Method for measuring the curl of an optical film and method for manufacturing an optical film

Abstract

This invention provides a method for measuring the curl value of optical films that can accurately measure the curl value in a short amount of time. [Solution] The curl measurement method according to the present invention is a method for measuring a curl value representing the degree of curl of a sheet-shaped optical film F using an optical sensor 1 equipped with a light emitter 11 and a light receiver 12, comprising: an arrangement step ST21 in which the light emitter is placed on one side of the optical film and the light receiver is placed on the other side of the optical film, sandwiching the optical film and facing the light emitter; an emission and reception step ST22 in which a light beam L extending vertically toward the optical film is emitted using the light emitter and the light that is transmitted through the light beam without being blocked by the optical film is received using the light receiver; and a curl value calculation step ST23 in which the curl value of the optical film is calculated based on the vertical length of the transmitted light.

Description

Technical Field

[0001] The present invention relates to a method for measuring the curl value of an optical film that can measure the curl value representing the degree of curl that may occur at the end of an optical film such as a sheet-like polarizing plate, and a method for manufacturing an optical film using the same. In particular, the present invention relates to a method for measuring the curl value of an optical film that can accurately measure the curl value in a short time, and a method for manufacturing an optical film using the same.

Background Art

[0002] Conventionally, a polarizing plate has been used as a constituent material for liquid crystal display devices, organic EL display devices, and the like. The polarizing plate includes a retardation film or the like according to the application, in addition to the polarizing film. The polarizing film is composed of, for example, a polarizer dyed with a dichroic substance such as iodine and a protective film for protecting the polarizer. The long-strip polarizing film is manufactured by laminating a long-strip protective film on at least one side of the long-strip polarizer. A long-strip retardation film or the like is laminated on one side of the manufactured long-strip polarizing film to manufacture a long-strip optical laminate. A long-strip release liner is laminated on one side of the manufactured long-strip optical laminate, and a long-strip surface protective film is laminated on the other side to manufacture a long-strip polarizing plate. The lamination of these long-strip films is usually performed by a roll-to-roll method or a roll-to-sheet method. The manufactured long-strip polarizing plate is cut into sheet form to have a size and shape according to the application, and is used in a liquid crystal display device or the like. When used in a liquid crystal display device or the like, the release liner is peeled off, and the remaining components of the polarizing plate are attached to the liquid crystal display device or the like.

[0003] However, in an optical film such as a sheet-like polarizing plate manufactured as described above, curl (warping at the end) that causes problems in use may occur. When the degree of curl becomes severe, it causes problems when laminating the optical film to a liquid crystal display device or the like. Therefore, the curl value representing the degree of curl is measured, and based on the magnitude thereof, it is determined whether the optical film is a good product or a defective product, and the defective products are discarded.

[0004] Figure 1 is a schematic diagram illustrating an example of a conventional method for measuring curl value. When measuring the curl value, the optical film F is placed on a flat mounting platform 5 so that its lower side is convex (the curve of the edges of the optical film F is upward), and the vertical distance H from the top surface of the mounting platform 5 to the outer edge of the optical film F (if the optical film F is rectangular, the vertical distance to its four corners) is measured. The distance H is measured by placing a scale that extends vertically near the outer edge of the optical film F and having the operator visually read the scale's markings. The maximum value of distance H is then taken as the curl value. In other words, when the optical film F is placed on a flat surface (the top surface of the mounting platform 5) with its lower side convex, the vertical distance between the lowest point of the optical film F (a point at the same position as the top surface of the mounting platform 5) and the highest point of the optical film F is taken as the curl value. If this curl value is below a predetermined threshold, the optical film F is judged to be a good product; if it exceeds the threshold, it is judged to be a defective product.

[0005] Conventional measurement methods, as shown in Figure 1, require manual measurement by workers, resulting in lengthy measurement times. Therefore, from the standpoint of optical film manufacturing efficiency, it is difficult to measure all optical films, necessitating sampling measurements, which carries the risk of defective products being released. Furthermore, because measurements are performed manually, there is a possibility of variability in measurement results from one worker to another. Therefore, there is a need to automatically measure the curl value of optical films using optical sensors.

[0006] Figure 2 is a schematic side view (viewed from a horizontal direction perpendicular to the optical film transport direction) illustrating a general configuration example of a conventional measuring device that automatically measures the curl value of an optical film using an optical sensor. In Figure 2, the X direction represents the horizontal direction which is the transport direction of the optical film F, the Y direction represents the horizontal direction perpendicular to the X direction, and the Z direction represents the vertical direction (thickness direction of the optical film F). The same applies to Figure 5, which will be described later. As shown in Figure 2, conventional measuring devices 100' generally use a reflective optical sensor equipped with a light emitter 11' and a light receiver 12'. Specifically, for example, a sensor that performs the light section method, a type of triangulation method, is used as the optical sensor, a laser light source that emits a linear laser beam L' extending in the Y direction is used as the light emitter 11', and an area sensor camera in which imaging elements such as CCDs and CMOS are arranged in a matrix is ​​used as the light receiver 12'. The laser beam L' is projected from the light emitter 11' downward in the Z direction toward the upper surface of the optical film F, and the reflected light of the laser beam L' reflected from the upper surface of the optical film F is received by the light receiver 12' which has a viewing axis tilted with respect to the Z direction (the laser beam L' irradiated onto the optical film F is imaged by the light receiver 12'). Based on the image obtained by analyzing the deformation state of the linear laser beam L', the position in the Z direction of the upper surface of the optical film F along the Y direction is measured. Since the optical film F is placed on the belt conveyor 3 and transported in the X direction, the position of the upper surface of the optical film F in the Z direction is continuously measured from the state in Figure 2(a) where the leading edge (downstream end in the transport direction) FT of the optical film F is directly below the light projector 11', to the state in Figure 2(b) where the rear end (upstream end in the transport direction) FR of the optical film F is directly below the light projector 11', and the curl value of the optical film F can be calculated based on these measurement results. Specifically, for example, the curl value can be calculated based on the difference between the highest Z-direction position of the upper surface of the optical film F measured and the Z-direction position of the upper surface of the transport belt constituting the belt conveyor 3.

