Retardation film manufacturing method

Abstract

The present invention provides a retardation film with which the weight reduction of VR goggles can be satisfactorily achieved while improving visibility. This retardation film manufacturing method includes turning a forming material that contains a resin having negative birefringence into the shape of a film, and annealing the formed film. The film formation is performed by coating a support body with a resin solution containing the forming material, and the annealing temperature is equal to or higher than the boiling point T(°C) of a solvent contained in the resin solution.

Description

Method for manufacturing retardation film

[0001] The present invention relates to a method for producing a retardation film.

[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 polarizing components and phase difference components are generally used to realize image display and improve image display performance (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. Since the use of VR goggles in various situations is being considered, there is a demand for lighter weight, improved visibility, and the like.

[0004] Japanese Patent Application Laid-Open No. 2021-103286

[0005] While the weight reduction of the VR goggles can be achieved by, for example, thinning the lenses used in the VR goggles, there is also a need for the development of optical components suitable for display systems using thin lenses.

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

[0007] 1. A method for producing a retardation film according to an embodiment of the present invention includes forming a film from a forming material containing a resin having negative birefringence, and annealing the formed film, wherein the film formation is carried out by applying a resin solution containing the forming material to a support, and the annealing temperature is equal to or higher than the boiling point T (°C) of the solvent contained in the resin solution. 2. In the production method described in 1 above, the annealing temperature may be 130°C or higher. 3. In the production method described in 1 or 2 above, the annealing time may be 15 seconds or longer. 4. In the annealing of the production method described in any one of 1 to 3 above, one main surface of the film may be protected by a protective member, and the other main surface may be exposed. 5. The production method described in 4 above may include, before the annealing, laminating a surface protective film as the protective member to the film, and peeling the support from the film. 6. In the production method described in any one of 1 to 5 above, the resin having negative birefringence may include a fumaric acid ester-based resin. 7. In the manufacturing method according to any one of the above items 1 to 6, the retardation film may have refractive index characteristics that satisfy the relationship nz>nx=ny.

[0008] According to the retardation film according to the embodiment of the present invention, it is possible to effectively achieve a reduction in the weight of VR goggles while improving visibility.

[0009] 1 is a schematic cross-sectional view showing an outline of a configuration of a retardation film according to one embodiment of the present invention. FIG. 2 is a view showing an example of a method for manufacturing a retardation film according to one embodiment of the present invention. FIG. 3 is a view continuing from FIG. 2A. FIG. 3B is a view continuing from FIG. 2C. FIG. 4 is a view showing an example of a method for integrating an optical laminate including a retardation film with a component. FIG. 4 is a view continuing from FIG. 3A. FIG. 4 is a view continuing from FIG. 3B. FIG. 5 is a schematic view showing an outline of a configuration of an example of a display system for VR goggles. FIG. 5 is a schematic partially enlarged cross-sectional view showing an outline of a configuration of an example of an optical film piece shown in FIG. 3C. FIG. 6 is an observation photograph (10x objective lens) of a retardation film after a durability test (80°C, 240 hours) of Experimental Example 10. FIG. 7 is an observation photograph (10x objective lens) of a retardation film after a durability test (80°C, 240 hours) of Experimental Example 4. FIG. 8 is an observation photograph (10x objective lens) of a retardation film after a durability test (65°C, 90% RH, 240 hours) of Experimental Example 10.

[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. 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 redundant explanations may be omitted.

[0011] (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 maximum (i.e., the slow axis direction), "ny" is the refractive index in the in-plane direction perpendicular to the slow axis (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-Plane Retardation (Re) "Re(λ)" is the in-plane retardation measured with light having a wavelength of λ nm at 23°C. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 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) Thickness Direction Retardation (Rth) "Rth(λ)" is the retardation in the thickness direction measured with light having a wavelength of λ nm at 23°C. For example, "Rth(550)" is the retardation in the thickness direction measured with light having a wavelength of 550 nm at 23°C. Rth(λ) is calculated by the formula: Rth(λ) = (nx - nz) x 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 an angle is mentioned in this specification, the angle includes both clockwise and counterclockwise angles relative to the reference direction. Therefore, for example, "45°" means ±45°.

