JP2013007789A - Multilayer uniaxially oriented film - Google Patents

Abstract

Reflected polarized light with improved polarization performance compared to the prior art, at the same time eliminating the hue shift of transmitted polarized light due to the obliquely incident angle with respect to light incident in the oblique direction, and excellent in heat-resistant dimensional stability To provide a multilayer uniaxially stretched film having a function.
A multi-layer uniaxially stretched film having 251 layers or more in which first layers and second layers are alternately laminated, wherein the first layer includes (i) a specific dicarboxylic acid containing a naphthoic acid component as a dicarboxylic acid component. A layer comprising a polyester containing a diol component having 5 to 50 mol% and a dicarboxylic acid component having a naphthalenediyl group, and (ii) a diol component having an alkylene group having 2 to 4 carbon atoms as a diol component The second layer is an optically isotropic layer having an average refractive index of 1.50 or more and 1.60 or less comprising a copolymerized polyester having a glass transition temperature of 80 ° C. or more and a copolymerization amount of 5 mol% or more and 85 mol% or less. And is achieved by a multilayer uniaxially stretched film having a heat shrinkage rate at 85 ° C. of 1.5% or less.
[Selection figure] None

Description

  The present invention relates to a multilayer uniaxially stretched film that selectively reflects a certain polarization component and selectively transmits a polarization component perpendicular to the polarization component. More specifically, it has excellent polarization performance that selectively reflects a certain polarization component and selectively transmits a polarization component perpendicular to the polarization component, and partially reflects light incident in an oblique direction. The present invention relates to a multilayer uniaxially stretched film in which a hue shift of transmitted polarized light is eliminated without occurrence and excellent in heat-resistant dimensional stability.

  A film in which low refractive index layers and high refractive index layers are alternately laminated can be an optical interference film that selectively reflects or transmits light of a specific wavelength by structural optical interference between the layers. In addition, such a multilayer film can obtain a high reflectance equivalent to that of a film using metal by gradually changing the film thickness or by bonding films having different reflection peaks. It can also be used as a film or a reflection mirror. Furthermore, by stretching such a multilayer film only in one direction, it can also be used as a polarization reflection film that reflects only a specific polarization component. It is known that these can be used as a brightness enhancement film for a liquid crystal display or the like by using the liquid crystal display or the like.

In general, a multilayer film composed of layers having different refractive indexes of 0.05 to 0.5 μm has a difference in refractive index between the layer constituting one layer and the layer constituting the other layer, Depending on the number of layers, there is a phenomenon such as increased reflection that reflects light of a specific wavelength. In general, the reflection wavelength is expressed by the following equation.
λ = 2 (n ₁ × d ₁ + n ₂ × d ₂ )
(In the above formula, λ is the reflection wavelength (nm), n ₁ and n ₂ are the refractive indexes of the respective layers, and d ₁ and d ₂ are the thicknesses (nm) of the respective layers)

For example, as shown in Patent Document 1, by using a resin having a positive stress optical coefficient in one layer, the refractive index of such a layer is birefringent by stretching in a uniaxial direction. By applying a method to increase the refractive index difference between layers in the stretching direction in the film plane, while reducing the refractive index difference between layers in the direction perpendicular to the stretching direction in the film plane, only a specific polarization component Can be reflected.
By utilizing this principle, it is possible to design a reflective polarizing film that reflects polarized light in one direction and transmits polarized light in the orthogonal direction, for example, and the desired birefringence at that time is expressed by the following equation: .
n _1X > n _2X , n _1Y = n _2Y
(In the above formula, n _1X and n _2X represent the refractive index in the stretching direction in each layer, and n _1Y and n _2Y represent the refractive index in the direction perpendicular to the stretching direction in each layer.)

In Patent Document 2, polyethylene-2,6-naphthalenedicarboxylate (hereinafter sometimes referred to as 2,6-PEN) is used for a layer having a high refractive index, and thermoplasticity is used for a layer having a low refractive index. The multilayer film using the PEN which copolymerized 30 mol% of elastomers and terephthalic acid is illustrated. This is because a resin having a positive stress optical coefficient is used in one layer and a resin having a very low stress optical coefficient (extremely low birefringence due to stretching) is used in the other layer. The reflective polarizing film which reflects only polarized light is illustrated.
Patent Document 3 describes a multilayer laminated film containing polyethylene-2,6-naphthalenedicarboxylate as a high refractive index layer and containing inert particles, but highly reflects one polarized light in a wide wavelength region. The concept of a reflective polarizing film has not been proposed.

  As described above, the use of 2,6-PEN for a layer having a high refractive index is conventionally known, but a multilayer uniaxially stretched film having a reflective polarization function using 2,6-PEN for a layer having a high refractive index. Then, a difference arises in the refractive index of the direction (Y direction) orthogonal to the extending | stretching direction in the PEN layer after extending | stretching, and the refractive index of a film thickness direction (Z direction). Therefore, if the stretching ratio is increased to increase the refractive index difference between the layers in the stretching direction (X direction) to improve the polarization performance, the refractive index difference between the layers in the Z direction increases accordingly, and the light enters the oblique direction. Since a hue shift of transmitted light occurs due to partial reflection on light, it is difficult to further increase the draw ratio and increase the degree of polarization.

  Patent Document 4 discloses a polymer containing copolyethylene naphthalate having a refractive index of 1.58 or less at 632.8 nm and a glass transition temperature of 90 ° C. or more, and a multilayer film using the polymer for a layer having low in-plane birefringence. Although it has been proposed, a conventional homo-PEN or terephthalic acid copolymerized PEN is used as the PEN-based polymer used in the high refractive index layer.

JP-A-4-268505 Japanese National Patent Publication No. 9-506837 International Publication No. 01/47711 Pamphlet Special table 2008-517139

  The object of the present invention is to eliminate the above-mentioned problems of the conventional multilayer film, further improve the polarization performance than before, and simultaneously shift the hue of transmitted polarized light due to the incident angle in the oblique direction with respect to the light incident in the oblique direction. Is to provide a multilayer uniaxially stretched film having a reflective polarization function and excellent in heat-resistant dimensional stability.

  The present invention is based on the following findings. That is, polyethylene-2,6-naphthalenedicarboxylate, which has been conventionally used as a resin for the first layer constituting the high refractive index layer, increases the refractive index in the stretching direction (X direction) by uniaxial stretching. In the Y direction, the refractive index hardly changes before and after stretching, while the Z direction has a characteristic that the refractive index decreases. Therefore, if the stretching ratio is increased to increase the refractive index difference between the layers in the stretching direction (X direction) to improve the polarization performance, the refractive index difference between the layers in the Z direction increases accordingly. Further, if the refractive index between the layers in the Z direction after stretching is made to coincide, the difference in the refractive index between the layers in the Y direction becomes large. Therefore, it is difficult to achieve both improvement in polarization performance and suppression of hue shift of transmitted polarized light with respect to obliquely incident light.

  The present inventors have replaced the polyethylene-2,6-naphthalenedicarboxylate as the first layer resin constituting the high refractive index layer with 6,6 ′-(alkylenedioxy) di-2-naphthoic acid. When a polyester having a high refractive index containing a component is used, the refractive index difference between the X direction and the Y direction of the first layer after uniaxial stretching can be increased, and in addition, the refraction between layers in both the Y direction and the Z direction. As a result of being able to reduce the rate difference, it is possible to achieve both the improvement in polarization performance, which is the subject of the present invention, and the elimination of the hue deviation of transmitted polarized light due to the oblique incident angle, and at the same time, the high refractive index layer of the present invention. The polymer used in the low refractive index layer was found to have an effect on the heat-resistant dimensional stability despite the fact that the heat-resistant dimensional stability was expected to be high due to low stress during stretching, and the present invention was completed. You It led to.

（式（Ａ）中、Ｒ^Ａは炭素数２〜４のアルキレン基を表わす）

（式（Ｂ）中、Ｒ^Ｂはナフタレンジイル基を表わす）
（ｉｉ）ジオール成分は９０モル％以上１００モル％以下の下記式（Ｃ）で表される成分を含有し、

（式（Ｃ）中、Ｒ^Ｃは炭素数２〜４のアルキレン基を表わす）
２）該第２層は、８０℃以上のガラス転移温度を有する共重合量５モル％以上８５モル％以下の共重合ポリエステルからなり、平均屈折率１．５０以上１．６０以下かつ光学等方性の層であって、
３）該多層一軸延伸フィルムの８５℃、３０分の条件における熱収縮率が１．５％以下であることを特徴とする多層一軸延伸フィルム。 That is, the object of the present invention is achieved by the following invention.
1. In the multi-layer uniaxially stretched film of 251 layers or more in which the first layer and the second layer are alternately laminated,
1) The first layer is a layer made of polyester of a dicarboxylic acid component and a diol component,
(I) The dicarboxylic acid component contains a component represented by the following formula (A) of 5 mol% or more and 50 mol% or less and a component represented by the following formula (B) of 50 mol% or more and 95 mol% or less,

(In the formula (A), R ^A represents an alkylene group having 2 to 4 carbon atoms)

(In formula (B), R ^B represents a naphthalenediyl group)
(Ii) The diol component contains 90 mol% or more and 100 mol% or less of a component represented by the following formula (C),

(In the formula (C), R ^C represents an alkylene group having 2 to 4 carbon atoms)
2) The second layer is made of a copolyester having a glass transition temperature of 80 ° C. or more and a copolymerization amount of 5 mol% to 85 mol%, and has an average refractive index of 1.50 to 1.60 and optical isotropy. A sex layer,
3) The multilayer uniaxially stretched film is characterized in that the thermal shrinkage rate of the multilayer uniaxially stretched film at 85 ° C. for 30 minutes is 1.5% or less.

