JPH0596218A - Reverse roll coater - Google Patents

Abstract

PURPOSE:To prevent a stripe from being formed in a coated film on a web by equipping both an applicator roll provided with numerous recesses on the outer circumferential face and a backup roll touched thereto via the web, and providing a doctor blade which butts the applicator roll on the outer circumferential surface thereof. CONSTITUTION:A reverse roll coater is equipped with both an applicator roll 1 closely provided with numerous recesses 5 in a lattice-shape in a range of the front face on the outer circumferential face and a backup roll 2 made of rubber which touches this roll 1 via a web 4 and is contrarotated for the roll 1. One part of the applicator roll 1 is immersed in coating liquid of the inside of a coating liquid tank 3. Further, the applicator roll 1 is provided with a doctor blade 6 which butts the outer circumferential face of the roll 1 in the lower part side in the direction of rotation than the contact point with the backup roll 2. In such a way, many recesses 5 are provided on the surface of the applicator roll 1. Thereby the contact area of the web 4 for the roll 1 is made small and coating liquid 7 is thinly and uniformly transferred on the web 4 and applied thereto.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two roll type reverse roll coater having an applicator roll and a backup roll which rotate in opposite directions.

[0002]

2. Description of the Related Art FIG. 2 exemplifies a typical three-roll reverse roll coater of the related art, and includes an applicator roll 1 having a smooth surface and a metalling roll 10 having a smooth surface which rotates in reverse to the applicator roll 1. And a backup roll 2 made of rubber. After adjusting the amount of the coating liquid 7 attached to the applicator roll 1 with the metering roll 10, the coating liquid 7 is transferred from the applicator roll 1 to the web 4. ing. There, the rotation speeds of the three rolls 1, 2 and 10 are controlled independently and individually, and the relative surface speed between the applicator roll 1 and the metering roll 10 and the applicator roll 1 and the backup roll are controlled. The relative surface speed with respect to 2 is changed.

On the other hand, a two-roll type gravure coater is also known, in which a gravure roll in which a myriad of cells are densely provided all over the outer peripheral surface and a backup roll which is in contact with the gravure roll via a web, Both rolls in the case are rotating in the same direction.

[0004]

In the conventional reverse roll coater, one of the main factors that determines the coating thickness on the web 4, that is, the thickness of the coating film 7a is the applicator roll 1
And the metering roll 10 has a nip distance. A problem with this is that the nip interval between the two rolls 1 and 10 cannot be set small when the main purpose is to make the coating film 7a uniform and thin. That is, the circularity of both rolls 1 and 10 is not perfect, and the runout of the bearings of both rolls 1 and 10 is synergistically added to this. Therefore, there is a limit in setting the size of the corresponding nip interval as small as possible. Therefore, in the conventional reverse roll coater, even though the surface smoothness of the coating film 7a was excellent, it was not possible to meet the demands for both uniformization and thinning.

Further, the pressing force of the backup roll 2 in the reverse roll coater needs to be transferred so that the measured coating liquid 7 is completely peeled off from the smooth surface of the applicator roll 1 by the web 4. Therefore, the pressing force of the backup roll 2 should ideally be set as small as possible. However, there were limits here as well. That is, the total pressure acting on the web in the nip between the rolls 1 and 2 tends to be too high. Furthermore, the smooth surface of the applicator roll 1 is in full contact with the rubber backup roll 2 via the web 4 in the roll axial direction, and the contact area is large. In addition, both rolls 1 and 2 are reversed, so both rolls 1 and 2
The frictional resistance to the web 4 at the nip is also large. These act in synergy to feed the web 4, that is, the rotation of the backup roll 2 intermittently hits against the gun, and the coating film 7a on the web 4 has horizontal stripes parallel to the roll axis. Moreover, wrinkles and tension fluctuations are likely to occur on the web 4.

