Optical film evaluation method

Abstract

To accurately evaluate an optical axis of an optical film.SOLUTION: A method for an evaluation according to an embodiment of the present invention is a method for evaluating an optical film, and the method includes the steps of: arranging the optical film on a substrate having a straight part in the outer periphery; measuring an optical axis of the optical film on the basis of the straight part of the substrate; and correcting the result of measurement on the basis of the positional relation between the substrate and the optical film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Image display devices, such as liquid crystal display devices and electroluminescence (EL) display devices (e.g., organic EL display devices), are rapidly becoming popular. In image display devices, optical components such as retardation components and polarizing components are generally used to realize image display and improve the performance of the image display (see, for example, Patent Document 1).

[0003] In recent years, new applications of image display devices have been developed. For example, goggles with displays (VR goggles) for realizing virtual reality (VR) have begun to be commercialized. As the applications of image display devices expand, optical films including the optical members described above are desired to have shapes suited to the applications. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-103286 Summary of the Invention [Problem to be solved by the invention]

[0005] However, depending on the shape, it may be difficult to accurately grasp the optical axis of the optical film.

[0006] In view of the above, a main object of the present invention is to accurately evaluate the optical axis of an optical film. [Means for solving the problem]

[0007] 1. An evaluation method according to an embodiment of the present invention is a method for evaluating an optical film, and includes placing the optical film on a substrate having a straight portion on its outer periphery, measuring the optical axis of the optical film based on the straight portion of the substrate, and correcting the measurement result based on the positional relationship between the substrate and the optical film. 2. In the evaluation method described in 1 above, a first linear portion extending in a first direction and a second linear portion extending in a second direction may be formed on the outer periphery of the substrate, and the substrate may have a corner where the first linear portion and the second linear portion intersect. 3. In the evaluation method according to 1 or 2 above, the substrate may be optically isotropic. 4. In the evaluation method according to any one of 1 to 3 above, the total light transmittance of the substrate may be 85% or more. 5. In the evaluation method according to any one of 1 to 4 above, the haze of the substrate may be 5% or less. 6. In the evaluation method according to any one of 1 to 5 above, the optical film does not need to have a linear portion on the periphery. 7. In the evaluation method according to any one of the above items 1 to 6, the optical film may have a positioning portion for positioning relative to the substrate.

[0008] 8. Another embodiment of the present invention provides a measuring device for measuring the optical axis of an optical film, comprising: a substrate having a straight portion on its outer periphery and on which the optical film is placed; a sample holding unit having a mounting surface on which the substrate is placed; and a regulating surface perpendicular to the mounting surface; and a measuring unit for measuring the optical axis of the optical film, wherein the measurement is performed with the straight portion of the substrate abutted against the regulating surface. 9. A substrate according to yet another embodiment of the present invention is used for measuring the optical axis of an optical film, and is a substrate on which the optical film is placed, and has a linear portion on the outer periphery. [Effects of the Invention]

[0009] According to the evaluation method of the embodiment of the present invention, the optical axis of the optical film can be accurately evaluated. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a top view of a measurement substrate according to one embodiment of the present invention. [Figure 2A] 2 is a top view of an example of a state in which the measurement substrate shown in FIG. 1 is placed on a jig of a measurement device. [Figure 2B] 2 is a side view of an example of a state in which the measurement substrate shown in FIG. 1 is placed on a jig of a measurement device. [Figure 3] FIG. 1 is a schematic diagram showing a general configuration of an example of a display system for VR goggles. [Figure 4] FIG. 2 is a schematic cross-sectional view showing an example of the details of an optical film. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In order to clarify the description, the drawings may schematically show the width, thickness, shape, etc. of each part compared to the embodiments, but these are merely examples and do not limit the interpretation of the present invention. Furthermore, in the drawings, the same or equivalent elements are given the same reference numerals, and duplicate explanations may be omitted.

[0012] (Definition of terms and symbols) The definitions of terms and symbols used in this specification are as follows. (1) Refractive index (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is greatest (i.e., the slow axis direction), "ny" is the refractive index in the direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-plane phase difference (Re) "Re(λ)" is the in-plane retardation measured with light of wavelength λ nm at 23°C. For example, "Re(550)" is the in-plane retardation measured with light of wavelength 550 nm at 23°C. Re(λ) is calculated by the formula: Re(λ)=(nx-ny)×d, where d (nm) is the thickness of the layer (film). (3) Retardation in the thickness direction (Rth) "Rth(λ)" is the retardation in the thickness direction measured with light of wavelength λ nm at 23°C. For example, "Rth(550)" is the retardation in the thickness direction measured with light of wavelength 550 nm at 23°C. Rth(λ) is calculated by the formula: Rth(λ) = (nx - nz) × d, where d (nm) is the thickness of the layer (film). (4) Nz coefficient The Nz coefficient is calculated by Nz=Rth / Re. (5)Angle When angles are referred to herein, the angles include both clockwise and counterclockwise angles relative to a reference direction, so for example, "45°" means ±45°.

