Measurement method and method for manufacturing optical film

Abstract

To provide a measuring method of a coating layer capable of acquiring accurate thickness of the coating layer, and a manufacturing method of optical film including the measuring method.SOLUTION: A measuring method according to one aspect measures thickness of a coating layer in an optical film including a base material and the coating layer laminated on the base material on the basis of an optical measurement method, and includes: a first measurement step of measuring the thickness of the base material using a first film thickness meter and the optical measurement method; a second measurement step of measuring thickness of an optical film obtained by applying the coating layer to the base material using a second film thickness meter and the optical measurement method; and a calculation step of calculating thickness of the coating layer on the basis of an optical measurement result obtained by the first film thickness meter and the second film thickness meter. The first film thickness meter and the second film thickness meter are spectroscopic interference type film thickness meters. A thickness correction value in a conversion formula for converting the optical measurement result of the second film thickness meter into thickness is different from a thickness correction value in a conversion formula for converting the optical measurement result of the first film thickness meter into thickness.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a measurement method and a method for producing an optical film. [Background technology]

[0002] Patent Document 1 discloses a technique for applying a coating liquid (coating agent) onto a sheet-like material (substrate) using a rotating roll (coating roll) while the sheet-like material is being transported, thereby producing an optical film having a substrate and a coating layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-024565 A Summary of the Invention [Problem to be solved by the invention]

[0004] In an optical film having a substrate and a coating layer, the thickness of the coating layer affects the performance of a product including the optical film, and therefore, in order to monitor the thickness of the coating layer, it is necessary to appropriately measure the thickness of the coating layer.

[0005] When a coating layer is applied to a substrate while the substrate is being transported as in Patent Document 1, the thickness of the coating layer can be measured in-line by using a non-contact spectral interference film thickness meter. When the thickness of the coating layer is measured in-line using a spectral interference film thickness meter in this way, the thickness of the substrate before the coating layer is formed on the substrate and the thickness of the optical film obtained by forming the coating layer on the substrate are measured with the spectral interference film thickness meter. The thickness of the coating layer can be obtained as the difference between the thickness of the optical film thus obtained and the thickness of the substrate.

[0006] However, there are cases where the difference between the thickness of the coating layer measured using a spectral interference film thickness meter and the actual thickness of the coating layer measured by observing the cross section of the optical film becomes large.

[0007] An object of one aspect of the present invention is to provide a method for measuring the thickness of a coating layer, which allows for more accurate measurement of the thickness of a coating layer, and a method for producing an optical film including the above-mentioned measuring method. [Means for solving the problem]

[0008] A measurement method according to one aspect of the present invention is a method for measuring the thickness of a coating layer in an optical film including a substrate and a coating layer laminated on the substrate by an optical measurement method, the method comprising: a first measurement step of measuring the thickness of the substrate by the optical measurement method using a first thickness gauge; a second measurement step of measuring the thickness of the optical film obtained by coating the coating layer on the substrate by the optical measurement method using a second thickness gauge; and a calculation step of calculating the thickness of the coating layer based on the optical measurement results obtained by the first thickness gauge and the second thickness gauge, wherein the first thickness gauge and the second thickness gauge are each a spectral interference thickness gauge, and a thickness correction value in a conversion formula for converting the optical measurement result of the second thickness gauge to a thickness is different from a thickness correction value in the conversion formula for converting the optical measurement result of the first thickness gauge to a thickness.

[0009] In the above measurement method, a thickness correction value in a conversion formula for converting the optical measurement result of the second thickness meter into a thickness is different from a thickness correction value in a conversion formula for converting the optical measurement result of the first thickness meter into a thickness. In this case, a thickness correction value according to the configuration of the optical film can be adopted, so that the thickness of the coating layer can be obtained more accurately.

[0010] The thickness correction value for the optical measurement result of the first film thickness meter may be an estimated refractive index of the substrate, and the thickness correction value for the optical measurement result of the second film thickness meter may be expressed by equation (1).

number

[0011] The above n1 and n2 may satisfy the relationship shown in formula (B) or formula (C). 0.77≦n2 / n1≦0.99 (B) 1.01≦n2 / n1≦1.20 (C)

[0012] The estimated refractive index of the substrate may be 1.4 or more and 1.8 or less. The thickness of the substrate may be 10 μm or more and 500 μm or less.

