JP2016024313A - Uniaxially oriented multilayer laminate film and optical member comprising the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a uniaxially oriented multilayer laminate film having a certain polarizing performance and improved interlayer adhesiveness while the film is a polymer film having a multilayer structure using a polyethylene naphthalate polymer in a layer having a high refractive index characteristic, and an optical member comprising the film.SOLUTION: The uniaxially oriented multilayer laminate film includes a first layer and a second layer alternately laminated and has such characteristics that (1) the first layer contains polyester, containing ethylene naphthalate units by 80 mol% or more and 100 mol% or less based on repeating units constituting the polyester; and (2) a polymer constituting the second layer is a copolymer polyester having a 2,6-naphthalene dicarboxylic acid component, an ethylene glycol component, and a trimethylene glycol component as copolymer components.SELECTED DRAWING: None

Description

  The present invention relates to a uniaxially stretched multilayer laminate film and an optical member comprising the same, and more specifically, a uniaxially stretched multilayer laminate film having a certain reflective polarization performance and interlayer adhesion while being a multilayer polymer film, and an optical composed thereof It relates to members.

A film in which a large number of low refractive index layers and high refractive index layers are alternately laminated may be an optical interference film that selectively reflects or transmits light of a specific wavelength by structural optical interference between layers. it can. In addition, such a multilayer laminated film can obtain a high reflectivity equivalent to a film using metal by gradually changing the film thickness or by laminating films having different reflection peaks. It can also be used as a glossy film or a reflection mirror. Furthermore, by stretching such a multilayer laminated film in one direction, it can also be used as a polarizing reflection film that reflects only a specific polarization component. By using these for a liquid crystal display or the like, brightness of a liquid crystal display or the like can be obtained. It is known that it can be used for an improvement film etc. (patent documents 1, 2, 3, 4, etc.).
However, the reflective polarizing polymer film using a multilayer structure which has been studied in the past may not have sufficient adhesion between the multilayer polymers, and the multilayer part may be peeled off during processing. there were.

For example, polyethylene-2,6-naphthalene dicarboxylate (hereinafter sometimes referred to as 2,6-PEN) described in Patent Document 2 is used for the high refractive index layer, and a thermoplastic elastomer or terephthalic acid is used. In the case of a multilayer laminated film using 30 mol% copolymerized PEN as a low refractive index layer, the refractive index difference between layers in the uniaxial stretching direction (X direction) is increased to increase the reflectance of P-polarized light, while in the film plane By reducing the difference in refractive index between layers in the direction perpendicular to the X direction (Y direction) and increasing the transmittance of S-polarized light, a certain level of polarization performance is exhibited.
However, in the combination of the above-mentioned polymers, when the multi-layer laminated film is post-processed, stress is applied to the multi-layered portion, so that the multi-layer portion is easily peeled off, and the improvement in adhesion between layers has been desired.

JP-A-4-268505 Japanese National Patent Publication No. 9-506837 Japanese National Patent Publication No. 9-506984 International Publication No. 01/47711 Pamphlet

  An object of the present invention is a uniaxially stretched multi-layer film having a certain polarization performance and improved adhesion between layers while being a multi-layer polymer film using a polyethylene naphthalate polymer in a layer having a high refractive index characteristic The object is to provide a laminated film and an optical member comprising the same.

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

  That is, an object of the present invention is a uniaxially stretched multi-layer laminated film in which a first layer and a second layer are alternately laminated, and 1) the first layer is a layer containing polyester and constitutes the polyester. 2) The ethylene naphthalate unit is contained in the range of 80 mol% or more and 100 mol% or less based on the repeating unit, and 2) the polymer forming the second layer is a 2,6-naphthalenedicarboxylic acid component, an ethylene glycol component and a triglyceride component. This is achieved by a uniaxially stretched multilayer laminated film which is a copolyester containing a methylene glycol component as a copolymerization component.

  According to the present invention, the uniaxially stretched multilayer laminate film of the present invention is a polymer film having a multilayer structure using a polyethylene naphthalate polymer in a layer having a high refractive index characteristic, and has a certain polarization performance and an interlayer. The adhesion is improved. For this reason, for example, when used as a brightness improving member or a reflective polarizing plate that requires polarization performance, delamination does not occur due to external force applied during bonding to other members, assembly to a liquid crystal display, use, etc. Therefore, a more reliable brightness improving member, a polarizing plate for a liquid crystal display, and the like can be provided.

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 laminated. About each configuration of the present invention, such as resin constituting each layer, polarization performance, etc. This will be described in detail below.

[Uniaxially stretched multilayer laminated film]
In the uniaxially stretched multilayer laminated film of the present invention, the first layer is a layer having a relatively higher refractive index characteristic than the second layer, and the second layer is a layer having a relatively lower refractive index characteristic than the first layer. Thus, the refractive index relationship is expressed by using the following specific types of polyester in each layer.

In the present invention, the uniaxial stretching direction is referred to as the X direction, the direction perpendicular to the X direction in the film plane is referred to as the Y direction, and the direction perpendicular to the film plane is referred to as the Z direction.
The P-polarized light in the present invention is defined as a polarized light component parallel to an incident surface including a uniaxially stretched direction (X direction) with a film surface as a reflective surface in a uniaxially stretched multilayer laminated film. The S-polarized light in the present invention is defined as a polarized light component perpendicular to an incident surface including a uniaxially stretched direction (X direction) in a uniaxially stretched multilayer laminated film with the film surface as a reflective surface.
In the present invention, the refractive index in the stretching direction (X direction) may be described as nX, the refractive index in the direction orthogonal to the stretching direction (Y direction) as nY, and the refractive index in the film thickness direction (Z direction) as nZ. .

[First layer]
The first layer constituting the uniaxially stretched multilayer laminated film of the present invention is a layer containing polyester, and the ethylene naphthalate unit is in the range of 80 mol% or more and 100 mol% or less based on the repeating unit constituting the polyester. contains.

(First dicarboxylic acid component)
A naphthalenedicarboxylic acid component is contained as a dicarboxylic acid component constituting the polyester of the first layer, and the content thereof is 80 mol% or more and 100 mol% or less based on the dicarboxylic acid component constituting the polyester.

