JP6309849B2 - Uniaxially stretched multilayer laminated film, polarizing plate for liquid crystal display comprising the same, optical member for liquid crystal display, and liquid crystal display - Google Patents

Description

  The present invention relates to a uniaxially stretched multilayer laminated film, a polarizing plate for a liquid crystal display comprising the same, an optical member for a liquid crystal display, and a liquid crystal display. More specifically, the present invention has a reflective polarizing performance and interlayer adhesion while being a multilayer polymer film. The present invention relates to a uniaxially stretched multilayer laminated film, a polarizing plate for liquid crystal display comprising the same, an optical member for liquid crystal display, and a liquid crystal display.

  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. It is said. 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.

  Since such an absorption type polarizing plate transmits polarized light in the transmission axis direction and absorbs most of the polarized light in the direction orthogonal to the transmission axis, about 50% of the light emitted from the light source device is the absorption type polarizing plate. It is pointed out that the light use efficiency is reduced. 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 a polarizing plate 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, a reflective polarizing plate having a planar multilayer structure in which three or more layers of birefringent films are laminated on the light source side, and an absorptive polarizing plate on the opposite side through a liquid crystal layer are disclosed.

Further, in Patent Document 3, when an absorptive polarizing plate and a reflective polarizing plate are used as polarizing plates disposed on both sides of a liquid crystal cell in which a liquid crystal is sandwiched between flexible substrates, the temperature changes of each polarizing plate. In order to eliminate the warpage caused by the difference in the amount of expansion and contraction, 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.
However, the reflective polarizing polymer film (for example, Patent Documents 4 to 6) using a birefringent multilayer structure which has been studied in the past does not have sufficient adhesion between the multilayer polymers. In some cases, the multilayer part peeled off.

For example, polyethylene-2,6-naphthalene dicarboxylate (hereinafter sometimes referred to as 2,6-PEN) described in Patent Document 5 is used for the high refractive index layer, and a thermoplastic elastomer or terephthalic acid is used. In the case of a multilayer laminated film using 30 mol% copolymerized PEN as a low refractive index layer, the refractive index difference between layers in the uniaxial stretching direction (X direction) is increased to increase the reflectance of P-polarized light, while in the film plane By reducing the difference in refractive index between layers in the direction perpendicular to the X direction (Y direction) and increasing the transmittance of S-polarized light, a certain level of polarization performance is exhibited.
However, the combination of the above-described polymers does not have a sufficient degree of polarization for use as a polarizing plate, and the adhesion between layers is also insufficient.

As a reflective polarizing polymer film having a multilayer structure that can be used as a reflective polarizing plate having a higher degree of polarization, the present inventors can use it as a polarizing plate adjacent to a liquid crystal cell in Patent Document 7 and substitute for an absorbing polarizing plate. A reflective polarizing plate made of a multi-layered polymer film is studied, and a specific polymer is used as the high refractive index layer and is uniaxially oriented to provide more polarizing performance than a conventional multi-layered reflective polarizing plate. Proposes an enhanced film.
However, although the reflective polarizing film proposed in Patent Document 7 achieves a high degree of polarization of around 97 to 98%, the interlaminar adhesion is still not sufficient, and further improvement is required.

JP-T 9-507308 JP 2005-316511 A JP 2009-103817 A JP-A-4-268505 Japanese National Patent Publication No. 9-506837 International Publication No. 01/47711 Pamphlet JP 2012-13919 A

  An object of the present invention is a uniaxially stretched multilayer laminated film having a polarizing performance and improved interlayer adhesion while being a multilayer polymer film using a polyethylene naphthalate-based polymer in a layer having a high refractive index characteristic Another object of the present invention is to provide a reflective polarizing film for a polarizing plate of a liquid crystal display, a polarizing plate for a liquid crystal display comprising the same, an optical member for a liquid crystal display, and a liquid crystal display.

  As a result of diligent investigations to solve the above problems, the present inventors have obtained polarization performance by using a copolymer polyester containing a specific copolymer component in a layer having a low refractive index characteristic in addition to conventional knowledge. It was found that the improvement of interlayer adhesion can be realized while maintaining the above, and the present invention has been completed.

  That is, an object of the present invention is a uniaxially stretched multi-layer laminated film in which a first layer and a second layer are alternately laminated, and 1) the first layer is a layer containing polyester and constitutes the polyester. The ethylene naphthalate unit is contained in the range of 50 mol% or more and 100 mol% or less based on the repeating unit to be used. 2) The polymer forming the second layer is 2,6-naphthalenedicarboxylic acid component, ethylene glycol component, fat This is achieved by a uniaxially stretched multilayer laminated film which is a copolyester containing a cyclic diol component and a trimethylene glycol component as copolymerization components.

  According to the present invention, the uniaxially stretched multilayer laminated film of the present invention is a polymer film having a multilayer structure using a polyethylene naphthalate-based polymer in a layer having a high refractive index characteristic, and has polarization performance and adhesion between layers. Improved. For this reason, for example, when used in a brightness improving member that requires polarization performance, a polarizing plate of a liquid crystal display that requires a high degree of polarization, etc., it is added to other members, assembled into a liquid crystal display, and used. Since delamination does not occur due to external force, it is possible to provide a more reliable brightness improving member and liquid crystal display polarizing plate.

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 polarization component (S polarization component) perpendicular to the surface. 1 is a schematic cross-sectional view of a liquid crystal display according to a preferred embodiment of the present invention. The dicarboxylic acid component is composed of a component derived from 2,6-naphthalenedicarboxylic acid and a component derived from 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, and the diol component is ethylene glycol. About the polymerization polyester, the glass transition point at the time of changing the ratio of a dicarboxylic acid component is represented. The dicarboxylic acid component is composed of a component derived from 2,6-naphthalenedicarboxylic acid and a component derived from 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, and the diol component is ethylene glycol. For the polymerized polyester, the melting point when the ratio of the dicarboxylic acid component is changed is shown.

