JP2020190553A - Method for inspecting optical film and method for manufacturing optical film - Google Patents

Abstract

To provide a method for inspecting an optical film and a method for manufacturing an optical film each of which enables the performance reliability of the optical film to be improved.SOLUTION: The method for inspecting an optical film comprises: a detection step in which an inspection surface 10a of an optical film 10 having a first phase difference layer, a second phase difference layer, a first adhesion layer disposed between the first and the second phase difference layers is irradiated with inspection light L1 from a light source unit 21 disposed on the inspection surface side, and light irradiated from the light source unit and reflected by the optical film is detected by a detection unit 22 arranged on an inspection surface side; and a determination step in which luminance distribution along a cross section in the optical film is acquired based on luminance of light detected by the detection unit to determine whether or not the optical film is the good product based on the luminance distribution.SELECTED DRAWING: Figure 4

Description

The present invention relates to an optical film inspection method and an optical film manufacturing method.

As an optical film, there is a retardation laminate having a first retardation layer and a second retardation layer. In the retardation laminate, the first retardation layer and the second retardation layer are bonded via an adhesive layer (for example, a layer formed of an ultraviolet curable resin adhesive). An example of a retardation laminate is a circular polarizing plate applied to an organic electroluminescence (organic EL) image display device (see Patent Document 1).

JP-A-2018-17996

When an optical film having a first retardation layer, an adhesive layer, and a second retardation layer in this order is applied to, for example, an image display device, it is required to reduce the interference unevenness of the optical film. Therefore, after forming the optical film, a quality inspection is performed according to the degree of interference unevenness of the optical film. This quality inspection is usually performed by irradiating an optical film with light and performing a visual inspection. However, in the visual inspection, the quality of the optical film tends to depend on the subjectivity, physical condition, etc. of the inspector, so that the reliability of the performance of the optical film tends to decrease.

Therefore, an object of the present invention is to provide an optical film inspection method and an optical film manufacturing method that can improve performance reliability.

In the method for inspecting an optical film according to one aspect of the present invention, a first retardation layer, a second retardation layer, and a first adhesive layer arranged between the first retardation layer and the second retardation layer are formed. The inspection surface of the optical film to be held is irradiated with the inspection light from the light source portion arranged on the inspection surface side, and the light emitted from the light source portion and reflected by the optical film is detected on the inspection surface side. Based on the detection step detected by the unit and the brightness of the light detected by the detection unit, the brightness distribution along the cross section of the optical film is acquired, and whether or not the optical film is a good product is determined based on the brightness distribution. A determination step for determining is provided.

In the above inspection method, the brightness distribution along the cross section of the optical film is acquired based on the brightness of the light detected by the detection unit, and it is determined whether or not the optical film is a good product based on the brightness distribution. Therefore, the quality of the optical film can be objectively determined, and the performance reliability of the optical film is improved.

The detection step and the determination step may be performed while transporting the optical film.

The cross section may be a cross section in the width direction of the optical film.

In the detection step, the inspection light from the light source unit is irradiated to the inspection surface through the first polarizing filter, and the light emitted from the light source unit to the optical film and reflected by the optical film is secondly polarized. It may be detected by the above-mentioned detection unit through a filter. In this case, for example, by adjusting the arrangement relationship of the first polarizing filter and the second polarizing filter, the influence of the surface reflection of the optical film can be reduced, and the optical film can be inspected more accurately.

One of the first retardation layer and the second retardation layer is a 1/2 wavelength layer and the other is a 1/4 wavelength layer, and the x-axis and y-axis orthogonal to each other are virtually placed on the inspection surface. When one of the x-axis and the y-axis is used as the reference axis and the counterclockwise direction is referred to as a positive angular direction with respect to the reference axis when viewed from the inspection surface side, the first retardation layer is used. In the optical film, the first retardation layer and the second retardation layer are arranged so that the first retardation axis and the second retardation axis of the second retardation layer satisfy the following conditions (1) to (3). The phase difference layer is arranged so that the first absorption axis of the first polarizing filter and the second absorption axis of the second polarizing filter satisfy the following conditions (4), (5) and (6). , The first polarizing filter and the second polarizing filter may be arranged with respect to the optical film.
(1) -40 ° <θ1 <-10 ° (θ1 is the angle between the first slow phase axis and the reference axis)
(2) + 15 ° <θ2 <+ 50 ° (θ2 is the angle between the second slow phase axis and the reference axis)
(3) + 55 ° <θ3 <+ 65 ° (θ3 is the angle between the first slow phase axis and the second slow phase axis)
(4) -20 ° <θ4 <+ 20 ° (θ4 is the angle between the first absorption axis and one of the second absorption axes and the reference axis).
(5) + 70 ° <θ5 <+ 110 ° (θ5 is the angle between the first absorption axis and the other of the second absorption axes and the reference axis).
(6) + 70 ° <θ6 <+ 110 ° (θ6 is the angle between the first absorption axis and the second absorption axis)

With the above configuration, the surface reflection of the optical film can be further reduced.

The optical film has a polarizing plate located on the opposite side of the 1/4 wavelength layer with respect to the 1/2 wavelength layer in the stacking direction, and a first located between the polarizing plate and the 1/2 wavelength layer. It may have two adhesive layers.

The first adhesive layer may be a cured layer of an active energy ray-curable adhesive.

The detection step may be carried out while transporting the optical film.

The peak wavelength of the inspection light may be in the range of 400 nm to 750 nm.

The detection step may be performed with the optical film arranged on the main surface of the support plate, and the specular reflectance of the main surface may be 45% or less. In this case, since the influence of reflection on the main surface of the support plate can be reduced, it is easy to accurately determine the quality of the optical film.

The method for producing an optical film according to another aspect of the present invention includes the method for inspecting the optical film according to the present invention.

In the above inspection method, the brightness distribution along the cross section of the optical film is acquired based on the brightness of the light detected by the detection unit, and it is determined whether or not the optical film is a good product based on the brightness distribution. Therefore, the quality of the optical film can be objectively determined, and the performance reliability of the optical film is improved. As a result, an optical film having improved performance reliability can be manufactured.

According to the present invention, it is possible to provide an optical film inspection method and an optical film manufacturing method that can improve performance reliability.

