JP5288068B1 - White polyester film for solar cell, solar cell back surface sealing sheet and solar cell module using the same - Google Patents

Abstract

  An object of the present invention is to provide a white polyester film for solar cells excellent in environmental durability represented by light resistance and hydrolysis resistance while having good light reflectivity, and a solar cell backside sealing sheet using the same And providing a solar cell module. The white polyester film for a solar cell of the present invention that has achieved the above object has a whiteness of 50 or more, an average reflectance of 50 to 95% in a wavelength range of 400 to 800 nm, and an acid value of 1 to 50 eq / ton. , A polyester film for solar cells having a thickness of 30 to 380 μm, and has a multilayer structure in which an inorganic fine particle concentration containing layer containing 10 to 35% by mass of inorganic fine particles is disposed as at least one outermost layer, The thickness of the inorganic fine particle concentration content layer is 5-30% with respect to the thickness of the whole polyester film, and the content of inorganic fine particles in the whole polyester film is 2-10% by mass.

Description

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

  In recent years, solar cells have attracted attention as a next-generation clean energy source. A constituent member such as a back surface sealing sheet for sealing the back surface is used for the solar cell module, and a base film is used for these constituent members. Since solar cells are used outdoors for a long period of time, durability to the natural environment is required for these components and the base films used for these components.

  As a base film for a solar cell backside sealing sheet, a fluorine-based film, a polyethylene-based film, or a polyester-based film to which a white pigment or the like is added has been used for the purpose of improving UV resistance, concealment, and the like ( Patent Documents 1 to 9).

JP-A-11-261085 JP 2000-114565 A JP 2004-247390 A JP 2002-134771 A JP 2006-270025 A JP 2007-184402 A JP 2007-208179 A JP 2008-85270 A WO 2007-105306

  As described in Patent Documents 1 to 9, by using a white base film as a constituent member of the solar cell back surface sealing sheet, it was possible to reflect sunlight and increase power generation efficiency. However, it is necessary to add a large amount of white pigment particles to these white base films, and in order to improve the dispersibility and mixing state of the particles added in a large amount, a process of preparing a raw material in which particles and a resin are premixed In addition, techniques such as increasing the melting time even in the normal extrusion process are adopted, and as a result of adding such a large number of thermal histories, the resin tends to deteriorate, and the obtained base film is attached to the back surface of the solar cell. When used for a sealing sheet, there is a problem that durability is poor under high temperature and high humidity.

  In view of the above problems, an object of the present invention is a white polyester film for solar cells, which has high whiteness and good light reflectivity, and is excellent in environmental durability represented by light resistance and hydrolysis resistance. It is providing the solar cell backside sealing sheet and solar cell module which used this.

  The white polyester film for solar cells according to the present invention that has solved 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, and an acid value of 1 to 50 eq / ton, which is a polyester film for solar cells having a thickness of 30 to 380 μm, and has a multilayer structure in which an inorganic fine particle concentration containing layer containing 10 to 35% by mass of inorganic fine particles is disposed as at least one outermost layer. The thickness of the inorganic fine particle concentration layer is 5 to 30% with respect to the thickness of the whole polyester film, and the content of inorganic fine particles in the whole polyester film is 2 to 10% by mass.

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

  The white polyester film for solar cell of the present invention preferably has a thermal shrinkage rate at 150 ° C. in the longitudinal direction of 0.2 to 3.0%. It is preferable that the breaking elongation retention after the accelerated hydrolysis test is 60 to 100% under the conditions of 105 ° C., 100% RH, 0.03 MPa, and 200 hours treatment.

The white polyester film for solar cells of the present invention has a breaking elongation retention ratio of 35% or more after the accelerated light deterioration test under the conditions of 63 ° C., 50% RH, UV irradiation intensity of 100 mW / cm ² , and irradiation for 100 hours. Is preferred. The change in the color b * value after the accelerated light deterioration test is preferably 12 or less.

  In the white polyester film for a solar cell of the present invention, a coating layer containing a polyurethane resin containing an aliphatic polycarbonate polyol as a constituent component may be disposed on at least one surface of the polyester film.

  In addition, this invention embeds in the solar cell backside sealing sheet using the said white polyester film for solar cells, and the filler layer adjacent to a solar cell backside sealing sheet and a solar cell backside sealing sheet, and a filler layer. A solar cell module including the solar cell element thus formed is also included.

