JP7766938B2 - Photocurable artificial nail composition - Google Patents

Description

The present invention relates to a photocurable artificial nail composition.

Nail art, which involves decorating natural fingernails or toenails or gluing artificial nails onto them, is becoming increasingly popular. Furthermore, artificial nails are often formed on top of natural nails to reinforce them and prevent them from cracking or peeling due to external forces.
For such nail decoration or reinforcement, resin-containing materials known as manicures, pedicures, and sculptures are applied to the nails.

Recently, photocurable artificial nail compositions known as gel nails have been attracting attention as materials used to decorate or reinforce nails. Gel nails are photocurable gel-like nail coating materials (photocurable artificial nail compositions), and are known to contain, for example, (meth)acrylate oligomers and (meth)acrylic monomers. Gel nails are applied to nails and cured by exposure to ultraviolet light, forming a crosslinked polymer coating through a radical polymerization reaction, which is said to create a tough coating that is resistant to peeling from the nail.

To date, photocurable artificial nail compositions such as gel nails have been primarily studied from the perspectives of adhesion of the cured coating film to the substrate (adhesion to the nail), durability of adhesion, curability, and the aesthetic appeal of the cured coating film. However, there has been a demand for further improvements in the properties of photocurable artificial nail compositions to date, in terms of adhesion of the cured coating film to the substrate (adhesion to the nail) and durability of adhesion. Furthermore, there is also a demand for photocurable artificial nail compositions with properties such as curability and the aesthetic appeal of the cured coating film.

In photocurable artificial nail compositions such as gel nails, the following studies have been conducted to improve the adhesion of the cured coating film to the substrate (adhesion strength to the nail) and the durability of adhesion.
Patent Document 1 describes an artificial nail compound containing (a) a compound having at least one radically polymerizable unsaturated double bond in the molecule, (b) an acidic phosphorus compound having at least one radically polymerizable unsaturated double bond in the molecule, and (c) a radical polymerization initiator.

Patent Document 2 describes a photocurable artificial nail composition containing a urethane (meth)acrylate oligomer, a radically polymerizable compound, and a photopolymerization initiator. This composition specifically uses a "radically polymerizable phosphate compound having a methacrylate group" such as methacryloxyethyl hexanoate phosphate or trismethacryloyloxyethyl acid phosphate as the radically polymerizable compound, but does not use a "radically polymerizable phosphate compound having an acrylate group."

JP 2010-53097 A Japanese Patent Application Laid-Open No. 2017-197532

The problem that the present invention aims to solve is to obtain a photocurable artificial nail composition that exhibits excellent adhesion to the substrate (adhesion to the nail) and adhesion durability of the cured coating film, as well as excellent properties such as curability and the aesthetic appeal of the cured coating film. Furthermore, the present invention aims to obtain a photocurable artificial nail composition that prevents the cured coating film formed on the nail from becoming cloudy over time, and that exhibits excellent properties such as curability and the aesthetic appeal of the cured coating film.

As a result of intensive research into solving the above problems, the present inventors have found that the above problems can be solved by forming a photocurable artificial nail composition with a specific composition, and have thus completed the present invention.
Specifically, the following applies:
Item 1: A photocurable artificial nail composition comprising: (a) a radically polymerizable phosphoric acid compound having an acrylate group; (b) a radically polymerizable compound having a (meth)acrylate group and no phosphorus atom; and (c) a photopolymerization initiator.
Item 2: The photocurable artificial nail composition according to Item 1, wherein (a) the radically polymerizable phosphoric acid compound having an acrylate group is a radically polymerizable phosphoric acid ester compound having an acrylate group.
Item 3: The photocurable artificial nail composition according to Item 1 or 2, wherein (a) the radically polymerizable phosphoric acid compound having an acrylate group is 2-acryloyloxyethyl phosphate and/or bis(2-acryloyloxyethyl) phosphate.
Item 4: The photocurable artificial nail composition according to any one of Items 1 to 3, wherein (b) the radically polymerizable compound having a (meth)acrylate group and no phosphorus atom is a radically polymerizable oligomer having a (meth)acrylate group.
Item 5: The photocurable artificial nail composition according to any one of Items 1 to 4, wherein the content of (a) the radically polymerizable phosphoric acid compound having an acrylate group is more than 0% by mass and not more than 4.4% by mass, based on the total amount of components of the photocurable artificial nail composition.

The photocurable artificial nail composition of the present invention exhibits remarkable effects, such as excellent adhesion of the cured coating film to the substrate (adhesion to the nail) and adhesion durability, as well as excellent properties such as curability and the aesthetic appearance of the cured coating film.

The photocurable artificial nail composition of the present invention will now be described.
The photocurable artificial nail composition of the present invention contains a radically polymerizable phosphoric acid compound having an acrylate group, a radically polymerizable compound having a (meth)acrylate group but not a phosphorus atom, and a photopolymerization initiator.
The mechanism by which the inclusion of a radically polymerizable phosphoric acid compound having an acrylate group in the photocurable composition of the present invention improves the adhesion of the cured coating film to a substrate (adhesion to a nail) and the durability of adhesion is unknown, but the present inventors speculate as follows.
Generally, acrylate groups have less steric hindrance and are more curable than methacrylate groups, and therefore are believed to cure reliably after penetrating the nail surface and to adhere strongly to the entire nail, thereby improving the adhesion of the cured coating film to the substrate (adhesion strength to the nail) and the durability of adhesion. However, the present invention is not limited to this conjecture.
Furthermore, in the photocurable artificial nail composition of the present invention, the content of the radically polymerizable phosphoric acid compound having an acrylate group is within a specific range (more than 0 mass %, preferably 0.1 mass % or more and 4.4 mass % or less, preferably 4.3 mass % or less) relative to the total amount of components of the photocurable artificial nail composition, thereby preventing the photocurable artificial nail composition coating film formed on the nail from becoming cloudy over time (clouding over time). Although the mechanism by which this can be prevented is unclear, the present inventors speculate as follows.
Generally, radical polymerizable phosphate compounds having an acrylate group are often provided as a mixture of a compound having one hydroxyl group bonded to a phosphorus atom and a compound having two hydroxyl groups bonded to a phosphorus atom. When a radical polymerizable phosphate compound having an acrylate group bonds (hydrogen bonds) with a nail, one hydroxyl group bonded to the phosphorus atom contributes, resulting in an excess of hydroxyl groups bonded to the phosphorus atom. It is believed that these excess hydroxyl groups react with moisture evaporated from the nail, causing the cured coating film to become cloudy over time. This is because the cured coating film does not become cloudy immediately after application, and does not become cloudy over time in systems that do not contain a radical polymerizable phosphate compound having an acrylate group. This suggests that the clouding over time of the cured coating film is due to the reaction between the excess hydroxyl groups from the radical polymerizable phosphate compound having an acrylate group and moisture evaporated from the nail. From this, it is believed that by setting the content of the radically polymerizable phosphate compound having an acrylate group within a specific range relative to the total amount of components of the photocurable artificial nail composition, it is possible to prevent the photocurable artificial nail composition coating film formed on the nail from becoming cloudy over time. However, the present invention is not limited to this speculation.

