JP7392344B2 - multilayer laminated film - Google Patents

Description

The present invention relates to multilayer laminate films.

A multilayer laminated film having a multilayer laminated structure in which a large number of layers with a low refractive index and layers with a high refractive index are laminated alternately is an optical interference film that selectively reflects or transmits light of a specific wavelength due to structural optical interference between layers. can do. In addition, such multilayer laminated films can reflect or reflect light over a wide wavelength range by gradually changing the thickness of each layer along the thickness direction or by laminating films with different reflection peaks. It can transmit light and achieve high reflectance equivalent to that of films using metals, and can also be used as metallic luster films or reflective mirrors. 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 light component, and can be used for brightness-enhancing materials such as liquid crystal displays. (For example, see Patent Documents 1 to 4).
Especially in mobile phones, tablet PCs, etc., these multilayer laminated films are widely used to suppress power consumption.

Here, in a multilayer laminated film, by providing a thick outermost layer, a protective layer, and a layer with a supporting function (also referred to as a "supporting layer"), a wide reflection wavelength band (that is, a reflectance in a wide wavelength band) can be achieved. High operability has been proposed while maintaining at least one of a high degree of polarization) and a moderately high degree of polarization (see Patent Documents 5 to 7). However, when such thick film layers are laminated, the thickness and weight of the optical film as a whole may increase. In particular, in the field of mobile phones, tablet PCs, etc., where smaller and lighter products are desired, further improvements are required in multilayer laminated films so as not to increase their thickness and weight.

Japanese Patent Application Publication No. 04-268505 Special Publication No. 9-506837 Special Publication No. 9-506984 International Publication No. 01/047711 Japanese Patent Application Publication No. 2003-251675 JP2016-24312A International Publication No. 13/080987

In order to reduce the size and weight of a multilayer laminate film, it is conceivable to make the multilayer laminate film thinner by making the support layer that does not contribute to optical properties thinner or not providing it. However, in a multilayer laminated film having a multilayer laminated structure that can maintain a wide reflection band and a moderately high degree of polarization by gradually changing the thickness of each layer along the thickness direction, attempts are made to thin the film as described above. If this happens, streak-like defects may occur near the surface layer on the thinner side of the inclined structure. Here, if a thick support layer is provided on the thin side surface of the inclined structure of the multilayer laminate structure in order to suppress streaks, the multilayer laminate structure will be made thinner than necessary due to the constraints of reducing the size and weight of the multilayer laminate film. Therefore, the reflection wavelength band becomes narrower and the reflectance of light decreases.
An object of the present invention is to provide a multilayer laminate film that can be made thinner, maintain a wide reflection band and a moderately high degree of polarization, and suppress the occurrence of streaks.

Means for solving the above problems include the following aspects.
<1>
A multilayer laminate film having a multilayer laminate structure in which a first layer mainly composed of resin and a second layer mainly composed of resin are alternately laminated, the multilayer laminate structure including the first layer and the second layer mainly composed of resin. and a layer thickness profile in terms of physical thickness of a repeating unit having at least and a second region whose thickness monotonically increases toward two surfaces, and the ratio of the number of repeating units in the first region to the number of repeating units in the multilayer laminate structure is 5% or more and 35% or less, A multilayer laminate film, wherein the ratio of the number of repeating units in the second region to the number of all repeating units in the multilayer laminate structure is 65% or more and 95% or less, and satisfies the following (A) or (B). (A) The physical thickness of the repeating unit at the end on the first surface side in the first region is 90 nm or more and 170 nm or less, and the physical thickness of the repeating unit at the end on the second surface side is 80 nm or more and 120 nm or less. , the physical thickness of the repeating unit at the end on the first surface side in the second region is greater than or equal to the average thickness of all the repeating units in the first region and less than or equal to the maximum thickness of the repeating unit in the first region; The physical thickness of the repeating unit at the end on the second surface side is 240 nm or more and 310 nm or less. (B) The physical thickness of the repeating unit at the end on the first surface side in the first region is 240 nm or more and 310 nm or less, and the physical thickness of the repeating unit at the end on the second surface side is 200 nm or more and 300 nm or less. , the physical thickness of the repeating unit at the end on the first surface side in the second region is 80 nm or more and 120 nm or less, and the physical thickness of the repeating unit at the end on the second surface side is the same as that of the repeating unit in the first region. The thickness is greater than or equal to the minimum thickness and less than or equal to the average thickness of all repeating units in the first region.
<2>
The multilayer laminate film according to <1>, wherein the total ratio of the first region and the second region to the total number of repeating units in the multilayer laminate structure is 85% or more.
<3>
The multilayer laminate film according to <1> or <2>, which has a support layer mainly made of resin and having a thickness of 4 μm or less on the surface of the multilayer laminate structure.

According to the present invention, a multilayer laminate film is provided that suppresses the occurrence of streaks while maintaining a wide reflection band and a moderately high degree of polarization while being thinned.

FIG. 2 is a schematic diagram showing an example of a layer thickness profile in the multilayer laminate structure of the multilayer laminate film according to the first embodiment. It is a schematic diagram which shows an example of the layer thickness profile in the multilayer laminated structure of the multilayer laminated film based on 2nd Embodiment.

Hereinafter, an embodiment that is an example of the present invention will be described. The present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the purpose of the present invention.

[Multilayer laminated film]
The multilayer laminate film of the present invention has a multilayer laminate structure in which a first layer mainly composed of resin and a second layer mainly composed of resin are alternately laminated.
Further, the multilayer laminate film may have a support layer mainly made of resin and having a thickness of 4 μm or less on the surface of the multilayer laminate structure.
Each component of the multilayer laminate film of the present invention will be explained below.

[Multilayer laminated structure]
The multilayer laminate structure of the present invention has a layer thickness profile based on the physical thickness of a repeating unit that includes at least a first layer mainly composed of resin and a second layer mainly composed of resin.
Preferably, the first layer is birefringent, and the second layer is isotropic, and due to the light interference effect of the first layer and the second layer, a wide range of wavelengths can be seen in the visible light region of 380 nm to 780 nm. It can be reflective over a range of wavelengths.

Here, "reflectable" means that, in at least one arbitrary direction within the plane of the film, the average reflectance of polarized light parallel to the direction perpendicularly incident is 50% or more. Such reflection may be 50% or more as an average reflectance in each wavelength range, preferably 60% or more, and more preferably 70% or more.

