JPH1053608A - Photopolymerizable composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a photopolymerizable composition suitable for obtaining acrylic adhesives excellent in initial adhesive forces and temporal adhesive forces to adherends having a machine oil such as a cutting oil or an anticorrosive oil on the surfaces. SOLUTION: This photopolymerizable composition comprises 100 pts.wt. of a photopolymerizable monomer mixture comprising a monomer mixture consisting of (A) an alkyl (meth)acrylate (the alkyl group has 4-14 carbon atoms) and (B) a polar group-containing vinylic monomer and having a Fedors theoretical solubility parameter of >=8.8(cal/cm<3> )<1/2> and (C) a photopolymerization initiator and 5-40 pts.wt. of an oil-absorbing resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photopolymerizable composition suitable for an acrylic pressure-sensitive adhesive having excellent oil-surface adhesion.

[0001]

2. Description of the Related Art In recent years, pressure-sensitive adhesives are often used in various applications in the form of tapes or sheets. However, the adhesive strength inherent in the pressure-sensitive adhesive tape is a necessary condition that the adherend surface is clean, and the initial adhesive strength is sufficient when the adherend surface is contaminated, particularly when oil is attached. Often cannot be demonstrated. For this reason, it is necessary to sufficiently clean the surface of the adherend using an organic solvent, an aqueous detergent, or the like in order to express a high initial adhesive strength. However, it was expensive, and it was not really desirable. In particular, cutting oils, rust-preventive oils, and the like often adhere to metal adherends used industrially, and the development of pressure-sensitive adhesives having excellent oil-surface adhesion is desired.

On the other hand, as an example of the above-mentioned pressure-sensitive adhesive tape having excellent oil-surface adhesion, Japanese Patent Application Laid-Open No. 3-292379 discloses an alkyl (meth) acrylate having 8 to 18 carbon atoms and a carboxyl group-containing monomer as main components. A pressure-sensitive adhesive tape comprising a pressure-sensitive adhesive containing 30% by weight or less of an unreacted monomer is disclosed.

[0003]

However, the pressure-sensitive adhesive tape disclosed in Japanese Patent Application Laid-Open No. 3-292379 has a problem in that the presence of a large amount of unreacted monomer reduces monomer odor and cohesive strength, and furthermore, bleeds to the adhesive interface. There is a problem that the adhesive force changes with time due to the out-flow, and it is not always preferable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a photopolymerizable material suitable for obtaining an acrylic pressure-sensitive adhesive excellent in initial adhesive strength and temporal adhesive strength to an adherend having a machine oil such as a cutting oil or a rust-preventive oil on its surface. It is to provide a composition.

[0005]

The photopolymerizable composition of the present invention comprises (A) an alkyl (meth) acrylate having an alkyl group having 4 to 14 carbon atoms and (B) a vinyl monomer having a polar group. 7. Theoretical solubility parameter is 8.
8 (cal / cm ³ ) ^1/2 or more, and 100 parts by weight of a photopolymerizable mixed monomer comprising a photopolymerizable initiator (C) and 5 to 40 parts by weight of an oil-absorbing resin. Is what you do.

[0006] The mixed monomer used in the present invention is:
(A) Alkyl (meth) having 4 to 14 carbon atoms in the alkyl group
It comprises an acrylate and (B) a polar group-containing vinyl monomer. The alkyl (meth) acrylate (A) is an alkyl (meth) acrylate having 4 to 14 carbon atoms in the alkyl group, and these have a homopolymer having a glass transition temperature of -50.
Since the temperature is extremely low at not more than ° C, it is possible to maintain a high pressure-sensitive adhesiveness of the obtained acrylic pressure-sensitive adhesive by using it as a main component. Examples of the alkyl (meth) acrylate (A) include n-butyl acrylate, hexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl (meth) acrylate, and n-nonyl ( Examples thereof include (meth) acrylate, isononyl (meth) acrylate, and lauryl (meth) acrylate, and these may be used alone or in combination of two or more.

As the content of the alkyl (meth) acrylate (A) decreases, the cohesive strength increases and the pressure-sensitive adhesiveness decreases, and as the content increases, the cohesive strength decreases and the shear strength decreases. , Preferably 50 to 98
%, More preferably 70 to 95% by weight.

