JP2011126181A - Uniaxially oriented laminated multilayer film, brightness improving member made of the film, composite member for liquid crystal display made of them, and liquid crystal display made of them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated multilayer film having a reflective polarization function in which the hue dislocation of transmitted polarized light by an incident angle in the oblique direction to light incident in the oblique direction simultaneously while polarization performance is raised further is not seen. <P>SOLUTION: In a uniaxially oriented laminated multilayer film of at least 251 layers, first layers and second layers are laminated alternately. The first layer (i) contains (i) 5-50 mole% of a predetermined dicarboxylic acid component containing a naphthoic acid component as a dicarboxylic acid component and a dicarboxylic acid component having a phenylene group or a naphthalenediyl group and (ii) is made of a polyester containing a diol component having a 2-10C alkylene group as a diol component. The second layer is a layer made of a thermoplastic resin having an average refractive index of 1.50-1.60 and refractive index differences in the uniaxial orientation direction, its orthogonal direction, and the film thickness direction before and after the orientation of 0.05 or below. In the uniaxially oriented laminated multilayer film, as regards a P polarization component, average reflectances to the incident polarized light at incident angles 0° and 50° are at least 90%, respectively, and as regards an S polarization component, average reflectances to the incident polarized light at incident angles 0°and 50° are 15% or below, respectively. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a uniaxially stretched multilayer laminated film that selectively reflects a certain polarization component and selectively transmits a polarization component perpendicular to the polarization component, a brightness enhancement member comprising the same, and a liquid crystal display composite comprising the same. The present invention relates to a member and a liquid crystal display device made of them.

  More specifically, the polarization performance of selectively reflecting a certain polarization component and selectively transmitting a polarization component in a direction perpendicular to the polarization component is superior to that of the prior art, and partially with respect to light incident in an oblique direction. The present invention relates to a uniaxially stretched multi-layer laminate film in which a hue shift of transmitted polarized light is eliminated without occurrence of reflection, a brightness improving member made of the same, a composite member for liquid crystal display made of them, and a liquid crystal display device made of them.

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

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

  For example, as shown in Patent Document 1, by using a resin having a positive stress optical coefficient in one layer, the refractive index of the layer is made birefringent by stretching in one axial direction, thereby making anisotropy. To increase the refractive index difference between layers in the stretching direction in the film plane, while reducing the refractive index difference between layers in the direction perpendicular to the stretching direction in the film plane. can do.

Utilizing this principle, for example, a reflective polarizing film that reflects P-polarized light and transmits S-polarized light can be designed. The desired birefringence at that time is expressed by the following equation.
n1 _X > n2 _X , n1 _Y = n2 _Y
(In the above formula, n1 _X and n2 _X represent the refractive index in the stretching direction in each layer, and n1 _Y and n2 _Y represent the refractive index in the direction orthogonal to the stretching direction in each layer)

  In Patent Documents 2 and 3, polyethylene-2,6-naphthalenedicarboxylate (hereinafter sometimes referred to as 2,6-PEN) is used for the layer having a high refractive index, and the refractive index is low. The multilayer film which uses PEN which copolymerized 30 mol% of thermoplastic elastomers and isophthalic acid for the layer is illustrated. This is because a resin having a positive stress optical coefficient is used in one layer and a resin having a very low stress optical coefficient (extremely low birefringence due to stretching) is used in the other layer. The reflective polarizing film which reflects only polarized light is illustrated.

  However, when 2,6-PEN is used for a layer having a high refractive index, the refractive index in the direction perpendicular to the stretching direction after stretching (Y direction) and the refractive index in the film thickness direction (Z direction) in such a layer. Due to the difference, if the stretching is increased to increase the refractive index difference between the layers in the stretching direction (X direction) to improve the polarization performance, the refractive index difference between the layers in the Z direction is increased accordingly. There is a problem that the hue shift of transmitted light is further increased by partial reflection of light incident in an oblique direction.

JP 04-268505 A Japanese National Patent Publication No. 9-506837 WO01 / 47711 pamphlet

  The object of the present invention is to solve the above-mentioned problems of the conventional multilayer laminated film and to improve the polarization performance further than before, while simultaneously transmitting the hue of transmitted polarized light by the obliquely incident angle with respect to the light incident in the oblique direction. An object of the present invention is to provide a multilayer laminated film having a reflective polarization function, in which no deviation is observed.

  As a result of intensive studies to solve the above problems, the present inventors have conventionally used a high refractive index and birefringent polyethylene-2,6-naphthalene as the first layer resin constituting the high refractive index layer. When dicarboxylate was often used, the change in refractive index in each direction due to uniaxial stretching of polyethylene-2,6-naphthalenedicarboxylate increased in the stretching direction (X direction), but the Y direction was before and after stretching. However, the refractive index hardly changes, while the Z direction has a characteristic of decreasing. Therefore, if the stretching is increased to increase the refractive index difference between the layers in the stretching direction (X direction) to improve the polarization performance, the refractive index difference between the layers in the Z direction increases accordingly, or Z after stretching If the refractive index between the layers in the direction is made to coincide, the difference in the refractive index between the layers in the Y direction will increase, and it will be difficult to achieve both improved polarization performance and a hue shift of transmitted polarized light with respect to obliquely incident light. I found it.

  On the other hand, instead of polyethylene-2,6-naphthalenedicarboxylate, as the first layer resin constituting the high refractive index layer, a polyester having a high refractive index characterized by having a specific copolymer component As a result, the difference in refractive index between the X direction and the Y direction of the first layer after uniaxial stretching can be increased as compared with the conventional one. As a result, the polarization performance is improved, and in both the Y direction and the Z direction. The difference in refractive index between the layers can be reduced, and it has been found that the improvement in polarization performance, which is the subject of the present invention, and the elimination of the hue deviation of transmitted polarized light due to the oblique incident angle can be achieved, and the present invention has been completed. It was.

