JP7600810B2 - Hard coat resin composition, cured product, and article including the cured product - Google Patents

Description

The present invention relates to a resin composition for hard coats, a cured product thereof, and an article having the cured product.

In the field of image display devices, flexible displays that can be bent and still retain their display function are attracting attention. Flexible plastics are used for the cover windows and housings of flexible displays, as they are more susceptible to scratches than glass and other materials. Therefore, a hard coat layer is generally formed on the surface of the plastic film.

For example, Patent Document 1 discloses an ultraviolet-curable hard coat resin composition that contains a polyfunctional (meth)acrylate having two or more (meth)acryloyl groups in the molecule and a urethane (meth)acrylate and/or an epoxy (meth)acrylate having two (meth)acryloyl groups in the molecule.

JP 2015-172194 A

In recent years, flexible displays such as foldable displays that can be folded and rollable displays that can be rolled up into a cylindrical shape have been developed. Accordingly, hard coat films are required to have high hardness, bending durability, and high adhesion in addition to scratch resistance. Furthermore, when hard coat films are applied to the outermost surface of plastics, they are also required to have excellent design properties such as an aesthetic appearance.

However, the UV-curable hard coat resin composition described in Patent Document 1 was prone to cracking and did not have sufficient bending durability. In addition, the UV-curable hard coat resin composition did not have sufficient adhesion to plastics, leaving room for improvement. Furthermore, when a low-molecular plasticizer is added to the UV-curable hard coat resin composition to improve the flexibility of the cured product, the plasticizer may seep out onto the surface of the cured product when the cured product is repeatedly bent (also known as bleed-out), which may impair the aesthetic appearance.

The present invention aims to solve these problems and provide a resin composition for hard coating that can produce a cured product with high hardness, excellent bending durability and adhesion, and good appearance, a cured product thereof, and an article including the cured product.

The present invention is based on the discovery that by using a specific urethane acrylate having a polyether chain and a urethane bond, it is possible to obtain a cured product that has high hardness, excellent bending durability and adhesion, and a good appearance.

The present invention provides the following means.
[1] A resin composition for hard coat comprising a monofunctional urethane (meth)acrylate, a polyfunctional (meth)acrylate having two or more (meth)acryloyloxy groups in the molecule, and an initiator,
The resin composition for hard coat, wherein the monofunctional urethane (meth)acrylate is one or more monomers selected from the reaction products of the following (i) to (iii):
(i) An equimolar reaction product of a polyether monol and a compound having a (meth)acryloyloxy group, the compound having a (meth)acryloyloxy group being a compound having one isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule.
(ii) A reaction product of an equimolar amount of a polyether monol, a diisocyanate, and a compound having a (meth)acryloyloxy group, wherein the compound having a (meth)acryloyloxy group has one group reactive with an isocyanate group in one molecule, and has one or two (meth)acryloyloxy groups in one molecule.
(iii) An equimolar reaction product of a polyether polyol and a compound having a (meth)acryloyloxy group, wherein the compound having a (meth)acryloyloxy group has one isocyanate group per molecule and one or two (meth)acryloyloxy groups per molecule.
[2] The resin composition for hard coat according to [1], further comprising a (meth)acrylate having an epoxy group and a (meth)acryloyloxy group.
[3] The content of the monofunctional urethane (meth)acrylate is 0.1 to 30.0 mass% based on 100 mass% of the solid content of the hard coat resin composition. [1] or [2]. The hard coat resin composition according to the above.
[4] The resin composition for hard coat according to any one of [1] to [3], wherein the monofunctional urethane (meth)acrylate has a number average molecular weight of 3,000 to 35,000.
[5] The resin composition for hard coat according to any one of [1] to [4], wherein the monofunctional urethane (meth)acrylate has a glass transition temperature of −55° C. or lower.
[6] A cured product obtained by curing the resin composition for hard coat according to any one of [1] to [5].
[7] The cured product according to [6], having a glass transition temperature of 50 to 200°C.
[8] The cured product according to [6] or [7], having a storage modulus E'(25°C) of 500 to 5000 MPa at 25°C.
[9] An article comprising the cured product according to any one of [6] to [8].
[10] A member having a substrate having a surface on at least a portion thereof made of the cured product according to any one of [6] to [8].

The present invention provides a resin composition for hard coating that can produce a cured product with high hardness, excellent bending durability and adhesion, and good appearance, a cured product thereof, and an article including the cured product.

The definitions and meanings of the terms and expressions used in this specification are given below.
The term "(meth)acryloyloxy group" is a general term for an acryloyloxy group and a methacryloyloxy group.
"(Meth)acrylate" is a general term for acrylate and methacrylate.
Similarly, "(meth)acrylic acid" is a general term for acrylic acid and methacrylic acid.
The term "functional group number" refers to the number of (meth)acryloyloxy groups in one molecule, unless otherwise specified. The term "average functional group number" refers to the average number of (meth)acryloyloxy groups in one molecule, where the formula weight or number average molecular weight based on a chemical formula is one unit, unless otherwise specified.
The term "monofunctional urethane (meth)acrylate" refers to a urethane (meth)acrylate having an average number of functional groups in one molecule that is substantially 1. A urethane (meth)acrylate having an average number of functional groups in one molecule that is 0.7 to 1.4, preferably 0.8 to 1.3, is considered to be a urethane (meth)acrylate having substantially one (meth)acryloyloxy group in one molecule, that is, a monofunctional urethane (meth)acrylate.
By "equimolar reaction product" is meant that the molar ratio of the reacting compounds is substantially 1, and a reaction product in which the molar ratio is 0.7 to 1.4, preferably 0.8 to 1.3, is considered to be an equimolar reaction product.
Similarly, the "equal number of moles" of reactive groups (or compounds) means that the molar ratio of the reactive groups (or compounds) is substantially 1, and when the molar ratio is 0.7 to 1.4, preferably 0.8 to 1.3, the molar numbers of the reactive groups (or compounds) are considered to be equal.
The "hydroxyl value" is determined by measurement in accordance with JIS K 1557: 2007. The "hydroxyl value-based molecular weight" is a value calculated from the formula 56100/(hydroxyl value)×(number of active hydrogens in the initiator).
The "NCO index" in the reaction of an isocyanate group-containing compound with a hydroxyl group-containing compound is a value obtained by multiplying by 100 the equivalent ratio of the isocyanate groups of the isocyanate group-containing compound to the hydroxyl groups of the hydroxyl group-containing compound.
Unless otherwise specified, the term "molecular weight" refers to the formula weight based on a chemical formula, or, in the case of a compound having a molecular weight distribution, the number average molecular weight. The "number average molecular weight" is a polystyrene-equivalent molecular weight determined by gel permeation chromatography (GPC) based on a calibration curve prepared using standard polystyrene samples.
"Hard coat layer" means a layer that imparts excellent surface hardness and scratch resistance.

[Hard Coat Resin Composition]
The hard coat resin composition of the present invention is a hard coat resin composition containing a monofunctional urethane (meth)acrylate, a polyfunctional (meth)acrylate having two or more (meth)acryloyloxy groups in the molecule (hereinafter, also simply referred to as "polyfunctional (meth)acrylate"), and an initiator,
The monofunctional urethane (meth)acrylate is one or more monomers selected from the reaction products of the following (i) to (iii):
(i) An equimolar reaction product of a polyether monol and a compound having a (meth)acryloyloxy group, the compound having a (meth)acryloyloxy group being a compound having one isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule.
(ii) A reaction product of an equimolar amount of a polyether monol, a diisocyanate, and a compound having a (meth)acryloyloxy group, wherein the compound having a (meth)acryloyloxy group has one group reactive with an isocyanate group in one molecule, and has one or two (meth)acryloyloxy groups in one molecule.
(iii) An equimolar reaction product of a polyether polyol and a compound having a (meth)acryloyloxy group, wherein the compound having a (meth)acryloyloxy group has one isocyanate group per molecule and one or two (meth)acryloyloxy groups per molecule.