[0013] The coating layer may have a refractive index of 1.4 or more and 1.8 or less, and a thickness of 0.5 μm or more and 5 μm or less.

[0014] The measuring method according to one embodiment may further include a coating step of coating the substrate with the coating layer to form the optical film including the substrate and the coating layer, and the first measuring step, the coating step, and the second measuring step may be performed while the substrate is being transported. In this case, the thickness of the coating layer can be obtained while the substrate is being coated with the coating layer.

[0015] A method for producing an optical film according to another aspect of the present invention includes a coating step of applying a coating layer to a substrate to form an optical film including the substrate and the coating layer, and a step of measuring a thickness of the coating layer by the measurement method, wherein the first measurement step in the measurement method is performed before the coating step, and the second measurement step in the measurement method is performed after the coating step.

[0016] In the manufacturing method, the first measurement step is performed before the coating step, and the second measurement step in the measurement method is performed after the coating step. Therefore, the thickness of the substrate can be measured in the first measurement step, and the thickness of the optical film can be measured in the second measurement step. The thickness correction value in the conversion formula for converting the optical measurement result of the second film thickness meter to thickness, which is adopted in the step of measuring the thickness of the coating layer in the manufacturing method, is different from the thickness correction value in the conversion formula for converting the optical measurement result of the first film thickness meter to thickness. In this case, since the thickness correction value according to the configuration of the optical film can be adopted, the thickness of the coating layer can be obtained more accurately.

[0017] The first measuring step, the coating step, and the second measuring step may be performed while the substrate is being transported, in which case the thickness of the coating layer can be obtained while the coating layer is being applied to the substrate. Effect of the Invention

[0018] According to one aspect of the present invention, there is provided a method for measuring the thickness of a coating layer, which can obtain the thickness of a coating layer more accurately, and a method for producing an optical film including the above-mentioned measuring method. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of an optical film according to an embodiment. [Diagram 2] FIG. 2 is a conceptual diagram for explaining a method for producing an optical film according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The same elements are given the same reference numerals, and duplicated explanations will be omitted. The dimensional ratios of the drawings do not necessarily match those in the description.

[0021] 1 is a schematic diagram showing the configuration of an optical film produced by a method for producing an optical film according to one embodiment. An optical film 10 shown in FIG. 1 is a film having a substrate 11 and a coating layer 12.

[0022] The substrate 11 is an optical laminate having a resin film 111 and an optical function layer 112 laminated on the resin film 111. An example of the thickness of the substrate 11 is 10 μm or more and 500 μm or less, and may be 10 μm or more and 200 μm or less. An example of the refractive index (or the estimated refractive index described later) of the substrate 11 is 1.4 or more and 1.8 or less, and may be 1.5 or more and 1.8 or less. An example of the length of the substrate 11 is 100 m or more and 30,000 m or less, and may be 100 m or more and 10,000 m or less. In one embodiment, the substrate 11 is a member having a thickness of 10 μm or more and 500 μm or less and a refractive index of 1.4 or more and 1.8 or less.

[0023] Examples of the resin constituting the resin film 111 include triacetyl cellulose (TAC), polyethylene terephthalate (PET), and polycycloolefin (COP). Examples of the optical function layer 112 include a retarder layer that imparts a phase difference to incident light, a linear polarizer layer that imparts linear polarization properties to incident light, and a circular polarization layer (including an elliptical polarization layer) in which the retarder layer and the linear polarizer layer are laminated via an adhesive layer. The base material 11 can be an optical film that functions as, for example, a phase plate, a linear polarizer, a circular polarizer, or the like, depending on the type of the optical function layer 112. The optical function layer 112 itself may be a phase plate, a linear polarizer, a circular polarizer, or the like, in which case the resin film 111 can be, for example, a protective film.

[0024] The substrate 11 may be a single-layer resin film. Examples of the resin film are the same as those described above. The substrate 11 may be a laminate of a plurality of resin layers (or resin films). One of the plurality of resin layers may be a hard coat layer.

[0025] The substrate 11 itself may also be an optical film. In this case, the optical film 10 is a laminated optical film.

