CN118829929A - Lens unit, laminate, display, method for manufacturing display, and display method - Google Patents
Lens unit, laminate, display, method for manufacturing display, and display method Download PDFInfo
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- CN118829929A CN118829929A CN202380024836.2A CN202380024836A CN118829929A CN 118829929 A CN118829929 A CN 118829929A CN 202380024836 A CN202380024836 A CN 202380024836A CN 118829929 A CN118829929 A CN 118829929A
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- polarizing member
- stretching
- laminate
- display
- lens
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Landscapes
- Polarising Elements (AREA)
Abstract
The invention provides a lens part capable of realizing light weight and high definition of VR goggles. A lens unit according to an embodiment of the present invention is a display system for displaying an image to a user, the lens unit including: a reflection unit that reflects light that is emitted from a display surface of a display element that displays an image toward the front and that has passed through a polarizing member and a1λ/4 th member, the reflection unit including a reflective polarizing member and an absorptive polarizing member that is disposed in front of the reflective polarizing member; a first lens unit disposed on an optical path between the display element and the reflection unit; a half mirror disposed between the display element and the first lens portion, and configured to transmit light emitted from the display element and reflect the light reflected by the reflecting portion toward the reflecting portion; and a2λ/4 th member disposed on an optical path between the half mirror and the reflecting section, wherein a thickness of an absorption-type polarizing film constituting the absorption-type polarizing member is 8 μm or less.
Description
Technical Field
The invention relates to a lens part, a laminated body, a display body, a manufacturing method of the display body and a display method.
Background
Image display devices, such as liquid crystal display devices and Electroluminescent (EL) display devices (for example, organic EL display devices), are rapidly spreading. In an image display device, an optical member such as a polarizing member or a phase difference member is generally used in order to realize image display and improve image display performance (for example, refer to patent document 1).
In recent years, new uses of image display devices have been developed. For example, goggles with displays (VR goggles) for achieving Virtual Reality (VR) have begun to be commercialized. As VR goggles have been studied for use in various scenes, light weight, high definition, and the like are desired. The weight reduction can be achieved by, for example, thinning a lens used for VR goggles. On the other hand, it is also desired to develop an optical member suitable for a display system using a thin lens.
Prior art literature
Patent literature
Patent document 1: japanese patent laid-open No. 2021-103286
Disclosure of Invention
Problems to be solved by the invention
In view of the above, a main object of the present invention is to provide a lens unit capable of realizing light weight and high definition of VR goggles.
Means for solving the problems
1. The lens portion of the embodiment of the present invention is used for a display system for displaying an image to a user,
The lens unit includes:
a reflection unit that reflects light that is emitted from a display surface of a display element that displays an image toward the front and that has passed through a polarizing member and a1λ/4 th member, the reflection unit including a reflective polarizing member and an absorptive polarizing member that is disposed in front of the reflective polarizing member;
A first lens unit disposed on an optical path between the display element and the reflection unit;
a half mirror disposed between the display element and the first lens portion, and configured to transmit light emitted from the display element and reflect the light reflected by the reflecting portion toward the reflecting portion; and
And a2λ/4 th member disposed on an optical path between the half mirror and the reflecting section, wherein a thickness of an absorption-type polarizing film constituting the absorption-type polarizing member is 8 μm or less.
2. The lens unit according to the above 1, wherein a reflection axis of the reflection type polarizing member and an absorption axis of the absorption type polarizing member may be arranged parallel to each other.
3. In the lens portion of 1 or 2, the first lens portion and the half mirror may be integrated.
4. The lens unit according to any one of the above 1 to 3, wherein the lens unit may include a second lens unit disposed in front of the reflecting unit.
5. In the lens unit according to any one of the above 1 to 4, an angle between an absorption axis of the polarizing member included in the display element and a slow axis of the 1λ/4 th 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 2λ/4 th member may be 40 ° to 50 °.
6. The lens unit according to any one of the above 1 to 5, wherein a ratio of a thickness of the absorption-type polarizing film to a thickness of the reflection-type polarizing member is 15% or less.
7. The laminate according to an embodiment of the present invention is the laminate for the reflection unit of the lens unit according to any one of the above 1 to 6, and includes the reflection type polarizing member and the absorption type polarizing member.
8. The laminate according to item 7, wherein the reflective polarizing member and the absorptive polarizing member are laminated via an adhesive layer.
9. The display according to an embodiment of the present invention includes the lens unit according to any one of 1 to 6.
10. The method for manufacturing a display according to an embodiment of the present invention is a method for manufacturing a display having the lens portion described in any one of 1 to 6.
11. The display method according to an embodiment of the present invention includes:
passing the light of the display image emitted through the polarizing member and the 1λ/4 th member through the half mirror and the first lens section; a step of passing the light passed through the half mirror and the first lens portion through a 2λ/4 th member;
Reflecting the light having passed through the 2λ/4 th member toward the half mirror at a reflecting portion including a reflective polarizing member;
A step of transmitting the light reflected by the reflecting section and the half mirror through the reflective polarizing member of the reflecting section by the 2λ/4 th member; and
A step of transmitting the light transmitted through the reflective polarizing member to the absorptive polarizing member,
Wherein the thickness of the absorption type polarizing film constituting the absorption type polarizing member is 8 μm or less.
12. A method for manufacturing an absorptive polarizing film for a lens unit according to an embodiment of the present invention includes:
Forming a polyvinyl alcohol resin layer containing a halide and a polyvinyl alcohol resin on one side of a long thermoplastic resin substrate to form a laminate;
The laminate is sequentially subjected to auxiliary stretching in a gas atmosphere, dyeing, stretching in an aqueous solution, and drying shrinkage by heating while being transported in the longitudinal direction so as to shrink by 2% or more in the width direction.
13. The production method according to the above 12, wherein the halide is contained in the polyvinyl alcohol resin layer in an amount of 5 to 20 parts by weight based on 100 parts by weight of the polyvinyl alcohol resin.
14. In the production method according to the above 12 or 13, the stretching ratio in the auxiliary stretching treatment in the gas atmosphere is 2.0 times or more.
15. The production method according to any one of 12 to 14, wherein the drying shrinkage treatment step is a step of heating with a heating roller.
16. The production method according to the above 15, wherein the temperature of the heating roller is 60 to 120 ℃, and the shrinkage ratio of the laminate in the width direction by the drying shrinkage treatment is 2% or more.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the lens unit of the embodiment of the present invention, the VR goggles can be made lightweight and highly slim.
Drawings
Fig. 1 is a schematic diagram showing a schematic configuration of a display system according to an embodiment of the present invention.
Fig. 2 is a schematic cross-sectional view showing an example of a laminate of reflection units used in the display system shown in fig. 1.
Fig. 3 is a schematic perspective view showing an example of a multilayer structure included in the reflective polarizing film.
Fig. 4 is a schematic diagram showing an example of the drying shrinkage treatment using the heating roller.
Fig. 5 is an observation photograph showing optical unevenness.
Symbol description
2. Display system
4. Lens part
12. Display element
14. Reflection part
16. A first lens part
18. Half mirror
20. First phase difference member
22. Second phase difference member
24. A second lens part
30. Laminate body
32. Reflective polarizing component
34. Absorption type polarizing component
36. Adhesive layer
Detailed Description
Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these embodiments. For the sake of more clear explanation, the drawings may schematically show the width, thickness, shape, etc. of each part in comparison with the embodiments, but the explanation of the present invention is not limited to the examples.
(Definition of terms and symbols)
The terms and symbols in the present specification are defined as follows.
(1) Refractive index (nx, ny, nz)
"Nx" is a refractive index in a direction in which the refractive index in the plane reaches the maximum (i.e., the slow axis direction), "ny" is a refractive index in a direction orthogonal to the slow axis in the plane (i.e., the fast axis direction), and "nz" is a refractive index in the thickness direction.
