JP2012179816A - White laminated polyester film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a white laminate polyester film for a reflective sheet capable reducing the generation of unevenness in luminance while maintaining high luminance in a backlight device for a thin type large screen installed with an LED light source at a side face, particularly, a back light device for a monitor of 20 inches or larger, in regard to the white laminated polyester film with superior reflection characteristics, concealment, rigidity, and scratch mark resistance.SOLUTION: The white laminated polyester film is a biaxially oriented polyester film having at least two layers being an A layer and a B layer composed of polyester. Cyclic olefin copolymers and inorganic particles are included in the B layer, and when a film surface is vertically cut, a cavity occupation ratio in a B layer cross section is ≥10% and ≤25%, and the cavity occupation ratio of the inorganic particles is ≥7% and ≤27%. 20-35 wt.% of the inorganic particles are included in the A layer, the thickness of the A layer is 2-16 μm, and the thickness of the whole white laminated polyester film is ≥150 μm and ≤350 μm.

Description

  The present invention relates to a white laminated polyester film suitable for use as a light reflecting plate. More specifically, the present invention relates to a polyester film containing voids inside the film, excellent in reflection characteristics, concealment properties, and reduced brightness unevenness, and includes a backlight device for image display and a reflection sheet for a lamp reflector, The present invention relates to a white laminated polyester film that can be suitably used for a reflective sheet for lighting equipment, a reflective sheet for lighting signs, a back reflective sheet for solar cells, and the like, and particularly suitable for a reflector of a backlight device for image display. Is.

  A white polyester film has a uniform and high brightness for applications such as reflectors and reflectors for surface light source devices, back reflector sheets for lighting signs, and back reflector sheets for solar cells in flat image display systems used in liquid crystal displays, etc. It is widely used because of its characteristics such as dimensional stability and low cost. As a method to achieve high brightness, polyester film contains many inorganic particles such as barium sulfate, and uses light reflection at the interface between the polyester resin and the particles and the hollow interface of the fine cavities generated using the particles as nuclei. (Refer to Patent Document 1), a method of utilizing light reflection at the cavity interface of fine cavities generated by mixing an incompatible resin with polyester and using an incompatible resin as a nucleus (Patent Document 2) Inorganic contained in the polyester film, such as a method utilizing light reflection at the interface of the cavity formed inside by impregnating the polyester film with an inert gas in a pressure vessel (see Patent Document 3) A method using a difference in refractive index between particles and polyester resin and a difference in refractive index between fine voids and polyester resin is widely used.

In recent years, in particular, the use of liquid crystal displays has been dramatically expanded, and in addition to conventional notebook computers, monitors, and portable terminals, it has been widely used for liquid crystal televisions, etc., with higher screen brightness and higher definition. There is a demand for larger screens. As the screen brightness increases, the reflective sheet is required to have higher brightness and higher hiding properties, and it is necessary to increase the reflective interface, such as increasing the amount of inorganic particles in the polyester film and increasing the number of cavities. It had been.
On the other hand, as the light source of the liquid crystal display, a method using an LED light source with low power consumption and high output is used. In addition to the method of arranging the light source on the back of the conventional backlight device, the light source is arranged on the side A system that is advantageous for reducing the thickness is adopted. Correspondingly, the LED backlight housing has an uneven shape with a height of 10 mm or less for improving the strength of the housing, storing the electrical wiring and the base, and heat dissipation at the edge of the housing near the LED light source. There may be a groove processing.

JP 2003-160682 A Japanese Patent Publication No. 8-16175 JP 2001-166295 A

  However, in response to the increase in screen size, the conventional reflective sheet that has increased the number of cavities and achieved high brightness has a low rigidity due to the large number of cavities, causing problems such as folding and wrinkling of the reflective sheet during processing and assembly, In order to ensure rigidity, it is necessary to increase the thickness of the film, resulting in an increase in cost.

  Further, in the method in which the LED light source is arranged on the side surface, the reflection sheet is installed on the above-described uneven housing, and the light guide plate is further superimposed on the reflection sheet. The reflection sheet is pressed against the uneven portion of the casing by the weight. For this reason, the conventional reflective sheet has scratches due to the uneven portions on the surface, and there is a concern that uneven brightness occurs. In addition, there is a problem that the reflection sheet is bent along the dent of the housing and uneven brightness occurs.

  An object of the present invention is to solve the above problems and provide a white laminated polyester film for a reflection sheet in which scratches caused by unevenness of a casing and luminance unevenness due to deflection of the reflection sheet are reduced. In particular, it is an object of the present invention to provide a white laminated polyester film for a reflection sheet that is suitably used in a monitor backlight device having a LED light source disposed on the side surface of 20 inches or more.

  The white laminated polyester film of the present invention that solves the above problems is a biaxially stretched polyester film having at least two layers of a layer A and a layer B composed of polyester, and a cyclic olefin copolymer in the layer B And the inorganic particles are included, the void occupancy in the cross section of the B layer when cut perpendicularly to the film surface is 10% or more and 25% or less, the occupancy of the inorganic particles is 7% or more and 27% or less, The layer A contains 20 to 35% by weight of inorganic particles, the layer A has a thickness of 2 to 16 μm, and the total thickness of the white laminated polyester film is 150 to 350 μm.

