JPH0552345B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention is suitable for use in metallic finishing methods for automobiles, where metallic base paints, especially metallic base coat coatings, are less likely to break and the underlying surface appears speckled (hereinafter referred to as metal staining). Regarding metallic-based paints that can be used. Conventional technology Metallic finishing for automobiles is a typical layered coating method, and its standard coating specifications include electrodeposition coating, 1 to 2 coats of intermediate coating, 4 to 5 coats of metallic base coating, clear coating, etc. It consists of painting. Metallic base paint and clear paint, which are part of the finishing process, are usually applied using a wet-on-wet two-coat, one-bake method. This 2-coat, 1-bake method is highly productive and has become a standard coating system because the metallic base paint is applied, the solvent is flashed off, and then the clear paint is applied and baked. Wet paint, where paint is applied over and over again.
Since it is an on-wet painting process, the metal powder contained in the metallic base may reflow, causing problems during the painting process. wet on
One of the problems with wet painting is that when applying metallic base paint and clear paint using the same resin system, even if you apply the metallic base paint and then flash off the solvent and apply the clear paint, they are not compatible. If the compatibility is poor, the solvent of the clear paint will re-dissolve the metallic base, causing metal unevenness, and if the compatibility is poor, metal smearing may occur. This phenomenon is particularly likely to occur when a clear paint is applied to a metallic base paint using a single acrylic resin, and when a top coat is applied without polishing the intermediate coat, or when a thin coat of metallic base paint is applied and the clear paint is applied wet-on-wet. This especially occurs when a thick film is applied. On the other hand, it is well known that recently, in order to obtain a high-quality paint film appearance, the number of cases in which a thin layer of metallic base paint is applied and then a thick layer of clear paint applied wet-on-wet is increasing. However, there is a problem that such a coating system tends to cause metal twisting. This is thought to be due to insufficient wettability of the metallic base paint to the base and the fact that the solvent in the clear paint tends to cause the metallic base to coagulate. As a prior art having a configuration similar to the present invention,
For example, there is Japanese Patent Application Laid-Open No. 57-30770, which describes acrylic resins with a weight average molecular weight of 3000 to 8000,
A top coating for automobiles with excellent weather resistance is disclosed, which is composed of three components: an acrylic resin and an amino resin having a weight average molecular weight of 10,000 to 50,000. However, since this system is a combination of resins with small molecular weights, there is a problem in that the compatibility between the base coat and clear coat is good and it is difficult to completely suppress the occurrence of metal unevenness. Problems to be Solved by the Invention The problems to be solved by the present invention are the problems of the prior art described above, namely, when there is a difference in compatibility between the metallic base coat and the clear coat in wet-on-wet painting, Metal twist occurs. Means for Solving the Problems The present inventors have discovered that the metal twist of the metallic base coat is caused by poor wetting between the metallic base coat and the clear coat and aggregation caused by the solvent in the clear paint,
This problem was solved by the following means. That is, the present invention includes (i) thermosetting resin (A) 98 to 70% by weight;
and (ii) an acrylic resin (B) with an SP value 0.4 or more lower and a weight average molecular weight 30,000 or more higher than the thermosetting resin (A).
2 to 30% by weight, and further contains alkoxymethyl melamine resin (C), and the blending ratio of thermosetting resin (A) and alkoxymethyl melamine resin (C) is 9/1 to 6/4.
(weight ratio), thermosetting resin (A), acrylic resin (B) and alkoxymethyl melamine resin
