JP2012226078A - Polarizing film, method for producing the same, and display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizing film capable of developing high isotropic scattering property and having high frontal brightness.SOLUTION: The polarizing film comprises a continuous phase formed of a first transparent resin and a planar dispersion phase formed of a second transparent resin in the continuous phase, with plate faces of the dispersion phase oriented substantially parallel to the film plane. On the planar shape of the dispersion phase, a ratio of the major axis to the minor axis is approximately from 1 to 1.5. The average size of the dispersion phase in the planar shape is from 0.2 to 5 μm, and the ratio of the average size to the average thickness may be from 2 to 50. The dispersion phase may have an approximately disk shape. The polarizing film comprises a biaxially oriented film, in which a difference in the refractive index between the continuous phase and the dispersion phase with respect to linearly polarized light may differ between one orientation direction and the other orientation direction.

Description

  The present invention relates to a polarizing film having light diffusibility and polarizing property, a method for producing the polarizing film, and a display device (a surface light source device, a transmission type or a reflection type liquid crystal display device, etc.) provided with the polarizing film.

  In liquid crystal display devices, iodine-based or dye-based absorption polarizing plates are generally used. Therefore, the brightness of the display surface is less than half the brightness of a light source such as outside light or irradiation light. Moreover, since the two absorption polarizing plates are used on the front and back of the liquid crystal panel, the brightness is actually reduced to 30 to 40% of the brightness of the light source. Therefore, in order to obtain higher luminance, an attempt has been made to compensate for the above-mentioned drawbacks by polarization conversion. Examples of the polarization conversion method include a method using a prism such as a polarization beam splitter, and a polarization conversion method using the circular polarization characteristics of cholesteric liquid crystal.

  However, in the method using the prism, the polarization depends on the angle and the wavelength, and the lightness and compactness are lacking. When using cholesteric liquid crystal, in order to cover all wavelengths, it is necessary to make the liquid crystal into multiple layers with different helical pitches, making the liquid crystal complicated and expensive. Furthermore, a polarizing sheet in which optical elements are laminated on both sides of a flat element made of a birefringent material such as calcite, a polarizer in which a film composed of a polyester resin, etc., is laminated, and a composite of liquid crystal and polymer is used. Methods are also known, but all of them are complicated and expensive and have not yet become widespread.

  On the other hand, a method has also been proposed in which a scattering sheet in which a dispersed phase having a refractive index different from that of the continuous phase is dispersed in the form of particles in the continuous phase is used as a polarizing element. For example, Japanese Patent Laid-Open No. 9-297204 (Patent Document 1) discloses an anisotropic scattering element in which inorganic scattering particles having an aspect ratio of 1 or more are dispersed and arranged in resins or polymers having different refractive indexes.

  However, in this scattering element, since the scattering is anisotropic, when this scattering element is used as a polarizing element, the front luminance is lowered. Further, in this scattering element, since the dispersed phase is composed of inorganic particles, when the scattering particles are arranged in a certain direction, voids are easily generated between the polymer and the inorganic particles, and cannot be stably manufactured.

  Therefore, a method has also been proposed in which the dispersed phase is made of a polymer and stretched to develop anisotropy in the dispersed phase. Japanese Patent Application Laid-Open No. 2008-129556 (Patent Document 2) discloses a scattering type polarizer having a continuous phase composed of a polyester-based resin (A) and a dispersed phase composed of a polystyrene-based resin (B). A scattering type polarizing element having a (YI value) in the range of −3 to 3 is disclosed.

  However, also in this polarizing element, since the scattering is anisotropic, the front luminance is lowered. Moreover, in order to improve a brightness | luminance, extending | stretching of the high magnification 4 times or more is required. On the other hand, when the draw ratio is 4 times or less, a general-purpose biaxial stretching device for polyester and a tenter device can be used, which is highly convenient. In addition, since the expensive polyester-based resin is used as the continuous phase, the material cost is high and the economy is low.

  Therefore, as a polarizing element capable of expressing excellent polarization characteristics and scattering characteristics by a simple method, WO2010 / 137450 (Patent Document 3) is composed of a transparent resin in a continuous phase composed of a polycarbonate-based resin. An element composed of a stretched sheet in which the dispersed phase is dispersed in the form of particles, wherein the in-plane birefringence of the continuous phase is less than 0.05, and the in-plane birefringence of the dispersed phase is 0.05. There has been disclosed a polarizing element in which the difference in refractive index between the continuous phase and the dispersed phase with respect to linearly polarized light is different between the stretching direction and the direction perpendicular to the stretching direction.

  However, even in this polarizing element, since the scattering is anisotropic, the front luminance is lowered.

JP-A-9-297204 (Claims and Examples) JP 2008-129556 A (Claims, paragraph [0024], Examples) WO2010 / 137450 (claims)

  Therefore, an object of the present invention is to provide a polarizing film that can exhibit high isotropic scattering and high front luminance, a method for manufacturing the polarizing film, and a display device (display device such as a surface light source device and a liquid crystal display device) provided with the polarizing film. Is to provide.

  Another object of the present invention is to provide a polarizing film capable of improving luminance by a simple method, a method for producing the same, and a display device including the polarizing film.

  As a result of intensive studies to achieve the above-described problems, the inventors of the present invention have formed a second transparent resin in a continuous phase that is stretched biaxially by a predetermined method and formed by the first transparent resin. In the film in which the plate-like dispersed phase is dispersed, it has been found that by orienting the plate surface of the dispersed phase substantially parallel to the film surface, high isotropic scattering can be expressed and front luminance can be improved. completed.

  That is, the polarizing film of the present invention is a polarizing film including a continuous phase formed of a first transparent resin and a dispersed phase formed of a second transparent resin, and the dispersed phase is plate-shaped. And the plate surface of the dispersed phase is oriented substantially parallel to the film surface. In the planar shape of the dispersed phase, the ratio of the major axis to the minor axis is about 1 to 1.5. The average size of the dispersed phase in the planar shape may be about 0.2 to 5 μm, and the ratio of the average size to the average thickness may be about 2 to 50. The dispersed phase may be substantially disk-shaped. The polarizing film of the present invention is a film stretched in two directions intersecting substantially at right angles, and the refractive index difference between the continuous phase and the dispersed phase with respect to linearly polarized light is different between one stretching direction and the other stretching direction. Also good. In the stretched film, the absolute value of the refractive index difference between the continuous phase and the dispersed phase in one stretching direction is 0.1 to 0.3, and the refractive index difference between the continuous phase and the dispersed phase in the other stretching direction. The absolute value of may be 0.1 or less. In the polarizing film of the present invention, the total light transmittance of linearly polarized light in the stretching direction with a small refractive index difference is 80% or more, and the reflectance of linearly polarized light in the stretching direction with a large refractive index difference is about 30 to 60%. There may be. In the polarizing film of the present invention, the in-plane birefringence of the continuous phase may be less than 0.05, and the in-plane birefringence of the dispersed phase may be 0.05 or more. The continuous phase may be formed of a polycarbonate resin, and the dispersed phase may be formed of a polyester resin. In the polarizing film of the present invention, the dispersed phase may be dispersed substantially uniformly in the continuous phase. The ratio of the continuous phase to the dispersed phase is about continuous phase / dispersed phase = 99/1 to 50/50 (weight ratio).

  The present invention also includes a method for producing the polarizing film by stretching a sheet formed by melting and mixing two kinds of transparent resins in two directions intersecting substantially at right angles. In this method, when the glass transition temperature of the transparent resin forming the continuous phase is Tg, one of the longitudinal and transverse directions is stretched at a temperature of Tg ° C. to (Tg + 80) ° C. under a tensile rate of 100 to 800 mm / The film is stretched 1.2 to 4 times in minutes, and the other stretch is stretched 1.2 to 4 times at a tensile speed of 5 to 100 mm / min under a temperature condition of (Tg + 15) ° C. to (Tg + 80) ° C. May be.

