JPH0613106B2 - Coating film formation method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for forming a coating film by two coats and one bake, and more specifically, it has an excellent finished appearance and is advantageous in resource saving and pollution control. Regarding the method.

Conventional technology Conventionally, the outer appearance of automobiles, motorcycles, electric appliances, etc., where cosmetic appearance is important, is an organic solvent that forms coating films with excellent coating performance such as smoothness, sharpness, and weather resistance. Finished with diluted thermosetting paint. As the painting method,
Generally, an organic solvent-type thermosetting enamel paint (hereinafter abbreviated as "base coat") containing a coloring pigment and / or a metallic pigment is applied, and after air-drying, an organic solvent-type thermosetting transparent clear paint is repeatedly applied to both coating films. The two-coat one-bake system (hereinafter abbreviated as “2c1b system”) that simultaneously cures the above is mainly used.

However, in recent years, there is a strong demand for improving the appearance of the coating, and various rheology control agents are added mainly for the purpose of smoothing the overcoat coating film, and measures such as polishing the intermediate coating film are taken into consideration. Has been. On the other hand, a high-solid type coating originally developed from the viewpoint of pollution control can easily obtain a film thickness, and its adoption as a clear material is advantageous for improving the appearance, so it is sometimes used in combination with a conventional base coat.

Problems to be Solved by the Invention However, in the method described above, an increase in man-hours due to polishing,
There is a problem that a sufficient improvement in appearance cannot be obtained, and a large amount of an organic solvent is added to the conventional base coat, which is not preferable from the viewpoint of resource saving and prevention of pollution. For this reason, there are base coats that are made into a high solid, but there is a limit to the reduction of organic solvent, and further, there is a drawback that a light-colored metallic such as silver is difficult to obtain a white finish.

Means for Solving the Invention Therefore, in view of the above situation, the present inventors have conducted extensive studies, and as a result, by using a specific water-based paint for the base coat, resource saving and pollution control can be achieved at the same time. In combination with forced drying, we succeeded in obtaining a very smooth and finished white metallic color or solid color base coat coating in a short time.Moreover, by applying top clear and heat curing, the finished appearance is extremely high. It was found that a 2c1b coating film having excellent coating film performance was obtained, and the present invention was completed.

Thus, according to the present invention, a water-dilutable paint containing a metallic pigment and / or a coloring pigment adjusted so that the solid content when applied to an object to be coated is 15 to 40% by weight is applied, and the coating film is applied. Using forced air with a wind velocity of 1 m / sec or more and a temperature of 100 ° C. or less, and forced drying under the condition that the value of wind velocity [m / sec] × temperature [° C.] × time [min] is 500 to 5000 After that, the present invention relates to a method for forming a coating film, which comprises coating a transparent top coating material thereon and heating and curing both of them at the same time.

In the present invention, the "solid content at the time of coating" means the non-volatile content% by weight of the coating film when it is coated on an object by spray coating or the like.
That is, it means the state of the coating liquid, including the effects of various coating machines and various conditions of the coating environment (temperature, humidity, wind speed, etc.).

In the method of the present invention, by using a specific water-dilutable coating material described below as the base coat, since it contains little or no organic solvent, it contributes to resource saving and pollution prevention, and a coating film having a specific solid content. By performing specific warm air drying, the base coat coating film with excellent smoothness and the arrangement of the aluminum pigments is very well arranged even when the aluminum pigments are included, and a transparent top clear layer is applied on top of it. 2c, which is smooth and has a very good finished appearance and excellent coating performance
The feature is that a 1b coating film can be obtained.

The water-dilutable metallic paint or solid color paint used in the present invention has a binder component of water or a water-dispersible resin extender in which a binder resin is dispersed in a mixture of water and a hydrophilic organic solvent, or It comprises a mixture of the water-dispersible resin color developing agent and water or a water-soluble resin color developing agent in which a binder resin is dissolved in a mixture of water and a hydrophilic organic solvent.

