JP7238946B2 - Multilayer laminated film, luminance enhancing member and polarizing plate using the same - Google Patents

Description

The present invention relates to multilayer laminated films.

A multi-layer laminated film, in which multiple layers of low refractive index (low refractive index layers) and high refractive index layers (high refractive index layers) are alternately laminated, selectively reflects light of a specific wavelength through structural optical interference between layers. Alternatively, it can be a transparent optical interference film.

Such a multi-layer laminate film reflects or transmits light over a wide wavelength range by gradually changing the thickness of each layer along the thickness direction or by bonding films with different reflection peaks. It is possible to obtain a high reflectance equivalent to that of a film using metal, and it can also be used as a metallic luster film or a reflective mirror. Furthermore, it is known that by stretching such a multilayer laminated film in one direction, it can be used as a reflective polarizing film that reflects only a specific polarized component, and can be used as a brightness enhancement member for liquid crystal displays and the like. (Patent Documents 1 to 4, etc.).

For example, polyethylene naphthalene dicarboxylate (hereinafter sometimes referred to as PEN) described in Patent Document 2 and the like is used for the high refractive index layer, and PEN obtained by copolymerizing 30 mol% of thermoplastic elastomer or terephthalic acid is used as a low refractive index layer. In the case of the multilayer laminated film used for the refractive index layer, the refractive index difference between the layers in the uniaxial stretching direction is increased to increase the reflectance of P-polarized light (polarized light parallel to the plane of incidence including the uniaxial stretching direction). On the other hand, in the in-plane direction of the film, the difference in refractive index between the layers in the direction orthogonal to the uniaxial stretching direction is reduced to increase the transmittance of S-polarized light (polarized light perpendicular to the plane of incidence including the uniaxial stretching direction). As a result, a certain level of polarization performance is exhibited.

In addition, such a multilayer laminated film may have a thick film layer in order to make the thickness of the film good for handling (Patent Document 5).

JP-A-04-268505 Japanese Patent Publication No. 9-506837 Japanese Patent Publication No. 9-506984 WO 01/47711 pamphlet JP-A-2003-251675 Japanese Patent Publication No. 2012-509496 Japanese Patent Publication No. 2002-509043 JP 2016-24313 A

However, in the conventionally studied multilayer laminated film, the adhesion between the layers may not be sufficient, and for example, there is a problem that the layers are peeled off due to stress applied during post-processing. was there. Here, "interlayer" mainly means between a high refractive index layer (or birefringent layer) and a low refractive index layer (or isotropic layer). In addition, in the case of having a thick film layer, between the multilayer laminated structure including the high refractive index layer (or birefringent layer) and the low refractive index layer (or isotropic layer) and the thick film layer There is also the problem of peeling off. In such a case, the space between the multilayer laminated structure and the thick film layer, more strictly, the space between the layer forming the surface of the multilayer laminated structure and the thick film layer may be called an interlayer.

In Patent Document 6, the second optical layer, which is an isotropic layer, contains the birefringent thermoplastic polymer of the first optical layer, which is a birefringent layer, in a copolymer blend to improve interlayer adhesion. A technique for doing so is disclosed. However, just changing the resin of the isotropic layer while using PEN for the birefringent layer as in Patent Document 6 has a limit in improving interlayer adhesion. Further, when a thick film layer is provided, no consideration is given to improving the adhesion between the multilayer structure and the thick film layer.

Further, in Patent Literatures 7 and 8, it is studied to chemically improve the adhesiveness by a copolymer component, but no study is made from the mechanical properties of the resin.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a multilayer laminated film having improved interlayer adhesion in a multilayer structure constituting the multilayer laminated film.

Another desirable object of the present invention is to provide a multilayer laminate film having a thick layer, in which the interlayer adhesion between the multilayer laminate structure and the thick layer is improved.

As a result of intensive studies on interlayer peeling, the present inventors found that the mechanical properties of the resin that constitutes the multilayer structure, particularly the birefringent layer, are related to the interlayer adhesion. I paid attention to this. That is, the birefringence of the first layer is usually imparted by stretching in many cases. A residual stress difference is generated between the layers, and the mechanism that separation is likely to occur when the difference is large was investigated.

In order to solve the above problems, the present invention employs the following configuration.
1. A multilayer laminated film having a multilayer laminated structure in which birefringent first layers mainly made of resin and isotropic second layers mainly made of resin are alternately laminated,
When a uniaxially stretched film is produced using the resin forming the first layer under the following conditions, the resulting uniaxially stretched film has a stress at 5% elongation (F5 value) in the stretching direction of 370 MPa or more. , 415 MPa or less.
Stretching temperature: glass transition temperature Tg + 25°C of the resin forming the first layer
Stretching speed: 400%/min. Stretching ratio: 5.0 times2. 2. The multilayer laminated film according to 1 above, which has a thick film layer in contact with the multilayer laminated structure.
3. 3. The multilayer laminated film as described in 1 or 2 above, wherein the resin constituting the first layer is an oriented crystalline polyester resin.
4. 4. The multilayer laminated film according to any one of 1 to 3 above, wherein the resin constituting the first layer is a copolymer polyester resin containing a naphthalene dicarboxylic acid component as a main component and an isophthalic acid component as a copolymer component.
5. The copolyester resin constituting the first layer is
The copolymerization amount of the isophthalic acid component is 4 mol% or more and 15 mol% or less with respect to the total dicarboxylic acid component constituting the copolymerized polyester resin,
5. The multilayer laminated film as described in 4 above, which has an intrinsic viscosity of 0.50 dL/g or more and 0.60 dL/g or less.
6. 4. The multilayer laminate film according to any one of 1 to 3 above, wherein the resin constituting the first layer is a copolymer polyester resin containing a naphthalene dicarboxylic acid component as a main component and a terephthalic acid component as a copolymer component.
7. The copolyester resin constituting the first layer is
The copolymerization amount of the terephthalic acid component is 10 mol% or more and 16 mol% or less with respect to the total dicarboxylic acid component constituting the copolymerized polyester resin,
7. The multilayer laminated film as described in 6 above, which has an intrinsic viscosity of 0.52 dL/g or more and 0.59 dL/g or less.
8. 8. The multilayer laminated film according to any one of 1 to 7 above, which is capable of broadly reflecting light with a wavelength of 380 to 780 nm due to optical interference between the first layer and the second layer.
9. A brightness enhancement member using the multilayer laminated film according to any one of 1 to 8 above.
10. A polarizing plate using the multilayer laminated film according to any one of 1 to 8 above.

ADVANTAGE OF THE INVENTION According to this invention, the multilayer laminated film which improved the interlayer adhesion in a multilayer laminated structure can be provided.

Further, according to a preferred embodiment of the present invention, it is possible to provide a multilayer laminated film having a thick film layer in which interlayer adhesion between the multilayer structure and the thick film layer is improved.

