JP2008164930A - Scatter type polarizer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To increase the brightness enhancement rate of a scatter type polarizer having a phase separation structure composed of two kinds of polymers by investigating factors negatively influencing the enhancement of the brightness. <P>SOLUTION: A composition including a polyester type resin (A) composing a continuous phase and a polystyrene type resin (B) composing a dispersion phase is formed into a film, and the obtained cast sheet is stretched to make a scatter type polarizer, wherein the crystallization temperature of the polystyrene type resin (B) is 20 °C or lower when the scatter type polarizer is cooled at a temperature fall rate of 20 °C/min in a differential scanning calorimetry. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a scattering polarizer that can be used as a brightness enhancement film, and more specifically, a scattering type having scattering anisotropy that transmits only light in a specific polarization direction and reflects light in other polarization directions. It relates to a polarizer.

  As a configuration example of a liquid crystal display (LCD), as shown in FIG. 1, on the back side (back side) of the liquid crystal cell, a glass substrate, a polarizing film, a brightness enhancement film, a diffusion film, a cold cathode tube (backlight unit), A configuration obtained by sequentially stacking reflection sheets and the like can be exemplified.

  In such a configuration, the polarizing film transmits only light of a specific polarization direction (linearly polarized light) and supplies it to the liquid crystal cell, and absorbs light of other polarization directions. The amount of light supplied decreases and the image becomes dark. Therefore, as described above, by arranging a brightness enhancement film on the light source side of the polarizing film, the amount of light that can be supplied to the liquid crystal cell can be increased by increasing the amount of light in the polarization direction that the polarizing film transmits, thereby brightening the image. To be done.

  As this kind of brightness enhancement film, a film using a scattering polarizer is known. When a scattering polarizer is used as a brightness enhancement film, if the polarization direction of light passing through the brightness enhancement film matches the polarization direction of light passing through the polarization film, light in the polarization direction absorbed by the polarization film can be obtained. The light is reflected on the light source side by the brightness enhancement film on the near side, and while the reflection and scattering are repeated between the brightness enhancement film and the reflection sheet, the polarization direction of the light changes and passes through the polarization film. As a result, the luminance of the image can be improved.

As such a scattering-type polarizer, for example, as disclosed in Patent Document 1, a polarizer in which films made of a polyester resin or the like are multilayered is known.
In addition, a scattering polarizer is known in which a polymer blend having a phase separation structure composed of two types of polymers having different birefringence is uniaxially stretched. Such a scattering type polarizer has scattering anisotropy in which the degree of scattering of polarized light is different between the stretching direction and the perpendicular direction, and therefore selectively transmits light in a specific polarization direction and light in other polarization directions. Can be selectively reflected or scattered. For example, in Patent Document 2, a sheet in which a second polymer such as polymethyl methacrylate or syndiotactic polystyrene is dispersed in a first polymer made of 2,6-polyethylene naphthalate or the like is stretched. Is disclosed.

Japanese National Patent Publication No. 9-506985 JP 2000-506990 A

  According to the present invention, in a scattering polarizer having a phase-separated structure composed of two types of polymers, it is possible to further improve the luminance by investigating factors that have a negative effect on luminance enhancement and reducing such factors. It is intended to provide a scattering polarizer.

  The inventor forms a composition containing the polyester resin (A) constituting the continuous phase and the polystyrene resin (B) constituting the dispersed phase, and when stretching the obtained cast sheet, It has been found that as crystallization progresses during stretching, the haze of the stretched sheet is reduced, and this has a negative effect on luminance improvement.

  Therefore, the present invention is formed by forming a composition containing a polyester resin (A) constituting a continuous phase and a polystyrene resin (B) constituting a dispersed phase, and stretching the obtained cast sheet. It is a scattering type polarizer, Comprising: In differential scanning calorimetry, the crystallization temperature of polystyrene-type resin (B) when cooling a scattering type polarizer with the temperature-fall rate of 20 degrees C / min is 200 degrees C or less. A characteristic scattering polarizer is proposed.

