JP5864128B2 - Laminated film - Google Patents

Description

  The present invention relates to a laminated film including a reflective polarizing film. More specifically, the polarizing performance of selectively reflecting a certain polarization component and selectively transmitting a polarization component perpendicular to the polarization component is superior to the conventional one. In addition, the present invention relates to a laminated film including a reflective polarizing film in which hue deviation is eliminated even with respect to incident light in an oblique direction and having less luminance unevenness.

  A film in which a plurality of layers having a low refractive index and a layer having a high refractive index 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, it is known that by stretching such a multilayer laminated film only in one direction, it can be used as a polarizing reflection film that reflects only a specific polarization component, and these can be used as a brightness enhancement film for liquid crystal displays and the like. ing.

In general, a multilayer optical film having a layer thickness of 0.05 to 0.5 μm and alternately laminated layers having different refractive indexes is different from the refractive index difference between the layer constituting one layer and the layer constituting the other layer. Depending on the thickness and the number of 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 (Japanese Patent Laid-Open No. 04-268505), by using a resin having a positive stress optical coefficient for one layer, the layer is stretched in a uniaxial direction. The refractive index of the film is made birefringent to provide anisotropy, and the difference in refractive index between layers in the stretching direction in the film plane is increased, while the difference in refractive index between layers in the direction perpendicular to the stretching direction in the film plane is increased. By making it small, only a specific polarization component can be reflected.

By utilizing this principle, it is possible to design a reflective polarizing film that reflects polarized light in one direction and transmits polarized light in the orthogonal direction, for example, and the desired birefringence at that time is expressed by the following equation: .
n _1X > n _2X , n _1Y = n _2Y
(In the above formula, n _1X and n _2X represent the refractive index in the stretching direction in each layer, and n _1Y and n _2Y represent the refractive index in the direction perpendicular to the stretching direction in each layer.)

  In Patent Document 2 (Japanese Patent Publication No. 9-506837), polyethylene-2,6-naphthalenedicarboxylate (hereinafter sometimes referred to as 2,6-PEN) is used for the layer having a high refractive index. A multilayer film using PEN obtained by copolymerizing 30 mol% of a thermoplastic elastomer or terephthalic acid in a layer having a low refractive index is exemplified. 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.

Further, Patent Document 3 (WO01 / 47711 pamphlet) also discloses a uniaxially stretched multilayer laminated film using polyethylene-2,6-naphthalenedicarboxylate in a layer having a high refractive index.
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. Differences occur. Therefore, if the stretching ratio is increased to increase the refractive index difference between the layers in the stretching direction (X direction) to improve the polarization performance, the refractive index difference between the layers in the Z direction increases accordingly, and the incident light in the oblique direction There is a problem that the hue shift of transmitted light tends to be large due to partial reflection of the light.

  On the other hand, a surface light source called a backlight is used for a liquid crystal display or the like, but in order to diffuse light emitted from the light source in such a liquid crystal display and make an image of the light source difficult to see, a light diffusion film Is used. Moreover, when a reflective polarizing film is installed in the display as the liquid crystal display becomes larger, there is a concern that the film may be deformed by heat emitted from an example cathode tube as a light source, and the flatness may be impaired. . As one of countermeasures against such deformation, a method of providing a flexible transparent dimensional stability layer on a reflective polarizing film was proposed in Patent Document 4 (Japanese Patent Application Laid-Open No. 2008-310348). It has been proposed that the conductive layer can be made to diffuse light.

  As described above, a large number of optical films having various functions are used in the liquid crystal display, and attempts have been made to integrate the functions of a plurality of optical films in a demand for further thinning. When a dimensionally stable layer is provided, the reflective polarizing film laminate is in contact with the other optical film, and the luminance unevenness of the display tends to be noticeable. By laminating the diffusion layer, when the polarized light from the light source passes through the reflective polarizing film laminate and is diffused through the diffusion layer, the polarization may be canceled depending on the diffusion layer, and the brightness enhancement effect may be impaired. Newly discovered and a solution is desired.

JP-A-4-268505 Japanese National Patent Publication No. 9-506837 WO01 / 47711 pamphlet JP 2008-310348 A

  The object of the present invention is to solve the above-mentioned problems of the multilayer laminated film having the conventional reflective polarization performance and the problems of the multilayer film of the multilayer laminated film and the diffusion layer, while further improving the polarization performance than before. It is another object of the present invention to provide a laminated film that eliminates a hue shift with respect to incident light in an oblique direction and has a high brightness improvement effect without deterioration in flatness and luminance unevenness even when used in a large display.

  As a result of intensive studies to solve the above problems, the present inventors have obtained the following knowledge. That is, in the conventional multilayer laminated reflective polarizing film, uniaxial stretching direction (X) is used instead of polyethylene-2,6-naphthalenedicarboxylate, which has been used as a resin constituting the high refractive index layer. A thermoplastic resin having a characteristic that both the refractive index in the direction perpendicular to the uniaxial stretching direction in the film plane (Y direction) and the refractive index in both the film thickness direction (Z direction) are decreased. By using it, the refractive index difference between the X direction and the Y direction of the first layer after uniaxial stretching can be made larger than before.

As a result, the polarized light parallel to the X direction, that is, the polarized light perpendicular to the transmission axis is higher than that of a conventional multilayer laminated reflective polarizing film using polyethylene-2,6-naphthalenedicarboxylate as a high refractive index layer. Reflective performance is obtained, polarized light in the orthogonal direction (transmission axis direction, Y direction in the present invention) can be selectively transmitted, and higher polarization performance than that of a conventional reflective polarizing film can be obtained. It was found that the hue shift of transmitted polarized light due to the incident angle of direction can be eliminated.
Furthermore, by laminating a diffusion film having a certain surface shape and retardation characteristics on at least one surface of such a reflective polarizing film, there is no reduction in flatness or brightness unevenness even when used for large displays, and high brightness. The present inventors have found that an improvement effect can be obtained and have completed the present invention.

That is, according to the present invention, an object of the present invention is a laminated film in which a diffusion film is laminated on at least one surface of a reflective polarizing film,
The diffusion film has a center line average roughness SRa of 0.3 to 1.0 μm and a peak count SPc of less than 500 counts / mm ² , and an in-plane retardation value (Re (550)) at a wavelength of 550 nm of the diffusion film. Is less than 100 nm, the retardation value in the direction perpendicular to the plane at a wavelength of 550 nm (Rth (550)) is less than 300 nm,
The reflective polarizing film comprises a total of 251 or more uniaxially stretched multilayer laminated films in which the first layer and the second layer are alternately laminated,
The uniaxially stretched multilayer laminated film is 1) The first layer has an average refractive index of 1.60 or more and 1.70 or less, and the refractive index n _{X in the} uniaxial stretching direction (X direction) is increased by stretching. a layer refractive index n _Z is formed of a thermoplastic resin to decrease by stretching the refractive index n _Y and the film thickness direction (Z direction) in a direction perpendicular inner in the uniaxial stretching direction (Y-direction),
2) 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) A layer made of a thermoplastic resin having a refractive index difference of 0.05 or less before and after stretching, and 3) a polarization component parallel to the incident surface including the X direction, with the film surface as a reflective surface The average reflectivity 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 90% or more,
4) 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 for the incident polarized light at an incident angle of 0 degrees and 50 degrees is 15% or less, respectively. This is achieved by the laminated film (Item 1).

