JPH0751225B2 - Powder coating equipment - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a powder coating apparatus for coating powder coating material on an object by electrostatic application.

(Prior Art) As a coating method, a method using a liquid paint (see, for example, Japanese Patent Laid-Open No.
61-25672, JP-A-61-220758) and powder coating using powder coating (for example, magazine "Painting Technology" P80-82, Riko Shuppan, November 1985 issue). The latter powder coating can be further divided into the fluidized-dip method and the electrostatic coating which is to be described.

As examples of the former, there are, for example, the Dobuzuke method in which an object to be coated is dipped in a water-based paint for coating, and the cationic electrodeposition coating method. Then, there is a problem that rust is easily generated.

In this respect, the cation electrodeposition coating method does not have any particular problems, but the equipment is large, and when it is used as a dedicated coating equipment for the shock absorber as the object to be coated, both the initial cost and the running cost are high. The cost will increase.

Therefore, electrostatic coating has recently attracted attention as a solution to these problems. Electrostatic coating is carried out by feeding powder coating material into an electrostatic field formed by using an object to be coated as an anode and a coating machine as a cathode.

By the way, conventionally, when coating an object to be coated, it has been conventionally performed as follows. That is, first, the object to be coated is pretreated by degreasing, chemical conversion treatment, etc., then the object to be coated after pretreatment is housed in a coating booth, the powder coating is sprayed onto the object to be coated by an electrostatic gun, and then baked. It is common to go through three roughly steps.

The coating booth usually has an opening through which the article to be coated enters and leaves and a powder recovery device is connected via a duct so that the article to be coated is stored in the coating booth from the opening. The powder paint is sprayed from the electrostatic gun, and the powder recovery device continues to operate during this period, and the powder paint that did not adhere to the object to be coated is absorbed from the duct by the suction force of the device.
It is recovered by the powder recovery device. The recovered powder paint is immediately reused.

(Problems to be Solved by the Invention) In the conventional example as described above, the object to be coated after pretreatment is stored in the coating booth as it is and electrostatically coated.
For example, if there are steps or gaps such as shock absorbers that are undercarriage parts of automobiles, it is difficult for powder coating material to enter the corners or gaps of the steps, so the coating thickness at these parts is uneven. It was.

In addition, electrostatic painting that sprays powder paint from the electrostatic gun,
Because it is done without closing the opening of the painting booth,
The powder coating material will be scattered outside the coating booth, and the powder coating material will be lost. Of course, leakage of powder paint from the coating booth is also prevented by an air curtain, but this is not preferable because considerable air movement occurs in the coating booth.

The present invention has been made to solve the above problems,
An object of the present invention is to obtain a powder coating apparatus capable of making the thickness of a coating film uniform even if there is a stepped portion or a gap in an object to be coated and reducing loss of the powder coating material as much as possible.

(Means for Solving Problems) The present invention provides a preheating device for preheating an object to be coated, a coating booth provided with an electrostatic gun for injecting powder coating material onto the object to be preheated, A post-heating device for post-heating an object to be electrostatically coated by the electrostatic gun is continuously installed, and a powder recovery device for sucking and recovering excess powder paint in the coating booth through a duct is installed. In the powder coating apparatus described above, a shutter is arranged in the opening for loading and unloading the object to be coated in the coating booth, and the electrostatic gun intersects the rotation axis of the object to be rotatably supported. The spraying direction is set so that the powder coating material is sprayed in the following direction, and a damper for adjusting the amount of suction air is arranged in the duct.

(Function) Since the object to be coated is preheated by the preheating device before being stored in the coating booth and electrostatically coated, the adhesion of the powder coating material to the object to be coated is increased and the conductivity of the coating material is increased. Since the insulating property of the coating film decreases due to the temperature dependence, the electrostatic application effect is improved, and therefore the coating efficiency is improved and the coating film on these parts even if there are steps or gaps on the object to be coated. The thickness can be made uniform.

