JP2708095B2 - Alcoholic silica sol composition and method for surface modification of plastic substrate using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alcoholic silica sol composition which can be applied to improve the scratch resistance, abrasion resistance, chemical resistance, weather resistance, etc. of the surface of plastic materials such as polycarbonate and polymethyl methacrylate. The present invention relates to an object and a hard coating of a plastic substrate using the same.

[0002]

2. Description of the Related Art Plastic materials are generally lightweight, easy to mold, and have excellent impact resistance and transparency, so they have a wide range of uses. It is easy to be damaged by wiping work to remove, friction, scratching, etc., so that gloss and transparency are easily lost during use. In addition, it is easily attacked by organic solvents,
There are problems with weather resistance, heat resistance, and combustion resistance.

[0003] These disadvantages can be largely covered by coating the substrate surface with a hard material. For example, as a conventionally known method, a method of directly applying a thermosetting resin such as a melamine resin and baking and hardening (Japanese Patent Publication No. 40-7392, Japanese Patent Publication No. 46-109), or a polyfunctional acrylic such as dimethacrylate of alkanediol is used. A method in which a cured film obtained by polymerizing a resin on the inner surface of a mold is transferred during cast polymerization of a methacrylic resin (Japanese Patent Publication No. 35-1)
7847, JP-B-37-9827), SiO 2 under high vacuum.
₂ and a method to deposit low melting point glass (G. Kienel: Kunststof
fe 59,76 (1969)). In particular, the method of applying a hard coating agent is low in cost and is an industrially advantageous method. For example, a melamine resin or an organosilane-based thermosetting (for example, Japanese Patent Publication No. 52-39691), diethylene glycol dimethacrylate, a phosphazene derivative, or the like can be used. (Ishikawa: reinforced plastics 32, 58-62, Kurahashi: painting and paint: '91 / 11 (No.485) 39-47).

[0004] However, melamine resin hard coats are inexpensive but take a long time to cure, and have poor weather resistance. Recently, the influence of acid rain has become a problem. Thermal curing of polyfunctional acrylic monomers such as diethylene glycol dimethacrylate takes a long time, and UV curing and electron beam curing, which have extremely short curing times, are used, but high-energy irradiation is performed in an inert atmosphere. However, there is a problem that the cost is high because equipment and a processing method for performing the above require high technology.

On the other hand, organosilane-based hard coatings generally have extremely long heat-curing times and are expensive in raw materials. However, hard coatings having excellent weather resistance and extremely high hardness can be obtained by a simple method. Therefore, various things have been proposed. Organosilanes are organopolysiloxanes that are cured by condensation through the formation of silanols by hydrolysis of alkoxysilanes. The organosilanes that constitute the organopolysiloxanes have structural units ranging from monofunctional to tetrafunctional. is there. A cured film made of tetrafunctional tetraethoxysilane is not used as it is because it has poor film-forming properties and lacks adhesiveness.
A method of fusing the formed silica particles at a temperature of not less than ° C is employed.
Examples of practical applications include the hydrolysis and polycondensation products of tetrafunctional alkylalkoxysilanes, which have been known for a long time, and fluorinated olefins such as tetrafluoroethylene. Complexes with an organic polymer consisting of a copolymer of the above are widely known (US Pat. No. 3,42
9,845 and 3,429,846 (both 1969)). In recent years, many studies have been made on organic-inorganic hybrid polymers using a sol-gel method using tetraethoxysilane. In the hard coating using these tetrafunctional alkoxysilanes, since an organic polymer is used, an organic solvent and a polymer composition, a curing catalyst, a surfactant, a coating condition, and the like constituting a paint are complicated.

On the other hand, in the case of a method using a trifunctional alkylalkoxysilane, Owens-Illinois is used.
Has been known for a long time (US Pat. No. 3,45
1,838 (1969), 3,554,6
98 (1971)). However, since the drying and curing rate is low (130 for methyltriethoxysilane).
Even when heating at 2 ° C. for 2 hours or more, it is tacky and requires 18 hours of heating for curing. ) 80-300 ° C. at first in said patent
After obtaining a partially condensable curable resin by heating to a temperature, the resin is dissolved in a solvent, a curing catalyst is further added, and the mixture is applied and cured by an ordinary method. In addition, alcoholic silica sol obtained by hydrolysis and polycondensation of methyltriethoxysilane is well wetted on a glass plate and forms an adherent film, but poorly wettable on plastic substrates such as polycarbonate, and requires a surfactant. Even when used in combination, the coating film formed lacks adhesion to the substrate, easily cracks and peels off, and thus has a problem of lacking abrasion resistance.

