JPH04367762A - Control of film thickness of powder painting - Google Patents

Abstract

PURPOSE:To uniformly, simply and certainly control film thickness in powder painting. CONSTITUTION:An adhesive 3a is preliminarily applied to the surface of a steel plate 2a to be painted and a powder 1 having an m.p. higher than the baking temp. of the adhesive 3a is received in a storage tank 5 to be arranged between the surface of the steel plate 2a and the electrodes 4 arranged in opposed relation to the steel plate 2a and DC voltage is applied to the electrodes 4 to bond the powder 1 to the surface of the steel plate 2a. Subsequently, the steel plate 2a is heated to bake the powder 1 through the adhesive 3a to form a film. In this powder painting, the thickness of the film of the powder bonded to the surface of the steel plate 2a is controlled on the basis of the change of applied voltage, the change of the distance between the steel plate 2a and the electrodes 4, the change of the areas of the electrodes 4 and the change of the area of a painting window region.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is applied in the field of powder coating, in which the texture of powder particles can be brought out on the painted surface, and it is possible to obtain coated steel sheets with high design quality. The present invention relates to a method for controlling film thickness.

0002

[Prior Art] As a material to be painted, for example, a painted metal plate is
Traditionally, it has been mainly used for exterior purposes, such as roofing and exterior wall materials. For this reason, material properties such as corrosion resistance and weather resistance, primarily rust prevention functions, were required. However, in recent years, painted boards have been increasingly used as interior materials, and there has been a strong demand for their properties as amenity materials. For this reason,
Aesthetics and tactility have come to be considered important as functions required of painted boards. Among these, textured coating materials are one of the materials that are welcomed as they give a sense of luxury and provide a psychologically calming environment.

[0003] Methods for obtaining a painted surface with this texture include spray coating or roll coating a low-gloss paint on a substrate such as a steel plate, aluminum plate, or plastic plate, or electrostatic powder coating. Examples include a method of obtaining a thick coating film with a peel-like coating, and a method of pressing a tool with a large uneven surface onto a thickly coated vinyl chloride steel plate.

[0004] This invention has been proposed by the same inventor in order to obtain a powder-coated steel plate with a high design having an uneven coating surface. Powder and granular material having a melting point higher than the baking temperature of the material is stored in a storage tank, and the storage tank containing the powder and granular material is placed between an electrode that is placed facing the material to be coated, and a direct current is applied to this electrode. The powder and granules are attached to one side of the material to be coated by applying a voltage, and then the material to be coated is introduced into a drying oven, the material to be coated is heated, and the material to be coated is coated through the adhesive. In a powder coating method characterized by baking and thus forming a coating film (see FIG. 6), the present invention provides a method for improving the variation in coating film thickness, which has been a problem in the past. Conventionally, in this method, the coating film thickness was controlled by changing the line speed of the material to be coated.

[0005]

[Problem to be solved by the invention] However, by changing the conventional line speed, the film thickness of powder coating can be adjusted.
That is, the method of controlling the amount of adhesion has the following problems. FIG. 6 shows a schematic diagram of a conventional method for controlling the amount of coating by changing the line speed regarding powder coating of steel plates and the like. The steel plate 2 a to be painted is unwound from the uncoiler 12 , cleaned by a steel plate cleaning pretreatment device 15 , and then coated with adhesive 3 by a roll coater 14 . On top of the electrode 4 placed on the insulator 7 and connected to the DC voltage generator 10, the powder 1 is placed in a storage tank 6 with an open top. The charged powder 1 flies toward and adheres to the surface of the steel plate 2a coated with the adhesive 3 due to the electric field generated between the steel plate 2a and the electrode 4. Next, the painted steel plate 2a
is placed in a drying oven 11, heated and baked through the adhesive. The coating is thus completed and the coiler 13 winds it up.

