WO2021220907A1 - 偏光板および該偏光板を用いた画像表示装置 - Google Patents
偏光板および該偏光板を用いた画像表示装置 Download PDFInfo
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- WO2021220907A1 WO2021220907A1 PCT/JP2021/016161 JP2021016161W WO2021220907A1 WO 2021220907 A1 WO2021220907 A1 WO 2021220907A1 JP 2021016161 W JP2021016161 W JP 2021016161W WO 2021220907 A1 WO2021220907 A1 WO 2021220907A1
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- WIPO (PCT)
- Prior art keywords
- pva
- polarizing plate
- stretching
- polarizer
- based resin
- Prior art date
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Images
Classifications
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
- H10K59/80—Constructional details
- H10K59/8791—Arrangements for improving contrast, e.g. preventing reflection of ambient light
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/30—Polarising elements
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B7/00—Layered products characterised by the relation between layers; Layered products characterised by the relative orientation of features between layers, or by the relative values of a measurable parameter between layers, i.e. products comprising layers having different physical, chemical or physicochemical properties; Layered products characterised by the interconnection of layers
- B32B7/02—Physical, chemical or physicochemical properties
- B32B7/023—Optical properties
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
- G02B1/04—Optical elements characterised by the material of which they are made; Optical coatings for optical elements made of organic materials, e.g. plastics
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/133528—Polarisers
-
- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09F—DISPLAYING; ADVERTISING; SIGNS; LABELS OR NAME-PLATES; SEALS
- G09F9/00—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements
- G09F9/30—Indicating arrangements for variable information in which the information is built-up on a support by selection or combination of individual elements in which the desired character or characters are formed by combining individual elements
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B3/00—Ohmic-resistance heating
- H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
- H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material
- H05B3/14—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material the material being non-metallic
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B33/00—Electroluminescent light sources
- H05B33/02—Details
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B32—LAYERED PRODUCTS
- B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
- B32B2329/00—Polyvinylalcohols, polyvinylethers, polyvinylaldehydes, polyvinylketones or polyvinylketals
- B32B2329/04—Polyvinylalcohol
Definitions
- the present invention relates to a polarizing plate and an image display device using the polarizing plate.
- a polarizing plate is often arranged on at least one side of a display cell due to the image forming method.
- an image display device having a camera unit has rapidly become widespread, and the camera unit can function not only as a photographing device but also as a main component of a face recognition system.
- the polarizing plate is often provided with a through hole or a transparent portion (non-polarized portion) at a position corresponding to the camera portion.
- the through hole or the transparent portion often impairs the design, a polarizing plate capable of sufficiently exerting the photographing function and the face recognition function without providing the through hole or the transparent portion is desired.
- the present invention has been made to solve the above-mentioned conventional problems, and its main purpose is to provide an excellent photographing function without providing a through hole or a transparent portion when applied to an image display device having a camera unit.
- An object of the present invention is to provide a polarizing plate capable of realizing a face recognition function.
- the polarizing plate according to the embodiment of the present invention has a polarizing element made of a polyvinyl alcohol-based resin film containing a dichroic substance, and a protective layer arranged on at least one side of the polarizing element, and is reflective.
- the image contrast index is 15 or less.
- the thickness of the polarizer is 12 ⁇ m or less.
- the reflected image contrast index is 13 or less.
- the polarizing plate has a protective layer on only one side of the polarizer.
- an image display device includes a display cell and the above-mentioned polarizing plate arranged on at least one side of the display cell.
- the reflected image contrast index to 15 or less, when applied to an image display device having a camera unit, an excellent photographing function and an excellent photographing function without providing a through hole or a transparent portion and A polarizing plate capable of realizing a face recognition function can be provided.
- FIG. 1 is a schematic cross-sectional view of a polarizing plate according to one embodiment of the present invention.
- the polarizing plate 100 is a first protective layer (outer protection) arranged on one side of the polarizing element 10 and the polarizing element 10 (for example, the side opposite to the display cell when the polarizing plate is applied to an image display device). It has a layer (20) 20 and a second protective layer (inner protective layer) 30 arranged on the other side of the polarizing element (for example, the display cell side when the polarizing plate is applied to the image display device). Either the first protective layer 20 or the second protective layer 30 may be omitted depending on the purpose or the like.
- the polarizer 10 is made of a polyvinyl alcohol (PVA) -based resin film containing a dichroic substance (typically iodine or a dichroic dye).
- PVA polyvinyl alcohol
- the reflected image contrast index is 15 or less, preferably 14.5 or less, more preferably 13 or less, and further preferably 12 or less.
- the transmitted wave surface aberration optical distortion of light transmitted through the polarizing plate, details will be described later
- the technical meaning of defining the reflected image contrast index will be described below.
- the surface roughness of the polarizer (for example, arithmetic mean roughness Ra) is related to one of the causes of the increased transmitted wave surface aberration.
- the present inventors have found that the transmitted wave surface aberration cannot be appropriately controlled even if the surface roughness of the polarizer is controlled.
- the transmitted wave surface aberration can be appropriately controlled by controlling the reflected image contrast index as a characteristic of the entire polarizing plate, and the present invention is completed. I arrived.
- the reflected image contrast index is a single and / or mutual optical factor of the constituent elements of the polarizing plate (for example, a streak of the polarizer, refraction and / or scattering of the interface between the polarizer and the protective layer, and a protective layer. It reflects the unevenness of.
- the reflected image contrast index can be measured as follows. In a dark room environment, the polarizing plate is irradiated with light from a special lighting device for inspection (“S-Light” manufactured by Japan Technology Center) at an angle of 45 °; the image of the reflected image is captured as digital data; 100 mm ⁇ 100 mm. Image processing is performed on the region to obtain the brightness variation as the standard deviation, and this is used as the reflected image contrast index. More specifically, the brightness of the pixels of the image is quantified in gradations of 0 to 255, the standard deviation thereof is obtained, and this is used as the reflected image contrast index.
- the polarizing plate preferably has a small transmitted wave surface aberration as described above.
- the transmitted wave surface aberration is an index showing the optical distortion of the light transmitted through the polarizing plate, and means the deviation of the light transmitted through the polarizing plate from the ideal wave surface (spherical surface). Therefore, if the transmitted wave surface aberration becomes too large, the deviation of the light transmitted through the polarizing plate from the ideal wave surface becomes large, and the light flux emitted from one point of the object does not converge to one point, so that the image is blurred. , May be distorted.
- the transmitted wave surface aberration is preferably 100 nm or less, more preferably 50 nm or less, still more preferably 30 nm or less, and particularly preferably 25 nm or less.
- Such transmitted wave surface aberration can be realized by controlling the reflected image contrast index to a predetermined value or less as described above.
- the transmitted wave surface aberration can be typically represented by Pv ⁇ ⁇ .
- Pv indicates the difference (Peek-Valley) between the maximum value and the minimum value of the transmitted wave surface aberration in the measurement range, and represents the ratio of the distance to the incident light wavelength.
- Pv 0.1.
- ⁇ is the wavelength (nm) of the incident light.
- the transmitted wave surface aberration can be measured using a HeNe laser with a wavelength of 632.8 nm.
- the polarizing element is composed of a PVA-based resin film containing a dichroic substance (typically, iodine or a dichroic dye).
- the dichroic substance is preferably iodine.
- the polarizer may be formed of a single-layer resin film or may be formed of a laminate of two or more layers.
- the polarizer formed from the single-layer resin film include a hydrophilic polymer film such as a polyvinyl alcohol (PVA) -based film, a partially formalized PVA-based film, and an ethylene / vinyl acetate copolymer system partially saponified film.
- a hydrophilic polymer film such as a polyvinyl alcohol (PVA) -based film, a partially formalized PVA-based film, and an ethylene / vinyl acetate copolymer system partially saponified film.
