JPH01210083A - Method for applying finishing coating - Google Patents

Abstract

PURPOSE:To reduce unevenness of films to improve brightness and luster, by forming a film composed of setting type paint as a first stage on the surface to be painted, applying setting type paint thereto by nonelectrostatic spray painting, while said film is still in an uncured state, and curing them thereafter. CONSTITUTION:A first-stage film is formed on the surface to be painted by application of setting type paint by electrostatic painting, following which, while said film is still in an uncured state, setting type paint is applied thereto by nonelectrostatic spray painting, and, thereafter, these films are cured to form finishing coat. Surfaces to be coated at a first stage are, for example, electrodeposition coating film, which is formed and baked on a metallic substrate by application of electrodeposition coating of anion or cation type, etc. As a setting type paint to be applied at first and second stage, a thermosetting resin paint composed of a base resin, such as acrylic resin, polyester resin, alkyd resin, etc., and isocyanate compounds is used.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a topcoating method. More specifically, the present invention relates to a top coating method that can form a film with an excellent finished appearance when applied particularly to coatings for automobile exterior panels.

(Prior art and its problems) Conventionally, coatings for automobile exterior panels have been applied by electrocoating using an anionic electrocoating paint or cationic electrocoating paint as an undercoat, or applying an intermediate coat to the electrocoating film. A thermosetting paint is applied using an electrostatic coating machine or a spray coating machine directly onto an undercoat paint film such as a paint film, or onto a film on which a base coat paint film is formed on the undercoat paint film, and then cured. A coating method has been implemented in which a cured film is formed using

The electrostatic coating method atomizes the paint using centrifugal force or compressed air, and at the same time applies a voltage to the mist, thereby imparting an electric charge to the paint particles. Since it can be electrically attached to the surface to be painted, it has advantages such as high adhesion efficiency to the surface to be painted, less paint loss, and good circulation of coating particles to the surface to be painted. It has been widely used since then.

Generally, when a thermosetting paint is applied to a surface to be painted using an electrostatic coating machine, the paint particles flying out from the electrostatic coating machine lose the organic solvent in the particles before being applied to the surface to be coated. It evaporates and changes to a substance with a high solid content and low fluidity, which is then applied to the surface to be coated and the particles are fused and flow even on vertical surfaces, resulting in less coating defects such as sagging. A film can be formed. The coating particles ejected from the electrostatic coating machine have particle sizes within a certain range, and when these particles are applied toward the surface to be coated, the particle size increases in the order of particle size from large to small. Repainting is performed accordingly. The coating is repeated until a predetermined film thickness is reached, but even after the predetermined film thickness has been applied, the coating particles with extremely fine particle diameters that are delayed in coating are themselves charged particles, so they may be scattered to others. It is applied in the form of dust (fine particles dotted) on the surface to be applied. Even during the baking process, the particles are not fused together and are scattered as fine particles on the surface of the coating, and the melt viscosity of the particles is higher than that of the previously formed coating, and there is a gap between the two. This results in a difference in viscosity, resulting in minute irregularities (approximately 0.01 to 1) on the baked-on film, resulting in poor finished appearance such as gloss and brightness.

Today, automotive exterior paints are required to have a mirror-like smooth coating surface (mirror finish), and how to achieve such high appearance quality has become a major issue. In the current top coating line using the electrostatic coating method, as described above, the final appearance of the coating is poor, and a high quality coating has not yet been obtained.

The present invention has been made for the purpose of providing a coating with high appearance quality that solves the above-mentioned problems.

(Means for Solving the Problems) As a result of various studies on methods to solve these problems, the inventor of the present invention formed a film by electrostatically applying a curable paint as the first step, and then It has been discovered that all of the above problems can be solved by non-electrostatic spray coating of a curable paint as a second step, and the present invention has been completed.

That is, in the present invention, a curable paint is electrostatically applied to the surface to be painted to form a film as a first stage, and then, as a second stage, the curable paint is applied in an uncured state while the first stage film is uncured. The present invention relates to a top coating method characterized by curing these coatings after repeated electrostatic spray coating.

In the coating method of the present invention, the surface to be coated in the first stage can be selected without particular limitation. For example, a metal base material may be coated with 7-ion type or cation-type electrodeposition coating. After that, an electrodeposition coating film is baked; an intermediate coating coating is applied on the above electrodeposition coating film and then baked; a metallic coating is a metallic coating applied to the above electrodeposition coating film or intermediate coating coating. Examples include a metallic paint film obtained by applying a metallic coating to the film or the above-mentioned electrodeposition coating film or intermediate coating film and then baking it; a surface to be coated for top coating such as a conductive plastic material.

Specifically, the coating method of the present invention includes 1, for example, using an electrodeposition coating film or an intermediate coating film as the surface to be coated for F coating, electrostatically coating this object with a solid color paint as a first step to form a coating, and then While the film is in an uncured state, a solid color paint is applied as a second layer by non-electrostatic spray coating, or a metallic paint film is used as the surface to be coated for topcoating,
As a first step, clear paint is applied electrostatically to this material to form a film.Next, while the film is uncured, clear paint is applied by non-electrostatic spraying as a second step, and the resulting film is heated. Alternatively, this can be done by simultaneously curing the first and second coats using moisture.

