WO2011118305A1 - White polyester film, light-reflective plate using the same, and liquid-crystal display backlight using the same - Google Patents

White polyester film, light-reflective plate using the same, and liquid-crystal display backlight using the same Download PDF

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Publication number
WO2011118305A1
WO2011118305A1 PCT/JP2011/053633 JP2011053633W WO2011118305A1 WO 2011118305 A1 WO2011118305 A1 WO 2011118305A1 JP 2011053633 W JP2011053633 W JP 2011053633W WO 2011118305 A1 WO2011118305 A1 WO 2011118305A1
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Prior art keywords
layer
polyester film
white polyester
light
film
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Application number
PCT/JP2011/053633
Other languages
French (fr)
Japanese (ja)
Inventor
舩冨剛志
長谷川正大
奥田昌寛
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東レ株式会社
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Application filed by 東レ株式会社 filed Critical 東レ株式会社
Priority to CN201180010943.7A priority Critical patent/CN102782532B/en
Priority to KR1020127022727A priority patent/KR101772015B1/en
Priority to JP2011522311A priority patent/JP5045851B2/en
Publication of WO2011118305A1 publication Critical patent/WO2011118305A1/en

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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/02—Diffusing elements; Afocal elements
    • G02B5/0205—Diffusing elements; Afocal elements characterised by the diffusing properties
    • G02B5/0236—Diffusing elements; Afocal elements characterised by the diffusing properties the diffusion taking place within the volume of the element
    • G02B5/0242—Diffusing elements; Afocal elements characterised by the diffusing properties the diffusion taking place within the volume of the element by means of dispersed particles
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/02—Diffusing elements; Afocal elements
    • G02B5/0273—Diffusing elements; Afocal elements characterized by the use
    • G02B5/0284—Diffusing elements; Afocal elements characterized by the use used in reflection
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/08—Mirrors
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033—Means for improving the coupling-out of light from the light guide
    • G02B6/005—Means for improving the coupling-out of light from the light guide provided by one optical element, or plurality thereof, placed on the light output side of the light guide
    • G02B6/0053—Prismatic sheet or layer; Brightness enhancement element, sheet or layer
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/0001—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems
    • G02B6/0011—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings specially adapted for lighting devices or systems the light guides being planar or of plate-like form
    • G02B6/0033—Means for improving the coupling-out of light from the light guide
    • G02B6/005—Means for improving the coupling-out of light from the light guide provided by one optical element, or plurality thereof, placed on the light output side of the light guide
    • G02B6/0055—Reflecting element, sheet or layer
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on liquid crystals, e.g. single liquid crystal display cells
    • G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
    • G02F1/1333—Constructional arrangements; Manufacturing methods
    • G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
    • G02F1/1336—Illuminating devices
    • G02F1/133602—Direct backlight
    • G02F1/133605—Direct backlight including specially adapted reflectors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/048—Encapsulation of modules
    • H01L31/049—Protective back sheets
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy

Definitions

  • the present invention relates to a white polyester film suitable for use as a light reflecting plate, a light reflecting plate using the same, and a backlight for a liquid crystal display.
  • a backlight method in which light is applied from the back of the display and a light reflecting plate are widely used because of a thin and uniform illumination.
  • a light reflector on the back of the screen, but this reflector is required to be thin and have high light reflectivity.
  • a white film or the like that is whitened by containing fine bubbles inside and reflecting light at the bubble interface is mainly used.
  • the light reflected by the reflector is diffused, and the light other than the light that has directivity directly is reflected by the prism, and is repeatedly reflected between the reflector and finally the liquid crystal cell with enhanced light directivity. Sent to. In this case, if the reflection efficiency of the reflector is low, or if there is a factor that causes light leakage or attenuation in the system, light loss will occur during repeated reflections and the energy efficiency will deteriorate, reducing the brightness of the screen. Or the economy is reduced.
  • Such a white polyester film is also used for a back sheet of a solar cell.
  • Patent Document 1 describes that a light reflecting plate is used as one member constituting a light source of a liquid crystal display.
  • Patent Document 2 describes that a white film whitened by containing fine bubbles inside the film and reflecting light at the bubble interface is used as the light reflecting plate.
  • Patent Documents 3 and 4 describe a white film in which an ultraviolet absorbing layer is laminated in order to prevent yellow discoloration of the film due to ultraviolet rays emitted from a cold cathode tube.
  • Patent Document 5 discloses a method of providing a light concealing layer on a film surface opposite to a light source in order to improve luminance in an edge light system.
  • Patent Document 6 discloses a method of controlling the light diffusibility by selecting the refractive index difference between the spherical particles and the binder and improving the front luminance by the light diffusion sheet.
  • Patent Document 7 discloses a method of improving luminance unevenness in a backlight by controlling the diffusibility of a film surface on the light source side in a reflection sheet in a direct type backlight.
  • Patent Document 1 The reflector described in Patent Document 1 was not sufficiently thin and highly reflective.
  • an ultraviolet absorbing layer is provided, or in a method in which the ultraviolet absorbing layer contains a trace amount of a fluorescent brightening agent, the absorbed ultraviolet energy is converted into heat, or the reflective film
  • the brightness of the screen is reduced because only a small amount of light that contributes to color adjustment is converted.
  • the reflectors described in Patent Documents 5 and 6 have a problem that the color change due to ultraviolet rays radiated from the cold cathode fluorescent lamp is large, and the use efficiency of light energy as a backlight is deteriorated and the luminance of the screen is lowered.
  • Patent Document 7 contains porous and hollow particles and particles with non-uniform shapes together with a small amount of fluorescent brightening agent, even with a small amount of light that contributes to color adjustment, depending on the contained particles There has been a problem that light is attenuated by refraction, reflection, scattering, and the like, and the luminance is not improved.
  • the white film In the reflection plate, it is necessary to prevent the white film from being deteriorated by the ultraviolet light (hereinafter referred to as UV) emitted from the lamp light source or with the white film while improving the reflection efficiency of the white film.
  • UV ultraviolet light
  • a conventionally known method for example, as disclosed in the aforementioned Patent Documents 3 and 4, a method of reducing the amount of ultraviolet rays reaching the polyester resin by thickly applying a layer containing a UV absorber to a white film was there.
  • the layer containing the UV absorber is processed by post-processing, there is a problem in economic efficiency and lead time.
  • the film used as the reflector is desirably thin from the viewpoints of miniaturization and weight reduction and processability.
  • the reflection efficiency is lowered, so that the leakage needs to be suppressed as much as possible.
  • the present invention eliminates the disadvantages of these conventional techniques, has high brightness, has little color change due to ultraviolet rays from the lamp or the sun, can prevent light leakage to the back surface, and further requires no post-processing, and is a white polyester film
  • the purpose is to provide.
  • an object of the present invention is a white polyester film having at least two layers of an A layer composed of polyester and a B layer composed of polyester, wherein the B layer has bubbles, and the A layer is rutile.
  • the total thickness of the white polyester film is 100 ⁇ m or more and 500 ⁇ m or less
  • the thickness of the A layer is 2 ⁇ m or more and 16 ⁇ m or less Is done.
  • the object of the present invention is achieved by a light reflector using the above white polyester film.
  • the object of the present invention is achieved by a backlight for a liquid crystal display in which the white polyester film is arranged with the layer A side facing the light source.
  • the A layer contains 2 to 6% by mass of the rutile-type titanium oxide with respect to the total mass of the A layer, and the barium sulfate to the total mass of the A layer.
  • the rutile titanium oxide preferably has a number average particle size of 0.1 ⁇ m or more and 1.0 ⁇ m or less.
  • the barium sulfate preferably has a number average particle diameter of 0.5 ⁇ m to 3.0 ⁇ m.
  • the number average particle diameter of the silicon dioxide is preferably 2.0 ⁇ m or more and 5.0 ⁇ m or less.
  • the layer B preferably contains a polymer incompatible with polyester, or a polymer incompatible with polyester and inorganic particles dispersed therein.
  • the white polyester film of the present invention is obtained by irradiating the layer A with ultraviolet rays under the conditions of illuminance: 100 mW / cm 2 , temperature: 60 ° C., relative humidity: 50% RH, and irradiation time: 48 hours. Yellowish change amount after UV irradiation: ⁇ b value is preferably less than 5.
  • a white polyester film that has high brightness, little color change due to ultraviolet rays from a lamp or the sun, can prevent light leakage to the back surface, and does not require post-processing.
  • the white polyester film of the present invention is suitably used for a large direct light type liquid crystal display used for televisions and the like, and a small sidelight type liquid crystal display used for notebook computers, mobile phones and the like. Moreover, it can be used as a back sheet for solar cells, and contributes to the efficiency of conversion from sunlight to electricity, and can impart resistance to ultraviolet rays from sunlight.
  • the white polyester film of the present invention is a white polyester film having at least a layer A composed of polyester and a layer B composed of polyester, wherein the layer B has bubbles, and the layer A is a rutile titanium oxide, Three types of inorganic particles of barium sulfate and silicon dioxide are contained, the total thickness of the white polyester film is 100 ⁇ m or more and 500 ⁇ m or less, and the thickness of the A layer is 2 ⁇ m or more and 16 ⁇ m or less.
  • the A layer is a layer in which inorganic particles are contained in polyester, and has a role of scattering the light and protecting the film from ultraviolet rays. It also has a role of preventing light leakage to the back surface and a role of a support layer for stabilizing the film formation.
  • the light scattering property of the A layer can be adjusted mainly by controlling the surface roughness.
  • a method of adding particles having different refractive indexes to a polyester resin can be mentioned.
  • the thickness of the A layer is 2 ⁇ m or more and 16 ⁇ m or less.
  • the B layer is a layer having bubbles. Therefore, if the thickness of the A layer is 2 ⁇ m or more and 16 ⁇ m or less, moderate irregularities are formed on the surface of the A layer due to the bubbles, The scattering property is extremely good.
  • inorganic particles having an ultraviolet absorbing ability and a light stabilizer are included, a film having good resistance to ultraviolet rays and high brightness can be obtained.
  • the A layer is disposed on the light source side, the A layer is gradually decomposed by the energy of ultraviolet rays.
  • a preferable range of the thickness of the A layer is 2 ⁇ m or more and 8 ⁇ m or less, and more preferably 2 ⁇ m or more and 6 ⁇ m or less.
  • the thickness of the A layer that is directed to the light source side at least at the outermost layer is 2 ⁇ m or more and 16 ⁇ m or less. Need to be. As described above, when the thickness of the A layer is less than 2 ⁇ m, the photolysis of the polyester has an adverse effect on the luminance, and the high luminance cannot be maintained. On the other hand, when the thickness of the A layer exceeds 16 ⁇ m, the loss of light energy in the A layer cannot be ignored, and the light does not sufficiently reach the voids in the B layer.
  • the total thickness of the white polyester film of the present invention is 100 ⁇ m or more and 500 ⁇ m or less. If the total thickness of the white polyester film is less than 100 ⁇ m, the reflectance is insufficient.
  • the upper limit is not particularly limited, but if the thickness exceeds 500 ⁇ m, no increase in reflectance can be expected even if the thickness is increased beyond this, and therefore the upper limit is usually 500 ⁇ m.
  • the surface of the layer A is arranged toward the light source side, so that UV resistance, reduction in luminance unevenness, high reflectance, scratches on the light guide plate, and suppression of occurrence of uneven contact screen are suppressed.
  • the layer structure may be a two-layer structure of A layer / B layer, a three-layer structure of A layer / B layer / A layer, or a structure of four or more layers, but it is easy on film formation. Considering this, a three-layer structure is preferable.
  • the resin constituting the A layer and the B layer is polyester.
  • polyethylene terephthalate and polyethylene naphthalate are preferable.
  • additives such as an antioxidant and an antistatic agent may be added to the polyester.
  • the B layer is whitened by containing fine bubbles inside the film.
  • the formation of fine bubbles is caused by finely dispersing a polymer incompatible with polyester or a polymer incompatible with polyester and inorganic particles in a film base material such as polyester and stretching it (for example, biaxially). This can be achieved by stretching.
  • the layer A contains rutile type titanium oxide.
  • rutile type titanium oxide When rutile type titanium oxide is used, there is less yellowing after irradiating the polyester film with light for a longer time than when anatase type titanium oxide is used, and the change in color difference can be suppressed.
  • this rutile-type titanium oxide is used after being treated with a fatty acid such as stearic acid or a derivative thereof, the dispersibility can be improved and the glossiness of the film can be further improved.
  • the number average particle diameter (diameter) of rutile type titanium oxide is preferably 0.1 ⁇ m or more and 1.0 ⁇ m or less. When the number average particle diameter of rutile type titanium oxide is within this range, aggregation is difficult to occur, uniform dispersibility is good, and light resistance is excellent, while film stretchability is also good, productivity is high, and light resistance is excellent. .
  • the addition amount of rutile type titanium oxide is preferably 2% by mass or more and 6% by mass or less with respect to the mass of the entire A layer.
