JPH032026B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for coating reactive injection molded articles. [Prior art] A reactive injection molded product is a resin molded product obtained by simultaneously curing and molding a thermosetting resin inside a molding mold. RIM (Reaction Injection)
Molding) is in practical use, and is mainly useful in the field of automobile parts because of its excellent strength, flexibility, and freedom of shape design during molding. In principle, urethane RIM is a molded product with a foamed interior and a smooth surface, but depending on the molding conditions, the surface often becomes partially porous. Particularly immediately after molding, it is normal that the material is highly porous. In coating such molded products, there is a need for paints and coating methods that can be rapidly cured to prevent micropores and form a coating film with flexibility that can follow the flexibility of the molded product. Conventional painting on urethane RIM is (1) Urethane RIM
A method of post-curing after molding to further reduce the micropores on the surface, and then applying a two-component polyurethane resin paint at a temperature close to room temperature, or a method of applying a low-temperature curing polyurethane resin paint containing a catalyst, etc. (2) Leave it for a few days after molding the urethane RIM.
A known method is to apply a low-temperature polyurethane resin paint after the surface has become smooth. Furthermore, (3) a method is known from Japanese Patent Publication No. 53-19038, in which a polyurethane paint is applied and then treated in an amine or ammonia atmosphere to cure the paint film. [Problems to be solved by the invention] However, the above-mentioned coating methods (1) and (2) require a long time to dry, and the low-temperature type polyurethane resin paint has a short pot life and is difficult to handle on site. It is complicated or difficult, and furthermore, it has the disadvantage of causing a large loss in the working process, and the obtained coating film also does not have performance sufficiently suitable for the flexibility of urethane RIM. Furthermore, even low-temperature curing polyurethane resin paints require heating to about 60 to 100°C to speed up the curing time, and thus require heating energy to achieve rapid curing. In addition, the method described in Japanese Patent Publication No. 53-19038 (3) above allows rapid curing of polyurethane resin paints, but when this method is applied to urethane RIM, which is a reactive injection molded product, the resulting paint film has a It had the disadvantage of poor water boiling properties and the formation of blisters in the coating film. Therefore, the present invention improves the drawbacks of the conventional coating methods described above, and provides a reaction coating that cures at low temperatures and in a short time, has excellent flexibility and can match the flexibility of urethane RIM, and has excellent boiling water resistance. An object of the present invention is to provide a method for painting a plastic injection molded product. [Means for Solving the Problems] The present invention provides a coating method in which a reactive injection molded product is coated with a polyurethane resin paint, and then the coating film is cured in an amine atmosphere in a gas phase. This is a method for coating a reactive injection molded article, which comprises exposing the reactive injection molded article in an amine atmosphere in a gaseous state immediately before coating. The reactive injection molded product used in the present invention is as described above, and includes urethane RIM, fiber-reinforced urethane RIM, and the like. In addition, polyurethane resin paints that are cured in a gas phase amine atmosphere use polyols such as acrylic polyols, polyester polyols, alkyd polyols, and polyolefin polyols, but acrylic polyols and polyester polyols are particularly suitable. Among these, polyols with Tg: -40°C to 30°C, hydroxyl value: 20 to 160, and number average molecular weight: 1000 to 10000 are suitable, especially Tg: -10°C to 10°C,
Hydroxyl value: 40-145, number average molecular weight: 3000-6000
acrylic polyols and polyester polyols are preferred. If the Tg is higher than 30℃, the flexibility of the polyurethane resin coating film formed will be insufficient, if it is lower than -40℃, the surface hardness will be insufficient, and if the hydroxyl value is higher than 160, the flexibility will be insufficient. However, if the number average molecular weight is less than 20, chemical performance such as durability and hot water resistance will be inferior, if the number average molecular weight is greater than 10,000, the appearance of the coating will be poor, and if it is less than 1,000, the moisture resistance and resistance will be poor. Chemical performance such as hot water properties becomes inferior. Polyisocyanates suitable for use in the present invention include toluylene diisocyanate (TDI), diphenylmetadiisocyanate (MDI), methylene diisocyanate, xylylene diisocyanate (XDI), heximethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), These include triphenylmethane triisocyanate, phenylene diisocyanate, lysine diisocyanate, the above-mentioned methylol adducts or trimers, and mixtures thereof. The polyol and polyisocyanate mentioned above have a ratio of OH equivalent to isocyanate equivalent.