Examples of the polar group-containing vinyl monomer (B) include carboxyl group-containing vinyl such as (meth) acrylic acid, crotonic acid, itaconic acid, (anhydride) maleic acid, fumaric acid, and carboxyethyl (meth) acrylate. Monomer, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate,
Hydroxyl-containing vinyl monomers such as 4-hydroxybutyl (meth) acrylate, modified caprolactone (meth) acrylate, polyethylene glycol (meth) acrylate, and polypropylene glycol (meth) acrylate, (meth) acrylonitrile, N-vinylpyrrolidone, and N-vinylcaprolactam , N-vinyl lauryl lactam, (meth) acryloyl morpholine, (meth) acrylamide, dimethyl (meth) acrylamide, N-
Methylol (meth) acrylamide, N-butoxymethyl (meth) acrylamide, dimethylaminopropyl (meth) acrylamide, dimethylaminomethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, diethylaminoethyl ( Examples thereof include nitrogen-containing vinyl monomers such as meth) acrylate, and these may be used alone or in combination of two or more.

When the content of the polar group-containing vinyl monomer (B) is reduced, the cohesive strength is reduced and the shear strength is hardly obtained, and the theoretical solubility parameter of Fedors is 8.8 (cal / cm ³ ) ^1/2. It is difficult to make it more than the above, and when the amount is too large, the cohesive strength becomes high and it becomes difficult to obtain pressure-sensitive adhesiveness. .

A part of the polar group-containing vinyl monomer (B) may be replaced by another vinyl monomer. Examples of the other vinyl monomer include methyl (meth) acrylate, ethyl (meth) acrylate, Examples include vinyl acetate, vinyl propionate, styrene, and isobornyl (meth) acrylate.

The content of the other vinyl monomer is preferably not more than 20% by weight, more preferably not more than 10% by weight in the above-mentioned mixed monomer, because as the content increases, the cohesive strength increases and the pressure-sensitive adhesiveness decreases. .

The mixed monomer used in the present invention is composed of the above-mentioned components, and the Fedors theoretical solubility parameter is 8.8 (cal / cm ³ ) ^1/2 or more. The theoretical solubility parameter of the Fedors is:
It is based on the calculation method devised by Fedors (Journal of the Adhesion Society of Japan, vol. 22, no. 10 (1986)).
(53) and (566)). In this calculation method, each atom or atomic group such as a polar group is a unique Δe _i
And Δv _i , if the structural formula is known, the Fedors theoretical solubility parameter of each vinyl monomer (hereinafter referred to as “SP
Value, and the unit is (cal / cm ³ ) ^1/2 ).

[0013] SP value _{= (ΣΔe i / ΣΔv i)} 1/2

The above Δe _i represents the binding energy and the molecular kinetic energy of the atoms constituting the alkyl (meth) acrylate (A) or the polar group-containing vinyl monomer (B) or the polar group.
shows the binding energy and molecular kinetic energy of the entire monomer mixture _i, also Delta] v _i is atom such atoms or polar groups constituting the alkyl (meth) acrylate (A) or polar group-containing vinyl monomer (B) indicates the volume occupied by the Dan shows the volume occupied by the total monomer mixture .SIGMA..DELTA.V _i.

The alkyl (meth) acrylate
SP of (A) or vinyl monomer containing polar group (B)
Δe of the main atom or atomic group required to calculate the value
_iAnd Δv _iShows that the acryloxy group is Δe_i= 636
0, Δv_i= 60, the methylene group is Δe_i= 1180, Δ
v_i= 16.1, methyl group is Δe_i= 1125, Δv_i
= 33.5, carboxyl group is Δe_i= 6600, Δv
_i= 28.5.

Based on the above values, the following alkyl (meth)
When the SP values of the acrylate (A) and the polar group-containing vinyl monomer (B) are calculated, for example, SP value = 8.82 for n-butyl acrylate, SP value = 8.62 for 2-ethylhexyl acrylate, and SP value for acrylic acid
Value = 11.1 and so on.

