TWI576244B - Uniaxially stretched multilayer laminated film - Google Patents

Description

Uniaxially stretched multilayer laminated film

The present invention relates to a uniaxially stretched multilayer laminated film which selectively reflects a certain polarizing component and selectively transmits the polarizing component and the polarizing component in the vertical direction. More specifically, the present invention relates to the selective reflection of the incident angle from the front side and the oblique direction of the film for a certain polarization component, and the incident angle from the front direction of the film for the polarization component of the polarized component and the vertical direction. A uniaxially-extending multilayer laminated film which selectively transmits light and has a certain reflectance from an incident angle in the oblique direction of the film and greatly increases the brightness in the front direction.

A thin film in which a layer having a low refractive index and a layer having a high refractive index are alternately laminated can be an optical interference film which selectively reflects or transmits light of a specific wavelength by structural light interference between layers. Further, such a multilayer laminated film can be bonded to a film having a different reflection peak by gradually changing the film thickness, and can obtain a high reflectance similar to that of a film using a metal, and can also be used as a metallic gloss film or a mirror. Further, by stretching such a multilayer laminated film only in a single direction, only a specific polarizing component can be reflected, and the polarizing component in the vertical direction can be directly transmitted, and since it can be used as a polarizing reflective film, it can be used as a liquid crystal. A film with improved brightness such as a display.

In general, a multilayer optical film comprising a layer having a layer thickness of 0.05 to 0.5 μm and having a different refractive index utilizes a refractive index difference and a film thickness and a number of laminations of a layer constituting one layer and a layer constituting another layer. A phenomenon of so-called increased reflection that reflects light of a specific wavelength is exhibited. Generally, the reflection wavelength thereof is expressed by the following formula.

λ=2(n ₁ ×d ₁ +n ₂ ×d ₂ )

(In the above formula, λ represents the reflection wavelength (nm), n ₁ and n ₂ represent the refractive indices of the respective layers, and d ₁ and d ₂ represent the thickness (nm) of each layer).

For example, as shown in Patent Document 1, by using a resin having a positive stress optical coefficient on one layer, the refractive index of the layer is birefringent by uniaxial stretching to become anisotropic, in-plane extension of the film. The difference in the refractive index between the layers in the direction is increased, and on the other hand, the difference in the refractive index difference between the layers in the direction perpendicular to the direction in which the film is extended can be made to reflect only the specific polarized component.

According to this principle, for example, a reflective polarizing film that reflects polarized light in one direction and transmits polarized light in the vertical direction can be designed. The ideal birefringence at this time is expressed by the following formula.

N1 _X >n2 _X ,n1 _Y =n2 _Y

(In the above formula, n1 _X and n2 _X represent the refractive indices of the extending directions of the respective layers, and n1 _Y and n2 _Y represent the refractive indices of the respective layers in the direction perpendicular to the extending direction).

Further, in Patent Document 2, polyethylene-2,6-naphthalene dicarboxylate (hereinafter sometimes referred to as 2,6-PEN) is used as a layer having a high refractive index, and is used in a layer having a low refractive index. A multilayer laminated film of 30 mol% of a thermoplastic elastomer or PEN of terephthalic acid was polymerized. This is exemplified by using a resin having a positive stress optical coefficient in one layer and a resin having a very small stress optical coefficient (very small birefringence due to elongation) in the other layer, and only reflecting the specific polarized reflection. Polarized film.

The review of the reflective polarizing film mainly focuses on the difference in refractive index between the layers in the extending direction, and the difference in the refractive index between the extending direction and the perpendicular direction in the plane of the film, and then using the light that is not transmitted through the polarized light on the light source side. Improve brightness and improve performance.

On the other hand, in the recycling technique focusing on the unpolarized polarizing component, it is difficult to further improve the brightness improving performance by using the polarizing method so that the reflectance of the polarizing component is close to 100%. .

Further, Patent Document 3 discloses a uniaxially stretched multilayer laminated film in which polyethylene 2,6-naphthalenedicarboxylic acid ethylene glycol and syndiotactic polystyrene are alternately laminated, but it is not proposed to reflect only a certain Part of the wavelength peak is the concept of brightness enhancement film which is the higher transmittance of the film.

(Patent Document 1) Japanese Patent Publication No. 04-268505

(Patent Document 2) Japanese Patent Publication No. 9-506837

(Patent Document 3) WO01/47711

It is an object of the present invention to provide a polarizing component that is transmitted through a polarizing component in the vertical direction, that is, a polarizing component that has been transmitted at a high angle in the vertical direction, and is incident on the oblique direction of the film, not only by reusing the polarizing component that has not passed through. The uniaxially-stretched multilayer laminated film in which the polarizing component has a certain reflectance and has a higher brightness in the front direction than the conventional one, and a uniaxially stretched multilayer laminated film laminate composed of the same.

Further, a second object of the present invention is to provide a uniaxially stretched multilayer laminated film having a large difference in luminance in the front direction and a small variation in hue in the front direction, and a uniaxially stretched multilayer laminated film laminate composed of the same.

The present invention is based on the following findings. In other words, it has been found that a multilayer laminated film having a function of reflecting a polarized light and transmitting polarized light in a vertical direction in a wavelength region of visible light has a high reflection characteristic of polarized light in the direction of the reflection axis. a polarizing component that transmits light from an incident angle in the front direction of the film in the direction of the axial direction, and a new function of reflecting the polarized component incident from the oblique direction of the film, thereby allowing polarization in the transmission axis direction to be emitted in an oblique direction The component can also be reflected on the light source side and reused, so that the front brightness is greatly improved.

As for the brightness enhancement film of the liquid crystal display, there is a brightness enhancement film as described above which is reused by polarized light, or a triangular column of about 50 micrometers juxtaposed on the polyethylene terephthalate film, so that the brightness in a specific direction is lowered. Increase the front brightness of the sheet, etc.

In the present invention, by controlling the birefringence characteristics of the multilayer laminated film, on the one hand, the polarizing is reused, and on the other hand, the light of the incident angle in the specific direction transmitted in the past is reflected to achieve the improvement of the front luminance. Furthermore, it is possible to integrate the functions of the two components of the front view brightness improvement and the viewing angle control of the liquid crystal display by combining the brightness enhancement film and the enamel formed by the multilayer laminated film.

Therefore, by using the multilayer laminated film of the present invention as the brightness improving film of the liquid crystal display, the ruthenium member can be reduced and the light use efficiency can be improved, and the power consumption of the liquid crystal display can be reduced. Further, the multilayer laminated film of the present invention is different from the three-dimensionally shaped enamel sheet, and since it is planar, it can be expected to be integrated with other optical films.

That is, the object of the present invention is achieved by the following invention.

A uniaxially stretched multilayer laminated film which is a uniaxially stretched multilayer laminated film in which a first layer and a second layer are alternately laminated 251 or more, and is characterized in that: 1) the first layer contains 2,6- The polyester having a naphthalene dicarboxylic acid component as a constituent component having a thickness of 0.01 μm or more and 0.5 μm 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. In the direction (Z direction), the refractive index difference between the Y direction and the Z direction of the first layer is 0.1 or more.

2) The second layer is a layer having a thickness of 0.01 μm or more and 0.5 μm or less with a thermoplastic resin as a constituent component, and the average refractive index of the thermoplastic resin is 1.60 or more and 1.65 or less, and is negative optical anisotropy or isotropic Resin,

3) The film surface is used as the reflecting surface, and the average reflectance of the incident polarized light having an incident angle of 0 to 50 degrees and the wavelength of 400 to 800 nm is 90% or more for the polarizing component having the incident surface perpendicular to the Y direction. ,

4) The film surface is used as the reflection surface, and the average reflectance of the incident polarized light having a wavelength of 400 to 800 nm at an incident angle of 0 degrees is 15% or less for the incident component including the Y-direction incident surface. The average reflectance of the incident polarized light having a 50-degree angle of 400 to 800 nm is 20% or more.

2. The uniaxially stretched multilayer laminated film according to the above item 1, wherein the negative optical anisotropic resin constituting the second layer is a syndiotactic polystyrene resin, and the incident surface including the Y direction is parallel. In the polarizing component, the average reflectance of the incident polarized light having an incident angle of 50 degrees of 400 to 800 nm is 50% or more.

