JPH03193160A - Method for continuously forming thin layer coating film - Google Patents

Abstract

PURPOSE:To form an extremely thin layer coating film having uniform thickness on a continuously running support by preliminarily applying a solvent to the continuously running support and electrostatically applying a coating solution having a film forming composition dissolved or dispersed therein to the support before the solvent is dried. CONSTITUTION:A solvent 8 is preliminarily applied to a continuously running support 3 by a roll coater composed of a coating roller 4 and a coating solution having a film forming composition dissolved or dispersed therein is electrostaticaly applied to the support 3 by a rotary atomizing spray head 1 before the solvent is dried. As a result, an extremely thin layer coating film having uniform thickness can be formed to the continuously running support.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of atomizing a water-based or organic solvent-based coating solution to form a continuous coating film on the surface of a moving support.

[Prior Art] Atomizing a coating liquid in which a coating film-forming composition such as a resin, pigment, dye, etc. is dissolved or dispersed and depositing it on a substrate has been practiced for a long time, mainly in the coating industry.

Further, Japanese Patent Application Laid-Open No. 53-5271 proposes a method for producing a matte film in which an electrostatic charge is applied.

[Problems to be Solved by the Invention] However, in the method of directly atomizing a coating liquid in which a coating film-forming composition such as a resin, dye, pigment, etc. It has not been used much in the past because it is difficult to uniformly obtain a thin film evenly.

The reason for this difficulty is that the atomized particles are made smaller in order to form a thin film. In other words, in order to form an extremely thin film, it is necessary to make the atomized particles of the coating liquid smaller, but as the diameter of the atomized particles becomes smaller, the amount of solvent evaporated per unit volume of the coating liquid increases. , the atomized particles become concentrated and their viscosity increases. Therefore, when the atomized particles adhere to the support, they do not spread smoothly, leaving unevenness in the coating film, making it difficult to obtain a smooth film. Since the atomized particles adhering to the surface of the support hardly spread, islands of the coating material are formed on the support surface, resulting in the appearance of areas without a coating film on the support surface. Therefore, it is difficult to obtain a smooth film unless the film is considerably thick.

Furthermore, the method described in Japanese Patent Application Laid-Open No. 53-5271 is as follows.

The thin film formed by the extrusion die is simply matted (formation of a minute pattern with a predetermined height and diameter) by the action of electrostatic charges.

An object of the present invention is to provide a method for continuously forming a thin coating film that solves the problems of the prior art described above.

[Means for Solving the Problems] According to the present invention, a solvent (which may contain 1% by weight or less of additives) is applied in advance to a continuously running support,
The above objective is achieved by a method for continuously forming a thin layer coating, in which a coating liquid in which the coating film forming composition is dissolved or dispersed is electrostatically applied before the solvent dries to form a uniform thin layer coating on the support. can do.

[Preferred Embodiment] As the solvent to be pre-coated on the continuously running support, it is preferable to use the solvent of the coating liquid for electrostatic coating, and when the solvent in the coating liquid consists of multiple components, a solvent with a high surface tension among them is used. It is more preferable to select the components. This is because if the surface tension of the solvent applied to the support in advance is lower than the surface tension of the coating liquid applied electrostatically thereafter, the coating liquid will not easily wet and spread.

Examples of the solvent include organic solvents, water, and the like. When the coating solution is electrostatically applied to the support, the solvent may be added in a small amount (1% by weight or less) to the extent that the increase in viscosity due to the addition of additives does not hinder smooth application of the coating solution to the support. It can contain things. These additives include, for example, substances such as surfactants that promote smooth application of the coating solution to the support, and various additives that are desired to be added in terms of quality.

Solvents or solvents containing 1% by weight or less of additives.

The atomized droplets are applied to the continuously running support at least to the extent that the atomized droplets can spread smoothly when attached to the support.

Various methods can be used to pre-coat the solvent or solvent containing up to 1% by weight of additives onto the support. For example, a method using a row coater as shown in Fig. 1, a method using a bar coater, a method using atomization which is the same as the means for applying a coating liquid such as a photosensitive liquid described later, a method using atomization using ultrasonic waves, etc. be. Although the roll coater varies depending on the speed as shown in FIG. 1, a roll coater having three reverse roll coaters, a gravure coater, and the like is used. Forward and reverse direct or offset gravure coaters can be used as well. A bar coater can apply the coating using the method shown in Japanese Patent Publication No. 58-4589.