[0007] In the conventional measuring device 100' having the above configuration, since a reflective optical sensor is used, as shown in Figure 2(a), when the tip FT of the optical film F, which is curled (bent) with its normal direction tilted towards the upstream side in the transport direction, is located directly below the light emitter 11', the reflected light of the laser beam L' with sufficient light intensity is easily reflected towards the light receiver 12', making it possible to measure the position in the Z direction of the upper surface of the optical film F with relatively good accuracy. However, as shown in Figure 2(b), when the rear end FR of the optical film F, which is curled with its normal direction tilted downstream in the transport direction, is located directly below the light emitter 11', the reflected light of the laser beam L' with sufficient light intensity may not be reflected towards the light receiver 12' depending on the surface condition of the optical film F. In this case, the measurement accuracy of the Z-direction position of the upper surface of the optical film F deteriorates. Furthermore, if the curl is extremely large, the light receiver 12' may not be able to receive the reflected light, and it may not be possible to measure the Z-direction position of the upper surface of the optical film F. Thus, conventional curl measurement methods using reflective optical sensors have a problem in that they may not be able to accurately measure the curl value due to the influence of the direction of curl and the surface condition of the optical film.

[0008] For example, Patent Document 1 proposes a method for analyzing the curl of a single-sheet (circular) optical film, but it uses a reflective optical sensor as a measuring device to measure the vertical distance to the optical film (paragraph 0044 of Patent Document 1, Figure 1), which can lead to the same problems as the conventional curl measurement method described above. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2020-85754 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The present invention was made to solve the problems of the prior art described above, and aims to provide a method for measuring the curl of an optical film that can measure the curl value accurately in a short time, and a method for manufacturing an optical film using the same. [Means for solving the problem]

[0011] To solve the aforementioned problems, the present invention provides a method for measuring the curl value of a sheet-shaped optical film using an optical sensor comprising a light emitter and a light receiver, the method comprising: an arrangement step of arranging the light emitter on one side of the optical film and arranging the light receiver on the other side of the optical film, with the optical film in between, so as to face the light emitter; an emission and light receiving step of using the light emitter to emit a light beam extending vertically toward the optical film and using the light receiver to receive the light from the light beam that has been transmitted without being blocked by the optical film; and a curl value calculation step of calculating the curl value of the optical film based on the vertical length of the transmitted light.

[0012] In this invention, "side of the optical film" means the direction along the in-plane direction of the optical film (the in-plane direction assuming a flat optical film without curl). Furthermore, in this invention, "curl value" refers to the vertical distance between the lowest point of the optical film and the highest point of the optical film when the optical film is placed on a flat surface with the lower side convex. According to the curl measurement method of the present invention, in the arrangement step, a light emitter and a light receiver are positioned opposite each other on one side and the other side of the optical film, with the optical film in between. Then, in the light emission and light reception step, a light beam extending vertically is emitted towards the optical film using the light emitter, and the light beam that is transmitted without being blocked by the optical film is received using the light receiver. The vertical length of this transmitted light changes depending on the curl value of the optical film. Specifically, when the curl (curl at the end) of the optical film increases (the curl value increases), the vertical length of the light beam that is blocked and not transmitted by the optical film increases, so the vertical length of the transmitted light decreases. When the curl of the optical film decreases (the curl value decreases), the vertical length of the light beam that is blocked and not transmitted by the optical film decreases, so the vertical length of the transmitted light increases. Therefore, in the curl value calculation step, the curl value of the optical film can be calculated based on the vertical length of the transmitted light. According to the curl measurement method of the present invention, automation is possible because an optical sensor is used, and the curl value can be measured in a shorter time compared to when an operator measures it manually. Furthermore, since a transmissive optical sensor is used as the optical sensor, which includes a light emitter that emits a light beam extending in the vertical direction and a light receiver that receives the light beam emitted from the light emitter that is transmitted without being obstructed, the method is less affected by the direction of curl and surface condition of the optical film, and the curl value can be measured with high accuracy.

[0013] The curl measurement method according to the present invention can also be performed with the light emission and reception process running while both the optical film and the optical sensor are stationary. Specifically, for example, the plane of the optical film can be divided into multiple regions, and a positioning process can be performed so that the optical film and optical sensor are in positions corresponding to one region. For this one region, with both the optical film and optical sensor stationary, the light emission and reception process and the curl value calculation process can be performed to measure the curl value for that region. Subsequently, a positioning process can be performed to move the optical film and optical sensor relatively to positions corresponding to other regions. Then, with both the optical film and optical sensor stationary, the light emission and reception process and the curl value calculation process can be performed similarly to measure the curl value for those other regions. It is conceivable that the maximum value of the curl value for each region obtained by repeating this process for all regions can be taken as the final curl value of the optical film. Alternatively, it is conceivable that multiple optical sensors corresponding to multiple regions can be used so that each process can be performed simultaneously for multiple regions. However, in the former case, although it takes less time than manual measurement, it requires repeated relative movement and stopping of the optical film and optical sensor, which increases the time required to measure the curl value. In the latter case, since multiple optical sensors are used, the equipment cost is higher.

[0014] As described above, in order to avoid the problems that occur when the light emission and reception process is performed with both the optical film and the optical sensor stationary, it is preferable that in the light emission and reception process, the light beam is emitted using the light emitter and the transmitted light is received using the light receiver while the optical film and the optical sensor are moved relative to each other in the in-plane direction of the optical film (i.e., the optical sensor is stationary and the optical film is moved, or the optical film is stationary and the optical sensor is moved, or both the optical film and the optical sensor are moved in opposite directions).

[0015] According to the preferred method described above, since the light transmission and reception process is performed while the optical film and optical sensor are moved relative to each other, there is no need to repeatedly move and stop the optical film and optical sensor relative to each other, which further shortens the measurement time for the curl value, and since there is no need to use multiple optical sensors, the equipment cost can be reduced.

[0016] In the preferred method described above, when the optical sensor is stationary and the optical film is moved during the light transmission / reception process, if the movement speed is too high, the leading edge of the optical film (the downstream end in the direction of movement) may lift due to air resistance, potentially causing the curl value to be measured as larger than the true value. To avoid this, it is preferable that in the light emission and reception process, the optical sensor is kept stationary while the optical film is moved in the in-plane direction of the optical film at a speed of 30 m / min or less, the light beam is emitted using the light emitter, and the transmitted light is received using the light receiver.

