EP3706515A1

EP3706515A1 - Web manufacturing method, charge control method, and charge control device

Info

Publication number: EP3706515A1
Application number: EP18871897.7A
Authority: EP
Inventors: Masato Okuno; Mitsuru Watanabe
Original assignee: Toray Industries Inc
Current assignee: Toray Industries Inc
Priority date: 2017-10-30
Filing date: 2018-10-29
Publication date: 2020-09-09
Anticipated expiration: 2038-10-29
Also published as: JP7347213B2; EP3706515A4; WO2019088052A1; JPWO2019088052A1; CN111512704A; EP3706515B1

Abstract

The purpose of the present invention is to manufacture a charge amount-controlled web without providing the web, such as an elongated polymer film, with an advance charge. Provided is a web manufacturing method comprising a transfer step of transferring a web, wherein a liquid is supplied to the interface of a transfer roll transferring the web and the web, and a charge amount on a surface of the web due to frictional charging between the transfer roll and the web is controlled. The liquid includes, for example, a liquid that produces, between the transfer roll and the web, a frictional charge of the opposite polarity from the charge polarity produced on the surface of the web due to frictional charge between the transfer roll and the web.

Description

Technical Field

The present invention relates to a method for manufacturing a web with a controlled amount of charge, a charge control method and charge control device that control the amount of charge on the web.

Background Art

In general, static electricity is generated when two substances rub against each other, causing one of the two substances to be relatively positively charged and the other to be relatively negatively charged. In general, the tendency of a substance to be positively or negatively charged when it rubs against another substance is common as triboelectric series for each substance, and by referring to the triboelectric series, it is possible to estimate a substance to be positively charged between two substances when frictional electrification is generated between the two substances. An example of triboelectric series is given in Non-Patent Literature 1.
For example, when a web such as a long-length polymer film is conveyed, the web is moved by rotating the conveying roller while supporting the web by the conveying roller, and this movement also generates static electricity between the web and the conveying roller, causing the surface of the conveyed web to be charged. When the amount of charge on the surface of the web increases, peeling discharge may occur between the web and the conveying roller at the position where the web being conveyed by the conveying roller separates from the conveying roller (called the roller separating point). This results in the formation of discharge marks on the surface of the web, which is a defect in the web. For example, when a web is subjected to a coating treatment, the discharge marks cause uneven coating. In addition, even if peeling discharge does not occur, there is a problem that various dust particles easily adhere to the charged surface.
There is a technology using a static eliminator that generates ions in the air to neutralize the charge on the surface of the web. However, in the case where a static eliminator is used, a space for the static eliminator is required, and depending on the structure around the conveying rollers, it may not be possible to install the static eliminator. Since a static eliminator generates ions by discharge, it is not possible to place the static eliminator in an environment in which explosion protection is required. In addition, in the case where the conveying speed of the web is large or the distance from the roller separating point to the static eliminator is large, the static elimination capacity may be insufficient and the static elimination may not be performed sufficiently. In addition, since the conveying rollers are generally made of metals and are electrically conductive, the ions for static elimination are absorbed by the conveying rollers, resulting in decrease in static elimination capability. In the case where the surface of the web is not uniformly charged but is charged unevenly, the apparent charging potential is low and the static elimination may not be sufficiently performed.
Patent Literature 1 discloses that a material that is positively charged by frictional electrification with the web and a material that is negatively charged by frictional electrification with the web are alternately arranged in a conveying direction of the web to constitute conveying rollers, so that the web is not apparently charged in the broad sense.
Patent Literature 2 discloses that an electric charge opposite in polarity to the frictional charge is imparted to a surface opposite to a surface charged by friction in a web, and the electric charge opposite in polarity neutralizes the electric charge of the frictional charge.
Patent Literature 3 discloses that an electric charge opposite in polarity to the charge by frictional electrification is given to the surface of the web which comes into contact with the roller in advance before the web comes into contact with the roller.

