JPS5912353B2 - Coating film formation method using slurry paint - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of forming a coating film using a slurry paint.

In recent years, efforts have been made to make paints and coatings pollution-free, and the use of water-based paints and powder paints that are suitable for this purpose is increasing. However, these non-polluting and resource-saving paints also have some drawbacks in terms of their characteristics and use.

5. For example, powder coatings require specific coating equipment and are therefore not as easy to apply as conventional solvent-based coatings, thereby limiting their use.

Further, among water-based paints, water-soluble paints cannot have a high solid content concentration of 10, and therefore cannot be coated in a thick film at one time.

Furthermore, since emulsion paints use a large amount of surfactant, the resulting paint film has problems with water resistance, chemical resistance, etc.
Slurry paints have been developed to eliminate or improve these problems15.

This slurry paint mainly uses water as a medium and has a
It is a paint in which resin particles of about μ size are dispersed in a medium at a solid concentration of about 20 to 60% by weight. Since this paint comes out with a high solid content concentration as mentioned above, it has the advantage that a thick film can be applied at one time, and that conventional solution paint coating equipment can be used as is. . Furthermore, since the paint does not contain a large amount of surfactant, it is possible to form a coating film with excellent water resistance and chemical resistance. However, since the volatile component of the paint is only water, it saves resources and has the excellent advantage of not causing pollution. However, even with this slurry paint, there are still fundamental problems that remain unresolved30.

One of the problems is that minute cracks (hereinafter referred to as cracks) are likely to occur during the process of forming a film by setting or preheating and drying the slurry paint after painting and then heating and drying.

35 The reason for this is thought to be that water evaporates during post-painting setting or preheating drying, causing the paint film to shrink.

Such cracks are often seen in areas that are prone to drying, such as edges and areas exposed to strong winds, and the width of cracks that occur during setting or preheating drying is determined by resin particles melted during heating and drying. This is further magnified by the surface tension of the film, resulting in undesirable coating defects. As a method to solve this problem, a method has been proposed in which a water-soluble resin or emulsion resin is added to the slurry paint to reduce shrinkage of the paint film and improve the adhesion between resin particles to prevent cracks. .

However, in this method, it is necessary to add 5% by weight or more of a water-soluble resin or emulsion resin in terms of solid content to the resin particles in the slurry paint, and if this is done, the above-mentioned drawbacks of water-based paints will appear, and The drawback was that it became extremely difficult to treat the paint wastewater generated during painting. An object of the present invention is to eliminate or improve the above-mentioned problems and to provide a method for forming a smooth coating film using a slurry paint.

That is, in the present invention, after coating a slurry-like paint in which resin particles of about 0.5 to 80 microns are dispersed in an aqueous medium with a solid content concentration of about 20 to 60% by weight, the object to be coated is heated. Until drying (hereinafter referred to as the setting process), the object to be coated is heated at a temperature between about room temperature and 100°C, at which the constituent resin particles do not melt, at a relative humidity of 80% or more, and at a wind speed of 0.3 m/min. This is achieved by maintaining the atmosphere in an atmosphere adjusted to below Sec.

According to the method of the present invention, the slurry paint applied to the object to be coated is heated in a heating drying oven to a temperature higher than the softening temperature of the resin particles, and the particles fuse together, causing the paint film to evaporate due to water evaporation. Until the ability to withstand shrinkage appears, a wet coating of slurry paint prevents rapid evaporation of water and prevents cracks from occurring.

In the present invention, humidification is performed during the setting process. That is, the relative humidity is set to 80% or more. In addition, the wind speed on the surface of the object to be coated by the ventilation system is maintained at 0.3 m/Se or less.

In the above, the relative humidity is lower than 80% or the wind speed is 0.
．． If the speed is faster than 3 m/Sec, cracks will occur in the coating film. In the present invention, among the above conditions, especially the relative humidity is 85%.
~900/I-, wind speed 0.3~0.05m/Sec (
7) is preferred.

In this respect, it will be clear that the present invention differs greatly from the setting conditions for coating films such as conventional solvent-based paints or water-soluble paints. In other words, solvent-based paints, water-soluble paints, etc. do not cause cracks even if the solvent evaporates rapidly in the setting.On the other hand, if a large amount of solvent evaporates during heating and drying, it can cause pinholes and cracks. The wind speed due to ventilation off the coast of the setting is normally 0.00 to prevent fires and explosions.
In contrast, it is 5 to 0.3 m/Sec, which is quite large. The temperature of the setting process of the present invention ranges from room temperature to 10°C.
Maintain at 0°C.

In the above case, if the temperature is higher than 100°C, the resin particles will fuse and form a continuous film while still containing a large amount of water in the coating, which will easily cause pinholes and wrinkles in the next heating drying process. There is a tendency to In the present invention, heating and drying is performed under pressure.

