JP7516457B2 - Lens portion, laminate, display, manufacturing method of display, and display method - Google Patents

Description

The present invention relates to a lens portion, a laminate, a display body, a manufacturing method for a display body, and a display method.

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).

In recent years, new applications for image display devices have been developed. For example, goggles with displays (VR goggles) for realizing Virtual Reality (VR) have begun to be commercialized. Since VR goggles are being considered for use in a variety of situations, there is a demand for them to be lightweight and have high definition. Lightweightness can be achieved, for example, by making the lenses used in VR goggles thinner. On the other hand, there is also a demand for the development of optical components suitable for display systems using thin lenses.

JP 2021-103286 A

In view of the above, the primary objective of the present invention is to provide a lens section that can achieve lightweight, high-definition VR goggles.

1. A lens unit according to an embodiment of the present invention is a lens unit used in a display system that displays an image to a user, comprising: a reflecting unit that reflects light that is emitted forward from a display surface of a display element that displays an image and passes through a polarizing element and a first λ/4 element, and includes a reflective polarizing element and an absorptive polarizing element disposed in front of the reflective polarizing element, a first lens unit that is disposed on an optical path between the display element and the reflecting unit, a half mirror that is disposed between the display element and the first lens unit, transmits the light emitted from the display element, and reflects the light reflected by the reflecting unit toward the reflecting unit, and a second λ/4 element that is disposed on the optical path between the half mirror and the reflecting unit, and the thickness of an absorptive polarizing film that constitutes the absorptive polarizing element is 8 μm or less.
2. In the lens portion described above in 1, the reflection axis of the reflective polarizing member and the absorption axis of the absorptive polarizing member may be arranged parallel to each other.
3. In the lens portion according to 1 or 2 above, the first lens portion and the half mirror may be integral with each other.
4. In the lens portion according to any one of 1 to 3 above, the lens portion may include a second lens portion disposed in front of the reflecting portion.
5. In the lens portion according to any one of 1 to 4 above, an angle between an absorption axis of the polarizing member included in the display element and a slow axis of the first λ/4 member may be 40° to 50°, and an angle between an absorption axis of the polarizing member included in the display element and a slow axis of the second λ/4 member may be 40° to 50°.
6. In the lens portion according to any one of the above items 1 to 5, a ratio of a thickness of the absorptive polarizing film to a thickness of the reflective polarizing member may be 15% or less.

7. A laminate according to an embodiment of the present invention is used in the reflective portion of the lens unit according to any one of 1 to 6 above, and has the reflective polarizing member and the absorptive polarizing member.
8. In the laminate according to the above item 7, the reflective polarizing member and the absorptive polarizing member may be laminated via an adhesive layer.

9. A display according to an embodiment of the present invention has a lens portion according to any one of 1 to 6 above.
10. A method for manufacturing a display according to an embodiment of the present invention, which is a method for manufacturing a display having a lens portion according to any one of 1 to 6 above.

11. A display method according to an embodiment of the present invention includes the steps of: passing light representing an image emitted through a polarizing element and a first λ/4 element through a half mirror and a first lens unit; passing the light that has passed through the half mirror and the first lens unit through a second λ/4 element; reflecting the light that has passed through the second λ/4 element toward the half mirror with a reflecting unit including a reflective polarizing element; allowing the light reflected by the reflecting unit and the half mirror to pass through the reflective polarizing element of the reflecting unit with the second λ/4 element; and transmitting the light that has passed through the reflective polarizing element through an absorbing polarizing element, and the thickness of the absorbing polarizing film that constitutes the absorbing polarizing element is 8 μm or less.

12. A method for producing an absorptive polarizing film for a lens portion according to an embodiment of the present invention includes forming a polyvinyl alcohol-based resin layer containing a halide and a polyvinyl alcohol-based resin on one side of a long thermoplastic resin substrate to form a laminate, and subjecting the laminate to an auxiliary air-stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in this order, in which the laminate is heated while being transported in the longitudinal direction to cause it to shrink by 2% or more in the width direction.
13. In the method according to 12 above, the content of the halide in the polyvinyl alcohol-based resin layer is 5 to 20 parts by weight based on 100 parts by weight of the polyvinyl alcohol-based resin.
14. In the manufacturing method according to 12 or 13 above, the stretching ratio in the auxiliary in-air stretching treatment is 2.0 times or more.
15. In the manufacturing method according to any one of the above 12 to 14, the drying and shrinking treatment step is a step of heating using a heating roll.
16. In the manufacturing method according to 15 above, the temperature of the heating roll is 60° C. to 120° C., and the shrinkage rate in the width direction of the laminate due to the drying shrinkage treatment is 2% or more.

The lens portion according to the embodiment of the present invention can achieve lighter weight and higher definition in VR goggles.

1 is a schematic diagram showing a general configuration of a display system according to an embodiment of the present invention. 2 is a schematic cross-sectional view showing an example of a laminate used in a reflector of the display system shown in FIG. 1 . FIG. 2 is a schematic perspective view showing an example of a multilayer structure included in a reflective polarizing film. FIG. 2 is a schematic diagram showing an example of a drying shrinkage treatment using a heating roll. 1 is an observation photograph showing optical unevenness.

Below, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. Furthermore, in order to make the description clearer, the drawings may show the width, thickness, shape, etc. of each part more diagrammatically than the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

(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 direction perpendicular to the slow axis in the plane (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction.
(2) In-plane phase difference (Re)
"Re(λ)" is the in-plane retardation measured with light 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) Retardation in the thickness direction (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)×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 referring to an angle in this specification, the angle includes both clockwise and counterclockwise angles with respect to a reference direction. Thus, for example, "45°" means ±45°.

FIG. 1 is a schematic diagram showing the general configuration of a display system according to one embodiment of the present invention. In FIG. 1, the arrangement and shape of each component of the display system 2 are illustrated. The display system 2 includes a display element 12, a reflecting section 14, a first lens section 16, a half mirror 18, a first phase difference member 20, a second phase difference member 22, and a second lens section 24. The reflecting section 14 is disposed in front of the display surface 12a side of the display element 12, and can reflect light emitted from the display element 12. The first lens section 16 is disposed on the optical path between the display element 12 and the reflecting section 14, and the half mirror 18 is disposed between the display element 12 and the first lens section 16. The first phase difference member 20 is disposed on the optical path between the display element 12 and the half mirror 18, and the second phase difference member 22 is disposed on the optical path between the half mirror 18 and the reflecting section 14.

