JPH1043671A - Electrostatic powder coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic powder coating method which is free of defects which appear when an electrostatic powder coating gun is used, can form a coating film without mottle without decreasing the particle size of a powdered coating more than necessity, eliminate useless consumption of the powdered coating, and easily form optional information such characters by a coating film having different hues on an object to be coated. SOLUTION: An electrostatic latent image formed on photosensitive materials 3a, 3b, 3c, 3d, is developed by sticking a thermosetting powdered coating by electrostatic force, and the coating is transferred on a transfer sheet 90. The coating is fixed temporarily on the sheet 90 by heating it at a temperature below a curing temperature. The temporarily fixed coating is pressed to an object to be coated and cured by heating to be baked on the object, and then the sheet 90 is peeled off from the coating which is baked on the object.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for performing electrostatic powder coating.

[0002]

2. Description of the Related Art In recent years, changes in the global environment have been regarded as a problem, and efforts have been made at the international level to prevent the global environment from deteriorating. Also in the field of coating technology, paint containing an organic solvent poses problems of pollution due to scattering of the organic solvent during coating, environmental pollution and volatile odors due to volatile organic substances (VOC). Therefore, a high-solid or water-based paint and a powder coating method have been developed. In particular, since the powder coating method uses a powder coating containing no organic solvent at all, it is preferable because there is no problem of pollution or disaster caused by the organic solvent. Further, the powder coating method has an advantage that thick coating is easy and automation is easy.

[0003] In such a powder coating method, for example, in a coating line for home electric appliances and the like, a coating film is formed in advance on a plate-shaped metal material before processing by PCM (Pre-Coated Metal).
In order to reduce the cost of coating equipment, make it compact, save labor, and improve the productivity by shortening the coating and baking time.

As one of the powder coating methods, there is an electrostatic powder coating method. This involves charging the thermosetting powder coating to the positive or negative electrode, spraying it onto the object to be coated, and then thermosetting so that the powder coating can be baked onto the object to be coated. To form. In order to perform this electrostatic powder coating method, a powder coating gun called a corona gun or a tribo gun is used to charge and eject the powder coating.

[0005] The corona gun uses, for example, a high-voltage generator to apply 70 to 10 to a corona electrode at an outlet of powder paint.
By applying a high voltage of 0 KV and discharging from the corona electrode, the powder paint conveyed by compressed air is charged. Thereby, the charged powder paint flies in an electric field formed between the corona gun and the object to be coated, and adheres to the object to be coated.

However, in the method using a corona gun, only a few percent of the ions discharged from the corona electrode are used for charging the powder coating. The unused ions generate ozone and generate odor. Also,
Since the electrostatic repulsion called back ionization is fast, craters and pinholes are easily generated in the coating film. In addition, a phenomenon called the Faraday cage effect, which deteriorates the penetration of the powder coating material into the concave portion to be coated, occurs. For this reason, there are drawbacks in that the efficiency of applying the powder coating is low and it is difficult to obtain a uniform coating film with a smooth surface. Also,
There is a problem that dust easily adheres to the coating film.

In a conventional tribo gun, powder paint is conveyed by pressurized air in a straight conveying path, and static electricity is generated by friction between the conveying surface surrounding the conveying path and the powder paint, thereby forming the powder. This is to charge the paint.

However, in the method using the tribo gun, since the powder paint conveying path is substantially straight, there is little chance of contact between the conveying surface and the powder paint particles, and the charging efficiency is poor. Therefore, when the maximum ejection amount is small, the coating efficiency is low, and the area to be coated is large, the coating takes a long time.

Further, the thickness of the coating film formed by the conventional powder coating has been about 100 μm to 300 μm, but in recent years, it has been increased to 40 μm.
It is also required to apply a thin film having a thickness of about 25 μm to 25 μm. Therefore, the average diameter of each particle constituting the powder coating,
What used to be about 40 μm to 30 μm,
It is necessary to reduce the diameter to about 10 to 10 μm. But,
As the particle size decreases, the specific surface area increases significantly.
Then, in the coating method using the conventional gun for electrostatic powder coating, it is difficult to sufficiently increase the chance of contact between the conveying surface and the powder coating particles, and the charging efficiency is greatly reduced. Therefore, the coating efficiency decreases.

Further, the gun for electrostatic powder coating forms a coating film of a single hue on an object to be coated. for that reason,
It has been difficult to form information such as letters, numbers, patterns, images, figures, and the like on the object to be coated with a coating film. In particular, it has been difficult to express such information using a plurality of hues. Then, after baking of the powder coating, information such as characters is added using a stamp or a label, but there is a problem that the information is easily erased.