[0007]

SUMMARY OF THE INVENTION In view of the above-mentioned prior art, the present invention aims at further improving the performance by improving an organoalkoxysilane-based hard coating.
It is an object of the present invention to provide an alcoholic silica sol composition capable of providing a coating film having excellent adhesion to a transparent plastic such as polycarbonate and having excellent scratch resistance by a simple ordinary coating method. Furthermore, the present invention provides a surface modification that greatly enhances the practical value by applying the above-mentioned alcoholic silica sol composition to a plastic material such as polycarbonate, thereby replacing plastic molded products with inorganic glass and extending the product life by improving surface properties. The purpose is to provide quality methods.

[0008]

In order to solve the above-mentioned problems, the present inventor has proposed a method of improving an organopolysiloxane-based hard coating by shortening the curing time, improving the hardness of a coating film, and adhering a substrate to a plastic. Various investigations were carried out diligently to improve the performance. As a result, the weight ratio of trifunctional methyltriethoxysilane to 1/3 to 1/1
An alcoholic silica sol produced by preliminarily mixing a 5-fold amount of tetrafunctional tetramethoxysilane with water and hydrolyzing / polycondensing in the presence of an acid catalyst is applied to a glass plate or the like in a usual manner. When applied and dried, curing is unexpectedly fast. When heated and dried at 120 ° C, it cures in about a few minutes. (If only methyltriethoxysilane is hydrolyzed and polycondensed, heat and cure at 120 ° C for 2 hours or more. The film was also insufficiently cured and was tacky), and it was found that a coating film having good adhesion was formed.

Also, as described above, the hydrolysis and hydrolysis of methyltriethoxysilane obtained by mixing a limited amount of a tetrafunctional alkoxysilane such as tetramethoxysilane.
The coating of the alcoholic silica sol composition composed of a polycondensate has poor wettability with plastics such as polycarbonate, but a water-dispersed system such as an acrylic reactive microgel, a specific polymer microsphere as a primer, When applied to the surface, it has good wettability and a coating film with excellent transparency and adhesion is formed. When this coating film is used as a primer layer and the above-mentioned alcoholic silica sol composition is applied, it is unexpected. Has very good wettability and affinity,
It hardens and dry even at room temperature, but especially when hardened and dried at 120 ° C on a hot plate, it rapidly dries and hardens, and has excellent adhesion, colorless transparency, high gloss, and high hardness with excellent scratch resistance. However, it was found that an unexpectedly rigid and impact-resistant coating film was formed. The present invention has been made based on this finding.

That is, the present invention provides (1) a trialkoxysilane and a tetraalkoxysilane in a weight ratio of 3: 1 to 15:
1/6 to 2 times the weight of water to the alkoxysilane contained in 1 is added, and the mixture is hydrolyzed in the presence of an acid catalyst.
A colorless, transparent, low-viscosity alcoholic silica sol composition obtained by polycondensation and (2) a functional group in the copolymerization component when the alcoholic silica sol composition according to claim 1 is applied to a plastic substrate. A method for modifying the surface of a plastic substrate, comprising applying and drying and curing the above-mentioned alcoholic silica sol composition after previously applying and drying a plastic surface on a plastic surface using an acrylic fine particle polymer microsphere as a primer. Is what you do.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION As the hydrolyzable alkylalkoxysilane used in the present invention, various commercially available trifunctional lower alkoxysilanes such as methyltriethoxysilane, methyltrimethoxysilane and phenyltriethoxysilane can be used. And the like, but they may be appropriately mixed and used. Examples of the tetrafunctional alkoxysilane used as a mixture with these alkylalkoxysilanes include tetramethoxysilane, tetraethoxysilane and methyl silicate 51, tetraethoxysilane widely used in industry as a condensate of tetramethoxysilane. Ethyl silicate 40 as a condensate is exemplified.

