JP6707908B2 - White polyester film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polyester film, and relates to a white polyester film that is preferably used as a backlight unit of a liquid crystal display.

In recent years, the use of liquid crystal displays has been remarkably expanded, and for thin-screen LCD TVs with a depth of 150 mm or less and a large screen of 26 inches or more, LED light sources with low power consumption and high output are used. The method has begun to be used, and the method that is advantageous for thinning is adopted by arranging the light source on the side surface or the front surface. In addition to liquid crystal display devices, LED light sources are used in many fields such as lighting fixtures and illuminated signboards. Most of the devices using the LED light source use a reflector in order to use the light efficiently.

In such an LED, a silicone resin has been used as an encapsulating material instead of an epoxy resin, which may cause yellowing over time, in response to the recent demand for increasing the amount of heat generation and improving the extraction efficiency of blue light. .. Silicone resin is more expensive than epoxy resin, but is less discolored by heat. Silicone itself is an effective solution with less discoloration due to heat, but has the disadvantage of high gas permeability. With respect to water, silicone has few ionic impurities and excellent adhesion, so it does not corrode, but sulfur and sulfide easily penetrate silicone, react with the silver-plated substrate in the LED, and turn black. There is a problem of causing it.

For this reason, it has been required that other members used in devices using the LED light source, such as a reflection plate, a diffusion plate, and a prism sheet, do not generate a gas containing sulfur and sulfide depending on the use environment.

On the other hand, the reflection plate is required to have further excellent light reflection performance (also simply referred to as “reflectivity”) in order to improve brightness. As a method of exhibiting excellent light reflection performance in a film, by utilizing the incompatibility of the incompatible resin in the process of adding an incompatible resin to a matrix resin, forming it into a sheet and stretching it A method in which a large number of voids are formed inside the film and light is reflected by using the voids, a method in which white inorganic particles are included in the film and light is reflected by the particles, and a sheet in which inorganic particles are added to a matrix resin To form a large number of voids at the interface between the inorganic particles and the matrix resin, and to use the voids to reflect light, or to add a foaming agent to the matrix resin and to foam when or after molding into a sheet. There are known methods such as a method in which light is reflected by using voids generated by such a method or a method in which these are combined. For example, barium sulfate particles easily form fine voids and are excellent in concealing property, and therefore a reflection plate containing polyester therein is preferably used (see Patent Documents 1 to 3).

Since barium sulfate particles are sulfates, it is very difficult to completely eliminate sulfate ions that are ionized only slightly, or impurities derived from sulfur that remain when being produced. The reflector using barium sulfate particles has high reflectivity and concealing property and is excellent in handleability, but problems such as deterioration of the LED due to sulfate ions and impurities may occur.

JP, 2000-037835, A JP, 2005-125700, A JP, 2006-015674, A

An object of the present invention is to eliminate the above-mentioned problems. That is, there is a need for a white polyester film that does not deteriorate the constituent members of the LED, has high reflectivity and hiding power, and is easy to handle.

The inventors of the present invention have the following configurations as a result of earnestly examining such problems.
(1) A white polyester film having a white layer (A layer) containing a polyester resin, titanium dioxide, and calcium carbonate, wherein the polyester resin in the A layer is 50% by weight or more and less than 80% by weight with respect to the A layer. Titanium is contained in the A layer in an amount of 1% by weight or more and less than 49% by weight, calcium carbonate in the A layer in an amount of 1% by weight or more and less than 49% by weight, and the total amount of calcium carbonate and titanium dioxide in the A layer is 20% by weight of the A layer. White polyester film (2), a white polyester film (2) having a specific gravity of 0.5 to 1.0, and a white layer (A layer) and an A layer satisfying the following (formula 1), which is not less than 50% by weight. The white polyester film according to (1) having a surface layer (B layer) laminated on at least one of the layers 1.2<{specific gravity of B layer}/{specific gravity of A layer}<2.0 (formula 1).
(3) The white polyester film according to (1) or (2), in which the amount of carboxylic acid terminal groups of the polyester resin forming the A layer is 10 to 30 eq/t, (4) the polyester resin forming the A layer is entirely The white polyester film according to any one of (1) to (3), wherein 5 to 20 mol% of the carboxylic acid component is an isophthalic acid residue.
(5) The polyester resin constituting the layer A is mainly composed of polyester obtained by polymerizing a dicarboxylic acid and a diol, and 5 to 60 mol% of all diol components are 1,4-cyclohexanedimethanol residues ( The white polyester film according to any one of 1) to (4).
(6) A white polyester film having a white layer (A layer) containing a polyester resin, titanium dioxide and calcium carbonate, which is substantially free of sulfate and sulfide (1) to (5) The white polyester film described in 1.
(7) The white polyester film as described in any one of (1) to (6), which has a film thickness of 150 μm or less and a total light transmittance of less than 3.0%.
(8) The white polyester film as described in any one of (1) to (7), which is used for a liquid crystal reflector.
(9) The polyester film according to any one of (1) to (7) used in an LED lighting unit.
(10) The white polyester film as described in any one of (1) to (7) used in an LED backlight unit.
(11) The white polyester film as described in any of (1) to (7), which is used for a direct type LED backlight unit.

According to the present invention, it is possible to provide a white polyester film which is not deteriorated in the constituent members of an LED, has high reflectivity and concealing property, and is easy to handle, and which is suitably used as a backlight unit of a liquid crystal display or the like.

As a result of diligent studies on the subject, the present inventors have found that it is effective to use a material containing inorganic particles as a reflector in the effective use of light, but a gas that is considered to be derived from the inorganic particles is used for the LED light source. It was clarified that it has a great influence on the life, and the present invention was completed. Sulfates such as barium sulphate and sulfides such as zinc sulphide are very difficult to completely eliminate sulfate ions which are only slightly ionized or sulfur-derived impurities that remain when produced. The reflector using barium sulfate particles has high reflectivity and concealing property and is easy to handle, but it sometimes deteriorates the constituent members of the LED.

According to the studies conducted by the inventors of the present invention, the use of titanium dioxide and calcium carbonate does not deteriorate the constituent members of the LED, has high reflectivity and concealing property, and has a good handleability and is a white polyester film. It was found that they can be.

[Structure of film]
The white polyester film of the present invention is a white polyester film having a white layer (A layer) containing a polyester resin, titanium dioxide and calcium carbonate, wherein the polyester resin in the A layer is 50% by weight or more with respect to the A layer. It must be contained less than wt%. More preferably, it is 55% by weight or more and less than 65% by weight. If it is less than 50% by weight, the mechanical strength, heat resistance and film-forming property of the film may deteriorate, which is not preferable. Further, if it is 80% by weight or more, a sufficient amount of titanium dioxide and calcium carbonate cannot be contained, which is not preferable.

