JP7846663B2 - Method for manufacturing phase difference films - Google Patents

Description

This invention relates to a method for manufacturing a phase difference film.

Image display devices, such as liquid crystal displays and electroluminescent (EL) displays (e.g., organic EL displays), are rapidly becoming widespread. In image display devices, optical components such as polarizing members and phase difference members are generally used to realize image display and improve image display performance (see, for example, Patent Document 1).

In recent years, new applications for image display devices have been developed. For example, goggles with displays for realizing Virtual Reality (VR) (VR goggles) are beginning to be commercialized. Since VR goggles are being considered for use in various situations, there is a demand for lighter weight and improved visibility.

Japanese Patent Publication No. 2021-103286

The weight reduction of the VR goggles mentioned above can be achieved, for example, by making the lenses used in the VR goggles thinner. On the other hand, the development of optical components suitable for display systems using thin lenses is also desired.

In view of the above, the primary objective of the present invention is to provide a phase difference film that can effectively achieve weight reduction of VR goggles while improving visibility.

1. A method for manufacturing a phase difference film according to an embodiment of the present invention comprises 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 coating a support with a resin solution containing the forming material, and the annealing temperature is equal to or greater than the boiling point T (°C) of the solvent contained in the resin solution.
2. In the manufacturing method described in item 1 above, the annealing temperature may be 130°C or higher.
3. In the manufacturing method described in 1 or 2 above, the annealing time may be 15 seconds or more.
4. In the annealing process described in any of items 1 to 3 above, one main surface of the film may be protected by a protective member, while the other main surface may be exposed.
5. The manufacturing method described in item 4 above may include laminating a surface protective film as the protective member to the film before annealing, and peeling the support from the film.
6. In the manufacturing method described in any of items 1 to 5 above, the resin having negative birefringence may include a fumarate ester resin.
7. In the manufacturing method described in any of items 1 to 6 above, the phase difference film may have refractive index characteristics that satisfy the relationship nz > nx = ny.

According to the phase difference film of the present invention, it is possible to achieve a significant reduction in the weight of VR goggles while improving visibility.

This is a schematic cross-sectional view showing the general configuration of a phase difference film according to one embodiment of the present invention. This figure shows an example of a method for manufacturing a phase difference film according to one embodiment of the present invention. This figure follows Figure 2A. This figure follows Figure 2B. This figure follows Figure 2C. This figure shows an example of a method for integrating an optical laminate containing a phase difference film into a component. This figure follows Figure 3A. This figure follows Figure 3B. This is a schematic diagram showing the general configuration of an example of a VR goggle display system. Figure 3C is a schematic, partially enlarged cross-sectional view showing the general configuration of an example of an optical film piece. This is an observation photograph (10x objective lens) of the phase contrast film after the durability test (80°C, 240 hours) of Experimental Example 10. This is an observation photograph (10x objective lens) of the phase contrast film after the durability test (80°C, 240 hours) in Experimental Example 4. This is an observation photograph (10x objective lens) of the phase contrast film after the durability test (65°C, 90% RH, 240 hours) of Experimental Example 10.

The embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. While the drawings may schematically represent the width, thickness, shape, etc., of parts in order to clarify the explanation, these are merely examples and do not limit the interpretation of the present invention. Furthermore, in the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant explanations may be omitted.

(Definitions 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 where the refractive index is maximum in the plane (i.e., the slow phase axis direction), "ny" is the refractive index in the direction perpendicular to the slow phase axis in the plane (i.e., the fast phase 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 λnm at 23°C. For example, "Re(550)" is the in-plane phase difference measured with light of wavelength 550nm at 23°C. Re(λ) can be calculated using 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 λnm at 23°C. For example, "Rth(550)" is the phase difference in the thickness direction measured with light of wavelength 550nm at 23°C. Rth(λ) can be calculated using the formula: Rth(λ) = (nx - nz) × d, where d (nm) is the thickness of the layer (film).
(4) Nz coefficient The Nz coefficient is calculated by Nz = Rth/Re.
(5) Angle In this specification, when an angle is referred to, the angle includes both clockwise and counterclockwise directions with respect to the reference direction. Thus, for example, "45°" means ±45°.

