JP2014126638A - Reflective film for liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflective film which does not cause screen irregularities of a liquid crystal display, especially a liquid crystal display having an LED backlight, and maintains a high reflective capability even after long use.SOLUTION: A reflective film is for use with backlights of liquid crystal displays and, when the height of the reflective film from a flat plate on which it is placed is measured after going through a process of mounting the reflective film on a backlight, turning the backlight on for 4 hours under a temperature of 60°C and a relative humidity of 80%, dismounting the reflective film from the backlight, and placing the reflective film on the flat plate, the maximum height is no more than 5 nm.

Description

  The present invention relates to a reflective film suitable for a liquid crystal display. The present invention relates to a reflection film that can be suitably used for a backlight device for image display and a reflection sheet of a lamp reflector, and can be particularly suitably used for a reflection plate of a backlight device for image display.

  In a planar image display type surface light source device or illumination signboard used for a liquid crystal display or the like, a reflective film is installed on the back surface for the purpose of improving luminance.

  As a method of developing high brightness, the polyester film contains a large number of inorganic particles such as barium sulfate, and reflects light at the interface between the polyester resin and the inorganic particles, and at the hollow interface of the fine cavities that are generated using the particles as nuclei. (Refer to Patent Document 1), a method of utilizing light reflection at the cavity interface of fine cavities produced by mixing incompatible resin with polyester and using incompatible resin as a nucleus (patent) Reference 2), adding inorganic particles to polypropylene resin, and stretching the formed film to form fine cavities in the film and utilizing light reflection (see Patent Document 3). A method in which compatible resins are mixed and biaxially stretched to generate cavities is used (see Patent Document 4).

  However, in these methods, liquid crystal display devices for liquid crystal televisions and personal computers are downsized and improved in performance, and the amount of heat generated by a light source (for example, LED) used for the backlight of the liquid crystal display is increased for a long time. In use, luminance unevenness occurs on the screen. In particular, in the edge light system that is advantageous for thinning by arranging the LED light source on the side surface, the temperature gradient inside the backlight tends to be large in the portion close to and away from the LED light source. Problems have become prominent.

JP 2003-160682 A Japanese Patent Publication No. 8-16175 JP-A-11-174213 JP 2008-158134 A

  An object of the present invention is to provide a reflective film in which screen unevenness is unlikely to occur in a liquid crystal display, particularly a liquid crystal display using an LED backlight, thereby maintaining high reflection performance even in long-term use.

In order to solve the above problems, the present invention adopts the following configuration.
(1) A reflective film for a backlight of a liquid crystal display, wherein the reflective film is incorporated into a backlight, the backlight is turned on for 4 hours at a temperature of 60 ° C. and a relative humidity of 80%, and then the reflective film is backlit. The reflective film is characterized in that the maximum height is 5 mm or less when the height of the reflective film from the flat plate is measured by taking it out from the flat plate and placing it on the flat plate.
(2) The reflective film as described in (1), wherein the reflective film is a white polyester film.
(3) The reflective film according to (1) or (2), wherein an average reflectance at a wavelength of 400 to 700 nm on at least one surface of the reflective film is 85% or more.
(4) The reflective film according to any one of (1) to (3), wherein the total thickness of the reflective film is 100 μm or more and 500 μm or less.

  According to the present invention, it is possible to improve luminance unevenness in a liquid crystal display, particularly a liquid crystal display using an LED backlight. As a result, high reflection performance can be maintained even during long-term use.

  Embodiments of the present invention will be described below.

[Reflective film]
Reflective film materials include polyester resins such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polylactic acid (PLA), polyethylene (PE), polypropylene (PP), and cycloolefin (COC, COP). Fluorine such as polyolefin resin such as resin, cellulose resin such as cellulose triacetate and acetate, acrylic resin such as polymethyl methacrylate (PMMA), polycarbonate (PC) resin, polytetrafluoroethylene (PTFE) A resin or the like can be used. Among these materials, it is preferable to use polyethylene terephthalate (PET), cyclic polyolefin (COC, COP), polymethyl methacrylate (PMMA), polycarbonate (PC), or the like that has little absorption of visible light.

  The reflective film of the present invention can be obtained by adding a resin (hereinafter referred to as an incompatible resin) incompatible with inorganic / organic particles or a base resin to a base material made of the above material.

