Continuous measurement method for optical characteristics of film, production method for film, and optical characteristic measurement device for film

Abstract

To provide a measurement method for optical characteristics, a production method for a film, an optical characteristic measurement device which can detect optical abnormality in a film with a simple and inexpensive structure in a film production device.SOLUTION: Provided is a continuous measurement method for optical characteristics of a traveling film in the longitudinal direction. The film is irradiated with light from one surface of the film by a light source. A polarizer is installed on the other surface of the film in parallel with the film. There are four or more polarizers. Each polarizer has different transmission axis angles and is arranged so as not to overlap with light from the light source. A photodetector is installed on the side opposite to the film of the polarizer. The photodetector receives the light transmitted through the film and the polarizer, and derives the optical characteristics of the film from the light intensity of the detected light.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for continuously measuring the optical properties of a film, a method for producing a film, and an apparatus for measuring the optical properties of a film. [Background technology]

[0002] In the continuous film production process, reducing problems such as tearing and ensuring stable production are important issues.

[0003] Polyester resins are used in a variety of applications due to their excellent mechanical properties, thermal properties, electrical properties, chemical resistance, moldability, etc. Polyester films made from polyester resins, particularly biaxially oriented polyester films obtained by stretching in two directions to achieve molecular orientation, are widely used as various industrial materials such as components for optical devices, solar cell backsheets, electrical insulating materials, thermal transfer applications, and process paper.

[0004] In the transverse stretching process of a film forming apparatus, the film is stretched to about 2 to 5 times its width, so a large force is applied to the film, and the film may break. In particular, the film often breaks near the ends in the width direction, because the film is stretched by holding both ends in the transverse stretching process, so a larger stress is concentrated near both ends of the film. If the film breaks, it takes a lot of time and effort to restore it, resulting in a large loss.

[0005] In particular, if there is an abnormality in the physical properties of the film, the film is more likely to break. One such abnormality is an abnormality in the film orientation angle. The orientation angle of a film can be detected as an optical property, and various methods have been proposed as devices for measuring the optical properties of a film (for example, Patent Documents 1, 2, and 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2016-70856 A [Patent Document 2] JP 2020-151909 A [Patent Document 3] JP 2022-134936 A Summary of the Invention [Problem to be solved by the invention]

[0007] However, the inspection device disclosed in Patent Document 1 can inspect the qualitative variation in the orientation angle, but cannot quantitatively measure the orientation angle.

[0008] Furthermore, although the inspection device disclosed in Patent Document 2 can determine the orientation angle of the film, it cannot determine the orientation angle at a location that may cause tearing during the transverse stretching process.

[0009] Furthermore, the inspection device disclosed in Patent Document 3 can detect optical defects in the film, but cannot quantitatively measure the orientation angle.

[0010] The present invention aims to solve the above problems by providing a method for continuously measuring the optical properties of a traveling film, a method for producing a film, and an optical property measuring device that can detect abnormalities in the optical properties of the film with a simple and inexpensive configuration. [Means for solving the problem]

