JP7383559B2 - Optical film inspection method and optical film manufacturing method - Google Patents

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 the retardation laminate is a circularly polarizing plate applied to an organic electroluminescence (organic EL) image display device (see Patent Document 1).

Japanese Patent Application Publication No. 2018-17996

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

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.

An optical film inspection method according to one aspect of the present invention includes a first retardation layer, a second retardation layer, and a first adhesive layer disposed between the first retardation layer and the second retardation layer. A light source section disposed on the inspection surface side irradiates the inspection surface of the optical film having the inspection surface with inspection light, and a detection section disposed on the inspection surface side detects the light irradiated from the light source section and reflected by the optical film. a detection step in which the optical film is detected by the detection unit, and a brightness distribution along the cross section of the optical film is obtained based on the brightness of the light detected by the detection unit, and it is determined whether the optical film is a good product based on the brightness distribution. and a determination step of making a determination.

In the above inspection method, a brightness distribution along a cross section of the optical film is obtained based on the brightness of light detected by the detection unit, and it is determined whether the optical film is a good product based on the brightness distribution. Therefore, since the quality of the optical film can be determined objectively, the performance reliability of the optical film is improved.

The detection step and the determination step may be performed while conveying 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 section is irradiated onto the inspection surface through a first polarizing filter, and the light irradiated from the light source section to the optical film and reflected by the optical film is irradiated with second polarized light. 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 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. , one of the x-axis and the y-axis is the reference axis when viewed from the inspection surface side, and when the counterclockwise direction with respect to the reference axis is referred to as a positive angular direction, the first retardation layer In the optical film, the first retardation layer and the second slow axis of the second retardation layer satisfy the following conditions (1) to (3). A retardation layer is arranged such that a first absorption axis of the first polarizing filter and a 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 axis and the reference axis)
(2) +15°<θ2<+50° (θ2 is the angle between the second slow axis and the reference axis)
(3) +55°<θ3<+65° (θ3 is the angle between the first slow axis and the second slow 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 axis 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, surface reflection of the optical film can be further reduced.

The optical film includes, in the lamination direction, a polarizing plate located on the opposite side to the 1/4 wavelength layer when viewed from the 1/2 wavelength layer, and a polarizing plate located between the polarizing plate and the 1/2 wavelength layer. 2 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 the optical film is being conveyed.

The peak wavelength of the test light may be within the range of 400 nm to 750 nm.

The detection step may be performed with the optical film disposed on the main surface of the support plate, and the regular 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.

A method for manufacturing an optical film according to another aspect of the present invention includes the above-mentioned method for inspecting an optical film according to the present invention.

In the above inspection method, a brightness distribution along a cross section of the optical film is obtained based on the brightness of light detected by the detection unit, and it is determined whether the optical film is a good product based on the brightness distribution. Therefore, since the quality of the optical film can be determined objectively, the performance reliability of the optical film is improved. As a result, an optical film with 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 diagram showing a schematic configuration of an optical film manufactured by an optical film manufacturing method according to an embodiment. FIG. 3 is a schematic diagram showing a schematic configuration of a modified example of the optical film. FIG. 4 is a diagram for explaining an optical film inspection method according to an embodiment. FIG. 5 is a diagram illustrating the arrangement relationship between the first retardation layer and the second retardation layer included in the optical film. FIG. 6 is a diagram illustrating 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 samples S1 to S4 used in the experimental examples. FIG. 8 is a schematic diagram showing the schematic structure of the optical film used for visual inspection.

Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant explanation will be omitted. The dimensional proportions in the drawings do not necessarily correspond to those in the description.

FIG. 1 is a flowchart of an optical film manufacturing method including an inspection method according to an embodiment. The method for manufacturing 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 recovering optical film that is a good product 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 electroluminescent device.

