JPH09328522A - Silica fine particles having a photopolymerization initiator on the surface and a film forming method using the silica fine particles - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain fine silica particles which give a film excellent in durability and clarity merely when a free-radical-polymerizable monomer contg. the same is cured by exposure to active rays of light by introducing a specific substance into the surfaces of fine silica particles. SOLUTION: A photopolymn. initiator is introduced into fine silica particles pref. having an average particle size of 5-300nm. The objective particles are produced by reacting fine silica particles obtd. by dropping a soln. of a tetrafunctional silane compd. (e.g. tetraethoxysilane) into an aq. alkali soln. under stirring with an alkoxysilane compd. having a photopolymn. initiator represented by formula I (wherein R<1> is a group represented by formula II, etc.; R<2> is H, halogen, or 1-12C alkyl; R<4> and R<5> are each H, 1-12C alkyl, 1-12C alkenyl, 1-12C alkoxy, or phenyl; R<6> is OR<8> , etc.; and R<8> is H, 1-6C alkyl, or 1-6C alkanoyl) at the molecular terminal.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to silica fine particles having a photopolymerization initiator on the surface and a film forming method using the silica fine particles.

[0002]

2. Description of the Related Art Conventionally, inorganic fine particles such as silica have been used as a modifier of a polymer material or a composite material with a polymer material, and attempts have been made to use the surface of the inorganic fine particles by chemically changing them. ing.

For example, there is known a technique for improving the performance of a film to be formed by grafting a polymer chain having an affinity for a dispersion medium onto the surface of inorganic fine particles to improve the dispersibility of the inorganic fine particles. For example, CO on the surface of inorganic fine particles
OK group, CO ⁺ ClO ₄ ^- after such by grafting the polymer having a graft chain as a polymerization initiator, further anionic polymerization, a method of performing cationic polymerization (Polymer Society Proceedings, vol.40, pp.1686 199
1), a vinyl-based monomer having a peroxycarbonate group is radical-polymerized on silica fine particles having a peroxy group or an azo group introduced on the surface of the inorganic fine particles, and the peroxycarbonate group on the side chain of the resulting graft chain is used as a polymerization initiation point. A method of graft-polymerizing a vinyl-based monomer on the surface of silica fine particles (JP-A-5-295052).
Are disclosed.

However, in order to form a resin film by these methods, it was necessary to carry out a polymerization reaction in two or more steps as described above. Further, there are disadvantages that the adjustment of the polymerization conditions is complicated and the polymerizable monomers are restricted.

[0005]

In view of the above problems, the present invention provides silica fine particles having a photopolymerization initiator on the surface thereof, which enables graft polymerization of various monomers in a simple process.

[0006]

The silica fine particles of the present invention are characterized by having a surface introduced with a photopolymerization initiator. The silica fine particles in which the photopolymerization initiator is introduced on the surface are silica fine particles obtained by a known method,
It is obtained by reacting an alkoxysilane compound having a photopolymerization initiator represented by the following formula at the terminal.

Embedded image

The silica fine particles having a photopolymerization initiator introduced on the surface thereof are added to a radical-polymerizable polyfunctional monomer and irradiated with an actinic ray to form a film excellent in durability and transparency. Can be done. The silica fine particles having a photopolymerization initiator introduced on the surface of the present invention have a great advantage in that a coating excellent in durability and transparency can be obtained without the need for any other step by only irradiating the above-mentioned actinic rays. It has a sex.

<Silica Fine Particles> The silica fine particles having a photopolymerization initiator introduced on the surface of the present invention react with silanol groups present on the surface of the silica fine particles and an alkoxysilane compound containing the photopolymerization initiator at the terminal. Can be obtained. The above reaction can be carried out by a known method in a solvent in which silica fine particles are uniformly dispersed. The reaction time may be appropriately adjusted according to the reactivity of the compound used.

As the silica fine particles, those having a particle size of not more than the wavelength of visible light are used in consideration of imparting transparency when formed into a film or a molded body. Specifically, the particle size is 300 nm or less, and more preferably 100 nm or less. Moreover, since those having a particle size of 5 nm or less are difficult to stably produce and are not practical, the average particle size of the silica fine particles used in the present invention is 5 to 5.
It is preferably 300 nm.

