Patent Publication Number: US-2010129630-A1

Title: Heat-ray shielding polyvinylchloride film and heat-ray shielding polyester film laminate

Description:
BACKGROUND 
     1. Technical Field 
     The present invention relates to a heat-ray shielding polyester film utilized in an opening part such as windows of buildings or vehicles, and having an excellent visible light transmittance and heat ray-shielding properties, and relates to a heat ray-shielding polyester film laminate in which the heat ray-shielding polyester film is laminated on other transparent base material. 
     2. Description of Related Art 
     Conventionally, a so-called opening part such as windows of each buildings and vehicles is made of a transparent glass plate or a resin plate, for taking in solar rays. However, the solar rays include ultraviolet rays and infrared rays in addition to visible light. A near infrared ray having wavelengths of 800 to 2500 nm out of the infrared rays included in the solar rays, is called a heat ray and this heat ray causes a temperature in a room to increase when it enters into the room from the opening part. 
     Therefore, in recent years, a heat ray-shielding material capable of shielding heat rays while sufficiently taking in the visible light, and simultaneously suppressing a temperature increase in a room while maintaining brightness, has been studied, and various means therefore have been proposed. 
     For example, patent document 1 proposes a heat ray-shielding plate, wherein a heat ray reflection film formed by vapor-depositing a metal on a transparent resin film, is bonded to a transparent base material such as a glass plate, an acrylic plate, and a polycarbonate plate. Also, for example, a plurality of heat ray shielding plates formed by directly vapor-depositing the metal or metal oxide on the surface of the transparent base material are proposed. 
     As a heat ray-shielding means, patent document 2 and patent document 3 propose the heat ray-shielding plate formed by kneading mica coated with titanium oxide as a heat ray-reflection particle, into transparent resin such as acrylic resin and polycarbonate resin, other than a method for applying a heat ray-reflecting film and a heat ray-shielding film on the aforementioned transparent base material. 
     Meanwhile, in patent document 4, an applicant of the present invention focuses on hexaboride nanoparticles having a large quantity of free electrons as components having a heat ray-shielding effect, and has already proposed the heat ray-shielding resin sheet material wherein the hexaboride nanoparticles are dispersed, or the hexaboride nanoparticles and ITO nanoparticles and/or ATO nanoparticles are dispersed in the polycarbonate resin and the acrylic resin. 
     In optical characteristics of the heat ray-shielding resin sheet material to which the hexaboride nanoparticles are singularly applied, or the hexaboride nanoparticles and ITO nanoparticles and/or ATO nanoparticles are applied, a visible light transmittance is improved to 70% or more and a solar light transmittance is improved to 50%, because the heat ray-shielding resin sheet material has a maximum transmittance in a visible ray region, and exhibits a strong absorption and hence a minimum transmittance in a near-infrared region. 
     Patent Document 1: 
     Japanese Patent Laid Open Publication No. 61-277437 
     Patent Document 2: 
     Japanese Patent Laid Open Publication No. 05-78544 
     Patent Document 3: 
     Japanese Patent Laid Open Publication No. 02-173060 
     Patent Document 4: 
     Japanese Patent Laid Open Publication No. 2003-327717 
     DISCLOSURE OF THE INVENTION 
     Problems to be Solved by the Invention 
     In a heat ray-shielding plate, with a heat ray-reflecting film bonded to a transparent substrate described in patent document 1, there is a problem that the heat ray-reflecting film itself incurs extremely high cost and also a complicated step such as a bonding step is required, thereby increasing a cost extremely high. Further, bonding properties between the transparent base material and the heat ray-reflecting film are inferior, thus involving a problem that the heat ray-reflecting film is peeled-off. 
     In the heat ray-shielding plate, with the heat ray-shielding film vapor-deposited on the transparent base material, a vapor deposition apparatus requiring an atmosphere control controlling the atmosphere to be in a high vacuum state with high precision must be used. Therefore, there is a problem that mass-productivity is low, universal usability is poor, and the heat ray-shielding plate is extremely expensive. 
     In the heat ray-shielding plate described in patent documents 2 and 3, in order to obtain a high heat ray-shielding properties, a large quantity of heat ray-reflecting particles are required to be added thereto. However, when an addition amount of the heat ray-reflecting particles are increased, there is a problem that the visible light transmittance is lowered this time. Reversely, when the addition amount of the heat ray-reflecting particles is reduced, it is difficult to simultaneously satisfy the heat ray-shielding properties and the visible light transmittance, because the heat ray-shielding properties are lowered in spite of increased visible light transmittance. Further, when a large quantity of heat ray reflection particles are mixed, there is also a problem from an aspect of strength, such that physical property of the transparent resin, being the base material, is deteriorated, and particularly impact resistance and toughness are deteriorated. 
     In a heat ray-shielding sheet material described in patent document 4, a sufficient solar light-shielding effect can be obtained in a region of a low visible light transmittance. However, the sufficient solar light transmittance can not be obtained in a region of a high visible light transmittance, and there is a room for improvement in this point. 
     In view of the above-described circumstance, an object of the present invention is to provide a heat ray-shielding film and a heat ray-shielding film laminate, which can be manufactured by a simple method without using a complicated process and a physical film deposition method at a high cost, and capable of maintaining excellent visible light transmittance and simultaneously exhibiting high heat ray-shielding properties. 
     Means for Solving the Problem 
     In order to solve the above-described problem, as a result of a strenuous study continued by inventors of the present invention, it is found that the above-described problems can be solved by applying tungsten oxide nanoparticles expressed by a general formula WO x  (satisfying 2.45≦x≦2.999) and/or composite tungsten oxide nanoparticles expressed by a general formula M y WO z  (satisfying 0.1≦y≦0.5, 2.2≦z≦3.0) and having a hexagonal crystal structure, as nanoparticles having a heat ray-shielding function. 
     Further, it is also found by the inventors of the present invention, that polyester used as a film material affixed to windows of vehicles and buildings, is suitable, for the reason that polyester has a high transparency and mechanical characteristics, as the film material of the aforementioned heat ray-shielding film and the heat ray-shielding film laminate. 
     Namely, in order to solve the above-described problems, in a first structure, there is provided a heat ray-shielding polyester film, with nanoparticles having a heat ray-shielding function dispersed therein, wherein the nanoparticles having the heat ray-shielding function are tungsten oxide nanoparticles expressed by a general formula WO x  (satisfying 2.45≦x≦2.999) and/or composite tungsten oxide nanoparticles expressed by a general formula M y WO z  (satisfying 0.1≦y≦0.5, 2.2≦z≦3.0) and having a hexagonal crystal structure, and an average dispersed particle size of the nanoparticles is 1 nm or more and 200 nm or less, a content of the nanoparticles is 0.1 wt % or more and 10 wt % or less, and a thickness of the polyester film is 10 μm or more and 300 μm or less. 
     In a second structure, there is provided the heat ray-shielding polyester film according to the first structure, wherein M contained in the composite tungsten oxide nanoparticles is one or more kinds of elements selected from Cs, Rb, K, Tl, In, Ba, Li, Ca, Sr, Fe, Sn, Al, and Cu. 
     Here, according to a study by the inventors of the present invention, in a case of the heat ray-shielding polyester film, with the tungsten oxide and composite tungsten oxide nanoparticles dispersed in a medium, which are transparent in a visible light region and having an absorption in a near infrared ray region, it is found that color tone is changed and a transmittance is lowered, when subjected to ultraviolet rays for a long time. 