Examples of the naphthalenedicarboxylic acid component include components derived from 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, or combinations thereof, and derivatives thereof. In particular, 2,6-naphthalenedicarboxylic acid or The derivative component is preferably exemplified.
The lower limit of the content of the naphthalenedicarboxylic acid component is preferably 85 mol%, more preferably 90 mol%. Further, the upper limit of the content of the naphthalenedicarboxylic acid component is preferably less than 100 mol%, more preferably 98 mol% or less, still more preferably 95 mol% or less.

  In addition to the naphthalenedicarboxylic acid component, the dicarboxylic acid component constituting the first layer polyester may further contain terephthalic acid, isophthalic acid, and the like as long as the object of the present invention is not impaired. Among them, terephthalic acid is preferable. The content is preferably in the range of more than 0 mol% and not more than 20 mol%. Further, the lower limit of the content of the second dicarboxylic acid component is more preferably 2 mol%, more preferably 5 mol%, and the upper limit of the content of the second dicarboxylic acid component is more preferably 15 mol%, More preferably, it is 10 mol%. If the second dicarboxylic acid component is less than the lower limit, the adhesion may decrease, and if the upper limit is exceeded, the difference in refractive index from the second layer cannot be increased, and the degree of polarization may decrease. is there.

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

(Diol component)
As the diol component constituting the polyester of the first layer, an ethylene glycol component is used, and the content thereof is preferably 80 mol% or more and 100 mol% or less, more preferably based on the thiol component constituting the polyester. It is 85 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less, and particularly preferably 90 mol% or more and 98 wt% or less. When the ratio of the diol component is less than the lower limit, the above-described uniaxial orientation may be impaired.

As the diol component constituting the polyester of the first layer, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol, diethylene glycol and the like may be contained in addition to the ethylene glycol component as long as the object of the present invention is not impaired.
The melting point of the polyester used for the first layer is preferably in the range of 220 to 290 ° C, more preferably in the range of 230 to 280 ° C, and still more preferably in the range of 240 to 270 ° C. The melting point can be determined by measuring with DSC.
If the melting point of the polyester exceeds the upper limit value, fluidity may be inferior when melt-extruded and molded, and discharge and the like may be made uneven. On the other hand, if the melting point is less than the lower limit, the film forming property is excellent, but the mechanical properties of the polyester are easily impaired, and the refractive index properties of the present invention are hardly exhibited.

The glass transition temperature (hereinafter sometimes referred to as Tg) of the polyester used for the first layer is preferably 80 to 120 ° C, more preferably 82 to 118 ° C, still more preferably 85 to 118 ° C, and particularly preferably. It exists in the range of 100-115 degreeC. When Tg is in this range, the heat resistance and dimensional stability are excellent, and the refractive index characteristics of the present invention are easily exhibited. Such melting point and glass transition temperature can be adjusted by controlling the kind and amount of copolymerization component and diethylene glycol as a by-product.
By using this polyester for the first layer and performing uniaxial stretching, a high refractive index characteristic of 1.80 to 1.90 is expressed with respect to the refractive index nX in the X direction of the first layer. When the refractive index in the X direction in the first layer is within such a range, the refractive index difference from the second layer becomes large, and 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.

[Second layer]
In the present invention, a copolymer polyester containing a 2,6-naphthalenedicarboxylic acid component, an ethylene glycol component and a trimethylene glycol component as copolymerization components may be used as the polymer forming the second layer of the uniaxially stretched multilayer laminated film. is necessary.
The copolymer component in the present invention means any component constituting the polyester, and is not limited to the copolymer component as a subordinate component, and includes the main component.

  In order to express the reflective polarization function, a polyester mainly composed of an ethylene naphthalate unit is used for the first layer as the high refractive index layer of the present invention, and the polymer component of the second layer is 2,6-naphthalenedicarboxylic acid. If the component is not included, the compatibility with the first layer is lowered, and delamination occurs, so that the interlayer adhesion with the first layer is lowered.

In the copolymer polyester of the second layer, the diol component contains at least two components of an ethylene glycol component and a trimethylene glycol component as essential components. Among these, the ethylene glycol component is preferably used as a main diol component from the viewpoint of film-forming properties.
The copolymer polyester of the second layer in the present invention further contains a trimethylene glycol component as a diol component. If the trimethylene glycol component is not included, the elasticity of the layer structure is insufficient and delamination occurs.
The 2,6-naphthalenedicarboxylic acid component is preferably 30 mol% to 100 mol%, more preferably 30 mol% to 80 mol% of the total carboxylic acid component constituting the copolymer polyester of the second layer. More preferably, it is 40 mol%-70 mol%. If the content of the 2,6-naphthalenedicarboxylic acid component is less than the lower limit, the adhesion may be lowered from the viewpoint of compatibility. The upper limit of the content of the 2,6-naphthalenedicarboxylic acid component is not particularly limited, but other dicarboxylic acid components may be copolymerized in order to adjust the refractive index relationship with the first layer.

The ethylene glycol component is preferably 50 mol% to 95 mol%, more preferably 50 mol% to 90 mol%, still more preferably 50 mol% to 85 mol% of the total diol component constituting the copolymer polyester of the second layer. The mol%, particularly preferably 50 mol% to 80 mol%.
The trimethylene glycol component is preferably from 3 mol% to 50 mol%, more preferably from 5 mol% to 40 mol%, more preferably from the total diol component constituting the copolymer polyester of the second layer. It is 10 mol%-40 mol%, Most preferably, it is 10 mol%-30 mol%. If the content of the trimethylene glycol component is less than the lower limit, it is difficult to ensure interlayer adhesion, and if the content exceeds the upper limit, a resin having a desired refractive index and glass transition temperature cannot be obtained.

  The copolymer polyester constituting the second layer preferably has an average refractive index of 1.55 to 1.65, more preferably 1.57 to 1.64, and even more preferably 1.59 to 1.63. Hereinafter, it is particularly preferably 1.60 or more and 1.63 or less, and most preferably 1.60 or more and 1.62 or less. The second layer is preferably an optically isotropic layer.

  The average refractive index of the second layer is obtained by melting the copolymer polyester constituting the second layer alone and extruding it from a die to create an unstretched film. Transition temperature) Stretched 5.5 times at + 20 ° C. to prepare a uniaxially stretched film, and in each of the X direction, Y direction, and Z direction of the obtained film at a wavelength of 633 nm using a metricon prism coupler The refractive index is measured, and the average value thereof is defined as the average refractive index.

