JP7616950B2 - Measurement method and method for manufacturing optical film - Google Patents

Description

The present invention relates to a measurement method and a manufacturing method for an optical film.

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. This produces an optical film having a substrate and a coating layer.

JP 2000-024565 A

In optical films having a substrate and a coating layer, the thickness of the coating layer affects the performance of products that include the optical film. Therefore, in order to monitor the thickness of the coating layer, it is necessary to measure the thickness of the coating layer appropriately.

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 measuring the thickness of a coating layer 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 obtained in this way and the thickness of the substrate.

However, there were cases where the thickness of the coating layer obtained using a spectroscopic interference film thickness meter differed greatly from the actual thickness of the coating layer obtained by observing the cross section of the optical film.

An object of one aspect of the present invention is to provide a method for measuring the thickness of a coating layer that can obtain the thickness of the coating layer more accurately, and a method for manufacturing an optical film that includes the above-mentioned measurement method.

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, based on an optical measurement method, and includes a first measurement step of measuring the thickness of the substrate by the optical measurement method using a first film thickness meter, a second measurement step of measuring the thickness of the optical film obtained by applying the coating layer to the substrate by the optical measurement method using a second film thickness meter, and a calculation step of calculating the thickness of the coating layer based on the optical measurement results obtained by the first film thickness meter and the second film thickness meter, wherein the first film thickness meter and the second film thickness meter are each a spectral interference film thickness meter, and a thickness correction value in a conversion formula for converting the optical measurement result of the second film thickness meter to 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 to a thickness.

In the above measurement method, the thickness correction value in the conversion formula for converting the optical measurement result of the second thickness meter to thickness is different from the thickness correction value in the conversion formula for converting the optical measurement result of the first thickness meter to 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.

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

(In formula (1), N represents the thickness correction value for the optical measurement result of the second thickness meter, _n1 represents the thickness correction value for the measurement result of the first thickness meter, _n2 represents the refractive index of the coating layer, _x1 represents the thickness of the substrate, and _x2 represents the thickness of the coating layer.)

The above _n1 and _n2 may satisfy the relationship shown in formula (B) or formula (C).
0.77≦n ₂ /n ₁ ≦0.99...(B)
1.01≦n ₂ /n ₁ ≦1.20...(C)

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.

The refractive index of the coating layer may be 1.4 or more and 1.8 or less. The thickness of the coating layer may be 0.5 μm or more and 5 μm or less.

The measurement 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 measurement step, the coating step, and the second measurement step may be performed while the substrate is being transported. In this case, the thickness of the coating layer can be obtained while the coating layer is being applied to the substrate.

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 the thickness of the coating layer by the measurement method, in which 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.

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 used 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, a thickness correction value according to the configuration of the optical film can be used, so that the thickness of the coating layer can be obtained more accurately.

The first measurement step, the coating step, and the second measurement step may be performed while the substrate is being transported. In this case, the thickness of the coating layer can be obtained while the coating layer is being applied to the substrate.

According to one aspect of the present invention, it is possible to provide a method for measuring the thickness of a coating layer that can obtain the thickness of the coating layer more accurately, and a method for manufacturing an optical film that includes the above-mentioned measurement method.

FIG. 1 is a schematic diagram illustrating the configuration of an optical film according to an embodiment. FIG. 2 is a conceptual diagram for explaining a method for producing an optical film according to an embodiment.

Below, an embodiment of the present invention will be described with reference to the drawings. Identical elements will be given the same reference numerals, and duplicate explanations will be omitted. The dimensional ratios in the drawings do not necessarily match those in the description.

Figure 1 is a schematic diagram showing the configuration of an optical film manufactured by an optical film manufacturing method according to one embodiment. The optical film 10 shown in Figure 1 is a film having a substrate 11 and a coating layer 12.

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. 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.

Examples of resins 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 substrate 11 may 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 may be, for example, a protective film.

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 multiple resin layers (or resin films). One of the multiple resin layers may be a hard coat layer.

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

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.