When the weight ratio of the tetrafunctional alkoxysilane to the trifunctional alkylalkoxysilane is more than 1/3, the coating film from the alcoholic silica sol formed by hydrolysis / polycondensation is Since the film formation property is impaired, such as the formation of numerous lines and cracks, and easy peeling, the mixing ratio depends on the type of alkylalkoxysilane, the type and composition of the polymer microspheres of the primer, the coating conditions such as the curing temperature and the coating method. It is necessary to decide in consideration of such factors. Preferably, the weight ratio of 4 to 1/7 times the amount of 4
A mixture of functional alkoxysilanes is used. Further, when the tetrafunctional alkoxysilane is mixed in less than 1/15 times, it is no different from the case where only the trifunctional methyltriethoxysilane is used, and the drying and curing of the produced alcoholic silica sol becomes extremely slow. Also, the scratch resistance became insufficient.

In the present invention, the hydrolysis / polycondensation of alkylalkoxysilanes is carried out while adding an equal volume of water and stirring at room temperature in the presence of an acid catalyst such as acetic acid or a 0.1N aqueous hydrochloric acid solution. It is preferable to form a colorless and transparent alcoholic silica sol in about 30 minutes. The produced alcoholic silica sol has no apparent change for about one week, and then gradually produces a translucent precipitate. The hardness and scratch resistance of the coating film were best immediately after the alcoholic silica sol was obtained, and the hardness of the resulting coating film tended to decrease over time. Although the amount of water is acceptable up to twice, it is not necessary to make the amount equal to or more than one because the viscosity is originally low. It is preferably an equal volume. Also, when the amount of water was set to 1/6 times the amount of alkoxysilane, a colorless and transparent alcoholic silica sol was formed, but the coating film formed from this alcoholic silica sol composition hardened considerably. It was late. However, the stability of the alcoholic silica sol is improved.

For hydrolysis and polycondensation of alkoxysilanes, an acid catalyst is preferably used. Examples of the acid catalyst include 0.1.
A 1N aqueous hydrochloric acid solution, glacial acetic acid, citric acid, or the like is suitably added to about 1 to 5% of the alkoxysilane so that a uniform alcoholic silica sol can be formed in about 10 to 60 minutes. When the amount of the catalyst is increased, the formation of the alcoholic silica sol is accelerated, but the stability of the sol is deteriorated, and a translucent gel is immediately formed, which is not desirable. The reaction temperature is usually 5
The temperature is 60C, preferably 10-30C. Alkaline catalysts such as aqueous ammonia are not desirable because the sol becomes translucent and promotes gelation to deteriorate the stability of the sol.

Next, the surface modification of plastic using the alcoholic silica sol composition of the present invention will be described. The alcoholic silica sol composition forms a hard coating film with good adhesion on a glass plate or the like,
Since plastic such as polycarbonate has poor wettability, it is necessary to coat a primer on the plastic surface in advance to improve wettability and adhesion when applying to plastic. As a primer, it was necessary to have not only adhesion to plastic but also affinity to the alcoholic silica sol composition. In the present invention, a water-dispersed polymer microsphere of acrylic ultrafine particles having functional groups such as a hydroxyl group, a glycidyl group, and an amide group and having a film forming property at room temperature is suitably used as a primer. It has good wettability to plastic base materials, can be freely adjusted in leveling properties, and has excellent coating workability, and can adopt various coating methods including dip coating, roll coating, curtain flow coating, etc. It is suitable. The thickness of the primer coating is not particularly different from the conventional method. Preferably it is 5 to 20 μm.

