JP3444664B2 - Electrostatic powder coating method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic powder coating method for electrostatically applying a charged powder coating on the surface of an object to be coated on which an undercoat insulating layer is formed.

[0002]

2. Description of the Related Art From the viewpoint of environmental protection, electrostatic powder coating has been attracting attention as a pollution-free coating method that can replace solvent coating. Electrostatic powder coating is a method in which powder coating material conveyed by air is sprayed from an electrostatic gun toward a grounded object to be coated, and electrostatically applied to the object to be coated. Powder paint is applied to the surface of the object to be coated in a charged state, but after being sprayed from the electrostatic gun, an external charging method that charges the powder outside the electrostatic gun and an electrostatic gun It is roughly classified into an internal charging method in which an electric charge is applied to powder inside an electrostatic gun before being sprayed.

A corona gun 1 shown in FIG. 6 is known as an electrostatic gun using the former external charging method. A pin-type corona electrode 2 is provided at the tip of the corona gun 1, and a high voltage is applied to this corona electrode 2. Since the object 3 to be coated is grounded, corona discharge is generated from the tip of the gun 1 toward the object 3 to be coated, and when powder coating material is conveyed by air and ejected from the gun 1, corona discharge causes The generated ions are attached to the powder particles and the powder particles are charged. Then, the charged powder particles are applied to the surface of the object to be coated 3 under the influence of the air flow from the gun 1 and the electric force along the electric force lines 4.

However, as shown in FIG. 6, the electric lines of force 4 are mostly not projected into the concave portion of the object to be coated 3 and are concentrated in the convex portion, so that the powder particles are mainly convex because of the so-called Faraday cage effect. Focus on the part and apply. That is, the powder particle layer 5 is formed only on the convex portion and is hardly formed on the concave portion. Of the ions generated by corona discharge,
Less than half of the ions adhere to the powder particles, and many ions move as free ions along the electric force lines 4 and adhere to the surface of the article to be coated 3. As the powder particle layer 5 on the article 3 is formed, free ions are also accumulated on the surface of the article 3. For this reason, the surface potential of the article 3 to be coated gradually increases, and the coating efficiency of the powder particles gradually decreases due to the influence of this surface potential. Further, in this way, when the electric field strength in the powder particle layer 5 increases and exceeds the dielectric breakdown electric field strength of air, a so-called reverse ionization phenomenon occurs in which a minute discharge occurs in the powder particle layer 5. The coating film becomes rough.

In order to solve such a problem of the conventional corona gun, as shown in FIG. 7, a free ion trap device 6 is provided behind the corona electrode 2, for example, 5 to 20 cm behind the corona electrode 2. Corona gun is proposed. In the free ion trap device 6, a plurality of pin-type trap electrodes 7, which are each grounded, are arranged on the same circumference. Since the trap electrode 7 is arranged at a position closer to the object to be coated 3 when viewed from the corona electrode 2, the lines of electric force 8 are concentrated on the trap electrode 7 and most of the free ions generated near the corona electrode 2 are electric. It moves along the force line 8 and is captured by the trap electrode 7. For this reason, free ions toward the article 3 to be coated are significantly reduced.

However, as shown in FIG. 7, when the object 3 to be coated has, for example, an undercoat insulating layer 3b formed on an iron plate 3a, and an overcoat layer is formed on the surface of the undercoat insulating layer 3b. Since the surface to be coated is an insulating layer, even if the free ions toward the object to be coated 3 are reduced,
When the charged powder coating material is laminated, the potential of the surface to be coated easily rises, which may cause a reverse ionization phenomenon. Although free ions can be reduced by providing the free ion trap device 6, on the other hand, the electric field E between the object to be coated 3 and the corona charging gun is weakened, so that F = qE (q: powder The adhesive force F of the powder particles, which is represented by the amount of electrostatic charge of the particles, becomes small, and there arises a problem that the coating efficiency on the surface of the article 3 is reduced.

On the other hand, a tribo gun 9 shown in FIG. 8 is known as an electrostatic gun utilizing the internal charging method. When the powder coating material is conveyed by air in the gun, it is charged by friction with a charging material made of resin or the like, and when jetted from the gun 9, the powder coating material moves along with the air flow 10 and moves to the surface of the object 3 to be coated. Apply to. In this tribo gun 9, gun 9
Since an electric field is not formed between the object to be coated 3 and the object to be coated 3, the charged powder particles are not affected by the electric field.
Is carried to the object 3 to be coated. Therefore, the object to be coated 3
The coating film 5 is also formed in the concave portions of the. Further, since no electric field is formed between the tribo gun 9 and the object to be coated 3, the problem of free ions unlike the corona gun does not occur.