- PVA polyvinyl alcohol
- a partially formalized PVA-based film ethylene / vinyl acetate copolymer system partially saponified film
- examples thereof include those which have been dyed and stretched with a bicolor substance such as iodine or a bicolor dye, and polyene-based oriented films such as a dehydrated product of PVA and a dehydrogenated product of polyvinyl chloride.
- the dyeing with iodine is performed, for example, by immersing a PVA-based film in an aqueous iodine solution.
- the draw ratio of the uniaxial stretching is preferably 3 to 7 times. Stretching may be performed after the dyeing treatment or while dyeing. Alternatively, it may be stretched and then dyed.
- the PVA-based film is subjected to a swelling treatment, a cross-linking treatment, a washing treatment, a drying treatment and the like. For example, by immersing the PVA-based film in water and washing it with water before dyeing, it is possible not only to clean the dirt and blocking inhibitor on the surface of the PVA-based film, but also to swell the PVA-based film to prevent uneven dyeing. Can be prevented.
- the polarizer obtained by using the laminate include a laminate of a resin base material and a PVA-based resin layer (PVA-based resin film) laminated on the resin base material, or a resin base material and the resin.
- Examples thereof include a polarizer obtained by using a laminate with a PVA-based resin layer coated and formed on a base material.
- the polarizer obtained by using the laminate of the resin base material and the PVA-based resin layer coated and formed on the resin base material is, for example, a resin base material obtained by applying a PVA-based resin solution to the resin base material and drying the resin base material.
- stretching typically includes immersing the laminate in an aqueous boric acid solution for stretching. Further, stretching may further include, if necessary, stretching the laminate in the air at a high temperature (eg, 95 ° C. or higher) prior to stretching in boric acid aqueous solution.
- a high temperature eg, 95 ° C. or higher
- the obtained resin base material / polarizer laminate may be used as it is (that is, the resin base material may be used as a protective film for the polarizer), or the resin base material is peeled off from the resin base material / polarizer laminate. Then, any suitable protective film according to the purpose may be laminated on the peeled surface. Details of the method for producing such a polarizer are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580 and Japanese Patent No. 6470455. The entire description of these publications is incorporated herein by reference.
- any suitable resin can be adopted as the PVA-based resin that forms the PVA-based resin film.
- polyvinyl alcohol and ethylene-vinyl alcohol copolymer can be mentioned.
- Polyvinyl alcohol is obtained by saponification of polyvinyl acetate.
- the ethylene-vinyl alcohol copolymer is obtained by saponifying the ethylene-vinyl acetate copolymer.
- the degree of saponification of the PVA-based resin is usually 85 mol% to 100 mol%, preferably 95.0 mol% to 99.9 mol%, and more preferably 99.0 mol% to 99.5 mol%. ..
- the degree of saponification can be determined according to JIS K 6726-1994. By using a PVA-based resin having such a degree of saponification, a polarizer having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.
- the average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose.
- the average degree of polymerization is usually 1000 to 10000, preferably 1200 to 5000, and more preferably 1500 to 4500.
- the average degree of polymerization can be determined according to JIS K 6726-1994.
- the iodine concentration in the PVA-based resin film (polarizer) is, for example, 5.0% by weight to 12.0% by weight.
- the boric acid concentration in the PVA-based resin film is, for example, 12% by weight to 25% by weight.
- the thickness of the polarizer is, for example, 12 ⁇ m or less, preferably 8 ⁇ m or less, more preferably 7 ⁇ m or less, still more preferably 6 ⁇ m or less.
- the thickness of the polarizer is preferably 1 ⁇ m or more, more preferably 2 ⁇ m or more. The thicker the polarizer, the easier it is to obtain the desired reflected image contrast index. However, according to the embodiment of the present invention, the desired reflected image contrast index can be realized in spite of such a thin polarizing element. Can be done.
- the polarizer preferably exhibits absorption dichroism at any wavelength of 380 nm to 780 nm.
- the simple substance transmittance of the polarizer is preferably 40.0% to 46.0%, more preferably 40.5% to 43.0%.
- the degree of polarization of the polarizer is preferably 99.9% or more, more preferably 99.95% or more, and further preferably 99.98% or more.
- the first and second protective layers are formed of any suitable film that can be used as a protective layer for the polarizer.
- the material that is the main component of the film include cellulose-based resins such as triacetyl cellulose (TAC), polyester-based, polyvinyl alcohol-based, polycarbonate-based, polyamide-based, polyimide-based, polyethersulfone-based, and polysulfone-based.
- TAC triacetyl cellulose
- polyester-based polyvinyl alcohol-based
- polycarbonate-based polycarbonate-based
- polyamide-based polyimide-based
- polyethersulfone-based polysulfone-based
- thermosetting resins such as (meth) acrylic, urethane, (meth) acrylic urethane, epoxy, and silicone, or ultraviolet curable resins can also be mentioned.
- glassy polymers such as siloxane-based polymers can also be mentioned.
- the polymer film described in JP-A-2001-343529 (WO01 / 37007) can also be used.
- a resin composition containing a thermoplastic resin having a substituted or unsubstituted imide group in the side chain and a thermoplastic resin having a substituted or unsubstituted phenyl group and a nitrile group in the side chain.
- the polymer film can be, for example, an extruded product of the above resin composition.
- the thickness of the first protective layer (outer protective layer) 20 arranged on the side opposite to the display cell is typically 300 ⁇ m or less, preferably 100 ⁇ m or less. , More preferably 5 ⁇ m to 80 ⁇ m, still more preferably 10 ⁇ m to 60 ⁇ m.
- the thickness of the outer protective layer is the thickness including the thickness of the surface treatment layer.
- the thickness of the second protective layer (inner protective layer) 30 arranged on the display cell side when the polarizing plate 100 is applied to the image display device is preferably 5 ⁇ m to 200 ⁇ m, more preferably 10 ⁇ m to 100 ⁇ m, and even more preferably. It is 10 ⁇ m to 60 ⁇ m.
- the inner protective layer is preferably optically isotropic. As used herein, “optically isotropic" means that the in-plane retardation Re (550) is 0 nm to 10 nm and the thickness direction retardation Rth (550) is -10 nm to +10 nm. say.
- the inner protective layer is a retardation layer having any suitable retardation value.
- the in-plane retardation Re (550) of the retardation layer is, for example, 110 nm to 150 nm, and the angle formed by the slow axis thereof and the absorption axis of the polarizer is, for example, 40 ° to 50 °.
- nx is the refractive index in the direction in which the in-plane refractive index is maximized (that is, the slow-phase axis direction), and “ny” is the in-plane direction orthogonal to the slow-phase axis (that is, phase-advance). It is the refractive index in the axial direction), “nz” is the refractive index in the thickness direction, and “d” is the thickness (nm) of the layer (film).
- the second protective layer (inner protective layer) 30 may be preferably omitted.
- the polarizer is a polyvinyl alcohol-based resin layer (PVA-based resin layer) containing a halide and a polyvinyl alcohol-based resin (PVA-based resin) on one side of a long thermoplastic resin base material.
- PVA-based resin layer polyvinyl alcohol-based resin layer
- PVA-based resin polyvinyl alcohol-based resin layer
- the content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.
- the drying shrinkage treatment is preferably carried out using a heating roll, and the temperature of the heating roll is preferably 60 ° C. to 120 ° C.
- the shrinkage ratio in the width direction of the laminated body by the drying shrinkage treatment is preferably 2% or more.
- the polarizer described in Section B above can be obtained.
- the laminated body can be uniformly shrunk over the entire laminated body while being conveyed.
- a heating roll in the drying shrinkage treatment step the laminated body can be uniformly shrunk over the entire laminated body while being conveyed.