Optical isotropy means that the refractive index difference between the two directions of the refractive index in the X direction, Y direction, and Z direction is 0.05 or less, preferably 0.03 or less.
Since the second layer has such an average refractive index and is an optically isotropic material having a small difference in refractive index in each direction by stretching, refraction in the X direction after stretching between the first layer and the second layer. A refractive index characteristic with a large refractive index difference and a small refractive index difference between layers in the Y direction can be obtained, and polarization performance is exhibited.
If the second layer in the present invention is within a range that does not impair the object of the present invention, a thermoplastic resin other than the copolymerized polyester is added to the second polymer within a range of 10% by weight or less based on the weight of the second layer. It may be contained as a component.

  In the present invention, the above-mentioned copolyester of the second layer preferably has a glass transition temperature of 85 ° C. or higher, more preferably 90 ° C. or higher and 150 ° C. or lower, still more preferably 90 ° C. or higher and 120 ° C. or lower, particularly preferably. Is 93 ° C. or higher and 110 ° C. or lower. When the glass transition temperature of the copolyester of the second layer is less than the lower limit, the heat resistance at 90 ° C. may not be sufficiently obtained, and the second layer includes a step such as heat treatment near the temperature. Crystallization or embrittlement of the haze may increase, which may be accompanied by a decrease in the degree of polarization. In addition, when the glass transition temperature of the copolymer polyester of the second layer is too high, the polyester of the second layer may also be birefringent due to stretching at the time of stretching, and accordingly, refraction with the first layer in the stretching direction. The rate difference is reduced, and the reflection performance may be reduced.

Among the above-described copolymer polyesters, amorphous copolymer polyesters are preferable from the viewpoint that no haze increase occurs due to crystallization by heat treatment at 90 ° C. × 1000 hours. The term “amorphous” as used herein means that the heat of crystal melting when the temperature is raised at a rate of temperature rise of 20 ° C./min in differential calorimetry (DSC) is less than 0.1 mJ / mg.
Specific examples of the second layer copolyester include (1) a copolyester containing a 2,6-naphthalenedicarboxylic acid component as a dicarboxylic acid component and an ethylene glycol component and a trimethylene glycol component as a diol component, (2) Examples thereof include a copolyester containing a 2,6-naphthalenedicarboxylic acid component and a terephthalic acid component as the dicarboxylic acid component, and an ethylene glycol component and a trimethylene glycol component as the diol component.

The copolyester preferably has an intrinsic viscosity of 0.50 to 0.70 dl / g measured at 35 ° C. using an o-chlorophenol solution, more preferably 0.55 to 0.65 dl / g. is there.
Since the copolymer polyester used in the second layer uses a trimethylene glycol component as a copolymer component, the film-forming property may be lowered, and the intrinsic viscosity of the copolymer polyester is adjusted to the above range to form a film. The sex can be increased. The intrinsic viscosity when using the above-described copolymer polyester as the second layer is preferably higher from the viewpoint of film forming property, but in the range exceeding the upper limit, the difference in melt viscosity from the polyester of the first layer becomes large, The thickness of each layer may be non-uniform.

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

The degree of polarization in the present invention can be measured using a degree of polarization measuring device.
This means that the higher the degree of polarization specified by the above equation (1), the more the transmission of the reflected polarization component is suppressed, and the higher the transmittance of the transmitted polarization component in the orthogonal direction. Even slight light leakage of the polarization component can 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 requiring reflective polarization characteristics such as a brightness enhancement member. Moreover, when it has a polarization degree of 99.5% or more, it can be applied alone as a reflective polarizing plate as a polarizing plate of a liquid crystal display having a high contrast, which has been difficult to apply unless it is an absorption polarizing plate.
Such polarization degree characteristics are obtained by using the above-mentioned types of polymers constituting the first layer and the second layer, and by making the refractive indexes between the layers in the X direction, the Y direction, and the Z direction a specific relationship by uniaxial stretching. can get.

(S-polarized average transmittance)
The average transmittance Ts of S-polarized light in the wavelength range of 400 to 800 nm of the uniaxially stretched multilayer laminated film of the present invention is preferably 60% or more, more preferably 70% or more, still more preferably 75% or more, particularly preferably. Is 80% or more.
The average transmittance of S-polarized light in the present invention is an incident angle of 0 degree with respect to a polarized light component perpendicular to an incident surface including a uniaxially stretched direction (X direction) in a uniaxially stretched multilayer laminated film. The average transmittance at a wavelength of 400 to 800 nm with respect to the incident polarized light is shown.
If the average transmittance of the S-polarized light is less than the lower limit, when used for a brightness improving member, a reflective polarizing plate, etc., the reflected polarized light component is reflected to the light source side without being absorbed by the film, and the light is effectively utilized again. Even when the light recycling function is taken into account, the superiority of the brightness enhancement effect may not be sufficient.

[Buffer layer, middle layer, and outermost layer]
The uniaxially stretched multilayer laminated film of the present invention may include an intermediate layer and / or an outermost layer in addition to the first layer and the second layer. The intermediate layer and / or the outermost layer preferably has a thickness of 5 μm or more and 50 μm or less, and such an intermediate layer may be included in the alternately laminated structure of the first layer and the second layer.
The intermediate layer is sometimes referred to as an internal thick film layer or the like in the present invention. In the present invention, the intermediate layer refers to a thick film layer existing inside an alternately laminated structure. In the present invention, a thick film layer (sometimes referred to as a thickness adjusting layer or a buffer layer) is formed on both sides of an alternating laminate of 101 layers or more at the initial stage of production of the multilayer laminated film, and then the number of laminated layers is determined by doubling. Is preferably used, but in that case, a method in which two buffer layers are laminated to form an intermediate layer is preferable, and the outermost thick film layer obtained by such a method is replaced with an intermediate layer. This is called the outermost layer.

