JP6411736B2 - Light selective reflection film and light selective reflective film for display - Google Patents

Description

  The present invention relates to a light selective reflection film, and more particularly to a light selective reflection film that reflects red light and green light and transmits blue light.

The laminated film can be an optical interference film that selectively reflects or transmits light of a specific wavelength due to structural optical interference between layers by alternately laminating low refractive index layers and high refractive layers. .
Such a laminated film is a film having a pearly luster that looks superior in design, for example, iridescent, if it is laminated in multiple layers and the wavelength of light that is selectively reflected or transmitted is in the visible light region. Can be obtained.
On the other hand, in a liquid crystal display, in order to increase the light use efficiency of the backlight, the phosphor layer is excited by blue light emitted from the backlight, thereby emitting red light and green light to obtain an image. Display is being considered.

In such a type of display, since the light emitted from the phosphor is isotropic, part of the light is emitted to the backlight side and is not emitted outside the display. Therefore, it is considered to improve the light utilization efficiency by installing a light selective reflection film that transmits blue light of the backlight and reflects red light and green light of the phosphor between the backlight and the phosphor layer. Has been. (For example, Patent Documents 1 and 2).
As such a light selective reflection film, for example, Patent Document 2 describes that it can be composed of a multilayer laminated film composed of a low refractive index material and a high refractive index material. An SiO ₂ film having a thickness of about 1 μm and an Nb film are described. A multilayer laminated film with ₂ O ₅ film is illustrated. However, the lamination of such inorganic substances tends to be complicated.

  In addition, as a light selective reflection film using a polymer, Patent Document 3 describes a multilayer laminated film composed of a low refractive index polymer and a high refractive index polymer. Polyethylene naphthalate (PEN) and polymethyl methacrylate (PMMA). A light ray selective reflection film that transmits blue light and reflects light having a wavelength of 500 to 700 nm, which is made of a multilayer laminated film, has been studied. However, when an amorphous resin is used as the low refractive index layer, the coefficient of thermal expansion is increased, and the deformation of the film is increased when the display is used.

JP 2006-309225 A JP 2009-115924 A Japanese translation of PCT publication No. 2002-509271

  The object of the present invention is to solve the above-mentioned problems of the prior art, have a low coefficient of thermal expansion, for example, to reduce the deformation of the film when using a display, and to reflect red light and green light with high reflection. It is to provide a light selective reflection film having high transmission characteristics with respect to characteristics and blue light.

  As a result of diligent studies to achieve the above object, the present inventors have found that if the combination of the resin constituting the high refractive index layer and the low refractive index layer of the multilayer laminated film is controlled, the reflection characteristics of red light and green light The inventors have found that a low thermal expansion characteristic can be achieved while maintaining the blue light transmission characteristic, and have completed the present invention.

That is, an object of the present invention is a film in which layers A and B are alternately laminated, and the number of laminated layers is 161 or more, and layer A includes ethylene-2,6-naphthalenedicarboxylate as a main repeating unit. Copolymer polyethylene terephthalate having a layer thickness in the range of 0.06 to 0.3 μm, and layer B having a proportion of ethylene terephthalate units of 50 to 95 mol% based on all repeating units. The layer thickness is in the range of 0.06 to 0.3 μm, and the thermal expansion coefficient of the film from 40 ° C. to 100 ° C. is 26 ppm / ° C. or less in both the length direction and the width direction of the film. , the film is an average reflectance of red light and green light more than 70%, the biaxially wherein the average transmittance of the blue light is 82% or more stretch It is accomplished by the line selective reflection film.

In addition, the light selective reflection film of the present invention preferably has “a ratio of the maximum thickness and the minimum thickness (maximum / minimum) in each layer in layers A and B is 1.2-2. it is 9 "," layer a is the ethylene-2,6-naphthalene dicarboxylate units all repeating units as a reference of an aromatic polyester, which accounts for more than 90 mol% "is for" display, light Including those having at least one requirement of “selective reflection film”.

  It is possible to provide a light selective reflection film that has high reflection characteristics with respect to red light and green light and transmits blue light while being a film having a smaller coefficient of thermal expansion than conventional ones.