  The present invention also includes a surface light source device and a liquid crystal display device provided with the polarizing film.

  In the present specification, the “plate shape” means a shape having a substantially planar shape, and the substantially planar shape does not need to be smooth throughout, but is partially or entirely swollen or You may have a hollow shape. That is, the “plate shape” means a shape having a generally smooth surface, and the “plate surface” means a surface having the planar shape. In this specification, “film” is used to mean including a sheet regardless of the thickness.

  In the present invention, the plate-like dispersed phase formed of the second transparent resin is oriented in the continuous phase formed of the first transparent resin so that the plate surface of the dispersed phase is substantially parallel to the film surface. For this reason, the scattered light isotropically exits from the dispersed phase, and the exit angle of the scattered light is appropriately narrowed, so that high isotropic scattering can be achieved and the front luminance can be improved. Furthermore, the brightness of the display device can be improved by a simple method.

FIG. 1 is a schematic sectional view showing an example of a transmissive liquid crystal display device using the surface light source device of the present invention. FIG. 2 is a schematic sectional view showing an example of the reflective liquid crystal display device of the present invention. FIG. 3 is a schematic sectional view showing another example of the reflective liquid crystal display device of the present invention.

[Polarized film]
The polarizing film of the present invention includes a continuous phase formed of a first transparent resin and a plate-like dispersed phase formed of a second transparent resin and having a plate surface oriented substantially parallel to the film surface. That is, the polarizing film is formed of a continuous phase that forms a matrix (matrix) of the polarizing film and a dispersed phase that exists in the matrix and expresses a polarizing function. Furthermore, the interface between the continuous phase and the dispersed phase is substantially free of voids, and the continuous phase and the dispersed phase are bonded or in close contact.

(Continuous phase)
The first transparent resin constituting the continuous phase includes thermoplastic resins [olefin resins, cyclic olefin resins, halogen-containing resins (including fluorine resins), vinyl alcohol resins, vinyl ester resins, vinyl ether resins. , (Meth) acrylic resins, styrene resins, polyester resins, polyamide resins, polycarbonate resins, thermoplastic polyurethane resins, polysulfone resins (polyethersulfone, polysulfone, etc.), polyphenylene ether resins (2,6- Xylenol polymers), cellulose derivatives (cellulose esters, cellulose carbamates, cellulose ethers, etc.), silicone resins (polydimethylsiloxane, polymethylphenylsiloxane, etc.)], rubber or elastomers (polybutadiene) Diene rubber such as polyisoprene, styrene-butadiene copolymer, acrylonitrile-butadiene copolymer, acrylic rubber, urethane rubber, silicone rubber, etc.), thermosetting resin (epoxy resin, unsaturated polyester resin, diallyl phthalate resin, Silicone resin, etc.). These transparent resins can be used alone or in combination of two or more. Of these transparent resins, polycarbonate resins are preferable because they are inexpensive and have high transparency.

  The polycarbonate-based resin has low in-plane birefringence (absolute value of the difference in refractive index between the stretching direction and the direction perpendicular to the stretching direction), and the in-plane birefringence is less than 0.05, for example, 0 to 0.00. 03, preferably 0 to 0.02, more preferably about 0 to 0.01. Therefore, in this invention, a draw ratio can be restrained low by combining with a dispersed phase with high in-plane birefringence. In particular, in the case of a bisphenol A type polycarbonate-based resin, the in-plane birefringence is substantially zero at a draw ratio of 3 to 5 times under the conditions of Examples described later. The refractive index can be measured at a wavelength of 633 nm using a prism coupler (manufactured by Metricon), as described in Examples described later.

  Polycarbonate resins include aromatic polycarbonates based on bisphenols, aliphatic polycarbonates such as diethylene glycol bisallyl carbonate, and the like. Of these, aromatic polycarbonates based on bisphenols are preferred because of their excellent optical properties and low cost.

Examples of bisphenols include biphenols such as dihydroxybiphenyl, bis (hydroxyaryl) alkanes such as bisphenol A, bisphenol F, bisphenol AD, bis (4-hydroxytolyl) alkane, and bis (4-hydroxyxylyl) alkane. [For example, bis (hydroxyaryl) C _1-10 alkanes, preferably bis (hydroxyaryl) C _1-6 alkanes], bis (hydroxyaryl) cycloalkanes such as bis (hydroxyphenyl) cyclohexane [for example, bis (Hydroxyaryl) C _3-12 cycloalkanes, preferably bis (hydroxyaryl) C _4-10 cycloalkanes], 4,4'-di (hydroxyphenyl) ether and other di (hydroxyphenyl) ethers Di (hydroxyphenyl) ketones such as 4,4'-di (hydroxyphenyl) ketone, di (hydroxyphenyl) sulfoxides such as bisphenol S, bis (hydroxyphenyl) sulfones, bisphenol fluorenes [for example, 9,9-bis (4-hydroxyphenyl) fluorene, 9,9-bis (4-hydroxy-3-methylphenyl) fluorene, etc.]. These bisphenols may be C _2-4 alkylene oxide adducts. These bisphenols can be used alone or in combination of two or more.

The polycarbonate resin may be a polyester carbonate resin obtained by copolymerizing a dicarboxylic acid component (such as an aliphatic, alicyclic or aromatic dicarboxylic acid or an acid halide thereof). These polycarbonate resins can be used alone or in combination of two or more. Preferred polycarbonate resins are resins based on bis (hydroxyphenyl) C _1-6 alkanes, for example, bisphenol A type polycarbonate resins. In the bisphenol A-type polycarbonate resin, the proportion of other copolymerizable monomer other than bisphenol A is, for example, about 20 mol% or less, preferably about 10 mol% or less (for example, 0.1 to 10 mol%). is there.

  The average molecular weight of the first transparent resin (particularly polycarbonate-based resin) is, for example, a viscosity average molecular weight determined from a viscosity measured in a methylene chloride solution having a concentration of 0.7 g / dL at 20 ° C. About 15000 to 120,000, preferably about 17000 to 100,000, and more preferably about 18000 to 50000 (especially 18000 to 30000). If the molecular weight of the first transparent resin is too small, the mechanical strength of the film tends to decrease, and if the molecular weight is too large, the melt fluidity decreases, and the handleability during film formation and the uniform dispersibility of the dispersed phase tend to decrease. .

  The melt flow rate (MFR) of the first transparent resin (particularly polycarbonate resin) is, for example, about 3 to 30 g / 10 minutes in accordance with ISO 1133 (300 ° C., 1.2 kg load (11.8 N)). It can be selected from the range, for example, 5 to 30 g / 10 minutes, preferably 6 to 25 g / 10 minutes, more preferably 7 to 20 g / 10 minutes (particularly 8 to 15 g / 10 minutes).

When the viscosity of the first transparent resin (particularly polycarbonate-based resin) is measured using a rotary rheometer (manufactured by Anton Paar) at 270 ° C. and a shear rate of 10 sec ⁻¹ , for example, 100 to 1500 Pa · s, preferably 200 to 1200 Pa · s, more preferably about 300 to 1000 Pa · s (particularly 500 to 750 Pa · s).

  The glass transition temperature of the first transparent resin (particularly polycarbonate-based resin) can be selected from a range of, for example, about 110 to 250 ° C. From the viewpoint that the stretching temperature can be set lower and the selection range of the resin in the dispersed phase is expanded. For example, it is about 110-180 degreeC, Preferably it is 120-160 degreeC, More preferably, it is about 130-160 degreeC (especially 140-155 degreeC). The glass transition temperature can be measured using a differential scanning calorimeter, for example, using a differential scanning calorimeter (“DSC6200” manufactured by Seiko Denshi Kogyo Co., Ltd.) under a nitrogen stream at a heating rate of 10 ° C./min. It can be measured.

