JPH09164353A - Roll coater coating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively remove bubbles in a coating material and to better the dispersion of particles such as pigment in the coating material and to continuously manufacture a metal plate having few defects in coating by installing a coating material tank for agitating a coating material and a coating material adjusting tank for making defoaming treatment separated from each other. SOLUTION: A coating material which has overflowed a coater pan 2 is recovered in a coating material recovery tank 3 through an overflow pipe 9. In the coating material recovery tank 3, bubbles in the coating material or bubbles generated during falling are floated and removed. The coating material after recovery is sent to a coating material tank 5 through piping 10 by a pump 4, and it is agitated by an agitator 24 there in order to uniformalize the concentration of the coating material or to uniformly disperse particles such as pigment and aggregate. While the flow rate of the coating material is adjusted by an adjusting device 12, it is sent to a coating material adjusting tank 1, and the bubbles in the coating material are enlarged by an ultrasonic oscillator 6 to effectively break them. In this way, the occurrence of defects in coating is lessened to reduce a variation in paint film thickness.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the efficient removal of air bubbles entrapped in a paint, or the efficient dispersion of particles such as pigments, aggregates, and metal powders such as aluminum in the paint to prevent coating defects. The present invention relates to a roll coater coating device for continuously producing a coated metal sheet with little generation.

[0002]

2. Description of the Related Art Many coated metal sheets are manufactured by roll coater coating. In roll coater coating, usually, a roll partially immersed in the paint in the coater pan is rotated to pump up the paint, and the pumped paint is directly transferred to the metal plate that is the material to be coated, or the pumped paint is transferred to another roll. Then, the coating material adhered to the transferred roll is applied to a metal plate as a coating material to form a coating film.

Referring to FIG. 4, a case where a steel sheet is coated by a roll coater coating device using three coater rolls will be described as an example. In FIG. 4, the three coater rolls are a pickup roll 15 and an applicator roll 1.
6 is a doctor roll 18, 5 is a paint tank,
2 is a coater pan, 21 is a paint circulation pump for sending paint from the paint tank 5 to the coater pan 2, and the paint tank 5
Is provided below the coater pan 2. A part of the pickup roll 15 is dipped in the coater pan 2 containing the paint, the pickup roll 15 is rotated, and the film thickness of the paint 20 drawn up from the coater pan 2 is adjusted by the doctor roll 18.
It is applied to the steel plate 17 that travels via 6. The steel sheet coated with the paint is baked by a baking facility (not shown) to form a coated steel plate. On the other hand, the paint 20 is sent from the paint tank 5 to the coater pan 2 by the paint circulation pump 21,
Some of the paint adheres to the steel plate 17, but the excess paint returns to the paint tank 5 again via the paint return pipe 23. In the paint tank 5, the paint is stirred by a stirring device 24 having stirring blades in order to make the paint concentration uniform. Further, in order to replenish the paint that has adhered to the steel plate and is reduced, the paint is replenished from the paint replenishment tank 25 to the paint tank 5 as necessary.

When the paint is circulated and coated on the steel sheet by the above-mentioned coating apparatus, bubbles generated during the circulation of the paint are entrained in the paint and brought into the coater pan.
The coating material adheres to the steel sheet through the pickup roll and the applicator roll while enclosing the air bubbles, so that coating film defects such as swelling and foaming occur on the coating surface of the steel sheet.

[0005] In recent years, with the expansion of applications of coated steel sheets in the fields of building materials and home appliances, diversification of products of coated steel sheets,
The quality is being further improved. Correspondingly, the composition of the paint resin components, auxiliaries, solvents, etc. becomes more complicated, and in addition to this, various additives are used in combination, and the paint becomes more likely to generate bubbles. There is. In addition, various pigments, aggregates, particles of aluminum powder and the like have been added to improve the design. Since these compound particles are settling particles, in order to improve the dispersion state in the paint, stirring is strengthened by stirring blades in the paint tank. It is easier to get caught in the inside.

The addition of an antifoaming agent has been studied in order to suppress the generation of bubbles. However, the addition of the defoaming agent may easily cause other coating defects such as repellency and leveling failure, and it is currently difficult to completely prevent the generation of bubbles with this type of additive.