  The uniaxially stretched multilayer laminate film of the present invention is a uniaxially stretched multilayer laminate film in which the first layer and the second layer are alternately laminated. About each configuration of the present invention, such as resin constituting each layer, polarization performance, etc. This will be described in detail below.

[Uniaxially stretched multilayer laminated film]
In the uniaxially stretched multilayer laminated film of the present invention, the first layer is a layer having a relatively higher refractive index characteristic than the second layer, and the second layer is a layer having a relatively lower refractive index characteristic than the first layer. Thus, the refractive index relationship is expressed by using the following specific types of polyester in each layer.
In the present invention, the uniaxial stretching direction is referred to as the X direction, the direction perpendicular to the X direction in the film plane is referred to as the Y direction, and the direction perpendicular to the film plane is referred to as the Z direction.
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. The S-polarized light in the present invention is defined as a polarized light component perpendicular to an incident surface including a uniaxially stretched direction (X direction) in a uniaxially stretched multilayer laminated film with the film surface as a reflective surface.
In the present invention, the refractive index in the stretching direction (X direction) may be described as nX, the refractive index in the direction orthogonal to the stretching direction (Y direction) as nY, and the refractive index in the film thickness direction (Z direction) as nZ. .

[First layer]
The first layer constituting the uniaxially stretched multilayer laminated film of the present invention is a layer containing polyester, and the ethylene naphthalate unit is in the range of 50 mol% or more and 100 mol% or less based on the repeating unit constituting the polyester. contains.

(First dicarboxylic acid component)
A naphthalenedicarboxylic acid component is contained as a dicarboxylic acid component constituting the polyester of the first layer, and the content thereof is 50 mol% or more and 100 mol% or less based on the dicarboxylic acid component constituting the polyester.
Examples of the naphthalenedicarboxylic acid component include components derived from 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, or combinations thereof, and derivatives thereof. In particular, 2,6-naphthalenedicarboxylic acid or The derivative component is preferably exemplified.

  The lower limit of the content of the naphthalenedicarboxylic acid component is preferably 55 mol%, more preferably 60 mol%, and even more preferably 65 mol%. The upper limit of the content of the naphthalenedicarboxylic acid component is preferably less than 100 mol%, more preferably 95 mol% or less, still more preferably 90 mol% or less, particularly preferably 80 mol% or less, and most preferably 70 mol. % Or less.

By using a polyester containing a naphthalenedicarboxylic acid component as a main component, it is possible to realize a birefringence characteristic having a high uniaxial orientation and a high refractive index in the X direction, and a refractive index with the second layer in the X direction. The difference can be increased, contributing to high polarization.
On the other hand, if the proportion of the naphthalenedicarboxylic acid component is less than the lower limit, the amorphous characteristics increase, and the difference between the refractive index nX in the stretch direction (X direction) and the refractive index nY in the Y direction in the stretched film is different. Therefore, sufficient reflection performance may not be obtained for the P-polarized component.

(Diol component)
As the diol component constituting the polyester of the first layer, an ethylene glycol component is used, and the content thereof is preferably 50 mol% or more and 100 mol% or less, more preferably based on the siale component constituting the polyester. It is 75 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less, and particularly preferably 90 mol% or more and 98 wt% or less. When the ratio of the diol component is less than the lower limit, the above-described uniaxial orientation may be impaired.
As the diol component constituting the polyester of the first layer, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol, diethylene glycol and the like may be contained in addition to the ethylene glycol component as long as the object of the present invention is not impaired.

(Second dicarboxylic acid component)
In the polyester constituting the first layer, it is preferable that a second dicarboxylic acid component is further used, and the component represented by the following formula (A) is contained in an amount exceeding 0 mol% and not more than 50 mol%,
(In the formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms)
Or it is preferable to contain the component represented by a following formula (B) more than 0 mol% and 50 mol% or less.
(In formula (B), R ^B represents a biphenyl group)

The content of the second dicarboxylic acid component is expressed on the basis of the dicarboxylic acid component constituting the polyester of the first layer, and the lower limit thereof is preferably 5 mol%, more preferably 10 mol%, still more preferably 20 mol%. Especially preferably, it is 30 mol%. Further, the upper limit of the content of the second dicarboxylic acid component is preferably 45 mol%, more preferably 40 mol%, still more preferably 35 mol%.
The aromatic polyester (I) further containing a component represented by the following formula (A) (hereinafter sometimes referred to as aromatic polyester (I)), and a component represented by the following formula (B) The aromatic polyester (II) to be contained (hereinafter sometimes referred to as aromatic polyester (II)) will be described.

(Aromatic polyester (I))
As one of the polyesters forming the first layer, an aromatic polyester (I) having an aromatic copolymer component having the following specific structure as a dicarboxylic acid component is exemplified.
In the present invention, preferred examples of the dicarboxylic acid component constituting the aromatic polyester (I) include a naphthalenedicarboxylic acid component of 50 mol% or more and less than 100 mol%, and the following formula (A) of more than 0 mol% and 50 mol% or less. It is preferable to contain a specific amount of the component represented by:

(In the formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms)

By using polyester containing such a copolymer component, the polarization performance can be further enhanced. On the other hand, if the proportion of the component represented by the formula (A) exceeds the upper limit value increases the characteristics of the amorphous, 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 refractive index difference between the first layer and the second layer in the X direction cannot be increased, and sufficient reflection performance may not be obtained for the P-polarized component.
Regarding the component represented by the formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms. Examples of the alkylene group include an ethylene group, a trimethylene 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 5 mol%, more preferably 10 mol%, still more preferably 20 mol%, particularly preferably 30 mol%. Further, the upper limit value of the content of the component represented by the formula (A) is more preferably 45 mol%, further preferably 40 mol%, particularly preferably 35 mol%.
The acid component represented by the formula (A) is 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, 6,6 ′-(trimethylenedioxy) di-2-naphthoic acid, or 6, 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.

