JPH03110B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reliably forming a coating film in a uniform chilimen pattern over the entire surface of an object to be coated.

Conventionally, when a coated object is baked and dried in a direct heating drying oven, sometimes it is not possible to obtain a smooth coating, and some coating defects such as crystal or chili-like patterns occur on the coating surface. is known to occur.

This phenomenon is called gas checking, and various studies have been conducted on the causes of gas checking.
This is thought to occur because when sulfur dioxide gas or the like comes into contact with the coating surface, surface hardening is accelerated by the catalytic action of the acidic gas, causing shrinkage due to internal strain in the coating. Additionally, many studies have reported indirect causes such as high humidity, insufficient ventilation, and incomplete pretreatment such as degreasing.

However, research into the causes of gas checking, whether direct or indirect, has been done with the aim of preventing the occurrence of gas checking, which is a defect. There was no idea that this was the case.

The present invention aims to uniformly and reliably generate a matte Chilimen pattern over the entire surface of the object by actively utilizing gas checking, which has traditionally been considered a defect. It was completed as a result of intensive research.

That is, in the present invention, after a thermosetting resin coating containing an inorganic pigment is applied to an object to be coated, the surface of the object to be coated is baked and dried in a heated acidic atmosphere containing 8 ppm or more of hydrogen chloride gas, or It is characterized in that it is brought into contact with the above acidic atmosphere and then baked and dried.

Further, the present invention will be explained in detail. First, the resin paint only needs to be thermosetting, and general thermosetting resin paints such as acrylic resin paint, polyester resin paint, acrylic-melamine resin paint can be used, and inorganic pigments can also be used. Carbon black, lithopone, lead white, yellow iron oxide, zinc white,
Yellow lead, titanium oxide, iron oxide, etc. may be added to the above-mentioned paint, either singly or in an appropriate mixture, depending on the desired color tone.

As described below, the present invention accelerates the curing reaction by bringing an uncured paint film into contact with a heated acidic atmosphere containing 8 ppm or more of hydrogen chloride gas, and forms a warping pattern by utilizing the internal strain of the paint film. However, since the paint of the present invention contains an inorganic pigment, due to the difference in thermal conductivity between the inorganic pigment and the resin,
This causes local differences in the degree of progress of the curing reaction of the paint film, expands the internal distortion of the paint film, and ensures the occurrence of chilimen patterns, and the paint contains inorganic pigments. This is an essential requirement of the present invention. Note that organic pigments do not have much difference in thermal conductivity from resin components, so the above effects cannot be expected.

The thickness of the coating film is not particularly limited, but it is preferably 7 μm or more in order to obtain a clear appearance, and the thicker the coating thickness, the more uneven the chilimen pattern becomes.

Furthermore, as for the coating method, conventionally known methods can be applied, and the above-mentioned paint may be applied by a water-soluble or solvent-based dip coating method, an electrodeposition coating method, an electrostatic coating method, etc.

The object coated in this way is then
It is baked and dried in an acidic atmosphere containing 8 ppm or more of hydrogen chloride gas, or after being brought into contact with the acidic atmosphere, it is baked and dried in a separate baking and drying oven. If hydrogen chloride gas is less than 8 ppm, it will not be possible to reliably form a uniform chilimen pattern coating on the entire surface of the object to be coated, and if carbon dioxide or other acidic gas is used, the chilimen pattern will not be formed on the entire surface. In order to reliably form the acid gas, the acid gas concentration would have to be extremely high, which is not realistic.

Regarding the temperature of the acidic atmosphere, since the method of the present invention utilizes the phenomenon that the paint hardens and causes internal distortion due to contact with hydrogen chloride gas,
It is necessary to set the temperature at least so that the paint hardens.

By the way, it has been found that the temperature at which a paint cures in an acidic gas atmosphere is lower than the temperature at which it cures in a normal atmosphere. For example, in the case of an acrylic-melamine resin paint that begins to harden at 160 to 170°C in a normal atmosphere, it was found that it also hardens at 130 to 140°C in an acidic atmosphere containing 8 ppm of hydrogen chloride gas.

Therefore, when setting the temperature of an acidic atmosphere,
There is no problem as long as the temperature is higher than that at which it hardens in a normal atmosphere.

Also, when baking and drying in an acidic atmosphere, a normal baking and drying temperature is sufficient, and furthermore, there are no special conditions for baking and drying in a separate dedicated baking and drying oven after contact with an acidic atmosphere.

Since the paint hardens quickly, the contact between the surface of the object to be coated and the acidic atmosphere can be instantaneous. However, even if the coating film is brought into contact with an acidic atmosphere after the surface of the coating has been cured in a normal atmosphere, a coating film with a chilimen pattern cannot be formed.

Examples of the present invention will be described below.

Example 1 Aluminum alloy A6063S-T5 material (length 300mm)
After normal pretreatment, sulfuric acid 150g/, 20
Anodic oxidation treatment was carried out for 20 minutes at a current density of 1.5 A/dm ² in an electrolytic bath at 0.degree. C. to form an anodic oxide film of 9 .mu.m. This aluminum alloy A6063S-T5 material was immersed vertically in a white acrylic-melamine resin bath (35% solids concentration, 45% pigment concentration) containing titanium oxide as an inorganic pigment at 60℃ for 3 minutes. It was pulled up at a pulling temperature of 1.8 m/min, and then baked and dried for 20 minutes at 170°C in an electric furnace in an acidic atmosphere with a hydrogen chloride gas concentration of 12 ppm while hanging vertically. A white coating film with a chilimen pattern was produced.

