JP6077299B2 - Uniaxially stretched multilayer laminated film, polarizing plate comprising the same, optical member for liquid crystal display device, and liquid crystal display device - Google Patents

Description

  The present invention relates to a uniaxially stretched multilayer laminated film, a polarizing plate comprising the same, an optical member for a liquid crystal display device, and a liquid crystal display device, and more specifically, selectively reflects a certain polarized component and is perpendicular to the polarized component. The present invention relates to a uniaxially stretched multilayer laminated film having excellent polarization performance for selectively transmitting a polarization component and excellent tear performance, a polarizing plate comprising the same, an optical member for a liquid crystal display device, and a liquid crystal display device.

  Liquid crystal display devices (LCDs) used in televisions, personal computers, mobile phones, etc. can be displayed by adjusting the amount of light emitted from the light source by a liquid crystal panel with polarizing plates on both sides of the liquid crystal cell. Yes. An absorption type polarizing plate generally called a light absorption type dichroic linear polarizing plate is used as a polarizing plate bonded to a liquid crystal cell, and a polarizing plate in which PVA containing iodine is protected with triacetyl cellulose (TAC). Is widely used.

Such an absorption type polarizing plate transmits polarized light in the direction of the transmission axis and absorbs most of the polarized light in the direction orthogonal to the transmission axis, so that about 50% of the non-polarized light emitted from the light source device is the absorption type. It has been pointed out that the light use efficiency is reduced by absorption by the polarizing plate. Therefore, in order to effectively use polarized light in the direction orthogonal to the transmission axis, a configuration in which a reflective polarizer called a brightness enhancement film is used between a light source and a liquid crystal panel has been studied. An example of such a reflective polarizer For example, a polymer type film using optical interference has been studied (for example, Patent Document 1).
On the other hand, the polarizing plate attached to the liquid crystal cell also has an absorption type polarizing plate depending on the type and purpose of light used in the display device, such as reflective display using external light and transmissive display using backlight. Various laminated structures combining a reflection type polarizing plate have been studied.

For example, Patent Document 2 discloses polarization used on both sides of a liquid crystal layer in a liquid crystal display device in which electrolysis is applied to the liquid crystal layer to change the retardation value of the liquid crystal to shift the phase difference of polarized light incident on the liquid crystal layer by a certain amount. As an example of a plate, a reflective polarizing plate having a planar multilayer structure in which three or more layers having birefringence are laminated on the light source side, and an absorptive polarizing plate on the opposite side through a liquid crystal layer are disclosed.
Further, Patent Document 3 discloses that when an absorptive polarizing plate and a reflective polarizing plate are used as a polarizing plate in a liquid crystal cell in which liquid crystal is sandwiched between flexible substrates, the amount of expansion and contraction associated with the temperature change of each polarizing plate is different. In order to eliminate the warpage that occurs in order to solve the problem, it has been proposed to eliminate the warpage by combining these polarizing plates into a specific laminated structure. As an example of the reflective polarizing plate, the use of a birefringent dielectric multilayer film is described. Specifically, a brightness enhancement film is disclosed.

Further, as a reflective polarizing plate that is used alone and bonded to a liquid crystal cell, for example, Patent Document 4 proposes a uniaxially stretched multilayer laminated film using a copolymer PEN having a specific copolymer component as a high refractive index layer. Has been.
On the other hand, liquid crystal display devices are sometimes exposed to high temperatures and high humidity for a long time, and stable performance is required for polarizing plates even in harsh environments. For example, Patent Document 5 uses a polymer having an effect of lowering the refractive index while increasing the glass transition temperature such as 2,6-PEN for the high refractive index layer and t-butyl-isophthalic acid for the low refractive index layer. Thus, a configuration that improves reflection and further has heat resistance is disclosed.

Patent Document 6 discloses that the polymer used in the low refractive index layer of the biaxially stretched film having a metal-like appearance contains residues derived from at least three kinds of diols, ethylene glycol, butylene glycol, and spiroglycol. Describes that whitening due to crystallization by high-temperature heat treatment at 200 ° C. or higher in the tenter is suppressed and moldability is improved.
On the other hand, in the case of a uniaxially stretched multilayer laminated film using a copolyester for the low refractive index layer, the copolyester constituting the low refractive index layer tends to crystallize at high temperatures in the production process and usage environment, affecting the degree of polarization. It has been found that there is a possibility that a haze change may occur, and that the tear resistance in the unstretched direction is likely to deteriorate because the stretch treatment is not performed in one direction, and the solution of such a problem Is desired.

JP-T 09-507308 JP 2005-316511 A JP 2009-103817 A JP 2011-126181 A Special table 2008-517139 JP 2010-184493 A

  The object of the present invention is to solve the above-mentioned problems of the conventional uniaxially stretched multilayer laminated film using a copolyester for the low refractive index layer, to have a small haze change at high temperature and to be excellent in tear resistance. An object is to provide a uniaxially stretched multilayer laminated film, a polarizing plate comprising the same, an optical member for a liquid crystal display device, and a liquid crystal display device.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that a conventional uniaxially stretched multilayer laminated film using a copolyester as a low refractive index layer has a reflective polarizing plate incorporated in a liquid crystal display device. There is a possibility of being subjected to a high temperature in the process of combining with the member of the above and during use. In such a case, the copolymer polyester used in the low refractive index layer is likely to be crystallized, and the haze of the film tends to be high, and it is not stretched. It was found that it was easy to tear in the direction. And it has been found that by increasing the glass transition temperature of the copolyester of the low refractive index layer and increasing the intrinsic viscosity of the uniaxially stretched multilayer laminated film, the haze change under high temperature is small and the tear resistance is also improved. The present invention has been completed.

That is, the object of the present invention is a uniaxially stretched multilayer laminated film in which the first layer and the second layer are alternately laminated.
1) The first layer comprises an aromatic 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. And
(In the formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms)
(In the formula (B), R ^B represents a phenylene group or a naphthalenediyl group)
(Ii) The diol component contains 90 to 100 mol% of a component represented by the following formula (C),
(In the formula (C), R ^C represents an alkylene group having 2 to 10 carbon atoms)
2) The second layer is made of a copolyester having a glass transition temperature of 90 ° C. or more and a copolymerization amount of 5 mol% to 90 mol%, and has an average refractive index of 1.50 to 1.60 and optical isotropy. A layer of
3) It is achieved by a uniaxially stretched multilayer laminate film having an intrinsic viscosity of 0.55 dl / g or more and 0.75 dl / g or less.

  According to the present invention, the uniaxially stretched multilayer laminated film of the present invention has a high polarization performance that selectively reflects a certain polarization component and selectively transmits a polarization component perpendicular to the polarization component, and at high temperatures. Therefore, it is possible to provide a reflective polarizing plate, an optical member for a liquid crystal display device, and a liquid crystal display device that can replace conventional absorption polarizing plates. Moreover, since the uniaxially stretched multilayer laminated film of the present invention has high tear strength and excellent tear resistance, the process yield is also improved.

