JP5817165B2 - White laminated polyester film for reflector and backlight device - Google Patents

Description

  The present invention relates to a white laminated polyester film for a reflector. More specifically, the present invention relates to a polyester film having a laminated structure, excellent in luminance, rigidity, heat deflection stability, and good productivity, and particularly suitable for use as a reflector of a backlight device for image display. It is related with the white laminated polyester film which can do.

  A white polyester film is widely used as a reflector and a reflective sheet of a surface light source device in a flat image display system used for a liquid crystal display or the like because of its uniform and high reflectance, dimensional stability, and low cost. Yes. As a method of expressing high reflective performance, the polyester film contains a large number of inorganic particles such as titanium oxide and barium sulfate, for example, at the interface between the polyester resin and the particles, and at the hollow interface of the fine cavities generated using the particles as nuclei. Light reflection (refer to Reference 1 and Reference 2), light reflection at the cavity interface of fine cavities generated by mixing incompatible resin with polyester and mixing incompatible resin (Refer to reference 3), a method of utilizing light reflection at the interface of the cavity generated inside by impregnating a polyester film with an inert gas in a pressure vessel (refer to reference 4), etc. Wide range of methods using the difference in refractive index between inorganic particles and polyester resin contained in the polyester film and the difference in refractive index between fine voids and polyester resin It is needed.

  In recent years, the use of liquid crystal displays has been dramatically expanded, and for LCD TV applications for thin screens with a depth of 150 mm or less and large screens with a size of 26 inches or more, LED light sources that have low power consumption and high output are used. In addition to the conventional method of arranging a light source on the back surface of a backlight device, a method that is advantageous for thinning is adopted in which the light source is arranged on the side surface.

JP 2002-138150 A JP 2004-330727 A Japanese Patent Laid-Open No. 04-239540 International Publication No. 97/01117 Pamphlet

  However, in the case of a thin large screen LED light source backlight device in which the light source is arranged on the side, there are the following problems. That is, in the conventional CCFL edge light method, the light source, the light guide plate, and the reflection plate are not in direct contact, but in the LED edge light method, the LED light source is in direct contact with the light guide plate. Is directly in contact with the reflector, so that the heat generated by the light source is directly received, the light guide plate and the reflector are likely to become high temperature, and thermal stability is important. In addition, the LED backlight housing for thin large screens is provided with uneven processing to improve the strength of the housing and to store the electrical wiring and board, and at the edge of the housing near the LED light source A groove for heat dissipation is provided. For this reason, there is a part of the reflector that floats in the air from the housing, so that when the light source is turned on after assembly, the reflector is thermally deflected along the recess of the housing by the heat of the light source, causing uneven brightness. There is.

  The present invention solves the above-mentioned problems, and in a backlight device for a thin large screen in which an LED light source is arranged on the side, white laminated polyester for a reflector that does not bend when the light source is lit, has high brightness, and does not cause uneven brightness Aim to provide a film.

The white laminated polyester film for a reflector of the present invention that achieves this object is a laminated polyester film in which a polyester layer (A) is laminated on both sides of a polyester layer (B) containing a cavity inside the laminated polyester film. film, meets all the requirements of the following (1) to (5), the average of the longitudinal and width directions of the bending moment at the bending angle 15 degrees by Taber stiffness tester 3.5~9.5mN A white laminated biaxially stretched polyester film for a reflector, characterized by being m .
(1) The thickness of the polyester layer (A) is 12 to 40 μm.
(2) The polyester layer (A) is a layer formed by using polyester and the polyester incompatible component (incompatible component), and the content of the incompatible component in the polyester layer (A) On the other hand, it should be 0.01 to 1.50% by weight.
(3) The thickness of the polyester layer (B) is 250 to 450 μm.
(4) The thermal contraction rate in the longitudinal direction and the width direction at 90 ° C. for 30 minutes of the laminated polyester film is 0.0 to 0.5%, respectively.
(5) The apparent density of the laminated polyester film is 0.5 to 0.9 g / cm ³ .
Moreover, the void-containing laminated white polyester film of the present invention has the following preferable modes ( b ) to (c) .
( B) The density of the polyester layer (A) is 1.1 to 1.5 g / cm ³ .
(C) a light guide plate, a plurality of point light sources arranged on at least one side end of the light guide plate, a reflector arranged on the side opposite to the light emitting surface side of the light guide plate, and the reflector A backlight device including a housing to be placed, wherein the housing has irregularities with a height of 5 to 20 mm on a surface facing the reflector, and the reflector includes the reflector. A backlight device characterized in that a white laminated biaxially stretched polyester film is used.

  ADVANTAGE OF THE INVENTION According to this invention, in the LED backlight apparatus for thin large screens, the white laminated polyester film for reflectors which does not carry out a heat deflection at the time of light source lighting, and a brightness nonuniformity does not generate | occur | produce can be obtained at low cost. In addition, the apparent density is low and it is easy to handle because it is easy to handle, and it is difficult to bend due to its own weight.Therefore, there is little loss during assembly processing, and it is not limited to thin LED backlight devices for large screens. It can be suitably used as a reflector.

The thermal deflection measuring method in this invention is shown. It is sectional drawing of the backlight apparatus of this invention.

  The present inventors have solved the above-mentioned problem, that is, a thin laminated large-screen LED backlight device in which an LED light source is arranged on the side surface. As a result of intensive studies on the film, the inventors have found and found that a polyester film having a specific configuration can solve such problems all at once.

  The white laminated polyester film for reflector of the present invention has a polyester layer (A) containing a component incompatible with polyester (incompatible component) on both sides of the polyester layer (B) containing a cavity inside. It is a laminated polyester film. In the present invention, the polyester layer (B) contains a cavity inside. By containing a large number of cavities inside, the reflectance can be increased while suppressing scattering loss by utilizing the difference in refractive index between the polyester resin and the cavities. As a method of causing the polyester layer (B) to contain cavities and exhibiting high reflectivity and concealment, (1) adding a foaming agent to the polyester, foaming by heating during extrusion or film formation, or chemical decomposition (2) A method of adding a gas or a vaporizable substance during extrusion of a polyester, (3) Add a thermoplastic resin (incompatible resin) incompatible with the polyester to the polyester And a method of generating fine cavities by uniaxially or biaxially stretching it, and (4) a method of adding a large amount of bubble-forming inorganic fine particles in place of the incompatible resin, etc. In the present invention, from the comprehensive points of film forming properties, ease of adjusting the amount of cavities contained therein, ease of forming finer and uniform cavities, and light weight, the above-mentioned (3 It is preferable to use a method of using the inorganic fine particles used in the incompatible resin and (4). In this method, the more the content of the resin and / or inorganic particles incompatible with the polyester, the higher the stretching ratio in the biaxial stretching process, the more the interface that reflects light is generated inside the polyester. It is possible to exhibit high reflectivity and concealment.

