JPH10118558A - Electrostatic coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and accurately apply a coating material having lightness equal to that of a conductive base body on a nonconductive base body. SOLUTION: A rotary atomizing coating device 16 is equipped with a coating gun 20 which injects a coating material 18 while high voltage is applied. The coating material 18 is a thermosetting coating material containing at least >=30wt.% aromatic org. solvent 22. The coating NV value of the coating material 18 is controlled to 55 to 75%. As for the aromatic org. solvent 22, for example, toluene and xylene can be used. Moreover, the coating material 18 contains a bright pigment 24 such as a metallic pigment and mica and a coloring pigment 26 containing a resin and pigments.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a method for coating a conductive primer on a surface of a non-conductive substrate, and then applying a coating containing a bright pigment on the conductive primer through a rotary atomizing electrostatic coating apparatus. The present invention relates to an electrostatic coating method to be applied.

[0002]

2. Description of the Related Art For example, it is common practice to apply the same color electrostatic coating treatment to an automobile body and a bumper using a paint containing a bright pigment such as metallic or mica. This type of electrostatic coating has advantages such as the ability to form high-quality coatings, and therefore, a rotary atomizing electrostatic coating device, commonly called a bell type coating machine, is widely used. ing.

When an automobile body is painted by the above-mentioned bell-type painting machine, as shown in FIG. 4, an undercoat layer 2a and an intermediate coat layer 2b are provided on the surface of a metal substrate 1, and then the intermediate coat layer 2b is provided. The coating material 4 is drawn out from the coating gun 3 on the surface 2b while a high voltage is applied. The paint 4 includes a bright pigment 5 such as metallic or mica, a colored pigment 6 containing a resin and a pigment,
And the thinner 7, and the paint 4 is applied on the intermediate coating layer 2 b.

On the other hand, when a bumper is coated by a bell type coating machine, a conductive primer layer 9 is provided on the surface of a resin base (non-conductive base) 8 such as polypropylene or polyethylene as shown in FIG. After that, the conductive primer layer 9
The paint 4a is drawn out from the paint gun 3a in a state where a high voltage is applied. The paint 4a contains a bright pigment 5 such as metallic or mica, a colored pigment 6 containing a resin and a pigment, and a thinner 7a containing a curing agent.
a is applied on the conductive primer layer 9.

[0005]

By the way, in the painting of the above-mentioned automobile body, various techniques have been used to improve the brightness.

[0006] However, in the above-mentioned bumper coating, the coating viscosity becomes low under the action of the curing agent contained in the thinner 7a, and the glitter pigment 5 is often not leveled. For this reason, it has been pointed out that the brightness is lowered, and the color of the vehicle body differs from that of the bumper. In order to increase the lightness, painting NV (nonv
It is conceivable to increase the olefin value to about 80%, but this causes a problem that the coating efficiency is significantly reduced.

The present invention solves this kind of problem and provides an electrostatic coating method capable of easily and reliably applying a coating having the same brightness as a conductive substrate on a non-conductive substrate. The purpose is to provide.

[0008]

In order to solve the above-mentioned problems, the present invention uses a paint containing at least 30% by weight or more of an aromatic organic solvent and has a coating NV value of this paint. , 55% to 75%. As a result, the aromatic organic solvent in the applied coating film immediately penetrates into the conductive primer, and the thickness of the coating film becomes thinner and the bright pigment is leveled, so that the brightness is effectively increased. In this case, the coating efficiency is further improved by setting the coating NV value of the paint to 55% to 70%.

In addition, since the conductive primer contains chlorinated polypropylene as a main component, the dissolving power of the aromatic organic solvent is improved, and the permeation of the aromatic organic solvent is more reliably performed.

[0010]

FIG. 1 is an explanatory view of an electrostatic coating method according to an embodiment of the present invention. A conductive primer layer 14 is provided in advance on the surface of a resin base (non-conductive base) 12 such as polypropylene or polyethylene that constitutes the bumper 10. The conductive primer layer 14 is formed by applying a primer containing chlorinated polypropylene as a main component.

The rotary atomizing type coating apparatus 16 is provided with a coating gun 20 for drawing out the coating material 18 in a state where a high voltage is applied. The coating material 18 is a thermosetting coating material containing at least 30% by weight or more of the aromatic organic solvent 22. The coating NV value of the coating material 18 is 55% to 75%, more preferably 5% to 75%.
It is set to 5% to 70%. The coating NV value is the ratio of the weight Wo of the paint 18 after drying to the weight W of the paint 18 one minute after coating, and (Wo / W) ×
It is determined from 100%.