Hereinafter, a photocurable artificial nail composition containing (a) a radically polymerizable phosphoric acid compound having an acrylate group, (b) a radically polymerizable compound having a (meth)acrylate group and no phosphorus atom, and (c) a photopolymerization initiator will be described in detail.
In this specification, (meth)acrylate refers to both acrylate and methacrylate.

[Radically polymerizable phosphate compound having an acrylate group]
The radical polymerizable phosphate compound having an acrylate group is not particularly limited as long as it has an acrylate group and a phosphate group (-P(=O)(OH) ₂ group or -P(=O)(OH)- group) in the molecule.
For example, the following formula:
CH ₂ =CH-COO-R ¹ -P(=O)(OH) ₂
CH ₂ =CH-COO-R ² -P(=O)(OH)-R ³ -OCO-CH=CH ₂
(In the formula, R ¹ , R ² and R ³ represent divalent organic groups.)
The compound may be one or more compounds selected from the group consisting of compounds represented by the following formula:

Examples of such radically polymerizable phosphate compounds having an acrylate group include 2-acryloyloxyethyl phosphate, 2-acryloyloxypropyl phosphate, 2-acryloyloxybutyl phosphate, 2-acryloyloxypentyl phosphate, 2-acryloyloxyhexyl phosphate, acryloyloxyethyl valerate phosphate, acryloyloxypropyl valerate, acryloyloxybutyl valerate phosphate, acryloyloxypentyl valerate, acryloyloxyhexyl valerate, acryloyloxyethyl caproate phosphate, acryloyloxypropyl caproate phosphate, acryloyloxybutyl caproate phosphate, acryloyloxypentyl caproate, acryloyloxyhexyl caproate phosphate, and acryloyloxy caprylate phosphate. Examples of the acrylate-containing radical polymerizable phosphate compound include one or more compounds selected from the group consisting of ethyl caprylate phosphate, acryloyloxypropyl caprylate phosphate, acryloyloxybutyl caprylate phosphate, acryloyloxypentyl caprylate phosphate, acryloyloxyhexyl caprylate, bis(2-acryloyloxyethyl) phosphate, bis(2-acryloyloxypropyl) phosphate, bis(2-acryloyloxybutyl) phosphate, bis(2-acryloyloxypentyl) phosphate, bis(2-acryloyloxyhexyl) phosphate, acid phosphooxypolyoxyethylene glycol monoacrylate, acid phosphooxypolyoxypropylene glycol monoacrylate, ethylene oxide-modified phosphate diacrylate, propylene oxide-modified phosphate diacrylate, and phosphate-modified epoxy acrylate. Examples of the radical polymerizable phosphate compound having an acrylate group include a radical polymerizable phosphate ester compound having an acrylate group.

In the photocurable artificial nail composition of the present invention, the content of the radically polymerizable phosphate compound having an acrylate group is not particularly limited. It may be, for example, more than 0% by mass, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 0.5% by mass or more, relative to the total amount of components of the photocurable artificial nail composition, and may be, for example, 10.0% by mass or less, preferably 7.0% by mass or less, and more preferably 5.0% by mass or less. By including the radically polymerizable phosphate compound having an acrylate group, the photocurable artificial nail composition of the present invention can have improved adhesion to nails.
In the photocurable artificial nail composition of the present invention, by setting the content of the radically polymerizable phosphoric acid compound having an acrylate group to more than 0 mass %, preferably 0.1 mass % or more, and 4.4 mass % or less, preferably 4.3 mass % or less, based on the total amount of components of the photocurable artificial nail composition, it is possible to prevent the photocurable artificial nail composition coating film formed on the nail from becoming cloudy over time (clouding over time).

[Radically polymerizable compound having a (meth)acrylate group but not a phosphorus atom]
The radical polymerizable compound having a (meth)acrylate group but not having a phosphorus atom is not particularly limited as long as it has one or more (meth)acrylate groups in the molecule and does not have a phosphorus atom in the molecule, and one type may be used alone or two or more types may be used in combination.
The number of (meth)acrylate groups contained in one molecule is not particularly limited, but from the viewpoints of the curability of the photocurable artificial nail composition, the hardness of the cured coating film, etc., it is 1 to 10, preferably 1 to 8. The number of (meth)acrylate groups can be confirmed by analysis using infrared absorption spectroscopy (IR), nuclear magnetic resonance (NMR), gas chromatography mass spectrometry (GC/MS), etc.

Examples of the radical polymerizable compound having a (meth)acrylate group but not a phosphorus atom include a radical polymerizable oligomer having a (meth)acrylate group but not a phosphorus atom (hereinafter sometimes referred to as an "oligomer having a (meth)acrylate group") and a radical polymerizable monomer having a (meth)acrylate group but not a phosphorus atom (hereinafter sometimes referred to as a "radical polymerizable monomer").
In the present invention, it is preferable to use a mixture of one or more oligomers having a (meth)acrylate group and one or more radical polymerizable monomers as the radical polymerizable compound having a (meth)acrylate group but not a phosphorus atom.

In the photocurable artificial nail composition of the present invention, the content of the radically polymerizable compound having a (meth)acrylate group but no phosphorus atom is not particularly limited. It can be, for example, 1% by mass or more, preferably 10% by mass or more, and more preferably 20% by mass or more, relative to the total amount of components of the photocurable artificial nail composition, and can be, for example, 99% by mass or less, preferably 98% by mass or less, and more preferably 95% by mass or less.

