JP3122806B2 - Primer for RIM urethane molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a primer (undercoat) suitable for coating a RIM urethane molding used for a bumper of an automobile.

[0002]

2. Description of the Related Art RIM (Reaction Injection)
On Molding) The urethane molded body is injected into a mold of a desired shape while mixing a polyol component selected from a polyester resin, an acrylic resin, a polyether resin and the like and a polyisocyanate in the presence of a foaming agent and the like. It is a foam having a skin layer on the cured surface, and is widely used for bumpers of automobiles.

[0003] A paint is applied to the surface of the molded article for the purpose of protection and decoration, and the paint is often applied by applying a primer and a top coat.

Conventionally, non-crosslinked paints mainly composed of thermoplastic polyurethane elastomer, two-pack paints composed of polyester polyol and polyisocyanate, polyester resin and melamine resin as the primers for RIM urethane moldings. Is generally used.

However, among these, the coating film of the non-crosslinked polyurethane elastomer-based primer has good chipping resistance and adhesion, but is susceptible to erosion by the organic solvent in the top coating material. The surface smoothness of the coated surface is not sufficient due to insufficient conversion, and a large amount of an organic solvent is required for adjusting the appropriate viscosity at the time of coating, which is not preferable from the viewpoint of resource saving and pollution prevention. Also,
The two-pack paint has excellent adhesion and smoothness, and has a high solid content in the paint, but has a short pot life, so it needs to be mixed at the painting site. Cleaning and disposal after painting Have to be done promptly.
It is difficult to apply to automotive coating lines. In addition, thermosetting primers containing polyester resin and melamine resin as main components have good smoothness and a high solid content at the time of coating, but the adhesion is not sufficient because the composition is different from that of RIM urethane moldings. In addition, it has a defect that pinholes and armpits are easily generated on the painted surface.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a primer for an RIM urethane molded article, which aims to eliminate all of the above-mentioned defects, and is characterized in that a specific polyurethane elastomer has a weight average molecular weight of 800 to 3000.
Melamine resin (crosslinking agent).

As a result, the solid content at the time of coating can be made higher than that of the polyurethane elastomer alone, so that the primer coating is not eroded by the organic solvent in the top coating, and the Has been improved, the smoothness of the coated surface has been improved, the chipping resistance and the adhesion to the RIM urethane molded article have been excellent, and a coating film having almost no pinholes or wrinkles has been formed. R
Succeeded in obtaining a primer for IM urethane moldings,
The present invention has been completed.

That is, according to the present invention, (A) the hydroxyl value is 2
0 to 50 to 95 parts by weight of a polyurethane elastomer having a urea bond and (B) a weight average molecular weight of 8
The present invention relates to a primer for an RIM urethane molded article containing 50 to 5 parts by weight of a melamine resin of 0.00 to 3000 as a main component.

Hereinafter, the coating composition which is the primer of the present invention will be described in more detail.

(A): Polyurethane elastomer This is mainly obtained by reacting a polyol component, a diamine, and a polyisocyanate compound. The urea bond and the urethane bond coexist in the molecule, and the hydroxyl value is It needs to be less than 0-20.

[0011] RIM by having a urea bond
Adhesion with the urethane molded article was remarkably improved, and when the hydroxyl value was less than 20, low-temperature impact resistance, chipping resistance, adhesion with the molded article, and the like were improved.

The polyol component for preparing the component (A) has two or more, preferably two, hydroxyl groups in one molecule. Examples thereof include ethylene glycol, propylene glycol, diethylene glycol, trimethylene glycol, and dipropylene glycol. Glycol, pentanediol,
Alkylene or ether group-containing low molecular weight polyols such as hexanediol, glycerin, trimethylolpropane, and trimethylolethane: using one or more selected from ethylene oxide, propylene oxide, butylene oxide, hexylene oxide, and the like. Particularly preferred are high molecular weight polyether diols: cyclohexane dimethanol and / or high molecular weight polyether diols of hydrogenated bisphenols (A, F) and alkylene oxides.