  • the addition amount of rutile-type titanium oxide is within this range, the stretchability of the film is good, and even after the polyester film is irradiated with light for a long time, there is little yellowing and the change in color difference can be suppressed. Further, it is difficult to cause a reduction in reflection performance and luminance unevenness, and the screen luminance can be improved.
  • the white polyester film of the present invention is complementary because of reduced reflection performance and uneven brightness. It is necessary to combine barium sulfate. Thus, when barium sulfate is complementarily combined, a favorable reflectance can be obtained and luminance unevenness can be reduced. Since barium sulfate is incompatible with polyester, many fine bubbles can exist even in the A layer, and there is little yellowing after irradiating the polyester film with light for a long time, suppressing the change in color difference. it can.
  • the number average particle diameter (diameter) of barium sulfate is preferably 0.5 ⁇ m or more and 3.0 ⁇ m or less.
  • the addition amount of barium sulfate is preferably 16% by mass or more and 24% by mass or less with respect to the total mass of the A layer.
  • the reflectance does not decrease, the yellowing after irradiating the polyester film with light for a long time is small, and it is easy to suppress the change in color difference. The stretchability is not impaired and the productivity is good.
  • the white film surface that is, the surface of the layer A has a certain degree of roughness, and is easily available for the purpose of reducing the adhesion between the screen and the white film.
  • the number average particle diameter (diameter) of silicon dioxide is preferably 2.0 ⁇ m or more and 5.0 ⁇ m or less.
  • the direct reflection component does not increase excessively, and the difference in brightness (brightness unevenness) according to the interval between the illumination light sources hardly occurs, so that the brightness of the liquid crystal screen can be kept uniform.
  • particles that have become too coarse will not fall off, and the light guide plate will not be scratched.
  • the direct type since there is a cold cathode tube between the light guide plate and the reflection plate, the light guide plate and the reflection plate are not in direct contact with each other, and there is no worry about the occurrence of scratches on the light guide plate and uneven contact screen.
  • the content of silicon dioxide is preferably 0.5% by mass or more and 3% by mass or less with respect to the mass of the entire A layer.
  • the content of silicon dioxide is within this range, the surface roughness becomes too low and luminance unevenness does not occur, and the brightness of the liquid crystal screen can be made uniform.
  • the stretchability of the film is not impaired and the productivity is good.
  • the total content of the three types of inorganic particles of rutile titanium oxide, barium sulfate and silicon dioxide per 100% by mass of the A layer is preferably 10% by mass or more and 50% by mass or less. More preferably, they are 12 mass% or more and 40 mass% or less, More preferably, they are 15 mass% or more and 30 mass% or less. When the total content of the inorganic particles is within this range, necessary UV resistance and reflectance can be easily obtained, while cutting during film formation hardly occurs.
  • the white polyester film of the present invention has a configuration in which a plurality of A layers are present such as A layer / B layer / A layer
  • the content of the aforementioned rutile titanium oxide, barium sulfate, and silicon dioxide is preferable.
  • the preferable range and the preferred range of the number average particle diameter apply to the A layer directed to the light source side at least in the outermost layer.
  • the white polyester film of the present invention has a yellowness change amount ( ⁇ b value) after irradiation with ultraviolet rays on layer A for illuminance: 100 mW / cm 2 , temperature: 60 ° C., relative humidity: 50% RH, irradiation time: 48 hours. Preferably it is less than 5.
  • the ⁇ b value is more preferably less than 4 and even more preferably less than 3.
  • the lower limit is not particularly limited and is theoretically zero.
  • the white polyester film of the present invention can easily achieve the above ⁇ b value by using three kinds of inorganic particles of rutile type titanium oxide, barium sulfate and silicon dioxide in combination. Even so, it is useful in that the color change can be reduced. Moreover, there is almost no loss of luminance as a reflector.
  • Cyclic olefin as an incompatible polymer polyethylene glycol, polybutylene terephthalate and polytetramethylene glycol copolymer as a low specific gravity agent are mixed with polyethylene terephthalate, thoroughly mixed and dried, and a temperature of 270 to 300 ° C.
  • barium sulfate and silicon dioxide is supplied to the extruder A by a conventional method, and the polymer of the extruder B layer is formed on both surface layers in the T-die three-layer die. A three-layer structure of A layer / B layer / A layer was obtained.
  • the melted sheet is closely cooled and solidified by electrostatic force on a drum cooled to a drum surface temperature of 10 to 60 ° C., and the unstretched film is led to a group of rolls heated to 80 to 120 ° C. in the longitudinal direction.
  • the film is stretched 2.0 to 5.0 times in length and cooled with a roll group of 20 to 50 ° C. Subsequently, the film is stretched in the direction perpendicular to the longitudinal direction in an atmosphere heated to 90 to 140 ° C. while being guided to a tenter while holding both ends of the film that has been stretched with clips.
  • the stretching ratio is 2.5 to 4.5 times in the longitudinal and lateral directions, and the area ratio (longitudinal stretching ratio ⁇ lateral stretching ratio) is preferably 9 to 16 times.
  • the white polyester film of the present invention preferably has an average reflectance of 90% or more, more preferably 95% or more, and particularly preferably 97% or more at a wavelength of 400 to 700 nm as measured from the layer A surface.
  • the average reflectance is less than 90%, the luminance may be insufficient depending on the applied liquid crystal display.
  • the white polyester film of the present invention thus obtained can improve the luminance of the liquid crystal backlight, and since the reflectance does not decrease much even when used for a long time, the edge light and the direct type light for liquid crystal screens. It can be conveniently used as a reflector for a surface light source and a reflector.
  • the white polyester film for reflecting a liquid crystal display according to the present invention thus obtained has a high reflectance because fine bubbles are formed inside the film, and is used as a reflector for liquid crystal displays of side light type and direct light type. In this case, high brightness can be obtained.
  • the physical property value evaluation method and the effect evaluation method of the present invention are as follows. (1) Film thickness / layer thickness The film thickness was measured according to JIS C2151-2006.
  • the film was cut in the thickness direction using a microtome to obtain a section sample.
  • the section of the slice sample was imaged at a magnification of 3,000 times using a Hitachi Field Emission Scanning Electron Microscope (FE-SEM) S-800, and the thickness of each layer was measured and the thickness ratio was calculated by measuring the thickness of the laminate. .
  • FE-SEM Hitachi Field Emission Scanning Electron Microscope
  • An integrating sphere is attached to a spectrophotometer (U-3310) manufactured by Hitachi High-Technologies, and the reflectance when the standard white plate (aluminum oxide) is 100% is measured over a wavelength range of 400 to 700 nm. The reflectance was read from the obtained chart at intervals of 5 nm to obtain spectral reflectance.
  • the reflecting plate laminated in the backlight of 181BLM07 manufactured by NEC Corporation
  • the backlight is formed by stacking elements of the light reflecting white polyester film 1, the cold cathode tube 2, the milky white plate 3, the diffusion plate 4, the prism sheet 5, and the polarizing prism sheet 6 in order from the bottom to the top in FIG. Composed.
  • the liquid crystal screen was photographed with a CCD camera 7 (DXC-390 manufactured by SONY), and an image was captured with an eye scale 8 manufactured by an image analyzer Eye System. Thereafter, the luminance level of the photographed image was controlled to 30,000 steps and automatically detected, and converted into luminance to obtain the relative luminance value (%).
  • Relative luminance was determined by the following standard using # 250E6SL manufactured by Toray Industries, Inc. as a reference sample (100%).
  • luminance unevenness (%) was obtained by the following equation.
  • Unevenness of luminance (%) (maximum relative luminance value ⁇ minimum relative luminance value) / average relative luminance value ⁇ 100
  • the brightness unevenness was determined according to the following criteria using # 250E6SL manufactured by Toray Industries, Inc. as a reference sample (100%).
  • the number average diameter when each particle was converted to a perfect circle was calculated and used as the average particle diameter of the inorganic particles.
  • Yellowness (b value), ⁇ b value Using an SM color computer (manufactured by Suga Test Instruments Co., Ltd.), a b value representing yellowness was determined by a reflection measurement method using a C / 2 ° light source.
  • Light resistance (yellowishness change: ⁇ b value) Light resistance was evaluated by irradiating the sample with ultraviolet rays using an iSuper UV tester (model number: SUV-W131) manufactured by Iwasaki Electric Co., Ltd. and measuring the color tone b value before and after the irradiation.
  • the change in b value before and after UV irradiation was defined as ⁇ b. That is, as shown in the following equation, the ⁇ b value is the difference between the yellowness b 2 after UV irradiation and the initial yellowness b 1 .
  • ⁇ b value yellowness b 2 after UV irradiation ⁇ initial yellowness b 1
  • the ultraviolet irradiation conditions were as follows.
  • Illuminance 100 mW / cm 2 , temperature: 60 ° C., relative humidity: 50% RH, irradiation time: 48 hours
  • Light resistance was graded according to the following criteria.
  • the film can be stably formed for 24 hours or more.
  • the film can be stably formed for 12 hours or more and less than 24 hours.
  • the presence or absence of scratches was visually confirmed, and the light guide plate scratches were determined according to the following criteria.
  • Example 1 Polyethylene glycol having a molecular weight of 4,000 and having a color tone of polyethylene terephthalate after polymerization (JIS K7105-1981, measured by stimulus value direct reading method) of L value 62.8, b value 0.5, haze 0.2% Using terephthalate, 57 parts by mass of polyethylene terephthalate, 10 parts by mass of (PBT / PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (trade name: Hytrel manufactured by Toray DuPont Co., Ltd.), against ethylene glycol 10 parts by mass of copolymerized polyethylene terephthalate (33 mol% CHDM copolymerized PET) in which 33 mol% of 1,4-cyclohexanedimethanol was copolymerized and 23 parts by mass of poly (5-methyl) norbornene were prepared and mixed at 180 ° C. for 3 hours. After drying,
  • Extruder A heated to 280 ° C. (A layer).
  • a layer A layer
  • the unstretched film obtained by cooling and solidifying this 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 3.7 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.
  • Examples 2 to 30 A white polyester 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 Table 1.
  • Example 1 since the content of silicon dioxide was small, the luminance unevenness was slightly inferior, and since the content of rutile-type titanium oxide was small, the light resistance was slightly lower than the other examples. It was inferior. Although the content of barium sulfate was small, the luminance was at a level that could be used practically.
  • Example 2 since the contents of silicon dioxide and barium sulfate were larger, the film-forming stability was slightly inferior to those of the other examples, and the content of rutile titanium oxide was larger. was slightly inferior to the other examples.
  • Example 3 since the number average particle diameter of silicon dioxide was smaller, the luminance unevenness was slightly inferior to the other examples, and the number average particle diameter of rutile-type titanium oxide was smaller, so that the light resistance was high. It was slightly inferior to the other examples. Although the number average particle size of barium sulfate was smaller, the luminance was at a level that could be used practically.
  • Example 4 since the number average molecular weights of silicon dioxide and barium sulfate were larger, the film-forming stability was slightly inferior to the other examples, and the number average particle diameter of rutile titanium oxide was larger. Therefore, the light resistance was slightly inferior to the other examples.
  • Example 5 since the content of silicon dioxide was small, the luminance unevenness was slightly inferior to the other examples, and the content of rutile type titanium oxide was small, so that the light resistance was another example. Was slightly inferior to. Although the content of barium sulfate was small, the luminance was at a level that could be used practically.
  • Example 6 since the contents of silicon dioxide and barium sulfate were higher, the film-forming stability was slightly inferior to those of the other examples, and the content of rutile titanium oxide was higher. was slightly inferior to the other examples.
  • Example 7 since the number average particle diameter of silicon dioxide was smaller, the luminance unevenness was slightly inferior to the other examples, and the number average particle diameter of rutile-type titanium oxide was smaller, so that the light resistance was high. It was slightly inferior to the other examples. Although the number average particle size of barium sulfate was smaller, the luminance was at a level that could be used practically.
  • Example 8 since the number average molecular weights of silicon dioxide and barium sulfate were larger, the film forming stability was slightly inferior to those of the other examples. Although the number average particle size of rutile type titanium oxide was large, the light resistance was at a level that could be used practically.
  • Comparative Example 1 A film having a thickness of 188 ⁇ m 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 1. Although the film formation is stable and the relative reflectance is 104.2% and high luminance is obtained even in the relative luminance, the silicon dioxide is not added to the A layer. It was insufficient.
  • Example 2 A film having a thickness of 188 ⁇ m 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 1. Although the relative reflectance was 104.3% and a high value was obtained even in the relative luminance, the light resistance was insufficient because no rutile-type titanium oxide was added to the A layer.
  • Comparative Example 3 A film having a thickness of 188 ⁇ m 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 1.
  • Example 5 A film having a thickness of 188 ⁇ m 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 1. The film was stable, the relative reflectance was 103.8%, and a high luminance was obtained even with the relative luminance, but the luminance unevenness was insufficient because the A layer was thick.