The above-mentioned resin composition for hard coat can provide a cured product having high hardness, excellent bending durability and adhesion, and good appearance.
[Monofunctional urethane (meth)acrylate]
The hard coat resin composition of the present invention contains a monofunctional urethane (meth)acrylate, and can be photopolymerized or thermally polymerized by its (meth)acryloyloxy group. The monofunctional urethane (meth)acrylate has a polyether chain as a flexible graft chain that does not contribute to crosslinking, and thus a cured product with excellent flexibility can be obtained. Furthermore, the cured product has a small temperature dependency of the storage modulus in a wide temperature range of -20 to 80°C, and can maintain excellent flexibility even at a low temperature range of 0°C or lower.
The (meth)acryloyloxy group of the monofunctional urethane (meth)acrylate is preferably an acryloyloxy group from the viewpoint of better polymerizability.

The monofunctional urethane (meth)acrylate in the present invention is one or more monomers selected from the reaction products of (i) to (iii) above (hereinafter also referred to as "monomer 1-1", "monomer 1-2" and "monomer 1-3"). The monofunctional urethane (meth)acrylate in the hard coat resin composition may be used alone or in combination of two or more types.

<Monomer 1-1>
Monomer 1-1 is a reaction product of (i), and is an equimolar reaction product of polyether monool (i-1) and a compound (i-2) having a (meth)acryloyloxy group, and the compound (i-2) having a (meth)acryloyloxy group is a compound having one isocyanate group per molecule and one or two (meth)acryloyloxy groups per molecule.

As monomer 1-1, a compound represented by formula (1) is preferred.

In formula (1), R ¹ is a monovalent organic group having one or two (meth)acryloyloxy groups.
R ¹² is preferably an alkylene group having 2 to 8 carbon atoms, more preferably an alkylene group having 2 to 4 carbon atoms. A plurality of R ¹² present in one molecule may be the same or different. When two or more types of R ¹² are present in one molecule, the chain of -OR ¹² - may be block or random. R ¹² is preferably one or more types selected from an ethylene group, a propylene group, a 1,2-dimethylethylene group, and a 1-ethylethylene group, more preferably one or more types selected from an ethylene group and a propylene group.

It is also preferred that (OR ¹² ) is a unit based on a monomer a having one epoxy group and an ether bond other than the ether bond of the epoxy group in one molecule. The unit based on the monomer a is preferably a unit represented by formula (11). The monomer a may be used alone or in combination of two or more kinds.

In formula (11), R ¹⁰¹ is a monovalent group represented by -R ¹⁰³ -O-R ¹⁰⁴ , and R ¹⁰² is a hydrogen atom or a monovalent group represented by -R ¹⁰⁵ -O-R ^106. R ¹⁰³ and R ¹⁰⁵ are each independently a linear or branched alkylene group having 1 to 3 carbon atoms, and R ¹⁰⁴ and R ¹⁰⁶ are each independently a linear or branched alkyl group having 1 to 18 carbon atoms.
The alkylene group of R ¹⁰³ and R ¹⁰⁵ is each independently preferably a methylene group, an ethylene group, an n-propylene group or an isopropylene group, more preferably a methylene group or an ethylene group, and further preferably a methylene group.
R ¹⁰⁴ and R ¹⁰⁶ each independently have 1 to 14 carbon atoms, more preferably 1 to 12 carbon atoms, and even more preferably 2 to 10 carbon atoms.
Examples of the linear alkyl group for R ¹⁰⁴ and R ¹⁰⁶ include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-octyl group, an n-decyl group, a lauryl group, a cetyl group, and a stearyl group, and preferably each independently is a methyl group, an ethyl group, or an n-butyl group. A branched alkyl group has a structure in which a hydrogen atom in the linear alkyl group (excluding a hydrogen atom bonded to a terminal carbon) is substituted with an alkyl group. Examples of the substituting alkyl group include a methyl group and an ethyl group. A preferred branched alkyl group is a 2-ethylhexyl group.

Monomer a is preferably a monomer represented by formula (12).

R ¹⁰¹ and R ¹⁰² in formula (12) are the same as R ¹⁰¹ and R ¹⁰² in formula (11).

Examples of the monomer represented by formula (12) include methyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, lauryl glycidyl ether, and hexyl glycidyl ether. From the viewpoint of the bending durability of the cured product of the hard coat resin composition, butyl glycidyl ether or 2-ethylhexyl glycidyl ether is preferred.

In formula (1), R ¹³ is an alkyl group having 1 to 20 carbon atoms. R ¹³ is preferably an alkyl group having 1 to 8 carbon atoms, more preferably a methyl group, an ethyl group, or a butyl group, and even more preferably a butyl group.
a is an integer from 20 to 600, preferably an integer from 35 to 500, and more preferably an integer from 65 to 250.

(Polyether monol (i-1))
The polyether monool (i-1) in the monomer 1-1 is a compound having an initiator residue, a polyether chain, and a hydroxyl group corresponding to the number of active hydrogens of the initiator, the compound being obtained by ring-opening polymerization of an alkylene oxide and/or the monomer a with an initiator having an active hydrogen-containing group and having one or more active hydrogens.

Examples of the active hydrogen-containing group of the initiator include a hydroxyl group, a carboxyl group, and an amino group having one hydrogen atom bonded to a nitrogen atom. The active hydrogen-containing group of the initiator is preferably a hydroxyl group or a carboxyl group, more preferably a hydroxyl group, and even more preferably an alcoholic hydroxyl group.

Examples of initiators having one active hydrogen include monohydric alcohols, monohydric phenols, monovalent carboxylic acids, and amine compounds having one hydrogen atom bonded to a nitrogen atom. The initiator is preferably a monohydric aliphatic alcohol or a monohydric aliphatic carboxylic acid, and more preferably a monohydric aliphatic alcohol. A polyoxyalkylene monool having a lower molecular weight than the target polyether monool may also be used as the initiator.

The number of carbon atoms of the monohydric aliphatic alcohol as the initiator is preferably 1 to 20, more preferably 2 to 8. Specific examples of the monohydric aliphatic alcohol as the initiator include ethanol, propanol, 2-propanol, and n-butanol.
The number of carbon atoms of the monovalent aliphatic carboxylic acid used as the initiator is preferably 2 to 20, more preferably 2 to 8, including the carbon atoms of the carboxy group.

When the alkylene oxide and the monomer a undergo ring-opening polymerization, the ratio of the mass of the monomer a to the total mass of the two is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 10 to 80% by mass, from the viewpoint of adjusting the hardness and bending durability of the cured product of the hard coat resin composition.

The number of carbon atoms in the alkylene oxide is preferably 2 to 8, and more preferably 2 to 4. Specific examples of the alkylene oxide include propylene oxide, ethylene oxide, 1,2-butylene oxide, and 2,3-butylene oxide.

The oxyalkylene group in the polyether monool (i-1) preferably consists of only an oxypropylene group or a combination of an oxypropylene group and a group other than the oxypropylene group. The oxyalkylene group other than the oxypropylene group is preferably an oxyethylene group.
The ratio of oxypropylene groups to all oxyalkylene groups in the polyether monool (i-1) is preferably 50 to 100% by mass, more preferably 60 to 100% by mass. When the initiator is a polyoxyalkylene monool having a lower molecular weight than the target polyether monool, the oxyalkylene groups in the initiator are regarded as oxyalkylene groups in the obtained polyether monool.

