JP6248724B2 - Laminated polyester film - Google Patents

Description

  The present invention requires the brightness of a light source for a reflective material such as an LED backlight member for a liquid crystal television, an LED backlight member for a personal computer, an LED light source member for a small monitor, or a reflective member for a lighting fixture. The present invention relates to a laminated polyester film that is suitably used as a substrate film.

  In recent years, many reflective films have been used for light source members such as televisions, personal computers, smartphones, lighting devices, and lighting signs. In particular, LED liquid crystal displays have been improved to light sources that are brighter than before, as screens have been increased in size and display brightness and so on. Therefore, although high performance of a reflective film is calculated | required, there exists a limit only by reflection by the bubble in a layer in the conventional laminated | multilayer film. In order to exceed this limit, a new technology for light enhancement performance is required, and this technology has been required. For example, the intensity of the light wavelength emitted from the LED light source used for the backlight of the liquid crystal display is 100, with the intensity of the blue light peak wavelength 450 nm being 100, and the yellow light in the broad wavelength region of 550 nm to 630 nm is about 40 in intensity. . This blue light and yellow light are mixed with the naked eye and appear as white light. In order to increase the light from the light source in the liquid crystal display device, a reflective film for a backlight member capable of particularly increasing the luminance of the yellow light wavelength from 500 nm to 550 nm is required, and the reflectance in the above wavelength band is particularly high. Reflective films have been required for backlight members. For example, in Patent Document 1, a mixture of an inorganic phosphor or an organic phosphor is applied to a white film or mixed in a layer, but when an organic phosphor is used, the content must be increased. Optical properties such as film color tone, whiteness, and chromaticity shift when used in a backlight are greatly inferior. In Patent Literature 2, Patent Literature 3, and Patent Literature 4, since the brightening agent is used, the reflection peak becomes 390 nm, and the light cannot be brightened at the yellow light wavelength, so the requirement cannot be satisfied. Under such circumstances, a laminated film excellent in luminance improvement is required for a film for a reflector.

JP 2011-6540 A JP 2009-86451 A JP 2007-230242 A JP 2007-30284 A

The present invention provides a laminated film that can be brightened when used for a backlight for liquid crystal display and illumination, and has little chromaticity shift, and a method for producing the film.

The laminated polyester film of the present invention has the following configuration. That is,
A laminated polyester film comprising a polyester resin, having a film configuration of A layer / B layer or A layer / B layer / A layer, wherein the B layer contains a cavity and contains a fluorescent colorant, the laminated polyester A laminated polyester film characterized in that the film satisfies all the following requirements (1) to (3).

(1) The B layer contains 10% by mass to 40% by mass of one or more selected from resins or inorganic particles incompatible with the polyester constituting the B layer, based on the mass of the B layer, and contains bubbles. (2) The B layer contains a fluorescent colorant having an absorption wavelength of greater than 350 nm and less than 550 nm and an emission wavelength band of greater than 390 nm and less than 620 nm, based on the mass of the B layer, from 0.1 μg / g to less than 1 μg / g (3) The A layer contains inorganic particles, and the content thereof is 0.01% by mass to 30% by mass based on the mass of the A layer.
It is.

  The laminated film of the present invention has the effect of increasing the light wavelength band of white light by adopting the above-described configuration. When used in a liquid crystal display, the LED backlight light is efficiently reflected and chromaticity deviation is small. The screen text and images can be easily seen even in daytime brightness. Alternatively, when used in a lighting fixture, it can be brightened even if power consumption is reduced.

It is the schematic sectional drawing of the liquid crystal screen incorporating the laminated | multilayer film, and the schematic of the brightness | luminance measuring method.

The present invention comprises a polyester resin, has a film configuration of A layer / B layer or A layer / B layer / A layer, and the B layer is a laminated polyester film containing cavities.
[polyester]
In the present invention, the polyester suitably used is preferably a polyester having a melting point of 250 ° C. or higher. Specifically, polyethylene terephthalate, polyethylene naphthalate, polymethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate Rate and so on. Particularly preferred is polyethylene terephthalate.
[A layer]
In the present invention, the A layer is a surface layer. In order to have the role of preventing light leakage to the back surface and the role of a support layer that stabilizes the film formation, the A layer needs to contain 0.01-30% by mass of inorganic particles in the polyester relative to the mass of the A layer. And has the role of scattering light. The light scattering property of the A layer can be adjusted mainly by controlling the surface roughness. As another method, for example, a method of adding particles having different refractive indexes to a polyester resin can be mentioned. Here, the kind of inorganic fine particles to be contained in the A layer is not particularly limited, but preferably has a Mohs hardness of 3.0 or more, for example, calcium carbonate, titanium dioxide, zinc oxide, silicon dioxide, zinc sulfide. , Barium sulfate, alumina, talc and the like. These inorganic particles can be used alone or in combination depending on the necessity of imparting surface functions such as glossiness adjustment, whiteness adjustment, and light resistance.