The optical film 10 has a retardation laminate 11. The retardation laminate 11 includes a first retardation layer 12, a second retardation layer 13, and a first adhesive layer 14 that adheres them. Usually, the optical film 10 has at least one of a first protective layer 15 and a second protective layer 16 that protect the retardation laminate 11 . Below, 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 provides a retardation 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 above-mentioned in-plane retardation is, for example, for a wavelength of 550 nm. The in-plane phase difference in this embodiment can be measured, for example, by AxoScan (manufactured by Axometrics).

When the first retardation layer 12 is a 1/2 wavelength layer, it can be manufactured by subjecting a translucent thermoplastic resin film to a stretching treatment or the like to provide a retardation of λ/2. In this case, the first retardation layer 12 is a birefringent film. Examples of thermoplastic resins are cellulose ester resins such as triacetyl cellulose.

The first retardation layer 12 may be manufactured by forming a first liquid crystal layer, a first alignment layer, etc. that provides a retardation of λ/2 on a base film. In this case, the first liquid crystal layer, the first alignment layer, etc. 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 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 provides a λ/4 retardation. An example of the thickness of the second retardation layer 13 is 0.1 μm to 2 μm. Examples of the 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 may 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 may be 116 nm±4 nm. The example of the above-mentioned in-plane retardation is, for example, for a wavelength of 550 nm. The angle between the slow axis of the second retardation layer 13 (second slow axis 13a described later) and the slow axis of the first retardation layer 12 (first slow axis 12a described later) is the angle between the optical film 10 It suffices if the angle is arranged so that it functions as a circularly 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 retardation of λ/4. In this case, the second retardation layer 13 is a birefringent film. Examples of the thermoplastic resin are the same as those for the first retardation layer 12.

The second retardation layer 13 may be manufactured by forming a liquid crystal layer, an alignment layer, etc. that provides a retardation of λ/4 on a base film. In this case, the second liquid crystal layer, second alignment layer, etc. 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 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 provide a retardation, and may be a 1/2 wavelength layer, a 1/4 wavelength layer, a positive C layer, etc., respectively. , or may be a reverse retardation layer exhibiting reverse wavelength dispersion.
The in-plane retardation value Re (550) of the positive C layer is usually in the range of 0 to 10 nm, preferably in the range of 0 to 5 nm, and the retardation value Rth in the thickness direction is usually in the range of -10 to -300 nm, preferably 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 above λ/4 layer and the second retardation layer 13 is the above 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 a positive C layer, or the first retardation layer 12 may be the λ/4 layer. The optical film may be a positive C layer, and the second retardation layer 13 may be a λ/4 layer.
The optical film 10 may be an optical film that further includes a retardation layer in addition to the first retardation layer 12 and the second retardation layer 13 described above. 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 or a reverse retardation layer may be further included.

<First adhesive layer>
The first adhesive layer 14 is a layer that is disposed between the first retardation layer 12 and the second retardation layer 13 and bonds the first retardation layer 12 and the second retardation layer 13 together. 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 from a pressure-sensitive adhesive or an adhesive. An example of the first adhesive layer 14 is a cured layer of an active energy ray-curable adhesive. An active energy ray-curable 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 resin components contained in the water-based adhesive include polyvinyl alcohol resins and urethane resins. The aqueous composition containing the polyvinyl alcohol resin can further contain a curable component and a crosslinking agent. Examples of the water-based composition containing a urethane resin include a water-based composition containing a polyester-based ionomer type urethane resin and a compound having a glycidyloxy group. A polyester-based ionomer type urethane resin is a urethane resin having a polyester skeleton into which a small amount of an ionic component (hydrophilic component) is introduced.

