JPS596705B2 - Electrostatic coating method for defective conductive articles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrostatic coating method, and more specifically:
This invention relates to an electrostatic coating method for defective conductive articles.

Electrostatic coating methods are widely used in the field of coating technology, and need not be described in detail here. The first method of this method is
As is well known, the advantage of this is a reduction in the amount of paint used.
However, even this excellent coating method has drawbacks; for example, when the object to be coated is made of poorly conductive materials such as plastic, wood, rubber, etc., it is virtually impossible to achieve electrostatic coating. It's impossible. This is because, in such a case, the electric charge of the paint deposited on the object to be coated by electrostatic printing does not escape and accumulates as it is, thereby causing an increase in the potential on the surface of the object to be coated. As the potential of the surface of the object to be coated increases, the effect of coating disappears, and therefore electrostatic coating becomes virtually impossible. Many improved methods have been proposed to overcome these drawbacks of conventional methods.

These improvement methods can be roughly divided into the following technical ideas: (
1) Immediately before electrostatic painting, treat the object to be coated with a suitable chemical to impart conductivity to its surface; and (2) place a ground behind the object to be coated or adjust the charging polarity of the paint. It is based on arranging electrodes with opposite polarity and thus utilizing the electrostatic force between the paint charge and the ground or electrode behind the object to be coated.

Although the method based on the first technical idea enables electrostatic coating on non-conductive articles, it is economically undesirable due to the increase in processing steps for imparting conductivity. Moreover, there is a tendency for coating defects such as poor adhesion to occur due to the chemicals used in the treatment. Furthermore, the method based on the second technical idea does not essentially solve the ultimate problem of discharging the electric charge and decreasing the potential on the surface of the object to be coated, but only in certain cases. In other words, it only produces a slight electrostatic effect when the surface resistance of the object to be coated is low and leaks are likely to occur, or when the object itself is thin and has some degree of conductivity. . The present inventors conducted research to develop an improved electrostatic coating method for poorly conductive articles that can provide excellent electrostatic coating effects without the above-mentioned drawbacks. As a result, we have now completed the present invention.

The electrostatic coating method according to the present invention places a ground conductor on a part of the painted surface of a defective conductive article, starts electrostatic coating with a paint having a certain degree of conductivity from near this conductor, and forms a wet coating film. It is characterized by painting while maintaining a continuous state.

The invention will now be described in more detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of an electrostatic coating system showing one preferred embodiment of the present invention.

1 in the figure is the object to be coated, that is, a defective conductive article.
2 is a jig (here, a holder) for the defective conductive article 1, and is grounded as shown.

3 and 3/ of the jig 2, which are the folded parts
indicates the ground conductor according to the present invention. Reference numeral 4 designates an electrostatic coating gun, and the paint sprayed by this gun is charged by an electrode 6 connected to a DC high-voltage generator 5, and electrostatically coated on the defective conductive article 1.

For painting, first place the electrostatic coating gun 4 near the ground conductor 3 (position I in the figure), start electrostatic coating with conductive paint from this position, and then move the gun in the direction of arrow 7. Painting is carried out continuously in staggered positions. The figure shows the intermediate position of the gun. Similarly, place the gun at the position shown in the figure and start electrostatic painting from this position.When performing such painting, the wet paint film (undried paint film) that is formed is continuous. Care must be taken to ensure that if the wet coating is discontinuous, the desired objective of paint charge escape cannot be achieved, as detailed below. When the wet coating film is in a continuous state as in the present invention, the conductivity of the paint itself may contribute to the escape of paint charges, so that the charges formed on the surface of the defective conductive article 1 are continuously removed. In other words, in the case of the present invention, the paint sprayed toward the defective conductive object 1 adheres to the object 1 and is continuously sprayed. Therefore, if the paint itself is conductive, electrical charges on the surface of the object to be coated can be released to the ground by making a part of the paint film conductive to the ground through some means. Yes, but what if there is no ground conductor, as in conventional electrostatic coating systems?

This can be considered by omitting the jig 2 and the ground conductor 3 from FIG. In this case, as a result of the conductive paint being sprayed toward the defective conductive object 1 by the electrostatic coating gun 4, the electric charge of the paint and the electric charge of ions incidentally generated during electrostatic painting are separated. After reaching the surface of the object to be coated, it cannot escape anywhere and remains there. As a result of the charge being accumulated on the object, the surface potential of the object is also increased. This surface potential is finally raised to the same level as the potential of the electrode 6 of the gun 4, at which point the paint is no longer charged at all, and therefore there is no electrostatic coating effect. This phenomenon occurs when the object to be coated 1
This occurs when the material is made of a completely insulating material, or when it is made of a conductive material but is completely insulated from earth. The potential increases to a state where the electrostatic coating effect is zero, and it becomes virtually impossible to carry out electrostatic coating. Figure 2 shows
FIG. 2 is a schematic diagram of a coated object showing another preferred embodiment of the present invention. As shown in the figure, a workpiece 1 having poor conductivity is held by a conductive jig 2, and the jig 2 is further grounded. What is important here is that a plurality of electrically conductive needle-shaped metal pieces 8 are embedded in the object to be coated, and their tips are inevitably connected to the coating film formed during electrostatic coating. It is configured so that it can be contacted. It should be understood that when carrying out the present invention, methods other than those shown in FIGS. 1 and 2 may be employed as a method for grounding a portion of the continuous film of paint. For example, it is possible to use a ground electrode placed separately from the jig. moreover,
The coating order can also be set as appropriate depending on the grounding method and location. According to the present invention, it is possible to apply the electrostatic coating method to objects to be coated with poor conductivity, so that it is possible to reduce the amount of paint used and the number of man-hours for painting work, which are the merits of this method.