According to the present invention, when used as, for example, a brightness improving member for a liquid crystal display or a reflective polarizing plate, delamination occurs due to an external force applied during lamination with other members, assembly into a liquid crystal display, use, or the like. Since it is less likely to occur, it is possible to provide a brightness improving member, a polarizing plate, and the like with higher reliability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an example of the laminated structure of the multilayer laminated film of the present invention;

Each configuration of the present invention will be described in detail below.

[Multilayer laminated film]
The multilayer laminated film of the present invention has a multilayer laminated structure in which first layers mainly made of resin and second layers mainly made of resin are alternately laminated. Here, "predominantly" means that resin accounts for 70% by mass or more in each layer, preferably 80% by mass or more, and more preferably 90% by mass or more.

In the present invention, an aspect may be employed in which the interference effect of light is exhibited by the first layer and the second layer, and in which the light can be reflected in an arbitrary wavelength range. In this case, it is usually preferred that the first layer is birefringent and the second layer is isotropic. Moreover, it is preferable that the total number of layers to be laminated is 30 or more in order to exhibit the interference effect.

In order to achieve such reflection characteristics, a birefringent first layer mainly made of resin and having a thickness of 10 to 1000 nm and an isotropic second layer mainly made of resin and having a thickness of 10 to 1000 nm It is preferable to have a structure in which a total of 30 or more layers are alternately laminated in the thickness direction. The details of the resin constituting each layer will be described later, but for the first layer, a resin that can exhibit specific mechanical properties and can form a birefringent layer, and for the second layer, etc. It is not particularly limited as long as it can form an anisotropic layer. Thermoplastic resins are preferable for all of them from the viewpoint of easy production of films. In the present invention, birefringence is defined when the difference between the maximum and minimum refractive indices in the longitudinal direction, transverse direction, and thickness direction is 0.1 or more, and isotropy is less than 0.1.

Furthermore, the multilayer laminated film of the present invention preferably has a thick film layer in contact with the multilayer laminated structure. In a multi-layered structure, the thickness of each layer affects the optical properties, so if there is a desired optical property, the thickness of each layer cannot be changed unnecessarily. Therefore, by having a thick film layer, the thickness of the multilayer laminate film as a whole can be increased, and for example, handling properties can be improved, which is preferable.

In addition, FIG. 1 shows a schematic diagram of an example of the laminated structure of the multilayer laminated film of the present invention. In FIG. 1, the multilayer laminate structure 3 is in contact with the thick film layers 1 and 2 .

[Structure of multilayer laminated film]
The effect of improving the adhesion between layers according to the present invention can be obtained regardless of the application as long as it is a multilayer laminated film having a multilayer laminated structure of a birefringent first layer and an isotropic second layer. .

A preferable application of the multilayer laminated film is an application that utilizes optical interference between the first layer and the second layer. A preferred configuration of a multilayer laminate film suitable for such applications utilizing optical interference will be described below.

[First layer]
In the first layer of the present invention, the resin forming the first layer is a uniaxially stretched film obtained when a uniaxially stretched film is prepared under the stretching conditions described later using the resin, and the stress at 5% elongation in the stretching direction of the obtained uniaxially stretched film (F5 value) is 370 MPa or more and 415 MPa or less. Here, the stretching conditions are such that the stretching temperature is the glass transition temperature Tg of the resin forming the first layer+25° C., the stretching speed is 400%/min, and the stretching ratio is 5.0 times. The thickness of the uniaxially stretched film to be obtained is preferably about 50 μm in consideration of the ease of film formation and the ease of measuring the F5 value.

When the F5 value is within the above range, the residual stress in the first layer is moderate while the first layer is birefringent, and the residual stress in the second layer is balanced. The interlayer adhesion between the two layers is improved. That is, the birefringence of the first layer is usually imparted by stretching or the like, but if this has residual stress inside due to stretching or the like, the second layer is isotropic and has almost no residual stress inside. A mechanism is presumed in which a difference in residual stress is generated between and when the difference is large, peeling is likely to occur. In the present invention, rather than improving adhesion by sharing chemical properties that the first layer and the second layer have common components, focusing on mechanical properties such as residual stress of the first layer and the second layer, While the first layer has birefringence and the second layer has isotropy, the adhesion between the layers is to be improved.

When the F5 value exceeds the upper limit, the residual stress in the first layer becomes high, so that the residual stress balance between the first layer and the second layer becomes unbalanced, thereby lowering the interlayer adhesion. From this point of view, the F5 value is preferably 410 MPa or less, more preferably 408 MPa or less, and even more preferably 405 MPa or less. If the F5 value is too low, the stress applied to the first layer during stretching tends to be low, which tends to make the film formation unstable and make it difficult to obtain the desired birefringence. Therefore, the F5 value is preferably 380 MPa or higher, more preferably 390 MPa or higher, and even more preferably 395 MPa or higher.

The F5 value tends to increase as the Young's modulus of the resin increases, and decrease as the Young's modulus decreases. For example, when the resin is an oriented or crystalline resin, the direction in which orientation and crystals are less likely to occur is the direction in which the Young's modulus is decreased and the F5 value is decreased. It is conceivable to lower the linearity of the molecule by increasing the molecular weight or by carrying out copolymerization. In particular, it is important that the orientation and crystallinity are affected by the molecular weight and cannot be determined only by the components and amounts of copolymerization. More specifically, it is preferable to use a polyester as described later.

The first layer constituting the multilayer laminated film of the present invention is a birefringent layer. In this case, the constituent resin is capable of forming a birefringent layer. Accordingly, a resin with oriented crystallinity is preferable as the resin constituting the first layer, and a polyester resin is particularly preferable as such a resin with oriented crystallinity. Based on the repeating units constituting the polyester resin, preferably ethylene terephthalate units and/or ethylene isophthalate units and/or ethylene naphthalate units, more preferably ethylene naphthalate units as main components, that is, 84 mol % or more, it is preferable because a layer with a higher refractive index can be easily formed, thereby easily increasing the difference in refractive index from the second layer. Here, in the case of combined use of resin, it is the total content.

(1st layer polyester)
As described above, in the present invention, the polyester for the first layer preferably contains a naphthalenedicarboxylic acid component as a main component as a dicarboxylic acid component from the viewpoint of the refractive index. The content as a main component is preferably 84 mol % or more based on the dicarboxylic acid component constituting the polyester. Such naphthalenedicarboxylic acid components include 2,6-naphthalenedicarboxylic acid components, 2,7-naphthalenedicarboxylic acid components, components derived from combinations thereof, or derivative components thereof, particularly 2,6- A naphthalenedicarboxylic acid component or a derivative component thereof is preferably exemplified. The content of the naphthalene dicarboxylic acid component is more preferably 85 mol % or more, still more preferably 88 mol % or more, even more preferably 90 mol % or more, and particularly preferably 91 mol % or more.