Therefore, measures against defoaming by improving the coating apparatus are being studied. (1) Japanese Patent Application Laid-Open No. 6-312152 describes a technique for removing bubbles from the coating material supplied to the coater pan. Specifically, for example, in Example 2 thereof, as shown in FIG. 5, a part of the pickup roll 15 is immersed in the paint pan 2 to adhere the paint to the roll surface,
In a roll coater for strip material that continuously applies to the strip material,
The paint pan 2 is horizontally divided into two sections 31a and 31c by a dam plate 30, a paint supply port 32 and a discharge port 33 are provided in the first section 31a, and a pickup roll 15 is provided in the second section 31c. And the bottom of the dam plate 30 is slightly higher than the bottom of the paint pan 2 so that the first section 31a and the second section 31c communicate with each other at the bottom of the paint pan 2. A paint pan in which the height of the paint outlet 33 in the section 31a is higher than the bottom surface of the paint pan 2 is described. With such a configuration, as the paint circulates, the bubbles contained in the paint rise in the section 31a of the paint pan partitioned by the weir plate 30 and come out to the liquid surface to disappear, so that the bubbles are picked up. It is prevented from moving into the section 31c on the roll 15 side and adhering to this roll.

(2) Japanese Laid-Open Patent Publication No. 56-81112 discloses a resonance frequency of 10 to 50 provided in the middle of a circulating device.
A technique for removing bubbles in the paint before reaching the coating part by a defoaming device having a KHz ultrasonic vibrator is described. Specifically, in Example 1, in the curtain coater coating using the apparatus shown in FIG. 6, the coating material provided in the lower portion of the coating material that drops in a film form from the head tank 40 provided in the upper portion of the object to be coated. It is collected in a tank 41, defoamed from the tank by a gear pump 42 in a defoaming processing chamber 43, and then returned to a head tank 40 provided in the upper part again. Conveyor device 4
4 is coated when the article to be coated passes over the surface.

The paint in the paint tank 41 is a gear pump 42.
Thus, it is fed into the defoaming processing chamber 43 equipped with the ultrasonic defoaming device. With respect to the paint sent into the defoaming processing chamber 43, the bubbles in the paint float on the surface by the action of the ultrasonic oscillator 45 and the oscillator 46. Compressed air is sent into the defoaming processing chamber 43 via a compressor 47 and a regulator 48,
The air bubbles are removed by increasing the pressure of the void portion of the defoaming chamber 43 and at the same time giving a certain wind speed to the liquid surface. The defoamed paint flows out from the paint discharge port 49 and is poured into the head tank 40 along the guide plate 50.

(3) Japanese Unexamined Patent Publication No. 62-97668 discloses a dip coating method in which an article to be dipped in a coating is
By applying ultrasonic waves of 0 KHz or more and 50 KHz or less, after coating, destroy the bubbles formed in the dents and voids of the coating object, and apply the coating material of the coating object with strong adhesion without unevenness. Is listed. Also, JP-A 2-3-3
According to Japanese Patent No. 1852, an ultrasonic oscillator is installed inside a paint tank in which an object to be coated is immersed, and it becomes possible to remove bubbles generated in the paint when the paint is supplied and to stir the paint for each application. It is described that application is possible.

[0011]

However, the technique described in the above publication has the following problems. (1) In the case of the technique described in Japanese Patent Laid-Open No. 6-312152, a first method for raising bubbles in a paint pan
Since the area of the section is small, the paint supplied into the coater pan flows into the second section on the pickup roll side before the bubbles therein sufficiently rise in the first section. Further, if the area of the first section is made to have a sufficient capacity for the rise of air bubbles, the settling of metal powder or the like mixed in the paint in this section will increase and the uniformity of the paint on the pick-up roll part will deteriorate, A uniform coating film is formed, and it is not possible to achieve both removal of air bubbles and good dispersion of metal powder and the like mixed in the coating material.