However, even if the tribo gun 9 is used,
When an overcoat layer is formed on the surface of an object to be coated on which an undercoat insulation layer has already been formed, the potential of the surface to be coated may easily rise due to the lamination of charged powder coating materials, which may cause the reverse ionization phenomenon. . Further, since an electric field is not formed between the tribo gun 9 and the object 3 to be coated, there is a problem that the coating efficiency on the surface of the object 3 to be coated is lower than that in the corona gun.

As a typical example of the multi-layer coating having an undercoat layer, the car body coating of an automobile will be described. The coating film of an automobile is formed by a multilayer coating film of which the lowermost layer is an electrodeposition layer, and an intermediate coating layer and a top coating layer (base coat, clear top coat) are formed thereon in this order. Powder coating is possible except for the electrodeposition layer and metallic base coat, but overcoating of such coatings is electrostatically limited compared with the case of coating on metal coated objects. Therefore, problems such as a decrease in coating efficiency and roughening of the coating film due to electrostatic repulsion occur.

For example, when a high voltage of about -80 kV is applied to a coating gun on an object to be coated on which an undercoat layer is formed, the surface of the undercoat layer on the object to be coated is charged by the charge of ions flying from the coating gun. To trap the surface charge density of the object to be coated. Therefore, the surface potential of the object to be coated becomes a high potential of minus several kV, and electrostatic repulsion between the charged powder particles ejected from the coating gun toward the object to be coated and the object to be coated is caused. Force is generated and the coating efficiency is reduced. Further, electrostatic repulsion also occurs between the powder coating materials deposited on the object to be coated, and as a result, an appearance defect such as rough skin of the coating film easily occurs.

[0011]

As described above, in the conventional electrostatic powder coating method, there is a problem that the surface of the coating film may be rough due to the reverse ionization phenomenon and the coating efficiency of the powder coating material is low. was there. The present invention has been made to solve such problems, and provides an electrostatic powder coating method capable of preventing the occurrence of the reverse ionization phenomenon and improving the coating efficiency of the powder coating material. With the goal.

[0012]

An electrostatic powder coating method according to a first aspect of the present invention is a method for coating an electrostatic powder coating in front of a coating gun for spraying powder coating.
It has an opening in the center facing the object to be painted and
Electrodes for forming an induction field whose opposite surfaces are made of an insulator
Then, powder the surface of the electrode for forming the induction field that faces the object to be coated.
An object to be coated while being charged to a first polarity that is the same polarity as the paint
The undercoat insulation layer to the second polarity that is opposite to the first polarity.
Underneath the electrode for forming the induction field and the object to be coated
The powder coating which has been charged to the first polarity between the coating insulating layer to form a substantially equal induced electric field to induce on the surface of the material to be coated, the first polarity powder coatings by spray gun a method of supplying in an induction field through an opening of the induced electric field forming electrode is charged. The electrostatic powder coating method according to a second aspect is the method according to the first aspect, in which the powder coating material is electrostatically charged by using a coating gun that traps free ions. The electrostatic powder coating method according to a third aspect is the method according to the first aspect, in which the powder coating material is electrostatically charged and coated using a coating gun having an external electric field forming electrode. The electrostatic powder coating method according to claim 4 is the method according to claim 1, wherein the powder coating material is electrostatically charged and coated using a coating gun having a free ion trap device and an external electric field forming electrode. Is the way.

The undercoat insulating layer of the article to be coated may be formed of a single layer or a multilayer of two or more layers. Furthermore, the undercoat insulating layer can be charged using corona discharge. Further, it is desirable to use fine powder having a particle diameter of 25 μm or less, preferably 5 to 20 μm as the powder coating material.

