Retardation film, optical laminate, and method of manufacturing optical film piece

Abstract

To provide a retardation film which enables effective weight reduction of VR goggles while improving visibility.SOLUTION: A retardation film 1 provided herein has a first principal surface 1a and a second principal surface 1b facing each other and contains a resin with negative birefringence. When heated at a temperature of 80°C for 240 hours, the number of cracks having a length of 200 μm or more appearing in the retardation film 1 is zero.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a retardation film, an optical laminate, and a method for manufacturing an optical film piece.

Background Art

[0002] Image display devices typified by liquid crystal display devices and electroluminescence (EL) display devices (for example, organic EL display devices) have been rapidly spreading. In image display devices, in order to realize image display and improve the performance of image display, generally, optical members such as polarizing members and retardation members are used (see, for example, Patent Document 1).

[0003] In recent years, new applications of image display devices have been developed. For example, goggles with a display (VR goggles) for realizing Virtual Reality (VR) have begun to be commercialized. Since VR goggles are being considered for use in various scenarios, weight reduction, improvement of visibility, etc. are desired.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The weight reduction of the VR goggles can be achieved, for example, by thinning the lenses used in the VR goggles. On the other hand, the development of an optical member suitable for a display system using thin lenses is also desired.

[0006] In view of the above, the main object of the present invention is to provide a retardation film that can satisfactorily achieve weight reduction of VR goggles while improving visibility.

Means for Solving the Problems

[0007] 1. The retardation film according to an embodiment of the present invention has a first major surface and a second major surface facing each other, and is a retardation film containing a resin having negative birefringence, and when heated at a temperature of 80° C. for 240 hours, the number of cracks having a length of 200 μm or more is zero. 2. In the retardation film according to 1 above, the solvent content may be less than 3200 μg / g. 3. In the retardation film according to 1 or 2 above, the solvent content may exceed 30 μg / g. 4. In the retardation film according to any one of 1 to 3 above, the difference in the dimensional change rate due to heating may be less than 0.03%. 5. In the retardation film according to any one of 1 to 4 above, the difference in the dimensional change rate due to heating may be -0.02% or more. 6. In the retardation film according to any one of 1 to 5 above, the amount of change in surface smoothness by placing it in an environment of a temperature of 65° C. and a relative humidity of 90% for 240 hours may be 0.04 arcmin or less. 7. In the retardation film according to any one of 1 to 6 above, the resin having the negative birefringence may contain a fumarate resin. 8. In the retardation film according to any one of 1 to 7 above, the refractive index characteristics may show a relationship of nz>nx = ny. 9. The optical laminate according to an embodiment of the present invention includes the retardation film according to any one of 1 to 8 above. 10. The optical laminate according to 9 above may include an adhesive layer disposed adjacent to the retardation film. 11. The method for manufacturing an optical film piece according to an embodiment of the present invention includes heating the optical laminate according to 9 or 10 above and integrating it with a component having a curved surface portion.

Advantages of the Invention

[0008] According to the retardation film according to an embodiment of the present invention, while improving visibility, weight reduction of the VR goggles can be satisfactorily achieved.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 2D

Figure 3A

Figure 3B

Figure 3C

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. For the sake of clearer explanation, the drawings may schematically represent the width, thickness, shape, etc. of each part as compared with the embodiments, but this is merely an example and does not limit the interpretation of the present invention. Also, for the drawings, the same or equivalent elements are denoted by the same reference numerals, and duplicate explanations may be omitted.

[0011] (Definitions of Terms and Symbols) The definitions of the terms and symbols in this specification are as follows. (1) Refractive Index (nx, ny, nz) “nx” is the refractive index in the direction where the in-plane refractive index is maximum (i.e., the slow axis direction), “ny” is the refractive index in the direction orthogonal 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 phase difference measured with light of wavelength λ nm at 23°C. For example, “Re(550)” is the in-plane phase difference measured with light of wavelength 550 nm at 23°C. Re(λ) is obtained by the formula: Re(λ) = (nx - ny) × d, where d (nm) is the thickness of the layer (film). (3) Phase Difference in the Thickness Direction (Rth) “Rth(λ)” is the phase difference in the thickness direction measured with light of wavelength λ nm at 23°C. For example, “Rth(550)” is the phase difference in the thickness direction measured with light of wavelength 550 nm at 23°C. Rth(λ) is obtained 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 obtained by Nz = Rth / Re. (5) Angle When referring to an angle in this specification, the angle includes both clockwise and counterclockwise directions with respect to the reference direction. Therefore, for example, “45°” means ±45°.

[0012] [Phase Difference Film] Figure 1 is a schematic cross-sectional view showing a schematic configuration of a retardation film according to one embodiment of the present invention.

[0013] The retardation film 1 is composed of, for example, a resin film. In this case, the retardation film 1 may contain a resin. The retardation film 1 has a first major surface 1a and a second major surface 1b facing each other.

