JP2012148260A - Roll coating device and roll coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a roll coating device and a roll coating method, capable of efficiently removing air bubbles generated around a pick-up roll within a coater pan and obtaining a base material having a coating film with excellent appearance characteristics.SOLUTION: The roll coating device 100 includes a roll 4 pumping up coating liquid within the coater pan 7, and applies the coating liquid to the base material traveling continuously. A suction port simultaneously sucking the coating liquid and gas is provided in a predetermined position in the vicinity of a coating liquid face in the coater pan 7 to efficiently remove air bubbles within the coater pan 7.

Description

  The present invention relates to a roll coating apparatus and a roll coating method for continuously coating a coating liquid on a long base material such as a steel strip using a roll.

  Conventionally, a process of forming various coating films on the surface of a base material in order to impart performance such as corrosion resistance, workability, aesthetics, and insulation to a continuously running base material (for example, a steel plate) has been performed. It has been broken. As this treatment method, a roll coater (roll coating apparatus) is generally used, and a two-roll coater using two rolls or a three-roll coater using three rolls is widely used.

  This method mainly consists of a pick-up roll that pumps the coating liquid from the coater pan filled with the coating liquid, an applicator roll that transfers the coating liquid to the substrate, and a coating liquid that is pumped by the pickup roll as necessary. It consists of rolls and blades that adjust the amount. The rotation direction of each roll is either a natural rotation that rotates in the same direction at the close point or close point between the rolls, or a reverse rotation that rotates in the reverse direction. When excess coating liquid scraped off with a blade flows into the coater pan, air bubbles are often generated, and if the coating liquid contains a surfactant, the coating liquid does not disappear easily. The problem of remaining on the surface occurs (see FIG. 6).

In this way, if a large amount of bubbles remain on the surface of the coating liquid, bubbles may overflow from the coater pan and contaminate the surroundings with the coating liquid. In some cases, the film passes through the substrate and is transferred to the surface of the substrate, which is the material to be coated, resulting in a pinhole-like coating film defect. Such pinhole-shaped coating film defect portions are often unpainted or thin films, and may not only deteriorate the appearance of the final product but also locally deteriorate the coating film performance such as corrosion resistance.
As a method for solving these problems, a defoaming device in which an ultrasonic defoaming means and a centrifugal defoaming means are sequentially arranged is disclosed (Patent Document 1).

Japanese Patent Laid-Open No. 11-253702

Generally, bubbles are likely to stay around a structure such as a roll, and it is important to remove bubbles at the periphery of the roll that draws up the coating liquid.
However, in the method of Patent Document 1, it is possible to remove bubbles in the coater pan to some extent by using a deaeration device. However, in order to increase productivity, the roll rotation speed is increased, or the high speed during high-speed application is increased. In the case where the amount of a component that causes bubbles, such as a surfactant, is increased in the coating solution in order to withstand the shearing force, the amount of bubbles generated increases and the bubbles cannot be removed in time.
In recent years, with the improvement of consumers' awareness of aesthetics, the demand for coating appearance has increased significantly, and the development of a roll coating apparatus and a roll coating method for obtaining a coating film with fewer coating defects is desired. It was.

  Therefore, in view of the above circumstances, the present invention can efficiently remove bubbles generated around the pick-up roll in the coater pan, and can obtain a base material having a coating film with excellent appearance characteristics. An object is to provide a coating apparatus and a roll coating method.

  Means of the present invention for solving the above problems are as follows.

[1] A roll coating apparatus that includes a roll that pumps up the coating liquid in the coater pan, and that coats the coating liquid on a continuously traveling substrate.
A discharge device that simultaneously sucks and discharges the coating liquid and gas through a suction port disposed over and below the coating liquid surface in the coater pan;
The average opening height (H1) obtained by dividing the total opening area (S1) of the suction port by the maximum horizontal width of the suction port is 1 mm or more,
The average opening height (H2) obtained by dividing the opening area (S2) of the suction port through which the gas passes by the horizontal width of the suction port at the coating liquid surface position is 0.5 mm or more,
A roll coating apparatus, wherein a ratio (S2 / S1) of the total opening area (S1) to the opening area (S2) is 0.8 or less.

[2] The roll coating apparatus according to [1], wherein the suction port is disposed on one end side in the axial direction of the roll so that a flow of the coating liquid is generated in the axial direction of the roll.