Citation List

Patent Literature

Patent Literaute 1: JP S62-131500 A
Patent Literature 2: Japan Patent No. 5885869
Patent Literature 3: JP H10-15812 A

Non-Patent Literature

Non-Patent Literature 1: Akinari Kasai, "Various Factors Influencing Charging Measurements," Journal of Polymer Science, The Society of Polymer Scienc, 1967, Vol. 16, No. 179, p. 323-329.

Summary of Invention

Technical Problem

However, in the technology of Patent Literature 1, there is still a risk of peeling discharge because the web is charged at the microscopic level, and it is difficult to actively control the amount of charge on the surface of the web.
In the method of Patent Literature 2, although the sum of the amount of charge on both sides of the front and back is zero and appears to be uncharged, there is actually an electric charge on each side, which causes, for example, uneven coating in the coating process, which is a later process. If one side of the web is contacted with the metal roller and is grounded under the state that there are electric charges on both sides of the web, the potential occurs due to the electric charge on the other side and the web may attract dust particles existing in the air.
In the method of Patent Literature 3, the web before contacting the roller has a high potential, so the web may absorb dust particles or cause discharge when it comes into contact with the roller.
As described above, there are cases where the technology using a static eliminator among the technologies for preventing charging in the webs conveyed by the conveying rollers cannot be applied, and there is a possibility that the static eliminator capacity may be insufficient. The technology described in Patent Literature 1 may not sufficiently prevent peeling discharge. The technologies described in Patent Literatures 2 and 3 have problems such as adsorption of dust particles or generation of discharge due to the charge imparted, although the technologies are designed to impart a charge opposite in polarity to the charge caused by frictional electrification in advance. It can be said that prevention of charging the web is one aspect of controlling the amount of charge on the web, but any general technology of controlling the amount of charge on the web by methods other than the method of imparting a charge is not known.
An object of the present invention is to provide a method for manufacturing a web in which the amount of charge is controlled without imparting a charge to the web in advance, and a charge control method and charge control device that control the amount of charge of the web.

Solution to Problem

The method for manufacturing a web in the present invention is directed to a method for manufacturing a web including a conveying step of conveying a web, the method including a step of supplying a liquid to an interface between the web and a conveying roller that conveys the web to control an amount of charge generated on a surface of the web by frictional electrification between the conveying roller and the web.
The charge control method in the present invention is directed to a charge control method for controlling an amount of charge on a web conveyed by a conveying roller, the charge control method including supplying a liquid to an interface between a web and a conveying roller that conveys the web to control an amount of charge generated on a surface of the web by frictional electrification between the conveying roller and the web.
The charge control device in the present invention is directed to a charge control device for controlling an amount of charge on a web to be conveyed, the charge control device including a conveying roller configured to convey the web, and a supplying means of supplying a liquid to an interface between the conveying roller and the web, wherein the amount of charge generated on a surface of the web by frictional electrification between the conveying roller and the web is controlled by the liquid.
Frictional electrification can occur not only between solids, but also between solids and liquids. In the present invention, in order to control the amount of charge on the surface of the web after being conveyed by the conveying roller, a liquid for controlling the amount of charge is supplied to the interface between the web and the conveying roller that conveys the web. The amount of charge generated on the surface of the web can be controlled by controlling the amount of the liquid supplied to the interface. Since frictional electrification occurs between the web and the liquid as well, the amount of charge on the surface of the web can be controlled by combining frictional electrification between the web and the conveying roller with frictional electrification between the web and the liquid. In particular, the use of a liquid capable of generating a frictional charge between the web and the liquid, the frictional charge being opposite in polarity to the charge generated on the surface of the web by frictional electrification between the conveying roller and the web, can reduce the charge on the surface of the web or prevent charging on the surface of the web. The kind of the liquid to be used can be determined based on the aforementioned triboelectric series, depending on the material of the web and the material of the surface of the conveying roller. In addition, when the amount of the liquid supplied to the interface between the conveying roller and the web is changed, the magnitude of the frictional charge between the web and the liquid changes, so the amount of the charge on the web can be controlled more precisely by controlling the amount of the liquid supplied to the interface.
In the present invention, the web is, for example, a long-length polymer film or an electrically insulating film. As a method of supplying the liquid to the interface between the conveying roller and the web, the liquid may be supplied directly to the interface from the direction of entry of the web with respect to the interface, or the liquid may be sprayed towards the surface of the rotating conveying roller. The liquid sprayed on the surface of the conveying roller is supplied to the interface between the conveying roller and the web by rotating the conveying roller. As to the method of supplying the liquid, in the case of supplying the liquid by spraying, the amount of the liquid consumed can be reduced and the amount of the liquid supplied can be precisely controlled, as compared with the case of supplying the liquid directly to the interface. In addition, in order to control the amount of charge in the width direction of the web (direction orthogonal to the conveying direction), the conveying roller may be divided into a plurality of regions along the longitudinal direction of the conveying roller, and the amount of the liquid to be supplied may be controlled in each of the divided regions.

