JPS6249973A - Formation of coated film - Google Patents

Abstract

PURPOSE:To shorten work period so as to reduce the cost of painting and to eliminate the inter-layer exfoliation by dirt by coating a two-liquid reaction type primer coat on a surface to be coated and coating a finish coat of single liquid type thereon while the coated film is in the wet state before drying to touch. CONSTITUTION:The two-liquid reaction type primer coat (e.g., urethane resin paint, epoxy resin paint) is coated on the surface to be coated and the finish coat (e.g. cold drying type paint selected from chlorinated rubber, alkyl resin and acrylic resin paints) of the single liquid type is coated thereon while the coated film is in the wet state before drying to touch. The surface prepn., primer coating and finish coating can be successively executed in nearly the same period according to the above-mentioned method for forming the coated film; therefore not only the cost of the painting operation is considerably reduced but also the insufficiency of the adhesive power between the coated film layers by the sticking of foreign matter is obviated. The coated film formed has the corrosion resistance and appearance which compare favorably with the coated film formed by the conventional painting stage which includes drying between painting stages.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of applying a paint to a substrate to be painted for the purpose of aesthetics, corrosion prevention, etc.

[Conventional technology]

When painting metal materials and metal products for the purpose of preventing M#I, multiple layers are usually applied.1For example, when painting metal materials, the surface of the landscape to be painted is subjected to blasting, sanding, etc. Surface treatment is performed for the purpose of removing rust and surface deposits by polishing, etc., then an undercoat is applied primarily to prevent corrosion, and after this paint has solidified and dried,
On top of that, if necessary, an intermediate coat is applied, and after this has solidified and dried, a top coat is applied primarily for aesthetic purposes. This is because paints with excellent adhesion to the substrate and corrosion resistance do not necessarily satisfy aesthetic requirements.
Also, in many cases, it is difficult to say that a paint that has excellent aesthetic properties and is resistant to the environment in which it comes into contact with the painted surface does not necessarily have the best adhesion to the base or corrosion resistance, so it is difficult to say that the paint has the best adhesion to the base or corrosion resistance. The objective is to obtain a coating film with excellent properties. Also, it is meant to reduce the probability that defects such as pinholes that may occur in two or more coats will remain, and in some cases, the adhesion between the undercoat and top coat may not be very good. For the purpose of improving corrosion resistance or imparting other coating properties, intermediate coatings that act as a bridge between surface coatings are also applied. In each of these painting steps, it is common knowledge in the industry that the next coating is applied after the coating layer formed by the undercoat has dried.

However, in the following cases, a top coat has been applied while the undercoat is still uncured. That is ■
Apply a baking-type phenolic resin-based or alkyd resin-based undercoat paint, apply an intermediate coat or top coat after the solvent has volatilized but not yet cured, and apply the undercoat and intermediate coat or top coat simultaneously in one baking process. Methods of curing paint films are being used.

■ When spraying the same paint multiple times to increase the thickness of the paint film or to prevent the aforementioned pinholes from remaining, the spray gun is moved back and forth many times to form the desired thick paint film. In some cases, since the paint is the same, the top coat is applied while the base coat is still wet.

■ As disclosed in Japanese Patent Publication No. 60-17588, if the main components of the undercoat and topcoat are the same vehicle, it is not recommended to apply the topcoat before the undercoat is completely cured. It is being said.

Method (2) normally requires two baking steps, but by curing the undercoat and topcoat at the same time in one baking, the process is shortened. Although the paint film is in an uncured state, the top coat is applied after it is dry to the touch.
Moreover, the desired coating film is formed only by baking, and it is not applied when the undercoat film is wet, nor is it a room-temperature curing type coating.

In the case of (2), since the paint is the same, there is no possibility of interaction between two or more coats, and it is clear that no problem will occur even if the undercoat is wet and the topcoat is applied. However, unlike the present invention, different types of paint are not applied.

In the case of (2), both the undercoat paint and the topcoat paint are epoxy resin or modified epoxy resin paints, and the main component vehicle is the same type of paint, so they are strictly different types of paints. isn't it.

In this way, for the same type of paint, it is customary to apply the top coat while the undercoat is still wet, but it is common practice to apply the top coat while the base coat is still wet;
For resins (according to paint classification), the top coat is not applied while the base coat is wet.

