WO2010137450A1 - Polarizing element and display device using same - Google Patents

Abstract

Disclosed is a polarizing element which can be obtained by a simple method and is capable of exhibiting excellent polarization characteristics and scattering characteristics. Specifically disclosed is a polarizing element which is configured of a stretched sheet obtained by uniaxially stretching a sheet that is formed by melt-mixing and molding a polycarbonate resin and a transparent resin, in said stretched sheet dispersed phases that are configured of the transparent resin being dispersed in the form of particles in the continuous phase that is configured of the polycarbonate resin. In the polarizing element, the absolute value of the refractive index difference of the continuous phase between the stretching direction and the direction perpendicular to the stretching direction is less than 0.05, the absolute value of the refractive index difference of the dispersed phases between the stretching direction and the direction perpendicular to the stretching direction is not less than 0.05, the refractive index difference between the continuous phase and the dispersed phases with respect to linearly polarized light in the stretching direction is different from that in the direction perpendicular to the stretching direction, and the reflectance of polarized light parallel to the stretching direction is not less than 30%.

Description

Polarizing element and display device using the same

The present invention relates to a polarizing element having a light diffusing property and a polarizing property, 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 element.

Liquid crystal display devices generally use iodine or dye type absorption polarizing plates. Therefore, the brightness of the display surface is less than half the brightness of a light source such as outside light or irradiation light. Further, 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 prism method, the polarization depends on the angle and 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 is also 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, JP-A-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, this element is liable to produce voids between the polymer and the inorganic particles when the scattering particles are arranged in a certain direction, and cannot be manufactured stably. In addition, although the method of performing ultraviolet curing while arranging inorganic particles in the polymer by calendaring using a roller as a processing method that hardly generates voids, the polymer to be used is limited.

In US Pat. No. 4,871,784 (Patent Document 2), a second polymer composed of a crystalline polypropylene resin is dispersed in a first polymer composed of an aromatic polyester resin. A method of stretching the resulting sheet to produce microvoids is disclosed. However, the method of generating elliptical microvoids around the dispersion is difficult to control the polarization properties of the sheet because of the varying interface geometry.

JP-T-2000-506990 (Patent Document 3) discloses a first phase having a birefringence of at least about 0.05 and a refractive index difference between the first phase and the first phase. And a second phase that is greater than about 0.05 along the first axis and less than about 0.05 along a second axis that is orthogonal to the first axis, the optical body comprising: An optical body is disclosed wherein the diffuse reflectance as a whole of the first and second phases is at least about 30% along at least one axis for at least one polarization of electromagnetic radiation. This document describes a combination of 2,6-polyethylene naphthalate and polymethyl methacrylate or syndiotactic polystyrene as a combination of the first and second polymers. It also describes that a small amount of naphthalenedicarboxylic acid can be used to improve the adhesion between phases, and that a compatibilizing agent is used to form voids (voids).

However, when a sheet in which the polymer constituting the second phase is dispersed in the polymer constituting the first phase, the bonding force between the two polymers is weak, and the continuous phase and A small amount of voids are formed between the dispersed phase and the sheet cannot be stably produced. Moreover, although the example which uses a polystyrene glycidyl methacrylate as a compatibilizing agent is described, even if a compatibilizing agent is blended, an abrupt increase in viscosity and gelation occur at the end, and it is stable and smooth in appearance. An excellent sheet cannot be obtained.

Japanese Patent Application Laid-Open No. 2003-075643 (Patent Document 4) discloses a stable and uniform polarizing element that eliminates these problems, has excellent scattering characteristics and polarization characteristics, and does not generate voids. An element composed of a stretched sheet in which a disperse phase composed of a second transparent resin is dispersed in a continuous phase composed of one transparent resin in the form of particles, A polarizing element is disclosed in which the difference in refractive index between the two phases is different and a gap is not substantially generated between the two phases. This document describes blending a second transparent resin having an epoxy group or a compatibilizer having an epoxy group with the first transparent resin composed of a polyester-based resin.

However, even with this resin composition, a special method such as stretching at a high magnification of 4 times or more and roll rolling is required, and a polarizing element stretched at 4 times or more is easily torn. Further, when a special method such as roll rolling is not used, a general-purpose stretching machine cannot be used because high-strength stretching is necessary.

Japanese Patent Application Laid-Open No. 2008-129556 (Patent Document 5) discloses a scattering 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, even in this polarizing element, it is necessary to stretch at a high magnification of 4 times or more in order to improve the luminance. 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. For example, if the uniaxial stretching is performed, a wide stretched sheet can be easily produced from a narrow unstretched sheet. In addition, since the expensive polyester-based resin is used as the continuous phase, the material cost is high and the economy is low.

In general, inexpensive resin materials include polyolefin resins, polymethyl methacrylate resins, styrene resins, polycarbonate resins, etc., but the refractive index change caused by stretching is small, and the above-mentioned continuous phase However, it is not suitable for forming a polarizing element of a type that causes anisotropy of refractive index. That is, when an inexpensive material is used as a continuous phase, since many inexpensive materials have a small change in refractive index, it is required to obtain higher luminance by polarization conversion in such a material. Conventionally, however, a resin that is more flexible than the continuous phase has been used as the dispersed phase. However, although it is deformed into a rugby ball or rod shape by stretching, the deformation stress is small and the molecular chains are easily relaxed in orientation. In the disperse phase, it was considered that a large difference in refractive index did not occur even when stretched. Therefore, a polarizing element using a cheap material such as polycarbonate as a continuous phase is not known.

