JPH04225864A - Coating method - Google Patents

Abstract

PURPOSE:To prevent generation of thick coating and striping fault at the starting time of coating and jointing time of web and also to prevent generation of striping, uneven and repelling fault at the stationary time, thus eneble a coating method uniformly applicable at high speed. CONSTITUTION:Quantity of charge at the starting time of coating and the jointing time of web is elevated more than quantity of charge at the stationary time.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating method. In particular, in the production of photographic light-sensitive materials such as photographic film and photographic paper, photolithographic materials, magnetic recording materials, pressure-sensitive copying paper, heat-sensitive copying paper, etc., long strip supports (hereinafter referred to as The present invention relates to a method in which a coating liquid such as a photographic emulsion or a magnetic agent is applied to a web (referred to as a "web") by forming a bead after the web is electrically charged.

0002

[Prior Art] Conventionally, in coating photographic light-sensitive materials, magnetic recording materials, recording paper, etc., a method has been widely known in which a web continuously running at high speed is charged and then a coating liquid is applied by forming beads. There is. That is, ■ the time of application start and/or
Or a coating method in which discharge treatment is applied only to the joint part (Japanese Patent Application Laid-open No. 5
5-142565). (2) A method in which a potential of 0.1 KV or more is applied to the bead-forming part of the coating liquid or to the surface of the support immediately before it (Japanese Patent Laid-Open No. 146369/1983). ■ A coating in which the support is charged with a constant charging potential and the degree of vacuum is kept below the steady state of vacuum before coating, the degree of vacuum is kept above the steady state of vacuum for a certain period of time after coating, and then the degree of vacuum shifts to the steady state of vacuum. Method (Unexamined Japanese Patent Publication No. 1-2587
Publication No. 72), etc.

0003

[Problem to be Solved by the Invention] However, although method (2) is useful for preventing thick coating and streak failures at the start of coating and when joining webs, it is not useful for speeding up coating under normal conditions; However, when such a voltage was applied, there were problems such as repellency failure. In addition, method (■) is useful for preventing repellency failures during steady state, but if a high amount of charge is applied to unsteady areas such as joints at the start of coating, streaks and uneven failures are likely to occur in steady areas, and vice versa. However, a low charge amount that does not cause streaks or uneven failures in the steady region is insufficient for stabilizing the unsteady region. Furthermore, since the method (2) charges at a constant charging potential that is reached during steady state, uniformity during application and when passing through a joint is achieved by maintaining the degree of vacuum at or above the steady state vacuum for a certain period of time.

[0004] The purpose of the present invention is to solve the problems of the above-mentioned methods, to eliminate the occurrence of thick coating and streak failures at the start of coating and when joining webs, and to eliminate the occurrence of streaks, unevenness, repelling failures, etc. even during steady state. The object of the present invention is to provide a coating method that enables uniform production at high speed.

[0005]

[Means and effects for solving the problems] The above-mentioned object of the present invention is to provide a coating method in which the surface of a long strip-shaped support is charged continuously at high speed, and then a coating liquid is applied by forming a bead. This is achieved by a coating method characterized in that the amount of charge at the start and when the web passes through the joint is higher than the amount of charge during steady coating.

[0006] In order to apply the coating continuously at high speed in the present invention, many joints of the web are required. For this reason, it is necessary to minimize the occurrence of thick coating and streak failures in the area downstream of the joint in order to improve yields. In the present invention, increasing the amount of charge at the start of coating and when the web passes through the joint to be higher than the amount of charge during steady coating means, specifically, to increase the amount of charge at 1K at the start of coating and when the web passes through the joint.
This means that the voltage should be 0.1 to 0.5 KV in the steady state. 1KV or more at the start of coating and when the web passes through the joint means thick coating rate (coating amount in thick coating area/
It is necessary to suppress the coating amount (in the normal area) to 130% or less, and the upper limit thereof is preferably increased to a level that does not cause spark discharge. Also, 0.1 in the steady region
~0.5 KV means that if it is 0.1 KV or less, repelling failure is likely to occur, and if it is 0.5 KV or more, charging unevenness is likely to occur as coating unevenness.

The adjustment of the amount of charge in the present invention is shown in terms of the applied voltage with respect to the coating time, as shown in FIG. 1. At the time of starting coating and passing through the bond, for example, an applied voltage of 8 KV is applied, and the amount of charge on the web at that time is 1000V. 5K during steady state
This means that when an applied voltage of V is applied, the amount of charge on the web becomes 150V.