[3] A gas injection device that is disposed on the other end side in the axial direction of the roll and that injects gas onto the coating liquid surface and causes the coating liquid to flow toward the suction port side. The roll coating apparatus according to [2].

[4] The opening shape of the suction port is a slit shape, and the suction port is provided so that the longitudinal direction of the suction port and the coating liquid surface are parallel to each other. Roll applicator.

[5] The coating liquid discharged from the suction port to the outside of the coater pan is sent to a degassing device, degassed, and then the degassed coating liquid is supplied into the coater pan. The roll coating apparatus according to any one of [1] to [4], further comprising a coating liquid circulation means for circulating the liquid.

[6] A roll coating method in which the coating liquid is applied to a continuously traveling substrate using the roll coating apparatus according to any one of [1] to [5].

  In the present invention, by providing a suction port for sucking the coating liquid and gas at a predetermined position, bubbles existing on the coating liquid surface can be efficiently removed, and there is no coating defect even at high speed operation. Thin film coating can be performed with high productivity.

It is a side view which shows the principal part structural example of one embodiment of the roll coating device of this invention. It is a top view which shows the principal part structural example of one embodiment of the roll coating device of this invention. FIG. 3 is a diagram showing a configuration example in the vicinity of the suction port of the roll coating apparatus of the present invention (the bubble in FIG. 3A is an image diagram, which is different from the actual size), and FIG. Is a front view. It is a side view which shows the principal part structural example of the other embodiment of the roll coating device of this invention. It is a top view which shows the principal part structural example of the other embodiment of the roll coating device of this invention. It is a photograph which shows the bubble generation | occurrence | production state of the coating liquid by the roll coating apparatus of a prior art.

  Hereinafter, a roll coating apparatus and a roll coating method of the present invention will be described with reference to the drawings.

(Embodiment 1)
FIG. 1 and FIG. 2 are a side view and a plan view, respectively, showing a configuration example of a main part of an embodiment of the roll coating apparatus of the present invention. A roll coating apparatus 100 shown in FIG. 1 is a three-roll coater (three-roll coater) in which a coating liquid is applied to one side of a base material 1 that is continuously passed while being wound around a backup roll 2.
In addition, various base materials can be used as the base material 1, for example, a cold-rolled steel plate, a surface-treated steel plate subjected to plating or chemical conversion treatment such as zinc, a steel plate such as an electromagnetic steel plate, or an aluminum plate. Paper, film, etc. can be used.

The roll coating apparatus 100 includes a pickup roll 4 that pumps the coating liquid 8 from the coater pan 7, a metering roll 5 that adjusts the amount of the coating liquid 8 on the pickup roll 4, and the adjusted coating liquid on the pickup roll 4. An applicator roll 3 for transferring 8 to the substrate 1 is provided.
As for the roll diameter and roll body length of each roll, the optimum diameter and body length are appropriately selected according to the substrate to be used. However, in the case of application to a thin steel plate, the roll diameter is usually preferably about 70 to 400 mmφ. . This is because when the roll diameter is smaller than 70 mmφ, the deflection tends to occur, and when the roll diameter is larger than 400 mmφ, the contact area between the rolls becomes larger and appearance defects tend to occur. The roll body length may be appropriately selected so as to be equal to or greater than the width to be applied.

The surface of the pick-up roll 4 may be appropriately selected according to the properties of the coating liquid, the target adhesion amount, and the coating conditions. For example, a gravure roll in which a large number of recesses are formed on the body surface, or the surface is mirror-finished Flat rolls and the like.
The surface of the applicator roll 3 may be appropriately selected depending on the properties of the coating solution, the target adhesion amount, and the coating conditions. However, if it is not desired to damage the steel plate or the like as the material to be coated, use a rubber roll with a rubber lining. Is preferred.
And the arrow in FIG. 1 shows the rotation direction of a roll, or the running direction of a base material. The rotation direction of each roll is the reverse direction between each roll and between the applicator roll 3 and the substrate 1, and a blade 6 that scrapes the coating liquid is installed on the mitering roll 5. In addition, the rotation direction of a roll is not specifically limited.

  As the coating liquid 8 to be used, various known coating liquids can be used. Especially, it can be effectively applied to a coating solution in which bubbles are generated and hardly disappear. For example, a coating liquid containing an emulsion resin containing a large amount of a surfactant in order to contain a resin in a water-based paint is likely to generate bubbles due to shearing force due to roll coating. Is very effective.