Advantageous Effects of Invention

In the present invention, it is possible to manufacture a web in which the amount of charge is controlled without imparting a charge to the web in advance, and it is also possible to control the amount of charge on the web.

Brief Description of Drawings

FIG. 1 is a diagram showing a configuration of the charge control device in an aspect of the present invention.
FIG. 2 is a diagram showing a configuration for controlling the amount of charge of web having a large width.

Description of Embodiments

Next, embodiments of the present invention are described with reference to the drawings. FIG. 1 shows the charge control device in an aspect of the present invention. This charge control device is used for manufacturing a web by the manufacturing method in the present invention.
The charge control device shown in FIG. 1 is configured to be used in the step of conveying the web 10, and includes a conveying roller 20 that conveys the web 10, and a spray nozzle 30 disposed so as to face the surface of the conveying roller 20 at a position opposite to the position where the conveying roller 20 contacts the web 10.
The web 10 may be, for example, a film for magnetic recording tapes, a film for mold release, a film for capacitors, a film for battery separators, or the like, and is not limited to these. In particular, in the case of the film for magnetic recording tapes, the film for mold release, or the film for battery separator, it is effective from the viewpoint of preventing uneven coating when the final product is obtained through a coating process. It is also effective in preventing the adhesion of dust particles or the like due to static electricity in the case of the film for battery separator, which requires strict control of foreign substances.
In the embodiment of the present invention, the conveying step includes at least one rotating conveying roller, and is a step of conveying a web by utilizing the frictional force generated between the conveying roller and the web in a state where the conveying roller and the web are in contact. Another rotating roller may be installed before and after the aforementioned conveying roller(s) and the web may be conveyed, or the ends of the web may be grasped by a running clip or the like, and the web may be conveyed.
The spray nozzle 30 is an atomizer that sprays a liquid b for charge control on the rotating conveying roller 20, and functions as a supplying means of supplying the liquid b for charge control to the interface between the conveying roller 20 and the web 10. In other words, the supplying means may be an atomizer that sprays a liquid on a rotating conveying roller. The liquid b for charge control is supplied to the spray nozzle 30, and compressed air a is also supplied thereto for spraying the liquid b for charge control. The spray nozzle 30 is covered with a nozzle cover 40 in order to prevent the liquid b for charge control from splashing at an unintended position. The nozzle cover 40 has a slit 41 extending in the longitudinal direction of the conveying roller 20 at a position facing the conveying roller 20, and the liquid b for charge control sprayed from this spray nozzle 30 passes through this slit 41 and reaches the conveying roller 20. The width of the slit 41 (length along the direction of rotation of the conveying roller 20) is adjustable within the range of, for example, 10 mm to 30 mm, and the gap between the position of the slit 41 and the surface of the conveying roller 20 is, for example, about 2 mm. One spray nozzle 30 can spray the liquid over an area of, e.g. about 30 cm in the longitudinal direction of the conveying roller 20.
Furthermore, in the charge control device shown in FIG. 1, an electrometer 50 is arranged at a position downstream of the conveying roller 20 in the conveying direction of the web 10 to measure the surface potential of the surface of the web 10 with which the conveying roller 20 is contact. Although the electrometer 50 is not essential, as is clear from the Examples described below, the surface potential of the web 10 changes depending on the supply amount of the liquid b for charge control and the amount of charge changes, so that the amount of charge of the web 10 can be more precisely controlled by providing the electrometer 50 and controlling the supply amount of the liquid b for charge control based on the measured value. The surface of the web 10 conveyed downstream from the conveying roller 20 may be wet with the liquid b for charge control, and this liquid b for charge control can be removed by, for example, air blowing, heating drying, scraping off with a nip roller, or the like.