The components arranged in front of the half mirror (in the illustrated example, the half mirror 18, the first lens section 16, the second phase difference member 22, the reflecting section 14, and the second lens section 24) may be 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. The light emitted from the display surface 12a passes through, for example, a polarizing member (typically, a polarizing film) that may be included in the display element 12, and is converted into a first linearly polarized light.

The first phase difference member 20 is a λ/4 member that can convert the first linearly polarized light incident on the first phase difference member 20 into the first circularly polarized light (hereinafter, the first phase difference member may be referred to as the first λ/4 member). The first phase difference member 20 may be provided integrally with the display element 12.

The half mirror 18 transmits the light emitted from the display element 12 and reflects the light reflected by the reflecting portion 14 toward the reflecting portion 14. The half mirror 18 is integrally provided with the first lens portion 16.

The second phase difference member 22 is a λ/4 member that can transmit the light reflected by the reflector 14 and the half mirror 18 through the reflector 14, which includes a reflective polarizing member (hereinafter, the second phase difference member may be referred to as a second λ/4 member). The second phase difference member 22 may be provided integrally with the first lens portion 16, or may be provided integrally with the reflective polarizing member included in the reflector 14.

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

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

Light that passes through the reflecting portion 14 passes through the second lens portion 24 and enters the user's eye 26.

For example, the absorption axis of the polarizing member included in the display element 12 and the reflection axis of the reflective polarizing member included in the reflecting section 14 may be arranged substantially parallel to each other or substantially 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 phase difference member 20 is, for example, 40° to 50°, may be 42° to 48°, or may be about 45°. The angle between the absorption axis of the polarizing member included in the display element 12 and the slow axis of the second phase difference member 22 is, for example, 40° to 50°, may be 42° to 48°, or may be about 45°.

The in-plane phase difference Re(550) of the first phase difference member 20 is, for example, 100 nm to 190 nm, may be 110 nm to 180 nm, may be 130 nm to 160 nm, or may be 135 nm to 155 nm.

The first phase difference member 20 preferably exhibits an inverse dispersion wavelength characteristic in which the phase difference value increases according to the wavelength of the measurement light. The Re(450)/Re(550) of the first phase difference member 20 is, for example, 0.75 or more and less than 1, and may be 0.8 or more and 0.95 or less.

The in-plane phase difference Re(550) of the second phase difference member 22 is, for example, 100 nm to 190 nm, may be 110 nm to 180 nm, may be 130 nm to 160 nm, or may be 135 nm to 155 nm.

The second phase difference member 22 preferably exhibits an inverse dispersion wavelength characteristic in which the phase difference value increases according to the wavelength of the measurement light. The Re(450)/Re(550) of the second phase difference member 22 is, for example, 0.75 or more and less than 1, and may be 0.8 or more and 0.95 or less.

Each retardation member is made of any suitable material. For example, it may be a resin film (typically a stretched film) or may be made of a liquid crystal compound. When the retardation member is a resin film, its thickness is, for example, 10 μm to 100 μm.

Examples of resins contained in the resin film include polycarbonate-based resins, polyester carbonate-based resins, polyester-based resins, polyvinyl acetal-based resins, polyarylate-based resins, cyclic olefin-based resins, cellulose-based resins, polyvinyl alcohol-based resins, polyamide-based resins, polyimide-based resins, polyether-based resins, polystyrene-based resins, acrylic-based resins, and the like. These resins may be used alone or in combination (e.g., blended or copolymerized). For example, a resin film containing a polycarbonate-based resin or a polyester carbonate-based resin (hereinafter sometimes simply referred to as a polycarbonate-based resin) can be suitably used. By using such a resin, for example, the above-mentioned reverse dispersion wavelength characteristic can be exhibited.

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

An absorptive polarizing member may be provided in front of the reflective polarizing member. Typically, the absorptive polarizing member may be provided between the reflective polarizing member and the second lens section 24. The reflection axis of the reflective polarizing member and the absorption axis of the absorptive polarizing member may be arranged approximately parallel to each other, and the transmission axis of the reflective polarizing member and the transmission axis of the absorptive polarizing member may be arranged approximately parallel to each other. The absorptive polarizing member may be included in the reflecting section 14. When the reflecting section 14 includes an absorptive polarizing member, the reflecting section 14 may include a laminate having a reflective polarizing member and an absorptive polarizing member.

Figure 2 is a schematic cross-sectional view showing an example of a laminate used in the reflector of the display system shown in Figure 1. The laminate 30 has a reflective polarizing element 32 and an absorptive polarizing element 34, and the reflective polarizing element 32 and the absorptive polarizing element 34 are laminated via an adhesive layer 36. By using the adhesive layer, the reflective polarizing element 32 and the absorptive polarizing element 34 are fixed, and the axial arrangement of the reflection axis and the absorption axis (transmission axis and transmission axis) can be prevented from being misaligned. In addition, the adverse effects of an air layer that may be formed between the reflective polarizing element 32 and the absorptive polarizing element 34 can be suppressed. The adhesive layer 36 may be formed of an adhesive or a pressure-sensitive adhesive. The thickness of the adhesive layer 36 is, for example, 0.05 μm to 30 μm, preferably 3 μm to 20 μm, and more preferably 5 μm to 15 μm. Although not shown, the second phase difference element 22 may be integrally provided with the reflective polarizing element 32, and therefore the laminate 30 may have the second phase difference element 22. In this case, the second phase difference member 22 can be laminated to the reflective polarizing member 32 via an adhesive layer.

The reflective polarizing element can transmit light polarized parallel to its transmission axis (typically, linearly polarized light) while maintaining its polarization state, and can reflect light in other polarization states. A typical reflective polarizing element is made of a film (sometimes called a reflective polarizing film) with a multilayer structure. In this case, the thickness of the reflective polarizing element is, for example, 10 μm to 150 μm, preferably 20 μm to 100 μm, and more preferably 30 μm to 60 μm.