Hereinafter, the present invention will be described in detail.
<Laminated structure>
The light selective reflection film of the present invention is a film in which layers A and B are alternately laminated and the number of laminated layers is 161 or more, and layer A is a repeating layer mainly composed of ethylene-2,6-naphthalenedicarboxylate units. Copolymer comprising an aromatic polyester as a unit, having a layer thickness in the range of 0.06 to 0.3 μm, and layer B having a proportion of ethylene terephthalate units of 50 to 95 mol% based on all repeating units. It consists of polyethylene terephthalate, and when the layer thickness is in the range of 0.06 to 0.3 μm, it reflects red light and green light and transmits blue light.

(Layer A)
Layer A in the present invention comprises an aromatic polyester having ethylene-2,6-naphthalenedicarboxylate units as main repeating units. As used herein, “main” means occupying 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more, based on all repeating units of the aromatic polyester in layer A. And particularly preferably a homopolyester containing no copolymerization component. When the ethylene-2,6-naphthalenedicarboxylate unit is less than 80 mol%, it becomes difficult to provide a sufficient refractive index difference with the second layer described later, and sufficient reflection characteristics are exhibited. Can be difficult.

  As the copolymerization component used in the aromatic polyester, conventionally known ones can be used. For example, isophthalic acid, terephthalic acid, orthophthalic acid, naphthalenedicarboxylic acid (excluding 2,6-naphthalenedicarboxylic acid), biphenyldicarboxylic acid Aromatic carboxylic acids such as: aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid and decanedicarboxylic acid; acid components such as alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, diethylene glycol, propylene glycol Aliphatic diols such as 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol and neopentyl glycol; alicyclic diols such as 1,4-cyclohexanedimethanol, polyethylene glycol, poly Tetramethylene It can be mentioned glycol component recall like. Of these, isophthalic acid, terephthalic acid, neopentyl glycol, 1,4-cyclohexanedimethanol and diethylene glycol are preferable, and isophthalic acid and terephthalic acid are particularly preferable. These copolymer components may be used alone or in combination of two or more components.

The intrinsic viscosity (orthochlorophenol, measured at 35 ° C.) of the aromatic polyester is preferably 0.40 to 0.80 dl / g, and more preferably 0.45 to 0.75 dl / g. If the intrinsic viscosity is within such a range, the film forming property when forming a film having a multilayer laminated structure with a second layer described later is good.
The layer A of the present invention may contain a small amount of other polymers and additives as long as the object of the present invention is not impaired. For example, lubricants such as inert particles, colorants such as pigments and dyes, Examples thereof include additives such as a stabilizer, a flame retardant, a foaming agent, and an ultraviolet absorber.

(Layer B)
Layer B in the present invention comprises a copolymerized polyethylene terephthalate (hereinafter referred to as polyester (B)) in which the proportion of ethylene terephthalate units is 50 to 95 mol%, preferably 60 to 90 mol%, based on all repeating units constituting the polyester. May be called). When the ratio of the ethylene terephthalate unit exceeds the upper limit, it is not preferable because it is easy to crystallize and orientate at the time of film formation and a difference in refractive index between the layer A and the reflection characteristic is lowered. On the other hand, when the ratio of the ethylene terephthalate unit is less than the lower limit, not only the heat resistance and film forming property during film formation (particularly during extrusion) are lowered, but the copolymer component is a component that imparts high refractive index. In some cases, there arises a problem that a difference in refractive index with the layer A is reduced by increasing the refractive index. When the ratio of the ethylene terephthalate unit is within the above range, it is possible to ensure a difference in refractive index from the layer A while maintaining good heat resistance and film forming property, and to provide sufficient reflectance. Will be able to.

  In order to secure a difference in refractive index from the layer A and improve reflection characteristics, the heat setting temperature during film formation described later is set to be equal to or higher than the melting point of the polyester (B) while maintaining the orientation of the layer A. It is preferable to melt the B polyester (B) and lower the orientation of the layer B to increase the refractive index difference between the layer A and the layer B. From this viewpoint, the melting point of the polyester (B) is preferably 10 ° C. or more, particularly 30 ° C. or more lower than the melting point of the aromatic polyester.

