JP7363538B2 - Film pinhole inspection method, film manufacturing method, and film pinhole inspection device - Google Patents

Description

The present invention relates to a film pinhole inspection method for inspecting the presence or absence of pinholes (fine through holes) in a film, particularly an electrically insulating film, a film manufacturing method including the inspection method, and a pinhole inspection device for the film. .

Electrical insulating films are inspected for pinholes during the manufacturing process for quality control. A pinhole is a microscopic hole that penetrates the front and back surfaces of a film. If a film with a pinhole formed is placed between electrodes and a voltage is applied, there is a possibility that a short circuit will occur between the electrodes and damage the power supply. There is. Therefore, in film production lines, pinhole inspection is performed before shipment to prevent films with pinholes from being shipped as final products.
For example, films produced on the same production line are wound into a plurality of rolls, and one of the rolls is selected as a sample. If a pinhole is detected in this sample, all of the films produced on the same production line are removed from shipment, cleaned, or remanufactured.

Conventional technology for inspecting pinholes in film involves applying a high voltage between a pair of electrodes placed opposite each other with the sheet being conveyed in between, and converting the discharge current caused by the pinholes in the film into an optical signal using a light emitting diode. Some are known (for example, see Patent Document 1). The converted optical signal is received and detected by a photodiode and converted into a current signal, and the presence or absence of a pinhole is determined by detecting this current signal. In addition, as another conventional technique, a pair of electrode plates are arranged in parallel with the sheet being conveyed in between, a high DC voltage is applied between these electrodes, and the discharge current generated when this application is applied is detected. There is also known a method in which the presence or absence of a pinhole is determined by (for example, see Patent Document 2).

Japanese Patent Application Publication No. 2000-111531 Japanese Patent Application Publication No. 2002-90346

In this way, in both of Patent Documents 1 and 2, pinholes are detected by utilizing the fact that when a voltage is applied to the film, the dielectric breakdown voltage becomes small at the inspection position. Regarding this applied voltage and dielectric breakdown voltage, the wider the gap (difference) between the detection voltage of the normal part (the part without pinholes) and the detection voltage of the pinhole occurrence part, the wider the so-called window, the higher the detection accuracy. This makes it possible to prevent erroneous detection and oversight of holes.

However, with the increasing integration and density of electronic devices such as electric cars and smartphones, the thickness of electrically insulating films has become noticeably thinner. There is a tendency for the window to decrease and the window to shrink. In other words, by making the film thinner, the difference in dielectric breakdown voltage between a location where a pinhole is formed and a location where a pinhole is not formed becomes smaller. As a result, test accuracy may deteriorate. In addition, due to roll manufacturing accuracy, each detection voltage varies depending on the inspection part, and in some cases, the detection voltage of a normal part is lower than the detection voltage of a pinhole occurrence part, resulting in false detection (a normal part is replaced by a pinhole). false positive detection may occur. The inspection methods disclosed in Patent Documents 1 and 2 cannot sufficiently cope with thinning of the film, and there is room for improvement.

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a method for inspecting pinholes in a film, a method for manufacturing a film, and a method for detecting pinholes in a film that can accurately detect pinholes even when the film is thinned. The purpose of the present invention is to provide a pinhole inspection device.

