JPH041674B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an intermediate coating method in a painting process for, for example, an automobile body. (Prior art) Generally, in the painting process of automobile bodies, etc.
In order to improve the appearance or finish after painting, three stages of painting are applied to the surface of the vehicle body, etc.: undercoating, intermediate coating, and top coating (see, for example, Japanese Patent Application Laid-Open No. 55-88874). In order to achieve the best possible finish within a limited amount of time, a method is usually adopted in which the same paint is applied in two separate coats. However, as for the paint for the above-mentioned intermediate coating, conventionally, the resin type is melamine-cured oil-free polyester, the non-volatile content is 45 to 55% by weight, and the resin and pigment are mixed.
A product that is formulated in a weight ratio of 0.8 to 1.2:1.0 and has a viscosity of 20 to 30 seconds at 20°C as measured with a food cup No. 4 is generally used. The film thickness was, for example, 20μ in the first application and 30μ in the second application. However, such conventional intermediate coating methods have the following problems. That is, as shown in FIG. 1, the surface 1a of the undercoat film 1 formed by electrodeposition or the like is generally uneven, and the surface of the vehicle body may also be uneven. Therefore,
When a first intermediate coat is applied on top of the paint 2, the surface 2a becomes smooth immediately after application as shown in Fig. 1, but the thinner contained in the paint 2 as a solvent By gradually diluting volatile components such as, the paint 2 becomes thinner as shown in the figure, and the same unevenness occurs on its surface 2a along the unevenness of the undercoat film surface 1a. Therefore, as shown in the figure, the surface 3a becomes smooth immediately after applying the paint 3 as the second intermediate coat, but especially after the second intermediate coat, the volatile components are extracted and the paint film is formed. Baking is performed at 140℃ for 20 minutes to harden, so
As shown in the figure, both paints 2 and 3 are further thinned, and the unevenness of the surface 3a becomes even more noticeable. In addition, especially in the first intermediate coating, if there is insufficient atomization during spraying of the paint or poor fluidity of the paint after application, as shown in Figure 2, this paint 2' In addition to this, as shown in the figure, the paint film 2' is affected by the unevenness of the undercoat film surface 1a due to the dilution of volatile components from the paint 2'. The unevenness on the surface 2a' becomes more noticeable,
Therefore, when the second intermediate coating 3' is applied and baked, as shown in FIG. 1, the unevenness of the surface 3a' of the coating 3' becomes more significant than in the case of FIG. Therefore, in the past, after baking these intermediate coats, it was necessary to perform water polishing work on the surfaces 3a and 3a' of the paints 3 and 3', which required a large amount of manpower and man-hours. . (Purpose of the Invention) The present invention addresses the above-mentioned problems in the prior art, and aims to use a paint with an optimal blend for each of the two intermediate coats in the car body painting process. This allows for a smooth intermediate coating film, which enables a good external finish to be obtained without the need for water sanding after intermediate coating, thereby reducing the number of personnel and processes required for water sanding. The purpose is to (Configuration of the Invention) In order to achieve the above object, the present invention is configured as follows. In other words, in an intermediate coating method in which the intermediate coating is applied in two parts in a three-coat system consisting of undercoat, intermediate coat, and top coat, the nonvolatile content is 65 to 85% by weight in the first intermediate coating process, and the resin and pigment are mixed. The weight distribution ratio is 0.4 to 0.8:1.0, and the viscosity is 30 with food cup No. 4.
~50 seconds / 20℃ paint is applied, without drying it in a drying oven, and as a second intermediate coating process, non-volatile content is 20 to 40% by weight, and a polymerization blend of resin and pigment is applied. Apply a paint with a ratio of 2.0 to 3.0:1.0 and a viscosity of 10 to 18 seconds/20°C using a No. 4 Ford cup. Here, the types of resin components in the paint are:
Melamine cured oil-free polyester is suitable. In addition, as a coating machine that applies paint, 1
For the second application, a rotary atomizing electrostatic type coating machine is used, and for the second application, a rotary atomizing electrostatic type or an air atomizing type coating machine is used. Furthermore, after applying the first intermediate coat as described above, without actively drying in a drying oven, let it stand naturally at 20°C for 2 to 5 minutes, and then apply the second intermediate coat. . In addition, the amount of paint applied is adjusted so that the coating thickness when drying is, for example, 35±5μ in the first intermediate coating, and similarly, the coating thickness is 15±5μ when drying in the second intermediate coating. Adjusted to be 5μ. The above configuration is summarized in Table 1. This table also includes the conventional example described above for comparison. In addition, after the second intermediate coating, for example, 140
Baking for 20 minutes at ℃ is carried out.

