JP2019179645A - Charging control method for web, charging controller and manufacturing method for web - Google Patents

Abstract

To achieve manufacture of a web with a controlled charging amount without causing a discharge phenomenon.SOLUTION: The charging control method, controlling a charging amount of a web, includes: a supply process for, while keeping a dry state of one of both surface of a web to be conveyed, supplying liquid to the other surface; a measurement process for measuring a web charging amount with a potentiometer at a more downstream process than the supply process; and a feedback process for controlling the liquid supply amount of the supply process on the basis of the charging amount measured by the measurement process.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a charge control method, a charge control device, and a web manufacturing method for controlling the charge amount of a web.

  In general, static electricity is generated when two materials rub against each other, and one of the two materials is relatively positively charged and the other is negatively charged. The tendency of each substance to be positively charged or negatively charged when rubbed against another substance is commonly known as a charge train, and by referring to the charge train, it can be between any two materials. Thus, it can be estimated which is positively charged when frictional charging occurs. An example of the charged column is shown in Non-Patent Document 1.

  For example, in a manufacturing process of an object in which at least a part of the surface is made of an insulator such as a plastic battery separator made of a polyolefin such as polyethylene or polypropylene, a manufacturing tool comes into contact with the insulator. It is well known that charged charges are generated on the surface of the insulator, causing various obstacles in the process. When the generated charge amount exceeds a certain value, a discharge may occur between the insulator and the transport roll or other object. Such a discharge phenomenon may cause various kinds of troubles, which is a big problem.

  In addition, a part of a plastic sheet or the like may be deformed by heat during discharge, or charging due to discharge may cause uneven coating of a solvent during processing. Moreover, when it has a grinding process, the grinding powder is adsorbed by a grinding tool or the like due to electrification, resulting in a problem that the processing efficiency is lowered. Furthermore, charging is a cause of foreign matter adhesion in every process.

  In order to suppress such a problem caused by charging, conventionally, ions are supplied to neutralize the charged charges generated on the insulator, thereby eliminating the charge.

As a specific example of a device for performing static elimination, for example, a discharge type static eliminator that generates ions by ionizing gas by corona discharge at a needle tip is known. In this static eliminator, an insulator is formed by an electric field of a charged charge. Reverse polarity ions are attracted, and the charged charge is electrically neutralized. (Patent Document 1)
However, since the static eliminator discharges when generating ions, it cannot be placed in an environment that requires explosion-proofing because it promotes an explosion or the like to be avoided in the environment. Further, in the static eliminator, when the web conveyance speed is high, the static eliminating capability is insufficient, and the static eliminator may not be sufficiently performed. Furthermore, the static eliminator cannot be used for adjusting to a specific charge amount other than zero volts.

JP 10-15812

Akinari Kasai, “Factors affecting electrification measurement values”, Polymer, The Society of Polymer Science, 1967, Vol. 16, No. 179, p. 323-329

  As described above, the technology using the static eliminator among the technologies for preventing charging in the conveyed web may not be applicable, and the static elimination capability may be insufficient. Although it can be said that the charge removal of the web is one form of controlling the charge amount of the web, a general technique for controlling the charge amount of the web by a method other than adding a charge is not known. In addition, in a manufacturing process in which the web is manufactured by performing various processes while the web is being transported, for example, the charge amount distribution in the web transport direction (MD direction) in accordance with changes in environmental temperature and humidity due to day and night or season. Furthermore, the charge amount distribution in the TD direction may fluctuate due to non-uniformity in the width direction of the web (TD direction, the direction orthogonal to the thickness direction among the directions orthogonal to the MD direction). That is, for example, when the web is charged by contact / separation with the transport roll, for example, the amount of charge of the web varies depending on the environmental temperature and humidity. Further, for example, the web film thickness may vary even in the MD direction or the TD direction, and in this case, the charge amount may change along the MD direction or the TD direction. In addition, when the static electricity is removed from the web in the middle of conveyance, there are cases where the front and back surfaces are actually charged even though the charge amount is zero and it appears that the web is not charged. May cause, for example, uneven coating in the coating process, which is a subsequent process.