Figure 3 is a schematic perspective view showing an example of a multilayer structure included in a reflective polarizing film. The multilayer structure 32a has alternating layers A having birefringence and layers B having substantially no birefringence. The total number of layers constituting the multilayer structure may be 50 to 1000. For example, the refractive index nx in the x-axis direction of layer A is larger than the refractive index ny in the y-axis direction, and the refractive index nx in the x-axis direction and the refractive index ny in the y-axis direction of layer B are substantially the same, and the refractive index difference between layers A and B is large in the x-axis direction and substantially zero in the y-axis direction. As a result, the x-axis direction can be the reflection axis, and the y-axis direction can be the transmission axis. The refractive index difference between layers A and B in the x-axis direction is preferably 0.2 to 0.3.

The A layer is typically made of a material that exhibits birefringence when stretched. Examples of such materials include naphthalene dicarboxylic acid polyesters (e.g., polyethylene naphthalate), polycarbonates, and acrylic resins (e.g., polymethyl methacrylate). The B layer is typically made of a material that does not substantially exhibit birefringence even when stretched. Examples of such materials include copolyesters of naphthalene dicarboxylic acid and terephthalic acid. The multilayer structure can be formed by combining coextrusion and stretching. For example, the material constituting the A layer and the material constituting the B layer are extruded and then multilayered (e.g., using a multiplier). The resulting multilayer laminate is then stretched. The x-axis direction in the illustrated example can correspond to the stretching direction.

Commercially available reflective polarizing films include, for example, "DBEF" and "APF" manufactured by 3M, and "APCF" manufactured by Nitto Denko Corporation.

The crossed transmittance (Tc) of the reflective polarizing member (reflective polarizing film) may be, for example, 0.01% to 3%. The single transmittance (Ts) of the reflective polarizing member (reflective polarizing film) may be, for example, 43% to 49%, and preferably 45% to 47%. The degree of polarization (P) of the reflective polarizing member (reflective polarizing film) may be, for example, 92% to 99.99%.

The single transmittance (Ts) is typically measured by an ultraviolet-visible spectrophotometer. The polarization degree (P) is typically measured by an ultraviolet-visible spectrophotometer and calculated by the following formula based on the parallel transmittance (Tp) and crossed transmittance (Tc) obtained by performing visibility correction. Ts, Tp, and Tc are Y values measured by a 2-degree visual field (C light source) according to JIS Z8701 and then subjected to visibility correction.
Polarization degree (P) = {(Tp-Tc)/(Tp+Tc)} ^1/2 ×100

The absorptive polarizing member may typically include a resin film (sometimes referred to as an absorptive polarizing film or simply a polarizing film) containing a dichroic material. Preferably, it includes a polyvinyl alcohol (PVA)-based film containing iodine. The thickness of the absorptive polarizing film is preferably 1 μm or more and 8 μm or less, more preferably 7 μm or less, and even more preferably 5 μm or less. By using an absorptive polarizing film of such a thickness, it is possible to suppress shrinkage that may occur due to environmental changes (e.g., temperature changes) and maintain excellent display characteristics. Specifically, in the above display system, since even slight shrinkage of the components can cause image distortion, by using an absorptive polarizing film of such a thickness, it is possible to extremely effectively suppress distortion of the displayed image.

The ratio of the thickness of the absorptive polarizing film to the thickness of the reflective polarizing element is preferably 15% or less, more preferably 10% or less. The ratio of the thickness of the absorptive polarizing film to the sum of the thickness of the second phase difference element, the thickness of the reflective polarizing element, and the thickness of the absorptive polarizing element is preferably 10% or less, more preferably 5% or less.

The cross transmittance (Tc) of the absorptive polarizing element (absorptive polarizing film) is preferably 0.5% or less, more preferably 0.1% or less, and even more preferably 0.05% or less. The single transmittance (Ts) of the absorptive polarizing element (absorptive polarizing film) is, for example, 41.0% to 45.0%, and preferably 42.0% or more. The polarization degree (P) of the absorptive polarizing element (absorptive polarizing film) is, for example, 99.0% to 99.997%, and preferably 99.9% or more. By combining the reflective polarizing element with the absorptive polarizing element, excellent display characteristics can be achieved. For example, the user's perception of afterimages (ghosts) can be suppressed.

The method for producing the absorptive polarizing film according to one embodiment includes forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin substrate to form a laminate, and subjecting the laminate to an air-assisted stretching process, a dyeing process, an underwater stretching process, and a drying shrinkage process in this order, in which the laminate is heated while being conveyed in the longitudinal direction to shrink the laminate by 2% or more in the width direction. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight per 100 parts by weight of the PVA-based resin. The stretching ratio in the air-assisted stretching process is preferably 2.0 times or more. The drying shrinkage process is preferably performed using a heating roll, and the temperature of the heating roll is preferably 60°C to 120°C. The shrinkage rate in the width direction of the laminate due to the drying shrinkage process is preferably 2% or more. A laminate containing a PVA-based resin layer containing a halide is prepared, the laminate is stretched in multiple stages including air-assisted stretching and underwater stretching, and the stretched laminate is heated with a heating roll to obtain a polarizing film having excellent optical properties (typically, single transmittance and polarization degree) and suppressed variation in optical properties. Specifically, by using a heating roll in the drying shrinkage treatment step, the laminate can be uniformly shrunk throughout the laminate while being transported. This not only improves the optical properties of the resulting polarizing film, but also enables stable production of polarizing films with excellent optical properties and suppresses variation in the optical properties of the polarizing film (particularly, single transmittance).

Any appropriate method may be used to prepare a laminate of a thermoplastic resin substrate and a PVA-based resin layer. Preferably, a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin substrate, and then dried to form a PVA-based resin layer on the thermoplastic resin substrate. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight per 100 parts by weight of the PVA-based resin.

Any appropriate method can be used to apply the coating liquid. Examples include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, and knife coating (comma coating, etc.). The application and drying temperature of the coating liquid is preferably 50°C or higher.

The thickness of the PVA-based resin layer is preferably 3 μm to 40 μm, and more preferably 3 μm to 20 μm.

Before forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to a surface treatment (e.g., corona treatment, etc.), or an easy-adhesion layer may be formed on the thermoplastic resin substrate. By carrying out such treatment, it is possible to improve the adhesion between the thermoplastic resin substrate and the PVA-based resin layer.

The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If it is less than 20 μm, it may be difficult to form a PVA-based resin layer. If it is more than 300 μm, for example, in the underwater stretching process described below, it may take a long time for the thermoplastic resin substrate to absorb water, and excessive load may be required for stretching.

