Film temperature and thickness measuring device and measuring method using the same

Abstract

The present invention relates to a film temperature and thickness measuring device and a measuring method using the same, which sequentially measures the surface temperature and thickness of a film being extruded or coated in an in-line manner at the same point, and controls the film temperature and thickness based on the measured data, thereby enabling the production of a film with a uniform thickness.

Description

[Technical field]

[0001] This invention claims the benefit of the filing date of Korean Patent Application No. 10-2022-0140518, filed with the Korean Intellectual Property Office on October 27, 2022, the entire contents of which are incorporated herein by reference. The present invention relates to a film temperature and thickness measuring device capable of sequentially measuring the temperature and thickness of a film produced during an in-line polymer film production process, and a measuring method using the same. [Background technology]

[0002] Generally, a porous polymer film is used as a separator for a secondary battery. The polymer film is usually produced by forming a polymer resin melt discharged from an extruder into a film, and then stretching and heat setting the film.

[0003] The film manufacturing process is carried out in an in-line manner with a roll-to-roll structure, and the resulting product is in the form of a rectangular separator roll, which is then cut to a predetermined size and used as a separator substrate.

[0004] The polymer film used in the separator preferably has a uniform thickness variation throughout the separator in order to improve product yield, and therefore, it is necessary to control the thickness uniformity of the produced film by measuring the thickness during the extrusion process of the polymer film.

[0005] Previously, only the thickness of the polymer film was measured, but the thickness of the film produced can change depending on the real-time process temperature due to the thermal expansion coefficient of the polymer material. If there is a difference in the uniformity of the film thickness, product defects can occur in the post-process due to waviness and thickness variations in the material.

[0006] Currently, there is no method for real-time measurement of film temperature changes, so it is impossible to measure film thickness changes and predict temperature changes. Therefore, in the past, after changing the process, products were manufactured through actual thickness measurements using a sampling method, sample measurements according to material characteristics, and calibration of measuring instruments.

[0007] Specifically, referring to FIG. 1, conventionally, after a film 1 is extruded by an extruder 10, the thickness of the film 1 is measured in a separate process using a scanning type loading level density meter 3. In this case, a preparatory work is required to confirm the thickness value of the product using the loading level density meter 3. That is, the thickness of the film 1 can be confirmed after a calibration work using a sample of the film 1.

[0008] However, the actual thickness measurement of the film 1 sample can only be performed with the manufacturing equipment after the rewinder of the winding roll 5 stopped, and there are cumbersome problems such as the need to measure the temperature of the film 1 sample using a separate infrared surface infrared temperature sensor. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the above problems, and aims to provide a film temperature and thickness measuring device and a measuring method using the same, which can sequentially measure the surface temperature and thickness of a film being extruded or coated in an in-line manner at the same point, and produce a film of uniform thickness by controlling the film temperature and thickness based on the measured data. [Means for solving the problem]

[0010] To achieve the above object, the film temperature and thickness measuring device according to the present invention is a measuring device for measuring the temperature and thickness of a film being extruded or coated, and includes a conveying unit having a rotating roll for conveying the film being formed in one direction, a thickness measuring unit installed at a distance from an outer circumferential surface of the rotating roll for measuring the thickness of the film being conveyed, a temperature measuring unit disposed adjacent to the thickness measuring unit for measuring the surface temperature of the film being conveyed, and a control unit for determining whether or not the measured values ​​measured by the thickness measuring unit and the temperature measuring unit exceed a reference value.

[0011] In this case, the temperature measuring unit and the thickness measuring unit are arranged on the same line in the transport direction of the film so that the surface temperature and thickness of the film can be measured successively at the same point on the transported film. Here, a thickness measuring section and a temperature measuring section are disposed in this order from upstream to downstream in the transport direction of the film. Alternatively, the temperature measuring section and the thickness measuring section may be disposed in this order from the upstream to the downstream in the transport direction of the film.

[0012] The thickness measuring unit may include a guide rail arranged parallel to and spaced apart from the central axis of the rotating roll, a movable plate connected to the guide rail so as to be movable back and forth by receiving power along the longitudinal direction of the guide rail, and a laser displacement sensor connected to the movable plate via a first bracket and configured to irradiate a laser toward a surface of the film transported by the rotating roll to measure the thickness of the film.