In FIG. 2, the coater pan 7 has a rectangular shape, but its shape is not particularly limited.
Further, the size of the coater pan 7 is not particularly limited as long as it is at least larger than the cross-sectional area of the portion where the pickup roll 4 is immersed in the coating solution. When the coater pan 7 is rectangular, as shown in FIG. 2, the coater pan 7 is often arranged so that the long side of the coater pan 7 is parallel to the axial direction of the roll.

  As shown in FIG. 2, the roll coating apparatus 100 has a suction port arranged on one end side in the axial direction of the pickup roll 4 so as to generate a flow of the coating liquid 8 in the axial direction of the pickup roll 4. A discharge device including a suction nozzle 9 is provided. Further, in FIG. 2, as a preferred mode, gas injection is arranged on the other end side in the axial direction of the pick-up roll 4 to inject gas to the coating liquid surface and flow the coating liquid to the suction port side. Although the form provided with the gas injection apparatus which has the nozzle 10 was shown, the gas injection nozzle 10 does not need to be installed. When the gas injection nozzle 10 is installed, as shown in FIG. 2, the suction port of the suction nozzle 9 and the injection port of the gas injection nozzle 10 are opposed to each other with the pickup roll 4 interposed therebetween (periphery of the coater pan 7). It is preferable to be disposed on the part).

  The configuration of the discharge device is not particularly limited as long as it has a suction port for sucking and discharging the coating liquid and gas, but normally, as shown in FIG. 2, a suction nozzle 9 having a suction port; It is preferable to include a suction device 11 to which the nozzle is connected. As shown in FIG. 2, the suction nozzle 9 and the suction device 11 may be connected by piping as necessary.

  As shown in FIG. 3, the discharging device sucks the coating liquid 8 and the gas through the suction port 9a. As shown in FIG. 3, the bubbles 20 are removed from the coater pan 7 by sucking the coating liquid in which the bubbles 20 are floating in the suction port 9 a. The suction port 9a is disposed in the vicinity of the coating liquid surface in the coater pan 7 at a position that satisfies a predetermined relationship described later with the coating liquid surface position.

In FIGS. 2 and 3, the shape of the suction port 9a is a slit shape, but is not particularly limited. For example, a substantially circular shape, a substantially elliptical shape, a shape in which a plurality of these are arranged, and the like are also included. What is necessary is just to select the width | variety of a suction port suitably according to the quantity and expansion | swelling state of a bubble. In order to efficiently suck as many bubbles as possible together with as little coating liquid as possible, the suction port is preferably slit-shaped, and its longitudinal direction is parallel to the liquid surface of the coating liquid 8 as shown in FIG. Thus, it is preferable to be installed. Moreover, it is preferable to arrange | position so that the transversal direction may become substantially orthogonal to the liquid level of the coating liquid 8 like FIG.
In FIG. 2, only one suction port 9a is shown, but a plurality of suction ports 9a may be used.

The average opening height (H1) obtained by dividing the total opening area (S1) of the suction port 9a by the maximum horizontal width of the suction port 9a is 1 mm or more (see FIG. 3). Average opening height (H1) has shown the average value of the opening height in the horizontal direction (width direction) of the suction port 9a. The average opening height (H1) is preferably 2 to 10 mm, and more preferably 5 to 8 mm in order to efficiently suck as many bubbles as possible together with as little coating solution as possible.
If the average opening height (H1) is less than 1 mm, it is difficult to maintain the positional relationship between the liquid level and the liquid level in a predetermined relationship, the flow for sucking the coating liquid is weakened, and the bubble suction efficiency is deteriorated. Since the desired effect is difficult to obtain, the average opening height (H1) is set to 1 mm or more.
For example, when the longitudinal direction of the slit-like suction port 9a is parallel to the liquid surface of the coating liquid 8 and the short side direction is inclined with a predetermined angle with respect to the liquid surface of the coating liquid 8, The opening area (S1) intends the area of the suction port 9a when the suction port 9a is viewed from the horizontal direction.