[0011] The optical property measuring method of the present invention, which solves the above problems, is a method for continuously measuring the optical properties of a traveling film in the longitudinal direction, which involves irradiating light from a light source onto the film from one side of the film, placing a polarizing plate on the other side of the film parallel to the film, and the number of polarizing plates is four or more, each of which has a different transmission axis angle and is arranged so as not to overlap with the light from the light source, and placing a light receiving unit on the opposite side of the polarizing plate from the film, which receives light that has passed through the film and the polarizing plate, and deriving the optical properties of the film from the light intensity of the received light, thereby continuously measuring the optical properties of the film in the longitudinal direction. The optical property measuring method, film manufacturing method, and optical property measuring device of the present invention can also be in the following forms. (1) A method for continuously measuring optical properties of a traveling film in the longitudinal direction, comprising the steps of: A method for continuously measuring the optical characteristics of a film in the longitudinal direction, comprising: irradiating light onto one side of the film from a light source; placing a polarizing plate parallel to the film on the other side of the film; and comprising four or more polarizing plates, each with a different transmission axis angle and positioned so as not to overlap with the light from the light source. A light receiving unit is placed on the opposite side of the polarizing plate from the film, and the light receiving unit receives light that has passed through the film and the polarizing plate, and deriving the optical characteristics of the film from the intensity of the received light. (2) A method for continuously measuring the optical properties of a film described in (1) in the longitudinal direction, wherein the polarizing plate is sized so that one side fits within a range of 100 mm square, and when the polarizing plate is projected onto the film, it is positioned within a range of 200 mm square. (3) A method for continuously measuring the optical properties of a film described in (1) or (2) in the longitudinal direction, in which the light receiving unit described in (1) is installed within 200 mm from at least one end of the film width direction toward the center in the film width direction. (4) A method for producing a film, comprising a step of melt-extruding a raw material for a film with an extruder, and then stretching the raw material in at least one axial direction, and a step of continuously measuring optical properties of the film in the longitudinal direction after the stretching step, A method for manufacturing a film, the method comprising the steps of: irradiating light onto the film from one side of the film using a light source; placing a polarizing plate on the other side of the film parallel to the film; and wherein the polarizing plates are four or more in number, each having a different transmission axis angle and being positioned so as not to overlap with the light from the light source; placing a light receiving unit on the opposite side of the polarizing plate from the film; and receiving light that has passed through the film and the polarizing plate and deriving the optical properties of the film from the intensity of the received light, and continuously measuring the optical properties of the film in the longitudinal direction. (5) An optical property measuring device in which light is irradiated onto a film from one side thereof using a light source, a polarizing plate is placed on the other side of the film parallel to the film, the polarizing plates are four or more in number, each having a different transmission axis angle and being positioned so as not to overlap with the light from the light source, a light receiving unit is placed on the opposite side of the polarizing plate from the film, the light receiving unit receives light that has passed through the film and the polarizing plate, and the optical properties of the film are derived from the intensity of the received light. Effect of the Invention

[0012] According to the present invention, it is possible to provide an optical property measuring method, a film manufacturing method, and an optical property measuring device that are capable of detecting optical abnormalities in a film despite having a simple configuration. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic perspective view showing an example of an optical characteristic measuring method of the present invention. [Diagram 2] 1 is a schematic side view showing an example of an optical characteristic measuring method of the present invention. [Diagram 3] This is a diagram showing the positions of the polarizing plates projected onto the film. [Figure 4] FIG. 2 is a top view showing an example of orientation in a film. [Diagram 5] FIG. 2 is a side view showing the configuration of the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The optical property measuring method of the present invention is a method for continuously measuring the optical properties of a traveling film in the longitudinal direction, characterized in that the film is irradiated with light from a light source from one side of the film, a polarizing plate is placed parallel to the film on the other side of the film, the polarizing plates are four or more, each of the polarizing plates has a different transmission axis angle and is arranged so as not to overlap with the light from the light source, a light receiving unit is placed on the opposite side of the polarizing plate from the film, the light receiving unit receives light transmitted through the film and the polarizing plate, and the optical properties of the film are derived from the light intensity of the received light. The optical property measuring method of the present invention will be specifically described below.

[0015] FIG. 1 is a schematic perspective view of one embodiment of the optical property measuring device of the present invention installed in a film forming apparatus, and FIG. 2 is a schematic side view seen from a direction perpendicular to the film running direction. In the embodiment shown in FIG. 1 and FIG. 2, a light source 2 is arranged on one side of the film 1, and light is irradiated onto the film. Four or more polarizing plates 3 are arranged on the other side of the film 1 in parallel with the film 1 so as not to overlap with the light from the light source 2. The arrows on the polarizing plates 3 indicate the transmission axis angles, and each polarizing plate 3 has a different transmission axis angle. In addition, a light receiving unit 4 is arranged on the opposite side of the polarizing plate 3 to the film 1, and the light receiving unit 4 receives the light transmitted through the film 1 and the polarizing plates 3.

[0016] FIG. 3 is a diagram showing the position of the polarizing plate 3 projected onto the film.

[0017] FIG. 4 is a top view of the film in the film-forming apparatus, with arrows indicating the orientation of the film.

[0018] As shown in Figures 1 and 2, the optical property measuring method of the present invention has a light source installed on one side of the film in the inspected area of ​​the traveling film surface, and four or more polarizing plates with different transmission axis angles are installed on the other side parallel to the film so as not to overlap, and a light receiving unit that receives the transmitted light that has passed through the film and the polarizing plates.