[Phase contrast film]
Figure 1 is a schematic cross-sectional view showing the general configuration of a phase difference film according to one embodiment of the present invention.

The phase difference film 1 is composed of, for example, a resin film. In this case, the phase difference film 1 may contain resin. The phase difference film 1 has a first main surface 1a and a second main surface 1b that face each other.

The thickness of the phase difference film 1 is, for example, 1 μm to 40 μm, preferably 3 μm to 35 μm, and more preferably 5 μm to 30 μm.

For example, it is preferable that the phase difference film 1 has zero cracks with a length of 200 μm or more when heated at 80°C for 240 hours. For example, the presence or absence of cracks can be evaluated within a 45 mm × 50 mm area. Furthermore, for example, it is preferable that the number of cracks with a length of 200 μm or more that occur when the phase difference film 1 is placed in an environment of 65°C and 90% relative humidity for 240 hours is 5 or less per 45 mm × 50 mm, more preferably 3 or less per 45 mm × 50 mm, and even more preferably 1 or less per 45 mm × 50 mm. It is particularly preferable that no such cracks occur.

The number and length of cracks that may occur in the phase-contrast film 1 can be confirmed, for example, by observation with an optical microscope.

The phase difference film 1 may contain a solvent. The solvent that the phase difference film 1 may contain is, for example, a solvent used in its manufacturing process. Examples of solvents that the phase difference film 1 may contain include ethyl acetate and methyl isobutyl ketone. These can be used individually or in combination of two or more. Among these, methyl isobutyl ketone is preferred.

The phase difference film 1 has a solvent content of, for example, less than 3200 μg/g, preferably 3150 μg/g or less, and more preferably 3100 μg/g or less. Satisfying this solvent content can result in excellent durability. For example, crack formation can be suppressed. On the other hand, the solvent content of the phase difference film 1 is preferably greater than 30 μg/g, more preferably 50 μg/g or more, and even more preferably 100 μg/g or more. Satisfying this solvent content can, for example, obtain a phase difference film 1 having a desired phase difference value.

The phase difference film 1 has a dimensional change rate difference due to heating that is, for example, less than 0.03%, preferably 0.02% or less. Satisfying this dimensional change rate difference allows for superior durability. For example, crack formation can be suppressed. On the other hand, the dimensional change rate difference of the phase difference film 1 due to heating is preferably -0.02% or more, more preferably 0.01% or more. Satisfying this dimensional change rate difference allows for obtaining a phase difference film 1 having, for example, a desired phase difference value.

The difference in the above-mentioned dimensional change rate can be determined by, for example, placing the sample in a heated environment at 65°C and 10% relative humidity for 60 minutes and measuring the dimensional change before and after heating.

The surface smoothness of the first main surface 1a and the second main surface 1b of the phase difference 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 change in surface smoothness after placing the phase difference film 1 in an environment of 65°C and 90% relative humidity for 240 hours is preferably 0.04 arcmin or less. Surface smoothness can be measured by focusing the irradiated light onto the target surface.

The resin film constituting the phase difference film 1 may, for example, include a resin having negative birefringence. A resin having negative birefringence may exhibit the property of having the maximum refractive index in the direction perpendicular to the stretching direction when uniaxially stretched. In the phase difference film 1 (resin film), the content of the resin having negative birefringence is, for example, 90% to 98% by weight, preferably 94% to 97% by weight.

Examples of resins having negative birefringence include resins in which highly polarized anisotropic chemical bonds or functional groups, 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, and fumarate ester resins. For specific examples, refer to the resins having negative birefringence described in Japanese Patent Publication No. 2021-076759, Japanese Patent Publication No. 2008-544304, and Japanese Patent Publication No. 2008-544317. These resins can be used individually or in combination of two or more. Fumarate ester resins are preferably used as resins having negative birefringence.

The phase difference film 1 (resin film) may further contain any suitable additives as needed. Specific examples of additives include plasticizers, heat stabilizers, light stabilizers, lubricants, antioxidants, UV absorbers, flame retardants, colorants, antistatic agents, compatibilizers, crosslinking agents, and thickeners. The type and content of additives may be appropriately determined depending on the purpose. The additive content in the phase difference film 1 (resin film) is, for example, 3% to 10% by weight.