Moreover, according to this invention, the following brightness improvement member using the said multilayer uniaxially stretched film, the composite member for liquid crystal displays, a liquid crystal display device, a polarizing plate, and the optical member for liquid crystal display devices are also provided.
2. 2. The multilayer uniaxially stretched film according to item 1, wherein the copolymer polyester constituting the second layer is a copolymerized polyethylene terephthalate having an alicyclic diol as a copolymer component.
3. 3. The multilayer uniaxially stretched film according to item 2 above, wherein the copolymer component constituting the copolymer polyethylene terephthalate is at least one selected from the group consisting of spiroglycol, tricyclodecane dimethanol and cyclohexane dimethanol.
4). 2. The multilayer uniaxially stretched film according to item 1, wherein the copolymer polyester constituting the second layer is a copolymerized polyethylene nafphthalate having at least one of alicyclic dicarboxylic acid or alicyclic diol as a copolymer component.
5). 5. The copolymerization component constituting the copolymerized polyethylene nafphthalate is at least one selected from the group consisting of cyclohexanedicarboxylic acid, decahydronaphthalenedicarboxylic acid, spiroglycol, tricyclodecane dimethanol and cyclohexanedimethanol. Multi-layer uniaxially stretched film.
6). The refractive index difference in the uniaxial stretching direction (X direction) of the first layer and the second layer of the multilayer uniaxially stretched film in the film plane is 0.10 to 0.45, and the direction orthogonal to the uniaxial stretch direction The refractive index difference between the first layer and the second layer in the (Y direction) and the refractive index difference between the first layer and the second layer in the film thickness direction (Z direction) are 0.05 or less, respectively. The multilayer uniaxially stretched film according to any one of 5.
7). The film surface is a reflecting surface, and the average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree and 50 degrees with respect to a polarized light component parallel to the incident surface including the X direction is 90% or more, With respect to the polarized light component perpendicular to the incident surface including the X direction with the film surface as the reflecting surface, the average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degrees and 50 degrees is 15% or less, respectively. The multilayer uniaxially stretched film according to any one of 1 to 6 above.
8). A reflective polarizing plate comprising the multilayer uniaxially stretched film according to any one of items 1 to 7.
9. 9. An optical member for a liquid crystal display device, wherein the first polarizing plate, the liquid crystal cell, and the second polarizing plate are sequentially arranged, and the first polarizing plate is the reflective polarizing plate according to item 8 above.
10. A liquid crystal display device comprising a light source and the optical member for a liquid crystal display device according to the preceding item 9, wherein the first polarizing plate is disposed on the light source side.

  The multilayer uniaxially stretched film of the present invention eliminates the hue shift of transmitted polarized light due to the incident angle in the oblique direction seen in the conventional reflective polarizing film, and has a higher polarization performance than the conventional one, and further has a heat resistant dimensional stability. Excellent in properties. Therefore, when used as a polarizing plate to be bonded to a brightness enhancement film or a liquid crystal cell, as an example, there is no deformation of the film due to heating even when a heating step is included when bonding to another member, and a high luminance improvement rate In addition, a liquid crystal display excellent in visibility with a high viewing angle and a small hue shift can be provided.

It is a schematic sectional drawing of the 1st aspect of the liquid crystal display device of this invention. It is a schematic sectional drawing of the 2nd aspect of the liquid crystal display device of this invention.

[Multilayer uniaxially stretched film]
The multilayer uniaxially stretched film of the present invention is a film in which the first layer and the second layer are alternately laminated, has 251 layers or more, and is stretched in at least a uniaxial direction. Here, the first layer represents a layer having a higher refractive index than the second layer, and the second layer represents a layer having a lower refractive index than the first layer.
A feature of the present invention is that the first layer and the second layer constituting the multilayer uniaxially stretched film use a polyester having a high refractive index characterized by having a specific copolymer component in the first layer, and the second layer And an optically isotropic polyester having an average refractive index of 1.50 or more and 1.60 or less and having a glass transition temperature of 80 ° C. or more and 155 ° C. or less. Here, the optical isotropy means that the refractive index difference in each of the stretching direction (X direction), the orthogonal direction (Y direction) and the film thickness direction (Z direction) is 0.05 or less. .

  By configuring the first layer using a specific polyester described later, it becomes possible to increase the refractive index difference between the X direction and the Y direction of the first layer after stretching, and in the Y direction and the Z direction. It becomes possible for the first time to reduce the refractive index difference between the layers in both directions. As described above, the specific polyester of the present invention, which has not been conventionally used for the first layer of the multilayer film having a reflective polarization function, is used for the first layer, and the second layer copolyester described later. By combining it with a multilayer uniaxially stretched film, it becomes possible to achieve both improvement in polarization performance and suppression of hue shift of transmitted polarized light with respect to obliquely incident light, which has been difficult until now.

Furthermore, the polyester for the first layer used in the present invention has a low stress during stretching, and has a high glass transition temperature and a lower refractive index than the first layer while having optical isotropy after stretching to the second layer. By using a copolyester, it has high heat-resistant dimensional stability at 85 ° C.
Here, the refractive index in the stretching direction (X direction) is described as n _X , the refractive index in the direction orthogonal to the stretching direction (Y direction) is expressed as n _Y , and the refractive index in the film thickness direction (Z direction) is described as _NZ. There is.
Hereinafter, the multilayer uniaxially stretched film of the present invention will be described in detail.

(First layer)
In the present invention, the polyester constituting the first layer (hereinafter sometimes referred to as aromatic polyester (I)) is obtained by polycondensation of the following dicarboxylic acid component and diol component.

(Dicarboxylic acid component)
As a dicarboxylic acid component (i) constituting the aromatic polyester (I) of the present invention, a component represented by the following formula (A) of 5 mol% or more and 50 mol% or less, and 50 mol% or more and 95 mol% or less of At least two kinds of aromatic dicarboxylic acid components of the component represented by the following formula (B) are used. Here, the content of each aromatic dicarboxylic acid component is a content based on the total number of moles of the dicarboxylic acid component.

（式（Ａ）中、Ｒ^Ａは炭素数２〜４のアルキレン基を表わす）

(In the formula (A), R ^A represents an alkylene group having 2 to 4 carbon atoms)

（式（Ｂ）中、Ｒ^Ｂはナフタレンジイル基を表わす）

(In formula (B), R ^B represents a naphthalenediyl group)

About the component represented by a formula (A), in formula, ^RA is a C2-C4 alkylene group. Examples of the alkylene group include an ethylene group, a trimethylene group, an isopropylene group, and a tetramethylene group, and an ethylene group is particularly preferable.
The lower limit of the content of the component represented by the formula (A) is preferably 7 mol%, more preferably 10 mol%, still more preferably 15 mol%. Moreover, the upper limit of the content of the component represented by the formula (A) is preferably 45 mol%, more preferably 40 mol%, still more preferably 35 mol%. Therefore, the content of the component represented by the formula (A) is preferably 5 mol% or more and 45 mol% or less, more preferably 7 mol% or more and 40 mol% or less, and further preferably 10 mol% or more and 35 mol% or less. Especially preferably, it is 15 mol% or more and 30 mol% or less.

The component represented by the formula (A) includes 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, 6,6 ′-(trimethylenedioxy) di-2-naphthoic acid, and 6,6 ′. A component derived from-(butyleneoxy) di-2-naphthoic acid is preferred. Among these, even-numbered carbon atoms of R ^A in formula (A) are preferable, and components derived from 6,6 ′-(ethylenedioxy) di-2-naphthoic acid are particularly preferable.

Such aromatic polyester (I) is characterized in that the dicarboxylic acid component contains a component represented by the formula (A) in an amount of 5 mol% to 50 mol%. If the proportion of the component represented by the formula (A) is less than the lower limit, since the decrease in the refractive index in the Y direction by stretching does not occur, the refractive index of the refractive index n _Y and Z direction Y direction in the stretched film n The difference in _Z becomes large, and it is difficult to improve the hue shift due to polarized light incident at an oblique incident angle. Further, if the proportion of the component represented by the formula (A) exceeds the upper limit value, amorphous characteristics becomes large, the difference between the refractive index n _Y in refractive index n _X and Y direction of the X-direction in the stretched film Therefore, sufficient performance as a reflective polarizing film is not exhibited.
Thus, by using the polyester containing the component represented by the formula (A), a multilayer uniaxially stretched film that does not cause a hue shift due to an incident angle in an oblique direction while improving the polarization performance as a reflective polarizing film as compared with the prior art. Can be manufactured.

Further, the component represented by formula (B), wherein, R ^B is a naphthalene-diyl group.
The component represented by the formula (B) is preferably 2,6-naphthalenedicarboxylic acid or 2,7-naphthalenedicarboxylic acid, and particularly preferably 2,6-naphthalenedicarboxylic acid.
The lower limit of the content of the component represented by the formula (B) is preferably 55 mol%, more preferably 60 mol%, still more preferably 65 mol%. Moreover, the upper limit of the content of the component represented by the formula (B) is preferably 93 mol%, more preferably 90 mol%, and still more preferably 85 mol%. Therefore, the content of the component represented by the formula (B) is preferably 55 mol% or more and 95 mol% or less, more preferably 60 mol% or more and 93 mol% or less, and further preferably 65 mol% or more and 90 mol% or less. Particularly preferred is 70 mol% or more and 85 mol% or less.

If the proportion of the component represented by the formula (B) is less than the lower limit value, amorphous characteristics becomes large, the difference between the refractive index n _Y in refractive index n _X and Y direction of the X-direction in the stretched film Since it becomes small, sufficient performance as a reflective polarizing film is not exhibited. Moreover, when the ratio of the component shown by Formula (B) exceeds an upper limit, since the ratio of the component shown by Formula (A) becomes relatively small, the refractive indexes n _Y and Z in the Y direction in the stretched film The difference in the refractive index _{NZ in} the direction becomes large, and it is difficult to improve the hue shift due to the polarized light incident at an oblique incident angle.
Thus, by using the polyester containing the component represented by the formula (B), it is possible to realize a birefringence characteristic having a high uniaxial orientation while exhibiting a high refractive index in the X direction.

(Diol component)
As the diol component (ii) constituting the aromatic polyester (I) of the present invention, a diol component represented by the following formula (C) of 90 mol% or more and 100 mol% or less is used. Here, the content of the diol component is a content based on the total number of moles of the diol component.

（式（Ｃ）中、Ｒ^Ｃは炭素数２〜４のアルキレン基を表わす）

(In the formula (C), R ^C represents an alkylene group having 2 to 4 carbon atoms)

In the formula (C), R ^C is an alkylene group having 2 to 4 carbon atoms, and examples thereof include an ethylene group, a propylene group, an isopropylene group, and a tetramethylene group. As the diol component represented by the formula (C), ethylene glycol, trimethylene glycol, tetramethylene glycol and the like are preferable, and ethylene glycol is particularly preferable.
The content of the diol component represented by the formula (C) is preferably 95 mol% to 100 mol%, more preferably 98 mol% to 100 mol%. When the ratio of the diol component represented by the formula (C) is less than the lower limit, the above-described uniaxial orientation is impaired.

