JP2013003410A - Multilayer oriented film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayer oriented film having a reflective polarization function, in which the polarizing performance is further enhanced compared to a conventional film as well as shift in a hue of transmitted polarized light depending on an incident angle in an oblique direction is prevented for the light obliquely incident to the film.SOLUTION: The multilayer oriented film comprises alternately laminated first layers and second layers in total 251 layers or more. The first layer is a layer having a thickness of 0.01 to 0.5 μm and comprising a polyester, which contains: (i) as a dicarboxylic acid component, a specified dicarboxylic acid component by 5 mol% or more and 70 mol% or less containing naphthoic acid component, and a dicarboxylic acid component having a phenylene group; and (ii) as a diol component, a diol component having a 2-4C alkylene group or a 6C alicyclic group. The second layer is a layer having a thickness of 0.01 to 0.5 μm and comprising an optically isotropic copolymer polyester having an average refractive index of 1.55 or more and 1.62 or less. The multilayer oriented film has a specified thickness ratio and a specified difference in the diffraction index between the first layer and the second layer, and shows an average reflectance of 90% or more for a P-polarized light component each at an incident angle of 0 degree and 50 degrees and an average reflectance of 15% or less for a S-polarized light component each at an incident angle of 0 degree and 50 degrees.

Description

  The present invention relates to a multilayer 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 stretched film in which a hue shift of transmitted polarized light is eliminated without being generated.

  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, it is conventionally known to use 2,6-PEN for a layer having a high refractive index. However, when 2,6-PEN is used for a layer having a high refractive index, There is a difference between the refractive index in the direction orthogonal to the stretching direction (Y direction) and the refractive index in the 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. For this reason, there has been a problem that the hue shift of transmitted light is further increased by partial reflection of light incident in an oblique direction.

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

  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 film having a reflective polarization function.

  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 has been found that 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 can be achieved, and the present invention is completed. It came.
That is, the object of the present invention is achieved by the following invention.

1. A multilayer 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 having a thickness of 0.01 μm or more and 0.5 μm or less made of a polyester of a dicarboxylic acid component and a diol component.
(I) The dicarboxylic acid component contains 5 mol% or more and 70 mol% or less of the component represented by the following formula (A) and 30 mol% or more and 95 mol% or less of the component represented by the following formula (B),
(In the formula (A), R ^A represents an alkylene group having 2 to 4 carbon atoms)
(In formula (B), R ^B represents a phenylene 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 or an alicyclic group having 6 carbon atoms)

The second layer comprises a copolymerized polyester having a copolymerization amount of 5 mol% or more and 50 mol% or less, and has an average refractive index of 1.55 or more and 1.62 or less and an optically isotropic thickness of 0.01 μm or more and 0.5 μm or less. Layer of
2) Refractive index difference in the uniaxial stretching direction (X direction) between the first layer and the second layer in the film plane is 0.10 to 0.45, and the direction perpendicular to the uniaxial stretching direction (Y direction) The difference in refractive index between the first layer and the second layer and the difference in refractive index between the first layer and the second layer in the film thickness direction (Z direction) is 0.06 or less,
3) The ratio between the maximum layer thickness and the minimum layer thickness of each of the first layer and the second layer is 2.0 or more and 5.0 or less, and 4) the incident surface includes the X direction as a reflection 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 degree and 50 degrees with respect to a polarized light component parallel to the surface is 90% or more, respectively.
5) With respect to the polarized light component perpendicular to the incident surface including the X direction, with the film surface as the reflective 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. Is,
A multilayer stretched film characterized by that.

Moreover, according to this invention, the following brightness improvement member, composite member for liquid crystal displays, and a liquid crystal display device using said multilayer stretched film are also provided.
2. A member for improving brightness comprising the multilayer stretched film according to item 1.
3. A composite member for a liquid crystal display, wherein a light diffusion film is laminated on at least one surface of the brightness enhancement member according to item 2.
4). 3. A liquid crystal display device comprising the brightness enhancement member according to item 2.
5. A liquid crystal display device comprising the composite member for a liquid crystal display according to item 3 above.