As the adhesive, an acrylic adhesive containing an acrylic copolymer and a crosslinking agent can be used. The above 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 above (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, 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 include meth)acrylate, nonyl(meth)acrylate, decyl(meth)acrylate, and lauryl(meth)acrylate, among which n-butyl acrylate, methyl acrylate, or a mixture thereof is preferred. These can be used alone or in combination of two or more.
The above-mentioned polymerizable monomer having a crosslinkable functional group is used as a component for reinforcing the cohesive force or adhesive strength of the adhesive through chemical bonding with the crosslinking agent described below and imparting durability and cuttability, for example. Examples include monomers having a hydroxy group, monomers having a carboxyl group, monomers having an amide group, monomers having a tertiary amine group, and these may be used alone or in combination of two or more. can be used.
The crosslinking agent is a component for strengthening the cohesive force of the adhesive by appropriately crosslinking the copolymer, and its type is not particularly limited. Examples include isocyanate compounds and epoxy compounds, which may be used alone or in combination of two or more.
A pressure-sensitive adhesive composition is obtained by dissolving each component constituting the pressure-sensitive adhesive in an appropriate solvent such as ethyl acetate, and the pressure-sensitive adhesive composition is applied onto a base material and then dried to form an adhesive layer. Ru. If there are components that are not partially soluble in the solvent, they may be in a dispersed state in the system.

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

Examples of materials for the first protective layer 15 and the second protective layer 16 include cyclic polyolefin resin; cellulose acetate resin such as triacetyl cellulose and diacetyl cellulose; polyethylene terephthalate, polyethylene naphthalate (PET), and polybutylene terephthalate. Materials in this field may include polyester resins; polycarbonate resin films; (meth)acrylic resins; polypropylene resins and the like. An example of the thickness of the first protective layer 15 and the second protective layer 16 is 30 μm to 100 μm. The thickness 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 formation step S01, or purchased products may be used. When forming the optical film 10, for example, after forming the retardation laminate 11 by laminating the first retardation layer 12 and the second retardation layer 13 via the first adhesive layer 14, the retardation layer 11 is formed. The first protective layer 15 and the second protective layer 16 may be bonded to the laminate 11. Alternatively, after laminating the first protective layer 15 to the first retardation layer 12 and laminating the second protective layer 16 to the second retardation layer 13, the first retardation layer 12 and the second retardation layer 13 may be bonded to each other via the first adhesive layer 14.

The optical film 10 manufactured in the forming step S01 may be the optical film 10A shown in FIG. 3. The optical film 10A differs from the optical film 10 mainly 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 explained focusing on this difference.

<Polarizing plate>
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 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 dyes having absorption anisotropy include dichroic dyes. Specifically, iodine or a dichroic organic dye is used as the dichroic dye. An example of the polarizer material is polyvinyl alcohol resin. The polarizer may be a layer formed by coating a base film with a dye having absorption anisotropy and curing the coating. 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 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, 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.

Examples of the material of the thermoplastic resin film may be the same as those of the first protective layer 15 (or 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 still more 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 (first slow axis 12a to be described later) of the first retardation layer 12 is preferably 71° to 74°.

<Second adhesive layer>
The second adhesive layer 18 may be a layer formed from the same adhesive or pressure-sensitive adhesive as the first adhesive layer 14, or may be a layer formed from a different adhesive or pressure-sensitive adhesive. The second adhesive layer 18 may be a layer formed of an adhesive. Examples of adhesives are adhesive compositions containing (meth)acrylic resins, rubber resins, urethane resins, ester resins, silicone resins, polyvinyl ether resins, etc. 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 materials for 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 formation step S01, or purchased products may be used.

In the following, unless otherwise specified, a case will be described in which the optical film 10 is formed in the forming step S01 and is inspected.

[Inspection process]
In the inspection step S02, interface reflection 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, and the first adhesive It is checked whether the degree of interference unevenness caused by the uniformity of the thickness of the layer 14 is within an allowable range.