  As a preferred embodiment of the aromatic polyester (I) in the present invention, in particular, the naphthalenedicarboxylic acid component is a component derived from 2,6-naphthalenedicarboxylic acid, and the dicarboxylic acid component represented by the formula (A) is 6 , 6 ′-(ethylenedioxy) di-2-naphthoic acid, and a diol component is preferably an ethylene glycol polyester.

The increase in the refractive index in the X direction by stretching is mainly affected by components having an aromatic ring such as a naphthalenedicarboxylic acid component and a component represented by the formula (A). Moreover, when the component represented by Formula (A) is included, the refractive index in the Y direction tends to decrease due to stretching. Specifically, since the component represented by the formula (A) has a molecular structure in which two aromatic rings are connected by an ether bond via an alkylene chain, the directions in which these aromatic rings are not in the plane direction when uniaxially stretched And the refractive index in the Y direction of the first layer tends to decrease due to stretching.
On the other hand, since the diol component of the aromatic polyester (I) in the present invention is aliphatic, the influence of the diol component on the refractive index characteristics of the first layer is smaller than that of the dicarboxylic acid component of the present invention.

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, in the case of a copolymer containing a naphthalene dicarboxylic acid component and a component of formula (A), compared to a homopolymer having only a naphthalene dicarboxylic acid component or a homopolymer having only a component of formula (A) Although it has a low melting point, it has an excellent characteristic that its mechanical strength is comparable.

  The glass transition point (hereinafter sometimes referred to as Tg) of the aromatic polyester (I) is preferably in the range of 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 a melting point and glass transition point can be adjusted by controlling the type and amount of copolymerization component and diethylene glycol as a by-product.

The naphthalenedicarboxylic acid component is a component derived from 2,6-naphthalenedicarboxylic acid, and the dicarboxylic acid component represented by the formula (A) is derived from 6,6 ′-(ethylenedioxy) di-2-naphthoic acid FIG. 3 and FIG. 4 show the glass transition point and the melting point when the ratio of the dicarboxylic acid component is changed for the polyester in which the diol component is ethylene glycol.
The method for producing the aromatic polyester (I) in the case of including the naphthalenedicarboxylic acid component and the component represented by the formula (A) is based on, for example, the method described on page 9 of International Publication No. 2008/153188. Can be manufactured.

(Refractive index characteristics of aromatic polyester (I))
When the aromatic polyester (I) containing such a specific copolymer component is used for the first layer and is uniaxially stretched, the refractive index nX in the X direction of the first layer is a high refractive index of 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.
The difference between the refractive index nY after uniaxial stretching in the Y direction and the refractive index nZ after uniaxial stretching in the Z direction is preferably 0.05 or less.

(Aromatic polyester (II))
As polyester which comprises the 1st layer of this invention, the aspect of the following aromatic polyesters (II) other than aromatic polyester (I) is illustrated preferably.
Specifically, instead of the component represented by the formula (A) of the aromatic polyester (I), the component represented by the following formula (B) is used as the dicarboxylic acid component, and more than 0 mol% and 50 mol% or less. The aromatic polyester contained in the range of.

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

  Of the dicarboxylic acid component and diol component constituting the aromatic polyester (II), the same components as the aromatic polyester (I) can be used for the components other than the component represented by the formula (B). The content is also in accordance with the aromatic polyester (I).

[Second layer]
In the present invention, a copolymer that includes a 2,6-naphthalenedicarboxylic acid component, an ethylene glycol component, an alicyclic diol component, and a trimethylene glycol component as a copolymer component as a polymer that forms the second layer of the uniaxially stretched multilayer laminated film. It is necessary to use polymerized polyester.
The copolymer component in the present invention means any component constituting the copolymer polyester, and is not limited to the copolymer component as a subordinate component, and includes the main component.
In order to express the reflective polarization function, a polyester containing a predetermined amount of an ethylene naphthalate unit is used for the first layer as the high refractive index layer of the present invention, and the polymer component of the second layer is a 2,6-naphthalenedicarboxylic acid component. If it is not included, the compatibility with the first layer is lowered and delamination occurs, so that the interlayer adhesion with the first layer is lowered.

In the copolymer polyester of the second layer, the diol component contains at least three components of an ethylene glycol component, an alicyclic diol component, and a trimethylene glycol component as essential components. Among these, the ethylene glycol component is preferably used as a main diol component from the viewpoint of film-forming properties.
The copolymer polyester of the second layer in the present invention further contains a trimethylene glycol component as a diol component. If the trimethylene glycol component is not included, the elasticity of the layer structure is insufficient and delamination occurs.
Furthermore, the copolymer polyester of the second layer in the present invention contains an alicyclic diol component. By containing the alicyclic diol component, it becomes possible to make the interlayer refractive index difference smaller according to the refractive index characteristics of the first layer, particularly in the Y direction, and the polarization performance can be improved. At the same time, a glass transition point capable of exhibiting sufficient heat resistance can be obtained.
Preferred examples of the alicyclic diol component include at least one selected from the group consisting of spiro glycol, tricyclodecane dimethanol and cyclohexane dimethanol.

  The 2,6-naphthalenedicarboxylic acid component is preferably 30 mol% to 100 mol%, more preferably 30 mol% to 80 mol% of the total carboxylic acid component constituting the copolymer polyester of the second layer. Is preferred. If the content of the 2,6-naphthalenedicarboxylic acid component is less than the lower limit, the adhesiveness is lowered from the viewpoint of compatibility. The upper limit of the content of the 2,6-naphthalenedicarboxylic acid component is not particularly limited, but other dicarboxylic acid components may be copolymerized in order to adjust the refractive index relationship with the first layer.