  The multilayer 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 higher polarization performance than the conventional one. Therefore, when used as a polarizing plate to be bonded to a brightness enhancement film or a liquid crystal cell, a high brightness improvement rate can be obtained, and a liquid crystal display excellent in visibility with a small viewing angle and a high viewing angle 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 stretched film]
The multilayer 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 one axial 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 a polyester having a high refractive index, characterized by having a specific copolymer component in the first layer in the first layer and the second layer constituting the multilayer stretched film with a constant layer thickness configuration. And an optically isotropic copolyester having an average refractive index of 1.55 or more and 1.62 or less is used for the second layer. 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 forming the first layer using a specific polyester described later, the refractive index difference between the X direction and the Y direction of the first layer after stretching has a certain amount, but the refraction between the layers in both the Y direction and the Z direction. It becomes possible to reduce the rate difference. 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. In combination with the above, a multilayer film having a constant layer thickness makes it possible to achieve both improvement in polarization performance and suppression of hue shift of transmitted polarized light with respect to incident light in an oblique direction, which has been difficult until now.
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 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 the dicarboxylic acid component (i) constituting the aromatic polyester (I) of the present invention, 5 mol% or more and 70 mol% or less of the component represented by the following formula (A), and 30 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.

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

  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 ′. -(Tetramethylenedioxy) di-2-naphthoic acid is preferred, and among these, 6,6 '-(ethylenedioxy) di-2-naphthoic acid is preferred.

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 70 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 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 phenylene group.
Examples of the component represented by the formula (B) include terephthalic acid and isophthalic acid, and terephthalic acid is particularly preferable.

  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.

(In the formula (C), R ^C represents an alkylene group having 2 to 4 carbon atoms or an alicyclic group having 6 carbon atoms)

In formula (C), R ^C is an alkylene group having 2 to 4 carbon atoms or an alicyclic group having 6 carbon atoms, and examples thereof include an ethylene group, a propylene group, an isopropylene group, a tetramethylene group, and a cyclohexanemethanol group. It is done. As the diol component represented by the formula (C), ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol 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 70 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.

  Other ester units constituting the aromatic polyester (I) include alkylene terephthalates such as ethylene terephthalate, trimethylene terephthalate and butylene terephthalate, and cyclohexanedimethylene terephthalate. Among these, ethylene terephthalate 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 terephthalic 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.

  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 in the range of 30 to 110 ° 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.

(Thickness of the first layer)
The 1st layer of this invention is a layer whose thickness of each layer is 0.01 micrometer or more and 0.5 micrometer or less. When the thickness of the first layer is within such a range, light can be selectively reflected by optical interference between layers.

(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. The difference in refractive index between n _Y and n _Z is small regardless of the draw ratio.

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 1.70 to 1.80. 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 0.06 or less, preferably 0.05 or less, More preferably, it is 0.03 or less. Since the difference in refractive index between these two directions is small, there is an effect that even when polarized light is incident at an oblique incident angle, a hue shift hardly occurs.

  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. In addition, since the diol component of aromatic polyester (I) in this invention is an aliphatic component, the influence which the diol component has on the refractive index characteristic of a 1st layer is small compared with the above-mentioned 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]
(Copolymerized polyester)
In the present invention, the second layer is a copolyester having a coweight of 5 to 50 mol%, preferably 10 to 40 mol%, based on all repeating units constituting the polyester, from the viewpoint of film forming property in uniaxial stretching. More preferably, the copolymerized amount of copolymerized polytrimethylene terephthalate or copolymerized polybutylene terephthalate. Examples of the copolymer component preferably used include aliphatic dicarboxylic acids such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid, and aliphatics such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid. Preferable examples include acid components such as alicyclic dicarboxylic acids such as dicarboxylic acid and cyclohexanedicarboxylic acid, aliphatic diols such as ethylene glycol and hexanediol, and glycol components such as alicyclic diol such as cyclohexanedimethanol. Among these, isophthalic acid, 2,6-naphthalenedicarboxylic acid, or copolymerized polytrimethylene terephthalate or copolymerized polybutylene terephthalate copolymerized with cyclohexanedimethanol is preferable. The copolymerization amount is preferably 10 mol% or less. Among these copolymer components, it is preferable to appropriately adjust the type and amount of copolymer component of the copolymer polyester of the second layer according to the refractive index in the Y direction of the first layer.
The copolymer polyester constituting the second layer may be, for example, one obtained by melt-kneading two or more kinds of polyesters at the stage of forming a film and transesterifying them.