FIG. 4 is a drawing for explaining an inspection method for inspecting the optical film 10. In this embodiment, the surface on the first retardation layer 12 side (in the configuration of FIG. 2, the surface of the first protective layer 15) is used as the inspection surface 10a, and an inspection optical system 20 having a light source section 21 and a detection section 22 is used. The optical film 10 is then inspected. The inspection optical system 20 is a reflective optical system in which a light source section 21 and a detection section 22 are located on the same side with respect to 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, while the optical film 10 is being conveyed in the direction of the white arrow in FIG. The light (hereinafter referred to as “reflected light L2”) is detected by the detection unit 22.
When the optical film 10 is sheet-shaped, the optical film 10 can be conveyed, for example, by a belt conveyor. When the optical film 10 is long, the optical film 10 may be conveyed, for example, by a conveyance roll. Hereinafter, the width direction (direction perpendicular to the transport direction) of the optical film 10 will be referred to as the TD direction, and the transport direction of the optical film 10 will be referred to as the MD direction. An example of the transport speed is 1 m/min to 100 m/min.

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

The light source section 21 outputs 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 even more preferably 600 nm to 650 nm.

The illuminance of the inspection light L1 at the light source section 21 is usually in the range of 1000 to 25000 [lx], preferably in the range of 1000 to 15000 [lx], at a position at a distance of 15 mm from the light source section 21, More preferably, it is in the range of 50,00 to 10,000 [lx].

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

The light source section 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 section 21 is perpendicular to the normal n of the optical film 10 and, for example, perpendicular to the MD direction.

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

The detection unit 22 receives 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 reflected light L2 that is the inspection light L1 reflected by the optical film 10. The size of the angle α2 between the optical axis of the detection unit 22 and the normal n to 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 section 22 and the inspection surface 10a may be the distance between the light receiving surface of the detection section 22 and the inspection surface 10a.

In the detection step S02A of this 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 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 section 21 and the optical film 10. The second polarizing filter 24 is arranged between the optical film 10 and the detection section 22. Therefore, the inspection light L1 output from the light source section 21 passes through the first polarizing filter 23 and is irradiated onto 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 placed on the optical path of the inspection light L1, and the second polarizing filter 24 is placed on the optical path of the reflected light L2, then the first polarizing filter 23 and the second polarizing filter 24 are arranged The location is not limited. However, it is more preferable to place the first polarizing filter 23 at a distance from the light source section 21 in consideration of the influence of heat emitted from the light source section 21. The distance from the light source section 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 explained using 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 diagram illustrating 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 axis 12a of the first retardation layer 12 and the second slow axis 13a of the second retardation layer 13 shows that the first retardation layer 12 and the second retardation The arrangement relationship of 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 the 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 axis 12a and the second slow 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 (left rotation) with respect to the reference axis RA is defined as a positive angle direction, and clockwise (right rotation) is defined as a negative angle direction. The angular direction is

As shown in FIG. 5, the angle between the first slow axis 12a and the reference axis RA is θ1, the angle between the second slow axis 13a and the reference axis RA is θ2, and the first slow axis When the angle between the axis 12a and the second slow axis 13a is θ3, the first retardation layer 12 and the second retardation layer 13 have the angle θ1, the angle θ2, and the angle θ3 under the following condition (1). - Arranged to satisfy 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 indicated by hatching. By satisfying condition (3), the optical film 10 functions as a circularly polarizing plate.

FIG. 6 is a diagram illustrating 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 determined by the relationship between the first absorption axis 23a of the first polarizing filter 23 and the second absorption axis 24a of the second polarizing filter 24. It shows. The x-axis and y-axis in FIG. 6 are the same as the x-axis and y-axis in FIG. 5. In other words, the first absorption axis 23a in FIG. 6 corresponds to the state in which the first polarizing filter 23 is moved to a position perpendicular to the normal n (rotated so that the angle α1 becomes 0°) in FIG. This corresponds to an axis obtained by projecting the first absorption axis 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 axis 23a and the reference axis RA is θ4, the angle between the second absorption axis 24a and the reference axis RA is θ5, and the angle between the first absorption axis 23a and the reference axis RA is θ5. When the angle with the second absorption axis 24a is θ6, the first polarizing filter 23 and the second polarizing filter 24 have an angle θ4, an angle θ5, and an angle θ6 that satisfy the following conditions (4) to (6). arranged to meet the needs.
(4) -20°<θ4<+20°
(5) +70°<θ5<+110°
(6) +70°<θ6<+110°
In FIG. 6, the allowable ranges of θ4 and θ5 are indicated by hatching. Condition (6) is such that the point where the first polarizing filter 23 and the second polarizing filter 24 are in a crossed nicol state is constant with respect to the state where the first absorption axis 23a and the second absorption axis 24a are ideally orthogonal. This is an expression that takes into account the allowable range of . Hereinafter, for convenience of explanation, the arrangement relationship between the first polarizing filter 23 and the second polarizing filter 24 that satisfies condition (6) will be referred to as a crossed Nicols state.