Moreover, when such a scattering-type polarizer pays attention to the cast sheet before extending | stretching, in the differential scanning calorimetry, the polystyrene-type resin (B) when the said cast sheet is heated with the temperature increase rate of 10 degrees C / min. It was found that the crystallization start temperature of was 150 ° C. or higher.
Therefore, the present invention is formed by forming a composition containing a polyester resin (A) constituting a continuous phase and a polystyrene resin (B) constituting a dispersed phase, and stretching the obtained cast sheet. It is a scattering type polarizer, and in the differential scanning calorimetry, the crystallization start temperature of the polystyrene resin (B) when the cast sheet is heated at a heating rate of 10 ° C./min is 150 ° C. or higher. We also propose a scattering polarizer characterized by

  With such a scattering-type polarizer, the haze is significantly low, and when incorporated in a liquid crystal display or the like as a brightness enhancement film, it is possible to further improve the image clarity and further increase the brightness improvement rate. be able to.

In the present invention, the form of the scattering polarizer is not particularly limited, and includes a plate form, a sheet form, a film form, a pellet form, and other forms.
In general, the term “sheet” refers to a product that is thin according to the definition in JIS and usually has a thickness that is small and flat for the length and width. In general, “film” refers to the length and width. Is a thin flat product whose thickness is extremely small compared to the standard, and the maximum thickness is arbitrarily limited. Usually, it is supplied in the form of a roll (Japanese Industrial Standard JISK6900). In the present invention, it is not necessary to distinguish between the two, and therefore, in the present invention, the term “film” includes “sheet”, and the term “sheet” includes “film”. Shall be.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail below, but the scope of the present invention is not limited to the embodiments described below.
In this specification, “X to Y” (X and Y are arbitrary numbers) is intended to mean “X or more and Y or less” unless otherwise specified, and simultaneously “greater than X and less than Y”. The intention of “preferably” is also included.

  The scattering polarizer according to the present embodiment (hereinafter referred to as “the present polarizer”) contains a polyester resin (A) constituting a continuous phase and a polystyrene resin (B) constituting a dispersed phase. It can be obtained by forming an article into a sheet and stretching the obtained sheet.

  Examples of the polyester resin (A) that can constitute the continuous phase include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, and naphthalenedicarboxylic acid, or esters thereof, ethylene glycol, diethylene glycol, 1,4-butanediol, neo Aromatic polyester resin obtained by polycondensation with glycols such as pentyl glycol and 1.4 cyclohexanedimethanol, aliphatic polyester resin obtained by ring-opening polymerization of lactone, such as polyε-caprolactam, polyethylene adipate, polyethylene Azelate, polyethylene succinate, polybutylene adipate, polybutylene azelate, polybutylene succinate, polybutylene succinate adipate, polytetramethylene succinate, cyclohexanedicarboxylic acid / An aliphatic polyester resin obtained by polymerizing a dibasic acid and a diol, such as chlorohexanedimethanol condensate, an aliphatic polyester resin obtained by polymerizing a hydroxycarboxylic acid such as polylactic acid or polyglycol, and the aliphatic polyester Examples thereof include aliphatic polyester resins in which a part of ester bonds, for example, 50% or less of all ester bonds are replaced with amide bonds, ether bonds, urethane bonds, and the like.

Among them, preferred is a crystalline polyester containing an aromatic molecule, such as polyethylene terephthalate (PET), polytrimethylene terephthalate, polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN). it can. Among these, a polymer blend or copolymer (copolymer) comprising a combination of two or more types is also preferred.
Among these, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or a copolymer thereof is particularly preferable.

  A commercial item can also be used as said polyethylene naphthalate (PEN). For example, Teonex TN8065S (polyethylene naphthalate homopolymer, manufactured by Teijin Chemicals Ltd., intrinsic viscosity 0.71 dl / g), Teonex TN8065SC (polyethylene naphthalate homopolymer, manufactured by Teijin Chemicals Ltd., intrinsic viscosity 0.55 dl / g) g), Teonex TN8756C (polyethylene naphthalate and polyethylene terephthalate copolymer, manufactured by Teijin Chemicals Ltd., intrinsic viscosity 0.65 dl / g) and the like can be mentioned as preferred examples.