[0026] The coating layer 12 is laminated on the substrate 11. An example of the thickness of the coating layer 12 is 0.5 μm or more and 5 μm or less, and may be 0.5 μm or more and 3 μm or less. An example of the refractive index of the coating layer 12 is 1.4 or more and 1.8 or less, and may be 1.4 or more and less than 1.5. In one embodiment, the coating layer 12 is a layer having a thickness of 0.5 μm or more and 5 μm or less and a refractive index of 1.4 or more and 1.8 or less.

[0027] An example of the material of the coating layer 12 is an adhesive or a pressure-sensitive adhesive. In this case, the coating layer 12 functions as an adhesive layer or a pressure-sensitive adhesive. The adhesive or pressure-sensitive adhesive may be a material known in the technical field to which the present disclosure relates. Examples of the adhesive include an active energy ray curable adhesive such as an ultraviolet (UV) curable resin, and a water-based adhesive such as an aqueous solution of a polyvinyl alcohol-based resin. Examples of the pressure-sensitive adhesive include a pressure-sensitive adhesive composition mainly composed of a (meth)acrylic resin, a rubber-based resin, a urethane-based resin, an ester-based resin, a silicone-based resin, a polyvinyl ether-based resin, or the like.

[0028] Next, a method for producing the optical film 10 will be described. Fig. 2 is a schematic diagram for explaining the method for producing the optical film according to one embodiment. Fig. 2 shows the substrate 11 and the coating layer 12 in a schematic manner, and examples of the configurations of the substrate 11 and the coating layer 12 are the same as those described with reference to Fig. 1.

[0029] 2, the optical film 10 is produced by forming a coating layer 12 on a long substrate 11 while transporting the substrate 11 by a transport device (not shown). That is, the method for producing an optical film includes a coating step of forming the optical film 10 by coating the substrate 11 with the coating layer 12.

[0030] In the coating step, as shown in FIG. 2, a coating device 20 is used to coat the substrate 11 with the coating agent 12a. This forms the coating layer 12. The coating agent 12a is a material that constitutes the coating layer 12, and is, for example, the adhesive or pressure-sensitive adhesive described above. The coating device 20 is not limited as long as it can coat the substrate 11 with the coating agent 12a, and various coating methods can be used, such as a gravure coater, a doctor blade, a wire bar, a die coater, and a comma coater. Of these, a gravure coater is preferred from the viewpoint of thin film coating.

[0031] In order to control (or monitor) the thickness of the coating layer 12, the manufacturing method of the optical film includes a step of measuring the thickness of the coating layer 12 using a thickness measuring method according to one embodiment. Hereinafter, the step of measuring the thickness of the coating layer 12 will be specifically described.

[0032] The step of measuring the thickness of the coating layer 12 is a step of measuring the thickness of the coating layer 12 based on an optical measurement method, and includes a first measuring step, a second measuring step, and a calculating step.

[0033] In the first measurement step, the thickness x1 of the substrate 11 is measured by an optical measurement method using a first thickness meter 30A. As shown in Fig. 2, in order to measure the thickness x1, the first thickness meter 30A is disposed upstream of the coating device 20 in the conveying direction of the substrate 11. In this embodiment, the first thickness meter 30A is disposed in the center of the width direction of the substrate 11 (direction perpendicular to the conveying direction).

[0034] The first film thickness meter 30A is a non-contact spectroscopic interference film thickness meter. The spectroscopic interference film thickness meter irradiates a measurement object (substrate 11 in the first measurement step) with measurement light 31 (for example, infrared light in a wide wavelength band) and obtains the optical path length of the measurement object (optical measurement result) based on the interference between the reflected light from the front surface of the measurement object and the reflected light from the back surface of the measurement object.

[0035] In the second measurement step, the thickness x3 of the optical film 10 is measured by an optical measurement method using the second thickness meter 30B. As shown in FIG. 2, the second thickness meter 30B is disposed downstream of the coating device 20 in the conveying direction of the substrate 11 in order to measure the thickness x3. The second thickness meter 30B is a non-contact spectral interference thickness meter. In this embodiment, the second thickness meter 30B is the same thickness meter as the first thickness meter 30A, and is disposed in the center of the substrate 11 in the width direction, similarly to the first thickness meter 30B.

