JPS5843152B2 - metallurgy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-coat metallic finish coating method that is highly aesthetically pleasing.

Paint finishes using solvent-free powder coatings are extremely effective in preventing pollution, and their use is rapidly expanding in recent years.

The electrostatic coating method is universally used as a powder coating method, and with this method, it is possible to apply a thick coat of approximately 50μ or more in one coat, and the uncoated powder coating can be collected. It has the advantages of being easy, reducing paint loss, and being economical.

However, in the case of powder coatings containing metal powder (for example, aluminum powder) or metal powder and colored pigments, the difference in the amount of charge between the metal powder and the resin that forms the film, and the melt viscosity of the powder coating Due to the uneven orientation of the metal powder in the film caused by the high temperature, it is extremely difficult to achieve the same metallic feel as conventional solution-based metallic paints using electrostatic coating methods, and the paint is still at a stage where it can be put to practical use. not reached.

The so-called 2nd method involves applying a solution-type undercoat containing metal powder, then applying a layer of transparent powder paint and then curing it by heating.
In the metallic finishing method using the one-coat one-bake method, the powder coating is often painted and baked with a considerable amount of volatile components remaining in the undercoat film, resulting in bubbles (foaming) in the finished paint film. There are still various problems that need to be solved with metallic finish coatings using powder coatings, such as defects such as rough skin, yellowing, and metallic unevenness.

As a result of intensive research in order to improve the above-mentioned defects, the present inventor used a thermosetting paint containing a foil pigment as an undercoat, and after painting, the volatile component content in this paint film was reduced to 6% (by weight). , hereinafter the same) If the following conditions are applied, the above-mentioned defects will not occur even if the thermosetting transparent powder coating (hereinafter referred to as top coat) is applied and cured by heating, and the metallic feel and durability will not be affected by the above two points. We have discovered that scales not only provide a much superior coating film compared to the one-to-one bake metallic finish, but also improve the top coat application efficiency.
The present invention has now been completed.

That is, the present invention applies a foil pigment or a thermosetting paint containing a foil pigment and a coloring agent (hereinafter referred to as base coat) to an object to be coated, and then heats it to reduce the volatile component content in the coating film to 6. % or less, then a top coat is applied and baked, and both coating films are simultaneously cured.

The volatile components in the base coat film mainly consist of solvents, diluents, etc., and the content thereof is determined by the following measurement and calculation method.

First, apply a base coat diluted to a paintable viscosity to a diameter of 60 mm, depth of 15 mm, and weight of approximately 101 mm. Tin plate or diameter 601nrIt, depth 1811Lrft
・About 29 samples were collected and weighed into an aluminum dish weighing approximately 1.51 cm, poured into a thin film, spread, and then placed in a dryer kept at 150±2°C and heated for 60 minutes.

Next, remove the plate from the dryer and dry it in a dessicator for about 60 minutes.
After cooling for 0 minutes, it was weighed, and the heating residue Ro (
%).

However, A: Weight of the sample after heating S') S: Weight of the sample before heating 2) The volatile component content in the diluted base coat is determined by subtracting Ro from 100.

The above heating conditions are intended to drive out all of the volatile components in the base coat, but the heating conditions are such that some of the volatile components in the base coat remain. (%) In this case Rn>
Ro) and the volatile component content is (%). Therefore, in order to apply a base coat of heating residue Ro and bring the volatile component content in this coating to the range set in the present invention, The heating residue Rn of the diluted base coat under several heating conditions is determined in advance by the method described above, and the heating conditions (temperature and time) such that ■ is 6% or less are first determined by the above formula.

Next, using the actual object to be coated and a heating device (drying oven),
Measure the surface temperature of the object to be coated under specified heating conditions, and check whether the surface temperature and its holding time match or approximate the specified heating conditions.

If there is a difference between the heating conditions and the prescribed heating conditions, further correction is made through trials, and the heating conditions for the actual object to be coated that approximate the heating conditions determined in the laboratory are determined. It can be applied to heating after applying the base coat.

The foil-like pigment blended into the base coat in the method of the present invention is a metallic pigment or a non-metallic pigment having a fine scale-like, foil-like, or strip-like external shape, and includes, for example, aluminum powder (non-leafing). mold or leafing mold), bronze powder, copper powder, mica powder, modified mica powder (e.g. mica powder with a thin film of titanium oxide deposited)
, foil-shaped iron oxide powder, etc. are used.

In addition to these foil pigments, a small amount of coloring agents such as inorganic pigments, organic pigments, and dyes used in ordinary paints may also be used.