[0013] The moving plate may be coupled to the guide rail so as to be reciprocally movable in a direction intersecting the longitudinal direction of the guide rail, thereby adjusting a distance between the moving plate and an outer circumferential surface of the rotating roll. The first bracket may be connected to the movable plate so as to be rotatable at a predetermined angle along the film transport direction with the first hinge axis of the movable plate as a rotation center, thereby enabling adjustment of the laser irradiation angle of the laser displacement sensor.

[0014] The temperature measurement unit may also include a second bracket connected to the first bracket so as to be movable back and forth along a direction intersecting the longitudinal direction of the rotating roll, and an infrared temperature sensor provided on the second bracket for measuring the surface temperature of the film transported by the rotating roll. The infrared temperature sensor may also be connected to the second bracket so as to be rotatable at a predetermined angle along the film transport direction with the second hinge axis of the second bracket as a rotation center, thereby enabling adjustment of the infrared irradiation position of the infrared temperature sensor.

[0015] Furthermore, when the film is extrusion molded, the temperature measuring section and the thickness measuring section can measure adjacent positions within 0 to 30 mm along the transport direction of the film. In addition, when the film is formed by coating, the temperature measuring unit and the thickness measuring unit can measure adjacent positions within 0 to 100 mm along the transport direction of the film.

[0016] On the other hand, the film temperature and thickness measuring method according to the present invention is The method may include the steps of forming a film by an extrusion or coating process, transporting the formed film in one direction by a rotating roll, irradiating an infrared ray toward a surface of the film transported by the rotating roll to measure the film temperature at a predetermined point, irradiating a laser to the same or a nearby position on the surface of the film where the temperature is measured to measure the thickness of the film, determining whether the measured film temperature and thickness values ​​exceed reference values, and changing conditions of the film manufacturing process if the measured values ​​exceed the reference values.

[0017] Here, the step of measuring the thickness of the film may include measuring the temperature of the film in the same line as the transport direction of the film and then measuring the thickness of the film so that the surface temperature and thickness of the film can be measured sequentially at the same point on the transported film.

[0018] Alternatively, the step of measuring the temperature of the film may include measuring the thickness of the film in the same line as the transport direction of the film and then measuring the temperature of the film so that the thickness and surface temperature of the film can be measured sequentially at the same point on the transported film.

[0019] In this case, the step of measuring the thickness of the film can include the steps of: irradiating a laser toward the surface of a rotating roll when the film is not being transported using a laser displacement sensor, measuring the outer diameter of the rotating roll and setting this as a basic value; irradiating a laser onto the surface of the film using the laser displacement sensor while the film is being transported using the rotating roll, measuring the measured distance from the film; and subtracting the basic value from the measured distance from the film to derive the thickness of the film. Effect of the Invention

[0020] The film temperature and thickness measuring device and the measuring method using the same according to the present invention configured as described above sequentially measure the surface temperature and thickness at the same point of a film being extruded or coated in an in-line manner, and the measured data values ​​are compared with reference values ​​to change various film manufacturing process conditions or perform processes such as heat setting.

[0021] In other words, by using the film temperature and thickness measuring device according to the present invention, the temperature changes and material changes of the film to be manufactured can be predicted in advance based on the measured film temperature and thickness values, and based on this, a film of uniform thickness can be manufactured.

[0022] In particular, by being able to measure the temperature and thickness of a film sequentially at the same adjacent position of the film being transported after film extrusion or coating molding, it is possible to eliminate the need for the conventional process of measuring samples of film products, thereby shortening the time required for the manufacturing process. [Brief description of the drawings]