That is, according to the present invention, an object of the present invention is a 251 or more uniaxially stretched multilayer laminated film in which the first layer and the second layer are alternately laminated,
1) The first layer is composed of (i) an acid component represented by the following formula (A) in which the dicarboxylic acid component is 5 mol% or more and 50 mol% or less, and the following formula (B) of 50 mol% or more and 95 mol% or less. Containing the acid component represented,
(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) A diol component represented by the following formula (C) in which the diol component is 90 mol% or more and 100 mol% or less
(In the formula (C), R ^C represents an alkylene group having 2 to 10 carbon atoms)
A layer having a thickness of 0.01 μm or more and 0.5 μm or less comprising a polyester with an aromatic dicarboxylic acid component and a diol component containing
The second layer has an average refractive index of 1.50 or more and 1.60 or less, a uniaxial stretching direction (X direction), a direction perpendicular to the uniaxial stretching direction in the film plane (Y direction), and a film thickness direction ( (Z direction) each refractive index difference is a layer having a thickness of 0.01 μm or more and 0.5 μm or less made of a thermoplastic resin that is 0.05 or less before and after stretching,
2) The film surface is a reflecting surface, and the average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree and 50 degrees with respect to the polarized light component parallel to the incident surface including the X direction is 90% or more, respectively. Yes,
3) With respect to a polarized light component perpendicular to the incident surface including the X direction, with the film surface as a reflective surface, the average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree and 50 degrees is 15% or less, respectively. And 4) achieved by a uniaxially stretched multilayer laminated film (Claim 1) in which the ratio between the maximum layer thickness and the minimum layer thickness in each of the first layer and the second layer is 2.0 or more and 5.0 or less. Is done.

Moreover, the uniaxially stretched multilayer laminated film of the present invention includes a film having at least one of the following as a preferred embodiment.
2. The uniaxially stretched multilayer laminated film according to 1 above, wherein the acid component represented by the formula (A) is the following formula (A-1).
3. The uniaxially stretched multilayer according to 1 or 2 above, wherein the hue change amounts Δx and Δy represented by the following formulas (1) and (2) are both equal to or less than 0.1 with respect to the polarization component parallel to the incident surface: Laminated film.
Δx = x (0 °) −x (50 °) (1)
(In the above formula (1), x (0 °) represents the hue x of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and x (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents hue x)
Δy = y (0 °) −y (50 °) (2)
(In the above formula (2), y (0 °) represents the hue y of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and y (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents the hue y)
4). 1 for the polarization component perpendicular to the incident surface, wherein the hue change amounts Δx and Δy represented by the following formulas (1) and (2) are both 0.01 or less: Axial stretched multilayer laminated film.
Δx = x (0 °) −x (50 °) (1)
(In the above formula (1), x (0 °) represents the hue x of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and x (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents hue x)
Δy = y (0 °) −y (50 °) (2)
(In the above formula (2), y (0 °) represents the hue y of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and y (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents the hue y)
5). The uniaxially stretched multilayer laminated film according to any one of 1 to 4 above, wherein the film thickness is 15 μm or more and 40 μm or less.
6). The uniaxially stretched multilayer laminated film according to any one of 1 to 5 above, wherein the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is in the range of 1.5 to 5.0.
7). The uniaxially stretched multilayer laminated film according to any one of the above 1 to 6, wherein a heat seal layer is further provided on at least one outermost layer surface of the alternate lamination of the first layer and the second layer.
8). 8. The heat seal layer is made of the same thermoplastic resin as the second layer, and the melting point of the thermoplastic resin is 20 ° C. lower than the melting point of the polyester of the first layer and is a layer having a thickness of 3 to 10 μm. Axial stretched multilayer laminated film.
9. The uniaxially stretched multilayer laminated film according to any one of 1 to 8 above, which is used as a brightness enhancement film for a liquid crystal display.

Moreover, this invention relates to the member for a brightness improvement which consists of a uniaxially stretched multilayer laminated film of this invention.
Furthermore, the present invention relates to a composite member for a liquid crystal display in which a light diffusion film is laminated on at least one surface of the brightness enhancement member of the present invention, and as a preferred embodiment, the brightness enhancement member and the light diffusion film are heat sealed. A composite member for a liquid crystal display that is laminated through layers, and a composite member for a liquid crystal display that further includes a prism layer on the opposite side of the brightness enhancement member through a light diffusion film are also included.
Others The present invention relates to a liquid crystal display device including the brightness enhancing member of the present invention and a liquid crystal display device including the composite member for a liquid crystal display of the present invention.

  According to the present invention, the uniaxially stretched multilayer laminated film of the present invention eliminates the hue shift of transmitted polarized light due to the oblique incident angle seen in the conventional reflective polarizing film, and has higher polarization performance than before. Therefore, when used as a brightness enhancement film, a high brightness improvement rate can be obtained, and a liquid crystal display excellent in visibility with a high viewing angle and little hue shift can be provided.

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.

[Uniaxially stretched multilayer laminated film]
The uniaxially stretched multilayer laminated film of the present invention is a uniaxially stretched multilayer laminated film having 251 layers or more in which the first layer and the second layer are alternately laminated. Here, the first layer represents a layer having a higher refractive index than the second layer, and the second layer represents a layer having a lower refractive index than the first layer.

The greatest feature of the present invention is that the first layer and the second layer constituting the uniaxially stretched multilayer laminated film have a specific copolymer component in the first layer with a constant layer thickness constitution. A polyester having a high refractive index is used, and a thermoplastic resin having an average refractive index of 1.50 to 1.60 is used for the second layer.
By configuring the first layer using a specific polyester described later, it becomes possible to increase the refractive index difference between the X direction and the Y direction of the first layer after stretching, and in the Y direction and the Z direction. It becomes possible for the first time to reduce the refractive index difference between the layers in both directions. As described above, the specific polyester of the present invention, which has not been conventionally used for the first layer of the multilayer laminated film having a reflective polarization function, is used for the first layer, and further, the second layer thermoplastic described later. By combining with a resin to form a multilayer laminated film having a constant layer thickness, it is possible to achieve both improvement in polarization performance and hue shift of transmitted polarized light with respect to obliquely incident light, which has been difficult until now. Furthermore, since the polarization performance is higher than before, the film thickness can be reduced to about 1/3 and the display thickness can be further reduced if the polarization performance is comparable to the conventional one.