As a method for electrostatically applying a coating liquid in which a coating film-forming composition is dissolved or dispersed, a conventionally known electrostatic airless spray method, single rotation atomization type electrostatic coating method, etc. can be used. When electrostatically applying a coating liquid in which a coating film-forming composition is dissolved or dispersed, the coating liquid is atomized into droplets.

Two different types of rotary atomization electrostatic coating methods are known.9 For example, a solution such as a resin is applied to the rear inner peripheral surface of a cup-shaped spray head that rotates at 5,000 to 50,000 per minute.
The solution in the spray head is continuously supplied at a rate of ~2000 cc/min, and the solution in the spray head is formed into a thin film on the inner circumferential surface by the centrifugal force caused by the rotation of the spray head. 30 to -140kV from the tip along with its centrifugal force
A fine liquid is emitted and atomized by the electrostatic action of the tip to which a voltage of The droplets can be ejected and deposited on the surface of the support.

[Example] (Example 1) Coating liquid A: A solution having the following composition and a viscosity of 2 cp Cresol formaldehyde resin 5 parts by weight Oil Blue #603 (manufactured by Orient Chemical Industry ■) 0.05 parts by weight Methyl ethyl ketone 14 parts by weight 2-methoxy Ethyl acetate 35 parts by weight Solvent B: 2-methoxyethyl acetate liquid Examples of the present invention will be explained with reference to FIG. It was rewound from the sending section 2. An aluminum foil support 3 with a thickness of 100 μm and a width of 300 mm was moved at a speed of 50 m/min.
The solvent B (pre-coating liquid 8) was coated in an amount of 2 by a roll coater consisting of a coating roller 4, etc.
cc / ni' to form a support 9 coated with the pre-coating solution, and before the coating film of solvent B dries, a rotary atomization electrostatic coating method using a rotary atomization spray head 1 is carried out. The coating liquid A was spray-coated at a voltage of -70 kV while feeding the liquid at 1.0,000 revolutions per minute at a rate of 100 cc/min to obtain a support 10 coated with the coating liquid. The droplet diameter is approximately 21
A uniform film surface with a thickness of 0.5 μm was obtained after coating and drying.

(Comparative Example 1) Using only the same coating liquid A as in Example 1 and using the same coating method,
Coating was carried out under the same coating conditions, ie, by a two-rotation atomization electrostatic coating method, at 10,000 revolutions per minute, at a voltage of -70 kV, and at the same liquid delivery rate. The surface of the coating after application was highly uneven, and there were some areas where the coating was not present.

(Example 2) Coating liquid C: A solution having the following composition and a viscosity of 10 ep Acrylic acid copolymer 5 parts by weight Oil Blue #603 (manufactured by Orient Kagaku Kogyo ■) 0.05 parts by weight Methyl glycol 100 parts by weight Methanol
20 parts by weight Solvent D = Methyl glycol Using the apparatus shown in Figure 1, thickness 100 μm 1 width 300 mm
Using an aluminum foil as a support, it was run at a speed of 50 m/min, and a coating amount of 3 c of solvent was applied using a roll coater.
c/rrf', and before the solvent coating film dries, the liquid was pumped at 120 cc/min at 15,000 revolutions per minute using the rotary atomization electrostatic coating method, until the coating film was -80 cc/rrf'.
Coating liquid C was applied by spraying at a voltage of kV. The droplet diameter is approximately 7
A uniform film surface with a thickness of 0.26 μm was obtained after coating and drying.

(Comparative Example 2) Only the same coating liquid C as in Example 2 was applied under exactly the same conditions as in Example 2. After application, the coating surface has large irregularities,
There were also some areas where there was no paint film.