JP-A-9-297204 (Claims and Examples) US Pat. No. 4,871,784 (Claims) JP 2000-506990 A (Claims, Examples) JP 2003-075643 A (Claims, Examples) JP 2008-129556 A (Claims, paragraph [0024], Examples)

Accordingly, an object of the present invention is to provide a polarizing element capable of exhibiting excellent polarization characteristics and scattering characteristics by a simple method and a display device (display device such as a surface light source device or a liquid crystal display device) provided with the polarizing element. There is.

Another object of the present invention is to provide a polarizing element that can improve the luminance of the display device even at a low stretch ratio, and a display device including the polarizing element.

Still another object of the present invention is to provide a polarizing element having excellent polarization characteristics without causing lacerations or voids due to stretching, and a display device including the polarizing element.

Another object of the present invention is to inexpensively and easily manufacture the polarizing element and a display device including the polarizing element.

As a result of intensive studies to achieve the above-mentioned problems, the inventors of the present invention have achieved a simple method by uniaxially stretching a sheet in which the matrix phase (continuous phase) is composed of a polycarbonate-based resin and the dispersed phase is composed of a predetermined transparent resin. Thus, the inventors have found that excellent polarization characteristics and scattering characteristics can be expressed, and completed the present invention.

That is, the polarizing element of the present invention is an element composed of a stretched sheet in which a disperse phase composed of a transparent resin is dispersed in a continuous phase composed of a polycarbonate-based resin, and the continuous phase The in-plane birefringence of the dispersed phase is less than 0.05, the in-plane birefringence of the dispersed phase is 0.05 or more, and the difference in refractive index between the continuous phase and the dispersed phase with respect to linearly polarized light is the stretching direction and the stretching direction. It differs in the direction perpendicular to. In this polarizing element, the absolute value of the difference in refractive index between the continuous phase and the dispersed phase in the stretching direction is 0.1 to 0.3, and the refraction between the continuous phase and the dispersed phase in the direction perpendicular to the stretching direction. The absolute value of the rate difference may be 0.1 or less. The dispersed phase may have an average length of a major axis and a minor axis of 0.8 to 10 μm and 0.05 to 0.8 μm, respectively, and an average aspect ratio of 2 to 200. In the polarizing element of the present invention, the total light transmittance of linearly polarized light in the direction perpendicular to the stretching direction is 80% or more, and the reflectance of linearly polarized light in the direction parallel to the stretching direction (regular reflection component and backscattering). 30% or more may be sufficient as the reflectance by a component. The polycarbonate resin may be a bisphenol A type polycarbonate resin having a glass transition temperature of 120 to 160 ° C. The dispersed phase may be composed of a polyester resin (particularly, a polyalkylene naphthalate resin such as a polyethylene naphthalate resin). 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 includes a method of producing the polarizing element by uniaxially stretching a sheet formed by melting and mixing a polycarbonate resin and a transparent resin. In this method, uniaxial stretching may be performed 1.2 to 4 times at a temperature of Tg ° C. to (Tg + 80) ° C., where Tg is the glass transition temperature of the polycarbonate resin. Furthermore, you may heat-process at the temperature more than extending | stretching temperature.

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

In this specification, “film” is used to mean including a sheet regardless of thickness.

In the present invention, since the sheet in which the continuous phase is composed of polycarbonate resin and the dispersed phase is composed of a predetermined transparent resin is uniaxially stretched, excellent polarization characteristics and scattering characteristics can be expressed by a simple method. Moreover, even if it is a low draw ratio, the brightness | luminance of a display apparatus can be improved and a polarization characteristic can be improved, without generating a tear and a void by extending | stretching. Furthermore, according to the present invention, such an excellent polarizing element can be manufactured inexpensively and easily.

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.

[Polarizing element]
The polarizing element of the present invention is composed of a stretched sheet in which a dispersed phase composed of a transparent resin is dispersed in the form of particles in a continuous phase composed of a polycarbonate-based resin. That is, the polarizing element is formed of a continuous phase that forms a matrix (matrix) of the polarizing element and a dispersed phase that is present in the matrix and exhibits a polarizing function. The interface between the continuous phase and the dispersed phase is substantially free from voids, and the continuous phase and the dispersed phase are bonded or in close contact with each other.

(Continuous phase)
The continuous phase is composed of a polycarbonate resin, and has an in-plane birefringence (absolute value of the difference in refractive index between the stretching direction and the direction perpendicular to the stretching direction) of less than 0.05, for example, 0 to 0 0.03, preferably 0 to 0.02, more preferably about 0 to 0.01. In the present invention, the draw ratio can also be suppressed low. 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 and aliphatic polycarbonates such as diethylene glycol bisallyl carbonate. 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. [Eg bis (hydroxyaryl) C _1-10 alkanes, preferably bis (hydroxyaryl) C _1-6 alkanes], bis (hydroxyaryl) cycloalkanes such as bis (hydroxyphenyl) cyclohexane [eg bis (hydroxyaryl) (Hydroxyaryl) C _3-12 cycloalkanes, preferably bis (hydroxyaryl) C _4-10 cycloalkanes], di (hydroxyphenyl) ether such as 4,4′-di (hydroxyphenyl) ether 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 the 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 polycarbonate-based resin is selected from a range of about 10,000 to 200,000 (for example, 15,000 to 150,000) as a viscosity average molecular weight obtained from a viscosity measured in a methylene chloride solution having a concentration of 0.7 g / dL at 20 ° C., for example. For example, it is about 15,000 to 120,000, preferably about 17,000 to 100,000, more preferably about 18,000 to 50,000 (particularly 18,000 to 30,000). If the molecular weight of the polycarbonate-based resin is too small, the mechanical strength of the film tends to be lowered. If the molecular weight is too large, the melt fluidity is lowered, and the handleability during film formation and the uniform dispersibility of the dispersed phase are likely to be lowered.