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

[0013] The retardation film 1 is made of, for example, a resin film. In this case, the retardation film 1 may contain resin. The retardation film 1 has a first main surface 1a and a second main surface 1b that face 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, the retardation film 1 preferably has zero cracks with a length of 200 μm or more that occur when heated at a temperature of 80 ° C. for 240 hours. For example, the presence or absence of cracks can be evaluated within a 45 mm × 50 mm range. Furthermore, for example, the retardation film 1 preferably has five cracks with a length of 200 μm or more that occur when placed in an environment of 65 ° C. and 90% relative humidity for 240 hours, more preferably three cracks per 45 mm × 50 mm or less, and even more preferably one crack per 45 mm × 50 mm or less. It is particularly preferable that no such cracks occur.

[0016] The number and length of cracks that may occur in the retardation film 1 can be confirmed, for example, by observation using 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 may be used alone or in combination of two or more. Among these, methyl isobutyl ketone is preferably used.

[0018] The solvent content of the retardation film 1 is, for example, less than 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 difference in dimensional change rate of the retardation film 1 due to heating is, for example, less than 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 of the retardation film 1 due to heating 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, for example, placing the measurement sample in a heated environment at a temperature of 65° C. and a relative humidity of 10% for 60 minutes and measuring the change in dimension before and after heating.

[0021] The surface smoothness of the first main surface 1a and the second main 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. The change in surface smoothness caused by placing the retardation film 1 in an environment of 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 irradiated light on the surface of the object.

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

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

[0024] The retardation film 1 (resin film) may further contain any appropriate additives as necessary. Specific examples of additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, UV absorbers, flame retardants, colorants, antistatic agents, compatibilizers, crosslinking agents, thickeners, etc. The type and content of the additives may be appropriately set depending on the purpose. The content of the additives 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 whose refractive index characteristics can exhibit the relationship nz>nx=ny (so-called positive C plate). In this case, the thickness direction retardation Rth(550) of the retardation film 1 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" includes 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 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, and 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 Science Research Institute).

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

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

[0029] 2A shows a state in which the above-mentioned forming material is formed into a film on a support (e.g., a base film such as a polyester film) 30 to form a film 31. The film is formed, for example, by applying a resin solution containing the above-mentioned forming material to the support 30 and drying the coated film. When the resin solution dries on the support 30, volume shrinkage generates stress, and the polymer molecular chains tend to orient in the in-plane direction. When a resin that has high birefringence expression and negative intrinsic birefringence is used, a film 31 with large thickness-direction birefringence can be formed on the support 30 due to the shrinkage action during drying.

[0030] Examples of solvents 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 solids concentration of the resin solution is, for example, 16% by weight to 20% by weight.

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

[0032] The formed film 31 can be used as a positive C-plate as is, for example, but it is preferable that the film 31 be annealed. Annealing can, for example, satisfy the solvent content and / or the difference in dimensional change rate, and provide a retardation film 1 with excellent durability. 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 viewpoint of preventing breakage, it is preferable that the surface of the film 31 be 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 this embodiment, for example, a retardation film 1 that satisfies the solvent content and / or the difference in dimensional change rate can be obtained. Furthermore, 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, a surface protection film 32 is attached as a protective member to the upper surface 31a of the film 31, and then, 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 in a state where the surface protection film 32 is attached as a protective member to the upper surface 31a of the film 31 and the lower surface 31b is exposed.