Moreover, the laminated film of this invention includes what comprises at least any one of the following as a preferable aspect.
Item 2. Item 2. The laminated film according to Item 1, wherein the diffusion film is laminated on both surfaces of the reflective polarizing film.
Item 3. The thermoplastic resin forming the first layer of the uniaxially stretched multilayer laminated film is made of polyester of a dicarboxylic acid component and a diol component,
(I) The dicarboxylic acid component contains a component represented by the following formula (A) of 5 mol% to 50 mol% and a component represented by the following formula (B) of 50 mol% to 95 mol%. ,
(In the formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms)
(In the formula (B), R ^B represents a phenylene group or a naphthalenediyl group)
(Ii) The diol component contains 90 to 100 mol% of a component represented by the following formula (C).
(In the formula (C), R ^C represents an alkylene group having 2 to 10 carbon atoms)
Item 3. The laminated film according to Item 1 or 2.
Item 4.
Item 4. The laminated film according to any one of Items 1 to 3, wherein the thermoplastic resin forming the second layer is a polyester mainly composed of an ethylene terephthalate component copolymerized with isophthalic acid or 2,6-naphthalenedicarboxylic acid.
Item 5.
Item 5. The laminated film according to any one of Items 1 to 4, wherein the resin forming the diffusion film is polycarbonate.
Item 6.
Item 6. The laminated film according to any one of Items 1 to 5, which is used as a brightness enhancement film for a liquid crystal display.

  Further, the present invention includes a brightness enhancement member made of the laminated film of the present invention, and further includes a liquid crystal display device having a surface light source, the brightness enhancement member of the present invention, and a liquid crystal display module.

  According to the present invention, the laminated film of the present invention eliminates the hue shift of transmitted polarized light due to the oblique incident angle seen in the conventional multilayer laminated 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. At the same time, since a diffusion film with a certain surface property is laminated, even if it is used for a large display, there is no reduction in flatness and luminance unevenness, and a diffusion effect can be obtained without impairing the luminance improvement effect of the reflective polarizing film, It can be suitably used as a luminance improving member for a large display.

FIG. 1 shows refractive indexes (n _X , n _Y , 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). n _Z ). FIG. 2 shows the refractive index in the stretching direction (X direction) after uniaxial stretching of the aromatic polyester (I) for the first layer in the present invention, the direction orthogonal to the stretching direction (Y direction), and the thickness direction (Z direction). (Represented as n _X , n _Y , and n _Z , respectively). FIG. 3 shows a film surface of the uniaxially stretched multilayer laminated film of the present invention as a reflective surface, a polarization component (p light component) parallel to the incident surface including the stretching direction (X direction), and the stretching direction (X direction). Is an example of a graph of the reflectance at an incident angle of 0 ° with respect to the wavelength of a polarized light component (s light component) perpendicular to the incident surface. FIG. 4 is a schematic cross-sectional view of a laminated film in which a diffusion film is laminated on one side of a reflective polarizing film via an adhesive layer, and the film surface on the diffusion film side is a diffusion surface. FIG. 5 is a schematic cross-sectional view of a laminated film in which a diffusion film is laminated on both sides of a reflective polarizing film via an adhesive layer, and the film surfaces of both diffusion films are diffusion surfaces.

[Laminated film]
In the laminated film of the present invention, a diffusion film is laminated on at least one surface of the reflective polarizing film, and the diffusion film has a surface shape of center line average roughness SRa and peak count SPc described later, and a certain retardation characteristic described later. The reflective polarizing film includes a uniaxially stretched multilayer laminated film in which the first layer and the second layer are alternately laminated, and the first layer has a refractive index characteristic that has not been obtained in the past. Thus, the uniaxially stretched multi-layer laminate film has a property that the reflection property of polarized light in the reflection axis direction is higher than the conventional one, and the transmittance of the polarization in the transmission axis direction is higher than the conventional one.
The present invention will be described in detail below.

[Reflective polarizing film]
The reflective polarizing film in the present invention is a film having a polarization performance that selectively reflects a certain polarization component and selectively transmits a polarization component perpendicular to the polarization component, and includes a first layer and a second layer. And a total of 251 layers or more of the following uniaxially stretched multilayer laminated films.

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

(First layer)
In the present invention, the first layer has an average refractive index of 1.60 or more and 1.70 or less, and the refractive index n _{X in the} uniaxial stretching direction (X direction) increases by stretching, and the uniaxial stretching direction in the film plane. a layer made of a thermoplastic resin refractive index n _Z has a characteristic to decrease by stretching the refractive index n _Y and the film thickness direction (Z direction) in the direction perpendicular (Y direction).

Polyethylene-2,6-naphthalene dicarboxylate has hitherto been known as the most suitable material as the first layer of the multilayer laminated film having a reflective polarization function. refractive index n _Y in the Y direction before and after stretching is mostly unchanging material. On the other hand, the thermoplastic resin constituting the first layer of the present invention is most characterized in that the refractive index nY in the _Y direction decreases with stretching, as the refractive index nZ in the _Z direction, due to stretching.
In the multilayer laminated film having the reflective polarization function, the thermoplastic resin having the refractive index characteristic of the present invention, which has not been conventionally known as the resin constituting the first layer, is further combined with the second layer thermoplastic resin described later. By using a multilayer laminated film, it is possible to achieve both high polarization performance, which has been difficult with conventional multilayer laminated films, and color shift with respect to incident light in an oblique direction.

  Here, the average refractive index in the present invention means that the thermoplastic resin constituting the first layer is melted alone, extruded from a die to create an unstretched film, and the obtained film in the X direction, Y direction, Z The refractive index in each direction 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.

Moreover, about the refractive index change of each direction by extending | stretching, it can obtain | require by the following method. That is, the thermoplastic resin constituting the first 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 first layer is melted alone and extruded from a die to create a uniaxially stretched film by applying 5 times at 135 ° C. in the uniaxial direction, 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 to obtain the refractive index in each direction after stretching.
By comparing the refractive index before stretching obtained by such a method with the refractive index in each direction after stretching, the change in the refractive index due to stretching can be confirmed.

  The lower limit value of the average refractive index of the thermoplastic resin constituting the first layer is more preferably 1.61, and still more preferably 1.62. The upper limit of the average refractive index of the thermoplastic resin constituting the first layer is more preferably 1.69, and still more preferably 1.68. When the average refractive index of the thermoplastic resin of the first layer is within this range, the refractive index difference in each direction between the stretched second layer and the second layer can be set to a desired range. On the other hand, when the average refractive index of the thermoplastic resin of the first layer is less than the lower limit value, the refractive index difference with the second layer is close, and the refractive index difference in the X direction after stretching cannot be sufficiently increased. . When the average refractive index of the thermoplastic resin of the first layer exceeds the upper limit value, the refractive index difference with the second layer after stretching becomes large, and the refractive index difference between the layers in the Y direction and Z direction after stretching becomes small. It is hard to do.

The refractive index n _X in the X direction of the thermoplastic resin of the first layer is preferably increased by 0.20 or more by stretching, more preferably 0.25 or more, and further preferably 0.27 or more. The larger the change in the refractive index, the higher the polarization performance can be improved, but the upper limit value is limited to 0.35 and further 0.30 because the film breaks when the draw ratio is too high. .