     Then, as a result of a research by the inventors of the present invention, it is possible to achieve a structure of containing a coloring preventing agent, together with the aforementioned tungsten oxide and composite tungsten oxide nanoparticles. Specifically, it is found that the heat ray-shielding polyester film, with a change of color by ultraviolet rays suppressed, can be obtained by containing and dispersing one or more kinds of coloring preventing agents selected from a phosphate-based coloring preventing agent, an amide-based coloring preventing agent, an amine-based coloring preventing agent, a hindered amine-based coloring preventing agent, a hindered phenol-based coloring preventing agent, and a sulfur-based coloring preventing agent, and the aforementioned change of color can be solved. 
     Namely, in order to solve the aforementioned problems, in a third structure, there is provided the heat ray-shielding polyester film according to the first or second structure, wherein coloring preventing agents are contained in the polyester film. 
     In a fourth structure, there is provided the heat ray-shielding polyester film according to the third structure, wherein a content of the coloring preventing agents is 0.1 wt % or more and 20 wt % or less. 
     In a fifth structure, there is provided the heat ray-shielding polyester film according to the third or fourth structure, wherein the coloring preventing agents are one or more kinds of coloring preventing agents selected from a phosphorus-based coloring preventing agent, an amide-based coloring preventing agent, an amine-based coloring preventing agent, a hindered amine-based coloring preventing agent, a hindered phenol-based coloring preventing agent, and a sulfur-based coloring preventing agent. 
     In a sixth structure, there is provided the heat ray-shielding polyester film according to any one of the third to fifth structures, wherein the coloring preventing agent is the phosphate-based coloring anent, containing one or more kinds of groups selected from any one of a phosphonate group, a phosphate group, a phosphonate ester group, and a phosphinate group. 
     In a seventh structure, there is provided the heat ray-shielding polyester film according to any one of the third to sixth structures, wherein a visible light transmittance of the heat ray-shielding polyester film is set to be 60% or more and 70% or less, and when a reduction rate of the visible light transmittance is standardized as 100% after emitting ultraviolet rays for 2 hours at intensity of 100 mW/cm 2  to a heat ray-shielding polyester film having the same composition with the composition of the aforementioned heat ray-shielding polyester film other than a point that the coloring preventing agent is not contained, the reduction rate of the visible light transmittance is 70% or less after emitting the ultraviolet rays to this heat ray-shielding polyester film, for the same hours, at the same intensity. 
     In an eighth structure, there is provided a heat ray-shielding polyester film, which is obtained by laminating the heat ray-shielding polyester film according to anyone of claims  1  to  7  on other transparent base material. 
     ADVANTAGE OF THE INVENTION 
     The heat ray-shielding polyester film of the present invention is the heat ray-shielding polyester film containing nanoparticles having a heat ray-shielding function in a transparent polyester film, wherein the nanoparticles having the heat ray-shielding function are constituted of tungsten oxide nanoparticles expressed by a general formula WO x  (satisfying 2.45≦x≦2.999) and/or composite tungsten oxide nanoparticles expressed by a general formula M y WO z  (satisfying 0.1≦y≦0.5, 2.2≦z≦3.0) and having a hexagonal crystal structure, with a diameter of the oxide nanoparticles being 1 nm or more and 200 nm or less, and a content of the oxide particles being 0.1 wt % to 10 wt %, and a thickness of the polyester film being 10 μm to 300 μm. Accordingly, a heat ray-shielding polyester film capable of maintaining an excellent visible light transmittance and exhibiting high heat ray-shielding properties, and a heat ray-shielding polyester film laminate, with the heat ray-shielding polyester film laminated on other resin base material can be obtained, which are useful in such a manner as being used in window materials for vehicles, buildings, and airplanes, being capable of efficiently shield solar rays, and being utilized suitably as inexpensive materials. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     1. Nanoparticles Having the Heat Ray-Shielding Function 
     Nanoparticles having the heat ray-shielding function applied to this embodiment are tungsten oxide nanoparticles expressed by a general formula WO x  (satisfying 2.45≦x≦2.999) and/or composite tungsten oxide nanoparticles expressed by a general formula M y WO z  (satisfying 0.1≦y≦0.5, 2.2≦z≦3.0) and having a hexagonal crystal structure. By using the aforementioned tungsten oxide nanoparticles and/or the composite tungsten oxide nanoparticles, desired optical characteristics can be obtained as the heat ray-shielding polyester film. 
     For example, W 18 O 49 , W 20 O 58 , W 4 O 11  can be give as the tungsten oxide nanoparticles expressed by the general formula WO x  (satisfying 2.45≦x≦2.999). When a value of x is 2.45 or more, it is possible to avoid a situation that a crystal phase of WO 2 , being an outside of a purpose, appears in the heat ray-shielding material, and also it is possible to obtain a chemical stability of the material. Meanwhile, when the value of x is 2.999 or less, a sufficient amount of free electrons are generated and the tungsten oxide nanoparticles become an efficient heat ray-shielding material. When the value of x is 2.95 or less, the tungsten oxide nanoparticles are further preferable as the heat ray-shielding material. Note that WO x  compound, with a range of x satisfying 2.45≦x≦2.999, is contained in a compound called a so-called a magneli phase. 
     As the composite tungsten oxide nanoparticles expressed by a general formula M y WO z  (satisfying 0.1≦y≦0.5, 2.2≦z≦3.0) and having a hexagonal crystal structure, for example, the composite tungsten oxide nanoparticles containing one or more kinds of elements selected from Cs, Rb, K, Tl, In, Ba, Li, Ca, Sr, Fe, Sn, Al, and Cu can be given. An addition amount y of added element M is preferably 0.1 or more and 0.5 or less, and is further preferably in the vicinity of 0.33. This is because the value theoretically calculated from the hexagonal crystal structure is 0.33, and in a case of an addition amount around this value, preferable optical characteristics can be obtained. 
     Also, the range of z is preferably set to be 2.2≦z≦3.0. This is because in the composite tungsten oxide material expressed by M y WO z  also, a similar mechanism works, which is similar to that of the tungsten oxide material expressed by WO x  as described above, and also in a range of z≦3.0, there is a supply of the free electrons by addition of the aforementioned element M. From the viewpoint of the optical characteristics, the range of z is more preferably set to be 2.2≦z≦2.99, and further preferably set to be 2.45≦z≦2.99. 
     Here, as a typical example of the composite tungsten oxide material, Cs 0.33 WO 3 , Rb 0.33 WO 3 , K 0.33 WO 3 , Ba 0.33 WO 3  can be given. However, when the values of y and z are set to be in the aforementioned range, useful heat ray-shielding characteristics can be obtained. 
     It is preferable that surface treatment is applied to surfaces of the tungsten oxide nanoparticles and the composite tungsten oxide nanoparticles of the present invention in such a manner as being coated with an oxide containing one or more kinds of elements selected from Si, Ti, Zr, and Al, from the viewpoint of improving weatherability. 
     In addition, in order to obtain a desired heat ray-shielding polyester film, it is desirable that powder colors of the tungsten oxide nanoparticles and/or the composite tungsten oxide nanoparticles satisfy conditions that L* is set to be 25 to 80, a* is set to be −10 to 10, and b* is set to be −15 to 15 in the powder colors of a L*a*b* color system (JIS Z 8729) recommended by Commission internationale de l&#39;eclairage (CIE). 