Use at a ratio of 0.5:1 to 2:1. If the OH equivalent is less than 0.5, the adhesion and flexibility will decrease, and if it is greater than 2, the water resistance and hot water resistance will decrease, and the crosslinking density will decrease, resulting in a decrease in the pinhole suppressing effect. . In the method of the present invention, the amine used in the gas phase to expose the urethane RIM before applying the polyurethane resin paint and the amine used in the gas phase after applying the polyurethane resin paint may be the same or different. The amine used is preferably a tertiary amine, such as aliphatic tertiary amines such as trimethylamine, triethylamine, tripropylamine, tributylamine, and triamylamine; aromatic amines such as dimethylaniline, diethylaniline, and tribunzylamine; N-methylmorpholine, N-ethylmorpholine, or triethanolamine, methyldiethanolamine, dimethylethanolamine, diethylethanolamine, dibutylethanolamine, di(2
-Ethylhexine) ethanolamine, ethyldiethanolamine, triisopropanolamine, dibutylisopropanolamine, and other alanolamines can be used, with dimethylethanolamine being preferred. The atmosphere with the above amines has an amine concentration in the gas phase of about 10 to 3000 ppm, preferably 300 ppm, both before and after applying the polyurethane resin paint.
-1200 ppm is suitable, and the temperature is 0-80°C, preferably 20-40°C. The curing time in an amine atmosphere varies depending on the fat composition film thickness, type of tertiary amine, temperature, concentration, etc., but generally it is 0.5 to 10 minutes before painting, preferably 1 to 10 minutes.
The duration is generally 1 to 10 minutes, preferably 2 to 4 minutes in an amine atmosphere after coating. Note that, if necessary, after the treatment in the amine atmosphere after coating, heating may be further performed at a temperature of 100° C. or less for 3 to 15 minutes. The polyurethane resin paint that is cured in the amine gas phase used in the present invention naturally contains various known pigments such as coloring pigments and extender pigments, surfactants, antifoaming agents, leveling agents, color separation prevention agents, etc. It can contain additives, esters, ketones, aliphatic or aromatic hydrocarbon solvents, and the like. It has been found that when painting with a polyurethane resin paint according to the method of the present invention and then curing the paint film in an amine atmosphere, the paint film formed at this time does not cause any abnormalities such as foaming even if it is subsequently exposed to high temperatures. did. Further, as a method for applying the polyurethane resin paint used in the present invention, known methods such as air spray, airless spray, and electrostatic painting can be applied. Furthermore, it is also possible to further coat a thermosetting resin paint or a urethane resin paint on the urethane coating film formed in the present invention. [Function] In the method of the present invention, by exposing the reactive injection molded product, urethane RIM, in advance in an amine atmosphere, the amine is adsorbed in the urethane RIM,
It acts on the hardening of the coating film by the polyurethane resin paint applied afterwards, thus preventing the occurrence of defects such as pinholes in the coating film. Therefore, the boiling water resistance of the coating film is improved. In addition, by treating the coating twice in an amine atmosphere before and after painting, the coating can be cured in a very short time, which also suppresses the occurrence of pinholes and matches the flexibility of urethane RIM. It is possible to form a coating film with the properties of: [Example] The present invention will be described below with reference to Examples. Parts in the examples are parts by weight unless otherwise specified. Example 1 (1) Preparation of polyol: 34.0 parts of methyl acrylate, 35.5 parts of butyl acrylate, 13.9 parts of ethyl acrylate and 2-hydroxyethyl methacrylate as monomers.
Polymerization was carried out in a conventional manner using 18.6 parts (monomer total 100 parts), 66 parts of xylene as a solvent, and 3.2 parts of azobisisobutyronitrile as a polymerization initiator to obtain an acrylic polyol.
The solids content of this solution was 65% by weight. The characteristics of the obtained acrylic polyol are Tg:
The temperature was 8°C, the hydroxyl value was 80, and the number average molecular weight was 5000. (2) Preparation of polyurethane resin paint: 100% of the acrylic polyol solution prepared in (1) above.
A base consisting of 52 parts of titanium oxide powder (manufactured by Ishihara Sangyo Co., Ltd., trade name TYPEQUE RC-97), 20 parts of Cellsolve Acetate, 5 parts of xylol, and xylylene diisocyanate (manufactured by Takeda Pharmaceutical Co., Ltd., trade name) as a curing agent. Name Takenate O-110N)
A two-component polyurethane resin paint consisting of 34 parts was prepared. The OH/NCO ratio was 1/1. (3) Painting: After degreasing the urethane RIM using a conventional method, it was left at 20°C for 3 minutes in an atmosphere containing 300 ppm of dimethylethanolamine at a wind speed of 0.5 m/sec.
Immediately, the paint prepared in (2) above was spray-coated to a film thickness of 35 μm, and allowed to set for 2 minutes at room temperature. then dimethylethanolamine
In an atmosphere of 600ppm, at an atmospheric wind speed of 1.2m/sec.
It was left at 20°C for 2 minutes. Thereafter, it was dried at 30°C for 10 minutes to obtain a cured coating film. Table 2 shows the test results of the obtained coating film. From the results shown in Table 2, it was found that this coating film was free of pinholes and had excellent flexibility, adhesion, and boiling water resistance. Examples 2 to 5 Polyols were prepared in the same manner as in Example 1 using the monomers, curing agents, and solvents shown in Table 1 below (Table 1 also shows the case of Example 1).
Values are parts by weight.