The diamine has two amino groups per molecule.
A compound having (-NH ₂ ), for example, an alkylenediamine having 2 to 10 carbon atoms such as ethylenediamine, propylenediamine, and diethylaminopropylamine; and an aromatic diamine such as phenylenediamine, diaminodiphenylmethane, and benzyldimethylamine. .

Further, the polyisocyanate compound is
Compounds having two or more isocyanate groups in the molecule, for example, aliphatic diisocyanates such as hexamethylene diisocyanate and trimethylhexamethylene diisocyanate: cycloaliphatic diisocyanates such as hydrogenated xylylene diisocyanate and isophorone diisocyanate: tolylene diisocyanate Aromatic diisocyanates such as diphenylmethane diisocyanate: isocyanate group-containing prepolymers obtained by reacting these diisocyanates with a polyhydric alcohol having 2 to 4 hydroxyl groups in one molecule: cyclized polymers of diisocyanate itself: can give. These can be used alone or in combination of two or more.

Although the ratio of these components is not particularly limited, for example, the isocyanate group of the polyisocyanate compound is preferably 0.7 to 1 per mole of the hydroxyl group of the polyol component.
It is preferable that 1 mol of the amino group of the diamine is in the range of 0.2 to 0.8 mol.

The urethanization reaction and ureation reaction with these components can be carried out under ordinary conditions.

The component (A) has a hydroxyl value of from 0 to 2
It is less than 0, especially 0-13, and the weight average molecular weight is 50
A range of from 00 to 100,000, particularly from 7000 to 20,000 is suitable. The SP value (solubility parameter, solubility parameter) of the component (A) itself is 11 to 1
3, especially 12 to 13, and the elongation is 50 to 500% (20 ° C., film thickness 15 to improve the impact resistance at low temperature).
μm), and particularly preferably 200 to 300%. In particular, when the hydroxyl value is 20 or more, the elongation percentage of the formed coating film is reduced, the low-temperature impact resistance is reduced, and the adhesion to the material is not sufficient, which is not preferable.

(B): weight average molecular weight of 800 to 300
This is a methylolated melamine resin obtained by reacting aldehyde with melamine, and an ether obtained by etherifying a part or all of the methylol group of the methylolated melamine resin with an alkyl group having 1 to 6 carbon atoms. Melamine resin is preferred. Aldehydes include formaldehyde, paraformaldehyde, acetaldehyde, benzaldehyde and the like. Examples of the monohydric alcohol having 1 to 6 carbon atoms used for etherification include methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, and 2-ethylhexyl alcohol.

The component (B) has a weight average molecular weight of 800 to 3000, particularly preferably 10 to increase the solid content in coating and to improve the atomization in spray coating.
It is preferable to set the SP value to 00 to 2000, and if necessary, to make the SP value the same as or approximate to the component (A). If the weight average molecular weight is less than 800, the low-temperature curability of the coating film is inferior, and if it is more than 3000, the solid content is reduced, and the smoothness of the coating film is undesirably reduced.

The methylol group of the component (B) is the same as the component (A)
It is thought that a crosslinking reaction occurs with -NH- based on a urethane bond in the component, but the ether group hardly undergoes a crosslinking reaction with the component (A), and it is presumed that the ether group is self-crosslinked.
Accordingly, the component (B) has a methylol group and an alkyl ether group, and further has an imino group (—NH
It is particularly preferable to use those which also have-).

The primer (A) and the component (B) are essential for the primer of the present invention, but if necessary, a polyester resin (C) can be added.

The component (C) causes an esterification reaction between a polyhydric alcohol having two or more hydroxyl groups in one molecule and a polybasic acid having two or more carboxyl groups in one molecule, which is known per se. Having a weight average molecular weight of 1,000 to 10,000, particularly 1500 to 800.
0, the hydroxyl value is preferably in the range of 30 to 100, and the acid value is preferably in the range of 4 to 50. By using the component (C), the curability of the primer coating film can be improved. It is preferable that the SP value of the component (C) is the same as or approximate to the components (A) and (B).