In the present invention, the resin forming the first layer satisfies the F5 value described above, and the F5 value can be satisfied in terms of copolymerization and molecular weight as described above. Copolymerization components include acid components such as terephthalic acid and isophthalic acid. The copolymerization amount can be in the range of 16 mol% or less based on the dicarboxylic acid component constituting the polyester, and can be in the range of 15 mol% or less, 12 mol% or less, 10 mol% or less, and 9 mol% or less. can do. Moreover, it can be in the range of 4 mol % or more, 5 mol % or more, 6 mol % or more, and 7 mol % or more.

In addition, the molecular weight can be expressed as an intrinsic viscosity, and the intrinsic viscosity (o-chlorophenol solution, value at 35 ° C.; hereinafter the same) is in the range of 0.5 dL / g or more and 0.60 dL / g or less. be able to. From these, it can be seen that the crystallinity and orientation tend to be lower for the copolymer components that are bent due to the chemical structure, the glass transition temperature tends to be lower, and the Young's modulus at room temperature tends to be lower, the crystallinity and orientation tend to be lower with a larger amount of copolymerization, the glass transition temperature tends to be lower, and the Young's modulus at room temperature tends to be lower. , the higher the molecular weight, the lower the crystallinity and orientation tend to be, and the higher the Young's modulus. do it.

Hereinafter, the case where the copolymerization component is an isophthalic acid component and the case where the copolymerization component is a terephthalic acid component, which are particularly preferred embodiments in the present invention, will be described.

(Polyester of first layer: isophthalic acid component copolymerized polyester resin)
A preferred embodiment of the resin constituting the first layer in the present invention is a copolymerized polyester resin containing a naphthalene dicarboxylic acid component as a main component and an isophthalic acid component as a copolymer component.

The copolymer polyester resin is not limited as long as it satisfies the F5 value while exhibiting birefringence. An embodiment in which it is 4 mol % or more and 15 mol % or less with respect to the total dicarboxylic acid component constituting the resin and the intrinsic viscosity is 0.50 dL/g or more and 0.60 dL/g or less can be mentioned. At this time, the naphthalene dicarboxylic acid component as the main component is 85 mol % or more and 96 mol % or less.

The copolymerization amount is more preferably 5 mol% or more, still more preferably 6 mol% or more, particularly preferably 7 mol% or more, more preferably 12 mol% or less, still more preferably 10 mol% or less, especially Preferably, it is 9 mol % or less. At this time, the naphthalene dicarboxylic acid component as the main component is 95 mol % or less, 94 mol % or less, 93 mol % or less, and 88 mol % or more, 90 mol % or more, 91 mol % or more.

The intrinsic viscosity is more preferably 0.51 dL/g or more, still more preferably 0.53 dL/g or more, particularly preferably 0.55 dL/g or more, and more preferably 0.59 dL/g or less, still more preferably is 0.58 dL/g or less.

If the amount of copolymerization and the intrinsic viscosity are outside the above ranges, basically, the product does not satisfy the F5 value specification in the present invention while having birefringence.

In the present invention, the isophthalic acid component as the copolymer component of the first layer provides a copolymer polyester resin that is moderately curved in terms of chemical structure. It is a copolymer component that is particularly preferable to the terephthalic acid component, which will be described later, because it is easy to exhibit refractive properties.

(Polyester of first layer: terephthalic acid component copolymerized polyester resin)
A preferred embodiment of the resin constituting the first layer in the present invention is a copolymerized polyester resin containing a naphthalene dicarboxylic acid component as a main component and a terephthalic acid component as a copolymer component.

The copolymer polyester resin is not limited as long as it satisfies the F5 value while exhibiting birefringence. An embodiment in which the content is 10 mol % or more and 16 mol % or less with respect to the total dicarboxylic acid component constituting the resin and the intrinsic viscosity is 0.52 dL/g or more and 0.59 dL/g or less is exemplified. At this time, the naphthalene dicarboxylic acid component as the main component is 84 mol % or more and 90 mol % or less.

The copolymerization amount is more preferably 11 mol % or more, still more preferably 12 mol % or more, particularly preferably 13 mol % or more, and more preferably 15 mol % or less. At this time, the naphthalenedicarboxylic acid component as the main component is 89 mol % or less, 88 mol % or less, 87 mol % or less, and 85 mol % or more.

The intrinsic viscosity is more preferably 0.53 dL/g or more, still more preferably 0.54 dL/g or more, particularly preferably 0.55 dL/g or more, and more preferably 0.58 dL/g or less, still more preferably is 0.57 dL/g or less.

If the amount of copolymerization and the intrinsic viscosity are outside the above ranges, basically, the product does not satisfy the F5 value specification in the present invention while having birefringence.

(1st layer polyester: diol component)
An ethylene glycol component is used as the diol component constituting the preferred polyester of the first layer, and the content thereof is preferably 80 mol% or more and 100 mol% or less based on the thiol component constituting the polyester, More preferably 85 mol% or more, still more preferably 90 mol% or more, particularly preferably 95 mol% or more, and more preferably 98 mol% or less. If the ratio of the diol component is less than the lower limit, the uniaxial orientation described above may be impaired.

As the diol component constituting the polyester of the first layer, in addition to the ethylene glycol component, a trimethylene glycol component, a tetramethylene glycol component, a cyclohexanedimethanol component, a diethylene glycol component, etc. are contained within a range that does not impair the object of the present invention. good too. The effect of the copolymerization of the glycol component on the F5 value may be considered in the same manner as the effect of the copolymerization of the acid component.

(Refractive index characteristics)
When used as a brightness enhancement member or a reflective polarizing plate used in liquid crystal displays, etc., the first layer is a layer having a relatively higher refractive index characteristic than the second layer, and the second layer is higher than the first layer. Preferably, the layer has relatively low refractive index properties and is uniaxially stretched. In this case, in the present invention, the uniaxial stretching direction is the TD direction, the direction perpendicular to the TD direction in the film plane is the MD direction (also referred to as the non-stretching direction), and the direction perpendicular to the film plane is the Z direction. It may be called a direction (also referred to as a thickness direction).

By using a polyester containing a naphthalene dicarboxylic acid component as a main component for the first layer as described above, it is possible to exhibit a high refractive index in the TD direction and at the same time achieve birefringence characteristics with high uniaxial orientation. The difference in refractive index with respect to the direction of the second layer can be increased, contributing to a high degree of polarization. On the other hand, if the content of the naphthalene dicarboxylic acid component is less than the lower limit, the amorphous property tends to increase, and the difference between the refractive index nTD in the TD direction and the refractive index nMD in the MD direction tends to decrease. In the multi-layer laminate film, it is difficult to obtain sufficient reflection performance for the P-polarized component in the present invention, which is defined as a polarized component parallel to the plane of incidence including the uniaxial stretching direction (TD direction) with the film surface as the reflecting surface. tend to become The S-polarized component in the present invention is defined as a polarized component perpendicular to the plane of incidence including the uniaxial stretching direction (TD direction) with the film surface as the reflecting surface in the multilayer laminated film.