  The continuous phase may be composed of a polymer alloy. When a polycarbonate-based resin is used as the first transparent resin, for example, the ratio of the other transparent resin is, for example, 100 parts by weight or less, preferably 50 parts by weight or less, with respect to 100 parts by weight of the polycarbonate-based resin. Preferably it is about 10 parts by weight or less (for example, 0.1 to 10 parts by weight). Specific examples of the polymer alloy include, for example, a polycarbonate resin composition disclosed in JP-A-9-183892 (a resin composition in which a polyester resin and a transesterification catalyst are blended with polycarbonate to reduce haze value and birefringence). ), A polycarbonate resin composition disclosed in Japanese Patent Application Laid-Open No. 11-3379969 (a resin composition in which an aromatic alkenyl compound or a vinyl cyanide compound is blended with polycarbonate), and a polycarbonate resin composition disclosed in Japanese Patent No. 4021741 (Resin composition in which polyester and epoxy-modified polyolefin are blended with polycarbonate).

(Dispersed phase)
The dispersed phase may be any transparent resin that is incompatible with the first transparent resin constituting the continuous phase and can exhibit in-plane birefringence different from the continuous phase in the polarizing film. It can be selected from the transparent resins exemplified as the transparent resin. The transparent resin constituting the dispersed phase is preferably a transparent resin having in-plane birefringence (the absolute value of the difference in refractive index in the vertical direction and the refractive index in the horizontal direction) of 0.05 or more. The in-plane birefringence is, for example, about 0.05 to 0.5, preferably about 0.1 to 0.4, and more preferably about 0.15 to 0.3 (particularly 0.2 to 0.25). . When the continuous phase is composed of the first transparent resin (for example, polycarbonate-based resin) and the disperse phase is composed of the transparent resin having a large intrinsic birefringence, the stretch between the continuous phase and the disperse phase is effectively achieved with low magnification. It is possible to produce a device having a high refractive index difference and having high scattering characteristics and polarization characteristics.

  Examples of such transparent resins include cyclic olefin resins, vinyl resins (polyvinyl chloride, vinyl chloride-vinyl acetate copolymers, polyvinyl pyrrolidone, etc.), styrene resins (styrene-acrylonitrile resin, etc.), acrylics, and the like. Resin (poly (meth) acrylic acid, poly (meth) acrylic acid alkyl ester such as poly (meth) acrylic acid methyl ester), acrylonitrile resin (poly (meth) acrylonitrile, etc.), polyester resin (non-crystalline fragrance) Aromatic polyester resins, aliphatic polyester resins, liquid crystal polyesters, etc.), polyamide resins (polyamide 6, polyamide 66, polyamide 610 etc.), cellulose derivatives (cellulose acetate etc.), synthetic rubber (polybutadiene, polyisoprene etc.), natural Rubber etc. Murrell. These transparent resins can be used alone or in combination of two or more.

Of these transparent resins, polyester resins, particularly polyalkylene arylate resins, are preferred because they have substantially the same refractive index as polycarbonate resins and can easily increase the refractive index in the stretching direction by stretching. In the polyalkylene arylate resin, the main component is an allene arylate unit, for example, 50 mol% or more, preferably 75 to 100 mol%, more preferably 80 to 100 mol% (particularly 90 to 100 mol%). Containing homo or copolyesters are included. The copolymerizable monomer constituting the copolyester includes a dicarboxylic acid component (for example, C _8-20 aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, 2,7-naphthalenedicarboxylic acid, 2,5-naphthalenedicarboxylic acid). Acid, adipic acid, azelaic acid, C _4-12 alkane dicarboxylic acid such as sebacic acid, C _4-12 cycloalkane dicarboxylic acid such as 1,4-cyclohexanedicarboxylic acid, etc.), diol component (for example, ethylene glycol, propylene glycol) , butanediol, _{C 2-10} alkanediol such as neopentyl glycol, diethylene glycol, _{C 4-12} cycloalkane diols such as poly _{C 2-4} alkylene glycol, 1,4-cyclohexanedimethanol, such as polyethylene glycol, bisphenol And aromatic diols such as), hydroxycarboxylic acid component (e.g., p- hydroxybenzoic acid, p- hydroxyethoxy benzoic acid) and the like. These copolymerizable monomers can be used alone or in combination of two or more. The polyalkylene arylate-series resin, for example, polyethylene terephthalate, polypropylene terephthalate, poly C _2-4 alkylene terephthalate-series resin such as polybutylene terephthalate, polyethylene naphthalate, polypropylene naphthalate, poly C _2-4, such as polybutylene naphthalate Examples include alkylene naphthalate resins.

Among these polyalkylene arylate resins, polyalkylene naphthalate resins (especially from the viewpoint that they have a refractive index equivalent to that of the polycarbonate resin before stretching and can easily increase the refractive index in the stretching direction by stretching. Poly _C2-4 alkylene naphthalate resins such as polyethylene naphthalate resins) are preferred. The polyalkylene naphthalate resin is a homopolyester of an alkylene naphthalate unit (especially a C _2-4 alkylene naphthalate unit such as ethylene-2,6-naphthalate) or an alkylene naphthalate unit content of 80 mol% or more. (Especially 90 mol% or more) copolyesters. Examples of the copolymerizable monomer constituting the copolyester include the aforementioned dicarboxylic acid component, diol component, and hydroxycarboxylic acid. Of these copolymerizable monomers, dicarboxylic acid components such as terephthalic acid are widely used.

  The average molecular weight of the second transparent resin (for example, a polyester-based resin such as a polyalkylene naphthalate-based resin) can be selected from a range of, for example, a number average molecular weight of about 5,000 to 1,000,000, for example, 10,000 to 500,000, preferably 12,000. ˜300000, more preferably about 15,000 to 100,000. When the molecular weight of the second transparent resin is too large, the melt fluidity is lowered and the aspect ratio of the dispersed phase is likely to be lowered. The number average molecular weight can be measured in terms of polystyrene using gel permeation chromatography.

The melt viscosity of the second transparent resin (for example, a polyester resin such as a polyalkylene naphthalate resin) is 270 ° C. and a shear rate of 10 sec ⁻¹ using a rotary rheometer (manufactured by Anton Paar). When measured, it is, for example, about 200 to 5000 Pa · s, preferably 300 to 4000 Pa · s, more preferably about 500 to 3000 Pa · s (particularly 1000 to 2000 Pa · s).

  The ratio of the first transparent resin (particularly polycarbonate resin) to the melt viscosity is, for example, the melt viscosity of the first transparent resin / the melt viscosity of the second transparent resin = 2/1 to 1/10, preferably It is about 2/1 to 1/5, more preferably about 2/1 to 1/3 (particularly 1/1 to 1 / 2.5). In such a range, both resins are sufficiently mixed, and a dispersed layer having an appropriate size can be uniformly formed in the continuous phase, and the dispersed phase can be controlled to an appropriate particle size. High in-plane birefringence can be imparted.

  The glass transition temperature of the second transparent resin (for example, a polyester-based resin such as a polyalkylene naphthalate-based resin) can be selected from a range of about 50 to 200 ° C., for example, but the aspect ratio of the dispersed phase can be easily increased by stretching. From the point which can raise, it is preferable that it is lower than the glass transition temperature of 1st transparent resin, for example, 1-100 degreeC, Preferably it is 5-80 degreeC, More preferably, it is about 10-50 degreeC (especially 20-40 degreeC) grade. It may be low. Specifically, the glass transition temperature of 2nd transparent resin is 60-180 degreeC, for example, Preferably it is 80-150 degreeC, More preferably, it is about 90-130 degreeC (especially 100-120 degreeC) grade. The glass transition temperature can be measured using a differential scanning calorimeter, for example, using a differential scanning calorimeter (“DSC6200” manufactured by Seiko Denshi Kogyo Co., Ltd.) under a nitrogen stream at a heating rate of 10 ° C./min. It can be measured.

