JP6411802B2 - Uniaxially Stretched Multilayer Laminated Film and Prismatic Layer-Containing Brightness Enhancement Film Consisting of It - Google Patents

Description

  The present invention relates to a uniaxially stretched multilayer laminate film and a brightness enhancement film with a prism layer comprising the same, and more particularly to a uniaxially stretched multilayer laminate film with improved adhesion to a prism layer and a brightness enhancement film with a prism layer composed thereof.

  Liquid crystal display devices (LCDs) used for portable terminals such as smartphones and tablet terminals adjust the transmission of light emitted from light sources by liquid crystal panels in which polarizing plates are disposed on both sides of a liquid crystal cell Enables the display. As a polarizing plate to be bonded to a liquid crystal cell, an absorption type polarizing plate generally called a light absorbing type dichroic linear polarizing plate is used, and a polarizing plate in which PVA containing iodine is protected with triacetyl cellulose (TAC) Is widely used.

  Since such an absorption type polarizing plate transmits polarized light in the transmission axis direction and absorbs most of polarized light in the direction orthogonal to the transmission axis, about 50% of non-polarized light emitted from the light source device is absorbed It is pointed out that the light is absorbed by the polarizing plate and the light utilization efficiency decreases. Therefore, in order to effectively use polarized light in the direction orthogonal to the transmission axis, a configuration in which a reflective polarizer called a brightness enhancement film is used between a light source and a liquid crystal panel has been studied. An example of such a reflective polarizer A polymer type multilayer laminate film using optical interference is being studied as (Patent Document 1 and the like).

With the spread of portable terminals, the need for thinner display terminals is increasing, and the thickness of the members such as the reflective polarization type brightness enhancement film, the diffusion film, the prism film, and the light guide plate installed inside the display is further reduced. There is a need for a composite optical film that can further integrate these functions.
As an example of such a composite functional film, as described in Patent Document 2 etc., there is proposed a reflective polarization-type brightness enhancement film with a prism layer in which a prism structure is formed on a reflective polarization-type brightness enhancement film. However, when the prism layer is formed on such a reflective polarization type brightness enhancement film, the adhesion may not be sufficient, and when the prism layer is cut and installed in a display terminal, the prism layer may be chipped or peeled off.

  On the other hand, in general, a prismatic film forms a prismatic layer on a PET film substrate. As a general prism layer formation method, it is formed by transferring a non-solvent type UV curable resin onto a PET film substrate, but in that case, adhesion is provided by providing a coated layer on the PET film substrate To raise Such an easy-adhesive coating layer is applied in the film forming process of PET film, and a thermosetting crosslinking agent is added to a binder component such as polyester, acrylic or urethane resin to form a substrate and a prism. Improves adhesion with layers. In particular, in a non-solvent type UV curable resin such as a prism layer, the improvement of the adhesion due to the dissolution of the substrate by the organic solvent can not be expected, so the coating film capable of securing the adhesion is extremely limited (Patent Document 3) , 4 etc.).

When such an easily adhesive coating film is formed on a reflective polarization-type brightness enhancement film, a polyester resin other than PET is often used as a reflective polarization-type brightness enhancement film, and a film forming process is further performed to exhibit reflective polarization performance. Since there is often no crystallization step inside, the reactivity of the thermosetting crosslinking agent decreases, and sufficient adhesion to the prism layer is secured even when using a coating liquid composition similar to that of the PET film substrate. It was difficult to do.
In addition, since the reflective polarization-type brightness enhancement film is easily scratched on the surface layer formed of a specific polyester resin other than PET, it was necessary to bond a protective film or the like during the process. It is also required not to use such a protective film, and it is desired to improve the adhesion between the prism layer and the reflective polarization type brightness improving film serving as a base thereof, and further to secure the winding property and the like.

Japanese Patent Publication No. 9-507308 Japanese Patent Publication No. 9-506985 JP 2008-36868 A JP 2008-189868 A

  An object of the present invention is a multilayer film having a polyalkylene naphthalate-based polyester as a high refractive index layer, uniaxially stretched with reflection polarization performance and high adhesion between a prism layer formed on the film and the film It is an object of the present invention to provide a multilayer laminated film, and a brightness enhancement film with a prism layer comprising the same.

  As a result of intensive studies to solve the above problems, the present inventors made a multilayer laminate film having a polyalkylene naphthalate polyester as a high refractive index layer and a copolyester having a high glass transition point as a low refractive index layer. In this case, the composition which can be used for the coating layer is limited as compared with the case of the PET film often used as the base material layer of the prism, and further focusing on the outermost layer of the multilayer laminated film It has been found that a uniaxially stretched multilayer laminate film having high adhesion between them and a prismatic layer-attached brightness enhancing film comprising the same can be obtained, and the present invention has been completed.

That is, an object of the present invention is a uniaxially stretched multilayer laminated film in which a first layer and a second layer are alternately laminated,
1) The first layer contains a polyester comprising ethylene naphthalate units,
2) The polymer forming the second layer is a copolyester having a glass transition point of 90 ° C. or more and an average refractive index of 1.55 to 1.65,
3) The number of alternating layers of the first layer and the second layer is 101 or more in total, and has an outermost layer of 5 μm to 50 μm consisting of the second layer on at least one surface,
4) A coated layer having a thickness of 0.02 to 0.50 μm is provided on at least one surface of the outermost layer comprising the second layer, and the coated layer is an acrylic binder and particles having an average particle diameter of 0.05 to 0.50 μm In an amount of 0.1 to 5.0% by weight based on the coating layer,
5) The total thickness of the film including the coating layer is 20 to 150 μm,
6) It is obtained by the uniaxially stretched multilayer laminated film whose polarization degree (P) represented by following formula (1) is 80% or more.
Degree of polarization (P) = {(Ts−Tp) / (Tp + Ts)} × 100 (1)
Wherein, in the formula (1), Tp is the average transmittance of P-polarized light in the wavelength range of 400 to 800 nm, Ts
Represents the average transmittance of S-polarized light in the wavelength range of 400 to 800 nm)

  According to the present invention, the uniaxially stretched multilayer laminate film of the present invention has a reflective polarization performance and high adhesion between the prism layer formed on the film and the film, and at the same time, is excellent in the winding property. It is possible to provide a high quality composite optical film in which the function of a brightness enhancement film and the function of a prism are integrated.

1 is a schematic cross-sectional view of a liquid crystal display according to a preferred embodiment of the present invention.

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

[Uniaxially stretched multilayer laminated film]
The uniaxially stretched multilayer laminate film of the present invention is a layer in which the first layer has a relatively high refractive index characteristic than the second layer, and the second layer has a relatively lower refractive index characteristic than the first layer. Such refractive index relationships are manifested by using the following specific types of polyester in each layer.
In the present invention, the uniaxial stretching direction is referred to as the X direction, the direction orthogonal to the X direction in the film plane is referred to as the Y direction, and the direction perpendicular to the film surface is referred to as the Z direction.
In the uniaxially stretched multilayer laminate film, P-polarization in the present invention is defined as a polarization component parallel to the incident surface including the uniaxial stretching direction (X direction), with the film surface as a reflection surface. Further, S-polarization in the present invention is defined as a polarization component perpendicular to the incident surface including the uniaxial stretching direction (X direction), with the film surface as a reflection surface in the uniaxially stretched multilayer laminated film.
In the present invention, the refractive index in the stretching direction (X direction) may be described as nX, the refractive index in the direction orthogonal to the stretching direction (Y direction) as nY, and the refractive index in the film thickness direction (Z direction) as nZ. .