The phase difference film 1 is, for example, a film whose refractive index characteristics exhibit the relationship nz > nx = ny (a so-called positive C plate). In this case, the phase difference Rth(550) in the thickness direction of the phase difference 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 exactly equal, but also the case where nx and ny are substantially equal. The in-plane phase difference Re(550) of the phase difference 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.

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

The phase difference 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 formation step), and annealing the formed film (annealing step). Here, it is preferable that the formed film is not substantially stretched.

Figures 2A to 2D show an example of a method for manufacturing a phase difference film according to one embodiment of the present invention.

Figure 2A shows a state in which the forming material is formed into a film 31 on a support (for example, a base film such as a polyester film) 30. Film formation is performed, for example, by coating the support 30 with a resin solution containing the forming material and drying the coated film. Stress is generated due to volume shrinkage when the resin solution dries on the support 30, causing the polymer molecular chains to tend to orient in the in-plane direction. By using a resin with high birefringence and negative intrinsic birefringence, a film 31 with large thickness-direction birefringence can be formed on the support 30 due to the shrinkage effect during drying.

Examples of solvents included in the above resin solution include ethyl acetate and methyl isobutyl ketone. These can be used individually or in combination of two or more. Among these, methyl isobutyl ketone is preferred. The solid content concentration of the resin solution is, for example, 16% to 20% by weight.

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

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 allows for the production of a phase difference film 1 that satisfies, for example, the difference in solvent content and/or dimensional change rate, and has excellent durability. During annealing, the film 31 can be in any suitable state. Specifically, during annealing, the surface of the film 31 (typically the main surface) may be protected by a protective member or exposed. For example, from the viewpoint 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, it is preferable that during annealing, one main surface of the film 31 is protected by a protective member and the other main surface is exposed. According to this configuration, for example, a phase difference film 1 that satisfies the difference in solvent content and/or dimensional change rate well can be obtained. Furthermore, for example, a phase difference film 1 having a desired phase difference value can be obtained.

In the illustrated example, before annealing the film 31, as shown in Figure 2B, a surface protection film 32 is bonded to the upper surface 31a of the film 31 as a protective member. Then, as shown in Figure 2C, the support 30 is peeled off from the lower surface 31b of the film 31. Finally, as shown in Figure 2D, the film 31 is annealed with the surface protection film 32 bonded to the upper surface 31a and the lower surface 31b exposed.

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 it, a phase difference film 1 with superior appearance can be obtained. Specifically, air tends to easily enter between the support 30 and the film 31, creating gaps. If annealing is performed with gaps present between the support 30 and the film 31, the areas where the gaps exist may leave marks, potentially impairing the appearance of the resulting phase difference film 1. By using a protective member separate from the support 30, a phase difference film 1 with superior appearance can be obtained.

The surface protection film 32 is typically a laminate of a base film 32a and an adhesive layer 32b. Examples of base film forming materials include polyester polymers such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polybutylene terephthalate (PBT); cellulosic polymers such as diacetylcellulose and triacetylcellulose; polycarbonate polymers; (meth)acrylic polymers such as polymethyl methacrylate; and cycloolefin polymers such as polynorbornene. These may be used individually 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. Alternatively, a self-adhesive film may be used as the surface protection film.

For example, by adjusting the annealing conditions, a phase difference film 1 that satisfies the above-mentioned difference in solvent content and/or dimensional change rate can be obtained. The annealing conditions (e.g., 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 between the boiling point T (°C) of the solvent contained in the resin solution and T+100°C, and may be T+20°C or higher, or T+70°C or higher. The annealing temperature is, for example, 50°C to 250°C, and may be 120°C or higher, 130°C or higher, or 140°C or higher. Also, for example, the annealing temperature can be set higher than the above-mentioned drying temperature. The annealing time is, for example, 5 seconds to 30 seconds, and preferably 15 seconds or more.

