JP2007178505A - White polyester film for display reflecting plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a white polyester film for a liquid crystal display reflection plate capable of ensuring high luminance, when it is used in a liquid crystal display. <P>SOLUTION: The white polyester film comprises a polyester and a resin, having an MFR of 230-500 g/10 min (ASTM D1238) and being incompatible with the polyester, wherein at least one surface of the film has an average relative reflectance in the wavelength region of light of 400-700 nm being 99% or higher. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a white polyester film. In particular, the white polyester film is most suitable for a liquid crystal display. When a liquid crystal screen is illuminated with a sidelight (also referred to as an edge light), a fluorescent tube is disposed just above a reflective film. The present invention relates to a white polyester film for a display-reflecting plate that can form a base material for a reflecting plate that has a clear structure (called a direct type) and can provide a brighter screen.

  In recent years, many displays using liquid crystals have been used as display devices for personal computers, televisions, mobile phones, and the like. Conventionally, when illuminating these liquid crystal displays, the backlight system in which light is applied from the back of the display and the sidelight system as disclosed in Japanese Patent Laid-Open No. 63-62104 are thin and can be illuminated uniformly. Widely used. The sidelight system is a system that applies various treatments such as halftone dot printing and embossing to one side of a transparent substrate such as an acrylic plate with a certain thickness, and illuminates a cold cathode tube from the edge of the acrylic plate. Illumination light is evenly distributed, and a screen with uniform brightness is obtained. In addition, since the illumination is installed not at the back of the screen but at the edge, it can be made thinner than the backlight method. In order to prevent the illumination light from escaping to the back of the screen, it is necessary to install a reflector on the back of the screen. This reflector is required to be thin and highly reflective. A white film or the like, which is whitened by containing fine bubbles and scattering light in the bubbles, is mainly used.

  On the other hand, a direct light system has been adopted for large screens such as liquid crystal televisions. In this system, cold cathode ray tubes are arranged in parallel at the bottom of the liquid crystal screen. The reflecting plate may be a flat plate or a cold cathode ray tube formed into a semicircular concave shape. Conventionally, a film added with a white pigment, a film containing fine bubbles inside, or a film obtained by bonding these films to a metal plate, a plastic plate or the like has been used. In particular, when a film containing fine bubbles inside is used, it is widely used because of its excellent brightness improvement effect and uniformity.

  The formation of the fine bubbles is achieved by finely dispersing a high melting point incompatible polymer in a film base material such as polyester and stretching it (for example, biaxial stretching). During stretching, voids (bubbles) are formed around the incompatible polymer particles, and this exhibits a scattering effect on the light, so that it becomes white and high reflectance can be obtained.

  On the other hand, an important characteristic of a liquid crystal display is the degree of brightness of the screen. In particular, in a display with a large screen, if the light reflected by the reflecting plate is not sufficiently scattered, brightness unevenness occurs in the screen and a beautiful image cannot be obtained. In order to maintain the brightness uniformity of the screen, it is known that the reflected light is sufficiently diffusely reflected by adding inorganic particles to the surface of the white film for the reflector.

In recent years, the adoption of the “reverse prism method” has begun to spread in the illumination of smaller liquid crystal displays such as notebook computers and mobile phones. This method will be described with reference to FIG. In this method, after the light emitted from the edge lamp passes through the light guide plate and is reflected by the reflecting plate, the light is bent in the vertical direction through the prism installed in the opposite direction to the conventional method, thereby providing directivity. To send to the liquid crystal cell. In the conventional method, the light reflected by the reflecting plate is diffused, and the light entering the upward-facing prism is reflected by the prism other than the one having directivity directly above, and is repeatedly reflected between the reflecting plate, The light is finally sent to the liquid crystal cell in a state in which the directivity of the light is increased. In this method, light is lost through the reflecting plate while the reflection is repeated, and the luminance cannot be sufficiently obtained. On the other hand, when the conventional reflector is used in the reverse prism system, the directivity cannot be sufficiently obtained by the prism facing in the reverse direction because the ratio of the diffused light is high, and sufficient luminance cannot be obtained. .
JP 63-62104 A JP-A-6-322153 JP-A-7-118433 Japanese Patent Laid-Open No. 2003-160682

  The present invention solves such a problem, and not only when used in a reverse prism type liquid crystal display, but also for a liquid crystal display reflector capable of obtaining high brightness in a conventional regular prism type liquid crystal display device. An object is to provide a white polyester film.

