JP2597123B2 - Coating composition and synthetic resin molded article using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a coating composition used for a synthetic resin molded product.

<Prior art> Compared to glass products, synthetic resin molded products not only have excellent properties such as lightness and toughness, but also have the advantages of being inexpensive and easy to mold, and are used in a wide range of fields. I have. However, these synthetic resin molded articles have a drawback that their surfaces are easily damaged by the action of contact, impact, scratching, etc., because their surface hardness and wear resistance are insufficient.

In order to improve these drawbacks, various methods for forming a crosslinked cured film on the surface of a synthetic resin molded product have been conventionally studied. For example, a method of applying a coating composition containing a polymerizable monomer or oligomer on the surface of a synthetic resin molded article, and then irradiating with ultraviolet rays to form a cross-linked cured film on the surface to obtain a film having excellent wear resistance. Has been proposed. (JP-B-48-42211, JP-B-49-2)
No. 2951, JP-A-53-102936, JP-A-53-1046
No. 38, JP-A-58-101121, JP-B-58-129018
However, although these methods can improve the abrasion resistance, which is a drawback of the synthetic resin molded product, the deterioration due to sunlight and artificial light remains a practical problem, and there is a strong demand for improved weatherability. .

As a method of improving such a defect, there is a method of applying a coating composition to which various light stabilizers are added, irradiating ultraviolet rays, forming a crosslinked cured film on the surface, and obtaining a film excellent in weather resistance. Proposed. (JP-A-56-141309
In addition, as a conventionally known technique, a light stabilizer and an antioxidant are combined for improving weather resistance, or two kinds of light stabilizers such as an ultraviolet absorber and a hindered amine light stabilizer are combined. Is known to be very effective.
(Chemical Industry 5, 72 (1985)) <Problems to be Solved by the Invention> However, using a coating composition using such an additive such as a light stabilizer and an antioxidant, a synthetic resin molded article is produced. Even if a coating is applied, sufficient weather resistance has not always been obtained. Further, there is a drawback in that if the hardness and the wear resistance are to be improved, there is a problem in that the flexibility is poor and cracks are easily generated in a heat cycle test. In particular, the improvement of hardness and abrasion resistance and the compatibility of flexibility and heat cycle resistance are important issues from a practical point of view. In addition, in terms of the manufacturing process, it is necessary to have excellent curing reactivity when irradiating with ultraviolet light in the air, which must be satisfied together with the above-mentioned quality problems. The present inventors have intensively studied to improve these points, and as a result, have arrived at the present invention.

<Means for Solving the Problems> Generally, a composition for an ultraviolet-curable coating contains a photopolymerizable prepolymer and a photopolymerizable monomer as main components therein, and is obtained separately. It is composed of a prepolymer and the monomer. The present inventors did not make up the composition by blending these prepolymers and monomers, but instead prepared a photopolymerizable prepolymer obtained by reacting a polyfunctional isocyanate compound with an excessive amount of a hydroxyl group-containing polyfunctional acrylic monomer. A reaction mixture containing a functional urethane acrylate and a hydroxyl group-containing polyfunctional acrylic monomer which is a photopolymerizable monomer at a specific ratio is used as a main component of an ultraviolet-curable coating composition as it is, and this coating composition is used as a synthetic resin molded product. When applied, surprisingly, compared to a general UV-curable coating composition by blending, it shows a better balance of appearance, abrasion resistance, and flexibility and prevention of crack formation in a heat cycle test. A film with excellent weather resistance (no change in wear resistance over time) and excellent adhesion is formed I found the door.

That is, the present invention provides: (a) 100 parts by weight of an acrylate mixture having 40 to 90 parts by weight of a polyfunctional urethane acrylate and 60 to 10 parts by weight of a hydroxyl group-containing polyfunctional acrylic monomer; and (b) a light stabilizer having a cyclic hindered amine structure.
To 5 parts by weight and (c) 0.01 to 5 parts by weight of an antioxidant, wherein the acrylate mixture is a reaction mixture obtained by reacting a polyfunctional isocyanate compound with an excessive amount of a hydroxyl group-containing polyfunctional acrylic monomer. A coating composition comprising a polyfunctional urethane acrylate and an unreacted hydroxyl-containing polyfunctional acrylic monomer.

