CN107405908B - Laminated film and method for producing same - Google Patents

Abstract

The present invention provides a laminated film which has various functions as a laminated film, has high mechanical strength, and can be processed with high yield and high precision in various processing steps. The laminated film of the present invention is characterized in that: the laminated film is formed by alternately laminating a layer A made of a crystalline polyester and a layer B made of a thermoplastic resin different from the crystalline polyester for a total of 11 or more layers, and the Young's modulus in the direction of the orientation axis (the direction in which the Young's modulus is the largest) of the laminated film is 6GPa or more.

Description

Laminated film and method for producing same

Technical Field

The present invention relates to a laminated film and a method for producing the same.

Background

Thermoplastic resin films, particularly biaxially stretched polyester films, have excellent properties such as mechanical properties, electrical properties, dimensional stability, transparency, and chemical resistance, and therefore are widely used as substrate films in various applications such as magnetic recording materials and packaging materials.

On the other hand, as the polyester film, a laminated film in which different resins are alternately laminated is used. Such a laminated film can be a film having a special function that cannot be obtained by a single-layer film, and examples thereof include: tear-resistant films having improved tear strength (see patent document 1), infrared-reflecting films that reflect infrared rays (see patent document 2), and polarizing-reflecting films having polarizing-reflecting properties (see patent document 3).

However, since the laminated film as described above has a structure in which different resins are alternately laminated, the mechanical strength and dimensional stability tend to be reduced by the influence of the lamination thickness as compared with a single-layer film. When the mechanical strength and dimensional stability of the laminated film are lowered, for example, when the laminated film is combined with various other films and members and subjected to processing such as punching, cutting, coating, and lamination to form a functional film, the film is deformed, broken, and the like due to a force applied to the film, and there are problems such as the following: a decrease in processing accuracy and yield during processing, and a decrease in optical characteristics and quality of the obtained film; or, when the film is actually mounted on a product or the like, a problem occurs due to a dimensional change.

Documents of the prior art

Patent document

Patent document 1 Japanese patent No. 3960194

Patent document 2 Japanese patent No. 4310312

Patent document 3 Japanese patent laid-open No. 2014-124845

Disclosure of Invention

Problems to be solved by the invention

Accordingly, an object of the present invention is to solve the above-described problems, and an object of the present invention is to provide a laminated film which has various functions as a laminated film, has high mechanical strength and dimensional stability, can be processed with high yield and high precision in various processing steps, and does not cause defects in practical use.

Means for solving the problems

The present invention has been made to solve the above problems, and a laminated film of the present invention is a laminated film in which a layer a made of a crystalline polyester and a layer B made of a thermoplastic resin different from the crystalline polyester are alternately laminated by a total of 11 or more layers, and the young's modulus in the direction of the orientation axis (the direction in which the young's modulus is the largest) of the laminated film is 6GPa or more.

According to a preferred embodiment of the laminated film of the present invention, the laminated film has a beam diameter of 1 μm and a wavelength of 1390cm^-1In the polarization Raman spectrum of (1), a ratio I max/I min of a peak intensity I max in a direction of a maximum reflectance to a peak intensity I min in a direction perpendicular thereto is 5 or more.

According to a preferred embodiment of the laminated film of the present invention, the carboxylic acid component constituting the crystalline polyester contains 90 mol% or more of naphthalenedicarboxylic acid.

According to a preferred embodiment of the laminated film of the present invention, the absolute value of the linear expansion coefficient at a temperature of 40 ℃ to 50 ℃ is 10 ppm/DEG C or less in either the direction of the orientation axis of the laminated film or the direction perpendicular to the direction of the orientation axis.

According to a preferred embodiment of the laminate film of the present invention, when a reflectance at an incident angle of 10 ° with respect to a polarized light component parallel to an incident plane including the orientation axis direction of the laminate film is denoted as R1, and a reflectance at an incident angle of 10 ° with respect to a polarized light component perpendicular to the incident plane including the orientation axis direction is denoted as R2, the reflectance at a wavelength of 550nm satisfies the following expressions (2) and (3).

·R2(550)≤40％···(2)

·R1(550)≥70％···(3)

According to a preferred embodiment of the present invention, the laminated film has a melting peak in a first temperature rise curve obtained by differential scanning calorimetry (hereinafter referred to as DSC) of the laminated film, and an exothermic peak in a range of Tm-110 ℃ to Tm-60 ℃ when the melting peak top temperature is taken as Tm.

According to a preferred embodiment of the present invention, the ratio of the young's modulus of the laminated film in the direction of the orientation axis to the direction perpendicular to the orientation axis in the same plane is 2 or more.

According to a preferred embodiment of the laminated film of the present invention, the heat shrinkage stress of the laminated film at a temperature of 100 ℃ in the orientation axis direction is 1MPa or less.

According to a preferred embodiment of the laminated film of the present invention, the absolute value of TMA at a temperature of 100 ℃ in the direction of the orientation axis of the laminated film is 0.5% or less.

According to a preferred embodiment of the laminated film of the present invention, a melting peak of the laminated film from the thermoplastic resin B measured by Differential Scanning Calorimetry (DSC) is 5J/g or less.

According to a preferred embodiment of the laminated film of the present invention, the layer a and the layer B satisfy the following conditions.

Layer A: the polyester resin composition is composed of an aromatic polyester containing a dicarboxylic acid component and a diol component as main components, wherein 80 to 100 mol% of the dicarboxylic acid component is 2, 6-naphthalenedicarboxylic acid, and 80 to 100 mol% of the diol component is ethylene glycol.

B layer: the polyester resin composition is composed of an aromatic polyester which mainly contains a dicarboxylic acid component and a diol component, wherein 40 to 75 mol% of 100 mol% of the dicarboxylic acid component is 2, 6-naphthalenedicarboxylic acid, 25 to 60 mol% of the dicarboxylic acid component is at least one component selected from isophthalic acid, 1, 8-naphthalenedicarboxylic acid and 2, 3-naphthalenedicarboxylic acid, and 80 to 100 mol% of the diol component is ethylene glycol.

According to a preferred embodiment of the laminated film of the present invention, the laminated film may be wound around an orientation axis of the laminated film to form a film roll.

According to a preferred embodiment of the film roll of the present invention, the width of the laminated film is 1000mm or more.

The method for producing a laminated film of the present invention is characterized in that an unstretched film in which a layer A made of a crystalline polyester and a layer B made of a thermoplastic resin different from the crystalline polyester are alternately laminated for a total of 11 or more layers is stretched at a magnification of 2 to 5 times in the film longitudinal direction, then stretched at a magnification of 2 to 5 times in the film width direction, and further stretched again at a magnification of 1.3 to 4 times in the film longitudinal direction.

ADVANTAGEOUS EFFECTS OF INVENTION

The present invention provides a laminated film which has high mechanical strength and dimensional stability, can be suitably used as various functional films in processing such as punching, cutting, coating, and laminating, or in use, and can be used without causing any trouble in actual mounting.

The laminated film of the present invention is a laminated film having a high young's modulus, and therefore is suitable for various optical films, engineering films, and the like.

Detailed Description

Next, the laminated film and the method for producing the same of the present invention will be described in detail.

The laminated film of the present invention is a laminated film in which a total of 11 or more layers (a layer) composed of a crystalline polyester (hereinafter, sometimes referred to as a crystalline polyester a.) and a layer (B layer) composed of a thermoplastic resin different from the crystalline polyester (hereinafter, sometimes referred to as a thermoplastic resin B.) are alternately laminated.

The crystalline polyester a is specifically the following polyester: according to JIS K7122(1999), a differential scanning calorimetry (hereinafter, also referred to as DSC.) was performed, and a polyester having a heat of crystal fusion DeltaHm of 15J/g or more was obtained by heating a resin from 25 ℃ to 300 ℃ (1stRUN) at a temperature rise rate of 20 ℃/min, holding the resin in this state for 5 minutes, then quenching the heated resin to a temperature of 25 ℃ or less, and raising the temperature from 25 ℃ to 300 ℃ again at a temperature rise rate of 20 ℃/min, and in the obtained differential scanning calorimetry chart of 2ndRUN, the heat of crystal fusion DeltaHm obtained from the peak area of the melting peak was 15J/g or more. The heat of crystal fusion is more preferably 20J/g or more, and still more preferably 25J/g or more.

The thermoplastic resin B is a thermoplastic resin that exhibits optical properties or thermal properties different from those of the crystalline polyester a used in the a layer. Specifically, the thermoplastic resin having a difference in refractive index of 0.01 or more in any of 2 perpendicular directions arbitrarily selected in the plane of the laminate film and a direction perpendicular to the plane, or the thermoplastic polyester having a melting point and a glass transition temperature different from those of the crystalline polyester a in DSC is used.

Here, the alternate lamination means that the a layer and the B layer are laminated in a regular array in the thickness direction. For example, a (ba) n (n is a natural number) is laminated in a regular array. By alternately laminating resins having different optical properties as described above, interference reflection that reflects light having a wavelength designed from the relationship between the difference in refractive index of each layer and the layer thickness can be exhibited.

Further, by alternately laminating resins having different thermal properties, it is possible to highly control the orientation state of each layer and control the optical properties, mechanical properties, and thermal shrinkage properties when producing a biaxially stretched film.

Preferred embodiments of the laminate film include: there are cases where the layer a is formed of a crystalline polyester a, the layer B is formed of a thermoplastic resin B different from the crystalline polyester a, and the layer C is formed of a thermoplastic resin C different from the crystalline polyester a and the thermoplastic resin B. In this case, a layer C such as CA (BA) n, CA (BA) nC, and a (BA) nca (BA) m may be laminated on the outermost layer or the intermediate layer.