【table】

[Table] According to such a configuration, as shown in FIG.
The first coat 12 of the intermediate coat applied on the base coat a has a high proportion of non-volatile matter and pigments, and accordingly has a high viscosity and a thick coating film. The unevenness on the film surface 11a is completely hidden by the paint 12. In addition, since this paint 12 has a low proportion of volatile components, it hardly causes thinning even after application, as shown in the figure, and therefore, the unevenness of the lower surface hardly appears on the surface 12a.
a is kept smooth. Furthermore, as shown in FIG. 3, the paint 13 applied as the second intermediate coat from above the paint 12 has a high resin content and volatile components and has a low viscosity, so it has excellent fine particle makeup and fluidity. As a result, the surface 13a of the paint 13 can be applied smoothly. Then, baking is performed after the second intermediate coating is performed as described above, and at that time, the volatile components contained in the second intermediate coating 13 are diluted and the paint 13 becomes thin.
Since the surface 12a of the first intermediate coating 12 is smooth, the surface 13a of the second intermediate coating 13 remains smooth even after thinning, as shown in FIG. On the other hand, when applying the first intermediate coat,
Due to poor atomization and poor fluidity of the paint, the fourth
As shown in the figure, unevenness may occur on the surface 12a' of the intermediate coating 12' applied for the first time.
However, even in this case, as shown in the figure, since the paint 12' has a low proportion of volatile components, almost no thinning occurs. Furthermore, before the first intermediate coat 12' dries and hardens, the second intermediate coat 13' is applied on the paint 12' as shown in Figure 1, so that the paint 13' contains The volatile components contained in the paint 12' permeate the paint 12' applied to the underside of the paint 12', as shown in Figure 2.
The interface between 3' and 12', that is, the surface 12a' of the first intermediate coat 12' is smoothed. For this reason, the paint 12',
The volatile components in 13' are diluted and the paint 12', 1
When 3' is cured, an intermediate coating film having a smooth surface 13a' is formed as shown in the figure. (Effects of the Invention) As described above, according to the present invention, since the first and second intermediate coats are configured to use paints with the optimum composition, the water polishing work after baking the intermediate coat, which was conventionally required, can be eliminated. A good appearance can be achieved without the need for polishing, and the number of personnel or man-hours involved in the sanding work can be reduced. (Example) Examples of the present invention will be described below. First, in the example, as the first intermediate coating, the resin type was melamine-cured oil-free polyester, the non-volatile content was 78% by weight, the weight mixing ratio of resin and pigment was 0.5:1.0, and Foud Cup No. 4 was used. A paint with a measured viscosity of 43 seconds/20°C was applied to give a dry film thickness of 38μ. After leaving this naturally under the specified conditions, 2
For the second intermediate coating, use the same resin type as above, with a non-volatile content of 32% by weight, a weight blending ratio of resin and pigment of 2.6:1.0, and a viscosity of Foord Cup No. 4 for 12 seconds/1.
The paint was applied at 20°C so that the dry film thickness was 16μ. Furthermore, after baking and drying these, a specified top coat is applied to a film thickness of 35 μm when dry.
It was applied and dried. Next, in the example, as the first intermediate coating, the nonvolatile content was 66% by weight, the weight mixing ratio of resin and pigment was 0.7:1.0, and the viscosity was Foord Cup No. 4.
Paint was applied for 34 seconds at 20°C so that the dry film thickness was 32μ, and as a second intermediate coat, the non-volatile content was 38% by weight and the polymerization ratio of resin and pigment was applied.
2.2/1.0, viscosity is 12 seconds/20 with food cup No. 4
℃ paint was applied so that the dry film thickness was 14 μm, and topcoating was performed in the same manner as in the above example.
In this example as well, the same resin type paint as in the above example was used. For the coating films finally formed in these examples, the PGD value and flow comparator value were measured using a sharpness gloss meter and a coating film smoothness meter, and the appearance and finish properties were determined based on these values. The evaluation was made by comparing with the conventional example. here,
The larger the PGD value, the smaller the flow comparator value, the more
Indicates that the finish is good. As a conventional example, a paint with a non-volatile content of 52% by weight, a weight blending ratio of resin and pigment of 0.9:1.0, a viscosity of Foord Cup No. 4, and a viscosity of 24 seconds/20°C is used. The film thickness (when dry) is 15μ the first time and 25μ the second time (conventional example), and the other is 20μ the first time and 35μ the second time. The test was carried out for the one coated in the same manner (conventional example). Of these, the water polishing work after baking the intermediate coat was performed only in the conventional example. The above conditions and results are shown in Table 2.

[Table] As a result, both the examples and the ones that were not subjected to water sanding using the conventional method (conventional example) had a superior external finish, and those that were water sanded using the conventional method (conventional example) A similar finish was obtained.

[Brief explanation of drawings]

1 and 2 are schematic sectional views of the coating film obtained in each step in the conventional intermediate coating method, and FIGS. 3 and 4 are schematic sectional views of the coating film obtained in each step in the intermediate coating method of the present invention.

Claims (1)

[Claims] 1 An intermediate coating method in which the intermediate coating in a three-coat system of undercoating, intermediate coating, and top coating is applied in two times, in which non-volatile content is applied as the first intermediate coating.
65-85% by weight, weight blending ratio of resin and pigment is 0.4
~0.8:1.0, viscosity is 30-50 with food cup No. 4
The paint is applied at a temperature of 20°C per second, and without being dried in a drying oven, a second intermediate coating process is applied with a non-volatile content of 20 to 40% by weight and a weight ratio of resin to pigment. 2.0-3.0: An intermediate coating method characterized by applying a paint with a viscosity of 1.0 and a No. 4 Ford Cup in 10-18 seconds at 20°C.