JPH0757340B2 - Method for coating reactive injection molded articles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for coating a reactive injection molded article. More specifically, the present invention relates to a method for coloring and coating a reactive injection-molded article, which can reduce the occurrence of defects in the appearance of a coating film in a coating process, reduce the cost for coating, and at the same time obtain a coating film having high gloss.

[Conventional technology]

A reactive injection molded article is a resin molded article obtained by simultaneously curing and molding a thermosetting resin inside a molding die, and for example, urethane RIM (RIM (R
eaction Injection Molding) has been put to practical use,
It is mainly useful in the field of automobile parts because of its excellent strength, flexibility, and freedom of shape design during molding.

Urethane RIM is a molded article that has a foamed interior and a smooth surface, in principle, but the surface is often partially porous due to molding conditions. In particular, the porosity is usually large immediately after molding. In the coating of such a molded article, a paint and a coating method which can be rapidly cured to prevent the fine pores and can form a flexible coating film that can follow the flexibility of the molded article are required.

For conventional urethane RIM coating, (1) after urethane RIM molding, post cure is performed to further reduce the fine pores on the surface,
A method of applying a two-component polyurethane resin paint at a temperature close to room temperature, or a method of applying a low temperature curing type polyurethane resin paint containing a catalyst, etc. (2) After leaving urethane RIM molding, leave it for several days to make the surface smooth A method of applying a low temperature type polyurethane resin paint after drip is known. Further, (3) Urethane RIM paints and coating methods are disclosed in
8-78737 is known.

[Problems to be solved by the invention]

However, the above-mentioned coating methods (1) and (2) require a long drying time, and the low temperature type polyurethane resin coating has a short pot life, which makes handling on site complicated or difficult. However, the coating film obtained did not have properties sufficiently suitable for the flexibility of urethane RIM.

Further, in the above-mentioned (3) Japanese Patent Laid-Open No. 58-78737, urethane RIM is used.
Although the paint used for painting is described, urethane RIM
The effect of suppressing the pinhole is not described, and the purpose is obviously different from the present invention.

Furthermore, in recent years, a high degree of durability, a variety of color tones, and a high degree of gloss have been required for coated products of reactive injection molded articles such as urethane RIM, and this requirement is particularly high in the automobile article field. Is large. That is, the coating film is required to have water resistance, weather resistance, durability such as flexibility at low temperature and the like, and in terms of design, finish with the same color as an automobile body, that is, solid color coating, as well as metallic coating. In order to deal with this, in the solid color coating, normally, the above-mentioned undercoat coating is followed by a two-coat coating in which a top-coat coating is further carried out. The cost is obviously disadvantageous in terms of the amount used, and the gloss of the coating film is not satisfactory. In addition, in metallic coating, the gloss of the coating film is generally lower than that of the solid color coating film. Therefore, following the undercoat coating described above, a metallic coating is applied, and then a clear coating is applied. Then, the number of processes is increased, and the cost for painting is further increased.

Therefore, the object of the present invention relates to the coating of reactive injection-molded articles, for example, urethane RIM, to eliminate defective coating appearance due to surface defects such as urethane RIM, and to provide a highly glossy and flexible coating film. It is to provide a method that can be formed in a small number of steps.

[Means for solving problems]

The present inventors have earnestly conducted research on a method for coating a reactive injection molded article, and as a result, finally completed the present invention.

That is, the present invention involves coating a reactive injection molded article with a colored polyurethane resin coating having free isocyanate groups and then curing the coating in an amine atmosphere in the gas phase, followed by a non-colored heat cure. A method for coating a reactive injection-molded article in which a reactive resin paint or a polyurethane resin paint is applied and cured by heating.

The reactive injection molded article used in the present invention is as described above, urethane RIM, fiber reinforced urethane RIM.
And so on.

Further, as the polyol of the colored polyurethane resin coating having a free isocyanate group which is cured in an amine atmosphere in a gas phase, a polyol such as an acrylic polyol, a polyester polyol, an alkyd polyol, or a polyolefin polyol is used, and particularly an acrylic Polyols and polyester polyols are suitable, and among these, Tg: -40 to 30 ° C, hydroxyl value: 20 to 16
A polyol having a number average molecular weight of 0, 1000 to 10,000 is suitable. In particular, polyester polyols and acrylic polyols having a Tg of −20 to 20 ° C., a hydroxyl value of 40 to 145, and a number average molecular weight of 1500 to 6000 are desirable.