(2) In-plane phase difference (Re)
"Re (λ)" is the in-plane retardation measured at 23℃with light of wavelength λnm. For example, "Re (550)" is the in-plane retardation measured at 23℃with light having a wavelength of 550 nm. When the thickness of the layer (film) is d (nm), the following formula can be used: re (λ) = (nx-ny) ×d was obtained as Re (λ).
(3) Retardation in thickness direction (Rth)
"Rth (λ)" is a phase difference in the thickness direction measured at 23℃with light having a wavelength of λnm. For example, "Rth (550)" is a phase difference in the thickness direction measured at 23℃with light having a wavelength of 550 nm. When the thickness of the layer (film) is d (nm), the following formula can be used: rth (λ) = (nx-nz) ×d to obtain Rth (λ).
(4) Nz coefficient
The Nz coefficient can be obtained by nz=rth/Re.
(5) Angle of
In this specification, when referring to an angle, the angle includes both clockwise and counterclockwise with respect to a reference direction. Thus, for example, "45" means ± 45 °.
Fig. 1 is a schematic diagram showing a schematic configuration of a display system according to an embodiment of the present invention. Fig. 1 schematically illustrates the arrangement, shape, and the like of the respective components of the display system 2. The display system 2 includes a display element 12, a reflecting portion 14, a first lens portion 16, a half mirror 18, a first phase difference member 20, a second phase difference member 22, and a second lens portion 24. The reflecting portion 14 is disposed on the display surface 12a side of the display element 12, that is, in front of the display element, and can reflect light emitted from the display element 12. The first lens portion 16 is disposed on the optical path between the display element 12 and the reflecting portion 14, and the half mirror 18 is disposed between the display element 12 and the first lens portion 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 portion 14.
The components (the half mirror 18, the first lens portion 16, the second phase difference member 22, the reflecting portion 14, and the second lens portion 24 in the illustrated example) disposed in front of the half mirror are sometimes collectively referred to as a lens portion (lens portion 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 a polarizing member (typically, a polarizing film) that may be included in the display element 12, for example, and is emitted as1 st linearly polarized light.
The first phase difference member 20 is a λ/4 member capable of converting 1 st linearly polarized light incident on the first phase difference member 20 into 1 st circularly polarized light (hereinafter, the first phase difference member may be referred to as a1λ/4 member). The first phase difference member 20 may be integrally provided 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 to the first lens portion 16.
The second phase difference member 22 is a λ/4 member (hereinafter, the second phase difference member may be referred to as a 2λ/4 th member) that transmits the light reflected by the reflecting portion 14 and the half mirror 18 through the reflecting portion 14 including the reflective polarizing member. The second phase difference member 22 may be integrally provided with the first lens portion 16 or may be integrally provided with a reflective polarizing member included in the reflecting portion 14.
The 1 st circularly polarized light emitted from the 1 st λ/4 th member 20 passes through the half mirror 18 and the first lens section 16, and is converted into 2 nd linearly polarized light by the 2 nd λ/4 th member 22. The 2 nd linear polarized light emitted from the 2λ/4 th member 22 is reflected toward the half mirror 18 without being transmitted by the reflective polarizing member included in the reflecting section 14. At this time, the polarization direction of the 2 nd linearly polarized light incident on the reflective polarizing member included in the reflecting portion 14 is the same as the reflection axis of the reflective polarizing member. Therefore, the 2 nd linearly polarized light incident on the reflecting portion is reflected by the reflective polarizing member.
The 2 nd linear polarized light reflected by the reflecting section 14 is converted into 2 nd circular polarized light by the 2λ/4 th member 22, and the 2 nd circular polarized light emitted from the 2λ/4 th member 22 is reflected by the half mirror 18 after passing through the first lens section 16. The 2 nd circularly polarized light reflected by the half mirror 18 passes through the first lens portion 16, and is converted into the 3 rd linearly polarized light by the 2λ/4 th member 22. The 3 rd linearly polarized light is transmitted by the reflective polarizing member included in the reflection section 14. At this time, the polarization direction of the 3 rd linearly polarized light incident on the reflective polarizing member included in the reflecting portion 14 is the same as the transmission axis of the reflective polarizing member. Therefore, the 3 rd linearly polarized light incident on the reflecting portion 14 is transmitted through the reflective polarizing member.
The light transmitted 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 reflection unit 14 may be arranged substantially parallel to each other or substantially orthogonal to each other. The angle between the absorption axis of the polarizing member included in the display element 12 and the slow axis of the first phase difference member 20 is, for example, 40 ° to 50 °, 42 ° to 48 °, or 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 °, 42 ° to 48 °, or about 45 °.
The in-plane retardation Re (550) of the first retardation member 20 may be, for example, 100nm to 190nm, 110nm to 180nm, 130nm to 160nm, or 135nm to 155nm.
The first phase difference member 20 preferably exhibits an inverse dispersion wavelength characteristic in which the phase difference value becomes large in accordance with the wavelength of the measurement light. 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 may be, for example, 100nm to 190nm, 110nm to 180nm, 130nm to 160nm, or 135nm to 155nm.
The second phase difference member 22 preferably exhibits inverse dispersion wavelength characteristics in which the phase difference value becomes large in accordance with the wavelength of the measurement light. 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 phase difference member may be formed of any suitable material. For example, the film may be a resin film (typically a stretched film) or may be formed of a liquid crystal compound. In the case where the phase difference member is a resin film, the thickness thereof is, for example, 10 μm to 100 μm.
The resin contained in the resin film includes: polycarbonate-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., blending, copolymerization). For example, a resin film containing a polycarbonate-based resin or a polyester carbonate-based resin (hereinafter, may be simply referred to as a polycarbonate-based resin) can be suitably used. By using such a resin, the above-described inverse dispersion wavelength characteristic can be exhibited, for example.
As the polycarbonate resin, any suitable polycarbonate resin can be used. For example, the polycarbonate resin contains a structural unit derived from a fluorene dihydroxy compound, a structural unit derived from an isosorbide dihydroxy compound, and a structural unit derived from at least one dihydroxy compound selected from alicyclic diols, alicyclic dimethanol, di-, tri-, or polyethylene glycols, and alkylene glycols or spirodiols. Preferably, the polycarbonate resin comprises a structural unit derived from a fluorene dihydroxy compound, a structural unit derived from an isosorbide dihydroxy compound, a structural unit derived from alicyclic dimethanol and/or a structural unit derived from di-, tri-or polyethylene glycol; it is further preferable that the composition further 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 resin may contain a structural unit derived from another dihydroxy compound, if necessary. Details of a polycarbonate resin that can be suitably used for a retardation member and a method for forming a retardation member are described in, for example, japanese patent application laid-open No. 2014-10291, japanese patent application laid-open No. 2014-26262, japanese patent application laid-open No. 2015-212816, japanese patent application laid-open No. 2015-212817, and Japanese patent application laid-open No. 2015-212818, and these publications are incorporated by reference into the present specification.
An absorptive polarizing member may be provided in front of the reflective polarizing member. Typically, an absorptive polarizing member may be disposed between the reflective polarizing member and the second lens portion 24. The reflection axis of the reflection type polarizing member and the absorption axis of the absorption type polarizing member may be disposed substantially parallel to each other, and the transmission axis of the reflection type polarizing member and the transmission axis of the absorption type polarizing member may be disposed substantially parallel to each other. The absorption-type polarizing member may be included in the reflection part 14. In the case where the reflection section 14 includes an absorption-type polarizing member, the reflection section 14 may include a laminate having a reflection-type polarizing member and an absorption-type polarizing member.