(2) In the case of the technique described in Japanese Patent Laid-Open No. 56-81112, the bubbles floating in the defoaming chamber are forcibly broken by the compressed air, so that the solvent evaporation from the paint surface is large. Nari paint viscosity changes greatly,
Also, the surface of the paint is skinned and this may be brought into the head tank. In addition, air bubbles that have floated above the paint in the defoaming chamber gather, but here large air bubbles that remain without being broken are brought into the head tank as they are, and small air bubbles that are not broken are sent to the head tank. After collection, they may aggregate into large bubbles. When this technique is applied to the roll coater coating which is the subject of the present invention, the above-mentioned bubbles may be brought into the coater pan, and the coater as described in JP-A-6-312152 of (1) is intended. It is difficult to solve the problems of the present invention by this technique, which requires countermeasures for defoaming the bread.

(3) The techniques described in JP-A-62-97668 and JP-A-2-31852 are intended for dip coating, and a method of continuously coating a steel sheet by roll coater coating while circulating the coating material. The present invention relates to a technology different from the technology targeted by the invention. All of the techniques described in these publications defoam using ultrasonic waves in the coating section, but when this technique is applied to the roll coater coating targeted by the present invention, in the process of defoaming Since the bubbles floating on the surface adhere to the steel sheet, it is difficult to solve the problem of the present invention by this technique.

The technique described in the above-mentioned publication is insufficient as a countermeasure against bubbles contained in the paint, or there is no description or suggestion of countermeasures against bubbles in the roll coater coating.

The present invention has been made in consideration of the above-mentioned circumstances. When the roll coater coating is performed on the metal plate while circulating the paint to be contained in the coater pan, the bubbles trapped in the paint are efficiently defoamed. Or to further improve the dispersion of particles of pigments, aggregates, metal powders such as aluminum in the paint, and to provide a coating apparatus capable of continuously producing a coated metal plate with few coating defects. With the goal.

[0016]

Means for Solving the Problems The present inventors have made various studies on the state of bubbles which are coating defects and the states of bubbles in the coater pan and various parts of the paint circulating apparatus.

As a result, large bubbles having a size of several hundreds of μm or more are easily broken at the coating stage and are less likely to cause a coating defect, but fine bubbles having a size of several tens of μm or less are pumped up by a pickup roll. It was found that when it was removed, it remained after the application and was likely to cause a coating defect.

Further, it has been found that the generation of fine bubbles having a size of about several tens of μm or less is due to the following reason. (Case 1) When the paint tank is lower than the position of the coater pan, during coating, air bubbles are entrained in the paint as the pick-up roll rotates, or paint squeezed between the pick-up roll and the applicator roll or between the applicator roll and the steel plate. Bubbles are generated due to falling into the coater pan. These bubbles are entrained in the paint that overflows from the coater pan and are delivered to the paint tank without disappearing.

When the paint overflowing from the coater pan falls into the paint tank, new bubbles are generated.

When the paint is replenished in the paint tank, or in order to make the paint concentration uniform, the paint is agitated by a stirrer equipped with a stirring blade. At that time, air bubbles are entrapped in the paint.

The bubbles mentioned above are mixed with bubbles of various sizes. When the paint is supplied from the paint tank to the coater pan by pressurizing it with the paint circulating pump while keeping these air bubbles in the paint, the discharge pressure is released, and the air bubbles in the paint are about several tens of μm. Become bubbles. Also, new air bubbles are generated in the paint circulation pump itself. The paint is sent to the coater pan while entraining these minute air bubbles.

(Case 2) When the position of the paint tank is higher than the position of the coater pan, large bubbles may be generated when the paint enters the paint tank, and the paint including these bubbles is directly sent to the coater pan. In some cases, it is worse than in case 1 above.

Therefore, in order to prevent the above-mentioned coating defects, the coating material is agitated in the coating tank to make the coating concentration uniform,
After uniformly dispersing particles such as metal powder mixed in the paint, reduce the bubbles in the paint in another tank, and install these tanks above the coater pan to prevent bubbles in the paint. It was considered effective to supply the paint from the paint adjustment tank to the coater pan without using the paint circulation pump, which has a large effect on the miniaturization of the paint.