  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 backside sealing sheet and a solar cell module having excellent light reflectivity and excellent environmental durability. It has become possible.

  The white polyester film for solar cells according to 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 thickness of 30 to 380 μm. A polyester film for solar cells, having a multilayer structure in which an inorganic fine particle concentration-containing layer containing 10 to 35% by mass of inorganic fine particles is disposed as at least one outermost layer, and the thickness of the inorganic fine particle concentration content layer Is 5 to 30% with respect to the thickness of the entire polyester film, and the content of 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 is an aromatic dicarboxylic acid or ester thereof such as terephthalic acid, isophthalic acid or naphthalenedicarboxylic acid, ethylene glycol, butylene glycol, diethylene glycol, 1,4- It is produced by polycondensation with glycols such as butanediol and neopentyl glycol, and may be a homopolymer or a copolymer obtained by copolymerizing a third component.

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

  When the third component is copolymerized, the molar ratio of ethylene terephthalate unit, butylene terephthalate unit or ethylene-2,6-naphthalate unit is preferably 70 mol% or more, more preferably 80 mol% or more, and 90 mol% or more. Further preferred.

  In addition to the method of directly polycondensing aromatic dicarboxylic acid and glycol, the above polyester resin is a method of polycondensation after transesterification of alkyl ester of aromatic dicarboxylic acid and glycol, diglycol of aromatic dicarboxylic acid It can be produced by a method in which an ester is polycondensed.

  Examples of the polycondensation catalyst include antimony compounds, titanium compounds, germanium compounds, tin compounds, aluminum and / or aluminum compounds, phosphorus compounds having an aromatic ring in the molecule, and aluminum salts of phosphorus compounds.

  After the polycondensation reaction, the thermal stability of the polyester resin can be further improved by removing the catalyst from the polyester resin or deactivating the catalyst by adding a phosphorus compound or the like. Further, an appropriate amount of the polycondensation catalyst may coexist within a range in which no problem occurs in the characteristics, processability, and color tone of the polyester resin.

  When the polyester resin is produced, dialkylene glycol is by-produced during the esterification reaction of terephthalic acid or the ester exchange reaction of dimethyl terephthalate. When a large amount of dialkylene glycol is contained in the polyester resin, the resulting film may have reduced heat resistance when exposed to a high temperature environment. Therefore, the content of dialkylene glycol in the polyester resin used in the present invention is preferably suppressed within a certain range.

  Specifically, taking diethylene glycol as an example of a representative dialkylene glycol, the content of diethylene glycol in the polyester resin is preferably 2.3 mol% or less, more preferably 2.0 mol% or less, and 1.8 mol%. The following is more preferable. When the content of diethylene glycol is 2.3 mol% or less, the thermal stability can be increased, and an increase in acid value due to decomposition during drying and molding can be suppressed. In addition, although it is better that there is little diethylene glycol, since it is by-produced when manufacturing a polyester resin, the lower limit of the content is realistically 1.0 mol%, Furthermore, 1.2 mol%.

  In the present invention, in order to impart durability to the polyester film, the intrinsic viscosity of the polyester resin used is preferably 0.65 dl / g or more, more preferably 0.67 dl / g or more, preferably 0.90 dl / g or less, 0 .75 dl / g or less is more preferable. By making the intrinsic viscosity of the polyester resin within the above range, good productivity can be obtained, and the hydrolysis resistance and heat resistance of the formed film can be enhanced. On the other hand, when the intrinsic viscosity is lower than 0.65 dl / g, the formed film may have poor hydrolysis resistance and heat resistance. On the other hand, if it is higher than 0.90 dl / g, the productivity may decrease. In order to adjust the intrinsic viscosity of the polyester resin within the above range, it is desirable to perform solid phase polymerization after polymerization.

  The carboxyl terminal of the polyester resin represented by the acid value has an action of promoting hydrolysis by autocatalysis. In order to obtain high hydrolysis resistance as a member for solar cell, it is important that the acid value of the white polyester film for solar cell of the present invention is in the range of 1 to 50 eq / ton relative to the polyester. The acid value is preferably 2 eq / ton or more, more preferably 3 eq / ton or more, preferably 40 eq / ton or less, more preferably 30 eq / ton or less with respect to the polyester. When an acid value is larger than 50 eq / ton, the hydrolysis resistance of a film falls and early deterioration tends to occur.