  The second layer made of such a copolyester has an average refractive index of 1.55 to 1.62 and optical isotropy. Here, the average refractive index is obtained by melting the copolymer polyester constituting the second layer alone, extruding from a die to create an unstretched film, and forming the film under the same conditions as the multilayer stretched film. The refractive index in each of the X direction, Y direction, and Z direction of the obtained 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 copolyester constituting the second layer is preferably 1.56 or more and 1.61 or less, 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, the refractive index difference in the X direction between the first layer and the second layer is large, and the refractive index difference in the Y direction and Refractive index characteristics having both small refractive index differences in the Z direction can be obtained. As a result, both the polarization performance and the hue shift due to the incident angle in the oblique direction can be achieved.

(Thickness of the second layer)
The second layer of the present invention is a layer having a thickness of each layer of 0.01 μm or more and 0.5 μm or less. When the thickness of the second layer is within such a range, light can be selectively reflected by optical interference between layers.

(Refractive index difference between the first layer and the second layer)
The difference in refractive index between the first layer and the second layer in the X direction (uniaxial stretching direction in the film plane) needs to be 0.10 to 0.45, preferably 0.10 to 0.30. is there. When the refractive index difference in the X direction is within such a range, the reflection characteristics can be improved efficiently.
The refractive index difference between the first layer and the second layer in the direction (Y direction) orthogonal to the uniaxial stretching direction in the film plane, and the refractive index between the first layer and the second layer in the film thickness direction (Z direction). The differences are each 0.06 or less. Further, the difference in refractive index between the first layer and the second layer in the Y direction is preferably 0.03 or less, more preferably 0.02 or less, and particularly preferably 0.01 or less. Further, the difference in refractive index between the first layer and the second layer in the Z direction is preferably 0.05 or less, more preferably 0.03 or less.

[Ingredients other than resin]
In order to improve the rollability of the film, the multilayer stretched film of the present invention contains at least one outermost layer of inert particles having an average particle diameter of 0.01 μm to 2 μm and 0.001 weight based on the weight of the layer. % To 0.5% by weight is preferred. If the average particle diameter of the inert particles is smaller than the lower limit value or the content is less than the lower limit value, the effect of improving the winding property of the multilayer stretched film tends to be insufficient, while the inclusion of the inert particles When the amount exceeds the upper limit value or the average particle diameter exceeds the upper limit value, deterioration of the optical properties of the multilayer stretched film due to the particles may become remarkable. The average particle diameter of the preferable inert particles is in the range of 0.02 μm to 1 μm, particularly preferably 0.1 μm to 0.3 μm. Moreover, content of a preferable inert particle is the range of 0.02 weight%-0.2 weight%.

  Examples of the inert particles included in the multilayer stretched film include inorganic inert particles such as silica, alumina, calcium carbonate, calcium phosphate, kaolin, and talc, and organic materials such as silicone, crosslinked polystyrene, and styrene-divinylbenzene copolymer. Mention may be made of inert particles. The particle shape is not particularly limited as long as it is a generally used shape such as agglomerated or spherical.

  The inert particles may be contained not only in the outermost layer but also in a layer composed of the same resin as the outermost layer. For example, the inert particles may be contained in at least one of the first layer and the second layer. Good. Alternatively, another layer different from the first layer and the second layer may be provided as the outermost layer, and when a heat seal layer is provided, inert particles may be included in the heat seal layer.