In the heat drying process, the atmospheric temperature of the furnace is adjusted to such a temperature that the rate of temperature rise of the object to be coated is such that the resin particles do not melt until the water in the coating film finishes evaporating, or the coating film remains porous. carry out. The humidifying device has a structure in which, for example, air taken in from the outside is filtered through a filter and then directly humidified with steam, or the air is passed through a hot water spray, humidified, and then heated or cooled by a heat exchanger as necessary. Conventionally known structures can be used as they are.

The present invention will be explained below with reference to Examples.

Note that all parts and weights in the examples indicate parts by weight and weight %.

Example 1 A 60Cfb acetone solution of an acrylic resin with a softening temperature of 45°C, a molecular weight of 17,000, and a hydroxyl value of 60 was prepared at 110° C. A 60% acetone solution of a block isocyanate resin with a softening temperature of 68°C and an isocyanate target of 770. 50 parts, Iso tin compound (catalyst for dissociation reaction of block isocyanate)
After uniformly mixing and dispersing 0.5 parts of surface conditioning agent, 0.5 parts of surface conditioner, 8 parts of phthalocyanine blue, and 0.3 parts of carbon black, the resin solution was sprayed into 5,000 parts of water under vigorous stirring. Resin particles were formed by emulsifying and extracting the solvent into water.

The resin particles were filtered with P, washed with an equal volume of water, and filtered to obtain a water-containing resin particle cake with a solid content of 60%. After mixing 100 parts of this water-containing cake with 0.2 parts of nonionic surfactant, 0.5 parts of polycarboxylate thickener, and 20 parts of water, the mixture was pulverized in a boiler mill to form resin particles. 70% of 5
A slurry paint suitable for spray coating with a particle size of ~30μ was obtained. This slurry-like paint was spray-painted onto a polished mild steel plate, and a coating film was formed by setting and heating and drying under the conditions shown in Table 1. The obtained coating surface condition is also shown in Table-1. Example 2 Softening temperature 41°C, molecular weight 15,0001, hydroxyl value 40,
56 parts of a 60% acetone solution of acrylic resin with an acid value of 18,
Melamine resin (product name RESIMENRF-3403M
24 parts of 60% acetone solution from 0NSANT0 (USA),
Add 0.5 part of a silicone surface conditioner to 5 parts of a 20% acetone solution of cellulose acetate (trade name EAB-551-02 Eastman Kodak, USA) and 8 parts of a 20% acetone solution of a plasticizer (dimethyl C7 tallate). A transparent resin paint was made by uniformly stirring and mixing.

93.5 parts of this transparent resin paint and 0.5 parts of carbon black.
1 part and 6 parts of phthalocyanine green were added and dispersed and kneaded in a ball mill to obtain a colored solution paint. The above transparent resin paint and colored solution paint were each sprayed into water in the same manner as in Example 1,
Resin particles were formed, washed with water, and filtered to obtain resin particles each having a solid content of about 68%.

For each 100 parts of these resin particles, 0.5 part of water-soluble thickening stabilizer, 0.2 part of nonionic surfactant, and 35 parts of water.
The mixture was pulverized using a ball mill to obtain a transparent resin slurry paint and a colored slurry paint in which 85% of the resin powder had a particle size of 10 to 30 μm.

On the other hand, an aliphatic hydrocarbon solvent dispersion containing 65% of aluminum pigment with a mesh size of 325 or less (trade name: Aluminum Paste H)
ighSPAKLE. 10. A xylene dispersion containing 12 parts of Toyo Aluminum (0 vermilion)) and 40 (Ft) of a flaky pearl pigment (trade name: HCGl5O, manufactured by Nihon Koken Kogyo Co., Ltd.).
5 parts of an emulsion with a solid content of 50% and a viscosity of 350 CPS (trade name Yodozol 32A108 Zhonbuchi Spinning (Mai)) 20
Then, 6 parts of a water-soluble aminoplast resin (trade name: SUMITEX M-40W, manufactured by Sumitomo Chemical Co., Ltd.) and 7.5 parts of water were added and mixed to obtain a pigment dispersion.

Claims (1)

[Scope of Claims] 1. A slurry-like paint in which resin particles of about 0.5 to 80 μm are dispersed in an aqueous medium with a solid content concentration of about 20 to 60% by weight is coated on an object and then heated and dried. A slurry-like paint characterized in that the object to be coated is maintained in an atmosphere at a temperature of 100° C. or less, at which the resin particles do not melt, a relative humidity of 80% or more, and a wind speed of 0.3 m/sec or less. coating film formation method. 2 Claim 1 in which the relative humidity is 85 to 90%
A method for forming a coating film using a slurry paint as described in . 3. The method of forming a coating film using a slurry paint according to claim 1, wherein the wind speed is 0.3 to 0.05 m/sec.