[0013] A method for evaluating the optical axis of an optical film according to an embodiment of the present invention includes preparing a measurement substrate by placing an optical film on a substrate having a straight portion on its outer periphery, measuring the optical axis of the optical film based on the straight portion of the substrate, and correcting the measurement results based on the positional relationship between the substrate and the optical film.

[0014] The optical film to be evaluated may have an optical axis. Specifically, the optical film may include at least a retardation member and may have a slow axis and a fast axis. The retardation member may have any appropriate in-plane retardation Re(550). The in-plane retardation Re(550) of the retardation member is, for example, 100 nm to 300 nm. For example, when the retardation member can function as a so-called λ / 4 member, its in-plane retardation Re(550) is, for example, 100 nm to 190 nm, or may be 110 nm to 180 nm, 130 nm to 160 nm, or 135 nm to 155 nm.

[0015] The retardation member may typically be a stretched resin film or an oriented and solidified layer of a liquid crystal compound.

[0016] Examples of resins contained in the resin film include polycarbonate resins, polyester carbonate resins, polyester resins, polyvinyl acetal resins, polyarylate resins, cyclic olefin resins, cellulose resins, polyvinyl alcohol resins, polyamide resins, polyimide resins, polyether resins, polystyrene resins, and acrylic resins. These resins may be used alone or in combination. Examples of methods for combining include blending and copolymerization. When the retardation member exhibits reverse dispersion wavelength characteristics, a resin film containing a polycarbonate resin or a polyester carbonate resin (hereinafter sometimes simply referred to as a polycarbonate resin) can be suitably used.

[0017] Any suitable polycarbonate-based resin can be used as the polycarbonate-based resin. For example, the polycarbonate-based resin contains structural units derived from a fluorene-based dihydroxy compound, structural units derived from an isosorbide-based dihydroxy compound, and structural units derived from at least one dihydroxy compound selected from the group consisting of alicyclic diols, alicyclic dimethanols, di-, tri-, or polyethylene glycols, and alkylene glycols or spiroglycols. Preferably, the polycarbonate-based resin contains structural units derived from a fluorene-based dihydroxy compound, structural units derived from an isosorbide-based dihydroxy compound, structural units derived from an alicyclic dimethanol, and / or structural units derived from di-, tri-, or polyethylene glycol; more preferably, it contains structural units derived from a fluorene-based dihydroxy compound, structural units derived from an isosorbide-based dihydroxy compound, and structural units derived from di-, tri-, or polyethylene glycol. The polycarbonate-based resin may contain structural units derived from other dihydroxy compounds as needed. Details of polycarbonate-based resins that can be suitably used for phase difference members and methods for forming phase difference members are described, for example, in JP-A-2014-10291, JP-A-2014-26266, JP-A-2015-212816, JP-A-2015-212817, and JP-A-2015-212818, and the descriptions in these publications are incorporated herein by reference.

[0018] The thickness of the retardation member made of a stretched resin film is, for example, 10 μm to 100 μm, preferably 10 μm to 70 μm, and more preferably 20 μm to 60 μm.

[0019] The above-mentioned liquid crystal compound alignment solidified layer is a layer in which the liquid crystal compound is aligned in a predetermined direction within the layer and the alignment state is fixed. The term "alignment solidified layer" encompasses an alignment solidified layer obtained by solidifying a liquid crystal monomer, as described below. In a retardation member, rod-shaped liquid crystal compounds are typically aligned in the slow axis direction of the retardation member (homogeneous alignment). Examples of rod-shaped liquid crystal compounds include liquid crystal polymers and liquid crystal monomers. The liquid crystal compound is preferably polymerizable. If the liquid crystal compound is polymerizable, the alignment state of the liquid crystal compound can be fixed by aligning the liquid crystal compound and then polymerizing it.