Further, it is considered that efficient defoaming is possible even in a small-capacity processing tank by carrying out the processing for reducing the bubbles in the paint by using ultrasonic waves. I investigated sex.

(Experimental Example 1) A sample in which about 100 ml (about 7 cm in height) of an aminoalkyd clear paint having a viscosity of 300 cp was put in a 1250 ml glass beaker and then air bubbles were forcibly entrained by using a small high speed disperser. Created. Samples were sampled with a dropper from a portion 2 cm from the bottom of the glass beaker containing this sample and a portion 2 cm below the liquid surface. Drop the sampled sample on a slide glass via a spacer,
After placing a cover glass on the upper part, the number of bubbles recognized as light spots was counted by microscopic observation with a magnification of 3 times. Further, the number of bubbles was similarly investigated for the sample sampled after 5 minutes had elapsed.

Further, as shown in FIG. 7, a glass beaker 61 containing a sample 60 prepared in the same manner as described above is placed in tap water 6
38KHz ultrasonic cleaner Ultrasonic C containing 2
The sample was placed on -20 (manufactured by Ultrasonics KK) 63, subjected to ultrasonic treatment for 1 minute and 5 minutes, and then sampled from a portion 2 cm from the bottom surface (point a) and a portion 2 cm below the bath surface (point b). The number of bubbles in the sample was examined in the same manner as above.

The survey results are shown in Table 1.

[0028]

[Table 1]

From Table 1, it can be seen that the number of bubbles was significantly reduced in a short time by the ultrasonic treatment, and in particular, it was remarkably reduced in the portion near the bottom of the glass beaker. It was found that defoaming was promoted and efficient defoaming treatment was possible.

The present invention has been made based on such findings, and means of the present invention for solving the above problems are as follows.

(1) A coater pan for putting paint for applying a coating on a metal plate by a coater roll, a paint collecting tank for receiving paint that overflows from the coater pan below the coater pan, and a paint for the paint above the coater pan. A paint tank for stirring and an ultrasonic oscillator for defoaming the paint sent from the paint tank are provided at the bottom, and a paint adjusting tank for supplying the paint to the coater pan is provided. A roll coater coating device in which a recovery tank and the paint tank are connected to each other via a paint supply pipe having a paint circulation pump for transferring the paint discharged from the paint recovery tank to the paint tank.

(2) The roll coater coating apparatus according to the above (1), wherein a partition plate for controlling the flow of the paint is provided in the paint adjusting tank.

(3) In the above (1) or (2), the roll coater coating device in which the paint adjusting tank is provided with a paint temperature adjusting means.

In the present invention, the paint tank for stirring the paint and the paint adjusting tank for defoaming are separated, so that the paint concentration in the paint tank is made uniform and the metal powder mixed in the paint is used. Sufficient stirring required for uniform dispersion of particles such as Also, some of the fine bubbles contained in the paint sent by the paint circulation pump are floated and removed in this tank.

Since the paint can be sent from the paint tank to the paint adjusting tank without using a paint circulation pump which has a great influence on the miniaturization of bubbles contained in the paint,
The load of defoaming treatment in the paint adjusting tank can be reduced.

The ultrasonic wave oscillator provided at the bottom of the paint preparation tank efficiently defoams the paint preparation tank. By providing a partition plate inside the paint adjustment tank, it is possible to control the flow of paint in the tank.
More efficient defoaming is possible. In addition, by installing an ultrasonic oscillator in the paint adjustment tank, the paint temperature rises, which changes the paint viscosity, which causes coating work such as film thickness fluctuations.
May affect coating quality. In addition, the same problem may occur due to the vertical change of the paint temperature due to the seasonal variation of the air temperature. In these cases, by providing the temperature adjusting means in the paint adjusting tank, it is possible to prevent the temperature change of the paint adjusting tank and prevent the above problems.

Further, since the paint can be sent from the paint adjusting tank to the coater pan without using a paint circulation pump which has a great influence on the miniaturization of the bubbles contained in the paint, the paint with few bubbles in the coater pan. Can be supplied.

[0038]

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

In the following drawings, the same parts as those shown in the already described drawings are designated by the same reference numerals and the description thereof will be omitted.