In this way, the powder shown in FIG. 6 adheres to the surface of the steel plate due to electrostatic force. In this case, the position of the top surface of the powder decreases over time. For this reason, the coating flow rate becomes gradually lower. In the case of coil coating, this can be corrected by lowering the line speed, but at the same time, the residence time in the drying oven 11 also changes, making it necessary to control the oven temperature, which requires complicated measures overall. Furthermore, since the coating flow rate changes depending on the type of powder or granular material, it is necessary to set the line speed each time, and accordingly, the furnace temperature setting and adhesive coating conditions must also be changed. in this way,
In the method shown in FIG. 6, it has been desired to develop a simple method for controlling the coating film thickness, which can replace the conventional method of controlling the amount of coating by changing the line speed. However, such a method for controlling coating film thickness has not yet been proposed.

[0007] Therefore, the present invention was made in view of the above circumstances, and an object thereof is to provide an excellent coating film thickness control method that can easily and reliably control uniform film thickness. do.

[0008]

[Means for Solving the Problems] The gist of the present invention is as follows. (1) An adhesive is applied to the surface of the material to be painted in advance, powder and granules having a melting point higher than the baking temperature of the adhesive are stored in a storage tank, and an electrode is placed facing the surface of the material to be painted. The storage tank containing the powder and granules is placed between them, and the powder and granules are applied to one surface of the material to be coated by applying a DC voltage to the electrodes. The to-be-painted material to which the paint has been adhered is introduced into a drying oven, the to-be-painted material is heated, and the powder and granules are baked onto the to-be-painted material via the adhesive, thus drying one of the to-be-painted materials. In a method for controlling the film thickness of powder coating, which is characterized by forming a coating film on a surface, by changing the applied voltage and/or the distance between the material to be coated and the electrode, A method for controlling the film thickness of powder coating, comprising controlling the coating film thickness of the powder particles to be adhered to one surface of a material. (2) The film thickness control method for powder coating described above is characterized in that the coating film thickness of the powder adhered to one surface of the material to be coated is controlled by changing the area of the electrode. A method for controlling the film thickness of powder coating. (3) In the powder coating film thickness control method described above, a movable member for blocking the powder and granules between the storage tank in which the powder and granules are placed in contact with the electrode and the material to be coated is provided. A type shielding plate is provided, and the area of the coating window area to which the powder particles can adhere is made variable by the movable shielding plate, and by changing the area of the coating window area, one side of the material to be coated is A method for controlling the film thickness of powder coating, the method comprising controlling the film thickness of the powder coating applied to a surface. (4) A coating film thickness control method by changing the applied voltage and/or the distance between the material to be coated and the electrode as described in (1), and changing the electrode area as described in (2). By combining the method of controlling the coating film thickness by changing the area of the coating window region described in (3), the method of controlling the coating film thickness by changing the area of the coating window region described in (3) can be used to A powder coating film thickness control method characterized by controlling the coating film thickness.

[0009]

[Operation] The coating film thickness h by the electrostatic method according to this invention is
As schematically shown in FIG. 1, which explains that the coating film thickness is controlled by the coating flow rate of the powder and the residence time of the material to be coated at the electrode part, It is governed by the residence time τ of the material 2 in the electrode section 4.

0010

[Math 1]

FIG. 2 illustrates how the electric field strength E (electric field strength E=electrode voltage V/distance d between the material to be coated and the electrode) affects the coating flow rate 2 of the powder 1. . When the electric field strength Ec is exceeded, the coating flow rate 3 increases as the electric field strength E increases.

0012

[Math 2]

[0013]

[Math 3]

Furthermore, when the electric field strength E is increased, dielectric breakdown of the air occurs and spark discharge occurs, resulting in large variations in the coating flow rate. Here, the critical electric field strength Ec varies depending on the material to be coated, but is generally within a range of 1×10 4 [V/m] or more and 2×10 6 [V/m] or less. Further, the electric field strength Es at which spark discharge occurs varies depending on the distance d between the material to be coated and the electrode and the atmospheric pressure of the atmosphere, and follows Baschen's law.