  When the intermediate layer having such a thickness is included in a part of the alternately laminated structure of the first layer and the second layer, the thickness of each layer constituting the first layer and the second layer is uniformly adjusted without affecting the polarization function. It becomes easy. The intermediate layer having such a thickness may be the same composition as either the first layer or the second layer, or a composition partially including these compositions. Since the layer thickness is thick, the intermediate layer does not contribute to the reflection characteristics. On the other hand, since the polarized light to be transmitted may be affected, when particles are included in the layer, it is preferably within the range of the particle concentration described in the description of the particles.

If the thickness of the intermediate layer is less than the lower limit, the layer configuration of the alternately laminated components may be disturbed, and the reflection performance may be deteriorated. On the other hand, if the thickness of the intermediate layer exceeds the upper limit, the total thickness of the uniaxially stretched multilayer laminated film after lamination is increased, and it is difficult to save space when used as a polarizing plate or a brightness enhancement member of a thin liquid crystal display. Sometimes. Moreover, when a some intermediate | middle layer is included in a uniaxially stretched multilayer laminated film, it is preferable that the thickness of each intermediate | middle layer exists in this range.
Furthermore, when it has the thick film layer (outermost layer) of the above-mentioned thickness which consists of a composition of a 2nd layer in both surface layers of a uniaxial stretching multilayer laminated film, the outermost layer of a glass transition point relatively lower than a 1st layer Is preferable because it functions as a cushioning material, can relieve some of the external stress on the uniaxially stretched multilayer laminated film, and can suppress delamination between layers.

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

[Coating layer]
In the present invention, it is preferable that a coating layer is further provided on at least one of the outermost layers of the uniaxially stretched multilayer laminated film, and the coating layer contains an acrylic binder.
The thickness of the coating layer is preferably 0.02 to 0.50 μm, and more preferably 0.02 to 0.20 μm, from the viewpoint of ensuring adhesion.

In general, when an easy-adhesion coating layer is provided on a polyethylene terephthalate film, a polyester resin, a urethane resin, an acrylic resin, or the like having a glass transition point of 30 ° C. or higher and lower than 100 ° C. is often used as a binder component. By adding, winding property can be secured at the same time.
In the case of the uniaxially stretched multilayer laminated film of the present invention, a mode in which a thick film layer composed of the composition of the second layer is provided as the outermost layer of the multilayer laminated is preferable from the viewpoint of production of the multilayer laminated, but the second layer is non-oriented When the coating layer is further provided on the surface layer due to being in a state and the like, if a polyester resin and / or urethane resin highly compatible with the polyester constituting the second layer is used, the coating film constitutes the second layer. Since it is mixed with the polyester, the winding property may not be sufficiently ensured even if particles are added to the coating layer.
Therefore, when providing a thick film layer composed of the composition of the second layer as the outermost layer of the multilayer stack and further providing a coating layer on at least one surface thereof, in order to improve the adhesion and winding properties with the outermost layer The coating layer preferably contains an acrylic binder, and preferably contains particles of a predetermined size.
Further, as described later, when a prism layer or a diffusion layer is laminated on at least one surface of the uniaxially stretched multilayer laminated film of the present invention, a solvent-free UV curable acrylic resin is generally used as the prism layer. Also from the viewpoint of adhesion to the prism layer, the coating layer preferably contains an acrylic binder.

  The type of the acrylic binder is not particularly limited, but an acrylic copolymer is preferable, and the main component is preferably composed of methyl methacrylate, ethyl methacrylate, butyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, or the like. Such a main component may use not only one type but also a plurality of components, 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, it is preferable to add an acrylic component containing a hydroxyl group, a carboxyl group, a nitrile group, an amide group, a cyano group or the like as a co-polymerization component as an adhesion improving component or a self-crosslinking component.
As a (meth) acrylate of the subsequent copolymerization component, for example, those exemplified below can be used. Acrylic acid, methacrylic acid, 2-hydroxyl acrylate, 2-hydroxyl methacrylate, 2-hydroxyl ethyl acrylate, 2-hydroxyl butyl acrylate, acrylamide, methacrylamide, ethyl acrylamide, butyl acrylamide, dimethyl acrylamide, diethyl acrylamide, hydroxy diethyl acrylamide N-methylolacrylamide, acrylonitrile, methacrylonitrile, acryloylmorpholine, oxetane methacrylate and the like.
Of these, acrylonitrile, N-methylolacrylamide, 2-hydroxylethyl acrylate and the like are preferable.

The acrylic binder is preferably an aqueous emulsion from the viewpoint of ensuring adhesion to the solventless prism layer and from the viewpoint of reducing the viscosity of the aqueous coating liquid.
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 film may be lowered. On the other hand, when the particle size of the emulsion is less than 20 nm, it becomes close to a water-soluble acrylic binder, and the adhesion to the prism layer may be lowered.

In order to apply the aqueous coating liquid in 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, while lowering the adhesion with the prism layer. Therefore, it is preferable to keep the content of the surfactant to the minimum amount within the range where the effect is manifested. Specifically, 0.02 to 0.30% by weight based on the weight of the aqueous coating liquid is added. It is preferable to keep the amount.

As the surfactant, an anionic surfactant, a cationic surfactant, a nonionic surfactant, or the like can be used. Of these, polyoxyalkylene phenyl ether is preferable from the viewpoint of improving adhesion to the prism layer, and examples thereof include polyoxyethylene tribenzylphenyl ether and polyoxyethylene distyrenated ether.
The amount of the coating layer composition added is preferably 1% by weight or more and 10% by weight or less based on the weight of the composition in terms of solid content. If it is less than 1% by weight, the stability of the coating film may be lowered, and coating defects such as coating stripes and repellency are likely to occur. If it is more than 10% by weight, the adhesion between the prism and the coating layer will be reduced. There is.

The coating layer in the present invention preferably further contains particles. When the coating layer contains an acrylic binder and further contains particles, the winding property is improved even when the coating layer has the outermost layer composed of the composition of the second layer of the present invention.
As such particles, it is preferable to add inert inorganic particles such as silica particles, inert organic particles such as acrylic particles, or organic-inorganic composite particles. Further, it is preferable to use particles having an average particle size of 100 nm or more and 1000 nm or less (hereinafter sometimes referred to as large particles). In the case of particles having an average particle size of less than 100 nm, the winding property may not be sufficiently exhibited. On the other hand, if the average particle size is larger than 1000 nm, the transparency of the coating layer may be lowered.
The amount of the particles used in the coating layer is preferably 0.1% by weight or more and 3.0% by weight or less when the total solid component of the coating layer composition is 100% by weight. When the addition amount is less than 0.1% by weight, the winding property may not be sufficiently exhibited, and when it is more than 3.0% by weight, the transparency of the coating layer may be deteriorated.