When a polymeric microsphere having no functional group such as a hydroxyl group is used as a primer,
When an alcoholic silica sol was coated thereon, the coating film was unsuitable, such as whitening and peeling. As the polymer microsphere used in the present invention, an acrylic polymer latex having a functional group such as a hydroxyl group is also used.More preferably, the ultrafine particles and the structure in which the inside of the particle is appropriately cross-linked, This is a case in which a reactive microgel having a low cross-linking degree having a film forming property itself is used as a primer. The reactive microgel forms a highly glossy coating film excellent in water resistance and solvent resistance by drying, so that when the above-mentioned alcoholic silica sol is applied on this coating film, the coated surface does not change, and This is because the cross-linked structure of the coating surface suppresses interpenetration, and the surface has a structure richer in polysiloxane bonds. Such reactive microgels are described in JP-B-7-80971, "Coating Engineering", Vol. 22, no. 9, 384 (1987).

In the present invention, the film thickness after coating and drying and curing the alcoholic silica sol composition on the substrate is usually 1 to 5
Although the thickness is 0 μm, the lower limit is 5 μm in terms of adhesion and hardness.
m or more and the upper limit is preferably 20 μm or less. After the application of the alcoholic silica sol, the coating is dried and cured, but may be at room temperature, preferably at 60 to 180 ° C, more preferably at 100 to 150 ° C. The curing time is usually 3 minutes or more if it is 100 ° C. or more, preferably 15 to 30 minutes. In the present invention, by using a polymer microsphere such as an acrylic reactive microgel having a functional group capable of hydrogen bonding with a polymer microsphere having film forming properties at room temperature as a primer, the adhesion between the organosiloxane and the plastic is improved. It ’s a big improvement, but interestingly,
Despite the high surface hardness of the coating film, the coating film has flexibility even though it has abrasion resistance, it does not crack even when bending slightly, and the coating film surface does not peel off even if the substrate is bent considerably It was found to exhibit properties. The coating film is steel wool with a pencil hardness of 7H or more and has No. 0 (center diameter 2
(5 μm) The surface was slightly scratched when rubbed, but no scratch was found with No. 0000 steel wool.

The hard coating film obtained according to the present invention has good water resistance, and shows no change even in water for a long time. In addition, polycarbonate, polymethyl methacrylate, etc. are easily attacked by organic solvents, but the hard coating significantly improves the solvent resistance of the substrate, and changes even when rubbed with a cloth containing alcohol, ketone, benzene, and hexane. Not seen. As a coating film forming method in the present invention, dipping, spraying, roll,
Normal coating methods such as flow, spin, and bar coating can be employed. The present invention is suitable as a colorless, transparent, high-gloss hard coating for transparent plastics, but it can also be coated with various color hues by incorporating a coloring agent. The method of the present invention comprises polycarbonate, polymethyl methacrylate, nylon, polyester, polystyrene,
It is suitable for surface modification of various plastics such as vinyl chloride resin plates, and is particularly useful for scratch resistance, abrasion resistance, weather resistance and solvent resistance of the surface of transparent plastics, especially polycarbonate. In particular, there is a great need to extend the life of products by improving the surface properties of transparent plastic, and various molded products such as sundries, daily necessities, aircraft windows and doors, motorcycle windshields, headlights and various lighting fixture covers, signs It is useful as a coating method for large materials such as displays, display panels, instrument panels, and equipment covers.

[0019]

Next, the present invention will be described in more detail based on Reference Examples and Examples, but the present invention is not limited to these Examples. In the examples, parts and ratios indicate parts by weight and weight ratio, respectively.

Reference Example 1 A 1000 ml four-necked flask equipped with a gas inlet tube, a reflux condenser, a composite glass electrode for pH measurement, and a stirring device was used, and the system concentration was 5.0 (as an emulsifier in 400 ml of distilled water). g / 100 ml) of a commercially available reactive emulsifier New Frontea A-229E (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd., phosphate ester emulsifier) and kept at 50 to 60 ° C. As a polymerization monomer, 300 g of a mixed monomer prepared by mixing ethyl acrylate and methyl methacrylate with 2-hydroxyethyl methacrylate at a weight mixing ratio of 60/40/5 was prepared, and 50 g of the mixed monomer was first dispersed in a polymerization flask. While emulsifying and maintaining a constant stirring state, a trace amount of copper sulfate aqueous solution (concentration in the system: 5.0 × 10 ⁻⁷ mol)
Per liter), and then a redox polymerization initiator consisting of equimolar amounts of potassium persulfate-sodium thiosulfate (concentration in the system: 3.0 × 10 ⁻³ mol / l) is used for 50 to 100 mol / l.
Initiate the polymerization at 60 ° C., pH 4-7. Then, while the remaining monomer mixture (250 g) was gradually dropped, polymerization was carried out while preventing temperature rise due to polymerization heat. The polymerization was completed in about 15 to 30 minutes, and a transparent ultrafine particle reactive microgel that appeared bluish white in reflected light and yellowish red in transmitted light was obtained. The average particle size of the obtained polymer microspheres is 5
It is 2 ± 11 nm and is a microgel with a loosely crosslinked structure in the particles (the swelling ratio of the resulting film to benzene is 16), but it has film-forming properties at room temperature and is colorless and transparent and has high gloss when applied to glass plates, polycarbonate, etc. A film having good adhesiveness was formed.