Further, as the thermosetting resin that is a film-forming component of the base coat, any thermosetting resin that is blended into ordinary solution-type resin coatings and dispersion-type resin coatings can be used without any problem.

An example of 2.3 is organic solution type thermosetting acrylic.
There are amino resins, water-soluble thermosetting acrylic/amino resins, non-water dispersible acrylic/amino resins, oil-free polyester emulsions/amino resins, acrylic copolymer emulsions/amino resins, etc.

A base coat is made by blending a foil pigment, a coloring agent, an additive, etc. into a liquid containing the above-mentioned thermosetting resin. Usually, the foil pigment is added to 10 parts (by weight, hereinafter the same) of resin. ~
A ratio of 30 copies will be adopted.

The top coat in the present invention is a powder coating whose main component is a thermosetting resin powder (which may also contain a crosslinking agent or a curing agent), and which contains colorants, additives, etc., if necessary. Examples 1.2 include those in which a thermosetting acrylic resin or a thermosetting polyester resin is used as a film-forming component.

Among these, for example, acrylic top coats include vinyl monomers having glycidyl or hydroxyl groups as functional monomers (e.g., glycidyl methacrylate, glycidyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, etc.) , a copolymer resin with a glass transition temperature of 40 to 70°C using an alkyl ester of acrylic acid or methacrylic acid, styrene, etc. as a non-functional monomer, and a polyhydric carboxylic acid, blocked isocyanate, or melamine/formaldehyde condensate as a curing component. Combined with
It is made by adding surface conditioners, anti-scratch agents, etc.

If desired, a topcoat with added colorant may also be applied to the method of the invention.

To obtain a colored and transparent top coat, use organic pigments, inorganic pigments, or dyes used in ordinary paints within a range that does not impair the metallic feel of the finished film when applied over the base coat film. Then, you can adjust the amount.

The coating method of the present invention can be easily carried out as follows.

First, adjust the base coat to a viscosity of 10 to 30 seconds with a specified thinner (Ford Cup #4, 20°C, the same measurement conditions apply for the following viscosities and seconds), and apply this to the unpainted surface. An object to be coated (for example, a steel plate or an aluminum plate) or an object to which a primer has been applied in advance is undercoated by spray coating or electrostatic coating to form a wet coating film to a dry film thickness of 10 to 40 μm.

After leaving this at room temperature for several minutes, use a hot air drying oven, infrared oven, or far infrared oven to determine the content of volatile components in the undercoat film using the method described above so that it is 6% or less. Heating is performed by applying the heating conditions for the coated object.

Immediately after heating, apply a top coat of 50 to 150
Electrostatically coated to a coating thickness of μ, then 160 to 22
Bake at 0 DEG C. for 45-15 minutes to simultaneously cure both the base coat and top coat to provide the metallic finish desired by the present invention.

If the content of volatile components in the undercoat film exceeds 6%, if a top coat is applied and baked on top of this film, it will cause wrinkles regardless of the type of base coat, loss of metallic feel, and damage to the skin. This is not desirable as it may cause such problems.

In the present invention, the content of volatile components in the base coat film is measured and calculated using the method described above, and the heating conditions for the undercoat are set in advance for the actual object to be coated, thereby achieving high efficiency in a continuous coating line. , a metallic paint finish with excellent aesthetics can be achieved.

In other words, powder coating on a base coat that still contains some volatile components improves the top coat's application efficiency, and baking hardens the base coat and top coat simultaneously, making it easier to use on the painting line. It is also possible to save labor.

Hereinafter, a detailed explanation will be given with reference to Examples and Comparative Examples.

All parts and percentages are by weight. Example 1 (a) Production of base coat A As a dispersion stabilizer, a graft product of polyto-2-hydroxystearic acid and methacrylic acid copolymer was mixed with vinyl monomers (30% styrene, 30% methyl methacrylate).
, a mixture consisting of 23% 2-ethylhexyl acrylate, 15% hydroxyethyl acrylate, and 2% acrylic acid)
A non-aqueous dispersion resin liquid was prepared in n-pentane using 210% of the resin.

The resin content of this resin liquid was 60%, and the degree of dispersion was 20%.

Using this non-aqueous dispersion resin liquid, paste aluminum powder was dispersed in the following formulation, and the heating residue was 60%.
Basecoat A was produced.