This invention relates to a metallic base paint made by mixing (C) at room temperature, and the above-mentioned problems have been solved by using such a metallic base paint. Examples of the thermosetting resin (A) to be incorporated into the metallic base paint of the present invention include acrylic resins, alkyd resins, and polyester resins. If the thermosetting resin (A) is an acrylic resin, the SP value is 10.6 to 11.5 and the weight average molecular weight is 30,000 to 95,000.
It is preferable to use If the SP value of the acrylic resin is less than 10.6, it will tend to mix with the clear paint and the finished appearance will deteriorate, such as not being sufficiently glossy.On the other hand, if it exceeds 11.5, the water resistance of the paint film will deteriorate and the weather resistance will deteriorate. It is on a declining trend. Furthermore, if the weight average molecular weight is less than 30,000, coating film performance such as durability will deteriorate, and if it exceeds 95,000, smoothness will tend to decrease, which is not preferable. The acrylic resin used in the present invention can be polymerized, for example, from the following monomers by a conventional method. (1) Hydroxylmethyl methacrylate, (meth)
Ethylene monomers having hydroxyl groups such as hydroxylethyl acrylate, hydroxylpropyl (meth)allylate, hydroxylbutyl (meth)acrylate, N-methylolacrylamine, (2) (meth)acrylic acid, crotonic acid, itaconic acid , fumaric acid, ethylenic monomers having a carboxyl group such as maleic acid, (3) methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate,
2-ethylhexyl acrylate, acrylic acid n
Ethylene monomers copolymerizable with the monomers (1) and (2), such as (meth)acrylic acid alkyl esters such as -octyl and n-dodecyl acrylate, as well as (meth)acrylonitrile, styrene, and the like are used. Next, when a polyester resin is used as the thermosetting resin (A) of the present invention, it preferably has an SP value of 10 to 11 and a weight average molecular weight of 1,500 to 12,000. SP value
If it is less than 10, it tends to dissolve in the solvent in the clear paint and cause unevenness, whereas if it exceeds 11, it tends to aggregate in the solvent and cause metal twisting, which is not preferable. Also, if the weight average molecular weight is less than 1500, the coating quality will not necessarily be sufficient;
Exceeding this is not preferable because the finished appearance tends to deteriorate. The above-mentioned polyester resin contains polybasic acids such as isophthalic acid, phthalic anhydride, succinic anhydride, adipic acid, sebacic acid, trimellitic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, and monobasic acids such as benzoic acid as an acid component. Basic acid, neobentyl alcohol, trimethylolethane, trimethylolpropane, 1,
It can be easily produced by polymerizing in a conventional manner using raw materials such as 6-hexanediol, 1,5-pentadiol, pentaerythritol, glycerin, and ethylene glycol.
In addition, as such a polyester resin, an alkyd resin modified with oil may be used, and in that case, from the viewpoint of compatibility with the resin, weather resistance, etc., coconut oil and its fatty acids, synthetic fatty acids such as octylic acid, etc. It is preferable to use those containing glycidyl esters of synthetic fatty acids in an amount of 30% by weight or less. Next, it is necessary that the acrylic resin (B) blended into the metallic base paint of the present invention has an SP value that is 0.4 or more lower than the SP value of the thermosetting resin (A).
If the difference does not reach 0.4, metal distortion will occur, which is not desirable. Also, the weight average molecular weight of the acrylic resin (B) is greater than the weight average molecular weight of the thermosetting resin (A).
It is necessary to have a value higher than 30,000, and if the difference does not reach 30,000, metal distortion will occur, which is not desirable. In order to cure the acrylic resin or polyester resin of the thermosetting resin (A), the metallic base paint of the present invention contains an alkoxymethyl melamine resin (C) in a ratio of thermosetting resin (A)/alkoxymethyl melamine resin = 9/1. It is blended at a ratio (weight ratio) of ~6/4. The preferred blending amount of the alkoxymethyl melamine resin is 8/2 to 7/3. Specific examples of alkoxymethyl melamine resin include alkoxy groups such as methoxy group, ethoxy group, n-butoxy group, i-