Here, the refractive index in the stretching direction (X direction) is described as n _X , the refractive index in the direction orthogonal to the stretching direction (Y direction) is expressed as n _Y , and the refractive index in the film thickness direction (Z direction) is described as _NZ. There is.
Hereinafter, the uniaxially stretched multilayer laminated film of the present invention will be described in detail.

[First layer]
In the present invention, the polyester constituting the first layer (hereinafter sometimes referred to as aromatic polyester (I)) is obtained by polycondensation of the following dicarboxylic acid component and diol component.
(Dicarboxylic acid component)
As the dicarboxylic acid component (i) constituting the aromatic polyester (I) of the present invention, an acid component represented by the following formula (A) of 5 mol% or more and 50 mol% or less, and 50 mol% or more and 95 mol% or less At least two types of aromatic dicarboxylic acid components represented by the acid component represented by the following formula (B) or derivatives thereof 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)

Regarding the acid component represented by the formula (A), R ^A is an alkylene group having 2 to 10 carbon atoms. 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.

  The lower limit of the content of the acid component represented by the formula (A) is preferably 7 mol%, more preferably 10 mol%, still more preferably 15 mol%. The upper limit of the content of the acid component represented by the formula (A) is preferably 45 mol%, more preferably 40 mol%, still more preferably 35 mol%, particularly preferably 30 mol%.

  Therefore, the content of the acid 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%. Hereinafter, it is particularly preferably 15 mol% or more and 30 mol% or less.

The acid 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 '-(Butylenedioxy) di-2-naphthoic acid is preferred. Among these, those having an even number of carbon atoms of ^RA in the formula (A) are preferable, and 6,6 ′-(ethylenedioxy) di-2-naphthoic acid represented by the following formula (A-1) is particularly preferable.

Such aromatic polyester (I) is characterized in that the dicarboxylic acid component contains an acid component represented by the formula (A) in an amount of 5 mol% to 50 mol%. When the ratio of the acid component represented by the formula (A) is less than the lower limit value, a decrease in the refractive index in the Y direction due to stretching does not occur.
The difference in refractive index n _Z of the refractive index n _Y and Z direction Y direction in the stretched film is increased, it is difficult to improve the hue shift due polarized light incident at an incident angle of an oblique direction. Further, if the proportion of the acid component represented by the formula (A) exceeds the upper limit value, amorphous characteristics becomes large, the refractive index n _Y in refractive index n _X and Y direction of the X-direction in the stretched film Since the difference is small, it does not exhibit sufficient performance as a reflective polarizing film.
As described above, by using the polyester containing the acid component represented by the formula (A), uniaxial stretching that improves the polarization performance as a reflective polarizing film and does not cause a hue shift due to an incident angle in an oblique direction. A multilayer laminated film can be produced.

Further, the acid component of the formula (B), wherein, R ^B is a phenylene group or naphthalene-diyl group.
Examples of the acid component represented by the formula (B) include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, or a combination thereof, and particularly 2,6-naphthalenedicarboxylic acid. Is preferably exemplified.

The lower limit of the content of the acid component represented by the formula (B) is preferably 55 mol%, more preferably 60 mol%, still more preferably 65 mol%, particularly preferably 70 mol%. Further, the upper limit value of the content of the acid component represented by the formula (B) is preferably 93 mol%, more preferably 90 mol%, still more preferably 85 mol%.
Therefore, the content of the acid 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. Hereinafter, it is particularly preferably 70 mol% or more and 85 mol% or less.

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

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

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

As the aromatic polyester (I), in particular, the dicarboxylic acid component represented by the formula (A) is a dicarboxylic acid component represented by the formula (A-1),
A polyester in which the dicarboxylic acid component represented by the formula (B) is an aromatic dicarboxylic acid 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 an acid component of the formula (A) and an acid component of the formula (B), and has a melting point compared to a homopolymer having only the acid component of the formula (A). Although it has a low mechanical strength, it has excellent properties.

The glass transition temperature (hereinafter sometimes referred to as Tg) of the aromatic polyester (I) is preferably 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 the pamphlet of WO2008 / 153188.

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

(Refractive index characteristics of the first layer)
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.

Further, the refractive index difference between the refractive index n _Y after uniaxial stretching in the Y direction and the refractive index n _Z after uniaxial stretching in the Z direction is 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 is likely to occur when polarized light is incident at an oblique incident angle.

[Second layer]
(Thermoplastic resin)
In the present invention, the second layer has an average refractive index of 1.50 or more and 1.60 or less, and a difference in refractive index between the X direction, the Y direction, and the Z direction is 0.05 or less before and after stretching. Consists of. Here, the average refractive index means that the thermoplastic resin constituting the second layer is melted alone, extruded from a die to create an unstretched film, and the direction of the obtained film in the X direction, Y direction, and Z direction, respectively. The refractive index is measured at a wavelength of 633 nm using a Metricon prism coupler, and the average value thereof is defined as the average refractive index.

  Regarding the difference in refractive index before and after stretching, first, the thermoplastic resin constituting the second layer is melted alone and extruded from a die to produce an unstretched film. For each of the X direction, Y direction, and Z direction of the obtained film, the refractive index at a wavelength of 633 nm is measured using a metricon prism coupler, the average refractive index is obtained from the average value of the refractive indexes in three directions, and stretched. The previous refractive index. Next, for the refractive index after stretching, the thermoplastic resin constituting the second layer is melted alone and extruded from a die, and a uniaxially stretched film is formed by applying 5 times at 135 ° C. in the uniaxial direction, For each direction in the X direction, Y direction, and Z direction of the obtained film, the refractive index at a wavelength of 633 nm is measured using a Metricon prism coupler to determine the refractive index in each direction after stretching, and each direction before and after stretching. It is obtained by comparing the difference in refractive index.

  The average refractive index of the thermoplastic resin 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 is an isotropic material having such an average refractive index and a small difference in refractive index before and after stretching, the refractive index difference in the X direction after stretching between the first layer and the second layer is reduced. A refractive index characteristic that is large and has a very small difference in refractive index in the Y direction and extremely small difference in refractive index in the Z direction can be obtained. As a result, both the polarization performance and the hue shift due to the incident angle in the oblique direction can be achieved.