[First layer]
The first layer constituting the uniaxially stretched multilayer laminate film of the present invention contains a polyester containing alkylene naphthalate units. By using a polyester containing an alkylene naphthalate unit in the first layer, which is a high refractive index layer, and stretching in a uniaxial direction, high stretch orientation birefringence is exhibited, and the second layer in the stretching direction (X direction) And the difference in refractive index between them can be increased, which contributes to high polarization.
Specifically, polyethylene-2,6-naphthalenedicarboxylate, polybutylene-2,6-naphthalenedicarboxylate, polypropylene-2,6-naphthalenedicarboxylate and copolymers thereof can be mentioned. Among these, polyesters or copolymers thereof in which the main repeating unit is composed of an ethylene-2,6-naphthalene dicarboxylate component are preferable.

  When the polyester constituting the first layer is a copolyester, it is preferable to further contain a second dicarboxylic acid component as a copolymerization component, and more specifically, it is represented by a terephthalic acid component and the following formula (A) A component is mentioned and can contain at least any one component of these components.

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

Among these copolymer components, a copolymer polyester using a component represented by the formula (A) exhibits extremely high uniaxial orientation characteristics, so that higher birefringence is exhibited.
For component represented by the formula (A), and wherein, ^{R A} represents an alkylene group having 2 to 10 carbon atoms. Examples of such an alkylene group include ethylene group, trimethylene group, isopropylene group, tetramethylene group, hexamethylene group, octamethylene group and the like, and ethylene group is particularly preferable.

The copolymerization component is preferably 5 to 50 mol%, more preferably 5 to 40 mol%, particularly 10 to 35 mol% based on the dicarboxylic acid component constituting the polyester. preferable.
The component represented by the formula (A) is preferably 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, 6,6 ′-(trimethylenedioxy) di-2-naphthoic acid, 6 ′-(butylenedioxy) di-2-naphthoic acid and the like, and among them, those having an even number of carbon atoms in ^RA in the formula (A) are preferable, and in particular 6,6 ′-(ethylenedioxy) Di-2-naphthoic acid is preferred.

  By using the above-described polyester as the polyester constituting the first layer and performing uniaxial stretching, the refractive index nX in the X direction of the first layer has a high refractive index characteristic of 1.80 to 1.90. When the refractive index in the X direction in the first layer is in such a range, the difference in refractive index with the second layer becomes large, and the reflective polarization performance can be exhibited. The difference between the refractive index nY after uniaxial stretching in the Y direction and the refractive index nZ after uniaxial stretching in the Z direction is preferably 0.05 or less.

The average refractive index of the first layer is obtained by melting the polyester forming the first layer alone and extruding from the die to form an unstretched film (cast film), uniaxially (glass transition point of the polyester + 20) The unstretched film and the stretched film thus obtained are stretched 5.5 times at a temperature of 5.5 ° C., and the obtained unstretched film and stretched film are stretched in the stretching direction (X direction) and in the orthogonal direction (Y direction), thickness direction (Z direction) The refractive index (referred to as nX, nY, nZ) of (a) is determined by measuring the refractive index at a wavelength of 633 nm using a Metriccon prism coupler, and is taken as the refractive index before stretching and after stretching.
About the average refractive index of polyester which comprises a 1st layer, the average value of the refractive index of each direction before extending | stretching was made into the average refractive index.

[The second layer]
In the present invention, a copolymerized polyester having a glass transition point of 90 ° C. or more and an average refractive index of 1.55 to 1.65 is used as a polymer for forming the second layer of the uniaxially stretched multilayer laminated film. The glass transition point of the copolymerized polyester forming the second layer more preferably has a glass transition point (Tg) of 90 ° C. or more and less than 120 ° C.
If the glass transition point of such a copolyester is less than the lower limit, deformation, fusion and the like occur at the actual use temperature of a liquid crystal display and the like, and it is difficult to endure practical use. On the other hand, the upper limit of the glass transition point of the copolymerized polyester of the present invention is not particularly limited as long as the characteristics of the present invention are not impaired, but the glass of the copolymerized polyester used for the second layer having low refractive index characteristics If the transition point is 120 ° C. or more, orientation tends to occur in the stretching step, and desired refractive index properties may not be obtained.

The average refractive index of the copolyester forming the second layer is required to be 1.55 to 1.65, and preferably 1.58 or more and 1.60 or less. The average refractive index of the copolymerized polyester of the second layer is adjusted in accordance with the refractive index in the direction (Y direction) orthogonal to the stretching direction of the first layer polyester.
The average refractive index of the second layer is obtained by melting the copolymerized polyester forming the second layer alone, extruding from a die to form an unstretched film, uniaxially (glass transition point of the copolymerized polyester + 20) The film is stretched 5.5 times at ° C. to form a uniaxially stretched film, and the refractive index at a wavelength of 633 nm is measured using the Metricon prism coupler for each of the obtained film in the X direction, Y direction, and Z direction. And their mean value as the mean refractive index.

The copolyester of the second layer is preferably optically isotropic. The optical isotropy in the present invention means that the refractive index difference between the refractive index in the X direction, the Y direction and the Z direction is 0.05 or less, preferably 0.03 or less.
Since the second layer has such an average refractive index and is an optical isotropic material having a small difference in refractive index in each direction by stretching, refraction in the X direction between the layers of the first layer and the second layer after stretching A refractive index characteristic having a large difference in index and a small difference in refractive index between layers in the Y direction can be obtained, and the polarization performance can be further enhanced, which is preferable.

Examples of the copolymerized polyester forming the second layer include copolymerized polyethylene terephthalate, copolymerized polyethylene naphthalene dicarboxylate, or a blend thereof. Examples of dicarboxylic acid-based copolymerization components include an isophthalic acid component in the case of copolymerized polyethylene terephthalate, a naphthalenedicarboxylic acid component, and a terephthalic acid component in the case of copolymerized polyethylene naphthalenedicarboxylate.
The copolymerized polyester forming the second layer preferably further contains an alicyclic diol component as a diol-based copolymer component, and as the alicyclic diol component, spiroglycol, tricyclodecanedimethanol and cyclo At least one selected from the group consisting of xanthimethanol is preferably exemplified.

Here, the copolymerization component in the present invention means that it is any component constituting the polyester, and is not limited to the copolymerization component as a secondary component, and may be used including the main component.
For example, when polyethylene-2,6-naphthalenedicarboxylate is used for the first layer, the average refractive index of the copolymerized polyester of the second layer is preferably about 1.62 because a higher degree of polarization can be obtained. It is preferable to use 40 mol% terephthalic acid copolymerized polyethylene-2,6-naphthalene dicarboxylate which is obtained by copolymerizing 40 mol% terephthalic acid component as an example of the second layer copolymer polyester having such refractive index characteristics. .

  In addition, 21 mol% of a dicarboxylic acid component such as the aforementioned 6,6 '-(ethylenedioxy) di-2-naphthoic acid or 6,6'-(trimethylenedioxy) di-2-naphthoic acid was copolymerized. In the case of using polyethylene-2,6-naphthalenedicarboxylate as the polyester of the first layer, the average refractive index of the copolymerized polyester of the second layer is about 1.58 to obtain a higher degree of polarization Preferably, a copolymerized polyethylene terephthalate containing a naphthalene dicarboxylic acid component and an alicyclic diol component (eg, naphthalene dicarboxylic acid component / terephthalic acid component / ethylene glycol) as an example of the second layer copolymer polyester having such refractive index characteristics Component / spiro glycol component = 25/75/90/10 mol% copolymer).