Examples of the above-mentioned polyfunctional isocyanate compound include hexamethylene diisocyanate, lysine diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, and diisocyanates obtained by hydrogenating aromatic isocyanates among these diisocyanate compounds. Compounds (for example, diisocyanate compounds such as hydrogenated tolylene diisocyanate and hydrogenated xylylene diisocyanate), divalent or trivalent polyfunctional isocyanate compounds and diisocyanate compounds such as triphenylmethane triisocyanate and dimethylene triphenyl triisocyanate. A polyfunctional isocyanate compound obtained by quantification, especially hexamethylene diisocyanate , Lysine diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate, hydrogenated tolylene diisocyanate, diisocyanate compounds such as hydrogenated xylylene diisocyanate are preferable.

Examples of the above-mentioned hydroxyl group-containing polyfunctional acrylic monomer include compounds having one or more hydroxyl groups and three or more acryloyloxy groups in one molecule, and specifically, pentaerythritol triacrylate, diglycerin triacrylate, Ditrimethylolethane triacrylate, ditrimethylolpropane triacrylate, dipentaerythritol triacrylate, dipentaerythritol tetraacrylate, dipentaerythritol pentaacrylate, tripentaerythritol triacrylate, tripentaerythritol tetraacrylate, tripentaerythritol pentaacrylate, tripenta Erythritol hexaacrylate and tripentaerythritol heptaacrylate.

As the light stabilizer to be added to the acrylate mixture, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine, 4-octanoyl-2,2,6,6-tetramethylpiperidine, bis-sebacate ( 2,2,6,6-tetramethyl-4-piperidyl), bis-sebacate- (N-methyl-2,2,6,6-tetramethyl-4-piperidyl), other oligomer types having a cyclic hindered amine structure and Light stabilizers of the polymer type are used.

Antioxidants include 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3- (3,5-di-
t-butyl-4-hydroxyphenyl) -propionate, 2,2-methylene-bis (4-methyl-6-tert-butylphenol), 2-tert-butyl-6- (3-tert-butyl-5-methyl- 2-hydroxybenzyl) -4-methylphenyl acrylate, tetrakis- [methylene-3
-(3,5-di-t-butyl-4-hydroxyphenyl)
Propionate] methane, trinonylphenyl phosphite, triphenyl phosphite and the like.

The polyfunctional urethane acrylate of the present invention has two or more urethane bonds and six or more acryloyloxy groups in one molecule obtained by reacting a polyfunctional isocyanate compound with a hydroxyl group-containing acrylic monomer.

The acrylate mixture obtained by the reaction between the polyfunctional isocyanate compound and an excess amount of the hydroxyl group-containing polyfunctional acrylic monomer is described in detail for the coating composition of the present invention comprising the acrylate mixture, the light stabilizer and the antioxidant described above. Containing a polyfunctional urethane acrylate which is a reaction product and an unreacted hydroxyl group-containing polyfunctional acrylic monomer, and performing the reaction so that the weight ratio of the two is in the range of 40/60 to 90/10. It is something that can be done.

10% by weight of hydroxyl group-containing polyfunctional acrylic monomer
If the composition is less than 90% by weight of the polyfunctional urethane acrylate, the viscosity increases with the reaction time during the synthesis and gelation is likely to occur. It is not preferable because abrasion resistance is reduced. In the case where the weight ratio of the hydroxyl group-containing polyfunctional acrylic monomer exceeds 60% and the weight ratio of the polyfunctional urethane acrylate is less than 40%, there is no problem such as gelation at the time of synthesis. When applied to a resin molded product, the flexibility and adhesion of the coating film are deteriorated, which is not preferable.