  The white laminated polyester film of the present invention is a white laminated polyester film having excellent reflection characteristics, concealing properties, rigidity, and scratch resistance by defining the cross-sectional structure of the B layer and the amount of inorganic particles in the A layer. Obtainable. Therefore, in a thin large-screen backlight device in which the LED light source is arranged on the side surface, it is possible to reduce the occurrence of luminance unevenness while maintaining high luminance, and in particular, the LED light source is arranged on the side surface of 20 inches or more. It can be used as a suitable reflective sheet in a monitor backlight device. In addition, because it is highly rigid and has excellent scratch resistance, it can reduce creases and scratches that occur during processing and assembly, and is not limited to thin large-screen LED backlight devices, but also as a reflective sheet for LCDs in general. It can be preferably used.

  The present inventors have solved the above problems, 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 following are mentioned as a component which the polyester resin used for the white laminated polyester film of this invention comprises. 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, etc. of the polyester film to be produced, it is preferable that the polyester resin in the present invention has 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 the copolymer component may be used as a pellet in which a copolymer component is polymerized in advance. For example, polybutylene terephthalate is used. Alternatively, a method may be used in which a mixture of pellets independently polymerized 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. %.

  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, a titanium compound and a germanium compound are preferable because a metal catalyst aggregate that absorbs light is difficult to generate, and a titanium compound is preferable from the viewpoint of cost. Specific examples of titanium compounds include titanium alkoxides such as titanium tetrabutoxide and titanium tetraisopropoxide, and composite oxides and titanium complexes in which the main metal element such as titanium dioxide silicon dioxide composite oxide is composed of titanium and silicon. Can be used. In addition, ultrafine titanium oxide such as titanium-silicon composite oxide (trade name: C-94) manufactured by Accordis may be used.

  In these polyester resins, various additives such as a fluorescent brightening agent, a crosslinking agent, a heat stabilizer, an oxidation stabilizer, an ultraviolet absorber, an organic lubricant, an inorganic lubricant, and the like within the range not impairing the effects of the present invention. Fine particles, fillers, light-proofing agents, antistatic agents, nucleating agents, dyes, dispersing agents, coupling agents, and the like may be added.

  In the present invention, the B layer composed of polyester needs to contain both the cyclic olefin copolymer and the inorganic particles. By containing the cyclic olefin copolymer in the polyester resin, a cavity having the cyclic olefin copolymer as a nucleus is formed at the time of stretching, and light reflection occurs at the cavity interface. Therefore, in order to obtain a high reflectance, this cavity should be increased. However, an increase in the number of cavities may reduce the reflective interface due to the coupling between the cavities, leading to a decrease in the strength of the reflective sheet, and the cavities are likely to be destroyed when a local force is applied to the reflective sheet. For this reason, when the reflective sheet is incorporated into a thin, large screen LED backlight housing, scratches may be formed on the reflective sheet due to the uneven portions of the housing, and uneven brightness may occur. Further, it is not preferable because a foreign matter mixed at the time of processing or assembling may cause scratches and reduce the yield. Furthermore, the increase in the cavities decreases the apparent density of the reflection sheet and decreases the rigidity, which deteriorates the crease resistance. Therefore, it is not preferable because the reflection sheet is bent by processing and assembling, and the reflection sheet is bent by the concavo-convex portion of the housing, resulting in uneven brightness. On the other hand, since inorganic particles scatter light, their addition improves the reflectance. However, excessive addition of inorganic particles is not preferable because the reflectance is lowered by light absorption of the inorganic particles and the effect of improving the reflectance is reduced by aggregation of the inorganic particles. Further, it is not preferable from the viewpoint of film formation stability. Furthermore, when used in combination with a cyclic olefin copolymer as in the present invention, it is not preferable because uniform formation of cavities with the cyclic olefin copolymer as a nucleus is inhibited and scratch resistance is deteriorated.

Therefore, in order to obtain a reflective sheet that is excellent in rigidity and scratch resistance, reduces unevenness in brightness, and maintains high brightness, the white laminated polyester film of the present invention is obtained by cutting perpendicularly to the film surface. It is necessary that the cavity occupation ratio in the cross section of the B layer is 10% or more and 25% or less, and the occupation ratio of the inorganic particles is 7% or more and 27% or less. If the cavity occupancy in the cross section of the B layer is less than 10%, the rigidity and scratch resistance are excellent, and the occurrence of uneven brightness can be reduced, but it is not preferable because sufficient brightness cannot be obtained. On the other hand, if the cavity occupancy in the cross section of the layer B exceeds 25%, the luminance increases, but the rigidity and scratch resistance are lowered and luminance unevenness occurs, which is not preferable. Furthermore, even if the cavity occupation ratio in the cross section of the B layer is 10% or more and 25% or less, if the occupation ratio of the inorganic particles in the cross section of the B layer is less than 7%, sufficient luminance cannot be obtained. Undesirably, if the occupancy ratio of the inorganic particles in the cross section of the layer B exceeds 27%, the film-forming stability is deteriorated and the brightness is lowered, and the scratch resistance is also deteriorated and uneven brightness may occur. It is not preferable.
In the present invention, the cyclic olefin copolymer contained in the layer B includes bicyclo [2,2,1] hept-2-ene, 6-methylbicyclo [2,2,1] hept-2-ene, 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 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-dece Amorphous cyclic olefin resin such as 10-methyl-tricyclo [4,4,0,12.5] -3-decene and a crystalline polyolefin resin such as ethylene, propylene, butene and methylpentene are copolymerized. Etc. These may be homopolymers or copolymers, or two or more of them may be used in combination. In particular, a resin having a large difference in critical surface tension from polyester and not easily deformed by heat treatment after stretching is preferred, and among these, a copolymer of ethylene and bicycloalkene is particularly preferred. Further, when the film is stretched, the cyclic olefin copolymer may be plastically deformed and the formation of the cavity may be hindered. Therefore, the glass transition temperature Tg of the cyclic olefin copolymer is preferably 160 to 220 ° C.