     The near infrared ray-shielding material containing the tungsten oxide nanoparticles and/or the composite tungsten oxide nanoparticles of this embodiment absorb light in a near infrared region and particularly the light of 1000 nm or more is greatly absorbed. Therefore, its transmission color tone is a bluish color tone in many cases. Further, sizes of the tungsten oxide nanoparticles and composite tungsten oxide nanoparticles can be suitably selected, according to a purpose of use. First, when used for an application of maintaining transparency, the tungsten oxide nanoparticles and the composite tungsten oxide nanoparticles have preferably a dispersed particle size of 200 nm or less. This is because when the dispersed particle size is 200 nm or less, the light is not completely shielded by scattering, and visibility in a visible light region can be maintained, and simultaneously transparency can be efficiently maintained. Particularly, when the transparency of the visible light region is emphasized, the scattering by particles is further preferably taken into consideration. 
     When reduction of the scattering by these particles is emphasized, the dispersed particle size of the tungsten oxide nanoparticles and the composite tungsten oxide nanoparticles are preferably set to be 200 nm or less. This is because when the dispersed particle size is smaller, scattering of the light in a visible light region of wavelengths 400 nm to 780 nm is reduced, due to geometrically scattering or Mie scattering, and as a result, a heat ray-shielding film is turned into a fogged glass, and it is possible to avoid a situation that a sharp transparency can not be obtained. 
     Namely, when the dispersed particle size is 200 nm or less, the geometric scattering or the Mie scattering is reduced, and an area becomes a Rayleigh scattering area. In the Rayleigh scattering area, scattered lights are reduced in inverse proportion to 6 th  power of the particle size, and therefore scattering is reduced with reduction of the dispersed particle size, and the transparency is improved. Further, when the dispersed particle size is 100 nm or less, the scattered lights are preferably extremely reduced. The dispersed particle size is preferably smaller, from a viewpoint of avoiding the scattering of the lights, and industrial manufacture is easy when the dispersed particle size is 1 nm or more. 
     The heat ray-shielding performance is determined by a content of the nanoparticles having the heat ray-shielding function and a thickness of the polyester film. Namely, the nanoparticles having the heat ray-shielding function can secure the heat ray-shielding characteristics by increasing the thickness of the film up to, for example, 300 μm, when its content is 0.1 wt %. Accordingly, as a content capable of exhibiting practical heat ray-shielding characteristics, the content is preferably set to be 0.1 wt % or more. Also, when the content of the nanoparticles having the heat ray-shielding function is 10 wt % or less, abrasion strength and impact resistance of the polyester film are not decreased. Meanwhile, when the thickness of the film is decreased, required content of the nanoparticles is increased for exhibiting the practical heat ray-shielding characteristics. For example, when the thickness of the film is decreased to 10 μm, the required content of the nanoparticles is 10 wt %. Accordingly, although described in detail in an item of “4. A manufacturing method of a heat ray-shielding polyester film and a heat ray-shielding polyester film” as will be described later, the thickness of the polyester film is preferably set to be in a range of 10 to 300 μm. 
     2. Coloring-Preventing Agent 
     It is found that the heat ray-shielding polyester film, in which a change of color due to ultraviolet rays is suppressed, can be obtained by containing and dispersing one or more kinds of coloring preventing agents selected from a phosphate-based coloring preventing agent, an amide-based coloring preventing agent, an amine-based coloring preventing agent, a hindered amine-based coloring preventing agent, a hindered phenol-based coloring preventing agent, and a sulfur-based coloring preventing agent, together with the aforementioned tungsten oxide nanoparticles and composite tungsten oxide nanoparticles. 
     The “coloring preventing agent” used in this embodiment refers to a compound having one or more functions of the functions of inhibiting initiation of a chain reaction, inhibiting the chain reaction, and decomposing peroxide. 
     Here, the function of inhibiting initiation of the chain reaction means the function, of deactivating a metal ion, being a catalyst for generating a hazardous peroxide radical, and inhibiting the initiation of the chain reaction due to the peroxide radical. 
     Also, the function of inhibiting the chain reaction means the function of deactivating the generated peroxide radical and suppressing the chain reaction of generating new peroxide radical due to an action of the peroxide radical. 
     Further, the function of decomposing the peroxide means the function of decomposing the peroxide into a deactivated compound, thereby inhibiting a reaction of the peroxide from being decomposed and radicalized. 
     By the aforementioned function, the coloring preventing agent of this embodiment functions to inhibit the generation and increase of the hazardous peroxide radical that reduces tungsten atoms in the tungsten oxide nanoparticles or/and composite tungsten oxide nanoparticles. 
     The kind of the coloring preventing agent used in this embodiment will be described. 
     In this embodiment, it is also possible to use the coloring preventing agent of any one of (a) phosphorus coloring preventing agent, (b) amide-based coloring preventing agent, (c) amine-based coloring preventing agent, (d) hindered amine-based coloring preventing agent, (e) hindered phenol-based coloring preventing agent, and (f) sulfur-based coloring preventing agent. Among them, (a) phosphorus coloring preventing agent is desirable, and particularly the phosphorus coloring preventing agent containing any one of the phosphonate group, phosphate group, phosphoric acid ester group, and phosphinate group is desirable, due to a high coloring suppressing effect during irradiation of ultraviolet rays. 
     Note that although the coloring preventing agent may be used singularly, two or more kinds of them may be combined and used. By a combined use of the coloring preventing agent mainly having the function of inhibiting initiation of the chain reaction, the coloring preventing agent mainly having the function of inhibiting the chain reaction, and the coloring preventing agent mainly having the function of decomposing the peroxide, depending on a used dispersing medium, a high coloring suppressing effect can be obtained in some cases. 
     An optimal content of the coloring preventing agent in the heat ray-shielding polyester film of this embodiment is different, depending on the kind of the used coloring preventing agent and the dispersing medium. However, generally, the content is preferably set to be 0.01 wt % or more, 20 wt % or less, and further preferably set to be 1 wt % or more and 15 wt % or less in the heat ray-shielding polyester film. 
     When the content of the coloring preventing agent in the heat ray-shielding polyester film is 0.01 wt % or more, the radical generated by the ultraviolet rays can be sufficiently trapped, and the generation of the chain reaction of hazardous radicals is suppressed. Therefore, the generation of pentavalent tungsten can be suppressed, and it is possible to obtain an effect of suppressing coloring due to the ultraviolet rays. Meanwhile, when the content in the dispersing medium is 20 wt % or less, radical polymerization of polymer resin is hardly inhibited by the coloring preventing agent, even when UV-curing resin is used as the dispersing medium. Therefore, the transparency and strength of the heat ray-shielding polyester film can preferably be maintained. Note that when a thermo-curing resin and/or thermoplastic resin is used as the dispersing medium, 20 wt % or more of them is acceptable to be contained in the dispersing medium. 
     Regarding the coloring preventing agent of each kind, specific examples and general functions will be described. 
     (a) Phosphorus Coloring Preventing Agent 
     The phosphorus coloring preventing agent containing phosphorus is given as a first specific example of the coloring preventing agent. Further, a compound having the phosphorus functional groups containing phosphorus is preferable. 
     Here, the phosphorus functional groups include the one containing trivalent phosphorus and the one containing pentavalent phosphorus, and either one of them may be acceptable in the “phosphorus functional groups” of this embodiment. 
     A general formula of the phosphorus coloring preventing agent having the phosphorus functional groups containing trivalent phosphorus is expressed by the following (formula 1), and the phosphorus coloring preventing agent having the phosphorus functional groups containing pentavalent phosphorus is expressed by the following (formula 2). 
     