Fig. 2 is a schematic cross-sectional view showing an example of a laminate of reflection units used in the display system shown in fig. 1. The laminate 30 includes a reflective polarizing member 32 and an absorptive polarizing member 34, and the reflective polarizing member 32 and the absorptive polarizing member 34 are laminated together via an adhesive layer 36. By using the adhesive layer, the reflective polarizing member 32 and the absorptive polarizing member 34 are fixed, and thus the shift of the axis arrangement of the reflection axis and the absorption axis (transmission axis and transmission axis) can be prevented. In addition, adverse effects caused by an air layer that may be formed between the reflective polarizing member 32 and the absorptive polarizing member 34 can be suppressed. The adhesive layer 36 may be formed of an adhesive or an adhesive. The thickness of the adhesive layer 36 is, for example, 0.05 μm to 30. Mu.m, preferably 3 μm to 20. Mu.m, and more preferably 5 μm to 15. Mu.m. Although not shown, the second phase difference member 22 may be integrally provided with the reflective polarizing member 32, and thus the laminated body 30 may have the second phase difference member 22. In this case, the second phase difference member 22 may be laminated to the reflective polarizing member 32 via an adhesive layer.
The reflective polarizing member transmits polarized light (typically, linearly polarized light) parallel to the transmission axis thereof while maintaining the polarization state thereof, and reflects light having other polarization states. As the reflective polarizing member, a film having a multilayer structure (sometimes referred to as a reflective polarizing film) is typically used. In this case, the thickness of the reflective polarizing member is, for example, 10 μm to 150 μm, preferably 20 μm to 100 μm, and more preferably 30 μm to 60 μm.
Fig. 3 is a schematic perspective view showing an example of a multilayer structure included in the reflective polarizing film. The multilayer structure 32a includes layers a having birefringence and layers B having substantially no birefringence alternately. 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 the a layer is larger than the refractive index ny in the y-axis direction, the refractive index nx in the x-axis direction of the B layer is substantially the same as the refractive index ny in the y-axis direction, and the refractive index difference between the a layer and the B layer is large in the x-axis direction and substantially zero in the y-axis direction. As a result, the x-axis direction can be made the reflection axis and the y-axis direction can be made the transmission axis. The refractive index difference between the a layer and the B layer in the x-axis direction is preferably 0.2 to 0.3.
The a layer is typically formed of a material exhibiting birefringence by stretching. Examples of such a material include naphthalene dicarboxylic acid polyesters (e.g., polyethylene naphthalate), polycarbonates, and acrylic resins (e.g., polymethyl methacrylate). The B layer is typically formed of a material that does not substantially exhibit birefringence even when stretched. Examples of such a material include a copolyester of naphthalene dicarboxylic acid and terephthalic acid. The above-described multilayer structure may be formed by combining coextrusion with stretching. For example, the material constituting the layer a and the material constituting the layer B are extruded and then multilayered (for example, using a multiplier). Subsequently, the obtained multilayer laminate is stretched. The x-axis direction of the illustrated example may correspond to the stretching direction.
Examples of the commercial products of the reflective polarizing film include trade names "DBEF", "APF" manufactured by 3M company and trade name "APCF" manufactured by niton electric company.
The orthogonal 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) is, for example, 43% to 49%, preferably 45% to 47%. The polarization degree (P) of the reflective polarizing member (reflective polarizing film) may be 92% to 99.99%, for example.
The above-mentioned monomer transmittance (Ts) can be representatively measured by an ultraviolet-visible spectrophotometer. The polarization degree (P) can be typically obtained based on the parallel transmittance (Tp) and the orthogonal transmittance (Tc) obtained by measuring with an ultraviolet-visible spectrophotometer and correcting the visibility. Ts, tp, and Tc are Y values obtained by measuring a 2-degree field of view (C light source) of JIS Z8701 and performing visibility correction.
Degree of polarization (P) = { (Tp-Tc)/(tp+tc) } 1/2 ×100
The above-mentioned absorption-type polarizing member may typically include a resin film containing a dichroic substance (sometimes referred to as an absorption-type polarizing film or simply a polarizing film). Preferably, the film contains a polyvinyl alcohol (PVA) film containing iodine. The thickness of the absorption-type polarizing film is preferably 1 μm or more and 8 μm or less, more preferably 7 μm or less, and still more preferably 5 μm or less. By using the absorbing-type polarizing film having such a thickness, shrinkage that may occur due to environmental changes (e.g., temperature changes) can be suppressed, and excellent display characteristics can be maintained. Specifically, in the display system described above, a small amount of shrinkage of the member may cause distortion of the image, and therefore, by using an absorbing-type polarizing film having such a thickness, distortion of the displayed image can be suppressed extremely well.
The ratio of the thickness of the absorption-type polarizing film to the thickness of the reflection-type polarizing member is preferably 15% or less, more preferably 10% or less. The ratio of the thickness of the absorption-type polarizing film to the sum of the thickness of the second phase difference member, the thickness of the reflection-type polarizing member, and the thickness of the absorption-type polarizing member is preferably 10% or less, more preferably 5% or less.
The orthogonal transmittance (Tc) of the absorption-type polarizing member (absorption-type polarizing film) is preferably 0.5% or less, more preferably 0.1% or less, and further preferably 0.05% or less. The single transmittance (Ts) of the absorption-type polarizing member (absorption-type polarizing film) is, for example, 41.0% to 45.0%, and preferably 42.0% or more. The polarization degree (P) of the absorptive polarizing member (absorptive polarizing film) is, for example, 99.0% to 99.997%, and preferably 99.9% or more. By combining the absorption-type polarizing member with the reflection-type polarizing member, excellent display characteristics can be achieved. For example, it is possible to suppress the user from visually recognizing an afterimage (right).
The method for producing an absorptive polarizing film according to one embodiment includes the steps of: forming a polyvinyl alcohol resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol resin (PVA-based resin) on one side of a long thermoplastic resin substrate to form a laminate; the laminate is sequentially subjected to an auxiliary stretching treatment in a gas atmosphere, a dyeing treatment, a stretching treatment in an aqueous solution, and a drying shrinkage treatment for shrinking the laminate by 2% or more in the width direction by heating while being transported in the longitudinal direction. The content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin. The stretching ratio in the auxiliary stretching treatment in the gas atmosphere is preferably 2.0 times or more. The drying shrinkage treatment is preferably performed by a heated roller, and the temperature of the heated roller is preferably 60 to 120 ℃. The shrinkage ratio of the laminate in the width direction based on the drying shrinkage treatment is preferably 2% or more. A laminate including a PVA-based resin layer containing a halide is produced, and stretching of the laminate is performed in a multistage manner including auxiliary stretching in a gas atmosphere and stretching in an aqueous solution, and the stretched laminate is heated by a heating roller, whereby a polarizing film having excellent optical characteristics (typically, a single body transmittance and a degree of polarization) and suppressed in variation of optical characteristics can be obtained. Specifically, by using the heating roller in the drying and shrinking process, the entire laminate can be uniformly shrunk while the laminate is conveyed. Thus, not only the optical characteristics of the obtained polarizing film can be improved, but also a polarizing film excellent in optical characteristics can be stably produced, and the variation in optical characteristics (particularly, the transmittance of the monomer) of the polarizing film can be suppressed.
As a method for producing a laminate of the thermoplastic resin base material and the PVA-based resin layer, any suitable method can be used. The PVA-based resin layer is preferably formed on the thermoplastic resin substrate by applying a coating liquid containing a halide and a PVA-based resin to the surface of the thermoplastic resin substrate and drying the coating liquid. As described above, the content of the halide in the PVA-based resin layer is preferably 5 to 20 parts by weight relative to 100 parts by weight of the PVA-based resin.
As a coating method of the coating liquid, any suitable method can be employed. Examples include: roll coating, spin coating, bar coating, dip coating, die coating, curtain coating, spray coating, knife coating (comma coating, etc.), and the like. The coating/drying temperature of the coating liquid is preferably 50℃or higher.