[0014]

In the coating method according to the first aspect of the invention, the coating gun is arranged in front of the coating gun.
The surface of the installed induction field forming electrode facing the object to be coated is
The first polarity, which is the same polarity as the powder coating, is used to prevent undercoating of the coated object.
The edge layer is charged to the second polarity which is opposite to the first polarity.
A substantially uniform induction electric field for inducing the charged powder coating material on the surface of the undercoat insulating layer is applied to the induction field forming electrode and the coating surface.
The powder coating material formed between the undercoat insulating layer of the package and charged to the first polarity is supplied to the induced electric field. According to the coating method of claim 2, in the method of claim 1, since the free ions are trapped by the coating gun, the problem caused by the free ions is avoided. According to a third aspect of the present invention, in the method of the first aspect, the powder coating material is charged by an external electric field formed by an external electric field forming electrode provided on the coating gun. According to a fourth aspect of the present invention, in the method of the first aspect, the powder coating material is charged by an external electric field formed by an external electric field forming electrode provided on the coating gun, and free ions generated when the external electric field is formed. It is trapped by a free ion trap device.

An undercoat insulating layer which is a single layer or a multilayer consisting of two or more layers may be used, and the undercoat insulating layer can be charged by using corona discharge.
Further, when fine powder having a particle size of 25 μm or less is used as the powder coating material, a coating film having excellent finish can be obtained.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Example 1. An electrostatic powder coating method according to Embodiment 1 of the present invention will be described with reference to FIGS. The object to be coated 13 is an iron plate 13.
An insulating layer 13b is formed as an undercoat layer on the surface of a, and the iron plate 13a is grounded. Before electrostatically coating as an overcoat layer on this undercoat insulating layer 13b, the surface of the undercoat insulating layer 13b is exposed to an electric field using a corona discharge device 30 as shown in FIG. 1 to precharge. Later, the corona gun 1 as shown in FIG.
1, the negatively charged powder particles are applied onto the undercoat insulating layer 13b, so that here, the undercoat insulating layer 13b is precharged to a potential having a polarity opposite to that of the charged powder particles, that is, a positive polarity. . The corona discharge device 30 includes a corona electrode 31 and a high voltage generator 32 that applies a positive high voltage to the corona electrode 31.

The surface potential of the precharged undercoat insulating layer 13b is appropriately selected by changing the applied voltage, the discharge distance, the discharge time, etc.
It is set to about 3 kV.

Next, by using an electrostatic powder coating apparatus as shown in FIG. 2, the powder coating material having a negative polarity is applied on the surface of the undercoat insulating layer 13b of the object 13 to be coated, and the top coating is applied. Form the layers. In this electrostatic powder coating apparatus, an induction electric field forming electrode 21 is arranged in front of the corona gun 11, and the induction electric field forming electrode 21 faces the undercoat insulating layer 13b of the object 13 to be grounded. A pin-shaped corona electrode 12 for forming an electric field outside the gun 11 to generate a corona discharge is provided at the tip of the corona gun 11, and a direct current for applying a high voltage to the corona electrode 12 is provided. The power supply 15 is connected. A free ion trap device 16 is provided behind the corona electrode 12. Figure 3
As shown in FIG. 1, the free ion trap device 16 includes a plurality of pin-type trap electrodes 17 each grounded.
Are arranged on the same circumference.

As shown in FIG. 4, an induction electric field forming electrode 2 disposed between the corona gun 11 and the article 13 to be coated.
In No. 1, a plurality of ring-shaped electrode members 23 are concentrically formed on the surface of an insulating plate 22 having an opening 22a formed in the center. These plural ring-shaped electrode members 23
Are electrically connected to each other and are also connected to the DC power supply 24, as shown in FIG. DC power supply 24
Is an electric field in the direction in which the powder particles charged by the corona gun 11 are induced in the article 13 to be coated and the electrode 21 and the article 1 to be coated.
3 is connected to the ring-shaped electrode member 23 with the same polarity as that of the DC power supply 15 connected to the corona electrode 12 of the corona gun 11.

First, a high voltage of, for example, about -80 kV is applied to the corona electrode 12 of the corona gun 11 from the DC power source 15, and corona discharge is generated from the corona electrode 12 toward the article to be coated 13. At this time, since the trap electrode 17 of the free ion trap device 16 is arranged near the corona electrode 12, the lines of electric force 18 are concentrated on the trap electrode 17 and most of the free ions generated near the corona electrode 12 are generated. The trap electrode 17 is moved along the line of electric force 18
Trapped in.

Further, from the DC power source 24 to the plurality of ring-shaped electrode members 23 of the electrode 21 for forming an induction electric field, −20 to 40 k.
A potential of about V is applied, and thereby an almost even induced electric field is formed between the induced electric field forming electrode 21 and the object to be coated 13.