  The weight average molecular weight of the polyester-based resin (A) that can constitute the continuous phase is preferably 30,000 or more, the intrinsic viscosity is preferably 0.5 dl / g or more, and the glass transition temperature is 70 ° C to 120 ° C. The range is preferable, and the melting point is preferably in the range of 240 ° C to 270 ° C.

  On the other hand, the polystyrene resin (B) capable of constituting the dispersed phase is a polymer having styrene and may be a homopolymer or copolymer of styrene monomer or a polymer blend thereof, such as polystyrene, styrene-acrylonitrile. Examples thereof include a copolymer, a styrene- (meth) acrylic acid ester copolymer, and a styrene-maleic anhydride copolymer. Further, examples of the polystyrene include polystyrene having an atactic structure, polystyrene having an isotactic structure, polystyrene having a syndiotactic structure, and among these, polystyrene having an atactic structure (simply “polystyrene” or “PS”). ), A syndiotactic polystyrene (hereinafter also referred to as “sPS”) is preferable, and sPS is particularly preferable.

Among the above sPS, syndiotactic polystyrene obtained by copolymerization of styrene and paramethylstyrene is preferable, and particularly styrene and paramethylstyrene are 99: 1 to 75:25, especially 99: 1 to 80:20, Among these, syndiotactic polystyrene obtained by copolymerization at a molar ratio of 99: 1 to 90:10 is preferable.
Such syndiotactic polystyrene is particularly excellent in dispersibility with respect to the polyester resin (A) constituting the continuous phase, the crystallization temperature described below is 200 ° C. or lower, and the crystallization start temperature is 150 ° C. The brightness of the scattering polarizer can be further improved by affecting the temperature.

The polystyrene-based resin (B) preferably has a weight average molecular weight of 250,000 or more, particularly preferably 250,000 to 350,000, and more preferably 270,000 to 300,000.
The melt index (MI) of the polystyrene resin (B) is preferably 10 g / 10 min or less, particularly preferably 2 to 10 g / 10 min, and more preferably 4 to 10 g / 10 min. In addition, this melt index (MI) is a measured value based on the conditions of temperature 300 degreeC and load 1.2kg based on JISK-7210.

The polystyrene resin (B) preferably has a melting point of 260 ° C. or lower, particularly preferably 240 to 260 ° C., particularly preferably 240 to 250 ° C.
Moreover, it is preferable that the glass transition temperature of a polystyrene-type resin (B) is 90-100 degreeC, especially 90-95 degreeC.

As a preferable combination of the polyester resin (A) and the polystyrene resin (B), the refractive index in one direction X after stretching is substantially the same among the above resins, more specifically, the difference in refractive index. Is within 0.05, preferably within 0.01, and the refractive index difference in the direction Y perpendicular to the direction X is large. For example, the refractive index difference is 0.1 or more, preferably 0.3 or more. It is preferable to select and use a combination. From this viewpoint, polyethylene naphthalate (PEN) and syndiotactic polystyrene (sPS), polyethylene naphthalate (PEN) and polystyrene (PS), polyethylene terephthalate (PET) and syndiotactic polystyrene (sPS), polyethylene terephthalate (PET) A combination of styrene and polystyrene (PS) can be mentioned as a preferred example.
Among these, a combination of a blend of polyethylene naphthalate (PEN) / polyethylene terephthalate (PET) and syndiotactic polystyrene (sPS) is particularly preferable. PEN has a large positive birefringence (Δn = 0.32), sPS has a large negative birefringence (Δn = −0.10), and the refractive index is PEN (1.64)> PET (1.59). ) ≈sPS (1.59). Therefore, when PEN and sPS are blended, when a sea-island structure is formed and stretched, the difference in refractive index between PEN and sPS increases in direction X, and the X-direction component of light increases. While it can be reflected, the refractive index difference between PEN and sPS is closer to 0 in the direction Y, and the Y-direction component of the light can be almost transmitted. Furthermore, by blending an appropriate amount of PET with PEN, the refractive index in the direction Y can be lowered, and the refractive index difference from sPS can be made closer to zero.

