TWI499064B - White polyester film for solar cell, solar cell back encapsulant and solar cell module using same - Google Patents

Description

White polyester film for solar cell, solar cell back encapsulant and solar cell module using same

The present invention relates to a white polyester film for a solar cell which has high whiteness and good light reflectivity, and which is excellent in light resistance and hydrolysis resistance, and a solar cell back encapsulating sheet and a solar cell module using the same.

In recent years, solar cells have attracted attention as the next generation of green energy. As the solar cell module, a constituent member such as a back encapsulating sheet on the back surface thereof is used, and the constituent members are made of a base film. Since the solar cell is continuously used during the long period of time, the base film used in the constituent members or the constituent members is required to have durability against the natural environment.

In order to improve the UV resistance and the shielding property, a fluorine-based film, a polyethylene film, or a polyester film to which a white pigment or the like is added has been conventionally used for the purpose of improving the UV resistance and the shielding property (Patent Document) 1~9).

Prior technical literature Patent literature

Patent Document 1 Japanese Patent Laid-Open No. Hei 11-261085

Patent Document 2 Japanese Patent Laid-Open Publication No. 2000-114565

Patent Document 3 Japanese Patent Laid-Open Publication No. 2004-247390

Patent Document 4 Japanese Patent Laid-Open Publication No. 2002-134771

Patent Document 5 Japanese Patent Laid-Open Publication No. 2006-270025

Patent Document 6 Japanese Patent Laid-Open Publication No. 2007-184402

Patent Document 7 Japanese Patent Laid-Open Publication No. 2007-208179

Patent Document 8 Japanese Patent Laid-Open Publication No. 2008-85270

Patent Document 9 W O 2007-105306

Patent Literatures 1 to 9 also disclose that by using a white base film as a solar cell back surface encapsulating sheet constituent member, it is possible to reflect sunlight and improve power generation efficiency. However, it is necessary to add a large amount of white pigment particles to the white base film, and to prepare the raw material of the premixed particles and the resin in a usual extrusion step in order to improve the dispersibility and the mixed state of the particles to be added in a large amount. The method of increasing the melting time and the like, but the resin is likely to be deteriorated as a result of applying such a large thermal history, and when the obtained base film is used for the solar cell back encapsulating sheet, there is a problem that durability is high at high temperature and high humidity.

The object of the present invention is to provide a white polyester film for a solar cell, a solar cell back encapsulating sheet and a solar cell module using the same, wherein the white polyester film for a solar cell has high whiteness and good At the same time of light reflectivity, it is excellent in environmental durability represented by light resistance and hydrolysis resistance.

The white polyester film for solar cells of the present invention which can solve the above problems has a whiteness of 50 or more, an average reflectance of 50 to 95% in a wavelength range of 400 to 800 nm, an acid value of 1 to 50 eq/ton, and a thickness. A polyester film for a solar cell of 30 to 380 μm, characterized in that it has a multilayer structure containing 10 to 35% by mass of inorganic particles. The inorganic fine particle concentration-containing layer is disposed as the outermost layer of at least one side, and the thickness of the inorganic fine particle-containing layer is 5 to 30% with respect to the thickness of the entire polyester film, and the inorganic layer of the polyester film as a whole The content of the fine particles is 2 to 10% by mass.

The inorganic fine particles are preferably titanium dioxide mainly composed of a rutile type.

The white polyester film for a solar cell of the present invention preferably has a heat shrinkage ratio of from 0.2 to 3.0% in the longitudinal direction at 150 °C. Under the conditions of 105 ° C, 100% RH, 0.03 MPa, and treatment for 200 hours, the elongation at break retention after the hydrolysis test is promoted is preferably 60 to 100%.

The white polyester film for solar cells of the present invention has a rate of elongation at break after the photodegradation test is promoted at 63% C, 50% RH, UV irradiation intensity of 100 mW/cm ² , and irradiation for 100 hours. It is better. The change in the COLOR b* value after the above-described photodegradation test is preferably 12 or less.

The white polyester film for a solar cell of the present invention may be provided with a coating layer containing a polyurethane resin on the surface of at least one side of the polyester film, wherein the polyurethane resin is aliphatic. A polycarbonate polyol is used as a constituent component.

Moreover, the present invention also includes a solar cell back encapsulating sheet using the above-described white polyester film for a solar cell, and a solar cell module comprising: a solar cell back encapsulating sheet, and a solar cell back encapsulating sheet a filler layer and a solar cell element embedded in the filler layer.

The white polyester film for solar cells of the present invention has both light reflectivity and environmental durability. By using the white polyester film for a solar cell of the present invention, it is possible to provide an inexpensive and lightweight solar cell back sheet and solar cell module which have excellent light reflectivity and excellent environmental durability.

The white polyester film for solar cells of the present invention has a whiteness of 50 or more, an average reflectance of 50 to 95% in a wavelength range of 400 to 800 nm, an acid value of 1 to 50 eq/ton, and a solar energy of 30 to 380 μm. A polyester film for a battery, characterized in that it has a multilayer structure containing 10 to 35% by mass of inorganic fine particles, and the inorganic fine particle-concentrated layer is disposed as an outermost layer of at least one side, and is opposite to the polyester film. The thickness of the inorganic fine particle-concentrated layer is 5 to 30%, and the content of the inorganic fine particles in the entire polyester film is 2 to 10% by mass.

<Polyester Resin>

The polyester resin used in the white polyester film for solar cells of the present invention means an aromatic dicarboxylic acid such as p-citric acid, isophthalic acid or naphthalene dicarboxylic acid or an ester thereof such as ethylene glycol or dibutyl. The diol of alcohol, diethylene glycol, 1,4-butanediol, and neopentyl glycol may be produced by polycondensation of a diol, or may be a copolymer copolymerized with a third component.

Representative examples of such a polyester resin include polyethylene terephthalate, polybutylene terephthalate, and polyethylene 2,6-naphthalenedicarboxylate.

When copolymerizing with the third component, the molar ratio of the ethylene phthalate unit, the p-butyl phthalate or the ethylene 2,6-naphthalate unit is preferably 70 mol% or more, and 80%. More than or equal to mol% is preferable, and more preferably 90 mol% or more.

In addition to the method of directly polycondensing an aromatic dicarboxylic acid and a diol, the polyester resin can also be subjected to a polycondensation reaction by subjecting an alkyl ester of an aromatic dicarboxylic acid to a transesterification reaction with a diol. A method of producing a method in which a glycol ester of an aromatic dicarboxylic acid is subjected to polycondensation or the like.

Examples of the polycondensation catalyst include a ruthenium compound, a titanium compound, a ruthenium compound, a tin compound, an aluminum and/or an aluminum compound, a phosphorus compound having an aromatic ring in the molecule, and an aluminum salt of a phosphorus compound.

After the polycondensation reaction, the catalyst is passivated by removing the catalyst from the polyester resin or by adding a phosphorus compound or the like, whereby the thermal stability of the polyester resin can be further improved. Further, the polycondensation catalyst system may coexist in an appropriate amount within a range in which the properties, workability, and color tone of the polyester resin are not problematic.

When a polyester resin is produced, a dialkylene glycol is produced as a by-product in the esterification reaction of citric acid or in the transesterification reaction to dimethyl phthalate. When the polyester resin contains a large amount of dialkyl diol, the heat resistance is lowered when the obtained film is exposed to a high temperature environment. Therefore, the dialkyl diol content of the polyester resin used in the present invention is preferably suppressed within a certain range.

Specifically, when diethylene glycol is used as an example of a dialkylene glycol, the diethylene glycol content of the polyester resin is preferably 2.3 mol% or less, and 2.0 mol% or less. Preferably, 1.8 mol% or less is more preferable. By making the content of diethylene glycol 2.3 mol% or less, it can be mentioned It has high heat stability and can suppress the increase in acid value caused by decomposition at the time of drying and molding. Further, diethylene glycol is preferably used in a small amount, but since it is a by-product in the production of a polyester resin, the lower limit of the content is actually 1.0 mol%, and 1.2 mol% is more preferable.