The refractive index n _Y in the Y direction of the thermoplastic resin constituting the first layer is preferably lowered in the range of 0.05 to 0.20 by stretching, more preferably 0.06 to 0.15, More preferably, it is 0.07 or more and 0.10 or less. When the amount of decrease in the refractive index is less than the lower limit, if the resins in both layers are selected so that the interlayer refractive index in the Y direction matches, the difference in the refractive index between the layers in the X direction increases. The refractive index shift between the layers increases, and it may be difficult to achieve both improvement in polarization performance and hue shift of transmitted polarized light with respect to obliquely incident light. On the other hand, when the amount of decrease in the refractive index exceeds the upper limit, the orientation is too high and the mechanical strength may not be sufficient.

The refractive index n _Z in the Z direction of the thermoplastic resin of the first layer is preferably lowered in the range of 0.05 to 0.20 by stretching, more preferably 0.06 to 0.15, and still more preferably. Is 0.07 or more and 0.10 or less. In order to make the amount of decrease in the refractive index less than the lower limit, the X direction must be lowly oriented, and the refractive index difference between the layers in the X direction may not be sufficiently large. On the other hand, when the amount of decrease in the refractive index exceeds the upper limit, the orientation is too high and the mechanical strength may not be sufficient.

The difference in refractive index between the Y-direction refractive index n _Y after stretching of the first layer and the Z-direction refractive index n _Z after stretching is preferably 0.05 or less, more preferably 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. Such polarized light is particularly effective for eliminating a hue shift with respect to a polarization component (s-polarized light) perpendicular to an incident surface including a stretching direction (X direction) of a uniaxially stretched film with a film surface as a reflecting surface. .
As the thermoplastic resin having such refractive index characteristics, specifically, an aromatic polyester having a copolymer component having a specific structure as described below as a dicarboxylic acid component (hereinafter sometimes referred to as aromatic polyester (I)). Is exemplified.

<Aromatic polyester (I)>
Examples of the thermoplastic resin forming the first layer include aromatic polyester (I) having a copolymer component having a specific structure as a dicarboxylic acid component. Such a polyester is obtained by polycondensation of a dicarboxylic acid component and a diol component described in detail below.

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

(In the formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms)
(In the formula (B), R ^B represents a phenylene group or a naphthalenediyl group)

About the component represented by Formula (A), in formula, ^RA is a C2-C10 alkylene group. Examples of the alkylene group include an ethylene group, a propylene group, an isopropylene group, a tetramethylene group, a hexamethylene group, and an octamethylene group.
The lower limit of the content of the component represented by the formula (A) is preferably 7 mol%, more preferably 10 mol%, still more preferably 15 mol%. Moreover, the upper limit of the content of the component represented by the formula (A) is preferably 45 mol%, more preferably 40 mol%, still more preferably 35 mol%, and particularly preferably 30 mol%.
Therefore, the content of the component represented by the formula (A) is preferably 5 mol% or more and 45 mol% or less, more preferably 7 mol% or more and 40 mol% or less, and further preferably 10 mol% or more and 35 mol% or less. Especially preferably, it is 15 mol% or more and 30 mol% or less.

The component represented by the formula (A) is preferably 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, 6,6 ′-(trimethylenedioxy) di-2-naphthoic acid, and 6,6 ′-(ethylenedioxy) di-2-naphthoic acid. Components derived from 6 ′-(butyleneoxy) di-2-naphthoic acid are preferred. Among these, those having an even number of carbon atoms of R ^A in formula (A) are preferable, particularly derived from 6,6 ′-(ethylenedioxy) di-2-naphthoic acid represented by the following formula (A-1). Are preferred.

Such aromatic polyester (I) is characterized in that the dicarboxylic acid component contains a component represented by the formula (A) in an amount of 5 mol% to 50 mol%. When the ratio of the acid component represented by the formula (A) is less than the lower limit value, it is difficult for the refractive index in the Y direction to decrease due to uniaxial stretching.
The difference in refractive index n _Z of the refractive index n _Y and Z direction Y direction in the stretched film is increased, which may hue deviation occurs for polarized light incident at an incident angle of an oblique direction. Further, if the proportion of the component represented by the formula (A) exceeds the upper limit value, amorphous characteristics becomes large, the difference between the refractive index n _Y in refractive index n _X and Y direction of the X-direction in the stretched film Therefore, sufficient reflection performance as a reflective polarizing film cannot be obtained.

Thus, by using the polyester containing the component represented by the formula (A), it is possible to produce a uniaxially stretched multilayer laminated film having higher polarization performance as a reflective polarizing film than in the past, and further in an oblique direction. It is possible to suppress the hue shift of polarized light due to the incident angle.
Further, the acid component of the formula (B), wherein, R ^B is a phenylene group or naphthalene-diyl group.
Examples of the component represented by the formula (B) include components derived from terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, or combinations thereof. -Preferred examples include components derived from naphthalenedicarboxylic acid.

The lower limit of the content of the component represented by the formula (B) is preferably 55 mol%, more preferably 60 mol%, still more preferably 65 mol%, and particularly preferably 70 mol%. Moreover, the upper limit of the content of the component represented by the formula (B) is preferably 93 mol%, more preferably 90 mol%, and still more preferably 85 mol%.
Therefore, the content of the component represented by the formula (B) is preferably 55 mol% or more and 95 mol% or less, more preferably 60 mol% or more and 93 mol% or less, and further preferably 65 mol% or more and 90 mol% or less. Particularly preferred is 70 mol% or more and 85 mol% or less.

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

<Diol component>
In the present invention, as the diol component (ii) constituting the aromatic polyester (I), a 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 components derived from ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol, and the like, and ethylene glycol, trimethylene glycol, tetramethylene. A component derived from glycol is preferred, and a component derived from 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 following 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 the component of the formula (A) and the component of the formula (B), and has a lower melting point than the homopolymer having only the component of the formula (A). The mechanical strength is excellent.

The glass transition temperature (hereinafter sometimes referred to as Tg) of the aromatic polyester (I) is preferably 80 to 120 ° C, more preferably 82 to 118 ° C, and still more preferably 85 to 118 ° C. When Tg is within this range, a film having excellent heat resistance and dimensional stability can be obtained. Such melting point and glass transition temperature can be adjusted by controlling the kind and copolymerization amount of the copolymerization component and dialkylene glycol as a by-product.
The method for producing the aromatic polyester (I) can be produced, for example, according to the method described on page 9 of the pamphlet of WO2008 / 153188.

<< Refractive index characteristics of aromatic polyester (I) >>
FIG. 2 shows an example of changes in the refractive index in each direction when the aromatic polyester (I) is uniaxially stretched. As shown in FIG. 2, the refractive index n _X in the X direction is in a direction that increases by stretching, the refractive index n _{Y in the Y} direction and the refractive index n _{Z in the} Z direction are both in a direction that decreases with stretching, and refractive index difference regardless of the draw ratio n _Y and n _Z is characterized by very small.
In addition, the first layer is uniaxially stretched using the aromatic polyester (I) containing the specific copolymer component, so that the refractive index n _{X in the} X direction is 1.80 to 1.90. Has characteristics. When the refractive index in the X direction in the first layer is within such a range, the refractive index difference from the second layer becomes large, and sufficient reflective polarization performance can be exhibited.

