JP5326519B2 - Roll coating method and roll coating apparatus - Google Patents

Description

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

  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. 2, this type of coating apparatus (three roll coater) includes a pickup roll 4 that draws up the coating liquid 7 from the coater pan 6 filled with the coating liquid, and an amount of the coating liquid pumped up by the pickup roll 4. And an applicator roll 3 that transfers the adjusted amount of coating solution from the pick-up roll 4 to the substrate 1.

  The direction of rotation of each roll may be a reverse rotation that rotates in the opposite direction to a natural rotation that rotates in the same direction at the proximity point between the rolls or at the close point, but in general the reverse rotation is the basis. Since it is easy to obtain a coating surface having a uniform film thickness along the unevenness of the material, reverse rotation is often performed particularly between the applicator roll 3 and the substrate 1. The applicator roll 3 uses a rubber roll in which a steel roll is lined with rubber 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 an appearance defect in which a streak pattern appears in the circumferential direction called roping. This roping is known as a defect that occurs when fluid pressure fluctuations exceed the effect of surface tension stabilization. In addition, the film thickness may be uneven due to the occurrence of rubbing due to air entrainment between the applicator roll 3 and the substrate 1, and the appearance may be deteriorated.

  Naturally, it is necessary to suppress the occurrence of such coating defects, but in addition to this, in recent years, due to increasing needs for workability and high electrical conductivity, the film thickness has been reduced (the film thickness after coating and drying is less than 0.1 μm). ) Is required.

  Conventionally, as a thin film coating technique, a micro gravure method using a small-diameter gravure roll (see, for example, Patent Document 1) and a die coater method (see, for example, Patent Document 2) are disclosed. In the microgravure method, the coating film thickness can be reduced to less than 3 μm and a minimum of about 1 μm. In addition, the die coater method can be applied to about 1 μm in recent years.

  However, in the case of the micro gravure method, since the coating liquid is transferred to the substrate using a metal roll, wrinkles are generated on the surface of the substrate when the substrate is a metal. In the case of a die coater method, in order to reduce the film thickness, it is necessary to bring the gap between the base material and the die for supplying the coating liquid close to the desired film thickness. However, in the case of a steel strip that runs continuously, shape variation occurs in both the width direction and the longitudinal direction, so that it is difficult to make the die close. In addition, in the case of the die coater method, when high-speed application is performed, a defect called air entrainment occurs, so that the application is limited to a low-speed region of about 10 mpm, and productivity is hindered.

In addition, when the coating is performed on the base material using a large roll coater having a width of about 1000 mm as in the production of a steel strip, it depends on the accuracy of the roll, but generally it can be applied without fading. The liquid film thickness is about 5 μm or more. In order to reduce the film thickness after coating and drying to less than 0.1 μm while ensuring the thickness of the liquid film, it is necessary to increase the dilution ratio of the coating liquid (decrease the concentration of the coating liquid). However, it is necessary to make the solid content concentration in the coating liquid as low as less than 2%. In particular, when a water-based coating solution is used, the surface tension increases due to the dilution rate, so that the wettability with the substrate is deteriorated, and rubbing is likely to occur in the line direction.
Japanese Patent Laid-Open No. 11-197569 JP 2004-230361 A

  The present invention has been made to solve the above-described problems, and improves the wettability of the coating solution with respect to a substrate that runs continuously at a high speed, and reduces the dilution rate of the coating solution for thinning. It is an object of the present invention to provide a roll coating method and a roll coating apparatus that do not cause defects such as rubbing even when raised.

  As described above, in the case of a roll coater, when a coating solution diluted to a solid content concentration of less than 2% is applied to a substrate, the surface tension increases and wettability deteriorates, so that rubbing occurs in the line direction. It becomes easy to do. The reason for the occurrence of rubbing is that liquid wetting on the base material is likely to occur due to deterioration of wettability between the base material and the coating liquid. Therefore, in order to obtain a uniform film thickness, the air accompanying the substrate should not affect the meniscus between the applicator roll and the substrate.

  Therefore, as a result of intensive studies, the inventors installed a plasma irradiation device upstream from the position of the applicator roll, and modified the surface of the substrate with the plasma irradiation device so that the wettability was good. After that, if it was brought into contact with the applicator roll, it came to the idea that even when the dilution rate of the coating solution was increased, the occurrence of rubbing would be eliminated.