- thermoplastic resin base material a thermoplastic resin base material
- a PVA-based resin layer a coating liquid containing a halide and a PVA-based resin is applied to the surface of the thermoplastic resin base material and dried to form a PVA-based resin layer on the thermoplastic resin base material.
- the content of the halide in the PVA-based resin layer is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.
- any appropriate method can be adopted as the application method of the coating liquid.
- a roll coating method, a spin coating method, a wire bar coating method, a dip coating method, a die coating method, a curtain coating method, a spray coating method, a knife coating method (comma coating method, etc.) and the like can be mentioned.
- the coating / drying temperature of the coating liquid is preferably 50 ° C. or higher.
- the thickness of the PVA-based resin layer is preferably 3 ⁇ m to 40 ⁇ m, more preferably 3 ⁇ m to 20 ⁇ m.
- the thermoplastic resin base material Before forming the PVA-based resin layer, the thermoplastic resin base material may be surface-treated (for example, corona treatment or the like), or the easy-adhesion layer may be formed on the thermoplastic resin base material. By performing such a treatment, the adhesion between the thermoplastic resin base material and the PVA-based resin layer can be improved.
- thermoplastic resin base material any suitable thermoplastic resin film can be adopted. Details of the thermoplastic resin base material are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580. The entire description of the publication is incorporated herein by reference.
- the coating liquid contains a halide and a PVA-based resin as described above.
- the coating liquid is typically a solution in which the halide and the PVA-based resin are dissolved in a solvent.
- the solvent include water, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, various glycols, polyhydric alcohols such as trimethylpropane, and amines such as ethylenediamine and diethylenetriamine. These can be used alone or in combination of two or more. Of these, water is preferred.
- the PVA-based resin concentration of the solution is preferably 3 parts by weight to 20 parts by weight with respect to 100 parts by weight of the solvent.
- the content of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin.
- Additives may be added to the coating liquid.
- the additive include a plasticizer, a surfactant and the like.
- the plasticizer include polyhydric alcohols such as ethylene glycol and glycerin.
- the surfactant include nonionic surfactants. These can be used for the purpose of further improving the uniformity, dyeability, and stretchability of the obtained PVA-based resin layer.
- any suitable resin can be adopted as the PVA-based resin.
- polyvinyl alcohol and ethylene-vinyl alcohol copolymers can be mentioned.
- Polyvinyl alcohol is obtained by saponification of polyvinyl acetate.
- the ethylene-vinyl alcohol copolymer is obtained by saponifying the ethylene-vinyl acetate copolymer.
- the degree of saponification 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 degree of saponification can be determined according to JIS K 6726-1994.
- the PVA-based resin By using a PVA-based resin having such a degree of saponification, a polarizer having excellent durability can be obtained. If the degree of saponification is too high, gelation may occur.
- the PVA-based resin preferably contains an acetoacetyl-modified PVA-based resin.
- the average degree of polymerization of the PVA-based resin can be appropriately selected according to the purpose.
- the average degree of polymerization is usually 1000 to 10000, preferably 1200 to 4500, and more preferably 1500 to 4300.
- the average degree of polymerization can be determined according to JIS K 6726-1994.
- any suitable halide can be adopted.
- iodide and sodium chloride can be mentioned.
- Iodides include, for example, potassium iodide, sodium iodide, and lithium iodide. Of these, potassium iodide is preferred.
- the amount of the halide in the coating liquid is preferably 5 parts by weight to 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, and more preferably 10 parts by weight to 15 parts by weight with respect to 100 parts by weight of the PVA-based resin. It is a department. If the amount of the halide exceeds 20 parts by weight with respect to 100 parts by weight of the PVA-based resin, the halide may bleed out and the finally obtained polarizer may become cloudy.
- the stretching of the PVA-based resin layer increases the orientation of the polyvinyl alcohol molecules in the PVA-based resin.
- the stretched PVA-based resin layer is immersed in a liquid containing water, the polyvinyl alcohol molecules become more oriented. The orientation may be disturbed and the orientation may decrease.
- the laminate of the thermoplastic resin and the PVA-based resin layer is stretched in boric acid water, when the laminate is stretched in boric acid water at a relatively high temperature in order to stabilize the stretching of the thermoplastic resin, The tendency of the degree of orientation to decrease is remarkable.
- stretching a PVA film alone in boric acid water is generally performed at 60 ° C.
- stretching of a laminate of A-PET (thermoplastic resin base material) and a PVA-based resin layer is performed. It is carried out at a high temperature of about 70 ° C., and in this case, the orientation of PVA at the initial stage of stretching may decrease before it is increased by stretching in water.
- a laminate of a PVA-based resin layer containing a halide and a thermoplastic resin base material is prepared, and the laminate is stretched at a high temperature (auxiliary stretching) in the air before being stretched in boric acid water.
- Crystallization of the PVA-based resin in the PVA-based resin layer of the laminated body after the auxiliary stretching can be promoted.
- the disorder of the orientation of the polyvinyl alcohol molecules and the decrease in the orientation can be suppressed as compared with the case where the PVA-based resin layer does not contain a halide.
- thermoplastic resin base material can be stretched while suppressing the crystallization of the thermoplastic resin base material, and the thermoplastic resin base material is excessively crystallized in the subsequent stretching in boric acid water. This solves the problem that the stretchability is lowered, and the laminated body can be stretched at a higher magnification.
- the PVA-based resin when the PVA-based resin is applied on the thermoplastic resin base material, it is compared with the case where the PVA-based resin is applied on a normal metal drum in order to suppress the influence of the glass transition temperature of the thermoplastic resin base material. Therefore, it is necessary to lower the coating temperature, and as a result, the crystallization of the PVA-based resin becomes relatively low, which may cause a problem that sufficient optical characteristics cannot be obtained. On the other hand, by introducing the auxiliary stretching, it is possible to increase the crystallinity of the PVA-based resin even when the PVA-based resin is coated on the thermoplastic resin, and it is possible to achieve high optical characteristics. Become.
- the stretching method of the aerial auxiliary stretching may be fixed-end stretching (for example, a method of stretching using a tenter stretching machine) or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). good.
- the stretching method for aerial auxiliary stretching can be, for example, biaxial stretching using a tenter stretching machine.
- the stretching ratio in the longitudinal direction in the aerial auxiliary stretching is preferably 2.3 times or more, and more preferably 2.4 times to 3.5 times.
- the width residual ratio (width after shrinkage with respect to the original width:%) is controlled by adopting biaxial stretching as described above.
- the difference between the residual width (that is, after the auxiliary stretching in the air) and the residual free shrinkage width in the aerial auxiliary stretching is preferably 2% or more, more preferably 3% or more, and further. It is preferably 5% or more.
- the maximum value of the difference can be, for example, 15%.
- the free shrinkage width residual rate is the width residual rate when the free end is stretched in the longitudinal direction at the same stretching ratio.
- the free shrinkage width residual rate when the draw ratio is x times can be calculated by (1 / x 1/2) ⁇ 100.
- the maximum stretching ratio (longitudinal direction) when the aerial auxiliary stretching and the underwater stretching are combined is preferably 5.0 times or more, more preferably 5.5 times or more, and further, with respect to the original length of the laminated body. It is preferably 6.0 times or more.
- the "maximum draw ratio" means the draw ratio immediately before the laminate breaks, and separately confirms the draw ratio at which the laminate breaks, and means a value 0.2 lower than that value.
- the stretching temperature of the aerial auxiliary stretching can be set to an arbitrary appropriate value depending on the forming material of the thermoplastic resin base material, the stretching method, and the like.
- the stretching temperature is preferably the glass transition temperature (Tg) or more of the thermoplastic resin base material, more preferably the glass transition temperature (Tg) of the thermoplastic resin base material (Tg) + 10 ° C. or higher, and particularly preferably Tg + 15 ° C. or higher.
