JP5396728B2 - Roll coating method and roll coating apparatus - Google Patents

Description

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

  Conventionally, in order to impart performance such as corrosion resistance, workability, aesthetics, insulation, etc. to a continuously running base material (for example, a steel strip), various coating films are formed on the surface of the base material. Yes. As this processing 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. In particular, the three-roll coater is a mainstream coating method because it has excellent controllability of the coating film thickness and has a relatively beautiful surface appearance.

  As shown in FIG. 4, this type of coating apparatus (three-roll coater) includes a pickup roll 4 that draws up the coating liquid 3 from the coater pan 2 filled with the coating liquid, and an amount of the coating liquid pumped up by the pickup roll 4. And a applicator roll 6 for transferring the adjusted coating liquid amount from the pickup roll 4 to the steel strip.

  The rotation direction of each roll may be in the vicinity of the rolls, or in the case of natural rotation that rotates in the same direction at the close point, and in reverse rotation that rotates in the opposite direction. Since it is easy to obtain a coating film surface having a uniform film thickness along the surface unevenness of the substrate, the surface of the substrate has unevenness, and particularly when the uniform film thickness along the surface unevenness is desired, In many cases, reverse rotation is performed between the substrates 1. The applicator roll 6 is often a rubber roll in which rubber is lined on a steel roll so as not to damage the surface of the substrate 1.

  However, as a typical coating defect of a roll coater including a three roll coater, there is a defect called roping. In this roping, streaks in the circumferential direction of the roll are transferred to the steel sheet, resulting in uneven film thickness and deterioration of appearance. Roping tends to occur more easily as the viscosity of the coating liquid is higher and as the roll peripheral speed is higher. In particular, when the steel plate speed is increased, the circumferential speed of each roll is also increased, so that the occurrence of roping becomes significant.

  As a technique for preventing roping, for example, Patent Document 1 discloses a technique for controlling a ratio of a line speed, an applicator roll circumferential speed, and a pickup roll circumferential speed to a specific range. Patent Document 2 discloses a method of keeping the paint temperature in the vicinity of the temperature at which the paint viscosity is minimized. Furthermore, in Patent Document 3, as a method for reducing the occurrence of roping in high-speed coating at a line speed of 200 mpm or higher, the peripheral speed of the pickup roll is 20 to 80 mpm, and the peripheral speed of the applicator roll is 200 to 1000 mpm which is higher than the line speed. A method for performing coating is disclosed.

  However, with the techniques disclosed in Patent Document 1 and Patent Document 2, even when the line speed is low, roping can be prevented. However, when the line speed is high, the effect of preventing roping is insufficient. The line speed at which a uniform appearance without roping can be obtained is less than 200 mpm, which can be a factor that hinders productivity.

  Further, in the method disclosed in Patent Document 3, when the peripheral speed of the applicator roll is increased, the roping pitch on the applicator roll becomes finer and the roping is less noticeable on the steel plate, but the peripheral speed of the applicator roll is increased. If the line speed is increased too much, the flow of the coating solution is disturbed at the position where the applicator roll and the steel plate are in contact with each other, and the interface of the coating solution locally vibrates in the width direction, causing unevenness of the film thickness on the steel plate. In some cases, a pattern was generated. Thus, increasing the peripheral speed of the applicator roll is an effective means for roping, but there is a risk of creating a new deterioration factor of the appearance of coating.

In any of the coating methods disclosed in Patent Documents 1 to 3, the coating film thickness (wet film thickness) in the liquid film state after coating is about 10 μm. When the wet film thickness is about 10 μm, even if the coating film immediately after coating is uneven, it is leveled in the middle of drying, so that the film thickness unevenness is suppressed to a level where there is no problem. Therefore, when the wet film thickness after application is about 10 μm, the problem of film thickness unevenness after drying has not been realized.
JP 2000-254580 A JP 9-47716 A JP-A-10-309512

  In recent years, from the viewpoint of improving functionality, it has been required to reduce the coating film thickness so that the film thickness after drying is less than 0.1 μm. In order to reduce the coating film thickness, it is necessary to reduce the coating thickness when the coating film is applied to the substrate in a liquid state.