  Examples of the copolymer component preferably used include aliphatic dicarboxylic acids such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 2,7-naphthalenedicarboxylic acid, and aliphatics such as adipic acid, azelaic acid, sebacic acid, and decanedicarboxylic acid. Examples thereof include acid components such as alicyclic dicarboxylic acids such as dicarboxylic acid and cyclohexanedicarboxylic acid, aliphatic diols such as butanediol and hexanediol, alicyclic diols such as cyclohexanedimethanol, and glycol components such as spiroglycol. Of these, isophthalic acid, 2,6-naphthalenedicarboxylic acid, cyclohexanedimethanol, and spiroglycol are preferable. When a copolymerization component other than these is included, the copolymerization amount is preferably 10 mol% or less.

Moreover, it is preferable that the glass transition temperature of polyester (B) is 90 degrees C or less. By using such a polyester, when it is stretched under such stretching conditions that the aromatic polyester of layer A is oriented, the orientation of the polyester (B) of layer B does not advance because of the high stretching temperature. It becomes easy to make a refractive index difference between A and the layer B.
The layer B in the present invention is preferably crystalline from the viewpoint of thermal dimensional stability of the resulting film. Here, the crystallinity means that the melting point derived from the layer B is observed when the light selective reflection film is subjected to DSC measurement at a heating rate of 20 ° C./min.

The intrinsic viscosity (orthochlorophenol, measured at 35 ° C.) of the polyester (B) is preferably 0.40 to 1.0 dl / g, more preferably 0.45 to 0.95 dl / g. If the intrinsic viscosity is not within such a range, the difference from the intrinsic viscosity of the aromatic polyester constituting the layer A may become large. Even if it is possible, the film forming property may be lowered.
The layer B of the present invention may contain a small amount of other polymers and additives as long as the purpose of the present invention is not impaired, as in the above-mentioned layer A. For example, lubricants such as inert particles, pigments, dyes, etc. And additives such as colorants, stabilizers, flame retardants, foaming agents, and ultraviolet absorbers.

(Additive)
Various additives may be used in the light selective reflection film of the present invention within the scope of the object of the present invention. For example, in order to improve the winding property of the film, the average particle diameter is at least 0.1 in the outermost layer. 0.001 to 0.5% by weight of inactive particles of 01 to 2 μm may be contained based on the weight of the layer. When the average particle diameter of the inert particles is smaller than the lower limit value or the content is less than the lower limit value, the effect of improving the winding property of the film may not be sufficiently exhibited, while the inclusion of the inert particles When the amount exceeds the upper limit value or the average particle size exceeds the upper limit value, the optical properties of the film may be deteriorated.
The average particle diameter of the preferable inert particles is 0.02 to 1 μm, particularly preferably 0.1 to 0.3 μm. Moreover, content of a preferable inert particle is the range of 0.02-0.2 weight%.

Examples of the inert particles contained in the light selective reflection film of the present invention include inorganic inert particles such as silica, alumina, calcium carbonate, calcium phosphate, kaolin and talc, silicone, crosslinked polystyrene, and styrene-divinylbenzene copolymer. Organic inert particles such as The particle shape is not particularly limited as long as it is a generally used shape such as agglomerated or spherical.
In addition, as long as the objective of this invention is show | played, an inert particle may be contained other than outermost layer, for example, may be contained in the internal layer comprised with the same resin as the outermost layer.

<Light selective reflection film>
The light selective reflection film of the present invention is obtained by alternately laminating the above-described layer A and layer B, but the desired light reflectivity can be improved by setting the number of laminated layers to 161 layers or more. The number of stacked layers is preferably 231 layers or more, more preferably 275 layers or more. As the number of layers increases, selective reflection due to multiple interference increases and the reflectance can be increased. However, if the desired reflection characteristics are obtained, in order to increase productivity or obtain a thin film The number of stacked layers may be reduced, for example, 2001 layers or less, preferably 1001 layers or less.

(Each layer thickness)
The layer thickness of the layer A in the present invention needs to be in the range of 0.06 to 0.3 μm, and the layer thickness of the layer B needs to be in the range of 0.06 to 0.3 μm. is there.
Light ray selection that transmits blue light and reflects red light and green light by using the above-mentioned polyester for each of layer A and layer B, and making the thickness of each layer within the range of 0.06 to 0.3 μm A reflective film can be obtained. If a layer having a layer thickness less than the lower limit is present, the reflection wavelength is in the blue light region, and the blue light transmittance is reduced, so that it is difficult to obtain a light selective reflection film having a function of transmitting blue light. If a layer having a layer thickness exceeding the upper limit exists, even if the secondary peak (1/2 wavelength of the main reflection peak) is removed by adjusting the thickness ratio described below, the tertiary peak (1 of the main reflection peak) is removed. / 3) occurs in the blue light region, the blue light transmittance is impaired, and it becomes difficult to obtain a light selective reflection film having a function of transmitting blue light.