In the polyether monool (i-1), a polyoxyalkylene monool having a low hydroxyl value, i.e., a high molecular weight, can be produced by ring-opening polymerization of an alkylene oxide having 3 or more carbon atoms, preferably propylene oxide, as an initiator in the presence of a composite metal cyanide complex catalyst.
The polyoxyalkylene monool having a low hydroxyl value includes polyoxyalkylene monools having a hydroxyl value of 40 mgKOH/g or less.
A polyoxyalkylene monool having a low hydroxyl value and an oxyethylene group can be produced by using a polyoxyalkylene monool having a high hydroxyl value and an oxyethylene group, for example, a hydroxyl value of 50 mgKOH/g or more, as an initiator and ring-opening polymerizing an alkylene oxide having 3 or more carbon atoms, preferably propylene oxide, in the presence of a composite metal cyanide complex catalyst.
In the polyether monool, the polyoxyalkylene monool having a high hydroxyl value and the polyoxyalkylene monool having a high hydroxyl value as the initiator can also be produced by using an alkali catalyst such as potassium hydroxide.

In the production of polyoxyalkylene monool, the initiator and alkylene oxide to be added to the reaction system are usually ones with low moisture content, with moisture removed by degassing under reduced pressure or the like. Usually, the lower the moisture content of the initiator in the production of polyoxyalkylene monool, the better, preferably 500 ppm by mass or less, more preferably 300 ppm by mass or less. If the moisture content is within the above range, the amount of polyoxyalkylene diol produced from water is suppressed, and as a result, the amount of by-products caused by polyoxyalkylene diol is suppressed, and it is easy to adjust the upper limit of the average number of hydroxyl groups in the obtained polyoxyalkylene monool to 1.2 or less.

The lower the water content of polyether monol (i-1) used as the raw material for monomer 1-1, the better. It is preferably 300 mass ppm or less, more preferably 250 mass ppm or less, and even more preferably 50 to 200 mass ppm relative to polyether monol (i-1). When the water content is within the above range, the generation of by-products of water and isocyanate group-containing compounds is small, and the stability of monomer 1-1, which is the reaction product, is improved. Furthermore, it is easy to suppress the change in appearance of the hard coat resin composition over time, and it is easy to obtain a cured product of the hard coat resin composition that has excellent bending durability.

The average number of hydroxyl groups in one molecule of the polyether monol (i-1) is preferably 0.80 to 1.20, more preferably 0.90 to 1.10.
The hydroxyl value of the polyether monool (i-1) is preferably from 1.6 to 18.1 mgKOH/g, more preferably from 2.8 to 14.0 mgKOH/g, and further preferably from 3.1 to 11.2 mgKOH/g.

The polyether monool (i-1) in monomer 1-1 may be a mixture of two or more polyether monools. In this case, each polyether monool is preferably a polyoxyalkylene monool that falls within the above category.

An example of polyether monool (i-1) is one represented by formula (1a).

In formula (1a), R ¹² , R ¹³ and a have the same symbols as those in formula (1).

(Compound (i-2) Having a (Meth)acryloyloxy Group)
The compound (i-2) having a (meth)acryloyloxy group is a compound having one isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule. The compound (i-2) having a (meth)acryloyloxy group is preferably a (meth)acrylate having an isocyanate group bonded to an aliphatic hydrocarbon group or an alicyclic hydrocarbon group, more preferably an isocyanate alkyl (meth)acrylate.
The number of carbon atoms in the alkylene group excluding the isocyanate group of the isocyanatoalkyl group is preferably 8 or less, and more preferably 4 or less.

An example of the compound (i-2) having a (meth)acryloyloxy group is a compound represented by formula (1b).

In formula (1b), R ¹¹ is a hydrogen atom or a methyl group, and is preferably a hydrogen atom.
s is an integer of 1 to 4, preferably 1 or 2.

Specific examples of the compound (i-2) having a (meth)acryloyloxy group include 2-isocyanate ethyl (meth)acrylate, isocyanate methyl methacrylate, etc. Commercially available products include, for example, Karenz (registered trademark; hereafter abbreviated) AOI and Karenz MOI (both manufactured by Showa Denko K.K.).

An example of the compound (i-2) having a (meth)acryloyloxy group is a compound represented by formula (1c).

In formula (1c), R ¹¹ is a hydrogen atom or a methyl group, and is preferably a hydrogen atom.
R ¹⁴ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and is preferably a methyl group.
t is an integer of 1 to 8, preferably an integer of 1 to 4, and more preferably an integer of 1 to 2.
u is an integer of 0 to 4, preferably an integer of 0 to 2.

Specific examples of the compound (i-2) having a (meth)acryloyloxy group include 2,2-(bisacryloyloxymethyl)propyl isocyanate and 1,1-(bisacryloyloxymethyl)ethyl isocyanate (product name "Kalends BEI", manufactured by Showa Denko K.K.), and preferably 1,1-(bisacryloyloxymethyl)ethyl isocyanate.

For example, when polyether monool (i-1) is polyoxypropylene monool, monomer 1-1 is preferably one or more selected from the compounds represented by formula (1-1-1), formula (1-1-2) and formula (1-1-3).

In formula (1-1-1), formula (1-1-2), and formula (1-1-3), m, n1, and n2 each independently represent an integer of preferably 20 to 600, more preferably an integer of 35 to 500, and even more preferably an integer of 65 to 250.
Bu is a butyl group.

<Monomer 1-2>
Monomer 1-2 is a reaction product of (ii), which is an equimolar reaction product of polyether monool (ii-1), diisocyanate (ii-2) and a compound (ii-3) having a (meth)acryloyloxy group, and the compound (ii-3) having a (meth)acryloyloxy group is a compound having one group reactive with an isocyanate group per molecule and having one or two (meth)acryloyloxy groups per molecule.

As monomer 1-2, a compound represented by formula (2) is preferred.

In formula (2), ^R2 is a monovalent organic group having one or two (meth)acryloyloxy groups.
R ²² is preferably an alkylene group having 2 to 8 carbon atoms, more preferably an alkylene group having 2 to 4 carbon atoms. A plurality of R ²² present in one molecule may be the same or different. When two or more types of R ²² are present in one molecule, the chain of -OR ²² - may be block or random. R ²² is preferably selected from an ethylene group, a propylene group, a 1,2-dimethylethylene group, and a 1-ethylethylene group, more preferably one or more types selected from an ethylene group and a propylene group.
Similarly to (OR ¹² ) in formula (1), (OR ²² ) is also preferably a unit based on a monomer a having one epoxy group and an ether bond other than the ether bond of the epoxy group in one molecule. The preferred embodiment of the monomer a is the same as that of the monomer 1-1.
R ²³ is an alkyl group having 1 to 20 carbon atoms, preferably an alkyl group having 2 to 8 carbon atoms, and more preferably a butyl group.
^R24 is a divalent group obtained by removing two isocyanate groups from a diisocyanate. Examples of diisocyanates will be described later.
b is an integer of 20 to 600, preferably an integer of 35 to 500, and more preferably an integer of 65 to 250.

(Polyether monol (ii-1))
The polyether monol (ii-1) is the same as the polyether monol (i-1) in the monomer 1-1, and the preferred embodiments are also the same.

An example of the polyether monool (ii-1) is one represented by formula (2a).

In formula (2a), R ²² , R ²³ and b have the same meanings as the same symbols in formula (2).

(Diisocyanate (ii-2))
The diisocyanate (ii-2) is a compound having two isocyanate groups in one molecule.
Examples of the diisocyanate (ii-2) include non-yellowing aromatic diisocyanates, aliphatic diisocyanates, alicyclic diisocyanates, and various modified products of these diisocyanates (modified products having two isocyanate groups). The diisocyanates may be used alone or in combination of two or more.
The diisocyanate (ii-2) is preferably at least one selected from aliphatic diisocyanates and alicyclic diisocyanates, from the viewpoint of further improving the bending durability of the cured product of the hard coat resin composition.

Specific examples of non-yellowing aromatic diisocyanates include xylylene diisocyanate and tetramethylxylylene diisocyanate.
Specific examples of the aliphatic diisocyanate include 1,6-hexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, and lysine diisocyanate.
Alicyclic diisocyanates include isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 2,5-norbornane diisocyanate, and 2,6-norbornane diisocyanate.