  The blending ratio of the polyester-based resin (A) and the polystyrene-based resin (B) is adjusted in a mass ratio of (A) :( B) = 95: 5 to 50:50, particularly 75:25 to 50:50. It is preferable to do this. As the compounding ratio is closer to 50:50, the number of interfaces can be increased. When the proportion of the polystyrene resin (B) is less than 5 parts by mass or exceeds 50 parts by mass, the difference in refractive index between the two components is increased. Tends to be insufficient.

Moreover, you may add additives, such as a compatibilizing agent (C), as needed for the purpose of improving the dispersibility of a dispersed phase.
The compatibilizer (C) can be selected from conventional compatibilizers according to the type of continuous phase and dispersed phase. For example, polycarbonate, ester resin, resin having an epoxy group, resin having an oxazoline ring, Examples thereof include a block copolymer or a graft copolymer comprising at least one resin selected from resins having an azlactone group and at least one resin selected from styrene resins, polyphenylene oxide, and polyamides. Among these, from the viewpoint of improving dispersibility, a resin having an epoxy group or an oxazoline group is particularly preferable, and an epoxy-modified one is particularly preferable.
Commercially available compatibilizers such as “Reseda” (manufactured by Toagosei Co., Ltd.), “Epocross” (manufactured by Nippon Shokubai Co., Ltd.), and “Modiper” (manufactured by Nippon Oil & Fats Co., Ltd.) can also be used. Among these, “reseda” that is epoxy-modified polystyrene and “epocros” that is an oxazoline group-containing polymer are preferable, and “reseda” can be used particularly advantageously.

  The blending ratio of the compatibilizer is, for example, preferably 0.2 to 10 parts by mass, particularly 1 to 10 parts by mass with respect to 100 parts by mass in total of the polyester resin (A) and the polystyrene resin (B). .

(Film forming method)
Although the form of this scattering type polarizer is not specifically limited, Here, the manufacturing method of a sheet-like scattering type polarizer is demonstrated.

  The composition containing the polyester resin (A) and the polystyrene resin (B) may be melted to form a sheet. For example, the composition is dried, supplied to an extruder, and melted by heating to a temperature equal to or higher than the melting point of the resin. Then, the melted composition may be extruded from the slit-shaped discharge port of the T die and adhered and solidified on a cooling roll to form a cast sheet (unstretched state). However, it is not limited to such a film forming method.

(Stretching method)
The cast sheet thus formed is preferably substantially uniaxially stretched. Here, “substantially uniaxial stretching” means stretching performed positively in only one direction. For example, it is intended to include a case where the film is naturally stretched in a direction different from the one direction in the process of film formation, heat treatment or winding. More objectively, it means that the stretching ratio in one direction is 4 times or more of the stretching ratio in the direction orthogonal thereto.
By substantially uniaxially stretching in this way, the dispersed phase can be arranged and fixed in a substantially constant direction in the continuous phase, and the anisotropic scattering function can be exhibited. That is, the refractive index in the stretching direction of the polyester resin (A) constituting the continuous phase is remarkably increased, and the refractive index in the non-stretching direction is decreased. In the polystyrene resin (B) constituting the dispersed phase, the refractive index in the stretching direction is significantly decreased, and the refractive index in the non-stretching direction is increased. By uniaxial stretching, the refractive index of the continuous phase and the disperse phase differ greatly in the stretching direction, the direction perpendicular to the stretching direction is almost the same, and polarized light having the same refractive index is almost transmitted. In addition, it is possible to produce a scattering-type polarizing element having a property of scattering polarized light having different refractive indexes.

