JPH06114327A - Atomizing electrostatic coating method under rotation - Google Patents

Abstract

PURPOSE:To improve the deposition efficiency of paint keeping a high quality of coated products in an atomizing electrostatic coating method under rotion using a metallic paint. CONSTITUTION:A base coating process A is composed of the first step A1 and the second step A2. In the first step A1, a colored metallic paint discharged from a paint nozzle is atomized at the high speed rotation of an atomization head 15, and shaping air is ejected to the atomized paint. In the second step, the colored metallic paint discharged from the paint nozzle is atomized at a rotational speed slower than that of the atomization head 15 in the first step A1, and the shaping air which has the ejection direction inclined by a given angle from the central axis line of the atomization head 15 and has a higher speed as compared with that in the first step A1 is ejected to the atomized paint.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotary atomizing electrostatic coating method using a metallic coloring paint, and more particularly to a rotary atomizing electrostatic coating method capable of improving coating efficiency while maintaining good coating quality. Regarding the painting method.

[0002]

2. Description of the Related Art A paint is atomized by a mechanical high-speed rotation force, and the atomized paint is negatively charged,
The rotary atomizing electrostatic coating method, in which atomized paint is applied to an object by electrostatic force, has been adopted in many fields because of its good coating efficiency.

For automobiles, the aesthetic appearance of painting is emphasized, and today, painting using metallic paint is often performed. Flake pigments such as aluminum and mica are mixed in the metallic paint, and it is required to arrange the flake pigments so as to be parallel to the surface of the object to be coated in order to increase the coating brightness.

In order to make the flake pigment substantially parallel to the surface of the object to be coated, it is necessary to blow the atomized paint particles toward the object to be coated by high-speed shaping air. This allows the flake pigment to collide with the surface of the object to be coated at high speed, and the flake pigment becomes substantially parallel to the surface of the object to be coated. A technique for increasing the metallic brightness by increasing the flow rate of shaping air is described in Japanese Patent Laid-Open No. 3-101858.

[0005]

However, in the case of the method in which the metallic paint is collided with the object to be coated at a high speed by increasing the flow rate of the shaping air, the amount of the paint scattered becomes large, and the amount of the paint is larger than that in the usual electrostatic painting. Therefore, there arises a problem that the coating efficiency is lowered.

The coating efficiency of the paint is greatly influenced by the flow velocity of the shaping air as described above, but is also influenced by the rotation speed of the atomizing head. That is, since the paint is discharged from the atomizing head and atomized by the centrifugal force generated by the high speed rotation of the atomizing head, it is desirable that the atomizing head rotates slowly in order to suppress the scattering of the paint. However, if the rotation of the atomizing head is low, atomization of the paint is not promoted, which causes a problem that the coating quality is deteriorated.

The present invention focuses on the above-mentioned problems, and in rotary atomization electrostatic coating using a metallic paint, it is possible to improve the coating efficiency of the paint while maintaining good coating quality. An object is to provide an electrostatic coating method.

[0008]

In order to achieve this object, an electrostatic coating method according to the present invention is a base coating process for electrostatically coating an object to be coated with a metallic colored coating mixed with flake pigment. And a finish coating step of electrostatically coating the metallically coated object using a coating material which is adjacent to the base coating step and in which the flake pigment is not mixed, and the rotary atomization electrostatic coating method comprises: In the process, the metallic colored paint discharged from the paint nozzle is atomized by the high speed rotation of the atomizing head, and the shaping air whose spraying direction is parallel to the central axis of the atomizing head is sprayed toward the atomized paint. And the first step, which is adjacent to the first step, atomizes the metallic colored paint discharged from the paint nozzle at a speed lower than the rotation speed of the atomizing head in the first step, and jets A second step of injecting shaping air toward the atomized paint, the direction of which is inclined by a predetermined angle with respect to the central axis of the atomizing head and which is faster than in the first step. .

[0009]

In the rotary atomizing electrostatic coating method thus constituted, the object to be coated is coated in the first step of the base coating step and then in the second step. In the first step, since the atomizing head is rotated at high speed, atomization of the paint discharged from the atomizing head is promoted. In addition, since the atomizing head rotates at high speed, the scattering of paint is also large due to centrifugal force,
Since the scattering of the paint is suppressed by the shaping air that is jetted in parallel to the central axis of the atomizing head, the paint application efficiency is improved.