The thickness of the PVA based resin layer is preferably 3 to 40. Mu.m, more preferably 3 to 20. Mu.m.
Before forming the PVA-based resin layer, the thermoplastic resin substrate may be subjected to a surface treatment (for example, corona treatment or the like), or an easy-to-adhere layer may be formed on the thermoplastic resin substrate. By performing such a treatment, the adhesion between the thermoplastic resin base material and the PVA-based resin layer can be improved.
The thickness of the thermoplastic resin substrate is preferably 20 μm to 300. Mu.m, more preferably 50 μm to 200. Mu.m. If the particle size is less than 20. Mu.m, it is difficult to form a PVA based resin layer. If the particle size exceeds 300. Mu.m, for example, in the stretching treatment in an aqueous solution described later, the thermoplastic resin substrate takes a long time to absorb water, and there is a concern that an excessive load is required for stretching.
The water absorption rate of the thermoplastic resin base material is preferably 0.2% or more, more preferably 0.3% or more. The thermoplastic resin substrate absorbs water, and the water can exert a plasticizer effect to achieve plasticization. As a result, the tensile stress can be greatly reduced, and the stretching can be performed at a high magnification. On the other hand, the water absorption rate of the thermoplastic resin base material is preferably 3.0% or less, and more preferably 1.0% or less. By using such a thermoplastic resin base material, it is possible to prevent defects such as a significant decrease in dimensional stability of the thermoplastic resin base material at the time of production, and deterioration in appearance of the obtained polarizing film. In addition, the substrate is prevented from breaking during stretching in an aqueous solution, or the PVA-based resin layer is prevented from peeling from the thermoplastic resin substrate. The water absorption of the thermoplastic resin base material can be adjusted by introducing a modifying group into the constituent material, for example. The water absorption was determined in accordance with JIS K7209.
The glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 120℃or lower. By using such a thermoplastic resin base material, crystallization of the PVA-based resin layer can be suppressed, and stretchability of the laminate can be sufficiently ensured. Further, if plasticization of the thermoplastic resin substrate based on water and stretching in an aqueous solution are considered to be performed satisfactorily, it is more preferably 100℃or less, and still more preferably 90℃or less. On the other hand, the glass transition temperature of the thermoplastic resin substrate is preferably 60℃or higher. By using such a thermoplastic resin base material, it is possible to prevent the thermoplastic resin base material from being deformed (for example, to generate irregularities, looseness, wrinkles, and the like) and the like when the PVA-based resin-containing coating liquid is coated and dried, thereby producing a laminate satisfactorily. In addition, the stretching of the PVA-based resin layer can be performed well at a suitable temperature (for example, about 60 ℃). The glass transition temperature of the thermoplastic resin base material can be adjusted by, for example, using a crystallization material in which a modifying group is introduced into a constituent material and heating the material. The glass transition temperature (Tg) is a value obtained in accordance with JIS K7121.
As the constituent material of the thermoplastic resin base material, any suitable thermoplastic resin may be used. Examples of the thermoplastic resin include: ester resins such as polyethylene terephthalate resins, cycloolefin resins such as norbornene resins, olefin resins such as polypropylene, polyamide resins, polycarbonate resins, copolymer resins thereof, and the like. Among them, norbornene-based resins and amorphous polyethylene terephthalate-based resins are preferable.
In one embodiment, an amorphous (uncrystallized) polyethylene terephthalate resin is preferably used. Among them, an amorphous (hardly crystallized) polyethylene terephthalate resin is particularly preferably used. Specific examples of the amorphous polyethylene terephthalate resin include copolymers further containing isophthalic acid and/or cyclohexanedicarboxylic acid as dicarboxylic acid and copolymers further containing cyclohexanedimethanol and diethylene glycol as diol.
In a preferred embodiment, the thermoplastic resin substrate is formed of a polyethylene terephthalate-based resin having isophthalic acid units. This is because such a thermoplastic resin base material is extremely excellent in stretchability and can suppress crystallization during stretching. This is considered to be because the main chain can be given a large degree of bending by introducing isophthalic acid units. The polyethylene terephthalate resin has terephthalic acid units and ethylene glycol units. The content of isophthalic acid units is preferably 0.1 mol% or more, more preferably 1.0 mol% or more, based on the total of all the repeating units. This is because a thermoplastic resin base material extremely excellent in stretchability can be obtained. On the other hand, the content ratio of isophthalic acid units is preferably 20 mol% or less, more preferably 10 mol% or less, based on the total of all the repeating units. By setting the content ratio as described above, the crystallinity can be improved favorably in the drying shrinkage treatment described later.
The thermoplastic resin base material may be stretched in advance (before forming the PVA-based resin layer). In one embodiment, stretching may be performed in the transverse direction of the elongated thermoplastic resin substrate. The transverse direction is preferably a direction perpendicular to the stretching direction of the laminate to be described later. In the present specification, the term "orthogonal" also includes a case of being substantially orthogonal. Here, the term "substantially orthogonal" includes a case of 90 ° ± 5.0 °, preferably 90 ° ± 3.0 °, and more preferably 90 ° ± 1.0 °.
The stretching temperature of the thermoplastic resin substrate is preferably Tg-10 to tg+50℃withrespect to the glass transition temperature (Tg). The stretching ratio of the thermoplastic resin base material is preferably 1.5 to 3.0 times.
As the stretching method of the thermoplastic resin substrate, any suitable method can be employed. Specifically, the stretching may be performed at the fixed end or at the free end. The stretching mode may be dry or wet. The stretching of the thermoplastic resin substrate may be performed in one stage or may be performed in multiple stages. In the case of performing in multiple stages, the stretching ratio is a product of stretching ratios in the respective stages.
The coating liquid contains a halide and a PVA-based resin as described above. The coating liquid may be typically a solution obtained by dissolving the halide and the PVA-based resin in a solvent. Examples of the solvent include: water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various diols, polyols such as trimethylolpropane, and amines such as ethylenediamine and diethylenetriamine. They may be used alone, or two or more kinds may be used in combination. Among them, water is preferable. The PVA-based resin concentration of the solution is preferably 3 to 20 parts by weight based on 100 parts by weight of the solvent. In such a resin concentration, a uniform coating film can be formed to adhere to the thermoplastic resin substrate. The halide content in the coating liquid is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin.
Additives may be blended into the coating liquid. Examples of the additive include: plasticizers, surfactants, and the like. Examples of the plasticizer include: polyhydric alcohols such as ethylene glycol and glycerol. Examples of the surfactant include: nonionic surfactants. These additives may be used for the purpose of further improving the uniformity, dyeing property, and stretchability of the resulting PVA-based resin layer.
As the PVA-based resin, any suitable resin may be used. For example, polyvinyl alcohol and an ethylene-vinyl alcohol copolymer are mentioned. The polyvinyl alcohol can be obtained by saponifying polyvinyl acetate. The ethylene-vinyl alcohol copolymer can be obtained by saponifying an 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 K6726-1994. By using the PVA-based resin having such a saponification degree, a polarizing film excellent in durability can be obtained. If the saponification degree is too high, gelation may occur.
The average polymerization degree of the PVA-based resin may be appropriately selected according to the purpose. The average polymerization degree is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300. The average polymerization degree can be determined in accordance with JIS K6726-1994.
As the above-mentioned halide, any suitable halide may be used. Examples thereof include iodide and sodium chloride. Examples of the iodide include potassium iodide, sodium iodide, and lithium iodide. Among them, potassium iodide is preferable.
The amount of the halide in the coating liquid is preferably 5 to 20 parts by weight based on 100 parts by weight of the PVA-based resin, and more preferably 10 to 15 parts by weight based on 100 parts by weight of the PVA-based resin. When the amount of the halide is more than 20 parts by weight relative to 100 parts by weight of the PVA-based resin, the halide may ooze out, and the finally obtained polarizing film may be clouded.