  The inorganic particles include at least one selected from the group consisting of calcium carbonate, titanium dioxide, zinc oxide, silicon dioxide, barium sulfate, alumina, talc, zirconium oxide, zinc sulfide and basic lead carbonate (lead white). Among them, a mixture comprising at least one kind selected from the group consisting of calcium carbonate, zinc oxide, barium sulfate and titanium dioxide, or a combination of two or more kinds is preferable.

  Examples of the organic particles include thermally crosslinkable resin particles such as polypropylene and polystyrene, and examples of incompatible resins include polyolefin resins such as polyethylene, polypropylene, polybutene, and polymethylpentene, cyclic polyolefin resins, polystyrene resins, and poly Examples thereof include acrylate resins, polycarbonate resins, polyacrylonitrile resins, polyphenylene sulfide resins, and fluorine resins.

  In the present invention, the reflective film may be a single layer or a laminate of two or more layers.

[White polyester film]
The reflective film in the present invention is preferably a white polyester film from the viewpoint of reflection performance and heat resistance. Moreover, the laminated body of at least 2 layer or more of the A layer and the B layer containing a cavity which are substantially made of polyester and do not contain a cavity may be used.

  The resin constituting the A layer and the B layer is preferably polyester, and particularly preferably polyethylene terephthalate (PET) or polyethylene naphthalate (PEN). Further, various known additives such as an antioxidant and an antistatic agent may be added to the polyester.

[A layer]
It is preferable that A layer is a layer which does not contain a bubble substantially. The phrase “substantially free of bubbles” refers to a layer state in which the porosity is less than 10%, and the thickness of the A layer is a cross-sectional direction in which bubbles are not substantially contained from the surface when the cross section is observed with an electron microscope. The thickness up to the depth is obtained, and the thickness of the layer substantially free of bubbles is defined as the A layer thickness.

  The layer A preferably contains inorganic particles. The A layer has a role of scattering light, a role of preventing light leakage to the back surface, and a role of a support for stabilizing the film formation. In addition, when the backlight is an edge light system, there is an effect of reducing unevenness caused by nonuniform contact between the light guide plate and the reflective film.

  The light scattering property of the A layer can be adjusted mainly by controlling the surface roughness. As another method, for example, particles having a refractive index different from that of the resin constituting the A layer are added to the A layer. A method is mentioned.

  Here, as a kind of inorganic particle contained in A layer, calcium carbonate, titanium dioxide, zinc oxide, silicon dioxide, barium sulfate, alumina, talc etc. are mentioned, for example. Among these, silicon dioxide is preferable because it has an effect of reducing uneven adhesion between the light guide plate and the reflective film. These inorganic particles can be used alone or in combination depending on the necessity of imparting surface functions such as glossiness adjustment, whiteness adjustment, and light resistance.

  The preferred content of the inorganic particles to be contained in the A layer is not particularly limited as long as the above properties can be obtained, and cannot be uniquely defined because of the influence of the particle diameter and specific gravity. It is preferable that it is 0.1 mass% or more with respect to the whole, More preferably, it is 0.5 mass% or more, More preferably, it is 1 mass% or more. Moreover, although an upper limit is not specifically limited, It is preferable that it is 50 mass% or less with respect to the whole A layer, More preferably, it is 40 mass% or less, More preferably, it is 30 mass% or less. If it is less than 0.1% by mass, necessary characteristics may not be obtained, and if it exceeds 50% by mass, the film forming property may be deteriorated.

  The preferable particle diameter of the inorganic particles to be contained in the layer A is not particularly limited as long as the above properties are obtained, but is preferably 1 μm or more, more preferably 3 μm or more, from the viewpoint of less adhesion unevenness between the light guide plate and the reflective film. Preferably it is 5 micrometers or more.

[B layer]
The layer B is preferably a layer that is whitened by containing fine bubbles inside the film. Formation of fine bubbles can be achieved by finely dispersing a polymer incompatible with polyester in a film substrate such as a polyester film and stretching (for example, biaxial stretching).

[Incompatible resin]
The B layer preferably contains a resin that is incompatible with the resin constituting the B layer. By containing the incompatible resin, a cavity having the incompatible resin as a nucleus is formed at the time of stretching, and light reflection occurs at the cavity interface. Polyesters that are incompatible with polyesters may be homopolymers or copolymers, polyolefin resins such as polyethylene, polypropylene, polybutene, and polymethylpentene, cyclic polyolefin resins, polystyrene resins, and polyacrylate resins. Polycarbonate resin, polyacrylonitrile resin, polyphenylene sulfide resin, fluororesin and the like are preferably used. Two or more of these may be used in combination.