When the number of laminated layers is less than 11, the lamination of different thermoplastic resins may affect various properties such as film formability and mechanical properties, and thus, for example, the production of a biaxially stretched film may be difficult, and a product obtained by combining the biaxially stretched film with other components may be defective.

On the other hand, in the case of a laminated film in which a total of 11 or more layers are alternately laminated like the laminated film of the present invention, since the thermoplastic resins can be uniformly arranged as compared with a laminated film in which the number of layers is less than 11, film formability and mechanical properties can be stabilized. Further, as the number of layers increases, the growth of orientation in each layer tends to be suppressed, and for example, as the tear resistance strength by surface tension is improved, it becomes easy to control mechanical properties and heat shrinkage properties, and it becomes possible to impart special optical properties such as an interference reflection function. The number of layers to be stacked is preferably 100 or more, and more preferably 200 or more. When 100 or more layers are laminated, the film can reflect light in a wide area with high reflectance, and when 200 or more layers are laminated, for example, substantially all visible light with a wavelength of 400 to 700nm can be reflected. Further, there is no upper limit to the number of layers to be laminated, but as the number of layers increases, it may cause an increase in manufacturing cost due to an increase in size and complexity of a manufacturing apparatus, and therefore, in practice, 10000 layers or less are within a practical range.

In the laminated film of the present invention, the young's modulus in the orientation axis direction of the laminated film needs to be 6GPa or more. The orientation axis direction of the laminated film here means a direction in which the Young's modulus of the film is measured while changing the direction at every 10 degrees within the film surface, and the Young's modulus is the largest. The young's modulus is an index indicating a force required for initial deformation of a film, and by increasing the young's modulus, even when a force is applied to a laminated film in a processing step such as punching, cutting, coating, and laminating, or when the film is used as a functional film, deformation can be suppressed, and processing defects associated with deformation of the film and changes in performance during use can be easily suppressed.

The Young's modulus of the laminated film in the orientation axis direction is preferably 8GPa or more, and more preferably 10GPa or more. As the young's modulus increases, the laminated film becomes less likely to deform, and the control range of the processing conditions during processing such as punching, cutting, coating, and laminating becomes wider, so that it is useful not only to suppress processing defects but also to improve the performance of the obtained product. In order to increase the young's modulus, as described later, the selection of a resin and the production method of a film are used.

In addition, when the number of layers is about one or several, the young's modulus of the laminated film in the orientation axis direction is 6GPa or more, the laminated film tends to be brittle due to the orientation strength of the resin, and the workability may be deteriorated.

On the other hand, in the case of a laminated film in which a layer a made of a crystalline polyester a and a layer B made of a thermoplastic resin B different from the crystalline polyester a are alternately laminated by a total of 11 or more layers as in the present invention, even if the young's modulus is 6GPa or more, the young's modulus can be improved without impairing the workability due to the interfacial tension at the lamination interface or the cushioning effect of the layer B made of the thermoplastic resin B, and further, even if a force is applied to the laminated film in the processing steps such as punching, cutting, coating, and laminating or in the use as a functional film, the effect of suppressing the deformation can be obtained.

In the laminated film of the present invention, it is also preferable that the ratio of the young's modulus of the laminated film in the direction of the orientation axis to the direction perpendicular to the orientation axis in the same plane is 2 or more. When the ratio of young's moduli is to be increased simply by selecting a resin or a method of producing a film, the young's modulus is limited to a laminated film having a uniform young's modulus in the in-plane direction of the laminated film. This is because the young's modulus depends on the strength of the orientation of the resin constituting the laminate film, and how strongly the orientation is in a direction in which the young's modulus is to be increased affects the magnitude of the young's modulus.

On the other hand, in the processing steps such as punching, cutting, coating, and laminating, particularly in the step of continuously processing using a roll-shaped film, it is effective to increase the young's modulus in the longitudinal direction of the laminated film for stabilization of the processing steps. Therefore, by setting the ratio of the young's modulus of the laminated film in the direction of the orientation axis to the young's modulus in the direction perpendicular to the direction in the same plane to 2 or more, the young's modulus on the orientation axis side can be further increased, and it becomes easy to set the young's modulus in the direction in which the young's modulus is the maximum (the direction of the orientation axis of the laminated film) to 6GPa or more. More preferably, the ratio of the young's modulus of the laminated film in the direction of the orientation axis to the young's modulus of the laminated film in the direction perpendicular to the direction in the same plane is 3 or more, and in this case, it is easy to make the young's modulus of the laminated film in the direction of the orientation axis to be 10GPa or more.

The laminated film of the present invention had a beam diameter of 1 μm and a wavelength of 1390cm^-1In the polarization raman spectrum of (1), a ratio I max/I min of a peak intensity I max in a direction of the maximum reflectance to a peak intensity I min in a direction perpendicular thereto is preferably 5 or more. The direction in which the reflectance is maximum here means: the polarization component was measured by changing the direction of the incident light at an angle of 0 DEG with respect to the incident plane of the laminated film and at an angle of 0 DEG within the plane of the laminated film at intervals of 10 DEGIn the case of the reflectance, the reflectance shows a direction of the maximum value.

Further, the wavelength observed in the polarization Raman spectrum was 1390cm^-1The peak of (2) is assigned to the CNC stretching band of naphthalene ring, and the orientation state of naphthalene ring can be determined by the ratio I max/I min of the peak intensity I max in the direction of maximum reflectance to the peak intensity I min in the direction perpendicular thereto. Wavelength 1390cm^-1The I max/I min is preferably 5.5 or more, more preferably 6 or more.

Wavelength 1390cm^-1When I max/l min is 5 or more, it means that the naphthalene rings are uniformly oriented, and as a result, the Young's modulus can be improved by increasing the orientation. 1390cm for a wavelength^-1The upper limit of I max/I min is preferably 20, more preferably 10, and particularly preferably 7 or less, from the viewpoint of preventing deterioration of interlayer adhesiveness due to a large difference in the orientation state and crystallinity between the a layer formed of the crystalline polyester a containing naphthalenedicarboxylic acid and the B layer formed of the thermoplastic resin B different from the crystalline polyester a. Wavelength 1390cm^-1The I max/I min of (A) can be adjusted by selecting a combination of resins for the A layer and the B layer and film forming conditions.

In the laminated film of the present invention, the light beam diameter is 1 μm and the wavelength is 1615cm^-1In the polarized raman spectrum of (3), it is preferable that the ratio I max/I min of the peak intensity I max in the direction of the maximum reflectance to the peak intensity I min in the direction perpendicular thereto is 4 or more.

Wavelength 1615cm observed in polarized Raman Spectroscopy^-1The orientation state of the benzene ring can be measured by the ratio I max/I min of the peak intensity I max in the direction of the maximum reflectance to the peak intensity I min in the direction perpendicular thereto. Wavelength 1615cm^-1The I max/I min is preferably 4.5 or more, more preferably 5 or more. Wavelength 1615cm^-1When I max/l min in the above-mentioned region is 4 or more, it means that the benzene rings are uniformly oriented, and as a result, the Young's modulus can be improved by increasing the orientation.

For a wavelength of 1615cm^-1The upper limit of I max/I min (in mm) is determined so as to prevent the formation of a layer due to the crystalline polyester A containing naphthalenedicarboxylic acid and the formation of crystalsFrom the viewpoint of deterioration of interlayer adhesiveness due to a large difference in the orientation state and crystallinity of the B layer formed of the thermoplastic resin B having different nature polyesters a, the upper limit is preferably 20 or less, more preferably 10 or less, and particularly preferably 6 or less. Wavelength 1615cm^-1The I max/I min of (A) can be adjusted by selecting a combination of resins for the A layer and the B layer and film forming conditions. Examples of the optimum combination thereof are as described above.

In addition, in the laminated film of the present invention, the diameter of the light beam is 1 μm and the wavelength is 1390cm^-1In the polarization raman spectrum of (1), a ratio I max/I min of a peak intensity I max in a direction of the maximum reflectance to a peak intensity I min in a direction perpendicular thereto is preferably 5 or more.

In the laminated film of the present invention, the absolute value of the linear expansion coefficient at a temperature of 40 to 50 ℃ in any one of the direction of the orientation axis of the laminated film and the direction perpendicular to the direction of the orientation axis of the laminated film needs to be 10 ppm/DEG C or less. The linear expansion coefficient is an index indicating the ease of change in the size of the film when the temperature is changed, and by making the absolute value of the thermal expansion coefficient small, deformation of the film can be suppressed even when the temperature of the laminated film is changed during processing steps such as punching, cutting, coating, and laminating, or when the laminated film is used as a functional film, and processing defects accompanying deformation of the film and performance changes during use can be suppressed easily.

Preferably, the absolute value of the linear expansion coefficient is 5 ppm/DEG C or less in either the direction of the oriented axis of the laminated film or the direction perpendicular to the direction of the oriented axis of the laminated film. As the absolute value of the thermal expansion coefficient decreases, the deformation of the laminated film with respect to a temperature change becomes smaller, and for example, the control range of the processing conditions during processing becomes wider, so that it is useful not only for suppressing a processing failure but also for improving the performance of the obtained product or suppressing dimensional deformation during actual use. In order to reduce the absolute value of the thermal expansion coefficient, as described later, the absolute value is achieved by a method for producing a laminated film in addition to the selection of a resin.