<Oligomer Having (Meth)acrylate Group>
The (meth)acrylate group-containing oligomer used as the radical polymerizable compound having a (meth)acrylate group but no phosphorus atom is not particularly limited as long as it is an oligomer having one or more (meth)acrylate groups. The number of (meth)acrylate groups contained in one molecule is not particularly limited, but is 1 to 10, preferably 2 to 8, from the viewpoints of the curability of the photocurable artificial nail composition, the hardness of the cured coating film, etc.
The number of (meth)acrylate groups can be confirmed by analysis using infrared absorption spectroscopy (IR), nuclear magnetic resonance (NMR), gas chromatography mass spectrometry (GC/MS), or the like.

The radically polymerizable phosphate compound having an acrylate group contained in the photocurable artificial nail composition of the present invention is highly reactive and generates a large amount of heat upon curing. For this reason, it is preferable to adjust the reactivity of the photocurable artificial nail composition and reduce the heat of curing of the photocurable artificial nail composition by incorporating an oligomer having a methacrylate group, which has relatively lower reactivity and generates less heat upon curing than the radically polymerizable phosphate compound having an acrylate group. This allows the heat of curing of the photocurable artificial nail composition to be, for example, 45°C or less, preferably 43°C or less, and more preferably 40°C or less.

According to the findings of the present inventors, in photocurable artificial nail compositions, curing heat is generated by the reaction of (meth)acrylate groups with radicals. Therefore, when a component with a high degree of polymerization (high weight-average molecular weight), such as a (meth)acrylate oligomer, is used, the number of (meth)acrylate groups per unit mass is reduced, and the number of reactive sites per unit mass is reduced, making it possible to control (reduce) the curing heat. On the other hand, when a polyfunctional (meth)acrylate is used, the curing heat tends to be high.
That is, for an oligomer having a (meth)acrylate group, the heat of curing can be reduced by increasing the degree of polymerization or by increasing the content of an oligomer having a high degree of polymerization (high molecular weight), whereas the heat of curing can be increased by using an oligomer having many (meth)acrylate groups, by decreasing the degree of polymerization of the oligomer, or by increasing the content of an oligomer having a low degree of polymerization (low molecular weight).
Furthermore, since the molecular structure of the acrylate group is not bulky, the reactivity is higher than that of the methacryloyl group, but the curing heat tends to be higher.
In the photocurable artificial nail composition of the present invention, the oligomer having a (meth)acrylate group may be, for example, an oligomer having a methacrylate group.

The oligomer having a (meth)acrylate group is not particularly limited, but examples thereof include:
an oligomer having, in its main skeleton (main chain), a (meth)acrylate group having at least one bond selected from the group consisting of a urethane bond, a bond formed by a ring-opening reaction of an epoxy group, an ester bond, an ether bond, a urea bond, a carbonate bond, and an amide bond;
an oligomer having a (meth)acrylate group, the main skeleton (main chain) of which has a molecular chain formed by polymerization of one or more monomers selected from the group consisting of styrene-based, (meth)acrylic-based, olefin-based, and diene-based monomers;
and the like.

Of these,
(a) urethane (meth)acrylate oligomer (oligomer having a (meth)acrylate group and a urethane bond in the main skeleton);
(b) an epoxy (meth)acrylate oligomer having a molecular chain formed by a ring-opening reaction of an epoxy group;
(c) ester (meth)acrylate oligomer (oligomer having an ester bond in the main skeleton (oligomer having a methacrylate group)),
(d) ether (meth)acrylate oligomer (oligomer having a (meth)acrylate group with an ether bond in the main skeleton);
The use of one or more selected from the group consisting of the above is advantageous in terms of adhesion and the like.
The oligomer having a (meth)acrylate group may be either a commercially available product or a synthetic product. In the present invention, from the viewpoint of nail adhesion and durability of the photocurable resin composition and/or its cured coating film, the composition may contain one or more oligomers having a urethane (meth)acrylate group.
The oligomer having a (meth)acrylate group can also be used in combination with an oligomer other than the oligomer having a (meth)acrylate group.

(Urethane (meth)acrylate oligomer)
The urethane (meth)acrylate oligomer can be synthesized, for example, by a method in which a polyol and a polyisocyanate are reacted to form an isocyanate group-containing urethane prepolymer, and then the prepolymer is reacted with a compound having an active hydrogen-containing group and a (meth)acrylate group in the molecule (e.g., hydroxyalkyl (meth)acrylate, (meth)acrylic acid, etc.), but the synthesis method is not limited to this.
Commercially available products include, for example, AH-600, AT-600, UA-306H, and UF-8001G (manufactured by Kyoeisha Chemical Co., Ltd.), RUA-071, RUA-003VE, RUA-075, and RUA-048 (manufactured by Asia Chemical Industry Co., Ltd.), UA-4200, UA200PA, UA-33H, and UA-1100H, SUA TH1 and SUA TH2 (manufactured by Shin-Nakamura Chemical Co., Ltd.), UV-3310B (manufactured by Mitsubishi Chemical Corporation), UN-9000PEP, UN-9200A, and AU-2040 (manufactured by Tokushiki Co., Ltd.), and KUA-PC2I (manufactured by KSM Co., Ltd.), and Art Resin Examples include, but are not limited to, one or more selected from the group consisting of UN-6303, UN-9200A, UN-900PEP (manufactured by Negami Chemical Industries Co., Ltd.).

When a urethane (meth)acrylate oligomer is used in a photocurable artificial nail composition, a cured coating film having excellent stretchability, adhesion, and strength can be obtained, and therefore it is preferably used.
The one or more urethane (meth)acrylate oligomers that can be used in the present invention can be selected from those having one or more skeletons selected from the group consisting of a non-aromatic polyether skeleton, an aromatic polyether skeleton, a non-aromatic polycarbonate skeleton, an aromatic polycarbonate skeleton, a non-aromatic polyester skeleton, and an aromatic polyester skeleton. Among these, those having one or more skeletons of a non-aromatic polyether skeleton or a (non)aromatic polycarbonate skeleton are preferred.

For example, a urethane (meth)acrylate oligomer having one or more types of non-aromatic polyether skeleton can be obtained by adding a (meth)acrylic compound having a hydroxyl group to an isocyanate group-containing polyether urethane prepolymer, and then subjecting 10% or more of the total number of isocyanate groups in the urethane prepolymer to an addition reaction with the (meth)acrylic compound having a hydroxyl group.
The isocyanate group-containing polyether urethane prepolymer is a product of reacting a polyol compound having an alkylene group with 3 or more carbon atoms with a polyisocyanate, and has a weight average molecular weight of, for example, 400 to 30,000. The polyol compound is preferably polypropylene polyol. The polyisocyanate may be one or more selected from the group consisting of non-aromatic polyisocyanates, such as isophorone diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, and their isocyanurates and biuret derivatives.