  • Comparative Example 6 A film having a thickness of 250 ⁇ m 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 1. Although the relative reflectance was 102.0% and the relative luminance was also high, there was a scratch on the light guide plate because no silicon dioxide was added to the A layer, and no rutile titanium oxide was added.
  • Example 7 A film having a thickness of 225 ⁇ m 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 1. However, in order to obtain a two-layer lamination of A / B layers, lamination was performed with a feed block, and a sheet was extruded from a T-die to obtain a molten sheet. Although the film-forming stability was insufficient, the relative reflectance was 103.0%, and a high value was obtained even in the relative luminance, but there was a scratch on the light guide plate and the light resistance was insufficient.
  • Example 8 A film having a thickness of 225 ⁇ m 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 1. However, since the raw material was not supplied to the extruder A and the A layer was not formed, it became a single layer film of only the B layer. There was film-forming stability, the relative reflectance was 100.0%, there were scratches on the light guide plate, and the relative luminance, luminance unevenness and light resistance were insufficient.
  • PET Polyethylene terephthalate
  • PET / I / PEG ethylene glycol / terephthalic acid / isophthalic acid cocondensate (polyethylene terephthalate copolymer in which 5 mol% of polyethylene glycol having a molecular weight of 1,000 is copolymerized)
  • PET / CHDM polyethylene-1,4-cyclohexylenedimethylene terephthalate (polyethylene terephthalate copolymer obtained by copolymerizing 33 mol% of 1,4-cyclohexanedimethanol with respect to ethylene glycol)
  • PBT / PTMG Polyester ether elastomer mabutylene / poly (alkylene ether) phthalate (copolymer having 30 mol% of alkylene glycol with respect to butylene terephthalate) (trade name: Hytrel manufactured by Toray DuPont) It is.
  • the white polyester film of the present invention is suitably used for large direct-type light-type liquid crystal displays used for televisions and the like, and small sidelight-type liquid crystal displays used for notebook computers and mobile phones. Moreover, it can be used as a back sheet for solar cells, and contributes to the efficiency of conversion from sunlight to electricity, and can impart resistance to ultraviolet rays from sunlight.

Abstract

Provided is a white polyester film which has at least an A layer made of polyester and a B layer made of polyester, wherein the B layer has bubbles, the A layer contains three inorganic components of rutile titanium oxide, barium sulfate and silicon dioxide, the white polyester film has a total thickness of 100-500 μm, and the A layer has a thickness of 2-16 μm. A light-reflective white polyester film is provided which can obtain a high degree of brightness when used for a liquid-crystal display, and which is excellent in terms of UV resistance and is cheaper than in the past. Furthermore, the white polyester film provides excellent reflection performance and UV resistance when used as a back sheet for a solar cell.

Description

白色ポリエステルフィルム、それを用いた光反射板および液晶ディスプレイ用バックライトWhite polyester film, light reflector using the same, and backlight for liquid crystal display
　本発明は、光反射板としての使用に好適な白色ポリエステルフィルム、それを用いた光反射板および液晶ディスプレイ用バックライトに関する。 The present invention relates to a white polyester film suitable for use as a light reflecting plate, a light reflecting plate using the same, and a backlight for a liquid crystal display.
　液晶ディスプレイの光源として、従来、ディスプレイの背面からライトをあてるバックライト方式や、光反射板が、薄型で均一に照明できるメリットから広く用いられている。その際、照明光の画面背面への逃げを防ぐため、画面の背面に光反射板を設置する必要があるが、この反射板には薄さと光の高反射性が要求されることから、フィルム内部に微細な気泡を含有させ気泡界面で光を反射させることにより白色化された白色フィルムなどが主に用いられる。 As a light source of a liquid crystal display, conventionally, a backlight method in which light is applied from the back of the display and a light reflecting plate are widely used because of a thin and uniform illumination. At that time, in order to prevent the illumination light from escaping to the back of the screen, it is necessary to install a light reflector on the back of the screen, but this reflector is required to be thin and have high light reflectivity. A white film or the like that is whitened by containing fine bubbles inside and reflecting light at the bubble interface is mainly used.
　反射板で反射された光は拡散され、真上に指向性がある光以外はプリズムで反射され、反射板との間で反射を繰り返し、最終的に光の指向性を高めた状態で液晶セルに送られる。この場合、反射板の反射効率が低かったり、系内に光の漏れや減衰させる要因があったりすると、反射を繰り返すうちに光ロスが発生してエネルギー効率が悪くなるため画面の輝度が低下したり、また経済性が低下したりする。 The light reflected by the reflector is diffused, and the light other than the light that has directivity directly is reflected by the prism, and is repeatedly reflected between the reflector and finally the liquid crystal cell with enhanced light directivity. Sent to. In this case, if the reflection efficiency of the reflector is low, or if there is a factor that causes light leakage or attenuation in the system, light loss will occur during repeated reflections and the energy efficiency will deteriorate, reducing the brightness of the screen. Or the economy is reduced.
　さらに、冷陰極管から放射される紫外線によるフィルムの黄変色を防ぐために紫外線吸収層を積層した白色フィルムも提案されている。 Furthermore, in order to prevent yellow discoloration of the film due to ultraviolet rays radiated from the cold cathode tube, a white film having an ultraviolet absorbing layer laminated thereon has also been proposed.
　これら反射板において、輝度の諸特性を改善するための様々な方法が開示されている。 In these reflectors, various methods for improving various characteristics of luminance are disclosed.
　また、このような白色ポリエステルフィルムは太陽電池のバックシートにも利用されている。 Moreover, such a white polyester film is also used for a back sheet of a solar cell.
　特許文献１には液晶ディスプレイの光源を構成する一部材として光反射板を用いることが記載されている。 Patent Document 1 describes that a light reflecting plate is used as one member constituting a light source of a liquid crystal display.
　特許文献２にはフィルム内部に微細な気泡を含有させ気泡界面で光を反射させることにより白色化された白色フィルムを光反射板として用いることが記載されている。 Patent Document 2 describes that a white film whitened by containing fine bubbles inside the film and reflecting light at the bubble interface is used as the light reflecting plate.
　特許文献３、４には冷陰極管から放射される紫外線によるフィルムの黄変色を防ぐために紫外線吸収層を積層した白色フィルムが記載されている。 Patent Documents 3 and 4 describe a white film in which an ultraviolet absorbing layer is laminated in order to prevent yellow discoloration of the film due to ultraviolet rays emitted from a cold cathode tube.
　特許文献５にはエッジライト方式での輝度向上を図るために、光源と反対側のフィルム面に光隠蔽層を設ける方法が開示されている。 Patent Document 5 discloses a method of providing a light concealing layer on a film surface opposite to a light source in order to improve luminance in an edge light system.
　特許文献６には球状粒子とバインダーとの屈折率差を選択することにより、光拡散性を制御し、光拡散シートによる正面輝度を改善する方法が開示されている。 Patent Document 6 discloses a method of controlling the light diffusibility by selecting the refractive index difference between the spherical particles and the binder and improving the front luminance by the light diffusion sheet.
　特許文献７には直下型バックライトにおける反射シートにおいて、光源側のフィルム面の拡散性を制御することにより、バックライトでの輝度ムラを改善する方法が開示されている。
特開2003-160682号公報 特公平8-16175号公報 特開2001-166295号公報 特開2002-90515号公報 特開2002-333510号公報 特開2001-324608号公報 特開2005-173546号公報 Patent Document 7 discloses a method of improving luminance unevenness in a backlight by controlling the diffusibility of a film surface on the light source side in a reflection sheet in a direct type backlight.
Japanese Patent Laid-Open No. 2003-160682 Japanese Patent Publication No.8-16175 JP 2001-166295 A JP 2002-90515 A JP 2002-333510 A JP 2001-324608 JP 2005-173546 A
　特許文献１に記載の反射板は薄さと光の高反射性が十分ではなかった。 The reflector described in Patent Document 1 was not sufficiently thin and highly reflective.
　特許文献２に記載の反射板は反射効率が低かったり、系内に光の漏れや減衰させる要因があったため、反射を繰り返すうちに光ロスが発生してエネルギー効率が悪くなって画面の輝度が低下したり、また経済性が低下したりする問題があった。 Since the reflection plate described in Patent Document 2 has low reflection efficiency or causes light leakage or attenuation in the system, light loss occurs during repeated reflection, resulting in poor energy efficiency and screen brightness. There is a problem that the cost is lowered and the economic efficiency is lowered.
　特許文献３、４に記載の反射板は紫外線吸収層を設けたり、その紫外線吸収層中に微量の蛍光増白剤を含有する方法では、吸収した紫外線エネルギーは熱に
変換するか、反射フィルムの色目調整に寄与する少量の光量にしか変換されず画面の輝度が低下する問題があった。
特許文献５，６に記載の反射板は冷陰極管から放射される紫外線による色調変化が大きく、バックライトとしての光エネルギーの利用効率が悪くなって画面の輝度が低下する問題があった。
特許文献７に記載の反射板は微量の蛍光増白剤と共に多孔質や中空の粒子や形状が不均一な粒子を含有したものは、色目調整に寄与する少量の光量でさえ、含有した粒子によって屈折や反射や散乱等によって光が減衰し輝度が向上しないという問題があった。 In the reflectors described in Patent Documents 3 and 4, an ultraviolet absorbing layer is provided, or in a method in which the ultraviolet absorbing layer contains a trace amount of a fluorescent brightening agent, the absorbed ultraviolet energy is converted into heat, or the reflective film There is a problem that the brightness of the screen is reduced because only a small amount of light that contributes to color adjustment is converted.
The reflectors described in Patent Documents 5 and 6 have a problem that the color change due to ultraviolet rays radiated from the cold cathode fluorescent lamp is large, and the use efficiency of light energy as a backlight is deteriorated and the luminance of the screen is lowered.
The reflector described in Patent Document 7 contains porous and hollow particles and particles with non-uniform shapes together with a small amount of fluorescent brightening agent, even with a small amount of light that contributes to color adjustment, depending on the contained particles There has been a problem that light is attenuated by refraction, reflection, scattering, and the like, and the luminance is not improved.
　反射板においては白色フィルムの反射効率を高めたまま、ランプ光源から放出されるあるいは太陽光の紫外線（以下、ＵＶという）から白色フィルムの劣化を防ぐ必要がある。従来知られた方法としては、例えば前記の特許文献３，４に開示されるように、白色フィルムにＵＶ吸収剤を含有した層を厚く塗布して、ポリエステル樹脂に到達する紫外線量を低減する方法があった。しかし、ＵＶ吸収剤を含有した層を後加工で処理するため、経済性、リードタイムに問題があった。また、小型軽量化や加工性の観点から反射板として用いるフィルムは薄い方が望ましいが、入射した光が背面に漏洩すると反射効率が低下するため漏洩は極力抑える必要がある。 In the reflection plate, it is necessary to prevent the white film from being deteriorated by the ultraviolet light (hereinafter referred to as UV) emitted from the lamp light source or with the white film while improving the reflection efficiency of the white film. As a conventionally known method, for example, as disclosed in the aforementioned Patent Documents 3 and 4, a method of reducing the amount of ultraviolet rays reaching the polyester resin by thickly applying a layer containing a UV absorber to a white film was there. However, since the layer containing the UV absorber is processed by post-processing, there is a problem in economic efficiency and lead time. In addition, the film used as the reflector is desirably thin from the viewpoints of miniaturization and weight reduction and processability. However, if incident light leaks to the back surface, the reflection efficiency is lowered, so that the leakage needs to be suppressed as much as possible.
　本発明は、これら従来の技術の欠点を解消し、輝度が高く、ランプまたは太陽からの紫外線による色調変化が少なく、背面への光漏洩を防ぐことができ、さらに後加工が不要な白色ポリエステルフィルムを提供することを目的とする。 The present invention eliminates the disadvantages of these conventional techniques, has high brightness, has little color change due to ultraviolet rays from the lamp or the sun, can prevent light leakage to the back surface, and further requires no post-processing, and is a white polyester film The purpose is to provide.
　すなわち本発明の目的は、ポリエステルで構成されたＡ層とポリエステルで構成されたＢ層との少なくとも２層を有する白色ポリエステルフィルムであって、該Ｂ層は気泡を有し、該Ａ層はルチル型酸化チタン、硫酸バリウムおよび二酸化珪素の３種類の無機粒子を含有し、白色ポリエステルフィルムの全厚みが１００μｍ以上５００μｍ以下であり、該Ａ層の厚みが２μｍ以上１６μｍ以下である白色ポリエステルフィルムにより達成される。 That is, an object of the present invention is a white polyester film having at least two layers of an A layer composed of polyester and a B layer composed of polyester, wherein the B layer has bubbles, and the A layer is rutile. Achieved by a white polyester film containing three types of inorganic particles of type titanium oxide, barium sulfate and silicon dioxide, the total thickness of the white polyester film is 100 μm or more and 500 μm or less, and the thickness of the A layer is 2 μm or more and 16 μm or less Is done.