  In the white laminated polyester film of the present invention, the cyclic olefin copolymer is dispersed in a matrix made of a polyester resin with a number average particle size of 0.4 to 3.0 μm. It is preferable for obtaining strength, and more preferably in the range of 0.5 to 1.5 μm. The number average particle size here refers to the area of 100 particles observed by using a scanning electron microscope (FE-SEM) S-2100A manufactured by Hitachi, Ltd. It is the average value of the diameter when converted into a yen.

  The copolymerization component of the copolymerized polyester resin to be mixed in the B layer is a copolymerized polyester resin in which the main component of the diol component is an alicyclic glycol among the above-described copolymerization components. This is preferable because it has a function of stabilizing the dispersion state of the olefin copolymer. The content of the copolymer component is preferably 1% by weight or more and 10% by weight or less, more preferably 1% by weight or more, with respect to the total amount of the constituent components of the layer containing the void (B layer). 6% by weight or less.

  Furthermore, in order to finely disperse a cyclic olefin copolymer incompatible with polyester into a preferred shape, a block of a polyalkylene glycol, a polyester resin composed of an aliphatic diol component having 2 to 6 carbon atoms and terephthalic acid It is preferable to add a copolymer resin. Among these, a block copolymer of polyalkylene glycol and polybutylene terephthalate is particularly preferable. Such a resin may be used as a polyester obtained by copolymerizing the resin in advance in a polymerization reaction or may be used directly as it is. The addition amount is preferably 2 to 10% by weight with respect to the total amount of the constituent components of the layer containing voids (B layer) in view of the effect of refining the cyclic olefin copolymer, more preferably 3 to 3%. 9% by weight. Excessive addition is not preferable because the film-forming stability is lowered and the cost is increased.

  In the present invention, examples of the inorganic particles contained in the layer B include calcium carbonate, titanium dioxide, zinc oxide, zirconium oxide, zinc sulfide, basic lead carbonate (lead white), and barium sulfate. Thus, 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, manufacturing costs, and the like. In the present invention, when calcium carbonate is used, it is preferable to use colloidal calcium carbonate in order to obtain stability and an appropriate dispersion diameter. In addition, when titanium dioxide is used, the rutile type has a higher refractive index because the crystal structure is denser than that of the anatase type. Since it can be obtained, it is preferable to use rutile type titanium dioxide. As the particle diameter, it is preferable to use a number average particle diameter of 0.1 to 0.7 μm in order to realize excellent reflectivity and concealment. More preferably, it is 0.2-0.5 micrometer.

In this invention, it is preferable that content of the cyclic olefin copolymer and inorganic particle contained in B layer satisfy | fill all the following formula | equation.
3 ≦ a ≦ 8, 10 ≦ b ≦ 30
Here, a: content of the cyclic olefin copolymer with respect to the total amount of the constituent components of the B layer (% by weight), b: content of inorganic particles with respect to the total amount of the constituent components of the B layer (% by weight) ). Since the number of cavities increases by increasing the content of the cyclic olefin copolymer, the cavity occupancy increases. Further, when the content of the inorganic particles increases, the inorganic particle occupation ratio in the layer B increases, but the inorganic particles may bind cavities generated by the cyclic olefin copolymer. The cavity occupancy depends on the stretching conditions and is not limited to this. However, the content of the cyclic olefin copolymer and inorganic particles contained in the B layer is within the above range, and the film was cut perpendicular to the film surface. Cavity occupancy in the cross section of layer B is preferably 10% or more and 25% or less, and inorganic particle occupancy is preferably 7% or more and 27% or less.

In the present invention, in order to obtain a reflection sheet having excellent rigidity and scratching properties and reduced luminance unevenness, it is not sufficient to set the void occupancy and particle occupancy of the B layer within the above ranges, and the surface layer is laminated. It is necessary that the A layer contains inorganic particles and the content of the inorganic particles is 20 to 35% by weight based on the total amount of the constituent components in the A layer. The thickness of the A layer needs to be 2 μm or more and 16 μm or less. The layer A laminated on the surface layer has a function of imparting functions such as surface glossiness adjustment, whiteness adjustment, and light resistance, and stabilizing the film formation, and also makes the B layer cavity difficult to crush. This is because it also plays a role of a protective layer to make it difficult for traces to occur.
In the present invention, it is necessary for the A layer to contain airless particles. By adding inorganic particles, the hardness of the film surface is improved, and the surface is also smooth, so that a film having excellent scratch resistance can be obtained. In addition, the improvement of surface slip is preferable from the viewpoint of handling properties.