[Laminated structure]
(Number of layers)
The multilayer stretched film of the present invention is obtained by alternately laminating a total of 251 layers of the first layer and the second layer described above. When the number of stacked layers is less than 251 layers, a certain average reflectance cannot be satisfied over a wavelength range of 400 to 800 nm with respect to an average reflectance characteristic of a polarized light 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 multilayer stretched film having a number of layers of 501 or more, a melt in an alternately laminated state is obtained in a range of 300 layers or less, and the layer configuration is maintained in a direction perpendicular to the laminating direction. It is possible to increase the number of layers by a method of dividing the layer so that the ratio is 1: 1 and then 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 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.
Since the reflection wavelength band shown by the multilayer stretched film of the present invention is from the visible light region to the near infrared region, it is necessary to set the layer thickness within the above range. When the layer thickness exceeds 0.5 μm, the reflection band becomes an infrared region, and usefulness as a reflective polarizing film cannot be obtained. On the other hand, when the layer thickness is less than 0.01 μm, the polyester component absorbs light and the reflection performance cannot 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 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 2.0 or more and 5.0 or less, preferably 2.0 or more and 4.0. Hereinafter, it is more preferably 2.0 or more and 3.5 or less, and further preferably 2.0 or more and 3.0 or less.
That is, the ratio between the maximum layer thickness and the minimum layer thickness in the first layer is 2.0 or more and 5.0 or less, and the ratio between the maximum layer thickness and the minimum layer thickness in the second layer is 2.0 or more and 5.0 or less. It is.

For example, in a multilayer stretched film having 126 first layers and 125 second layers, the maximum layer thickness of the first layer is the thickness of the largest layer among the first layers of 126 layers. is there. The minimum layer thickness of the first layer is the thickness of the smallest layer among the 126 first layers.
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 the multilayer stretched film, 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, when each of the laminated first and second layers has a constant thickness, only a specific wavelength is reflected. The average reflectance of the polarization component parallel to the incident surface including the stretching direction (X direction) cannot be increased uniformly over a wide wavelength range of 400 to 800 nm. Further, 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) decreases.

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.
The method for laminating the multilayer stretched film of the present invention is not particularly limited. For example, the first layer and the second layer are alternately divided into 138 layers for the first layer polyester and 137 layers for the second layer copolyester. And a multi-layer feed block device in which the flow path is continuously changed by 2.0 to 5.0 times.

(Average layer thickness ratio of the first layer and the second layer)
In the multilayer 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)
In addition to the first layer and the second layer, the multilayer stretched film of the present invention may have 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. . 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. On the other hand, since it may affect the transmitted polarized light, when the particles are included in the layer, it is preferably within the range of the particle concentration described above.

[Uniaxially stretched film]
The multilayer stretched film of the present invention is stretched in at least a uniaxial direction in order to satisfy the optical properties of 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 in terms of enhancing 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 the more stretched direction in the biaxial 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 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 stretched film of the present invention has the film surface as a reflection surface, and the incident polarized 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. The average reflectance 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. Each average reflectance is 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, not only the polarization reflection performance as a reflective polarizing film, but also the hue shift of the reflected light occurs, resulting in a display. Coloring occurs. 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 case, and 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 13.5% or less, still more preferably 5% or more and 13.5% or less, and particularly preferably 8% or more and 13.5% 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 is lowered, so that it is bonded to a brightness enhancement film such as a liquid crystal display or a liquid crystal cell. It does not exhibit sufficient performance as a polarizing plate.

  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 12% or less as well as the above-mentioned 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 that of a conventional absorption polarizing plate. Polarization performance is obtained, and it can be suitably used as a polarizing plate to be bonded to a liquid crystal cell alone as in the second aspect 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.