  The present invention has the following features based on the above-described concept.

[1] In a roll coating method in which a coating liquid is applied to a base material made of a continuously traveling metal by a roll in contact with or close to the base material , the base material before the coating liquid is applied to the base material A roll coating method comprising performing plasma irradiation over the entire width direction of a substrate .

  [2] The roll coating method according to [1], wherein in the plasma irradiation, a plasma irradiation time to the base material is 0.2 seconds or more and 10 seconds or less.

  [3] The roll coating method according to [1] or [2], wherein in the plasma irradiation, a plasma irradiation distance to the substrate is 50 mm or less.

  [4] In the plasma irradiation, the plasma is arc plasma generated between the electrodes, and has a mechanism for changing the direction of discharge by injecting air into the arc plasma, and the air injection speed at that time is 30 to 260 m. / S is the roll coating method according to any one of [1] to [3].

[5] the base material consisting of continuously traveling metal, the roll coating apparatus for applying a coating liquid by a roll in contact with or in close proximity to the substrate, upstream of the position from the position of the roll, the group A roll coating apparatus , wherein a plasma irradiation apparatus for performing plasma irradiation is installed over the entire width direction of the material .

  [6] The roll coating apparatus according to [5], wherein a plasma irradiation distance from the plasma irradiation apparatus to the substrate is 50 mm or less.

  [7] The plasma irradiation apparatus generates arc plasma between electrodes, and includes a mechanism for changing the direction of discharge by injecting air into the arc plasma. [6] The roll coating apparatus according to [6].

  In the present invention, when the coating liquid is applied to the base material by the roll coater, the base material is preliminarily irradiated with plasma, so that the surface of the base material is modified and the wettability is good. The coating solution is applied, and even when the dilution rate of the coating solution is increased to reduce the thickness of the coating solution, the occurrence of rubbing is eliminated, and the thin film coating without coating defects can be performed on the high-speed line. .

  An embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a roll coating apparatus according to an embodiment of the present invention. This roll coating apparatus is a three-roll coater of a type 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, and a pickup roll 4 that draws the coating liquid 7 from a coater pan 6, And a applicator roll 3 for transferring the adjusted coating liquid 7 on the pick-up roll 5 to the substrate 1.

  In addition, the pick-up roll 4 uses the gravure roll in which many recessed parts were formed in the trunk | drum surface, or the flat roll by which the surface was mirror-finished. When the substrate 1 is a metal plate such as a steel strip, the applicator roll 3 is a rubber roll lined with rubber. The rotation direction of each roll is opposite between each roll and between the applicator roll and the base material, and a blade 8 that scrapes the coating solution is installed on the mitering roll 3.

  In addition, in the roll coating apparatus according to this embodiment, the plasma irradiation device 9 is installed at a position upstream from the position of the applicator roll 3, and the substrate 1 is irradiated with plasma from the plasma irradiation device 9. Then, after the surface of the substrate 1 is modified and the wettability is good, the application liquid 7 is applied by the applicator roll 3.

  Here, the plasma irradiation device 9 includes a power supply device, an electrode, a ground, and an air supply device, and is an arc plasma type. There are various methods for generating plasma under atmospheric pressure, but since arc plasma can be generated in the atmosphere, surface modification by plasma irradiation can be easily performed without the need for vacuum equipment. In the atmospheric pressure glow discharge method, it is necessary to use a rare gas such as argon or helium as a carrier gas in order to stably generate plasma, but in the arc plasma method, the direction of discharge is changed by using air. Therefore, the process is easy without requiring an exhaust facility. Also, plasma irradiation equipment that requires vacuum equipment increases the cost of equipment installation and maintenance, making it impossible to make profits on a line that continuously produces inexpensive products. Therefore, arc plasma irradiation equipment that can be used in the atmosphere is superior. It is.

  The results of investigations on conditions under which the wettability of the substrate is improved by surface modification of the substrate by plasma irradiation are described below. The wettability was evaluated by measuring static and dynamic contact angles using a contact angle meter PG-X (manufactured by Matsubo Co., Ltd.).