The SP value of these mixed monomers as a whole can be calculated based on the sum of the mole fractions of the vinyl monomer components to be mixed. Thus, for example, 2
When the main component is an alkyl (meth) acrylate (A) having an SP value of less than 8.8, such as ethylhexyl acrylate (SP value = 8.62), the SP value of the mixed monomer is 8.8 or more. Therefore, it is necessary to mix a polar group-containing vinyl monomer having a high SP value such as acrylic acid.

The lower the SP value, the lower the oil-surface adhesion of the acrylic pressure-sensitive adhesive obtained when polymerized,
It is at least 8.8 (cal / cm ³ ) ^1/2 , preferably at least 9.0 (cal / cm ³ ) ^1/2 .

The mixed monomer used in the present invention comprises the above-mentioned components, but it is preferable to add a polyfunctional vinyl monomer in advance in order to simultaneously carry out polymerization and crosslinking during photopolymerization. Examples of the polyfunctional vinyl monomer include 1,4-butanediol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,9-nonanediol di (meth) acrylate,
(Poly) ethylene glycol di (meth) acrylate,
(Poly) propylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate,
Glycerin methacrylate acrylate, pentaerythritol di (meth) acrylate, pentaerythritol tri (meth) acrylate, trimethylolpropane tri (meth) acrylate, allyl (meth) acrylate, vinyl (meth) acrylate, divinylbenzene,
Epoxy (meth) acrylate and the like can be mentioned. These may be used alone or in combination of two or more.

The amount of the polyfunctional vinyl monomer added is
The less the degree of crosslinking, the lower the degree of cross-linking, the lower the heat resistance and shear strength, and the greater the degree of cross-linking, the higher the degree of cross-linking.
Since the flexibility is impaired and the pressure-sensitive adhesiveness is reduced, the amount is preferably from 0.01 to 100 parts by weight of the mixed monomer.
1 part by weight, more preferably 0.02 to 0.8 part by weight.

The photopolymerizable mixed monomer used in the present invention comprises the above-mentioned mixed monomer and photopolymerizable initiator (C). Examples of the photopolymerizable initiator (C) include:
(2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone [manufactured by Ciba-Geigy, trade name “Darocur 2959”], α-hydroxy-α,
α'-Dimethylacetophenone [Ciba Geigy, trade name “Darocur 1173”], 1-hydroxycyclohexyl phenyl ketone [Ciba Geigy, trade name “Irgacure 184”], methoxyacetophenone, 2,2-dimethoxy-2-phenyl Acetophenone [trade name "IRGACURE 65" manufactured by Ciba Geigy
1 "], benzoin ether initiators such as benzoin ethyl ether and benzoin propyl ether, ketal initiators such as benzyl dimethyl ketal, and others, halogenated ketones, acyl phosphine oxides, acyl phosphinates, etc. And these may be used alone or in combination of two or more.

When the amount of the photopolymerizable initiator (C) is small, a polymer having a strong monomer odor is obtained, and when the amount is large, the amount of generated radicals is increased and the cohesive force is reduced. On the other hand, it is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 4 parts by weight.

The photopolymerizable composition used in the present invention comprises the above-mentioned photopolymerizable mixed monomer and an oil-absorbing resin, and the above-mentioned oil-absorbing resin has a property of absorbing oil when it comes into contact with an oil surface. For example, a polynorbornene-based elastomer, a t-butylstyrene-divinylbenzene copolymer, or the like can be used, and a polynorbornene-based elastomer is particularly preferable in that it has a high oil-absorbing ability. Examples of the polynorbornene-based elastomer include “polynorbornene” (trade name, manufactured by Shinko Giken Co., Ltd.) as a commercial product.

If the amount of the oil-absorbing resin is small, it is difficult to obtain oil-absorbing performance, and if the amount is large, the cohesive strength of the obtained acrylic pressure-sensitive adhesive is reduced and the adhesive strength is reduced. 5 to 40 parts by weight, preferably 10 to 4 parts by weight based on 100 parts by weight of
0 parts by weight.