Furthermore, according to the present invention, various coating defects are not caused as in conventional methods.
In the present invention, coated objects (articles) with poor electrical conductivity can be used. Such articles are not particularly limited as long as they have poor electrical conductivity. Typical products include, for example, natural rubber, EPDM rubber,
Modified vinyl, polyethylene, polypropylene, ABS
, articles made from poorly conductive materials such as nylon. Specifically, if we take electrostatic painting of automobile parts as an example, we will apply the fascia panel that constitutes the outer panel of the vehicle body, the sight shield attached to the gap between the bumper and the vehicle body, and the outer panel of the energy absorbing bumper. etc. can be given. Note that "poor conductivity", as used herein, means that the volume resistivity of the object (article) to be coated exceeds 101 to 11 Ω·m. The ground conductor to be placed on a part of the painted surface of the defective conductive article may be made of various conductive metal materials such as iron, aluminum, copper, or brass, as well as materials that have been given conductivity. It can also be achieved from plastic materials. The paint used in this invention must have some degree of good conductivity, ie, low electrical resistance.

The present inventors have discovered through experiments that it is desirable that the volume resistivity of the paint used is 105 Ω·m or less. In addition, in the case of paints that require dilution prior to painting, the volume resistivity of the paint after dilution is 10.
It is desirable that it be 5Ω·m or less. Generally, if the specific volume resistivity of the paint used is as above,
The surface potential of the poorly conductive article (coated article) will fall within a range that does not interfere with the effectiveness of electrostatic effects. However, if the conductivity of the paint used is given by the highly volatile solvent contained in the paint, and the resistance value of the paint differs greatly between when it is sprayed and when it is attached to the object, the above-mentioned volume resistivity , 105 Ω·m. Furthermore, if the specific volume resistivity of the paint used is extremely low, for example on the order of 102Ω・m or less, in other words, if the paint used has extremely high conductivity, the paint supply path In order to avoid high-pressure leaks through the paint that may occur depending on the setting conditions of You can also do it. In addition, the conductivity of a paint is quantitatively shown by its specific volume resistivity, and the quality of the conductivity of a paint is determined by (current due to charges escaping to the ground) x (specific volume resistivity of the paint) It affects the quality of electrostatic coating by applying a potential equal to x (a constant based on the coating film formed and the shape of the object to be coated) to the surface of the object to be coated.

If the potential applied to the surface of the object to be coated is sufficiently smaller than the potential of the electrode applied by the high-pressure generator, then
That is, the potential of the electrode is 60, which is commonly used in electrostatic painting.
-70, and if the former is on the order of 2 to 3 KV, substantially the same electrostatic coating effect as when the object to be coated is conductive can be obtained.

However, if the former potential reaches the order of several 10 K, it goes without saying that a desirable electrostatic coating effect cannot be obtained. Next, the present invention will be explained in more detail with reference to the following examples.

Example 1 Electrostatic coating was carried out on an object to be coated using an air atomizing electrostatic coating gun.

The object to be coated was a urethane bumper for automobiles, and it was fixed using a painting jig commonly used for painting such objects. The paint used was a thermosetting urethane one-component type refrigerant (volume specific resistivity = 103Ω・m), and it was applied with the electrostatic paint gun at a voltage of 0 KV applied to the gun.
It was hand-painted. The coating efficiency of the obtained cold film was measured and found to be 18%. Example 2 Electrostatic coating was carried out on an object to be coated using an air atomizing electrostatic coating gun.

As in Example 1 above, a urethane bumper for an automobile was used as the object to be coated. However, in the case of this example, a painting jig as shown in FIG. 1 was used instead of the commonly used painting jig, and a ground conductor as shown was also provided. The paint used was a thermosetting urethane one-component type paint (volume specific resistivity = 103 Ω·m), which was continuously applied using the electrostatic paint gun at a gun applied voltage of 1-60K. The direction of movement of the gun was opposite to arrows 7 and 7' shown in FIG. The coating efficiency of the resulting coating film was measured and found to be 24%. Example 3 The procedure described in Example 2 above was repeated.

However, in this example, the electrostatic coating gun was moved in the same direction as arrows 7 and 7' shown in FIG. The coating efficiency of the resulting coating film was measured and found to be 42%. Example 4 The procedure described in Example 3 above was repeated.

However, in this example, the object to be coated was fixed using an insulating coating jig. When the coating efficiency of the obtained coating film was measured,
It was 18%. It will be understood from the results described in Examples 1 to 4 that excellent electrostatic coating effects are achieved when electrostatic coating is carried out according to the present invention.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a static N coating system showing one preferred embodiment of the present invention, and FIG. 2 is a schematic Q diagram of the object to be coated showing another preferred embodiment of the present invention. In the figure, 1 is a defective conductive object, 2 is a jig, 3 is a flat conductor, 4 is an electrostatic coating gun, and 8 is a needle-shaped object. There are 2 pieces.

Claims (1)

[Scope of Claims] 1. A ground conductor is placed on a part of the painted surface of the defective conductive article, and electrostatic painting is started from near this conductor with a paint having a specific volume resistivity of 10^5 Ω・m or less. , an electrostatic coating method for defective conductive articles, characterized in that coating is carried out while maintaining a continuous state of a wet coating film. 2. The electrostatic coating method according to claim 1, wherein the ground conductor constitutes a part of a jig for the defective conductive article.