　また、本発明の目的は、上記白色ポリエステルフィルムを用いた光反射板により達成される。 Also, the object of the present invention is achieved by a light reflector using the above white polyester film.
　また、本発明の目的は、上記白色ポリエステルフィルムがそのＡ層面側を光源側に向けて配されている液晶ディスプレイ用バックライトにより達成される。 Also, the object of the present invention is achieved by a backlight for a liquid crystal display in which the white polyester film is arranged with the layer A side facing the light source.
　なお、本発明の白色ポリエステルフィルムは、前記Ａ層が、前記ルチル型酸化チタンを該Ａ層の全質量に対して２質量％以上６質量％以下、前記硫酸バリウムを該Ａ層の全質量に対して１６質量％以上２４質量％以下、前記二酸化珪素を該Ａ層の全質量に対して０．５質量％以上３質量％以下含有することが好ましい。 In the white polyester film of the present invention, the A layer contains 2 to 6% by mass of the rutile-type titanium oxide with respect to the total mass of the A layer, and the barium sulfate to the total mass of the A layer. On the other hand, it is preferable to contain 16 mass% or more and 24 mass% or less, and the said silicon dioxide contains 0.5 mass% or more and 3 mass% or less with respect to the total mass of this A layer.
　本発明の白色ポリエステルフィルムは、前記ルチル型酸化チタンの数平均粒径が０．１μｍ以上１．０μｍ以下であることが好ましい。 In the white polyester film of the present invention, the rutile titanium oxide preferably has a number average particle size of 0.1 μm or more and 1.0 μm or less.
　本発明の白色ポリエステルフィルムは、前記硫酸バリウムの数平均粒径が０．５μｍ以上３．０μｍ以下であることが好ましい。 In the white polyester film of the present invention, the barium sulfate preferably has a number average particle diameter of 0.5 μm to 3.0 μm.
　本発明の白色ポリエステルフィルムは、前記二酸化珪素の数平均粒径が２．０μｍ以上５．０μｍ以下であることが好ましい。 In the white polyester film of the present invention, the number average particle diameter of the silicon dioxide is preferably 2.0 μm or more and 5.0 μm or less.
　本発明の白色ポリエステルフィルムは、前記Ｂ層が、ポリエステルと非相溶なポリマーまたは、ポリエステルと非相溶なポリマーおよび無機粒子を分散して含有することが好ましい。 In the white polyester film of the present invention, the layer B preferably contains a polymer incompatible with polyester, or a polymer incompatible with polyester and inorganic particles dispersed therein.
　本発明の白色ポリエステルフィルムは、前記Ａ層に照度：１００ｍＷ／ｃｍ２、温度：６０℃、相対湿度：５０％ＲＨ、照射時間：４８時間の条件で紫外線を照射したときの、紫外線照射前と紫外線照射後とでの黄色味変化量：Δｂ値が５未満であることが好ましい。 The white polyester film of the present invention is obtained by irradiating the layer A with ultraviolet rays under the conditions of illuminance: 100 mW / cm 2 , temperature: 60 ° C., relative humidity: 50% RH, and irradiation time: 48 hours. Yellowish change amount after UV irradiation: Δb value is preferably less than 5.
　本発明によれば、輝度が高く、ランプまたは太陽からの紫外線による色調変化が少なく、背面への光漏洩を防ぐことができ、さらに後加工が不要な白色ポリエステルフィルムが提供される。本発明の白色ポリエステルフィルムは、テレビなどに使用される大型の直下型ライト方式の液晶ディスプレイや、ノートパソコンや携帯電話などに使用される小型のサイドライト方式の液晶ディスプレイに好適に使用される。また、太陽電池用のバックシートとしても使用でき、太陽光から電気へ変換する効率に寄与するほか太陽光からの紫外線についても耐性を付与することができる。 According to the present invention, there is provided a white polyester film that has high brightness, little color change due to ultraviolet rays from a lamp or the sun, can prevent light leakage to the back surface, and does not require post-processing. The white polyester film of the present invention is suitably used for a large direct light type liquid crystal display used for televisions and the like, and a small sidelight type liquid crystal display used for notebook computers, mobile phones and the like. Moreover, it can be used as a back sheet for solar cells, and contributes to the efficiency of conversion from sunlight to electricity, and can impart resistance to ultraviolet rays from sunlight.
本発明の白色ポリエステルフィルムを組み込んだ液晶画面の概略断面及び輝度測定法の概略を示した図である。It is the figure which showed the general | schematic cross section of the liquid crystal screen incorporating the white polyester film of this invention, and the outline of the brightness | luminance measuring method. 本発明の白色ポリエステルフィルムを組み込んだサイドライト方式の液晶画面を示す概略断面図である。It is a schematic sectional drawing which shows the liquid crystal screen of the sidelight system incorporating the white polyester film of this invention.
　本発明の白色ポリエステルフィルムは、ポリエステルで構成されたＡ層とポリエステルで構成されたＢ層とを少なくとも有する白色ポリエステルフィルムであって、Ｂ層が気泡を有し、Ａ層がルチル型酸化チタン、硫酸バリウムおよび二酸化珪素の３種類の無機粒子を含有し、該白色ポリエステルフィルムの全厚みが１００μｍ以上５００μｍ以下であり、かつ該Ａ層の厚みが２μｍ以上１６μｍ以下である。 The white polyester film of the present invention is a white polyester film having at least a layer A composed of polyester and a layer B composed of polyester, wherein the layer B has bubbles, and the layer A is a rutile titanium oxide, Three types of inorganic particles of barium sulfate and silicon dioxide are contained, the total thickness of the white polyester film is 100 μm or more and 500 μm or less, and the thickness of the A layer is 2 μm or more and 16 μm or less.
　Ａ層はポリエステルに無機粒子を含有させた層であり、光を散乱させる役割と共に紫外線からフィルムを保護する役割がある。また背面への光漏洩を防ぐ役割、製膜を安定化させる支持層の役割がある。 The A layer is a layer in which inorganic particles are contained in polyester, and has a role of scattering the light and protecting the film from ultraviolet rays. It also has a role of preventing light leakage to the back surface and a role of a support layer for stabilizing the film formation.
　Ａ層の光散乱性は主に表面粗さを制御することにより調整することができる。例えば、ポリエステル樹脂に屈折率の異なる粒子を添加する方法が挙げられる。 The light scattering property of the A layer can be adjusted mainly by controlling the surface roughness. For example, a method of adding particles having different refractive indexes to a polyester resin can be mentioned.
　本発明の白色ポリエステルフィルムにおいては、Ａ層の厚みは２μｍ以上１６μｍ以下である。本発明の白色ポリエステルフィルムはＢ層が気泡を有する層であるために、Ａ層の厚みが２μｍ以上１６μｍ以下であると気泡に起因してＡ層の表面に適度な凹凸が形成され、光の散乱性が極めて良好になる。加えて、紫外線吸収能を有する無機粒子や光安定剤を含んだときには紫外線への耐性も良好で、輝度の高いフィルムとすることができる。Ａ層を光源側に配置すると紫外線のエネルギーによってＡ層は徐々に分解を受ける。そのため、Ａ層の厚みが２μｍ未満であると、ポリエステルの光分解が輝度に対して悪影響を及ぼし、高い輝度を維持することができない。一方、Ａ層の厚みが１６μｍを超える場合は、Ａ層における光エネルギーのロスが無視できなく、Ｂ層のボイドへ光が十分に届かなくなる。またＢ層に届いた光もボイド界面で多重反射したのち効率的にフィルム外部に出射出来ないため、光路長が長くなり、ロスとなる。そのため、高い輝度を得ることができない。Ａ層の厚みの好ましい範囲は２μｍ以上８μｍ以下であり、更に好ましくは、２μｍ以上６μｍ以下である。 In the white polyester film of the present invention, the thickness of the A layer is 2 μm or more and 16 μm or less. In the white polyester film of the present invention, the B layer is a layer having bubbles. Therefore, if the thickness of the A layer is 2 μm or more and 16 μm or less, moderate irregularities are formed on the surface of the A layer due to the bubbles, The scattering property is extremely good. In addition, when inorganic particles having an ultraviolet absorbing ability and a light stabilizer are included, a film having good resistance to ultraviolet rays and high brightness can be obtained. When the A layer is disposed on the light source side, the A layer is gradually decomposed by the energy of ultraviolet rays. Therefore, if the thickness of the A layer is less than 2 μm, the photolysis of the polyester has an adverse effect on the luminance, and high luminance cannot be maintained. On the other hand, when the thickness of the A layer exceeds 16 μm, the loss of light energy in the A layer cannot be ignored, and the light does not sufficiently reach the voids in the B layer. Further, since the light reaching the B layer cannot be efficiently emitted outside the film after being multiple-reflected at the void interface, the optical path length becomes long and a loss occurs. Therefore, high brightness cannot be obtained. A preferable range of the thickness of the A layer is 2 μm or more and 8 μm or less, and more preferably 2 μm or more and 6 μm or less.
　なお、本発明の白色ポリエステルフィルムにおいて、Ａ層／Ｂ層／Ａ層のように複数のＡ層が存在する構成の場合、少なくとも最外層で光源側に向けられるＡ層の厚みが２μｍ以上１６μｍ以下である必要がある。上述のようにＡ層の厚みが２μｍ未満であると、ポリエステルの光分解が輝度に対して悪影響を及ぼし、高い輝度を維持することができない。一方、Ａ層の厚みが１６μｍを超える場合は、Ａ層における光エネルギーのロスが無視できなく、Ｂ層のボイドへ光が十分に届かなくなる。 In the white polyester film of the present invention, when a plurality of A layers are present such as A layer / B layer / A layer, the thickness of the A layer that is directed to the light source side at least at the outermost layer is 2 μm or more and 16 μm or less. Need to be. As described above, when the thickness of the A layer is less than 2 μm, the photolysis of the polyester has an adverse effect on the luminance, and the high luminance cannot be maintained. On the other hand, when the thickness of the A layer exceeds 16 μm, the loss of light energy in the A layer cannot be ignored, and the light does not sufficiently reach the voids in the B layer.
　本発明の白色ポリエステルフィルムの全厚みは１００μｍ以上５００μｍ以下である。白色ポリエステルフィルムの全厚みが１００μｍ未満であると反射率が不足する。また、上限は特に制限する必要はないが、５００μｍを超えるとこれ以上厚くしても反射率の上昇が望めないので、上限としては通常５００μｍである。 The total thickness of the white polyester film of the present invention is 100 μm or more and 500 μm or less. If the total thickness of the white polyester film is less than 100 μm, the reflectance is insufficient. The upper limit is not particularly limited, but if the thickness exceeds 500 μm, no increase in reflectance can be expected even if the thickness is increased beyond this, and therefore the upper limit is usually 500 μm.
　本発明の白色ポリエステルフィルムは、Ａ層表面が光源側に向けて配されていることで、耐ＵＶ性、輝度ムラの低減、高反射率、導光板のキズおよび密着画面ムラの発生の抑制を得ることができる。層構成は、Ａ層／Ｂ層の２層構成であってもよく、Ａ層／Ｂ層／Ａ層の３層構成、あるいは４層以上の構成であってもよいが、製膜上の容易さを考慮すると３層構成が好ましい。 In the white polyester film of the present invention, the surface of the layer A is arranged toward the light source side, so that UV resistance, reduction in luminance unevenness, high reflectance, scratches on the light guide plate, and suppression of occurrence of uneven contact screen are suppressed. Obtainable. The layer structure may be a two-layer structure of A layer / B layer, a three-layer structure of A layer / B layer / A layer, or a structure of four or more layers, but it is easy on film formation. Considering this, a three-layer structure is preferable.
　本発明においてＡ層およびＢ層を構成する樹脂はポリエステルである。特に、ポリエチレンテレフタレート、ポリエチレンナフタレートが好ましい。 In the present invention, the resin constituting the A layer and the B layer is polyester. In particular, polyethylene terephthalate and polyethylene naphthalate are preferable.
　また、このポリエステルの中には、公知の各種添加剤、例えば、酸化防止剤、帯電防止剤などが添加されていても良い。 In addition, various known additives such as an antioxidant and an antistatic agent may be added to the polyester.
　Ｂ層はフィルム内部に微細な気泡を含有することによって白色化されている。微細な気泡の形成は、フィルム母材、たとえばポリエステル中に、ポリエステルと非相溶なポリマーまたは、ポリエステルと非相溶なポリマーおよび無機粒子を細かく分散して含有させ、それを延伸（たとえば二軸延伸）することにより達成できる。 The B layer is whitened by containing fine bubbles inside the film. The formation of fine bubbles is caused by finely dispersing a polymer incompatible with polyester or a polymer incompatible with polyester and inorganic particles in a film base material such as polyester and stretching it (for example, biaxially). This can be achieved by stretching.
