Curable resin composition for flexible film coating

Abstract

Provided is a curable resin composition, for flexible film coating, capable of forming a cured film excellent in flexibility and scratch resistance. A curable resin composition for flexible film coating according to an embodiment includes urethane (meth)acrylate and a tetrafunctional thiol compound. The urethane (meth)acrylate is a reaction product of a feedstock containing an aliphatic polyisocyanate and pentaerythritol (meth)acrylate having a hydroxyl value of 150-240 mgKOH / g.

Description

Curable resin composition for flexible film coating

[0001] The present invention relates to a curable resin composition used to coat flexible films.

[0002] It is known that a curable resin composition that can be cured by irradiation with active energy rays such as ultraviolet rays is used as a coating agent for protecting the surface of a film. For example, Patent Document 1 discloses a curable resin composition that includes a specific urethane (meth)acrylate and a reaction product of a polyfunctional (meth)acrylate and a polyfunctional thiol.

[0003] In recent years, flexible displays that are repeatedly bent and used for display purposes have become increasingly popular. Flexible displays include foldable displays that can be folded and rollable displays that can be rolled up into a cylindrical shape, and are incorporated into mobile electronic devices such as smartphones and tablet devices.

[0004] JP 2015-113414 A

[0005] In optical films used in such flexible displays, the coating film formed on the surface is required to have flexibility, i.e., resistance to creases even when repeatedly bent, and also to have resistance to scratches even when the surface is rubbed, i.e., scratch resistance. In general, scratch resistance tends to improve by increasing the surface hardness, but increasing the hardness tends to decrease flexibility and bendability, and it is not easy to achieve both flexibility and scratch resistance.

[0006] In view of the above, an object of an embodiment of the present invention is to provide a curable resin composition for flexible film coating that can form a cured film that is excellent in flexibility and scratch resistance.

[0007] The present invention includes the following embodiments. [1] A curable resin composition for flexible film coating, comprising: a urethane (meth)acrylate that is a reaction product of raw materials comprising pentaerythritol (meth)acrylate having a hydroxyl value of 150 to 240 mg KOH / g and an aliphatic polyisocyanate; and a tetrafunctional thiol compound. [2] The curable resin composition for flexible film coating according to [1], wherein the tetrafunctional thiol compound comprises a tetrafunctional thiol compound derived from pentaerythritol. [3] The curable resin composition for flexible film coating according to [1] or [2], wherein the mass ratio of the urethane (meth)acrylate to the tetrafunctional thiol compound is 90 / 10 to 98 / 2. [4] The curable resin composition for flexible film coating according to any one of [1] to [3], wherein the pentaerythritol (meth)acrylate is a mixture of pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate. [5] Use of a curable resin composition for flexible film coating, the curable resin composition comprising: a urethane (meth)acrylate that is a reaction product of raw materials containing pentaerythritol (meth)acrylate having a hydroxyl value of 150 to 240 mg KOH / g and an aliphatic polyisocyanate; and a tetrafunctional thiol compound.

[0008] The curable resin composition for flexible film coating according to the embodiment of the present invention can form a cured film that is excellent in flexibility and scratch resistance.

[0009] The curable resin composition for flexible film coating according to this embodiment (hereinafter simply referred to as the "curable resin composition") contains the following components (A) and (B): Component (A): a urethane (meth)acrylate that is a reaction product of raw materials containing pentaerythritol (meth)acrylate having a hydroxyl value of 150 to 240 mg KOH / g and an aliphatic polyisocyanate; Component (B): a tetrafunctional thiol compound.

[0010] In this specification, (meth)acrylate refers to acrylate and / or methacrylate, (meth)acrylic acid refers to acrylic acid and / or methacrylic acid, and (meth)acryloyl refers to acryloyl and / or methacryloyl.

[0011] [Component (A): Urethane (meth)acrylate] The urethane (meth)acrylate of component (A) is obtained by reacting pentaerythritol (meth)acrylate having a hydroxyl value of 150 to 240 mgKOH / g with an aliphatic polyisocyanate as essential raw materials, and a urethane bond is formed by reaction of the hydroxyl group contained in the pentaerythritol (meth)acrylate with the isocyanate group of the aliphatic polyisocyanate.