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

The viscosity of the polycarbonate-based resin, using a rotary rheometer (Anton Paar Co. Ltd.), 270 ° C., measured at the conditions of a shear rate of 10 sec ^-1, for example, 100 ~ 1500 Pa · s, preferably 200 ~ 1200 Pa · s, more preferably about 300 to 1000 Pa · s (particularly 500 to 750 Pa · s).

The glass transition temperature of the polycarbonate-based resin can be selected, for example, from a range of about 110 to 250 ° C., but from the viewpoint that the stretching temperature can be set low and the selection range of the resin for the dispersed phase is expanded, for example, 110 to 180 ° C. The temperature is preferably 120 to 160 ° C, more preferably about 130 to 160 ° C (particularly 140 to 155 ° C). 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 of a polycarbonate resin and another resin (particularly a transparent resin) as long as the optical properties and mechanical properties of the polycarbonate resin are not impaired. As other resin (transparent resin etc.), the transparent resin etc. which comprise the continuous phase mentioned later are mentioned. The ratio of the other resin is, for example, 100 parts by weight or less, preferably 50 parts by weight or less, more preferably 10 parts by weight or less (for example, 0.1 to 10 parts by weight) with respect to 100 parts by weight of the polycarbonate resin. ) Specific examples of the polymer alloy include, for example, a polycarbonate resin composition disclosed in Japanese Patent Application Laid-Open No. 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 JP-A-11-3479969 (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 is incompatible with the polycarbonate-based resin constituting the continuous phase, and in-plane birefringence (the absolute value of the difference in refractive index between the refractive index in the stretching direction and the direction perpendicular to the stretching direction). ) Is not particularly limited as long as it is a transparent resin 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, more preferably about 0.15 to 0.3 (particularly 0.2 to 0.25). . In the present invention, the continuous phase is composed of a polycarbonate-based resin and the dispersed phase is composed of a transparent resin having a large intrinsic birefringence, so that a high degree of efficiency can be effectively achieved between the continuous phase and the dispersed phase at low magnification. An element having a refractive index difference and having high scattering characteristics and high polarization characteristics can be prepared.

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 resins, etc.), acrylic 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. It is included. 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. The polyalkylene arylate resin has, as a main component, an alkylene arylate unit, for example, at a ratio of 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. Examples of the copolymerizable monomer constituting the copolyester include dicarboxylic acid components (for example, C _8-20 aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, 2,7-naphthalenedicarboxylic acid, and 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 (eg, 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.

In the present invention, among these polyalkylene arylate resins, polyalkylene naphthalate has 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. Resin (especially poly C _2-4 alkylene naphthalate resin such as polyethylene naphthalate resin) is preferable. 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 polyester-based resin (for example, polyalkylene naphthalate-based resin) can be selected from the range of, for example, about 5,000 to 1,000,000 in terms of number average molecular weight, for example, 10,000 to 500,000, preferably 12,000 to 300,000, and more preferably 15,000. It is about ~ 100,000. If the molecular weight of the polyethylene naphthalate resin is too large, the melt fluidity is lowered and the aspect ratio of the dispersed phase tends to be lowered. The number average molecular weight can be measured in terms of polystyrene using gel permeation chromatography.

The viscosity of the polyester resin, by using a rotary rheometer (Anton Paar Co. Ltd.), 270 ° C., measured at the conditions of a shear rate of 10 sec ^-1, for example, 200 ~ 5000Pa · s, · preferably 300 ~ 4000 Pa s, more preferably about 500 to 3000 Pa · s (particularly 1000 to 2000 Pa · s).

The ratio of the viscosity of the polycarbonate resin is, for example, the viscosity of the polycarbonate resin / viscosity of the polyester resin = 2/1 to 1/10, preferably 2/1 to 1/5, more preferably 2/1 to 1. / 3 (particularly 1/1 to 1 / 2.5). When the ratio of the viscosities is in such a range, both resins are sufficiently mixed to form a dispersion layer having an appropriate size in the continuous phase, and the dispersion phase has an appropriate particle size. It can be controlled, and high in-plane birefringence can be imparted to the dispersed phase.

The glass transition temperature of the polyester-based resin (for example, polyalkylene naphthalate-based resin) can be selected from the range of, for example, about 50 to 200 ° C. From the viewpoint that the aspect ratio of the dispersed phase can be easily increased by stretching. The glass transition temperature is preferably lower than the glass transition temperature of the resin, for example, 1 to 100 ° C., preferably 5 to 80 ° C., more preferably 10 to 50 ° C. (especially 20 to 40 ° C.). Specifically, the glass transition temperature of the polyester resin is, for example, about 60 to 180 ° C., preferably about 80 to 150 ° C., more preferably about 90 to 130 ° C. (particularly about 100 to 120 ° C.). 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 average diameter in the major axis direction of the dispersed phase is 0.8 to 10 μm, preferably 1 to 5 μm, more preferably about 1.5 to 3 μm. The average diameter in the minor axis direction of the dispersed phase is 0.05 to 0.8 μm, preferably 0.1 to 0.7 μm, more preferably about 0.2 to 0.6 μm. The average aspect ratio of the dispersed phase is 2 to 1000 (for example, 2 to 200), preferably 3 to 500, more preferably 5 to 100 (especially 7 to 30). The dispersed phase is phase-separated from the continuous phase by stretching, and changes from a spherical shape to an anisotropic shape. The anisotropic shape may be, for example, a rugby ball shape (an ellipsoid such as a spheroid), a flat body, a rectangular parallelepiped shape, a fibrous shape, a filamentous shape, or the like. The average diameter of the dispersed phase before orientation processing by stretching may be, for example, about 0.3 to 3 μm.