FIG. 1 is a flowchart of an optical film manufacturing method including an inspection method according to an embodiment. FIG. 2 is a schematic view showing a schematic configuration of an optical film manufactured by the method for manufacturing an optical film according to an embodiment. FIG. 3 is a schematic view showing a schematic configuration of a modified example of the optical film. FIG. 4 is a drawing for explaining an inspection method of an optical film according to an embodiment. FIG. 5 is a drawing for explaining the arrangement relationship between the first retardation layer and the second retardation layer of the optical film. FIG. 6 is a drawing for explaining the arrangement relationship of the first polarizing filter and the second polarizing filter with respect to the optical film. FIG. 7 is a chart showing the detection results of the samples S1 to S4 used in the experimental example. FIG. 8 is a schematic view showing a schematic configuration of an optical film used for visual inspection.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and duplicate description will be omitted. The dimensional ratios in the drawings do not always match those described.

FIG. 1 is a flowchart of an optical film manufacturing method including an inspection method according to an embodiment. The method for producing an optical film includes an optical film forming step S01, an optical film inspection step S02, an optical film forming condition changing step S03, and a non-defective optical film recovery step S04.

[Formation process]
In the forming step S01, the optical film 10 shown in FIG. 2 is formed. The optical film 10 is a circularly polarizing plate and can be applied to, for example, an organic electroluminescence apparatus.

The optical film 10 has a retardation laminate 11. The retardation laminate 11 has a first retardation layer 12, a second retardation layer 13, and a first adhesive layer 14 for adhering them. Usually, the optical film 10 has at least one of a first protective layer 15 and a second protective layer 16 that protects the retardation laminate 11. Hereinafter, unless otherwise specified, the case where the optical film 10 has the first protective layer 15 and the second protective layer 16 will be described.

<First retardation layer>
The first retardation layer 12 is, for example, a λ / 2 plate (1/2 wavelength layer) that gives a phase difference of λ / 2. An example of the thickness of the first retardation layer 12 is 1 μm to 3 μm. Examples of the in-plane retardation (R0) of the first retardation layer 12 include 236 nm ± 4 nm, 234 nm ± 5 nm and 240 nm ± 5 nm. The example of the in-plane phase difference is, for example, an example for a wavelength of 550 nm. The in-plane phase difference in the present embodiment can be measured by, for example, AxoScan (manufactured by Axometrics).

When the first retardation layer 12 is a 1/2 wavelength layer, it can be manufactured by subjecting a film of a translucent thermoplastic resin to a stretching treatment or the like so as to give a phase difference of λ / 2. In this case, the first retardation layer 12 is a birefringent film. An example of a thermoplastic resin is a cellulosic ester resin such as triacetyl cellulose.

The first retardation layer 12 may be manufactured by forming a first liquid crystal layer, a first alignment layer, or the like that gives a retardation of λ / 2 on the base film. In this case, the first liquid crystal layer, the first alignment layer, and the like correspond to the first retardation layer 12. The base film may be peeled off after forming the first retardation layer 12. Alternatively, the base film may also be a component of the first retardation layer 12. The example of the base film is the same as that of the first protective layer 15. The first protective layer 15 may also serve as a base film.

<Second retardation layer>
The second retardation layer 13 is, for example, a λ / 4 plate (1/4 wavelength layer) that gives a phase difference of λ / 4. An example of the thickness of the second retardation layer 13 is 0.1 μm to 2 μm. Examples of in-plane retardation (R0) of the second retardation layer 13 include 116 nm ± 4 nm and 120 nm ± 5 nm. When the in-plane retardation of the first retardation layer 12 is 236 nm ± 4 nm or 234 nm ± 5 nm, the in-plane retardation of the second retardation layer 13 can be 116 nm ± 4 nm. When the in-plane retardation of the first retardation layer 12 is 240 nm ± 5 nm, the in-plane retardation of the second retardation layer 13 can be 116 nm ± 4 nm. The example of the in-plane phase difference is, for example, an example for a wavelength of 550 nm. The angle formed by the slow axis of the second retardation layer 13 (the second slow axis 13a described later) and the slow axis of the first retardation layer 12 (the first slow axis 12a described later) is the optical film 10. It suffices if it is arranged so as to function as a circular polarizing plate, and is usually 60 ° ± 1 °.

When the second retardation layer 13 is a 1/4 wavelength layer, it can be manufactured by subjecting a translucent thermoplastic resin film to a stretching treatment or the like so as to give a phase difference of λ / 4. In this case, the second retardation layer 13 is a birefringent film. The example of the thermoplastic resin is the same as that of the first retardation layer 12.

The second retardation layer 13 may be manufactured by forming a liquid crystal layer, an alignment layer, or the like that gives a retardation of λ / 4 on the base film. In this case, the second liquid crystal layer, the second alignment layer, and the like correspond to the second retardation layer 13. The base film may be peeled off after forming the second retardation layer 13. Alternatively, the base film may also be a component of the second retardation layer 13. The example of the base film is the same as that of the second protective layer 16. The second protective layer 16 may also serve as a base film.

The first retardation layer 12 and the second retardation layer 13 are not particularly limited as long as they are layers that give a retardation, and may be a 1/2 wavelength layer, a 1/4 wavelength layer, a positive C layer, or the like, respectively. , It may be an anti-phase difference layer exhibiting anti-wavelength dispersibility.
The in-plane retardation value Re (550) of the positive C layer is usually in the range of 0 to 10 nm, preferably 0 to 5 nm, and the retardation value Rth in the thickness direction is usually in the range of -10 to −300 nm, preferably in the range of -10 to −300 nm. Is in the range of -20 to -200 nm.

The optical film 10 may be an optical film in which the first retardation layer 12 is the λ / 4 layer and the second retardation layer 13 is the λ / 2 layer.
The optical film 10 may be an optical film in which the first retardation layer 12 is the λ / 4 layer and the second retardation layer 13 is the positive C layer, or the first retardation layer 12 is It may be an optical film which is a positive C layer and the second retardation layer 13 is a λ / 4 layer.
The optical film 10 may be an optical film including a retardation layer in addition to the first retardation layer 12 and the second retardation layer 13. For example, when the first retardation layer 12 is the λ / 2 layer and the second retardation layer 13 is the λ / 4 layer, a positive C layer and an anti-phase difference layer may be further included.