Since the angles θ1 to θ6 of conditions (1) to (6) are defined with respect to the common reference axis RA, conditions (1) to (6) are based on the first phase difference in the detection step S02A. The arrangement relationship between 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 conditions (1) to (6) using FIGS. 5 and 6, the y-axis is taken 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 of 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 relation of the optical film 10, the first polarizing filter 23, and the second polarizing filter 24 at the time of inspecting the optical film 10. By adjusting, angles θ1 to θ6 of conditions (1) to (6) can be realized.

As shown in FIG. 4, the optical film 10 may be placed on a back plate (support plate) 25. The regular 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. The back plate 25 may be a plate made of a material having a specular reflectance within the range exemplified above, or a sheet made of a material having a specular reflectance within the range exemplified above may be pasted on the surface of the plate member. It may also have a combined configuration.

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

In the determination step S02B, it is sufficient to determine interference unevenness in the interference fringes (changes in amplitude) represented by the brightness distribution according to an index (determination index) that can determine interference unevenness. For example, the determination may be made using the ratio of the minimum brightness to the maximum brightness in the brightness distribution ([minimum brightness/maximum brightness] (%)), or the maximum brightness and the average value of the brightness distribution (average brightness) may be used as a determination index. Determination may be made using the difference between (maximum brightness - average brightness) as a determination index. Whether or not the optical film 10 is a non-defective product may be determined by setting a standard in advance, for example, by experiment, depending on the determination method.

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

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

When the changing step S03 is performed, the forming step S01 is performed 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 non-defective in the determining step S02B.

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

[Collection process]
In the collection step S04, the optical film 10 may be formed under the same conditions as when the optical film 10 for inspection was formed, and the formed optical film 10 may be collected. For example, when the optical film 10 is long and the inspection step S02 is carried out while conveying the optical film 10 formed in the forming step S01, the optical film 10 that has passed through the inspection step S02 is rolled up, 10 may be collected.

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

For example, when performing a visual inspection, the inspection results may vary depending on individual differences among inspectors (including differences in viewing angles, etc.), the condition of the same inspector (for example, physical condition, fatigue during the inspection, etc.), and the manufacturing factory of the optical film 10. There is a possibility that there may be differences between the two. 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, the inspection light L1, etc. to be used are fixed, and the determination is made based on the brightness distribution. Differences between inspectors (or between the same inspectors), differences in inspection methods between factories, etc. are eliminated. Therefore, the quality of the optical film 10 can be determined objectively.

In the method for manufacturing the optical film 10, since the quality of the optical film 10 is objectively determined by the above-mentioned inspection method, it is possible to efficiently manufacture the optical film 10 of good quality. As a result, the manufacturing yield of the optical film 10 is improved.

In the method for manufacturing the optical film 10, since the above-mentioned detection step S02A and determination step S02B can be performed automatically while the optical film 10 is being transported, it is possible to immediately detect the occurrence of a defective product. As a result, the optical film 10 of good quality can be manufactured more efficiently.

The brightness distribution used in the determination step S02B represents interference fringes of the reflected light L2. Therefore, 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 material of the optical film 10, etc. can be reduced. Therefore, the ratio of the minimum brightness to the maximum brightness can have general versatility.

When using the first polarizing filter 23 and the second polarizing filter 24, 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. 14 (including the influence of the interface between layers adjacent to the first adhesive layer 14) can be evaluated more accurately. Therefore, 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, it is possible to determine whether the optical film 10 is good or not. can be determined more accurately.