[0036] In the calculation step, the thickness x2 of the coating layer 12 is calculated based on the optical measurement results obtained by the first thickness gauge 30A and the second thickness gauge 30B. The optical measurement results are the optical path lengths of the substrate 11 and the optical film 10, which are the measurement targets of the first thickness gauge 30A and the second thickness gauge 30B.

[0037] If the optical path length of the substrate 11 obtained by the first thickness meter 30A is called OL1, and the optical path length of the optical film 10 obtained by the second thickness meter 30B is called OL2, then OL1 and OL2 can be converted to thicknesses x1 and x3 using the conversion equations expressed by formulas (1) and (2). N0 and N in formulas (1) and (2) are thickness correction values ​​for converting the optical path length to thickness, and are known as scaling values. x1 = (OL1) / N0 (1) x3=(OL2) / N (2)

[0038] The thickness x2 of the coating layer 12 is obtained as the difference between the thickness x3 and the thickness x1. That is, the thickness x2 is calculated by the formula (3). x2=x3-x1=(OL2) / N-(OL1) / N0...(3)

[0039] N0 and N in formula (3) (formulas (1) and (2)) will be explained in detail.

[0040] (Thickness correction value N0) In this embodiment, the thickness correction value N0 is the estimated refractive index n1 of the substrate 11. As shown in FIG. 1, when the substrate 11 has a multilayer structure, the refractive index of the substrate 11 deviates from the refractive index of the resin film 111 or the optical function layer 112. Even if the substrate 11 is formed of a resin film 111, the refractive index of the resin film 111 may also deviate from the theoretical value due to tension generated in the substrate 11 during transportation. The estimated refractive index n1 is a refractive index that takes the deviation into account, and is the substantial refractive index of the substrate 11 in the manufacturing process of the optical film 10.

[0041] The thickness correction value N0 as the estimated refractive index n1 can be obtained as follows. The optical path length OL1 of the substrate 11 is obtained in advance using the first film thickness meter 30A while the substrate 11 is being transported as shown in FIG. 2. The actual thickness of the substrate 11 (hereinafter also referred to as "actual film thickness") is obtained by observing a cross section of the substrate 11. A thickness correction value is calculated from the optical path length OL1 and the actual film thickness of the substrate 11 so that the optical path length OL1 coincides with the actual film thickness of the substrate 11 obtained by the cross section observation.

[0042] By using such a thickness correction value N0, even if the substrate 11 has a layered structure, it is possible to use an optimal thickness correction value N0 for the substrate 11. As a result, it is possible to calculate the thickness x1 more accurately.

[0043] (Thickness correction value N) The thickness correction value N is different from the thickness correction value NO. The thickness correction value N may be the refractive index of the optical film 10 taking into consideration that the optical film 10 is a laminate of the substrate 11 and the coating layer 12. In one embodiment, the thickness correction value N is expressed by formula (4).

number

[0044] When equation (4) is used as the thickness correction value N, OL1 and OL2 in equation (3) are known as the measurement results of the first thickness meter 30A and the second thickness meter 30B, the refractive index n2 of the coating layer 12 is also known, and further, the estimated refractive index n1 is also known, so that the thickness x2 can be calculated by substituting equation (4) into equation (3).

[0045] In one embodiment, the thickness x2 calculated in the calculation step is a value calculated using the measurement result of the second film thickness gauge 30B and the optical measurement result of the first film thickness gauge 30A at the same location on the substrate 11 (for convenience of explanation, referred to as "measurement position a"). The thickness x2 may be calculated using the measurement result at the measurement position a, among the measurement results of the first film thickness gauge 30A and the second film thickness gauge 30B, based on the installation distance between the first film thickness gauge 30A and the second film thickness gauge 30B and the conveyance speed of the substrate 11. The calculation of the thickness x2 using the optical measurement results of the first film thickness gauge 30A and the second film thickness gauge 30B may be automatically performed using a control device to which the measurement results of the first film thickness gauge 30A and the second film thickness gauge 30B are input.

[0046] In the manufacturing method of the optical film 10, the thickness x2 is obtained using a first thickness meter 30A and a second thickness meter 30B, which are spectral interference thickness meters. Therefore, since the thickness x2 of the coating layer 12 can be obtained in-line, it is possible to check whether the coating layer 12 is formed to the desired thickness while manufacturing the optical film 10. For example, if there is a discrepancy between the thickness x2 of the coating layer 12 obtained by the above measurement method and the desired thickness (thickness at the design stage), the coating conditions can be adjusted to form the coating layer 12 having the desired thickness. Therefore, it is possible to improve the quality of the optical film 10 and the manufacturing yield.