  In addition to the particles having the above average particle diameter, particles having an average particle diameter of 10 nm to 80 nm (hereinafter sometimes referred to as small particles) are added in the range of 0.5 wt% to 5.0 wt%. It is preferable to do. If the added amount of such small particles is less than 0.5% by weight, the effect of improving the winding property may not be sufficiently exhibited. On the other hand, if the added amount of small particles is more than 5% by weight, the transparency may be lowered. There is. The kind of particles used for the small particles is preferably any of inert inorganic particles represented by silica particles, inert organic particles represented by acrylic particles, or organic-inorganic composite particles, similar to the large particles, Further, it is more preferable to use the same type as the large particles.

[Lamination structure of uniaxially stretched multilayer laminated film]
(Number of layers)
In the uniaxially stretched multilayer laminated film of the present invention, it is preferable that the first layer and the second layer described above are alternately laminated in a total of 101 or more layers. When the number of laminated layers is 100 or less, a certain average reflectance may not be obtained over a wavelength range of 400 to 800 nm with respect to an average reflectance characteristic of a polarization component parallel to the incident surface including the stretching direction (X direction). is there.
The upper limit of the number of layers is preferably 2001 layers or less from the viewpoint of productivity and film handling properties, etc. However, if the desired average reflectance characteristic is obtained, the number of layers can be further reduced from the viewpoint of productivity and handling properties. For example, it may be 1001, 501 or 301 layers. The thickness of the optical member obtained by the present invention can be further reduced by setting the number of laminated layers to a smaller number within a range that satisfies the target reflection characteristics.

(Each layer thickness)
The thickness of each of the first layer and the second layer is preferably 0.01 μm or more and 0.5 μm or less. The thickness of each layer of the first layer is more preferably 0.01 μm or more and 0.1 μm or less, and the thickness of each layer of the second layer is more preferably 0.01 μm or more and 0.3 μm or less. The thickness of each layer can be determined based on a photograph taken using a transmission electron microscope.
When the uniaxially stretched multilayer laminated film in the present invention is used as a reflective polarizing plate such as a brightness enhancement member or a liquid crystal display, the reflection wavelength band is preferably from the visible light region to the near infrared region, and the first layer and the first layer By setting the thickness of each of the two layers within such a range, light in such a wavelength region can be selectively reflected by optical interference between layers. On the other hand, when the layer thickness exceeds 0.5 μm, the reflection band becomes the infrared region. On the other hand, when the layer thickness is less than 0.01 μm, the polyester component absorbs light and the reflection performance cannot be obtained.

(Ratio of maximum layer thickness to minimum layer thickness)
In the uniaxially stretched multilayer laminated film of the present invention, the ratio between the maximum layer thickness and the minimum layer thickness in each of the first layer and the second layer is preferably 2.0 or more and 5.0 or less, more preferably It is 2.0 or more and 4.0 or less, more preferably 2.0 or more and 3.5 or less, and particularly preferably 2.0 or more and 3.0 or less. The ratio of the layer thickness is specifically represented by the ratio of the maximum layer thickness to the minimum layer thickness. The maximum layer thickness and the minimum layer thickness in each of the first layer and the second layer can be obtained based on a photograph taken using a transmission electron microscope.
In the multilayer laminated film, the wavelength to be reflected is determined by the difference in refractive index between layers, the number of layers, and the thickness of the layer. However, when each of the laminated first and second layers has a constant thickness, only a specific wavelength is reflected. The average reflectance of the polarization component parallel to the incident surface including the stretching direction (X direction) cannot be increased uniformly over a wide wavelength range of 400 to 800 nm, It is preferable to use layers having different thicknesses.

On the other hand, when the ratio between the maximum layer thickness and the minimum layer thickness exceeds the upper limit value, the reflection band is wider than 400 to 800 nm, and the reflectance of the polarization component parallel to the incident surface including the stretching direction (X direction) May be accompanied by a decline.
The layer thicknesses of the first layer and the second layer may change stepwise or may change continuously. By changing each of the first layer and the second layer laminated in this way, light in a wider wavelength range can be reflected.
The method of laminating the multilayer structure in the uniaxially stretched multilayer laminated film of the present invention is not particularly limited. For example, the first layer and the first layer obtained by branching the polyester for the first layer into 138 layers and the polyester for the second layer into 137 layers and the first layer There is a method of using a multilayer feed block device in which two layers are alternately laminated and the flow path is continuously changed by 2.0 to 5.0 times.

(Average layer thickness ratio of the first layer and the second layer)
In the uniaxially stretched multilayer laminated film of the present invention, the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is preferably in the range of 0.5 times to 4.0 times. The lower limit of the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is more preferably 0.8. The upper limit of the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is more preferably 3.0. The most preferred range is 1.1 or more and 3.0 or less.
By setting the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer to an optimum thickness ratio, light leakage due to multiple reflection can be further improved. The optimum thickness ratio here is (the refractive index in the stretching direction of the first layer) × (the average layer thickness of the first layer) and (the refractive index in the stretching direction of the second layer) × The value (optical thickness) represented by (average layer thickness of the second layer) is a uniform thickness, and when converted from the refractive index characteristics of each layer of the present invention, the second with respect to the average layer thickness of the first layer. A preferable range of the ratio of the average layer thickness of the layers is about 1.1 to 3.0.

[Uniaxially stretched film]
The uniaxially stretched multilayer laminated film of the present invention is stretched in at least a uniaxial direction in order to obtain optical characteristics as a target reflective polarizing film. The uniaxial stretching in the present invention includes a film stretched in a biaxial direction in addition to a film stretched only in a uniaxial direction and a film stretched in one direction. The uniaxial stretching direction (X direction) may be either the film longitudinal direction or the width direction. Further, in the case of a film stretched in a biaxial direction and stretched in one direction, the direction (X direction) that is more stretched may be either the film longitudinal direction or the width direction. In the direction where the draw ratio is low, it is preferable that the draw ratio is about 1.03 to 1.20 times from the viewpoint of improving the polarization performance. In the case of a film stretched in a biaxial direction and stretched in one direction, the “stretch direction” in relation to polarized light and refractive index refers to a more stretched direction.
As the stretching method, known stretching methods such as heat stretching with a rod heater, roll heat stretching, and tenter stretching can be used, but tenter stretching is preferable from the viewpoint of reducing scratches due to contact with the roll and stretching speed.

