JP2010264398A - Coating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gravure coating method which can measure an amount of coating while keeping the liquid surface stable, can minimize lowering of the amount of coating caused by clogging of gravure, and can maintain the amount of coating at a fixed level. <P>SOLUTION: The gravure coating method includes a means 5 measuring pan weight in which an electronic balance of a load cell type, an electromagnetic type, or a tuning fork type, a spring balance or the like, is installed underneath a pan 3, and a means 9 controlling the speed of a gravure roll, and the speed of the gravure roll is controlled to keep the weight of the pan at a fixed level by feeding a coating liquid to the pan in an amount equal to the desired amount of coating. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for maintaining a constant coating amount in a method for applying a coating liquid onto a web.

  For the purpose of imparting functions such as easy adhesion, slipperiness, gas barrier properties, moisture proofing, and antistatic properties to a plastic film, a coating film having these functions is applied to the film surface. Is widely practiced. As a coating method for such a film, a roll coating method represented by a gravure roll method, a reverse roll method, or the like is mainly used.

  In recent years, as the functionality of coating films has increased, it has been required to increase the uniformity of the thickness of the coating film in order to maintain the uniformity of the function, and the management of the coating amount has become increasingly important.

  The coating amount is determined from the web running speed and the coating liquid consumption speed. Conventionally, the coating liquid consumption speed is determined by stopping the supply of the coating liquid to the pan for a certain period of time. A method of measuring the weight and obtaining from the difference weight has been adopted (Patent Document 1). However, in the method of obtaining from the difference weight, since the supply of the coating liquid to the pan is interrupted for a certain period of time, the liquid level in the pan decreases during that time, the pickup amount to the roll changes, and the coating amount becomes unstable. There was a drawback. In addition, if the decrease in the liquid level in the pan is reduced, the difference in weight is reduced, so that the measurement error of the coating amount is increased.

  In the gravure coating method, the coating liquid gradually adheres to the plate, causing clogging, and the coating amount decreases over time.Therefore, the coating is applied before the coating amount decreases beyond the allowable range. There was a drawback that the plate had to be interrupted to clean the plate.

Japanese Laid-Open Patent Publication No. 1-245876

  The present invention can measure the coating amount while keeping the liquid level constant, and is intended to solve the decrease in the coating amount due to clogging of the gravure, and a gravure coating method for maintaining a constant coating amount. It is something to be offered.

As a result of intensive studies to solve the above problems, the present inventors measured the weight of the pan while feeding a certain amount of coating liquid to the pan, and the gravure roll was adjusted so that the weight of the pan was constant. The inventors have found that the above-mentioned problems can be solved by controlling the speed, and have reached the present invention.
That is, the gist of the present invention is as follows.

  It is equipped with pan weight measurement means and gravure roll speed control means. The coating liquid is fed to the pan so as to match the desired coating amount, and the gravure roll speed is adjusted so that the bread weight is constant. A coating method characterized by controlling.

  According to the present invention, since the coating liquid is always supplied to the pan, the height of the liquid level is constant, and the coating amount does not become unstable. Further, when the plate starts to be clogged and the coating amount starts to decrease, the bread weight starts to increase. Accordingly, the gravure roll speed increases accordingly, so that the coating amount decrease due to clogging is compensated. As a result, since the coating amount of the coating liquid on the web is constant, for example, a coating film having a uniform film thickness is obtained in coating on a film, and coating spots are less likely to occur even in thin coating. The effect is obtained. Further, the frequency of cleaning the plate can be greatly reduced, and the production cost can be reduced.

It is the schematic which shows an example of the coating apparatus as an embodiment of this invention.

  Hereinafter, the coating method of the present invention will be described in detail.

  The coating apparatus schematically shown in FIG. 1 is a gravure roll (2) engraved with a fixed shape cell for applying a coating liquid to a plastic film (1), and the coating liquid is soaked in a gravure roll. And a doctor (4) for scraping off excess coating liquid from the gravure roll. The coating liquid is lifted by the gravure roll soaked in the coating liquid, and the doctor applies the excess coating liquid. The working liquid is scraped off, and the coating liquid is transferred to the plastic film by being brought into contact with the plastic film.