[0015] Powder is charged in an electric field, and the amount of charge is q
Then, it is attracted to the surface to be painted by the Coulomb force F shown by the following equation [1]. F=qE ─ [1] Formula. The powder coating flow rate 4 increases as the Coulomb force F increases, and FIG. 2, which shows the relationship between the coating flow rate and electric field strength, clearly supports this fact. Here, the electric field strength E is proportional to the applied voltage V and inversely proportional to the inter-electrode distance d, as described above. In other words, by changing the voltage V, the coating flow rate 5 can be changed, and the coating film thickness h can be changed. This holds true even if the inter-electrode distance d is changed.

[0016]

[Math 4]

[0017]

[Math 5]

[0018] The longer the residence time τ in the electrostatic coating section, the thicker the coating film becomes. This residence time τ is inversely proportional to the sheet passing speed v and proportional to the electrode length l. In other words, even if the plate passing speed v is constant, the amount of adhesion can be changed by making the electrode length l variable. FIG. 3 schematically shows a method for making the electrode length variable. The electrode 4 is divided in the direction of movement of the material to be coated 2, and each electrode is energized or electrically interrupted as necessary. As shown in FIG. 4, which explains the coating window area, this is a window in which the opening is variable between the material 2 to be coated and the powder 1 in order to change the apparent length of the electrode. A movable painting window shielding plate 5 may be provided in the moving direction of the painting window 2, and the area of the painting window region may be controlled by this painting window shielding plate 5. As described above, according to the method of the present invention, it is possible to easily achieve uniform coating film thickness, which has been a problem in the past.

[0019]

[Example] Next, the present invention will be explained by referring to an example. An embodiment of coating film thickness control according to the present invention is shown in FIG. This embodiment is a method of controlling the coating film thickness by changing the applied voltage, the distance between the steel plate and the electrode, the electrode area, and the area of the coating window area. In this example, a steel strip was used as the material to be coated, which was unwound and wound into a coil. In the figure, 2a is a steel plate (steel strip) to be painted. On the surface of the steel plate 2a, a polyethylene adhesive 3a whose coating amount, viscosity, and volatile/nonvolatile content ratio are controlled in advance is applied at 17 g/m2. 1a is a granular material. In this example, polyurethane beads 1a having an average particle diameter of 74 μm before coating and which had been subjected to conductivity improvement treatment were used as the powder 1a. Polyurethane beads 1a are placed in an open-topped reservoir 6 placed on top of an electrode 4. As shown in FIG. 3, the electrode 4 disposed facing the surface of the steel plate 2a is divided in the direction of movement of the steel plate 2a, and each can be independently energized or electrically interrupted as necessary. The total electrode area can be changed. This electrode 4
At the same time, the storage tank 6 can be moved in the vertical direction, and the distance between it and the steel plate 2a can be changed. The electrode 4 and the storage tank 6 are mounted and fixed on an insulator 7,
These vertical movements are performed by an elevator 9 that is movable up and down and is provided under a concrete base 8 that supports them. 10 is a DC voltage generator connected to the electrode 4, 5 is a steel plate 2
This is a shielding plate that can change the area of a movable painting window area in the moving direction of a. Painted steel plate 2a,
The painted window area shielding plate 5 is grounded.