[0020] The alignment and solidification layer of the liquid crystal compound (liquid crystal alignment and solidification layer) can be formed by performing an alignment treatment on the surface of a predetermined substrate, applying a coating liquid containing a liquid crystal compound to the surface to align the liquid crystal compound in a direction corresponding to the alignment treatment, and fixing the alignment state. Any appropriate alignment treatment can be used as the alignment treatment. Specific examples include mechanical alignment treatment, physical alignment treatment, and chemical alignment treatment. Specific examples of mechanical alignment treatment include rubbing treatment and stretching treatment. Specific examples of physical alignment treatment include magnetic field alignment treatment and electric field alignment treatment. Specific examples of chemical alignment treatment include oblique vapor deposition and photoalignment treatment. Any appropriate treatment conditions can be used for the various alignment treatments depending on the purpose.

[0021] The alignment of liquid crystal compounds is achieved by treating them at a temperature at which they exhibit a liquid crystal phase depending on the type of liquid crystal compound. By performing such temperature treatment, the liquid crystal compounds assume a liquid crystal state and are aligned in accordance with the alignment treatment direction on the substrate surface.

[0022] In one embodiment, the alignment state is fixed by cooling the liquid crystal compound aligned as described above. When the liquid crystal compound is polymerizable or crosslinkable, the alignment state is fixed by subjecting the liquid crystal compound aligned as described above to a polymerization treatment or crosslinking treatment.

[0023] Any suitable liquid crystal polymer and / or liquid crystal monomer can be used as the liquid crystal compound. The liquid crystal polymer and the liquid crystal monomer can be used alone or in combination. Specific examples of liquid crystal compounds and methods for producing a liquid crystal alignment solidified layer are described in, for example, JP 2006-163343 A, JP 2006-178389 A, and WO 2018 / 123551 A. The descriptions in these publications are incorporated herein by reference.

[0024] The thickness of the retardation member formed of the liquid crystal alignment solidified layer is, for example, 1 μm to 10 μm, preferably 1 μm to 8 μm, more preferably 1 μm to 6 μm, and further preferably 1 μm to 4 μm.

[0025] FIG. 1 is a top view of a measurement substrate according to one embodiment of the present invention. The measurement substrate 6 includes a substrate 4 and an optical film 2 disposed on the substrate 4. The substrate 4 has a predetermined thickness (e.g., 0.5 mm to 10 mm), and both opposing main surfaces are horizontal. The substrate 4 has linear portions in a planar view on its periphery. The substrate 4 has a first linear portion 4a extending in a first direction and a second linear portion 4b extending in a second direction on its periphery. The substrate 4 also has a corner 4c where the first linear portion 4a and the second linear portion 4b intersect. The first direction and the second direction of the substrate 4 are substantially perpendicular to each other, and the substrate 4 has a substantially rectangular shape in a planar view. However, the shape of the substrate in a planar view is not particularly limited as long as linear portions are formed on at least a portion of the periphery. For example, this means that the ratio of the length of the longest linear portion to the total length of the periphery exceeds 0.1.

[0026] The substrate used for the measurement substrate is preferably optically isotropic. By using an optically isotropic substrate, the influence on the evaluation of the optical axis of the optical film can be suppressed. In this specification, "optically isotropic" means that the in-plane retardation Re(590) is 0 nm to 10 nm. The in-plane retardation Re(590) of the substrate used for the measurement substrate is more preferably 1 nm or less, even more preferably 0.1 nm or less, particularly preferably 0.05 nm or less, and most preferably 0.01 nm or less. The retardation Rth(590) in the thickness direction of the substrate used for the measurement substrate is preferably -10 nm to +10 nm.

[0027] The total light transmittance of the substrate is preferably 85% or more, more preferably 88% or more, and even more preferably 90% or more. The haze of the substrate is preferably 5% or less, more preferably 3% or less, and even more preferably 1% or less. By using such a substrate, the influence on the evaluation of the optical axis of the optical film can be suppressed. As the substrate, for example, a glass substrate is preferably used.

[0028] The optical film 2 does not have a straight line portion on the periphery. In this specification, "does not have a straight line portion on the periphery" means that the ratio of the length of the longest straight line portion to the total length of the periphery is 0.1 or less. In the illustrated example, the optical film is substantially elliptical, but is not limited to this and may be, for example, substantially circular.

[0029] Although not shown, the optical film 2 may be disposed on the substrate 4 via any appropriate layer. For example, the optical film 2 is preferably fixed to the substrate 4 via an adhesive layer such as an adhesive layer or a pressure-sensitive adhesive layer.

[0030] The optical axis of the optical film is measured using the measurement substrate. Any appropriate device can be used as the optical axis measuring device. For example, KOBRA-WPR manufactured by Oji Scientific Instruments Co., Ltd. can be used as the optical axis measuring device.