　Ａ層にはルチル型酸化チタンを含有させる。ルチル型酸化チタンを用いると、アナターゼ型酸化チタンを用いた場合よりも、光線を長時間ポリエステルフィルムに照射した後の黄変が少なく、色差の変化を抑制することができる。このルチル型酸化チタンは、ステアリン酸等の脂肪酸およびその誘導体等を用いて処理して用いると、分散性を向上させることができ、フィルムの光沢度を一層向上させることができる。 The layer A contains rutile type titanium oxide. When rutile type titanium oxide is used, there is less yellowing after irradiating the polyester film with light for a longer time than when anatase type titanium oxide is used, and the change in color difference can be suppressed. When this rutile-type titanium oxide is used after being treated with a fatty acid such as stearic acid or a derivative thereof, the dispersibility can be improved and the glossiness of the film can be further improved.
　ルチル型酸化チタンの数平均粒径（直径）は０．１μｍ以上１．０μｍ以下が好ましい。ルチル型酸化チタンの数平均粒径がこの範囲であると、凝集が生じ難く均一分散性良好で、耐光性に優れる一方、フィルムの延伸性も良好で、生産性が高く、また耐光性に優れる。ルチル型酸化チタンの添加量は、Ａ層全体の質量に対し２質量％以上６質量％以下が好ましい。ルチル型酸化チタンの添加量がこの範囲であると、フィルムの延伸性も良好で、光線を長時間ポリエステルフィルムに照射した後においても黄変が少なく、色差の変化を抑制することができる。また、反射性能の低下や輝度ムラも生じにくく、画面輝度を向上することができる。 The number average particle diameter (diameter) of rutile type titanium oxide is preferably 0.1 μm or more and 1.0 μm or less. When the number average particle diameter of rutile type titanium oxide is within this range, aggregation is difficult to occur, uniform dispersibility is good, and light resistance is excellent, while film stretchability is also good, productivity is high, and light resistance is excellent. . The addition amount of rutile type titanium oxide is preferably 2% by mass or more and 6% by mass or less with respect to the mass of the entire A layer. When the addition amount of rutile-type titanium oxide is within this range, the stretchability of the film is good, and even after the polyester film is irradiated with light for a long time, there is little yellowing and the change in color difference can be suppressed. Further, it is difficult to cause a reduction in reflection performance and luminance unevenness, and the screen luminance can be improved.
　耐光性付与のためルチル型酸化チタン単独で用いる場合、添加量を多くすることで耐ＵＶ性は向上するが、反射性能の低下、輝度ムラが生じるため本発明の白色ポリエステルフィルムにおいては補完的に硫酸バリウムを組み合わせることが必要である。このように補完的に硫酸バリウムを組み合わせると、良好な反射率が得られ、輝度ムラを低減できる。硫酸バリウムはポリエステルと非相溶であるため、Ａ層でも微細な気泡を多数存在させることが出来、光線を長時間ポリエステルフィルムに照射した後の黄変が少なく、色差の変化を抑制することができる。 When using rutile-type titanium oxide alone to provide light resistance, UV resistance is improved by increasing the amount of addition, but the white polyester film of the present invention is complementary because of reduced reflection performance and uneven brightness. It is necessary to combine barium sulfate. Thus, when barium sulfate is complementarily combined, a favorable reflectance can be obtained and luminance unevenness can be reduced. Since barium sulfate is incompatible with polyester, many fine bubbles can exist even in the A layer, and there is little yellowing after irradiating the polyester film with light for a long time, suppressing the change in color difference. it can.
　ここで、硫酸バリウムの数平均粒径（直径）は０．５μｍ以上３．０μｍ以下が好ましい。数平均粒径をこの範囲とすると凝集が生じ難く粒子が粗大化し難いため、均一分散性が良好で、耐光性に優れる一方、フィルムの延伸性が損なわれず、生産性が良好である。硫酸バリウムの添加量は、Ａ層の全質量に対し１６質量％以上２４質量％以下が好ましい。硫酸バリウムの添加量がこの範囲であると、反射率が低下せず、光線を長時間ポリエステルフィルムに照射した後の黄変が少なく、色差の変化を抑制することが容易である一方、フィルムの延伸性が損なわれず、生産性が良好である。 Here, the number average particle diameter (diameter) of barium sulfate is preferably 0.5 μm or more and 3.0 μm or less. When the number average particle size is in this range, aggregation is difficult to occur and the particles are difficult to coarsen, so that uniform dispersibility is good and light resistance is excellent, while film stretchability is not impaired and productivity is good. The addition amount of barium sulfate is preferably 16% by mass or more and 24% by mass or less with respect to the total mass of the A layer. When the addition amount of barium sulfate is within this range, the reflectance does not decrease, the yellowing after irradiating the polyester film with light for a long time is small, and it is easy to suppress the change in color difference. The stretchability is not impaired and the productivity is good.
　上記のとおり、ルチル型酸化チタンおよび硫酸バリウムを併用することで、Ａ層に微細な気泡を多数存在させることが出来、耐ＵＶ性が向上するため、ルチル型酸化チタン単独で用いるよりもその添加量を低減させることが出来る。その結果、耐光性、輝度ムラの低減、および高反射率を両立できる飛躍的な効果が生まれる。 As described above, by using rutile titanium oxide and barium sulfate in combination, many fine bubbles can be present in the A layer, and UV resistance is improved. The amount can be reduced. As a result, a dramatic effect capable of achieving both light resistance, reduction in luminance unevenness, and high reflectance is produced.
　エッジライト方式では白色フィルムの平面性が高すぎるとフィルムと導光板が強く密着する箇所ができてしまい、そこで光の反射角度が変わることにより液晶画面内輝度にムラが発生してしまうことがある。そこで本発明においては、このエッジライト方式にも対応すべく、白色フィルム表面、つまりＡ層の表面にある程度の粗さを持たせ、画面と白色フィルムの密着性を低下させる目的で入手の容易さから二酸化珪素を添加する。二酸化珪素の数平均粒径（直径）は２．０μｍ以上５．０μｍ以下が好ましい。二酸化珪素の数平均粒径がこの範囲であると、表面の粗さが低くなり過ぎてフィルムと導光板の密着性が高くなってしまうことがなく、また、液晶画面上に照明光源の光を直接反射する成分が増え過ぎず、照明光源の間隔に応じた明暗の差（輝度ムラ）が発生し難いため、液晶画面の明るさを均一に保つことができる。一方、粒子が粗大化し過ぎた粒子が脱落することはなく、導光板にキズをつけることもない。なお、直下型方式では導光板と反射板の間に冷陰極管があるため、導光板と反射板が直接接することがなく導光板のキズ及び密着画面ムラの発生の心配はない。 In the edge light method, if the flatness of the white film is too high, a portion where the film and the light guide plate are in close contact with each other is formed, and the brightness of the liquid crystal screen may be uneven by changing the light reflection angle there. . Therefore, in the present invention, in order to cope with this edge light system, the white film surface, that is, the surface of the layer A has a certain degree of roughness, and is easily available for the purpose of reducing the adhesion between the screen and the white film. Add silicon dioxide. The number average particle diameter (diameter) of silicon dioxide is preferably 2.0 μm or more and 5.0 μm or less. If the number average particle diameter of silicon dioxide is within this range, the surface roughness will not be too low, and the adhesion between the film and the light guide plate will not be increased. The direct reflection component does not increase excessively, and the difference in brightness (brightness unevenness) according to the interval between the illumination light sources hardly occurs, so that the brightness of the liquid crystal screen can be kept uniform. On the other hand, particles that have become too coarse will not fall off, and the light guide plate will not be scratched. In the direct type, since there is a cold cathode tube between the light guide plate and the reflection plate, the light guide plate and the reflection plate are not in direct contact with each other, and there is no worry about the occurrence of scratches on the light guide plate and uneven contact screen.
　また、本発明の白色フィルムにおいて、二酸化珪素の含有量は、Ａ層全体の質量に対し０．５質量％以上３質量％以下が好ましい。二酸化珪素の含有量がこの範囲であると、表面の粗さが低くなり過ぎて輝度ムラが発生することはなく、液晶画面の明るさを均一にできる。一方、フィルムの延伸性が損なわれず、生産性が良好である。 In the white film of the present invention, the content of silicon dioxide is preferably 0.5% by mass or more and 3% by mass or less with respect to the mass of the entire A layer. When the content of silicon dioxide is within this range, the surface roughness becomes too low and luminance unevenness does not occur, and the brightness of the liquid crystal screen can be made uniform. On the other hand, the stretchability of the film is not impaired and the productivity is good.
　Ａ層の質量１００質量％あたりの、ルチル型酸化チタン、硫酸バリウムおよび二酸化珪素の３種類の無機粒子の合計含有量は、好ましくは１０質量％以上５０質量％以下である。より好ましくは１２質量％以上４０質量％以下、さらに好ましくは１５質量％以上３０質量％以下である。無機粒子の合計含有量がこの範囲であると必要な耐ＵＶ性や反射率が容易に得られる一方、製膜時の切断が発生し難い。 The total content of the three types of inorganic particles of rutile titanium oxide, barium sulfate and silicon dioxide per 100% by mass of the A layer is preferably 10% by mass or more and 50% by mass or less. More preferably, they are 12 mass% or more and 40 mass% or less, More preferably, they are 15 mass% or more and 30 mass% or less. When the total content of the inorganic particles is within this range, necessary UV resistance and reflectance can be easily obtained, while cutting during film formation hardly occurs.
　ルチル型酸化チタン、硫酸バリウムおよび二酸化珪素の３種類の無機粒子を併用することにより、耐ＵＶ性、輝度ムラの低減、高反射率、導光板のキズ及び密着画面ムラの発生の抑制を同時に満たすことができる。 Combined use of three types of inorganic particles of rutile titanium oxide, barium sulfate and silicon dioxide satisfy simultaneously UV resistance, reduction of luminance unevenness, high reflectivity, light guide plate scratches, and suppression of unevenness of contact screen. be able to.
　なお、本発明の白色ポリエステルフィルムが、Ａ層／Ｂ層／Ａ層のように複数のＡ層が存在する構成の場合、前述のルチル型酸化チタン、硫酸バリウム、二酸化珪素についての含有量の好ましい範囲や数平均粒子径の好ましい範囲は、少なくとも最外層で光源側に向けられるＡ層についてあてはまる。 In addition, when the white polyester film of the present invention has a configuration in which a plurality of A layers are present such as A layer / B layer / A layer, the content of the aforementioned rutile titanium oxide, barium sulfate, and silicon dioxide is preferable. The preferable range and the preferred range of the number average particle diameter apply to the A layer directed to the light source side at least in the outermost layer.
　本発明の白色ポリエステルフィルムは、Ａ層に照度：１００ｍＷ／ｃｍ２、温度：６０℃、相対湿度：５０％ＲＨ、照射時間：４８時間で紫外線照射した後の黄色み変化量（Δｂ値）が５未満であることが好ましい。Δｂ値はより好ましく４未満であり、さらに好ましくは３未満である。下限は特に限定されるものではなく、理論的にはゼロである。本発明の白色ポリエステルフィルムはルチル型酸化チタン、硫酸バリウムおよび二酸化珪素の３種類の無機粒子を併用することで上記Δｂ値を容易に達成できるので、バックライト光源や太陽光の照射を長時間受けたとしても色変化を少なくできる点で有用である。また、反射板として輝度を損なうことがほとんど無い。 The white polyester film of the present invention has a yellowness change amount (Δb value) after irradiation with ultraviolet rays on layer A for illuminance: 100 mW / cm 2 , temperature: 60 ° C., relative humidity: 50% RH, irradiation time: 48 hours. Preferably it is less than 5. The Δb value is more preferably less than 4 and even more preferably less than 3. The lower limit is not particularly limited and is theoretically zero. The white polyester film of the present invention can easily achieve the above Δb value by using three kinds of inorganic particles of rutile type titanium oxide, barium sulfate and silicon dioxide in combination. Even so, it is useful in that the color change can be reduced. Moreover, there is almost no loss of luminance as a reflector.
　次に、本発明の白色ポリエステルフィルムの製造方法について説明するが、この例に限定されるものではない。 Next, although the manufacturing method of the white polyester film of this invention is demonstrated, it is not limited to this example.