  The incompatible resin referred to here is a thermoplastic resin other than polyester and is incompatible with polyester, dispersed in the form of particles in the polyester, and stretched in the film. A resin having a large effect of forming cavities is preferred.

  Among these incompatible resins, polyolefin resins, polyamide resins, polyimide resins, polyether resins, polyester amide resins, polyether ester resins, acrylic resins, polyurethane resins, polycarbonate resins, polyvinyl chlorides Preferable examples thereof are based resins. Specifically, linear, branched or cyclic polyolefin resins such as polyethylene, polypropylene, polybutene, polymethylpentene, and cyclopentadiene, acrylic resins such as poly (meth) acrylate, polystyrene, and fluorine-based resins Resins are preferably used. These incompatible resins may be a homopolymer or a copolymer, and two or more incompatible resins may be used in combination. Among these, a polyolefin-based resin having a small surface tension is preferably used in that it has excellent void formability. More specifically, polypropylene and polymethylpentene are preferably used. Polymethylpentene has a relatively large difference in surface tension with polyester and is excellent in void formation, not only has a large effect of forming bubbles per added amount, but also has a high melting point, so that deformation due to heat treatment is unlikely to occur. It is particularly preferable as an incompatible resin that becomes the core of voids because it can be sufficiently heat treated during production, and as a result, the mechanical strength and dimensional stability of the formed film can be improved. .

  Here, as polymethylpentene, what contains the derivative | guide_unit from 4-methylpentene-1 in a molecular skeleton is preferable. Examples of other derived units include hydrocarbons having 6 to 12 carbon atoms other than ethylene units, propylene units, butene-1 units, 3-methylbutene-1, or 4-methylpentene-1. The polymethylpentene may be a homopolymer or a copolymer. A plurality of polymethylpentenes having different compositions and melt viscosities may be used, or other olefinic resins and other resins may be used in combination.

  Further, as the incompatible resin used in the present invention, a cyclic olefin copolymer is particularly preferably used. The cyclic olefin copolymer is a copolymer composed of at least one cyclic olefin selected from the group consisting of cycloalkene, bicycloalkene, tricycloalkene and tetracycloalkene, and linear olefin such as ethylene and propylene. is there. Representative examples of such cyclic olefins include bicyclo [2,2,1] hept-2-ene, 6-methylbicyclo [2,2,1] hept-2-ene, and 5,6-dimethylbicyclo [2,2 , 1] hept-2-ene, 1-methylbicyclo [2,2,1] hept-2-ene, 6-ethylbicyclo [2,2,1] hept-2-ene, 6-n-butylbicyclo [ 2,2,1] hept-2-ene, 6-i-butylbicyclo [2,2,1] hept-2-ene, 7-methylbicyclo [2,2,1] hept-2-ene, tricyclo [ 4,3,0,12.5] -3-decene, 2-methyl-tricyclo [4,3,0,12.5] -3-decene, 5-methyl-tricyclo [4,3,0,12. 5] -3-decene, tricyclo [4,4,0,12.5] -3-decene, 10-methyl-tricycl B [4,4,0,12.5] -3-decene and the like. In particular, bicyclo [2,2,1] hept-2-ene (norbornene) and its derivatives are preferable from the viewpoint of productivity, transparency, and high Tg (glass transition point).

In the present invention, the content of the incompatible resin in the polyester layer (B) is preferably 12 to 35% by weight, more preferably 18 to 30% by weight, based on the entire polyester layer (B). When the content of the incompatible resin is within the above range, the film has excellent reflectivity and concealment properties, and the film has low apparent density, but hardly breaks during stretching and has a rigidity. It is preferable because the film is easy to handle because it is high and difficult to bend.
In the present invention, the presence or absence of fine cavities inside the polyester layer (B) is confirmed by observing the cross section of the polyester layer (B) with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). be able to.

  In the present invention, when the polyester layer (B) contains an incompatible resin, the cavities generated with the incompatible resin as a nucleus are preferably independent of each other. In addition, the longitudinal direction said here is a direction where a film flows in the process at the time of film manufacture, and let the direction orthogonal to a longitudinal direction be a width direction in a film plane.

  A method for controlling the average dispersion diameter of the incompatible resin within a preferable range is not particularly limited. For example, in addition to the above-described polyester and incompatible resin, it is preferable to add a dispersant. Can be mentioned. By adding a dispersant, the dispersion diameter of the incompatible resin is reduced, so that the cavities generated by stretching can be made finer, resulting in improved film reflectivity, total light transmittance, and film formation stability. Can be made. The incompatible resin in the polyester layer (B) preferably has a volume average particle size of 1.0 to 6.0 μm. Examples of the dispersant exhibiting the above effects include olefin polymers or copolymers having a polar group such as a carboxyl group or an epoxy group, or a functional group reactive with polyester, polyethylene glycol, cyclohexane dimethanol copolymer polyester , Polyalkylene glycols such as methoxypolyethylene glycol, polytetramethylene glycol, polypropylene glycol, and others, ethylene / propylene oxide copolymer, sodium dodecylbenzenesulfonate, alkylsulfonate sodium salt, glycerin monostearate Surfactant such as rate, tetrabutylphosphonium paraaminobenzene sulfonate, thermal adhesive resin, and the like can be used. Of course, these may be used alone or in combination of two or more. Among them, a copolymer resin of a polyalkylene glycol, an aliphatic diol component having 2 to 6 carbon atoms, and a polyester resin composed of terephthalic acid is compatible with a polyester resin which is a main constituent unit of the polyester layer (B) and a polyolefin. From the viewpoint of improving the dispersibility of the resin, a block copolymer of polyethylene glycol and polybutylene terephthalate is particularly preferable. Such a dispersant may be used as a polyester obtained by copolymerizing a dispersant in a polymerization reaction in advance, or may be used directly as it is.

  The amount of the dispersant used in the present invention is preferably 3 to 35% by weight, more preferably 15 to 30% by weight, based on the entire polyester layer (B) containing the dispersant. When the addition amount is within the above range, the effect of refining the bubbles becomes high, it has an excellent light reflection function, has high production stability, and can be produced at low cost, which is preferable.

  Such a polyester layer (B) has an excellent light reflecting function because it contains a cavity inside, but has a high cushioning property and flexibility, so it is greatly inferior in terms of rigidity.

  Therefore, in the present invention, it is necessary to laminate the polyester layer (A) described below on both sides of the polyester layer (B). By laminating the polyester layer (A), the rigidity of the laminated polyester film can be maintained and the film-forming property can be improved, and high rigidity, high reflectance, and productivity that cannot be achieved with a single layer structure. It is possible to obtain a film having both.