  Here, the kind of inorganic fine particles to be contained in the layer A is not particularly limited, but preferably has a Mohs hardness of 3.0 or more from the viewpoint of scratch resistance, such as calcium carbonate, titanium dioxide, Examples thereof include zinc oxide, zirconium oxide, zinc sulfide, basic lead carbonate (lead white), barium sulfate, and alumina. Among these, from the viewpoint of ultraviolet resistance, titanium oxide, zinc oxide, alumina and the like are preferable because they have an ultraviolet absorbing function. These inorganic particles can be used alone or in combination depending on the necessity of imparting surface functions other than scratch resistance such as glossiness adjustment, whiteness adjustment, and light resistance.

  In the present invention, the content of the inorganic particles in the A layer needs to be 20 to 35% by weight, more preferably 24 to 30% by weight, based on the total amount of the constituent components in the A layer. preferable. When the content of the inorganic particles is less than 20% by weight, the surface hardness is lowered and scratch resistance is lowered, which is not preferable. In addition, when the content of the inorganic particles exceeds 35% by weight, it is not preferable because scraping due to particle dropping occurs. Moreover, when the film forming stability deteriorates due to deterioration of the stretchability of the film, or when inorganic particles having absorption in the visible light region of 400 to 700 nm are used, the amount of light reaching the B layer which is a reflective layer is decreased. As a result, the luminance may be lowered, which is not preferable.

  The number average particle diameter (diameter) of the inorganic particles contained in the A layer of the present invention is preferably 0.1 μm or more and 5.0 μm or less, more preferably 0.1 μm or more and 3.0 μm or less. If the thickness is less than 0.1 μm, the particles are aggregated and easily coarsened, and the scratch resistance is lowered. On the other hand, if the thickness exceeds 5.0 μm, the particles are likely to drop off, so that the scratch resistance may be lowered, or the dropped particles may be a foreign substance and damage the light guide plate.

  In the present invention, the thickness of the A layer needs to be 2 μm or more and 16 μm or less, and more preferably 4 μm or more and 8 μm or less. The reflective sheet of the present invention improves the scratch resistance by laminating the A layer containing inorganic particles on the surface layer of the B layer containing cavities, but the thickness of the A layer is less than 2 μm. If so, the effect of improving scratch resistance may not be sufficiently exhibited, and problems such as peeling off of the A layer may occur. In addition, when titanium oxide, zinc oxide, alumina or the like is used for the purpose of imparting light resistance to the A layer, or when barium sulfate, calcium carbonate or the like is used for improving the reflectance, the thickness of the A layer is If it is less than 2 μm, the function is not sufficiently exhibited, which is not preferable. On the other hand, when the thickness of the A layer exceeds 16 μm, the loss of light energy in the A layer cannot be ignored, and the light does not sufficiently reach the B layer that is the reflective layer. Further, since the light reaching the B layer cannot be efficiently emitted outside the film after being multiple-reflected at the cavity interface, the optical path length becomes long and a loss occurs. Therefore, high luminance cannot be obtained, which is not preferable. Moreover, when the thickness of A layer exceeds 16 micrometers, it is unpreferable also from a viewpoint that the reuse of the waste chip collect | recovered from the manufacturing process of a film is difficult.

  In the present invention, the total thickness of the white laminated polyester film is 150 μm or more and 350 μm or less, preferably 180 μm or more and 250 μm or less. If the total thickness of the white laminated polyester film is less than 150 μm, the reflectance is insufficient and the rigidity is lowered, which is not preferable. Further, the upper limit is not particularly limited, but if it exceeds 350 μm, an increase in the reflectance cannot be expected even if it is thicker than this, and the cost increases, which is not preferable.

  The white laminated polyester film of the present invention may have a two-layer configuration of A layer / B layer, a three-layer configuration of A layer / B layer / A layer, or a configuration of four or more layers, In consideration of easiness in film formation, a three-layer structure is preferable.

  In the white laminated polyester film of the present invention, the rigidity is preferably 1.0 mN · m or more and less than 10 mN · m, more preferably 1.1 mN · m or more and less than 10 mN · m. It is preferable that the rigidity is 1.0 mN · m or more in order to suppress luminance unevenness due to bending during processing and assembly, and bending of the reflection sheet due to the uneven portion of the housing. Further, from the viewpoints of film conveyance and winding properties, the film preferably has flexibility, and the rigidity is preferably less than 10 mN · m.

Furthermore, in the present invention, the overall apparent density of the white laminated polyester film is preferably 0.8 to 1.1 g / cm ³ , more preferably 0.85 to 1.1 g / cm ³ . When the apparent density is 0.8 g / cm ³ or more, the rigidity is increased, and it is possible to suppress luminance unevenness due to bending that occurs during processing and assembly, and bending of the reflection sheet due to the uneven portion of the housing. Further, setting the apparent density to 1.1 g / cm ³ or less is suitable for making the cavity occupancy of the B layer within the above range.

  In the white laminated polyester film of the present invention, the total light transmittance is preferably less than 5% in order to maintain concealability. In order to make the total light transmittance less than 5%, the thickness of the entire film is increased, the appropriate void ratio is increased, or the number average particle diameter of the cyclic olefin copolymer and inorganic particles in the film is reduced. Can be achieved. The total light transmittance is more preferably 3% or less.

  In addition, it is preferable that the relative reflectance at a wavelength of 560 nm on at least one surface of the white laminated polyester film of the present invention is 98.0% or more in order to obtain high luminance when incorporated in a backlight. In order to set the relative reflectance to 98.0% or more, the thickness of the entire film is increased or the number average particle diameters of the cyclic olefin copolymer and the inorganic particles are made fine after the layer B of the present invention is formed. It can be achieved by doing. The relative reflectance is more preferably 99% or more, and most preferably 100% or more.