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 related to the present disclosure. Examples of adhesives include active energy ray curing adhesives such as ultraviolet (UV) curing resins, and water-based adhesives such as aqueous polyvinyl alcohol resin solutions. Examples of pressure-sensitive adhesives include pressure-sensitive adhesive compositions mainly composed of (meth)acrylic resins, rubber resins, urethane resins, ester resins, silicone resins, polyvinyl ether resins, etc.

Next, a method for producing the optical film 10 will be described. FIG. 2 is a schematic diagram for explaining a method for producing an optical film according to one embodiment. In FIG. 2, the substrate 11 and the coating layer 12 are shown in schematic form, but examples of the configurations of the substrate 11 and the coating layer 12 are as described with reference to FIG. 1.

As shown in FIG. 2, the optical film 10 is manufactured by forming a coating layer 12 on a long substrate 11 while the substrate 11 is transported by a transport device (not shown). That is, the method for manufacturing an optical film includes a coating step in which the substrate 11 is coated with the coating layer 12 to form the optical film 10.

In the coating process, 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, doctor blade, wire bar, die coater, and comma coater. Of these, a gravure coater is preferred from the viewpoint of thin-film coating.

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 measurement method according to one embodiment. The step of measuring the thickness of the coating layer 12 will be described in detail below.

The process of measuring the thickness of the coating layer 12 is a process of measuring the thickness of the coating layer 12 based on an optical measurement method, and includes a first measurement process, a second measurement process, and a calculation process.

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).

The first thickness meter 30A is a non-contact spectral interference thickness meter. The spectral interference thickness meter irradiates the 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 light reflected from the front surface of the measurement object and the light reflected from the back surface of the measurement object.

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.

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 meter 30A and the second thickness meter 30B. The optical measurement results are the optical path lengths of the substrate 11 and the optical film 10, which are the objects of measurement by the first thickness meter 30A and the second thickness meter 30B.

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, OL1 and OL2 can be converted to thicknesses _x1 and _x3 using the conversion formulas 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.
x ₁ = (OL1)/N ₀ ...(1)
x ₃ = (OL2)/N...(2)

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).
x ₂ = x ₃ - x ₁ = (OL2)/N-(OL1)/N ₀ ...(3)

_N0 and N in formula (3) (formula (1) and formula (2)) will be described in detail.

(Thickness correction value N ₀ )
In this embodiment, the estimated refractive index _n1 of the substrate 11 is used as the thickness correction value _N0 . As shown in FIG. 1, when the substrate 11 has a multi-layer 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.

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.

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 a more accurate thickness _x1 .

(Thickness correction value N)
The thickness correction value N is different from the thickness correction value N _0. 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).

(In formula (4), _n1 is the estimated refractive index (thickness correction value) of the substrate 11, _n2 is the refractive index of the coating layer 12, _x1 is the thickness of the substrate 11, and _x2 is the thickness of the coating layer 12.)

When formula (4) is used as the thickness correction value N, OL1 and OL2 in formula (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. Therefore, the thickness x2 can be calculated by substituting formula (4) into formula (3).

In one embodiment, the thickness _x2 calculated in the calculation step is a value calculated using the measurement result of the second thickness gauge 30B and the optical measurement result of the first 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, based on the installation distance between the first thickness gauge 30A and the second thickness gauge 30B and the conveying speed of the substrate 11, among the measurement results of the first thickness gauge 30A and the second thickness gauge 30B. The calculation of the thickness _x2 using the optical measurement results of the first thickness gauge 30A and the second thickness gauge 30B can be performed automatically using a control device to which the measurement results of the first thickness gauge 30A and the second thickness gauge 30B are input.

In the manufacturing method of the optical film 10, the thickness _x2 is obtained using the first thickness meter 30A and the 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 improve the manufacturing yield.

In the above-described thickness measurement method, different thickness correction values N0 _, N are applied to the optical measurement results of the first thickness gauge 30A and the second thickness gauge 30B. The effect of this point will be described 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.

As shown in FIG. 2, the manufacturing method of manufacturing an optical film while conveying the 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, from the viewpoint of preventing 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.

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, so that 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.