In the present invention, in order to impart durability to the polyester film, the inherent viscosity of the polyester resin to be used is preferably 0.65 dl/g or more, more preferably 0.67 dl/g or more, and most preferably 0.90 dl/g or less. Preferably, it is 0.75 dl/g or less. When the intrinsic viscosity of the polyester resin is in the above range, good productivity can be obtained, and hydrolysis resistance and heat resistance of the formed film can be improved. On the other hand, when the intrinsic viscosity is less than 0.65 dl/g, the hydrolysis resistance and heat resistance of the formed film may be deteriorated. Further, when it is higher than 0.90 dl/g, there is a case where productivity is low. In order to adjust the intrinsic viscosity of the polyester resin to the above range, it is preferred to carry out solid phase polymerization after the polymerization.

The carboxyl terminal of the polyester resin represented by the acid value has an action of promoting hydrolysis by self-catalytic action. In order to obtain a high degree of hydrolysis resistance, the acid value of the white polyester film for a solar cell of the present invention is important in the range of 1 to 50 eq/ton with respect to the polyester. The acid value is preferably 2 eq/ton or more with respect to the polyester, more preferably 3 eq/ton or more, more preferably 40 eq/ton or less, and still more preferably 30 eq/ton or less. When the acid value is more than 50 eq/ton, the hydrolysis resistance of the film is low and early deterioration is likely to occur.

In order to make the acid value of the film in the above range, it is preferred to suppress the acid value of the polyester resin used as the raw material resin to a certain range. Specifically, the acid value of the polyester resin is preferably less than 50 eq/ton, and is 25 eq/ton. The following is preferred, and it is more preferably 20 eq/ton or less. Further, the acid value of the film is preferably small, but from the viewpoint of productivity, the lower limit is 0.5 eq/ton. The acid value of the polyester resin and the film can be measured by a titration method to be described later.

In order to control the acid value of the polyester resin in the above range, the polymerization conditions of the resin, in detail, the important factors of the production apparatus such as the structure of the esterification reactor, and the dicarboxylic acid supplied to the slurry of the esterification reactor The composition ratio of the diol, the esterification reaction temperature, the reaction pressure, the reaction time, and the like, the esterification reaction conditions, the solid layer polymerization conditions, and the like may be appropriately set. Further, it is also effective to control the moisture content of the polyester crystal grains supplied to the extruder or to control the resin temperature in the melting step. Further, it is also preferred to block the carboxyl terminal by an epoxy compound or a carbodiimide compound or the like.

For example, when the polyester crystal grains are supplied to the extruder, in order to suppress an increase in the acid value, it is preferred to use a sufficiently dried polyester crystal grain. Specifically, the moisture content of the polyester crystal grains is preferably 100 ppm or less, more preferably 50 ppm or less, and still more preferably 30 ppm or less.

The drying method of the polyester crystal grains can be a well-known method such as vacuum drying or heat drying. For example, when heating and drying, the heating temperature is preferably 100 to 200 ° C, and more preferably 120 to 180 ° C. The drying time is preferably 1 hour or more, more preferably 3 hours or more, and still more preferably 6 hours or more.

Further, in order to suppress the acid value of the polyester resin, it is also effective to control the temperature of the resin in the melting step to a certain range. Specifically, the melting temperature is preferably 280 to 310 ° C, more preferably 290 to 300 ° C. By raising the melting temperature, the back pressure during filtration in the extruder is reduced, and good results can be achieved. Productivity, but when the melting temperature is higher than 310 ° C, the hydrolysis resistance of the obtained film is lowered because the resin is thermally deteriorated and the acid value of the resin is increased.

Further, the polyester resin may contain one or more kinds of fluorescent whitening agents, ultraviolet rays, infrared absorbing dyes, thermal stabilizers, surfactants, antioxidants, etc., depending on the purpose of use. Various additives.

For the antioxidant, an antioxidant such as an aromatic amine or a phenol can be used, and as the thermal stabilizer, a phosphorus stabilizer such as phosphoric acid or a phosphate ester, a sulfur-based or an amine-based thermal stabilizer can be used.

<Inorganic microparticles>

The inorganic fine particles used in the white polyester film for a solar cell of the present invention are not particularly limited, and examples thereof include titanium oxide, barium sulfate, cerium oxide, kaolin, talc, calcium carbonate, zeolite, alumina, and carbon. Black, zinc oxide, zinc sulfide, and the like. From the viewpoint of improving whiteness and productivity, titanium dioxide or barium sulfate of a white pigment is preferred, and titanium dioxide is more preferred.

The average particle diameter of the inorganic fine particles is preferably 0.1 μm or more, more preferably 0.5 μm or more, still more preferably 3 μm or less, and still more preferably 2.5 μm or less. By setting the average particle diameter of the inorganic fine particles within the above range, the whiteness of the film due to the light scattering effect can be improved, and film formation can be suitably performed. On the other hand, when the average particle diameter is less than 0.1 μm, the light scattering effect is insufficient, and there is a possibility that the whiteness necessary for the film cannot be obtained. Moreover, when the average particle diameter is more than 3 μm, there is a possibility that the film is likely to be broken or the film formation cannot be performed satisfactorily in the film formation.

In the present invention, the average particle diameter of the inorganic fine particles can be determined by the following electron microscopic method. Specifically, the inorganic microparticles are observed by a scanning electron microscope, the magnification is appropriately changed according to the size of the particles, a photograph is taken, and the photograph taken is enlarged and reproduced, and at least 100 or more microparticles are randomly selected, and the outer periphery of each particle is drawn. The equivalent diameter of the particles was measured from the maps using a video analysis device, and the average value of the particles was set as the average particle diameter.

Since the solar cell is exposed to sunlight for a long time outside the house, durability against light deterioration (light resistance) is required. From the viewpoint of improving the light resistance, the inorganic fine particles used in the film of the present invention are preferably titanium dioxide fine particles mainly composed of a rutile type.

The titanium dioxide system is known to be mainly two crystal forms of the rutile type and the anatase type. The spectral reflectance of the ultraviolet light of the anatase type is very large, and the rutile type has a characteristic that the ultraviolet absorption rate is large (that is, the spectral reflectance is small). The difference in the spectral characteristics of the titanium oxide crystal form is remarkable. By utilizing the rutile-type ultraviolet absorbing property, the light resistance of the film can be preferably improved, and the coloring due to photodegradation of the film can be reduced. Therefore, in the preferred aspect of the present invention, even if the ultraviolet absorber is not substantially added, the light resistance is excellent. Therefore, it is not easy to cause problems such as contamination or poor adhesion caused by bleeding of the ultraviolet absorber.

In addition, the term "main body" as used herein means that the content of rutile-type titanium dioxide in the total titanium dioxide fine particles is more than 50% by mass. Further, the content of the anatase titanium dioxide in the total titanium dioxide fine particles is preferably 10% by mass or less, more preferably 5% by mass or less, and 0% by mass. optimal. When the content of the anatase type titanium dioxide is more than 10% by mass, the content of the rutile-type titanium oxide which is contained in the total titanium dioxide fine particles is small, and the photocatalytic effect of the anatase-type titanium dioxide is higher than the case where the ultraviolet absorption performance is insufficient. Strong, due to this effect, the light resistance tends to be low. The rutile-type titanium dioxide and the anatase-type titanium dioxide system can be distinguished by the X-ray structure diffraction or spectral absorption characteristics.

Further, the surface of the titanium dioxide fine particles mainly composed of the rutile type of the present invention may be subjected to an inorganic treatment using alumina or cerium oxide or an organic treatment using a polyfluorene-based or alcohol-based method.

