Optical film piece and method for manufacturing same

Abstract

Provided is an optical film piece whereby it is possible to satisfactorily achieve weight reduction in VR goggles while improving visibility. The optical film piece is provided with an absorption-type polarizing film. The absorption-type polarizing film is composed of polyvinyl alcohol-based resin. On the main surface of the absorption-type polarizing film, an orientation function of a first portion located in the central portion is different from an orientation function of a second portion located outside the first portion.

Description

Optical film piece and method for manufacturing the same

[0001] The present invention relates to optical film pieces and methods for making the same.

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

[0003] In recent years, new applications of image display devices have been developed. For example, goggles with displays (VR goggles) for realizing virtual reality (VR) have begun to be commercialized. Since the use of VR goggles in various situations is being considered, there is a demand for lighter weight, improved visibility, and the like.

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

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

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

[0007] 1. An optical film piece according to an embodiment of the present invention is an optical film piece including an absorptive polarizing film, the absorptive polarizing film being made of a polyvinyl alcohol-based resin, and the orientation function of a first portion located in the center of a main surface of the absorptive polarizing film is different from the orientation function of a second portion located outside the first portion. 2. In the optical film piece described in 1 above, the absorptive polarizing film may have a portion with an orientation function of 0.30 or less. 3. In the optical film piece described in 1 or 2 above, the absolute value of the difference between the orientation function of the first portion and the orientation function of the second portion may be 0.02 or more. 4. In the optical film piece described in any one of 1 to 3 above, the main surface may be curved. 5. A method for manufacturing an optical film piece according to an embodiment of the present invention is the method for manufacturing an optical film piece described in any one of 1 to 4 above, and includes heating and stretching a member including a polyvinyl alcohol-based resin film to integrate it with a part having a curved portion, and the orientation function of the polyvinyl alcohol-based resin film is 0.30 or less. 6. In the method for manufacturing an optical film piece described above in 5, the radius of curvature of the curved surface of the component may be 150 mm or less. 7. In the method for manufacturing an optical film piece described above in 5 or 6, the radius of curvature of the curved surface of the component may be 40 mm or less.

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

[0009] Fig. 4B is a top view of an optical film piece according to one embodiment of the present invention. Fig. 5 is a schematic partially enlarged cross-sectional view showing the general configuration of the optical film piece shown in Fig. 1. Fig. 6 is a schematic cross-sectional view showing a state in which the optical film piece shown in Fig. 1 is integrated with an optical component. Fig. 7 is a view showing an example of a method for manufacturing an optical film piece according to one embodiment of the present invention. Fig. 8 is a view continuing from Fig. 4A. Fig. 9 is a view continuing from Fig. 5B. Fig. 10 is a view continuing from Fig. 1C. Fig. 11 is a schematic view showing the general configuration of an example of a display system for VR goggles.

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In order to clarify the description, the drawings may schematically show the width, thickness, shape, etc. of each part compared to the embodiments, but these are merely examples and do not limit the interpretation of the present invention. Furthermore, in the drawings, the same or equivalent elements are given the same reference numerals, and redundant explanations may be omitted.

[0011] (Definition of Terms and Symbols) The definitions of terms and symbols used in this specification are as follows. (1) Refractive Index (nx, ny, nz) "nx" is the refractive index in the direction in which the in-plane refractive index is maximum (i.e., the slow axis direction), "ny" is the refractive index in the in-plane direction perpendicular to the slow axis (i.e., the fast axis direction), and "nz" is the refractive index in the thickness direction. (2) In-Plane Retardation (Re) "Re(λ)" is the in-plane retardation measured with light having a wavelength of λ nm at 23°C. For example, "Re(550)" is the in-plane retardation measured with light having a wavelength of 550 nm at 23°C. Re(λ) is calculated by the formula: Re(λ) = (nx - ny) × d, where d (nm) is the thickness of the layer (film). (3) Thickness Direction Retardation (Rth) "Rth(λ)" is the retardation in the thickness direction measured with light having a wavelength of λ nm at 23°C. For example, "Rth(550)" is the retardation in the thickness direction measured with light having a wavelength of 550 nm at 23°C. Rth(λ) is calculated by the formula: Rth(λ) = (nx - nz) x d, where d (nm) is the thickness of the layer (film). (4) Nz coefficient The Nz coefficient is calculated by Nz = Rth / Re. (5) Angle When an angle is mentioned in this specification, the angle includes both clockwise and counterclockwise angles relative to the reference direction. Therefore, for example, "45°" means ±45°.

[0012] [Optical Film Piece] Fig. 1 is a top view of an optical film piece according to one embodiment of the present invention, Fig. 2 is a schematic partially enlarged cross-sectional view showing the general configuration of the optical film piece shown in Fig. 1, and Fig. 3 is a schematic cross-sectional view showing the optical film piece shown in Fig. 1 integrated with an optical component. Note that in Fig. 3, cross sections of the optical component and the optical film piece are not hatched to make the drawing easier to see. Also, details of the optical film piece are omitted.

[0013] The optical film piece 1 includes an absorptive polarizing element 28 and a pressure-sensitive adhesive layer 30. The absorptive polarizing element 28 includes at least an absorptive polarizing film 28a. In the illustrated example, the absorptive polarizing element 28 includes a protective layer 29 in addition to the absorptive polarizing film 28a. Unlike the illustrated example, the protective layer 29 may be omitted. In this case, the absorptive polarizing element 28 may correspond to an absorptive polarizing film.

[0014] The optical film piece 1 has a substantially circular shape in plan view, but is not limited to this. For example, the optical film piece 1 may have a substantially elliptical shape or a rounded rectangular shape. The major axis of the optical film piece 1 in plan view is, for example, 10 mm to 100 mm. Here, the major axis in plan view is the distance between the two most distant points on the periphery of the optical film piece when viewed from above.

[0015] The optical film piece 1 has a first main surface 1a and a second main surface 1b facing each other. The first main surface 1a and the second main surface 1b of the optical film piece 1 are curved. In the illustrated example, the optical film piece 1 has a convex curvature toward the second main surface 1b, the first main surface 1a has a concave curve, and the second main surface 1b has a convex curve. In the example shown in FIG. 3 , the optical film piece 1 is attached to the concave surface of an optical component (e.g., a lens) L having a curved surface by its pressure-sensitive adhesive layer 30 (not shown in FIG. 3 ), and the absorptive polarizing film 28a has a convex curvature toward the pressure-sensitive adhesive layer 30, and the main surface of the absorptive polarizing film 28a has a curved surface. Unlike the illustrated example, the optical film piece 1 may be attached to the convex surface of the optical component L. The radius of curvature of the main surface of the optical film piece 1 is, for example, 10 mm or more and 150 mm or less, preferably 100 mm or less, and more preferably 90 mm or less. The radius of curvature can be confirmed using, for example, a laser displacement meter.