In this state, when the powder coating material is conveyed by air and ejected from the corona gun 11, negative ions generated by the corona discharge adhere to the powder particles and the powder particles are negatively charged. It rides on the air flow and moves toward the induction field forming electrode 21. Thus, the powder particles that have passed through the opening 22a of the insulating plate 22 of the electric field forming electrode 21 are affected by the induced electric field formed between the induced electric field forming electrode 21 and the object to be coated 13. Is guided to the article 13 to be coated, and is applied to the surface of the undercoat insulating layer 13b of the article 13 to be coated.

At this time, the positive charges forming the surface potential of the undercoat insulating layer 13b and the negative charges of the charged powder particles cancel each other out and are neutralized, so that the coated surface has such a high potential that reverse ionization occurs. It never becomes. Therefore, a coating film having an excellent finish is formed. In order to obtain a smooth coating film surface, fine powder having a particle diameter of 25 μm or less, preferably 5 to 20 μm is used as the powder coating material.

In addition, in the first embodiment, since a large amount of free ions are trapped by the free ion trap device 16, the free ions toward the object to be coated 13 are significantly reduced, and the adverse effect caused by the free ions is prevented. be able to. Further, since the electric field for inducing the charged powder particles is formed between the induction electric field forming electrode 21 and the object to be coated 13, the efficiency of coating on the surface of the object to be coated 13 is improved even if the free ions are reduced. be able to.

The undercoat insulating layer 13b is not limited to a single layer, but may be an insulating layer composed of two or more layers.

Example 2. When performing electrostatic coating, instead of the corona gun 11, a tribo gun 19 as shown in FIG.
Can also be used. A charging material made of resin or the like is provided inside the tribo gun 19, and is charged by friction with the charging material when the powder coating material is conveyed in the gun.
The charging polarity is generally determined by the material such as resin used as the charging material, but when a charging material made of Teflon is used, the powder particles are positively charged.
The tribo gun 19 shown in FIG. 5 is for ejecting powder particles charged with a positive polarity and injecting the powder particles to the object to be coated 13.
The DC power supply 24 is connected so as to have a polarity opposite to that in the above case.

In this second embodiment, in which the charged powder particles having the positive polarity are applied, the undercoat of the object to be coated 13 is applied to a potential having a polarity opposite to that of the charged powder particles, that is, a negative polarity, before the electrostatic application. The insulating layer 13b is precharged.

When the positively charged powder coating material is sprayed from the tribo gun 19, the powder coating material moves along the air flow toward the induction electric field forming electrode 21 and is guided through the opening 22a of the insulating plate 22. It reaches the induction electric field formed between the electric field forming electrode 21 and the object to be coated 13. Here, the powder particles are guided to the article 13 to be coated by receiving a force from the electric field, and adhere to the surface of the undercoat insulating layer 13b of the article 13 to be coated.

At this time, the negative charges forming the surface potential of the undercoat insulating layer 13b and the positive charges of the charged powder particles cancel each other and are neutralized, so that the coated surface has a high potential such that reverse ionization occurs. It never becomes. Therefore, a coating film having an excellent finish is formed.

Further, since the electric field for inducing the charged powder particles is formed between the induction electric field forming electrode 21 and the object 13 to be coated, even if the tribo gun 19 is used as the electrostatic gun, the object 13 to be coated can be efficiently treated. It can be applied to the surface.

[0031]

As described above, according to the electrostatic powder coating method of the present invention, the front side of the coating gun for spraying the powder coating material is used.
Has an opening in the center facing the object to be coated and
An electrode for forming an induced electric field whose surface facing the
The surface of the induction field forming electrode facing the object to be coated.
It is charged while being charged to a first polarity that is the same polarity as the powder coating.
The second polarity of the undercoat insulation layer of the article that is opposite to the first polarity
Electrodes for forming induction field and objects to be coated
Of the powder coating material is charged to a first polarity between the undercoat insulating layer to form a substantially equal induced electric field to induce on the surface of the material to be coated, the spray gun a powder coating material first Since it is charged with polarity and supplied into the induction electric field through the opening of the induction electric field forming electrode, the coating efficiency of the powder coating material can be improved. In addition, the undercoat insulation layer of the object to be coated is powder coated.
Since it is charged to the second polarity, which is the opposite polarity to
The charge of the powder coating is medium due to the charge on the surface of the undercoat insulating layer
The finish is excellent because it prevents the occurrence of the reverse ionization phenomenon.
A coated film is obtained.

