JP2017078139A - Cured film, resin laminate, and method of manufacturing resin laminate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cured film excellent in moldability, surface hardness, and scratch resistance, a resin laminate having the cured film, and a method of manufacturing the resin laminate.SOLUTION: The cured film contains: more than 50 mass% and 75 mass% or less of a repeating unit derived from a monomer (a1) having one isocyanuric acid skeleton and two or three (meth)acryloyl groups in the molecule; and 25 mass% or more and less than 50 mass% of a repeating unit derived from a monomer (a2) having two (meth)acryloyl groups in the molecule (provided that an isocyanuric acid skeleton is not contained in the molecule). The film thickness of the cured film is 2 μm or more and 18 μm or less. The resin laminate has the cured film laminated on at least one surface of a resin substrate comprising a (meth)acrylic resin composition.SELECTED DRAWING: Figure 1

Description

The present invention relates to a cured film, a resin laminate, and a method for producing a resin laminate.
More specifically, the present invention relates to a cured film excellent in moldability, surface hardness, and scratch resistance, a resin laminate, and a method for producing the resin laminate.

  Conventionally, a transparent glass plate or resin plate is used as a display front plate in order to protect the surface of various displays such as a CRT display device, a liquid crystal television, and a mobile phone. Recently, many touch panel displays have been adopted.

  A glass plate is used for a display front plate used for a touch panel type display because of excellent scratch resistance and surface hardness. However, the glass plate has a problem that it is easily broken when it is thinned, and it is difficult to use it for in-vehicle materials such as instrument panel and glazing, and products having complicated shapes such as a display front plate.

  Therefore, recently, studies have been made to use a resin plate having high transparency and excellent workability as compared with a glass plate. However, since the surface hardness of the resin plate is low, the problem is that scratches due to scratching or the like are likely to occur.

  In order to solve the above problems, a cured film containing a polyfunctional monomer such as polyfunctional (meth) acrylate is formed on the substrate surface of the resin plate so that the scratch resistance and surface hardness of the resin plate are improved. Techniques for improvement are known (Patent Documents 1 to 4).

  For example, Patent Document 1 discloses a method for producing an acrylic resin laminate, in which after a cured film is formed on a mold surface, a raw material for an acrylic resin base material is injected onto the surface of the cured film and cast polymerization is performed. Proposed.

  In Patent Document 2, as a curable composition for forming an intermediate layer of an optical recording medium, a curing shrinkage rate at the time of polymerization is low, and transparency, heat resistance, and releasability from a resin mold are good. Curable compositions have been proposed.

  Patent Document 3 proposes a laminate in which a cured film having a high surface hardness is laminated.

  Patent Document 4 proposes a hard coat film having high hardness and excellent scratch recovery properties.

JP-A-2005-248,070 JP 2005-112952 A WO2014 / 184833 WO2012 / 085651

  In the technique described in Patent Document 1, although the scratch resistance of the resin laminate is improved by the cured coating, the surface hardness of the resin laminate is not sufficient because the adhesion between the resin substrate and the cured coating is not sufficient.

  Further, in the technique disclosed in Patent Document 2, since the curable composition has a high viscosity, it is difficult to apply a thin layer of the cured film, and a complicated shape such as a square-shaped portion having a small curvature radius is difficult. It is difficult to use for manufacturing a display front plate having a shape.

  In the technique described in Patent Document 3, the cured film has a surface hardness of pencil hardness 9H and good scratch resistance, but the moldability and bending resistance of the obtained laminate are insufficient. .

  In the technique described in Patent Document 4, since the viscosity of the raw material and the curing liquid used in the hard coating film curing liquid is high and the coating property is poor, it is necessary to add a solvent to the curing liquid to lower the viscosity. . As a result, the solvent remains in the obtained product, and the scratch resistance of the cured film becomes insufficient.

  The present invention aims to solve these problems. That is, an object of the present invention is to provide a cured film excellent in moldability, surface hardness and scratch resistance, a resin laminate having the cured film, and a method for producing the resin laminate.

The first gist of the present invention is a repeating unit derived from a monomer (a1) having one isocyanuric acid skeleton in the molecule and two or three (meth) acryloyl groups,
A cured film containing a repeating unit derived from the monomer (a2) having two (meth) acryloyl groups in the molecule (however, the molecule does not contain an isocyanuric acid skeleton),
With respect to the total mass of the cured film, the repeating unit derived from the monomer (a1) exceeds 50% by mass and is 75% by mass or less,
A cured film comprising a resin composition containing a repeating unit derived from the monomer (a2) containing 25% by mass or more and less than 50% by mass, wherein the cured film has a thickness of 2 μm or more and 18 μm or less. is there.

The second gist of the present invention is a repeating unit derived from a monomer (a1) having one isocyanuric acid skeleton in the molecule and two or three (meth) acryloyl groups,
A cured film containing a repeating unit derived from the monomer (a2) having two (meth) acryloyl groups in the molecule (however, the molecule does not contain an isocyanuric acid skeleton),
In the cured film, the repeating unit derived from the monomer (a1) contains more than 50% by mass and 75% by mass or less, and the repeating unit derived from the monomer (a2) contains 25% by mass or more and less than 50% by mass. The curable composition is cured, and the cured film has a thickness of 2 μm or more and 18 μm or less.

  According to a third aspect of the present invention, there is provided a resin laminate in which the cured film is laminated on at least one surface of a resin base material made of a (meth) acrylic resin composition containing 50% by mass or more of a repeating unit derived from methyl methacrylate. It is in.

  In the resin laminate, the cured film may have a mixed layer formed on the resin substrate side by the resin substrate forming composition penetrating the hard film.

Furthermore, the 4th summary of this invention exists in the manufacturing method of the resin laminated body which consists of a series of processes of following (1) and (2).
(1) monomer (a1) having one isocyanuric acid skeleton in the molecule and 2 or 3 (meth) acryloyl groups (a1) exceeding 50% by mass and 75% by mass or less;
A curable composition containing 25% by mass or more and less than 50% by mass of a monomer (a2) having two (meth) acryloyl groups in the molecule (provided that the molecule does not contain an isocyanuric acid skeleton) and a polymerization initiator After the product is applied to the inner surface of the mold, the curable composition is irradiated with active energy rays and cured to form a cured film.
(2) The resin base material (b1) containing a mixture of polymerizable monomers is poured onto the surface of the cured film formed in the step (1), and then heat polymerized by cast polymerization to obtain a resin. A laminate is formed.