An example of diisocyanate (ii-2) is a compound represented by formula (2b).

In formula (2b), R ²⁴ has the same meaning as the same symbol in formula (2).
As the diisocyanate, from the viewpoint of further improving the bending durability of the cured product of the hard coat resin composition, 1,6-hexamethylene diisocyanate, isophorone diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate are preferred.

(Compound (ii-3) Having a (Meth)acryloyloxy Group)
The compound (ii-3) having a (meth)acryloyloxy group is a compound having one group reactive with an isocyanate group in one molecule and having one or two (meth)acryloyloxy groups in one molecule.
Examples of the group that reacts with an isocyanate group include a hydroxyl group and an amino group having a nitrogen atom bonded to a hydrogen atom. The number of hydroxyl groups and the number of hydrogen atoms bonded to the nitrogen atom in the group that reacts with an isocyanate group are preferably each 1. In addition, the group that reacts with an isocyanate group is preferably a hydroxyl group bonded to an aliphatic hydrocarbon group or an alicyclic hydrocarbon group.

As the compound (ii-3) having a (meth)acryloyloxy group, hydroxyalkyl (meth)acrylates and hydroxycycloalkyl (meth)acrylates are preferred, and hydroxyalkyl (meth)acrylates in which the hydroxyalkyl group has 8 or less carbon atoms are particularly preferred.

An example of the compound (ii-3) having a (meth)acryloyloxy group is a compound represented by formula (2c).

In formula (2c), R ²¹ is a hydrogen atom or a methyl group, and is preferably a hydrogen atom.
p is an integer of 1 to 4, and preferably an integer of 1 or 2.

Specific examples of the compound (ii-3) having a (meth)acryloyloxy group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, and 6-hydroxyhexyl (meth)acrylate. Commercially available products include Light Ester HO-250(N), Light Ester HOP(N), Light Ester HOA(N), Light Ester HOP-A(N), and Light Ester HOB(N) (all manufactured by Kyoeisha Chemical Co., Ltd.), and 4-HBA (manufactured by Osaka Organic Chemical Industry Ltd.).

An example of the compound (ii-3) having a (meth)acryloyloxy group is a compound represented by formula (2d).

In formula (2d), R ²¹ is a hydrogen atom or a methyl group, and is preferably a hydrogen atom.
R ²⁵ is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and is preferably a methyl group.
q is an integer of 1 to 8, preferably an integer of 1 to 4, and more preferably an integer of 1 to 2.
r is an integer of 0 to 4, preferably an integer of 0 to 2.

Specific examples of the compound (ii-3) having a (meth)acryloyloxy group include 2,2-(bisacryloyloxymethyl)propan-1-ol and 1,1-(bisacryloyloxymethyl)ethane-1-ol, with 1,1-(bisacryloyloxymethyl)ethane-1-ol being preferred.

<Monomer 1-3>
Monomer 1-3 is a reaction product of (iii), and is an equimolar reaction product of polyether polyol (iii-1) and a compound (iii-2) having a (meth)acryloyloxy group, and the compound (iii-2) having a (meth)acryloyloxy group is a compound having one isocyanate group per molecule and one or two (meth)acryloyloxy groups per molecule.

As the monomer 1-3, a compound represented by the formula (III) is preferable.
R ³ -NH-C(=O)-Z ¹ ...(III)
In formula (III), ^R3 is a monovalent organic group having one or two (meth)acryloyloxy groups.
^Z1 is a residue of a polyether polyol obtained by removing one hydrogen atom from one of the hydroxyl groups in the polyether polyol.

More preferably, monomer 1-3 is a compound represented by formula (3).

In formula (3), ^R3 is the same as ^R3 in formula (III).
R ³² is preferably an alkylene group having 2 to 8 carbon atoms, more preferably an alkylene group having 2 to 4 carbon atoms. A plurality of R ³² present in one molecule may be the same as or different from each other. When two or more types of R ³² are present in one molecule, the chain of -OR ³² - may be block or random. R ³² is preferably one or more types selected from an ethylene group, a propylene group, a 1,2-dimethylethylene group, and a 1-ethylethylene group, more preferably one or more types selected from an ethylene group and a propylene group.
Similarly to (OR ¹² ) in formula (1), (OR ³² ) is also preferably a unit based on a monomer a having one epoxy group and an ether bond other than the ether bond of the epoxy group in one molecule. The preferred embodiment of the monomer a is the same as that of the monomer 1-1.
c is an integer of 20 to 600, preferably an integer of 35 to 500, and more preferably an integer of 65 to 250.

(Polyether polyol (iii-1))
The polyether polyol (iii-1) is a compound obtained by ring-opening polymerization of an alkylene oxide and/or the monomer a with an initiator having an active hydrogen-containing group and having two or more active hydrogens, and having an initiator residue, a polyether chain, and hydroxyl groups corresponding to the number of active hydrogens of the initiator.

The alkylene oxide is preferably an alkylene oxide having a carbon number of 2 to 4. Specific examples of the alkylene oxide having a carbon number of 2 to 4 include propylene oxide, ethylene oxide, 1,2-butylene oxide, and 2,3-butylene oxide.
Moreover, the monomer a is preferably a monomer represented by the above formula (12). Examples of the monomer represented by formula (12) include methyl glycidyl ether, butyl glycidyl ether, 2-ethylhexyl glycidyl ether, lauryl glycidyl ether, and hexyl glycidyl ether. From the viewpoint of further improving the bending durability of the cured product of the hard coat resin composition, butyl glycidyl ether or 2-ethylhexyl glycidyl ether is preferable.

When the alkylene oxide and the monomer a undergo ring-opening polymerization, the ratio of the mass of the monomer a to the total mass of the two is preferably 90% by mass or less, more preferably 85% by mass or less, and even more preferably 10 to 80% by mass, from the viewpoint of adjusting the hardness and bending durability of the cured product of the hard coat resin composition.

The active hydrogen-containing group of the initiator includes a hydroxyl group, a carboxyl group, and an amino group having a hydrogen atom bonded to a nitrogen atom. The active hydrogen-containing group of the initiator is preferably a hydroxyl group, more preferably an alcoholic hydroxyl group.

Examples of initiators having two or more active hydrogen atoms include water, polyhydric alcohols, polyhydric phenols, polycarboxylic acids, and amine compounds having two or more hydrogen atoms bonded to nitrogen atoms. The initiator is preferably water or a dihydric aliphatic alcohol, more preferably a dihydric aliphatic alcohol. A polyoxyalkylene polyol having a lower molecular weight than the target polyether polyol may also be used as the initiator.

The carbon number of the dihydric aliphatic alcohol used as the initiator is preferably 2 to 8. Specific examples of the dihydric aliphatic alcohol used as the initiator include ethylene glycol, propylene glycol, polypropylene glycol such as dipropylene glycol, and 1,4-butanediol.

The oxyalkylene groups in the polyether polyol (iii-1) are preferably composed of only oxypropylene groups, or a combination of oxypropylene groups and other groups. The oxyalkylene groups other than oxypropylene groups are preferably one or more selected from oxyethylene groups and oxytetramethylene groups. The ratio of oxypropylene groups to all oxyalkylene groups in the polyether polyol is preferably 50 to 100 mass%, more preferably 80 to 100 mass%.
When the initiator is a polyoxyalkylene polyol having a lower molecular weight than the target polyether polyol, the oxyalkylene group in the initiator is regarded as the oxyalkylene group in the obtained polyether polyol.

