JP5069806B2 - Liquid crystal cell laminating polarizing plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polarizing plate to be bonded to a liquid crystal cell, which has high polarization performance comparable to a conventional absorptive polarizing plate and a function as a brightness-enhancing film which reflects polarized light not transmitted to reuse the polarized light, and is free from a hue shift of transmitted light with respect to light impinging in an oblique direction and comprises a multilayer laminate reflective polarizing film. <P>SOLUTION: The polarizing plate to be bonded to a liquid crystal cell comprises a uniaxially drawn multilayer laminate film, where a first layer is made of a polyester comprising a specific aromatic dicarboxylic acid component and a diol component and a second layer is made of a thermoplastic resin having an average refractive index of no less than 1.50 but no more than 1.60 and having a difference of 0.05 or less between a refractive index before drawing and that after drawing in each of a X-direction, Y-direction and Z-direction, where the thermoplastic resin is a blend of a copolymerized polyethylene terephthalate or a copolymerized polyethylene naphthalene dicarboxylate and a polycyclohexane dimethylene terephthalate-isophthalate copolymer. With a film surface as a reflecting surface, an average reflectance at a wavelength of 400 to 800 nm of incident polarized light having incidence angles of 0&deg; and 50&deg; with respect to a polarization component parallel with an incidence surface including a uniaxial drawing direction (X-direction) is 95% or higher. With the film surface as the reflecting surface, an average reflectance at a wavelength of 400 to 800 nm of the incident polarized light having incidence angles of 0&deg; and 50&deg; with respect to a polarization component perpendicular to the incidence surface including the X-direction is 12% or lower. <P>COPYRIGHT: (C)2012,JPO&amp;INPIT

Description

  The present invention relates to a polarizing plate having a high degree of polarization suitable for bonding to a liquid crystal cell, and more particularly to a polarizing plate for laminating a liquid crystal cell having a high degree of polarization using a uniaxially stretched multilayer laminated film.

  Liquid crystal display devices (LCDs) used in televisions, personal computers, mobile phones, etc. can be displayed by adjusting the amount of light emitted from the light source by a liquid crystal panel with polarizing plates on both sides of the liquid crystal cell. Yes. An absorption type polarizing plate generally called a light absorption type dichroic linear polarizing plate is used as a polarizing plate bonded to a liquid crystal cell, and a polarizing plate in which PVA containing iodine is protected with triacetyl cellulose (TAC). Is widely used.

  Such an absorption type polarizing plate transmits polarized light in the direction of the transmission axis and absorbs most of the polarized light in the direction orthogonal to the transmission axis, so about 50% of the unpolarized light emitted from the light source device is about 50%. It has been pointed out that the absorption efficiency of light decreases due to absorption by the absorption-type polarizing plate. Therefore, in order to effectively use polarized light orthogonal to the transmission axis, a configuration in which a reflective polarizer called a brightness enhancement film is used between a light source and a liquid crystal panel has been studied. As an example, a polymer type film using optical interference has been studied (for example, Patent Document 1).

On the other hand, the polarizing plate attached to the liquid crystal cell also has an absorption type polarizing plate depending on the type and purpose of light used in the display device, such as reflective display using external light and transmissive display using backlight. Various laminated structures combining a reflection type polarizing plate have been studied.
For example, Patent Document 2 discloses polarization used on both sides of a liquid crystal layer in a liquid crystal display device in which electrolysis is applied to the liquid crystal layer to change the retardation value of the liquid crystal to shift the phase difference of polarized light incident on the liquid crystal layer by a certain amount. As an example of a plate, a reflective polarizing plate having a planar multilayer structure in which three or more layers having birefringence are laminated on the light source side, and an absorptive polarizing plate on the opposite side through a liquid crystal layer are disclosed.
Further, Patent Document 3 discloses that when an absorptive polarizing plate and a reflective polarizing plate are used as a polarizing plate in a liquid crystal cell in which liquid crystal is sandwiched between flexible substrates, the amount of expansion and contraction associated with the temperature change of each polarizing plate is different. In order to eliminate the warpage that occurs in order to solve the problem, it has been proposed to eliminate the warpage by combining these polarizing plates into a specific laminated structure. As an example of the reflective polarizing plate, the use of a birefringent dielectric multilayer film is described. Specifically, a brightness enhancement film is disclosed.

However, the reflective polarizing polymer film (for example, Patent Documents 4 to 6) using a birefringent multilayer structure as conventionally studied has a function of reflecting p-polarized light and transmitting s-polarized light. The degree of polarization does not reach the same level as that of the dichroic linear polarizing plate.
For example, polyethylene-2,6-naphthalene dicarboxylate (hereinafter sometimes referred to as 2,6-PEN) described in Patent Document 5 is used for the high refractive index layer, and a thermoplastic elastomer or isophthalic acid is used. In the case of a multilayer laminated film using 30 mol% copolymerized PEN as a low refractive index layer, the refractive index difference between the layers in the stretching direction (X direction) is increased by stretching to increase the reflectance of p-polarized light, while in the film plane By increasing the transmittance of s-polarized light by reducing the refractive index difference between layers in the direction orthogonal to the X direction (Y direction), a certain level of polarization performance is manifested. If the polarization performance is to be increased to the level of the dichroic linear polarizing plate, the refractive index in the Y direction and the refractive index in the film thickness direction (Z direction) are accompanied by stretching in the X direction due to the nature of the 2,6-PEN polymer. When the Y-direction interlayer refractive index difference is matched, the Z-direction interlayer refractive index difference increases, and the hue deviation of transmitted light increases due to partial reflection of light incident in an oblique direction. .

  Therefore, a liquid crystal display device using such a multilayer polymer film alone as one polarizing plate of a liquid crystal cell has not yet been put into practical use.

JP-T 09-507308 JP 2005-316511 A JP 2009-103817 A JP 04-268505 A Japanese National Patent Publication No. 9-506837 International Publication No. 01/47711 Pamphlet

  The object of the present invention is to provide high polarization performance comparable to that of a conventional absorption-type polarizing plate and a function as a brightness enhancement film that reflects and reuses polarized light that is not transmitted, and transmits light incident in an oblique direction. An object of the present invention is to provide a polarizing plate for laminating a liquid crystal cell, which is composed of a multilayered reflective polarizing film, in which the hue shift of light is eliminated.

  As a result of intensive studies to solve the above problems, the present inventors have found that polyethylene-2,6-naphthalenedicarboxy, which has been used as a resin constituting the high refractive index layer of conventional multilayer laminated reflective polarizing films, Instead of the rate, the first layer after uniaxial stretching is obtained by using a thermoplastic resin that has the property that the refractive index in the X direction increases by uniaxial stretching while the refractive index in both the Y and Z directions decreases. As a result, the difference in refractive index between the X direction and the Y direction can be made larger than before, and as a result, p is higher than that of a multilayer laminated reflective polarizing film using polyethylene-2,6-naphthalenedicarboxylate. Polarized reflection performance is obtained, high polarization performance that selectively transmits s-polarized light by not transmitting p-polarized light, and inter-layer refraction in both the Y and Z directions The difference can be reduced and the hue shift of the transmitted light with respect to the light incident in the oblique direction is eliminated, so that the multilayer laminated film alone can be used as one polarizing plate of the liquid crystal cell, and the present invention is It came to be completed.

That is, an object of the present invention is a polarizing plate composed of a uniaxially stretched multilayer laminate film, wherein the uniaxially stretched multilayer laminate film has a multilayer structure of 251 layers or more in which the first layer and the second layer are alternately laminated. Have
1) The thermoplastic resin forming the first layer is (i) an acid component represented by the following formula (A-1) in which the dicarboxylic acid component is 5 mol% or more and 50 mol% or less, and 50 mol% or more and 95 mol% or less. Containing an acid component represented by the following formula (B):
(In formula (B), R ^B represents a naphthalenediyl group)
(Ii) A diol component represented by the following formula (C) in which the diol component is 90 mol% or more and 100 mol% or less
(In the formula (C), R ^C represents an ethylene group)
A polyester with an aromatic dicarboxylic acid component and a diol component containing
2) The thermoplastic resin constituting the second layer has an average refractive index of 1.50 or more and 1.60 or less, and the respective refractive index differences in the X direction, Y direction and Z direction are 0.05 or less before and after stretching. A thermoplastic resin, wherein the thermoplastic resin is a copolymerized polyethylene terephthalate or a blend of a copolymerized polyethylene naphthalene dicarboxylate and a polycyclohexanedimethylene terephthalate-isophthalate copolymer;
3) An average reflectance of a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degrees and 50 degrees with respect to a polarized light component parallel to the incident surface including the uniaxial stretching direction (X direction) with the film surface as a reflecting surface. 95% or more, with respect to a polarized light component perpendicular to the incident surface including the X direction, with the film surface as a reflective surface, an average reflectance of 400 to 800 nm with respect to the incident polarized light at incident angles of 0 degrees and 50 degrees Is achieved by a polarizing plate for laminating a liquid crystal cell, which is 12% or less.

  In the polarizing plate for laminating a liquid crystal cell of the present invention, the thermoplastic resin forming the second layer is a polyester mainly composed of an ethylene terephthalate component copolymerized with isophthalic acid or 2,6-naphthalenedicarboxylic acid. Is included as a preferred embodiment.