(Characteristics of the polyester of the first layer)
The melting point of the polyester used in the first layer is preferably in the range of 230-280°C, more preferably in the range of 240-270°C, still more preferably in the range of 245-260°C. The melting point can be determined by measuring with a differential scanning calorimeter (DSC). If the melting point of the polyester exceeds the upper limit, the flowability tends to be poor during molding by melt extrusion, and the discharge, etc., tends to become non-uniform. On the other hand, when the melting point is less than the lower limit, although the film formability is excellent, it tends to be difficult to exhibit refractive index characteristics when used as a brightness improving member or a reflective polarizing plate.

The glass transition temperature (hereinafter sometimes referred to as Tg) of the polyester used in the first layer is preferably 100° C. or higher, more preferably 105° C. or higher, and still more preferably 108° C. or higher. It is 120° C. or lower, more preferably 118° C. or lower, and still more preferably 115° C. or lower. When the Tg is in this range, the heat resistance and dimensional stability are excellent, and refractive index characteristics are easily exhibited when used as a brightness enhancement member or a reflective polarizing plate.

The melting point and glass transition temperature can be adjusted by controlling the type and amount of copolymerization components, diethylene glycol as a by-product, and the like.

[Second layer]
The second layer constituting the multilayer laminated film of the present invention is an isotropic layer. In this case, the constituent resin is capable of forming an isotropic layer. Therefore, amorphous resin is preferable as the resin constituting the second layer. Among them, amorphous polyester resins are preferred. Here, the term "amorphous" does not exclude having slight crystallinity, as long as the second layer can be made isotropic to the extent that the multilayer laminated film of the present invention exhibits the intended function. .

(Copolyester for the second layer)
Copolyester is preferable as the resin constituting the second layer, and in particular, naphthalenedicarboxylic acid component, isophthalic acid component, terephthalic acid component, ethylene glycol component and/or trimethylene glycol component, cyclohexanedimethanol component, and neopentyl glycol. It is preferable to use a copolymerized polyester containing other components as a copolymerized component. The naphthalenedicarboxylic acid component includes a 2,6-naphthalenedicarboxylic acid component, a 2,7-naphthalenedicarboxylic acid component, a component derived from a combination thereof, or a derivative component thereof, particularly 2, A preferred example is a 6-naphthalenedicarboxylic acid component or a derivative component thereof. The copolymerization component of the second layer in the present invention means any one of the components constituting the polyester, and the secondary component (as a copolymerization amount, relative to the total acid component or the total diol component) less than 50 mol %), and the main component (50 mol % or more of all acid components or all diol components as a copolymerization amount) is also used.

In the present invention, as the resin for the second layer, it is preferable to use a copolyester in which the acid component is a terephthalic acid component as a main component. In particular, as the resin for the second layer, it is preferable to use a copolyester containing a terephthalic acid component as a main component and a naphthalenedicarboxylic acid component as a secondary component. This makes it easy to make the second layer isotropic in accordance with the aspect of the polyester in the first layer. In addition, there is a tendency to increase the effect of improving adhesion from a chemical point of view.

As the copolyester for the second layer, it is preferable to use a copolyester in which the diol component is an ethylene glycol component as a main component. This tends to improve the film formability. A trimethylene glycol component can also be contained as a secondary component, which is expected to further increase the adhesion between layers.

The naphthalenedicarboxylic acid component, preferably 2,6-naphthalenedicarboxylic acid component, is preferably 30 mol % or more and 100 mol % or less of the total carboxylic acid component constituting the copolymerized polyester of the second layer, more preferably It is 30 mol % or more and 80 mol % or less, more preferably 40 mol % or more and 70 mol % or less. This tends to increase the effect of improving the adhesion from the chemical point of view that the compatibility with the first layer can be increased. If the content of the naphthalenedicarboxylic acid component is less than the lower limit, the effect of improving the compatibility may decrease. The upper limit of the content of the naphthalene dicarboxylic acid component is not particularly limited, but if it is too large, it tends to be difficult to develop a refractive index difference with the first layer. In addition, other dicarboxylic acid components may be copolymerized in order to adjust the refractive index relationship with the first layer.

The isophthalic acid component and the terephthalic acid component, each or a combination of both, preferably accounts for 5 mol% or more and 70 mol% or less, more preferably 10 mol%, of the total carboxylic acid components constituting the copolyester of the second layer. mol % or more and 65 mol % or less, more preferably 30 mol % or more and 60 mol % or less. This tends to increase the effect of improving the adhesion from the chemical point of view that the compatibility with the first layer can be increased. If the content is less than the lower limit, the effect of improving compatibility may decrease. Furthermore, it is preferable to copolymerize the same dicarboxylic acid component among the copolyesters used for the first layer, because the adhesion is more likely to be improved from the viewpoint of compatibility between the layers. Above all, it is more preferable that the isophthalic acid component accounts for 1 mol % or more and 15 mol % or less of the total carboxylic acid components constituting the copolyester of the second layer. By using a copolymerized polyester containing an isophthalic acid component as the resin for the second layer, the presence of a bending component in the chemical structure of the isophthalic acid facilitates the occurrence of an anchor effect at the molecular level with the first layer, It is more preferable because it tends to further improve interlayer adhesion and tends to make interlayer separation less likely to occur.

The ethylene glycol component is preferably 50 mol% or more and 95 mol% or less, more preferably 50 mol% or more and 90 mol% or less, still more preferably 50 mol % or more and 85 mol % or less, particularly preferably 50 mol % or more and 80 mol % or less. This tends to make it easier to develop a refractive index difference with the first layer.

The trimethylene glycol component is preferably 3 mol% or more and 50 mol% or less, more preferably 5 mol% or more and 40 mol% or less, of the total diol component constituting the copolyester of the second layer. , more preferably 10 mol % or more and 40 mol % or less, particularly preferably 10 mol % or more and 30 mol % or less. Thereby, the interlayer adhesion with the first layer can be made higher. In addition, there is a tendency that a difference in refractive index from that of the first layer is likely to occur. If the content of the trimethylene glycol component is less than the lower limit, the effect of improving interlayer adhesion tends to be low, and if it exceeds the upper limit, it tends to be difficult to obtain a resin having a desired refractive index and glass transition temperature. .

As the diol component constituting the polyester of the second layer, in addition to the above components such as the ethylene glycol component, a tetramethylene glycol component, a cyclohexanedimethanol component, a diethylene glycol component, a neopentyl glycol component, and the like are further added within a range that does not impair the object of the present invention. may contain.

The second layer in the present invention contains a thermoplastic resin other than the copolymerized polyester within a range of 10% by mass or less based on the mass of the second layer as long as it does not impair the object of the present invention. It may be contained as a component.