[0047] In the above-described thickness measurement method, a thickness correction value N is applied to the optical measurement results of the first thickness gauge 30A and the second thickness gauge 30B. 0, N is different. The effect of this point will be explained in comparison with the case where the same thickness correction value is applied to the optical measurement results of the first thickness gauge 30A and the second thickness gauge 30B.

[0048] As shown in FIG. 2, the manufacturing method of manufacturing an optical film while conveying a substrate 11 is suitable for continuous production of a long optical film 10. In this way, when the optical film is continuously produced, if a mistake occurs in setting the thickness correction value when different values ​​are used for the first thickness gauge 30A and the second thickness gauge 30B, a large amount of defective optical films with reduced quality are produced. Therefore, in order to prevent the above-mentioned setting mistake, the same value is usually used as the thickness correction value for the first thickness gauge 30A and the second thickness gauge 30B. However, the present inventors have found that there are cases where a deviation occurs between the thickness of the coating layer obtained by optical measurement and the actual thickness of the coating layer, and further, the deviation increases.

[0049] In the above measurement method, a value different from the thickness correction value N0 for the first thickness gauge 30A is adopted as the thickness correction value N for the second thickness gauge 30B. For example, a value considering that the optical film 10 is a laminate of the substrate 11 and the coating layer 12 can be adopted as the thickness correction value for the second thickness gauge 30B. In this way, the thickness correction value N is different from the thickness correction value N0, so that the thickness x2 can be calculated more accurately. As a result, the coating layer 12 having a desired thickness can be formed, and the quality of the optical film 10 can be improved. When the thickness correction value N is expressed by formula (4), the thickness x2 can be calculated more accurately.

[0050] When the difference between the estimated refractive index n1 of the substrate 11 and the refractive index n2 of the coating layer 12 is large, the difference between the estimated refractive index n1 of the substrate 11 and the refractive index of the optical film 10 also becomes large. Therefore, the difference between the thickness of the coating layer obtained by applying the same value as the thickness correction value for the first thickness meter 30A and the second thickness meter 30B to the optical measurement result and the actual thickness of the coating layer also increases. Therefore, the above measurement method is effective when the difference between the estimated refractive index n1 of the substrate 11 and the refractive index n2 of the coating layer 12 is large. In one embodiment, the above measurement method is even more effective when the estimated refractive index n1 of the substrate 11 and the refractive index n2 of the optical film 10 satisfy the relationship shown in formula (5) or formula (6). 0.77≦n2 / n1≦0.99 (5) 1.01≦n2 / n1≦1.20 (6)

[0051] When the thickness x2 of the coating layer 12 is 0.5 μm or more and 5 μm or less, it is difficult to directly measure the thickness x2 of the coating layer 12 with a spectral interference film thickness gauge from the viewpoints of the resolution, measurement accuracy, etc. of the spectral interference film thickness gauge. Therefore, the above method of calculating the thickness x2 based on the thickness x3 of the optical film 10 and the thickness x1 of the substrate 11 is effective.

[0052] The above measurement method is effective, for example, when forming a coating layer 12 having an exemplary refractive index n2 and thickness on a substrate 11 having an exemplary refractive index (or estimated refractive index n1) and thickness in this specification.

[0053] Next, experimental examples for the above-mentioned measurement method will be described, but the present invention is not limited to these examples. In the following description, "%" and "parts" mean mass % and mass parts unless otherwise specified. In the description of the experimental examples, for convenience of explanation, the same elements as those in the embodiment described using FIG. 1 and FIG. 2 are given the same reference numerals. Furthermore, the thickness obtained using the first thickness meter 30A and the second thickness meter 30B is referred to as "in-line thickness", and the thickness obtained by observing the cross section of the substrate 11 or the optical film 10 is referred to as "actual thickness". (Experimental Example 1) [Preparation of substrate] (Preparation of composition (A) for forming alignment layer) The following components were mixed, and the resulting mixture was stirred at a temperature of 80° C. for 1 hour to obtain a composition for forming an alignment layer (A). Oriented materials (part 5): [ka] Solvent (95 parts): Cyclopentanone