  In the present invention, the polyester layer (A) is a layer formed by using a polyester and an incompatible component (incompatible component) with the polyester, and the content of the incompatible component is a polyester layer ( It is preferable that it is 0.01-1.50 weight% with respect to A). The content of the incompatible component is more preferably 0.02 to 0.80% by weight, still more preferably 0.20 to 0.60% by weight. If the content of the incompatible component is below the above numerical range, the contact area with the roll increases, the film is easily damaged when there are foreign objects or scratches on the roll, and the film does not slip on the roll, and the meander It becomes easy and film formation becomes unstable. Moreover, when content of this incompatible component exceeds the said numerical range, rigidity will fall because the cavity of a polyester layer (A) increases. Moreover, since internal absorption of the light in a polyester layer (A) becomes large, it is not preferable.

  In the present invention, since the highly rigid polyester layer (A) is provided on both sides of the polyester layer (B), the laminated polyester film can have sufficient rigidity. The rigidity is expressed by a bending moment value of an angle of 15 degrees, and is preferably 3.5 to 9.5 mN · m. If it is less than 3.5 mN · m, the rigidity becomes insufficient and thermal deflection occurs, resulting in uneven brightness. Moreover, when exceeding 9.5 mN * m, it becomes difficult to wind as a roll, and since a severe curl and a crease generate | occur | produce, it is unpreferable.

  Examples of incompatible components contained in the polyester layer (A) of the present invention include silicon dioxide, barium sulfate, calcium carbonate, titanium dioxide, zinc oxide, zirconium oxide, zinc sulfide, basic lead carbonate (lead white), and the like. However, silicon dioxide particles are preferred from the standpoint of slipperiness and a small difference in refractive index from polyester. Moreover, it is preferable that the number average particle diameter of this incompatible component is 1.0-4.0 micrometers from a viewpoint of the protrusion property to the polyester surface.

  In the present invention, the polyester layer (A) needs to have a thickness of 12 to 40 μm. In the present invention, the polyester layer (A) is provided on both sides of the B layer, but each thickness needs to be 12 to 40 μm.

  When the thickness of the polyester layer (A) is less than 12 μm, the rigidity of the laminated polyester film becomes small, causing heat deflection when exposed to a high temperature environment when the light source is turned on in the backlight. Unevenness occurs. When the thickness of the polyester layer (A) exceeds 40 μm, the reflectance decreases due to an increase in loss due to light absorption in the polyester layer (A).

  On the other hand, in the present invention, the polyester layer (B) needs to have a thickness of 250 to 450 μm. The main light reflection performance is expressed by the cavity in the polyester layer (B), and when the thickness of the polyester layer (B) is less than 250 μm, the film has poor reflectivity, concealability and rigidity. . When the thickness of the polyester layer (A) exceeds 450 μm, the production stability of the film is lowered.

  In addition, the polyester layer (A) and the polyester layer (B) are preferably laminated at once in a film production line by a coextrusion method, and then stretched in a biaxial direction to be biaxially oriented. In addition, in the method of providing the polyester layer (A) by a coating method, it may be difficult to stably provide a film thickness necessary for exhibiting sufficient rigidity. Further, the bonding method is not preferable because the cost becomes high.

  In this invention, a polyester layer (A) and a polyester layer (B) are comprised using a polyester resin. The following components are mentioned as a component which comprises the polyester resin used by this invention. Examples of the dicarboxylic acid component include terephthalic acid, isophthalic acid, 5-sodium sulfoisophthalic acid, phthalic acid, diphenic acid and ester derivatives thereof for aromatic dicarboxylic acids, and adipic acid, for aliphatic dicarboxylic acids. Examples of sebacic acid, dodecadioic acid, eicoic acid, dimer acid and ester derivatives thereof include 1,4-cyclohexanedicarboxylic acid and ester derivatives thereof for alicyclic dicarboxylic acids, and trimellitic acid, pyrophosphate for polyfunctional acids. A merit acid and its ester derivative are mentioned as a representative example. Examples of the diol component include ethylene glycol, propanediol, butanediol, neopentyl glycol, pentanediol, hexanediol, octanediol, decanediol, cyclohexanedimethanol, diethylene glycol, triethylene glycol, polyethylene glycol, and tetramethylene glycol. Typical examples include polyethers such as polyethylene glycol and polytetramethylene glycol. Considering the mechanical strength, heat resistance, production cost, and the like of the produced polyester film, it is preferable that the polyester layer (A) and the polyester layer (B) in the present invention have polyethylene terephthalate as a basic structure. The basic constitution in this case means that 50% by weight or more of polyethylene terephthalate is contained with respect to the contained polyester resin.

  In the present invention, a copolymer component may be introduced into the basic structure of polyethylene terephthalate. As a method for introducing a copolymer component, a copolymer component may be added at the time of polymerization of a polyester pellet as a raw material and used as a pellet in which a copolymer component has been polymerized in advance. A method may be used in which a mixture of butylene terephthalate pellets and polyethylene terephthalate pellets is supplied to an extruder and copolymerized by transesterification at the time of melting. The amount of these copolymerization components is not particularly limited, but from the viewpoint of each characteristic, the dicarboxylic acid component and the diol component are each preferably 1 to 50 mol%, more preferably 1 to 20 mol, with respect to each component. %. Moreover, it is preferable to use isophthalic acid as a copolymerization component from a viewpoint of cleavage prevention between a polyester layer (A) and a polyester layer (B), film-forming stability, and manufacturing cost. In addition, it is preferable that the polyester layer (A) and the polyester layer (B) contain a common copolymer component because the cleavage preventing property between the polyester layer (A) and the polyester layer (B) is further improved.

  As a catalyst used for the polycondensation reaction of the said polyester resin, an antimony compound, a titanium compound, a germanium compound, a manganese compound etc. are mentioned preferably, for example. These catalysts can be used alone or in combination. Of these catalysts, the antimony compound is easy to control the polymerization reaction and is advantageous in terms of cost. In addition, titanium compounds and germanium compounds are advantageous in that they do not easily form metal catalyst aggregates, and titanium compounds are preferred from the viewpoint of cost.

  In this way, the polyester layer (A) that increases the rigidity of the polyester film on the surface side while exhibiting basic light reflection performance is laminated by the thick layer of the polyester layer (B) with little loss of light absorption. Thereby, although there are many cavities as a whole film and the apparent density is low, a high rigidity and an effect of increasing the reflectance can be obtained. In addition, the thickness of each polyester layer measures the length of the thickness direction of each polyester layer from the observation photograph with the scanning microscope of the said cross section, and calculates | requires the thickness of each layer by calculating backward from magnification. In addition, when calculating | requiring the thickness of each polyester layer, the cross-sectional photograph arbitrarily selected from the mutually different measurement visual field in the cut surface cut out along the width direction is used, and it calculates as the average value. When the longitudinal direction and the width direction are unknown, a cross section in an arbitrary direction may be measured.