Also, at the time of electrostatically applied powder coating, by closing the opening of the coating booth with a shutter and squeezing the duct with a damper,
It is possible to reduce the movement of air in the coating booth, and thus suppress the temperature decrease of the preheated coating object.

Furthermore, since the electrostatic gun is arranged so as to intersect the rotation axis of the object to be coated, the coating rate of the powder coating material does not decrease even if the object to be coated has a step.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows the overall structure of a powder coating apparatus according to the present invention, in which 1 is a trolley conveyor erected in a loop,
A plurality of hangers 2 capable of suspending an object to be coated are movably attached to the trolley conveyor 1 at appropriate intervals, and are intermittently driven clockwise by a drive device (not shown).

Below the trolley conveyor 1, an attachment zone 3 for attaching an object to be coated on the hanger 2, a degreasing zone 4, a water washing zone 5, a surface conditioning zone 6, a chemical conversion treatment zone 7, a water washing zone 8,
Hot water washing zone 9, air blow zone 10, pre-heating zone 11,
The coating zone 12, the post-heating zone 13, the water cooling zone 14, the air cooling zone 15, and the removal zone 16 for removing the object to be coated from the hanger 2.
Is provided. Reference numeral 17 is a coating machine, and 18 is a paint collecting device.

Next, these will be described in more detail. A degreasing zone 4 for degreasing an object to be coated, a water washing zone 5, 8, a surface conditioning zone 6, a chemical conversion treatment zone 7, a hot water washing zone 9, an air blow zone 10, a water cooling zone 14, Regarding the technical contents in each zone of the air-cooling zone 15, it is omitted to name the documents one by one, but since various techniques have already been disclosed and implemented, detailed description thereof will be omitted.

Therefore, here, the preheating zone 11 will be described first. In the preheating, the article to be coated is heated to 150 to 200 ° C by electromagnetic induction heating.

The reason for performing preheating is that the electrical conductivity of the paint has a temperature dependency, so preheating the coated object reduces the insulating property of the coating film and improves the electrostatic application effect. By increasing the viscosity of the powder coating material by the heat of 1, the uniformity of the coating film thickness in the dents and gaps of the coated object is improved.

The preheating method is preferably high-frequency electromagnetic induction heating, which can raise the temperature for a short time and has excellent energy efficiency by heat conversion. For example, JP-A-61-45592 and JP-A-61-96504
As described in the publication, in the conventional method of surrounding an object to be coated with a high-frequency exciting coil and performing induction heating, in the case where the shape of the high-frequency exciting coil has a margin with respect to a dimensional change of the object to be coated. , The change in temperature distribution becomes large.

Therefore, in the present invention, as described in, for example, Japanese Utility Model Laid-Open No. 61-96503, by inserting a high-frequency exciting coil formed in a rod-shaped body inside a hollow body to be coated, Prevents changes in temperature distribution due to changes.

Here, the temperature change of the article to be coated means that the shape based on the function of the article to be coated is generally similar, but the dimensions of the details change depending on the model, year or vehicle type.

When the preheating of the object to be coated is completed as described above, electrostatic application coating is then performed.

In this coating process, in order to prevent the preheating temperature from decreasing due to preheating of the object to be coated, electrostatically applied powder coating is performed in a hermetically closed state by allowing the opening of the coating booth to be closed.

FIG. 2 shows an apparatus used for electrostatically-applied powder coating. 19 is a coating booth, and a pair of electrostatic guns 20 and 21 are installed in the coating booth 19 so as to face each other. The electrostatic gun 20 is supported by a gun moving device 22 so as to be movable in a direction orthogonal to the spray direction of the powder coating material.

The coating booth 19 can be sealed as described above. That is, the coating booth 19 needs an opening for taking in and out the object to be coated, but in the present invention, this opening is closed by the shutter 23.