  However, even when any of the methods described in Patent Documents 1 to 3 above is used, if the film is thinned at the time of applying the coating film, there is a problem that unevenness remains in the film thickness after drying. Will occur. This is because the minute unevenness of the film thickness at the time of applying the coating film is not eliminated by the subsequent leveling and remains as the film thickness unevenness after drying.

  Therefore, the present invention does not hinder productivity even when a thin coating film having a film thickness after drying of less than 0.1 μm, for example, is formed on a continuously running substrate, and An object of the present invention is to provide a roll coating method and a roll coating apparatus capable of forming a coating film without causing film thickness unevenness on the surface of the substrate.

  In order to solve the above problems, the present invention has the following features.

[1] The amount of the coating liquid supplied to the pick-up roll is adjusted with a mitering roll, the adjusted amount of coating liquid is supplied to the applicator roll, and the applicator roll supplied with the coating liquid is In a roll coating method using a three-roll coater that contacts a continuously running substrate and applies a coating solution to the substrate surface,
When applying the coating liquid so that the thickness of the coating film after drying is less than 0.1 μm by using a steel strip as the base material and water-based paint as the coating liquid and running the base material continuously at a high speed of 100 mpm or higher. ,
The concentration of the coating solution is 1.00% to 4.80% and the coating film thickness is 3 μm or less.
As the applicator roll, a rubber lining roll in which rubber having a hardness of 60 degrees or more is lined is used,
First, using a precoater having at least one roll on the upstream side in the substrate running direction of the three-roll coater, the surface of the substrate to which the coating solution is applied has the same composition as the coating solution applied by the three-roll coater. The coating liquid is precoated with a liquid film thickness of less than 5 μm , and then the coating liquid on the precoated substrate is in a liquid state, and the coating liquid is applied to the substrate by the three-roll coater. Roll coating method.

[ 2 ] A roll coating apparatus used in the roll coating method according to [1],
A pickup roll supplied with the coating liquid, a metering roll for adjusting the amount of the coating liquid supplied to the pickup roll, and the coating liquid supplied from the pickup roll with the liquid amount adjusted A three-roll coater provided with an applicator roll for applying a coating solution to a continuously running substrate;
On the upstream side of the substrate running direction of the three-roll coater, a surface of the substrate to which the coating solution is applied is precoated with a coating solution having the same composition as the coating solution applied with the three-roll coater, and the precoated coating is applied. A roll coater provided with a precoater provided at a position where the liquid reaches the three-roll coater in a liquid state,
An applicator roll constituting the three-roll coater is a rubber lining roll in which rubber having a hardness of 60 degrees or more is lined.

  According to the present invention, even when a thin coating film having a dried film thickness of less than 0.1 μm is formed on a continuously running substrate, productivity is not hindered, and There are provided a roll coating method and a roll coating apparatus capable of forming a coating film without causing film thickness unevenness on the surface of the substrate.

  In order to reduce the film thickness after coating and drying, a method of diluting the coating liquid can be considered. However, it has been found that the appearance often deteriorates when diluted too much, and it is necessary to reduce the film thickness when it is applied to the substrate in a liquid state. The concentration that can be diluted varies slightly depending on the type of treatment liquid, and in some cases, even if there is an additive such as a surfactant, the film thickness is more uniform when applied at a concentration of about 1% or more. The result that it was easy to ensure the property and the good appearance was obtained. Therefore, in order to form a film having a film thickness of less than 0.1 μm after drying, it is considered that the thickness of the liquid film at the time of application needs to be less than 3 μm, preferably about 1 μm. We studied diligently.

  One embodiment of the present invention is described below.

  FIG. 1 is a diagram showing a roll coating apparatus used in an embodiment of the present invention. As shown in FIG. 1, the roll coating apparatus used in this embodiment applies (transfers) a coating solution by a roll to the surface of a substrate 1 that is continuously passed through, and includes a three-roll coater A, A precoater (precoat device) B is provided on the upstream side.