(Aromatic polyester (I))
In the aromatic polyester (I), the content of the repeating unit ((A)-(C)) formed by the component represented by the formula (A) and the diol component represented by the formula (C) is all repeated. It is 5 mol% or more and 50 mol% or less of the unit, preferably 5 mol% or more and 45 mol% or less, more preferably 10 mol% or more and 40 mol% or less.
As other ester units constituting the aromatic polyester (I), alkylene such as ethylene-2,6-naphthalene dicarboxylate, trimethylene-2,6-naphthalene dicarboxylate, butylene-2,6-naphthalene dicarboxylate -2,6-naphthalenedicarboxylate units. Among these, ethylene-2,6-naphthalenedicarboxylate units are preferable from the viewpoint of high refractive index.
As the aromatic polyester (I), in particular, the dicarboxylic acid component represented by the formula (A) is 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, and the dicarboxylic acid represented by the formula (B) A polyester in which the acid component is 2,6-naphthalenedicarboxylic acid and the diol component is ethylene glycol is preferred.

The aromatic polyester (I) has an intrinsic viscosity of 0.4 to 3 dl / measured at 35 ° C. using a mixed solvent of P-chlorophenol / 1,1,2,2-tetrachloroethane (weight ratio 40/60). It is preferable that it is g, More preferably, it is 0.4-1.5 dl / g, Most preferably, it is 0.5-1.2 dl / g.
The melting point of the aromatic polyester (I) is preferably in the range of 200 to 260 ° C, more preferably in the range of 205 to 255 ° C, and still more preferably in the range of 210 to 250 ° C. The melting point can be determined by measuring with DSC.

If the melting point of the polyester exceeds the upper limit value, fluidity may be inferior when melt-extruded and molded, and discharge and the like may be made uneven. On the other hand, if the melting point is less than the lower limit, the film forming property is excellent, but the mechanical properties of the polyester are easily impaired, and the refractive index properties of the present invention are hardly exhibited.
In general, a copolymer has a lower melting point than a homopolymer and tends to decrease mechanical strength. However, the polyester of the present invention is a copolymer containing the component of formula (A) and the component of formula (B) as an acid component, and has a melting point as compared with a homopolymer having only the component of formula (A). Although it has a low mechanical strength, it has excellent properties.

The glass transition temperature (hereinafter sometimes referred to as Tg) of the aromatic polyester (I) is preferably 60 to 120 ° C, more preferably 80 to 118 ° C, and still more preferably 85 to 118 ° C. When Tg is within this range, a film having excellent heat resistance and dimensional stability can be obtained. Such melting point and glass transition temperature can be adjusted by controlling the kind and copolymerization amount of the copolymerization component and dialkylene glycol as a by-product.
The method for producing the aromatic polyester (I) can be produced, for example, according to the method described on page 9 of the pamphlet of WO2008 / 153188.

(Refractive index of the first layer)
When the aromatic polyester (I) is uniaxially stretched, the refractive index n _{X in} the X direction is in the direction of increasing by stretching, and the refractive index n _{Y in the Y} direction and the refractive index n _{Z in the} Z direction both decrease with stretching. to have a direction, yet the refractive index difference n _Y and n _Z regardless of the draw ratio is characterized by very small.
In addition, the first layer is uniaxially stretched using the aromatic polyester (I) containing the specific copolymer component, so that the refractive index n _{X in the} X direction is a high refractive index of 1.70 to 1.90. Has characteristics. When the refractive index in the X direction in the first layer is within such a range, the refractive index difference from the second layer becomes large, and sufficient reflective polarization performance can be exhibited.
Moreover, the refractive index difference between the refractive index n _Y after uniaxial stretching in the Y direction and the refractive index n _Z after uniaxial stretching in the Z direction is specifically 0.05 or less, preferably 0.03 or less. Especially preferably, it is 0.01 or less. Since the difference in refractive index between these two directions is very small, there is an effect that no hue shift occurs even when polarized light is incident at an oblique incident angle.

  As a mechanism by which the aromatic polyester (I) exhibits the refractive index characteristics as described above by uniaxial stretching, for increasing the refractive index in the X direction by stretching, a component represented by the formula (A), which is an aromatic component, The component represented by the formula (B) mainly affects. Moreover, about the fall of the refractive index of the Y direction by extending | stretching, the component represented by Formula (A) mainly influences, and two aromatic rings contained in the component represented by Formula (A) are ether-bonded via an alkylene chain. It is considered that when the uniaxial stretching is performed, these aromatic rings are easily rotated in a direction other than the plane direction, and the refractive index characteristic in the Y direction of the first layer is expressed. Moreover, since the diol component of the aromatic polyester (I) in the present invention is an aliphatic component, the influence of the diol component on the refractive index characteristics of the first layer is smaller than that of the above-described dicarboxylic acid component.

On the other hand, if the polyester constituting the first layer is polyethylene-2,6-naphthalene dicarboxylate, 1 regardless of the axial draw ratio to the refractive index n _Y in the Y direction is not observed decrease at a constant On the other hand, the refractive index n _Z in the Z direction decreases as the uniaxial stretching ratio increases. Therefore, the difference between the refractive index n _{Y in the Y} direction and the refractive index n _{Z in} the Z direction becomes large, and a hue shift is likely to occur when polarized light is incident at an oblique incident angle.

(Second layer)
In the present invention, the second layer of the uniaxially stretched multilayer laminated film is made of a copolymerized polyester having a glass transition temperature of 80 ° C. or higher and a copolymerization amount of 5 mol% to 85 mol%, and has an average refractive index of 1.50. The layer is an optically isotropic layer with a value of 1.60 or less.
Here, the average refractive index is obtained by melting the polyester constituting the second layer alone, extruding from a die to create an unstretched film, and forming the film under the same conditions as those for the multilayer uniaxially stretched film. The refractive index in each of the X direction, Y direction and Z direction of the film was measured at a wavelength of 633 nm using a metricon prism coupler, and the average value thereof was defined as the average refractive index. Optical isotropy means that the refractive index difference between the two directions of the refractive index in the X direction, Y direction, and Z direction is 0.05 or less, preferably 0.03 or less.

  The average refractive index of the polyester constituting the second layer is 1.50 to 1.60, preferably 1.53 to 1.60, more preferably 1.55 to 1.60, and even more preferably 1. .58 or more and 1.60 or less. Since the second layer has such an average refractive index and is an optically isotropic material having a small difference in refractive index in each direction by stretching, refraction in the X direction after stretching between the first layer and the second layer. The rate difference is large, and as a result, high polarization performance is obtained. At the same time, it is possible to obtain a refractive index characteristic in which both the refractive index difference in the Y direction and the refractive index difference in the Z direction between the layers are extremely small. As a result, both the polarization performance and the hue shift due to the incident angle in the oblique direction can be achieved. .

The copolyester of the second layer in the present invention needs to have a glass transition temperature of 80 ° C. or higher, preferably 90 ° C. or higher and 155 ° C. or lower, more preferably 90 ° C. or higher and 120 ° C. or lower.
If the glass transition temperature of the polyester of the second layer is less than the lower limit, the heat shrinkage rate after stretching cannot be suppressed, and when used continuously as a display, the polarization performance deteriorates due to shrinkage. Within the scope of the present invention, the glass transition temperature of the polyester of the second layer is preferably higher. On the other hand, when the glass transition temperature is too high, the polyester of the second layer may also be birefringent due to stretching during stretching, and the refractive index difference with the first layer in the stretching direction will be small, and the reflection performance will deteriorate. There is.

  In particular, with regard to heat-resistant dimensional stability, by using a copolymer polyester having a glass transition temperature applied to the second layer, the heat-resistant dimensional stability of the second layer itself can be increased. Since it has the characteristic of low stress during stretching, it has a high heat-resistant dimensional stability of 1.5% or less under heating conditions of 85 ° C. for 30 minutes in both the uniaxial stretching direction (X direction) and its orthogonal direction (Y direction). A multilayer uniaxially stretched film having high reflective polarization characteristics can be obtained.

  In the present invention, the copolymerization amount of the copolymer polyester of the second layer indicates the proportion of the secondary copolymer component when the polyester repeating unit is 100 mol%. Further, the subordinate component represents the total amount of the components excluding the component having the highest ratio in the diol component and the component having the highest ratio in the dicarboxylic acid component. For example, in the example of Table 1 of the present invention, the copolymer polyester described as CHDC35SPG70PEN has 35 mol% of cyclohexanedicarboxylic acid and 65 mol% of naphthalenedicarboxylic acid component with respect to 100 mol% of dicarboxylic acid component, 70 mol% of spiroglycol and 30 mol% of ethylene glycol with respect to 100 mol% of the diol component, 35 mol% of cyclohexanedicarboxylic acid, which is a subordinate component of the dicarboxylic acid component, and ethylene, a subordinate component of the diol component The amount of copolymerization is 65 mol%, which is the total of 30 mol% of glycol.

  Among the copolyesters having such a glass transition temperature, refractive index characteristics and optical isotropy at the same time, from the viewpoint of film-forming properties in uniaxial stretching and a difference in refractive index from the first layer, all repeating units constituting the polyester Preferred examples include copolymer polyesters such as copolymer polyethylene terephthalate and copolymer polyethylene naphthalene dicarboxylate having a copolymer weight of 5 to 85 mol%, preferably 10 to 70 mol% based on the above.

  In order to improve the glass transition temperature, an aromatic component having high rigidity is often introduced. However, such a component often increases the refractive index as the glass transition temperature is improved. Therefore, in this invention, it is preferable to introduce | transduce alicyclic components, such as alicyclic dicarboxylic acid and alicyclic diol, as a copolymerization component.

  Among the copolymerized polyethylene terephthalates, it is preferable to use a copolymerized polyethylene terephthalate having an alicyclic diol as a copolymerization component. By substituting a part of ethylene glycol with an alicyclic diol without reducing the amount of aromatic groups derived from terephthalic acid, the refractive index characteristics of the present invention can be provided while having a glass transition temperature in this range. . As such alicyclic diol, it is preferable to use at least one selected from the group consisting of spiro glycol, tricyclodecane dimethanol and cyclohexane dimethanol.

Among the copolymerized polyethylene naphthalene dicarboxylates, it is preferable to use a copolymerized polyethylene nafphthalate having at least one alicyclic dicarboxylic acid or alicyclic diol as a copolymerization component, and including such a copolymer component. Thus, the glass transition temperature described above can be provided. As these copolymerization components, it is preferable to use at least one selected from the group consisting of cyclohexanedicarboxylic acid, decahydronaphthalenedicarboxylic acid, spiroglycol, tricyclodecane dimethanol and cyclohexanedimethanol. Examples of the spiroglycol component include 3,9-bis (2-hydroxy-1,1-dimethylethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane.
The copolymer polyester containing these copolymer components may be obtained by a method in which the copolymer components of the monomers are subjected to a polycondensation after an ester exchange reaction or an esterification reaction, and a plurality of polyesters are blended. Polyester obtained in this way may be used.