[0016] <Absorptive Polarizing Film> The absorptive polarizing film 28 a is typically made of a polyvinyl alcohol resin (PVA resin) containing a dichroic material such as iodine, an organic dye, etc. The thickness of the absorptive polarizing film 28 a is, for example, 1 μm or more and 20 μm or less, or may be 2 μm or more and 15 μm or less, 12 μm or less, 10 μm or less, or 8 μm or less.

[0017] The absorptive polarizing film 28a preferably exhibits absorptive dichroism at any wavelength between 380 nm and 780 nm. The crossed transmittance (Tc) of the absorptive polarizing film 28a 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 film 28a is, for example, 40.0% to 45.0%, and preferably 41.0% or more. The polarization degree (P) of the absorptive polarizing film 28a is, for example, 99.0% to 99.997%, and preferably 99.8% or more.

[0018] The crossed transmittance, single transmittance, and degree of polarization can be measured, for example, using an ultraviolet-visible spectrophotometer. The degree of polarization P can be calculated from the obtained Tp and Tc by measuring the single transmittance Ts, parallel transmittance Tp, and crossed transmittance Tc using an ultraviolet-visible spectrophotometer, using the following formula: Ts, Tp, and Tc are Y values ​​measured using a 2-degree visual field (C light source) according to JIS Z 8701 and corrected for visibility. Degree of polarization P (%) = {(Tp - Tc) / (Tp + Tc)} １／２ ×100

[0019] In the absorptive polarizing film 28a, polyvinyl alcohol molecules are typically oriented. The orientation state of the polyvinyl alcohol molecules may vary across the principal surface 28b of the absorptive polarizing film 28a. Specifically, the principal surface 28b of the absorptive polarizing film 28a may have a distribution of orientation functions that can represent the orientation state of the polyvinyl alcohol molecules. For example, the orientation function of the first region 28c located in the center of the principal surface of the absorptive polarizing film 28a may differ from the orientation function of the second region 28d located outside the first region 28c. Specifically, the absolute value of the difference between the orientation function of the first region 28c and the orientation function of the second region 28d is, for example, 0.02 or more, and may be 0.05 or more. Such a relationship suppresses the occurrence of cracks in the optical film piece 1, resulting in excellent appearance. Furthermore, the optical film piece 1 can be well integrated with an optical component L having a curved surface. For example, the optical film piece 1 can be integrated with the curved surface without leaving any gaps. Therefore, the optical film piece 1 can achieve, for example, improved visibility and weight reduction of VR goggles.

[0020] The absorptive polarizing film 28a may have a region with a low orientation function (sometimes referred to as a low orientation region) on the principal surface 28b. For example, the orientation function of the low orientation region on the principal surface 28b of the absorptive polarizing film 28a may be 0.30 or less, 0.29 or less, preferably 0.285 or less, more preferably 0.28 or less, and even more preferably 0.25 or less, and may even be 0.22 or less. By having such a region, the above-described orientation function distribution can be satisfied. Furthermore, the radius of curvature of the principal surface of the optical film piece 1 can be reduced. For example, the radius of curvature of the principal surface of the optical film piece 1 can be 40 mm or less. Note that when the radius of curvature is greater than 40 mm and less than 70 mm, the orientation function of the low orientation region may be, for example, 0.45 or less, 0.42 or less, 0.40 or less, 0.35 or less, or less than 0.31. When the radius of curvature exceeds 70 mm, the orientation function of the low orientation portion may be 0.50 or less, 0.45 or less, 0.42 or less, or 0.40 or less.

[0021] In one embodiment, the low-alignment portion may be formed at the periphery or end of the absorptive polarizing film 28 a, while in another embodiment, the low-alignment portion may be formed at the center of the absorptive polarizing film 28 a.

[0022] A method for producing the polyvinyl alcohol-based resin film (PVA-based resin film) constituting the absorptive polarizing film 28 a includes, for example, forming a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a polyvinyl alcohol-based resin (PVA-based resin) and a halide on one side of a long thermoplastic resin substrate to form a laminate, and subjecting the laminate to an in-air auxiliary stretching treatment, a dyeing treatment, an underwater stretching treatment, and a drying shrinkage treatment in which the laminate is heated while being transported in the longitudinal direction to shrink the laminate by 2% or more in the width direction, in that order.

[0023] The PVA-based resin layer is preferably formed by applying a coating liquid containing a PVA-based resin and a halide to a thermoplastic resin substrate and drying the coating liquid. 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 thickness of the PVA-based resin layer is preferably 3 to 40 μm, more preferably 3 to 20 μm.

[0024] Examples of the method for applying the coating liquid include roll coating, spin coating, wire bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (comma coating, etc.), etc. The temperature for applying and drying the coating liquid is preferably 50° C. or higher.

[0025] In order to improve the adhesion between the thermoplastic resin substrate and the PVA-based resin layer, the thermoplastic resin substrate may be subjected to a surface treatment such as a corona treatment before forming the PVA-based resin layer, or an easy-adhesion layer may be formed on the thermoplastic resin substrate.

[0026] The thickness of the thermoplastic resin substrate is preferably 20 μm to 300 μm, more preferably 50 μm to 200 μm. If the thickness is less than 20 μm, for example, it may be difficult to form a PVA-based resin layer. If the thickness is more than 300 μm, for example, in the underwater stretching treatment described below, it may take a long time for the thermoplastic resin substrate to absorb water, and an excessive load may be required for stretching.

[0027] The water absorption of the thermoplastic resin substrate is preferably 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, allowing the substrate to be stretched at a high ratio. On the other hand, the water absorption of the thermoplastic resin substrate is preferably 3.0% or less, more preferably 1.0% or less. The use of such a thermoplastic resin substrate can prevent problems such as a significant decrease in the dimensional stability of the substrate during production, resulting in a poor appearance of the resulting PVA-based resin film. Furthermore, it can prevent the substrate from breaking or the PVA-based resin layer from peeling off from the substrate during underwater stretching. The water absorption of the thermoplastic resin substrate can be adjusted, for example, by introducing a modifying group into the constituent materials. The water absorption is a value determined in accordance with JIS K 7209.