On the other hand, when the polyester constituting the first layer is polyethylene-2,6-naphthalenedicarboxylate, 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. In contrast, the refractive index n _{Z in} the Z direction decreases as the uniaxial stretching ratio increases. According therefore uniaxial stretching ratio is high, the difference in refractive index n _Y and Z directions of the refractive index n _Z in the Y-direction is increased, the hue shift is likely to occur with respect to the polarization at an incident angle of an oblique direction.

(Second layer)
<Thermoplastic resin>
In the second layer of the present invention, the average refractive index in the X direction, Y direction, and Z direction before stretching is 1.50 or more and 1.60 or less, and the average refractive index before stretching and the X direction after stretching, It consists of a thermoplastic resin in which the difference between the refractive index in the Y direction and the Z direction is 0.05 or less in all three directions.
Here, the average refractive index in the X direction, Y direction, and Z direction before stretching in the second layer means that the thermoplastic resin constituting the second layer is melted alone and extruded from a die to create an unstretched film. The refractive index in each of the X direction, Y direction and Z direction of the obtained film was measured at a wavelength of 633 nm using a metricon prism coupler, and the average value thereof was defined as the average refractive index.

Regarding the refractive indices in the X direction, Y direction, and Z direction after stretching in the second layer, the thermoplastic resin constituting the second layer is melted alone and extruded from a die, and is 5 at 135 ° C. in a uniaxial direction. A uniaxially stretched film is prepared by stretching the film twice, and after stretching by measuring the refractive index at a wavelength of 633 nm using a metricon prism coupler in each of the X direction, Y direction, and Z direction of the obtained film. The refractive index in each direction is obtained.
The difference between the average refractive index before stretching determined in this way and the refractive index in the X direction, Y direction, and Z direction after stretching is obtained, and the difference is 0.05 or less in absolute value in all three directions. A thermoplastic resin having a refractive index characteristic is used for the second layer.
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. As a result, high polarization performance can be obtained. At the same time, it is possible to obtain a refractive index characteristic in which both the refractive index difference in the Y direction and the refractive index difference in the Z direction between the layers are extremely small, and it is also favorable for the hue deviation of polarized light due to the incident angle in the oblique direction.

  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 crystalline polyesters having such refractive index characteristics, copolymerized polyesters such as copolymerized polyethylene terephthalate and copolymerized polyethylene naphthalene dicarboxylate, blends of crystalline copolymerized polyesters, crystalline copolymerized polyesters and amorphous polyesters A blend with is preferably exemplified.

  Among the crystalline copolyesters, copolyethylene terephthalate is preferable, and polyesters mainly composed of an ethylene terephthalate component copolymerized with isophthalic acid or 2,6-naphthalenedicarboxylic acid are preferable, and particularly isophthalic acid or 2,6- A polyester having an ethylene terephthalate component copolymerized with naphthalenedicarboxylic acid as a main component and having a melting point of 220 ° C. or lower is preferable.

  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 copolymerization component among dicarboxylic acids and 2,7-naphthalenedicarboxylic acids; Aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid; Alicyclic rings such as cyclohexanedicarboxylic acid Preferred examples include acid components such as aliphatic dicarboxylic acids, aliphatic diols such as butanediol and hexanediol; and glycol components such as alicyclic diols such as cyclohexanedimethanol.

Moreover, you may use aromatic polyester (I) used by the 1st layer of this invention as copolymer polyethylene naphthalene dicarboxylate. In such a case, in order to obtain the refractive index characteristic of the second layer of the present invention, it is preferable to blend with another copolymerized polyester. As the other copolyester, copolyethylene terephthalate having a refractive index lower than that of the copolyethylene terephthalate is preferable. Examples of copolymer components include alicyclic dicarboxylic acid components such as cyclohexanedicarboxylic acid, decalin dicarboxylic acid, and tetralindicarboxylic acid, and alicyclic diolic acids such as cyclohexanedimethanol, adamantanediol, spiroglycol, and tricyclodecanedimethanol. Ingredients.
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.

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

(Number of layers)
In the uniaxially stretched multilayer laminated film in the present invention, the above-mentioned first layer and second layer are alternately laminated in total of 251 layers. When the number of stacked layers is less than 251 layers, the average reflectance characteristics of the polarization component parallel to the incident surface including the stretching direction (X direction) may satisfy a certain average reflectance over a wavelength range of 400 to 800 nm. Can not.
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 preferably 0.01 μm or more and 0.5 μm or less. The thickness of each layer of the first layer is preferably 0.01 μm or more and 0.1 μm or less, and the thickness of each layer of the second layer is preferably 0.01 μm or more and 0.3 μm or less. The thickness of each layer can be determined based on a photograph taken using a transmission electron microscope.
In the present invention, the reflection wavelength band exhibited by the uniaxially stretched multilayer laminated film is from the visible light region to the near infrared region, so that the thicknesses of the respective layers of the first layer and the second layer are efficiently visible. The reflectance characteristics from the light region to the near infrared region can 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 the first layer is 2.0 or more and 5.0 or less, and the ratio between the maximum layer thickness and the minimum layer thickness in the second layer. Is preferably 2.0 or more and 5.0 or less. More preferably, both layers are 2.0 or more and 4.0 or less, More preferably, they are 2.0 or more and 3.5 or less, Most preferably, they are 2.0 or more and 3.0 or less.

For example, in a multilayer stretched film having 126 first layers and 125 second layers, the maximum layer thickness of the first layer refers to the thickness of the largest layer among the first layers of 126 layers, The minimum layer thickness of the first layer refers to the thickness of the smallest layer among the 126 first layers.
The ratio of the layer thickness is specifically represented by the ratio of the maximum layer thickness to the minimum layer thickness. The maximum layer thickness and the minimum layer thickness in each of the first layer and the second layer can be obtained based on a photograph taken using a transmission electron microscope.

In the multilayer 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. In addition, when the ratio between the maximum layer thickness and the minimum layer thickness exceeds the upper limit value, the reflection band is too wide, and the reflectivity of the polarization component parallel to the incident surface including the stretching direction (X direction) is decreased. There is.
The layer thicknesses of the first layer and the second layer may change stepwise or may change continuously.
As a method for obtaining such a layer thickness ratio, for example, the first layer and the second layer obtained by branching the polyester for the first layer into 137 layers and the thermoplastic resin for the second layer into 138 layers are alternately laminated, and the flow path Is a method using a multi-layer feed block device in which the value continuously changes from 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 1.5 times 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 film obtained can be adjusted while maintaining the adhesion between the layers and without changing the resin used. And has the 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 in the present invention has a thickness adjusting layer having a layer thickness of 2 μm or more as a part of the alternately laminated structure of the first layer and the second layer or the alternately laminated structure. You may have on both sides. 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.

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

[Average reflectance]
The uniaxially stretched multilayer laminated film in the present invention has a wavelength 400 for the incident polarized light at an incident angle of 0 degree with respect to a polarization component parallel to the incident surface including the uniaxially stretched direction (X direction). The average reflectance of ˜800 nm is 90% or more, and at the same time, the wavelength of the polarized light component perpendicular to the incident surface including the X direction with the film surface as the reflecting surface is 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree. The average reflectance is 15% or less.