  Furthermore, a load cell (5) for measuring the weight of the pan and the coating liquid is provided under the pan, and the pan is connected to the coating liquid feed pump (7) via the pipe (6). The coating liquid is fed from the storage tank (8). Then, the gravure roll speed is controlled by the controller (9) so that the weight measured by the load cell is constant.

  In the present invention, as a means for measuring the weight of the pan, an electronic balance such as a load cell type, an electromagnetic type, or a tuning fork type, a spring balance, or the like is preferable.

  In the present invention, the liquid feeding means for feeding the coating liquid to the pan is not particularly limited, but is set so that the same amount of coating liquid as the desired coating amount is fed to the pan by a feed pump or the like. It is preferable to use a positive displacement pump in order to send liquid quantitatively, and examples of the positive displacement pump include a piston pump, a plunger pump, a diaphragm pump, a gear pump, a vane pump, a screw pump, and a tube pump. When the liquid feeding amount pulsates, the weight of the coating liquid accumulated in the pan fluctuates and the coating amount tends to become unstable. Therefore, it is preferable to use a pump with little pulsation. Although depending on the coating amount and the characteristics of the coating liquid, a screw pump or a tube pump can be preferably used.

  In the present invention, it is necessary to change the gravure roll speed using a controller or the like so that the pan weight measured as described above becomes constant. By doing in this way, the liquid feeding amount of a pump and the actual coating amount can be made to correspond.

  In general, the reverse gravure coating method has a characteristic that the coating amount changes in accordance with the ratio of the web running speed and the gravure roll speed. Specifically, there is a region where the coating amount is the largest in the range where the ratio between the web running speed and the gravure roll speed is 1.2 to 1.5, and the ratio between the web running speed and the gravure roll speed is higher than that. As the size increases or decreases, the coating amount decreases.

  In the gravure coating method, the coating liquid gradually adheres to the plate, causing clogging, and the coating amount decreases with time, so the coating amount is the largest at the start of coating, so the web running speed It is preferable that the ratio between the gravure roll speed and the gravure roll speed is made small at the start of coating, and the ratio between the web running speed and the gravure roll speed is increased so as to compensate for the decrease in coating amount due to clogging. The ratio of the web running speed and the gravure roll speed at the start of coating is more preferably 0.9 to 1.1. This is because if the ratio of the web running speed to the gravure roll speed is less than 0.9, the surface of the coated surface may be deteriorated. Further, it is not preferable that the ratio between the web running speed and the gravure roll speed is larger than 1.5 because the surface of the coated surface may be deteriorated.

  The coating method of the present invention can be preferably applied to coating on a plastic film, but is not particularly limited. It can be applied to both in-line coating applied during the plastic film formation or stretching process and offline coating applied outside the plastic film formation or stretching process, but the loss due to coating interruption is large. It can be applied particularly effectively with in-line coating.

[Example 1]
Polyethylene terephthalate is melted with an extruder, extruded from a T-die, brought into close contact with a cooling drum, rapidly cooled, and stretched 4 times with a longitudinal stretching machine to continuously stretch a longitudinally stretched polyester film having a width of 500 mm and a thickness of 50 μm. Obtained. Here, using a tube pump, a polyester-based easy-adhesive coating agent (solid content concentration 5 mass%) is fed to the pan at 200 g / min, and a # 200 lattice cell (cell capacity 12 cm ³ / m ² ) is supplied. The engraved gravure roll is soaked in a coating solution on a pan placed on a load cell, the excess coating solution is scraped off from the gravure roll using a doctor, and the longitudinally stretched polyester film traveling at a speed of 100 m / min is used. The coating solution was transferred to the film by contact and applied to a coating width of 400 mm. At this time, the gravure roll speed at the start of coating (linear speed on the surface of the gravure roll, hereinafter the same) was 105 m / min, and the weight shown by the load cell was 30.00 kg.

  Subsequently, the coated longitudinally stretched polyester film is guided to a tenter-type stretching machine and stretched transversely by 5 times, followed by heat treatment and relaxation treatment. The stretched end portion was trimmed to obtain an easy-adhesion biaxially stretched polyester film having a thickness of 12 μm and a width of 2000 mm.