Here, "based mainly on resin" means that the 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 order to achieve such reflection characteristics, a birefringent first layer is made of resin and has a thickness of 10 to 1000 nm, and an isotropic second layer is made of resin and has a thickness of 10 to 1000 nm. It is preferable to have a structure in which a total of 30 or more layers are laminated alternately in the thickness direction. The total number of layers is more preferably 100 layers or more, still more preferably 150 layers or more, particularly preferably 190 layers or more, and the upper limit of the total number of layers is preferably 2000 layers or less, more preferably 1000 layers or less. , more preferably 500 layers or less, particularly preferably 360 layers or less.

The multilayer laminated structure may have a third layer in addition to the first and second layers described above, and when it has a third layer, the first layer, second layer, and third layer are arranged in the order of the first layer, second layer, and third layer. It is preferable to have a structure in which repeating units are stacked.

Further, the resin constituting each layer will be described in detail later, but is not particularly limited as long as it can form a birefringent layer and an isotropic layer. In all cases, thermoplastic resins are preferred from the viewpoint of easy production of films.
In addition, in each layer of the present invention, the film forming machine axis direction (sometimes referred to as longitudinal direction, longitudinal direction, or MD direction), the direction perpendicular to the film forming machine axis direction within the film plane (transverse direction, width direction, (Also referred to as TD direction.) Regarding the refractive index in the thickness direction, those with a difference of 0.1 or more between the maximum and minimum are considered birefringent, and those with a difference of less than 0.1 are considered isotropic.

(Layer thickness profile)
The layer thickness profile of the multilayer laminate structure in the present invention includes a first region where the thickness monotonically decreases from the first surface of the multilayer laminate structure, and a second region where the thickness monotonically increases toward the second surface of the multilayer laminate structure. and the ratio of the number of repeating units in the first region to the total number of repeating units in the multilayer laminate structure is 5% or more and 35% or less, and the ratio of the number of repeating units in the second region to the total number of repeating units in the multilayer laminate structure is The ratio of the number of repeating units is 65% or more and 95% or less, and the following (A) or (B) is satisfied.

(A) The physical thickness of the repeating unit at the end on the first surface side in the first region is 90 nm or more and 170 nm or less, and the physical thickness of the repeating unit at the end on the second surface side is 80 nm or more and 120 nm or less, The physical thickness of the repeating unit at the end on the first surface side in the second region is greater than or equal to the average thickness of all repeating units in the first region and less than or equal to the maximum thickness of the repeating unit in the first region, and The physical thickness of the repeating unit at the side edge is 240 nm or more and 310 nm or less.

(B) The physical thickness of the repeating unit at the end on the first surface side in the first region is 240 nm or more and 310 nm or less, and the physical thickness of the repeating unit at the end on the second surface side is 200 nm or more and 300 nm or less, The physical thickness of the repeating unit at the end on the first surface side in the second region is 80 nm or more and 120 nm or less, and the physical thickness of the repeating unit at the end on the second surface side is the minimum thickness of the repeating unit in the first region. The above is less than or equal to the average thickness of all the repeating units in the first region.

Regarding the embodiment of the multilayer laminated film of the present invention, when the layer thickness profile satisfies the above (A), it is also referred to as the "first embodiment", and when the above (B) is satisfied, it is also referred to as the "second embodiment". ” is also called. The “first embodiment” and the “second embodiment” will be collectively referred to as the “present embodiment”.

Here, even when the multilayer laminate structure has a third layer, it similarly has a layer thickness profile based on the physical thickness of the repeating unit, and such layer thickness profile is determined by the thickness from the first surface of the multilayer laminate structure. a first region whose thickness monotonically decreases, and a second region whose thickness monotonically increases toward a second surface of the multilayer laminate structure, wherein the first region is repeated for every number of repeating units in the multilayer laminate structure. The ratio of the number of units is 5% or more and 35% or less, and the ratio of the number of repeating units in the second region to all the number of repeating units in the multilayer laminate structure is 65% or more and 95% or less, and (A) Or satisfies (B).
Next, the "first embodiment" and "second embodiment" of the multilayer laminated film of the present invention will be described in detail.

[First embodiment]
When the multilayer laminated film of the present invention is the first embodiment, from the viewpoint of suppressing the generation of streaks, it is preferable that the physical thickness of the repeating unit at the end on the first surface side in the first region is 105 nm or more, and 110 nm or more. The thickness is more preferably 120 nm or more, and even more preferably 120 nm or more. Further, the upper limit of the physical thickness of the repeating unit at the end on the first surface side in the first region is not particularly limited, but from the viewpoint of thinning the film, it is preferably 160 nm or less, and 150 nm or less. is more preferable, and even more preferably 140 nm or less.
The physical thickness of the repeating unit at the end on the second surface side in the first region is preferably 90 nm or more, and preferably 105 nm or more, from the viewpoint of ensuring a wide reflection band and a moderately high degree of polarization while making the film thin. More preferably, it is 115 nm or less. Note that since the first region monotonically decreases, the physical thickness is selected to be thinner than the physical thickness of the repeating unit at the end on the first surface side.
The average thickness of all repeating units in the first region is preferably 95 nm or more, more preferably 105 nm or more, even more preferably 115 nm or more, and preferably 145 nm or less, more preferably 135 nm or less, and even more preferably 125 nm or less.
In addition, from the viewpoint of suppressing the occurrence of streaks while maintaining a wide reflection band and a moderately high degree of polarization while making the film thinner, the physical thickness of the repeating unit at the end on the second surface side in the second region should be 250 nm or more. is preferable, and preferably 300 nm or less.

FIG. 1A is a schematic diagram showing an example of a layer thickness profile in the multilayer laminate structure of the multilayer laminate film according to the first embodiment.
For example, as shown in FIG. 1A, the multilayer laminated structure 100A has a first region 10A whose thickness monotonically decreases from the first surface 50A and a second region 20A whose thickness monotonically increases toward the second surface 70A. .
The physical thickness of the repeating unit at the end on the first surface 50A side in the first region 10A is 140 nm, and the physical thickness of the repeating unit at the end on the second surface 70A side is 110 nm.
Further, the physical thickness of the repeating unit at the end on the second surface 70A side in the second region 20A is 250 nm.

[Second embodiment]
When the multilayer laminated film of the present invention is the second embodiment, from the viewpoint of suppressing the occurrence of streaks while maintaining a wide reflection band and a moderately high degree of polarization while reducing the thickness, the first surface side in the first region The physical thickness of the repeating unit at the end of is preferably 250 nm or more, and preferably 300 nm or less.
Further, the physical thickness of the repeating unit at the end on the second surface side in the first region is preferably 205 nm or more and 295 nm or less, from the viewpoint of ensuring a wide reflection band and a suitably high degree of polarization while making the film thin. Note that since the first region monotonically decreases, the physical thickness is selected to be thinner than the physical thickness of the repeating unit at the end on the first surface side.
The average thickness of all repeating units in the first region is preferably 225 nm or more, more preferably 230 nm or more, even more preferably 235 nm or more, and is preferably 295 nm or less, more preferably 285 nm or less, and even more preferably 270 nm or less.
In addition, from the viewpoint of ensuring a wide reflection band and a moderately high degree of polarization while making the film thin, the physical thickness of the repeating unit at the end on the first surface side in the second region is preferably 90 nm or more, and preferably 105 nm or more. is more preferable, and also preferably 115 nm or less.