FIG. 1 is a diagram showing a first embodiment of the present invention. In FIG. 1, 1 is a paint adjustment tank, 3 is a paint recovery tank, 4 is a paint circulation pump, 6 is an ultrasonic oscillator, 9 is an overflow pipe, 10 is paint supply pipe, and 11 is paint tank 5 to paint adjustment tank 1. Paint piping to send paint, 13
Is a paint pipe for sending paint from the paint adjusting tank 1 to the coater pan 2, and 12 and 14 are flow rate adjusting devices.

The paint overflowed from the coater pan 2 is recovered in the paint recovery tank 3 via the overflow pipe 9. The lower part of the overflow pipe 9 is immersed in the paint collected in the paint collecting tank 3. The paint recovery tank 3 is provided with air bubbles brought from the coater pan 2 or the coater pan 2
It is possible to float and eliminate the bubbles generated when the liquid drops from the surface, and reduce the bubbles in the paint flowing out from here. Therefore,
Since this leads to a reduction in the load when performing defoaming processing in the paint adjustment tank 1, it contributes to downsizing of the paint adjustment tank capacity, reduction of the output of the ultrasonic oscillator, and the like. In particular, when the paint recovery tank is a hopper, the linear flow velocity of the paint can be changed to improve the floating and defoaming effect of bubbles, which contributes to the reduction of the capacity of the tank.

The paint collected in the paint collecting tank 3 is passed through the paint supply pipe 10 by the paint circulating pump 4 and the paint tank 5.
Sent to In the paint tank 5, a paint supply tank (not shown) replenishes the paint reduced due to the adhesion to the metal plate, a solvent for viscosity adjustment, and the like. In the paint tank 5, in order to make the concentrations of these paints uniform or to uniformly disperse particles such as pigments, aggregates, and metal powders such as aluminum in the paint, they are stirred by a stirring device 24 having stirring blades. . In addition, a part of fine bubbles contained in the paint sent from the paint circulation pump is floated and removed in this tank.

Next, the paint is sent from the paint tank 5 to the paint adjusting tank 1 via the paint pipe 11. A flow rate adjusting device 12 for controlling the flow rate of the paint supplied from the paint tank 5 to the paint adjusting tank 1 is installed between the paint tank 5 and the paint adjusting tank 1, and is linked with a pump to control the paint tank. The liquid surface position can be controlled. The paint tank 5 is provided above the coater pan 2, and when the paint is sent to the paint adjusting tank 1, it is possible to prevent the bubbles contained in the paint from becoming fine and new bubbles to be generated.

An ultrasonic oscillator 6 is provided at the bottom of the paint adjusting tank 1.
Is provided. The cavitation of the ultrasonic oscillator 6 causes the bubbles in the paint to collide with each other to form a large bubble, which rises and breaks, so that the bubbles in the paint in the paint adjusting tank 1 can be efficiently removed. Further, since the paint is agitated at that time, it is possible to make the paint concentration and the dispersion of particles such as metal powder mixed in the paint uniform.

The frequency of the ultrasonic oscillator is 20 to 50 KH
z, and more preferably 25-40 KHz, the defoaming efficiency is good. If this frequency is less than 20 KHz, cavitation is less likely to occur, and the defoaming efficiency decreases. Further, if the frequency exceeds 50 KHz, problems in working environment occur, which is not preferable. As the ultrasonic oscillator, it is possible to use an ultrasonic oscillator whose output can be varied so that the defoaming efficiency and the dispersion efficiency differ depending on the type of paint.

A magnetostrictive oscillator, a piezoelectric oscillator, an electrostrictive oscillator, or the like can be used as the oscillator of the ultrasonic wave generation source. Examples of the magnetostrictive oscillator include nickel, ferrite, and Alfel alloy, examples of the piezoelectric oscillator include crystal, Rochelle salt, and examples of the electrostrictive oscillator include barium titanate and lead titanium zirconate.

It is advantageous in terms of defoaming that the ultrasonic oscillator 6 is installed at the bottom of the paint adjusting tank 1. The installation method may be a throw-in type inside the paint adjusting tank or a built-in type inside or inside the paint adjusting tank, but is not limited to these installing methods.