[0017] According to the preferred method described above, by moving the optical film in the in-plane direction at a speed of 30 m / min or less, the lifting of the leading edge of the optical film is suppressed, and the accuracy of the curl value measurement can be maintained. However, if the movement speed of the optical film is too low, the measurement time for the curl value will be long, so it is preferable to move it at a speed of 5 m / min or more.

[0018] In the preferred method described above, one possible method for moving the optical film while keeping the optical sensor stationary during the light emission / reception process is to place the optical film on a conveyor belt and transport it. In this case, if the in-plane flatness of the conveyor belt, particularly the in-plane flatness of the area of ​​the conveyor belt on which the optical film is placed during the light emission / reception process, is poor, the orientation of the optical film may change during transport, potentially worsening the accuracy of the curl value measurement. Therefore, in the light projecting and receiving process, while keeping the optical sensor stationary, place the optical film on the conveying belt of the belt conveyor and convey it. When projecting the light beam using the light projector and receiving the transmitted light using the light receiver, it is preferable that the in-plane flatness of the area of the conveying belt on which the optical film is placed during the execution of the light projecting and receiving process is 1.5 mm or less.

[0019] In the above preferred method, "in-plane flatness" means the difference between the maximum value and the minimum value of the vertical distances from the same vertical position serving as a reference to a plurality of points within the area of the conveying belt on which the optical film is placed during the execution of the light projecting and receiving process. According to the above preferred method, since the in-plane flatness of the area of the conveying belt on which the optical film is placed during the execution of the light projecting and receiving process is as small as 1.5 mm or less (the in-plane flatness is good), it is difficult for the posture of the optical film to change during conveyance, and it is possible to maintain the measurement accuracy of the curl value.

[0020] As described above, when placing and conveying the optical film on the conveying belt of the belt conveyor, in order to reduce the in-plane flatness of the area of the conveying belt on which the optical film is placed during the execution of the light projecting and receiving process, it is conceivable to arrange a flat support plate that contacts the lower surface of the said area of the conveying belt. Therefore, in the light projecting and receiving process, while placing the optical film on the conveying belt of the belt conveyor and conveying it, when projecting the light beam using the light projector and receiving the transmitted light using the light receiver, it is preferable that a flat support plate that contacts the lower surface of the area of the conveying belt is arranged below the area of the conveying belt on which the optical film is placed during the execution of the light projecting and receiving process.

[0021] In the above preferred method, "flat support plate" means a support plate whose contact surface with at least the conveying belt is flat. According to the above preferred method, when performing the light emitting and receiving process, since the flat support plate disposed below the area of the conveyor belt on which the optical film is placed contacts the lower surface of the said area of the conveyor belt, the said area of the conveyor belt follows along the flat support plate, and it is possible to easily reduce the in-plane flatness of the said area of the conveyor belt.

[0022] Also, in order to solve the above problems, the present invention provides a manufacturing method of an optical film, which includes a manufacturing process of manufacturing a sheet-like optical film, an inspection process of inspecting the optical film, and a sorting process of sorting the optical film. In the inspection process, the curl measurement method is executed, and based on the magnitude of the measured curl value of the optical film, it is determined whether the optical film is a good product or a defective product. In the sorting process, the optical film is sorted according to whether it is determined to be a good product or a defective product.

[0023] According to the manufacturing method of the present invention, in the inspection process, since the above curl measurement method is executed, it is possible to automate the inspection process, and the sorting process following the inspection process can also be automated using a known sorting mechanism. Therefore, the inspection (measurement of the curl value) of the optical film and the sorting of good and defective products can be continuously and automatically executed, and it is possible to improve the manufacturing efficiency of the optical film. Also, in the inspection process, since the above curl measurement method is executed, it is possible to accurately determine good and defective products, and it is possible to reduce the risk of mis-sorting in the sorting process.

Effects of the Invention

[0024] According to the present invention, it is possible to accurately measure the curl value of the optical film in a short time, and it is possible to improve the manufacturing efficiency of the optical film.

Brief Description of the Drawings

[0025] [Figure 1] It is a diagram schematically explaining an example of a conventional method for measuring the curl value. [Figure 2] This is a schematic side view illustrating a general configuration example of a conventional measuring device that automatically measures the curl value of an optical film using an optical sensor. [Figure 3] This is a flowchart showing the general steps of a method for manufacturing an optical film according to one embodiment of the present invention. [Figure 4] This is a schematic cross-sectional view showing an example of the general structure of an optical film manufactured by a manufacturing method according to one embodiment of the present invention. [Figure 5] This figure schematically shows an example of the configuration of an inspection device that performs the inspection process ST2 shown in Figure 3. [Modes for carrying out the invention]

[0026] The following describes a method for measuring the curl of an optical film according to one embodiment of the present invention and a method for manufacturing an optical film using the same, with appropriate reference to the attached drawings. In this embodiment, the case in which the optical film is a polarizing plate will be used as an example. Note that the figures are for reference only, and the dimensions, scale, and shape of the optical film and device components shown in the figures may differ from those of the actual product.

[0027] Figure 3 is a flowchart showing the schematic steps of the method for manufacturing an optical film according to this embodiment. As shown in Figure 3, the manufacturing method according to this embodiment includes a manufacturing step ST1, an inspection step ST2, and a sorting step ST3. Each step ST1 to ST3 will be described below.

[0028] <Manufacturing process ST1> In manufacturing process ST1, a sheet-shaped optical film is manufactured. Figure 4 is a schematic cross-sectional view showing an example of the general structure of an optical film manufactured by the manufacturing method according to this embodiment. As shown in Figure 4, the optical film F of this embodiment comprises a polarizing film F1, a phase difference film F2, an adhesive layer F3, a release liner F4, and a surface protection film F5.

[0029] [Polarizing film F1] The polarizing film F1 consists of a polarizer F11 and protective films F12 and F13 that protect the polarizer F11. In this embodiment, protective films F12 and F13 are bonded to both sides of the polarizer F11, but this is not the only option; it is sufficient if protective films are bonded to at least one side of the polarizer F11.

