CN115524777A - Phase difference film, polarizing plate, and image display device - Google Patents
Phase difference film, polarizing plate, and image display device Download PDFInfo
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- CN115524777A CN115524777A CN202210732447.2A CN202210732447A CN115524777A CN 115524777 A CN115524777 A CN 115524777A CN 202210732447 A CN202210732447 A CN 202210732447A CN 115524777 A CN115524777 A CN 115524777A
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- KPGXUAIFQMJJFB-UHFFFAOYSA-H tungsten hexachloride Chemical class Cl[W](Cl)(Cl)(Cl)(Cl)Cl KPGXUAIFQMJJFB-UHFFFAOYSA-H 0.000 description 1
- 239000004711 α-olefin Substances 0.000 description 1
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/30—Polarising elements
- G02B5/3083—Birefringent or phase retarding elements
-
- 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
- G02F1/133528—Polarisers
-
- 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
- G02F1/13363—Birefringent elements, e.g. for optical compensation
- G02F1/133634—Birefringent elements, e.g. for optical compensation the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis
-
- 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
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K50/00—Organic light-emitting devices
- H10K50/80—Constructional details
- H10K50/868—Arrangements for polarized light emission
-
- 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
Landscapes
- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- General Physics & Mathematics (AREA)
- Nonlinear Science (AREA)
- Mathematical Physics (AREA)
- Chemical & Material Sciences (AREA)
- Crystallography & Structural Chemistry (AREA)
- Polarising Elements (AREA)
- Devices For Indicating Variable Information By Combining Individual Elements (AREA)
- Liquid Crystal (AREA)
- Shaping By String And By Release Of Stress In Plastics And The Like (AREA)
- Manufacture Of Macromolecular Shaped Articles (AREA)
Abstract
The invention provides a phase difference film which is not easy to generate cracks in a solvent resistance test. The retardation film of the present invention is a stretched film of a cyclic polyolefin resin. The glass transition temperature of the retardation film is preferably 145 ℃ or higher. The interaction radius Ro of the retardation film in the Hansen Solubility Parameter (HSP) space and the distance Ra between the coordinates of HSP of the retardation film in the HSP space and the coordinates of HSP of hexane preferably satisfy 1 < Ra/Ro < 2.
Description
Technical Field
The invention relates to a phase difference film, a polarizing plate and an image display device.
Background
In displays such as liquid crystal display devices, retardation films are used for optical compensation such as contrast enhancement and view angle enlargement, and for shielding (antireflection) of external light reflected by metal electrodes. In a retardation film using a non-liquid crystal polymer, optical anisotropy is imparted by stretching a polymer film in at least one direction. A large number of polymers have positive intrinsic birefringence and the refractive index in the stretching direction increases.
The phase difference film is classified into uniaxial films such as a positive a plate (nx > ny = nz), a negative a plate (nz = nx > ny), a positive C plate (nx = ny < nz), a negative C plate (nx = ny > nz), a positive B plate (nz > nx > ny), a negative B plate (nx > ny > nz), a Z plate (nx > nz > ny) and the like, according to the magnitude relation among the refractive index nx in the slow axis direction in the plane, the refractive index ny in the fast axis direction in the plane, and the refractive index nz in the thickness direction.
If a polymer film is longitudinally stretched (free-end uniaxial stretching), the molecular chains of the polymer are oriented in the longitudinal direction (stretching direction) along with the stretching, and a shrinking action is generated in the width direction and the thickness direction. When a film of a polymer having a positive intrinsic refractive index is longitudinally stretched, the refractive index (nx) in the longitudinal direction is increased, and the refractive index (ny) in the width direction and the refractive index (nz) in the thickness direction are decreased, so that a positive a plate having refractive index anisotropy of nx > ny = nz can be obtained.
If the polymer film is stretched in the longitudinal direction in a state where a heat-shrinkable film is laminated on at least one surface thereof, the amount of shrinkage in the width direction becomes larger due to the influence of the shrinkage force of the heat-shrinkable film than in the case of ordinary free-end uniaxial stretching. Therefore, in the case of a polymer having positive intrinsic birefringence, the refractive index ny in the fast axis direction becomes smaller and the refractive index nz in the thickness direction becomes relatively larger, and therefore, a retardation film having refractive index anisotropy of nx > nz > ny can be obtained (for example, see patent document 1).
A retardation film is generally used by being bonded to a polarizer, and an image display panel can be formed by bonding a polarizing plate in which a polarizer and a retardation film are laminated to an image display unit such as a liquid crystal cell or an organic EL cell. The image display device can be formed by connecting the image display panel to a drive circuit, and housing the image display panel in a case in combination with a cover glass, a backlight, and the like as necessary.