In addition, when the coating liquid 7 is handled in a wide range, the viscosity, density, web feed speed, nip pressure, etc. are comprehensively taken into consideration, and the three rolls 1, 2, 10 are ideal. There is also a problem in that it is necessary to adjust the speed ratio, which makes this setting work extremely difficult. Even in the best adjustment, the conventional reverse roll coater still produces the coating film 7a.
Was difficult to make uniform and thin. On the other hand, in the gravure coater, the coating amount is mainly determined by the shape and size of the cell and the angle of the doctor blade, so that the coating film 7a can be made uniform. Therefore, it is possible to cope with thinning to some extent. However, in this case, since a gravure pattern appears on the coating film on the web, the greatest problem is that it is necessary to subsequently carry out a leveling process.

Therefore, it is an object of the present invention to effectively achieve uniformization and thinning of the coating film on the web in the reverse roll coater without causing streaks in the coating film on the web.
Another object of the present invention is to obtain an easy-to-use reverse roll coater that does not require strictness in adjusting the rotational speed ratio between rolls.

[0008]

As shown in FIG. 1, the present invention comprises an applicator roll 1 and a backup roll 2 which is in contact with the applicator roll 1 via a web 4. The backup roll 2 is rotating in the reverse direction, innumerable dents 5 are densely provided on the entire outer peripheral surface of the applicator roll 1, and the applicator roll 1 rotates more than the contact point with the backup roll 2. On the lower side in the direction, it is required to have a doctor blade 6 that abuts against the outer peripheral surface of the applicator roll 1.

[0009]

The coating liquid 7 is filled in the recesses 5 on the applicator roll 1, and the excess coating liquid 7 is scraped off the roll surface by the doctor blade 6. Next, the coating liquid 7 in the recess 5
It is transferred to the surface of the web 4 guided by the backup roll 2. However, since the two rolls 1 and 2 are rotating in opposite directions, the coating film 7a on the web 4 is in a state of being erased from the pattern of the recesses 5 and being in a smooth and solid coating state. At that time, in the nip between the rolls 1 and 2, the web 4 is in line contact with the surface of the applicator roll 1, but the contact area between the web 4 and the applicator roll 1 is small due to the presence of the recess 5. Therefore, the frictional resistance to the web 4 is reduced. If the frictional resistance with respect to the web 4 becomes small, the tension of the web 4 becomes uniform without fluctuation, and the coating film 7a on the web can be made uniform. At the same time, the pressing force of the backup roll 2 can be dramatically reduced.

[0010]

Therefore, according to the present invention, it is possible to make the coating film 7a infinitely thin by simply selecting the size and shape of the recess 5 while ensuring the smoothness of the coating film 7a of the reverse roll coater itself. Uniformity can be achieved at the same time. Specifically, in the case of the aqueous coating liquid 7, the lower limit of the coating film 7a on the web 4 was 10 g / m ² when wet in the past, but in the present invention, it is applied to a very thin thickness of ² g / m ² when wet. It can be formed. The coating film 7a does not have streaks in the vertical direction or the horizontal direction.

The metering of the coating liquid 7 on the applicator roll 1 can be accomplished by scraping off with the doctor blade 6, and therefore the reverse roll coater of the present invention is sufficient with the two-roll system in which the conventional metering roll 10 is omitted. As a result, it is possible to eliminate the streak phenomenon of the coating film 7a on the web 4 due to the roundness of the conventional metering roll 10 and the deflection of the bearing portion.

Moreover, even if the rotation speed ratio between the applicator roll 1 and the backup roll 2 is not strictly set, the coating film 7a can be thinly and evenly applied and formed even with a ratio of 1: 1.

[0013]

FIG. 1 shows a two-roll reverse roll coater according to the present invention, in which 1 is an applicator roll and 2 is a roll.
Is an elastic rubber backup roll, 3 is a coating liquid tank, and 4 is a web. The backup roll 2 is in elastic contact with the applicator roll 1 via the web 4.

