JPS5844433B2 - How to finish the paint film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for finishing paint films used for applications such as automobile exterior paints that require long-term weather resistance and excellent painted surface appearance.

Conventionally, paints used outdoors, such as top coats for automobiles, require not only film performance such as chemical resistance, solvent resistance, and physical properties, but also long-term weather resistance and excellent painted surface appearance. .

Coupled with the social demand for resource conservation in recent years, the requirements for weather resistance have become even more sophisticated.For example, in the case of passenger cars, it used to be that the coating was warranted until the first vehicle inspection (2 years), but recently It has become necessary to guarantee the paint film until at least the second vehicle inspection (4 years).

On the other hand, regarding the appearance of the coated surface, especially in the case of top coat paints for automobiles, which is the main application of the coating composition of the present invention, the quality of the appearance of the coated surface has a significant impact on its commercial value, and it is extremely important to improve the appearance. big.

As a method of simultaneously improving both weather resistance and the appearance of the painted surface, increasing the thickness of the top coat, particularly the clear coat, has been considered and various studies have been conducted.

However, it is extremely difficult to thicken the film all at once because it causes wrinkles and sagging.

Therefore, in recent years, the main finishing method has been to apply a base paint containing metallic powder and/or colored pigments, then apply a clear paint to the painted surface, and then simultaneously heat and harden it. A new finishing method has begun to be considered, in which a clear coating is applied and baked on top of the coating.

According to this finishing method, although the number of man-hours increases, there are no problems such as wrinkles or sagging, and the normal clear film thickness is 25 to 30 μm.
As a result, it is possible to easily form a coating film twice as thick as that of the coating film, and as a result, it is possible to obtain a coating film with extremely excellent weather resistance and surface resistance.

However, when this finishing method is used, adhesion between the first clear and second clear becomes a problem, and if peeling occurs at this interface, the intended purpose cannot be achieved.

Adhesion can be improved by sanding the first clear coating, then applying a second clear coating and baking it, but this requires a great deal of time and effort, resulting in a large increase in cost and is not practical.

In view of the current situation, the inventors of the present invention have completed the present invention as a result of intensive studies on a method for finishing a coating film with excellent adhesion between the first clear coat and the second clear coat and a good appearance of the coated surface.

The present invention relates to a paint (mainly composed of a thermosetting resin and an amino resin mixed with a metallic powder and/or a colored pigment).
After applying a clear paint (first clear) containing thermosetting resin A and amino resin as main components to the painted surface and baking it, further coat it with thermosetting resin B and amino resin as main components. clear paint (
In a finishing method in which a second clear coat is applied and burnt, thermosetting resin A and thermosetting resin B are hydroxyalkyl α/β unsaturated carboxylic acids, α°β unsaturated carboxylic acids, and other copolymerizable vinyl monomers. Consisting of
A first clear and a second clear, characterized in that both the resin hydroxyl groups (in terms of solid content) and (or) the resin acid (in terms of solid content) of thermosetting resin A are higher than those of thermosetting resin B. This is a coating finishing method that provides excellent adhesion and a good appearance of the coated surface.

The hydroxyalkyl α/β unsaturated carboxylates used in thermosetting resin A and thermosetting resin B of the present invention include 2-hydroxyethyl acrylate or methacrylate, 2-hydroxypropyl acrylate or methacrylate, and 3-hydroxypropyl acrylate. or methacrylate, 4-hydroxybutyl acrylate, 5-
Hydroxyamyl acrylate, 6-hydroxyhexyl acrylate or methacrylate, 7-hydroxyhebutyl acrylate, 9-hydroxynonyl acrylate, 8-hydroxyoctyl methacrylate, 10-hydroxydecyl methacrylate, 3-hydroxypropyl crotonate, 5-hydroxyamyl crotonate ,6
-Hydroxyhexyl crotonate, 7-hydroxyhebutyl crotonate, 10-hydroxydecyl crotonate, di(2-hydroxyethyl) maleate, cy(4
-hydroxybutyl) maleate, di(6-hydroxyhexyl) maleate, di(9-hydroxynonyl) maleate, di(10-hydroxydecyl) maleate, di(2-hydroxyethyl) fumarate, di(4-hydroxybutyl) fumarate, Examples include di(6-hydroxyhexyl) fumarate and di(10-hydroxydecyl) fumarate.