Additives such as fillers and tackifier resins may be added to the photopolymerizable composition as needed. Examples of the filler include inorganic hollow fillers such as glass balloons, alumina balloons, shirasu balloons, fly ash balloons, glass beads, silica beads, silica gel, alumina silica, fly ash,
Inorganic filler such as synthetic mica, diatomaceous earth, porous filler such as porous silica, polymethyl methacrylate, acrylonitrile-vinylidene chloride copolymer, organic hollow filler composed of polystyrene, phenol resin, etc., polymethacrylic acid Methyl beads, polystyrene beads, nylon beads, styrene acrylic beads, urethane beads, silicon beads, polyethylene beads, polypropylene beads, ethylene-vinyl acetate copolymer beads,
Organic fillers such as polyethyl acrylate beads, cubic alumina silica, glass flakes, glass fibers,
Chain clay minerals and the like may be mentioned, and these may be used alone or in combination of two or more.

The preferred range of the amount of the filler varies depending on the specific gravity. Generally, a hollow filler having a low specific gravity is used in an amount of 100 parts by weight of the photopolymerizable mixed monomer.
In the case of a hollow filler or an organic filler having a specific gravity of about 0.7 to 10 parts by weight and an inorganic filler having a specific gravity of 2 or more, the above-mentioned photopolymerizable mixed monomer is used in the case of a hollow filler or an organic filler. The amount is preferably 70 to 150 parts by weight based on 100 parts by weight of the ionic mixed monomer.

Usually, when the volume fraction of the filler in the photopolymerizable mixed monomer is small, the shear strength is decreased, and when the volume fraction is large, the pressure-sensitive adhesive property is decreased. is there.

Examples of the tackifying resin include C5
-Based and C9-based hydrogenated petroleum resins, hydrogenated rosin resins, hydrogenated rosin ester resins, hydrogenated terpene resins, hydrogenated terpene phenol resins, hydrogenated coumarone-indene resins, disproportionated rosin resins, disproportionated rosin ester resins , Polymerized rosin resin,
Resins having relatively few unsaturated bonds, such as polymerized rosin ester resins, may be used, and these may be used alone or in combination of two or more. When the addition of the tackifier resin causes polymerization inhibition such as a decrease in molecular weight or a decrease in the polymerization rate, it is necessary to appropriately adjust the addition amount of the polyfunctional vinyl monomer or a chain transfer agent described below.

Next, the polymerization process conditions for the photopolymerizable composition will be described. As a basic process, a method of applying the above-described photopolymerizable composition to at least one surface of a substrate using a coating machine such as a roll coater, and then performing light irradiation and polymerizing the substrate. .

In the photopolymerization, a chain transfer agent may be added to the photopolymerizable composition for the purpose of appropriately controlling the molecular weight of the obtained copolymer. N-dodecyl mercaptan, 2-mercaptoethanol, β-mercaptopropionic acid, octyl β-mercaptopropionate, methoxybutyl β-mercaptopropionate, trimethylolpropane tris (β-thiopropionate), butyl thioglycolate, Examples thereof include thiol compounds such as propanethiols, butanethiols, and thiophosphites, and halogen compounds such as carbon tetrachloride. These may be used alone or in combination of two or more.

When the photopolymerizable composition is formed into a sheet having a thickness of 100 μm or less, the composition can be applied with a viscosity of 1,000 cps or less or a TI value (thixotropic index) of about 1.5. In the case of shaping into a sheet having a thickness exceeding the above range, it is preferable to adjust the viscosity by using a thickener, since it flows at a low viscosity and it is difficult to control it to a constant thickness.

Examples of the above thickener include elastomers such as acrylic rubber, nitrile rubber, epichlorohydrin rubber, isoprene rubber, butyl rubber, styrene-isoprene-styrene (SIS), and thermoplastic resins such as polymethyl methacrylate and polystyrene. Alternatively, inorganic particles such as hydrophobic silica and alumina having an average particle size of 5 μm or less can be used. When adding inorganic particles, it is preferable that the particles are subjected to a hydrophobizing treatment because dispersion to primary particles is fast.

When the amount of the thickener is increased, the cohesive strength of the acrylic copolymer decreases and the shear strength decreases, so that preferably 20 parts by weight based on 100 parts by weight of the photopolymerizable mixed monomer. Or less, more preferably 10 parts by weight or less, particularly preferably 5 parts by weight or less.