(Refractive index characteristics between the first layer and the second layer)
The refractive index difference in the X direction between the first layer and the second layer in the film plane is preferably 0.10 to 0.45, more preferably 0.20 to 0.40, and even more preferably 0.25 to 0.25. 0.30. When the refractive index difference in the X direction is within such a range, the reflection characteristics can be improved efficiently, and a high reflectance can be obtained with a smaller number of layers.
Moreover, it is preferable that the difference in refractive index in the Y direction between the first layer and the second layer and the difference in refractive index in the Z direction between the first layer and the second layer are 0.05 or less, respectively. Since the refractive index difference between the layers in the Y direction and the Z direction is both in the above-described range, a hue shift can be suppressed when polarized light is incident at an oblique incident angle.

(Number of layers)
The multilayer uniaxially stretched film of the present invention is obtained by alternately laminating the above-described first layer and second layer in total of 251 layers. By providing such a number of layers, it is possible to obtain a constant high average reflectance over a wavelength range of 400 to 800 nm with respect to the average reflectance characteristic of the polarization component parallel to the incident surface including the stretching direction.
The number of stacked layers is not particularly limited as long as it is within such a range, but as the number of stacked layers increases, a higher reflectance is obtained for polarized light parallel to the reflection axis direction, preferably 301 layers or more, more preferably 401 layers or more, More preferably, it is 501 layers or more.

Further, as a more preferable method for obtaining a multi-layer uniaxially stretched film having 501 layers or more, a melt in an alternately laminated state is obtained in a range of 300 layers or less, and while maintaining such a layer configuration, a direction perpendicular to the lamination direction The number of layers can be increased by a method of dividing the layers so as to have a ratio of 1: 1 and stacking again so that the number of layers (doubling number) is 2 to 4 times.
The upper limit of the number of layers is limited to 2001 layers from the viewpoints of productivity and film handling. As long as the average reflectance characteristic of the present invention is obtained, the upper limit value of the number of layers may be further reduced from the viewpoint of productivity and handling properties, and may be, for example, 1001 layers or 901 layers.

(Each layer thickness)
Since the first layer and the second layer selectively reflect light by optical interference between layers, the thickness of each layer is preferably 0.01 μm or more and 0.5 μm or less. The thickness of each layer can be determined based on a photograph taken using a transmission electron microscope.
The reflection wavelength band exhibited by the multilayer uniaxially stretched film of the present invention is preferably from the visible light region to the near infrared region, and is preferably in the range of the layer thickness. When the layer thickness exceeds 0.5 μm, the reflection band becomes an infrared region, and usefulness as a reflective polarizing film may not be obtained. On the other hand, when the layer thickness is less than 0.01 μm, the polyester component may absorb light and the reflection performance may not be obtained.
The thickness of each layer of the first layer is preferably 0.01 μm or more and 0.1 μm or less. The thickness of each layer of the second layer is preferably 0.01 μm or more and 0.3 μm or less.

(Ratio of maximum layer thickness to minimum layer thickness)
In the multilayer uniaxially stretched film of the present invention, the ratio between the maximum layer thickness and the minimum layer thickness in each of the first layer and the second layer is preferably 2.0 or more and 5.0 or less, more preferably 2. It is 0 or more and 4.0 or less, more preferably 2.0 or more and 3.5 or less, and particularly preferably 2.0 or more and 3.0 or less.
The ratio of the layer thickness is specifically represented by the ratio of the maximum layer thickness to the minimum layer thickness. The maximum layer thickness and the minimum layer thickness in each of the first layer and the second layer can be obtained based on a photograph taken using a transmission electron microscope.

  In multilayer uniaxially stretched films, the wavelength to be reflected is determined by the difference in refractive index between layers, the number of layers, and the thickness of the layers. However, if each of the laminated first and second layers has a constant thickness, only a specific wavelength is reflected. It is difficult to increase the average reflectance uniformly over a wide wavelength band such as a wavelength of 400 to 800 nm with respect to the average reflectance characteristics of the polarization component parallel to the incident surface including the stretching direction (X direction). Sometimes. In addition, when the ratio between the maximum layer thickness and the minimum layer thickness exceeds the upper limit value, the reflection band is excessively widened, and the reflectance of the polarization component parallel to the incident surface including the stretching direction (X direction) may decrease. is there.

The first layer and the second layer may change stepwise or may change continuously. By changing each of the first layer and the second layer laminated in this way, light in a wider wavelength range can be reflected.
Although the lamination | stacking method of the multilayer uniaxially stretched film of this invention is not specifically limited, For example, the 1st layer and the 2nd layer which branched the polyester for 1st layers into 138 layers, the copolymer polyester for 2nd layers into 137 layers, The method of using the multilayer feed block apparatus which is laminated | stacked alternately and the flow path changes continuously 2.0 to 5.0 times is mentioned.

(Average layer thickness ratio of the first layer and the second layer)
In the multilayer uniaxially stretched film of the present invention, the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is preferably in the range of 1.5 to 5.0 times. The lower limit value of the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is more preferably 2.0. The upper limit of the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is more preferably 4.0, and even more preferably 3.5.
Since the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is in such a range, secondary reflection occurring at a half wavelength of the reflection wavelength can be effectively used. Therefore, each of the first layer and the second layer The ratio of the maximum layer thickness to the minimum layer thickness can be minimized, which is preferable from the viewpoint of optical characteristics. In addition, by changing the thickness ratio of the first layer and the second layer in this way, the mechanical properties of the obtained film are also adjusted while maintaining the adhesion between the layers and without changing the resin used. And has an effect of making the film difficult to tear.
On the other hand, when the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer deviates from this range, the secondary reflection that occurs at the half wavelength of the reflection wavelength becomes small, and the reflectance may decrease. .

(Thickness adjustment layer)
The multilayer uniaxially stretched film of the present invention may have, in addition to the first layer and the second layer, a thickness adjusting layer having a layer thickness of 2 μm or more in a part of the alternately laminated structure of the first layer and the second layer. Good. By having the thickness adjusting layer having such a thickness in a part of the alternately laminated structure of the first layer and the second layer, the thickness of each layer constituting the first layer and the second layer is made uniform without affecting the polarization function. Easy to adjust. The thickness adjusting layer having such a thickness may be the same composition as either the first layer or the second layer, or a composition partially including these compositions. Since the layer thickness is thick, the thickness adjusting layer does not contribute to the reflection characteristics.

(Uniaxially stretched film)
The multilayer uniaxially stretched film in the present invention is stretched in at least a uniaxial direction in order to satisfy the optical characteristics as the target reflective polarizing film. The uniaxial stretching in the present invention includes not only a film stretched only in a uniaxial direction but also a film stretched in a biaxial direction and further stretched in one direction. The uniaxial stretching direction (X direction) may be either the film longitudinal direction or the width direction. Further, in the case of a film stretched in a biaxial direction and stretched in one direction, the direction (X direction) that is more stretched may be either the film longitudinal direction or the width direction. In the direction where the draw ratio is low, it is preferable that the draw ratio is about 1.05 to 1.20 times from the viewpoint of improving the polarization performance. In the case of a film stretched in a biaxial direction and stretched in one direction, the “stretch direction” in relation to polarized light and refractive index refers to a more stretched direction.
As the stretching method, known stretching methods such as heat stretching with a rod heater, roll heat stretching, and tenter stretching can be used, but tenter stretching is preferable from the viewpoint of reducing scratches due to contact with the roll and stretching speed.

(Film thickness)
The multilayer uniaxially stretched film of the present invention preferably has a film thickness of 15 μm to 150 μm, more preferably 25 μm to 100 μm, and still more preferably 30 μm to 80 μm.

[Average reflectance]
The multilayer uniaxially stretched film of the present invention has a film surface as a reflection surface, and the incident light at an incident angle of 0 degrees and 50 degrees with respect to a polarization component parallel to the incident surface including the stretching direction (X direction) of the uniaxially stretched film. It is preferable that the average reflectance with respect to polarized light at a wavelength of 400 to 800 nm is 90% or more.
In addition, with respect to the polarization component perpendicular to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as the reflecting surface, the wavelength of the incident polarized light at an incident angle of 0 degrees and 50 degrees is 400 to 800 nm. The average reflectance is preferably 15% or less.
Here, the incident surface refers to a surface that is perpendicular to the reflecting surface and includes the incident light beam and the reflected light beam. In addition, the polarization component parallel to the incident surface including the film surface as a reflection surface and including the stretching direction (X direction) of the uniaxially stretched film is generally referred to as P-polarized light. In addition, a polarized light component having a film surface as a reflection surface and perpendicular to an incident surface including a stretching direction (X direction) of a uniaxially stretched film is generally referred to as S-polarized light. Furthermore, the incident angle represents an incident angle with respect to a direction perpendicular to the film surface.

For a polarized light component (P-polarized light) parallel to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as a reflecting surface, the wavelength 400 for the incident polarized light at incident angles of 0 degrees and 50 degrees The average reflectance of ˜800 nm is more preferably 95% or more and 100% or less, and particularly preferably 97% or more and 100% or less.
When the average reflectance at a wavelength of 400 to 800 nm with respect to the P-polarized light component at such an incident angle is less than the lower limit, the polarization reflection performance as a reflective polarizing film may not be sufficiently high, and the hue shift of the reflected light may be Coloring may occur when a display is formed. Further, the higher the average reflectance within such a range, the higher the polarization reflection performance.
As a member for improving brightness in the first aspect of the liquid crystal display device of the present invention, it has such a high average reflectance characteristic with respect to the P-polarized component and also has a reflectance characteristic described later with respect to the S-polarized component. It can be used suitably.

  Further, in this average reflectance range, the average reflectance for the P-polarized light component is 95% or more with respect to the incident angles of 0 degrees and 50 degrees, so that the transmission amount of the P-polarized light can be suppressed as compared with the conventional one, and the S-polarized light. A high polarization performance that selectively transmits light is exhibited, and a high polarization performance comparable to that of a conventional absorption-type polarizing plate is obtained. As in the second embodiment of the liquid crystal display device of the present invention, the liquid crystal cell is bonded alone. It can be used as a polarizing plate. At the same time, the P-polarized light in the direction orthogonal to the transmission axis is highly reflected without being absorbed by the film, so that it can also function as a brightness enhancement film for reusing such light. In addition, for the P-polarized light at an incident angle of 50 degrees, since the average reflectance is thus high, high polarization performance is obtained, and transmission of light incident in an oblique direction is highly suppressed. Hue shift is suppressed.