According to the above configuration, the film of the present invention can achieve excellent light resistance even under light irradiation. Specifically, when UV irradiation is performed for 100 hours at an irradiation intensity of 100 mW/cm ² at 63 ° C and 50% RH, the elongation at break of the film is preferably 35% or more, and preferably 40% or more. . As described above, the film of the present invention is suitable as a back surface encapsulating sheet of a solar cell that can be used outdoors, because it can suppress photodecomposition or deterioration even by light irradiation.

The addition of the inorganic fine particles to the film can be carried out by a well-known method, and the master batch method (MB method) in which the polyester resin and the inorganic fine particles are mixed in advance using an extruder is preferred from the viewpoint of reducing the heat history. In addition, it is possible to use a method in which a masterbatch is produced by deaerating moisture, air, or the like while the undried polyester resin and the inorganic fine particles are put into an extruder in advance, in order to suppress an increase in the acid value of the polyester resin. It is preferred to produce a masterbatch by drying the polyester resin as much as possible. In this case, a method of producing a master batch while degassing, and a method of producing a sufficiently dried polyester resin without deaeration may be mentioned. By controlling the addition of inorganic microparticles to the polyester In the aspect of the resin, since it can contain a high concentration of inorganic fine particles while appropriately keeping the acid value of the polyester resin low, it is easy to obtain both light resistance and water resistance while having high whiteness and light reflectance. A solution film.

As described above, in the case of producing a master batch, it is preferred that the polyester resin to be charged is reduced in moisture content by pre-drying. The drying condition is preferably 100 to 200 ° C, preferably 120 to 180 ° C, preferably 1 hour or more, more preferably 3 hours or more, still more preferably 6 hours or more. Thereby, the moisture content of the polyester resin is preferably 50 ppm or less, preferably 30 ppm or less, to sufficiently dry.

When the master batch is produced by degassing, the polyester resin is melted at a temperature of 250 to 300 ° C, preferably 270 to 280 ° C, and one of the premixers is set, preferably two or more. It is preferable that the gas port is subjected to continuous suction and degassing of 0.05 MPa or more, preferably 0.1 MPa or more, and the pressure reduction in the mixer is maintained.

Further, the method of premixing is not particularly limited, and a batch method may be used, and a uniaxial or biaxial or higher kneading extruder may be used.

<Inorganic microparticles contain a layer>

In the white polyester film for a solar cell of the present invention, the inorganic fine particles containing 10 to 35% by mass of the inorganic fine particles contain a layer which is disposed as the outermost layer of at least one side. In addition, the content of the inorganic fine particles containing the layer in the inorganic fine particle concentration is preferably 11% by mass or more, more preferably 28% by mass or less, and still more preferably 21% by mass or less. By setting the content of the inorganic fine particles within the above range, it is possible to obtain a white polyester thin film for solar cells having high whiteness and reflectance and excellent environmental durability. membrane. On the other hand, when the content is less than 10% by mass, the whiteness and reflectance of the film become insufficient and photodegradation of the film is easily performed. Further, when it is more than 35% by mass, in order to uniformly disperse it in the resin, it is necessary to carry out most of the heat, and the above-mentioned previous problems cannot be solved.

Moreover, the content of the inorganic fine particles in the entire film is 2 to 10% by mass. It is preferably 3% by mass or more and 8% by mass or less.

The white polyester film for a solar cell of the present invention has a laminated structure of at least two layers, and the above multilayer structure may be used. However, a layer having a large content of inorganic fine particles (a layer containing inorganic fine particles in a concentrated layer) is the outermost layer of at least one side. The composition. For example, when the inorganic fine particle concentration-containing layer is used as the A layer and the inorganic fine particle content is smaller than the inorganic fine particle concentration-containing layer, the A layer/B layer, the A layer/B layer/A layer, or the like can be used. Composition. The preferred structure is a two-layer structure, and when the back sheet is used, the layer containing a large amount of inorganic particles is disposed on the outermost layer directly contacting the sunlight, thereby effectively preventing the film itself and the composition. The member film, the sheet, and the adhesive layer of the inner layer of the back sheet are deteriorated by ultraviolet rays or the like.

In order to prevent the layer provided by deterioration due to ultraviolet rays or the like, the surface roughness is also increased and the adhesion between the layers is not easily obtained because a certain amount of high-concentration inorganic fine particles are added thereto. One of the preferable reasons for the advantage of the two-layer configuration is that the concentration of the inorganic fine particles on the opposite side can be suppressed to be low, and such a problem does not occur.

When it is composed of a two-layer structure (A layer/B layer) or a three-layer structure (A layer/B layer/A layer), the thickness of the outermost surface layer (layer A) with respect to the entire film layer (one layer, or both surfaces) The total thickness is set to 5 to 30%. Surface layer (A layer) The thickness ratio is preferably 8% or more, more preferably 10% or more, and still more preferably 15% or more. Further, it is preferably 28% or less, more preferably 25% or less, and still more preferably 25% or less. By setting the thickness ratio of the surface layer to the above range, a white polyester film for solar cell encapsulation having both whiteness, reflectance and environmental durability can be obtained. On the other hand, when the thickness ratio of the surface layer is less than the above lower limit, there is a possibility that the film photodegradation gradually proceeds in the thickness direction. Further, when the thickness ratio of the surface layer is higher than the above upper limit, the hydrolysis resistance of the entire film tends to be deteriorated.

The white polyester film for a solar cell of the present invention is particularly preferably composed of a two-layer structure which satisfies the above thickness ratio. The photodegradation proceeds slowly from the outermost layer on the side directly invading the sunlight to the thickness direction. Therefore, the layer containing the inorganic fine particles is disposed separately from the plurality of layers, and by providing one layer on the outermost layer on the direct intrusion side of the sunlight, the layer can be efficiently concentrated to prevent the function of light deterioration. In addition, when the intermediate layer is placed in the inorganic fine particle-concentrated layer, there is a possibility that the film is peeled off due to deterioration of the resin. From this viewpoint, the inorganic fine particle-concentrated layer is preferably the outermost layer which is only present on the side directly infiltrated by sunlight. The film of the present invention has a two-layer structure, and by concentrating the inorganic fine particle content on the outermost layer on the side directly infiltrated by sunlight, the inorganic fine particle content can be suppressed to a low level as a whole, and the height can be made high. High whiteness, light reflectivity, UV resistance, hydrolysis resistance.

<Other layers with less inorganic fine particles>

The white polyester film for a solar cell of the present invention may further contain another layer having a smaller content of inorganic fine particles than the layer containing the inorganic fine particles. The content of inorganic fine particles in the other layers is as long as In the above-mentioned inorganic fine particles, the content of the inorganic fine particles is small, and the content of the inorganic fine particles is small. For the above reason, the difference between the content of the inorganic fine particles and the inorganic fine particles contained in the inorganic fine particle concentration is preferably 10% by mass or more.

<Function giving layer>

When the white polyester film for a solar cell of the present invention requires various functions such as easy adhesion, insulation, and scratch resistance, the polymer resin may be coated on the surface thereof by coating or the like. Further, when slipperiness is required, the coating layer may contain inorganic and/or organic particles.

When the adhesion is required, it is preferable to provide a coating layer on the surface of at least one side of the film, wherein the aqueous coating liquid contains a water-soluble or water-dispersible copolymerized polyester resin, an acrylic resin, and At least one of the polyurethane resins. For example, the aqueous coating liquid disclosed in Japanese Patent No. 3,567, 927, Japanese Patent No. 3,589, 232, and Japanese Patent No. 3,589, 233, and the like.

