JP7357986B1 - Electrostatic auxiliary coating method using a backing roll with internal electrodes capable of applying high voltage - Google Patents

Abstract

An object of the present invention is to provide a coating method for a wide web that enables stable coating at high speed and has excellent uniformity in coating thickness. [Solution] A method for coating a flexible plastic web with a coating solution involves transporting the web to a backing roll for coating, and applying a DC voltage to a part of the surface of the rotating backing roll to apply an electrostatic field of the backing roll. The process of passing the coating point while closely supporting the second surface of the web, and the electrostatic force generated by the coordination of charges of the same polarity as the DC voltage applied to the first surface of the web, the backing roll is provided with an outermost layer, an internal electrode layer, and an insulating layer in this order, and a predetermined voltage is applied to the internal electrode layer. The outermost layer is a ceramic material layer having a volume resistivity of 107 to 1013 Ωcm at 25 to 100°C. [Selection diagram] Figure 1

Description

The present invention applies a liquid composition, particularly a coating liquid consisting of a water-soluble composition, or In the process of applying multiple layers by curtain coating, bead coating, etc., electrostatic force is applied to the contact line where the coating liquid contacts the web (hereinafter referred to as the coating point) to coat the surface of the web (coating surface). The present invention relates to a method of increasing coating thickness uniformity and coating speed by preventing entrained air layers from becoming trapped between the coating solution and the web and promoting uniform wetting of the coating solution onto the web.

In addition, the present invention brings the back side of the web (backing roll side) into close contact with the backing roll surface to prevent an air layer accompanying the web back side and the roll surface from entering between the web and the roll. This invention relates to a method that makes it possible to raise the limit of web speed before running troubles such as fluctuations in tension and speed and oscillation occur.

INDUSTRIAL APPLICATION This invention is applied to the improvement of the coating method of a liquid composition, mainly a water-soluble composition, in the production of photographic film, photographic paper, magnetic recording tape, adhesive tape, pressure-sensitive/thermal recording paper, coated paper, etc. .

In curtain coating and bead coating, air layers accompany the front and back sides of a web that moves at high speed.

The thickness of these entrained air layers on the front and back sides increases with the speed of web movement, so when a certain threshold speed is reached, coating uniformity deteriorates or web slippage and oscillation occur. , stable coating will not be possible, and the coating speed will not be able to be increased beyond the respective limit speed. In order to maintain coating uniformity and increase coating speed, a method is needed that can simultaneously counteract the effects of entrained air layers on both the front and back sides of the web.

On the front side of the web, when the moving speed of the web increases and the entrained air layer increases beyond a certain limit, an air layer enters below the coating liquid transferred to the web at the coating point and is pushed out by the coating liquid. become unable to do so. If an air layer enters under the coating layer, it will prevent the coating solution from wetting the surface of the web and spread, or the air layer will be incorporated into the coating solution and form bubbles, reducing the uniformity of the coating layer. You won't be able to increase your speed.

Conventionally, in curtain coating and bead coating, when an electrostatic field is assisted at the coating point, the electrostatic force on ions and dipolar molecules in the coating liquid makes it possible to attract the coating liquid to the web surface and make it adhere to the web surface. It is well known to increase the upper limit of speed. Methods for assisting the electrostatic field at the coating point include 1) a method in which an electrostatic charge is applied to the web from a corona discharge electrode placed in a space, and then the web is passed through the coating point while being supported by a grounded coating backing roll; 2) 3) A method in which a DC voltage is applied to a conductive coating backing roll (hereinafter referred to as backing roll) insulated from the ground to form an electric field between the web surface and the coating liquid at the coating point, or 3) or a combination of these two. A method is disclosed.

For example, Patent Documents 1 to 4 disclose the method 1) of imparting an electric charge to a dielectric web such as polyester. A web of polarized dielectric material bound between its opposing back and front surfaces is supported on a grounded conductive backing roll surface and conveyed to a coating point. The remaining polar charge attracts the coating solution and acts to more forcefully eliminate the air layer below the coating solution, resulting in an increase in coating speed. Furthermore, in Patent Documents 5 to 7, a DC voltage is applied to a conductive backing roll insulated from earth to charge the surface thereof, and the web is supported on the surface and transferred to a coating point. Method 2) is disclosed, in which an electric field is applied between the coating liquids to bring the coating liquids into close contact with the web. Further, Patent Document 7 also discloses a method of combining 2) and 3).

The effect of imparting static charge to the web, or the effect of adding static electricity to the surface of the conductive backing roll, is a phenomenon in which an air layer accompanying the web is caught between the surface of the web and the coating liquid, making it impossible for the coating liquid to get wet. The aim is to suppress this and raise the critical speed at which coating transparency and thickness become non-uniform. In conventional electrostatic auxiliary coatings 1) to 3), the higher the adhesion of the coating liquid to the surface of the web, the more strongly the entrained air layer is eliminated. Alternatively, it is known that the higher the voltage on the backing roll surface, the higher the coating speed. However, in electrostatic auxiliary coatings in which voltage is applied to a conductive backing roll, if the applied voltage exceeds 1500V, spark discharge from the backing roll to peripheral equipment and short-circuit current penetrating the web are likely to occur. It has been known. In addition, in the method of imparting an electrostatic charge to the web, when the charged potential on the surface side of the web increases, the web is separated between the coating liquid and the surface of the conductive backing roll at pinholes in the web or in places where insulation resistance is low. Penetrating short circuit currents may occur. Therefore, the surface potential of the web due to the charged charges disclosed in Patent Document 1 is 1200V or less. In addition, for example, in Patent Document 4, the surface potential of the web was set lower than 700 to 800 V by combining the polarization effect of a coating liquid containing a surfactant, and in Patent Document 2, by combining the method of charging the web with a conductive brush. Although electrostatically assisted coating techniques are disclosed, the standard recommended surface potential is much lower, 400-500V. Thus, electrostatically assisted coatings using conventional conductive backing rolls are unable to apply sufficient electrical potential to the coating point, resulting in a critical speed limit before coating failure occurs due to increased entrained air. The effect of raising the

Furthermore, the back side of the web and the surface of the backing roll each have an air layer associated therewith. Therefore, the combined entrained air causes the web to float, and the flying height increases as the web speed increases. When the flying height of the web exceeds a certain limit, there is a problem that the conveyance of the web becomes unstable, and an increase in the entrained air layer on the back side of the web also causes the inability to increase the coating speed.

When the air temperature is 25°C, the flying height h (μm) of the web is: backing roll radius R (m), roller speed U _R (m/s), web speed U _W (m/s), web tension T ( N/m), it is given by the following equation (1).