Documents of the prior art
Patent literature
Patent document 1: japanese patent laid-open publication No. 2006-72309
Disclosure of Invention
Problems to be solved by the invention
In assembling an image display device, an adhesive is used when a cover glass is attached to the surface of a polarizing plate, and the end face of the film may be exposed to a solvent contained in the adhesive. In addition, when the image display device is assembled, cleaning may be performed using a solvent. Therefore, the retardation film is required to have solvent resistance.
The cyclic polyolefin is excellent in transparency and heat resistance and also excellent in chemical resistance, and is suitable as an optical film material for displays. However, if a solvent resistance test is performed in a state where a stretched retardation film of a cyclic polyolefin is inserted into an image display panel, when a hydrocarbon-based solvent such as hexane is used, fine cracks may occur at the end faces of the film. Particularly in a stretched film having refractive index anisotropy of nx > nz > ny, the occurrence of cracks in a solvent resistance test is significant.
In view of the above circumstances, an object of the present invention is to provide a stretched retardation film in which edge cracks are less likely to occur even in a solvent resistance test using a hydrocarbon solvent such as hexane.
Means for solving the problems
The retardation film according to one embodiment of the present invention is a stretched film of a cyclic polyolefin resin. The glass transition temperature of the retardation film is preferably 145 ℃ or higher. The rate of change in heated dimension of the retardation film at a temperature of 95 ℃ may be 0.40% or less.
The interaction radius Ro of the retardation film in the Hansen Solubility Parameter (HSP) space and the distance Ra between the coordinates of the retardation film in the HSP space and the coordinates of hexane preferably satisfy 1 < Ra/Ro < 2.
The front retardation of the retardation film may be 200nm or more. The thickness of the retardation film may be 10 to 300 μm. The in-plane birefringence (Δ n = nx-ny) of the retardation film may be 1.0 × 10 -3 The above. The phase difference film may have refractive index anisotropy of nx > nz > ny.
nx is a refractive index in a slow axis direction in the plane of the retardation film, ny is a refractive index in a fast axis direction in the plane of the retardation film, and nz is a refractive index in a thickness direction of the retardation film.
The polarizing plate provided with the retardation film can be obtained by laminating and integrating the retardation film and the polarizer. The polarizing plate can be suitably used for forming an image display device such as a liquid crystal display device or an organic EL display device.
Effects of the invention
The retardation film described above can suppress the occurrence of cracks even when it is heated or brought into contact with a solvent by cleaning or the like in the process of producing an image display device.
Detailed Description
The retardation film of the present invention is a stretched retardation film obtained by stretching a cyclic polyolefin film. The cyclic polyolefin is a polymer comprising an alicyclic structure in a repeating unit of a main chain.
Examples of the cyclic polyolefin resin include: resins described in, for example, japanese patent application laid-open Nos. H1-240517, H3-14882, and H3-122137. Specific examples thereof include: ring-opened (copolymer) polymers of cyclic olefins, addition polymers of cyclic olefins, copolymers of cyclic olefins with α -olefins such as ethylene and propylene (typically random copolymers), graft polymers obtained by modifying these with unsaturated carboxylic acids or their derivatives, and hydrogenated products. Commercially available products of cyclic polyolefin resins include: "ZEONOR" and "ZEONEX" manufactured by Kakuzuki, "ARTON" manufactured by JSR, "APEL" manufactured by Mitsui Chemicals, and "TOPAS" manufactured by TOPAS ADVANCEDPolyMERS.
As described in detail later, the cyclic polyolefin resin constituting the retardation film is preferably such that the distance Ra between the cyclic polyolefin resin and the HSP of hexane is large in the coordinate space of the Hansen Solubility Parameter (HSP).
The cyclic polyolefin film preferably contains 50 wt% or more of the cyclic polyolefin resin. The content of the cyclic polyolefin resin in the cyclic polyolefin film is more preferably 70% by weight or more, still more preferably 80% by weight or more, and may be 90% by weight or more or 95% by weight or more.
As a method for producing the cyclic polyolefin film, a known method such as a solution casting method or a melt extrusion method can be used. The thickness of the film is not particularly limited, but is generally about 5 μm to 300. Mu.m. The film may contain additives such as ultraviolet absorbers, stabilizers, lubricants, plasticizers, and the like.