Further, other substituents may be introduced into the alkyl chain, including secondary hydroxy groups, halide groups, nitrile groups, and the like, such as 2,3 dihydroxypropyl acrylate, 3,5 dihydroxy amyl crotonate, 6,10 dihydroxydecyl methacrylate, di2
・6-Sihydroxyl maleate, di-2-chlor 7-
Examples include hydroxyhebutyl fumarate.

The appropriate amount to be used is an amount corresponding to a resin hydroxyl group number of 20 to 150, preferably 35 to 130, for both thermosetting resin A and thermosetting resin B.

Furthermore, among these hydroxyalkyl α/β unsaturated carboxylic acids, from the viewpoint of copolymerizability and reactivity with amino resins, hydroxyalkyl (meth)acrylates with an alkyl group having 2 to 5 carbon atoms, i.e. 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 2-hydroxyisopropyl (meth)acrylate, etc. are suitable.

If the amount of α/β-unsaturated hydroxyalkyl carboxylate used is less than the above range, curing will be insufficient and solvent resistance will be unsatisfactory, and if it is more than the above range, the crosslinking density will be too high and flexibility will be insufficient. or acid resistance decreases,
It doesn't suit the purpose.

Examples of the α/β unsaturated carboxylic acids used in thermosetting resin A and thermosetting resin B of the present invention include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, monoalkyl esters thereof, and croton. acid, α-methylene geltaroic acid, aconitic acid, atorobic acid, acid anhydrides such as maleic anhydride, succinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, trimellitic acid, and hydroxyalkyl αβ unsaturated carboxylic acids. Examples include adducts with.

These α/β unsaturated carboxylic acids not only play an important role as a catalyst for the crosslinking reaction between the hydroxyalkyl α/β unsaturated carboxylic acid and the amino resin, but also act as crosslinking reactive groups themselves.

The amount of α/β unsaturated carboxylic acid used is determined when the resin acid value is 6 to 4 in both thermosetting resin A and thermosetting resin B.
An amount corresponding to 0, preferably in the range 10 to 30 is suitable.

If the amount used is less than the above range, the above effects will be insufficient, and if it is more than the above range, the viscosity of the resulting copolymer will increase, and the water resistance etc. will decrease, which is not preferable.

Furthermore, in order to achieve a practical level of adhesion between the first clear and second clear, which is the object of the present invention, the hydroxyl group content and/or acid value of the thermosetting resin A, which is the main component of the first clear, must be increased. It is necessary to use a thermosetting resin B which is the main component of the second clear.

In order to improve adhesion, the larger the difference between the hydroxyl groups and the acid value between the two, the better.

In other words, the hydroxyl group content and acid value of thermosetting resin A are designed to be as high as possible without impairing other properties, and the hydroxyl group content and acid value of thermosetting resin B are designed to be as low as possible without impairing other properties. This improves the adhesion between the first clear and second clear.

Further, the α/β unsaturated carboxylic acid used in the thermosetting resin B, which is the main component of the second clear, is (a) fumaric acid, maleic acid, itaconic acid, or a monoalkyl ester thereof, (b) crotonic acid, or The present invention is that it consists of at least one adduct of an acid anhydride such as maleic anhydride, succinic anhydride, phthalic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, and a hydroxyalkyl α/β unsaturated carboxylic acid. It shows a favorable effect for the purpose of the invention, that is, improving the adhesion of second clear and first clear.

There is no problem in using these acids in combination with other α/β unsaturated carboxylic acids.