The applicator roll 1 and the backup roll 2 independently control the rotation speed, and the backup roll 2 rotates in the reverse direction with respect to the applicator roll 1. The relative surface velocity ratio (linear velocity ratio) of both rolls 1 and 2 may be 1: 1 but is within the range of 1.0 to 3.0: 1, more preferably 1.1 to 1.3: 1. Can be set.
The rotation speed of the applicator roll 1 may be slower than that of the backup roll 2. On the outer peripheral surface of the applicator roll 1, innumerable recesses 5 are densely provided in a lattice pattern over the entire surface. The total opening area of the recess 5 is about 70 to 80%.

Incidentally, if the opening area of each recess 5 is reduced, the surface speed ratio of both rolls 1 and 2 can be increased, but there is a limit to the processing accuracy of the recess 5, and the applicator roll 1 is limited to this extent. If the linear velocity of the above exceeds 1.5 times the linear velocity of the backup roll 2, thin coating of the coating liquid 7 on the web 4 becomes difficult. In this sense, the surface velocity ratio of both rolls 1 and 2 is
1.0-1.5: 1.0 is preferable. The depth of each depression 5 is not so important for uniform coating, and about 30 μm is sufficient. The applicator roll 1 is provided with a doctor blade 6 that abuts against the outer peripheral surface of the applicator roll 1 on the lower side in the rotation direction than the contact point with the backup roll 2.

The coating liquid 7 in the coating liquid tank 3 is directly picked up on the outer surface of the applicator roll 1. Then, each recess 5 on the roll 1 is filled with the coating liquid 7, and the excess coating liquid 7 is scraped off from the roll surface by the doctor blade 6. Next, the applicator roll 1 is attached to the web 4 pressed against the applicator roll 1 by the backup roll 2.
The upper coating liquid 7, that is, the coating liquid 7 in the recess 5 is transferred. Since both rolls 1 and 2 are rotating in reverse to each other at the time of this transition, the coating liquid 7 is applied to the web 4 in a smooth and solid state instead of the pattern of the depressions 5.

A large number of recesses 5 are densely formed in the applicator roll 1, and the contact area of the web 4 with the roll 1 is small due to the existence of the recesses 5, so that the web 4
The frictional resistance applied to is also low. Accordingly, the tension of the web 4 did not fluctuate, and the coating liquid 7 could be thinly and uniformly transferred and applied to the web 4 by making the shape and size of the recess 5 precise. At that time, the nip pressure between the applicator roll 1 and the backup roll 2 is usually 2.0 to 5.0 kg.
Although it is set to / cm, in the present invention, it is 1/10, and further 1
/ 100 to 0.02 to 0.05 Kg / cm could be set.

Specifically, the linear velocity ratio between the backup roll 2 and the applicator roll 1 is 1: while using the coating liquid 7 and feeding the web 4 at a line speed of 200 m / min.
Set to 1.3 and nip pressure between both rolls 1 and 2 is 0.03Kg
/ Cm, the coating film 7a of the coating liquid 7 transferred to the web 4 could be formed as thin and smooth as 6 g / m ² when wet. Similar good results were obtained even when the linear velocity ratio of both rolls 1 and 2 was 1: 1.

[Brief description of drawings]

FIG. 1 is a side view of a reverse roll coater according to the present invention.

FIG. 2 is a side view of a conventional reverse roll coater.

[Explanation of symbols]

 1 Applicator roll 2 Backup roll 3 Coating liquid tank 4 Web 5 Recess 6 Doctor blade 7 Coating liquid

Claims (1)

[Claims] 1. An applicator roll 1 and a backup roll 2 in contact with the applicator roll 1 via a web 4 are provided. Innumerable recesses 5 are densely provided all over the outer peripheral surface, and the applicator roll 1 abuts against the outer peripheral surface of the applicator roll 1 on the rotation direction lower side than the contact point with the backup roll 2. A reverse roll coater equipped with a doctor blade 6.