The average opening height (H2) obtained by dividing the opening area (S2) through which the gas of the suction port 9a passes by the horizontal width of the suction port 9a at the coating liquid surface position is 0.5 mm or more. (See FIG. 3). The horizontal width of the suction port at the coating liquid surface position corresponds to the width represented by W in FIG. The opening area (S2) corresponds to the opening area of the suction port 9 located above the coating liquid surface.
Average opening height (H2) has shown the average value of the opening height in the horizontal direction (width direction) of the part through which the gas of the suction port 9a passes. In other words, it is the average value in the horizontal direction of the height from the coating liquid surface to the suction port 9a. The average opening height (H2) is preferably 1 to 8 mm, and more preferably 2 to 5 mm.
When the average opening height (H2) is less than 0.5 mm, the coating liquid closes the suction port due to the effect of the surface tension of the coating liquid, and as a result, only the coating liquid is sucked and a desired effect is obtained. I can't.

Further, the suction port 9a is arranged so that the ratio (S2 / S1) of the total opening area (S1) to the opening area (S2) is 0.8 or less.
When the ratio (S2 / S1) is more than 0.8, the flow of sucking the coating liquid is weakened, the bubble suction efficiency is deteriorated, and a desired effect cannot be obtained. Further, if the ratio (S2 / S1) is too small, the suction amount of the coating liquid becomes too large compared to the suction amount of bubbles, and the efficiency is lowered. The ratio (S2 / S1) is preferably 0.2 to 0.6, and more preferably 0.3 to 0.5.
Area of the total open area (S1) is not particularly limited, but coater pan size by properly optimum size such as to be used is employed, usually, preferably about 400~2000mm ^2, 600~1600mm ² about Is more preferable.

As shown in FIG. 2, among the two areas of the coater pan 7 separated by a vertical plane passing through the central axis of the pickup roll 4, bubbles are likely to be generated in the area where the pickup roll 4 pumps up the coating liquid 8, Moreover, when there are bubbles, there is a risk of reaching a base material that is wound around a roll and applied. Therefore, the suction nozzle 9 having the suction port 9a is preferably provided in a region on the side where the pickup roll 4 draws up the coating liquid 8.
As shown in FIG. 2, the suction port 9 a of the suction nozzle 9 is arranged on one end side (near) in the axial direction of the pickup roll 4 so that the flow of the coating liquid is generated in the axial direction of the pickup roll 4. It is preferred that

Further, the suction port 9 a of the suction nozzle 9 may be disposed at a position parallel to the axis of the pickup roll 4 and facing the outer peripheral surface of the pickup roll 4. In this case, the coating liquid 8 on the side where the pickup roll 4 draws up the coating liquid 8 flows away from the outer peripheral surface of the pickup roll 4.
The flow rate of the coating liquid 8 in the coater pan 7 is not particularly limited, but the liquid surface flow rate at a position 1 cm away from the coating liquid scraping portion of the pick-up roll is 0. It is preferable that it is 05-0.5 m / s, and 0.1-0.3 m / s is more preferable.

  The suction amount of the coating liquid 8 from the suction port 9a is not particularly limited, but is preferably 10 to 60 L / min, and more preferably 20 to 50 L / min.

  The suction nozzle 9 having the suction port 9a is connected to a suction device 11 such as a gas-liquid suction pump, a vacuum pump, and a defoaming pump, and may be connected via a pipe as shown in FIG.

The gas injection device is an optional component provided as necessary. By using the gas injection device, the bubbles in the coating liquid 8 can be more efficiently removed.
The configuration of the gas injection device is not particularly limited as long as the gas can be injected onto the coating liquid surface. Usually, as shown in FIG. 2, a gas injection nozzle 10 having an injection port for injecting gas, and a gas injection nozzle And a gas supply device 12 connected to 10. As shown in FIG. 2, the gas injection nozzle 10 and the gas supply device 12 may be connected via a pipe or the like as necessary.

The gas injection nozzle 10 is a nozzle that injects gas to the liquid surface of the coating liquid 8. By injecting gas from the nozzle, the flow of the coating liquid 8 is more efficiently generated, and the air bubbles floating on the liquid surface of the coating liquid 8 are more efficiently near the outside of the roll edge where there is no danger of being pumped up by the pickup roll 4. Can be moved.
The gas injection nozzle 10 is connected to a gas supply device 12 such as a compressor, a blower, and a fan through a pipe, and examples of the supplied gas include air.