When Tg is higher than 30 ° C, flexibility is insufficient, when it is lower than -40 ° C, surface hardness is insufficient, when hydroxyl value is higher than 160, flexibility is insufficient, and when it is lower than 20, moisture resistance and resistance are low. The chemical performance such as warm water becomes inferior, and when the number average molecular weight is more than 10,000, the appearance of the coating film becomes poor, and when it is less than 1000, the chemical performance such as moisture resistance and hot water resistance becomes poor. .

Suitable polyisocyanates for use in the present invention in colored polyurethane resin coatings having free isocyanate groups are toluylene diisocyanate (TDI),
Diphenylmethane diisocyanate (MDI), methylene diisocyanate, xylylene diisocyanate (XD
I), hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), triphenylmethane triisocyanate, phenylene diisocyanate, lysine diisocyanate, and the above-mentioned methylol adducts or 3-5 mer, and mixtures thereof. .

The above-mentioned polyol and polyisocyanate are OH
It is used so that the ratio of equivalents to isocyanate equivalents is 0.5: 1 to 2: 1. When the OH equivalent is less than 0.5, the adhesiveness and flexibility are deteriorated, and when the OH equivalent is more than 2, the water resistance, the warm water resistance and the crosslink density are decreased, so that the pinhole suppressing effect is decreased.

The colored polyurethane resin coating material having a free isocyanate group used in the present invention contains various pigments depending on the required color of the coating film. As the pigment, inorganic pigments such as titanium dioxide and carb black and various organic pigments are used. Also, in the case of metallic coating, aluminum powder is used. These may be used alone or in combination of two or more, and the type and content of the pigment may be determined according to the required color.

Further, the colored polyurethane coating used in the present invention may optionally contain various additives such as antifoaming agents, leveling agents, color separation preventing agents, fluidity adjusting agents, and various solvents such as esters, ketones and aromatics. It may contain hydrocarbons and the like.

In the present invention, the above-mentioned colored polyurethane resin paint is applied and then cured in an amine atmosphere in a gas phase state. The amine usable at this time is the third one.
Amines are preferred, for example, aliphatic tertiary amines such as trimethylamine, triethylamine, tripropylamine, tributylamine, triamylamine, aromatic amines such as dimethylaniline, diethylaniline, tribenzylamine, N-methylmorpholine, N-ethyl. Morpholine or alkanolamines such as triethanolamine, methyldiethanolamine, dimethylethanolamine, diethylethanolamine, dibutylethanolamine, di (2-ethylhexyl) ethanolamine, ethyldiethanolamine, triisopropanolamine, dibutylisopropanolamine can be used, among them dimethylethanol Amine is preferred.

As the atmosphere of the above amines, an amine concentration in the gas phase of about 10 to 300 ppm, preferably 300 to 1200 ppm is suitable. Suitably the temperature is between 0 and 80 ° C, preferably between 20 and 40 ° C. The curing time in the amine atmosphere varies depending on the resin composition, the film thickness to be formed, the type of the tertiary amine, the temperature and the concentration, etc., but is generally 1 to 10 minutes, preferably 2 to 4 minutes. If necessary after the treatment in the amine gas phase, heat treatment may be further performed at a temperature of 100 ° C. or lower for 3 to 15 minutes.

The uncolored thermosetting resin coating or polyurethane resin coating used as the top coating in the present invention is a so-called clear coating, and as the thermosetting resin coating, acrylic melamine resin coating, alkyd melamine resin coating, etc. can be used. . These are those in which the melamine resin and acrylic resin or alkyd resin contained in the coating material are condensed by heating to obtain a cured coating film.Acryl resin, alkyd resin, and melamine resin are variously selected depending on the desired coating property. can do. As the polyurethane resin paint, various one-component or two-component polyurethane resin paints can be used. The one-pack type polyurethane resin coating material contains a blocked polyisocyanate resin and a resin having a hydroxyl group in the coating material, and the heated compound is dissociated to generate a free isocyanate group by heating at 120 to 140 ° C. It is a coating material that forms a urethane bond by the reaction of a hydroxyl group with a hydroxyl group to obtain a cured coating film. The two-component polyurethane resin paint is a paint that is applied after mixing a main agent containing a resin having a hydroxyl group and a curing agent containing a resin having an isocyanate group, and is usually heated at 80 to 100 ° C for 20 to 60 minutes. Thus, a cured coating film is obtained. The resin having an isocyanate group used here is preferably a non-yellowing type isocyanate-containing resin, and for example, a hexamethylene diisocyanate-based isocyanate-containing resin is used.