The above object of the present invention is achieved by the following configuration.
(1)
a voltage application step of applying a DC voltage between a pair of electrodes arranged opposite to each other so as to sandwich both sides of the film;
a detection step of detecting a current flowing between the pair of electrodes or a voltage drop between the pair of electrodes;
a determination step of determining the presence or absence of a pinhole in the film based on the detection result of the detection step,
One of the first electrodes of the pair of electrodes is placed in contact with a first surface that is the front or back surface of the film,
The other second electrode of the pair of electrodes is spaced apart from a second surface opposite to the first surface,
The polarity of the voltage applied to the second electrode is set to be negative relative to the first electrode.
Film pinhole inspection method.
(2) the distance between the first electrode and the second electrode is set in a range of 50 μm to 200 μm;
The method for inspecting pinholes in a film according to (1).
(3) further comprising a conveying step of conveying the film between the pair of electrodes,
The first electrode is a conductive roller that conveys the film by contacting the first surface of the film with its peripheral surface, and also functions as an electrode while conveying the film in the conveying process.
The method for inspecting pinholes in a film according to (1) or (2).
(4) The second electrode is formed in a cylindrical shape and is arranged such that its longitudinal direction is perpendicular to the transport direction of the film and parallel to the width direction of the film.
The method for inspecting pinholes in a film according to any one of (1) to (3).
(5) an inspection step of inspecting the film for the presence or absence of pinholes by the film pinhole inspection method according to any one of (1) to (4);
a winding step of winding the film subjected to the inspection step;
Film manufacturing method.
(6) a winding step of winding films produced on the same production line into a plurality of rolls;
One of the plurality of wound bodies is selected as a specimen, and the presence or absence of the pinhole is determined in the film of the specimen by the film pinhole inspection method according to any one of (1) to (4). an inspection process for inspecting the
a shipping step of shipping the remainder of the plurality of wound bodies as a final product if the pinhole is not detected in the inspection step;
Film manufacturing method.
(7) further comprising a re-winding step of re-winding the specimen;
In the shipping step, all of the plurality of rolled bodies including the specimen are shipped;
The film manufacturing method described in (6).
(8) a winding step of winding the film produced on the production line into a rolled body;
An inspection step of inspecting a part of the film of the rolled body for the presence or absence of the pinhole by the film pinhole inspection method according to any one of (1) to (4);
If the pinhole is not detected in the inspection step, the portion of the film that has been inspected for the presence or absence of the pinhole is cut off, and the remaining portion is shipped as a final product.
Film manufacturing method.
(9) The production line is
a solution preparation step of preparing a polyolefin solution by kneading a polyolefin resin and a plasticizer;
a sheet forming step of discharging the polyolefin solution from a die and cooling it to form a gel-like sheet;
a sheet stretching step of stretching the gel-like sheet to form a stretched sheet;
a plasticizer removal step of removing the plasticizer from the stretched sheet to obtain a microporous membrane;
The film manufacturing method according to any one of (6) to (8).
(10) a pair of electrodes arranged opposite to each other so as to sandwich both sides of the film;
a voltage application unit that applies a DC voltage between the pair of electrodes;
a detection unit that detects a current flowing between the pair of electrodes or a voltage drop between the pair of electrodes;
a determination unit that determines the presence or absence of a pinhole in the film based on the detection result of the detection unit,
One of the first electrodes of the pair of electrodes is placed in contact with the first surface, which is the front or back surface of the film,
The other second electrode of the pair of electrodes is spaced apart from a second surface opposite to the first surface,
The polarity of the voltage applied to the second electrode is set to be negative relative to the first electrode.
Film pinhole inspection device.
(11) The separation distance between the first electrode and the second electrode is set in a range of 50 μm to 200 μm.
The film pinhole inspection device according to (10).
(12) The voltage application unit further includes a transport unit that transports the film,
The first electrode is a conductive roller that conveys the film by contacting the first surface of the film with its circumferential surface, and is provided integrally with the conveyance section and serves as an electrode while conveying the film. Function,
The film pinhole inspection device according to (10) or (11).
(13) The second electrode is formed in a cylindrical shape and is arranged so that its longitudinal direction is perpendicular to the transport direction of the film and parallel to the width direction of the film.
The film pinhole inspection device according to any one of (10) to (12).

Note that an electrically insulating film is suitable as the film to be applied to the film pinhole inspection method according to the present invention.

According to the present invention, one of the pair of electrodes, the first electrode, is disposed in contact with the first surface, which is the front or back surface of the film, and the other second electrode of the pair of electrodes is disposed on the first surface. The polarity of the voltage applied to the second electrode is set to be negative relative to the first electrode. Therefore, since the window for detection can be widened, pinholes can be detected with high accuracy even when the film is thinned.

The present invention has been briefly described above. Furthermore, the details of the present invention will be further clarified by reading the mode for carrying out the invention (hereinafter referred to as "embodiment") described below with reference to the accompanying drawings. .

FIG. 1 is a flowchart illustrating a production line of a film production method according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a film pinhole inspection device for realizing an inspection line according to an embodiment of the present invention. FIG. 3 is a schematic diagram of the film pinhole inspection device shown in FIG. 2 viewed from above. FIG. 4 is a flowchart illustrating the inspection line according to the embodiment of the present invention. FIG. 5 is a schematic diagram illustrating the detection results of the detection step shown in FIG. 4. FIG. 6 is a graph showing comparative test results of Examples and Comparative Examples according to the present invention. FIG. 7 is a block diagram schematically showing a system between a bar electrode and a conductive roller, with FIG. 7(a) showing a normal portion of the film and FIG. 7(b) showing a portion where a pinhole has occurred.