The primer for molded RIM urethane of the present invention comprises the above components (A) and (B) as main components, and the composition ratio of both components can be arbitrarily selected depending on the purpose of use. Based on solids weight,
The component (A) is suitably 50 to 95% by weight, particularly 60 to 80% by weight, and the component (B) is suitably 50 to 5% by weight, particularly 40 to 20% by weight. The component (C) is suitably used in an amount of 0 to 15 parts by weight, especially 2 to 13 parts by weight, per 100 parts by weight of the total of the components (A) and (B).

The primer of the present invention can be obtained by dissolving or dispersing each of the above components in an organic solvent. If necessary, a coloring pigment, an extender pigment, an anti-settling agent, an anti-sagging agent, etc. can be added. .

The primer of the present invention preferably has a solid content of about 20 to 50% by weight at the time of spray coating, for example. In addition, the coating film thickness is 10 to 10 based on the cured coating film.
About 20 μm is suitable. And the coating film is 80-1
About 30 ° C, preferably 100 to 130 ° C, 10 to 3
It is suitable to cure by heating for about 0 minutes. The primer coating film is free from pinholes and wrinkles and has good adhesion, but is more preferably heated and cured at 100 to 130 ° C. because the smoothness after overcoating is further improved.

The primer coating surface can be coated with a known overcoat for plastics. As the top coating, for example, acrylic resin, polyester resin,
A cross-linking-curable organic solvent-based coating containing as a main component at least one base resin selected from a fluororesin, an alkyd resin and the like and at least one cross-linking agent selected from a polyisocyanate compound, a melamine resin and the like is preferable. is there. A color pigment, a metallic pigment, or the like can be added to these overcoat paints as needed. As the coating method of the top coat itself, one coat and one bake method, two coats and one bake method, two coats and two bake methods
There is a baking method. In addition, it is also possible to apply the top coat in a state where the above-mentioned primer coat is uncured, and to cure both coats simultaneously by heating.

The technical effects of the primer for RIM urethane molding of the present invention are as follows.

(1) Adhesion with the RIM urethane molded article (coated surface) was remarkably improved.

(2) Almost no pinholes or cracks are observed, and the smoothness is good.

(3) The atomization during spray coating was improved, and the solid content was increased, so that the smoothness of the coating film surface was significantly improved.

(4) Since the primer coating is cross-linked and hardened, there is almost no possibility of being eroded by the top coating.

(5) The chipping resistance is also good.

(6) Since the solid content at the time of spray coating is higher than that of the conventional polyurethane elastomer alone primer, it was possible to contribute to resource saving and prevention of pollution.

[0034]

EXAMPLES Examples and comparative examples according to the present invention will be described below.

The components (A) to (C) used in each example are
It is as follows.

(A) Polyurethane elastomer (A-1): "SAMPLEN PU-816" (trade name, manufactured by Sanyo Chemical Industries, Ltd.).

Weight average molecular weight: about 15,000, elongation: 25
0% (film thickness 15 μm), SP value 12.5, hydroxyl value 0.

(A-2): "SAMPLEN PU-816L
M "(trade name, manufactured by Sanyo Chemical Industries, Ltd.).

Weight average molecular weight: about 9000, elongation 250
% (Film thickness: 15 μm), SP value: 12.5, hydroxyl value: 12.

(A-3): "SAMPLEN PU-71X"
3 "(trade name, manufactured by Sanyo Chemical Industries, Ltd.).

Weight average molecular weight: about 15,000, elongation 25
0% (film thickness 15 μm), SP value 12.5, hydroxyl value 30
It is.

(B) Melamine resin (B-1): "Super Beckamine L-127" (trade name, manufactured by Sumitomo Chemical Co., Ltd.).