Next, the control method of the amount of charge by using this charge control device is described. When the web 10 is conveyed by rotating the conveying roller 20 while spraying the liquid b for charge control from the spray nozzle 30 toward the conveying roller 20, the sprayed liquid b for charge control is continuously supplied to the interface between the web 10 and the conveying roller 20. As a result, frictional electrification occurs between the conveying roller 20 and the web 10, and frictional electrification also occurs between the supplied liquid and the web 10. In the case where these two frictional charges are of the same polarity with respect to the web 10, the absolute value of the surface potential of the web 10 increases and the amount of charge on the web 10 increases. In the case where these frictional charges are opposite in polarity, the electric charge by frictional electrification between the conveying roller 20 and the web 10 is neutralized by frictional electrification between the liquid b for charge control and the web 10, and when the frictional charge between the liquid b for charge control and the web 10 is of an appropriate degree, these charges are canceled each other and the amount of charge on the web 10 becomes extremely small. Therefore, in the charge control device in the present embodiment, the amount of the charge on the web 10 can be controlled, and in particular, the amount of the charge on the web 10 can be reduced to almost zero by using the liquid b for charge control capable of generating a frictional charge between the web and the liquid, the frictional charge being opposite in polarity to the charge generated on the surface of the web by frictional electrification between the conveying roller and the web, and controlling the supplied amount of the liquid b.
What liquid is used as the liquid b for charge control can be determined based on the triboelectric series, depending on the target charge amount, the material of the web 10, and the material of the surface of the conveying roller 20, but it is preferable to select a liquid that does not change the properties of the web 10. For example, in the case where the web 10 is a polyethylene film, as the surface material of the conveying roller 20 that tends to generate positive frictional charge, examples thereof include silicon rubber, hard chrome plating and the like, and as the liquid that tends to generate negative frictional charge, examples thereof include water and the like. On the other hand, as the surface material of the conveying roller 20 that tends to generate negative frictional charge with respect to the polyethylene film, examples thereof include glass and the like, and as the liquid that tends to generate positive frictional charge, examples thereof include a halogen-based solvent such as trichlorobenzene and dichloromethane.
The width of the web 10 (i.e., in a direction orthogonal to the conveying direction) may be larger than the width to which the liquid b for charge control can be sprayed from one atomizer as a supplying means. In such a case, in the case of using only one atomizer, the charge control can be performed only in a part of the web 10. FIG. 2 shows an arrangement of atomizers (spray nozzles 30) in a charge control device corresponding to the web 10 having a large width. For ease of explanation, the web 10 is not shown in FIG. 2.
The charge control device shown in FIG. 2 is similar to the one shown in FIG. 1, and supplies the liquid b for charge control to the interface between the web 10 and the conveying roller 20 by spraying the liquid b for charge control from the spray nozzle 30 to control the amount of the charge on the web 10. Here, water is assumed to be used as the liquid b for charge control. Assuming that the length of the conveying roller 20 is larger than the width of the web 10, in the charge control device shown in FIG. 2, a plurality of spray nozzles 30 (three in this case) that are atomizers are provided, and these spray nozzles 30 are arranged within a single nozzle cover 40 in the longitudinal direction of the conveying roller 20. Air a used for spraying water is commonly supplied to the plurality of spray nozzles 30. The slit 41 in the nozzle cover 40 is provided over almost the entire length of the conveying roller 20 in the longitudinal direction so as to face the conveying roller 20. In the illustrated case, the conveying roller 20 is divided into three regions (L region, C region and R region, each shown therein) along the longitudinal direction. The water used for spraying is supplied via a pressure reducing valve 31, and is branched into three pipes 32 to 34 at the outlet side of the pressure reducing valve 31, and a spray nozzle 30 is provided at the end of each of the pipes 32 to 34. The pipes 32 to 34 correspond to the L region, C region and R region, and each of them is equipped with a valve 35 and a flowmeter 36.
In the case shown in FIG. 2, when the conveying roller 20 is divided into a plurality of regions in the longitudinal direction thereof, it is possible to control the amount of water supplied to each of the divided areas by controlling each of the valves 35. This makes it possible to control the amount of charge on the web in the width direction. In particular, since the flowmeter 36 is provided for each of the L region, C region, and R region, it is possible to control the amount of charge with high precision in each of the L region, C region, and R region by controlling the opening degree of the valve 35 based on the measurement value of the flowmeter 36.