In this invention, content of the inorganic particle contained in A layer is 0.01 to 30 mass% with respect to A layer mass. If it is less than 0.01% by mass, the scattered light is insufficient and sufficient reflection performance cannot be obtained, and if it exceeds 30% by mass, the film-forming property is deteriorated.
[B layer]
The B layer is whitened by containing fine bubbles inside the film. Formation of fine bubbles can be achieved by dispersing a resin or inorganic particles incompatible with polyester in a film base material such as polyester, and stretching (for example, biaxial stretching).
In the present invention, the B layer needs to contain one or more selected from resins or inorganic particles that are incompatible with the polyester constituting the B layer. As a resin incompatible with polyester (hereinafter sometimes abbreviated as incompatible resin), it may be a homopolymer or a copolymer, such as polyethylene, polypropylene, polybutene, polymethylpentene, etc. A polyolefin resin, a cyclic polyolefin resin, a polystyrene resin, a polyacrylate resin, a polycarbonate resin, a polyacrylonitrile resin, a polyphenylene sulfide resin, a fluorine resin, or the like is preferably used. Two or more of these may be used in combination. In particular, a resin having a large difference in critical surface tension from polyester and being hardly deformed by heat treatment after stretching is preferable, and specifically, a polyolefin-based resin is preferable. Examples of the polyolefin resin include polyolefin resins such as polyethylene, polypropylene, polybutene, and polymethylpentene, cyclic polyolefin resins, and copolymers thereof. Among these, a copolymer of ethylene and bicycloalkene, which is a cyclic olefin copolymer, is particularly preferable. By containing the incompatible resin, bubbles having the incompatible resin as a core are produced at the time of stretching, and light reflection occurs at the bubble interface.

In the present invention, the incompatible resin to be contained in the B layer is dispersed in a matrix composed of a polyester resin with a number average particle size of 0.4 μm or more and 3.0 μm or less. It is preferable for obtaining film strength, and more preferably in the range of 0.5 μm or more and 1.5 μm or less. The number average particle size referred to here is a cross section of the film in the width direction (TD), and the B layer portion of the cross section is observed using a scanning electron microscope (FE-SEM) S-2100A manufactured by Hitachi, Ltd. It is the average value of the diameter when the area of 100 particles is calculated and converted into a perfect circle.
Examples of the inorganic particles include calcium carbonate, titanium dioxide, zinc oxide, zirconium oxide, zinc sulfide, basic lead carbonate (lead white), and barium sulfate. Among these, visible wavelengths of 400 to 700 nm are included. Calcium carbonate, barium sulfate, titanium dioxide, and the like, which absorb less in the light region, are preferable from the viewpoints of reflection characteristics, concealment properties, production costs, and the like. In the present invention, barium sulfate and titanium dioxide are the most preferable from the viewpoints of rollability of the film, long-term film-forming stability, and improved reflection characteristics. As the particle size of the inorganic particles, it is preferable to use particles having a number average particle size of 0.1 μm or more and 3.0 μm or less in order to realize excellent reflectivity and concealability.
The B layer contains 10% by mass to 40% by mass of one or more selected from the resins or inorganic particles incompatible with the polyester constituting the B layer, and has bubbles. is necessary. If it is less than 10% by mass, desired bubbles do not appear and high luminance cannot be obtained. On the other hand, when it exceeds 40 mass%, film forming property may deteriorate.
(Fluorescent colorant)
In the present invention, the content of the fluorescent colorant needs to be 0.1 μg / g or more and less than 1 μg / g based on the mass of the B layer. If the content of the fluorescent colorant is less than 0.1 μg / g, the fluorescent colorant emits less light and the effect of increasing the luminance does not appear. If it is less than 1 μg / g, the chromaticity difference in the backlight is particularly small, so that color correction on the liquid crystal display is not necessary.
For accurate color reproduction, it is preferable that the chromaticity difference Δx, Δy value in the backlight is within 3/1000. In order to achieve the above range, it is necessary that the content of the fluorescent colorant is 0.1 μg / g or more and less than 1 μg / g.