  The shape of the dispersed phase may be a plate shape (or a flat shape), and the planar shape of the plate surface is not particularly limited, and may be, for example, an indefinite shape, a polygonal shape, etc. A perfect circle shape) and an elliptical shape are preferable. In other words, the shape of the dispersed phase is preferably a disk shape or an elliptical plate shape, and a substantially disk shape is particularly preferable. In the present invention, since it has a plate shape such as a substantially disk shape, it is possible to exhibit an appropriate isotropic scattering property and to improve luminance. The reason is not clear, but the isotropic property in the direction of scattered light emission is improved, the angle of emission of the scattered light is moderately narrowed and focused in the direction perpendicular to the film surface, and the front brightness is also improved. It is estimated that this is because the scattered light is also effectively used to improve the luminance.

  The planar shape of the plate surface of the dispersed phase can be selected according to the required scattering characteristics and luminance, and may be an anisotropic shape, but isotropic because it has an excellent balance between the scattering characteristics and the luminance improvement effect. The shape (substantially circular shape) is preferable.

  In the planar shape, the size of the dispersed phase (in the case of an anisotropic shape such as an elliptical shape, the average addition size of the major axis and the minor axis in the planar shape) is about 0.1 to 10 μm on average. It is 2-5 micrometers, Preferably it is 0.3-4 micrometers, More preferably, it is about 0.5-3 micrometers (especially 1-2 micrometers). In the planar shape of the disperse phase (particularly elliptical or substantially circular planar shape), the ratio of the major axis to the minor axis can be selected from the range of about 1 to 10, for example, 1 to 5, preferably 1 to 3, Preferably, it is about 1 to 2 (particularly 1 to 1.5), and may be about 1 to 1.2 (particularly 1 to 1.1), for example, depending on the application.

  The average thickness of the dispersed phase is, for example, about 0.01 to 1 μm, preferably about 0.03 to 0.8 μm, and more preferably about 0.05 to 0.5 μm (particularly 0.1 to 0.4 μm). The ratio of the average size to the average thickness can be selected from the range of about 1.5 to 100, for example, 2 to 50, preferably 3 to 30, and more preferably 4 to 20 (particularly 5 to 10). In the present invention, for example, by stretching the sheet phase-separated into a sea-island structure in the biaxial direction, the ratio of the major axis to the minor axis and the ratio of the average size to the average thickness can be controlled. The luminance can be improved by controlling the anisotropy of scattering.

  The ratio (weight ratio) between the continuous phase (resin component constituting the continuous phase) and the dispersed phase (resin component constituting the dispersed phase) can be selected according to the type of resin, melt viscosity, light diffusibility, etc. , Continuous phase / dispersed phase = 99/1 to 50/50, preferably 98/2 to 70/30, more preferably about 96/4 to 80/20, usually 95/5 to 85 / About 15. When used in such a ratio, the dispersed phase can be uniformly dispersed even if the pellets of each component are directly melt-kneaded without compounding both components in advance, and voids are generated due to orientation treatment such as uniaxial stretching. Can be prevented, and a good polarizing film can be obtained.

(Additive)
In the polarizing film of the present invention, the dispersed phase is bonded or closely adhered to the continuous phase without substantially forming voids at the interface with the continuous phase, but if necessary, a compatibilizing agent is blended. May be. When a compatibilizing agent is blended, the dispersed phase may be bonded or adhered to the continuous phase via the compatibilizing agent.

  As a compatibilizing agent, a polymer (random, block or graft copolymer) having the same or common components as the resin constituting the continuous phase and the dispersed phase, and the resin constituting the continuous phase and the dispersed phase are usually used. An affinity polymer (random, block or graft copolymer) or the like is used. Specifically, a polyester elastomer, a compatibilizer having an epoxy group in the main chain, particularly an epoxy-modified aromatic vinyl-diene block copolymer [for example, an epoxidized styrene-butadiene-styrene (SBS) block copolymer). And an epoxidized styrene-diene copolymer such as a polymer and an epoxidized styrene-butadiene block copolymer (SB) or an epoxy-modified styrene-diene copolymer]. The epoxidized aromatic vinyl-diene copolymer not only has high transparency, but also has a relatively high softening temperature of about 70 ° C., which makes the resin compatible in many combinations of a continuous phase and a dispersed phase, The dispersed phase can be uniformly dispersed.

  The ratio of the compatibilizer is, for example, as the ratio (weight ratio) to the dispersed phase, dispersed phase / compatibilizer (weight ratio) = 99/1 to 50/50, preferably 99/1 to 70/30, more preferably Is about 98/2 to 80/20. Furthermore, the proportion of the compatibilizer is, for example, 0.1 to 20 parts by weight, preferably 0.5 to 15 parts by weight, and more preferably 1 to 10 parts by weight with respect to a total of 100 parts by weight of the continuous phase and the dispersed phase. About a part.

  The polarizing film of the present invention is a conventional additive, for example, a stabilizer such as an antioxidant or a heat stabilizer, a plasticizer, an antistatic agent, a flame retardant, a filler, an ultraviolet ray, as long as the optical properties are not impaired. It may contain an absorbent or the like.

(Characteristics of polarizing film)
In the polarizing film of the present invention, the difference in refractive index between the continuous phase and the dispersed phase with respect to linearly polarized light is the longitudinal direction of the film (MD direction, length direction or flow direction, hereinafter sometimes referred to as “X-axis direction”). And the horizontal direction (CD direction or width direction, hereinafter referred to as “Y-axis direction”). Therefore, the polarizing film has a property of scattering polarized light in a direction in which the refractive index difference is large. Some polarized light is scattered in front of the film, and the remaining polarized light is scattered in the rear of the film and hardly absorbed. . Further, polarized light in a direction with a small difference in refractive index has a characteristic of almost transmitting. That is, the polarizing film largely scatters linearly polarized light in one direction (for example, the X-axis direction), and linearly polarized light in a direction perpendicular to this direction scatters smaller than or substantially scatters in the X-axis direction. do not do.

  Regarding the refractive index difference, the absolute value of the refractive index difference between the continuous phase and the dispersed phase in one direction (for example, the X-axis direction) is 0.1 or more (for example, 0.1 to 0.5), preferably The absolute value of the difference in refractive index between the continuous phase and the dispersed phase in the other direction (for example, the Y-axis direction) is about 0.1 to 0.3, more preferably about 0.1 to 0.2. 1 or less, for example, 0.05 or less, preferably 0.04 or less, more preferably 0.03 or less (for example, about 0.001 to 0.03). When the absolute value of the refractive index difference between the two is in the above range, the balance between backscattering (reflection) and transmission scattering is excellent, and excellent polarization characteristics and scattering characteristics can be exhibited, and the brightness of the display device can also be improved. .

  The polarizing film of the present invention is preferably a film stretched in two directions intersecting substantially at right angles. However, in the polarizing film having a difference in refractive index, the continuous phase and the dispersed phase are the sheets at the time of film formation (so-called At the stage of the cast sheet), it is preferable that each refractive index has a small anisotropy and has substantially the same refractive index. For example, the absolute value of the refractive index difference between the polycarbonate resin before stretching and the polyester resin constituting the dispersed phase may be 0.05 or less, preferably 0.04 or less, more preferably 0.03 or less. . If the refractive index difference between the two resins before stretching is in this range, the refractive index difference can be easily expressed in the stretching direction by ordinary stretching. That is, when stretched under normal conditions, the polycarbonate constituting the continuous phase does not change the refractive index much by stretching, whereas the dispersed phase is deformed into a disk shape or an elliptical plate shape by stretching. At the same time, a large difference in refractive index occurs. On the other hand, by stretching under specific conditions (such as stretching at low temperature and low speed), only the shape of the dispersed phase is deformed without significantly changing the molecular orientation, that is, without changing the refractive index much before stretching. Can do. Therefore, in biaxial stretching, by changing the stretching conditions, anisotropy can be expressed in the refractive index, and excellent polarization characteristics can be expressed.