  The refractive index and the glass transition point of the polyester are determined by the ratio of the monomer components constituting the polyester, and naphthalenedicarboxylic acid component, bisphenol fluorene component, biscresol fluorene component, etc. are raised as polyester forming components to enhance the refractive index and the glass transition point. Be On the other hand, an alicyclic diol component is mentioned as a polyester formation component which reduces a refractive index and raises a glass transition point. By appropriately adjusting these components, the average refractive index can be adjusted to 1.55 to 1.65 at a glass transition temperature of 90 ° C. or higher for the copolymerized polyester forming the second layer.

Among the copolyesters having such a glass transition point and refractive index properties, low copolyester copolyesters are preferable from the viewpoints of suppression of birefringence during stretching and suppression of thermal crystallization. Among them, amorphous polyester is particularly preferred. Amorphous as used herein means that the heat of crystal fusion when the temperature is raised at a temperature rising rate of 20 ° C./min in differential thermal analysis (DSC) is less than 0.1 mJ / mg.
The glass transition point of the copolymerized polyester forming the second layer does not have to be 90 ° C. or more from the stage before forming the film, and may be 90 ° C. or more after the stretching treatment. For example, two or more types of polyesters may be blended and transesterified at the time of melt-kneading.

[The outermost layer]
The uniaxially stretched multilayer laminate film of the present invention has an outermost layer of 5 μm to 50 μm consisting of the second layer on at least one surface, and the thickness thereof is preferably 5 to 45 μm, more preferably 7 to 20 μm, and further Preferably it is 5-15 micrometers.
If the thickness of the outermost layer of the second layer is less than the lower limit, the adhesion between the prism layer and the uniaxially stretched multilayer laminate film is not sufficient, and the prism layer tends to be peeled off. The upper limit of the thickness of the outermost layer is preferably in the above range from the viewpoint of production and the viewpoint of thinning of the entire uniaxially stretched multilayer laminated film.

In the present invention, as a mechanism for improving the prism adhesion by making the second layer of a certain thickness the outermost layer, the outermost layer comprising the second layer exhibits a cushioning effect, and the prism layer and the uniaxially stretched multilayer laminate film Since a part of the stress applied to the interface is relaxed, it is considered to contribute to the improvement of the prism adhesion, and the effect is not sufficiently exhibited unless the thickness of the outermost layer is less than the lower limit.
The outermost layer may be one whose layer thickness has been adjusted by the design of slits at the time of production of a uniaxially stretched multilayer laminate film, or may be one further laminated in a separate step after production of the laminate film. In addition, in the case of increasing the number of laminations of the alternate laminate by using a doubling method described later, the buffer layer may be an intermediate layer (hereinafter, may be referred to as an internal thick film layer) located inside the uniaxially stretched multilayer laminate film. It is preferable that it is arrange | positioned as outermost layer.

In the present invention, in the case of increasing the number of laminated uniaxially stretched multi-layered films, thick layers (referred to as a thickness adjusting layer and buffer layer) on both sides of alternate laminated layers of 101 layers or more In some cases, the method of forming the (possibly) and then doubling the number of laminations is preferably used.
The doubling is a method in which, for example, when an alternate stack of 101 layers is formed first, it is stacked by dividing it into 2 divisions, 3 divisions, or 4 divisions, and the block is formed when the first alternate lamination is one block. The number of stacked ones is called doubling number. Such doubling process can be performed using a branch block called a layer doubling block.

When the number of doublings is 2 or more, two buffer layers present on both sides of the first alternate stack are double-stacked by doubling and arranged in the middle of the alternate stack after doubling, which is referred to as an intermediate layer in the present invention. Further, the buffer layer finally disposed on the outermost layer by doubling corresponds to the outermost layer in the present invention.
By the presence of such an intermediate layer inside the alternate laminate, the thickness of each layer constituting the first layer and the second layer can be easily adjusted uniformly without affecting the polarization function, and the reflection performance can be enhanced. it can. In the case of disposing a buffer layer or an intermediate layer in the present invention, the same composition as the second layer is preferable. When the polyester forming the first layer is used for the buffer layer, physical durability such as tearing and cracking may be reduced.

[Coated layer]
The uniaxially stretched multilayer laminate film of the present invention has a coated layer having a thickness of 0.02 to 0.50 μm on at least one surface of the outermost layer comprising the above-mentioned second layer, and the coated layer contains an acrylic binder And 0.1 to 5.0% by weight of particles having an average particle diameter of 0.05 to 0.50 μm based on the coating layer.
Generally, when an easily adhesive coating layer is provided on a polyethylene terephthalate film, polyester resin having a glass transition temperature of about 30 to 100 ° C., urethane resin, acrylic resin, etc. is often used as a binder component, and particles are further added to the coating layer. At the same time, it is possible to secure the winding property.

  The uniaxially stretched multilayer laminate film of the present invention has a thick film layer comprising the composition of the second layer as the outermost layer of the multilayer laminate, and further has the coated layer of the present invention on at least one side of the outermost layer composed of the second layer. Thus, the adhesion to the prism layer can be enhanced. It is difficult to reduce peeling of the prism layer to a practical level with only one of the outermost layer and the coating layer.

  In the present invention, the second layer is preferably optically isotropic in order to enhance the degree of polarization, and as a method of enhancing the isotropy, the second layer may be in a non-oriented state or heat fixing treatment may be used. There is a way not to do it. Therefore, when a coating layer is further provided on the surface layer of the outermost layer, if a polyester resin, urethane resin, or the like having high compatibility with the copolyester forming the second layer is used for the coating layer, the coating film forms the second layer. Mixed with the copolymerized polyester, and even if particles are added to the coating layer, it is difficult to secure sufficient winding property.

Therefore, when the thick film layer having the composition of the second layer is provided as the outermost layer, and the coated layer is further provided on at least one side thereof, the coated layer is acrylic in order to enhance the adhesion with the outermost layer and the winding property. It is necessary to include a binder and to contain a certain amount of particles of a predetermined size. While the adhesion between the prism layer and the uniaxially stretched multilayer laminate film of the present invention is enhanced by the combination of the acrylic binder and the particles, it is sufficient even if it has the outermost layer comprising the composition of the second layer of the present invention Can be obtained.
In addition, when laminating a prism layer on at least one surface of the uniaxially stretched multilayer laminated film of the present invention, a non-solvent type UV curable acrylic resin is generally used as the prism layer, so the viewpoint of adhesion with the prism layer Also, it is preferable that the coating layer contains an acrylic binder.

  The type of the acrylic binder is not particularly limited, but an acrylic copolymer is preferred, and the main component is preferably composed of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate or the like. Not only one kind of main component but also plural components may be used, and the glass transition point can be adjusted by changing the composition ratio. Among these, a methyl acrylate-ethyl acrylate copolymer is preferable because the glass transition point can be easily adjusted.

Furthermore, in addition to the above-mentioned acrylic binder, an acrylic component containing a hydroxyl group, a carboxyl group, a nitrile group, an amide group, a cyano group or the like as an adhesion improving component or a self-crosslinking component may be added as a copolymer component preferable.
As the (meth) acrylate of the conventional copolymerization component, for example, those exemplified below can be used. That is, acrylic acid, methacrylic acid, 2-hydroxy acrylate, 2-hydroxy methacrylate, 2-hydroxy ethyl acrylate, 2-hydroxy butyl acrylate, acrylamide, methacrylamide, ethyl acrylamide, butyl acrylamide, dimethyl acrylamide, diethyl acrylamide, hydroxy diethyl acrylamide And acrylonitrile, methacrylonitrile, acryloyl morpholine, oxetane methacrylate, N-methylol acrylamide and the like.
Among them, acrylonitrile, N-methylol acrylamide, 2-hydroxy ethyl acrylate and the like are preferable.