When the white polyester film for a solar cell of the present invention is used in contact with a filler layer of an olefin resin such as EVA or PVB, in order to achieve easy adhesion to the filler layer, it is particularly suitable for the aqueous coating liquid to contain a polyurethane. Resin. In particular, in view of being excellent in heat resistance and hydrolysis resistance and preventing yellowing caused by sunlight, it is preferred to contain a polyurethane resin having an aliphatic polycarbonate polyol as a constituent component. By including such a polyurethane resin, the adhesion of the film under moist heat can be improved.

The aliphatic polycarbonate polyol may, for example, be an aliphatic polycarbonate diol or an aliphatic polycarbonate triol. The number average molecular weight of the polycarbonate diol is preferably 1,500 to 4,000, more preferably 2,000 to 3,000. When the number average molecular weight of the aliphatic polycarbonate diol is less than 1,500, the tough urethane component is added and the stress caused by the heat shrinkage of the substrate cannot be alleviated, and the adhesion is lowered. Further, when the number average molecular weight is more than 4,000, there is a case where the adhesion and the strength after the high-temperature and high-humidity treatment are lowered.

When the total polyisocyanate component of the polyurethane resin is 100 mol%, the molar ratio of the aliphatic polycarbonate polyol is preferably 3 mol% or more, and 5 mol% or more. Preferably, it is preferably 60 mol% or less, more preferably 40 mol% or less. When the molar ratio is less than 3 mol%, water dispersibility becomes difficult. Moreover, when it is more than 60 mol%, since the water resistance is low, the moist heat resistance is low.

The glass transition temperature of the above urethane resin is not particularly limited, and is preferably less than 0 ° C, more preferably less than -5 ° C. Thereby, when the pressure is applied, the viscosity is close to the partially melted olefin resin such as EVA or PVB, and by partial mixing, the adhesion is improved and the appropriate flexibility is easily achieved.

<Method for Producing White Polyester Film for Solar Cell>

The method for producing the white polyester film for a solar cell of the present invention is not particularly limited, and it is preferably a co-extrusion method in which polyester granules for forming each layer are supplied to respective extruders, and laminated in a molten state. And extruded from the same mold. For example, when a film comprising two layers of a layer containing inorganic fine particles is produced, a polyester crystal grain containing a large amount of inorganic fine particles (a resin crystal grain containing a layer of inorganic fine particles) and a small amount of inorganic fine particles are aggregated. Ester grain (resin grain for other layers) After being supplied to the respective extruders, lamination is carried out in a molten state and extrusion is carried out from the same mold.

When the polyester crystal grains are supplied to the extruder, in order to suppress an increase in the acid value, it is preferred to use a sufficiently dried polyester crystal grain. Specifically, the moisture content of the polyester crystal grains is preferably 100 ppm or less, more preferably 50 ppm or less, and still more preferably 30 ppm or less.

The drying method of the polyester crystal grains can be a well-known method such as drying under reduced pressure, drying by heating, or the like. For example, when heating and drying, the heating temperature is preferably 100 to 200 ° C, more preferably 120 to 180 ° C. The drying time is preferably 1 hour or more, more preferably 3 hours or more, and still more preferably 6 hours or more.

The melting temperature of the polyester crystal grains in the extruder is preferably 280 to 310 ° C, more preferably 290 to 300 ° C. By increasing the melting temperature, the back pressure during filtration in the extruder is lowered, and good productivity can be achieved. However, when the melting temperature is higher than 310 ° C, the resin is thermally deteriorated and the acid value of the resin is increased. The film has a low hydrolysis resistance.

Next, the polyester resin for forming each layer after melting in each extruder is laminated in a molten state, extruded from the same mold into a film shape, and formed by unwinding by using a chill roll. film.

The resulting unstretched film was stretched by biaxial alignment treatment. As the stretching method, there may be mentioned a sequential biaxial stretching method, a simultaneous biaxial stretching method, a blow stretching method, and the like, wherein the successive biaxial stretching method uses the heated roll or non-contact of the obtained unstretched film. After the heater is heated, the extension is carried out between the rolls having the speed difference (roll extension), and secondly, After the uniaxially stretched film ends are held by the jig and heated in the oven, the extension in the width direction (the tenter extension) is performed, and high heat is applied to perform heat fixation; the simultaneous biaxial stretching method is The extension is carried out by a tenter having a mechanism capable of simultaneously extending in the longitudinal direction and the lateral direction (the tenter is simultaneously biaxially extended); and the blow extension method is performed by an expansion of the air pressure. In the stretching step, in order to appropriately maintain the elongation at break of the obtained film, it is preferable to obtain the vertical and horizontal alignment balance by appropriately controlling the stretching ratio of the aspect ratio.

When a high degree of thermal dimensional stability is required, it is preferred to subject the film to longitudinal relaxation treatment. In the method of the longitudinal relaxation treatment, a well-known method, for example, a method in which the tenter jig is gradually narrowed and the longitudinal relaxation treatment is performed (Japanese Patent Publication No. 4-028218), and placed in the tenter A method in which the end portion of the film is cut into a razor and the longitudinal relaxation treatment is performed to avoid the influence of the jig (Japanese Patent Publication No. Sho 57-54290). Further, a method of relaxing by applying heat to the offline may be used. Moreover, in the above-described stretching step, it is possible to impart a high thermal dimensional stability to the film by appropriately controlling the stretching conditions.

Further, in order to impart various functions to the film, it is also possible to coat the surface of the film with a polymer resin by coating or the like, or to contain inorganic and/or organic particles in the coating layer. The coating method is not particularly limited. For example, when a coating layer for imparting adhesion or the like is formed, a coating layer may be provided after film formation (off-line coating method), or may be formed in a film formation (on-line coating method). Settings. In terms of productivity, it is preferably set in a film forming film.

<Characteristics of White Polyester Film for Solar Cells>

The thickness of the white polyester film for solar cells of the present invention is set to 30 to 380 μm. The thickness is preferably 35 μm or more, more preferably 40 μm or more, still more preferably 250 μm or less, and still more preferably 230 μm or less. When the thickness of the film is in the above range, electrical insulation is excellent, and weight reduction or thinning is facilitated. On the other hand, when the thickness of the film is more than 380 μm, it is not easy to reduce the weight or film. Moreover, when it is less than 30 micrometer, it is not easy to achieve an electrical insulation effect.

The white polyester film for solar cells of the present invention has a whiteness of 50 or more, preferably 60 or more. When the whiteness is less than 50, the shielding property is poor, and it is difficult to visually confirm the film system during processing of the solar cell module, and the processing efficiency may be lowered.

The white polyester film for solar cells of the present invention has an average reflectance of 50% or more, preferably 60% or more, in the range of wavelengths of 400 to 800 nm. Further, the higher the average reflectance is, the better, but in practice, the upper limit is about 95%. When the reflectance is less than 50%, it is not preferable because the film itself and the internal components of the solar cell are deteriorated due to light.

The heat shrinkage ratio of the white polyester film for a solar cell of the present invention at 150 ° C is preferably 0.2% or more in the longitudinal direction, preferably 0.4% or more, more preferably 3.0% or less, and 1.8% or less. good. Thereby, it is possible to suppress occurrence of warpage or the like at the time of heat processing or in a laminated state. On the other hand, when the heat shrinkage ratio is less than 0.2%, the film may be deflected during processing. Further, when it is more than 3.0%, the shrinkage during processing is large, and wrinkles in the shape of a washboard are generated. So that the heat shrinkage at 150 ° C is in the above range In the method, it can be carried out by controlling the stretching conditions or performing the longitudinal relaxation treatment and the transverse relaxation treatment in the heat fixation step.

The white polyester film for a solar cell of the present invention preferably has a vertical and horizontal alignment balance. In other words, when the film thickness is 50 μm, the MOR value (MOR-C) is preferably 1.0 or more, preferably 1.3 or more, more preferably 2.0 or less, and still more preferably 1.8 or less. Thereby, the alignment balance of the longitudinal and lateral directions of the film can be adjusted, and mechanical strength and durability can be easily maintained. Moreover, it is possible to suppress warpage during lamination and to improve adhesion. The method of making the MOR-C in the above range can be carried out by controlling the ratio of the stretching ratio in the aspect ratio of the stretching step.