Here, the polyester in the present invention is a general term for polymer compounds in which the main bond in the main chain is an ester bond, and can usually be obtained by polycondensation reaction of a dicarboxylic acid component and a glycol component. .. Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as terephthalic acid, 2,6-naphthalenedicarboxylic acid, isophthalic acid, 5-sodium sulfoisophthalic acid, phthalic acid, diphenic acid and ester derivatives thereof. Group dicarboxylic acids include adipic acid, sebacic acid, dodecadioic acid, eicoic acid, dimer acid and ester derivatives thereof, and alicyclic dicarboxylic acids include 1,4-cyclohexanedicarboxylic acid and ester derivatives thereof, and diols. Examples of the component include ethylene glycol, propanediol, butanediol, neopentyl glycol, pentanediol, hexanediol, octanediol, decanediol, 1,4-cyclohexanedimethanol (CHDM), diethylene glycol, triethylene glycol, tetramethylene. Typical examples include glycol, polyethylene glycol, and polyethers such as polytetramethylene glycol. These may be used alone or in combination of two or more. Considering the mechanical strength, heat resistance, production cost, etc. of the film, it is preferable that the polyester resin used in the present invention has a basic constitution of polyethylene terephthalate (PET). The basic structure in this case means that 40 mol% or more of the polyester resin is an ethylene terephthalate unit.

The white polyester film of the present invention is a white polyester film having a white layer (A layer) containing a polyester resin, titanium dioxide and calcium carbonate, wherein titanium dioxide in the A layer is 1% by weight or more based on the A layer. It must be contained less than wt%. It is more preferably 5% by weight or more and less than 40% by weight, and further preferably 10% by weight or more and less than 35% by weight. Most preferably, it is 15% by weight or more and less than 25% by weight. If the content of titanium dioxide is less than 1% by weight, the reflection and concealing properties of titanium dioxide may not be fully exhibited, which is not preferable. On the other hand, if it is more than 49% by weight, productivity may be lowered, which is not preferable.

Titanium dioxide is known to have a crystalline form of rutile type, anatase type, and brookite type. Among them, rutile type titanium dioxide having excellent whiteness, light reflectivity and masking property is preferable. Further, it is particularly preferable to use high-purity titanium dioxide having high purity among titanium dioxide. Here, the high-purity titanium dioxide means titanium dioxide having a small light absorption capacity for visible light, that is, titanium dioxide having a small content of coloring elements such as vanadium, iron, niobium, copper, and manganese. Examples of high-purity titanium dioxide include those produced by the chlorine method process. In the chlorine method process, rutile ore containing titanium dioxide as a main component is reacted with chlorine gas in a high temperature furnace at about 1000° C. to first generate titanium tetrachloride. Then, by burning this titanium tetrachloride with oxygen, high-purity titanium dioxide can be obtained. There is also a sulfuric acid process as an industrial production method of titanium dioxide, but since titanium dioxide obtained by this method contains many coloring elements such as vanadium, iron, copper, manganese, and niobium, visible light is used. The light absorption capacity for Therefore, it is difficult to obtain high-purity titanium dioxide by the sulfuric acid method process.

Since titanium dioxide may deteriorate the resin by a photocatalytic action, it is preferable that the surface thereof is coated with silicon dioxide and/or alumina. The photocatalytic activity of titanium dioxide can be suppressed by coating the surface with an inert inorganic oxide such as silicon dioxide or alumina. If it is coated with silicon dioxide and/or alumina, it is coated with zinc oxide and other oxides such as aluminum, silicon, zirconium, tin, titanium, antimony, hydroxides, hydrated oxides, etc. It may be contained as an agent. The method for obtaining such titanium dioxide is not particularly limited, and titanium dioxide particles obtained by a known method can be used.

Further, in order to improve the dispersibility of titanium dioxide in the resin, the surface may be treated with an appropriate surface treatment agent. Examples thereof include polyhydric alcohols, alkanolamines or derivatives thereof, organosilicon compounds, higher fatty acids or metal salts thereof. Specifically, examples of the polyhydric alcohol include trimethylolethane, trimethylolpropane, and pentaerythritol. Examples of the alkanolamine include triethylamine and the like. Examples of the organosilicon compound include polysiloxanes such as dimethylpolysiloxane and methylhydrogenpolysiloxane, alkylsilanes such as hexyltrimethoxysilane, and organosilanes such as silane coupling agents such as aminosilane and vinylsilane. Examples of higher fatty acids include stearic acid, and examples of metal salts of higher fatty acids include magnesium stearate and zinc stearate. You may use 2 or more types of these.

The titanium dioxide of the present invention is more preferably titanium dioxide which has been surface-treated by combining one or more organic compounds together with the coating treatment with silicon dioxide and/or alumina. Specific preferred embodiments include titanium dioxide surface-treated with a polyhydric alcohol as an organic compound, titanium dioxide surface-treated with a polysiloxane, and the like. Titanium dioxide surface-treated by combining one or more of these organic compounds can be produced by a known method, or a commercially available product can be used.

The particle size (number average particle size) of titanium dioxide is preferably 0.05 to 5 μm. The thickness is more preferably 0.07 to 3 μm, and further preferably 0.1 μm to 2 μm. If the particle size is smaller than 0.05 μm, titanium dioxide may easily aggregate, which is not preferable. If it is larger than 5 μm, the productivity may be lowered, which is not preferable. Here, the number average particle diameter is 100 times with a scanning electron microscope (SEM) at a magnification of 10000, and 100 particles of each particle before being added to the resin (film) are arbitrarily measured to obtain the average particle diameter. The value obtained. (When the particles are not spherical, they are approximated to the closest ellipse, and the ellipse is calculated by (major axis+minor axis)/2).

The white polyester film of the present invention is a white polyester film having a white layer (A layer) containing a polyester resin, titanium dioxide and calcium carbonate, wherein calcium carbonate in the A layer is 1% by weight or more based on the A layer. It must be contained less than wt%. It is more preferably 5% by weight or more and less than 40% by weight, and further preferably 10% by weight or more and less than 35% by weight. Most preferably, it is 20% by weight or more and less than 35% by weight. The white polyester film of the present invention can have high reflection performance by utilizing light reflection at the interface by forming fine bubbles with the inorganic nucleating agent as a base point. The inorganic nucleating agent needs to be calcium carbonate from the viewpoint of dispersibility in polyester, light reflectivity, and hiding power. Inorganic nucleating agents include, in addition to calcium carbonate, titanium dioxide, magnesium carbonate, zinc carbonate, zinc oxide, cerium oxide, magnesium oxide, calcium phosphate, mica, titanium mica, talc, clay, kaolin, lithium fluoride, calcium fluoride, etc. May be included. These inorganic particles may be used alone or in combination of two or more kinds. Further, the inorganic particles may be in a form such as porous or hollow porous, and further, in order not to impair the effects of the present invention, surface treatment is performed in order to improve dispersibility in the resin. May be.