As the method for producing the fine silica particles by controlling the particle size as described above, a solution of a tetrafunctional silane compound such as tetraethoxysilane is dropped into an acidic or alkaline aqueous solution and stirred (wet method), A method (sintering method) by combustion hydrolysis of purified silicon tetrachloride and the like can be mentioned. Among these methods, it is relatively easy to control the particle size, and since the silanol groups with high reactivity are sufficiently present on the surface of the obtained silica fine particles, a solution of a tetrafunctional silane compound such as tetraethoxysilane is used. A method of dropping into an alkaline aqueous solution and stirring is advantageous. The particle size of the silica fine particles can be controlled by adjusting the alkali concentration of the alkaline aqueous solution and the reaction temperature in consideration of the stirring efficiency of the stirring device used.

The alkoxysilane compound having the photopolymerization initiator at the terminal can be synthesized by a known method. The reaction represented by the following formula is one example.

Embedded image (In the formula, R ¹ represents any functional group capable of reacting with R ² ,
Examples of the combination of R ¹ and R ² include a carboxyl group and an epoxy group, an isocyanate group and a hydroxyl group, and an isocyanate group and an amino group. Examples of R ³ include an ester bond and a urethane bond, which are the result of the reaction between R ¹ and R ² . )

As the above-mentioned photopolymerization initiator, known ones can be used, but from the viewpoint that the silica fine particles of the present invention can be cured at a low temperature and in a short time when forming a film, radical cleavage is performed. It is preferable to use a photopolymerization initiator of the type. Examples of the radical cleavage type photopolymerization initiator include those having a structure represented by the following formula.

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<Method of Using Silica Fine Particles> The silica fine particles having a photopolymerization initiator introduced on the surface of the present invention are added to a radical-polymerizable polyfunctional monomer and irradiated with an actinic ray to obtain durability and transparency. An excellent film can be obtained. The silica fine particles having a photopolymerization initiator introduced on the surface of the present invention have a great advantage in that a coating excellent in durability and transparency can be obtained without the need for any other step by only irradiating the above-mentioned actinic rays. It has a sex.

Ultraviolet rays, electron beams, etc. can be used as the actinic rays. The wave number and irradiation amount of the above-mentioned actinic rays are determined in consideration of the type of photopolymerization initiator modified on the surface of the silica fine particles.

<Radical-Polymerizable Polyfunctional Monomer> The radical-polymerizable polyfunctional monomer is not particularly limited as long as it is soluble in a solvent or the like or has a proper fluidity by itself. From the viewpoint of hardness and durability of the film, it is preferable to use one having high crosslinking performance.
In particular, it is particularly preferable to use an acrylate having two or more (meth) acryloyl groups in the molecule because it can achieve high hardness and can be easily cured by irradiation with ultraviolet rays or electron beams.

Examples of the acrylate having two or more (meth) acryloyl groups in the molecule include ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, triethylene glycol di (meth) acrylate and tetraethylene glycol di. (Meth) acrylate, nonaethylene glycol di (meth)
Acrylate, polyethylene glycol di (meth) acrylate, tripropylene glycol di (meth) acrylate, tetrapropylene glycol di (meth) acrylate, nonapropylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 2,2-bis [4- (acryloxydiethoxy) phenyl] propane, 2,2-bis [4- (methacryloxydiethoxy) phenyl] propane, 3-phenoxy-
Examples thereof include 2-functional (meth) acrylates such as 2-propanoyl acrylate and 1,6-bis (3-acryloxy-2-hydroxypropyl) -hexyl ether.
These can also be used for adjusting the viscosity of the coating composition.

Further, pentaerythritol tri (meth)
Trifunctional (meth) acrylates such as acrylate, trimethylolpropane tri (meth) acrylate, and glycerol tri (meth) acrylate, other pentaerythritol tetra (meth) acrylate, dipentaerythritol penta (meth) acrylate, dipentaerythritol hexa (meth) ) Acrylate, caprolactone-modified dipentaerythritol hexaacrylate (DPCA series: Nippon Kayaku) obtained by reacting (meth) acrylic acid with a polyol obtained by adding ε-caprolactone to dipentaerythritol, 1, 1, 3, 3, 5, A tetra- or higher functional (meth) acrylate such as 5-hexa ((meth) acryloylalkylenedioxy) cyclotriphosphazene is advantageous for improving the film hardness.