In the second step, since the high-speed shaping air is blown to the paint discharged from the atomizing head, the flake pigment in the paint becomes almost parallel to the surface of the object to be coated, and the metallic paint is applied. It is possible to increase the brightness. In the second step, since the shaping air has a high speed, the paint is likely to be scattered, but since the rotation speed of the atomizing head is slower than that in the first step, the scattering of the paint due to the centrifugal force is suppressed. The coating efficiency can be improved by just that much.

When the shaping air is high speed,
Since the atomized paint will go straight, the coating pattern may be small, but since the shaping air is jetted obliquely with respect to the center axis of the atomizing head in the second step, the shaping air Will spread radially outward, and it will be possible to prevent the paint pattern from contracting significantly. This suppresses uneven coating.

In the second step, since the rotation speed of the atomizing head is reduced, the paint is less likely to be atomized, but the high speed shaping air collides with the paint discharged from the atomizing head. The atomization of the paint is promoted by this high-speed shaping air.

As described above, by appropriately controlling the rotation speed of the atomizing head, the flow velocity of the shaping air, and the injection direction, the coating efficiency can be increased in the first step and the coating quality can be improved in the second step. It is possible to maintain.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the rotary atomizing electrostatic coating method according to the present invention will be described below with reference to the drawings.

FIGS. 1 to 8 show an embodiment of the present invention, particularly when it is applied to the top coating of a vehicle body. First, the coating device used in the present invention and the arrangement of the coating device will be described. In FIG. 1, reference numeral 1 denotes a coating booth, and a transportation conveyor 3 for transporting a vehicle body 2 as an object to be coated is laid in the coating booth 1.

The coating booth 1 has a base coating process A and a finish coating process B, and the finish coating process B is located after the base coating process A. The base painting process A is
It is composed of a _first step A ₁ and a second step A ₂ . A drying furnace 71 is arranged between the base coating process A and the finish coating process B in the coating booth 1.

In the first step A ₁ , a side automatic coating device 31 arranged on both sides of the conveyor 3 and a top automatic coating device 41 arranged directly above the conveyor 3 are arranged. The top automatic coating device 41 is arranged in front of the side automatic coating device 31 in the traveling direction of the vehicle body 2. The side automatic coating device 31 has a plurality of rotary atomizing electrostatic coating machines 32, 33, 34. The top automatic coating device 41 comprises a plurality of rotary atomizing electrostatic coating machines 42, 43, 4
Have four.

The side automatic coating device 31 has a function of coating the side surface of the vehicle body 2, and the top automatic coating device 41 has a function of coating the upper surface portion, front portion, and rear portion of the vehicle body 2.

In the second step A ₂ , the side automatic devices 51 arranged on both sides of the transfer conveyor 3 and the transfer conveyor 3 are used.
And a top automatic coating device 61 arranged immediately above the above. The top automatic coating device 61 is arranged in front of the side automatic coating device 51 in the traveling direction of the vehicle body 2. The side automatic coating device 51 has a plurality of rotary atomizing electrostatic coating machines 52 and 53. Top automatic painting equipment 61
Has a plurality of rotary atomizing electrostatic coaters 62, 63, 64.

The side automatic coating device 51 has a function of coating the side surface of the vehicle body 2, and the top automatic coating device 61 has a function of coating the upper surface portion, front portion, and rear portion of the vehicle body 2.

In the finish coating step B, a side automatic coating device 81 arranged on both sides of the conveyor 3 and a top automatic coating device 91 arranged directly above the conveyor 3 are arranged. The top automatic coating device 91 is arranged in front of the side automatic coating device 81 in the traveling direction of the vehicle body 2. The side automatic coating device 81 has a plurality of rotary atomizing electrostatic coating machines 82, 83, 84, 85. The top automatic coating device 91 includes a plurality of rotary atomizing electrostatic coating machines 92, 9
It has 3, 94.

The side automatic coating device 81 has a function of coating the side surface of the vehicle body 2, and the top automatic coating device 91 has a function of coating the upper surface portion, front portion, and rear portion of the vehicle body 2.