  An object of the present invention is to provide a method for manufacturing a web in which the charge amount is controlled without causing a discharge phenomenon, and a method and apparatus for controlling the charge amount of the web.

  The present invention is a charge control method for controlling the amount of charge of a web, wherein a liquid for charge control is supplied to one surface of both surfaces of a web being conveyed while a liquid is substantially applied to the other surface. A first supply step that does not supply the web, a first measurement step that measures the charge amount of the web downstream from the first supply step, and a charge amount that is measured in the first measurement step. And a first feedback step for controlling at least one of the type and amount of liquid supplied in the first supply step.

  The first feedback step preferably includes a step of switching between a liquid for positively charging the web and a liquid for negatively charging the web based on the charge amount measured in the first measurement step.

  In the first measurement step, it is also preferable to measure the surface charge amount on the other surface of the web in a state where the one surface of the web is in close contact with a grounded conductive roll.

  After the first feedback step, charging liquid is supplied to the surface of the web opposite to the one where the liquid was supplied in the first supply step, while the other surface is substantially A second supply step in which no liquid is supplied to the liquid, a second measurement step in which the charge amount of the web is measured downstream of the second supply step, and a charge amount measured in the second measurement step It is also preferable to perform a second feedback step for controlling at least one of the type and amount of liquid supplied in the second supply step based on the above.

  In the first feedback step and / or the second feedback step, the web is positively charged based on the charge amount measured in the first measurement step and / or the second measurement step immediately after that. It is also preferable to include a step of switching between the liquid to be charged and the liquid to be negatively charged.

  In the first measurement step and / or the second measurement step, a surface charge amount on the other surface of the web may be measured in a state where the one surface of the web is in close contact with a grounded conductive roll. preferable.

  The present invention provides a liquid supply unit for supplying a liquid to one side of a web, and an electrometer for measuring the charge amount of the web, which is provided downstream of the liquid supply unit in the web conveyance direction. A control unit that adjusts at least one of the amount of liquid supplied from the liquid supply unit and the type of liquid based on the charge amount measured by the electrometer, and the liquid supplied from the liquid supply unit among both surfaces of the web. A charge control device comprising: a drying holding region provided to face a surface opposite to a surface to be supplied, and to keep the surface on the opposite side in a dry state.

  Provided in close contact with the surface of the web opposite to the surface facing the electrometer, and provided with a grounded conductive roll, the electrometer in the measurement step is attached to the conductive roll It is also preferable that the surface charge amount of the web is measured while the web is in close contact.

  The present invention is a method for manufacturing a battery separator, comprising the step of controlling the charge of the web by the charge control method of the present invention.

  According to the present invention, it is possible to manufacture a web in which the charge amount is controlled without accompanying a discharge phenomenon, and it is possible to control the charge amount of the web.

It is a figure which shows the structure in an example of the charging control apparatus of this invention. It is a block diagram which shows the example of arrangement | positioning around the liquid supply apparatus in this invention. It is a figure which shows the structure in another example of the charging control apparatus of this invention.

  The present invention uses a liquid as a means for controlling the charge amount of the web. By supplying a liquid to the web, it is possible to manufacture a web in which the charge amount is controlled without previously applying a charge to the web. Tribocharging can occur not only between solids, but also between solids (webs) and liquids. By utilizing frictional charging between the web and the liquid, the amount of charge on the web surface is controlled. In particular, the use of a liquid that generates a triboelectric charge with the web having a polarity opposite to the polarity of the charge generated on the surface of the web as the liquid can quickly reduce or eliminate the charge on the web surface. What kind of liquid should be used may be determined based on the above-described charging train according to the material of the web. In addition, the amount of triboelectric charge generated between the web and the liquid also changes according to the amount of liquid supplied to the surface of the web. Therefore, by controlling the amount of liquid supplied, the amount of web charge can be made finer. Control can be performed.