[0012] (Pentaerythritol (meth)acrylate) In this embodiment, pentaerythritol (meth)acrylate with a hydroxyl value of 150 to 240 mgKOH / g is used as the raw material (reaction component) of component (A). A hydroxyl value of 240 mgKOH / g or less can prevent a decrease in the scratch resistance of the cured film. A hydroxyl value of 150 mgKOH / g or more makes the cured film more easily stretchable, and can prevent streaking due to repeated bending. The hydroxyl value of pentaerythritol (meth)acrylate is preferably 155 to 230 mgKOH / g, and more preferably 180 to 230 mgKOH / g.

[0013] In this specification, the hydroxyl value is measured in accordance with JIS K0070-1992. Specifically, a sample (pentaerythritol (meth)acrylate) is dissolved in acetic anhydride / pyridine (15 parts by mass / 85 parts by mass). After reacting at 90°C for 1.5 hours, a small amount of water is added, and the mixture is reacted for an additional 10 minutes, after which it is cooled to room temperature. Phenolphthalein is then added as an indicator, and the hydroxyl value is determined by titration with a 1 mol / L potassium hydroxide (KOH) ethanol solution.

[0014] Pentaerythritol (meth)acrylate is obtained by reacting pentaerythritol with (meth)acrylic acid, and the hydrogen atoms of the hydroxyl groups of pentaerythritol are substituted with (meth)acryloyl groups. The hydroxyl value corresponds to the number of substituted hydroxyl groups. The reaction of pentaerythritol with (meth)acrylic acid can be carried out by a known method. This may result in pentaerythritol mono(meth)acrylate, in which one (meth)acrylic acid unit is added to pentaerythritol, pentaerythritol di(meth)acrylate, in which two (meth)acrylic acid units are added, pentaerythritol tri(meth)acrylate, in which three (meth)acrylic acid units are added, or pentaerythritol tetra(meth)acrylate, in which four (meth)acrylic acid units are added, and the resulting product is usually a mixture containing two or more of these (meth)acrylates. Pentaerythritol tetra(meth)acrylate does not have a hydroxyl group and therefore does not react with aliphatic polyisocyanates. However, in this embodiment, pentaerythritol tetra(meth)acrylate is also included as a raw material (reactive component).

[0015] In this embodiment, the pentaerythritol (meth)acrylate is preferably a mixture of pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate. In one embodiment, 100% by mass of pentaerythritol (meth)acrylate preferably contains 5 to 35% by mass of pentaerythritol di(meth)acrylate, 35 to 55% by mass of pentaerythritol tri(meth)acrylate, and 20 to 45% by mass of pentaerythritol tetra(meth)acrylate, and more preferably contains 10 to 30% by mass of pentaerythritol di(meth)acrylate, 40 to 55% by mass of pentaerythritol tri(meth)acrylate, and 25 to 40% by mass of pentaerythritol tetra(meth)acrylate. The content of pentaerythritol mono(meth)acrylate may be, for example, 5% by mass or less, or may be 0 to 3% by mass.

[0016] In this embodiment, the component to be reacted with the aliphatic polyisocyanate may be only pentaerythritol (meth)acrylate having a hydroxyl value of 150 to 240 mgKOH / g, but may also contain other hydroxyl group-containing components such as polyols as long as the effect is not impaired. In a preferred embodiment, the hydroxyl group-containing component contains 90% by mass or more of the above-mentioned pentaerythritol (meth)acrylate. In other words, it is preferable that the above-mentioned pentaerythritol (meth)acrylate is contained in 90% by mass or more of 100% by mass of the hydroxyl group-containing component.

[0017] The other hydroxyl group-containing components are not particularly limited, and examples thereof include dipentaerythritol (meth)acrylate, glycerin (meth)acrylate, trimethylolpropane (meth)acrylate, and ditrimethylolpropane (meth)acrylate.

[0018] (Aliphatic Polyisocyanate) In this embodiment, an aliphatic polyisocyanate is used as a raw material (reaction component) for component (A). By using a urethane (meth)acrylate obtained by reacting an aliphatic polyisocyanate with pentaerythritol (meth)acrylate having the above-mentioned specific hydroxyl value, the scratch resistance of the cured film can be improved.