  In particular, a resin having a large difference in critical surface tension from polyester and being hardly deformed by heat treatment after stretching is preferable, and specifically, a polyolefin-based resin is preferable. Examples of the polyolefin resin include polyolefin resins such as polyethylene, polypropylene, polybutene, and polymethylpentene, cyclic polyolefin resins, and copolymers thereof. Among these, a copolymer of ethylene and bicycloalkene, which is a cyclic olefin copolymer, is particularly preferable.

  A preferable content of the incompatible resin to be contained in the B layer is 5% by mass or more and 25% by mass or less. In addition, the incompatible resin contained in the B layer is dispersed in a matrix made of a polyester resin so that the number average particle diameter is 0.4 μm or more and 3.0 μm or less. In the range of 0.5 μm or more and 1.5 μm or less.

  The number average particle size referred to here is a cross section in the width direction (TD) of the film, and the B layer portion of the cross section is a scanning electron microscope (FE-SEM) S-2100A manufactured by Hitachi, Ltd. The average value of the diameters when the area of 100 particles observed in this way is obtained and converted to a perfect circle.

  In the B layer, inorganic particles may be contained, and examples thereof include calcium carbonate, titanium dioxide, zinc oxide, zirconium oxide, zinc sulfide, basic lead carbonate (lead white), and barium sulfate. Among them, calcium carbonate, barium sulfate, titanium dioxide, and the like, which absorb less in the visible light range of 400 to 700 nm, are preferable from the viewpoints of reflection characteristics, concealment properties, production costs, and the like. In the present invention, barium sulfate and titanium dioxide are most preferable from the viewpoints of film winding property, long-term film-forming stability, and improvement in reflection characteristics. As the particle size of the inorganic particles, it is preferable to use particles having a number average particle size of 0.1 μm or more and 3.0 μm or less in order to realize excellent reflectivity and concealability.

[Copolyester]
Copolymer polyester is preferably used for the B layer. Even when the B layer contains inorganic particles at a high concentration, it can be stably formed and has a role as a dispersant for the incompatible resin in the B layer.

  The copolymer polyester has a main dicarboxylic acid component of terephthalic acid, a main glycol component of ethylene glycol, and a copolymer component of aromatic carboxylic acid or aliphatic carboxylic acid such as isophthalic acid or naphthalene dicarboxylic acid, and tetra It is a polyester containing at least one selected from the group consisting of aliphatic diols such as methylene glycol, cyclohexanedimethanol, polyethylene glycol and polytetramethylene glycol.

  The copolymer polyester used is based on polyethylene terephthalate, a copolymer of polyethylene terephthalate and isophthalic acid, a copolymer of polyethylene terephthalate and cyclohexanedimethanol, and a copolymer of polybutylene terephthalate and polytetramethylene terephthalate. It is preferable to contain at least two or more types of copolyesters selected from the coalescence.

[Coating layer]
An application layer may be provided on at least one surface of the reflective film in the present invention. Moreover, it is preferable that a coating layer contains a granular particle and a binder at least. By providing the coating layer, there is an effect of improving the luminance of the backlight. Further, when the backlight is an edge light system, effects such as reduction in uneven adhesion between the light guide plate and the reflective film and reduction in damage to the light guide plate due to the reflection plate can be obtained.

  The type of granular particles is not particularly limited, and any organic or inorganic type can be used. As the organic spherical particles, acrylic resin particles, silicone resin particles, nylon resin particles, polystyrene resin particles, polyethylene resin particles, polyamide resin particles such as benzoguanamine, urethane resin particles, and the like can be used. As the inorganic spherical particles, silicon oxide, aluminum hydroxide, aluminum oxide, zinc oxide, barium sulfide, magnesium silicate, or a mixture thereof can be used.

  The binder resin is not particularly limited, but a resin mainly composed of an organic component is preferable. For example, polyester resin, polyurethane resin, acrylic resin, methacrylic resin, polyamide resin, polyethylene resin, polypropylene resin, polyvinyl chloride resin, polyvinylidene chloride Examples thereof include resins, polystyrene resins, polyvinyl acetate resins, and fluorine resins. These resins may be used alone, or two or more copolymers or a mixture thereof may be used. Of these, polyester resins, polyurethane resins, acrylic resins or methacrylic resins are preferably used in terms of heat resistance, particle dispersibility, coatability, and glossiness.

