JPH02214563A - Web coating device - Google Patents

Abstract

PURPOSE:To prevent a contact accident at a boundary region between a web holding part and a web not holding part by making the amt. of gas to be injected at the boundary region larger than that at the other region on the web holding surface. CONSTITUTION:A coater 2 and a gas injector 11 are arranged practically in opposition to each other with a continuously traveling web 3 in between. The amt. of gas to be injected from the injector at the boundary region 11c between the web holding surface 11a and web not holding surface 11b of the injector is made larger than that at the other region of the web holding surface 11a. As a result, the rapid depressurization of the gas contributing to the floating and supporting of the web 3 at the boundary region 11c is prevented, and the contact accident of the web 3 at the boundary region 11c is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an apparatus for floatingly supporting a web (band-shaped flexible support) and applying a coating liquid to an extremely uniform film thickness.

More specifically, it relates to a device that applies one or more coating liquids to the surface of a web of photographic material, etc., opposite to the surface to be coated, by continuously moving the surface of the web while floating and supporting it. The present invention relates to a web coating device suitable for double-sided coating.

[Conventional technology]

Conventionally, various means and methods are known as techniques for coating both sides of a web.

For example, ■Method of coating one side of the web and gelling it, then bringing the gelled side directly into contact with a support roll and continuously applying the coating to the opposite side (Special Publication No. 4B-44171) ■Innumerable methods A coating machine (coater) emits gas from the curved surface of the roll having small holes or slits to float the web.
Method of applying by pressing the tip of the
No. 9-17853) are known.

However, with the above conventional technology, even if there is slight dust or scratches on the support roll that supports the gelled surface, the gelled coating surface will be disturbed, and a part of the coating layer may be left on the roll. The same problem occurs even if the adhesive remains, and maintenance is extremely difficult.

(2) If the peripheral speed of the support roll deviates even slightly from the conveyance speed of the web, the gelled coating layer will be greatly disturbed.

In addition, the technology described in Japanese Patent Publication No. 49-17853,
■As the width of the web increases, the difference in density in the direction along the center of the web increases, making it impossible to press the tip of the coating machine evenly against the web, making it difficult to obtain a uniform coating layer over the entire surface of the web.

■ No consideration has been taken to suppress vibrations of the web before and after the coating machine, which tends to cause uneven coating.

(2) Since the method involves pressing the coating machine, there is a drawback that bead coating methods such as slide hoppers, which are generally used for coating photographic materials, cannot be applied.

For this reason, the present inventors installed a coater and a gas ejector at positions substantially facing each other across the continuously running web, and ejected gas from the gas ejector toward the web. proposed and put into practical use a coating method and an apparatus for coating the web using the coater while floating and supporting the web (Japanese Patent Application No. 175801/1983).
).

[Problem to be solved by the invention]

However, in the above-described conventional web coating device, as shown in FIG. This is because the high static pressure air interposed between the web 3 and the web holding surface 11a may cause contact with the boundary area 11c.
This is because the web is opened to the outside air and the pressure suddenly decreases, making it impossible to float and support the web. In order to prevent this phenomenon, it is possible to increase the amount of gas ejected from the web-closing surface or to supply gas to the boundary area from the non-web-closing surface side, but either method will completely prevent contact accidents. There is a problem in that it cannot be prevented and the running web becomes unstable.

In view of the above points, it is an object of the present invention to provide a web coating device in which there is no fear that the flying height of the web will decrease even in the boundary area.

[Means to solve the problem]

In order to achieve the above object, the present invention disposes a coater and a gas ejector at positions substantially facing each other across a continuously running web, and ejects gas from the web-closing surface of the gas ejector. In the web coating device that performs coating while floating and supporting the web, the amount of gas ejected in a boundary area between the web holding surface and the non-web holding surface is larger than the amount of gas ejected in other areas of the web holding surface. However, it is possible to prevent sudden decompression from occurring in the boundary area.

〔Example〕

The present invention will be described below based on embodiments shown in the accompanying drawings.

Fig. 1 is a longitudinal sectional view showing the overall configuration of the web coating device of the present invention, Fig. 2 is a sectional view of the gas ejector and the vicinity of the second coater, and Fig. 3 is a gas ejector configured using a porous body. It is an explanatory diagram of an example.

In the figure, 1 is the first coater, 2 is the second coater,
The first and second coaters 1.2 are connected to the introduction section D of the web 3.
1 and the deriving section D2 in this order.

The coater 1.2 is provided with outlet slits la, lb and 2a, 2b, respectively, the outlet slits la, lb and 2
The coating liquid gushing out from a and 2b enables two-layer coating. That is, the first coater 1 applies the coating liquid to the front surface 3a of the web 3 near the introduction section, and the second coater 2 applies the coating liquid to the back surface 3b of the web 3 near the exit section D2, thereby coating both sides of the web 3. It is structured so that it can be achieved.