  In FIG. 2, the gas injection nozzle 10 is arranged at the peripheral edge of the coater pan 7 with the injection port facing the axial direction of the pickup roll 4, but the arrangement position is not particularly limited. As shown in FIG. 2, the gas injection nozzle 10 is normally disposed on the other end side in the axial direction of the pickup roll 4 and at a position facing the suction nozzle 9 and the pickup roll 4.

The installation height of the gas injection nozzle 10 is not particularly limited, but is usually arranged near the coating liquid surface. Usually, the position of the injection port of the gas injection nozzle 10 is preferably located at a height of 10 to 100 mm from the coating liquid surface.
The inclination angle of the gas injection nozzle 10 with respect to the coating liquid surface is preferably 30 ° or less, and more preferably 5 to 15 ° from the viewpoint of suppressing generation of bubbles due to gas injection.
The amount of gas injected from the gas injection nozzle 10 is not particularly limited, but the gas velocity of the nozzle injection port that easily generates the flow of the coating liquid while suppressing the generation of bubbles is preferably 30 to 100 m / s, more preferably 40-60 m / s is preferable.

The shape of the injection port of the gas injection nozzle 10 is not particularly limited, and examples thereof include a slit shape and a circular shape. From the viewpoint of uniformly injecting gas over a wide range, a slit shape is preferable.
The size of the injection port of the gas injection nozzle 10 is not particularly limited, and an optimal size is appropriately selected depending on the size of the roll and the size of the coater pan.
In FIG. 2, only one gas injection nozzle 10 is shown, but a plurality of gas injection nozzles 10 may be used. When using two or more, you may use in parallel and may arrange | position up and down.

The level of the coating liquid 8 in the coater pan 7 is preferably constant so that the amount of the coating liquid pumped up by the pickup roll 4 does not change.
At the same time as the coating liquid 8 is sucked and discharged from the suction port 9a, the coating liquid 8 may be appropriately supplied to the coater pan 7 so that the level of the coating liquid 8 is kept constant.
In particular, the roll coating apparatus 100 sends the coating liquid discharged from the suction port 9a to the outside of the coater pan 7 to the degassing apparatus, and after degassing with the degassing apparatus, the degassed coating liquid is supplied. It is preferable to have a coating liquid circulating means for circulating the coating liquid by supplying it into the coater pan 7. In FIG. 2, the coating liquid circulating means is omitted.
The coating liquid circulating means is degassed by a first liquid feeding device for feeding the coating liquid discharged from the suction port 9a to the outside of the coater pan 7 to the degassing device, a deaeration device for degassing the coating liquid. It is preferable to include a second liquid feeding device that supplies the coated liquid to the coater pan 7.
As the first liquid feeding device and the second liquid feeding device, a liquid feeding device such as a metering pump is used.

The deaeration device is not particularly limited, and examples thereof include a centrifuge. In addition, when performing centrifugation with a centrifuge, you may carry out under reduced pressure.
Further, the coating liquid circulating means may include a coating liquid tank that stores the degassed coating liquid after the deaeration device.

When returning the coating liquid deaerated by the deaerator into the coater pan 7, a slope or the like is used in order not to generate bubbles at the pouring position through the coating liquid supply port connected to the coater pan 7. It is preferable to return slowly.
Alternatively, the coating liquid may be returned to the coater pan 7 by using a liquid feeding pump that sucks the coating liquid stored in the coating liquid tank and feeds the coating liquid from the coating liquid supply port into the coater pan 7.

  In addition, between the suction port 9a and the deaerator, between the deaerator and the coating liquid tank, between the coating liquid tank and the coating liquid supply port, and the like may be appropriately connected by piping.

Next, a coating method using the roll coating apparatus according to the first embodiment shown in FIGS. 1 and 2 will be described.
First, the coating liquid 8 in the coater pan 7 is pumped up by the pick-up roll 4, the amount of the pumped coating liquid 8 is adjusted by the mitering roll 5, transferred to the applicator roll 3, and the applicator roll 3 runs continuously. The coating liquid 8 on the surface of the applicator roll 3 is transferred to the surface of the base material 1 by bringing the coating liquid 8 into contact with the base material 1 to be transferred. The substrate 1 having the coating liquid 8 applied on the surface is then passed through a heating facility or a drying facility (not shown) and dried by heating to form a required coating film on the surface of the substrate 1. The coating liquid 8 adhering to the surface of the mitering roll 5 is scraped off by a blade 6 arranged with one end pressed against the surface of the mitering roll 5 and returns to the coater pan 7.