[0054] (Preparation of composition (B) for forming alignment layer) 2-Butoxyethanol was added to Sunever SE-610 (manufactured by Nissan Chemical Industries, Ltd.), a commercially available oriented polymer, to obtain an orientation layer forming composition (B). The obtained orientation layer forming composition (B) had a solid content of 1% relative to the total amount of the composition, and a solvent content of 99% relative to the total amount of the composition. The solid content of Sunever SE-610 was calculated from the concentration listed in the delivery specifications.

[0055] (Preparation of Liquid Crystal Layer Forming Composition (C)) A liquid crystal layer-forming composition (C) was obtained by mixing the following components and stirring the resulting mixture at 80° C. for 1 hour. Polymerizable liquid crystal compounds C1 and C2 were synthesized by the method described in JP-A-2010-31223. ·Polymerizable liquid crystal compound C1 (80 parts): [ka] ·Polymerizable liquid crystal compound C2 (20 parts): [ka] Polymerization initiator (6 parts): 2-Dimethylamino-2-benzyl-1-(4-morpholinophenyl)butan-1-one (Irgacure 369; manufactured by Chiba Specialty Chemicals) Solvent (400 parts): Cyclopentanone

[0056] (Manufacture of substrate) A polyethylene terephthalate (PET) film having a thickness of 100 μm (corresponding to the resin film 111 in FIG. 1) was treated using a corona treatment device under conditions of an output of 0.3 kW and a treatment speed of 3 m / min. The photoalignment layer forming composition (A) was applied to the corona-treated surface with a bar coater, dried at 80° C. for 1 minute, and then irradiated with 100 mJ / cm 2 using a polarized UV irradiation device (SPOT CURE SP-7; manufactured by Ushio Inc.). 2An alignment layer was obtained by carrying out polarized UV exposure with an integrated light amount of 100 nm. The thickness of the alignment layer was measured with a laser microscope (LEXT, manufactured by Olympus Corporation) and found to be 100 nm.

[0057] Next, the liquid crystal layer-forming composition (C) was applied onto the alignment layer using a bar coater and dried at 120°C for 1 minute, after which ultraviolet light was irradiated using a high-pressure mercury lamp (Unicur VB-15201BY-A, manufactured by Ushio Inc.) (under a nitrogen atmosphere, wavelength: 365 nm, cumulative light amount at wavelength 365 nm: 1000 mJ / cm 2 ) to form a liquid crystal layer as a retarder layer, thereby obtaining a substrate 11 as a retardation plate. The liquid crystal layer had a thickness of 2 μm. In the substrate 11 thus produced, the laminate of the alignment layer and the liquid crystal layer corresponds to the optical function layer 112 in FIG.

[0058] <Optical film manufacturing> The substrate 11 prepared as described above was conveyed as shown in Fig. 2, while which was coated with the coating agent 12a using a coating device 20. In this manner, an optical film 10 including the substrate 11 and the coating layer 12 laminated on the substrate 11 was produced. The conveying speed of the substrate 11 was 20 m / min, and the tension applied to the substrate 11 during conveyance was 200 N.

[0059] A gravure coater was used as the coating device 20. The coating agent 12a was an ultraviolet-curable adhesive, and the coating layer 12 was an adhesive layer. The refractive index n2 of the coating layer 12 (the refractive index of the coating agent 12a) was 1.482. In Experimental Example 1, the target film thickness of the coating layer 12 was 1.3 μm.

[0060] In Experimental Example 1, the in-line film thickness x2 of the coating layer 12 was obtained by applying the measurement method described in the above embodiment during the production of the optical film 10. Specifically, as shown in Fig. 2, the optical path length OL1 and the optical path length OL2 of the substrate 11 and the optical film 10 were measured by a first film thickness meter 30A and a second film thickness meter 30B installed upstream and downstream of the coating device 20, and the in-line film thickness x2 of the coating layer 12 was calculated using the measurement results and formula (3). In Experimental Example 1, the in-line film thickness x2 was obtained at nine points in the transport direction (longitudinal direction) of the substrate 11 while the substrate 11 was transported.