[0031] Typically, when measuring the optical axis, the measurement substrate is placed on a jig of a measurement device. FIG. 2A is a top view of an example of the state in which the measurement substrate shown in FIG. 1 is placed on the jig of the measurement device, and FIG. 2B is a side view of an example of the state in which the measurement substrate shown in FIG. 1 is placed on the jig of the measurement device. The sample holding jig 8 of the measurement device has a horizontal mounting surface 8a and a regulating surface 8b perpendicular to the mounting surface 8a. The measurement substrate 6 (substrate 4) is placed on the mounting surface 8a with the first linear portion 4a abutting against the regulating surface 8b of the sample holding jig 8. The substrate 4 has an end surface 41 including the first linear portion 4a, and the end surface 41 abuts against the regulating surface 8b. Evaluating the optical axis of the optical film 2 using the substrate 4 can significantly improve evaluation accuracy compared to when the substrate 4 is not used. Abutting the first linear portion 4a forming the corner portion 4c against the regulating surface 8b can further improve evaluation accuracy. Although not shown, the sample holder 8 may be provided with a reference portion or the like for mounting the sample holder 8 on a measuring device in addition to the regulating surface 8b.

[0032] The measurement result of the optical axis of the optical film using a measurement substrate is corrected based on the positional relationship between the substrate and the optical film. The positional relationship between the substrate and the optical film can be converted into coordinates (quantified) using, for example, an image measuring instrument. Examples of image measuring instruments include the NEXIV series manufactured by Nikon Corporation.

[0033] The positional relationship between the substrate and the optical film is determined, for example, by the distance or angle between a straight line portion of the substrate and an arbitrary point on the optical film or a line connecting two arbitrary points. The optical film 2 has positioning portions 2a, 2a that position the optical film 2 relative to a first straight line portion 4a of the substrate 4. In the illustrated example, the positioning portions 2a are cutout portions in which the outer periphery is partially cut out in a planar view, but are not limited to this. The positioning portions may be, for example, protrusions in which the outer periphery is partially protruding in a planar view, or marks provided within the surface of the optical film.

[0034] The optical film may include other members in addition to the retardation member. Specific examples of the other members include optical members such as polarizing members. The optical film may be used in any appropriate image display device. The optical film may be used, for example, in VR goggles.

[0035] FIG. 3 is a schematic diagram showing the overall configuration of an example of a display system for VR goggles, illustrating the arrangement and shape of each component of the display system. The display system 10 includes a display element 12, a reflective polarizing element 14, a first lens unit 16, a half mirror 18, a first λ / 4 element 20, a second λ / 4 element 22, and a second lens unit 24. The reflective polarizing element 14 is disposed in front of the display surface 12a of the display element 12 and can reflect light emitted from the display element 12. The first lens unit 16 is disposed on the optical path between the display element 12 and the reflective polarizing element 14, and the half mirror 18 is disposed between the display element 12 and the first lens unit 16. The first λ / 4 element 20 is disposed on the optical path between the display element 12 and the half mirror 18, and the second λ / 4 element 22 is disposed on the optical path between the half mirror 18 and the reflective polarizing element 14.

[0036] The display element 12 is, for example, a liquid crystal display or an organic EL display, and has a display surface 12a for displaying an image. The light emitted from the display surface 12a passes through, for example, a polarizing member that may be included in the display element 12, and is converted into a first linearly polarized light.

[0037] The first λ / 4 member 20 can convert the first linearly polarized light incident on the first λ / 4 member 20 into first circularly polarized light. The first λ / 4 member 20 may be provided integrally with the display element 12.

[0038] The half mirror 18 transmits the light emitted from the display element 12 and reflects the light reflected by the reflective polarizing member 14 back toward the reflective polarizing member 14. The half mirror 18 is provided integrally with the first lens portion 16.

[0039] The second λ / 4 member 22 can transmit light reflected by the reflective polarizing member 14 and the half mirror 18 through the reflective polarizing member 14. The second λ / 4 member 22 may be provided integrally with the first lens portion 16.

[0040] The first circularly polarized light output from the first λ / 4 element 20 passes through the half mirror 18 and the first lens unit 16, and is converted into the second linearly polarized light by the second λ / 4 element 22. The second linearly polarized light output from the second λ / 4 element 22 is reflected toward the half mirror 18 without passing through the reflective polarizing element 14. At this time, the polarization direction of the second linearly polarized light incident on the reflective polarizing element 14 is the same as the reflection axis of the reflective polarizing element 14. Therefore, the second linearly polarized light incident on the reflective polarizing element 14 is reflected by the reflective polarizing element 14.