  Here, the incident surface refers to a surface that is perpendicular to the reflecting surface and includes the incident light beam and the reflected light beam. In addition, in the present invention, the polarized light component parallel to the incident surface including the stretching direction (X direction) of the uniaxially stretched film is p-polarized light, polarized light orthogonal to the transmission axis, and extinction axis direction. Sometimes referred to as polarized light or polarized light in the direction of the reflection axis. Further, in the present invention, the polarization component perpendicular to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as the reflective surface may be referred to as s-polarized light and polarized light in the transmission axis direction. Furthermore, the incident angle represents an incident angle with respect to a direction perpendicular to the film surface.

With respect to a polarized light component (p-polarized light) parallel to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as a reflective surface, the wavelength of the incident polarized light at an incident angle of 0 degree is 400 to 800 nm. The average reflectance is more preferably 95% or more and 100% or less, and particularly preferably 98% or more and 100% or less.
This high average reflectivity for the p-polarized component reduces the amount of transmission of p-polarized light compared to the conventional one, and exhibits high polarization performance that selectively transmits s-polarized light, improving the brightness of liquid crystal displays, etc. When used as a film, a high brightness improvement effect is obtained.

Further, with respect to a polarized light component (p-polarized light) parallel to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as a reflecting surface, the wavelength 400 to the incident polarized light at an incident angle of 50 degrees. The average reflectance at 800 nm is preferably 93% or more and 99% or less, and more preferably 95% or more and 98% or less.
Since the average reflectance of p-polarized light at an incident angle of 50 degrees is high in this way, high polarization performance is obtained, and transmission of light incident in an oblique direction is highly suppressed. Is suppressed.

The average of the wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree with respect to the polarization component (s-polarized light) perpendicular to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as the reflecting surface. The reflectance is more preferably 5% or more and 12% or less, further preferably 8% or more and 12% or less, and particularly preferably 9% or more and 11% or less.
Further, with the film surface as a reflection surface, a wavelength component of 400 to 800 nm with respect to the incident polarized light at an incident angle of 50 degrees with respect to a polarization component (s-polarized light) perpendicular to the incident surface including the stretching direction (X direction) of the uniaxially stretched film. The average reflectance is preferably 12% or less, more preferably 5% or more and 10% or less, and particularly preferably 8% or more and 10% or less.

  By limiting the average reflectance of the wavelength 400 to 800 nm with respect to the s-polarized component within this range, the amount of s-polarized light transmitted to the side opposite to the light source increases, and the transmittance for s-polarized light increases. On the other hand, when the average reflectance with respect to the s-polarized component 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 not exhibited. On the other hand, the transmittance of the s-polarized component is higher when the reflectance with respect to the s-polarized light is lower within such a range, but it may be difficult to make it lower than the lower limit due to the composition and stretching.

  In order to obtain such an average reflectance characteristic for the p-polarized component, the polymer having the refractive index characteristic described above is used as the polymer constituting each of the first layer and the second layer, and the film is stretched constant in the stretching direction (X direction). This is achieved by increasing the refractive index difference between the first layer and the second layer in the stretching direction (X direction) by stretching the film at a magnification to make the film in-plane direction of the first layer have a birefringence. Moreover, in order to obtain this average reflectance in the wavelength range of 400 to 800 nm, a method of adjusting the thickness and the number of layers of the first layer and the second layer can be mentioned.

  In order to obtain such an average reflectance characteristic for the s-polarized component, the polymer having the refractive index characteristic described above is used as the polymer component constituting the first layer and the second layer, and the direction orthogonal to the stretching direction ( This is achieved by making the difference in refractive index between the first layer and the second layer in the orthogonal direction (Y direction) extremely small by not stretching in the Y direction) or by only stretching at a low draw ratio.

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

[Film thickness]
The uniaxially stretched multilayer laminated film in the present invention preferably has a film thickness of 15 μm or more and 40 μm or less. The conventional multilayer laminated film having a reflective polarization function needs to increase the number of layers in order to increase the average reflectance of p-polarized light, and the thickness of about 100 μm is necessary. The present invention constitutes the first layer. By using a resin whose refractive index in the Y direction decreases as a result of stretching as a thermoplastic resin, and combining it with the above-mentioned second layer thermoplastic resin, a multilayer multilayer film having a constant layer thickness is obtained. The film thickness can be made thinner.

[Diffusion film]
In the laminated film of the present invention, it is preferable that a diffusion film is laminated on at least one surface of the reflective polarizing film, and further, a diffusion film is laminated on both surfaces of the reflective polarizing film. It is preferable that the reflective polarizing film and the diffusion film are laminated via an adhesive layer. Although it does not specifically limit about the kind of adhesion layer, or the lamination | stacking method, The method of bonding with an acrylic adhesive etc. is mentioned as an example.

As an example of a laminated structure, as shown in FIG. 4, it is necessary to laminate | stack so that the diffusion surface of a diffusion film may become an outermost surface from ensuring a diffusion performance. As shown in FIG. 5, you may paste a diffusion film on both surfaces of a reflective polarizing film. It is preferable to bond a diffusion film on both sides from the viewpoint of securing flatness during a practical test.
By laminating a diffusion film on a reflective polarizing film, a single optical member can express a plurality of functions that were conventionally separate optical members such as a brightness enhancement member and a diffusion plate. In addition, since the reflective polarizing film of the present invention has a thin film thickness, it is difficult to maintain flatness with the reflective polarizing film alone when used as an optical member for a large display. Is suppressed. At the same time, the reflective polarizing film and the other optical film are laminated via the diffusion film of the present invention, so that the contact surface between the reflective polarizing film and the other optical film is reduced, and the brightness of the liquid crystal display is increased. Spots do not occur. Furthermore, there is an effect that luminance spots do not occur even in a large area of a large display.

(Diffusion film surface roughness)
The surface roughness of the diffusion film in the present invention is such that the center line average roughness SRa is 0.3 to 1.0 μm, the evaluation length is 2 mm, the cutoff value is 0.25 mm, and the peak count SPc per unit evaluation area is It has a form of less than 500 counts / mm ² . The peak count SPc is preferably 50 or more and 450 or less, more preferably 100 or more and 450 or less, and particularly preferably 150 or more and 450 or less.

  In the range where the center line average roughness SRa is not more than the lower limit value, sufficient diffusion performance cannot be exhibited. On the other hand, in the range where the center line average roughness SRa and the peak count SPc exceed the upper limit values, there is a diffusion effect when polarized light from the light source passes through the reflective polarizing film and is diffused to the viewer side. If it is too high, the high polarization performance obtained by the reflective polarizing film is eliminated, the depolarization is increased, and the luminance is significantly reduced.

(Diffusion film retardation characteristics)
In the present invention, the diffusion film has an in-plane retardation value (Re (550)) of 100 nm or less at a wavelength of 550 nm. When the in-plane retardation value Re (550) exceeds 100 nm, a phase difference is caused during lamination, and the polarized light that has passed through the uniaxially stretched multilayer laminated film is disturbed, resulting in a decrease in luminance.

Here, the retardation value Re in the diffusing film plane is represented by the following formula (1), and is a characteristic representing the retardation of the retardation of light transmitted in the direction perpendicular to the film.
Re = ((n′x−n′y) × d (1)
(Where n′x is the refractive index of the slow axis (highest refractive index) in the diffusion film surface, n′y is the refractive index perpendicular to n′x in the diffusion film surface, and d is diffusion) (Represents each film thickness)

  The in-plane retardation value Re (550) is more preferably 80 nm or less. The in-plane retardation value Re (550) is preferably smaller within such a range, so that the phase difference is less likely to occur. However, the lower limit value is naturally constrained due to the properties of the thermoplastic resin constituting the diffusion film. 5 or more, and 7 or more.

