JP2001046939A - Coating device and coating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of coating defect by using a plate glass as an edge guide liquid contact surface to stabilize a curtain film. SOLUTION: A liquid contact part material of an edge guide 6 is made of the plate glass 3. The curtain film 7 falls down along the surface of the plate glass 3 attached to the edge guide 6. An assistant liquid film 10 is preferably formed on the surface of the plate glass 3 and the curtain film 7 falls down along the assistant liquid film 10. The plate glass 3 consists essentially of raw materials such as silica sand, soda lime and is formed by a float method or the like to have uniform thickness. The surface of the plate glass 3 is preferably surface roughened. As the method for surface roughening the surface of the plate glass 3, the sand blast method is used to form frosted plate glass like. The surface roughness of the plate glass 3 is preferably >=0.5 μm, more preferably 1.0-1.5 μm. As the result, viscosity resistance generated to the curtain film 7 is remarkably reduced and film forming property is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the production of a silver halide photographic material, a magnetic recording material, a pressure- and heat-sensitive recording paper, an art paper, a coated paper, and an ink jet recording sheet, and relates to a belt-shaped support which runs continuously. The present invention relates to a method and an apparatus for applying a liquid thin film (hereinafter, referred to as a curtain film) to a web (hereinafter, referred to as a web).

[0002]

2. Description of the Related Art As a multi-layer simultaneous coating method, a slide bead method or an extrusion method is generally known, but in recent years, a curtain coating method has been frequently used in accordance with a demand for high-speed coating. The curtain coating method is a method in which a curtain film is freely dropped and applied onto a continuously running web, and is disclosed as a basic technique in Japanese Patent Publication Nos. 49-24133 and 49-35447.

[0003] When a curtain coating apparatus is applied on a web, the instability of a curtain film that falls freely has a great effect on product quality. Typical phenomena that hinder the stability of the curtain film include a phenomenon behind the curtain film (hereinafter referred to as a teapot phenomenon) and a phenomenon of thinning the curtain film near the edge guide wall. These phenomena are described by SFKistler and Schweizer,
1997, LIQUID FILM COATING ”.

[0004] The teapot phenomenon is a phenomenon in which the curtain film does not fall vertically and tries to go around the rear of the lip, and is due to an imbalance in the momentum at the lip tip of the coating solution flowing down the slide surface. The teapot phenomenon is remarkable when the viscosity of the coating solution is decreased or the coating amount is increased, that is, when the Reynolds number of the coating solution is relatively large. Since both ends of the curtain film are fixed by edge guides, free deformation of the curtain film due to the teapot phenomenon cannot be allowed, and distortion occurs in the curtain film. As a result, the coating amount in the curtain film width direction becomes non-uniform, and good coating surface quality cannot be obtained.

As a method for suppressing such a teapot phenomenon, for example, a coating method characterized by increasing the viscosity of a coating liquid in the lowermost layer to 40 cP or more in order to reduce the momentum of the coating liquid on the slide surface is disclosed in Japanese Patent Application Laid-Open No. HEI 9-163568. 1-1131549
JP-A-1-38166 and JP-T-6-509505 disclose an apparatus for optimizing the shape of a lip to straighten a wetting line and stabilize a curtain film.

Although the teapot phenomenon can be effectively suppressed by these disclosed methods, there is a problem that a large viscous resistance acts on the edge guide wall due to an increase in the viscosity of the coating solution, so that the flow is easily generated. are doing. Further, even if the shape of the lip is optimized, it has not been a sufficient measure against various kinds of coating liquid physical properties and flow rates.

On the other hand, a method has been disclosed in which the shape of the edge guide is devised to reduce curtain film distortion caused by the teapot phenomenon. For example, JP-A-51-
Japanese Patent No. 57734 discloses a coating apparatus using a flat plate type edge guide. Although the curtain film distortion due to the teapot phenomenon is effectively suppressed by the disclosed method, some problems have been pointed out.