The thermoplastic resin substrate preferably has a water absorption rate of 0.2% or more, more preferably 0.3% or more. The thermoplastic resin substrate can absorb water, and the water can act as a plasticizer to plasticize the substrate. As a result, the stretching stress can be significantly reduced, and the substrate can be stretched at a high ratio. On the other hand, the water absorption rate of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. By using such a thermoplastic resin substrate, it is possible to prevent problems such as a significant decrease in the dimensional stability of the thermoplastic resin substrate during production, which leads to a deterioration in the appearance of the resulting polarizing film. It is also possible to prevent the substrate from breaking during underwater stretching, and the PVA-based resin layer from peeling off from the thermoplastic resin substrate. The water absorption rate of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent material. The water absorption rate is a value determined in accordance with JIS K 7209.

The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or less. By using such a thermoplastic resin substrate, the stretchability of the laminate can be sufficiently ensured while suppressing the crystallization of the PVA-based resin layer. Furthermore, in consideration of the plasticization of the thermoplastic resin substrate by water and the good underwater stretching, it is more preferable that the temperature is 100°C or less, and even more preferable that the temperature is 90°C or less. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60°C or more. By using such a thermoplastic resin substrate, defects such as deformation of the thermoplastic resin substrate (e.g., generation of unevenness, sagging, wrinkles, etc.) when applying and drying the coating liquid containing the PVA-based resin can be prevented, and the laminate can be well prepared. In addition, the stretching of the PVA-based resin layer can be well performed at a suitable temperature (e.g., about 60°C). The glass transition temperature of the thermoplastic resin substrate can be adjusted, for example, by introducing a modified group into the constituent material and heating using a crystallization material. The glass transition temperature (Tg) is a value determined in accordance with JIS K 7121.

Any suitable thermoplastic resin may be used as the material for the thermoplastic resin substrate. Examples of thermoplastic resins include ester-based resins such as polyethylene terephthalate-based resins, cycloolefin-based resins such as norbornene-based resins, olefin-based resins such as polypropylene, polyamide-based resins, polycarbonate-based resins, and copolymer resins of these. Of these, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferred.

In one embodiment, amorphous (uncrystallized) polyethylene terephthalate resins are preferably used. Among them, amorphous (hardly crystallized) polyethylene terephthalate resins are particularly preferably used. Specific examples of amorphous polyethylene terephthalate resins include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acids, and copolymers further containing cyclohexanedimethanol or diethylene glycol as glycols.

In a preferred embodiment, the thermoplastic resin substrate is made of a polyethylene terephthalate resin having an isophthalic acid unit. This is because such a thermoplastic resin substrate has excellent stretchability and can suppress crystallization during stretching. This is thought to be due to the introduction of an isophthalic acid unit, which imparts a large bend to the main chain. The polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content ratio of the isophthalic acid unit is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, based on the total of all repeating units. This is because a thermoplastic resin substrate with extremely excellent stretchability can be obtained. On the other hand, the content ratio of the isophthalic acid unit is preferably 20 mol% or less, more preferably 10 mol% or less, based on the total of all repeating units. By setting such a content ratio, the crystallinity can be increased satisfactorily in the drying shrinkage treatment described below.

The thermoplastic resin substrate may be stretched in advance (before the PVA-based resin layer is formed). In one embodiment, the long thermoplastic resin substrate is stretched in the transverse direction. The transverse direction is preferably a direction perpendicular to the stretching direction of the laminate described below. In this specification, "perpendicular" also includes the case where the direction is substantially perpendicular. Here, "substantially perpendicular" includes the case where the direction is 90°±5.0°, and is preferably 90°±3.0°, and more preferably 90°±1.0°.

The stretching temperature of the thermoplastic resin substrate is preferably Tg-10°C to Tg+50°C relative to the glass transition temperature (Tg). The stretching ratio of the thermoplastic resin substrate is preferably 1.5 to 3.0 times.

Any appropriate method may be adopted as the method for stretching the thermoplastic resin substrate. Specifically, it may be fixed-end stretching or free-end stretching. The stretching method may be dry or wet. The stretching of the thermoplastic resin substrate may be performed in one stage or in multiple stages. When it is performed in multiple stages, the above-mentioned stretching ratio is the product of the stretching ratios in each stage.

As described above, the coating liquid contains a halide and a PVA-based resin. The coating liquid is typically a solution in which the halide and the PVA-based resin are dissolved in a solvent. Examples of the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Of these, water is preferred. The concentration of the PVA-based resin in the solution is preferably 3 to 20 parts by weight per 100 parts by weight of the solvent. With such a resin concentration, a uniform coating film that is in close contact with the thermoplastic resin substrate can be formed. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight per 100 parts by weight of the PVA-based resin.

Additives may be added to the coating liquid. Examples of additives include plasticizers and surfactants. Examples of plasticizers include polyhydric alcohols such as ethylene glycol and glycerin. Examples of surfactants include nonionic surfactants. These can be used to further improve the uniformity, dyeability, and stretchability of the resulting PVA-based resin layer.

Any suitable resin may be used as the PVA-based resin. Examples include polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Polyvinyl alcohol is obtained by saponifying polyvinyl acetate. Ethylene-vinyl alcohol copolymer is obtained by saponifying ethylene-vinyl acetate copolymer. The saponification degree of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.95 mol%, and more preferably 99.0 mol% to 99.93 mol%. The saponification degree can be determined in accordance with JIS K 6726-1994. By using a PVA-based resin with such a saponification degree, a polarizing film with excellent durability can be obtained. If the saponification degree is too high, there is a risk of gelation.

The average degree of polymerization of the PVA-based resin can be appropriately selected depending on the purpose. The average degree of polymerization is usually 1,000 to 10,000, preferably 1,200 to 4,500, and more preferably 1,500 to 4,300. The average degree of polymerization can be determined in accordance with JIS K 6726-1994.

As the halide, any suitable halide may be used. Examples include iodide and sodium chloride. Examples of iodide include potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred.

The amount of halide in the coating solution is preferably 5 to 20 parts by weight per 100 parts by weight of PVA-based resin, and more preferably 10 to 15 parts by weight per 100 parts by weight of PVA-based resin. If the amount of halide exceeds 20 parts by weight per 100 parts by weight of PVA-based resin, the halide may bleed out and the final polarizing film may become cloudy.