The acrylic binder is preferably an aqueous emulsion from the viewpoint of securing the adhesion to the non-solvent prism layer and the viewpoint of reducing the viscosity of the aqueous coating solution.
The particle size of such an emulsion is preferably in the range of 20-80 nm. When the particle size of the emulsion exceeds 80 nm, the transparency of the coating may be reduced. On the other hand, if the particle size of the emulsion is less than 20 nm, it will be close to a water-soluble acrylic binder, and the adhesion to the prism layer may be lowered.

  Further, as particles used in the coating layer, it is preferable to add inert inorganic particles such as silica particles, inert organic particles such as acrylic particles, or organic-inorganic composite particles. As particles used in the coating layer, particles having an average particle diameter of 0.05 to 0.50 μm are used, and more preferably, particles having an average particle diameter of 0.10 to 0.40 μm. If the average particle size is less than the lower limit, sufficient rollability can not be obtained. In addition, even if particles having an average particle diameter larger than the upper limit are used, it is difficult to obtain a further improvement effect of the winding property, but the transparency of the coated layer is lowered.

  The content of particles used in the coating layer is preferably 0.1 to 5.0% by weight based on the weight of the coating layer (hereinafter sometimes referred to as the solid content of the coating layer or coating layer composition), and is preferably Is 0.1 to 3.0% by weight, more preferably 0.3 to 2.5% by weight. If the content of the particles is less than the lower limit, sufficient winding property is not expressed, and on the other hand, even if the particle content is increased from the upper limit, the effect of further improving the winding property is difficult to be obtained Sex is reduced.

Further, in order to apply the aqueous coating solution in the form of a thin film, it is preferable to add a surfactant to the composition of the coating layer.
The surfactant may improve and stabilize the dispersibility of the emulsion, but may reduce the adhesion to the prism layer. Therefore, it is preferable to limit the content of surfactant to a minimum amount within the range where the effect is exhibited, and specifically, the addition of 0.02 to 0.30% by weight based on the weight of the aqueous coating liquid The amount is preferably limited, and the content is preferably 2 to 20% by weight based on the coating layer (based on the solids of the coating layer composition).

  As examples of surfactants, anionic surfactants, cationic surfactants, nonionic surfactants and the like can be used. For example, polyoxyalkylene-fatty acid ether, polyoxyalkylene-aromatic acid ether, polyoxyalkylene-fatty acid ester, polyoxyalkylene-aromatic acid ester, polyoxyethylene-polyoxypropylene (copolymer) -fatty acid ester, poly Oxyethylene-polyoxypropylene (copolymer)-aromatic acid ester, sorbitan fatty acid ester, glycerin fatty acid ester, fatty acid metal soap, alkyl sulfate, alkyl sulfonate, alkyl sulfosuccinate, etc. anionic type, nonionic type interface Activators can be used.

Among them, polyoxyalkylene-fatty acid ether and polyoxyalkylene-aromatic acid ether are preferable from the viewpoint of improving adhesion to the prism layer, and, for example, polyoxyethylene tribenzyl phenyl ether, polyoxyethylene di-styrenated phenyl ether, polyoxy Ethylene oleyl ether etc. are mentioned.
The amount of the coating layer composition added is preferably such that the solid content is 1% by weight or more and 10% by weight or less based on the coating solution. If the addition amount is less than 1% by weight, the stability of the coating may be reduced, coating defects such as coating streaks and repelling may easily occur, and if it is more than 10% by weight, the adhesion may be reduced. .

  The thickness of the coating layer in the present invention is 0.02 to 0.50 μm, preferably 0.05 to 0.30 μm, and more preferably 0.05 to 0.20 μm. If the thickness of the coating layer is less than the lower limit, the adhesion effect with the prism layer is not sufficiently exhibited. Even if the thickness of the coating layer is increased beyond the upper limit, further improvement in adhesion becomes difficult.

[Lamination structure of uniaxially stretched multilayer laminated film]
(Number of stacks)
The uniaxially stretched multilayer laminate film of the present invention has a configuration in which the above-mentioned first layer and second layer are alternately laminated in a total of 101 layers or more. When the number of laminated layers is 100 or less, a certain average reflectance may not be expressed over a wavelength of 400 to 800 nm with respect to the average reflectance characteristics of polarization components parallel to the incident plane including the stretching direction (X direction) .
The upper limit of the number of laminations is preferably 2001 from the viewpoint of productivity and film handling properties, but if the target average reflectance characteristics are obtained, the number of laminations may be further reduced from the viewpoint of productivity and handling. For example, it may be 1001 layers, 501 layers, or 301 layers. The thickness of the optical member obtained in the present invention can be made thinner by setting the number of laminations smaller within the range in which the target reflection characteristics are satisfied.

(Layer thickness)
The thickness of each layer of the first layer and the second layer is preferably 0.01 μm or more and 0.5 μm or less. The thickness of each layer of the first layer is more preferably 0.01 μm or more and 0.1 μm or less, and the thickness of each layer of the second layer is more preferably 0.01 μm or more and 0.3 μm or less. The thickness of each layer can be determined based on a photograph taken using a transmission electron microscope.
When the uniaxially stretched multilayer laminate film of the present invention is used as a brightness enhancement film, the light of the light source can be efficiently reused by reflecting the light in the visible light region to the near infrared region. By setting the thickness of each layer of the first layer and the second layer in such a range, it is possible to selectively reflect light in such a wavelength range by light interference between layers. On the other hand, if the layer thickness exceeds 0.5 μm, the reflection band is in the infrared region, which does not affect the visibility of the display, and the contribution to the light utilization efficiency is reduced. When the layer thickness is less than 0.01 μm, the polyester component absorbs light and the reflection performance can not be obtained.

(Ratio of maximum layer thickness to minimum layer thickness)
In the uniaxially stretched multilayer laminate film of the present invention, the ratio of the maximum layer thickness to the minimum layer thickness in each of the first layer and the second layer is preferably 2.0 or more and 5.0 or less, and more preferably 2.0 or more and 4.0 or less, more preferably 2.0 or more and 3.5 or less, and particularly preferably 2.0 or more and 3.0 or less. The ratio of the layer thickness is specifically represented by the ratio of the maximum layer thickness to the minimum layer thickness. The maximum layer thickness and the minimum layer thickness of each of the first layer and the second layer can be determined based on a photograph taken using a transmission electron microscope.

In multilayer laminated films, the refractive index difference between layers, the number of layers, and the thickness of layers determine the wavelength of light reflected, but when each of the laminated first and second layers has a constant thickness, it reflects only a specific wavelength The average reflectance characteristic of the polarization component parallel to the incident plane including the stretching direction (X direction) can not be uniformly increased over a wide wavelength band of 400 to 800 nm. It is preferred to use layers of different thickness.
On the other hand, when the ratio of the maximum layer thickness to the minimum layer thickness exceeds the upper limit, the reflection band extends more than 400 to 800 nm, and the visible light region of the polarization component parallel to the incident plane including the stretching direction (X direction) It may be accompanied by a decrease in the reflectance of the

The layer thicknesses of the first layer and the second layer may be changed stepwise or continuously. By changing each of the first and second layers stacked in this manner, light in a wider wavelength range can be reflected.
Although the method of laminating the multilayer structure in the uniaxially stretched multilayer laminated film of the present invention is not particularly limited, for example, the first layer in which the first layer polyester is branched into 138 layers and the second layer polyester is branched into 137 layers. There is a method of using a multi-layered feed block device in which two layers are alternately stacked and the flow path changes continuously by 2.0 to 5.0 times.

