resistance of optical films is generally evaluated using steel wool, but steel wool is literally a hard, thin metal wire, and the degree of abrasion caused by a touch pen is completely different, so abrasion resistance caused by a touch pen cannot be evaluated using steel wool.

The eraser used in the above eraser test is a Korean MINOAN (product name: manufactured by MUNBANGSAWOO, diameter 6 mm), which is the eraser used in the abrasion resistance test. Using a flat friction tester manufactured by Toyo Seiki Seisakusho, the eraser is rubbed back and forth 1,000 times under conditions of a load of 1 kg, a rubbing speed of 40 rpm, and a stroke width of 50 mm, and the water contact angle is measured before and after. In this specification, the water contact angle is the value measured based on the sessile drop method of JIS R 3257:1999.

The water contact angle before the eraser test is 100° or more, preferably 105° or more, and more preferably 110° or more. If it is less than 100°, it cannot be said to have sufficient anti-fouling properties, and it is difficult to suppress the adhesion of fingerprints and dirt. The water contact angle after the eraser test is reduced by less than 20% from the measured value before the test, preferably less than 10%, and more preferably less than 6%. If it is 20% or more, it cannot be said to have sufficient abrasion resistance, and the anti-fouling properties decrease significantly over time when rubbed with a touch pen.

The present invention will be described in detail below based on examples and comparative examples, but these are specific examples and are not intended to be limiting. Unless otherwise specified, measurements were performed at room temperature of 25°C and relative humidity of 65%. The amounts are shown in parts by weight, and are expressed in terms of solid content except for the dilution solvent.

Example 1
Example 1, which is an HC resin composition, was prepared by using Z-885B-AS (product name: manufactured by AICA Corporation, polythiophene-based compound: PEDOT/PSS was 1% of the total solid content, binder: hexafunctional urethane acrylate obtained by reacting HDI and PETA) as (A), X-71-1203M (product name: manufactured by Shin-Etsu Chemical Co., Ltd., solid content 20%) as (B), Omnirad 184 (product name: manufactured by Shin-Etsu Chemical Co., Ltd., α-hydroxyacetophenone-based) as (C), and butyl acetate, MEK, PGM, and diacetone alcohol as dilution solvents in the formulation shown in Table 1, and stirring until uniformly dissolved and dispersed, to prepare Example 1, which is an HC resin composition.

Examples 2 to 6
In addition to the materials used in Example 1, Z-702 B -AS (product name: manufactured by AICA Corporation, polythiophene-based compound: PEDOT/PSS was 1.4% of the total solid content, binder: DPHA, hexafunctional) was used as (A) and KY-1216 (product name: manufactured by Shin-Etsu Chemical Co., Ltd., solid content 20%) was used as (B), and these were stirred until uniformly dissolved and dispersed in the formulation described in 1 to prepare HC resin compositions of Examples 2 to 6.

Comparative Examples 1 to 5
In addition to the materials used in the examples, Z-879A-AS (trade name: manufactured by Aica Kogyo Co., Ltd., polythiophene-based compound: PEDOT/PSS was 1% of the total solids, binder: 5-functional urethane acrylate obtained by reacting HDI flat with PETA and 2-hydroxyethyl acrylate) and Z-850A-AS (trade name: manufactured by Aica Kogyo Co., Ltd., polythiophene-based compound: PEDOT/PSS was 1.4% of the total solids, binder: ditrimethylolpropane triacrylate, 4-functional) and DPHA and Urea A (6-functional urethane acrylate obtained by reacting HDI with PETA) were mixed as binders and stirred until uniformly dissolved and dispersed in the formulation shown in Table 2 to prepare Comparative Examples 1 to 5, which are HC resin compositions.

Preparation of HC film: The coating was applied to an A4-sized polyethylene terephthalate film U403 (product name: manufactured by Toray Industries, 100 μm, with easy-adhesion layers on both sides) so that the film thickness when cured would be 2 μm, and after drying at 80°C for 1 minute in a thermostatic chamber, the coating was purged with nitrogen and cured with ultraviolet light using an electrodeless UV irradiation device F300S/LC-6B manufactured by Fusion UV Systems Japan, with an output of 1200 mW/cm2 with an H bulb and an accumulated light quantity of 200 mJ/cm2.

Table 1

Table 2

The evaluation method was as follows:

Appearance: The coated surface of the HC film created above was visually inspected, and if it was in good condition with no defects such as bumps, repelling, or uneven coating, it was marked with an ◯, and if it had defects, it was marked with an X.

Total light transmittance: Measured in accordance with JIS K7361-1 using a Haze-GARD2 made by Toyo Seiki Seisakusho, with 90% or more marked as ◯ and less than 90% marked as ×.

Haze: Measured in accordance with JIS K7361-1 using a Haze-GARD2 made by Toyo Seiki Seisakusho, with 1% or less marked as ◯ and over 1% marked as ×.

Surface resistivity: The coated surface of the HC film prepared above was measured in accordance with JIS K6911 using a high resistivity meter HIRESTA-UX manufactured by Nitto Seiko Analytech Co., Ltd., and a value exceeding 1.00×10 ¹² Ω/□ was marked as x.

Water contact angle: Using MINOAN (product name: manufactured by MUNBANGSAWOO, diameter 6 mm), 1000 reciprocal rubs were performed under conditions of a load of 1 kg, a rub speed of 40 rpm, and a stroke width of 50 mm using a flat friction tester manufactured by Toyo Seiki Seisakusho, and the water contact angle was measured before and after. The water contact angle was measured according to the static drop method of JIS R 3257:1999, using a DMs-400 manufactured by Kyowa Interface Science Co., Ltd., after dropping water at room temperature and leaving it to stand for 30 seconds. The difference between the initial water contact angle and the water contact rate after abrasion with an eraser was used as the water contact angle change rate, with less than 10% being rated as ◎, 10-20% being ◯, and 20% or more being ×.

Evaluation result 1

Evaluation result 2

The examples were good with no problems in terms of appearance, total light transmittance, haze, or water contact angle.

On the other hand, Comparative Example 1 in which the amount of (B) was less than the lower limit, Comparative Examples 2 and 3 in which the number of functional groups in (A) was less than 6, and Comparative Examples 4 and 5 in which the binder did not contain a polythiophene-based compound all had large rates of change in water contact angle, and all of these were unsuitable for the present invention.

Claims (4)

On a plastic film substrate,
The composition includes a binder (A) containing a polythiophene-based compound, a fluorine-based silicone compound (B) having a reactive functional group, and a photopolymerization initiator (C),
The (A) contains a hexa- or higher functional (meth)acrylate,
The ratio of the (B) to 100 parts by weight of the photopolymerization component is 0.3 to 12.0 parts by weight,
a cured layer of a hard coat resin composition, the cured film having a water contact angle of 100° or more, and a decrease in the water contact angle of less than 20% after 1000 reciprocating strokes with an eraser under a load of 1 kg;
A hard coat film having a total light transmittance of 90% or more . 2. The hard coat film according to claim 1, comprising a cured layer of a hard coat resin composition, the content of the polythiophene compound contained in (A) being 0.8 to 5.0% by weight based on the total solid content . 2. The hard coat film according to claim 1, which has a cured layer of a hard coat resin composition, the cured film having a water contact angle of 110.1° or more . 4. The hard coat film according to claim 1, wherein the haze is 1% or less .