(Characteristics of the polyester of the second layer)
In the present invention, the copolyester of the second layer described above preferably has a glass transition temperature of 80° C. or higher, more preferably 85° C. or higher and 150° C. or lower, still more preferably 88° C. or higher and 120° C. or lower. be. Thereby, it is excellent in heat resistance. In addition, there is a tendency that a difference in refractive index from that of the first layer is likely to occur. If the glass transition temperature of the copolyester of the second layer is less than the lower limit, sufficient heat resistance may not be obtained. The haze increases due to brittleness and embrittlement, and the degree of polarization may decrease when used as a brightness enhancement member or a reflective polarizing plate. In addition, if the glass transition temperature of the copolyester of the second layer is too high, the polyester of the second layer may also have birefringence due to stretching during stretching, and accordingly, the refractive index of the polyester of the second layer is different from that of the first layer in the stretching direction. The index difference becomes small, and the reflection performance may deteriorate.

Among the copolyesters described above, amorphous copolyesters are preferred because they can remarkably suppress the increase in haze due to crystallization by heat treatment at 80° C. for 1000 hours. The term "amorphous" as used herein means that the heat of crystal fusion is less than 0.1 mJ/mg when the temperature is increased at a temperature increase rate of 20°C/min in DSC.

Specific examples of the copolyester for the second layer include (1) a copolyester containing a 2,6-naphthalene dicarboxylic acid component and isophthalic acid as dicarboxylic acid components and an ethylene glycol component and a trimethylene glycol component as diol components; (2) A copolymer polyester containing a 2,6-naphthalene dicarboxylic acid component and a terephthalic acid component as dicarboxylic acid components and an ethylene glycol component and trimethylene glycol component as diol components.

The copolyester of the second layer preferably has an intrinsic viscosity of 0.50 to 0.70 dl/g, more preferably 0.52 to 0.65 dl, measured at 35°C using an o-chlorophenol solution. /g. When the copolyester used in the second layer contains a trimethylene glycol component as a copolymerization component, the film formability may deteriorate. can be further enhanced. In the case of using the above-described copolyester as the second layer, the intrinsic viscosity is preferably higher from the viewpoint of film-forming properties, but in the range exceeding the upper limit, the difference in melt viscosity from the polyester of the second layer increases, The thickness of each layer may be uneven.

[Refractive index]
In the present invention, the refractive index of each of the first layer and the second layer can be designed to produce an optical interference effect.

For example, the first layer preferably has a high refractive index characteristic of 1.80 to 1.90 with respect to the refractive index nTD in the uniaxial stretching direction (TD direction). When the refractive index in the TD direction of the first layer is within such a range, the difference in refractive index from that of the second layer increases, and the reflective polarization performance can be exhibited. Moreover, the difference between the refractive index nMD after uniaxial stretching in the MD direction and the refractive index nZ after uniaxial stretching in the Z direction is preferably 0.05 or less. Such a refractive index characteristic can be obtained by subjecting the polyester resin as described above to uniaxial stretching or the like.

The second layer preferably has an average refractive index of 1.55 or more and 1.65 or less, more preferably 1.57 or more and 1.64 or less, still more preferably 1.59 or more and 1.63 or less. 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 average refractive index of the second layer is obtained by melting the copolyester constituting the second layer alone, extruding it through a die to create an unstretched film, and uniaxially (copolyester glass of the second layer Transition temperature) A uniaxially stretched film was prepared by stretching 5.0 times at +25 ° C., and the TD, MD, and Z directions of the obtained film were measured using a Metricon prism coupler at a wavelength of 633 nm. Refractive indices are measured and their average value is defined as the average refractive index.

[Thick film layer]
In the present invention, the multilayer laminate film may have a thick film layer. The thick film layer in the present invention includes the outermost layer and the intermediate layer described below.

The multilayer laminate film of the present invention may have a thick outermost layer on one or both surfaces. Here, a thick film means an optically thick film. Such an outermost layer is mainly made of resin. Here, "mainly" means that the resin accounts for 70% by mass or more in the layer, preferably 80% by mass or more, and more preferably 90% by mass or more. In addition, the outermost layer is preferably an isotropic layer, and from the viewpoint of ease of production, it may be the same resin as the second layer, and is composed of the above-described copolymerized polyester of the second layer. possible, and such an embodiment is preferred.

The multilayer laminate film of the present invention may have an intermediate layer. The intermediate layer, which may be referred to as an internal thick film layer or the like in the present invention, refers to a thick film layer present inside the multilayer structure. In the present invention, thick layers (sometimes referred to as thickness adjusting layers or buffer layers) are formed on both sides of the alternately laminated structure in the initial stage of manufacturing the multilayer laminated film, and then the number of laminated layers is increased by doubling. method is preferably used, in which case two thick layers are laminated to form an intermediate layer, and the thick layer formed inside becomes the intermediate layer and is formed on the outside. The layer of the thick film that has been coated becomes the outermost layer.

More specifically, the thickness of the outermost layer is preferably more than 1 μm, more preferably 3 μm or more, still more preferably 5 μm or more, and preferably 25 μm or less, more preferably 20 μm or less. Thickness is preferred. The intermediate layer preferably has a layer thickness of, for example, 5 μm or more, preferably 100 μm or less, and more preferably 50 μm or less. When such an outermost layer and/or intermediate layer is part of the multilayer structure, the thickness of each layer constituting the first layer and the second layer is adjusted uniformly without affecting the optical function such as the polarization function. easier. The outermost layer and the intermediate layer may have the same composition as either the first layer or the second layer, or a composition partially containing these compositions, and the layer thickness is optically thick, so it contributes to the reflection characteristics. do not. On the other hand, since it may affect the transmission characteristics, when particles are included in the layer, the particle diameter and particle concentration should be selected in consideration of the light transmittance. In addition, the outermost layer and the intermediate layer can increase the overall thickness of the film, thereby improving handling properties, for example.

If the thickness of the outermost layer and/or the intermediate layer is less than the lower limit, the handleability may be deteriorated during film formation and processing. On the other hand, if the thickness of the outermost layer and/or the intermediate layer exceeds the upper limit, the thickness of the multilayer laminated film as a whole becomes too thick, which saves space when used as a reflective polarizing plate or a brightness enhancement member for a thin liquid crystal display. can be difficult to convert. In addition, when the multilayer laminated film has outermost layers on both surface layers, or when the multilayer laminated film includes a plurality of intermediate layers, the thickness of each outermost layer and/or intermediate layer is within the above thickness range. The total thickness of the outermost layers and/or the total thickness of the intermediate layers is preferably less than or equal to the upper limit of each thickness range.

The polymer used for the outermost layer and the intermediate layer may be a resin different from that of the first layer or the second layer, provided that it can be present in the multilayer structure using the method for producing a multilayer laminated film of the present invention. From the viewpoint of increasing the inter-layer adhesion, it is preferable that the layer has the same composition as either the first layer or the second layer, or a composition that partially contains these compositions.