[Refractive index characteristics between the first layer and the second layer]
The X-direction refractive index difference between the first layer and the second layer is preferably 0.10 to 0.45. When the refractive index difference in the X direction is within such a range, the reflection characteristics can be improved efficiently, and a high reflectance can be obtained with a smaller number of layers, which is preferable.
The difference in refractive index between the first layer and the second layer in the Y direction is preferably 0.05 or less. It is preferable that the refractive index difference between the layers in the Y direction is within such a range that the polarization performance is improved.

[Film thickness]
The film thickness of the uniaxially stretched multilayer laminated film of the present invention is preferably 15 μm or more and 200 μm or less, and more preferably 35 μm or more and 150 μm or less.

[Method for producing uniaxially stretched multilayer laminated film]
Below, the manufacturing method of the uniaxially stretched multilayer laminated film of this invention is explained in full detail.
The uniaxially stretched multi-layer laminate film of the present invention creates an alternating laminate of 101 layers or more in total by alternately superposing the polymer constituting the first layer and the polymer constituting the second layer in a molten state, Thick film layers (buffer layers) are provided on both sides, and an alternate laminate having the buffer layer is divided into, for example, 2 to 4 using a device called layer doubling, and the alternate laminate having the buffer layer is blocked as one block. The number of stacked layers can be increased by a method of stacking again so that the number of stacked layers (doubling number) is 2 to 4 times. By such a method, an uniaxially stretched multilayer laminated film having an intermediate layer in which two buffer layers are laminated in a multilayer structure and an outermost layer composed of one buffer layer on both surfaces can be obtained.
Such an alternate laminate is laminated so that the thickness of each layer changes stepwise or continuously in a range of 2.0 to 5.0 times.

  The multilayer unstretched film laminated in a desired number of layers by the above-described method is stretched in the film forming direction or at least one axial direction (direction along the film surface) in the width direction perpendicular thereto. The stretching temperature is preferably in the range of the glass transition temperature (Tg) to (Tg + 20) ° C. of the polymer of the first layer. By performing stretching at a temperature lower than before, the orientation characteristics of the film can be controlled to a higher degree.

  The draw ratio is preferably 2 to 7.0 times, more preferably 4.5 to 6.5 times. Within such a range, the larger the draw ratio, the smaller the variation in the plane direction of the individual layers in the first layer and the second layer, and the light interference of the multilayer stretched film is made uniform in the plane direction. Moreover, since the refractive index difference of the extending direction of a 1st layer and a 2nd layer becomes large, it is preferable. As the stretching method at this time, known stretching methods such as heat stretching with a rod heater, roll heating stretching, and tenter stretching can be used. From the viewpoints of reducing scratches due to contact with the roll and stretching speed, tenter stretching is performed. preferable.

Moreover, when performing a extending | stretching process also in the direction (Y direction) orthogonal to this extending | stretching direction and performing biaxial stretching, it is preferable to limit to a draw ratio of about 1.03-1.20 times. If the stretch ratio in the Y direction is further increased, the polarization performance may be deteriorated.
Moreover, the uniaxially stretched multilayer laminated film obtained by toe-out (re-stretching) in the stretching direction within a range of 5 to 15% while further heat-setting at a temperature of (Tg) to (Tg + 30) ° C. after stretching. It is possible to highly control the orientation characteristics.
In the present invention, when the above-mentioned coating layer is provided, 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 member]
The uniaxially stretched multilayer laminated film of the present invention uses the polyester of the above-described composition for each of the first layer and the second layer, and alternately laminates in multiple layers and stretches in one direction to selectively select one polarization component. It can be used as a brightness enhancement member for liquid crystal displays and the like because it exhibits the performance of selectively transmitting the polarized light component and the polarized light component perpendicular to the polarized light component. When used as a brightness enhancement member, a good brightness improvement rate can be obtained, and light can be reused by reflecting the polarization component that has not been transmitted to the light source side.
In addition, 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. In that case, it is preferable that a prism layer or a diffusion layer is laminated via the coating layer described above.

By using the uniaxially stretched multilayer laminated film of the present invention and bonding to a member such as a prism layer to form a unit, the number of members during assembly can be reduced, and the thickness of the liquid crystal display can be further reduced. Moreover, since the delamination by the external force added at the time of a process etc. can be suppressed by bonding with these members using the uniaxially stretched multilayer laminated film of this invention, a more reliable brightness improvement member can be provided.
When the uniaxially stretched multilayer laminated film of the present invention is used as a brightness enhancement member, it can be used in a liquid crystal display device having a configuration as shown in FIG.
Specifically, a liquid crystal display device in which the brightness enhancement member 4 is disposed between the light source 5 of the liquid crystal display and the liquid crystal panel 6 composed of the polarizing plate 1 / liquid crystal cell 2 / polarizing plate 3 is exemplified. . When further providing a prism layer, it is preferable to dispose the prism layer on the liquid crystal panel 6 side.

[LCD polarizing plate]
Among the uniaxially stretched multi-layer laminated films of the present invention, those having a high degree of polarization of 99.5% or more, the polarization of a liquid crystal display used alone adjacent to the liquid crystal cell without using an absorptive polarizing plate in combination. It can be used as a plate.
The present invention also includes an optical member for liquid crystal display (liquid crystal panel) in which the first polarizing plate, the liquid crystal cell, and the second polarizing plate, which are the polarizing plates for liquid crystal display of the present invention, are laminated in this order. Included as an aspect.
Conventionally, as a polarizing plate on both sides of a liquid crystal cell, high polarizing performance has been obtained by having at least an absorptive polarizing plate. If it is a polarizing plate using the uniaxially stretched multilayer laminated film of the present invention, Since high polarization performance that could not be achieved by the multilayer laminated film is obtained, it can be used as a polarizing plate used adjacent to the liquid crystal cell instead of the absorption polarizing plate.