  The three-roll coater A includes a pickup roll 4 that draws up the coating liquid 3 from the coater pan 2, a metering roll 5 that adjusts the amount of the coating liquid on the pickup roll 4, and the adjusted coating liquid on the pickup roll 4. And an applicator roll 6 to be transferred to the substrate 1.

  The rotation direction of each roll 4, 5, 6 of the three-roll coater A is the reverse direction between each roll or between the applicator roll 6 and the substrate 1, and the blade that scrapes the coating liquid 3 on the mitering roll 5. 7 is installed.

  And the applicator roll 6 which contacts the base material 1 is a rubber lining roll in which rubber having a hardness of 60 degrees or more is lined.

  On the other hand, the precoater B preliminarily applies the coating liquid to the substrate 1 at a position upstream of the three-roll coater A, and includes a precoat roll 9 and a coating liquid supply roll 10 that supplies the coating liquid to the precoat roll 9. The coater pan 12 filled with the coating liquid 13 is provided. A rubber lining roll with a rubber lining is used as the precoat roll 9 that comes into contact with the substrate 1. On the other hand, the coating liquid supply roll 10 uses a metal roll.

  Here, the coater pan 12 is filled with the same type of coating solution 13 as the coating solution 3 applied to the substrate 1 with the three-roll coater A. Further, the precoater B is disposed at a position where the coating liquid 13 on the substrate 1 applied by the precoater B reaches the three-roll coater A while being in a liquid state.

  And when forming the thin film from which the film thickness after drying becomes less than 0.1 micrometer, for example with respect to the base material 1 which drive | works continuously using the roll coating device comprised as mentioned above, The coating liquid 13 is applied to the substrate 1 by the precoater B, and then the coating liquid 13 on the substrate 1 applied by the precoater B remains in a liquid state, and the coating liquid 3 is applied thereon by the three-roll coater A. Apply.

  Here, as described above, the applicator roll 6 is a rubber lining roll lined with rubber, and the rubber has a hardness of 60 degrees or more.

  Further, in order to make the liquid film thickness of the coating liquid applied by the 3-roll coater A less than 3 μm, the liquid film thickness (precoat film thickness) of the coating liquid applied (pre-coated) by the pre-coater B is less than 5 μm. It is preferable.

  Hereinafter, the reason why the hardness of the rubber of the applicator roll 6 and the thickness of the liquid film of the coating solution applied by the 3-roll coater A and the pre-coater B are within the above ranges will be described.

  First, in the three-roll type roll coater system configured as described above, a basic investigation was performed on the relationship between the hardness of the rubber on the surface of the applicator roll 6, which is a rubber lining roll, and the film thickness unevenness after coating and drying. That is, using the roll coater apparatus shown in FIG. 1, the situation and application of the meniscus portion between the applicator roll 6 and the substrate 1 when the rubber hardness of the surface of the applicator roll 6 is changed in the range of 30 to 90 degrees. The film thickness distribution in the subsequent transport direction was investigated.

  In addition, the running speed (line speed) of the base material 1 was 100 mpm, and a galvanized steel sheet having a thickness of 0.6 mm was used for the base material 1. In addition, the applicator roll 6, the pickup roll 4 and the mitering roll 5 each had a diameter of 300 mm. Also, the coating solution 3 contains a phosphoric acid-based water-based paint (containing a phosphoric acid compound, an Mg compound, silica, and a tetravalent vanadium compound) (concentration 3%, viscosity at a liquid temperature of 20 ° C .: 3 mPa · s, surface tension) : 40 dyn / cm, specific gravity of the film: 1.2).

And in order to make the coating film thickness in the liquid film state after application | coating by 3 roll coater A into less than 3 micrometers, as an example, the gravure whose surface recessed part volume is 5.8 cm < ³ > / m < ² > is included in the pick-up roll 4. A roll was used. Moreover, the roll peripheral speed of the pick-up roll 4 was adjusted so that the coating film thickness in the liquid film state after application was 2.6 μm and the film thickness after drying was 0.08 μm.