  Incidentally, the improvement of the wettability of the substrate is manifested by surface oxidation. Surface oxidation occurs when radicals generated on the surface of the substrate by discharge react with oxygen in the air. Oxidation treatment can introduce a polar functional group, such as a hydroxyl group-OH, on the surface of the substrate, increasing the surface free energy and making it hydrophilic.

  And about the plasma irradiation time to a base material, the wettability improvement of a base material became remarkable from 0.2 second. And during the irradiation time up to 10 seconds, the wettability of the substrate was improved as the irradiation time increased. However, when the irradiation time exceeded 10 seconds, there was almost no change in wettability compared to the case of irradiation for 10 seconds. Therefore, the plasma irradiation time is preferably set to 0.2 seconds or more and 10 seconds or less.

  Further, regarding the plasma irradiation distance to the base material, it was difficult to irradiate the base material with plasma generated stably when the irradiation distance was 50 mm or more, and no improvement in wettability was observed. Therefore, the plasma irradiation distance (that is, the gap between the plasma irradiation apparatus and the substrate) is preferably 50 mm or less. However, in order to avoid the occurrence of defects due to the contact between the plasma irradiation apparatus and the base material, it is preferable to make the gap larger than the thickness variation of the base material.

  Moreover, it is preferable that the air velocity to be jetted to change the direction of the plasma is 30 m / s or more and 260 m / s or less. If the air speed is less than 30 m / s, the direction of the plasma cannot be easily changed, and it becomes difficult to irradiate the substrate with plasma. If the air speed exceeds 260 m / s, the plasma is stable. This is because it becomes difficult to generate plasma and the wettability improving effect is reduced.

  Next, the results of investigation on the peripheral speed condition range of the roll where the appearance after application is uniform will be described. As described above, as a typical coating defect of a roll coater including a three-roll coater, a streak pattern in the circumferential direction of a roll called roping is transferred to a base material, resulting in uneven film thickness, which may deteriorate the appearance. . This roping tends to occur more easily as the viscosity of the coating solution is higher and the roll peripheral speed is higher. The conditions for the occurrence of roping mainly depend on the peripheral speed of each roll, the pressing pressure, the gap between rolls, and the physical properties of the coating liquid (viscosity, surface tension). Since the speed is increased and the peripheral speed of each roll is inevitably increased, it is difficult to avoid the occurrence of roping. Although roping may occur between the metering roll and the pickup roll and between the pickup roll and the applicator roll, it always occurs in the latter in high-speed coating. Further, when roping occurs in the latter, the roping generated in the former is canceled, so it is only necessary to pay attention to only between the pickup roll and the applicator roll.

  As a result of various experiments, as the peripheral speed of the pick-up roll is increased, the roping pitch on the applicator roll decreases, and the peripheral speed of the pick-up roll is 0 with respect to the peripheral speed of the applicator roll. Very fine roping was obtained above 5 times. When the pitch of roping is reduced, the coating unevenness may become inconspicuous, but the leveling effect increases between after application and after drying, so that the appearance after drying is improved.

  Moreover, it is preferable that the peripheral speed of an applicator roll shall be 0.7 times or more and 1.4 times or less with respect to the running speed (line speed) of a base material. Also between the applicator roll and the base material, as between the pick-up roll and the applicator roll, roping appears more markedly as the applicator roll peripheral speed is slower than the line speed. When the peripheral speed of the applicator roll is increased and the peripheral speed ratio is 0.7 or more, roping is reduced and a good appearance is obtained. However, when the peripheral speed of the applicator roll is excessively increased, the appearance is deteriorated. This is because, when the applicator roll peripheral speed is too high, roping that occurs between the pickup roll and the applicator roll is unavoidable. In other words, considering only the applicator roll and the base material, a faster applicator roll peripheral speed provides a better appearance, but roping tends to occur between the pick-up roll and the applicator roll, and if roping occurs, the applicator It is transferred as it is from the roll to the substrate. To avoid roping between the pick-up roll and the applicator roll, the pick-up roll peripheral speed should be increased as described above. However, as the applicator roll peripheral speed increases, the pick-up roll peripheral speed must also be increased accordingly. Don't be. However, if the peripheral speed of the pick-up roll is too high, the coating liquid scatters when the coating liquid is drawn from the coater pan. Further, the progress of wear of the mitering roll or applicator roll is accelerated, which is not preferable for actual operation. Moreover, if the applicator roll peripheral speed exceeds 1.4 times the line speed, the liquid pool of the coating liquid between the base material and the applicator roll tends to vibrate and uneven coating occurs. The speed is preferably 1.4 times or less.