When the ultrasonic oscillator 6 is provided on the entire bottom surface of the paint adjusting tank 1, the ultrasonic wave generator 6 is moved from the paint adjusting tank 1 to the coater pan 2.
Bubbles generated by cavitation generated near the paint discharge port 13a may flow out to the coater pan. Therefore, when coating defects due to air bubbles are likely to occur, it is desirable not to provide the ultrasonic oscillator 6 near the paint discharge port 13a from the paint adjusting tank 1 to the coater pan 2.

The paint from which air bubbles have been removed is the paint adjustment tank 1
It is sent to the coater pan 2 through the paint pipe 13 from the paint discharge port 13a provided in the vicinity of the bottom part of the. A flow rate adjusting device 14 for controlling the flow rate of the paint supplied from the paint adjusting tank 1 to the coater pan 2 is installed between the paint adjusting tank 1 and the coater pan 2, and is linked with a pump to adjust the paint adjusting tank. The liquid level position of 1 can be controlled.

The coating material supplied to the coater pan 2 is applied to the steel plate 17 via the pick-up roll 15 and the applicator roll 16, and the product is passed through the necessary steps.

Since the paint adjusting tank 1 is provided above the coater pan 2, the paint can be supplied to the coater pan 2 without using the paint circulating pump. The problem of bubbles generated by itself disappears.

The paint outlet 13a from the paint adjusting tank 1 to the coater pan 2 is preferably provided at a position near the bottom of the paint adjusting tank 1. Since the bubbles in the paint float by the action of ultrasonic waves, there are less bubbles at the bottom. Therefore, by discharging the paint to the coater pan 2 from the position near the bottom, it is possible to supply the paint with few bubbles to the coater pan. Further, even if sedimentable foreign matter such as sludge exists at the bottom, it is not discharged to the coater pan 2.

Further, the paint supply port 1 to the paint adjusting tank 1
1b and the paint discharge port 13a from the paint adjusting tank 1 to the coater pan 2 are preferably provided on the opposite side of the paint adjusting tank 1. With this arrangement,
Better removal of bubbles.

A second embodiment of the present invention is shown in FIG. In FIG. 2, 7a and 7b are partition plates provided in the paint adjusting tank 1, 7a has a paint flow section at the bottom, and 7b has an overflow section at the top. In the case of this embodiment, since the flow of the paint in the paint adjusting tank 1 can be controlled by the partition plates 7a and 7b, in addition to the effect of the second embodiment, more efficient defoaming can be performed.

The partition plate 7 includes a partition plate 7a having a paint circulating portion at the bottom and a partition plate 7b at the top of which the paint overflows.
And is preferably provided. A plurality of these partition plates may be provided alternately. Partition plate 7a having a paint distribution section at the bottom
It is also possible to use only. A part of the lower part of the partition plate of the partition plate 7a having a paint circulating portion at the bottom may be concave. The partition plate 7b on which the paint overflows may have a shape in which a part of the partition plate has a concave shape. The partition plate 7a having a paint circulating portion at the bottom traps the air bubbles floating in the tank, breaks the air bubbles, and prevents the air bubbles from being sent to the coater pan 2. The partition plate 7b, on which the paint overflows, traps settling foreign matter such as sludge, and also contributes to preventing these foreign matter from being sent to the coater pan 2.

When the number of partition plates is increased, the ability to separate air bubbles in the paint is increased, but the ability to disperse particles such as pigments, aggregates and aluminum powder is reduced. It is desirable to properly select the number of partition plates.

A third embodiment of the present invention is shown in FIG. In FIG. 3, reference numeral 8 is a water jacket provided on the outer side of the paint adjusting tank 1. The paint temperature in the paint adjusting tank is detected by a temperature detector (not shown), the water temperature in the water jacket is adjusted, and the paint temperature is maintained at a constant temperature. In the case of the present embodiment, since the temperature in the paint adjusting tank can be made constant, in addition to the effect of the second embodiment, it is possible to further reduce fluctuations in the applied coating film thickness.