If the amount of calcium carbonate in the layer A is less than 1% by weight, the reflection performance may be insufficient, which is not preferable. On the other hand, if it is more than 49% by weight, productivity may be lowered, which is not preferable.
When calcium carbonate is used for the white polyester film of the present invention, it may be either a natural product or a synthetic product, and its crystal form may be calcite, aragonite, vaterite, etc. From the viewpoints of properties and hiding properties, natural products are preferable, and calcite is preferable as the crystal form. Further, other metal compounds such as magnesium oxide, aluminum oxide, silicon dioxide, etc. may be contained.

The calcium carbonate used in the present invention may be in a form of porous or hollow porous, and further, a surface treatment for further promoting the formation of fine bubbles or a surface for improving dispersibility in a resin. You may use what was processed.

The calcium carbonate used in the present invention is preferably surface-treated with a polyvalent carboxylic acid compound, a phosphorus compound, a silane coupling agent or the like from the viewpoint of dispersibility in a resin, suppression of hydrolysis of polyester, and the like. Examples of the polycarboxylic acid compound used in the present invention include aromatic carboxylic acids such as phthalic acid, isophthalic acid and terephthalic acid, sebacic acid, azelaic acid, suberic acid, pimelic acid, adipic acid, glutaric acid and succinic acid. Unsaturated dicarboxylic acids such as saturated dicarboxylic acid, maleic acid, fumaric acid, acrylic acid and methacrylic acid, polyacrylic acid, polymethacrylic acid, copolymers of acrylic acid and methacrylic acid, and metal salts, ammonium salts and alkyl esters thereof. And glycol ester. From the viewpoint of the affinity between the calcite-type calcium carbonate particles and the polyester and the particle dispersibility, a copolymer of polyacrylic acid and its derivative and a metal salt thereof are particularly preferable. Examples of the phosphorus compound include phosphoric acid, phosphorous acid, phosphinic acid, phosphonic acid and their derivatives. Specifically, phosphoric acid, phosphorous acid, phosphoric acid trimethyl ester, phosphoric acid tributyl ester, phosphoric acid triphenyl ester, phosphoric acid mono- or dimethyl ester, dimethylphosphinic acid, phenylphosphinic acid, phenylphosphonic acid dimethyl ester, phenylphosphon Examples thereof include acid diethyl ester, metal phosphates such as calcium phosphate, sodium phosphate, magnesium phosphate, manganese phosphate, and phosphorus compounds such as ammonium phosphate. Examples of the silane coupling agent include vinyltrichlorosilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, γ-( 2-aminoethyl)aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltrimethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-methacryloxypropylmethyldimethoxysilane , Γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, N-β (aminoethyl ) Γ-aminopropyltrimethoxysilane, N-β(aminoethyl)γ-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane Silane, γ-chloropropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, bis-(3-[triethoxysilyl]-propyl)-tetrasulfane (TESPT), bis-(3-[triethoxysilyl]-propyl)-disulfane and the like can be mentioned. Particularly, represented by γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltrimethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane. It is preferable to use epoxy silane.

A method for performing these surface treatments is not particularly limited, and a known technique can be used.

The particle size (number average particle size) of calcium carbonate contained in the white polyester film of the present invention is preferably 0.05 to 5 μm. If the particle size is smaller than 0.05 μm, aggregation may be likely to occur, which is not preferable. If it is larger than 5 μm, the productivity may be lowered, which is not preferable. Here, the number average particle diameter is 100 times with a scanning electron microscope (SEM) at a magnification of 10000, and 100 particles of each particle before being added to the resin (film) are arbitrarily measured to obtain the average particle diameter. The value obtained is referred to (when the particles are not spherical, the shape is approximated to an ellipse having the closest shape, and the ellipse is (major axis+minor axis)/2).

In the white polyester film of the present invention, the total of calcium carbonate and titanium dioxide in the A layer needs to be 20% by weight or more and less than 50% by weight with respect to the A layer. More preferably, it is more than 35% by weight and less than 45% by weight. By setting the calcium carbonate and titanium dioxide in the layer A in the above ranges, it is possible to obtain a white polyester film having an excellent balance of reflectivity and hiding power. When the total amount of titanium dioxide and calcium carbonate in the A layer is 20% by weight or less based on the A layer, sufficient reflectance and hiding property may not be obtained, which is not preferable. Further, if the total amount of titanium dioxide and calcium carbonate in the A layer is 50% by weight or more based on the A layer, the film forming property of the film becomes insufficient, which is not preferable. In order to contain titanium dioxide and calcium carbonate in a total amount of more than 20% by weight in the layer A, it is preferable to use titanium dioxide and calcium carbonate as described above. By setting the particle diameters of titanium dioxide and calcium carbonate within the above ranges, it is possible to suppress film breakage originating from aggregates or coarse particles. Further, titanium dioxide and calcium carbonate have a high water content due to the large surface area, and when added in a large amount, hydrolysis of the polyester may occur during extrusion. In addition, titanium dioxide is likely to be charged on the surface and may easily form an aggregate due to interaction with different kinds of inorganic particles. Increasing the content in the film after using titanium dioxide and calcium carbonate, as described above, the surface treatment suitable for titanium dioxide and calcium carbonate, respectively, is performed, and the polyester resin as specified below is specified. It can be achieved by using in a range. The method for measuring the contents of titanium dioxide and calcium carbonate is not particularly limited, and known techniques can be used. For example, a platinum crucible is weighed, sulfuric acid is added, carbonization is performed using a hot plate and a burner, and heating is performed at 550° C. for 2 hours in an electric furnace to perform ashing treatment. A mixture flux of sodium carbonate-boric acid was added to the obtained ash, and the mixture was heated by a burner to perform a melting treatment, allowed to cool, and diluted nitric acid and hydrogen peroxide solution were added to dissolve the sample solution. Then, it is introduced into an ICP emission spectrometer (OPTIMA 4300 DV manufactured by Perkin Elmer Co., Ltd.) to quantify inorganic elements, trifluoroacetic acid or 1,1,1,3,3,3-hexafluoro-2-propanol. , O-chlorophenol or the like is used to dissolve the polyester resin, and the residue is centrifuged to quantify it, and other methods can be used. The polyester resin used in the present invention preferably contains a copolymerization component from the viewpoint of stretchability and film-forming stability. Examples of the copolymerization component include a dicarboxylic acid component and a diol component. Examples of the dicarboxylic acid component include aromatic dicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, isophthalic acid, 5-sodium sulfoisophthalic acid, phthalic acid, diphenic acid and ester derivatives thereof, and aliphatic dicarboxylic acid. Then, adipic acid, sebacic acid, dodecadioic acid, eicosic acid, dimer acid and its ester derivative, alicyclic dicarboxylic acid, 1,4-cyclohexanedicarboxylic acid and its ester derivative, and polyfunctional acid, Typical examples are trimellitic acid, pyromellitic acid and ester derivatives thereof. Of these dicarboxylic acid components, 2,6-naphthalenedicarboxylic acid, isophthalic acid, 5-sodium sulfoisophthalic acid and 1,4-cyclohexanedicarboxylic acid are preferable, but among them, isophthalic acid is excellent in stretchability and film-forming stability. It is particularly preferable because In the white polyester film of the present invention, it is preferable that 3 to 20 mol% of all dicarboxylic acid components are isophthalic acid residues. It is more preferably 4 to 15 mol %, and further preferably 5 to 12 mol %. By containing isophthalic acid as a copolymerization component, film breakage during film formation can be suppressed and film formation stability can be improved. As a method of introducing the copolymerization component, the copolymerization component may be added at the time of polymerization of the polyester pellets as a raw material and used as pellets in which the copolymerization component is preliminarily polymerized, and, for example, polybutylene terephthalate may be used. Alternatively, a method may be used in which a mixture of pellets polymerized alone and polyethylene terephthalate pellets is supplied to an extruder and copolymerized by a transesterification reaction at the time of melting. The method for adjusting the ratio of the isophthalic acid residue to the above range is not particularly limited, but a method of adding it as an isophthalic acid copolymerized PET obtained by copolymerizing isophthalic acid as a dicarboxylic acid component, an isophthalic acid copolymerized polybutylene terephthalate (PBT) And a method of adding as isophthalic acid copolymerized polycyclohexylene dimethylene terephthalate. Examples of the diol component include propanediol, butanediol, neopentyl glycol, pentanediol, hexanediol, octanediol, decanediol, 1,4-cyclohexanedimethanol (CHDM), diethylene glycol, triethylene glycol, polyethylene glycol and tetra. Representative examples include methylene glycol, polyethylene glycol, and polyethers such as polytetramethylene glycol. Further, these copolymerization components may be used alone or in combination of two or more. Of these diol acid components, butanediol, neopentyl glycol and 1,4-cyclohexanedimethanol are preferably used. Among them, 1,4-cyclohexanedimethanol is preferable because the molecule is bulky and thus the carbonyl group of the ester bond is less susceptible to nucleophilic attack of water molecules and is less likely to be hydrolyzed. In the white polyester film of the present invention, it is preferable that 5 to 60 mol% of all diol components are 1,4-cyclohexanedimethanol residues. It is more preferably 9 to 55 mol %, and even more preferably 12 to 40 mol %. When the 1,4-cyclohexanedimethanol residue is less than 5 mol %, the hydrolysis resistance of the polyester may be deteriorated, which is not preferable. On the other hand, if it is more than 60 mol %, the film-forming property may be deteriorated, which is not preferable. The method for setting the ratio of 1,4-cyclohexanedimethanol residues in the above range is not particularly limited, but a method in which 1,4-cyclohexanedimethanol is copolymerized with CHDM copolymerized PET as a diol component, poly- Examples thereof include a method of adding as 1,4-cyclohexylene dimethylene terephthalate and a method of adding as isophthalic acid copolymer poly-1,4-cyclohexylene dimethylene terephthalate. For example, master pellets of titanium dioxide particles or calcium carbonate particles can be made using poly-1,4-cyclohexylene dimethylene terephthalate. Titanium dioxide particles and calcium carbonate particles tend to form aggregates, but either titanium dioxide particles or calcium carbonate particles are master pelletized using poly-1,4-cyclohexylene dimethylene terephthalate and the other particles When polyethylene terephthalate is used as a master pellet, aggregation can be suppressed.