The orientation coefficient as the degree of alignment of the particles constituting the dispersed phase is preferably as high as possible, for example, 0.34 or more (about 0.34 to 1), preferably 0.4 to 1 (eg 0.5 to 1), More preferably, it may be about 0.7 to 1 (particularly 0.8 to 1). Higher polarization characteristics can be imparted as the orientation coefficient of the dispersed phase particles is higher.

The orientation coefficient can be calculated based on the following formula.

Orientation coefficient = (3 <cos ² θ> −1) / 2
[Wherein θ represents the angle between the long axis of the particulate dispersed phase and the X axis of the film (when the long axis and the X axis are parallel, θ = 0 °), and <cos ² θ> represents each The average of cos ² θ calculated for the dispersed phase particles is shown and is represented by the following formula.

<Cos ² θ> = ∫n (θ) · cos ² θ · dθ
(In the formula, n (θ) represents the ratio (weight ratio) of dispersed phase particles having an angle θ in all dispersed phase particles)].

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, and 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 element can be obtained.

(Additive)
In the polarizing element of the present invention, the dispersed phase is bonded or closely adhered to the continuous phase without substantially generating 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, polyester elastomers, compatibilizers having an epoxy group in the main chain, particularly epoxy-modified aromatic vinyl-diene block copolymers [for example, epoxidized styrene-butadiene-styrene (SBS) block copolymers And an epoxidized styrene-diene copolymer or an epoxy-modified styrene-diene copolymer such as an epoxidized styrene-butadiene block copolymer (SB)]. 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 compatibilizing agent is, for example, as a ratio (weight ratio) to the dispersed phase, dispersed phase / compatibilizing agent (weight ratio) = 99/1 to 50/50, preferably 99/1 to 70/30, more preferably Is about 98/2 to 80/20. Further, the proportion of the compatibilizer is, for example, 0.1 to 20 parts by weight, preferably 0.5 to 15 parts by weight, more preferably 1 to 10 parts by weight with respect to 100 parts by weight of the total of the continuous phase and the dispersed phase. About a part.

The polarizing element 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 element)
In the polarizing element of the present invention, the refractive index difference between the continuous phase and the dispersed phase with respect to the linearly polarized light is large in the sheet stretching direction (hereinafter sometimes referred to as “X-axis direction”) and is perpendicular to the stretching direction. The direction (hereinafter, sometimes referred to as “Y-axis direction”) is small. Therefore, the polarizing element has a property of scattering polarized light in a direction in which the refractive index difference is large. A part of the polarized light is scattered in front of the stretched sheet, and the remaining polarized light is scattered behind the stretched sheet. Not absorbed. Further, polarized light in a direction with a small difference in refractive index has a characteristic of almost transmitting. That is, the polarizing element greatly scatters linearly polarized light in the stretching direction, and linearly polarized light in a direction perpendicular to the stretching direction scatters less than or substantially not in the stretching direction.

Regarding the refractive index difference, the absolute value of the refractive index difference between the continuous phase and the dispersed phase in the X-axis direction is 0.1 or more (for example, 0.1 to 0.5), preferably 0.1 to 0.3. More preferably, it is about 0.1 to 0.2, and the absolute value of the refractive index difference between the continuous phase and the dispersed phase in the Y-axis direction may be 0.1 or less, for example, 0.05 or less It is 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. .

In the polarizing element having the refractive index difference, the continuous phase and the disperse phase have a small refractive index anisotropy at the stage of film formation (so-called cast sheet) and have substantially the same refractive index. It is preferable to have it. For example, the absolute value of the difference in refractive index between the polycarbonate resin before stretching and the transparent resin constituting the dispersed phase may be 0.05 or less, preferably 0.04 or less, and more preferably 0.03 or less. When the refractive index difference between the two resins before stretching is in this range, the anisotropy of the refractive index difference can be easily expressed by stretching.

Generally, it is known that when a cast sheet is uniaxially stretched, the refractive index is remarkably increased in the stretch direction of the continuous phase (X-axis direction). A polarizing element is prepared by increasing the refractive index in the X-axis direction of a transparent resin in a continuous phase without significantly changing the refractive index in the Y-axis direction. On the other hand, in the polarizing element of the present invention, the change in refractive index is small even when the continuous phase is in the X-axis direction, and the refractive index of the fine particle dispersed phase is remarkably changed between the X-axis direction and the Y-axis direction. That is, while the continuous phase does not cause a large difference in refractive index due to stretching, the dispersed phase deforms into an anisotropic shape such as a rugby ball shape or a rod shape due to stretching and also causes a large difference in refractive index.