Specific embodiments of the film pinhole inspection method, film manufacturing method, and film pinhole inspection apparatus of the present invention will be described below with reference to the respective figures.
Note that the drawings should be viewed according to the direction of the symbols. In addition, in the following explanation, the downstream side refers to the direction in which the formed film is transported and wound, and along the transport direction, the left side of the paper in FIGS. 2 and 3 is the upstream side, and the The right side of the paper in No. 3 is also called the downstream side.

Additionally, the figures and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the claimed subject matter. Further, in the embodiment according to the present invention (hereinafter also referred to as "the present embodiment"), a microporous polyolefin film, which is an electrically insulating film, will be cited and explained as an example of the film, but the present invention is not limited thereto. Various electrically insulating films can be used, and the present invention is not limited to electrically insulating films, and can be applied to various other films as appropriate.

Furthermore, the pinholes to be inspected by the pinhole inspection method according to the present embodiment are through-holes whose diameter or length is much larger than the micropores formed in the material of the microporous polyolefin membrane. If a pinhole is formed in the film, if a pair of electrodes is placed to sandwich the film and a dielectric breakdown voltage (DC voltage) is applied, the discharge current will be reduced because the voltage is approximately as low as the air withstand voltage. Occur. On the other hand, in a normal portion where no pinhole is formed, the dielectric breakdown voltage is higher than in a portion where a pinhole is formed. Therefore, when a DC voltage between these breakdown voltages is applied to the film, breakdown occurs only in the portion where the pinhole is formed.

The film manufacturing method according to the present embodiment includes a manufacturing line for manufacturing an electrically insulating film (hereinafter also referred to as "film"), and an inspection line (inspection process) for testing the manufactured film for the presence or absence of pinholes. , mainly includes. The inspection line is executed as a post-process of the manufacturing line. In addition, the inspection line L2 is realized by a film pinhole inspection device (hereinafter also referred to as “inspection device”) of the present embodiment, as described later.

First, with reference to FIG. 1, a manufacturing line L1 for film F in the method for manufacturing film F according to the present embodiment will be described. FIG. 1 is a flowchart illustrating the production line L1 of the film production method according to the embodiment of the present invention.

The production line L1 is equipped with a plurality of rollers, and these rollers suitably convey the film F from the upstream side to the downstream side, and finally wind it around the core without any winding deviation to form a film product reel (final Manufactured products). As shown in FIG. 1, the production line L1 includes a solution preparation process (S11), a sheet forming process (S12), a sheet stretching process (S13), a plasticizer removal process (S14), and a heat setting process ( S15) and a winding step (S16).

In the solution preparation step, a polyolefin resin and a plasticizer are kneaded to prepare a polyolefin solution. In the sheet forming step, the polyolefin solution prepared in the solution preparation step is discharged from a predetermined die and cooled to form a gel-like sheet. In the sheet stretching process, the gel-like sheet formed in the sheet forming process is stretched to form a stretched sheet.

Here, inside the stretched sheet, a large number of plasticizers are scattered in the form of particles inside the polyolefin resin, and in the plasticizer removal step, the stretched sheet stretched in the sheet stretching step is washed to remove the plasticizer contained in the stretched sheet. Replace plasticizer with solvent. Then, the stretched sheet substituted with this solvent is dried to volatilize the solvent. As a result, countless micropores are formed inside the sheet. That is, in the plasticizer removal step, the plasticizer is removed from the stretched sheet and the film F is formed. In the heat setting process, heat is applied to the film F from which the plasticizer has been removed to stabilize it as a film body. After the treatment in the heat setting process, the film F is further conveyed to the downstream side and is wound around the core by a predetermined winding means (not shown) (that is, a winding process).

In the winding process, the film F is laminated in the radial direction of the roll R (wound body) by winding the film F, and the roll R of the film F is obtained as a raw material. Also, at this time, the films F produced on the same production line L1 are wound into a plurality of rolls R, respectively. One of the plurality of rolls R wound in this manner is selected as a sample, and the film F of this sample is inspected for the presence or absence of pinholes in the inspection line L2 in the post-process. As will be described later, if it is determined that no pinholes are detected as a result of the inspection, at least the remainder of the plurality of rolls R is used as a film product reel (final product) by a manufacturer that uses battery separator film, such as a battery manufacturer. will be shipped to.