FIG. 1B is a schematic diagram showing an example of a layer thickness profile in the multilayer laminate structure of the multilayer laminate film according to the second embodiment.
For example, as shown in FIG. 1B, the multilayer laminated structure 100B has a first region 10B whose thickness monotonically decreases from the first surface 50B and a second region 20A whose thickness monotonically increases toward the second surface 70B. .
The physical thickness of the repeating unit at the end on the first surface 50B side in the first region 10B is 250 nm, and the physical thickness of the repeating unit at the end on the second surface 70B side is 237 nm.
Further, the physical thickness of the repeating unit at the end on the first surface 50B side in the second region 20B is 110 nm.

By having the above structure, the multilayer laminated film according to the present embodiment can suppress the occurrence of streaks while maintaining a wide reflection band and a moderately high degree of polarization while being made thin.
Although the reason is not certain, it is assumed as follows.

In a multilayer laminated film having a multilayer laminated structure, the reason why streaks occur when thinning the film is attempted is that the layer forming the surface of one end of the multilayer laminated structure is caused by resin flow originating from the manufacturing process of the multilayer laminated film. It is possible that they are easily affected. Therefore, if the layer forming the surface of the multilayer laminated structure is too thin, the layer structure will be disturbed due to the influence of resin flow, and streaks will likely occur.
On the other hand, the multilayer laminate film of this embodiment has a structure in which the thin layer described above is formed inside the multilayer laminate structure rather than on the surface layer, so that resin flow caused by the manufacturing process of the multilayer laminate film is reduced. It is thought that the influence is reduced and the occurrence of streaks can be suppressed.
In addition, the multilayer laminated film of this embodiment has a structure in which the overlapping area of the physical thickness of the repeating unit in the first region and the second region of the multilayer laminated structure is kept to the minimum or necessary minimum. It is believed that a wide reflection band and a suitably high degree of polarization can be maintained without significantly increasing the thickness of the structure.

By appropriately distributing repeating units having a refractive index and thickness corresponding to each reflection wavelength in the first region and the second region, it is possible to have a first layer and a second layer with a wide range of optical thickness. It becomes possible to reflect light within a range.
This is because the reflected wavelength depends on the optical thickness of each layer constituting the multilayer laminated film. Generally, the reflection wavelength of a multilayer laminated film is expressed by the following (Formula 1).
λ=2(n1×d1+n2×d2) (Formula 1)
(In the above formula, λ represents the reflection wavelength (nm), n1 and n2 represent the refractive index of each layer, and d1 and d2 represent the physical thickness (nm) of each layer)

Further, the optical thickness λM (nm) is expressed as the product of the refractive index nk and the physical thickness dk (nm) of each layer, as shown in (Equation 2) below. The physical thickness here may be determined from a photograph taken using a transmission electron microscope.
λM (nm) = nk x dk (Formula 2)

In the present invention, if the thickness of the first region and the second region is set as in the first embodiment and the second embodiment described above, the layer thickness can be set such that the light having a wavelength of 380 nm to 780 nm can be widely reflected. It can be a profile. Further, by adjusting the ratio of repeating units in the first region and the second region, a wider reflection band and a higher reflectance can be achieved.

In the present invention, the physical thickness of the repeating unit is represented by the following (Formula 3).
dp=d1+d2 (Formula 3)
In the above formula, dp represents the physical thickness (nm) of the repeating unit, and d1 and d2 represent the physical thicknesses (nm) of the first and second layers constituting the repeating unit, respectively.
The physical thickness here may be determined from a photograph taken using a transmission electron microscope.

(First area)
In the present invention, the first region in which the thickness monotonically decreases from the first surface of the multilayer laminate structure refers to the first region in which the thickness decreases monotonically from the first surface of the multilayer laminate structure, starting from one surface in the thickness direction of the multilayer laminate structure, and extending from one surface (first surface) to the other surface. It has a layer thickness profile in which the physical thickness of the repeating unit monotonically decreases toward the second surface.

In the present invention, "monotonically decreasing" means that in the first region, the physical thickness of the repeating unit at the end on one surface (first surface) side of the multilayer laminate structure is the largest, and Preferably, this means that the physical thickness of the repeating unit decreases in all of the first regions, but is not limited thereto. For example, when looking at the entire first region, it is sufficient if there is a tendency for the physical thickness of the repeating unit to decrease. Specifically, starting from the end on the first surface side, numbers are assigned to the repeating unit from the thicker side to the thinner side of the physical thickness of the repeating unit, and using this as the horizontal axis, the repeating unit is numbered. When the physical thickness is plotted on the vertical axis, the number of repeating units is divided into approximately five equal parts within the range where the thickness shows a decreasing tendency, and the physical thickness of the repeating unit in each equally divided area is calculated in the direction of decreasing thickness. If all the average values of are decreasing, it is considered to be monotonically decreasing, otherwise it is not monotonically decreasing.
However, only when the number of repeating units is 4 or less, the number of repeating units is divided into approximately three equal parts, and in each equally divided area, it is determined whether or not there is a monotonous decrease using the same method as above.

(Second area)
In the present invention, the second region whose thickness increases monotonically toward the second surface of the multilayer laminate structure is the surface of the multilayer laminate structure that is opposite to the starting point of the first region in the thickness direction of the multilayer laminate structure. (second surface) as the end point, and has a layer thickness profile in which the physical thickness of the repeating unit increases monotonically toward the other surface (second surface).

In the present invention, "monotonically increasing" refers to the physical properties of the repeating unit at the end of the surface (second surface) of the multilayer laminated structure opposite to the starting point of the first region in the second region. It is preferable that the physical thickness of the repeating unit is the thickest and that the physical thickness of the repeating unit increases in all of the second regions, but is not limited thereto. For example, when looking at the entire second region, it is sufficient if there is a tendency for the physical thickness of the repeating units to increase. Specifically, numbers are assigned to repeating units from the thinner physical thickness side to the thicker side of the physical thickness of the repeating unit, with the end on the second surface side as the end point. When the physical thickness is plotted on the vertical axis, the number of repeating units is divided into approximately five equal parts within the range where the thickness shows an increasing tendency, and the physical thickness of the repeating unit in each equally divided area is calculated in the direction of increasing thickness. If all the average values of are increasing, it is considered to be monotonically increasing, otherwise it is considered not to be monotonically increasing.