To further explain the present invention, the material of the corona discharge electrode in the present invention may be metal, carbon fiber, etc., and the shape thereof may be a thin wire, a brush shape, a tough edge shape, a flat plate shape, etc. Other supports used in the present invention include paper, plastic film, resin-coated paper, synthetic paper, and the like. Examples of the material of the plastic film include polyolefins such as polyethylene and polypropylene, vinyl polymers such as polyvinyl acetate, polyvinyl chloride, and polystyrene;
- Polyamides such as nylon and 6-nylon, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polycarbonates, and cellulose acetates such as cellulose triacetate and cellulose diacetate are used. The resin used for resin-coated paper is typically polyolefin such as polyethylene, and there are papers laminated on one or both sides. However, it is not necessarily limited to these. Furthermore, the term "coating liquid" includes liquid compositions of various types depending on the application, such as coating liquids for photosensitive emulsion layers, undercoat layers, protective layers, back layers, etc. in photographic light-sensitive materials. ; magnetic layer, undercoat layer, etc. as in magnetic recording media;
Coating liquids for lubricating layers, protective layers, backing layers, etc.; and coating liquids for adhesive layers, colored layers, antirust layers, etc., and these coating liquids contain water-soluble binders or organic binders. Slide coating, roller bead coating, extrusion coating, curtain coating, etc. can be used as a method for applying the coating liquid onto the support, and other methods are also possible.

Embodiments of the present invention will be explained using the drawings. In FIG. 2, the coating liquid 6a is pumped 2 into the liquid injector 1.
The liquid 6 is supplied to the cavity 3, spread to the full coating width in the cavity 3, and flowed through the slot 4 onto the slide surface 5.
A coating liquid bead 8 is formed in an overlapping relationship with b, and is applied onto the support 7 supported by the backing roller 9.
At the start of coating and when passing through a joint, when the coating liquid bead 8 comes into contact with the web 7, the coating tends to be thicker than usual. An electrode 11 is installed and a voltage from a high-voltage power source 15 is used to cause corona discharge, thereby strengthening the adhesion of the coating liquid to the web surface. On the other hand, the vacuum chamber 10, which reduces the pressure of the part of the liquid injector before application using the vacuum pump 14, performs constant pressure reduction to increase the coating speed. The present invention is a coating method characterized by changing the voltage so that the amount of charge at the start of coating and when the web passes through a joint is higher than the amount of charge during steady coating.

0010

EXAMPLE An example will be described in order to clearly demonstrate the effects of the present invention. However, the present invention is not limited to this embodiment. A 5% gelatin solution with a viscosity of 2 is used as a coating solution.
When applying 0cp from a liquid injector using the slide bead coater having the vacuum chamber, the degree of vacuum in the vacuum chamber was kept constant at -50 mmH2O, and the coating speed was 150 m/m.
The conditions of the coated surface at the start of coating, at steady state, and when passing through the bonding were compared based on the amount of charge at in and 300 m/min. The results are shown in Table 1.

[0011]

[Table 1]

As shown in Table 1, the coating speed was 150 m/mi.
n shows a change in the thick coating rate at the start of coating, but at a coating speed of 300 m/min, the charge amount is preferably 1000 V or more at the start of coating and when passing through the joint, and preferably about 200 V during normal times. It is clear that a change in quantity is desired.

[0013]

[Effects of the Invention] The coating method of the present invention makes the amount of charge higher at the start of coating and when passing through the joint higher than the amount of charge during steady state.
It has become possible to eliminate the occurrence of thick coating and streak failures at the start of coating and when passing through joints during high-speed continuous coating, as well as unevenness and repelling failures during steady state, making it possible to achieve uniform production with high efficiency.

[Brief explanation of the drawing]

FIG. 1 is a chart showing how to apply applied voltage with respect to continuous coating time in the coating method of the present invention.

FIG. 2 is a side view of an embodiment of a coating apparatus for carrying out the coating method of the present invention.

[Explanation of symbols]

1. Liquid injection device 2 Pump 3 Cavity 4 Slot 5 Slide surface 6a, 6b Coating liquid 7 Support 8 Coating liquid bead 9 Backing roller 10　Decompression chamber 11 Electrode 12 Earth roller 13　Charging part 14　Reducing pressure pump 15 High voltage power supply

Claims (1)

[Claims] 1. A method in which the surface of a long strip-shaped support that runs continuously at high speed is electrically charged, and then a coating liquid is applied by forming a bead, in which the charging is performed at the start of coating and when the web passes through a joint. A coating method characterized by making the amount of charge higher than the amount of charge during steady coating.