Reference numeral 18 is the above-mentioned paint collecting device, which is equipped with a dust collecting duct 25 attached to the bottom of the paint booth 19
Connected to 19. The paint collecting device 18 has a vacuuming device (not shown) for exhausting the inside of the coating booth 19, and the powder paint that does not adhere to the object to be coated is sucked and collected by the paint collecting device 18 via the dust collecting duct 25. It Reference numeral 26 denotes a damper provided inside the dust collecting duct 25 for adjusting the air volume in the duct 25.

The powder coating material collected by the coating material collecting device 18 is supplied to a coating machine 17 having a vibrating screen 27. The vibrating screen 27 is for removing foreign matter mixed in the powder coating material, and the powder coating material from which the foreign material is removed is supplied to the electrostatic guns 20, 21.

By the way, the reason for providing the shutter 23 and the damper 26, if the shutter 23 is not provided, it is necessary to prevent leakage of the powder coating material from the opening of the coating booth 19 by an air curtain, In such a case, the air moves in the coating booth 19, so that the temperature of the preheated coating object decreases.

In addition, when electrostatically applied powder is sucked without adjusting the air volume in the dust collection duct 25, the same coating booth as above
Significant air movement will occur within 19.

In the case where the shutter 23 and the damper 26 are not provided in this way, a considerable amount of air is moved in the coating booth 19, so that the temperature of the preheated coating object is lowered as described above.

Therefore, in the present invention, the opening for the entrance and exit of the object to be coated at the time of electrostatically applied powder coating is closed by the shutter 23, and the damper 26 is interlocked with the shutter 23, and the opening degree of the damper 26 is reduced when the shutter 23 is closed. By reducing the air flow rate, the amount of powder paint collected is reduced, and the air flow rate is increased by increasing the opening degree of the damper 26 when the shutter 23 is opened after taking out the object to be coated from the coating booth 19. Then, the powder paint is quickly collected.

By doing so, the movement of air in the coating booth 19 at the time of electrostatically applied powder coating can be reduced, and the temperature decrease of the object to be coated can be suppressed as much as possible.

In addition, it is preferable to line a vinyl chloride resin plastic plate on the inner surface of the booth 19 during painting. The reason for this is to prevent the electrostatic effect from the electrostatic guns 20 and 21 from being absorbed by the wall surface of the coating booth 19. By doing so, it is expected that the coating film thickness of the object to be coated is uniform, the coating efficiency is improved, and the paint recovery rate is improved, and as a result, the volume of the coating booth 19 can be reduced.

Fig. 3 shows the coating state with electrostatic guns 20 and 21.
8 is an object to be coated. Here, a shock absorber will be described as an example of the article to be coated 28. In the case of a shock absorber, since the step portions 28a and 28b are formed on both ends, the electrostatic guns 20 and 21 should be attached so that the powder coating easily adheres to the corners of the step portions 28a and 28b. The powder coating material is arranged obliquely upward so that the powder coating material is sprayed onto the stepped portions 28a, 28b from diagonally below to improve the adhesiveness of the powder coating material.

More specifically, one electrostatic gun 20 is replaced with the other electrostatic gun 21.
When the electrostatic gun 20 is applied by electrostatic force, the one electrostatic gun 20 is held in the same posture and stroked in the vertical direction, and the other electrostatic gun 21 is fixed.

Most preferably, the inclination angle θ ₁ of _one electrostatic gun 20 is about 15 ° and the inclination angle θ ₂ of the other electrostatic gun 21 is about 75 °. The stroke of one electrostatic gun 20 is 350mm,
The stroke speed is preferably 300 mm / sec.

Further, the object to be coated 28 is rotated during electrostatically applied powder coating. This rotation speed is regulated by the coating time.

Next, a more specific example of the coating conditions using the above apparatus will be described.

When applying static electricity, use one of the electrostatic guns 20 to 9-10
Once, and the other electrostatic gun 21 is applied 2-3 times. In this case, the rotation speed of the object to be coated 28 is set to 44 rpm when the coating time of one electrostatic gun 20 is 10 seconds and the coating time of the other electrostatic gun 21 is 4 seconds.