[0019] The light receiving unit receives light from the light source that has passed through the film and the polarizing plate, and derives the optical characteristics of the film from the amount of light (light intensity). The light receiving unit is not particularly limited as long as it can receive light from the light source that has passed through the film and the polarizing plate and measure the amount of light (light intensity), but it is preferable to use a commercially available CCD camera or CMOS camera in terms of cost and ease of signal processing. As described later, in the film production process, the ends of the film in the width direction are held by clips in the transverse stretching process, so that a larger force is applied to the ends of the film in the width direction than to the center of the film in the width direction, and optical abnormalities are likely to occur at the ends of the film in the width direction. Therefore, it is preferable to install the light receiving unit within 200 mm from the end on one side of the film in the width direction to the center of the film in the width direction. Furthermore, from the viewpoint of easily detecting optical abnormalities, the distance between the film and the light receiving unit is preferably 1 mm or more and 2000 mm or less, more preferably 10 mm or more and 1500 mm or less, even more preferably 100 mm or more and 1200 mm or less, and particularly preferably 250 mm or more and 1000 mm or less.

[0020] There are no limitations on the light source as long as it is unpolarized, transmits through the polarizing plate and film, and emits an amount of light that can be measured by the light receiving unit. In particular, LED lighting, which has high illuminance and a long life, is preferable. In addition, a bandpass filter or a circular polarizing filter may be added between the light source and the light receiving unit as appropriate.

[0021] Four or more polarizing plates are installed parallel to the film on the other side of the side where the light source is installed. Here, "parallel to the film" means that the angle between the film surface and the polarizing plate surface is 15° or less. The angle between the film surface and the polarizing plate surface is preferably 10° or less, and more preferably 5° or less. The applicable polarizing plate may be any size that can polarize the light from the light source and measure the luminance by the light receiving unit, and a commercially available general-purpose polarizing plate can be applied. However, it is preferable that the polarizing plates are arranged so as not to overlap with the light from the light source, and that each polarizing plate is arranged so as to be within a range of 100 mm square so that there is no significant difference in the way the light from the light source hits the film, and each polarizing plate is preferably arranged close to each other. Similarly, it is preferable that the distance between each polarizing plate and the film is the same or the difference is small so that there is no significant difference in the way the light from the light source hits the film. FIG. 3 is a diagram showing a case where a certain polarizing plate and another polarizing plate are arranged at different distances from the film. Even if the distance between each polarizing plate and the film is different as shown in FIG. 3, it is preferable to project the polarizing plates onto the film and arrange them within a 200 mm square range as shown in FIG. 3, because the difference in the amount of light from the light source is small. In addition, since the luminance of each polarizing plate is measured by the light receiving unit and the orientation angle is derived from the difference, the transmission axis angles of each polarizing plate are different, and the transmission axis angles are preferably as far apart as possible to derive the orientation angle with high accuracy. In the case of using four polarizing plates, it is preferable that the transmission axis angle of a certain polarizing plate is 45°, 90°, and 135° when the transmission axis angle of the certain polarizing plate is set as 0°. In addition, from the viewpoint of easy detection of optical abnormalities, the distance between the film and the polarizing plate is preferably 1 mm or more and 1500 mm or less, more preferably 5 mm or more and 1000 mm or less, even more preferably 10 mm or more and 800 mm or less, and particularly preferably 50 mm or more and 700 mm or less.

[0022] As a method for calculating the orientation angle of the film, it is preferable to use the Jones calculation method, which mathematically calculates polarized light. Since the square of the absolute value of each component of the Jones matrix is ​​proportional to the brightness, it is possible to calculate the orientation angle of the film from the brightness of each polarizing plate. As an example of the calculation method, the following formula (1) is the Jones matrix when the light source passes through the film and the polarizing plate, and the brightness is given by formula (2). Here, L is the brightness, θ is the transmission axis angle of the polarizing plate, β is the orientation angle of the film, δ is the phase difference of the film, and E is a component of the Jones matrix. This is a formula that calculates L by inputting θ, β, and δ for each polarizing plate. Here, since the brightness is measured for each of multiple polarizing plates, β and δ that minimize the error between the brightness calculated by the Jones calculation method from θ, β, and δ for the combination of the transmission axis angle and brightness of each polarizing plate and the brightness can be calculated numerically. As a method for calculating by numerical analysis, commercially available software (such as Microsoft Excel) or a self-made program may be used.