Refractive index (represented as n _X , n _Y , and n _Z respectively) in the stretching direction (X direction) after uniaxial stretching of 2,6-PEN, the direction orthogonal to the stretching direction (Y direction), and the thickness direction (Z direction). ) Is shown in FIG. In the present invention, the first layer aromatic polyester (I) has a uniaxially stretched stretch direction (X direction), a direction perpendicular to the stretch direction (Y direction), and a refractive index in the thickness direction (Z direction) (each of n _X , N _Y and n _Z ) are shown in FIG. The film surface of the uniaxially stretched multilayer laminated film of the present invention is a reflective surface, and the polarization component (P-polarized component) parallel to the incident surface including the stretching direction (X direction) and the incident including the stretching direction (X direction) It is an example of the graph of the reflectance with respect to the wavelength of a polarized light component (S polarized light component) perpendicular | vertical with respect to a surface. 1 is a schematic cross-sectional view of a liquid crystal display device according to a preferred embodiment of the present invention.

In the uniaxially stretched multilayer laminate film of the present invention, the uniaxially stretched multilayer laminate film in which the first layer and the second layer are alternately laminated,
1) The first layer comprises a polyester of a dicarboxylic acid component and a diol component,
(I) The dicarboxylic acid component is an acid 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. Contains,
(In the formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms)
(In the formula (B), R ^B represents a phenylene group or a naphthalenediyl group)
(Ii) The diol component contains 90 to 100 mol% of a component represented by the following formula (C),
(In the formula (C), R ^C represents an alkylene group having 2 to 10 carbon atoms)
2) The second layer is made of a copolyester having a glass transition temperature of 90 ° C. or more and a copolymerization amount of 5 mol% to 90 mol%, and has an average refractive index of 1.50 to 1.60 and optical isotropy. A layer of
3) The intrinsic viscosity of the uniaxially stretched multilayer laminated film is 0.55 dl / g or more and 0.75 dl / g or less.

  The uniaxially stretched multilayer laminated film of the present invention has high polarization performance and suppresses haze change under high temperature due to crystallization of the second layer polymer by increasing the glass transition temperature of the second layer copolymer polyester. It is possible to increase the high temperature heat resistance. Further, by increasing the intrinsic viscosity of the uniaxially stretched multilayer laminated film, the tear resistance can be enhanced without accompanying a decrease in tear strength in the unstretched direction. Hereinafter, each configuration of the present invention will be described in detail.

[Uniaxially stretched multilayer laminated film]
The uniaxially stretched multilayer laminated film in the present invention is a uniaxially stretched film having a multilayer structure in which the first layer and the second layer are alternately laminated. In the present invention, the first layer is more than the second layer. A layer having a higher refractive index and a second layer represent layers having a lower refractive index than the first layer. Further, the refractive index in the stretching direction (X direction) may be described as n _X , the refractive index in the direction orthogonal to the stretching direction (Y direction) as n _Y , and the refractive index in the film thickness direction (Z direction) as _NZ. is there.

As the uniaxially stretched multilayer laminated film used in the present invention, an aromatic polyester having a high refractive index characterized by having a specific copolymer component in the first layer and optically isotropic in the second layer A copolymer polyester having a small refractive index change due to stretching, an average refractive index of 1.50 or more and 1.60 or less, and a glass transition temperature of 90 ° C. or more is used.
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. The refractive index difference between the first layer and the second layer in both directions can be reduced. Therefore, a polyethylene-2,6-naphthalene dicarboxylate copolymer using a polyethylene-2,6-naphthalene dicarboxylate homopolymer or a commonly used copolymer component such as isophthalic acid or terephthalic acid was used as the first layer. Compared with a uniaxially stretched multilayer laminated film, the polarization performance is greatly improved, and the hue shift of transmitted polarized light with respect to obliquely incident light is also improved.

[First layer]
The first layer in the present invention is composed of an aromatic polyester having a specific structural component as a dicarboxylic acid component (hereinafter sometimes referred to as aromatic polyester (I)). Such an aromatic polyester is obtained by polycondensation of a dicarboxylic acid component and a diol component described in detail below.

(Dicarboxylic acid component)
In the present invention, the dicarboxylic acid component (i) constituting the aromatic polyester (I) is 5 mol% to 50 mol% of the following formula (A), and 50 mol% to 95 mol% At least two types of aromatic dicarboxylic acid components represented by 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 10 carbon atoms)
(In the formula (B), R ^B represents a phenylene group or a naphthalenediyl group)

About the component represented by Formula (A), in formula, ^RA is a C2-C10 alkylene group. Examples of the alkylene group include an ethylene group, a propylene group, an isopropylene group, a tetramethylene group, a hexamethylene group, and an octamethylene 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%, and particularly preferably 30 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) is preferably 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, 6,6 ′-(trimethylenedioxy) di-2-naphthoic acid, and 6,6 ′-(ethylenedioxy) di-2-naphthoic acid. Components derived from 6 ′-(butyleneoxy) di-2-naphthoic acid are 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 by containing a specific amount of a component represented by the formula (A) as a dicarboxylic acid component. When the ratio of the component represented by the formula (A) is less than the lower limit, the refractive index n _Y in the Y direction and the refraction in the Z direction in the stretched film are unlikely to occur due to uniaxial stretching. differences rate n _Z increases, polarization performance is lowered and also the hue shift is likely to occur for polarized light incident at an incident angle of an oblique direction. 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, the difference in refractive index between the first layer and the second layer in the X direction cannot be increased, and sufficient reflection performance cannot be obtained for the P-polarized component.
Thus, by using the polyester containing the component represented by the formula (A), it is possible to produce a uniaxially stretched multilayer laminated film having higher polarization performance as a reflective polarizing film than in the past, and further in an oblique direction. It is possible to suppress the hue shift of polarized light due to the incident angle.

Further, the component represented by formula (B), where, R ^B is a phenylene group or naphthalene-diyl group.
Examples of the component represented by the formula (B) include components derived from terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, or combinations thereof, or derivative components thereof. In particular, 2,6-naphthalenedicarboxylic acid or its derivative component is preferably exemplified.
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%, and particularly preferably 70 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 Accordingly, the refractive index difference between the first layer and the second layer in the X direction cannot be increased, and sufficient reflection performance cannot be obtained for the P-polarized component. 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, the polarization performance deteriorates, and a hue shift is likely to occur with respect 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)
In the present invention, as the diol component (ii) constituting the aromatic polyester (I), a 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 10 carbon atoms)

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%.
In the formula (C), R ^C is an alkylene group having 2 to 10 carbon atoms, and examples of the alkylene group include an ethylene group, a propylene group, an isopropylene group, a tetramethylene group, a hexamethylene group, and an octamethylene group. . Among these, preferred examples of the diol component represented by the formula (C) include ethylene glycol, trimethylene glycol, tetramethylene glycol, and cyclohexanedimethanol, and ethylene glycol is particularly preferred. 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 ester unit (-(A)-(C)-) composed of the acid component represented by the formula (A) and the diol component represented by the formula (C) is , 5 mol% or more and 50 mol% or less of all repeating units, 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 terephthalate units such as ethylene terephthalate, trimethylene terephthalate, butylene terephthalate, ethylene-2,6-naphthalene dicarboxylate, trimethylene-2,6-naphthalene dicarboxylate And alkylene-2,6-naphthalenedicarboxylate units such as butyl and butylene-2,6-naphthalenedicarboxylate. Among these, ethylene terephthalate units and ethylene-2,6-naphthalenedicarboxylate units are preferable, and ethylene-2,6-naphthalenedicarboxylate units are particularly preferable from the viewpoint of high refractive index.