By always using the light stabilizer and the antioxidant in combination, the weather resistance can be improved. The amount of the light stabilizer is 0.01 to 5 parts by weight, preferably 0.1 to 2 parts by weight, based on 100 parts by weight of the acrylate mixture of the present invention, and the amount of the antioxidant used is 100 parts by weight of the acrylate mixture of the present invention. 0.0
1-5 parts by weight, preferably 0.05-1 part by weight, is used. However, if the amount of the light stabilizer used is too small, the effect of reducing deterioration is diminished. If the amount is too large, whitening or poor adhesion is not preferred. The same applies to the amount of the antioxidant used. The light stabilizer and the antioxidant may be used alone or in combination of two or more.

Here, when only the light stabilizer is added, the effect of reducing deterioration is slightly reduced as compared with the case where the light stabilizer is used in combination, and the weather resistance is slightly improved but not sufficient. When only an antioxidant is added, there is no effect of reducing deterioration and no improvement in weather resistance is observed as compared with the case where a light stabilizer is used in combination.

Next, a method for using the coating composition of the present invention will be described in detail. The coating composition of the present invention is mixed with a suitable solvent, an ultraviolet absorber and a photosensitizer, applied to a synthetic resin molded article, and then cured by irradiation with ultraviolet rays. In addition, curing may be performed by irradiating active energy rays such as α rays, β rays, γ rays, and electron beams.

Examples of the photosensitizer include benzoin, benzoin ethyl ether, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexylphenyl ketone, azobisisobutyronitrile, benzoyl peroxide, and other general compounds. Known photosensitizers are used. These photosensitizers are used in an amount of 1 to 10 parts by weight, preferably 2 to 5 parts by weight, based on 100 parts by weight of the coating composition of the present invention. If the amount is too large, the cured film will be colored, and if it is too small, curing will be insufficient.

The composition of the present invention may contain a solvent and various additives such as an ultraviolet absorber.

Examples of the ultraviolet absorber include hydroxybenzoate derivatives such as 2,4-di-t-butylphenyl-3,5-di-t-butyl-4-hydroxybenzoate, phenyl salicylate, and 4-t-butylphenyl salicylate. Salicylate derivatives, benzophenone derivatives such as 2,4-dihydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone, cyanoacrylate derivatives such as ethyl-2-cyano-3,3-diphenylacrylate, 2- (2-hydroxy -5-methylphenyl) benzotriazole, 2- (2-hydroxy-3)
Benzotriazole derivatives such as -t-butyl-5-methylphenyl) -5-chlorobenzotriazole are exemplified.

Examples of the solvent include alcohols such as ethanol, propanol, isopropanol and butanol; aromatic hydrocarbons such as benzene and toluene; acetates such as ethyl acetate and butyl acetate; ketones such as acetone and methyl ethyl ketone; Ethoxyethoxy) ethanol,
Ethers such as glycol monomethyl ether, glycol monoethyl ether and dioxane are used.

As the synthetic resin for surface-coating the coating composition of the present invention, a thermoplastic resin and a thermosetting resin are used without distinction.For example, polymethyl methacrylate, polycarbonate, polyallyl diglycol carbonate resin, ABS resin, polystyrene , PVC, polyester resin, acetate resin and the like. Further, as the shape of the synthetic resin molded product, in addition to a general molded product, a sheet, a film and the like are also targeted.

As a coating method, a known method such as brush coating, spray coating, roll coating, and dipping may be used as appropriate. The point is that any method can be used as long as a desired uniform thickness and a smooth surface can be obtained. As the thickness of the coating, 1 ~ 30μ, preferably 2.5
If it is less than 1 μ, sufficient hardness cannot be obtained, and if it exceeds 30 μ, cracks and the like are likely to occur.

<Effects of the Invention> As is apparent from Table 1, a comparative example in which a polyfunctional urethane acrylate was synthesized alone and a hydroxyl group-containing polyfunctional acrylic monomer was blended and used, a hydroxyl group-containing polyfunctional acrylic monomer outside the scope of the present invention Compared to the comparative example using
It can be seen that the examples of the acrylate mixture obtained from the synthesis of the present invention, ie, the mixture of the polyfunctional urethane acrylate and the hydroxyl group-containing polyfunctional acrylic monomer, are excellent in weather resistance, abrasion resistance and adhesion.