(Kyo Hashimoto, “Basic Theory and Applications of Web Handling,” p. 73, published by the Processing Technology Research Group)

According to equation (1), the thickness of the entrained air layer caught between the back side of the web and the roll surface decreases as the web tension T increases, and increases as the roll radius R, web speed U _W or backing roll speed U _R increases. (Usually U _W ≒ U _R ).

In electrostatically assisted coating, where a voltage is applied to a conductive backing roll, as the web conveyance speed increases and the web floats due to the entrained air layer between the web and the backing roll, the distance from the backing roll surface to the front side of the web increases. is lengthened, and the air layer between the conductive backing roll and the back side of the web reduces capacitance. This reduces the amount of polar charge stored in the web and reduces the electrostatic force between the web and the coating liquid.

Additionally, if the thickness of the accompanying air layer on the back side of the web exceeds the sum of the surface roughness of the roll and the surface roughness of the back side of the web, the contact between the web and the backing roll surface will decrease, and the force that pulls the web will decrease. . As the web traction decreases, the web tension and speed begin to fluctuate, causing problems such as web meandering and scratches on the back side of the web. Therefore, in order to increase the coating speed, it is absolutely necessary to take measures against floating the web by using an entrained air layer sandwiched between the back side of the web and the backing roll.

The relationship between the web conveyance speed and the flying height calculated from equation (1) is shown in FIGS. 7 and 8. As shown in FIG. 7, it is possible to suppress floating of the web by increasing the web tension T. However, increasing web tension increases the load on the web transport system and increases the amount of deflection of the backing roll and guide rolls in the web transport path. Furthermore, if the web is thin, wrinkles are likely to occur, so there is a limit to how the web tension can be increased.

Further, as shown in FIG. 8, when the diameter of the backing roll is reduced, the flying height of the web is reduced. However, reducing the diameter of the backing roll reduces the rigidity of the roll and increases the amount of deflection. Furthermore, as the roll diameter decreases, the rotational speed of the roll increases accordingly, so the higher the web speed and the wider the web, the more the roll vibrates, causing a vibration pattern on the coating film. In roller curtain coating or bead coating for a wide web with a width of 1500 mm or more, the diameter of the backing roll is preferably 100 mm or more in consideration of ensuring the bending strength of the roll and the area required to install the coating head (applicator). The web tension depends on the strength and thickness of the web, but is usually around 75 to 300 N/m, taking into account elongation and deformation of the web. According to Fig. 7, when a backing roll with a diameter of 100 mm is used, even if the web tension is set to 150 N/m, the flying height of the web is already 6 μm at a moving speed of 100 m/min. The traction force decreases and tension and speed fluctuations occur. Judging from the web flying height shown in Figures 7 and 8, when the diameter of the backing roll is set to 100 mm or more, in order to increase the web conveyance speed to 100 m/min or more, air is required to be entrained on the back side of the web. The layer should prevent the web from floating.

In electrostatic auxiliary curtain coating in which a DC voltage is applied to a conductive backing roll having a diameter of 100 mm or more, a countermeasure against floating of the web due to an accompanying air layer on the back side of the web is disclosed in Patent Document 7. In Patent Document 7, in its example, circumferential grooves (groove depth 0.15 mm, width 0.43 mm, pitch 1 mm) are formed on the backing roll surface with a diameter of 200 mm at a ratio of 10 to 30% of the roll surface area. However, the accompanying air layer is discharged into the microgroove, thereby making it possible to suppress floating of the web and increase the conveyance speed. However, the voltage applied to the conductive backing roll is 800 V or less, and furthermore, the electrostatic auxiliary effect is reduced in the grooves, so coating unevenness is likely to occur. Therefore, the amount of increase in coating speed when microgrooves and electrostatic assistance are used together is 144 m/min at the maximum, which is not so large.

Patent No. 2835659 Special Publication No. 01-035702 Japanese Patent Application Publication No. 08-252517 Patent No. 2509316 Special Publication No. 06-009671 Special Publication No. 46-027423 US Patent No. 6177141

Masaru Hashimoto, “Basic Theory and Applications of Web Handling,” published by Machining Technology Research Group, p. 73

In curtain coating and bead coating, the front side (coating side) and back side (backing roll side) of the web moving at high speed are accompanied by an air layer on both sides, and the thickness of both sides depends on the movement of the web. Increases with increasing speed. However, the problems caused by the entrained air layer are different on the front and back sides. This is a phenomenon in which the coating liquid does not wet the web on the front side, but on the back side, the web floats due to the accompanying air layer that enters between the back side of the web and the backing roll, making the web running unstable. . There is a need for high-speed coating technology that can simultaneously address these different problems caused by entrained airflow on the front and back sides of the web.

By using a backing roll that can increase the voltage applied to the roll surface to 1.5 kV or more, preferably to about 3.5 kV, the dielectric web is more strongly polarized, and the contact line between the coating liquid and the web (coating point) Since the electric field between the web surface and the coating solution can be made much stronger than in conventional methods, the coating speed can be increased as needed simply by adjusting the applied voltage.

At the same time, the back side of the web, which is strongly polarized by the high voltage of the backing roll, is strongly attracted to the backing roll by the electric field caused by the positive charge on the backing roll surface, pushing out the accompanying air layer and adhering to the back roll surface, causing web running problems. It becomes possible to raise the critical speed before this occurs.

In order to achieve the above object, the present invention employs the following method.

In the process of applying a liquid composition (particularly a water-soluble composition) to a continuously running web supported by rolls, the present invention prevents spark discharge from occurring to peripheral equipment even when a DC high voltage of up to 6 kV is applied. To provide an electrostatic auxiliary coating method using a highly safe backing roll that does not generate short-circuit current in the web and does not cause electric shock even if a human body touches the roll surface. This backing roll uses highly insulating ceramics for the bottom layer, conductive metal for the internal electrode layer, and a high-resistance ceramic material layer for the outermost layer. A three-layer structure is formed on the roll surface. The internal electrode layer is completely electrically shielded from the core bar of the backing roll and peripheral equipment by the outermost layer and the bottom layer. Since the dielectric strength of the outermost and bottom layers is 6kV or more, spark discharge to peripheral devices and short-circuit current in the web are completely prevented even if a maximum DC high voltage of 6kV is applied to the internal electrode layer. Ru.