[0041] The second linearly polarized light reflected by the reflective polarizing element 14 is converted into second circularly polarized light by the second λ / 4 element 22, and the second circularly polarized light emitted from the second λ / 4 element 22 passes through the first lens unit 16 and is reflected by the half mirror 18. The second circularly polarized light reflected by the half mirror 18 passes through the first lens unit 16 and is converted into third linearly polarized light by the second λ / 4 element 22. The third linearly polarized light is transmitted through the reflective polarizing element 14. At this time, the polarization direction of the third linearly polarized light incident on the reflective polarizing element 14 is the same as the transmission axis of the reflective polarizing element 14. Therefore, the third linearly polarized light incident on the reflective polarizing element 14 is transmitted through the reflective polarizing element 14.

[0042] The light transmitted through the reflective polarizing member 14 passes through the second lens portion 24 and enters the eye 26 of the user.

[0043] The absorption axis of the polarizing member included in the display element 12 and the reflection axis of the reflective polarizing member 14 may be disposed approximately parallel to each other or approximately perpendicular to each other. The angle formed between the absorption axis of the polarizing member included in the display element 12 and the slow axis of the first λ / 4 member 20 is, for example, 40° to 50°, or may be 42° to 48°, or may be approximately 45°. The angle formed between the absorption axis of the polarizing member included in the display element 12 and the slow axis of the second λ / 4 member 22 is, for example, 40° to 50°, or may be 42° to 48°, or may be approximately 45°.

[0044] The in-plane retardation Re(550) of the first λ / 4 component 20 is, for example, 100 nm to 190 nm, or alternatively, 110 nm to 180 nm, 130 nm to 160 nm, or 135 nm to 155 nm. The first λ / 4 component 20 preferably exhibits inverse dispersion wavelength characteristics in which the retardation value increases according to the wavelength of the measurement light. The Re(450) / Re(550) of the first λ / 4 component 20 may be, for example, 0.75 or more and less than 1, or 0.8 or more and 0.95 or less.

[0045] The in-plane retardation Re(550) of the second λ / 4 component 22 is, for example, 100 nm to 190 nm, or alternatively, 110 nm to 180 nm, 130 nm to 160 nm, or 135 nm to 155 nm. The second λ / 4 component 22 preferably exhibits inverse dispersion wavelength characteristics in which the retardation value increases according to the wavelength of the measurement light. The Re(450) / Re(550) of the second λ / 4 component 22 may be, for example, 0.75 or more and less than 1, or 0.8 or more and 0.95 or less.

[0046] Although not shown, display system 10 may also include an absorptive polarizer disposed in front of reflective polarizer 14. The reflective axis of the reflective polarizer and the absorption axis of the absorptive polarizer may be disposed approximately parallel to each other.

[0047] The above optical film can include, for example, members provided in the above display system. Specifically, the optical film can include a retardation member such as a λ / 4 member. Further, the optical film can include a polarizing member such as a reflective polarizing member or an absorptive polarizing member. Furthermore, the optical film can include other members such as a protective member and an adhesive layer for integrating adjacent members. The thickness of the optical film varies depending on, for example, the type and number of the included members, but is, for example, 50 μm to 400 μm. The optical film applied to the above display system can have a shape corresponding to the shape of the first lens portion or the second lens portion. For example, it can be designed to have a shape without a straight portion on the outer periphery such as a substantially circular shape or a substantially elliptical shape. In this case, the optical film can be provided integrally with the first lens portion or the second lens portion.

[0048] FIG. 4 is a schematic cross-sectional view showing an example of the details of the optical film. The optical film 2 includes a second λ / 4 member 22 that can correspond to the above retardation member, another retardation member 28 disposed on one side of the second λ / 4 member 22, and a protective member 30 disposed on the other side of the second λ / 4 member 22.

[0049] The second λ / 4 member 22 preferably exhibits a refractive index characteristic showing a relationship of nx > ny ≧ nz. Here, "ny = nz" includes not only the case where ny and nz are exactly equal but also the case where they are substantially equal. Therefore, within a range not impairing the effects of the present invention, ny < nz may occur. The Nz coefficient of the second λ / 4 member is preferably 0.9 to 3, more preferably 0.9 to 2.5, still more preferably 0.9 to 1.5, and particularly preferably 0.9 to 1.3.