Further, when forming a coating film of a large number of hues by using an electrostatic powder coating gun, it is difficult to have a number of electrostatic powder coating guns corresponding to the number of hues. Therefore, when a coating film having a plurality of hues is formed, it is necessary to frequently change the powder coating sprayed from one electrostatic powder coating gun. However, it takes time to change the powder coating, so that the operation time is greatly reduced.

In the production of powder coatings, first,
The resin for the binder, the curing agent, other additives, etc., and the toned pigment are mixed and melt-kneaded in a mixer. The mixture is cooled and then pulverized to obtain a powder coating for testing. A test coating is performed using this powder coating to form a coating film. If the hue of the coating film deviates from the desired hue, the powder paint for test is supplemented with the powder paint, and the process of manufacturing the powder paint for test is repeated. Further, when the heat history is a problem, a powder coating for a test is manufactured from a new resin for a binder, a curing agent, other additives, and the like, and a newly toned pigment.
Therefore, toning the powder coating requires time and effort. Therefore, it has been proposed to perform toning by mixing a plurality of types of powder coating materials having mutually different hues. However, when toning is performed by mixing a plurality of types of powder coatings, a uniform hue without color unevenness cannot be obtained unless the average particle diameter of each type of powder coating is 10 μm or less. That is, in obtaining a uniform hue, the influence of the diameter of the powder coating particles is large. This is because each type of powder coating has different physical properties such as fluidity and charging performance, so that it is difficult to uniformly mix the powder coatings, and thus it is difficult to uniformly charge the mixed powder coatings. It depends. Therefore, it is necessary to improve the uniformity after mixing by reducing the diameter of the powder coating particles. Further, it is practically impossible to separate each type of powder coating once mixed. Therefore, the powder coating once mixed cannot be reused to form a coating film having a different hue.

An object of the present invention is to provide an electrostatic powder coating method capable of solving the above-mentioned problems by utilizing electrophotographic technology in electrostatic powder coating technology.

[0014]

According to the present invention, there is provided an electrostatic powder coating method comprising: a latent image forming step of forming an electrostatic latent image on a photoreceptor;
A developing step of developing an electrostatic latent image by applying a thermosetting powder coating to the photoconductor by electrostatic force, and a first transfer step of transferring the powder coating on the photoconductor to a transfer sheet. A temporary fixing step in which the powder coating is heated at a temperature lower than the curing temperature of the powder coating so that the powder coating can be temporarily fixed to the transfer sheet; Thus, a baking step of baking the object to be coated and a peeling step of peeling the transfer sheet from the powder coating baked on the object to be coated are provided.

According to the electrostatic powder coating method of the present invention, the powder coating adhered on the photoreceptor is transferred onto the object to be coated via the transfer sheet by electrostatic force. A coating film can be formed without using it. In addition, since the coating film corresponds to the shape of the electrostatic latent image, any characters, numbers, patterns, images, figures, and the like can be formed by the coating film.

In the electrostatic powder coating method of the present invention, a plurality of types of powder coatings having different hues are sequentially transferred onto a transfer sheet by the latent image forming step, the developing step, and the transferring step. Then, it is preferable that the plurality of types of powder coatings are temporarily fixed on the transfer sheet by the temporary fixing step, and thereafter, the plurality of types of powder coatings are baked on the object to be coated by the baking step. . As a result, an arbitrary character, numeral, pattern, image, graphic, or the like can be formed by a coating film having a plurality of hues. The hue of the coating film is determined according to the hue of each type of powder coating and the amount of adhesion on the object to be coated. This makes it possible to form a coating film having a desired hue without mixing a plurality of types of powder coatings. Therefore, in obtaining a coating film having a uniform hue, the influence of the diameter of the powder coating particles can be reduced.

In the electrostatic powder coating method of the present invention, it is preferable that the plurality of types of powder coatings include powder coatings of three primary colors. Thereby, a coating film having an arbitrary hue can be obtained in accordance with the amount of the powder coating of the three primary colors adhered to the object to be coated.

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

The electrostatic powder coating apparatus 1 shown in FIG.
Fourth coating device 2a, 2b, 2c, 2d and each coating device 2
a, a transfer device 11 disposed below 2b, 2c, 2d
And

Each of the coating devices 2a, 2b, 2c, 2d has a drum-shaped photosensitive member 3a, 3
b, 3c, 3d, a mechanism for forming an electrostatic latent image on each of the photoconductors 3a, 3b, 3c, 3d (not shown), and a developing device 4a, 4b having a developing roller that is driven to rotate in the direction of the arrow in the figure.
4c and 4d.