Of the polyether polyols (iii-1), a polyoxyalkylene polyol having a low hydroxyl value, i.e., a high molecular weight, can be produced by ring-opening polymerization of an alkylene oxide having 3 or more carbon atoms, preferably propylene oxide, as an initiator in the presence of a composite metal cyanide complex catalyst.
Examples of polyoxyalkylene polyols having a low hydroxyl value include polyoxyalkylene polyols having a hydroxyl value of 40 mgKOH/g or less.
Of the polyether polyols (iii-1), a polyoxyalkylene polyol having a low hydroxyl value and an oxyethylene group can be produced by ring-opening polymerization of an alkylene oxide having 3 or more carbon atoms, preferably propylene oxide, using a polyoxyalkylene polyol having a high hydroxyl value and an oxyethylene group, for example a hydroxyl value of 50 mgKOH/g or more, as an initiator in the presence of a composite metal cyanide complex catalyst.
Among the polyether polyols (iii-1), the polyoxyalkylene polyol having a high hydroxyl value and the polyoxyalkylene polyol having a high hydroxyl value serving as the initiator can also be produced using an alkali catalyst such as potassium hydroxide.

The average number of hydroxyl groups in one molecule of the polyether polyol (iii-1) is preferably 1.60 to 2.00, more preferably 1.70 to 2.00, and even more preferably 1.80 to 1.96. A polyether polyol having an average number of hydroxyl groups in one molecule of 1.60 to 2.00 is sometimes called a polyether diol.
The hydroxyl value of the polyether polyol (iii-1) is preferably from 1.6 to 18.1 mgKOH/g, more preferably from 2.8 to 14 mgKOH/g.

Polyether polyol (iii-1) may be a mixture of two or more polyether polyols. In this case, each polyether polyol is preferably a polyether polyol that falls within the above category.

An example of polyether polyol (iii-1) is one represented by formula (3a).

In formula (3a), R ³² and c have the same meanings as the same symbols in formula (3).

(Compound (iii-2) Having a (Meth)acryloyloxy Group)
The compound (iii-2) having a (meth)acryloyloxy group is a compound having one isocyanate group in one molecule and one or two (meth)acryloyloxy groups in one molecule. The compound (iii-2) having a (meth)acryloyloxy group is the same as the compound (i-2) having a (meth)acryloyloxy group in the monomer 1-1, and the preferred embodiments are also the same.

The content of the monofunctional urethane (meth)acrylate is preferably 0.1 to 30.0% by mass, more preferably 0.5 to 20.0% by mass, and even more preferably 1.0 to 15.0% by mass, based on 100% by mass of the solid content of the hard coat resin composition. When the content of the monofunctional urethane (meth)acrylate is within the above range, a cured product having high hardness, excellent bending durability and adhesion, and a good appearance can be obtained.

From the viewpoint of obtaining a cured product of a resin composition for hard coat having excellent bending durability, the molecular weight of the monofunctional urethane (meth)acrylate is preferably 3,000 to 35,000, more preferably 3,000 to 30,000, even more preferably 4,000 to 25,000, and even more preferably 5,000 to 20,000. When two or more types of monomers (monofunctional urethane (meth)acrylates) are used in combination, it is preferable that the molecular weight of each is within the above range.

From the viewpoint of obtaining a cured product of a resin composition for hard coat having excellent bending durability, the monofunctional urethane (meth)acrylate has a glass transition temperature of preferably −55° C. or lower, more preferably −85 to −58° C., and even more preferably −80 to −60° C.
The glass transition temperature of the monofunctional urethane (meth)acrylate in the present invention is a value determined by dynamic viscoelasticity measurement of a homopolymer of the monofunctional urethane (meth)acrylate. Specifically, it is determined by the method described in the examples.

From the viewpoint of obtaining a cured product of a resin composition for hard coat having excellent bending durability, the monofunctional urethane (meth)acrylate has a storage modulus at −20 to 80° C. of preferably 5 to 150 kPa, more preferably 5 to 130 kPa, and even more preferably 5 to 100 kPa.
The storage modulus of the monofunctional urethane (meth)acrylate in the present invention is a value determined by dynamic viscoelasticity measurement of a homopolymer of the monofunctional urethane (meth)acrylate. Specifically, it is determined by the method described in the examples.

[Polyfunctional (meth)acrylate]
The hard coat resin composition of the present invention can obtain a cured product with high hardness by including a polyfunctional (meth)acrylate. The polyfunctional (meth)acrylate is not particularly limited as long as it has two or more (meth)acryloyloxy groups in the molecule, and examples thereof include alkanediol di(meth)acrylates such as 1,4-butanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, and tricyclodecanedimethylol di(meth)acrylate; bisphenol-modified di(meth)acrylates such as bisphenol A ethylene oxide-modified di(meth)acrylate and bisphenol F ethylene oxide-modified di(meth)acrylate; polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, and the like. Examples of the polyisocyanuric acid modified tri(meth)acrylate include isocyanuric acid modified tri(meth)acrylates such as gold di(meth)acrylate, epoxy di(meth)acrylate, pentaerythritol (meth)acrylate, dipentaerythritol (meth)acrylate, dipentaerythritol hexa(meth)acrylate, pentaerythritol tetra(meth)acrylate, ditrimethylolpropane tetra(meth)acrylate, pentaerythritol tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, tripentaerythritol poly(meth)acrylate, isocyanuric acid ethylene oxide modified tri(meth)acrylate, and ε-caprolactone modified tris(acryloxyethyl)isocyanurate.
The polyfunctional (meth)acrylates may be used alone or in combination of two or more kinds.

Commercially available products of the polyfunctional (meth)acrylate include "Viscoat (registered trademark; hereafter abbreviated) #802", "Viscoat #295", "Viscoat #300" (manufactured by Osaka Organic Chemical Industry Ltd.), "NK Ester A-HD-N", "NK Ester HD-N", "NK Ester A-NOD-N", "NK Ester NOD-N", "NK Ester A-DCP", "NK Ester DCP", "NK Ester A-BEP-2.2", "NK Ester A-TMPT", "NK Ester TMPT", and "NK Ester M-DPH-12E" (manufactured by Shin-Nakamura Chemical Co., Ltd.).

The content of the polyfunctional (meth)acrylate is preferably 5 to 70% by mass, more preferably 10 to 65% by mass, and even more preferably 20 to 60% by mass, based on 100% by mass of the solid content of the hard coat resin composition. If the content of the polyfunctional (meth)acrylate is 5% by mass or more, the hardness of the cured product of the hard coat resin composition can be increased, and if the content is 70% by mass or less, a cured product with high hardness, excellent bending durability and adhesion, and good appearance can be obtained.

[(Meth)acrylate having an epoxy group and a (meth)acryloyloxy group]
From the viewpoint of further increasing the hardness of the cured product, the resin composition for hard coat of the present invention preferably further contains a (meth)acrylate having an epoxy group and a (meth)acryloyloxy group (hereinafter also referred to as "epoxy (meth)acrylate").
Examples of the epoxy (meth)acrylate include epoxy (meth)acrylates which are reaction products of polyglycidyl compounds such as bisphenol A type epoxy resin, bisphenol F type epoxy resin, phenol novolac type epoxy resin, trisphenolmethane type epoxy resin, polyethylene glycol diglycidyl ether, glycerin polyglycidyl ether, and trimethylolpropane polyglycidyl ether with (meth)acrylic acid.
Specific examples include bisphenol type epoxy (meth)acrylates such as bisphenol A type epoxy (meth)acrylate, bisphenol F type epoxy (meth)acrylate, and bisphenol S type epoxy (meth)acrylate; cresol novolac type epoxy (meth)acrylate, amine modified bisphenol type epoxy (meth)acrylate, caprolactone modified bisphenol type epoxy (meth)acrylate, carboxylic anhydride modified epoxy (meth)acrylate, and phenol novolac type epoxy (meth)acrylate. Among these, from the viewpoint of further increasing the hardness of the cured product, bisphenol A type epoxy (meth)acrylate, bisphenol F type epoxy (meth)acrylate, and phenol novolac type epoxy (meth)acrylate are preferred.
The epoxy (meth)acrylate may be used alone or in combination of two or more kinds.