The method for producing the film F is not limited to the wet method as described above, but may also be a dry method in which a molten resin film is stretched by uniaxial stretching or the like to form holes. Further, the surface of the film F manufactured by the above-mentioned wet method or dry method may be coated with a resin film containing, for example, resin or inorganic particles. In this case, the following steps are taken. Specifically, the film F is unwound from the roll R wound as described above. After unrolling, a coated separator is obtained by impregnating the inside of the slurry containing resin and particles with the film F, or by applying the slurry to the front and back surfaces of the film F, and then performing a drying process.

Next, with reference to FIGS. 2 and 3, the configuration of the inspection apparatus 10 for realizing the inspection line L2 of the film F in the film manufacturing method according to the present embodiment will be described. FIG. 2 is a schematic diagram illustrating the inspection apparatus 10 for realizing the inspection line L2 according to this embodiment. FIG. 3 is a schematic diagram of the inspection apparatus 10 shown in FIG. 2 viewed from above.

As shown in FIGS. 2 and 3, the inspection device 10 of this embodiment includes a conductive roller 11 (conveying section, first electrode) that conveys the film F, and a film F that is conveyed and in contact with the conductive roller 11. A bar electrode 12 (second electrode) placed on the opposite side of the conductive roller 11 with the bar electrode 12 in between, a voltage application section 13 that applies a DC voltage between these electrodes, and a discharge current generated between these electrodes. It includes a detection unit (not shown) that detects a current flowing in accordance with the current, and a determination unit (not shown) that determines the presence or absence of a pinhole.

The conductive roller 11 conveys the film F by closely contacting the back surface (first surface) of the film F. The conductive roller 11 is formed into a cylindrical shape and is a conductive member having a metal member or a resin shaft whose outer peripheral surface is coated with a metal film, and at least its outer peripheral surface is grounded. The conductive roller 11 is a driving roller and generates a driving force for conveying the film F. The conductive roller 11 conveys the film F to the downstream side while frictionally contacting the back surface of the film F with its outer peripheral surface. Further, as shown in FIG. 3, the width direction dimension of the conductive roller 11 is set to be approximately the same as or larger than the width direction of the film F.

The conductive roller 11 and the bar electrode 12 are arranged opposite to each other so as to sandwich both sides of the transported film F, and constitute a pair of electrodes for applying a dielectric breakdown voltage to the film F. . That is, in the present embodiment, one of the first electrodes of the pair of electrodes is the conductive roller 11 that conveys the film F by contacting the back surface (first surface) of the film F with its peripheral surface, and It is provided integrally with the transport unit that transports the film F, and functions as an electrode while transporting the film F.

The other bar electrode 12 of the pair of electrodes is spaced apart from the surface of the film F being transported. Moreover, the bar electrode 12 is formed in a cylindrical shape and is arranged so that its longitudinal direction is perpendicular to the transport direction of the film F and parallel to the width direction of the film F (see FIG. 3). Since the bar electrode 12 has a circular cross section and a uniform shape in the circumferential direction, it is possible to obtain the same voltage characteristics no matter which position on the circumferential surface of the bar electrode 12 faces the conductive roller 11. becomes. Note that the cross-sectional shape of the bar electrode 12 may be nonuniform in the circumferential direction, but in this case, the distance of the gap between the pair of electrodes depends on which position of the bar electrode 12 faces the conductive roller 11. changes, so if not only the position of the bar electrode 12 with respect to the conductive roller 11 but also the position of the bar electrode 12 in the circumferential direction is not precisely performed, the voltage characteristics of dielectric breakdown may change and the inspection accuracy may decrease. be.

In this embodiment, the polarity of the voltage applied to the bar electrode 12 is set to be negative relative to that of the conductive roller 11. Further, the distance between the outer peripheral surface of the bar electrode 12 and the surface of the conductive roller 11 is set in a range of 50 μm to 200 μm.

The voltage application unit 13 has a DC power supply 14 and applies a DC voltage as a dielectric breakdown voltage between the conductive roller 11 and the bar electrode 12 that constitute this pair of electrodes. Then, the determination section determines the presence or absence of a pinhole in the film F based on the detection result of the detection section.
Note that the determination unit is composed of a general-purpose minicomputer or the like, and includes a CPU (central processing circuit), ROM (read-only memory circuit), RAM (writable memory circuit), and the like.