- Ratio of maximum thickness to minimum thickness [maximum thickness/minimum thickness] -
In this embodiment, the ratio of the maximum physical thickness to the minimum physical thickness of the repeating unit in the first region and the second region of the multilayer laminate structure is preferably within a specific range.
From the viewpoint of having a wide reflection band and a moderately high degree of polarization, and maintaining an appropriate amount of reflection in the reflection band, in the first region, the ratio of the maximum physical thickness to the minimum physical thickness of the repeating unit is 1. It is preferably 01 or more and 1.50 or less, more preferably 1.03 or more and 1.47 or less, and even more preferably 1.05 or more and 1.45 or less. Further, from the same viewpoint, in the second region, the ratio of the maximum physical thickness to the minimum physical thickness of the repeating unit is preferably 1.51 or more and 3.50 or less, and 1.55 or more and 3.30 or less. More preferably, it is 1.58 or more and 3.20 or less.

The ratio of the number of repeating units in the first region to the total number of repeating units in the multilayer laminated structure of the present invention is 5% or more and 35% or less, which prevents the occurrence of streaks while maintaining a wide reflection band and a moderately high degree of polarization. From the viewpoint of suppression, it is preferably 10% or more and 30% or less, and more preferably 10% or more and 25% or less.
The ratio of the number of repeating units in the second region to the total number of repeating units in the multilayer laminated structure of the present invention is 65% or more and 95% or less, and the generation of streaks is prevented while maintaining a wide reflection band and a moderately high degree of polarization. From the viewpoint of suppression, it is preferably 70% or more and 95% or less, and more preferably 75% or more and 90% or less.

In the present invention, the total ratio of the first region and the second region to the total number of repeating units in the multilayer laminated structure is 85% or more from the viewpoint of maintaining a wide reflection band and a moderately high degree of polarization while making the film thin. It is preferably 90% or more, even more preferably 95% or more.
In addition to the above-mentioned first region and second region, the multilayer laminate structure of the present invention has optical properties of the multilayer laminate film between the first region and the second region, within a range that does not impede the object of the present invention. It may have a layer that contributes to the improvement of the performance or a layer that does not contribute to the improvement of the performance. For example, as a layer that contributes to improving the optical properties of the multilayer laminated film, it may have a region having a sloped structure similar to the first region and second region in the first and second embodiments described above. . Furthermore, for the purpose of improving the reflectance in a specific wavelength band, a region having no sloped structure may be included in the same thickness range as the first region and the second region. Furthermore, examples of layers that do not contribute to improving the optical properties of the multilayer laminated film include a thick intermediate layer (for example, a layer with a physical thickness of more than 1 μm).

-Multilayer laminate structure-
[First layer]
The first layer constituting the multilayer laminate structure of the present invention is preferably a birefringent layer, that is, the resin constituting this is preferably one capable of forming a birefringent layer. Therefore, the resin constituting the first layer is preferably an oriented crystalline resin, and polyester is particularly preferred as the oriented crystalline resin. The polyester preferably contains ethylene terephthalate units and/or ethylene naphthalate units, more preferably ethylene naphthalate units, in a range of 80 mol% or more and 100 mol% or less, based on the repeating units constituting it. This is preferable because it is easier to form a layer with a higher refractive index, thereby making it easier to increase the difference in refractive index with the second layer. When resins are used together, this refers to the total content.

(1st layer resin)
The first layer resin is preferably polyester, and the polyester contains a naphthalene dicarboxylic acid component as a dicarboxylic acid component, and the content thereof is 80 mol% or more and 100 mol% or less based on the dicarboxylic acid component constituting the polyester. It is preferable that Such naphthalene dicarboxylic acid components include components derived from 2,6-naphthalene dicarboxylic acid components, 2,7-naphthalene dicarboxylic acid components, or combinations thereof, or derivative components thereof, particularly 2,6-naphthalene dicarboxylic acid components. Preferred examples include naphthalene dicarboxylic acid components and derivative components thereof. The content of the naphthalene dicarboxylic acid component is preferably 85 mol% or more, more preferably 90 mol% or more, and preferably less than 100 mol%, more preferably 98 mol% or less, and still more preferably 95 mol% or less. It is.

In addition to the naphthalene dicarboxylic acid component, the dicarboxylic acid component constituting the polyester of the first layer may further contain a terephthalic acid component, an isophthalic acid component, etc. within a range that does not impair the object of the present invention. It is preferable to contain. The content is preferably in the range of more than 0 mol% and 20 mol% or less. The content of the second dicarboxylic acid component is more preferably 2 mol% or more, even more preferably 5 mol% or more, and more preferably 15 mol% or less, even more preferably 10 mol% or less.

When the multilayer laminated film of the present invention is used as a brightness-enhancing member or reflective polarizing plate used in liquid crystal displays, etc., the first layer is a layer having a relatively higher refractive index than the second layer, and the second layer is a layer having a relatively higher refractive index than the second layer. Preferably, the layer has a relatively lower refractive index than the first layer and is uniaxially stretched.
In this case, in the present invention, the uniaxial stretching direction is the X direction (also referred to as the longitudinal direction), and the direction orthogonal to the X direction in the film plane is the Y direction (also referred to as the lateral direction or non-stretching direction). The direction perpendicular to the film surface is sometimes referred to as the Z direction (also referred to as the thickness direction).

By using polyester containing a naphthalene dicarboxylic acid component as a main component as described above for the first layer, it is possible to achieve a high refractive index in the X direction and a birefringence characteristic with high uniaxial orientation. It is possible to increase the difference in refractive index with the second layer with respect to the direction, 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 will increase and the difference between the refractive index nX in the X direction and the refractive index nY in the Y direction will tend to become smaller. In a multilayer laminated film, it is difficult to obtain sufficient reflection performance for the P-polarized light component in the present invention, which is defined as a polarized light component parallel to the incident plane including the uniaxial stretching direction (X direction), with the film surface as the reflective surface. There is a tendency to
Note that the S-polarized component in the present invention is defined as a polarized component that is perpendicular to the incident plane including the uniaxial stretching direction (X direction), with the film surface serving as a reflective surface in a multilayer laminated film.

As the diol component constituting the preferred polyester of the first layer, an ethylene glycol component is used, and its content is preferably 80 mol% or more and 100 mol% or less based on the diol component constituting the polyester. More preferably 85 mol% or more and 100 mol% or less, still more preferably 90 mol% or more and 100 mol% or less, particularly preferably 90 mol% or more and 98 mol% or less. If the proportion of the diol component is less than the lower limit, the above-mentioned uniaxial orientation may be impaired.