[0019] Examples of the aliphatic polyisocyanate include aliphatic diisocyanates such as hexamethylene diisocyanate (HDI), pentamethylene diisocyanate, tetramethylene diisocyanate, dodecamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate, as well as isocyanurates, allophanates, and adducts of these aliphatic diisocyanates. Any of these may be used alone or in combination of two or more.

[0020] In this embodiment, the component to be reacted with pentaerythritol (meth)acrylate may be only an aliphatic polyisocyanate, but may also contain other polyisocyanates as long as the effect is not impaired. In a preferred embodiment, the polyisocyanate contains 90% by mass or more of an aliphatic polyisocyanate (preferably hexamethylene diisocyanate). That is, it is preferable that the aliphatic polyisocyanate is contained in 90% by mass or more of 100% by mass of the polyisocyanate.

[0021] The other polyisocyanates are not particularly limited, and examples thereof include tolylene diisocyanate, diphenylmethane diisocyanate, xylylene diisocyanate, polyphenylmethane polyisocyanate, phenylene diisocyanate, naphthalene diisocyanate, hydrogenated diphenylmethane diisocyanate, hydrogenated xylylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, and isocyanurates, allophanates, and adducts thereof.

[0022] The reaction of the raw materials containing pentaerythritol (meth)acrylate and aliphatic polyisocyanate can be carried out by a known method, and is not particularly limited. From the viewpoint of hardness and safety of the cured film, the charge ratio of pentaerythritol to aliphatic polyisocyanate is, for example, preferably 1.01 to 1.30, more preferably 1.05 to 1.20, in terms of the molar ratio ([OH] / [NCO]) of hydroxyl groups (OH) to isocyanate groups (NCO).

[0023] The content of the pentaerythritol (meth)acrylate and the aliphatic polyisocyanate in the raw materials is, in terms of the total amount of both, preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass, relative to 100% by mass of the raw materials (reaction components).

[0024] During the reaction, a polymerization inhibitor that inhibits polymerization of the (meth)acryloyl group may be added. Examples of the polymerization inhibitor include p-benzoquinone, naphthoquinone, toluquinone, 2,5-diphenyl-p-benzoquinone, hydroquinone, 2,5-di-t-butylhydroquinone, methylhydroquinone, mono-t-butylhydroquinone, hydroquinone monomethyl ether, 2,6-di-t-butylcresol, and p-t-butylcatechol.

[0025] A catalyst may be added to promote the reaction during the reaction, such as dibutyltin dilaurate, dibutyltin diacetate, tin octoate, zinc hexanoate, cobalt naphthenate, triethylamine, triethylenediamine, bismuth nitrate, bismuth bromide, or 1,8-diazabicyclo[5.4.0]undecene.

[0026] In the reaction, an organic solvent such as ethyl acetate, butyl acetate, methyl ethyl ketone, or toluene may be used.

[0027] [Component (B): Tetrafunctional Thiol Compound] The curable resin composition according to this embodiment contains a tetrafunctional thiol compound as component (B). The thiol group (SH) of the tetrafunctional thiol compound reacts with the carbon-carbon double bond of the urethane (meth)acrylate to form a C-S bond when the curable resin composition is cured. By combining the specific urethane (meth)acrylate with a tetrafunctional thiol compound, it is possible to improve flexibility and abrasion resistance.

[0028] The tetrafunctional thiol compound is a compound having four thiol groups in the molecule. The tetrafunctional thiol compound preferably includes a pentaerythritol-derived tetrafunctional thiol compound. The pentaerythritol-derived tetrafunctional thiol compound is an ester of a thiol-containing fatty acid (preferably a saturated fatty acid) and pentaerythritol. The number of carbon atoms in the thiol-containing fatty acid is preferably 2 to 5, more preferably 2 to 4.

[0029] In one embodiment, a compound represented by the following general formula (1) is preferably used as the tetrafunctional thiol compound.

[0030] In the formula, R １ ~R ４ each independently represents an alkanediyl group having 1 to 4 carbon atoms, more preferably an alkanediyl group having 1 to 3 carbon atoms. The thiol group may be a primary thiol group bonded to a primary carbon, a secondary thiol group bonded to a secondary carbon, or a tertiary thiol group bonded to a tertiary carbon, but is preferably a secondary thiol group. That is, the tetrafunctional thiol compound may be a primary thiol, a secondary thiol, or a tertiary thiol, but is preferably a secondary thiol.