3. The uniaxially stretched multilayer laminated film according to the above item 2, wherein a ratio of an average layer thickness of the first layer to an average layer thickness of the second layer (average layer thickness of the first layer / average layer thickness of the second layer) ) is 0.1 or more and 5.0 or less.

4. The uniaxially stretched multilayer laminated film according to the above item 1, wherein the isotropic resin constituting the second layer is a benzoic acid in a range of 30 mol% or more and 70 mol% or less based on all repeating units. A copolymerized polyethylene naphthalate formed by copolymerization of at least one component of a dicarboxylic acid component or an isophthalic acid component.

5. The uniaxially stretched multilayer laminated film according to the above item 4, wherein a ratio of an average layer thickness of the first layer to an average layer thickness of the second layer (average layer thickness of the first layer / average layer thickness of the second layer) ) is 1.2 or more and 5.0 or less.

6. The uniaxially stretched multilayer laminated film according to the above item 4 or 5, wherein the uniaxially stretched multilayer laminated film has a crystal orientation in the thickness direction of the film of -0.30 or more and 0.05 or less.

7. The uniaxially stretched multilayer laminated film according to the above item 1, wherein the polyester of the first layer is polyethylene-2,6-naphthalenedicarboxylate.

8. The uniaxially stretched multilayer laminated film according to Item 1, wherein the first layer and the second layer are free of particles.

9. The uniaxially stretched multilayer laminated film according to the above item 1, which is used as a brightness enhancement film of a liquid crystal display.

A uniaxially-stretched multilayer laminated film laminate which is obtained by laminating at least one surface of a uniaxially stretched multilayer laminated film according to any one of the above items 1 to 9 and further comprising a heat-resistant thermoplastic resin film. .

A brightness enhancement film for a liquid crystal display, which is obtained by the uniaxially-stretched multilayer laminated film according to any one of the above items 1 to 9.

[Single-axis extended multilayer laminated film]

The uniaxially stretched multilayer laminated film of the present invention is a uniaxially stretched multilayer laminated film in which 251 layers or more of the first layer and the second layer are alternately laminated. The first layer, the second layer and the reflection characteristics of the uniaxially stretched multilayer laminated film constituting the present invention are explained below.

In the present invention, the first layer represents a layer having a higher refractive index than the second layer, and the second layer represents a layer having a lower refractive index than the first layer.

Further, the term "reflecting surface" as used in the present invention means a film surface. In the present invention, the incident surface is in a perpendicular relationship with the reflective surface layer, and refers to a surface including incident light and reflected light. The polarized light component having a film surface as a reflecting surface and parallel to the incident surface including the non-extended direction (Y direction) of the uniaxial film is also referred to as P-polarized light in the present invention. Further, the film surface is used as the reflecting surface, and the polarizing component perpendicular to the incident surface including the non-extension direction (Y direction) of the uniaxially stretched film is also referred to as S-polarized light in the present invention.

Further, the incident angle is expressed by an incident angle with respect to a direction perpendicular to the film surface. In the present invention, the incident direction of the uniaxially stretched film including the non-extended direction (Y direction) is taken as 0 degree in the Z direction, and the incident is incident. The angle between the incident ray in the plane and the Z direction is called the incident angle.

Further, in the present invention, the non-stretching direction (Y direction) of the uniaxially stretched film may be referred to as the transmission axis direction, and the extending direction (X direction) of the uniaxially stretched film may be the direction of the reflection axis.

[level one]

The first layer of the present invention is a layer containing a polyester containing a 2,6-naphthalenedicarboxylic acid component as a constituent component. By using a polyester containing a 2,6-naphthalene dicarboxylic acid component, a large birefringence is generated by stretching, and the refractive index characteristics suitable for reflecting the polarizing film are exhibited.

Specifically, the polyester containing a 2,6-naphthalenedicarboxylic acid component is preferably a monomer component of 90 mol% or more of 2,6-naphthalene dicarboxylic acid as a monomer component based on all repeating units of the polyester. The crystalline polyester obtained by the polycondensation is more preferably a content of the 2,6-naphthalenedicarboxylic acid component of 95 mol% or more. The crystalline polyester herein means a polyester having a melting point.

As the polyester, specifically, it is polyethylene 2,6-naphthalenedicarboxylic acid ethylene glycol, poly 2,6-naphthalenedicarboxylic acid butyl diester, poly 2,6-naphthalenedicarboxylic acid propylene glycol or Copolymer. The main repeating unit is preferably a polyester composed of ethylene 2,6-naphthalenedicarboxylate.

In the polyester, in order to maintain the alignment state in an ideal state, it is preferably polyethylene-2,6-naphthalenedicarboxylic acid ethylene glycol, or based on all repeating units of the polyester, 2 mol% or more and 5 mol. 6,6'-(Exoethyldioxy)di-2-naphthoic acid, 6,6'-(trimethylenedioxy)di-2-naphthoic acid or 6, as an acid component 6'-(butylene dioxy)di-2-naphthoic acid is a copolymerized polyethylene-2,6-naphthalenedicarboxylate or the like. As for other copolymerization components, fats such as other aromatic carboxylic acids such as isophthalic acid and 2,7-naphthalenedicarboxylic acid, adipic acid, pimelic acid, suberic acid, and stilbene dicarboxylic acid are listed. An acid component such as an alicyclic dicarboxylic acid such as a dicarboxylic acid or a cyclohexanedicarboxylic acid; an aliphatic diol such as butanediol or hexanediol; or an alicyclic diol such as cyclohexanedimethanol; Alcohol content.

The thickness of each layer constituting the first layer is 0.01 μm or more and 0.5 μm or less. This layer thickness can be obtained by photographing using a transmission electron microscope and based on a photograph. Each of the layers constituting the first layer exhibits reflection performance by light interference between layers in a wavelength region of 400 to 800 nm by having a layer thickness in the range. When the layer thickness of the first layer exceeds 0.5 μm, the reflection band is in the infrared region, and the usability as a reflective polarizing film cannot be obtained. On the other hand, when the layer thickness is less than 0.01 μm, the polyester component absorbs light and cannot obtain reflection performance.

Further, in the uniaxial stretching direction (X direction) of the film, in the direction perpendicular to the uniaxial stretching direction (Y direction) and the film thickness direction (Z direction) in the film plane, the Y-direction and the Z-direction refraction of the first layer The rate difference requirement is 0.1 or more.

Here, the refractive index in the Y direction of the first layer and the refractive index in the Z direction are formed by stretching the polyester constituting the first layer separately and extruding from the die, and stretching at 135 ° C in a uniaxial direction. The Y direction and the Z direction of the film obtained by the uniaxially stretched film were measured by a value of a refractive index at a wavelength of 633 nm measured by a 稜鏡 coupler manufactured by Metricon.

A polyester containing birefringence 2,6-naphthalene dicarboxylic acid is used as the first layer, and the refractive index difference between the Y direction and the Z direction of the first layer is large, and the average refractive index is 1.60 or more and 1.65 by using Hereinafter, a negative optical anisotropic or isotropic thermoplastic resin is used as the second layer, so that the refractive index difference between the first layer and the second layer in the Y direction in the film surface is small, and the Y direction is included. Among the polarized components parallel to the incident surface, the polarized light incident from the vertical direction (incident polarization at an incident angle of 0 degrees) and the incident polarized light at an angle close to the vertical direction achieve high transmission performance.

On the other hand, when the incident angle of the incident light is deflected in the incident surface including the Y direction, it is affected not only by the interlayer refractive index difference in the Y direction but also by the interlayer refractive index difference in the X direction and the interlayer refractive index in the Z direction. The influence of the rate difference causes the interlayer refractive index difference at the time of oblique incidence to become large. Therefore, the present invention is characterized in that high-reflection performance is obtained for polarized light incident obliquely in the polarizing component including the incident surface in the Y direction, and the oblique incident light can be effectively reused to greatly increase the front luminance. .

