JPH0761463B2 - Method for coating reactive injection molded articles - Google Patents

Description

The present invention relates to a method for coating reactive injection molded articles.

[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 automobiles because of its excellent strength, flexibility, and freedom of shape design during molding.

Urethane RIM is a molded product 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 product, a coating material 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 product 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. (4) The present inventors filed a patent application (Japanese Patent Application No. 61-313986) filed on December 25, 1986 for the improvement method of the above-mentioned coating method.

[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.

Further, Japanese Patent Application Laid-Open No. 61-31533 filed by the present applicants mainly aims at coating hard molded products, and this method alone is not sufficiently suitable for flexible molded products such as urethane RIM.

Further, the coating method of the prior invention of (4) above is an excellent coating method which is a great improvement over the conventional coating method described above.
It turns out that this method also has drawbacks. That is, when a reactive injection-molded article is molded in a molding die, a mold release agent is generally used to improve its mold release property.
Therefore, after removing the reactive injection molded article from the mold,
It is usually washed before painting. However, if this cleaning is not complete and there are traces of release agent remaining, this may cause repelling during or after painting.
It has been found that defects such as scratches and poor adhesion may occur, and the above-mentioned coating film defects cannot be avoided unless cleaning is performed.

Therefore, the object of the present invention relates to the coating of reactive injection-molded articles, for example, urethane RIM, eliminating the defect of the coating film appearance due to the surface defects of urethane RIM, and curing at low temperature in a short time,
It is an object of the present invention to provide a further improved coating method for urethane RIM capable of forming a flexible coating film.

[Means for solving problems]

The present invention is to coat a reactive injection molded article with a polyurethane resin undercoating material, and then to cure the coating film in an amine atmosphere in a vapor phase state, and then to apply a thermosetting resin coating material or a polyurethane resin coating material, A method for coating a reactive injection-molded article to be cured, wherein the undercoating polyurethane resin coating which is cured in the amine atmosphere is (a) Tg: -40 to 30
C., a hydroxyl value: 20 to 160, a number average molecular weight: containing a polyol consisting of 1000 to 10000 and (b) polyisocyanate,
(C) The ratio of OH equivalent to isocyanate equivalent is 0.5: 1 to 2: 1, and the TI value of the coating is 1.5 or more and the surface tension is 3
A method for coating a reactive injection-molded article having a rate of 2 dyne / cm or less.

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 polyurethane resin undercoating 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 an acrylic polyol and a polyester polyol are particularly suitable. , Tg: -40 ~ 30 ℃,
A polyol having a hydroxyl value of 20 to 160 and a number average molecular weight of 1,000 to 10,000 is suitable. Especially Tg: -20 ~ 20 ℃, hydroxyl value: 40 ~
145, number average molecular weight: 1500-6000 acrylic polyol and polyester polyol 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. .

Polyisocyanates suitable for use in polyurethane resin undercoats which are cured in the amine atmosphere in the present invention include toluylene diisocyanate (TDI), diphenylmethadiisocyanate (MDI), methylene diisocyanate, xylylene diisocyanate (XDI), Hexamethylene diisocyanate (HMDI), isophorone diisocyanate (IPDI), triphenylmethane triisocyanate, phenylene diisocyanate, lysine diisocyanate, and the above methylol adduct or 3 to 5
Polymers, 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 polyurethane resin undercoat used in the present invention which is cured in an amine atmosphere has a TI value of 1.5 or more and a surface tension of 32 dyne / cm or less. These coating properties are properties that are imparted to further reduce coating defects due to unevenness or holes present on the surface of a reactive injection-molded article and a trace amount of a release agent that may remain on the surface during coating. is there.

The TI value is the thixotropic index of the paint, and the TI value is 1.
When it is less than 5, when the paint is applied to the reactive injection-molded article immediately after molding, the surface of the reactive injection-molded article is affected by irregularities or holes in the surface of the reactive injection-molded article, and the coating is applied at the uncured coating film stage immediately after coating A so-called "blurring" phenomenon occurs in which through-holes occur and a uniform coating film is not formed, which leads to pinholes in the coating film.
The above phenomenon can be solved by keeping the TI value at 1.5 or more, but as a method for keeping the TI value at 1.5 or more, it is generally preferable to add ultrafine silicate, organoclay or polyamide modified fatty acid. The addition amount depends on the desired TI value and the kind of the added substance, but it is usually 0.2 to 4% by weight in order to achieve the TI value of 1.5 or more. If added in excess of 4% by weight, the TI value becomes unnecessarily high and the smoothness of the coating film deteriorates, which is not preferable.