  Further, by using a liquid as a means for controlling the charge amount of the web, the charge control can be performed even in a process that requires an explosion-proof measure. As a process requiring such an explosion-proof measure, specifically, a process of forming a coating layer on the surface of a porous battery separator made of polyolefin may be mentioned. In this process, an inorganic filler such as alumina and a resin component are kneaded together with an organic solvent such as acetone to form a slurry, and the acetone is volatilized and removed after the slurry is applied to the surface of the battery separator. As a result, a coating layer is formed. And, when the acetone is volatilized and removed, the processing chamber in which the battery separator is transported is explosion-proof, but the battery separator transported in the chamber generates static electricity when it touches a member such as a transport roll. In such a processing chamber, acetone may be ignited if the discharge type static eliminator is used to eliminate static electricity. Therefore, the static elimination method of the present invention is effectively used in an explosion-proof environment.

  In the present invention, in order to control the charge amount of the web surface, the liquid for charge control is supplied to one surface of both surfaces of the web to be conveyed, but the liquid is not substantially supplied to the other surface. “Substantially no liquid supply” means that a step of actively supplying liquid is not provided, and the degree to which gaseous moisture contained in the atmosphere adheres to the web is allowed. Further, the surface on the side that does not substantially supply the liquid may be kept in a dry state by contacting with a dry atmosphere, or when the liquid adheres, a heater for drying by heating, or the liquid is forced By attaching a nip roll or the like to be scraped off, the attached liquid may be removed before the measurement step immediately after described later. When the charge amount of the web is measured in a measurement process described later, the total charge amount on both surfaces (hereinafter referred to as “net charge amount”) is measured. When the charge control liquid is supplied to one surface of the web and the liquid is supplied to the other surface, the liquid is removed from the other surface (or when dried). In some cases, a charged state other than the phenomenon described in the above-described charge train may occur. For example, if a charge control liquid is supplied to one surface and charged negatively, the liquid is supplied from one surface or via a liquid to ease the charge when the other surface dries. If unintentionally connected, a positive charge is attracted from the connected ground or the like, and when viewed as a whole web, the result may be an unintended charged state. Therefore, in controlling the net charge amount as described above, it is important that the liquid is not substantially supplied to the other surface opposite to the one surface to which the liquid is supplied.

  Next, embodiments of the present invention will be specifically described with reference to the drawings. The web to which the static elimination method of the present invention is applied is, for example, a long polymer film or an electrically insulating film, and specifically a porous battery separator made of polyolefin such as polyethylene or polypropylene. FIG. 1 shows an example of a charge control device according to an embodiment of the present invention. This charge control device is used when a web is manufactured by the manufacturing method of the present invention. FIG. 1 schematically depicts a part of a process in which a web 10 which is a wide and long thin film such as a film or a strip is conveyed from the lower side to the upper side in FIG. The web 10 in FIG. 5 shows a state in which the thickness portion is viewed from the side along the MD direction.

  The illustrated charging control device is configured to be used in the process of transporting the web 10 that is the above-described battery separator, and the web is controlled by transport rolls 11 and 12 provided on the upper side and the lower side, respectively. 10 is vertically conveyed from the lower side to the upper side. The conveyance speed of the web 10 is, for example, 5 m / min to 100 m / min. A liquid supply device 20 is provided on one side (in this example, the right side in FIG. 1) of the web 10 conveyed from the lower side to the upper side. The liquid supply device 20 is, for example, a slit nozzle, and functions as a supply unit that supplies a charge control liquid to one side of the web 10 being conveyed. As a method for supplying a liquid to the web surface to be conveyed, it is preferable to use a slit nozzle because it can be easily obtained and it is easy to control and control the flow and flow of the liquid.