In the case of a single layer or a few layers, when the absolute value of the linear expansion coefficient of the laminated film at a temperature of 40 to 50 ℃ in the orientation axis direction is 10 ppm/DEG C or less, the film tends to become brittle due to the orientation strength of the resin, and the handling properties may be lowered. On the other hand, in the case of a laminated film in which a layer a made of a crystalline polyester a and a layer B made of a thermoplastic resin B different from the crystalline polyester a are alternately laminated by at least 11 layers in total as in the present invention, even if the absolute value of the linear expansion coefficient at a temperature of 40 to 50 ℃ is 10ppm/° c or less, the linear expansion coefficient can be reduced without impairing the workability due to the interfacial tension at the lamination interface and the cushioning effect of the layer B made of the thermoplastic resin B, and further, even when a force is applied to the laminated film in the processing steps such as punching, cutting, coating, and laminating or in the case of using the laminated film as a functional film, the effect of suppressing the deformation can be obtained.

In the laminated film of the present invention, it is also preferable that the heat shrinkage stress at a temperature of 100 ℃ in the orientation axis direction of the laminated film is 1MPa or less. The thermal shrinkage stress is an index indicating the magnitude of a force acting in the direction in which the laminated film shrinks when the temperature is changed, and by reducing the thermal shrinkage stress, deformation can be suppressed when the laminated film is heated during use, and processing defects and changes in the properties of the laminated film can be suppressed. More preferably, the thermal shrinkage stress at a temperature of 100 ℃ is 0.5MPa or less, and in this case, even during the processing or during actual use, thermal deformation of the laminated film can be suppressed.

In the laminated film of the present invention, it is also preferable that the absolute value of TMA represented by the following formula (1) in the orientation axis direction of the laminated film is 0.5% or less at a temperature of 100 ℃. In the following formula (1), L and Δ L represent the length of the laminated film in the axial direction when the temperature is 25 ℃ and the displacement of the length of the laminated film when the temperature is changed from 25 ℃. TMA is an index indicating the ratio of shrinkage or elongation of the laminated film at varying temperatures, and by reducing the absolute value of TMA, deformation can be suppressed when the laminated film is heated during use, and processing defects and changes in film properties can be suppressed. Preferably, the absolute value of TMA at a temperature of 100 ℃ is also 0.5% or less, and in this case, thermal deformation of the film can be suppressed even during the processing step or during actual use.

·TMA＝|ΔL/L|×100％···(1)

In the present invention, the laminated film may be formed into a film roll wound along an orientation axis of the laminated film. As described above, in the processing steps such as punching, cutting, coating, and laminating, particularly in the step of continuously processing using a rolled film, it is effective to increase the young's modulus in the longitudinal direction of the laminated film for stabilization of the processing steps, and by obtaining a film roll wound along the orientation axis of the laminated film, a high-quality product can be easily obtained even when a product is obtained using the laminated film of the present invention.

In order to obtain such a film roll, it is preferable that the angle formed by the orientation axis direction of the laminated film and the flow direction in the film production process is 10 ° or less. When the angle formed by the orientation axis direction of the laminated film and the flow direction in the film production process is 10 ° or less, the obtained laminated film is continuously wound in a roll shape, and therefore, in the processing steps such as punching, cutting, coating, and laminating, particularly the step of continuously processing using the roll-shaped film, the orientation axis direction and the flow direction in the processing steps become the same, and therefore, the processing steps are easily stabilized.

In practice, the winding direction of the film roll can be regarded as the flow direction in the film production process, and in an actual product, the angle formed between the orientation axis direction of the laminated film and the winding direction of the film roll is 10 ° or less.

In the laminate film of the present invention, the layer a formed of the crystalline polyester a is preferably the outermost layer. In this case, the crystalline polyester a is an outermost layer, and therefore, a biaxially stretched film can be produced in the same manner as a crystalline polyester film such as a polyethylene terephthalate film or a polyethylene naphthalate film. When the thermoplastic resin B, which is not a crystalline polyester but is formed of, for example, an amorphous resin, is an outermost layer, a biaxially stretched film obtained by the same operation as the crystalline polyester film may have problems such as film formation failure and deterioration of surface properties due to adhesion to a manufacturing apparatus such as a roll or a clip (clip).

As the crystalline polyester a usable in the present invention, a polyester obtained by polymerization of a monomer containing an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid and a diol as main components can be preferably used.

Examples of the aromatic dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, 1, 4-naphthalenedicarboxylic acid, 1, 5-naphthalenedicarboxylic acid, 2, 6-naphthalenedicarboxylic acid, 4 ' -biphenyldicarboxylic acid, 4 ' -diphenyl ether dicarboxylic acid, and 4,4 ' -diphenylsulfone dicarboxylic acid. Examples of the aliphatic dicarboxylic acid include adipic acid, suberic acid, sebacic acid, dimer acid, dodecanedioic acid, cyclohexanedicarboxylic acid, and ester derivatives thereof. These acid components can be used in only 1 kind, also can be combined with more than 2 kinds.

In particular, terephthalic acid and 2, 6-naphthalenedicarboxylic acid are preferably used as the carboxylic acid component constituting the crystalline polyester a used in the laminate film of the present invention, from the viewpoint of exhibiting a high refractive index and improving the young's modulus. Since terephthalic acid and 2, 6-naphthalenedicarboxylic acid contain aromatic rings having high symmetry, it is easy to achieve both a high refractive index and a high young's modulus by orienting and crystallizing the aromatic rings. In particular, when the carboxylic acid component constituting the crystalline polyester a contains 2, 6-naphthalenedicarboxylic acid, the volume ratio of the aromatic ring is increased, whereby a high young's modulus can be realized, and the polyester can be obtained industrially and universally, and therefore, a low-cost product can be obtained.

It is further preferable that the carboxylic acid component constituting the crystalline polyester contains 80 mol% or more of 2, 6-naphthalenedicarboxylic acid. By containing 80 mol% or more of naphthalenedicarboxylic acid, orientation crystallization can be easily performed by stretching and heat treatment during the production of the laminated film, and the Young's modulus can be easily increased.

Examples of the diol component include ethylene glycol, 1, 2-propanediol, 1, 3-propanediol, neopentyl glycol, 1, 3-butanediol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1, 2-cyclohexanedimethanol, 1, 3-cyclohexanedimethanol, 1, 4-cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyalkylene glycol, 2-bis (4-hydroxyethoxyphenyl) propane, isosorbide (isosbate), and spiroglycol. Among them, ethylene glycol is a preferable embodiment from the viewpoint of ease of polymerization.

The main component herein means 80 mol% or more of the diol component. More preferably 90 mol% or more. These diol components may be used alone in 1 kind, or 2 or more kinds may be used in combination. Some of hydroxy acids such as hydroxybenzoic acid may be copolymerized.

As the thermoplastic resin B usable in the present invention, there can be used chain polyolefins such as polyethylene, polypropylene and poly (4-methyl-1-pentene); alicyclic polyolefins which are ring-opening metathesis polymers, addition polymers, and addition copolymers with other olefins of norbornene type; polyamides such as nylon 6, nylon 11, nylon 12, and nylon 66, aromatic polyamides, polymethyl methacrylate, polyvinyl chloride, polyvinylidene chloride, polyvinyl alcohol, polyvinyl butyral, ethylene vinyl acetate copolymer, polyacetal, polyglycolic acid, polystyrene, styrene-copolymerized polymethyl methacrylate, and polycarbonate; polyesters such as polytrimethylene terephthalate, polyethylene terephthalate, polybutylene terephthalate, polyethylene-2, 6-naphthalate, polylactic acid, and polybutylene succinate; polyether sulfone, polyether ether ketone, modified polyphenylene ether, polyphenylene sulfide, polyether imide, polyimide, polyarylate, a tetrafluoroethylene resin, a trifluoroethylene resin, a chlorotrifluoroethylene resin, a tetrafluoroethylene-hexafluoropropylene copolymer, polyvinylidene fluoride, and the like.

Among these, polyesters are preferably used from the viewpoints of strength, heat resistance, transparency and general versatility, and from the viewpoints of adhesion to the crystalline polyester a used in the layer a and lamination properties. They can be used both as copolymers and as mixtures.

In the case where the thermoplastic resin B is a polyester in the laminated film of the present invention, a polyester obtained by polymerization of a monomer containing an aromatic dicarboxylic acid component and/or an aliphatic dicarboxylic acid component and a diol component as main constituent components can be preferably used. Here, as the aromatic dicarboxylic acid component, the aliphatic dicarboxylic acid component, and the diol component, the components listed in the crystalline polyester a can be suitably used.

In the laminated film of the present invention, the thermoplastic resin B is preferably an aromatic polyester containing an aromatic dicarboxylic acid component and a diol component as main components. In particular, it is more preferable that 40 to 75 mol% of the dicarboxylic acid component is 2, 6-naphthalenedicarboxylic acid, 25 to 60 mol% is a component selected from isophthalic acid, 1, 8-naphthalenedicarboxylic acid, and 2, 3-naphthalenedicarboxylic acid, and 80 to 100 mol% of the glycol component is ethylene glycol, based on 100 mol%.

Isophthalic acid, 1, 8-naphthalenedicarboxylic acid and 2, 3-naphthalenedicarboxylic acid have an effect of bending molecular chains depending on the molecular skeleton, and as a result, it is possible to reduce the crystallinity of thermoplastic resin B and the orientation during stretching. As a result, in the production of the stretched film, the increase in refractive index due to the oriented crystallization of the B layer can be suppressed, and the difference in refractive index from the a layer made of the crystalline polyester a (in the case of the polarized light reflectance performance, the difference in refractive index from the orientation axis of the a layer) can be easily generated. As a result, it becomes possible to exhibit higher optical characteristics particularly in the case of exhibiting polarized light reflection characteristics.