  According to the present invention, it has a high polarization performance comparable to that of a conventional absorption polarizing plate and a function as a brightness enhancement film that reflects and reuses polarized light that is not transmitted, and transmits light incident in an oblique direction. It is possible to provide a polarizing plate which is bonded to a liquid crystal cell in which the hue shift of light is eliminated.

Refractive index (represented as n _X , n _Y , and n _Z respectively) in the stretching direction (X direction) after uniaxial stretching of 2,6-PEN, the direction orthogonal to the stretching direction (Y direction), and the thickness direction (Z direction). ) Is shown in FIG. In the present invention, the first layer aromatic polyester (I) has a uniaxially stretched stretch direction (X direction), a direction perpendicular to the stretch direction (Y direction), and a refractive index in the thickness direction (Z direction) (each of n _X , N _Y and n _Z ) are shown in FIG. The film surface of the uniaxially stretched multilayer laminated film of the present invention is a reflective surface, and the polarization component (p light component) parallel to the incident surface including the stretching direction (X direction) and the incident including the stretching direction (X direction) It is an example of the graph of the reflectance with respect to the wavelength of a polarized light component (s light component) perpendicular | vertical with respect to a surface. 1 is a schematic cross-sectional view of a liquid crystal display device according to a preferred embodiment of the present invention.

[Uniaxially stretched multilayer laminated film]
(Average reflectance)
The reflective polarizing film for laminating a liquid crystal cell of the present invention is a reflective polarizing film composed of a uniaxially stretched multilayer laminated film, and the film surface is a reflective surface and is parallel to an incident surface including a uniaxially stretched direction (X direction). The average reflectance of the polarized light component at a wavelength of 400 to 800 nm with respect to the incident polarized light at incident angles of 0 degrees and 50 degrees is 95% or more, the film surface is the reflective surface, and the perpendicular surface is perpendicular to the incident surface including the X direction. The polarization component is characterized in that an average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at incident angles of 0 degrees and 50 degrees is 12% or less.

  Here, the incident surface refers to a surface that is perpendicular to the reflecting surface and includes the incident light beam and the reflected light beam. In addition, a polarization component parallel to an incident surface including a film surface as a reflection surface and including a stretching direction (X direction) of a uniaxially stretched film is generally referred to as p-polarized light. In addition, a polarization component perpendicular to an incident surface including a film surface as a reflection surface and including a stretching direction (X direction) of a uniaxially stretched film is generally referred to as s-polarized light. Furthermore, the incident angle represents an incident angle with respect to a direction perpendicular to the film surface.

With respect to the polarization component parallel to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as the reflecting surface, the average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree is More preferably, it is 98% or more and 100% or less. Since the average reflectance with respect to the p-polarized light component is thus high, the transmission amount of the p-polarized light is suppressed as compared with the conventional one, and a high polarization performance for selectively transmitting the s-polarized light is exhibited, which is comparable to the conventional absorption polarizing plate. High polarization performance is obtained, and it can be used as a polarizing plate to be bonded to a liquid crystal cell alone. At the same time, p-polarized light in a direction orthogonal to the transmission axis is highly reflected without being absorbed by the film, so that it can also function as a brightness enhancement film for reusing such light.
In addition, with respect to the polarization component parallel to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as the reflecting surface, the average reflection at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 50 degrees. The rate is more preferably 96% or more and 99% or less. This high average reflectivity for p-polarized light at an incident angle of 50 degrees can provide high polarization performance, and the transmission of light incident in an oblique direction is highly suppressed. Is suppressed.
The average reflectance at a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degree with respect to the polarized light component perpendicular to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as the reflecting surface is More preferably, it is 5% or more and 12% or less, and particularly preferably 8% or more and 12% or less.
Moreover, the average reflectance of the wavelength 400-800 nm with respect to the incident polarized light at an incident angle of 50 degrees with respect to a polarized light component perpendicular to the incident surface including the stretching direction (X direction) of the uniaxially stretched film with the film surface as a reflecting surface. Is more preferably 5% or more and 10% or less, and particularly preferably 8% or more and 10% or less.

  By limiting the average reflectance of the wavelength 400 to 800 nm with respect to the s-polarized component incident in the vertical direction and the oblique direction within this range, the amount of s-polarized light transmitted to the side opposite to the light source increases. On the other hand, when the average reflectance with respect to the s-polarized component exceeds the upper limit value, the polarization transmittance as a reflective polarizing film is lowered, so that sufficient performance as a polarizing plate to be bonded to a liquid crystal cell is not exhibited. On the other hand, although the transmittance of the s-polarized component is higher when the polarization reflectance is lower than the above range, it may be difficult to lower the lower limit than the lower limit.

  In order to obtain an average reflectance characteristic for the p-polarized component, in a uniaxially stretched multilayer laminated film constituted by alternately laminating a first layer and a second layer, a refractive index characteristic described later as a polymer constituting each layer is obtained. The first layer and the second layer in the stretching direction (X direction) are formed by stretching the film in the in-plane direction of the first layer by birefringence by stretching at a constant stretching ratio in the stretching direction (X direction). This is achieved by increasing the refractive index difference of the layers. Moreover, in order to obtain this average reflectance in a wavelength range of 400 to 800 nm, a method of adjusting the thicknesses of the first layer and the second layer can be mentioned.

  In addition, in order to obtain an average reflectance characteristic for the s-polarized component, in a uniaxially stretched multilayer laminated film constituted by alternately laminating a first layer and a second layer, a refractive index described later as a polymer component constituting each layer. The first layer and the second layer in the orthogonal direction (Y direction) by using a polymer having characteristics and not stretching in the direction orthogonal to the stretching direction (Y direction) or by only stretching at a low stretching ratio This is achieved by making the difference in the refractive index of the extremely small. Moreover, in order to obtain this average reflectance in a wavelength range of 400 to 800 nm, a method of adjusting the thicknesses of the first layer and the second layer can be mentioned.

[First layer]
The uniaxially stretched multilayer laminated film of the present invention has a multilayer structure in which first layers and second layers are alternately laminated. In the present invention, the first layer represents a layer having a higher refractive index than the second layer, and the second layer represents a layer having a lower refractive index than the first layer. The refractive index in the stretching direction (X direction) may be described as nX, the refractive index in the direction orthogonal to the stretching direction (Y direction) as nY, and the refractive index in the film thickness direction (Z direction) as nZ.

  In the present invention, the thermoplastic resin constituting the first layer has an average refractive index of 1.60 or more and 1.70 or less, the refractive index nX in the uniaxial stretching direction (X direction) is increased by stretching, and the film is in-plane. The refractive index nY in the direction perpendicular to the uniaxial stretching direction (Y direction) and the refractive index nZ in the film thickness direction (Z direction) are reduced by stretching.

Polyethylene-2,6-naphthalene dicarboxylate has hitherto been known as the most suitable material as the first layer of the multilayer laminated film having a reflective polarization function. While the refractive index nY in the Y direction hardly changes before and after stretching, the thermoplastic resin constituting the first layer of the present invention has a refractive index nY in the Y direction similar to the refractive index nZ in the Z direction by stretching. The most characteristic is that it decreases with stretching.
The thermoplastic resin having the refractive index characteristics of the present invention, which has not been conventionally used for the first layer of the multilayer laminated film having a reflective polarization function, is used for the first layer, and the second layer heat described later. By combining with a plastic resin to form a multilayer laminated film, high polarization performance comparable to that of conventional absorption type polarizing plates, which was difficult with conventional multilayer laminated films, is exhibited, and transmission of light incident in an oblique direction is achieved. Since the hue shift of polarized light is eliminated, it can be suitably used for a polarizing plate used by being attached to a liquid crystal cell.

  Here, the average refractive index in the present invention means that the thermoplastic resin constituting the first layer is melted alone, extruded from a die to create an unstretched film, and the obtained film in the X direction, Y direction, Z The refractive index in each direction is measured at a wavelength of 633 nm using a Metricon prism coupler, and the average value thereof is defined as the average refractive index.

Moreover, about the refractive index change of each direction by extending | stretching, it can obtain | require by the following method. That is, the thermoplastic resin constituting the first layer is melted alone and extruded from a die to produce an unstretched film. For each of the X direction, Y direction, and Z direction of the obtained film, the refractive index at a wavelength of 633 nm is measured using a metricon prism coupler, the average refractive index is obtained from the average value of the refractive indexes in three directions, and stretched. The previous refractive index.
Next, for the refractive index after stretching, the thermoplastic resin constituting the first layer is melted alone and extruded from a die to create a uniaxially stretched film by applying 5 times at 135 ° C. in the uniaxial direction, For each of the X direction, Y direction, and Z direction of the obtained film, the refractive index at a wavelength of 633 nm is measured using a metricon prism coupler to obtain the refractive index in each direction after stretching.
By comparing the refractive index before stretching obtained by such a method with the refractive index in each direction after stretching, the change in the refractive index due to stretching can be confirmed.