When the layer thicknesses of the layer A and the layer B are in the range of 0.06 to 0.3 μm, respectively, red light and green light can be selectively reflected by multiple interference due to the multilayer stack structure. The layer thicknesses of the layer A and the layer B are more preferably in the range of 0.07 to 0.2 μm.
The reflection wavelength of the light selective reflection film corresponds to twice the total optical thickness of the adjacent layers A and B. This optical thickness is represented by the product of the refractive index of each layer and the thickness of each layer.

In addition, Radford et al., “Reflectivity of Irradient Co-extracted Multilayered Plastic Films”, Polymer Engineering and Science, Vol. 13, no. 3, as in the May 1973 issue, a multilayer film using multilayer interference due to a quarter wavelength has a higher-order reflection peak in the visible light region even if the main reflection peak does not occur in the blue light region. In some cases, coloring due to higher-order reflection may be exhibited, and thus it is necessary to set an appropriate optical thickness for removing higher-order reflection.
In the light selective reflection film of the present invention, when the ratio of the optical thickness of the layer B to the optical thickness of the layer A is 1.0 for the adjacent layers A and B, the secondary ( It is possible to remove the ½ wavelength of the main reflection peak) and the fourth order (¼ wavelength of the main reflection peak).

In the case of the light selective reflection film of the present invention, the ratio of the thickness of the layer B to the thickness of the adjacent layer A (layer A / layer B, actual thickness ratio) is 0. By increasing the number of combinations in the range of 6 to 1.1, higher-order peaks generated in the blue light region can be reduced, and the blue light transmittance can be further increased.
This relationship only needs to hold for most of the layers of the laminated film, and is 70% or more, preferably 80% or more, more preferably 90% or more, particularly preferably 95% or more of the total number of layers in the laminated component. It only has to be established.

  Further, in the layer A and the layer B, the thickness of each layer improves the reflectance in the red light and green light regions, so that the ratio of the maximum thickness to the minimum thickness in the layer A is 1.2-2. 9 is preferably changed continuously. Further, the thickness of each layer of the layer B is also continuously changed from 1.2 to 2.9 at the maximum / minimum thickness ratio in order to improve the reflectance in the red light and green light regions. Is preferred.

  In addition to the layers A and B, the light selective reflection film of the present invention has a thick film layer exceeding 0.5 μm in the surface layer or intermediate layer of the laminated component (sometimes referred to as a light interference layer). Also good. By having a layer having such a thickness in a part of the alternately laminated structure of the layer A and the layer B, the layer thickness of the layer A and the layer B can be easily adjusted without affecting the reflection function. Such a thick film layer may have the same composition as either layer A or layer B, or a composition partially including these compositions, and does not contribute to reflection characteristics because the layer thickness is thick. When such a thick film layer is present on the surface layer, it may be referred to as a protective layer.

(Film thickness)
The film thickness of the light selective reflection film of the present invention is preferably 10 μm or more, more preferably 20 μm or more, and the upper limit is preferably 200 μm or less, more preferably 151 μm or less, in consideration of handleability and the like.

(Stretched film)
The light selective reflection film of the present invention is preferably a stretched film stretched in at least a uniaxial direction, and more preferably a biaxially stretched film stretched in a biaxial direction. By making the stretched film, the refractive index of the layer A in the stretching direction can be increased, the refractive index difference between the layers A and B can be further increased, and the number of layers can be reduced. The film thickness can be reduced while providing reflection characteristics.

(Coating layer)
In the light selective reflection film of the present invention, it is preferable to provide an easy-sliding coating layer on at least one surface of the film from the viewpoint of ensuring the slipperiness of the film.
Examples of the resin component constituting the coating layer include a polyester resin and an acrylic resin, and it is preferable to add a lubricant (filler, wax) in order to impart slipperiness.
Examples of the method for forming the coating layer include a method in which an aqueous coating liquid containing a composition constituting the coating layer is coated on the film at any stage of film formation.