[0050] The other retardation member 28 may be, for example, a member whose refractive index characteristics can exhibit the relationship nz>nx=ny (so-called positive C plate). The thickness direction retardation Rth(550) of the positive C plate is preferably −50 nm to −300 nm, more preferably −70 nm to −250 nm, even more preferably −90 nm to −200 nm, and particularly preferably −100 nm to −180 nm. Here, “nx=ny” encompasses not only the case where nx and ny are strictly equal, but also the case where nx and ny are substantially equal. The in-plane retardation Re(550) of the positive C plate is, for example, less than 10 nm.

[0051] The positive C plate can be formed from any suitable material, but is preferably composed of a film containing a liquid crystal material fixed in homeotropic alignment. The liquid crystal material (liquid crystal compound) that can be homeotropically aligned may be a liquid crystal monomer or a liquid crystal polymer. Specific examples of such liquid crystal compounds and methods for forming a positive C plate include the liquid crystal compounds and methods for forming the retardation layer described in

[0020] to

[0028] of JP 2002-333642 A. In this case, the thickness of the positive C plate is preferably 0.5 μm to 5 μm.

[0052] The protective member 30 typically includes a substrate. The substrate can be made of any appropriate film. Examples of materials that form the main component of the film constituting the substrate include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, polysulfone-based, polystyrene-based, cycloolefin-based resins such as polynorbornene, polyolefin-based, (meth)acrylic-based, and acetate-based resins. The thickness of the substrate is preferably 5 μm to 80 μm, more preferably 10 μm to 40 μm, and even more preferably 15 μm to 35 μm.

[0053] The protective member 30 may preferably have a substrate and a surface treatment layer formed on the substrate. A protective member having a surface treatment layer can be disposed so that the substrate is located on the second λ / 4 member 22 side. The surface treatment layer can have any appropriate function. For example, the surface treatment layer preferably has an anti-reflection function. The thickness of the surface treatment layer is preferably 1 μm to 20 μm, more preferably 2 μm to 15 μm, and even more preferably 3 μm to 10 μm.

[0054] Although not shown, each member included in the optical film 2 is preferably integrated via an adhesive layer. The optical film 2 may also be provided integrally with the first lens portion of the display system via an adhesive layer (for example, a pressure-sensitive adhesive layer) not shown. Specifically, an adhesive layer may be provided on the surface of another retardation member 28, and the optical film 2 may be bonded to the first lens portion via this adhesive layer. The adhesive layer may be formed of an adhesive or a pressure-sensitive adhesive. The thickness of the adhesive layer is, for example, 0.05 μm to 30 μm, preferably 3 μm to 20 μm, and more preferably 5 μm to 15 μm. [Example]

[0055] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. The thickness, retardation value, transmittance, and haze are values ​​measured by the following measurement methods. <Thickness> Thicknesses of 1 μm or less were measured using a scanning electron microscope (manufactured by JEOL Ltd., product name "JSM-7100F"), and thicknesses of more than 1 μm were measured using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C"). <Phase difference value> Measurements were made using a KOBRA-WPR manufactured by Oji Scientific Instruments Co., Ltd. Measurement wavelengths were 450 nm, 550 nm, and 590 nm, and the measurement temperature was 23°C. <Total light transmittance> Measurement was carried out in accordance with JIS K 7361 using an MDH-4000 manufactured by Nippon Denshoku Co., Ltd. <Haze> Measurement was carried out in accordance with JIS 7136 using a haze meter (manufactured by Murakami Color Science Laboratory, product name "HN-150").

[0056] [Example 1] A glass substrate having a thickness of 1.3 mm and a size of 65 mm x 165 mm was prepared. The in-plane retardation Re(590) of this glass substrate was 0 nm, the total light transmittance was 92.26%, and the haze was 0.16%.