  The lower limit value of the average refractive index of the thermoplastic resin of the first layer is more preferably 1.61, and still more preferably 1.62. The upper limit of the average refractive index of the thermoplastic resin of the first layer is more preferably 1.69, and still more preferably 1.68. When the average refractive index of the thermoplastic resin of the first layer is within such a range, the refractive index difference in each direction between the stretched second layer and the second layer can be set to a desired range. On the other hand, when the average refractive index of the thermoplastic resin of the first layer is less than the lower limit value, the refractive index difference with the second layer is close, and the refractive index difference in the X direction after stretching cannot be sufficiently increased. . When the average refractive index of the thermoplastic resin of the first layer exceeds the upper limit value, the refractive index difference with the second layer after stretching becomes large, and the refractive index difference between the layers in the Y direction and Z direction after stretching becomes small. It is hard to do.

  The refractive index nX in the X direction of the thermoplastic resin of the first layer is preferably increased by 0.20 or more by stretching, more preferably 0.25 or more, and further preferably 0.27 or more. The larger the change in the refractive index, the higher the polarization performance can be improved, but the upper limit value is limited to 0.35 and further 0.30 because the film breaks when the draw ratio is too high. .

  The refractive index nY in the Y direction of the thermoplastic resin of the first layer is preferably lowered in the range of 0.05 or more and 0.20 or less by stretching, more preferably 0.06 or more and 0.15 or less, and still more preferably. It is 0.07 or more and 0.10 or less. When the amount of decrease in the refractive index is less than the lower limit, if the resins in both layers are selected so that the interlayer refractive index in the Y direction matches, the difference in the refractive index between the layers in the X direction increases. The refractive index shift between the layers increases, and it may be difficult to achieve both improvement in polarization performance and hue shift of transmitted polarized light with respect to obliquely incident light. On the other hand, when the amount of decrease in the refractive index exceeds the upper limit, the orientation is too high and the mechanical strength may not be sufficient.

  The refractive index nZ in the Z direction of the thermoplastic resin of the first layer is preferably lowered in the range of 0.05 or more and 0.20 or less by stretching, more preferably 0.06 or more and 0.15 or less, and still more preferably. It is 0.07 or more and 0.10 or less. In order to make the amount of decrease in the refractive index less than the lower limit, the X direction must be lowly oriented, and the refractive index difference between the layers in the X direction may not be sufficiently large. On the other hand, when the amount of decrease in the refractive index exceeds the upper limit, the orientation is too high and the mechanical strength may not be sufficient.

  The difference in refractive index between the Y-direction refractive index nY after stretching of the first layer and the Z-direction refractive index nZ after stretching is preferably 0.05 or less, more preferably 0.03 or less, and particularly preferably 0.00. 01 or less. Since the difference in refractive index between these two directions is very small, there is an effect that no hue shift occurs even when polarized light is incident at an oblique incident angle. Such polarized light is particularly effective for eliminating a hue shift with respect to a polarization component (s-polarized light) perpendicular to an incident surface including a stretching direction (X direction) of a uniaxially stretched film with a film surface as a reflecting surface. .

  As the thermoplastic resin having such refractive index characteristics, specifically, an aromatic polyester having a copolymer component having a specific structure as described below as a dicarboxylic acid component (hereinafter sometimes referred to as aromatic polyester (I)). And polyethylene-2,7-naphthalenedicarboxylate.

<Aromatic polyester (I)>
As one of the thermoplastic resins forming the first layer, aromatic polyester (I) having a copolymer component having a specific structure as a dicarboxylic acid component is exemplified. Such a polyester is obtained by polycondensation of a dicarboxylic acid component and a diol component described in detail below.
(Dicarboxylic acid component)
As the dicarboxylic acid component (i) constituting the aromatic polyester (I) of the present invention, an acid component represented by the following formula (A) of 5 mol% or more and 50 mol% or less, and 50 mol% or more and 95 mol% or less At least two types of aromatic dicarboxylic acid components represented by the acid component represented by the following formula (B) or derivatives thereof are used. Here, the content of each aromatic dicarboxylic acid component is a content based on the total number of moles of the dicarboxylic acid component.

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

(In the formula (B), R ^B represents a phenylene group or a naphthalenediyl group)

Regarding the acid component represented by the formula (A), R ^A is an alkylene group having 2 to 10 carbon atoms. Examples of the alkylene group include an ethylene group, a propylene group, an isopropylene group, a tetramethylene group, a hexamethylene group, and an octamethylene group.

The lower limit of the content of the acid component represented by the formula (A) is preferably 7 mol%, more preferably 10 mol%, still more preferably 15 mol%. Further, the upper limit value of the content of the acid component represented by the formula (A) is preferably 45 mol%, more preferably 40 mol%, still more preferably 35 mol%, particularly preferably 30 mol%.
Therefore, the content of the acid component represented by the formula (A) is preferably 5 mol% or more and 45 mol% or less, more preferably 7 mol% or more and 40 mol% or less, and further preferably 10 mol% or more and 35 mol%. Hereinafter, it is particularly preferably 15 mol% or more and 30 mol% or less.

The acid component represented by the formula (A) is preferably 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, 6,6 ′-(trimethylenedioxy) di-2-naphthoic acid and 6 , 6 '-(Butylenedioxy) di-2-naphthoic acid is preferred. Among these, those having an even number of carbon atoms of ^RA in the formula (A) are preferable, and 6,6 ′-(ethylenedioxy) di-2-naphthoic acid represented by the following formula (A-1) is particularly preferable.

  Such aromatic polyester (I) is characterized in that the dicarboxylic acid component contains an acid component represented by the formula (A) in an amount of 5 mol% to 50 mol%. When the ratio of the acid component represented by the formula (A) is less than the lower limit, the refractive index in the Y direction due to uniaxial stretching is unlikely to decrease. The difference in the rate nZ becomes large, and it is difficult to improve the hue shift due to polarized light incident at an oblique incident angle. In addition, when the ratio of the acid component represented by the formula (A) exceeds the upper limit, the amorphous characteristics are increased, and the difference between the refractive index nX in the X direction and the refractive index nY in the Y direction in the stretched film is Therefore, the refractive index difference between the first layer and the second layer in the X direction cannot be increased, and sufficient reflection performance cannot be obtained for the p-polarized component.

  As described above, by using the polyester containing the acid component represented by the formula (A), uniaxial stretching that improves the polarization performance as a reflective polarizing film and does not cause a hue shift due to an incident angle in an oblique direction. A multilayer laminated film can be produced.

Further, the acid component of the formula (B), wherein, R ^B is a phenylene group or naphthalene-diyl group.
Examples of the acid component represented by the formula (B) include terephthalic acid, isophthalic acid, 2,6-naphthalenedicarboxylic acid, 2,7-naphthalenedicarboxylic acid, or a combination thereof, and particularly 2,6-naphthalenedicarboxylic acid. Is preferably exemplified.

The lower limit of the content of the acid component represented by the formula (B) is preferably 55 mol%, more preferably 60 mol%, still more preferably 65 mol%, particularly preferably 70 mol%. Further, the upper limit value of the content of the acid component represented by the formula (B) is preferably 93 mol%, more preferably 90 mol%, still more preferably 85 mol%.
Therefore, the content of the acid component represented by the formula (B) is preferably 55 mol% or more and 95 mol% or less, more preferably 60 mol% or more and 93 mol% or less, and further preferably 65 mol% or more and 90 mol% or less. Hereinafter, it is particularly preferably 70 mol% or more and 85 mol% or less.

When the ratio of the acid component represented by the formula (B) is less than the lower limit, the amorphous characteristics are increased, and the difference between the refractive index nX in the X direction and the refractive index nY in the Y direction in the stretched film is small. Therefore, the refractive index difference between the first layer and the second layer in the X direction cannot be increased, and sufficient reflection performance cannot be obtained for the p-polarized component. In addition, when the ratio of the acid component represented by the formula (B) exceeds the upper limit, the ratio of the acid component represented by the formula (A) is relatively small, so that the refractive index nY in the Y direction in the stretched film and The difference in the refractive index nZ in the Z direction becomes large, and it is difficult to improve the hue shift due to polarized light incident at an oblique incident angle.
Thus, by using the polyester containing the acid component represented by the formula (B), it is possible to realize a birefringence characteristic having a high uniaxial orientation while exhibiting a high refractive index in the X direction.

(Diol component)
As the diol component (ii) constituting the aromatic polyester (I) of the present invention, a diol component represented by the following formula (C) of 90 mol% or more and 100 mol% or less is used. Here, the content of the diol component is a content based on the total number of moles of the diol component.

(In the formula (C), R ^C represents an alkylene group having 2 to 10 carbon atoms)
The content of the diol component represented by the formula (C) is preferably 95 mol% to 100 mol%, more preferably 98 mol% to 100 mol%.

In the formula (C), R ^C is an alkylene group having 2 to 10 carbon atoms, and examples of the alkylene group include an ethylene group, a propylene group, an isopropylene group, a tetramethylene group, a hexamethylene group, and an octamethylene group. . Among these, preferred examples of the diol component represented by the formula (C) include ethylene glycol, trimethylene glycol, tetramethylene glycol, and cyclohexanedimethanol, and ethylene glycol is particularly preferred. When the ratio of the diol component represented by the formula (C) is less than the lower limit, the above-described uniaxial orientation is impaired.

