JPS592541B2 - Painting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating method for obtaining a coating film with excellent performance by overcoating a powder coating and a non-aqueous dispersion coating.

Painting is applied to achieve various purposes, but since one type of paint cannot satisfy all of them, the reality is that two or more types of paint are applied in layers.

Therefore, we combined a powder coating that forms a coating film with a thickness of 50 microns or more with excellent corrosion resistance and excellent chemical and physical performance using the same mold with a non-aqueous dispersion coating that has an excellent coating appearance and suitability for metallics. It is possible to apply multiple coats. However, when a non-aqueous dispersion paint is applied over a paint film obtained by baking a powder paint, the resulting paint film is inferior in all physical and chemical properties and cannot be put to practical use. After various studies on this point, it was found that the cause was poor adhesion between the overcoated coatings. Therefore, it has been found that sanding the surface of the powder coating film and then overcoating with a non-aqueous dispersion coating can significantly improve the problem, but it is still not satisfactory and has the drawback of requiring significant manpower. After further research into these drawbacks, we found that by applying a top coat with a non-aqueous dispersion paint when the gel fraction of the powder paint film used as an undercoat is 90% or less, an extremely excellent multi-coat film can be obtained. This brings us to the heading of the present invention.

The "gel fraction" referred to here means that the coating film test piece is
It is the value obtained by dividing the weight of a coating film test piece after immersing it in twice its weight of acetone at 25℃ for 24 hours and drying it at normal pressure of 40℃ for 24 hours by the initial weight. The gel fraction of the painted film in the baked state is well above 95%. The present invention involves heating a thermosetting powder coating applied to the surface of an object to form a continuous coating film with a gel fraction of 90% or less, and then applying a non-aqueous dispersion coating on the top surface and baking it. It's in the painting method.

The powder coating for the undercoat is a thermosetting one,
Any known thermosetting paint can be used.

These resin components include, for example, epoxy group-containing resins (glycidyl polyether, epoxy group-containing polyesters, and copolymers thereof), carboxyl group-containing compounds (including carboxyl group-containing polyesters and copolymers), epoxy group-containing resins, and amino group-containing compounds. , hydroxyl group-containing resin (hydroxyl group-containing polyester, copolymer) and amino resin,
It is composed of a hydroxyl group-containing resin, a blocked isocyanate compound, a carboxyl group-containing resin (carboxyl group-containing polyester or copolymer thereof), an epoxy group-containing compound (including the above-mentioned epoxy group-containing resin), and the like. These thermosetting powder coatings are applied onto an object to be coated by a method such as an electrostatic spraying method or a fluidized dipping method, and then heated.

Unlike normal baking, this heating forms a continuous coating film, but the heating temperature is such that the gel fraction is 90% or less, preferably 20 to 70%. and/or the heating time is slower than normal baking conditions. At that time, the gel fraction of the continuous coating film of powder coating was 90.
If the gel fraction exceeds 20%, the interlayer adhesion between the undercoat and topcoat tends to decrease, making it impossible to obtain a multilayer film with satisfactory performance. The organic solvent in the paint tends to wet the undercoat film and cause film defects, and in order to avoid this, measures such as setting are required, making the work complicated. On the other hand, the applied powder coating may not be heated at all,
Alternatively, if a non-aqueous dispersion paint is applied and baked in a state where no continuous coating film is formed even after heating, the resulting coating film will have a significantly poor appearance and is therefore unsuitable. A non-aqueous dispersion paint is applied onto the powder paint film thus obtained.

There are no particular restrictions on the coating method, but a spraying method is suitable. After application, set as necessary and then bake the paint film. This baking is carried out in order to sufficiently harden the undercoat powder coating layer and to form an excellent topcoat from the topcoat non-aqueous dispersion coating. The baking conditions vary depending on the type of undercoat, the degree of gel fraction, the type of topcoat, etc., but usually a temperature of 160 to 200°C for 5 to 30 minutes is appropriate. For example, the non-aqueous dispersion paint for top coating is described in [
As described in "Polymer Processing", pages 331 to 336, it is a dispersion type paint in which resin components are dispersed in a non-aqueous solvent using a special dispersion stabilizer.