In the coating method of the present invention, the clear paint and solid color paint applied in the first and second stages, and the metallic paint forming the surface to be coated for topcoating, are curable paints whose main vehicle component is a resin that hardens with moisture or heat. Any known resin paint can be used without any particular restriction. Specifically, for example, it is obtained by combining a base resin selected from acrylic resins, polyester resins, alkyd resins, cellulose resins, etc. and a crosslinking agent selected from amine resins, incyanate compounds, polybasic acid compounds, etc. Examples include thermosetting resins containing N-methylol groups, self-thermosetting resins containing N-methylol groups, and moisture-curing resins containing polyisocyanate groups and alkoxysilane groups. Paints containing the above-mentioned thermosetting resin as a vehicle component can be used in any form, either dispersed or dissolved in an organic solvent (including water), and paints containing a moisture-curing resin as a vehicle component can be used in any form other than water. A dispersion or a solution using an organic solvent as a medium can be used.

Furthermore, a metallic paint can be obtained by incorporating an aluminum powder or a burr mica pigment and, if necessary, a coloring pigment into the curable resin, and a solid color paint can be obtained by incorporating a coloring pigment into the curable resin. be able to.

The method of electrostatically coating the metallic paint or solid color paint on the above-mentioned base material for top coating is to apply the diluted paint using, for example, an electric atomizing electrostatic coating machine, a centrifugal force atomizing electrostatic coating machine, an air atomizing electrostatic coating machine, or an air atomizing electrostatic coating machine. Coating can be performed using an electrostatic coating machine such as an airless atomizing electrostatic coating machine. The coating film thickness is approximately l in dry film thickness.
0 to 50 JL, preferably about 20 to 40 p, seems to be sufficient.

Next, the method of non-electrostatic spray painting with clear paint or solid color paint is to set the coating coated using the electrostatic coating machine described above under conditions that do not harden it, and then apply the diluted spray paint to the surface of the coating. Apply non-electrostatic spraying using an air spray or airless sprayer. The setting conditions are such that if the paint sticks to your finger when you press it with your finger, it is considered an uncured film.
At a temperature of 0°C, the time is about 10 minutes or less, preferably 3 minutes or less. The non-electrostatic spray coating has a dry film thickness of about 1 to 20 #L, preferably 5 to 1 OJL. If the paint film thickness is less than about 1W, the gloss and brightness of the paint film will be poor, and in order to improve work efficiency, the output of the paint machine is generally increased and the paint is painted in a short period of time. This increases the amount of uncoated paint, which is economically disadvantageous.

Furthermore, the coating applied using a non-electrostatic spray coating machine is
Usually at a temperature of 0-100°C, preferably 20-80°C,
After setting for about 1-20 minutes, preferably about 5-10 minutes, it is dried and cured at room temperature for 30 minutes or more or at a temperature of 60-160 DEG C. for 10-40 minutes.

The coating method of the present invention is suitably used for articles where finish quality and coating performance are important, such as automobile exterior panels, electrical product exteriors, and the like.

(Effects of the Invention) Conventionally, in the top coating method of the present invention, when a curable coating is applied using an electrostatic coating machine, fine charged coating particles with little fusion or fluidity are coated on the surface of the formed film, This material forms small irregularities on the surface of the film, resulting in a film with poor brightness and gloss, but when a curable paint is applied to this material using a non-electrostatic sprayer, it will fly out from the non-electrostatic sprayer. It is presumed that the coating particles having a relatively large particle size adhere and fuse together to form a thin film, resulting in a film with less uneven surfaces and excellent sharpness and gloss.

Next, the present invention will be explained with reference to Examples, but the present invention is not limited to these Examples in any way.

The coating was performed using a surface-treated steel plate (Bonderite-Br3114, manufactured by Nippon Test Panel) that had been electrodeposited and intermediate coated, with an epoxy cationic electrodeposition coating and a polyester intermediate coating formed in this order. The coating was applied to the surface of the object under the conditions shown in Table 1 and Table 2 using the top coating paint and coating machine shown in Table 1 and Table 2.

Next, the obtained coated board was baked for 140'0-30 minutes to form a cured coating film. The results of the workability of this product are shown in Tables 1 and 2.

The coating machine used for E-coating and its conditions are as follows.

Electrostatic rotary atomization coating machine Mini Be1l: Tarpo G Mini Bell (manufactured by Nippon Landsburg Co., Ltd.) Applied voltage
-90KV Rotation speed 1700 Orpm Electrostatic air atomization coating machine REA gun (manufactured by Japan Ransburg) Applied voltage -60KV Air atomization pressure 4,0 kg/am2 Non-electrostatic air atomization coating machine Air atomization: Large automatic gun LA-70B (Iwata Painting Machine Industry ■) Table -
1 Table-2 Finish evaluation method and standard gloss> 20°Gloss: N Murakami Color Technology Institute type, gloss meter model GM-260. Measurements were made at a specular reflection angle of 20''.

Clearance>D OI: ) Lunter Lab, manufactured by DOR
An IGONQ optical gloss meter was used.

PGD: PGd (Portable Glass
s Distinctness)! A photosensitive tester was used.

1.0 is the upper limit or 0.1 is the lower limit. The higher the value, the better the image clarity. show.

Visual Evaluation> The condition of the painted surface was evaluated visually.

0 No abnormality Δ There are considerable dust-like irregularities on the painted surface.Surface roughness> Ra (center line average roughness): ■Tokyo Seimitsu Surfcom 5
It was measured with a 50A tester.

(Measurement condition) Measurement length 2III11 Pulling speed 0, 06mm/s Magnification 50000 Cutoff O, 16mm

Claims (1)

[Claims] 1. As a first step, a curable paint is applied electrostatically to the surface to be painted to form a film, and then, as a second step, a curable paint is applied by non-electrostatic spraying while the first layer is uncured. A top-coating method characterized by curing these films after applying multiple coats.