  In the present invention, the fluorescent colorant is a fluorescent dye that colors the polyester resin, and is different from the fluorescent whitening agent. It has a molecular structure that absorbs and excites directional light emitted from an LED light source, and has an absorption wavelength of 350 nm or more and less than 550 nm. Further, by adding to the B layer, the fluorescent colorant molecules are oriented along with the polyester molecules by stretching. Although the refraction difference is generated between the B layer and the A layer by the molecular structure with this plane orientation, when directional light is incident from the A layer, the inside of the B layer is reflected at the interface of the B layer while the light is reflected at the interface. Light diffuses in the surface direction. For example, when light enters from the film surface, the fluorescent colorant molecules in the B layer absorb the transmitted light, and the fluorescent colorant molecules emit light in all directions. At this time, since the interface of the B layer which is a fluorescent layer has a refractive index difference with respect to the outer layer, the fluorescence is totally reflected and light diffuses in the surface direction, so that high luminance can be obtained.

  The fluorescent colorant used in the B layer of the present invention has an absorption wavelength of 350 nm or more and less than 550 nm, more preferably an absorption wavelength of 360 nm or more and less than 540 nm, and more preferably an absorption wavelength of 370 nm or more and less than 530 nm. A fluorescent colorant having an absorption wavelength of less than 350 nm is not preferable for a liquid crystal display because the emission start wavelength is less than 390 nm, the emission color is shifted to blue-violet, and the luminance is lowered. A fluorescent colorant having an absorption wavelength of 550 nm or more is not preferable for a liquid crystal display because the emission wavelength peak is 620 nm, the emission color is shifted to red, and the luminance is lowered.

The emission wavelength is preferably 390 nm or more and less than 520 nm. When the emission wavelength is in this range, it is possible to obtain a reflective film with little coloration and high brightness when used in a liquid crystal display.

Fluorescent colorants used in the present invention are stilbene, distilbene, benzoxazole, styryl / oxazole, pyrene / oxazole, coumarin, imidazole, benzimidazole, pyrazoline, aminocoumarin, naphthalimide, perylene. It is preferable to contain one or more selected from the system compounds. Among these, perylene-based Lumogen (registered trademark) F Yellow 083 (manufactured by BASF), Lumogen (registered trademark) F Yellow 170 (manufactured by BASF), Lumogen because of its high durability and high effect of improving luminance. (Registered trademark) F Orange 240 (manufactured by BASF) or naphthalimide-based Lumogen (registered trademark) F Violet 570 (manufactured by BASF) can be used. Moreover, FX305 LemonYellow (manufactured by Sinloihi Co., Ltd.), FX305 LemonYellow (manufactured by Sinloihi Co., Ltd.), FX306 Orange Yellow (manufactured by Sinroihi Co., Ltd.), FM-12 Green (manufactured by Sinroihi Co., Ltd.), FM-14 Orange Sinloihi), FM-15 Lemon Yellow (Shinloihi), FM-16 Orange Yellow (Shinloihi), FM-25 Greenish Yellow (Sinroihi), FM-35 Yellow (Manufactured by Sinloihi), FM-105 Lemon Yellow (manufactured by Sinroihi), FA-005 Lemon Yellow (manufactured by Sinloihi), FM-006 Orange Yellow (Shinloi ( However, it is not particularly limited to these. If these fluorescent colorants are used, the luminance of the display can be efficiently increased by the laminated film by the light emission in the emission wavelength band described above.
[Total thickness]
In the present invention, the total thickness of the laminated polyester film is preferably from 50 μm to 500 μm, more preferably from 150 μm to 350 μm. The total thickness of the white polyester film is preferably 50 μm or more from the viewpoint of reflectivity. The upper limit is not particularly limited, but is preferably 500 μm or less, more preferably 350 μm or less from the viewpoint of reflectance, workability, and cost. If the thickness exceeds 500 μm, an increase in reflectivity cannot be expected even if the thickness is greater than this, and workability (handling properties) deteriorates due to the increase in mass when working as a single wafer for incorporation into a backlight.

[Production method]
Although the manufacturing method of the laminated | multilayer film of this invention is demonstrated, the additive which is not limited to this example (1) Polyester composition and the manufacturing method of the polyester composition containing a white particle (master pellet method)
Polyester, white particles, and a surface treatment agent are mixed, the mixture is put into an extruder, melt-kneaded and extruded, and pelletized to obtain master pellets.