Therefore, in the polarizing element of the present invention, due to uniaxial stretching, the refractive index of the continuous phase and the disperse phase are greatly different in the X-axis direction and substantially coincide with each other in the Y-axis direction. As a result, a polarizing element having a characteristic that the polarized light in the direction having substantially the same refractive index is substantially transmitted and the polarized light in the direction having a different refractive index is scattered is produced.

In the present invention, unlike the conventional polarizing element, the disperse phase has a large difference in refractive index between the X-axis direction and the Y-axis direction. In the axial direction, the greater the difference in refractive index between the continuous phase and the dispersed phase, the greater the scattering property for polarized light in that direction, and the ratio of backscattering (reflected light) also increases. On the other hand, if the refractive index of the continuous phase and the refractive index of the disperse phase completely coincide, the polarized light in the Y-axis direction is transmitted as a complete transparent body without being scattered. In the present invention, the refractive index difference in the Y-axis direction can be selected according to the application, and by using a transparent resin in which the refractive index difference before stretching is in the above-described range, the refractive indexes of both phases are substantially matched, The transmission / scattering property in the Y-axis direction may be improved. On the other hand, the diffusion effect may be reduced by making the refractive indexes of both phases slightly different.

Since the polarizing element of the present invention has such a refractive index difference, the total light transmittance in the Y-axis direction is high, for example, 80% or more (for example, 80 to 99%), preferably 82 to 98%, More preferably, it is about 85 to 95%. Further, when used as a diffusion sheet, the diffuse light transmittance in the Y-axis direction is, for example, 30% or more (for example, 30 to 90%), preferably 40 to 80%, more preferably about 50 to 70%. When not used as a diffusion sheet, for example, it may be 30% or less, preferably 20% or less, and more preferably 10% or less.

On the other hand, the polarizing element of the present invention has excellent scattering characteristics in the X-axis direction, and the total light transmittance in the X-axis direction is 75% or less (for example, 10 to 75%), preferably 70% or less (for example, 20 to 70%), more preferably 60% or less (25 to 60%). That is, the polarizing element of the present invention has a high reflectance (backscattering rate), and the reflectance in the stretching direction (backscattering rate) is 25% or more (for example, 25 to 90%), preferably 30% or more ( For example, 30 to 80%), more preferably 40% or more (for example, 40 to 75%), particularly 50% or more (for example, 50 to 70%) may be used.

That is, the polarizing element of the present invention has a total light transmittance in the Y-axis direction of 80% or more and a reflectance in the X-axis direction (reflectance due to regular reflection components and backscattering components) of 30% or more. In order to impart light diffusion and polarization to transmitted light, it has properties similar to those of an 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 in luminance, the polarizing element of the present invention can be used as a luminance improvement sheet for liquid crystal display devices and the like.

The total light transmittance and the diffuse light transmittance are measured using a polarization measuring device (haze meter) (manufactured by Nippon Denshoku Industries Co., Ltd., NDH-300A), as described in Examples below. The total light can be measured by a method according to JIS K7361-1, and the haze (diffused light) can be measured by a method according to JIS K7136.

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

The polarizing element 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 element 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 element 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 preferred transparent resin layer is formed of the same series (particularly the same) polycarbonate resin 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 the same as that of the polarizing element, for example. In particular, when the thickness of the polarizing element layer is about 3 to 500 μm, the thickness of the transparent resin layer can be selected from about 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 element and the total thickness of the transparent resin layer can be selected, for example, from the range of polarizing element / 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.

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

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

Next, the orientation treatment of the dispersed phase is performed by, for example, (1) a method of stretching an extruded sheet, (2) a method of forming a film while drawing the extruded sheet, solidifying the sheet, and then stretching the sheet. Can do. In order to express the excellent characteristics of the polarizing element of the present invention, a cast obtained by solidifying and cooling a sheet in which a dispersed phase, which is a transparent resin, is dispersed in a continuous phase, which is a polycarbonate-based resin, is formed by the melt film formation. It is preferable to reheat the sheet and then perform orientation processing by stretching.

The stretching may be simple free width uniaxial stretching or constant width (fixed width) uniaxial stretching. The uniaxial stretching method is not particularly limited. For example, a method of pulling both ends of a solidified film (tensile stretching), and a plurality of series (for example, two series) of a pair of opposed rolls (two rolls) are prepared in parallel. The film is inserted between the two rolls on the feeding side and the two rolls on the feeding side, and the film feeding speed of the two rolls on the feeding side is set. A method of stretching by making it faster than two rolls on the feeding side (stretching between rolls), a method of inserting a film between a pair of rolls facing each other, rolling the film with a roll pressure (roll rolling), and a tenter method Examples include fixed width uniaxial stretching.

Of these uniaxial stretches, a free-width uniaxial stretch can be preferably used from the viewpoint that tensile stretching, in particular, the deformation can be surely generated in the dispersed phase and the in-plane birefringence of the dispersed phase can be increased.

Also, fixed width uniaxial stretching by a tenter method can be preferably used. Fixed-width uniaxial stretching by the tenter method is different from free-width uniaxial stretching in which the width in the direction perpendicular to the stretching direction decreases with stretching and the thickness tends to be non-uniform across the entire width. This is a method that 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 uniaxial stretching by the tenter method, the stretching direction may be the sheet flow direction or the sheet width direction. When the flow direction is set, the production speed is improved, but in order to obtain a polarizing element having a desired width, it is necessary to increase the width of the cast sheet. On the other hand, when the width direction is set, since the film is stretched in the horizontal direction, a polarizing element having a desired width can be obtained even if the width of the cast sheet is small, but the production speed is lowered. These methods can be selected according to the application. In the uniaxial stretching by the tenter method, the tensile speed can be selected from the range of, for example, about 50 to 1000 mm / min depending on the stretching temperature and the magnification, for example, 100 to 800 mm / min, preferably 150 to 700 mm / min, Preferably, it is about 200 to 600 mm / min (particularly 400 to 600 mm / min).