In addition to the ethylene glycol component, the diol component constituting the polyester of the first layer may further contain a trimethylene glycol component, a tetramethylene glycol component, a cyclohexanedimethanol component, a diethylene glycol component, etc. within a range that does not impair the object of the present invention. Good too.

(Characteristics of first layer polyester)
The melting point of the polyester used in the first layer is preferably in the range of 220 to 290°C, more preferably in the range of 230 to 280°C, even more preferably in the range of 240 to 270°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, fluidity may be poor during melt extrusion and molding, and discharging may become uneven. On the other hand, if the melting point is less than the lower limit, although the film forming properties are excellent, the mechanical properties of polyester are likely to be impaired, and the refraction when used as a brightness-improving member of a liquid crystal display or a reflective polarizing plate. rate characteristics tend to be difficult to express.

The glass transition temperature (hereinafter sometimes referred to as Tg) of the polyester used in the first layer is preferably 80 to 120°C, more preferably 82 to 118°C, even more preferably 85 to 118°C, and particularly preferably It is in the range of 100-115°C. When Tg is within this range, it has excellent heat resistance and dimensional stability, and also tends to exhibit refractive index characteristics when used as a brightness improving member of a liquid crystal display or a reflective polarizing plate. The melting point and glass transition temperature can be adjusted by controlling the type and amount of copolymerization components, and by-product diethylene glycol.

The polyester used in the first layer preferably has an intrinsic viscosity of 0.50 to 0.75 dl/g, more preferably 0.55 to 0.72 dl, as measured at 35°C using an o-chlorophenol solution. /g, more preferably 0.56 to 0.71 dl/g. As a result, it tends to have appropriate oriented crystallinity, and tends to exhibit a difference in refractive index with the second layer.

[Second layer]
The second layer constituting the multilayer laminate structure of the present invention is preferably an isotropic layer, that is, the resin constituting this is preferably one capable of forming an isotropic layer. Therefore, the resin constituting the second layer is preferably an amorphous resin. Among these, amorphous polyester is preferred. Note that the term "amorphous" here does not exclude having extremely slight crystallinity, but only if the second layer can be made isotropic to the extent that the multilayer laminated film of the present invention can perform the intended function. good.

(Second layer resin)
As the resin constituting the second layer, a copolymerized polyester is preferable, and it is particularly preferable to use a copolymerized polyester containing a naphthalene dicarboxylic acid component, an ethylene glycol component, and a trimethylene glycol component as copolymerized components. The naphthalene dicarboxylic acid component includes a 2,6-naphthalene dicarboxylic acid component, a 2,7-naphthalene dicarboxylic acid component, a component derived from a combination thereof, or a derivative component thereof, particularly 2, Preferred examples include 6-naphthalene dicarboxylic acid component or its derivative component. The naphthalene dicarboxylic acid component, preferably the 2,6-naphthalene dicarboxylic acid component, is preferably 30 mol% or more and 100 mol% or less, more preferably is 30 mol% or more and 80 mol% or less, more preferably 40 mol% or more and 70 mol% or less. This allows for higher adhesion with the first layer. If the content of the naphthalene dicarboxylic acid component is less than the lower limit, adhesion may decrease from the viewpoint of compatibility. Further, 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 become difficult to express a difference in refractive index with the first layer. Note that other dicarboxylic acid components may be copolymerized in order to adjust the refractive index relationship with the first layer.

In addition, the copolymerization component in the present invention means any component constituting the polyester, and the secondary component (copolymerization amount less than 50 mol% based on the total acid component or total diol component) ), the main component (copolymerization amount of 50 mol % or more based on the total acid component or total diol component) can also be used.

In the present invention, as described above, it is preferable to use a polyester containing ethylene naphthalate units as a main component as the resin for the first layer, and in this case, a copolymer polyester containing a naphthalene dicarboxylic acid component as the resin for the second layer. By using , the compatibility with the first layer tends to increase, interlayer adhesion with the first layer tends to improve, and delamination becomes less likely to occur, which is preferable.
In the copolymerized polyester of the second layer, the diol component preferably contains at least two components: an ethylene glycol component and a trimethylene glycol component. Among these, the ethylene glycol component is preferably used as the main diol component from the viewpoint of film formability and the like.

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, even more preferably It is 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 copolyester of the second layer in the present invention preferably further contains a trimethylene glycol component as a diol component. Containing the trimethylene glycol component supplements the elasticity of the layered structure and increases the effect of suppressing interlayer peeling.

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 components constituting the copolymerized polyester 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. This allows for higher interlayer adhesion with the first layer. Moreover, there is a tendency for a difference in refractive index with the first layer to occur easily. If the content of the trimethylene glycol component is less than the lower limit, it will tend to be difficult to ensure interlayer adhesion, and if it exceeds the upper limit, it will be difficult to obtain a resin with a desired refractive index and glass transition temperature.
The second layer in the present invention may contain a thermoplastic resin other than the copolyester in an amount of 10% by mass or less based on the mass of the second layer as long as it does not impair the purpose of the present invention. It may be contained as a component.

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

(Characteristics of second layer copolyester)
In the present invention, the copolyester of the second layer described above preferably has a glass transition temperature of 85°C or higher, more preferably 90°C or higher and 150°C or lower, even more preferably 90°C or higher and 120°C or lower, Particularly preferably the temperature is 92°C or higher and 110°C or lower. This provides better heat resistance. Moreover, there is a tendency for a difference in refractive index with the first layer to occur easily. If the glass transition temperature of the copolyester of the second layer is below the lower limit, sufficient heat resistance may not be obtained. Haze increases due to embrittlement and embrittlement, which may be accompanied by a decrease in the degree of polarization when used as a brightness-enhancing member or 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 develop birefringence due to stretching, and as a result, the refraction with the first layer in the stretching direction may occur. The difference in index becomes small, and the reflection performance may deteriorate.

Among the above-mentioned copolyesters, amorphous copolyesters are preferred because they can extremely effectively suppress an increase in haze due to crystallization by heat treatment at 90° C. for 1000 hours. Amorphous here means that the heat of crystal fusion is less than 0.1 mJ/mg when the temperature is raised at a temperature increase rate of 20° C./min in DSC.

The copolymerized polyester of the second layer preferably has an intrinsic viscosity of 0.50 to 0.70 dl/g, more preferably 0.55 to 0.65 dl, as measured at 35°C using an o-chlorophenol solution. /g. If the copolymerized polyester used in the second layer has a trimethylene glycol component as a copolymerization component, film-forming properties may decrease. can be further increased. When using the copolymerized polyester described above as the second layer, a higher intrinsic viscosity is preferable from the viewpoint of film formability, but if the upper limit is exceeded, the difference in melt viscosity from the polyester of the second layer becomes large. The thickness of each layer may be non-uniform.