In the present invention, the apparent density of the entire film needs to be 0.5 to 0.9 g / cm ³ . The apparent density of the void-containing laminated white polyester film is increased by the thickness of the polyester layer (A), reduced by the thickness of the polyester layer (B) and the fine voids contained therein, and finally within the above range. is important. If the apparent density is less than 0.5, the strength of the film is inferior and breakage occurs, wrinkles occur during three-dimensional processing, and breakage occurs frequently in the film manufacturing process, resulting in poor productivity, and incorporation into a backlight. Thereafter, there arises a problem that heat deflection is easily caused when the light source is turned on, which is not preferable. On the other hand, when the apparent density exceeds 0.9 g / cm ³ , the amount of voids present in the polyester film is insufficient, and thus the reflectance is deteriorated. In addition, the large screen size is not preferable because it is easily bent due to its own weight and breaks during handling. In addition, the apparent density in this invention cuts a film into the magnitude | size of 100 mm x 100 mm, measures the thickness of 10 points | pieces by attaching the measuring element of diameter 10mm to a dial gauge, and average value d (thickness value d ( After calculating (μm), the film was weighed with a direct balance, and the weight w (g) was read to the unit of 10 ⁻⁴ g, and the calculated value.

Moreover, in this invention, it is preferable that the density of a polyester layer (A) is 1.1-1.5 g / cm < ³ >. Since the polyester layer (A) has no cavities, high rigidity can be obtained as a whole film even if the density of the whole film is low. As a method of bringing the density of the polyester layer (A) into the above range, the surface layer of the inorganic particles not containing particles that form cavities such as incompatible resin and inorganic particles in the polyester layer (A) is subjected to organic treatment, Examples thereof include a method of setting the content to 5% or less to make it difficult to form a cavity by stretching, and irradiating hot air or an infrared heater at 200 ° C. or higher after stretching to eliminate voids in the polyester layer (A).

  The internal haze of the polyester layer (A) is preferably 1 to 40%. More preferably, it is 5 to 20%. If the internal haze of the polyester layer (A) is less than 1%, part of the light incident on the film in the polyester layer (A) propagates in the in-plane direction to the end surface of the film and does not exit the front surface of the film. This is not preferable because it absorbs light and the reflectivity of the film decreases. When the internal haze of the polyester layer (A) is in the above range, the propagating light is scattered and the light is emitted to the front side of the film, so that the reflectance of the film can be improved. On the other hand, if the internal haze is larger than 40%, the light reflected by the polyester layer (B) is scattered by the polyester layer (A), the transmittance is lowered and the reflectance of the film is lowered. As a method for adjusting the internal haze to the above range, an incompatible component having a refractive index different from that of polyester is contained in the polyester layer (A) in an amount of 0.01 to 1.50% by weight based on the weight of the polyester layer (A). The method is preferably used. In particular, as a method for adjusting the internal haze to 5 to 20%, an incompatible component having a refractive index different from that of polyester in the polyester layer (A) is 0.20 to 0.60 weight relative to the weight of the polyester layer (A). % Is preferably used. At this time, the formation of a cavity in the polyester layer (A) by stretching in the film production process is not preferable because not only the internal haze does not fall within the above range but also the rigidity of the film decreases. Examples of incompatible components include silicon dioxide, barium sulfate, calcium carbonate, titanium dioxide, zinc oxide, zirconium oxide, zinc sulfide, and basic lead carbonate (lead white). In terms of easy control, silicon dioxide and barium sulfate are preferably used.

  In the present invention, an antioxidant is preferably added to the polyester layer (B) in an amount of 0.05 to 1.0% by weight, more preferably 0.1 to 0.5% by weight, based on the polyester layer (B). By making it contain, it becomes possible to perform more stable polymer extrusion and film formation. As the antioxidant, a hindered phenol-based or hindered amine-based antioxidant is particularly preferable from the viewpoint of dispersibility.

  In the white laminated polyester film for a reflector of the present invention, the average value of the heat shrinkage when exposed to 90 ° C. for 30 minutes in the longitudinal direction and the width direction is required to be 0.0 to 0.5%. Preferably, it is 0.0 to 0.3%. When the thermal shrinkage rate exceeds 0.5%, the dimensional change due to the thermal shrinkage of the film for the reflector is increased, and the flatness of the film is deteriorated. Further, the heat shrinkage rate is preferably larger than 0.0%. When it is less than 0.0%, that is, in the direction in which the film is stretched during heating, the film is stretched by the heat of the light source after being incorporated in the backlight unit, so that bending and undulation are likely to occur. The method for adjusting the heat shrinkage rate at 90 ° C. to 0.0 to 0.5% is not particularly limited, but usually the biaxially stretched film is reduced in the draw ratio during production, the heat treatment temperature is increased, and the width direction simultaneously with the heat treatment. And / or a method of performing relaxation treatment in the longitudinal direction. In order to obtain a predetermined heat shrinkage rate in both the longitudinal direction and the width direction, it is preferable to perform relaxation treatment also in the longitudinal direction. For this relaxation treatment, a method (in-line treatment) performed during the production of the biaxially stretched polyester film is preferable from the viewpoint of production cost, but a method of performing relaxation treatment by passing the film once formed into the oven again (offline) Processing).

  Next, although an example is demonstrated about the manufacturing method of the white laminated polyester film for reflectors of this invention, this invention is not limited only to this example.

  In a composite film-forming apparatus having an extruder (A) and an extruder (B), first, in order to form a polyester layer (A), a polyester pellet having a melting point of 230 to 280 ° C. and a master pellet containing an incompatible component, Mix so that the incompatible component is 0.01 to 1.50% by weight, and dry sufficiently. You may add a ultraviolet absorber to this dry raw material as needed. Next, the dried raw material is supplied to an extruder (A) heated to a temperature of 240 to 300 ° C., filtered through a 10 to 50 μm cut filter after melt extrusion, and then introduced into a T-die composite die. . On the other hand, in order to form the polyester layer (B), the polyester pellets vacuum-dried and the pellets of resin incompatible with the vacuum-dried polyester as necessary are mixed and heated to a temperature of 260 to 300 ° C. It is supplied to the extruder (B), melted in the same manner as in the case of the polyester (A) layer, filtered and introduced into the T-die composite die. In addition, you may add a dispersing agent to this raw material as needed. In addition, the incompatible resin may be added by previously drying a master chip in a vacuum. In the T-die composite die, the polymer of the extruder (B) is laminated at the center so that the polymer of the extruder (A) is A / B / A on both surface sides, and coextruded into a sheet and melted A laminated sheet is obtained.