  Among thermoplastic resins having such a refractive index characteristic, a crystalline polyester is preferable from the viewpoint of film forming property in uniaxial stretching. As the crystalline polyester having such refractive index characteristics, copolymerized polyethylene terephthalate, copolymerized polyethylene naphthalene dicarboxylate, or a blend of these copolymerized polyester and amorphous polyester is preferable, and copolymerized polyethylene terephthalate is particularly preferable. Among such copolymerized polyethylene terephthalates, polyesters mainly composed of an ethylene terephthalate component copolymerized with isophthalic acid or 2,6-naphthalenedicarboxylic acid are preferred, and in particular, ethylene copolymerized with isophthalic acid or 2,6-naphthalenedicarboxylic acid. A polyester having a melting point of 220 ° C. or lower, mainly composed of a terephthalate component, is preferred.

  In the case of copolymerized polyethylene terephthalate, the copolymer components other than the above components may be isophthalic acid or 2,6-naphthalene within a range of 10 mol% or less based on all repeating units constituting the polyester of the second layer. Aromatic carboxylic acids other than the main copolymer component among dicarboxylic acids and 2,7-naphthalenedicarboxylic acids; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid; fats such as cyclohexanedicarboxylic acid Preferable examples include acid components such as cyclic dicarboxylic acids, aliphatic diols such as butanediol and hexanediol; and glycol components such as alicyclic diols such as cyclohexanedimethanol.

  Among these, two copolymer components of isophthalic acid and 2,6-naphthalenedicarboxylic acid are preferable because the melting point is easily lowered while maintaining stretchability. In addition, the melting point of the thermoplastic resin constituting the second layer does not have to be low from the stage before forming the film, and may be low after the stretching treatment. For example, two or more kinds of polyesters may be blended and transesterified at the time of melt kneading.

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

[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, deterioration of the optical properties of the multilayer stretched film due to the particles may become remarkable. The average particle diameter of the preferable inert particles is in the range of 0.02 μm to 1 μm, particularly preferably 0.1 μm to 0.3 μm. Moreover, content of a preferable inert particle is the range of 0.02 weight%-0.2 weight%.

Examples of the inert particles contained 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)
The uniaxially stretched multilayer laminated film of the present invention is obtained by alternately laminating a total of 251 layers of the above-mentioned first layer and second layer. When the number of laminated layers is less than 251 layers, a certain average reflectance cannot be satisfied over a wavelength range of 400 to 800 nm with respect to an average reflectance characteristic of a polarized light component parallel to the incident surface including the stretching direction.
The upper limit of the number of layers is limited to 2001 layers from the viewpoints of productivity and film handling. As long as the average reflectance characteristic of the present invention is obtained, the upper limit value of the number of layers may be further reduced from the viewpoint of productivity and handling properties, and may be, for example, 1001, 501 and 301 layers.

(Each layer thickness)
Since the first layer and the second layer selectively reflect light by optical interference between layers, the thickness of each layer is 0.01 μm or more and 0.5 μm or less. The thickness of each layer can be determined based on a photograph taken using a transmission electron microscope.

Since the reflection wavelength band shown by the uniaxially stretched multilayer laminated film of the present invention is from the visible light region to the near infrared region, it is necessary to set the layer thickness within the above range. When the layer thickness exceeds 0.5 μm, the reflection band becomes an infrared region, and usefulness as a reflective polarizing film cannot be obtained. On the other hand, when the layer thickness is less than 0.01 μm, the polyester component absorbs light and the reflection performance cannot be obtained.
The thickness of each layer of the first layer is preferably 0.01 μm or more and 0.1 μm or less. The thickness of each layer of the second layer is preferably 0.01 μm or more and 0.3 μm or less.

(Ratio of maximum layer thickness to minimum layer thickness)
In the 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 2.0 or more and 5.0 or less, preferably 2.0 or more. It is 4.0 or less, more preferably 2.0 or more and 3.5 or less, and further 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. Further, when the ratio between the maximum layer thickness and the minimum layer thickness exceeds the upper limit value, the reflection band is excessively widened, and the reflectance of the polarization component parallel to the incident surface including the stretching direction (X direction) decreases.

The first layer and the second layer may change stepwise or may change continuously. By changing each of the first layer and the second layer laminated in this way, light in a wider wavelength range can be reflected.
The method for laminating the multilayer 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 1.5 to 5.0 times. The lower limit value of the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is more preferably 2.0. The upper limit of the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is more preferably 4.0, and even more preferably 3.5.

Since the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is in such a range, secondary reflection occurring at a half wavelength of the reflection wavelength can be effectively used. Therefore, each of the first layer and the second layer The ratio of the maximum layer thickness to the minimum layer thickness can be minimized, which is preferable from the viewpoint of optical characteristics. In addition, by changing the thickness ratio of the first layer and the second layer in this way, the mechanical properties of the obtained film are also adjusted while maintaining the adhesion between the layers and without changing the resin used. And has an effect of making the film difficult to tear.
On the other hand, when the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer deviates from this range, the secondary reflection that occurs at the half wavelength of the reflection wavelength becomes small, and the reflectance may decrease. .

(Thickness adjustment layer)
In addition to the first layer and the second layer, the uniaxially stretched multilayer laminated film of the present invention has a thickness adjusting layer having a layer thickness of 2 μm or more in a part of the alternately laminated structure of the first layer and the second layer. May be. By having the thickness adjusting layer having such a thickness as 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 can be made uniform without affecting the polarization function. Easy to adjust. The thickness adjusting layer having such a thickness may be the same composition as either the first layer or the second layer, or a composition partially including these compositions. Since the layer thickness is thick, the thickness adjusting layer does not contribute to the reflection characteristics. On the other hand, since it may affect the transmitted polarized light, when the particles are included in the layer, it is preferably within the range of the particle concentration described above.

[Uniaxially stretched film]
The 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.