In general, the orientation of the polyvinyl alcohol molecules in the PVA-based resin is improved by stretching the PVA-based resin layer, but if the PVA-based resin layer after stretching is immersed in a liquid containing water, the orientation of the polyvinyl alcohol molecules may be disturbed and the orientation may be reduced. In particular, when a laminate of a thermoplastic resin and a PVA-based resin layer is stretched in an aqueous boric acid solution, the degree of orientation tends to be significantly reduced when the laminate is stretched in an aqueous boric acid solution at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin. For example, stretching of a PVA film monomer in an aqueous boric acid solution is usually performed at 60 ℃, whereas stretching of a laminate of an a-PET (thermoplastic resin substrate) and a PVA-based resin layer is performed at a high temperature of about 70 ℃, in which case the orientation of PVA at the initial stage of stretching is reduced at a stage before the stretching in an aqueous solution is increased. In contrast, by producing a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin substrate and stretching the laminate in an aqueous boric acid solution at a high temperature in air (auxiliary stretching), crystallization of the PVA-based resin in the PVA-based resin layer of the laminate after the auxiliary stretching can be promoted. As a result, when the PVA-based resin layer is immersed in a liquid, disorder of orientation of polyvinyl alcohol molecules and decrease of orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide. This improves the optical characteristics of the polarizing film obtained by the treatment step of immersing the laminate in a liquid, such as dyeing treatment and stretching treatment in an aqueous solution.
In particular, in order to obtain high optical characteristics, a method of stretching in 2 stages in which dry stretching (auxiliary stretching) and stretching in an aqueous boric acid solution are combined may be selected. By introducing the auxiliary stretching as in the case of the stretching in 2 stages, the stretching can be performed while suppressing the crystallization of the thermoplastic resin base material, and the problem of the decrease in stretchability due to the excessive crystallization of the thermoplastic resin base material in the subsequent stretching in the aqueous boric acid solution can be solved, and the laminate can be stretched at a higher magnification. In addition, when the PVA-based resin is coated on the 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 coating temperature as compared with the case of coating the PVA-based resin on a metal drum in general, and as a result, there is a problem that crystallization of the PVA-based resin is relatively lowered, and sufficient optical characteristics cannot be obtained. In contrast, by introducing the auxiliary stretching, even when the PVA-based resin is coated on the thermoplastic resin, crystallinity of the PVA-based resin can be improved, and high optical characteristics can be realized. In addition, by simultaneously improving the orientation of the PVA-based resin in advance, when immersed in water in the subsequent dyeing step and stretching step, problems such as a decrease in the orientation and dissolution of the PVA-based resin can be prevented, and high optical characteristics can be achieved.
The stretching method of the auxiliary stretching in the gas atmosphere may be fixed-end stretching (for example, stretching using a tenter), or free-end stretching (for example, stretching the laminate in one direction by passing it between rolls having different circumferential speeds), and the free-end stretching may be positively employed in order to obtain high optical characteristics. In one embodiment, the stretching treatment in the gas atmosphere includes a heated roll stretching step of stretching the laminate by a circumferential velocity difference between heated rolls while conveying the laminate in the longitudinal direction thereof. The stretching treatment in the gas atmosphere typically includes a region stretching process and a heated roller stretching process. The order of the region stretching step and the heat roller stretching step is not limited, and the region stretching step may be performed first, or the heat roller stretching step may be performed first. The zone stretching process may be omitted. In one embodiment, the zone stretching step and the heated roll stretching step are performed sequentially. In another embodiment, the film end is gripped in a tenter stretching machine, and the distance between tenters is stretched in the conveying direction (the distance between the tenters is stretched to a stretching ratio). At this time, the distance of the tenter in the width direction (the direction perpendicular to the conveying direction) is arbitrarily set close to the set. It is preferable that the stretching ratio in the conveying direction be set so as to be closer to the free end. In the case of the free end stretching, it is calculated by shrinkage= (1/stretch ratio) 1/2 in the width direction.
The auxiliary stretching in the gas atmosphere may be performed in one stage or may be performed in multiple stages. In the case of performing in multiple stages, the stretching ratio is the product of stretching ratios in the respective stages. The stretching direction in the auxiliary stretching in the gas atmosphere is preferably substantially the same as the stretching direction in the stretching in the aqueous solution.
The stretching ratio in the auxiliary stretching in the gas atmosphere is preferably 2.0 to 3.5 times. The maximum stretching ratio in the case of combining auxiliary stretching in a gas atmosphere and stretching in an aqueous solution is preferably 5.0 times or more, more preferably 5.5 times or more, and still more preferably 6.0 times or more with respect to the original length of the laminate. In the present specification, "maximum stretch ratio" means a stretch ratio immediately before the laminate breaks, and additionally, a stretch ratio at which the laminate breaks is confirmed, and "maximum stretch ratio" means a value smaller than this by 0.2.
The stretching temperature of the auxiliary stretching in the gas atmosphere may be set to any appropriate value depending on the material forming the thermoplastic resin base material, the stretching method, and the like. The stretching temperature is preferably not less than the glass transition temperature (Tg) of the thermoplastic resin substrate, more preferably not less than the glass transition temperature (Tg) +10 ℃ of the thermoplastic resin substrate, and particularly preferably not less than tg+15 ℃. On the other hand, the upper limit of the stretching temperature is preferably 170 ℃. By stretching at such a temperature, rapid progress of crystallization of the PVA-based resin can be suppressed, and defects caused by the crystallization (e.g., inhibition of orientation of the PVA-based resin layer due to stretching) can be suppressed. The crystallization index of the PVA-based resin after auxiliary stretching in a gas atmosphere 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 ATR method using a fourier transform infrared spectrophotometer. Specifically, the crystallization index was calculated by measuring polarized light as measurement light and using intensities of 1141cm -1 and 1440cm -1 in the obtained spectrum.
Crystallization index= (I C/IR)
Wherein,
I C: when the measurement light is incident and measured, the intensity of the measurement light is 1141cm -1
I R: the intensity of the measurement light was 1440cm -1 when the measurement light was incident.
If necessary, the insolubilization treatment is performed after the auxiliary stretching treatment in a gas atmosphere and before the stretching treatment in an aqueous solution and 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 can be imparted to the PVA-based resin layer, and the PVA can be prevented from being lowered in orientation when immersed in water. The concentration of the aqueous boric acid solution is preferably 1 to 4 parts by weight based on 100 parts by weight of water. The temperature of the insoluble bath (boric acid aqueous solution) is preferably 20 to 50 ℃.
The dyeing treatment is typically performed by dyeing the PVA-based resin layer with iodine. Specifically, iodine is adsorbed to the PVA-based resin layer. Examples of the adsorption method include: a method in which a PVA-based resin layer (laminate) is immersed in a dyeing liquid containing iodine; a method of applying the dyeing liquid to the PVA-based resin layer; and a method of spraying the dyeing liquid on the PVA-based resin layer. A method of immersing the laminate in a dyeing liquid (dyeing bath) is preferable. This is because iodine can be adsorbed well.
The staining solution is preferably an aqueous iodine solution. The amount of iodine to be blended is preferably 0.05 to 0.5 parts by weight based on 100 parts by weight of water. In order to increase the solubility of iodine in water, it is preferable to add iodide to the aqueous iodine solution. Examples of the iodide include: potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide, barium iodide, calcium iodide, tin iodide, titanium iodide, and the like. Among them, potassium iodide is preferable. The amount of the iodide to be blended is preferably 0.1 to 10 parts by weight, more preferably 0.3 to 5 parts by weight, based on 100 parts by weight of water. In order to suppress dissolution of the PVA-based resin, the liquid temperature at the time of dyeing with the dyeing liquid is preferably 20 to 50 ℃. When the PVA-based resin layer is immersed in the dyeing liquid, 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.
