JPH03123669A - Coating method - Google Patents

Abstract

PURPOSE:To prevent thick coating by setting the approach speed of a liquid injector to a web to about 1-10cm/sec corresponding to the running speed of the web and applying single-pole charge to the surface to be coated of the web by corona discharge immediately before the injector. CONSTITUTION:Before a coating solution 5 is applied to the web 1 allowed to run at a high speed by a backup roller 2, corona discharge is applied to the surface to be coated of the web 1 by an electrode 11 and single-pole charge is applied to the surface of the web 1. Subsequently, a liquid injector 3 is moved toward the surface of the web 1 running at a high speed in parallel to the surface of the web 1 at a predetermined speed and the coating solution 5 is brought into contact with the surface of the web 1. This predetermined moving speed is set to 1-10cm/sec corresponding to the running speed of the web 1. Therefore, the coating solution 5 is stably applied to the web 1 by the inertial force of the coating solution 5 due to the proper approach-stop operation of the liquid injector 3 and the electrostatic attraction force due to single-pole charge and thick coating at the initial time of coating is eliminated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to films for photographic light-sensitive materials, photographic paper, magnetic recording materials such as magnetic recording tapes, information recording papers such as adhesive tapes, pressure-sensitive paper, and thermal paper. The present invention relates to a method of applying various liquid compositions onto a continuously running belt-shaped support (hereinafter referred to as a web) used in the production of other photographic printing plate materials and the like. In particular, the present invention relates to a coating method using a slide hopper type and extrusion type liquid injection device in which beads are formed.

[Conventional technology]

Conventionally, in this type of coating method, when the coating liquid starts to be applied to the web, even if the coating liquid comes into contact with the running web, the coating liquid is not applied to the web immediately, but is applied after passing through a slight guidance period. be done. Moreover, at the point where the coating liquid starts to be applied to the web, the coating film becomes thicker than in other parts. This thickly coated area requires a longer drying process, even though it is only a small portion of the whole.

Furthermore, if this thickly coated area is insufficiently dried, the undried portion may adhere to the reversing roller or the like during the drying process, contaminating the process or disturbing the subsequent coated surface.

A coating method for preventing thick coating of the coating liquid at the start of coating is disclosed in Japanese Patent Laid-Open No. 59-206080. In this coating method, when forming a bead at the start of coating, the speed at which the liquid dispenser approaches the web is approximately 1 c.
m/see to 5 cm/sec, which allows the web running speed to be approximately 20 m/sec.
It is stated that thick coating of a coating film can be prevented by a simple structure in the range of 200 m/ff1 inch from 100 m/in.

The outline of the device is shown in FIG.

[Problem to be solved by the invention]

However, in the coating method described in JP-A-59-206080, the thick coating at the start of coating is reduced compared to when the approach speed is slower than 1 cm/sec, but the coating does not reach the same thickness as the steady portion. Not yet.

In addition, when the running speed of the web is in the range of 200 m/+win or more, the wettability between the coating liquid and the coated surface of the web deteriorates, resulting in smearing (and the liquid is inevitably fed from the liquid injection device). The flow rate of the coating liquid is 20m/sin ~2
00 m/win, which increases the amount of thick coating at the start of coating, but in such a web running speed range, the coating method described in JP-A-59-206080 cannot prevent thick coating. The effect is not sufficient.

The purpose of the present invention is to solve the drawbacks of the prior art and provide a coating method that enables smooth coating with less thick coating in coating methods using slide hopper type and extrusion type liquid injection device. It's about doing.

[Means and effects for solving the problems] The above object of the present invention is to form a bead on a continuously running web and apply a coating liquid to the web when forming the bead at the start of coating. or the approach speed of the backup roller around which the web is wound to the injector is approximately 1 effl/se depending on the running speed of the web.
e to 10 cm/see, and is achieved by a coating method characterized by applying a unipolar charge to the coated surface of the web immediately before the liquid dispenser by corona discharge using a high voltage generator and an electrode. .

The present invention has an approach speed of 2 cta/sec to 6 cm/sec.
c, and when the amount of charge on the coated surface due to corona discharge is 20 V/C1m-1000V/Cl11 as measured by a surface electrometer, the most excellent effect on thick coating is achieved.

Below is a schematic cross-sectional view (Fig. 1) of an embodiment of the present invention.
This will be explained in detail based on the following.

In FIG. 1, a web l to which a coating liquid is applied is conveyed at high speed via a backup roller 2. As shown in FIG.

Although the liquid injector 3 is a slide type hopper in this embodiment, it may be an extrusion type hopper. The liquid injector 3 is located close to the backup roller 2. This liquid injector 3 is wound around a backup roller 2 and is movable parallel to the surface of the running web 1.

Then, the coating liquid 5 is applied to the liquid supply passages 4a, 4b, 4c, and 4d by a pump (3a) at a given flow rate.

6b, 6c, and 6d are injected continuously. Coating liquid 5
The next narrow vertical extrusion slits 7l-7a, 7b.

It flows out from 7c and 7d onto the slide surface 8 that slopes downward. Each of the flowing coating liquids flows in a layer by gravity on the sliding surface 8 and forms a bead 5 between the surface of the web 1 to be coated and the end 9 of the liquid dispenser 3.
a and is continuously applied. A negative pressure chamber 10 is formed between the backup roller 2 and the juice dispenser 3, and the inside of the negative pressure chamber 10 is depressurized by a pressure reducing means to create a bead 5a.
The drips are attracted so that they are applied to the web l. In addition, in order to apply a unipolar charge to the coated surface of the web immediately before the juice dispenser 3 by corona discharge, an electrode 11 and a high voltage generator 12. And the earth roller 13 is attached in front of the backup roller 2 in the web traveling direction.