[Table] Table 2 shows the characteristics of the polyol used in the above examples and the test results of the coating film obtained by coating urethane RIM using the polyol in the same manner as in Example 1. In addition, only in Example 2, after molding the urethane RIM,
I used one that had been used for some time. The resulting coating film had no pinholes and had excellent flexibility, adhesion, and boiling water resistance. Comparative Example 1 The polyurethane resin paint used in Example 1 was applied to urethane RIM, but in this example, treatment in an amine atmosphere before and after the above painting was not performed, and
It was heated and dried at ℃ for 30 minutes. The results are shown in Table 2. Pinholes were observed in the resulting coating film. Comparative Example 2 After degreasing the urethane RIM in accordance with a conventional method, immediately spray-paint the polyurethane paint used in Example 1 to a film thickness of 35 μm without performing amine atmosphere treatment, and then spray it at 20°C for 2 minutes. After setting,
In an atmosphere of 600ppm dimethylethanolamine,
It was left at 20° C. for 2 minutes at an atmospheric air velocity of 1.2 m/sec.
Thereafter, it was dried at 30°C for 10 minutes to obtain a cured film. Table 2 shows the test results of the obtained coating film. Although the coating film was in good condition with no pinholes, blisters occurred after the boiling water test (immersion for 2 hours). Examples 6 to 10 Example 1 was carried out by using polyols having special properties as shown in Table 2 and using them at the OH/NCO ratios shown in Table 2.
Table 2 shows the results of coating urethane RIM in the same manner as above. The coating films formed as shown in Table 2 were somewhat inferior to Examples 1 to 5, but had better boiling water resistance than Comparative Examples 1 and 2.

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〔Effect of the invention〕

According to the present invention, reactive injection molded products can be coated quickly, coating film defects such as pinholes can be prevented, and a flexible coating that can follow the flexibility of the molded product can be obtained. A coating film with excellent boiling properties can be obtained.

Claims (1)

[Scope of Claims] 1. In a coating method in which a reactive injection molded product is coated with a polyurethane resin paint and then the coating film is cured in an amine atmosphere in a gas phase, the reaction occurs immediately before coating with the polyurethane resin paint. 1. A method for coating a reactive injection molded article, which comprises exposing the reactive injection molded article in advance to an amine atmosphere in a gaseous state. 2 The above polyurethane resin paint has (a) Tg: -40℃
~30℃, hydroxyl value: 20-160, number average molecular weight:
1000 to 10000, and (b) a polyisocyanate, the coating method according to claim 1, wherein the ratio of (c) OH equivalent to isocyanate equivalent is 0.5:1 to 2:1.