That is, the method of the present invention
(1) A method of applying a liquid composition by flowing a coating liquid from a grounded applicator onto a first surface of a continuously moving flexible plastic web having opposing first and second surfaces. And,
The web is conveyed along a path to a backing roll for coating, and a second surface of the web is brought into close contact with a part of the surface of the rotating backing roll to which a DC voltage is applied by an electrostatic field of the backing roll. passing through a coating point while supporting;
Applying the coating liquid to the first surface of the web by attracting the coating liquid at the coating point using an electrostatic force generated by coordination of a charge having the same polarity as the DC voltage applied to the backing roll on the first surface of the web. and a step of
The backing roll has an outermost layer that the web is in close contact with, a conductive monopolar internal electrode layer that is adjacent to the inner side of the outermost layer, and an insulating layer that is adjacent to the inner side of the inner electrode layer. The backing roll is configured to be able to apply a predetermined voltage to the internal electrode layer, and the outermost layer has a volume resistivity of 10 ⁷ to 10 ¹³ Ωcm at 25 to 100°C. a ceramic material layer, the surface of the backing roll is charged with a charge having the same sign as the voltage applied to the inner electrode on the outermost layer in a state where the predetermined voltage is applied to the inner electrode layer; The second surface of the web that is in contact with the outermost layer is brought into close contact with the outermost layer by the electrostatic force of the charge, and the coating liquid is brought into contact with the first surface of the web that is being rotated and transferred. and depositing it on the first surface of the web.

In the coating method,
(2) Apply a charge having a polarity opposite to the DC voltage applied to the internal electrode layer to a second surface of the web opposite to the second surface of the web before the coating liquid contacts the web during rotational transfer. Apply to the surface of 1,
(3) the DC voltage applied to the internal electrode layer is 0.3 to 6.0 KV;
(4) the diameter of the backing roll is 100 mm or more;
(5) At least one of the insulating layer, the internal electrode layer, and the outermost layer is made of a material formed by a thermal spraying method, or a material using an inorganic or organic binder. and at least one of the insulating layer, the internal electrode layer, and the outermost layer of the backing roll is subjected to a sealing treatment.
(6) The outermost layer is made of a ceramic material, and the ceramic material is alumina-based or zirconium oxide containing a compound selected from titanium oxide, chromium oxide, silicon oxide, manganese oxide, nickel oxide, and iron oxide. or magnesium oxide ceramics, or aluminum oxide ceramics containing 5 to 17% by weight of titanium oxide.
(7) The ceramic material includes at least one selected from aluminum nitride, silicon carbide, and silicon nitride, and an organic or inorganic binder.
(8) the outermost layer has a thickness of 50 to 500 μm;
(9) The centerline average surface roughness Ra of the outermost layer is 0.01 to 5 μm.
(10) The internal electrode layer is made of a conductive material containing tungsten or molybdenum.
(11) The thickness of the internal electrode layer is 5 to 50 μm.
(12) The insulating layer is an aluminum oxide-based, magnesium oxide-based, beryllium oxide-based, aluminum nitride-based material containing 2 to 4% by weight of aluminum oxide or titanium oxide, or a ceramic material containing silicon nitride, porcelain, and containing at least one highly insulating material selected from enamel;
(13) The volume resistivity value of the insulating layer is 10 ¹³ Ωcm or more,
(14) The thickness of the insulating layer is 50 to 500 μm.
It is characterized by

In the process of applying a liquid composition (particularly a water-soluble composition) to a continuously running web supported by rolls, the present invention prevents spark discharge from occurring to peripheral equipment even when a DC high voltage of up to 6 kV is applied. This is an electrostatic auxiliary coating method that uses a highly safe backing roll that does not generate short-circuit current in the web and does not cause electric shock even if a person touches the roll surface. This backing roll uses highly insulating ceramics for the bottom layer, conductive metal for the internal electrode layer, and a high resistance ceramic material layer for the outermost layer.The gap between the outermost layer/internal electrode layer/insulating layer is A three-layer structure is formed on the roll surface. The internal electrode layer is completely electrically shielded from the core metal of the backing roll and peripheral equipment by the outermost layer and the bottom layer. Since the dielectric strength of the outermost layer and the bottom layer is 6 kV or more, spark discharge to peripheral devices is completely prevented even if a maximum DC high voltage of 6 kV is applied to the internal electrode layer.

The volume resistivity of the high-resistance semiconductor ceramic that is the outermost layer is 10 ⁷ to 10 ¹³ Ωcm, so when a DC voltage is applied to the internal electrode, charges move from the internal electrode to the outermost surface, and the surface of the outermost layer Charged with the same polarity as the electrode. At the same time, the web that is in contact with the outermost surface of the backing roll is dielectrically polarized by the electric field of the internal electrode, and the internal electric dipole changes the back surface direction to a charge of opposite polarity to the internal electrode potential, and the front surface direction are arranged so that they have charges of the same polarity. Then, the coating liquid is attracted to the web surface by the electrostatic charge of the same polarity as the internal electrode arranged on the web surface side, and the air layer entrained on the web surface side is eliminated, and the coating liquid is Promote wetting the web. At the same time, charges of opposite polarity to the internal electrodes arranged on the back side of the web are attracted to free charges of the same polarity as the internal electrodes charged on the surface of the high-resistance semiconductor ceramic, which is the outermost layer of the backing roll. Adheres to the backing roll surface. In this way, in the present invention, the influence of the entrained air layer on both the front and back sides of the web is eliminated, making it possible to significantly increase the coating speed on the web.

According to the present invention, the following effects can be obtained.
1. A high DC voltage of up to 6 kV is applied to the internal electrodes installed on the outside surface of the backing roll to control the electrostatically assisted liquid flow without spark discharge to surrounding equipment or damage to the web due to short circuit currents. Coating of compositions (particularly water-soluble compositions) becomes possible.
2. While applying a high DC voltage to the internal electrode of the backing roll, at the same time an external auxiliary electrode is installed in the space above the front side of the web, and a DC voltage of 1.5 to 6 kV with the opposite polarity to the internal electrode is applied. , an electrostatically assisted coating that imparts a charge of opposite polarity to the internal electrode on the front side of the web is possible.
3. Even if the diameter of the backing roll is 100 mm or more, it is possible to completely adhere the web to the backing roll by the electrostatic force generated by the electrostatic charge on the surface of the high-resistance semiconductor ceramic on the outermost surface, and the electrostatic force on the web surface Auxiliary coating can be carried out effectively, swinging and slipping caused by floating of the web can be prevented, and the web conveyance speed can be increased to 400 m/min or more.
4. Since the diameter of the backing roll can be increased according to the length of the roll, the rigidity of the roll can be increased, making it easier to make the web wider.