The stretching temperature is preferably a temperature equal to or higher than the glass transition temperature of the polycarbonate resin. When the glass transition temperature of the polycarbonate resin is Tg, for example, Tg to (Tg + 80) ° C., preferably (Tg + 5) to (Tg + 50) ° C. More preferably, the temperature may be as high as (Tg + 5) to (Tg + 30) ° C. [particularly (Tg + 8) to (Tg + 20) ° C.]. The specific stretching temperature may be, for example, about 120 to 180 ° C., preferably 150 to 175 ° C., more preferably about 150 to 170 ° C. (especially 160 to 170 ° C.).

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. It may be about 2 to 5 times (for example, 1.5 to 4 times), preferably about 2 to 4 times, more preferably about 2.5 to 3.8 times (especially 2.5 to 3.5 times). . 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 the primary stretching by the tenter method described above.

The polarizing element of the present invention is subjected to tension heat treatment (heat treatment while maintaining the length of the sheet) at a stretching temperature or a temperature higher than the stretching temperature in order to relax the birefringence of the continuous phase and develop 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 the stretching temperature to a temperature that is about 50 ° C. higher than the stretching temperature, and may be, for example, a temperature that is about 30 ° C. higher than the stretching temperature. Substantially the same temperature may be used. 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, when the temperature is about 165 ° C., 2 to 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 element and strength can be improved.

The laminated film is obtained by laminating a transparent resin layer on at least one surface of the polarizing element layer by a conventional method, for example, a coextrusion molding method, a laminating method (extrusion laminating method, dry laminating method, etc.), or the like. 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 element disposed on the side. In the surface light source device, the polarizing element 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 in which luminance is improved using the polarizing element 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 element 5 disposed between the cell 7 and a diffusion sheet 6 that diffuses light transmitted through the polarizing element 5 is 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 element 5, the emitted light is almost transmitted through the polarizing element 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 element 5 and is transmitted therethrough. The light whose polarization direction has not changed is reflected again by the polarizing element 5, but the light whose polarization direction has been rotated again by 90 degrees due to reflection by the reflecting plate 3 passes through the polarizing element 5. The light that has passed through the polarizing element 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 element 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 element of the present invention used for this application has a total light transmittance of linearly polarized light in the Y-axis direction of 80% or more, and the reflectance of linearly polarized light in the X-axis direction (reflectance by regular reflection component and backscattering component). 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 element 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 improvement effect of the polarizing element 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 element of the present invention and the reflecting plate, and the polarizing element 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 element 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 element 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 absorptive polarizing plate 18 for guiding light to the liquid crystal cell 17 and a polarizing element 15 disposed between the reflecting plate 13 and the liquid crystal cell 17 for scattering light emitted from the reflecting plate 13 are provided. Yes.

In the reflective liquid crystal display device 10, only the light having the same polarization axis as that of the polarizing plate is transmitted among the external light incident on the absorption polarizing plate 18 and reaches the liquid crystal cell 17. The light incident on the liquid crystal cell 17 rotates the polarization direction and reaches the polarizing element 15.

When the display of the liquid crystal cell is a dark display, the polarizing element 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 element 15. The polarized light that has passed through the absorptive polarizing plate 18 passes through the polarizing element 15 again, and the direction of the polarized light is rotated by the liquid crystal cell 17 and becomes a direction perpendicular to the polarizing axis of the absorptive 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 element 15 is arranged so that the polarization direction of the external light that has passed through the liquid crystal cell 17 coincides with the X-axis direction of the polarizing element 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 element 15 without rotating the polarization direction in the liquid crystal cell 17. The polarized light incident on the polarizing element 15 is scattered in the reflection direction or the transmission direction. The light scattered in the transmission direction is reflected by the reflecting plate 13, merged with the light already scattered by the polarizing element 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 element 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 element 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. Further, 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 element 25. When the polarizing element 25 is arranged so that the direction of the linearly polarized light passing therethrough coincides with the Y-axis direction of the polarizing element 8, the polarized light emitted from the polarizing element 25 is reflected 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 element 25. The incident light becomes polarized light in the X-axis direction of the polarizing element 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 element 25. The incident light passes through the polarizing element 25 as it is, with the polarization in the Y-axis direction intact, but the polarization in the X-axis direction is scattered. Next, the polarized light emitted from the polarizing element 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 element 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 element of the present invention is used, high scattering and polarization 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 element 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 prism couplers (Metricon Corporation) with respect to the stretching direction (X-axis direction) and the vertical direction (Y-axis direction) when each resin single sheet is stretched under the same conditions as in Examples and Comparative Examples. And made 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., NDH-300A), all rays were measured by a method according to JIS K7361-1, and haze (diffuse rays) was measured according to JIS K7136. Measured by different methods. Measurement is performed by inserting an absorption type polarizing plate on the light source side, inserting only the linearly polarized light that vertically polarizes the light source, and inserting the polarizing elements of Examples and Comparative Examples, and the total light transmittance for the polarized light of the polarizing element, Diffuse light transmittance and total light reflectance (total light reflectance = 1−calculated by 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 3), the refractive index between the continuous phase and the dispersed phase. The measurement was performed for the case where the direction in which the difference was large coincided with the polarization axis of the absorption polarizing plate (“vertical” in Table 3).