Furthermore, when an acrylic urethane oligomer having a urethane bond in the molecule of an acrylic monomer is used, the abrasion resistance of the coating surface after curing is further improved. The urethane oligomer having an acryloyl group or a methacryloyl group at the molecular end can be obtained, for example, by reacting a compound having two or more isocyanate groups in one molecule with an acrylate or methacrylate having active hydrogen. Examples of the compound having two or more isocyanates in one molecule include m-phenylene diisocyanate, p-phenylene diisocyanate,
Toluene-2,4-diisocyanate, toluene-2,
6-diisocyanate, toluene-2,5-diisocyanate, toluene-3,5-diisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, isophorone diisocyanate, 4,4 ′ -Diphenylmethane diisocyanate, 4,4'-diisocyanate-3,3'-dimethylbiphenyl, 4,4'-diisocyanate-3,3'-
Dimethylbiphenylmethane and the like can be mentioned. The above-mentioned active hydrogen-containing acrylate or methacrylate is 2
-Hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, glycerin di (meth) acrylate, 1,6-bis (3-acryloxy-
2-hydroxypropyl) -hexyl ether, pentaerythritol tri (meth) acrylate, tris-
(2-hydroxyethyl) -isocyanuric acid ester (meth) acrylate, (meth) acrylic acid, etc. are mentioned.

At this time, metal soaps such as cobalt naphthenate, cobalt octenoate and manganese naphthenate as curing accelerators, aromatics such as dimethylaniline, tertiary amines, and quaternary ammonium salts such as dimethylbenzylammonium chloride. Etc. may be used.

The addition amount of the silica fine particles having the photopolymerization initiator introduced on the surface of the present invention varies depending on the amount of the photopolymerization initiator introduced on the surface of the silica fine particles and the particle size of the silica fine particles. As in the case of adding the photopolymerization initiator, it may be determined in consideration of the ratio of the crosslinkable resin and the photopolymerization initiator, which are the objects of the polymerization. When silica fine particles having a particle size of 5 to 300 nm are used, it is preferably about 0.1 to 50 parts by weight with respect to 100 parts by weight of the radical-polymerizable polyfunctional monomer. If the amount added is too small, the reaction will be slow and uncured, or crosslinking will take a long time. If the amount added is too large, the weather resistance of the resin after curing will decrease, and yellowing tends to occur, such being undesirable.

Further, an amine compound may be added in order to prevent a decrease in sensitivity due to oxygen inhibition. The amine compound is not particularly limited as long as it is a non-volatile compound such as an aliphatic amine or an aromatic amine. For example, triethanolamine and methyldiethanolamine are often used. Of the compounds exemplified as the photopolymerization initiator, an amino group-containing compound such as dialkylaminobenzoic acid ester and Michler's ketone can be used to serve also as an oxygen inhibition inhibitor.

<Additives> In addition to the above components, a coating composition containing silica fine particles having a photopolymerization initiator introduced on the surface thereof and a radically polymerizable polyfunctional monomer, in addition to the above components, a pigment, a thixotropic agent, and a filler. Various additives such as an ultraviolet absorber, an antioxidant, a surface modifier and a defoaming agent may be added.

Further, the viscosity of the composition can be adjusted by adding a solvent and a thickener so that the work of forming a film on the surface of the article becomes easy. As the above-mentioned solvent, a solvent having a low boiling point or a solvent having a strong volatility evaporates during the construction to change the viscosity, and a solvent having a high boiling point requires a time for the drying step, and thus a solvent having a boiling point of about 60 to 160 ° C is desirable. . Specifically, cyclohexanone, ethylene glycol monomethyl ether (methyl cellosolve), ethylene glycol monoethyl ether (ethyl cellosolve), diethylene glycol dimethyl ether, tetrahydrofuran, dioxane, butyl acetate, ethyl acetate, methyl isopropyl ketone, methyl ethyl ketone, toluene, xylene, anisole. , Methanol, ethanol, isopropanol, butanol and the like. As the thickener, a polymer that can be dissolved in a solvent is used, and for example, an acrylic resin, an acrylic silicon resin, a polysiloxane resin, a fluororesin, a vinyl chloride-vinyl acetate copolymer, or the like is preferably used.

The mixing method is not particularly limited, but in general, silica fine particles are previously dispersed in a solvent, and then a crosslinking agent, a thickener, and various additives are added. A general stirring device such as a mechanical stirrer or a mixer can be used for stirring, and if necessary, heating may be performed during dispersion or stirring.