  In order to make the acid value of a film into the said range, it is preferable to suppress the acid value of the polyester resin used as raw material resin to a fixed range. Specifically, the acid value of the polyester resin is preferably less than 50 eq / ton, more preferably 25 eq / ton or less, and further preferably 20 eq / ton or less. Moreover, although the one where the acid value of a film is small is preferable, 0.5 eq / ton is a minimum from the point of productivity. The acid value of the polyester resin or film can be measured by a titration method described later.

  In order to control the acid value of the polyester resin within the above range, the polymerization conditions of the resin, specifically, the production equipment factors such as the structure of the esterification reactor, and the dicarboxylic acid and glycol of the slurry supplied to the esterification reactor What is necessary is just to set suitably esterification reaction conditions, such as composition ratio, esterification reaction temperature, reaction pressure, and reaction time, or solid layer polymerization conditions. It is also effective to control the moisture content of the polyester chip supplied to the extruder or to control the resin temperature in the melting step. Furthermore, it is also a preferable method to block the carboxyl terminal with an epoxy compound or a carbodiimide compound.

  For example, when supplying polyester chips to an extruder, it is preferable to use sufficiently dried polyester chips in order to suppress an increase in acid value. Specifically, the moisture content of the polyester chip is preferably 100 ppm or less, more preferably 50 ppm or less, and even more preferably 30 ppm or less.

  As a method for drying the polyester chip, a known method such as vacuum drying or heat drying can be used. For example, in the case of heat drying, the heating temperature is preferably 100 to 200 ° C, more preferably 120 to 180 ° C. The drying time is preferably 1 hour or longer, more preferably 3 hours or longer, and even more preferably 6 hours or longer.

  In order to suppress the acid value of the polyester resin, it is also effective to control the resin temperature in the melting step within a certain range. Specifically, the melting temperature is preferably 280 to 310 ° C, and more preferably 290 to 300 ° C. By increasing the melting temperature, the back pressure during filtration in the extruder can be reduced, and good productivity can be achieved. However, when the melting temperature is higher than 310 ° C., thermal degradation of the resin proceeds, Since an acid value rises, the hydrolysis resistance of the obtained film may fall.

  The polyester resin contains one or many kinds of various additives such as a fluorescent brightening agent, an ultraviolet ray inhibitor, an infrared absorbing dye, a heat stabilizer, a surfactant, and an antioxidant depending on the purpose of use. It can also be made.

  Antioxidants such as aromatic amines and phenols can be used as antioxidants, and thermal stabilizers such as phosphoric acid and phosphoric acid esters such as phosphorous, sulfur esters, and amines can be used. The agent can be used.

<Inorganic fine particles>
The inorganic fine particles used for the white polyester film for solar cells of the present invention are not particularly limited, and are titanium dioxide, barium sulfate, silica, kaolinite, talc, calcium carbonate, zeolite, alumina, carbon black, oxidation. Examples thereof include zinc and zinc sulfide. From the viewpoint of improving whiteness and productivity, titanium dioxide or barium sulfate which is a white pigment is preferable, and titanium dioxide is more preferable.

  The average particle size of the inorganic fine particles is preferably 0.1 μm or more, more preferably 0.5 μm or more, preferably 3 μm or less, and more preferably 2.5 μm or less. By setting the average particle size of the inorganic fine particles within the above range, the whiteness of the film due to the light scattering effect can be increased and film formation can be suitably performed. On the other hand, when the average particle size is less than 0.1 μm, the whiteness necessary for the film may not be obtained due to insufficient light scattering effect. On the other hand, when the average particle size is more than 3 μm, the film is easily broken during film formation, and there is a possibility that film formation cannot be performed well.

  In the present invention, the average particle size of the inorganic fine particles can be determined by the following electron microscope method. Specifically, the inorganic fine particles are observed with a scanning electron microscope, the magnification is appropriately changed according to the size of the particles, a photograph is taken, and the photographed photograph is enlarged and at least 100 or more randomly selected. The outer circumference of each particle is traced, and the equivalent circle diameter of the particle is measured from these trace images with an image analyzer, and the average value thereof is taken as the average particle diameter.