<First adhesive layer>
The first adhesive layer 14 is a layer that is arranged between the first retardation layer 12 and the second retardation layer 13 and adheres the first retardation layer 12 and the second retardation layer 13. An example of the thickness of the first adhesive layer 14 is 0.1 μm to 5.0 μm, preferably 0.5 μm to 4.0 μm, and more preferably 1.0 μm to 3.0 μm. The first adhesive layer 14 can be formed by an adhesive or an adhesive. An example of the first adhesive layer 14 is a cured layer of an active energy ray-curable adhesive. The active energy ray-curing adhesive is an adhesive that is cured by irradiation with active energy rays such as ultraviolet rays, visible light, electron beams, and X-rays.

The first adhesive layer 14 may be formed of a known water-based adhesive in which a curable resin component is dissolved or dispersed in water. Examples of the resin component contained in the water-based adhesive include polyvinyl alcohol-based resin and urethane resin. The water-based composition containing the polyvinyl alcohol-based resin can further contain a curable component and a cross-linking agent. Examples of the aqueous composition containing a urethane resin include an aqueous composition containing a polyester ionomer type urethane resin and a compound having a glycidyloxy group. The polyester-based ionomer type urethane resin is a urethane resin having a polyester skeleton, in which a small amount of an ionic component (hydrophilic component) is introduced.

As the pressure-sensitive adhesive, an acrylic pressure-sensitive adhesive containing an acrylic copolymer and a cross-linking agent can be used. The acrylic copolymer can be produced by radical polymerization of a (meth) acrylate monomer having an alkyl group having 1 to 12 carbon atoms and a polymerizable monomer having a crosslinkable functional group. The (meth) acrylate means acrylate and methacrylate.
Specific examples of the (meth) acrylate monomer having an alkyl group having 1 to 12 carbon atoms include n-butyl (meth) acrylate, 2-butyl (meth) acrylate, t-butyl (meth) acrylate, and the like. 2-Ethylhexyl (meth) acrylate, ethyl (meth) acrylate, methyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, pentyl (meth) acrylate, n-octyl (meth) acrylate, isooctyl ( Examples thereof include meta) acrylate, nonyl (meth) acrylate, decyl (meth) acrylate, and lauryl (meth) acrylate, and among these, n-butyl acrylate, methyl acrylate, or a mixture thereof is preferable. These can be used alone or in combination of two or more.
The polymerizable monomer having a crosslinkable functional group is, for example, as a component for reinforcing the cohesive force or adhesive strength of the pressure-sensitive adhesive by a chemical bond with the following cross-linking agent to impart durability and cutability. Examples thereof include a monomer having a hydroxy group, a monomer having a carboxy group, a monomer having an amide group, a monomer having a tertiary amine group, and the like, and these may be used alone or in combination of two or more. Can be used.
The type of the cross-linking agent is not particularly limited as a component for strengthening the cohesive force of the pressure-sensitive adhesive by appropriately cross-linking the copolymer. For example, isocyanate compounds, epoxy compounds and the like can be mentioned, and these can be used alone or in combination of two or more.
Each component constituting the pressure-sensitive adhesive is dissolved in an appropriate solvent such as ethyl acetate to obtain a pressure-sensitive adhesive composition, and the pressure-sensitive adhesive composition is applied onto a substrate and then dried to form an adhesive layer. To. If some components are insoluble in the solvent, they may be dispersed in the system.

In the present embodiment, the first protective layer 15 and the second protective layer 16 are provided on both sides of the retardation laminated body 11. Specifically, the first protective layer 15 is provided on the side opposite to the first adhesive layer 14 when viewed from the first retardation layer 12. The second protective layer 16 is provided on the side opposite to the first adhesive layer 14 when viewed from the second retardation layer 13.

Examples of the materials of the first protective layer 15 and the second protective layer 16 include cyclic polyolefin resins; cellulose acetate resins such as triacetyl cellulose and diacetyl cellulose; polyethylene terephthalate, polyethylene naphthalate (PET), polybutylene terephthalate and the like. Materials in this field such as polyester resin; polycarbonate resin film; (meth) acrylic resin; polypropylene resin can be mentioned. An example of the thickness of the first protective layer 15 and the second protective layer 16 is 30 μm to 100 μm. The thicknesses of the first protective layer 15 and the second protective layer 16 may be different.

The optical film 10 can be formed by preparing each layer and then laminating them. Each layer may be manufactured in the forming step S01, or a purchased product may be used. When forming the optical film 10, for example, the first retardation layer 12 and the second retardation layer 13 are bonded to each other via the first adhesive layer 14 to form the retardation laminate 11, and then the retardation layer 11. The first protective layer 15 and the second protective layer 16 may be bonded to the laminated body 11. Alternatively, after the first protective layer 15 is bonded to the first retardation layer 12 and the second protective layer 16 is bonded to the second retardation layer 13, the first retardation layer 12 and the second retardation layer are bonded. 13 may be bonded to each other via the first adhesive layer 14.

The optical film 10 produced in the forming step S01 may be the optical film 10A shown in FIG. The optical film 10A is mainly different from the optical film 10 in that a polarizing plate 17 is laminated on the first retardation layer 12 via a second adhesive layer 18. The optical film 10A will be described focusing on this difference.

<Polarizer>
The polarizing plate 17 is a linear polarizing plate. The polarizing plate 17 has a polarizer having linear polarization characteristics. The polarizing plate may have a thermoplastic resin film laminated on one side or both sides of the polarizer.

The polarizer is, for example, a stretched film (or stretched layer) on which a dye having absorption anisotropy is adsorbed. Examples of the dye having absorption anisotropy include a dichroic dye. Specifically, as the dichroic dye, iodine or a dichroic organic dye is used. An example of a material for a polarizer is a polyvinyl alcohol-based resin. The polarizer may be a layer formed by applying a dye having absorption anisotropy to a base film and curing it. The base film may be a part of the polarizer, or may be peeled off after forming the polarizer. The material of the base film is the same as that of the thermoplastic resin film, and the thermoplastic resin film may also serve as the base film.

The thickness of the polarizer is usually 30 μm or less, preferably 18 μm or less, and more preferably 15 μm or less. The thickness of the polarizer is usually 1 μm or more, and may be, for example, 5 μm or more.

The example of the material of the thermoplastic resin film may be the same as the example of the material of the first protective layer 15 (or the second protective layer 16). The thickness of the thermoplastic resin film is preferably 5 μm or more and 150 μm or less, more preferably 5 μm or more and 100 μm or less, and further preferably 10 μm or more and 50 μm or less.