When base coat A is diluted with a thinning solution (a mixture of 40 parts of petroleum-based aliphatic hydrocarbon solvent, 50 parts of ethylene glycol monoethyl ether acetate, and 10 parts of diethylene glycol monoethyl ether acetate), the heating residue Ro is 45 It was .4%.

This diluted base coat) A was dried in a hot air drying oven (manufactured by Saga Chemical Industry Co., Ltd., with an air velocity of 0 in the oven) using the heating residue measurement method described above.
．． 5 to 1.0 m/see) at 170°C.
The heating residue Rn after heating for 0 minutes was 47.6%, and the volatile component content was 4.6%.

In addition, base coat A diluted to the above viscosity was heated using a far-infrared heater (Infrajet, manufactured by JARD Co., Ltd.) at a distance of 12 to 13 cr, IL1, voltage of 90 to 100 V, using a far-infrared heater (manufactured by JARD Co., Ltd., Infrajet) according to the heating residue measurement method described above. 3 with conditions
The heating residue Rn after heating for one minute was 46.1%, and the volatile component content was 1.5%.

(b) Production of top coat Styrene 2 Qq, 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, Add 1.5 parts of benzoyl peroxide to a three-bottle flask equipped with a stirrer and a reflux condenser, and bring the temperature of the contents to 90-10.
It was heated to 0°C.

After maintaining this temperature for 3 hours, 2 parts of benzoyl peroxide was further added and the temperature was maintained for 4 hours to complete the copolymerization.

Next, a cooling tube was installed so that the cooled and condensed solvent flowed out of the flask, and stirring was continued while heating at an external temperature of 120 to 140°C, thereby removing about 60% of the doluol.

After that, the pressure inside the flask was reduced to about 200 mmHg,
The external temperature was raised by 1 to 140 to 150°C, and the remaining doluol was almost completely distilled off.

After the copolymer thus obtained was allowed to cool and solidify,
Acrylic resin powder was prepared by pulverizing it into fine particles that could pass through a 6-mesh sieve using a pulverizer.

The above mixture was melted and kneaded at about 100 DEG C. for 10 minutes using heated rolls, and after cooling was ground to a particle size of 20 to 100 .mu.m to produce a 7''r-t.

f'→ Paint Surface-treated steel plate with epoxy ester resin electrodeposition primer (Nileclone A1200 primer manufactured by Kansai Paint Co., Ltd.) (JIS G3310 steel plate subjected to zinc phosphate chemical conversion treatment, 300 words 90XO, g'= ) on top of Boehmeco A diluted to a viscosity of 14 seconds with the thinner used in (a), using an air spray gun (Binks JGA502) in a painting booth at room temperature of 25°C, to measure the dry film thickness. The coating was applied so that the thickness was 15 to 25μ.

After this was left at room temperature for 2 minutes, it was heated at 170° C. for 10 minutes in a hot air drying oven (same as the one used in (a)), and the volatile component content in the coating film of BaseCo) A was adjusted to 5%.

Immediately, a top coat was applied over the top coat using an electrostatic spraying machine (Sames Co., Ltd., Starjet) while applying 80 KV to give a dry film thickness of 60 to 80 μm.

Then baked at 180℃ for 25 minutes in a hot air drying oven.
Both the base coat and top coat were cured simultaneously.

The coating film thus obtained was completely free of coating defects such as flaking, yellowing, and rough skin, had an excellent metallic feel with a rich texture, and had good gloss and sharpness.

The test results are shown in Table 1.

Comparative Example 1 Base coat) A ((a) of Example 1) was applied to a surface-treated steel plate coated with an electrodeposition primer similar to that of Example 1, according to the coating method of Example 1. After coating, it was left at room temperature for 2 minutes, heated at 150° C. for 10 minutes, and then a top coat ((b) of Example 1) was applied and baked.

The resulting coating film had wrinkles, had a slightly low gloss, and was poor in metallic feel and texture.

The test results are shown in Table 1.

Incidentally, after heating basecoe) A diluted to a viscosity of 14 seconds at 150°C for 10 minutes using the heating residue measurement method described above, the heating residue Rn was 4962%, and the volatile component content was 7.
It was 7%.

The volatile component content of the coating film on the steel plate is estimated to be about 8%.

Example 2 Base coat A ((a) of Example 1) was applied on a surface-treated steel plate coated with an electrodeposition primer similar to (/→ of Example 1) according to the coating method of ←→ of Example 1. Painted.

Next, using a far-infrared heater (same as the one used in (a) of Example 1), the distance between the heating element and the object to be coated was 12 to 13 cm.
It was heated for 3 minutes under the conditions of IfL and voltage of 90 to 100 V to bring the content of volatile components in the coating film of BASECO) A to 2%.