In order to improve the reflection performance of the oblique polarization, it is effective to make the thickness of the first layer thicker than the thickness of the second layer depending on the type of the resin.

The method of making the refractive index difference between the Y direction and the Z direction of the first layer 0.1 or more is exemplified by using a polyester having a birefringence 2,6-naphthalenedicarboxylic acid component in the first layer, in the film. A method of extending a film within the range described in the manufacturing method.

[Second floor]

The second layer of the present invention is a layer having a thickness of 0.01 μm or more and 0.5 μm or less of a thermoplastic resin as a constituent component, and the thermoplastic resin has an average refractive index of 1.60 or more and 1.65 or less, and is negative optical anisotropy or isotropic. Sex resin.

By using a negative refractive resin or an isotropic resin having the above refractive index characteristics as the thermoplastic resin constituting the second layer, the following mechanism is employed to exhibit parallel polarization of the incident surface including the Y direction. The function of reflecting the polarized component incident from the oblique direction of the film.

First, when a negative optical anisotropic resin having an average refractive index of 1.60 or more and 1.65 or less is used as the second layer, the refractive index in the extending direction (X direction) is made larger than the average refractive index before stretching by performing uniaxial stretching. Small, so that the refractive index in the direction perpendicular to the direction in which the uniaxial direction extends (Y direction) and the thickness direction of the film (Z direction) becomes larger than the average refractive index before stretching, and the so-called negative optical anisotropy is exhibited. . When the thermoplastic resin exhibiting the negative optical anisotropy is uniaxially stretched, the refractive index of the second layer is larger in the Y direction and the Z direction than in the X direction.

By using a polyester containing 2,6-naphthalene dicarboxylic acid as the first layer, and using the optically anisotropic resin having a negative average refractive index as the second layer, the first layer and the second layer in the X direction can be increased. The difference in refractive index between the layers of the layer reduces the difference in refractive index between the first layer and the second layer in the Y direction. Further, the difference in refractive index between the layers of the first layer and the second layer in the Z direction also increases due to the characteristics of the first layer. When these resins are combined, in particular, the difference in the refractive index between the layers in the X direction is increased.

Therefore, in the P-polarized light incident in the oblique direction among the parallel polarized lights including the incident surface in the Y direction, high reflectance is obtained by affecting the interlayer refractive index difference in all of the X direction, the Y direction, and the Z direction as described above, Therefore, the reflected light of the oblique incident polarized light can be effectively reused, and the front luminance is greatly improved.

Further, when an isotropic resin having an average refractive index of 1.60 or more and 1.65 or less is used as the second layer, the second layer has a refractive index characteristic in which the refractive index difference in the X direction, the Y direction, and the Z direction after uniaxial stretching is small. In the present invention, the isotropic property specifically means that the difference between the average refractive index before stretching and the refractive index in the X direction, the Y direction, and the Z direction after stretching is 0.05 or less in all three directions, or the X direction after stretching, The refractive index difference between the Y direction and the Z direction is 0.05 or less.

By using the isotropic resin having the refractive index characteristic in the second layer and using the polyester containing the above-mentioned 2,6-naphthalenedicarboxylic acid component as the resin of the first layer, the number in the X direction can be simultaneously increased. The difference in refractive index between the layers of one layer and the second layer and the difference in refractive index between the layers of the first layer and the second layer in the Z direction, and the difference in refractive index between the layers of the first layer and the second layer in the Y direction is reduced. According to this, in addition to the function of the reflective polarizing film which selectively reflects the polarized light in a specific direction, the reflection performance of the P-polarized light incident in the oblique direction can be obtained. Further, when the isotropic resin is used as the second layer, the difference in the refractive index between the layers in the X direction is smaller than that in the case where a negative optical anisotropic resin is used, but since the reflection performance of the P-polarized light in the oblique direction is exhibited, the first It is more effective that the thickness of the layer is thicker than the second layer. The influence of the refractive index characteristics of the first layer can be improved by making the first layer having a high surface orientation in the extending direction relatively thicker than the second layer.

Further, the average refractive index before stretching is such that the thermoplastic resin constituting the second layer is separately melted, extruded from the nozzle to form an unstretched film, and the refractive index of the obtained film in the X direction, the Y direction, and the Z direction. The 稜鏡 coupling made by Metricon was used to measure at a wavelength of 633 nm, and the average value of these was defined as the average refractive index.

Further, the refractive index in the X direction, the Y direction, and the Z direction after the extension of the second layer is such that the thermoplastic resin constituting the second layer is separately melted and extruded from the die, and is five times in the uniaxial direction at 135 ° C. The film was stretched to form a uniaxially stretched film, and the refractive index of the film was measured at a wavelength of 633 nm using a 稜鏡 coupling made by Metricon in the X direction, the Y direction, and the Z direction of the obtained film.

The average refractive index of the thermoplastic resin used in the second layer is preferably 1.61 or more and 1.64 or less, more preferably 1.62 or more and 1.63 or less. In the above resin, the Y-direction refraction of the first layer and the second layer after the uniaxial stretching is used. The resin having a close ratio is preferably a resin having a refractive index difference of 0.1 or less in the Y direction, more preferably 0.05 or less.

(negative optical anisotropic resin)

The optically anisotropic resin having an average refractive index in the above range is exemplified by syndiotactic polystyrene resin, polymethyl methacrylate, maleic anhydride modified polystyrene, ruthenium modified polycarbonate, and the like. . Among them, a syndiotactic polystyrene resin is preferable in consideration of the refractive index in each direction due to elongation.

The syndiotactic polystyrene resin has a three-dimensional structure, which is a three-dimensional structure in which a phenyl group or a substituted phenyl group of a side chain is located in a mutually opposite direction with respect to a main chain formed of a carbon-carbon bond. The stereotacticity is quantified by nuclear magnetic resonance using isotope carbon. The stereoregularity measured by the method may be a ratio of the existence of a plurality of constituent units, for example, diad in two cases, triad in three cases, and five-part in five times, but In the invention, the polystyrene-based resin is exemplified by a racemic diad of 75% or more, preferably 85% or more, or a racemic pentad of 30% or more, preferably More than 50% of polystyrene polystyrene, polyalkylstyrene, polyhalogenated styrene, polyalkoxystyrene, polyvinylbenzoic acid, or such hydrogenated polymers and copolymerization thereof Things.

The polystyrene resin having such a syndiotactic structure in the present invention is collectively referred to as a syndiotactic polystyrene resin.

Among these, it is preferred that the polystyrene-based resin has a melting point of 220 to 270 ° C, more preferably 240 to 270 ° C.

Further, a copolymer may be used as the syndiotactic polystyrene resin, and a copolymer of syndiotactic polystyrene and p-methylstyrene is preferred. Wherein, the melting point of the syndiotactic polystyrene homopolymer is 270 ° C, and the melting point can be adjusted by adjusting the copolymerization amount of p-methyl styrene, but the melting point is decreased when the p-methyl styrene is large, and the crystallinity is also decline. The amount of the copolymerization is preferably in the range of 20 mol% or less. When the melting point is lower than 220 ° C, the crystallinity of the polystyrene-based resin is too low, and it is difficult to form a film, and heat resistance (change in dimensionality upon heat treatment) is lowered.

The second layer made of the syndiotactic polystyrene resin may be added with inert particles in a range where the optical properties are not deteriorated, but it is preferred that the inert particles are not substantially contained.

Atactic polystyrene or isotactic polystyrene has low crystallinity and is difficult to form a film, and since it has no crystal structure or a loose structure, heat resistance is poor.

The polyester containing a 2,6-naphthalene dicarboxylic acid component increases the refractive index in the extending direction by stretching, but the syndiotactic polystyrene resin exhibits a negative optical anisotropy, so the refractive index in the extending direction is rather decreased. The difference in refractive index between the two layers in the X direction can be increased.

Further, the difference between the melting point of the layer (the first layer) composed of the polyester containing 2,6-naphthalenedicarboxylic acid and the layer (the second layer) of the negative optical anisotropic resin of the present invention is preferably Within 30 °C. When the difference is more than 30 ° C, after the melt lamination, when the unstretched sheet is formed by curing, peeling between the layers may occur, and peeling may occur at the time of subsequent stretching.