(Aromatic polyester (I))
In the aromatic polyester (I), the content of the ester unit (-(A)-(C)-) composed of the acid component represented by the formula (A) and the diol component represented by the formula (C) is , 5 mol% or more and 50 mol% or less of all repeating units, preferably 5 mol% or more and 45 mol% or less, more preferably 10 mol% or more and 40 mol% or less.

  As other ester units constituting the aromatic polyester (I), alkylene terephthalate units such as ethylene terephthalate, trimethylene terephthalate, butylene terephthalate, ethylene-2,6-naphthalene dicarboxylate, trimethylene-2,6-naphthalene dicarboxylate And alkylene-2,6-naphthalenedicarboxylate units such as butyl and butylene-2,6-naphthalenedicarboxylate. Among these, ethylene terephthalate units and ethylene-2,6-naphthalenedicarboxylate units are preferable, and ethylene-2,6-naphthalenedicarboxylate units are particularly preferable from the viewpoint of high refractive index.

As the aromatic polyester (I), in particular, the dicarboxylic acid component represented by the formula (A) is a dicarboxylic acid component represented by the formula (A-1),
A polyester in which the dicarboxylic acid component represented by the formula (B) is an aromatic dicarboxylic acid component derived from 2,6-naphthalenedicarboxylic acid and the diol component is ethylene glycol is preferred.

  The aromatic polyester (I) has an intrinsic viscosity of 0.4 to 3 dl / measured at 35 ° C. using a mixed solvent of P-chlorophenol / 1,1,2,2-tetrachloroethane (weight ratio 40/60). It is preferable that it is g, More preferably, it is 0.4-1.5 dl / g, Most preferably, it is 0.5-1.2 dl / g.

The melting point of the aromatic polyester (I) is preferably in the range of 200 to 260 ° C, more preferably in the range of 205 to 255 ° C, and still more preferably in the range of 210 to 250 ° C. The melting point can be determined by measuring with DSC.
If the melting point of the polyester exceeds the upper limit value, fluidity may be inferior when melt-extruded and molded, and discharge and the like may be made uneven. On the other hand, if the melting point is less than the lower limit, the film forming property is excellent, but the mechanical properties of the polyester are easily impaired, and the refractive index properties of the present invention are hardly exhibited.
In general, a copolymer has a lower melting point than a homopolymer and tends to decrease mechanical strength. However, the polyester of the present invention is a copolymer containing an acid component of the formula (A) and an acid component of the formula (B), and has a melting point compared to a homopolymer having only the acid component of the formula (A). Although it has a low mechanical strength, it has excellent properties.

The glass transition temperature (hereinafter sometimes referred to as Tg) of the aromatic polyester (I) is preferably 80 to 120 ° C, more preferably 82 to 118 ° C, and still more preferably 85 to 118 ° C. When Tg is within this range, a film having excellent heat resistance and dimensional stability can be obtained. Such melting point and glass transition temperature can be adjusted by controlling the kind and copolymerization amount of the copolymerization component and dialkylene glycol as a by-product.
The method for producing the aromatic polyester (I) can be produced, for example, according to the method described on page 9 of International Publication No. 2008/153188.

(Refractive index characteristics of aromatic polyester (I))
FIG. 2 shows an example of changes in the refractive index in each direction when the aromatic polyester (I) is uniaxially stretched. As shown in FIG. 2, the refractive index nX in the X direction is in the direction of increasing by stretching, the refractive index nY in the Y direction and the refractive index nZ in the Z direction are both decreasing with stretching, and Regardless of this, the difference in refractive index between nY and nZ is very small.

  Further, the first layer is uniaxially stretched using the aromatic polyester (I) containing the specific copolymer component, so that the refractive index nX in the X direction is 1.80 to 1.90. Have When the refractive index in the X direction in the first layer is within such a range, the refractive index difference from the second layer becomes large, and sufficient reflective polarization performance can be exhibited.

  On the other hand, when the polyester constituting the first layer is polyethylene-2,6-naphthalenedicarboxylate, as shown in FIG. 1, the refractive index nY in the Y direction is constant regardless of the stretching ratio in the uniaxial direction. While no decrease is observed, the refractive index nZ in the Z direction decreases as the uniaxial stretching magnification increases. Therefore, the difference between the refractive index nY in the Y direction and the refractive index nZ in the Z direction becomes large, and a hue shift tends to occur when polarized light is incident at an oblique incident angle.

<Polyethylene-2,7-naphthalenedicarboxylate>
An example of another thermoplastic resin forming the first layer is polyethylene-2,7-naphthalenedicarboxylate (hereinafter sometimes referred to as 2,7-PEN). Such polyester is obtained by polycondensation using 2,7-naphthalenedicarboxylic acid as a dicarboxylic acid component and ethylene glycol as a diol component. Moreover, you may have a copolymerization component in the range of 10 mol% or less based on the total repeating unit amount, More preferably, it is 5 mol% or less. As the copolymer component, one or more of the dicarboxylic acid components and diol components described in the aromatic polyester (I) can be used.

  2,7-PEN has the same constituents as polyethylene-2,6-naphthalenedicarboxylate, but due to the different coordination of carboxylic acid, the crystal structure due to stretching is different. In 2,6-PEN, Since the refractive index nY in the Y direction is reduced due to the stretching that was not observed, both the improvement of the polarization performance and the hue shift of the transmitted polarized light with respect to the incident light in the oblique direction can be achieved together with the aromatic polyester (I).

[Second layer]
<Thermoplastic resin>
In the present invention, the second layer has an average refractive index of 1.50 or more and 1.60 or less, and a difference in refractive index between the X direction, the Y direction, and the Z direction is 0.05 or less before and after stretching. Consists of. Here, the average refractive index is the same as the average refractive index of the thermoplastic resin constituting the first layer, the thermoplastic resin constituting the second layer is melted alone, and extruded from a die to create an unstretched film, The refractive index in each of the X direction, Y direction, and Z direction of the obtained film is measured at a wavelength of 633 nm using a metricon prism coupler, and the average value thereof is defined as the average refractive index.

  As for the difference in refractive index before and after stretching, as in the case of the first layer, first, the thermoplastic resin constituting the second layer is melted alone and extruded from a die to produce an unstretched film. For each of the X direction, Y direction, and Z direction of the obtained film, the refractive index at a wavelength of 633 nm is measured using a metricon prism coupler, the average refractive index is obtained from the average value of the refractive indexes in three directions, and stretched. The previous refractive index. Next, for the refractive index after stretching, the thermoplastic resin constituting the second layer is melted alone and extruded from a die, and a uniaxially stretched film is formed by applying 5 times at 135 ° C. in the uniaxial direction, For each direction in the X direction, Y direction, and Z direction of the obtained film, the refractive index at a wavelength of 633 nm is measured using a Metricon prism coupler to determine the refractive index in each direction after stretching, and each direction before and after stretching. It is obtained by comparing the difference in refractive index.

  The average refractive index of the thermoplastic resin constituting the second layer is preferably from 1.53 to 1.60, more preferably from 1.55 to 1.60, and even more preferably from 1.58 to 1.60. is there. Since the second layer is an isotropic material having such an average refractive index and a small difference in refractive index before and after stretching, the refractive index difference in the X direction after stretching between the first layer and the second layer is reduced. Refractive index characteristics that are large and extremely small in both the Y-direction refractive index difference and the Z-direction refractive index difference can be obtained, and as a result, both high polarization performance and hue shift due to an oblique incident angle can be achieved. .

  Among thermoplastic resins having such a refractive index characteristic, a crystalline polyester is preferable from the viewpoint of film forming property in uniaxial stretching. As the crystalline polyester having such refractive index characteristics, copolymerized polyethylene terephthalate, copolymerized polyethylene naphthalene dicarboxylate, or a blend of these copolymerized polyester and amorphous polyester is preferable, and copolymerized polyethylene terephthalate is particularly preferable. Among such copolymerized polyethylene terephthalates, polyesters mainly composed of an ethylene terephthalate component copolymerized with isophthalic acid or 2,6-naphthalenedicarboxylic acid are preferred, and in particular, ethylene copolymerized with isophthalic acid or 2,6-naphthalenedicarboxylic acid. A polyester having a melting point of 220 ° C. or lower, mainly composed of a terephthalate component, is preferred.

  In the case of copolymerized polyethylene terephthalate, the copolymer components other than the above components may be isophthalic acid or 2,6-naphthalene within a range of 10 mol% or less based on all repeating units constituting the polyester of the second layer. Aromatic carboxylic acids other than the main copolymer component among dicarboxylic acids and 2,7-naphthalenedicarboxylic acids; aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid, decanedicarboxylic acid; fats such as cyclohexanedicarboxylic acid Preferable examples include acid components such as cyclic dicarboxylic acids, aliphatic diols such as butanediol and hexanediol; and glycol components such as alicyclic diols such as cyclohexanedimethanol.

  Among these, two copolymer components of isophthalic acid and 2,6-naphthalenedicarboxylic acid are preferable because the melting point is easily lowered while maintaining stretchability. In addition, the melting point of the thermoplastic resin constituting the second layer does not have to be low from the stage before forming the film, and may be low after the stretching treatment. For example, two or more kinds of polyesters may be blended and transesterified at the time of melt kneading.