Any well-known thermoplastic or thermosetting non-aqueous dispersion paint can be used for the topcoat, but if the basecoat and topcoat react with each other, an extremely superior overcoat can be obtained. Therefore, the resin content of non-aqueous dispersion paint is
It is preferable that it contains a functional group that is mutually reactive with the functional group of the resin component of the powder coating. For example, when the functional group of a powder coating is a hydroxyl group, the functional group of a non-aqueous dispersion coating is an alkoxymethylol group, a methylol group, etc., and when it is a carboxyl group, it is an epoxy group, a hydroxyl group, etc.; is a carboxyl group, an amino group, an amide group, etc. The multi-coated coating film obtained in this way is extremely useful because it has excellent properties due to the mutually improving effects of the powder coating film as the undercoat and the coating film made of the non-aqueous dispersion paint as the topcoat.

The present invention will be explained below based on examples.

Parts and % in the text indicate parts by weight and % by weight. Example 1 Methyl methacrylate 30%, styrene 30(?l),
Butyl acrylate 15%, glycidyl acrylate 1
0 (fl), and β-methylglycidyl methacrylate 150! ) with a number average molecular weight of 7,000 and a ring and ball softening point of 112°C, 15 parts of decanedioic acid, 7 parts of Epiclon 1050 (Dainippon Ink Chemical Industry System, bisphenol type epoxy resin with an epoxy equivalent of 500), and oxidation. 35 parts of titanium was added, kneaded, and then ground.

The obtained powder coating was applied to a zinc phosphate-treated iron plate by electrostatic spraying, and then heated at 150° C. for 10 minutes to obtain a continuous coating film with a gel fraction of 55%. On top of this continuous coating film, the following non-aqueous dispersion paint was spray-coated and baked at 150°C for 10 minutes and at 170°C for 20 minutes.

The resulting overcoated coating film had good gloss, smoothness, sharpness, and physical and chemical properties, and had excellent interlayer adhesion. 900 parts of aliphatic hydrocarbon, 100 parts of toluene, 40 parts of methyl methacrylate, 5 parts of methyl glycidyl methacrylate, 5 parts of methacrylic acid, 5 parts of azobisisobutyronitrile, dispersion stabilizer solution (self-condensate of 12-hydroxystearic acid) After reacting the terminal carboxyl group of (penta-hexamer) with glycidyl methacrylate to introduce a terminal unsaturated bond, 5 parts (50% butyl acetate solution) of the product grafted with methyl methacrylate were added at 75°C in a nitrogen gas stream. After heating under reflux for 30 minutes at 95 parts were added dropwise over 4 hours under reflux, and the mixture was kept at the same temperature for an additional 30 minutes.

To 150 parts of the obtained milky-white dispersion having a non-volatile content of about 50% and a viscosity of A3, 25 parts of titanium oxide milled with the methacrylate adduct of the 12-hydroxystearic acid self-condensate mentioned above was added to form a non-aqueous dispersion. Got the paint. Comparative Example 1 In Example 1, the powder coating was baked at 170°C for 30 minutes (gel fraction 98%), and the non-aqueous dispersion coating was applied on top of the powder coating and baked at 150°C for 30 minutes.

The resulting coating film had very poor interlayer adhesion and poor physical performance, and also whitened when immersed in boiling water. Example
2 An adduct of 3 moles of xylylene diisocyanate and 1 mole of trimethylolpropane to 70 parts of a polymer having a number average molecular weight of 9000 and a softening point of 109°C consisting of 40% styrene, 20% β-hydroxyethyl methacrylate, and 40% butyl methacrylate. 30 parts of ε-caprolactam-blocked isocyanate, 2 parts of dibutyltin diacetate, 1 part of carbon, and 40 parts of titanium oxide were added to the mixture, and the mixture was kneaded and pulverized.

The obtained powder coating was applied to a zinc phosphate treated iron plate, and 17
It was heated at 0° C. for 10 minutes to obtain a continuous coating film with a gel fraction of 45%. On top of this continuous coating film, a paint prepared by mixing the following non-aqueous dispersion with aluminum paste (metallic aluminum content: 3%) was sprayed and baked at 140° C. for 20 minutes and at 1800° C. for 10 minutes.

The obtained multilayer coating film had excellent interlayer adhesion and good coating properties. Butyl formaldehyde (formaldehyde:water:n-butanol di40°10:50
) 504 parts, melamine 144 parts, n-butanol 112 parts
parts, xylene 40 parts, phthalic anhydride 0.24 parts, formic acid 1
．． 36 parts were heated to 100° C. for 3 hours, during which time the distillate was removed, and a butylated melamine resin (approximately 70% non-volatile content, viscosity approximately 90 poise, mineral spirits tolerance of 50 cc per 19, 1.5 cc methanol) was prepared. tolerance)
On the other hand, 75 parts of xylene and 15 parts of n-butanol were heated to 110°C, and 30 parts of methyl methacrylate, 38 parts of n-butyl acrylate, 10 parts of isobutyl methacrylate, and 20 parts of dihydroxyethyl methacrylate were added thereto. 1 part, 2 parts of acrylic acid, 10 parts of xylene, 1 part of dit-butyl peroxide, and 1.5 parts of azobisisobutyronitrile were added dropwise over 3 hours, and further kept at 110°C for 5 hours to obtain a non-volatile content of about 50%. , a polymer having a viscosity of MN was obtained.