If coating is performed using a coating gun that traps free ions, it is possible to prevent the occurrence of reverse ionization phenomenon due to free ions. Further, it is possible to spray the powder coating material using a coating gun having an external electric field forming electrode and electrostatically charge the sprayed powder coating material by the external electric field. If a coating gun having a free ion trap device and an external electric field forming electrode is used, free ions generated at the time of forming an external electric field can be trapped by the free ion trap device, and problems caused by free ions can be avoided.

Charging of the undercoat insulating layer of a single layer or a multi-layer of two or more layers can be carried out by utilizing corona discharge. Further, if a fine powder having a particle diameter of 25 μm or less is used as the powder coating material, a coating film having a more excellent finish can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a precharge step in an electrostatic powder coating method according to a first embodiment of the present invention.

2 is a diagram showing a coating step in the electrostatic powder coating method of Example 1. FIG.

3 is a diagram showing a corona gun free ion trap device used in Example 1. FIG.

4 is a front view showing an electric field forming electrode used in Example 1. FIG.

FIG. 5 is a diagram showing a coating step in the electrostatic powder coating method of Example 2.

FIG. 6 is a schematic view showing a state of coating with a conventional corona gun.

FIG. 7 is a diagram showing a state of coating with another conventional corona gun.

FIG. 8 is a schematic view showing a state of coating with a conventional tribo gun.

[Explanation of symbols]

11 corona gun, 12, 31 corona electrode, 13 coated object, 13a iron plate, 13b undercoat insulation layer, 15,
24 DC power supply, 16 free ion trap device, 1
7 trap electrode, 19 tribogan, 21 induction field forming electrode, 32 high voltage generator.

─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masahiro Yamamoto 2-13-27 Shinonome, Koto-ku, Tokyo Onoda Cement Co., Ltd. Ionics Technology Center (72) Inventor Mitsuyoshi Kumada 2-13 Shinonome, Koto-ku, Tokyo −27 Onoda Cement Co., Ltd. Ionics Technology Center (72) Inventor Atsushi Kondo 2-13-27 Shinonome, Koto-ku, Tokyo Onoda Cement Co. Ltd. Ionics Technology Center (72) Inventor Koichi Tsutsui Osaka Prefecture 19-17 Ikedanaka-cho, Neyagawa City, Japan Paint Co., Ltd., Neyagawa Works (72) Inventor, Shannon Riveki, 19-17 Ikedanaka-cho, Neyagawa City, Osaka Prefecture Japan Paint Co., Ltd., Neyagawa Works (56) References JP-A-53- 59737 (JP, A) JP 61-171568 (JP, A) JP 6-114297 (JP, A) Open flat 5-192632 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) B05D 1/06

Claims (7)

(57) [Claims] 1. An electrically grounded and preformed insulating layer
Is charged to the first polarity on the surface of the object being coated
And the powder coating an electrostatic powder coating method for electrostatically coating deposition, faces of the front of the spray gun that injects powder coating to an object to be coated
In addition, it has an opening in the center and the surface facing the painting gun is
An induction field forming electrode composed of a rim is arranged, and the surface of the induction field forming electrode facing the object to be coated is powder coating.
Under the object to be coated and charged to a first polarity that is the same polarity as
The coating insulation layer is charged to a second polarity that is opposite to the first polarity.
By coating the electrode for forming the induction field and the undercoat of the object to be coated.
An almost uniform induction electric field is formed between the insulating layer and the powder coating material charged to the first polarity on the surface of the object to be coated, and the coating gun sets the powder coating material to the first polarity. Charged and induced
An electrostatic powder coating method, characterized in that the electric field is supplied into an induction electric field through an opening of a field forming electrode . 2. The electrostatic powder coating method according to claim 1, wherein the powder coating material is electrostatically charged and coated using a coating gun that traps free ions. 3. The electrostatic powder coating method according to claim 1, wherein the powder coating material is electrostatically charged and coated using a coating gun having an external electric field forming electrode. 4. The electrostatic powder coating according to claim 1, wherein the powder coating is electrostatically charged by using a coating gun having a free ion trap device and an external electric field forming electrode. Method. 5. The electrostatic powder coating method according to claim 1, wherein the undercoat insulating layer of the article to be coated is composed of a single layer or a multilayer of two or more layers. 6. claims 1, characterized in that charging with an undercoat insulating layer of material to be coated using corona discharge 5
The electrostatic powder coating method according to any one of 1 . 7. A powder coating electrostatic powder coating method according to any one of claims 1 to 6, characterized in that a fine powder having a particle size 25 [mu] m.