Each of the photoreceptors 3a, 3b, 3c and 3d has a residual latent image erased by a pre-exposure device of an electrostatic latent image forming mechanism.
After being charged by the charging electrode, exposure is performed by an exposure device, whereby an electrostatic latent image is formed on the outer peripheral surface. Each of the developing devices 4a, 4b, 4c, and 4d causes the charged thermosetting powder coating to adhere to the opposing photoconductors 3a, 3b, 3c, and 3d by electrostatic force by rotation of the developing roller. As the developer, a two-component developer obtained by mixing magnetic particles in a powder coating as a carrier or a non-magnetic one-component developer incorporating non-magnetic particles in a powder coating can be used.
Further, in the case of applying a black color, a one-component developer containing magnetic particles in a powder coating can be used. The electrostatic latent image forming mechanism, the photoconductors 3a, 3b, 3c, and 3d, and the developing devices 4a, 4b, 4c, and 4d can have the same structures as those used in an electrophotographic copying machine. .

In the present embodiment, the transport device 11 is constituted by a belt conveyor, and has a conductive conveyor belt 12 which is driven to rotate in the direction of the arrow in the figure. The transfer sheet 90 is conveyed by being placed on the upper surface of the conveyor belt 12. Each of the photoconductors 3a, 3b, 3c, and 3d is sequentially pressed against the upper surface of the conveyed transfer sheet 90, so that the powder coating on the outer peripheral surfaces of the photoconductors 3a, 3b, 3c, and 3d is coated. 10 is transferred. This transfer is performed, for example, by bringing the outer peripheral surfaces of the photoconductors 3a, 3b, 3c, and 3d into close contact with the upper surface of the transfer sheet 90, and charging the powder coatings on the photoconductors 3a, 3b, 3c, and 3d. The charging can be performed by charging the conveyor belt 12 to the pole opposite to the pole. Therefore, one pole of the DC power supply 32 is connected to the conveyor belt 12, and the other pole is grounded.

As shown in FIG. 2A, the hue of the powder coating 42 applied to the transfer sheet 90 by the first coating device 2a is black. As shown in (2) of FIG. 2, the hue of the powder coating material 43 attached to the transfer sheet 90 by the second coating device 2b is cyan. FIG.
As shown in (3) of FIG.
The hue of the powder coating 44 attached by the coating device 2c is magenta. As shown in FIG. 2 (4), the hue of the powder coating material 45 attached to the transfer sheet 90 by the fourth coating device 2d is yellow. Thereby, a plurality of types of powder coating materials having different hues are sequentially attached to the transfer sheet 90. The order in which the yellow, magenta, and cyan paints adhere is not particularly limited.

The transfer sheet 90 to which the powder coatings 42, 43, 44, and 45 are attached is sent out from the transfer device 11 and then transferred to a fixing device (not shown) by another transfer device 11 '. The fixing device is, for example, a transfer sheet 90
As a heating means for the powder coatings 42, 43, 44, and 45 attached thereon, a pressure pinch roller having a built-in heater can be used. The powder coatings 42, 43, 44, 45
Is temporarily fixed to the transfer sheet 90 by being heated at a temperature lower than the curing temperature by the fixing device.
The temporarily fixed powder coatings 42, 43, 44, 4
5 is preferably covered with a protective film such as a PET film, polyethylene, or Teflon until the later-described baking is performed.

The material of the transfer sheet 90 is flexible, and the powder coatings 42, 4 heated at a temperature lower than the curing temperature are used.
3, 44, and 45 can adhere due to viscosity, and powder coatings 42, 43,
44 and 45 do not seize and can exhibit heat resistance. For example, a Teflon film or a heat-resistant silicone film is used. Further, on the transfer sheet 90, on a Teflon or silicone-based film surface, so as to be easily separated from the powder coatings 42, 43, 44, 45 baked on the coating object 10 in a baking process described later. For example, it is preferable to apply a release agent such as paraffin wax, carnauba wax and silicone wax.

As shown in FIG. 3A, the powder coatings 42, 43, 4 temporarily fixed on the transfer sheet 90 are provided.
The members 4 and 45 are heated by the heating device 91 in a state where the members 4 and 45 are pressed against the object to be coated 10, and are thereby thermally cured to be baked on the object to be coated 10. As the heating device 91, for example, a device that blows out hot air, an infrared heater called a radiant heating device, or the like can be used. Next, as shown in FIG.
The transfer sheet 90 is peeled off from the powder coatings 42, 43, 44, 45 baked to zero.

In the above embodiment, first, the first coating device 2
a, an electrostatic latent image is formed on the photoreceptor 3a, and a black thermosetting powder coating 42 is applied on the photoreceptor 3a by electrostatic force to develop the electrostatic latent image. The powder coating 42 on the photoreceptor 3 a is transferred onto the transfer sheet 90. Next, similarly, the cyan powder coating material 43 is transferred onto the transfer sheet 90 by the second coating device 2b.
Next, similarly, the magenta powder coating material 44 is transferred onto the transfer sheet 90 by the third coating device 2c. Next, similarly, the yellow powder coating material 45 is transferred onto the transfer sheet 90 by the fourth coating device 2d. Next, the respective powder coatings 42, 43, 4 on the transfer sheet 90
4 and 45 are heated at a temperature lower than the curing temperature and are temporarily fixed to the transfer sheet 90. Next, the transfer sheet 90
Each of the upper powder coatings 42, 43, 44, and 45 is pressed against the object to be coated and thermally cured, so that it is baked on the object 10 to be coated. Thereafter, the transfer sheet 90 is obtained from the powder coatings 42, 43, 44, 45 baked on the coating target 10.
Is peeled off.