The ethylene glycol component is preferably 50 mol% to 92 mol%, more preferably 50 mol% to 80 mol% of the total diol component constituting the copolymer polyester of the second layer.
The alicyclic diol component is preferably 3 mol% to 40 mol%, more preferably 3 mol% to 30 mol% of the total diol component constituting the copolymer polyester of the second layer. If the content of the alicyclic diol component is less than the lower limit, it is difficult to obtain a resin having a desired refractive index and glass transition point, and if it exceeds the upper limit, it is difficult to ensure adhesion.
The trimethylene glycol component is preferably 5 mol% to 47 mol%, more preferably 10 mol% to 40 mol% of the total diol component constituting the copolymer polyester of the second layer. If the content of the trimethylene glycol component is less than the lower limit, it is difficult to ensure adhesion, and if it exceeds the upper limit, a resin having a desired refractive index and glass transition point cannot be obtained.

The copolyester constituting the second layer preferably has an average refractive index of 1.50 or more and 1.65 or less, more preferably 1.53 or more and 1.63 or less, and further preferably 1.55 or more and 1.61. Hereinafter, it is particularly preferably 1.58 or more and 1.60 or less. The second layer is preferably an optically isotropic layer.
The average refractive index of the second layer is obtained by melting the copolymer polyester constituting the second layer alone and extruding it from a die to create an unstretched film. Transition temperature) A uniaxially stretched film was stretched 5 times at + 20 ° C., and the refractive index at a wavelength of 633 nm using a metricon prism coupler in each of the X, Y and Z directions of the obtained film. And the average value thereof is defined as the average refractive index.
Optical isotropy means that the refractive index difference between the two directions of the refractive index in the X direction, Y direction, and Z direction is 0.05 or less, preferably 0.03 or less.

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. A refractive index characteristic having a large refractive index difference and a small refractive index difference between layers in the Y direction can be obtained, and polarization performance can be enhanced to a high degree, which is preferable.
Further, when the component represented by the formula (A) or the formula (B) is used as the copolymerization component of the first layer, not only the characteristics in the X direction and the Y direction but also the Z-direction refractive index difference in each direction, Z The difference in refractive index in the direction is also small, and the hue shift due to the oblique incident angle can be reduced, which is preferable.
If the second layer in the present invention is in a range that does not affect the degree of polarization of the present invention, the thermoplastic resin other than the copolyester is within the range of 10% by weight or less based on the weight of the second layer. You may contain as a polymer component of 2.

In the present invention, the above-mentioned copolymer polyester of the second layer preferably has a glass transition point of 70 ° C. or higher, more preferably 70 ° C. or higher and 150 ° C. or lower, more preferably 70 ° C. or higher and 120 ° C. or lower, particularly preferably. Is 75 ° C. or higher and 110 ° C. or lower. When the glass transition point of the copolyester of the second layer is less than the lower limit, sufficient heat resistance may not be obtained, and the second is included when a process such as heat treatment near the glass transition point or at a higher temperature is included. Crystallization or embrittlement of the layer may increase haze and may cause a decrease in the degree of polarization. In addition, when the glass transition point of the copolymer polyester of the second layer is too high, the polyester of the second layer may also be birefringent due to stretching at the time of stretching, and accordingly, refraction with the first layer in the stretching direction. The rate difference is reduced, and the reflection performance may be reduced.
Among the copolyesters having such a refractive index characteristic, amorphous copolyesters are preferable from the viewpoint that no haze increase due to crystallization occurs at high heat treatment. 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.

  Specific examples of the second layer copolyester include (1) a copolyester containing a 2,6-naphthalenedicarboxylic acid component as a dicarboxylic acid component and an ethylene glycol component, a trimethylene glycol component and a spiroglycol component as a diol component. And (2) a copolyester containing a 2,6-naphthalenedicarboxylic acid component and terephthalic acid as the dicarboxylic acid component and an ethylene glycol component, a trimethylene glycol component and a spiroglycol component as the diol component. In addition to the above-described copolymer component, a copolymer polyester containing a component represented by the following formula (A) as a dicarboxylic acid component is also preferred.

(In the formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms)

Examples of the alkylene group include an ethylene group, a trimethylene group, an isopropylene group, a tetramethylene group, a hexamethylene group, and an octamethylene group, and an ethylene group is particularly preferable.
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.

  Since the copolymer polyester of the second layer uses an alicyclic diol component or the like as a copolymer component, the tear strength in the unstretched direction may be reduced, and the intrinsic viscosity of the copolymer polyester should be in the above range. Can improve the tear resistance. In the case where the above-described copolymer polyester is used as the second layer, the intrinsic viscosity is preferably higher from the viewpoint of tear resistance, but in the range exceeding the upper limit, the difference in melt viscosity from the aromatic polyester of the first layer is large. Accordingly, the thickness of each layer may be non-uniform.

(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 90.0% or more, and more preferably 95.0% or more. The degree of polarization is more preferably 99.0% or more, particularly preferably 99.5% or more, and most preferably 99.9% 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 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. When the uniaxially stretched multilayer laminated film of the present invention has a polarization degree of 98.0% or more, it can be suitably used as an application such as a brightness enhancement member. Moreover, by having a degree of polarization of 99.5% or more, a reflective polarizing plate alone can be applied as a polarizing plate of a liquid crystal display having a high contrast, which has conventionally been difficult to apply unless it is an absorptive polarizing plate.