These thermosetting resin paints or polyurethane resin paints do not contain pigments, but may contain various additives such as antifoaming agents, leveling agents, fluidity adjusting agents, ultraviolet absorbers, and light stabilizers. Particularly, the ultraviolet absorber and the light stabilizer are useful for the purpose of improving the weather resistance or light resistance of the coating film. Examples of the ultraviolet absorber include benzophenone-based compounds such as 2,4-dihydroxybenzophenone and 2-hydroxy-4-methoxybenzophenone, and benzo compounds such as 2- (2'-hydroxy-5'-methylphenyl) -benzotriazole. A compound such as triazole is used, and a hindered amine such as bis- (2,2,6,6-tetramethyl-4-piperidyl) -sebacate is used as the light stabilizer.

Furthermore, the non-colored thermosetting resin coating material or polyurethane resin coating material used in the present invention may contain a solvent such as an ester, a ketone or an aromatic hydrocarbon, if necessary.

Generally, the heat curing conditions after coating these top coats are
80 to 140 ° C, 20 to 60 minutes.

Known methods such as air spraying, airless spraying, and electrostatic coating are applied as the coating method of the colored polyurethane resin coating containing a free isocyanate group and the uncolored thermosetting resin coating or polyurethane resin coating used in the present invention. To be done.

[Action]

In the present invention, after coating the colored polyurethane resin coating material containing the free isocyanate group, by curing the coating film in the amine atmosphere in the gas phase, low temperature, it is possible to cure in a short time, It is possible to save energy and improve productivity. Also, the coating film has sufficient strength after being cured in an amine atmosphere in a gas phase state, and then is coated with a thermosetting resin paint or a polyurethane resin paint which is not colored and is cured by heating. In addition, there is no appearance defect such as pinhole due to the micropores existing in the base material of the reactive injection molded article.

Furthermore, the coating film obtained by applying an uncolored thermosetting resin paint or polyurethane paint has high gloss and satisfies the market demand. Particularly in metallurgical coating, the conventional coating method requires three coats consisting of an undercoat, a base coat (aluminum powder-containing coat) and a clear coat, whereas according to the method of the present invention, aluminum powder is directly added to the undercoat paint. Since it can be contained in 2 coats,
The present invention is more useful for metallic coating.

[Examples] In order to more specifically describe the present invention, examples will be described below. The present invention is not limited to these examples. In the examples, all parts mean parts by weight.

Example 1 (1) Preparation of Polyol Methyl methacrylate (35.0 parts), butyl acrylate (36.0 parts), ethyl acrylate (13.9 parts) and 2-hydroxyethyl methacrylate (15.1 parts) (monomer total: 100 parts) were used as a monomer, and a solvent was used. Then, 66 parts of xylol and 3.4 parts of azobisisobutyronitrile as a polymerization initiator were used to carry out polymerization in a usual manner to obtain an acrylic polyol. The solid content of this solution was 65% by weight.

The characteristics of the obtained acrylic polyol were Tg: 5 ° C., hydroxyl value: 65, and number average molecular weight: 4,500.

(2) Preparation of colored polyurethane resin paint (hereinafter referred to as coloring paint) A 6 parts of aluminum powder (manufactured by Toyo Aluminum Co., trade name Alpaste 1100NA) in 100 parts of the acrylic polyol solution prepared in (1) above, 50 parts of cellosolve acetate,
With a base consisting of 50 parts of xylol and 0.5 part of fluidity modifier,
Xylylene diisocyanate-based polyisocyanate as a curing agent (Takenate D-11, manufactured by Takeda Pharmaceutical Co., Ltd.)
(0N) 25 parts were mixed to prepare Colored Paint A.

(3) Preparation of uncolored top coating (hereinafter referred to as clear coating) a Polyester polyol (Sumitomo Bayer Urethane Co.,
Product name Desmofuen 670) 100 parts Toluene 50 parts, Butyl acetate 49 parts, UV absorber (Ciba Geigy Co., product name Tinuvin 328) 1 part is added to form a clear paint base and a curing agent, hexamethylene diisocyanate polyisocyanate. 65 parts (Sumitomo Bayer Urethane Co., Ltd., trade name Sumijuule N-75) were mixed to obtain a clear paint a.