Examples include alkoxymethylmelamine resins having butoxy groups. If the blending ratio of the alkoxymethyl melamine resin is less than 9/1, the crosslinking density of the coating film will not increase, resulting in weak coating film strength.On the other hand, if it exceeds 6/4, the coating film will be easily hydrolyzed, or This is not preferable because it also deteriorates the finished appearance of the coating film. Further, in the metallic base paint according to the present invention, metallic pigments commonly used in conventional metallic base paints such as aluminum, bronze powder, mica powder, titanium coated mica, etc. can be used as the metallic pigment (D). There is no particular limitation on the amount of metallic pigment (D) to be added, but as in the general case, it is usually 1 per solid weight of the resin.
~30% by weight is sufficient. The metallic base paint of the present invention may further contain coloring pigments, such as inorganic pigments such as carbon black and titanium dioxide, and organic pigments such as phthalocyanine blue, phthalocyanine green, and sinker sand, as required. When producing the metallic base paint according to the present invention, the thermosetting resin (A) and the acrylic resin (B)
must be mixed at ambient temperature without heating. It is not preferable to use a mixture at a temperature of 100°C or higher because a paint with the desired performance cannot be obtained. The reason for this is not clear, but when mixed uniformly under heating, resins with low SP values are mixed uniformly, whereas in the paint of the present invention, which is mixed at room temperature, the parts with low SP values remain. It is assumed that ivy resin is effective against metal twisting. In addition to the essential components, the metallic base coating composition of the present invention contains 25% by weight of acrylic resin, polyester resin, alkyd resin, cellulose, acetate, butyrate resin, blocked isocyanate, etc., which are different from the above-mentioned specific acrylic resin. It can be included in the following amounts. The metallic base paint produced in this way can be applied by, for example, air spraying or electrostatic painting, and after flashing off the solvent at a temperature of about 50°C or less, a clear coat is applied on top of it according to a conventional method. The coat can be painted. There are no particular restrictions on the resin used for the clear coat, and any resin vehicle commonly used as a clear paint may be used. Note that the longer the setting time of the metallic base coat is, the less likely metal twisting will occur. In the present invention, the weight average molecular weight is measured by gel permeation chromatography using styrene as a standard.
CORBETT equation (Journal of Applied Polymer
Science, 12 , 2359, 1968). √Vml・δml+√Vmh・δmh/√Vml+√Vmh (in the formula: V: molecular volume, δ: solubility parameter,
ml: low SP solvent, mh: high SP solvent) Examples The present invention will be explained in more detail based on Examples below, but it goes without saying that the scope of the present invention is not limited to these Examples. Nor. The SP value in the following examples is the KW
With the value calculated using the formula of SUH and JMCORBETT, the solvent in the sample resin was volatilized, the remaining resin solid content 0.5 g was redissolved in 10 ml of acetone, and n-hexane and high SP value solvent were used as a low SP value solvent. It was calculated by performing turbidity titration using ion-exchanged water and substituting the titre into the following formula. Vml=(10+H)/(n-hexane molecular weight+acetone molecular weight) Vmh=(10+D)/(water molecular weight+acetone molecular weight) δml=9.75+10/10+H+7.24×H/10+H δmh=9.75+10/10+D+23.43×D /10+D H: Titration amount (ml) when using n-hexane D: Titration amount (ml) when using ion-exchanged water Production of acrylic resin (A) Monomers, initiators and solvents shown in Table 1 Acrylic resin (A)-1 and A as follows using
-2 was manufactured. A reaction vessel equipped with a stirrer was first charged with the first component (#1) in Table 1 and heated to a temperature of 110°C. Next, while maintaining this temperature, a liquid mixture of the second component (#2) in Table 1 was added dropwise over a period of 3 hours. After the addition was completed, the mixture was aged for 30 minutes, and then the third component (#3) in Table 1 was added dropwise for 30 minutes. 2 more at a temperature of 110℃
The reaction was continued for a period of time to produce acrylic resins (A)-1 and A-2 having the physical properties shown in Table 1.