Next, with reference to FIGS. 4 and 5, an inspection method according to the present embodiment, which is realized using the above-described inspection apparatus 10, will be described. FIG. 4 is a flowchart illustrating the inspection line L2 according to the embodiment of the invention. FIG. 5 is a schematic diagram illustrating the detection results of the detection step shown in FIG. 4.

As shown in FIG. 4, the inspection line L2 includes a transportation process (S21), a voltage application process (S22), a detection process (S23), a determination process (S24), a rewinding process (S25), The shipping process (S26) is included.
In addition, in this embodiment, since it is estimated that the films F produced on the same production line L1 have the same characteristics, one of the plurality of rolls R is selected as a sample as described above, and this Specimens are used for testing. On the other hand, instead of using a sample, the rolls R may be set and each pinhole inspection may be performed on the first portion of the film F that has started to be conveyed (in-line inspection). In this case, the part used in the test is cut out and discarded after the test. Note that if there are no pinholes, no dielectric breakdown will occur in the film F, so the portion used in the inspection may be left without being cut out.

In the conveyance process, the conductive roller 11 of the inspection device 10 conveys the film F unwound from the sample roll R to the voltage application section 13. In a plurality of rolls R of film F produced on the same production line L1, the overall quality of the plurality of rolls R is judged and managed by inspecting the sample film F for the presence or absence of pinholes. In the voltage application process, the voltage application unit 13 of the inspection device 10 applies a DC voltage between a pair of electrodes constituted by the conductive roller 11 and the bar electrode 12 to the film F of the specimen being transported in the transport process. do. This voltage is preset to a value between the dielectric breakdown voltage (substrate breakdown voltage) when the film F is normal and the dielectric breakdown voltage (pinhole breakdown voltage) when pinholes are generated. In the detection process, the detection unit of the inspection device 10 detects a current corresponding to a discharge current generated in the film F when a DC voltage is applied in the voltage application process, that is, a current that flows when dielectric breakdown occurs in the film F, or Detect voltage drop.

In the determination step, the determination section of the inspection device 10 determines the presence or absence of pinholes in the film F based on the detection result of the detection section. That is, the determination unit determines that there is a pinhole if the detection unit detects a current or voltage drop that corresponds to the discharge current, and determines that there is a pinhole if the current or voltage drop that corresponds to the discharge current is not detected. It is determined that there is no. At this time, in this embodiment, as shown in FIG. 5, even if the film F is thinned, the dielectric breakdown voltage (substrate breakdown voltage) of the normal part of the film F and the dielectric breakdown of the pinhole generated part of the film F are It is possible to make the gap, or window, with respect to the voltage (pinhole withstand voltage) wider than before. Therefore, if the DC voltage applied to the film F by the voltage applying section 13 is set near the center of this expanded window, dielectric breakdown may occur even though there are no pinholes, or even when there are pinholes. Therefore, the phenomenon that no dielectric breakdown occurs can be suppressed, and the determination unit of the inspection device 10 can accurately determine the presence or absence of a pinhole. In the re-winding step, the sample film F is re-wound to the roll R state.

Here, if a pinhole is detected in the determination step, a predetermined alarm device outputs an alarm. The process then stops and does not proceed to the shipping process.
Note that if a pinhole is detected during the above-mentioned in-line inspection, cleaning of the equipment in the previous process is started, or cleaning is encouraged to remove deposits on the roll R in the previous process.

On the other hand, if no pinhole is detected in the specimen film F in the determination step, the process proceeds to the shipping step. In the shipping process, assuming that no pinholes are detected in the specimen, the remainder of the plurality of rolls R other than the specimen is shipped as a film product reel.
Note that during inspection, the specimen becomes charged due to the voltage applied by the conductive roller 11 and the bar electrode 12, but as long as no pinholes are detected, there is no quality problem. The entire roll R may be shipped as a film product reel.
In addition, a voltage is applied to a part of the film F unwound from the roll R to determine the presence or absence of a pinhole, and if it is determined that there is no pinhole, the part of the roll R used for the inspection is The film F may be cut and the remaining portion may be shipped as a film product reel. In this case, for example, the presence or absence of a pinhole may be determined in a part of the film F in the width direction, and the remaining part in the width direction may be used as a film product reel (slit), or one part in the length direction of the roll R may be used as a film product reel (slit). The presence or absence of pinholes may be determined for the part of the film F, and the remaining length of the roll R may be used as a film product reel.