  The liquid supply path 21 extending toward the upstream side of the liquid supply apparatus 20 is branched into two and connected to the liquid reservoirs 22 and 23, respectively. The liquid reservoir 22 stores a liquid A that charges polyethylene positively, for example, a halogen-based solvent such as chloroform, and the liquid reservoir 23 stores a liquid B that charges polyethylene negatively, such as water. The type of the liquid is determined according to the type of the web 10 in the charging train.

  A valve 24 and a flow meter 25 are provided between the liquid supply device 20 and the liquid storage unit 22, and a valve 26 and a flow meter 27 are provided between the liquid supply device 20 and the liquid storage unit 23. It has been. Therefore, by switching the opening and closing of the valves 24 and 26, the liquid supplied to the web 10 is switched between the liquid A and the liquid B, and the flow rate of the liquid can be adjusted according to the opening degree of the valve 24 (26). It has become. Moreover, about the slit nozzle of the liquid supply apparatus 20, you may provide a slit nozzle for exclusive use for A liquid and B liquid, respectively. That is, the liquid supply device 20 for the A liquid and the liquid supply device 20 for the B liquid are provided separately, and are supplied to the web 10 by switching the valves 24 and 26 in the liquid supply devices 20 and 20. The type of liquid may be switched.

  A liquid receiving portion 14 for receiving the liquid is provided on the lower side of the conveying roll 12 provided on the lower side of the conveying rolls 11 and 12, and the liquid supplied to the web 10 from the liquid supply device 20 is It is configured to be stored when it flows down along the web 20. With the above configuration, the liquid supply device 20 is disposed opposite to one surface (the right surface in FIG. 1) of both surfaces of the web 10 to supply the liquid, and the other surface (the left surface in FIG. 1). Is provided with an air surface and substantially no liquid is supplied. In this way, when substantially not supplying the liquid to the other surface, the nozzle for blowing air and the web 10 are heated and dried below the liquid supply device 20 (upstream in the conveyance direction of the web 10). A heater or a nip roll that forcibly scrapes off the liquid may be provided, or if the liquid adheres to the surface of the web 10 by the processing in the previous process, the liquid will make the surface 10 water repellent. Based on this, the conveyance distance may be set longer until it is separated.

  Further, in the charging control device shown in FIG. 1, an electrometer 40 is provided at a position downstream (above in this example) from the liquid supply device 20 described above. Measures the net charge amount of the surface supplied with. The separation dimension between the liquid supply device 20 and the electrometer 40 is set to be, for example, 0.5 m to 20.0 m, and the web is conveyed from the lower side to the upper side at the above-described conveyance speed. When 10 reaches the height position of the electrometer 40, the liquid supplied from the liquid supply device 20 is shaken off to be in a dry state. That is, when the net charge amount is measured by the electrometer 40, the electrometer according to the conveyance speed of the web 10, the wettability of the liquid in the web 10, and the type of the liquid so that the web 10 is completely dried. A height position of 40 is set. If the web 10 is wet when the potential is measured by the electrometer 40, an unexpectedly charged state may occur due to drawing of charges from the atmosphere when the web 10 is subsequently dried. At the time of measuring the potential, the web 10 is dried.

  Further, the charging control device is provided with a control unit 50, which determines the type and flow rate of the charge control liquid 30 according to the net charge amount measured by the electrometer 40, Feedback is continuously performed by repeating a series of flows in which the charge control liquid 30 is supplied from the liquid supply device 20 to the web 10 at the determined liquid type and flow rate. When the net charge amount measured by the electrometer 40 is negative, the liquid A is supplied, and when it is positive, the liquid is switched to the liquid B and supplied. The feedback may be performed continuously, or may be performed every several hours in order to suppress day and night fluctuations. As described above, the web 10 that has reached the potential measurement position in the electrometer 40 has been sufficiently drained and dried, but the electrometer 40 can be largely separated from the liquid supply device 20. If not, a nozzle for blowing air, a heater for heating and drying the web 10, or a nip roll for forcibly scraping off the liquid may be provided between the electrometer 40 and the liquid supply device 20.