  Therefore, the polarizing film of the present invention can appropriately adjust the refractive index difference in both the X-axis direction and the Y-axis direction by stretching in two directions intersecting substantially at right angles. By making it the same, since the shape of the dispersed phase becomes a substantially disk shape, it is possible to improve the luminance such as the front luminance while maintaining high isotropic scattering characteristics.

  The polarizing film of the present invention has a high total light transmittance of linearly polarized light in a direction in which the refractive index difference is small (stretching direction in which the refractive index difference is small) among the X-axis direction and the Y-axis direction. The total light transmittance of linearly polarized light in the small direction is 80% or more, for example, 80 to 99%, preferably 85 to 98%, and more preferably about 90 to 95%. Furthermore, the diffused light transmittance of linearly polarized light in the above direction is, for example, 20% or more (for example, 20 to 90%), preferably 30 to 80%, and more preferably 35 to 60% from the viewpoint of improving luminance. It may be about (especially 40 to 50%). The direction showing such a high total light transmittance may be either the X-axis direction or the Y-axis direction, but the Y-axis direction is preferable from the viewpoint of productivity.

  On the other hand, the polarizing film of the present invention has excellent scattering characteristics in the direction with a large refractive index difference (stretching direction with a large refractive index difference) in the X-axis direction and the Y-axis direction. The total light transmittance is 70% or less (for example, 10 to 70%), preferably 60% or less (for example, 30 to 60%), and more preferably 50% or less (for example, 40 to 50%). That is, the polarizing film of the present invention has high reflectance (reflectance due to regular reflection components and backscattering components), and the reflectance (backscattering rate) in the above direction is 30% or more (for example, 30 to 90%). , Preferably 40% or more (for example, 40 to 80%), more preferably 50% or more (for example, 50 to 60%), for example, about 30 to 60% (particularly 40 to 60%). Good. The direction showing such reflectance may be either the X-axis direction or the Y-axis direction, but the X-axis direction is preferable from the viewpoint of productivity.

  That is, the polarizing film of the present invention has a total light transmittance of 80% or more in a direction where the refractive index difference is small, and a reflectance in a direction where the refractive index difference is large (the reflectance due to the regular reflection component and the backscattering component). ) Is 30% or more, and imparts light diffusion and polarization to the transmitted light, and therefore has properties similar to those of the absorption polarizing plate. Moreover, since it reflects without absorbing polarized light, it does not increase in temperature due to absorption of one of the polarized light, which is a defect of the absorption type, and becomes a good scattering type polarizing plate similar to a transmission type polarizing plate. Furthermore, since the reflected light contributes to the improvement of the luminance, the polarizing film of the present invention can also be used as a luminance improvement sheet for a liquid crystal display device or the like.

  In addition, the total light transmittance and the diffused light transmittance are all light rays using a polarization measuring device (haze meter) (manufactured by Nippon Denshoku Industries Co., Ltd., NDH5000W) as described in Examples described later. Can be measured by a method according to JIS K7361-1, and haze (diffuse light) can be measured by a method according to JIS K7136.

  The thickness of the polarizing film of the present invention is about 3 to 500 μm, preferably about 5 to 400 μm (for example, 30 to 400 μm), and more preferably about 5 to 300 μm (for example, 50 to 300 μm).

  The polarizing film of the present invention may be a single layer film, or may be a laminated film in which a transparent resin layer that does not impair optical properties is laminated on at least one side (particularly both sides). When the polarizing film is protected by the transparent resin layer, the dispersed phase particles can be prevented from falling off and adhering, and the scratch resistance and production stability of the polarizing film can be improved, and the strength and handleability can be improved.

  The resin of the transparent resin layer can be selected from the resins exemplified as the constituent components of the continuous phase or the dispersed phase. A preferable transparent resin layer is formed of a transparent resin (particularly, a polycarbonate resin) of the same system (particularly, the same) as the continuous phase. The transparent resin layer may also contain the aforementioned conventional additives as long as the optical properties are not impaired.

  The total thickness of the transparent resin layer may be, for example, the same level as the polarizing film. In particular, when the thickness of the polarizing film layer is about 3 to 500 μm, the thickness of the transparent resin layer can be selected from 3 to 150 μm, preferably 5 to 50 μm, and more preferably about 5 to 15 μm.

  The ratio between the thickness of the polarizing film and the total thickness of the transparent resin layer can be selected from the range of, for example, polarizing film / transparent resin layer = 5/95 to 99/1, and is usually 50/50 to 99/1, preferably Is about 70/30 to 95/5. The thickness of the laminated film is, for example, about 6 to 800 μm, preferably about 10 to 600 μm, and more preferably about 20 to 450 μm.

  A release agent such as silicone oil may be applied to the surface of the polarizing film as long as the optical properties are not hindered, or a corona discharge treatment may be performed. In addition, you may form the uneven | corrugated | grooved part of a film in the surface of a polarizing film. When such an uneven part is formed, antiglare properties can be imparted.

[Production method of polarizing film]
The polarizing film can be obtained by dispersing and orienting the second transparent resin constituting the dispersed phase in the first transparent resin constituting the continuous phase. For example, a polycarbonate resin and a polyester resin and, if necessary, an additive such as a compatibilizer are blended by a conventional method (for example, a melt blending method, a tumbler method, etc.) as necessary, and melt-mixed. The dispersed phase can be dispersed in the continuous phase by extrusion from a die or ring die to form a film. The melting temperature is preferably equal to or higher than the melting points of the first and second transparent resins, and varies depending on the type of resin, but is, for example, about 150 to 290 ° C, preferably about 200 to 260 ° C.

  The orientation treatment of the dispersed phase can be performed by, for example, (1) a method of stretching an extruded sheet, (2) a method of forming a film while drawing the extruded sheet to solidify the sheet, and then stretching the sheet. In order to express the excellent characteristics of the polarizing film of the present invention, the molten phase is used to disperse the dispersed phase composed of the second transparent resin in the form of particles in the continuous phase composed of the first transparent resin. It is preferable to reheat the cast sheet that has been solidified and cooled, and then to perform orientation processing by stretching.

  Stretching may be performed in two directions intersecting substantially at right angles, and may be simultaneous biaxial stretching. However, the longitudinal and lateral stretching conditions (orientation conditions) can be easily adjusted to different conditions. Biaxial stretching is preferred. In sequential biaxial stretching, an unstretched sheet is stretched in a uniaxial direction, and then stretched in a direction orthogonal to the stretching direction. In addition, it is not limited to so-called sequential biaxial stretching, for example, a mode in which deformation of the domain at the first stage (first) of sequential stretching is performed by extrusion sheeting (a mode in which stretching is performed at the same time as forming the extruded sheet) ).

  The biaxial stretching may be simple free-width biaxial stretching or constant width (fixed width) biaxial stretching. The biaxial stretching method is not particularly limited. For example, a method of pulling both ends of the solidified sheet (tensile stretching), and a plurality of series (for example, two series) of a pair of rolls (two rolls) facing each other are prepared. Installed in parallel, inserts the film into each of the two rolls, stretches the film between the two rolls on the feeding side and the two rolls on the feeding side, and feeds the film on the two rolls on the feeding side Stretching by making it faster than the two rolls on the feeding side (stretching between rolls), inserting a film between a pair of opposed rolls and rolling the film with roll pressure (roll rolling), tenter method And fixed width biaxial stretching.

  Fixed-width biaxial stretching by the tenter method is a method in which the width in the direction perpendicular to the stretching direction does not change, and is advantageous for producing a uniform sheet over the entire width while maintaining the anisotropic orientation of the dispersed phase. . Furthermore, although the details of the action are unknown, it is also effective for changing the refractive index of the dispersed phase.