The web 3 is supported in contact with the auxiliary roller 4 and carried into the introduction section, and then is supported in contact with the main roller 5 and goes around, and when passing near the first coater 1, the web 3 is transferred to the introduction section.
It is applied to the surface 3a and transported to the cold air zone 6.

Reference numeral 7.8 denotes a vacuum chamber, and the vacuum chamber 7.8 appropriately sucks the bead (coating liquid from the coater in a cross-linked state onto the web surface) consisting of the coating liquid from each coater 1.2, and converts the coating liquid into the coating liquid. This is to stabilize the transfer of water to the web surface. Among the decompression chambers 78, one chamber 7 is provided below the bead gap B+ of the first coater 1, and the other chamber 8 is provided below the bead gap Bz of the second coater 2.

The cold air zone 6 is for cooling the coating liquid applied to the surface 3a of the web 3 to promote gelation, and supports the back surface 3b (uncoated surface) of the web 3 while cooling it. Conveyance roller group 9 to be conveyed and surface 3a of web 3
It is equipped with a group of small holes (or) slits 10 that cool the (already coated surface) by applying cold air to it. The temperature in this cold air zone 6 depends on coating conditions (temperature of coating solution, coating thickness, coating speed, etc.) and web running conditions (web temperature, web thickness, web running speed, etc.), but usually, The temperature of the web 3 when it leaves the cold air zone 6 and is conveyed to the second coater 2 is 10
It is adjusted to be around °C.

1 is a gas ejector, and the gas ejector 11 floats and supports the web 3 to protect its front surface 3a (already coated surface), then wraps the web 3 in the vicinity of the second coater 2 and sprays the back surface 3b (
This is for applying the coating liquid to the uncoated surface. That is, the web holding surface 11a of the outer shell of the gas ejector 11 is provided with a large number of fine gas ejection holes F, and the gas in the gas ejector 11 is ejected toward the surface 3a of the web 3, and the coater 2
The web 3 can be floated and conveyed while being coated.

Here, the amount of gas ejected (per unit area) in the boundary areas 11c and llc between the web-holding surface 11a and the non-web-holding surface 11b is larger than the amount of gas ejected (per unit area) from the web-holding surface 11a.

That is, a sufficient amount of gas to replenish the air flowing out from the web-holding surface 11a to the non-web-holding surface 11b side is supplied to the boundary region 11c, thereby preventing a decrease in the flying height of the web 3. ing.

Various means can be considered to increase the amount of gas ejected from this boundary region 11c, such as increasing the number of micro gas ejection holes F or increasing the diameter of the micro gas ejection holes F, as shown in the second figure. , it is practical to increase the porosity.

In addition, it is of course possible to make the ejection pressure in the boundary region 11c larger than in other regions while keeping the pore size constant.

The amount of ejection from this boundary area 11c depends on the web running conditions (web thickness, web running speed, distance between the web and web holding surface, etc.) and coating conditions (coating film thickness, coating liquid viscosity, etc.) However, it is desirable that the amount of ejection per unit area be at least 20 times the ejection amount of the web holding surface 11a.

What is important here is that the amount of gas ejected is closely related to the vibration of the web, and if the vibration of the web is not sufficiently suppressed, the thickness of the coating layer on the back side 3b of the web will become uneven. It is.

Therefore, an important point in this invention is to balance the ejection amount between the web holding surface 11a and the boundary area 11c while considering the suppression of web vibration.
The number double has a special meaning.

The gas used for floating support here may be any gas such as N2 gas, air, inert gas, etc. as long as it does not pose a safety problem, but air is most commonly used. The coated web coated on the opposite side in the floating support section is then exposed to cold air on both sides in a non-contact state in a cold air zone (not shown) to gel the coating layer, and then passes through the lead-out section D2 to be coated in a non-contact state. The coated web is conveyed to the drying zone, but in this non-contact gelling area or the non-contact drying zone, the coated web fluctuates (or vibrates) in the direction perpendicular to the running direction.
Even if the liquid is applied, it is absorbed by the floating support section and does not propagate, making it possible to apply it uniformly.

The web 3, which has not been coated on both sides, is conveyed into the introduction section DI while being supported in contact with the auxiliary roller 4, passes around the first coater 1 while being supported in contact with the main roller 5, and is gushed out from the gushing slits la and lb. Two layers are applied to the surface 3a using a coating liquid.