[Ingredients other than resin]
In order to improve the winding property of the film, the uniaxially stretched multilayer laminated film of the present invention is provided with inert particles having an average particle diameter of 0.01 μm to 2 μm in at least one outermost layer based on the weight of the layer. It is preferable to contain 0.001 to 0.5 weight%. If the average particle diameter of the inert particles is smaller than the lower limit value or the content is less than the lower limit value, the effect of improving the winding property of the multilayer stretched film tends to be insufficient, while the inclusion of the inert particles When the amount exceeds the upper limit value or the average particle diameter exceeds the upper limit value, the optical properties of the multilayer stretched film may be deteriorated due to the particles. The average particle diameter of the preferable inert particles is in the range of 0.02 μm to 1 μm, particularly preferably 0.1 μm to 0.3 μm. Moreover, content of a preferable inert particle is the range of 0.02 weight%-0.2 weight%.

  Examples of the inert particles included in the uniaxially stretched multilayer laminated film include inorganic inert particles such as silica, alumina, calcium carbonate, calcium phosphate, kaolin, and talc, silicone, crosslinked polystyrene, and styrene-divinylbenzene copolymer. Such organic inert particles can be mentioned. The particle shape is not particularly limited as long as it is a generally used shape such as agglomerated or spherical.

  The inert particles may be contained not only in the outermost layer but also in a layer composed of the same resin as the outermost layer. For example, the inert particles may be contained in at least one of the first layer and the second layer. Good. Alternatively, another layer different from the first layer and the second layer may be provided as the outermost layer, and when a heat seal layer is provided, inert particles may be included in the heat seal layer.

[Lamination structure of uniaxially stretched multilayer laminated film]
(Number of layers)
In the uniaxially stretched multilayer laminated film of the present invention, it is preferable that the above-mentioned first layer and second layer are alternately laminated in a total of 251 layers. When the number of stacked layers is less than 251 layers, the average reflectance characteristics of the polarization component parallel to the incident surface including the stretching direction (X direction) may satisfy a certain average reflectance over a wavelength range of 400 to 800 nm. There are things that cannot be done.
The upper limit of the number of layers is limited to 2001 layers from the viewpoints of productivity and film handling. As long as the average reflectance characteristic of the present invention is obtained, the upper limit value of the number of layers may be further reduced from the viewpoint of productivity and handling properties, and may be, for example, 1001, 501 and 301 layers.

(Each layer thickness)
The thickness of each layer of the first layer and the second layer is 0.01 μm or more and 0.5 μm or less. The thickness of each layer of the first layer is preferably 0.01 μm or more and 0.1 μm or less, and the thickness of each layer of the second layer is preferably 0.01 μm or more and 0.3 μm or less. The thickness of each layer can be determined based on a photograph taken using a transmission electron microscope.

  Since the reflection wavelength band shown by the uniaxially stretched multilayer laminated film of the present invention is from the visible light region to the near infrared region, the thickness of each layer of the first layer and the second layer is within such a wavelength range. Can be selectively reflected by optical interference between layers. On the other hand, when the layer thickness exceeds 0.5 μm, the reflection band becomes the infrared region. On the other hand, when the layer thickness is less than 0.01 μm, the polyester component absorbs light and the reflection performance cannot be obtained.

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

In the multilayer laminated film, the wavelength to be reflected is determined by the difference in refractive index between layers, the number of layers, and the thickness of the layer. However, when each of the laminated first and second layers has a constant thickness, only a specific wavelength is reflected. The average reflectance of the polarization component parallel to the incident surface including the stretching direction (X direction) cannot be increased uniformly over a wide wavelength range of 400 to 800 nm, Use layers with different thicknesses.
On the other hand, when the ratio between the maximum layer thickness and the minimum layer thickness exceeds the upper limit value, the reflection band is wider than 400 to 800 nm, and the reflectance of the polarization component parallel to the incident surface including the stretching direction (X direction) May be accompanied by a decline.

The layer thicknesses of the first layer and the second layer may change stepwise or may change continuously. By changing each of the first layer and the second layer laminated in this way, light in a wider wavelength range can be reflected.
The method for laminating the multilayer structure in the uniaxially stretched multilayer laminated film of the present invention is not particularly limited. For example, the first layer is obtained by branching 137 layers of polyester for the first layer and 138 layers of thermoplastic resin for the second layer. And a second layer are alternately laminated, and a method of using a multilayer feed block device in which the flow path continuously changes by 2.0 to 5.0 times is mentioned.

(Average layer thickness ratio of the first layer and the second layer)
In the uniaxially stretched multilayer laminated film of the present invention, the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is preferably in the range of 1.5 to 5.0 times. The lower limit value of the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is more preferably 2.0. The upper limit of the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is more preferably 4.0, and even more preferably 3.5.

Since the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer is in such a range, secondary reflection occurring at a half wavelength of the reflection wavelength can be effectively used. Therefore, each of the first layer and the second layer The ratio of the maximum layer thickness to the minimum layer thickness can be minimized, which is preferable from the viewpoint of optical characteristics. In addition, by changing the thickness ratio of the first layer and the second layer in this way, the mechanical properties of the obtained film are also adjusted while maintaining the adhesion between the layers and without changing the resin used. And has an effect of making the film difficult to tear.
On the other hand, when the ratio of the average layer thickness of the second layer to the average layer thickness of the first layer deviates from this range, the secondary reflection that occurs at the half wavelength of the reflection wavelength becomes small, and the reflectance may decrease. .

(Thickness adjustment layer)
In addition to the first layer and the second layer, the uniaxially stretched multilayer laminated film of the present invention has a thickness adjusting layer having a layer thickness of 2 μm or more in a part of the alternately laminated structure of the first layer and the second layer. May be. By having the thickness adjusting layer having such a thickness as a part of the alternately laminated structure of the first layer and the second layer, the thickness of each layer constituting the first layer and the second layer can be made uniform without affecting the polarization function. Easy to adjust. The thickness adjusting layer having such a thickness may be the same composition as either the first layer or the second layer, or a composition partially including these compositions. Since the layer thickness is thick, the thickness adjusting layer does not contribute to the reflection characteristics. On the other hand, since it may affect the transmitted polarized light, when the particles are included in the layer, it is preferably within the range of the particle concentration described above.

[Uniaxially stretched film]
The uniaxially stretched multilayer laminated film of the present invention is stretched in at least a uniaxial direction in order to satisfy the optical properties as the target reflective polarizing film. The uniaxial stretching in the present invention includes a film stretched in a biaxial direction in addition to a film stretched only in a uniaxial direction and a film stretched in one direction. The uniaxial stretching direction (X direction) may be either the film longitudinal direction or the width direction. Further, in the case of a film stretched in a biaxial direction and stretched in one direction, the direction (X direction) that is more stretched may be either the film longitudinal direction or the width direction. In the direction where the draw ratio is low, it is preferable that the draw ratio is about 1.05 to 1.20 times in terms of enhancing the polarization performance. In the case of a film stretched in a biaxial direction and stretched in one direction, the “stretch direction” in relation to polarized light and refractive index refers to a more stretched direction.

  As the stretching method, known stretching methods such as heat stretching with a rod heater, roll heat stretching, and tenter stretching can be used, but tenter stretching is preferable from the viewpoint of reducing scratches due to contact with the roll and stretching speed.

[Refractive index characteristics between the first layer and the second layer]
The X-direction refractive index difference between the first layer and the second layer is preferably 0.10 to 0.45, more preferably 0.20 to 0.40, and particularly preferably 0.25 to 0.30. is there. When the refractive index difference in the X direction is within such a range, the reflection characteristics can be improved efficiently, and a high reflectance can be obtained with a smaller number of layers.

  Moreover, it is preferable that the difference in refractive index in the Y direction between the first layer and the second layer and the difference in refractive index in the Z direction between the first layer and the second layer are 0.05 or less, respectively. Since the refractive index difference between the layers in the Y direction and the Z direction is both in the above-described range, hue deviation can be suppressed when polarized light is incident at an oblique incident angle.

[Film thickness]
The uniaxially stretched multilayer laminated film of the present invention preferably has a film thickness of 15 μm or more and 40 μm or less. The conventional multilayer laminated film having a reflective polarization function needs to increase the number of layers in order to increase the average reflectance of p-polarized light, and the thickness of about 100 μm is necessary. The present invention constitutes the first layer. By using a resin whose refractive index in the Y direction decreases as a result of stretching as a thermoplastic resin, and combining it with the above-mentioned second layer thermoplastic resin, a multilayer multilayer film having a constant layer thickness is obtained. Thus, the film thickness can be made thinner and the optical member for the liquid crystal optical device can be made thinner.

[Method for producing uniaxially stretched multilayer laminated film]
Below, the manufacturing method of the uniaxially stretched multilayer laminated film of this invention is explained in full detail.
The uniaxially stretched multilayer laminated film of the present invention is extruded in a state in which the thermoplastic resin constituting the first layer and the thermoplastic resin constituting the second layer are alternately superposed in the molten state, and the multilayer unstretched film (sheet) Process). At this time, the laminate is laminated so that the thickness of each layer changes stepwise or continuously within a range of 2.0 times or more, preferably 5.0 times or less.