The increase in the refractive index in the X direction by stretching is mainly affected by the component represented by the formula (A) and the component represented by the formula (B) having an aromatic ring. Further, the decrease in the refractive index in the Y direction due to stretching has a molecular structure in which the component represented by the formula (A) is mainly influenced and two aromatic rings are connected by an ether bond via an alkylene chain. When stretched, 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 exhibited.
On the other hand, 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.

As the aromatic polyester (I), in particular, the dicarboxylic acid component represented by the formula (A) is a component derived from 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, and the formula (B) A polyester in which the dicarboxylic acid component represented by is a component derived from 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 the formula (A) and the component of the formula (B), and has a lower melting point than the homopolymer having only the component of the formula (A). The mechanical strength is excellent.

The glass transition temperature (hereinafter sometimes referred to as Tg) of the aromatic polyester (I) is preferably 80 to 120 ° C, more preferably 82 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 International Publication No. 2008/153188.

(Refractive index characteristics of aromatic polyester (I))
FIG. 2 shows an example of changes in the refractive index in each direction when the aromatic polyester (I) is uniaxially stretched. As shown in FIG. 2, the refractive index n _X in the X direction is in a direction that increases by stretching, the refractive index n _{Y in the Y} direction and the refractive index n _{Z in the} Z direction are both in a direction that decreases with stretching, and refractive index difference regardless of the draw ratio n _Y and n _Z 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 1.80 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.

In addition, the 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 preferably 0.05 or less, more preferably 0. 0.03 or less, particularly preferably 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.
On the other hand, when the polyester constituting the first layer is polyethylene-2,6-naphthalene dicarboxylate, as shown in FIG. 1, the refractive index n _{Y in the} Y direction is constant regardless of the stretching ratio in the uniaxial direction. While no decrease is observed, the refractive index n _{Z in} the Z direction decreases as the uniaxial stretching magnification 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 tends to occur when polarized light is incident at an oblique incident angle.

[Second layer]
<Copolymerized polyester of the 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 90 ° C. or more and a copolymerization amount of 5 mol% or more and 90 mol% or less, and has an average refractive index of 1.50 or more and 1 .60 or less and an optically isotropic layer.
The average refractive index of the second layer is 1 by melting the copolymer polyester constituting the second layer alone, extruding it from a die to create an unstretched film, and stretching it five times at 120 ° C. in a uniaxial direction. An axially stretched film was prepared, and the refractive index at a wavelength of 633 nm was measured using a metricon prism coupler for each of the X direction, Y direction, and Z direction of the obtained film, and the average value thereof was taken as the average refractive index. It is specified.
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 from 1.53 to 1.60, more preferably from 1.55 to 1.60, and even more preferably from 1.58 to 1.60. is there. 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. Deviation can also be suppressed.

  The copolyester of the second layer in the present invention needs to have a glass transition temperature of 90 ° C. or higher, preferably 90 ° C. or higher and 150 ° C. or lower, more preferably 90 ° C. or higher and 120 ° C. or lower. If the glass transition temperature of the copolyester of the second layer is less than the lower limit, the heat resistance at 90 ° C. is not sufficient, and haze increases due to crystallization and embrittlement of the second layer when heat-treated at this temperature. , Leading to a decrease in the degree of polarization. On the other hand, if the glass transition temperature of the copolyester of the second layer is too high, the polyester of the second layer may also be birefringent due to stretching during stretching, and the difference in refractive index from the first layer in the stretching direction will be small. The reflection performance may be deteriorated.

Among the copolyesters having such a refractive index characteristic, amorphous copolyesters are preferred from the viewpoint that no haze increase occurs due to crystallization by heat treatment at 90 ° C. for 1000 hours. The term “amorphous” as used herein means that the heat of crystal melting when the temperature is raised at a rate of temperature rise of 20 ° C./min in differential calorimetry (DSC) is less than 0.1 mJ / mg.
As an amorphous copolyester having such refractive index characteristics, a copolyester terephthalate, copolyethylene naphthalene dicarboxylate, or a blend thereof, wherein the copolyester is an alicyclic diol is used. Among them, copolymer polyethylene terephthalate in which the copolymer component is an alicyclic diol is preferable. The alicyclic diol used as a copolymerization component of the copolymer polyester is preferably at least one selected from the group consisting of spiroglycol, tricyclodecane dimethanol and cyclohexane dimethanol, and these alicyclic rings. In addition to the group diol, the main acid component of isophthalic acid, terephthalic acid, and 2,6-naphthalenedicarboxylic acid is used in order to obtain the above glass transition temperature while adjusting the relationship with the refractive index with the first layer. Acid components other than those may be used as a copolymerization component. As the copolyester of the second layer, a polyester mainly composed of an ethylene terephthalate component obtained by copolymerizing 2,6-naphthalenedicarboxylic acid and spiroglycol is particularly preferable. Spiroglycol is preferable in that it has a higher crystal binding force than other alicyclic glycol components such as cyclohexanedimethanol, and suppresses haze-up due to crystallization of the second layer during long-term heat treatment at 90 ° C. × 1000 hours. The copolymerization component may be a copolymerized polyester having one or two aromatic dicarboxylic acids, and is preferably a copolymerized polyethylene terephthalate containing naphthalenedicarboxylic acid as a copolymerization component, and the amount of copolymerization is the glass transition temperature. Is adjusted to 90 ° C. or higher. In addition, it is easier to adjust the refractive index relationship with the polyester of the first layer when the alicyclic diol is a copolymer component.

When the copolymer component constituting the copolymer polyester of the second layer is only an alicyclic diol, spiroglycol is preferable, and the copolymerization amount is preferably 20 to 45 mol%. Moreover, when the copolymerization component which comprises the copolymerization polyester of a 2nd layer consists of alicyclic diol and another copolymerization component, alicyclic diol is 10-30 mol%, and another copolymerization component is 10-10. It is preferably 60 mol%.
Here, the copolymerization amount of the copolymerized polyester constituting the second layer in the present invention will be described by taking a copolymerized polyethylene terephthalate as an example. When the repeating unit of the polyester constituting the second layer is 100 mol%, It is represented by the ratio of the copolymer component. The subordinate component is represented by the total amount of components excluding the ethylene glycol component in the diol component and the terephthalic acid component in the dicarboxylic acid component.

Further, the copolymer polyester of the second layer is an aliphatic dicarboxylic acid such as adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid or the like as a copolymerization component other than the above components within a range of 10 mol% or less; cyclohexanedicarboxylic acid An acid component such as an alicyclic dicarboxylic acid such as an acid, or a glycol component such as an aliphatic diol such as butanediol or hexanediol may be used.
The glass transition temperature of the copolyester constituting the second layer is not necessarily 90 ° C. or higher from the stage before forming the film, and may be 90 ° C. or higher after the stretching treatment. For example, two or more kinds of polyesters may be blended and transesterified at the time of melt kneading.
The copolyester of the second layer preferably has an intrinsic viscosity measured at 35 ° C. using an o-chlorophenol solution of 0.55 to 0.75 dl / g, more preferably 0.60 to 0.70 dl. / G.