In order to obtain a multilayer film having an interference reflection function, it is also preferable that the thermoplastic resin B is an amorphous resin. The amorphous resin is less likely to be oriented when a biaxially stretched film is produced than the crystalline resin, and therefore, an increase in refractive index due to oriented crystallization of the B layer formed of the thermoplastic resin B can be suppressed, and a difference in refractive index from the a layer formed of the crystalline polyester a can be easily generated. In particular, when a heat treatment step is provided in the production of a stretched film, this effect becomes remarkable.

Among the orientations generated in the stretching process, the orientation generated in the B layer can be completely relaxed in the heat treatment process, and the difference in refractive index from the a layer formed of the crystalline polyester can be maximized.

The amorphous resin herein means the following resin: according to JIS K7122(1999), the resin is heated from 25 ℃ to 300 ℃ (1 stun) at a temperature rise rate of 20 ℃/min, kept in this state for 5 minutes, then quenched to a temperature of 25 ℃ or less, and then heated again from room temperature to 300 ℃ at a temperature rise rate of 20 ℃/min, and in the obtained differential scanning calorimetry chart of 2ndRUN, the heat of crystal fusion Δ Hm obtained from the peak area of the melting peak is 5J/g or less, and more preferably a resin not showing a peak corresponding to the crystal melting.

In order to obtain a laminate film having an interference reflection function, it is also preferable to use a crystalline resin having a melting point lower by 20 ℃ or more than the melting point of the crystalline polyester a as the thermoplastic resin B. In this case, by performing the heat treatment at a temperature between the melting point of the thermoplastic resin B and the melting point of the crystalline polyester a in the heat treatment step, the heat treatment can be completely relaxed in the heat treatment step, and the difference in refractive index from the layer a formed of the crystalline polyester a can be maximized. The difference in melting point between the crystalline polyester A and the thermoplastic resin B is preferably 40 ℃ or more. In this case, since the selection range of the temperature in the heat treatment step is wide, the promotion of orientation relaxation of the thermoplastic resin B and the control of the orientation of the crystalline polyester become easier.

The preferable combination of the crystalline polyester a and the thermoplastic resin B is preferably such that the absolute value of the difference in SP values between the two is 1.0 or less. When the absolute value of the difference in SP values is 1.0 or less, delamination between the a layer and the B layer is less likely to occur. More preferably, the crystalline polyester a and the thermoplastic resin B are formed of a combination providing the same basic skeleton.

The basic skeleton herein means a repeating unit constituting the resin. For example, when polyethylene naphthalate having a carboxylic acid component composed of only 2, 6-naphthalenedicarboxylic acid or a polyethylene naphthalate copolymer having 2, 6-naphthalenedicarboxylic acid as a main component of the carboxylic acid component (the carboxylic acid component contains 80% or more of 2, 6-naphthalenedicarboxylic acid) is used as the crystalline polyester a, it is preferable to use an amorphous polyethylene naphthalate copolymer or a crystalline polyethylene naphthalate copolymer having a melting point lower than that of the crystalline polyester a as the thermoplastic resin B.

In order to obtain a laminate film having an interference reflection function, the glass transition temperature of the thermoplastic resin B is preferably lower than the glass transition temperature of the crystalline polyester a by 10 ℃. In this case, when the optimum stretching temperature is used for stretching the crystalline polyester in the stretching step, the orientation in the thermoplastic resin B does not progress, and therefore, the difference in refractive index from the layer a formed of the crystalline polyester can be made large. More preferably, the glass transition temperature of the thermoplastic resin B is 20 ℃ or more lower than the glass transition temperature of the crystalline polyester A.

In a suitable production method for obtaining the laminated film of the present invention, which will be described later, oriented crystallization of the thermoplastic resin B may easily progress and the desired interference reflection function may not be obtained, but oriented crystallization can be suppressed by lowering the glass transition temperature of the thermoplastic resin B by 20 ℃ or more than the glass transition temperature of the crystalline polyester a.

Various additives such as antioxidants, heat stabilizers, weather stabilizers, ultraviolet absorbers, organic lubricants, pigments, dyes, organic or inorganic fine particles, fillers, antistatic agents, and nucleating agents may be added to the thermoplastic resin to such an extent that the properties thereof are not deteriorated.

In the laminated film of the present invention, it is preferable that when the reflectance at an incident angle of 10 ° with respect to a polarized light component parallel to the incident plane including the orientation axis direction of the laminated film is represented as R1 and the reflectance at an incident angle of 10 ° with respect to a polarized light component perpendicular to the incident plane including the orientation axis direction of the laminated film is represented as R2, the reflectance at a wavelength of 550nm satisfies the following expressions (2) and (3). By satisfying the following equations (2) and (3), it is possible to impart a polarized light reflection characteristic such that one polarized light is reflected and the other polarized light is transmitted.

In order to obtain a film satisfying the following formula (2), the difference in refractive index between the a layer and the B layer in the axial direction of the laminated film is adjusted by a combination of resins such that the difference in refractive index is 0.02 or less, more preferably 0.01 or less, and still more preferably 0.005 or less. In order to obtain a film satisfying the following formula (3), the difference in refractive index between the a layer and the B layer in the direction perpendicular to the direction of the orientation axis of the laminated film can be adjusted by selection of a combination of resins and film formation conditions such that the difference in refractive index between the a layer and the B layer is 0.08 or more, more preferably 0.1 or more, and still more preferably 0.15 or more. Examples of the most suitable combinations thereof are as described above.

·R2(550)≤40％···(2)

·R1(550)≥70％···(3)。

In the laminate film of the present invention, it is preferable that the laminate film has a melting peak Tm in a first temperature rise curve in DSC, and has an exothermic peak in a range of Tm-110 ℃ or higher and Tm-60 ℃ or lower at a peak top temperature of the melting peak. In order to exhibit the above-described polarization characteristics, control of the refractive index of each layer becomes important, which makes control of orientation and crystallinity important. In this control, the a layer made of the crystalline polyester a is highly oriented in one direction, whereby the difference in refractive index between the orientation direction and the direction perpendicular thereto is increased. On the other hand, it is necessary to match one of the refractive indices of the B layer and the a layer (mainly, in the direction in which the refractive index is low) and increase the refractive index difference between the other refractive index and the B layer (mainly, in the direction in which the refractive index is high), and it is important to control the orientation and crystallinity of the B layer.

As a result of intensive studies, the present inventors have found that a laminate film has a melting peak Tm in a first temperature rise curve in DSC and an exothermic peak in a range of Tm-110 ℃ to Tm-60 ℃ inclusive, as an index for controlling the B layer, and thus high optical properties can be obtained.

This exothermic peak is a peak indicating the heat release due to crystallization of the B layer, and thus is an index of the orientation and crystallinity of the B layer. In the absence of this exothermic peak, the B layer undergoes oriented crystallization in the film formation step, or the crystallinity is very low, and the like, so that the relationship with the refractive index of the a layer is out of the desired range, and the optical characteristics are degraded.

Even if an exothermic peak exists, when the peak is outside the range of Tm-110 ℃ to Tm-60 ℃, the B layer is excessively oriented to exhibit anisotropy or the crystallinity is extremely lowered; and so on, resulting in a relationship with the refractive index of the a layer out of a desired range, the optical characteristics are degraded. Therefore, the laminate film of the present invention has an exothermic peak in the range of Tm-110 ℃ or higher and Tm-60 ℃ or lower, which is necessary for obtaining high optical characteristics.

Examples of a method for forming a laminated film having an exothermic peak at a temperature of from Tm-110 ℃ to Tm-60 ℃ include the following methods: the layer A and the layer B are in the preferred forms described above; in the production method described later, the temperature, the magnification, and the stretching speed in the stretching step are preferably set to the ranges. These methods are also preferably carried out in combination of a plurality of them.

The heat release amount in the heat release peak of the laminate film of the present invention is preferably 0.1J/g or more and 10J/g or less. The heat release amount is more preferably 0.5J/g to 5J/g, still more preferably 1.5J/g to 4J/g. When the heat release is out of the range of 0.1J/g to 10J/g, the B layer is excessively oriented to exhibit anisotropy, or the crystallinity is extremely lowered; and so on, resulting in a relationship with the refractive index of the a layer out of a desired range, the optical characteristics are degraded. In the laminated film of the present invention, high optical characteristics can be obtained by setting the amount of heat generated in the heat generation peak to 0.1J/g or more and 10J/g or less.

The laminate film of the present invention preferably has a melting peak temperature Tm of 255 ℃ or higher. The melting peak temperature is more preferably 258 ℃ or higher. In order to satisfy the range of the melting peak temperature, a more preferable range of the resin is selected from the above resins, whereby the optical properties can be improved and a film having high heat resistance can be formed.

Next, a preferred method for producing the laminated film of the present invention will be described below.

The laminated structure of the laminated film usable in the present invention can be easily realized by the same method as described in paragraphs [0053] to [0063] of Japanese patent application laid-open No. 2007-307893.

First, crystalline polyester a and thermoplastic resin B are prepared in the form of pellets or the like. The pellets are dried in hot air or under vacuum as needed, and then fed to separate extruders. In the extruder, the extrusion amount of the resin melted by heating is made uniform by a gear pump or the like, and foreign matter, modified resin, or the like is removed by a filter or the like. These resins were fed into a multilayer lamination apparatus.