[0023] [Figure 1] Schematic diagram showing a conventional in-line film manufacturing process; [Diagram 2] FIG. 1 is a schematic diagram showing an in-line film manufacturing process to which the film temperature and thickness measuring device according to the present invention is applied; [Diagram 3] 1 is a schematic diagram of a film temperature and thickness measuring device according to the present invention; [Figure 4] FIG. 1 is a perspective view of a film temperature and thickness measuring device according to the present invention; [Diagram 5] FIG. 2 is a perspective view of a main part of a film temperature and thickness measuring device according to the present invention; [Figure 6] FIG. 2 is a side view of a film temperature and thickness measuring device according to the present invention; [Figure 7] FIG. 2 is a side view showing the structure of a thickness measuring unit according to the present invention; [Figure 8] FIG. 2 is a schematic diagram showing the thickness measurement principle of the thickness measurement unit according to the present invention; [Figure 9] FIG. 2 is a side view showing the structure of a temperature measuring unit according to the present invention; [Figure 10] FIG. 2 is a detailed view of the main part of the film temperature and thickness measuring device according to the present invention; [Figure 11] FIG. 2 is a diagram showing the arrangement of a film temperature and thickness measuring device according to the present invention; [Figure 12] 1 is a flow chart showing a process for measuring film temperature and thickness according to the present invention; [Figure 13] 1 is a photograph substituting a drawing comparing a film temperature and thickness measuring method according to the present invention with a conventional thickness measuring method. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the configuration and operation of specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. Here, when assigning reference symbols to components in each drawing, it should be noted that identical components are represented by the same symbols as much as possible, even if they are shown in different drawings.

[0025] FIG. 2 is a schematic diagram showing an in-line film production process to which the film temperature and thickness measuring device according to the present invention is applied, and FIG. 3 is a schematic diagram showing the configuration of the film temperature and thickness measuring device according to the present invention.

[0026] 2 and 3, a film temperature and thickness measuring device 100 according to a preferred embodiment of the present invention may include a conveying unit 110, a thickness measuring unit 120, a temperature measuring unit 130, and a control unit 140.

[0027] For reference, for ease of explanation, an example of measuring the temperature and thickness of a film 1 extruded by an extruder 10 using the film temperature and thickness measuring device 100 according to the present invention will be illustrated and described below. Of course, the present invention is not limited to this, and the measuring device 100 according to the present invention can be used to measure the temperature and thickness of a film 1 on which a coating layer is formed, even during a manufacturing process of a film 1 in which a coating layer (wet coating) is formed by applying a coating slurry to a substrate.

[0028] The configuration of the present invention will be specifically described as follows. First, the conveying unit 110 conveys the polymer film 1 (hereinafter, abbreviated as "film") extruded from the extruder 10 in one direction. The conveying unit 110 is adapted to an in-line method having a roll-to-roll structure, so that the film 1 can be continuously manufactured.

[0029] Specifically, the transport section 110 may include a plurality of rotating rolls 111 that are driven by a motor and rotate at a predetermined speed to transport the film 1 . In this case, the film temperature and thickness measuring device 100 according to the present invention is provided on any one of the multiple rotating rolls 111 .

[0030] 4 and 5, the thickness measuring unit 120 is installed at a predetermined distance from the outer circumferential surface of the rotating roll 111 and can measure the thickness of the transported film 1 in real time.

[0031] Specifically, the thickness measuring unit 120 may include a guide rail 121 arranged at a distance parallel to the central axis of the rotating roll 111, a movable plate 123 connected to the guide rail 121 so as to be capable of moving back and forth by receiving power along the longitudinal direction of the guide rail 121, and a laser displacement sensor 127 connected to the movable plate 123 via a first bracket 125 and configured to irradiate a laser toward the surface of the film 1 transported by the rotating roll 111 to measure the thickness of the film 1.

[0032] 6, the moving plate 123 is coupled to be reciprocally movable in a direction intersecting with the longitudinal direction of the guide rail 121, and can adjust the distance between the moving plate 123 and the outer circumferential surface of the rotating roll 111. In this case, the distance between the moving plate 123 can be automatically adjusted by receiving power or manually adjusted. In the present invention, the case where the distance between the moving plate 123 is manually adjusted is taken as an example.

[0033] 7, the first bracket 125 is connected to the moving plate 123 so as to be rotatable at a predetermined angle in the transport direction of the film 1 around the first hinge shaft 125a of the moving plate 123. This makes it possible to adjust the laser irradiation angle of the laser displacement sensor 127 irradiated toward the surface of the film 1.

[0034] In this case, the structure for sliding the laser displacement sensor 127 in the longitudinal direction of the film 1 or in a direction intersecting the longitudinal direction can be constructed by selectively applying various conventionally known components, and therefore a detailed description of the structure will be omitted.