- the upper limit of the stretching temperature is preferably 170 ° C.
- the crystallization index of the PVA-based resin after the aerial auxiliary stretching is preferably 1.3 to 1.8, and more preferably 1.4 to 1.7.
- an insolubilization treatment is performed after the aerial auxiliary stretching treatment and before the underwater stretching treatment or the dyeing treatment.
- the insolubilization treatment is typically performed by immersing a PVA-based resin layer in an aqueous boric acid solution.
- the dyeing treatment is typically performed by dyeing the PVA-based resin layer with a dichroic substance (typically iodine).
- a cross-linking treatment is performed after the dyeing treatment and before the underwater stretching treatment.
- the cross-linking treatment is typically performed by immersing a PVA-based resin layer in an aqueous boric acid solution. Details of the insolubilization treatment, the dyeing treatment and the cross-linking treatment are described in, for example, Japanese Patent Application Laid-Open No. 2012-73580 (above).
- the underwater stretching treatment is performed by immersing the laminate in a stretching bath. According to the underwater stretching treatment, the thermoplastic resin base material or the PVA-based resin layer can be stretched at a temperature lower than the glass transition temperature (typically, about 80 ° C.), and the PVA-based resin layer is crystallized. It is possible to stretch at a high magnification while suppressing the above. As a result, a polarizer having excellent optical characteristics can be produced.
- any appropriate method can be adopted as the stretching method of the laminated body. Specifically, it may be fixed-end stretching or free-end stretching (for example, a method of uniaxial stretching through a laminate between rolls having different peripheral speeds). Preferably, free end stretching is selected.
- the stretching of the laminate may be carried out in one step or in multiple steps. In the case of performing in multiple stages, the draw ratio (maximum draw ratio) of the laminated body described later is the product of the draw ratios of each stage.
- the underwater stretching is preferably carried out by immersing the laminate in a boric acid aqueous solution (boric acid water stretching).
- a boric acid aqueous solution as the stretching bath, it is possible to impart rigidity to withstand the tension applied during stretching and water resistance that does not dissolve in water to the PVA-based resin layer.
- boric acid can generate a tetrahydroxyboric acid anion in an aqueous solution and crosslink with a PVA-based resin by hydrogen bonding.
- the PVA-based resin layer can be imparted with rigidity and water resistance, can be stretched satisfactorily, and a polarizer having excellent optical characteristics can be produced.
- the boric acid aqueous solution is preferably obtained by dissolving boric acid and / or borate in water as a solvent.
- the boric acid concentration is preferably 1 part by weight to 10 parts by weight, more preferably 2.5 parts by weight to 6 parts by weight, and particularly preferably 3 parts by weight to 5 parts by weight with respect to 100 parts by weight of water. Is.
- an aqueous solution obtained by dissolving a boron compound such as borax, glyoxal, glutaraldehyde or the like in a solvent can also be used.
- iodide is added to the above stretching bath (boric acid aqueous solution).
- the elution of iodine adsorbed on the PVA-based resin layer can be suppressed.
- Specific examples of iodide are as described above.
- the concentration of iodide is preferably 0.05 parts by weight to 15 parts by weight, and more preferably 0.5 parts by weight to 8 parts by weight with respect to 100 parts by weight of water.
- the stretching temperature (liquid temperature of the stretching bath) and the immersion time of the laminate in the stretching bath are determined by the composition of the protective layer (typically, the material and whether it is arranged on one side or both sides of the polarizer. ) Can be set appropriately.
- the stretching temperature may be, for example, 70 ° C. or lower, 67 ° C. or lower, 66 ° C. or lower, or 65 ° C. or lower.
- the lower limit of the stretching temperature may be, for example, 50 ° C., or may be, for example, 55 ° C.
- the immersion time of the laminate in the stretching bath may be, for example, 50 seconds or longer, 55 seconds or longer, or 60 seconds or longer.
- the upper limit of the immersion time can be, for example, 100 seconds.
- the combination of the stretching temperature and the immersion time may be, for example, 55 ° C. to 66 ° C./55 seconds or more, or may be, for example, 60 ° C. to 66 ° C./60 seconds to 80 seconds.
- Boric acid stretching in water is usually carried out at around 70 ° C. for about 50 seconds, but the present inventors lower the stretching temperature by several ° C. and lengthen the immersion time to reduce the optical characteristics of the polarizer. It was found that the reflected image contrast index can be remarkably reduced. This is an unexpectedly excellent effect. Furthermore, it has been found that the same effect can be obtained only by lowering the stretching temperature or increasing the immersion time depending on the composition of the protective layer.
- the stretching ratio by stretching in water is preferably 1.5 times or more, more preferably 3.0 times or more.
- the total draw ratio of the laminated body is preferably 5.0 times or more, more preferably 5.5 times or more, with respect to the original length of the laminated body.
- drying shrinkage treatment may be carried out by heating the entire zone, or by heating the transport roll (using a so-called heating roll) (heating roll drying method). Preferably, both are used.
- heating roll heating roll drying method
- the crystallization of the thermoplastic resin base material can be efficiently promoted and the crystallinity can be increased, which is relatively low. Even at the drying temperature, the crystallinity of the thermoplastic resin base material can be satisfactorily increased.
- the rigidity of the thermoplastic resin base material is increased, and the thermoplastic resin base material is in a state of being able to withstand the shrinkage of the PVA-based resin layer due to drying, and curling is suppressed.
- the laminated body can be dried while being maintained in a flat state, so that not only curling but also wrinkles can be suppressed.
- the laminated body can be improved in optical characteristics by shrinking in the width direction by a drying shrinkage treatment. This is because the orientation of PVA and the PVA / iodine complex can be effectively enhanced.
- the shrinkage ratio in the width direction of the laminate by the drying shrinkage treatment is preferably 1% to 10%, more preferably 2% to 8%, and particularly preferably 4% to 6%.
- FIG. 2 is a schematic view showing an example of the drying shrinkage treatment.
- the laminate 200 is dried while being transported by the transport rolls R1 to R6 heated to a predetermined temperature and the guide rolls G1 to G4.
- the transport rolls R1 to R6 are arranged so as to alternately and continuously heat the surface of the PVA resin layer and the surface of the thermoplastic resin base material.
- one surface of the laminate 200 (for example, thermoplastic) is arranged.
- the transport rolls R1 to R6 may be arranged so as to continuously heat only the resin base material surface).
- Drying conditions can be controlled by adjusting the heating temperature of the transport roll (temperature of the heating roll), the number of heating rolls, the contact time with the heating roll, and the like.
- the temperature of the heating roll is preferably 60 ° C. to 120 ° C., more preferably 65 ° C. to 100 ° C., and particularly preferably 70 ° C. to 80 ° C.
- the crystallinity of the thermoplastic resin can be satisfactorily increased, curling can be satisfactorily suppressed, and an optical laminate having extremely excellent durability can be produced.
- the temperature of the heating roll can be measured with a contact thermometer. In the illustrated example, six transport rolls are provided, but there is no particular limitation as long as there are a plurality of transport rolls.
- the number of transport rolls is usually 2 to 40, preferably 4 to 30.
- the contact time (total contact time) between the laminate and the heating roll is preferably 1 second to 300 seconds, more preferably 1 to 20 seconds, and further preferably 1 to 10 seconds.
- the heating roll may be provided in a heating furnace (for example, an oven) or in a normal production line (in a room temperature environment). Preferably, it is provided in a heating furnace provided with a blowing means.
- a heating furnace provided with a blowing means.
- the temperature of hot air drying is preferably 30 ° C to 100 ° C.
- the hot air drying time is preferably 1 second to 300 seconds.
- the wind speed of hot air is preferably about 10 m / s to 30 m / s. The wind speed is the wind speed in the heating furnace and can be measured by a mini-vane type digital anemometer.