　非相溶ポリマーとして環状オレフィンを、低比重化剤としてポリエチレングリコール、ポリブチレンテレフタレートとポリテトラメチレングリコール共重合物を、ポリエチレンテレフタレートに混合し、それを充分混合・乾燥させて２７０～３００℃の温度に加熱された押出機Ｂに供給する。ルチル型酸化チタン、硫酸バリウムおよび二酸化珪素の３種類の無機粒子を含んだポリエチレンテレフタレートを常法により押出機Ａに供給して、Ｔダイ３層口金内で押出機Ｂ層のポリマーが両表層にくるようＡ層／Ｂ層／Ａ層なる３層構成を得た。 Cyclic olefin as an incompatible polymer, polyethylene glycol, polybutylene terephthalate and polytetramethylene glycol copolymer as a low specific gravity agent are mixed with polyethylene terephthalate, thoroughly mixed and dried, and a temperature of 270 to 300 ° C. To the extruder B heated to Polyethylene terephthalate containing three kinds of inorganic particles of rutile type titanium oxide, barium sulfate and silicon dioxide is supplied to the extruder A by a conventional method, and the polymer of the extruder B layer is formed on both surface layers in the T-die three-layer die. A three-layer structure of A layer / B layer / A layer was obtained.
　この溶融されたシートを、ドラム表面温度１０～６０℃に冷却されたドラム上で静電気力にて密着冷却固化し、該未延伸フィルムを８０～１２０℃に加熱したロール群に導き、長手方向に２．０～５．０倍縦延伸し、２０～５０℃のロール群で冷却する。続いて、縦延伸したフィルムの両端をクリップで把持しながらテンターに導き９０～１４０℃に加熱された雰囲気中で長手に垂直な方向に横延伸する。延伸倍率は、縦、横それぞれ２．５～４．５倍に延伸するが、その面積倍率（縦延伸倍率×横延伸倍率）は９～１６倍であることが好ましい。面積倍率が９倍未満であると得られるフィルムの白さが不良となり、逆に１６倍を越えると延伸時に破れを生じやすくなり製膜性が不良となる傾向がある。こうして二軸延伸されたフィルムの平面性、寸法安定性を付与するために、テンター内で１５０～２３０℃の熱固定を行い、均一に徐冷後、室温まで冷却して巻き取り本発明の白色ポリエステルフィルムを得る。 The melted sheet is closely cooled and solidified by electrostatic force on a drum cooled to a drum surface temperature of 10 to 60 ° C., and the unstretched film is led to a group of rolls heated to 80 to 120 ° C. in the longitudinal direction. The film is stretched 2.0 to 5.0 times in length and cooled with a roll group of 20 to 50 ° C. Subsequently, the film is stretched in the direction perpendicular to the longitudinal direction in an atmosphere heated to 90 to 140 ° C. while being guided to a tenter while holding both ends of the film that has been stretched with clips. The stretching ratio is 2.5 to 4.5 times in the longitudinal and lateral directions, and the area ratio (longitudinal stretching ratio × lateral stretching ratio) is preferably 9 to 16 times. If the area magnification is less than 9 times, the whiteness of the resulting film becomes poor. Conversely, if it exceeds 16 times, the film tends to be broken during stretching and the film forming property tends to be poor. In order to give the flatness and dimensional stability of the biaxially stretched film in this manner, heat setting at 150 to 230 ° C. is performed in a tenter, uniformly cooled, cooled to room temperature, and wound up. A polyester film is obtained.
　本発明の白色ポリエステルフィルムは、Ａ層面から測定した４００～７００nmの波長における平均反射率が９０％以上であることが好ましく、より好ましくは９５％以上、特に好ましくは９７％以上である。平均反射率が９０％未満の場合には、適用する液晶ディスプレイによっては輝度が不足する場合がある。 The white polyester film of the present invention preferably has an average reflectance of 90% or more, more preferably 95% or more, and particularly preferably 97% or more at a wavelength of 400 to 700 nm as measured from the layer A surface. When the average reflectance is less than 90%, the luminance may be insufficient depending on the applied liquid crystal display.
　このようにして得られる本発明の白色ポリエステルフィルムは、液晶バックライトの輝度向上を図ることができ、長時間使用しても反射率の低下が少ないので、液晶画面用のエッジライトおよび直下型ライトの面光源の反射板、およびリフレクターとして好都合に使用することができる。かくして得られた本発明の液晶ディスプレイ反射用白色ポリエステルフィルムは、フィルム内部に微細な気泡が形成され高反射率が達成されており、サイドライトタイプ及び直下型ライトタイプの液晶ディスプレイの反射板として使用された場合に高い輝度を得ることができる。
〔物性の測定ならびに効果の評価方法〕
　本発明の物性値の評価方法ならびに効果の評価方法は次の通りである。
（１）フィルム厚み・層厚み
　フィルムの厚みは、JIS C2151-2006に準じて測定した。 The white polyester film of the present invention thus obtained can improve the luminance of the liquid crystal backlight, and since the reflectance does not decrease much even when used for a long time, the edge light and the direct type light for liquid crystal screens. It can be conveniently used as a reflector for a surface light source and a reflector. The white polyester film for reflecting a liquid crystal display according to the present invention thus obtained has a high reflectance because fine bubbles are formed inside the film, and is used as a reflector for liquid crystal displays of side light type and direct light type. In this case, high brightness can be obtained.
[Measurement of physical properties and evaluation method of effects]
The physical property value evaluation method and the effect evaluation method of the present invention are as follows.
(1) Film thickness / layer thickness The film thickness was measured according to JIS C2151-2006.
　フィルムをミクロトームを用いて厚み方向に切断し、切片サンプルを得た。
該切片サンプルの断面を日立製作所製電界放射型走査電子顕微鏡（FE-SEM）S-800を用いて、3,000倍の倍率で撮像し、撮像から積層厚みを採寸し各層厚みと厚み比を算出した。
（２）相対平均反射率
　日立ハイテクノロジーズ製分光光度計（U―3310）に積分球を取り付け、標準白色板（酸化アルミニウム）を１００％とした時の反射率を波長４００～７００nmにわたって測定する。得られたチャートより５nm間隔で反射率を読み取り、分光反射率とした。
（３）見かけ比重
　フィルムを１００×１００mm角に切取り、ダイアルゲージを取り付けたものにて１０点の厚みを測定し、厚みの平均値ｄ（μｍ）を計算する。また、このフィルムを直示天秤にて秤量し、重さｗ（ｇ）を１０－４ｇの単位まで読み取る。このとき、見かけ比重を次式により求めた。 The film was cut in the thickness direction using a microtome to obtain a section sample.
The section of the slice sample was imaged at a magnification of 3,000 times using a Hitachi Field Emission Scanning Electron Microscope (FE-SEM) S-800, and the thickness of each layer was measured and the thickness ratio was calculated by measuring the thickness of the laminate. .
(2) Relative average reflectance An integrating sphere is attached to a spectrophotometer (U-3310) manufactured by Hitachi High-Technologies, and the reflectance when the standard white plate (aluminum oxide) is 100% is measured over a wavelength range of 400 to 700 nm. The reflectance was read from the obtained chart at intervals of 5 nm to obtain spectral reflectance.
(3) Apparent specific gravity A film is cut into a 100 × 100 mm square, 10 points of thickness are measured with a dial gauge attached, and an average thickness d (μm) is calculated. Further, this film is weighed with a direct balance, and the weight w (g) is read to a unit of 10 −4 g. At this time, the apparent specific gravity was determined by the following equation.
　　　見かけ比重＝ｗ／ｄ×１００
（４）相対輝度および輝度ムラ（直下型方式輝度）
　図１に示したように181BLM07（ＮＥＣ（株）製）のバックライト内に張り合わせてある反射板を所定の光反射用白色ポリエステルフィルム１のサンプルに変更し、点灯させた。ここで、バックライトは、図１において下から上の順に、光反射用白色ポリエステルフィルム１、冷陰極管２、乳白板３、拡散板４、プリズムシート５、偏光プリズムシート６の要素を積み重ねて構成される。点灯状態で１時間待機して光源を安定化させた後、液晶画面部をＣＣＤカメラ７（ＳＯＮＹ製DXC-390）にて撮影し、画像解析装置アイシステム製アイスケール８で画像を取り込んだ。その後、撮影した画像の輝度レベルを３万ステップに制御し自動検出させ、輝度に変換して相対輝度の値（％）を求めた。 Apparent specific gravity = w / d × 100
(4) Relative luminance and luminance unevenness (direct type luminance)
As shown in FIG. 1, the reflecting plate laminated in the backlight of 181BLM07 (manufactured by NEC Corporation) was changed to a predetermined sample of white polyester film 1 for light reflection and turned on. Here, the backlight is formed by stacking elements of the light reflecting white polyester film 1, the cold cathode tube 2, the milky white plate 3, the diffusion plate 4, the prism sheet 5, and the polarizing prism sheet 6 in order from the bottom to the top in FIG. Composed. After waiting for 1 hour in the lighting state to stabilize the light source, the liquid crystal screen was photographed with a CCD camera 7 (DXC-390 manufactured by SONY), and an image was captured with an eye scale 8 manufactured by an image analyzer Eye System. Thereafter, the luminance level of the photographed image was controlled to 30,000 steps and automatically detected, and converted into luminance to obtain the relative luminance value (%).
　相対輝度は、東レ株式会社製#250E6SLを基準サンプル（１００％）とし、次の基準で級判定した。 Relative luminance was determined by the following standard using # 250E6SL manufactured by Toray Industries, Inc. as a reference sample (100%).
　Ａ：１０２％以上
　Ｂ：１０１％以上１０２％未満
　Ｃ：１００％以上１０１％未満
　Ｆ：１００％未満。 A: 102% or more B: 101% or more and less than 102% C: 100% or more and less than 101% F: Less than 100%.
　また、輝度ムラ（％）は次式により求めた。 Also, luminance unevenness (%) was obtained by the following equation.
　　　輝度ムラ（％）＝（相対輝度最大値－相対輝度最小値）／相対輝度平均値×１００
　輝度ムラは、東レ株式会社製#250E6SLを基準サンプル（１００％）とし、次の基準で級判定した。 Unevenness of luminance (%) = (maximum relative luminance value−minimum relative luminance value) / average relative luminance value × 100
The brightness unevenness was determined according to the following criteria using # 250E6SL manufactured by Toray Industries, Inc. as a reference sample (100%).
　Ａ：８０％未満
　Ｂ：８０％以上９０％未満
　Ｃ：９０％以上１００％未満
　Ｆ：１００％以上。
（５）フィルム中の無機粒子の平均粒径（直径）
　透過型電子顕微鏡HU-12型（（株）日立製作所製）を用い、Ａ層およびＢ層の断面を10,0000倍に拡大観察した断面写真から求めた。すなわち、断面写真の粒子部分を粒子形状に沿ってマーキングして、その粒子部分をハイビジョン画像解析処理装置PIAS-IV（（株）ピアス製）を用いて画像処理を行い、測定視野内の計１００個の粒子を真円に換算した時の数平均径を算出し、無機粒子の平均粒径とした。
（６）黄色味（ｂ値）、Δｂ値
　ＳＭカラーコンピューター（スガ試験機（株）製）を用い、Ｃ／２°光源による反射測定法により、黄色味を表すｂ値を求めた。
（７）耐光性（黄色味変化：Δｂ値）
　岩崎電気（株）製アイスーパーＵＶテスター（型番：SUV-W131）を用いてサンプルに紫外線を照射し、照射前後の色調ｂ値を測定することで、耐光性の評価を行った。紫外線照射前後のｂ値の変化をΔｂとした。すなわち、Δｂ値は、次式に示すとおり、ＵＶ照射後の黄色味ｂ2と初期の黄色味ｂ１との差をいう。 A: Less than 80% B: 80% or more and less than 90% C: 90% or more and less than 100% F: 100% or more.
(5) Average particle diameter (diameter) of inorganic particles in the film
Using a transmission electron microscope HU-12 type (manufactured by Hitachi, Ltd.), it was determined from a cross-sectional photograph obtained by observing the cross sections of the A layer and the B layer at a magnification of 10,0000. That is, the particle portion of the cross-sectional photograph is marked along the particle shape, and the particle portion is subjected to image processing using a high-definition image analysis processing device PIAS-IV (manufactured by Pierce Co., Ltd.). The number average diameter when each particle was converted to a perfect circle was calculated and used as the average particle diameter of the inorganic particles.
(6) Yellowness (b value), Δb value Using an SM color computer (manufactured by Suga Test Instruments Co., Ltd.), a b value representing yellowness was determined by a reflection measurement method using a C / 2 ° light source.
(7) Light resistance (yellowishness change: Δb value)
Light resistance was evaluated by irradiating the sample with ultraviolet rays using an iSuper UV tester (model number: SUV-W131) manufactured by Iwasaki Electric Co., Ltd. and measuring the color tone b value before and after the irradiation. The change in b value before and after UV irradiation was defined as Δb. That is, as shown in the following equation, the Δb value is the difference between the yellowness b 2 after UV irradiation and the initial yellowness b 1 .
　　　Δｂ値＝ＵＶ照射後の黄色味ｂ2－初期の黄色味ｂ１
　ここで、紫外線照射条件を次のとおりとした。 Δb value = yellowness b 2 after UV irradiation−initial yellowness b 1
Here, the ultraviolet irradiation conditions were as follows.