The white polyester film for a liquid crystal display reflector of the present invention that meets this purpose is:
(1) A white polyester film using a resin incompatible with polyester having a polyester and MFR of 230 to 500 g / 10 min (ASTM D1238), and having an average relative reflectance in a light wavelength range of 400 to 700 nm. A white polyester film for a display reflector that is 99% or more on at least one side of the film;
(2) The white polyester film for display reflector according to (1), wherein the resin incompatible with polyester is polymethylpentene,
(3) An interface formed by a three-layer configuration of A layer / B layer / A layer or A layer / B layer / C layer, wherein the B layer is a layer containing fine bubbles, and is formed by the fine bubbles in the B layer. The white polyester film for display reflector according to (1) or (2), wherein the number of
(4) The white polyester film for a liquid crystal display reflector according to any one of (1) to (3), wherein the number of interfaces is 80 or more per 100 μm of film thickness,
As a display device,
(5) A display device using the white polyester film for display reflector according to any one of (1) to (4),
It is.

  According to the white polyester film for a display reflector of the present invention, it is possible to obtain a high brightness that has not been achieved in the past in the screen brightness in a display device. The present invention relates to a white polyester film. In particular, the present invention exhibits high brightness as a display such as a notebook personal computer, a monitor, a mobile phone, or other direct liquid crystal television, and a brighter image can be obtained.

  The polyester constituting the present invention is a polymer obtained by condensation polymerization from a diol and a dicarboxylic acid. Examples of the dicarboxylic acid include terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, adipic acid, sebacic acid, and the like. The diol is represented by ethylene glycol, trimethylene glycol, tetramethylene glycol, cyclohexanedimethanol and the like. Specific examples include polymethylene terephthalate, polytetramethylene terephthalate, polyethylene-p-oxybenzoate, poly-1,4-cyclohexylenedimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate. In the present invention, polyethylene terephthalate and polyethylene naphthalate are particularly preferable.

  Of course, these polyesters may be homopolyesters or copolyesters. Examples of copolymer components include diol components such as diethylene glycol, neopentyl glycol, and polyalkylene glycol, adipic acid, sebacic acid, and phthalic acid. And dicarboxylic acid components such as isophthalic acid, 2,6-naphthalenedicarboxylic acid, and 5-sodiumsulfoisophthalic acid.

  In addition, various known additives such as an antioxidant and an antistatic agent may be added to the polyester. The polyester used in the present invention is preferably polyethylene terephthalate. Polyethylene terephthalate film is excellent in water resistance, durability, chemical resistance and the like.

  In the present invention, the average reflectance in the wavelength region of light of 400 to 700 nm needs to be 99% or more on at least one side of the film. This is because if it is less than 99%, the luminance as a backlight may decrease. In the present invention, the average reflectance is measured over a range of 400 to 700 nm when an integrating sphere is attached to a spectrophotometer (U-3310) manufactured by Hitachi High-Technologies and the standard white plate (aluminum oxide) is taken as 100%. . The reflectance is read from the obtained chart at intervals of 5 nm and averaged.

  In order to make the reflectance 99% or more, it is important that fine bubbles are contained in the film to make it white, and since this exhibits a scattering action on light, the reflectance can be improved. Preferably, the reflectance is 100% or more, more preferably 101% or more. There is no particular upper limit for the reflectivity, but in order to increase the reflectivity, it is necessary to increase the addition amount of the nucleating agent, and in that case, the film forming property may become unstable, so it may be 110% or less. preferable.