(Isotropic resin)

The isotropic resin having an average refractive index in the above range is a thermoplastic resin having the refractive index property, and is not particularly limited as long as it does not exhibit birefringence after stretching, and is exemplified by, for example, polyester, polycarbonate, or acrylic resin. Wait. Among them, from the viewpoint of interlayer adhesion or elongation, it is preferred to copolymerize polyalkylene naphthalate.

The copolymerized polynaphthalene dicarboxylate diester is exemplified by at least 30 mol% or more and 70 mol% or less of the terephthalic acid component or the isophthalic acid component based on the total repeating unit. A copolymerized polyethylene naphthalate or a copolymerized polybutylene naphthalate, copolymerized by one component. Further, the copolymerized polyethylene naphthalate is preferably used as the second layer from the viewpoint of the film forming property or the interlayer adhesion of the first layer. The copolymerization amount of the copolymerized polyester is more preferably from 40 mol% to 65 mol%.

(thickness of each layer of the second layer)

The thickness of each layer constituting the second layer is 0.01 μm or more and 0.5 μm or less. This layer thickness can be photographed using a transmission electron microscope and determined based on photographs. By having the layers constituting the second layer have a layer thickness in the range, the reflection performance is exhibited by the light interference between the layers in the wavelength region of 400 to 800 nm. When the layer thickness of the second layer exceeds 0.5 μm, the reflection band becomes an infrared region, and the usability as a reflective polarizing film cannot be obtained. On the other hand, when the layer thickness is less than 0.01 μm, the polyester component absorbs light and cannot obtain reflection performance.

[particle]

The uniaxially stretched multi-layer laminated film of the present invention may have a roll-up property of the film in a range satisfying the reflectance characteristic, and may also contain 0.001% by weight to 0.5% by weight based on the weight of the layer on at least one outermost layer. % of inert particles having an average particle diameter of from 0.01 μm to 2 μm. When the inert particles are added, the average particle diameter of the inert particles is preferably 0.02 μm to 1 μm, preferably 0.1 μm to 0.3 μm. Further, the content of the inert particles is preferably in the range of 0.02% by weight to 0.2% by weight.

The inert particles contained in the uniaxially stretched multilayer laminated film are exemplified by inorganic inert particles such as cerium oxide, aluminum oxide, calcium carbonate, calcium phosphate, kaolin, talc, argon, crosslinked polystyrene, and benzene. Organic inert particles of an ethylene-divinylbenzene copolymer. The shape of the particles is not particularly limited as long as it is a generally used shape such as agglomerated shape or a spherical shape.

Further, if the range of the reflectance characteristics is satisfied, the outermost layer may be included in the layer composed of the same resin as the outermost layer, and may be contained in the first layer or the second layer, for example. In the first floor. Alternatively, another layer different from the first layer and the second layer may be provided as the outermost layer.

In order to achieve better optical properties, it is preferred that the first layer and the second layer do not contain particles. By not including particles in the film, the transmittance of P-polarized light incident at an incident angle of 0° can be improved, and the average reflectance for the wavelength of the P-polarized light of 400 to 800 nm can be further reduced, and the front luminance can be further improved.

[Layered composition] (laminal number)

The uniaxially stretched multilayer laminated film of the present invention is obtained by laminating 251 layers or more of the first layer and the second layer. The number of laminations of the uniaxially stretched multilayer laminated film is preferably 301 or more, more preferably 401 or more, still more preferably 501 or more, and most preferably 551 or more. When the number of laminations is less than the lower limit, the average reflectance characteristic of the polarizing component (S-polarized light) perpendicular to the incident surface including the non-extension direction (Y direction) cannot satisfy a certain average of the entire wavelength of 400 to 800 nm. Reflectivity. At the same time, when the number of laminations does not reach the lower limit value, the average reflectance characteristic of the incident angle of 50 degrees with respect to the polarization component (P-polarized light) having parallel incident planes in the non-extension direction (Y direction) cannot satisfy the entire wavelength. A certain average reflectance of 400 to 800 nm.

The upper limit of the number of laminations is preferably 2001 in terms of productivity and rationality of the film. The upper limit of the number of laminations is such that, in view of the average reflectance characteristics of the present invention, the number of laminations can be further reduced from the viewpoint of productivity or handleability, and for example, it can be 1001 layers or 801 layers.

(average layer thickness ratio of the first layer to the second layer)

When the above-mentioned isotropic resin is used as the thermoplastic resin constituting the second layer, in addition to the refractive index characteristics of the respective directions due to the resin, the ratio of the average layer thickness of the first layer to the average layer thickness of the second layer (the The average layer thickness of one layer/the average layer thickness of the second layer) affects the reflection characteristics of the obliquely incident polarized component of the P-polarized light having parallel incident planes in the Y direction, by making the average layer of the first layer The thickness is thicker than the average layer thickness of the second layer, and the reflection of the incident polarized light in the oblique direction can be effectively reused, which can effectively improve the front brightness.

When the ratio of the average layer thickness of the first layer to the average layer thickness of the second layer (the average layer thickness of the first layer / the average layer thickness of the second layer) is in the range of 0.5 or more and 5.0 or less, 150% or more can be obtained. The front brightness improvement rate is good, but in order to obtain a front brightness improvement rate of 160% or more, the layer thickness is preferably 1.2 or more and 5.0 or less. Further, the upper limit of the layer thickness ratio is preferably 4.0, more preferably 3.5.

When the ratio of the average layer thickness of the first layer to the average layer thickness of the second layer (the average layer thickness of the first layer/the average layer thickness of the second layer) exceeds the upper limit value, the light interference between the layers is lowered, and S-polarized light cannot be ensured. Full reflection characteristics. When the ratio of the thickness of the layer does not reach the lower limit value, the reuse of the oblique incident light in the P-polarized light becomes insufficient, and the front luminance cannot be greatly improved.

When the negative optical anisotropic resin is used as the thermoplastic resin constituting the second layer, the reflectance of the resin is increased by the refractive index characteristic of the resin, and the reflectance of the obliquely incident light to the P-polarized light is applied to the first layer and the second layer. The relationship of the average layer thickness is not particularly specified, but the layer thickness ratio (the average layer thickness of the first layer/the average layer thickness of the second layer) is preferably in the range of 0.1 or more and 5.0 or less. By making the layer thickness ratio fall within this range, a substantial increase in frontal brightness is obtained.

Further, when a negative optical anisotropic resin is used, the layer thickness ratio (average layer thickness of the first layer / average layer thickness of the second layer) is preferably in the range of 0.2 or more and 3.0 or less, more preferably 0.3 or more and 3.0 or less. The range is preferably 0.5 or more and 2.0 or less, and more preferably 0.7 or more and 1.5 or less. When the thickness ratio of the layer is in the range of 0.2 or more and 3.0 or less, the hue deviation is large, and when the film is used as the brightness improving film of the liquid crystal display, the reproducibility of the image is lacking, and the visibility is lowered.

(the ratio of the maximum layer thickness to the minimum layer thickness)

The multilayer laminated film generally determines the wavelength of reflection depending on the refractive index, the number of layers, and the thickness of the layer, but the layers of the first layer and the second layer which are laminated have a certain thickness and can only reflect only a specific wavelength. Therefore, the uniaxially stretched multi-layer laminated film of the present invention can increase the visible light at a wavelength of 400 to 800 nm by setting the ratio of the maximum layer thickness to the minimum layer thickness of each of the first layer and the second layer to be 2.0 or more and 5.0 or less. Reflective properties throughout the region.

The lower limit of the ratio of the maximum layer thickness to the minimum layer thickness of each of the first layer and the second layer layer is preferably 2.1, and the upper limit value is preferably 4.0, more preferably 3.5, more preferably 3.0, and the first layer is When the ratio of the maximum thickness to the minimum thickness of each layer of the second layer is less than the lower limit, the reflection of the S-polarized light and the reflection characteristic of the oblique direction of the P-polarized light cannot be obtained in the entire wavelength range of 400 to 800 nm. characteristic. On the other hand, when the ratio of the maximum thickness to the minimum thickness of the first layer and the second layer exceeds the upper limit, the reflection band is too wide, and the average reflectance in the wavelength region of 400 to 800 nm is lowered, so that the target cannot be obtained. Reflection characteristics.