The method of obtaining the proportion of the copolymerization component is not particularly limited, but a method of combining a plurality of analysis methods can be considered. Possible methods include IR (infrared spectroscopy), 1H-NMR and 13C-NMR analysis methods, and gas chromatography after hydrolysis using hydrochloric acid and the like.

The white polyester film of the present invention preferably has a carboxylic acid terminal group amount of 10 to 30 equivalents/ton. In the polyester, the carbonyl group of the ester bond is hydrolyzed by the nucleophilic attack of a water molecule, and the molecular chain is cleaved. If the molecular chain becomes short, crystallization is likely to occur, and it may be broken during stretching. When the amount of the carboxylic acid terminal group is more than 30 equivalents/ton, the film forming stability may be deteriorated due to the short molecular chain, which is not preferable. Further, if the amount of the carboxylic acid terminal group is less than 10 equivalents/ton, the stress during stretching becomes high and the film-forming property may deteriorate, which is not preferable. The method for adjusting the amount of the carboxylic acid terminal group to such a range is not particularly limited, but for example, by carrying out solid-phase polymerization of polyester at a melting point Tm-30°C or lower, Tm-60°C or higher, and a vacuum degree of 0.3 Torr or lower, the carboxylic acid terminal group is reduced. A method of reducing the amount, by performing the surface treatment of the inorganic particles described above, a method of suppressing hydrolysis at the time of extrusion, a method of suppressing the hydrolysis by adding the inorganic particles together with a difficult-to-hydrolyze polyester, or Examples include a method of combining these. As the polyester which is difficult to hydrolyze, poly-1,4-cyclohexylene dimethylene terephthalate (PCHT), its isophthalic acid copolymer (PCHT/I), etc. are preferably used.

The white polyester film of the present invention preferably has a specific gravity of 0.5 to 1.0. It is more preferably 0.6 to 0.95, and even more preferably 0.7 to 0.9. When the specific gravity is higher than 1.0, the reflectivity derived from the bubble-containing structure may be insufficient. When the specific gravity is lower than 0.5, the rigidity of the film is lowered and the handleability is deteriorated, which is not preferable. The method of setting the specific gravity in the above range is not particularly limited, but a method of adding fine particles to the resin and uniaxially or biaxially stretching it to generate fine bubbles is preferable. For example, if the white polyester film of the present invention has a single-layer structure consisting only of a white layer (A layer) containing a polyester resin, titanium dioxide and calcium carbonate, 1% by weight of calcium carbonate as described above is contained in the A layer. By containing the above and stretching under a specific condition, a white polyester film having a specific gravity in the range can be obtained.

The white polyester film of the present invention may be either a single-layer film or a multi-layer film, but it is composed of at least two layers and is a white layer (A layer) containing a polyester resin, titanium dioxide and calcium carbonate. A structure in which a surface layer (B layer) is laminated on at least one side is preferable. For example, it may have a two-layer structure of A/B, a three-layer structure of B/A/B, or a structure of four or more layers. A layer structure is preferred.

In the case of a structure having two or more layers, the stacking ratio of the total of all A layers and the total of all B layers is preferably 1/18<B layer/A layer<1/2 in weight ratio. With the above-mentioned laminated structure and weight ratio, the specific gravity can be 0.5 to 1.0 even when the white polyester film of the present invention has a structure of two or more layers. When the lamination ratio of the surface layers is large, it is difficult to set the specific gravity in such a range, and the reflection performance and the hiding property may be deteriorated, which is not preferable.