(Example 3) Coating liquid E: solution acrylic acid latex with the following composition and viscosity of 2 cp 5 parts by weight aqueous dye
0.05 parts by weight surfactant
0.1 parts by weight water 90
Parts by weight Solution F: 100 parts by weight Water (solvent) 0.05 parts by weight Surfactant (additive) 0.05 parts by weight Using the apparatus shown in FIG. After running at high speed and applying solution F (an aqueous solution containing a surfactant as an additive) in advance to a coating amount of 2 cc/rrt using a roll coater, a rotary atomizing electrostatic machine was applied before solution F was dry. 110 at 12,000 revolutions per minute depending on the coating method.
Coating liquid E was fed at a rate of cc/min and applied at a voltage of -80 kV.
was applied by spraying. The droplet diameter was approximately 6 μm, and a uniform film surface with a thickness of 0.32 μm was obtained after coating and drying.

(Comparative Example 3) The same coating solution E as in Example 3 was applied under exactly the same conditions as in Example 3 without applying solution F in advance.

After application, the surface of the coating was very uneven and there were some areas where there was no coating.

(Example 4) This will be explained with reference to FIG. Solution F shown in Example 3 was
A rotating atomizing spray head 14 is placed on an aluminum foil support ■6 placed on a 50 cm square pedestal (support plate 15).
Atomization was carried out for 1 second at 8,000 revolutions per minute and a voltage of -80 kV using a rotary atomization electrostatic coating method using a rotary atomizer. Thereafter, the coating solution E shown in Example 3 was quickly applied using the rotary atomization electrostatic coating method using the rotary atomization spray head 17 at 12,000 revolutions per minute and a voltage of -80 kV. , spray coating was performed for 1 second to obtain a support 19 coated with the coating solution. The droplet diameter was approximately 6 μm, and a uniform film surface with a thickness of 0.51 μm was obtained after coating and drying.

(Comparative Example 4) The same coating liquid E as in Example 4 was applied under exactly the same conditions without applying solution F in advance. The surface of the coating after application was highly uneven, and there were some areas where the coating was not present.

0 In Examples 1 to 4, smoothness (thickness difference) 0.01 to
While it was 0.1 μm, in Comparative Examples 1 to 4, the thickness difference was 0.5 μm or more, and the minimum film thickness was about 2 μl.

In Examples 1 to 3, the apparatus shown in FIG. 2, 3, or 5 may be used instead of the apparatus shown in FIG. 1 to form a thin coating film of uniform thickness. .

FIG. 2 shows a support 9 coated with a coating liquid (solvent) before running.
2 shows that the coating liquid is electrostatically applied using an airless spray nozzle 12 to form a support 10 coated with the coating liquid.

FIG. 3 shows that the pre-coating liquid (solvent) is electrostatically applied to the support 3 unwound from the delivery section 2 by the rotary atomizing spray head 13.
A support 9 coated with a pre-coating solution (solvent) is electrostatically coated with a coating solution using a nine-rotation atomizing spray head 1 to form a support 10 coated with a coating solution.

In FIG. 5, a pre-coating liquid (solvent, etc.) 23 is applied to a support 24 using a coating roller 20, this support 1 is moved by a conveyor belt 25, and an airless spray nozzle 26 is used to apply the coating liquid to the support. Indicates electrostatic application.

[Effects of the Invention] The method for continuously forming a thin coating film of the present invention can form an extremely thin thin coating film with a uniform thickness on a continuously running support.

[Brief explanation of drawings]

1-5 are schematic cross-sectional views of one example of a coating and delivery line for carrying out the present invention. 1, 13.14.17...Rotating atomization spray head 2...Delivery section 3...Support 4...Coating roller 5...Metering roller 6...Backup roller 7...Liquid Pan 8... Pre-coating liquid (solvent B, D or solution F) 9... Support coated with pre-coating liquid 10... Support body 2 coated with coating liquid 11... Pass roller 1226... Airless spray Nozzles 15, 18...
・Support support plate! , [i, 19...Support 20...Coating roller 21...Backup roller 22...Liquid reservoir roller 23...Pre-coating liquid (solvent, etc.)

Claims (1)

[Claims] 1. A method for continuously forming a thin coating film, which comprises applying a solvent in advance to a continuously running support, and electrostatically coating a coating liquid in which a coating film-forming composition is dissolved or dispersed before the solvent dries.