The amount of painting used is as follows. The length of the circular tube of the electrostatic gun 20, 21 is 350 mm, the diameter of the circular tube is 53 mm, and the diameters d ₁ and d ₂ of the steps 28a and 28b of the shock absorber (coated article 28) are 200 mm.
In the case of; a coating film having an average film thickness of 42 μm, a maximum film thickness of 60 μm and a minimum film thickness of 30 μm was obtained under the above conditions.

The weight of the paint at this time was 12 g.

Here, the above conditions are as follows. That is, the discharge amount of one electrostatic gun 20 is 56 g / min, the other electrostatic gun 20
21 discharge time 4 seconds, coating object 28 rotation speed 44 rpm, one electrostatic gun 20 stroke speed 300 mm / sec, stroke 350 m
m.

From the above, it can be seen that the coating rate is 94.5% and the residual paint is 5.5%.

As shown in FIG.
After being removed by the vibrating screen 27, the foreign matter is removed and then reused immediately after passing through a paint tank (not shown).

After the electrostatically applied powder coating of the coating object is completed as described above, the coating film is baked by post-heating in order to completely weld the coating material adhered to the coating object.

A high temperature infrared heating device is used as the coating baking device. Since the color of the coating film is mainly black, the absorption efficiency of infrared rays is high regardless of the frequency of the infrared rays. Therefore, by heating the surface temperature of the infrared source to 500 to 1000 ° C Will be possible.

As a concrete example of a heating device, the heat coil is made of Kanthal wire, and the Kanthal wire is attached to a ceramic fiber heat insulation board with a thermal conductivity of about 0.1 to 0.2 Kcal / nh, and there are two types of panel structures with ratings of 10.5KW and 21KW. As an example, a heating furnace in which a body is formed and these panel structures are combined into a box shape can be given.

Similar to a coating booth, a shutter was provided at the opening and exit opening of the coated object in such a heating furnace, and the coated object was charged while the movement of internal air was suppressed and the temperature was measured. A baking temperature of 180 ° C. and a baking time of 2 minutes were obtained with the interior entering time of 2 minutes and 40 seconds. At this time, the surface temperature of the infrared-generating heat source was 500 ° C in the lower part of the heating furnace and 700 ° C in the upper part.

Next, the powder coating material used for the above coating will be described.
Powder coatings that cure at a baking temperature of 180 ° C and a baking time of 2 minutes, such as epoxy resin (average molecular weight of about 12
Bisphenol A with 00-1600 and epoxy equivalent 700-1000
Type epoxy resin), a polyester resin having a carboxyl group (average molecular weight 2800 to 3800, acid value 50 to 70), and a powder coating composed of a glycol-modified imidazole catalyst that accelerates the curing reaction rate of these resins is used. As a concrete example of this, with the product name "Pawette TM-85 Black" relating to the manufacturing of Tokyo Paint Co., Ltd., the maximum particle size is 100μ
m, and the average particle size is adjusted to 42 μm.

However, the powder coating material is not limited to the above temperature 180-250 ℃,
Any material that can be hardened in a baking time of 2 minutes can be appropriately selected.

As described above, in this embodiment, in addition to the property that the resin is hardened in a short time, the heating furnace capable of rapid heating is used, and the object to be coated is preheated, so that the baking time is greatly shortened.

Such a powder coating material is advantageous not only in shortening the baking time but also in coating. That is, in the present invention, preheating is performed to increase the viscosity of the powder coating material as described above, but in order to further increase this effect, the powder coating material is fused to the object to be coated at around 110 ° C. It is preferable that the resins exemplified above satisfy this.

When the bake hardening is completed, cooling is then performed. This cooling is performed by a water spray device or a dipping device for quenching the object to be coated and cooling with a fan.