[0031] Specific examples of tetrafunctional thiol compounds represented by the above general formula (1) include pentaerythritol tetrakis(mercaptoacetate), pentaerythritol tetrakis(3-mercaptopropionate), and pentaerythritol tetrakis(3-mercaptobutyrate). These can be used alone or in combination of two or more. Of these, pentaerythritol tetrakis(3-mercaptobutyrate) is particularly preferred.

[0032] The tetrafunctional thiol compound of component (B) preferably contains 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more of a pentaerythritol-derived tetrafunctional thiol compound (preferably a compound represented by general formula (1)), and may be 100% by mass.

[0033] [Curable Resin Composition] The curable resin composition according to this embodiment contains the urethane (meth)acrylate of component (A) and the tetrafunctional thiol compound of component (B), and is an active energy ray-curable resin composition that can be cured by irradiation with active energy rays.

[0034] In the curable resin composition, the mass ratio (A) / (B) of the urethane (meth)acrylate of component (A) to the tetrafunctional thiol compound of component (B) is preferably 90 / 10 to 98 / 2. When the mass ratio (A) / (B) is 90 / 10 or more, the effect of improving scratch resistance can be enhanced. When the mass ratio (A) / (B) is 98 / 2 or less, the effect of improving flexibility can be enhanced. The mass ratio (A) / (B) is more preferably 92 / 8 to 97 / 3, and even more preferably 93 / 7 to 96 / 4.

[0035] The content of the component (A) in the curable resin composition is not particularly limited, and may be 70 to 98 mass %, 80 to 97 mass %, or 90 to 96 mass % in terms of the amount of the component (A) relative to 100 mass % of the solid content.

[0036] The curable resin composition may be composed only of a urethane (meth)acrylate and a tetrafunctional thiol, but preferably further contains a photopolymerization initiator. Examples of the photopolymerization initiator include alkylphenone photopolymerization initiators such as 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methylpropiophenone, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, benzyl dimethyl ketal, and benzoin isopropyl ether, and acylphosphine oxide photopolymerization initiators such as 2,4,6-trimethylbenzoyl-diphenylphosphine oxide and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide. These can be used alone or in combination of two or more.

[0037] The content of the photopolymerization initiator is not particularly limited, and may be, for example, 0.1 to 20 parts by mass, 0.5 to 10 parts by mass, or 1 to 5 parts by mass relative to 100 parts by mass of the total amount of the components (A) and (B).

[0038] The curable resin composition may contain an organic solvent, if necessary, to adjust the viscosity during application. Examples of organic solvents include alcohols such as methanol, ethanol, propanol, n-butanol, and isobutanol; ketones such as acetone, methyl isobutyl ketone, methyl ethyl ketone, and cyclohexanone; cellosolves such as ethyl cellosolve; aromatic solvents such as toluene and xylene; glycol ethers such as propylene glycol monomethyl ether; acetate esters such as methyl acetate and ethyl acetate; and diacetone alcohol. These organic solvents may be used alone or in combination.

[0039] The curable resin composition may further contain, within the scope that does not impair the effects of the present embodiment, a urethane (meth)acrylate other than component (A), an ethylenically unsaturated monomer other than a urethane (meth)acrylate, a non-tetrafunctional thiol compound, an acrylic resin, a surface conditioner, a leveling agent, a polymerization inhibitor, a filler, a dye, a pigment, an oil, a plasticizer, waxes, a drying agent, a dispersant, a wetting agent, a gelling agent, a stabilizer, an antifoaming agent, a surfactant, a thixotropy-imparting agent, an antioxidant, a flame retardant, an antistatic agent, a matting agent, a crosslinking agent, silica, a zirconium compound, a preservative, and the like.

[0040] The curable resin composition can be used to coat a flexible film, thereby protecting the surface of the flexible film. The curable resin composition can be applied to a flexible film substrate and then cured by irradiating with active energy rays, forming a cured film on the surface of the substrate. When the curable resin composition contains an organic solvent, the composition may be dried after application to remove the organic solvent, and then cured by irradiating with active energy rays.