  In the biaxial stretching of the present invention, by making the stretching conditions in the machine direction and the transverse direction different, the refractive index difference between the continuous phase and the dispersed phase with respect to the linearly polarized light is drawn so as to be different in the machine direction and the transverse direction. To do. For example, in biaxial stretching by the tenter method, from the viewpoint of productivity, the stretching direction that increases the refractive index difference may be the sheet flow direction, and a small refractive index difference is expressed (refractive index difference is not expressed). The direction may be the width direction of the sheet.

  As stretching conditions (stretching conditions in the direction in which the refractive index is large in the flow direction and width direction of the sheet) for expressing the difference in refractive index, normal stretching conditions can be used. The stretching temperature is preferably equal to or higher than the glass transition temperature of the first transparent resin. When the glass transition temperature of the first transparent resin is Tg, for example, Tg to (Tg + 80) ° C., preferably (Tg + 5) to ( Tg + 50) ° C., more preferably (Tg + 5) to (Tg + 30) ° C. [particularly (Tg + 8) to (Tg + 20) ° C.] may be used. When the first transparent resin is a polycarbonate resin, the specific stretching temperature is, for example, about 120 to 180 ° C., preferably 130 to 175 ° C., more preferably 140 to 170 ° C. (especially 150 to 170 ° C.). There may be.

  In the biaxial stretching by the tenter method, the tensile speed can be selected from the range of about 50 to 1000 mm / min, for example, depending on the stretching temperature and magnification, for example, 100 to 800 mm / min, preferably 150 to 700 mm / min. More preferably, it is about 200-600 mm / min (especially 400-600 mm / min).

  Although the draw ratio can be selected from a wide range, in the present invention, even at a relatively low draw ratio, a large difference can be caused between the refractive index in the stretching direction and the refractive index in the direction perpendicular to the stretching direction. 1 to 5 times (for example, 1.2 to 4 times), preferably 1.3 to 3.5 times, more preferably 1.5 to 3 times (especially 1.8 to 2.5 times) Also good. In particular, in the present invention, since a sheet having excellent scattering characteristics can be produced even at a draw ratio of 4 times or less, it can be easily produced using a general-purpose stretching apparatus such as biaxial stretching by the tenter method described above.

  On the other hand, as the stretching conditions for not expressing the refractive index difference (stretching conditions in the direction in which the refractive index is small among the flow direction and the width direction of the sheet), for the stretching conditions for increasing the refractive index difference, Conditions of high temperature and gradually stretching are used. The stretching temperature may be a stretching temperature that is 1 to 50 ° C. higher than the stretching temperature for expressing the difference in refractive index, preferably 3 to 30 ° C. higher, more preferably 5 to 20 ° C. higher. Specifically, (Tg + 5) to (Tg + 100) ° C., preferably (Tg + 10) to (Tg + 90) ° C., more preferably (Tg + 15) to (Tg + 80) ° C. [particularly (Tg + 20) to (Tg + 60) ° C.]. It may be.

  In the biaxial stretching by the tenter method, the tensile speed is smaller than the tensile speed for increasing the refractive index difference, for example, 1 to 100 mm / min, preferably 5 to 100 mm / min, more preferably 6 to 50 mm / min. It is about (especially 8-30 mm / min).

  The draw ratio can be selected from the range of the draw ratio for increasing the refractive index difference, for example, 1.1 to 5 times (for example, 1.2 to 4 times), preferably 1.3 to 3.5 times. More preferably, it is about 1.5 to 3 times (particularly 1.8 to 2.5 times). From the viewpoint of improving the isotropic scattering property, the magnification may be approximately the same as the draw ratio for increasing the refractive index difference.

  The polarizing film of the present invention is subjected to tension heat treatment (heat treatment while maintaining the length of the sheet) at a temperature higher than the stretching temperature or the stretching temperature in order to relax the birefringence of the continuous phase and express the polarization characteristics. Thus, heat resistance can be imparted while maintaining polarization characteristics. The heat treatment temperature can be selected from, for example, a range from a stretching temperature for not causing a refractive index difference to a temperature that is about 50 ° C. higher than the stretching temperature, for example, a temperature that is about 30 ° C. higher than the stretching temperature from the stretching temperature. For example, the temperature may be substantially the same as the stretching temperature so as not to cause a difference in refractive index. The heat treatment time is, for example, 0.1 to 30 minutes, preferably 1 to 10 minutes, more preferably about 2 to 5 minutes, and can be selected according to the temperature. For example, in the case of a temperature of about 165 ° C., 2 to 2 It takes about 3 minutes. By this heat treatment, the refractive index difference between the continuous phases can be reduced, and the refractive index of the continuous phase and the dispersed phase can be matched in the direction perpendicular to the stretching direction, so that the optical characteristics can be improved. Furthermore, heat resistance such as dimensional stability of the polarizing film and strength can be improved.

  The laminated film is obtained by laminating a transparent resin layer on at least one surface of the polarizing film layer by a conventional method, for example, a coextrusion molding method, a laminating method (extrusion laminating method, dry laminating method, etc.). be able to.

[Surface light source device and transmissive liquid crystal display device]
The surface light source device of the present invention includes a tubular light source (such as a fluorescent tube), a light guide member for allowing light from the tubular light source to be incident from the side surface and emitted from a flat light exit surface, and light emitted from the light guide member. And a polarizing film disposed on the side. In the surface light source device, the polarizing film is used as a scattering element.

  FIG. 1 is a schematic cross-sectional view showing an example of a transmissive liquid crystal display device using a surface light source device whose luminance is improved by using the polarizing film of the present invention. The liquid crystal display device 1 is provided with a fluorescent tube 2 serving as a tubular light source and a side portion of the fluorescent tube 2, and guides the light from the fluorescent tube 2 to be incident from a side surface and emitted from a flat emission surface. An optical member (light guide plate) 4, a TN liquid crystal cell 7 illuminated by light emitted from the light guide plate 4, a reflective member (reflecting plate) 3 that reflects the incident light, the light guide plate 4, and the liquid crystal A polarizing film 5 disposed between the cells 7 and a diffusion sheet 6 that diffuses light transmitted through the polarizing film 5 are provided.

  In the liquid crystal display device 1, the light from the fluorescent tube 2 passes through the light guide plate 4, is reflected by the reflection plate 3, and is emitted from the light guide plate 4. In the polarizing film 5, the emitted light is almost transmitted through the polarizing film 5 in the direction where the refractive index difference between the continuous phase and the dispersed phase is small (Y-axis direction), and is polarized in the direction where the refractive index difference is large (X-axis direction). Scattered and transmitted or reflected.

  The reflected light again passes through the light guide plate 4 and is reflected by the reflection plate 3. This reflection generates light whose polarization direction is partially rotated by 90 degrees. The light whose polarization direction is rotated passes through the light guide plate 4 again, reaches the polarizing film 5 and is transmitted therethrough. The light whose polarization direction has not changed is reflected again by the polarizing film 5, but the light whose polarization direction has been rotated by 90 degrees again due to reflection by the reflecting plate 3 passes through the polarizing film 5. The light that has passed through the polarizing film 5 is scattered by the diffusion sheet 6 and irradiates the liquid crystal cell 7.

  Therefore, most of the light from the fluorescent tube 2 is made to coincide with the polarization axis and is emitted from the polarization film 5, so that the polarization axis of the absorption polarizing plate (not shown) on the incident side of the liquid crystal cell 7 is If matched with the axis, the light of the fluorescent tube 2 that was conventionally used only about 50% can be used with higher efficiency.

