JP2000254571A - Electrification device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a spark from being generated while a sufficient charge is given to the surface of a web even at the time of rapid coating by providing an insulator cover for protecting a ground roll between an electrode and the ground roll, in an electrification device having the electrode and the ground roll disposed so as to pinch the travelling web. SOLUTION: A power terminal 3 is connected to a power source device 2, to which an electrode 1 is connected, and an A.C. source is converted to a D.C. by the power source device 2 to supply the D.C. to the electrode 1. A ground roll 5 is installed opposite to the electrode 1, and the web 6 is conveyed through the ground roll 5, the web travels at a set gap from the electrode 1, although the web 6 is in contact with the ground roll 5. An insulator cover 4 protecting the ground roll 5 is provided between the electrode 1 and the ground roll 5, and the cover 4 is arranged so that the ground roll 5 is not directly influened by a D.C. high voltage from the electrode 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a power supply device.
Specifically, before applying a coating liquid to a running web (referred to as a “long belt-shaped support”), an applied voltage is applied to the electrodes to apply a potential to the running web (hereinafter referred to as “electrical treatment”). Calling device), more specifically, using a coating method such as a lip coater, a slide bead coater, a curtain coater, especially a photographic film,
The present invention relates to a power supply device used for producing a photographic photosensitive material such as photographic paper, a photoengraving material, an ink jet recording material, a magnetic recording material, a heat-sensitive recording material, a pressure-sensitive copying material and the like.

[0002]

2. Description of the Related Art Conventional photographic photosensitive materials, photoengraving materials, ink jet recording materials, magnetic recording materials, heat-sensitive recording materials,
In a coating method for producing a pressure-sensitive copying material or the like, a coating liquid applied to a web is a coating liquid mainly containing water as a dispersion medium. On the other hand, the web to which the coating liquid is applied is based on paper, and various substances are applied on the front and back, regardless of whether it is organic or inorganic, for each purpose, or a bonded web or a plastic film web is used. . For that reason,
Affinity does not match with a hydrophilic coating solution containing water as a main dispersion medium, which may cause defects such as repelling and uneven coating at the time of coating. In particular, polyethylene represented by a web such as a photographic material, polyethylene terephthalate However, in the case of a web having a hydrophobic surface such as polyolefin, problems such as repelling and uneven coating tend to occur, and these problems must be completely avoided from the viewpoint of the quality required in the market. is there.

[0003] In recent years, the coating speed has been increased in order to increase the production efficiency, and a problem called coating unevenness has arisen in connection with the increase in the coating speed. In other words, in addition to the affinity problem that the coating liquid adapts to the web as the coating speed increases, the flow of air around the web due to the running of the web affects the coating section, and air that enters between the coating liquid and the web. A phenomenon called entrainment has occurred, and it is necessary to have a stronger attraction force between the web and the coating solution to prevent air entrainment than chemical affinity.

[0004] Regarding these problems, a method of applying an electric charge by applying an electric potential to the web and giving an attractive force to the coating liquid is effective, and several proposals have been made on this method. For example, JP-A-61-146369 and JP-A-6-146369
A method described in, for example, JP-A-1-147070 and the like is a method of applying a DC electric field to a web to apply electric power.
No. 881 is known.

In these charging methods, a charging device is usually used between the electrode and the earth roll immediately before or at the coating section (when the charging section is charged, the electrode is coated with a coater head and the earth roll is coated). A backing roll for a coater head such as a roll) is passed through the web while contacting the web with an earth roll to apply a potential to the web. Normally, a high DC voltage is applied between the electrode and the earth roll, an electric field is generated between the electrodes, and a dielectric polarization phenomenon is generated on the surface of the web, thereby inducing a charge having a sign opposite to that of the opposing electrode. The surface can be charged. As a result, an electrostatic field is generated between the web and the coating liquid in the coating section, and an attractive force between the web and the coating liquid is generated by the electrostatic force. Therefore, if the surface potential of the web surface is further increased, a higher static electric field (increased electric field strength) is generated, and the web-
The attraction between the coating liquids is further increased.