Specific examples of the water-dispersible resin color developing agent include acrylic resins. The acrylic resin is prepared by polymerizing an acrylic monomer in the presence of a conventionally known dispersion stabilizer such as a nonionic or anionic surfactant and a water-soluble resin. Examples of the acrylic monomer used for the polymerization include α, β-ethylenically unsaturated carboxylic acids such as acrylic acid and methacrylic acid; methyl (meth)
(Meth) acrylic acid esters such as acrylate, ethyl (meth) acrylate, propyl (meth) acrylate and butyl (meth) acrylate; hydroxyl group-containing (meth) acrylic substances such as hydroxyethyl (meth) acrylate and hydroxypropyl (meth) acrylate Acid ester; polymerizable unsaturated monomers such as styrene, (meth) acrylamide, glycidyl methacrylate, vinyl acetate, and the like.

In addition, according to the multi-stage polymerization method, first, a monomer containing no or a small amount of α, β-ethylenically unsaturated acid is polymerized, and then a monomer containing a large amount of α, β-ethylenically unsaturated acid is copolymerized. A multi-stage polymerized emulsion obtained by polymerization is mentioned. The multi-stage polymerized emulsion thickens by being made alkaline, which is particularly desirable for the purpose of the present invention.

Next, as the water-soluble resin used in combination with the above-mentioned water-dispersible resin color developing agent, a conventionally known one is used, and in principle, a hydrophilic group sufficient to solubilize the resin, for example, a carboxyl group (- COOH), hydroxyl group (-OH), methylol group (-
CH ₂ OH), amino group _(-NH 2), sulfone group (-
SO ₃ H), polyoxyethylene bond The most common ones are those in which a carboxyl group is introduced and an alkali salt is made to be water-soluble. The amount of carboxyl groups that can be water-soluble varies depending on the skeleton of the resin, the content of other hydrophilic groups, the type of neutralizing agent, and the neutralization equivalent, but an acid value of at least 30 is required. The water-soluble resin is completely water-solubilized by being neutralized with an alkaline substance such as sodium hydroxide or amine.

Specific examples of the water-soluble resin include acrylic resin-based resin,
Examples thereof include alkyd resin type and epoxy resin type. As the acrylic resin system, (meth) acrylic acid ester having a functional group such as α, β-ethylenically unsaturated carboxylic acid, hydroxyl group, amide group and methylol group, and other (meth) acrylic acid ester, styrene, etc. Acid value of 30 to 100 and hydroxyl value of about 20
~ 200 can be mentioned. The raw material of the alkyd resin is the same as that of a conventional solvent type alkyd resin, and it is obtained by subjecting a polybasic acid, a polyhydric alcohol and a modified oil to a condensation reaction by a conventional method. As the epoxy resin system, a method of synthesizing an epoxy ester by reacting an epoxy group with an unsaturated fatty acid and adding an α, β-unsaturated acid to the unsaturated group, a hydroxyl group of the epoxy ester, a phthalic acid or a tricarboxylic acid Examples thereof include epoxy ester resins obtained by a method of esterifying a polybasic acid such as mellitic acid.

The mixing ratio of the water-dispersible resin color developing agent and the water-soluble resin color developing agent is 100/0 to 60/4 in terms of solid content weight percentage.
The range is 0, preferably 95/5 to 75/25. If it is out of this range, the hot air drying property will be poor, and it will be difficult to obtain a sufficient finish even after top clear coating.

The water-dilutable paint used in the present invention, in addition to the binder,
As the cross-linking agent, an amino resin obtained by condensation or co-condensation of melamine, benzoguanamine, urea or the like with formaldehyde is used. Further, as the pigment, a coloring pigment, a metallic pigment, an extender pigment and the like which are usually used in the field of paints are blended. In addition, a small amount of hydrophilic organic solvent is used to disperse the pigment. Further, an organic or inorganic thickener may be used for the purpose of preventing unevenness and sagging.

As the transparent top clear used in the present invention, conventionally known ones are used, and specifically, for example, amino alkyd resin, acrylic resin, amino acrylic resin, amino oil free alkyd resin, silicone polyester resin, fluororesin, urethane. Resin-based paints are examples. From the viewpoint of preventing pollution, a high solid type is preferable, and a powder coating can be used.

Specific embodiments of the method of the present invention are as follows, for example.