[0014] The thickness of the retardation film 1 is, for example, 1 μm to 40 μm, preferably 3 μm to 35 μm, and more preferably 5 μm to 30 μm.

[0015] For example, it is preferable that the retardation film 1 has 0 cracks with a length of 200 μm or more when heated at a temperature of 80 °C for 240 hours. For example, the presence or absence of crack generation can be evaluated within a range of 45 mm × 50 mm. Also, for example, when the retardation film 1 is placed in an environment of a temperature of 65 °C and a relative humidity of 90% for 240 hours, it is preferable that the number of cracks with a length of 200 μm or more is 5 or less per 45 mm × 50 mm, more preferably 3 or less per 45 mm × 50 mm, still more preferably 1 or less per 45 mm × 50 mm, and it is particularly preferable that such cracks do not occur.

[0016] The number and length of cracks that can occur in the retardation film 1 can be confirmed, for example, by observation with an optical microscope.

[0017] The retardation film 1 may contain a solvent. The solvent that the retardation film 1 may contain is, for example, a solvent used in its manufacturing process. Examples of the solvent that the retardation film 1 may contain include ethyl acetate and methyl isobutyl ketone. These can be used alone or in combination of two or more. Among these, methyl isobutyl ketone is preferably used.

[0018] The retardation film 1 has a solvent content of less than, for example, 3200 μg / g, preferably 3150 μg / g or less, and more preferably 3100 μg / g or less. By satisfying such a solvent content, excellent durability can be achieved. For example, the occurrence of cracks can be suppressed. On the other hand, the solvent content of the retardation film 1 is preferably more than 30 μg / g, more preferably 50 μg / g or more, and even more preferably 100 μg / g or more. By satisfying such a solvent content, for example, a retardation film 1 having a desired retardation value can be obtained.

[0019] The retardation film 1 has a difference in dimensional change rate due to heating of less than, for example, 0.03%, preferably 0.02% or less. By satisfying such a difference in dimensional change rate, excellent durability can be achieved. For example, the occurrence of cracks can be suppressed. On the other hand, the difference in dimensional change rate due to heating of the retardation film 1 is preferably -0.02% or more, more preferably 0.01% or more. By satisfying such a difference in dimensional change rate, for example, a retardation film 1 having a desired retardation value can be obtained.

[0020] The difference in the dimensional change rate can be determined by placing a measurement sample, for example, in a heating environment at a temperature of 65°C and a relative humidity of 10% for 60 minutes and measuring the change in dimensions before and after heating.

[0021] The surface smoothness of the first major surface 1a and the second major surface 1b of the retardation film 1 is, for example, 0.10 arcmin or more and 0.50 arcmin or less, preferably 0.40 arcmin or less, and more preferably 0.30 arcmin or less, respectively. The amount of change in surface smoothness by placing the retardation film 1 in an environment at a temperature of 65°C and a relative humidity of 90% for 240 hours is preferably 0.04 arcmin or less. The surface smoothness can be measured by focusing the irradiation light on the surface of the object.

[0022] The resin film constituting the retardation film 1 can contain, for example, a resin having negative birefringence. The resin having negative birefringence can be a resin that exhibits the property that the refractive index in the direction perpendicular to the stretching direction is maximized when uniaxially stretched. In the retardation film 1 (resin film), the content ratio of the resin having negative birefringence is, for example, 90% by weight to 98% by weight, preferably 94% by weight to 97% by weight.

[0023] Examples of the resin having negative birefringence include resins in which chemical bonds or functional groups with large polarization anisotropy such as aromatic rings and carbonyl groups are introduced into the side chains. Specific examples of the resin having negative birefringence include acrylic resins, styrene resins, maleimide resins, modified polyolefin resins, fumarate resins, etc. As specific examples thereof, reference can be made to the resins having negative birefringence described in JP-A-2021-076759, JP-T-2008-544304, JP-T-2008-544317, etc. The above resins can be used alone or in combination of two or more. As the resin having negative birefringence, a fumarate resin is preferably used.

[0024] The retardation film 1 (resin film) can further contain any appropriate additive as required. Specific examples of the additive include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, ultraviolet absorbers, flame retardants, colorants, antistatic agents, compatibilizers, crosslinking agents, thickeners, etc. The type and content of the additive can be appropriately set according to the purpose. The content of the additive in the retardation film 1 (resin film) is, for example, 3% by weight to 10% by weight.

[0025] The retardation film 1 is, for example, a film (so-called positive C-plate) whose refractive index characteristics may exhibit the relationship nz > nx = ny. In this case, the retardation Rth(550) in the thickness direction of the retardation film 1 is preferably from -50 nm to -300 nm, more preferably from -70 nm to -250 nm, still more preferably from -90 nm to -200 nm, and particularly preferably from -100 nm to -180 nm. Here, "nx = ny" includes not only the case where nx and ny are exactly equal, but also the case where nx and ny are substantially equal. The in-plane retardation Re(550) of the retardation film 1 is, for example, less than 10 nm, preferably 5 nm or less, more preferably 3 nm or less, particularly preferably 1 nm or less, and most preferably 0.5 nm or less.