(Refractive index characteristics of the first layer)
The refractive index n _X in the X direction of the polyester of the first layer is preferably increased by 0.1 or more by stretching. The larger the change in the refractive index, the higher the polarization performance, but the upper limit is limited to 0.3 because the film breaks when the draw ratio is too high.

Refractive index n _Z in the refractive index n _Y and Z directions in the Y-direction of the polyester of the first layer is preferably reduced in the range of 0.1 or less by stretching. If the amount of decrease in the refractive index exceeds the upper limit, the orientation may be too high and the mechanical strength may not be sufficient.

The difference in refractive index between the Y-direction refractive index n _Y after stretching of the first layer and the Z-direction refractive index n _Z after stretching is preferably 0.06 or less, more preferably 0.05 or less, and still more preferably. 0.03 or less. Since the difference in refractive index between these two directions is small, there is an effect that even when polarized light is incident at an oblique incident angle, a hue shift hardly occurs. Such polarized light is particularly effective in eliminating a hue shift with respect to a polarization component (S-polarized light) perpendicular to an incident surface including a stretching direction (X direction) of a uniaxially stretched film with a film surface as a reflecting surface. .

[Hue]
The multilayer stretched film in the present invention preferably has a small amount of change in hue with respect to incident light in an oblique direction, and specifically, 0 to about at least one of x and y values in the CIE color system in accordance with JIS standard Z8729. It is preferable that the maximum change amount in the 80-degree field of view 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 seal layer]
The multilayer 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. Further, when the copolyester is amorphous and does not exhibit a melting point, or has a melting point, it is preferably a layer having a melting point of 20 ° C. or more lower than the melting point of the first layer polyester and a thickness of 3 to 10 μm. By providing the layer having such characteristics, 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 stretched film of the present invention selectively reflects the P-polarized light component, selectively transmits the S-polarized light component perpendicular to the polarized light component, and transmits the hue of the transmitted polarized light with respect to the incident light in the oblique direction. The deviation 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.

[Composite materials for liquid crystal displays]
It is preferable that the brightness enhancement member prepared using the multilayer stretched film of the present invention is further used as a composite member for a liquid crystal display by further laminating a light diffusion film on at least one surface thereof. Moreover, it is preferable that the brightness enhancement member and the light diffusion film are laminated by being bonded via a heat seal layer.
Moreover, the aspect which laminates | stacks a light-diffusion film on the both surfaces of the member for brightness improvement is preferable for the composite member for liquid crystal displays of this invention. By providing the light diffusing film on the surface layer of the brightness enhancement member, the heat-resistant dimensional stability is improved, and the brightness uniformity is improved.

[Liquid Crystal Display Device Including Brightness Improvement Member]
When the multilayer stretched film of the present invention is used as a member for improving brightness, 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 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 stretched film of the present invention, for the P-polarized light component, 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 is 95% or more, respectively, and the S-polarized light component The multilayer stretched film having 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 of 12% or less can be used as a reflective polarizing plate to be bonded to a liquid crystal cell.
A polarizing plate having such reflectance characteristics has 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.

[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 comprising the multilayer stretched film of the present invention are laminated in this order (this book) In the 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, as a polarizing plate on both sides of a liquid crystal cell, a polarizing property using a multilayer stretched film of the present invention has been obtained by having at least an absorptive polarizing plate. Since high polarization performance that could not be achieved with a film can be obtained, it can be used in combination with a liquid crystal cell instead of a conventional absorption polarizing plate.

That is, the feature of the present invention is that a polarizing plate comprising the multilayer stretched film of the present invention is used alone as one first polarizing plate in one of the liquid crystal cells. A plurality of the multilayer stretched films of the present invention may be laminated to form the first polarizing plate. A laminate in which the multilayer 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 stretched film of the present invention and the absorption polarizing plate are laminated is 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 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 type 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. Instead of the polarizing plate, it can be used in combination with a liquid crystal cell.
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 Containing 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 stretched film]
Below, the manufacturing method of the multilayer stretched film of this invention is explained in full detail.
The multilayer stretched film of the present invention is formed by extruding the polyester constituting the first layer and the copolymer polyester constituting the second layer alternately in a molten state in a state where at least 251 layers or more are superposed on each other. Process). 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 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 light interference of the multilayer stretched film becomes uniform in the plane direction. This is preferable because the difference in refractive index between the layers 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.