The maximum layer thickness and the minimum layer thickness of each of the first layer and the second layer can be photographed by a transmission electron microscope and determined based on photographs.

Moreover, the first layer and the second layer may be changed stepwise or continuously.

As a method of obtaining the thickness characteristic of the layer, for example, when the first layer resin and the second layer resin are alternately laminated, a multi-layer feed block device is used to continuously change the thickness of the flow path of the feed tube. . Further, the method of gradual change is exemplified by laminating a layer of uniform thickness by a multi-layer feeding tube device, then laminating a layer of uniform thickness composed of different layer thicknesses, and further laminating the laminated fluids to make the layer thickness The method of phase change. An example of a stepwise change in layer thickness is exemplified by a layer varying in a ratio of 1.0:1.3:2.0.

Further, a method of laminating the above-mentioned multilayered fluids perpendicular to the surface and re-layering 251 layers or more may be used, and for example, a method of increasing the number of laminations by three branches may be exemplified.

(other layers)

In addition to the first layer and the second layer, the uniaxially stretched multi-layer laminated film of the present invention may have a thick film layer of more than 0.5 μm in the surface layer or the intermediate layer of the laminated film. By having the thick layer in one of the first layer and the second layer alternately laminating, the thickness of each layer constituting the first layer and the second layer can be easily adjusted to be uniform without affecting the polarizing function. The thick layer may be the same composition as any of the first layer and the second layer, or may partially comprise the composition of the components. Since the layer thickness is thick, it does not contribute to the reflective property. On the other hand, since the polarized light is transmitted, the layer is preferably free of particles.

(membrane thickness)

The film thickness of the uniaxially stretched multilayer laminated film of the present invention is preferably 15 μm or more and 150 μm or less, more preferably 30 μm or more and 100 μm or less.

[Single-axis stretch film]

The uniaxially stretched multilayer laminated film of the present invention is formed to extend at least on a single axis in order to satisfy the optical characteristics of the target reflective polarizing film. The uniaxial stretching in the present invention includes, in addition to the film extending only in the uniaxial direction, a film extending in one direction in the film extending in the biaxial direction. The uniaxial stretching direction (X direction) may be any one of the longitudinal direction and the width direction of the film. Further, in the film extending in one direction in the film extending in the biaxial direction, the direction in which the film is extended again (the X direction) may be any one of the longitudinal direction and the width direction of the film, and the direction in which the stretching ratio is low is limited to the stretching ratio of 1.05. When it is about 1.20 times, it is preferable in terms of improving the polarizing performance. In the case of a film extending in one direction extending in the biaxial direction, the so-called "extension direction" in relation to the polarization or the refractive index means the direction of re-expansion.

The stretching method may use a conventional stretching method such as heating extension by a rod heater, roll heating extension, tenter stretching, etc., but it is preferable from the viewpoint of reducing the hiccup or the stretching speed caused by contact with the roller. The tenter extends.

[reflection characteristics]

The uniaxially stretched multi-layer laminated film of the present invention has a film surface as a reflecting surface, and the incident polarizing light having an incident angle of 0 degrees and 50 degrees in a polarizing component (S-polarized light) perpendicular to an incident surface including the Y direction. The average reflectance of the wavelength of 400 to 800 nm (may be referred to as an average reflectance at an incident angle of 0 degrees, and an average reflectance at an incident angle of 50 degrees, respectively) is 90% or more.

Further, in the polarizing component (P-polarized light) in which the film surface is used as the reflecting surface in parallel with the incident surface including the Y direction, the average reflectance of the incident polarized light having an incident angle of 0 degrees is 400 to 800 nm (sometimes The average reflectance at an incident angle of 0 degrees is 15% or less, and the average reflectance at a wavelength of 400 to 800 nm of the incident polarized light at an incident angle of 50 degrees (sometimes referred to as an average reflectance at an incident angle of 50 degrees). ) is 20% or more.

In the S-polarized component, the average reflectance of the incident polarized light at an incident angle of 0 degrees and 50 degrees is preferably from 95% to 100%, more preferably from 98% to 100%.

When the average reflectance in the S-polarized component is less than the lower limit, the polarized reflection performance as the reflective polarizing film is insufficient, and sufficient performance as a brightness-enhancing film such as a liquid crystal display cannot be exhibited.

In order to obtain the reflectance characteristics of the S-polarized component, in addition to the thickness of each layer and the number of laminations, the refractive index difference between the first layer and the second layer in the film extending direction (X direction) is increased, and is preferably 0.15. the above. Specifically, the method of using the resin for the first layer and the resin for the second layer in the present invention to extend in a certain range in the X direction to increase the birefringence of the first layer is exemplified. Further, in order to increase the reflectance in a wide wavelength range of 400 to 800 nm, a method of setting the ratio of the maximum layer thickness to the minimum layer thickness in the above range is exemplified.

In the P-polarized component, the average reflectance at a wavelength of 400 to 800 nm of the incident polarized light at an incident angle of 0 degrees is preferably 13% or less, more preferably 5% or more and 13% or less.

Further, in the P-polarized component, when the average optical reflectance of the incident polarized light having an incident angle of 50 degrees is 400 to 800 nm, when the negative optical anisotropic resin of the present invention is used as the resin of the second layer, it is preferably 50% or more, more preferably 70% or more and 100% or less, and more preferably 80% or more and 99% or less. When the isotropic resin of the present invention is used as the resin of the second layer, the average reflectance of the wavelength of the incident polarized light of 400 to 800 nm at an incident angle of 50 degrees is preferably 20% or more and 50% or less. More preferably 25% or more and 40% or less.

In the P-polarized component, the average reflectance at an incident angle of 0 degrees is suppressed in the range, and on the other hand, the average reflectance at an incident angle of 50 degrees is higher than the average reflectance at 0 degrees, by falling within the above range. The P-polarized component incident from the oblique direction can be reflected to the light source side and reused, so that the brightness improvement performance of the film can be improved higher than the conventional brightness.

In the P-polarized component, when the average reflectance of the incident polarized light having an incident angle of 0 to 400 nm and 800 nm exceeds the upper limit value, the polarized light transmittance of the reflective polarizing film is lowered, so that the brightness of the liquid crystal display or the like cannot be exhibited. The full performance of the film. On the other hand, when the average reflectance of the P-polarized component at a wavelength of 400 to 800 nm of the incident polarized light having an incident angle of 50 degrees does not reach the lower limit value, most of the P-polarized component incident from the oblique direction directly passes through the film. Since the polarized light reflected to the light source side is reduced, the reuse efficiency of the P-polarized light is insufficient, and the front luminance improvement performance of the conventional reflective polarizing film cannot be achieved.

In order to obtain the reflectance characteristics of the P-polarized component, in addition to the thickness of each layer and the number of laminations, the difference in the refractive index difference between the layers in the X direction and the interlayer in the Z direction is increased as described above, so that the interlayer in the Y direction is formed. The refractive index difference is preferably 0.02 or less, and the ratio of the average layer thickness of the first layer to the average layer thickness of the second layer is in a predetermined range depending on the kind of the resin.

Further, in order to increase the reflectance of the P-polarized light incident obliquely in the entire wide wavelength range of the wavelength of 400 to 800 nm, a method of setting the ratio of the maximum layer thickness to the minimum layer thickness within the above range is exemplified.

The uniaxially-stretched multilayer laminated film of the present invention preferably has a difference between a maximum reflectance and a minimum reflectance in each of wavelengths of 400 to 800 nm in the S-polarized component of 10% or less, and a wavelength of 400 to 800 nm in the P-polarized component. The difference between the maximum reflectance and the minimum reflectance at each wavelength is also within 10%. When the difference between the maximum reflectance and the minimum reflectance of each of the above-described polarizing components is 10% or more, there is a problem in that it is used in a liquid crystal display or the like due to a hue deviation of reflected or transmitted light.