In the figures showing these embodiments, 3
Although it is illustrated using a book roll,
The device of the present invention does not depend on the number of rolls used,
The effect can be exhibited when coating with a roll coater.

The coating material used for coating with the apparatus of the present invention is not only a low-viscosity water-based coating material, but also known resins, pigments,
It is also possible to use a high-viscosity paint having a viscosity of 50 cp or more (measured value at 20 ° C.), which is obtained by selecting and combining a modifier, an additive, and a solvent as necessary. Examples of the resin include amino resin, alkyd resin, polyester resin, epoxy resin, acrylic resin, urethane resin and phenol resin. As the pigment, titanium oxide, carbon black, iron oxide, yellow lead, ferrocyanine blue, phthalocyanine green and other inorganic pigments / organic pigments, barium sulfate, talc, extender pigments such as mica, aluminum powder, paints such as copper powder, What is used for ink etc. can be applied. As the additive, a pigment dispersant, a leveling agent, an anti-settling agent, an ultraviolet absorber or the like can be used. As the solvent, toluene,
Xiene, sorbet 100, sorbet 150, butyl acetate, ethyl acetate, butanol, cellosolve, butyl cellosolve, methyl isobutyl ketone, cyclohexane, cellosolve acetate and the like which are generally used as paint diluents can be used.

[0060]

EXAMPLE Using the apparatus of the above-mentioned embodiment, a polyester-based coating was used to produce 100,0
The amount of coating defects caused by bubbles and the variation in coating film thickness with respect to the reference film thickness were investigated. The number of coating defects was examined by visually observing the appearance of the coated steel sheet, and the variation in coating film thickness was examined by a fluorescent X-ray film thickness meter. Table 2 shows the results. In addition, for comparison, using the coating apparatus shown in FIG.
The same survey as above was conducted. The results are shown in Table 2.

[0061]

[Table 2]

Inventive Example 1 causes less coating film defects than Comparative Example. In Invention Examples 2 and 3 in which a partition plate was used for the paint tank, the occurrence of coating film defects was not recognized. In Invention Example 1 and Invention Example 2, the coating temperature increased somewhat with the elapse of time, and thus the coating film thickness fluctuated slightly, but in Invention Example 3 in which the coating temperature was constant, the coating film thickness fluctuation was small.

[0063]

When a steel sheet is coated using the apparatus of the present invention, the occurrence of coating defects can be reduced, or the variation in coating thickness can be further reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a third embodiment of the present invention.

FIG. 4 is a diagram for explaining a conventional coating device.

FIG. 5 is a diagram for explaining measures against bubbles in a coater pan according to a conventional technique.

FIG. 6 is a view for explaining a defoaming equipment for coating material by ultrasonic waves in a conventional technique.

FIG. 7 is a diagram showing an experimental facility used for investigating the defoaming property of a paint by ultrasonic waves

[Explanation of symbols]

 1 Paint Adjustment Tank 2 Coater Pan 3 Paint Recovery Tank 4 Paint Circulation Pump 5 Paint Tank 6 Ultrasonic Oscillator 7, 7a, 7b Partition Plate 8 Cooling Device 10 Paint Supply Pipe 15 Pickup Roll 16 Applicator Roll 17 Steel Plate

Claims (3)

[Claims] 1. A coater pan in which a paint for coating a metal plate with a coater roll is put, a paint collecting tank for receiving a paint overflowed from the coater pan below the coater pan, and a paint agitator above the coater pan. A paint tank for performing the above and an ultrasonic oscillator for defoaming the paint sent from the paint tank are provided at the bottom, and a paint adjusting tank for supplying the paint to the coater pan is provided, and the paint recovery Roll coater coating characterized in that the tank and the paint tank are connected via a paint supply pipe having a paint circulating pump for transferring paint discharged from the paint collecting tank to the paint tank in the middle of the tank apparatus 2. The roll coater coating apparatus according to claim 1, wherein a partition plate for controlling the flow of the paint is provided in the paint adjusting tank. 3. The roll coater coating apparatus according to claim 1, wherein the paint adjusting tank is provided with a paint temperature adjusting means.