FIG. 2 is a cross-sectional view showing an example of the method of the present invention for performing electrostatic auxiliary coating using only a backing roll to which a high voltage is applied to the internal electrodes. FIG. 2 is a diagram schematically showing the state of charge distribution in part A of FIG. 1. FIG. FIG. 2 is an external view of the method of the present invention viewed from an oblique direction. FIG. 6 is a cross-sectional view of a modified method of the present invention in which electrostatically assisted coating is performed using a backing roll with a high voltage applied to the internal electrode and a method of imparting an electrostatic charge to the web. FIG. 5 is a diagram schematically showing the state of charge distribution in part B of FIG. 4. FIG. FIG. 7 is an external view of a method according to a modified example of the present invention as viewed from an oblique direction. It is a graph showing changes in web flying height with respect to tension and web speed in a backing roll having a diameter of 200 mm. 2 is a graph showing changes in web flying height with respect to backing roll diameter and web speed at a web tension of 150 N/m.

1 to 3 illustrate the method of the invention. FIG. 2 schematically shows the state of charge distribution in section A shown in FIG.

(1) In order to increase the coating capacity, in addition to increasing the web conveyance speed, it is important to lengthen the backing roll and widen the web. However, when the web tension is constant, the amount of deflection of the roll increases rapidly when the backing roll is lengthened, so in order to prevent the backing roll from deflecting, it is necessary to simultaneously increase the diameter of the backing roll and increase the rigidity of the roll ( The amount of deflection of the roll is proportional to the cube of the roll length and inversely proportional to the fourth power of the moment of inertia (approximately proportional to the roll diameter). However, as shown in equation (1) above, when the roll diameter is increased, the entrained air layer on the back side of the web also increases proportionally. An increase in the entrained air layer lowers the upper limit of the web conveyance speed, making it impossible to increase the diameter of the backing roll and making it impossible to lengthen the roll. On the other hand, since the present invention can eliminate the influence of the entrained air layer on the back side of the web, it becomes possible to widen the web by increasing the diameter of the backing roll and the roll length as necessary. Judging from FIG. 8, the influence of the entrained air layer becomes significant when the diameter of the web conveyance roll becomes 100 mm or more, so the present invention is more effective when applied to a backing roll with a diameter of 100 mm or more. .

The internal electrode layer 3 of the backing roll 1 of the present invention is a conductive layer that is adjacent to the outermost layer 4 without any gap therebetween and is in contact with the outermost layer 4 . The internal electrode layer 3 is of a unipolar type, and is connected to a DC high-voltage power source 5 so that a DC voltage can be applied. It is completely insulated from the core metal 16.

Generally, there are two types of internal electrode layers 3, a monopolar type and a bipolar type, depending on the voltage application method. The monopolar type has only a single internal electrode, either positive (+) or negative (-), and a voltage is applied only between this single electrode with respect to the ground. A bipolar type is a method that has two or more internal electrodes with different polarities, but when the web that is the object to be attracted is connected to ground, electric charge (current) leaks to the ground side and electrostatic adsorption occurs. power becomes unstable. In the present invention, a monopolar type is used for the internal electrode layer 3. The internal electrode layer 3 is continuously and uniformly provided over a wider range than the width of the web 7 in the axial direction of the backing roll 1 and further over the entire circumference of the backing roll 1 in the rotational direction of the backing roll 1. . When the internal electrode 3 has a comb-like shape, a band shape, or a spiral shape, unevenness occurs in the coating layer. Note that the internal electrode layer 3 may not be formed at both end portions of the cylindrical surface of the backing roll 1 that are outside the support range of the web 7.

The outermost layer 4 is made of a high-resistance ceramic material, and has a volume resistivity of 10 ⁷ to 10 ¹³ Ωcm, more preferably 10 ⁸ to 10 ¹² Ωcm, at 25 to 100°C. In the field of dealing with static electricity, materials with a volume resistivity of 10 ¹³ Ωcm or more are classified as insulators because static electricity is difficult to move. Materials with a volume resistivity value lower than 10 ⁶ Ωcm are called electrostatic conductors, which allow static electricity to move easily and become equipotential when a voltage is applied. Materials with a volume resistivity value of 10 ⁷ to 10 ¹³ are classified as intermediate between conductors and insulators, and are classified as "electrostatic semiconductors." It is known that when a voltage is applied, a minute current flows, and free charges move to the surface and become electrically charged, just like in a conductor. The amount of this free charge depends on the applied voltage. Unlike conductive metal surfaces, on the surface of such high-resistance semiconductor ceramic materials, even when a high voltage of 3.5 to 6 kV is applied, a small current of about 0.001 to 10 μA/cm ² is generated locally. It only flows. Therefore, discharge due to free charges on the surface becomes a minute corona and does not develop into arc discharge, and no spark discharge is generated toward surrounding equipment.

In the present invention, as shown in FIG. 2, when a DC voltage is applied to the internal electrode layer 3, free charges 17 having the same polarity as the internal electrode 3 move to the surface of the outermost layer 4 and are charged. When the second surface 13 (back surface) of the web 7 comes into contact with the surface of the outermost layer 4, the dipole 18 inside the web 7 has a polarity opposite to that of the free charge 17 due to dielectric polarization caused by the electric field of the internal electrode. It is coordinated toward the surface of the outermost layer 4. The web 7 is brought into close contact with the surface of the outermost layer 4 by the electrostatic force between the charges 17 on the surface of the outermost layer 4 and the opposite charges of the dipoles coordinated on the second surface 13 of the web 7 . At this time, the first surface 12 (front side) of the web, which is the coating surface, is polarized and charged to have the same polarity as the internal electrode due to the electrostatic field of the internal electrode 3. This "polar charge" attracts the coating liquid toward the first surface 12 of the web 7 during rotational transfer, causing an entrained air layer to enter between the coating liquid 9 and the first surface 12 of the web 7. Therefore, it becomes possible to form a uniform coating layer 11 on the first surface 12 of the web 7. The higher the voltage applied to the internal electrode 3, the more the web 7 is dielectrically polarized and the amount of polar charge accumulated on the first surface 12 increases, and the electric field becomes stronger, making it possible to greatly increase the coating speed. .

(2) FIGS. 4 and 5 are side views showing an example of a modified method of the present invention. FIG. 5 schematically shows the state of charge distribution in section B of FIG. 4. In FIG.

In the method of the modified example of the present invention, in the same equipment configuration as the method of the present invention, a space auxiliary electrode 14 is additionally installed at a position upstream of the coating point, and a high voltage of opposite polarity to the internal electrode 4 is applied to corona. This is a method of generating electric discharge to charge the first surface 12 of the web 7 with free charges 19 having a polarity opposite to that of the internal electrode layer 3.