  The polarizing film of the present invention used for this application has a total light transmittance of 80% or more of linearly polarized light in the Y-axis direction, and the reflectance of linearly polarized light in the X-axis direction (reflectance due to regular reflection components and backscattering components). Is preferably used for a transmissive liquid crystal display device having a scattering characteristic of 30% or more. The effect of improving the luminance of the polarizing film of the present invention is effective even when laminated on a light guide plate / diffusion plate / prism sheet, which is usually used. Furthermore, the brightness enhancement effect of the polarizing film of the present invention is also preferable for a direct type backlight (surface light source device) that does not use a light guide plate and a transmissive liquid crystal display device using the same.

[Reflective liquid crystal display]
In the reflective liquid crystal display device of the present invention, a liquid crystal cell may be disposed between the polarizing film of the present invention and the reflecting plate, and the polarizing film of the present invention is disposed between the liquid crystal cell and the reflecting plate. May be. Of these devices, a reflective liquid crystal display device in which the polarizing film is disposed between a liquid crystal cell and a reflector is preferable.

  FIG. 2 is a schematic cross-sectional view showing an example of a reflective liquid crystal display device in which the luminance is improved by using the polarizing film of the present invention. The reflective liquid crystal display device 10 includes a reflective member (reflective plate) 13 for reflecting external light, a TN liquid crystal cell 17 (for a reflective liquid crystal device) illuminated by light emitted from the reflective plate 13, an external An absorption polarizing plate 18 for guiding light to the liquid crystal cell 17, and a polarizing film 15 disposed between the reflection plate 13 and the liquid crystal cell 17 and for scattering light emitted from the reflection plate 13 are provided. Yes.

  In the reflection type liquid crystal display device 10, only the light having the polarization axis coincident with the polarization axis among the external light incident on the absorption type polarization plate 18 is transmitted and reaches the liquid crystal cell 17. The light incident on the liquid crystal cell 17 rotates in the polarization direction and reaches the polarizing film 15.

  When the display of the liquid crystal cell is a dark display, the polarizing film 15 is arranged so that the polarization direction of the external light that has passed through the liquid crystal cell 17 coincides with the Y-axis direction of the polarizing film 15. The polarized light that has passed through the absorption polarizing plate 18 passes through the polarizing film 15 again and is rotated in the direction of the polarization by the liquid crystal cell 17 and becomes a direction perpendicular to the polarization axis of the absorption polarizing plate 18, so that dark display is obtained.

  On the other hand, when the display of the liquid crystal cell is a bright display, the polarizing film 15 is arranged so that the polarization direction of the external light that has passed through the liquid crystal cell 17 matches the X-axis direction of the polarizing film 15. Of the external light incident on the absorption-type polarizing plate 18, only the light whose polarization axis coincides with the polarizing plate 18 is transmitted to the liquid crystal cell 17 and reaches the polarizing film 15 without rotating the polarization direction in the liquid crystal cell 17. The polarized light incident on the polarizing film 15 is scattered in the reflection direction or the transmission direction. The light scattered in the transmission direction is reflected by the reflection plate 13, merged with the light already scattered by the polarizing film 15, reaches the absorption polarizing plate 18, and is transmitted as it is. Since this transmitted light is sufficiently scattered by the polarizer 15, it shows a good white display with little viewing angle dependency.

  FIG. 3 is a schematic cross-sectional view showing another example of the reflective liquid crystal display device in which the luminance is improved by using the polarizing film of the present invention. The reflective liquid crystal display device 20 includes a reflective liquid crystal device liquid crystal cell 27 that is illuminated by light emitted from the reflective plate 23, a reflective member (reflective plate) 23 for reflecting external light, and the liquid crystal cell 27 and the reflective liquid crystal cell 27. A quarter-wave plate 29 disposed between the plate 23 and a polarizing film disposed between the quarter-wave plate 29 and the liquid crystal cell 27 for scattering light emitted from the reflector plate 23. 25. The liquid crystal cell 27 is a type of liquid crystal containing a dichroic dye.

  In the reflective liquid crystal display device 20, in the liquid crystal cell 27, when no voltage is applied, the liquid crystal molecules are aligned in the liquid crystal alignment processing direction (the direction parallel to the glass substrate of the liquid crystal cell), and the dichroic dye is similarly aligned. To do. Of the external light incident on the liquid crystal cell 27, the linearly polarized light component parallel to the long axis direction of the dichroic dye molecule is absorbed by the dichroic dye. The linearly polarized light component in the direction perpendicular to the major axis direction of the dichroic dye molecule passes through the liquid crystal cell 27 and enters the polarizing film 25. When the polarizing film 25 is arranged so that the direction of the linearly polarized light passing therethrough coincides with the Y-axis direction of the polarizing film 8, the polarized light emitted from the polarizing film 25 is caused by the quarter wavelength plate (phase difference plate) 29. It becomes circularly polarized light. Further, the circularly polarized light is reflected by the reflecting plate 23, rotates the direction of the circularly polarized light, enters the quarter wavelength plate 29 again, rotates the direction of the original linearly polarized light by 90 degrees, and again , Enters the polarizing film 25. The incident light becomes polarized light in the X axis direction of the polarizing film 25 and is scattered as linearly polarized light parallel to the long axis direction of the molecules of the dichroic dye, and is absorbed by the dichroic dye in the liquid crystal cell 27. The display of the cell 27 is a good black display.

  On the other hand, in the liquid crystal cell 27, when a voltage is applied, the liquid crystal molecules are aligned perpendicular to the glass substrate, and the dichroic dye is similarly aligned. The incident external light passes through the liquid crystal cell 27 without being absorbed by the dichroic dye of the liquid crystal cell 27 containing the dichroic dye, and enters the polarizing film 25. The incident light passes through the polarizing film 25 as it is with respect to the polarization in the Y-axis direction, but the polarization in the X-axis direction is scattered. Next, the polarized light emitted from the polarizing film 25 becomes circularly polarized light by the quarter wavelength plate 29 and is reflected by the reflecting plate 23. The reflected light is reversed in the direction of the circularly polarized light and is incident on the quarter-wave plate 29 again. Of the incident light, the polarized light in the Y-axis direction passes as it is, and the polarized light that has become circularly polarized light is rotated by 90 degrees and scattered by the polarizing film 25. Therefore, since all the light that has passed through the liquid crystal cell 27 containing the dichroic dye becomes scattered reflected light, a good white display can be realized.

  When the polarizing film of the present invention is used, high scattering property and polarization property can be imparted to transmitted light and reflected light, so that the visibility of the liquid crystal display screen can be improved. In particular, even a liquid crystal display surface having a large area can be brightly displayed throughout. Therefore, the transmissive or reflective liquid crystal display device can be widely used for display parts of electric products such as personal computers (personal computers), word processors, liquid crystal televisions, mobile phones, watches, calculators, and the like. In particular, it can be suitably used for a liquid crystal display device of a portable information device.

  Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. In addition, the characteristic of the polarizing film obtained by the Example and the comparative example was evaluated in accordance with the following method.

[Section observation of sheet]
Microsections are cut out in two directions (in the case of a stretched sheet, parallel to and perpendicular to the stretching direction) from the unstretched original sheet and the stretched sheet after stretching, and a transmission electron microscope (JEM 1200EXII, manufactured by JEOL Ltd.) When observed in, the polymer of the dispersed phase forms ellipsoidal (or elongated linear) scatterers (particulate dispersed phase) arranged in the extrusion direction, and the major axis length and minor axis length thereof. Were measured for 50 dispersed phase particles and averaged.

[Refractive index]
The refractive indexes of the continuous and dispersed phases are the prism couplers (X-axis direction) and transverse-stretching direction (Y-axis direction) when each resin single sheet is stretched under the same conditions as in the examples and comparative examples. Measured at a wavelength of 633 nm. Further, the refractive index difference was determined based on the measured refractive index.