The whiteness of at least one surface of the white laminated polyester film of the present invention is preferably 80% or more. Whiteness is an X value that is a tristimulus value of color under optical conditions according to JIS Z-8722 (2000) using a spectroscopic color difference meter SE-2000 type (manufactured by Nippon Denshoku Industries Co., Ltd.). , Y value and Z value were measured and obtained from the following formula.
Whiteness (%) = 4 × 0.847 × Z value−3 × Y value Next, a method for producing a white laminated polyester film of the present invention will be described, but the present invention is not limited to this example.

  In the composite film forming apparatus having an extruder (M) and an extruder (S), first, in order to form the A layer, polyester pellets having a melting point of 230 to 280 ° C. and master pellets of inorganic particles, Mix so as to be 10 to 30% by weight with respect to the total amount of the constituent components, and dry sufficiently. An additive such as an ultraviolet absorber may be added to the dry raw material as necessary. Next, this dry raw material is supplied to an extruder (S) 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. . In addition, you may add 1-10 weight% of copolyester resin to this raw material as needed.

  On the other hand, in order to form the B layer, the vacuum-dried polyester pellets, the vacuum-dried cyclic olefin copolymer master pellets, and the inorganic particle master pellets were added to the B layer. Mix 10 wt% and inorganic particles 10-30 wt%. Each resin is melt-extruded at a uniform ratio to achieve uniform film performance, discharge fluctuation during extrusion, pressure fluctuation to the filter is prevented, and the particle size distribution of the cyclic olefin copolymer in the film is smaller. Therefore, it is preferable to use a raw material obtained by melt-kneading a polyester resin and a cyclic olefin copolymer in advance using an extruder or the like. The mixed resin is supplied to an extruder (M) heated to a temperature of 260 to 300 ° C., melted in the same manner as in the case of the polyester A layer, filtered and introduced into a T-die composite die. In addition, 1-10 weight% of copolyester resin may be added to this raw material as needed, and 2-10 weight% of block copolymers of polyalkylene glycol and polybutylene terephthalate may be added. . Furthermore, the loss generated when the white film of the present invention is once produced may be recycled and used as a recovered raw material.

  In the T-die composite die, the polymer of the extruder (M) is laminated at the center so that the polymer of the extruder (S) 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 5 times in each of the longitudinal direction and the width direction, and the area ratio (longitudinal stretching ratio x lateral stretching ratio) is preferably 9 to 15 times. When the area magnification is less than 9 times, the strength of the obtained biaxially stretched laminated film is insufficient, and conversely, when the area magnification exceeds 15 times, there is a tendency that tearing tends to occur. Further, as the area magnification is increased, the cavity occupation ratio of the B layer increases and the cavities are easily bonded to each other. Therefore, the area magnification is preferably within the above range from the viewpoint of the cavity occupation ratio.

  In order to complete the crystal orientation of the obtained biaxially stretched laminated film and to impart flatness and dimensional stability, it is continuously [Tg-10] (° C) or more and [Tg + 10] (° C) or less in the tenter. By performing heat treatment for 1 to 30 seconds at a temperature, cooling uniformly to room temperature, then cooling to room temperature, and then performing corona discharge treatment or the like to further improve the adhesion to other materials, if necessary, and winding up The white polyester film of the present invention can be obtained. Here, Tg is the glass transition temperature of the cyclic olefin copolymer. During the heat treatment step, a relaxation treatment of 3 to 12% may be performed in the width direction or the longitudinal direction as necessary.

  The 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, or transfer defects caused by sticking to a heating roll. Is unlikely to occur. Further, after biaxial stretching, the film may be re-stretched in either the longitudinal direction or the width direction.

  The white polyester film of the present invention thus obtained has reduced luminance unevenness while maintaining the luminance of the liquid crystal backlight, so that the reflection sheet for the surface light source of the edge light for liquid crystal screens and the direct light, And it can be suitably used as a reflector. In particular, it can be suitably used in a monitor backlight device in which the diagonal dimension of the screen in which the LED light source is arranged on the side surface is 20 inches or more.

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

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

(2) Cavity occupancy and inorganic particle occupancy of layer B From the cross-sectional photograph taken with a scanning electron microscope as in (1) above, only the cavity or inorganic particles are traced on the OHP transparent film with an oil pen. Then, using the image analyzer, the occupied area (A) of the cavity filled with the oil-based pen or the occupied area (B) of the inorganic particles was calculated. Using the obtained occupied areas (A) and (B) and the area of the entire B layer, the values calculated by the following formulas are defined as the cavity occupation ratio and the inorganic particle occupation ratio.

Cavity occupancy in layer B = (A) / B layer total area × 100 (%)
Occupancy ratio of inorganic particles in the B layer = (B) / area of the entire B layer × 100 (%).

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

(4) Rigidity The rigidity was measured at a bending angle of 15 ° according to JIS P-8125-2000, and a taper type stiffness tester TELEDYNE MODEL150-D (NORTH Tonowanda, manufactured by New York USA) was used.