Powder coating of the steel plate 2a was carried out using the equipment shown in FIG. 5 through the following steps. That is, the steel plate 2a
is uncoiled from the uncoiler 12, cleaned by the steel plate cleaning pretreatment device 15, and then an adhesive 3a is applied in advance to the surface of the steel plate 2a by the roll coater 14,
Next, the powder 1a placed in the storage tank 6 placed on the electrode 4 is transferred to the steel plate 2a by applying a DC voltage to the electrode 4.
The adhesive 3 is charged by the electric field generated between the electrode 4 and the
It was made to adhere by flying toward the target surface of the steel plate 2a coated with a. At this time, the coating film thickness of the powder 1a adhered to the surface of the steel plate 2a was controlled by changing the applied voltage, the distance between the steel plate 2a and the electrode 4, the electrode area, and the area of the coating window area. Next, the painted steel plate 2a is placed in a drying oven 11, and the steel plate 2a is heated.
The powder 1a was baked onto the steel plate 2a via an adhesive to complete the coating, and the steel plate 2a was wound up into a coiler 13. Then, the thickness of the film formed on the surface of the steel plate coated in this manner was measured. Table 1 shows the film thickness measurement results (μ). Furthermore, in this example, the applied voltage V (Kv), the distance d (mm) between the steel plate and the electrode, and the electrode area S (m2)
and the painted window area (m2) are also shown in Table 1.

[0021]

[Table 1]

As shown in Table 1, it can be seen from conditions No. 1 and No. 2 that a thicker film can be obtained by increasing the electric field strength E (electric field strength E=applied voltage V/distance d between the steel plate and the electrode). However, the electric field strength E has a limit value corresponding to the distance between the steel plate and the electrode, and if the electric field strength E is made larger than the limit value, spark discharge occurs, resulting in insufficient powder adhesion and aesthetic defects on the painted surface. From conditions No. 1 and No. 3, it can be seen that even with the same electric field strength, increasing the distance d between the steel plate and the electrode results in a somewhat thicker film. This is because the larger the distance d between the steel plate and the electrode, the faster the powder particles reach the painted surface, and the more particles can be embedded deeper into the adhesive surface, allowing more powder particles to be coated. It is. From conditions No. 1 and No. 4, it can be seen that if the electrode area is increased, the amount of powder supplied increases, resulting in a thick film, and if the electrode area is decreased, the amount of powder supplied is reduced, resulting in a thin film. Similarly, regarding the painting window area, it can be seen from conditions No. 1 and No. 5 that increasing the area of the painting window area results in a thick film, and decreasing the area of the painting window area results in a thin film. This example shows that the coating film thickness can be controlled by varying the applied voltage, the distance between the steel plate and the electrode, the electrode area, and the area of the coating window region.

[0023] Regarding a cut steel plate, the surface of the steel plate that is not the surface to be painted is supported by means such as an electromagnet, adhesive is applied, electrostatic painting is performed, and then the cut steel plate is turned over. The coating is completed in the same way as steel strip by separating it from the support such as an electromagnet, placing it on a rotating conveyor roller with the painted side up and the unpainted side down, and placing it in a drying oven. can do.

[0024]

[Effects of the Invention] As explained above, according to the present invention, a method for controlling coating film thickness in powder coating can be achieved by (1)
Applied voltage and/or distance between the material to be coated and the electrode,
(2) Electrode area, (3) Painted window area area, (
4) Furthermore, since we have adopted a method of controlling the coating film thickness by varying the combination of these four conditions, the coating film thickness can be controlled more reliably and easily than the conventional method of varying the line speed. Moreover, a uniform film thickness can be obtained.

[Brief explanation of drawings]

[Figure 1] A diagram explaining that the coating film thickness is controlled by the coating flow rate of powder and the residence time of the material to be coated at the electrode section.

[Figure 2] Diagram showing the relationship between coating flow rate and electric field strength

[Figure 3] Diagram showing an electrode that is divided in the direction of movement of the material to be coated and the total electrode area can be changed by individually energizing or electrically cutting off each part as necessary.