JP-A No. 60-92365 proposes a top coat clear paint composition to be applied on a base coat by a wet-on-wet method. In either case, only an acrylic resin isocyanate curing paint is cited as a two-component reactive undercoat paint. This is coated with a clear paint composition containing an acrylic polymer, a diluent, a crosslinking agent, and crosslinked polymer fine particles having a particle size of 0.01 to 10 mm, and the base coat paint is 1.
Mainly liquid type, and in the case of two-component type, the top coat is also two-component, and although it cannot be said to be the same type, it uses the same type of paint. It is also aimed at line painting of automobiles.

Unlike the present invention, the present invention is not intended for large structures such as buildings, bridges, and tanks, and the composition itself is different.

[Problem that the invention seeks to solve]

In conventional painting processes, if foreign matter such as dirt or dust adheres to the painted surface during the drying process between the undercoating process and the intermediate coating process, or between the intermediate coating process and the topcoating process, each coating It is a well-known phenomenon that the adhesion between film layers becomes insufficient, leading to delamination problems. Furthermore, in the conventional process, the work period from base preparation to topcoat painting is long, and there is also the problem that painting costs increase accordingly for large buildings and bridges.

The present invention was devised in view of this point of view, and provides a coating film forming method different from conventional coating methods, which reduces coating costs by shortening the construction period, and reduces delamination due to dirt and dust. It also attempts to solve the problem of

[Means for solving problems]

The present invention applies a two-component reactive undercoat paint to the substrate to be painted,
This coating film forming method is characterized in that a one-component top coat is applied while the coating film is in a wet state before it is dry to the touch.

Epoxy resin or urethane resin paint is suitable as the two-liquid reactive undercoat paint. As a two-component reactive paint,
Although a relatively low molecular weight resin that is liquid at room temperature may be used, a resin that is solid at room temperature is preferred.

The resins used in epoxy resin undercoat paints include:
Any ordinary epoxy resin obtained by the reaction of epichlorohydrin and bisphenol A may be used, specifically Epicote (Shell Chemical Registered Trademark) 828.834.1
001.1004.1007.1009 etc., Araldite (Japan Ciba Geigy registered trademark) 6071°7071
, 6084.7097.6097, Sumiepoxy (Sumitomo Chemical registered trademark) ESA-011,014, and other general-purpose resins may be used.

The curing agent for epoxy resin used in this case is preferably a polyamide curing agent. Other compounding materials include Cumaron resin 1
Extending agents such as oil resin or white tar, extender pigments such as silica, talc, and calcium carbonate, coloring pigments such as Bengara, titanium oxide, and carbon black, and thixotropic agents such as organic bentonite and silicic anhydride fine powder. A solvent may be used if necessary.

The resins used in urethane resin paints include regular polyester and hydroxyl group-containing epoxy resins.

Alternatively, a vehicle such as a modified epoxy resin in which the number of hydroxyl groups is increased by modifying an epoxy resin with an alkanolamine is used in combination with a resin containing active isocyanate groups for curing the resin.

As isocyanate group-containing resins, methylene diisocyanate (MDI) type, tolylene diisocyanate (TDI) type
) type, hexamethylene diisocyanate (HMDI) type, etc. are generally known, but any of them can be used. However, the use of MDI and TDI resins may cause them to stand out on the surface of the top coat and cause the paint film to change color over time; however, if HMDI resins are used as a curing agent, this will not happen. No such phenomenon occurs. As other compounding materials, those used in the above-mentioned epoxy resin paints can be used as desired. However, if a bituminous material such as tar or asphalt, or a tar oil resin having properties equivalent to these is added as an extender to an epoxy resin or urethane resin as an undercoat, its moisture (-e
t) If a top coat is applied over the condition, the above-mentioned bituminous substance will bleed out after the coating is applied, so emphasis should be placed on corrosion resistance.
This is good when aesthetics are not so required, but when aesthetics are required, it is preferable not to use paints containing bituminous substances or tar oil resins as undercoat paints.

Examples of the top coat include chlorinated rubber paints that are solvent-volatile synthetic resin paints, acrylic resin paints, and oxidative polymerization alkyd resin paints.

Other alkyd resin-containing chlorinated rubber paints can also be used.

In the present invention, after applying the two-component reactive undercoating paint,
The main feature is that the top coat is applied while the base coat is still wet.

This wet state is defined by JIS K-5400-
This refers to the condition before dry to the touch as described in 1970 "General Test Methods for Paints 5.10J. Conventional common sense has it that when different types of paints are applied as an undercoat and a topcoat, interlayer separation occurs. The reality is that such a coating method has not been used because of the preconception that blistering, foaming, or disturbances will occur in the coating film.