Next, the operation of the powder coating device having the above configuration will be described. First, after the article to be coated is attached to the hanger 2 in the attachment zone 3 shown in FIG. 1, the hanger 2 is intermittently driven to stop the article to be coated in each zone, and degreasing, water washing, surface conditioning, chemical conversion treatment,
After washing with water, washing with hot water and air blowing, the article to be coated is heated to 150 to 200 ° C. in the preheating zone 11 by the means described above.

Then, the preheated object to be coated is housed in the coating booth 19 through the opening of the coating booth 19, and after closing the opening with the shutter 23, the powder coating is applied to the object 28 to be coated as described above. To jet.

When the coating is completed in this way, the powder coating adhered to the article to be coated 28 is baked in the post-heating zone 13. Here, as described above, the article to be coated 28 is put in the heating furnace for 2 minutes and 40 seconds,
Bake for 2 minutes at a temperature of °.

After baking, the object to be coated is cooled in the water cooling zone 14 and the air cooling zone 15, and then the object to be coated is removed from the hanger 2 in the removal zone 16.

4 and 5 show the measurement results of the thickness of the coating film coated as described above, and FIG. 3 shows the coated object (shock absorber) coated by the electrostatic gun 20 that strokes up and down. ) Shows the coating film thickness on the shell portion 28c, and FIG. 4 shows the lower step portion 28b coated by the fixed electrostatic gun 21.
The coating thickness in (spring receiving) is shown.

In the figure, the graph connecting ● is the membrane pressure at the A site of the shock absorber shown in FIG. 6, and the graph connecting × is B.
The film thickness of the portion, the graph connecting Δ shows the film thickness of the C portion, and the graph connecting O shows the film thickness at the D portion. The graph connecting ▲ shows the film thickness obtained by the conventional electrostatic coating.

4 and 5, the range of P indicates the thickness of the shell portion 28c 10 mm below the lower surface of the upper step portion 28a, and the range of R is 10 m from the outer peripheral surface of the shell portion 28c in the radial direction.
The film thickness on the lower surface of the lower step 28b up to m is shown.

As can be seen from the figure, in the case of the present invention, a film thickness of 40 μm or more can be obtained, and the film thickness is almost uniform, and this coating state is as shown in P and R of the graph. There is almost no change in the corners.

(Effects of the Invention) As described above, in the present invention, after preheating, electrostatic application coating is performed by an electrostatic gun with a devised spraying direction. The improved and thick film thickness can be obtained, and the film thickness can be made uniform, so that stable quality can be ensured in continuous operation.

Also, by operating the shutter in the coating booth and the damper in the duct, the flow of air in the coating booth can be suppressed to a small level, so it is possible to maximize the adhesiveness of the powder coating and the electrostatic application effect. Therefore, the coating efficiency can be further improved.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a powder coating apparatus according to the present invention, FIG. 2 is a plan view showing a concrete example of the coating zone in FIG. 1, and FIG. 3 is a schematic diagram showing the arrangement of electrostatic guns. 4 and 5 are graphs showing the coating film thickness, and FIG. 6 is a bottom view of the lower step of the shock absorber. 11 …… Pre-heating zone (pre-heating device) 13 …… Post-heating zone (post-heating device) 19 …… Painting booth 20, 21 …… Electrostatic gun 28 …… Object to be coated

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tatsuo Sugimoto 1-1-7 Toyosu, Koto-ku, Tokyo (56) References JP-A-51-38324 (JP, A)

Claims (1)

[Claims] 1. A pre-heating device for pre-heating an article to be coated, a coating booth equipped with an electrostatic gun for spraying powder coating onto the pre-heated article, and electrostatic coating by the electrostatic gun. In the powder coating device, a post-heating device for post-heating an object to be coated is continuously installed, and a powder recovery device for suction-recovering excess powder paint in the coating booth through a duct is installed. A shutter is arranged in an opening of the booth for loading and unloading the article to be coated, and the electrostatic gun sprays the powder coating material in a direction intersecting the rotation axis of the article to be rotatably supported. The powder coating apparatus is characterized in that the injection direction is set as described above, and a damper for adjusting the suction scene is arranged in the duct.