JP2817056B2 - Application method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a coating method. Particularly, in the production of photographic photosensitive materials such as photographic films and photographic papers, photoengraving materials, magnetic recording materials, pressure-sensitive copying papers, and thermosensitive copying papers, etc., a continuously running long strip-shaped support (hereinafter referred to as "web"). To apply a coating solution such as a photographic emulsion or a magnetic agent
More specifically, the present invention relates to a method of coating by averaging charging unevenness on a web in order to uniformly apply a coating solution to a web.

[Conventional technology]

Conventionally, as a method of averaging uneven charging on a web,
A method in which a high voltage is applied to an electrode to generate both positive and negative ions, thereby neutralizing the charge on the web and eliminating the charge (for example, "Electrostatic Handbook" edited by the Society of Polymer Science, Japan).

Initially, a positive charge is applied to the web and then a negative charge is applied to make the charge on the web uniform (Japanese Patent Laid-Open No. 60-9589).
No. 9).

[Problems to be solved by the invention]

However, the former method has a much higher capacity than the self-discharge type static eliminator, but when the web or charge voltage is difficult to eliminate, a large number of electrodes and a high voltage power supply are required accordingly. It is costly and space for equipment installation is also a problem.

In the latter method, when the electric charge on the web was easily fixed, the smoothing of the uneven charging as shown by this method did not occur so much, and the effect was small.

The object of the present invention is to address the conventional problems as described above,
An object of the present invention is to provide a coating method which can reduce the problems of equipment cost and space and more effectively smooth out charging unevenness.

[Means and actions for solving the problem]

The above objects of the present invention are as follows: (1) Immediately before applying a coating liquid onto a continuously running long strip-shaped support, the maximum value and the minimum value of the charged voltage on the long strip-shaped support are detected. By applying a charge having the opposite sign to the potential of the median value on the web, the maximum value and the minimum value of the charge on the web were made positive and negative, respectively, so that the values were equal, and a voltage applied type static eliminator was used. A coating method characterized by performing coating later.

 Achieved by

When the maximum and minimum median values and the average value almost coincide with each other, the average value may be detected and used instead of the median value.

In the present invention, the maximum value and the minimum value of the charged voltage on the long belt-shaped support are detected, and the charge having the opposite sign to the potential of the median value is applied to the web, thereby obtaining the maximum value of the charge on the web. When the minimum value is positive and negative, respectively, and the values are made equal, the median value of the charged voltage on the web fluctuates considerably in the length direction or lot on the long strip-shaped support. The voltage of the charging device may be controlled based on the value. In addition, two or more charging electrodes may be used in order to compensate for non-uniformity in the width direction of one charging electrode.

In the present invention, a charge having the opposite sign to the potential of the median value is applied to the web, and the maximum value and the minimum value of the charge on the web are positive and negative with respect to the zero value, respectively. By distributing, the effect is remarkable even when the following voltage application type static eliminator is used, and a large number of electrodes and a high voltage power supply are not required unlike the conventional case.

The voltage-applied static eliminator used here generally uses an AC high-voltage power supply and generates positive and negative ions from the electrodes to neutralize the charged charges on the object.

The relationship between the electrostatic attractive force and the charged voltage is F = C · V ² , where F is the electrostatic attractive force, C is a constant, and V; the charged voltage attracts the coating liquid according to the above equation.

In the case of the conventional charge distribution as shown in FIG. 2, the fluctuation of the electrostatic attraction is ΔFa = C (b ² −a ² ) where a: minimum voltage, b: maximum voltage, shown in FIG. In the case of such a charge distribution of the present invention, Here, k is a leveling rate, (a coefficient that makes it easy for the previously charged electric charge to be somewhat uniform by applying the electric charge) k ≦ 1 Therefore, the variation of the electrostatic attractive force can be obtained by the method of the present invention from the above equation. By using, compared to the conventional The difference in coating unevenness due to uneven electrostatic attraction is extremely small, for example, about 1/10.

 An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic side view of one embodiment of a coating apparatus to which the coating method of the present invention is applied. However, the present invention is not limited to this embodiment.

Immediately before applying the coating liquid 2 onto the continuously running web 1 from the coating head 3, the charged voltage on the web 1 is measured by the potentiometer 4, and the maximum value and the minimum value of the charged voltage are determined by the control unit 5.
And a charge having the opposite sign to the potential of the median value is applied to the web by the charging electrode 7 and the earth roller 8 by the DC high-voltage power supply 6 under the control of the control unit 5. As a result, the maximum value and the minimum value of the charge on the web 1 are positive and negative, respectively.
They are negatively charged so that their values are equal.