  Next, charge amount control using this charge control device will be described. The web 10 conveyed toward the liquid supply apparatus 20 by the conveying rolls 11 and 12 is in a dry state on both surfaces, and one surface and the other surface of both surfaces are charged to different potentials. In some cases, the polarity of the charge itself may be different. As described above, there is a case where the charge amount and the polarity of the charge vary in the MD direction of the web 10 due to variations in the film thickness of the web 10. Then, the charge control liquid 30 is supplied from the liquid supply device 20 to one surface of both surfaces of the web 10, and the web 10 is conveyed without supplying the liquid to the other surface. When the charge control liquid 30 is continuously supplied onto the web 10, frictional charging occurs between the liquid supplied in the first supply process and the web 10. If this triboelectric charge has the same polarity as the charging polarity of the web 10, the absolute value of the net charging amount of the web 10 increases, whereas if it is the opposite polarity, the net charging amount of the web decreases. In this way, the net charge amount of the web 10 is adjusted to a specific value (in this example, zero volts). When the charge amount measured by the electrometer 40 as the first measurement step increases or decreases, the flow rate of the liquid is adjusted according to the increase or decrease, and when the polarity of the charge is reversed, the type of the liquid is changed. And the flow rate of the liquid is set. The step of controlling at least one of the flow rate and type of the liquid constitutes a first feedback step. When the type of liquid is changed, it is only necessary to switch between opening and closing of the valves 24 and 26 as described above. Therefore, a blank time associated with the switching of the type of liquid (the time during which the web 10 is conveyed without being supplied with liquid). ) Does not occur.

  Therefore, according to the charge control device of the present embodiment, the net charge amount of the web 10 can be controlled. In particular, the flow rate and type of the charge control liquid 30 are controlled based on the net charge amount of the web 10 measured at a position downstream of the supply process of supplying the charge control liquid in the web 10 conveyance direction. Therefore, the net charge amount of the web 10 can be made almost zero. What is used as the charge control liquid can be determined based on the charge train according to the target net charge amount and the material of the web 10. And since the liquid is not substantially supplied to the other surface opposite to the one surface to which the liquid is supplied, the charge generated as the liquid adhering to the other surface dries is charged. The web 10 can be adjusted to the intended charged state.

  By the way, the width dimension of the web 10 may be wider than the width in which the liquid can be supplied from one liquid supply device 20 as the supply means. Further, even if the entire TD direction of the web 10 can be wetted by the liquid supplied from one liquid supply device 20, the charge amount and the polarity of the charge may change in the TD direction of the web 10. In such a case, only one part of the web 10 can be charged with only one liquid supply device 20. Therefore, FIG. 2 shows the arrangement of the liquid supply device 20 in the charge control device corresponding to an example in which the charge control is performed at a plurality of positions in the web 10 having a wide width dimension or in the TD direction.

  As in FIG. 1, the charge control device shown in FIG. 2 supplies the charge control liquid 30 from the liquid supply device 20 to one of the two surfaces of the web 10, while the other surface on the opposite side. Controls the net charge amount of the web 10 by substantially not supplying a liquid, and schematically shows the web 10 viewed from above. Therefore, the web 10 in FIG. 2 is in a state in which the thickness portion is viewed along the TD direction. The liquid supply devices 20 are arranged at equal intervals at a plurality of locations (here, 3 locations) along the TD direction of the web 10. With respect to the plurality of liquid supply devices 20, when the reference numerals “20a”, “20b”, and “20c” are attached from the left side to the right side in FIG. 2, the electrometer 40 is, as shown by the one-dot chain line in FIG. The same number (three in this example) of liquid supply devices 20a to 20c is arranged above the liquid supply devices 20a to 20c so as to correspond to the arrangement positions of the liquid supply devices 20a to 20c. In FIG. 2, the plurality of liquid supply systems (valves 24 and 26 and flow meters 25 and 27), the charge control liquid 30 and the electrometer 40 are moved from the left to the right as in the liquid supply devices 20 a to 20 c. Subscripts “a”, “b” and “c” are added. Further, the electrometers 40a to 40c are drawn with a one-dot broken line.