  The copolymer polyester having the glass transition temperature described above uses an alicyclic diol component or the like as a copolymer component, so that the tear strength particularly in the unstretched direction tends to decrease. Therefore, tear resistance can be improved by setting the intrinsic viscosity of the copolyester within the above range. When the intrinsic viscosity of the copolyester is less than the lower limit, the tear resistance is not sufficient. Although the higher intrinsic viscosity of the copolyester of the second layer is preferable from the viewpoint of tear resistance, the difference in melt viscosity with the aromatic polyester of the first layer is large in the range exceeding the upper limit, and the thickness of each layer is It tends to be uneven.

[Ingredients other than resin]
In order to improve the winding property of the film, the uniaxially stretched multilayer laminated film of the present invention is provided with inert particles having an average particle diameter of 0.01 μm to 2 μm in at least one outermost layer based on the weight of the layer. It is preferable to contain 0.001 to 0.5 weight%. 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, the optical properties of the multilayer stretched film may be deteriorated due to the particles. 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 uniaxially stretched multilayer laminated film include inorganic inert particles such as silica, alumina, calcium carbonate, calcium phosphate, kaolin, and talc, silicone, crosslinked polystyrene, and styrene-divinylbenzene copolymer. Such organic inert particles can be mentioned. 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.

[Lamination structure of uniaxially stretched multilayer laminated film]
(Number of layers)
In the uniaxially stretched multilayer laminated film of the present invention, it is preferable that the above-mentioned first layer and second layer are alternately laminated in a total of 251 layers. When the number of laminated layers is less than 251 layers, a constant average reflectance may not be obtained 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 (X direction). is there.
The upper limit of the number of layers is preferably 2001 layers or less from the viewpoint of productivity and film handling properties, etc. However, if the desired average reflectance characteristic is obtained, the number of layers can be further reduced from the viewpoint of productivity and handling properties. For example, it may be 1001, 501 or 301 layers.

(Each layer thickness)
The thickness of each layer of the first layer and the second layer is 0.01 μm or more and 0.5 μm or less. The thickness of each layer of the first layer is preferably 0.01 μm or more and 0.1 μm or less, and the thickness of each layer of the second layer is preferably 0.01 μm or more and 0.3 μm or less. The thickness of each layer can be determined based on a photograph taken using a transmission electron microscope.
When the uniaxially stretched multilayer laminated film of the present invention is used as a reflective polarizing plate of a liquid crystal display device, the reflection wavelength band is preferably from the visible light region to the near infrared region, and the first layer and the second layer. By setting the thickness of each layer in such a range, light in such a wavelength region can be selectively reflected by optical interference between layers. On the other hand, when the layer thickness exceeds 0.5 μm, the reflection band becomes the infrared region. 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.

(Ratio of maximum layer thickness to minimum layer thickness)
In the uniaxially stretched multilayer laminated 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 It is 2.0 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 the multilayer laminated 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 layer. 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, It is preferable to use layers having different thicknesses.

On the other hand, when the ratio between the maximum layer thickness and the minimum layer thickness exceeds the upper limit value, the reflection band is wider than 400 to 800 nm, and the reflectance of the polarization component parallel to the incident surface including the stretching direction (X direction) May be accompanied by a decline.
The layer thicknesses of 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 structure in the uniaxially stretched multilayer laminated film of the present invention is not particularly limited. For example, the first layer is obtained by branching 137 layers of polyester for the first layer and 138 layers of thermoplastic resin for the second layer. And a second layer are alternately laminated, and a method of using a multilayer feed block device in which the flow path continuously changes by 2.0 to 5.0 times is mentioned.

(Average layer thickness ratio of the first layer and the second layer)
In the uniaxially stretched multilayer laminated 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 0.5 to 2.0 times. The lower 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 0.8. 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 1.5. The most preferred range is 1.1 or more and 1.3 or less.
By setting the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer to an optimum thickness ratio, light leakage due to multiple reflection can be minimized. The optimum thickness ratio here is (the refractive index in the stretching direction of the first layer) × (the average layer thickness of the first layer) and (the refractive index in the stretching direction of the second layer) × The value (optical thickness) represented by (average layer thickness of the second layer) is a uniform thickness, and when converted from the refractive index characteristics of each layer of the present invention, the second with respect to the average layer thickness of the first layer. A preferable range of the ratio of the average layer thickness of the layers is about 1.1 to 1.3.

[Buffer layer / intermediate layer]
In addition to the first layer and the second layer, the uniaxially stretched multilayer laminated film of the present invention may have an intermediate layer having a layer thickness of 2 μm or more inside the alternately laminated structure of the first layer and the second layer. Good. The intermediate layer is sometimes referred to as an internal thick film layer or the like in the present invention. In the present invention, the intermediate layer refers to a thick film layer existing inside an alternately laminated structure. In the present invention, thick film layers (sometimes referred to as a thickness adjusting layer or a buffer layer) are formed on both sides of an alternating laminate of 300 layers or less in the initial stage of production of a multilayer laminated film, and then laminated by doubling. A method of increasing the number is preferably used. In that case, two buffer layers are laminated to form an intermediate layer.
By having an intermediate layer with 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 uniformly adjusted without affecting the polarization function. It becomes easy to do. The intermediate layer having such a thickness may have the same composition as either the first layer or the second layer, or a composition partially including these compositions, and does not contribute to the reflection characteristics because the layer thickness is thick. On the other hand, since it may affect the transmitted polarized light, it is preferable that the particle concentration is within the above-described range when the particles are included in the layer. The intermediate layer may contain 10 ppm or more and 2000 ppm or less of a visible light absorber based on the weight of the layer.

The thickness of the intermediate layer is preferably 2 μm or more and 50 μm or less. If the thickness is less than the lower limit, the layer configuration of the alternately laminated components may be disturbed, and the degree of polarization (or color loss) may occur due to reflection leakage on the reflection axis side (or transmission axis). On the other hand, if the thickness of the intermediate layer exceeds the upper limit, the thickness after lamination increases, which is not practical in production. The thickness of the intermediate layer is preferably 5 μm or more and 20 μm or less.
The method of forming the intermediate layer is not particularly limited. For example, a thick film layer (buffer layer) is provided at both ends of a 277 layered structure, and the layer is divided into two using a branch block called a layer doubling block. Can be provided to form one internal thick film layer (intermediate layer). A plurality of intermediate layers can be provided by three branches and four branches in the same manner.

[Uniaxially stretched film]
The uniaxially stretched multilayer laminated film of the present invention is stretched in at least a uniaxial direction in order to satisfy the optical properties as the target reflective polarizing film. The uniaxial stretching in the present invention includes a film stretched in a biaxial direction in addition to a film stretched only in a uniaxial direction and a film 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.

[Refractive index characteristics between the first layer and the second layer]
The X-direction refractive index difference between the first layer and the second layer is preferably 0.10 to 0.45, more preferably 0.20 to 0.40, and particularly preferably 0.25 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, 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.

[Intrinsic viscosity]
The uniaxially stretched multilayer laminated film of the present invention has an intrinsic viscosity of 0.55 dl / g or more and 0.75 dl / g or less, preferably 0.57 dl / g or more and 0.70 dl / g or less. If the intrinsic viscosity of the film is less than the lower limit, the tear strength in the unstretched direction is lowered, and breakage is likely to occur during the process of forming a uniaxially stretched multilayer laminated film or manufacturing an optical member for a liquid crystal display device. On the other hand, if the intrinsic viscosity of the film exceeds the upper limit, the melt viscosity will increase, so the amount of resin that can be extruded per unit time will decrease and productivity will decrease.In addition, the shear heat generation during extrusion will increase and the resin temperature will increase. The disassembly due to can not be ignored.