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≦n ₂ /n ₁ ≦0.99 (5)
1.01≦ _n2 / _n1 ≦1.20...(6)

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 meter from the viewpoints of the resolution, measurement accuracy, etc. of the spectral interference film thickness meter. 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.

The above measurement method is effective, for example, when forming a coating layer 12 having the exemplified refractive index _n2 and thickness on a substrate 11 having the exemplified refractive index (or estimated refractive index _n1 ) and thickness in this specification.

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 called "in-line thickness", and the thickness obtained by observing the cross section of the substrate 11 or the optical film 10 is called "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 (A) for forming an alignment layer.
Orientable material (5 parts):

Solvent (95 parts): Cyclopentanone

(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 stated in the delivery specifications.

(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 compound C1 and polymerizable liquid crystal compound C2 were synthesized by the method described in JP-A-2010-31223.
・Polymerizable liquid crystal compound C1 (80 parts):

・Polymerizable liquid crystal compound C2 (20 parts):

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

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

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 that, a high pressure mercury lamp (Unicur VB-15201BY-A, manufactured by Ushio Inc.) was used to irradiate with ultraviolet light (under a nitrogen atmosphere, wavelength: 365 nm, accumulated 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 thickness of the liquid crystal layer was 2 μm. In the substrate 11 thus manufactured, the laminate of the alignment layer and the liquid crystal layer corresponds to the optical function layer 112 in FIG. 1.

<Production of Optical Film>
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.

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 n ₂ 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.

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 lengths OL1 and 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, respectively, 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.

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

In calculating the in-line film thickness _x2 , the thickness correction value N for the first film thickness meter 30A was calculated as follows.

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 n _{1 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 n 1 of} the substrate 11 calculated in this manner was adopted as the thickness correction value N ₀ for the first thickness meter 30A. The thickness correction value N ₀ used in Experimental Example 1 was 1.715.

The thickness correction value N for the second thickness gauge 30B was calculated using the formula (4).

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.

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).

(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 locations where the thickness was obtained based on the above measurement method was three. In Experimental Example 2, cross-sectional observation was also performed at the locations where the in-line film thickness _x2 was obtained, and the actual film thickness of the coating layer 12 was also obtained.

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).

Comparative Experimental Example 1
In 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 film thickness of the coating layer was obtained. The in-line film thickness was obtained at one location. At the in-line film thickness obtaining location, the actual film thickness of the coating layer was obtained in the same manner as in Experimental Example 1. The in-line film thickness and actual film thickness in Comparative Experimental Example 1 were as shown in Table 2. The "difference" in Table 2 is the difference between the actual film thickness and the in-line film thickness (actual film thickness - in-line film thickness), as in Experimental Example 1.

Comparative Experimental Example 2
In 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.

From a comparison between Experimental Example 1 and Comparative Experimental Example 1 and a comparison between Experimental Example 2 and Comparative Experimental Example 2, it can be understood 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 the thickness close to the actual thickness can be obtained by using equation (4).

The above describes an embodiment of the present invention. However, the present invention is not limited to the exemplified embodiment, and includes the scope indicated by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.

The placement locations 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 are not limited to the center of the substrate. The first and second thickness gauges may each be provided in multiple 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 multiple first thickness gauges and the average value of the optical measurement results of the multiple second thickness gauges.

The first and second thickness gauges do not have to be the same model, as long as they are both spectral interference thickness gauges.

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

Claims (12)

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.
How to measure? 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.

(In formula (1), N represents the thickness correction value for the optical measurement result of the second thickness meter, _n1 represents the thickness correction value for the measurement result of the first thickness meter, _n2 represents the refractive index of the coating layer, _x1 represents the thickness of the substrate, and _x2 represents the thickness of the coating layer.) The _n1 and _n2 satisfy the relationship shown in formula (2).
The measurement method according to claim 2.
0.77≦n ₂ /n ₁ ≦0.99...(2) The _n1 and _n2 satisfy the relationship shown in formula (3).
The measurement method according to claim 2.
1.01≦n ₂ /n ₁ ≦1.20...(3) 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. 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. 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. 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. The substrate has a multi-layer structure.
The measurement method according to any one of claims 1 to 8. 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 . 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. 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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