[0061] The first thickness gauge 30A and the second thickness gauge 30B were SI-T80 manufactured by Keyence Corporation.

[0062] In calculating the in-line film thickness x2, the thickness correction value N for the first film thickness gauge 30A was calculated as follows.

[0063] First, the thickness of the substrate 11 manufactured in Experimental Example 1 was measured by the first thickness meter 30A while being transported as shown in FIG. 2. The transport conditions of the substrate 11 were the same as those in the case of manufacturing the optical film 10. The actual thickness of the substrate 11 was obtained by observing the cross section of the substrate 11. The estimated refractive index n1 of the substrate 11 was calculated using the optical path length OL1, which is the optical measurement result of the first thickness meter 30A, and the actual thickness of the substrate 11 obtained by the cross section observation. The estimated refractive index n1 of the substrate 11 calculated in this manner was adopted as the thickness correction value N0 for the first thickness meter 30A. The thickness correction value N0 used in Experimental Example 1 was 1.715.

[0064] The thickness correction value N for the second thickness gauge 30B was determined as N expressed by the formula (4).

[0065] In Experimental Example 1, a cross-section of the produced optical film 10 was observed at the location where the in-line film thickness x2 was obtained, and the actual film thickness of the coating layer 12 was also obtained.

[0066] The in-line film thickness x2 of the substrate 11 at each thickness acquisition point based on the measurement method and the actual film thickness based on cross-sectional observation were as shown in Table 1. The "difference" in Table 1 is the difference between the actual film thickness and the in-line film thickness x2 (actual film thickness - in-line film thickness).

[0067] (Experimental Example 2) In Experimental Example 2, the optical film 10 was produced in the same manner as in Experimental Example 1, except that the target film thickness when forming the coating layer 12 was set to 1.5 μm and the number of points at which the thickness was obtained based on the above measurement method was three. In Experimental Example 2, cross-sectional observation was also performed at the points at which the in-line film thickness x2 was obtained, and the actual film thickness of the coating layer 12 was also obtained.

[0068] The in-line film thickness x2 of the coating layer 12 at each thickness acquisition point based on the measurement method and the actual film thickness of the coating layer 12 based on cross-sectional observation were as shown in Table 1. As in Experimental Example 1, the "difference" in Table 1 is the difference between the actual film thickness and the in-line film thickness x2 (actual film thickness - in-line film thickness).

[0069] [Table 1]

[0070] (Comparative Experimental Example 1) As Comparative Experimental Example 1, an optical film was manufactured in the same manner as in Experimental Example 1, except that the thickness correction value for the second thickness gauge 30B was the same as the thickness correction value for the first thickness gauge 30A, i.e., 1.715, and the in-line thickness of the coating layer was obtained. The in-line thickness was obtained at one location. At the location where the in-line thickness was obtained, the actual thickness of the coating layer was obtained in the same manner as in Experimental Example 1. The in-line thickness and actual thickness in Comparative Experimental Example 1 were as shown in Table 2. The "difference" in Table 2 is the difference between the actual thickness and the in-line thickness (actual thickness - in-line thickness), as in Experimental Example 1.

[0071] (Comparative Experimental Example 2) As Comparative Experimental Example 2, an optical film was manufactured in the same manner as in Experimental Example 2, except that the thickness correction value for the second thickness gauge was the same as the thickness correction value for the first thickness gauge 30A, i.e., 1.715, and the in-line thickness of the coating layer was obtained. The in-line thickness was obtained at one location. At the location where the in-line thickness was obtained, the actual thickness of the coating layer was obtained in the same manner as in Experimental Example 1. The in-line thickness and actual thickness in Comparative Experimental Example 2 were as shown in Table 2. The "difference" in Table 2 is the difference between the actual thickness and the in-line thickness (actual thickness - in-line thickness), as in Experimental Example 1.

[0072] [Table 2]

[0073] A comparison between Experimental Example 1 and Comparative Experimental Example 1 and a comparison between Experimental Example 2 and Comparative Experimental Example 2 reveals that by adopting a thickness correction value N for the second thickness gauge 30B that is different from the thickness correction value N0 for the first thickness gauge 30A, a thickness closer to the actual thickness can be obtained, that is, a thickness x2 can be obtained more accurately. In the above Experimental Examples 1 and 2, the thickness correction value for the second thickness gauge 30B is used as the thickness correction value expressed by equation (4), and it was verified that by using equation (4), a thickness closer to the actual thickness can be obtained.