When the coating solution is prepared, it is preferable that the content of silica fine particles in the coating composition is 0.5 to 50% by weight of the total solid content. This is because if the content of the solid content is too small, there is a possibility that sufficient radicals for polymerizing and curing the entire resin component may not be generated with respect to the amount of radicals generated by ultraviolet irradiation. If the content of silica fine particles in the solid content is too large, the transparency may be deteriorated and a brittle film may be formed, or the adhesion to the substrate may be deteriorated.

<Film Forming Method> The obtained film coating liquid composition is applied to the surface of an article and irradiated with ultraviolet rays to be cured to form a film. For the coating, an appropriate method can be used depending on the physical properties of the coating composition and the article. Generally, brush coating, spray coating method, curtain coating method, flow coating method, bar coating method, doctor blade method, roll coating method, dip coating method, air knife method, spin coating method and the like are used. The film thickness of the film can be changed as necessary. Generally, it is between 1 μm and 1 mm, but not limited to this.

The article on which the film of the present invention is formed is not particularly limited, and its material includes plastic materials such as plastic plates and films, wood plywood, inorganic materials such as cement and glass, roof tiles and the like. Ceramic materials, metals, etc. The shape is not limited, and a plate-shaped product, a plate-shaped product having an embossed surface, a molded product molded into various shapes, and the like can be used.

[0028]

【Example】

Example 1 <Synthesis of Silica Fine Particles> A solution prepared by mixing 40 g of tetraethoxysilane (manufactured by Nacalai Tesque, Inc.) with 200 ml of methanol (manufactured by Nacalai Tesque, Inc.) was mixed with 475 m of methanol.
1 and ammonia water (28% aqueous solution) (manufactured by Nacalai Tesque, Inc.) in a mixed solution of 60 ml while being stirred with a mechanical stirrer (manufactured by Shinto Kagaku) to obtain a solution in which silica fine particles were suspended. . The ammonia and methanol components in this solution were replaced by ethanol (Nacalai Tesque, Inc.) by distillation.

<Measurement of Particle Size of Silica Fine Particles> The silica fine particles obtained by the above method were dispersed on a glass substrate to which a double-sided tape was attached in advance and photographed with a scanning electron microscope. The particle size of the particles shown in this photograph was directly measured and the average particle size was calculated.
Met.

<Synthesis of alkoxysilane having photopolymerization initiator portion> 4 (2-hydroxyethoxy) -phenyl (2-hydroxy-2-propyl) ketone (manufactured by Ciba-Geigy, Irgacure 2959) in 30 g of THF.
0 g was dissolved, and further di-n-butyltin dilaurate 100 mg and 3-triethoxysilylpropyl isocyanate (manufactured by Shin-Etsu Chemical Co., Ltd., KBE9007) were added.
5 g was added, and the mixture was stirred at room temperature for 3 hours. After that, the reaction solution was heated to 50 ° C. and left for 3 hours.

The reaction solution obtained above was depressurized to remove the solvent to obtain a waxy solid crude product. After dissolving this solid in a mixed solvent of hexane and tetrahydrofuran, the tetrahydrofuran is gradually evaporated by heating, and the solid produced at this time is collected by filtration to obtain a tripolymer having a photopolymerization initiator moiety at the end. A purified powder of ethoxysilane (formula below) was obtained.

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<Introduction on the Surface of Silica Fine Particles> To 150 g of a 1 wt% ethanol solution in which the silica fine particles obtained above are uniformly dispersed, 1.18 g of triethoxysilane having the photopolymerization initiator portion is added. Up to 90 ° C,
The reaction mixture was allowed to reflux for 8 hours with stirring. Then, evaporation to dryness was performed to obtain silica fine particles having a photopolymerization initiator introduced on the surface.

<Preparation of Composition Containing Silica Fine Particles> 100 parts by weight of caprolactone-modified dipentaerythritol hexaacrylate (Kayarad DPCA-30 manufactured by Nippon Kayaku Co., Ltd.) as a radical-polymerizable polyfunctional monomer was coated with a photopolymerization initiator on the surface. 0.5 parts by weight of the introduced silica fine particles were added and sufficiently stirred.

<Formation of film> The above composition was applied onto a polymethylmethacrylate resin plate having a thickness of 3 mm using a wire bar or the like, and an irradiation dose of 5 was applied using a high pressure mercury lamp.
Ultraviolet irradiation was performed so as to obtain J / cm ² to form a film.