(Epoxy (meth)acrylate oligomer)
An epoxy (meth)acrylate oligomer having a molecular chain generated by a ring-opening reaction of an epoxy group can be synthesized, for example, by reacting a polyfunctional epoxy resin with a (meth)acrylate having a functional group reactive with an epoxy group, but the synthesis method is not limited to this.
Examples of commercially available products include, but are not limited to, one or more selected from the group consisting of EBECRYL 1259, 605, and 1606 (manufactured by Daicel-Cytec Co., Ltd.), and EPOXY ESTER 3000A, 3000MK, 3002A(N), 3002M(N), and 40EM (manufactured by Kyoeisha Chemical Co., Ltd.).

(Ester (meth)acrylate oligomer)
The ester (meth)acrylate oligomer having an ester bond can be synthesized, for example, by adding a compound having a hydroxyl group and a (meth)acrylate group in the molecule and/or (meth)acrylic acid or an acrylic compound having a carboxyl group to the carboxyl group and/or hydroxyl group of an ester oligomer obtained by reacting a polyol with a polycarboxylic acid, but the synthesis method is not limited to this.
Examples of commercially available products include, but are not limited to, one or more types selected from the group consisting of Aronix (registered trademark) M-6100, M-6200, M-6250, M-6500, M-7100, M-7300K, M-8030, M-8060, M-8100, M-8530, M-8560, and M-9050 (manufactured by Toagosei Co., Ltd.), and UV-3500BA, UV3520TL, UV-3200B, and UV-3000B (manufactured by Mitsubishi Chemical Corporation).

(Ether (meth)acrylate oligomer)
The ether (meth)acrylate oligomer having an ether bond can be synthesized, for example, by adding one or more members selected from the group consisting of a compound having a hydroxyl group and a (meth)acrylate group in the molecule, (meth)acrylic acid, and a compound having a carboxyl group and a (meth)acrylate group in the molecule to the hydroxyl group of an aliphatic polyether polyol or a hydroxyl group of an aromatic polyether polyol made from a raw material such as bisphenol, but the synthesis method is not limited to this.
Examples of commercially available products include, but are not limited to, one or more selected from the group consisting of UV-6640B, UV-6100B, UV-3700B (manufactured by Mitsubishi Chemical Corporation), Light Acrylate (registered trademark) 3EG-A, 4EG-A, 9EG-A, 14EG-A, PTMGA-250, BP-4EA, BP-4PA, BP-10EA, Light Ester 4EG, 9EG, 14EG (manufactured by Kyoeisha Chemical Co., Ltd.), and EBECRYL (registered trademark) 3700 (manufactured by Daicel-Cytec Co., Ltd.).

(Weight-average molecular weight and content of oligomer having (meth)acrylate group)
The weight-average molecular weight of the oligomer having a (meth)acrylate group is not particularly limited. For example, it is 1,000 or more, preferably 2,000 or more, more preferably 3,000 or more, and for example, it is 100,000 or less, preferably 30,000 or less, more preferably 20,000 or less. By setting the weight-average molecular weight within this range, it is possible to improve the durability of the cured coating film while maintaining a low viscosity.

In the photocurable artificial nail composition of the present invention, the content of the oligomer having a (meth)acrylate group is not particularly limited and can be, for example, 10% by mass or more, preferably 20% by mass or more, and for example, 90% by mass or less, preferably 70% by mass or less, more preferably 50% by mass or less, based on the total amount of the components of the photocurable artificial nail composition.
The content of the oligomer having a (meth)acrylate group relative to the total amount of the radical polymerizable compound having a (meth)acrylate group but not a phosphorus atom is not particularly limited, and can be, for example, 0% by mass or more, preferably 5% by mass or more, more preferably 20% by mass or more, and can be, for example, 100% by mass or less, preferably 50% by mass or less.

<Radical polymerizable monomer>
Examples of the radical polymerizable monomer include a radical polymerizable monomer having a (meth)acrylate group (hereinafter, sometimes referred to as a "(meth)acrylate monomer") and a compound having a radical polymerizable unsaturated group other than a (meth)acrylate group.

((Meth)acrylate Monomer)
The (meth)acrylate monomer is not particularly limited as long as it has one or more (meth)acrylate groups and does not have a phosphorus atom in the molecule. The number of (meth)acrylate groups contained in one molecule is not particularly limited, but from the viewpoints of the curability of the photocurable artificial nail composition, the hardness of the cured coating film, etc., it is one or more, and for example, 10 or less, preferably 8 or less, and more preferably 6 or less.
In the present invention, it is preferable to use, as the (meth)acrylate monomer, one or more types selected from (meth)acrylate monomers having one (meth)acrylate group, or a mixture of one or more types selected from (meth)acrylate monomers having one (meth)acrylate group and one or more types selected from (meth)acrylate monomers having two or more (meth)acrylate groups.