[0028] The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120°C or lower. By using such a thermoplastic resin substrate, the stretchability of the laminate can be sufficiently ensured while suppressing crystallization of the PVA-based resin layer. Considering the plasticization of the thermoplastic resin substrate with water and the smooth underwater stretching, the Tg is more preferably 100°C or lower, and even more preferably 90°C or lower. On the other hand, the Tg of the thermoplastic resin substrate is preferably 60°C or higher. By using such a thermoplastic resin substrate, defects such as deformation of the substrate (e.g., the occurrence of unevenness, sagging, wrinkles, etc.) during the application and drying of the coating liquid can be prevented, allowing for the production of a satisfactory laminate. Furthermore, the PVA-based resin layer can be stretched 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 modifying group into the constituent material or by heating using a crystallizing material. The glass transition temperature (Tg) is a value determined in accordance with JIS K 7121.

[0029] Examples of thermoplastic resins include ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, and copolymer resins thereof. Among these, norbornene resins and amorphous polyethylene terephthalate resins are preferably used.

[0030] In one embodiment, an amorphous (non-crystallized) polyethylene terephthalate resin is preferably used. Among them, an amorphous (hard to crystallize) polyethylene terephthalate resin is preferably used. Specific examples of the amorphous polyethylene terephthalate resin include copolymers further containing isophthalic acid and / or cyclohexanedicarboxylic acid as a dicarboxylic acid, and copolymers further containing cyclohexanedimethanol or diethylene glycol as a glycol.

[0031] In a preferred embodiment, the thermoplastic resin substrate is composed of a polyethylene terephthalate resin having an isophthalic acid unit. Such a thermoplastic resin substrate has excellent stretchability and can suppress crystallization during stretching. This is thought to be due to the introduction of the isophthalic acid unit, which imparts a large curvature to the main chain. The polyethylene terephthalate resin has a terephthalic acid unit and an ethylene glycol unit. The content 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 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 favorably increased during the drying shrinkage treatment described below.

[0032] The thermoplastic resin substrate may be stretched by any appropriate method before forming the PVA-based resin layer. For example, the long thermoplastic resin substrate may be stretched in the transverse direction. The transverse direction is preferably a direction approximately perpendicular to the stretching direction of the laminate described below. 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.

[0033] As described above, the coating liquid may contain a PVA-based resin and a halide. The coating liquid may typically be a solution in which a PVA-based resin and a halide 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. Among these, water is preferably used. The concentration of the PVA-based resin is preferably 3 to 20 parts by weight per 100 parts by weight of the solvent. The content of the halide in the coating liquid is preferably 5 to 20 parts by weight, more preferably 10 to 15 parts by weight, per 100 parts by weight of the PVA-based resin.

[0034] Examples of the PVA-based resin 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, for example, 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. The average polymerization degree of the PVA-based resin is, for example, 1,000 to 10,000, preferably 1,200 to 4,500, and more preferably 1,500 to 4,300. The average polymerization degree can be determined in accordance with JIS K 6726-1994. Examples of the halide include iodides such as potassium iodide, sodium iodide, and lithium iodide, and sodium chloride. Of these, potassium iodide is preferably used.

[0035] The coating liquid may contain additives. 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.

[0036] Stretching a PVA-based resin layer can increase the orientation of polyvinyl alcohol molecules in the PVA-based resin. However, immersing the stretched PVA-based resin layer in a liquid containing water can disrupt the orientation of the polyvinyl alcohol molecules, resulting in a decrease in the orientation. When a laminate of a thermoplastic resin substrate and a PVA-based resin layer is stretched in boric acid water at a relatively high temperature to stabilize the stretching of the thermoplastic resin substrate, the orientation tends to decrease significantly. In contrast, high-temperature stretching (auxiliary stretching) in air of a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate before stretching in boric acid water can promote crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after auxiliary stretching. As a result, when the PVA-based resin layer is immersed in a liquid, the disruption of the orientation of polyvinyl alcohol molecules and the decrease in the orientation can be suppressed compared to when the PVA-based resin layer does not contain a halide. This can improve the optical properties of the PVA-based resin film obtained through a process in which the laminate is immersed in a liquid, such as a dyeing process and an underwater stretching process.

[0037] To obtain high optical properties, a two-stage stretching method can be selected, combining in-air stretching (auxiliary stretching) and stretching in boric acid water. By introducing auxiliary stretching, stretching can be performed while suppressing crystallization of the thermoplastic resin substrate, thereby solving the problem of reduced stretchability due to excessive crystallization of the thermoplastic resin substrate during subsequent stretching in boric acid water, and allowing the laminate to be stretched at a high magnification. Furthermore, when a PVA-based resin is applied to a thermoplastic resin substrate, the application temperature must be lower than, for example, when the PVA-based resin is applied to a metal drum in order to suppress the influence of the glass transition temperature of the thermoplastic resin substrate. As a result, the crystallization of the PVA-based resin is relatively low, which can lead to problems such as insufficient optical properties being obtained. In contrast, by introducing auxiliary stretching, it is possible to increase the crystallinity of the PVA-based resin, even when the PVA-based resin is applied to a thermoplastic resin substrate, and high optical properties can be achieved. 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 when the PVA-based resin is immersed in water during subsequent dyeing or stretching treatments can be prevented, and high optical properties can be achieved.

[0038] The method of the auxiliary in-air stretching may be fixed-end stretching (e.g., a method of stretching using a tenter stretching machine) or free-end stretching (e.g., a method of uniaxially stretching a laminate by passing it between rolls having different peripheral speeds). From the viewpoint of obtaining high optical properties, free-end stretching is preferably used.

[0039] The draw ratio of the auxiliary in-air stretching is preferably 2.0 to 3.5. The auxiliary in-air stretching may be carried out in one stage or in multiple stages. When carried out in multiple stages, the draw ratio is the product of the draw ratios in each stage. The stretching direction in the auxiliary in-air stretching is preferably approximately the same as the stretching direction in the underwater stretching.

[0040] The stretching temperature for the auxiliary in-air stretching is preferably equal to or higher than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably equal to or higher than Tg of the thermoplastic resin substrate + 10°C, and even more preferably equal to or higher than Tg of the thermoplastic resin substrate + 15°C. On the other hand, the upper limit of the stretching temperature is preferably 170°C. By stretching at such a temperature, rapid crystallization of the PVA-based resin can be suppressed, thereby suppressing defects due to crystallization (for example, preventing the orientation of the PVA-based resin layer due to stretching). The crystallization index of the PVA-based resin after the auxiliary in-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 performed using polarized light as the measurement light, and the crystallization index at 1141 cm of the obtained spectrum is measured. －１ and 1440 cm －１ The crystallization index is calculated using the intensity according to the following formula: Crystallization index = (I Ｃ / I Ｒ ) where I Ｃ is 1141 cm when measured with incident measuring light －１ is the intensity of I Ｒ is 1440 cm when measured with incident measuring light －１ is the strength.