The diffusion film in the present invention has a retardation value (Rth (550)) in a direction perpendicular to the film plane at a wavelength of 550 nm of less than 300, preferably 280 nm or less. When Rth (550) exceeds the upper limit value, the luminance is significantly lowered when observed from an oblique direction.
Rth (550) is preferably smaller within this range, but the lower limit is naturally limited due to the properties of the thermoplastic resin constituting the diffusion film, and is 50 or more, and more preferably 100 or more.

Here, the retardation value Rth in the direction perpendicular to the plane of the diffusing film is represented by the following formula (2), and is a characteristic representing the retardation of the retardation of light transmitted through the film in an oblique direction.
Rth = ((n′x−n′y) ÷ 2−n′z) × d (2)
(Where n′x is the refractive index of the slow axis (highest refractive index) in the plane of the diffusion film, n′y is the refractive index perpendicular to n′x in the plane of the diffusion film, n′z) Is the refractive index in the thickness direction of the diffusion film, and d is the film thickness)

(Diffusion film type)
The type of the resin forming the diffusion film in the present invention is not particularly limited, but polycarbonate is particularly preferable from the viewpoints of glass transition temperature and transparency. A polymer material collectively called polycarbonate is a generic term for a polymer material in which a polycondensation reaction is used in its synthesis method and the main chain is linked by a carbonic acid bond. Among these, a phenol derivative, phosgene, diphenyl are generally used. It means that obtained by polycondensation from carbonate or the like.

Usually, a polycarbonate having 2,2-bis (4-hydroxyphenyl) propane, which is called bisphenol-A, as a bisphenol component is preferably selected. By appropriately selecting various bisphenol derivatives, a polycarbonate copolymer is formed. can do.
In addition to this bisphenol-A, bis (4-hydroxyphenyl) methane, 1,1-bis (4-hydroxyphenyl) cyclohexane, 9,9-bis (4-hydroxyphenyl) fluorene, 1,1 -Bis (4-hydroxyphenyl) -3,3,5-trimethylcyclohexane, 2,2-bis (4-hydroxy-3-methylphenyl) propane, 2,2-bis (4-hydroxyphenyl) -2-phenyl Ethane, 2,2-bis (4-hydroxyphenyl) -1,1,1,3,3,3-hexafluoropropane, bis (4-hydroxyphenyl) diphenylmethane, bis (4-hydroxyphenyl) sulfide, bis ( 4-hydroxyphenyl) sulfone and the like.
The proportion of the copolymer component is preferably 2 to 20 mol%, more preferably 5 to 10 mol%, in all repeating units of the polycarbonate copolymer.

[Diffusion film surface forming method]
As a method of imparting surface properties of the center line average roughness SRa and peak count SPc to the diffusion film, a method of adding polymer beads or inorganic particles to the diffusion film, embossing on one side of the thermoplastic resin film, and forming irregularities The method of forming and making it a diffusion film is illustrated.
In the present invention, a method of forming irregularities on the surface by a method of producing a polycarbonate film by a T-die method using a cooling roll and a guide roll as described in JP-A-1-72833 is preferable. Specifically, a matted cooling roll is used as the cooling roll, and a mirror guide roll made of heat-resistant silicon is used as the guide roll.

[Usage]
The laminated film of the reflective polarizing film and the diffusing film of the present invention also has a diffusion function while maintaining the high polarization performance of the reflective polarizing film and the effect of reducing the hue shift of transmitted polarized light with respect to obliquely incident light, Moreover, since the flatness of the reflective polarizing film is maintained and there is no luminance unevenness, it can be suitably used as a luminance improving film for a liquid crystal display and can be processed into a luminance improving member.
In particular, since it has a higher polarization performance than conventional ones, it is possible to provide a liquid crystal display device that has a high luminance improvement rate when used as a luminance enhancement film, and has a high viewing angle and excellent hue and low visibility. it can.
Moreover, the liquid crystal display device which has a surface light source, the brightness improvement member of this invention, and a liquid crystal display module is illustrated as a display apparatus.

[Production method of laminated film]
The uniaxially stretched multilayer laminated film in the present invention is extruded in a state in which the thermoplastic resin constituting the first layer and the thermoplastic resin constituting the second layer are alternately superposed in the molten state, and the multilayer unstretched film (sheet) Process). At this time, the laminate is laminated so that the thickness of each layer changes stepwise or continuously within a range of 2.0 times or more, preferably 5.0 times or less.

  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 variations in the plane direction of the individual layers in the first layer and the second layer, and the light interference of the multilayer stretched film is made uniform in the plane direction. This is preferable because the difference in refractive index between the layers and the second layer in the stretching direction becomes large. As the stretching method at this time, known stretching methods such as heat stretching with a rod heater, roll heating stretching, and tenter stretching can be used. From the viewpoints of reducing scratches due to contact with the roll and stretching speed, tenter stretching is performed. preferable. In addition, a method of forming a uniaxially stretched film without performing a stretching process in the direction orthogonal to the stretching direction (Y direction) is preferable. It is preferable to limit the draw ratio to about 05 to 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.

As an example of a method for obtaining a diffusion film, a resin used for the diffusion film is melt-extruded through a T-die of an extruder, and a resin sheet is sandwiched between a cooling roll and a guide roll whose surface is roughened to a certain roughness. By pressing with, the rough surface of the cooling roll is embossed on the film surface to obtain a diffusion film having a diffusion surface having the surface characteristics of the present invention. In order to obtain the surface characteristics of the present invention, the surface design, pressing and the like of the cooling roll may be adjusted.
The obtained uniaxially stretched multilayer laminate film and, if necessary, another surface provided with another layer on the surface of the uniaxially stretched multilayer laminate film are used as a reflective polarizing film, and the reflective polarizing film and the diffusion film are laminated and bonded together. Processed into a laminated film. The reflective polarizing film and the diffusion film are preferably laminated via an adhesive layer. Although it does not specifically limit about the kind of adhesion layer, or the lamination | stacking method, The method of bonding with an acrylic adhesive etc. is mentioned as an example.

  The present invention will be further described below with reference to examples. In addition, the physical property and characteristic in an Example were measured or evaluated by the following method. Moreover, unless otherwise indicated, the part and% in an Example mean a weight part and weight%, respectively.

(1) Refractive index and average refractive index before stretching in each direction and average refractive index Each resin constituting each layer was melted and extruded from a die, and a film cast on a casting drum was prepared. Further, a stretched film was prepared by stretching the obtained film at 135 ° C. in a uniaxial direction 5 times. For each of the obtained cast film and stretched film, the stretching direction (X direction) and its orthogonal direction (Y direction), the refractive index in the thickness direction (Z direction) (respectively n _X , n _Y , n _Z ), It was determined by measuring at a wavelength of 633 nm using a metricon prism coupler, and was defined as the refractive index before stretching and after stretching. About the average refractive index before extending | stretching of each layer, it calculated | required from the average value of the refractive index of 3 directions before extending | stretching.