REFERENCE EXAMPLE 2 In the same manner as in Reference Example 1, in producing a polymer microsphere, ethyl acrylate and methyl methacrylate were used as polymerization monomers and glycidyl methacrylate was used as a reactive monomer in a mixing ratio of 60/40/2. And then polymerized in the same manner as in Reference Example 1 to obtain a particle diameter of 57 ± 9 nm.
, A translucent viscous reactive microgel was obtained. The degree of cross-linking in the particles is rather high (the swelling ratio of the formed film to benzene is 5), and the film formability is poor at room temperature. However, when dried on a hot plate at 120 ° C, a colorless, transparent, high-gloss, smooth film is formed. Was done.

REFERENCE EXAMPLE 3 Under the same method and under the same polymerization conditions as in Reference Example 1, a reactive microgel obtained by polymerizing ethyl acrylate and 2-hydroxyethyl methacrylate as the polymerization monomer at a mixing ratio of 100/2 was used. Since the glass transition temperature Tg was low because it did not contain methyl methacrylate, a soft film was formed.

Example 1 6 parts of water (mixing ratio of alkoxysilane and water is 1: 1) was added to an alkoxysilane (mixing ratio of 5: 1) obtained by mixing 1 part of tetramethoxysilane with 5 parts of methyltriethoxysilane and an acid. Mix the catalyst (0.1 part for acetic acid or 0.1 part for 0.1N hydrochloric acid, 0.025 part for citric acid crystals) and stir with a magnetic stirrer at room temperature for 10-20 minutes. Was hydrolyzed and polycondensed to form a colorless and transparent alcoholic silica sol solution. This alcoholic silica sol did not change in appearance for about one week, and then gradually became translucent and turbid, and a sticky solid precipitated. In this case, the storage stability of the alcoholic silica sol increases as the amount of the acid catalyst decreases, but the hardness of the formed film immediately after preparation increases as the amount of the acid catalyst increases.

Example 2 Hydrolysis and polycondensation were carried out in the same manner as in Example 1 except that the mixing ratio of methyltriethoxysilane and tetramethoxysilane was changed to 3: 1. A colorless and transparent alcoholic silica sol was obtained.

Example 3 A mixture of methyltriethoxysilane and tetramethoxysilane was used as a mixture of alkoxysilanes at a mixing ratio of 5: 1.
Hydrolysis and polycondensation were carried out in the same manner as in Example 1 except that the amount of water was added to the alkoxysilane in a 6-fold amount rather than a 1-fold amount. A colorless and transparent alcoholic silica sol was obtained by stirring for 10 to 30 minutes. was gotten.

Example 4 An aqueous dispersion prepared in Reference Example 1 was applied to a test piece from which a protective film of a polycarbonate sheet (manufactured by Nippon GE Plastics Co., Ltd., Lexan; thickness 0.5 mm, with a protective film on both sides) was removed. A polymer microsphere (acrylic reactive microgel) is cast, or a YBA type baker applicator manufactured by Yoshimitsu Seiki Co., Ltd.
m) and dried on a hot plate with a surface temperature of 130 ° C. for several minutes. Then, the alcoholic silica sol prepared in Example 1 was cast thereon, and immediately dried on a hot plate at 130 ° C. for about 10 to 15 minutes to form a coating film having high gloss and good adhesion and a hard surface. Was. The coating film is colorless, transparent and smooth. It is not scratched even if it is strongly scratched with nails. Was scarred little. The adhesion of the coating film was very good, and the X-cut tape test scored 10 points with no peeling, and the cross-cut tape peel test was 100/100.
No change was observed in the coating film even when the sheet was slightly bent. The water resistance of the coating film is good, the surface does not change at all even when immersed in water for more than one week, and it is rubbed with a cloth containing various organic solvents (alcohol, ketone, tetrahydrofuran, benzene). No change was seen.