[0034] The support 30 used in 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 tends to easily get trapped between the support 30 and the film 31, making gaps more likely to form. If annealing is performed with a gap between the support 30 and the film 31, the gap may leave a mark, damaging the appearance of the resulting retardation film 1. By using a protective member separate 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 a pressure-sensitive adhesive layer 32b. Materials for forming the base film include polyester-based polymers such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBT); cellulose-based polymers such as diacetyl cellulose and triacetyl cellulose; polycarbonate-based polymers; (meth)acrylic polymers such as polymethyl methacrylate; and cycloolefin-based 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 pressure-sensitive adhesive layer is, for example, 5 μm to 15 μm. Furthermore, 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 can be obtained that satisfies the solvent content and / or the difference in dimensional change rate. The annealing conditions (e.g., annealing temperature, annealing time) can be set to any appropriate conditions. For example, the annealing temperature can be set depending on the solvent contained in the resin solution. Specifically, the annealing temperature is preferably equal to or higher than the boiling point T (°C) of the solvent contained in the resin solution and equal to or lower than T + 100°C, and may be equal to or higher than T + 20°C, or may be equal to or higher than T + 70°C. The annealing temperature is, for example, equal to or higher than 50°C and equal to or lower than 250°C, and may be equal to or higher than 120°C, 130°C, or 140°C. Furthermore, for example, the annealing temperature can be set higher than the drying temperature. The annealing time is, for example, 5 to 30 seconds, preferably equal to or higher than 15 seconds.

[0037] The retardation film 1 can be used by being integrated with, for example, 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 stretched as necessary. For example, when integrating the retardation film 1 into a curved surface portion, the retardation film 1 can be heated and stretched as necessary. Note that the retardation film 1 can typically be integrated into 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 can be obtained by integrating an optical laminate including the retardation film 1 with a curved surface portion of an optical component. A pressure-sensitive adhesive (pressure-sensitive adhesive layer) is typically used for integration.

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

[0040] 3A shows a state in which a work (optical laminate) 4 is prepared by providing a pressure-sensitive adhesive layer 3 on a laminate 2 including a retardation film, and the work 4 is placed above an optical component (lens) L, which is an adherend. Note that details of the laminate 2 are omitted in FIG. 3 .

[0041] The lens L is, for example, circular in plan view and concave 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 workpiece 4 can easily become 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 is in a state where it is easily deformed, the entire surface of the workpiece 4 is bonded to the lens L by any appropriate method (for example, by utilizing a pressure difference), as shown in Fig. 3B. Thereafter, as shown in Fig. 3C, unnecessary portions of the workpiece 4 (for example, portions that do not overlap with the lens L in a plan view) are removed, thereby obtaining the optical film piece 5.

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

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

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

[0046] [Display System] Figure 4 is a schematic diagram showing the general configuration of an example of a display system for VR goggles, and schematically illustrates 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.

[0047] The half mirror or the components arranged forward from the first lens unit (in the illustrated example, the half mirror 18, first lens unit 16, second λ / 4 member 22, reflective polarizing member 14, and second lens unit 24) may be collectively referred to as the 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 12 a for displaying an image. The light emitted from the display surface 12 a passes through, for example, a polarizing member that may be included in the display element 12, and is converted into 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 the 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 back toward the reflective polarizing member 14. The half mirror 18 is provided integrally with the first lens portion 16.

[0051] 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.

[0052] The first circularly polarized light output from the first λ / 4 member 20 passes through the half mirror 18 and the first lens portion 16, and is converted into the second linearly polarized light by the second λ / 4 member 22. The second linearly polarized light output 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 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 direction 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.

[0054] The light transmitted through the reflective polarizing member 14 passes through the second lens portion 24 (the absorptive polarizing member 28 and the second lens portion 24, which will be described later), and enters the eye 26 of the user.

[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 disposed approximately parallel to each other or approximately perpendicular to each other. The angle 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 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°.