       
         
         
             
             
         
       
     
     Note that in the formula 1 and the formula 2, values of x, y, z is 0 or 1. Further, R 1 , R 2 , and R 3  are each a hydrocarbon group having a straight-chain, a branched structure or a cyclic structure expressed by a general formula C m H n , or a halogen atom or a hydrogen atom such as fluorine, chlorine, and bromine. Further, when y or z is 1, R 2  or R 3  may be a metal atom. 
     In this embodiment, the “phosphorus functional groups” refer to a part excluding R 1  in the formula 1 and the formula 2 (namely, general formula: —O x —P(O y R 2 )(O z R 3 ), or general formula: —O x —P(O)(O y R 2 )(O z R 3 ). Specifically, the phosphonate group (—P(O)(OH) 2 ), the phosphate group (—O—P(O)(OH) 2 ), the phosphonic acid ester group (—P(O)(OR 2 )(OR 3 )), the phosphate ester group (—O—P(O)(OR 2 )(OR 3 )), and the phosphinate group (—P(R 2 )(R 3 )), etc, can be given as examples of the phosphorous functional groups. 
     Out of these phosphorus functional groups, the functional group containing pentavalent phosphorous such as phosphonate group, phosphate group, phosphonic acid ester group, and phosphate ester group have mainly the function of inhibiting initiation of the chain reaction (namely, the function of chelating and trapping the metal ions by the adjacent phosphorus functional groups). 
     Meanwhile, it is so considered that the phosphorus functional groups containing trivalent phosphorus such as the phosphinate group have mainly the function of decomposing peroxide (namely, the function of decomposing the peroxide into a stable compound by self-oxidation of a P-atom). 
     Among these phosphorus functional groups, the phosphonate coloring preventing agent having the phosphonate group can efficiently trap the metal ions and excellent in stability such as a resistance to hydrolysis, and therefore is particularly suitable as the coloring preventing agent. 
     As a suitable example of a low molecular type phosphorus coloring preventing agent, specifically, phosphoric acid (HC 3 PO 4 ), triphenyl phosphite ((C 6 H 5 O) 3 P) trioctadecyl phosphite ((C 18 H 27 O) 3 P), tridecyl phosphite ((C 10 H 21 O) 3 P), trilauryltrithio phosphate ([CH 3 (CH 2 ) 11 S] 3 P), etc, can be given. 
     Further, as suitable examples of polymer phosphorus coloring preventing agents, specifically, polyvinylsulfonic acid, polystyrenesulfonic acid, vinyl-based phosphoric acid (for example, acrylic phosphorus ester (CH 2 ═CHCOOPO(OH) 2 ), vinyl alkyl phosphoric ester (CH 2 ═CHR—O—PO(OH) 2 , R is a polymer such as —(CH 2 ) n —), polyether sulfone resin introduced with the phosphonate group, polyether ketone resin, straight type poly(trifluoro styrene) resin, crosslinking type (trifluoro styrene) resin, poly(2,3-diphenyl-1,4-phenyleneoxide) resin, poly(allyl ether ketone) resin, poly(allylene ether sulfone) resin, poly(phenyl quinoxaline), poly(benzyl silane) resin, polystyrene-graft-ethylen tetrafluoroethylene resin, polystyrene-graft-polyvinylidene fluoride, polystyrene-graft-tetrafluoroethylene resin, etc, can be given. 
     Further, in order to give excellent cloudless transparency to the infrared ray shielding material containing the tungsten oxide nanoparticles and/or the composite tungsten oxide nanoparticles of this embodiment, and effectively suppress coloring of the tungsten oxide nanoparticles and/or the composite tungsten oxide nanoparticles due to ultraviolet rays, a polymer phosphorous coloring preventing agent is preferable in some cases, depending on the kind of the dispersing medium. Further in addition, the polymer phosphorus coloring preventing agent, in which a crosslink structure is introduced to the polymer phosphorous coloring agent, is preferable in some cases. 
     (b) Amide-Based Coloring Preventing Agent 
     A second specific example of the coloring preventing agent is a coloring preventing agent composed of a compound (called “an amide-based coloring preventing agent” in some cases in this embodiment) having an amide bond (—CO—NH—) in a molecule. It is so considered that the amide-based coloring preventing agent has mainly the function of inhibiting initiation of a chain reaction (namely, the function of chelating and trapping the metal ions by O atom and N atom of amide bond). 
     As suitable examples of low molecular type amide-based coloring preventing agents, N-salicyloyl-N′-aldehyde hydrazine (C 6 H 4 (OH)—CONHNHCHO), N-salicyloyl N′-acetyl hydrazine (C 6 H 4 (OH)—CONHNHCOCH 3 ), N,N′-diphenyl-oxamide (C 6 H 5 —NHCOCONH—C 6 H 5 ), N,N′-di(2-hydroxy phenyl)oxamide (C 6 H 4 (OH)—NHCOCONH—C 6 H 4 (OH)), etc, can be given. 
     Further, as suitable examples of polymer amid coloring preventing agents, a polymer of monomer such as vinyl, acrylic, methacryl, styryl having the aforementioned low molecular type amide-based coloring preventing agents on side chains, and a polymer with the aforementioned low molecular type amide-based coloring preventing agent incorporated into main chains, can be given. 
     Note that the polymer compound is sometimes more preferable than the low molecular-type compound, and when the polymer compound is used, the crosslink structure may be further introduced, and these points are the same as a case of the phosphorus coloring preventing agent. 
     (c) Amine-Based Coloring Preventing Agent 
     A third specific example of the coloring preventing agent is a coloring preventing agent composed of a compound having a benzene ring in a molecule and an amino group (—NH 2 ) or an imino bond (—NH—) bonded to the benzene ring (called an “amine-based coloring preventing agent in some cases in this embodiment). 
     The amine-based coloring preventing agent is considered to have mainly the function of inhibiting a chain reaction (namely, the function of suppressing the chain reaction due to radical, by trapping the radical by the amino group or the imino bond bonded to the benzene rings). 
     As suitable examples of low molecular type amine-based coloring preventing agents, phenyl-β-naphryl amine (C 6 H 5 —NH—C 10 H 7 ), α-naphthyl amine (C 10 H 7 NH 2 ), N,N′-di-second butyl-p-phenylenediamine ((CH 3 ) 2 CNH—C 6 H 4 —NHC(CH 3 ) 2 ), phenothiazine (C 6 H 4 SNHC 6 H 4 ), N,N′-diphenyl-p-phenylenediamine (C 6 H 5 —NH—C 6 H 4 —NH—C 6 H 5 ), etc, can be given. 
     Further, as suitable examples of polymer amine-based coloring preventing agents, the polymer of monomer such as vinyl, acrylic, methacryl, styryl having the aforementioned amine-based coloring preventing agents on the side chains, and a polymer with the aforementioned low molecular type amide-based coloring preventing agent incorporated into the main chains, can be given. 
     Note that the polymer compound is sometimes more preferable than the low molecular-type compound, and when the polymer compound is used, the crosslink structure may be further introduced, and these points are the same as a case of the phosphorus coloring preventing agent. 
     (d) Hindered Amine-Based Coloring Preventing Agent 
     A fourth specific example of the coloring preventing agent is a 2,2,6,6,-tetramethyl piperidine derivative or 1,2,2,6,6-pentamethyl-4-piperidine derivative (called a “hindered amine-based coloring preventing agent” in some cases in this embodiment.). 
     The hindered amine-based coloring preventing agent is considered to have mainly the function of inhibiting the chain reaction (namely, the function of trapping the radical and suppressing the chain reaction due to the radical). 
     As examples of the low molecular type hindered amine-based coloring preventing agents, 4-benzoyloxy-2,2,6,6-tetramethyl piperidine, 4-stearoyloxy-2,2,6,6-tetramethyl piperidine, 4-stearoyloxy-1,2,2,6,6-pentamethylpiperidine, 4-methacryloyloxy-1,2,2,6,6-tetramethylpiperidine, 4-methacryloyloxy-1,2,2,6,6-pentamethylpiperidine, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-1-octoxypiperidyl)sebacate, 4-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}-1-[2-{3-(3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy}ethyl]-2,2,6,6-tetramethylpiperidine, bis(1,2,2,6,6-pentamethyl-4-piperidyl)2-butyl-2-(3,5-di-t-butyl-4-hydroxybenzyl)malonate, 8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro[4.5]decane-2,4-dion, tetrakis(2,2,6,6-tetramethyl-4-piperidyl)1,2,3,4-butanetetracarboxylate, tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)1,2,3,4-butanetetracarboxylate, tridecyl.tris(2,2,6,6-tetramethyl-4-piperidyl) 1,2,3,4-butanetetracarboxylate, tridecyl.tris(1,2,2,6,6-pentamethyl-4-piperidyl)1,2,3,4-butanetetracarboxylate, ditridecyl.bis(2,2,6,6-tetramethyl-4-piperidyl) 1,2,3,4-butanetetracarboxylate, ditridecyl.bis(1,2,2,6,6-pentamethyl-4-piperidyl)1,2,3,4-butanetetracarboxylate, 3,9-bis[1,1-dimethyl-2-{tris(2,2,6,6-tetramethyl-4-pi peridyloxy carbonyl)butylcarbonyloxy}ethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane, 3,9-bis[1,1-dimethyl-2-{tris(1,2,2,6,6-pentamethyl-4-piperidyloxy carbonyl)butyl carbonyloxy}ethyl]-2,4,8,10-tetraoxaspiro[5,5]undecane, 2,2,4,4-tetramethyl20-(β-lauryloxycarbonyl)-ethyl-7-oxa-3,20-diazadispiro[5,1,11,2]-heneicosan-21-one, 2,4,6-tris{N-cyclohexyl-N-(2-oxo-3,3,5,5-tetramethylpiperazinedione)ethyl}-1,3,5-triazine, etc, can be given. 