[0026] The haze of the retardation film 1 is preferably 2.0% or less, more preferably 1.5% or less. The haze of the retardation film 1 is, for example, 0.1% or more, and may be 1.0% or more. The haze of the retardation film 1 can be measured, for example, in accordance with JIS K7136 using a haze meter (for example, "HN-150" manufactured by Murakami Color Research Laboratory).

[0027] The retardation film 1 can be obtained, for example, by a method including forming a film (film-forming step) of a forming material containing the resin having the above-described negative birefringence in a film form, and annealing the formed film (annealing step). Here, it is preferable that the formed film is not substantially stretched.

[0028] Figures 2A to 2D are diagrams showing an example of a method for manufacturing a retardation film according to one embodiment of the present invention.

[0029] Figure 2A shows a state in which the above forming material is formed into a film on a support (for example, a base film such as a polyester film) 30 to form a film 31. The film formation is performed, for example, by applying a resin solution containing the above forming material to the support 30 and drying the applied film. When the resin solution is dried on the support 30, stress is generated due to volume shrinkage, and the molecular chains of the polymer tend to be oriented in the in-plane direction. When a resin having high birefringence development property and negative intrinsic birefringence is used, a film 31 having a large thickness-direction birefringence can be formed on the support 30 by the shrinkage action during drying.

[0030] Examples of the solvent contained in the resin solution include ethyl acetate and methyl isobutyl ketone. These can be used alone or in combination of two or more. Among these, methyl isobutyl ketone is preferably used. The solid content concentration of the resin solution is, for example, 16% by weight to 20% by weight.

[0031] The drying temperature of the applied film is, for example, 50°C to 160°C. The drying time of the applied film is, for example, 120 seconds to 240 seconds.

[0032] The formed film 31 can be used as a positive C plate as it is, for example, but the film 31 is preferably annealed. By annealing, for example, a retardation film 1 with excellent durability can be obtained that satisfies the difference in the content of the above solvent and / or the dimensional change rate. During annealing, the film 31 can be in any appropriate state. Specifically, during annealing, the surface (typically, the main surface) of the film 31 may be protected by a protective member or may be exposed. For example, from the perspective of suppressing breakage, it is preferable that the surface of the film 31 is protected by a protective member during annealing. When the main surface of the film 31 is protected, only one main surface may be protected, or both main surfaces may be protected. In a preferred embodiment, during annealing, it is preferable that one main surface of the film 31 is protected by a protective member and the other main surface is exposed. According to such a form, for example, a retardation film 1 that satisfactorily satisfies the difference in the content of the above solvent and / or the dimensional change rate can be obtained. Also, for example, a retardation film 1 having a desired retardation value can be obtained.

[0033] In the illustrated example, before annealing the film 31, as shown in FIG. 2B, after laminating a surface protection film 32 as a protective member on the upper surface 31a of the film 31, as shown in FIG. 2C, the support 30 is peeled off from the lower surface 31b of the film 31. Then, as shown in FIG. 2D, the film 31 is annealed with the surface protection film 32 laminated as a protective member on the upper surface 31a of the film 31 and the lower surface 31b exposed.

[0034] The support 30 used for film formation can be used as a protective member, but by peeling the support 30 from the film 31 and annealing, a retardation film 1 with excellent appearance can be obtained. Specifically, air easily enters between the support 30 and the film 31, and there is a tendency for a gap to occur. If annealing is performed with a gap existing between the support 30 and the film 31, the location where the gap exists may become a mark and may damage the appearance of the resulting retardation film 1. By using a protective member separately from the support 30, a retardation film 1 with excellent appearance can be obtained.

[0035] The surface protection film 32 is typically a laminate of a base film 32a and an adhesive layer 32b. Examples of the material for forming the base film include polyester polymers such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBT); cellulose polymers such as diacetyl cellulose and triacetyl cellulose; polycarbonate polymers; (meth)acrylic polymers such as polymethyl methacrylate; cycloolefin polymers such as polynorbornene. These may be used alone or in combination of two or more. The thickness of the base film is preferably 15 μm to 70 μm, more preferably 20 μm to 60 μm, and even more preferably 25 μm to 50 μm. The thickness of the adhesive layer is, for example, 5 μm to 15 μm. Also, for example, a self-adhesive film may be used as the surface protection film.