Comparative Example 1 Aluminum alloy A6063S subjected to the same pretreatment, anodizing treatment, and dip painting treatment as in Example 1
-T5 material was baked and dried at 170℃ for 20 minutes in an electric furnace in an atmosphere that does not contain hydrogen chloride gas.
A smooth and glossy coating film was formed on the entire surface.

Comparative Example 2 A vertically suspended aluminum alloy A6063S-T5 material (length 300 mm) subjected to the same pretreatment, anodizing treatment, and dip coating treatment as in Example 1 was placed in an electric furnace in an acidic atmosphere with a hydrogen chloride gas concentration of 6 ppm. 170℃ within
When baked for 20 minutes, approximately 160
A matte chilimen pattern was produced up to mm, but the appearance became uneven with a glossy and smooth coating toward the bottom.

Comparative Example 3 Aluminum alloy A6063S subjected to the same pretreatment, anodizing treatment, and dip painting treatment as in Example 1
When the -T5 material was baked and dried at 170°C for 20 minutes in an electric furnace in a nitrogen dioxide atmosphere with a concentration of 12 ppm, a smooth and glossy white coating was formed on the entire surface.

Similarly, when baking and drying was performed in an electric furnace in an atmosphere containing 12 ppm of nitrogen monoxide, carbon dioxide, and carbon monoxide instead of using nitrogen dioxide, a white coating film with the same appearance as the case with nitrogen dioxide was produced in each case. .

Comparative Example 4 An aluminum alloy A6063S-T5 material subjected to the same pretreatment and anodizing treatment as in Example 1 was immersed in a pigment-free acrylic-melamine resin bath (solid content concentration 20%) at 60°C for 3 minutes. After that, it was pulled up at a pulling speed of 1.8 m/min, and then baked and dried in the same electric furnace as in Example 1, and a glossy clear coating film was obtained.

Example 2 After subjecting aluminum plate A1200P to the same pretreatment and anodizing treatment as in Example 1, a cream-colored acrylic-melamine resin bath (solid) containing titanium oxide and yellow lead as inorganic pigments was added. 35% pigment concentration, 40% pigment concentration) for 3 minutes at 40°C, then pulled up at a pulling speed of 1.0 m/min, and then set the hydrogen chloride gas concentration to 15 ppm and the temperature to 180°C.
When baked for 30 minutes in an electric furnace in an acidic atmosphere set at ℃, a cream-colored coating film with a uniform matte chilimen pattern was obtained.

Comparative Example 5 Aluminum plate material A1200P subjected to the same pretreatment, anodization treatment, and dip coating treatment as in Example 2
was introduced into an electric furnace set at 180°C in an atmosphere that does not contain hydrogen chloride gas, and the aluminum plate material
When the actual temperature of A1200P reached 180℃, hydrogen chloride gas was sent into the electric furnace to make the hydrogen chloride gas concentration 15ppm, and then baked for another 15 minutes. A coating was obtained. The lower limit of curing of the paint used in Comparative Example 5 (same as the paint used in Example 2) in an atmosphere containing 15 ppm of hydrogen chloride gas was measured and found to be 130 to 140°C.

Example 3 An aluminum plate A1200P that had been pretreated, anodized, and dip-painted using the same paint as in Example 2 was treated with hydrogen chloride gas.
After being in contact with an acidic atmosphere at 150°C containing 15ppm for 10 seconds, this aluminum plate A1200P was introduced into an electric furnace that did not contain hydrogen chloride gas and was set at 180°C, and was baked and dried for 30 minutes, which was the same as in Example 2. A chilimen-patterned coating film was obtained.

Example 4 An aluminum alloy A6063S-T5 material subjected to the same pretreatment and anodizing treatment as in Example 1 was immersed in pure water at 80°C for 10 minutes to temporarily seal the holes, then drained and dried, and then used as an inorganic pigment. Black polyester resin paint including bone black (pigment concentration 20
%, viscosity Iwata cup 12 seconds) to obtain a coating film of 10 μm. This aluminum alloy
When the A6063S-T5 material was baked and dried for 30 minutes at 190°C in an electric furnace with a hydrogen chloride gas concentration of 8 ppm, a black coating film with a uniform matte chilimen pattern was formed on the entire surface.

Example 5 An aluminum plate A1200P that had been pretreated and anodized in the same manner as in Example 1 was coated in a white acrylic-melamine electrodeposition paint bath containing titanium oxide as an inorganic pigment (solid content 12%, pigment concentration 25%). %), electrodeposited at 150V for 2 minutes, and then set for 10 minutes. When this aluminum plate material A1200P was baked and dried for 30 minutes in an electric furnace set at 180°C with a hydrogen chloride gas atmosphere at a concentration of 10 ppm, a white coating film with a uniform chilimen pattern that was completely matte was obtained.

As described above, according to the method of the present invention, it is possible to reliably and uniformly form a chilimen-patterned coating film over the entire surface of the object to be coated, and to easily provide the object to be coated with a coating film with a beautiful appearance. It has an effect.

In each of the examples, only aluminum material is used as the object to be coated, but any material can be used as long as it can withstand the baking drying temperature, and the material is not limited to aluminum material.

Claims (1)

[Claims] 1 After applying thermosetting resin paint containing inorganic pigments to the object, the surface of the object is exposed to hydrogen chloride gas.
A method for forming a chilimen pattern coating film, which comprises baking and drying in a heated acidic atmosphere containing 8 ppm or more, or bringing it into contact with the acidic atmosphere, and then baking and drying.