[Support layer]
The multilayer laminate film of the present invention preferably does not have a support layer from the viewpoint of thinning, but may have a support layer mainly made of resin with a thickness of 4 μm or less on the surface of the multilayer laminate structure. When the multilayer laminate structure has a support layer, the operability of the multilayer laminate structure and the finally obtained multilayer laminate film are improved.
Such a support layer is mainly made of resin. Here, "consisting 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. Further, the support layer is preferably an isotropic layer, and from the viewpoint of ease of manufacture, it may be made of the same resin as the second layer, and may be made of the copolymerized polyester of the second layer described above. possible, and such embodiments are preferred.

The thickness of the support layer is more preferably 3 μm or less, still more preferably 2 μm or less. The lower limit of the support layer may be in a range exceeding 1 μm. If the support layer is too thin, it tends to affect the optical properties of the multilayer laminate film, which may lead to deterioration of the optical properties.

(coating layer)
The multilayer laminated film of one embodiment of the present invention can have a coating layer on at least one surface.
Examples of such coating layers include an easy-sliding layer for imparting slipperiness and a primer layer for imparting adhesiveness to a prism layer, a diffusion layer, and the like. The coating layer contains a binder component, and in order to impart slipperiness, it is preferable to contain particles, for example. In order to provide easy adhesion, the binder component used should be chemically close to the component of the layer to be bonded. Furthermore, from an environmental point of view, the coating solution for forming the coating layer is preferably an aqueous coating solution that uses water as a solvent, but especially in such cases, it is important to A surfactant may be included for the purpose of improving the composition. In addition, functional agents such as a crosslinking agent may be added to increase the strength of the coating layer.

[Method for manufacturing multilayer laminated film]
A method for producing a multilayer laminate film according to an embodiment of the present invention will be described in detail. Note that the manufacturing method shown below is an example, and the present invention is not limited thereto. Further, different aspects can also be obtained with reference to the following.
The multilayer laminate structure of the multilayer laminate film according to an embodiment of the present invention is obtained by alternately stacking the resin constituting the first layer and the resin constituting the second layer in a molten state using a multilayer feedblock device. For example, alternating laminate configurations with a total of 30 or more layers can be created and obtained. At this time, a support layer can be formed by providing a buffer layer on one or both sides of the alternately laminated structure.

In such an alternately laminated structure, the first layer and the second layer are laminated such that the thickness of each layer has a desired gradient structure. This can be achieved, for example, by varying the spacing and length of the slits in a multilayer feedblock device.
After laminating the desired number of layers by the method described above, the layers are extruded through a die and cooled on a casting drum to obtain a multilayer unstretched body. Thereafter, a multilayer laminated film is obtained by stretching as described below.

The multilayer unstretched body obtained by the above method has at least one axial direction (such uniaxial direction is the direction along the film surface). The stretching temperature is preferably in the range of the glass transition temperature (Tg) of the first layer resin to (Tg+20)°C. By performing stretching at a lower temperature than conventionally, the orientation characteristics of the film can be controlled to a higher degree.

The multilayer unstretched body is preferably stretched at a magnification of 2.0 to 7.0 times, more preferably 4.5 to 6.5 times. The larger the stretching ratio within this range, the smaller the variation in the refractive index of the individual layers in the first and second layers in the plane direction due to the thinning of the layers by stretching, and the more uniform the optical interference in the multilayer laminated structure is in the plane direction. This is preferable because it increases the refractive index difference between the first layer and the second layer in the stretching direction. As for the stretching method at this time, known stretching methods such as heating stretching with a rod-shaped heater, roll heating stretching, and tenter stretching can be used. preferable.

In addition, when performing biaxial stretching by performing a stretching process in a direction (Y direction) perpendicular to the stretching direction in the film plane, depending on the application, if you want to provide reflective polarization characteristics, 1. It is preferable to limit the stretching ratio to about 0.01 to 1.20 times. If the stretching ratio in the Y direction is increased more than this, the polarization performance may deteriorate.
In addition, after stretching, the orientation properties of the obtained multilayer laminated film can be improved by toe-out (re-stretching) in the stretching direction in the range of 5 to 15% while further heat-setting at a temperature of (Tg) to (Tg + 30) °C. can be highly controlled.

When providing the above-mentioned coating layer in an embodiment of the present invention, the coating on the multilayer laminated film can be carried out at any stage, but it is preferably carried out during the film manufacturing process, and the coating is applied to the film before stretching. It is preferable to apply it by
In this way, a multilayer laminate film according to one embodiment of the present invention is obtained.

In addition, when the multilayer laminated film is used for a metallic gloss film or a reflective mirror, it is preferable to make it a biaxially stretched film, and in this case, it is manufactured by either the sequential biaxial stretching method or the simultaneous biaxial stretching method. It's okay. In addition, the stretching ratio may be adjusted so that the refractive index and film thickness of each layer of the first layer and the second layer can obtain the desired reflection characteristics. Taking this into consideration, it is sufficient to set the size to about 2.5 to 6.5 times in both the vertical and horizontal directions.

- Optical properties of multilayer laminate structures and multilayer laminate films -
In the present invention, the average transmittance of the multilayer structure in the transmission axis at a wavelength of 380 nm to 780 nm is preferably 70% or more, more preferably 80% or more, and most preferably 85% or more. Further, the average reflectance on the reflection axis at a wavelength of 380 nm to 780 nm is preferably 70% or more, more preferably 75% or more, and most preferably 80% or more.

[Application]
Applications to which the multilayer laminate film of the present invention can be preferably applied will be described below. The multilayer laminated film of the present invention is particularly preferably used as a color filter, a heat ray reflective film, a brightness improving member, a reflective polarizing plate, or a security film.