  In the apparatus shown in FIG. 2, the net charge amount in the TD direction is supplied to each liquid supply by controlling the opening and opening / closing of the valves 24a-24c, 26a-26c based on the measurement results of the electrometers 40a-40c. It can adjust separately for every apparatus 20a-20c. As a result, the net charge amount in the width direction of the web 10 can be controlled with high accuracy. When the charge amount and the charge polarity in the TD direction are uniform, only one electrometer 40 is provided, and a plurality of liquid supplies arranged in the TD direction based on the measurement result of the electrometer 40 are provided. The amount of liquid supplied from the devices 20a to 20c and the type of liquid may be changed collectively. In this case, the electrometer 40 may be provided at the center in the TD direction as a place where the electrometer 40 is disposed (a place where the charge amount is measured).

  In the example described above, the potential measured by the electrometer 40 (40a to 40c) is the net charge amount already described in detail, and the charge amount on one surface of both surfaces of the web 10 and the other surface. The charge amount is the sum of the charge amount and the charge amount. Therefore, when performing neutralization of the web 10, there may be a case in which the one surface and the other surface are charged, but the charge amount when the both surfaces are viewed together is zero volts. Further, when adjusting the charge amount of the web 10 to a specific value, even if one surface and the other surface of the web 10 are deviated from the specific value, both surfaces are viewed together. In some cases, the specific value may be obtained. Therefore, in the embodiment of the present invention described in FIG. 3, the surface charge amounts of the one surface and the other surface of the web 10 are individually adjusted. The “surface charge amount” here is a charge amount measured when the potential of one surface of the web 10 is measured and the other surface is grounded (grounded) and forced to zero volts. Specifically, the potential of the web 10 on the non-contact side is measured in a state where the back surface of the web 10 is in close contact with a grounded conductive roll. Hereinafter, the embodiment of FIG. 3 will be specifically described with reference to the drawings.

  In FIG. 3, the web 10 is conveyed from the lower side to the upper side as described above in the description of FIG. In the embodiment of FIG. 3, in addition to the transport rolls 11 and 12 in the embodiment of FIG. 1, another transport roll 13 provided above the transport rolls 11 and 12 (downstream in the transport direction of the web 10). Is used. Therefore, the conveyance roll 11, the conveyance roll 12, and the conveyance roll 13 are located in order from the lower side toward the upper side. A first conductive roll 60 a is provided between the transport rolls 11 and 12, and a second conductive roll 60 b is provided between the transport rolls 12 and 13. In the region between the lowermost transport roll 11 and the first conductive roll 60a, the web 10 is transported vertically from the lower side to the upper side, and the side surface facing the region (in this example, the right side) ) Is provided with the liquid supply device 20 described above, and in the region between the transport roll 12 and the second conductive roll 60b, the liquid supply device is provided on the surface (left side) opposite to the side surface side. 120 is provided.

  And the 1st electroconductive roll 60a is provided in the upper side of the liquid supply apparatus 20, and this 1st electroconductive roll 60a is earth | grounded and is set to zero volt | bolt. The web 10 is closely attached so as to be held by the first conductive roll 60a, and the traveling path is bent in the horizontal direction, and further extends horizontally toward the upstream conveying roll 12. Moreover, the electrometer 40 is provided so that the web 10 closely_contact | adhered to the 1st electroconductive roll 60a may be provided, and the electric potential of the surface side in the web 10 which the back side adhered to the 1st electroconductive roll 60a is measured. It is configured to be able to. Also in this example, the separation dimension between the liquid supply device 20 and the electrometer 40 is set in the same manner as the example described above with reference to FIG. Similarly, the first supply process and the first measurement process are respectively performed, and at least one of the type and supply amount of the liquid supplied from the liquid supply device 20 based on the potential measured by the electrometer 40 is the first. 1 as a feedback process.