To apply the coating liquid 5 to the web 1, as shown in FIG. 2, first, before starting coating, a corona discharge is applied to the surface of the web 1 to be coated from the electrode 11 to give a unipolar charge to the surface of the web. . Next, the liquid injector 3 is moved at a predetermined speed parallel to the surface of the web 1 that is running at high speed, and the coating liquid 5 is brought into contact with the surface of the web 1. The coating liquid 5 is stably coated on the web surface due to the inertial force of the coating liquid due to the approaching and stopping operations of the liquid injection fii3 and the electrostatic attraction of the unipolarly charged web, and coating is started.

The approach speed of the liquid dispenser 3 at this time is effective in the range of 1 crtr/see to 10 cm/sec depending on the running speed of the web. More preferably, the approaching speed of the juicer 3 is
2cra/see to 6cta/sec, and
The most effective charge amount of the surface to be coated due to corona discharge is 20 V/cm to 1000 V/cm as measured by a surface electrometer.

The material of the corona discharge electrode 11 in the present invention is metal, carbon fiber, etc., and the shape is thin wire, brush shape, etc.
A knife shape, a flat plate shape, etc. can be used.

In addition, the web (band-shaped support) used in the present invention includes paper, plastic film, resin coated paper, synthetic paper, and the like. The material of the plastic film is, for example, polyolefin such as polyethylene or polypropylene, or polyvinyl acetate. Vinyl polymers such as polyvinyl chloride and polystyrene, polyamides such as 16,6-nylon and 6-nylon, polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polycarbonate, cellulose acetate such as cellulose triacetate and cellulose diacetate, etc. used. Further, the resin used for resin coated paper is typically polyolefin such as polyethylene, and some are 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 those used in photographic light-sensitive materials.
Coating liquid for photosensitive emulsion layer, undercoat layer, protective layer, back layer, etc. Coating liquid for magnetic layer, undercoat layer, lubricating layer, protective layer, back layer, etc. in magnetic recording media; Oil adhesive layer 1 colored layer,
Examples include coating liquids for rust prevention layers, etc., and these coating liquids contain a water-soluble binder or an organic binder.

〔Example〕

(Example-1) An example will be given to further clarify the effects of the present invention.

Coating was carried out by the method of the present invention using an apparatus as shown in FIG.

The coating liquid was 70 parts by weight of alkali-treated photographic gelatin and 1 part by weight of sodium dodecylsulfonate.

A solution of 0.6 parts by weight of potassium polyvinylbenzenesulfonate in 928.4 parts by weight of water was used.

The viscosity of the coating liquid was 4Qcps at 40°C, and the surface tension was 40dyne/cm. This coating liquid is sent from the pump 6a, and the flow rate per 1 cm width is 1.8 cc/se.
Only one layer was applied to a gelatin-subbed polyethylene terephthalate web running at a speed of 150 m/sin at e.

The distance between the end 9 of the slide hopper and the web 1 is 0.3 m.
The pressure in the negative pressure chamber 10 was set to -40 wa HzO, the approach speed of the slide hopper was set to 5 c+i/see, and the amount of charge on the coated surface due to corona discharge was set to 100 V/c+a as measured by a surface electrometer (Trek Corporation, Model 344). In this case, the ratio of the film thickness of the thickly coated portion at the tip to the steady position was 1.0 to 1.5.

(Comparative Example-1) Using the coating liquid and support of Example-1, JP-A-59-20
According to the method of Publication No. 6080, using the apparatus shown in FIG. 3, the distance between the end 9 of the slide hopper and the web 1 is 0.3 mm, the pressure in the negative pressure chamber 10 is -40 ff, and the approach speed of the slide hopper is 5 cm/sec. When the film thickness was set at 1, the ratio of the film thickness of the thickly coated portion at the tip to the steady position was 1.2 to 2.5.

(Comparative Example-2) Using the coating liquid and support of Example-1, the distance between the end 9 of the slide hopper and the web 1 was set to 0 using the apparatus shown in FIG.
．． 3 layers m, the pressure of the negative pressure chamber 10 -40mH, o, the approach speed of the slide hopper 0.3c+a/! iec 1
When the amount of charge on the coated surface due to corona discharge is set to 100 V/cm as measured by a surface electrometer (Trek model 344), the ratio of the film thickness of the first thickly coated area to the steady position is 1.2.
It was ~2.5.

〔Effect of the invention〕

According to the present invention, in a coating method in which a bead is formed on a continuously running web for coating, when a bead is formed at the start of coating, thick coating that occurs in some areas can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of one embodiment of the present invention, FIG. 2 is a schematic sectional view showing the state immediately before the application of the present invention starts, and FIG.
The figure is a schematic cross-sectional view of the conventional technology.
5a...Beads 6a, 6b, 6c, 6d--Pump 7a, 7b, 7c, 1d=Extrusion slit 8...Sliding surface 9...End IO...Negative pressure chamber 11...Electrode 12...High voltage generation Device 13: Earth roller (and 3 others)

Claims (1)

[Claims] In a method of applying a coating liquid by forming a bead on a continuously running web, when forming the bead at the start of coating, the speed at which the liquid injector approaches the web or the liquid injection of the backup roller around which the web is wound The approaching speed to the container varies from about 1 cm/sec to 1 cm/sec depending on the running speed of the web.
0 cm/sec, and is characterized in that a unipolar charge is applied to the coated surface of the web by corona discharge from a high voltage generator and an electrode immediately before a liquid injector.