  Further, the precoat roll 9 having a diameter of 300 mm was used.

  FIG. 2 shows the relationship between the rubber hardness of the roll surface of the applicator roll 6 and the film thickness unevenness after coating and drying. Here, the film thickness unevenness is measured by measuring the film thickness at a pitch of 10 μm in each of the 3 mm regions in the transport direction and the width direction of the coated substrate (galvanized steel sheet) 1, and the maximum and minimum values of the measured values. Calculated from the difference.

  As shown in FIG. 2, when the hardness of the rubber on the surface of the applicator roll 6 is 60 degrees or more, the film thickness unevenness is less than 0.004 μm and less than 5% with respect to the target film thickness of 0.08 μm. It became clear that this would be possible. When the hardness of the rubber on the surface of the applicator roll 6 is small, the contact length of the coating liquid at the meniscus portion between the applicator roll 6 and the base material 1 becomes long, so that the vibration of the meniscus portion becomes remarkable and the film thickness unevenness. It is thought that generated. By increasing the hardness of the rubber on the surface of the applicator roll 6, the vibration of the meniscus portion is reduced, and when the hardness of the rubber is 60 degrees or more, there is almost no vibration and it is confirmed that it is uniformly applied. did. The upper limit of the hardness of the rubber is not particularly limited, but it may be used at the hardness of rubber that does not cause wrinkles on the base material, and may be appropriately selected depending on the hardness of the base material.

  Next, the relationship between the film thickness (precoat film thickness) of the coating liquid precoated (preliminary coating) with the precoater B and the film thickness of the coating liquid after coating with the 3 roll coater A was investigated. In the same manner as described above, a galvanized steel sheet having a plate thickness of 0.6 mm was used as the substrate 1 at a line speed of 100 mpm. Further, a phosphoric acid-based water-based paint (concentration: 3%, viscosity at a liquid temperature of 20 ° C .: 3 mPa · s, surface tension: 40 dyn / cm, specific gravity of film: 1.2) was used as the coating liquid 13. And the investigation of the influence of a precoat film thickness was implemented on the peripheral speed conditions from which the measurement result of the liquid film thickness in the state without a precoat will be 2.6 micrometers.

  In FIG. 3, the relationship between the film thickness (precoat film thickness) of the coating liquid precoated with the precoater B and the film thickness of the coating liquid after coating with the 3 roll coater A is shown.

  As shown in FIG. 3, when the precoat film thickness is thick, the precoated liquid film slips through the contact portion between the applicator roll 6 and the substrate 1. The film thickness becomes thicker than when no pre-coating is performed. Therefore, in order to realize thin film coating of less than 3 μm in the 3-roll coater A, it has become clear that the film thickness of the coating solution pre-coated with the pre-coater B should be less than 5 μm.

  And in the roll coating device which concerns on this embodiment, as shown in FIG. 1, it has the precoater B in the upstream of the base material 1 running direction of the 3 roll coater A. As shown in FIG.

  As shown in FIG. 4, in the case of a roll coating apparatus that does not have a pre-coater, when a coating having a film thickness of less than 3 μm is applied, streak patterns and creases are easily generated in the line direction. Become. The reason why the streaky pattern is generated is considered to be that the air flow accompanying the substrate 1 disturbs the meniscus between the substrate 1 and the applicator roll 6. The reason for the occurrence of scumming is that when the applied film thickness is as thin as less than 3 μm, the amount of liquid applied to the protrusions becomes extremely thin due to the unevenness of the surface of the substrate 1. It is thought that this is because the liquid breakage easily occurs. Therefore, in order to obtain a uniform film thickness without streaking, it is necessary to prevent the air accompanying the base material 1 from affecting the meniscus between the applicator roll 6 and the base material 1. It is.