[Film thickness]
The uniaxially stretched multilayer laminated film of the present invention preferably has a film thickness of 15 μm or more and 40 μm or less. In order to obtain an average reflectance of about 90% for the P-polarized light, the conventional multilayer laminated film having a reflective polarizing function needs to have a larger number of layers than the present invention, and a thickness of about 100 μm is required. In the present invention, the aromatic polyester (I) having a specific copolymerization component is used as the resin constituting the first layer, and the multilayer lamination having a constant layer thickness is combined with the second-layer thermoplastic resin described above. By making it into a film, if it has the same level of polarization performance as before, it can be achieved even if the number of layers is reduced, and the film thickness can be reduced to about 1/3 of 40 μm or less. is there. With such a film thickness, the display thickness can be further reduced.

[Average reflectance]
The uniaxially stretched multilayer laminated film of the present invention has a film surface as a reflection surface and a polarization component parallel to the incident surface including the stretching direction (X direction) of the uniaxially stretched film at an incident angle of 0 degrees and 50 degrees. About a polarized light component perpendicular to the incident surface including the stretching direction (X direction) of the uniaxially stretched film, the average reflectance of the wavelength of 400 to 800 nm with respect to the incident polarized light is 90% or more, respectively. The average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at incident angles of 0 degrees and 50 degrees is 15% or less, respectively.

  Here, the incident surface refers to a surface that is perpendicular to the reflecting surface and includes the incident light beam and the reflected light beam. In addition, the polarization component parallel to the incident surface including the film surface as a reflection surface and including the stretching direction (X direction) of the uniaxially stretched film is generally referred to as P-polarized light. Moreover, the polarization component perpendicular to the incident surface including the film surface as a reflection surface and including the stretching direction (X direction) of the uniaxially stretched film is generally also referred to as S-polarized light. Furthermore, the incident angle represents an incident angle with respect to a direction perpendicular to the film surface.

With respect to the polarization component parallel to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as the reflecting surface, the average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree is More preferably, it is 95% or more and 100% or less, and particularly preferably 98% or more and 100% or less.
In addition, with respect to the polarization component parallel to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as the reflecting surface, the average reflection at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 50 degrees. The rate is more preferably 93% or more and 99% or less, and particularly preferably 95% or more and 98% or less.

  When the average reflectance at a wavelength of 400 to 800 nm with respect to the P-polarized light component at such an incident angle is less than the lower limit, not only the polarization reflection performance as a reflective polarizing film, but also the hue shift of the reflected light occurs, resulting in a display. Coloring occurs. On the other hand, the higher the average reflectance within this range, the higher the polarization reflection performance, but it may be difficult to increase it to an extent exceeding the upper limit due to the composition and stretching.

The average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree with respect to the polarized light component perpendicular to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as the reflecting surface is More preferably, it is 5% or more and 12% or less, and particularly preferably 8% or more and 12% or less.
Moreover, the average reflectance of the wavelength 400-800 nm with respect to the incident polarized light at an incident angle of 50 degrees with respect to a polarized light component perpendicular to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as a reflecting surface. Is more preferably 5% or more and 10% or less, and particularly preferably 8% or more and 10% or less.

  When the average reflectance of a wavelength of 400 to 800 nm with respect to the S-polarized light component at such an incident angle exceeds the upper limit value, the polarization transmittance as a reflective polarizing film is lowered, so that sufficient performance as a brightness enhancement film such as a liquid crystal display is obtained. Not expressed. On the other hand, although the transmittance of the S-polarized component is higher when the polarization reflectance is lower than the above range, it may be difficult to lower the lower limit than the lower limit.

  In order to obtain an average reflectance characteristic for such a P-polarized component, in addition to the thickness of each layer and the number of layers, a polymer having the above-described characteristics is used as the polymer component constituting the first layer and the second layer, and the stretching direction ( In the X direction, the film is stretched at a constant draw ratio to increase the birefringence in the in-plane direction of the first layer, thereby increasing the refractive index difference between the first layer and the second layer in the stretching direction (X direction). Is achieved.

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

[Hue change]
In the uniaxially stretched multilayer laminated film of the present invention, the amount of hue change Δx, Δy represented by the following formulas (1) and (2) is 0.1 or less for the polarization component parallel to the incident surface. It is preferably 0.09 or less, more preferably 0.08 or less.
Δx = x (0 °) −x (50 °) (1)
(In the above formula (1), x (0 °) represents the hue x of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and x (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents hue x)
Δy = y (0 °) −y (50 °) (2)
(In the above formula (2), y (0 °) represents the hue y of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and y (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents the hue y)

The hues x and y related to the polarization component parallel to the incident surface (P-polarized light) are standard according to JIS standard Z8729 based on transmission spectra measured at 0 ° and 50 ° incident angles for P-polarized light of the film. Y, x, and y in the CIE color system for the light source C are represented by calculated values.
Further, the hue change amounts Δx and Δy represented by the equations (1) and (2) are incident on the incident polarization component perpendicular to the film surface (0 degree) and incident obliquely by 50 degrees from the direction perpendicular to the film surface. This represents the magnitude of the amount of change in hue x and y with respect to the polarization component, and corresponds to the hue shift of transmitted P-polarized light.
When the hue change amounts Δx and Δy exceed the upper limit, the hue shift of the transmitted P-polarized light due to the incident angle in the oblique direction is large, and when used as a brightness enhancement film, the hue shift at a high viewing angle is large and the visibility is high. May decrease.