As the multilayer laminating apparatus, a manifold die, a feed block (feed block), a static mixer, or the like can be used, and in order to effectively obtain the configuration of the present invention, a feed block having 11 or more fine slits is preferably used. By using such a feed head, the apparatus does not become very large, and therefore, foreign matter due to thermal degradation is small, and even when the number of stacked layers is very large, highly accurate stacking can be performed. Further, the lamination accuracy in the width direction is also significantly improved as compared with the conventional technique. In addition, according to this apparatus, since the thickness of each layer can be adjusted by the shape (length and width) of the slit, an arbitrary layer thickness can be realized.

The laminated sheet discharged from the die is extruded onto a cooling body such as a casting drum, cooled and solidified, and thereby a casting film is obtained. In this case, it is preferable to use an electrode in the form of a wire, a tape, a needle, a knife, or the like, to bring the discharged sheet into close contact with a cooling body by an electrostatic force, and to rapidly cool and solidify the sheet. Further, as a method of bringing the discharged sheet into close contact with the cooling body, a method of blowing air from a slit-shaped, dot-shaped, or planar device, and a method using a nip roll (nip roll) are also preferable.

The cast film obtained in the above manner is preferably subjected to biaxial stretching. Here, biaxial stretching means stretching the film in the longitudinal direction and the width direction.

In addition, as a preferable biaxial stretching method for obtaining the laminated film of the present invention, it is necessary to stretch the film at a magnification of 2 to 5 times in the film longitudinal direction, then stretch the film at a magnification of 2 to 5 times in the film width direction, and further stretch the film again at a magnification of 1.3 to 4 times in the film longitudinal direction. The details of which are described below.

The obtained cast film was first stretched in the longitudinal direction. Stretching in the longitudinal direction can generally be carried out using a difference in the peripheral speed of the rolls. The stretching may be performed in 1 stage, or may be performed in multiple stages using a plurality of roller pairs. The stretching magnification varies depending on the type of resin, but is preferably 2 to 5 times. The purpose of this 1st lengthwise stretching is: in order to improve uniform stretchability in subsequent stretching in the film width direction, the required minimum orientation is set. Therefore, when the stretch ratio is set to a ratio of more than 5, a film having a sufficient stretch ratio may not be obtained in stretching in the film width direction and re-stretching in the longitudinal direction performed after the above-described stretching step. If the stretch ratio is less than 2 times, the minimum orientation required for stretching may not be imparted, and thickness unevenness may occur in the longitudinal direction of the film, resulting in a decrease in quality. The stretching temperature is preferably a temperature of from the glass transition temperature to the glass transition temperature of the crystalline polyester a constituting the laminate film +30 ℃.

The uniaxially stretched film obtained as described above may be subjected to surface treatment such as corona treatment, flame treatment, or plasma treatment, and then subjected to in-line coating to impart functions such as slipperiness, adhesiveness, and antistatic properties, as necessary.

Next, the uniaxially stretched film is stretched in the width direction. In the stretching in the width direction, the film is generally stretched in the width direction by conveying the film while holding both ends of the film with clips using a tenter. The stretching ratio varies depending on the type of resin, and is preferably 2 to 5 times. The purpose of this widthwise stretching is to set the minimum orientation required for imparting high stretchability upon subsequent stretching in the film lengthwise direction. Therefore, when the stretch ratio is set to a ratio of more than 5, a film having a sufficient stretch ratio may not be obtained in the case of redrawing in the film longitudinal direction performed subsequent to this step. When the stretch ratio is less than 2 times, thickness unevenness may occur in the film width direction during stretching, resulting in a decrease in quality. The stretching temperature is preferably from the glass transition temperature of the crystalline polyester a constituting the laminate film to the glass transition temperature +30 ℃ or from the glass transition temperature to the crystallization temperature of the crystalline polyester.

Next, the obtained biaxially stretched film is stretched again in the longitudinal direction. The stretching in the longitudinal direction may be generally performed by using a difference in the peripheral speed of the rolls. The stretching may be performed in 1 stage, or may be performed in multiple stages using a plurality of roller pairs. The stretching ratio varies depending on the type of resin, but is preferably 1.3 to 4 times. The 2nd stretching in the longitudinal direction aims at orienting the film in the longitudinal direction as strongly as possible, and the resin is strongly oriented by further stretching in the longitudinal direction as described above, and as a result, the young's modulus in the orientation axis direction of the laminated film is 6GPa or more, and the linear expansion coefficient in the direction in which the young's modulus is maximum (the orientation axis direction of the laminated film) is 10 ppm/c or less. In particular, the higher the stretch ratio in the longitudinal direction, the higher the Young's modulus can be increased, or the linear expansion coefficient can be suppressed, and it is easy to set the Young's modulus to 10GPa or more and the absolute value of the linear expansion coefficient to 5 ppm/DEG C or less at 40 ℃ to 50 ℃. The stretching temperature is preferably from the glass transition temperature to the glass transition temperature +80 ℃ of the crystalline polyester a constituting the laminate film.

In order to impart flatness and dimensional stability to the film biaxially stretched as described above, it is preferable to perform heat treatment in a tenter at a temperature not lower than the stretching temperature and not higher than the melting point. By performing the heat treatment, not only the effect of promoting the orientation crystallization and increasing the young's modulus is obtained, but also the dimensional stability is improved with the promotion of the orientation crystallization, and as a result, it is possible to set the absolute value of the linear expansion coefficient at a temperature of 40 to 50 ℃ or less in either the direction in which the young's modulus is maximized (the direction of the orientation axis of the laminated film) or the direction perpendicular to the direction of the orientation axis of the laminated film to 5ppm/° c or less. Further, it is also possible to set the thermal shrinkage stress at a temperature of 100 ℃ in the axial direction to 1MPa or less and the absolute value of TMA at a temperature of 100 ℃ in the axial direction to 0.5% or less. After the heat treatment as described above, the steel sheet is uniformly cooled slowly, and then cooled to room temperature to be wound. If necessary, when the heat treatment is followed by slow cooling, a relaxation treatment or the like may be performed.

The laminated film obtained by the above-described production method can be used to form a laminated film having a high young's modulus and having a polarization reflection characteristic satisfying the above-described formulas (2) and (3). This is because, at the 2nd stretching in the film longitudinal direction, the orientation of the a layer formed of the crystalline polyester a can be made stronger in the film longitudinal direction, and as a result, a difference is generated between the refractive index in the film longitudinal direction and the refractive index in the film width direction perpendicular to the film longitudinal direction. Further, by selecting an amorphous resin as the thermoplastic resin B or selecting a combination of the crystalline polyester a and the thermoplastic resin B which can relax the difference in glass transition temperature and melting point of orientation in the stretching step and the heat treatment step, the orientation of the thermoplastic resin B can be suppressed, and the polarized light reflection characteristic can be imparted.

(method of measuring Properties and method of evaluating Effect)

The methods for measuring the characteristics and evaluating the effects of the present invention are as follows.

(1) Number of stacked layers:

the layer structure of the laminated film was determined by observing a sample, which had been cut out in cross section using a microtome, using a Transmission Electron Microscope (TEM). That is, a cross-sectional photograph of the film was taken under an acceleration voltage of 75kV using a transmission electron microscope H-7100FA model (manufactured by Hitachi, Ltd.), and the layer structure and the thickness of each layer were measured. According to circumstances, RuO is used to improve contrast₄、OsO₄And the like. Further, depending on the thickness of the thinnest layer (thin film layer) among all the layers in an image taken, observation was performed at a magnification of 10 ten thousand times when the thin film layer thickness was less than 50nm, observation was performed at a magnification of 4 ten thousand times when the thin film layer thickness was 50nm or more and less than 500nm, and observation was performed at an enlargement magnification of 1 ten thousand times when the thin film layer thickness was 500nm or more.

(2) The layer thickness and layer number calculating method comprises the following steps:

the TEM photograph image obtained in item (1) above was taken at an image size of 720dpi using a scanner (CanoScan D1230U, canon (inc.). The Image was stored in a personal computer in the form of a bitmap file (BMP) or a compressed Image file (JPEG), and then the file was opened using Image-Pro Plus ver.4 (vendor: プラネトロン (ltd)) to analyze the Image. For the image analysis processing, the relationship between the thickness direction position and the average luminance of the region sandwiched between 2 lines in the width direction is read in the form of numerical data in the vertical thickness profile mode.

Data acquisition was performed using the table calculation software (Excel 2000) for position (nm) and brightness data using the sampling step 2 (thinning out 2), and then numerical processing of 5-point moving average was performed. The obtained data on the periodic variation in luminance was differentiated, and the maximum value and the minimum value of the differential curve were read by vba (visual Basic for applications) program, and the interval between the adjacent maximum luminance region and minimum luminance region was defined as the layer thickness of 1 layer, and the layer thickness was calculated. This operation was performed for each photograph, and the layer thickness and the number of layers were calculated for all the layers.

(3) Young's modulus:

the laminated film was cut into a long strip having a length of 150mm × a width of 10mm, and this was used as a sample. A tensile test was carried out by using a tensile tester (テンシロン UCT-100, manufactured by オリエンテック) with an initial distance between tensile grips of 50mm and a tensile speed of 300 mm/min. The Young's modulus was determined from the obtained load-strain line by performing measurement at 23 ℃ under an atmosphere of 65% relative humidity. Each sample was measured 5 times, and the average value was used for evaluation.