Example 2 In the preparation of a composition containing fine silica particles, a photopolymerization initiator was introduced onto the surface of 100 parts by weight of caprolactone-modified dipentaerythritol hexaacrylate (Kayarad DPCA-30 manufactured by Nippon Kayaku Co., Ltd.). A film was formed in the same manner as in Example 1 except that 20 parts by weight of silica fine particles were used.

Examples 3 and 4 In the preparation of silica fine particle-containing compositions, dipentaerythritol was replaced with dipentaerythritol hexaacrylate (Kayarad DPCA-30 manufactured by Nippon Kayaku Co., Ltd.) as a radically polymerizable polyfunctional monomer. A film was formed in the same manner as in Examples 1 and 2 except that hexaacrylate (DPHA manufactured by Nippon Kayaku Co., Ltd.) was used.

Comparative Example 1 The silica fine particles prepared in Example 1 were used as they were without introducing a photopolymerization initiator on the surface. 100 parts by weight of caprolactone-modified dipentaerythritol hexaacrylate (manufactured by Nippon Kayaku Co., Ltd., Kayarad DPCA-30), 0.5 parts by weight of the silica fine particles, and 4- (2-hydroxyethoxy) -phenyl (2 as a photopolymerization initiator) -Hydroxy-2-propyl) ketone (manufactured by Ciba Geigy,
A film was formed in the same manner as in Example 1 except that 0.5 part by weight of Irgacure 2959) was added to obtain a composition containing silica fine particles.

Comparative Example 2 100 parts by weight of dipentaerythritol hexaacrylate (DPHA, manufactured by Nippon Kayaku Co., Ltd.), 20 parts by weight of silica fine particles having no photopolymerization initiator introduced on the surface, and 4-part by weight as a photopolymerization initiator Example 1 except that 0.5 part by weight of (2-hydroxyethoxy) -phenyl (2-hydroxy-2-propyl) ketone (manufactured by Ciba-Geigy, Irgacure 2959) was added to obtain a silica fine particle-containing composition. A film was formed in the same manner as in.

The following methods were used to evaluate the wiping resistance, scratch resistance and substrate adhesion. The results are shown in Table 1.

[Table 1]

<Evaluation of Adhesion to Substrate> 100 scratches of 1 mm square were made on the surface of the film formed in Examples and Comparative Examples by a cutter, and Sekisui Cello Tape (manufactured by Sekisui Chemical Co., Ltd.) was adhered to the surface. Let The tape was peeled off at once, and the number of remaining grids was measured.

<Evaluation of Wiping Resistance> Steel wool (# 0000) was applied to the films formed in the examples and comparative examples under a load of 100 g per 1 cmφ unit circle.
The presence or absence of scratches after wiping 0 times was observed. Those without scratches were marked with ◯, and those with scratches were marked with x.

<Evaluation of scratch resistance> Scratch tester (manufactured by Resca, CSR-02, needle used: 212 gf / m)
m, radius of curvature 15 μm), the scratch resistance test of the coatings formed in Examples and Comparative Examples was performed.

[0043]

EFFECT OF THE INVENTION The silica fine particles having a photopolymerization initiator introduced on the surface of the present invention are durable and transparent by a simple process of adding them to a radically polymerizable polyfunctional monomer and curing them by irradiating with actinic rays. A film with excellent properties can be obtained. Further, by reacting the silica fine particles with an alkoxysilane compound having a photopolymerization initiator represented by the following formula at the terminal, the silica fine particles having the photopolymerization initiator of the present invention introduced therein can be easily obtained. According to the film forming method of the present invention, it has abrasion resistance and wiping resistance that cannot be obtained when a film is formed using a composition obtained by simply mixing a curable resin, a photopolymerization initiator, and inorganic fine particles. A film can be obtained.

Claims (3)

[Claims] 1. A silica fine particle having a surface on which a photopolymerization initiator is introduced. 2. The method for producing silica fine particles according to claim 1, wherein the silica fine particles are reacted with an alkoxysilane compound having a photopolymerization initiator represented by the following formula at the terminal. Embedded image 3. A method for forming a film, which comprises adding the silica fine particles according to claim 1 or 2 to a radical-polymerizable polyfunctional monomer and curing the same by irradiating with actinic rays.