- a washing treatment is performed after the underwater stretching treatment and before the drying shrinkage treatment.
- the cleaning treatment is typically performed by immersing a PVA-based resin layer in an aqueous potassium iodide solution.
- the polarizing plate according to the above items A and B can be applied to an image display device. Therefore, such an image display device is also included in the embodiment of the present invention.
- the image display device includes a display cell and the polarizing plate according to items A and B arranged on at least one side of the display cell. Examples of the image display device include a liquid crystal display device and an organic electroluminescence (EL) display device. Since the configuration of the image display device is well known in the industry, detailed description thereof will be omitted.
- the polarizing plates obtained in Examples and Comparative Examples were placed on a horizontal surface in a small dark room.
- a special lighting device for inspection (“S-Light” manufactured by Nippon Gijutsu Center Co., Ltd.) was used as a light source, and the light from the light source was applied to the polarizing plate at an angle of 45 °.
- the polarizing plate was set so that the absorption axis direction of the polarizing plate and the irradiation direction of the light source were perpendicular to each other.
- the polarizing plate was laminated on a light-shielding black acrylic plate via an acrylic adhesive (thickness 20 ⁇ m).
- a polarizing plate having a protective layer on one side has a polarizing element surface in contact with an adhesive
- a polarizing plate having a protective layer on both sides has an inner protective layer surface in contact with an adhesive. Since the reflected image contrast index of the black acrylic plate is sufficiently smaller than that of the polarizing plate, it does not affect the measurement result.
- the reflected image projected on the screen installed on the wall surface of the dark room was captured by a camera, and the image of the reflected image was captured as digital data. Image processing was performed on a region of 100 mm ⁇ 100 mm of the captured image to obtain the brightness variation as the standard deviation, and this was used as the reflected image contrast index.
- the brightness of the pixels of the image was quantified in gradations of 0 to 255, the standard deviation was obtained, and this was used as the reflected image contrast index.
- the polarizing plates obtained in Examples and Comparative Examples were placed in a measuring device (Verifire interferometer system manufactured by ZYGO) and measured. A HeNe laser having a wavelength of 632.8 nm was used as a light source, and the spot diameter of the incident light was set to 1 mm. Using the application of spherical transmitted wave surface measurement, the transmitted wave surface aberration calculated from the interference light was obtained.
- Example 1 Fabrication of Polarizer
- a thermoplastic resin base material an amorphous isophthal copolymer polyethylene terephthalate film (thickness: 100 ⁇ m) having a Tg of about 75 ° C. was used, and one side of the resin base material was treated with corona. Was given. 100 parts by weight of PVA-based resin in which polyvinyl alcohol (degree of polymerization 4200, degree of saponification 99.2 mol%) and acetoacetyl-modified PVA (manufactured by Nippon Synthetic Chemical Industry Co., Ltd., trade name "Gosefimmer”) are mixed at a ratio of 9: 1.
- a PVA aqueous solution (coating solution) was prepared by dissolving 13 parts by weight of potassium iodide in water.
- the PVA aqueous solution was applied to the corona-treated surface of the resin base material and dried at 60 ° C. to form a PVA-based resin layer having a thickness of 13 ⁇ m to prepare a laminate.
- the obtained laminate was uniaxially stretched 2.4 times in the longitudinal direction (longitudinal direction) in an oven at 130 ° C. (aerial auxiliary stretching treatment). Next, the laminate was immersed in an insolubilizing bath at a liquid temperature of 40 ° C.
- the laminate was immersed in a washing bath at a liquid temperature of 20 ° C. (an aqueous solution obtained by blending 4 parts by weight of potassium iodide with 100 parts by weight of water) (cleaning treatment). Then, while drying in an oven kept at about 90 ° C., it was brought into contact with a heating roll made of SUS whose surface temperature was kept at about 75 ° C. (dry shrinkage treatment). In this way, a polarizer having a thickness of about 5 ⁇ m was formed on the resin substrate.
- Polarizing Plate A polycarbonate-based resin film (40 ⁇ m) was bonded to the surface of the polarizer obtained above (the surface opposite to the resin base material) as a protective layer via an ultraviolet curable adhesive. Specifically, the curable adhesive was coated so as to have a total thickness of about 1.0 ⁇ m, and bonded using a roll machine. Then, UV light was irradiated from the cycloolefin film side to cure the adhesive. Next, the resin base material was peeled off to obtain a polarizing plate having a polycarbonate-based resin film (protective layer) / polarizing element. The obtained polarizing plate was used for the evaluation of (1) and (2) above. The results are shown in Table 1.
- the polycarbonate resin film was produced as follows. To 81.98 parts by mass of isosorbide (hereinafter sometimes abbreviated as "ISB”), 47.19 parts by mass of tricyclodecanedimethanol (hereinafter sometimes abbreviated as “TCDDM”) and diphenyl carbonate (hereinafter “" 175.1 parts by mass (sometimes abbreviated as “DPC”) and 0.979 parts by mass of a 0.2% by mass aqueous solution of cesium carbonate as a catalyst were put into the reaction vessel, and the first stage of the reaction was carried out under a nitrogen atmosphere. As the step of, the heating tank temperature was heated to 150 ° C., and the raw materials were dissolved while stirring as necessary (about 15 minutes).
- ISB isosorbide
- TCDDM tricyclodecanedimethanol
- DPC diphenyl carbonate
- 0.979 parts by mass of a 0.2% by mass aqueous solution of cesium carbonate as a catalyst were put into the reaction vessel, and the
- the pressure was changed from normal pressure to 13.3 kPa, and the generated phenol was extracted from the reaction vessel while raising the heating tank temperature to 190 ° C. in 1 hour.
- the pressure inside the reaction vessel is set to 6.67 kPa, the heating tank temperature is raised to 230 ° C. in 15 minutes, and the generated phenol is generated. It was taken out of the reaction vessel. Since the stirring torque of the stirrer increased, the temperature was raised to 250 ° C. in 8 minutes, and the pressure in the reaction vessel was brought to 0.200 kPa or less in order to remove the generated phenol.
- Example 2 The temperature of the boric acid aqueous solution in the underwater stretching treatment was set to 66 ° C., the immersion time in the boric acid aqueous solution was set to 60 seconds, and a cycloolefin film (manufactured by Nippon Zeon Corporation, 17 ⁇ m) was used as the protective layer.
- a polarizing plate was produced in the same manner as in Example 1 except for the above. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.
- Example 3 Except that the temperature of the boric acid aqueous solution in the underwater stretching treatment was 64 ° C., the immersion time in the boric acid aqueous solution was 50 seconds, and an acrylic resin film (thickness 40 ⁇ m) was used as the protective layer.
- a polarizing plate was produced in the same manner as in Example 1. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.
- the obtained imidized MS resin had a glutarimide unit, a (meth) acrylic acid ester unit, and a styrene unit, and had an acid value of 0.5 mmol / g.
- the obtained imidized MS resin was formed into a film by melt extrusion molding. At that time, 0.66 parts by weight of the ultraviolet absorber was supplied to 100 parts by weight of the resin.
- Example 4 A polarizer having a thickness of about 5 ⁇ m was formed on the resin substrate in the same manner as in Example 2.
- a cycloolefin-based film manufactured by Zeon Corporation, 17 ⁇ m was bonded to the surface of the obtained polarizer (the surface opposite to the resin substrate) as a protective layer via an ultraviolet curable adhesive.
- the curable adhesive was coated so as to have a total thickness of about 1.0 ⁇ m, and bonded using a roll machine. Then, UV light was irradiated from the cycloolefin film side to cure the adhesive.
