JPS5837866B2 - Coating method and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a coating method and apparatus, and more particularly to a method and apparatus for coating a coating solution by colliding a coating liquid in the form of a thin film against a support. The present invention relates to a method and apparatus for applying the same.

Among the methods of applying a thin film of coating liquid by colliding with a support, a typical method is the curtain coating method.

The curtain coating method is a method in which a free-falling curtain made of one or more coating liquids is formed and the curtain is made to collide with the object to be coated to form a coating film on the object. However, due to the demand for improved coating quality, high-precision coating is gradually required, and in recent years, Japanese Patent Publications No. 49-24133 and No. 49-
Attempts have been made to apply the curtain coating method, as disclosed in Japanese Patent No. 35447, to fields where precision is particularly required, such as the production of photographic materials.

The method disclosed in Japanese Patent Publication Nos. 49-24133 and 49-35447 involves supplying one or more types of coating liquid between two edge guides using a slide type or extrusion type liquid injection device. This method forms a thin, free-falling curtain that is applied to a continuously running web.

The reason why the coating liquid is supplied between the two edge guides is to regulate the coating width and to stabilize the curtain film.

As described above, many improvements have been made to the curtain coating method, but there has been almost no research on edge guides. Generally, they were of a fixed type, such as the flat plate disclosed in Japanese Patent No. 57734.

However, when coating from the left using such a fixed edge guide, if the coating liquid leaves the part supported by the edge guide even a little, the coating liquid will contract. As shown in the figure, coating liquid 1
It has been found that when the coating film is applied to the surface of the web 2, the thickness of the coating film at both side edges in the width direction of the web is thicker than that at the center.

This phenomenon has been observed even when the clearance between the lower end of the edge guide and the web is reduced to almost zero.

This phenomenon occurs in addition to the general flow contraction caused by interfacial tension, etc.
When a fixed edge guide is used, an uneven distribution of the falling speed of the coating liquid applied near the edge guide inevitably occurs; in other words, the falling speed of the coating liquid near the edge guide is lower than the falling speed of the coating liquid near the center of the curtain film. Due to the phenomenon that the velocity is small (that is, the falling momentum is small), the liquid constricts without being able to break through the air layer adhering to the web, and when a certain amount of liquid has accumulated (the momentum increases), it is applied. It can be assumed that this is because of the

The phenomenon that the flow contracts when the part supported by the edge guide is even slightly removed cannot be avoided even by conventional coating methods, for example, the method disclosed in Fig. 10 of the above-mentioned Japanese Patent Publication No. 49-35447. .

The reason for this coating method is that, as shown in FIG.
A slot 3s is provided in the axial direction along the side surface in contact with the curtain membrane 1c, and an inert liquid such as a transparent gelatin solution is forced into the hollow part 3h from the top of the edge guide 3, and the liquid is passed through the slot 3h into the curtain membrane 1c. The liquid is made to ooze out in the width direction, but even when the liquid oozes out in this way, no force is applied in the downward direction of the coating liquid, so the distribution of the flowing velocity is shown by the arrows in Figure 2. This is because, compared to the central portion, the velocity distribution on the side of the bead guide 3 is still small, showing the same velocity distribution as the flat plate and thin rond mentioned above, and does not contribute to preventing the contraction of the coating liquid 1 for a long time.

It goes without saying that if the paint film applied to the web surface is locally thick, it will not only cause a quality problem, but also cause problems in the drying process of the paint film, such as uniform drying and solidification of the paint film. In extreme cases, this could be the cause of so-called wet failures.

The object of the present invention is to eliminate the above-mentioned drawbacks of conventional coating methods, and to provide a coating method that does not cause localized thick coating and can consistently provide a uniform coating thickness.

Another object of the invention is to provide an apparatus for carrying out the above method.

These objects of the present invention are achieved by supporting both ends of a thin film of coating liquid with liquid jetted in the same direction as the moving direction of the coating liquid.

Hereinafter, embodiments of the present invention will be described in detail based on the accompanying drawings.

FIG. 3 is a schematic front view of a curtain coating device showing an embodiment of the present invention, and FIG. 2 is a side view thereof.

3 and 4, the coating liquid 1 is sent to the extrusion liquid injector 4 by a pump shown in the figure, and is discharged from the slot 4B to the edge guides 3, 3 sleeves.

The edge guides 3, 3' are made of stainless steel plate with a smooth surface, and one end is in close contact with the tip of the slot 4s of the liquid injector 4.
The other end is provided at a position some distance from the upper surface of the coating roll 5, and holds the curtain film 1c of the coating liquid 1 flowing down from the slot 4s from the width direction, thereby regulating the coating width.

Below the edge guides 3 and 3' is a small inner diameter pipe 6.
, 6' are embedded in the edge guides 3, 3', respectively.