  In the said manufacturing method, an active energy ray can be irradiated to the curable composition of a process (1) in oxygen atmosphere.

  According to the present invention, a cured film excellent in moldability, surface hardness, and scratch resistance, and a resin laminate having the cured film can be provided. Such a cured film and a resin laminate are suitable for products having a complicated curved surface structure such as a display front plate, an in-vehicle material such as an instrument panel and glazing.

It is the schematic diagram which showed the cross section of the resin laminated body which one embodiment of this invention laminated | stacked the cured film on the one surface of the resin base material. It is the schematic diagram which showed the cross section of the resin laminated body which was one Embodiment of this invention and the cured film laminated | stacked on both surfaces of the resin base material.

  Hereinafter, the present invention will be described in detail. In the present invention, “(meth) acrylate” and “(meth) acrylic acid” are each at least one selected from “acrylate” and “methacrylate”, and at least one selected from “acrylic acid” and “methacrylic acid”. Means.

  “Monomer” means an unpolymerized compound, and “repeating unit” means a unit derived from the monomer formed by polymerization of the monomer. The repeating unit may be a unit directly formed by a polymerization reaction, or may be a part of the unit converted into another structure by treating the polymer.

  Further, “mass%” indicates the content of a predetermined component contained in the total amount of 100 mass%.

<Curing film>
The cured film used in the present invention has more than 50% by mass of the repeating unit derived from the monomer (a1) having one isocyanuric acid skeleton and two or three (meth) acryloyl groups in the molecule, and is 75% by mass. And
It is a cured film containing 25% by mass or more and less than 50% by mass of a repeating unit derived from the monomer (a2) having two (meth) acryloyl groups in the molecule (however, the molecule does not include an isocyanuric acid skeleton). .

  The thickness of the cured film is preferably 2 μm or more and 18 μm or less. A film thickness of 2 μm or more is preferable because the cured film has good scratch resistance and surface hardness, and 4 μm or more is more preferable. Moreover, if the film thickness of the said cured film is 18 micrometers or less, since the moldability of a cured film becomes favorable, it is preferable and 12 micrometers or less are more preferable.

  In addition, the film thickness of a cured film can be measured with the measuring method described in the Example mentioned later.

In the cured film of the present invention, the surface of the cured film was scratched 100 times with # 000 steel wool at a pressure of 480 g / cm ² for 100 reciprocal scratches, and then the change amount ΔH (unit: haze value calculated by the following formula (1) :%) Can be 3.0% or less.

[Change in haze value ΔH (%)] = [Haze value after scratching (%)] − [Haze value before scratching (%)] (Formula 1)
If the amount of change ΔH in the haze value of the cured film is 3.0% or less, it can be used for products requiring scratch resistance such as a display full board. More preferably, it is 2.0% or less.

<Mixed layer>
The cured film used in the present invention can have a mixed layer formed by penetrating the hard film into the resin substrate-forming composition, which will be described later.

  Here, the said mixed layer means the layer from which the density | concentration of the composition for resin base material formation which forms the said resin base material becomes high continuously from the said cured film side to the said resin base material side.

  In the resin laminate of the present invention, the formation of the mixed layer improves the adhesion between the cured layer and the resin substrate, thereby suppressing the occurrence of cracks when the resin laminate is bent. The effect which improves, and the effect which surface hardness and abrasion resistance improve are acquired.

  The swelling layer preferably has a thickness of the swelling layer of 0.05 μm or more and 10 μm or less. If the minimum of thickness is 0.05 micrometer or more, it is preferable from a viewpoint of a moldability, and if the upper limit of thickness is 10 micrometers or less, it is preferable from a viewpoint of hardness and scratch resistance. In addition, the thickness of the said mixed layer can be measured with the measuring method described in the Example mentioned later.

<Curable composition>
In the cured film of the present invention, the monomer (a1) described later exceeds 50% by mass and is 75% by mass or less, the monomer (a2) described later is 25% by mass or more and less than 50% by mass, a polymerization initiator (B ) Can be obtained by curing.

  If necessary, the curable composition may contain a monomer having one (meth) acryloyl group to adjust the viscosity of the curable composition or the crosslinking density of the cured film. In addition, release agents, lubricants, plasticizers, antioxidants, antistatic agents, light stabilizers, UV absorbers, flame retardants, flame retardant aids, polymerization inhibitors, fillers, pigments, dyes in curable compositions Various additives such as a silane coupling agent, a leveling agent, an antifoaming agent, or a fluorescent agent can be contained.

<Monomer (a1)>
The monomer (a1) is a compound having one isocyanuric acid skeleton and two or three (meth) acryloyl groups in the molecule.

  When the monomer (a1) has one isocyanuric acid skeleton in the molecule, an effect of improving the crack resistance of the obtained resin molded body is obtained. In addition, when the monomer (a1) has 2 or 3 (meth) acryloyl groups in the molecule, an effect of improving the surface hardness and scratch resistance of the obtained resin molded body can be obtained.

  Examples of the monomer (a1) include the following compounds. These can be used alone or in combination of two or more.

(1) (meth) acryloyl isocyanates;
For example, tris [(meth) acryloyloxyethyl] isocyanurate, tris [2- (meth) acryloyloxypropyl] isocyanurate, bis [(meth) acryloyloxyethyl] hydroxyethyl isocyanurate, bis [2- (meth) acryloyl Oxypropyl] -2-ethoxypropyl isocyanurate, tris [(meth) acryloyloxyethoxyethyl] isocyanurate and mixtures thereof.

(2) Urethane (meth) acrylates;
(2-1) A compound obtained by reacting a hydroxyl group-containing (meth) acrylate with an isocyanate group of a compound obtained by isocyanurating an isocyanate compound such as hexamethylene diisocyanate;
Examples of the hydroxy group-containing (meth) acrylate include hydroxyalkyl (meth) acrylate and compounds obtained by modifying these hydroxyalkyl (meth) acrylates with caprolactone. Examples of the hydroxyalkyl (meth) acrylate include 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and the like.