The polymer film is stretched to improve the molecular orientation in a specific direction, thereby obtaining a retardation film. Examples of the stretching method include: a longitudinal uniaxial stretching method, a transverse uniaxial stretching method, a longitudinal and transverse sequential biaxial stretching method, a longitudinal and transverse simultaneous biaxial stretching method, and the like. As the stretching mechanism, any suitable stretching machine such as a roll stretching machine, a tenter stretching machine, a telescopic or linear motor type biaxial stretching machine, or the like can be used.
When a heat-shrinkable film is stretched in one direction in a state where the film is laminated on at least one surface of a polymer film, the film is shrunk in a direction orthogonal to the stretching direction by the shrinking force of the heat-shrinkable film, and the refractive index in the thickness direction is increased relative to the shrinking direction (fast axis direction), whereby a stretched retardation film having refractive index anisotropy of nx > nz > ny can be obtained. nx is a refractive index in a slow axis direction (stretching direction) in a plane, ny is a refractive index in a fast axis direction in a plane, and nz is a refractive index in a thickness direction.
For example, if a laminate in which a heat-shrinkable film is laminated on one or both sides of a polymer film is subjected to free-end uniaxial stretching, the shrinkage in the direction (width direction) orthogonal to the stretching direction is increased by the action of the heat-shrinkable film, and a stretched retardation film having refractive index anisotropy of nx > nz > ny can be obtained. A simultaneous biaxial stretching machine may be used to stretch the film in the longitudinal direction while controlling the amount of shrinkage in the width direction, with the film held at both ends in the width direction by a jig or the like. Further, by shrinking the heat-shrinkable film in the longitudinal direction by the shrinking force of the heat-shrinkable film while stretching the film in the width direction, a retardation film having a slow axis direction in the width direction and having a refractive index anisotropy of nx > nz > ny can be produced.
The heat-shrinkable film is not particularly limited as long as it is heat-shrunk in a direction orthogonal to the stretching direction when it is stretched while being laminated to the polymer film. The heat shrinkable film may have anisotropy in shrinkage rate. For example, the following heat shrinkable film may be used: when a laminate of a polymer film and a heat-shrinkable film is stretched in the width direction and shrunk in the longitudinal direction during stretching, the amount of shrinkage in the longitudinal direction is greater than the amount of shrinkage in the width direction. As an example, in the production (stretching) of a heat-shrinkable film, clips are moved so as to increase the interval between tenter clips in the longitudinal direction while holding both ends of the film with tenter clips or the like and maintaining the distance between the clips in the width direction, whereby a heat-shrinkable film which is easily shrunk in the longitudinal direction can be obtained.
The material constituting the heat-shrinkable film is not particularly limited, and a material heat-shrinkable at around the stretching temperature of the cyclic polyolefin film is preferable. Since the heat shrinkable film is excellent in versatility and inexpensive, polyolefins such as polyethylene and polypropylene, and polyesters can be preferably used as the material of the heat shrinkable film.
The retardation film may have a front retardation Re of, for example, about 15nm to 400nm, or 100nm or more, or 150nm or more. The NZ coefficient of the phase difference film, which is defined by NZ = (nx-NZ)/(nx-ny), may be about 0 to 3. The NZ coefficient may be 1.5 or less, may be 1.0 or less, may be 0.1 to 0.9, 0.2 to 0.8, or 0.3 to 0.7. The front retardation and the NZ coefficient of the retardation film can be appropriately set according to the application of the retardation film, the optical design of the image display device, and the like. Examples of applications of the retardation film having an NZ coefficient of less than 1 include a circularly polarizing plate used for optical compensation of a liquid crystal display device and for shielding reflected light from an organic EL display device.
For example, in the IPS mode liquid crystal display device, when the liquid crystal display device is viewed from an oblique direction at an angle of 45 degrees (azimuth angles of 45 degrees, 135 degrees, 225 degrees, and 315 degrees) with respect to the absorption axis of the polarizer, light leakage in black display is large, and a decrease in contrast and color shift are likely to occur. By disposing a retardation film having a front retardation of 1/2 of the wavelength λ and an NZ coefficient of 0.5 between the liquid crystal cell and the polarizer, the black luminance in the oblique direction can be reduced, and the contrast can be improved.