Additive (2) A method for producing a polyester composition comprising a polyester composition and a fluorescent colorant (master pellet method)
Polyester and fluorescent colorant are mixed, and the mixture is put into an extruder, melt-kneaded and extruded, and pelletized to obtain master pellets.

Manufacturing method of three-layer laminated film (biaxial stretching method)
Using an extruder having an extruder A, an extruder B, and a T-die three-layer die, the raw materials are charged into the extruder A and the extruder B, melt-kneaded, and melt extrusion comprising A layer / B layer / A layer Create a sheet.

  Specifically, as a raw material for the A layer, a master pellet containing the additive (1) obtained by the above-described production method and polyester as necessary are mixed and dried to a temperature of 250 to 300 ° C. To an extruder A heated to

  Next, as a raw material for the B layer, a resin incompatible with polyester (for example, polymethylpentene), additive (2) and polyester are mixed, dried and heated to a temperature of 250 to 300 ° C. To the extruder B.

  Lamination is performed so that the polyester composition charged into the extruder A in the T-die three-layer die comes to both surface layers and the polyester composition thrown into the extruder B comes to the inner layer, and is melted in three layers. The extruded sheet is discharged.

The melted sheet is closely cooled and solidified by electrostatic force on a drum cooled to a drum surface temperature of 10 ° C. to 40 ° C., and the unstretched film is led to a roll group heated to 70 ° C. to 120 ° C. The film is longitudinally stretched 2.0 times to 5.0 times in the direction and cooled with a roll group of 20 ° C to 30 ° C. Subsequently, the film was stretched in a longitudinally heated atmosphere at 90 ° C. to 150 ° C. while holding both ends of the longitudinally stretched film with clips, and gradually stretched uniformly through heat fixation at 180 ° C. to 240 ° C. After cooling, after cooling to room temperature and winding, slitting is performed to obtain the laminated film of the present invention.
Moreover, the manufacturing method of a two-layer laminated film uses the extruder which has a T-die two-layer nozzle | cap | die, throws a raw material into the extruder A and the extruder B, melts and knead | mixes it, and melt-extrusion which consists of A layer / B layer A sheet is formed by the same method as the above-mentioned three-layer lamination per sheet to obtain the laminated film of the present invention.

[Measuring method]
(1) Film thickness / layer thickness The thickness of the film was measured according to JIS C2151-2006.
The film was cut using a microtome without crushing in the thickness direction to obtain a slice sample.
The cross section of the section sample was imaged at a magnification of 3000 times using a scanning electron microscope (FE-SEM) S-2100A manufactured by Hitachi, Ltd., and the thickness of each layer was measured and the thickness ratio was calculated.

(2) Apparent density The film was cut into a 100 × 100 mm square, and a thickness of 10 points was measured with a dial gauge (No. 2109-10, manufactured by Mitoyo Seisakusho) attached with a 10 mm diameter probe (No. 7002). Then, the average thickness d (μm) is calculated. Further, this film is weighed with a direct balance, and the weight w (g) is read up to a unit of 10 ⁻⁴ g. The value calculated by the following formula is the apparent density.
Apparent density = w / d × 100 (g / cm ³ ).

(3) Luminance (direct-type luminance) and chromaticity difference As shown in FIG. 1, the reflective film pasted in the backlight of 181BLM07 (manufactured by NEC Corporation) is changed to a reference sample or an evaluation sample and turned on. I let you. In this state, after waiting for 1 hour to stabilize the light source, the liquid crystal screen was photographed with a CCD camera (DXC-390 manufactured by SONY), and an image was captured using an eye scale manufactured by an image analyzer Eye System. Thereafter, the brightness level of the photographed image was controlled to 30,000 steps and automatically detected, and converted into brightness and chromaticity.
As a luminance and chromaticity evaluation, a reference sample of Toray Co., Ltd. # 250E6SL was used. The relative luminance of the film sample was obtained by the following formula, and this numerical value was evaluated as luminance.
Brightness (%) = (Brightness of film sample (%)) / (Brightness of reference sample (%)) × 100.
The luminance was evaluated according to the following criteria.
：: 103% or more ◯: 101% or more and less than 103% ×: less than 101% The above ◎ and ○ were regarded as acceptable.
The chromaticity difference was evaluated using the following formula.
Chromaticity difference Δx = (x value of film sample) − (x value of reference sample)
Chromaticity difference Δy = (y value of film sample) − (y value of reference sample)
A: Excellent 0.000 or more and less than 0.002 B: Good 0.002 or more and less than 0.003 X: Inferior The above A and B exceeding 0.003 were regarded as acceptable.
Here, the x value and the y value are indices representing coordinates in the chromaticity diagram (CIE 1931).