The amount of bubbles generated in the coater pan 7 is proportional to the amount of coating liquid to be scraped off. That is, it is proportional to the amount of coating liquid to be pumped up, in other words, the rotational speed of the pickup roll 4. In addition, when the substrate speed is increased in order to increase productivity, the rotational speed of the pickup roll 4 is often increased accordingly, and a coating stabilized with a surfactant or the like is added. In the liquid, bubbles are likely to be generated. In that case, since the shearing force increases between the rolls and between the rolls / base materials, the amount of the surfactant and the like in the coating liquid 8 is often increased, and a large amount of the surfactant is added. In addition, the surface tension is also lowered, and it becomes easier to form bubbles. As a result, bubbles generated in the coater pan 7 are wound up by the pickup roll 4.
According to the roll coating apparatus 100 described above, bubbles generated around the pickup roll 4 can be sufficiently removed, and bubbles can be prevented from adhering to the base material and being bitten between the rolls.

(Other embodiments)
Although the said embodiment described the coating system by a 3 roll system, in this invention, it is not limited to a 3 roll system, A 1 roll system and a 2 roll system may be sufficient.
4 and 5 show a side view and a plan view, respectively, of a two-roll system embodiment. Also in the case of the two-roll method, the bubbles present on the liquid surface of the coating liquid 8 can be removed by providing the suction port described above.

  4 adjusts the amount of the application liquid 8 on the pickup roll 4 that picks up the application liquid 8 from the coater pan 7 and the pickup roll 4, and uses the application liquid 8 on the pickup roll 4 as a base material. 1 is provided with an applicator roll 3 to be transferred. The arrows in the figure indicate the rotation direction of the roll or the traveling direction of the substrate. When the coating liquid 8 pumped up by the pickup roll 4 is transferred to the applicator roll 3, the amount of the liquid is adjusted.

As shown in FIG. 5, the roll coating apparatus 200 has a suction port disposed on one end side in the axial direction of the pickup roll 4 so as to generate a flow of the coating liquid 8 in the axial direction of the pickup roll 4. Discharge device provided with a suction nozzle 9 and gas injection, which is arranged on the other end side of the pickup roll 4 in the axial direction, for injecting gas to the coating liquid surface and flowing the coating liquid to the suction port 9a side A gas injection device having a nozzle 10. As shown in FIG. 5, the suction port of the suction nozzle 9 and the spray port of the gas spray nozzle 10 are preferably arranged at positions facing each other (on the peripheral edge of the coater pan 7) across the pickup roll 4.
As described above, the gas injection device is an optional component provided as necessary.
As shown in FIG. 5, the suction nozzle 9 is an area on the side where the pickup roll 4 pumps up the coating liquid 8 out of two areas of the coater pan 7 divided by a vertical plane passing through the central axis of the pickup roll 4. It is preferable to be provided.

  In the present invention described above, bubbles existing on the surface of the coating liquid generated around the pickup roll can be easily removed, and it is possible to manufacture a product free from defects in appearance and performance due to bubbles. became.

  The present invention will be described in detail by the following examples and comparative examples.

Using the roll coating apparatus shown in FIGS. 1 and 2 on a coil of a galvanized steel sheet having a plate thickness of 0.8 mm and a plate width of 1100 mm, coating is performed under the coating conditions shown in Table 1, and the obtained steel sheet Appearance characteristics were evaluated.
As each roll, a rubber lining roll obtained by lining rubber to a metal roll was used for the applicator roll 3, and a metal roll having a flat surface was used for the pickup roll 4 and the metering roll 5. The roll diameter of each roll is 300 mmφ for the applicator roll 3 and the pickup roll 4 and 200 mmφ for the mitering roll 5. The roll body length of each roll was 1.6 m, and the gap between the pickup roll 4 and the metering roll 5 was 90 μm. The area of the coater pan 7 was 1000 mm × 1900 mm.
The substrate speed (line speed) was 100 m / min, and the rotation speeds of the applicator roll 3, the pickup roll 4 and the mitering roll 5 were 100 m / min, 70 m / min and 30 m / min.