[0041] The substrate of the flexible film is not particularly limited as long as it has flexibility that allows repeated bending, and examples include resin films made of polyester-based resins, polyimide-based resins, polyolefin-based resins, polycarbonate-based resins, acrylonitrile butadiene styrene copolymers (ABS), polystyrene-based resins, etc., and glass films.

[0042] In this specification, the term "film" is a concept that also includes sheets. The thickness of the substrate of the flexible film such as the resin film or glass film is not particularly limited, and may be, for example, 10 to 250 μm, 20 to 100 μm, or 30 to 80 μm.

[0043] The method for applying the curable resin composition is not particularly limited, and examples thereof include wet coating methods such as spraying, gravure, dipping, roll, spin, and screen printing.

[0044] Examples of active energy rays used to cure the curable resin composition applied to a substrate include light rays such as far ultraviolet rays, ultraviolet rays, near ultraviolet rays, and infrared rays, electromagnetic waves such as X-rays and gamma rays, as well as electron beams, proton beams, and neutron beams. Among these, curing by ultraviolet irradiation is preferred. In this case, for example, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a carbon arc lamp, a metal halide lamp, a xenon lamp, an LED lamp, or the like is used to cure the composition at an intensity of 30 to 3,000 mJ / cm. ２ Alternatively, the composition may be cured by irradiating it with ultraviolet light.

[0045] The thickness of the cured film formed from the curable resin composition is not particularly limited, and may be, for example, 1 to 10 μm, or 2 to 5 μm.

[0046] The hardness of the cured film is not particularly limited, and may be, for example, 3H or higher, or 3H to 5H in pencil hardness measured in accordance with JIS K5600-5-4:1999.

[0047] Flexible films having a cured film formed from the curable resin composition according to this embodiment are used in a variety of applications. Examples include optical films for flexible displays, films for the interior or exterior of vehicles, decorative films for building materials, etc. Among these, the flexible films are particularly preferably used as optical films for flexible displays.

[0048] Optical films for flexible displays are optical films used in flexible displays that are repeatedly bent during use. Examples of flexible displays include foldable displays, which are displays that can be folded, and rollable displays, which are displays that can be rolled up into a cylindrical shape. Examples include flexible displays that are incorporated into mobile electronic devices such as smartphones and tablet devices.

[0049] The present invention will be explained in more detail below based on examples and comparative examples, but the present invention is not limited thereto.

[0050] Examples of the synthesis of pentaerythritol acrylates 1 to 3 are shown below.

[0051] [Pentaerythritol acrylate 1] (Pentaerythritol acrylate with a hydroxyl value of 205 mg KOH / g) Into a four-neck flask equipped with a thermometer, a stirrer, and a water-cooled condenser, 1,151 parts by mass (16.0 mol) of acrylic acid, 604 parts by mass (4.44 mol) of pentaerythritol ("Pentaerythritol mono" manufactured by Perstorp), 43.9 parts by mass of paratoluenesulfonic acid, 2.1 parts by mass of hydroquinone monomethyl ether, and 552 parts by mass of toluene were added and mixed. Then, under reduced pressure, while blowing in air, the reaction temperature was maintained at approximately 100°C, and the reaction was carried out until 56% of the total hydroxyl groups in the reacting pentaerythritol were esterified. The reaction was carried out while removing the condensed water. After completion of the reaction, 353 parts by mass of toluene was added. A 20% by weight aqueous solution of sodium hydroxide, equivalent to 1.1 times the molar amount of the acid content of the reaction solution to which toluene had been added, was added with stirring to neutralize the solution, thereby removing excess acrylic acid and paratoluenesulfonic acid. The organic layer was then separated, and a water washing treatment was performed by adding 10 parts by weight of water per 100 parts by weight of the organic layer with stirring. The organic layer was then separated again, and the toluene was distilled off by heating under reduced pressure. The resulting pentaerythritol acrylate 1 was 860 parts by weight and had a hydroxyl value of 205 mgKOH / g.