In the uniaxially stretched multilayer laminated film of the present invention, the hue change amounts Δx and Δy represented by the following formulas (1) and (2) are both 0.01 or less with respect to the polarization component perpendicular to the incident surface. Preferably, it is 0.005 or less, particularly preferably 0.003 or less.
Δx = x (0 °) −x (50 °) (1)
(In the above formula (1), x (0 °) represents the hue x of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and x (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents hue x)
Δy = y (0 °) −y (50 °) (2)
(In the above formula (2), y (0 °) represents the hue y of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and y (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents the hue y)

The hues x and y related to the polarization component perpendicular to the incident surface (S-polarized light) are standard according to JIS standard Z8729 based on transmission spectra measured at 0 ° and 50 ° incident angles for S-polarized light of the film. Y, x, and y in the CIE color system for the light source C are represented by calculated values.
The hue change amounts Δx and Δy are the change amounts of the hue x and y between the incident polarized light component perpendicular to the film surface (0 degree) and the incident polarized light component inclined at 50 degrees from the direction perpendicular to the film surface. It represents the magnitude and corresponds to the hue shift of transmitted S-polarized light.
When the hue change amounts Δx and Δy exceed the upper limit, the hue shift of the transmitted S-polarized light due to the incident angle in the oblique direction is large, and when used as a brightness enhancement film, the hue shift at a high viewing angle is large and the visibility is high. May decrease.
Such a hue change amount is achieved by using the above-described specific polyester as the thermoplastic resin constituting the first layer and the second layer, respectively.

[Heat seal layer]
In the uniaxially stretched multilayer laminated film of the present invention, a heat seal layer can be further provided on at least one outermost layer surface of the alternate lamination of the first layer and the second layer. By having a heat seal layer, when laminating | stacking with another member as a member of a liquid crystal display, for example, members can be bonded together via a heat seal layer by heat processing.
As such a heat seal layer, it is preferable to use a thermoplastic resin having a melting point equal to or lower than the melting point of the outermost layer of the alternately laminated layers, but as an advantage that can be formed simultaneously with the alternately laminated layers, the same thermoplastic resin as the second layer is used. It is preferable to use it. Furthermore, it is preferable that the thermoplastic resin has a melting point of 20 ° C. or more lower than the melting point of the thermoplastic resin of the first layer and has a thickness of 3 to 10 μm. By having the melting point and the layer thickness, the members can be firmly bonded as a heat seal layer.

When the same thermoplastic resin as the second layer is used as the heat seal layer, the heat seal layer has a layer thickness of 3 to 10 μm, which is compared with 0.5 μm which is the maximum thickness of the layers constituting such an alternately laminated layer. Thus, the layer having a thickness of 4 times or more is a layer that does not contribute to the reflectance in the wavelength band of 400 to 800 nm, and is distinguished from the alternate lamination of the first layer and the second layer.
Moreover, even if it uses the blend of the 1st layer and the 2nd layer in the range which does not impair the characteristic as a heat seal layer, it is satisfactory.

[Brightness enhancement film]
The uniaxially stretched multilayer laminated film of the present invention selectively reflects the P-polarized component with high reflection, selectively transmits the S-polarized component perpendicular to the polarized component, and transmits light incident in an oblique direction. Since the deviation of the hue of polarized light is eliminated, it can be suitably used as a brightness enhancement film for liquid crystal displays, and can be processed into a brightness enhancement member. In particular, since it has higher polarization performance than before, it can provide a high brightness improvement rate when used as a brightness enhancement film, and can provide a liquid crystal display excellent in visibility with a high viewing angle and little hue shift. Moreover, the film thickness can be made 40 μm or less.

[Composite materials for liquid crystal displays]
It is preferable that the brightness enhancement member prepared using the uniaxially stretched multilayer laminate film of the present invention is further used by laminating a light diffusion film on at least one surface thereof and used as a composite member for a liquid crystal display. Moreover, it is preferable that the brightness enhancement member and the light diffusion film are laminated by being bonded via a heat seal layer. Conventionally, it was used in a layer configuration of 800 layers or more, and the total thickness as a composite member was about 100 microns, but by adopting the layer configuration of the composite member for liquid crystal display of the present invention, the total as a composite member The thickness can be reduced to about 50 microns, and the liquid crystal display can be made thinner.

  In the composite member for a liquid crystal display according to the present invention, the light diffusion film is laminated on at least one surface of the brightness enhancement member, and a prism layer is further provided on the opposite side of the brightness enhancement member via the light diffusion film. The configuration is also preferably exemplified. By having such a layer structure, the display can be made thinner and at the same time the brightness enhancement performance is enhanced as compared with the conventional composite member having a layer structure of 800 layers or more.

[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 extruded in a state where at least 251 layers or more of the thermoplastic resin constituting the first layer and the thermoplastic resin constituting the second layer are alternately superposed in the molten state. It is set as a stretched film (process made into a sheet-like material). At this time, the laminated body of 251 layers or more laminated | stacked so that the thickness of each layer may change in the range of 2.0 times-5.0 times in steps or continuously.

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

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

(1) Melting point (Tm) and glass transition point (Tg) of polyester and film
10 mg of a polyester sample or a film sample was sampled, and a DSC (manufactured by TA Instruments, trade name: DSC2920) was used. The melting point and the glass transition point are measured at a temperature rising rate of.

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

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

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

(5) Refractive index and average refractive index after stretching in each direction Each resin constituting each layer was melted, extruded from a die, and cast on a casting drum. Further, a stretched film was prepared by stretching the obtained film at 135 ° 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 average refractive index, the average value of each refractive index before extending | stretching was made into the average refractive index.

(6) Reflectivity, reflection wavelength Using a spectrophotometer (manufactured by Shimadzu Corporation, MPC-3100), a polarizing filter is mounted on the light source side, and the relative specular reflectivity with respect to the aluminum-deposited mirror at each wavelength is measured from a wavelength of 400 nm. Measure in the range of 800 nm. In this case, the measured value when the transmission axis of the polarizing filter is aligned with the film stretching direction (X direction) is P-polarized light, and the transmission axis of the polarizing filter is disposed perpendicular to the film stretching direction. Was measured as S-polarized light. For each polarization component, the average reflectance in the range of 400 to 800 nm was defined as the average reflectance.