Commercially available products of the epoxy (meth)acrylate include "KAYARAD R-115" (manufactured by Nippon Kayaku Co., Ltd.), "Epoxy Ester 3000KM", "Epoxy Ester 3000A" (manufactured by Kyoeisha Chemical Co., Ltd.), "BAEM-50", "MAEA-100", "BAEM-100" (manufactured by KSM Co., Ltd.), "NK Oligo EA-1010N", "NK Oligo EA-1010LC", "NK Oligo EA-1010NT2", "NK Oligo EA-1020LC3" (manufactured by Shin-Nakamura Chemical Co., Ltd.), "EBECRYL 600", "EBECRYL 3603" (manufactured by Daicel-Allnex Co., Ltd.), etc.

The content of the epoxy (meth)acrylate is preferably 70% by mass or less, more preferably 1 to 60% by mass, even more preferably 3 to 50% by mass, and even more preferably 10 to 50% by mass, based on 100% by mass of the solid content of the hard coat resin composition. If the content of the epoxy (meth)acrylate is within the above range, the hardness of the cured product of the hard coat resin composition can be further increased.

[Initiator]
The initiator used in the present invention includes a radical polymerization initiator. As the radical polymerization initiator, a known one can be used, and a photoradical polymerization initiator or a thermal radical polymerization initiator is preferably used.

<Photoradical polymerization initiator>
Examples of the photoradical polymerization initiator include 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methylpropiophenone, diethoxyacetophenone, 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropanone, 1-(4-dodecylphenyl)-2-hydroxy-2-methylpropanone, 4-(2-hydroxyethoxy)-phenyl(2-hydroxy-2-propyl)ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, and benzoin-n -butyl ether, benzoin phenyl ether, benzyl dimethyl ketal, benzophenone, benzoylbenzoic acid, methyl benzoylbenzoate, 4-phenylbenzophenone-4-methoxybenzophenone, thioxanthone, 2-chlorothioxanthone, 2-methylthioxanthone, 2,4-dimethylthioxanthone, isopropylthioxanthone, 2,4-dichlorothioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, methylphenyl glyoxylate, benzyl, camphorquinone, and the like.
In addition, commercially available products such as those having the trade names "Irgacure 184", "Irgacure 127", "Irgacure 149", "Irgacure 261", "Irgacure 369", "Irgacure 500", "Irgacure 651", "Irgacure 754", "Irgacure 784", "Irgacure 819", "Irgacure 907", "Irgacure 1116", "Irgacure 1173", "Irgacure 1664", "Irgacure 1700", "Irgacure 1800", "Irgacure 1850", "Irgacure 2959", "Irgacure 4043", "Darocure (registered trademark; hereinafter, abbreviated) 1173", and "Darocure MBF" (all manufactured by BASF Corporation) are preferably used.

<Thermal Radical Polymerization Initiator>
Examples of the thermal radical polymerization initiator include azo compounds; and organic peroxides such as hydroperoxides, dialkyl peroxides, peroxy esters, diacyl peroxides, peroxydicarbonates, peroxyketals, and ketone peroxides. Specific examples of the thermal radical polymerization initiator include azobisisobutyronitrile, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, 2,5-dimethyl-2,5-di(2-ethylhexanoyl)peroxyhexane, t-butylperoxybenzoate, t-butyl peroxide, cumene hydroperoxide, dicumyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-dibutylperoxyhexane, 2,4-dichlorobenzoyl peroxide, 1,4-di(2-t-butylperoxyisopropyl)benzene, 1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, methyl ethyl ketone peroxide, and 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate.

From the viewpoint of an appropriate polymerization rate, the content of the initiator is preferably 0.01 to 20 parts by mass, more preferably 0.05 to 10 parts by mass, and even more preferably 0.1 to 8 parts by mass, per 100 parts by mass of the monofunctional urethane (meth)acrylate, the polyfunctional (meth)acrylate, and the epoxy (meth)acrylate combined.

〔silica〕
From the viewpoint of further increasing the hardness of the cured product, the resin composition for hard coat of the present invention preferably further contains silica. The silica is not particularly limited, and known silica such as colloidal silica can be used.
The colloidal silica can be used in the form of a normal aqueous dispersion or in the form dispersed in an organic solvent. As the colloidal silica, from the viewpoint of uniformly and stably dispersing it in the hard coat resin composition, colloidal silica dispersed in an organic solvent is preferred.
Examples of the organic solvent include methanol, isopropyl alcohol, n-butanol, ethylene glycol, xylene/butanol, ethyl cellosolve, butyl cellosolve, N,N-dimethylformamide, N,N-dimethylacetamide, methyl ethyl ketone, methyl isobutyl ketone, toluene, etc. The organic solvent may be used alone or in combination of two or more kinds.

As the colloidal silica dispersed in an organic solvent, commercially available products can be used, and examples thereof include silica sol dispersed in methanol, IPA-ST (silica sol dispersed in isopropyl alcohol), NBA-ST (silica sol dispersed in n-butanol), EG-ST (silica sol dispersed in ethylene glycol), XBA-ST (silica sol dispersed in xylene/butanol), ETC-ST (silica sol dispersed in ethyl cellosolve), BTC-ST (silica sol dispersed in butyl cellosolve), DBF-ST (silica sol dispersed in dimethylformamide), DMAC-ST (silica sol dispersed in dimethylacetamide), MEK-ST (silica sol dispersed in methyl ethyl ketone), and MIBK-ST (silica sol dispersed in methyl isobutyl ketone), all of which are commercially available from Nissan Chemical Industries, Ltd.
The colloidal silica dispersed in an organic solvent may be used alone or in combination of two or more kinds.

The average particle size of the silica is preferably 1 to 200 nm, more preferably 2 to 150 nm, even more preferably 5 to 100 nm, and even more preferably 8 to 50 nm. When the average particle size of the silica is 1 nm or more, the hardness of the cured product can be further increased, and when it is 200 nm or less, the transparency of the cured product of the hard coat resin composition can be increased.
The average particle size of silica refers to the average primary particle size.
The average particle size of silica is the cumulative 50% value (number basis) in the equivalent sphericity distribution measured by a dynamic light scattering particle size distribution measuring device.

The shape of the silica is not particularly limited, and examples include spherical, hollow, porous, rod-like, plate-like, fibrous, and amorphous shapes.

When the hard coat resin composition of the present invention contains silica, the content of silica is preferably 1 to 70 mass %, more preferably 1 to 50 mass %, and even more preferably 3 to 30 mass %, based on 100 mass % of the solid content of the hard coat resin composition, from the viewpoint of increasing the hardness of the cured product.

〔solvent〕
The hard coat resin composition of the present invention may contain a solvent. Examples of the solvent include lactones such as γ-butyrolactone, γ-valerolactone, γ-caprolactone, γ-heptalactone, α-acetyl-γ-butyrolactone, and ε-caprolactone; ethers such as dioxane, 1,2-dimethoxymethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, tetraethylene glycol dimethyl ether, and tetraethylene glycol diethyl ether; carbonates such as ethylene carbonate and propylene carbonate; ketones such as methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, and acetophenone; and solvents such as phenol, cresol, and xylenol. Examples of the solvent include phenols; esters such as ethyl acetate, butyl acetate, ethyl lactate, ethyl cellosolve acetate, butyl cellosolve acetate, carbitol acetate, butyl carbitol acetate, and propylene glycol monomethyl ether acetate; hydrocarbons such as toluene, xylene, diethylbenzene, and cyclohexane; halogenated hydrocarbons such as trichloroethane, tetrachloroethane, and monochlorobenzene; organic solvents such as petroleum-based solvents such as petroleum ether and petroleum naphtha; fluorine-based alcohols such as 2H,3H-tetrafluoropropanol; hydrofluoroethers such as perfluorobutyl methyl ether and perfluorobutyl ethyl ether; alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, and n-propyl alcohol; and diacetone alcohol which has the properties of both a ketone and an alcohol.
As the solvent, from the viewpoint of ease of application work, esters, ethers, alcohols and ketones are preferable, ketones are more preferable, and methyl ethyl ketone and methyl isobutyl ketone are further preferable.
The solvent may be used alone or in combination of two or more kinds.