[Tear strength]
The uniaxially stretched multilayer laminated film of the present invention preferably has a tear strength of 7.5 N / mm or more, and more preferably 8.0 N / mm or more. If the tear strength is less than the lower limit, the film tends to break during the production of the uniaxially stretched multilayer laminated film or in the manufacturing process of the optical member for a liquid crystal display device. Such tear strength is achieved by setting the intrinsic viscosity of the film within the above-mentioned range.

[Haze]
In the uniaxially stretched multilayer laminated film of the present invention, the difference between the haze after heat treatment at 90 ° C. for 1000 hours and the haze before treatment is preferably 2.0% or less, and more preferably 1.0% or less. Is more preferable. By having such haze characteristics, the change in optical characteristics is small even after heat treatment, and when used in a liquid crystal display device, the change in polarization performance is small even in a high temperature environment and can be suitably used. When the haze difference before and after the heat treatment exceeds the upper limit value, the polarization performance after the heat treatment tends to be lower than the polarization performance before the heat treatment due to the influence of scattered light due to the haze.

[Degree of polarization]
In the uniaxially stretched multilayer laminated film of the present invention, the degree of polarization (P%) represented by the following formula (1) is preferably 99.5 or more, more preferably 99.6% or more, and particularly preferably 99. .7% or more.
Degree of polarization (P) = {(Ts−Tp) / (Tp + Ts)} × 100 (1)
(In formula (1), Tp represents the average transmittance of P-polarized light in the wavelength range of 400 to 800 nm, and Ts represents the average transmittance of S-polarized light in the wavelength range of 400 to 800 nm)

The P-polarized light in the present invention is defined as a polarized light component parallel to an incident surface including a uniaxially stretched direction (X direction) with a film surface as a reflective surface in a uniaxially stretched multilayer laminated film. S-polarized light is defined as a polarized light component perpendicular to an incident surface including a uniaxially stretched direction (X direction) with a film surface as a reflective surface in a uniaxially stretched multilayer laminated film.
The degree of polarization in the present invention can be measured using a degree of polarization measuring device.

This means that the higher the degree of polarization specified by the above equation (1), the more the transmission of the reflected polarization component is suppressed, and the higher the transmittance of the transmitted polarization component in the orthogonal direction. Even slight light leakage of the components can be reduced. As the polarizing degree of the uniaxially stretched multilayer laminated film of the present invention is 99.5% or more, a reflective polarizing plate is used as a polarizing plate for a liquid crystal display device having a high contrast, which has conventionally been difficult to apply unless it is an absorptive polarizing plate. Can be applied alone.
In order to achieve such polarization degree characteristics while being a multilayer film, the first layer (high refractive index layer) and the second layer (low refractive index layer) constituting the uniaxially stretched multilayer laminated film are used in the present invention. Each of the specific polyesters may be used, and the uniaxially stretched multilayer laminated film may have an intermediate layer having a certain thickness that does not affect light interference, and the intermediate layer may contain a certain amount of visible light absorber. Also good.

(S-polarized average transmittance)
The average transmittance Ts of S-polarized light in the wavelength range of 400 to 800 nm of the uniaxially stretched multilayer laminated film of the present invention is preferably 60% or more, more preferably 70% or more, still more preferably 75% or more, particularly preferably. Is 80% or more.
The average transmittance of S-polarized light in the present invention is such that, in a uniaxially stretched multilayer laminated film, the incident angle is 0 with respect to a polarized light component perpendicular to the incident surface including the uniaxially stretched direction (X direction). It represents the average transmittance at a wavelength of 400 to 800 nm for the incident polarized light in degrees.

The uniaxially stretched multilayer laminated film of the present invention preferably has a higher transmittance for the S-polarized light that is the transmission axis direction, but a certain amount of visible light absorber is added to the intermediate layer in order to increase the degree of polarization described above. When it is contained, S-polarized light is also absorbed, and the average transmittance of S-polarized light may decrease. If the average transmittance of S-polarized light is within such a range, it is a characteristic of the reflective polarizing plate, which reflects the reflected polarized light to the light source side without being absorbed by the polarizing plate, and again by the light recycling function that effectively uses the light. Although a brightness enhancement effect can be obtained, if the average transmittance of S-polarized light is less than the lower limit, the superiority of the brightness enhancement effect may be less than that of the absorption polarizing plate.
In order to obtain the transmittance characteristic of the S-polarized component, the difference in refractive index between the first layer and the second layer in the Y direction of the uniaxially stretched multilayer laminated film of the present invention is 0.05 or less, and the intermediate layer When mix | blending a visible light absorber in it, it is mentioned that the content does not exceed an upper limit.

(Average reflectance)
The uniaxially stretched multilayer laminated film of the present invention has a film surface as a reflection surface, and the incident light at an incident angle of 0 degree 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 with a wavelength of 400 to 800 nm for polarized light is preferably 98% or more and 100% or less.
Since the average reflectance with respect to the P-polarized component is thus high, a high polarization performance that selectively transmits the S-polarized light while suppressing the transmission amount of the P-polarized light is exhibited, and the high polarization degree of the present invention is obtained. The polarizing plate can be used alone as a polarizing plate adjacent to the liquid crystal cell without using an absorptive polarizing plate in combination. At the same time, the P-polarized light in the direction orthogonal to the transmission axis is highly reflected without being absorbed by the reflective polarizing film, so that it can also function as a brightness enhancement film that reuses the reflected light.

  Moreover, the uniaxially stretched multilayer laminated film of the present invention has a film surface as a reflection surface, and a polarization component perpendicular to the incident surface including the stretching direction (X direction) of the uniaxially stretched film at an incident angle of 0 degree. The average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light is preferably 40% or less, more preferably 35 or less, further preferably 30% or less, particularly preferably 25% or less, and most preferably 20% or less. . Moreover, it is preferable that the minimum of the average reflectance with a wavelength of 400-800 nm with respect to this incident polarized light at an incident angle of 0 degree is 5%.

  When the average reflectance at a wavelength of 400 to 800 nm with respect to the S-polarized light component incident in the vertical direction is within such a range, the amount of S-polarized light transmitted to the side opposite to the light source increases. On the other hand, when the average reflectance with respect to the S-polarized light component exceeds the upper limit, the polarization transmittance as the reflective polarizing film is lowered, so that sufficient performance as a polarizing plate adjacent to the liquid crystal cell may not be exhibited. On the other hand, although the transmittance of the S-polarized component is higher when the reflectance of the S-polarized component is lower than the above range, it may be difficult to make it lower than the lower limit because of the composition and stretching.

  In order to obtain the above-described average reflectance characteristics for the P-polarized light component, in the uniaxially stretched multilayer laminated film constituted by alternately laminating the first layer and the second layer, the refractive index characteristic of the present invention as a polymer constituting each layer. The first layer in the stretching direction (X direction) and the first layer are stretched at a constant stretching ratio in the stretching direction (X direction) to increase the birefringence in the in-plane direction of the film of the first layer. The refractive index difference between the two layers can be increased and achieved. Moreover, in order to obtain this average reflectance in a wavelength range of 400 to 800 nm, a method of adjusting the thicknesses of the first layer and the second layer can be mentioned.