[0036] For example, by adjusting the annealing conditions, a retardation film 1 that satisfactorily meets the difference in the solvent content and / or the dimensional change rate can be obtained. The annealing conditions (for example, annealing temperature, annealing time) can be set to any appropriate conditions. For example, the annealing temperature can be set according to the solvent contained in the resin solution. Specifically, the annealing temperature is preferably not lower than the boiling point T (°C) of the solvent contained in the resin solution and not higher than T + 100 °C, and may be not lower than T + 20 °C or not lower than T + 70 °C. The annealing temperature is, for example, not lower than 50 °C and not higher than 250 °C, and may be not lower than 120 °C, not lower than 130 °C, or not lower than 140 °C. Also, for example, the annealing temperature can be set higher than the drying temperature. The annealing time is, for example, 5 seconds to 30 seconds, and preferably not less than 15 seconds.

[0037] The retardation film 1 can be used, for example, by being integrated with a component (e.g., an optical component such as a lens). The integration is typically performed by bonding the retardation film 1 to the component via an adhesive layer. Depending on the shape of the component to be integrated, the retardation film 1 can be heated and, if necessary, stretched. For example, when integrating with a curved surface portion, the retardation film 1 can be heated and, if necessary, stretched. Note that the retardation film 1 can typically be integrated with a component together with other optical members.

[0038] In one embodiment, an optical film piece can be obtained by integrating an optical laminate including the retardation film 1 with a curved surface portion of an optical component (e.g., a lens). Specifically, an optical film piece including the retardation film 1 can be obtained by integrating an optical laminate including the retardation film 1 with a curved surface portion of an optical component. Typically, an adhesive (adhesive layer) is used for the integration.

[0039] FIGS. 3A to 3C are diagrams showing an example of a method for integrating an optical laminate including a retardation film with a component.

[0040] FIG. 3A shows a state where an adhesive layer 3 is provided on a laminated portion 2 including a retardation film to prepare a workpiece (optical laminate) 4, and the workpiece 4 is disposed above an optical component (lens) L that is an adherend. Note that in FIG. 3, details of the laminated portion 2 are omitted.

[0041] The lens L is, for example, circular in plan view and has a concave shape in cross section. The workpiece 4 is held above the concave surface (upper surface) of the lens L by a holder (not shown). In this state, the workpiece 4 can be heated. The shape of the workpiece 4 can be more easily deformed by heating. The heating temperature of the workpiece 4 is, for example, 50°C or higher and 150°C or lower.

[0042] When the workpiece 4 becomes easily deformable, by any suitable method (for example, utilizing the air pressure difference), as shown in FIG. 3B, the workpiece 4 is bonded to the entire surface of the lens L. Thereafter, as shown in FIG. 3C, unnecessary portions of the workpiece 4 (for example, portions that do not overlap with the lens L in plan view) are removed, and the optical film piece 5 can be obtained.

[0043] When integrating with the curved surface portion, the retardation film is heated and can be stretched as necessary. For example, by using a retardation film that satisfies the difference in the content of the above solvent and / or the dimensional change rate, the integration with the curved surface portion can be performed well. Specifically, when integrating with the curved surface portion, problems such as cracks occurring in the retardation film can be suppressed.

[0044] The shape of the optical film piece 5 in plan view is, for example, substantially circular, but is not limited thereto. Specifically, the optical film piece 5 may be substantially elliptical or may be a rounded rectangular shape. The optical film piece 5 has an upper surface and a lower surface facing each other. The upper surface and the lower surface of the optical film piece 5 have curved surfaces. In the illustrated example, the optical film piece 5 has a convex curvature on the lower surface side, the upper surface has a concave curved surface, and the lower surface has a convex curved surface. In the example shown in FIG. 3C, the optical film piece 5 is bonded to the concave surface of the lens L having the curved surface portion by its adhesive layer 3.

[0045] The optical film piece according to the embodiment of the present invention can include any suitable other optical member in addition to the retardation film. And the optical film piece can be used for any suitable display body. The optical film piece can be suitably used for, for example, VR goggles.

[0046] [Display system] FIG. 4 is a schematic diagram showing a schematic configuration of an example of a display system of a VR goggle, schematically illustrating the arrangement and shape of each component of the display system. The display system 10 includes a display element 12, a reflective polarizing member 14, a first lens unit 16, a half mirror 18, a first λ / 4 member 20, a second λ / 4 member 22, and a second lens unit 24. The reflective polarizing member 14 is disposed in front of the display surface 12a side of the display element 12 and can reflect the 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 member 14, and the half mirror 18 is disposed between the display element 12 and the first lens unit 16. The first λ / 4 member 20 is disposed on the optical path between the display element 12 and the half mirror 18, and the second λ / 4 member 22 is disposed on the optical path between the half mirror 18 and the reflective polarizing member 14.

[0047] The components disposed forward from the half mirror or the first lens unit (in the illustrated example, the half mirror 18, the first lens unit 16, the second λ / 4 member 22, the reflective polarizing member 14, and the second lens unit 24) may be collectively referred to as a lens unit (lens unit 4).

[0048] 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 emitted as a first linearly polarized light.