The stretching method may be any of free-width uniaxial stretching and constant-width uniaxial stretching, and any of stretching method, inter-roll stretching method, roll rolling method, and other methods may be employed.
The stretching temperature is preferably a temperature in the range of about the glass transition temperature (Tg) of the resin to (Tg + 50 ° C.), and particularly preferably 128 ° C. or less. When the stretching temperature is within this range, stretching can be performed stably without breaking during stretching.
The draw ratio is not particularly limited, but for example, it is preferably 4 times or more for TD or MD, preferably 4 to 5 times for TD or MD, and more preferably 4 to 4.5 times for TD or MD.

The stretched sheet is preferably heat-treated to impart heat resistance and dimensional stability. Under the present circumstances, it is preferable that the heat processing temperature shall be 180-230 degreeC, and it is more preferable to set it as 180-200 degreeC. The treatment time required for the heat treatment is preferably 1 second to 5 minutes.
When heat treatment is performed after stretching as described above, it is preferable to use a tenter stretching device capable of performing heat treatment after stretching as the stretching device.

  The thickness of the polarizer is not particularly limited. For example, when used for a brightness enhancement film, the thickness is preferably 100 μm to 250 μm, particularly preferably 100 μm to 200 μm.

(This polarizer)
In this differential scanning calorimetry, it is important that the crystallization temperature of the polystyrene resin (B) is 200 ° C. or lower when the scattering polarizer is cooled at a rate of temperature decrease of 20 ° C./min. Preferably, it is 150-200 degreeC, Most preferably, it is 180-200 degreeC.

  In addition, the fact that the crystallization temperature of the polystyrene resin (B) when the scattering polarizer is cooled as described above is 200 ° C. or less is 10 The crystallization start temperature of the polystyrene-based resin (B) when the cast sheet is heated at a rate of temperature rise of ° C./min is 150 ° C. or higher, preferably 150 to 180 ° C., particularly preferably 150 to 170 ° C.

  In order to prepare such a scattering polarizer, for example, the main component resin of the composition as a raw material, that is, the type of polyester resin (A) and polystyrene resin (B), the type of compatibilizer, the sheet It can be adjusted by the type and amount of impurities such as crystal nucleating agent (silica) or metal, among which styrene and paramethylstyrene are copolymerized as polystyrene resin (B). It is preferable to prepare syndiotactic polystyrene, particularly syndiotactic polystyrene obtained by copolymerizing styrene and paramethylstyrene in a molar ratio of 99: 1 to 75:25.

For example, when the polarizer having the above configuration is measured by being laminated on a backlight unit, the luminance is improved by 1.20 times or more, particularly preferably 1.40 times or more, compared with the case where the polarizer is not laminated. Can do.
Therefore, the present polarizer is used as a brightness enhancement film, and after adjusting the polarization direction of light passing through the brightness enhancement film and the polarization direction of light passing through the polarization film, for example as shown in FIG. In addition, a glass substrate, a polarizing film, a brightness enhancement film, a diffusion film, a cold-cathode tube (backlight unit), a reflective sheet, etc. are sequentially laminated on the back side (back side) of the liquid crystal cell to form a liquid crystal display (LCD). If comprised, compared with the case where the said brightness enhancement film is not laminated | stacked, the brightness | luminance of an image can be improved 1.20 times or more, Especially preferably, it is 1.40 times or more.
At this time, if light emitted from a cold cathode tube (backlight) as a light source is represented by light having one polarization direction and light having a polarization direction orthogonal thereto, the light incident on the brightness enhancement film In this case, the polarized light in the non-scattering direction passes through as it is, but the light in the other polarization direction perpendicular to this is reflected to the light source side, and scattering and reflection are repeated between the brightness enhancement film and the reflection sheet to form a brightness enhancement film. If the light is incident again and changed to light having a polarization direction that is not scattered, it passes, otherwise it is reflected again to the light source side, and this is repeated. Thus, since most of the light emitted from the light source can be supplied to the liquid crystal cell before long, the amount of light supplied to the liquid crystal cell can be increased, and the luminance of the image can be improved.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to these examples, and various applications are possible without departing from the technical idea of the present invention.
Here, the take-up (flow) direction of the sheet or film when the sheet or film is manufactured is indicated by MD, and the orthogonal direction thereof is indicated by TD.