[0057] (Fabrication of λ / 4 components) Polymerization was carried out using a batch polymerization apparatus consisting of two vertical reactors equipped with stirring blades and reflux condensers controlled at 100° C. The polymerization mixture contained 29.60 parts by mass (0.046 mol) of bis[9-(2-phenoxycarbonylethyl)fluoren-9-yl]methane, 29.21 parts by mass (0.200 mol) of isosorbide (ISB), 42.28 parts by mass (0.139 mol) of spiroglycol (SPG), 63.77 parts by mass (0.298 mol) of diphenyl carbonate (DPC), and 1.19 × 10 calcium acetate monohydrate as a catalyst. -2 Part of mass (6.78×10 -5 (mol) was charged. After purging the reactor with nitrogen under reduced pressure, heating was performed using a heat transfer medium. Stirring was initiated when the internal temperature reached 100°C. Forty minutes after the start of the temperature increase, the internal temperature reached 220°C. This temperature was maintained while simultaneously reducing the pressure. 90 minutes after reaching 220°C, the pressure was reduced to 13.3 kPa. Phenol vapor by-produced during the polymerization reaction was introduced into a reflux condenser at 100°C, and the small amount of monomer components contained in the phenol vapor was returned to the reactor. Uncondensed phenol vapor was collected by introducing nitrogen into the first reactor and temporarily restoring the pressure to atmospheric pressure. The oligomerized reaction liquid in the first reactor was then transferred to the second reactor. Next, heating and depressurization of the second reactor were initiated, and the internal temperature reached 240°C and the pressure reached 0.2 kPa in 50 minutes. The polymerization was then allowed to proceed until the specified stirring power was reached. When the predetermined power was reached, nitrogen was introduced into the reactor to restore pressure, and the polyester carbonate resin produced was extruded into water, and the strands were cut to obtain pellets.

[0058] The resulting polyester carbonate resin pellets were vacuum-dried at 80°C for 5 hours and then used in a film-making machine equipped with a single-screw extruder (manufactured by Toshiba Machine Co., Ltd., cylinder temperature setting: 250°C), a T-die (width: 200 mm, temperature setting: 250°C), a chill roll (temperature setting: 120-130°C), and a winder to produce a 135 μm-thick long resin film. The resulting long resin film was stretched in the width direction at a stretching temperature of 143°C and a stretch ratio of 2.8 to obtain a 47 μm-thick stretched film. The resulting stretched film had an Re(590) of 145 nm, an Re(450) / Re(550) ratio of 0.86, and an Nz coefficient of 1.12. The stretched film also had a total light transmittance of 96.81% and a haze of 0.48%.

[0059] (Positive C-plate formation) A liquid crystal coating solution was prepared by dissolving 20 parts by weight of a side-chain liquid crystal polymer represented by the following chemical formula (1) (the numbers 65 and 35 in the formula represent the mole percent of the monomer unit, and are conveniently expressed as a block polymer; weight-average molecular weight 5000), 80 parts by weight of a polymerizable liquid crystal exhibiting a nematic liquid crystal phase (BASF: trade name Paliocolor LC242), and 5 parts by weight of a photopolymerization initiator (Ciba Specialty Chemicals: trade name Irgacure 907) in 200 parts by weight of cyclopentanone. The coating solution was then applied to a PET substrate that had been subjected to vertical alignment treatment using a bar coater, and the liquid crystal was aligned by heating and drying at 80°C for 4 minutes. The liquid crystal layer was irradiated with ultraviolet light to harden it, forming a positive C-plate with a thickness of 4 μm and an Rth(550) of -100 nm on the substrate. [ka]

[0060] (Production of protective material) The anti-reflection layer-forming material shown below was applied to an acrylic film having a lactone ring structure and heated at 80°C for 1 minute. After heating, the coating layer was irradiated with a high-pressure mercury lamp at an integrated light intensity of 300 mJ / cm. 2The coating layer was cured by irradiation with ultraviolet light of 1000 kJ / cm, to obtain an acrylic film (thickness: 44 μm) on which an antireflection layer having a thickness of 0.1 μm was formed.

[0061] (Anti-reflection layer forming material) 100 parts by weight of a polyfunctional acrylate containing pentaerythritol triacrylate as the main component (manufactured by Osaka Organic Chemical Industry Co., Ltd., trade name "Viscoat #300", solid content 100 wt%), 150 parts by weight of hollow nanosilica particles (manufactured by JGC Catalysts and Chemicals Industries, Ltd., trade name "Sururia 5320", solid content 20 wt%, weight average particle diameter 75 nm), 50 parts by weight of solid nanosilica particles (manufactured by Nissan Chemical Industries, Ltd., trade name "MEK-2140Z-AC", solid content 30 wt%, weight average particle diameter 10 nm), 12 parts by weight of a fluorine-containing additive (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "KY-1203", solid content 20 wt%), and 3 parts by weight of a photopolymerization initiator (manufactured by BASF, trade name "OMNIRAD907", solid content 100 wt%) were mixed. To this mixture, a mixed solvent of TBA (tertiary butyl alcohol), MIBK (methyl isobutyl ketone), and PMA (propylene glycol monomethyl ether acetate) in a weight ratio of 60:25:15 was added as a dilution solvent to make the total solid content 4% by weight, and the mixture was stirred to prepare a coating liquid for forming an anti-reflection layer.