  Furthermore, as the hydroxy group-containing (meth) acrylate, for example, a reaction product of glycidyl (meth) acrylate and (meth) acrylic acid, pentaerythritol mono (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri ( And (meth) acrylate and pentaerythritol tetra (meth) acrylate.

(2-2) A compound obtained by reacting tris (2-hydroxyethyl) isocyanurate with a hydroxy group-containing (meth) acrylate;
Examples of the hydroxy group-containing (meth) acrylate include hydroxyalkyl (meth) acrylate and compounds obtained by modifying these hydroxyalkyl (meth) acrylates with caprolactone.

  Examples of the hydroxyalkyl (meth) acrylate include 2- (meth) acryloyloxyethyl isocyanate, isophorone diisocyanate and 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth). An acrylate etc. are mentioned.

  Furthermore, as a hydroxy group-containing (meth) acrylate, a reaction product of glycidyl (meth) acrylate and (meth) acrylic acid, pentaerythritol mono (meth) acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, Examples include pentaerythritol tetra (meth) acrylate.

  It is preferable that the lower limit of the content of the repeating unit derived from the monomer (a1) exceeds 50% by mass because the scratch resistance, surface hardness, and moldability of the cured film are improved. Moreover, if the upper limit of the repeating unit derived from the monomer (a1) is 75% by mass or less, the content of the monomer (a2) will be relatively increased, and the appearance of the cured film will be increased for the reasons described later. Since it becomes favorable, it is preferable.

<Monomer (a2)>
The monomer (a2) is a monomer having two (meth) acryloyl groups in the molecule (however, the molecule does not contain an isocyanuric acid skeleton).

  Since the monomer (a2) does not have an isocyanuric acid skeleton in the molecule, the viscosity is lower than that of the monomer (a1), so that the viscosity of the curable composition is reduced and the curable composition The coatability is stable, and the appearance of the resin molded body is improved.

  Since the monomer (a2) has two (meth) acryloyl groups in the molecule, the surface hardness and scratch resistance of the resin molded article can be favorably maintained.

  Examples of the monomer (a2) include ethylene glycol di (meth) acrylate, dicyclopentenyl di (meth) acrylate, triethylene glycol di (meth) acrylate, tetraethylene glycol di (meth) acrylate, and polyethylene glycol di ( (Meth) acrylate, trimethylolpropane di (meth) acrylate, ethylene oxide adduct trimethylolpropane di (meth) acrylate, tripropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,4-butanediol di (Meth) acrylate, 1,6-hexanediol di (meth) acrylate, polyester di (meth) acrylate, polyethylene glycol di (meth) acrylate, tricyclodecane dimethylo Di (meth) acrylate, hydroxypivalate neopentyl glycol di (meth) acrylate, bisphenol A polyethoxydi (meth) acrylate, 1,10-decanediol di (meth) acrylate, hydroxypivalate neopentyl glycol di (meth) acrylate, etc. Is mentioned.

  One of the above monomers can be used alone or in combination of two or more monomers.

  Among these, 1,6-hexanediol di (meth) acrylate is preferable from the viewpoint of reducing the viscosity of the curable composition and improving the coating property of the curable composition.

  If the repeating unit derived from the monomer (a2) (however, the molecule does not contain an isocyanuric acid skeleton) is 30% by mass or more, the viscosity of the curable composition is lowered and the appearance of the cured film is good. Therefore, it is preferable. Further, if the repeating unit derived from the monomer (a2) is less than 50% by mass, the content of the monomer (a1) is relatively increased, so that the cured film has crack resistance, scratch resistance and surface hardness. Is preferable because

<Component (a3), Component (a4)>
In addition, the cured film of the present invention cures (meth) acrylic acid esters other than the component (a1) and the component (a2) for the purpose of adjusting the viscosity of the curable composition or the crosslinking density of the cured film. You may make it contain so that content in a film | membrane may be the range of 20 mass% or less.

  Specifically, (meth) acrylic acid ester (component (a3)) having three or more (meth) acryloyl groups in the molecule, or (meth) acrylic having one (meth) acryloyl group in the molecule And (meth) acrylic acid esters such as acid esters (component (a4)).

  Specific examples of the component (a3) include, for example, an aliphatic hydrocarbon-modified trimethylolpropane tri (meth) acrylate having 2 to 5 carbon atoms and an aliphatic hydrocarbon-modified dipentaerythritol penta (meth) having 2 to 5 carbon atoms. Examples thereof include acrylates and aliphatic hydrocarbon-modified dipentaerythritol tetra (meth) acrylates having 2 to 5 carbon atoms.

  Specific examples of the component (a4) include, for example, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate, cyclohexyl (meth) acrylate, ( Isobornyl (meth) acrylate, norbornyl (meth) acrylate, adamantyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, dicyclopentenyl (meth) acrylate, dicyclo (meth) acrylate Pentanyl, tetracyclododecanyl (meth) acrylate, cyclohexanedimethanol mono (meth) acrylate, 4-acryloyloxymethyl-2-methyl-2-ethyl-1,3-dioxolane, 4-acryloyloxymethyl-2- Methyl-2-isobutyl-1,3-dioxo Emissions, trimethylolpropane formal (meth) acrylate.

  These can be used individually by 1 type or in combination of 2 or more types.

<Polymerization initiator (B)>
The polymerization initiator (B) is a component for curing the curable composition. In the present invention, the type of the polymerization initiator is not particularly limited, and a known photopolymerization initiator and / or thermal polymerization initiator can be used depending on the method for producing the resin laminate.