(2) Reflectivity and reflection wavelength Using a spectrophotometer (manufactured by Shimadzu Corporation, MPC-3100), a polarizing filter is mounted on the light source side, and the relative specular reflectance with respect to an aluminum-deposited mirror at each wavelength is changed from a wavelength of 400 nm to 800 nm. Measure in the range of. In this case, 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 transmission axis of the polarizing filter is disposed so as to be orthogonal to the stretching direction of the film Was measured as s-polarized light. For each polarization component, the average reflectance in the range of 400 to 800 nm was defined as the average reflectance.
In addition, the case where the measuring light was incident from the direction perpendicular to the film surface of the film sample was defined as 0 degree incidence. The measurement at an incident angle of 50 degrees was performed by arranging the film obliquely with respect to the light source so that the measurement light is incident at an angle of 50 degrees from the direction perpendicular to the film surface.

(3) Three-dimensional surface roughness (SRa, SPc)
In accordance with JIS-B0601, B0651, using a three-dimensional surface roughness meter (trade name: SURF CORDER SE-3CK, manufactured by Kosaka Laboratory Ltd.), stylus tip R2 μm, scanning pitch 2 μm, scanning length 1 mm, scanning Centerline average roughness SRa (um) and peak count SPc (count / mm ² ) were measured under the conditions of 100 lines and a cutoff of 0.25 mm.

(4) Melting point (Tm) and glass transition point (Tg) of thermoplastic resin and film
10 mg of a polymer sample or a film sample was sampled, and a melting point and a glass transition point were measured using a DSC (TA Instruments, trade name: DSC2920) at a heating rate of 20 ° C./min.

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

(6) Thickness and number of layers 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 (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 and the number of layers were 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.

(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) Total light transmittance, haze It measured using the haze measuring device (NDH-2000 by Nippon Denshoku Industries Co., Ltd.) according to JIS-K7136. In the table, the total light transmittance was described as Tt, and the haze as Hz.

(9) Retardation The refractive index of the diffusion film is determined by measuring the refractive index at a wavelength of 633 nm using a laser refractometer (Model 2010 prism coupler manufactured by Metricon), and the diffusion film at a wavelength of 550 nm is measured using an ellipsometer manufactured by JASCO. The retardation (in-plane retardation: Re, thickness direction retardation Rth) was determined.

(10) Brightness improvement effect, hue Instead of the optical film (diffuse film, prism sheet) in the LCD panel (Madeshita Electric's VIERA TH-32LZ80 2007), the produced laminated film (uniaxially stretched multilayer laminated film and diffusion) A laminated film with a film) was inserted between a light source and a polarizing plate, and the front luminance when white was displayed on a PC was evaluated by an FPD viewing angle measurement evaluation apparatus (ErgoScope 88) manufactured by Opto Design.
The rate of increase in luminance after inserting the sample film relative to the luminance before inserting the sample film was calculated, and the luminance improvement effect was evaluated according to the following criteria.
◎: Brightness improvement effect is 160% or more. ○: Brightness improvement effect is 150% or more and less than 160%. △: Brightness improvement effect is 140% or more and less than 150%. X: Brightness improvement effect is less than 140%. The maximum change in hue x or y at an omnidirectional viewing angle of 80 degrees was evaluated according to the following criteria.
○: Maximum change in both x and y is less than 0.03 Δ: Maximum change in either x or y is 0.03 or more ×: Maximum change in both x and y is 0.03 or more

(11) Luminance spot evaluation Instead of the optical film (diffusion film, prism sheet) in the LCD panel (Madeshita Electric's VIERA TH-32LZ80 2007), the produced laminated film (uniaxially stretched multilayer laminated film and diffusion film) The laminated film was inserted between the light source and the polarizing plate, the backlight was turned on, the appearance of the panel displaying white color on the PC in the dark room was observed with the naked eye, and evaluated based on the following criteria.
Evaluation criteria:
○: Luminance spots due to cold cathode tubes are completely invisible △: Luminance spots due to cold cathode tubes are slightly confirmed ×: Luminance spots due to cold cathode tubes are clearly confirmed

(12) Heat resistance evaluation test The prepared laminated film (laminated film of uniaxially stretched multilayer laminated film and diffusion film) is placed between the light source and the polarizing plate in the LCD panel (Made by Panasonic Vera TH-32LZ80 2007). Then, after the backlight was turned on continuously for 3000 hours, the sheet was taken out and the appearance of the sheet was observed with the naked eye, and the appearance of the laminated film continuously used in the heated state was evaluated based on the following criteria.
Evaluation criteria:
◎: No change in the appearance of the film after continuous use, or slight changes (unmeasured irregularities with a height of less than 0.5 mm) visually observed on the film after continuous use ○: Continuous use Irregularities with a height of less than 1 mm can be seen on the film after the film. Δ: Irregularities with a height of 1 mm or more can be seen on the film after continuous use.

[Example 1]
(Creation of uniaxially stretched multilayer laminated film)
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 a thermoplastic resin 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 thermoplastic resin for the second layer. .

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 configuration of each layer of the obtained uniaxially stretched multilayer laminated film, the characteristics and physical properties of each layer.

(Creation of diffusion film)
To a reactor equipped with a thermometer, a stirrer and a reflux condenser, 9809 parts of ion-exchanged water and 2271 parts of 48% sodium hydroxide aqueous solution were added, and 1775 parts of 2,2-bis (4-hydroxyphenyl) propane and sodium hydrosulfite were added. After dissolving 3.5 parts and adding 7925 parts of methylene chloride, 1000 parts of phosgene was blown in at a temperature of 16 to 20 ° C. with stirring for 60 minutes. After completion of the phosgene blowing, 32.7 parts of p-tert-butylphenol and 327 parts of 48% aqueous sodium hydroxide solution were added, and 1.57 parts of triethylamine was further added, followed by stirring at 20 to 27 ° C. for 40 minutes to complete the reaction. .
The methylene chloride layer containing the product was washed with dilute hydrochloric acid and pure water, and then methylene chloride was evaporated to obtain a polycarbonate resin. The number average molecular weight (Mn) of the obtained resin was 19,000 and Tg was 149 ° C.

The obtained polycarbonate resin is heated to 240 to be in a molten state, supplied to a single screw extruder, led to a die, and the surface and centerline of this molten polycarbonate adjusted to a temperature of 190 to 195 ° C. and a temperature of 120 to 130 ° C. A mirror roller guide roll made of silicon rubber having a surface hardness of 70 ° from the opposite surface of the polycarbonate resin is brought into contact with a cooling roll having an average roughness Ra of 0.3 μm and a 10-point average roughness Rz of 0.50 μm. By pressing with an average linear pressure of 4 kg / cm, a single-sided mat having a thickness of 0.25 mm and a polycarbonate film having a mirror surface on the other side were obtained. At this time, Re (550) was 75 nm, and Rth (550) was 255 nm. The properties of the obtained diffusion film are shown in Table 2.
Then, it laminated | stacked on both surfaces of the obtained uniaxial stretching multilayer laminated film through the mirror surface side of the obtained single-sided mat and the polycarbonate film of the other side mirror surface, and an acrylic adhesive, and obtained the laminated film. Table 2 shows the characteristics of the obtained laminated film.

[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 the resin composition or the layer thickness of each layer was changed. The single-sided mat obtained on both surfaces of the obtained uniaxially stretched multilayer laminated film, the mirror surface side of the polycarbonate film on the other side mirror surface, and an acrylic adhesive were laminated to obtain a laminated film. Table 2 shows the characteristics of the obtained laminated film.
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 polyester for the second layer in Example 4 is the ENA21PEN which is the polyester for the first layer of Example 4 (79 mol% of the acid component is a 2,6-naphthalenedicarboxylic acid component, 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.