The angle between the absorption axis of the polarizing plate 17 and the slow axis of the first retardation layer 12 (first slow axis 12a described later) is preferably 71 ° to 74 °.

<Second adhesive layer>
The second adhesive layer 18 may be a layer formed of the same adhesive or adhesive as the first adhesive layer 14, or may be a layer formed of a different adhesive or adhesive. The second adhesive layer 18 may be a layer formed by an adhesive. An example of the pressure-sensitive adhesive is a pressure-sensitive adhesive composition containing (meth) acrylic resin, rubber-based resin, urethane-based resin, ester-based resin, silicone-based resin, polyvinyl ether-based resin and the like as main components. The thickness of the second adhesive layer 18 is, for example, 0.1 μm to 10 μm.

The optical film 10A may have a first protective layer 15A on the polarizing plate 17. Examples of the material of the first protective layer 15A include polyethylene terephthalate (PET), polypropylene (PP), and polyethylene (PE). An example of the thickness of the first protective layer 15A is 30 μm to 100 μm.

The optical film 10A can be manufactured by preparing each layer and then laminating them, as in the case of the optical film 10. Each layer may be manufactured in the forming step S01, or a purchased product may be used.

Hereinafter, unless otherwise specified, a case where the optical film 10 is formed in the forming step S01 and inspected thereof will be described.

[Inspection process]
In the inspection step S02, interfacial reflection and first adhesion caused by at least one of the refractive index difference between the first adhesive layer 14 and the first retardation layer 12 and the refractive index difference between the first adhesive layer 14 and the second retardation layer 13 It is inspected whether or not the degree of interference unevenness caused by the influence of the uniformity of the thickness of the layer 14 is within the allowable range.

FIG. 4 is a drawing for explaining an inspection method for inspecting the optical film 10. In the present embodiment, the surface on the first retardation layer 12 side (the surface of the first protective layer 15 in the configuration of FIG. 2) is the inspection surface 10a, and the inspection optical system 20 having the light source unit 21 and the detection unit 22 is used. Then, the optical film 10 is inspected. The inspection optical system 20 is a catadioptric system in which the light source unit 21 and the detection unit 22 are located on the same side of the optical film 10. As shown in FIG. 1, the inspection method includes a detection step S02A and a determination step S02B.

<Detection process>
In the detection step S02A, the inspection surface 10a is irradiated with the inspection light L1 from the light source unit 21 and reflected by the optical film 10 while being conveyed from the light source unit 21 while conveying the optical film 10 in the direction of the white arrow in FIG. Light (hereinafter referred to as "reflected light L2") is detected by the detection unit 22.
When the optical film 10 is sheet-fed, the optical film 10 can be conveyed by, for example, a belt conveyor. When the optical film 10 is long, the optical film 10 can be conveyed by, for example, a conveying roll. Hereinafter, the width direction of the optical film 10 (the direction orthogonal to the transport direction) is referred to as the TD direction, and the transport direction of the optical film 10 is referred to as the MD direction. An example of the transport speed is 1 m / min to 100 m / min.

The light source unit 21 and the detection unit 22 included in the inspection optical system 20 will be described.

The light source unit 21 outputs the inspection light L1. The peak wavelength of the inspection light L1 is, for example, 400 nm to 750 nm, preferably 500 nm to 700 nm, more preferably 550 nm to 680 nm, and further preferably 600 nm to 650 nm.

The illuminance in the light source unit 21 of the inspection light L1 is usually in the range of 1000 to 25000 [lux], preferably in the range of 1000 to 15000 [lux] at a position where the distance from the light source unit 21 is 15 mm. More preferably, it is in the range of 50,000 to 10000 [lp].

The inspection light L1 may be irradiated to one point on the inspection surface 10a, or may be irradiated over the entire film width.

The light source unit 21 is, for example, a line LED light source in which a plurality of LEDs are arranged in a line. In this case, the extending direction of the light source unit 21 is orthogonal to the normal line n of the optical film 10 and, for example, the direction orthogonal to the MD direction.

The light source unit 21 is arranged on the inspection surface 10a side. The distance d1 between the light source unit 21 and the inspection surface 10a is usually 100 mm to 2000 mm. The distance d1 is, for example, the distance between the light emitting surface of the light source unit 21 and the inspection surface 10a. The angle α1 [°] between the optical axis of the light source unit 21 and the normal line n (thickness direction of the optical film 10) of the inspection surface 10a is usually 1 ° to 60 °, preferably 5 ° to 50 °. It is more preferably 10 ° to 45 °.

The detection unit 22 receives the reflected light L2 from the inspection surface 10a. The detection unit 22 is a two-dimensional luminance meter. An example of the detection unit 22 is an area sensor camera (two-dimensional sensor camera), and an example of the area sensor camera is a CCD camera. The detection unit 22 may be a line-shaped luminance meter (for example, a line sensor camera).

The detection unit 22 is arranged on the inspection surface 10a side so as to be able to receive the reflected light L2 reflected by the inspection light L1 by the optical film 10. The size of the angle α2 formed by the optical axis of the detection unit 22 and the normal line n of the inspection surface 10a is substantially the same as the size of the angle α1. An example of the distance d2 between the detection unit 22 and the inspection surface 10a is 100 mm to 2000 mm. The distance d2 between the detection unit 22 and the inspection surface 10a may be the distance between the light receiving surface of the detection unit 22 and the inspection surface 10a.

In the detection step S02A of the present embodiment, the first polarizing filter 23 and the second polarizing filter 24 are used. The first polarizing filter 23 and the second polarizing filter 24 may be a part of the inspection optical system 20.

The first polarizing filter 23 and the second polarizing filter 24 are filters having linear polarization characteristics. The first polarizing filter 23 is arranged between the light source unit 21 and the optical film 10. The second polarizing filter 24 is arranged between the optical film 10 and the detection unit 22. Therefore, the inspection light L1 output from the light source unit 21 passes through the first polarizing filter 23 and is irradiated to the optical film 10 as linearly polarized light. The reflected light L2, which is the inspection light L1 reflected by the optical film 10, enters the detection unit 22 via the second polarizing filter 24. If the first polarizing filter 23 is arranged on the optical path of the inspection light L1 and the second polarizing filter 24 is arranged on the optical path of the reflected light L2, the arrangement of the first polarizing filter 23 and the second polarizing filter 24 The position is not limited. However, it is more preferable that the first polarizing filter 23 is separated from the light source unit 21 in consideration of the influence of heat generated from the light source unit 21. The distance from the light source unit 21 to the first polarizing filter 23 is preferably 50 mm or more.