Examples of (meth)acrylate monomers having one (meth)acrylate group include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, neopentyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, and esters of monohydric alcohols such as N-acryloyloxyethylhexahydrophthalimide with (meth)acrylic acid; acrylamide, hydroxyethylacrylamide, dimethylacrylamide, diethylacrylamide, methacrylamide, N-methyl (meth)acrylamide, and N-hydroxypropyl methyl acrylate. N-methylol(meth)acrylamide, N-methoxymethyl(meth)acrylamide, N-butoxymethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N,N-dipropyl(meth)acrylamide, N,N-diisopropyl(meth)acrylamide, N,N-dibutyl(meth)acrylamide, N,N-diisobutyl(meth)acrylamide, N,N-di-tert-butyl(meth)acrylamide, N,N-diheptyl(meth)acrylamide, N,N-dioctyl(meth)acrylamide, N,N-di-tert-octyl(meth)acrylamide, N,N-didodecyl(meth)acrylamide, N,N-dioctadecyl(meth)acrylamide, N,N-dimethylaminopropyl(meth)acrylamide, N,N-dimethylaminoethyl(meth)acrylamide (meth)acrylate group-containing amide compounds such as acrylate; hydroxyl group-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate; nitrogen-containing alkyl (meth)acrylates such as N,N-dimethylaminoethyl (meth)acrylate, N,N-diethylaminoethyl (meth)acrylate, and N-t-butylaminoethyl (meth)acrylate; glycidyl (meth)acrylate; 4-(meth)acryloyloxymethyl-2-cyclohexyl-1,3-dioxolane, adamantyl (meth)acrylate, (2-methyl-2-ethyl-1,3-dioxolan-4yl)methyl (meth)acrylate, cyclic trimethylolpropane formal (meth)acrylate, (2-isobutyl-2-methyl-1,3-dioxolan-4yl)methyl (meth)acrylate, (2-ethyl-2-methyl-1,3-dioxolan-4yl)methyl (meth)acrylate (1,4-dioxolan-4yl)methyl (meth)acrylate, (1,4-dioxaspiro[4,5]decan-2yl)methyl (meth)acrylate, tetrafurfuryl alcohol oligo(meth)acrylate, alkoxylated tetrahydrofurfuryl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, (3-ethyloxetan-3-yl)methyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate glycidyl ether, (meth ) Examples include one or more selected from the group consisting of heterocycle-containing (meth)acrylates such as acryloylmorpholine, N-(meth)acryloyloxyethylhexahydrophthalimide, pentamethylpiperidyl (meth)acrylate, isocyanuric acid di(meth)acrylate, isocyanuric acid tri(meth)acrylate, triazine tri(meth)acrylate, N-(meth)acryloxysuccinimide, and N-(meth)acryloxyphthalimide.

Among these (meth)acrylate monomers having one (meth)acrylate group, (i) esters of monohydric alcohols with (meth)acrylic acid, such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, neopentyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, and isobornyl (meth)acrylate;
(ii) hydroxyl group-containing (meth)acrylates such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate;
Preferably, one or more selected from the group consisting of:

Examples of (meth)acrylate monomers having two or more (meth)acrylate groups include ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene di(meth)acrylate, ethoxylated polypropylene glycol di(meth)acrylate, ethoxylated propylene glycol di(meth)acrylate, 1,3-butanediol di(meth)acrylate, and 1,4-butanediol di(meth)acrylate. Acrylate, 1,9-nonanediol di(meth)acrylate, glycerin di(meth)acrylate, trimethylolpropane di(meth)acrylate, pentaerythritol di(meth)acrylate, neopentyl glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, pentaerythritol di(meth)acrylate, bisphenol A ethylene oxide modified di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate, propoxylated bisphenol A di(meth)acrylate (isopyridenediphenylbis(methacrylic acid oxyhydroxy) di(meth)acrylate monomers such as propoxylated and ethoxylated bisphenol A di(meth)acrylate; tri(meth)acrylate monomers such as glycerin tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, ditrimethylolpropane tri(meth)acrylate, trimethylolpropane propylene oxide-modified tri(meth)acrylate, trimethylolpropane ethylene oxide-modified tri(meth)acrylate, pentaerythritol tri(meth)acrylate, and ε-caprolactone-modified tris(acryloxyethyl)isocyanurate; tetra(meth)acrylate monomers such as pentaerythritol tetra(meth)acrylate; polypentaerythritol (meth)acrylates such as dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, tripentaerythritol (meth)acrylate, and tetrapentaerythritol (meth)acrylate; (meth)acrylate monomers having four or more (meth)acrylate groups such as ethoxylated isocyanuric acid triacrylate and ethoxylated pentaerythritol tetraacrylate; and the like.

Among these (meth)acrylate monomers having two or more (meth)acrylate groups, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, polypropylene di(meth)acrylate, 1,3-butanediol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate,
It is preferable to use one or more selected from the group consisting of propoxylated bisphenol A dimethacrylate represented by the formula (I), trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, pentaerythritol tetra(meth)acrylate, dipentaerythritol penta(meth)acrylate, dipentaerythritol hexa(meth)acrylate, and the like.

(Compounds Having Radically Polymerizable Unsaturated Groups Other Than (Meth)acrylate Groups)
Examples of the compound having a radically polymerizable unsaturated group other than a (meth)acrylate group include compounds having a radically polymerizable unsaturated group (a functional group having a polymerizable carbon-carbon double bond), such as a vinyl group, a vinyl ether group, or an allyl group.
Examples of such compounds include one or more selected from the group consisting of allyl glycidyl ether, styrene, α-methylstyrene, vinyltoluene, α-chlorostyrene, vinyl acetate, and the like.

The content of the radical polymerizable monomer in the photocurable artificial nail composition of the present invention is, for example, 1% by mass or more, preferably 10% by mass or more, and can be, for example, 90% by mass or less, preferably 80% by mass or less.
Furthermore, by adjusting the type and amount of the radical polymerizable monomer contained in the photocurable artificial nail composition, the reactivity and curing heat of the photocurable artificial nail composition can be adjusted.
In the present invention, it is preferable to use, as the radical polymerizable monomer, a radical polymerizable monomer having a functional group, such as a (meth)acrylate monomer having a hydroxyl group, or a (meth)acrylate compound having a cyclic structure in the molecule, such as cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, isobornyl (meth)acrylate, or (meth)acryloylmorpholine, in terms of the adhesion of the cured coating film of the photocurable artificial nail composition to the substrate (adhesion strength to the nail), adhesion durability, curability, and aesthetic appearance of the cured coating film.

<Photopolymerization initiator>
The photopolymerization initiator generates radicals when irradiated with light of a wavelength emitted from a light source for photocuring. Examples of the photopolymerization initiator include one or more photopolymerization initiators selected from the group consisting of acylphosphine oxides, α-hydroxyalkylphenones, benzoin ethers, benzil ketals, acid esters, α-aminoalkylphenones, benzophenones, thioxanthones, titanocenes, quinones, and the like.
The photopolymerization initiator can impart good curability to the photocurable artificial nail composition even when irradiated with light using various light sources including a UV-LED light source.