(Average layer thickness ratio of the first layer and the second layer)
In the uniaxially stretched multilayer laminated film of the present invention, the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is preferably in the range of 0.5 times to 2.0 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 0.8. The upper limit of the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is more preferably 1.5. The most preferable range is 1.0 or more and 1.3 or less.
By making the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer an optimal thickness ratio, light leakage due to multiple reflection can be minimized. Here, the optimum thickness ratio is a value represented by (refractive index of first layer in stretching direction) × (average layer thickness of first layer), (refractive index of second layer in stretching direction) × The thickness is such that the value (optical thickness) represented by (the average layer thickness of the second layer) becomes equal.

[Uniaxially stretched film]
The uniaxially stretched multilayer laminate film of the present invention is stretched in at least one axial direction in order to obtain optical properties as a target reflective polarizing film. The uniaxial stretching in the present invention includes a film stretched in two axial directions in addition to a film stretched only in one uniaxial direction, and also includes a film stretched in one direction. The uniaxial stretching direction (X direction) may be either the film longitudinal direction or the width direction. In addition, in the case of a film stretched in two axial directions, in the case of a film stretched in one direction, the more stretched direction (X direction) may be either the film longitudinal direction or the width direction. The direction in which the draw ratio is low is preferably limited to a draw ratio of about 1.03 to 1.20, from the viewpoint of enhancing the polarization performance. In the case of a film stretched in two axial directions and stretched in one direction, the “stretching direction” in relation to polarization and refractive index refers to a more stretched direction.
As a stretching method, known stretching methods such as heating stretching by a rod-shaped heater, roll heating stretching, tenter stretching can be used, but tenter stretching is preferable from the viewpoints of reduction of flaws due to contact with rolls and stretching speed.

[Refractive index characteristics between layers of the first layer and the second layer]
The refractive index difference between the first layer and the second layer in the X direction 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 in such a range, the reflection characteristics can be efficiently enhanced, and high reflectance can be obtained with a smaller number of laminations.
Moreover, it is preferable that the refractive index difference of the Y direction of 1st layer and 2nd layer is 0.05 or less. When the refractive index difference between layers in the Y direction is in such a range, the polarization performance is preferably enhanced.

[Film thickness]
The uniaxially stretched multilayer laminate film of the present invention has a total film thickness including the coating layer of 20 to 150 μm, more preferably 30 to 130 μm, and still more preferably 50 to 100 μm. By using the uniaxially stretched multilayer laminate film of such a thickness as a brightness enhancement film, it is possible to provide a thin-walled member suitable for a member of a display terminal.

Degree of polarization
The uniaxially stretched multilayer laminated film of the present invention has a degree of polarization (P) represented by the following formula (1) of 80% or more, preferably 85% or more.
Degree of polarization (P) = {(Ts−Tp) / (Tp + Ts)} × 100 (1)
(In the formula (1), Tp represents the average transmittance of P-polarized light in the wavelength range of 400 to 800 nm, and Ts represents the average transmittance of S-polarized light in the wavelength range of 400 to 800 nm.

The measurement of the degree of polarization in the present invention can be measured using a degree of polarization measurement device.
The higher the degree of polarization specified by the above equation (1) is, the more transmission of the reflected polarized light component is suppressed, which means that the transmittance of the transmitted polarized light component in the orthogonal direction is higher. The slight light leakage of the polarization component can also be reduced. When the uniaxially stretched multilayer laminated film of the present invention has such a degree of polarization, it can be used for applications where a reflective polarization characteristic such as a brightness enhancement film is required. Further, in the case of having a degree of polarization of 99.5% or more, the reflective polarizing plate alone can be applied as a polarizing plate for a liquid crystal display having a high contrast which has been difficult to apply unless it is a conventional absorbing polarizing plate.
Such polarization degree characteristics are obtained by using the above-mentioned types of polymers constituting the first layer and the second layer, and making the refractive indices of the layers in the X direction, the Y direction, and the Z direction into a specific relationship by uniaxial stretching. can get.

[S-polarization average transmittance]
The average transmittance Ts of S polarized light in the wavelength range of 400 to 800 nm of the uniaxially stretched multilayer laminate film of the present invention is preferably 60% or more, more preferably 70% or more, still more preferably 75% or more, particularly preferably Is 80% or more.
The S-polarization average transmittance in the present invention is a uniaxially stretched multi-layer laminated film, in which the film surface is a reflective surface, and the incident angle is 0 degree for a polarization component perpendicular to the incident surface including the uniaxial stretching direction (X direction). Represents the average transmittance of the wavelength of 400 to 800 nm for the incident polarization at.
When the S-polarization average transmittance is less than the lower limit, when it is used for a brightness enhancement film etc., a light recycling function is considered in which the reflected polarized light component is not absorbed by the film but reflected to the light source side and the light is used effectively again. However, the superiority of the luminance improvement effect may not be sufficient.

[Method of producing uniaxially stretched multilayer laminated film]
Below, the manufacturing method of the uniaxially stretched multilayer laminated film of this invention is explained in full detail.
The uniaxially stretched multi-layer laminate film of the present invention is obtained by alternately laminating the polymer constituting the first layer and the polymer constituting the second layer in a molten state to create an alternate laminate of 101 or more layers in total A thick film layer (buffer layer) is provided on both sides, and an alternating stack having the buffer layer is divided into, for example, 2 to 4 using a device called layer doubling, and the alternating stack having the buffer layer is divided into one block. The number of laminations can be increased by the method of laminating again so that the number of laminations (number of doublings) becomes 2 to 4 times. By this method, it is possible to obtain a uniaxially stretched multilayer laminated film having an intermediate layer in which two buffer layers are laminated inside the multilayer structure, and an outermost layer consisting of one buffer layer on both surfaces.

In addition, the uniaxially stretched multilayer laminated film of the present invention has a total of 101 layers in which the polymer constituting the first layer and the polymer constituting the second layer are alternately superposed in a molten state, in addition to using the above-mentioned doubling method. With the above-described target number of laminations, the thickness of each layer may be laminated stepwise or continuously so as to change in the range of 2.0 to 5.0 times.
The multilayer unstretched film laminated to the desired number of laminations by the method described above is stretched in at least one axial direction (direction along the film surface) in the film forming direction or in the width direction orthogonal thereto. The stretching temperature is preferably in the range of temperature (Tg) to (Tg + 50) ° C. of the glass transition point of the polymer of the first layer, and more preferably in the range of (Tg + 20) ° C. or less. When stretched at a stretching temperature of (Tg + 20) ° C. or less, the orientation characteristics of the film can be controlled to a higher degree.

The draw ratio at this time is preferably 2 to 10 times, more preferably 2 to 7 times, still more preferably 2.5 to 7 times, and particularly preferably 4.5 to 6.5 times. Within this range, the greater the stretching ratio, the smaller the variation in the surface direction of the individual layers in the first layer and the second layer due to the thinning due to stretching, and the light interference of the multilayer stretched film becomes more uniform in the surface direction, Moreover, since the refractive index difference of the extending | stretching direction of 1st layer and 2nd layer becomes large, it is preferable.
The drawing method at this time may be a known drawing method such as heating drawing by a rod heater, roll heating drawing, tenter drawing, etc., but from the viewpoint of reduction of flaws due to contact with the roll and drawing speed, tenter drawing preferable.