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

  In titanium dioxide, two crystal forms of rutile type and anatase type are mainly known. The anatase type has a characteristic that the spectral reflectance of ultraviolet rays is very large, whereas the rutile type has a characteristic that the absorption rate of ultraviolet rays is large (that is, the spectral reflectance is small). Paying attention to the difference in spectral characteristics of titanium dioxide crystal form, it is possible to improve the light resistance of the film suitably by using the rutile UV absorption performance, and to reduce the coloration due to light deterioration of the film. Is possible. Thereby, in the more suitable aspect of this invention, it is excellent in light resistance, even if it does not add another ultraviolet absorber substantially. For this reason, problems such as contamination due to bleeding out of the ultraviolet absorber and a decrease in adhesion are unlikely to occur.

  Here, “main body” means that the content of rutile-type titanium dioxide in all titanium dioxide fine particles exceeds 50 mass%. Further, the content of anatase-type titanium dioxide in all the titanium dioxide fine particles is preferably 10% by mass or less, more preferably 5% by mass or less, and most preferably 0% by mass. If the content of anatase-type titanium dioxide exceeds 10% by mass, the content of rutile-type titanium dioxide in the total fine titanium dioxide particles will be reduced, resulting in insufficient UV absorption performance. Titanium has a strong photocatalytic action, and this action also tends to reduce light resistance. Rutile titanium dioxide and anatase titanium dioxide can be distinguished by X-ray structure diffraction and spectral absorption characteristics.

  The surface of the titanium dioxide fine particles mainly composed of the rutile type of the present invention may be subjected to inorganic treatment with alumina or silica, or organic treatment with silicone or alcohol.

In the above structure, the film of the present invention can exhibit excellent light resistance even under light irradiation. Specifically, when UV irradiation is performed for 100 hours at 63 ° C., 50% RH and irradiation intensity of 100 mW / cm ² , the elongation at break of the film is preferably maintained at 35% or more, more preferably 40% or more. Can do. As described above, the film of the present invention is also suitable as a back surface sealing sheet for solar cells used outdoors because the photodecomposition and deterioration are suppressed by light irradiation.

  A known method can be used to add inorganic fine particles to the film. However, from the viewpoint of reducing the heat history, a master batch method (MB method) in which a polyester resin and inorganic fine particles are previously mixed with an extruder. ) Is preferred. Among them, a polyester resin that has not been dried in advance and inorganic fine particles are put into an extruder, and a method of preparing a master batch while degassing moisture and air can be adopted. It is preferable to prepare a masterbatch by using it because an increase in the acid value of the polyester resin can be suppressed. In this case, a method of producing a masterbatch while degassing or a method of producing a masterbatch without deaeration using a sufficiently dried polyester resin can be mentioned. By controlling the addition mode of the inorganic fine particles to the polyester resin in this way, the acid value of the polyester resin can be suitably kept low while containing high concentrations of inorganic fine particles, so that high whiteness and light reflectance are achieved. While having it, it is easy to obtain a film having both light resistance and hydrolysis resistance.

  As mentioned above, when producing a masterbatch, it is preferable to reduce the moisture content of the polyester resin to be charged in advance by drying. Drying conditions are preferably 100 to 200 ° C., more preferably 120 to 180 ° C., preferably 1 hour or more, more preferably 3 hours or more, and further preferably 6 hours or more. Thereby, it is sufficiently dried so that the moisture content of the polyester resin is preferably 50 ppm or less, more preferably 30 ppm or less.

  When producing a masterbatch while degassing, melt the polyester resin at a temperature of 250 to 300 ° C, preferably 270 to 280 ° C, and provide one, preferably two or more degassing ports in the preliminary kneader. It is preferable to adopt a method such as continuous suction deaeration of 0.05 MPa or more, preferably 0.1 MPa or more, and maintaining the reduced pressure in the mixer.

  The premixing method is not particularly limited, and may be a batch method or a single-screw or biaxial or more kneading extruder.

<Concentrated layer containing inorganic fine particles>
In the white polyester film for a solar cell of the present invention, an inorganic fine particle concentration containing layer containing 10 to 35% by mass of inorganic fine particles is disposed as at least one outermost layer. Moreover, 11 mass% or more is preferable, as for content of the inorganic fine particle in an inorganic fine particle concentration containing layer, 28 mass% or less is preferable, and 21 mass% or less is more preferable. By setting the content of the inorganic fine particles in the above range, it is possible to obtain a white polyester film for a solar cell excellent in environmental durability while having high whiteness and reflectance. On the other hand, when the content is lower than 10% by mass, the whiteness and reflectance of the film are insufficient, and the film is easily deteriorated by light. On the other hand, if it exceeds 35% by mass, the resin is uniformly dispersed in the resin, so that a large number of heat histories are required, and the conventional problems described above cannot be solved.