First, there is a problem of viscous resistance generated when the curtain film contacts the edge guide wall. Due to the action of the viscous resistance, an uneven distribution of the curtain film falling velocity is recognized near the edge guide wall, and a thinned portion is generated near the edge guide wall. The thinning phenomenon is considered to be caused by the Marangoni effect, and is described in detail in JP-B-60-14624.

The phenomenon of thinning causes fatal coating defects in the field of photographic light-sensitive materials that require precise coating, and significantly lowers the product yield. In particular, in recent years, high viscosity by coating solution concentration for the purpose of high-speed coating and reduction of drying load tends to further increase the viscous resistance, and the phenomenon of thinning further proceeds. Since the progress of the thinning phenomenon promotes the contraction, the curtain film comes off the edge guide,
Eventually, the curtain film may be destroyed.

Various methods and apparatuses have been disclosed to prevent the thinning phenomenon. For example, Japanese Patent Publication No. 49-35447
JP, JP-A-61-75876, JP-A-1-1-1
No. 99668, Japanese Patent Publication No. 5-70507, No. 6
No. 61517 describes a method of supplying a low-viscosity auxiliary liquid along an edge guide. According to the method of the present disclosure, even with a high-viscosity coating liquid, the viscous resistance at the edge guide wall can be greatly reduced, so that a stable curtain film can be obtained with a low coating amount without a thinning phenomenon.

Second, a flat plate type edge guide is disclosed in
There is a problem that agglomerates such as a coating solution are more likely to be deposited on the edge guide wall than the rod type described in Japanese Patent No. 24133. The flow of the curtain film near the edge guide wall is disturbed by the accumulation of the aggregates, so that the contraction is likely to occur.

Recently, an edge guide curved in accordance with the shape of a curtain film has been disclosed in Japanese Patent Application Laid-Open No. 9-253552. According to the disclosed method, although the curtain film distortion due to the teapot phenomenon is eliminated, the degree of deformation of the curtain film due to the teapot phenomenon greatly varies depending on operating conditions such as coating liquid physical properties and flow rates, so that the edge guide needs to be changed for each condition change. It is necessary to change the shape, it is necessary to accurately predict the shape of the curtain film in order to optimize the shape of the edge guide, and a known auxiliary liquid is supplied to the edge guide to avoid the phenomenon of thinning In this case, the flow state of the curtain film at the curved portion of the edge guide tends to be disturbed, and is not practically sufficient.

On the other hand, as a material of an edge guide used in a conventional curtain coating apparatus, Japanese Patent Laid-Open No. 4-94761 is used.
And Japanese Patent Publication No. 4-46629, metals such as stainless steel and aluminum are common, and other materials such as plastics such as polyethylene and polytetrafluoroethylene and rubbers are also known. .

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and has as its object to reduce curtain film distortion due to a teapot phenomenon which is a phenomenon peculiar to a curtain coating method. An object of the present invention is to provide a coating apparatus and a coating method for stabilizing a curtain film by simultaneously avoiding a phenomenon of thinning, thereby preventing generation of coating defects. Another object of the present invention is to provide a coating apparatus and a coating method capable of preventing the aggregates from adhering to the edge guide liquid contact surface and stably and uniformly forming the auxiliary liquid film on the edge guide liquid contact surface. To provide.

[0015]

The above object is achieved by the following coating apparatus and coating method. (1) In a curtain coating apparatus in which at least one or more coating liquids are supported on both sides by an edge guide to form a free-falling coating liquid film of the coating liquid and coat the coating on a support, the edge guide contacting surface is preferably A curtain coating apparatus, which is a sheet glass. (2) The curtain coating device according to (1), wherein the surface of the plate glass is roughened. (3) The curtain coating device according to (1) or (2), wherein the surface roughness of the plate glass is 0.5 μm or more. (4) In the coating apparatus of (1) to (3), a uniform thin auxiliary liquid film is formed on the surface of the plate glass, and both ends of the free-falling coating liquid film are supported by the auxiliary liquid film. Curtain coating method.