[Evaluation of polarization and scattering characteristics]
Using a polarimeter (Nippon Denshoku Industries Co., Ltd., NDH5000W), the total light is measured by a method according to JIS K7361-1, and the haze (diffused light) is a method according to JIS K7136. Measured with The measurement is performed by inserting the polarizing films obtained in Examples and Comparative Examples between the light source and the absorptive polarizing plate, and making the light source only linearly polarized light vertically polarized, and the total light transmittance with respect to the polarized light of the polarizing film. , Diffuse light transmittance, total light reflectance (calculated by total light reflectance = 1−total light transmittance) were measured. This total light reflectivity coincides with the reflectivity (the reflectivity due to the regular reflection component and the backscattering component). In the measurement, when the direction in which the refractive index difference between the continuous phase and the dispersed phase is small coincides with the polarization axis of the absorption polarizing plate ("parallel" in Table 2), the refractive index between the continuous phase and the dispersed phase. The measurement was performed with respect to the case where the direction in which the difference was large coincided with the polarization axis of the absorption polarizing plate (“vertical” in Table 2).

[Front brightness]
Using an automatic variable angle photometer ("GP-200" manufactured by Murakami Color Research Laboratory Co., Ltd.), evaluation was performed with a configuration of diffusion sheet / prism / diffusion sheet / brightness enhancement sheet.

Example 1
Polyethylene naphthalate resin (PEN, manufactured by Teijin Chemicals Ltd., “Teonex TN8065S”, viscosity at 270 ° C. and shear rate 10 sec ⁻¹ : 1578 Pa · s) as a resin constituting the dispersed phase, 10 parts by weight, constituting the continuous phase Bisphenol A type polycarbonate resin (PC, manufactured by Mitsubishi Engineering Plastics Co., Ltd., “medium viscosity product Iupilon S-2000”, viscosity average molecular weight 18000 to 20000, MFR 10 g / 10 min, 270 ° C. and shear rate 10 sec ⁻¹ Viscosity: 681 Pa · s) 90 parts by weight were melt-kneaded and extruded at a cylinder temperature of 280 ° C. using a twin screw extruder (manufactured by Ikekai Tekko Co., Ltd., PCM30), and cooled to produce pellets. The obtained pellets were press-molded for 3 minutes at a press pressure of 270 ° C. and 10 MPa using a small press machine (Toyo Seiki Seisakusho, Mini Test Press 10) to prepare a press sheet having a thickness of 1 mm. The obtained sheet was cut into a width of 40 mm and a length of 70 mm, and pre-heated at 165 ° C. for 3 minutes at 40 mm between chucks using a tenter type biaxial stretching machine (Tensilon UCT-5 with thermostatic bath), and then a tensile speed of 10 mm. After stretching in the transverse direction by 1.5 times at a rate of 1 / min, stretched in the longitudinal direction at a speed of 155 ° C. and twice at a pulling speed of 500 mm / min, and then heat-treated at 165 ° C. for 3 minutes while being held in a chuck. Was rapidly cooled to obtain a biaxially stretched sheet.

Example 2
A biaxially stretched sheet was produced in the same manner as in Example 1 except that the stretching ratio in the transverse direction was 1.7 times.

Example 3
A biaxially stretched sheet was produced in the same manner as in Example 1 except that the stretching ratio in the transverse direction was 1.9 times.

Comparative Example 1
A uniaxially stretched sheet was produced in the same manner as in Example 1 except that the film was not stretched in the transverse direction and was stretched in the longitudinal direction at 155 ° C. and a tensile speed of 500 mm / min.

Comparative Example 2
A uniaxially stretched sheet was produced in the same manner as in Example 1 except that the film was not stretched in the transverse direction and was stretched in the longitudinal direction at 165 ° C. and a tensile speed of 500 mm / min three times.

  Table 1 shows the stretching temperature and magnification, the thickness of the stretched film, and the size of the dispersed phase in Examples 1-3 and Comparative Examples 1-2. Further, Table 2 shows the results regarding the total light transmittance, reflectance, diffuse light transmittance, omnidirectional luminance, and front luminance of the stretched sheet.

  As is clear from the table, the polarizing films of the examples (particularly the polarizing film of Example 1) have a lower omnidirectional luminance than the comparative polarizing film, although the reflectance in the X-axis direction is small. It has almost the same performance as the example. This can be presumed to be because the scattering characteristics in the X-axis direction were improved by controlling the domain shape in the example, and as a result, the light recycling efficiency was improved. In Examples 2 and 3, the front luminance is high although the omnidirectional luminance is slightly lower than that of the comparative example. It can be estimated that the front luminance is improved by controlling the domain shape and improving the scattering characteristics in the Y-axis direction.

  The polarizing film of the present invention can be used for various surface light source devices. In particular, a transmissive or reflective liquid crystal display device (for example, display of electrical products such as personal computers, word processors, liquid crystal televisions, mobile phones, watches, calculators, etc.) Part)

DESCRIPTION OF SYMBOLS 1,10,20 ... Liquid crystal display device 2 ... Fluorescent tube 3,13,23 ... Reflecting member or reflecting layer 4 ... Light guide plate 5,15,25 ... Polarizing film 6 ... Diffusion sheet 7,17,27 ... Liquid crystal cell 18 ... Absorption type polarizing plate 29 ... 1/4 wavelength plate

Claims (15)

  A polarizing film including a continuous phase formed of a first transparent resin and a dispersed phase formed of a second transparent resin, wherein the dispersed phase is plate-shaped, and a plate surface of the dispersed phase is A polarizing film oriented substantially parallel to the film surface.   The polarizing film according to claim 1, wherein in the planar shape of the dispersed phase, the ratio of the major axis to the minor axis is 1 to 1.5.   The polarizing film according to claim 1 or 2, wherein the average size of the dispersed phase in a planar shape is 0.2 to 5 µm, and the ratio of the average size to the average thickness is 2 to 50.   The polarizing film according to claim 1, wherein the dispersed phase is substantially disc-shaped.   The film stretched in two directions intersecting substantially at right angles, wherein the refractive index difference between the continuous phase and the dispersed phase with respect to linearly polarized light is different in one stretching direction and the other stretching direction. A polarizing film according to 1.   The absolute value of the refractive index difference between the continuous phase and the dispersed phase in one stretching direction is 0.1 to 0.3, and the absolute value of the refractive index difference between the continuous phase and the dispersed phase in the other stretching direction is 0. The polarizing film according to claim 5, which is 1 or less.   6. The polarizing film according to claim 5, wherein the total light transmittance of the linearly polarized light in the stretching direction having a small refractive index difference is 80% or more, and the reflectance of the linearly polarized light in the stretching direction having a large refractive index difference is from 30 to 60%. .   The polarizing film according to claim 1, wherein the in-plane birefringence of the continuous phase is less than 0.05 and the in-plane birefringence of the dispersed phase is 0.05 or more.   The polarizing film according to claim 1, wherein the continuous phase is formed of a polycarbonate-based resin and the dispersed phase is formed of a polyester-based resin.   The polarizing film according to any one of claims 1 to 9, wherein the dispersed phase is dispersed substantially uniformly in the continuous phase.   The polarizing film according to claim 1, wherein the ratio of the continuous phase to the dispersed phase is continuous phase / dispersed phase = 99/1 to 50/50 (weight ratio).   The method for producing a polarizing film according to claim 1, wherein a sheet formed by melting and mixing two kinds of transparent resins is stretched in two directions intersecting substantially at right angles.   When the glass transition temperature of the transparent resin forming the continuous phase is Tg, one of the longitudinal and transverse directions is stretched at a temperature of Tg ° C. to (Tg + 80) ° C. under a tensile rate of 100 to 800 mm / min. The film is stretched 2 to 4 times, and the other is stretched 1.2 to 4 times at a tensile rate of 5 to 100 mm / min under a temperature condition of (Tg + 15) ° C to (Tg + 80) ° C. the method of.   The surface light source device provided with the polarizing film in any one of Claims 1-11.   The liquid crystal display device provided with the polarizing film in any one of Claims 1-11.

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