As explained above, according to the present embodiment, one of the conductive rollers 11 (first electrode) of the pair of electrodes is disposed in contact with the back surface (first surface) of the film F, and The other bar electrode 12 (second electrode) is arranged apart from the front surface (second surface), and the polarity of the voltage applied to the bar electrode 12 is set to be negative relative to the conductive roller 11. be done. Therefore, the gap, that is, the window, between the base material breakdown voltage (dielectric breakdown voltage in a normal portion) and the pinhole breakdown voltage (dielectric breakdown voltage in a pinhole generated portion) in the film F can be made wider than in the past. Thereby, the window for detection can be widened, so even if the film F is thinned, pinholes can be detected with high accuracy.

Further, according to the present embodiment, since the distance between the bar electrode 12 (second electrode) and the surface of the conductive roller 11 is set in the range of 50 μm to 200 μm, pinholes can be detected with higher accuracy. can.

Further, according to the present embodiment, the conductive roller 11 (first electrode) is a conductive roller 11 that conveys the film F by contacting the back surface (first surface) of the film F with its circumferential surface. In (S21), it also functions as an electrode while transporting the film F. Therefore, the film F can be inspected for pinholes efficiently.

Further, according to this embodiment, the bar electrode 12 (second electrode) is formed in a cylindrical shape, and is arranged so that its longitudinal direction is perpendicular to the transport direction of the film F and parallel to the width direction of the film F. . Therefore, since the bar electrode 12 has a circular cross section and a uniform shape in the circumferential direction, the same voltage characteristics can be obtained no matter which position on the circumferential surface of the bar electrode 12 faces the conductive roller 11. Therefore, it is possible to prevent a decrease in pinhole detection accuracy.

In order to confirm the effectiveness of the present invention, a comparative test was conducted to compare dielectric breakdown voltages. In this comparative test, inspection devices (10) of a comparative example and an example (corresponding to the above embodiment) were prepared. In the inspection device (10) of the comparative example, the polarity of the voltage applied to the bar electrode (second electrode, 12) was set to be positive relative to that of the conductive roller (first electrode, 11). That is, between the comparative example and the example, the first electrode and the second electrode were set to be opposite to each other, and the other configurations were the same. Furthermore, the film (F) to be tested was also the same. The comparative test results at that time are shown in FIG. FIG. 6 is a graph showing comparative test results of Examples and Comparative Examples according to the present invention.

As shown in FIG. 6, when comparing the detection results of the comparative example and the example, it can be seen that the pinhole withstand voltage is the same, but the base material withstand voltage is about 0.2 kV higher in the example. . In other words, the window of the example is wider than that of the comparative example, and it can be seen that pinhole detection can be performed with high accuracy. In other words, this comparative test demonstrated the effectiveness of the present invention. Here, the reason why only the base material breakdown voltage changed and the pinhole breakdown voltage did not change depending on the polarity of the applied voltage will be explained using FIG. 7. Figure 7 is a block diagram schematically showing the system between the bar electrode and the conductive roller. Figure 7 (a) shows the inspection of a normal part of the film, and Figure 7 (b) shows the part where a pinhole has occurred. Shows the time of inspection. It is generally known that the dielectric breakdown phenomenon exhibits different behavior depending on the positive and negative polarities, but since the system in Figure 7(a) is vertically asymmetric, the system changes when the polarity is reversed, and the withstand voltage of the base material is Differences due to polarity appear. On the other hand, since the system shown in FIG. 7B is vertically symmetrical, the system remains substantially the same even if the polarity is reversed, and it is considered that the pinhole breakdown voltage does not differ depending on the polarity.

This concludes the description of the specific embodiments, but the aspects of the present invention are not limited to the above embodiments, and modifications and improvements can be made as appropriate.
For example, in the above embodiment, nothing was inserted between the second electrode and the film (F), but a dielectric may be placed between them. Therefore, for example, the second electrode may be constituted by a roller having a dielectric layer on the outer periphery.

The manufacturing process to which the inspection method of the present invention is applied is applicable to electrically insulating films (e.g., polyolefin battery separator films, coating separators, nonwoven fabric battery separators, capacitor films, etc.) as well as polyolefin microporous films used for high-precision filtration. It is also suitable for manufacturing processes of films and the like.