  Gravure roll plate clogging occurred gradually after the start of coating, so the gravure roll speed was gradually increased so that the weight indicated by the load cell was maintained at 30.00 kg. The gravure roll speed was 118 m / min after 16 minutes from the start of coating, and the gravure roll speed was 120 m / min after 24 hours from the start of coating. After 24 hours, the gravure roll was cleaned and returned to the state after the start of coating. However, since the liquid feeding amount and the weight indicated by the load cell were always constant, the coating amount was constant at 5 g / min.

[Comparative Example 1]
Regardless of the weight indicated by the load cell, the gravure roll speed is constant at 105 m / min, the feeding rate of the tube pump is 300 g / min, and the coating liquid is made to overflow so that the liquid level of the pan is constant. The tube pump was stopped for 10 minutes at the start, 8 hours, 16 hours, and 24 hours after the start of coating, and the same procedure as in Example 1 was performed except that the coating amount was determined from the weight difference indicated by the load cell.

  The coating amount was 5 g / min at the start of coating, 4.6 g / min after 8 hours of coating, 4.3 g / min after 16 hours, and 4.1 g / min after 24 hours. The amount of work has decreased.

  The film after 8 hours from the start of coating was insufficient in the desired coating amount and was poor in easy adhesion. It can be said that the gravure roll needs to be cleaned every 8 hours after the start of coating.

[Comparative Example 2]
The same as Comparative Example 2 except that the coating amount was adjusted to 5 g / min by changing the gravure roll speed to 114 m / min and 118 m / min, respectively, after measuring the coating amount 8 hours after starting the coating and 16 hours later. Went to.

  The coating amount was 5 g / min at the start of coating, 4.6 g / min after 8 hours from the start of coating, 4.6 g / min after 16 hours, and 4.5 g / min after 24 hours. It varied between 5 and 5.0 g / min.

[Example 2]
After the nylon 6 was melted by an extruder, it was extruded from a T-die, brought into close contact with a cooling drum, and rapidly cooled to obtain an unstretched nylon 6 film having a width of 500 mm and a thickness of 150 μm continuously. Subsequently, using a tube pump, a polyurethane-based easy-adhesive coating agent (solid concentration: 10% by mass) is fed to the pan at 66 g / min, and a # 200 lattice cell (cell capacity: 12 cm ³ / m ² ) is supplied. The unstretched nylon 6 film that drips the engraved gravure roll in the coating liquid on the pan placed on the load cell, scrapes off the excess coating liquid from the gravure roll using a doctor, and runs at a speed of 33 m / min. The coating solution was transferred to the film by being brought into contact with the coating film, and coated to a coating width of 400 mm. The gravure roll speed at the start of coating was 35 m / min, and the weight shown by the load cell was 30.00 kg.

  Subsequently, the coated unstretched nylon 6 film is guided to a tenter type simultaneous biaxial stretching machine, and is simultaneously biaxially stretched 3 times in the longitudinal direction and 3.3 times in the transverse direction, followed by heat treatment and relaxation treatment. The stretched end portion was trimmed to obtain an easily bonded biaxially stretched nylon 6 film having a thickness of 15 μm and a width of 1300 mm.

  Since gravure roll clogging gradually occurred after the start of coating, the gravure roll speed was gradually increased so that the weight indicated by the load cell was maintained at 30.00 kg. The gravure roll speed was 37 m / min after 16 hours from the start of coating, and the gravure roll speed was 39 m / min after 24 hours from the start of coating. However, since the liquid feeding amount and the weight indicated by the load cell were always constant, the coating amount was constant at 5 g / min.

1 Plastic film 2 Gravure roll 3 Pan 4 Doctor 5 Load cell 6 Piping 7 Feed pump 8 Coating liquid tank 9 Controller

Claims (1)

It is equipped with pan weight measurement means and gravure roll speed control means. The coating liquid is fed to the pan so as to match the desired coating amount, and the gravure roll speed is adjusted so that the bread weight is constant. A coating method characterized by controlling.