The phase difference film 1 can be used, for example, integrated into a component (e.g., an optical component such as a lens). Integration is typically performed by bonding the phase difference film 1 to the component via an adhesive layer. Depending on the shape of the component to be integrated, the phase difference film 1 may be heated and stretched as needed. For example, when integrating it into a curved surface, the phase difference film 1 may be heated and stretched as needed. The phase difference film 1 can also typically be integrated into a component together with other optical components.

In one embodiment, an optical film piece can be obtained by integrating an optical laminate containing a phase difference film 1 onto the curved surface of an optical component (e.g., a lens). Specifically, an optical film piece containing the phase difference film 1 can be obtained by integrating an optical laminate containing the phase difference film 1 onto the curved surface of an optical component. Typically, an adhesive (adhesive layer) is used for this integration.

Figures 3A to 3C illustrate an example of a method for integrating an optical laminate containing a phase difference film into a component.

Figure 3A shows the state in which a workpiece (optical laminate) 4 is prepared by applying an adhesive layer 3 to the laminated portion 2 containing the phase difference film, and the workpiece 4 is placed above the optical component (lens) L, which is the object to be adhered. Note that details of the laminated portion 2 are omitted in Figure 3.

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. Heating can make the workpiece 4 more susceptible to deformation. The heating temperature of the workpiece 4 is, for example, between 50°C and 150°C.

Once workpiece 4 is in a state where it can be easily deformed, it is bonded to lens L across its entire surface using any appropriate method (for example, by utilizing a pressure difference), as shown in Figure 3B. Then, as shown in Figure 3C, unnecessary portions of workpiece 4 (for example, parts that do not overlap with lens L in a plan view) are removed to obtain optical film piece 5.

During integration with a curved surface, the phase difference film is heated and, if necessary, stretched. For example, by using a phase difference film that satisfies the above-mentioned solvent content and/or dimensional change rate differences, integration with the curved surface can be achieved effectively. Specifically, defects such as cracks in the phase difference film during integration with a curved surface can be suppressed.

The planar shape of the optical film piece 5 is, for example, approximately circular, but is not limited thereto. Specifically, the optical film piece 5 may be approximately elliptical or a rounded rectangle. The optical film piece 5 has an upper surface and a lower surface 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 curve on the lower surface, a concave curve on the upper surface, and a convex curve on the lower surface. In the example shown in Figure 3C, the optical film piece 5 is bonded to the concave surface of the lens L, which has a curved portion, by its adhesive layer 3.

The optical film piece according to the embodiment of the present invention may include any other suitable optical component in addition to the phase difference film. The optical film piece can be used in any suitable display device. For example, the optical film piece can be suitably used in VR goggles.

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

The components positioned in front of the half-mirror or first lens section (in the illustrated example, the half-mirror 18, the first lens section 16, the second λ/4 member 22, the reflective polarizing member 14, and the second lens section 24) are sometimes collectively referred to as the lens section (lens section 4).

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. 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 then emitted as first linearly polarized light.

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 integrally provided with the display element 12.

The half-mirror 18 transmits light emitted from the display element 12 and reflects the light reflected by the reflective polarizing member 14 back towards the reflective polarizing member 14. The half-mirror 18 is integrally mounted on the first lens portion 16.

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 integrally provided with the first lens portion 16.

The first circularly polarized light emitted from the first λ/4 member 20 passes through the half-mirror 18 and the first lens portion 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 towards 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 direction 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.

The second linearly polarized light reflected by the reflective polarizing member 14 is converted into a second circularly polarized light by the second λ/4 member 22. The second circularly polarized light emitted from the second λ/4 member 22 passes through the first lens portion 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 portion 16 and is converted into a third linearly polarized light by the second λ/4 member 22. The third linearly polarized light is transmitted 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 direction as the transmission axis of the reflective polarizing member 14. Therefore, the third linearly polarized light incident on the reflective polarizing member 14 is transmitted through the reflective polarizing member 14.

Light transmitted through the reflective polarizing member 14 passes through the second lens portion 24 (the absorbing polarizing member 28 and the second lens portion 24, described later) and enters the user's eye 26.

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 orthogonal 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°, may be 42° to 48°, or 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°, may be 42° to 48°, or approximately 45°.