[Crystal alignment]

The uniaxially stretched multilayer laminated film of the present invention preferably has a crystal orientation in the thickness direction of the film of -0.30 or more and 0.05 or less, more preferably -0.10 or more and 0.00 or less. The larger the value of the crystal orientation in the thickness direction of the film, the smaller the surface alignment property and the higher the uniaxial alignment property. When the crystal orientation exceeds the upper limit, the uniaxial alignment property is too strong, and the refractive index characteristics of the respective sides cannot be simultaneously satisfied. On the other hand, when the crystal alignment degree is less than the lower limit value, the surface alignment becomes excessive and biaxial alignment property occurs, so that the polarized reflection characteristics of the present invention cannot be obtained.

In the present invention, the crystal orientation in the thickness direction of the film is determined by the crystal orientation of the polyester resin mainly constituting the first layer, and the crystal structure of the film using the X-ray diffraction device is parallel to the naphthalene ring. The crystal orientation index <cos ² Φ _{010 , ND} > in the thickness direction (ND) of the plane (110 surface) and the crystal plane (010 surface) which is a plane perpendicular to the direction of the molecular chain (206 surface), and The crystal orientation degree f _{010, ND} obtained by the following formula (1) is represented _{by ND} .

[Manufacturing method of uniaxially stretched multilayer laminated film]

Next, a method of producing the uniaxially stretched multilayer laminated film of the present invention will be described in detail.

The uniaxially stretched multilayer laminated film of the present invention is a polyester comprising 2,6-naphthalenedicarboxylic acid (for the first layer) and a thermoplastic resin exhibiting the refractive index characteristics of the second layer of the present invention (second layer) It is extruded in a molten state with at least 251 layers superposed on each other to form a multilayer unstretched film (step of being a sheet). In this case, the laminate of 251 or more layers is laminated so that the thickness stepwise or continuous of each layer is changed in the range of 2.0 times to 5.0 times.

The multilayer unstretched film thus obtained is stretched in at least a uniaxial direction (direction along the film surface) in the film forming direction or the width direction perpendicular thereto (X direction). The elongation temperature is preferably in the range of the glass transition point temperature (Tg) to Tg + 50 ° C of the polyester of the first layer. The stretching ratio at this time is preferably from 2 to 10 times, more preferably from 2.5 to 7 times, still more preferably from 3 to 6 times, and most preferably from 4.5 to 5.5 times. When the stretching ratio is large, the surface direction deviation of each of the first layer and the second layer is reduced by thinning due to stretching, and the light interference of the extended multilayer laminated film becomes uniform in the plane direction, so that it is preferable. Further, the difference in refractive index between the extending direction of the first layer and the second layer and the difference in refractive index in the thickness direction are preferably increased. The extension method at this time may use a conventional extension method such as heating extension by a rod heater, roll heating extension, tenter extension, etc., but from the viewpoint of reducing the kiss mark or the extension speed caused by contact with the roller, It is preferred to extend the tenter. Further, the stretching treatment is also applied in a direction (Y direction) perpendicular to the extending direction, and when biaxial stretching is performed, the stretching ratio is preferably limited to about 1.05 to 1.20 times. When the stretching ratio in the Y direction is higher than the above, the polarizing performance may be lowered. Further, after the stretching, it is preferably further subjected to heat setting treatment.

[Brightness Enhancement Film]

In the uniaxially-stretched multilayer laminated film of the present invention, since the S-polarized component is selectively and highly reflective, the light in the vicinity of the incident angle of 0 degrees in the P-polarized component perpendicular to the S-polarized component is selectively transmitted through the light, and is inclined. Since the P-polarized component incident in the direction is reflected, the S-polarized component and the P-polarized component which are reflected can be reused by using the brightness enhancement film as a liquid crystal display, and a part of the P-polarized light can be reused to obtain the front luminance. More substantial than ever.

Further, by providing the multilayer laminated film itself with this function, the front side brightness improvement and the viewing angle control of the liquid crystal display are improved by combining the brightness enhancement film and the enamel sheet formed by the multilayer laminated film. By using the multilayer laminated film of the present invention, the functions of the conventional brightness improving film and the second member can be integrated, and on the other hand, the member can be reduced in light efficiency, and the power consumption of the liquid crystal display can be reduced.

[Uniaxially stretched multilayer laminated film laminate]

When the uniaxially stretched multilayer laminated film of the present invention is used as a brightness improving film such as a liquid crystal display, heat resistance thermoplasticity can be laminated on at least one side of the uniaxially stretched multilayer laminated film of the present invention from the viewpoint of ensuring planarity. Resin film.

The resin constituting the heat-resistant thermoplastic resin film is not particularly limited, and examples thereof include a polyester resin, a polycarbonate resin, an acrylic resin, and a polyamide resin. Among them, a polycarbonate resin is preferred from the viewpoint of transparency and heat resistance. A polymer material generally referred to as polycarbonate, although it is generally referred to as a polycondensation reaction in its synthesis method, and the main chain is bonded by a carbonic acid bond, but generally also means a phenol derivative and carbon ruthenium, A polycondensation product such as diphenyl carbonate. In general, a 2,2-bis(4-hydroxyphenyl)propane called bisphenol A is preferably selected as the polycarbonate of the bisphenol component, but a polycarbonate can be formed by selecting various bisphenol derivatives as appropriate. Copolymer.

The copolymerization component may be exemplified by bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)cyclohexane, and 9,9-bis(4-hydroxyl) in addition to the bisphenol A. Phenyl) fluorene, 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane, 2,2-bis(4-hydroxy-3-methylphenyl)propane, 2,2-bis(4-hydroxyphenyl)-2-phenylethane, 2,2-bis(4-hydroxyphenyl)-1,1,1,3,3,3-hexafluoropropane, double (4-Hydroxyphenyl)diphenylmethane, bis(4-hydroxyphenyl) sulfide, bis(4-hydroxyphenyl)fluorene, and the like.

The proportion of the copolymerization component is preferably from 2 to 20 mol%, more preferably from 5 to 10 mol%, based on the total repeating unit of the polycarbonate copolymer.

The polycarbonate resin used herein preferably has a viscosity average molecular weight of 10,000 or more and 200,000 or less. When the viscosity average molecular weight is less than 10,000, the mechanical strength of the obtained film is insufficient, and when the high molecular weight is 200,000 or more, the viscosity of the dopant is too large, and there is a lack of workability.

A method of laminating a heat-resistant thermoplastic resin film on at least one side of a uniaxially stretched multilayer laminated film, and applying an adhesive layer on one surface of a heat-resistant thermoplastic resin film such as a roll coater, and then attaching it at room temperature A method of stretching a multi-layer laminated film by uniaxially, applying a heat-sealing layer on one side of a heat-resistant thermoplastic resin film, heating and pressing it by a laminator or the like, and one side of a heat-resistant thermoplastic resin film A suitable conventional technique such as a method in which an ultraviolet curable resin is applied and then irradiated with ultraviolet rays.

Example

The invention is further illustrated by the examples. Further, the physical properties or characteristics in the examples were measured or evaluated by the following methods.

(1) Melting point of resin and film (Tm)

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

(2) Specificity of the resin and the specificity of the copolymerized component and the amount of each component

The respective resin components, the copolymerization components, and the respective component amounts were determined by ¹ H-NMR measurement for each layer of the film sample.

(3) Thickness of each layer

The film sample was cut into a film having a length of 2 mm and a width of 2 cm, and was fixed in an embedding capsule, and then embedded in an epoxy resin (EPOMOUNT manufactured by REFINETEC Co., Ltd.). The encapsulated sample was vertically cut in the width direction by MICROTOME (ULTRACUT UCT manufactured by LEICA) to form a 5 nm thick film slice. The transmission was observed at an acceleration voltage of 100 kV using a transmission electron microscope (Hitachi S-4300), and the thickness of each layer was measured from the photograph.

And, based on the thicknesses of the obtained layers, the ratio of the maximum layer thickness to the minimum layer thickness in the first layer, and the ratio of the thickness of the largest layer in the second layer to the thickness of the minimum layer, respectively.

Further, the average layer thickness of the first layer and the average layer thickness of the second layer were determined based on the thicknesses of the obtained layers, and the average layer thickness of the first layer and the average layer thickness of the second layer were calculated.