[Maximum height from flat plate]
The reflective film of the present invention is incorporated into a backlight, the backlight is turned on for 4 hours under the conditions of a temperature of 60 ° C. and a relative humidity of 80%, then taken out of the backlight and placed on a flat plate, and the height from the flat plate is measured. The maximum height is preferably 5 mm or less, more preferably 4 mm or less, and particularly preferably 3 mm or less. When it is larger than 5 mm, the dimensional stability is insufficient, and luminance unevenness occurs due to long-term use.

  Here, the maximum height is the height of the portion where the lift of the film edge from the flat plate is the largest among a plurality of samples prepared by cutting out the reflective film taken out from the backlight in a predetermined direction and width. Details of the measurement method will be described later.

[Average reflectance]
The average reflectance at a wavelength of 400 to 700 nm on at least one surface of the reflective film of the present invention is preferably 85% or more, more preferably 87% or more, and particularly preferably 90% or more. When the average reflectance is less than 85%, the luminance may be insufficient depending on the applied liquid crystal display.

[Total thickness]
The total thickness of the reflective film of the present invention is preferably from 100 μm to 500 μm, more preferably from 150 μm to 350 μm. If the total thickness of the reflective film is 100 μm or more, it is preferable from the viewpoint of reflectivity, and the thicker the thickness, the higher the rigidity and the less likely to cause deformation. The upper limit is not particularly limited, but is 500 μm or less, more preferably 350 μm or less from the viewpoint of reflectance, workability, and cost. If the thickness exceeds 500 μm, an increase in reflectivity cannot be expected even if the thickness is increased beyond this, and workability (handling properties) may deteriorate due to the increase in mass when working as a single wafer for incorporation into a backlight.

[Production method]
Next, a white polyester film will be described as an example as a method for producing the reflective film of the present invention, but the present invention is not limited to this example.

  Cyclic olefin as incompatible resin, copolymer of 1,4-cyclohexanedimethanol and polyethylene terephthalate as dispersant (copolyester), copolymer of polybutylene terephthalate and polytetramethylene glycol as polyethylene terephthalate The mixture is sufficiently mixed and dried, and then supplied to the extruder B heated to a temperature of 270 to 300 ° C. Polyethylene terephthalate containing inorganic particles of silicon dioxide is supplied to the extruder A to obtain a three-layer structure of A layer / B layer / A layer so that the polymer of the A layer becomes both surface layers in the T-die three-layer die. It was.

  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 roll group heated to 80 to 120 ° C. However, it is stretched 2.8 to 4.0 times in the longitudinal direction.

  More preferably, it is 3.1 to 3.4 times. If it is less than 2.8 times, the reflective properties may not be sufficient, or the thickness unevenness of the film may deteriorate and a good film may not be obtained. If it exceeds 4.0 times, the film may be easily broken during film formation, and the thermal shrinkage in the longitudinal direction may be increased. The film stretched in the longitudinal direction is subsequently subjected to stretching (transverse stretching) in the direction orthogonal to the longitudinal direction (hereinafter referred to as the transverse direction), heat setting, and thermal relaxation to form a biaxially oriented film. However, these processes are performed while the film is running. The transverse stretching process starts from a temperature higher than the glass transition temperature (Tg) of the polyester. And it heats up to (5-70) degreeC temperature higher than Tg. The temperature increase in the transverse stretching process may be continuous or stepwise (sequential), but it is usually preferable to increase the temperature sequentially. For example, the transverse stretching zone of the tenter is divided into a plurality along the film running direction, and the temperature is raised by flowing a heating medium having a predetermined temperature for each zone. The transverse stretching ratio is preferably 2.5 to 4.5 times, more preferably 2.8 to 3.9 times, although it depends on the required characteristics of the application. If it is less than 2.5 times, the thickness unevenness of the film may be deteriorated, and if it exceeds 4.5 times, breakage may easily occur during film formation.

  In this way, by stretching the obtained unstretched film in at least one direction, a cavity can be developed with a resin or inorganic particles incompatible with the polyester as a nucleus. Here, the case of stretching by the sequential biaxial stretching method has been described in detail as an example, but the stretching may be performed by any of the sequential biaxial stretching method and the simultaneous biaxial stretching method.

  In order to complete the crystal orientation of the obtained biaxially stretched film and to impart flatness and thermal dimensional stability, it is subsequently heat-set at a temperature of 180 to 220 ° C. for 1 to 30 seconds in a tenter, After gradually cooling uniformly, cool to room temperature and wind up.