(1) Method for measuring crystallization temperature When the scattering polarizer is cooled at a rate of temperature decrease of 20 ° C./min based on JIS K-7121 using differential scanning calorimetry (DSC-7) manufactured by PerkinElmer The crystallization temperature of the polystyrene resin (B) was measured from the obtained thermogram.

(2) Method for measuring crystallization start temperature When cast sheet is heated at a rate of temperature increase of 10 ° C./min based on JIS K-7121 using differential scanning calorimetry (DSC-7) manufactured by PerkinElmer The crystallization start temperature of the polystyrene resin (B) was measured from the obtained thermogram.

(3) Evaluation method of polarized light transmittance The polarized light transmittance was measured by attaching an integrating sphere to a spectrophotometer (manufactured by Hitachi, Ltd .: U-4000). A polarizing film is attached to the incident light side of a light source having a wavelength of 380 nm to 800 nm, an absorption type polarizing film is inserted on the light source side, and the light source is only linearly polarized light that is polarized in the vertical direction. A polarizer was inserted, and the polarization transmittance of the scattered polarized light was measured for MD and TD, respectively.
The evaluation criteria for MD are: “O” when the average polarization transmittance of 400 nm to 700 nm is 80% or more, “△” when 70% or more and less than 80%, and “70” or less polarization transmission. The rate was evaluated as “x”.
As evaluation criteria for TD, a polarization transmittance of 20% or less was evaluated as “◯”, a polarization transmittance of more than 20% and 25% or less as “Δ”, and a polarization transmittance of more than 25% as “x”.

(4) Luminance evaluation A sample unit (brightness enhancement film) and a polarizing film were sequentially laminated and fixed on a backlight unit (Sharp “Aquos” 13-inch, model number: LC-13S4-S), and the screen was separated by 50 cm. The central luminance was measured with a luminance meter (manufactured by Minolta, model: LS-100). The luminance when the sample sheet was not incorporated was measured, and the ratio to the luminance was calculated as the luminance improvement rate (see the following formula (1)). The larger this value, the higher the brightness.
As evaluation criteria, a luminance improvement rate of 1.20 or more was evaluated as “◯”, a luminance improvement rate of 1.10 or more and less than 1.20 was evaluated as “Δ”, and a luminance improvement rate of less than 1.10 was evaluated as “x”. .

  Formula (1): Brightness improvement rate = (luminance when the sample sheet is assembled / luminance before incorporation of the sample sheet)

(5) Haze evaluation method
Based on Japanese Industrial Standard JIS K7105, total light transmittance and diffuse transmittance were measured for stretched sheets (scattering polarizers) of Examples and Comparative Examples, and a haze value was calculated based on the following formula.
In addition, the sheet of sPS alone (100 μm thickness) used in Examples and Comparative Examples was subjected to stretching and heat treatment in the same manner as in each Example or Comparative Example, and the total light transmittance and diffuse transmittance were measured. The haze value was calculated based on the formula.
Haze value = (diffuse transmittance / total light transmittance) × 100
As evaluation criteria, a haze having a haze value of less than 40% was evaluated as “◯”, a haze of 40% or more and less than 50% as “Δ”, and a haze of 50% or more as “x”.

<Example 1>
Polyethylene naphthalate (PEN, refractive index: 1.64, intrinsic viscosity: 0.7 dl / g, Tg: 120 ° C., weight average molecular weight: 54000, melting point: 265 ° C.) and polyethylene terephthalate (PET, refractive index: 1. 58, intrinsic viscosity: 1.2 dl / g, Tg: 80 ° C., weight average molecular weight: 110000, melting point: 255 ° C.), syndiotactic polystyrene (sPS), and epoxy as a compatibilizer, graft-polymerized with polystyrene Modified polystyrene (epoxy-modified PS-graft-PS, refractive index: 1.58, Tg: 90 ° C.) is blended at a mass ratio of PEN: PET: sPS: Compatibilizer = 50: 10: 40: 2. After mixing well, while feeding with a constant mass feeder, extrusion kneading at a resin temperature of 290 ° C. with a twin screw extruder, cooling and solidifying to form a cast sheet with a thickness of 450 μm did.
The obtained cast sheet was uniaxially stretched 4.5 times to TD at 130 ° C. using a small tenter device (manufactured by Kyoto Machine Co., Ltd.), heat-treated at 180 ° C. for 1 minute, and a sheet-like scattering type having a thickness of 100 μm. A polarizer was obtained.