[0041] After the auxiliary air-stretching treatment, an insolubilization treatment may be carried out before the underwater stretching treatment or the dyeing treatment. The insolubilization treatment is typically carried out by immersing the PVA-based resin layer in an aqueous boric acid solution. The insolubilization treatment imparts water resistance to the PVA-based resin layer, thereby preventing a decrease in the orientation of the PVA when immersed in water. The concentration of the aqueous boric acid solution used in the insolubilization treatment 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 to 50°C.

[0042] The dyeing treatment is typically carried out by dyeing the PVA-based resin layer with iodine. Specifically, the dyeing treatment is carried out by allowing the PVA-based resin layer to adsorb iodine. A preferred method for adsorbing iodine is to immerse the PVA-based resin layer (laminate) in a dye solution (dye bath) containing iodine.

[0043] The dye solution is preferably an aqueous iodine solution. In this case, the amount of iodine blended is preferably 0.05 to 0.5 parts by weight per 100 parts by weight of water. To increase the solubility of iodine in water, it is preferable to blend an iodide into 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. Among these, potassium iodide is preferably used. The amount of iodide blended 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 dye solution during dyeing is preferably 20 to 50°C 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, more preferably 30 seconds to 90 seconds, in order to ensure the transmittance of the PVA-based resin layer.

[0044] The dyeing conditions (concentration, solution temperature, immersion time) can be set so that the single transmittance and polarization degree of the resulting PVA-based resin film fall within the above-mentioned ranges. For example, the ratio of the iodine content to the potassium iodide content in the iodine aqueous solution used as the dyeing solution is preferably 1:5 to 1:20, more preferably 1:5 to 1:10.

[0045] When a dyeing process is performed consecutively after a treatment (e.g., an insolubilization treatment) in which a laminate is immersed in a treatment bath containing boric acid, the boric acid contained in the treatment bath may be mixed into the dye bath, causing the boric acid concentration of the dye bath to change over time, resulting in unstable dyeability. To prevent this instability in dyeability, the upper limit of the boric acid concentration of the dye bath is preferably adjusted to 4 parts by weight, more preferably 2 parts by weight, per 100 parts by weight of water. Meanwhile, the lower limit of the boric acid concentration of the dye 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, a dye bath containing boric acid is used in advance. This can reduce the rate of change in boric acid concentration when the boric acid from the treatment bath is mixed into the dye bath. The amount of boric acid to be blended in advance 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.

[0046] A crosslinking treatment may be 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, thereby preventing a decrease in the orientation of the PVA when the layer is immersed in high-temperature water during the subsequent underwater stretching treatment. The concentration of the aqueous boric acid solution used in the crosslinking treatment is preferably 1 to 5 parts by weight per 100 parts by weight of water. Furthermore, when the crosslinking treatment is performed after the dyeing treatment, it is preferable to further incorporate an iodide. The incorporation of an iodide can suppress the elution of iodine adsorbed to the PVA-based resin layer. The amount of iodide incorporated 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 to 50°C.

[0047] The underwater stretching treatment is carried out by immersing the laminate in a stretching bath. Underwater stretching treatment 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 while suppressing crystallization. As a result, a PVA-based resin film with excellent optical properties can be produced.

[0048] Any appropriate method can be adopted as the stretching method for the laminate. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method in which the laminate is uniaxially stretched by passing it between rolls with different peripheral speeds). Preferably, free-end stretching is selected. The stretching of the laminate may be carried out in one stage or in multiple stages. When it is carried out in multiple stages, the stretching ratio of the laminate described below is the product of the stretching ratios in each stage.

[0049] The underwater stretching is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in boric acid solution). Using an aqueous boric acid solution as a stretching bath can impart to the PVA-based resin layer rigidity sufficient to withstand the tension applied during stretching and water resistance sufficient to prevent dissolution in water. Specifically, boric acid generates tetrahydroxyborate anions in the aqueous solution, which can crosslink with the PVA-based resin through hydrogen bonding. As a result, the PVA-based resin layer is imparted with rigidity and water resistance, allowing for satisfactory stretching, and a PVA-based resin film with excellent optical properties can be produced.

[0050] The boric acid aqueous solution is preferably obtained by dissolving boric acid and / or a borate in water as a solvent. The boric acid concentration is preferably 1 to 10 parts by weight, more preferably 2.5 to 7 parts by weight, and even more preferably 3 to 6 parts by weight, per 100 parts by weight of water. By setting the boric acid concentration to 1 part by weight or more, dissolution of the PVA-based resin layer can be effectively suppressed, allowing the production of a PVA-based resin film with higher performance. In addition to boric acid or a borate, aqueous solutions obtained by dissolving boron compounds such as borax, glyoxal, glutaraldehyde, or the like in a solvent can also be used.

[0051] Preferably, an iodide is added to the stretching bath (boric acid aqueous solution). By adding an iodide, it is possible to suppress the elution of iodine adsorbed in the PVA-based resin layer. Specific examples of iodides are as described above. The concentration of the 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.

[0052] The stretching temperature (liquid temperature of the stretching bath) is preferably 40°C or higher, more preferably 60°C or higher. At such a temperature, good stretching can be achieved. 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 lower than 40°C, good stretching may not be achieved, even taking into account the plasticization of the thermoplastic resin substrate by water. On the other hand, the stretching temperature (liquid temperature of the stretching bath) is preferably 85°C or lower, more preferably 75°C or lower. The higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, which may result in poor optical properties. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.

[0053] The orientation function, breaking point, and elastic modulus of the PVA-based resin film described below can be controlled, for example, by adjusting the stretching ratio in underwater stretching. In one embodiment, the stretching ratio in underwater stretching is preferably 1.8 times or less, more preferably 1.7 times or less, and may even be 1.6 times or less. The total stretching ratio of the laminate is preferably 4.3 times or less, more preferably 4.0 times or less, and even more preferably 3.7 times or less, relative to the original length of the laminate.

[0054] The stretching ratio in underwater stretching is, for example, more than 1.0, preferably 1.1 or more, more preferably 1.2 or more, and even more preferably 1.3 or more. The total stretching ratio of the laminate is, for example, more than 2.5, preferably 3.0 or more, and more preferably 3.2 or more, relative to the original length of the laminate. Such a stretching ratio allows the production of a PVA-based resin film with excellent optical properties. Such a stretching ratio can be satisfactorily achieved by employing underwater stretching (stretching in boric acid water).

