JPH0353994B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for forming coating layers on both sides of a plastic film or sheet-like substrate, and in particular, it coats both sides of the substrate substantially simultaneously, uniformly and The present invention relates to a double-sided coating method for forming a coat layer with good appearance.

[Prior Art] Film or sheet-like substrates (hereinafter simply referred to as film-like substrates or films) such as cellophane or plastic films are coated with a coating process for the purpose of imparting various properties such as gas barrier properties, moisture proofing properties, and chemical resistance. The process itself is known. A coating processing device consists of a film-like base material feeding section, a coating head, a drying section, a cooling section, a winding section, etc. It is also known that the coating performance in the coating head has a large effect on the quality of the coating appearance. There is. Conventionally used coating heads include the knife coater type shown in FIG. 2a and the kiss roll coater type shown in FIG. 2b. A relatively highly viscous coating liquid 2 is applied little by little onto the film 3 which is brought close to each other and advances in the direction of arrow A between the rubber blanket 4 and the doctor knife 1. On the other hand, in the latter kiss roll coater type, the coating liquid 2 lifted up by a gravure roll 6 partially immersed in the coating liquid 2 is transferred to a coating roll 5, and the coated surface of the film 3 is transferred by the coating roll 5. Apply coating liquid on top. In addition to the above methods, gravure roll type, air knife coater type, reverse roll coater type, etc. are known.
Different methods are used depending on the type and properties of the film base material and coating liquid.

Each of the above-mentioned methods is a method of applying the coating liquid 2 to one side of the film 3, and if you try to perform double-sided coating using these methods,
First, we must consider a method of coating one side of the film, allowing it to dry completely, and then coating the other side. However, when coating both sides using this method, the material must pass through the coating processing device twice, which is very disadvantageous in terms of work efficiency.

Against this background, a method as shown in FIG. 3 has been devised as a method for simultaneously coating both sides of a film-like base material, and is currently widely used. That is, a pair of coating rolls 5, 5 are arranged at positions facing each other with the running film 3 in between, and the coating liquid 2 is applied to the circumferential surface of each coating roll 5, 5 via an intermediate roll 8 and a gravure roll 6. Supplied. Theoretically speaking, it is conceivable to form an extremely fine gap between both surfaces of the film 3 and the surface of each coating roll 5, and to allow the coating liquid to penetrate into the gap, but in actual work, Since the distance varies depending on the dimensional and shape accuracy of the coating roll 5 and the vibration of the film 3, a good coating appearance cannot be obtained with the above-mentioned non-contact type. Therefore coating roll 5
There is a contact type or nip type method for double-sided coating in which a rubber roll is used as the coating roll and the film 3 is compressed by a coating roll, that is, one coating roll 5 acts as a back-up roll for the other coating roll 5. It's being used. Therefore, from a microscopic perspective, the rubber coating roll that presses the film 3 from both sides has a flat appearance on the pressing surface, and the rotation direction and speed of the coating roll 5 are set in the running direction A of the film 3. and must be synchronized with the traveling speed. The positional relationship between the film 3 and the coating rolls 5, 5 is such that the coating liquid is applied evenly to both the left and right sides.
The film 3 is arranged so as to run in each tangential direction. That is, the virtual straight line (broken line in FIG. 3) connecting the axes of the coating roll 5 and the travel trajectory of the film 3 must be perpendicular to each other.

[Problems to be Solved by the Invention] When double-sided coating is applied by the means shown in FIG. 3, the pressing surface is microscopically flat as described above, and the film 3 and each coating roll 5 come into line contact. become. Therefore coating roll 5
A pool of coating liquid is formed near the entry point of the film 3, and as the operation continues for a long time, the pool gradually increases, causing the following inconvenience.

That is, when the film advances vertically upward, the coating liquid drips, which impedes the stability of the coating operation, and when the film advances in the horizontal direction, the coating liquid is cast on the upper surface of the film, causing the film to drop. It spreads to the lateral edge, commonly known as the ear, and sometimes extends to the lower side ear.
In either case, it becomes impossible to form a good coating on the film surface.
If it were possible to change the speed ratio between the film and the coating roll, it might be possible to avoid the above disadvantages, but this is not possible as long as the nip method is used. Therefore, efforts have been made to improve the appearance of the coating by introducing a smoothing process after the coating process. In the smoothing process, as shown in Fig. 4, a smoothing bar 9 or the like is arranged along the travel path of the film 3 to remove excess coating liquid from the surface of the film 3 to obtain a uniform film thickness. That is. However, depending on the viscosity of the coating liquid, it may not be possible to obtain a sufficient smoothing effect, and the compounds used in the coating liquid may be subject to restrictions or the film thickness adjustment may become uncertain. When a coating liquid is used, the particles applied to the film surface may be scraped off by the smoothing bar 9, and the compounds used as the coating liquid are thus considerably limited. Although attempts have been made to make the smoothing bar 9 rotatable, the adjustment operation becomes even more complicated, making it difficult to obtain a good coating appearance with a high yield.