Generally, the orientation of the polyvinyl alcohol molecules in the PVA-based resin increases when the PVA-based resin layer is stretched, but when the stretched PVA-based resin layer is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules may become disordered, and the orientation may decrease. In particular, when a laminate of a thermoplastic resin and a PVA-based resin layer is stretched in boric acid water, the tendency for the degree of orientation to decrease is remarkable when the laminate is stretched in boric acid water at a relatively high temperature to stabilize the stretching of the thermoplastic resin. For example, while a PVA film alone is generally stretched in boric acid water at 60°C, a laminate of A-PET (thermoplastic resin substrate) and a PVA-based resin layer is stretched at a high temperature of around 70°C, in this case, the orientation of the PVA at the beginning of the stretching may decrease before it increases due to the stretching in water. In response to this, a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate is prepared, and the laminate is stretched at high temperature (auxiliary stretching) in air before being stretched in boric acid water, so that crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, the orientation of the polyvinyl alcohol molecules is disturbed and the orientation is reduced, compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of the polarizing film obtained through a process in which the laminate is immersed in a liquid, such as a dyeing process and an underwater stretching process.

In particular, in order to obtain high optical properties, a two-stage stretching method is selected that combines dry stretching (auxiliary stretching) and stretching in boric acid water. By introducing auxiliary stretching like two-stage stretching, it is possible to stretch while suppressing the crystallization of the thermoplastic resin substrate, which solves the problem of the thermoplastic resin substrate being excessively crystallized and reduced in stretchability in the subsequent stretching in boric acid water, and the laminate can be stretched at a higher magnification. Furthermore, when applying a PVA-based resin to a thermoplastic resin substrate, in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate, it is necessary to lower the application temperature compared to when applying a PVA-based resin to a normal metal drum, which may result in a problem that the crystallization of the PVA-based resin is relatively low and sufficient optical properties cannot be obtained. In contrast, by introducing auxiliary stretching, it is possible to increase the crystallinity of the PVA-based resin even when applying a PVA-based resin to a thermoplastic resin, and it is possible to achieve high optical properties. At the same time, by increasing the orientation of the PVA-based resin in advance, problems such as a decrease in the orientation of the PVA-based resin or dissolution can be prevented when the resin is immersed in water during the subsequent dyeing and stretching processes, making it possible to achieve high optical properties.

The stretching method of the auxiliary air stretching may be fixed end stretching (for example, a method of stretching using a tenter stretching machine) or free end stretching (for example, a method of uniaxially stretching a laminate between rolls with different peripheral speeds), but in order to obtain high optical properties, free end stretching can be actively adopted. In one embodiment, the air stretching process includes a heated roll stretching process in which the laminate is stretched by the difference in peripheral speed between heated rolls while being transported in its longitudinal direction. The air stretching process typically includes a zone stretching process and a heated roll stretching process. The order of the zone stretching process and the heated roll stretching process is not limited, and the zone stretching process may be performed first, or the heated roll stretching process may be performed first. The zone stretching process may be omitted. In one embodiment, the zone stretching process and the heated roll stretching process are performed in this order. In another embodiment, the film is stretched by gripping the film end in a tenter stretching machine and widening the distance between the tenters in the flow direction (the widening of the distance between the tenters is the stretching ratio). In this case, the tenter distance in the width direction (perpendicular to the machine direction) is set to be as close as possible. Preferably, it can be set to be as close as possible to the free end stretching ratio in the machine direction. In the case of free end stretching, the shrinkage ratio in the width direction is calculated as (1/stretching ratio) ^1/2 .

The air-assisted stretching may be performed in one step or in multiple steps. When the air-assisted stretching is performed in multiple steps, the stretching ratio is the product of the stretching ratios in each step. The stretching direction in the air-assisted stretching is preferably approximately the same as the stretching direction in the underwater stretching.

The stretching ratio in the air-assisted stretching is preferably 2.0 to 3.5 times. The maximum stretching ratio when air-assisted stretching and underwater stretching are combined is preferably 5.0 times or more, more preferably 5.5 times or more, and even more preferably 6.0 times or more, relative to the original length of the laminate. In this specification, the "maximum stretching ratio" refers to the stretching ratio just before the laminate breaks, and refers to a value 0.2 lower than the stretching ratio at which the laminate breaks, which is determined separately.

The stretching temperature of the auxiliary air stretching can be set to any appropriate value depending on the material of the thermoplastic resin substrate, the stretching method, etc. The stretching temperature is preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate + 10°C, and particularly preferably equal to or higher than Tg + 15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, the crystallization of the PVA-based resin can be suppressed from proceeding rapidly, and defects due to the crystallization (for example, preventing the orientation of the PVA-based resin layer by stretching) can be suppressed. The crystallization index of the PVA-based resin after the auxiliary air stretching is preferably 1.3 to 1.8, more preferably 1.4 to 1.7. The crystallization index of the PVA-based resin can be measured by the ATR method using a Fourier transform infrared spectrophotometer. Specifically, the measurement is carried out using polarized light as the measuring light, and the crystallization index is calculated according to the following formula using the intensities at 1141 cm ⁻¹ and 1440 cm ⁻¹ of the obtained spectrum.
Crystallization index = (I _C /I _R )
however,
I _C : Intensity at 1141 cm ⁻¹ when the measurement light is incident and measured. I _R : Intensity at 1440 cm ⁻¹ when the measurement light is incident and measured.

If necessary, an insolubilization treatment is performed after the auxiliary air stretching treatment and before the underwater stretching treatment or dyeing treatment. The insolubilization treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing the insolubilization treatment, water resistance is imparted to the PVA-based resin layer, and it is possible to prevent a decrease in the orientation of the PVA when immersed in water. The concentration of the aqueous boric acid solution is preferably 1 to 4 parts by weight per 100 parts by weight of water. The liquid temperature of the insolubilization bath (aqueous boric acid solution) is preferably 20°C to 50°C.

The dyeing process is typically performed by dyeing the PVA-based resin layer with iodine. Specifically, the dyeing process is performed by adsorbing iodine to the PVA-based resin layer. Examples of the adsorption method include a method of immersing the PVA-based resin layer (laminate) in a dyeing solution containing iodine, a method of applying the dyeing solution to the PVA-based resin layer, and a method of spraying the dyeing solution onto the PVA-based resin layer. A method of immersing the laminate in a dyeing solution (dye bath) is preferable, because iodine can be well adsorbed in this method.