[0055] The drying shrinkage treatment may be performed by zone heating, which heats the entire zone, or by heating the transport rolls (using so-called heated rolls). Preferably, both methods are used. Drying using heated rolls efficiently suppresses heat curling of the laminate, resulting in the production of a PVA-based resin film with excellent appearance. Specifically, drying the laminate while it is aligned with the heated rolls efficiently promotes crystallization of the thermoplastic resin substrate, thereby increasing the crystallinity. Even at relatively low drying temperatures, the crystallinity of the thermoplastic resin substrate can be favorably increased. As a result, the rigidity of the thermoplastic resin substrate increases, enabling it to withstand shrinkage of the PVA-based resin layer due to drying, thereby suppressing curling. Furthermore, using heated rolls allows the laminate to be dried while maintaining a flat state, thereby suppressing not only curling but also wrinkling. At this time, the optical properties of the laminate can be improved by shrinking it in the width direction through the drying shrinkage treatment. This is because the orientation of the PVA and the PVA / iodine complex can be effectively enhanced. 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, thereby achieving high productivity.

[0056] For example, drying conditions can be controlled by adjusting the heating temperature of the transport rolls (heating roll temperature), 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 even more preferably 70°C to 80°C. This effectively increases the crystallinity of the thermoplastic resin substrate, effectively suppressing curling and imparting excellent strength to the laminate. The temperature of the heating rolls can be measured using a contact thermometer. Typically, 2 to 40 transport rolls, preferably 4 to 30 rolls, are used. The contact time (total contact time) between the laminate and the heating rolls is preferably 1 second to 300 seconds, more preferably 1 second to 20 seconds, and even more preferably 1 second to 10 seconds.

[0057] The heating rolls may be installed in a heating furnace (e.g., an oven) or in a normal production line (under room temperature). Preferably, they are installed in a heating furnace equipped with a blower. By using both heating roll drying and hot air drying, it is possible to suppress abrupt temperature changes between the heating rolls, and 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. Note that this air speed is the air speed inside the heating furnace and can be measured using a mini-vane type digital anemometer.

[0058] Preferably, after the underwater stretching treatment and before the drying shrinkage treatment, a washing treatment is carried out by, for example, immersing the PVA-based resin layer in an aqueous potassium iodide solution.

[0059] For example, the orientation function of the PVA-based resin film may be 0.30 or less, 0.29 or less, preferably 0.285 or less, more preferably 0.28 or less, even more preferably 0.25 or less, and may be 0.22 or less. On the other hand, the orientation function is, for example, 0.05 or more, preferably 0.10 or more, more preferably 0.15 or more. If the orientation function is too small, excellent optical properties (e.g., single transmittance and / or polarization degree) may not be obtained. Note that the formation of low-orientation portions having an orientation function exceeding 0.30 can be achieved, for example, by increasing the stretching ratio in the underwater stretching.

[0060] The absorption axis direction of the PVA-based resin film may substantially correspond to the stretching direction (MD direction) of the PVA-based resin layer. The transmission axis direction of the PVA-based resin film may substantially correspond to the direction (TD direction) perpendicular to the stretching direction (MD direction) of the PVA-based resin layer. The break point of the PVA-based resin film in the absorption axis direction is, for example, 3.0% to 20%, and preferably 3.2% or more. The break point of the PVA-based resin film in the transmission axis direction is, for example, 10% to 50%. The ratio of the break point of the PVA-based resin film in the transmission axis direction to the break point of the PVA-based resin film in the absorption axis direction (break point in transmission axis direction / break point in absorption axis direction) is, for example, 10 or less, and preferably 9 or less. The elastic modulus of the PVA-based resin film in the absorption axis direction is, for example, 1000 MPa to 2500 MPa, and preferably 2200 MPa or less. The elastic modulus of the PVA-based resin film in the transmission axis direction is preferably 1200 MPa to 2500 MPa. The ratio of the elastic modulus of the PVA-based resin film in the transmission axis direction to the elastic modulus of the PVA-based resin film in the absorption axis direction (elastic modulus of the transmission axis direction / elastic modulus of the absorption axis direction) is, for example, 0.5 or more, preferably 0.7 or more. Here, the breaking point and elastic modulus of the PVA-based resin film may each be values ​​at 120°C.

[0061] <Protective Layer> The protective layer 29 that can be included in the absorptive polarizing member 28 can be composed of any appropriate film. Examples of materials that serve as the main component of the film that constitutes the protective layer include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, polysulfone-based, polystyrene-based, cycloolefin-based resins such as polynorbornene, polyolefin-based, (meth)acrylic, and acetate-based resins. Note that the resin substrate used in producing the PVA-based resin film may be used directly as the protective layer of the absorptive polarizing film.

[0062] The thickness of the protective layer is preferably 5 μm to 80 μm, more preferably 10 μm to 50 μm, and even more preferably 15 μm to 40 μm.

[0063] The optical film piece 1 can be obtained by integrating a member containing the PVA-based resin film with the curved surface of an optical component (e.g., lens L shown in FIG. 3). Specifically, by integrating a member containing a PVA-based resin film with an optical component, an optical film piece 1 including an absorptive polarizing member 28 including an absorptive polarizing film 28a can be obtained. The integration can be typically performed by bonding the member containing the PVA-based resin film to the curved surface of the optical component (e.g., lens L) using a pressure-sensitive adhesive layer. The obtained optical film piece 1 can then include a pressure-sensitive adhesive layer (pressure-sensitive adhesive layer 30 shown in FIG. 2).

[0064] 4A-4D are diagrams illustrating an example method for manufacturing an optical film piece according to one embodiment of the present invention.

[0065] FIG. 4A shows a state in which a workpiece 2 is prepared by providing a pressure-sensitive adhesive layer or the like on a member including a PVA-based resin film, and the workpiece 2 is placed above a lens L, which is an adherend. The lens L is, for example, circular in plan view and concave in cross section. The radius of curvature of the curved surface of the lens L is, for example, 10 mm or more and 150 mm or less, preferably 100 mm or less, more preferably 90 mm or less, and may be 70 mm or less, or may be 40 mm or less. The workpiece 2 is placed at a predetermined distance from the concave surface (top surface) of the lens L. The lens L is placed on a holder 52 on a liftable holding table 51 housed in a lower chamber 50. The end 2a of the workpiece 2 is sandwiched between the upper chamber 60 and the lower chamber 50.

[0066] 4B shows a state in which the space in which the workpiece 2 is placed is depressurized and the workpiece 2 is heated. Specifically, the upper chamber 60 and the lower chamber 50 are depressurized using a vacuum device (not shown) or the like, and then the workpiece 2 is heated. The shape of the workpiece 2 may be easily deformed by heating. The heating temperature of the workpiece 2 is preferably 50°C or higher and 150°C or lower.