Therefore, the inventors of the present invention have conducted various researches with the aim of perfecting a coating method that can efficiently coat both sides of the film at the same time and provide a good coating appearance.
The present invention has now been completed.

[Means for solving the problem] In order to coat both sides of a plastic film or sheet-like base material with a coating liquid at the same time in a good condition, a coating film 1 is provided on both sides of the traveling film or sheet with the running film or sheet in between. A method in which both sides of a film or sheet are coated using a pair of coating rolls, and the film or sheet is coated on both sides so that the intersection angle of the running trajectory of the film or sheet with respect to a virtual plane including the respective axes of the coating rolls is not 90 degrees. Coating rolls are provided back and forth in the direction in which the film or sheet travels, and the film or sheet is brought into contact with the outer periphery of the two coating rolls with a contact length of 1 to 100 mm, and the film or sheet is run under tension between the coating rolls. The gist of the present invention resides in that the two coating rolls are rotated in a direction opposite to the traveling direction of the film or sheet while coating the film or sheet so that both sides of the film or sheet are coated one after another.

[Function] Conventional coating rolls were disposed facing each other so that the imaginary plane including the axis of rotation and the film running trajectory were at right angles, but in the present invention, the intersection angle between the imaginary plane and the film running trajectory was 90°. The coating rolls are arranged in a non-contact arrangement by arranging the coating rolls at positions shifted from each other back and forth to prevent the coating rolls from coming into contact with each other. The recommended intersection angle range is 20 to 80 degrees, and the optimal range is preferably 40 to 75 degrees. The film is then independently supported in contact with two coating rolls,
The coating rolls are suspended so that they are in contact with each other with a contact length of 1 to 100 mm on the circumferential surface of the coating rolls, so that both rolls are running under tension. Therefore, the rotation of each coating roll can be controlled independently of the film running direction, and the coating roll can be rotated in a direction opposite to the film running direction. The rotational speed of the coating roll can be set independently of the film traveling speed, and the rotational speed ratio of the coating roll to the film traveling speed, as well as the mutual rotational speed ratio of each coating roll, can be freely set. . Also, since it is freed from the restriction that the direction of rotation must match the film running direction, when rotating in the reverse direction, any speed ratio can be set according to the characteristics of the coating liquid without the need for a smoothing process. It becomes possible to provide a good coating appearance on both sides almost simultaneously.

EXAMPLE A schematic diagram of a coating head suitable for carrying out the method of the invention is shown in FIG. 1a. Film 3 is arrow A
As shown in FIG. 3, a coating roll 5a is disposed on the left side of the film 3, and an intermediate roll 8 and a gravure roll 6 are used to supply the coating liquid 2 to the coating roll 5a.
are arranged in contact with each other from the position of the coating roll 5a. In this embodiment, the same diameter is used as the coating roll 5a, intermediate roll 8, and gravure roll 6, but the diameter of each roll can be freely selected depending on the type of coating liquid, etc. can. On the other hand, on the right side of the film 3, a coating roll 5b, an intermediate roll 8 and a gravure roll 6 are arranged in contact with each other. Coating roll 5a and coating roll 5b
As shown in the figure, the rolls 5b are shifted back and forth so that they are lower than the rolls 5a. Of course, the roll 5a may be placed downward. In other words, the virtual plane X (indicated by broken lines) including the rotation axes of the coating rolls 5a and 5b does not intersect perpendicularly to the traveling locus 3 of the film 3. Further, in order to run the film 3 under tension between the rolls 5a and 5b, the film 3 is made to advance (slightly meander) along each circumferential surface of the rolls 5b and 5a.

When applying the coating liquid 2 to the film 3, first the coating roll 5b located on the lower side
The coating liquid 2 is applied to the right side of the film 3 by means of the following steps. At this time, the film 3 and the coating roll 5b have a finite contact length 1 as shown in FIG.
0, while the coating roll 5
Point a also has a similar finite length and comes into contact with the film 3, and its left side surface is coated with the coating liquid 2. Such a film 3 has a very slight meandering shape due to the coating rolls 5a and 5b, and the film 3 is
Since the tension is applied by a and 5b, vibration of the film is prevented and stable running is ensured, resulting in a uniform and good coating film. Furthermore, contact length 1
The preferred range of 0 varies depending on the rigidity of the film, the roll diameter, the film running speed, and the properties of the coating liquid, but as a result of repeated experiments, a range of 5 to 20 mm is the most preferable range, and the running resistance of the film It was found that a range of 1 to 100 mm is the limit for maintaining a good coating appearance, taking into account the increase in . That is, when the contact length 10 exceeds 100 mm, scratches tend to occur on the outer surface of the coating layer, and in an experimental example where the contact length was 130 mm, many scratches were generated on the outer surface of the coating, resulting in poor appearance.