The dyeing conditions (concentration, liquid temperature, immersion time) may be set so that the monomer transmittance and polarization degree of the finally obtained polarizing film fall within the above ranges. As such dyeing conditions, an aqueous iodine solution is preferably used as the dyeing solution, and the ratio of the iodine content to the potassium iodide content in the aqueous iodine solution is preferably 1:5 to 1:20. The ratio of iodine to potassium iodide content in the aqueous iodine solution is preferably 1:5 to 1:10. Thus, a polarizing film having the above-described optical characteristics can be obtained.
When the dyeing treatment is continuously performed after the laminate is immersed in the treatment bath containing boric acid (typically, the insolubilization treatment), the boric acid contained in the treatment bath is mixed into the dyeing bath, and the boric acid concentration in the dyeing bath changes with time, and as a result, the dyeing property may become unstable. In order to suppress the instability of the dyeing property as described above, the upper limit of the boric acid concentration of the dyeing bath is adjusted so as to be preferably 4 parts by weight, more preferably 2 parts by weight, relative to 100 parts by weight of water. On the other hand, the lower limit of the boric acid concentration in the dyeing bath is preferably 0.1 part by weight, more preferably 0.2 part by weight, and further preferably 0.5 part by weight relative to 100 parts by weight of water. In one embodiment, the dyeing treatment is performed using a dyeing bath in which boric acid is previously mixed. This reduces the ratio of change in boric acid concentration when boric acid in the treatment bath is mixed into the dyeing bath. The amount of boric acid to be previously mixed in the dyeing bath (i.e., the amount of boric acid not originating from the treatment bath) is preferably 0.1 to 2 parts by weight, more preferably 0.5 to 1.5 parts by weight, based on 100 parts by weight of water.
If necessary, the crosslinking treatment is performed after the dyeing treatment and before the stretching treatment in an aqueous solution. The crosslinking treatment is typically performed by immersing the PVA-based resin layer in an aqueous boric acid solution. By performing the crosslinking treatment, water resistance can be imparted to the PVA-based resin layer, and in the subsequent stretching in an aqueous solution, the decrease in the orientation of PVA when immersed in high-temperature water can be prevented. The concentration of the aqueous boric acid solution is preferably 1 to 5 parts by weight based on 100 parts by weight of water. In the case of performing the crosslinking treatment after the dyeing treatment, it is preferable to further add an iodide. By adding iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. The amount of iodide to be blended is preferably 1 to 5 parts by weight based on 100 parts by weight of water. Specific examples of iodides are described above. The liquid temperature of the crosslinking bath (aqueous boric acid solution) is preferably 20℃to 50 ℃.
The stretching treatment in an aqueous solution is performed by immersing the laminate in a stretching bath. According to the stretching treatment in an aqueous solution, stretching can be performed at a temperature lower than the glass transition temperature (typically about 80 ℃) of the thermoplastic resin base material and the PVA-based resin layer, and stretching can be performed at a high magnification while suppressing crystallization of the PVA-based resin layer. As a result, a polarizing film having excellent optical characteristics can be produced.
Any suitable method may be used for stretching the laminate. Specifically, the stretching may be performed at a fixed end or at a free end (for example, a method in which a laminate is uniaxially stretched by passing the laminate between rolls having different peripheral speeds). The free end stretch is preferably selected. Stretching of the laminate may be performed in one stage or in multiple stages. In the case of performing in multiple stages, the stretching ratio (maximum stretching ratio) of the laminate to be described later is the product of the stretching ratios in the respective stages.
The stretching in the aqueous solution is preferably performed by immersing the laminate in an aqueous boric acid solution (stretching in the aqueous boric acid solution). By using an aqueous boric acid solution as the stretching bath, the PVA-based resin layer can be provided with rigidity capable of withstanding tension applied during stretching and water resistance insoluble in water. Specifically, boric acid can form a tetrahydroxyboric acid anion in an aqueous solution and crosslink with the PVA-based resin by hydrogen bonding. As a result, the PVA-based resin layer can be given rigidity and water resistance, and stretched well, and a polarizing film having excellent optical characteristics can be produced.
The aqueous boric acid 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 3.5 to 7 parts by weight, particularly preferably 4 to 6 parts by weight, relative to 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, and a polarizing film having higher characteristics can be produced. It is also possible to use an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde, or the like other than boric acid or borate in a solvent.
Preferably, iodide is blended in the stretching bath (boric acid aqueous solution). By adding iodide, elution of iodine adsorbed to the PVA-based resin layer can be suppressed. Specific examples of iodides are described above. The concentration of iodide is preferably 0.05 to 15 parts by weight, more preferably 0.5 to 8 parts by weight, relative to 100 parts by weight of water.
The stretching temperature (liquid temperature of the stretching bath) is preferably 40 to 85 ℃, more preferably 60 to 75 ℃. If the temperature is such, the PVA-based resin layer can be stretched at a high rate while suppressing dissolution. Specifically, as described above, the glass transition temperature (Tg) of the thermoplastic resin substrate is preferably 60 ℃ or higher from the viewpoint of forming a PVA-based resin layer. In this case, when the stretching temperature is lower than 40 ℃, there is a risk that the thermoplastic resin base material cannot be stretched well even if plasticization by water is considered. On the other hand, the higher the temperature of the stretching bath, the higher the solubility of the PVA-based resin layer, and there is a possibility that excellent optical characteristics cannot be obtained. The immersion time of the laminate in the stretching bath is preferably 15 seconds to 5 minutes.
The stretching ratio by stretching in an aqueous solution is preferably 1.5 times or more, more preferably 3.0 times or more. The total stretch 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 realizing such a high stretching ratio, a polarizing film having very excellent optical characteristics can be produced. Such a high stretching ratio can be achieved by using an aqueous stretching method (stretching in an aqueous boric acid solution).
The drying shrinkage treatment may be performed by zone heating in which the entire zone is heated, or may be performed by heating a conveying roller (using a so-called heating roller) (heating roller drying method). Preferably both are utilized. By drying with the heating roller, the laminate can be efficiently suppressed from being curled by heating, and a polarizing film excellent in appearance can be produced. Specifically, by drying the laminate while the laminate is in a state of being brought along the heated roller, crystallization of the thermoplastic resin base material can be efficiently promoted, and the crystallinity can be increased, and even at a relatively low drying temperature, the crystallinity of the thermoplastic resin base material can be satisfactorily increased. As a result, the rigidity of the thermoplastic resin base material increases, and the PVA-based resin layer is allowed to shrink due to drying, thereby suppressing curling. Further, since the laminate can be dried while being kept flat by using the heating roller, not only curling but also the occurrence of wrinkles can be suppressed. At this time, the laminate is shrunk in the width direction by the drying shrinkage treatment, whereby the optical characteristics can be improved. This is because the orientation of PVA and PVA/iodine complex can be effectively improved. The shrinkage ratio of the laminate in the width direction by the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%. By using the heating roller, the laminate can be continuously contracted in the width direction while being conveyed, and high productivity can be achieved.
Fig. 4 is a schematic diagram showing an example of the drying shrinkage treatment. In the drying shrinkage process, the laminate 200 is dried while being conveyed by the conveying rollers R1 to R6 and the guide rollers G1 to G4 heated to a predetermined temperature. In the illustrated example, the conveyance rollers R1 to R6 are disposed so as to alternately continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin substrate, but the conveyance rollers R1 to R6 may be disposed so as to continuously heat only one surface (for example, the surface of the thermoplastic resin substrate) of the laminate 200, for example.