The white polyester film of the present invention preferably has at least two layers, the A layer satisfies (formula 1), and has a surface layer (B layer) laminated on at least one of the A layers.
1.2<{specific gravity of surface layer (B layer)}/{specific gravity of white layer (A layer)}<2.0 (Equation 1)
The rigidity of the film is improved in correlation with the specific gravity, but by stacking the surface layer (B layer) satisfying (Equation 1) on at least one of the white layers (A layer), high rigidity is obtained even if the specific gravity is low. You may be able to. When {specific gravity of surface layer}/{specific gravity of white layer} is 2.0 or more, peeling or film breakage at the interface easily occurs due to a large difference in specific gravity, which is not preferable. Further, if {specific gravity of surface layer}/{specific gravity of white layer} is 1.2 or less, the reflection performance is low due to insufficient formation of bubbles, or the rigidity is high because the specific gravity of the entire film is low. Is low, and the handleability may deteriorate. The method for making the specific gravity of the A layer and the B layer satisfy (Formula 1) is not particularly limited, but a method of containing calcium carbonate in the B layer in an amount of 1% by weight or more and less than 10% by weight based on the weight of the B layer. Can be given. It is more preferably 3% by weight or more and less than 8% by weight. If the calcium carbonate in the B layer is less than 1% by weight, the specific gravity of the B layer may be (specific gravity of B layer)/(specific gravity of A layer)≧2.0, which is not preferable. Further, when the calcium carbonate in the B layer is 10% by weight or more, (B layer specific gravity)/(A layer specific gravity)≦1.2 may be unfavorable. The white layer (A layer) and the surface layer (B layer) are preferably laminated in a film-forming line by a co-extrusion method and then stretched biaxially. Further, if necessary, longitudinal re-stretching and/or transverse re-stretching may be performed.

The white polyester film of the present invention is a white polyester film having a white layer (A layer) containing a polyester resin, titanium dioxide and calcium carbonate, and preferably contains substantially no sulfate or sulfide. By substantially not containing the sulfate and the sulfide, it is possible to eliminate problems such as deterioration of the LED and other constituent members due to impurities derived from sulfate ions and sulfur. Here, "substantially free from" means that the film contains less than 1% by weight of sulfates and sulfides. It is more preferably less than 100 ppm, still more preferably less than 1 ppm. The method for determining the content of sulfates and sulfides is not particularly limited, but TOF-SIMS (time of flight secondary ion mass spectrometry), IR (infrared spectroscopy), gas chromatography, etc. are combined. A method can be considered.

The total thickness of the white polyester film of the present invention is 70 μm or more and 400 μm or less, preferably 90 μm or more and 380 μm or less. When the total thickness of the white polyester film is less than 70 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 400 μm, the reflection performance cannot be expected to increase even if the thickness is further increased, and the cost becomes high, which is not preferable.

The white polyester film of the present invention preferably has a thickness of 150 μm or less and a total light transmittance of less than 3.0%. It is more preferably less than 2.5% and even more preferably less than 2.0%. Generally, the larger the thickness of the reflector, the higher the reflection performance and the lower the total light transmittance. By achieving a low total light transmittance with a relatively thin film, it is possible to contribute to cost reduction of the reflector and thinning of the display. The method of making the white polyester film of the present invention 150 μm or less and the total light transmittance of less than 2.5% is not particularly limited, but for example, the content of titanium dioxide in the white polyester film of the present invention is 5% by weight or more. Thus, a white polyester film having a total light transmittance within the above range can be obtained.

In addition, various coating liquids are applied to the white polyester film of the present invention by using a well-known technique in order to impart easy adhesion, antistatic property, etc., or a hard coat layer for enhancing impact resistance, etc. May be provided, and if necessary, suitable additives in an amount that does not impair the effects of the present invention, for example, a heat stabilizer, an oxidation stabilizer, a UV absorber, a UV stabilizer, an organic system. The lubricants, organic fine particles, fillers, nucleating agents, dyes, dispersants, coupling agents and the like may be added.

INDUSTRIAL APPLICABILITY The white polyester film of the present invention has less deterioration of the other constituent members, has high reflectivity and concealing property, and is easy to handle, and therefore, in addition to the backlight unit of the liquid crystal display, the LED lighting unit, the solar cell back sheet. It can also be suitably used for printing base materials, dust-free paper, packaging materials such as labels, and the like.

Next, a specific method for producing the polyester film of the present invention will be described, but the present invention is not limited thereto.

In a composite film forming machine having at least two single-screw or twin-screw extruders, a main extruder and a sub-extruder, a polyester resin, titanium dioxide particles or master pellets used as a raw material of a white layer (A layer) in the main extruder. , And calcium carbonate particles or master pellets, and the polyester resin and the inorganic particles or master pellets as the raw material of the surface layer (B layer) are charged into the auxiliary extruder. It is preferable that each of the raw materials is dried so that the water content is 50 ppm or less. In addition, it is preferable that the inorganic particles are compounded in advance and added as master pellets in terms of handleability and dispersibility. Furthermore, it is preferable to prepare the master pellet of calcium carbonate using poly-1,4-cyclohexylene dimethylene terephthalate. Alternatively, it is preferable to prepare titanium dioxide master pellets using poly-1,4-cyclohexylene dimethylene terephthalate. Agglomeration of titanium dioxide and calcium carbonate can be suppressed by preparing one of the master pellets of titanium dioxide and calcium carbonate using poly-1,4-cyclohexylene dimethylene terephthalate. More preferably, titanium dioxide master pellets are prepared using poly-1,4-cyclohexylene dimethylene terephthalate. In the master pellet, if necessary, an appropriate additive in an amount that does not impair the effects of the present invention, for example, a heat resistance stabilizer, an oxidation resistance stabilizer, an ultraviolet absorber, an ultraviolet stabilizer, an organic slippery agent, an organic compound. Fine particles, fillers, nucleating agents, dyes, dispersants, coupling agents and the like may be added. For example, a three-layer laminated film of B layer/A layer/B layer can be formed by using two extruders and a feed block or a multi-manifold installed above the T die. The extruded unstretched sheet is cooled and solidified by a casting drum to form an unstretched film.

This unstretched film is heated to a glass transition temperature (Tg) or higher of the polymer by roll heating and, if necessary, infrared heating and the like, and stretched in the longitudinal direction (hereinafter referred to as the longitudinal direction) to obtain a longitudinally stretched film. This stretching is performed by utilizing the peripheral speed difference between two or more rolls. The longitudinal stretching ratio is preferably 2 to 6 times, more preferably 3 to 4 times, although it depends on the required characteristics of the application. If it is less than 2 times, the reflectance may be low, and if it exceeds 6 times, breakage may easily occur during film formation. The film after the longitudinal stretching is subsequently subjected to a treatment of stretching in the direction orthogonal to the longitudinal direction (hereinafter referred to as the transverse direction), heat setting, and heat relaxation in order to obtain a biaxially oriented film. While running. At this time, it is preferable that the preheating and the stretching temperature for the lateral stretching are carried out at the glass transition temperature (Tg) of the polymer or higher (Tg+20° C.). The transverse stretching ratio is preferably 2.5 to 6 times, more preferably 3 to 4 times, although it depends on the required characteristics of the application. If it is less than 2.5 times, the reflectance may be low. If it exceeds 6 times, breakage may easily occur during film formation. In order to complete the crystal orientation of the obtained biaxially stretched laminated film and impart flatness and dimensional stability, heat treatment is continuously performed at a temperature of 180 to 230° C. for 1 to 60 seconds in a tenter to obtain a uniform film. After gradual cooling, cool to room temperature and wind on a roll. The heat treatment may be performed while relaxing the film in the longitudinal direction and/or the width direction.