Since the outermost layer 4 of the backing roll 1 has a maximum withstand voltage of 6 kV and a volume resistivity of 10 ⁷ to 10 ¹³ Ωcm, there may be pinholes or places with weak insulation resistance in the web to which the charge 19 is applied. This also prevents short-circuit current from flowing from the coating liquid to the backing roll 1 at these defective locations. Therefore, it is possible to increase the amount of free charges 19 on the first surface 12 of the web 7 by raising the corona discharge potential of the external auxiliary electrode 14 installed in the space upstream of the coating point as necessary. possible, and it becomes possible to further increase the electrostatically assisted coating speed. The voltage applied to the external auxiliary electrode is DC (-) 3.5 to 6 kV, which is sufficiently effective, and if it is installed at an appropriate distance from peripheral devices, spark discharge will not occur.

Furthermore, due to the electrostatic force between the charge 17 on the surface of the outermost layer 4 and the charge 19 charged on the first surface of the web, the web 7 is even more strongly adhered to the surface of the outermost layer 4, and the web 7 is pushed to the back side of the web 7. This makes it possible to completely prevent the intrusion of accompanying airflow. Therefore, as the coating speed increases, the web conveyance speed can also be greatly increased as required.

(3) Since the web 7, which is the adsorbed object of the present invention, is flexible, there is no loose contact between the web 7 and the backing roll 1, and a uniform and strong adhesion force is required. be. In order to obtain the electrostatic force necessary for electrostatic adhesion of the web 7, a voltage of DC(+) 0.3 to 3.5 kV is usually sufficient to be applied to the internal electrode layer 3. The higher the applied voltage, the stronger the electrostatic auxiliary effect becomes, and when the applied voltage is 0.3 kV or less, the electrostatic force is insufficient. Since the maximum withstand voltage of the outermost layer 4 is 6 kV or more, spark discharge does not occur even if DC+3.5 kV is applied.

(4) At least one of the insulating layer 4, internal electrode layer 3, and outermost layer 2 of the backing roll 1 is made of a material formed by a thermal spraying method, or a binder of either an inorganic or organic type. These are the materials used, and at least one of them has been subjected to a sealing treatment.

Thermal spraying as used in the present invention refers to forming a coating by melting or softening the coating material by heating, accelerating it into fine particles, and colliding with the surface of the object to be coated, solidifying and depositing the flattened particles. It is a coating technology. There are various methods of thermal spraying, and they are classified according to the materials used, the type of heat source, etc., but atmospheric plasma spraying is particularly suitable for the present invention.

Further, when a thermal sprayed ceramic material is used for the outermost layer 4 and the outermost layer 2, it is preferable that at least one of the insulating layer 2, the internal electrode layer 3, and the outermost layer 4 is subjected to a sealing treatment. A thermal sprayed ceramic coating is a collection of flat thermal sprayed particles, but there are fine gaps between the thermal sprayed particles, forming interconnected pores corresponding to 3 to 10 Vol% of the total volume of the thermal sprayed coating. In a normal atmospheric environment, humid air or liquid permeates into these pores and water molecules are adsorbed on the inner walls of the pores, so the thermal sprayed coating has extremely low insulation resistance and withstand voltage. By impregnating thermal sprayed ceramics with an insulating sealant, connected pores disappear, the volume resistivity becomes stable, and the material becomes a ceramic material with high withstand voltage and excellent corrosion resistance. The sealing treatment after coating the ceramic material is a practical method that can be performed even on large backing rolls with a diameter of 200 mm or more used in actual machines. The materials used for the sealing treatment include low-viscosity silicone oligomers (e.g., viscosity 8-40 mPs, 25°C), low-viscosity epoxy resins (e.g., viscosity 80-400 mPs, 25°C), polyester resins, and inorganic coatings. A liquid sealing agent such as a lithium silicate aqueous solution to form or a metal alkoxide to form an inorganic sol can be used after diluting it with a solvent to lower its viscosity. In the case of the present invention, low-viscosity silicone oligomers and low-viscosity epoxy resins are preferred because they exhibit excellent impregnation properties, insulation performance, and voltage resistance properties. As for the thickness range of the sealing layer, it is preferable that the entire thermal sprayed layer is sealed. In this manner, it is important to infiltrate the pores of the thermally sprayed coating to seal the pores, and then heat and harden the pores to stabilize the volume resistivity and withstand voltage characteristics of the pore sealer. Unless the pores inside the sprayed coating are reliably sealed, neither the insulating layer 2 nor the outermost layer 4 can be adjusted to their original volume resistivity and withstand voltage.

The volume resistivity value of the outermost layer 4 after the sealing treatment at 25 to 100°C is 10 ⁷ to 10 ¹³ Ωcm, preferably 10 ⁸ to 10 ¹² Ωcm, and more preferably 10 ⁹ to 10 ¹² Ωcm. . If the volume resistivity value is smaller than 10 ⁷ Ωcm, it becomes impossible to prevent the occurrence of short circuit current or spark discharge to peripheral devices from the coating liquid connected to the ground through the web 7 in contact with the surface of the backing roll 1. . That is, if the volume resistivity value of the outermost layer 4 is less than 10 ⁷ , it is not preferable to perform electrostatic auxiliary coating in which a high voltage of 1.5 kV or more is applied to the surfaces of the back roll and web.

On the other hand, when the volume resistivity value of the outermost layer 4 exceeds 10 ¹³ Ωcm, the outermost layer 4 becomes an insulating dielectric, and substantially no free charge 17 flows from the internal electrode layer 3 . As a result, the surface of the outermost layer 4 cannot be charged with free charges 17 of the same polarity as the internal electrodes, which is not preferable. If the outermost layer 4 is a dielectric with insulating electrical properties, the dipole 18 is oriented so that the surface direction of the outermost layer 4 has the same polarity of charge as the inner electrode 3 due to dielectric polarization caused by the voltage of the inner electrode 3. do. Here, the electrification on the surface of the outermost layer 4 is due to charges fixed to dipoles, and cannot be neutralized and eliminated with free charges. When the web 7 leaves the backing roll, a reverse charge remains on the surface of the outermost layer 4 due to peel-off charging. When a voltage is applied to the backing roll, this reverse charge is trapped by the fixed charge at the dipole end of the outermost layer 4, and although the apparent charging potential decreases, it does not disappear and remains as it is. There is. When the surface of the outermost layer 4 becomes like this, the web 7 is repelled from the surface of the outermost layer 4. That is, if the outermost layer 4 has a volume resistivity higher than 10 ¹³ Ωcm, it becomes an insulating dielectric, and the peeled charge of the web remains on its surface without being neutralized. 4, and problems occur in the running of the web.

(5) The outermost layer 4 is made of a ceramic material, and the ceramic material is an alumina-based or zirconium oxide-based material containing a compound selected from titanium oxide, chromium oxide, silicon oxide, manganese oxide, nickel oxide, and iron oxide. Or magnesium oxide ceramics, or aluminum oxide ceramics containing 5 to 17% by weight of titanium oxide.