The dyeing solution is preferably an aqueous iodine solution. The amount of iodine is preferably 0.05 to 0.5 parts by weight per 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add an iodide to the aqueous iodine solution. Examples of iodides include potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, and titanium iodide. Of these, potassium iodide is preferable. The amount of iodide is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, per 100 parts by weight of water. The temperature of the dyeing solution during dyeing is preferably 20°C to 50°C in order to suppress dissolution of the PVA-based resin. When the PVA-based resin layer is immersed in the dye solution, the immersion time is preferably 5 seconds to 5 minutes, and more preferably 30 seconds to 90 seconds, in order to ensure the transmittance of the PVA-based resin layer.

The dyeing conditions (concentration, liquid temperature, immersion time) can be set so that the single transmittance and polarization degree of the final polarizing film are within the above-mentioned ranges. As for such dyeing conditions, preferably, an iodine aqueous solution is used as the dyeing solution, and the content ratio of iodine and potassium iodide in the iodine aqueous solution is 1:5 to 1:20. The content ratio of iodine and potassium iodide in the iodine aqueous solution is preferably 1:5 to 1:10. This makes it possible to obtain a polarizing film having the optical properties described above.

When a dyeing process is performed continuously after a process (typically, an insolubilization process) in which the laminate is immersed in a treatment bath containing boric acid, the boric acid concentration of the dyeing bath may change over time due to the boric acid contained in the treatment bath being mixed into the dyeing bath, resulting in unstable dyeability. In order to suppress the above-mentioned instability of dyeability, the upper limit of the boric acid concentration of the dyeing bath is adjusted to preferably 4 parts by weight, more preferably 2 parts by weight, per 100 parts by weight of water. On the other hand, the lower limit of the boric acid concentration of the dyeing bath is preferably 0.1 parts by weight, more preferably 0.2 parts by weight, and even more preferably 0.5 parts by weight, per 100 parts by weight of water. In one embodiment, the dyeing process is performed using a dyeing bath in which boric acid has been blended in advance. This can reduce the rate of change in the boric acid concentration when the boric acid of the treatment bath is mixed into the dyeing bath. The amount of boric acid preliminarily mixed into the dye bath (i.e., the content of boric acid not derived from the treatment bath) is preferably 0.1 to 2 parts by weight, and more preferably 0.5 to 1.5 parts by weight, per 100 parts by weight of water.

If necessary, a crosslinking treatment is performed after the dyeing treatment and before the underwater stretching treatment. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. The crosslinking treatment imparts water resistance to the PVA-based resin layer, and prevents the orientation of the PVA from decreasing when the layer is immersed in high-temperature water during the subsequent underwater stretching. The concentration of the aqueous boric acid solution is preferably 1 to 5 parts by weight per 100 parts by weight of water. In addition, when the crosslinking treatment is performed after the dyeing treatment, it is preferable to further add an iodide. By adding an iodide, it is possible to suppress the elution of iodine adsorbed to the PVA-based resin layer. The amount of iodide to be added is preferably 1 to 5 parts by weight per 100 parts by weight of water. Specific examples of iodides are as described above. The liquid temperature of the crosslinking bath (aqueous boric acid solution) is preferably 20°C to 50°C.

The underwater stretching process is performed by immersing the laminate in a stretching bath. The underwater stretching process allows stretching at a temperature lower than the glass transition temperature (typically about 80°C) of the thermoplastic resin substrate or the PVA-based resin layer, and allows the PVA-based resin layer to be stretched at a high magnification while suppressing crystallization. As a result, a polarizing film with excellent optical properties can be produced.

The stretching method of the laminate can be any appropriate method. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method of uniaxially stretching the laminate by passing it between rolls with different peripheral speeds). Free-end stretching is preferably selected. The stretching of the laminate may be performed in one stage or in multiple stages. When it is performed in multiple stages, the stretching ratio (maximum stretching ratio) of the laminate described below is the product of the stretching ratios in each stage.

The underwater stretching is preferably performed by immersing the laminate in an aqueous solution of boric acid (underwater stretching in boric acid). By using an aqueous solution of boric acid as the stretching bath, it is possible to impart to the PVA-based resin layer the rigidity required to withstand the tension applied during stretching, and the water resistance required to prevent dissolution in water. Specifically, boric acid can generate tetrahydroxyborate anions in the aqueous solution and crosslink with the PVA-based resin through hydrogen bonds. As a result, the PVA-based resin layer is imparted with rigidity and water resistance, allowing it to be stretched well, and a polarizing film with excellent optical properties can be produced.

The boric acid aqueous solution is preferably obtained by dissolving boric acid and/or a borate in water, which is a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 3.5 to 7 parts by weight, and particularly preferably 4 to 6 parts by weight, per 100 parts by weight of water. By making the boric acid concentration 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, and a polarizing film with higher characteristics can be produced. In addition to boric acid or a borate, an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.

Preferably, iodide is added to the stretching bath (boric acid aqueous solution). By adding iodide, it is possible to suppress the elution of iodine adsorbed in the PVA-based resin layer. Specific examples of iodide are as described above. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, per 100 parts by weight of water.

The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C to 85°C, more preferably 60°C to 75°C. At such a temperature, the PVA-based resin layer can be stretched at a high ratio while suppressing dissolution. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60°C or higher in relation to the formation of the PVA-based resin layer. In this case, if the stretching temperature is below 40°C, even if the plasticization of the thermoplastic resin substrate by water is taken into consideration, there is a risk that the substrate cannot be stretched well. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and the higher the risk that excellent optical properties cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

The stretching ratio in underwater stretching is preferably 1.5 times or more, more preferably 3.0 times or more. The total stretching ratio of the laminate is preferably 5.0 times or more, more preferably 5.5 times or more, relative to the original length of the laminate. By achieving such a high stretching ratio, a polarizing film with extremely excellent optical properties can be produced. Such a high stretching ratio can be achieved by employing the underwater stretching method (stretching in boric acid water).