Examples of the photopolymerization initiator include the following compounds. These 1 type compounds can be used individually or in combination of 2 or more types.
-Known thioxanthone compounds such as benzophenone, 4-phenylbenzophenone and anthraquinone;
-Known acetophenone compounds such as diethoxyacetophenone and benzyldimethyl ketal;
-Known benzoin ether compounds such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether;
-Known acylphosphine oxide compounds such as 2,4,6-trimethylbenzoyldiphenylphosphine oxide and bis (2,6-dimethoxybenzoyl) -2,4,4-trimethylpentylphosphine oxide;
Methyl benzoyl formate; 1,7-bisacridinyl heptane;
-Known acridine compounds such as 9-phenylacridine Thermal polymerization initiators include, for example, methyl ethyl ketone peroxide, benzoyl peroxide, dicumyl peroxide, t-butyl hydroperoxide, cumene hydroperoxide, t-butyl peroxide Organic peroxides such as oxyoctoate, t-butylperoxybenzoate, lauroyl peroxide; azo compounds such as azobisisobutyronitrile; and N, N-dimethylaniline, N, N- Examples thereof include redox polymerization initiators combined with amines such as dimethyl-p-toluidine. These 1 type compounds can be used individually or in combination of 2 or more types.

  Content of the polymerization initiator (B) in a curable composition is 0.1-10 mass parts with respect to 100 mass parts of total amounts of a monomer (a1)-monomer (a4) (curing liquid). However, it is not particularly limited.

  Among the polymerization initiators (B), the photopolymerization initiator is preferable from the viewpoint of efficiently producing the cured film of the present invention by irradiating the curable composition with active energy rays.

  Examples of the active energy rays include electron beams, ultraviolet rays, and visible rays, but ultraviolet rays are preferable from the viewpoints of apparatus cost and productivity. The cumulative amount of active energy rays is preferably 5 to 2000 mJ / cm2.

  Examples of the active energy ray light source include a fluorescent ultraviolet lamp, an ultrahigh pressure mercury lamp, a high pressure mercury lamp, a medium pressure mercury lamp, a low pressure mercury lamp, a metal halide lamp, an Ar laser, a He-Cd laser, a solid laser, a xenon lamp, and a high frequency. Examples include induction mercury lamps and sunlight. Among these, a fluorescent ultraviolet lamp and a high-pressure mercury lamp are preferable from the viewpoint of the curing rate of the curable composition.

  As a polymerization initiator (B), when hardening a curable composition by heating using a thermal polymerization initiator, a well-known hot air drying furnace etc. can be used as a heating apparatus. The heating temperature is usually 40 ° C to 120 ° C, and the heating time is usually 1 minute to 48 hours.

<Resin base material (b1)>
As resin which comprises the resin base material used by this invention, polyolefin resin, (meth) acrylic resin, an epoxy resin, a polyimide resin, a phenol resin, a polyester resin, a polycarbonate resin etc. are mentioned, for example.

  Among these, a (meth) acrylic resin having a methyl methacrylate unit as a main component is preferable from the viewpoint of excellent transparency and appearance.

  “A (meth) acrylic resin having a methyl methacrylate unit as a main component” means that 50 to 100% by mass of methyl methacrylate units and methyl methacrylate can be copolymerized with respect to all structural units constituting the (meth) acrylic resin. It means a polymer containing 0 to 50% by mass of monomer units and the total amount of the respective components does not exceed 100% by mass.

Examples of the monomer copolymerizable with the methyl methacrylate unit include a) to k) below.
a) Methacrylic acid esters such as ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, benzyl methacrylate;
b) acrylic esters such as methyl acrylate, ethyl acrylate, n-butyl acrylate, iso-butyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate;
c) unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, itaconic acid;
d) unsaturated carboxylic acid anhydrides such as maleic anhydride, itaconic anhydride;
e) maleimides such as N-phenylmaleimide, N-cyclohexylmaleimide;
f) Hydroxy group-containing vinyl monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate;
g) Vinyl esters such as vinyl acetate and vinyl benzoate;
h) vinyl chloride, vinylidene chloride and derivatives thereof;
i) Nitrogen-containing vinyl monomers such as methacrylamide and acrylonitrile;
j) Epoxy group-containing monomers such as glycidyl acrylate and glycidyl methacrylate;
k) Aromatic vinyl monomers such as styrene and α-methylstyrene Further, examples of the monomer copolymerizable with the methyl methacrylate unit include, in addition to the above monomers, the following l) to p). Can be mentioned.
l) Alkanediol di (meth) acrylate such as ethylene glycol di (meth) acrylate, 1,2-propylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate (Meth) acrylate;
m) Diethylene glycol di (meth) acrylate, dipropylene glycol di (meth) acrylate, triethylene glycol (meth) acrylate, tetraethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, neopentyl glycol di (meth) Polyoxyalkylene glycol di (meth) acrylates such as acrylates;
n) vinyl monomers having two or more ethylenically unsaturated bonds in the molecule such as divinylbenzene;
o) an unsaturated polyester prepolymer obtained from at least one polycarboxylic acid comprising an ethylenically unsaturated polycarboxylic acid and at least one diol;
p) Vinyl ester prepolymer obtained by acrylic modification of the end of the epoxy group When using a (meth) acrylic resin containing a methyl methacrylate unit as a main component as a resin base material, radical polymerization having a methyl methacrylate as a main component Mixture of monomers, ie, 50% by mass to 100% by mass of methyl methacrylate and 0% by mass to 50% by mass of monomer copolymerizable with methyl methacrylate, based on the total mass of (meth) acrylic resin Can be used as the resin base material (b1).

  Alternatively, a mixed solution (syrup) of a partial polymer obtained by polymerizing a part of the mixture of the radical polymerizable monomers and the remaining radical polymerizable monomer may be used as the resin base material (b1). it can.

  Moreover, the liquid mixture (syrup) which dissolved the (meth) acrylic resin in the mixture of the said radical polymerizable monomer can be used as a resin base material (b1).

  A resin base material of (meth) acrylic resin can be obtained by curing the above-mentioned resin base material (b1) by a known method.

  The molecular weight of the partial polymer in the syrup or the (meth) acrylic resin as the resin base material is preferably a mass average molecular weight of 300,000 or less. Moreover, as a polymerization rate of a partial polymer, 5 mass% or more and 50 mass% or less are preferable with respect to the total mass of a partial polymer. The mixing ratio of the partial polymer or (meth) acrylic resin in the syrup and the radical polymerizable monomer is preferably 2:98 to 50:50 in terms of mass ratio.

  A known polymerization initiator can be added to the resin base material (b1). Examples of the polymerization initiator include organic oxides, azo compounds, and derivatives thereof exemplified as the polymerization initiator (B) described above. The addition amount of a polymerization initiator can be 0.005-5 mass parts with respect to 100 mass parts of radically polymerizable monomers in a (meth) acrylic resin base material.