In an organic EL display device, a circularly polarizing plate is disposed on the visible side of an organic EL cell in order to prevent light from being reflected by a metal electrode and reflected light from being visually recognized from the outside as a mirror surface. The circularly polarizing plate has a structure in which a λ/4 plate having a front retardation of 1/4 of the wavelength λ is disposed on one surface of a polarizer (surface on the organic EL cell side). Since the retardation film having the refractive index anisotropy of nx > nz > ny has a small change in retardation at a viewing angle, if the retardation film having the refractive index anisotropy of nx > nz > ny is used as the λ/4 plate of the circularly polarizing plate, the light shielding property is improved not only in the front surface (normal direction) of the display device but also in an oblique direction.
The thickness of the retardation film is not particularly limited, but is preferably 5 to 300 μm from the viewpoint of handling properties such as strength and handling properties. In order to increase the front retardation, the thickness of the retardation film is preferably 10 μm or more, more preferably 20 μm or more, and may be 30 μm or more, 40 μm or more, or 50 μm or more. The thickness of the retardation film may be 250 μm or less or 200 μm or less.
The in-plane birefringence [ Delta ] n of the retardation film may be 1.0X 10 -3 As described above. The in-plane birefringence Δ n = nx-ny is a difference between a refractive index nx in the slow axis direction in the plane and a refractive index ny in the fast axis direction in the plane, and is a value obtained by dividing the front retardation Re by the thickness. In the stretched retardation film, Δ n tends to be larger as the stretching magnification is larger, and larger Δ n makes it possible to realize a large front retardation with a smaller thickness. The retardation film may have Δ n of 1.3 × 10 -3 Above, or 1.5X 10 -3 The above.
The glass transition temperature (Tg) of the retardation film is preferably 145 ℃ or higher, and may be 147 ℃ or higher. The higher the Tg of the retardation film, the less the retardation film is likely to change due to heating. The retardation film preferably has a dimensional change rate of 0.40% or less at 95 ℃. The dimensional change rate at 95 ℃ is a measurement value based on thermomechanical analysis (TMA). The higher the Tg, the smaller the dimensional change at 95 ℃.
In the manufacturing process of an image display device, after a polarizing plate is bonded to the surface of an image display cell, heating may be performed for the purpose of adjusting the moisture content of the polarizer. In the lighting test, the temperature of the panel may rise to about 80 to 100 ℃. The higher the Tg of the retardation film, the smaller the dimensional change rate at 95 ℃, the more likely the generation of cracks in the retardation film is suppressed when the solvent resistance test is performed after the image display panel is heated.
From the viewpoint of suppressing the occurrence of cracks in the solvent resistance test, the cyclic polyolefin resin constituting the retardation film preferably has a large distance Ra from the Hansen Solubility Parameter (HSP) in the coordinate space of the HSP.
The Hansen Solubility Parameter (HSP) is the division of the solubility parameter delta of Hildebrand (Hildebrand) into dispersion terms delta d Polar term delta p And hydrogen bonding term delta h These three components are represented in a three-dimensional coordinate space, and δ 2 ＝δ d 2 +δ p 2 +δ h 2 The relationship of (1) holds. Dispersion term delta d Indicating the effect based on the dispersion force, the polarity term δ p Representing the effect based on dipole forces, the hydrogen bond term δ h Indicating the effect based on hydrogen bonding force. Distance Ra of HSP of two substances is determined by difference Delta of dispersion terms between the two substances d The difference of the polarity terms delta p And the difference of hydrogen bond terms Δ δ h Ra = {4 Δ δ d 2 +Δδ p 2 +Δδ h 2 } 1/2 It is shown that the smaller Ra, the higher the compatibility, and the larger Ra, the lower the compatibility.
The solubility of a particular polymer relative to a solvent may be determined by the HSP (δ) of the polymer d ，δ p ，δ h ) And the radius of interaction Ro, and HSP of the solvent. The radius of interaction Ro is also referred to as the "radius of the lytic sphere", and the ratio Ra/Ro of the distance Ra of HSP to the radius of interaction Ro is also referred to as the Relative Energy Difference (RED). In the case of assuming a sphere (dissolving sphere) of radius Ro centered on the coordinates of HSP of the polymer, when the coordinates of HSP of the solvent are inside the dissolving sphere of the polymer (i.e., when Ra/Ro < 1), the polymer is predicted to be soluble in the solvent, and when the coordinates of HSP of the solvent are outside the dissolving sphere of the polymer (i.e., when Ra/Ro > 1), the polymer is predicted to be insoluble in the solvent. Coordinates of HSP of solvent at the surface of the dissolution sphere of the polymer (i.e., ra/Ro = 1), the polymer is predicted to be partially soluble in the solvent.