  The present invention is preferably whitened by containing fine bubbles inside the film. Formation of fine bubbles is achieved by finely dispersing a polymer incompatible with the high melting point polyester in a film base material such as polyester and stretching it (for example, biaxial stretching). During stretching, voids (bubbles) are formed around the incompatible polymer particles, which exhibit a scattering action on the light, so that it becomes white and high reflectance can be obtained. Incompatible polymers include, for example, poly-3-methylbutene-1, poly-4-methylpentene-1, polyvinyl-t-butane, 1,4-trans-poly-2,3-dimethylbutadiene, polyvinylcyclohexane, polystyrene , Polymethylstyrene, polydimethylstyrene, polyfluorostyrene, poly-2-methyl-4-fluorostyrene, polyvinyl-t-butyl ether, cellulose triacetate, cellulose tripropionate, polyvinyl fluoride, polychlorotrifluoroethylene, etc. A polymer having a melting point of 200 ° C. or higher selected from Among them, polyolefin, particularly polymethylpentene is preferable for the polyester base material.

  The MFR of the resin incompatible with the polyester in the present invention is a melt flow rate, the resin temperature is heated to 260 ° C., the measured resin amount is 5 kg, and other conditions are measured according to ASTM D 1238. Value. The higher the value, the lower the viscosity. In the present invention, since the melt flow rate is 230 g / 10 min or more, a finer effect appears than before, and an effect of increasing the interface around the thickness is seen. In addition, with the increase in MFR, the fine effect is further promoted. There is no upper limit, but if it exceeds 500 g / 10 min, it is often impossible to produce substantially. Therefore, preferably, MFR is 250 to 450 g / 10 min, and more preferably, MFR is 350 to 450 g / 10 min.

Since the method for controlling MFR depends on the polymerization time during polymerization and the extrusion temperature during resin molding, the desired MFR can be obtained freely by changing the polymerization time and the extrusion temperature.
The addition amount of the incompatible polymer (for example, polyolefin) is preferably 5% by weight or more and 25% by weight or less when the entire layer containing the incompatible polymer is 100% by weight. If it is too small, the effect of whitening will be diminished and it will be difficult to obtain a high reflectance, and if it is too high, the mechanical properties such as the strength of the film itself will be too low, which is not preferable.

  The incompatible polymer is more preferably dispersed uniformly. By uniform dispersion, bubbles are uniformly formed inside the film, and the degree of whitening and thus the reflectance becomes uniform. In order to uniformly disperse the incompatible polymer, it is effective to add a low specific gravity agent as a dispersion aid. The low specific gravity agent is a compound having an effect of reducing the specific gravity, and the effect is recognized in a specific compound. For example, for polyester, polyalkylene glycol such as polyethylene glycol, methoxypolyethylene glycol, polytetramethylene glycol, polypropylene glycol, ethylene / propylene oxide copolymer, sodium dodecylbenzenesulfonate, alkylsulfonate It is represented by sodium salt, glycerin monostearate, tetrabutylphosphonium paraaminobenzenesulfonate and the like. In the case of the film of the present invention, polyalkylene glycol, particularly polyethylene glycol is particularly preferable. A copolymer of polybutylene terephthalate and polytetramethylene glycol is also preferably used for improving the dispersibility of the incompatible polymer. The addition amount is preferably 3% by weight or more and 20% by weight or less based on 100% by weight of the entire layer containing the incompatible polymer. If the amount is too small, the effect of the addition is diminished, and if it is too large, the original properties of the film base material may be impaired. Such a low specific gravity agent can be added to the film base polymer in advance and adjusted as a master polymer (master chip).

  As described above, when the white polyester film contains fine bubbles, the apparent specific gravity of the polyester film is lower than that of a normal polyester film. If a lower specific gravity agent is further added, the specific gravity is further lowered. That is, a white and light film can be obtained. In order to reduce the weight of this white polyester film while maintaining the mechanical properties as a substrate for a liquid crystal display reflector, the apparent specific gravity is preferably 0.5 or more and 1.2 or less.

In order to make the apparent specific gravity 0.5 or more and 1.2 or less, when a low specific gravity agent such as polymethylpentene having a specific gravity of 0.83 is used as described above, it is 5% by weight or more and 25% by weight with respect to the whole layer. % Or less, and a draw ratio of 2.5 to 4.5 can be achieved. When the apparent specific gravity is within the range of the present invention, when used as a liquid crystal display reflector, the brightness of the screen is remarkably excellent.