As a more preferable method, a voltage applying type static eliminator is passed immediately before the coater after passing through the potentiometer, and the AC high voltage power supply 9 and the static eliminator electrode 10 discharge both sides of the web to further reduce the charging voltage. This is a method of performing coating after the application.

As the voltage applying type static eliminator, 25 charged electrodes were used on one side of the web, and a sine wave of 50 Hz, 7 Kv, PP was used as a power source.

The material of the corona discharge electrode in the present invention may be metal, carbon fiber, or the like, and the shape may be a thin wire, brush, knife edge, flat plate, or the like.

In addition, examples of the support used in the present invention include paper, plastic film, resin-coated paper, and synthetic paper. 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 6,6-nylon and 6-nylon; polyethylene terephthalate;
Polyesters such as 2,6-naphthalate, polycarbonates, cellulose acetates such as cellulose triacetate and cellulose diacetate are used. The resin used for the resin-coated paper is typically a polyolefin such as polyethylene, and may be one-sided or double-sided. However, it is not necessarily limited to these.

The term "coating liquid" includes various liquid compositions depending on the intended use. For example, coating liquids such as photosensitive emulsion layers, undercoat layers, protective layers, back layers, etc., as in photographic materials. Liquid; other coating liquids such as an adhesive layer, a colored layer, and a rust-preventing layer. These coating liquids contain a water-soluble binder or an organic binder.

As a method of applying the coating liquid on the support, a slide coat, a roller beat coat, a spray coat,
Extrusion coats, curtain coats and the like can be used, and other methods are also possible.

〔Example〕

Polyethylene terephthalate film 10 as web
Using 0μ, a two-layer gelatin aqueous solution using a slide bead coater was used to coat 50 cc / m ² , and the lower layer was a solution containing a dye to determine coating unevenness. The coating speed was 20 cc / m ^2.
The coating was performed at 0 m / min by changing the static elimination method. Since this web has a surface resistance of about 10 ¹⁰ Ω or less on the anti-coated surface, the charge on the coated surface is very easily stabilized, and coating unevenness due to uneven charging is very likely to occur.

FIG. 4 shows changes in the charged state on the web in the following examples and comparative examples. In order to clarify the effect, positive forced charging unevenness was periodically given in advance.

Example 1 According to the charging method of the present invention, the maximum value and the minimum value of the charge on the web were made positive and negative, respectively, so that the values were equal, and the charge amount was further reduced by using a voltage application type static eliminator. When post-coating was performed, no coating unevenness occurred.

Example 2 In the case where the coating was performed after the maximum value and the minimum value of the electric charge on the web were made positive and negative, respectively, and the values were equal by the charging method of the present invention, the periodic coating unevenness was reduced. Although it did not occur, slight application unevenness due to charging unevenness was felt to some extent.

In Examples 1-2, a = 30 V, b = 200 V, and at this time, the leveling rate K was about 0.8.

The electrostatic attraction is The change in the electrostatic attraction is reduced to about 1/9 theoretically.

Comparative Example 1 When coating was performed after positively charging and then negatively charging as shown in JP-A-60-95899, periodic coating unevenness slightly occurred, and coating unevenness due to minute charging unevenness was also observed. Occurred.

Comparative Example-2 When the coating was performed after using only the voltage applying type static eliminator,
As in Comparative Example 1, periodic and other coating unevenness also occurred.

〔The invention's effect〕

According to the coating method of the present invention, it is possible to reduce the facility cost and space problem for eliminating the uneven charging, and to more effectively smooth the uneven charging.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a coating apparatus according to one embodiment of the coating method of the present invention, FIG. 2 illustrates the charging status on a web, FIG. 3 is a graph illustrating the charging status according to the present invention, and FIG. FIG. 7 is an explanatory graph of a change in the charging state of the web in the example and the comparative example. DESCRIPTION OF SYMBOLS 1 ... Web 2 ... Coating liquid 3 ... Coating head 4 ... Potentiometer 5 ... Control part 6 ... DC high voltage power supply 7 ... Charging electrode 8 ... Earth roller 9 ... AC high voltage power supply 10 ... Static eliminator electrode

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Claims (1)

(57) [Claims] 1. Immediately before coating a coating solution on a continuously running elongate strip-shaped support, the maximum value and the minimum value of the charged voltage on the elongate strip-shaped support are detected, and the potential of the median value is detected. By applying a charge of the opposite sign to the web, the maximum value and the minimum value of the charge on the web are made equal to the positive and negative values, respectively. Coating method.