(4) Coating After degreasing the urethane RIM by a conventional method, the colored paint A prepared in (2) above is spray-coated to a film thickness of 25μ, set at room temperature for 2 minutes, and then dimethylethanolamine vapor 600ppm. Atmosphere wind speed 1.
It was left for 2 minutes at a temperature of 20 ° C. at 2 m / sec. Then 10 at 30 ℃
After drying for a minute, the clear coating composition (3) above was spray coated to a film thickness of 30 μm and heated at 100 ° C. for 40 minutes. The obtained coating film had high gloss without pinholes. The obtained coating film performance is shown in Table 1.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the colored paint was not left in the atmosphere containing the dimethylethanolamine vapor. The resulting coating film had many pinholes and was not practical. Table 1 for other performance
Shown in.

Example 2 (1) Preparation of Colored Paint B Polyester polyol (manufactured by Dainippon Ink and Chemicals, Inc.,
Product name Panotsuku D-161) 100 parts, cyanine blue (manufactured by Toyo Ink Mfg. Co., Ltd., product name cyanine blue MR-3) 10
Part, aluminum powder (trade name, manufactured by Toyo Aluminum Co., Ltd.
HS-2) 1 part, toluene 50 parts, cellosolve acetate 39
80 parts of hexamethylene diisocyanate-based polyol (manufactured by Dainippon Ink and Chemicals, Inc., trade name DN-980) as a curing agent was mixed with a base consisting of 10 parts to prepare a colored coating material B.

(2) Coating After degreasing the urethane RIM by a conventional method, spray paint the colored paint B prepared in (1) above to a film thickness of 30μ, set at 20 ° C for 2 minutes, and add 800ppm of triethylamine vapor. 20 ° C in an atmosphere containing air with an air velocity of 1.5 m / sec
Let stand for 2 minutes. Then, after drying at 50 ° C. for 10 minutes, an acrylic melamine resin coating (manufactured by NOF CORPORATION, trade name Primatuk 3000) as a clear coating for baking was spray-coated to a film thickness of 25 μm, and dried by heating at 120 ° C. for 40 minutes. The obtained coating film was satisfactory without any irregularities such as pinholes and gloss. The performance is shown in Table-1.

Comparative Example 2 In Example 2, 100 parts of a thermoplastic urethane resin (manufactured by Sumitomo Bayer Urethane Co., trade name Desmorac 4125), titanium dioxide (manufactured by Ishihara Sangyo Co., trade name Type Iku CR-90) 15 without using the colored paint B Parts and 85 parts of methyl ethyl ketone were used in the same manner as in Example 2 except that a one-pack type colored coating material containing no free isocyanate group was used.

The obtained coating film had high gloss, but it was unusable for practical use due to many pinholes. The performance is shown in Table-1.

Examples 3 to 6 The same procedure as in Example 1 was carried out except that a colored coating material having the characteristics shown in Table 2 was used. The performance of the resulting coating film is shown in Table 2.

Comparative Example 3 Example 1 is different from Example 1 except that a commercially available silver metallic color paint for urethane RIM (manufactured by NOF CORPORATION, trade name Primat # 5000) is used instead of the clear coating a.
Same as above.

The obtained coating film had low gloss.

[Effects of the Invention] According to the method of the present invention, in the coating of a reactive injection molded article, a urethane coating film having high strength can be formed at low temperature in a short time, and then a clear coating material is applied to form a pinhole or the like. A coating having a high gloss without coating defects is obtained.

Claims (2)

[Claims] 1. A reactive injection molded article having a Tg: -40.degree. C. to 30.
℃, hydroxyl value: 20 ~ 160, number average molecular weight of 100 ~ 10000 coated with a colored polyurethane resin paint having a free isocyanate group produced as a polyol component, then applied in an amine atmosphere in the gas phase A method for coating a reactive injection-molded article, which comprises curing a film, then coating an uncolored thermosetting resin coating or polyurethane resin coating, and curing by heating. 2. The method for coating a reactive injection-molded article according to claim 1, wherein the colored polyurethane resin coating material containing free isocyanate groups is a two-component polyurethane resin coating material.