  The interface in the present invention is an interface between the air layer and the resin layer that has invaded into fine bubbles mainly expressed by stretching the film formation between the polyester and the incompatible resin. This is caused by interface reflection occurring at the boundary between the air layer and the resin layer. Although reflection at one interface is small but many fine bubbles overlap each other, interface multiple reflection is caused and a function is imparted as a highly reflective material. The number of interfaces of the present invention was cut using a microtome without crushing the film cross section in the thickness direction, and then the cut interfaces were scanned using a scanning electron microscope S-2100A type (Hitachi, Ltd.). From the image obtained by magnifying the image at 10000 times, when a straight line is drawn perpendicularly to the film surface from one arbitrary point on the film surface to the other, the interface existing on the line Obtain by measuring the number. The number of interfaces is counted by counting one interface even when the interface is from the gas phase to the solid phase, and counting one interface even when the interface is from the solid phase to the gas phase. The number of interfaces in the present invention needs to be 150 or more, and is 2000 or less. High reflection characteristics and concealment can be obtained by increasing the number of interfaces.

  The average thickness of the fine bubbles in the film thickness direction is preferably 0.1 μm to 10 μm, more preferably 0.4 μm to 8 μm, in terms of light reflectivity and light diffusibility. If the thickness is less than 0.1 μm, the reflectance varies depending on the wavelength due to an optical interference effect or the like, and the reflected light may be colored. When the thickness is 10 μm or more, in order to secure 150 or more interfaces, it is necessary to considerably increase the film thickness, which is not suitable for the current practical use of thinning and weight reduction.

  It is preferable that 80 or more interfaces exist per 100 μm of film thickness. More preferably, it is 90 or more and 3000 or less. By providing 80 or more interfaces per 100 μm of film thickness, it is possible to obtain a light reflecting film having high reflectivity and high concealment property even though it is a thin film. 3000 or more are saturated, and the effect is minute.

  The white polyester film for a liquid crystal display reflector has a three-layer structure of A layer / B layer / A layer or A layer / B layer / C layer, and the B layer contains the fine bubbles. A layer is preferable in order to achieve both high reflectivity and film formability. Further, the A layer and / or the C layer corresponding to the film surface can be used as a layer containing inorganic particles and / or organic particles in the polyester. Moreover, when carbon black is added to the C layer, it can be suitably used as a reflective film having high concealment.

Next, although the manufacturing method of the white polyester film of this invention is demonstrated, it is not limited to this example. Polymethylpentene with an MFR of 400 g / 10 min as an incompatible polymer and polyethylene glycol, polybutylene terephthalate and polytetramethylene glycol copolymer as a low specific gravity agent are mixed with polyethylene terephthalate, and then thoroughly mixed and dried. And fed to an extruder A heated to a temperature of 270 to 300 ° C. If necessary, polyethylene terephthalate containing an inorganic additive such as SiO ₂ is supplied to extruder B by a conventional method, and the polymer of extruder B layer is placed on both surface layers in the T-die three-layer die. You may laminate to 3 layers of the structure of / B layer / A layer.

  The melted sheet is tightly 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 longitudinally 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 longitudinally stretched film 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 x lateral stretching ratio) is preferably 9 to 16 times. If the area magnification is less than 9 times, the whiteness of the film obtained 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. in a tenter, uniform cooling, and cooling to room temperature, winding up the film of the present invention. obtain.

  The white polyester film for a liquid crystal display reflector of the present invention thus obtained has high reflectivity because fine bubbles are formed inside the film, and has high brightness when used as a reflector of a display such as a liquid crystal display. 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) Average relative 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 400 to 700 nm. The reflectance is read from the obtained chart at intervals of 5 nm, and the average value is calculated to obtain the average relative reflectance.

(2) Number of interfaces inside the film Using a microtome, the film was cut without crushing the film cross section in the thickness direction. Next, from the image obtained by magnifying the cut interface at a magnification of 10,000 times using a scanning electron microscope S-2100A type (Hitachi Ltd.), the film surface is changed from an arbitrary point on the film surface to the other side. When a straight line was drawn perpendicularly to the film surface, the number of interfaces existing on the line was measured. The number of interfaces was counted as one interface even when the interface was from the gas phase to the solid phase, and one interface was counted even when the interface was from the solid phase to the gas phase. The number of interfaces per 100 μm of the film was calculated by calculating the average thickness d (μm) by measuring the total thickness of the film (film was cut into a 100 × 100 mm square and a dial gauge was attached to at least 10 points). ) Was converted to a value per 100 μm. (3) The apparent specific gravity film was cut into a 100 × 100 mm square, the thickness of at least 10 points was measured with a dial gauge attached, and the average thickness d (μm) was calculated. Moreover, 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 set to w / d × 100.