[0049] The first λ / 4 member 20 can convert the first linearly polarized light incident on the first λ / 4 member 20 into a first circularly polarized light. The first λ / 4 member 20 may be provided integrally with the display element 12.

[0050] The half mirror 18 transmits the light emitted from the display element 12 and reflects the light reflected by the reflective polarizing member 14 toward the reflective polarizing member 14. The half mirror 18 is provided integrally with the first lens unit 16.

[0051] The second λ / 4 member 22 can transmit the 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 unit 16.

[0052] The first circularly polarized light emitted from the first λ / 4 member 20 passes through the half mirror 18 and the first lens unit 16 and is converted into second linearly polarized light by the second λ / 4 member 22. The second linearly polarized light emitted from the second λ / 4 member 22 is reflected toward the half mirror 18 without passing through the reflective polarizing member 14. At this time, the polarization direction of the second linearly polarized light incident on the reflective polarizing member 14 is the same as the reflection axis of the reflective polarizing member 14. Therefore, the second linearly polarized light incident on the reflective polarizing member 14 is reflected by the reflective polarizing member 14.

[0053] The second linearly polarized light reflected by the reflective polarizing member 14 is converted into second circularly polarized light by the second λ / 4 member 22, and the second circularly polarized light emitted from the second λ / 4 member 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 member 22. The third linearly polarized light passes through the reflective polarizing member 14. At this time, the polarization direction of the third linearly polarized light incident on the reflective polarizing member 14 is the same as the transmission axis of the reflective polarizing member 14. Therefore, the third linearly polarized light incident on the reflective polarizing member 14 passes through the reflective polarizing member 14.

[0054] The light transmitted through the reflective polarizing member 14 passes through the second lens unit 24 (the absorption type polarizing member 28 and the second lens unit 24 described later) and enters the user's eye 26.

[0055] 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 arranged substantially parallel to each other or substantially perpendicular to each other. The angle formed by 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°, may be 42° to 48°, or may be about 45°. The angle formed by 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°, may be 42° to 48°, or may be about 45°.

[0056] The in-plane retardation Re(550) of the first λ / 4 member 20 is, for example, 100 nm to 190 nm, may be 110 nm to 180 nm, may be 130 nm to 160 nm, or may be 135 nm to 155 nm. The first λ / 4 member 20 preferably exhibits an inverse-dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light. Re(450) / Re(550) of the first λ / 4 member 20 is, for example, 0.75 or more and less than 1, and may be 0.8 or more and 0.95 or less.

[0057] The in-plane retardation Re(550) of the second λ / 4 member 22 is, for example, 100 nm to 190 nm, may be 110 nm to 180 nm, may be 130 nm to 160 nm, or may be 135 nm to 155 nm. The second λ / 4 member 22 preferably exhibits an inverse-dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light. Re(450) / Re(550) of the second λ / 4 member 22 is, for example, 0.75 or more and less than 1, and may be 0.8 or more and 0.95 or less.

[0058] The display system 10 may include an absorption-type polarizing member 28. The absorption-type polarizing member 28 can be arranged in front of the reflective polarizing member. The reflection axis of the reflective polarizing member 14 and the absorption axis of the absorption-type polarizing member 28 can be arranged substantially parallel to each other, and the transmission axis of the reflective polarizing member 14 and the transmission axis of the absorption-type polarizing member 28 can be arranged substantially parallel to each other. The reflective polarizing member 14 and the absorption-type polarizing member 28 may be integrated. The absorption-type polarizing member 28 can be used, for example, from the viewpoint of improving visibility in the above display system.

[0059] In the display system 10, a space may be formed between the first lens unit 16 and the second lens unit 24. In this case, the member disposed between the first lens unit 16 and the second lens unit 24 is preferably provided integrally with either the first lens unit 16 or the second lens unit 24. For example, the member disposed between the first lens unit 16 and the second lens unit 24 is integrated with either the first lens unit 16 or the second lens unit 24 via an adhesive layer. According to such a form, for example, the handleability of each member can be excellent. The adhesive layer may be formed of an adhesive or a pressure-sensitive adhesive. Specifically, the adhesive layer may be an adhesive layer or a pressure-sensitive adhesive layer. The thickness of the adhesive layer is, for example, 0.01 μm to 60 μm.

[0060] The optical film piece according to an embodiment of the present invention can include, for example, an optical member provided in the above display system. The optical film piece can include other members such as an adhesive layer for integrating adjacent optical members. The thickness of the optical film piece varies depending on, for example, the types and numbers of the included members, but is, for example, 50 μm to 400 μm.

[0061] For example, the optical film piece 5 can include the second λ / 4 member 22. Further, the optical film piece 5 may include the reflective polarizing member 14, or both the reflective polarizing member 14 and the absorptive polarizing member 28. And the optical film piece can be integrated with, for example, the first lens unit 16 or the second lens unit 24. Typically, it can be bonded to the first lens unit 16 or the second lens unit 24, which is an adherend, via an adhesive layer. For example, the first lens unit 16 shown in FIG. 4 has a curved surface portion and can correspond to the above optical component (lens L).