If the peak wavelength of the inspection light L1 output from the light source section 21 is in the range of, for example, 400 nm to 750 nm, preferably 500 nm to 700 nm, more preferably 600 nm to 650 nm, interference unevenness may occur because the wavelength range is limited. easy to detect. Furthermore, the maximum and minimum values of the brightness distribution become clearer in the data. Also 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 section 21 and the optical film 10 is 100 mm to 2000 mm, the installation space for the inspection optical system 20 can be reduced. Furthermore, the brightness of the reflected light L2 is likely to improve. Similarly, when the distance d2 between the optical film 10 and the detection section 22 is 100 mm to 2000 mm, the installation space for the inspection optical system 20 can be reduced.

If the regular 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.

An experimental example using a sample of the optical film 10 will be described below.

[Experiment 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, sample S1 has the second protective layer 16, the second retardation layer 13, the first adhesive layer 14, the first retardation layer 12, and the 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 in this order on the second protective layer 16. The plan view shape of sample S1 was a rectangle.

The first protective layer 15 and the second protective layer 16 were triacetylcellulose 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 retardation was 236 nm. The second retardation layer 13 was a λ/4 plate. The in-plane retardation was 116 nm. The angle θ3 (see FIG. 5) between the first slow axis 12a of the first retardation layer 12 and the second slow axis 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)
Sample S4 uses an epoxy resin-based ultraviolet curable adhesive (refractive index at a wavelength of 589 nm: 1.51) as the material for the first adhesive layer 14, and the thickness of the first adhesive layer 14 is 1.51 nm. It had the same configuration as sample S1 except that it was 5 μm.

The detection step S02A described using FIG. 4 was performed on the prepared samples S1 to S4. Since the conditions were the same except that the test targets were different, the samples S1 to S4 will be referred to as samples S, and the detection step S02A in the experimental example will be specifically explained.

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

In the detection step S02A, an area scan camera (product 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 conditions (1) to (6). Specifically, angles θ1 to θ6 were 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 brightness distribution in the figure is a cross-sectional brightness distribution (brightness distribution along the width direction) of the samples S1 to S4 at the center in the transverse 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 0 mm), and the vertical axis shows the brightness.

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

The following samples S1a, S2a, S3a, and S4a were used for 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 sample S1a, an optical system consisting of a third adhesive layer 32, a second retardation layer 13, a first adhesive layer 14, a first retardation layer 12, a second adhesive layer 18, and a polarizing plate 33 is used. A film 30 was produced.

The second retardation layer 13, first adhesive layer 14, and first retardation layer 12 constituting sample S1a were the same as the corresponding layers of sample S1. The material of the second adhesive layer 18 (thickness: 5 μm) and the third adhesive layer 32 (thickness: 25 μm) was an acrylic adhesive. 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 using FIG. The angle between the absorption axis of the polarizing plate 33 and the first slow axis 12a of the first retardation layer 12 was 72.1° to 72.9°.

During the visual evaluation, the surface of the third adhesive layer 32 was placed on a black acrylic plate 31 as a support in order to support the sample S1a. Furthermore, in order to reduce color unevenness on the surface of the polarizing plate 33, a water layer 34 (thickness: approximately 1 mm) and a glass plate 35 (thickness: 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 samples S2a to S4a were the same as the configuration of optical film 30, except that they had the same differences as those between samples S2 to S4 and sample S1. When visually evaluating the samples S2a to S4a, the samples S2a to S4a are placed on the black acrylic plate 31, and a water layer is placed on the surface of the polarizing plate 33 that the samples S2a to S4a have. 34 and glass plate 35 were laminated.

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

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

In addition to the embodiment described above, various modifications have been described. However, the present invention is not limited to the above embodiments and various modifications, but is indicated by the claims, and includes all changes within the meaning and range equivalent to the claims. is intended.