Methyl / butyl mixed etherified melamine resin, weight average molecular weight 1000, containing imino group, SP value 1
2.

(B-2): Methyl / butyl mixed etherified melamine resin.

Weight average molecular weight 5000, containing imino group,
The SP value is 10.

(C) Polyester resin (C-1): polyester resin.

Weight average molecular weight 13000, hydroxyl value 6
8, acid value 9.5, SP value 10.8.

(C-2): polyester resin.

Weight average molecular weight 5000, hydroxyl value 10
0, acid value 40, SP value 11.5.

Examples 1 to 5 and Comparative Examples 1 to 8 The above components and pigments were mixed according to the compounding ratio shown in Table 1 below, and an organic solvent (methyl ethyl ketone / methoxybutyl acetate / butyl acetate = 20/40/40, (Weight ratio), the viscosity was adjusted to 19 seconds / Ford cup # 4/20 ° C. to obtain a primer for RIM urethane.

In Table 1, (B-
The component 2) is a polyisocyanate compound having a free isocyanate group ("Takenate D-16KN", manufactured by Takeda Pharmaceutical Co., Ltd.), and Comparative Example 8 is a two-pack type paint.

[0052]

[Table 1]

The primer shown in Table 1 was spray-coated on the RIM urethane molded body so as to have a thickness of 15 μm based on the cured coating film, and was left at room temperature for 3 minutes, and then cured by heating (heating conditions are shown in Table 2). Was). Then, a plastic overcoat “SOFLEX # 1211” (trade name, manufactured by Kansai Paint Co., Ltd., trade name, polyester resin / melamine resin black paint) was applied to a film thickness of 30 μm (cured coating film).
The composition was cured by heating at 0 ° C. for 20 minutes.

Table 2 also shows the performance test results of the coating film thus cured.

[0055]

[Table 2]

The performance test results in Table 2 above were obtained by the following methods.

Adhesion: A test result of a primer coating film which was cured by heating under the above conditions. The primer coating surface was cut with a knife to reach the substrate, and the size was 1 × 1 m.
100 m-thick mounds were formed, an adhesive cellophane tape was stuck on the coated surface, and the number of the remaining knit-mesh coatings after abrupt peeling at room temperature was examined.

〇 indicates 100 remaining, △ indicates 99 to 80 remaining, and × indicates 79 or less remaining.

Pinhole resistance: The coated surface after top coating was visually judged.

[Delta] indicates that no pinholes or armpits are observed, [Delta] indicates that pinholes or armpits are slightly observed, and X indicates that pinholes or armpits are often observed.

Sharpness: Sharpness after top coating was measured using a sharpness measuring device “JCRI-GGD-166 type Gd meter” (sold by Nihon Color Research Institute) at an angle of 55 °. It was measured.

Low-temperature impact resistance: The state of the coated surface when a 500 g weight was dropped from a height of 50 cm onto the coated surface at −20 ° C. using a DuPont impact tester was examined.
〇 indicates that cracks were slightly observed on the coated surface, and X indicates that cracks occurred frequently.

Compatibility: (A)
A mixture of the components (B) and (C) at the above ratio was coated on a glass plate to a thickness of 50 μm (cured coating film), and the transparency was visually evaluated.

〇 indicates transparent and good compatibility, and X indicates cloudy and poor compatibility.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takahiro Sakurai, Aichi, Miyoshi-cho, Nishi-kamo-gun, Aichi Prefecture, Kanagawa Paint Co., Ltd. Kansai Paint Co., Ltd. (56) References JP-A-56-161473 (JP, A) JP-A-2-187171 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09D 1 / 00-201/10 C08K 3/00-13/08 C08L 1/00-101/16

Claims (1)

(57) [Claims] The main components are (A) 50 to 95 parts by weight of a polyurethane elastomer having a hydroxyl value of less than 20 and having a urea bond, and (B) 50 to 5 parts by weight of a melamine resin having a weight average molecular weight of 800 to 3000. RIM urethane molded product primer.