Details of Hansen Solubility Parameters are described in Charles m. Hansen, hansen Solubility Parameters: a Users Handbook (CRC Press, 2007). HSPs of various organic solvents are known. HSP and Ra of the polymer can be calculated based on the results of Solubility tests for solvents by the Sphere program of computer software Hansen Solubility Parameters In Practice (HSPiP).
HSP and Ro of cyclic polyolefin were calculated as follows: a dissolution test was performed using toluene, hexane, methanol, trichlorobenzene, and γ -butyrolactone, and a mixed solvent of toluene and hexane, a mixed solvent of toluene and methanol, a mixed solvent of toluene and trichlorobenzene, and a mixed solvent of toluene and γ -butyrolactone as solvents, and the case of dissolution was assumed to be "1", and the case of non-dissolution was assumed to be "0", and the results were calculated by inputting the results in the above-described program. When the retardation film contains a plurality of polymers, a dissolution test may be performed on the retardation film, and HSP and Ro may be calculated by the above-described procedure.
The interaction radius Ro of the retardation film (cyclic polyolefin resin) in the HSP space and the distance Ra between the HSP coordinate of the retardation film and the HSP coordinate of hexane in the HSP space preferably satisfy 1 < Ra/Ro. Furthermore, hexane HSP is well known, (delta.) d ，δ p ，δ h ) = (14.9,0,0). Therefore, by obtaining HSP of the retardation film (cyclic polyolefin resin), the distance Ra = {4 Δ δ = between coordinates in HSP space can be calculated d 2 +Δδ p 2 +Δδ h 2 } 1/2 。
As described above, in addition to the high glass transition temperature of the retardation film, the Ra/Ro is made larger than 1 (that is, coordinates of HSP of hexane are outside the dissolved spheres of the polymer), and thus the generation of cracks at the end portions of the retardation film in the solvent resistance test tends to be suppressed. Ra/Ro is preferably 1.03 or more, and may be 1.05 or more or 1.07 or more. In the cyclic polyolefin resin, ra/Ro is generally less than 2, and Ra/Ro may be 1.8 or less, 1.6 or less, or 1.5 or less.
The generation of cracks at the end portions of the retardation film in the solvent resistance test is considered to be influenced by the strain of the stretched retardation film and the local dissolution of the organic solvent. In a stretched retardation film, polymer chains are oriented in the stretching direction, and generally, cracks tend to occur along the stretching direction. In particular, since cyclic polyolefins have low intrinsic birefringence, it is necessary to increase the stretching ratio in order to obtain a retardation film having large in-plane birefringence Δ n and large front retardation. In addition, since a stretched film having refractive index anisotropy of nx > nz > ny is stretched in a stretching direction (slow axis direction) and is highly shrunk in a direction (fast axis direction) orthogonal to the stretching direction, the degree of orientation of polymer chains in the stretching direction is high, and cracks are likely to occur.
In an image display panel, a retardation film is bonded and fixed to other members such as a polarizing plate (polarizer) and an image display unit. When a heating and lighting test for adjusting the moisture content of the polarizer is performed in this state, the temperature of the image display panel rises to about 80 to 100 ℃. In contrast to the image display unit which undergoes very little dimensional change when heated to about 100 ℃, a resin material such as a retardation film expands when heated.
In a state where the retardation film is bonded to an image display unit or the like, a force of expansion of the film due to heating is accumulated in the film as a stress. It is considered that if the end face of the film comes into contact with the solvent in a state where a large stress is accumulated, the stress is locally relaxed at the solvent contact portion, but the stress is rather concentrated at the periphery thereof, which causes the generation of cracks. It is considered that a film having a low glass transition temperature and a large change in heated dimension has a large stress accumulated therein in a state of being bonded to an image display unit or the like, and therefore cracks are likely to occur due to contact with a solvent. In particular, in the case of a stretched retardation film having refractive index anisotropy of nx > nz > ny, a film having a high molecular chain orientation tends to be cracked due to a high molecular orientation, and the stress generated by heating is also large, which is a factor of the tendency to generate cracks.
In the present invention, since the glass transition temperature of the film is high, dimensional change during heating is small, and stress accumulated in the film in the image display device is reduced. Further, it is considered that since Ra/Ro is larger than 1 and solubility in hexane is low, local stress relaxation due to contact with a solvent and stress concentration on the periphery thereof are less likely to occur, and even when the molecular chains are highly oriented like a stretched film exhibiting refractive index anisotropy of nx > nz > ny, the occurrence of cracks can be suppressed.
