JPH035226B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a coating system suitable for automobiles, bicycles, and other objects to be coated that require corrosion protection and durability. Furthermore, the present invention relates to a coating system that provides an excellent finish in a shortened process. Prior Art In conventional automobile coating systems, etc., in order to shorten the process, the object to be coated is coated with electrodeposition paint and/or powder paint, and then a top coat is sometimes directly laminated. When creating a solid finish with the above-mentioned coating system that ``lays the top coat directly on top of the electrodeposition paint or/and powder paint,'' the top coat may be damaged due to bleeding of the electrodeposition paint or powder paint. There is a phenomenon in which even the film turns yellow. As a way to solve these defects,
Although it is possible to make the yellowing less noticeable to some extent by using a top clear coat as in 60-18223, which is commonly known as a "turbid clear" containing coloring pigments or extender pigments, it is not at a sufficient level. In addition, the problem can be solved by applying a primer such as electrocoating paint and/or powder paint as in the past, and then applying an intermediate coat, but there are problems with the cost, productivity, and economics of the intermediate coat itself, not to mention the painting process. It was a deterioration of sex. Purpose of the Invention The object of the present invention is to prevent the phenomenon of yellowing of the top coat film in a coating system in which a top coat is directly laminated wet-on-wet on top of the base coat. Structure of the Invention The present invention consists of applying an electrodeposition paint or/and powder paint as an undercoat film, a first layer of topcoat with high hiding power, and then a second layer of topcoat with less than normal hiding power. This is a wet-on-wet lamination method to obtain a coating with an excellent finish. The electrodeposition paint used as the undercoat is a known electrodeposition paint containing a conventional pigment in a vehicle such as epoxy resin or blocking isocyanate as a curing agent. This electrodeposition paint has yellowing of the isocyanate itself.
Alternatively, due to volatilization of the isocyanate blocking agent, etc., there is a tendency for yellowing during curing or after coating film formation. On the other hand, powder coating is a well-known powder coating that is made by blending ordinary pigments into a vehicle such as epoxy resin or polyester resin, but this powder coating hardens due to additives used as leveling agents and other yellowing substances. It has a tendency to yellow over time or after film formation. These yellowings have unfavorable effects such as bleeding on the top coat, especially on white or light colored finishes such as pink and yellow. Next, what is important in the present invention is to apply a top coat that has a specific relationship to the hiding power of the two-layer top coat. In the present invention, the hiding power is [second layer top coat]/[first layer top coat] = 1.3 to 3.5. If this ratio is less than 1.3, prevention of yellowing will be insufficient, and if this ratio exceeds 3.5, the hiding power of the second layer will be insufficient or the appearance of the coating will be poor. Furthermore, the hiding power of the first layer top coat is 20 to 40 μ, and the hiding power of the second layer top coat is 40 to 40μ.
It is 70μ. The hiding power in the present invention is determined by the dry film thickness that results in a white/black △E of 0.3 or less when coated on JIS K54006.3 hiding power test paper. The dry hiding film thickness of the first layer top coat with high hiding power is preferably 30μ or less, which has better hiding power than the dry hiding film thickness of 40μ for ordinary solid colors. Further, the top coat of the first layer may have a function of sealing the bleed of the undercoat with high hiding power, and gloss is not necessarily an essential expected property. The vehicle is preferably acrylic resin, polyester resin, or the like. In order to ensure this function, one of the requirements of the present invention is that the first and second layer top coats be made of different resins. The acrylic resin here is an acrylic resin commonly used for automotive metallic bases, etc.
The polyester resin can be a polyester resin commonly used for automobile interior coatings, top coatings, etc., and the molecular weight of acrylic resin is 10,000 to 10,000 in number average molecular weight.
30000th place is preferable. If the number average molecular weight is less than 10,000, the heat reflow properties of the first top coat layer will be too good, and when baked at the same time as the second layer paint, it will melt and cause the first and second layers to melt. The paint causes a "mixing" phenomenon,
If it exceeds 30,000, the leveling of the first layer will deteriorate, causing poor appearance. The curing agent for acrylic resin has a number average molecular weight of 500.
~1500 melamine resin can be used in an amount of 20 to 40%, preferably 25 to 35%, based on the acrylic resin. If it is less than 20%, it will be difficult to obtain the desired coating film strength for the first layer, and if it exceeds 40%, the molecular weight of the melamine resin will be low, and if the wet-on-wet coating that is the object of the present invention is applied, the second layer will be difficult to obtain. Solvents dissolve the melamine resin, resulting in poor appearance, which is undesirable. The molecular weight of polyester resin is the number average molecular weight.
2000 to 3800 is preferable. If the number average molecular weight is less than 2,000, the reflow properties under heat will be too good, resulting in a "mixing" phenomenon similar to acrylic resins, and if the number average molecular weight exceeds 3,800, the reflow properties during heat will deteriorate, which is undesirable. As a means to compensate for the difficulty of using polyester resin, it is also effective to use cellulose, acetate butyrate (hereinafter referred to as CAB), wax, etc. in combination. The curing agent for polyester resin has a number average molecular weight.
Approximately 500 to 1,500 melamine resin is used in an amount of 20 to 50%, preferably 30 to 45%, based on the polyester resin. If it is less than 20%, the curing of the first layer will be insufficient, and if it exceeds 50%, when the second layer is applied wet-on-wet, the melamine resin will swell and the appearance of the paint film will deteriorate, so it is preferable. do not have. Coloring pigments include titanium oxide, carbon black,
Cyanine blue, cyanine green, quinacridone, red iron oxide, yellow iron oxide, isoindolinone, anthrapyridine, quinophthalone, perylene, deoxazine, etc. are used, and to obtain the desired hiding power, for example, titanium oxide is added in the solid content of the paint. The total pigment content is about 45 to 60%, with a few percent of colored pigments added as the main ingredient. The hiding power of the first layer designed in this way is 20 to 40μ in dry film thickness.
It is necessary to cover the base with (the same applies below). Preferably, it is 30μ or less. Other additives such as a solvent and a leveling agent are appropriately blended into this paint. The second layer then needs to be a different resin than the vehicle for the top coat of the first layer. In the present invention, there is no problem if the different resins are acrylic resin/polyester resin or polyester resin/acrylic resin, but there are also cases where there is a difference in curing speed as seen in the following combinations. Permissible. First layer Second layer Polyester resin / CAB Polyester resin Acrylic resin / CAB Polyester resin Polyester resin / CAB Acrylic resin Acrylic resin / CAB Acrylic resin The molecular weight of the polyester resin used for the top coat of the second layer is 1000 in number average molecular weight. ~3000 is preferable. If the number average molecular weight is less than 1,000, the film forming property will be poor and the sag (flow of the coating film) will be low, and if it exceeds 3,000, the appearance will be poor, which is not preferable. The curing agent for polyester resin has a number average molecular weight.
Approximately 500 to 1000 melamine resin is used in an amount of 20 to 60%, preferably 30 to 45%, based on the polyester resin. The number average molecular weight of the acrylic resin used in the top coating of the second layer is preferably 5,000 to 10,000. If the number average molecular weight is less than 5,000, weather resistance will deteriorate, and if it exceeds 10,000, the appearance will deteriorate, which is not preferred. As a curing agent for polyester resins and acrylic resins, melamine resin with a number average molecular weight of about 500 to 1500 is used in an amount of 20 to 40%, preferably 25 to 40%, of the acrylic resin.
35% can be used. If it is less than 20%, curing will be insufficient and coating film strength will not be obtained, and pinholes exceeding 40% may occur, which is not preferable. Titanium oxide, carbon black, cyanine blue, cyanine green, quinacridone, perylene, red iron oxide, yellow iron oxide, isoindolinone, anthrapyrimidine, etc. are used as coloring pigments in the second layer top coat to achieve the desired hiding power. For example, by mixing 30 to 50% titanium oxide and a few percent of other coloring pigments, the hiding power of the base can be increased to 40 to 50%.
Design around 70μ. Other additives such as a solvent and a leveling agent are appropriately blended into this paint. Next, examples of the coating method of the present invention include the following methods. The object to be coated is subjected to a chemical conversion treatment using, for example, a zinc phosphate-based treatment agent, and then an electrodeposition paint or/and powder paint is applied as an undercoat, and then a first layer of topcoat and a second layer of topcoat are applied. 2 coats of wet on wet paint 1 bake (hereinafter referred to as W/W)
Paint with. Since applying the first and second top coat paints W/W is the worst condition for preventing bleeding, this process does not preclude two coats and two bakes. Electrodeposition coating is a so-called electrodeposition coating film of 10 to 50μ,
The powder coating is applied using an electrostatic coating method to form a film thickness of 40 to 150μ. The present invention will be explained in more detail with reference to Examples below.
The present invention is not limited to this range. Paint manufacturing example 1 The compounding amount is weight%