  Moreover, content of the inorganic fine particle in the whole film shall be 2-10 mass%. Preferably, they are 3 mass% or more and 8 mass% or less.

  The white polyester film for solar cells of the present invention has a laminated structure of at least two layers, and may have a multilayer structure higher than that, but at least one of the layers containing a large amount of inorganic fine particles (inorganic fine particle concentration containing layer) is present. The structure is the outermost layer. For example, when the layer containing inorganic fine particles is the A layer and the other layer having a smaller content of inorganic fine particles than the layer containing the inorganic fine particles is the B layer, the A layer / B layer, A layer / B layer / A layer, etc. Configuration can be taken. Preferred configurations include a two-layer configuration, and when the back sheet is formed, the film itself and the inner layer constituting the back sheet are arranged by arranging a layer containing a large amount of inorganic particles in the outermost layer on the side in direct contact with sunlight. It effectively prevents deterioration of member films, sheets and adhesive layers due to ultraviolet rays.

  Since inorganic fine particles having a certain high concentration are added to the layer provided for preventing deterioration due to ultraviolet rays or the like, the surface roughness increases and it becomes difficult to obtain adhesion between the layers. One advantage of having a two-layer structure is that such a problem does not occur because the concentration of inorganic fine particles on the opposite surface can be kept low.

  In the case of a two-layer configuration (A layer / B layer) or a three-layer configuration (A layer / B layer / A layer), the thickness (one side or The total thickness of the double-sided skin layers is 5-30%. The thickness ratio of the skin layer (A layer) is preferably 8% or more, more preferably 10% or more, and further preferably 15% or more. Moreover, 28% or less is preferable, 25% or less is more preferable, and 25% or less is further more preferable. By setting the thickness ratio of the skin layer within the above range, a white polyester film for sealing solar cells in which whiteness, reflectance, and environmental durability are compatible can be obtained. On the other hand, when the thickness ratio of the skin layer is lower than the lower limit, film light deterioration may gradually progress in the thickness direction. Moreover, when the thickness ratio of a skin layer is higher than the said upper limit, it exists in the tendency for the hydrolysis resistance of the whole film to be inferior.

  In particular, the white polyester film for solar cells of the present invention preferably has a two-layer structure that satisfies the above thickness ratio. Photodegradation progresses gradually in the thickness direction from the outermost layer where sunlight directly enters. Therefore, the concentration of the inorganic fine particle concentration layer is provided in the outermost layer on the side where sunlight directly enters rather than being divided into several layers, thereby concentrating the function of efficiently preventing light deterioration on this layer. be able to. In addition, when an inorganic fine particle concentration-containing layer is disposed in the intermediate layer, there is a risk of film peeling due to resin deterioration. From such a viewpoint, the inorganic fine particle concentration-containing layer is the most on the side where sunlight directly enters. It is preferable to exist only in the outer layer. The film of the present invention has a two-layer structure, and the concentration of inorganic fine particles is concentrated in the outermost layer on the side where sunlight directly enters, and the entire film is kept low in inorganic fine particle content, resulting in high whiteness and light reflection. Rate, UV resistance, and hydrolysis resistance can be made highly compatible.

<Other layers with low content of inorganic fine particles>
In the white polyester film for solar cells of the present invention, another layer having a smaller content of inorganic fine particles than the above-mentioned concentration layer containing inorganic fine particles may be included. The content of the inorganic fine particles in the other layer should be less than the content of the inorganic fine particles in the inorganic fine particle concentration-containing layer, but for the above reason, the difference from the content of the inorganic fine particles in the inorganic fine particle concentration-containing layer is different. 10 mass% or more is preferable.

<Functional layer>
When various functions such as easy adhesion, insulation, and scratch resistance are required for the white polyester film for solar cell of the present invention, the surface thereof may be coated with a polymer resin by coating or the like. Moreover, when slipperiness is requested | required, an inorganic and / or organic particle | grain may be contained in the said coating layer.

  When easy adhesion is required, the coating layer is formed on at least one surface of the film using an aqueous coating solution containing at least one of water-soluble or water-dispersible copolymer polyester resin, acrylic resin and polyurethane resin. It is preferable to provide it. Examples of these coating liquids include aqueous coating liquids disclosed in Japanese Patent No. 3567927, Japanese Patent No. 3589232, Japanese Patent No. 3589233, and the like.