(4) Orientation axis direction of the laminated film:

the Young's modulus of the laminated film was measured while changing the direction at every 10 degrees within the film surface, and the direction in which the Young's modulus became maximum was defined as the orientation axis direction of the laminated film.

(5) Coefficient of linear expansion:

the laminated film was cut into a long strip of 25mm in length by 4mm in width in the direction of the orientation axis thereof, and this was used as a sample. TMA measurement was performed on the orientation axis direction of the laminate film by using a TMA tester (TMA/SS 6000, manufactured by セイコーインスツルメンツ) in which the distance between the initial tensile chucks was set to 15mm and the tensile tension was set to 29.4mN, and in this state, the temperature in the tester was raised from 25 ℃ to 150 ℃ at 5 ℃/min. From the obtained TMA-temperature curve, the linear expansion coefficient at a temperature of 40 ℃ to 50 ℃ was determined.

(6) Thermal shrinkage stress:

the laminated film was cut into a long strip of 25mm in length by 4mm in width in the direction of the orientation axis thereof, and this was used as a sample. The thermal shrinkage stress was measured in the direction of the orientation axis of the laminate film by using a TMA tester (TMA/SS 6000 manufactured by セイコーインスツルメンツ) in which the distance between tensile chucks was kept constant at 15mm and the temperature in the tester was raised from 25 ℃ to 150 ℃ at 5 ℃/min. From the obtained stress-temperature curve, the thermal shrinkage stress was determined.

(7)TMA：

The laminated film was cut into a long strip of 25mm in length by 4mm in width in the direction of the orientation axis thereof, and this was used as a sample. TMA measurement was performed on the orientation axis direction of the laminate film by using a TMA tester (TMA/SS 6000, manufactured by セイコーインスツルメンツ) in which the distance between the initial tensile chucks was set to 15mm and the tensile tension was set to 29.4mN, and in this state, the temperature in the tester was raised from 25 ℃ to 150 ℃ at 5 ℃/min. From the obtained TMA-temperature curve, TMA was determined.

(8) Measurement of reflectance and transmittance of incident light having a polarized light component:

the sample was cut at 5cm × 5cm from the center in the direction of the orientation axis on the line segment having the largest length in the direction of the orientation axis. The measurement was performed using a basic configuration using an integrating sphere attached to a spectrophotometer (U-4100 Spectrophotometer) manufactured by Hitachi, with reference to a sub-white plate of alumina attached to the apparatus. The sample was set behind the integrating sphere with the orientation axis direction of the laminated film as the vertical direction. Further, a polarizer manufactured by グランテーラ company was attached, and linear polarized light having polarized light components of 0 and 90 degrees was incident, and the reflectance at a wavelength of 250 to 1500nm was measured.

The measurement conditions are as follows. The slit is set to 2nm (visible)/automatic control (infrared), the gain (gain) is set to 2, and the reflectance with the azimuth angle of 0-180 degrees is obtained by measuring at a scanning speed of 600 nm/min. When the reflection measurement of the sample was performed, the sample was blackened with マジックインキ (registered trademark) in order to eliminate interference due to reflection from the back surface.

Further, with respect to the samples cut out in the same manner, transmittance was measured in the same manner without being blackened, and from the obtained transmittance data, the extinction ratio at a wavelength of 550nm was determined by the following equation.

Extinction ratio T2/T1

(here, T1 represents the transmittance of a polarized light component parallel to the incident plane including the orientation axis direction of the laminated film at an incident angle of 0 °, and T2 represents the transmittance of a polarized light component perpendicular to the incident plane including the orientation axis direction of the laminated film at an incident angle of 0 °)

(9) Peak intensity ratio of polarized raman spectrum I max/I min:

the polarization Raman spectrum was measured using a laser Raman spectrometer T-64000 manufactured by Jovin Yvon Corp. In the laminated film, a cross section is cut with a microtome so that a cut surface in each direction becomes a measurement surface, with the direction in which the reflectance specified in the above item (4) is the maximum being denoted as imax and the direction perpendicular thereto being denoted as imin. In the polarization raman spectrum, the polarization axis of the laser beam from the sample cross section and the transmission axis of the film were measured as parallel conditions, and the polarization axis of the laser beam and the transmission axis of the film were measured as perpendicular conditions. For the measurement, the center of each layer was measured at 3 points with changing positions, and the average value was defined as the measurement value. The detailed measurement conditions are as follows.

Measurement mode: micro-Raman

Objective lens: x 100

Beam diameter: 1 μm

Cross slit: 100 μm

Light source: ar + laser/514.5 nm

Laser power: 15mW

Diffraction grating: spectrograph 600gr/mm

Dispersion: single 21 Angstrom/mm

Slit: 100 μm

The detector: CCD/Jobin Yvon 1024 × 256.

1390cm for a wavelength^-1And a wavelength of 1615cm^-1The peak intensity ratio I max/I min of the polarized Raman spectrum at the time of measurement was 1390cm from the CNC stretched band of naphthalene ring obtained by the measurement of the polarized Raman spectrum^-1Peak intensity of (3), and 1615cm of C ═ C stretch band derived from benzene ring^-1The ratio of the peak intensities of (1) was calculated from the peak intensities of the sample whose measurement surface was a cross section in the direction of I max and the sample whose measurement surface was a cross section in the direction of I min.

(10) Enthalpy of fusion and glass transition temperature:

the laminate film thus measured was sampled, and the DSC curve of the sample was measured by differential calorimetry (DSC) according to JIS-K-7122 (1987). For the test, the enthalpy of fusion at this time and the glass transition temperature were measured at a temperature of 20 ℃/min from 25 ℃ to 290 ℃. The apparatus and the like used are as follows.

An apparatus: セイコー electronic engineering (Inc. 'ロボット DSC-RDC 220'

Data analysis "ディスクセッション SSC/5200"

Sample mass: 5 mg.

(11) Processability:

the rolled film was introduced into a punching machine to have a length of 500mm, and punching was performed using a rectangular die having a width-wise length of 95% of the film width. The punching interval in the longitudinal direction was set to 40 mm. The following A, B and C evaluations were carried out. A and B were accepted as passed.

A: the film can be continuously conveyed and processed without breaking.

B: although the film is partially broken, the film can be continuously conveyed in the longitudinal direction and can be continuously processed.

C: the film was completely broken, and continuous processing in the longitudinal direction was not performed.

(12) And (3) mounting test:

a laminated film as a sample was cut out from the position of the center in the film width direction with dimensions of 1450mm in the longitudinal direction and 820mm in the width direction. Next, the flatness of the polarized light reflector after the heat resistance test for 12 hours was visually evaluated at 50 ℃ and 85 ℃ in the order of a 50% diffusion plate, a microlens sheet, a polarized light reflector, and a polarizing plate on a 32-type liquid crystal TV LHD32K15JP backlight manufactured by ハイセンスジャパン co.

The planarity was evaluated by A, B and C described below. And taking A as qualified.

A: at 50 ℃ and 85 ℃, the appearance was not problematic

B: at a temperature of 50 ℃, the appearance was problematic.

(13) Content of naphthalenedicarboxylic acid:

the layer a of the laminate film formed of the crystalline polyester was dissolved in deuterated Hexafluoroisopropanol (HFIP) or a mixed solvent of HFIP and deuterated chloroform, and composition analysis was performed by using 1H-NMR and 13C-NMR.

Examples

(example 1)

As the crystalline polyester A, 2, 6-polyethylene naphthalate (PEN) having a melting point of 266 ℃ and a glass transition temperature of 122 ℃ was used. Further, as the thermoplastic resin B, a copolymerized PEN (copolymerized PEN1) obtained by copolymerizing 25 mol% of 2, 6-naphthalenedicarboxylic acid spiroglycol, 25 mol% of terephthalic acid and 50 mol% of ethylene glycol, which is an amorphous resin having no melting point and having a glass transition temperature of 103 ℃ was used.

The prepared crystalline polyester A and thermoplastic resin B were fed into 2 single-screw extruders and melt-kneaded at 290 ℃. Next, the crystalline polyester a and the thermoplastic resin B were passed through 5 FSS type disk filters (leaf disk filters), respectively, and then combined together by a laminating apparatus having 11 slits while measuring with a gear pump, to obtain a laminate in which 11 layers were alternately laminated in the thickness direction. The method for producing a laminate is carried out according to the method described in Japanese patent laid-open No. 2007-307893 [0053] to [ 0056 ].

Here, the length and the interval of the slits are all constant. The obtained laminate had a laminate structure in which 6 layers of the crystalline polyester a and 5 layers of the thermoplastic resin B were alternately laminated in the thickness direction. Further, the value obtained by dividing the length of the die lip in the film width direction by the length of the die lip in the film width direction at the inlet of the die, which is the widening ratio of the inside of the die, was 2.5. The width of the obtained casting film was 600 mm.

The resulting cast film was heated with a roll set to a temperature of 120 ℃, then stretched to 3.0 times in the film length direction with a roll set to a temperature of 135 ℃, and then cooled once. The uniaxially stretched film obtained in the above manner was introduced into a tenter, preheated with hot air at a temperature of 115 ℃ and then stretched at a temperature of 135 ℃ by 3.0 times in the film width direction to obtain a biaxially stretched film in the form of a film roll. The width of the biaxially stretched film obtained here was 1500 mm.

Further, the biaxially stretched film was heated with a roller set to a temperature of 120 ℃, and then stretched to 3.0 times in the film length direction with a roller set to a temperature of 160 ℃, and both ends of the film were trimmed to obtain a target laminate film in the form of a film roll having a film width of 1000mm and a length of 200 m.