[0056] The in-plane retardation Re(550) of the first λ / 4 member 20 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. 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. The Re(450) / Re(550) of the first λ / 4 member 20 may be, for example, 0.75 or more and less than 1, or 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, or may be 110 nm to 180 nm, 130 nm to 160 nm, or 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. The Re(450) / Re(550) of the second λ / 4 member 22 may be, for example, 0.75 or more and less than 1, or 0.8 or more and 0.95 or less.

[0058] The display system 10 may include an absorptive polarizing element 28. The absorptive polarizing element 28 may be disposed in front of the reflective polarizing element. The reflection axis of the reflective polarizing element 14 and the absorption axis of the absorptive polarizing element 28 may be disposed approximately parallel to each other, and the transmission axis of the reflective polarizing element 14 and the transmission axis of the absorptive polarizing element 28 may be disposed approximately parallel to each other. The reflective polarizing element 14 and the absorptive polarizing element 28 may be integrated together. The absorptive polarizing element 28 may be used in the above-described display system, for example, from the viewpoint of improving visibility.

[0059] In the display system 10, a space may be formed between the first lens portion 16 and the second lens portion 24. In this case, it is preferable that the member disposed between the first lens portion 16 and the second lens portion 24 is integrally formed with either the first lens portion 16 or the second lens portion 24. For example, the member disposed between the first lens portion 16 and the second lens portion 24 is integrated with either the first lens portion 16 or the second lens portion 24 via an adhesive layer. This configuration may provide, for example, excellent ease of handling of each member. 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 the embodiment of the present invention may include, for example, an optical element provided in the display system. The optical film piece may also include other elements such as an adhesive layer for integrating adjacent optical elements. The thickness of the optical film piece varies depending on the type and number of elements included, but is, for example, 50 μm to 400 μm.

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

[0062] FIG. 5 is a schematic, partially enlarged cross-sectional view showing the general configuration of an example of the optical film piece shown in FIG. 3C . The optical film piece 5 includes, in this order, a pressure-sensitive adhesive layer 3, a retardation member 23, a reflective polarizing member 14, and an absorptive polarizing member 28. 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 that satisfies the relationship nz > nx = ny. Using such a retardation film 1 can prevent light leakage (e.g., light leakage in oblique directions). As shown in FIG. 5 , in the retardation member 23, the second λ / 4 member 22 is preferably located forward (upper in FIG. 5 ) than the positive C plate 1. Then, a pressure-sensitive 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). Furthermore, the retardation member 23 and the reflective polarizing member 14 are laminated via an adhesive layer (for example, a pressure-sensitive adhesive layer), and the reflective polarizing member 14 and the absorptive polarizing member 28 are laminated via an adhesive layer (for example, a pressure-sensitive adhesive layer).

[0064] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The thickness values ​​are measured by the following measurement method. <Thickness> Thicknesses of 10 μm or less were measured using a scanning electron microscope (manufactured by JEOL Ltd., product name "JSM-7100F"). Thicknesses exceeding 10 μm were measured using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C").

[0065] Experimental Example 1 (Dope Preparation) 48 parts by weight of hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "Metolose 60SH-50"), 15,601 parts by weight of distilled water, 8,161 parts by weight of diisopropyl fumarate, 240 parts by weight of 3-ethyl-3-oxetanylmethyl acrylate, and 45 parts by weight of a polymerization initiator, t-butyl peroxypivalate, were placed in an autoclave equipped with a stirrer, a condenser, a nitrogen inlet tube, and a thermometer. Nitrogen bubbling was performed for 1 hour, and then the mixture was stirred at 49°C for 24 hours to carry out radical suspension polymerization. The mixture was then 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 ester-based resin. The obtained fumarate ester-based resin was dissolved in a mixed solvent of methyl isobutyl ketone (MIBK, boiling point: 116°C) and ethyl acetate (boiling point: 77°C) to prepare a solution with a solid content of 20% by weight. Further, 5 parts by weight of tributyl trimellitate as a plasticizer was added to 100 parts by weight of the fumarate ester-based resin to prepare a dope.