The arrangement relationship of the optical film 10, the first polarizing filter 23, and the second polarizing filter 24 in the inspection step S02A will be described with reference to FIGS. 5 and 6. In the description of the arrangement relationship, the in-plane retardation of the first retardation layer 12 is 236 nm ± 4 nm or 234 nm ± 5 nm, and the in-plane retardation of the second retardation layer 13 is 116 nm ± 4 nm. Alternatively, the in-plane retardation of the first retardation layer 12 is 240 nm ± 5 nm, and the in-plane retardation of the second retardation layer 13 is 120 nm ± 4 nm.

FIG. 5 is a drawing for explaining the arrangement relationship between the first retardation layer 12 and the second retardation layer 13 included in the optical film 10. In FIG. 5, the relationship between the first slow phase axis 12a of the first retardation layer 12 and the second slow phase axis 13a of the second retardation layer 13 causes a first phase difference layer 12 and a second phase difference. The arrangement relationship of the layers 13 is shown.

The x-axis and y-axis in FIG. 5 are virtual axes set on the inspection surface 10a. The x-axis and y-axis can be arbitrarily set as long as they are orthogonal to each other. As an example, the x-axis direction is the MD direction. In order to define the angles of the first slow phase axis 12a and the second slow phase axis 13a, the y axis is set as the reference axis RA. When defining the angle with respect to the reference axis RA, when the optical film 10 is viewed from the inspection surface 10a side, counterclockwise (counterclockwise) is set as a positive angle direction and clockwise (clockwise) is negative with respect to the reference axis RA. In the angle direction of.

As shown in FIG. 5, the angle between the first slow phase axis 12a and the reference axis RA is θ1, the angle between the second slow phase axis 13a and the reference axis RA is θ2, and the first slow phase When the angle between the shaft 12a and the second slow-phase shaft 13a is θ3, the first retardation layer 12 and the second retardation layer 13 have the following conditions (1) of the angle θ1, the angle θ2, and the angle θ3. ~ Arranged so as to satisfy the condition (3).
(1) -40 ° <θ1 <-10 °
(2) + 15 ° <θ2 <+ 50 °
(3) + 55 ° <θ3 <+ 65 °
In FIG. 5, the allowable ranges of θ1 and θ2 are shown by hatching. When the condition (3) is satisfied, the optical film 10 functions as a circularly polarizing plate.

FIG. 6 is a drawing for explaining the arrangement relationship of the first polarizing filter 23 and the second polarizing filter 24 with respect to the optical film 10. In FIG. 6, the arrangement relationship between the first polarizing filter 23 and the second polarizing filter 24 is shown in relation to the first absorption shaft 23a of the first polarizing filter 23 and the second absorption shaft 24a of the second polarizing filter 24. Shown. The x-axis and y-axis in FIG. 6 are the same as the x-axis and y-axis in FIG. In other words, the first absorption axis 23a in FIG. 6 is a state in which the first polarizing filter 23 is moved to a position orthogonal to the normal line n (rotated so that the angle α1 becomes 0 °) in FIG. This corresponds to the axis obtained by projecting the first absorption shaft 23a of the first polarizing filter 23 onto the inspection surface 10a. The same applies to the second absorption shaft 24a in FIG.

As shown in FIG. 6, the angle between the first absorption shaft 23a and the reference axis RA is θ4, the angle between the second absorption shaft 24a and the reference shaft RA is θ5, and the first absorption shaft 23a When the angle between the second absorption shaft 24a and the second absorption shaft 24a is θ6, the first polarizing filter 23 and the second polarizing filter 24 satisfy the following conditions (4) to (6) for the angles θ4, the angle θ5, and the angle θ6. Arranged to meet.
(4) -20 ° <θ4 <+ 20 °
(5) + 70 ° <θ5 <+ 110 °
(6) + 70 ° <θ6 <+ 110 °
In FIG. 6, the allowable ranges of θ4 and θ5 are shown by hatching. The condition (6) is constant with respect to the state where the first polarizing filter 23 and the second polarizing filter 24 are in the cross Nicol state with respect to the state where the first absorption axis 23a and the second absorption axis 24a are ideally orthogonal to each other. It is an equation expressed in consideration of the permissible range of. Hereinafter, for convenience of explanation, the arrangement relationship of the first polarizing filter 23 and the second polarizing filter 24 satisfying the condition (6) is referred to as a cross Nicol state.

Since the angles θ1 to θ6 of the conditions (1) to (6) are defined with respect to the common reference axis RA, the conditions (1) to (6) are the first phase difference in the detection step S02A. The arrangement relationship of the layer 12, the second retardation layer 13, the first polarizing filter 23, and the second polarizing filter 24 is defined. In the explanation of the relationship between the conditions (1) and (6) using FIGS. 5 and 6, the y-axis is set as the reference axis RA. However, the reference axis RA may be the x-axis. In other words, the optical film 10 may be rotated by ± 90 ° or 180 °, or the arrangement relationship between the first polarizing filter 23 and the second polarizing filter 24 may be reversed.

The arrangement relationship of the first retardation layer 12 and the second retardation layer 13 at the time of forming the optical film 10 and the arrangement relationship of the optical film 10, the first polarizing filter 23 and the second polarizing filter 24 at the time of inspection of the optical film 10. By adjusting, the angles θ1 to θ6 of the conditions (1) to (6) can be realized.

As shown in FIG. 4, the optical film 10 may be arranged on the back plate (support plate) 25. The specular reflectance of the main surface 25a (the surface on the optical film 10 side) of the back plate 25 is, for example, 45% or less. As the back plate 25, a plate made of a material having a specular reflectance in the above-exemplified range may be used, or a sheet of a material having a specular reflectance in the above-exemplified range is attached to the surface of the plate member. It may have a combined configuration.