The resulting laminated film exhibited the physical properties shown in table 1, and exhibited a high young's modulus and a low linear expansion coefficient (40 to 50 ℃) in the MD direction. In addition, the interference reflection characteristics due to the difference in refractive index between the crystalline polyester a and the thermoplastic resin B are shown. The laminate film of the present invention can be suitably used in the case of processing into a product or in the case of actual use.

(example 2)

A laminated film was obtained in the same manner as in example 1, except that a device having 101 slits was used as the laminating device to be used.

The resulting laminated film exhibited the physical properties shown in Table 1, and exhibited a high Young's modulus and a low linear expansion coefficient (40 to 50 ℃) in the longitudinal direction of the film in the same manner as in example 1. Further, the interference reflection characteristic due to the difference in refractive index between the crystalline polyester a and the thermoplastic resin B was exhibited, and the high polarized light reflection characteristic was exhibited as compared with example 1. The laminated film can be stably and continuously produced with high precision when processed into a product, and can be used without any problem even when actually used.

(example 3)

A laminated film was obtained in the same manner as in example 1, except that a device having 201 slits was used as the laminating device to be used.

The resulting laminated film exhibited the physical properties shown in table 1, and exhibited a high young's modulus and a low linear expansion coefficient (40 to 50 ℃) in the MD direction as in example 1. Further, the interference reflection characteristic due to the difference in refractive index between the crystalline polyester a and the thermoplastic resin B was exhibited, and the interference reflection characteristic was higher than that of example 2, and was at a level that it could be used as a polarized light reflection member. The laminated film can be stably and continuously produced with high precision when processed into a product, and can be used without any problem even when actually used.

(example 4)

A laminated film was obtained in the same manner as in example 1, except that a device having 801 slits was used as the laminating device. The resulting laminated film exhibited the physical properties shown in table 1, and exhibited a high young's modulus and a low linear expansion coefficient (40 to 50 ℃) in the MD direction as in example 1. Further, the interference reflection characteristic due to the difference in refractive index between the crystalline polyester a and the thermoplastic resin B was exhibited, and the polarized light reflection member exhibited a high polarized light reflection characteristic as compared with example 3, and had very good performance. The laminated film can be stably and continuously produced with high precision when processed into a product, and can be used without any problem even when actually used.

(example 5)

A laminated film was obtained in the same manner as in example 4 except that the ratio of stretching the biaxially stretched film in the film longitudinal direction was 2.5 times. The resulting laminated film exhibited the physical properties shown in Table 1, and exhibited a high Young's modulus and a low coefficient of linear expansion (40 to 50 ℃ C.). In addition, as in example 4, the polarizing reflective member exhibited high polarized light reflection characteristics and had very good performance. The laminated film can be stably and continuously produced with high precision when processed into a product, and can be used without any problem even when actually used.

(example 6)

A laminated film was obtained in the same manner as in example 4 except that the ratio of stretching the biaxially stretched film in the film longitudinal direction was 2.2 times. The resulting laminated film exhibited the physical properties shown in Table 1, and exhibited a high Young's modulus and a low coefficient of linear expansion (40 to 50 ℃ C.). The laminated film can be continuously produced even when processed into a product under specific conditions, and can be used without any problem even when actually used.

(example 7)

A laminated film was obtained in the same manner as in example 4 except that the ratio of stretching the biaxially stretched film in the film longitudinal direction was 2.0 times. The resulting laminated film exhibited the physical properties shown in Table 1, and exhibited a high Young's modulus and a low coefficient of linear expansion (40 to 50 ℃ C.). The laminated film can be continuously produced even when processed into a product under specific conditions, and can be used without any problem even when actually used.

(example 8)

A laminated film was obtained in the same manner as in example 4, except that the biaxially stretched film was stretched again in the longitudinal direction and then conveyed into an oven heated to a temperature of 180 ℃. The resulting laminated film exhibited the physical properties shown in Table 1, and exhibited a high Young's modulus and a low coefficient of linear expansion (40 to 50 ℃ C.). In addition, as in example 4, the polarizing reflective member exhibited high polarized light reflection characteristics and had very good performance. Further, the obtained film was able to suppress the heat shrinkage stress at 100 ℃ in the film longitudinal direction and the absolute value of TMA to be lower than those of example 4, and the laminated film was able to be continuously produced with high precision and stability when processed into a product under specific conditions, and was able to be used without any problem even under severer conditions than those of example 4 in practical use.

(example 9)

A laminated film was obtained in the same manner as in example 4, except that the biaxially stretched film was stretched again in the longitudinal direction and then conveyed into an oven heated to a temperature of 220 ℃. The resulting laminated film exhibited the physical properties shown in Table 2, and exhibited a high Young's modulus and a low coefficient of linear expansion (40 to 50 ℃ C.). In addition, as in example 4, the polarizing reflective member exhibited high polarized light reflection characteristics and had very good performance. Further, the obtained laminated film can suppress the heat shrinkage stress at 100 ℃ in the film longitudinal direction and the absolute value of TMA to be lower than those of example 4, and the laminated film can be stably and continuously produced with high accuracy when processed into a product under specific conditions, and can be used without any problem even under severer conditions than those of example 4 in practical use.

(example 10)

A laminated film was obtained in the same manner as in example 4 except that a copolymerized PEN (copolymerized PEN2) obtained by copolymerizing 50 mol% of 2, 6-naphthalenedicarboxylic acid, 5 mol% of a spiroglycol, and 45 mol% of ethylene glycol, having a melting point of 240 ℃ and a glass transition temperature of 118 ℃, was used as the crystalline polyester. The obtained laminated film exhibited physical properties as shown in table 2, and exhibited a high young's modulus. The laminated film can be continuously produced even when processed into a product under specific conditions, and can be used without any problem even when actually used.

(example 11)

A laminated film was obtained in the same manner as in example 4, except that copolymerized PEN2 was used as the thermoplastic resin B. The obtained laminated film showed physical properties as shown in table 2, and high young's modulus as in example 4. On the other hand, since the difference in glass transition temperature between the crystalline polyester and the thermoplastic resin B is small, the reflection performance is about the same as that of example 1. The laminated film can be stably and continuously produced with high precision when processed into a product, and can be used without any problem even when actually used.

(example 12)

A laminated film was obtained in the same manner as in example 4, except that polyethylene terephthalate (PET) having a melting point of 256 ℃ and a glass transition temperature of 81 ℃ was used as the crystalline polyester, and cyclohexanedimethanol copolymerized PET (copolymerized PET) having a glass transition temperature of 78 ℃ was used as the amorphous resin B. The obtained laminated film exhibited physical properties as shown in Table 2, and exhibited a high Young's modulus as compared with comparative examples 1 to 5. The laminated film can be continuously produced even when processed into a product under specific conditions, and can be used without any problem in practical use. On the other hand, since the crystalline polyester was PET, the reflectance was lower than that of example 4.

(example 13)

A laminated film was obtained in the same manner as in example 4 except that a copolymerized PEN (copolymerized PEN3) obtained by copolymerizing 70 mol% of 2, 6-naphthalenedicarboxylic acid and 30 mol% of isophthalic acid having a glass transition temperature of 96 ℃ as dicarboxylic acid components and ethylene glycol as a glycol component was used as the thermoplastic resin B. The obtained laminated film exhibited physical properties as shown in table 3, and exhibited a high young's modulus. The laminated film can be continuously produced when processed into a product, and can be used without any problem even when actually used.

(example 14)

A laminated film was obtained in the same manner as in example 13, except that the speed of stretching the film in the longitudinal direction was set to 400%/sec after the biaxial stretching. The obtained laminated film exhibited physical properties as shown in table 3, and exhibited a high young's modulus. The laminated film can be continuously produced when processed into a product, and can be used without any problem even when actually used. Further, the extinction ratio showing the polarization characteristics was higher than that of example 4, and the polarization light reflectance was excellent.

(example 15)

A laminated film was obtained in the same manner as in example 4 except that a copolymerized PEN (copolymerized PEN4) obtained by copolymerizing 50 mol% of 2, 6-naphthalenedicarboxylic acid and 50 mol% of isophthalic acid as dicarboxylic acid components and ethylene glycol as glycol components, having a glass transition temperature of 90 ℃. The obtained laminated film exhibited physical properties as shown in table 3, and exhibited a high young's modulus. The laminated film can be continuously produced when processed into a product, and can be used without any problem even when actually used. Further, the extinction ratio showing the polarization characteristics was higher than that of example 4, and the polarization light reflectance was excellent.

(example 16)

A laminated film was obtained in the same manner as in example 4 except that a copolymerized PEN (copolymerized PEN5) obtained by copolymerizing 75 mol% of 2, 6-naphthalenedicarboxylic acid and 25 mol% of isophthalic acid as dicarboxylic acid components and ethylene glycol as glycol components, having a glass transition temperature of 98 ℃. The obtained laminated film exhibited physical properties as shown in table 3, and exhibited a high young's modulus. The laminated film can be continuously produced when processed into a product, and can be used without any problem even when actually used. Further, the extinction ratio showing the polarization characteristics was higher than that of example 4, and the polarization light reflectance was excellent.