  The average of the wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree with respect to the polarization component (S-polarized light) perpendicular to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as the reflecting surface The reflectance is more preferably 12% or less, further preferably 5% or more and 12% or less, and particularly preferably 8% or more and 12% or less.

Moreover, the average reflectance of the wavelength 400-800 nm with respect to the incident polarized light at an incident angle of 50 degrees with respect to a polarized light component perpendicular to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as a reflecting surface. Is more preferably 13% or less, still more preferably 5% or more and 12.5% or less, and particularly preferably 8% or more and 12% or less.
When the average reflectance at a wavelength of 400 to 800 nm with respect to the S-polarized light component at such an incident angle exceeds the upper limit value, the polarization transmittance as a reflective polarizing film may be reduced, which may cause a brightness enhancement film such as a liquid crystal display or a liquid crystal cell. In some cases, sufficient performance as a polarizing plate to be bonded is not exhibited.

On the other hand, although the transmittance of the S-polarized component is higher when the polarization reflectance is lower than the above range, it may be difficult to lower the lower limit than the lower limit. In particular, when the reflectance for S-polarized light is within a more preferable range as well as the above-described high average reflectance for P-polarized light, the amount of S-polarized light transmitted to the side opposite to the light source is increased, which is comparable to the conventional absorption polarizing plate. High polarization performance is obtained, and it can be suitably used as a polarizing plate that is independently bonded to a liquid crystal cell as in the second embodiment of the liquid crystal display device of the present invention.
In order to obtain an average reflectance characteristic for such a P-polarized component, in addition to the thickness of each layer and the number of layers, a polymer having the above-described characteristics is used as the polymer component constituting the first layer and the second layer, and the stretching direction ( In the X direction, the film is stretched at a constant draw ratio to increase the birefringence in the in-plane direction of the first layer, thereby increasing the refractive index difference between the first layer and the second layer in the stretching direction (X direction). Is achieved.

  Further, in order to obtain an average reflectance characteristic for the S-polarized component, a polymer having the above-described characteristics is used as a polymer component constituting the first layer and the second layer, and a direction perpendicular to the stretching direction (Y direction) This is achieved by making the difference in the refractive index between the first layer and the second layer in the orthogonal direction (Y direction) extremely small.

[Hue]
The multilayer uniaxially stretched film in the present invention preferably has a small amount of change in hue with respect to incident light in an oblique direction. Specifically, according to JIS standard Z8729, at least one of the x and y values in the CIE color system is 0. It is preferable that the maximum change amount in a field of -80 degrees is less than 0.03, and it is preferable that the maximum change in both x and y is less than 0.03. In the case of the maximum change amount exceeding this range, the hue shift of the transmitted polarized light due to the incident angle in the oblique direction is large, and when used as a brightness enhancement film, the hue shift at a high viewing angle becomes large, and the visibility may be lowered. is there.
In order to make the hue change amount in such a range, the above-mentioned specific polyester is used as the polymer constituting the first layer and the second layer, respectively, and the relationship between the refractive indexes in the above-mentioned X direction, Y direction, and Z direction by stretching. To achieve this.

[Heat shrinkage characteristics]
The multilayer uniaxially stretched film of the present invention preferably has a heat shrinkage rate of 1.5% or less, more preferably 1.0% or less at 85 ° C. for 30 minutes. Such heat shrinkage characteristics are characteristics in both the uniaxial stretching direction and the orthogonal direction.
Although the present invention is a multilayer uniaxially stretched film having reflective polarization performance, it has a high heat-resistant dimensional stability in both the stretching direction and the orthogonal direction thereof, and therefore is a case where the heat treatment is performed or the use environment includes a high-temperature environment. However, the shrinkage does not cause a decrease in polarization performance, and high polarization performance can be maintained.
As a method for obtaining such heat-resistant dimensional stability, a copolymer polyester having the above-mentioned high glass transition temperature on the low refractive index side, using the aromatic polyester (I) having a low stress property during stretching on the high refractive index layer side. The method using is mentioned.

[Haze characteristics]
The multilayer uniaxially stretched film of the present invention preferably has a haze value of 1.0% or less, and more preferably 0.5% or less. By having such a haze value characteristic, the transmittance of S-polarized light is increased, and a higher degree of polarization can be obtained. Such a haze value is obtained by using a copolymer polyester having a high glass transition temperature as the polyester of the second layer, and each layer constituting the multilayer uniaxially stretched film of the present invention contains or does not contain an additive such as a lubricant. It can be obtained by making it within a range of 0.1% by weight or less based on the weight.

[Heat seal layer]
The multilayer uniaxially stretched film of the present invention can be further provided with a heat seal layer (hereinafter sometimes referred to as a protective layer) on at least one outermost layer surface of the alternate lamination of the first layer and the second layer. By having a heat seal layer, when laminating | stacking with another member as a member of a liquid crystal display, for example, members can be bonded together via a heat seal layer by heat processing.
As such a heat seal layer, it is preferable to use a thermoplastic resin having a melting point equal to or lower than the melting point of the outermost layer of the alternately laminated layers. It is preferable to use it. Moreover, it is preferable that the heat seal layer thickness is 3-10 micrometers. By providing such a layer, the members can be firmly bonded to each other.

In addition, when providing the above-mentioned thickness adjustment layer on the outermost layer surface of an alternating lamination, when it has the above-mentioned characteristic, it functions also as a heat seal layer. Moreover, when the above-mentioned thickness adjustment layer exists in the outermost layer surface of alternate lamination, a heat seal layer may be further provided on the thickness adjustment layer.
When the same copolymer polyester as the second layer is used as the heat seal layer, the heat seal layer has a layer thickness of 3 to 10 μm, compared to 0.5 μm, which is the maximum thickness of the layers constituting such an alternate lamination. The layer having a thickness of 4 times or more is a layer that does not contribute to the reflectance in the wavelength band of 400 to 800 nm, and is distinguished from the alternate lamination of the first layer and the second layer. Moreover, even if it uses the blend of the 1st layer and the 2nd layer in the range which does not impair the characteristic as a heat seal layer, it is satisfactory.

[Brightness improvement member]
The multilayer uniaxially stretched film of the present invention selectively reflects the P-polarized component with high reflection, selectively transmits the S-polarized component perpendicular to the polarization component with high transmission, and transmits polarized light with respect to light incident in an oblique direction. Hue shift is eliminated. Therefore, it can be suitably used as a brightness enhancement film for a liquid crystal display, and can be processed into a brightness enhancement member. In particular, since it has a higher polarization performance than the conventional one, it is possible to provide a liquid crystal display which has a high luminance improvement rate when used as a member for improving luminance and has a high viewing angle and excellent visibility with little hue shift. it can. In addition, the multilayer uniaxially stretched film of the present invention is a multilayer uniaxially stretched film having reflective polarization performance, and has high heat stability in both the stretching direction and its orthogonal direction. In order to impart heat-resistant dimensional stability, it is necessary to use a layer made of a resin having high heat-resistant dimensional stability on both sides of the film. Therefore, high heat-resistant stability can be provided without using such a layer.

[Liquid Crystal Display Device Including Brightness Improvement Member]
When the multilayer uniaxially stretched film of the present invention is used as a brightness enhancement member, it can be used in a liquid crystal display device with the configuration of the first embodiment as shown in FIG.
Specifically, there is exemplified a liquid crystal display device in which a brightness enhancement member 4 is disposed between a light source 5 of a liquid crystal display and a liquid crystal panel 6 composed of a polarizing plate 1 / a liquid crystal cell 2 / a polarizing plate 3. The

[Reflective polarizing plate for bonding liquid crystal cells]
The multilayer uniaxially stretched film of the present invention can be used as a reflective polarizing plate to be bonded to a liquid crystal cell.
Specifically, in the multilayer uniaxially stretched film of the present invention, the P-polarized component has an average reflectance of a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree and 50 degrees, respectively, of 95% or more, and S polarized light. As a component, a multilayer uniaxially stretched film having an average reflectance of 400 to 800 nm with respect to the incident polarized light at incident angles of 0 degrees and 50 degrees is 12.5% or less is used as a reflective polarizing plate to be bonded to a liquid crystal cell. be able to.
A polarizing plate having such reflectance characteristics has a high polarization performance comparable to that of a conventional absorption polarizing plate, a function as a brightness enhancement film that reflects and reuses polarized light that is not transmitted, and is incident in an oblique direction. The hue shift of the transmitted light with respect to the transmitted light is eliminated. Further, in the bonding with the liquid crystal cell, it is often bonded by heating through an adhesive layer, and the dimensional change is small after such a process, so that the high polarization performance of the present invention is maintained.

[Optical members for liquid crystal display devices]
The present invention also includes an optical member for a liquid crystal display device in which a first polarizing plate, a liquid crystal cell, and a second polarizing plate made of the multilayer uniaxially stretched film of the present invention are laminated in this order. In the present invention, it may be referred to as a second aspect of the liquid crystal display device). Such an optical member is also referred to as a liquid crystal panel. The optical member corresponds to 11 in FIG. 2, the first polarizing plate corresponds to 9, the liquid crystal cell corresponds to 8, and the second polarizing plate corresponds to 7.
Conventionally, a polarizing plate using the multilayer uniaxially stretched film of the present invention has been obtained by having at least an absorptive polarizing plate as polarizing plates on both sides of the liquid crystal cell. Since high polarization performance that cannot be achieved with a uniaxially stretched film can be obtained, it can be used in combination with a liquid crystal cell in place of a conventional absorption polarizing plate.

That is, the feature of the present invention is that a polarizing plate comprising the multilayer uniaxially stretched film of the present invention is used alone as one first polarizing plate in one of the liquid crystal cells. A plurality of multilayer uniaxially stretched films of the present invention may be laminated to form the first polarizing plate. A laminate in which the multilayer uniaxially stretched film of the present invention is laminated with another film may be used as the first polarizing plate, but preferably the configuration in which the multilayer uniaxially stretched film of the present invention and the absorption polarizing plate are laminated. Excluded.
The type of the liquid crystal cell is not particularly limited, and any type of liquid crystal cell such as a VA mode, an IPS mode, a TN mode, an STN mode, or a bend alignment (π type) can be used.