[0030] (Polarizer F11) A polarizer F11 is typically composed of a resin film containing a dichroic substance. Any suitable resin film that can be used as a polarizer can be employed. Typically, the resin film is a polyvinyl alcohol-based resin (hereinafter referred to as "PVA-based resin") film.

[0031] Any suitable resin can be used as the PVA resin for forming the above-mentioned PVA resin film. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer is obtained by saponifying ethylene-vinyl acetate copolymer.

[0032] Examples of dichroic substances included in the resin film include iodine and organic dyes. These can be used individually or in combination of two or more. Iodine is preferably used.

[0033] The resin film may be a single-layer resin film or a laminate of two or more layers.

[0034] A specific example of a polarizer composed of a single layer of resin film is one in which a PVA-based resin film has been subjected to iodine dyeing and stretching (typically uniaxial stretching). Iodine dyeing is performed, for example, by immersing the PVA-based film in an iodine aqueous solution. The stretching ratio for uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after dyeing, or during dyeing. Dyeing may also be performed after stretching. If necessary, the PVA-based resin film may be subjected to swelling, crosslinking, washing, drying, etc.

[0035] Specific examples of polarizers composed of laminates include polarizers composed of a laminate of a resin substrate and a PVA-based resin layer (PVA-based resin film) laminated on the resin substrate, or polarizers composed of a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate. A polarizer composed of a laminate of a resin substrate and a PVA-based resin layer coated on the resin substrate can be manufactured, for example, by applying a PVA-based resin solution to a resin substrate, drying it to form a PVA-based resin layer on the resin substrate, obtaining a laminate of the resin substrate and the PVA-based resin layer, and then stretching and dyeing this laminate to make the PVA-based resin layer a polarizer. In this embodiment, stretching typically includes immersing the laminate in a boric acid aqueous solution and stretching it. Furthermore, stretching may, if necessary, include air stretching the laminate at a high temperature (e.g., 95°C or higher) before stretching in the boric acid aqueous solution. The resulting resin substrate / polarizer laminate may be used as is (i.e., the resin substrate may be used as a protective layer for the polarizer), or the resin substrate may be peeled off from the resin substrate / polarizer laminate, and any appropriate protective layer may be laminated onto this peeled surface according to the purpose. Details of such a polarizer manufacturing method are described, for example, in Japanese Patent Application Publication No. 2012-73580. The entire description of this publication is incorporated herein by reference.

[0036] The thickness of the polarizer F11 is preferably 15 μm or less, more preferably 1 μm to 12 μm, even more preferably 3 μm to 10 μm, and particularly preferably 3 μm to 8 μm.

[0037] The polarizer F11 preferably exhibits absorption dichroism at any wavelength within the range of 380 nm to 780 nm. The transmittance of polarizer F11 is preferably 40.0% to 45.0%, more preferably 41.5% to 43.5%. The degree of polarization of polarizer F11 is preferably 97.0% or higher, more preferably 99.0% or higher, and even more preferably 99.9% or higher.

[0038] In manufacturing process ST1, a long strip of resin film is used as the raw material film. This raw material film is transported in the longitudinal direction (MD direction) and immersed in various treatment baths to perform various treatments such as dyeing and stretching, thereby manufacturing a long strip of polarizer F11 having the above configuration.

[0039] (Protective film F12, F13) Any suitable resin film can be used as the protective films F12 and F13. Examples of resin film forming materials include (meth)acrylic resins, cellulose resins such as diacetylcellulose and triacetylcellulose, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, ester resins such as polyethylene terephthalate resins, polyamide resins, polycarbonate resins, and copolymer resins thereof. Note that "(meth)acrylic resin" means acrylic resin and / or methacrylic resin. The forming materials of protective films F12 and F13 may be the same or different.

[0040] The thickness of protective films F12 and F13 is typically 10 μm to 100 μm, preferably 20 μm to 40 μm. The thicknesses of protective films F12 and F13 may be the same or different.

[0041] The surface of protective films F12 and F13 opposite to the polarizer F11 may be treated as needed with a hard coat, anti-reflective coating, anti-sticking coating, anti-glare coating, or other surface treatments. Furthermore / or, the surface of protective films F12 and F13 opposite to the polarizer F11 may be treated as needed with a treatment to improve visibility when viewed through polarized sunglasses (typically, a treatment to impart (elliptical) circular polarization function, or a treatment to impart ultra-high phase difference). Note that if a surface treatment is applied and a surface treatment layer is formed, the thickness of protective films F12 and F13 includes the thickness of the surface treatment layer.

[0042] The protective films F12 and F13 are laminated to the polarizer F11 via an arbitrary and suitable adhesive layer (not shown). Typical adhesives that make up the adhesive layer include PVA-based adhesives and activated energy ray-curing adhesives.

[0043] In manufacturing process ST1, a long strip polarizing film F1 is manufactured by laminating long strip protective films F12 and F13 having the above configuration onto a long strip polarizer F11.

[0044] [Phase contrast film F2] The phase difference film F2 may be, for example, a compensating plate that provides a wide viewing angle, or it may be a phase difference plate (circular polarizer) such as a half-wave plate or a quarter-wave plate used with a polarizing film to generate circularly polarized light. The thickness of the phase difference film F2 is, for example, 1 to 200 μm.

[0045] The phase difference film F2 is laminated to the polarizing film F1 (protective film F13) via an arbitrary suitable adhesive layer or tack layer (not shown). Typical adhesives that make up the adhesive layer include PVA-based adhesives and activated energy ray-curing adhesives.

[0046] In manufacturing process ST1, a long, strip-shaped optical laminate is manufactured by laminating a long, strip-shaped phase difference film F2 having the above configuration onto one side (protective film F13) of a long, strip-shaped polarizing film F1.

[0047] [Adhesive layer F3] The adhesive layer F3 is formed by applying adhesive to one side of the release liner F4 and then curing the applied adhesive by heating and drying it in an oven or the like. The heating temperature of the adhesive is preferably set in the range of 100°C to 160°C, and more preferably in the range of 140°C to 160°C. At this heating temperature, it is preferably heated for 20 seconds to 3 minutes, and more preferably for 1 minute to 3 minutes.