When the hard coat resin composition of the present invention contains a solvent, the content of the solvent is preferably 20 to 80% by mass, more preferably 30 to 70% by mass, and even more preferably 40 to 60% by mass, based on the total amount of the hard coat resin composition.

[Other ingredients]
The resin composition for hard coat of the present invention may contain other components in addition to the above-mentioned components from the viewpoint of good handling, hardness of the cured product, bending durability, etc. Examples of the other components include leveling agents, defoaming agents, ultraviolet absorbers, light stabilizers, antioxidants, polymerization inhibitors, crosslinking agents, etc. Examples of the leveling agents include fluorine-based compounds, silicone-based compounds, acrylic compounds, etc.
These other components may be blended in the resin composition for hard coat in a content range that does not impair the effects of the present invention.

[Production of hard coat resin composition]
The hard coat resin composition of the present invention can be produced by uniformly mixing a monofunctional urethane (meth)acrylate, a polyfunctional (meth)acrylate, a polymerization initiator, and optionally an epoxy (meth)acrylate, a solvent, and other components using a known mixing device such as a self-revolving stirring and defoaming device, a homogenizer, a planetary mixer, a three-roll mill, a bead mill, etc. The components in the hard coat resin composition may be mixed simultaneously or by successive addition.

[Cured product of hard coat resin composition]
The cured product of the present invention can be obtained by quickly curing the above-mentioned resin composition for hard coat of the present invention by applying light irradiation or heat treatment. Alternatively, the resin composition for hard coat of the present invention can be applied onto a substrate, dried, and then irradiated with light to cure the composition, thereby forming a hard coat layer, which can be used as a hard coat film.

The thickness of the hard coat layer after curing is usually 0.1 to 100 μm, preferably 1 to 20 μm.

Examples of substrates include polyester, polypropylene, polyethylene, polyacrylate, polycarbonate, triacetyl cellulose, polyethersulfone, and cycloolefin polymers.

Examples of methods for applying the hard coat resin composition include bar coater coating, Mayer bar coating, air knife coating, gravure coating, reverse gravure coating, microgravure coating, micro reverse gravure coater coating, die coater coating, dip coating, spin coat coating, spray coating, etc.

When the hard coat resin composition is irradiated with light to cure, the light source can be appropriately set according to the light absorption ability of the photopolymerization initiator. For example, ultraviolet light emitting diodes (LEDs), low pressure mercury lamps, high pressure mercury lamps, mercury xenon lamps, metal halide lamps, tungsten lamps, arc lamps, excimer lamps, excimer lasers, semiconductor lasers, YAG lasers, laser systems combining lasers and nonlinear optical crystals, high frequency induced ultraviolet generators, etc. can be used as light sources. The integrated light amount is, for example, about 0.01 to 5 J/cm ^2. After the light irradiation, a heat treatment may be further performed. By performing a heat treatment, the composition can be cured better. Usually, the heating temperature is about 40 to 200°C, and the heating time is about 1 minute to 15 hours. Also, the curability can be improved by leaving the composition at room temperature (about 15 to 25°C) for about 1 to 48 hours.

When the hard coat resin composition is cured by heat treatment, the heating temperature is usually about 40 to 250°C, and the heating time is about 5 minutes to 24 hours. Preferably, the heating time is shortened when the heating temperature is high, and the heating time is lengthened when the heating temperature is low.

[Physical Properties]
The cured product of the resin composition for hard coat of the present invention preferably has a glass transition temperature of 50 to 200°C, more preferably 70 to 180°C, and even more preferably 80 to 150°C.

The cured product of the resin composition for hard coat of the present invention has a storage modulus E' (25°C) at 25°C of preferably 500 to 5000 MPa, more preferably 700 to 4000 MPa, and even more preferably 900 to 3500 MPa.
The glass transition temperature and storage modulus of the cured product are values determined by dynamic viscoelasticity measurement, specifically, by the method described in the Examples.

The cured product of the resin composition for hard coat of the present invention preferably has a pencil hardness of F or more, more preferably H or more, as measured by the pencil hardness method of JIS K5600.
The pencil hardness of the cured product is measured by the method described in the Examples.

[Application]
The resin composition for hard coat of the present invention can be suitably used as a hard coat in electronic devices such as foldable phones and rollable displays.
Applications of the cured product of the hard coat resin composition of the present invention, articles comprising the cured product, and members comprising the cured product on at least a portion of the substrate surface include, for example, cover windows and housings of flexible displays such as foldable displays, rollable displays, and wearable displays.

The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples.

[Raw material compounds]
Details of the raw material compounds used in Synthesis Example 1 and Examples 1 to 4 are as follows.
DMC-TBA: zinc hexacyanocobaltate-tert-butyl alcohol complex AOI: 2-acryloyloxyethyl isocyanate; "Karens AOI" manufactured by Showa Denko K.K. Photopolymerization initiator: 2-hydroxy-2-methylpropiophenone; "Irgacure 1173" manufactured by BASF Corporation Multifunctional (meth)acrylate: mixture of tripentaerythritol acrylate, mono- and dipentaerythritol acrylate, and polypentaerythritol acrylate; "Viscoat #802" manufactured by Osaka Organic Chemical Industry Co., Ltd. Epoxy (meth)acrylate: bisphenol A-based epoxy acrylate; "KAYARAD R-115" manufactured by Nippon Kayaku Co., Ltd. Solvent 1: methyl ethyl ketone (MEK), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Solvent 2: methyl isobutyl ketone (MIBK), manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. Leveling agent: acrylic leveling agent; "BYK-361N", manufactured by BYK-Chemie Plasticizer: diisononyl phthalate (DINP), manufactured by Tokyo Chemical Industry Co., Ltd.

Synthesis Example 1 Synthesis of Monofunctional Urethane Acrylate 0.5 g of DMC-TBA and 112 g of n-butanol as an initiator were placed in a pressure-resistant reactor equipped with a stirrer and a nitrogen inlet tube, and 4,887 g of propylene oxide (hereinafter abbreviated as "PO") was added at a constant rate under a nitrogen atmosphere at 130°C to obtain intermediate A. 1,148 g of the intermediate A and 0.2 g of DMC-TBA were placed in a pressure-resistant vessel, and 2,325 g of PO was added at a constant rate over 5.5 hours under a nitrogen atmosphere at 130°C.
It was confirmed that the internal pressure of the pressure-resistant reactor had stopped decreasing, and polyether monol (hydroxyl value: 5.6 mg KOH/g, hydroxyl value-based molecular weight: 10,020, average number of hydroxyl groups: 1.08) was obtained.
Into a reaction vessel equipped with a stirrer and a nitrogen inlet tube, 500.0 g of the above polyether monool, 7.04 g of AOI (NCO index 100), and 0.04 g of a 25% by mass toluene solution of bismuth 2-ethylhexanoate were placed and stirred at 70° C. for 3 hours to obtain a monofunctional urethane acrylate (number average molecular weight 16,200, storage modulus at 25° C. 80 kPa, glass transition temperature −69° C.).