- Example 2 the same polycarbonate-based resin film as in Example 1 was attached to the exposed surface of the polarizer by peeling off the resin base material in the same manner as described above. In this way, a polarizing plate having a cycloolefin-based film (inner protective layer) / polarizer / polycarbonate-based resin film (outer protective layer) was obtained. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1. The cycloolefin-based film was produced as follows.
- Example 5 Acrylic in the same manner as in Example 4 except that the same acrylic resin film as in Example 3 was used as the inner protective layer and the same cycloolefin-based film as in Example 4 was used as the outer protective layer.
- Example 1 A polarizing plate was produced in the same manner as in Example 2 except that the temperature of the boric acid aqueous solution in the underwater stretching treatment was 70 ° C. and the immersion time was 50 seconds. The obtained polarizing plate was subjected to the same evaluation as in Example 1. The results are shown in Table 1.
- Example 2 A polarizer having a thickness of about 5 ⁇ m was formed on the resin substrate in the same manner as in Example 1 except that the temperature of the boric acid aqueous solution in the underwater stretching treatment was 70 ° C. and the immersion time was 50 seconds.
- a cycloolefin-based film (manufactured by Zeon Corporation, 17 ⁇ m) was bonded to the surface of the obtained polarizer (the surface opposite to the resin substrate) as a protective layer via an ultraviolet curable adhesive. Specifically, the curable adhesive was coated so as to have a total thickness of about 1.0 ⁇ m, and bonded using a roll machine. Then, UV light was irradiated from the cycloolefin film side to cure the adhesive.
- the polarizing plate of the embodiment of the present invention has a small reflected image contrast index, and as a result, a small transmitted wave surface aberration. Therefore, it is understood that the polarizing plate of the embodiment of the present invention can realize an excellent photographing function and face recognition function without providing a through hole or a transparent portion when applied to an image display device having a camera portion. Will be done.
- Such a polarizing plate can be realized by lowering the temperature of the boric acid aqueous solution and lengthening the immersion time in the underwater stretching treatment in the production of the polarizer.
- the polarizing plate according to the embodiment of the present invention is suitably used for an image display device (for example, a liquid crystal display device, an organic EL display device, a quantum dot display device).
- an image display device for example, a liquid crystal display device, an organic EL display device, a quantum dot display device.
- Polarizer 10 Polarizer 20 First protective layer 30 Second protective layer 100 Polarizing plate
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Abstract
Description
1つの実施形態においては、上記偏光子の厚みは12μm以下である。
1つの実施形態においては、上記反射像コントラスト指標は13以下である。
1つの実施形態においては、上記偏光板は、上記偏光子の一方の側のみに保護層を有する。
本発明の別の局面によれば、画像表示装置が提供される。この画像表示装置は、表示セルと、該表示セルの少なくとも一方の側に配置された上記の偏光板と、を備える。
図1は、本発明の1つの実施形態による偏光板の概略断面図である。偏光板100は、偏光子10と、偏光子10の一方の側(例えば、偏光板を画像表示装置に適用したときに表示セルとは反対側)に配置された第1の保護層(外側保護層)20と、偏光子10の他方の側(例えば、偏光板を画像表示装置に適用したときに表示セル側)に配置された第2の保護層(内側保護層)30とを有する。目的等に応じて、第1の保護層20または第2の保護層30のいずれか一方は省略されてもよい。偏光子10は、二色性物質(代表的には、ヨウ素、二色性染料)を含むポリビニルアルコール(PVA)系樹脂フィルムで構成されている。
偏光子は、上記のとおり、二色性物質(代表的には、ヨウ素、二色性染料)を含むPVA系樹脂フィルムから構成される。二色性物質は、好ましくはヨウ素である。偏光子は、単層の樹脂フィルムから形成されてもよく、二層以上の積層体から形成されてもよい。