  Subsequently, the traveling direction of the web 10 is bent vertically by the transport roll 12 and is stretched vertically over the area between the second conductive roll 60b. A liquid supply device 120 composed of a slit nozzle is disposed so as to face this region from the side (in this example, the left side in FIG. 3), and is configured to supply liquid to the web 10. ing. Therefore, the surface opposite to the surface to which the liquid is supplied in the region between the transport roll 11 and the first conductive roll 60a is between the transport roll 12 and the second conductive roll 60b. Thus, the liquid is supplied as the second supply step. Similarly to the first conductive roll 60a, the conductive roll 60b is also grounded.

  As in the embodiment of FIG. 1, the liquid supply device 120 is connected to a liquid storage portion 122 in which liquid A is stored and a liquid storage portion 123 in which liquid B is stored. A valve 124 and a flow meter 125 are provided between the unit 122 and a valve 126 and a flow meter 127 are provided between the liquid supply device 120 and the liquid storage unit 123. A liquid receiving part 114 for receiving the charge control liquid 130 supplied from the liquid supply device 120 to the web 10 is provided below the transport roll 12.

  The web 10 is in close contact with the second conductive roll 60b and the travel path is bent in the horizontal direction, and is transported toward the apparatus performing another process by the transport roll 13 ahead. And the electrometer 140 is provided so that the web 10 closely_contact | adhered to the 2nd electroconductive roll 60b may be provided, and based on the measurement result of the electric potential which is a measurement result of the 2nd measurement process by this electrometer 140. Thus, at least one of the flow rate and type of the liquid supplied between the transport roll 12 and the second conductive roll 60b is controlled as the second feedback process. The separation dimension between the liquid supply device 120 and the electrometer 140 is set similarly to the example of FIG. Further, the control unit 50 may be provided for each of the two liquid supply units 20 and 120.

  In the embodiment of FIG. 3 described above, for both surfaces of the web 10, the back surface side is set to zero volts, and the surface side potential is individually measured and adjusted to zero volts. Even if the amount of potential is measured individually on both surfaces, it becomes zero volts. Here, when the web 10 is in contact with the first conductive roll 60a, the surface that is in contact with the first conductive roll 60a is apparently zero volt while being in contact with the conductive roll 60a. Since it is charged again after leaving the conductive roll 60a, the amount of potential is individually adjusted for both surfaces.

  3 is summarized, the electrometers 40 and 140 measure the surface charge amount of the web 10 with the back surface of the web 10 in close contact with the conductive rolls 60a and 60b connected to the ground. In other words, the charge control method of the embodiment of FIG. 1 is performed on both sides of the web 10. As a result, since the charge amount can be measured and controlled on each side, the charge amount on both surfaces of the web 10 can be set to zero volts.

  Here, a method of adjusting the web 10 to a desired charge amount other than zero volts using the configuration of the embodiment of FIG. 3 will be described. In this case, for the downstream electrometer 140 out of the two electrometers 40, 140, the arrangement position is further shifted downstream between the second conductive roll 60b and the transport roll 13, so that both surfaces The total charge amount (the net charge amount described above) can be measured. Based on the measurement result of the downstream electrometer 140, the flow rate and type of the liquid supplied from the liquid supply device 120 between the transport roll 12 and the second conductive roll 60b are adjusted.