The retardation film of the present invention may be laminated and integrated with a polarizer to form a polarizing plate. The polarizing plate can be obtained by bonding a retardation film to one main surface of the polarizer via an appropriate adhesive layer or pressure-sensitive adhesive layer. Other films may be laminated between the polarizer and the phase difference film.
Examples of the polarizer include films obtained by uniaxially stretching hydrophilic polymer films such as polyvinyl alcohol films, partially formalized polyvinyl alcohol films, and ethylene-vinyl acetate copolymer partially saponified films, and polyene-based oriented films such as polyvinyl alcohol dehydrated products and polyvinyl chloride desalted products.
Among them, a polyvinyl alcohol (PVA) polarizer in which a dichroic material such as iodine or a dichroic dye is adsorbed to a polyvinyl alcohol film such as polyvinyl alcohol or partially formalized polyvinyl alcohol and oriented in a predetermined direction is preferable because of its high degree of polarization. For example, a PVA-based polarizer can be obtained by subjecting a polyvinyl alcohol-based film to iodine dyeing and stretching.
As the PVA polarizer, a thin polarizer having a thickness of 10 μm or less may be used. Examples of the thin polarizer include: examples of the polarizing film include thin polarizing films described in Japanese patent laid-open Nos. Sho 51-069644, 2000-338329, WO2010/100917, japanese patent No. 4691205, and Japanese patent No. 4751481. Such a thin polarizer can be obtained, for example, by stretching a PVA-based resin layer and a stretching resin base material in a state of being laminated and then dyeing with iodine.
The arrangement angle of the polarizer and the retardation film is not particularly limited. For example, when the retardation film is used for the purpose of optical compensation to suppress light leakage when the liquid crystal display device is viewed from an oblique direction, it is preferable that the absorption axis direction of the polarizer and the slow axis direction of the retardation film are arranged in parallel or orthogonal to each other. When the circularly polarizing plate is formed by laminating the polarizer and the retardation film, it is preferable that the polarizer and the retardation film are arranged so that an angle formed by the absorption axis direction of the polarizer and the slow axis direction of the retardation film is 45 °. The arrangement angle does not need to be strictly in the above range, and may include an error of about ± 2 °.
A transparent film as a polarizer protective film may be bonded to the other surface of the polarizer via an appropriate adhesive layer or pressure-sensitive adhesive layer. An optical film other than the retardation film and the polarizer protective film described above may be laminated on the polarizer. An adhesive layer or an adhesive layer for bonding to an image display unit or the like may be laminated on the polarizing plate.
The retardation film and the polarizing plate can be used as an optical film for an image display device. For example, an image display panel can be obtained by bonding a polarizing plate provided with a phase difference film to the surface of an image display unit via an appropriate adhesive. When the image display unit is a liquid crystal unit, a backlight as a light source is further combined, whereby a liquid crystal display device can be formed.
After a polarizing plate is bonded to the surface of the image display unit, heating may be performed for the purpose of adjusting the moisture content of the polarizer. In the lighting test, the panel was heated to a high temperature of about 80 to 100 ℃. In the present invention, since the glass transition temperature of the retardation film is high, even when the temperature is increased by heating, a lighting test, or the like, the stress accumulated in the inside or the interface of the retardation film is small. Further, since the solubility of the resin material constituting the retardation film in a hydrocarbon solvent such as hexane is low (Ra/Ro is large), the occurrence of cracks at the end face of the retardation film is suppressed even when the end face of the retardation film is brought into contact with an organic solvent after heating.
Examples
The present invention will be described in more detail below by way of examples and comparative examples, but the present invention is not limited to these examples.
[ Synthesis example 1]
Into a reaction vessel purged with nitrogen gas were charged dicyclopentadiene: 21 parts by weight of 8-methyl-8-carboxymethyltetracyclo [4.4.0.1 2，5 .1 7，10 ]-3-dodecene: 78 parts by weight, and 2-norbornene: 1 part by weight of 1-hexene as a molecular weight modifier: 14.7 parts by weight, and toluene as a solvent: 150 parts by weight, heated to 107 ℃. In thatTo this solution were added a toluene solution of ethylaluminum (0.6 mol/l) and 0.4 part by weight and a toluene solution of methanol-modified tungsten hexachloride (0.025 mol/l) and 1.8 parts by weight, and reacted at 107 ℃ for 1 hour to obtain a ring-opened polymer. To 360 parts by weight of the solution of the ring-opened polymer thus obtained was added Ru 4-CH as a hydrogenation catalyst 3 (CH 2 ) 4 C 6 H 4 CO 2 ]H(CO)[P(C 6 H 5 ) 3 ]:0.04 part by weight, 9 to 10MPa in hydrogen pressure, and reacted at 160 to 165 ℃ for 3 hours. After completion of the reaction, the obtained product (hydride) was precipitated in methanol and vacuum-dried to obtain a cyclic polyolefin resin (weight average molecular weight: 46000, glass transition temperature: 148 ℃ C.). The obtained resin was melt-kneaded using a twin-screw extruder, extruded in a strand-like form, and water-cooled and then fed to a feed extruder (Feeder-Ruder) to obtain pellets.