Next, the structure of the rotary atomizing electrostatic coating machine arranged in each step will be described. The configurations of the electrostatic coating machines arranged in the base coating step A and the finish coating step B are basically the same, but the second step A ₂ of the base coating step A ₂
Rotary atomizing electrostatic coating machines 52, 53, 62, 6 arranged in
Only 3 and 64 are different in the configuration of the shaping air nozzle. Therefore, the common structure of the electrostatic coating machine will be described first, and different parts will be described with reference to FIGS.

In FIG. 2, reference numeral 11 indicates a rotary atomizing electrostatic coating machine. The rotary atomizing electrostatic coating machine 11 has a resin housing 12. Inside the resin housing 12, a hollow rotating shaft 13 supported by an air bearing (not shown) is arranged. The rotary shaft 13 is rotationally driven by an air motor 14.

A bell-shaped atomizing head 15 is attached to the tip of the rotary shaft 14. A paint nozzle 16 for supplying the metallic coloring paint 4 to the atomizing head 15 is arranged in the hollow portion of the rotary shaft 14. A flake pigment is mixed in the metallic coloring paint 4. The metallic coloring paint 4 supplied to the atomizing head 15 is discharged outward in the radial direction by the rotational force of the atomizing head 15 by the air motor 14. Second step A _{2 of} base coating step A
The peripheral speed of the atomizing head 15 in each electrostatic coating machine arranged in the finishing coating process B is set to 120 m / sec or less. The peripheral speed of the atomizing head 15 in each electrostatic coating machine arranged in the first step A ₁ is set to 120 m / sec or more.

A ring-shaped shaping air cap 18 is attached to the end of the resin housing 12 on the side of the atomizing head 15. Air is pumped into the shaping air cap 18 via an air passage 20. A plurality of shaping nozzles 19 are formed at the tip of the shaping air cap 18. The shaping nozzles 19 are arranged in a circle.

The shaping air 5 is jetted from each shaping nozzle 19 in parallel with the central axis Y of the atomizing head 15. Shaping air 5
It is adapted to be sprayed toward the paint 4a atomized by the atomizing head 15. The shaping nozzle 19 formed so that the shaping air 5 is parallel to the central axis Y of the atomizing head 15 is provided in each of the first step A ₁ of the base coating step A and the finish coating step B. It is provided only on the rotary atomizing electrostatic coating machine.

5 and 6 show the arrangement of the external electrode 21 for charging the paint 4a atomized by the atomizing head 15 with a negative charge. A plurality of external electrodes 21 are radially provided. One of the external electrodes 21 is fixed to the resin housing 12, and the other extends in parallel along the central axis Y of the atomizing head 15. The tip of the external electrode 21 is formed on the electrode pin 21a. The electrode pin 21a of the external electrode 21 is located slightly behind the tip of the atomizing head 15 in the _first step A ₁ . In the second step A ₂ , the electrode pin 21 a projects slightly forward of the end surface of the atomizing head 15. It is desirable that this protrusion amount be 50 mm or less.

Each outer electrode 21 has a circumference of 6 in this embodiment.
It is placed in equal parts. A high voltage generator 22 is connected to the external electrode 21. The external electrode 21 is used only in the case of electrostatic coating using a water-based metallic paint instead of a solvent-based metallic paint. In the case of a solvent-based metallic paint, the external electrode 21 is directly applied to the resin housing 12 side. A voltage is applied. It is desirable that the attachment radius R of the external electrode 21 from the central axis Y be less than or equal to twice the diameter of the atomizing head 15.

7 and 8 show a jetting configuration of shaping air in the rotary atomizing electrostatic coating machine used in the second step A ₂ of the base coating step A. A plurality of shaping nozzles 25 are formed at the tip of the shaping air cap 18. Shaping nozzle 25
From the predetermined angle θ with respect to the central axis Y of the atomizing head 15.
Only, the shaping air 5 is jetted in the direction inclining in the direction opposite to the rotation direction of the atomizing head 15.
The angle θ is set to, for example, 10 to 60 °. The flow velocity of the shaping air 5 in the _second step A ₂ is higher than the flow velocity of the shaping air 5 in the _first step A ₁ .

Next, the procedure and operation of the rotary atomizing electrostatic method of the present invention will be described. When the vehicle body 2 transported into the coating booth 1 reaches the base coating process A, the coating work by the side automatic coating device 31 and the top automatic coating device 41 arranged in the first process A ₁ is started.