  The multilayer unstretched film thus obtained is stretched in the film forming direction or at least one axial direction (direction along the film surface) in the width direction perpendicular thereto. The stretching temperature is preferably in the range of the temperature (Tg) to Tg + 50 ° C. of the glass transition point of the thermoplastic resin of the first layer. The draw ratio at this time is preferably 2 to 10 times, more preferably 2.5 to 7 times, further preferably 3 to 6 times, and particularly preferably 4.5 to 5.5 times. The larger the draw ratio, the smaller the variations in the plane direction of the individual layers in the first layer and the second layer, and the light interference of the multilayer stretched film is made uniform in the plane direction. This is preferable because the difference in refractive index between the layers and the second layer in the stretching direction becomes large. As the stretching method at this time, known stretching methods such as heat stretching with a rod heater, roll heating stretching, and tenter stretching can be used. From the viewpoints of reducing scratches due to contact with the roll and stretching speed, tenter stretching is performed. preferable. Moreover, when performing a extending | stretching process also in the direction (Y direction) orthogonal to this extending | stretching direction and performing biaxial stretching, it is preferable to limit to a draw ratio of about 1.05-1.20 times. If the stretch ratio in the Y direction is further increased, the polarization performance may be deteriorated. Moreover, it is preferable to perform a heat setting process after extending | stretching.

[Reflective polarizing film for bonding liquid crystal cells]
The uniaxially stretched multilayer laminated film of the present invention has a high polarization performance comparable to that of a conventional absorption polarizing plate, and a function as a brightness enhancement film that reflects and reuses polarized light that is not transmitted, and in an oblique direction. Since the hue shift of the transmitted light with respect to the incident light is eliminated, the uniaxially stretched multilayer laminated film can be used as a polarizing plate to be bonded to the liquid crystal cell alone.

[Optical members for liquid crystal display devices]
The present invention also includes an optical member for a liquid crystal display device in which the first polarizing plate, the liquid crystal cell, and the second polarizing plate made of the reflective polarizing film for bonding a liquid crystal cell of the present invention are laminated in this order. Included as an aspect. Such an optical member is also referred to as a liquid crystal panel. Such an optical member corresponds to 5 in FIG. 4, the first polarizing plate corresponds to 3, the liquid crystal cell corresponds to 2, and the second polarizing plate corresponds to 1.

  Conventionally, as a polarizing plate on both sides of the liquid crystal cell, high polarizing performance has been obtained by having at least an absorptive polarizing plate. If it is a polarizing plate using the multilayer laminated film of the present invention, the conventional multilayer laminated film is used. Since high polarization performance that could not be achieved with a film can be obtained, it can be used in combination with a liquid crystal cell instead of a conventional absorption polarizing plate.

  That is, the feature of the present invention is that a polarizing plate comprising the multilayer laminated film of the present invention is used alone in one of the liquid crystal cells as the first polarizing plate. Preferably, the first polarizing plate is an absorption polarizing plate. Laminated configurations are excluded.

The type of the liquid crystal cell is not particularly limited, and any type of liquid crystal cell such as a VA mode, an IPS mode, a TN mode, an STN mode, or a bend alignment (π type) can be used.
Moreover, the kind of 2nd polarizing plate is not specifically limited, Both an absorption type polarizing plate and a reflection type polarizing plate can be used. When a reflective polarizing plate is used as the second polarizing plate, it is preferable to use the reflective polarizing film for bonding a liquid crystal cell of the present invention.

  In the optical member for a liquid crystal display device of the present invention, the first polarizing plate, the liquid crystal cell, and the second polarizing plate are preferably laminated in this order, and these members may be laminated directly, Further, the layers may be laminated through a layer called an adhesive layer or an adhesive layer that enhances adhesion between layers (hereinafter sometimes referred to as an adhesive layer), a protective layer, or the like.

[Formation of optical member for liquid crystal display device]
As a method of disposing the polarizing plate in the liquid crystal cell, it is preferable to laminate both with an adhesive layer. The pressure-sensitive adhesive forming the pressure-sensitive adhesive layer is not particularly limited. For example, an acrylic polymer, silicone-based polymer, polyester, polyurethane, polyamide, polyether, fluorine-based or rubber-based polymer is appropriately selected. Can be used. In particular, an acrylic pressure-sensitive adhesive that is excellent in transparency, has suitable wettability, cohesiveness, and adhesive pressure-sensitive adhesive properties, and is excellent in weather resistance, heat resistance, and the like. The adhesive layer may be provided with a plurality of layers having different compositions or types.

  From the viewpoint of workability when laminating the liquid crystal cell and the polarizing plate, the adhesive layer is preferably attached in advance to one or both of the polarizing plate and the liquid crystal cell. The thickness of the pressure-sensitive adhesive layer can be appropriately determined according to the purpose of use and adhesive force, and is generally 1 to 500 μm, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

(Release film)
Moreover, it is preferable that a release film (separator) is temporarily attached to the exposed surface of the pressure-sensitive adhesive layer for the purpose of preventing contamination or the like until it is practically used. Thereby, it can prevent contacting an adhesion layer in the usual handling state. Examples of release films include plastic films, rubber sheets, paper, cloth, non-woven fabrics, nets, foam sheets, metal foils, laminates thereof, and the like, silicone-based or long-chain alkyl-based, fluorine-based or molybdenum sulfide. Those coated with a release agent such as can be used.

[Liquid Crystal Display]
The present invention also includes a liquid crystal display device including a light source and the optical member for a liquid crystal display device of the present invention, in which the first polarizing plate is disposed on the light source side.

  FIG. 4 is a schematic cross-sectional view of a liquid crystal display device which is one embodiment of the present invention. The liquid crystal display device has a light source 4 and a liquid crystal panel 5, and further incorporates a drive circuit and the like as necessary. The liquid crystal panel 5 includes the first polarizing plate 3 on the light source 4 side of the liquid crystal cell 2. In addition, the second polarizing plate 1 is provided on the side opposite to the light source side of the liquid crystal cell 2, that is, on the viewing side. As the liquid crystal cell 2, for example, an arbitrary type such as a VA mode, an IPS mode, a TN mode, an STN mode, or a bend alignment (π type) can be used.

The liquid crystal display device of the present invention has a conventional absorption type by disposing the first polarizing plate 3 made of the reflective polarizing film for bonding a liquid crystal cell of the present invention having high polarization performance on the light source side of the liquid crystal cell 2. Instead of the polarizing plate, it can be used in combination with a liquid crystal cell.
The first polarizing plate comprising the reflective polarizing film for laminating a liquid crystal cell of the present invention has a high polarizing performance comparable to a conventional absorption polarizing plate, and a brightness enhancement film that reflects and reuses polarized light that is not transmitted. Therefore, it is not necessary to use a reflective polarizing plate called a brightness enhancement film between the light source 4 and the first polarizing plate 3, and the function of a polarizing plate to be bonded to the brightness enhancement film and the liquid crystal cell is provided. Since they can be integrated, the number of members can be reduced.

  Furthermore, the liquid crystal display device of the present invention uses the reflective polarizing film for laminating a liquid crystal cell of the present invention as the first polarizing plate, so that almost no p-polarized component incident in the oblique direction is incident on the light incident in the oblique direction. Since the s-polarized component that is not transmitted and is incident in the oblique direction at the same time is transmitted while suppressing reflection, the hue deviation of the transmitted light with respect to the light incident in the oblique direction is suppressed. Therefore, it can be visually recognized as the color of the projected image as the liquid crystal display device.

  Further, normally, as shown in FIG. 4, the second polarizing plate 1 is disposed on the viewing side of the liquid crystal cell 2. The second polarizing plate 1 is not particularly limited, and a known one such as an absorption polarizing plate can be used. When the influence of external light is very small, the same type of reflective polarizing plate as the first polarizing plate may be used as the second polarizing plate. In addition to the second polarizing plate, for example, various optical layers such as an optical compensation film can be provided on the viewing side of the liquid crystal cell 2.

[Formation of liquid crystal display device]
The liquid crystal display device of the present invention can be obtained by combining an optical member for liquid crystal display device (liquid crystal panel) and a light source, and further incorporating a drive circuit or the like as necessary. In addition to these, various members necessary for the formation of the liquid crystal display device can be combined, but the liquid crystal display device of the present invention allows light emitted from the light source to enter the first polarizing plate. Is preferred.

Generally, the light source of a liquid crystal display device is roughly classified into a direct type and a side light type, but the liquid crystal display device of the present invention can be used without any limitation.
The liquid crystal display device thus obtained is, for example, an OA device such as a personal computer monitor, a notebook personal computer or a copy machine, a mobile device such as a mobile phone, a clock, a digital camera, a personal digital assistant (PDA), a portable game machine, Household electrical equipment such as video cameras, TVs, microwave ovens, back monitors, car navigation system monitors, car audio equipment, in-vehicle equipment, display equipment such as commercial store information monitors, security equipment such as monitoring monitors, It can be used for various applications such as nursing care and medical equipment such as nursing monitors and medical monitors.

  Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited to the examples shown below.