Hereinafter, the present invention will be described in more detail with reference to Examples, but these are illustrative, and the present invention is not limited thereto.

Synthesis Example 1 300 g of toluene, 353 g of pentaerythritol triacrylate, 0.6 g of hydroquinone monomethyl ether as a polymerization inhibitor, and 0.16 g of dibutyltin dilaurate as a catalyst were placed in one glass reactor equipped with a stirrer, a thermometer, and a dropping funnel. While maintaining the temperature at 60 ° C., 47 g of hexamethylene diisocyanate was added dropwise over 1 hour. Then, the reaction was continued at the same temperature for 2 hours to complete the reaction, and toluene was distilled off to obtain a polyfunctional urethane acrylate.
400 g of an acrylate mixture consisting of 214 g and 186 g of a hydroxyl group-containing polyfunctional acrylic monomer was obtained. Its isocyanate content was 0.03%.

Synthesis Example 2 47 g of hexamethylene diisocyanate of Synthesis Example 1 was
The reaction was carried out in the same manner as in Synthesis Example 1 except that 73 g of dicyclohexylmethane diisocyanate was used, to obtain 426 g of an acrylate mixture composed of 240 g of a polyfunctional urethane acrylate and 186 g of a hydroxyl group-containing polyfunctional acrylic monomer. Its isocyanate content was 0.02%.

Synthesis Example 3 47 g of hexamethylene diisocyanate of Synthesis Example 1 was used.
The reaction was carried out in the same manner as in Synthesis Example 1 except that isophorone diisocyanate was changed to 62 g to obtain 415 g of an acrylate mixture composed of 229 g of polyfunctional urethane acrylate and 186 g of hydroxyl-containing polyfunctional acrylic monomer. Its isocyanate content was 0.03%.

Synthesis Example 4 Pentaerythritol triacrylate 35 of Synthesis Example 1
3 g, dipentaerythritol pentaacrylate 550 g
The reaction was carried out in the same manner as in Synthesis Example 1 except that
597 g of an acrylate mixture comprising 340 g of polyfunctional urethane acrylate and 257 g of hydroxyl-containing polyfunctional acrylic monomer was obtained. Its isocyanate content was 0.03%.

Synthesis Example 5 Pentaerythritol triacrylate 35 of Synthesis Example 2
3 g, dipentaerythritol pentaacrylate 550 g
The reaction was carried out in the same manner as in Synthesis Example 1 except that
623 g of an acrylate mixture composed of 366 g of a polyfunctional urethane acrylate and 257 g of a hydroxyl group-containing polyfunctional acrylic monomer was obtained. Its isocyanate content was 0.03%.

Comparative Synthesis Example 1 Pentaerythritol triacrylate 35 of Synthesis Example 1
The reaction was carried out in the same manner as in Synthesis Example 1 except that 3 g was changed to 166 g, to obtain 214 g of a polyfunctional urethane acrylate. Its isocyanate content was 0.03%.

Comparative Synthesis Example 2 A reaction was carried out in the same manner as in Synthesis Example 4 except that 550 g of dipentaerythritol pentaacrylate in Synthesis Example 4 was changed to 292 g to obtain 340 g of a polyfunctional urethane acrylate.
Its isocyanate content was 0.03%.

Comparative Synthesis Example 3 Pentaerythritol triacrylate 35 of Synthesis Example 1
The reaction was carried out in the same manner as in Synthesis Example 1 except that 3 g was changed to 137 g of hydroxyethyl acrylate to obtain 184 g of an acrylate mixture composed of 112 g of a polyfunctional urethane acrylate and 72 g of a monofunctional acrylic monomer. Its isocyanate content was 0.02%.