Among these, acylphosphine oxide-based photopolymerization initiators generate radicals when irradiated with ultraviolet light having a wavelength of 365 nm or more and 405 nm or less, which is emitted from commonly used UV-LED light sources. Therefore, they can impart good curability even when curing is performed by irradiating light using various light sources, including UV-LED light sources. Furthermore, when curing is performed by irradiating light using a UV-LED light source, yellowing of the cured coating film can be prevented.
Examples of the acylphosphine oxide photopolymerization initiator include one or more selected from the group consisting of 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide, and the like.
In particular, 2,4,6-trimethylbenzoyldiphenylphosphine oxide can be preferably used in the present invention because it also functions as a skin conditioning agent.

Examples of photopolymerization initiators other than acylphosphine oxide photopolymerization initiators include 2,4-diethylthioxanthone, 2-isopropylthioxanthone, thioxanthone, 2-chlorothioxanthone, isopropylthioxanthone, 1-chloro-4-propylthioxanthone, 3-[3,4-dimethyl-9-oxo-9H-thioxanthone-2-yl-oxy]-2-hydroxypropyl-N,N,N-trimethylammonium chloride, fluorothioxanthone, 2-benzoxanthone, and 2-benzoxanthone. 2-methyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one, oligo(2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone), 4-benzoyl-4'-methyl-diphenyl sulfide, 1,2-octanedione, 1-(4-(phenylthio)-2,2-(O-benzoyloxime))1-hydroxycyclohexyl phenyl ketone, benzoyl-4'-methyl-diphenyl sulfide ... Zoin ethyl ether, benzyl dimethyl ketal, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxy-cyclohexyl-phenyl-ketone (IRGACURE 184), 1-(4-isopropylphenyl)-2-hydroxy-2-methylpropan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)-benzyl]-phenyl}-2-methylpropan-1-one, 1-[4-(2-hydroxyethoxy)phenyl]- Examples include one or more selected from the group consisting of [benzyl]-2-hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methylpropionyl)-benzyl]phenyl}-2-methylpropane, benzophenone, 4-phenylbenzophenone, isophthalphenone, methyl phenylglyoxylate, ethyl anthraquinone, phenanthrenequinone, camphorquinone, 1-hydroxy-cyclohexyl-phenyl-ketone, etc.

In the present invention, it is preferable to use a photopolymerization initiator containing an acylphosphine oxide-based photopolymerization initiator, and it is more preferable to use a photopolymerization initiator containing an acylphosphine oxide-based photopolymerization initiator and an α-hydroxyalkylphenone-based photopolymerization initiator.

The content of the photopolymerization initiator in the photocurable artificial nail composition of the present invention is not particularly limited. It is, for example, 0.05% by mass or more, preferably 0.07% by mass or more, more preferably 0.1% by mass or more, and for example, 5.0% by mass or less, preferably 4.0% by mass or less, more preferably 3.0% by mass or less, based on the total amount of components of the photocurable artificial nail composition. If the content exceeds 5.0% by mass, the molecular weight of the cured coating film may decrease, making the cured coating film brittle, and the cured coating film of the photocurable artificial nail composition may yellow (turn yellowish). If the content is less than 0.05% by mass, the photocurable artificial nail composition may take a long time to cure and may not cure properly.

[Other ingredients]
In addition to the radically polymerizable phosphate compound having an acrylate group, the radically polymerizable compound having a (meth)acrylate group but not a phosphorus atom, and the photopolymerization initiator, various other components can be blended into the photocurable artificial nail composition of the present invention, provided that such components do not adversely affect the viscosity, coatability, handleability, cured coating film durability, etc. Examples of such components include one or more selected from the group consisting of various additives such as colorants, polyfunctional thiol compounds, polyol compounds, fragrances, silicone-based or fluorine-based antifoaming agents, silane coupling agents such as γ-glycidoxypropyltrimethoxysilane, photopolymerization accelerators such as tertiary amines, chain transfer agents, fillers, surface tension modifiers, polymerization inhibitors, flame retardants, antioxidants, ion adsorbents, stress reducers, preservatives, antibacterial agents, flexibility-imparting agents, waxes, halogen trapping agents, leveling agents, and wetting improvers.

The colorant may be one or more selected from the group consisting of pigments, luster materials, and dyes, and may be used in any amount to impart a desired color tone to the photocurable artificial nail composition. In particular, the colorant may be one or more selected from the group consisting of inorganic pigments, luster materials, organic pigments, and dyes used in nail coatings, and does not significantly inhibit curing by ultraviolet irradiation (light irradiation).
The photocurable artificial nail composition before curing can contain not only pigments but also resin particles and decorative materials that can be incorporated into known photocurable artificial nail compositions.

Examples of colorants include Brown No. 201, Black No. 401, Purple No. 201, Purple No. 401, Blue No. 1, Blue No. 2, Blue No. 201, Blue No. 202, Blue No. 203, Blue No. 204, Blue No. 205, Blue No. 403, Blue No. 404, Green No. 201, Green No. 202, Green No. 204, Green No. 205, Green No. 3, Green No. 401, Green No. 402, Yellow No. 201, Yellow No. 202-(1), and Yellow No. 20 No. 2-(2), Yellow No. 203, Yellow No. 204, Yellow No. 205, Yellow No. 4, Yellow No. 401, Yellow No. 402, Yellow No. 403-(1), Yellow No. 404, Yellow No. 405, Yellow No. 406, Orange 201 No., Orange No. 203, Orange No. 204, Orange No. 205, Orange No. 206, Orange No. 207, Orange No. 401, Orange No. 402, Orange No. 403, Red No. 102, Red No. 104-(1), Red No. 105-(1) ), Red No. 106, Red No. 2, Red No. 201, Red No. 202, Red No. 203, Red No. 204, Red No. 205, Red No. 206, Red No. 207, Red No. 208, Red No. 213, Red No. 214, Red No. 215, Red No. 218, Red No. 219, Red No. 220, Red No. 221, Red No. 223, Red No. 225, Red No. 226, Red No. 227, Red No. 228, Red No. 230-(1), Red No. 23 0-(2), Red No. 231, Red No. 232, Red No. 3, Red No. 401, Red No. 405, Red No. 501, Red No. 502, Red No. 503, Red No. 504, Red No. 505, Red No. 506, titanium oxide, iron oxide, chromium oxide, manganese violet, carbon black, metal powder, metal flakes, metal oxide flakes, glass flakes, etc.