  Such polarization degree characteristics are obtained by using the above-mentioned types of polymers constituting the first layer and the second layer, and by making the refractive indexes between the layers in the X direction, the Y direction, and the Z direction a specific relationship by uniaxial stretching. can get. Further, in order to obtain a high degree of polarization of 99.5% or more, among the polyesters of the first layer, aromatic polyester (I) or aromatic polyester (II) is used, and the second dicarboxylic acid of these polyesters is used. The orientation characteristics of the uniaxially stretched multilayer laminated film can be controlled to a high degree by performing the toe-out (re-stretching) and heat setting treatment within a predetermined range after uniaxial stretching with the component being 10 mol% or more. Is obtained.

(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 an incident angle of 0 degree with respect to a polarized light component perpendicular to an incident surface including a uniaxially stretched direction (X direction) in a uniaxially stretched multilayer laminated film. The average transmittance at a wavelength of 400 to 800 nm with respect to the incident polarized light is shown.
When the average transmittance of the S-polarized light is less than the lower limit, when used as a reflective polarizing plate, a light recycling function for reflecting the reflected polarized light to the light source side without absorbing it by the polarizing plate and effectively utilizing the light again is considered. Even so, the superiority of the brightness enhancement effect may not be sufficient as compared with the absorption-type polarizing plate.

[Buffer layer / intermediate layer]
The uniaxially stretched multilayer laminated film of the present invention may contain an intermediate layer in addition to the first layer and the second layer. The intermediate layer preferably has a thickness of 2 μm or more and 30 μm or less, and such an intermediate layer may be included in the alternately laminated structure of the first layer and the second layer.
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, a thick film layer (sometimes referred to as a thickness adjusting layer or a buffer layer) is 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 the number of laminated layers is determined by doubling. In this case, a method in which two buffer layers are laminated to form an intermediate layer is preferable.

When the intermediate layer having such a thickness is included 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. 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 the polarized light to be transmitted may be affected, when particles are included in the layer, it is preferably within the range of the particle concentration described in the description of the particles.
If the thickness of the intermediate layer is less than the lower limit, the layer configuration of the alternately laminated components may be disturbed, and the reflection performance may be deteriorated. On the other hand, if the thickness of the intermediate layer exceeds the upper limit, the total thickness of the uniaxially stretched multilayer laminated film after lamination increases, saving space when used as a polarizing plate or a brightness enhancement member for thin liquid crystal display devices. It may be difficult. Moreover, when a some intermediate | middle layer is included in a uniaxially stretched multilayer laminated film, it is preferable that the thickness of each intermediate | middle layer exists in this range.

The polymer used for the intermediate layer may be a resin different from the first layer or the second layer, as long as it can be present in the multilayer structure using the method for producing a uniaxially stretched multilayer laminated film of the present invention. From the viewpoint of interlayer adhesion, the composition is preferably the same as that of either the first layer or the second layer, or may be a composition partially including these compositions.
The method for forming the intermediate layer is not particularly limited. For example, thick film layers (buffers) are formed on both sides of an alternating laminate of 300 layers or less before doubling, which is described in the column for producing a uniaxially stretched multilayer laminate film. Layer) is divided into two using a branch block called a layer doubling block, and one layer of an internal thick film layer (intermediate layer) can be provided by re-stacking them. A plurality of intermediate layers can be provided by three branches and four branches in the same manner.

[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 of the first layer and the second layer is preferably 0.01 μm or more and 0.5 μm or less. The thickness of each layer of the first layer is more preferably 0.01 μm or more and 0.1 μm or less, and the thickness of each layer of the second layer is more 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 according to the present invention is used as a reflective polarizing plate or a brightness enhancement member for a liquid crystal display, 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 of laminating the multilayer structure in the uniaxially stretched multilayer laminated film of the present invention is not particularly limited. For example, the first layer and the first layer obtained by branching the polyester for the first layer into 138 layers and the polyester for the second layer into 137 layers and the first layer There is a method of using a multilayer feed block device in which two layers are alternately laminated and the flow path is continuously changed by 2.0 to 5.0 times.

(Average layer thickness ratio of the first layer and the second layer)
In the 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 times to 4.0 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 3.0. The most preferred range is 1.1 or more and 3.0 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 further improved. 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 3.0.

[Uniaxially stretched film]
The uniaxially stretched multilayer laminated film of the present invention is stretched in at least a uniaxial direction in order to obtain optical characteristics as a 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. 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, which is preferable.
The difference in refractive index between the first layer and the second layer in the Y direction is preferably 0.05 or less. It is preferable that the refractive index difference between the layers in the Y direction is within such a range that the polarization performance is improved.

[Film thickness]
The film thickness of the uniaxially stretched multilayer laminated film of the present invention is preferably 15 μm or more and 200 μm or less, and more preferably 50 μm or more and 180 μm or less.

[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 multi-layer laminated film of the present invention is formed by alternately laminating the polymer constituting the first layer and the polymer 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 + 20) ° C. of the polymer of the first layer. By performing stretching at a temperature lower than before, the orientation characteristics of the film can be controlled to a higher degree.

  The draw ratio is preferably 2 to 5.8 times, more preferably 4.5 to 5.5 times. Within such a range, the larger the draw ratio, the smaller the variation in the plane direction of the individual layers in the first layer and the second layer, and the light interference of the multilayer stretched film is made uniform in the plane direction. Moreover, since the refractive index difference of the extending | stretching direction of a 1st layer and a 2nd layer becomes large, it 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.
Moreover, the uniaxially stretched multilayer laminated film obtained by toe-out (re-stretching) in the stretching direction within a range of 5 to 15% while further heat-setting at a temperature of (Tg) to (Tg + 30) ° C. after stretching. It is possible to highly control the orientation characteristics.

[Liquid crystal for liquid crystal display]
Among the uniaxially stretched multi-layer laminated films of the present invention, those having a high degree of polarization of 99.5% or more, the polarization of a liquid crystal display used alone adjacent to the liquid crystal cell without using an absorptive polarizing plate in combination. It can be used as a plate.