The above-mentioned prior art does not disclose a comprehensive and specific coating technique for stabilizing a curtain film by simultaneously avoiding a curtain film distortion and a thinning phenomenon due to a teapot phenomenon. Therefore,
As a result of the inventor's intensive experiments, as a method of simultaneously avoiding the curtain film distortion and the thinning phenomenon due to the teapot phenomenon and stabilizing the curtain film, it is enough to allow the free deformation of the curtain film due to the teapot phenomenon. That the edge guide width is required, that the flat glass is suitable for improving the wettability of the edge guide liquid contact portion in order to solve the problems of the flat edge guide and to avoid the thinning phenomenon, It has been found that the wettability is remarkably improved by roughening the surface, and that the curtain film is further stabilized by forming a uniform water film on the surface of the plate glass.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
FIG. 1 shows a perspective view of a curtain coating apparatus. As described in JP-B-49-24133, curtain coating is performed by uniformly supplying a coating liquid from a slit 5 to form a coating liquid 8 in a thin layer state on a slide surface 4 and a pair of edge guides. The coating film 6 is dropped freely from the lip tip 1 along the web 6 as a curtain film 7 and collides with the continuously running web 2 to perform coating.

In the present invention, the curtain film 7 is dropped along the surface of the glass sheet 3 attached to the edge guide 6.
As another preferred embodiment of the present invention, as shown in FIG. 2, an auxiliary liquid film 10 can be formed on the surface of the glass sheet 3 and the curtain film 7 can be dropped along the auxiliary liquid film 10.

As described above, conventionally, the material of the edge guide 6 is disclosed in Japanese Patent Application Laid-Open No. Hei 4-94761 and Japanese Patent Publication No. 4-4662.
As described in Japanese Patent Publication No. 9 (KOKAI), metals such as stainless steel and aluminum are generally used.
Materials such as plastic and rubber such as polytetrafluoroethylene have also been known. The liquid contact member of the edge guide 6 is made of the glass sheet 3 to improve the wettability of the liquid contact portion, and the auxiliary liquid film 10 is stably and uniformly formed on the surface of the glass sheet 3 to form a contact with the curtain film 7. It has been clarified by experiments by the present inventors that the viscous resistance generated between them is drastically reduced and the film forming property is remarkably improved. In particular, it has become clear that roughening the surface of the plate glass 3 is extremely effective in stably and uniformly forming the auxiliary liquid film 10 which is a preferred embodiment of the present invention.

In the present invention, the auxiliary liquid film 10 is a liquid film formed by flowing an auxiliary liquid onto the glass sheet 3 attached to the edge guide 6 so as to cover the entire surface of the glass sheet with a uniform thickness. In order to allow the auxiliary liquid to flow to the surface of the plate glass 3 with a uniform thickness, for example, as shown in FIG. 2, the clearance of the auxiliary liquid supply channel 11 is set to 100 μm or more and 800 μm or more.
The following is preferable, and more preferably 300 μm
The range is at least 500 μm.

The thickness of the auxiliary liquid film 10 is preferably 1
It is not less than 00 μm and not more than 1000 μm, and more preferably in the range of 200 μm to 500 μm.

As a method of forming the auxiliary liquid film 10, for example, the auxiliary liquid is supplied to the manifold 12 of the edge guide 6 by a liquid feed pump not shown in FIG. Auxiliary liquid supply flow path 1 connected to manifold 12
The auxiliary liquid flows out of the substrate 1 and an auxiliary liquid film 10 having a uniform thickness is formed on the plate glass 3 attached to the edge guide 6.

The preferred range of the flow rate of the auxiliary liquid is 0.1.
2 ml / sec / cm or more and 1.5 ml / sec / cm or less, more preferably 0.5 ml / sec / cm or more.
It is within the range of 1.0 ml / sec / cm.