In the first step A ₁ , since the atomizing head 15 is rotated at a high speed, atomization of the paint discharged from the atomizing head 15 is promoted. Further, since the atomizing head 15 rotates at high speed, the scattering of the paint becomes large due to the centrifugal force, but the scattering of the discharged paint 4a is injected in parallel with the axis Y of the atomizing head 15. Since it is suppressed by the air 5, the coating efficiency of the paint is improved. That is, in the first step A ₁ , in order to maximize the suction effect due to the electrostatic voltage, the atomized paint is gently pushed forward by using air of low pressure (1-2 kg / cm ² ). ing.

When the painting operation in the first step A ₁ is completed, the vehicle body 2 is moved by the conveyor 3 to the second step A ₂
Then, the coating work by the side automatic coating device 51 and the top automatic coating device 61 is started. In the second step A ₂ , since the high-speed shaping air 5 is blown to the paint 4 that has separated from the atomizing head 15, the flake pigment in the metallic coloring paint 4 becomes substantially parallel to the surface of the vehicle body 2, and It is possible to increase the brightness.
In the second step A _2, but the paint 4a tends to scatter because the shaping air 5 becomes faster, the rotational speed of the atomizing head 15 is first lower than step A _1, the coating materials of the centrifugal force Scattering is suppressed, and the coating efficiency of the coating material 4a is increased accordingly.

When the shaping air 5 is at a high speed, the atomized paint will go straight, which may cause a small coating pattern. However, in the second step A ₂ , the shaping air 5 is slanted. Since the shaping air 5 is spread in the radial direction, the coating pattern is prevented from becoming extremely small. This enables uniform coating.

In the second step A ₂ , since the rotation speed of the atomizing head 15 decreases, the paint 4 is less likely to be atomized, but the paint 4 separated from the atomizing head 15 has a high-speed shaping air 5
Are collided with each other, the atomization of the paint 4 is promoted by the high-speed shaping air 5. That is, in the second step A ₂ , in order to improve the coating quality, the flake pigment is arranged in parallel with the surface of the vehicle body 2 by using high pressure air (3 to 4 kg / cm ² ), and It promotes atomization.

When the painting operation in the second step A ₂ is completed, the vehicle body 2 is transported to the drying furnace 71 by the transport conveyor 3. The vehicle body 2 is heated by the drying oven 71 to accelerate the drying of the paint. In this embodiment, the base coating process A
Since the water-based paint is used, the drying furnace 71 is provided in the coating booth 1. However, when the metallic coloring paint 4 used in the base coating process A is a solvent-based paint, forced drying is performed. There is no need, and the drying oven 71 becomes unnecessary.

When the coating material is completely dried by the drying oven 71, the body 2 is finished by the conveyor 3 in the finish coating step B.
Be transported to. When the vehicle body 2 reaches the finish coating process B,
Side automatic coating device 81 and top automatic coating device 91
The painting work is started. In the finish coating step B, an electrostatic coating operation using a metallic clear paint or a solid paint is performed. The flake pigments are not mixed in these coating materials used in the finish coating step B.

In the finish coating step B, the peripheral speed of the atomizing head 15 is 120 m / m as in the second step A ₂ of the base coating step A.
It is set to be equal to or less than a second, and the injection of the shaping air 5 is made parallel to the axis Y of the atomizing head 15 and at a low speed as in the first step A ₁ .

As described above, in the base coating process A, the coating process is divided into the first process A ₁ and the second process A ₂ , and the rotation speed of the atomizing head 15 and the flow velocity of the shaping air 5 are calculated in each process. Since the jetting directions are set to be different from each other, the coating efficiency can be enhanced in the first step A ₁ and the coating quality can be enhanced in the second step A ₂ . In the present embodiment, coating efficiency of the paint 4a is 70 to 80% in the first step A ₁ in the second step A ₂ 5
It becomes 0 to 60%.

In this embodiment, the paint used in the painting work in the base painting process A is explained by using the water-based paint, but the same can be applied to the painting work using the solvent. Furthermore, although the present invention has been described as applied to automatic painting of a vehicle body, the article to be coated is not limited to the vehicle body 2 and may be various products.