The in-plane phase difference Re(550) of the first λ/4 member 20 is, for example, 100 nm to 190 nm, but may also be 110 nm to 180 nm, 130 nm to 160 nm, or 135 nm to 155 nm. Preferably, the first λ/4 member 20 exhibits an inverse dispersion wavelength characteristic in which the phase difference value increases with the wavelength of the measured light. The Re(450)/Re(550) of the first λ/4 member 20 is, for example, 0.75 or more and less than 1, and may also be 0.8 or more and 0.95 or less.

The in-plane phase difference Re(550) of the second λ/4 member 22 is, for example, 100 nm to 190 nm, but may also be 110 nm to 180 nm, 130 nm to 160 nm, or 135 nm to 155 nm. Preferably, the second λ/4 member 22 exhibits an inverse dispersion wavelength characteristic in which the phase difference value increases with the wavelength of the measured light. The Re(450)/Re(550) of the second λ/4 member 22 is, for example, 0.75 or more and less than 1, and may also be 0.8 or more and 0.95 or less.

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

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 placed between the first lens portion 16 and the second lens portion 24 is integrally provided with either the first lens portion 16 or the second lens portion 24. For example, the member placed 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 allows for, for example, excellent handling of each member. The adhesive layer may be formed of an adhesive or a tack. Specifically, the adhesive layer may be an adhesive layer or a tack layer. The thickness of the adhesive layer is, for example, 0.01 μm to 60 μm.

The optical film piece according to the embodiment of the present invention may, for example, include optical components provided in the above-mentioned display system. The optical film piece may also include other components, such as an adhesive layer for integrating adjacent optical components. The thickness of the optical film piece varies depending on the type and number of components included, but is, for example, 50 μm to 400 μm.

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

Figure 5 is a schematic partially enlarged cross-sectional view showing the general configuration of an example of an optical film piece shown in Figure 3C. The optical film piece 5 includes, in this order, an adhesive layer 3, a phase difference member 23, a reflective polarizing member 14, and an absorbing polarizing member 28. The phase difference member 23 has a laminated structure of a second λ/4 member 22 and a phase difference film 1. The phase difference film 1 is, for example, a positive C plate exhibiting the relationship nz > nx = ny. By using such a phase difference film 1, light leakage (for example, light leakage in an oblique direction) can be prevented. As shown in Figure 5, it is preferable that the second λ/4 member 22 is positioned forward (above in Figure 5) of the positive C plate 1 in the phase difference member 23. The adhesive layer 3 can be arranged adjacent to the positive C plate 1.

Although not shown in the diagram, typically, the second λ/4 member 22 and the phase difference film 1 are laminated via an adhesive layer (e.g., an adhesive layer). Furthermore, the phase difference member 23 and the reflective polarizing member 14 are laminated via an adhesive layer (e.g., an adhesive layer), and the reflective polarizing member 14 and the absorbing polarizing member 28 are laminated via an adhesive layer (e.g., an adhesive layer).

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

[Experimental Example 1]
(Preparation of dope)
In an autoclave equipped with a stirrer, condenser, nitrogen inlet tube, and thermometer, 48 parts by weight of hydroxypropyl methylcellulose (manufactured by Shin-Etsu Chemical Co., Ltd., trade name "Metholose 60SH-50"), 15601 parts by weight of distilled water, 8161 parts by weight of diisopropyl fumarate, 240 parts by weight of 3-ethyl-3-oxetanylmethyl acrylate, and 45 parts by weight of t-butyl peroxypivalate, a polymerization initiator, were placed. After 1 hour of nitrogen bubbling, radical suspension polymerization was carried out by holding the mixture at 49°C for 24 hours while stirring. The mixture was then cooled to room temperature, and the suspension containing the resulting 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 resin.
The obtained fumarate ester resin was dissolved in a mixed solvent of methyl isobutyl ketone (MIBK, boiling point: 116°C) and ethyl acetate (boiling point: 77°C) to obtain a solution with a solid content of 20% by weight. Furthermore, 5 parts by weight of tributyl trimellitate was added as a plasticizer to 100 parts by weight of the fumarate ester resin to prepare a dope.