[0052] HPLC analysis revealed that the ratios of di-, tri-, and tetra-isomers of Pentaerythritol Acrylate 1 were as follows: Pentaerythritol diacrylate 24% by mass Pentaerythritol triacrylate 45% by mass Pentaerythritol tetraacrylate 31% by mass

[0053] [Pentaerythritol acrylate 2] (Pentaerythritol acrylate with a hydroxyl value of 158 mg KOH / g) 1,151 parts by mass (16.0 mol) of acrylic acid, 604 parts by mass (4.44 mol) of pentaerythritol ("Pentaerythritol mono" manufactured by Perstorp), 43.9 parts by mass of paratoluenesulfonic acid, 2.1 parts by mass of hydroquinone monomethyl ether, and 552 parts by mass of toluene were added to a four-neck flask equipped with a thermometer, a stirrer, and a water-cooled condenser, and mixed. Then, under reduced pressure, the reaction temperature was maintained at approximately 100°C while blowing in air, and the reaction was continued until 68% of the total hydroxyl groups in the reacting pentaerythritol were esterified. The reaction was carried out while removing the condensed water. After completion of the reaction, 353 parts by mass of toluene was added. A 20% by weight aqueous solution of sodium hydroxide, equivalent to 1.1 times the molar amount of the acid content of the reaction solution to which toluene had been added, was added with stirring to neutralize the solution, thereby removing excess acrylic acid and paratoluenesulfonic acid. The organic layer was then separated, and a water washing treatment was performed by adding 10 parts by weight of water per 100 parts by weight of the organic layer with stirring. The organic layer was then separated again, and the toluene was distilled off by heating under reduced pressure. The resulting pentaerythritol acrylate 2 was 649 parts by weight and had a hydroxyl value of 158 mgKOH / g.

[0054] HPLC analysis revealed that the ratios of di-, tri- and tetra-isomers of pentaerythritol acrylate 2 were as follows: pentaerythritol diacrylate 10% by mass pentaerythritol triacrylate 51% by mass pentaerythritol tetraacrylate 39% by mass

[0055] [Pentaerythritol acrylate 3] (Pentaerythritol acrylate with a hydroxyl value of 229 mg KOH / g) 1,151 parts by weight (16.0 mol) of acrylic acid, 604 parts by weight (4.44 mol) of pentaerythritol ("Pentaerythritol mono" manufactured by Perstorp), 43.9 parts by weight of paratoluenesulfonic acid, 2.1 parts by weight of hydroquinone monomethyl ether, and 552 parts by weight of toluene were added to a four-neck flask equipped with a thermometer, a stirrer, and a water-cooled condenser, and mixed. The mixture was then reacted under reduced pressure while blowing in air, maintaining the reaction temperature at approximately 100°C, until 50% of the total hydroxyl groups in the reacting pentaerythritol were esterified. The reaction was carried out while removing the condensed water. After completion of the reaction, 353 parts by weight of toluene was added. A 20% by weight aqueous solution of sodium hydroxide, equivalent to 1.1 times the molar amount of the acid content of the reaction solution to which toluene had been added, was added with stirring to neutralize the solution, thereby removing excess acrylic acid and paratoluenesulfonic acid. The organic layer was then separated, and a water washing treatment was performed by adding 10 parts by weight of water per 100 parts by weight of the organic layer with stirring. The organic layer was then separated again, and the toluene was distilled off by heating under reduced pressure. The resulting pentaerythritol acrylate 3 was 807 parts by weight and had a hydroxyl value of 229 mgKOH / g.

[0056] HPLC analysis revealed that the ratios of di-, tri- and tetra-isomers of Pentaerythritol Acrylate 3 were as follows: Pentaerythritol diacrylate 30% by mass Pentaerythritol triacrylate 44% by mass Pentaerythritol tetraacrylate 26% by mass

[0057] The content ratio of each component in pentaerythritol acrylate was determined by high performance liquid chromatography (HPLC, "Prominence-iLC2050C" manufactured by Shimadzu Corporation). Specifically, the measurement was performed using a column ("Inertsil ODS-2" manufactured by GL Sciences, Inc., inner diameter 4.6 mm x length 250 mm), a column temperature of 40°C, and a gradient elution method using a mobile phase of methanol / water = 20 / 80 to 100 / 0.

[0058] Details of pentaerythritol acrylates 4 and 5 are as follows.

[0059] Pentaerythritol acrylate 4: "Aronix M-933" manufactured by Toagosei Co., Ltd., hydroxyl value 280 mg KOH / g.

[0060] Pentaerythritol acrylate 5: "New Frontier PET-3" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., hydroxyl value 120 mg KOH / g.