  The resin base material (b1) may include a colorant, a release agent, an antioxidant, a stabilizer, a flame retardant, an impact modifier, a light stabilizer, an ultraviolet absorber, a polymerization inhibitor, if necessary. Various additives such as a chain transfer agent can be added.

  Examples of the polymerization method of the resin base material (b1) include a bulk polymerization method, a solution polymerization method, an emulsion polymerization method, and a suspension polymerization method, but the production cost of the (meth) acrylic resin composition, the use of a solvent, and the like. From the viewpoint of the environmental load due to the above, the productivity of the (meth) acrylic resin molded product, and the transparency, the bulk polymerization method is preferred.

<Resin laminate>
The resin laminate according to an embodiment of the present invention is a laminate in which a cured film having a thickness of 2 μm or more and 18 μm or less is laminated on the surface of a resin base material.

  In the evaluation of crack resistance by the following evaluation method, the resin laminate according to one embodiment of the present invention is crack resistant so that cracks do not occur in the resin laminate when the resin laminate is bent to a radius of curvature of 15 mm or less. Can have. Furthermore, when the resin laminate is bent to a curvature radius of 5 mm or less, it can have crack resistance that does not generate cracks.

  When the resin laminate has crack resistance when bent to a radius of curvature of 15 mm or less, the handleability of the resin laminate is improved, and the resin laminate of the present invention is used for manufacturing a display front plate having a complicated curved shape. The body can be used.

<Method for producing resin laminate>
Examples of the method for producing the resin laminate of the present invention include the following two methods.
(1) A method of obtaining a resin laminate by applying a curable composition to the surface of a resin substrate and then curing the curable composition.
(2) A method of obtaining a resin laminate by polymerizing a resin base material layer after forming a resin base material layer on the surface of a cured film obtained by curing the curable composition .

  Here, the curable composition means that the monomer (a1) having one isocyanuric acid skeleton and two or three (meth) acryloyl groups in the molecule exceeds 50% by mass and 75% by mass or less, A monomer (a2) having two (meth) acryloyl groups in the molecule (however, it does not contain an isocyanuric acid skeleton in the molecule) 25% by mass or more and less than 50% by mass, and a polymerization initiator That means.

  Among the methods described above, the method (2) is preferable from the viewpoint of excellent balance between the pencil hardness and scratch resistance of the cured film and the critical curvature radius of the resin laminate.

  Specific examples of the method (2) include the method (2-1) described below.

<Method (2-1)>
The curable composition is applied to the inner surface of the mold, and then the active energy ray is irradiated to cure the curable composition to obtain a laminated mold in which a cured film is formed on the inner surface of the mold.

  Next, the resin base material (b1) is injected into the obtained laminated mold so as to cover the cured film, and then the resin base material (b1) is cured by cast polymerization, so that the surface of the cured film is A resin substrate layer is formed on the substrate.

  Next, the resin laminate having a cured film laminated on the surface is peeled from the mold to obtain a resin laminate.

That is, the method for producing a resin laminate of the method (2-1) is a method for producing a resin laminate including the following.
(1) applying a curable composition to the inner surface of the mold;
(2) irradiating active energy rays to cure the curable composition to obtain a laminated mold in which a cured film is laminated on the inner surface of the mold;
(3) A resin base material is injected into the laminated mold, and the resin base material is cured by cast polymerization to form a resin base layer;
(4) The resin laminate in which a cured film is laminated on the surface of the resin base material is peeled off from the mold. Further, the resin laminate has a crack resistance that does not generate cracks when bent to the curvature radius of 15 mm or less, and is cured. As a resin laminated body with which the variation | change_quantity ((DELTA) H) of the haze value of a film | membrane satisfy | fills 3% or less, monomer (a1) 50 mass on the surface of a resin base material, for example by said method (2-1). The curable composition containing 75% by mass or less and the compound and the monomer (a2) of 25% by mass or more and less than 50% by mass is coated, and then the curable ancestor composition is cured to form a resin group A resin molded body in which a cured film having a film thickness of 25 to 40 μm is formed on the surface of the material can be mentioned.

  Examples of the method for applying the curable composition to the inner surface of the mold include a fluency method, a roller coating method, a bar coating method, a spray coating method, and an air knife coating method.

  Here, in the resin laminate finally obtained by irradiating the curable composition with active energy rays in an oxygen atmosphere, the cured film is on the resin substrate side, The composition for forming a resin base material may have a mixed layer formed by penetrating the hard film. Here, the oxygen atmosphere is not particularly limited as long as it is in the presence of a gas containing oxygen, and air is particularly excellent in view of economy and safety.

  Furthermore, the reaction constant A defined by the following formula of the cured film obtained immediately after the step (1) is not particularly limited, but can be, for example, in the range of 0.03 to 0.5. If the lower limit of the reaction constant A is 0.03 or more, the curing reaction of the cured film can be sufficiently completed in the obtained resin laminate. If the upper limit of the reaction constant A is 0.5 or less, the mixed layer can be formed efficiently.

Reaction constant A = a / b
a: Peak height of infrared absorption spectrum in the range of 790 to 820 cm ⁻¹ measured by the total reflection measurement method on the surface of the cured coating (A) b: Measured by the total reflection measurement method on the surface of the cured coating (A) The peak height of the infrared absorption spectrum in the range of 1700 to 1740 cm ⁻¹ The reaction constant A of the cured film obtained immediately after the step (1) is adjusted by adjusting the amount of active energy, heating polymerization temperature, time, etc. Can be controlled.

  Examples of the mold type include molds such as molds and sheets. The mold is usually prepared by facing two molds so that the surface on which the cured film is laminated faces the inner surface. The surface on which the mold cured film is laminated preferably has a smooth surface.

  Examples of the mold material include stainless steel, glass, and resin.

  As the mold, a mold in which two molds of the same material or different materials are arranged to face each other can be used. Examples of the method for producing the template include the following methods.