Moreover, the kind of 2nd polarizing plate is not specifically limited, Both an absorption type polarizing plate and a reflection type polarizing plate can be used. When a reflective polarizing plate is used as the second polarizing plate, it is preferable to use a reflective polarizing plate made of the multilayer uniaxially stretched film of the present invention.
In the optical member for a liquid crystal display device of the present invention, the first polarizing plate, the liquid crystal cell, and the second polarizing plate are preferably laminated in this order, and these members may be laminated directly, Further, the layers may be laminated through a layer called an adhesive layer or an adhesive layer that enhances adhesion between layers (hereinafter sometimes referred to as an adhesive layer), a protective layer, or the like.

[Formation of optical member for liquid crystal display device]
As a method of disposing the polarizing plate in the liquid crystal cell, it is preferable to laminate both with an adhesive layer. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited. For example, an acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is appropriately selected. Can be used. In particular, an acrylic pressure-sensitive adhesive that is excellent in transparency, has suitable wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and is excellent in weather resistance, heat resistance, and the like. The adhesive layer may be provided with a plurality of layers having different compositions or types.
From the viewpoint of workability when laminating the liquid crystal cell and the polarizing plate, the adhesive layer is preferably attached in advance to one or both of the polarizing plate and the liquid crystal cell. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 to 500 μm, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

(Release film)
Moreover, it is preferable that a release film (separator) is temporarily attached to the exposed surface of the pressure-sensitive adhesive layer for the purpose of preventing contamination or the like until it is practically used. Thereby, it can prevent contacting an adhesion layer in the usual handling state. Examples of release films include plastic films, rubber sheets, paper, cloth, non-woven fabrics, nets, foam sheets, metal foils, laminates thereof, and the like, silicone-based or long-chain alkyl-based, fluorine-based or molybdenum sulfide. Those coated with a release agent such as can be used.

[Liquid crystal display device including reflective polarizing plate for bonding liquid crystal cells]
The present invention also includes a liquid crystal display device comprising a light source and the optical member for a liquid crystal display device of the present invention, wherein the first polarizing plate is disposed on the light source side.
FIG. 2 is a schematic sectional view of a liquid crystal display device according to the second embodiment of the present invention. The liquid crystal display device has a light source 10 and a liquid crystal panel 11, and further incorporates a drive circuit and the like as necessary. The liquid crystal panel 11 includes a first polarizing plate 9 on the light source 10 side of the liquid crystal cell 8. Further, the second polarizing plate 7 is provided on the side opposite to the light source side of the liquid crystal cell 8, that is, on the viewing side. As the liquid crystal cell 8, an arbitrary type such as a VA mode, an IPS mode, a TN mode, an STN mode, a bend alignment (π type), or the like can be used.

The liquid crystal display device of the present invention has a conventional absorption by disposing the first polarizing plate 9 made of the reflective polarizing plate for bonding a liquid crystal cell of the present invention having high polarization performance on the light source side of the liquid crystal cell 8. It can be used in combination with a liquid crystal cell instead of a mold polarizing plate.
Since the polarizing plate of the present invention has a high polarization performance comparable to that of a conventional absorption polarizing plate and a function as a brightness enhancement film that reflects and reuses polarized light that is not transmitted, the light source 10 and the first polarization There is no need to use a reflective polarizing plate called a brightness enhancement film between the plate 9 and the function of the polarizing plate to be bonded to the brightness enhancement film and the liquid crystal cell can be integrated, thereby reducing the number of members. Can do.

Furthermore, the liquid crystal display device of the present invention uses the polarizing plate of the present invention as the first polarizing plate, so that the light incident in the oblique direction hardly transmits the P-polarized component incident in the oblique direction, and at the same time obliquely Since the S-polarized component incident in the direction is transmitted while suppressing reflection, the hue deviation of the transmitted light with respect to the light incident in the oblique direction is suppressed. Therefore, it can be visually recognized as the color of the image projected as the liquid crystal display device.
Further, normally, as shown in FIG. 2, the second polarizing plate 7 is disposed on the viewing side of the liquid crystal cell 8. The second polarizing plate 7 is not particularly limited, and a known one such as an absorption polarizing plate can be used. When the influence of external light is very small, the same type of reflective polarizing plate as the first polarizing plate may be used as the second polarizing plate. In addition to the second polarizing plate, for example, various optical layers such as an optical compensation film can be provided on the viewing side of the liquid crystal cell 8.

[Formation of liquid crystal display device including reflective polarizing plate for bonding liquid crystal cell]
The liquid crystal display device of the second aspect of the present invention can be obtained by combining the optical member for liquid crystal display device (liquid crystal panel) of the present invention and a light source, and further incorporating a drive circuit and the like as necessary. In addition to these, various members necessary for the formation of the liquid crystal display device can be combined. However, the liquid crystal display device of the present invention allows light emitted from the light source to enter the first polarizing plate. Is preferred.
Generally, the light source of a liquid crystal display device is roughly classified into a direct type and a side light type, but the liquid crystal display device of the present invention can be used without any limitation.

  The liquid crystal display device thus obtained includes, for example, OA equipment such as a personal computer monitor, notebook personal computer, copy machine, etc., mobile equipment such as a mobile phone, a clock, a digital camera, a personal digital assistant (PDA), a mobile game machine, Household electrical equipment such as video cameras, TVs, microwave ovens, back monitors, car navigation system monitors, car audio equipment, in-vehicle equipment, display equipment such as commercial store information monitors, security equipment such as monitoring monitors, It can be used for various applications such as nursing care and medical equipment such as nursing monitors and medical monitors.

[Method for producing multilayer uniaxially stretched film]
Below, the manufacturing method of the multilayer uniaxially stretched film of this invention is explained in full detail.
The multilayer uniaxially stretched film of the present invention is obtained by extruding an aromatic polyester constituting the first layer and a copolymer polyester constituting the second layer alternately in a molten state in a state where at least 251 layers or more are superposed. (Step of making a sheet-like material). At this time, the laminated body of 251 layers or more laminated | stacked so that the thickness of each layer may change in the range of 2.0 times-5.0 times in steps or continuously.

  The multilayer unstretched film thus obtained is stretched in the film forming direction or at least one axial direction (direction along the film surface) in the width direction perpendicular thereto. The stretching temperature is preferably in the range of the glass transition temperature (Tg) to Tg + 50 ° C. of the polyester of the first layer. The draw ratio at this time is preferably 2 to 10 times, more preferably 2.5 to 7 times, still more preferably 3 to 6 times, and particularly preferably 4.5 to 5.5 times. The larger the draw ratio, the smaller the variation in the plane direction of the individual layers in the first layer and the second layer due to the thinning by stretching, and the optical interference of the multilayer uniaxially stretched film becomes uniform in the plane direction. This is preferable because the difference in refractive index between the first layer and the second layer in the stretching direction becomes large. As the stretching method at this time, known stretching methods such as heat stretching with a rod heater, roll heating stretching, and tenter stretching can be used. From the viewpoints of reducing scratches due to contact with the roll and stretching speed, tenter stretching is performed. preferable. Moreover, when performing a extending | stretching process also in the direction (Y direction) orthogonal to this extending | stretching direction and performing biaxial stretching, it is preferable to limit to a draw ratio of about 1.05-1.20 times. If the stretch ratio in the Y direction is further increased, the polarization performance may be deteriorated. Moreover, it is preferable to perform a heat setting process after extending | stretching.

  In the present invention, for example, as a more preferable method for obtaining a multilayer uniaxially stretched film having 501 layers or more, a melt in an alternately laminated state is obtained in a range of 300 layers or less, and while maintaining such a layer configuration, a direction perpendicular to the lamination direction The number of layers can be increased by a method of dividing the layers so as to have a ratio of 1: 1 and stacking again so that the number of layers (doubling number) is 2 to 4 times. When performing such doubling treatment, it can be carried out by a known method, and after the obtained melt in the laminated state is cast on a cast drum to obtain a multilayer unstretched film, the multilayer uniaxial is obtained through the stretching process described above. A stretched film can be obtained.

  The invention is further described by way of examples. In addition, the physical property and characteristic in an Example were measured or evaluated by the following method.

(1) Melting point (Tm) and glass transition point (Tg) of polyester and film
10 mg of a polyester sample or a film sample is sampled, and a melting point and a glass transition point are measured at a temperature increase rate of 20 ° C./min using DSC (trade name: DSC2920, manufactured by TA Instruments).

(2) Identification of resin and identification of copolymer component and amount of each component For each layer of the film sample, the component of the resin, the copolymer component and the amount of each component were identified by ¹ H-NMR measurement.

(3) Thickness of each layer A film sample was cut into a film length direction of 2 mm and a width direction of 2 cm, fixed to an embedding capsule, and then embedded with an epoxy resin (Refotech Co., Ltd. Epomount). The embedded sample was cut perpendicularly in the width direction with a microtome (LETRAC ULCT UCT manufactured by LEICA) to form a thin film slice having a thickness of 5 nm. Using a transmission electron microscope (Hitachi S-4300), the film was observed and photographed at an acceleration voltage of 100 kV, and the thickness of each layer was measured from the photograph.
Moreover, based on the thickness of each obtained layer, the ratio of the maximum layer thickness to the minimum layer thickness in the first layer and the ratio of the maximum layer thickness to the minimum layer thickness in the second layer were determined.
Moreover, based on the thickness of each obtained layer, the average layer thickness of the first layer and the average layer thickness of the second layer were determined, respectively, and the average layer thickness of the second layer relative to the average layer thickness of the first layer was calculated. .
In addition, the thickness adjustment layer of the outermost layer was excluded from the first layer and the second layer. Further, when a thickness adjusting layer having a thickness of 2 μm or more exists in the alternate lamination, such a layer was also excluded from the first layer and the second layer.

(4) Total film thickness A film sample is sandwiched between spindle detectors (K107C manufactured by Anritsu Electric Co., Ltd.), and 10 points of thickness are measured at different positions using a digital differential electronic micrometer (K351 manufactured by Anritsu Electric Co., Ltd.). And the average value was calculated | required and it was set as the film thickness.

(5) Refractive index and average refractive index in each direction Each polymer constituting each layer is melted and extruded from a die, and a film cast on a casting drum is prepared. The obtained film is made into a multilayer stretched film. A stretched film was prepared by forming a film under the same conditions as the film conditions. With respect to the obtained stretched film, the refractive index (respectively expressed as n _X , n _Y , and n _Z ) in the stretching direction (X direction), the orthogonal direction (Y direction), and the thickness direction (Z direction) is determined by Metricon. The refractive index at a wavelength of 633 nm was measured by using a prism coupler manufactured, and the average value of n _X , n _Y , and n _Z was determined for the average refractive index.