For example, the inspection surface 10a of the optical film 10 may be the surface on the second retardation layer 13 side (in the configurations shown in FIGS. 2 and 3, the surface of the second protective layer 16). Although the inspection process 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 only needs to have a first retardation layer, a second retardation layer, and an adhesive layer that adheres them.

The first retardation layer is not limited to a layer that provides a retardation of λ/2, and the second retardation layer is not limited to a layer that provides a retardation of λ/4. The retardation provided by the first retardation layer and the second retardation layer may be set so as to realize desired optical properties 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 conditions (1) to (6) are the first retardation layer and the second retardation layer. It may be set in accordance with the retardation provided by the second retardation layer to be suitable for determining the quality of the optical film.

In the detection step, it is not necessary to transport 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... Retardation laminate, 12... First retardation layer, 12a... First slow axis, 13... Second retardation layer, 13a... Second slow axis , 14... First adhesive layer, 15, 15A... First protective layer, 16... Second protective layer, 17... Polarizing plate, 18... Second adhesive layer, 20... Inspection optical system, 21... Light source section, 22... Detection 23...First polarizing filter, 23a...First absorption axis, 24...Second polarizing filter, 24a...Second absorption axis, 25...Back plate, 25a...Main surface of the back plate.

Claims (10)

Disposed on the inspection surface side of an optical film having a first retardation layer, a second retardation layer, and a first adhesive layer disposed between the first retardation layer and the second retardation layer. a detection step of irradiating inspection light from the light source section and detecting the light irradiated from the light source section and reflected by the optical film by a detection section disposed on the inspection surface side;
a determination step of obtaining a brightness distribution along a cross section of the optical film based on the brightness of the light detected by the detection unit, and determining whether the optical film is a good product based on the brightness distribution;
Equipped with
In the detection step, the inspection light from the light source section is irradiated onto the inspection surface through a first polarizing filter, and the light irradiated from the light source section to the optical film and reflected by the optical film is converted into second polarized light. Detected by the detection unit through a filter,
An x-axis and a y-axis that are 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, and the counterclockwise direction is set as a positive axis with respect to the reference axis. When referred to as the angular direction of
The first polarizing filter and the second polarizing filter are arranged in the optical film such that the first absorption axis of the first polarizing filter and the second absorption axis of the second polarizing filter satisfy the following condition (A). is located against
Inspection method for optical film.
(A) +70°<θ6<+110° (θ6 is the angle between the first absorption axis and the second absorption axis) performing a detection step and a determination step while conveying 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. 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,
In the optical film, the first retardation layer and the second retardation layer are arranged,
The first polarizing filter and the second polarizing filter such 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) and (5). is arranged with respect to the optical film,
The method for inspecting an optical film according to any one of claims 1 to 3.
(1) -40°<θ1<-10° (θ1 is the angle between the first slow axis and the reference axis)
(2) +15°<θ2<+50° (θ2 is the angle between the second slow axis and the reference axis)
(3) +55°<θ3<+65° (θ3 is the angle between the first slow axis and the second slow axis)
(4) -20°<θ4<+20° (θ4 is the angle between one of the first absorption axis and the second absorption axis and the reference axis)
(5) +70°<θ5<+110° (θ5 is the angle between the first absorption axis and the other of the second absorption axis and the reference axis) The optical film is
a polarizing plate located on the opposite side of the 1/4 wavelength layer when viewed 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;
has,
The method for inspecting an optical film according to claim 4. 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 5. carrying out the detection step while conveying the optical film;
The method for inspecting an optical film according to any one of claims 1 to 6. The peak wavelength of the inspection light is within the range of 400 nm to 750 nm.
The method for inspecting an optical film according to any one of claims 1 to 7. Performing the detection step with the optical film disposed on the main surface of the support plate,
The regular reflectance of the main surface is 45% or less,
The method for inspecting an optical film according to any one of claims 1 to 8. A method for producing an optical film, comprising the method for inspecting an optical film according to any one of claims 1 to 9.

Images