[0067] FIG. 4C shows the state in which bonding of the workpiece 2 to the lens L has begun. When the workpiece 2 is in a state where it is easily deformed, the holding table 51 is raised, and a portion of the lens L (in the illustrated example, the peripheral portion) is brought into contact with the workpiece 2. After contact, the air pressure in the upper chamber 60 is gradually increased. The air pressure in the upper chamber 60 becomes higher than the air pressure in the lower chamber 50, which can create a pressure difference between the two spaces. This pressure difference gradually draws the workpiece 2 downward, allowing the entire workpiece 2 to be bonded to the lens L, as shown in FIG. 4D. In the illustrated example, after the peripheral portion of the lens L is brought into contact with the workpiece 2, the workpiece 2 can be bonded from the peripheral portion toward the center of the lens L. After bonding, unnecessary portions of the workpiece 2 (e.g., portions that do not overlap with the lens L in a planar view) are removed to obtain the optical film piece 1 shown in FIG. 3.

[0068] The PVA-based resin film may be stretched during integration with the curved surface. Stretching can change the orientation of the PVA-based resin film. For example, stretching can increase the orientation of the PVA-based resin film. In the example shown in FIGS. 4A to 4D , the workpiece 2 (PVA-based resin film) may be stretched more from the periphery (edge) of the lens L toward the center. For example, using a PVA-based resin film that satisfies the above orientation function can facilitate successful integration with the curved surface. Specifically, a member including the PVA-based resin film can be conformed to the shape of the curved surface, allowing it to be integrated with the curved surface without leaving any gaps. Furthermore, defects such as cracks in the PVA-based resin film can be suppressed during integration with the curved surface.

[0069] The optical film piece according to the embodiment of the present invention may include any other suitable optical element in addition to the absorptive polarizing element, and may be used in any suitable display device, such as VR goggles.

[0070] [Display System] Figure 5 is a schematic diagram showing the general configuration of an example of a display system for VR goggles, and schematically illustrates the arrangement and shape of each component of the display system. The display system 10 includes a display element 12, a reflective polarizing element 14, a first lens unit 16, a half mirror 18, a first λ / 4 element 20, a second λ / 4 element 22, and a second lens unit 24. The reflective polarizing element 14 is disposed in front of the display surface 12a of the display element 12 and can reflect light emitted from the display element 12. The first lens unit 16 is disposed on the optical path between the display element 12 and the reflective polarizing element 14, and the half mirror 18 is disposed between the display element 12 and the first lens unit 16. The first λ / 4 element 20 is disposed on the optical path between the display element 12 and the half mirror 18, and the second λ / 4 element 22 is disposed on the optical path between the half mirror 18 and the reflective polarizing element 14.

[0071] The half mirror or the components arranged forward from the first lens unit (in the illustrated example, the half mirror 18, first lens unit 16, second λ / 4 member 22, reflective polarizing member 14, and second lens unit 24) may be collectively referred to as the lens unit (lens unit 4).

[0072] The display element 12 is, for example, a liquid crystal display or an organic EL display, and has a display surface 12 a for displaying an image. The light emitted from the display surface 12 a passes through, for example, a polarizing member that may be included in the display element 12, and is converted into first linearly polarized light.

[0073] The first λ / 4 member 20 can convert the first linearly polarized light incident on the first λ / 4 member 20 into the first circularly polarized light. The first λ / 4 member 20 may be provided integrally with the display element 12.

[0074] The half mirror 18 transmits the light emitted from the display element 12 and reflects the light reflected by the reflective polarizing member 14 back toward the reflective polarizing member 14. The half mirror 18 is provided integrally with the first lens portion 16.

[0075] The second λ / 4 member 22 can transmit the light reflected by the reflective polarizing member 14 and the half mirror 18 through the reflective polarizing member 14. The second λ / 4 member 22 may be provided integrally with the first lens portion 16.

[0076] The first circularly polarized light output from the first λ / 4 member 20 passes through the half mirror 18 and the first lens portion 16, and is converted into the second linearly polarized light by the second λ / 4 member 22. The second linearly polarized light output from the second λ / 4 member 22 is reflected toward the half mirror 18 without passing through the reflective polarizing member 14. At this time, the polarization direction of the second linearly polarized light incident on the reflective polarizing member 14 is the same as the reflection axis of the reflective polarizing member 14. Therefore, the second linearly polarized light incident on the reflective polarizing member 14 is reflected by the reflective polarizing member 14.

[0077] The second linearly polarized light reflected by the reflective polarizing element 14 is converted into second circularly polarized light by the second λ / 4 element 22, and the second circularly polarized light emitted from the second λ / 4 element 22 passes through the first lens unit 16 and is reflected by the half mirror 18. The second circularly polarized light reflected by the half mirror 18 passes through the first lens unit 16 and is converted into third linearly polarized light by the second λ / 4 element 22. The third linearly polarized light is transmitted through the reflective polarizing element 14. At this time, the polarization direction of the third linearly polarized light incident on the reflective polarizing element 14 is the same direction as the transmission axis of the reflective polarizing element 14. Therefore, the third linearly polarized light incident on the reflective polarizing element 14 is transmitted through the reflective polarizing element 14.

[0078] The light transmitted through the reflective polarizing member 14 passes through the second lens portion 24 (the absorptive polarizing member 28 and the second lens portion 24 ) and enters the eye 26 of the user.

[0079] The absorption axis of the polarizing member included in the display element 12 and the reflection axis of the reflective polarizing member 14 may be disposed approximately parallel to each other or approximately perpendicular to each other. The angle between the absorption axis of the polarizing member included in the display element 12 and the slow axis of the first λ / 4 member 20 is, for example, 40° to 50°, or may be 42° to 48°, or may be approximately 45°. The angle between the absorption axis of the polarizing member included in the display element 12 and the slow axis of the second λ / 4 member 22 is, for example, 40° to 50°, or may be 42° to 48°, or may be approximately 45°.

[0080] The in-plane retardation Re(550) of the first λ / 4 member 20 is, for example, 100 nm to 190 nm, or may be 110 nm to 180 nm, 130 nm to 160 nm, or 135 nm to 155 nm. The first λ / 4 member 20 preferably exhibits an inverse dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light. The Re(450) / Re(550) of the first λ / 4 member 20 may be, for example, 0.75 or more and less than 1, or 0.8 or more and 0.95 or less.

[0081] The in-plane retardation Re(550) of the second λ / 4 member 22 is, for example, 100 nm to 190 nm, or may be 110 nm to 180 nm, 130 nm to 160 nm, or 135 nm to 155 nm. The second λ / 4 member 22 preferably exhibits an inverse dispersion wavelength characteristic in which the retardation value increases according to the wavelength of the measurement light. The Re(450) / Re(550) of the second λ / 4 member 22 may be, for example, 0.75 or more and less than 1, or 0.8 or more and 0.95 or less.