The polyfunctional thiol compound is blended as a curability modifier, a crosslinking agent, and a viscosity modifier in the photocurable artificial nail composition. In addition, blending the polyfunctional thiol compound in the photocurable artificial nail composition can improve the wiping properties when wiping off the cured coating film to remove it.
Examples of polyfunctional thiol compounds include those obtained by reacting a hydroxyl group of a polyol compound such as trimethylolpropane, pentaerythritol, dipentaerythritol, etc. with a compound having a thiol group or a group that reacts to become a thiol group. For example, one or more compounds selected from the group consisting of trimethylolpropane tris(3-mercaptopropionate), tris[(3-mercaptopropionyloxy)-ethyl]-isocyanurate, pentaerythritol tetrakis(3-mercaptobutyrate), pentaerythritol tetrakis(3-mercaptopropionate), dipentaerythritol hexakis(3-mercaptopropionate), etc.
When the polyfunctional thiol compound is contained in the photocurable artificial nail composition, it is preferably contained in an amount of 1.0 to 10.0% by mass.

The polyol compound functions as a diluent and an adhesion improver for the photocurable artificial nail composition. Examples of the polyol compound include one or more selected from the group consisting of alkyl polyols, polyester polyols, polyether polyols, acrylic polyols, polybutadiene polyols, and phenolic polyols. Among these, alkyl polyols, polyester polyols, and polyether polyols are preferred.
The alkyl polyol may be at least one selected from the group consisting of ethylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, neopentyl glycol, cyclohexanedimethanol, trimethylolpropane, pentaerythritol, and the like.

The polyester polyol may be one or more selected from the group consisting of condensation polyester polyols, addition polymerization polyester polyols, polycarbonate polyols, etc. The condensation polyester polyol may be obtained by a condensation reaction of one or more diol compounds selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,9-nonanediol, 1,4-hexanedimethanol, diol dimer acid, polyethylene glycol, etc. with one or more organic polybasic acids selected from the group consisting of adipic acid, isophthalic acid, terephthalic acid, sebacic acid, etc., and preferably has a weight average molecular weight of 100 or more and 100,000 or less. The addition polymerization polyester polyol may be polycaprolactone, and preferably has a weight average molecular weight of 100 or more and 100,000 or less. Polycarbonate polyols are synthesized by direct phosgenation of polyols, transesterification with diphenyl carbonate, or the like, and preferably have a weight average molecular weight of 100 or more and 100,000 or less.
The polyether polyol may be, for example, a polyether polyol obtained by the opening polymerization of an alkylene oxide.

The polymerization inhibitor may be, for example, one or more selected from the group consisting of quinone compounds, salicylic acid hydrazide, tocopherol compounds, and the like.
When a polymerization inhibitor is contained in the photocurable artificial nail composition, it can be blended in an amount of, for example, 500 ppm or more, preferably 1,000 ppm or more, and for example, 5,000 ppm or less, preferably 4,500 ppm or less, based on the total amount of the photocurable artificial nail composition.

[Uses and properties of photocurable artificial nail composition]
The cured coating film of the photocurable artificial nail composition of the present invention has excellent adhesion to a substrate, maintains adhesion to the substrate for a long period of time, and has an appropriate hardness.
The photocurable artificial nail composition of the present invention is a composition for coating the surface of a nail, similar to so-called common manicures and pedicures, and may be coated on the surface of the user's own nail, which may be roughened by sanding or the like, as needed. It is particularly suitable for use as a gel nail, and can be used, for example, in any of a base coat layer that is applied directly to the user's nail, a color coat that is applied on the base coat layer, and a top coat layer that is further applied on top of that.
When used as a color coat, the color can be adjusted to a variety of colors, such as solid colors, glitter, metallic luster, dark colors, and bright colors, using a colorant.
When forming a cured coating film of the photocurable artificial nail composition of the present invention, equipment similar to that used for conventional radically polymerizable nail polishes that are cured by ultraviolet light or the like, or general ultraviolet curing equipment can be used.
When the photocurable artificial nail composition of the present invention is used in any layer, the cured coating film will not chip or peel off for a long period of time (e.g., at least two weeks after curing), and lifting from the underlying layer or the user's nail can be suppressed.

The photocurable artificial nail composition of the present invention only needs to have a viscosity that allows it to be applied sufficiently with an application tool such as a brush.
The photocurable artificial nail composition preferably has a stress (maximum stress) at break in a tensile test of the cured coating film of 15.0 MPa or more, more preferably 18.0 MPa or more, and even more preferably 20.0 MPa or more. If the stress is less than 15.0 MPa, the composition may be prone to peeling due to rubbing.
The strain at break of the cured coating film is preferably 95.0% or more, more preferably 97.0% or more, and even more preferably 100.0% or more.

[Coating of nails with photocurable artificial nail composition]
The nails to be coated with the photocurable composition of the present invention may be human fingernails or toenails, or may be the nails of animals such as dogs and cats.
When the photocurable artificial nail composition of the present invention is applied to a nail or an (un)cured coating film on the nail to form a coating, the applied surface may or may not be sanded. The method for applying the photocurable artificial nail composition is not particularly limited, and for example, an application tool such as a brush or an application method such as an inkjet can be used.
The photocurable artificial nail composition of the present invention can be used as any of a base coat layer (gel base; primer layer), an intermediate layer (color layer), and a top coat layer in a gel nail. In particular, because of its excellent adhesion to the substrate, it is suitable for use as a base coat layer (gel base; primer layer).
After applying the photocurable artificial nail composition of the present invention, small decorations, powder, etc. can be attached to the coating surface of the photocurable artificial nail composition before curing to enhance the design.

Alternatively, a layer having the shape of a nail or the like can be prepared on one side of a sheet using the uncured photocurable artificial nail composition of the present invention, and after bringing this layer into contact (transferring) with the nail surface, the layer can be cured by irradiating it with ultraviolet light, with or without peeling off the sheet.
By using a method in which a layer is formed on the surface of a sheet in advance using a photocurable artificial nail composition and then transferred, it is possible to coat the surface of the nail with a uniform and accurate pattern without using an applicator such as a brush, and there is no need to wash the applicator after use.