[0035] 8, the principle of measuring the thickness of the film 1 using the thickness measuring unit 120 configured as above is as follows: first, using the laser displacement sensor 127, a laser is irradiated toward the surface of the rotating roll 111 on which the film 1 is not being conveyed, and the outer diameter d of the rotating roll 111 is measured based on the distance from the surface of the rotating roll 111, and this is set as a basic value. As a reference, the basic value may be the roundness of the rotating roll 111, etc. Then, while the film 1 is being conveyed using the rotating roll 111, the laser displacement sensor 127 irradiates the surface of the film 1 with a laser to measure the measured distance from the film 1. Then, the thickness t of the film 1 can be derived by subtracting the basic value from the measured value obtained by measuring the distance from the surface of the film 1 using the laser displacement sensor 127.

[0036] Referring again to FIG. 6, the temperature measuring unit 130 is disposed adjacent to the thickness measuring unit 120 and can measure the surface temperature of the transported film 1 in real time.

[0037] Explaining in detail with reference to FIG. 9, the temperature measuring unit 130 may include a second bracket 131 connected to the first bracket 125 so as to be movable forward and backward in a direction intersecting the longitudinal direction of the rotating roll 111 (the transport direction of the film 1), and an infrared temperature sensor 133 installed on the second bracket 131 to measure the surface temperature of the film 1 transported by the rotating roll 111.

[0038] In this case, the infrared temperature sensor 133 is connected to the second bracket 131 so as to be rotatable at a predetermined angle in the transport direction of the film 1 around the second hinge shaft 131a of the second bracket 131. This makes it possible to adjust the infrared irradiation position of the infrared temperature sensor 133. The temperature and thickness measuring device 100 having the above-mentioned temperature measuring unit 130 and thickness measuring unit 120 is preferably provided on the first rotating roll 111 (see FIG. 2) among the multiple rotating rolls 111 in the transport direction of the film 1.

[0039] That is, after the film 1 is extruded, the film 1 may shrink or expand due to heat while being transported by a plurality of rotating rolls 111. Therefore, accurate measurement data can be obtained by measuring the temperature and thickness of the film 1 before it shrinks or expands during the transport process and immediately after the film 1 is extruded.

[0040] However, the present invention does not particularly limit the temperature / thickness measurement position of the film 1 using the measuring device 100. That is, the measuring device 100 may be applied to the first rotating roll (chill or cooling roll) immediately after the extrusion process of the film 1, or the second or third rotating roll, or may be applied to the rotating roll after the stretching process in the width direction or length direction of the film.

[0041] In this case, the temperature measuring unit 130 and the thickness measuring unit 120 are arranged on the same line as the transport direction of the film 1 so that the temperature and thickness of the film 1 at the same point on the transported film 1 can be measured sequentially. Of course, this is not limited to this, and the temperature measuring unit 130 and the thickness measuring unit 120 can also be arranged adjacent to each other in the width direction of the transported film 1 to measure the temperature and thickness at the adjacent positions. In the present invention, an example in which the temperature measuring unit 130 and the thickness measuring unit 120 are arranged on the same line as the transported film 1 is illustrated and described.

[0042] 10, when the film 1 is extrusion molded, it is preferable that the measurement position L of the temperature measuring unit 130 and the thickness measuring unit 120 is within 0 to 30 mm, preferably within 0 to 10 mm, in the transport direction of the film 1, and sequentially measures the same adjacent position. That is, if the measurement position L of the temperature measuring unit 130 and the thickness measuring unit 120 exceeds 30 mm, an error may occur due to a temperature change after the film is extruded.

[0043] When the film 1 is coated, it is preferable that the measurement position L of the temperature measuring unit 130 and the thickness measuring unit 120 measure adjacent positions within 0 to 100 mm along the transport direction of the film 1. That is, when the film 1 is coated, the film 1 is transported at a transport speed faster than that of the extrusion molding. Thus, the range of the measurement position L can be increased in proportion to the speed. Referring to FIG. 11, the temperature measuring unit 130 and thickness measuring unit 120 having the above-described structure are arranged at intervals along the longitudinal direction of the guide rail 121, and can sequentially measure the temperature and thickness at multiple points on the film 1.

[0044] In this case, the present invention has been illustrated and described with an example of first measuring the temperature at a specific point on the film 1 being extruded and then measuring the thickness of the film 1 at the same point, but this is not limited to this and can be modified and applied to a case where the thickness of the film 1 being extruded and then the temperature of the film 1 is measured.