[0061] Examples of the synthesis of urethane acrylates UA1 to UA3 and UAC1 to UAC4 are shown below.

[0062] [Urethane acrylate UA1] A flask was charged with 21.4 parts by mass of hexamethylene diisocyanate (HDI), 0.05 parts by mass of hydroquinone monomethyl ether as a polymerization inhibitor, 0.02 parts by mass of dioctyltin dineodecanoate as a reaction catalyst, and 78.6 parts by mass of pentaerythritol acrylate (acrylate 1) having a hydroxyl value of 205 mgKOH / g (molar ratio [OH] / [NCO]=1.13). The mixture was then reacted at 50 to 80°C until the amount of free isocyanate reached 0.1% or less, thereby obtaining urethane acrylate UA1.

[0063] [Urethane acrylates UA2 to UA3 and UAC1 to UAC4] Urethane acrylates UA2 to UA3 and UAC1 to UAC4 were synthesized in the same manner as for urethane acrylate UA1, except that the type and charged amount of pentaerythritol acrylate and the type and charged amount of polyisocyanate were changed as shown in Table 1. In Table 1, IPDI represents isophorone diisocyanate, which is an alicyclic polyisocyanate, and XDI represents xylylene diisocyanate, which is an aromatic polyisocyanate.

[0064]

[0065] [Examples 1 to 6 and Comparative Examples 1 to 6] Coating solutions (curable resin compositions) with a solid content concentration of 40% by mass were prepared by adding methyl ethyl ketone to the formulations (parts by mass) shown in Tables 2 and 3. Details of the components in Tables 2 and 3 other than urethane acrylates UA1 to UA3 and UAC1 to UAC4 are as follows:

[0066] Thiol compound 1: pentaerythritol tetrakis(3-mercaptobutyrate), "Karenz MT PE1" manufactured by Resonac Co., Ltd., a tetrafunctional secondary thiol compound

[0067] Thiol compound 2: 1,3,5-tris(2-(3-sulfanylbutanoyloxy)ethyl)-1,3,5-triazinane-2,4,6-trione, "Karenz MT NR1" manufactured by Resonac Co., Ltd., a trifunctional secondary thiol compound

[0068] - Polymerization initiator 1: IGM Resins B. V. "Omnirad 184" manufactured by

[0069] - Polymerization initiator 2: IGM Resins B. V. "Omnirad TPO H"

[0070] The coating liquid (curable resin composition) obtained above was evaluated for pencil hardness, flexibility, scratch resistance, and elongation. The evaluation methods were as follows.

[0071] [Pencil hardness] The coating solution was applied to a glass plate so that the film thickness in a dried state was about 3 μm, and the coating was dried for 1 minute in an oven at 80° C. Thereafter, the coating was measured under a nitrogen atmosphere using a high-pressure mercury lamp (80 W / cm×1 lamp) with an integrated illuminance of 600 mJ / cm ２ The coating was cured by irradiation to obtain a test piece, and the pencil hardness of this test piece was measured in accordance with JIS K5600-5-4:1999.

[0072] The coating solution was applied to a 100 μm-thick PET film (Cosmoshine A4360 manufactured by Toyobo Co., Ltd.) so that the film thickness in a dried state would be approximately 3 μm, and the film was dried in an oven at 80° C. for 1 minute. Thereafter, the film was irradiated with a high-pressure mercury lamp (80 W / cm×1 lamp) under a nitrogen atmosphere with an integrated illuminance of 600 mJ / cm ２ A film with a cured coating was obtained by irradiating the film with the cured coating. Measurements were carried out on the film with the cured coating in accordance with JIS K5600-5-1:1999, and flexibility was evaluated according to the following criteria. From the viewpoint of flexibility, i.e., resistance to creases even after repeated bending, it is preferable that this rating is B or higher and that the following elongation rating is B or higher. A: No creases with a mandrel diameter of 2 mm. B: Creases with a mandrel diameter of 2 mm. C: Creases with a mandrel diameter of 3 mm or more.