In the present invention, the temperature of the auxiliary liquid is not particularly limited, but when the coating liquid is an aqueous gelatin solution, the temperature of the auxiliary liquid should be higher than the temperature of the coating liquid in order to prevent sticking. preferable. A more preferable temperature range of the auxiliary liquid is 40 ° C. or more and 70 ° C. or less.

As the auxiliary liquid used in the present invention, water is generally used, but it is not limited thereto, and a volatile solvent for the purpose of reducing the drying load, for example, Japanese Patent Application Laid-Open No.
An aqueous alcohol solution such as methanol or ethanol described in 1997668 can also be used.

The plate glass 3 in the present invention is mainly composed of generally known raw materials such as silica sand, soda ash and lime,
It is formed into a uniform thickness by a known float method or the like, and is standardized in JIS-R3202. It is commercially available under the trade name of float plate glass.

In the present invention, the surface of the plate glass 3 is preferably roughened in order to improve the wettability with the curtain film or to make the auxiliary liquid film 10 have a uniform thickness.

As a method of roughening the surface of the sheet glass 3, for example, a method of blowing abrasive sand onto the surface of the sheet glass at a high speed by an air pressure of a compressor or the like to collide with the surface of the sheet glass, that is, a so-called sand blast method, can be formed into a sheet glass form. By adjusting the particle diameter and the blowing pressure of the polishing sand, it is possible to appropriately change the roughness of the surface of the sheet glass.

In the present invention, the surface roughness of the plate glass 3 is preferably 0.5 μm or more. More preferably, it is in the range of 1.0 to 1.5 μm.

In the present invention, surface roughness refers to JIS-B
0601 means the center line average roughness Ra, and a surface roughness profile measuring instrument (Surfcom 500B) manufactured by Tokyo Seimitsu was used as a measuring device.

The sheet glass width W needs to be large enough to allow the amount of deformation of the curtain film due to the teapot phenomenon. From the experimental results of the present inventors, when the position of the lip tip 1 is set at a half position of the sheet glass width W, the sheet glass width W is preferably 5 mm or more, more preferably 15 mm or more and 30 mm or less. .

In the present invention, the thickness of the sheet glass 3 is not particularly limited, but is preferably 1 mm or more in terms of strength.

The material of the edge guide body 6 in the present invention is preferably made of stainless steel from the viewpoints of corrosion resistance, processing accuracy and strength, but is not limited to this. For example, plastic, rubber, etc. are used as appropriate. be able to.

In the present invention, although not an essential device,
When the drying load is increased due to the thick coating on both edges of the coated material, Japanese Utility Model Application Laid-Open No. Sho 61-15069, JP-A-56-73579,
JP-B 5-70507, JP-A-6-233954,
The apparatus and method disclosed in JP-A-7-299410 can be appropriately used in combination.

[0035]

EXAMPLES Example 1 Coating was performed by the curtain coating apparatus shown in FIG. 1 under the following conditions. Web: 140 μm thick polyethylene resin coated paper Curtain film width: 1000 mm Curtain height: 100 mm Coating speed: 200 m / min

Coating solution: Temperature setting: 40 ° C., 8 wt% aqueous gelatin solution adjusted to 40 cP with a thickener Layer composition: 3 layers Coating amount of all layers Moisture: 90 ml / m ² (BM type manufactured by TOKIMEC).

The following edge guide was prepared. Edge guide A1: Rod type (stainless steel, diameter 2 mm) described in JP-B-49-24133. Edge guide A2: Flat type (stainless steel, plate width 20 mm, surface roughness 0) described in JP-A-51-57734. .1 μm or less) Edge guide B1: Plate type edge guide with sheet glass attached to liquid contact surface (sheet glass width: 20 mm, surface roughness: 0.01 μm) Edge guide B2: sheet glass surface of B1 roughened (sheet glass width) 20 mm, surface roughness 1.5 μm)

Using the various edge guides described above, the state of formation of the curtain film during coating was evaluated according to the following criteria. Table 1 shows the results. Evaluation criteria for curtain film distortion due to teapot phenomenon ：: No film distortion was observed. Δ: Weak film distortion was observed. ×: Strong film distortion was observed, and a streak-like coating defect occurred in the coated product.