Next, the web 3 is conveyed with contact support by conveying rollers 9 while receiving cold air from the small hole group 10 in the cold air zone 6.
It is cooled down to around °C and conveyed to the gas ejector 11. The web 3 is floated and supported on the surface 3a, which is the already coated surface, by the ejected gas from the web holding surface 11 of the gas ejector 11, and wraps around the vicinity of the second coater 2, but the boundary between the web holding surface 11a and the non-web holding surface 11b Since the ejection amount of the area 11c is larger than that of the other holding surfaces, there is no risk that the web floating amount will decrease to the extent that it comes into contact with the gas ejector, both when the web 3 starts and ends its wraparound. .

Incidentally, the ejection amount ■1 of the web holding surface 11a and the boundary area 1
If the ejection amount (2) of 1c is specifically shown, good coating is possible with the ejection amount per unit area of V+ -20cc/sin·d Vz -500cc/5in-c4.

Then, the second coater 2 coats the back surface 3a,
The web 3, which has been uniformly coated on both sides, is led out from the lead-out section Dt and conveyed to a cooling/drying process, where the both-side coating process is completed.

The web to be coated used in the present invention may be a plastic film such as polyethylene terephthalate or cellulose triacetate, or a web for photosensitive materials such as paper.

There are no particular restrictions on the material that makes up the curved surface of the floating support part, and any material can be used as long as it can withstand the internal pressure of the hollow part, but it is preferable to use brass steel or stainless steel with hard chrome plating on the surface. In view of ease of processing, plastic materials such as Bakelite or acrylic resin can also be used.

In carrying out the present invention, in order to prevent the gas from colliding with the gelled coating layer in the floating support section and preventing the coating layer from being disturbed by the dynamic pressure of this gas, it is necessary to It is desirable to lower the temperature of the coating layer to about 10° C. to increase the gel strength of the coating layer.

Although the embodiments have been described above, the embodiments of the present invention are not limited thereto, and the gas ejector has a continuous curved surface as the outer surface of the non-contact support part in order to maintain high static pressure in the gap with the web. Any material may be used as long as the curved surface is capable of ejecting gas and satisfies the conditions of the present invention, and may have a roll-like external shape, or may have a through-hole through which the gas passes from the inside to the outside of the gas ejector. For example, the shape of the gas ejector may be semi-cylindrical or elliptical, or the outer surface of the floating support may be The shape may have a curvature and the rest may be flat.

On the other hand, the main role of the part that allows the gas supplied inside the gas ejector to pass outside is to allow the gas to pass through as well as to provide pressure loss, so the cross-sectional shape of the through hole may be round or polygonal. It may be a hole, or it may be a form in which the outer shell of the gas ejector of the floating support part is constituted by a porous body P made of sintered metal or the like (Fig. 3). In this case, the boundary area 1
At the portion 1c, the amount of gas ejected from that portion is increased by increasing the porosity of the porous body.

Furthermore, instead of making the gas ejector hollow, it is also possible to construct the entire structure from the gas inlet to the outer surface of the floating support part from a porous body as described above.

〔Effect of the invention〕

As described above, the present invention disposes a coater and a gas ejector at substantially opposite positions with a continuously running web in between, and ejects gas from the web-closing surface of the gas ejector to blow the web. A web coating device that performs coating while floating and supporting the web, characterized in that the amount of gas ejected in the boundary area between the web holding surface and the non-web holding surface is larger than the amount of gas ejected in other areas of the web holding surface. Therefore, it is possible to prevent sudden decompression of the gas that contributes to floating support of the web in the boundary area. Therefore, there is no fear of web contact accidents occurring in the boundary area, which is highly effective in improving productivity and maintaining quality.

[Brief explanation of the drawing]

Fig. 1 is a longitudinal sectional view showing the overall configuration of the web coating device of the present invention, Fig. 2 is a sectional view of the gas ejector and the vicinity of the second coater, and Fig. 3 is a gas ejector configured using a porous body. An explanatory diagram of an example, FIG. 4 is a cross-sectional view showing a phenomenon in which the flying height of the web decreases in the boundary region of a gas jet device of a conventional device. - First coater 2 - Second coater 3 - Web 3a - Web front side 3b - Web back side 4 - Auxiliary roller 5 - Main roller 6 - Cold air zone 7.8 - Decompression chamber 9 - Conveyance roller Group l〇-Small hole group 11-Gas ejector 11a-1-Web holding surface 1 l b-11 non-nib holding surface 11 c-Boundary area ri, -Introduction part Dt=Output part B, , B, - Bead gap L・-Coating liquid F・-Minute gas ejection hole

Claims (1)

[Claims] A coater and a gas ejector are arranged at positions substantially facing each other across a continuously running web, and coating is performed while the web is supported floatingly by ejecting gas from the web-closing surface of the gas ejector. What is claimed is: 1. A web coating apparatus, characterized in that the amount of gas ejected in a boundary area between the web-holding surface and the non-web-holding surface is larger than the amount of gas ejected in other areas of the web-holding surface.