[0041]

According to the present invention, the following effects can be obtained.

(1) The base coating process is composed of a first process and a second process. In the first process, the metallic colored paint discharged from the paint nozzle is atomized by the high speed rotation of the atomizing head. , Since the shaping air whose spraying direction is parallel to the central axis of the atomizing head is sprayed toward the atomized paint, the atomization of the paint discharged from the atomizing head can be promoted. In addition, it is possible to prevent the paint from scattering. Therefore, it is possible to maintain good coating quality due to the atomization of the coating material, and it is possible to enhance the coating efficiency of the coating material.

(2) In the second step, the metallic colored paint discharged from the paint nozzle is atomized at a speed lower than the rotation speed of the atomizing head in the first step, and the injection direction is the central axis of the atomizing head. On the other hand, since the shaping air, which is inclined at a predetermined angle and is faster than the first step, is jetted toward the atomized paint, the flake pigment in the metallic colored paint is applied to the surface of the object to be coated. Are almost parallel, and metallic brightness can be increased.

(3) In the second step, since the flow velocity of the shaping air is high, the paint is easily scattered, but since the rotation speed of the atomizing head is lower than that in the first step, centrifugal force is applied. Scattering is suppressed, and the coating efficiency of the paint can be maintained high. Further, since the shaping air is jetted obliquely in the second step in which the shaping air has a high speed, it is possible to prevent the coating pattern from becoming extremely small.

(4) In the second step, since the number of revolutions of the atomizing head decreases, the paint is less likely to be atomized, but the high speed shaping air collides with the paint discharged from the atomizing head. Therefore, the atomization of the paint is promoted by this high-speed shaping air. Therefore, even in the second step, although the coating efficiency is slightly lower than that in the first step, the coating efficiency can be maintained high and the coating quality is also good.

(5) As described above, since it is possible to improve the coating efficiency of the coating material, it is possible to reduce the amount of the metallic colored coating material used in the base coating process and to reduce the amount of the coating waste in the coating booth. The amount generated can also be reduced.

[Brief description of drawings]

FIG. 1 is a plan view of a vehicle body top coating process to which an electrostatic coating method according to an embodiment of the present invention is applied.

FIG. 2 is a partially enlarged cross-sectional view of a rotary atomizing electrostatic coating machine used in the top coating process of FIG.

FIG. 3 is a side view showing a spraying state of shaping air in the first step and finish coating step of FIG. 1.

FIG. 4 is a front view of FIG.

5 is a side view of the rotary atomizing electrostatic coating machine arranged in the base coating process of FIG. 1. FIG.

FIG. 6 is a front view of FIG.

FIG. 7 is a side view showing the injection state of shaping air in the second step of FIG.

8 is a front view of FIG. 7. FIG.

[Explanation of symbols]

1 Coating booth 2 Car body as an object to be coated 3 Conveyor 4a Atomized paint 5 Shaping air 11 Rotary atomization electrostatic coating machine 15 Atomization head 16 Paint nozzle 19 Shaping nozzle 21 External electrode A Base coating process A ₁ No. ₁ 1st process A ₂ 2nd process B Finish coating process Y Central axis of atomizing head θ Shaping air injection angle

Front Page Continuation (72) Inventor Masashi Murate 1 Toyota Town, Toyota City, Aichi Toyota Automobile Co., Ltd.

Claims (1)

[Claims] 1. A base coating step of electrostatically coating an object to be coated using a metallic coloring coating material in which flake pigments are mixed, and a metallic coating which is adjacent to the base coating step and in which the flake pigments are not mixed. A rotary atomization electrostatic coating method comprising a finish coating step of electrostatically coating a coated object, wherein the base coating step comprises the step of atomizing a metallic colored paint discharged from a paint nozzle into fine particles by high-speed rotation of a head. And spraying shaping air in which the spraying direction is parallel to the central axis of the atomizing head toward the atomized paint, and adjacent to the first step, and is discharged from the paint nozzle. The metallic coloring paint is atomized at a speed lower than the rotation speed of the atomizing head in the first step, and the injection direction is inclined at a predetermined angle with respect to the central axis of the atomizing head A rotary atomizing electrostatic coating method comprising a second step of spraying high-speed shaping air toward atomized paint.