  This melt-laminated sheet is closely cooled and solidified by static electricity on a drum cooled to a surface temperature of 10 to 60 ° C. to produce an unstretched laminated film. The unstretched laminated film is led to a group of rolls heated to a temperature of 70 to 120 ° C., stretched 3 to 4 times in the longitudinal direction (longitudinal direction, that is, the traveling direction of the film), and a group of rolls having a temperature of 20 to 50 ° C. Cool with.

  Subsequently, the both ends of the film are guided to a tenter while being gripped by clips, and stretched 3 to 4 times in a direction (width direction) perpendicular to the longitudinal direction in an atmosphere heated to a temperature of 90 to 150 ° C.

  The stretching ratio is 3 to 4 times in the longitudinal direction and the width direction, respectively, but 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 resulting biaxially stretched laminated film has insufficient reflectivity, concealability, and film strength. Conversely, if the area magnification exceeds 16 times, the film tends to be easily broken during stretching. is there.

  In order to complete the crystal orientation of the obtained biaxially stretched laminated film and to give flatness and dimensional stability, heat treatment is continuously performed in a tenter at a temperature of 150 to 240 ° C. for 1 to 30 seconds, and uniform. After cooling to room temperature, it is cooled to room temperature, and then, if necessary, a corona discharge treatment or the like is performed to further improve the adhesion to other materials, and winding is performed to obtain the void-containing white laminated polyester film of the present invention. be able to. During the heat treatment and the slow cooling step, 1 to 12% relaxation treatment may be performed in the width direction and the longitudinal direction as necessary.

  Biaxial stretching may be either sequential stretching or simultaneous biaxial stretching. However, when the simultaneous biaxial stretching method is used, film breakage in the manufacturing process can be prevented, and the polyester layer (A) can be used as a heating roll. Transfer defects caused by sticking are less likely to occur. Further, after biaxial stretching, the film may be re-stretched in either the longitudinal direction or the width direction.

  The present invention also relates to a backlight device using the above-described white laminated biaxially stretched polyester film for a reflector. Hereinafter, embodiments of a backlight device according to the present invention will be described with reference to the drawings. In addition, although embodiment of this invention is described based on drawing below, those drawings are provided for illustration and this invention is not limited to those drawings.

FIG. 2 is a schematic sectional view showing the configuration of the embodiment of the backlight device according to the present invention.
In the backlight device of this embodiment, a plurality of point light sources 7 are disposed at one end of the light guide plate 4 made of a light transmissive material, and a reflector 5 is provided on the side opposite to the light emitting surface side of the light guide plate 4. The reflector 5 is placed on the housing 6.

  Here, the housing 6 is configured to have irregularities with a height of 5 to 10 mm on the surface facing the reflector 5. Moreover, the white laminated biaxially stretched polyester film for reflectors mentioned above is used for the reflector 5. About the point light source 7, the structure made into any arrangement | positioning of the one side edge part of the light-guide plate 4, a both-sides edge part, and a four side edge part may be sufficient. The light guide plate 4 is not a feature of the present invention, and a detailed description thereof will be omitted.

  In the backlight device of this embodiment, since the above-described white laminated biaxially stretched polyester film for a reflector is used for the reflector 5, even if the reflector 5 is placed on the uneven housing 5, the light source It is possible to suppress the bending of the reflecting plate 5 at the groove portion due to the heat generated from the light source during lighting. Therefore, a backlight device with little luminance unevenness can be obtained.

  Moreover, in the backlight device of this embodiment, the housing 6 has irregularities with a height of 5 to 20 mm on the surface facing the reflector 5, so that the rigidity of the housing itself is increased. Further, the concave portion serves as a vent hole to release heat inside the backlight to the outside, and an abnormal increase in the temperature of the backlight can be suppressed. Furthermore, a wiring board can be accommodated on the back side of the convex portion. In addition, the height of the unevenness was measured by using another scale for the distance of the recess from the scale placed on the convex surface. When the height of the unevenness is less than 5 mm, it is difficult to store the wiring board. When the height is more than 20 mm, it is difficult to make the backlight thin, which is not preferable.

  In the present invention, the size of the backlight device is preferably 26 inches or more and 70 inches or less. Here, the size of the backlight device refers to the length of the diagonal line of the backlight device. Backlights within the above range are less susceptible to bending due to the weight of the film itself constituting the reflector. In addition, a brightness non-uniformity prevention effect is sufficiently obtained with a backlight exceeding the above range.

The present invention will be described with reference to the following examples, but the present invention is not limited thereto.
Moreover, the measuring method and evaluation method of various physical property values are shown below.

[Measurement and evaluation method of characteristics]
(1) Thickness of polyester layer After freezing the film, a cross section is cut out along the longitudinal direction and the width direction, and the cross section is scanned with a scanning electron microscope (SEM) S-2100A (manufactured by Hitachi, Ltd.). The presence or absence of the inclusion of fine cavities was examined from a cross-sectional photograph taken by magnifying and magnifying 4000 times.

  The thickness of each polyester layer was determined by measuring the length in the thickness direction of each polyester layer from the observation photograph of the cross section with a scanning microscope and calculating backward from the magnification. In determining the thickness of each polyester layer, a total of five cross-sectional photographs arbitrarily selected from measurement fields different from each other on the cut surfaces cut out in the longitudinal direction and the width direction were used, and the average value was calculated. . In addition, when the longitudinal direction and the width direction are unknown, a cut surface cut in two mutually perpendicular directions is measured.

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

(3) Relative reflectance Relative reflection with a spectrophotometer (Shimadzu Corporation UV2450) attached with an integrating sphere attachment (ISR2200, Shimadzu Corporation), with barium sulfate as the standard plate and the standard plate as 100% The rate was measured. The relative reflectance at a wavelength of 550 nm was determined according to the following criteria. In addition, (circle) and (triangle | delta) are pass.
○: Good (104% or more)
Δ: Slightly inferior (102% or more and less than 104%)
X: Inferior (less than 102%).

<Standard plate creation method>
34 g of barium sulfate white standard reagent (EASTMAN White Reflectance Standard Cat No.6091) was put into a cylindrical recess having a diameter of 50.8 mm and a depth of 9.5 mm, and compressed using a glass plate, and the compression density was about 2 g / cm. ³ barium sulfate white standard plate was prepared.

(4) Concealing property Using a haze meter (HZ-2 manufactured by Suga Test Instruments Co., Ltd.), the polyester film was measured for total light transmittance according to JIS K7105 (1981), and the concealability was determined according to the following criteria. Went. In addition, (circle) and (triangle | delta) are pass.
○: Good (total light transmittance is less than 2.5%)
Δ: Slightly inferior (total light transmittance is 2.5% or more and less than 3.0%)
X: Inferior (total light transmittance is 3.0% or more).