(5) Relative reflectance When a spectrophotometer (Shimadzu Corporation UV2450) is attached with an integrating sphere attachment device (ISR2200, Shimadzu Corporation), barium sulfate is used as the standard plate, and the standard plate is 100%. The relative reflectance at a wavelength of 550 nm was measured.
：: 100% or more ◯: 99% or more and less than 100% Δ: 98% or more and less than 99% x: less than 98%

(6) Relative luminance (direct type luminance)
As shown in FIG. 1, the film laminated in the backlight of 181BLM07 (manufactured by NEC Corporation) 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.
For brightness evaluation, Toray Industries, Inc. # 250E6SL was used as a reference sample (100%),
The evaluation results were as follows.
A: 102% or more B: 101% or more and less than 102% Δ: 100% or more and less than 101% x: less than 100%.

  Above (circle) and (circle) were set as the pass.

(7) Brightness unevenness The reflective film pasted in the backlight of the 21.5 type liquid crystal display E2240V manufactured by LG Electronics Japan Co., Ltd. was changed to a predetermined film sample and turned on. In this state, after waiting for 1 hour to stabilize the light source, what can be visually recognized as luminance unevenness in a 500 lx illumination environment or a dark environment was observed, and the following evaluation results were obtained. Note that the luminance unevenness referred to here is due to bending of the reflection sheet and scratches.
◎: Excellent (Uneven brightness in 500 lx lighting environment and dark environment)
○: Good (Luminance unevenness is visible in a 500 lx lighting environment, but no luminance unevenness is visible in a dark environment.)
Δ: Inferior (Brightness unevenness is visible both in a 500 lx lighting environment and in a dark environment.)
×: Very inferior (A very strong luminance unevenness is seen in both a 500 lx lighting environment and a dark environment.)
Above (circle) and (circle) were set as the pass.

(8) Scratch resistance A pencil (Mitsubishi uni) having a hardness of 4B was shaved only so that the core became a columnar shape, and the core was exposed by 5 to 6 mm. Using HEIDON manufactured by Shinto Kagaku Co., Ltd., a pencil with only the core portion exposed was applied to the film surface at an angle of 45 degrees, and a distance of 10 mm was scratched at a speed of 30 mm / min and a load of 100 g. The measurement was performed three times, and the depth of scratch marks by a pencil was measured using a Zygo New View 200 (three-dimensional surface structure analysis microscope) manufactured by Canon Sales Co., Ltd., and evaluated according to the following criteria.
An average value of three measurements was obtained and evaluated for the depth of the scratch mark.
◎: Excellent No scratches by pencil ○: Good A scratch mark with a depth of less than 1 μm can be produced. ◎ and ○ were accepted.

(9) Film formation stability It was evaluated according to the following criteria whether the film could be formed stably.
○: A film can be stably formed for 24 hours or more.
Δ: Film can be stably formed for 12 hours or more and less than 24 hours.
X: Breakage occurs within 12 hours, and stable film formation is not possible.

  The present invention will be described based on examples.

<Example 1>
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.

  To 72 parts by mass of this polyethylene terephthalate (PET), 4 parts by mass of a copolymer of polybutylene terephthalate and polytetramethylene glycol (PBT / PTMG, “Hytrel” (registered trademark) manufactured by Toray DuPont), 1 part to ethylene glycol 4,4-cyclohexanedimethanol copolymer polyethylene terephthalate (PET / CHDM) 4 parts by mass, cyclic olefin copolymer having an ethylene-norbornene copolymer (COC) having a glass transition temperature Tg of 190 ° C. ) 5 parts by mass, 15 parts by mass of titanium dioxide having a number average particle size of 0.25 μm as inorganic particles were mixed and dried at 160 ° C. for 2 hours, and then supplied to Extruder B heated to 270 to 300 ° C. ( B layer).

  On the other hand, a polyethylene terephthalate chip, a rutile titanium oxide polyethylene terephthalate master having a number average particle size of 0.25 μm, a silicon dioxide particle polyethylene terephthalate master having a number average particle size of 3.5 μm, and a sulfuric acid having a number average particle size of 1.4 μm. Barium particle polyethylene terephthalate master and polyethylene terephthalate copolymerized with 15 mol% of isophthalic acid (PET / I), 56 parts by mass of polyethylene terephthalate, 4 parts by mass of titanium oxide, 1 part by mass of silicon dioxide, barium sulfate Is 20 parts by mass and PET / I is 19 parts by mass, vacuum-dried at 160 ° C. for 2 hours, and then supplied to Extruder A heated to 280 ° C. (A layer). Laminate through the laminator so that layer / B layer / A layer It was molded into a sheet. Furthermore, the unstretched film obtained by cooling and solidifying this film with a cooling drum having a surface temperature of 25 ° C. was led to a roll group heated to 85 to 98 ° C., longitudinally stretched 3.5 times in the longitudinal direction, and cooled with a roll group at 21 ° C. . Subsequently, the film was stretched by 3.6 times in a direction perpendicular to the longitudinal direction in an atmosphere heated to 120 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 190 ° C. in a tenter, and after uniform cooling, the mixture was cooled to room temperature and biaxially stretched white laminated polyester film was obtained. The physical properties of the substrate for light reflection are as shown in Table 1. The relative luminance, scratch resistance, and luminance unevenness were excellent.

<Example 2>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the layers were laminated through a laminating apparatus so as to be A layer / B layer. The physical properties of the substrate for light reflection are as shown in Table 1. The relative luminance, scratch resistance, and luminance unevenness were excellent. The reflectance, luminance, and scratch resistance were measured from the A layer side, and the film was placed so that the A layer was on the casing side in the measurement of luminance unevenness.