The white polyester film for a solar cell of the present invention is capable of achieving high hydrolysis resistance which can be prevented from being used for a long period of time outside the house. Specifically, in terms of the evaluation index of hydrolysis resistance, the elongation at break retention of the film after the hydrolysis test (105 ° C, 100% RH, 0.03 MPa, and treatment for 200 hours) can be maintained at 60% or more. Good is 70% or more and 100% or less.

In the white polyester film for a solar cell of the present invention, it is possible to suppress photodecomposition and deterioration even under light irradiation, and it is possible to achieve excellent light resistance which can be prevented from being used for a long period of time outside the house. Specifically, in terms of the evaluation index of light resistance, the elongation at break retention rate of the film after the photodegradation test (63° C., 50% RH, UV irradiation intensity: 100 mW/cm ² , and 100 hours of irradiation) can be maintained. More than 35%, preferably more than 40%.

In the white polyester film for a solar cell of the present invention, the change in the COLOR b* value after the photodegradation test is preferably 12 or less. It is better to be 10 or less. When the change in the COLOR b* value is greater than 12, it is not preferable because the appearance changes over the years.

The white polyester film for a solar cell of the present invention can be further used as a solar cell back encapsulating sheet by laminating it, and the film surface is preferably smoothed. Specifically, the three-dimensional surface roughness (SRa) of the white polyester film for solar cells of the present invention is preferably 0.1 μm or less.

As described above, the white polyester film for solar cells of the present invention has environmental durability, whiteness, and light reflectivity, which are represented by light resistance and hydrolysis resistance, and achieves excellent electrical insulation properties. The durable layer (hydrolysis resistant layer), the white layer and the insulating layer are integrated. Therefore, by using the white polyester film for a solar cell of the present invention in a solar cell back surface encapsulating sheet, it is possible to reduce weight and film thickness.

<Solar battery back encapsulation sheet>

In the white polyester film for a solar cell of the present invention, a base film (base film) which is a bonding material of a solar cell back encapsulating sheet and a flexible electronic member can be used. In particular, it is suitable as a base film for a solar cell back encapsulant sheet requiring high environmental durability.

The solar cell back encapsulating sheet of the present invention protects the solar cell module on the back side of the solar cell by using the surface on the side in contact with the filler layer of the solar cell module and/or the outermost surface of the solar cell module. It is characterized by using the white polyester film for solar cells of the present invention.

The white polyester film for solar cells of the present invention can be used alone or in combination of two or more sheets as a solar cell back surface encapsulating sheet. also, In order to impart water vapor barrier properties, a white polyester film for a solar cell of the present invention may be provided with a water vapor barrier film such as a water vapor barrier film or an aluminum foil. The layered form of the water vapor barrier layer can be laminated through the subsequent layer or directly laminated to form a sandwich structure.

As the water vapor barrier film, a polyvinylidene fluoride coating film, a cerium oxide vapor deposition film, an alumina vapor deposition film, an aluminum vapor deposition film, or the like can be used.

<Solar battery module>

The solar battery module of the present invention is a system that stores incident light such as sunlight or indoor light and converts it into electricity and stores the electricity, and is characterized in that it includes the solar cell back surface encapsulating sheet and the adjacent solar cell rear side encapsulating sheet. a filler layer and a solar cell element embedded in the filler layer.

The resin to be used in the filler layer is not particularly limited, and an olefin resin such as EVA or PVB can be exemplified.

Further, the solar cell module of the present invention may contain a surface protective sheet, a high light transmitting material, or the like, and may be used in a flexible form depending on the application.

This application claims priority rights based on Japanese Patent Application No. 2011-223049, filed on Oct. 7, 2011. The entire contents of the specification of Japanese Patent Application No. 2011-223049, filed on Jan.

Example

The present invention is not limited by the examples and the comparative examples, and the invention is not limited thereto, and all modifications that are made without departing from the spirit and scope of the invention are included in the technical scope of the present invention. The measurement and evaluation methods used in the present invention are as follows.

<Average particle size of inorganic fine particles>

The inorganic fine particles were observed using a scanning electron microscope, and the magnification was appropriately changed according to the size of the particles, and photographs were taken. The photographed photographs are enlarged and copied, and at least 100 or more microparticles are randomly selected, the outer circumference of each particle is drawn, and the equivalent diameter of the particles is measured from the maps using a video analysis device, and the average value of the particles is set as an average. Particle size.

<Intrinsic viscosity (IV) of polyester>

The polyester was dissolved in a 6/4 (mass ratio) mixed solvent of phenol/1,1,2,2-tetrachloroethane, and the intrinsic viscosity was measured at a temperature of 30 °C. In the case of a masterbatch containing a fine particle and a film, the solid component is removed by centrifugation and then measured.

<Diethylene glycol (DEG) content>

After 0.1 g of the polyester was decomposed by heating at 250 ° C in 2 ml of methanol, it was quantified by gas chromatography.

<acid price>

The acid value of the film or the raw material polyester resin was measured by the following method.

(1) Modulation of sample

The film or the raw material polyester resin is pulverized and vacuum-dried at 70 ° C for 24 hours, and then weighed using a scale in a range of 0.20 ± 0.0005 g. And the quality at this time is set to W (g). 10 ml of benzyl alcohol and the weighed sample were added to the test tube, and the test tube was immersed in a benzyl alcohol bath heated to 205 ° C, and the sample was dissolved while stirring with a glass rod, and the dissolution time was set to 3 minutes, 5 minutes, and 7 minutes. The samples at the time were set as A, B, and C, respectively. Next, the test tube was re-prepared, and only benzyl alcohol was placed and treated according to the same procedure, and the samples having a dissolution time of 3 minutes, 5 minutes, and 7 minutes were set as a, b, and c, respectively.

(2) titration

The titration was carried out using a potassium hydroxide solution (ethanol solution) of 0.04 mol/L which was previously known to have a factor (NF). When the phenol red of the indicator is changed from yellow-green to light red, the end point is set to determine the titer of the potassium hydroxide solution. The titration amounts of the samples A, B, and C were set to XA, XB, and XC (ml), and the titration amounts of the samples a, b, and c were set to Xa, Xb, and Xc (ml).

(3) Calculation of acid value

The titration amount V (ml) at a dissolution time of 0 minutes was determined by the least square method from the titrations XA, XB, and XC with respect to each dissolution time. Similarly, a titration V0 (ml) at a dissolution time of 0 minutes was obtained from Xa, Xb, and Xc. Next, the acid value (eq/ton) is obtained according to the following formula.

Acid value (eq/ton) = [(V-V0) × 0.04 × NF × 1000] / W

<Appearance density of film>

The apparent density of the film was measured in accordance with JIS K 7222 "Foaming Plastics and Rubber - Determination of Appearance Density". However, in order to make the mark simple, the unit is converted into g/cm ³ .

<Whiteness of film>

The whiteness of the film was carried out in accordance with JIS L 1015-1981-B and using Z-1001DP manufactured by Nippon Denshoku Industries Co., Ltd.

<Average reflectance of film>

The integrating sphere was attached to a spectrophotometer (manufactured by Shimadzu Corporation, self-recording spectrophotometer "UV-3150"), and the reflectance of a standard white plate (manufactured by SphereOptics Co., Ltd., white standard plate "ZRS-99-010-W") was set. The calibration was performed at 100% and the spectral reflectance was measured. The measurement was performed at a wavelength of 400 to 800 nm at a pitch of 1 nm and an average value was obtained. Further, in the case of a film single film, the black paper having no reflection was placed on the back surface of the sample film and measured. The light was measured by irradiating light from the side of the layer containing the inorganic fine particles.