In addition, the physical property and characteristic in an Example were measured or evaluated by the following method.
(1) Reflectivity, reflection wavelength Using a spectrophotometer (manufactured by Shimadzu Corporation, MPC-3100), a polarizing filter is mounted on the light source side, and the relative specular reflectance with the aluminum-deposited mirror at each wavelength is measured from a wavelength of 400 nm. Measure in the range of 800 nm. In this case, the measured value when the transmission axis of the polarizing filter is aligned with the stretching direction (X direction) of the film is p-polarized light, and the transmission axis of the polarizing filter is disposed so as to be orthogonal to the stretching direction of the film Was measured as s-polarized light. For each polarization component, the average reflectance in the range of 400 to 800 nm was defined as the average reflectance.

(2) Refractive index and average refractive index before stretching in each direction and average refractive index Each resin constituting each layer was melted and extruded from a die, and a film cast on a casting drum was prepared. Further, a stretched film was prepared by stretching the obtained film at 135 ° C. in a uniaxial direction 5 times. With respect to the obtained cast film and stretched film, the refractive index (respectively, nX, nY, nZ) in the stretching direction (X direction), the orthogonal direction (Y direction), and the thickness direction (Z direction) is measured. The refractive index at a wavelength of 633 nm was measured by using a prism coupler manufactured and obtained as the refractive index before stretching and after stretching. About average refractive index, the average value of each refractive index before extending | stretching was made into the average refractive index.

(3) Melting point (Tm) and glass transition point (Tg) of thermoplastic resin and film
10 mg of a polymer sample or a film sample was sampled, and a DSC (manufactured by TA Instruments, trade name: DSC2920) was used. The melting point and the glass transition point are measured at a temperature rising rate of.

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

(5) Thickness of each layer A film sample was cut into a film length direction of 2 mm and a width direction of 2 cm, fixed to an embedding capsule, and then embedded with an epoxy resin (Refotech Co., Ltd. Epomount). The embedded sample was cut perpendicularly in the width direction with a microtome (LETRAC ULCT UCT manufactured by LEICA) to form a thin film slice having a thickness of 5 nm. Using a transmission electron microscope (Hitachi S-4300), the film was observed and photographed at an acceleration voltage of 100 kV, and the thickness of each layer was measured from the photograph.
Moreover, based on the thickness of each obtained layer, the ratio of the maximum layer thickness to the minimum layer thickness in the first layer and the ratio of the maximum layer thickness to the minimum layer thickness in the second layer were determined.
Moreover, based on the thickness of each obtained layer, the average layer thickness of the first layer and the average layer thickness of the second layer were determined, respectively, and the average layer thickness of the second layer relative to the average layer thickness of the first layer was calculated. .
The outermost heat seal layer was excluded from the first layer and the second layer. Further, when a thickness adjusting layer having a thickness of 2 μm or more exists in the alternate lamination, such a layer was also excluded from the first layer and the second layer.

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

(7) Three-dimensional surface roughness (Ra, Rz, Rmax)
In accordance with JIS-B0601, B0651, using a three-dimensional surface roughness meter (trade name: SURF CORDER SE-3CK, manufactured by Kosaka Laboratory Ltd.), stylus tip R2 μm, scanning pitch 2 μm, scanning length 1 mm, scanning Centerline average roughness Ra, 10-point average roughness Rz, and maximum height Rmax were measured under the conditions of 100 pieces and a cutoff of 0.25 mm.

(8) Luminance improvement effect, hue Using a liquid crystal display device obtained as a personal computer display, the front luminance of the screen of the liquid crystal display device when white is displayed on the personal computer is measured by an FPD viewing angle measurement evaluation device (ErgoScope 88) manufactured by Optodesign. ), The luminance increase rate and the color relative to Comparative Example 1 were calculated, and the luminance improvement effect was evaluated according to the following criteria.
◎: Brightness improvement effect is 160% or more ○: Brightness improvement effect is 150% or more and less than 160% △: Brightness improvement effect is 140% or more and less than 150% ×: Brightness improvement effect is less than 140% The maximum change in hue x or y at all azimuth viewing angles of 0 to 80 degrees was evaluated according to the following criteria.
A: Maximum change of both x and y is less than 0.03 ○: Maximum change of either x or y is less than 0.03 Δ: Maximum change of either x or y is 0.03 or more X: x, y Maximum change of 0.03 or more for both

(9) Contrast evaluation
Using the liquid crystal display device obtained as a personal computer display, the front luminance of the screen of the liquid crystal display device when a white and black screen is displayed on the personal computer is measured with an FPD viewing angle measurement evaluation device (ErgoScope 88) manufactured by Opto Design. The brightness obtained from the white screen and the dark brightness from the black screen were obtained, and the contrast obtained from the bright brightness / dark brightness was evaluated according to the following criteria.
A: Contrast (bright luminance / dark luminance) 1000 or more ○: Contrast (bright luminance / dark luminance) 200 or more and less than 1000 ×: Contrast (bright luminance / dark luminance) Less than 200

[Comparative Example 1]
(Creating a polarizer)
Dyeing a polymer film composed mainly of polyvinyl alcohol [Kuraray's trade name “9P75R (thickness: 75 μm, average polymerization degree: 2,400, saponification degree 99.9 mol%)”] between rolls having different peripheral speeds While being stretched and conveyed. First, it was immersed in a 30 ° C. water bath for 1 minute to swell the polyvinyl alcohol film and stretched 1.2 times in the conveying direction, and then a 30 ° C. potassium iodide concentration of 0.03% by weight and an iodine concentration of 0.3 By immersing in a weight% aqueous solution for 1 minute, the film was stretched 3 times in the transport direction while dyeing, based on a film that was not stretched at all (original length). Next, the film was stretched 6 times in the conveying direction on the basis of the original length while being immersed in an aqueous solution having a boric acid concentration of 4% by weight and a potassium iodide concentration of 5% by weight for 30 seconds. Next, the obtained stretched film was dried at 70 ° C. for 2 minutes to obtain a polarizer. The polarizer had a thickness of 30 μm and a moisture content of 14.3% by weight.

(Create adhesive)
Polyvinyl alcohol resin having an acetoacetyl group (average polymerization degree 1200, saponification degree 98.5% mol%, acetoacetylation degree 5 mol%) 100 parts by weight, 50 parts by weight of methylol melamine at 30 ° C. Under the conditions, it was dissolved in pure water to prepare an aqueous solution having a solid content concentration of 3.7% by weight. An aqueous adhesive solution was prepared by adding 18 parts by weight of an aqueous solution containing alumina colloid having a positive charge (average particle diameter of 15 nm) at a solid content concentration of 10% by weight to 100 parts by weight of this aqueous solution. The viscosity of the adhesive solution was 9.6 mPa · s, the pH was in the range of 4 to 4.5, and the compounding amount of the alumina colloid was 74 parts by weight with respect to 100 parts by weight of the polyvinyl alcohol resin.

(Creation of absorption type polarizing plate)
An optical isotropic element having a thickness of 80 μm, a front retardation of 0.1 nm, and a thickness direction retardation of 1.0 nm (trade name “Fujitack ZRF80S”, manufactured by Fuji Film Co., Ltd.) Was applied to one side of the polarizer by roll-to-roll so that the conveying direction of both was parallel, and the same was applied to the opposite side of the polarizer. The above-mentioned alumina colloid-containing adhesive was applied to one side of an optically isotropic element (trade name “Fujitack ZRF80S” manufactured by Fuji Film Co., Ltd.) so that the thickness after drying was 80 nm. Then, the film was laminated by roll-to-roll, and then dried at 55 ° C. for 6 minutes to obtain a polarizing plate, which will be referred to as “polarizing plate X”.

(Creation of LCD panel)
The liquid crystal panel is taken out from a liquid crystal television (manufactured by Matsushita Electric Vera TH-32LZ80 2007) having an IPS mode liquid crystal cell and adopting a direct backlight, and polarizing plates and optical compensation arranged above and below the liquid crystal cell The film was removed, and the glass surfaces (front and back) of the liquid crystal cell were washed. Subsequently, an acrylic pressure-sensitive adhesive is applied to the light source side surface of the liquid crystal cell so that the polarizing plate X is in the same direction as the absorption axis direction of the light source side polarizing plate arranged in the original liquid crystal panel. The polarizing plate X was disposed in the liquid crystal cell.

  Next, the polarizing plate X is placed on the viewing side surface of the liquid crystal cell with an acrylic pressure-sensitive adhesive in the same direction as the absorption axis direction of the viewing side polarizing plate arranged in the original liquid crystal panel. The polarizing plate X was placed in a liquid crystal cell. In this way, a liquid crystal panel in which the polarizing plate X was disposed on one main surface of the liquid crystal cell and the polarizing plate X was disposed on the other main surface was obtained.

(Creation of liquid crystal display device)
The above liquid crystal panel was incorporated into the original liquid crystal display device, the light source of the liquid crystal display device was turned on, and a white screen and a black screen were displayed on a personal computer, and the luminance of the liquid crystal display device was evaluated.