[0073] [Abrasion Resistance] The coating liquid was applied to a 100 μm-thick PET film (Cosmoshine A4360 manufactured by Toyobo Co., Ltd.) so that the film thickness in a dry state would be approximately 3 μm, and the film was dried in an oven at 80° C. for 1 minute. Thereafter, the film was irradiated with a high-pressure mercury lamp (80 W / cm×1 lamp) under a nitrogen atmosphere with an integrated illuminance of 600 mJ / cm ２ The film with the cured coating was subjected to irradiation with #0000 steel wool at a load of 250 g / cm. ２ The scratch test was carried out under the condition of 1000 reciprocating strokes of 6 cm, and the film after the test in which the coating film had been cured was visually inspected and evaluated according to the following criteria: A: 2 or less scratches B: 3 to 4 scratches C: 5 or more scratches

[0074] [Extensibility] The coating solution was applied to a 100 μm-thick PET film (Cosmoshine A4360 manufactured by Toyobo Co., Ltd.) so that the film thickness in a dried state would be approximately 3 μm, and the film was dried in an oven at 80° C. for 1 minute. Thereafter, the film was exposed to a high-pressure mercury lamp (80 W / cm×1 lamp) under a nitrogen atmosphere with an integrated illuminance of 600 mJ / cm ２ A film with a cured coating was obtained by irradiating with light at 1000 K. The film was then subjected to irradiation with light at 1000 K. The coating was cured by irradiating with light at 1000 K. The film was subjected to irradiation with light at 1000 K. The coating was cured by irradiating ... Elongation = (average of three closely measured values ​​(mm) / 30 (mm)) x 100 (%) A: 10% or more B: 8% or more but less than 10% C: Less than 8%

[0075]

[0076]

[0077] The results are shown in Tables 2 and 3. Comparative Examples 1 and 2 are examples in which urethane acrylate, a reaction product of pentaerythritol acrylate and aliphatic polyisocyanate, was used in combination with a tetrafunctional thiol compound. However, in Comparative Example 1, the hydroxyl value of the pentaerythritol acrylate was larger than the specified value, resulting in poor scratch resistance. In Comparative Example 2, the hydroxyl value of the pentaerythritol acrylate was smaller than the specified value, resulting in poor elongation and poor flexibility, such as resistance to creases even after repeated bending.

[0078] In Comparative Example 3, the polyisocyanate constituting the urethane acrylate was an alicyclic polyisocyanate, and therefore the hardness was low and the scratch resistance was poor.In Comparative Example 4, the polyisocyanate constituting the urethane acrylate was an aromatic polyisocyanate, and therefore the scratch resistance and flexibility were poor.

[0079] In Comparative Example 5, since no thiol compound was blended, the flexibility was poor. In Comparative Example 6, since the thiol compound used in combination with the urethane acrylate was a trifunctional thiol compound, the scratch resistance was poor.

[0080] In contrast, in Examples 1 to 6, in which urethane acrylate, a reaction product of pentaerythritol acrylate having a specific hydroxyl value and aliphatic polyisocyanate, was used in combination with a tetrafunctional thiol compound, the resulting films had excellent scratch resistance, flexibility, and elongation.

[0081] The various numerical ranges described in this specification can be arbitrarily combined with their respective upper and lower limit values, and all such combinations are considered to be preferred numerical ranges described in this specification. Furthermore, a numerical range described as "X to Y" means from X to Y.

[0082] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their omissions, substitutions, modifications, etc. are included within the scope and spirit of the invention, as well as within the scope of the invention described in the claims and their equivalents.

Claims

1. A curable resin composition for flexible film coating, comprising: a urethane (meth)acrylate which is a reaction product of raw materials including pentaerythritol (meth)acrylate having a hydroxyl value of 150 to 240 mg KOH / g and an aliphatic polyisocyanate; and a tetrafunctional thiol compound.

2. The curable resin composition for flexible film coating according to claim 1, wherein the tetrafunctional thiol compound comprises a pentaerythritol-derived tetrafunctional thiol compound.

3. The curable resin composition for flexible film coating according to claim 1, wherein the mass ratio of the urethane (meth)acrylate to the tetrafunctional thiol compound is 90 / 10 to 98 / 2.

4. The curable resin composition for flexible film coating according to claim 1, wherein the pentaerythritol (meth)acrylate is a mixture of pentaerythritol di(meth)acrylate, pentaerythritol tri(meth)acrylate, and pentaerythritol tetra(meth)acrylate.

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