(Application as a brightness improving member)
By adopting the above-described polymer composition, layer structure, and orientation, the multilayer laminated film of the present invention selectively reflects one polarized light component and selectively transmits a polarized light component in a direction perpendicular to the polarized light component. performance. More specifically, it is a uniaxially stretched mode. Utilizing this performance, it can be used as a brightness improving member for liquid crystal displays and the like. When used as a brightness-enhancing member, one polarized component is transmitted, and the other polarized component that is not transmitted is reflected back to the light source without being absorbed, allowing the light to be reused and providing a good brightness-improving effect. .
Further, a curable resin layer such as a prism layer or a diffusion layer may be laminated on at least one surface of the multilayer laminated film of the present invention. Here, the curable resin layer is a thermosetting resin layer or an electron beam curable resin layer. In this case, it is also possible and preferable to laminate these prism layers or diffusion layers via a coating layer having a primer function or the like.
By using the multilayer laminated film of the present invention and bonding it with members such as a prism layer, or by forming a prism etc. on the surface of the multilayer laminated film of the present invention and making it into a unit, the number of parts during assembly can be reduced. The thickness of the liquid crystal display can be made thinner. Further, by bonding these members using the multilayer laminated film of the present invention, it is possible to suppress delamination between layers due to external forces applied during processing, etc., so that a more reliable brightness improving member can be provided.
When the multilayer laminated film of the present invention is used as a brightness-improving member, a liquid crystal display device in which the brightness-improving member is arranged between a light source of the liquid crystal display and a liquid crystal panel composed of a polarizing plate/liquid crystal cell/polarizing plate is used. Illustrated. When a prism layer or prism is further provided, it is preferable to arrange the prism layer or prism on the liquid crystal panel side of the brightness improving member.

(Application as reflective polarizing plate)
The multilayer laminated film of the present invention can be used in combination with an absorption type polarizing plate or alone as a polarizing plate for liquid crystal displays and the like. In particular, for those that have high reflective polarization performance and have a high polarization degree (P) described below of 80% or more, preferably 85% or more, more preferably 87% or more, an absorption type polarizing plate should be used in combination. Instead, it can be used alone as a polarizing plate for a liquid crystal display that is used adjacent to a liquid crystal cell.
More specifically, the laminated multilayer film of the present invention is used for a liquid crystal display in which a first polarizing plate, a liquid crystal cell, and a second polarizing plate made of the laminated multilayer film of the present invention are laminated in this order. Can be mentioned.

EXAMPLES The present invention will be described below with reference to Examples, but the present invention is not limited to the Examples shown below. In addition, the physical properties and characteristics in the examples were measured or evaluated by the following methods.

- Measuring the thickness of each layer -
The multilayer laminated film was cut out to a length of 2 mm in the longitudinal direction and 2 cm in the width direction, 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 using a microtome (ULTRACUT UCT manufactured by LEICA) to obtain thin film sections with a thickness of 50 nm. It was observed and photographed 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 photograph.
Note that whether the layer is the first layer or the second layer can be determined based on the aspect of the refractive index, but if this is difficult, it is also possible to determine based on the electronic state by NMR analysis or TEM analysis.

-Measurement of refractive index after stretching-
The refractive index of the first layer and the second layer of the multilayer laminate structure was determined by creating a two-layer laminate film with a layer thickness ratio of 1:1 under the same manufacturing conditions as the obtained multilayer laminate structure, and The refractive indices of the first layer and the second layer measured using the method are determined as the refractive index of the first layer and the second layer of the multilayer stacked structure, respectively.
For example, in this embodiment, a film with a total thickness of 75 μm was created under the same conditions as in Example 1, which will be described later, except that a two-layer laminated film with a thickness ratio of first layer:second layer = 1:1 was used. , for each of the first layer and the second layer, the refractive index (nX, nY, nZ, respectively) in the stretching direction (X direction), the orthogonal direction (Y direction), and the thickness direction (Z direction), respectively. The refractive index at a wavelength of 633 nm was measured using a prism coupler manufactured by Metricon Co., Ltd., and was determined as the refractive index after stretching of each of the first layer and the second layer.

-Judgment of monotonous decrease-
To judge whether a multilayer laminate structure is monotonically decreasing, consider the combination of the first layer and the second layer as one repeating unit, input the value of the physical thickness of this repeating unit on the vertical axis, and calculate the layer number of each repeating unit (multilayer In any region of the layer thickness profile when the numbers assigned sequentially from the first surface side of the laminated structure are entered on the horizontal axis, the film thickness tends to decrease from the first surface side to the second surface side. The number of repeating units within the range shown is divided into approximately five equal parts, and if the average value of the film thickness in each equally divided area is all decreasing in the direction of decreasing film thickness, it is assumed that the film thickness is monotonically decreasing. If this is not the case, it is assumed that the value is not monotonically decreasing.
However, only when the number of repeating units is 4 or less, the number of repeating units is divided into approximately three equal parts, and in each equally divided area, it is determined whether or not there is a monotonous decrease using the same method as above.

-Judgment of monotonous increase-
To determine whether a multilayer laminate structure is monotonically increasing, consider the combination of the first layer and the second layer as one repeating unit, input the value of the physical thickness of this repeating unit on the vertical axis, and calculate the layer number of each repeating unit (multilayer In any region of the layer thickness profile when the numbers assigned in order from the second surface side of the laminated structure are entered on the horizontal axis, the film thickness tends to increase from the first surface side to the second surface side. The number of repeating units within the range shown is divided into approximately five equal parts, and if the average value of the film thickness in each of the equally divided areas is all increasing in the direction of increasing film thickness, it is assumed that the film thickness increases monotonically. If this is not the case, it is assumed that the value is not monotonically increasing.

-Evaluation of polarization degree-
Using a polarizing film measuring device ("VAP7070S" manufactured by JASCO Corporation), the visibility-corrected degree of polarization of the obtained multilayer laminated film was measured and defined as the degree of polarization (P) (unit: %). The measurement was performed using a Glan-Taylor prism, a spot diameter adjustment mask Φ1.4, and a declination stage.The incident angle of the measurement light was set to 0 degrees, and the transmission axis of the multilayer laminated film was determined by crossed Nicol search (650 nm). It is calculated based on the average transmittance (wavelength range 380 to 780 nm) of each axis perpendicular to the transmission axis.
Here, the degree of polarization is preferably 76% or more. When used for optical purposes such as brightness improving members, it is preferably 80% or more, more preferably 85% or more, and still more preferably 87% or more.

-Measurement of reflection axis average reflectance-
The transmission spectra of the obtained multilayer laminate and multilayer laminate film were measured using a polarizing film measuring device ("VAP7070S" manufactured by JASCO Corporation).
The measurement was performed using a Glan-Taylor prism, a spot diameter adjustment mask Φ1.4, and a declination stage.The incident angle of the measurement light was set to 0 degrees, and the transmission axis of the multilayer laminated film was determined by crossed Nicol search (650 nm). and the average transmittance in the wavelength range of 380 nm to 780 nm on the axis (reflection axis) perpendicular to the transmission axis (also referred to as "transmission axis average transmittance" and "reflection axis average transmittance", respectively) at 5 nm intervals. did. Note that the "reflection axis average reflectance" was determined as 100-reflection axis average transmittance.