In connection with the recent increase in coating speed for improving production efficiency, a stronger web-coating liquid attraction force is required. Even in the prior art, it was possible to simply increase the attractive force by increasing the applied voltage. However, when the applied voltage is increased, the effect of the electric treatment is increased, but when the electric field strength reaches the dielectric breakdown strength, a short-circuit phenomenon occurs immediately and dielectric breakdown, that is, current spark occurs. In the case of a product to be manufactured, for example, a photosensitive material or the like, this spark may result in a large quality defect. In addition, the impact of the electric current spark is not preferable because it results in the generation of scratches and cracks on the surface of the earth roll.

Therefore, even if the applied voltage is simply increased, the electric field strength is increased, the applied surface potential is increased, and the attraction force between the web and the coating solution is increased, a problem such as a spark occurs. Typically, only a certain amount of voltage could be applied. According to the results of the actual charging test performed by the present inventors, when a metal high carbon steel roll is used as the earth roll, only about 4.5 KV can be applied to prevent sparking at a high applied voltage. Although the surface potential varies depending on the speed and type of the web, the thickness, the type and shape of the electrodes, the number of the webs, the distance between the earth roll and the electrodes, etc., the surface potential on the web should be about 0.1 KV even under the optimal conditions. It was finally. That is, if the surface potential on the web is to be further increased, a problem such as a spark occurs, which is incomplete with respect to the recent demand for an increase in the coating speed. There is a high demand for a solution.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a power supply device in which an electrode and an earth roll are arranged so as to sandwich a running web, and that a sufficient attraction force between the web and the coating liquid can be obtained even during high-speed coating. It is an object of the present invention to provide a power supply device which prevents the occurrence of sparks and prevents product defects and deterioration of earth rolls, while applying a charge having a surface potential exhibiting the following to the web surface.

[0009]

A problem to be solved is a power supply device in which an electrode and an earth roll are arranged so as to sandwich a running web.
The problem can be solved by a power supply device characterized in that an insulator cover for protecting the earth roll is provided.

[0010]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments, and various forms are possible. Needless to say.

FIG. 1 is a diagram showing a power supply device used in one embodiment of the present invention. FIG. 2 is a diagram illustrating each portion in the web width direction of the power supply device according to the present invention.

As shown in FIG. 1, a power supply terminal 3 and a power supply 2 are generally connected, and a power supply 2 and an electrode 1 are generally connected. Since the normal power supply 1 is an alternating current, it is converted into a direct current by the power supply device 2 and supplied to the electrode 1. An earth roll 5 is provided so as to face the electrode 1, and the web 6 is transported via the earth roll 5. The web 6 is in contact with the earth roll 5, but does not contact the electrode 1, and runs with a certain gap. The ground roll 5 is installed because, when a conductor is present on the electrode-facing surface and the conductor is grounded, electrostatic induction is more effectively performed, and as a result, the electric field density is reduced. This is because it is possible to increase the height.

A feature of the power supply device of the present invention is that an insulator cover 4 for protecting the earth roll 5 is provided between the electrode 1 and the earth roll 5. The insulator cover 4 is arranged so that the ground roll 5 is not directly affected by the DC high voltage from the electrode 1. That is, the portion of the ground roll 5 that is not covered with the web 6 and that is affected by the electrode is covered with at least the insulator cover 4. Specifically, the relationship is as shown in FIG. The web 6 is usually provided with an uncoated portion 9,
The insulator cover 4 is provided so as to cover the ground roll 5 from the uncoated portion 9 to the uncovered portion 7 not covered with the web 6.

As the electrode 1, a wire-shaped electrode as shown in FIG. 1 is usually used, but may be another shape, for example, a blade-like, needle-like, brush-like electrode or the like. In the case of using a wire-shaped electrode, the wire diameter affects the electric field density of the electric field to be formed. The thinner the wire, the higher the electric field density, and the surface potential applied to the web surface can be increased with a relatively low applied voltage. However, the conditions under which the present invention is used industrially are based on the premise that high-speed coating is performed, so that the surface potential of the web surface is relatively high. When applying at a coating speed of several hundred m / min with a bead coater that performs application while forming, a surface potential of at least about 0.2 KV to 1.0 KV is required. It is necessary to select the wire diameter. Although FIG. 1 shows the case of one electrode 1, a plurality of electrodes 1 can be applied, and a plurality of electrodes 1 can be provided along the running direction of the web 6 through the earth roll 5. If installed, it is possible to increase the charging effect. However, according to the results of the present inventors' research, the charging effect of the number of wires and the wire diameter, that is, the influence on the surface potential applied to the web is larger than that of the wire diameter. However, the effect was several orders of magnitude stronger.