Preferred materials for the outermost layer 4 of the present invention are materials whose volume resistivity can be adjusted to 10 ⁷ to 10 ¹³ Ωcm and are easy to handle. In terms of adhesion and density with the internal electrode layer 2, stability of volume resistivity, and ease of handling, an aluminum oxide-based material containing 5 to 17% by weight, preferably 7 to 15% by weight of titanium oxide by thermal spraying is used. A ceramic material layer is best.

(6) In the same sense, in the present invention, the outermost layer 4 and the insulating layer 2 are preferably non-oxide ceramic material layers using an organic or inorganic binder by coating. The outermost layer 4 and the insulating layer 2 may be made of an organic binder such as polyimide, or an inorganic binder such as aluminum phosphate, water glass, silicon, etc., as long as the volume resistivity and withstand voltage can be ensured. Apply a coating material made of a ceramic material containing at least one selected from aluminum nitride, silicon carbide, and silicon nitride and an organic or inorganic binder blended to have a volume resistivity appropriate for the It may also be a coating layer formed by.

(7) The thickness of the outermost layer 4 is preferably 50 μm or more, more preferably 80 to 500 μm. The lower limit of this thickness is the minimum thickness necessary to ensure that there are no pinholes penetrating the outermost layer 4 to the internal electrode layer 3, and the minimum thickness necessary for stable adhesion of the web 7. The film thickness is such that it can withstand voltage against the applied voltage. The upper limit of this thickness is set in consideration of the maximum applied voltage. In order to obtain a stronger electrostatic auxiliary effect, a higher applied voltage is required, and it is necessary to increase the thickness of the outermost layer 4 to increase the withstand voltage. However, since a sufficient effect can be obtained with a voltage applied to the internal electrode layer of 3.5 kV, a maximum withstand voltage of 6 kV is sufficient in consideration of the safety factor. It is not preferable for the thickness of the outermost layer 4 to be greater than 500 μm, at which the withstand voltage can be obtained, because this only increases the spraying time.

(8) The surface roughness of the outermost layer 4 of the backing roll 1 of the present invention has a centerline average surface roughness Ra of 0.01 to 5 μm. A smooth surface of less than 0.01 μm is difficult to obtain using actual polishing techniques for ceramic layers. The greater the surface roughness of the outermost layer 4, the more stable the running of the web at high speeds, but if it exceeds 5 μm, the surface roughness of the outermost layer 4 will be transferred to the back surface of the web, which is not preferable.

(9) As the material for the internal electrode layer 3, sintered conductive pastes such as tungsten, molybdenum, high-performance activated carbon, copper, and silver can be used. It has a high efficiency and is also easy to handle.

(10) Since the volume resistivity value of the outermost layer 4 is as high as 10 ⁷ to 10 ¹³ Ωcm, even when a high voltage of 6 kV is applied to the internal electrodes, the total current flowing from the internal electrodes to the web surface is extremely low, at a few mA or less. Therefore, a thickness of 5 to 50 μm is sufficient for the internal electrode layer 3, and it is preferable that the internal electrode layer 3 be as thin as possible in order to smooth the boundaries at both ends of the roll.

(11) Highly insulating materials for the insulating layer 2 include ceramic sprayed coatings such as high-purity alumina of 99.6% or more or alumina containing 2 to 4 wt% titanium oxide, magnesium oxide, beryllium oxide (BeO), and aluminum nitride. A coating material made of a ceramic material selected from (AlN) series, silicon nitride (Si3N4) series, etc. is preferable. In addition, polymer resins selected from polyimide, polyphenylene oxide, polytetrafluoroethylene (Teflon (registered trademark)), polytrifluorochloroethylene, polyethylene, polypropylene, polystyrene, etc., SiO2-based glass such as porcelain, and enamel. However, in the case of the present invention, a ceramic sprayed coating made of 99.6% or more high-purity alumina or alumina containing 2 to 4 wt% titanium oxide is preferred due to insulation performance, thermal conductivity, ease of handling, price, etc. Most preferred.

(12) The volume resistivity value of the insulating layer 2, which is the innermost layer in contact with the core metal 16 of the backing roll 1 of the present invention, is preferably 10 ¹³ Ωcm or more. This is to reduce the leakage current from the internal electrode layer 3 to the core metal 16 via the insulating layer 2 to a level that has no effect.

(13) The thickness of the insulating layer 2 is preferably 50 to 500 μm; if it is less than 50 μm, the withstand voltage is insufficient to apply the minimum voltage of 0.3 kV to the internal electrode layer 3 to obtain the necessary adhesion. Run short. In order to make it possible to apply a voltage of up to 6 kV to the internal electrode layers, it is desirable that the dielectric strength of the insulating layer 3 is 6 kV or more, but a thickness of 500 μm is sufficient for this dielectric strength.

(14) The web used in the present invention includes 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 6,6-nylon and 6-nylon, polyethylene terephthalate, polyethylene-2, Polyesters such as 6-naphthalate, polycarbonates, cellulose acetates such as cellulose triacetate, cellulose diacetate, etc. are used. Further, the resin used for resin-coated paper is typically polyolefin such as polyethylene, but is not necessarily limited thereto. The web can have one or several layers previously coated.

(15) Furthermore, the term "coating liquid" includes liquid compositions of various types depending on the application, such as photosensitive emulsion layers, undercoat layers, protective layers, backing layers, and antistatic layers of photographic light-sensitive materials. Or it can be used to form an ink absorbing layer in the case of an inkjet receiving medium, such as an antihalation layer. Magnetic layers, undercoat layers, lubricating layers, protective layers, back layers, adhesive layers, colored layers, anti-rust layers, etc. of magnetic recording media. These coating solutions can contain water-soluble binders or organic binders.

(16) Surfactants can be used to modify the surface tension and coating suitability of coating solutions. Surfactants include nonionic surfactants such as polyalkylene oxides and water-soluble adducts of glycidol and alkylphenols, anionic surfactants such as alkylaryl polyether sulfates and sulfonates, arylalkyl taurines, N-alkyl and N Amphoteric surfactants such as -acyl β-aminopropionates, saponins, alkylammonium sulfonate betaines, etc. can be used.

(17) A thickener can be used in the coating liquid to adjust the viscosity.

(17) Coating applicators to which the present invention is applicable are bead coating applicators, curtain coating applicators, extrusion coating applicators, and slide extrusion coating applicators.

[Measuring method]
The method for measuring physical property values used in the present invention is as follows.