第1および第2の保護層は、偏光子の保護層として使用できる任意の適切なフィルムで形成される。当該フィルムの主成分となる材料の具体例としては、トリアセチルセルロース(TAC)等のセルロース系樹脂や、ポリエステル系、ポリビニルアルコール系、ポリカーボネート系、ポリアミド系、ポリイミド系、ポリエーテルスルホン系、ポリスルホン系、ポリスチレン系、ポリノルボルネン系、ポリオレフィン系、(メタ)アクリル系、アセテート系等の透明樹脂等が挙げられる。また、(メタ)アクリル系、ウレタン系、(メタ)アクリルウレタン系、エポキシ系、シリコーン系等の熱硬化型樹脂または紫外線硬化型樹脂等も挙げられる。この他にも、例えば、シロキサン系ポリマー等のガラス質系ポリマーも挙げられる。また、特開2001-343529号公報(WO01/37007)に記載のポリマーフィルムも使用できる。このフィルムの材料としては、例えば、側鎖に置換または非置換のイミド基を有する熱可塑性樹脂と、側鎖に置換または非置換のフェニル基ならびにニトリル基を有する熱可塑性樹脂を含有する樹脂組成物が使用でき、例えば、イソブテンとN-メチルマレイミドからなる交互共重合体と、アクリロニトリル・スチレン共重合体とを有する樹脂組成物が挙げられる。当該ポリマーフィルムは、例えば、上記樹脂組成物の押出成形物であり得る。
偏光子は、例えば、長尺状の熱可塑性樹脂基材の片側に、ハロゲン化物とポリビニルアルコール系樹脂(PVA系樹脂)とを含むポリビニルアルコール系樹脂層(PVA系樹脂層)を形成して積層体とすること、および、積層体に、空中補助延伸処理と、染色処理と、水中延伸処理と、長手方向に搬送しながら加熱することにより幅方向に2%以上収縮させる乾燥収縮処理と、をこの順に施すことを含む方法により作製され得る。PVA系樹脂層におけるハロゲン化物の含有量は、好ましくは、PVA系樹脂100重量部に対して5重量部~20重量部である。乾燥収縮処理は、加熱ロールを用いて処理することが好ましく、加熱ロールの温度は、好ましくは、60℃~120℃である。乾燥収縮処理による積層体の幅方向の収縮率は、好ましくは、2%以上である。このような製造方法によれば、上記B項で説明した偏光子を得ることができる。特に、ハロゲン化物を含むPVA系樹脂層を含む積層体を作製し、上記積層体の延伸を空中補助延伸及び水中延伸を含む多段階延伸とし、延伸後の積層体を加熱ロールで加熱することにより、優れた光学特性(代表的には、単体透過率および偏光度)を有するとともに、光学特性のバラつきが抑制された偏光子を得ることができる。具体的には、乾燥収縮処理工程において加熱ロールを用いることにより、積層体を搬送しながら、積層体全体に亘って均一に収縮することができる。これにより、得られる偏光子の光学特性を高めることができるだけでなく、光学特性に優れる偏光子を安定して生産することができ、偏光子の光学特性(特に、単体透過率)のバラつきを抑制することができる。
熱可塑性樹脂基材とPVA系樹脂層との積層体を作製する方法としては、任意の適切な方法が採用され得る。好ましくは、熱可塑性樹脂基材の表面に、ハロゲン化物とPVA系樹脂とを含む塗布液を塗布し、乾燥することにより、熱可塑性樹脂基材上にPVA系樹脂層を形成する。上記のとおり、PVA系樹脂層におけるハロゲン化物の含有量は、好ましくは、PVA系樹脂100重量部に対して5重量部~20重量部である。
熱可塑性樹脂基材としては、任意の適切な熱可塑性樹脂フィルムが採用され得る。熱可塑性樹脂基材の詳細については、例えば特開2012-73580号公報に記載されている。当該公報は、その全体の記載が本明細書に参考として援用される。
塗布液は、上記のとおり、ハロゲン化物とPVA系樹脂とを含む。上記塗布液は、代表的には、上記ハロゲン化物および上記PVA系樹脂を溶媒に溶解させた溶液である。溶媒としては、例えば、水、ジメチルスルホキシド、ジメチルホルムアミド、ジメチルアセトアミド、N-メチルピロリドン、各種グリコール類、トリメチロールプロパン等の多価アルコール類、エチレンジアミン、ジエチレントリアミン等のアミン類が挙げられる。これらは単独で、または、二種以上組み合わせて用いることができる。これらの中でも、好ましくは、水である。溶液のPVA系樹脂濃度は、溶媒100重量部に対して、好ましくは3重量部~20重量部である。このような樹脂濃度であれば、熱可塑性樹脂基材に密着した均一な塗布膜を形成することができる。塗布液におけるハロゲン化物の含有量は、好ましくは、PVA系樹脂100重量部に対して5重量部~20重量部である。
特に、高い光学特性を得るためには、乾式延伸(補助延伸)とホウ酸水中延伸を組み合わせる、2段延伸の方法が選択される。2段延伸のように、補助延伸を導入することにより、熱可塑性樹脂基材の結晶化を抑制しながら延伸することができ、後のホウ酸水中延伸において熱可塑性樹脂基材の過度の結晶化により延伸性が低下するという問題を解決し、積層体をより高倍率に延伸することができる。さらには、熱可塑性樹脂基材上にPVA系樹脂を塗布する場合、熱可塑性樹脂基材のガラス転移温度の影響を抑制するために、通常の金属ドラム上にPVA系樹脂を塗布する場合と比べて塗布温度を低くする必要があり、その結果、PVA系樹脂の結晶化が相対的に低くなり、十分な光学特性が得られない、という問題が生じ得る。これに対して、補助延伸を導入することにより、熱可塑性樹脂上にPVA系樹脂を塗布する場合でも、PVA系樹脂の結晶性を高めることが可能となり、高い光学特性を達成することが可能となる。また、同時にPVA系樹脂の配向性を事前に高めることで、後の染色工程や延伸工程で水に浸漬された時に、PVA系樹脂の配向性の低下や溶解などの問題を防止することができ、高い光学特性を達成することが可能になる。
結晶化指数=(IC/IR)
ただし、
IC :測定光を入射して測定したときの1141cm-1の強度
IR :測定光を入射して測定したときの1440cm-1の強度
である。
必要に応じて、空中補助延伸処理の後、水中延伸処理や染色処理の前に、不溶化処理を施す。上記不溶化処理は、代表的には、ホウ酸水溶液にPVA系樹脂層を浸漬することにより行う。上記染色処理は、代表的には、PVA系樹脂層を二色性物質(代表的には、ヨウ素)で染色することにより行う。必要に応じて、染色処理の後、水中延伸処理の前に、架橋処理を施す。上記架橋処理は、代表的には、ホウ酸水溶液にPVA系樹脂層を浸漬させることにより行う。不溶化処理、染色処理および架橋処理の詳細については、例えば特開2012-73580号公報(上記)に記載されている。
水中延伸処理は、積層体を延伸浴に浸漬させて行う。水中延伸処理によれば、上記熱可塑性樹脂基材やPVA系樹脂層のガラス転移温度(代表的には、80℃程度)よりも低い温度で延伸し得、PVA系樹脂層を、その結晶化を抑えながら、高倍率に延伸することができる。その結果、優れた光学特性を有する偏光子を製造することができる。
上記乾燥収縮処理は、ゾーン全体を加熱して行うゾーン加熱により行ってもよいし、搬送ロールを加熱する(いわゆる加熱ロールを用いる)ことにより行う(加熱ロール乾燥方式)こともできる。好ましくは、その両方を用いる。加熱ロールを用いて乾燥させることにより、効率的に積層体の加熱カールを抑制して、外観に優れた偏光子を製造することができる。具体的には、加熱ロールに積層体を沿わせた状態で乾燥することにより、上記熱可塑性樹脂基材の結晶化を効率的に促進させて結晶化度を増加させることができ、比較的低い乾燥温度であっても、熱可塑性樹脂基材の結晶化度を良好に増加させることができる。その結果、熱可塑性樹脂基材は、その剛性が増加して、乾燥によるPVA系樹脂層の収縮に耐え得る状態となり、カールが抑制される。また、加熱ロールを用いることにより、積層体を平らな状態に維持しながら乾燥できるので、カールだけでなくシワの発生も抑制することができる。この時、積層体は、乾燥収縮処理により幅方向に収縮させることにより、光学特性を向上させることができる。PVAおよびPVA/ヨウ素錯体の配向性を効果的に高めることができるからである。乾燥収縮処理による積層体の幅方向の収縮率は、好ましくは1%~10%であり、より好ましくは2%~8%であり、特に好ましくは4%~6%である。加熱ロールを用いることにより、積層体を搬送しながら連続的に幅方向に収縮させることができ、高い生産性を実現することができる。
好ましくは、水中延伸処理の後、乾燥収縮処理の前に、洗浄処理を施す。上記洗浄処理は、代表的には、ヨウ化カリウム水溶液にPVA系樹脂層を浸漬させることにより行う。
上記A項およびB項に記載の偏光板は、画像表示装置に適用され得る。したがって、このような画像表示装置も、本発明の実施形態に包含される。画像表示装置は、表示セルと、表示セルの少なくとも一方の側に配置された上記A項およびB項に記載の偏光板と、を備える。画像表示装置としては、例えば、液晶表示装置、有機エレクトロルミネセンス(EL)表示装置が挙げられる。画像表示装置の構成は業界で周知であるので、詳細な説明は省略する。