Further, as described above, the charging effect is also affected by the earth roll 5, and the higher the dielectric constant of the earth roll 5, the stronger the charging effect. Therefore, a desired surface potential can be obtained by combining the wire diameter and the material of the earth roll depending on the level of the surface potential that is usually required.

However, even if the wire diameter and the material of the earth roll are combined, the problem due to sparks cannot be avoided. That is, since sparks are generated when the dielectric breakdown strength is reached, the electric field density changes even if the wire diameter is changed, but the electric field strength is determined by the applied voltage and the distance between the electrode 1 and the earth roll 5, so that the spark is prevented. Therefore, even if the electric field density is reduced by using a thick wire,
Only lowers the surface potential applied to the surface, and has no effect on spark prevention. If the distance between the electrode 1 and the earth roll 5 is increased, sufficient electric field strength cannot be obtained, and in this case, the surface potential also decreases. Next, with respect to the earth roll, if an insulating film is applied on the roll to prevent sparking, there is a contradictory relationship that the surface potential decreases, and it is very difficult to balance the two. In fact, the present inventors conducted intensive research on many roll materials,
Eventually, these balances could not be achieved. To be more specific, a material (ceramic material) having a high dielectric breakdown strength and a high dielectric constant was considered to be able to balance these, and various investigations were conducted. In any case, spark prevention is complete. When the film thickness is provided as described above, it is impossible to obtain a surface potential required for high-speed coating. Conversely, when the film thickness is adjusted so as to obtain the minimum surface potential (0.2 KV) required for high-speed coating, the portion where the web does not cover the roll, that is, the portion where the ceramic coating portion is bare and the portion between the electrode and the electrode. A short circuit occurred, sparking. That is, an earth roll surface coating material satisfying the surface potential required for spark prevention and high-speed coating was not found.

Therefore, in the present invention, the combination of the electrode 1 and the earth roll 5, the height of the applied voltage, and other conditions are not particularly limited. It is necessary to constitute a heating device that can apply the surface potential of the web 6 to the web 6.

Next, in the present invention, the portion where the coating liquid is applied to the web 6 is narrower than the width of the web, and it is necessary to provide the uncoated portions 9 at both web edges. Usually, the width of the uncoated portion 9 is 5 mm to 20 mm. In the width direction of the earth roll 5, the web 6 is placed between the ground roll 5 and the electrode 1 so that the web 6 covers the uncovered part 7 not covering the earth roll 5 and a part of the uncoated part 9 not coated with the coating liquid. It is necessary to install the insulator cover 4 in the first place. That is, in order to prevent the radius roll from being affected by the impact due to the spark, it is necessary to completely prevent the spark from being generated. For this purpose, the uncovered portion 7 where the web 6 does not cover the radius roll 5 is completely covered with the insulator. 4 needs to be covered. Normally, the width of the uncoated portion 9 covered by the insulator cover 4 may be about 3 mm from the edge of the web edge.

The insulator cover 4 is made of an insulator material, and is made of various insulator materials, such as rubbers, glasses, and the like.
A plate-like cover made of a material such as ceramics and organic polymers, and is provided to prevent spark generation due to a short circuit between the electrode 1 and the earth roll 5.
As the insulator material used for the insulator cover 4, various materials known to date can be applied. However, in the structure of the present invention, a soft material whose cover is deformed by weight or slight impact is grounded. It is not preferable because it may easily come into contact with the roll 5. However, it is necessary to use a sufficiently high dielectric breakdown property (dielectric breakdown strength). In practical use for stably preventing sparks, the dielectric breakdown strength is set to 2.5 KV / mm or more. , The thickness of the material must be 4 mm or less. That is, the entire cover must be able to withstand an applied voltage of at least 10 KV. This is because, as a result of research conducted by the present inventors, it is necessary to apply at least a voltage of 5 KV or more, and in some cases, an applied voltage of up to about 7 KV is required to impart a surface potential to a web required for high-speed coating. This is because In practical use, it is necessary to provide a cover that can withstand about 10 KV in consideration of safety. Here, when a material having a dielectric breakdown strength of less than 2.5 KV / mm is used, it is necessary to make the thickness greater than 4 mm. In the present invention, the insulator cover 4 is provided between the electrode 1 and the earth roll 5. If a too thick cover is installed, the distance between the electrode 1 and the earth roll 5 must be increased, and a gap between the cover and the earth roll is required.
The distance between the ground roll 5 and the ground roll 5 must be increased to at least 5 mm or more, and in practice, to 10 mm or more. As a result, a desired surface potential may not be obtained.