<Examples 3 to 14>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the raw material compositions of the A and B layers, the thickness of the A layer, and the total film thickness were changed as described in Table 1. The physical properties of the substrate for light reflection are as shown in Table 1. In any of the examples, the relative luminance, scratch resistance, and luminance unevenness were good.
However, in Example 4, since the content of the inorganic particles in the A layer was less than the preferred range, the scratch resistance was slightly inferior and the luminance unevenness was slightly inferior, but was in a practically usable range.

  In Example 6, although the thickness of the entire film was thinner than the preferred range, the rigidity was slightly low, and brightness unevenness due to the deflection of the reflecting sheet was slightly generated, it was within a practically usable range.

  In Example 8, the cavity occupation ratio of the B layer was slightly high, the scratch resistance was slightly inferior, and the luminance unevenness was slightly inferior, but it was within a practical range.

  In Example 9, although the cavity occupation ratio was slightly low and the relative luminance was slightly low, it was within a practically usable range.

  In Example 10, although the cavity occupation ratio was slightly low and the relative luminance was slightly low, it was within a practically usable range. Moreover, although the thickness of the whole film was thinner than the preferable range, the rigidity was a little low, and the brightness nonuniformity by some bending of the reflecting sheet generate | occur | produced, it was in the range which can be used practically.

  In Example 11, the proportion of inorganic particles in the B layer was large and the film forming property was slightly inferior although it was within the range where there was no problem.

  In Example 12, although the thickness of the A layer was thin and the scratch resistance was slightly inferior and the luminance unevenness was slightly inferior, it was within a practically usable range. Moreover, although it was in the range without a problem, the film forming property was also somewhat inferior.

  In Example 14, although the thickness of the A layer was thick and the relative luminance was slightly inferior, it was within a practically usable range.

<Example 15>
The white laminated polyester film was prepared in the same manner as in Example 1 except that the raw material composition of layer B was changed as described in Table 1 and the longitudinal draw ratio was 3.3 times and the transverse draw ratio was 3.5 times. Got. The physical properties of the substrate for light reflection are as shown in Table 1, and excellent relative luminance was obtained. However, although the cavity occupation ratio of the B layer was slightly high, the scratch resistance was slightly inferior and the luminance unevenness was slightly inferior, but it was in a practically usable range.

<Example 16>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the longitudinal draw ratio was 3.7 times and the transverse draw ratio was 3.7 times. The physical properties of the substrate for light reflection are as shown in Table 1. The relative luminance, scratch resistance, and luminance unevenness were excellent. However, the film forming property was slightly inferior although it was within the range without any problem.

<Example 17>
Example 1 except that an ethylene-norbornene copolymer (COC) having a glass transition temperature of 180 ° C. was used as the cyclic olefin copolymer of the B layer and the raw material composition of the A layer was changed as described in Table 1. A white laminated polyester film was obtained in the same manner. The physical properties of the substrate for light reflection are as shown in Table 1. The relative luminance, scratch resistance, and luminance unevenness were excellent.

<Example 18>
An ethylene-norbornene copolymer (COC) having a glass transition temperature of 180 ° C. is used as the cyclic olefin copolymer of the B layer, and barium sulfate having a number average particle diameter of 0.5 μm is used as the inorganic particles. A white laminated polyester film was obtained in the same manner as in Example 1 except that the raw material composition was changed as described in Table 1. The physical properties of the substrate for light reflection are as shown in Table 1. In any of the examples, the relative luminance, scratch resistance, and luminance unevenness were excellent.

<Example 19>
An ethylene-norbornene copolymer (COC) having a glass transition temperature of 160 ° C. is used as the cyclic olefin copolymer of the B layer, and barium sulfate having a number average particle size of 0.5 μm is used as the inorganic particles. A white laminated polyester film was obtained in the same manner as in Example 1 except that the raw material composition was changed as described in Table 1. The physical properties of the substrate for light reflection are as shown in Table 1. In any of the examples, the relative luminance, scratch resistance, and luminance unevenness were excellent.

<Comparative Example 1>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the B layer was not laminated, and only the A layer was made a single layer. Table 2 shows the physical properties of the light reflecting substrate. Although good relative luminance and rigidity were obtained, scratch resistance was insufficient because the B layer was not laminated, and luminance unevenness was insufficient.

<Comparative example 2>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the raw material composition of the A layer was changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Although good relative luminance and rigidity were obtained, the amount of inorganic particles in the layer A was large and the scratching property was inferior, and the luminance unevenness was inferior. Moreover, although it was in the range without a problem, the film forming property was also somewhat inferior.

<Comparative Example 3>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the raw material composition of the A layer was changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Although good relative luminance and rigidity were obtained, the amount of inorganic particles in layer A was small, scratch resistance was inferior, and luminance unevenness was inferior.

<Comparative example 4>
A white laminated polyester film was obtained in the same manner as in Comparative Example 3 except that the raw material composition of the B layer was changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Although good rigidity was obtained, the scratch occupancy was further deteriorated from Comparative Example 3 due to the large cavity occupancy ratio of the B layer, and the luminance unevenness was insufficient.

<Comparative Example 5>
A white laminated polyester film was obtained in the same manner as in Example 12 except that the raw material composition of the B layer was changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Since the void content was large, the scratch resistance and rigidity were inferior, and the brightness unevenness was inferior.