According to the electrostatic powder coating method of the above embodiment, the powder coatings 42, 43, 44, and 45 attached to the photoconductors 3a, 3b, 3c, and 3d by electrostatic force are transferred to the transfer sheet 9.
Since the image is transferred onto the coating object 10 through the line 0, a coating film can be formed without using an electrostatic powder coating gun. In addition, since the coating film corresponds to the shape of the electrostatic latent image, any characters, numbers, patterns, images, figures, and the like can be formed by the coating film. Furthermore, after sequentially transferring a plurality of types of powder coating materials 42, 43, 44, and 45 having different hues onto a transfer sheet 90, and baking the coating object 10, a coating film having a plurality of hues can be formed. Characters, numbers, patterns, images, figures, etc. can be formed. The hue of the coating film is determined according to the hue of each type of powder coating materials 42, 43, 44, and 45 and the amount of the coating material to be coated. This makes it possible to form a desired coating film having a uniform hue without mixing a plurality of types of powder coatings 42, 43, 44, and 45. That is, in obtaining a coating film having a uniform hue, the influence of the diameter of the powder coatings 42, 43, 44, 45 can be reduced, and the powder coatings 42, 43, 44, 45 are not wasted. In the present embodiment, the powder paints 43, 4 of the three primary colors are used.
By adhering 4, 45, the three primary color powder coatings 4
Depending on the amount of 3, 44, 45 deposited on the coating object 10,
A coating film of any hue can be formed.

According to the above-mentioned electrostatic powder coating method, a uniform coating film can be obtained. Therefore, by mixing powder coatings of two or more hues, it is possible to obtain a coating film of a single uniform hue. Are suitable. In this case, in order to uniformly apply the powder paint to the object to be coated, the difference in charge amount between the powder paints to be mixed is 10%.
μC / g or less, and the difference in permittivity is 0.3
And the resistance ratio is preferably 1/10 to 10. In order to uniformly cure the applied powder coating, the difference in softening point between the powder coatings to be mixed is preferably within 10 ° C. The softening point can be measured by a Koka type flow tester. The difference in melt viscosity at the paint baking temperature between each powder paint to be mixed is 300c
It is preferably within p, and the difference in curing time is preferably within 120 seconds.

The present invention is not limited to the above embodiment. For example, the hue of the powder coating is not particularly limited.

[0031]

According to the electrostatic powder coating method of the present invention, there are no disadvantages when using a gun for electrostatic powder coating, and the color unevenness can be reduced without making the diameter of the powder coating particles unnecessarily small. It is possible to form a coating film free of powder, to eliminate waste of the powder coating, and to easily form arbitrary information such as characters on a coating object by using a coating film of a plurality of hues.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view of an apparatus for performing a powder coating method according to an embodiment of the present invention.

FIGS. 2 (1) to (4) are explanatory diagrams of a powder coating process according to an embodiment of the present invention.

FIGS. 3 (1) and (2) are explanatory diagrams of a powder coating process according to an embodiment of the present invention.

[Explanation of symbols]

 3a, 3b, 3c, 3d Photoreceptor 10 Object 42, 43, 44, 45 Powder paint 90 Transfer sheet

Claims (3)

[Claims] 1. A latent image forming step of forming an electrostatic latent image on a photoreceptor, and a developing step of developing the electrostatic latent image by applying a thermosetting powder coating to the photoreceptor by electrostatic force. And a transfer step of transferring the powder coating on the photoreceptor to a transfer sheet; and a temperature lower than the curing temperature of the powder coating so that the powder coating can be temporarily fixed on the transfer sheet. Temporary fixing step of heating, and baking step of baking the paint object by pressing the powder paint against the object to be cured, and peeling the transfer sheet from the powder paint baked to the object to be painted And an electrostatic powder coating method. 2. A plurality of types of powder coating materials having different hues are sequentially transferred onto a transfer sheet by the latent image forming step, the developing step, and the transferring step, and then the plurality of types of powder coatings are successively transferred. 2. The electrostatic powder coating method according to claim 1, wherein the powder coating is temporarily fixed on the transfer sheet by the temporary fixing step, and thereafter, the plurality of kinds of powder coatings are baked on the object to be coated by the baking step. . 3. The electrostatic powder coating method according to claim 2, wherein the plurality of types of powder coatings include powder coatings of three primary colors.