(7) Hue For each of the P-polarized light and S-polarized light of the sample film, Y, x, and y in the CIE color system for the standard light source C are obtained from the transmission spectrum measured at an incident angle of 0 ° and 50 ° according to JISZ8729. It was. In addition, for each of P-polarized light and S-polarized light, a difference (amount of change in hue) for x and y at 0 ° and 50 ° was obtained by the following equations (1) and (2).
Δx = x (0 °) −x (50 °) (1)
(In the above formula (1), x (0 °) represents the hue x of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and x (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents hue x)
Δy = y (0 °) −y (50 °) (2)
(In the above formula (2), y (0 °) represents the hue y of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and y (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents the hue y)

(8) Brightness improvement effect The laminated sample film is inserted between the polarizing plates in the LCD panel (Diamond Crysta RDT158V-N 2004 manufactured by Mitsubishi Electric Corporation), and the front brightness when displaying white on the PC is 500 mm. The luminance was measured with a Topcon luminance meter (BM-7) from a remote location, and the rate of increase in luminance after inserting the sample film relative to the luminance before inserting the sample film was calculated to evaluate the effect of improving luminance.

(9) Heat seal strength The heat seal surfaces of the films were put together, leaving a chuck grip, and pressure-bonded at 140 ° C. and 275 kPa for 2 seconds to prepare a laminate sample. The obtained laminate sample was slit to a width of 25 mm, and the position of the crosshead was adjusted so as not to sag by sandwiching the grip margin with the chuck of the crosshead of a tensile tester (trade name “Tensilon” manufactured by Toyo Baldwin). The laminate was pulled at a crosshead speed of 100 mm / min, the laminate sample was peeled off, and the load was measured with a load cell attached to a testing machine to obtain heat seal strength (unit: N / 25 mm).

[Example 1]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, and ethylene glycol are subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and Subsequently, a polycondensation reaction was performed, and the intrinsic viscosity was 0.62 dl / g, 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 (described as ENA in the table) and an aromatic polyester whose glycol component is ethylene glycol. To this, 0.10 wt% of spherical silica particles (average particle size: 0.3 μm, ratio of major axis to minor axis: 1.02, average deviation of particle size: 0.1) based on the weight of the first layer This was used as polyester for the first layer, and 20 mol% of isophthalic acid copolymerized polyethylene terephthalate (IA20PET) having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.62 dl / g was prepared as the second layer thermoplastic resin.

  The prepared polyester for the first layer and polyester for the second layer are each dried at 170 ° C. for 5 hours, then supplied to the first and second extruders, heated to 300 ° C. to be in a molten state, and used for the first layer After branching the polyester to 137 layers and the second layer polyester to 138 layers, the first layer and the second layer are alternately laminated, and the maximum layer thickness and the minimum layer thickness of the first layer and the second layer, respectively. Using a multi-layer feedblock device in which the maximum value is continuously changed up to 2.2 times at the minimum, and a total of 275 layers of the melt in which the first layer and the second layer are alternately stacked, While maintaining the laminated state, the same polyester as the second layer polyester is led from the third extruder to the three-layer die on both sides thereof, and a heat seal layer is further provided on both sides of the melt in the laminated state of 275 layers in total. Laminated. The supply amount of the third extruder was adjusted so that both end layers (heat seal layers) were 18% of the whole. The laminated state is led to a die, cast on a casting drum, adjusted so that the average layer thickness ratio of the first layer and the second layer is 1.0: 2.6, and a total of 277 layers. An unstretched multilayer laminated film was prepared.

This multilayer unstretched film was stretched 5.2 times in the width direction at a temperature of 135 ° C., and heat-set at 140 ° C. for 3 seconds. The thickness of the obtained film was 33 μm.
Table 1 shows the resin composition of each layer of the obtained uniaxially stretched multilayer laminated film, the characteristics of each layer, and Table 2 shows the physical properties.
Further, the obtained uniaxially stretched multilayer laminated film was bonded to the back coat surface of a light diffusion film (Eiwa Co., Ltd .: Opulse BS-912) by pressure bonding at 140 ° C. and 275 kPa for 2 seconds to bond the laminated film. Obtained.

[Examples 2 to 4, 6]
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 or the layer thickness of each layer was changed. Table 2 shows the physical properties of the obtained uniaxially stretched multilayer laminated film. Further, the obtained uniaxially stretched multilayer laminated film was bonded to the back coat surface of a light diffusion film (Eiwa Co., Ltd .: Opulse BS-912) by pressure bonding at 140 ° C. and 275 kPa for 2 seconds to bond the laminated film. Obtained.
In addition, NDC20PET used as the second layer polyester in Example 2 is a copolymer component of 20 mol% isophthalic acid copolymerized polyethylene terephthalate (IA20PET) used as the second layer polyester in Example 1 with 2,6- It is a copolyester changed to naphthalenedicarboxylic acid.

  Further, the ENA21PEN / PCT blend used as the second layer polyester in Example 4 is ENA21PEN (79 mol% of the acid component is a 2,6-naphthalenedicarboxylic acid component, which is the first layer polyester of Example 4). 21 mol% of the acid component is 6,6 '-(ethylenedioxy) di-2-naphthoic acid component, aromatic polyester whose glycol component is ethylene glycol) and Eastman Chemical's PCTA AN004 (polycyclohexanedimethylene terephthalate- Isophthalate copolymer) is mixed so as to have a weight ratio of 2: 1.

[Example 5]
A monoaxially stretched multilayer laminated film was prepared by changing the copolymerization ratio of the polyester for the first layer as shown in Table 1 and performing the same operation as in Example 1 except that the layer thickness was changed as shown in Table 1. did. Table 1 shows the resin composition of each layer of the obtained uniaxially stretched multilayer laminated film, the characteristics of each layer, and Table 2 shows the physical properties.
Further, the back coat surface of a light diffusion film (Eiwa Co., Ltd .: Opulse BS-912) is provided on one side of the obtained uniaxially stretched multilayer laminated film, and the prism sheet (Made by Mitsubishi Rayon: “Diaart” Y) is provided on the opposite side. The back coat surface of the type (M268Y) was sandwiched and bonded together at 140 ° C. and 275 kPa for 2 seconds to obtain a laminate film. When the luminance enhancement effect was measured using the obtained laminate film, a luminance enhancement effect of 210% was obtained.