1) The solid content at the time of application of the water-dilutable coating composition having the above composition is adjusted by using deionized water to a value 1 to 5% lower than the target solid content at the time of application, and the solid content at the time of spray application is adjusted. Minutes. If necessary, add a thickener to increase the viscosity to 2000-60.
After adjusting to 00cps / 6rpm, B type viscometer,
Spray coating is performed so that the dry film thickness is 0 to 40 μm. If the solid content at the time of coating is less than 15% by weight, the hiding power is poor, and if it exceeds 40% by weight, a smooth coating film cannot be obtained.

2) Then, in the forced drying, using a warm air with a wind speed of 1 m / sec or more and a temperature of 100 ° C. or less, the wind velocity [m / sec]
Forced drying is performed under the condition that the value of × temperature [° C.] × time [minute] satisfies 500 to 5000. If the above value is 500 or less, cracking, deterioration of gloss, and unevenness in the subsequent steps are caused. On the other hand, when it is 5,000 or more, the surface of the base coat surface has unevenness, unevenness, and the object to be coated is not completely cooled, which hinders clear coating in the next step.

3) Then, the transparent top clear is applied repeatedly by electrostatic spray coating so as to have a dry film thickness of 20 to 50 μm.

4) 120 ~ 15 after making the usual settings
Heat at 0 ° C. for 30 to 20 minutes to obtain a cured coating film.

Effect and Effect of the Invention In the 2c1b coating film forming method of the present invention, the solid content of the base coat at the time of application is adjusted to 15 to 40% by weight, and the wind speed is 1 m.
/ M 2 or more and warm air with a temperature of 100 ° C or less is used.
/ Sec] x temperature [° C] x time [min] is 500 to 500
By drying at 0, a base coat coating film having an extremely large volume shrinkage can be efficiently obtained. That is, since the volumetric shrinkage is large, the unevenness of the coating surface generated at the time of coating is extremely smoothed, and at the same time, the metallic pigment such as aluminum is arranged more parallel along the object to be coated,
A very smooth and bright coating is obtained. Also, by adopting the drying conditions, without impairing the finish,
Since the desired volumetric contraction can be obtained efficiently, it is extremely effective in terms of coating line space and production efficiency in continuous production of automobiles, home appliances and the like.

In addition, conventional solvent-based base coats required a large amount of organic solvent at the time of coating, rather than clear paint, due to restrictions in spraying workability, but by making this base coat aqueous, the amount of organic solvent used can be reduced. Can be significantly reduced,
It is extremely effective in saving resources and preventing pollution.

EXAMPLES The present invention will be described based on examples. In addition, a part and% show a weight part and weight%.

[Preparation of sample]

1. Preparation of coating object Electron No. 9200 (Kansai Paint Co., Ltd., epoxy resin-based cationic electrodeposition coating) is electrodeposited on a steel plate surface-treated with Bonderite # 3030 (Nihon Parker Rising Co., Ltd., zinc phosphate treatment). , Amilak N on it
-2 Sealer (Aminopolyester resin-based intermediate coating manufactured by Kansai Paint Co., Ltd.) was used.

2. Manufacture of aqueous resin for base coat 1) Manufacture of acrylic resin water dispersion (W-1) In a reaction vessel, 113 parts of deionized water, 30% Newcol 707SF (surfactant, manufactured by Nippon Emulsifier Co., Ltd.), 5 parts, 5% excess 10 parts of an ammonium sulfate aqueous solution and 20 parts of the following monomer mixture are added and heated to 75 ° C.

Then 80 parts of the following monomer mixture is added over 2 hours using a metering pump. After the addition was completed, the mixture was aged at 75 ° C. for 1 hour, and then passed through a nylon cloth of 200 mesh at 30 ° C. to pass it. The obtained aqueous dispersion had a nonvolatile content of 44% and a glass transition temperature (Tg) of 41 ° C. Deionized water was further added to this product and the pH was adjusted to 7.5 with dimethylaminoethanol to obtain 40% acrylic resin water foot solution W-1.