Immediately apply a top coat ((b) in Example 1) on top of this.
Electrostatic coating was performed under the same coating conditions as ←→ in Example 1, and 180
Both the basecoat and topcoat films were cured simultaneously by baking at 0C for 25 minutes.

The finish of the coating after baking is the same as in Example 1 (
It had no coating defects and had an excellent metallic feel, solid feel, sharpness, and gloss.

The test results are shown in Table 1.

Example 3 (a) Production of base coat B A water-dilutable base coat B with a heating residue of 48% was produced by dispersing paste-like aluminum powder in the above-mentioned formulation.

When BaseCo) B was diluted with a diluted solution consisting of 80 parts of deionized water and 20 parts of diethylene glycol monobutyl ether to a viscosity of 26 seconds, the heating residue RO was 39.9%.

The heating residue R after heating this diluted base coat) B at 150°C for 10 minutes using the heating residue measurement method described above.
n was 41.8%, and volatile component content was 4.5%.

In addition, basecoe) B diluted to the above viscosity was heated using a far-infrared heater (the same as that used in (a) of Example 1) and the distance between the heating element and the device according to the heating residue measurement method described above. 3 under the conditions of 12-13crrL, voltage 90-1oov
The heating residue Rn after heating for minutes was 41.7%, and the volatile component content was 4.3%.

(B) On a surface-treated steel plate coated with an electrodeposition primer similar to f'→ in Coating Example 1, basecoe) B diluted to a viscosity of 26 seconds with the same thinner as in (A) above was applied using an air spray gun ( Using Hinx JGA502), the room temperature is 25℃ and the humidity is 5.
The coating was carried out in a coating booth at 0% RH to give a dry film thickness of 15 to 25 μm.

After leaving this at room temperature for 5 minutes, dry it for 15 minutes using a hot air drying oven.
It was heated at 0° C. for 10 minutes, and the content of volatile components in the coating film of BASECO) B was set to 5%.

On top of this, a top coat ((b) of Example 1) was immediately electrostatically applied under the same coating conditions as in Example 1, and the temperature was 180°C.
The base coat and top coat were cured at the same time by baking for 25 minutes.

The coating film thus obtained was completely free of metallic unevenness, which is a drawback of water-soluble metallic paints, and had excellent metallic feel, texture, and sharpness and gloss.

The test results are shown in Table 1.

Comparative Example 2 Base coat) B ((/f) of Example 3 was applied to a surface-treated steel plate coated with an electrodeposition primer similar to that of Example 1, according to the coating method of (B) of Example 3. ) was applied, left at room temperature for 5 minutes, heated at 130° C. for 10 minutes, and then a top coat ((b) of Example 1) was applied and baked.

Yellowing of the armpits was observed in the resulting coating film, and the gloss, metallic feel, and texture were also inferior to the finished coating film of Example 3.

The test results are shown in Table 1.

Note that after heating base coat B diluted to a viscosity of 26 seconds at 130° C. for 10 minutes using the heating residue measuring method described above, the heating residue Rn was 43.6%, and the volatile component content was 8.
It was 5%.

The volatile component content of the coating film on the steel plate is estimated to be about 9%.

Example 4 Base coat) B ((a) of Example 3) was applied on a surface-treated steel plate coated with an electrodeposition primer similar to that of Example 1 according to the coating method of (b) of Example 3. After coating and leaving it at room temperature for 5 minutes, using a far-infrared heater (same as the one used in (a) of Example 1), heat it for 3 minutes under the same conditions as Example 2 to determine the amount of paint in the coating film of Base Coat) B. The volatile component content was 5%.

On top of this, a top coat ((b) of Example 1) was immediately electrostatically applied under the same coating conditions as in Example 1, and the temperature was 180°C.
Baking was carried out for 25 minutes to cure both the base coat and top coat' at the same time.

As in Example 3, the resulting coating film was free from metallic unevenness and had excellent metallic feel, solid feel, and sharpness and gloss.

The test results are shown in Table 1.

Claims (1)

[Claims] 1 After applying a foil-like pigment or a thermosetting paint containing a foil-like pigment and a coloring agent to an object to be coated, heating is performed to reduce the content of volatile components in the coating film to 6% by weight or less, and then a thermosetting transparent coating is applied. A metallic finish coating method characterized by applying a top coat of powder coating and baking it, curing both coatings at the same time.