(5) Thermal contraction rate According to ASTM D1204 (1984), the thermal contraction rate at 90 ° C. for 30 minutes was measured. What averaged the value measured in the longitudinal direction and the width direction was made into the thermal contraction rate of the film.

(6) Bending moment (rigidity)
The bending moment (mN · m) was at a bending angle of 15 ° according to JIS P-8125 (2000), and a taper type stiffness tester TELEDYNE TABER MODEL150-D (manufactured by North Tonawanda, New York USA) was used.

(7) Heat deflection value A film with a length of 297 mm and a width of 210 mm is placed on an iron block with a width of 120 mm, a length of 155 mm, and a height of 25 mm, and the film is aligned at the center on the iron block at 90 ° C. After being left in the hot air oven for 3 minutes, the deflection distance shown in FIG. 1 was measured at four corners of the film in the oven, and the average value was taken as the thermal deflection value. When there is no thermal deflection, it is 0 mm, and when the thermal deflection is 25 mm or more, it is 25 mm.

(8) Uneven brightness
Samsung Co., Ltd. C7000 series 46-inch model backlight (light guide plate with pattern printing of 5 mm thickness, a plurality of LED light sources arranged on the left and right sides of the light guide plate, and the light emitting surface side of the light guide plate The backlight is provided with a reflecting plate disposed on the opposite side of the housing and a casing on which the reflecting plate is placed, and is arranged substantially parallel to each other on the reflecting plate side of the casing. A backlight having an electronic board stored on the back side of the convex portion of the casing, which has four concave portions connected to the portion and a convex portion (height 7 mm) partitioned by the concave portion and the upper and lower sides of the casing. The reflection film that was pasted together was changed to a predetermined film sample and turned on. In this state, after waiting for 1 hour to stabilize the light source, the liquid crystal screen was photographed with a CCD camera (DXC-390 manufactured by SONY), and an image was captured using an eye scale manufactured by an image analyzer Eye System. Thereafter, the brightness level of the photographed image was controlled to 30,000 steps to be automatically detected and converted to brightness. The luminance uniformity was evaluated according to the following formula. Those that could not be visually recognized as unevenness were evaluated as acceptable (◯) and evaluated as follows.
Brightness unevenness (%) = (maximum value−minimum value) / average value × 100
○: Good (Luminance unevenness is less than 10%)
Δ: Somewhat inferior (brightness unevenness of 10% or more and less than 20%)
X: Inferior (brightness unevenness of 20% or more).

(9) Density of polyester layer (A) (adjustment of sample) A blade is put in the film cross section, and the polyester layer (A) portion is peeled off. When the polyester layer (B) is adhered, it is scraped off with a single blade or a file, and five 30 mm × 30 mm samples are prepared.
(Density measurement)
The sample was measured using an electronic hydrometer based on JIS K7112 (1980). In addition, five samples were prepared, each was measured, and the average value was made into the density of the polyester layer (A). SD-120L manufactured by Mirage Trading Co., Ltd. was used as the electronic hydrometer.

(10) Insert a blade into the internal haze (sample adjustment) film cross section of the polyester layer (A), and peel off the polyester layer (A). When the polyester layer (B) is adhered, it is scraped off with a single blade or a file, and five 30 mm × 30 mm samples are prepared.
(Measurement of internal haze)
Based on JIS K7105 (1985), it measured using the haze meter (HGM-2DP by Suga Test Instruments Co., Ltd.). An internal haze was obtained by placing a film in a glass cell for liquid measurement, filling the periphery with tetralin, and performing measurement. Five samples were prepared, each was measured, and the average value was taken as the internal haze of the polyester layer (A).

<Example 1>
(Manufacture of polyethylene terephthalate pellets (PET))
Using terephthalic acid as the acid component and ethylene glycol as the glycol component, adding to the polyester pellets that can obtain antimony trioxide (polymerization catalyst) to 300 ppm in terms of antimony atoms, performing a polycondensation reaction, limiting viscosity Polyethylene terephthalate pellets (PET) having 0.63 dl / g and carboxyl end group amount of 40 equivalents / ton were obtained.

  In a composite film-forming apparatus having an extruder (a) and an extruder (b), the raw material master pellet mixture shown in Table 1 was vacuum-dried at a temperature of 160 ° C. for 5 hours in order to form a polyester layer (A). Thereafter, the mixture was supplied to the extruder (a) side, melt-extruded at a temperature of 280 ° C., filtered with a 30 μm cut filter, and then introduced into a T-die composite die.

Abbreviations in Table 1 have the following meanings.
SiO ₂ : silicon dioxide (volume average particle diameter 1.5 μm)
BaSO ₄ : Barium sulfate (average particle size 0.5 μm)
・ PMP: Polymethylpentene (“TPX” manufactured by Mitsui Chemicals, Inc.)
PBT / PAG: Block copolymer of polybutylene terephthalate (PBT) and polyalkylene glycol (PAG) (“Hytrel (R)” (registered trademark) manufactured by Toray DuPont)
COC: Cyclic olefin copolymer (copolymer resin of ethylene and norbornene) (“TOPAS” manufactured by Polyplastics)
On the other hand, in order to form the polyester layer (B), the raw material mixture shown in Table 1 was vacuum-dried at a temperature of 160 ° C. for 5 hours, then supplied to the extruder (b) side and melt-extruded at a temperature of 280 ° C. After the foreign matter was filtered with a 30 μm cut filter, it was introduced into a T-die composite die.

  Next, in the T-die composite die, the polyester layer (A) is merged so as to be laminated (A / B / A) on both surface layers of the polyester layer (B), and then co-extruded into a sheet to obtain a melt-laminated sheet. The melt-laminated sheet was closely cooled and solidified by an electrostatic charge method on a drum maintained at a surface temperature of 18 ° C. to obtain an unstretched laminated film. Subsequently, the unstretched laminated film is preheated with a roll group heated to a temperature of 85 ° C. according to a conventional method, and then stretched 3.4 times in the longitudinal direction (longitudinal direction) using a heating roll having a temperature of 90 ° C. And cooled with a roll group at a temperature of 25 ° C. to obtain a uniaxially stretched film.

  While holding both ends of the obtained uniaxially stretched film with clips, it is guided to a preheating zone at a temperature of 90 ° C. in the tenter, and continuously in a heating zone at a temperature of 100 ° C. in a direction perpendicular to the longitudinal direction (width direction). The film was stretched by a factor of 3.4. Subsequently, after a heat treatment for 10 seconds at a temperature of 190 ° C. in a heat treatment zone in the tenter, a relaxation treatment was performed in a 4% width direction at a temperature of 180 ° C., and then a 1% width direction at a temperature of 150 ° C. The relaxation treatment was performed. Next, while uniformly cooling slowly, the film relaxes in the longitudinal direction by 0.3% at the tenter outlet, is wound, and the thickness of the polyester layer (A) and the polyester layer (B) having a cavity inside is 23/274/23. A white laminated polyester film having a thickness of 320 μm having a (μm) A / B / A three-layer composite structure was obtained. This white laminated polyester film contained many fine cavities in the polyester layer (B).