-Evaluation of streaks-
Regarding the obtained multilayer laminated film, an area measuring 1 m in length x 1 m in width was used as an evaluation area for streaks. The obtained streak evaluation area was visually observed under a fluorescent lamp, and the streak suppression effect of the multilayer laminated film was evaluated based on the following evaluation criteria.
A: No streaks are visible at all. B: Only faint streaks are visible, and they do not look like color streaks. C: Color streaks can be seen partially, not on the entire surface. D: Color streaks can be easily seen on almost the entire surface. , The film looks cloudy, but the unevenness is not noticeable when you touch the surface E: Streaks appear on the entire surface, and the unevenness is clear even when you touch it.

[Production Example 1] Polyester A
As the polyester for the first layer, dimethyl 2,6-naphthalene dicarboxylate, dimethyl terephthalate, and ethylene glycol were transesterified in the presence of titanium tetrabutoxide, and then polycondensation reaction was performed to form the acid component. A copolymerized polyester (intrinsic viscosity 0.64 dl/g) in which 95 mol% of the acid component is a 2,6-naphthalene dicarboxylic acid component, 5 mol% of the acid component is a terephthalic acid component, and the glycol component is an ethylene glycol component (intrinsic viscosity 0.64 dl/g) (o-chlorophenol) , 35°C, hereinafter the same) were prepared.

[Production Example 2] Polyester B
As the polyester for the second layer, dimethyl 2,6-naphthalene dicarboxylate, dimethyl terephthalate, ethylene glycol, and trimethylene glycol were transesterified in the presence of titanium tetrabutoxide, and then polycondensation reaction was performed. Therefore, 50 mol% of the acid component is a 2,6-naphthalene dicarboxylic acid component, 50 mol% of the acid component is a terephthalic acid component, 85 mol% of the glycol component is an ethylene glycol component, and 15 mol% of the glycol component is trimethylene glycol. A copolymerized polyester (intrinsic viscosity: 0.63 dl/g) as a component was prepared.

[Examples A1 to A8, Examples B1 to B8, Comparative Examples 1 to 4]
<Example A1>
After drying polyester A for the first layer at 170°C for 5 hours, and drying polyester B for the second layer at 85°C for 8 hours, they were supplied to the first and second extruders, respectively, and heated to 300°C. After heating to melt and branching the polyester for the first layer into 138 layers and the polyester for the second layer into 138 layers, the first layer and the second layer were laminated alternately, and as shown in Tables 1 and 2. Using a multilayer feedblock device equipped with comb teeth to provide the layer thickness profile shown in the figure, a melted material with a total of 276 layers in a laminated state is formed, and the laminated state is extruded through a die to form an unstretched multilayer laminated structure. was created.
This unstretched multilayer laminate was stretched 5.9 times in the width direction at a temperature of 130°C. The thickness of the obtained uniaxially stretched multilayer laminate film was 28 μm.
This multilayer laminated film was evaluated using the evaluation method described above, and the results are shown in Tables 1 and 2.
Furthermore, from the refractive index after stretching described above, it was confirmed that the first layer was birefringent and the second layer was isotropic.

<Examples A2 to A8 and Examples B1 to B8>
A multilayer laminate film was produced in the same manner as in Example 1, except that the multilayer feedblock device used was changed so that the layer thickness profiles shown in Tables 1 and 2 were obtained.
Tables 1 and 2 show the evaluation results of the multilayer laminate films obtained in Examples A2 to A8 and Examples B1 to B8.
Note that "(A)" in Table 1 indicates the case where the layer thickness profile is the first embodiment described above, and "(B)" in Table 2 indicates the case where the layer thickness profile is the second embodiment described above. This shows an embodiment.

Furthermore, in all of the films obtained in Examples A2 to A8 and Examples B1 to B8, the first layer was birefringent and the second layer was isotropic, based on the above-mentioned evaluation of the refractive index after stretching. It was confirmed that

<Comparative Examples 1 to 4>
A multilayer laminate film was produced in the same manner as in Example 1, except that the multilayer feedblock device used was changed so that the layer thickness profiles shown in Tables 1 and 2 were obtained.
The evaluation results of the multilayer laminate films obtained in Comparative Examples 1 to 4 are shown in Tables 1 and 2.

As can be seen from Tables 1 and 2, in the multilayer laminate films of Examples, the generation of streaks was suppressed while maintaining a wide reflection band and a moderately high degree of polarization while being thin.

Therefore, in the multilayer laminate film of the example, the generation of streaks can be suppressed while maintaining a wide reflection band and a moderately high degree of polarization while being thinned, so the multilayer laminate film of the example can be used as an optical film. For example, when applied to liquid crystal displays and devices equipped with the same, it can contribute to making them smaller and lighter.

Claims (3)

A multilayer laminate film having a multilayer laminate structure in which a first layer mainly composed of resin and a second layer mainly composed of resin are alternately laminated,
The multilayer laminate structure has a layer thickness profile in physical thickness of a repeating unit having at least the first layer and the second layer, and the layer thickness profile is:
A first region whose thickness monotonically decreases from the first surface of the multilayer laminate structure and a second region whose thickness monotonically increases toward the second surface of the multilayer laminate structure, The ratio of the number of repeating units in the first region to the total number of repeating units is 5% or more and 35% or less, and the ratio of the number of repeating units in the second region to the total number of repeating units in the multilayer laminate structure is 65%. 95% or less,
A multilayer laminate film that satisfies the following (A) or (B).
(A)
The physical thickness of the repeating unit at the end on the first surface side in the first region is 90 nm or more and 170 nm or less, and the physical thickness of the repeating unit at the end on the second surface side is 80 nm or more and 120 nm or less,
The physical thickness of the repeating unit at the end on the first surface side in the second region is greater than or equal to the average thickness of all the repeating units in the first region and less than or equal to the maximum thickness of the repeating unit in the first region, and The physical thickness of the repeating unit at the end on the surface side is 240 nm or more and 310 nm or less.
(B)
The physical thickness of the repeating unit at the end on the first surface side in the first region is 240 nm or more and 310 nm or less, and the physical thickness of the repeating unit at the end on the second surface side is 200 nm or more and 300 nm or less,
The physical thickness of the repeating unit at the end on the first surface side in the second region is 80 nm or more and 120 nm or less, and the physical thickness of the repeating unit at the end on the second surface side is the smallest of the repeating units in the first region. The thickness is greater than or equal to the average thickness of all the repeating units in the first region. The multilayer laminate film according to claim 1, wherein the total ratio of the first region and the second region to the total number of repeating units in the multilayer laminate structure is 85% or more. The multilayer laminate film according to claim 1 or 2, further comprising a support layer mainly composed of resin and having a thickness of 4 μm or less on the surface of the multilayer laminate structure.