In addition to the addition of the above-mentioned thickener, there is also a thickening method in which a photopolymerizable mixed monomer or a photopolymerizable composition to which an oil absorbing resin is added in advance is partially prepolymerized. Such prepolymerization should be performed before the addition of the polyfunctional vinyl monomer to prevent microgel formation. This is because, when the gel is partially generated, it causes defects such as streaks during coating.

The conversion of the above-mentioned mixed monomer by the prepolymerization becomes lower as the viscosity decreases, and as it increases, the cohesive force of the pressure-sensitive adhesive after photopolymerization decreases and the shear strength decreases. It is preferably from 60 to 60% by weight, more preferably from 10 to 40% by weight.

The lamp used for the light irradiation includes:
Those having an emission distribution at a light wavelength of 400 nm or less are used, and examples thereof include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, chemical lamps, black light lamps, microwave-excited mercury lamps, and metal halide lamps. Among the above-mentioned lamps, black light lamps, chemical lamps, and the like are known in that they efficiently emit light in a wavelength region (usually 330 to 400 nm) effective for decomposing a photopolymerizable initiator and can efficiently polymerize a thick film sheet. preferable.

Further, since the irradiation light intensity of the lamp affects the degree of polymerization of the copolymer obtained from the photopolymerizable composition,
It is appropriately selected according to the performance of the target product. For example,
In the case of a cleavage-type photopolymerizable initiator having a normal acetophenone group, the irradiation light intensity is low, and the time until the start of the reaction varies due to inhibition of polymerization by oxygen, and a polymer having a constant polymerization degree is obtained. When the molecular weight is increased, the molecular weight is reduced, so that it becomes difficult to balance pressure-sensitive adhesiveness, cohesive force and stress relaxation.
The range of W / cm ² is preferred.

Radical polymerization such as the above-mentioned photopolymerization generally has a polymerization inhibition by oxygen, and is particularly caused by intrusion of oxygen in the air and dissolved oxygen in the photopolymerizable composition. For this reason, a process capable of removing polymerization inhibition by oxygen is preferable.For example, as a method for suppressing intrusion of oxygen in the air, a light-transmitting material such as polyethylene terephthalate or Teflon in which the surface of the photopolymerizable composition is release-treated. A method of covering with a release sheet, irradiating the photopolymerizable composition through the release sheet, or an inert box having a light-transmitting window and replacing oxygen with an inert gas such as nitrogen gas or carbon dioxide gas. And the like. At this time, the atmosphere oxygen concentration in the inert box is 5,000 ppm or less, preferably 300 pp.
m or less.

The film or cover film to be coated may be stretched by heating due to the radiation heat from the lamp or the heat of polymerization when polymerization occurs rapidly. In such a case,
When the obtained pressure-sensitive adhesive is, for example, in a sheet shape, shape defects such as vertical stripes may occur. In order to solve such a problem, a method of suppressing radiant heat by an optical filter, or a method of removing heat of polymerization by bringing a cooling plate into contact with the back surface of the film to be coated may be used.

[0040]

Embodiments of the present invention will be described below. (Examples 1-3 and Comparative Examples 1-4) "Preparation of photopolymerizable composition" According to the composition shown in Table 1, 2-ethylhexyl acrylate, acrylic acid, 2,2-dimethoxy-2 were placed in a separable flask. -Phenylacetophenone (Circa Geigy, trade name "Irgacure 651"), n-dodecylmercaptan and polynorbornene-based elastomer (Shinko Giken Co., Ltd., trade name "Polynorbornene") are added and stirred and mixed until uniformly dispersed. The dissolved oxygen was removed by bubbling nitrogen gas. In addition, Table 1 shows the result of calculating the theoretical solubility parameter of the mixed monomer from the molar ratio of 2-ethylhexyl acrylate and acrylic acid.

Thereafter, using a black light lamp having a maximum wavelength peak at 365 nm, an irradiation intensity of 1 mW / c
When irradiated with ultraviolet rays of m ^2, the viscosity gradually increased as the temperature of the photopolymerizable composition increased. When the temperature of the photopolymerizable composition increased by 5 ° C., the ultraviolet irradiation was stopped. The prepolymerized photopolymerizable composition was obtained by the above operation (monomer conversion: 3.8% by weight, viscosity at 25 ° C: 2,300 cps).