The earth roll 5 of the power supply device in the present invention
May be usually a metal roll for conveying the web 6, but it is also possible to use a roll whose entire roll surface is covered with an insulating coating layer containing a high dielectric substance or a roll which has been subjected to another roll surface treatment. I don't care.

However, in order to obtain the surface potential for obtaining the above-mentioned high-speed coating property, the type and content of the high dielectric substance, the insulating substance forming the insulating coating layer, the thickness of the coating layer, and the like are controlled. There is a need to. If these conditions are determined in accordance with practical use, the present invention can be applied under any conditions. However, for example, a high dielectric substance has a relative permittivity of 10%.
No. 00 or more, an insulating substance 1 forming an insulating coating layer
0.3 to 3 parts by weight with respect to parts by weight. Rubbers, glasses, ceramics, organic polymers, and the like can be used as the insulating material. The coating layer thickness is usually 1 to 10 m
m, but is not particularly limited.

Next, the coating solution, the web,
The coating device will be described.

In the present invention, a coating solution is a photographic emulsion solution for producing a photographic light-sensitive material or a photoengraving material prepared by dispersing silver halide or the like in an aqueous gelatin solution or an ink-jet recording material. An ink-jet coating liquid in which an ink-absorbing pigment such as silica and an adhesive are dispersed, or a water-soluble polymer such as gelatin, polyvinylpyrrolilone (PVP), carboxymethylcellulose (CMC) or the like which forms the ink-absorbing layer is dissolved. , A magnetic coating material for manufacturing magnetic recording materials, magnetic particles dispersed in water or an organic solvent, and a heat-sensitive coloring material coating solution for developing heat-sensitive recording materials. Containing a color former or a color developer as a pressure-sensitive color-forming body coating liquid when producing a pressure-sensitive copying material. Capsule etc. those dispersed, said solid concentration if necessary, the viscosity, the coating liquid such as temperature or the like is adjusted, can be used without limitation. However, in view of the characteristics of the type of web used and the degree of industrial demand, it is preferable to adapt to the field of photographic light-sensitive materials and photoengraving materials.

As the web 6 used in the present invention, generally used high quality paper, medium quality paper, paper renewal, machine coated paper, art paper, cast coated paper, synthetic paper, resin coated paper, plastic film, metal Board, rubber board,
Includes fabrics woven from natural or synthetic fibers.

The coating apparatus used in the present invention is mainly a non-contact pre-measurement type coating apparatus such as a lip coater, a slide bead coater, a curtain coater and the like, and a post-metering coating apparatus such as a blade coater and a rod. It can be applied before application sections such as a coater and an air knife coater, and can also be used for a size press coater, a gate roll coater, a gravure coater and the like.

However, the power supply device of the present invention is preferably applied to a slide bead coater that forms a bead in a coating section and performs coating. That is, the slide bead coater is a method in which the coating liquid is applied to the web by a slide contact method, and is a coating method in which the contact force between the coating liquid and the web is the weakest among the coating methods. Therefore, as described above, air easily enters between the coating liquid and the web, and as a result, a problem such as uneven coating is likely to occur. Therefore, usually, on the upstream side in the running direction of the web, a pressure reducing section is provided immediately before the coating section where the coating liquid and the web come into contact with each other to increase the contact force between the coating liquid and the web, and the coating liquid and the web are coated in close contact. Coating method. Therefore, if the contact force is increased by another method other than the pressure reduction, the applicability is improved, and as a result, a product having no application unevenness is obtained.