<Judgment process>
In the determination step S02B, the brightness distribution along the cross section in the width direction (TD direction) of the optical film 10 is acquired based on the brightness of the reflected light L2 detected by the detection unit 22. Next, it is determined whether or not the optical film 10 is a non-defective product based on the brightness distribution. The luminance distribution can be created, for example, based on the luminance data acquired by the detection unit 22 in the analyzer. The analysis device may be, for example, a dedicated device for carrying out the detection method, or a personal computer in which a program for analysis is installed.

In the determination step S02B, in the interference fringes (change in amplitude) represented by the luminance distribution, the interference unevenness may be determined according to an index (determination index) that can be determined. For example, the judgment may be performed using the ratio of the minimum brightness to the maximum brightness in the brightness distribution ([minimum brightness / maximum brightness] (%)) as a determination index, or the maximum brightness and the average value (average brightness) of the brightness distribution. (The determination may be made using [maximum brightness-average brightness] as a determination index. Whether or not the optical film 10 is a non-defective product may be determined in advance according to the determination method, for example, according to an experiment or the like.

When the optical film 10 is determined to be defective in the determination step S02B (“NO” in the determination step S02B), the change step S03 is performed.

[Change process]
In the changing step S03, the forming conditions of the optical film 10 are changed. Changes in the forming conditions include, for example, changing the thickness of the first adhesive layer 14, adjusting the flatness of the member underlying the first adhesive layer 14, and the characteristics of the adhesive which is the material of the first adhesive layer 14. Including adjustment.

When the changing step S03 is carried out, the forming step S01 is carried out again. The forming step S01, the inspection step S02, and the changing step S03 may be repeated until the optical film 10 is determined to be a non-defective product in the determination step S02B.

When the optical film 10 is determined to be a non-defective product in the determination step S02B (“YES” in the determination step S02B), the recovery step S04 is performed.

[Recovery process]
In the recovery step S04, the optical film 10 may be formed and the formed optical film 10 may be recovered under the same conditions as when the optical film 10 for inspection is formed. For example, when the optical film 10 is long and the inspection step S02 is carried out while transporting the optical film 10 formed in the forming step S01, the optical film 10 that has undergone the inspection step S02 is wound up, for example. 10 may be collected.

In the inspection method of the present embodiment, as described above, the inspection light L1 is irradiated to the optical film 10 from the light source unit 21, and the reflected light L2 is detected by the detection unit 22. The luminance distribution of the cross section of the optical film 10 in the TD direction is acquired based on the luminance data of the reflected light L2 detected by the detection unit 22, and the quality of the optical film 10 is determined based on the luminance distribution. Therefore, the quality of the optical film 10 can be objectively determined.

For example, when performing a visual inspection, the inspection results include individual differences between inspectors (including differences in viewing angles), the condition of the same inspector (for example, physical condition, tiredness during inspection, etc.), and the manufacturing plant of the optical film 10. There may be differences between them. On the other hand, in the optical film inspection method of the present embodiment, the arrangement relationship between the inspection optical system 20 and the optical film 10 and the inspection light L1 to be used are fixed, and the determination is made based on the brightness distribution. Differences between inspectors (or between the same inspectors) and differences in inspection methods between factories have been eliminated. Therefore, the quality of the optical film 10 can be objectively determined.

In the method for manufacturing the optical film 10, since the quality of the optical film 10 is objectively determined by the above inspection method, a good optical film 10 can be efficiently manufactured. As a result, the manufacturing yield of the optical film 10 is improved.

In the method for manufacturing the optical film 10, the above-mentioned detection step S02A and determination step S02B can be automatically performed while transporting the optical film 10, so that the occurrence of defective products can be detected immediately. As a result, a non-defective optical film 10 can be manufactured more efficiently.

The luminance distribution used in the determination step S02B shows the interference fringes of the reflected light L2. Therefore, the interference unevenness can be evaluated based on the brightness distribution.

When the ratio of the minimum brightness to the maximum brightness in the brightness distribution is used as a determination index, the influence of differences in the materials of the optical film 10 can be reduced. Therefore, the ratio of the minimum brightness to the maximum brightness can have versatility.

When the first polarizing filter 23 and the second polarizing filter 24 are used, the influence of surface reflection on the inspection surface 10a can be reduced. When the optical film 10, the first polarizing filter 23, and the second polarizing filter 24 are arranged so as to satisfy the above conditions (1) to (6), the influence of surface reflection can be further reduced, so that the first adhesive layer Interference unevenness caused by the influence of 14 (including the influence of the interface of the layer adjacent to the first adhesive layer 14) can be evaluated more accurately. Therefore, the quality of the optical film 10 is improved by arranging the optical film 10, the first polarizing filter 23, and the second polarizing filter 24 so as to satisfy the above conditions (1) to (6) and performing the detection step S02A. Can be determined more accurately.

When the peak wavelength of the inspection light L1 output from the light source unit 21 is, for example, 400 nm to 750 nm, preferably 500 nm to 700 nm, and more preferably 600 nm to 650 nm, the wavelength region is limited, so that interference unevenness occurs. Is easy to detect. Furthermore, the maximum and minimum values of the luminance distribution become clearer on the data. From this point of view, it is easier to detect interference unevenness. As a result, the quality of the optical film 10 can be determined more accurately.

When the distance d1 between the light source unit 21 and the optical film 10 is 100 mm to 2000 mm, the installation space of the inspection optical system 20 can be reduced. Further, the brightness of the reflected light L2 is likely to be improved. Similarly, when the distance d2 between the optical film 10 and the detection unit 22 is 100 mm to 2000 mm, the installation space of the inspection optical system 20 can be reduced.

When the specular reflectance of the back plate 25 is 45% or less, the influence of reflection from the back plate 25 can be reduced. As a result, the quality of the optical film 10 can be determined more accurately.

Hereinafter, an experimental example using the sample of the optical film 10 will be described.

[Experimental example]
In the experimental example, sample S1, sample S2, sample S3, and sample S4 were prepared as specific samples of the optical film 10. The width of each sample was 1340 mm.

(Sample S1)
Sample S1 had the configuration shown in FIG. That is, the sample S1 has a second protective layer 16, a second retardation layer 13, a first adhesive layer 14, a first retardation layer 12, and a first protective layer 15, and the second retardation layer 13, the first. The adhesive layer 14, the first retardation layer 12, and the first protective layer 15 were laminated on the second protective layer 16 in this order. The plan view shape of sample S1 was rectangular.