  The syndiotactic polystyrene (sPS) used in this example is syndiotactic polystyrene obtained by copolymerizing styrene and paramethylstyrene at a molar ratio of 94: 6. The refractive index is 1.59. Tg: 95 ° C., melting point 249 ° C., weight average molecular weight 300,000, MI: 4 g / 10 min.

<Example 2>
A scattering type polarizer was obtained in the same manner as in Example 1 except that the cast sheet was uniaxially stretched 4.5 times to TD at 140 ° C.

<Example 3>
Syndiotactic polystyrene (sPS) used is obtained by copolymerizing styrene and paramethylstyrene in a molar ratio of 94: 6 (refractive index: 1.59, Tg: 95 ° C., melting point 247 ° C.). A scattering polarizer was obtained in the same manner as in Example 1, except that the weight average molecular weight was changed to 250,000 and MI was 14 g / 10 min.

<Comparative Example 1>
The syndiotactic polystyrene (sPS) used was syndiotactic polystyrene composed of a homopolymer of styrene (refractive index: 1.59, Tg: 93 ° C., melting point 271 ° C., weight average molecular weight 300,000, MI: 3 g / 10 min). A scattering polarizer was obtained in the same manner as in Example 1 except that

<Comparative example 2>
Except that the cast sheet was uniaxially stretched 4.5 times to TD at 140 ° C., an attempt was made to form a scattering polarizer in the same manner as in Comparative Example 1.
It broke during stretching.

  As is clear from Table 1, the embodiments of Examples 1 to 3 were all superior to the embodiments of Comparative Examples 1 and 2. Further, among the examples, the modes of Examples 1 and 2 were superior to the mode of Example 3.

It is sectional drawing which showed an example of the general structure of a liquid crystal display (LCD).

Claims (8)

A scattering type polarizer obtained by forming a composition containing a polyester-based resin (A) constituting a continuous phase and a polystyrene-based resin (B) constituting a dispersed phase, and stretching the obtained cast sheet There,
In the differential scanning calorimetry, the crystallization temperature of the polystyrene-based resin (B) when the scattering polarizer is cooled at a temperature decrease rate of 20 ° C./min is 200 ° C. or less. A scattering type polarizer obtained by forming a composition containing a polyester-based resin (A) constituting a continuous phase and a polystyrene-based resin (B) constituting a dispersed phase, and stretching the obtained cast sheet There,
In differential scanning calorimetry, the crystallization start temperature of polystyrene-based resin (B) when the cast sheet is heated at a heating rate of 10 ° C./min is 150 ° C. or more, and a scattering type polarizer .   The scattering polarizer according to claim 1 or 2, wherein the polystyrene-based resin (B) has a melting point of 260 ° C or lower.   The scattering polarizer according to any one of claims 1 to 3, wherein the polystyrene resin (B) is syndiotactic polystyrene obtained by copolymerization of styrene and paramethylstyrene.   The scattering type according to claim 4, wherein the polystyrene resin (B) is syndiotactic polystyrene obtained by copolymerizing styrene and paramethylstyrene in a molar ratio of 99: 1 to 90:10. Polarizer.   The above composition contains the polyester resin (A) and the polystyrene resin (B) in a mass ratio of 95: 5 to 50:50, and the total of the polyester resin (A) and the polystyrene resin (B). The scattering polarizer according to any one of claims 1 to 5, comprising 0.2 to 10 parts by mass of a compatibilizer (C) with respect to 100 parts by mass.   The brightness improvement rate is 1.20 or more, the scattering type polarizer according to any one of claims 1 to 6. A liquid crystal display device comprising the scattering polarizer according to claim 1.

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