Example 5 A coating was performed in the same manner as in Example 4, except that the reactive microgel prepared in Reference Example 2 was used instead of the reactive microgel prepared in Reference Example 1. The same physical properties as in the case of No. 1 were shown. When the coating film was naturally dried and cured, similarly to the case where the coating film was dried by heating at 120 ° C., a film having excellent scratch resistance and excellent water resistance and chemical resistance was formed.

Comparative Example 1 In Example 4, the alcoholic silica sol prepared in Example 1 was directly coated on a polycarbonate sheet without coating the polycarbonate with water-dispersed polymer microspheres as a primer.
And dried and cured on a hot plate. Although the wettability was slightly poor, a colorless and transparent hard coating film was formed in about several minutes. However, the adhesion between the coating film and the polycarbonate sheet is poor.
Also, when rubbed with steel wool, it was easily peeled off and was not practical.

Example 6 In Example 1, instead of using the acrylic reactive microgel of Reference Example 1, a soft reactive microgel having a lower glass transition temperature prepared in Reference Example 3 was used as a primer. When the alcoholic silica sol prepared in Example 1 was coated on the primer layer, a transparent coating film having good adhesion was formed. However, it was easily scratched by scratching with nails and had no abrasion resistance. However, when the alcoholic silica sol is repeatedly coated three or more times,
Even if it was strongly scratched with a nail, no scratch was formed at all, and a good coating film having excellent scratch resistance and good adhesion was formed.

Comparative Example 2 In Example 4, instead of using the acrylic reactive microgel of Reference Example 1, various commercially available polymer latexes or acrylic polymer latexes having no functional group involved in hydrogen bonding were used as primers. If used,
When coating with the alcoholic silica sol, it was observed that the coating film of the primer layer was whitened or swelled to impair the transparency. In addition, the alcoholic silica sol easily penetrates into the primer layer underneath, and the resulting coating film is undesirably softened and easily scratched with a nail.

Example 7 In the same manner as in Example 4, an alcoholic silica sol made of alkoxysilane having a mixing ratio of methyltriethoxysilane and tetramethoxysilane of 3: 1 prepared in Example 2 was applied to the surface of polycarbonate. In the case of coating, a slightly thin streak was generated, but a coating film which was firm and had good adhesion was formed.

[0032]

The colorless, transparent and low-viscosity alcoholic silica sol composition of the present invention is coated on a plastic material, and particularly on a transparent plastic material such as polycarbonate or methacrylic resin by the method of the present invention. As a result, the scratch resistance, abrasion resistance, chemical resistance, weather resistance, and the like of the surface can be significantly improved. In addition, it can be modified simply by using ordinary coating methods, which is advantageous in terms of cost as well. The service life of plastic products is improved by improving the surface characteristics of large plastic products such as window glass, door materials, signboards, windshields, and various lighting equipment covers. It is extremely significant in practical use such as extension.

Claims (2)

(57) [Claims] An acid catalyst is prepared by adding 1/6 to 2 times by weight of water to an alkoxysilane containing trialkoxysilane and tetraalkoxysilane in a weight ratio of 3: 1 to 15: 1. A colorless, transparent and low-viscosity alcoholic silica sol composition obtained by hydrolysis and polycondensation in the presence. 2. In applying the alcoholic silica sol composition according to claim 1 to a plastic substrate, an acrylic fine particle polymer microsphere containing a functional group in a copolymer component is used as a primer on a plastic surface, A method for modifying the surface of a plastic substrate, comprising applying the above-mentioned alcoholic silica sol composition after application in advance and drying and curing the composition.