Examples of the present invention will be described below, but the present invention is not limited to the examples shown below.
In addition, the physical property and characteristic in an Example were measured or evaluated by the following method.

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

(2) Interlayer adhesion An ultraviolet curable acrylic resin having 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 to form a glass. The resin is cured by irradiation with a UV lamp (irradiation intensity: 80 W / cm, 6.4 KW) from a distance of 30 cm on the surface side of the mold, and the resin is cured. A lens layer was formed to obtain a brightness enhancement sheet. The processed surface of the obtained brightness enhancement sheet is subjected to cross cut (100 squares of 1 mm ² ), and a cellophane tape having a width of 24 mm (manufactured by Nichiban Co., Ltd.) is pasted thereon and peeled at 90 °. After abrupt peeling 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 (R-604, manufactured by Nippon Kayaku Chemical Co., Ltd.) 25% by weight
27% by weight of phenoxyethyl acrylate (Biscoat 192 manufactured by Osaka Organic Chemical Industry Co., Ltd.)
2-Hydroxy-2-methyl-1-phenylpropan-1-one (Darocur 1173 manufactured by Merck) 2% by weight
<Adhesion evaluation criteria>
A: peeling area of 0% or more and less than 5% (very good adhesion)
○: peeling area is 5% or more and less than 20% (adhesive strength is good)
X: Peeling area is 20% or more (adhesive strength is poor)

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

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

(5) Average refractive index after stretching in each direction Each resin constituting each layer was melted, extruded from a die, and cast on a casting drum. Further, a stretched film was prepared by stretching the obtained film 5.5 times in the uniaxial direction at (glass transition temperature of resin) + 20 ° C. With respect to the obtained cast film and stretched film, the refractive index (respectively, nX, nY, nZ) in the stretching direction (X direction), the orthogonal direction (Y direction), and the thickness direction (Z direction) is measured. It was determined by measuring at a wavelength of 633 nm using a prism coupler. About the average refractive index of polyester which comprises a 2nd layer, the average value of the refractive index of each direction after extending | stretching was made into the average refractive index.

(6) Thickness of each layer A uniaxially stretched multilayer laminated film was cut into a film longitudinal direction of 2 mm and a width direction of 2 cm, fixed to an embedding capsule, and then embedded with an epoxy resin (Epomount manufactured by Refinetech Co., Ltd.). The embedded sample was cut perpendicularly in the width direction with a microtome (LETRAC ULCT UCT manufactured by LEICA) to form a thin film slice having a thickness of 5 nm. Using a transmission electron microscope (Hitachi S-4300), the film was observed and photographed at an acceleration voltage of 100 kV, and the thickness of each layer was measured from the photograph.
With respect to a layer having a thickness of 1 μm or more, the thickness existing in the multilayer structure was defined as the intermediate layer, and the thickness present in the outermost layer was defined as the outermost layer, and each thickness was measured. When a plurality of intermediate layers existed, the intermediate layer thickness was determined from the average value thereof.
Moreover, based on the thickness of each obtained layer, the ratio of the maximum layer thickness to the minimum layer thickness in the first layer and the ratio of the maximum layer thickness to the minimum layer thickness in the second layer were determined.
Moreover, based on the thickness of each obtained layer, the average layer thickness of the first layer and the average layer thickness of the second layer were determined, respectively, and the average layer thickness of the second layer relative to the average layer thickness of the first layer was calculated.
In determining the thicknesses of the first layer and the second layer, the intermediate layer and the outermost layer were excluded from the first layer and the second layer.

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

(8) Brightness improvement effect (brightness improvement rate)
Using a VA liquid crystal display panel (AQUAOS LC-20E90 manufactured by Sharp), the prism film and the upper diffusion film are removed, and the resulting brightness enhancement film with a prism layer is replaced with a white display. Was measured with an FPD viewing angle measurement and evaluation apparatus (ErgoScope 88) manufactured by Opto Design, and the rate of increase in luminance relative to the configuration before replacement was calculated, and the luminance improvement effect was evaluated according to the following criteria.
A: Brightness improvement effect is 150% or more B: Brightness improvement effect is 120% or more and less than 150% X: Brightness improvement effect is less than 120%

(9) Durability at 90 ° C. A uniaxially stretched multilayer laminated film was attached to a transparent optical glass having a thickness of 10 mm via an adhesive film, and the initial degree of polarization was measured. After processing at 90 ° C. for 500 hours in a heating oven (manufactured by ESPEC Corp., model number SH241), the film was taken out and left at room temperature for 1 hour to measure the degree of polarization. The 90 ° C. durability was evaluated according to the following criteria.
A: Initial contrast, decrease in degree of polarization after durability is less than 2% B: Initial contrast, decrease in degree of polarization after durability is 2% or more and less than 4% x: Initial contrast, decrease in degree of polarization after durability 4% or more

[Example 1]
As the polyester for the first layer, dimethyl 2,6-naphthalenedicarboxylate, dimethyl terephthalate, and ethylene glycol are transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction to produce an acid component. Copolymer in which 95 mol% of the 2,6-naphthalenedicarboxylic acid component (described as PEN in the table), 5 mol% of the acid component is terephthalic acid component (described in the table as DMT), and the glycol component is ethylene glycol Polyester (DMT5PEN) (intrinsic viscosity 0.64 dl / g) was prepared.
As the polyester for the second layer, dimethyl 2,6-naphthalenedicarboxylate, dimethyl terephthalate, and ethylene glycol and trimethylene glycol are transesterified in the presence of titanium tetrabutoxide, followed by a polycondensation reaction. 50 mol% of the acid component is 2,6-naphthalenedicarboxylic acid component (described as PEN in the table), 50 mol% of the acid component is terephthalic acid component (described as DMT in the table), glycol component A copolymerized polyester (DMT50C3G15PEN) (intrinsic viscosity 0.63 dl / g) in which 15 mol% was trimethylene glycol was prepared.