Further, here, the case of stretching by the sequential biaxial stretching method has been described in detail as an example, but the polyester film of the present invention may be stretched by any of the sequential biaxial stretching method and the simultaneous biaxial stretching method, Further, if necessary, after the biaxial stretching, the longitudinal re-stretching and/or the transverse re-stretching may be performed.

Hereinafter, the present invention will be described in detail with reference to examples. The characteristic values were measured by the following methods.

(1) Specific gravity Five square samples each having a side of 5 cm were cut out from the film and measured using an electronic hydrometer SD-120L (manufactured by Mirage Trading Co., Ltd.) based on JIS K7112-1980. The arithmetic mean of the obtained measured values of 5 points in total was determined and used as the specific gravity of the film. When measuring the specific gravity of only the surface layer and the white layer, the respective layers were peeled off or unnecessary layers were scraped off with sandpaper or the like, and the measurement was performed for each layer.

(2) Carboxylic acid terminal group amount It was measured by the method of Maurice. (Reference MJ Maurice, F. Huizinga. Anal. Chim. Acta, 22363 (1960)). When measuring the amount of carboxylic acid terminal groups only in the surface layer and the reflective layer, each was peeled off and the measurement was performed for each layer.

(3) Total light transmittance Using a turbidimeter “NDH5000” manufactured by Nippon Denshoku Industries Co., Ltd., the total light transmittance was measured according to JIS “Testing method for total light transmittance of plastic transparent material” (K7361-1). , 1997 edition).
⊚: Less than 2.0% ◯: Less than 2.5% Δ: Less than 3.0% ×: 3.0% or more Δ or more was accepted.

(4) Reflectivity When a 60 mmφ integrating sphere was attached to a Hitachi High-Technologies spectrophotometer (U-3310), and a standard white plate of aluminum oxide (Hitachi High-Technologies, Part No. 210-0740) was set to 100%. The reflectance is measured over 400-700 nm. The reflectance is read from the obtained chart at intervals of 5 nm, and the arithmetic mean value is calculated to obtain the reflectance.
A: Greater than 101%, Good: Greater than 99%, Good: Greater than 96%, Poor: 96% or less Good or bad was accepted.

(5) Film-forming stability It was evaluated whether or not the film could be formed without breaking during film formation.
◯: A film can be formed without tearing.
Δ: Film breakage occurs to some extent, but the film can be collected.
×: Film cannot be collected due to film breakage.
△ or above was regarded as acceptable.

(6) Tg, Tm, heat of crystal fusion The heat of crystal fusion and the melting point Tm were measured by the following methods. According to JIS K7122 (1999), the measurement was performed using EXSTAR DSC6220 manufactured by Seiko Instruments Inc. The disk session "SSC/5200" was used for data analysis. The measurement shall be performed in a nitrogen atmosphere. First, 5 mg of a resin as a sample was weighed and packed in a sample pan, the sample pan was heated from 20° C. to 300° C. at a temperature rising rate of 10° C./min, and kept at 300° C. for 5 minutes. Of the endothermic peaks obtained from the DSC curve of the differential scanning calorimetry chart (endothermic and exothermic curve) obtained at this time, the area of the peak having the maximum area is the heat of crystal fusion, the peak temperature is the melting point Tm, and the crystallization peak is not visible. Was taken as the glass transition temperature Tg.

(7) Intrinsic viscosity IV
The P layer was dissolved in 100 ml of orthochlorophenol (solution concentration C=1.2 g/ml), and the viscosity of the solution at 25° C. was measured using an Ostwald viscometer. Also, the viscosity of the solvent was measured in the same manner. [Η] was calculated by the following formula (3) using the obtained solution viscosity and solvent viscosity, and the obtained value was taken as the intrinsic viscosity (IV).

ηsp/C=[η]+K[η]2·C (3)
(Here, ηsp=(solution viscosity/solvent viscosity)-1 and K is the Huggins constant (assumed to be 0.343).)
(8) Particle size (number average particle size)
Using a S-2100A scanning electron microscope manufactured by Hitachi Ltd., each particle before being added to the resin (film) was observed at a magnification of 10000 times, and 100 particles were arbitrarily measured to measure the average particle diameter. Was calculated (if the particles are not spherical, the shape is approximated to an ellipse having the closest shape, and is calculated by (major axis+minor axis)/2 of the ellipse).

(9) Handleability The handleability was judged by the broken state when the film was bent. Using a coating film bending tester MODEL HD-5110 (manufactured by Kamijima Seisakusho Co., Ltd.), confirm the state of film breakage when wrapped around an 8 mm and 16 mm mandrel at a bending angle of 180° in accordance with JIS K5600-5-1 type 1. did.

◯: The film has no crease or crack at 8 mm.

Δ: A crease was formed on the film at 8 mm, but there was no crease or crack on the film at 16 mm.

×: 16 mm, the film had a crease and was cracked.

(10) LED chip discoloration test The L value, a value, and b value of the central portion of the LED chip “NSSW157T” manufactured by Nichia Corporation are measured and used as the L value, a value, and b value before heat treatment. .. Then, 100 g of a sample obtained by cutting the LED chip and the white polyester film into a 10 mm square was weighed, and put in a glass container having a total volume of 1000 ml together with a filter paper containing an amount of water calculated so that the relative humidity was 95%. It was sealed and heat-treated at 80° C. for 24 hours. After the treatment, the temperature was allowed to cool to room temperature, and the L value, a value, and b value of the central portion of the LED chip taken out from the container were measured and used as the L value, a value, and b value after the wet heat treatment. From the values obtained by these, ΔL, Δa, and Δb values were obtained from the following equations (2) to (4).

ΔL value=(L value before wet heat treatment)−(L value after wet heat treatment) (2)
Δa value=(a value before wet heat treatment)−(a value after wet heat treatment) (3)
Δb value=(b value before wet heat treatment)−(b value after wet heat treatment) (4)
◯: ΔL value is less than 1.0 ×: ΔL value is 1.0 or more (11) L, a, b value measuring method A microfacet spectrocolor difference meter VSS400 (manufactured by Nippon Denshoku Industries Co., Ltd.) was used and a light source D65 was used. And the measurement diameter was set to 0.5 mmφ under the optical condition according to JIS Z-8722 (2000), and the color difference L value, a value, and b value according to JIS K-7105 (1981) were obtained.