[Comparative Example 1]
The thermoplastic resin for the first layer is made of polyethylene-2,6-naphthalenedicarboxylate (PEN) having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.62 dl / g, and the thermoplastic resin for the second layer is made of intrinsic viscosity (ortho Chlorophenol, 35 ° C.) Example 1 with the exception of changing to 0.62 dl / g terephthalic acid 64 mol% copolymerized polyethylene-2,6-naphthalenedicarboxylate (TA64PEN) and changing to the production conditions shown in Table 1. Similarly, a uniaxially stretched multilayer laminated film was obtained. Table 1 shows the resin composition of each layer of the obtained uniaxially stretched multilayer laminated film, the characteristics of each layer, and Table 2 shows the physical properties.
In the obtained uniaxially stretched multilayer laminated film, the average reflectance of S-polarized light exceeded 15% at both incident angles of 0 ° and 50 °, and the polarization performance was deteriorated as compared with Examples. Further, the amount of hue change of Δx of P-polarized light was larger than that of the example, and a hue shift occurred.

[Comparative Examples 2 to 6]
As shown in Table 1, a uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1 except that any of the resin composition, the layer thickness, and the production conditions was changed. Table 1 shows the resin composition of each layer of the obtained uniaxially stretched multilayer laminated film, the characteristics of each layer, and Table 2 shows the physical properties. As for the obtained film, polarization performance fell compared with the Example. Further, the hue change amount of either P-polarized light or S-polarized light was large, and a hue shift occurred.

  According to the present invention, the uniaxially stretched multilayer laminated film of the present invention eliminates the hue shift of transmitted polarized light due to the oblique incident angle seen in the conventional reflective polarizing film, and has higher polarization performance than before. Therefore, when used as a brightness enhancement film, a high brightness improvement rate can be obtained, and a liquid crystal display excellent in visibility with a high viewing angle and little hue shift can be provided.

Claims (15)

A uniaxially stretched multilayer laminated film having 251 layers or more in which the first layer and the second layer are alternately laminated,
1) The first layer is composed of (i) an acid component represented by the following formula (A) in which the dicarboxylic acid component is 5 mol% or more and 50 mol% or less, and the following formula (B) of 50 mol% or more and 95 mol% or less. Containing the acid component represented,
(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) A diol component represented by the following formula (C) in which the diol component is 90 mol% or more and 100 mol% or less
(In the formula (C), R ^C represents an alkylene group having 2 to 10 carbon atoms)
A layer having a thickness of 0.01 μm or more and 0.5 μm or less comprising a polyester with an aromatic dicarboxylic acid component and a diol component containing
The second layer has an average refractive index of 1.50 or more and 1.60 or less, a uniaxial stretching direction (X direction), a direction perpendicular to the uniaxial stretching direction in the film plane (Y direction), and a film thickness direction ( (Z direction) each refractive index difference is a layer having a thickness of 0.01 μm or more and 0.5 μm or less made of a thermoplastic resin that is 0.05 or less before and after stretching,
2) The film surface is a reflecting surface, and the average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree and 50 degrees with respect to the polarized light component parallel to the incident surface including the X direction is 90% or more, respectively. Yes,
3) With respect to a polarized light component perpendicular to the incident surface including the X direction, with the film surface as a reflective surface, the average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree and 50 degrees is 15% or less, respectively. 4) A uniaxially stretched multilayer laminated film characterized in that the ratio between the maximum layer thickness and the minimum layer thickness in each of the first layer and the second layer is 2.0 or more and 5.0 or less. The uniaxially stretched multilayer laminated film according to claim 1, wherein the acid component represented by the formula (A) is the following formula (A-1).
The uniaxial stretching according to claim 1 or 2, wherein the amount of hue change Δx, Δy represented by the following formulas (1), (2) is 0.1 or less for a polarized light component parallel to the incident surface: Multi-layer laminated film.
Δx = x (0 °) −x (50 °) (1)
(In the above formula (1), x (0 °) represents the hue x of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and x (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents hue x)
Δy = y (0 °) −y (50 °) (2)
(In the above formula (2), y (0 °) represents the hue y of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and y (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents the hue y) The hue change amounts Δx and Δy represented by the following formulas (1) and (2) are both 0.01 or less for the polarization component perpendicular to the incident surface: Uniaxially stretched multilayer laminated film.
Δx = x (0 °) −x (50 °) (1)
(In the above formula (1), x (0 °) represents the hue x of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and x (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents hue x)
Δy = y (0 °) −y (50 °) (2)
(In the above formula (2), y (0 °) represents the hue y of the transmission spectrum of the incident polarized light at an incident angle of 0 degrees, and y (50 °) represents the transmission spectrum of the incident polarized light at an incident angle of 50 degrees. Represents the hue y)   The uniaxially stretched multilayer laminated film according to claim 1, wherein the film thickness is 15 μm or more and 40 μm or less.   The ratio of the average layer thickness of a 2nd layer with respect to the average layer thickness of a 1st layer is the range of 1.5 times or more and 5.0 times or less, The uniaxial stretching multilayer laminated film in any one of Claims 1-5.   The uniaxially stretched multilayer laminated film according to any one of claims 1 to 6, wherein a heat seal layer is further provided on at least one outermost layer surface of the alternate lamination of the first layer and the second layer.   The heat seal layer is made of the same thermoplastic resin as the second layer, and the melting point of the thermoplastic resin is 20 ° C lower than the melting point of the polyester of the first layer and is a layer having a thickness of 3 to 10 µm. Uniaxially stretched multilayer laminated film.   The uniaxially stretched multilayer laminated film according to any one of claims 1 to 8, which is used as a brightness enhancement film for a liquid crystal display.   The brightness improvement member which consists of a uniaxially stretched multilayer laminated film in any one of Claims 1-9.   A composite member for a liquid crystal display, wherein a light diffusion film is laminated on at least one surface of the brightness enhancement member according to claim 10.   The composite member for a liquid crystal display according to claim 11, wherein the brightness enhancement member and the light diffusion film are laminated via a heat seal layer.   The composite member for a liquid crystal display according to claim 11 or 12, further comprising a prism layer on the side opposite to the member for improving brightness via a light diffusion film.   A liquid crystal display device comprising the brightness enhancement member according to claim 10.   The liquid crystal display device containing the composite member for liquid crystal displays in any one of Claims 11-13.