(4) Film-forming property Evaluation was performed by the number of occurrences of film breakage. Evaluation was performed based on the number of tears per day, and the determination was made according to the following criteria. In addition, (circle) and (triangle | delta) are pass.
○: Good (No tearing occurs (less than once / day))
Δ: Slightly inferior (breakage occurs occasionally (1 to 2 times / day))
X: Inferior (Many tears (twice / day or more)).

(5) The maximum absorption / emission wavelength spectroscopic color difference meter SE-2000 type (manufactured by Nippon Denshoku Industries Co., Ltd.) of the fluorescent colorant is used, and the reflection mode of the A layer side according to JIS Z-8722 (2000). The light reflectance was measured. The number of samples was set to n = 5, and each light reflectance was measured, and the average value was calculated. The sample measurement diameter is 30 mmφ. The method for measuring the light reflectance is shown below. The light reflectance on the surface on the A layer side is measured over 350 nm or more and 900 nm or less when the standard white plate made of aluminum oxide (Nippon Denshoku Industries Co., Ltd., part No. SE-11628) is 100%. The reflectance was read from the obtained reflectance chart at intervals of 5 nm, the arithmetic average value was calculated, and the reflectance was obtained. In addition, the emission wavelength was read from a reflectance chart in the wavelength range where the spectral reflectance was measured from the A layer side, and the peak value was 0.5% or more according to the emission wavelength specific to the fluorescent colorant. Sometimes it was determined that there was light emission, and the maximum value was taken as the maximum absorption wavelength. On the other hand, in the same manner as described above, when the peak value was lowered by 0.5% or more, it was determined that there was absorption, and the minimum value was taken as the maximum absorption wavelength.
In order to identify the absorption / emission wavelength specific to the fluorescent colorant used in the present invention, the absorption / emission wavelength of each fluorescent colorant can be determined by measuring the single absorption / emission wavelength with various fluorescent colorant samples in advance. The emission wavelength and the position of the visible light wave region are determined. Using this, the absorption / emission wavelength of the sample and the position of the visible light wavelength region are taken and collated and specified.
The absorption and emission wavelengths of the fluorescent colorant used in the present invention are as shown in Table 1.

  The present invention will be described based on examples.

[Example 1]
Polyethylene glycol having a molecular weight of 4000 and a color tone of polyethylene terephthalate after polymerization (measured by JIS K7105-1981, stimulus value direct reading method) of L value 62.8, b value 0.5, haze 0.2% Using terephthalate, 53 parts by mass of polyethylene terephthalate, 8 parts by mass of (PBT / PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (trade name: Hytrel manufactured by Toray DuPont), 1,4 to ethylene glycol -8 parts by mass of copolymerized polyethylene terephthalate (33 mol% CHDM copolymerized PET) in which 33 mol% of cyclohexanedimethanol is copolymerized, 10 parts by mass of poly (5-methyl) norbornene, 20 parts by mass of barium sulfate, fluorescent colorant master pellet ( Master Pele 1 part by weight of Lumogen FYello083: BASF Co., containing 10 μg / g) was adjusted and mixed, dried at 180 ° C. for 3 hours, and then supplied to Extruder B heated to 270 to 300 ° C. ( B layer). Meanwhile, 99 parts by mass of polyethylene terephthalate and 1 part by mass of silicon terephthalate master containing silicon dioxide particles having a number average particle size of 0.6 μm (containing 1% by mass of silicon dioxide based on the total amount of the master chip) were vacuum-dried at 180 ° C. for 3 hours. Thereafter, the polymer was supplied to an extruder A heated to 280 ° C. (A layer), and these polymers were laminated through a laminating apparatus so as to be A layer / B layer / A layer, and formed into a sheet form from a T die. Furthermore, the unstretched film obtained by cooling and solidifying the film with a cooling drum having a surface temperature of 25 ° C. was led to a roll group heated to 85 to 98 ° C., longitudinally stretched 3.6 times in the longitudinal direction, and cooled with a roll group at 21 ° C. . Subsequently, the film was stretched by 3.6 times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 120 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, the film was heat-set at 200 ° C. in a tenter, uniformly cooled, cooled to room temperature, and a biaxially stretched laminated film was obtained. Table 2 shows the physical properties of the light reflecting substrate.