[0048] Specific examples of adhesives that form the adhesive layer F3 include acrylic adhesives, rubber adhesives, silicone adhesives, polyester adhesives, urethane adhesives, epoxy adhesives, and polyether adhesives. By adjusting the type, number, combination and blending ratio of monomers that form the base resin of the adhesive, as well as the amount of crosslinking agent, reaction temperature, reaction time, etc., an adhesive with desired properties according to the purpose can be prepared. The base resin of the adhesive may be used alone or in combination of two or more types. From the viewpoint of transparency, processability and durability, acrylic adhesives are preferred. Details of the adhesives constituting the adhesive layer F3 are described, for example, in Japanese Patent Application Publication No. 2014-115468, and the description in said publication is incorporated herein by reference. The thickness of the adhesive layer F3 can be, for example, 10 μm to 100 μm.

[0049] [Release Liner F4] Any suitable material can be used as the release liner F4. Specific examples include plastic films, nonwoven fabrics, or paper coated with a release agent. Specific examples of release agents include silicone-based release agents, fluorine-based release agents, and long-chain alkyl acrylate-based release agents. Specific examples of plastic films include polyethylene terephthalate (PET) film, polyethylene film, and polypropylene film. The thickness of the release liner F4 can be, for example, 10 μm to 100 μm.

[0050] In manufacturing process ST1, an adhesive is applied to a long strip-shaped release liner F4 having the above configuration while it is being transported in the longitudinal direction (MD direction). The applied adhesive is then heated and dried in an oven or the like to harden it and form the aforementioned adhesive layer F3. Then, the release liner F4 is bonded to a long strip-shaped optical laminate (a laminate of polarizer F1 and phase difference film F2) via the adhesive layer 3 formed on the long strip-shaped release liner F4. Specifically, the adhesive layer F3 side of the long strip-shaped release liner F4 (release liner F4 with adhesive layer 3) is bonded to one side (phase difference film F2) of the long strip-shaped optical laminate. This produces a long strip-shaped optical laminate in which the polarizer F1, phase difference film F2, adhesive layer F3, and release liner F4 are laminated.

[0051] [Surface protection film F5] The surface protection film F5 typically comprises a substrate and an adhesive layer. In this embodiment, the thickness of the surface protection film F5 is, for example, 30 μm or more. The upper limit of the thickness of the surface protection film F5 is, for example, 150 μm. In this specification, "thickness of the surface protection film" refers to the total thickness of the substrate and the adhesive layer.

[0052] The base material can be made of any suitable resin film. Examples of resin film forming materials include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Preferably, it is an ester resin (particularly polyethylene terephthalate resin).

[0053] Any suitable adhesive can be used to form the adhesive layer. Examples of base resins for the adhesive include acrylic resins, styrene resins, silicone resins, urethane resins, and rubber resins.

[0054] In manufacturing process ST1, a long, strip-shaped surface protection film F5 is bonded to a long, strip-shaped optical laminate (a laminate of polarizer F1, phase difference film F2, adhesive layer F3, and release liner F4). Specifically, the long, strip-shaped surface protection film F5 is bonded to the side of the optical laminate (a laminate of polarizer F1, phase difference film F2, adhesive layer F3, and release liner F4) opposite to the side to which the release liner F4 is bonded. This produces a long, strip-shaped optical film (polarizer) F.

[0055] Finally, in manufacturing process ST1, a long strip of optical film F is cut into sizes and shapes (for example, rectangles) according to the application to produce a single sheet of optical film F.

[0056] <Inspection Process ST2> In inspection step ST2, the sheet-shaped optical film F manufactured in manufacturing step ST1 is inspected. As shown in Figure 3, inspection step ST2 includes a placement step ST21, a light emission / reception step ST22, a curl value calculation step ST23, and a determination step ST24. The placement step ST21, light emission / reception step ST22, and curl value calculation step ST23 in inspection step ST2 correspond to the curl measurement method according to this embodiment.

[0057] Figure 5 is a schematic diagram showing an example of the configuration of an inspection device that performs the inspection process ST2. Figure 5(a) is a side view of the inspection device (viewed from a horizontal direction perpendicular to the transport direction of the optical film F). Figure 5(b) is a front view of the area around the optical sensor provided in the inspection device (viewed from the transport direction of the optical film F). As shown in Figure 5, the inspection device 100 of this embodiment includes a transmissive optical sensor 1 having a light emitter 11 that emits a light beam extending in the Z direction (vertical direction), and a light receiver 12 positioned opposite the light emitter 11 with the object to be measured (optical film F in this embodiment) in between, and receiving the light from the light beam L that is transmitted without being blocked by the object to be measured (optical film F in this embodiment). For example, an LED light source that emits parallel light can be used as the light emitter 11, and for example, a line sensor camera in which imaging elements such as CCDs and CMOSs ​​are arranged in a straight line extending in the Z direction can be used as the light receiver 12. As an optical sensor 1 having such a configuration, for example, the "Ultra-high-speed, high-precision dimensional measuring instrument LS-9120" manufactured by Keyence Corporation can be used. Furthermore, the inspection device 100 of this embodiment includes a calculation device 2 connected to the optical sensor 1 (light receiver 12) that performs predetermined calculation processing. As the calculation device 2, for example, a computer on which a program for performing predetermined calculation processing is installed can be used. Furthermore, the inspection apparatus 100 of this embodiment includes a belt conveyor 3 that transports the optical film F in its in-plane direction (in this embodiment, the X direction). The belt conveyor 3 has a pair of rollers 31 and a transport belt 32 stretched between the pair of rollers 31. Furthermore, the inspection device 100 of this embodiment includes a flat support plate 4 positioned to contact the lower surface of the conveyor belt 32. The support plate 4 is formed, for example, from a metal plate material whose upper surface is flat. The following describes the steps ST21 to ST24 of the inspection process ST2 performed by the inspection apparatus 100 having the above configuration, with reference to Figure 5 as appropriate.