  First, a first laminated mold having a cured film formed on the inner surface of the mold is placed. Next, a second mold (with or without a cured film formed on the inner surface of the mold) is placed so as to face the laminated mold, and the first mold and the second mold are arranged. By providing a gasket as a sealing material at the periphery of the space formed between the molds, a laminated mold having a constant volume on the inside is produced, and this is used as the mold.

  In the present invention, the cured film may be formed on the inner surface of the first mold or on the inner surfaces of the first and second molds.

  The material of the gasket is preferably polyvinyl chloride, and more preferably soft polyvinyl chloride.

  The resin base material (b1) is injected into the obtained laminated mold, and then cast polymerization is performed with the resin base material (b1) covering the surface of the cured film to form a resin base layer. To do.

  Next, the resin laminate can be obtained by taking out the obtained resin base material from the mold in a state where the cured film and the resin base material are integrated.

  In the present specification and claims, “cast polymerization” means, for example, a mold composed of two molds arranged to face each other at a predetermined interval, and a sealing material arranged on the peripheral edge of the mold. This refers to a method in which a laminated mold composed of (gaskets or the like) is used and a resin base material is injected into the laminated mold and then polymerized.

  Examples of the casting polymerization used industrially include a cell casting method in which a resin base material is injected into a laminated mold made of a glass plate or a metal plate and then heated, and a continuous belt polymerization method.

  The continuous casting polymerization method is a first stainless steel endless belt having a cured film laminated on the belt surface, and is disposed to face the first belt, and runs at the same speed in the same direction as the first belt. The resin base material is continuously injected from the upstream side of the belt into the space portion formed by the second stainless steel endless belt and the gaskets disposed at both end portions of both endless belts, and heated continuously. This is a polymerization method.

  As a method for heating the laminated mold, a known method can be used. For example, the method of heating a lamination | stacking casting_mold | template with heat sources, such as 30-98 degreeC warm water, is mentioned. The polymerization time is appropriately determined according to the progress of the polymerization.

  In order to increase the polymerization rate of the resin base material, heat treatment at 90 to 150 ° C. can be performed by a heat source such as a far infrared heater in an air atmosphere as necessary. The polymerization time is appropriately determined according to the progress of the polymerization. Further, after the heat treatment, a cooling treatment such as blowing can be performed as necessary.

  The thickness of the resin laminate is not particularly limited, but may be 0.2 mm or more and 10 mm or less, and preferably 0.3 mm or more and 5 mm or less.

  Hereinafter, the present invention will be described in detail by way of examples. In addition, various evaluation in an Example was implemented with the following method.

(1) Film thickness measurement of cured film The resin laminate was cut in a direction parallel to the thickness direction using a cutting machine such as a panel saw. Next, the cut surface of the cut resin laminate was polished using an end mirror finisher. The film thickness was measured by observing the polished cross section using a digital microscope.

(2) Appearance The resin laminate was irradiated with a fluorescent lamp, and the appearance of the surface of the resin laminate was visually observed and evaluated in three stages.

No abnormality in the resin laminate: ○
There is a minute defect on a part of the resin laminate surface: △
There is a minute defect on the entire surface of the resin laminate: ×
(3) Scratch resistance The scratch resistance of the surface of the resin laminate was evaluated by the change in haze value (ΔH) (%) before and after the scratch test. Place a round pad with a diameter of 24 mm with # 000 steel wool (manufactured by Nippon Steel Wool Co., Ltd., trade name: Bonstar No. 000) on the surface of the cured resin layer of the resin laminate, and load of 2,000 g The distance of 50 mm was reciprocated 100 times below. Using a haze analyzer (manufactured by Nippon Denshoku Industries Co., Ltd., product name: HAZE METER NDH4000), in accordance with the measurement method shown in JIS K7136, the haze value of the resin laminate before and after the abrasion test The haze value change amount (ΔH) was calculated from the following formula. .

[Change in haze value (ΔH) (%))] = [Haze value after abrasion (%)] − [Haze value before abrasion (%)]
(4) Pencil hardness The pencil hardness of the surface of the resin laminate was measured according to JIS K5400.

(5) <Crack resistance>
The crack resistance of the resin laminate is measured by the curvature radius (molding R) at which cracking occurs when the resin laminate is bent to a radius of curvature of 5 mm, 7.5 mm, 10 mm, 15 mm and 20 mm by the following method. And evaluated.

  After cutting the resin laminate parallel to the thickness direction and cutting out 15 laminate pieces having a width of 30 mm, a length of 120 mm and a thickness of 1 mm, the cut surface of the laminate piece is polished with an end mirror polishing machine, A test piece for evaluation of crack resistance was obtained. Next, the test piece is stored in a heating furnace at 140 ° C. for 15 minutes and heat-treated and then taken out. Immediately, the test piece after the heat treatment is opposite to the surface of the bending jig with the surface having the cured film of the test piece. It was placed on the side and bent for 5 seconds while closely contacting the male-shaped surface of the bending jig. The surface of the test piece after being held for 5 seconds was visually observed, and a case where no crack was observed was accepted, and a case where one or more cracks were observed was rejected. Measurement was performed using three samples for bending jigs having five kinds of curvature radii. The smallest radius of curvature value that passed two of the three samples was recorded as forming R.

(6) Mixed layer thickness (Bt)
The resin laminates obtained in the examples and comparative examples were cut in the direction perpendicular to the main surface. Next, a small piece for a transmission electron microscope was cut out from the cut surface of the resin laminate using a microtome. Next, using a transmission electron microscope (TEM: manufactured by JEOL Ltd., model: JEM-10111, acceleration voltage: 100 V, magnification: 10000 times), a cross section of the small piece was observed to obtain a TEM observation image. did. In the region where the three-layer structure of the obtained TEM observation image was observed, the film thickness Bt of the mixed layer was measured as a layer of the resin base material / mixed layer / cured film in order.

(Reaction constant A)
The surface of the cured coating obtained immediately after the step (1) is subjected to a multiple reflection total reflection measurement method using a Fourier transform infrared spectrophotometer (ATR: manufactured by Thermo Fisher Scientific Co., Ltd .: Model iS10). , measured peak height of the infrared absorption spectrum in the range of 790～820Cm ^-1 to (a), the peak height of the infrared absorption spectrum in the range of 1700~1740cm ^-1 (b), the reaction constant a from the following equation Was calculated.