[Examples 2 to 21]
A laminated film was obtained in the same manner as in Example 1, except that the raw material composition of the A layer and B layer, the thickness of the A layer, and the total film thickness were changed as described in Tables 2 and 3. In all examples, the relative luminance, chromaticity difference, and film formation stability were good.

[Comparative Example 1]
A film having a thickness of 225 μm was obtained in the same manner as in Example 1 except that the laminated structure and the raw material composition were changed as described in Table 4. The chromaticity differences Δx and Δy values were within 3/1000, but the relative luminance was insufficient at 100.9% because the concentration of the fluorescent colorant was low.

[Comparative Examples 2 and 3]
A film having a thickness of 225 μm was obtained in the same manner as in Example 1 except that the laminated structure and the raw material composition were changed as described in Table 4. Since the concentration of the fluorescent colorant was high, the relative luminance was high, but the chromaticity difference was insufficient.

[Comparative Example 4]
A film having a thickness of 225 μm was obtained in the same manner as in Example 1 except that the laminated structure and the raw material composition were changed as described in Table 4. Since no fluorescent colorant was added, the chromaticity differences Δx and Δy values were within 3/1000, but the relative luminance was insufficient.

[Comparative Example 5]
A film having a thickness of 225 μm was obtained in the same manner as in Example 1 except that the laminated structure and the raw material composition were changed as described in Table 4. The chromaticity differences Δx and Δy values were within 3/1000 and the relative luminance was high, but the content of inorganic particles in the B layer was high and the film formation stability was insufficient.

[Comparative Example 6]
A film having a thickness of 225 μm was obtained in the same manner as in Example 1 except that the laminated structure and the raw material composition were changed as described in Table 4. Since the optical brightener was added, the chromaticity differences Δx and Δy values were within 3/1000, but the relative luminance was insufficient.

[Comparative Example 7]
The same method as in Example 1 was carried out except that the laminated structure and the raw material composition were changed as shown in Table 4, but the content of the inorganic particles in the A layer was high and film formation was impossible.

[Comparative Example 8]
A film having a thickness of 150 μm was obtained in the same manner as in Example 1 except that the laminated structure and the raw material composition were changed as described in Table 4. The chromaticity differences Δx and Δy values were within 3/1000, but the content of inorganic particles in the A layer was low and the relative luminance was insufficient.

  The laminated film of the present invention is a backlight member for a liquid crystal television, a backlight member for a personal computer, a light source member for a small monitor, a reflection sheet for a lighting fixture, etc., for applications that require high reflectivity and high brightness. Can be used widely.

1; laminated film 2; cold cathode tube 3; milk white plate 4; diffuser plate 5; prism sheet 6; polarizing prism sheet 7; CCD camera 8;

Claims (4)

A laminated polyester film comprising a polyester resin, having a film configuration of A layer / B layer or A layer / B layer / A layer, wherein the B layer contains a cavity and contains a fluorescent colorant, the laminated polyester A laminated polyester film characterized in that the film satisfies all the following requirements (1) to (3).
(1) The B layer contains 10% by mass to 40% by mass of one or more selected from resins or inorganic particles incompatible with the polyester constituting the B layer, based on the mass of the B layer, and contains bubbles. (2) The B layer contains a fluorescent colorant having an absorption wavelength of greater than 350 nm and less than 550 nm and an emission wavelength band of greater than 390 nm and less than 620 nm, based on the mass of the B layer, from 0.1 μg / g to less than 1 μg / g (3) The A layer contains inorganic particles, and the content thereof is 0.01% by mass to 30% by mass based on the mass of the A layer.   The fluorescent colorant is a stilbene, distilbene, benzoxazole, styryl / oxazole, pyrene / oxazole, coumarin, imidazole, benzimidazole, pyrazoline, aminocoumarin, naphthalimide, or perylene compound. The laminated polyester film according to claim 1, comprising at least one selected from among them. The laminated polyester film according to claim 1 or 2, wherein the total thickness of the laminated polyester film is 50 µm or more and 500 µm or less. The backlight reflective film of a liquid crystal display device or a liquid crystal display device, a reflective plate film for blue cut, a back sheet of a lighting device, a back sheet for a display plate, a wallpaper film, or a wavelength conversion film. The laminated polyester film according to any one of the above.

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