[0058] [Placement process ST21] In the arrangement step ST21, of the light emitter 11 and light receiver 12 of the optical sensor 1, the light emitter 11 is placed on one side of the optical film F (in this embodiment, in the Y direction) (the left side in the example shown in Figure 5(b)), and the light receiver 12 is placed opposite the light emitter 11, on the other side of the optical film F (in this embodiment, in the Y direction) (the right side in the example shown in Figure 5(b)). Specifically, in this embodiment, in the light emission and reception process ST22 described later, the optical sensor 1 is kept stationary while the optical film F is placed on the conveyor belt 32 of the belt conveyor 3 for transport. Therefore, the light emitter 11 and the light receiver 12 are fixed in positions so that they face each other in the Y direction, with the conveyor belt 32 in between. As a result, from the time the leading edge (downstream end in the transport direction) FT of the optical film F being transported by the belt conveyor 3 reaches the position where the optical sensor 1 is located until the trailing edge (upstream end in the transport direction) FR of the optical film F leaves the position where the optical sensor 1 is located, the light emitter 11 and the light receiver 12 are positioned so that they face each other with the optical film F in between. It is preferable to place the optical film F on the conveyor belt 32 so that its lower side is convex. If the optical film F is a mass-produced product with the same configuration, the direction of curl will generally be the same, so it is also possible to accumulate them in a stocker (not shown) in advance so that their lower sides are convex, and then sequentially discharge the optical film F from this stocker onto the conveyor belt 32.

[0059] [Light emission / reception process ST22] In the light emission and reception process ST22, the light emitter 11 emits a light beam L extending in the Z direction toward the optical film F, and the light receiver 12 receives the light from the light beam L that is not blocked by the optical film F (transmitted light). Specifically, in this embodiment, the optical sensor 1 is kept stationary (remaining in a fixed position), while the optical film F is placed on the conveyor belt 32 of the belt conveyor 3 and transported, a light beam L is emitted using the light emitter 11 and transmitted light is received using the light receiver 12.

[0060] Here, if the conveying speed of the belt conveyor 3 (corresponding to the movement speed of the optical film F in the X direction) is too high, the leading edge FT of the optical film F may lift due to air resistance, which may cause the curl value calculated in the curl value calculation step ST23 described later to be measured as larger than the true value. To avoid this, it is preferable to set the conveying speed of the belt conveyor 3 to 30 m / min or less, preferably 20 m / min or less, more preferably 15 m / min or less, and even more preferably 10 m / min or less. However, if the conveying speed of the belt conveyor 3 is set too low, the measurement time for the curl value (the time required to perform the light emission / reception step ST22 and the curl value calculation step ST23 described later) will be long, so it is preferable to set the conveying speed to 5 m / min or more.

[0061] Furthermore, if the in-plane flatness of the conveyor belt 32 of the belt conveyor 3 is poor, in particular, if the in-plane flatness of the region S of the conveyor belt 32 on which the optical film F is placed when the light transmission / reception process ST22 is executed (i.e., the region of the conveyor belt 32 on which the optical film F is placed from the time the leading edge FT of the optical film F reaches the position where the optical sensor 1 is located until the trailing edge FR of the optical film F leaves the position where the optical sensor 1 is located), the posture of the optical film F will change during transport, which may worsen the measurement accuracy of the curl value calculated in the curl value calculation process ST23 described later. To avoid this, the in-plane flatness of the region S of the conveyor belt 32 (the difference between the maximum and minimum distances in the Z direction from a reference Z-direction position to multiple points within the region S of the conveyor belt 32 (for example, nine points arranged in a matrix at equal intervals)) is set to 1.5 mm or less, preferably 1.0 mm or less, more preferably 0.8 mm or less, and even more preferably 0.5 mm or less. This in-plane flatness can be evaluated, for example, by placing multiple laser distance meters (not shown) at the same Z-direction position above the conveyor belt 32 and measuring the distance to the upper surface of the conveyor belt 32 with each laser distance meter when the optical film F is not placed on it.

[0062] To reduce the in-plane flatness of the region S of the conveyor belt 32, it is possible to increase the tension of the conveyor belt 32 by adjusting the distance between a pair of rollers 31 (the distance in the conveying direction of the belt conveyor 3), or to place multiple other rollers between the pair of rollers 31. However, this alone may not be sufficient. For this reason, in this embodiment, a flat support plate 4 is placed so as to contact the lower surface of the conveyor belt 32, specifically the lower surface of the region S of the conveyor belt 32 (in the example shown in Figure 5, it contacts a region slightly wider than region S). As a result, the region S of the conveyor belt follows the flat support plate 4, making it possible to easily reduce the in-plane flatness of the region S of the conveyor belt 32 (to 1.5 mm or less).

[0063] Furthermore, in order to calculate the curl value in the curl value calculation step ST23 described later, it is sufficient to perform the emission of the light beam L by the light emitter 11 and the reception of the transmitted light by the light receiver 12 only from the time the leading edge FT of the optical film F reaches the position where the optical sensor 1 is located until the trailing edge FR of the optical film F leaves the position where the optical sensor 1 is located. For this reason, it is preferable to place a known proximity sensor (not shown) to detect the time when the leading edge FT of the optical film F reaches the position where the optical sensor 1 is located and the time when the trailing edge FR of the optical film F leaves the position where the optical sensor 1 is located, and to perform the emission of the light beam L by the light emitter 11 and the reception of the transmitted light by the light receiver 12 only from the time when the arrival of the leading edge FT is detected by this proximity sensor until the departure of the trailing edge FR is detected.

[0064] [Curl value calculation process ST23] In the curl value calculation step ST23, the curl value of the optical film F is calculated based on the length of the transmitted light in the Z direction obtained by performing the light transmission and reception step ST22. Specifically, as shown in Figure 5(b), when the optical film F is not placed on the conveyor belt 32, the light receiver 12 receives transmitted light with a length of L0 in the Z direction, and when the optical film F is placed on the conveyor belt 32, the light receiver 12 receives transmitted light with a length of L1 in the Z direction. The light receiver 12 then calculates the L0-L1 value and outputs it to the arithmetic unit 2. More specifically, if the light receiver 12 is a line sensor camera as described above, when the optical film F is not placed on the conveyor belt 32, the number of imaging elements that receive more than a predetermined amount of light increases, and when the optical film F is placed on the conveyor belt 32, the number of imaging elements that receive more than a predetermined amount of light decreases. Therefore, the difference in the number of elements is converted into a length (i.e., the L0-L1 value) and output to the arithmetic unit 2. The L0-L1 values ​​are sequentially output to the arithmetic unit 2 according to the scan rate of the photodetector 12 (line sensor camera) from the time the leading edge FT of the optical film F reaches the position where the optical sensor 1 is located until the trailing edge FR of the optical film F leaves the position where the optical sensor 1 is located. The value of LO is constant, but the value of L1 fluctuates according to the degree of curl of the optical film F, so the L0-L1 values ​​also fluctuate according to the degree of curl of the optical film F. Then, the arithmetic unit 2 calculates the maximum value of L0-L1, which is sequentially input from the light receiver 12, as the curl value.