  In addition, in order to obtain the above-mentioned average reflectance characteristics for the S-polarized component, in the uniaxially stretched multilayer laminated film constituted by alternately laminating the first layer and the second layer, the polymer component constituting each layer of the present invention The first layer and the second layer in the orthogonal direction (Y direction) are obtained by using a polyester having a refractive index characteristic and not stretching in the direction orthogonal to the stretching direction (Y direction) or by only stretching at a low stretching ratio. The difference in refractive index between the two layers can be extremely small, which is achieved. Moreover, when making a visible light absorber contain in an intermediate | middle layer, setting it as fixed amount is mentioned. Moreover, in order to obtain this average reflectance in a wavelength range of 400 to 800 nm, a method of adjusting the thicknesses of the first layer and the second layer can be mentioned.

[Method for producing uniaxially stretched multilayer laminated film]
Below, the manufacturing method of the uniaxially stretched multilayer laminated film of this invention is explained in full detail.
The uniaxially stretched multilayer laminated film of the present invention is produced by alternately laminating the polyester constituting the first layer and the polyester constituting the second layer in a molten state to produce an alternating laminate having a total of 300 layers or less. A layer (buffer layer) with a film thickness is provided on both sides, and an alternating laminate having the buffer layer is divided into, for example, 2 to 4 using a device called layer doubling, and the alternating laminate having the buffer layer is blocked as one block. The number of stacked layers can be increased by a method of stacking again so that the number of stacked layers (doubling number) is 2 to 4 times. By such a method, a uniaxially stretched multilayer laminated film having an intermediate layer in which two buffer layers are laminated inside a multilayer structure can be obtained.

Such an alternate laminate is laminated so that the thickness of each layer changes stepwise or continuously in a range of 2.0 to 5.0 times.
The multilayer unstretched film laminated in a desired number of layers by the above-described method 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 thermoplastic resin of the first layer, and (Tg) to (Tg + 30) in order to highly control the orientation characteristics of the film. ) C. is preferred.

  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 variations in the plane direction of the individual layers in the first layer and the second layer, and the light interference of the multilayer stretched film is made uniform in the plane direction. And the refractive index difference in the stretching direction of the second layer is preferable. 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. Further, it is preferable to further heat-set after stretching, and it was obtained by toe-out (re-stretching) in the stretching direction in a range of 5 to 15% while performing at a temperature of (Tg) to (Tg + 30) ° C. The orientation characteristics of the uniaxially stretched multilayer laminated film can be highly controlled.

[Reflective polarizing film for polarizing plates of liquid crystal display devices]
Although the uniaxially stretched multilayer laminated film of the present invention is a reflective polarizing film having a multilayer structure, it has a high degree of polarization and a function as a brightness enhancement film that can be reused by reflecting polarized light that is not transmitted. Without using a polarizing plate in combination, it can be used as a polarizing plate for a liquid crystal display device used alone adjacent to a liquid crystal cell.

[Optical members for liquid crystal display devices]
In the present invention, 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 uniaxially stretched multilayer laminated film of the present invention are laminated in this order is also an aspect of the invention. included. Such an optical member is also referred to as a liquid crystal panel. Such an optical member corresponds to 5 in FIG. 4, the first polarizing plate corresponds to 3, the liquid crystal cell corresponds to 2, and the second polarizing plate corresponds to 1.
Conventionally, as a polarizing plate on both sides of the liquid crystal cell, high polarizing performance has been obtained by having at least an absorptive polarizing plate. Since a high polarization performance that could not be achieved with the multilayer laminated film is obtained, it can be used as a polarizing plate used adjacent to a liquid crystal cell in place of the conventional absorption polarizing plate.

That is, the present invention is characterized in that a polarizing plate comprising the uniaxially stretched multilayer laminated film of the present invention is used alone in one of the liquid crystal cells as the first polarizing plate, and preferably the first polarizing plate is an absorption type. The configuration laminated with the polarizing plate 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, the uniaxially stretched multilayer laminated film of the present invention is preferably used.
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]
The present invention also includes a liquid crystal display device (hereinafter sometimes referred to as a liquid crystal display) 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. It is included as one aspect.
FIG. 4 is a schematic cross-sectional view of a liquid crystal display device which is one embodiment of the present invention. The liquid crystal display device has a light source 4 and a liquid crystal panel 5, and further incorporates a drive circuit and the like as necessary. The liquid crystal panel 5 includes the first polarizing plate 3 on the light source 4 side of the liquid crystal cell 2. In addition, the second polarizing plate 1 is provided on the side opposite to the light source side of the liquid crystal cell 2, that is, on the viewing side. As the liquid crystal cell 2, for example, an arbitrary type such as a VA mode, an IPS mode, a TN mode, an STN mode, or a bend alignment (π type) can be used.

The liquid crystal display device of the present invention has a conventional absorption type by disposing the first polarizing plate 3 made of the reflective polarizing film for bonding a liquid crystal cell of the present invention having high polarization performance on the light source side of the liquid crystal cell 2. Instead of the polarizing plate, it can be used in combination with a liquid crystal cell. In particular, when the degree of polarization of the uniaxially stretched multi-layer laminate film is 99.5% or higher, the contrast required from the brightness / darkness of the liquid crystal display is very high as practically required for a liquid crystal television. Can be obtained.
The first polarizing plate comprising the uniaxially stretched multilayer laminated film 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 can be reused by reflecting non-transmitted polarized light. Therefore, it is not necessary to use a reflective polarizing plate called a brightness enhancement film between the light source 4 and the first polarizing plate 3, and the function of the brightness enhancement film and the polarizing plate bonded to the liquid crystal cell is integrated. Therefore, the number of members can be reduced.

Furthermore, the liquid crystal display device of the present invention uses the uniaxially stretched multilayer laminated film of the present invention as the first polarizing plate, so that even the light incident in the oblique direction transmits almost the P-polarized component incident in the oblique direction. However, since the S-polarized component incident in the oblique direction is transmitted while suppressing reflection, the hue shift 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 projected image as the liquid crystal display device.
Further, normally, as shown in FIG. 4, the second polarizing plate 1 is disposed on the viewing side of the liquid crystal cell 2. The second polarizing plate 1 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 2.

[Formation of liquid crystal display device]
The liquid crystal display device of the present invention can be obtained by combining an optical member for liquid crystal display device (liquid crystal panel) and a light source, and further incorporating a drive circuit or the like as necessary. In addition to these, various members necessary for the formation of the liquid crystal display device can be combined, but 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 is, for example, an OA device such as a personal computer monitor, a notebook personal computer or a copy machine, a mobile device such as a mobile phone, a clock, a digital camera, a personal digital assistant (PDA), a portable 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.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the examples shown below.
In addition, the physical property and characteristic in an Example were measured or evaluated by the following method.

(1) Refractive index and average refractive index before stretching in each direction and average refractive index Each resin constituting each layer was melted and extruded from a die, and a film cast on a casting drum was prepared. In addition, a stretched film was prepared by stretching the obtained film at 120 ° C. in a uniaxial direction 5 times. About the obtained cast film and stretched film, the respective refractive indexes in the stretching direction (X direction), the orthogonal direction (Y direction), and the thickness direction (Z direction) (referred to as n _X , n _Y , and n _Z respectively). Was determined by measuring the refractive index at a wavelength of 633 nm using a metricon prism coupler, and the refractive index was determined before and after stretching.
About the average refractive index of polyester which comprises a 1st layer, the average value of the refractive index of each direction before extending | stretching was made into the average refractive index. Moreover, about the average refractive index of polyester which comprises a 2nd layer, the average value of the refractive index of each direction after extending | stretching was made into the average refractive index.