The rear ends of the pipes 6, 6' communicate with the illustrated auxiliary liquid supply tank, and the auxiliary liquid discharge holes 6h, 6h on the tip side thereof coincide with the flow direction of the curtain membrane 1c, and the center of the hole is located in the curtain membrane 1.
It is provided so as to be located approximately on the side edge of c.

The auxiliary liquid supplied to the pipes 6 and 6' varies depending on the properties of the coating liquid 1 used, but is generally a liquid that does not impair the original physical properties of the coating liquid 1, and Any liquid may be used as long as it has a surface tension that can sufficiently hold the side edges of the curtain film 1c. For example, when the coating liquid 1 is an aqueous gelatin solution, the auxiliary liquid may be a volatile aqueous solution such as a methanol aqueous solution, as described later. Experiments conducted by the present inventor have revealed that the solution is particularly effective in reducing the drying load.

Next, the operation of the curtain coating apparatus constructed as described above will be explained.

The coating liquid 1 discharged from the slot 4s of the liquid injector 4 becomes a free-falling curtain film 1c while its width direction length is regulated by the edge guides 3 and 3', and falls onto the web 2 running on the coating roll 5. Flows down onto the surface.

(In this example, the width of the web 2 is larger than the coating width.

) At this time, the auxiliary liquid is supplied to the pipes 6, 6' and is discharged in a jet form from the discharge holes 6h, 6'h.

In particular, from the viewpoint of retaining the curtain film 1c, it is theoretically preferable for the discharge amount of the auxiliary liquid to be as large as possible and as the flow rate is high.
It is also necessary to consider the drying load of the coating film, and the appropriate amount is determined by experimentally determining the balance between the two.

As described above, when coating is carried out while supporting the curtain film 1c with the auxiliary liquid jetted out along the side edges of the curtain film 1c, the thickness of the coating film becomes uneven, and Even when the flow rate was low, the curtain film 1c was unlikely to break midway, making stable coating possible.

This is because the flow rate of the coating liquid 1 flowing down along the edge guides 3, 3' is actively increased by the auxiliary liquid, so that the coating liquid 1 flows from the lower end of the edge guides 3, 3' onto the web 2. This is believed to be because the flow does not contract before reaching the surface, in other words, the flow velocity distribution of the coating liquid 1 is made uniform in the width direction.

Although the above description is based on one embodiment of the present invention, the present invention is not limited to this embodiment and can be modified as described below.

Further, for the embodiment described above, the edge guides 3, 3'
Although a stainless steel plate with a smooth surface is used as the material, the material is not necessarily limited to this, and materials such as plastics and rubber other than those having water-repellent surface properties such as polyethylene and polytetrafluoroethylene may also be used.

Further, in the embodiment described above, nine free-falling curtains are formed using an extrusion-type liquid injector, but the invention is not limited to this, and is disclosed in U.S. Pat. It is also possible to use a so-called slide type liquid injector.

Further, in the above embodiment, a curtain coating method is used, but the method is not necessarily limited to the curtain coating method, and a thin film coating liquid as disclosed in FIG. It can also be applied to a general method of coating by colliding with the web to be coated.

Moreover, the coating liquid to be supplied to the free-falling curtain is not limited to one type, and two or more types of coating liquids may be supplied in a superimposed relationship.

Although the coating liquid used in the present invention is not particularly limited, it can be particularly suitably applied to the production of photographic light-sensitive materials, magnetic recording materials, and pressure-sensitive copying paper.

When the present invention is used in the production of photographic light-sensitive materials, the manufacturing method, composition, necessary additives, material of the web, various treatments, etc. of the photographic coating solution are described in Japanese Patent Publication No. 49-14130 and Japanese Patent Publication No. 49-241.
All of the materials disclosed in No. 33 and No. 49-35447 can be used.

The photographic coating liquid here includes not only photosensitive ones such as photographic emulsions, but also all kinds of coating liquids used in the production of photographic light-sensitive materials, such as undercoat coating liquids, antihalation coating liquids, and back layer coating liquids. It will be done.

When the present invention is used to manufacture magnetic recording materials, the manufacturing method, composition, necessary additives, material of the web, various treatments, etc. of the coating liquid for magnetic recording materials are disclosed in Japanese Patent Application No. 154491/1982. Everything is available for use.

Here, as the coating liquid for magnetic recording material, magnetic coating liquid,
It includes all coating liquids used in the production of magnetic recording materials, such as coating liquids for back coats.

In addition, when the coating method according to the present invention is applied to the production of magnetic recording materials, an orientation device is provided in the thin film portion made of the coating liquid to improve the orientation and to improve the stability of the thin film, which is better than the coating liquid. Although it is necessary to set specific implementation conditions for the homomagnetic coating liquid and the magnetic recording material, all of the conditions disclosed in Japanese Patent Application No. 51-96675 can be used for this purpose.