  The characteristics of the white laminated polyester film thus obtained are as shown in Table 2 and Table 3. The polyester layer (A) is thick and has high rigidity and is not easily heat-deflected, and also has uniform brightness, reflectivity, and concealment. It was particularly excellent.

<Example 2>
Using the raw materials shown in Table 1, in the same manner as in Example 1, the polyester layer (A) and the polyester layer (B) having a cavity inside had a thickness of 13/274/13 (μm) A / A white laminated polyester film having a thickness of 300 μm having a B / A three-layer composite structure was obtained. The characteristics of the obtained white laminated polyester film were as shown in Tables 2 and 3, and were within the acceptable range although the rigidity, thermal deflection, and luminance uniformity were slightly inferior.

<Example 3>
Using the raw materials shown in Table 1, in the same manner as in Example 1, the polyester layer (A) and the polyester layer (B) having cavities inside had a thickness of 38/274/38 (μm). A white laminated polyester film having a thickness of 350 μm having a B / A three-layer composite structure was obtained. The characteristics of the obtained white laminated polyester film are as shown in Table 2 and Table 3. Although the polyester layer (A) has high rigidity and is difficult to bend due to heat, the thicker the polyester layer (A), the greater the internal absorption of light. Although it was a little inferior, it was in the range of the pass.

<Example 4>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 320 μm having a 23/274/23 (μm) A / B / A three-layer composite structure similar to Example 1 was obtained. The characteristics of the obtained white laminated polyester film are as shown in Table 2 and Table 3, and although it has high rigidity and is difficult to bend, the film may meander because the amount of particles of the polyester layer (A) is small. Yes, the film formation stability was slightly inferior, but was within the acceptable range.

<Example 5>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 320 μm having a 23/274/23 (μm) A / B / A three-layer composite structure similar to Example 1 was obtained. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3, and since the polyester layer (A) has a large amount of particles, a large number of voids are formed in the polyester layer (A), so the rigidity is slightly inferior. Although the relative reflectance was somewhat low, it was within the acceptable range.

<Example 6>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 301 μm was obtained in the same manner as in Example 1 and having a 23/255/23 (μm) A / B / A three-layer composite structure. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3, and the overall thickness was thin, but the rigidity, thermal deflection, relative reflectivity, and concealment were somewhat inferior, but within the acceptable range. .

<Example 7>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 486 μm was obtained in the same manner as in Example 1 and having a 23/440/23 (μm) A / B / A three-layer composite structure. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3, and the polyester layer (B) is thick and has high rigidity and is not easily thermally deformed, but is slightly inferior in film formation stability but passed. It was within the range.

<Example 8>
Using the raw materials shown in Table 1, after performing a relaxation treatment in the 3% width direction at a temperature of 180 ° C., further performing a relaxation treatment in a 1.5% width direction at a temperature of 150 ° C. A white laminated polyester film having a thickness of 320 μm having a similar A / B / A three-layer composite structure of 23/274/23 (μm) was obtained. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3, and although it is somewhat easy to bend by heat, it has high rigidity, high reflectivity and concealability, and has excellent characteristics.

<Example 9>
23/274/23 (μm) A / B / A three-layer composite structure as in Example 1 using the raw materials shown in Table 1 and performing 3.7-fold stretching in the longitudinal direction (longitudinal direction) A white laminated polyester film having a thickness of 320 μm was obtained. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3, and although it is somewhat inferior in rigidity, heat deflection, and film formation, it has particularly high reflectance and concealment, and has excellent characteristics. It was.

<Example 10>
23/274/23 (μm) A / B / A three-layer composite structure as in Example 1 using the raw materials shown in Table 1 and stretching 3.1 times in the longitudinal direction (longitudinal direction) A white laminated polyester film having a thickness of 320 μm was obtained. The characteristics of the obtained white laminated polyester film were as shown in Tables 2 and 3, and although they had high rigidity, they were easy to bend due to heat and were slightly inferior in reflectance and concealment, but were in the acceptable range.

<Example 11>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 320 μm having a 23/274/23 (μm) A / B / A three-layer composite structure similar to Example 1 was obtained. The characteristics of the obtained white laminated polyester film were as shown in Tables 2 and 3, and improved in reflectivity and concealment properties, but were somewhat susceptible to heat deflection, but were within the acceptable range.

<Example 12>
Using the raw materials shown in Table 1, in the same manner as in Example 1, the polyester layer (A) and the polyester layer (B) having cavities inside had a thickness of 38/274/38 (μm). A white laminated polyester film having a thickness of 350 μm having a B / A three-layer composite structure was obtained. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3. The polyester layer (A) is thick and has large light internal absorption, but the reflectivity and concealability are slightly improved, but the rigidity is high. And the heat deflection was within the acceptable range.

<Example 13>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 486 μm was obtained in the same manner as in Example 1 and having a 23/440/23 (μm) A / B / A three-layer composite structure. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3, and since the polyester layer (B) is thick, the rigidity is very high. However, because there is a little PBT / PAG, heat deflection is easy. Since the apparent density was low, the film formation stability was slightly inferior, but it was within the acceptable range.

<Example 14>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 320 μm was obtained in the same manner as in Example 1 and having an A / B / A three-layer composite structure of 23/274/23 (μm). The results obtained by incorporating the obtained white laminated polyester film into a backlight casing having a concavo-convex height of 20 mm different from those in the above examples are as shown in Tables 2 and 3, and the polyester layer (A) is thick. It had high rigidity and was not easily heat-deflected, and was particularly excellent in luminance uniformity, reflectivity, and concealment.

<Example 15>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 320 μm was obtained in the same manner as in Example 1 and having an A / B / A three-layer composite structure of 23/274/23 (μm). The characteristics of the obtained white laminated polyester film are as shown in Table 2 and Table 3. The properties were high in rigidity, good luminance uniformity, and particularly excellent in reflectance and concealment.