(2) Average transmittance and polarization degree of P-polarized light and S-polarized light About the obtained uniaxially stretched multilayer laminated film, the transmittance of P-polarized light and S-polarized light using a polarization degree measuring device (“VAP7070S” manufactured by JASCO Corporation) The transmittance and the degree of polarization were measured.
The measured value when the transmission axis of the polarizing filter is aligned with the stretching direction (X direction) of the film is P-polarized light, and the measured value when the transmission axis of the polarizing filter is disposed perpendicular to the stretching direction of the film The degree of polarization (P%, unit%) when S is S-polarized light is expressed by the following formula.
Degree of polarization (P) = {(Ts−Tp) / (Tp + Ts)} × 100 (1)
(In formula (1), Tp represents the average transmittance of P-polarized light in the wavelength range of 400 to 800 nm, and Ts represents the average transmittance of S-polarized light in the wavelength range of 400 to 800 nm)
The measurement light was measured with the incident angle set to 0 degree.

(3) Glass transition temperature (Tg) of the second layer
10 mg of the second layer sample was sampled, and the melting point and the glass transition point were measured at a temperature increase rate of 20 ° C./min using DSC (trade name: DSC2920, manufactured by TA Instruments).

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

(5) Thickness of each layer A uniaxially stretched multilayer laminated film was cut into a film longitudinal direction of 2 mm and a width direction of 2 cm, fixed to an embedding capsule, and then embedded with an epoxy resin (Epomount manufactured by Refinetech Co., Ltd.). 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.
With respect to a layer having a thickness of 1 μm or more, the thickness existing in the multilayer structure was defined as the intermediate layer, and the thickness present in the outermost layer was defined as the outermost layer, and each thickness was measured. When a plurality of intermediate layers existed, the intermediate layer thickness was determined from the average value thereof.
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 determining the thicknesses of the first layer and the second layer, the intermediate layer and the outermost layer were excluded from the first layer and the second layer.

(6) Total film thickness A film sample is sandwiched between spindle detectors (K107C manufactured by Anritsu Electric Co., Ltd.), and a digital differential electronic micrometer (K351 manufactured by Anritsu Electric Co., Ltd.) is used to measure 10 thicknesses at different positions. Measurement was made to obtain the average value, and the film thickness was obtained.

(7) Haze According to JIS K7136, using a haze measuring device (NDH-2000) manufactured by Nippon Denshoku Industries Co., Ltd., haze before and after heat treatment of a uniaxially stretched multilayer laminated film from the following formula (2) Difference, ΔHz was measured.
ΔHz = (haze after heat treatment at 90 ° C. × 1000 hr) − (haze before heat treatment at 90 ° C. × 1000 hr) (2)
◎: 1.0% or less ○: Greater than 1.0% and 2.0% or less △: Greater than 2.0% and 5.0% or less ×: Greater than 5.0%

(8) Intrinsic Viscosity For the polyester for the first layer, a solution measured at a temperature of 35 [° C.] after dissolving in P-chlorophenol / 1,1,2,2-tetrachloroethane having a weight ratio of 6: 4 From the viscosity, the value calculated by the following formula was used.
About the polyester and film for 2nd layers, the value computed by the following Formula from the solution viscosity measured at the temperature of 35 [degreeC] after melt | dissolving in an o-chlorophenol solution was used.
ηsp / C = [η] + K [η] 2 · C
Here, ηsp = (solution viscosity / solvent viscosity) −1, C is the dissolved polymer weight per 100 [ml] of solvent [g / 100 ml], and K is the Huggins constant. The solution viscosity and solvent viscosity were measured using an Ostwald viscometer. The unit is indicated by [dl / g].

(9) Tear strength According to JIS K-7128, tear strength was measured at a tensile speed of 200 mm / min using Tensilon UCT-100 manufactured by Orientec. The test was conducted by Method A (trouser tear method). Measurement is performed in the machine direction (MD) and transverse direction (TD) of the film, and only values that have been completely torn in the tear direction are used. No value "-".

(10) Brightness improvement effect The front luminance of the screen of the liquid crystal display device when white display is performed on the personal computer using the liquid crystal display device obtained as the display display of the personal computer with the FPD viewing angle measurement evaluation device (ErgoScope 88) manufactured by Optodesign. Measurement was performed to calculate the luminance increase rate relative to Reference Example 1, 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%

(11) Contrast evaluation Using a liquid crystal display device obtained as a personal computer display, the front luminance of the liquid crystal display screen when a white and black screen is displayed on the personal computer is measured by an FPD viewing angle measurement evaluation device manufactured by Optodesign ( ErgoScope 88), bright luminance was determined from the white screen, and dark luminance was determined from the black screen, and the contrast determined from the bright luminance / dark luminance was evaluated according to the following criteria.
A: Contrast (bright luminance / dark luminance) 2000 or more B: Contrast (bright luminance / dark luminance) 1000 or more and less than 2000 ×: Contrast (bright luminance / dark luminance) Less than 1000

[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 0.63 dl / g, 65 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component (described as PEN in the table), and 35 mol% of the acid component was 6 mol%. , 6 ′-(ethylenedioxy) di-2-naphthoic acid component (denoted as ENA in the table), aromatic polyester whose glycol component is ethylene glycol is used as the first layer polyester, and is inherent as the second layer polyester Copolymerized polyethylene terephthalate having a viscosity of 0.70 dl / g and 2,6-naphthalenedicarboxylic acid 30 mol% and spiroglycol 20 mol% It was prepared rate (NDC30SPG20PET).

The prepared polyester for the first layer is dried at 170 ° C. for 5 hours, the polyester for the second layer is dried at 70 ° C. for 10 hours, then supplied to the first and second extruders, heated to 300 ° C. to be in a molten state, After branching the polyester for the first layer into 138 layers and the polyester for the second layer into 137 layers, the first layer and the second layer are alternately laminated, and the maximum layer thickness in each of the first layer and the second layer Using a multi-layer feedblock device in which the minimum layer thickness continuously changes up to 2.2 times at the maximum / minimum, a total of 275 layers in which the first layer and the second layer are alternately stacked While maintaining the laminated state of the melt, the same polyester as the second layer polyester is led from the third extruder to the three-layer feed block on both sides of the melt, and the lamination direction of the melt in the laminated state of 275 layers in total Further buffer layers on both sides And the layers. The supply amount of the third extruder was adjusted so that the total of the buffer layers on both sides was 30% of the whole. The layered state is further divided into three layers in a layer doubling block and laminated at a ratio of 1: 1: 1, and the total number of layers is 829 including two intermediate layers inside and two outermost layers on the outermost layer. The film is guided to the die while being held, cast on a casting drum, and adjusted so that the average layer thickness ratio of the first layer and the second layer is 1.0: 1.2. An unstretched multilayer laminated film was prepared.
This multilayer unstretched film was stretched 5.2 times in the width direction at a temperature of 120 ° C., and further subjected to heat setting treatment at 120 ° C. for 3 seconds while stretching 15% in the same direction at 120 ° C. The thickness of the obtained uniaxially stretched multilayer laminated film was 105 μm.