【table】

【table】 Paint manufacturing example 2 Compounding amount is weight%

【table】 Example

【table】

【table】 Paint manufacturing example 3 Compounding amount is weight%

【table】

【table】 Comparative example

【table】

[Table] Evaluation method PGD value Sharpness measuring machine manufactured by Nihon Koken Co., Ltd. Yellowing SM color computer manufactured by Suga Test Instruments Co., Ltd.
△E measurement value according to JIS-Z-8730 using SM-4 After forming a coating film, bake at 180℃ for 30 minutes Hiding power Painted on hiding power test paper of JIS-K5400 6.3, white/black △E 0.3 or less Let be the hidden film thickness. The results of visual appearance are as follows: ◎ Good smoothness and smoothness 〇 〃 Normal △ Slightly poor × Bending and other poor smoothness Effects of the invention Even with a coating system that shortens the process, no bleeding occurs, A coating film with an extremely clear hue was obtained. In addition, a method to shorten the intermediate coating process has been established, so
This invention is industrially highly effective, as it provides many additional benefits such as reducing the price of intermediate paint, reducing the number of painting processes, and improving production efficiency.

Claims (1)

[Scope of Claims] 1. An undercoat is applied on the object to be coated, and then the ratio of the hiding power of the top coat of the two layers is as follows: Hiding power of the top coat of the second layer/hiding power of the top coat of the first layer = 1.3 to 3.5 and a first layer of topcoat with a hiding power of 20 to 40μ, followed by a second layer of topcoat with a hiding power of 40 to 70μ wet on wet. . 2. The anti-yellowing coating method according to claim 1, wherein the first layer uses an acrylic resin and the second layer uses a polyester resin as a vehicle.