[0066] (Film Formation) A biaxially stretched polyethylene terephthalate film having a thickness of 75 μm and a width of 1,350 mm was prepared as a support. The roll of the support was set in the unwinding section of a film-forming apparatus, and while the support was unwound and transported downstream, the dope was applied onto the support to a film thickness of 18 μm after drying, and dried at 145° C. for 40 seconds.

[0067] (Annealing) After drying, a surface protection film (E-MASK RP series manufactured by Nitto Denko Corporation) consisting of a 38 μm thick PET film with a 5 μm thick adhesive layer formed thereon was laminated to the surface of the formed film, and then the support was peeled off from the film. The film was subjected to an annealing treatment while only one side of the film was protected by the surface protection film. Specifically, the film with the surface protection film laminated thereon was placed in an environment at a temperature (annealing temperature) of 50° C. for 15 seconds. In this way, 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 70°C.

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

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

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

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

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

[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.

[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 bonding a surface protective film to the 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 The retardation value at a wavelength of 587 nm was measured at 23°C using a retardation / ellipsoidal polarization measurement device (parallel Nicol rotation type, manufactured by Oji Scientific Instruments, product name "KOBRA-WPR"). The in-plane retardation Re(587) was measured at 10 arbitrary positions on a retardation film measuring 50 mm x 50 mm, and the average value was calculated. The thickness direction retardation Rth(587) was measured at 6 arbitrary positions on a retardation film measuring 50 mm x 50 mm, and the average value was calculated. 2. Solvent Content (Remaining Solvent Amount) The measurement sample (retardation film cut into a size of 10 mm x 50 mm) was placed in a 20 mL vial and sealed. The 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) measurement device using a headspace autosampler (HSS). The settings for 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 (remaining solvent amount) by applying a calibration curve prepared in advance. The calibration curve was prepared by diluting MIBK with acetone to prepare a standard of a certain concentration, sealing 1 μL of the standard in a 20 mL headspace vial, heating it in the same manner as the measurement sample, and then injecting 1 mL of the gas phase portion into the GC. The calibration curve was created from the GC peak area of ​​the standard and the prepared concentration.HSS: 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 apparatus: 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 10°C / min, then heated to 300°C at 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 10:1) Inlet temperature: 250°C Detector: FID Detector temperature: 250°C 3. Dimensional change rate The obtained retardation film was cut into a size of 25 mm length x 4 mm width to obtain a measurement sample. A 2.5 mm range from each end of the measurement sample in the longitudinal direction was chucked, and the dimensional change in the longitudinal direction due to heating was measured by a tensile method using a thermomechanical analyzer (TMA, "HC-TMA4000SA" manufactured by NETSCH Corporation), and the dimensional change rate (%) was calculated using the following formula: Dimensional change rate = dimensional change in the longitudinal direction / longitudinal dimension before heating × 100 Here, the dimensional change in the longitudinal direction is the value obtained by subtracting the dimension before heating from the dimension during heating, and the longitudinal dimension 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 Atmospheric gas: Nitrogen (200 mL / min) Measurement load: 2 g Moisture rise rate: 5% / min Temperature rise rate: 0.5°C / min Table 1 shows the value (difference in dimensional change rate) obtained by subtracting the dimensional change rate at the time when the specified temperature and relative humidity shown in the heating conditions above were reached (0 minutes later) from the dimensional change rate after the specified temperature and relative humidity shown in the heating conditions above were maintained for 60 minutes after reaching the specified temperature and relative humidity shown in the heating conditions above (60 minutes later).4. Surface Smoothness Using a phase-shifting laser interferometer (manufactured by Zygo, product name "DynaFiz"), the surface smoothness of the obtained retardation film and the retardation film after 240 hours in an environment of 65 ° C and 90% relative humidity was measured. Specifically, the measurement sample was placed on a measurement table with a vibration-proof table, and a single-wavelength (633 nm) laser was used to interfere with a standard with guaranteed flatness, and the relative displacement within a predetermined area (circle with a diameter of 50 mm) was measured. For analysis, the value obtained by doubling the "Slope magnitude RMS" angle index obtained by extracting frequency values ​​from 0.1 / mm to 1 / mm (equivalent to 2σ) was defined as the surface smoothness (unit: arcmin). Measurements were performed at six arbitrary locations on a 45 mm x 50 mm retardation film, and the average value was calculated. The difference in surface smoothness shown in Table 1 is the surface smoothness (average value of any six points) of the retardation film after 240 hours in an environment of 65 ° C and 90% relative humidity minus the surface smoothness (average value of any six points) of the retardation film before 240 hours in an environment of 65 ° C and 90% relative humidity. 5. Durability The obtained retardation film (retardation film with a surface protective film attached) was cut into a size of 45 mm x 50 mm. Then, a corona treatment was performed on the surface of the retardation film on the side where the surface protective film was not attached, and then a 12 μm thick adhesive layer was formed, and the retardation film with the surface protective film attached via the adhesive layer was attached to a glass plate. Thereafter, the surface protective film was peeled off from the retardation film, and the retardation film attached to the glass plate was placed in an environment of 80 ° C (oven) and an environment of 65 ° C and 90% relative humidity for 240 hours, and then the retardation film was observed with an optical microscope. Specifically, the number of cracks (pcs / 45 mm×50 mm) that occurred in a retardation film having a size of 45 mm×50 mm was counted.