Reaction constant A = a / b
Hereinafter, the abbreviations of the compounds indicate the following compounds.

Monomer (a1): A mixture of tris (2-hydroxyethyl) isocyanurate and bis (2-hydroxyethyl) isocyanurate (manufactured by Toagosei Co., Ltd., trade name: Aronix M315)
Monomer (a2): 1,6-hexanediol diacrylate (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name: C6DA)
Monomer (a3): A mixture of pentaerythritol triacrylate and pentaerythritol tetraacrylate (manufactured by Toagosei Co., Ltd., trade name: Aronix M305)
Monomer (a4): urethane monomer obtained by reacting 3 mol of 3-acryloyloxy-2-hydroxypropyl methacrylate with 1 mol of triisocyanate obtained by trimerizing hexamethylene diisocyanate (Shin Nakamura) Kogyo Co., Ltd., trade name: U6HA)
Polymerization initiator (b1): 1-hydroxycyclohexyl phenyl ketone (manufactured by BASF Japan Ltd., trade name: IRGACURE 184)
Polymerization initiator (b2): Bis (2,4,6-trimethylbenzoyl) -phenylphosphine oxide (manufactured by BASF Japan Ltd., trade name: IRGACURE 819)
[Example 1]
(Creation of curable composition (1))
To 100 parts by mass of the curing liquid consisting of 52% by mass of monomer (a1) and 48% by mass of monomer (a2), 2.0 parts by mass of polymerization initiator (b1) and polymerization initiator (b2): 0.5 After mixing parts by mass, the mixture was stirred using a warm water bath at a temperature of 40 ° C. for 30 minutes to obtain a curable composition (1).

(Preparation of resin base material (b1))
100 parts by weight of a mixture comprising 20 parts by weight of polymethyl methacrylate having a mass average molecular weight of 220,000 and 80 parts by weight of methyl methacrylate, 0.01 parts by weight of 2- (5-methyl-2-hydroxyphenyl) -benzotriazole, azobis After mixing 0.05 part by weight of dimethylvaleronitrile and 0.005 part by weight of sodium salt of dioctylsulfosuccinate, the mixture was stirred at room temperature for 10 minutes to obtain a resin base material. Next, the dissolved air in the resin base material was removed under reduced pressure to obtain a resin base material (b1).

(Creation of pre-curing film)
A SUS304 plate (1) having a mirror surface was used as a mold, and the curable composition (1) was applied onto the mold by a bar coating method to obtain a pre-curing film (1-1) having a thickness of 10 μm.

(Create a resin laminate)
The SUS304 plate (1) coated with the pre-curing coating (1-1) is passed at a speed of 2 m / min at a position 17 cm below the high-pressure mercury lamp (manufactured by Toshiba Corporation, trade name: FL40BL, output 120 W). However, the pre-curing coating (1-1) was irradiated with light from a high-pressure mercury lamp, and the pre-curing coating was cured in contact with air, and a laminated mold (1-2) having a cured film formed on the mold surface. Got. The reaction constant of the cured film at this time was A0.2.

  The obtained laminated mold (1-2) and the SUS304 plate (2) on which the cured film is not formed are opposed to each other so that the cured film of the laminated mold (1-2) is on the inside. The peripheral portion of the space sandwiched between the SUS304 plates (1) and (2) was sealed with a gasket made of soft polyvinyl chloride to produce a laminated mold (1-3).

  The resin base material (b1) was poured into the laminated mold (1-3) and polymerized in a hot water bath at 80 ° C. for 1 hour and then in a heated air furnace at 130 ° C. for 1 hour. After cooling the laminated mold (1-3) after No. 10, the two SUS304 plates (1) and (2) on both sides are peeled from the laminated mold (1-3), and a cured film is provided on one surface. A resin laminate (1-4) having a thickness of 1 mm was obtained.

  Table 1 shows the evaluation results of the composition of the cured film, the thickness of the cured film, the appearance, the scratch resistance, the pencil hardness, and the crack resistance of the obtained resin laminate (1-4).

  The resin laminate (1-4) had a scratch resistance of 0.2%, a pencil hardness of 4H, and a molding R of 10 mm, and was excellent in scratch resistance, surface hardness, and moldability.

  Furthermore, in the cured film, a 1 μm-thick mixed layer was observed on the resin substrate side, which was formed by the resin substrate forming composition penetrating into the hard film.

[Examples 2 to 6]
A resin laminate was obtained in the same manner as in Example 1 except that the composition of the curable composition shown in Table 1 and the film thickness of the cured coating were used. The evaluation results of the obtained resin laminate are shown in Table 1.

[Comparative Examples 1-6]
A resin laminate was obtained in the same manner as in Example 1 except that the composition of the curable composition and the thickness of the cured film were as shown in Table 1. The evaluation results of the obtained resin laminate are shown in Table 1.

  Since Comparative Example 1 was thick, it had excellent pencil hardness and scratch resistance, but molding R was poor.

  In Comparative Examples 2 and 3, since the content of the monomer (a1) was high, the appearance of the cured film was poor.

  In Comparative Example 4, since the content of the monomer (a2) was high, the cured film had poor scratch resistance.

  Since Comparative Examples 5 and 6 were compounds other than the monomer (a2), the molding R was poor.

[Comparative Example 7]
As the resin base material, Acrylite L manufactured by Mitsubishi Rayon Co., Ltd. was used. Next, after applying the curable composition (1) shown in Table 1 to the surface of the resin substrate by the bar coating method, the activity of the high-pressure mercury lamp (manufactured by Toshiba Corporation, trade name: FL40BL, output 120 W) The curable composition (1) was irradiated with energy rays to cure the curable composition to obtain a resin laminate. The evaluation results of the obtained resin laminate are shown in Table 1.

  The obtained resin laminate was evaluated for the film thickness appearance, scratch resistance, pencil hardness, presence / absence of a mixed layer, and crack resistance of the cured coating film by the evaluation method described above. The evaluation results are shown in Table 1.