Since coating is applied to both sides of the film 3 as described above, the speed ratio between the film and the coating roll is adjusted according to the properties of the coating liquid, and the direction of rotation of the coating roll is adjusted as shown in Figure 1a. By rotating the film in a direction counter to the running direction of the film, a film having a desired coating thickness and a good coating appearance can be produced.

The apparatus for coating both sides of the film 3 while applying tension by shifting the positions of the coating rolls 5a and 5b back and forth is not limited to the embodiment shown in FIG. It does not matter whether the rolls are removed or the coating rolls 5a, 5b, intermediate roll 8 and gravure roll 6 are arranged in a straight line as shown in Fig. 1f. b, c, and d show examples of various combinations of these changes. Figures 1 a to f show an example in which the film 3 runs vertically from bottom to top as shown by arrow A, while Figures 6 a and b show an example in which the film 3 runs horizontally along arrow B. An example of its application is shown.

In addition, since the present invention employs a method of tensioning the film 3 using the coating rolls 5a and 5b, the contact pressure between the rolls 5a and 5b and the film 3 is small compared to the nip method, and each coating roll 5a, Even if the direction of rotation of 5b is the same as that shown in FIG. 1a, the rotation speed can be freely selected. Therefore, the rotational speed of the coatings 5a, 5b can be adjusted independently of the running speed of the film 3.

(Experimental example) Using the apparatus shown in FIG. 1a as an example of the method of the present invention, and using the apparatus shown in FIG. 3 as a conventional example,
In each case, the coating performance of each film was compared when both sides of a 25 μm stretched polyester film were coated with an ether-type polyurethane resin emulsion (manufactured by Dai-ichi Kogyo Co., Ltd.). The coating conditions were the same for both the present invention and the conventional example as follows.

(a) A 200 mesh gravure roll is used, and the intermediate roll is an NBR rubber roll with a hardness of 80.
The coating roll used was a mirror-finished metal roll with the same diameter of 200 mm. The rotation direction of each roll is as shown in FIG. 3 and FIG. 1a.

(b) The film was run at a speed of 50 m/min, and the coating liquid was an ether-type polyurethane resin emulsion mixed with water.
A 10% concentration (viscosity 100 cps) was used, and a drying zone at 70°C was used for drying.

(c) In the coating method of the present invention, the roll rotation speed was 55 m/min, the roll was rotated in the opposite direction to the film running direction, and the contact length between the film and the coating roll was set to 10 mm. In the conventional method, the direction of rotation of the roll and the direction of film travel are the same.

(d) In the conventional method, after the coating process was completed, a smoothing process was added using a smoothing device as shown in FIG.

As a result of long-time coating processing under the conditions (a) to (d), the conventional method sometimes gave a good coating appearance, but uneven coating of the coating solution occurred in some places, and the quality of the product deteriorated. It wasn't stable. On the other hand, the appearance of the coating obtained by the method of the present invention remained in good condition until the end, and the coating process could be continued.

In the above experiment, a case was shown in which a single layer of coating was applied on a film-like base material, but even when applying another coating on top of a coated film, the above-mentioned method can be applied. Similarly, a good coating surface can be formed.

[Effects of the Invention] Since the present invention is configured as described above, the range of selection of coating conditions is widened, and even during long-term continuous operation, defects such as dripping do not occur, and the coating is always in good condition. It has become possible to perform double-sided coating processing with a beautiful appearance.

[Brief explanation of drawings]

1A to 1F are schematic explanatory diagrams showing an outline of the coating head used in the present invention, FIGS. FIG. 4 is a schematic explanatory diagram showing a contact type coating head used for double-sided coating. FIG. 4 is an explanatory diagram showing a smoothing device. FIG. Figures a and b are explanatory diagrams showing an embodiment in which the present invention is applied to a horizontally traveling film. 1... Knife, 2... Coating liquid, 3... Film, 4... Rubber bracket, 5, 5a, 5b...
Coating roll, 6... Gravure roll, 7
...Doctor blade, 8...Intermediate roll, 9...
...Smoothing bar, 10...Contact length.

Claims (1)

[Claims] 1. A method of coating both surfaces of a traveling plastic film or sheet with a coating liquid using a pair of coating rolls disposed on both sides of the film or sheet, the axis of each of the coating rolls being Both coating rolls are placed one behind the other in the traveling direction of the film or sheet so that the intersecting angle of the running trajectory of the film or sheet with respect to the virtual surface included is not 90 degrees. The two coating rolls are rotated in a direction opposite to the traveling direction of the film or sheet, while the coating rolls are brought into contact with the outer periphery of the roll at the contact length, and the coating rolls are run under tension, and both sides of the film or sheet are rotated. 1. A method for coating both sides of a film or sheet, characterized by coating both sides of the film or sheet one after the other.