The drying shrinkage treatment may be performed by zone heating, which heats the entire zone, or by heating the transport roll (using a so-called heating roll) (heat roll drying method). Preferably, both are used. By drying using a heating roll, it is possible to efficiently suppress the heat curl of the laminate and produce a polarizing film with excellent appearance. Specifically, by drying the laminate in a state where it is aligned with the heating roll, it is possible to efficiently promote the crystallization of the thermoplastic resin substrate and increase the crystallinity, and even at a relatively low drying temperature, it is possible to satisfactorily increase the crystallinity of the thermoplastic resin substrate. As a result, the rigidity of the thermoplastic resin substrate increases and it becomes in a state where it can withstand the shrinkage of the PVA-based resin layer due to drying, and curling is suppressed. In addition, by using a heating roll, the laminate can be dried while being maintained in a flat state, so that not only curling but also the occurrence of wrinkles can be suppressed. At this time, the laminate can be shrunk in the width direction by the drying shrinkage treatment, thereby improving the optical properties. This is because the orientation of the PVA and the PVA/iodine complex can be effectively increased. The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using a heated roll, the laminate can be continuously shrunk in the width direction while being transported, achieving high productivity.

Figure 4 is a schematic diagram showing an example of a drying shrinkage process. In the drying shrinkage process, the laminate 200 is dried while being transported by transport rolls R1 to R6 heated to a predetermined temperature and guide rolls G1 to G4. In the illustrated example, the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but, for example, the transport rolls R1 to R6 may be arranged so as to continuously heat only one surface of the laminate 200 (for example, the thermoplastic resin substrate surface).

Drying conditions can be controlled by adjusting the heating temperature of the transport rolls (temperature of the heating rolls), the number of heating rolls, the contact time with the heating rolls, etc. The temperature of the heating rolls is preferably 60°C to 120°C, more preferably 65°C to 100°C, and particularly preferably 70°C to 80°C. The crystallization degree of the thermoplastic resin can be increased well, curling can be suppressed well, and the laminate can be given extremely excellent durability. The temperature of the heating rolls can be measured by a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular restriction as long as there are multiple transport rolls. The number of transport rolls is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating rolls is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and even more preferably 1 to 10 seconds.

The heating rolls may be installed in a heating furnace (e.g., an oven) or in a normal production line (at room temperature). Preferably, they are installed in a heating furnace equipped with a blowing means. By using both drying with the heating rolls and hot air drying, it is possible to suppress abrupt temperature changes between the heating rolls, and it is possible to easily control shrinkage in the width direction. The hot air drying temperature is preferably 30°C to 100°C. The hot air drying time is preferably 1 second to 300 seconds. The hot air speed is preferably about 10 m/s to 30 m/s. The air speed is the air speed in the heating furnace, and can be measured by a mini-vane type digital anemometer.

Preferably, after the underwater stretching process, a cleaning process is performed before the drying shrinkage process. The cleaning process is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.

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

[Example 1]
The thermoplastic resin substrate used was a long amorphous isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) having a water absorption rate of 0.75% and a Tg of about 75° C. One side of the resin substrate was subjected to a corona treatment.
A PVA aqueous solution (coating solution) was prepared by adding 13 parts by weight of potassium iodide to 100 parts by weight of a PVA-based resin prepared by mixing polyvinyl alcohol (polymerization degree 4,200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Mitsubishi Chemical Corporation, product name "GOHSENEX Z410") in a ratio of 9:1, and dissolving the resultant in water.
The above PVA aqueous solution was applied to the corona-treated surface of a resin substrate and dried at 60° C. to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.
The obtained laminate was uniaxially stretched at its free end to 2.4 times its original size in the machine direction (longitudinal direction) between rolls having different peripheral speeds in an oven at 130° C. (auxiliary air stretching treatment).
Next, the laminate was immersed in an insolubilizing bath (a boric acid aqueous solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (insolubilizing treatment).
Next, the film was immersed in a dye bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) having a liquid temperature of 30° C. for 60 seconds while adjusting the concentration so that the single transmittance (Ts) of the finally obtained polarizing film would be 43.0% (dyeing treatment).
Next, the plate was immersed in a crosslinking bath (a boric acid aqueous solution obtained by mixing 3 parts by weight of potassium iodide and 5 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40° C. for 30 seconds (crosslinking treatment).
Thereafter, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4 wt %, potassium iodide concentration: 5 wt %) at a liquid temperature of 70° C., and uniaxially stretched in the longitudinal direction (longitudinal direction) between rolls with different peripheral speeds to a total stretch ratio of 5.5 times (underwater stretching treatment).
Thereafter, the laminate was immersed in a cleaning bath (an aqueous solution obtained by mixing 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20° C. (cleaning treatment).
Thereafter, while drying in an oven maintained at 90° C., the laminate was brought into contact with a SUS heated roll having a surface temperature maintained at 75° C. for about 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment was 5.2%.
In this manner, a polarizing film (absorption type polarizing film) having a thickness of 5 μm was formed on the resin substrate.

A cycloolefin resin film with a thickness of 25 μm was attached as a protective layer to the surface of the obtained polarizing film (the surface of the laminate facing the polarizing film) via an ultraviolet-curing adhesive. Specifically, the adhesive was applied so that the thickness of the adhesive layer after curing was approximately 1 μm, and the films were laminated using a rolling machine. The adhesive was then cured by irradiating it with UV light from the cycloolefin resin film side. The resin substrate was then peeled off to obtain a polarizing film (absorptive polarizing film) having a cycloolefin resin film/absorptive polarizing film configuration.

[Example 2]
A polarizing film including a polarizing membrane having a thickness of 7 μm was obtained in the same manner as in Example 1, except that a PVA-based resin layer having a thickness of 18 μm was formed on the resin substrate.