  Comparative Example 7 was insufficient in pencil hardness and scratch resistance. Moreover, the mixed layer was not observed. The manufacturing method of the resin laminate of Comparative Example 7 is the same as the manufacturing method of the resin laminate of Example 1, the point that the cured film was formed on the surface of the cured resin substrate, and the resin substrate of the cured film The difference is that the side surfaces are cured without contact with air. As a result, in the resin laminate of Comparative Example 7, a mixed layer was not formed between the cured film and the resin base material, and it is assumed that pencil hardness and scratch resistance were insufficient.

The resin laminate of the present invention is excellent in appearance, surface hardness, scratch resistance, and crack resistance, and further excellent in processability of the resin laminate, so that it is complicated for automotive use materials such as display front plate, instrument panel and glazing. Can be used for products with shape.

DESCRIPTION OF SYMBOLS 1 Resin base material 2 Cured film 3 Resin laminated body

Claims (18)

A monomer (a1) having one isocyanuric acid skeleton in the molecule and two or three (meth) acryloyl groups;
Curing comprising a resin composition obtained by curing a curable composition containing a monomer (a2) having two (meth) acryloyl groups in the molecule (but not including an isocyanuric acid skeleton in the molecule) A membrane,
The said curable composition contains the said monomer (a1) more than 50 mass% and 75 mass% or less, and the said monomer (a2) 25 mass% or more and less than 50 mass%. And
The cured film has a thickness of 2 μm or more and 18 μm or less. The cured film is a repeating unit derived from a monomer (a1) having one isocyanuric acid skeleton in the molecule and two or three (meth) acryloyl groups,
A cured film containing a repeating unit derived from the monomer (a2) having two (meth) acryloyl groups in the molecule (however, the molecule does not contain an isocyanuric acid skeleton),
In the cured film, the repeating unit derived from the monomer (a1) exceeds 50% by mass and is 75% by mass or less, and the repeating unit derived from the monomer (a2) is 25% based on the total mass of the cured film. The cured film of Claim 1 which consists of a resin composition containing the mass% or more and less than 50 mass%. After the surface of the cured film was scratched 100 times with # 000 steel wool at a pressure of 480 g / cm ² for 100 reciprocal scratches, the change in haze value (ΔH) calculated by the following formula (1) was 3.0% or less. The cured film according to claim 1 or 2.
[Change in haze value (ΔH) (%)] = [Haze value after scratch (%)] − [Haze value before scratch (%)] (Formula 1)   In the cured film, the total amount of the repeating unit derived from the monomer (a1) and the repeating unit derived from the monomer (a2) exceeds 100% by mass with respect to the total mass of the cured film. The cured film in any one of Claims 1-3 containing% or less.   The cured film in any one of Claims 1-4 whose molecular weight of the said monomer (a2) is 300 or less.   The cured film in any one of Claims 1-5 whose film thickness of the said cured film is 4 micrometers or more and 12 micrometers or less.   The cured film in any one of Claims 1-6 whose variation | change_quantity ((DELTA) H) of the haze value of the said cured film is 1.0% or less.   The resin lamination by which the cured film in any one of Claims 1-7 was laminated | stacked on the at least one surface of the resin base material which consists of a (meth) acrylic resin composition containing 50 mass% or more of repeating units derived from methyl methacrylate. body.   The said cured film is a resin laminated body of Claim 8 which has the mixed layer in which the composition for resin base material infiltrated the said hard film on the said resin base material side.   The resin laminate according to claim 9, wherein in the mixed layer, the concentration of the composition for forming a resin substrate that forms the resin substrate is continuously increased from the cured film side to the resin substrate side. The resin laminate according to claim 9 or 10, wherein the thickness of the mixed layer measured by the following method 1 is 0.05 µm or more and 10 µm or less.
<Method 1>
The resin laminate is cut in a direction perpendicular to the main surface, and then a small piece for a transmission electron microscope is cut out from the cut surface using a microtome. About the cut out small piece, a TEM observation image is acquired using a transmission electron microscope (acceleration voltage 100V, magnification 10,000 times). In the region where the three-layer structure of the obtained TEM observation image was observed, the film thickness Bt of the mixed layer was measured as a layer of the resin base material / mixed layer / cured film in order. The manufacturing method of the resin laminated body which consists of a series of processes of following (1) and (2).
(1) monomer (a1) having one isocyanuric acid skeleton in the molecule and 2 or 3 (meth) acryloyl groups (a1) exceeding 50% by mass and 75% by mass or less;
100 parts by mass of a curing liquid containing 25% by mass or more and less than 50% by mass of a monomer (a2) having two (meth) acryloyl groups in the molecule (however, the molecule does not include an isocyanuric acid skeleton) After applying a curable composition containing 0.1 to 10 parts by weight of an initiator to the inner surface of the mold,
The curable composition is cured by irradiating active energy rays to form a cured film.
(2) The resin base material (b1) containing a mixture of polymerizable monomers is poured onto the surface of the cured film formed in the step (1), and then heat polymerized by cast polymerization to obtain a resin. A laminate is formed.   The manufacturing method of the resin laminated body of Claim 12 whose film thickness of the said cured film is 2 micrometers or more and 18 micrometers or less.   The manufacturing method of the resin laminated body of Claim 12 or 13 which irradiates an active energy ray to the curable composition of the said process (1) in oxygen atmosphere. About the cured film obtained immediately after the said process (1), the reaction constant A defined by a following formula is 0.03-0.5, It is any one of Claims 12-14 characterized by the above-mentioned. The manufacturing method of the resin laminated body of this.
A = a / b
a: Peak height of infrared absorption spectrum in the range of 790 to 820 cm ⁻¹ measured by the total reflection measurement method on the surface of the cured coating (A) b: Measured by the total reflection measurement method on the surface of the cured coating (A) Infrared absorption spectrum peak height in the range of 1700-1740 cm ⁻¹   In the cured film, the total amount of the repeating unit derived from the monomer (a1) and the repeating unit derived from the monomer (a2) exceeds 100% by mass with respect to the total mass of the cured film. The manufacturing method of the resin laminated body in any one of Claims 12-15 containing the following.   The manufacturing method of the resin laminated body in any one of Claims 12-16 whose molecular weight of the said monomer (a2) is 300 or less. The method for producing a resin laminate according to any one of claims 12 to 17, wherein the mixture of the radical polymerizable monomers contains 50% by mass or more of methyl methacrylate.