(4) Screen brightness (luminance)
As shown in FIG. 1, the reverse prism type reflective film 12 of the backlight of VAIO (VGN-S52B / S) manufactured by Sony Corporation was changed to the reflective film produced in each Example and Comparative Example and measured. For the luminance measurement, an inverter was used for the cold cathode tube 11, and after AC12V was applied, it waited for 1 hour and waited until the brightness of the cold cathode tube became uniform and constant. Thereafter, the luminance was measured at a measurement distance of 850 mm with a luminance meter 15 (BM-7fast manufactured by topcon). The number of measurements is 3 times, and the average value is taken. As the luminance evaluation, 3000 cd / ^{m 2} or more ◎, 2950cd / ^{m 2} or more, less than ^{3000cd / m 2 ○, 2900cd /} m 2 or more, less than 2950cd / ^{m 2} △, was × less than 2900 cd / ^{m 2.} The same measurement was performed for the positive prism type shown in FIG.

(5) Glossiness Using a digital variable angle gloss meter (UGU-4D) manufactured by Suga Test Instruments Co., Ltd., the incidence angle and the light reception angle were evaluated according to JIS K7105 in accordance with 60 °.

(6) MFR
According to ASTM D1238, the resin temperature was 260 ° C. and the resin amount was 5 kg.

The present invention will be described based on examples.

[Example 1]
A polyethylene terephthalate chip (F20S manufactured by Toray Industries, Inc.) and a polyethylene glycol having a molecular weight of 4000, a copolymer of polybutylene terephthalate and polytetramethylene glycol (“Hytrel” manufactured by Toray DuPont Co., Ltd.) are used for polymerization of polyethylene terephthalate. The added master chip was vacuum-dried at 180 ° C. for 3 hours, and then 65 parts by weight of polyethylene terephthalate, 10% by weight of polyethylene terephthalate, 10 mol% of isophthalic acid and 5 mol% of polyethylene glycol (T794M manufactured by Toray Industries, Inc.) 5 parts by weight of a copolymer of polybutylene terephthalate and polytetramethylene glycol (“Hytrel” manufactured by Toray DuPont Co., Ltd.), an extrusion temperature set at 320 ° C., and an MFR of 230 g / 10 min. Chillene pentene is mixed to 20 parts by weight and supplied to Extruder B heated to 270 to 300 ° C. (layer B), while polyethylene terephthalate chips are added to 98 parts by weight and the number average particle diameter is 2.5 μm. A mixture of 2 parts by weight of 2% by weight of silicon dioxide master chip was vacuum-dried at 180 ° C. for 3 hours, and then supplied to Extruder A heated to 280 ° C. (A layer). / A layer was laminated through a laminating apparatus so that the thickness ratio was 1: 8: 1, and formed into a sheet form from a T-die. Further, the unstretched film obtained by cooling and solidifying this film with a cooling drum having a surface temperature of 25 ° C. is led to a roll group heated to 85 to 98 ° C., stretched 3.4 times in the longitudinal direction, and cooled with a roll group at 25 ° C. . Subsequently, the film was stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 230 ° C. in a tenter, and after uniform cooling, the film was cooled to room temperature to obtain a film having a winding thickness of 250 μm. The glossiness (60 °) of the obtained film is 132%, and the physical properties as a white polyester film (base material) for a liquid crystal display reflector are shown in Table 1.

[Example 2]
In Example 1, the composition of the raw material to be sent to the extruder A is 86 parts by weight of polyethylene terephthalate and 14 parts by weight of calcium carbonate 50% by weight. Among the raw materials to be sent to the extruder B, the extrusion temperature is set to 400 ° C. A film having a thickness of 250 μm was obtained in the same manner as in Example 1 except that 20 parts by weight of polymethylpentene having an MFR of 500 g / 10 min was used. The glossiness (60 °) of the obtained film is 52%, and the physical properties as a white polyester film (base material) for a liquid crystal display reflector are shown in Table 1.