(example 17)

A laminated film was obtained in the same manner as in example 4 except that a copolymerized PEN (copolymerized PEN6) obtained by copolymerizing 80 mol% of 2, 6-naphthalenedicarboxylic acid and 20 mol% of isophthalic acid as dicarboxylic acid components and ethylene glycol as glycol components, having a glass transition temperature of 103 ℃. The obtained laminated film exhibited physical properties as shown in table 3, and exhibited a high young's modulus. The laminated film can be continuously produced when processed into a product, and can be used without any problem even when actually used. Further, the extinction ratio showing the polarization characteristics was higher than that of example 4, and the polarization light reflectance was excellent.

(example 18)

A laminated film was obtained in the same manner as in example 4 except that a copolymerized PEN (copolymerized PEN7) obtained by copolymerizing 70 mol% of 2, 6-naphthalenedicarboxylic acid and 30 mol% of 1, 8-naphthalenedicarboxylic acid having a glass transition temperature of 103 ℃ as dicarboxylic acid components and ethylene glycol as a glycol component was used as the thermoplastic resin B. The obtained laminated film exhibited physical properties as shown in table 3, and exhibited a high young's modulus. The laminated film can be continuously produced when processed into a product, and can be used without any problem even when actually used. Further, the extinction ratio showing the polarization characteristics was higher than that of example 4, and the polarization light reflectance was excellent.

(example 19)

A laminated film was obtained in the same manner as in example 4 except that a copolymerized PEN (copolymerized PEN8) obtained by copolymerizing 70 mol% of 2, 6-naphthalenedicarboxylic acid, 30 mol% of 2, 3-naphthalenedicarboxylic acid and ethylene glycol as glycol components and having a glass transition temperature of 103 ℃ was used as the thermoplastic resin B. The obtained laminated film exhibited physical properties as shown in table 3, and exhibited a high young's modulus. The laminated film can be continuously produced when processed into a product, and can be used without any problem even when actually used. Further, the extinction ratio showing the polarization characteristics was higher than that of example 4, and the polarization light reflectance was excellent.

Comparative example 1

A film was obtained in the same manner as in example 4, except that a single-layer PEN film was used as the casting film. The obtained film showed physical properties as shown in table 2, and high young's modulus as in example 4. On the other hand, since the film had no laminated structure, it did not exhibit a peculiar reflection property, and the film became brittle as compared with the film of example 1, and thus the handling property was degraded. This film is inferior in continuous productivity because film breakage occurs when the film is processed into an article.

Comparative example 2

A laminated film was obtained in the same manner as in example 1, except that a device having 3 slits was used as the laminating device to be used. The obtained laminated film exhibited physical properties as shown in table 2, and exhibited a high young's modulus in the film longitudinal direction in the same manner as in example 1. On the other hand, since the number of layers was as small as 3, the reflection performance peculiar to the laminated structure was not exhibited, and the film was brittle as compared with the film of example 1, and therefore, the handling property was slightly lowered. This laminated film is inferior in continuous productivity because of film breakage when processed into a product.

Comparative example 3

The cast film obtained in the same manner as in example 4 was heated with a roll set having been set to a temperature of 120 ℃, and then stretched to 4.5 times in the film length direction with a roll set having been set to a temperature of 135 ℃, followed by cooling once.

The uniaxially stretched film obtained in the above manner was introduced into a tenter, preheated with hot air at a temperature of 135 ℃, then stretched 4.5 times in the film width direction at a temperature of 150 ℃, and then subjected to heat treatment by being conveyed into an oven heated to 220 ℃. The obtained biaxially stretched film was trimmed at both ends to obtain a target laminate film in the form of a film roll having a film width of 1500mm and a length of 200 m.

The resulting laminated film exhibited the physical properties shown in table 2, and the young's modulus was lower than that of example 4. This laminated film is inferior in continuous productivity because of film breakage when processed into a product.

Comparative example 4

The casting film obtained in the same manner as in example 4 was introduced into a tenter, preheated with hot air at a temperature of 135 ℃, and then stretched 5.0 times in the film width direction at a temperature of 150 ℃, and both ends of the film were trimmed to obtain a 200 m-target laminated film in a roll shape having a film width of 2000 mm.

The resulting laminated film exhibited the physical properties shown in table 2, and the young's modulus was lower than that of example 4. Further, since the film roll has an orientation axis in the width direction thereof, the strength of the film roll in the winding axis direction is very weak. This laminated film is inferior in continuous productivity because of film breakage when processed into a product.

Comparative example 5

The cast film obtained in the same manner as in example 4 was heated with a roll set to a temperature of 120 ℃, and then stretched 4.0 times in the film longitudinal direction with a roll set to a temperature of 135 ℃ and trimmed, thereby obtaining a film roll of a laminated film having a film width of 500mm and a length of 200m as an object.

The resulting laminated film exhibited the physical properties shown in table 2, and the young's modulus was lower than that of example 4. Further, the reflection performance was also greatly reduced as compared with the examples, with the orientation of the thermoplastic resin B generated during stretching. This laminated film is inferior in continuous productivity because of film breakage when processed into a product.

[ Table 1]

TABLE 1

[ Table 2]

[ Table 3]

Claims (12)

1. A laminated film comprising 11 or more layers in total, wherein a layer A comprising a crystalline polyester and a layer B comprising a thermoplastic resin different from the crystalline polyester are alternately laminated, and the Young's modulus in the orientation axis direction of the laminated film is 6GPa or more, and the ratio of the Young's modulus in the orientation axis direction to that in a direction perpendicular to the orientation axis direction in the same plane is 10.2/3.1 or more,

and the layer A and the layer B satisfy the following condition,

layer A: an aromatic polyester comprising a dicarboxylic acid component and a diol component as main components, wherein 80 to 100 mol% of the dicarboxylic acid component is 2, 6-naphthalenedicarboxylic acid, and 80 to 100 mol% of the diol component is ethylene glycol;

b layer: the polyester resin composition is composed of an aromatic polyester which mainly contains a dicarboxylic acid component and a diol component, wherein 40 to 75 mol% of 100 mol% of the dicarboxylic acid component is 2, 6-naphthalenedicarboxylic acid, 25 to 60 mol% of the dicarboxylic acid component is at least one component selected from isophthalic acid, 1, 8-naphthalenedicarboxylic acid and 2, 3-naphthalenedicarboxylic acid, and 80 to 100 mol% of the diol component is ethylene glycol.

2. The laminate film of claim 1, wherein the optical beam diameter is 1 μm and the wavelength is 1390cm^-1In the polarized Raman spectrum of (1), the reflectance is the largestThe ratio I max/I min of the direction peak intensity I max to the direction peak intensity I min perpendicular thereto is 5 or more.

3. The laminate film according to claim 1, wherein the carboxylic acid component constituting the crystalline polyester contains 90 mol% or more of naphthalenedicarboxylic acid.

4. The laminate film according to claim 1 or 2, wherein an absolute value of a linear expansion coefficient at a temperature of 40 ℃ or higher and 50 ℃ or lower in any one of an orientation axis direction and a direction perpendicular to the orientation axis direction is 10ppm/° c or lower.

5. The laminate film according to claim 1 or 2, wherein when a reflectance at an incident angle of 10 ° with respect to a polarized light component parallel to an incident plane including the orientation axis direction is denoted as R1, and a reflectance at an incident angle of 10 ° with respect to a polarized light component perpendicular to the incident plane including the orientation axis direction is denoted as R2, the reflectance at a wavelength of 550nm satisfies the following formulae (2) and (3),

·R2(550)≤40％ (2)

·R1(550)≥70％ (3)。

6. the laminate film according to claim 1 or 2, which has a melting peak in a first temperature rise curve obtained by Differential Scanning Calorimetry (DSC), and an exothermic peak in a range of from Tm-110 ℃ to Tm-60 ℃ when the melting peak top temperature is taken as Tm.

7. The laminate film according to claim 1 or 2, wherein a thermal shrinkage stress at a temperature of 100 ℃ in the axial direction is 1MPa or less.

8. The laminate film according to claim 1 or 2, wherein the absolute value of TMA at a temperature of 100 ℃ in the axial direction is 0.5% or less.

9. The laminate film according to claim 1 or 2, wherein a melting peak derived from the thermoplastic resin B measured by Differential Scanning Calorimetry (DSC) is 5J/g or less.

10. A film roll obtained by winding the laminated film according to any one of claims 1 and 2 along an orientation axis of the laminated film.

11. The film roll according to claim 10, wherein the width of the laminated film is 1000mm or more.

12. A method for producing a laminated film, characterized in that an unstretched film obtained by alternately laminating a layer A made of a crystalline polyester and a layer B made of a thermoplastic resin different from the crystalline polyester for a total of 11 or more layers is stretched at a ratio of 2 to 5 times in a film longitudinal direction, then stretched at a ratio of 2 to 5 times in a film width direction, and further stretched again at a ratio of 1.3 to 4 times in the film longitudinal direction,

and the layer A and the layer B satisfy the following condition,

layer A: an aromatic polyester comprising a dicarboxylic acid component and a diol component as main components, wherein 80 to 100 mol% of the dicarboxylic acid component is 2, 6-naphthalenedicarboxylic acid, and 80 to 100 mol% of the diol component is ethylene glycol;

b layer: the polyester resin composition is composed of an aromatic polyester which mainly contains a dicarboxylic acid component and a diol component, wherein 40 to 75 mol% of 100 mol% of the dicarboxylic acid component is 2, 6-naphthalenedicarboxylic acid, 25 to 60 mol% of the dicarboxylic acid component is at least one component selected from isophthalic acid, 1, 8-naphthalenedicarboxylic acid and 2, 3-naphthalenedicarboxylic acid, and 80 to 100 mol% of the diol component is ethylene glycol.