To 202.5 parts of this polymer, 142.9 parts of the butyl himelamine resin, 0.1 part of p-toluenesulfonic acid, and 57.1 parts of aliphatic hydrocarbon were added, and the mixture was heated at 100°C for 2 hours and 30 minutes to reduce the viscosity. A product of QR was obtained. This product 402,
Add 200 parts of aliphatic hydrocarbon to 6 parts and heat at 80°C.
90 parts of methyl methacrylate, 117 parts of n-butyl acrylate
1, 60 parts of isobutyl methacrylate, 30 parts of dihydroxypropyl methacrylate, 3 parts of acrylic acid, 100 parts of aliphatic hydrocarbon, and 7.5 parts of benzoyl peroxide were added dropwise over 5 hours, and the mixture was kept at 80°C for an additional 3 hours. A milky white non-aqueous dispersion having a non-volatile content of about 50% and a viscosity of X-Y was obtained. Comparative Example 2 In Example 2, the powder coating was baked at 180°C for 20 minutes (gel fraction 98%), and the non-aqueous dispersion coating was applied on top of the powder coating, and baked at 150°C for 30 minutes.

The resulting coating film had poor interlayer adhesion and poor physical performance. Example 3 Neopentyl glycol was added to 94.8 parts of a polyester with an acid value of 32, a hydroxyl value of 12, and a number average molecular weight of 2,600, consisting of 384 parts of dimethyl terephthalate, 440 parts of neopentyl glycol, 298 parts of isophthalic acid, and 96 parts of dodecynyl succinic anhydride. 5.2 parts were reacted to give an acid value of 11.5.
A polyester having a number average molecular weight of 48,000 and a softening point of 108° C. was obtained.

To 100 parts of this polyester, 10 parts of hexamethoxymethylmelamine, 2 parts of cyanine blue, and 1 part of 2-ethylhexyl acrylate polymer were added, kneaded, and then ground.
This powder coating was applied to a zinc phosphate-treated iron plate and heated at 150° C. for 10 minutes to obtain a continuous coating film with a gel fraction of 65%. The non-aqueous dispersed metallic paint used in Example 2 was applied to the top surface and baked at 150°C for 10 minutes and at 170°C for 30 minutes to obtain a coating film with excellent interlayer adhesion and coating properties.

Example 4 Isophthalic acid 47.0 equivalent %, ethylene oxide adduct of bisphenol A 34.9 equivalent %, 2-ethyl 1,3
An adduct of 3 moles of hexamethylene diisocyanate and 1 mole of trimethylolpropane to 80 parts of a polyester with a hydroxyl value of 53, a softening point of 92°C, and a number average molecular weight of 2000, consisting of 13.0 equivalents of hexanediol and 5.1 equivalents of glycerin. 20 parts of prolactam prolactam, 7 parts of Epiclon 4050 (manufactured by Dainippon Ink & Chemicals Co., Ltd., a bisphenol type epoxy resin with an epoxy equivalent of 1000), 1 part of dibutyltin dilaurate, and 2 parts of cyanine purulate. The mixture was added, kneaded, and then ground.

The obtained powder coating was applied to a zinc phosphate treated iron plate, and 17
A continuous coating film with a gel fraction of 65% was obtained by heating at 0° C. for 30 minutes. The non-aqueous dispersion metallic paint used in Example 2 was applied to the upper surface, and baked in the same manner as in Example 2. The resulting coating film had excellent interlayer adhesion and coating properties. Example 5 In Example 4, after forming a coating film of powder paint, the following non-aqueous dispersion paint was applied on the top surface, and the following Example 4 was applied.
By baking in the same manner as above, a coating film with excellent interlayer adhesion and coating properties was obtained.

An alkyd resin having a number average molecular weight of 4,000 and consisting of 65 parts of soybean oil, 13 parts of pentaerythritol, and 22 parts of phthalic acid was dissolved in 200 parts of mineral spirits.

Claims (1)

[Claims] 1 The thermosetting powder coating applied to the surface of the object to be coated is heated to form a continuous coating film with a gel fraction of 90% or less, and a non-aqueous dispersion coating is applied on top of the coating and baked. Painting method.