In addition, in the case where the drawing treatment is also performed in the direction (Y direction) orthogonal to the drawing direction and biaxial drawing is performed, it is preferable to limit the drawing ratio to about 1.03 to 1.20. If the draw ratio in the Y direction is further increased, the polarization performance may be degraded.
Further, after heat drawing, while performing heat setting at a temperature of (Tg) to (Tg + 30) ° C, toe-out (re-stretching) may be performed in the drawing direction in a range of 5 to 15%. The orientation properties of the film can be more highly controlled.
When the above-mentioned coating layer is provided in the present invention, the application to the uniaxially stretched multilayer laminated film can be carried out at any stage, but it is preferably carried out in the process of producing the film. It is preferable to apply.

[Brightness Improvement Film]
The uniaxially stretched multilayer laminate film of the present invention uses polyester of the above composition for each of the first layer and the second layer, laminates alternately in multiple layers, and selectively stretches one polarization component by stretching in one direction. Can be used as a brightness enhancement film for a liquid crystal display or the like because it exhibits the ability to reflect light and selectively transmit the polarized light component in the direction perpendicular to the polarized light component. When it is used as a brightness enhancement film, a good brightness enhancement rate can be obtained, and light can be reused by reflecting untransmitted polarized components to the light source side.
Also, a prism layer or a diffusion layer may be laminated on at least one surface of the uniaxially stretched multilayer laminated film of the present invention. At that time, it is preferable that a prism layer or a diffusion layer be laminated via the above-mentioned coating layer.

  Furthermore, a brightness enhancement film with a prism layer in which a prism layer is provided on the uniaxially stretched multilayer laminate film of the present invention is also included as a preferred embodiment of the present invention. By unitizing the brightness enhancement film and the prism layer, the number of members at the time of assembly can be reduced, and a high quality composite optical film can be provided in which the function of the brightness enhancement film and the function of the prism are integrated. Further, by bonding the prism layer with the uniaxially stretched multilayer laminated film of the present invention, it is possible to suppress peeling of the prism layer due to an external force applied at the time of processing etc., and thus a more reliable luminance improvement film can be provided. .

When the uniaxially stretched multilayer laminate film of the present invention is used as a brightness enhancement film, it can be used in a liquid crystal display device as shown in FIG.
Specifically, a liquid crystal display device in which the brightness improving member 4 is disposed between the light source 5 of the liquid crystal display and the liquid crystal panel 6 configured of the polarizing plate 1 / liquid crystal cell 2 / polarizing plate 3 is exemplified. . Although the installation position of the prism layer is not particularly limited, the apex angle is preferably about 90 degrees when installed on the panel side, and is preferably about 60 degrees when installed on the backlight side.

Hereinafter, the present invention will be described by way of examples, but the present invention is not limited to the examples shown below.
Physical properties and characteristics in the examples were measured or evaluated by the following methods.

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

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

(3) Identification of Polymer and Identification of Copolymerization Component and Amount of Each Component For each layer of the film, the polymer component and the copolymerization component and the amount of each component were identified by ¹ H-NMR measurement.

(4) Average Refractive Index The individual resins constituting the respective layers were melted and extruded from a die to prepare films cast on a casting drum. In addition, a stretched film was prepared by stretching the obtained film 5.5 times in uniaxial direction at (glass transition temperature of resin) + 20 ° C. Regarding the cast film and the stretched film thus obtained, the refractive index (each taken as nX, nY, nZ) of the stretching direction (X direction), the orthogonal direction (Y direction) and the thickness direction (Z direction) thereof are It measures by wavelength 633nm using a prism coupler made, and it was considered as the refractive index before extending, and after extending.
About the average refractive index of polyester which comprises a 1st layer, the average value of the refractive index of each direction before extending | stretching was made into the average refractive index. Moreover, about the average refractive index of polyester which comprises a 2nd layer, the average value of the refractive index of each direction after extending | stretching was made into the average refractive index.

(5) Thickness of Each Layer A uniaxially stretched multilayer laminated film was cut out in a film longitudinal direction 2 mm and a width direction 2 cm, fixed in an embedding capsule, and then embedded in an epoxy resin (Epomount manufactured by Refintech Co., Ltd.). The embedded sample was cut vertically with a microtome (ULTRACUT UCT, manufactured by LEICA) into a thin film section of 5 nm thickness. The film was observed and photographed at an accelerating voltage of 100 kV using a transmission electron microscope (Hitachi S-4300), and the thickness of each layer was measured from the photograph.
Based on the thickness of each layer obtained, 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 respectively determined.
Further, based on the thickness of each layer obtained, the average layer thickness of the first layer and the average layer thickness of the second layer were respectively determined, and the average layer thickness of the second layer to the average layer thickness of the first layer was calculated.
In addition, when calculating | requiring the thickness of 1st layer and 2nd layer, the intermediate | middle layer and outermost layer were remove | excluded from 1st layer and 2nd layer.
With respect to the layer having a thickness of 1 μm or more constituting the uniaxially stretched multilayer laminate film, the one existing inside the multilayer structure is taken as the intermediate layer, the one present in the outermost layer is taken as the outermost layer, It was measured. Moreover, when two or more intermediate layers existed, the intermediate layer thickness was calculated | required from those average value.
Further, the thickness of the applied layer was determined by the same method as described above.

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

(7) Average Particle Size of Particles The same measurement as in the layer thickness measurement was performed, the particle sizes of 100 particles in the coating layer were measured, and the average value was defined as the average particle size.

(8) Content of particle The binder component which forms the coating layer is dissolved, the solvent which does not dissolve the particle is selected, the coating layer subjected to sampling is dissolved, and then the particles are centrifuged, and the ratio to the total weight of particles ( %) Was taken as the content of particles.

(9) Coefficient of friction The coefficient of static friction μs and the coefficient of dynamic friction μk were measured according to JIS-K7125. The measurement was performed 5 times, and the average value was taken as the result.

(10) Haze Measured according to JIS-K7136 using a haze measuring instrument (NDH-2000 manufactured by Nippon Denshoku Kogyo Co., Ltd.).

(11) Brightness improvement effect (brightness improvement rate)
The liquid crystal display screen when white is displayed by removing the prism film and the upper diffusion film using a VA type liquid crystal display panel (manufactured by Sharp AQUOS LC-20E90 2011) and replacing it with the obtained brightness enhancement film with a prism layer The front luminance of was measured with an FPD viewing angle measurement and evaluation apparatus (ErgoScope 88) manufactured by Opto Design Co., Ltd., the rate of increase in luminance relative to the configuration before replacement was calculated, and the luminance improvement effect was evaluated based on the following criteria.
○: 150% or more of luminance improvement effect Δ: 120% or more and less than 150% of luminance improvement effect ×: less than 120% of luminance improvement effect