[Example 1]
Dimethyl 2,6-naphthalenedicarboxylate, 6,6 ′-(ethylenedioxy) di-2-naphthoic acid, and ethylene glycol are subjected to esterification and transesterification in the presence of titanium tetrabutoxide, and Subsequently, a polycondensation reaction was performed, and the intrinsic viscosity was 0.62 dl / g, 65 mol% of the acid component was 2,6-naphthalenedicarboxylic acid component (described as PEN in the table), and 35 mol% of the acid component was 6 mol%. , 6 '-(ethylenedioxy) di-2-naphthoic acid component (described as ENA in the table) and an aromatic polyester whose glycol component is ethylene glycol. To this, 0.10 wt% of spherical silica particles (average particle size: 0.3 μm, ratio of major axis to minor axis: 1.02, average deviation of particle size: 0.1) based on the weight of the first layer This was used as a thermoplastic resin for the first layer, and 20 mol% of isophthalic acid copolymerized polyethylene terephthalate (IA20PET) having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.62 dl / g was prepared as the thermoplastic resin for the second layer. .
The prepared polyester for the first layer and polyester for the second layer are each dried at 170 ° C. for 5 hours, then supplied to the first and second extruders, heated to 300 ° C. to be in a molten state, and used for the first layer After branching the polyester to 137 layers and the second layer polyester to 138 layers, the first layer and the second layer are alternately laminated, and the maximum layer thickness and the minimum layer thickness of the first layer and the second layer, respectively. Using a multi-layer feedblock device in which the maximum value is continuously changed up to 2.2 times at the minimum, and a total of 275 layers of the melt in which the first layer and the second layer are alternately stacked, While maintaining the laminated state, the same polyester as the second layer polyester is led from the third extruder to the three-layer die on both sides thereof, and a heat seal layer is further provided on both sides of the melt in the laminated state of 275 layers in total. Laminated. The supply amount of the third extruder was adjusted so that both end layers (heat seal layers) were 18% of the whole. The laminated state is led to a die, cast on a casting drum, adjusted so that the average layer thickness ratio of the first layer and the second layer is 1.0: 2.6, and a total of 277 layers. An unstretched multilayer laminated film was prepared.
This multilayer unstretched film was stretched 5.2 times in the width direction at a temperature of 135 ° C., and heat-set at 140 ° C. for 3 seconds. The thickness of the obtained reflective polarizing film was 33 μm.
(Formation of liquid crystal panel)
In Comparative Example 1, the light source side main surface of the liquid crystal cell was obtained in the same manner as in Comparative Example 1 except that the obtained reflective polarizing film was used instead of the polarizing plate X as the first polarizing plate on the light source side. The obtained reflective polarizing film (first polarizing plate) and a liquid crystal panel in which a polarizing plate X (second polarizing plate) was disposed on the viewing-side main surface were obtained.
(Creation of liquid crystal display device)
The above liquid crystal panel was incorporated into the original liquid crystal display device, the light source of the liquid crystal display device was turned on, and the brightness of the white screen and the black screen was evaluated with a personal computer.
The resin configuration of each layer of the uniaxially stretched multilayer laminate film thus obtained and the characteristics of each layer are shown in Table 1, and the physical properties of the uniaxially stretched multilayer laminate film and the properties of the liquid crystal display device are shown in Table 2.

[Examples 2 to 6]
As shown in Table 1, a reflective polarizing film composed of a uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1 except that the resin composition or the layer thickness of each layer was changed.
In addition, NDC20PET used as the second layer polyester in Example 2 is a copolymer component of 20 mol% isophthalic acid copolymerized polyethylene terephthalate (IA20PET) used as the second layer polyester in Example 1 with 2,6- It is a copolyester changed to naphthalenedicarboxylic acid.
Further, the ENA21PEN / PCT blend used as the polyester for the second layer in Example 4 is the ENA21PEN which is the polyester for the first layer of Example 4 (79 mol% of the acid component is a 2,6-naphthalenedicarboxylic acid component, 21 mol% of the acid component is 6,6 ′-(ethylenedioxy) di-2-naphthoic acid component, aromatic polyester whose glycol component is ethylene glycol, and PCTA AN004 (polycyclohexanedimethylene terephthalate manufactured by Eastman Chemical) -Isophthalate copolymer) is mixed at a weight ratio of 2: 1.
Moreover, in the said comparative example 1, it replaced with the polarizing plate X as a 1st polarizing plate by the side of a light source, and was used similarly to the comparative example 1 except having used the obtained reflective polarizing film on the light source side main surface of a liquid crystal cell. The obtained reflective polarizing film (first polarizing plate) and a liquid crystal panel in which a polarizing plate X (second polarizing plate) was disposed on the viewing-side main surface were obtained.
The above liquid crystal panel was incorporated into the original liquid crystal display device, the light source of the liquid crystal display device was turned on, and the brightness of the white screen and the black screen was evaluated with a personal computer.
The resin configuration of each layer of the uniaxially stretched multilayer laminate film thus obtained and the characteristics of each layer are shown in Table 1, and the physical properties of the uniaxially stretched multilayer laminate film and the properties of the liquid crystal display device are shown in Table 2.

[Example 7]
The same operation as in Example 1 was repeated except that three reflective polarizing films obtained in Example 1 were bonded in parallel and used as the first polarizing plate.

[Comparative Example 2]
The thermoplastic resin for the first layer is made of polyethylene-2,6-naphthalenedicarboxylate (PEN) having an intrinsic viscosity (orthochlorophenol, 35 ° C.) of 0.62 dl / g, and the thermoplastic resin for the second layer is made of intrinsic viscosity (ortho Chlorophenol, 35 ° C.) Example 1 with the exception of changing to 0.62 dl / g terephthalic acid 64 mol% copolymerized polyethylene-2,6-naphthalenedicarboxylate (TA64PEN) and changing to the production conditions shown in Table 1. Similarly, a uniaxially stretched multilayer laminated film was obtained, and a liquid crystal panel was formed using such a film as a first polarizing plate, thereby producing a liquid crystal display device.
The obtained uniaxially stretched multilayer laminated film has an average reflectance of p-polarized light of less than 95% for both incident angles of 0 ° and 50 °, and an average reflectance of s-polarized light of 12% for both incident angles of 0 ° and 50 °. Thus, the polarization performance was deteriorated as compared with Examples, and a sufficient luminance improvement rate could not be obtained. In addition, the maximum change in hue for both x and y was 0.03 or more, which was larger than in the example.

[Comparative Examples 3 to 7]
As shown in Table 1, a uniaxially stretched multilayer laminated film was obtained in the same manner as in Example 1 except that any of the resin composition, layer thickness, and production conditions was changed, and this film was used as a first polarizing plate for a liquid crystal panel To form a liquid crystal display device.
As for the obtained film, the polarization performance fell compared with the Example, and sufficient brightness improvement rate was not obtained. Also, at least the hue change amount of either x or y was larger than that of the example.

  According to the present invention, it has a high polarization performance comparable to that of a conventional absorption polarizing plate and a function as a brightness enhancement film that reflects and reuses polarized light that is not transmitted, and transmits light incident in an oblique direction. It is possible to provide a polarizing plate which is bonded to a liquid crystal cell in which the hue shift of light is eliminated.

DESCRIPTION OF SYMBOLS 1 2nd polarizing plate 2 Liquid crystal cell 3 1st polarizing plate 4 Light source 5 Liquid crystal panel

Claims (2)

A polarizing plate comprising a uniaxially stretched multilayer laminate film, wherein the uniaxially stretched multilayer laminate film has a multilayer structure of 251 layers or more in which the first layer and the second layer are alternately laminated,
1) The thermoplastic resin forming the first layer is (i) an acid component represented by the following formula (A-1) in which the dicarboxylic acid component is 5 mol% or more and 50 mol% or less, and 50 mol% or more and 95 mol% or less. Containing an acid component represented by the following formula (B):
(In formula (B), R ^B represents a naphthalenediyl group)
(Ii) A diol component represented by the following formula (C) in which the diol component is 90 mol% or more and 100 mol% or less
(In the formula (C), R ^C represents an ethylene group)
A polyester with an aromatic dicarboxylic acid component and a diol component containing
2) The thermoplastic resin constituting the second layer has an average refractive index of 1.50 or more and 1.60 or less, and the respective refractive index differences in the X direction, Y direction and Z direction are 0.05 or less before and after stretching. A thermoplastic resin, wherein the thermoplastic resin is a copolymerized polyethylene terephthalate or a blend of a copolymerized polyethylene naphthalene dicarboxylate and a polycyclohexanedimethylene terephthalate-isophthalate copolymer;
3) An average reflectance of a wavelength of 400 to 800 nm with respect to the incident polarized light at an incident angle of 0 degrees and 50 degrees with respect to a polarized light component parallel to the incident surface including the uniaxial stretching direction (X direction) with the film surface as a reflecting surface. 95% or more, with respect to a polarized light component perpendicular to the incident surface including the X direction, with the film surface as a reflective surface, an average reflectance of 400 to 800 nm with respect to the incident polarized light at incident angles of 0 degrees and 50 degrees Is 12% or less, A polarizing plate for laminating a liquid crystal cell.   The polarizing plate for laminating liquid crystal cells according to claim 1, wherein the thermoplastic resin forming the second layer is a polyester mainly composed of an ethylene terephthalate component copolymerized with isophthalic acid or 2,6-naphthalenedicarboxylic acid.