The power supply device of the present invention is suitable for a web having a hydrophobic surface whose surface is typified by resin-coated paper or plastic film, such as polyethylene, polyterephthalate, or polyolefin. In general, when a hydrophilic coating solution is applied to a web, if the web is more hydrophilic, repelling and uneven coating due to the repelling are less likely to occur, but the above-listed webs have an affinity with the hydrophilic coating solution. It is difficult to apply a hydrophilic coating solution due to low coating properties, and it belongs to the category of difficult coating technology. Therefore, when compared with other webs that are relatively hydrophilic, the effect of the present invention can be more fully applied when the coating liquid is applied to a web having a hydrophobic surface.

[0028]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to these Examples, and various applications can be made within the scope of the claims.

As a coating solution, sodium chloride, an aqueous silver nitrate solution, a halogen solution containing iridium salt and rhodium salt and the like are mixed in a 7% gelatin solution to prepare a photographic emulsion. Then, an organic precipitant is added, and the precipitate is washed with water. Dissolution, gold sensitization and the like were performed to prepare a coating solution for a photographic photosensitive material having a B-type viscosity of 11 cps. As the web, a web was prepared in which a polyethylene layer having a thickness of 30 micrometers was resin-coated on both sides of a paper substrate having a basis weight of 160 g / m ² . A slide bead coater was used as a coating device.

An insulator cover made of alumina ceramic (dielectric breakdown strength 10 kV / mm) and having a thickness of 1.2 mm was used. The electrode is a wire type, made of tungsten, 0.1 mm in diameter. The earth roll contains 0.4 parts by weight of barium titanate (dielectric constant: 1600) as a ceramic material on a high carbon steel roll or a high carbon steel roll. Then, a ceramic coating roll having a film thickness of 3 mm was used. The type of roll used is shown in Table 1. The distance between the wire electrode and the earth roll was 4 mm.

The coating was performed at a coating speed of 250 m / min using the above-mentioned coating solution, web and coating device. Regarding the results, the spark prevention effect of the insulator cover as shown in FIG. 1 was confirmed by the presence or absence of sparks, and whether or not the coating was possible was confirmed. Table 1 shows the results.

[0032]

[Table 1]

[0033]

The results as shown in Table 1 above were obtained.
In order to enable high-speed coating at a rate of / min, it is impossible if the surface potential is less than 0.2, and at least the surface potential must be at least 0.2 kV. Surface potential 0.2k
In order to increase the voltage to V or more, it is necessary to increase the applied voltage, etc., depending on the conditions of the earth roll, and accordingly, a spark is generated in the heating device without the insulator cover of the present invention, and the surface potential is unstable. And good coating is impossible. On the other hand, in the heating device provided with the insulator cover of the present invention, no spark was generated even when the applied voltage was increased, and the surface potential was reduced to 0.2.
It is clear that it is easy to increase the voltage to kV or more.
High-speed application of 50 m / min is possible. In the case where sparks occurred in Comparative Examples 1 and 4, scratches due to the impact of the sparks were observed on the surface of the Earl roll. Therefore, the power supply device of the present invention is a power supply device for applying an electric potential to the running web before applying the coating liquid to the web, and the power supply device in which the electrode and the earth roll are arranged so as to sandwich the web. At the time of high-speed coating, while applying a charge having a surface potential that sufficiently exerts the attraction force between the web and the coating liquid even at the time of high-speed coating, the generation of sparks is prevented, and product defects and deterioration of the earth roll are prevented. An enabling power supply can be supplied.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a power supply device used in one embodiment of the present invention.

FIG. 2 is a diagram illustrating each portion in the web width direction of the power supply device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrode 2 Power supply device 3 Power supply terminal 4 Insulator cover 5 Ground roll 6 Web 7 Uncovered part 8 Web edge end 9 Uncoated part

Claims (1)

[Claims] In an electric power supply device having an electrode and an earth roll sandwiching a running web, an insulator cover for protecting the earth roll is provided between the electrode and the earth roll. A heating device characterized by the above-mentioned.