[0082] The display system 10 may include an absorptive polarizing element 28. The absorptive polarizing element 28 may be disposed in front of the reflective polarizing element 14. The reflection axis of the reflective polarizing element 14 and the absorption axis of the absorptive polarizing element 28 (absorptive polarizing film 28 a) may be disposed approximately parallel to each other, and the transmission axis of the reflective polarizing element 14 and the transmission axis of the absorptive polarizing element 28 (absorptive polarizing film 28 a) may be disposed approximately parallel to each other. The reflective polarizing element 14 and the absorptive polarizing element 28 may be integrated. The absorptive polarizing element 28 may be used in the above-described display system, for example, from the viewpoint of improving visibility.

[0083] In the display system 10, a space may be formed between the first lens portion 16 and the second lens portion 24. In this case, it is preferable that the member disposed between the first lens portion 16 and the second lens portion 24 is integrally formed with either the first lens portion 16 or the second lens portion 24. For example, the member disposed between the first lens portion 16 and the second lens portion 24 is integrated with either the first lens portion 16 or the second lens portion 24 via an adhesive layer. This configuration may provide, for example, excellent ease of handling of each member. The adhesive layer may be formed of an adhesive or a pressure-sensitive adhesive. Specifically, the adhesive layer may be an adhesive layer or a pressure-sensitive adhesive layer. The thickness of the adhesive layer is, for example, 0.01 μm to 60 μm.

[0084] The optical film piece according to the embodiment of the present invention may include, for example, components provided in the display system. The optical film piece may also include other components, such as an adhesive layer, for integrating adjacent components. The thickness of the optical film piece varies depending on, for example, the type and number of components included, but is, for example, 50 μm to 400 μm.

[0085] For example, an optical film piece according to an embodiment of the present invention may include a reflective polarizing element 14. The optical film piece may also include a second λ / 4 element 22. The optical film piece may then be integrated with, for example, the first lens portion 16 or the second lens portion 24. Typically, it may be bonded to the adherend, that is, the first lens portion 16 or the second lens portion 24, via an adhesive layer. For example, the first lens portion 16 shown in FIG. 5 has a curved surface portion and may correspond to the optical component (lens L) described above.

[0086] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. The thickness, orientation function, single-substrate transmittance, and degree of polarization were measured using the following measurement methods. <Thickness> Thicknesses of 10 μm or less were measured using a scanning electron microscope (manufactured by JEOL Ltd., product name "JSM-7100F"). Thicknesses of more than 10 μm were measured using a digital micrometer (manufactured by Anritsu Corporation, product name "KC-351C"). <Orientation Function> Using a Fourier transform infrared spectrometer (manufactured by PerkinElmer, model "Frontier FT-IR"), polarized light was used as the measurement light, and the spectra of the measurement samples (PVA-based resin film and absorption-type polarizing film) were measured by attenuated total reflection spectroscopy (ATR), and the orientation function (PVA orientation) of the measurement samples was calculated from the obtained spectral results. Specifically, germanium was used as the crystallite to which the measurement sample was adhered, the incident angle of the measurement light was set to 45°, and the incident polarized infrared light (measurement light) was polarized light (s-polarized light) that vibrated parallel to the surface of the germanium crystal to which the sample was adhered. The measurement was carried out with the stretching direction of the measurement sample arranged parallel and perpendicular to the polarization direction of the measurement light, and the peak at 2941 cm of the obtained absorbance spectrum －１ The intensity I was calculated according to the following formula using the intensity of 3330 cm －１ is used as the reference peak, and 2941 cm －１ / 3330cm －１ The value is: When f = 1, it is perfectly oriented, and when f = 0, it is random. Also, 2941 cm －１The peak is due to the main chain (-CH ２ It is believed that the absorption is due to the vibration of f = (3 < cos ２ θ>-1) / 2 = (1-D) / [c(2D+1)] = -2 x (1-D) / (2D+1) where c = (3cos ２ β-1) / 2, 2941 cm －１ In the case of vibration of the PVA type, β = 90°. θ: angle of molecular chain with respect to the stretching direction β: angle of transition dipole moment with respect to the molecular chain axis D = (I⊥) / (I / / ) (In this case, D increases as the PVA molecules become more oriented.) I⊥: absorption intensity when the polarization direction of the measurement light and the stretching direction of the measurement sample are perpendicular I / / : absorption intensity when the polarization direction of the measurement light and the stretching direction of the measurement sample are parallel <Single Transmittance and Degree of Polarization> The single transmittance Ts, parallel transmittance Tp, and crossed transmittance Tc of the PVA type resin film / resin substrate laminates obtained in the Examples and Comparative Examples were measured using a UV-visible spectrophotometer (LPF200, manufactured by Otsuka Electronics Co., Ltd.) and were taken as Ts, Tp, and Tc of the PVA type resin film, respectively. These Ts, Tp, and Tc are Y values ​​measured using a 2-degree visual field (C light source) according to JIS Z 8701 and corrected for luminosity. The degree of polarization P was calculated from the obtained Tp and Tc using the above formula.

[0087] Example 1 (Formation of a PVA-Based Resin Film) A long, amorphous, isophthalic copolymerized polyethylene terephthalate film (thickness: 100 μm) with a water absorption rate of 0.75% and a Tg of approximately 75°C was used as a thermoplastic resin substrate. One side of the resin substrate was subjected to a corona treatment. A PVA-based resin (100 parts by weight) containing a 9:1 mixture of polyvinyl alcohol (degree of polymerization: 4200, degree of saponification: 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Mitsubishi Chemical Corporation, trade name "GOHSENEX Z410") was dissolved in water to prepare an aqueous PVA solution (coating solution). The PVA aqueous solution was applied to the corona-treated surface of the resin substrate and dried at 60°C to form a 13 μm-thick PVA-based resin layer, producing a laminate. The resulting laminate was free-end uniaxially stretched 2.4 times in the longitudinal direction (machine direction) between rolls with different peripheral speeds in an oven at 130°C (in-air auxiliary stretching treatment). The laminate was then immersed in an insolubilizing bath (a boric acid aqueous solution obtained by blending 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40°C for 30 seconds (insolubilization treatment). The laminate was then immersed in a dyeing bath (an iodine aqueous solution obtained by blending iodine and potassium iodide in a weight ratio of 1:7 with 100 parts by weight of water) at a liquid temperature of 30°C for 60 seconds while adjusting the concentration so that the final polarizing film had a single transmittance (Ts) of 40.0% or higher (dyeing treatment). The laminate was then immersed in a crosslinking bath (a boric acid aqueous solution obtained by blending 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). The laminate was then immersed in a boric acid aqueous 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) by 1.46 times (total stretch ratio 3.5 times) between rolls operating at different peripheral speeds (underwater stretching treatment). The laminate was then immersed in a cleaning bath (aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) at a liquid temperature of 20°C (washing treatment). The laminate was then dried in an oven maintained at 90°C and brought into contact with a SUS heated roll maintained at a surface temperature of 75°C for approximately 2 seconds (drying shrinkage treatment). The shrinkage rate of the laminate in the width direction due to the drying shrinkage treatment was 2%.In this way, a PVA-based resin film having a thickness of 7 μm, an orientation function of 0.24, a single transmittance Ts of 41.5%, and a polarization degree P of 99.9% was formed on the resin substrate.