[0062] FIG. 5 is a schematic partial enlarged cross-sectional view showing a schematic configuration of an example of the optical film piece shown in FIG. 3C. The optical film piece 5 includes an adhesive layer 3, a retardation member 23, a reflective polarizing member 14, and an absorptive polarizing member 28 in this order. The retardation member 23 has a laminated structure of a second λ / 4 member 22 and a retardation film 1. The retardation film 1 is, for example, a positive C-plate showing a relationship of nz>nx = ny. By using such a retardation film 1, light leakage (for example, light leakage in an oblique direction) can be prevented. As shown in FIG. 5, in the retardation member 23, it is preferable that the second λ / 4 member 22 is located forward (upward in FIG. 5) than the positive C-plate 1. And the adhesive layer 3 can be disposed adjacent to the positive C-plate 1.

[0063] Although not shown, typically, the second λ / 4 member 22 and the retardation film 1 are laminated via an adhesive layer (for example, an adhesive layer). Also, the retardation member 23 and the reflective polarizing member 14 are laminated via an adhesive layer (for example, an adhesive layer), and the reflective polarizing member 14 and the absorptive polarizing member 28 are laminated via an adhesive layer (for example, an adhesive layer).

Example

[0064] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited by these examples. The thickness is a value measured by the following measurement method. <Thickness> For a thickness of 10 μm or less, it was measured using a scanning electron microscope (manufactured by JEOL Ltd., product name “JSM-7100F”). For a thickness exceeding 10 μm, it was measured using a digital micrometer (manufactured by Anritsu Corporation, product name “KC-351C”).

[0065] [Experimental Example 1] (Preparation of Dope) Into an autoclave equipped with a stirrer, a cooling pipe, a nitrogen inlet pipe, and a thermometer, 48 parts by weight of hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "METHOCEL 60SH-50"), 15601 parts by weight of distilled water, 8161 parts by weight of diisopropyl fumarate, 240 parts by weight of 3-ethyl-3-oxetanemethyl acrylate, and 45 parts by weight of t-butylperoxy pivalate as a polymerization initiator were added. After nitrogen bubbling was carried out for 1 hour, radical suspension polymerization was carried out by holding at 49 °C for 24 hours while stirring. Next, it was cooled to room temperature, and the suspension containing the produced polymer particles was centrifuged. The obtained polymer was washed twice with distilled water and twice with methanol, and then dried under reduced pressure to obtain a fumarate resin. The obtained fumarate resin was dissolved in a mixed solvent of methyl isobutyl ketone (MIBK, boiling point: 116 °C) and ethyl acetate (boiling point: 77 °C) to form a solution with a solid content concentration of 20% by weight. Further, 5 parts by weight of tributyl trimellitate was added as a plasticizer to 100 parts by weight of the fumarate resin to prepare a dope.

[0066] (Film formation) As a support, a biaxially stretched polyethylene terephthalate film with a thickness of 75 μm and a width of 1350 mm was prepared. The wound body of the support was set at the feeding part of the film forming apparatus, the support was fed out, and while being conveyed downstream, the above dope was applied onto the support so that the dried film thickness would be 18 μm, and it was dried at 145 °C for 40 seconds.

[0067] (Annealing) After drying, a surface protection film (E-MASK RP series manufactured by Nitto Denko Corporation) in which an adhesive layer with a thickness of 5 μm was formed on a PET-based film with a thickness of 38 μm was laminated on the surface of the formed film, and then the support was peeled off from the film. Annealing treatment was performed in a state where only one side of the film was protected by the surface protection film. Specifically, the film laminated with the surface protection film was placed in an environment at a temperature (annealing temperature) of 50 °C for 15 seconds. Thus, a retardation film was obtained.

[0068] [Experimental Example 2] A retardation film was obtained in the same manner as in Experimental Example 1, except that the annealing temperature was set to 70°C during annealing.

[0069] [Experimental Example 3] A retardation film was obtained in the same manner as in Experimental Example 1, except that the annealing temperature was set to 90°C during annealing.

[0070] [Experimental Example 4] A retardation film was obtained in the same manner as in Experimental Example 1, except that the annealing temperature was set to 120°C during annealing.

[0071] [Experimental Example 5] A retardation film was obtained in the same manner as in Experimental Example 1, except that the annealing temperature was set to 140°C during annealing.

[0072] [Experimental Example 6] A retardation film was obtained in the same manner as in Experimental Example 1, except that the annealing temperature was set to 160°C during annealing.

[0073] [Experimental Example 7] A retardation film was obtained in the same manner as in Experimental Example 1, except that the annealing temperature was set to 180°C during annealing.

[0074] [Experimental Example 8] A retardation film was obtained in the same manner as in Experimental Example 1, except that the annealing temperature was set to 200°C during annealing.