Comparative Synthesis Example 4 Pentaerythritol triacrylate 35 of Synthesis Example 2
The reaction was carried out in the same manner as in Synthesis Example 2 except that 3 g was changed to 154 g of hydroxypropyl acrylate to obtain 227 g of an acrylate mixture composed of 140 g of polyfunctional urethane acrylate and 87 g of monofunctional acrylic monomer. Its isocyanate content was 0.02%.

Examples 1 to 8 and Comparative Examples 1 to 8 As shown in Table 1, a solvent and a photosensitizer were added to the coating composition of the present invention, and a 2 mm-thick methacrylic resin plate (SUMIPEX # 000) was added thereto. … Sumitomo Chemical Industries, Ltd.
Immersed in a high pressure mercury lamp (manufactured by Eye Graphics Co., Ltd., Eye Cure UE021-403C, 500V, H02-L41) in air.
Using (2)), ultraviolet light was irradiated from a distance of 250 mm to 120 W for 5 seconds. Table 1 shows the obtained results.

Note 1) Solvent: isopropyl alcohol: toluene = 1: 1 2) Photosensitizer: 1-hydroxycyclohexyl phenyl ketone 3) Curing time: UV irradiation time to make the film tack-free 4) Irradiation time: UV irradiation to the film Time 5) Made of abrasion resistant: Scratch test with # 0000 steel wool A: Does not hurt even when rubbed hard B: Slightly scratches with strong rubbing C: Slightly scratches with light rubbing D: Lightly rubs 6) Hardness: Pencil hardness according to JIS K5651-1966 7) Adhesion: Cross cut cellophane tape peel test ...
… Embeds the film cutting lines reaching the substrate at 1 mm intervals in 11 rows and 11 lines each to make 100 1 mm stitches, then attach cellophane tape on it and peel off rapidly. This cellophane tape operation is repeated three times at the same location, and is expressed by the number of stitches that have not been peeled off.

8) Weather resistance: Atlas Yubucon (Toyo Seiki Seisakusho) was used as an accelerated exposure acceleration test device. Condition is 4 at 60 ℃
Exposure to UV light for 4 hours and then wet exposure at 40 ° C. for 4 hours are repeated. After 500 hours and 1000 hours under these cycle conditions, the appearance, steel wool test, and adhesion were performed.

9) Light stabilizer: bis-sebacate (2,2,6,6-tetramethyl-4-piperidine) 10) Light stabilizer: bis-sebacate (N-methyl-2,2,6,
6-Tetramethyl-4-piperidine 11) Light stabilizer: 4-benzoyloxy-2,2,6,6-tetramethylpiperidine 12) Light stabilizer: 4-octanoyl-2,2,6,6-tetramethyl Piperidine 13) Antioxidant: tetrakis- [methylene-3- (3,5
-Di-t-butyl-4-hydroxyphenyl) propionate] methane 14) Antioxidant: n-octadecyl-3- (3,5-di-t
-Butyl-4-hydroxyphenyl) propionate 15) Antioxidant: trinonylphenyl phosphite 16) Antioxidant: triphenyl phosphite

Claims (3)

(57) [Claims] (1) (a) polyfunctional urethane acrylate 40 to 90
100 parts by weight of an acrylate mixture having 60 parts by weight of a hydroxyl group-containing polyfunctional acrylic monomer and 60 parts by weight of a hydroxyl group-containing poly (acrylic monomer) (b) Light stabilizer 0.01 having a cyclic hindered amine structure
To 5 parts by weight and (c) 0.01 to 5 parts by weight of an antioxidant, wherein the acrylate mixture is a reaction mixture obtained by reacting a polyfunctional isocyanate compound with an excessive amount of a hydroxyl group-containing polyfunctional acrylic monomer. A coating composition comprising a polyfunctional urethane acrylate and an unreacted hydroxyl group-containing polyfunctional acrylic monomer. 2. The coating composition according to claim 1, wherein the polyfunctional isocyanate compound is a diisocyanate compound. 3. The method according to claim 1, wherein the polyfunctional acrylic monomer having a hydroxyl group comprises 1
2. The coating composition according to claim 1, wherein the molecule has one or more hydroxyl groups and three or more acryloyloxy groups in the molecule.