<Optical characteristics>
The light selective reflection film of the present invention has optical characteristics of reflecting red light and green light and transmitting blue light. Here, the red light may include a wavelength in the near infrared region.
In the light selective reflection film of the present invention, the average reflectance in the range from red to green is preferably 70% or more, more preferably 80% or more, and further preferably 90% or more. By keeping the reflectance of both red light and green light high, blue light was used as a backlight, and it was used as a reflection film for a display that obtains an image by emitting red light and green light by excitation with a phosphor layer. In this case, the light emitted from the phosphor to the backlight side can be efficiently reflected and emitted to the outside of the display, so that the light utilization efficiency of the display can be increased.

Moreover, it is preferable that the average transmittance | permeability of the blue light of the light selective reflection film of this invention is 50% or more, More preferably, it is 60% or more, More preferably, it is 70% or more. If the transmittance of the blue light is less than the lower limit value, the backlight light is reflected, and a sufficient amount of light cannot be emitted outside the display, leading to a decrease in light use efficiency of the display.
The light selective reflection film of the present invention is thus provided with a high transmission characteristic and a high reflection characteristic selectively in a specific wavelength range, so that blue light is used as a backlight, and red light and green are excited by excitation with a phosphor layer. It can be suitably used as a reflective film for a display that uses light to emit an image, and the light utilization efficiency of the display can be increased.

<Thermal dimensional stability>
The light selective reflection film of the present invention has good thermal dimensional stability by using the polyester described above for the layer A and the layer B, and can reduce deformation of the film when the display is used.
Specifically, in the longitudinal direction (continuous film-forming direction, longitudinal direction, MD direction) and width direction (transverse direction, TD direction) of the light selective reflection film of the present invention may be 40. It is preferable that the thermal expansion coefficient in -100 degreeC is 26 ppm / degrees C or less, More preferably, it is 25 ppm / degrees C or less. In the case where the light selective reflection film of the present invention is stretched, such a thermal expansion coefficient can be easily achieved in this stretching direction.

<Film production method>
Below, the biaxially stretched film is demonstrated as an example about the method of manufacturing the light selective reflection film of this invention.
In order to obtain the light selective reflection film of the present invention, an aromatic polyester (resin for layer A) having ethylene-2,6-naphthalenedicarboxylate units as main repeating units and ethylene terephthalate units based on all repeating units. A copolymerized polyethylene terephthalate (resin for layer B) having a ratio of 50 to 95 mol% is extruded in a molten state and superimposed on a desired number of laminations, and a laminated unstretched film (step for forming a sheet-like material) To do. At this time, it is preferable to laminate | stack so that the film thickness of the layer A and the layer B may change to the thickness direction of a film stepwise or continuously about each.

The laminated unstretched film thus obtained is stretched in the film forming direction and in the width direction perpendicular thereto. The stretching temperature is preferably in the range of the glass transition temperature (Tg) to (Tg + 50) ° C. of the resin of the layer A. In this case, the draw ratio is preferably 2 to 6 times, more preferably 2.5 to 5 times, and still more preferably 3 to 5 times. The larger the draw ratio, the smaller the variation in the plane direction of the individual layers in layer A and layer B due to the thinning due to stretching, so that the light interference becomes uniform in the plane direction, and the stretching direction between layer A and layer B The difference in refractive index and the difference in refractive index in the film thickness direction are preferable. Moreover, since the orientation of the layer A and the layer B advances and a thermal expansion coefficient becomes low, so that a draw ratio is large, it is preferable.
As the stretching method at this time, known stretching methods such as heat stretching with a rod heater, roll heating stretching, and tenter stretching can be used. From the viewpoints of reducing scratches due to contact with the roll and stretching speed, tenter stretching is performed. preferable. Moreover, it is preferable to perform a heat setting process after extending | stretching.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention does not receive any limitation by this. In addition, each value in a present Example was calculated | required according to the following method.

(1) Melting point (Tm) and glass transition temperature (Tg) of resin and film constituting each layer
10 mg of a polymer sample or a film sample was sampled, and a melting point and a glass transition temperature (Tg) were measured at a rate of temperature increase of 20 ° C./min using DSC (TA Instruments, trade name: DSC2920).