(Film forming)
As a support, a biaxially oriented polyethylene terephthalate film with a thickness of 75 μm and a width of 1350 mm was prepared.
The wound support was set in the feeding section of the film-forming apparatus, and the support was fed out and conveyed downstream while the dope was applied to the support so that the film thickness after drying would be 18 μm. It was then dried at 145°C for 40 seconds.

(Anneal)
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, was laminated to the surface of the formed film, and then the support was peeled off from the film. Annealing treatment was performed with only one side of the film protected by the surface protection film. Specifically, the film with the surface protection film laminated to it was placed in an environment with a temperature (annealing temperature) of 50°C for 15 seconds.
Thus, a phase difference film was obtained.

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

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

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

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

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

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

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

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

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

The following evaluations were performed on the phase contrast films for each experimental example. The evaluation results are summarized in Table 1.
<Evaluation>
1. Phase Difference Values The phase difference values at a wavelength of 587 nm were measured at 23°C using a phase difference/elliptic polarization measuring device (parallel nicol rotation type, manufactured by Oji Instruments Co., Ltd., product name "KOBRA-WPR").
For the in-plane phase difference Re(587), measurements were taken at 10 arbitrary locations on a 50mm x 50mm phase difference film, and the average value was calculated. For the thickness-direction phase difference Rth(587), measurements were taken at 6 arbitrary locations on a 50mm x 50mm phase difference film, and the average value was calculated.
2. Solvent content (amount of remaining solvent)
The sample (phase contrast film cut to a size of 10 mm x 50 mm) was placed in a 20 mL vial and sealed tightly. 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 HSS and GC settings were as follows.
Based on the obtained gas chromatogram, the amount of gas generated from the sample was determined as the solvent content (residual solvent amount) by applying a pre-prepared calibration curve. The calibration curve was created by preparing a standard of constant concentration by diluting MIBK with acetone, sealing 1 μL of this standard in a 20 mL headspace vial, heating it in the same manner as the sample, injecting 1 mL of the gas phase into GC, and then analyzing the GC peak area of the standard 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 equilibrium 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 HP-1 capillary column (model number 19091Z-233, inner diameter 0.25 mm, length 30 m, film thickness 1.0 μm)
Column temperature: 300°C (Increase temperature from 40°C to 120°C at a rate of 10°C/min, then continue increasing temperature to 300°C at a rate of 20°C/min and hold 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℃
Detector: FID
Detector temperature: 250°C
3. Dimensional Change Rate The obtained phase difference film was cut to a size of 25 mm in length and 4 mm in width to obtain a measurement sample. A range of 2.5 mm was chucked from both ends in the longitudinal direction of the measurement sample, and the amount of dimensional change in the longitudinal direction due to heating was measured by the tensile method using a thermomechanical analyzer (TMA, "HC-TMA4000SA" manufactured by NETSCH). The dimensional change rate (%) was calculated using the following formula.
Dimensional change rate = Change in lengthwise dimension / Lengthwise dimension before heating × 100
Here, the change in length is the value obtained by subtracting the dimension before heating from the dimension during heating, and the length 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: 2g
・Humidity rise rate: 5%/min
• Heating rate: 0.5°C/min
Table 1 shows the difference in dimensional change rates obtained by subtracting the dimensional change rate at the point when the predetermined temperature and relative humidity shown in the above heating conditions are reached (0 minutes later) from the dimensional change rate after maintaining the temperature and relative humidity for 60 minutes after reaching the predetermined temperature and relative humidity shown in the above heating conditions (60 minutes later).
4. Surface Smoothness 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 using a phase-shift laser interferometer (manufactured by Zygo, product name "DynaFiz"). Specifically, the sample was placed on a measurement platform with vibration isolation, and a single-wavelength laser (wavelength 633 nm) was used to interfere with a standard instrument with guaranteed flatness, and the relative displacement within a predetermined area (a circle with a diameter of 50 mm) was measured.
For the analysis, the angle index "Slope Magnitude RMS," obtained by extracting frequency values from 0.1/mm to 1/mm, was doubled (corresponding to 2σ) and defined as surface smoothness (unit: arcmin).
Measurements were taken at six arbitrary locations on a 45 mm x 50 mm phase difference film, and the average value was calculated. The difference in surface smoothness shown in Table 1 is the value obtained by subtracting the surface smoothness of the phase difference film before exposure to the environment at 65°C and 90% relative humidity (average value at six arbitrary locations) from the surface smoothness of the phase difference film after exposure to the environment at 65°C and 90% relative humidity for 240 hours (average value at six arbitrary locations).
5. Durability The obtained phase difference film (phase difference film with a surface protective film laminated to it) was cut to a size of 45 mm x 50 mm. Then, the surface of the phase difference film on the side without the surface protective film was subjected to corona treatment, and a 12 μm thick adhesive layer was formed. The phase difference film with the surface protective film laminated to it was then laminated to a glass plate via the adhesive layer. After that, the surface protective film was peeled off the phase difference film, and the phase difference film laminated to the glass plate was placed in an environment at a temperature of 80°C (oven) and in an environment at a temperature of 65°C and a relative humidity of 90% for 240 hours. The phase difference film was then observed using an optical microscope. Specifically, the number of cracks (cracks/45 mm x 50 mm) that occurred in the 45 mm x 50 mm phase difference film was counted.