     Preferably, bis(2,2,6,6-tetramethyl-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, bis(2,2,6,6-tetramethyl-1-octyloxy-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)2-butyl-(3,5-ji-t-butyl-4-hydroxybenzyl)malonate, 8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro[4.5]decane-2,4-dion, 2,2,4,4-tetramethyl-20-(β-lauryloxycarbonyl)-ethyl-7-oxa-3,20-diazadispiro[5,1,11,2]-heneicosan-21-one, tetrakis(1,2,2,6,6-pentamethyl-4-piperidyl)1,2,3,4-butanetetracarboxylate, tridecyl.tris(1,2,2,6,6-pentamethyl-4-piperidyl)1,2,3,4-butanetetracarboxylate, 4-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}-1-[2-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}ethyl]-2,2,6,6-tetramethyl piperidine, and more preferably bis(1,2,2,6,6-pentamethyl-4-piperidyl)sebacate, bis(2,2,6,6-octyloxy-4-piperidyl)sebacate, bis(1,2,2,6,6-pentamethyl-4-piperidyl)2-butyl-(3,5-ji-t-butyl-4-hydroxybenzyl)malonate, 8-acetyl-3-dodecyl-7,7,9,9-tetramethyl-1,3,8-triazaspiro[4.5]decane-2,4-dion, 2,2,4,4-tetramethyl-20-(β-lauryloxycarbonyl)-ethyl-7-oxa-3,20-diazadispiro[5,1,11,2]-heneicosan-21-one, tridecyl.tris(1,2,2,6,6-pentamethyl-4-piperidyl)-1,2,3,4-butanetetracarboxylate, 4-{3-(3,5-di-t-butyl-4-hydroxyphenyl)propionyloxy}-1-[2-{3-(3,5-di-t-butyl-4-hydroxyphenylpropionyloxy}ethyl]-2,2,6,6-tetramethyl piperidine, can be given. 
     Further, as suitable examples of hindered amine-based coloring preventing agents, the polymer of the monomer such as vinyl, acrylic, methacryl, styryl having the hindered amine-based coloring preventing agents on its side chains, and the monomer with a structure of the hindered amine-based coloring preventing agents incorporated into the main chains, can be given. 
     Note that the polymer compound is sometimes more preferable than the low molecular-type compound, and when the polymer compound is used, the crosslink structure may be further introduced, and these points are the same as a case of the phosphorus coloring preventing agent. 
     (e) Hindered Amine-Based Coloring Preventing Agents 
     A fifth example of the coloring preventing agent is a compound with a large group such as tertiary butyl group introduced to a first order of “o” of the phenol OH group (called a “hindered phenol-based coloring preventing agent” in some cases in this embodiment). Similarly to the aforementioned hindered amine-based coloring preventing agent, it is so considered that the hindered phenol-based coloring preventing agent has mainly the function of inhibiting the chain reaction (namely, the function of trapping the radical by the phenol OH group and suppressing the chain reaction due to the radical). 
     As suitable examples of low molecular type hindered phenol-based coloring preventing agents, 2,6-tertiary butyl-p-cresol, 2,6-di-tertiary butyl-phenol, 2,4-di-methyl-6-tertiary butyl-phenol, butylhydroxyanisole, 2,2′-methylenebis(4-methyl-6-tertiary butylphenol), 4,4′-butylidenebis(3-methyl-6-tertiary butylphenol), 4,4′-thiobis(3-methyl-6-tertiary butylphenol), tetrakis[methylene-3(3,5-di-tertiary butyl-4-hydroxyphenyl)propionate]methane, 1,1,3-tris(2-methyl-4-hydroxy-5-tertiary butylphenyl)butane, etc, can be given. 
     Further, as suitable examples of polymer hindered phenol-based coloring preventing agents, the polymer of the monomer such as vinyl, acrylic, methacryl, styryl having the hindered amine-based coloring preventing agents on its side chains, and the monomer with a structure of the hindered amine-based coloring preventing agents incorporated into the main chains, can be given. 
     Note that the polymer compound is sometimes more preferable than the low molecular-type compound, and when the polymer compound is used, the crosslink structure may be further introduced, and these points are the same as a case of the phosphorus coloring preventing agent. 
     However, there are a lot of unexplained points in a trapping process of a hazardous radical of the aforementioned each kind of coloring preventing agent, and there is also a possibility that an action other than the aforementioned ones work, and the action is not limited to the aforementioned actions. 
     (f) Sulfur-Based Coloring Preventing Agent 
     A sixth specific example of the coloring preventing agent is a compound having bivalent sulfur in a molecule (called a “sulfur-based coloring preventing agent” in some cases in this embodiment). It is so considered that the sulfur-based coloring preventing agent has mainly the function of decomposing the peroxide (namely, the function of decomposing the peroxide into a stable compound by self-oxidation of S-atom). 
     As suitable examples of low molecular type sulfur-based coloring preventing agents, dilauryl thiodipropionate (S(CH 2 CH 2 COOC 12 H 25 ) 2 ), distearyl thiodipropionate (S(CH 2 CH 2 COOC 18 H 37 ) 2 ), lauryl stearyl thiodipropionate (S(CH 2 CH 2 COOC 18 H 37 )(CH 2 CH 2 COOC 12 H 25 )), dimyristylthiodipropionate (S(CH 2 CH 2 COOC 14 H 29 ) 2 ), distearyl β,β′-thiodibutilate (S(CH(CH 3 )CH 2 COOC 18 H 39 ) 2 ), 2-mercaptobenzimidazole (C 6 H 4 NHNCSH), dilaurylsulfide (S(C 12 H 25 ) 2 ), etc, can be given. 
     Further, as suitable examples of polymer sulfur-based coloring preventing agents, a polymer of monomer such as vinyl, acrylic, methacryl, styryl having the aforementioned sulfur-based coloring preventing agents on the side chains, and a polymer with the aforementioned sulfur-based coloring preventing agents incorporated into the main chains, can be given. 
     Note that the polymer compound is sometimes more preferable than the low molecular-type compound, and when the polymer compound is used, the crosslink structure may be further introduced, and these points are the same as a case of the phosphorus coloring preventing agent. 
     3. A Coloring Mechanism by Ultraviolet Rays of the Tungsten Oxide Nanoparticles and the Composite Tungsten Oxide Nanoparticles, and an Action Mechanism of the Coloring Preventing Agents to this Coloring Mechanism 
     First, the coloring mechanism by the tungsten oxide nanoparticles and the composite tungsten oxide nanoparticles of this embodiment will be described. 
     When the resin constituting the heat ray-shielding polyester film of this embodiment is irradiated with the ultraviolet rays, secondary substances such as proton, heavy metal ions, dehydrogenation radical, peroxide radical, and hydroxyl radical, being hazardous radicals, are generated one after the other, in a reaction of a process in which a high polymer chain of this medium resin is cut and decomposed by an energy of the ultraviolet rays. Then, the hazardous radicals, being the secondary substances, cut the polymer chain of the medium resin this time, and therefore deterioration of the polymer and generation of the hazardous radicals are progressed in a chain reaction manner. Then, any one of the hazardous radicals generated in a chain reaction manner reductively acts on the tungsten atoms in the tungsten oxide nanoparticles and/or the composite tungsten oxide nanoparticles, to thereby newly generate pentavalent tungsten. This pentavalent tungsten produces deep blue color, and therefore it can be estimated that coloring concentration is increased, with an increase of the pentavalent tungsten in the heat ray-shielding polyester film. 
     There are a lot of unexplained parts, regarding a mechanism of coloring the tungsten oxide nanoparticles and the composite tungsten oxide nanoparticles by the radicals generated in the medium resin. However, the aforementioned mechanism can be estimated as an assumption. Further, it can be estimated that radicalization of a polymer framework of the medium resin contributes to the coloring of the tungsten oxide nanoparticles and the composite tungsten oxide nanoparticles. Therefore, the inventors reach a conclusion that suppression of such generation reaction of the radicals and chain reaction of radical generation leads to an improvement of a durability of the heat ray-shielding polyester film. Namely, by making the aforementioned coloring preventing agents exist in the heat ray-shielding polyester film containing the tungsten oxide nanoparticles and the composite tungsten oxide nanoparticles, the hazardous radicals generated in this coloring preventing agents due to the ultraviolet rays can be trapped. It is found that by trapping the hazardous radicals, coloring of the tungsten oxide nanoparticles and the composite tungsten oxide nanoparticles (generation of new pentavalent tungsten) can be prevented and the change of the color tone of the heat ray-shielding polyester film due to the ultraviolet rays can be suppressed. 