<Light reflection variation rate of film>

For the obtained film roll, the roll was started to be rolled up to 0%, and when the roll up was set to 100%, 1 m × 1.8 m was cut out from the center of the 10%, 50%, and 90% length positions. Film sheet. Five 20 cm square film samples were sampled from the four corners and the center of the respective film sheets, and the respective average reflectances were measured by the above-mentioned "average reflectance of the film". The average value of the average reflectance of each film sample was set as a center value, and the value obtained by dividing the difference between the maximum value and the minimum value of the average reflectance by the center value was set as the light reflection variation rate.

<Promotes photodegradation test>

Using an EYE SUPER UV tester (manufactured by Iwasaki Electric Co., Ltd., SUV-W151), the inorganic fine particles of the film were concentrated on the layer side, and were subjected to continuous irradiation with UV treatment at 63 ° C and 50% RH for 100 hours at an irradiation intensity of 100 mW/cm ² .

<Promoted hydrolysis test>

The normalized HAST (Highly Accelerated Temperature and Humidity Stress Test) was carried out in accordance with JIS C 60068-2-66. The sample film was cut into 70 mm × 190 mm, and was set using a jig and keeping the distances that were not in contact with each other. The treatment was carried out for 200 hours at 105 ° C, 100% RH, and 0.03 MPa using EHS-221 manufactured by ESPEC.

<Elongation at break elongation>

The evaluation of light resistance and hydrolysis resistance was carried out by the elongation at break retention. According to JIS C 2318-1997, 5.3.31 (tensile strength and elongation), the elongation at break before and after the respective processes for promoting the photodegradation test and the accelerated hydrolysis test were measured, and the elongation at break retention ratio (%) was calculated according to the following formula.

Elongation at break (%) = [(elongation at break after treatment) × 100] / (elongation at break before treatment)

The elongation retention ratio after the photodegradation test was promoted was evaluated as × when it was less than 35%, ○ was evaluated as 35% or more and less than 60%, and ◎ was evaluated as 60% or more.

The elongation retention rate after the hydrolysis test was promoted was evaluated as × when less than 60%, 60% or less, and ○, and 80% or more was evaluated as ◎.

<COLOR b* value change>

The sample film was cut into 40 mm × 40 mm, using a standard white plate of X = 94.19, Y = 92.22, Z = 10.05.58, by COLOR b* value color difference meter (manufactured by Nippon Denshoku Co., Ltd., ZE-2000) and in accordance with JIS K 7105-1981 5.3.5 (a) The COLOR b* value of the sample film before and after the photodegradation test was measured. The change in the COLOR b* value is obtained according to the following formula.

Change in COLOR b* value = (COLOR b* value after promoting photodegradation test) - (COLOR b* value before photodegradation test is promoted)

For the change in the COLOR b* value, those higher than 12 were evaluated as ×, 5 to 12 were evaluated as ○, and those less than 5 were evaluated as ◎.

<Heat shrinkage ratio (HS150) at a length of 150 ° C>

The sample film was cut into 10 mm × 250 mm, and the long side was aligned with the direction to be measured, and the mark was drawn at intervals of 200 mm, and the interval A of the mark was measured under a constant tension of 5 g. Next, the sample film was allowed to stand in an oven without load and at 150 ° C for 30 minutes, and then taken out from the oven and cooled to room temperature. Subsequently, under a certain tension of 5 g, the interval B of the marks was obtained and the heat shrinkage ratio (%) was determined according to the following formula. Further, the heat shrinkage rate is measured in the width direction of the sample film at a position of three equal parts, and the average value of the three points is rounded off to the third digit after the decimal point, and the decimal point is adjusted. Use 2 digits.

Heat shrinkage rate (%) = [(A-B) × 100] / A

<MOR-C>

The obtained film was divided into five equal parts in the width direction, and a square sample of 100 mm was taken in the longitudinal direction and the width direction at each position, and the measurement was performed using a microwave transmission type molecular alignment meter (manufactured by Oji Scientific Instruments Co., Ltd., MOA-6004). The thickness correction was set to 50 μm, and MOR-C was obtained and an average value of 5 points was used.

<surface strength>

A sample film of 5 cm × 20 cm was cut out, and the double-sided adhesive tape A was used to completely follow the flat glass in such a manner that the inorganic fine particle-concentrated layer side was outside. On the surface of the sample film, an adhesive tape B (CELLO-TAPE (registered trademark) manufactured by NICHIBAN Co., Ltd.) having a width of 24 mm was adhered to a range of 35 mm in length and allowed to stand for 1 minute. Subsequently, the adhesive tape B was peeled off in a direction perpendicular to the glass surface to observe the surface on the side of the layer containing the inorganic fine particles.

50% or more of the area of the peeling portion of the adhesive tape B, and the peeling of the surface of the sample film was evaluated as "peeling", and the case where the frequency of the peeling was repeated five times or more and the frequency of "peeling" was less than half was evaluated as "○" (excellent surface strength) ), more than half of the cases are rated as "X" (surface strength is deteriorated).

<adhesion>

The film obtained in Example 13 was cut into 100 mm × 100 mm, and the EVA film described below was cut into 70 mm × 90 mm, and the film/EVA film/film (in any film, the coating layer was opposed to the EVA film). The configuration of the setting was superposed, and the sample was produced by heating and pressing under the following conditions. The prepared sample was cut into 20 mm × 100 mm, and then adhered to a SUS plate, and the peel strength of the film layer and the EVA film layer was measured using a tensile tester under the following conditions. After the peeling strength is set to exceed the maximum point, the average value of the portion to be peeled off is determined stably. The grades are classified according to the following criteria.

◎: 100N/20mm or more, or the material of the film is broken.

○: 75N/20mm or more and less than 100N/20mm

△: 50N/20mm or more and less than 75N/20mm

×: less than 50N/20mm

(Production conditions of the sample)

Device: Vacuum laminating machine (made by NPC, LM-30×30 type)

Pressurization: 1 air pressure

EVA film:

A. Standard ripening type

I.SANVIC company, Urtla Pearl (registered trademark) PV (0.4μm)

Lamination step: 100 ° C (vacuum for 5 minutes, vacuum press for 5 minutes)

Curing step: heat treatment at 150 ° C (normal pressure for 45 minutes)

II. manufactured by Mitsui FABRO Co., Ltd., SOLAR EVA (registered trademark) SC4 (0.4μm)

Lamination step: 130 ° C (vacuum for 5 minutes, vacuum press for 5 minutes)

Curing step: heat treatment at 150 ° C (normal pressure for 45 minutes)

B. Rapid ripening type

I. SANVIC Corporation Urtla Pearl (registered trademark) PV (0.45 μm)

Lamination step: 135 ° C (vacuum for 5 minutes, vacuum for 15 minutes)

II. SOLAR EVA (registered trademark) RC02B (0.45μm) manufactured by Mitsui FABRO Co., Ltd.

Lamination step: 150 ° C (vacuum for 5 minutes, vacuum press for 15 minutes)

<Manufacture of Polyester Resin Particles> (1) Manufacture of PET resin pellet I (PET-I)

The temperature of the esterification reactor was raised, and when it reached 200 ° C, a slurry composed of 86.4 parts by mass of citric acid and 64.4 parts by mass of ethylene glycol was added, and 0.017 parts by mass of antimony trioxide as a catalyst was added while stirring. 0.16 parts by mass of triethylamine. Next, the pressure was raised, and the pressure esterification reaction was carried out under the conditions of a pressure of 3.5 kgf/cm ² (343 kPa) and 240 ° C. Subsequently, the inside of the esterification reaction tank was returned to normal pressure, and 0.071 parts by mass of magnesium acetate tetrahydrate was added, followed by 0.014 parts by mass of trimethyl phosphate. Further, the temperature was raised to 260 ° C in 15 minutes, and 0.012 parts by mass of trimethyl phosphate was added, followed by 0.0036 parts by mass of sodium acetate. After 15 minutes, the obtained esterification reaction product was transferred to a polycondensation reaction tank, and the temperature was gradually raised from 260 ° C to 280 ° C under reduced pressure, and a polycondensation reaction was carried out at 285 ° C.