  Then, it is preferable to heat-process the obtained film, and you may give a 0.5-10% relaxation process to a horizontal direction or a longitudinal direction as needed. It is preferable that the temperature of heat processing is below melting | fusing point (Tm) of polyester, specifically, 100-200 degreeC is preferable, More preferably, it is 120-180 degreeC. If the temperature of the heat treatment is lower than 100 ° C, the thermal shrinkage rate may not be sufficiently reduced, and if it is higher than 200 ° C, the flatness of the film may be deteriorated. Further, the heat treatment time is preferably 5 seconds or longer, more preferably 10 seconds or longer. The thermal dimensional stability can be improved by setting the heat treatment time to 5 seconds or longer. In addition, since the flatness of a film may deteriorate when heat treatment is performed for a long time, the upper limit of the heat treatment time is preferably 60 seconds.

[Measurement of physical properties and evaluation of effects]
The physical property value evaluation method and the effect evaluation method of the present invention are as follows.

[Average reflectance]
The average reflectance is a wavelength range of 400 to 700 nm with a spectrophotometer U-3410 (Hitachi Ltd.) attached with a φ60 integrating sphere 130-0632 (Hitachi Ltd.) and a 10 ° C. inclined spacer. It is obtained by measuring the relative reflectance with respect to the standard white plate at intervals of 10 nm and calculating the average value thereof. In addition, part number 210-0740 by Hitachi Instruments Service Co., Ltd. was used for the standard white board, and the average value was calculated about 3 samples, and these average reflectances were employ | adopted.

[Total thickness, thickness of each layer, porosity]
The total thickness of the film was measured with a micrometer in accordance with JIS C2151 (2006). Each layer thickness is cut in the width direction (TD) without crushing the film in the thickness direction using a microtome to create a section sample, and the section of the section sample is a scanning electron microscope manufactured by Hitachi, Ltd. Using the (FE-SEM) S-2100A model, an image was taken at a magnification of 3,000, and the thickness of each layer was measured from the image. At the same time, voids (bubbles) were observed, and the area of the portion observed as bubbles was divided by the area of the observed layer and multiplied by 100 to obtain the porosity. The void (bubble) portion is a portion in which there is no constituent of the reflection film such as resin and particles in the section, and was determined by the contrast of the SEM image. A layer having a porosity of less than 10% was judged as layer A.

[Constant temperature and humidity test]
Only the reflective film in the 32-inch LCD TV LHD32K15JP backlight manufactured by Hisense Japan Co., Ltd. was changed to the film sample of Example and Comparative Example, and after the TV was returned to the original state, the temperature was 60 ° C. and the relative humidity was 80%. The backlight was turned on for 4 hours. The brightness (brightness) setting during the test was set to the maximum value. Three samples of each level were prepared for shape evaluation and confirmation of luminance unevenness described later. A constant temperature and humidity chamber TBL-3HA4PAC (manufactured by Espec Corp.) was used for the test tank.

[Shape evaluation]
The reflective film was taken out from the backlight unit of the liquid crystal TV after the test, and one sample was cut out by the full width at intervals of 3 cm in the long side direction, and the other one sample was cut out by the full width at intervals of 3 cm in the short side direction. The cut sample was placed on a flat plate, and the maximum value of the floating height from the flat plate to the edge of the reflective film was measured in total. The maximum value in the cut sample was taken as the result of that level. There was no designation as the upper surface when placing on a flat plate, and both sides were confirmed.

[Check brightness unevenness]
The reflective film in Hisense Japan Co., Ltd. 32-inch liquid crystal TV (model number: LHD32K15JP) backlight was replaced with a reflective film subjected to a constant temperature and humidity test, and the backlight was turned on. In that state, after waiting for 1 hour to stabilize the light source, 10 people conducted visual inspection in the dark room, compared with the same type TV incorporating a reflective film that was not subjected to constant temperature and humidity test, The number of people who could see the unevenness was compared. Moreover, the case where the number of persons who could visually recognize unevenness was 3 or less was determined to be good.

[Evaluation of adhesion unevenness between light guide plate and reflective film]
The backlight of the CIMEI 24-inch LED monitor (model number: 24LH) was taken out and disassembled, and three glass beads, a reflector, and a light guide plate were set in this order on the backlight casing, and the backlight was turned on. A donut-shaped load (16 kg, inner diameter 115 mm) is placed on the light guide plate so that the glass beads are in the center, and whether or not uneven adhesion between the reflective film and the light guide plate due to the glass beads is visible is 50 cm from the light guide plate. From a distance, it was visually observed in a dark room. As the glass beads, BZ-02 (particle size 0.2 mm) manufactured by ASONE was used. Visual observation was carried out by 10 people, and the number of people who were able to visually recognize uneven adhesion was counted.