Comparative example 1
Using pellets of a cyclic polyolefin resin ("ARTON R5000" made by JSR), an unstretched film having a thickness of 135 μm was produced by a melt extrusion method. This film was subjected to free-end uniaxial stretching (longitudinal stretching) at a temperature of 150 ℃ at a magnification of 1.5 times to obtain a stretched retardation film.
[ example 1]
Using the pellets of the cyclic polyolefin resin obtained in Synthesis example 1, an unstretched film having a thickness of 60 μm was produced by a melt extrusion method. This film was longitudinally stretched under the conditions shown in table 1 to obtain a stretched retardation film.
Comparative example 2
Using pellets of a cyclic polyolefin resin ("ARTON R5000" manufactured by JSR), an unstretched film having a thickness of 135 μm was produced by a melt extrusion method. A biaxially stretched propylene film (Torayfan, manufactured by dongli) having heat shrinkability was bonded to each surface of the film via an adhesive to obtain a laminate. The laminate was longitudinally stretched at a temperature of 150 ℃ at a magnification of 1.3 times, and then the heat shrinkable films laminated on both sides were peeled off and removed to obtain a stretched retardation film (hereinafter, this stretching method is referred to as "Z stretching").
Comparative examples 3 and 4 and example 2
Unstretched films were produced by changing the kind of cyclic polyolefin resin and the film thickness as shown in table 1, and were Z-stretched under the conditions shown in table 1. Except for this, a stretched retardation film was obtained in the same manner as in comparative example 2.
Comparative example 5
A commercially available product of a cyclic polyolefin film ("ZEONOR film ZF16" manufactured by japanese swiss) was Z-stretched under the conditions shown in table 1 to obtain a stretched retardation film.
Comparative example 6
A commercially available product of a cyclic polyolefin film ("ZEONOR film ZF14" manufactured by japanese swiss) was Z-stretched under the conditions shown in table 1 to obtain a stretched retardation film.
[ example 3]
Resin pellets of a Cyclic Olefin Polymer (COP) (ARTON R5000, manufactured by JSR) were dissolved in methylene chloride, an unstretched film having a thickness of 100 μm was produced by a solution film forming method, and Z-stretching was performed under the conditions shown in table 1 to obtain a stretched retardation film.
[ evaluation ]
< phase Difference characteristics >
The retardation film was cut out to have a size of 50mm × 50mm, and the front retardation and the retardation in a state where the sample was tilted by 40 ° with the slow axis direction as the rotation center were measured at a measurement wavelength of 550nm by a polarization-phase difference measurement system ("AxoScan" manufactured by Axometrics). From these measurements, the frontal retardation at a wavelength of 550nm was calculated: re = (nx-ny) × d and NZ coefficient: NZ = (nx-NZ)/(nx-ny). nx is a refractive index in a slow axis direction in a plane, ny is a refractive index in a fast axis direction in a plane, nz is a refractive index in a thickness direction, and d is a thickness. In calculating the NZ coefficient, the average refractive index of the film measured by an abbe refractometer manufactured by ATAGO corporation was used.
< Hansen Solubility Parameter (HSP) >
About 10g of the resin pellets (film pieces in comparative examples 5 and 6) were dissolved in 50mL of a solvent in an environment of 25 ℃ and whether or not the resin pellets were dissolved was visually checked. As the solvent used in the dissolution test, toluene, hexane, methanol, trichlorobenzene, γ -butyrolactone, a mixed solvent of toluene and hexane, a mixed solvent of toluene and methanol, a mixed solvent of toluene and trichlorobenzene, and a mixed solvent of toluene and γ -butyrolactone were used. Mixing the solvent in a ratio of 10: 90-90: the mixing ratio was changed to five or more levels in the range of 10, and a dissolution test was performed for each mixed solvent.
The resin pellets (polymer) were subjected to a fusion procedure using a fusion protocol of "1" and an insolubilization protocol of "0" and then subjected to a fusion procedure using computer software, hansen Solubility Parameters In Practice (HSPiP), to calculate the Hansen Solubility Parameter (HSP). Delta., (HSP) delta.) (the polymer) d 、δ p And delta h And the radius Ro of the dissolving sphere.