[0065] [Judgment process ST24] In the determination step ST24, it is determined whether the optical film F is a good product or a defective product based on the magnitude of the curl value of the optical film F measured (calculated) in the curl value calculation step ST23. Specifically, the computing device 2 compares the calculated curl value of the optical film F with a pre-set threshold value (for example, 5 mm). If the curl value is less than or equal to the threshold value, the optical film F is determined to be a good product; if it exceeds the threshold value, the optical film F is determined to be a defective product.

[0066] <Distribution Process ST3> In the sorting process ST3, the optical film F is sorted according to whether it was determined to be a good product or a defective product in the judgment process ST24 of the inspection process ST2. Specifically, for example, a sorting mechanism (not shown) that operates based on a control signal from the computing device 2 is located downstream of the belt conveyor 3, and the optical film F is sorted by this sorting mechanism. For example, if the optical film F is determined to be a good product, the sorting mechanism receives a control signal from the computing device 2 indicating that it has been determined to be a good product, and transports the optical film F, which has been conveyed to the sorting mechanism via the belt conveyor 3, to a collection container for good products (not shown) for collection. On the other hand, if the optical film F is determined to be a defective product, the sorting mechanism receives a control signal from the computing device 2 indicating that it has been determined to be a defective product, and transports the optical film F, which has been conveyed to the sorting mechanism via the belt conveyor 3, to a collection container for defective products (not shown) for collection. Since various known configurations can be used for the distribution mechanism, a detailed explanation will be omitted here.

[0067] According to the curl measurement method for the optical film F of this embodiment described above (arrangement step ST21, light emission / receiving step ST22, and curl value calculation step ST23), automation is possible because an optical sensor 1 is used, and the curl value can be measured in a shorter time compared to when an operator measures it manually. Furthermore, since a transmissive optical sensor 1 is used as the optical sensor 1, which includes a light emitter 11 that emits a light beam L extending in the vertical direction (Z direction) and a light receiver 12 that receives the light from the light beam L emitted from the light emitter 11 that is transmitted without being shielded, the curl value can be measured with high accuracy as it is less affected by the direction of curl and surface condition of the optical film F. Furthermore, according to the manufacturing method of the optical film F according to this embodiment, the inspection step ST2 can be automated because the curl measurement method according to this embodiment is performed in the inspection step ST2, and the sorting step ST3 that follows the inspection step ST2 can also be automated using a sorting mechanism. Therefore, the inspection (measurement of curl value) and sorting of good and defective products of the optical film F can be performed continuously and automatically, thereby increasing the manufacturing efficiency of the optical film F. In addition, because the curl measurement method according to this embodiment is performed in the inspection step ST2, good and defective products can be determined with high accuracy, and the risk of incorrect sorting in the sorting step ST3 can be reduced.

[0068] In this embodiment, the case in which the optical film F is placed on the conveyor belt 32 of the belt conveyor 3 and transported in the light transmission / reception process ST22 was described as an example, but the present invention is not limited to this, and other configurations in which the optical film F is moved in its in-plane direction can also be adopted. Furthermore, in the light transmission and reception process ST22, instead of keeping the optical sensor 1 stationary and moving the optical film F in the in-plane direction, it is also possible to keep the optical film F stationary and move the optical sensor 1 in the in-plane direction of the optical film F using a uniaxial stage or the like, or to adopt a configuration in which both the optical film F and the optical sensor 1 are moved in opposite directions in the in-plane direction of the optical film F. Furthermore, it is also possible to perform the light transmission / reception process ST22 while both the optical film F and the optical sensor 1 are stationary. Specifically, for example, the plane of the optical film F can be divided into multiple regions, and the positioning process ST21 can be performed so that the optical film F and the optical sensor 1 are in positions corresponding to one region. For this one region, the light transmission / reception process ST22 and the curl value calculation process ST23 can be performed while both the optical film F and the optical sensor 1 are stationary, and the curl value for that region can be measured. After that, the positioning process ST21 can be performed to move the optical film F and the optical sensor 1 relatively to positions corresponding to other regions. Then, while both the optical film F and the optical sensor 1 are stationary, the light transmission / reception process ST22 and the curl value calculation process ST23 can be performed in the same way to measure the curl value for those other regions. It is conceivable that the maximum value of the curl value for each region obtained by repeatedly performing this for all regions can be taken as the final curl value of the optical film F. Alternatively, it is conceivable to use multiple optical sensors 1 corresponding to multiple regions so that each process ST21 to ST23 can be performed simultaneously for multiple regions.

[0069] Below, we will describe examples of the results of measuring the curl value of optical film F using the curl measurement method according to this embodiment (Examples 1 to 4), and examples of the results of measuring the curl value of optical film F using a conventional curl measurement method (Comparative Examples 1 and 2). The optical films F used in Examples 1-4 and Comparative Examples 1 and 2 all have the following configuration (see Figure 4). (1) Dimensions of optical film F: Length in the vertical direction (transport direction) 160 mm, length in the horizontal direction (horizontal direction perpendicular to the transport direction) 230 mm, thickness 216 μm (2) Surface protective film F5: Composed of a base material made of polyethylene terephthalate resin and an adhesive layer made of acrylic adhesive, with a total thickness of 60 μm between the base material and the adhesive layer. (3) Protective film F12: Formed from triacetylcellulose, with a thickness of 50 μm (4) Polarizer F11: Formed from polyvinyl alcohol, 20 μm thick (5) Protective film F13: Formed from triacetylcellulose, thickness 20 μm (6) Phase difference film F2: Formed from a cycloolefin resin, with a thickness of 6 μm (7) Adhesive layer F3: Formed from an acrylic adhesive, with a thickness of 20 μm (8) Release liner F4: Formed from polyethylene terephthalate, with a thickness of 40 μm

[0070] <Example 1> In Example 1, the optical film F was transported on a belt conveyor 3 set to a transport speed of 5 m / min while the light emission / reception process ST22 was performed, and the curl value was calculated in the curl value calculation process ST23. This was repeated 10 times for each of the four directions in which the optical film F was transported (i.e., the direction in which the optical film F was placed on the transport belt 32 was changed in four directions at 90° intervals), and the curl value was measured a total of 40 times. In Example 1, the in-plane flatness of the transport belt 32 was 0.5 mm by positioning the flat support plate 4 in contact with the lower surface of the area S of the transport belt 32.