After completion of the polycondensation reaction, it was subjected to filtration treatment using a filter of NASLON (registered trademark) having a cut diameter of 5 μm of 95%, and was extruded from a nozzle into a strand shape, and was cooled by a predetermined filtration treatment (pore diameter: 1 μm or less). The water is allowed to cool, solidify and cut into pellets. The obtained PET resin pellet (PET-I) had an intrinsic viscosity of 0.616 dl/g, an acid value of 15.1 eq/ton, and substantially no inert particles and internal precipitated particles.

(2) Manufacture of PET Resin II (PET-II)

After pre-crystallizing PET resin pellet I (PET-I) at 160 ° C, solid phase polymerization was carried out in a nitrogen atmosphere at a temperature of 220 ° C to obtain a PET resin pellet having an intrinsic viscosity of 0.71 dl / g and an acid value of 11 eq / ton. II (PET-II).

(3) Manufacture of PET resin pellet III (PET-III)

A PET resin pellet III (PET-III) having an intrinsic viscosity of 0.51 dl/g and an acid value of 39 eq/ton was obtained by the same method as the PET resin pellet I (PET-I) except that the time of the polycondensation reaction was changed.

(4) Manufacture of PET resin particle IV (PET-IV) (Modulation of polycondensation catalyst solution) I) Preparation of phosphorus compound in ethylene glycol solution

After adding 2.0 liters of ethylene glycol to a flask equipped with a nitrogen inlet tube and a cooling tube, 200 g of Irganox (registered trademark) 1222 (CIBA SPECIALTY) as a phosphorus compound was added while stirring at 200 rpm under a nitrogen atmosphere. CHEMICALS (now BASF)). In addition, after adding 2.0 liters of ethylene glycol, the temperature of the jacket was changed to 196 ° C and the temperature was raised. When the internal temperature was 185 ° C or higher, the mixture was stirred under reflux for 60 minutes. Subsequently, the heating was stopped and the solution was immediately taken away from the heat source, kept under a nitrogen atmosphere, and cooled to below 120 ° C within 30 minutes. The molar fraction of Irganox1222 in the obtained solution was 40%, and the molar fraction of the compound changed from the structure of Irganox1222 was 60%.

II) Modification of aluminum compound in ethylene glycol solution

In a flask equipped with a cooling tube, 5.0 liters of pure water was added under normal temperature and normal pressure, and then 200 g of basic aluminum acetate was added as a slurry with pure water while stirring at 200 rpm. Further, pure water was added so as to have a total of 10.0 liters, and the mixture was stirred at normal temperature and normal pressure for 12 hours. Subsequently, the temperature of the jacket was changed to 100.5 ° C to raise the temperature, and the mixture was stirred under reflux for 3 hours from the time when the internal temperature became 95 ° C or higher. Stirring was stopped and allowed to cool to room temperature to obtain an aqueous solution of an aluminum compound.

After adding an equal volume of ethylene glycol to the obtained aqueous solution of the aluminum compound and stirring at room temperature for 30 minutes, the internal temperature was controlled at 80 to 90 ° C and the pressure was gradually reduced to 27 hPa. The water was distilled off from the system in an hour to obtain an ethylene glycol solution of 20 g/l of the aluminum compound. The peak integrated value ratio of the ²⁷ Al-NMR spectrum of the obtained aluminum solution was 2.2.

(esterification reaction and polycondensation)

It is composed of three continuous esterification reaction tanks and three polycondensation reaction tanks, and a continuous line mixer with a high-speed stirrer is provided in the transfer line from the third esterification reaction tank to the first polycondensation reaction tank. In the polyester production apparatus, 0.75 parts by mass of 0.75 parts by mass of ethylene glycol is continuously supplied to the slurry preparation tank with respect to 1 part by mass of high purity paraxamic acid. The first esterification reaction tank was set to 250 ° C and 110 kPa, the second esterification reaction tank was set to 260 ° C and 105 kPa, and the third esterification reaction tank was set to 260 ° C and 105 kPa, and the prepared slurry was prepared. The material was continuously supplied to obtain a polyester oligomer. Further, 0.025 parts by mass of ethylene glycol was continuously supplied to the second esterification reaction tank. The obtained oligomer is continuously transferred to a continuous polycondensation device composed of three reaction tanks, and an ethylene glycol solution and a phosphorus compound of the aluminum compound prepared by the above method are used in a mixer disposed on the line of the transfer line. The ethylene glycol solution is continuously added while stirring with a continuous mixer in an amount of 0.015 mol% and 0.036 mol% based on the acid component of the respective polyesters in terms of aluminum atoms and phosphorus atoms. The polycondensation reaction tank was set to 265 ° C and 9 kPa, the medium-term polycondensation reaction tank was set to 265 to 268 ° C and 0.7 kPa, and the final polycondensation reaction tank was set to 273 ° C and 13.3 Pa. A PET resin particle IV (PET-IV) having an intrinsic viscosity of 0.63 dl/g and an acid value of 10.5 eq/ton was obtained.

(5) Manufacture of PET resin pellet V (PET-V)

The obtained PET resin particle IV (PET-IV) was subjected to solid phase polymerization at 220 ° C under a reduced pressure of 0.5 mmHg using a rotary vacuum polymerization apparatus to obtain an intrinsic viscosity of 0.73 dl/g and an acid value of 5.0. PET resin pellet V (PET-V) of eq/ton.

<Manufacture of masterbatch containing microparticles> (6) Manufacture of masterbatch I (MB-I)

In the case of the raw material, 50% by mass of PET resin particles I (PET-I) after drying at 120 ° C, 10 ^-3 torr (about 0.133 Pa) for about 8 hours, mixed with 50% by mass average particle diameter 0.3 μm The rutile-type titanium dioxide (the value obtained by the electron microscopy method) is supplied to a vented twin-screw extruder, and kneaded and degassed, and extruded at 275 ° C to obtain rutile. Master batch particle I (MB-I) of the type titanium dioxide fine particles having an intrinsic viscosity of 0.45 dl/g and an acid value of 42.2 eq/ton.

(7) Manufacture of masterbatch II (MB-II)

Using a masterbatch I (MB-I) and solid phase polymerization at 220 ° C under a reduced pressure of 0.5 mmHg using a master batch I (MB-I), an intrinsic viscosity of 0.71 dl/g and an acid value of 23.5 eq/ton were obtained. Masterbatch II (MB-II).

(8) Manufacture of masterbatch III (MB-III)

A masterbatch containing rutile-type titanium dioxide fine particles was obtained by the same method as the master batch I (MB-I) except that PET resin particles IV (PET-IV) was used instead of PET resin particles I (PET-I). III (MB-III). The particles had an intrinsic viscosity of 0.46 dl/g and an acid value of 36.3 eq/ton.

(9) Manufacture of masterbatch IV (MB-IV)

Using a masterbatch III (MB-III) and solid phase polymerization at 220 ° C under a reduced pressure of 0.5 mmHg using a master batch III (MB-III), an intrinsic viscosity of 0.70 dl/g and an acid value of 19.4 eq/ton were obtained. Masterbatch granule IV (MB-IV) containing rutile-type titanium dioxide fine particles.