When the present invention is used in the production of pressure-sensitive copying paper, the manufacturing method, composition, necessary additives, web material, various treatments, etc. of the coating liquid for pressure-sensitive copying paper can be found in Japanese Patent Application No. 76743/1983. Everything disclosed can be used.

The coating liquid for pressure-sensitive copying paper includes any coating liquid used in the production of pressure-sensitive copying paper, such as a coating liquid containing microcapsules as a main component and a coating liquid containing a color developer as a main component.

In addition, when applying the coating method according to the present invention to the production of pressure-sensitive copying paper, it is necessary to set specific implementation conditions for the coating liquid for pressure-sensitive copying paper, but this is described in Japanese Patent Application No. 51-76.
The material disclosed in No. 743 can be used.

Water is generally used as the auxiliary liquid in the present invention, but liquids that can satisfy both sufficient support of the curtain film and reduction of the drying load of the coating film include, for example, methanol, ethanol, etc. Alcohol aqueous solutions, lower alkyl acetates such as ethyl acetate, butyl acetate, ethyl propionate, secondary butyl alcohol, methyl isobutyl ketone, β-ethoxyethyl acetate, methyl cellosolve acetate, etc. have a boiling point of approximately 30°C. Preferably, the solution is a volatile solution such as a low boiling point organic solvent of ~150°C.

As mentioned above, such an auxiliary liquid should not impair the physical properties of the coating liquid used, that is, the quality of the coating film, and therefore, it should be used as appropriate depending on the type of coating liquid. It is selected.

Examples and comparative examples are given below in order to make the effects of the present invention even clearer.

Example 1 A coating solution having the composition and physical properties shown in Table 1 was coated with an extrusion type curtain coating device as shown in FIG.
Thickness 180μ, width 1 being conveyed at a speed of 60m/min
8k on 8cm polyethylene terephthalate film
/rr? (in wet condition).

Here, the curtain height is 15cm, the application width is 15cm,
An edge guide made of stainless steel plate has an inner diameter of 0.0 mm at a position approximately 10 mm measured vertically from the lower end. 2 rra
n, a liquid injection pipe with an outer diameter of 1 m++ is bent as shown in the diagram,
Water was pumped through this pipe as an auxiliary liquid at a flow rate of 15 a/min.

When we observed the support part of the curtain film during the coating operation, we found that there was no contraction of the coating liquid even in the part away from the edge guide, and after the coating film applied to the film was sufficiently gelled with cold air, we applied the usual method. After drying, the thickness was measured using a thickness meter, and as a result, local thick coating was substantially observed and remained long.

In this example, the distance d between the lower end of the edge guide and the web was varied in the range of 1 to 5 WrL, but no contraction was observed and no substantial difference was observed.

Example 2 Same as Example 1, except that the auxiliary liquid was 5 methanol instead of water.
When a 0% aqueous solution was used, the same results as in Example 1 were obtained, and when gelling and drying was performed in the same manner as in Example 1, the time required to dry the coating film was longer than that in the case of water. It was confirmed that the time was reduced by about 15% on average.

Comparative Example When the auxiliary liquid pipe was removed by pressing the button in Example 1 and the auxiliary liquid supply was removed, the coating liquid contracted at the lower end of the edge guide and spread in a predetermined range of about 5 m inward from the side edge of the coating width. Local thick coating occurred continuously, with an average thickness of 1.5 times (maximum 1.8 times) the coating thickness.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a coating film obtained by a conventional coating method, Fig. 2 is an explanatory diagram of the operation of the conventional coating method, Fig. 3 is a schematic front view of a curtain coating device showing an embodiment of the present invention, and Fig. 4 is a cross-sectional view of a coating film obtained by a conventional coating method. It is a schematic side view. 1: Coating liquid, 1c: Curtain film, 2: Web, 3, 3'
: Edge guide, 4: Liquid injector, 5: Application roll, 6, 6
': Liquid injection pipe.

Claims (1)

[Scope of Claims] 1. A method of coating at least one coating liquid in the form of a thin film by colliding with a support to be coated, wherein both ends of the coating liquid in the form of a thin film are jetted in the same direction as the outflow direction of the coating liquid. A coating method characterized by supporting with a liquid discharged in a shape. 2. The coating method according to claim 1, wherein the liquid discharged in a jet form has volatility. 3. Press a button on the device that applies at least one type of coating liquid in the form of a thin film by colliding with the support to be coated, and apply the coating liquid to the outflow side end of the edge guide that supports both ends of the coating liquid in the form of a thin film. 1. A coating device comprising a liquid injection means that has a liquid injection hole in the same direction as a liquid outflow direction and discharges liquid in a jet form.