[Example 3]
In Example 1, 72 parts by weight of polyethylene terephthalate and 28 parts by weight of calcium carbonate master by 28 parts are added to the composition of the raw material to be sent to the extruder A. Of the raw materials to be sent to the extruder B, the extrusion temperature is 350 ° C. A film having a thickness of 250 μm was obtained in the same manner as in Example 1 except that 20 parts by weight of polymethylpentene having a set MFR of 360 g / 10 min was used. The glossiness (60 °) of the obtained film was 29%, and the physical properties as a substrate for a liquid crystal display reflector were as shown in Table 1 and high brightness was obtained.

[Example 4]
In Example 1, among the raw materials to be sent to the extruder B, the thickness was determined in the same manner as in Example 1 except that the extrusion temperature was set to 370 ° C. and 20 parts by weight of polymethylpentene having an MFR of 400 g / 10 min was used. A film of 250 μm was obtained. The glossiness (60 °) of the obtained film is 132%, and the physical properties as a substrate for a liquid crystal display reflector are shown in Table 1.

[Comparative Example 1]
In Example 1, as the raw material charged into the extruder B, the thickness was measured in the same manner as in Example 1 except that 20 parts by weight of polymethylpentene having an extrusion temperature set to 300 ° C. and MFR of 180 g / 10 min was used. A film of 250 μm was obtained. The glossiness (60 °) of the obtained film was 132%, and the physical properties as a substrate for a reverse prism type liquid crystal display reflector were as shown in Table 1, which was inferior to Example 1.

[Comparative Example 2]
In Example 1, as a raw material to be fed into the extruder B, a thickness of 250 μm was obtained in the same manner as in Example 1 except that 20 parts by weight of polymethylpentene having an extrusion temperature of 430 ° C. and an MFR of 550 g / 10 min was used. I got the film. The glossiness (60 °) of the obtained film was 132%, and the physical properties as a substrate for a reverse prism type liquid crystal display reflector were as shown in Table 1, which was inferior to Example 1.

[Comparative Example 3]
In Example 2, the raw material to be sent to the extruder B has a thickness of 250 μm in the same manner as in Example 1 except that 20 parts by weight of polymethylpentene having an extrusion temperature of 330 ° C. and an MFR of 26 g / 10 min was used. I got the film. The glossiness (60 °) of the obtained film is 52%, and the physical properties as a substrate for a liquid crystal display reflector are shown in Table 1.

  As shown in Table 1, using a resin PMP that is incompatible with polyester having a polyester and MFR of 230 to 500 g / 10 min (ASTM D1238), both the reflectance and the luminance increase as the number of interfaces increases. Recognize. In addition, the reverse prism type as shown in FIG. 1 and a regular prism type backlight that has been widely used in the past can be suitably used, and the luminance can be improved. By improving the brightness of the backlight, the brightness of the liquid crystal screen is improved and a bright and vivid image can be obtained.

It is a schematic sectional drawing of the backlight screen (reverse prism system) incorporating the reflecting plate. It is a schematic sectional drawing of the backlight screen (positive prism system) incorporating the reflecting plate.

Explanation of symbols

11; Cold cathode tube 12; Reflector plate 13; Light guide plate 14; Prism sheet 15; Luminance meter 16; Cold cathode tube 17; Reflector plate 18; Light guide plate 19;

Claims (5)

A white polyester film using a polyester and an MFR of 230 to 500 g / 10 min (ASTM D1238) incompatible with a polyester, wherein the average relative reflectance in the wavelength range of 400 to 700 nm is at least that of the film. A white polyester film for a display reflector, which is 99% or more on one side. The white polyester film for display reflector according to claim 1, wherein the resin incompatible with polyester is polymethylpentene. It has a three-layer structure of A layer / B layer / A layer or A layer / B layer / C layer, the B layer contains fine bubbles, and the number of interfaces formed by the fine bubbles is 150 or more per total film thickness The white polyester film for a display reflector according to claim 1 or 2. The white polyester film for a liquid crystal display reflector according to claim 1, wherein the number of interfaces is 80 or more per 100 μm of film thickness. A liquid crystal display device using the white polyester film for a display reflector according to claim 1.

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