[0074] The above describes the embodiments of the present invention. However, the present invention is not limited to the illustrated embodiments, and includes the scope of the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0075] The location of the first and second thickness gauges in the width direction (direction perpendicular to the longitudinal direction) of the long substrate in the above embodiment is not limited to the center of the substrate. The first and second thickness gauges may each be provided in a plurality of locations along the width direction (direction perpendicular to the longitudinal direction) of the long substrate in the above embodiment. In this case, for example, the thickness of the coating layer may be calculated using the average value of the optical measurement results of the plurality of first thickness gauges and the average value of the optical measurement results of the plurality of second thickness gauges.

[0076] The first and second thickness gauges do not have to be the same model as long as they are each a spectral interference type thickness gauge. [Explanation of symbols]

[0077] 10...optical film, 11...substrate, 12...coating layer, 30A...first film thickness gauge, 30B...second film thickness gauge.

Claims

1. A method for measuring a thickness of a coating layer in an optical film including a substrate and a coating layer laminated on the substrate, the method comprising the steps of: a first measuring step of measuring the thickness of the substrate by an optical measurement method using a first film thickness meter; a second measuring step of measuring a thickness of the optical film obtained by coating the coating layer on the substrate by an optical measurement method using a second film thickness meter; a calculation step of calculating a thickness of the coating layer based on optical measurement results obtained by the first thickness meter and the second thickness meter; Equipped with the first thickness meter and the second thickness meter are each a spectral interference thickness meter, a thickness correction value in a conversion formula for converting the optical measurement result of the second film thickness meter into a thickness is different from a thickness correction value in a conversion formula for converting the optical measurement result of the first film thickness meter into a thickness; the thickness correction value for the optical measurement result of the first film thickness meter is an estimated refractive index of the substrate; The estimated refractive index is a refractive index calculated in advance from an optical path length of the substrate obtained by using the first film thickness meter while transporting the substrate and a thickness of the substrate obtained by observing a cross section of the substrate. Measurement method.

2. The thickness correction value for the optical measurement result of the second film thickness meter is expressed by Equation (1): The measurement method according to claim 1. [0010] (In formula (1), N represents the thickness correction value for the optical measurement result of the second film thickness meter, and n １ represents the thickness correction value for the measurement result of the first thickness gauge, and n ２ represents the refractive index of the coating layer, and x １ represents the thickness of the substrate, and x ２ represents the thickness of the coating layer.)

3. The n １ and the n ２ satisfies the relationship shown in formula (2). The measurement method according to claim 2. 0.77≦n ２ / n １ ≦0.99・・・(2)

4. The n １ and the n ２ satisfies the relationship shown in formula (3). The measurement method according to claim 2. 1.01≦n ２ / n １ ≦1.20・・・(3)

5. The estimated refractive index of the substrate is 1.4 or more and 1.8 or less. The measurement method according to any one of claims 1 to 4.

6. The thickness of the substrate is 10 μm or more and 500 μm or less. The measurement method according to any one of claims 1 to 5.

7. The refractive index of the coating layer is 1.4 or more and 1.8 or less. The measurement method according to any one of claims 1 to 6.

8. The thickness of the coating layer is 0.5 μm or more and 5 μm or less. The measurement method according to any one of claims 1 to 7.

9. The substrate has a multilayer structure. The measurement method according to any one of claims 1 to 8.

10. The method further includes a coating step of coating the coating layer on the substrate to form the optical film including the substrate and the coating layer, The first measuring step, the coating step, and the second measuring step are carried out while transporting the substrate. The measurement method according to any one of claims 1 to 9.

11. a coating step of coating a substrate with a coating layer to form an optical film including the substrate and the coating layer; measuring the thickness of the coating layer by the method according to any one of claims 1 to 9; Equipped with The first measurement step in the measurement method is carried out before the coating step, The second measurement step in the measurement method is carried out after the coating step. A method for producing an optical film.

12. The first measuring step, the coating step, and the second measuring step are carried out while transporting the substrate. The method for producing an optical film according to claim 11 .

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