[Table] Production of acrylic resin (B) Acrylic resin B-1, B-
2, B-3 and B-4 were produced. First, the first component (#1) in Table 2 was charged into a reaction vessel equipped with a stirrer and heated to a temperature of 100°C. Next, while maintaining this temperature, a mixed solution of the second component (#2) in Table 2 was added dropwise over 3 hours. After the addition was completed, the mixture was aged for 30 minutes, and the third component (#3) in Table 2 was added dropwise over 30 minutes, and the reaction was continued at a temperature of 100° C. for another 2 hours. Acrylic resin B-3 and B-
For 4, further add the fourth component (#4).
The reaction was carried out at 100°C for about 4 hours while monitoring the viscosity.
After the reaction was completed, 20 parts by weight of toluene was added to dilute and cooled. In this way, acrylic resins B-1 to B-4 having the physical properties shown in Table 2 were produced.

[Table] *2 to *5: Refer to footnotes in Table 1 Examples 1 to 6 and Comparative Examples 1 to 5 Acrylic resin (A) and acrylic resin (B) synthesized above
and other components with the composition shown in Table 3 in a tin container and mixed with a disper for 15 minutes to prepare metallic base paints (Examples 1 to 6 and Comparative Examples 1 to 3).
5) was prepared.

[Table] Next, a cationic electrodeposited intermediate coat was applied to a 0.8 x 300 x 300 mm dull steel plate that had been chemically treated with zinc phosphate, and a 5:5 mixture of toluene: ethyl acetate: Solbetsuso 150 was applied to the sanded test piece. 14 in a #4 food cup with a 3:2 mixture of solvents.
The above-mentioned metallic base paint whose viscosity was adjusted to have a viscosity of 1.2 seconds was coated to a film thickness of 5 μm. Coating was carried out using Wider 61 at an atomization pressure of 4 kg/cm ² . The atmosphere in the booth during painting was at a temperature of 25℃±2℃.
The humidity was maintained at 75±5%. After setting in the booth atmosphere for 1 minute, the viscosity was adjusted to 27 seconds with a #4 food cup using a solvent mixed with Solbetsuso 100 and Solbetsuso 150 at a ratio of 2:1.
SPO-70 clear paint (SP value of the base resin in the clear paint is 9.3) was applied to the metallic base paint film. After painting, set for 5 minutes, then 140
Baked at ℃ for 20 minutes. The performance results of these coatings were as shown in Table 4.

【table】

[Table] Effects of the invention As is clear from the above explanation, the acrylic resin (B) in the base resin of the metallic base paint of the present invention
If the SP value of the thermosetting resin (A) is lowered by 0.4 or more than that of the thermosetting resin (A), a material close to the SP value of the base resin of the top coat will be mixed in, which will prevent metal twisting (film breakage) and reduce the weight average molecular weight to 30,000 yen. Blending the above-mentioned resins increases the viscosity of the base coat, suppresses film movement and prevents metal smearing, and at the same time reduces the effect of the base coat being attacked by the solvent in the top coat, preventing metal smearing. In this manner, the present invention provides a metallic base coating composition that simultaneously solves metal distortion and metal unevenness.

Claims (1)

[Scope of Claims] 1. (i) 98 to 70% by weight of thermosetting resin (A) and (ii) SP value defined in the text is 0.4 or more lower than that of thermosetting resin (A) and weight average molecular weight 30000 or more, it consists of 2 to 30% by weight of acrylic resin (B), and further contains alkoxymethyl melamine resin (C), and the blending ratio of thermosetting resin (A) and alkoxymethyl melamine resin (C) is 9/1 to 9/1.
Contains thermosetting resin in an amount of 6/4 (weight ratio)
A metallic base paint comprising (A), an acrylic resin (B), an alkoxymethylmelamine resin (C) and a metallic pigment (D) mixed at room temperature. 2 The thermosetting resin (A) is an acrylic resin with an SP value of 10.6 to 11.5 and a weight average molecular weight of 30,000 to 95,000, and
The metallic base paint according to claim 1, which is a resin whose main component is at least one of polyester resins having an SP value of 10 to 11 and a weight average molecular weight of 1,500 to 12,000. 3. The metallic base paint according to claim 1, wherein the acrylic resin (B) is a melamine-modified acrylic resin containing 3 to 10% by weight of an alkoxymethylmelamine resin component. 4 The thermosetting resin (A) is an acrylic resin with an SP value of 10.7 to 11.3, and the acrylic resin (B) has an SP value of 10.2 to 10.7.
A metallic base paint according to claim 1.