[Optical members for liquid crystal displays]
The present invention also includes an optical member for a liquid crystal display in which the first polarizing plate, the liquid crystal cell, and the second polarizing plate, which are the polarizing plates for a liquid crystal display of the present invention, are laminated in this order. . Such an optical member is also referred to as a liquid crystal panel. The optical member corresponds to 5 in FIG. 2, 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 a liquid crystal cell, high polarizing performance has been obtained by having at least an absorptive polarizing plate. If it is a polarizing plate using the uniaxially stretched multilayer laminated film of the present invention, Since a high polarization performance that could not be achieved with a multilayer laminated film can be obtained, it can be used as a polarizing plate used adjacent to a liquid crystal cell instead of an absorptive 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. Among them, the present invention is particularly preferably used for the VA mode and the IPS mode, which generally require high viewing angle characteristics from an oblique 45 ° azimuth.

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 liquid crystal display polarizing plate of the present invention is preferably used.
In the optical member for a liquid crystal display 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, You may laminate | stack through the layer (henceforth an adhesive layer) which improves the adhesiveness of the interlayer called an adhesion layer or an adhesion layer, a protective layer, etc.

[Formation of optical members for liquid crystal displays]
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 includes a liquid crystal display including the light source and the optical member for a liquid crystal display of the present invention, in which the first polarizing plate is disposed on the light source side, as one aspect of the present invention.
FIG. 2 is a schematic cross-sectional view of a liquid crystal display which is one embodiment of the present invention. The liquid crystal display 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 present invention is particularly preferably used for the VA mode and the IPS mode.

  The liquid crystal display of the present invention replaces the conventional absorption polarizing plate by disposing the first polarizing plate 3 comprising the polarizing plate for liquid crystal display of the present invention having high polarization performance on the light source side of the liquid crystal cell 2. In the case where it can be used alone and bonded to a liquid crystal cell and has a very high polarization performance of 99.5% or more, it is practically used in a liquid crystal television regarding the contrast required from the brightness / dark brightness of the liquid crystal display. A very high level of contrast required can be obtained.

The first polarizing plate comprising the polarizing plate for a liquid crystal display of the present invention has a high polarizing performance of 99.5% or more comparable to that of a conventional absorption polarizing plate, and 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 it is used adjacent to the brightness enhancement film and the liquid crystal cell. Since the functions of the polarizing plate can be integrated, the number of members can be reduced.
Further, normally, as shown in FIG. 2, 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]
The liquid crystal display of the present invention can be obtained by combining a liquid crystal display optical member (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 can be combined, but the liquid crystal display of the present invention preferably allows light emitted from the light source to enter the first polarizing plate. .

In general, the light source of a liquid crystal display is roughly classified into a direct type and a side light type, but the liquid crystal display of the present invention can be used without any limitation.
The liquid crystal display thus obtained is, for example, an OA device such as a personal computer monitor, a notebook computer, a copy machine, a mobile phone, a clock, a digital camera, a portable information terminal (PDA), a portable device such as a portable game machine, a video Household electrical equipment such as cameras, televisions, microwave ovens, back monitors, car navigation system monitors, car audio equipment, in-vehicle equipment, display equipment such as information monitors for commercial stores, surveillance equipment such as surveillance monitors, nursing care It can be used for various applications such as nursing care and medical equipment such as medical monitors and medical monitors.

Examples of the present invention will be described below, 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) Average transmittance of P-polarized light and S-polarized light, degree of polarization Using 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 (1).
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.

(2) Interlayer adhesion Using the obtained uniaxially stretched multi-layer laminated film, a cross cut (100 squares of 1 mm ² ) is applied, and a cellophane tape 24 mm wide (manufactured by Nichiban Co., Ltd.) is applied thereon. After affixing and peeling off at a 90 ° peeling angle, the peeled surface was observed and evaluated according to the following criteria.
A: peeling area of 0% or more and less than 5% (very good adhesion)
○: peeling area is 5% or more and less than 20% (adhesive strength is good)
X: Peeling area exceeds 20% (adhesive strength is poor)

(3) Polymer melting point (Tm) and glass transition point (Tg)
10 mg of each layer sample was sampled and used at 20 ° C./min. Using DSC (trade name: DSC Q400, manufactured by TA Instruments). The melting point and the glass transition point of the polymer constituting each layer are measured at a temperature rising rate of.

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

(5) 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. Further, a stretched film was prepared by stretching the obtained film 5 times in the uniaxial direction at (resin glass transition temperature) + 20 ° C. With respect to the obtained cast film and stretched film, the refractive index (respectively, nX, nY, nZ) in the stretching direction (X direction), the orthogonal direction (Y direction), and the thickness direction (Z direction) is measured. The refractive index was determined by measuring at a wavelength of 633 nm using a prism coupler made from 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.

(6) 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.

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

(8) Brightness improvement effect Using a VA type liquid crystal display panel (manufactured by Sharp AQUAS LC-20E90 2011), the lower polarizing plate (light source side polarizing plate) and the optical compensation film therein are removed, and a multilayer laminated film sample The front luminance of the liquid crystal display screen when white is displayed is measured with an FPD viewing angle measurement and evaluation device (ErgoScope 88) manufactured by Opto Design, and the rate of increase in luminance relative to Comparative Example 1 is calculated. Evaluated by criteria.
○: Brightness improvement effect is 160% or more Δ: Brightness improvement effect is 140% or more and less than 160% ×: Brightness improvement effect is less than 140%

(9) Contrast Using a liquid crystal display 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 with an FPD viewing angle measurement evaluation device (ErgoScope 88) manufactured by Optodesign. Then, the bright luminance was obtained from the white screen and the dark luminance was obtained from the black screen, and the contrast obtained 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

[Comparative 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. Then, it was dissolved in pure water to prepare an aqueous solution having a solid content concentration of 3.7% by weight. An aqueous adhesive solution was prepared by adding 18 parts by weight of an aqueous solution containing alumina colloid having a positive charge (average particle diameter of 15 nm) at a solid content concentration of 10% by weight to 100 parts by weight of this aqueous solution. The viscosity of the adhesive solution was 9.6 mPa · s, the pH was in the range of 4 to 4.5, and the compounding amount of the alumina colloid was 74 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol resin.