The prepared polyester for the first layer was dried at 170 ° C. for 5 hours, the polyester for the second layer was dried at 85 ° C. for 8 hours, then supplied to the first and second extruders, respectively, heated to 300 ° C. and melted The first layer polyester is branched into 138 layers and the second layer polyester is branched into 137 layers, and then the first layer and the second layer are alternately laminated, and the maximum in each of the first layer and the second layer is The first layer and the second layer were alternately laminated by using a multilayer feed block apparatus in which the layer thickness and the minimum layer thickness were continuously changed up to 3.1 times and 3.0 times at the maximum / minimum. A total of 275 layers of molten material is used, and the same polyester as the second layer polyester is led from the third extruder to the three-layer feed block on both sides of the melt while maintaining the laminated state. Both sides of the lamination direction of the melt in the state It was further laminated a buffer layer. The supply amount of the third extruder was adjusted so that the total of the buffer layers on both sides was 47% of the total. The layered state is further divided into two layers at a layer doubling block and laminated at a ratio of 1: 1, and the layered state of 553 layers including the intermediate layer inside and the two outermost layers in the outermost layer is maintained. Guided to a die, cast on a casting drum, adjusted so that the average layer thickness ratio of the first layer and the second layer is 1.0: 1.3, and an unstretched multi-layer stack with a total number of 553 layers A film was created.
On one side of this unstretched multilayer laminated film, a coating liquid A having an acrylic binder composition shown below with a solid content concentration of 4% was uniformly applied with a roll coater so that the coating thickness after stretching and drying was 0.1 μm.
This unstretched multilayer laminated film was stretched 5.5 times in the width direction at a temperature of 130 ° C. The thickness of the obtained uniaxially stretched multilayer laminated film was 85 μm.

[Examples 2-4, Comparative Examples 1-2]
As shown in Table 1, a uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1 except that the resin composition, layer thickness, and stretching conditions of each layer were changed. Table 1 shows the resin configuration of each layer of the uniaxially stretched multilayer laminated film thus obtained, and the characteristics of each layer. Table 1 shows the physical properties of the uniaxially stretched multilayer laminated film.

[Coating liquid A]
(Acrylic binder)
It consists of 60 mol% methyl methacrylate / 30 mol% ethyl acrylate / 2 mol% 2-hydroxyethyl acrylate / 5 mol% N-methylolacrylamide (Tg = 40 ° C.). Charge 302 parts of ion-exchanged water to a four-necked flask and raise the temperature to 60 ° C. in a nitrogen stream, then add 0.5 parts of ammonium persulfate and 0.2 part of sodium bisulfite 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 over 3 hours, with a liquid temperature of 60 to 70 ° C. It was dripped while adjusting. After the completion of dropping, the reaction was continued with stirring while maintaining the same temperature range for 2 hours, and then cooled to obtain an acrylic aqueous dispersion having a solid content of 25% by weight.
(Surfactant) Polyoxyethylene tribenzylphenyl ether (particles) Acrylic spherical particles (average particle diameter: 150 nm: manufactured by Nippon Shokubai Co., Ltd., trade name “Eposter MX-100W”)
These were prepared in the following composition ratio.
Acrylic binder: Surfactant: Particle = 89 wt%: 10 wt%: 1 wt% (added amount in terms of solid content)

  Although the uniaxially stretched multilayer laminated film of the present invention is a polymer film having a multilayer structure using a polyethylene naphthalate polymer in a layer having a high refractive index characteristic, it has a certain polarization performance and improved adhesion between layers. The For this reason, for example, when used in a brightness improving member or a reflective polarizing plate that requires polarization performance, delamination does not occur due to external force applied during bonding to other members, assembly to a liquid crystal display, use, etc. Therefore, a more reliable brightness improving member, a polarizing plate for a liquid crystal display, and the like can be provided.

DESCRIPTION OF SYMBOLS 1 Polarizing plate 2 Liquid crystal cell 3 Polarizing plate 4 Brightness improving member 5 Light source 6 Liquid crystal panel

Claims (10)

  A uniaxially stretched multilayer laminated film in which a first layer and a second layer are alternately laminated. 1) The first layer is a layer containing a polyester, and ethylene is based on a repeating unit constituting the polyester. It contains naphthalate units in the range of 80 mol% to 100 mol%. 2) The polymer that forms the second layer is a copolymer of 2,6-naphthalenedicarboxylic acid component, ethylene glycol component, and trimethylene glycol component. A uniaxially stretched multilayer laminated film, which is a copolyester contained as a component. The uniaxially stretched multilayer laminate film according to claim 1, wherein the degree of polarization (P) represented by the following formula (1) of the uniaxially stretched multilayer laminate film is 80% or more.
Degree of polarization (P) = {(Ts−Tp) / (Tp + Ts)} × 100 (1)
(In formula (1), Tp represents the average transmittance of P-polarized light in the wavelength range of 400 to 800 nm, and Ts represents the average transmittance of S-polarized light in the wavelength range of 400 to 800 nm)   The trimethylene glycol component is 3 mol% to 50 mol% of the total diol component constituting the copolymer polyester of the second layer, and the glass transition point of the copolymer polyester of the second layer is 85 ° C or higher. Item 3. The uniaxially stretched multilayer laminated film according to item 1 or 2.   The uniaxially stretched multilayer laminated film according to any one of claims 1 to 3, wherein an average refractive index of the second layer is 1.55 or more and 1.65 or less.   The uniaxially stretched multilayer laminated film according to any one of claims 1 to 4, wherein the first layer further contains a terephthalic acid component as a dicarboxylic acid component in a range of more than 0 mol% and 20 mol% or less.   The uniaxially stretched multilayer laminate film according to any one of claims 1 to 5, wherein the number of the uniaxially stretched multilayer laminate film is 101 or more.   The uniaxially stretched multilayer laminate film according to any one of claims 1 to 6, further comprising a thick film layer having a thickness of 5 µm or more and 50 µm or less composed of the composition of the second layer on both surface layers of the uniaxially stretched multilayer laminate film.   The uniaxially stretched multilayer laminated film according to any one of claims 1 to 7, further comprising a coating layer on at least one surface of the film thickness layer, wherein the coating layer contains an acrylic binder.   The uniaxially stretched multilayer laminated film according to any one of claims 1 to 8, which is used as a brightness improving member or a reflective polarizing plate.   An optical member in which a prism layer or a diffusion layer is laminated on at least one surface of the uniaxially stretched multilayer laminated film according to claim 1.