Examples

The present invention is described in more detail by the following examples.

[Example 1]

The device shown in FIG. 1 was assembled. Here, a soft polyethylene sheet (manufactured by Kokugo Co., Ltd.) having a thickness of 30 µm was used as the web 10, and a metal roller having a diameter of 150 mm and a hard chrome plated surface was used as the conveying roller 20. A two-fluid nozzle (model number: SCBIMV 80005 S) manufactured by H. Ikeuchi & Co., Ltd. was used as the spray nozzle 30 being an atomizer. Tap water was used as the liquid b for charge control, and this tap water and air a were supplied to the spray nozzle 30 so that water could be sprayed on the conveying roller 20. The web 10 was conveyed at 30 m/min by rotating the conveying roller 20. Then, the surface potential of the web 10 was measured with the electrometer 50 installed on the downstream side of the conveying roller 20 while changing the presence or absence of water spray and the flow rate of water spray. The results are shown in Table 1.
From Table 1, it can be found that, in the case of not spraying water, the surface potential of the web 10 was about +15 kV and was positive, but in the case of spraying water, the surface potential changed in a negative direction. In the case where the flow rate of water spray was 7 mL/min, the surface potential decreased to about +8 kV, and in the case where the s flow rate of water spray was 11 mL/min, the surface potential became almost 0 kV. In other words, by controlling the flow rate of water spray to 10 mL/min to 12 mL/min, the frictional electrification of web 10 can be prevented. By increasing the flow rate of water spray to 16 mL/min, the surface potential could be lowered to -17 kV. It has been found that the surface potential of the web 10, i.e., the amount of charge on the web 10 can be controlled by controlling the flow rate of water spray, i.e., the amount of water supplied to the interface between the conveying roller 20 and the web 10. Table 1

Flow rate of water spray [mL/min] 0 7 11 16

Surface potential [kV] +15 +8 0 -17

[Example 2]