1. Center line average roughness Ra
To measure the surface roughness of the backing roll, the average roughness Ra of the surface was actually measured using a portable surface roughness meter when measurement was possible in the roll state. The measuring device was in accordance with JISB0651, and the stylus had a conical shape with an apex angle of 60 degrees, and the radius of curvature of the spherical tip was 2 μm.The measurement method was in accordance with JISB0601-2013, with a cutoff value of 0.8 mm. to determine the center line average roughness Ra. The measurement was carried out using a Surfcoder SE1700α manufactured by Kosaka Institute Co., Ltd. as a measuring instrument.

2. Volume resistivity value The volume resistivity value of the outermost layer 4 on the surface of the backing roll 1 is measured according to the test method for electrically insulating ceramic materials JISC2141-1992. Cut out a main electrode with an outer diameter of 26 mm and a guard electrode with an outer diameter of 48 mm and an inner diameter of 38 mm from a conductive adhesive sheet. Paste so that they form concentric circles. A conductive wire with a conductive wire terminal attached with conductive adhesive tape is used as a contact point on the surface of the main electrode and the guard electrode. The internal electrode layer 3 of the backing roll is used as the counter electrode. For the measurement, the value taken 1 minute after the start of the measurement is adopted. A super insulation meter R-503 manufactured by Kawaguchi Electric Seisakusho was used as a measuring instrument. A DC voltage of 500 V is applied between the main electrode, internal electrode layer 3, and guard electrode, and the volume resistance R _V is determined from the current value I (A) flowing through the main electrode and counter electrode (internal electrode layer 3) at that time. (=V/I) and calculate the volume resistivity value _ρV using the following formula.

ρ _V (Ωcm)=R _V ×A/d
A=π×D ² /4
here,
V: Applied voltage (V)
R _V : Volume resistance (Ω)
ρ _V : Volume specific resistance value (Ωcm)
A: Area of main electrode (cm ² )
D: Main electrode outer diameter (cm)
d: Outermost layer thickness (cm)
Note that the thickness d is measured using a magnetic or eddy current thickness gauge. As a measuring instrument, a magnetic/eddy current film thickness meter FMP20 manufactured by Fisher Instruments Co., Ltd. was used.

(Example 1)
In the method shown in FIG. 1, the web 7 was continuously conveyed to the backing roll 1, and a DC voltage was applied only to the internal electrode 3 of the backing roll to carry out electrostatic auxiliary curtain coating according to the method of the present invention.

The backing roll 1 used here was manufactured as follows.

After sandblasting, an 80 wt% Ni/20 wt% Cr alloy with a thickness of 50 μm is applied to the entire surface of the body of the cylindrical core metal 16, which is made of steel and has a diameter of 200 mm, as a bonding layer to improve the adhesion of the ceramic layer. Laminated by plasma spraying. Subsequently, on the surface of the bonding layer, aluminum oxide (alumina) (99.6 wt% Al ₂ O ₃ ) as a highly insulating material was laminated to a thickness of 250 μm by plasma spraying, and then the sprayed alumina layer was sealed with a low-viscosity epoxy resin. Thus, an insulating layer 2 having a volume resistivity value of 10 ¹⁴ Ωcm or more was formed. Tungsten (W) having a thickness of 30 μm was laminated on the insulating layer 2 by plasma spraying to form the internal electrode layer 3. At this time, masking was performed to a width of 20 mm from both ends of the backing roll 1 in the width direction, so that the internal electrode layer 3 was not formed in this range. After removing the masks at both ends, both ends and the upper surface of the internal electrode layer 3, that is, the entire cylindrical surface of the backing roll 1, contain 10 wt% titanium oxide (TiO ₂ ), and the remaining 90 wt% contains alumina (Al ₂ O ₃ ) was laminated by plasma spraying to a thickness of 400 μm as the outermost layer 4. Similarly, the alumina ceramic material layer and the tungsten layer of the internal electrode layer 3 were sealed with a low-viscosity epoxy resin to obtain the outermost layer 4 having a volume resistivity value of 5.6×10 ¹⁰ Ωcm.

After the sealing treatment, the outermost layer 4 was polished with a diamond grindstone so that the residual thickness was 300 μm and the surface roughness Ra after polishing was 0.05 μm. In order to enable electrical connection to the internal electrode layer 3, when spraying the outermost layer 4, a rectangular area of 20 mm x 30 mm was masked at one end of the roll, and after the outermost layer 4 was sprayed, the internal electrode layer 3 was A width of 20 mm x 10 mm was exposed at the end of the roll. A slip ring 6 was connected to the exposed internal electrode layer 3. A DC high voltage power supply 5 was connected to the slip ring 6, and a DC voltage (+) of 3.5 kV was applied to the internal electrode 3. Here, even if the surface of the outermost layer 4 was touched with a finger while a voltage was applied to the internal electrodes, no current felt by the human body flowed.

The web 7 is a polyethylene terephthalate film with a thickness of 100 μm, and has a gelatin undercoat layer with a thickness of 0.3 μm formed thereon. The web 7 is heated in advance in a heating furnace at a temperature of 90 to 100°C, and the back and front surfaces are alternately brought into contact with a roll connected to earth to remove the charge until the surface potential becomes ±50V or less, and then cooled to 25°C. did.

The curtain height of the coating liquid 9 is 10 cm, the coating angle is 30° forward from the top of the roll, the tension of the web 7 is 150 N/m, and the conveyance speed of the web 7 is 400 m/min, so that the thickness of the wet coating layer 11 is 60 μm. A gelatin composition was applied to the surface. The coating liquid used was a 15% aqueous gelatin solution containing 0.1% dodecyl benzene and sodium sulfonate, the low shear viscosity was adjusted to 100 mPa・s using a thickener, and the flow rate of the coating liquid was set per 1 cm of coating width. It was set at 4cc/sec.

The back surface 12 of the web 7 was in close contact with the surface of the backing roll 1, and the running of the web was stable. The coating could be maintained without any coating failure caused by the air layer accompanying the surface of the web 7 getting caught under the coating liquid, and the wet coating layer 11 had good thickness uniformity and a smooth surface. . There was no spark discharge from the back roll to the surroundings, and no short-circuit current passing through the web 7 from the coating liquid 9 toward the roll surface.

(Comparative example 1)
When coating is performed with the voltage applied to the internal electrode 3 being 0 (zero) under the same configuration and conditions as in Example 1, the curtain of the coating liquid 9 alone cannot eliminate the entrained air layer, and the coating liquid covers the surface of the web 7. Uniform application was impossible because it did not get wet with 12. Further, since the web 7 floated up from the backing roll, the pulling force of the web 7 by the backing roll 1 decreased, the tension and speed of the web 7 fluctuated, and the running became unstable, so that the coating could not be maintained.