<Comparative Example 6>
A white laminated polyester film was obtained in the same manner as in Comparative Example 5 except that the raw material composition of the A layer was changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Since the inorganic particles in the A layer are few, the scratch resistance is worse than that of Comparative Example 3 and is insufficient, and the luminance unevenness is insufficient.

<Comparative Example 7>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the raw material composition of the A and B layers, the thickness of the A layer, and the total film thickness were changed as described in Table 2. In addition, as a nucleating agent for forming a cavity, polymethylpentene (“TPX” manufactured by Mitsui Chemicals, Inc.) was used instead of the cyclic olefin copolymer. Table 2 shows the physical properties of the light reflecting substrate. Although it was inferior in rigidity, it was within the practical range. However, since there were few inorganic particles in layer A and the void occupation ratio in layer B was large, scratch resistance was inferior and luminance unevenness was inferior. . Moreover, since the B layer did not contain inorganic particles, the relative luminance was inferior.

<Comparative Example 8>
A white laminated polyester film was obtained in the same manner as in Comparative Example 7 except that the raw material compositions of the A and B layers were changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Compared to Comparative Example 7, the layer A had fewer inorganic particles, and the cavity occupation ratio was large, so the rigidity, scratch resistance and rigidity were insufficient, and the luminance unevenness was insufficient.

<Comparative Example 9>
A white laminated polyester film was obtained in the same manner as in Comparative Example 8, except that the raw material composition of the A layer, the thickness of the A layer, and the total film thickness were changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Compared with Comparative Example 8, the thickness of the entire film was thick and the rigidity was good. In addition, since the inorganic particles of the A layer are within the preferable range, the scratch resistance is slightly improved as compared with Comparative Example 8, but the cavity occupation ratio is large, so that it is still inferior and the luminance unevenness is inferior. Met.

<Comparative Example 10>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the raw material composition of the B layer was changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Although good rigidity and relative luminance were obtained, the cavity occupation ratio was large, scratch resistance was inferior, and luminance unevenness was inferior.

<Comparative Example 11>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the raw material compositions of the A layer and the B layer were changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Although good rigidity and scratch resistance were obtained and the brightness unevenness was good, the cyclic olefin copolymer was not contained and the brightness was insufficient.

<Comparative Example 12>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the raw material composition of the B layer was changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Although good rigidity and scratch resistance were obtained and brightness unevenness was good, the inorganic particle occupancy in the B layer was low and the brightness was poor.

<Comparative Example 13>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the raw material composition of the B layer was changed as described in Table 2. Table 2 shows the physical properties of the obtained film as a light reflecting substrate. Although good rigidity and scratch resistance were obtained and brightness unevenness was good, the film was broken during film formation, and the film formation stability was insufficient.

<Comparative example 14>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the thickness of the A layer and the raw material composition of the B layer were changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Although good rigidity and relative luminance were obtained, the thickness of the A layer was thin, scratch resistance was inferior, and luminance unevenness was inferior. Moreover, although it was in the range without a problem, it was somewhat inferior to film forming property.

<Comparative Example 15>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the thickness of the A layer, the raw material composition of the A layer, and the B layer were changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Although good rigidity and scratch resistance were obtained, the A layer was thick and the relative luminance was poor.

<Comparative Example 16>
A white laminated polyester film was obtained in the same manner as in Example 1 except that the thickness of the entire film and the material composition of the B layer were changed as described in Table 2. Table 2 shows the physical properties of the light reflecting substrate. Although good scratch resistance was obtained, the thickness of the entire film was thin, the rigidity was insufficient, and the luminance unevenness was insufficient.

However,
PET: Polyethylene terephthalate,
PET / I: Polyethylene terephthalate copolymerized with 15 mol% of 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 (trade name: Hytrel manufactured by Toray DuPont)
COC: Cyclic olefin copolymer (copolymer resin of ethylene and norbornene)

Claims (6)

A biaxially stretched white film having at least two layers of an A layer composed of polyester and a B layer containing voids and satisfying all the requirements of (1) to (5) below Laminated polyester film.
(1) The layer B contains both a cyclic olefin copolymer and inorganic particles. (2) The void occupancy in the section of the layer B when cut perpendicular to the film surface is 10% or more and 25% or less, inorganic. (3) The thickness of the A layer is 2 μm to 16 μm (4) The content of inorganic particles in the A layer is 20 to 35% (5 ) The thickness of the whole white laminated polyester film is 150 μm or more and 350 μm or less. The white laminated polyester film according to claim 1, wherein the contents of the cyclic olefin copolymer and the inorganic particles in the B layer satisfy the following formula.
3 <a ≦ 8, 10 ≦ b ≦ 30
Where, a: cyclic olefin copolymer content (% by weight), b: inorganic particle content (% by weight) The white laminated polyester film according to claim 1 or 2, wherein an apparent density is 0.8 g / cm ³ or more and 1.1 g / cm ³ or less.   The white laminated polyester film according to any one of claims 1 to 3, which has a rigidity of 1.0 mN / m or more and less than 10 mN / m.   The white laminated polyester film according to any one of claims 1 to 4, wherein the relative reflectance at a wavelength of 560 nm on at least one side surface is 98.0% or more. The light reflection sheet using the white laminated polyester film in any one of Claims 1-6.