α・β unsaturated carboxylic acid hydroxyalkyl and α・β
Other copolymerizable vinyl monomers other than unsaturated carboxylic acids include, for example, α.

There are β-unsaturated alkyl carboxylates, such as acrylates having an alkyl group of 1 to 18 carbon atoms,
Methacrylates are mentioned, and specific examples of alkyl groups include methyl group, ethyl group, butyl group, isobutyl group,
They are n-propyl group, 2-ethylhexyl group, lauryl group, stearyl group, and cyclohexyl group.

In addition, styrene and its derivatives, organic nitriles such as acrylonitrile, methacrylatetrile, methylene geltalonitrile, vinyl acetate, vinyl propionate,
Vinyl esters of organic acids such as vinyl isopropionate, dibutyl fumarate, dibutyl itaconate, di-2-
Mention may be made of dialkyl fumarates such as ethylhexyl itaconate and dialkyl itaconates.

Furthermore, if necessary, a functional group monomer other than hydroxyalkyl α/β unsaturated carboxylate, such as glycidyl (meth)
Acrylates, (meth)acrylamides, and N-alkoxy(meth)acrylamides may be used within the range that does not impair the purpose of the present invention.

In addition, vinyl monomers having extremely thick absorption in the wavelength range of 300 nm or more and 400 nm or less, such as 2-hydroxy-4 (3-methacryloxy-2-hydroxypropoxy) benzophenone, 2-hydroxy-4 (3-
Acryloxy-2-hydroxypropoxy)benzophenone, 2,2'-dihydroxy-4(3-methacryloxy-2hydroxypropoxy)benzophenone, etc. can be used for the purpose of improving weather resistance.

Thermosetting resin A and thermosetting resin B are, for example, toluene,
It can be obtained by polymerization in a non-polar solvent such as xylene or Trupetz #100 or in a mixed solvent system with a polar solvent such as n-butanol.

As the polymerization initiator, a peroxide type such as benzoyl peroxide or cumene hydroperoxide or an azo compound type such as azobisisobutyronitrile or azobisvaleronitrile is used.

Furthermore, to adjust the degree of polymerization, normal dodecyl mercaptan, 2-mercaptoethanol, etc.
It will be done.

Examples of the amino resin used as a crosslinking agent with thermosetting resins A and B include melamine resin and benzoguanamine resin, but melamine resin is preferred in this application.

The blend ratio of thermosetting resin A or B and melamine resin is preferably in the range of 90/10 to 50150 in terms of solid content; if thermosetting resin A or B exceeds 90% by weight, crosslinking will be insufficient. , solvent resistance etc. become unsatisfactory.

If the amount is less than 50% by weight, the coating film becomes too hard (too adhesive) and is not suitable for this purpose.

Further, crosslinking agents other than amino resins, such as incyanate resins and epoxy resins, can also be used in small amounts in combination without impairing the purpose.

Furthermore, various weather resistance improving aids and various leveling agents that have been conventionally used for this purpose can also be used within the range that does not impair the purpose of the present invention.

In the following examples, parts represent parts by weight.

Examples 1 to 4 and Comparative Examples 1 to 4 By solution polymerization, resin compositions, hydroxyl groups, and
Acrylic copolymers L-1 to L-5 having the following acid values were obtained.

Next, these copolymers and amino resin knee pants 208E
(manufactured by Mitsui Toatsu Co., Ltd.) at a solid content ratio of 70/30.

The resulting mixture was diluted with Ford Cup #4 at 25° C. for 25 seconds using Tsurupetz #100 as a thinner to obtain a clear coat paint.

Next, the metallic enamel was mixed in the following manner.