実施例および比較例で得られた偏光板を、小型暗室内の水平面に載置した。光源として検査用特殊照明装置(日本技術センター社製、「S-Light」)を用い、当該光源からの光を角度45°で偏光板に照射した。その際、偏光板の吸収軸方向と光源の照射方向は垂直になるように、偏光板をセットした。偏光板は遮光性の黒色アクリル板上にアクリル系粘着剤(厚み20μm)を介して貼り合わせた。片側に保護層を有する偏光板は偏光子面を粘着剤と接するようにし、両側に保護層を有する偏光板は内側保護層面を粘着剤と接するようにした。なお、黒色アクリル板は偏光板に比べて反射像コントラスト指標が十分に小さいので測定結果には影響しない。暗室内の壁面に設置されたスクリーンに投影された反射像をカメラで撮像し、反射像の画像をデジタルデータとして取り込んだ。取り込んだ画像の100mm×100mmの領域について画像処理を施して輝度ばらつきを標準偏差として求め、これを反射像コントラスト指標とした。より詳細には、画像の画素の明るさを0~255の階調で数値化し、その標準偏差を求め、これを反射像コントラスト指標とした。
(2)透過波面収差
実施例および比較例で得られた偏光板を、測定装置(ZYGO社製、Verifire干渉計システム)へ配置し測定した。光源は波長632.8nmのHeNeレーザーを用い、入射光のスポット径を1mmとした。球面透過波面測定のアプリケーションを使用し、干渉光から計算される透過波面収差を得た。
1.偏光子の作製
熱可塑性樹脂基材として、長尺状で、Tg約75℃である、非晶質のイソフタル共重合ポリエチレンテレフタレートフィルム(厚み:100μm)を用い、樹脂基材の片面に、コロナ処理を施した。
ポリビニルアルコール(重合度4200、ケン化度99.2モル%)およびアセトアセチル変性PVA(日本合成化学工業社製、商品名「ゴーセファイマー」)を9:1で混合したPVA系樹脂100重量部に、ヨウ化カリウム13重量部を添加したものを水に溶かし、PVA水溶液(塗布液)を調製した。
樹脂基材のコロナ処理面に、上記PVA水溶液を塗布して60℃で乾燥することにより、厚み13μmのPVA系樹脂層を形成し、積層体を作製した。
得られた積層体を、130℃のオーブン内で縦方向(長手方向)に2.4倍に一軸延伸した(空中補助延伸処理)。
次いで、積層体を、液温40℃の不溶化浴(水100重量部に対して、ホウ酸を4重量部配合して得られたホウ酸水溶液)に30秒間浸漬させた(不溶化処理)。
次いで、液温30℃の染色浴(水100重量部に対して、ヨウ素とヨウ化カリウムを1:7の重量比で配合して得られたヨウ素水溶液)に、最終的に得られる偏光子の単体透過率(Ts)が所望の値となるように濃度を調整しながら60秒間浸漬させた(染色処理)。
次いで、液温40℃の架橋浴(水100重量部に対して、ヨウ化カリウムを3重量部配合し、ホウ酸を5重量部配合して得られたホウ酸水溶液)に30秒間浸漬させた(架橋処理)。
その後、積層体を、液温64℃のホウ酸水溶液(ホウ酸濃度4重量%、ヨウ化カリウム濃度5重量%)に浸漬させながら、周速の異なるロール間で縦方向(長手方向)に総延伸倍率が5.5倍となるように一軸延伸を行った(水中延伸処理)。なお、水中延伸処理における積層体のホウ酸水溶液への浸漬時間は75秒であった。
その後、積層体を液温20℃の洗浄浴(水100重量部に対して、ヨウ化カリウムを4重量部配合して得られた水溶液)に浸漬させた(洗浄処理)。
その後、約90℃に保たれたオーブン中で乾燥しながら、表面温度が約75℃に保たれたSUS製の加熱ロールに接触させた(乾燥収縮処理)。
このようにして、樹脂基材上に厚み約5μmの偏光子を形成した。
上記で得られた偏光子の表面(樹脂基材とは反対側の面)に、保護層として、ポリカーボネート系樹脂フィルム(40μm)を紫外線硬化型接着剤を介して貼り合せた。具体的には、硬化型接着剤の総厚みが約1.0μmになるように塗工し、ロール機を使用して貼り合わせた。その後、UV光線をシクロオレフィン系フィルム側から照射して接着剤を硬化させた。次いで、樹脂基材を剥離して、ポリカーボネート系樹脂フィルム(保護層)/偏光子の構成を有する偏光板を得た。得られた偏光板を上記(1)および(2)の評価に供した。結果を表1に示す。
水中延伸処理におけるホウ酸水溶液の温度を66℃としたこと、ホウ酸水溶液への浸漬時間を60秒としたこと、および、保護層としてシクロオレフィン系フィルム(日本ゼオン社製、17μm)を用いたこと以外は実施例1と同様にして偏光板を作製した。得られた偏光板を実施例1と同様の評価に供した。結果を表1に示す。
水中延伸処理におけるホウ酸水溶液の温度を64℃としたこと、ホウ酸水溶液への浸漬時間を50秒としたこと、および、保護層としてアクリル系樹脂フィルム(厚み40μm)を用いたこと以外は実施例1と同様にして偏光板を作製した。得られた偏光板を実施例1と同様の評価に供した。結果を表1に示す。なお、アクリル系樹脂フィルムは以下のようにして作製した。MS樹脂(メタクリル酸メチル/スチレン(モル比)=80/20の共重合体)をモノメチルアミンでイミド化した(イミド化率:5%)。得られたイミド化MS樹脂は、グルタルイミド単位と(メタ)アクリル酸エステル単位とスチレン単位とを有し、酸価は0.5mmol/gであった。得られたイミド化MS樹脂を溶融押出成形によりフィルム化した。その際、樹脂100重量部に対して紫外線吸収剤0.66重量部を供給した。
実施例2と同様にして樹脂基材上に厚み約5μmの偏光子を形成した。得られた偏光子の表面(樹脂基材とは反対側の面)に、保護層として、シクロオレフィン系フィルム(日本ゼオン社製、17μm)を紫外線硬化型接着剤を介して貼り合せた。具体的には、硬化型接着剤の総厚みが約1.0μmになるように塗工し、ロール機を使用して貼り合わせた。その後、UV光線をシクロオレフィン系フィルム側から照射して接着剤を硬化させた。次いで、樹脂基材を剥離して露出した偏光子表面に実施例1と同様のポリカーボネート系樹脂フィルムを上記と同様にして貼り合せた。このようにして、シクロオレフィン系フィルム(内側保護層)/偏光子/ポリカーボネート系樹脂フィルム(外側保護層)の構成を有する偏光板を得た。得られた偏光板を実施例1と同様の評価に供した。結果を表1に示す。なお、シクロオレフィン系フィルムは以下のようにして作製した。シクロオレフィンポリマー(ノルボルネン系モノマーの開環重合体の水素添加物、商品名「ZEONOR1420R」、日本ゼオン社製、ガラス転移温度:136℃)のペレットを用意し、100.5kPa、100℃で12時間乾燥させた。樹脂重量(100重量部)に対して、下記式で表される色素化合物を1.5重量部添加し、単軸押出機にてダイス温度260℃でTダイ式のフィルム溶融押出成形機を使用して、シクロオレフィン系フィルムを成形した。
内側保護層として実施例3と同様のアクリル系樹脂フィルムを用いたこと、および、外側保護層として実施例4と同様のシクロオレフィン系フィルムを用いたこと以外は実施例4と同様にして、アクリル系樹脂フィルム(内側保護層)/偏光子/シクロオレフィン系フィルム(外側保護層)の構成を有する偏光板を得た。得られた偏光板を実施例1と同様の評価に供した。結果を表1に示す。
水中延伸処理におけるホウ酸水溶液の温度を70℃としたこと、および、ホウ酸水溶液への浸漬時間を60秒としたこと以外は実施例5と同様にして偏光板を作製した。得られた偏光板を実施例1と同様の評価に供した。結果を表1に示す。
水中延伸処理におけるホウ酸水溶液の温度を70℃としたこと、および、浸漬時間を50秒としたこと以外は実施例2と同様にして偏光板を作製した。得られた偏光板を実施例1と同様の評価に供した。結果を表1に示す。
水中延伸処理におけるホウ酸水溶液の温度を70℃としたこと、および、浸漬時間を50秒としたこと以外は実施例1と同様にして樹脂基材上に厚み約5μmの偏光子を形成した。得られた偏光子の表面(樹脂基材とは反対側の面)に、保護層として、シクロオレフィン系フィルム(日本ゼオン社製、17μm)を紫外線硬化型接着剤を介して貼り合せた。具体的には、硬化型接着剤の総厚みが約1.0μmになるように塗工し、ロール機を使用して貼り合わせた。その後、UV光線をシクロオレフィン系フィルム側から照射して接着剤を硬化させた。次いで、樹脂基材を剥離して露出した偏光子表面にアクリル系フィルム(東洋鋼鈑社製、40μm)を上記と同様にして貼り合せた。このようにして、アクリル系フィルム(内側保護層)/偏光子/シクロオレフィン系フィルム(外側保護層)の構成を有する偏光板を得た。得られた偏光板を実施例1と同様の評価に供した。結果を表1に示す。
20 第1の保護層
30 第2の保護層
100 偏光板
Claims (5)
- 二色性物質を含むポリビニルアルコール系樹脂フィルムで構成された偏光子と、該偏光子の少なくとも一方の側に配置された保護層と、を有し、
反射像コントラスト指標が15以下である、
偏光板。 - 前記偏光子の厚みが12μm以下である、請求項1に記載の偏光板。
- 前記反射像コントラスト指標が13以下である、請求項2に記載の偏光板。
- 前記偏光子の一方の側のみに保護層を有する、請求項1から3のいずれかに記載の偏光板。
- 表示セルと、該表示セルの少なくとも一方の側に配置された請求項1から4のいずれかに記載の偏光板と、を備える、画像表示装置。
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