[0023]

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[0024]

number

[0025] Next, the film manufacturing method of the present invention will be described. The film manufacturing method of the present invention is characterized by using the optical property measuring method of the present invention. For example, the film manufacturing method includes a step of melt-extruding a raw material of the film with an extruder, and then stretching the raw material in at least one axial direction, and a step of continuously measuring the optical properties of the film in the longitudinal direction after the stretching step, The optical properties of the film may be measured by a method for producing a film, the method comprising the steps of: irradiating the film with light from a light source from one side of the film; arranging a polarizing plate on the other side of the film in parallel with the film; and, the number of polarizing plates is four or more, each of which has a different transmission axis angle and is arranged so as not to overlap with the light from the light source; and, on the opposite side of the polarizing plate from the film, a light receiving unit is provided, which receives light transmitted through the film and the polarizing plate, and deriving the optical properties of the film from the light intensity of the received light. By adopting such an embodiment, an abnormality in the film orientation angle can be detected early, and thus the film can be produced stably.

[0026] The film production method of the present invention will be specifically described below using a polyester film produced by a sequential biaxial stretching method as an example, although this is merely one embodiment of the present invention and the present invention is not limited thereto.

[0027] First, polyester resin pellets are fed to the raw material input section of the extruder, and the polyester resin is heated and melted. Then, the amount of extrusion is made uniform by a gear pump or the like, and the molten polyester resin is extruded, and foreign matter, gelled matter, etc. are removed through a filter. At this time, the extruder may be one or more, and when multiple extruders are used, the thermoplastic resin that has passed through the filter is sent to a lamination device. As the lamination device, a multi-manifold die, a feed block, a static mixer, etc. can be used, and these may be combined arbitrarily.

[0028] The type of polyester resin is not particularly limited as long as it does not impair the effects of the present invention, and for example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene-2,6-naphthalate (PEN), polybutylene naphthalate (PBN), polytrimethylene terephthalate (PPT), polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate (PCT), etc. can be used alone or in combination. In addition, each of the above polyester resins can also contain a copolymerization component within a range that does not impair the effects of the present invention.

[0029] The molten polyester resin thus obtained is discharged from a die into a sheet form and cooled and solidified on a cooling drum to obtain a non-oriented polyester sheet. In this step, it is preferable to strengthen the adhesion to the cooling drum by applying electrostatic force.

[0030] Next, the non-oriented polyester sheet is heated to a temperature equal to or higher than the glass transition temperature of the polyester resin by contacting and passing it through several temperature-controlled rolls or by heating it with radiant heat from a heater such as an infrared heater, and stretched in the machine direction (longitudinal stretching) by using the difference in peripheral speed between the front and rear rolls. The stretching ratio of this longitudinal stretching depends on the application of the film to be produced and the type of polyester resin, but is preferably 2 to 8 times when the polyester resin is PET. The longitudinal stretching may be performed in one step or in two or more steps.

[0031] The uniaxially oriented polyester sheet obtained by the longitudinal stretching is then cooled once, and subsequently stretched in the width direction (transverse stretching) by a tenter device to become a biaxially oriented polyester film. The uniaxially oriented polyester sheet is held at both ends in the width direction by clips near the entrance of the tenter device, and the clips equipped with bearings run along the clip rails to run toward the exit of the tenter device. Meanwhile, the uniaxially oriented polyester sheet is heated again to a temperature equal to or higher than the glass transition temperature of the polyester resin in the tenter device, stretched in the width direction as the rail on which the clips run widens, and then heat-treated and cooled. The stretch ratio in the width direction depends on the application of the film to be produced and the type of polyester resin, but is preferably 2 to 5 times when the polyester resin is PET. In addition, when the polyester resin is PET, the heat treatment can be performed at a relatively high temperature of 180°C to 250°C. By performing the heat treatment, the dimensional stability when exposed to high temperatures in the subsequent processing steps or when used as a final product is improved. In addition, after the heat treatment, the biaxially oriented polyester film can be relaxed by 1% to 10% in at least one of the longitudinal and transverse directions to further improve the dimensional stability. The process after the transverse stretching may be performed in the same tenter apparatus as the transverse stretching, or may be performed in a tenter apparatus different from the tenter apparatus used for the transverse stretching.

[0032] The biaxially oriented polyester film thus obtained is once wound up as an intermediate product roll on a wide winding machine, then cut to the required width and length by a slitter and wound up again to become the final product.

[0033] Here, when the film is stretched, the molecules are oriented as shown in FIG. 4, but thickness and temperature variations can cause abnormal orientation angles. Since physical properties differ when the orientation angle is different, a large force is applied to the film, particularly in the transverse stretching step, and the film may break due to abnormal orientation angles. In addition, since the film ends are held by clips in the transverse stretching step, a large force is applied to the film ends. Therefore, the optical property measuring method of the present invention is preferably carried out after a step of stretching in at least one direction, and more preferably carried out between the longitudinal stretching step and the transverse stretching step, or immediately after the transverse stretching step. EXAMPLES

[0034] Hereinafter, an example in which a polyester film was used as the film will be described, but the present invention is not limited to this example.