  As shown in the roll coating apparatus according to this embodiment in FIG. 1, the precoater B is installed on the upstream side in the traveling direction of the base material 1 of the three-roll coater A, so that the coating liquid precoated on the base material 1 is applied to the applicator. It flows into the gap between the roll 6 and the substrate 1 and functions to effectively block the air accompanying the substrate 1. As a result, uniform application was possible without generating streak patterns. Moreover, since pre-coating (preliminary application) is performed by the pre-coater B, the coating film 6 is brought into contact with the applicator roll 6 in a state where the coating film is formed on the surface of the steel plate 1, so that generation of creases (wrinkles) is eliminated.

  Thus, in this embodiment, even when a thin coating film having a film thickness after drying of less than 0.1 μm, for example, is formed on the continuously running substrate 1, productivity is improved. A coating film can be formed without hindering and without causing unevenness of film thickness on the surface of the substrate.

  In addition, in said embodiment, although the case where the base material 1 is apply | coated to the single side | surface of the base material 1 in the state wound around the backup roll 8 as usual is shown, this invention is a base material. The present invention can also be applied to the case of simultaneous double-sided coating in which roll coaters are arranged on both sides of 1 and no backup roll is required. Furthermore, the plate-passing direction of the substrate 1 may be either a horizontal pass or a vertical pass.

  Moreover, although the case where 2 rolls are used as the precoater B is shown in the above embodiment, the number of rolls may be one or more, and a 1 roll coater or a 3 roll coater may be used. A three-roll coater is more desirable than a two-roll coater because it has higher film thickness controllability and is more advantageous, but it is expensive. As described above, since the final film thickness is not affected if the film thickness (precoat thickness) applied by the precoater B is less than 5 μm, when a coating liquid supply device capable of controlling the film thickness is provided. Even a single roll can sufficiently achieve the object.

  Further, the supply method of the coating liquid in the precoater B may not be a method of pumping the coating solution 13 from the coater pan 12 but may be a method of spraying the coating solution from the nozzle to the roll.

  The invention is illustrated in detail by the following examples.

  As an example of the present invention, using a coil coating (steel strip) of a galvanized steel sheet having a thickness of 0.6 mm and a width of 1200 mm as a base material, using the roll coating apparatus shown in FIG. Coating was performed, and the film thickness after coating, the appearance of coating, the presence or absence of film thickness unevenness, the coating film concentration, the film thickness after drying, and the film specific gravity were calculated from the coating film thickness. For film thickness unevenness after drying, measure the film thickness distribution in the running direction (conveying direction) and width direction of the substrate, find the difference between the maximum and minimum values of the measured value, and the film thickness difference becomes the target film thickness. On the other hand, when it was 5% or less, there was no film thickness unevenness, and when it exceeded 5%, it was determined that there was film thickness unevenness. The used coating liquids 3 and 13 were prepared by adjusting the above-described phosphoric acid-based water-based paint to various concentrations.

  Here, for the three-roll coater A, the material of each roll is a rubber lining roll in which an applicator roll 6 is lined with rubber, a gravure roll in which a pickup roll 4 is formed with a large number of recesses on its surface, and a mitering roll 5. A rubber lining roll lined with rubber was used. The roll diameter of each roll was 300 mm for the applicator roll 6, 300 mm for the pickup roll 4, and 200 mm for the mitering roll 5. The peripheral speed of the mitering roll 5 was adjusted in the range of 5 to 150 mpm so that the coating film thickness was constant.

  As for the precoater B, the material of each roll was a precoat roll 9 having a rubber lining roll, a coating liquid supply roll 10 having a metal roll, and a roll diameter of 300 mm. And it was made to become predetermined | prescribed coating film thickness (precoat thickness) by adjusting the peripheral speed and nip pressure of a roll.

  On the other hand, as a comparative example, when the precoater (precoat apparatus) B is not used or the hardness of the rubber on the surface of the applicator roll 6 is less than 60 degrees, the coating conditions described in Table 1 are outside the scope of the present invention. Was applied. The other points were the same as in the example of the present invention.

  As shown in Table 1, in the example of the present invention, it became possible to uniformly apply a thin film having a film thickness after drying of less than 0.1 μm.