  The present invention will be described based on examples.

[Example 1]
Polyethylene terephthalate having a color tone of polyethylene terephthalate after polymerization (JIS K7105 (1981), measured by stimulus value direct reading method) having an L value of 62.8, a b value of 0.5, and a haze of 0.2% is used. 94 parts by mass, 0.5 part by mass of (PBT / PTMG) copolymer of polybutylene terephthalate and polytetramethylene glycol (trade name: “Hytrel” (registered trademark), manufactured by Toray DuPont Co., Ltd.), diol component A cycloolefin copolymer (trade name) having 0.5 parts by mass of copolymerized polyethylene terephthalate (33 mol% PET / CHDM copolymer) obtained by copolymerizing 33 mol% of 1,4-cyclohexanedimethanol with a glass transition temperature of 210 ° C. : 5 parts by mass of Polyplastics TOPAS) The resulting mixture was dried at 180 ° C. for 3 hours, and then supplied to the extruder B heated to 270 to 300 ° C.

  On the other hand, 63 parts by mass of polyethylene terephthalate, 17 parts by mass of silicon dioxide particles polyethylene terephthalate master having a number average particle size of 3.5 μm (containing 6% by mass of silicon dioxide based on the total amount of the master chip), 18 mol% of isophthalic acid in polyethylene terephthalate. 20 parts by mass of the polymerized material (PET / I) was vacuum-dried at 180 ° C. for 3 hours, and then supplied to the extruder A heated to 280 ° C. These polymers were laminated through a laminating apparatus so as to be A layer / B layer / A layer, and formed into a sheet form from a T-die. 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., stretched 3.4 times in the longitudinal direction, and cooled with a roll group at 21 ° C. Subsequently, the film stretched in the longitudinal direction was guided to a tenter while being gripped by clips, and was stretched by 3.6 times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 120 ° C. Thereafter, heat setting at 190 ° C. was performed in a tenter, followed by a relaxation treatment of 6% in the width direction at the same temperature, and then uniformly cooled, then cooled to room temperature and a biaxially stretched laminated film was obtained. . Then, after standing at 25 ° C. for 24 hours, heat treatment was performed in an oven at 150 ° C. for 20 seconds. Table 1 shows the physical properties and evaluation results. The maximum height from the flat plate was 0.5 mm, and the luminance unevenness evaluation was good.

[Examples 2 to 6]
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 film forming conditions, and the heat treatment conditions were changed as described in Table 1. In all the examples, the maximum height from the flat plate was 5 mm or less, and the luminance unevenness evaluation was good.

[Comparative Examples 1-2]
A film having a total thickness of 225 μm was obtained in the same manner as in Example 1 except that the raw material composition of the A layer and the B layer and the film forming conditions were changed as described in Table 1. The maximum height from the flat plate is 7.0 mm and 6.0 mm, respectively, depending on the content of the copolymer component in layer B and the presence or absence of heat treatment, and both comparative examples are higher than 5 mm. Was visually recognized.

Here, the abbreviations in Table 1 represent the following contents. That is,
PET: Polyethylene terephthalate,
PET / I: Polyethylene terephthalate copolymerized with 18 mol% isophthalic acid,
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% by mole of alkylene glycol based on butylene terephthalate) It is.

  The reflective film for liquid crystal displays of the present invention can be suitably used for a backlight.

Claims (4)

  A reflective film for a backlight of a liquid crystal display, wherein the reflective film is incorporated into a backlight, the backlight is turned on for 4 hours at a temperature of 60 ° C. and a relative humidity of 80%, and then the reflective film is taken out from the backlight. A reflective film characterized by having a maximum height of 5 mm or less when placed on a flat plate and measuring the height of the reflective film from the flat plate.   The reflective film according to claim 1, wherein the reflective film is a white polyester film.   The reflective film according to claim 1 or 2, wherein an average reflectance at a wavelength of 400 to 700 nm of at least one surface of the reflective film is 85% or more.   The total thickness of the said reflective film is 100 micrometers or more and 500 micrometers or less, The reflective film in any one of Claims 1-3 characterized by the above-mentioned.