Further, when an adjustment layer having a thickness exceeding 0.5 μm exists in the outermost layer or the interactive laminate layer, it is excluded from the first layer and the second layer.

(4) Overall thickness of the film

The film sample was placed in a rotor detector (K107C manufactured by Anritsu Electric Co., Ltd.), and a digital differential electronic micrometer (K351 manufactured by Anritsu Electric Co., Ltd.) was used to measure the thickness of 10 points at different positions, and the average value was obtained. membrane thickness.

(5) Refractive index before and after extension in all directions

Each of the resins constituting each layer was separately melted and extruded from a die, and cast on a casting drum to obtain an unstretched film. Further, the obtained unstretched film was then stretched five times in the uniaxial direction at 135 ° C to prepare a stretched film. Using the obtained unstretched film and the stretched film, Metricon is used for each refractive index (n _x , n _Y , n _Z ) in the extending direction (X direction), the vertical direction (Y direction), and the thickness direction (Z direction). The produced tantalum coupler was measured at a wavelength of 633 nm, and the refractive index before stretching and the refractive index after stretching were obtained.

The average refractive index before extension of each layer is obtained by averaging the refractive indices in the three directions before stretching. Further, the average refractive index after stretching of each layer is obtained by averaging the refractive indices in the three directions after stretching.

(6) Reflectance, reflection wavelength

A spectrophotometer (manufactured by Shimadzu Corporation, MPC-3100) was used, and a polarizing filter was attached to the light source side to measure the total light reflectance with respect to the integrating sphere at each wavelength in a wavelength range of 400 nm to 800 nm. In this case, the measured value when the transmission axis of the polarizing filter is aligned with the non-extension direction (Y direction) of the film is referred to as "polarized light (P-polarized light) in parallel with the incident surface including the Y direction", The measured value when the transmission axis of the polarizing filter is arranged perpendicular to the non-extension direction of the film is referred to as "polarized light (S-polarized light) perpendicular to the incident surface of the Y-containing direction".

Among the polarizing components, an average value was obtained based on reflectance data in the range of 400 to 800 nm as an average reflectance. Further, the measurement of the incident angle of 0 degrees is such that the light source is placed perpendicular to the film surface, and the film sample is placed at an incident angle of 50 degrees so that the light source is positioned over the extension of the incident angle. get on.

(7) Crystalline alignment

Using an X-ray diffraction device (ROTAFLEX RINT 2500HL manufactured by Rigaku Motor Co., Ltd.), the crystal orientation index <cos ² Φ _{010, ND} > in the thickness direction ND of the crystal face (010) of the film was obtained, and the following formula (1) was obtained. Crystalline orientation f _{010, ND} .

Further, the crystal orientation in the ND direction was measured using a pole sample stage (multipurpose sample stage manufactured by Rigaku Motor).

(8) Brightness improvement effect

The obtained uniaxially stretched multilayer laminated film is inserted into the LCD panel by taking out the state of the optical film (diffusion film, enamel sheet) in the LCD panel (manufactured by Matsushita Electric Co., Ltd., manufactured by VIERA TH-32LZ80, 2007) as a reference. Between the liquid crystal cell polarizer and the light source, the FPD viewing angle evaluation device (ErgoScope 88) manufactured by Opto Design Co., Ltd. was used to measure the front brightness when white was displayed on the PC, and the insertion of the uniaxially stretched multilayer laminated film was calculated. The rate of increase in front luminance before the multilayer laminated film was evaluated by the following criteria.

AA: The front brightness improvement effect is 180% or more

A: The front brightness improvement effect is 160% or more, less than 180%

B: The front brightness improvement effect is 150% or more, less than 160%

C: The front brightness improvement effect is 140% or more, less than 150%

D: The front brightness improvement effect is less than 140%

(9) Hue

The color is also measured by the measurement method of the front brightness enhancement effect, and the difference between the values of the hue x and y in the front luminance before inserting the sample film and the values of the hue x and y in the front luminance after the sample is inserted is as follows. The baseline is evaluated for hue.

◎: The difference between x and y is less than 0.03

○: The maximum change of x or y is 0.03 or more

×: The maximum change of x and y is 0.03 or more

(10) Endurance evaluation test

The back-coating surface of the heat-diffusing thermoplastic resin film (manufactured by Huihe Co., Ltd.: OPALUS BS-912) pressed on both sides of the obtained uniaxially stretched multilayer laminated film at 140 ° C and 275 kPa for 2 The film was laminated and formed into a laminate film and inserted between the liquid crystal polarizing plate and the light source in an LCD panel (manufactured by Matsushita Electric Co., Ltd., manufactured by VIERA TH-32LZ80, 2007), and the backlight was continuously lit for 3000 hr, and then observed with the naked eye. The appearance of the removed sheet was evaluated based on the following criteria.

◎: The appearance of the film after continuous lighting was not found at all, or the film after continuous lighting was visually recognized to be changed, but the height was not measured up to 0.5 mm.

○: On the film after continuous lighting, a bump of 0.5 mm or more and less than 1 mm in height was observed.

×: A bump of 1 mm or more is seen on the film after continuous lighting

[Example 1]

Poly(ethylene-2,6-naphthalenedicarboxylate) (PEN) having an intrinsic viscosity (o-chlorophenol, 35 ° C) of 0.62 dl/g was used as the polyester for the first layer, and the copolymer was prepared to have a copolymer of 8 mol% - A polystyrene copolymer between methyl styrene is used as the thermoplastic resin for the second layer.

Next, the first layer was dried with polyester at 170 ° C for 5 hours, and the second layer was dried at 100 ° C for 3 hours with a resin, and then supplied to the first and second extruders, and heated to 300 ° C to be in a molten state. The first layer is divided into 276 layers by polyester, and the second layer is divided into 275 layers by resin. The first layer and the second layer are alternately laminated, and the maximum layer thickness and the minimum layer in the first layer and the second layer are respectively The thickness is changed to a maximum/minimum continuous change to 2.2 times, and a multilayer feeding tube device designed to make the average layer thickness of the first layer and the second layer 1.0:1.0 is used, and the die is introduced while maintaining the laminated state. In the casting drum, the first layer and the second layer have an average layer thickness of 1.0:1.0, and the first layer and the second layer are alternately laminated to form a total of 551 layers of the unstretched multilayer laminated film.

The multilayer unstretched film was stretched to 5.2 times in the width direction at a temperature of 135 ° C, and heat-fixed at 150 ° C for 3 seconds. The resulting film had a thickness of 55 μm.

The resin composition of each layer of the obtained uniaxially stretched multilayer laminated film and the characteristics of each layer are shown in Table 1, and the physical properties are shown in Table 2.

[Examples 2 to 4]

The uniaxially stretched multilayer laminated film was obtained by the same operation as in Example 1 except that the resin composition of each layer as shown in Table 1 was changed. The resin composition of each layer of the obtained uniaxially stretched multilayer laminated film and the characteristics of each layer are shown in Table 1, and the physical properties are shown in Table 2.

[Examples 5 and 6]

The uniaxially stretched multilayer laminated film was obtained by the same operation as in Example 1 except that the layer thicknesses of the respective layers as shown in Table 1 were changed. The resin composition of each layer of the obtained uniaxially stretched multilayer laminated film and the characteristics of each layer are shown in Table 1, and the physical properties are shown in Table 2.

[Comparative Examples 1 to 2]

The uniaxially stretched multilayer laminated film was obtained by the same operation as in Example 1 except that the resin composition and the production conditions of the respective layers shown in Table 1 were changed. The resin composition of each layer of the obtained uniaxially stretched multilayer laminated film and the characteristics of each layer are shown in Table 1, and the physical properties are shown in Table 2.

[Embodiment 7]

In the polyethylene 2,6-naphthalenedicarboxylate (PEN) having an intrinsic viscosity (o-chlorophenol, 35 ° C) of 0.62 dl / g, 0.15 wt% of true spherical shape is added based on the weight of the first layer. As the bismuth dioxide particles (average particle diameter: 0.3 μm, ratio of long diameter to short diameter: 1.02, average deviation of particle diameter: 0.1), as the polyester for the first layer, 64% by weight of the intrinsic viscosity is prepared for copolymerization (o. Chlorophenol, 35 ° C) 0.62 dl / g of terephthalic acid poly 2,6-naphthalenedicarboxylate (TA64PEN) as a thermoplastic resin for the second layer.