In addition, HSP by polymer and HSP by hexane (. Delta.) ( d ，δ p ，δ h ) = {4 Δ δ) = (14.9,0,0) calculation of HSP distance Ra of polymer to hexane d 2 +Δδ p 2 +Δδ h 2 } 1/2 The ratio Ra/Ro of the HSP distance Ra to the radius Ro of the lysosphere was determined.
< glass transition temperature >
Differential thermal analysis of the stretched retardation film was carried out by a differential scanning calorimetry analyzer ("DSC 6200", manufactured by SII) under the following conditions, and the inflection point of the obtained DSC curve was set to the glass transition temperature.
Sample amount: 7-9 mg
Reference is made to: aluminum pot
Introducing gas: nitrogen is present in
Temperature range: room temperature to 230 DEG C
Temperature rise rate: 10 ℃/min
< Heat dimensional Change Rate >
The stretched retardation film was cut into a long strip of 16mm × 4mm in the longitudinal direction of the stretched retardation film, and subjected to thermomechanical analysis using a thermomechanical analyzer (TMA 7100 manufactured by High-Tech Science) under the following conditions, and the obtained TMA curve was based on the room temperatureLength L of the sample 0 And the sample length L at 95 ℃ were calculated to calculate the 95 ℃ dimensional change ratio (%) =100 × (L-L) 0 )/L 0 。
Introducing gas: nitrogen is present in
Loading: 0.0196N
Temperature range: room temperature to 100 DEG C
Temperature rise rate: 10 ℃/min
< solvent resistance test >
The retardation film was cut into a size of 50mm × 50mm, and attached to a glass plate with an adhesive. The sample was heated at 95 ℃ for 3 hours, naturally cooled at room temperature for 20 minutes, and then hexane was added dropwise to the ends (all four sides) of the film, and visually confirmed. The case where cracks were generated at the ends of the film was NG, and the case where no cracks were observed was OK.
The production conditions and evaluation results of the stretched retardation films of examples and comparative examples are shown in table 1.
The uniaxially stretched retardation film of example 1 using the cyclic polyolefin having Ra/Ro of more than 1 had no crack even after the solvent resistance test using hexane. The same applies to example 2 in which Z-stretching was performed, and to example 3 in which a cyclic polyolefin different from that in examples 1 and 2 was used.
The Z-stretched films of comparative examples 5 and 6 having Ra/Ro of less than 1 were cracked after the solvent resistance test. In comparative examples 1 to 4, the Ra/Ro was greater than 1, and the solubility in hexane was low, but cracks were generated after the solvent resistance test. In comparative examples 1 to 4, it is estimated that the case where the glass transition temperature is low and the dimensional change during heating is large is a factor of the occurrence of cracks, as compared with examples 1 and 2.
From the above results, it is found that a retardation film having a high glass transition temperature and a large Ra/Ro is less likely to cause cracks at the end face even when it is brought into contact with an organic solvent such as hexane after heating.
Claims (8)
1. A retardation film formed from a stretched film of a cyclic polyolefin resin,
wherein the glass transition temperature is 145 ℃ or higher,
the interaction radius Ro of the phase difference film in the Hansen solubility parameter space and the distance Ra between the coordinates of the phase difference film in the Hansen solubility parameter space and the coordinates of the hexane in the Hansen solubility parameter space satisfy 1 & lt Ra/Ro & lt 2.
2. The retardation film of claim 1, wherein the front retardation is 200nm or more.
3. The retardation film according to claim 1 or 2, which has a thickness of 10 to 300 μm.
4. The retardation film according to claim 1 or 2, wherein an in-plane birefringence Δ n as a difference between a refractive index nx in an in-plane slow axis direction and a refractive index ny in an in-plane fast axis direction is 1.0 x 10 -3 The above.
5. The retardation film according to claim 1 or 2, wherein a refractive index nx in a slow axis direction in a plane, a refractive index ny in a fast axis direction in a plane, and a refractive index nz in a thickness direction satisfy nx > nz > ny.
6. The retardation film according to claim 1 or 2, which has a dimensional change rate by heating at a temperature of 95 ℃ of 0.40% or less.
7. A polarizing plate comprising a polarizer and the retardation film according to any one of claims 1 to 6 laminated on one surface of the polarizer.
8. An image display device is provided with: an image display unit, and the polarizing plate according to claim 7.
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