(Example 2)
In the same coating apparatus as in Example 1, the web 7 was conveyed to the backing roll 1 with a diameter of 200 mm, the voltage applied to the internal electrode 3 was set to +3.5 kV, and the tungsten wire electrode 14 with a diameter of 0.5 mm was used as shown in FIG. is additionally installed at a distance of 10 mm from the web, and a voltage of -3 kV is applied to attach a negative charge (-) from the electrode 14 to the first surface of the web 7. Electrical auxiliary curtain coating was performed.

The web 7 is a polyethylene coated paper having a thickness of 100 μm, and has a gelatin undercoat layer having a thickness of 0.6 μm formed thereon. The web 7 is heated in advance in a heating furnace at a temperature of 90 to 100°C, and the back and front surfaces are alternately brought into contact with a roll connected to earth to remove the charge until the surface potential becomes ±50V or less, and then cooled to 25°C. It has been done.

The gelatin composition was coated to a wet thickness of 35 μm at a curtain height of 10 cm, a coating angle of 30° forward from the apex of the roll, a web 7 tension of 150 N/m, and a web conveyance speed of 400 m/min. Coating solution 9 was a 12% gelatin aqueous solution to which 0.1% dodecyl benzene sodium sulfonate was added, the low shear viscosity was adjusted to 21 mPa·s using a thickener, and the flow rate of the coating solution was set to a coating width of 1 cm. It was set at 2.3 cc/sec. The second surface 13 of the web 7 was in close contact with the surface of the backing roll 1, and the running was stable. The first surface 12 of the web 7 can stably maintain the coating without causing any coating failure due to the entrainment of the accompanying air layer into the coating solution, and the wet coating layer 11 has good thickness homogeneity and surface smoothness. Met. There were no spark discharges or glow discharges from the back roll to the surroundings, and no short-circuit current passing through the web 7 from the coating liquid 9 toward the roll surface.

(Comparative example 2)
When coating is performed with the voltage applied to the internal electrode 3 at 0 (zero) under the same configuration conditions as in Example 2, the coating liquid 9 forms a wet coating layer 11 that is in close contact with the entire first surface 12 of the web. I was able to do it. However, since an entrained air layer entered between the back surface 13 of the web and the backing roll and the web 7 floated, the tension and speed of the web 7 became unstable and swayed, making the running unstable and the surface smooth. It was not possible to sustainably form a wet coating layer 11.

1 Backing roll 2 Insulating layer 3 Internal electrode (+)
4 Outermost layer 5 DC high voltage power supply (for internal electrodes)
6 Slip ring 7 Band-shaped support (web)
8 Applicator (application head)
9 Coating liquid curtain 10 Coating liquid contact line (coating point)
11 Wet coating layer 12 Web first surface (surface)
13 Web second side (back side)
14 Spatial auxiliary electrode (-)
15 DC high voltage power supply (for space auxiliary electrode)
16 Roll core metal 17 Free charge (+)
18 Dipole inside the web 19 Surface charge (-)

Claims (14)

A method of coating a first surface of a continuously moving flexible plastic web having opposing first and second surfaces by discharging a coating solution comprising a liquid composition from a grounded applicator, the method comprising: ,
The web is conveyed along a path to a backing roll for coating, and a second surface of the web is brought into close contact with a part of the surface of the rotating backing roll to which a DC voltage is applied by an electrostatic field of the backing roll. passing through a coating point while supporting;
Applying the coating liquid to the first surface of the web by attracting the coating liquid at the coating point using an electrostatic force generated by coordination of a charge having the same polarity as the DC voltage applied to the backing roll on the first surface of the web. and a step of
The backing roll has an outermost layer that the web is in close contact with, a conductive monopolar internal electrode layer that is adjacent to the inner side of the outermost layer, and an insulating layer that is adjacent to the inner side of the inner electrode layer. The backing roll is configured to be able to apply a predetermined voltage to the internal electrode layer, and the outermost layer has a volume resistivity of 10 ⁷ to 10 ¹³ Ωcm at 25 to 100°C. The surface of the backing roll is a ceramic material layer, and when the predetermined voltage is applied to the internal electrode layer, the outermost layer is charged with a charge having the same sign as the voltage applied to the internal electrode layer . , the second surface of the web that is in contact with the outermost layer is brought into close contact with the outermost layer by the electrostatic force of the charge, and the coating liquid is attracted to the first surface of the web that is being rotated and transferred; A method of application, characterized in that it is brought into contact and deposited on a first surface of the web. A charge having a polarity opposite to the DC voltage applied to the internal electrode layer is applied to a first surface of the web opposite to the second surface of the web before the coating liquid contacts the web during rotational transfer. The coating method according to claim 1, wherein the coating method is applied to The coating method according to claim 1, wherein the DC voltage applied to the internal electrode layer is 0.3 to 6.0 KV. The coating method according to claim 1, wherein the backing roll has a diameter of 100 mm or more. At least one of the insulating layer, the internal electrode layer, and the outermost layer is a material formed by a thermal spraying method, or a material using an inorganic or organic binder, and the The coating method according to claim 1, wherein at least one of the insulating layer, the internal electrode layer, and the outermost layer of the backing roll is subjected to a sealing treatment. The outermost layer is made of a ceramic material, and the ceramic material is an alumina-based or zirconium oxide-based material containing a compound selected from titanium oxide, chromium oxide, silicon oxide, manganese oxide, nickel oxide, and iron oxide. The coating method according to claim 1, wherein the coating method is a magnesium ceramic or an aluminum oxide ceramic containing 5 to 17% by weight of titanium oxide. 1 . The outermost layer is made of a ceramic material, and the ceramic material includes at least one selected from aluminum nitride, silicon carbide, and silicon nitride, and an organic or inorganic binder. Application method described in. The coating method according to claim 1, wherein the outermost layer has a thickness of 50 to 500 μm. The coating method according to claim 1, wherein the outermost layer of the backing roll has a centerline average surface roughness Ra of 0.01 μm to 5 μm. The coating method according to claim 1, wherein the internal electrode layer is made of a conductive material containing tungsten or molybdenum. The coating method according to claim 1, wherein the internal electrode layer has a thickness of 5 to 50 μm. The insulating layer is selected from aluminum oxide, aluminum oxide containing 2 to 4% by weight of titanium oxide, magnesium oxide, beryllium oxide, aluminum nitride, or a ceramic material containing silicon nitride, porcelain, and enamel. 2. The coating method of claim 1, comprising at least one highly insulating material. The coating method according to claim 1, wherein the volume resistivity value of the insulating layer is 10 ¹³ Ωcm or more. The coating method according to claim 1, wherein the insulating layer has a thickness of 50 to 500 μm.