     The heat ray-shielding polyester film of this embodiment has a structure that the tungsten oxide nanoparticles and/or the composite tungsten oxide nanoparticles are dispersed in the medium resin. With this structure, the generation of the pentavalent tungsten involved in irradiation of the ultraviolet rays can be suppressed and the change of coloring can be suppressed. As a result, it becomes possible to suppress a reduction rate of the visible light transmittance in the infrared ray-shielding nanoparticles dispersion, after emitting the ultraviolet rays to the infrared ray-shielding nanoparticles dispersion of this embodiment. 
     4. A Manufacturing Method of the Heat Ray-Shielding Polyester Film, and the Heat Ray-Shielding Polyester Film 
     A manufacturing method of the heat ray-shielding polyester film can be arbitrarily selected, provided that it is a method of uniformly dispersing the nanoparticles having the heat ray-shielding function into resin. For example, it is possible to use a method of directly adding the nanoparticles to the resin and uniformly melting and mixing them. Particularly, it is easy and preferable to use a method of preparing a dispersion liquid in which the nanoparticles of the heat ray-shielding components are dispersed in an organic solvent together with a dispersant, then preparing a powder raw material obtained by removing the organic solvent from this dispersion liquid, and molding the heat ray-shielding polyester film by using a composition for molding, which is mixed with the resin or resin raw materials. 
     A method for dispersing the nanoparticles into the resin having the heat ray-shielding function is not particularly limited, provided that it is a method capable of uniformly dispersing the nanoparticles into the resin. However, it is more preferable to use a method of using the powder raw material obtained by removing the organic solvent from the dispersion liquid, with the nanoparticles dispersed in an arbitrary solvent as described above. 
     Specifically, by a method using, for example, a beads mill, a ball mill, a sand mill, and ultrasonic wave dispersion, the particles are dispersed in an arbitrary solvent together with the dispersant, to thereby obtain the dispersion liquid. A solvent is removed from the dispersion liquid by using a method such as reduced pressure drying, to thereby obtain the powder raw material. 
     A dispersion solvent used in the dispersion liquid is not particularly limited, and can be selected according to dispersability and solubility of the particles, and a general organic solvent can be used. Moreover, pH may be adjusted by adding acid and alkali as needed. 
     In order to manufacture the heat ray-shielding polyester film by using the aforementioned powder raw material, generally the powder raw material is added to polyester resin, and by a method of mixing them using a ribbon blender, and uniformly melting and mixing them using a mixing machine such as a tumbler, a Nauta mixer, a Henschel mixer, a super mixer, and a planetary mixer, and a kneading machine such as a Banbury mixer, a kneader, a roll, a single screw extruder, and a twin screw extruder, a mixture, with the nanoparticles uniformly dispersed in the polyester resin, is prepared. 
     The heat ray-shielding polyester film of this embodiment can be prepared by molding the mixture, with nanoparticles uniformly dispersed in the polyester resin as described above, by a publicly-known molding method such as a calender process. Further, it is also possible that the mixture, with nanoparticles uniformly dispersed in the resin, is palletized once by a granulation apparatus, and thereafter the heat ray-shielding polyester film is prepared by the same method. 
     A resin coating containing an ultraviolet absorber may also be formed on at least one film surface of the heat ray-shielding polyester film. For example, an ultraviolet absorbing film can be formed, by coating the surface of the heat ray-shielding resin sheet material with a coating liquid, with a benzotriazole-based or a benzophenone-based organic ultraviolet absorber, or an inorganic ultraviolet absorber such as zinc oxide and cerium oxide, dissolved in each kind of binder, and curing it. By such a formation of the ultraviolet absorbing film, the weatherability of the heat ray-shielding polyester film can be improved, and the ultraviolet ray-shielding effect can also be given to this heat ray-shielding polyester film. 
     As the polyester resin used in this embodiment, for example as acid components, an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, naphthalanedicarboxylic acid; and alicyclic dicarboxylic acid such as adipic acid, sebacic acid, dodecadione acid, azelaic acid; and alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid, are used, and as alcoholic components, alicyclic glycol such as ethylene glycol, diethylene glycol, polyethylene glycol; and aromatic glycol such as cyclohexanedimethanol, are used. These polyester resins may be used singularly or may be copolymerized with other component. Specifically, polyethylene terephthalate, or polyethylene-2,6-naphthalate is suitable from the viewpoint of a cost and characteristics. 
     Each kind of additive may be added to this polyester resin, as needed. As the additive, each kind of inorganic and organic particle can be used, and as its particle shape, each kind of particle shapes such as a pearly state, an agglomerating state, a scaly state, and beads state, can be used. The organic particle composed of thermoplastic resin such as cross-linked polystyrene, cross-linked acrylic resin, fluorine resin, and imide resin, can also be used. 
     Further, in the polyester film, total haze (wherein, film thickness: 25 μm conversion) is preferably set to be 2.5% or less. In a case of the haze of 2.5% or less, transparency can be ensured, when this polyester film is used for covering windows or covering each kind of equipment. 
     Further, the thickness of the polyester film is preferably set in a range of 10 to 300 μm. In a case of a film having a thickness of 10 μm or more, a sufficient resistance to weather can be obtained, and a thin film having 300 μm or less is excellent in processability and handling, and is suitable for being used for covering windows or covering each kind of equipment. 
     In addition, in this embodiment, an easy adhesion layer made of water soluble or water dispersible resin can also be provided on the surface of the polyester film. 
     The water soluble or water dispersible resin layer is not particularly limited. For example, acrylic resin, urethane resin, polyester resin, olefin resin, fluorine resin, vinyl resin, chlorine resin, styrene resin, each kind of graft resin, epoxy resin, and silicone resin, etc, can be used, and also the mixture of them can also be used. 
     Thus, it is possible to provide the heat ray-shielding polyester film having the heat ray-shielding function, and having a high transmittance capability in the visible light region, and further capable of suppressing the change of color tone due to ultraviolet rays, without using a physical film forming method involving a high cost and a complicated adhesion process, by dispersing the tungsten oxide nanoparticles and/or the composite tungsten oxide nanoparticles having a strong absorption in the near infrared region, uniformly in the polyester resin as the heat ray-shielding components, and molding this polyester resin into a film shape. 
     It is also preferable that the aforementioned any one of the heat ray-shielding polyester films is formed into a heat ray-shielding polyester film laminate, by being laminated on other transparent base material, according to a purpose of use. By forming the heat ray-shielding polyester film into the heat ray-shielding polyester film laminate, the laminate showing various mechanical characteristics can be obtained, and also by using the heat ray-shielding polyester film, in a part or the whole part of the laminate, the laminate having desired optical characteristics can be obtained. 
     5. Characteristics Evaluation of the Heat Ray-Shielding Polyester Film 
     In the heat ray-shielding polyester film of this embodiment, an evaluation method for the effect of suppressing the change of coloring due to irradiation of ultraviolet rays, will be explained. 
     (1) The heat ray-shielding polyester film not containing the coloring preventing agent of this embodiment is prepared. Then, a prescribed amount of ultraviolet rays is emitted to this heat ray-shielding polyester film, and reduction of the visible light transmittance due to the change of color tone caused by the irradiation of the ultraviolet rays, is measured.
 