  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 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.

(7) Luminance improvement rate and hue when used as a member for improving luminance A laminated film prepared in place of the optical film (diffuse film, prism sheet) in the LCD panel (manufactured by Matsushita Electric's VIERA TH-32LZ80 2007) (Diffusion film / multilayer stretched film / diffusion film laminate film) is inserted between the light source and the polarizing plate, and the front luminance when white is displayed on a PC is measured by an FPD viewing angle measurement evaluation device (ErgoScope 88) manufactured by Optodesign. It was evaluated by.
The rate of increase in luminance after inserting the sample film relative to the luminance before inserting the sample film was 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% Together with JIS standard Z8729 In accordance with the above, the hue x and y values in the CIE color system were measured for the maximum change in hue x or y at all azimuth viewing angles of 0 to 80 degrees and evaluated according to the following criteria.
○: Maximum change in both x and y is less than 0.03 Δ: Maximum change in either x or y is 0.03 or more ×: Maximum change in both x and y is 0.03 or more

[Example 1]
Dimethyl terephthalate, 6,6 '-(ethylenedioxy) di-2-naphthoic acid, and ethylene glycol are subjected to esterification and transesterification in the presence of titanium tetrabutoxide, followed by polycondensation. And an intrinsic viscosity of 0.62 dl / g, 74 mol% of the acid component is terephthalic acid component, 26 mol% of the acid component is 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component, glycol An aromatic polyester whose component is ethylene glycol was obtained. To this, 0.10 wt% of spherical silica particles (average particle size: 0.3 μm, ratio of major axis to minor axis: 1.02, average deviation of particle size: 0.1) based on the weight of the first layer The polyester for the first layer was used as the polyester for the second layer, and 20 mol% of 2,6-naphthalenedicarboxylic acid copolymerized polytrimethylene terephthalate (NDC20PTT) having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.62 dl / g as the polyester for the second layer. Prepared.

  The prepared polyester for the first layer was dried at 170 ° C. for 5 hours and supplied to the first extruder, and the polyester for the second layer was dried at 160 ° C. for 5 hours and then supplied to the second extruder. Subsequently, the first extruder is heated to 300 ° C. to be in a molten state, the second extruder is heated to 240 ° C. to be in a molten state, 138 layers of polyester for the first layer, and polyester for the second layer After branching to 137 layers, the first layer and the second layer are alternately laminated, and the maximum layer thickness and the minimum layer thickness of each of the first layer and the second layer are continuous up to 2.2 times at maximum / minimum. Using a multi-layer feedblock device that changes in a layered manner, a total of 275 layers of melts in which the first layer and the second layer are alternately stacked are formed on both sides while maintaining the stacked state. The same polyester as the polyester for the second layer was led from the third extruder to a three-layer die, and a thickness adjusting layer was further laminated on both sides of the laminated state melt of 275 layers in total. 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 4.0 times in the width direction at a temperature of 90 ° C., and heat-fixed at 90 ° 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.
Table 1 shows the polymer structure of each layer of the obtained multilayer stretched film, the characteristics of each layer, and Table 2 shows the physical properties. In addition, a light-diffusing polycarbonate film (Lexan 8A35-0.25, manufactured by SABIC) was bonded to the thickness adjusting layers on both sides constituting the outermost layer of the obtained multilayer stretched film with an adhesive to obtain a laminate film. .

[Examples 2 to 7]
As shown in Table 1, a multilayer stretched film was obtained in the same manner as in Example 1 except that the polymer composition 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 stretched film. Further, a light diffusing polycarbonate film was bonded to both surfaces (thickness adjusting layer) of the obtained multilayer stretched film in the same manner as in Example 1 to obtain a laminate film.