[Comparative Example 1]
A long roll of a polyvinyl alcohol (PVA)-based resin film (manufactured by Kuraray, product name "PE3000") having a thickness of 30 μm was uniaxially stretched in the longitudinal direction to 5.9 times its original length using a roll stretching machine while simultaneously undergoing swelling, dyeing, crosslinking, and washing treatments in this order, and finally a drying treatment was performed to produce a polarizing film (absorptive polarizing film) having a thickness of 12 μm.
The above swelling treatment was performed by stretching the film 2.2 times while treating with pure water at 20°C. Next, the dyeing treatment was performed by stretching the film 1.4 times while treating it in an aqueous solution at 30°C in which the weight ratio of iodine to potassium iodide was 1:7, and the iodine concentration was adjusted so that the single transmittance of the resulting polarizing film was 45.0%. Next, the crosslinking treatment was performed in two stages, and the first stage was stretched 1.2 times while treating it in an aqueous solution at 40°C in which boric acid and potassium iodide were dissolved. The aqueous solution at the first stage had a boric acid content of 5.0% by weight and a potassium iodide content of 3.0% by weight. The second stage was stretched 1.6 times while treating it in an aqueous solution at 65°C in which boric acid and potassium iodide were dissolved. The aqueous solution at the second stage was stretched 1.6 times while treating it in an aqueous solution at 65°C in which boric acid and potassium iodide were dissolved. The aqueous solution at the second stage was stretched 4.3% by weight and 5.0% by weight. Next, the film was washed with an aqueous potassium iodide solution at 20° C. The aqueous solution used for the washing treatment had a potassium iodide content of 2.6% by weight. Finally, the film was dried at 70° C. for 5 minutes to obtain a polarizing film.

A cycloolefin resin film with a thickness of 25 μm was attached as a protective layer to the obtained polarizing film using a 3% aqueous solution of a PVA-based adhesive (manufactured by Mitsubishi Chemical Corporation, product name "GOHSENOL Z200") to obtain a polarizing film.

[Comparative Example 2]
A polarizing film including a polarizing membrane having a thickness of 17 μm was obtained in the same manner as in Comparative Example 1, except that a PVA-based resin film having a thickness of 45 μm was used.

[Comparative Example 3]
A polarizing film including a polarizing membrane having a thickness of 23 μm was obtained in the same manner as in Comparative Example 1, except that a PVA-based resin film having a thickness of 60 μm was used.

[Comparative Example 4]
A polarizing film including a polarizing membrane having a thickness of 30 μm was obtained in the same manner as in Comparative Example 1, except that a PVA-based resin film having a thickness of 75 μm was used.

The following evaluations were carried out for the Examples and Comparative Examples. The evaluation results are summarized in Table 1.
<Evaluation>
1. Dimensional change rate (%)
A test piece measuring 100 mm×100 mm was cut out from the obtained polarizing film along the stretching direction and the direction perpendicular thereto, and attached to a glass plate via an acrylic adhesive layer having a thickness of 20 μm. This was heated in an oven at 80° C. for 500 hours, and the size before and after heating was measured, and the dimensional change rate before and after heating was calculated.
2. Contraction stress (N/4mm)
From the obtained polarizing film (before laminating the protective film), test pieces with a size of 20 mm x 4 mm were cut out along the stretching direction and the direction perpendicular thereto, and were set in a TMA analyzer ("TMA7100E" manufactured by Hitachi High-Tech Science Corporation). While maintaining this state, the test pieces were heated at 50°C for 30 minutes, and the shrinkage stress generated by the test pieces was measured.
3. Optical Unevenness The obtained polarizing film was cut into a size of 200 mm x 150 mm, and the obtained sample was attached to a glass plate via a 20 μm acrylic adhesive layer, and placed in a heating tester at 80° C. for 120 hours. Then, another standard polarizing plate (manufactured by Nitto Denko Corporation, "CRT1794") was superimposed on the removed sample so that their absorption axes were perpendicular to each other, and this was placed on a backlight, and in this state, the in-plane unevenness was confirmed.

In the comparative example, optical unevenness (especially at the corners) was observed, as shown in Figure 5.

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 embodiments can be replaced with configurations that are substantially the same as those shown in the above-described embodiments, that have the same effects, or that can achieve the same purpose.

The lens portion according to the embodiment of the present invention can be used, for example, in a display such as a VR goggle.

2 display system 4 lens portion 12 display element 14 reflecting portion 16 first lens portion 18 half mirror 20 first phase difference member 22 second phase difference member 24 second lens portion 30 laminate 32 reflective polarizing member 34 absorptive polarizing member 36 adhesive layer

Claims (10)

1. A lens unit for use in a display system for displaying an image to a user, comprising:
a reflecting section that reflects light that is emitted forward from a display surface of a display element that displays an image and that has passed through a polarizing member and a first λ/4 member, the reflecting section including a reflective polarizing member and an absorptive polarizing member that is disposed in front of the reflective polarizing member;
a first lens portion disposed on an optical path between the display element and the reflector;
a half mirror disposed between the display element and the first lens portion, the half mirror transmitting light emitted from the display element and reflecting the light reflected by the reflecting portion toward the reflecting portion;
a second λ/4 member disposed on an optical path between the half mirror and the reflecting portion,
The thickness of the absorptive polarizing film constituting the absorptive polarizing member is 8 μm or less.
Lens part. The lens portion according to claim 1, wherein the reflection axis of the reflective polarizing element and the absorption axis of the absorptive polarizing element are arranged parallel to each other. The lens unit according to claim 1, wherein the first lens unit and the half mirror are integral. The lens unit according to claim 1, further comprising a second lens unit disposed in front of the reflecting unit. the angle between the absorption axis of the polarizing member included in the display element and the slow axis of the first λ/4 member is 40° to 50°;
2. The lens portion according to claim 1, wherein an angle between an absorption axis of the polarizing member included in the display element and a slow axis of the second λ/4 member is 40° to 50°. The lens portion according to claim 1, wherein the ratio of the thickness of the absorptive polarizing film to the thickness of the reflective polarizing member is 15% or less. The lens unit according to claim 1 is used in the reflecting portion of the lens unit.
The reflective polarizing member and the absorptive polarizing member are included.
A laminate for the lens portion of the display system . The laminate for the lens portion of the display system according to claim 7 , wherein the reflective polarizing member and the absorptive polarizing member are laminated via an adhesive layer. A display having a lens portion according to any one of claims 1 to 6. A step of passing light representing an image outputted through the polarizing member and the first λ/4 member through a half mirror and a first lens unit;
A step of passing the light that has passed through the half mirror and the first lens portion through a second λ/4 member;
A step of reflecting the light that has passed through the second λ/4 member toward the half mirror by a reflecting section including a reflective polarizing member;
allowing the light reflected by the reflecting unit and the half mirror to pass through the reflective polarizing member of the reflecting unit by the second λ/4 member;
and transmitting the light transmitted through the reflective polarizing member through an absorptive polarizing member,
The thickness of the absorptive polarizing film constituting the absorptive polarizing member is 8 μm or less.
Display method.

Images