Evaluation criteria for thinning phenomenon of curtain film ：: No thinning phenomenon was observed at all. Δ: A local thinning phenomenon was observed at the lower end of the edge guide. X: A large-scale thinning phenomenon was observed in a wide range near the edge guide.

The following evaluation shows the result of visual observation of the edge guide liquid contact surface after continuous 50 hours of application. Criteria for evaluating the state of adhesion of aggregates on the liquid contact surface of the edge guide ：: No adhesion of aggregates was observed. Δ: Agglomeration was locally observed. ×: Adhesion of aggregates was observed on the entire surface of the liquid contact portion.

[0041]

[Table 1] ────────────────────────────── Edge guide Film distortion Film thinning Aggregate adhesion status Remarks ──── Ａ A1 × △ △ Comparative example A2 ○ × × Comparative example B1 ○ △ ○ The present invention B2 ○ ○ ○ The present invention ──────────────────────────────

Example 2 Using the edge guides A2 and B2 of Example 1, an auxiliary liquid film (hot water of 50 ° C., 0.5 ml / s) was applied to the surface of the edge guides.
at a flow rate of ec / cm). A3 having the auxiliary liquid film formed on the edge guide A2 was designated as A3, and B3 having the auxiliary liquid film formed on the edge guide B2. The coating was performed under the same conditions as in Example 1 except for the type of the edge guide and the coating time. The following evaluation shows the result of visually observing the liquid contact surface of the edge guide after continuous 200 hours of application. Auxiliary liquid film formation status evaluation criteria ：: Auxiliary liquid film was uniformly formed on the entire surface of the liquid contact portion. Δ: Local destruction was observed in the auxiliary liquid film. X: The auxiliary liquid film was completely destroyed. Criteria for evaluating the state of adhesion of aggregates on the liquid contact surface of the edge guide ：: No adhesion of aggregates was observed. Δ: Agglomeration was locally observed. ×: Adhesion of aggregates was observed on the entire surface of the liquid contact portion.

[0043]

[Table 2] エ ッ ジ Edge guide Auxiliary liquid film formation status Aggregate adhesion status Remarks ─ ─────────────────────────────── A3 △ △ Comparative example B3 ○ ○ The present invention ───────── ───────────────────────

[0044]

According to the present invention, in a method of applying at least one kind of coating liquid by a curtain coating apparatus, a curtain film is stabilized by simultaneously avoiding a curtain film distortion and a thinning phenomenon due to a teapot phenomenon, and thereby coating defects are prevented. It was possible to provide a coating method and a coating apparatus for preventing generation.

[Brief description of the drawings]

FIG. 1 is a perspective view of a curtain coating apparatus according to one embodiment of the present invention.

FIG. 2 is a side sectional view of an edge guide according to an embodiment of the present invention.

[Explanation of symbols]

 2 Web 3 Sheet glass 4 Sliding surface 5 Slit 6 Edge guide body 7 Curtain film 10 Auxiliary liquid film W Sheet glass width

Claims (4)

[Claims] 1. A curtain coating apparatus in which at least one or more coating liquids are supported on both sides by an edge guide to form a free-falling coating liquid film of the coating liquid and apply the coating liquid on a support, A curtain coating apparatus characterized in that the surface is a sheet glass. 2. The curtain coating apparatus according to claim 1, wherein the surface of the plate glass is roughened. 3. The curtain coating apparatus according to claim 1, wherein the surface roughness of the plate glass is 0.5 μm or more. 4. A uniform thin auxiliary liquid film is formed on the surface of the plate glass using the coating apparatus according to claim 1, and both ends of the free-falling coating liquid film are supported by the auxiliary liquid film. A curtain coating method.