(2) Thickness of each layer A film sample was cut into 2 mm in the film longitudinal direction and 2 cm in the width direction, fixed to an embedded capsule, and then embedded in an epoxy resin (Refotech Co., Ltd. Epomount). The embedded sample was cut perpendicularly to the film width direction with a microtome (“ULTRACUT” (registered trademark) UCT manufactured by Leica Microsystems) to form a thin film slice having a thickness of 5 nm. Using a transmission electron microscope (S-4300, manufactured by Hitachi High-Technologies Corporation), the film was observed and photographed at an acceleration voltage of 100 kV, and the thickness of each layer was measured from the photograph.
Further, the ratio of the maximum layer thickness to the minimum layer thickness in the layer A and the ratio of the maximum layer thickness to the minimum layer thickness in the layer B were determined based on the obtained thicknesses of the respective layers.
Moreover, based on the thickness of each obtained layer, the average layer thickness of layer A and the average layer thickness of layer B were determined, and the average layer thickness of layer B with respect to the average layer thickness of layer A was calculated.
In addition, when a thick film layer having a thickness of more than 0.5 μm was present in the outermost layer or the alternate lamination, they were excluded from the layer A and the layer B.

(3) Overall film thickness A film sample is sandwiched between spindle detectors (K107C manufactured by Anritsu Co., Ltd.), and 10 points of thickness are measured at different positions using a digital differential electronic micrometer (K351 manufactured by Anritsu Co., Ltd.) The average value was obtained and used as the film thickness.

(4) Optical characteristics (average reflectance of red light and green light)
An integrating sphere was attached to a spectrophotometer (Shimadzu Corporation UV-3101PC), and the reflectance when the BaSO ₄ white plate was 100% was measured over a wavelength range of 300 to 1300 nm. The measurement conditions were a scan speed of 200 nm / second, a slit width of 20 nm, and a sampling pitch of 2.0 nm. The reflectance was read from the obtained chart at intervals of 2 nm, and the average value was obtained in the range of 500 to 800 nm.

(5) Optical characteristics (average transmittance of blue light)
Using a spectrophotometer (manufactured by Shimadzu Corporation, MPC-3100), the relative spectral transmittance with respect to the barium sulfate integrating sphere at each wavelength was measured in the wavelength range of 300 nm to 1300 nm. The transmittance was read from the obtained chart at intervals of 2 nm, and the average value was obtained in the range of 400 to 490 nm.

(6) Thermal dimensional stability (thermal expansion coefficient)
The obtained film was cut into a width of 4 mm so that the film forming direction or the width direction of the film was the measurement direction, set in TMA3000 manufactured by Vacuum Riko, and the measurement was performed in an air atmosphere with a distance between chucks of 20 mm. . The film was heated from 30 ° C. to 170 ° C. at 5 ° C./min with a load of 49 mN per 50 μm of film thickness, held at 170 ° C. for 30 minutes, and then cooled to room temperature. Thereafter, the temperature was raised from 30 ° C. to 170 ° C. at 2 ° C./min, and the temperature expansion coefficient (αt: ppm / ° C.) was calculated from the following formula, which was defined as the coefficient of thermal expansion.
αt = {(L ₁₀₀ −L ₄₀ )} / (L × ΔT)} × 10 ⁶ +0.5
Here, L ₄₀ in the above formula is a sample length (mm) at 40 ° C., L ₁₀₀ is a sample length (mm) at 100 ° C., L is 20 mm (= distance between chucks), and ΔT is 60 ( = 100-40) ° C., 0.5 is the temperature expansion coefficient (ppm / ° C.) of quartz glass.