The first protective layer 15 and the second protective layer 16 were triacetyl cellulose resin films. The thickness of the first protective layer 15 and the second protective layer 16 was 80 μm.

The first retardation layer 12 was a λ / 2 plate. The in-plane phase difference was 236 nm. The second retardation layer 13 was a λ / 4 plate. The in-plane phase difference was 116 nm. The angle θ3 (see FIG. 5) between the first slow-phase shaft 12a of the first retardation layer 12 and the second slow-phase shaft 13a of the second retardation layer 13 was 60 °. The thickness of the first retardation layer 12 was 2 μm, and the thickness of the second retardation layer 13 was 1 μm.

The material of the first adhesive layer 14 was an epoxy resin-based ultraviolet curable adhesive (refractive index at a wavelength of 589 nm was 1.54). The thickness of the first adhesive layer 14 was 3.0 μm.

(Sample S2)
Sample S2 had the same configuration as sample S1 except that the thickness of the first adhesive layer 14 was 2.5 μm.
(Sample S3)
Sample S3 had the same configuration as sample S1 except that the thickness of the first adhesive layer 14 was 2.0 μm.
(Sample S4)
In sample S4, an epoxy resin-based ultraviolet curable adhesive (refractive index at a wavelength of 589 nm is 1.51) was used as the material of the first adhesive layer 14, and the thickness of the first adhesive layer 14 was 1. It had the same configuration as sample S1 except that it was 5 μm.

The detection step S02A described with reference to FIG. 4 was carried out on the prepared samples S1 to S4. Since the conditions were the same except that the inspection targets were different, the detection steps S02A in the experimental example will be specifically described with reference to samples S1 to S4.

As the light source unit 21, a line light source in which a plurality of red LEDs are arranged was used. The light source unit 21 was installed so that the inspection light L1 was applied to the central portion of the width of the film (sample S) to be inspected. The peak wavelength of the inspection light L1 was 600 nm to 650 nm. The angle α1 between the optical axis of the light source unit 21 and the normal line n between the inspection surface 10a was 20 °. Similarly, the angle α2 between the normal line n with the inspection surface 10a and the normal line n of the detection unit 22 was 20 °. The distance between the light source unit 21 and the inspection surface 10a was 135 mm. The distance d2 between the inspection surface 10a and the detection unit 22 was 760 mm. The illuminance of the inspection light L1 was 6570 [lux] at a position where the distance from the light source unit 21 was 15 mm.

In the detection step S02A, an area scan camera (trade name: G0-5000M-PGE, manufactured by JAI), a first polarizing filter 23, and a second polarizing filter 24 were used. The sample S, the first polarizing filter 23, and the second polarizing filter 24 were arranged so as to satisfy the conditions (1) to (6). Specifically, the angles θ1 to θ6 are as follows.
Angle θ1: -26.5 °
Angle θ2: 33.5 °
Angle θ3: 60 °
Angle θ4: 0 °
Angle θ5: 90 °
Angle θ6: 90 °
The detection step S02A was carried out while transporting the sample S at a transport speed of 500 mm / s.

FIG. 7 is a chart showing the detection results of samples S1 to S4. The luminance distribution in the figure is the luminance distribution (luminance distribution along the width direction) of the cross section in the central portion of the samples S1 to S4 in the lateral direction (width direction). The horizontal axis of the brightness distribution indicates the position in the width direction (unit: mm, the position at one end of the detection point is displayed as 0 mm), and the vertical axis indicates the brightness.

In the luminance distribution shown in FIG. 7, the ratio of the minimum luminance to the maximum luminance ([minimum luminance / maximum luminance]) (%) was used as a determination index, and the relationship with the visual evaluation was verified.

The following samples S1a, sample S2a, sample S3a and sample S4a were used for the visual evaluation. Sample S1a, sample S2a, sample S3a and sample S4a correspond to samples for visual evaluation of sample S1, sample S2, sample S3 and sample S4.

(Sample S1a)
As shown in FIG. 8, as the sample S1a, the optical composition including the third adhesive layer 32, the second retardation layer 13, the first adhesive layer 14, the first retardation layer 12, the second adhesive layer 18 and the polarizing plate 33. A film 30 was produced.

The second retardation layer 13, the first adhesive layer 14, and the first retardation layer 12 constituting the sample S1a were the same as the corresponding layers of the sample S1. The materials of the second adhesive layer 18 (thickness 5 μm) and the third adhesive layer 32 (thickness 25 μm) were acrylic pressure-sensitive adhesives. That is, the second adhesive layer 18 and the third adhesive layer 32 were adhesive layers. The polarizing plate 33 was a linear polarizing plate similar to the polarizing plate 17 described with reference to FIG. The angle between the absorption axis of the polarizing plate 33 and the first slow phase axis 12a of the first retardation layer 12 was 72.1 ° to 72.9 °.

At the time of visual evaluation, in order to support the sample S1a, the surface of the third adhesive layer 32 was arranged on the black acrylic plate 31 as a support. Further, in order to reduce color unevenness on the surface of the polarizing plate 33, a water layer 34 (thickness of about 1 mm) and a glass plate 35 (thickness of 1.1 mm) were laminated in this order on the surface of the polarizing plate 33 (see FIG. 8). ..

(Samples S2a to S4a)
The configurations of the optical films as the samples S2a to S4a were the same as those of the optical films 30 except that they had the same differences as the samples S2 to S4 and the samples S1. When visually evaluating the samples S2a to S4a, the samples S2a to S4a are arranged on the black acrylic plate 31 and the aqueous layer is placed on the surface of the polarizing plate 33 of the samples S2a to S4a as in the case of the sample S1a. 34 and the glass plate 35 were laminated.

In the visual evaluation, the visual results were evaluated from 1 to 4 (the larger the number, the higher the evaluation). The visual evaluation was performed according to a visual evaluation method predetermined by four persons, and the average of the four persons with respect to each sample S1a to S4a was adopted as the visual evaluation result of each sample S1a to S4a. When the samples S1a to S4a were referred to as sample Sa, the visual evaluation was performed as follows. That is, the sample Sa was arranged at an angle with respect to the horizontal plane. The sample Sa was irradiated with light from a three-wavelength fluorescent lamp from the direction orthogonal to the horizontal plane. The tilted sample Sa was viewed from a direction perpendicular to the surface thereof, and interference unevenness due to the light incident on and reflected from the fluorescent lamp was visually observed. Samples S1a to S4a had the same configuration except that they had the same differences as samples S1 to S4. Therefore, the difference in the visual evaluation of the samples S1a to S4a corresponds to the difference in the visual evaluation of the samples S1 to S4.