<Preparation of coating liquid>

43.75 parts by mass of 4,4-diphenylmethane diisocyanate, 12.85 parts by mass of dimethylolbutanoic acid, 154.31 parts by mass of polyhexamethylene carbonate diol having a number average molecular weight of 2000, and 0.03 parts by mass of dilauric acid Butyltin and 84.00 parts by mass of acetone as a solvent were stirred at 75 ° C for 3 hours under a nitrogen atmosphere, and after the reaction liquid was cooled to 40 ° C, 8.77 parts by mass of triethylamine was added to obtain a polyurethane pre-preparation. Polymer solution. Water dispersion was carried out by adding 450 parts by mass of water to the polyurethane prepolymer solution, and adjusting to 25 ° C and stirring and mixing at 2000 min ^-1 . Subsequently, a solution of 35% of the water-soluble polyurethane resin having a solid content was prepared by removing a part of acetone and water under reduced pressure. The glass transition temperature of the obtained polyurethane resin was -30 °C.

Next, a polyurethane resin solution obtained by the above-mentioned 55.86% by mass of water, 30.00% by mass of isopropyl alcohol, and 13.52% by mass, and 0.59% by mass of particles (cerium oxide sol having an average particle diameter of 40 nm, solid content concentration) 40% by mass) and 0.03 mass% of a surfactant (polyoxymethylene system, solid content concentration: 100% by mass) were mixed to prepare a coating liquid.

<Manufacture of white polyester film for solar cells> Example 1

The fine particles of 60% by mass of PET-II and 40% by mass of MB-II are mixed and the raw material of the layer (layer A) is concentrated, and the other layer (layer B) of 86% by mass of PET-II and 14% by mass of MB-II is mixed. The raw materials were each placed in separate extruders, mixed and melted at 285 ° C, and then joined in a molten state by using a feed block to form an A layer/B layer. At this point, layer A The discharge ratio to the B layer is controlled using a gear pump. Subsequently, an unstretched film was produced by extruding onto a cooling drum adjusted to 30 ° C using a T-die.

The obtained unstretched film was uniformly heated to 75 ° C using a heating roll, and heated to 100 ° C using a non-contact heater to carry out a 3.3-fold roll extension (longitudinal extension). The obtained uniaxially stretched film was guided to a tenter, heated to 140 ° C, and stretched 4.0 times in the transverse direction, fixed at a width of 215 ° C for 5 seconds, and further relaxed at a width of 4% at 210 ° C. A white polyester film roll for a solar cell having a thickness of 80 μm.

Example 2

A white polyester film roll for a solar cell was obtained in the same manner as in Example 1 except that the raw material compositions of the A layer and the B layer were changed as shown in Table 1.

Example 3

A white polyester film roll for a solar cell was obtained in the same manner as in Example 1 except that the raw material compositions of the A layer and the B layer were changed as shown in Table 1.

Example 4

A white polyester film roll for a solar cell was obtained in the same manner as in Example 1 except that the raw material compositions of the A layer and the B layer were changed as shown in Table 1.

Example 5

A white polyester film roll for a solar cell was obtained in the same manner as in Example 4 except that the discharge amount and the speed were changed so that the film roll thickness was 50 μm.

Example 6

A white polyester film roll for a solar cell was obtained in the same manner as in Example 5 except that the raw material compositions of the A layer and the B layer were changed as shown in Table 1.

Example 7

A white polyester film roll for a solar cell was obtained in the same manner as in Example 5 except that the raw material compositions of the A layer and the B layer were changed as shown in Table 1.

Example 8

A white polyester film roll for a solar cell was obtained in the same manner as in Example 5 except that the longitudinal stretching ratio was 3.1 times and the discharge amount and speed were changed so that the thickness of the film roll was 188 μm.

Example 9

A white polyester for solar cells was obtained in the same manner as in Example 5 except that the longitudinal stretching ratio was 3.0 times and the lateral stretching ratio was 3.7 times, and the discharge amount and speed were changed so that the thickness of the film roll was 350 μm. Film roll.

Example 10

A white polyester film roll for a solar cell was obtained in the same manner as in Example 5 except that the raw material compositions of the A layer and the B layer were changed as shown in Table 1.

Example 11

The film roll obtained in Example 1 was subjected to a relaxation treatment by an off-line coater set at a temperature of 160 ° C, and the speed and tension were adjusted to obtain a white polyester film roll for a solar cell.

Example 12

A white polyester film roll for a solar cell was obtained in the same manner as in Example 1 except that the feed block was changed to have the A layer/B layer/A layer.

Example 13

The coating amount of the above-prepared coating liquid after drying (after biaxial stretching) was 0.15 g/m ² by a roll coating method except for the B layer side of the uniaxially stretched film which was extended in the longitudinal direction. After the application, the film was dried at 80 ° C for 20 seconds, and a white polyester film roll for a solar cell was obtained in the same manner as in Example 1.

The physical properties of the film roll obtained in Examples 1 to 13 are shown in Table 2.

Comparative example 1, 2

A white polyester film roll for a solar cell was obtained in the same manner as in Example 1 except that the composition of the A layer and the B layer was changed as shown in Table 3.

Comparative example 3~5

A white polyester film roll for a solar cell was obtained in the same manner as in Example 1 except that the composition of the A layer and the B layer was changed as shown in Table 3, and the discharge amount and the speed were changed so that the film roll thickness was 50 μm. .

The physical properties of the film roll obtained in Comparative Examples 1 to 5 are shown in Table 4.

Industrial use possibility

The white polyester film for solar cells of the present invention has good whiteness and light reflectivity, and is excellent in environmental durability and achieves good electrical insulation. By using the white polyester film for a solar cell of the present invention, it is possible to provide a solar cell backside encapsulating sheet and a solar cell module which are excellent in environmental durability, inexpensive, and lightweight.

Claims (9)

A white polyester film for solar cells, having a whiteness of 50 or more, an average reflectance of 50 to 95% in a wavelength range of 400 to 800 nm, an acid value of 1 to 50 eq/ton, and a solar energy having a thickness of 30 to 380 μm. A polyester film for a battery, which has a multilayer structure in which inorganic fine particles containing 10 to 35% by mass of inorganic fine particles are contained in a concentrated layer containing at least one outermost layer, and are integrated with the polyester film as a whole. The thickness of the inorganic fine particle-concentrated layer is 5 to 30%, and the content of the inorganic fine particles in the entire polyester film is 2 to 10% by mass. A white polyester film for a solar cell according to the first aspect of the invention, wherein the inorganic fine particles are titanium dioxide having a rutile type as a main component. A white polyester film for a solar cell according to claim 1 or 2, wherein a heat shrinkage ratio at a temperature of 150 ° C in the longitudinal direction is 0.2 to 3.0%. The white polyester film for solar cells according to claim 1 or 2, wherein the elongation at break after the hydrolysis test is promoted at 105 ° C, 100% RH, 0.03 MPa, and treated for 200 hours. 100%. A white polyester film for a solar cell according to claim 1 or 2, wherein the photo-degradation test is accelerated under conditions of 63 ° C, 50% RH, ultraviolet light irradiation intensity of 100 mW/cm ² , and irradiation for 100 hours. The elongation retention rate is 35% or more. The white polyester film for solar cells according to claim 1 or 2, wherein the COLOR after the photodegradation test is promoted under the conditions of 63 ° C, 50% RH, ultraviolet light irradiation intensity of 100 mW/cm ² , and irradiation for 100 hours. The change in the b* value is 12 or less. The white polyester film for solar cells according to claim 1 or 2, wherein a coating layer containing a polyurethane resin is disposed on a surface of at least one side of the polyester film, wherein the polyaminocarboxylic acid The ester resin is composed of an aliphatic polycarbonate polyol as a constituent component. A solar cell back encapsulating sheet characterized by using a white polyester film for a solar cell according to any one of claims 1 to 7. A solar cell module comprising a solar cell back encapsulating sheet according to claim 8 of the patent application, a filler layer adjacent to a solar cell back encapsulating sheet, and a solar cell element embedded in the filler layer.