Monomer mixture Methyl methacrylate 50 parts Styrene 10 Butyl acrylate 27 Acrylic acid 3 2-Hydroxyethyl methacrylate 10 2) Production of acrylic resin water dispersion (W-2) In a reaction vessel, 140 parts of deionized water, 30% Newcol70
2.5 parts of 7SF and 1 part of the following monomer mixture (1) were added,
Stir and mix in a nitrogen stream and add 3 parts of 3% ammonium persulfate at 60 ° C. Then, after raising the temperature to 80 ° C., 99 parts of the following monomer mixture (1), 30% Newcol 70
A monomer emulsion consisting of 2.5 parts of 7SF and 4 parts of 3% ammonium persulfate and 42 parts of deionized water is added to the reaction vessel using a metering pump over 4 hours. After the addition is completed, aging is carried out for 1 hour.

Furthermore, the following monomer mixture (2) was added to the reaction vessel at 80 ° C. over 1.5 hours, aged for 1 hour after the addition was completed, and passed through a nylon cloth of 200 mesh at 30 ° C. Deionized water was added to this, and the pH was adjusted to 7 with dimethylaminoethanol.
It was adjusted to 5 to obtain a 20% acrylic resin aqueous dispersion W-2 having a Tg of 46 ° C.

Monomer mixture (1) Methyl methacrylate 55 parts Styrene 10 n-Butyl acrylate 9 2-hydroxyethyl acrylate 5 Methacrylic acid 1 Monomer mixture (2) Methyl methacrylate 5 parts n-Butyl acrylate 7 Acrylic acid 2-Ethylhexyl 5 Methacrylic acid 3 30% Newcol 707SF 0.5 3% Ammonium persulfate aqueous solution 4 Deionized water 30 3) Production of acrylic resin aqueous solution (W-3) 60 parts of butyl cellosolve and 15 parts of isobutyl alcohol were added to a reaction vessel in a nitrogen stream. Warm to 115 ° C. When the temperature reached 115 ° C, 26 parts of n-butyl acrylate,
A mixture of 47 parts of methyl methacrylate, 10 parts of styrene, 10 parts of 2-hydroxyethyl methacrylate, 6 parts of acrylic acid and 1 part of azoisobutyronitrile is added over 3 hours. After completion of the addition, the mixture was aged at 115 ° C. for 30 minutes, a mixture of 1 part of azobisisobutyronitrile and 115 parts of butyl cellosolve was added over 1 hour, and then aged for 30 minutes.
Pass with 200 mesh nylon cloth at ℃.

The acid value of the obtained reaction product was 48, the viscosity was Z ₄ (Gardner foam viscometer), the nonvolatile content was 55%, and the Tg was 45 ° C.
This was neutralized with dimethylaminoethanol in an equivalent amount, and deionized water was further added to obtain a 50% acrylic resin aqueous solution.

3. Manufacture of base coat 1) Manufacture of aqueous metallic paint M-1 Acrylic resin aqueous dispersion W-2 275 parts Acrylic resin aqueous solution W-3 40 Cymel 350 25 (Mitsui Toatsu Chemicals, Inc., amino resin) Aluminum paste AW-500B 20 (Asahi Kasei Metals Co., Ltd.) Butyl cellosolve 20 Deionized water 253 was mixed, and Tikusol K-130B (a thickener manufactured by Kyoeisha Oil and Fat Chemical Co., Ltd.) was added, and adjusted to 3000 cps with a B-type viscometer (rotor rotation speed 6 rpm). Thus, an aqueous metallic paint M-1 was obtained.

2) Production of Aqueous Metallic Paint M-2 Water-based metallic paint M-2 was obtained by further adding 507 parts of deionized water to the above aqueous metallic paint M-1 and adjusting the viscosity in the same manner.

3) Manufacture of water-based metallic paint M-3 Acrylic resin water dispersion W-1 137.5 parts Acrylic resin aqueous solution W-3 40 Cymel 350 25 Aluminum paste AW-500B 20 Butyl cellosolve 20 Deionized water 43 is mixed, and Chikusol K-130B. Was added and the viscosity was adjusted to 2500 cps with a B-type viscometer (rotor rotation speed 6 rpm) to obtain an aqueous metallic paint M-3.

4) Production of Aqueous Metallic Paint M-4 To the above aqueous metallic paint M-3, 40 parts of deionized water was added, and the viscosity was adjusted in the same manner to obtain an aqueous metallic paint M-4.