[Raw materials used]
(1) Polyester resin (a)
[Esterification reaction step]
To the esterification reaction vessel, 105 parts by weight of bishydroxyethyl terephthalate (corresponding to 100 parts by weight of polyethylene terephthalate) was charged and dissolved at 255°C. After the dissolution, 86 parts by weight of terephthalic acid and 37 parts by weight of ethylene glycol were supplied to the reaction vessel, the esterification reaction was allowed to proceed at 255° C., and water was discharged. The esterification reaction was terminated when the reaction rate reached 95% based on the amount of water flowed out.
[Polymerization process]
105 parts by weight of the esterification reaction product (100 parts by weight of polyethylene terephthalate) was transferred to a polymerization reaction vessel, and 0.09 part by weight of magnesium acetate and 0.03 part by weight of antimony trioxide were added to ethylene glycol while maintaining the temperature at 235°C. A mixture prepared by dissolving 0.02 part by weight of phosphoric acid in 1.6 parts by weight of ethylene glycol was added to the esterification reaction product. Then, the temperature in the polymerization reaction container was raised from 235° C. to 280° C. over 90 minutes, and the pressure in the container was gradually reduced from normal pressure to 150 Pa to allow the reaction to proceed. The reaction was terminated when the intrinsic viscosity (IV) reached 0.55 dl/g to obtain a polyester resin (a). The amount of carboxylic acid end groups was 33 equivalents/ton.

(2) Polyester resin (b)
[Solid Phase Polymerization Step] The polyester resin (a) was placed under vacuum at 160° C. for 6 hours to be dried and crystallized. Then, this was placed in a vacuum at 220° C. for 8 hours for solid phase polymerization to obtain a polyester resin (b). The obtained polyester resin (b) had an IV of 0.80 dl/g and a carboxylic acid terminal group amount of 10.5 equivalent/ton.

(3) Copolyester resin (c)
In the esterification reaction step, polymerization was carried out in the same manner as in the polyester resin (a) except that 71 parts by weight of terephthalic acid, 15 parts by weight of isophthalic acid and 37 parts by weight of ethylene glycol were supplied to the reaction vessel to remove isophthalic acid residues. A copolyester resin (c) containing 17.5 mol% was obtained. The IV was 0.55 dl/g and the amount of carboxylic acid end groups was 33 equivalents/ton.

(4) Calcium carbonate master pellet (d)
40 parts by weight of polyester resin (a) and 60 parts by weight of calcium carbonate particles (number average particle size 0.5 μm) were kneaded by a twin-screw extruder to obtain calcium carbonate master pellets (d).

(5) Calcium carbonate master pellet (e)
40 parts by weight of the copolyester resin (c) and 60 parts by weight of calcium carbonate particles (number average particle size 0.5 μm) were kneaded with a twin-screw extruder to obtain calcium carbonate master pellets (e).

(6) Titanium dioxide master pellet (f)
40 parts by weight of polyester resin (a) and 60 parts by weight of titanium dioxide particles (number average particle size 0.5 μm) were kneaded with a twin-screw extruder to obtain titanium dioxide master pellets (f).

(7) Titanium dioxide master pellet (g)
40 parts by weight of the copolyester resin (c) and 60 parts by weight of titanium dioxide particles (number average particle size 0.5 μm) were kneaded with a twin-screw extruder to obtain titanium dioxide master pellets (g).

(8) Titanium dioxide master pellet (h)
40 parts by weight of poly-1,4-cyclohexylene dimethylene terephthalate (PCHT) resin and 60 parts by weight of titanium dioxide particles (number average particle size 0.5 μm) were kneaded by a twin-screw extruder, and titanium dioxide master pellets ( h) was obtained.

(9) Calcium carbonate master pellet (i)
40 parts by weight of poly-1,4-cyclohexylene dimethylene terephthalate (PCHT) resin and 60 parts by weight of calcium carbonate particles (number average particle size 0.5 μm) were kneaded by a twin-screw extruder to prepare calcium carbonate particle master pellets. (I) was obtained.

(10) Barium sulfate master pellet (j)
40 parts by weight of the copolyester resin (c) and 60 parts by weight of barium sulfate particles (number average particle size 0.5 μm) were kneaded with a twin-screw extruder to obtain barium sulfate master pellets (j).

(Example 1)
The raw materials having the compositions shown in Tables 1 and 2 were vacuum-dried at a temperature of 180° C. for 6 hours, and then the raw material of the white layer (A layer) was melt-extruded into a main extruder at a temperature of 280° C. and then filtered with a 30 μm cut filter. And then introduced into the T-die base.

Then, the sheet was extruded into a molten sheet, and the molten sheet was contact-cooled and solidified by an electrostatic application method on a drum kept at a surface temperature of 25° C. to obtain an unstretched film. Subsequently, the unstretched film was preheated by a group of rolls heated to a temperature of 70° C., and then stretched in the longitudinal direction (longitudinal direction) at a magnification of Table 3 while irradiating from both sides with an infrared heater, and the temperature was 25° C. It cooled by the roll group of the temperature of, and the uniaxially stretched film was obtained. Then, while holding both ends of the uniaxially stretched film with clips, the uniaxially stretched film was guided to a preheating zone of 110°C in the tenter and slightly stretched by 5%, and continuously continuously at 120°C in the direction perpendicular to the longitudinal direction (transverse direction) of Table 3. It was stretched at a magnification. Further subsequently, heat treatment was carried out at a temperature shown in Table 3 in a heat treatment zone in the tenter, followed by uniform slow cooling and winding on a roll to obtain a white polyester film having a thickness shown in Table 3.
The properties of the white polyester film thus obtained are shown in Table 3, and the film was suitable for use as a reflector.

(Examples 2 to 11)
After vacuum-drying the raw materials having the compositions shown in Tables 1 and 2 at a temperature of 180° C. for 6 hours, the raw material of the reflective layer (A layer) was supplied to the main extruder and the raw material of the surface layer (B layer) was supplied to the auxiliary extruder. Each of them was melt-extruded at a temperature of 280° C., filtered through a 30 μm cut filter, and then introduced into a T-die composite die.

Then, in the T-die composite die, the surface layer (B layer) was combined so as to be laminated (B layer/A layer/B layer) on both surface layers of the white layer (A layer), and then coextruded into a sheet. A melt-laminated sheet was obtained, and the melt-laminated sheet was contact-cooled and solidified on a drum kept at a surface temperature of 25° C. by an electrostatic application method to obtain an unstretched film. Thereafter, in the same manner as in Example 1, a white polyester film of B layer/A layer/B layer 3 layer was obtained.
The properties of the white polyester film thus obtained are shown in Table 3, and the film was suitable for use as a reflector.