[0045] That is, based on the upstream-to-downstream direction of the conveying direction of the film 1 being extruded and conveyed by the rotating roll 111, the thickness measurement unit 120 is formed on the upstream side, and the temperature measurement unit 130 is formed on the downstream side. Alternatively, based on the upstream-to-downstream direction of the conveying direction of the film 1 being extruded and conveyed by the rotating roll 111, the temperature measurement unit 130 may be formed on the upstream side, and the temperature measurement unit 120 may be formed on the upstream side.

[0046] Meanwhile, the control unit 140 (see FIG. 3) can determine whether the measured values ​​respectively measured by the thickness measuring unit 120 and the temperature measuring unit 130 exceed a reference value.

[0047] That is, the control unit 140 can change the conditions of the extrusion molding film 1 manufacturing process based on the thickness and temperature measurements of the film 1 by the thickness measurement unit 120 and the temperature measurement unit 130, thereby manufacturing a film 1 of uniform thickness.

[0048] For example, the control unit 140 can heat-treat the film 1 by stretching and heat-setting after extrusion molding of the film 1 to remove localized twists and the like that occur during molding. This can suppress shrinkage and wrinkles in the film 1 and improve dimensional stability, such as maintaining a uniform thickness of the film 1.

[0049] Hereinafter, a process of measuring the film temperature and thickness using the film temperature and thickness measuring device 100 of the present invention will be described with reference to FIG. First, a film is extruded by the extruder 10 (S1). Thereafter, the extruded film is transported in one direction by a rotating roll 111 (S2). Thereafter, after the film 1 is extrusion-molded, infrared rays are irradiated from the rotating roll 111 conveyed toward a predetermined point on the surface of the film 1, and the temperature of the film 1 is measured (S3).

[0050] At the same time, a laser is irradiated onto the same point of the film 1 where the temperature was measured, and the thickness of the film 1 is measured (S4). In this case, the present invention has been described in the order of first measuring the temperature of film 1 (S3) and then measuring the thickness of film 1 (S4). However, this can be changed conversely to measuring the thickness of film 1 first (S3') and then measuring the temperature of film 1 by irradiating infrared light toward the same point on film 1 where the thickness of film 1 was measured (S4').

[0051] That is, in order to sequentially measure the surface temperature and thickness of the film 1 at the same point on the transported film 1, the temperature of the film 1 can be measured on the same line as the transport direction of the film 1, and then the thickness of the film 1 can be measured. Alternatively, in order to sequentially measure the thickness and surface temperature of the film 1 at the same point on the transported film 1, the thickness of the film 1 can be measured on the same line as the transport direction of the film 1, and then the temperature of the film 1 can be measured.

[0052] Then, the control unit 140 compares the measured temperature and thickness values ​​of the film 1 to determine whether they exceed reference values ​​(S5), and if the measured values ​​exceed the reference values, changes the conditions of the film 1 manufacturing process (S6).

[0053] The film temperature and thickness measuring device 100 according to the present invention configured as above, as shown in Fig. 13, sequentially measures the surface temperature and thickness at the same point of the film 1 formed in-line, and can predict the temperature change and material change of the film in advance by comparing the measured values ​​with the reference values ​​in real time. Based on this, it is possible to manufacture a film of uniform thickness by changing the conditions of the film manufacturing process or by going through a process such as heat fixing.

[0054] In particular, the present invention can sequentially measure the temperature and thickness of film 1 in real time during the extrusion or coating process of film 1, thereby eliminating the need for a sample measurement process of the film product as in the conventional method, and thereby shortening the time required for the manufacturing process.

[0055] Although the present invention has been illustrated and described above by way of specific examples, it is of course possible to change and modify the present invention in various ways without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0056] 1: Film, 100: Temperature and thickness measuring device 110: conveying section, 111: rotating roll 120: thickness measuring section, 121: guide rail 123: moving plate, 125: first bracket 125a: first hinge axis, 127: laser displacement sensor 130: temperature measuring unit, 131: second bracket 131a: second hinge axis, 133: infrared temperature sensor 140: Control unit

Claims

1. A measuring device for measuring the temperature and thickness of a film being extruded or coated, A conveying section including a rotating roll for conveying the formed film in one direction; a thickness measuring unit disposed apart from an outer circumferential surface of the rotating roll and configured to measure a thickness of the transported film; a temperature measuring unit arranged adjacent to the thickness measuring unit and configured to measure a surface temperature of the film being transported; and a control unit that determines whether or not the measured values ​​measured by the thickness measuring unit and the temperature measuring unit respectively exceed a reference value.