5) Manufacture of water-based metallic paint M-5 Acrylic resin aqueous dispersion W-2 225 parts Acrylic resin aqueous solution W-3 60 Cymel 25 Aluminum paste AW-500B 20 Butyl cellosolve 20 Deionized water 283 is mixed, and the viscosity is adjusted in the same manner as the preceding paragraph. Thus, an aqueous metallic paint M-5 was obtained.

6) Manufacture of aqueous white enamel paint S-1 Acrylic resin aqueous solution W-3 40 parts Titanium white 100 butyl cellosolve 20 is dispersed by a pebble mill to 5 μ or less, and acrylic resin water dispersion W-2 275 Cymel 350 25 deionized water 111 Was added and the viscosity was adjusted to 2500 cps in the same manner as in the previous section to obtain an aqueous white enamel paint S-1.

4. Manufacture of top coat 1) Manufacture of top coat T-1 <Manufacture of acrylic resin for top coat> 25 parts of methyl acrylate, 25 parts of ethyl acrylate
Parts, n-butyl acrylate 36.5 parts, 2-hydroxyethyl acrylate 12 parts, acrylic acid 1.5 parts and a polymerization initiator (α, α′-azobisisobutyronitrile) were used for polymerization in xylene to obtain a resin solid content. A 60% acrylic resin solution was obtained. The resin had a hydroxyl value of 58 and an acid value of 12.

This resin and U-Van 20SE (manufactured by Mitsui Toatsu Chemicals, Inc., n-
Butylated melamine resin) is mixed at a solid content ratio of 75/25, and the viscosity is adjusted to 25 seconds (Ford cup No. 4/20 ° C.) with an organic solvent (Swazol # 1500) and top coat T-1 is added. Got

2) Manufacture of top coat T-2 Melamine resin of the above top coat T-1 (U-Van 20
Duranate 24A (made by Asahi Kasei Corporation) instead of SE)
Hexamethylene diisocyanate water adduct)
The mixture was mixed so that H / NCO = 1/1 (molar ratio), and the viscosity was adjusted in the same manner to obtain Top Clear T-2.

3) Production of Topcoat T-3 20 parts of styrene, 43 parts of methyl methacrylate, 18 parts of n-butyl acrylate, 3 parts of ethyl acrylate, 13 parts of glycidyl methacrylate, 3 parts of hydroxyethyl methacrylate and 100 parts of toluene. The mixture was put into a three-necked flask equipped with a stirrer and a reflux condenser, 1.5 parts of benzoyl peroxide was added thereto, and the contents were heated to a temperature of 90 to 100 ° C. After maintaining at this temperature for 3 hours, 2 parts of benzoyl peroxide was further added and maintained at the above temperature for 4 hours to complete the copolymerization. The copolymer thus obtained was allowed to cool and solidify, and then pulverized by a pulverizer into fine particles that passed through a 6-mesh sieve to prepare an acrylic resin powder.

The above blend was melted and kneaded at about 100 ° C. for 10 minutes with a heating roll, cooled, and then finely pulverized to a particle size of 20 to 100 μ to produce a top coat T-3.

Examples 1 to 7 and Comparative Examples 8 to 13 The base coat and the top coat obtained as described above were applied to an object to be coated under the following conditions. Table 1 shows the performance test results of the obtained coating films. The conditions such as the drying condition, the baking condition, the solid content at the time of coating, and the film thickness were in accordance with Table 1.

Spray gun: Devilbiss JGA502 Air pressure: 5Kg / cm ² Gun distance: 35cm Painting booth temperature: 25 ℃ 〃 Wind speed: 0.5m / sec 〃 Humidity: 70%

Claims (1)

[Claims] 1. A solid content of 15 to 4 when applied to an object to be coated.
Metallic pigment adjusted to be 0% by weight and /
Alternatively, a water-dilutable coating material containing a coloring pigment is applied, and the coating film is heated at a wind speed of 1 m / sec or more with warm air having a temperature of 100 ° C. or less,
And the value of wind speed [m / sec] x temperature [° C] x time [min] is 5
A method for forming a coating film, which comprises performing forced drying under the condition of satisfying the condition of 0 to 5000, and then applying a transparent top-coat paint thereon and heating and curing both at the same time.