(2) The heat ray-shielding polyester film same as that of the aforementioned (1) is prepared, other than a point that the coloring preventing agent of this embodiment is contained. Then, a prescribed amount of ultraviolet rays is emitted to this heat ray-shielding polyester film, and the reduction of the visible light transmittance due to the change of color tone by this irradiation is measured.
 
(3) When the reduction of the visible light transmittance obtained by (1) is standardized as 100%, the reduction of the visible light transmittance obtained in (2) is calculated and from this calculated value, the capability of the heat ray-shielding polyester film containing the coloring preventing agent of this embodiment to suppress the change of color due to ultraviolet rays, is evaluated.
 
     For example, when it is assumed that the heat ray-shielding polyester film not containing the coloring preventing agent of this embodiment has 70% visible light transmittance before irradiation of the ultraviolet rays, and 50% visible light transmittance after irradiation of the ultraviolet rays, and the heat ray-shielding polyester film containing the coloring preventing agent of this embodiment has 68% visible light transmittance after irradiation of the ultraviolet rays, it is found that variation Δ of the visible light transmittance of the heat ray-shielding polyester film not containing the coloring preventing agent of this embodiment is 70%−50%=20%. Meanwhile, the variation Δ of the visible light transmittance of the heat ray-shielding polyester film containing the coloring preventing agent of this embodiment is 70%−68%=2%. 
     Accordingly, when the variation Δ of the visible light transmittance of the heat ray-shielding polyester film not containing the coloring preventing agent of this embodiment is standardized as 100%, the variation Δ of the visible light transmittance of the heat ray-shielding polyester film containing the coloring preventing agent of this embodiment is calculated to be 10%. 
     However, the prescribed amount of the ultraviolet rays means the amount of the ultraviolet rays, under continuous irradiation for 2 hours at intensity of 100 mW/cm 2 , by using EYE SUPER UV TESTER (SUV-W131) by Iwasaki Electric Co., Ltd. (At this time, temperature of a black panel is set to be 60° C.). 
     According to this calculation method, it is possible to objectively evaluate the capability of the coloring preventing agent of the heat ray-shielding polyester film of this embodiment to suppress the change of color due to ultraviolet rays. 
     Further, according to an examination by the inventors of the present invention, it is found that when the variation Δ of the visible light transmittance of, the heat ray-shielding polyester film containing the coloring preventing agent of this embodiment is 70% or less, sufficient capability of the coloring preventing agent of this embodiment to suppress the change of color due to ultraviolet rays can be confirmed, and also in a practical use, the change of coloring due to ultraviolet rays included in solar rays is suppressed. 
     EXAMPLES 
     Examples of the present invention will be specifically explained, together with comparative examples, with reference to table 1. However, the present invention is not limited to the examples described below. 
     Moreover, in each example, powder colors (10° visual field, light source D65) of the tungsten oxide nanoparticles and the composite tungsten oxide nanoparticles, and the visible light transmittance and the solar light transmittance of the heat ray-shielding resin sheet material were measured by using a spectrophoto-meter produced by HITACHI. The solar light transmittance is an index showing the heat ray-shielding capability. Further, the haze value was measured based on JIS K 7105, by using HR-200 produced by MURAKAMI COLOR RESEARCH LABORATORY. 
     Example 1 
     A quartz boat, with 50 g of H 2 WO 4  put therein, was set in a quartz tubular furnace, which was then heated while 5% of H 2  gas was supplied, with N 2  gas as a carrier, and reduced for 1 hour at a temperature of 600° C., and thereafter baked for 30 minutes at 800° C. in an N 2  gas atmosphere, to thereby obtain particle “a”. As the powder color of this particle “a”, L* was 36.9288, a* was 1.2573, b* was −9.1526, and as a result of identifying the crystal phase by powder X-ray diffraction, the crystal phase of W 18 O 49  was observed. 
     Next, 5 wt % of the particle “a”, 5 wt % of the polymer dispersant, and 90 wt % of methyl isobutyl ketone were weighed, which were then pulverized/dispersed for 6 hours by a paint shaker, with 0.3 mmΦ of ZrO 2  beads put therein, to thereby prepare the tungsten oxide nanoparticle dispersion liquid (liquid A). Here, when the dispersed particle size of the tungsten oxide nanoparticles in the dispersion liquid (liquid A) was measured by a particle size distribution meter ELS-800 produced by OTSUKA ELECTRONICS CO, LTD., it was 86 nm. 
     Next, from the obtained dispersion liquid (liquid A), methyl isobutyl ketone was removed by vacuum distillation, to thereby obtain a powder raw material (powder A). The powder raw material (powder A) was added to the polyester resin, so that the content of the particle “a” was 1.2 wt %, which were then mixed by the blender, and uniformly kneaded by the twin screw extruder, and thereafter molded into a film having a thickness of 50 μm by using a T-die, to thereby prepare the heat ray-shielding polyester film (sample 1) of an example 1, with the heat ray-shielding nanoparticles uniformly dispersed overall. 
     The dispersed particle size of the oxide particles in the obtained heat ray-shielding polyester film was 88 nm when observed by the cross-section TEM observation. 
     The solar light transmittance was 47.5% when the visible light transmittance was 65.1%, and the haze value was 1.5%. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                   
                   
                 Thickness 
                   
                   
                   
               
               
                   
                 Dispersed particle size 
                 Content 
                 of 
                 Visible 
                 Solar 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                 Indispersion 
                   
                 of 
                 polycator 
                 light 
                 light 
                   
                   
               
               
                   
                   
                 liquid 
                 In film 
                 particle 
                 film 
                 transmittance 
                 transmittance 
                 Haze 
               
               
                   
                 Composition 
                 (nm) 
                 (nm) 
                 (wt %) 
                 (μm) 
                 (%) 
                 (%) 
                 (%) 
                 Remark 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
            
               
                 Example1 
                 W 18 O 49   
                 86 
                 88 
                 1.2 
                 50 
                 65.1 
                 47.5 
                 1.5 
                   
               
               
                 Example2 
                 W 18 O 49   
                 86 
                 62 
                 0.2 
                 300 
                 64.3 
                 47.3 
                 1.4 
               