[0075] [Experimental Example 9] A retardation film was obtained in the same manner as in Experimental Example 1, except that the film was annealed without laminating a surface protection film (without protecting the film with a protective member) and the annealing temperature was set to 200°C.

[0076] [Experimental Example 10] A retardation film was obtained in the same manner as in Experimental Example 1, except that annealing was not performed.

[0077] The following evaluations were performed on the retardation films of each experimental example. The evaluation results are summarized in Table 1. <Evaluation> 1. Retardation value Using a retardation / elliptical polarization measuring device (parallel Nicol rotation type, manufactured by Oji Scientific Instruments Co., Ltd., product name "KOBRA-WPR"), the retardation value at a wavelength of 587 nm was measured at 23°C. Regarding the in-plane retardation Re(587), measurements were performed at 10 arbitrary locations on a retardation film with a size of 50 mm × 50 mm, and the average value was calculated. Regarding the retardation Rth(587) in the thickness direction, measurements were performed at 6 arbitrary locations on a retardation film with a size of 50 mm × 50 mm, and the average value was calculated. 2. Solvent content (residual solvent amount) The measurement sample (a retardation film cut into a size of 10 mm × 50 mm) was placed in a 20 mL vial and sealed. This vial was heated at 150°C for 30 minutes, and 1.0 mL of the heated gas (sample gas) was injected into a gas chromatograph (GC) measuring device using a headspace autosampler (HSS). The settings of the HSS and GC were as follows. Based on the obtained gas chromatogram, the amount of gas generated from the measurement sample was determined as the solvent content (residual solvent amount) by applying a calibration curve prepared in advance. The calibration curve was prepared by diluting MIBK with acetone to prepare a standard sample with a certain concentration, enclosing 1 μL of the standard sample in a 20 mL headspace vial, heating it in the same manner as the measurement sample, injecting 1 mL of the gas phase part into the GC, and creating it from the GC peak area of the standard sample and the prepared concentration. · HSS: Manufactured by Shimadzu Corporation, model "HS-20" Heating time: 30 minutes Pressurization time: 0.20 minutes Loop filling time: 0.20 minutes Loop equilibration time: 0.05 minutes Injection time: 0.5 minutes Sample loop temperature: 160°C Transfer line temperature: 200°C · GC device: Manufactured by Shimadzu Corporation, model "GC-2030" Column: Agilent Technologies capillary column "HP-1" (model number 19091Z-233, inner diameter 0.25 mm, length 30 m, film thickness 1.0 μm) Column temperature: 300 °C (heated from 40 °C to 120 °C at a rate of 10 °C / min, then continued to be heated to 300 °C at a rate of 20 °C / min and held for 5 minutes) Column pressure: 75 kPa (constant flow mode) Carrier gas: Nitrogen (5.0 mL / min) Inlet: Split (split ratio is 10:1) Inlet temperature: 250 °C Detector: FID Detector temperature: 250 °C 3. Dimensional change rate The obtained phase difference film was cut into a size of 25 mm in length and 4 mm in width to obtain a measurement sample. The ranges of 2.5 mm from both ends in the length direction of the measurement sample were checked, and using a thermomechanical analyzer (TMA, "HC-TMA4000SA" manufactured by NETSCH), the dimensional change amount in the length direction due to heating was measured by the tensile method, and the dimensional change rate (%) was calculated from the following formula. Dimensional change rate = Dimensional change amount in the length direction / Dimensional length in the length direction before heating × 100 Here, the dimensional change amount in the length direction is the value obtained by subtracting the dimension before heating from the dimension during heating, and the dimensional length in the length direction before heating is 20 mm. The measurement conditions (heating conditions) are as follows. · Heating condition 1: Placed in an environment with a temperature of 65 °C and a relative humidity of 10% for 60 minutes · Heating condition 2: Placed in an environment with a temperature of 65 °C and a relative humidity of 90% for 60 minutes · Atmosphere gas: Nitrogen (200 mL / min) · Measurement load: 2 g · Humidity increase rate: 5% / min · Heating rate: 0.5 °C / min The value obtained by subtracting the dimensional change rate at the time (0 minutes later) when reaching the predetermined temperature and relative humidity shown in the above heating conditions from the dimensional change rate after maintaining for 60 minutes (60 minutes later) after reaching the predetermined temperature and relative humidity shown in the above heating conditions (the difference in dimensional change rate) is shown in Table 1. 4. Surface smoothness Using a phase-shifting laser interferometer (manufactured by Zygo, product name "DynaFiz"), the surface smoothness of the obtained phase difference film and the phase difference film after being placed in an environment of 65°C and 90% relative humidity for 240 hours was measured. Specifically, the measurement sample was placed on a measurement table with a vibration isolator, and using a laser with a single wavelength (wavelength 633 nm), it was interfered with a reference device with guaranteed flatness, and the relative displacement within a predetermined region (a circle with a diameter of 50 mm) was measured. Regarding the analysis, a value obtained by doubling the angular index "Slope magnitude RMS" (corresponding to 2σ) obtained by extracting frequency values from 0.1 / mm to 1 / mm was defined as the surface smoothness (unit: arcmin). In addition, measurements were performed at six arbitrary locations on a phase difference film with a size of 45 mm × 50 mm, and the average value was calculated. The difference in surface smoothness shown in Table 1 is the value obtained by subtracting the surface smoothness (average value of six arbitrary locations) of the phase difference film before being placed in an environment of 65°C and 90% relative humidity from the surface smoothness (average value of six arbitrary locations) of the phase difference film after being placed in an environment of 65°C and 90% relative humidity for 240 hours. 5. Durability The obtained phase difference film (phase difference film with a surface protection film laminated) was cut into a size of 45 mm × 50 mm. Then, after corona treatment was performed on the surface of the phase difference film on the side where the surface protection film was not laminated, an adhesive layer with a thickness of 12 μm was formed, and the phase difference film with the surface protection film laminated via the adhesive layer was laminated to a glass plate. After that, the surface protection film was peeled off from the phase difference film, and the phase difference film laminated to the glass plate was observed with an optical microscope after being placed in an environment of 80°C (oven) and an environment of 65°C and 90% relative humidity for 240 hours. Specifically, the number of cracks (pieces / 45 mm × 50 mm) generated in the phase difference film with a size of 45 mm × 50 mm was counted.