The photocurable artificial nail composition after application can also be cured using a known UV curing device. Although the irradiation energy required for curing varies depending on the composition of the photocurable artificial nail composition, the irradiation energy (cumulative light amount) by light irradiation is 5 mJ/cm2 or ^more and 1,000 mJ/cm2 or ^less , preferably 10 mJ/cm2 or ^more and 800 mJ/ ^cm2 or less. If the irradiation energy is within this range, nail art with sufficient adhesion and abrasion resistance can be obtained.
As the light source, for example, a known ultraviolet light source such as a mercury lamp, a metal halide lamp, an ultraviolet light emitting diode (UV-LED), or an ultraviolet laser diode (UV-LD) can be used.
Among these, ultraviolet light emitting diodes (UV-LEDs) and ultraviolet laser diodes (UV-LDs) are preferred from the viewpoints of small size, long life, high efficiency, and low cost.

The present invention will be explained in more detail below using examples, but the present invention is not limited to these examples. Unless otherwise specified, "%" means "% by mass" and "parts" means "parts by mass."

<Examples 1 to 9, Comparative Examples 1 to 5>
The components shown in Table 1 were placed in a container in the amounts (parts by mass) shown in Table 1, and the mixture was heated to 50°C while stirring with a dissolver. After stirring, the mixture was left to stand at 80°C for 2 hours and degassed to obtain a photocurable artificial nail composition. All of these steps were performed in the dark.

The components in Table 1 are as follows:
PA: A mixture containing 2-acryloyloxyethyl phosphate and bis(2-acryloyloxyethyl) phosphate PU: Polycarbonate polyurethane methacrylate obtained from hydroxyethyl methacrylate, isophorone diisocyanate, and polycarbonate diol IBXA: Isobornyl acrylate HEMA: Hydroxyethyl methacrylate TPO: 2,4,6-trimethylbenzoyldiphenylphosphine oxide HPK: 1-hydroxycyclohexyl phenyl ketone PM1: Bismethacryloyloxyethyl phosphate PM2: Methacryloyloxyethyl caproate phosphate

<Peel-off load>
The adhesion of the resulting photocurable artificial nail composition was evaluated based on the peel-off load. The peel-off load was measured by a 90° peel-off test as follows. The results are also shown in Table 1.
(90° peel-off test)
The surface of the nylon plate was wiped with ethanol to remove any dirt, and then the photocurable artificial nail composition was applied to the surface so that the cured film thickness was 100 μm. The composition was cured for 30 seconds using a 30 W LED light to form a cured coating film measuring 10 mm in length and 50 mm in width.
The widthwise edge of the cured coating film was clamped with clips attached to a digital force gauge (Imada Co., Ltd., ZTA-100N), and the cured coating film was peeled off from the nylon plate in the widthwise direction at a peel angle of 90° at 100 mm/sec, and the peel-off load (the maximum load (kg) required to peel off the cured coating film) was measured.

<Peel-off load increase/decrease rate>
The peel-off load change rate was calculated using the peel-off load of Example 1 as the reference value according to the following formula: The results are also shown in Table 1.
Peel-off load increase/decrease rate (%)=(peel-off load)/(peel-off load of Example 1)×100

<Opacity test>
The photocurable artificial nail compositions of Examples 1 to 9 and Comparative Example 1 were applied to the nails of test subjects and cured to form a base coat layer (gel base) for gel nails. A transparent color gel was then applied and cured to form a transparent color layer, and a transparent top coat gel was applied and dried to form a transparent top coat layer, producing gel nails. The curing conditions were irradiation with a 30 W LED light for 30 seconds.
Four weeks after the gel nail formation, the condition of the gel nail was visually checked to see if it had become cloudy. The evaluation was graded as A if it was not cloudy after four weeks, and graded as B if it was cloudy after four weeks. The results are shown in Table 2.

From Table 1, it can be seen that the photocurable artificial nail compositions of Examples 1 to 9, which contain a "radical polymerizable phosphate compound having an acrylate group," have larger peel-off loads and peel-off load change rates, which are indicators of the adhesion of a cured coating film to a substrate (adhesion strength to a nail), and thus have higher adhesion and adhesion strength of a cured coating film to a substrate (nail), compared to the photocurable artificial nail compositions of Comparative Examples 1 to 5, which do not contain a "radical polymerizable phosphate compound having an acrylate group."
Furthermore, there were no problems with curability or the aesthetic appeal of the cured coating film, making it suitable for use as a gel nail. Furthermore, Table 2 shows that by adjusting the content of the "radical polymerizable phosphate compound having an acrylate group" to more than 0% by mass (preferably 0.01% by mass or more) and 4.4% by mass or less (preferably 4.3% by mass or less) of the total amount of components of the photocurable artificial nail composition, it is possible to form a base coat layer that maintains high adhesion to the nail while preventing clouding over time. This is extremely useful, especially when the color layer is transparent, as it eliminates the risk of the gel nail losing its aesthetic appeal over time due to clouding.

On the other hand, the photocurable artificial nail composition of Comparative Example 1, which did not contain a radically polymerizable phosphate compound having an acrylate group, and the photocurable artificial nail compositions of Comparative Examples 2 to 5, which contained a radically polymerizable phosphate compound having a methacrylate group instead of a radically polymerizable phosphate compound having an acrylate group, all had lower peel-off load values, which are an indicator of the adhesion of the cured coating film to the substrate (adhesion strength to the nail), than Examples 1 to 9, posing problems with adhesion and making them unsatisfactory when used as gel nails.

Claims (5)

(a) a radically polymerizable phosphoric acid compound having an acrylate group;
(b) a radical polymerizable compound having a (meth)acrylate group and no phosphorus atom;
(c) a photopolymerization initiator;
and (a) a content of a radically polymerizable phosphoric acid compound having an acrylate group is more than 0 mass % and 10.0 mass % or less based on the total amount of components of the photocurable artificial nail composition . The photocurable artificial nail composition according to claim 1, wherein (a) the radically polymerizable phosphate compound having an acrylate group is a radically polymerizable phosphate ester compound having an acrylate group. The photocurable artificial nail composition according to claim 1 or 2, wherein (a) the radically polymerizable phosphate compound having an acrylate group is 2-acryloyloxyethyl phosphate and/or bis(2-acryloyloxyethyl) phosphate. The photocurable artificial nail composition according to any one of claims 1 to 3, wherein (b) the radically polymerizable compound having a (meth)acrylate group and no phosphorus atom is a radically polymerizable oligomer having a (meth)acrylate group. The photocurable artificial nail composition according to any one of claims 1 to 4, wherein the content of (a) the radically polymerizable phosphoric acid compound having an acrylate group is greater than 0% by mass and not more than 4.4% by mass, based on the total amount of components of the photocurable artificial nail composition.