[Example 8]
A multilayer 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 stretched film. Further, a light diffusing polycarbonate film was bonded to both surfaces (thickness adjusting layer) of the obtained multilayer stretched film in the same manner as in Example 1 to obtain a laminate film.

[Example 9]
A multilayer 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 stretched film. Further, a light diffusing polycarbonate film was bonded to both surfaces (thickness adjusting layer) of the obtained multilayer stretched film in the same manner as in Example 1 to obtain a laminate 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 stretched film was obtained in the same manner as in Example 1 except that (doubling) was not performed. The stretching temperature and heat setting temperature were changed as shown in Table 1 for film formation.
Table 2 shows the physical properties of the obtained multilayer stretched film. Further, a light diffusing polycarbonate film was bonded to both surfaces (thickness adjusting layer) of the obtained multilayer stretched film in the same manner as in Example 1 to obtain a laminate 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 stretched film was obtained in the same manner as in Comparative Example 1.
Table 2 shows the physical properties of the obtained multilayer stretched film. Further, a light diffusing polycarbonate film was bonded to both surfaces (thickness adjusting layer) of the obtained multilayer stretched film in the same manner as in Example 1 to obtain a laminate film.

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

C2NA: 6,6 ′-(ethylenedioxy) di-2-naphthoic acid TA: terephthalic acid EG: ethylene glycol PET: polyethylene terephthalate C3NA: 6,6 ′-(trimethylenedioxy) di-2-naphthoic acid C4NA : 6,6 '-(tetramethylenedioxy) di-2-naphthoic acid TMG: trimethylene glycol PTT: polytrimethylene terephthalate CHDM: cyclohexane dimethanol PCT: polycyclohexane dimethylene terephthalate NDC: 2,6-naphthalenedicarboxylic acid PEN: Polyethylene-2,6-naphthalene dicarboxylate BD: 1,4-butanediol PBT: Polybutylene terephthalate IA: Isophthalic acid

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

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

Claims (5)

A multilayer 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 having a thickness of 0.01 μm or more and 0.5 μm or less made of a polyester of a dicarboxylic acid component and a diol component.
(I) The dicarboxylic acid component contains 5 mol% or more and 70 mol% or less of the component represented by the following formula (A) and 30 mol% or more and 95 mol% or less of the component represented by the following formula (B),
(In the formula (A), R ^A represents an alkylene group having 2 to 4 carbon atoms)
(In formula (B), R ^B represents a phenylene 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 or an alicyclic group having 6 carbon atoms)
The second layer comprises a copolymerized polyester having a copolymerization amount of 5 mol% or more and 50 mol% or less, and has an average refractive index of 1.55 or more and 1.62 or less and an optically isotropic thickness of 0.01 μm or more and 0.5 μm or less. Layer of
2) Refractive index difference in the uniaxial stretching direction (X direction) between the first layer and the second layer in the film plane is 0.10 to 0.45, and the direction perpendicular to the uniaxial stretching direction (Y direction) The difference in refractive index between the first layer and the second layer and the difference in refractive index between the first layer and the second layer in the film thickness direction (Z direction) is 0.06 or less,
3) The ratio between the maximum layer thickness and the minimum layer thickness of each of the first layer and the second layer is 2.0 or more and 5.0 or less, and 4) the incident surface includes the X direction as a reflection 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 degree and 50 degrees with respect to a polarized light component parallel to the surface is 90% or more, respectively.
5) With respect to the polarized light component perpendicular to the incident surface including the X direction, with the film surface as the reflective 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. Is,
A multilayer stretched film characterized by that.   A brightness enhancement member comprising the multilayer stretched film according to claim 1.   A composite member for a liquid crystal display, wherein a light diffusion film is laminated on at least one surface of the brightness enhancement member according to claim 2.   A liquid crystal display device comprising the brightness enhancement member according to claim 2.   A liquid crystal display device comprising the composite member for a liquid crystal display according to claim 3.