[Figure 4] Diagram explaining the painting window area

[Figure 5] Schematic diagram of painting showing one embodiment of the present invention

[Figure 6] Schematic diagram of conventional powder coating in which coating film thickness is controlled by changing line speed

[Explanation of symbols]

1 Powder material 1a Polyurethane beads 2 Material to be painted 2a Steel plate to be painted 3 Adhesive material 3a Polyethylene adhesive 4 Electrode 5 Painted window shielding board 6 Storage tank 7 Insulator 8. Foundation 9 Elevator 10 DC voltage generator 11 Drying oven 12 Uncoiler 13 Coiler 14 Adhesive application roll coater 15 Pre-treatment equipment for steel plate cleaning.

Claims (6)

[Claims] Claim 1: An adhesive is applied in advance to the surface of the material to be painted, and a granular material having a melting point higher than the baking temperature of the adhesive is stored in a storage tank and placed opposite to the surface of the material to be painted. The storage tank containing the granular material is arranged between the electrode and the granular material is attached to one surface of the material to be coated by applying a DC voltage to the electrode, and then,
The material to be coated to which the powder and granules are attached is introduced into a drying oven, the material to be coated is heated, and the powder and granules are baked onto the material to be coated via the adhesive, thus, the material to be coated is heated. In a powder coating film thickness control method characterized by forming a coating film on one side of a material, the applied voltage and/or
A powder coating film characterized in that the thickness of the coating film of the powder particles attached to one surface of the material to be coated is controlled by changing the distance between the material to be coated and the electrode. Thickness control method. 2. An adhesive is applied in advance to the surface of the material to be painted, and powder and granules having a melting point higher than the baking temperature of the adhesive are stored in a storage tank and placed opposite to the surface of the material to be painted. A storage tank containing the powder and granules is arranged between the electrode and the powder is applied to one side of the material to be coated by applying a DC voltage to the electrode, and then the powder The material to be coated with the body attached thereto is introduced into a drying oven, the material to be coated is heated, the powder and granules are baked onto the material to be coated via the adhesive, and one side of the material to be coated is heated. In the method for controlling the film thickness of powder coating, which is characterized in that a coating film is formed on the surface of the coating material, the powder coating is applied to one surface of the material to be coated by changing the area of the electrode. A powder coating film thickness control method characterized by controlling the film thickness. 3. An adhesive is applied in advance to the surface of the material to be painted, and powder and granules having a melting point higher than the baking temperature of the adhesive are stored in a storage tank and placed opposite to the surface of the material to be painted. A storage tank containing the powder is placed between the electrode and the powder is applied to one surface of the material to be coated by applying a DC voltage to the electrode. The material to be coated with the granules attached is introduced into a drying oven, the material to be coated is heated, and the powder and granules are baked onto the material to be coated via the adhesive, thus drying the material to be coated. In a powder coating film thickness control method characterized in that a coating film is formed on one surface, the powder coating is blocked between the storage tank disposed in contact with the electrode and the material to be coated. A movable shielding plate is provided, the area of the coating window area to which the powder particles can adhere is made variable by the movable shielding plate, and by changing the area of the coating window area, the area of the coating window area is changed. A method for controlling the film thickness of powder coating, comprising controlling the coating film thickness of the powder and granular material adhered to one surface. 4. A film thickness control method by changing the applied voltage and/or the distance between the material to be coated and the electrode according to claim 1, and by changing the electrode area according to claim 2. By combining the film thickness control method and the coating film thickness control method by changing the area of the coating window region according to claim 3, the coating film thickness of the powder particles attached to the surface of the material to be coated is controlled. A method for controlling film thickness of powder coating. 5. The material to be coated is a strip metal plate,
The method for controlling film thickness of powder coating according to claim 1, 2, 3 or 4, wherein the metal plate is a cut plate-like metal plate. 6. An electric field strength between the material to be coated and the electrode, which is a value obtained by dividing the applied voltage by the distance between the material to be coated and the electrode, is 1×104 [V
6. The method for controlling film thickness of powder coating according to claim 1, 2, 3, 4, or 5, wherein the film thickness is within a range of 2×10 6 [V/m] or more and 2×10 6 [V/m] or less.