When the polymer used for the thick film layer has the same composition as the first layer or a composition partially containing this composition, the layer forming the surface of the multi-layer laminate structure in contact with the thick film layer is the first layer. is preferable, and the interlayer adhesion between the thick film layer and the multilayer structure can be further improved. When the polymer used for the thick film layer has the same composition as the second layer or a composition partially containing this composition, the layer forming the surface of the multilayer laminate structure in contact with such thick film layer is the second layer. is preferable, and the interlayer adhesion between the thick film layer and the multilayer structure can be further improved. Also in this case, as described above, the thick layer preferably has less optical influence, so it is preferably isotropic, and therefore preferably has the same composition as the second layer. In that case, it is preferable that the layer forming the surface of the multilayer laminate structure is the second layer.

The method of forming the outermost layer and the intermediate layer is not particularly limited. is used to divide the laminate into two in the direction perpendicular to the alternate lamination direction, and these are relaminated in the alternate lamination direction to provide two outermost layers and one intermediate layer. A plurality of intermediate layers can also be provided by increasing the number of divisions, increasing the number of divisions, or by dividing into three or four in a similar manner.

[Other layers]
(Coating layer)
The multilayer laminate film of the present invention can have a coating layer on at least one surface. Examples of such a coating layer include a slippery layer for imparting slipperiness and a primer layer for imparting adhesiveness to a prism layer, a diffusion layer, or the like. The coating layer contains a binder component, and may contain, for example, particles in order to impart lubricity. In order to impart easy adhesion, the binder component to be used should be chemically close to the component of the layer to be adhered. The coating liquid for forming the coating layer is preferably a water-based coating liquid using water as a solvent from an environmental point of view. Surfactants can be included for enhancement purposes. In addition, a functional agent such as a cross-linking agent may be added to increase the strength of the coating layer.

[Method for producing multilayer laminated film]
A method for producing the multilayer laminate film of the present invention will be described in detail. In addition, the manufacturing method shown below here is an example, and the present invention is not limited to this. Different aspects can also be obtained by reference to the following.

The multilayer laminated film of the present invention is produced by alternately superimposing the polymer constituting the first layer and the polymer constituting the second layer in a molten state using a multilayer feed block apparatus to obtain, for example, a total of 30 layers or more. Alternating stacks may be created with buffer layers on both sides. After that, using a device called layer doubling, the alternately laminated structure is divided into, for example, 2 to 4 parts, and the alternately laminated structure is used as one block, and laminated again so that the number of laminated blocks (doubling number) becomes 2 to 4 times. It can be obtained by increasing the number. According to this method, when there is a buffer layer, it is possible to obtain a 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 sides. .

Such alternate lamination structure is laminated so that the thickness of each layer of the first layer and the second layer has a desired gradient structure. This can be achieved, for example, by varying the spacing and length of the slits in a multi-layer feedblock device. For example, the interval and length of the slit may be adjusted so as to have a portion forming a monotonically increasing region so as to reflect light over a wide wavelength range.

After laminating a desired number of layers by the method described above, the laminate is extruded through a die and cooled on a casting drum to obtain a multilayer unstretched film. The multilayer unstretched film has at least one axial direction (sometimes called the machine direction or the longitudinal direction) or a direction perpendicular to it in the film plane (sometimes called the transverse direction or the width direction). Such a uniaxial direction is a direction along the film plane.). The stretching temperature is preferably in the range of the glass transition temperature (Tg) of the polymer of the first layer to (Tg+25)°C. By stretching at a temperature lower than conventional, the orientation properties of the film can be more highly controlled.

The draw ratio is preferably 2.0 to 7.0 times, more preferably 4.5 to 6.5 times. The larger the draw ratio within this range, the smaller the variation in the refractive index in the plane direction of the individual layers in the first layer and the second layer due to the thinning due to stretching, and the optical interference of the multilayer laminated film becomes uniform in the plane direction. It is preferable because the difference in refractive index between the first layer and the second layer in the stretching direction becomes large. As the stretching method at this time, a known stretching method such as heating stretching with a rod-shaped heater, roll heating stretching, and tenter stretching can be used. preferable.

In addition, when stretching is performed in a direction (MD direction) perpendicular to the stretching direction (TD direction) in the film plane and biaxial stretching is performed, depending on the application, when it is desired to have reflective polarization properties. is preferably limited to a draw ratio of about 1.01 to 1.20 times. If the draw ratio in the MD direction is made higher than this, the polarizing performance may deteriorate.

Further, after the stretching, the orientation characteristics of the multilayer laminated film obtained by toe-out (re-stretching) in the stretching direction in the range of 5 to 15% while heat setting at a temperature of (Tg) to (Tg + 30) ° C. can be highly controlled.

In the present invention, when the above coating layer is provided, the coating on the multilayer laminated film can be performed at any stage, but it is preferably performed during the production process of the film, and the coating is applied to the film before stretching. is preferred.
Thus, the multilayer laminate film of the present invention is obtained.

In the case of a multi-layer laminate film used for a metallic luster film or a reflective mirror, it is preferably a biaxially stretched film. In this case, either successive biaxial stretching or simultaneous biaxial stretching can be used. good too. Moreover, the draw ratio may be adjusted so that the refractive index and film thickness of each layer of the first layer and the second layer exhibit desired reflection characteristics. Considering the refractive index of , it should be about 2.5 to 6.5 times both in the vertical and horizontal directions.

EXAMPLES The present invention will be described below with reference to 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) Overall thickness of the film and thickness of each layer A film sample was sandwiched between spindle detectors (K107C manufactured by Anritsu Electric Co., Ltd.), and a digital differential electronic micrometer (K351 manufactured by Anritsu Electric Co., Ltd.) was used to measure the thickness at different positions. was measured at 10 points, and the average value was determined as the total thickness of the film.

The multilayer laminated film was cut into a lengthwise direction of 2 mm and a width direction of 2 cm, fixed in an embedding capsule, and then embedded in an epoxy resin (Epomount manufactured by Refinetech Co., Ltd.). The embedded sample was cut perpendicularly to the width direction with a microtome (ULTRACUT UCT manufactured by LEICA) to obtain thin slices with a thickness of 5 nm. Observation and photographing were performed using a transmission electron microscope (Hitachi S-4300) at an accelerating voltage of 100 kV, and the thickness (physical thickness) of each layer was measured from the photographs.

Regarding layers having a thickness of more than 1 μm, the layer existing inside the multilayer structure was defined as the intermediate layer, and the layer existing on the outermost layer was defined as the outermost layer, and the thickness of each layer was measured.

Whether the layer is the first layer or the second layer can be determined based on the refractive index, but if this is difficult, it can be determined based on the electronic state obtained by NMR analysis or TEM analysis. Moreover, the refractive index of each layer can also be determined from a single-layer film having the same composition as that of each layer but having a larger thickness.

(2) Preparation of Uniaxially Stretched Film for Checking Stress Characteristics of Film An unstretched sheet was prepared from the resin forming the first layer of the multilayer laminated film using an extruder (Laboplastomill manufactured by TOYO SEIKI). The conditions for extrusion molding were as follows: the resin was melted at a set temperature of 300°C, extruded into a sheet from a die, placed on cast rolls set at a temperature of 70°C, and the sheet was solidified. The unstretched sheet obtained was about 250 μm.