[Example 1]
For layer A, melting point 267 ° C., intrinsic viscosity (orthochlorophenol, measured at 35 ° C.) 0.62 dl / g polyethylene-2,6-naphthalenedicarboxylate (PEN), for layer B, melting point 224 ° C., intrinsic viscosity (Orthochlorophenol, measured at 35 ° C.) Using 0.65 dl / g of isophthalic acid component 12 mol% copolymerized polyethylene terephthalate (IA12PET), each was dried and then fed to the extruder. PEN was 300 ° C., IA12PET Is heated to 280 ° C. to a molten state, and after branching 90 layers of PEN for layer A and 91 layers of IA12PET for layer B, a multilayer feedblock device in which layers A and B are alternately stacked Use and laminate, keep the laminated state, and supply PEN from the third extruder, the total number of 181 layers of laminated state The protective layer was further laminated on both sides of the melt. At that time, the layer A and the layer B are formed so that the ratio of the maximum layer thickness to the minimum layer thickness of each layer continuously changes up to 1.7 times at the maximum / minimum, The film thickness ratio was adjusted to 0.9: 1. Moreover, the supply amount of the 3rd extruder was adjusted so that a protective layer might be 30% of the whole.
The laminated state was led to a die, cast on a casting drum, and an unstretched laminated film having a total of 181 layers (the above protective layers were not counted) in which layers A and B were alternately laminated was prepared. This unstretched laminated film is stretched 4.5 times in the film forming direction at a temperature of 130 ° C., further stretched 4.5 times in the width direction at a temperature of 135 ° C., and subjected to heat setting treatment at 235 ° C. for 30 seconds, A biaxially stretched laminated film (light selective reflection film) having a thickness of 29 μm was obtained. Table 2 shows the physical properties of the obtained film.

[Examples 2-3]
A biaxially stretched laminated film was obtained in the same manner as in Example 1 except that the number of laminated layers and the thicknesses of Layer A, Layer B and protective layer were changed as shown in Table 1. Table 2 shows the physical properties of the obtained film.

[Examples 4 to 5]
A biaxially stretched laminated film was obtained in the same manner as in Example 1 except that the stretching ratio was changed as shown in Table 1. Table 2 shows the physical properties of the obtained film.

[Examples 6 and 7]
A biaxially stretched laminated film was obtained in the same manner as in Example 2 except that the thicknesses of the layer A, the layer B, and the protective layer were changed as shown in Table 1. Table 2 shows the physical properties of the obtained film.

[Comparative Example 1]
A biaxially stretched laminated film was obtained in the same manner as in Example 2 except that polymethyl methacrylate (PMMA) was used as the resin for the layer B. Table 2 shows the physical properties of the obtained film.

[Comparative Example 2]
A biaxially stretched laminated film was obtained in the same manner as in Example 3 except that the thicknesses of Layer A and Layer B were changed as shown in Table 1. Table 2 shows the physical properties of the obtained film.

[Comparative Example 3]
A biaxially stretched laminated film was obtained in the same manner as in Example 2 except that the thicknesses of the protective layer, layer A, and layer B were changed as shown in Table 1. Table 2 shows the physical properties of the obtained film.

[Comparative Example 4]
A biaxially stretched laminated film was obtained in the same manner as in Example 1 except that the number of laminated layers and the thicknesses of Layer A, Layer B and protective layer were changed as shown in Table 1. Table 2 shows the physical properties of the obtained film.

  The light selective reflection film of the present invention has high reflection characteristics for red light and green light, and has a transmission characteristic for blue light, but has a smaller coefficient of thermal expansion than conventional ones. By installing in between, it can be used suitably for the use which improves light utilization efficiency.

Claims (4)

Layer A and layer B are alternately laminated, and the number of laminated layers is 161 or more films, and layer A is composed of an aromatic polyester mainly composed of ethylene-2,6-naphthalenedicarboxylate, The layer thickness is in the range of 0.06 to 0.3 μm, and the layer B is made of copolymer polyethylene terephthalate in which the ratio of ethylene terephthalate units is 50 to 95 mol% based on all repeating units, and the layer thickness is 0 In the range of 0.06 to 0.3 μm, the coefficient of thermal expansion of the film from 40 ° C. to 100 ° C. is 26 ppm / ° C. or less in both the length direction and the width direction of the film, A biaxially stretched light selective reflection film characterized in that the average reflectance of light is 70% or more and the average transmittance of blue light is 82 % or more.   2. The light selective reflection film according to claim 1, wherein the ratio of the maximum thickness and the minimum thickness (maximum / minimum) in each of layers A and B is 1.2 to 2.9. Layer A is ethylene-2,6-naphthalene dicarboxylate units all repeating units as a reference of an aromatic polyester, which accounts for more than 90 mol%, light selective reflection film according to claim 1 or 2. The light selective reflection film according to any one of claims 1 to 3 , which is used for a display.