2. The temperature measuring unit and the thickness measuring unit are 2. The film temperature and thickness measuring device according to claim 1, which is arranged in the same line as the film transport direction so that the surface temperature and thickness of the film can be measured successively at the same point on the transported film.

3. 3. The film temperature and thickness measuring device according to claim 2, wherein a thickness measuring section and a temperature measuring section are disposed in this order from upstream to downstream in the film transport direction.

4. 3. The film temperature and thickness measuring device according to claim 2, wherein a temperature measuring section and a thickness measuring section are disposed in this order from upstream to downstream in the film transport direction.

5. The thickness measuring unit includes: A guide rail arranged parallel to the central axis of the rotating roll and spaced apart from the central axis of the rotating roll; a moving plate coupled to the guide rail so as to be reciprocally movable in a longitudinal direction of the guide rail by receiving a power; 2. The film temperature and thickness measuring device of claim 1, further comprising: a laser displacement sensor coupled to the moving plate via a first bracket and configured to measure a thickness of the film by irradiating a laser toward a surface of the film transported by the rotating roll.

6. The moving plate is 6. The film temperature and thickness measuring device according to claim 5, further comprising a guide rail connected to the guide rail so as to be movable back and forth in a direction intersecting the longitudinal direction of the guide rail, so that a distance between the guide rail and an outer circumferential surface of the rotating roll can be adjusted.

7. The first bracket is 6. The film temperature and thickness measuring device according to claim 5, further comprising a first hinge axis of the movable plate that is connected to the movable plate so as to be rotatable by a predetermined angle along the film transport direction, the first hinge axis being a rotation center, thereby enabling adjustment of the laser irradiation angle of the laser displacement sensor.

8. The temperature measuring unit is a second bracket coupled to the first bracket so as to be movable forward and backward along a direction intersecting the longitudinal direction of the rotating roll; 6. The film temperature and thickness measuring device according to claim 5, further comprising: an infrared temperature sensor provided on the second bracket for measuring a surface temperature of the film being transported by the rotating roll.

9. The infrared temperature sensor is 9. The film temperature and thickness measuring device of claim 8, further comprising a second hinge axis of the second bracket that is rotatably connected to the film transport direction by a predetermined angle around the second hinge axis, thereby enabling adjustment of the infrared irradiation position of the infrared temperature sensor.

10. The temperature measuring unit and the thickness measuring unit are 3. The film temperature and thickness measuring device according to claim 2, which measures a proximity position within 0 to 30 mm along the transport direction of the film when the film is extruded.

11. The temperature measuring unit and the thickness measuring unit are 3. The film temperature and thickness measuring device according to claim 2, which measures a proximity position within 0 to 100 mm along the transport direction of the film when the film is coated.

12. forming a film by an extrusion or coating process; A step of conveying the formed film in one direction by a rotating roll; a step of irradiating an infrared ray toward a surface of the film transported by the rotating roll to measure a temperature of the film at a predetermined point; measuring a thickness of the film by irradiating a laser at the same or a nearby position on the surface of the film where the temperature was measured; determining whether the film temperature and thickness measurements exceed reference values; and if the measured value exceeds a reference value, changing conditions of the film manufacturing process.

13. The step of measuring the thickness of the film comprises: The method for measuring film temperature and thickness according to claim 12, further comprising measuring the temperature of the film on the same line as the transport direction of the film and then measuring the thickness of the film so that the surface temperature and thickness of the film can be measured sequentially at the same point on the transported film.

14. The step of measuring the temperature of the film includes: The method for measuring film temperature and thickness according to claim 12, further comprising measuring the thickness of the film on the same line as the transport direction of the film, and then measuring the temperature of the film, so that the thickness and surface temperature of the film can be measured sequentially at the same point on the transported film.

15. The step of measuring the thickness of the film comprises: a step of measuring the outer diameter of the rotating roll by irradiating a laser toward the surface of the rotating roll while the film is not being transported using a laser displacement sensor, and setting the outer diameter as a basic value; a step of irradiating a laser onto a surface of the film by the laser displacement sensor during transport of the film using the rotating roll, and measuring a distance measurement value between the film and the surface; and subtracting a base value from the distance measurement to the film to derive a thickness of the film.

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