<Example 16>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 320 μm was obtained in the same manner as in Example 1 and having an A / B / A three-layer composite structure of 23/274/23 (μm). The characteristics of the obtained white laminated polyester film are as shown in Table 2 and Table 3. The properties were high in rigidity, good luminance uniformity, and particularly excellent in reflectance and concealment.
<Example 17>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 400 μm having an A / B / A three-layer composite structure of 23/354/23 (μm) was obtained in the same manner as in Example 1. The characteristics of the obtained white laminated polyester film are as shown in Table 2 and Table 3. The properties were high in rigidity, good luminance uniformity, and particularly excellent in reflectance and concealment.
<Example 18>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 320 μm having a 23/274/23 (μm) A / B / A three-layer composite structure similar to Example 1 was obtained. The characteristics of the obtained white laminated polyester film are as shown in Table 2 and Table 3, where the amount of particles of the polyester layer (A) is large, and since many voids are formed in the polyester layer (A), the rigidity is slightly inferior, Although the relative reflectance was somewhat low, it was within the acceptable range.
<Example 19>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 320 μm having a 23/274/23 (μm) A / B / A three-layer composite structure similar to Example 1 was obtained. The characteristics of the obtained white laminated polyester film are as shown in Table 2 and Table 3, where the amount of particles of the polyester layer (A) is large, and since many voids are formed in the polyester layer (A), the rigidity is slightly inferior, Although the relative reflectance was somewhat low, it was within the acceptable range.

<Comparative Example 1>
Using the raw materials shown in Table 1, in the same manner as in Example 1, the polyester layer (A) and the polyester layer (B) having cavities inside had a thickness of 10/274/10 (μm) A / A white laminated polyester film having a thickness of 294 μm having a B / A three-layer composite structure was obtained. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3, and the rigidity was low, the film was easily deformed by heat, and the brightness uniformity was very poor.

<Comparative Example 2>
Using the raw materials shown in Table 1, in the same manner as in Example 1, the polyester layer (A) and the polyester layer (B) having a cavity inside had a thickness of 42/274/42 (μm) A / A white laminated polyester film having a thickness of 358 μm having a B / A three-layer composite structure was obtained. The characteristics of the obtained white laminated polyester film are as shown in Table 2 and Table 3, and although they have high rigidity and are difficult to bend thermally, the relative reflectance was low.

<Comparative Example 3>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 320 μm having a 23/274/23 (μm) A / B / A three-layer composite structure similar to Example 1 was obtained. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3, and the film formation was unstable although it was highly rigid and difficult to bend.

<Comparative Example 4>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 320 μm having a 23/274/23 (μm) A / B / A three-layer composite structure similar to Example 1 was obtained. The characteristics of the obtained white laminated polyester film were as shown in Table 2 and Table 3, and were low in rigidity and slightly low in relative reflectance.

<Comparative Example 5>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 258 μm was obtained in the same manner as in Example 1 and having a 23/212/23 (μm) A / B / A three-layer composite structure. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3, and because the rigidity is low and heat deflection is easy, the luminance uniformity is poor, and the relative reflectance and the hiding property are very inferior.

<Comparative Example 6>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 516 μm was obtained in the same manner as in Example 1 and having a 23/470/23 (μm) A / B / A three-layer composite structure. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3, and the film formation was very unstable although it had high rigidity and was difficult to bend.

<Comparative Example 7>
Using the raw materials shown in Table 1, after performing a relaxation treatment in the 2% width direction at a temperature of 180 ° C., further performing a relaxation treatment in the 1% width direction at a temperature of 150 ° C., the same as in Example 1 A white laminated polyester film having a thickness of 320 μm having an A / B / A three-layer composite structure of 23/274/23 (μm) was obtained. The characteristics of the obtained white laminated polyester film were as shown in Tables 2 and 3, and the heat uniformity was high and the luminance uniformity was slightly inferior because of the high thermal shrinkage.

<Comparative Example 8>
23/274/23 (μm) A / B / A three-layer composite structure as in Example 1 using the raw materials shown in Table 1 and stretching 3.9 times in the longitudinal direction (longitudinal direction) A white laminated polyester film having a thickness of 320 μm was obtained. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3, and the rigidity was low and the film was easily deformed, and the film formation was very unstable.

<Comparative Example 9>
23/274/23 (μm) A / B / A three-layer composite structure as in Example 1 using the raw materials shown in Table 1 and stretching 2.9 times in the longitudinal direction (longitudinal direction) A white laminated polyester film having a thickness of 320 μm was obtained. The characteristics of the obtained white laminated polyester film were as shown in Tables 2 and 3, and although they had very high rigidity, they were easy to bend due to heat and poor in reflectance and concealment.

<Comparative Example 10>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 516 μm was obtained in the same manner as in Example 1 and having a 23/470/23 (μm) A / B / A three-layer composite structure. The characteristics of the obtained white laminated polyester film are as shown in Tables 2 and 3, and have high rigidity, reflectivity and concealment, but are easily deformed by heat, and the film formation was very unstable. .

<Comparative Example 11>
Using the raw materials shown in Table 1, a white laminated polyester film having a thickness of 320 μm having a 23/274/23 (μm) A / B / A three-layer composite structure similar to Example 1 was obtained. The characteristics of the obtained white laminated polyester film are as shown in Table 2 and Table 3, and the heat shrinkage rate was high and the film was easily deformed.

DESCRIPTION OF SYMBOLS 1 Iron block 2 Film 3 Heat deflection value 4 Light guide plate 5 Reflector plate 6 Case 7 Light source

Claims (3)

A laminated polyester film in which a polyester layer (A) is laminated on both sides of a polyester layer (B) containing a cavity therein, and the laminated polyester film satisfies all the following requirements (1) to (5) The white laminated biaxial stretching for a reflector is characterized in that the average of the bending moment in the longitudinal direction and the width direction at a bending angle of 15 degrees by a Taber stiffness tester is 3.5 to 9.5 mN · m. Polyester film.
(1) The thickness of the polyester layer (A) is 12 to 40 μm.
(2) The polyester layer (A) is a layer formed by using polyester and the polyester incompatible component (incompatible component), and the content of the incompatible component in the polyester layer (A) On the other hand, it should be 0.01 to 1.50% by weight.
(3) The thickness of the polyester layer (B) is 250 to 450 μm.
(4) The thermal contraction rate in the longitudinal direction and the width direction at 90 ° C. for 30 minutes of the laminated polyester film is 0.0 to 0.5%.
(5) The apparent density of the laminated polyester film is 0.5 to 0.9 g / cm ³ . The laminated polyester film for a reflector according to claim 1, wherein the density of the polyester layer (A) is 1.1 to 1.5 g / cm ³ . A light guide plate, a plurality of point light sources arranged at least on one side end of the light guide plate, a reflection plate arranged on the side opposite to the light emitting surface side of the light guide plate, and a housing for mounting the reflection plate It is a backlight apparatus provided with the body, Comprising: The said housing | casing has the unevenness | corrugation of 5-20 mm in height in the surface which opposes a reflecting plate, The said reflecting plate is Claim 1 or 2 . A backlight device characterized by being a white laminated biaxially stretched polyester film for a reflector.

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