[0035] (Measurement method) The light source 2 was an ITEC Systems Corporation uniform light emitting surface luminaire LMWG200X400-32WD-4, the light receiving unit 4 was a Keyence Corporation CV-035M, and the polarizing plates 3 were four pieces cut into a square with one side measuring 25 mm. Furthermore, the four polarizing plates were arranged parallel to the film and at equal intervals within a range of 60 mm square when projected onto the film, and the respective transmission axis angles were set to 0°, 45°, 90°, and 135°.

[0036] The measurement method was as shown in Figure 5, in which a light source was placed below the film, and the light transmitted through the film and polarizing plate was received by the light receiving unit to determine the luminance for each polarizing plate. The orientation angle of the film was derived by applying each luminance value to the Jones matrix that calculates the polarization state. Here, a circular polarizing filter 5 and a bandpass filter 6 were used to reduce measurement error. The distance between the film and the polarizing plate was 200 mm, and the distance between the film and the camera (light receiving unit) was 700 mm. The measurement results showed that the luminance values ​​of the polarizers with transmission axis angles of 0°, 45°, 90°, and 135° were 143, 133, 38, and 145, respectively, and the calculation results showed that the orientation angle of the film was 77°. The luminance values ​​referred to here are shades divided into 0 to 255 gradations. In addition, when using the Jones matrix formula to numerically analyze the orientation angle of the film, the solver function of Microsoft Excel was used. [Industrial Applicability]

[0037] According to the present invention, it is possible to provide an optical property measuring method, a film manufacturing method, and an optical property measuring device that can detect optical abnormalities in a film with a simple and inexpensive configuration. By using the optical property measuring method of the present invention, it is possible to detect abnormalities in the film orientation angle, thereby reducing film breakage and improving film productivity. [Explanation of symbols]

[0038] 1:Film 2:Light source 3: Polarizing plate 4: Light receiving part 5: Circular polarizing filter 6: Bandpass filter

Claims

1. A method for continuously measuring optical properties of a traveling film in the longitudinal direction, comprising the steps of: A light source shines light onto the film from one side, a polarizing plate is disposed on the other surface of the film in parallel to the film, and the number of the polarizing plates is four or more, the polarizing plates have different transmission axis angles, and are disposed so as not to overlap with the light from the light source; A light receiving section is disposed on the opposite side of the polarizing plate from the film, The light receiving section receives light that has passed through the film and the polarizing plate, and derives the optical characteristics of the film from the intensity of the received light, thereby measuring the optical characteristics of the film continuously in the longitudinal direction.

2. The polarizing plate is sized to fit within a 100 mm square area, The method for continuously measuring optical characteristics of a film in the longitudinal direction according to claim 1 , wherein the polarizing plate is arranged within an area of ​​200 mm square when projected onto the film.

3. 3. A method for continuously measuring optical properties of a film in the longitudinal direction according to claim 1 or 2, wherein the light receiving section according to claim 1 is installed within 200 mm from at least one end of the film in the width direction towards the center in the width direction of the film.

4. A method for producing a film, comprising a step of melt-extruding a raw material for a film with an extruder, and then stretching the raw material in at least one axial direction, and a step of continuously measuring optical properties of the film in a longitudinal direction after the stretching step, A method for manufacturing a film, the method including a step of continuously measuring the optical properties of a film in the longitudinal direction, the step of measuring the optical properties of the film including: irradiating the film with light from a light source from one side of the film; placing a polarizing plate on the other side of the film parallel to the film; the polarizing plates being four or more in number, each having a different transmission axis angle and being positioned so as not to overlap with the light from the light source; placing a light receiving unit on the opposite side of the polarizing plate from the film, the light receiving unit receiving light that has passed through the film and the polarizing plate, and deriving the optical properties of the film from the intensity of the received light.

5. A light source shines light onto the film from one side, a polarizing plate is disposed on the other surface of the film in parallel to the film, and the number of the polarizing plates is four or more, the polarizing plates have different transmission axis angles, and are disposed so as not to overlap with the light from the light source; A light receiving section is disposed on the opposite side of the polarizing plate from the film, The light receiving section receives light that has passed through the film and the polarizing plate, and derives the optical characteristics of the film from the intensity of the received light.

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