However, the present inventors thought that if this type of coating could be applied, the construction period would be considerably shortened and there would be significant economic benefits.As a result, the inventors deliberately researched recoating in wet conditions, which goes against common sense. The inventors have discovered that by employing the combination of undercoat and topcoat as in the present invention, a coating film with no defects in corrosion resistance can be formed, and the present invention has been completed.

At first glance, this method of forming a coating film seems absurd, as if it goes beyond common sense, but the results are of a surprising level. The top coat is applied while the base coat is still wet.

Naturally, a composite coating film is formed in which the undercoat film component and the topcoat film component are mixed at the interface. The reason why good results are obtained is not clear, but it may be due to differences in the solvent composition in the paint or a type of solvent shock, etc. - The components of the undercoat and topcoat do not mix together, and This is thought to be because only the interface between the two exists as a mixed layer. If you use a two-component reaction type such as an epoxy resin or urethane resin as the undercoat and apply a chlorinated rubber, acrylic, or alkyd resin as the topcoat, the acceptance curing mechanism will be different, so even better results will be obtained. It is thought that this can be obtained. In this case, the paint vehicle used for the undercoat is preferably one that has a large molecular weight and is solid at room temperature.

As for the painting method, it is best to use regular air spray or airless spray. Brush painting, roller painting, etc. are difficult to apply because the undercoat film is in a wet state. To achieve the present invention, one of the two painters should apply the undercoat and the other should immediately apply the topcoat, but painting on scaffolding involves work hazards, and Such coatings are often difficult. However, if two spray nozzles are installed in one coating machine, and the first spray nozzle applies the undercoat and the second spray nozzle applies the topcoat, the present invention can be applied in one operation of the coating machine. Since the desired coating film is formed, coating costs can be drastically reduced.

If such a coating machine is further equipped with a device for surface treatment, each step of the normal painting process of base treatment, undercoat, and topcoat can be performed in one operation of the paint machine.
Work becomes more efficient and costs are further reduced.

The coating film thickness is not particularly limited for this reason and may be arbitrarily determined depending on the purpose, but in consideration of corrosion resistance, the dry film thickness of the undercoat should be 60 to 250 μm, preferably 100 to 250 μm. The dry film thickness of the top coat should be 10 to 50 μm.

Preferably, the coating should be applied to a thickness of 20 to 30 μm.

After application, dry under normal conditions. This coating film is comparable in performance to a conventional coating in which an undercoat is dried and then a topcoat is applied.

[Example 1] As a substrate to be coated, a test plate obtained by degreasing a 150 x 70 x 1 mm mild steel plate and then subjecting it to shot blasting treatment was used. Approximately 5% thinner was added to the surface of this test plate in a two-component reactive urethane resin paint (product name: NB Coat 3000 GW gray color, manufactured by Nippon Steel Chemical Co., Ltd.), and the film thickness after drying was Apply with an airless spray method to a thickness of 100 to 120 μm, and immediately apply white chlorinated rubber synthetic resin paint (Nippon Steel Chemical Co., Ltd., trade name 2NB Coat C).
Approximately 20% by weight of thinner is added to R-503 chloride rubber topcoat) or alkyd resin paint (Nippon Steel Chemical Co., Ltd. trade name 2NB Coat FE-503 topcoat) to give a film thickness of 20 to 30 μm after drying. It was applied using an air spray method so that Temperature of 20±1℃, humidity (R, H,) 75±
It was cured for 7 days in a 5% constant temperature and humidity chamber.

Various tests were conducted on each of the composite coating films thus formed. The results are shown in Table 1. For comparison,
Coatings applied with conventional coating intervals (basecoat applied, dried for 16 hours, then topcoat applied) were tested at the same time.

[Example 2] The same test plate as in Example 1 was used, the same base treatment was applied, and a two-component reactive epoxy resin paint (Nippon Steel Chemical Co., Ltd. product name: NB Coat EP) was used as the undercoat. The same topcoat as in Example 1 was applied, except that blue) was used, and the coating was cured in the same manner. The test results for the coating film are shown in Table 2.

〔Effect of the invention〕

Claims (3)

[Claims] (1) A method for forming a coating film, which comprises applying a two-component reactive undercoating paint to a substrate to be coated, and then applying a one-component topcoat paint while the coating film is wet before being dry to the touch. (2) The coating film forming method according to claim 1, wherein the two-component reactive paint for the undercoat is a urethane resin-based or an epoxy resin-based paint. (3) The method for forming a coating film according to claim 1, wherein the top coating is a room temperature drying coating selected from chlorinated rubber, alkyd resin, and acrylic resin.