　照度：１００ｍＷ／ｃｍ２、温度：６０℃、相対湿度：５０％ＲＨ、照射時間：４８時間
　耐光性を下記基準により級判定した。 Illuminance: 100 mW / cm 2 , temperature: 60 ° C., relative humidity: 50% RH, irradiation time: 48 hours Light resistance was graded according to the following criteria.
　Ａ：黄色味変化量Δｂ値が３未満
　Ｂ：黄色味変化量Δｂ値が３以上４未満
　Ｃ：黄色味変化量Δｂ値が４以上５未満
　Ｆ：黄色味変化量Δｂ値が５以上
（８）製膜安定性
　安定に製膜できるか否かの程度を次の基準により級判定した。 A: Yellowish change Δb value is less than 3 B: Yellowish change Δb value is 3 or more and less than 4 C: Yellowish change Δb value is 4 or more and less than 5 F: Yellowish change Δb value is 5 or more (8 ) Film formation stability The grade of whether or not the film can be stably formed was determined according to the following criteria.
　Ａ：２４時間以上安定に製膜できる。 A: The film can be stably formed for 24 hours or more.
　Ｂ：１２時間以上２４時間未満安定に製膜できる。 B: The film can be stably formed for 12 hours or more and less than 24 hours.
　Ｆ：１２時間以内に破断が発生し、安定な製膜ができない。
（９）導光板キズ（サイドライト方式）
　図２に示したようなソニー（株）製ＶＡＩＯ（ＶＧＮ－Ｓ５２Ｂ／Ｓ）のバックライト内に張り合わせてある反射板を所定の光反射用白色ポリエステルフィルム１０のサンプルに変更し、導光板１３に接触させた後、光反射用白色ポリエステルフィルムを外して、導光板の表面を観察した。ここで、バックライトは、図２において下から上の順に、冷陰極管９、光反射用白色ポリエステルフィルム１０、導光板１１、プリズムシート１２の要素を積み重ねて構成される。 F: Breakage occurs within 12 hours, and stable film formation cannot be performed.
(9) Light guide plate scratches (side light method)
The reflective plate attached in the backlight of Sony Corporation VAIO (VGN-S52B / S) as shown in FIG. 2 is changed to a sample of a predetermined white polyester film 10 for light reflection. After making contact, the white polyester film for light reflection was removed, and the surface of the light guide plate was observed. Here, the backlight is configured by stacking elements of a cold cathode tube 9, a light reflecting white polyester film 10, a light guide plate 11, and a prism sheet 12 in order from the bottom to the top in FIG.
　キズの有無を目視にて確認し、導光板キズを次の基準により級判定した。 The presence or absence of scratches was visually confirmed, and the light guide plate scratches were determined according to the following criteria.
　Ａ：キズがないもの
　Ｂ：少々のキズはあるが実用可能レベル
　Ｆ：キズがあり実用不可能レベル A: No scratches B: Slight scratches but practical level F: Scratches practical level
　本発明を実施例に基づいて説明する。
［実施例１］
　分子量4,000のポリエチレングリコールを使用し、重合後のポリエチレンテレフタレートの色調（JIS K7105-1981、刺激値直読方法で測定）がＬ値６２．８、ｂ値０．５、ヘイズ０．２％であるポリエチレンテレフタレートを使用し、ポリエチレンテレフタレート５７質量部、ポリブチレンテレフタレートとポリテトラメチレングリコールの（ＰＢＴ／ＰＴＭＧ）共重合物を１０質量部（商品名：東レ・デュポン（株）製ハイトレル）、エチレングリコールに対し１，４－シクロヘキサンジメタノールが３３mol％共重合された共重合ポリエチレンテレフタレート（３３mol％ＣＨＤＭ共重合ＰＥＴ）１０質量部、ポリ（５－メチル）ノルボルネン２３質量部を調整混合し、１８０℃で３時間乾燥させた後、２７０～３００℃に加熱された押出機Ｂに供給（Ｂ層）した。 The present invention will be described based on examples.
[Example 1]
Polyethylene glycol having a molecular weight of 4,000 and having a color tone of polyethylene terephthalate after polymerization (JIS K7105-1981, measured by stimulus value direct reading method) of L value 62.8, b value 0.5, haze 0.2% Using terephthalate, 57 parts by mass of polyethylene terephthalate, 10 parts by mass of (PBT / PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (trade name: Hytrel manufactured by Toray DuPont Co., Ltd.), against ethylene glycol 10 parts by mass of copolymerized polyethylene terephthalate (33 mol% CHDM copolymerized PET) in which 33 mol% of 1,4-cyclohexanedimethanol was copolymerized and 23 parts by mass of poly (5-methyl) norbornene were prepared and mixed at 180 ° C. for 3 hours. After drying, supply to Extruder B heated to 270-300 ° C (B layer).
　一方、ポリエチレンテレフタレートのチップ４８．７質量部に、数平均粒径０．２５μｍのルチル型酸化チタンポリエチレンテレフタレートマスター（マスターチップ総量に対してルチル型酸化チタン３６質量％含有）を３質量部と、数平均粒径３．５μｍの二酸化珪素粒子ポリエチレンテレフタレートマスター０．３質量部（マスターチップ総量に対して二酸化珪素６質量％含有）と、数平均粒径１．４μｍの硫酸バリウム粒子ポリエチレンテレフタレートマスター１６質量部（マスターチップ総量に対して硫酸バリウム６０質量％含有）と、ポリエチレンテレフタレートにイソフタル酸を１８mol％共重合したもの（ＰＥＴ／Ｉ）を１７質量部と、ドデシルベンゼンスルホン酸ナトリウム１質量部と、ポリエチレンテレフタレート／ポリエチレングリコール重縮合物を１４質量部とを１８０℃で３時間真空乾燥した後、２８０℃に加熱された押出機Ａに供給し（Ａ層）、これらポリマーをＡ層／Ｂ層／Ａ層となるように積層装置を通して積層し、Ｔダイよりシート状に成形した。さらにこのフィルムを表面温度２５℃の冷却ドラムで冷却固化した未延伸フィルムを８５～９８℃に加熱したロール群に導き、長手方向に３．７倍縦延伸し、２１℃のロール群で冷却した。続いて、縦延伸したフィルムの両端をクリップで把持しながらテンターに導き１２０℃に加熱された雰囲気中で長手に垂直な方向に３．６倍横延伸した。その後テンター内で２００℃の熱固定を行い、均一に徐冷後、室温まで冷却し二軸延伸された積層フィルムを得た。光反射用基材としての物性は表１に示した。
［実施例２～３０］
　Ａ層、Ｂ層の原料組成、Ａ層の厚み、フィルム全厚みを表１に記載したとおりに変更した以外は、実施例１と同様の方法で白色ポリエステルフィルムを得た。 Meanwhile, 38.7 parts by mass of 48.7 parts by mass of polyethylene terephthalate chips, 3 parts by mass of rutile titanium oxide polyethylene terephthalate master having a number average particle size of 0.25 μm (containing 36% by mass of rutile titanium oxide based on the total amount of master chips), 0.3 parts by mass of silicon dioxide particle polyethylene terephthalate master having a number average particle size of 3.5 μm (containing 6% by mass of silicon dioxide with respect to the total amount of the master chip) and barium sulfate particle polyethylene terephthalate master 16 having a number average particle size of 1.4 μm Parts by weight (containing 60% by weight of barium sulfate based on the total amount of the master chip), 17 parts by weight of polyethylene terephthalate copolymerized with 18 mol% of isophthalic acid (PET / I), and 1 part by weight of sodium dodecylbenzenesulfonate , Polyethylene terephthalate / polyethylene 14 parts by weight of the polyglycol polycondensate was vacuum-dried at 180 ° C. for 3 hours, and then supplied to Extruder A heated to 280 ° C. (A layer). These polymers were combined with A layer / B layer / A layer. It laminated | stacked so that it might become, and it shape | molded in the sheet form from T-die. Further, the unstretched film obtained by cooling and solidifying this 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 3.7 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. The physical properties of the light reflecting substrate are shown in Table 1.
[Examples 2 to 30]
A white polyester 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 Table 1.
　いずれの実施例も相対輝度、輝度ムラ、耐光性は良好であった。 In all examples, the relative luminance, luminance unevenness, and light resistance were good.
　ただし、実施例１は二酸化珪素の含有量が少なめであったので輝度ムラがわずかに劣っており、ルチル型酸化チタンの含有量が少なめであったので耐光性が他の実施例よりもわずかに劣っていた。硫酸バリウムの含有量は少なめであったが、輝度は実用上使用できるレベルであった。 However, in Example 1, since the content of silicon dioxide was small, the luminance unevenness was slightly inferior, and since the content of rutile-type titanium oxide was small, the light resistance was slightly lower than the other examples. It was inferior. Although the content of barium sulfate was small, the luminance was at a level that could be used practically.
　実施例２は二酸化珪素、硫酸バリウムの含有量が多めであったので製膜安定性が他の実施例よりもわずかに劣っており、ルチル型酸化チタンの含有量が多めであったので輝度ムラが他の実施例よりもわずかに劣っていた。 In Example 2, since the contents of silicon dioxide and barium sulfate were larger, the film-forming stability was slightly inferior to those of the other examples, and the content of rutile titanium oxide was larger. Was slightly inferior to the other examples.
　実施例３は二酸化珪素の数平均粒子径が小さめであったので輝度ムラが他の実施例よりもわずかに劣っており、ルチル型酸化チタンの数平均粒子径が小さめであったので耐光性が他の実施例よりもわずかに劣っていた。硫酸バリウムの数平均粒子径は小さめであったが輝度は実用上使用できるレベルであった。 In Example 3, since the number average particle diameter of silicon dioxide was smaller, the luminance unevenness was slightly inferior to the other examples, and the number average particle diameter of rutile-type titanium oxide was smaller, so that the light resistance was high. It was slightly inferior to the other examples. Although the number average particle size of barium sulfate was smaller, the luminance was at a level that could be used practically.
　実施例４は二酸化珪素および硫酸バリウムの数平均分子量が大きめであったので製膜安定性が他の実施例よりもわずかに劣っており、ルチル型酸化チタンの数平均粒子径が大きめであったので耐光性が他の実施例よりもわずかに劣っていた。 In Example 4, since the number average molecular weights of silicon dioxide and barium sulfate were larger, the film-forming stability was slightly inferior to the other examples, and the number average particle diameter of rutile titanium oxide was larger. Therefore, the light resistance was slightly inferior to the other examples.
　実施例５は二酸化珪素の含有量が少なめであったので輝度ムラが他の実施例よりもわずかに劣っており、ルチル型酸化チタンの含有量が少なめであったので耐光性が他の実施例よりもわずかに劣っていた。硫酸バリウムの含有量は少なめであったが輝度は実用上使用できるレベルであった。 In Example 5, since the content of silicon dioxide was small, the luminance unevenness was slightly inferior to the other examples, and the content of rutile type titanium oxide was small, so that the light resistance was another example. Was slightly inferior to. Although the content of barium sulfate was small, the luminance was at a level that could be used practically.
　実施例６は二酸化珪素、硫酸バリウムの含有量が多めであったので製膜安定性が他の実施例よりもわずかに劣っており、ルチル型酸化チタンの含有量が多めであったので輝度ムラが他の実施例よりもわずかに劣っていた。 In Example 6, since the contents of silicon dioxide and barium sulfate were higher, the film-forming stability was slightly inferior to those of the other examples, and the content of rutile titanium oxide was higher. Was slightly inferior to the other examples.
　実施例７は二酸化珪素の数平均粒子径が小さめであったので輝度ムラが他の実施例よりもわずかに劣っており、ルチル型酸化チタンの数平均粒子径が小さめであったので耐光性が他の実施例よりもわずかに劣っていた。硫酸バリウムの数平均粒子径は小さめであったが輝度は実用上使用できるレベルであった。 In Example 7, since the number average particle diameter of silicon dioxide was smaller, the luminance unevenness was slightly inferior to the other examples, and the number average particle diameter of rutile-type titanium oxide was smaller, so that the light resistance was high. It was slightly inferior to the other examples. Although the number average particle size of barium sulfate was smaller, the luminance was at a level that could be used practically.