[0071] <Example 2> In Example 2, the curl value of the optical film F was measured in the same manner as in Example 1, except that the transport speed was set to 17 m / min.

[0072] <Example 3> In Example 3, the curl value of the optical film F was measured in the same manner as in Example 1, except that the transport speed was set to 27 m / min.

[0073] <Example 4> In Example 4, the curl value of the optical film F was measured in the same manner as in Example 2, except that a flat support plate 4 was not provided. In Example 4, the in-plane flatness of the conveyor belt 32 was 1.2 mm.

[0074] <Comparative Example 1> In Comparative Example 1, as shown in Figure 1, the curl value of optical film F was manually measured 10 times using a scale.

[0075] <Comparative Example 2> In Comparative Example 2, the curl value of the optical film F was measured in the same manner as in Example 1, except that a reflective optical sensor (light emitter 11', light receiver 12') as shown in Figure 2 was used.

[0076] <Measurement results> Table 1 shows the measurement results for Examples 1-4 and Comparative Examples 1 and 2. [Table 1] Table 1 shows that "Cycle Time" refers to the time required to measure the curl value of one optical film F once. "Cycle Time Evaluation" indicates that a cycle time greater than 5 seconds is marked with "×", a cycle time of 5 seconds or less but greater than 2 seconds is marked with "〇", and a cycle time of 2 seconds or less is marked with "◎". "Error" is the difference between the true value and the curl value with the largest difference from the true value, with the average of 10 curl values ​​measured in Comparative Example 1 being taken as the true value, and the curl values ​​measured 40 times each in Examples 1-4 and Comparative Example 2. "Error Evaluation" indicates that an error greater than 1.5 mm is marked with "×", an error of 1.5 mm or less but greater than 1.0 mm is marked with "△", and an error less than 1.0 mm is marked with "〇".

[0077] As shown in Table 1, Examples 1 to 4 exhibit smaller cycle times compared to Comparative Example 1, demonstrating that curl values ​​can be measured in a shorter time. Furthermore, Examples 1 to 4 show smaller error values ​​compared to Comparative Example 2, indicating that curl values ​​can be measured with greater accuracy. In particular, in Examples 1 and 2, the conveying speed of the belt conveyor 3 was 20 m / min or less, so the lifting of the leading edge FT of the optical film F was sufficiently suppressed. Also, in Examples 1 and 2, the in-plane flatness of the conveyor belt 32 was 1.0 mm or less, so the change in the posture of the optical film F during conveyance was sufficiently suppressed. As a result, it was possible to improve the measurement accuracy of the curl value compared to Example 3, where the conveying speed of the belt conveyor 3 exceeded 20 m / min, and Example 4, where the in-plane flatness of the conveyor belt 32 exceeded 1.0 mm. [Explanation of symbols]

[0078] 1. Optical sensor 2...Arithmetic unit 3. Belt conveyor 4...Support plate 11. Floodlight 12...Receiver 100... Inspection device F... Optical film L...Luminous flux ST1...Manufacturing process ST2...Inspection process ST3... Sorting process ST21...Placement process ST22...Light emission / reception process ST23... Curl value calculation process ST24...Judgment process

Claims

1. A method for measuring the curl value, which represents the degree of curl of a single-sheet optical film, using an optical sensor equipped with a light emitter and a light receiver, Arrangement step: Arrange the light emitter on one side of the optical film, and arrange the light receiver on the other side of the optical film, with the optical film in between, so as to face the light emitter. A light projection and receiving step, in which a light beam extending vertically toward the optical film is projected using the light projector, and the light beam that is transmitted through without being blocked by the optical film is received using the light receiver, The process includes a curl value calculation step, which calculates the curl value of the optical film based on the vertical length of the transmitted light. Method for measuring the curl of optical films.

2. In the light emission and reception process, the optical film and the optical sensor are moved relative to each other in the in-plane direction of the optical film, the light beam is emitted using the light emitter, and the transmitted light is received using the light receiver. A method for measuring the curl of an optical film according to claim 1.

3. In the light emission and reception process, while the optical sensor is kept stationary, the optical film is moved in the in-plane direction of the optical film at a speed of 30 m / min or less, the light beam is emitted using the light emitter, and the transmitted light is received using the light receiver. The method for measuring the curl of an optical film according to claim 2.

4. In the light emission and reception process, while the optical sensor is kept stationary, the optical film is placed on the conveyor belt of the belt conveyor and transported, the light beam is emitted using the light emitter, and the transmitted light is received using the light receiver. When the light emission and reception process is performed, the in-plane flatness of the area of ​​the conveyor belt on which the optical film is placed is 1.5 mm or less. The method for measuring the curl of an optical film according to claim 2.

5. In the light emission and reception process, the optical film is placed on a conveyor belt and transported while the light beam is emitted using the light emitter and the transmitted light is received using the light receiver. When the light transmission and reception process is performed, a flat support plate is positioned below the area of ​​the conveyor belt on which the optical film is placed, and contacts the lower surface of the area of ​​the conveyor belt. The method for measuring the curl of an optical film according to claim 2.

6. The manufacturing process for producing sheet-shaped optical films, An inspection process for inspecting the optical film, The process includes a sorting step for sorting the optical films, In the inspection step, the curl measurement method described in any of claims 1 to 5 is performed, and based on the magnitude of the measured curl value of the optical film, it is determined whether the optical film is a good product or a defective product. In the sorting process, the optical films are sorted according to whether they are determined to be good products or defective products. A method for manufacturing optical films.

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