Figure 6 shows an observation photograph (10x objective lens) of the phase contrast film after the durability test (80°C, 240 hours) of Experimental Example 10, and Figure 7 shows an observation photograph (10x objective lens) of the phase contrast film after the durability test (80°C, 240 hours) of Experimental Example 4. Furthermore, Figure 8 shows an observation photograph (10x objective lens) of the phase contrast film after the durability test (65°C, 90% RH, 240 hours) of Experimental Example 10.

As shown in Figure 6, after the durability test (80°C, 240 hours), one crack approximately 2 mm in length was observed in the phase difference film of Experimental Example 10. As shown in Figure 7, after the durability test (80°C, 240 hours), one crack approximately 1.3 mm in length was observed in the phase difference film of Experimental Example 4. As shown in Figure 8, after the durability test (65°C, 90% RH, 240 hours), numerous cracks ranging from 200 μm to over 2 mm in length were observed in the phase difference film of Experimental Example 10. The cracks that occurred in each test originated from the adhesive layer side of the phase difference film, and some of the observed cracks penetrated from the adhesive layer side to the other side (exposed surface).

The present invention is not limited to the embodiments described above, and various modifications are possible. For example, the configurations shown in the above embodiments can be replaced with configurations that are substantially identical, that produce the same effects, or that achieve the same objectives.

The optical film piece according to the embodiment of the present invention can be used, for example, in a display device such as VR goggles.

1. Phase difference film 1a. First main surface 1b. Second main surface 2. Laminated section 3. Adhesive layer 4. Workpiece (optical laminate)
5 Optical film piece 10 Display system 12 Display element 14 Reflective polarizing member 16 First lens part 18 Half mirror 20 First λ/4 member 22 Second λ/4 member 23 Phase difference member 24 Second lens part 28 Absorbing type 30 Support 31 Film 32 Surface protective film

Claims (6)

Forming a film-like material containing a resin having negative birefringence, and
This includes annealing the aforementioned film-formed film,
The film formation is carried out by coating a support with a resin solution containing the forming material.
The annealing temperature is equal to or greater than the boiling point T (°C) of the solvent contained in the resin solution.
In the annealing process described above, one main surface of the film is protected by a protective member, while the other main surface is exposed.
The protective member is a surface protective film.
A method for manufacturing a phase difference film. The method for manufacturing a phase difference film according to claim 1, wherein the annealing temperature is 130°C or higher. The method for manufacturing a phase difference film according to claim 1, wherein the annealing time is 15 seconds or more. A method for manufacturing a phase difference film according to claim 1 , comprising laminating a surface protective film as the protective member to the film before the annealing, and peeling the support from the film. The method for producing a phase difference film according to claim 1, wherein the resin having negative birefringence includes a fumarate ester resin. The method for manufacturing a phase difference film according to claim 1, wherein the phase difference film exhibits the relationship nz > nx = ny in its refractive index characteristics.