  Thus, in this embodiment, when the coating liquid 7 is applied to the base material 1 by the three-roll coater, the surface of the base material 1 is modified by previously irradiating the base material 1 with plasma from the plasma irradiation device 9. Since the coating liquid 7 is applied in a state where the wettability is improved, the occurrence of rubbing is eliminated even when the dilution ratio of the coating liquid is increased to reduce the thickness of the coating liquid. It becomes possible to perform a thin film coating without any.

  In the above-described embodiment, the single-sided coating method is generally used. The single-sided coating method is applied in a state where the base material is wound around the backup roll, but the present invention has a roll coater disposed on both sides of the base material. Therefore, the present invention can be similarly applied to a double-sided simultaneous application method that does not require a backup roll. Needless to say, the present invention can also be applied to roll coaters other than the three roll coater.

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

  As an example of the present invention, a coil (steel strip) of a galvanized steel sheet having a plate thickness of 0.9 mm and a plate width of 1250 mm is used as a base material, and using the roll coating apparatus shown in FIG. Application was performed, and the film thickness and appearance after drying were evaluated.

  At that time, as for the material of each roll, a rubber lining roll in which rubber was lined was used for the applicator roll 3 and the mitering roll 5, and a gravure roll having a large number of recesses formed on the surface was used for the pickup roll 4. . The roll diameter of each roll is 300 mm for the applicator roll 3 and the pickup roll 4 and 200 mm for the mitering roll 5. As the coating solution, a phosphoric acid-based aqueous paint having a viscosity of 3 mPa · s, a surface tension of 40 dyn / cm, and a solid content concentration of 5% at a liquid temperature of 20 ° C. was diluted with water.

  On the other hand, as a comparative example, using a roll coating apparatus in which a plasma irradiation apparatus is not installed, as shown in FIG. The film thickness and the appearance after drying were evaluated.

  In addition, evaluation of the external appearance after application | coating and drying of these invention examples and comparative examples was performed by visual observation under a sufficiently bright fluorescent lamp.

  Table 1 shows the evaluation results of the inventive examples and the comparative examples.

  As shown in Table 1, in the example of the present invention, even when the solid content concentration is less than 2%, it is possible to uniformly apply a film having a film thickness after drying of less than 0.1 μm with almost no rubbing. did it. On the other hand, in the comparative example, remarkable rubbing occurred even at a solid content concentration of 2%.

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

It is a side view which shows the roll coating device which concerns on one Embodiment of this invention. It is a side view which shows the conventional roll coating device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base material 2 Backup roll 3 Applicator roll 4 Pickup roll 5 Mitering roll 6 Coater pan 7 Coating liquid 8 Blade 9 Plasma irradiation apparatus

Claims (7)

In a roll coating method in which a coating solution is applied to a substrate made of metal that continuously travels with a roll that is in contact with or close to the substrate, the substrate is not coated with the coating solution . A roll coating method characterized by performing plasma irradiation in the entire width direction . 2. The roll coating method according to claim 1, wherein, in the plasma irradiation, a plasma irradiation time to the substrate is set to 0.2 seconds to 10 seconds. In the said plasma irradiation, the plasma irradiation distance to a base material shall be 50 mm or less, The roll coating method of Claim 1 or 2 characterized by the above-mentioned. In the plasma irradiation, the plasma is arc plasma generated between electrodes, and has a mechanism for changing the direction of discharge by injecting air into the arc plasma, and the air injection speed at that time is 30 to 260 m / s. The roll coating method according to claim 1, wherein the roll coating method is performed. In a roll coating apparatus that applies a coating solution with a roll that is in contact with or close to a base material made of metal that travels continuously, the width of the base material at a position upstream of the roll position. A roll coating apparatus characterized in that a plasma irradiation apparatus for performing plasma irradiation in the entire direction is installed. The roll coating apparatus according to claim 5, wherein a plasma irradiation distance from the plasma irradiation apparatus to the substrate is 50 mm or less. The said plasma irradiation apparatus produces | generates arc plasma between electrodes, and is provided with the mechanism in which the direction of discharge is changed by injecting air to arc plasma. Roll applicator.

Images