  On the other hand, in the comparative example, when the hardness of the rubber on the surface of the applicator roll 6 is less than 60 degrees and the precoater B is not used, the film is caused by the influence of coating unevenness generated at the meniscus portion between the applicator roll 6 and the steel plate 1. Thickness unevenness occurred. At that time, when the coating solution film thickness was 3 μm or more, no blur occurred, but repelling occurred and the film thickness unevenness after drying became remarkable. Further, when the coating film thickness was less than 3 μm, blurring occurred.

  Moreover, in the comparative example, when the hardness of the rubber on the surface of the applicator roll 6 was less than 60 degrees and the precoater B was used, the film thickness was nonuniform. In particular, when the precoat film thickness was 5 μm or more, the film thickness after application by the 3-roll coater A was 3 μm or more, and repellency occurred, resulting in remarkable film thickness unevenness after drying.

  In this example, a galvanized steel sheet was used as a base material. However, the present invention is not particularly limited to a steel sheet, and can be applied to other metal plates such as aluminum, paper, and films. .

It is a side view which shows the roll coating device used in one Embodiment of this invention. It is a figure which shows the relationship between the hardness of applicator roll surface rubber, and film thickness nonuniformity. It is a figure which shows the relationship between a precoat film thickness and the film thickness after application | coating with a 3 roll coater. It is a side view which shows the conventional roll coating device.

Explanation of symbols

A 3 roll coater B precoater 1 substrate 2 coater pan 3 coating solution 4 pickup roll 5 mitering roll 6 applicator roll 7 blade 8 backup roll 9 precoat roll 10 coating solution supply roll 12 coater pan 13 coating solution

Claims (2)

The amount of the coating liquid supplied to the pick-up roll is adjusted with a metering roll, the adjusted amount of coating liquid is supplied to the applicator roll, and the applicator roll to which the coating liquid is supplied is continuously A roll coating method using a three-roll coater that contacts a traveling substrate and applies a coating solution onto the surface of the substrate, and a precoater that applies the coating solution to the substrate in advance at a position upstream of the three-roll coater. In
When applying the coating liquid so that the thickness of the coating film after drying is less than 0.1 μm by using a steel strip as the base material and water-based paint as the coating liquid and running the base material continuously at a high speed of 100 mpm or higher. ,
The concentration of the coating solution is 1.00% to 4.80% and the coating film thickness is 3 μm or less.
As the applicator roll, you have use a rubber lining roll hardness 60 degrees or more of rubber lined,
The precoater has a precoat roll and a coating liquid supply roll for supplying a coating liquid to the precoat roll, the precoat roll is a rubber lining roll, and the coating liquid supply roll is a metal roll,
First, using the Purekota, the surface of coating a coating solution of a substrate, a coating solution having the same composition as the coating liquid for coating with the 3 roll coater precoated thickness of the liquid film is less than 5 [mu], followed by the A roll coating method, wherein the coating liquid is applied to a substrate by the three-roll coater when the coating liquid on the precoated substrate is in a liquid state. A roll coating apparatus used in the roll coating method according to claim 1,
A pickup roll supplied with the coating liquid, a metering roll for adjusting the amount of the coating liquid supplied to the pickup roll, and the coating liquid supplied from the pickup roll with the liquid amount adjusted A three-roll coater provided with an applicator roll for applying a coating solution to a continuously running substrate;
On the upstream side of the substrate running direction of the three-roll coater, a surface of the substrate to which the coating solution is applied is precoated with a coating solution having the same composition as the coating solution applied with the three-roll coater, and the precoated coating is applied. e Bei a liquid is provided at a position to reach the 3 roll coater in a liquid state Purekota,
Applicator roll which constitutes the 3 roll coater, Ri Oh rubber lining roll hardness 60 degrees or more of rubber lined,
The precoater includes a precoat roll and a coating liquid supply roll for supplying a coating liquid to the precoat roll, the precoat roll is a rubber lining roll, and the coating liquid supply roll is a metal roll. Roll applicator.

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