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

(Creation of LCD panel)
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 polarized light is passed through the acrylic pressure-sensitive adhesive so that the same absorption axis direction as that of the light source side polarizing plate arranged on the original liquid crystal panel is placed on the light source side surface of the liquid crystal cell. Plate X was placed in the liquid crystal cell.
Next, the above polarizing plate X is interposed through an acrylic pressure-sensitive adhesive so that the absorption axis direction is the same as the absorption axis direction of the viewing side polarizing plate disposed on the original liquid crystal panel on the viewing side surface of the liquid crystal cell. Was placed in a liquid crystal cell. In this way, a liquid crystal panel in which the polarizing plate X was disposed on one main surface of the liquid crystal cell and the polarizing plate X was disposed on the other main surface was obtained.

(Creation of liquid crystal display)
The above liquid crystal panel was incorporated into the original liquid crystal television, the light source of the liquid crystal television 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 was evaluated.

[Example 1]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, and ethylene glycol were subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and then further The polycondensation reaction was performed, and the intrinsic viscosity was 0.63 dl / g, 70 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 30 mol% of the acid component was 6,6 ′-(ethylenedioxy). Di-2-naphthoic acid component (denoted as ENA in the table), aromatic polyester whose glycol component is ethylene glycol (denoted as ENA30PEN in the table) as the first layer polyester, second layer polyester as 2 , 6-Naphthalenedicarboxylic acid 75 mol%, terephthalic acid 25 mol%, ethylene glycol 62 mol%, trimethyle Glycol 33 mol%, were prepared copolyester (intrinsic viscosity of 0.70 dl / g) consisting of spiroglycol 5 mol%.

The prepared polyester for the first layer is dried at 170 ° C. for 5 hours, and the polyester for the second layer is dried at 85 ° C. for 8 hours. The first layer polyester is branched into 138 layers and the second layer polyester is branched into 137 layers, and then the first layer and the second layer are alternately laminated, and the maximum layers of the first layer and the second layer are respectively laminated. Total number of first and second layers stacked alternately, using a multi-layer feedblock device where the thickness and minimum layer thickness varies continuously up to 3.1 times and 3.0 times at maximum / minimum A melt of 275 layers is produced, and the same polyester as the second layer polyester is guided from the third extruder to the three-layer feed block on both sides of the melt while maintaining the laminate state. On both sides of the melt lamination direction Ffa layer was further laminated. The supply amount of the third extruder was adjusted so that the total of the buffer layers on both sides was 23% of the total. 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, and cast on a casting drum to adjust the average layer thickness ratio of the first layer to the second layer to be 1.0: 2.6. An unstretched multilayer laminated film was prepared.
This multilayer unstretched film was stretched 5.0 times in the width direction at a temperature of 115 ° C., and further subjected to heat setting at 120 ° C. for 3 seconds while stretching 15% in the same direction at 115 ° C. The thickness of the obtained uniaxially stretched multilayer laminated film was 105 μm.

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

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

[Examples 2 to 4]
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, layer thickness, and stretching conditions of each layer were changed. The resin configuration of each layer of the uniaxially stretched multilayer laminated film thus obtained and the characteristics of each layer are shown in Table 1, and the physical properties of the uniaxially stretched multilayer laminated film and the properties of the liquid crystal display are shown in Table 2.
In Example 2, ENA40PEN (60 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component, and 40 mol% of the acid component was 6,6 '-(ethylenedioxy) di-2- A naphthoic acid component, an aromatic polyester whose glycol component is ethylene glycol), a copolymer polyester resin B shown in Table 3 as the polyester for the second layer, a stretching temperature of 120 ° C., and a stretching ratio of 5.1 times. Except having changed, it carried out similarly to Example 1, and obtained the uniaxially stretched multilayer laminated film.

In Example 3, ENA35PEN (65 mol% of the acid component is 2,6-naphthalenedicarboxylic acid component and 35 mol% of the acid component is 6,6 ′-(ethylenedioxy) di-2-naphthoate is added to the first layer polyester. Aromatic polyester having an acid component and a glycol component of ethylene glycol), and using a copolymer polyester resin C shown in Table 3 as the polyester for the second layer, in the width direction at a stretching temperature of 130 ° C. and a stretching ratio of 5.8 times. A uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1 except that the film was stretched and further subjected to heat setting at 130 ° C. for 3 seconds while stretching 10% in the same direction at 130 ° C.
In Example 4, the first layer polyester is BB30PEN (70 mol% of the acid component is 2,6-naphthalenedicarboxylic acid component, 30 mol% of the acid component is diphenyldicarboxylic acid component, and the glycol component is ethylene glycol) ), The polyester resin D shown in Table 3 is used as the polyester for the second layer, stretched in the width direction at a stretching temperature of 125 ° C. and a stretching ratio of 4.6 times, and further stretched by 10% in the same direction at 125 ° C. However, a uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1 except that the heat setting treatment was performed at 125 ° C. for 3 seconds.

Moreover, in the said comparative example 1, it replaced with the polarizing plate X as a 1st polarizing plate by the side of a light source, and was using the obtained uniaxial stretching multilayer laminated film similarly to the comparative example 1, and the light source side of a 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.
The above liquid crystal panel was incorporated into the original liquid crystal display, the light source of the liquid crystal display was turned on, and the brightness of the white screen and the black screen was evaluated with a personal computer.