The drying condition can be controlled by adjusting the heating temperature of the conveying roller (temperature of the heating roller), the number of heating rollers, the contact time with the heating roller, and the like. The temperature of the heating roller is preferably 60 to 120 ℃, more preferably 65 to 100 ℃, and particularly preferably 70 to 80 ℃. The crystallinity of the thermoplastic resin can be satisfactorily increased, curling can be satisfactorily suppressed, and extremely excellent durability can be imparted to the laminate. The temperature of the heating roller may be measured by a contact thermometer. In the example of the figure, 6 conveying rollers are provided, but there is no particular limitation as long as the conveying rollers are plural. The number of the conveying rollers is usually 2 to 40, preferably 4 to 30. The contact time (total contact time) between the laminate and the heating roller is preferably 1 to 300 seconds, more preferably 1 to 20 seconds, and still more preferably 1 to 10 seconds.
The heating roller may be provided in a heating furnace (for example, an oven) or may be provided in a normal manufacturing line (in a room temperature environment). Preferably, the air blower is provided in a heating furnace provided with an air blowing mechanism. By using the drying by the heating roller and the hot air drying in combination, abrupt temperature change between the heating rollers can be suppressed, and shrinkage in the width direction can be easily controlled. The temperature of the hot air drying is preferably 30 to 100 ℃. The hot air drying time is preferably 1 to 300 seconds. The wind speed of the hot air is preferably about 10m/s to 30 m/s. The wind speed is the wind speed in the heating furnace, and can be measured by a mini-blade type digital anemometer.
The washing treatment is preferably performed after the stretching treatment in the aqueous solution and before the drying shrinkage treatment. The above-mentioned washing treatment is typically performed by immersing the PVA-based resin layer in an aqueous potassium iodide solution.
Examples
Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. The thickness is a value measured by the following measurement method.
< Thickness >
The thickness of 10 μm or less was measured by a scanning electron microscope (product name "JSM-7100F", manufactured by Japanese electronics Co., ltd.). The thickness exceeding 10 μm was measured by a digital micrometer (manufactured by An Li Co., ltd., product name "KC-351C").
Example 1
As the thermoplastic resin substrate, an amorphous isophthalic acid copolymerized polyethylene terephthalate film (thickness: 100 μm) having a long shape, a water absorption of 0.75% and a Tg of about 75℃was used. One side of the resin base material was subjected to corona treatment.
To 100 parts by weight of a PVA based resin obtained by mixing polyvinyl alcohol (polymerization degree 4200, saponification degree 99.2 mol%) and acetoacetyl-modified PVA (trade name "GOHSENX Z410", manufactured by Mitsubishi chemical corporation) at a ratio of 9:1, 13 parts by weight of potassium iodide was added, and the resulting mixture was dissolved in water to prepare a PVA aqueous solution (coating liquid).
The PVA aqueous solution was applied to the corona treated surface of the resin substrate, and dried at 60 ℃ to form a PVA-based resin layer having a thickness of 13 μm, thereby producing a laminate.
The resulting laminate was subjected to free-end unidirectional stretching to 2.4 times (auxiliary stretching treatment in a gas atmosphere) in a 130 ℃ oven between rolls having different peripheral speeds along the machine direction (longitudinal direction).
Subsequently, the laminate was immersed in an insolubilization bath (an aqueous boric acid solution obtained by mixing 4 parts by weight of boric acid with 100 parts by weight of water) at a liquid temperature of 40 ℃ for 30 seconds (insolubilization treatment).
Next, in a dyeing bath (an aqueous iodine solution obtained by mixing iodine and potassium iodide in a weight ratio of 1:7 with respect to 100 parts by weight of water) at a liquid temperature of 30 ℃, the resultant polarizing film was immersed for 60 seconds while adjusting the concentration so that the monomer transmittance (Ts) of the finally obtained polarizing film became 43.0% (dyeing treatment).
Then, the resultant solution was immersed in a crosslinking bath (aqueous boric acid solution obtained by mixing 3 parts by weight of potassium iodide with 100 parts by weight of water and 5 parts by weight of boric acid) at a liquid temperature of 40℃for 30 seconds (crosslinking treatment).
Then, the laminate was immersed in an aqueous boric acid solution (boric acid concentration: 4 wt% and potassium iodide concentration: 5 wt%) at a liquid temperature of 70 ℃ and uniaxially stretched (stretching treatment in aqueous solution) between rolls having different peripheral speeds in the longitudinal direction (longitudinal direction) so that the total stretching ratio became 5.5 times.
Then, the laminate was immersed in a washing bath (an aqueous solution obtained by mixing 100 parts by weight of water with 4 parts by weight of potassium iodide) at a liquid temperature of 20 ℃ (washing treatment).
Then, the resultant was dried in an oven maintained at 90℃and contacted with a SUS-made heating roller maintained at a surface temperature of about 75℃for about 2 seconds (drying shrinkage treatment). The shrinkage in the width direction of the laminate based on the drying shrinkage treatment was 5.2%.
In this way, a polarizing film (absorption type polarizing film) having a thickness of 5 μm was formed on the resin substrate.
A cycloolefin resin film having a thickness of 25 μm as a protective layer was bonded to the surface of the obtained polarizing film (the surface on the polarizing film side of the laminate) via an ultraviolet curable adhesive. Specifically, the adhesive layer after curing was applied so that the thickness of the adhesive layer became about 1 μm, and the adhesive layer was bonded using a roll press. Then, UV light is irradiated from the cycloolefin resin film side to cure the adhesive. Then, the resin substrate was peeled off to obtain a polarizing film (absorption-type polarizing film) having a configuration of cycloolefin resin film/absorption-type polarizing film.
Example 2
A polarizing film including a polarizing film 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 polarizing film (absorption type polarizing film) having a thickness of 12 μm was produced by sequentially subjecting a long roll of a polyvinyl alcohol (PVA) -based resin film (trade name "PE3000" manufactured by kohly) having a thickness of 30 μm to a swelling, dyeing, crosslinking, and cleaning treatment while stretching the film in the longitudinal direction to 5.9 times in the longitudinal direction by a roll stretcher, and finally subjecting the film to a drying treatment.
The swelling treatment was carried out in pure water at 20℃and stretched to 2.2 times. Then, the polarizing film was stretched to 1.4 times by dyeing in an aqueous solution at 30℃in which the weight ratio of iodine to potassium iodide was adjusted to 1:7 so that the monomer transmittance of the obtained polarizing film became 45.0%. Then, the crosslinking treatment was carried out in 2 stages, and the crosslinking treatment in stage 1 was carried out in an aqueous solution containing boric acid and potassium iodide at 40℃and stretched to 1.2 times. The boric acid content of the aqueous solution of the crosslinking treatment in the stage 1 was 5.0 wt% and the potassium iodide content was 3.0 wt%. The crosslinking treatment in stage 2 was carried out in an aqueous solution containing boric acid and potassium iodide at 65℃and stretched to 1.6 times. The boric acid content of the aqueous solution of the crosslinking treatment in the 2 nd stage was 4.3 wt% and the potassium iodide content was 5.0 wt%. Next, the washing treatment was performed in an aqueous potassium iodide solution at 20 ℃. The potassium iodide content of the aqueous solution for the washing treatment was 2.6 wt%. Finally, a drying treatment was performed at 70℃for 5 minutes to obtain a polarizing film.
A cycloolefin resin film having a thickness of 25 μm was laminated on the obtained polarizing film as a protective layer using a 3% aqueous solution of a PVA based adhesive (trade name "GOHSENOL Z" manufactured by Mitsubishi chemical corporation) to obtain a polarizing film.
Comparative example 2
A polarizing film including a polarizing film 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 film 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 film 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 performed for examples and comparative examples. The evaluation results are summarized in table 1.
< Evaluation >
1. Dimensional change ratio (%)
From the obtained polarizing film, test pieces having dimensions of 100mm×100mm were cut out in the stretching direction and the direction perpendicular thereto, and the test pieces were bonded to a glass plate via an acrylic pressure-sensitive adhesive layer having a thickness of 20 μm. The resultant was placed in an oven at 80℃for 500 hours and heated, and the dimensions before and after heating were measured to calculate the dimensional change rate before and after heating.