(Formation of liquid crystal panel)
In Reference Example 1 to be described later, in the same manner as in Reference Example 1 except that the obtained uniaxially stretched multilayer laminated film was used instead of the polarizing plate X as the first polarizing plate on the light source side, the light source side of the liquid crystal cell A uniaxially stretched multilayer laminated film (first polarizing plate) obtained on the main surface 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, 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 uniaxially stretched multilayer laminate film thus obtained, the characteristics of each layer, the physical properties of the uniaxially stretched multilayer laminate film, and the properties of the liquid crystal display device.

[Examples 2 to 9]
As shown in Table 1, a uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1 except that the resin composition of each layer was changed.
Examples 2 and 3 are examples in which the intrinsic viscosity of the film is different. In Example 2, the intrinsic viscosity of the polyester in the second layer was changed to 0.60 dl / g. In Example 3, the intrinsic viscosity of the polyester in the second layer was changed. The same operation as in Example 1 was repeated except that was changed to 0.75 dl / g.

  Note that NDC38PET used as the second layer polyester in Example 4 was changed from the copolymerization component of copolymerized polyethylene terephthalate (NDC30SPG20PET) used as the second layer polyester in Example 1 to obtain 2,6-naphthalene. This is a copolymerized polyester having a dicarboxylic acid of 38 mol%. Similarly, Examples 5 to 6 are spiroglycol 45 mol% and 23 mol% copolymerized polyethylene terephthalate (SPG45PET, SPG23PET), and Example 8 is isophthalic acid 15 mol%, 2 Polyethylene terephthalate (IA15NDC20PET) copolymerized with 20 mol% of 1,6-naphthalenedicarboxylic acid, Example 9 is a copolymer of 20 mol% of 2,6-naphthalenedicarboxylic acid and 30 mol% of tricyclodecane dimethanol. And it is obtained by a polyethylene terephthalate (NDC20TCDM30PET). The polyester for the second layer of Example 7 represents spiroglycol 40 mol% copolymerized polyethylene-2,6-naphthalenedicarboxylate (SPG40PEN).

[Comparative Examples 1-4]
As shown in Table 1 as in Example, a uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1 except that the resin composition was changed, and this film was used as a first polarizing plate to form a liquid crystal panel. A liquid crystal display device was created. Comparative Example 1 is an example in which the intrinsic viscosity of the film is different, and the same operation as in Example 1 was repeated except that the intrinsic viscosity of the polyester of the second layer was changed to 0.50 dl / g. Table 1 shows the resin configuration of each layer of the uniaxially stretched multilayer laminated film thus obtained, the characteristics of each layer, the physical properties of the uniaxially stretched multilayer laminated film, and the properties of the liquid crystal display device.

[Reference Example 1]
(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. Under the conditions, 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)
A liquid crystal panel with a VA mode liquid crystal cell and a direct-type backlight (Sharp AQUAS LC-20E90 2011 made) was taken out from the liquid crystal panel, and the polarizing plate and the optical compensation film arranged above and below the liquid crystal cell The glass surface (front and back) of the liquid crystal cell was washed. Subsequently, the polarizing plate is placed on the surface on the light source side of the liquid crystal cell via an acrylic pressure-sensitive adhesive so as to be in the same direction as the absorption axis direction of the light source side polarizing plate arranged in the original liquid crystal panel. X was placed in a liquid crystal cell.
Next, the polarizing plate X is put on the surface on the viewing side of the liquid crystal cell via an acrylic adhesive so as to be in the same direction as the absorption axis direction of the viewing-side polarizing plate arranged in the original liquid crystal panel. Arranged 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.

  According to the present invention, the uniaxially stretched multilayer laminated film of the present invention has a high polarization performance that selectively reflects a certain polarization component and selectively transmits a polarization component perpendicular to the polarization component, and at high temperatures. Therefore, it is possible to provide a reflective polarizing plate, an optical member for a liquid crystal display device, and a liquid crystal display device that can replace conventional absorption polarizing plates. Moreover, since the uniaxially stretched multilayer laminated film of the present invention has high tear strength and excellent tear resistance, the process yield is also improved.

DESCRIPTION OF SYMBOLS 1 2nd polarizing plate 2 Liquid crystal cell 3 1st polarizing plate 4 Light source 5 Liquid crystal panel

Claims (14)

In the uniaxially stretched multilayer laminated film in which the first layer and the second layer are alternately laminated,
1) The first layer comprises an aromatic 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. And
(In the formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms)
(In the formula (B), R ^B represents a phenylene group or a naphthalenediyl group)
(Ii) The diol component contains 90 to 100 mol% of a component represented by the following formula (C),
(In the formula (C), R ^C represents an alkylene group having 2 to 10 carbon atoms)
2) The second layer is made of a copolyester having a glass transition temperature of 90 ° C. or more and a copolymerization amount of 5 mol% to 90 mol%, and has an average refractive index of 1.50 to 1.60 and optical isotropy. A layer of
3) The uniaxially stretched multilayer laminate film has an intrinsic viscosity of 0.55 dl / g or more and 0.75 dl / g or less. Copolymerization component of the copolyester constituting the second layer Ri Ah with alicyclic diols, the copolymerization amount is Ru as or 10-30 mole% der 20-45 mol%, in claim 1 The uniaxially stretched multilayer laminated film described.
  The uniaxially stretched multilayer laminated film according to claim 2, wherein the alicyclic diol is at least one selected from the group consisting of spiroglycol, tricyclodecane dimethanol and cyclohexane dimethanol.   The uniaxially stretched multilayer laminated film according to any one of claims 1 to 3, wherein the tear strength of the film is 7.5 N / mm or more.   The uniaxially stretched multilayer laminated film according to any one of claims 1 to 4, wherein a haze difference between the film before and after the treatment at 90 ° C for 1000 hours is 2.0% or less. The degree of polarization (P%) represented by the following formula (1) is 99.5 or more,
Degree of polarization (P) = {(Ts−Tp) / (Tp + Ts)} × 100 (1)
(In formula (1), Tp represents the average transmittance of P-polarized light in the wavelength range of 400 to 800 nm, and Ts represents the average transmittance of S-polarized light in the wavelength range of 400 to 800 nm)
The uniaxially stretched multilayer laminated film according to any one of claims 1 to 5, wherein an average transmittance Ts of S-polarized light in a wavelength range of 400 to 800 nm is 60% or more.   The uniaxially stretched multilayer laminated film according to any one of claims 1 to 6, which is used adjacent to a liquid crystal cell.   The polarizing plate which consists of a uniaxial stretching multilayer laminated film in any one of Claims 1-7.   An optical member for a liquid crystal display device, wherein the first polarizing plate comprising the polarizing plate according to claim 8, a liquid crystal cell, and a second polarizing plate are laminated in this order.   The optical member for a liquid crystal display device according to claim 9, wherein the optical member for a liquid crystal display device excluding a configuration in which the first polarizing plate is laminated with an absorption polarizing plate.   The optical member for a liquid crystal display device according to claim 9 or 10, wherein the second polarizing plate is an absorptive polarizing plate.   An optical member for a liquid crystal display device, comprising: a first polarizing plate, a liquid crystal cell, and a second polarizing plate, wherein the first polarizing plate and the second polarizing plate comprise the 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.   The liquid crystal display device according to claim 13, further comprising no reflective polarizing plate between the light source and the first polarizing plate.