               
                 Example3 
                 Cs 0.3 WO 3   
                 86 
                 62 
                 1.2 
                 50 
                 77.5 
                 48.3 
                 1.4 
               
               
                 Example4 
                 Cs 0.3 WO 3   
                 86 
                 62 
                 6 
                 10 
                 77.5 
                 48.3 
                 1.4 
               
               
                 Example5 
                 Cs 0.3 WO 3   
                 86 
                 62 
                 0.2 
                 300 
                 78.1 
                 48.8 
                 1.2 
               
               
                 Comparative 
                 Cs 0.3 WO 3   
                 86 
                   
                 0.09 
                 300 
                 87.1 
                 75.1 
                 1 
               
               
                 Example 1 
               
               
                 Comparative 
                 Cs 0.3 WO 3   
                 86 
                   
                 10.1 
                 10 
                 70.1 
                 37.1 
                 1 
                 Abrasion 
               
               
                 Example 2 
                   
                   
                   
                   
                   
                   
                   
                   
                 strength is low 
               
               
                   
               
            
           
         
       
     
     Example 2 
     The heat ray-shielding polyester film (sample 2) was prepared in the same way as the example 1, other than a point that the powder raw material (powder A) was added to the polyester resin, so that the content of the particle “a” was 0.2 wt % and this polyester resin was molded into a film having a thickness of 300 μm. 
     The dispersed particle size of the oxide nanoparticles in the obtained heat ray-shielding polyester film was 62 nm when observed by the cross-section TEM observation. 
     The solar light transmittance was 47.3% when the visible light transmittance was 64.3%, and the haze value was 1.4%. 
     Example 3 
     The powder obtained by sufficiently mixing 50 g of H 2 WO 4  and 17.0 g of Ca(OH) 2  by the agate mortar was heated while 5% of H 2  gas was supplied, with N 2  gas as a carrier, and reduced for 1 hour at a temperature of 600° C., and thereafter baked for 30 minutes at 800° C. in the N 2  gas atmosphere, to thereby obtain particle “b” (composition formula was expressed by Cs 0.3 WO 3 , and in the powder color of this particle “b”, L* was 35.2745, a* was 1.4918, b* was −5.3118). 
     Next, 5 wt % of the particle “b”, 5 wt % of the polymer dispersant, and 90 wt % of methyl isobutyl ketone were weighed, which were then pulverized/dispersed for 6 hours by a paint shaker, with 0.3 mmΦ of ZrO 2  beads put therein, to thereby prepare the composite tungsten oxide nanoparticle dispersion liquid (liquid B). Here, when the dispersed particle size of the tungsten oxide nanoparticles in the dispersion liquid (liquid B) was measured by a particle size distribution meter ELS-800 produced by OTSUKA ELECTRONICS CO, LTD., it was 86 nm. 
     Next, from the obtained dispersion liquid (liquid B), methyl isobutyl ketone was removed by vacuum distillation, to thereby obtain a powder raw material (powder B). The powder raw material (powder B) was added to the polyester resin, so that the content of the particle “b” was 1.2 wt %, which were then mixed by the blender, and uniformly kneaded by the twin screw extruder, and thereafter molded into a film having a thickness of 50 μm by using a T-die, to thereby prepare the heat ray-shielding polyester film (sample 3) of an example 3, with the heat ray-shielding nanoparticles uniformly dispersed overall. 
     The dispersed particle size of the oxide nanoparticles in the obtained heat ray-shielding polyester film was 62 nm when observed by the cross-section TEM observation. 
     The solar light transmittance was 48.3% when the visible light transmittance was 77.5%, and the haze value was 1.4%. 
     Example 4 
     The heat ray-shielding polyester film (sample 4) of an example 4 was obtained in the same way as the example 3, other than a point that the powder raw material (powder B) was added to the polyester resin so that the content of the particle “b” was 6 wt %, and this polyester resin was molded into a film having a thickness of 10 μm. 
     The dispersed particle size of the oxide nanoparticles in the obtained heat ray-shielding polyester film was 62 nm, when observed by the cross-section TEM observation. 
     The solar light transmittance was 48.3% when the visible light transmittance was 77.5%, and the haze value was 1.4%. 
     Example 5 
     The heat ray-shielding polyester film (sample 5) of an example 5 was obtained in the same way as the example 3, other than a point that the powder raw material (powder B) was added to the polyester resin so that the content of the particle “b” was 0.2 wt %, and this polyester resin was molded into a film having a thickness of 300 μm. 
     The dispersed particle size of the oxide nanoparticles in the obtained heat ray-shielding polyester film was 62 nm, when observed by the cross-section TEM observation. 
     The solar light transmittance was 48.8% when the visible light transmittance was 78.1%, and the haze value was 1.2%. 
     Comparative Example 1 
     The heat ray-shielding polyester film (sample 6) of an example 6 was obtained in the same way as the example 3, other than a point that the powder raw material (powder B) was added to the polyester resin so that the content of the particle “b” was 0.09 wt %, and this polyester resin was molded into a film having a thickness of 300 μm. 
     The solar light transmittance was 75.1% when the visible light transmittance was 87.1%, and the haze value was 1.0%. 
     There is less content of the particle “b”, which is 0.09 wt %, and therefore the solar light transmittance is high, thus failing to exhibit practical heat ray-shielding characteristics. 
     Comparative Example 2 
     The heat ray-shielding polyester film (sample 7) of an example 7 was obtained in the same way as the example 3, other than a point that the powder raw material (powder B) was added to the polyester resin so that the content of the particle “b” was 10.1 wt %, and this polyester resin was molded into a film having a thickness of 10 μm. The solar light transmittance was 37.1% when the visible light transmittance was 70.1%, and the haze value was 1.0%. 
     There is much content of the particle “b”, which is 10.1 wt %, and therefore the abrasion resistance of the surface of the heat ray-shielding polyester film is remarkably lowered, thus easily damaging the surface by being rubbed with fingernails, which is unpractical. 
     Example 6 
     The heat ray-shielding polyester film (sample 8) of an example 6 was prepared in the same way as the example 1, other than a point that the powder raw material (powder A) was added to the polyester resin so that the content of the particle “a”, was 0.2 wt %, and resorcinol-bis(diphenyl-phosphate) [produced by AJINOMOTO, product name: “REOFOS” RDP], being the phosphorous coloring preventing agent, was 0.4 wt %, and this polyester resin was molded into a film having a thickness of 300 μm. 
     The dispersed particle size of the oxide nanoparticles in the obtained heat ray-shielding polyester film was 64 nm when observed by the cross-section TEM observation. The solar light transmittance was 48.3% when the visible light transmittance was 65.4%, and the haze value was 1.5%. 
     When this heat ray-shielding polyester film was irradiated with ultraviolet rays for 2 hours and thereafter the optical characteristics were measured, it was found that the visible light transmittance was 64.0%, and the haze value was 1.5%. It was also found that the reduction of the visible light transmittance due to irradiation of the ultraviolet rays was 1.4%, which was small, and there was less change of color tone. Further, even after irradiation of the ultraviolet rays, it was found that the haze value was not varied, and the transparency was maintained. 
     Meanwhile, when the heat ray-shielding polyester film obtained by the example 1 was similarly irradiated with ultraviolet rays for 2 hours, and the variation Δ of the visible light transmittance was calculated. Then, it was found that the variation Δ was 6.8% and this heat ray-shielding polyester film had a sufficient capability to suppress the change of color due to ultraviolet rays, by adding the coloring preventing agent. 
     Note that continuous irradiation of the ultraviolet rays for 2 hours was performed by using EYE SUPER UV TESTER (SUV-W131) produced by Iwasaki Electric Co., Ltd., at intensity of 100 mW/cm 2 .