Then, the polyester for the first layer and the polyester for the second layer were respectively dried at 170 ° C for 5 hours, and then supplied to the first and second extruders, and heated to 300 ° C to be in a molten state, and the first layer was used for polymerization. The ester is divided into 276 layers, and the second layer is divided into 275 layers by resin, and the first layer and the second layer are alternately laminated, and the maximum layer thickness and the minimum layer thickness in the first layer and the second layer are maximized/minimum. Continuously changing to 2.2 times, and using a multi-layer feeding tube device designed to have an average layer thickness of 1.0:0.8 of the first layer and the second layer, is introduced into the nozzle while maintaining the lamination, and is cast on the casting drum. The average layer thickness of the first layer and the second layer is 1.0:0.8, and the first layer and the second layer are alternately laminated to form a total of 551 layers of the unstretched multilayer laminated film.

The multilayer unstretched film was stretched to 5.2 times in the width direction at a temperature of 135 ° C, and heat-fixed at 150 ° C for 3 seconds. The resulting film had a thickness of 55 μm.

The resin composition of each layer of the obtained uniaxially stretched multilayer laminated film, the characteristics of each layer are shown in Table 3, and the physical properties are shown in Table 4.

[Example 8, Comparative Examples 3 to 7]

The uniaxially stretched multilayer laminated film was obtained by the same operation as in Example 1 except that the resin composition, the layer thickness, and the production conditions of the respective layers shown in Table 1 were changed. The resin composition of each layer of the obtained uniaxially stretched multilayer laminated film, the characteristics of each layer are shown in Table 3, and the physical properties are shown in Table 4.

[Effects of the Invention]

The uniaxially-stretched multilayer laminated film of the present invention selectively has a polarizing component having an incident angle from the front direction of the film in the polarization direction of the transmission axis direction, in addition to the high reflection characteristic of the polarization direction in the direction of the reflection axis. Through the function of reflecting the polarized light component obliquely incident from the film, even if the polarized component that is incident on the oblique axis in the oblique direction can be reflected to the light source side and reused, the front luminance is greatly improved.

[Industry possible use]

By providing the multi-layered laminated film itself with the function, the front side brightness improvement and the viewing angle control of the liquid crystal display are performed with respect to the conventional method of improving the film and the enamel by combining the brightness of the multi-layer laminated film. According to the multilayer laminated film of the present invention, the functions of the conventional brightness enhancement film and the second member can be integrated, and on the one hand, the member can be reduced in light efficiency, and the power consumption of the liquid crystal display can be reduced.

Figure 1 is the refractive index of the uniaxial stretching ratio of 2,6-PEN and the direction of extension (X direction) after uniaxial stretching, the direction perpendicular to the extending direction (Y direction), and the thickness direction (Z direction) (respectively expressed as n _X , n _Y , n _Z ).

Fig. 2 is a view showing an example of the reflectance characteristics of the uniaxially-stretched multilayer laminated film of the present invention using a syndiotactic polystyrene resin in the second layer, relating to the film surface as a reflecting surface, and the inclusion of non-extension The incident surface of the direction (Y direction) is a parallel polarizing component (the P-polarized component in the present invention), And a reflectance characteristic of a polarizing component (the S-polarized component in the present invention) which is perpendicular to the incident surface including the non-extension direction (Y direction).

3 is an explanatory view of an incident surface (including an incident surface in the non-extended direction (Y direction)=YZ plane) and an incident angle of FIG. 2, which corresponds to an incident angle of 0 degrees in the Z-axis direction in the incident surface, The incident angle of the angle θ with 0 degrees as the reference in the incident surface.

4 is a view showing only the reflectance characteristics when the incident surface of the uniaxially stretched multilayer laminated film of the present invention using the syndiotactic polystyrene resin in the second layer is changed, in order to change the incident surface to the opposite side. When the extending direction (X direction) is parallel, the reflectance characteristics of the polarizing component (the S-polarized component in FIG. 4) perpendicular to the incident surface and the polarizing component (the P-polarized component in FIG. 4) parallel to the incident surface are shown.

5 is an explanatory diagram of an incident surface (including an incident surface (X direction) in the extending direction (X direction) and an incident angle of FIG. 4, and corresponds to an incident angle in the Z-axis direction of the incident surface as 0 degree, the incident The incident angle of the angle θ with 0 degrees as the reference in the plane.

Claims (10)

A uniaxially stretched multi-layer laminated film characterized in that a first layer and a second layer are alternately laminated with 251 layers or more, and 1) the first layer is composed of a polyester containing a 2,6-naphthalenedicarboxylic acid component as a constituent component. a layer having a thickness of 0.01 μm or more and 0.5 μm or less, a uniaxial stretching direction (X direction), a direction perpendicular to the uniaxial direction of the film (Y direction), and a film thickness direction (Z direction), Y of the first layer The difference in refractive index between the direction and the Z direction is 0.1 or more, and 2) the second layer is a layer having a thickness of 0.01 μm or more and 0.5 μm or less of a thermoplastic resin as a constituent component, and the average refractive index of the thermoplastic resin is 1.60 or more and 1.65 or less. And a negative optical anisotropy or isotropic resin, wherein the ratio of the average layer thickness of the first layer to the average layer thickness of the second layer in the case where the thermoplastic resin constituting the second layer is an isotropic resin (the average layer thickness of the first layer/the average layer thickness of the second layer) is 1.2 or more and 5.0 or less, and 3) the film surface is used as the reflection surface, and the incident angle is perpendicular to the incident surface including the Y direction, and the incident angle is The average reflectance of the incident polarized light at a wavelength of 400 to 800 nm at 0 and 50 degrees 20% or more, 4) using a film surface as a reflecting surface, and for a polarizing component including a parallel direction of the incident surface in the Y direction, an average reflectance of 400 to 800 nm for the incident polarized light at an incident angle of 0 degrees is 15 % or less, the average reflectance of the wavelength of the incident polarized light of 400 to 800 nm at an incident angle of 50 degrees is 20% or more. The uniaxially stretched multi-layer laminated film according to claim 1, wherein the negative optical anisotropic resin constituting the second layer is a syndiotactic polystyrene resin, and the incident surface containing the Y direction is used. Among the parallel polarization components, the average reflectance of the incident polarization of 400 to 800 nm at an incident angle of 50 degrees is 50% or more. The ratio of the average layer thickness of the first layer to the average layer thickness of the second layer (the average layer thickness of the first layer / the average layer thickness of the second layer), as in the uniaxially stretched multilayer laminated film of claim 2 ) is 0.1 or more and 5.0 or less. The uniaxially stretched multi-layer laminated film according to claim 1, wherein the constitutive resin constituting the second layer is a benzoic acid in a range of 30 mol% or more and 70 mol% or less based on all repeating units. A copolymerized polyethylene naphthalate formed by copolymerization of at least one component of a dicarboxylic acid component or an isophthalic acid component. The uniaxially stretched multilayer laminated film according to claim 3 or 4, wherein the uniaxially stretched multilayer laminated film has a crystal orientation in the thickness direction of the film of -0.30 or more and 0.05 or less. The uniaxially stretched multilayer laminated film of claim 1, wherein the polyester of the first layer is polyethylene-2,6-naphthalenedicarboxylate. The uniaxially stretched multilayer laminated film of claim 1, wherein the first layer and the second layer are free of particles. The uniaxially stretched multilayer laminated film of claim 1 is used as a brightness enhancement film for a liquid crystal display. A uniaxially stretched multi-layer laminated film laminate, which is attached as an application The heat-resistant thermoplastic resin film is laminated on at least one surface of the uniaxially stretched multilayer laminated film according to any one of the first to eighth aspects of the invention. A brightness enhancement film for a liquid crystal display, which is obtained by uniaxially stretching a multilayer laminated film according to any one of claims 1 to 8.