　実施例８は二酸化珪素、硫酸バリウムの数平均分子量が大めであったので製膜安定性が他の実施例よりもわずかに劣っていた。ルチル型酸化チタンの数平均粒子径は大きめであったが耐光性は実用上使用できるレベルであった。
［比較例１］
　積層構成および原料組成を表１に記載したとおりに変更した以外は、実施例１と同様の方法で厚み１８８μｍのフィルムを得た。製膜安定性があり、相対反射率は、１０４．２％、相対輝度でも高い輝度が得られたものの、Ａ層に二酸化珪素を添加していないため導光板へのキズがあり、輝度ムラが不十分であった。
［比較例２］
　積層構成および原料組成を表１に記載したとおりに変更した以外は、実施例１と同様の方法で厚み１８８μｍのフィルムを得た。相対反射率は１０４．３％であり、相対輝度でも高い値が得られたものの、Ａ層にルチル型酸化チタンを添加していないため耐光性が不十分であった。
［比較例３］
　積層構成および原料組成を表１に記載したとおりに変更した以外は、実施例１と同様の方法で厚み１８８μｍのフィルムを得た。製膜安定性があり、相対反射率は１０３．５％であり、相対輝度でも高い値が得られたものの、Ａ層に硫酸バリウムを添加していないため、Ａ層において微細な気泡を発現させることができず、耐光性が不十分であった。
［比較例４］
　積層構成および原料組成を表１に記載したとおりに変更した以外は、実施例１と同様の方法で厚み１８８μｍのフィルムを得た。製膜安定性があり、相対反射率は１０４．４％であり、相対輝度でも高い値が得られたものの、Ａ層の厚みが薄いため製膜安定性が不足しており、耐光性も不十分であった。
［比較例５］
　積層構成および原料組成を表１に記載した様に変更した他は、実施例１と同様の方法で厚み１８８μｍのフィルムを得た。製膜安定性があり、相対反射率は、１０３．８％、相対輝度でも高い輝度が得られたが、Ａ層の厚みが厚いため輝度ムラが不十分であった。
［比較例６］
　積層構成および原料組成を表１に記載したとおりに変更した以外は、実施例１と同様の方法で厚み２５０μｍのフィルムを得た。相対反射率は１０２．０％であり、相対輝度も高い値が得られたものの、Ａ層に二酸化珪素を添加していないため導光板へのキズがあり、ルチル型酸化チタンを添加していないため耐光性が不十分であった。
［比較例７］
　積層構成および原料組成を表１に記載したとおりに変更した以外は、実施例１と同様の方法で厚み２２５μｍのフィルムを得た。ただし、Ａ／Ｂ層の２層積層とするためフィードブロックにて積層し、Ｔダイよりシート状に押出して溶融シートとした。製膜安定性が不足しており、相対反射率は１０３．０％であり、相対輝度でも高い値が得られたものの、導光板へのキズがあり、耐光性が不十分であった。
［比較例８］
　積層構成および原料組成を表１に記載したとおりに変更した以外は実施例１と同様の方法で厚み２２５μｍのフィルムを得た。ただし、押出機Ａには原料を供給せず、Ａ層を形成していないので、Ｂ層のみの単層フィルムとなった。製膜安定性があり、相対反射率は１００．０％であり、導光板へのキズがあり、相対輝度、輝度ムラおよび耐光性が不十分であった。 In Example 8, since the number average molecular weights of silicon dioxide and barium sulfate were larger, the film forming stability was slightly inferior to those of the other examples. Although the number average particle size of rutile type titanium oxide was large, the light resistance was at a level that could be used practically.
[Comparative Example 1]
A film having a thickness of 188 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 1. Although the film formation is stable and the relative reflectance is 104.2% and high luminance is obtained even in the relative luminance, the silicon dioxide is not added to the A layer. It was insufficient.
[Comparative Example 2]
A film having a thickness of 188 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 1. Although the relative reflectance was 104.3% and a high value was obtained even in the relative luminance, the light resistance was insufficient because no rutile-type titanium oxide was added to the A layer.
[Comparative Example 3]
A film having a thickness of 188 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 1. Although there is film-forming stability, the relative reflectance is 103.5%, and a high value is obtained even in the relative luminance, but since no barium sulfate is added to the A layer, fine bubbles are expressed in the A layer. The light resistance was insufficient.
[Comparative Example 4]
A film having a thickness of 188 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 1. Although it has film-forming stability, the relative reflectance is 104.4%, and a high value is also obtained in the relative luminance, but the film-forming stability is insufficient because the thickness of the A layer is thin, and the light resistance is not good. It was enough.
[Comparative Example 5]
A film having a thickness of 188 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 1. The film was stable, the relative reflectance was 103.8%, and a high luminance was obtained even with the relative luminance, but the luminance unevenness was insufficient because the A layer was thick.
[Comparative Example 6]
A film having a thickness of 250 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 1. Although the relative reflectance was 102.0% and the relative luminance was also high, there was a scratch on the light guide plate because no silicon dioxide was added to the A layer, and no rutile titanium oxide was added. Therefore, the light resistance was insufficient.
[Comparative Example 7]
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 1. However, in order to obtain a two-layer lamination of A / B layers, lamination was performed with a feed block, and a sheet was extruded from a T-die to obtain a molten sheet. Although the film-forming stability was insufficient, the relative reflectance was 103.0%, and a high value was obtained even in the relative luminance, but there was a scratch on the light guide plate and the light resistance was insufficient.
[Comparative Example 8]
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 1. However, since the raw material was not supplied to the extruder A and the A layer was not formed, it became a single layer film of only the B layer. There was film-forming stability, the relative reflectance was 100.0%, there were scratches on the light guide plate, and the relative luminance, luminance unevenness and light resistance were insufficient.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
　ここで、表１～表４中の略号は次の内容を表す。すなわち、
　ＰＥＴ：ポリエチレンテレフタレート、
　ＰＥＴ／Ｉ／ＰＥＧ：エチレングリコール／テレフタル酸／イソフタル酸共縮合物（分子量1,000のポリエチレングリコール５mol％が共重合されたポリエチレンテレフタレート共重合体）、
　ＰＥＴ／ＣＨＤＭ：ポリエチレン－１，４－シクロヘキシレンジメチレンテレフタレート（エチレングリコールに対し１，４－シクロヘキサンジメタノールが３３mol％共重合されたポリエチレンテレフタレート共重合体）、
　ＰＢＴ／ＰＴＭＧ：ポリエステルエーテルエラストマブチレン／ポリ（アルキレンエーテル）フタレート（ブチレンテレフタレートに対し、アルキレングリコールが３０mol％の共重合体）（商品名：東レデュポン社製ハイトレル）、
である。 Here, the abbreviations in Tables 1 to 4 represent the following contents. That is,
PET: Polyethylene terephthalate,
PET / I / PEG: ethylene glycol / terephthalic acid / isophthalic acid cocondensate (polyethylene terephthalate copolymer in which 5 mol% of polyethylene glycol having a molecular weight of 1,000 is copolymerized),
PET / CHDM: polyethylene-1,4-cyclohexylenedimethylene terephthalate (polyethylene terephthalate copolymer obtained by copolymerizing 33 mol% of 1,4-cyclohexanedimethanol with respect to ethylene glycol),
PBT / PTMG: Polyester ether elastomer mabutylene / poly (alkylene ether) phthalate (copolymer having 30 mol% of alkylene glycol with respect to butylene terephthalate) (trade name: Hytrel manufactured by Toray DuPont)
It is.
　本発明の白色ポリエステルフィルムは、テレビなどに使用される大型の直下型ライト方式の液晶ディスプレイや、ノートパソコンや携帯電話などに使用される小型のサイドライト方式の液晶ディスプレイに好適に使用される。また、太陽電池用のバックシートとしても使用でき、太陽光から電気へ変換する効率に寄与するほか太陽光からの紫外線についても耐性を付与することができる。 The white polyester film of the present invention is suitably used for large direct-type light-type liquid crystal displays used for televisions and the like, and small sidelight-type liquid crystal displays used for notebook computers and mobile phones. Moreover, it can be used as a back sheet for solar cells, and contributes to the efficiency of conversion from sunlight to electricity, and can impart resistance to ultraviolet rays from sunlight.
１：光反射用白色ポリエステルフィルム
２：冷陰極管
３：乳白板
４：拡散板
５：プリズムシート
６：偏光プリズムシート
７：ＣＣＤカメラ
８：画像解析装置（アイスケール）
９：冷陰極管
１０：光反射用白色ポリエステルフィルム
１１：導光板
１２：プリズムシート
１３：ＣＣＤカメラ 1: White polyester film for light reflection 2: Cold cathode tube 3: Milky white plate 4: Diffuser plate 5: Prism sheet 6: Polarizing prism sheet 7: CCD camera 8: Image analyzer (eye scale)
9: Cold cathode tube 10: White polyester film for light reflection 11: Light guide plate 12: Prism sheet 13: CCD camera

Claims (9)

  1. ポリエステルで構成されたＡ層とポリエステルで構成されたＢ層との少なくとも２層を有する白色ポリエステルフィルムであって、該Ｂ層は気泡を有し、該Ａ層はルチル型酸化チタン、硫酸バリウムおよび二酸化珪素の３種類の無機粒子を含有し、該白色ポリエステルフィルムの全厚みが１００μｍ以上５００μｍ以下であり、かつ該Ａ層の厚みが２μｍ以上１６μｍ以下である白色ポリエステルフィルム。 A white polyester film having at least two layers of an A layer composed of polyester and a B layer composed of polyester, wherein the B layer has air bubbles, and the A layer comprises rutile titanium oxide, barium sulfate, and A white polyester film containing three types of inorganic particles of silicon dioxide, wherein the total thickness of the white polyester film is from 100 μm to 500 μm, and the thickness of the A layer is from 2 μm to 16 μm.
  2. 前記Ａ層が、前記ルチル型酸化チタンを該Ａ層の全質量に対して２質量％以上６質量％以下、前記硫酸バリウムを該Ａ層の全質量に対して１６質量％以上２４質量％以下、前記二酸化珪素を該Ａ層の全質量に対して０．５質量％以上３質量％以下含有する請求項１記載の白色ポリエステルフィルム。 In the A layer, the rutile titanium oxide is 2% by mass to 6% by mass with respect to the total mass of the A layer, and the barium sulfate is 16% by mass to 24% by mass with respect to the total mass of the A layer. The white polyester film according to claim 1, wherein the silicon dioxide is contained in an amount of 0.5% by mass to 3% by mass with respect to the total mass of the A layer.
  3. 前記ルチル型酸化チタンの数平均粒径が０．１μｍ以上１．０μｍ以下である請求項１または２記載の白色ポリエステルフィルム。 The white polyester film according to claim 1 or 2, wherein the rutile-type titanium oxide has a number average particle size of 0.1 µm or more and 1.0 µm or less.
  4. 前記硫酸バリウムの数平均粒径が０．５μｍ以上３．０μｍ以下である請求項１～３のいずれかに記載の白色ポリエステルフィルム。 The white polyester film according to any one of claims 1 to 3, wherein the barium sulfate has a number average particle size of 0.5 to 3.0 µm.
  5. 前記二酸化珪素の数平均粒径が２．０μｍ以上５．０μｍ以下である請求項１～４のいずれかに記載の白色ポリエステルフィルム。 The white polyester film according to any one of claims 1 to 4, wherein the number average particle diameter of the silicon dioxide is 2.0 袖 m to 5.0 袖 m.
  6. 前記Ｂ層が、ポリエステルと非相溶なポリマーまたは、ポリエステルと非相溶なポリマーおよび無機粒子を分散して含有する請求項１～５のいずれかに記載の白色ポリエステルフィルム。 The white polyester film according to any one of claims 1 to 5, wherein the layer B contains a polymer incompatible with polyester, or a polymer incompatible with polyester and inorganic particles dispersed therein.
  7. 前記Ａ層に照度：１００ｍＷ／ｃｍ２、温度：６０℃、相対湿度：５０％ＲＨ、照射時間：４８時間の条件で紫外線を照射したときの、紫外線照射前と紫外線照射後とでの黄色味変化量：Δｂ値が５未満である請求項１～６のいずれかに記載の白色ポリエステルフィルム。 Yellowness before and after ultraviolet irradiation when the layer A is irradiated with ultraviolet rays under the conditions of illuminance: 100 mW / cm 2 , temperature: 60 ° C., relative humidity: 50% RH, and irradiation time: 48 hours. The white polyester film according to any one of claims 1 to 6, wherein the change: Δb value is less than 5.
  8. 請求項１～７のいずれかに記載の白色ポリエステルフィルムを用いた光反射板。 A light reflector using the white polyester film according to any one of claims 1 to 7.
  9. 請求項１～７のいずれかに記載の白色ポリエステルフィルムがそのＡ層面側を光源側に向けて配されている液晶ディスプレイ用バックライト。 A backlight for a liquid crystal display, wherein the white polyester film according to any one of claims 1 to 7 is disposed with its layer A surface facing the light source.
PCT/JP2011/053633 2010-03-23 2011-02-21 White polyester film, light-reflective plate using the same, and liquid-crystal display backlight using the same WO2011118305A1 (en)

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KR1020127022727A KR101772015B1 (en) 2010-03-23 2011-02-21 White polyester film, light-reflective plate using the same, and liquid-crystal display backlight using the same
JP2011522311A JP5045851B2 (en) 2010-03-23 2011-02-21 White polyester film, light reflector using the same, and backlight for liquid crystal display

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CN102782532B (en) 2015-04-15
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KR20130018668A (en) 2013-02-25
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TWI495898B (en) 2015-08-11
JPWO2011118305A1 (en) 2013-07-04
KR101772015B1 (en) 2017-08-28

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