[0078]

[0079] An observation photograph (10x objective lens) of the retardation film after the durability test (80°C, 240 hours) of Experimental Example 10 is shown in Fig. 6, and an observation photograph (10x objective lens) of the retardation film after the durability test (80°C, 240 hours) of Experimental Example 4 is shown in Fig. 7. Also, an observation photograph (10x objective lens) of the retardation film after the durability test (65°C, 90% RH, 240 hours) of Experimental Example 10 is 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 of 200 μm to 2 mm or more were confirmed in the retardation film of Experimental Example 10. The cracks that occurred in each test occurred from the pressure-sensitive adhesive layer side of the retardation film, and some of the confirmed cracks penetrated from the pressure-sensitive adhesive layer side to the other side (exposed surface).

[0081] 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.

[0082] Optical film pieces according to embodiments of the present invention can be used in displays such as VR goggles, for example.

[0083] REFERENCE SIGNS LIST 1 Retardation film 1a First main surface 1b Second main surface 2 Laminated portion 3 Pressure-sensitive adhesive layer 4 Work (optical laminate) 5 Optical film piece 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 23 Retardation member 24 Second lens portion 28 Absorption type 30 Support 31 Film 32 Surface protective film

Claims

1. A method for producing a retardation film, comprising: forming a film from a forming material containing a resin having negative birefringence; and annealing the formed film, wherein the film is formed by applying a resin solution containing the forming material to a support, and the annealing temperature is equal to or higher than the boiling point T (°C) of a solvent contained in the resin solution.

2. The method for producing a retardation film according to claim 1, wherein the annealing temperature is 130° C. or higher.

3. The method for producing a retardation film according to claim 1, wherein the annealing time is 15 seconds or more.

4. The method for producing a retardation film according to claim 1, wherein, during the annealing, one of the main surfaces of the film is protected by a protective member, and the other main surface is exposed.

5. The method for producing a retardation film according to claim 4, further comprising the steps of: laminating a surface protective film as the protective member to the film before the annealing; and peeling off the support from the film.

6. The method for producing a retardation film according to claim 1, wherein the resin having negative birefringence includes a fumaric acid ester resin.

7. The method for producing a retardation film according to claim 1, wherein the retardation film has refractive index characteristics that satisfy the relationship nz>nx=ny.

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