[0078]

Table 1

[0079] Observation photos (10x objective lens) of the retardation film after the durability test (80 °C, 240 hours) in Experimental Example 10 are shown in Fig. 6, and observation photos (10x objective lens) of the retardation film after the durability test (80 °C, 240 hours) in Experimental Example 4 are shown in Fig. 7. Further, observation photos (10x objective lens) of the retardation film after the durability test (65 °C, 90% RH, 240 hours) in Experimental Example 10 are shown in Fig. 8.

[0080] As shown in Fig. 6, after the durability test (80 °C, 240 hours), one crack with a length of about 2 mm was confirmed in the retardation film of Experimental Example 10. As shown in Fig. 7, after the durability test (80 °C, 240 hours), one crack with a length of about 1.3 mm was confirmed in the retardation film of Experimental Example 4. As shown in Fig. 8, after the durability test (65 °C, 90% RH, 240 hours), many cracks with lengths ranging from 200 μm to 2 mm or more were confirmed in the retardation film of Experimental Example 10. The cracks generated in each test originated from the surface of the retardation film on the adhesive layer side, and among the confirmed cracks, there were also cracks that penetrated from the surface on the adhesive layer side to the other surface (exposed surface).

[0081] The present invention is not limited to the above-described embodiments, and various modifications are possible. For example, it can be replaced with a configuration that is substantially the same as the configuration shown in the above-described embodiments, a configuration that exhibits the same operational effects, or a configuration that can achieve the same purpose.

Industrial Applicability

[0082] The optical film piece according to the embodiment of the present invention can be used, for example, in a display body such as a VR goggle.

Explanation of Reference Numerals

[0083] 1 Retardation film 1a First main surface 1b Second main surface 2 Laminated portion 3 Adhesive layer 4 Workpiece (optical laminate) 5 Optical film piece 10 Display system 12 Display element 14 Reflective polarizing member 16 First lens unit 18 Half mirror 20 First λ / 4 member 22 Second λ / 4 member 23 Retardation member 24 Second lens unit 28 Absorptive type 30 Support 31 Film 32 Surface protection film

Claims

1. A retardation film having a first main surface and a second main surface facing each other and containing a resin having negative birefringence, having zero cracks with a length of 200 μm or more when heated at 80° C. for 240 hours, The retardation film.

2. The retardation film according to claim 1, wherein the solvent content is less than 3200 μg / g.

3. The retardation film according to claim 1, wherein the solvent content exceeds 30 μg / g.

4. The retardation film according to claim 1, wherein the difference in the dimensional change rate due to heating is less than 0.03%.

5. The retardation film according to claim 1, wherein the difference in the dimensional change rate due to heating is -0.02% or more.

6. The retardation film according to claim 1, wherein the change amount of surface smoothness by placing in an environment of 65° C. and 90% relative humidity for 240 hours is 0.04 arcmin or less.

7. The retardation film according to claim 1, wherein the resin having negative birefringence contains a fumarate resin.

8. The retardation film according to claim 1, wherein the refractive index characteristics exhibit a relationship of nz > nx = ny.

9. An optical laminate including the retardation film according to claim 1.

10. The optical laminate according to claim 9, including an adhesive layer disposed adjacent to the retardation film.

11. A method for manufacturing an optical film piece, including heating the optical laminate according to claim 9 and integrating it with a component having a curved surface portion.

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