2. Shrinkage stress (N/4 mm)
Test pieces of 20mm×4mm in size were cut out from the obtained polarizing film (polarizing film before the protective film was attached) along the stretching direction and the direction perpendicular thereto, and set in a TMA analyzer (manufactured by HITACHI HIGH-TECH SCIENCE corporation, "TMA 7100E"). While maintaining the state, the test piece was directly heated at 50℃for 30 minutes, and the shrinkage stress generated by the test piece was measured.
3. Optical unevenness
The obtained polarizing film was cut out to a size of 200mm×150mm, and bonded to a glass plate via a 20 μm acrylic pressure-sensitive adhesive layer, and the thus obtained sample was put into a heat tester at 80 ℃ for 120 hours. Then, another standard polarizing plate (CRT 1794 manufactured by nindong corporation) was superimposed on the extracted sample so that the absorption axes thereof were orthogonal to each other, and the sample was placed on a backlight, and in this state, in-plane unevenness was confirmed.
TABLE 1
In the comparative example, as shown in fig. 5, optical unevenness (particularly, in the corner portion) was confirmed.
The present invention is not limited to the above embodiment, and various modifications can be made. For example, the components may be replaced with components substantially identical to those described in the above embodiments, components exhibiting the same operational effects, or components achieving the same purpose.
Industrial applicability
The lens unit according to the embodiment of the present invention can be used for a display body such as VR goggles.
Claims (16)
1. A lens section for a display system for displaying an image to a user,
The lens section includes:
A reflection unit that reflects light that is emitted from a display surface of a display element that displays an image toward the front and that has passed through a polarizing member and a1λ/4 th member, the reflection unit 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 reflection portion;
a half mirror disposed between the display element and the first lens portion, and configured to transmit light emitted from the display element and reflect light reflected by the reflecting portion toward the reflecting portion; and
A2λ/4 th member disposed on an optical path between the half mirror and the reflecting portion,
Wherein the thickness of the absorption type polarizing film constituting the absorption type polarizing member is 8 μm or less.
2. The lens portion according to claim 1, wherein,
The reflection axis of the reflection type polarizing member and the absorption axis of the absorption type polarizing member are arranged parallel to each other.
3. The lens portion according to claim 1, wherein,
The first lens portion is integral with the half mirror.
4. The lens unit according to claim 1, comprising a second lens unit disposed in front of the reflecting unit.
5. The lens portion according to claim 1, wherein,
An angle formed by an absorption axis of the polarizing member included in the display element and a slow axis of the 1λ/4 th member is 40 ° to 50%,
An angle formed by an absorption axis of the polarizing member included in the display element and a slow axis of the 2λ/4 th member is 40 ° to 50 °.
6. The lens portion according to claim 1, wherein,
The ratio of the thickness of the absorption-type polarizing film to the thickness of the reflection-type polarizing member is 15% or less.
7. A laminate for use in the reflection section of the lens section according to any one of claims 1 to 6,
The laminate has the reflective polarizing member and the absorptive polarizing member.
8. The laminate according to claim 7, wherein,
The reflective polarizing member and the absorptive polarizing member are laminated via an adhesive layer.
9. A display body having the lens portion according to any one of claims 1 to 6.
10. A method for manufacturing a display body having the lens portion according to any one of claims 1 to 6.
11. A display method, the method comprising:
Passing the light of the display image emitted through the polarizing member and the 1λ/4 th member through the half mirror and the first lens section;
a step of passing the light passing through the half mirror and the first lens portion through a2λ/4 th member;
a step of reflecting the light passing through the 2λ/4 th member toward the half mirror at a reflecting section including a reflective polarizing member;
a step of transmitting the light reflected by the reflecting section and the half mirror through the 2 nd λ/4 member to the reflective polarizing member of the reflecting section; and
A step of transmitting the light transmitted through the reflective polarizing member to the absorptive polarizing member,
Wherein the thickness of the absorption type polarizing film constituting the absorption type polarizing member is 8 μm or less.
12. A method for producing the absorptive polarizing film for a lens unit according to any one of claims 1 to 6, comprising:
Forming a polyvinyl alcohol resin layer containing a halide and a polyvinyl alcohol resin on one side of a long thermoplastic resin substrate to form a laminate;
The laminate is sequentially subjected to an auxiliary stretching treatment in a gas atmosphere, a dyeing treatment, a stretching treatment in an aqueous solution, and a drying shrinkage treatment for shrinking the laminate by 2% or more in the width direction by heating while being transported in the longitudinal direction.
13. The manufacturing method according to claim 12, wherein,
The halide content in the polyvinyl alcohol resin layer is 5 to 20 parts by weight per 100 parts by weight of the polyvinyl alcohol resin.
14. The manufacturing method according to claim 12, wherein,
The stretching ratio in the auxiliary stretching treatment in the gas atmosphere is more than 2.0 times.
15. The manufacturing method according to claim 12, wherein,
The drying shrinkage treatment step is a step of heating with a heating roller.
16. The manufacturing method according to claim 15, wherein,
The temperature of the heating roller is 60-120 ℃, and the shrinkage rate of the laminated body in the width direction based on the drying shrinkage treatment is more than 2%.
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| JP2022-039286 | 2022-03-14 | ||
| JP2022-039285 | 2022-03-14 | ||
| JP2022077634A JP7516457B2 (en) | 2022-05-10 | 2022-05-10 | Lens portion, laminate, display, manufacturing method of display, and display method |
| JP2022-077634 | 2022-05-10 | ||
| PCT/JP2023/006727 WO2023176360A1 (en) | 2022-03-14 | 2023-02-24 | Lens part, laminate, display body, and manufacturing method and display method for display body |
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| JP2002107655A (en) | 2000-09-27 | 2002-04-10 | Minolta Co Ltd | Video display device |
| JP2006251095A (en) | 2005-03-08 | 2006-09-21 | Fuji Photo Film Co Ltd | Liquid crystal display device |
| JP2008102274A (en) | 2006-10-18 | 2008-05-01 | Nitto Denko Corp | Polarizer, polarization plate, optical film and image display apparatus |
| JP6686178B2 (en) | 2016-01-28 | 2020-04-22 | 深▲セン▼多▲ドゥオ▼新技術有限責任公司Ｓｈｅｎｚｈｅｎ Ｄｌｏｄｌｏ Ｎｅｗ Ｔｅｃｈｎｏｌｏｇｙ Ｃｏ．， Ｌｔｄ． | Short-range light expanding module, short-range light expanding method and short-range light expanding system |
| JP6699514B2 (en) | 2016-05-27 | 2020-05-27 | 住友化学株式会社 | Set of polarizing plates for IPS mode and IPS mode liquid crystal display device using the same |
| JP2019197181A (en) | 2018-05-11 | 2019-11-14 | 住友化学株式会社 | Polarizing plate and display device |
| CN112262329A (en) | 2018-06-07 | 2021-01-22 | 日东电工株式会社 | Polarizing film and polarizing plate with phase difference layer |
| CN110161692A (en) | 2018-07-16 | 2019-08-23 | 上海视涯信息科技有限公司 | A kind of virtual reality display device |
| WO2021106742A1 (en) | 2019-11-28 | 2021-06-03 | 日東電工株式会社 | Optical laminate, optical device, and image display device |
| JP7046127B6 (en) | 2020-07-28 | 2023-12-18 | 日東電工株式会社 | Image display device including an optical laminate and a polarizing plate with a retardation layer of the optical laminate |
| JP2022055640A (en) | 2020-09-29 | 2022-04-08 | 日東電工株式会社 | Decorative film and optical device |
| CN113448101A (en) | 2021-06-28 | 2021-09-28 | 歌尔股份有限公司 | Optical module and head-mounted display device |
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