The number average molecular weight of the obtained monofunctional urethane acrylate was measured by gel permeation chromatography (GPC) under the following measurement conditions.
<Measurement conditions>
Equipment used: "HLC-8120GPC", manufactured by Tosoh Corporation Columns used: The following two types of columns were connected in series in this order: "TSKgel (registered trademark) G7000H _XL ", manufactured by Tosoh Corporation, 1 column "TSKgel (registered trademark) GMH _XL ", manufactured by Tosoh Corporation, 2 columns Column temperature: 40°C
Detector: Refractive index (RI) detector Eluent: Tetrahydrofuran Flow rate: 0.8 mL/min Sample concentration: 0.5% by mass
Sample injection volume: 100 μL
・Standard sample: polystyrene

The glass transition temperature and storage modulus of the monofunctional urethane acrylate were determined by dynamic viscoelasticity measurement as follows.
0.3 parts by mass of a photoradical polymerization initiator ("Irgacure 819", manufactured by BASF) was added to 100 parts by mass of a monofunctional urethane acrylate, and mixed with a planetary stirrer. The resulting mixture was irradiated under a nitrogen gas atmosphere with a conveyor-type UV irradiator (manufactured by Oak Manufacturing Co., Ltd.; mercury xenon lamp, illuminance 100 mW/ ^cm2 , accumulated light amount 3 J/ ^cm2 ) to obtain a cured sample of the monofunctional urethane acrylate (homopolymer; length 15 mm, width 5 mm, thickness 2 mm).
The storage modulus (25°C) and loss modulus of the cured sample were measured using a dynamic viscoelasticity measuring device ("EXSTAR TMA/SS6100", manufactured by Hitachi High-Tech Science Corporation; tensile mode, temperature range: -80 to 130°C, heating rate: 3°C/min, measurement frequency: 1 Hz, strain: 1%), and the temperature at the peak was taken as the glass transition temperature.

Example 1
The hard coat resin composition of Example 1 was produced by adding and mixing 5 parts by mass of the monofunctional urethane acrylate obtained in Synthesis Example 1, 45 parts by mass of a polyfunctional (meth)acrylate (Viscoat #802), 45 parts by mass of an epoxy (meth)acrylate (KAYARAD R-115), 4 parts by mass of a photopolymerization initiator (Irgacure 1173), 50 parts by mass of a solvent 1 (MEK), 50 parts by mass of a solvent 2 (MIBK), and 0.1 parts by mass of a leveling agent (BYK-361N).

[Examples 2 to 4]
Using the blending compositions shown in Table 1, hard coat resin compositions of Examples 2 to 4 were produced in the same manner as in Example 1.

[evaluation]
Test specimens were prepared using each of the hard coat resin compositions produced in Examples 1 to 4, and were evaluated by the following tests. The evaluation results are shown in Table 1. Examples 1 and 2 are working examples, and Examples 3 and 4 are comparative examples.
[Preparation of test specimen]
Each of the hard coat resin compositions of Examples 1 to 4 was applied to an easily-adhesive treated PET film ("A4300 (product name)" manufactured by Toyobo Co., Ltd., thickness 38 μm) using a bar coater at a coating speed of 600 mm/min to form a coating film. The coating film was dried at 100°C for 120 seconds to remove the solvent. Next, the coating film was irradiated with ultraviolet light using a conveyor-type UV irradiator (manufactured by Oak Manufacturing Co., Ltd.; mercury xenon lamp) under conditions of a nitrogen gas atmosphere, an illuminance of 300 mW/cm ² , and an accumulated light quantity of 200 mJ/cm ² to cure the coating film, thereby obtaining a hard coat film having a hard coat layer having a thickness of 5 μm after curing. The obtained hard coat film was cut into a length of 30 mm and a width of 10 mm to prepare a test specimen.

[Pencil hardness]
The pencil hardness of the above test specimen was measured using a pencil scratch tester based on JIS K5600. Specifically, the hard coat layer of the test specimen was scratched about 5 mm with a pencil at a 45 degree angle and a load of 1 kg applied from above, and the pencil hardness was expressed as the hardness of the pencil that did not scratch 4 or more times out of 5 times.

[Bending durability (cracks)]
The test specimen was wrapped around a rod having a diameter of 10 mm with the hard coat layer side facing inward, and the test specimen was slid five times, after which the surface of the hard coat layer was visually observed and evaluated according to the following evaluation criteria.
<Evaluation criteria>
A: No cracks C: Cracks

[Appearance (static bending test)]
The test specimen was wrapped around a rod having a diameter of 10 mm with the hard coat layer side facing inward and allowed to stand at 80° C. for 48 hours, after which the surface of the hard coat layer of the test specimen was visually observed and evaluated according to the following criteria.
<Evaluation criteria: Bleeding out>
A: No bleeding was observed. C: Bleeding was observed. <Evaluation criteria: peeling>
A: No peeling occurred at the PET film interface. C: Peeling occurred at the PET film interface.

[Glass transition temperature/storage modulus]
The glass transition temperature and storage modulus of the hard coat resin composition were determined by dynamic viscoelasticity measurement as follows.
The hard coat resin composition obtained in each example was dried at 100°C for 10 minutes to remove the solvent. Next, the composition was poured into a silicone mold so as to obtain a cured sample of 5 mm wide x 15 mm long x 2 mm thick, and then a cured sample of the hard coat resin composition was obtained using a conveyor-type UV irradiator (Oak Manufacturing Co., Ltd.; mercury xenon lamp, illuminance 100 mW/cm ² , cumulative light amount 3 J/cm ² ) under a nitrogen gas atmosphere. The storage modulus (25°C) and glass transition temperature (°C) of the obtained cured sample were measured using a dynamic viscoelasticity measuring device (EXSTAR 6100, Hitachi High-Tech Science Co., Ltd.; tensile mode, temperature range: -100 to 200°C, heating rate: 3°C/min, measurement frequency: 1 Hz, strain 1%). The glass transition temperature was taken as the peak temperature of tan δ.

The hard coat resin composition of the present invention was found to have high hardness, excellent bending durability and adhesion, and a good appearance.

Claims (9)

A resin composition for hard coat comprising a monofunctional urethane (meth)acrylate, a polyfunctional (meth)acrylate having two or more (meth)acryloyloxy groups in the molecule, and an initiator,
The content of the monofunctional urethane (meth)acrylate is 0.1 to 30.0% by mass based on 100% by mass of the solid content of the hard coat resin composition,
The content of the polyfunctional (meth)acrylate is 5 to 70% by mass based on 100% by mass of the solid content of the hard coat resin composition,
The resin composition for hard coat, wherein the monofunctional urethane (meth)acrylate is one or more monomers selected from the reaction products of the following (i) to (iii):
(i) An equimolar reaction product of a polyether monol and a compound having a (meth)acryloyloxy group, the compound having a (meth)acryloyloxy group having one isocyanate group per molecule and one (meth)acryloyloxy group per molecule.
(ii) A reaction product of an equimolar amount of a polyether monool, a diisocyanate, and a compound having a (meth)acryloyloxy group, wherein the compound having a (meth)acryloyloxy group has one group reactive with an isocyanate group in one molecule, and has one (meth)acryloyloxy group in one molecule.
(iii) An equimolar reaction product of a polyether polyol and a compound having a (meth)acryloyloxy group, wherein the compound having a (meth)acryloyloxy group has one isocyanate group per molecule and one (meth)acryloyloxy group per molecule. The hard coat resin composition according to claim 1, further comprising a (meth)acrylate having an epoxy group and a (meth)acryloyloxy group. 3. The resin composition for hard coat according to claim 1, wherein the monofunctional urethane (meth)acrylate has a number average molecular weight of 3,000 to 35,000. 4. The resin composition for hard coat according to claim 1, wherein the monofunctional urethane (meth)acrylate has a glass transition temperature of -55°C or lower. A cured product obtained by curing the resin composition for hard coat according to any one of claims 1 to 4 . The cured product according to claim 5 , having a glass transition temperature of 50 to 200°C. The cured product according to claim 5 or 6 , having a storage modulus E'(25°C) of 500 to 5000 MPa at 25°C. An article comprising the cured product according to any one of claims 5 to 7 . A member comprising a substrate having the cured product according to any one of claims 5 to 7 on at least a part of the surface thereof.