The unstretched sheet obtained above was stretched using a stretching machine (manufactured by TOYO SEIKI, batch stretching machine) to prepare a uniaxially stretched film. Stretching is carried out at a glass transition temperature Tg of the resin forming the first layer + 25 ° C. for 60 seconds, then stretching at the same temperature at a stretching speed of 400% / min and a uniaxial stretching ratio of 5 times in the TD direction. The temperature was held for 3 seconds. The obtained uniaxially stretched film was about 50 µm.

(3) F5 value The stress at 5% elongation (F5 value) of the film was measured using a tensile tester (manufactured by Toyo Baldwin Co., Ltd., trade name "Tensilon") in a room adjusted to a temperature of 20 ° C. and a humidity of 50%. It was measured. Cut the sample film into a width of 10 mm and a length of 100 mm, attach the sample with a chuck interval of 30 mm, and perform a tensile test at a tensile speed of 100 mm / min according to JIS-C2318 5.3.3 (2007). The load at 5% elongation was read from the curve. The stress was calculated by dividing the load at 5% elongation by the cross-sectional area of the sample before the test (unit: MPa). Each stress measurement was evaluated with the number of samples n=5, and the average value was used.

(4) Interlayer Adhesion A sample was prepared by partially exfoliating the layers by, for example, applying an impact to the edge portion of the multilayer laminated film with a needle or the like. After that, in order to reduce measurement variation, the sample was allowed to stand for one day under conditions of a temperature of 23° C. and a relative humidity of 55% RH, and then cut into strips having a width of 25 mm and a length of 100 mm. A sample was attached to an acrylic plate having a clean surface and a thickness of 3 mm with a double-faced tape, and was pressed directly with a rubber roller to adhere. At this time, when the layers were peeled off, the thicker side was attached to the acrylic plate. This is set in a tensile tester (strograph manufactured by Toyo Seiki Co., Ltd.), and when the layers are peeled, the thin side is fixed to the chuck, and the strength is measured by peeling 90° at a tensile speed of 300 mm / min. bottom. By this method, the respective strengths in the MD direction and the TD direction of the multilayer laminated film were measured, and the average value was taken as the interlaminar adhesion strength.

In the present invention, the interlayer adhesion is preferably 100 g/25 mm or more, more preferably 130 g/25 mm or more, still more preferably 150 g/25 mm or more, and particularly preferably 170 g as the average value in the MD direction and the TD direction. /25 mm or more, preferably high. Moreover, it is preferably 100 g/25 mm or more, more preferably 120 g/25 mm or more, and still more preferably 140 g/25 mm or more in both the MD direction and the TD direction.

(5) Melting point (Tm) and glass transition temperature (Tg) of resin
10 mg of each layer sample was sampled from the resin before being made into a film, and was measured at 20° C./min. The temperature was raised from room temperature to 300°C at a temperature elevation rate of , held at 300°C for 3 minutes, then taken out and immediately transferred to ice for quenching. and again at 20°C/min. , and the melting point and glass transition temperature (extrapolation start temperature) of the polymer constituting each layer were measured.

Regarding the resin after making the film, 1 mg of each layer sample was sampled by scraping from the film, etc., and was measured at 20° C./min. The temperature was raised from room temperature to 300° C. at a temperature elevation rate of , held at 300° C. for 3 minutes, then taken out and immediately transferred to ice for quenching. and again at 20°C/min. , and the melting point and glass transition temperature (extrapolation start temperature) of the polymer constituting each layer were measured.

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

(7) Refractive index after stretching in each direction Each resin constituting each layer was melted, extruded from a die, and cast on a casting drum to prepare a film. Further, a stretched film was prepared by stretching the obtained film 5.0 times in the uniaxial direction at (the glass transition temperature of the resin) +25°C. Regarding the obtained cast film and stretched film, the respective refractive indices in the stretching direction (TD direction), the orthogonal direction (MD direction), and the thickness direction (Z direction) (respectively nX, nY, and nZ) were measured as metricons. It was obtained by measuring at a wavelength of 633 nm using a prism coupler manufactured by the company. Regarding the average refractive index of the polyester constituting the second layer, the average refractive index in each direction after stretching was taken as the average refractive index.

(8) Average reflectance (reflection spectrum)
Using a polarizing film measurement device (“VAP7070S” manufactured by JASCO Corporation), the reflection spectrum of the obtained multilayer laminated film was measured. For measurement, a spot diameter adjusting mask Φ1.4 mm and a deflection angle stage were used, and the incident angle of the measurement light was set to 0 degrees. The transmittance at each wavelength of the axis perpendicular to the was measured in the range of 380 to 780 nm at intervals of 5 nm. An average value of the reflectance was taken in the range of 380 to 780 nm, and this was taken as the average reflectance of the reflection axis at normal incidence. If the average reflectance was 50% or more, it was determined that the measured reflection axis of the multilayer laminate film could be reflected. When used for optical purposes such as brightness enhancement members, the average reflectance is 85% or more, preferably 87% or more, and more preferably 90% or more.

[Production Example 1] Polyester A
Dimethyl 2,6-naphthalenedicarboxylate, dimethyl isophthalate, and ethylene glycol as the polyester for the first layer were subjected to transesterification reaction in the presence of titanium tetrabutoxide, followed by polycondensation reaction to obtain an acid component. 96 mol% of the 2,6-naphthalene dicarboxylic acid component, 4 mol% of the isophthalic acid component, and a copolymer polyester (intrinsic viscosity of 0.56 dl / g) in which the glycol component is an ethylene glycol component (o-chlorophenol, 35° C., hereinafter the same) (represented as IA4PEN) was prepared.

[Production Example 2] Polyester B
As the polyester for the second layer, dimethyl 2,6-naphthalenedicarboxylate, dimethyl terephthalate, dimethyl isophthalate, and ethylene glycol were subjected to transesterification reaction in the presence of titanium tetrabutoxide, followed by polycondensation reaction. 41 mol% of the acid component is a 2,6-naphthalenedicarboxylic acid component, 50 mol% is a terephthalic acid component, 9 mol% is an isophthalic acid component, and a copolymer polyester (intrinsic viscosity 0.55 dl/g) (referred to as TA50IA9PEN) was prepared.