[Evaluation of brightness improvement]
Using a polarization measuring device (NDH-300A, manufactured by Nippon Denshoku Industries Co., Ltd.), a reflector and an absorption polarizing plate are inserted on the light source side, and the total light transmittance is measured. did. The polarizing elements of Examples and Comparative Examples were inserted between the reflecting plate and the absorbing polarizing plate so that the direction in which the refractive index difference between the continuous phase and the dispersed phase is small and the transmission direction of the absorbing polarizing plate coincided with each other. The transmittance was measured. A value obtained by normalizing the measured value with respect to the previous reference value as shown in the following formula was defined as the luminance improvement degree.

(Brightness improvement level) = [(measured value) / (reference value)] × 100.

[Trouser tearing]
The tear strength was determined by a trouser tear method according to JIS K7128-1. Under constant temperature conditions (23 ° C., relative humidity 50%), a test piece was cut into a predetermined size, a 75 mm slit was inserted in the stretching direction, and a tear test was performed at a speed of 200 mm / min. 20 mm at the start of tearing and 5 mm before the end of tearing were excluded, and the average value of the remaining 50 mm tear strength was obtained. The test was performed at N = 5, and the average value was obtained.

Example 1
Polyethylene naphthalate resin (PEN, manufactured by Teijin Chemicals Ltd., “Teonex TN8065S”, viscosity at 270 ° C. and shear rate of 10 sec ⁻¹ ) 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 preheated at 165 ° C. for 5 minutes at 50 mm between chucks using a tensile tester (Orientec Co., Ltd., Tensilon UCT-5T) equipped with a constant temperature unit. Thereafter, the film was stretched 3.5 times at a pulling speed of 500 mm / min, heat-treated at 165 ° C. for 3 minutes while being held in the chuck, and then rapidly cooled to room temperature to obtain a stretched sheet.

Example 2
A stretched sheet was produced in the same manner as in Example 1 except that a press sheet having a thickness of 500 μm was produced by press molding.

Example 3
A stretched sheet was produced in the same manner as in Example 1 except that a press sheet having a thickness of 500 μm was prepared by press molding and the obtained sheet was stretched 5 times.

Example 4
A stretched sheet was produced in the same manner as in Example 1 except that a press sheet having a thickness of 500 μm was produced by press molding and the obtained sheet was stretched three times.

Example 5
A stretched sheet was produced in the same manner as in Example 1 except that a press sheet having a thickness of 300 μm was produced by press molding and the obtained sheet was stretched twice.

Example 6
In the same manner as in Example 1, a press sheet having a thickness of 300 μm was produced by press molding. The obtained sheet was cut into a width of 40 mm and a length of 70 mm, and pre-heated at 155 ° C. for 5 minutes at 50 mm between chucks using a tensile tester equipped with a constant temperature unit, and then stretched twice at a tensile rate of 200 mm / min. Then, after being heat-treated at 155 ° C. for 3 minutes while being held on the chuck, it was rapidly cooled to room temperature to obtain a stretched sheet.

Example 7
5 parts by weight of polyethylene naphthalate resin as the resin constituting the dispersed phase and 95 parts by weight of bisphenol A type polycarbonate resin as the resin constituting the continuous phase are melt kneaded at a cylinder temperature of 280 ° C. using a twin screw extruder. Extruded and cooled to produce pellets. The obtained pellets were press-molded for 3 minutes at a pressure of 270 ° C. and 10 MPa using a small press machine to produce a press sheet having a thickness of 300 μm. The obtained sheet was cut into a width of 40 mm and a length of 70 mm, and pre-heated at 155 ° C. for 5 minutes at 50 mm between chucks using a tensile tester equipped with a constant temperature unit, and then stretched twice at a tensile rate of 200 mm / min. Then, after being heat-treated at 155 ° C. for 3 minutes while being held on the chuck, it was rapidly cooled to room temperature to obtain a stretched sheet.

Example 8
In the same manner as in Example 1, a press sheet having a thickness of 300 μm was produced by press molding. The obtained sheet was cut into a width of 40 mm and a length of 70 mm, and pre-heated at 155 ° C. for 5 minutes at 50 mm between chucks using a tensile tester equipped with a constant temperature unit, and then stretched twice at a tensile rate of 200 mm / min. Thereafter, it was rapidly cooled to room temperature to obtain a stretched sheet.

Comparative Example 1
8 parts by weight of polystyrene resin (PS, manufactured by Toyo Styrol Co., Ltd., “GPMW4D”) as the resin constituting the dispersed phase, 92 parts by weight of polyethylene naphthalate resin as the resin constituting the continuous phase, It was melted and kneaded at a cylinder temperature of 280 ° C., extruded, and cooled to produce pellets. The obtained pellets were press-molded for 3 minutes at a pressure of 270 ° C. and 10 MPa using a small press machine to produce a press sheet having a thickness of 550 μm. The obtained sheet was cut into a width of 40 mm and a length of 70 mm, and preheated at 133 ° C. for 5 minutes using a tensile tester equipped with a thermostatic unit, and then stretched 4 times at a pulling rate of 100 mm / min. Thereafter, it was rapidly cooled to room temperature to obtain a stretched sheet.

Comparative Example 2
A stretched sheet was produced in the same manner as in Comparative Example 1 except that the press sheet was stretched 5 times.