As the coating solution used, an aqueous coating solution having a viscosity of 0.003 [Pa · s], a surface tension of 0.035 [N / m], and a solid content concentration of 8% at a liquid temperature of 20 ° C. was used.
As the gas injection nozzle 10, a nozzle having the shape shown in Table 1 was used, and the injection port was disposed at a height of 20 mm from the liquid surface of the coating liquid 8 and inclined 5 ° with respect to the liquid surface.
The coating liquid sucked from the suction port 9a arranged as shown in FIG. 3 was sent to the deaerator. As the deaerator, an apparatus that performs centrifugation in an atmosphere reduced in pressure by a vacuum pump was used. The suction amount of the coating liquid 8 from the suction port 9a was 30 L / min. The coating liquid sucked from the suction port 9a by the action of the vacuum pump of the degassing device is sent to the degassing device via a pipe, and after degassing, is sent to the coating liquid tank via the pipe. Thereafter, the solution was returned from the coating solution tank to the inside of the coater pan 7 through a pipe by a solution feeding pump through a pipe.
The steel plate surface having the coating film obtained by the above method was visually observed and evaluated according to the following criteria. The results are summarized in Table 1.
"(Double-circle)": A bubble flaw defect is not observed in the obtained coating-film surface (2000 mm x 1100 mm).
“◯”: One or more bubble defects are observed on the surface (2000 mm × 1100 mm) of the obtained coating film.
“Δ”: On the surface of the obtained coating film (2000 mm × 1100 mm), more than three bubble defects are observed.
“X”: On the surface of the obtained coating film (2000 mm × 1100 mm), more than 10 bubble defects or streak defects are observed.

As can be seen from the results in Table 1, when the roll coating apparatus of the present invention is used, even when the roll rotation speed is high and bubbles are likely to be generated, there is no occurrence of defects due to the bubbles being rolled up, and the coating is beautiful and uniform. It was possible to produce a steel plate with a film.
On the other hand, in Comparative Examples 1 to 3 in which the suction port does not satisfy the predetermined condition, the bubble defect tends to increase.
Furthermore, in Comparative Example 4 in which no suction nozzle was provided, streak-like defects occurred due to entrapment of bubbles between the rolls.

DESCRIPTION OF SYMBOLS 1 Base material 2 Backup roll 3 Applicator roll 4 Pickup roll 5 Mitering roll 6 Blade 7 Coater pan 8 Coating liquid 9 Suction nozzle 9a Suction port 10 Gas injection nozzle 11 Suction device 12 Gas supply device 20 Bubble 100, 200 Roll coating device H1 Average opening height H2 Average opening height W Width of suction port at coating liquid level

Claims (6)

A roll coating apparatus that includes a roll that pumps up the coating liquid in the coater pan, and that applies the coating liquid to a continuously running substrate,
A discharge device that simultaneously sucks and discharges the coating liquid and gas through a suction port disposed over and below the coating liquid surface in the coater pan;
The average opening height (H1) obtained by dividing the total opening area (S1) of the suction port by the maximum horizontal width of the suction port is 1 mm or more,
The average opening height (H2) obtained by dividing the opening area (S2) of the suction port through which the gas passes by the horizontal width of the suction port at the coating liquid surface position is 0.5 mm or more,
A roll coating apparatus, wherein a ratio (S2 / S1) of the total opening area (S1) to the opening area (S2) is 0.8 or less.   The roll coating apparatus according to claim 1, wherein the suction port is disposed on one end side in the axial direction of the roll so that a flow of the coating liquid is generated in the axial direction of the roll.   The roll of Claim 2 provided with the gas injection apparatus which is arrange | positioned at the other end part side of the axial direction of the said roll, injects gas with respect to a coating liquid surface, and flows a coating liquid to the said suction opening side. Coating device.   The roll coating apparatus according to any one of claims 1 to 3, wherein the suction port has a slit shape, and the suction port is provided so that a longitudinal direction of the suction port and a coating liquid surface are parallel to each other.   The coating liquid discharged from the suction port to the outside of the coater pan is fed to a deaerator and deaerated, and then the degassed coating liquid is supplied into the coater pan to circulate the coating liquid. The roll coating apparatus according to any one of claims 1 to 4, comprising a coating liquid circulation means. A roll coating method in which the coating liquid is applied to a continuously running substrate using the roll coating apparatus according to claim 1.