[Example 1]
After drying the polyester A for the first layer at 170°C for 5 hours and the polyester B for the second layer at 85°C for 8 hours, they are supplied to the first and second extruders and heated to 300°C. to a molten state, and using a multi-layer feed block device equipped with comb teeth, the polyester for the first layer is branched into 138 layers and the polyester for the second layer is branched into 139 layers, and the first layer and the second layer are alternately formed. to obtain a melt in a laminated state of a total of 277 layers. At this time, the extrusion amount was adjusted so that the average layer thickness ratio between the first layer and the second layer in the final film was 1.0:1.3. In addition, the first layer and the second layer each have a layer thickness profile in which the thickness (physical thickness) of each layer increases monotonically from one end to the other end, and the ratio of the maximum film thickness/minimum film thickness in the first layer is 2.8. The ratio of maximum film thickness/minimum film thickness was set to 2.6 in the second layer so as to achieve the above. While maintaining the laminated state, the same polyester as the polyester for the second layer is led from the third extruder to the three-layer feed block on both sides thereof, and the laminated state of 277 layers (both surface layers are the second layer) A buffer layer was laminated on both sides in the lamination direction of the melt of No. 1). Here, the feed rate of the third extruder was adjusted so that the sum of the thicknesses of the buffer layers on both sides was 30% of the total thickness. The laminated state is further bifurcated with a layer doubling block and laminated at a ratio of 1:1 to produce an unstretched multilayer laminated film with a total of 557 layers including an intermediate layer inside and two outermost layers as the outermost layer. bottom.

This unstretched multilayer laminated film was stretched 6.0 times in the width direction at a temperature of 135°C. The thickness of the obtained uniaxially stretched multilayer laminate film was 66 μm. As a result of refractive index measurement, the first layer was birefringent and the second layer was isotropic.

[Examples 2-4, Example 6, Comparative Examples 1-2]
A uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1, except that the polyester resins of the first layer and the second layer were changed as shown in Table 1.

note that,
92 mol% of the acid component is a 2,6-naphthalene dicarboxylic acid component, 8 mol% is an isophthalic acid component, and a copolymer polyester (intrinsic viscosity of 0.57 dl / g) in which the glycol component is an ethylene glycol component (represented as IA8PEN) ), a copolymer polyester (intrinsic viscosity of 0.58 dl/g) ( represented as IA12PEN),
85 mol% of the acid component is a 2,6-naphthalene dicarboxylic acid component, 15 mol% is a terephthalic acid component, and a copolymer polyester (intrinsic viscosity of 0.57 dl / g) (TA15PEN) in which the glycol component is an ethylene glycol component ),
a polyester (intrinsic viscosity of 0.57 dl/g) (expressed as PEN) in which the acid component is a 2,6-naphthalene dicarboxylic acid component and the glycol component is an ethylene glycol component;
92 mol% of the acid component is a 2,6-naphthalene dicarboxylic acid component, 8 mol% is a terephthalic acid component, and a copolymer polyester (intrinsic viscosity of 0.57 dl / g) (TA8PEN) in which the glycol component is an ethylene glycol component .)
was obtained by changing the monomer amount in Production Example 1. The intrinsic viscosity was adjusted from the polycondensation time.
again,
40 mol % of the acid component is a 2,6-naphthalene dicarboxylic acid component, 60 mol % is a terephthalic acid component, and a copolymer polyester (intrinsic viscosity of 0.56 l / g) (TA60PEN) in which the glycol component is an ethylene glycol component .)
was obtained by changing the monomer amount in Production Example 2. The intrinsic viscosity was adjusted by the polycondensation time.

[Example 5]
After drying the polyester A for the first layer at 170°C for 5 hours and the polyester B for the second layer at 85°C for 8 hours, they are supplied to the first and second extruders and heated to 300°C. to a molten state, and using a multi-layer feed block device equipped with comb teeth, the polyester for the first layer is branched into 139 layers and the polyester for the second layer is branched into 138 layers, and the first layer and the second layer are alternately formed. to form a melt in a laminated state with a total of 277 layers, and the laminated state was maintained. In the same manner as in Example 1, 1 An axially stretched multilayer laminated film was obtained.

In both cases, the first layer was birefringent and the second layer was isotropic.

According to the present invention, the multilayer laminated film of the present invention makes it possible to realize a multilayer laminated film that is difficult to delaminate. Therefore, when used as an optical member such as a brightness enhancement member or a reflective polarizing plate, delamination does not occur due to external force applied during lamination with other members, assembly into a liquid crystal display, use, etc. It is possible to provide more reliable luminance improving members, polarizing plates for liquid crystal displays, and the like.

1 thick film layer (outermost layer)
2 thick film layer (middle layer)
3 Multilayer laminated structure

Claims (6)

A multilayer laminate film having a multilayer laminate structure in which a birefringent first layer containing 70% by mass or more of a resin and an optically isotropic second layer containing 70% by mass or more of a resin are alternately laminated. hand,
The resin forming the first layer was obtained by using an extruder to create a uniaxially stretched film under the following stretching conditions from an unstretched sheet produced under the following sheeting conditions. The stress (F5 value) at 5% elongation in the stretching direction of the uniaxially stretched film is 370 MPa or more and 415 MPa or less,
The resin constituting the first layer is a copolymer polyester resin containing a naphthalene dicarboxylic acid component and a terephthalic acid component,
The copolymerization amount of the terephthalic acid component is 10 mol% or more and 16 mol% or less with respect to the total dicarboxylic acid component constituting the copolymerized polyester resin,
The copolymerization amount of the naphthalenedicarboxylic acid component is 84 mol% or more and 90 mol% or less with respect to the total dicarboxylic acid component constituting the copolymerized polyester resin,
The copolyester resin has an intrinsic viscosity of 0.55 dL/g or more and 0.58 dL/g or less,
The resin constituting the second layer is a copolymer polyester resin containing a naphthalene dicarboxylic acid component, a terephthalic acid component, an isophthalic acid component and ethylene glycol,
The copolymerization amount of the terephthalic acid component and the isophthalic acid component is 30 mol% or more and 60 mol% or less with respect to the total dicarboxylic acid component constituting the copolymerized polyester resin of the second layer,
The copolymerization amount of the naphthalene dicarboxylic acid component is 40 mol% or more and 70 mol% or less with respect to the total dicarboxylic acid component constituting the copolymerized polyester resin of the second layer,
The copolyester resin of the second layer has an intrinsic viscosity of 0.52 dL/g or more and 0.65 dL/g or less.
Multilayer laminated film.
Sheet Forming Conditions The resin is melted at a set temperature of 300° C., extruded into a sheet from a die, grounded on a cast roll set at a temperature of 70° C., and solidified into a sheet.
Stretching conditions Stretching temperature: Glass transition temperature Tg of the resin forming the first layer + 25 ° C.
Stretching speed: 400%/min Stretch ratio: 5.0 times 2. The multilayer laminated film according to claim 1, having a thick layer in contact with the multilayer laminated structure. 3. The multilayer laminated film according to claim 1, wherein the resin constituting the first layer is an oriented crystalline polyester resin. 4. The multilayer laminated film according to any one of claims 1 to 3 , which reflects light having a wavelength of 380 to 780 nm with an average reflectance of 85% or more due to optical interference between the first layer and the second layer. A brightness enhancement member using the multilayer laminated film according to any one of claims 1 to 4. A polarizing plate using the multilayer laminated film according to any one of claims 1 to 4.

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