Comparative Example 3
A stretched sheet was produced in the same manner as in Comparative Example 1 except that the press sheet was stretched 6 times.

Comparative Example 4
A press sheet obtained in the same manner as in Comparative Example 1 was cut into a width of 40 mm and a length of 70 mm, and pre-heated at 133 ° C. for 5 minutes with a chuck of 50 mm between chucks and a tensile speed. The film was stretched 5 times at 100 mm / min and then heat treated at 133 ° C. for 3 minutes while being held on the chuck, and then rapidly cooled to room temperature to obtain a stretched sheet.

Comparative Example 5
4 parts by weight of polystyrene resin as the resin constituting the dispersed phase and 96 parts by weight of polyethylene naphthalate resin as the resin constituting the continuous phase were melt kneaded and extruded at a cylinder temperature of 280 ° C. using a twin screw extruder, Cooled to produce pellets. The obtained pellets were press-molded for 3 minutes at a pressure of 270 ° C. and 10 MPa using a small press machine to produce 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 preheated at 133 ° C. for 5 minutes using a tensile tester equipped with a thermostatic unit, and then stretched 6 times at a pulling rate of 100 mm / min. Thereafter, it was rapidly cooled to room temperature to obtain a stretched sheet.

Comparative Example 6
12 parts by weight of polystyrene resin as the resin constituting the dispersed phase and 88 parts by weight of polyethylene naphthalate resin as the resin constituting the continuous phase were melt-kneaded and extruded at a cylinder temperature of 280 ° C. using a twin screw extruder, Cooled to produce pellets. The obtained pellets were press-molded for 3 minutes at a pressure of 270 ° C. and 10 MPa using a small press machine to produce 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 preheated at 133 ° C. for 5 minutes using a tensile tester equipped with a thermostatic unit, and then stretched 6 times at a pulling rate of 100 mm / min. Thereafter, it was rapidly cooled to room temperature to obtain a stretched sheet.

Table 1 shows the blending composition, stretching temperature and magnification, heat treatment temperature, and stretched sheet thickness in Examples 1 to 8 and Comparative Examples 1 to 6. Table 2 shows the results of measurement of the average diameter and refractive index of the dispersed phase in the raw sheet and stretched sheet. Further, Table 3 shows the results regarding the total light transmittance, reflectance, diffused light transmittance, brightness enhancement degree, and trouser tear of the stretched sheet.

As is clear from the table, the polarizing elements of the examples can improve luminance and have high tear strength. In particular, the polarizing elements of Examples 1 and 2 exhibit high brightness enhancement and scattering characteristics despite the draw ratio of 3.5. On the other hand, although the polarizing element of the comparative example has a low tear strength and a high draw ratio, the brightness improvement degree and the scattering characteristics are not sufficiently improved. Furthermore, whitening was observed in the polarizing elements of the comparative examples (particularly Comparative Examples 3, 5 and 6) due to the generation of voids.

The polarizing element 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 ... Reflective member or reflective layer 4 ... Light guide plate 5,15,25 ... Polarizing element 6 ... Diffusion sheet 7,17,27 ... Liquid crystal cell 18 ... Absorption type polarizing plate 29 ... 1/4 wavelength plate

Claims (13)

1. A polarizing element composed of a stretched sheet in which a dispersed phase composed of a transparent resin is dispersed in a continuous phase composed of a polycarbonate-based resin, wherein the in-plane birefringence of the continuous phase is 0.00. Is less than 05, the in-plane birefringence of the dispersed phase is 0.05 or more, and the refractive index difference 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. Different polarizing elements.
2. The absolute value of the refractive index difference between the continuous phase and the dispersed phase in the 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 direction perpendicular to the stretching direction. The polarizing element according to claim 1, wherein is 0.1 or less.
3. The average length of the major axis and the minor axis of the dispersed phase is 0.8 to 10 µm and 0.05 to 0.8 µm, respectively, and the average aspect ratio of the dispersed phase is 2 to 200. Polarizing element.
4. 4. The total light transmittance of linearly polarized light in a direction perpendicular to the stretching direction is 80% or more, and the reflectance of linearly polarized light in a direction parallel to the stretching direction is 30% or more. A polarizing element according to 1.
5. 5. The polarizing element according to claim 1, wherein the polycarbonate resin is a bisphenol A type polycarbonate resin having a glass transition temperature of 120 to 160 ° C.
6. 6. The polarizing element according to claim 1, wherein the dispersed phase is composed of a polyester resin.
7. 7. The polarizing element according to claim 1, wherein the dispersed phase is composed of a polyalkylene naphthalate resin.
8. The polarizing element according to any one of claims 1 to 7, wherein the ratio of the continuous phase to the dispersed phase is continuous phase / dispersed phase = 99/1 to 50/50 (weight ratio).
9. A method for producing a polarizing element according to claim 1, wherein a sheet formed by melting and mixing a polycarbonate-based resin and a transparent resin is uniaxially stretched.
10. The method according to claim 9, wherein the polycarbonate resin is uniaxially stretched 1.2 to 4 times at a temperature of Tg ° C to (Tg + 80) ° C, where Tg is a glass transition temperature.
11. Furthermore, the method of Claim 9 or 10 which heat-processes at the temperature more than extending | stretching temperature.
12. A surface light source device comprising the polarizing element according to any one of claims 1 to 8.
13. A liquid crystal display device comprising the polarizing element according to any one of claims 1 to 8.

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