  As described in detail, in the embodiment of FIG. 3, the liquid for charging control is supplied to both surfaces of the web 10, and the liquid supply location for one surface and the other surface of the web 10 is changed. ing. The reason for this is that when a conductive liquid is used, if both surfaces of the web 10 are wetted at the same time, the charge in the liquid is induced according to the drying timing of both surfaces, and the intended charged state is lost. This is because they may shift. However, this is not the case when the influence of the inductive action is small, such as when both liquids are insulative and the relative dielectric constant is close to 1, and both surfaces may be supplied simultaneously.

  A web manufacturing method to which the above-described charging control method is applied will be briefly described by taking the battery separator described above as an example. First, a polyolefin solution is formed by melting and kneading a plasticizer in a polyolefin resin made of polyethylene or polypropylene. Then, the polyolefin solution is extruded through a die in which slit-like openings are formed, and cooled on a chill roll to form a gel sheet. Next, after the gel sheet is stretched in the TD direction and MD direction, the plasticizer is removed to form a microporous film as a web, and a washing process and a heat treatment process are performed and wound around a core. When the microporous film is transported through such a series of steps, the microporous film is charged because it contacts the transport roll, the core, and the like. Further, when the microporous film after winding is subjected to the above-described coating treatment using the organic solvent, it is similarly charged. Therefore, by applying the charge control method of the present invention to such a microporous film being transported, the microporous film is manufactured to have a specific charge amount.

10 Web 20, 120 Liquid supply device 24, 26 Valve 25, 27 Flow meter 30, 130 Charge control liquid 40, 140 Electrometer 50 Control unit 60a, 60b Conductive roll

Claims (9)

A charge control method for controlling the charge amount of a web,
A first supply step of supplying a liquid for charge control to one side of both surfaces of the web to be conveyed and substantially not supplying a liquid to the other side;
A first measurement step of measuring the charge amount of the web on the downstream side of the first supply step;
And a first feedback step of controlling at least one of the type and amount of liquid supplied in the first supply step based on the charge amount measured in the first measurement step.   The first feedback step includes a step of switching between a liquid for positively charging the web and a liquid for negatively charging the web based on the charge amount measured in the first measurement step. Charge control method.   The said 1st measurement process measures the surface charge amount in the other surface of the said web in the state which contact | adhered one surface of the said web to the earth | grounded electroconductive roll. The charge control method described in 1. After the first feedback step,
The second supply of supplying the liquid for charge control to the surface of the web opposite to the one supplied with the liquid in the first supply step, but supplying substantially no liquid to the other surface. Process,
A second measurement step of measuring the charge amount of the web downstream of the second supply step;
2. A second feedback step for controlling at least one of the type and amount of liquid supplied in the second supply step based on the charge amount measured in the second measurement step. The charge control method according to any one of?   In the first feedback step and / or the second feedback step, the web is positively charged based on the charge amount measured in the first measurement step and / or the second measurement step immediately after that. The charge control method according to claim 4, comprising a step of switching between a liquid to be charged and a liquid to be negatively charged.   In the first measurement step and / or the second measurement step, the surface charge amount on the other surface of the web is measured in a state where the one surface of the web is in close contact with a grounded conductive roll. The charge control method according to claim 4 or 5, characterized in that A liquid supply unit for supplying liquid to one side of the web;
An electrometer for measuring the charge amount of the web, provided downstream of the liquid supply unit in the web conveyance direction;
A control unit that adjusts at least one of the amount of liquid and the type of liquid supplied from the liquid supply unit based on the charge amount measured by the electrometer;
A drying holding region provided to face a surface opposite to a surface to which liquid is supplied from the liquid supply unit among both surfaces of the web, and to keep the opposite surface in a dry state; A charge control device characterized by that. Provided in close contact with the surface opposite to the surface facing the electrometer of the both surfaces of the web, comprising a grounded conductive roll,
The charge control device according to claim 7, wherein the electrometer in the measurement step is provided to measure a surface charge amount of the web in a state where the web is in close contact with the conductive roll. . A method for manufacturing a battery separator, comprising the step of controlling the charge of the web by the charge control method according to any one of claims 1 to 6.