(12) Adhesion to prism layer A UV curable acrylic resin of the following composition is poured into a glass mold on which a prism lens pattern is formed, and the coated layer surface of the polyester film obtained thereon is adhered to the resin side The resin is cured by using an ultraviolet lamp (irradiation intensity 80 W / cm, 6.4 KW) for 30 seconds from a distance of 30 cm on the surface side of the glass mold to cure the resin, 90 ° apex angle, pitch 50 μm, height A 30 μm prism lens layer was formed to obtain a brightness enhancement sheet. A cross cut (100 squares of 1 mm ² ) is cut on the machined surface of the obtained brightness enhancement sheet, and a cellophane tape (manufactured by Nichiban Co., Ltd.) with a width of 24 mm is pasted thereon, and peeled off at 90 °. After peeling rapidly at an angle, the peeled surface was observed and evaluated according to the following criteria.
<UV-curable acrylic resin>
Ethylene oxide modified bisphenol A dimethacrylate (FA-321M manufactured by Hitachi Chemical Co., Ltd.) 46% by weight
Neopentyl glycol modified trimethylolpropane diacrylate (Nippon Kayaku Chemical Industry Co., Ltd. R-604) 25% by weight
Phenoxyethyl acrylate (Osaka Organic Chemical Industry Co., Ltd. Biscoat 192) 27% by weight
2% by weight of 2-hydroxy-2-methyl-1-phenylpropan-1-one (Darocur 1173 manufactured by Merck)
<Evaluation criteria of adhesion>
○: Peeling area less than 5% (Good adhesion)
Δ: Peeling area is 5% or more and less than 30% ×: Peeling area is 30% or more (adhesion is poor)

(13) Anti-blocking property Two sample films are superposed so that the coated layer forming surfaces are in contact with each other, and a pressure of 0.6 kg / cm ² is applied thereto for 17 hours under an atmosphere of 80 ° C. and 80% RH. Then, it peeled, and the blocking resistance was evaluated by the following reference | standard by the peeling force at the time of peeling.
○: Peeling force <98 mN / 5 cm width (good)
:: 98 mN / 5 cm width ≦ peel force <196 mN / 5 cm width (slightly good)
×: 196 mN / 5 cm width ≦ peel force (defect)

Example 1
As a polyester for the first layer, an ester exchange reaction is performed with dimethyl 2,6-naphthalenedicarboxylate and ethylene glycol in the presence of titanium tetrabutoxide, and a polycondensation reaction is subsequently performed to obtain an intrinsic viscosity of 0.55 dl / g. Of polyethylene-2,6-naphthalenedicarboxylate (PEN) were prepared.
In addition, as polyester for the second layer, a transesterification reaction is performed with dimethyl 2,6-naphthalenedicarboxylate, dimethyl terephthalate and ethylene glycol in the presence of titanium tetrabutoxide, and a polycondensation reaction is subsequently performed. 60% by mole of the acid component is 2,6-naphthalenedicarboxylic acid component (denoted as PEN in the table), 40 mole% of the acid component is terephthalic acid component (denoted as DMT in the table), and the glycol component is ethylene glycol A copolyester (DMT 40 PEN) (inherent viscosity 0.63 dl / g) was prepared.

  After branching the polyester for the first layer into 138 layers and the polyester for the second layer into 137 layers, the first layer and the second layer are alternately laminated, and the maximum layer thickness in each of the first layer and the second layer And a total of 275 layers of alternating first and second layers, using a multi-layer feed block device where the maximum and minimum layer thickness varies continuously up to 2.2 times at maximum / minimum As a melt, keeping the laminated state, lead the same polyester as the polyester for the second layer from the third extruder on both sides to a three-layer feed block, and put a total of 275 layers of laminated melt on both sides The buffer layer was further laminated. The feed rate of the third extruder was adjusted so that both end layers (buffer layers) would be 42% of the total. The layering state is further divided into two layers by a layer doubling block and laminated at a ratio of 1: 1, and the layering state of a total of 553 layers including one intermediate layer inside and two outermost layers in the outermost layer is maintained Guide to the die as it is, cast on the casting drum, adjust the average layer thickness ratio of the first layer to the second layer to be 1.0: 1.2, and do not stretch 553 layers in total Multilayer laminated film was made.

Coating solution A having a solid content concentration of 4% and a composition shown in Table 2 was uniformly coated on one surface of this unstretched multilayer laminated film by a roll coater so that the coating thickness after drying was 0.1 μm.
The unstretched multilayer laminated film was stretched 5.2 times in the width direction at a temperature of 130 ° C. The thickness of the obtained uniaxially stretched multilayer laminate film was 85 μm. Using the brightness enhancement film with a prism layer in which the prism layer is laminated on the coated layer surface of the obtained uniaxially stretched multilayer laminate film according to the method of measurement method (12), the brightness improvement effect is obtained by the method of measurement method (11) Was measured.
The uniaxially stretched multilayer laminate film of the present invention has high adhesion between the prism layer and the film, and the peeling of the prism layer is reduced. Moreover, since it was excellent also in blocking resistance, the winding property was favorable.

[Examples 2 to 4, Comparative Examples 1 to 4]
As shown in Tables 1 and 2, a uniaxially stretched multilayer laminated film and a prism layer-attached luminance improving film were obtained in the same manner as in Example 1 except that the resin composition, the laminated constitution, and the composition of the coating layer were changed. Further, in the fourth embodiment, the branching process by the layer doubling block was not performed.

[Example 5]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 '-(ethylenedioxy) di-2-naphthoic acid, and ethylene glycol are subjected to esterification reaction and transesterification reaction in the presence of titanium tetrabutoxide, and the subsequent reaction The polycondensation reaction is carried out, and the intrinsic viscosity is 0.63 dl / g, 70 mol% of the acid component is 2,6-naphthalenedicarboxylic acid component, and 30 mol% of the acid component is 6,6 '-(ethylenedioxy) Di-2-naphthoic acid component (denoted as ENA in the table), aromatic polyester whose glycol component is ethylene glycol (denoted as ENA30PEN in the table) as polyester for the first layer and polyester for the second layer 6, 6- naphthalene dicarboxylic acid (denoted as NDC in the table) 66 mol%, 34 mol% terephthalic acid, ethylene glycol 50 ol%, spiroglycol (Tables in SPG and forth) 15 mol%, trimethylene glycol (described in the Table TMG) 35 mol%, were prepared copolyester (intrinsic viscosity of 0.70 dl / g) consisting of.

  The prepared first layer polyester is dried at 170 ° C. for 5 hours, and the second layer polyester is dried at 85 ° C. for 8 hours, and then supplied to the first and second extruders, respectively, and heated to 300 ° C. to be melted. After branching the polyester for the first layer into 138 layers and the polyester for the second layer into 137 layers, the first layer and the second layer are alternately laminated, and the maximum layer in each of the first layer and the second layer Total number of alternating first and second layers stacked using a multi-layer feed block device where the thickness and minimum layer thickness vary continuously up to 3.1x and 3.0x max / min The melt is in the form of a stack of 275 layers, and while maintaining the stack, the third extruder guides the same polyester as the polyester for the second layer to a three-layer feed block on both sides, for a total stack of 275 layers On both sides of the stack direction of the melt The Ffa layer is further stacked. The feed rate of the third extruder was adjusted so that the total of the buffer layers (outmost layers) on both sides was 80% of the total.

While maintaining the laminated state of 277 layers in total including the outermost layer, it is led to a die and cast on a casting drum, and the average layer thickness ratio of the first layer to the second layer is 1.0: 1.0 The unstretched multilayer laminated film of 277 layers in total was prepared.
Coating solution A having a solid content concentration of 4% and a composition shown in Table 2 was uniformly coated on one surface of this unstretched multilayer laminated film by a roll coater so that the coating thickness after drying was 0.1 μm.
This multilayer unstretched film was stretched 6.5 times in the width direction at a temperature of 120 ° C., and further heat-set at 120 ° C. for 3 seconds while being stretched 15% in the same direction at 120 ° C. The thickness of the obtained uniaxially stretched multilayer laminate film was 112 μm.
Using the brightness enhancement film with a prism layer in which the prism layer is laminated on the coated layer surface of the obtained uniaxially stretched multilayer laminate film according to the method of measurement method (12), the brightness improvement effect is obtained by the method of measurement method (11) Was measured.
The uniaxially stretched multilayer laminate film of the present invention has high adhesion between the prism layer and the film, and the peeling of the prism layer is reduced. Moreover, since it was excellent also in blocking resistance, the winding property was favorable.