The relationship between the visual evaluation and the quantitative evaluation (evaluation using the luminance data in the detection step S02A) is as shown in Table 1. From the results in Table 1, it was found that there is a high correlation between the visual evaluation and the evaluation based on the luminance distribution (quantitative evaluation). That is, it was verified that the quality of the optical film 10 can be objectively determined based on the brightness distribution obtained by performing the detection step S02A.

Various modifications have been described along with the embodiments described above. However, the present invention is not limited to the above-described embodiment and various modifications, and is indicated by the scope of claims, and includes all modifications within the meaning and scope equivalent to the scope of claims. Is intended.

For example, the inspection surface 10a of the optical film 10 may be a surface on the second retardation layer 13 side (in the configuration shown in FIGS. 2 and 3, the surface of the second protective layer 16). Although the inspection steps S02 and subsequent steps have been described using the optical film 10, the optical film 10A may be used instead of the optical film 10. The optical film may have a first retardation layer, a second retardation layer, and an adhesive layer for adhering them.

The first retardation layer is not limited to the layer giving the phase difference of λ / 2, and the second retardation layer is not limited to the layer giving the phase difference of λ / 4. The retardation provided by the first retardation layer and the second retardation layer may be any retardation set so as to realize the desired optical characteristics of the optical film containing them. When the first retardation layer and the second retardation layer are not layers that give a retardation of λ / 2 and λ / 4, respectively, the conditions corresponding to the conditions (1) to (6) are the first retardation layer and the condition (6). It may be set so as to be suitable for the quality determination of the optical film according to the phase difference given by the second retardation layer.

In the detection step, it is not necessary to convey the optical film.

The various embodiments and modifications described above may be combined as appropriate without departing from the spirit of the present invention.

10, 10A ... Optical film, 10a ... Inspection surface, 11 ... Phase difference laminate, 12 ... First retardation layer, 12a ... First slow phase axis, 13 ... Second retardation layer, 13a ... Second slow phase axis , 14 ... 1st adhesive layer, 15, 15A ... 1st protective layer, 16 ... 2nd protective layer, 17 ... Polarizing plate, 18 ... 2nd adhesive layer, 20 ... Inspection optical system, 21 ... Light source unit, 22 ... Detection Part, 23 ... 1st polarizing filter, 23a ... 1st absorption shaft, 24 ... 2nd polarizing filter, 24a ... 2nd absorption shaft, 25 ... back plate, 25a ... main surface of back plate.

Claims (11)

Arranged on the inspection surface side of an optical film having a first retardation layer, a second retardation layer, and a first adhesive layer arranged between the first retardation layer and the second retardation layer. A detection step of irradiating the inspection light from the light source unit and detecting the light emitted from the light source unit and reflected by the optical film by the detection unit arranged on the inspection surface side.
A determination step of acquiring a luminance distribution along a cross section of the optical film based on the brightness of light detected by the detection unit and determining whether or not the optical film is a good product based on the luminance distribution.
A method of inspecting an optical film comprising. The detection step and the determination step are performed while transporting the optical film.
The method for inspecting an optical film according to claim 1. The cross section is a cross section in the width direction of the optical film.
The method for inspecting an optical film according to claim 1 or 2. In the detection step, the inspection light from the light source unit is irradiated to the inspection surface through the first polarizing filter, and the light emitted from the light source unit to the optical film and reflected by the optical film is secondly polarized. Detected by the detector through a filter,
The method for inspecting an optical film according to any one of claims 1 to 3. One of the first retardation layer and the second retardation layer is a 1/2 wavelength layer, and the other is a 1/4 wavelength layer.
The x-axis and y-axis orthogonal to each other are virtually set on the inspection surface, one of the x-axis and the y-axis is set as a reference axis when viewed from the inspection surface side, and the counterclockwise direction is positive with respect to the reference axis. In the case of referring to the angular direction of
In the optical film, the first phase difference is such that the first slow axis of the first retardation layer and the second slow axis of the second retardation layer satisfy the following conditions (1) to (3). The layer and the second phase difference layer are arranged,
The first polarizing filter and the second polarizing filter so that the first absorption shaft of the first polarizing filter and the second absorption shaft of the second polarizing filter satisfy the following conditions (4), (5) and (6). A second polarizing filter is arranged with respect to the optical film.
The method for inspecting an optical film according to claim 4.
(1) -40 ° <θ1 <-10 ° (θ1 is the angle between the first slow phase axis and the reference axis)
(2) + 15 ° <θ2 <+ 50 ° (θ2 is the angle between the second slow phase axis and the reference axis)
(3) + 55 ° <θ3 <+ 65 ° (θ3 is the angle between the first slow phase axis and the second slow phase axis)
(4) -20 ° <θ4 <+ 20 ° (θ4 is the angle between the first absorption axis and one of the second absorption axes and the reference axis).
(5) + 70 ° <θ5 <+ 110 ° (θ5 is the angle between the first absorption axis and the other of the second absorption axes and the reference axis).
(6) + 70 ° <θ6 <+ 110 ° (θ6 is the angle between the first absorption axis and the second absorption axis) The optical film is
A polarizing plate located on the opposite side of the 1/4 wavelength layer from the 1/2 wavelength layer in the stacking direction.
A second adhesive layer located between the polarizing plate and the 1/2 wavelength layer,
Have,
The method for inspecting an optical film according to claim 5. The first adhesive layer is a cured layer of an active energy ray-curable adhesive.
The method for inspecting an optical film according to any one of claims 1 to 6. The detection step is carried out while transporting the optical film.
The method for inspecting an optical film according to any one of claims 1 to 7. The peak wavelength of the inspection light is in the range of 400 nm to 750 nm.
The method for inspecting an optical film according to any one of claims 1 to 8. The detection step was carried out with the optical film placed on the main surface of the support plate.
The specular reflectance of the main surface is 45% or less.
The method for inspecting an optical film according to any one of claims 1 to 9. A method for producing an optical film, which comprises the method for inspecting an optical film according to any one of claims 1 to 10.

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