[Preparation of Acrylic Adhesive Sheet] After blending 0.2 parts by weight of 1,6-hexanediol diacrylate with the above prepolymerized photopolymerizable composition, a 38 μm transparent mold release treatment was performed on one side. Polyethylene terephthalate (PET) film is coated on the release surface, and then covered with the same PET film so that the release surface is in contact with the exposed surface, and then a chemical lamp having a maximum wavelength peak at 365 nm is obtained. Irradiation with ultraviolet light having an irradiation intensity of ² mW / cm ² for 8 minutes using a
m of the acrylic pressure-sensitive adhesive sheet was obtained. The monomer conversion, weight average molecular weight and gel fraction of the obtained acrylic pressure-sensitive adhesive sheet were measured, and the results are shown in Table 1.

(Measurement of Conversion Rate of Monomer) A part of the obtained acrylic pressure-sensitive adhesive sheet was dissolved in methyl acetate, and the amount of 2-ethylhexyl acrylate present in the acrylic pressure-sensitive adhesive sheet was measured by gas chromatography. Thus, the monomer conversion was measured. However, the unit is% by weight.

(Weight average molecular weight) An uncrosslinked acrylic resin for molecular weight measurement was prepared in the same manner as above except that the oil absorbing resin and 1,6-hexanediol diacrylate were not separately added to the photopolymerizable composition. An adhesive sheet was obtained.
The obtained acrylic pressure-sensitive adhesive sheet was dissolved in tetrahydrofuran (hereinafter referred to as “THF”), and 0.5% by weight of T
An HF solution was obtained. This was measured as a weight average molecular weight in terms of standard polystyrene by gel permeation chromatography (GPC).

(Gel Fraction) A crosslinked acrylic pressure-sensitive adhesive sheet obtained by photopolymerization in the same manner except that no oil-absorbing resin was added to the photopolymerizable composition was immersed in an excess of THF. Then, after standing overnight, filtered through a 200-mesh stainless steel wire mesh, the residue was used as a crosslinking component,
The gel fraction was measured from the ratio. However, the unit is% by weight.

"Performance evaluation" (peel strength) The obtained acrylic pressure-sensitive adhesive sheet was 20 m wide.
After cutting to mx 80 mm length, the PET film on one side was peeled off, and aluminum foil of JIS H-4000 standard (product number "1100P", width 20 mm x length 100 mm x
(Thickness: 0.05 mm). Then, JIS H-
4000 standard aluminum plate (part number "1100P",
Rust-preventive oil was previously applied to a width of 50 mm × length 100 mm × thickness 2.0 mm) using an applicator so as to have a thickness of 5 μm. The PET film on the other side of the system-based pressure-sensitive adhesive sheet was peeled off and adhered by reciprocating two times with a 2 kg pressure roller at 23 ° C., and after 10 minutes using a tensile tester and 72 hours later.
90 ° peel strength after time (tensile speed 300mm / mi
n) was measured, and the results are shown in Table 1. However, the unit is kg /
20 mm.

[0047]

[Table 1]

[0048]

The composition of the photopolymerizable composition of the present invention is as described above, and the pressure-sensitive adhesive obtained by photopolymerization has a coating surface having a mechanical oil such as cutting oil or rust-preventive oil. It has excellent initial adhesion to the body, and has excellent adhesion over time without any change in adhesion over time.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location C09J 7/02 JJU C09J 7/02 JJU JJW JJW JKK JKK JKK JKKZ JKK

Claims (1)

[Claims] 1. A method comprising: (A) an alkyl (meth) acrylate having 4 to 14 carbon atoms in an alkyl group; and (B) a vinyl monomer having a polar group, wherein the theoretical solubility parameter of Fedors is 8.8 (cal / cm ³ ) ^{1. A} photopolymerizable composition comprising: 100 parts by weight of a photopolymerizable mixed monomer comprising a mixed monomer having a ratio of at least ^1/2 and (C) a photopolymerizable initiator; and 5 to 40 parts by weight of an oil-absorbing resin. [0001]