[Comparative Example 2]
ENA35PEN (65 mol% of the acid component is 2,6-naphthalenedicarboxylic acid component, 35 mol% of the acid component is 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component, glycol) Using a copolymer polyester resin E shown in Table 3 as the polyester for the second layer, and stretching in the width direction at a stretching temperature of 135 ° C. and a stretching ratio of 6.0 times. A uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1 except that heat setting was performed at 120 ° C. for 3 seconds while stretching 15% in the same direction at 135 ° C.

Moreover, in the said comparative example 1, it replaced with the polarizing plate X as a 1st polarizing plate by the side of a light source, and was using the obtained uniaxial stretching multilayer laminated film similarly to the comparative example 1, and the light source side of a 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.
The above liquid crystal panel was incorporated into the original liquid crystal display, the light source of the liquid crystal display was turned on, and the brightness of the white screen and the black screen was evaluated with a personal computer.
Table 2 shows the physical properties of the obtained uniaxially stretched multilayer laminated film and the liquid crystal display.

[Comparative Example 3]
ENA21PEN (79 mol% of the acid component is 2,6-naphthalenedicarboxylic acid component, 21 mol% of the acid component is 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component, glycol) Using a copolymer polyester resin F shown in Table 3 as the polyester for the second layer, and stretching in the width direction at a stretching temperature of 120 ° C. and a stretching ratio of 5.2 times. A uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1 except that heat setting was performed at 120 ° C. for 3 seconds while stretching 15% in the same direction at 120 ° C.

Moreover, in the said comparative example 1, it replaced with the polarizing plate X as a 1st polarizing plate by the side of a light source, and was using the obtained uniaxial stretching multilayer laminated film similarly to the comparative example 1, and the light source side of a 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.
The above liquid crystal panel was incorporated into the original liquid crystal display, the light source of the liquid crystal display was turned on, and the brightness of the white screen and the black screen was evaluated with a personal computer.
Table 2 shows the physical properties of the obtained uniaxially stretched multilayer laminated film and the liquid crystal display.

  The uniaxially stretched multilayer laminated film of the present invention is a polymer film having a multilayer structure in which a polyethylene naphthalate-based polymer is used for a layer having a high refractive index characteristic, and has polarization performance and improved interlayer adhesion. For this reason, for example, when used in a brightness improving member that requires polarization performance, a polarizing plate of a liquid crystal display that requires a high degree of polarization, etc., it is added to other members, assembled into a liquid crystal display, and used. Since delamination does not occur due to external force, it is possible to provide a more reliable brightness improving member and liquid crystal display polarizing plate.

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

Claims (15)

  A uniaxially stretched multilayer laminated film in which a first layer and a second layer are alternately laminated. 1) The first layer is a layer containing a polyester, and ethylene is based on a repeating unit constituting the polyester. It contains naphthalate units in the range of 50 mol% to 100 mol%. 2) The polymer forming the second layer is a 2,6-naphthalenedicarboxylic acid component, an ethylene glycol component, an alicyclic diol component, and trimethylene. A uniaxially stretched multilayer laminated film, which is a copolyester containing a glycol component as a copolymerization component. The uniaxially stretched multilayer laminate film according to claim 1, wherein the degree of polarization (P) represented by the following formula (1) of the uniaxially stretched multilayer laminate film 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 according to claim 1 or 2, wherein the first layer further contains a component represented by the following formula (A) as a dicarboxylic acid component in a range of more than 0 mol% and 50 mol% or less. Laminated film.
(In the formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms) The uniaxially stretched multilayer according to claim 1 or 2, wherein the first layer further contains a component represented by the following formula (B) as a dicarboxylic acid component in a range of more than 0 mol% and 50 mol% or less. Laminated film.
(In formula (B), R ^B represents a biphenyl group)   The uniaxially stretched multilayer laminated film according to any one of claims 1 to 4, wherein the alicyclic diol component is at least one selected from the group consisting of spiro glycol, tricyclodecane dimethanol and cyclohexane dimethanol. . The uniaxially stretched multilayer laminated film according to any one of claims 1 to 5, wherein the copolyester forming the second layer further contains a dicarboxylic acid component represented by the following formula (A).
(In the formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms)   The number of lamination | stacking of this uniaxial stretching multilayer laminated film is 251 layers or more, The uniaxial stretching multilayer laminated film in any one of Claims 1-6.   The uniaxially stretched multilayer laminated film according to any one of claims 1 to 7, which is used as a liquid crystal display polarizing plate adjacent to a liquid crystal cell.   The polarizing plate for liquid crystal displays which consists of a uniaxially stretched multilayer laminated film in any one of Claims 1-8.   The optical member for liquid crystal displays in which the 1st polarizing plate which consists of a polarizing plate for liquid crystal displays of Claim 9, a liquid crystal cell, and a 2nd polarizing plate are laminated | stacked in this order.   The optical member for a liquid crystal display according to claim 10, wherein the first polarizing plate is an optical member for a liquid crystal display excluding a configuration in which the first polarizing plate is laminated with an absorption polarizing plate.   The optical member for liquid crystal display according to claim 10 or 11, wherein the second polarizing plate is an absorptive polarizing plate.   A first polarizing plate, a liquid crystal cell, and a second polarizing plate are laminated, and the first polarizing plate and the second polarizing plate comprise the polarizing plate for a liquid crystal display according to claim 9. Optical member.   A liquid crystal display comprising a light source and the optical member for liquid crystal display according to claim 10, wherein the first polarizing plate is disposed on the light source side.   The liquid crystal display according to claim 14, further comprising no reflective polarizing plate between the light source and the first polarizing plate.