The experiment was performed in the same manner as Example 1 other than a glass-coating roller was used as the conveying roller 20 and 1,2,4-trichlorobenzene was used as the liquid b for charge control. The results are shown in Table 2. From Table 2, it can be found that, in the case of not spraying the liquid, the surface potential of the web 10 was -9 kV and was negative, but in the case of spraying the liquid, the surface potential changed in a positive direction. In the case where the flow rate of liquid spray was 10 mL/min, the surface potential shifted to the positive side and became about -5 kV. In the case where the flow rate of liquid spray was 15 mL/min, the surface potential became almost 0 kV. In other words, the frictional charge on the web 10 can be prevented by controlling the flow rate of liquid spray to 14 mL/min to 16 mL/min. By increasing the flow rate of liquid spray to 20 mL/min, the surface potential could be shifted to +8 kV. Even when the web 10 was negatively charged by frictional electrification with the conveying roller 20, the amount of the charge on the web 10 can be controlled by controlling the flow rate of the liquid that generates the frictional charge opposite in polarity. Table 2

Flow rate of liquid spray [mL/min] 0 10 15 20

Surface potential [kV] -9 -5 0 +8

Industrial availability.

In the present invention, a method for manufacturing a web, charge control method, and charge control device, which can manufacture a web with a controlled charge without imparting a charge to the web in advance, and can control the amount of the charge on the web, are provided.
Although the present invention are described in detail and with reference to the specific embodiments, it will be clear to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention.
This application is based on Japanese patent application No. 2017-209140 filed on October 30, 2017 , the contents of which are incorporated herein by reference.

Reference Sign List

10: Web
20: Conveying roller
30: Spray nozzle
40: Nozzle cover
50: Electrometer
a: Air
b: Liquid for charge control
w: Water

Claims

A method for manufacturing a web, comprising a conveying step of conveying a web,
the method comprising a step of supplying a liquid to an interface between the web and a conveying roller that conveys the web to control an amount of charge generated on a surface of the web by frictional electrification between the conveying roller and the web.
The method according to claim 1, wherein the liquid is a liquid capable of generating a frictional charge between the web and the liquid, the frictional charge being opposite in polarity to the charge generated on the surface of the web by frictional electrification between the conveying roller and the web.
The method according to claim 1 or 2, wherein the amount of charge generated on the surface of the web is controlled by controlling an amount of the liquid supplied to the interface.
The method according to claim 3, wherein the conveying roller is divided into a plurality of regions along a longitudinal direction of the conveying roller, and the amount of the liquid is controlled in each of the divided regions.
A charge control method for controlling an amount of charge on a web conveyed by a conveying roller,
the charge control method comprising supplying a liquid to an interface between a web and a conveying roller that conveys the web to control an amount of charge generated on a surface of the web by frictional electrification between the conveying roller and the web.
The charge control method according to claim 5, wherein the liquid is a liquid capable of generating a frictional charge between the web and the liquid, the frictional charge being opposite in polarity to the charge generated on the surface of the web by frictional electrification between the conveying roller and the web.
The charge control method according to claim 5 or 6, wherein the amount of charge generated on the surface of the web is controlled by controlling an amount of the liquid supplied to the interface.
The charge control method according to claim 7, wherein the conveying roller is divided into a plurality of regions along a longitudinal direction of the conveying roller, and the amount of the liquid is controlled in each of the divided regions.
A charge control device for controlling an amount of charge on a web to be conveyed, the charge control device comprising:
a conveying roller configured to convey the web; and

a supplying means of supplying a liquid to an interface between the conveying roller and the web,

wherein an amount of charge generated on a surface of the web by frictional electrification between the conveying roller and the web is controlled by the liquid.
The charge control device according to claim 9, wherein the liquid is a liquid capable of generating a frictional charge between the web and the liquid, the frictional charge being opposite in polarity to the charge generated on the surface of the web by frictional electrification between the conveying roller and the web.
The charge control device according to claim 9 or 10, wherein the amount of charge generated on the surface of the web is controlled by controlling an amount of the liquid supplied to the interface by the supplying means.
The charge control device according to claim 11, wherein the conveying roller is divided into a plurality of regions along a longitudinal direction of the conveying roller, and the supplying means is included in each of the divided regions.
The charge control device according to any one of claims 9 to 12, wherein the supplying means is an atomizer from which the liquid is sprayed on the rotating conveying roller.