[Reference Example 1]
Melted polyethylene terephthalate ([η] = 0.62 dl / g, Tg = 78 ° C) is extruded from a die, cooled by a cooling drum according to a conventional method to form an unstretched film, and then 4.0 times in the width direction at 95 ° C. After stretching, a coating solution D (solid content concentration 4% by weight) consisting of the coating layer components shown in Table 2 was uniformly coated on one side by a roll coater so as to have a coating thickness of 0.1 μm after drying. Subsequently, this coated film was dried at 95 ° C. successively, shrunk by 3% in the width direction at 180 ° C. and heat-set, and a film of 50 μm in thickness was obtained in the same manner as in Example 1.
Using the brightness enhancement film with a prism layer in which the prism layer is laminated on the coated layer surface of the obtained uniaxially stretched multilayer laminate film according to the method of measurement method (12), the brightness improvement effect is obtained by the method of measurement method (11) Was measured.
In the case of a polyethylene terephthalate single-layer film, adhesion to the prism layer could be enhanced by using a coating layer containing polyester as a binder component.

[Coated layer component]
(Acryl A)
It consists of 60 mol% of methyl methacrylate / 30 mol% of ethyl acrylate / 2 mol% of 2-hydroxyethyl acrylate / 5 mol% of N-methylol acrylamide (Tg = 40 ° C.). In a four-necked flask, 302 parts of ion exchanged water is charged and the temperature is raised to 60 ° C. in a nitrogen stream, then 0.5 parts of ammonium persulfate and 0.2 parts of sodium bisulfite are added as a polymerization initiator, A mixture of 46.7 parts of methyl methacrylate, 23.3 parts of ethyl acrylate, 4.5 parts of 2-hydroxyethyl acrylate, and 3.4 parts of N-methylol acrylamide for 3 hours at a liquid temperature of 60 to 70 ° C. It dripped, adjusting so that it might become. After completion of the dropwise addition, the reaction was continued with stirring while maintaining the same temperature range for 2 hours, and then cooled to obtain an aqueous dispersion of acrylic 1 having a solid content of 25% by weight.

(Acrylic B)
Synthesis was carried out in the same manner as for acrylic A, except that the monomer composition was adjusted to have a composition constituted by 60 mol% of methyl methacrylate / 35 mol% of ethyl acrylate / 5 mol% of N-methylol acrylamide.

(Polyester A)
The acid component is composed of 75 mol% of 2,6-naphthalenedicarboxylic acid / 20 mol% of isophthalic acid / 5 mol% of 5-sodiumsulfoisophthalic acid, and the glycol component is 90 mol% of ethylene glycol / 10 mol% of diethylene glycol (Tg = 80 ° C, average molecular weight 15000).
Polyester A was produced as follows. That is, 51 parts of dimethyl 2,6-naphthalenedicarboxylate, 11 parts of dimethyl isophthalate, 4 parts of dimethyl 5-sodium sulfoisophthalate, 31 parts of ethylene glycol and 2 parts of diethylene glycol are charged in a reactor, 05 parts were added, the temperature was controlled to 230 ° C. under a nitrogen atmosphere, and heating was performed to distill off generated methanol to carry out a transesterification reaction. Subsequently, the temperature of the reaction system was gradually raised to 255 ° C. in a polymerization kettle with high motor torque of a stirrer, and the pressure in the system was reduced to 1 mmHg to carry out a polycondensation reaction to obtain polyester A having an intrinsic viscosity of 0.56. . 25 parts of this polyester is dissolved in 75 parts of tetrahydrofuran, and 75 parts of water is dropped into the obtained solution under high-speed stirring at 10000 rpm to obtain a milky white dispersion, and then this dispersion is subjected to a reduced pressure of 20 mmHg. Distilled and distilled off tetrahydrofuran. An aqueous dispersion of polyester A having a solid content of 25% by weight was obtained.

(Polyester B)
The acid component is composed of 90 mol% of terephthalic acid / 5 mol% of isophthalic acid / 5 mol% of 5-sodium sulfoisophthalic acid, and the glycol component is 90 mol% of ethylene glycol / 10 mol% of diethylene glycol (Tg = 70 ° C., average molecular weight 15000) Polymerization was carried out in the same manner as polyester A, except that the monomer composition was adjusted so as to obtain the following composition.

(Surfactant A) Polyoxyethylene tribenzyl phenyl ether (Surfactant B) Polyoxyethylene distyrenated phenyl ether (Surfactant C) Polyoxyethylene oleyl ether

(Particle A)
Acrylic spherical particles (average particle size: 150 nm: manufactured by Nippon Shokubai Co., Ltd., trade name "Eposter MX-100W")
(Particle B)
Acrylic spherical particles (average particle size: 300 nm: manufactured by Nippon Shokubai Co., Ltd., trade name "Eposter MX-200W")
(Particle C)
Silica spherical particles (average particle size: 500 nm: manufactured by Nippon Shokubai Co., Ltd., trade name "Sea Hoster KE-W 50")

  The uniaxially stretched multi-layer laminate film of the present invention has a reflective polarization performance, high adhesion between the prism layer formed on the film and the film, and at the same time is excellent in winding property, so the function of the brightness enhancement film It is possible to provide a high quality composite optical film that integrates the functions of the lens and the prism.

Reference Signs List 1 polarizing plate 2 liquid crystal cell 3 polarizing plate 4 brightness enhancement film 5 light source 6 liquid crystal panel

Claims (4)

A uniaxially stretched multilayer laminated film in which a first layer and a second layer are alternately laminated,
1) The first layer contains a polyester comprising ethylene naphthalate units,
2) The polymer forming the second layer is a copolyester having a glass transition point of 90 ° C. or more and an average refractive index of 1.55 to 1.65,
3) The number of alternating layers of the first layer and the second layer is 101 or more in total, and has an outermost layer of 5 μm to 50 μm consisting of the second layer on at least one surface,
4) A coated layer having a thickness of 0.02 to 0.50 μm is provided on at least one surface of the outermost layer comprising the second layer, and the coated layer is an acrylic binder and particles having an average particle diameter of 0.05 to 0.50 μm In an amount of 0.1 to 5.0% by weight based on the coating layer,
5) The total thickness of the film including the coating layer is 20 to 150 μm,
6) A uniaxially stretched multilayer laminated film characterized in that the degree of polarization (P) represented by the following formula (1) is 80% or more.
Degree of polarization (P) = {(Ts−Tp) / (Tp + Ts)} × 100 (1)
(In the formula (1), Tp represents the average transmittance of P-polarized light in the wavelength range of 400 to 800 nm, and Ts represents the average transmittance of S-polarized light in the wavelength range of 400 to 800 nm. The uniaxially stretched multilayer laminate film according to claim 1, wherein the first layer further contains, as a dicarboxylic acid component, at least one of a terephthalic acid component and a component represented by the following formula (A).
(In formula (A), R ^A represents an alkylene group having 2 to 10 carbon atoms)   The copolyester forming the second layer contains at least one alicyclic diol component, and the alicyclic diol component is at least one selected from the group consisting of spiroglycol, tricyclodecanedimethanol and cyclohexanedimethanol. The uniaxially stretched multilayer laminated film according to claim 1 or 2.   The brightness improving film with a prism layer which provided the prism layer on the uniaxially stretched multilayer laminated film in any one of Claims 1-3.