[Examples 7 to 12]
A laminated film was obtained in the same manner as in Example 1 except that the thickness, retardation and surface roughness of the diffusion film used in Example 1 were changed as shown in Table 2. Table 2 shows the characteristics of the obtained laminated film.

[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 configuration of each layer of the obtained uniaxially stretched multilayer laminated film, the characteristics and physical properties of each layer.
Subsequently, a laminated film was obtained by pasting in the same manner as in Example 1 except that a single-sided mat used in Example 1 and a polycarbonate film having a double-sided mirror surface were used instead of the polycarbonate film having a double-sided mirror surface. Table 2 shows the characteristics of the obtained laminated film.
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 deteriorated as compared with the Examples. Moreover, the hue change amount of the laminated film was larger than that of the example, and a hue shift occurred. Further, since the surface of the polycarbonate film laminated on the uniaxially stretched multilayer laminated film was a mirror surface, luminance spots were generated.

[Comparative Examples 2 to 6]
As shown in Table 1, a uniaxially stretched multilayer laminated film and a laminated film were 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 configuration of each layer of the obtained uniaxially stretched multilayer laminated film, the characteristics and physical properties of each layer. As for the obtained uniaxially stretched multilayer laminated film, the polarization performance deteriorated as compared with the examples (reflectance characteristics in Table 1). Moreover, the hue change amount of the laminated film was larger than that of the example, and a hue shift occurred. Further, since the surface of the polycarbonate film laminated on the uniaxially stretched multilayer laminated film was a mirror surface, luminance spots were generated.

[Comparative Example 7]
A laminated film was obtained by laminating in the same manner as in Example 1 except that a single-sided mat used in Example 1 and a polycarbonate film having a double-sided mirror surface were used instead of the polycarbonate film having a double-sided mirror surface. Table 2 shows the characteristics of the obtained laminated film.

[Comparative Examples 8 and 9]
A laminated film was obtained in the same manner as in Example 1 except that instead of the diffusion film used in Example 1, a diffusion film whose thickness, retardation and surface roughness were changed as shown in Table 2 was used. Table 2 shows the characteristics of the obtained laminated film.
Since a diffusion film having a roughness whose SRa or peak count SPc exceeds the upper limit was used, the high brightness enhancement effect was eliminated while being the same uniaxially stretched multilayer laminated film as in Example 1, and more than in Example 1. The brightness improvement rate decreased.

[Comparative Example 10]
A laminated film was obtained in the same manner as in Example 1 except that a highly transparent biaxially stretched PET film (OLPFW-125 μm manufactured by Teijin DuPont Film) was used instead of the diffusion film used in Example 1. Table 2 shows the characteristics of the obtained laminated film. The retardation of the diffusion film was high in both the in-plane and thickness directions, and the peak count number exceeded 500. Thus, a sufficient luminance improvement effect was not obtained, the hue shift was large, and luminance spots were generated.

[Comparative Example 11]
A polycarbonate film having a thickness of 100 μm was stretched 5% at 150 ° C. to obtain a stretched film, and a laminated film was obtained in the same manner as in Example 1 except that this was used instead of the diffusion film used in Example 1. . Table 2 shows the characteristics of the obtained laminated film. The in-plane phase difference of the diffusion film was large, and the peak count number was over 500, so that a sufficient luminance improvement effect could not be obtained, the hue shift was large, and luminance spots were generated.

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

NDC: 2,6-naphthalenedicarboxylic acid ENA: 6,6 ′-(ethylenedioxy) di-2-naphthoic acid EG: ethylene glycol IA: isophthalic acid TA: terephthalic acid PEN: polyethylene-2,6-naphthalenedicarboxy Rate PET: Polyethylene terephthalate

  The laminated film of the present invention eliminates the hue shift of transmitted polarized light due to the oblique incident angle seen in the conventional multilayer laminated reflective polarizing film, and has a higher polarization performance than the conventional film. When used as a liquid crystal display, a high luminance improvement rate can be obtained, and a high viewing angle and a small hue shift can be provided. At the same time, since a diffusion film with a certain surface property is laminated, even if it is used for a large display, there is no reduction in flatness and luminance unevenness, and a diffusion effect can be obtained without impairing the luminance improvement effect of the reflective polarizing film, It can be suitably used as a luminance improving member for a large display.

A: Diffusion film B: Adhesive layer C: Reflective polarizing film D: Diffusion surface

Claims (8)

A laminated film in which a diffusion film is laminated on at least one surface of a reflective polarizing film,
The diffusion film has a center line average roughness SRa of 0.3 to 1.0 μm and a peak count SPc of less than 500 counts / mm ² , and an in-plane retardation value (Re (550)) at a wavelength of 550 nm of the diffusion film. Is less than 100 nm, the retardation value in the direction perpendicular to the plane at a wavelength of 550 nm (Rth (550)) is less than 300 nm,
The reflective polarizing film comprises a total of 251 or more uniaxially stretched multilayer laminated films in which the first layer and the second layer are alternately laminated,
The uniaxially stretched multilayer laminated film is 1) The first layer has an average refractive index of 1.60 or more and 1.70 or less, and the refractive index n _{X in the} uniaxial stretching direction (X direction) is increased by stretching. a layer refractive index n _Z is formed of a thermoplastic resin to decrease by stretching the refractive index n _Y and the film thickness direction (Z direction) in a direction perpendicular inner in the uniaxial stretching direction (Y-direction),
2) 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) A layer made of a thermoplastic resin having a refractive index difference of 0.05 or less before and after stretching, and 3) a polarization component parallel to the incident surface including the X direction, with the film surface as a reflective surface The average reflectivity 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 90% or more,
4) 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 for the incident polarized light at an incident angle of 0 degrees and 50 degrees is 15% or less, respectively. A laminated film characterized by the above.   The laminated film according to claim 1, wherein the diffusion film is laminated on both surfaces of the reflective polarizing film. The thermoplastic resin forming the first layer of the uniaxially stretched multilayer laminated film is made of polyester of a dicarboxylic acid component and a diol component,
(I) The dicarboxylic acid component contains a component represented by the following formula (A) of 5 mol% to 50 mol% and a component represented by the following formula (B) of 50 mol% to 95 mol%. ,
(In the formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms)
(In the formula (B), R ^B represents a phenylene group or a naphthalenediyl group)
(Ii) The diol component contains 90 to 100 mol% of a component represented by the following formula (C).
(In the formula (C), R ^C represents an alkylene group having 2 to 10 carbon atoms)
The laminated film according to claim 1 or 2.   The laminated film according to any one of claims 1 to 3, wherein the thermoplastic resin forming the second layer is a polyester mainly composed of an ethylene terephthalate component copolymerized with isophthalic acid or 2,6-naphthalenedicarboxylic acid.   The laminated film according to claim 1, wherein the resin forming the diffusion film is polycarbonate.   The laminated film according to any one of claims 1 to 5, which is used as a brightness enhancement film for a liquid crystal display.   The brightness improvement member which consists of a laminated | multilayer film in any one of Claims 1-6.   A liquid crystal display device comprising a surface light source, the brightness enhancement member according to claim 7 and a liquid crystal display module.