[0088] (Preparation of Workpiece) An acrylic pressure-sensitive adhesive composition was applied to the PVA-based resin film side of a laminate of a resin substrate and a PVA-based resin film and dried to form a pressure-sensitive adhesive layer with a thickness of 40 μm, thereby obtaining a workpiece.

[0089] [Example 2] In the production of an absorptive polarizing element, a workpiece was obtained in the same manner as in Example 1, except that the underwater stretching ratio was 1.67 times (total stretching ratio was 4.0 times), and an absorptive polarizing film having a thickness of 7 μm, an orientation function of 0.28, a single transmittance Ts of 41.2%, and a polarization degree P of 99.9% was formed.

[0090] [Example 3] In the production of an absorptive polarizing element, a workpiece was obtained in the same manner as in Example 1, except that the underwater stretching ratio was 1.25 times (total stretching ratio was 3.0 times), and an absorptive polarizing film having a thickness of 7 μm, an orientation function of 0.20, a single transmittance Ts of 41.8%, and a polarization degree P of 99.9% was formed.

[0091] Comparative Example 1 In the production of an absorptive polarizing member, a workpiece was obtained in the same manner as in Example 1, except that the underwater stretching ratio was 1.88 times (total stretching ratio was 4.5 times), and an absorptive polarizing film having a thickness of 6 μm, an orientation function of 0.31, a single transmittance Ts of 40.9%, and a polarization degree P of 99.9% was formed.

[0092] Comparative Example 2 In the production of an absorptive polarizing member, a workpiece was obtained in the same manner as in Example 1, except that the underwater stretching ratio was 2.3 times (total stretching ratio was 5.5 times), and an absorptive polarizing film having a thickness of 5 μm, an orientation function of 0.39, a single transmittance Ts of 40.5%, and a polarization degree P of 99.9% was formed.

[0093] The PVA-based resin films and workpieces of each Example and Comparative Example were evaluated as follows. The evaluation results are summarized in Table 1, along with the orientation function and optical properties of the PVA-based resin films. <Evaluation> 1. Breaking Point and Elastic Modulus of PVA-Based Resin Film The obtained PVA-based resin films were punched using a blade measuring 150 mm (long side) x 25 mm (short side) to obtain rectangular measurement samples. The punching was performed so that the long side was aligned with the MD direction (absorption axis direction). The punching was also performed so that the long side was aligned with the TD direction (transmission axis direction). The obtained measurement samples were chucked in a tensile tester (Shimadzu Corporation, "Autograph AG-Xplus") with a chucking distance of 80 mm and heated to 120°C. After leaving the samples in this state for 1 minute, they were pulled in the long side direction at a pulling rate of 0.8 mm / min while heated to 120°C, and the change in stress with respect to the pulling distance was measured. The elastic modulus (tensile modulus) was calculated from the slope of the initial line in the obtained stress-strain curve (strain (pulling distance / chucking interval): stress line at 0.050% to 0.250%). The point at which the stress suddenly dropped was calculated as the break point. 2. Bonding of Workpiece As shown in Figures 4A to 4D, bonding of the obtained workpiece to the curved surface (concave surface) of a lens with a diameter (major axis) of 50 mm and a curvature radius of 35 mm was attempted multiple times at 120°C. The occurrence of cracks, bonding defects, etc. during bonding was checked. 3. Orientation Function Distribution of Absorptive Polarizing Film The orientation function was measured for an optical film piece (absorptive polarizing film) obtained by bonding the workpiece to the curved surface of the lens. Specifically, the optical film piece was peeled from the lens, and 10 mm x 10 mm test pieces were cut out from the center and peripheral portions and used for measurement. The specimen was cut out so that one side was parallel to the absorption axis of the absorptive polarizing film. The orientation function was measured as described above.

[0094]

[0095] In Examples 1, 2, and 3, the workpiece could be bonded to the curved surface of the lens while suppressing the occurrence of cracks. On the other hand, in Comparative Example 1, the workpiece could be bonded to the lens, but many cracks occurred during bonding. In Comparative Example 2, the workpiece could not be bonded to the lens. Specifically, the workpiece did not stretch, and a gap occurred between the lens and the workpiece. The cracks tended to occur along a direction approximately perpendicular to the absorption axis direction (the stretching direction of the PVA-based resin layer).

[0096] The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, the configurations shown in the above-described embodiment can be replaced with configurations that are substantially the same as those shown in the above-described embodiment, that have the same effects, or that can achieve the same purpose.

[0097] Optical film pieces according to embodiments of the present invention can be used in displays such as VR goggles, for example.

[0098] REFERENCE SIGNS LIST 1 Optical film piece 10 Display system 12 Display element 14 Reflective polarizing member 16 First lens portion 18 Half mirror 20 First λ / 4 member 22 Second λ / 4 member 24 Second lens portion 28 Absorptive polarizing member 28a Absorptive polarizing film 28b Main surface 28c First portion 28d Second portion 29 Protective layer 30 Pressure-sensitive adhesive layer

Claims

1. An optical film piece comprising an absorptive polarizing film, the absorptive polarizing film being made of a polyvinyl alcohol-based resin, and an orientation function of a first portion located at the center of a main surface of the absorptive polarizing film is different from an orientation function of a second portion located outside the first portion.

2. The optical film piece according to claim 1, wherein the absorptive polarizing film has a portion having an orientation function of 0.30 or less.

3. The optical film piece according to claim 1, wherein the absolute value of the difference between the orientation function of the first region and the orientation function of the second region is 0.02 or more.

4. The optical film piece according to claim 1, wherein the major surface has a curved surface.

5. A method for producing an optical film piece according to claim 1, comprising heating and stretching a member containing a polyvinyl alcohol-based resin film to integrate it with a part having a curved surface, and the orientation function of the polyvinyl alcohol-based resin film is 0.30 or less.

6. The method for manufacturing an optical film piece according to claim 5, wherein the radius of curvature of the curved surface of the component is 150 mm or less.

7. The method for manufacturing an optical film piece according to claim 5, wherein the radius of curvature of the curved surface of the component is 40 mm or less.

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