Next, the surface tension of the polyurethane resin undercoat was adjusted to 32 dyne / c.
The purpose of keeping m or less is to obtain a good coating film appearance and coating film performance even when a slight amount of the release agent remains on the surface of the reactive injection molded article. In general, a reactive injection-molded article is coated with a mold release agent such as a fluorine-based or silicon-based mold during molding to facilitate the demolding work. The release agent is generally completely removed by cleaning before coating, but depending on the process conditions, cleaning before coating may be insufficient and a slight amount of release agent may remain. possible. Generally, the surface tension of reactive injection-molded articles has a critical surface tension of 35 dyne / cm to 40 d.
yne / cm, but when the release agent remains, the critical surface tension is 32.
dyne / cm to 34 dyne / cm, which may lead to defects such as repellency during application and after application, scratches, and poor adhesion.

The polyurethane resin undercoat used in the present invention prevents the occurrence of the above defects by keeping the surface tension at 32 dyne / cm or less, that is, at the critical surface tension of the reactive injection molded article as the substrate. To keep the surface tension below 32 dyne / cm, perfluoroalkyl sulfonate, perfluoroalkyl carboxylate, perfluoroalkyl ethylene oxide adduct, perfluoroalkyl phosphate,
A fluorine-based additive such as perfluoroalkyltrimethylammonium salt or a silicon-based additive such as polydimethylsiloxane, polymethylphenylsiloxane, polyester-modified polydimethylsiloxane, or polyether-modified polydimethylsiloxane is added. A variety of these fluorine-based or silicon-based additives are commercially available, and the addition amount varies depending on the type of additive used, but it is 0.01-2.
It is 0% by weight. Below 0.01% by weight, the surface tension is 32 dyne /
If it is 2.0% by weight or more, interlayer adhesion to the thermosetting resin coating material or polyurethane resin coating material, which is the top coating material, is lowered, which is not preferable.

In the polyurethane resin undercoating material to be cured in the amine atmosphere used in the present invention, various known additives, pigments such as coloring pigments and extender pigments, surfactants, defoaming agents,
Further, a leveling agent, a color separation preventing agent and the like may further contain an ester, a ketone, an aliphatic or aromatic hydrocarbon solvent and the like.

In the present invention, the above-mentioned polyurethane resin undercoat paint is applied and then cured in an amine atmosphere in a gas phase. As an amine which can be used at this time, a tertiary amine is preferable, for example, trimethylamine, triethylamine, tripropyl. Aliphatic tertiary amines such as amines, tributylamine and triamylamine, aromatic amines such as dimethylaniline, diethylaniline and tribenzylamine, N-methylmorpholine, N-ethylmorpholine or triethanolamine, methyldiethanolamine, dimethylethanol. Amine, diethylethanolamine, dibutylethanolamine, di (2-ethylhexyl) ethanolamine, ethyldiethanolamine, triisopropanolamine, dibutylisopropanolamine, etc. Luke alkanolamines even in use dimethylethanolamine are preferred.

As the atmosphere of the above amines, an amine concentration in the gas phase of about 10 to 3000 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 atmosphere, heat treatment may be further performed at a temperature of 100 ° C. or lower for 3 to 15 minutes.

Among the thermosetting resin coatings or polyurethane resin coatings used as the top coating in the present invention, acrylic melamine resin coatings, alkyd melamine resin coatings and the like can be used as the thermosetting resin coatings. 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. Heating temperature is 10
It is 0 to 140 ° C. 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 by heating at 120 to 140 ° C., the blocked compound dissociates to form a free isocyanate group,
It is a paint that produces a cured coating film by forming a urethane bond by the reaction of an isocyanate group and a hydroxyl group. 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 include various coloring pigments, various additives such as defoaming agents, leveling agents, fluidity modifiers, ultraviolet absorbers, light stabilizers, etc., and esters, ketones, aromatic hydrocarbons. And the like.

Known methods such as air spraying, airless spraying, and electrostatic coating are applied as the coating method of the polyurethane resin undercoating and topcoating which are cured in the amine atmosphere used in the present invention.

[Action]

The method of the present invention is capable of being cured at room temperature for a short time. It is possible to suppress the foaming of a coating film caused by the porosity of urethane RIM and to obtain a coating film having the ability to follow the flexibility of urethane RIM. Can be formed. Further, in addition to these features, the method of the present invention has the advantages that it can be cured at room temperature, so that economical savings can be obtained in terms of energy and that a long pot life can be maintained. Further, in the method of the present invention, even when the release agent is not completely washed, no coating film defect occurs, so that the process control is easy.

〔Example〕

In order to explain the present invention more specifically, 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 special properties of the obtained acrylic polyol were Tg: 5 ° C., hydroxyl value: 65, and number average molecular weight: 4,500.