(Comparative Examples 2, 3, 7)
After vacuum-drying the raw materials having the compositions shown in Tables 1 and 2 at a temperature of 180° C. for 6 hours, the raw material of the white layer (A layer) was supplied to the main extruder and the raw material of the surface layer (B layer) was supplied to the auxiliary extruder. Each of them was melt-extruded at a temperature of 280° C., filtered through a 30 μm cut filter, and then introduced into a T-die composite die.
Then, in the T-die composite die, the surface layer (B layer) was combined so as to be laminated (B layer/A layer/B layer) on both surface layers of the white layer (A layer), and then coextruded into a sheet. A melt-laminated sheet was obtained, and the melt-laminated sheet was contact-cooled and solidified on a drum kept at a surface temperature of 25° C. by an electrostatic application method to obtain an unstretched film. Thereafter, in the same manner as in Example 1, a biaxially stretched film of B layer/A layer/B layer 3 layer was obtained. The properties of the biaxially stretched film thus obtained are as shown in Table 3, and the film was not suitable for use as a reflector.

(Comparative Examples 4 and 5)
After vacuum-drying the raw materials having the compositions shown in Tables 1 and 2 at a temperature of 180° C. for 6 hours, the raw material of the white layer (A layer) was supplied to the main extruder and the raw material of the surface layer (B layer) was supplied to the auxiliary extruder. Each of them was melt-extruded at a temperature of 280° C., filtered through a 30 μm cut filter, and then introduced into a T-die composite die. Titanium dioxide was added as powder to the layer A.
Then, in the T-die composite die, the surface layer (B layer) was combined so as to be laminated (B layer/A layer/B layer) on both surface layers of the white layer (A layer), and then coextruded into a sheet. A melt-laminated sheet was obtained, and the melt-laminated sheet was contact-cooled and solidified on a drum kept at a surface temperature of 25° C. by an electrostatic application method to obtain an unstretched film. After that, the same film formation as in Example 1 was tried, but a biaxially stretched film could not be collected due to film breakage during stretching.

(Comparative example 6)
After vacuum-drying the raw materials having the compositions shown in Tables 1 and 2 at a temperature of 180° C. for 6 hours, the raw material of the white layer (A layer) was supplied to the main extruder and the raw material of the surface layer (B layer) was supplied to the auxiliary extruder. Each of them was melt-extruded at a temperature of 280° C., filtered through a 30 μm cut filter, and then introduced into a T-die composite die.
Next, in the T-die composite die, the surface layer (B layer) was combined so as to be laminated (B layer/A layer/B layer) on both surface layers of the white layer (A layer), and then coextruded into a sheet. A melt-laminated sheet was obtained, and the melt-laminated sheet was contact-cooled and solidified on a drum kept at a surface temperature of 25° C. by an electrostatic application method to obtain an unstretched film.
The properties of the unstretched film thus obtained are shown in Table 3 and were not suitable for use as a reflector.

(Reference example 1)
After vacuum-drying the raw materials having the compositions shown in Tables 1 and 2 at a temperature of 180° C. for 6 hours, the raw material of the white layer (A layer) was supplied to the main extruder and the raw material of the surface layer (B layer) was supplied to the auxiliary extruder. Each of them was melt-extruded at a temperature of 280° C., filtered through a 30 μm cut filter, and then introduced into a T-die composite die.
Then, in the T-die composite die, the surface layer (B layer) was combined so as to be laminated (B layer/A layer/B layer) on both surface layers of the white layer (A layer), and then coextruded into a sheet. A melt-laminated sheet was obtained, and the melt-laminated sheet was contact-cooled and solidified on a drum kept at a surface temperature of 25° C. by an electrostatic application method to obtain an unstretched film. After that, the same film formation as in Example 1 was tried, but a biaxially stretched film could not be collected due to film breakage during stretching.

(Reference example 2)
After vacuum-drying the raw materials having the compositions shown in Tables 1 and 2 at a temperature of 180° C. for 6 hours, the raw material of the white layer (A layer) was supplied to the main extruder and the raw material of the surface layer (B layer) was supplied to the auxiliary extruder. Each of them was melt-extruded at a temperature of 280° C., filtered through a 30 μm cut filter, and then introduced into a T-die composite die.
Then, in the T-die composite die, the surface layer (B layer) was combined so as to be laminated (B layer/A layer/B layer) on both surface layers of the white layer (A layer), and then coextruded into a sheet. A melt-laminated sheet was obtained, and the melt-laminated sheet was contact-cooled and solidified on a drum kept at a surface temperature of 25° C. by an electrostatic application method to obtain an unstretched film. Thereafter, in the same manner as in Example 1, a biaxially stretched film of B layer/A layer/B layer 3 layer was obtained. The properties of the biaxially stretched film thus obtained are as shown in Table 3, and the reflectivity, hiding property, handleability and film-forming property were good, but the LED chip discolored due to the impurities of barium sulfate. did.

According to the present invention, it is possible to provide a white polyester film that is preferably used as a backlight unit of a liquid crystal display.

Claims (12)

A white polyester film having a white layer (A layer) containing a polyester resin, titanium dioxide and calcium carbonate, wherein the polyester resin in the A layer is 50% by weight or more and less than 80% by weight relative to the A layer, and the titanium dioxide is A 1% by weight or more and less than 49% by weight of the layer, calcium carbonate is contained in the A layer by 1% by weight or more and less than 49% by weight, and the total amount of calcium carbonate and titanium dioxide in the A layer is 20% by weight or more of the A layer. less than 50 wt% der is, specific gravity of 0.5 to 1.0, with the a layer is less than (equation 1) meets the surface layer laminated on at least one of a layer (B layer) , White polyester film.
1.2<{specific gravity of layer B}/{specific gravity of layer A}<2.0 (Equation 1) The white polyester film according to claim 1, wherein the amount of carboxylic acid terminal groups of the polyester resin forming the layer A is 10 to 30 eq/t. The white polyester film according to claim 1 or 2, wherein the polyester resin constituting the layer A has an isophthalic acid residue in an amount of 3 to 20 mol% of all carboxylic acid components. The polyester resin constituting the layer A is mainly composed of a polyester obtained by polymerizing a dicarboxylic acid and a diol, and 5 to 60 mol% of all diol components are 1,4-cyclohexanedimethanol residues. The white polyester film according to any one of 3 above. A white polyester film having a white layer (A layer) containing a polyester resin, titanium dioxide and calcium carbonate, which is substantially free of sulfate and sulfide. the film. The white polyester film according to claim 1, wherein the film has a thickness of 150 μm or less and a total light transmittance of less than 3.0%. The white polyester film according to any one of claims 1 to 6, which is used for a liquid crystal reflector. The polyester film according to claim 1, which is used for an LED lighting unit. The white polyester film according to claim 1, which is used for an LED backlight unit. The white polyester film according to claim 1, which is used for a direct type LED backlight unit. A method for producing a white polyester having a white layer (A layer) containing a polyester resin, titanium dioxide and calcium carbonate, wherein master pellets of calcium carbonate are prepared using poly-1,4-cyclohexylene dimethylene terephthalate. The method for producing a white polyester film according to any one of claims 1 to 10. A method for producing a white polyester having a white layer (A layer) containing a polyester resin, titanium dioxide and calcium carbonate, wherein master pellets of titanium dioxide are produced using poly-1,4-cyclohexylene dimethylene terephthalate. The method for producing a white polyester film according to any one of claims 1 to 10.