10 Inspection device (film pinhole inspection device)
11 Conductive roller (first electrode)
12 Bar electrode (second electrode)
13 Voltage application section 14 DC power supply F Film L1 Production line L2 Inspection line

Claims (13)

a voltage application step of applying a DC voltage between a pair of electrodes arranged opposite to each other so as to sandwich both sides of the film;
a detection step of detecting a current flowing between the pair of electrodes or a voltage drop between the pair of electrodes;
a determination step of determining the presence or absence of a pinhole in the film based on the detection result of the detection step,
One of the first electrodes of the pair of electrodes is placed in contact with a first surface that is the front or back surface of the film,
The other second electrode of the pair of electrodes is spaced apart from a second surface opposite to the first surface,
The polarity of the voltage applied to the second electrode is set to be negative relative to the first electrode.
Film pinhole inspection method. A separation distance between the first electrode and the second electrode is set in a range of 50 μm to 200 μm,
The method for inspecting pinholes in a film according to claim 1. further comprising a conveying step of conveying the film between the pair of electrodes,
The first electrode is a conductive roller that conveys the film by contacting the first surface of the film with its peripheral surface, and also functions as an electrode while conveying the film in the conveying process.
The method for inspecting pinholes in a film according to claim 1 or 2. The second electrode is formed in a cylindrical shape and arranged so that its longitudinal direction is perpendicular to the transport direction of the film and parallel to the width direction of the film.
The method for inspecting pinholes in a film according to any one of claims 1 to 3. an inspection step of inspecting the film for the presence or absence of pinholes by the film pinhole inspection method according to any one of claims 1 to 4;
a winding step of winding the film subjected to the inspection step;
Film manufacturing method. a winding step of winding films produced on the same production line into a plurality of rolls;
Selecting one of the plurality of wound bodies as a specimen, and inspecting the film of the specimen for the presence or absence of the pinhole by the film pinhole inspection method according to any one of claims 1 to 4. An inspection process to
a shipping step of shipping the remainder of the plurality of wound bodies as a final product if the pinhole is not detected in the inspection step;
Film manufacturing method. further comprising a re-winding step of re-winding the specimen;
In the shipping step, all of the plurality of rolled bodies including the specimen are shipped;
The film manufacturing method according to claim 6. a winding step of winding the film produced on the production line into a rolled body;
an inspection step of inspecting a part of the film of the rolled body for the presence or absence of the pinhole by the film pinhole inspection method according to any one of claims 1 to 4;
If the pinhole is not detected in the inspection step, the portion of the film that has been inspected for the presence or absence of the pinhole is cut off, and the remaining portion is shipped as a final product.
Film manufacturing method. The production line is
a solution preparation step of preparing a polyolefin solution by kneading a polyolefin resin and a plasticizer;
a sheet forming step of discharging the polyolefin solution from a die and cooling it to form a gel-like sheet;
a sheet stretching step of stretching the gel-like sheet to form a stretched sheet;
a plasticizer removal step of removing the plasticizer from the stretched sheet to obtain a microporous membrane;
The film manufacturing method according to any one of claims 6 to 8. a pair of electrodes arranged opposite to each other so as to sandwich both sides of the film;
a voltage application unit that applies a DC voltage between the pair of electrodes;
a detection unit that detects a current flowing between the pair of electrodes or a voltage drop between the pair of electrodes;
a determination unit that determines the presence or absence of a pinhole in the film based on the detection result of the detection unit,
One of the first electrodes of the pair of electrodes is placed in contact with the first surface, which is the front or back surface of the film,
The other second electrode of the pair of electrodes is spaced apart from a second surface opposite to the first surface,
The polarity of the voltage applied to the second electrode is set to be negative relative to the first electrode.
Film pinhole inspection device. A separation distance between the first electrode and the second electrode is set in a range of 50 μm to 200 μm,
The film pinhole inspection device according to claim 10. further including a conveyance section that conveys the film to the voltage application section,
The first electrode is a conductive roller that conveys the film by contacting the first surface of the film with its circumferential surface, and is provided integrally with the conveyance section and serves as an electrode while conveying the film. Function,
The film pinhole inspection device according to claim 10 or 11. The second electrode is formed in a cylindrical shape and arranged so that its longitudinal direction is perpendicular to the transport direction of the film and parallel to the width direction of the film.
The film pinhole inspection device according to any one of claims 10 to 12.

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