Dianal ■HR-560 (Thermosetting acrylic resin manufactured by Mitsubishi Rayon Co., Ltd.), Kneepan 208E (Mitsui Toatsu (Mitsui Toatsu)
Butylated melamine (solid content: 60%) and Alpaste #1109MA (aluminum paste, manufactured by Toyo Aluminum Co., Ltd.) were blended at a solid content ratio of 80/20/IO,
Toluene/n-butyl acetate/butyl cellosolve/Turupetz #150 as thinner = 70/10/10/10
(weight ratio) and dilute with 4 1 and 2 with cassof #4.
The temperature was adjusted to 5° C. for 14 seconds to obtain a metallic enamel paint.

The metallic enamel paint was applied to a mild steel plate that had been degreased and subjected to phosphorization treatment to a dry film thickness of 1.
After painting to a thickness of 5μ, let it set for 3 minutes, apply first clear paint wet-on-wet to a dry film thickness of 25 to 30μ, leave it for 10 minutes, and dry it in an electric hot air dryer at 140℃ x 30mm (adhesive). test is 1
First cure was performed at 50°C x 90WlvL.

After 10 hours of taking it out of the dryer, apply a second clear paint to a dry film thickness of 25-30μ, leave it for 10 minutes, and then dry it again in an electric hot air dryer at 140°C x 30rIu.
! 1 (an adhesion test was also conducted at 130° C. x 30 m).

The evaluation results of the coating film thus obtained are shown in Table 2.

Examples 5 to 8 and Comparative Examples 5 to 8 Dianal ■HR-56070 parts, knee pants 208E
25 parts, titanium oxide R-820 (6 Hara Sangyo Co., Ltd.) 2 parts, Irgazine Yellow 2GLT (Ciba Geigy)
Co., Ltd.) was used as a thinner toluene/n-butyl acetate/butyl cellosolve/Turupetz #150 = 70/10/10/10 (weight ratio)
diluted with a mixed solvent of 25% in a Ford cup #4.
The temperature was adjusted to 14 seconds to obtain a solid enamel paint.

The above solid enamel paint was applied to a mild steel plate which had been degreased and phosphate chemically treated in exactly the same manner as in the previous example, and then coated with an electrodeposition primer for automobiles and an intermediate coat surfer. After painting to 15μ,
Set for 3 minutes and apply first clear paint to a dry film thickness of 2
Painted wet on wet to a thickness of 5 to 30μ,
After leaving it for 10 minutes, dry it in an electric hot air dryer at 140℃ x 30℃.
(Adhesion test was also conducted at 150℃ x 90rru!t)
One hour after removing the paint from the hot air dryer where the first cure was performed, the second clear paint was applied to a dry film thickness of 25 to 30 mm.
After coating it so that it has a coating thickness of
A second cure was also performed after 30 years of training.

The evaluation results of the coating film thus obtained are shown in Table 3.

Claims (1)

[Scope of Claims] 1. A paint (base coat) whose main components are a thermosetting resin and an amino resin blended with metallic powder and/or color pigments is applied, and then the painted surface is coated with thermosetting resins A and A. A finishing method in which a clear paint (first clear) whose main ingredients are resin is applied and baked, and then a clear paint (second clear) whose main ingredients are thermosetting resin B and amino resin is applied and baked. , thermosetting resin A and thermosetting resin B are composed of hydroxyalkyl α/β unsaturated carboxylic acid α/β unsaturated carboxylic acid and other copolymerizable vinyl monomers, and the resin hydroxyl groups of thermosetting resin A are and (or) a resin acid bag,
A method for finishing a coating film with excellent adhesion between a first clear coat and a second clear coat and a good appearance of the coated surface, which is characterized in that it is stronger than that of thermosetting resin B. 2 At least a part of the α/β unsaturated carboxylic acids used in the thermosetting resin B is a, fumaric acid, maleic acid, itaconic acid, or monoalkyl ester residue thereof, crotonic acid, maleic anhydride, anhydride. Claim 1, which is an adduct of an acid anhydride such as succinic acid, phthalic anhydride, tetrahydrophthalic anhydride, trimellitic anhydride, and a hydroxyalkyl α/β unsaturated carboxylic acid How to finish the paint film.