As the aromatic organic solvent 22, for example, toluene and xylene having a high dissolving power for the conductive primer layer 14 are used. The paint 18 further contains a bright pigment 24 such as metallic or mica, and a colored pigment 26 containing a resin and a pigment.

In such a configuration, a coating material 18 is drawn out from a coating gun 20 constituting the rotary atomizing type coating device 16 in a state where a high voltage is applied, and the coating material 18 is applied on the conductive primer layer 14. Thus, a coating layer 28 is formed.

At this time, the aromatic organic solvent 22 in the coating layer 28 immediately permeates the conductive primer layer 14. Thereby, in the present embodiment, the thickness of the coating layer 28 is reduced,
Since the bright pigment 24 is leveled along the painted surface, the effect that the lightness of the coating layer 28 is effectively increased can be obtained.

Table 1 and FIG. 2 show aromatic organic solvent 2
The relationship between the content ratio of No. 2 and lightness (lightness index L value) is shown.

[0016]

[Table 1]

Therefore, when the content of the aromatic organic solvent 22 was 30% by weight or more, the brightness was greatly improved and a desired color was obtained. For this reason, the content of the aromatic organic solvent 22 was set to 30% by weight or more.

Further, the relationship between the content of the aromatic organic solvent 22 and the brightness was experimentally obtained using the red pearl paint 18 and the silver paint 18. The results are shown in Tables 2 and 3.

[0019]

[Table 2]

[0020]

[Table 3]

Thus, it was found that the desired lightness could not be obtained when the content of the aromatic organic solvent 22 was less than 30% by weight.

Next, in Table 4 and FIG. 3, two types of green metallic paints 18 in which the content of the aromatic organic solvent 22 was set to 8% and 44% were used. The result of experimentally detecting the relationship between the value and the lightness (lightness index L value) is shown. In this experiment, the coating speed was set to 600 mm / sec, the number of passes was set to 2, the discharge amount was set to 114 g / min, and the film thickness was set to 14 to 16 μm.

[0023]

[Table 4]

Thus, the applied NV value of the paint 18 is 55
In the range of% to 75%, the lightness increased. Also,
When the coating NV value becomes 70% or more, the coating efficiency of the coating material 18 decreases. Therefore, the applied NV value of the paint 18 is in the range of 55% to 75%, more preferably 55% to 7%.
By setting it within the range of 0%, it is possible to reliably and efficiently obtain the coating layer 28 having a desired brightness.

A similar experiment was conducted with various changes in the content of the aromatic organic solvent 22. In the above-mentioned case where the content of the aromatic organic solvent 22 was set to 8% and 44%, respectively. The same result was obtained. Therefore, these detailed explanations are omitted.

[0026]

As described above, in the electrostatic coating method according to the present invention, a paint containing at least 30% by weight or more of an aromatic organic solvent is used, and the coating N
The V value is set between 55% and 75%. As a result, the aromatic organic solvent in the applied coating film immediately penetrates into the conductive primer, and the thickness of the coating film becomes thinner and the bright pigment is leveled, so that the brightness is effectively increased. Therefore, it is possible to easily and reliably form a coating film having the same brightness as the conductive substrate on the non-conductive substrate.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an electrostatic coating method according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the content of an aromatic organic solvent and brightness.

FIG. 3 is a diagram illustrating a relationship between a coating NV value and lightness.

FIG. 4 is a general explanatory view when applying an electrostatic coating to a metal substrate.

FIG. 5 is a general explanatory view when applying an electrostatic coating to a resin base.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Bumper 12 ... Resin base 14 ... Conductive primer layer 16 ... Rotary atomization type coating device 18 ... Paint 20 ... Coating gun 22 ... Aromatic organic solvent 24 ... Bright pigment 26 ... Colored pigment 28 ... Coating layer

Claims (2)

[Claims] An electrostatic coating method in which a conductive primer is applied to the surface of a non-conductive substrate, and then the conductive primer is coated with a paint containing a bright pigment via a rotary atomizing electrostatic coating device. The conductive primer contains chlorinated polypropylene as a main component, and the paint contains at least 30% by weight or more of an aromatic organic solvent, and the coating NV value of the paint is 55% or more.
% To 75%. 2. The electrostatic coating method according to claim 1, wherein the applied NV value of the paint is set to 55% to 70%.