(6) Reflectance, reflection wavelength Using a spectrophotometer (manufactured by Shimadzu Corporation, MPC-3100), a polarizing filter is mounted on the light source side, and the relative specular reflectance with the aluminum-deposited mirror at each wavelength is calculated. Measurement is performed in the wavelength range of 400 nm to 800 nm. In this case, the measured value when the transmission axis of the polarizing filter is aligned with the film stretching direction (X direction) is P-polarized light, and the transmission axis of the polarizing filter is disposed perpendicular to the film stretching direction. Was measured as S-polarized light. For each polarization component, the average reflectance in the range of 400 to 800 nm was defined as the average reflectance.
In the measurement, the multilayer uniaxially stretched film sample described in each specific example was used, and the reflectance characteristic at 0 degree incidence was measured at a 0 degree incident angle where measurement light was incident from the direction perpendicular to the film surface of the film sample. Went. Also, the reflectance characteristics at 50 degrees incidence is such that the measured polarized light is incident on the light source so that the perpendicular direction to the film surface of the film sample is 0 degrees and the measured polarized light is incident at a position tilted from 0 degrees to 50 degrees within the incident plane. The position of was adjusted and measured.

(7) Heat shrinkage rate Marks are applied to the film samples at intervals of 30 cm, heat treatment is performed in an oven at 80 ° C. for 30 minutes without applying a load, the interval between the heat marks after the heat treatment is measured, In the orthogonal direction, the thermal contraction rate was calculated by the following formula.
Thermal contraction rate (%) = ((distance between the pre-heat treatment gauge points−distance between the heat treatment gauge points) / distance between the heat treatment gauge points) × 100

(8) Film haze It measured using the haze measuring device (NDH-2000 by Nippon Denshoku Industries Co., Ltd.) according to JIS-K7136.

(9) Brightness improvement effect, hue Using a liquid crystal display device obtained as a personal computer display, the front luminance of the screen of the liquid crystal display device when white display is performed by a personal computer is an FPD viewing angle measurement evaluation device (ErgoScope 88) manufactured by Optodesign. ), The luminance increase rate and the color relative to Comparative Example 1 were calculated, and the luminance improvement effect was evaluated according to the following criteria.
◎: Brightness improvement effect is 160% or more ○: Brightness improvement effect is 150% or more and less than 160% △: Brightness improvement effect is 140% or more and less than 150% ×: Brightness improvement effect is less than 140% The maximum change in hue x and the maximum change in y at all viewing angles from 0 to 80 degrees were evaluated according to the following criteria.
A: Maximum change in both x and y is less than 0.03 ○: Maximum change in either x or y is less than 0.03 x: Maximum change in both x and y is 0.03 or more

(10) Contrast evaluation (degree of polarization)
Using the liquid crystal display device obtained as a personal computer display, the front luminance of the screen of the liquid crystal display device when a white and black screen is displayed on the personal computer is measured with an FPD viewing angle measurement evaluation device (ErgoScope 88) manufactured by Opto Design. The brightness obtained from the white screen and the dark brightness from the black screen were obtained, and the contrast obtained from the bright brightness / dark brightness was evaluated according to the following criteria.
◎: Contrast (bright luminance / dark luminance) 500 or more ○: Contrast (bright luminance / dark luminance) 200 or more and less than 500 Δ: Contrast (bright luminance / dark luminance) 100 or more and less than 200 ×: Contrast (bright luminance / dark luminance) Less than 100

(11) Durability evaluation
Using a liquid crystal display device obtained as a display for a personal computer, the backlight was continuously turned on for 3000 hr, the liquid crystal panel was taken out, the appearance was observed with the naked eye, and evaluation was performed based on the following criteria.
Evaluation criteria:
◎ No change in film appearance after heating
○ Changes in the film after heating are observed visually, but irregularities with a height of less than 0.5 mm are observed.
△ Unevenness with a height of less than 1 mm is seen in the heated film
X Unevenness with a height of 1 mm or more is observed in the heated film.

[Reference example]
(Creating a polarizer)
Dyeing a polymer film composed mainly of polyvinyl alcohol [Kuraray's trade name “9P75R (thickness: 75 μm, average polymerization degree: 2,400, saponification degree 99.9 mol%)”] between rolls having different peripheral speeds While being stretched and conveyed. First, it was immersed in a 30 ° C. water bath for 1 minute to swell the polyvinyl alcohol film and stretched 1.2 times in the conveying direction, and then a 30 ° C. potassium iodide concentration of 0.03% by weight and an iodine concentration of 0.3 By immersing in a weight% aqueous solution for 1 minute, the film was stretched 3 times in the transport direction while dyeing, based on a film that was not stretched at all (original length). Next, the film was stretched 6 times in the conveying direction on the basis of the original length while being immersed in an aqueous solution having a boric acid concentration of 4% by weight and a potassium iodide concentration of 5% by weight for 30 seconds. Next, the obtained stretched film was dried at 70 ° C. for 2 minutes to obtain a polarizer. The polarizer had a thickness of 30 μm and a moisture content of 14.3% by weight.

(Create adhesive)
Polyvinyl alcohol resin having an acetoacetyl group (average polymerization degree 1200, saponification degree 98.5 mol%, acetoacetylation degree 5 mol%) 100 parts by weight 50 parts by weight of methylol melamine at 30 ° C. Then, it was dissolved in pure water to prepare an aqueous solution having a solid content concentration of 3.7% by weight. An aqueous adhesive solution was prepared by adding 18 parts by weight of an aqueous solution containing alumina colloid having a positive charge (average particle diameter of 15 nm) at a solid content concentration of 10% by weight to 100 parts by weight of this aqueous solution. The viscosity of the adhesive solution was 9.6 mPa · s, the pH was in the range of 4 to 4.5, and the compounding amount of the alumina colloid was 74 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol resin.

(Creation of absorption type polarizing plate)
An optically isotropic element having a thickness of 80 μm, a front retardation of 0.1 nm, and a thickness direction retardation of 1.0 nm (the Fuji Colloid product name “Fujitack ZRF80S”) Was applied to one side of the polarizer by roll-to-roll so that the conveying direction of both was parallel, and the same was applied to the opposite side of the polarizer. Then, the above-mentioned alumina colloid-containing adhesive is applied to one side of an optical isotropic element (Fuji Film product name “Fujitack ZRF80S”) so that the thickness after drying is 80 nm. Then, the film was laminated by roll-to-roll, and then dried at 55 ° C. for 6 minutes to obtain a polarizing plate, which will be referred to as “polarizing plate X”.

(Creation of LCD panel)
Taking out the liquid crystal panel from a liquid crystal television (LG Electronics INFINA 22LE5300 2010), which has an IPS mode liquid crystal cell and adopts a direct type backlight, polarizing plates and optical compensation films disposed above and below the liquid crystal cell After removing, the glass surface (front and back) of the liquid crystal cell was washed. Subsequently, an acrylic pressure-sensitive adhesive is applied to the light source side surface of the liquid crystal cell so that the polarizing plate X is in the same direction as the absorption axis direction of the light source side polarizing plate arranged in the original liquid crystal panel. The polarizing plate X was disposed in the liquid crystal cell.
Next, the polarizing plate X is placed on the viewing side surface of the liquid crystal cell with an acrylic pressure-sensitive adhesive in the same direction as the absorption axis direction of the viewing side polarizing plate arranged in the original liquid crystal panel. The polarizing plate X was placed in a liquid crystal cell. In this way, a liquid crystal panel in which the polarizing plate X was disposed on one main surface of the liquid crystal cell and the polarizing plate X was disposed on the other main surface was obtained.

(Creation of liquid crystal display device)
The above liquid crystal panel was incorporated into the original liquid crystal display device, the light source of the liquid crystal display device was turned on, and a white screen and a black screen were displayed on a personal computer, and the luminance of the liquid crystal display device was evaluated.

[Example 1]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, and ethylene glycol are subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and Subsequently, a polycondensation reaction was performed, and the intrinsic viscosity was 0.62 dl / g, 85 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component (described as PEN in the table), and 15 mol% of the acid component was 6 mol%. , 6 ′-(ethylenedioxy) di-2-naphthoic acid component (described as ENA in the table) and an aromatic polyester whose glycol component is ethylene glycol were obtained as a polyester for the first layer.
Further, as the polyester for the second layer, tricyclodecane dimethanol, ethylene glycol and terephthalic acid are subjected to esterification reaction and transesterification reaction in the presence of titanium tetrabutoxide, followed by polycondensation reaction, Fragrance having an intrinsic viscosity of 0.60 dl / g, 30 mol% of the diol component being tricyclodecane dimethanol component (described as TCDM in the table), 70 mol% of the diol component being ethylene glycol component, and acid component being terephthalic acid A group polyester was obtained and used as the second layer polyester.

The prepared polyester for the first layer and polyester for the second layer are each dried at 170 ° C. for 5 hours, then supplied to the first and second extruders, heated to 300 ° C. to be in a molten state, and used for the first layer After branching the polyester to 138 layers and the second layer polyester to 137 layers, the first layer and the second layer are alternately laminated, and the maximum layer thickness and the minimum layer thickness in the first layer and the second layer, respectively. Using a multi-layer feedblock device in which the maximum value is continuously changed up to 2.2 times at the minimum, and a total of 275 layers of the melt in which the first layer and the second layer are alternately stacked, While maintaining the laminated state, the same polyester as the polyester for the second layer is led from the third extruder to the three-layer die on both sides thereof, and a thickness adjusting layer is further provided on both sides of the melt in a total of 275 layers. Laminated. The supply amount of the third extruder was adjusted so that the both end layers (thickness adjusting layers) were 18% of the whole. Next, while maintaining such a stacking state (hereinafter sometimes referred to as one unit), it is divided so as to have a ratio of 1: 1 in the stacking direction and the vertical direction, and the stacking number (doubling number) is doubled. In such a manner, the layers are again laminated, guided to the die while maintaining the laminated state, and cast on the casting drum so that the average layer thickness ratio of the first layer and the second layer is 1.0: 2.6. A multilayer unstretched film was prepared.
This multilayer unstretched film was stretched 5.2 times in the width direction at a temperature of 135 ° C., and heat-set at 130 ° C. for 3 seconds. The total thickness of the obtained film was 66 μm, and the number of layers in the alternately laminated (optical interference layer) portion of the first layer and the second layer was 550 layers.