[0062] (Optical film) The positive C-plate described below was attached to the λ / 4 member (stretched film) via an ultraviolet-curable adhesive (thickness after curing: 1 μm). Next, the protective member was attached to the λ / 4 member via the pressure-sensitive adhesive layer having a thickness of 5 μm, to obtain a laminate. From the obtained laminate, 32 elliptical optical films were punched out as shown in Fig. 1. The films were punched out so that the slow axis direction of the λ / 4 component, which had been determined in advance, was at an angle of 45° to the short side direction of the obtained optical film.

[0063] (Measuring shaft angle) The optical film was placed on the glass substrate to obtain a measurement substrate. Specifically, the optical film was attached to the glass substrate via a 12 μm thick adhesive layer to obtain a measurement substrate. The obtained measurement substrate was placed on the sample holder of a retardation measurement device (Oji Scientific Instruments, product name "KOBRA-WPR"). Specifically, as shown in Figure 2, the linear portion of the measurement substrate was abutted against the regulating surface of the sample holder. The slow axis direction of the optical film was then measured under conditions of a measurement wavelength of 590 nm, a measurement temperature of 23°C ± 2°C, and a measurement humidity of 60% ± 2%. Specifically, the axial angle formed by the slow axis direction of the optical film with respect to the regulating surface of the sample holder was measured.

[0064] (correction) The axis angle obtained by the above measurement was corrected to evaluate the slow axis of the optical film. Specifically, the position of the optical film relative to the upper edge of the glass substrate on the measurement substrate was converted into a coordinate system to calculate the misalignment of the laminate, and the axis angle obtained by the above measurement was corrected using the calculated misalignment. The coordinate system for the positions of the glass substrate and the optical film was used with an image measuring instrument (Nikon Corporation, "NEXIV VMZ-R6555").

[0065] [Comparative Example 1] The slow axis of the optical film was evaluated in the same manner as in Example 1, except for the following points. In measuring the axial angle, the optical film was placed directly on the sample holder without using a glass substrate. Specifically, the elliptical optical film was butted against the regulating surface of the sample holder so that the short side direction was perpendicular to the jig. - Shaft angle correction was not performed.

[0066] The standard deviations (degree of variation) of the evaluation results of Example 1 and the measurement results of Comparative Example 1 are shown below. In Comparative Example 1, misalignment is likely to occur when the optical film is placed on the jig, which can be said to cause variation in the measurement values. On the other hand, in Example 1, the use of a glass substrate makes the above-mentioned misalignment less likely to occur, and correction is performed, so the variation in the evaluation values ​​is extremely low.

[0067] [Table 1]

[0068] The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the configurations shown in the above-described embodiment can be replaced with configurations that are substantially the same as those shown in the above-described embodiment, that have the same effects, or that can achieve the same purpose. [Industrial Applicability]

[0069] The evaluation method according to the embodiment of the present invention can be suitably used to evaluate the optical axis of an optical film. [Explanation of symbols]

[0070] 2 optical film, 2a positioning portion, 4 substrate, 4a first linear portion, 4b second linear portion, 4c corner portion, 6 measurement substrate, 8 sample holding jig, 8a mounting surface, 8b regulating surface, 10 display system, 12 display element, 14 reflective polarizing member, 16 first lens portion, 18 half mirror, 20 first λ / 4 member, 22 second λ / 4 member, 24 second lens portion.

Claims

1. A method for evaluating an optical film, comprising: disposing the optical film on a substrate having a linear portion on its outer periphery; measuring an optical axis of the optical film based on the linear portion of the substrate; correcting the measurement results based on a positional relationship between the substrate and the optical film; Evaluation methods, including:

2. 2. The evaluation method according to claim 1, wherein a first linear portion extending in a first direction and a second linear portion extending in a second direction are formed on an outer periphery of the substrate, and the substrate has a corner where the first linear portion and the second linear portion intersect.

3. The evaluation method according to claim 1 , wherein the substrate is optically isotropic.

4. The evaluation method according to claim 1 , wherein the substrate has a total light transmittance of 85% or more.

5. The evaluation method according to claim 1 , wherein the haze of the substrate is 5% or less.

6. The evaluation method according to claim 1 , wherein the optical film does not have a linear portion on its outer periphery.

7. The evaluation method according to claim 1 , wherein the optical film has a positioning portion relative to the substrate.

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