(2) Preparation of polyurethane resin paint Titanium oxide powder (made by Ishihara Sangyo Co., Ltd., trade name Tybak CR-9 in 100 parts of the acrylic polyol solution prepared in (1) above
0) 30 parts, extender pigment (Hayashi Kasei Co., Ltd., trade name Diaclay) 15 parts, organic clay (NL Chemicals Benton SD-
2) 2 parts, a silicon-based additive (BYK-Chemie, trade name BYK-300) 0.2 parts, cellosolve acetate 20 parts and xylol 10 parts base material, and tolylene diisocyanate as a curing agent (Sumitomo Bayer Urethane A two-pack type polyurethane resin coating consisting of 24 parts of the product, Sumidule L-75 manufactured by the company, was prepared. The OH / NCO ratio was 1/1. The TI value was 2.5 and the surface tension was 31.5 dyne / cm.

(3) Coating The urethane RIM immediately after molding using a mold coated with a release agent (Chukyo Yushi Co., Ltd., trade name E-421) is exposed to saturated steam of trichloroethane for 2 minutes to completely wash the release agent. did. The critical surface tension of urethane RIM was 35 dyne / cm.
After that, spray paint the coating prepared in (2) above to a film thickness of 25μ, set at room temperature for 2 minutes, and then in an atmosphere of dimethylethanolamine 600ppm, at an air velocity of 1.2m / sec and a temperature of 20 ° C. Left for 2 minutes. After that, it was dried at 30 ° C. for 10 minutes, and then spray-coated with a urethane resin paint (trade name Porin No. 1RS, manufactured by Shinto Paint Co., Ltd.) to a film thickness of 30 μ, and heated at 100 ° C. for 30 minutes. Table 2 shows the test results of the obtained coating film. From the results in Table 2 (No. 1), it can be seen that a coating film free from pinholes and excellent in flexibility and adhesion was obtained.

Comparative Example 1 The polyurethane resin coating material used in Example 1 was applied in the same manner as in Example 1 and then treated at 100 ° C. for 30 minutes without amine atmosphere treatment.
After drying for a minute, a top coat was applied in the same manner as in Example 1. The formed coating film had many pinholes as shown in Table 2 (No. 2).

Example 2 Immediately after molding, the urethane RIM used in Example 1 was exposed to trichloroethane in saturated steam for 10 seconds to be incompletely washed. At this time, the critical surface tension of urethane RIM is 33d.
It was yne / cm. Thereafter, an undercoat paint and a topcoat paint were applied in the same manner as in Example 1. The test results of the obtained coating film are shown in Table 2 (No. 1). The results are exactly the same as in Example 1, and good results can be obtained even if the cleaning of the release agent is incomplete. Wakatsuta.

Comparative Example 2 The procedure of Example 2 was repeated, except that the silicone-based additive was not used during the blending of the polyurethane resin undercoat paint. The surface tension of the undercoat paint is 34.5 dyne
It was / cm. The results are shown in Table 2 (No. 2), but the coating film appearance and adhesion were poor.

Examples 3 to 5 Three kinds of polyols were prepared in the same manner as in Example 1 using the monomers, the initiator and the solvent shown in Table 1.

Three polyurethane resin paints were prepared by the same formulation as in Example 1 except that the above three polyols were used.

Table 2 (part 1) shows the characteristics of the polyol used in each of the above-mentioned examples and the test results of the coating film obtained by coating urethane RIM using the same in the same manner as in Example 1.

The obtained coating films were all excellent in flexibility without pinholes.

It is indicated by the value of.

Comparative Examples 3 to 8 Polyols having the characteristics as shown in Table 2 (Part 2) were used, and polyurethane resin paints having the OH / NCO ratio, TI value and surface tension shown in Table 2 (Part 2) were used. Example 1
Made in the same way.

However, in Comparative Examples 3, 4, 5, 7, and 8, a silicon-based additive (BYK-Chemie, trade name BYK-300) was added as in Example 1, but in Comparative Example 6, a silicon-based additive was added. Never used.

The results of coating urethane RIM using these in the same manner as in Example 1 are shown in Table 2 (No. 2). The coating film formed is shown in Table 2.
As shown in (Part 2), the coating film had many pinholes, was inflexible, or had a defect.

[Advantages of the Invention] According to the method of the present invention, a polyurethane undercoating film can be formed by rapid curing when coating a reactive injection-molded article, and therefore coating film defects such as pinholes of the reactive injection-molded article can be prevented. Moreover, a flexible coating is obtained which can follow the flexibility of the reactive injection molded article.

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Claims (1)

[Claims] 1. A reactive injection-molded article is coated with a polyurethane resin undercoating material, and then the coating film is cured in an amine atmosphere in a vapor phase state, and then a thermosetting resin coating material or polyurethane resin coating material is further applied as a topcoating material. Is applied and cured, wherein the undercoating polyurethane resin coating is (a) Tg: −40 ° C. to 30 ° C., hydroxyl group: 20 to
160, a polyol having a number average molecular weight of 1,000 to 10,000,
(B) polyisocyanate, (c) the ratio of OH equivalent to isocyanate equivalent is 0.5: 1 to 2: 1.
A method for coating a reactive injection-molded article, which has a TI value of 1.5 or more and a surface tension of 32 dyne / cm or less.