(Formation of liquid crystal panel)
In the reference example, the light source side main surface of the liquid crystal cell was obtained in the same manner as in Comparative Example 1, except that the obtained reflective polarizing film was used instead of the polarizing plate X as the first polarizing plate on the light source side. A reflective polarizing film (first polarizing plate) and a liquid crystal panel in which a polarizing plate X (second polarizing plate) was disposed on the viewing-side main surface were obtained.

(Creation of liquid crystal display device)
The above liquid crystal panel was incorporated into the original liquid crystal display device, the light source of the liquid crystal display device was turned on, and the brightness of the white screen and the black screen was evaluated with a personal computer.
Table 1 shows the resin configuration of each layer of the multilayer uniaxially stretched film thus obtained and the characteristics of each layer, and Table 2 shows the physical properties of the multilayer uniaxially stretched film and the liquid crystal display device.

[Examples 2 to 11]
As shown in Table 1, a multilayer uniaxially stretched film was obtained in the same manner as in Example 1 except that the resin composition or the layer thickness of each layer was changed. At that time, the stretching temperature and the heat setting temperature were adjusted according to the Tg of the polymer constituting the first layer. Table 2 shows the physical properties of the obtained multilayer uniaxially stretched film.

[Example 12]
A multilayer uniaxially stretched film was obtained in the same manner as in Example 1 except that the number of layers (doubling number) after obtaining a laminated state of 1 unit was changed to 3 times. Table 2 shows the physical properties of the obtained multilayer uniaxially stretched film.

[Example 13]
A multilayer uniaxially stretched film was obtained in the same manner as in Example 1 except that the lamination (doubling) after obtaining the laminated state of 1 unit was not performed. Table 2 shows the physical properties of the obtained multilayer uniaxially stretched film.

[Comparative Example 1]
Lamination after changing the polyester for the first layer to polyethylene-2,6-naphthalenedicarboxylate (PEN) having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.62 dl / g and obtaining a laminated state of 1 unit A multilayer uniaxially stretched film was obtained in the same manner as in Example 1 except that (doubling) was not performed. Table 2 shows the physical properties of the obtained multilayer uniaxially stretched film.

[Comparative Example 2]
As shown in Table 1, the polyester for the second layer was changed to terephthalic acid 45 mol% copolymerized polyethylene-2,6-naphthalenedicarboxylate (TA45PEN) having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.62 dl / g. Except for the above, a multilayer uniaxially stretched film was obtained in the same manner as in Comparative Example 1. Table 2 shows the physical properties of the obtained multilayer uniaxially stretched film.

  In addition, the composition of polyester in Table 1 is as follows.

C2NA: 6,6 ′-(ethylenedioxy) di-2-naphthoic acid NDC: 2,6-naphthalenedicarboxylic acid EG: ethylene glycol PEN: polyethylene-2,6-naphthalenedicarboxylate TMG: trimethylene glycol PTN: Polytrimethylene-2,6-naphthalenedicarboxylate BD: 1,4-butanediol PBN: Polybutylene-2,6-naphthalenedicarboxylate C3NA: 6,6 ′-(trimethylenedioxy) di-2-naphtho Acid TA: Terephthalic acid PET: Polyethylene terephthalate TCDM: Tricyclodecane dimethanol SPG: Spiroglycol CHDC: Cyclohexanedicarboxylic acid DHQE: Decahydronaphthalenedicarboxylic acid IA: Isophthalic acid

  The multilayer uniaxially stretched film of the present invention can be used for a brightness enhancement film, a polarizing plate to be bonded to a liquid crystal cell, and a liquid crystal display.

DESCRIPTION OF SYMBOLS 1 Polarizing plate 2 Liquid crystal cell 3 Polarizing plate 4 Brightness improving member 5 Light source 6 Liquid crystal panel 7 Second polarizing plate 8 Liquid crystal cell 9 First polarizing plate 10 Light source 11 Liquid crystal panel

Moreover, according to this invention, the following brightness improvement member using the said multilayer uniaxially stretched film, the composite member for liquid crystal displays, a liquid crystal display device, a polarizing plate, and the optical member for liquid crystal display devices are also provided.
2. 2. The multilayer uniaxially stretched film according to item 1, wherein the copolymer polyester constituting the second layer is a copolymerized polyethylene terephthalate having an alicyclic diol as a copolymer component.
3. 3. The multilayer uniaxially stretched film according to item 2 above, wherein the copolymer component constituting the copolymer polyethylene terephthalate is at least one selected from the group consisting of spiroglycol, tricyclodecane dimethanol and cyclohexane dimethanol.
4). Multilayer uniaxially stretched film according to item 1 copolyester is a copolymer of polyethylene Na phthalate and alicyclic dicarboxylic acids or of at least one copolymerizable component of the alicyclic diol constituting the second layer.
5). Copolymerization component constituting the copolymer of polyethylene Na phthalate cyclohexane dicarboxylic acid, decahydronaphthalene dicarboxylic acid, spiro glycol, according to item 4 is at least one selected from the group consisting of tricyclodecane and cyclohexanedimethanol Multilayer uniaxially stretched film.
6). The refractive index difference in the uniaxial stretching direction (X direction) of the first layer and the second layer of the multilayer uniaxially stretched film in the film plane is 0.10 to 0.45, and the direction orthogonal to the uniaxial stretch direction The refractive index difference between the first layer and the second layer in the (Y direction) and the refractive index difference between the first layer and the second layer in the film thickness direction (Z direction) are 0.05 or less, respectively. The multilayer uniaxially stretched film according to any one of 5.
7). The film surface is a reflecting surface, and the average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree and 50 degrees with respect to a polarized light component parallel to the incident surface including the X direction is 90% or more, With respect to the polarized light component perpendicular to the incident surface including the X direction with the film surface as the reflecting surface, the average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degrees and 50 degrees is 15% or less, respectively. The multilayer uniaxially stretched film according to any one of 1 to 6 above.
8). A reflective polarizing plate comprising the multilayer uniaxially stretched film according to any one of items 1 to 7.
9. 9. An optical member for a liquid crystal display device, wherein the first polarizing plate, the liquid crystal cell, and the second polarizing plate are sequentially arranged, and the first polarizing plate is the reflective polarizing plate according to item 8 above.
10. A liquid crystal display device comprising a light source and the optical member for a liquid crystal display device according to the preceding item 9, wherein the first polarizing plate is disposed on the light source side.

Among the polyethylene copolymer naphthalene dicarboxylate, it is preferable to use a copolymerized polyethylene Na phthalate and alicyclic dicarboxylic acids or of at least one copolymerizable component alicyclic diols, including such copolymerizable component Thus, the glass transition temperature described above can be provided. As these copolymerization components, it is preferable to use at least one selected from the group consisting of cyclohexanedicarboxylic acid, decahydronaphthalenedicarboxylic acid, spiroglycol, tricyclodecane dimethanol and cyclohexanedimethanol. Examples of the spiroglycol component include 3,9-bis (2-hydroxy-1,1-dimethylethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane.
The copolymer polyester containing these copolymer components may be obtained by a method in which the copolymer components of the monomers are subjected to a polycondensation after an ester exchange reaction or an esterification reaction, and a plurality of polyesters are blended. Polyester obtained in this way may be used.

Claims (10)

In the multi-layer uniaxially stretched film of 251 layers or more in which the first layer and the second layer are alternately laminated,
1) The first layer is a layer made of polyester of a dicarboxylic acid component and a diol component,
(I) The dicarboxylic acid component contains a component represented by the following formula (A) of 5 mol% or more and 50 mol% or less and a component represented by the following formula (B) of 50 mol% or more and 95 mol% or less,

(In the formula (A), R ^A represents an alkylene group having 2 to 4 carbon atoms)

(In formula (B), R ^B represents a naphthalenediyl group)
(Ii) The diol component contains 90 mol% or more and 100 mol% or less of a component represented by the following formula (C),

(In the formula (C), R ^C represents an alkylene group having 2 to 4 carbon atoms)
2) The second layer is made of a copolyester having a glass transition temperature of 80 ° C. or more and a copolymerization amount of 5 mol% to 85 mol%, and has an average refractive index of 1.50 to 1.60 and optical isotropy. A sex layer,
3) The multilayer uniaxially stretched film is characterized in that the thermal shrinkage rate of the multilayer uniaxially stretched film at 85 ° C. for 30 minutes is 1.5% or less.   The multilayer uniaxially stretched film according to claim 1, wherein the copolymer polyester constituting the second layer is a copolymerized polyethylene terephthalate having an alicyclic diol as a copolymer component.   The multilayer uniaxially stretched film according to claim 2, wherein the copolymerization component constituting the copolymerized polyethylene terephthalate is at least one selected from the group consisting of spiroglycol, tricyclodecane dimethanol and cyclohexane dimethanol.   The multilayer uniaxially stretched film according to claim 1, wherein the copolymer polyester constituting the second layer is a copolymerized polyethylene nafphthalate having at least one of alicyclic dicarboxylic acid or alicyclic diol as a copolymer component.   The copolymerization component constituting the copolymerized polyethylene nafphthalate is at least one selected from the group consisting of cyclohexanedicarboxylic acid, decahydronaphthalenedicarboxylic acid, spiroglycol, tricyclodecane dimethanol and cyclohexanedimethanol. Multilayer uniaxially stretched film.   The refractive index difference in the uniaxial stretching direction (X direction) of the first layer and the second layer of the multilayer uniaxially stretched film in the film plane is 0.10 to 0.45, and the direction orthogonal to the uniaxial stretch direction The refractive index difference between the first layer and the second layer in the (Y direction) and the refractive index difference between the first layer and the second layer in the film thickness direction (Z direction) are each 0.05 or less. The multilayer uniaxially stretched film in any one of -5.   The film surface is a reflecting surface, and the average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree and 50 degrees with respect to a polarized light component parallel to the incident surface including the X direction is 90% or more, With respect to the polarized light component perpendicular to the incident surface including the X direction with the film surface as the reflecting surface, the average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degrees and 50 degrees is 15% or less, respectively. The multilayer uniaxially stretched film according to any one of claims 1 to 6.   A reflective polarizing plate comprising the multilayer uniaxially stretched film according to claim 1.   The optical member for a liquid crystal display device, wherein the first polarizing plate, the liquid crystal cell, and the second polarizing plate are sequentially disposed, and the first polarizing plate is the reflective polarizing plate according to claim 8.   A liquid crystal display device comprising a light source and the optical member for a liquid crystal display device according to claim 9, wherein the first polarizing plate is disposed on the light source side.

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