  In particular, when the white polyester film for solar cells of the present invention is used on a surface in contact with a filler layer of an olefin resin such as EVA or PVB, a polyurethane resin is included in the aqueous coating liquid in order to exhibit easy adhesion to the filler layer. Is preferred. Especially, it is excellent in heat resistance and hydrolysis resistance, and it is preferable to contain the polyurethane resin which uses aliphatic polycarbonate polyol as a structural component from the point of yellowing prevention by sunlight. By including such a polyurethane resin, the adhesiveness of the film under wet heat can be improved.

  Examples of the aliphatic polycarbonate polyol include aliphatic polycarbonate diol and aliphatic polycarbonate triol. The number average molecular weight of the aliphatic polycarbonate diol is preferably 1500 to 4000, more preferably 2000 to 2000. 3000. If the number average molecular weight of the aliphatic polycarbonate diol is less than 1500, a hard urethane component increases, stress due to thermal contraction of the substrate cannot be relieved, and adhesiveness may decrease. Moreover, when a number average molecular weight exceeds 4000, the adhesiveness and the intensity | strength after a high temperature, high humidity process may fall.

  The molar ratio of the aliphatic polycarbonate polyol is preferably 3 mol% or more, more preferably 5 mol% or more, preferably 60 mol% or less, when the total polyisocyanate component of the polyurethane resin is 100 mol%, preferably 40 mol% or less. % Or less is more preferable. If the molar ratio is less than 3 mol%, water dispersibility may be difficult. On the other hand, if it exceeds 60 mol%, the water resistance is lowered and the heat and moisture resistance is lowered.

  The glass transition temperature of the polyurethane resin is not particularly limited, but is preferably less than 0 ° C and more preferably less than -5 ° C. As a result, the viscosity is close to that of partially melted olefin resin such as EVA or PVB at the time of pressure bonding, and the adhesiveness is improved by partial mixing, and suitable flexibility is easily achieved.

<Method for producing white polyester film for solar cell>
Although the manufacturing method of the white polyester film for solar cells of this invention is not restrict | limited especially, after supplying the polyester chip for each layer formation to a separate extruder, it laminates | stacks in a molten state and it extrudes from the same die | dye. A coextrusion method is preferred. For example, when manufacturing a film having a two-layer structure including a layer containing inorganic fine particles, a polyester chip containing a large amount of inorganic fine particles (resin chip for a layer containing inorganic fine particles) and a polyester chip containing less inorganic fine particles After supplying (resin chips for other layers) to separate extruders, they may be laminated in a molten state and extruded from the same die.

  When supplying the polyester chip to the extruder, it is preferable to use a sufficiently dried polyester chip in order to suppress an increase in acid value. Specifically, the moisture content of the polyester chip is preferably 100 ppm or less, more preferably 50 ppm or less, and even more preferably 30 ppm or less.

  As a method for drying the polyester chip, a known method such as vacuum drying or heat drying can be used. For example, in the case of heat drying, the heating temperature is preferably 100 to 200 ° C, more preferably 120 to 180 ° C. The drying time is preferably 1 hour or longer, more preferably 3 hours or longer, and even more preferably 6 hours or longer.

  The melting temperature of the polyester chip 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 can be reduced, and good productivity can be achieved. However, when the melting temperature is higher than 310 ° C., thermal degradation of the resin proceeds, Since an acid value rises, the hydrolysis resistance of the obtained film may fall.

  Next, the polyester resin for forming each layer melted by separate extruders is laminated in a molten state, extruded from the same die into a sheet, and taken out by a cooling roll to form an unstretched film.

  The obtained unstretched film is stretched by a biaxial orientation treatment. As the stretching method, the obtained unstretched film is heated with a heating roll or a non-contact heater, then stretched between rolls having a speed difference (roll stretching), and then uniaxially stretched with a clip. It is equipped with a sequential biaxial stretching method that stretches in the width direction (tenter stretching) after heating in the oven and then heat-sets by applying higher heat, and a mechanism that can simultaneously stretch in the vertical and horizontal directions Examples thereof include a simultaneous biaxial stretching method in which stretching is performed with a tenter (tenter simultaneous biaxial stretching), and an inflation stretching method in which stretching is performed by expanding with air pressure. In these stretching steps, in order to suitably maintain the elongation at break of the obtained film, it is preferable to maintain a longitudinal and lateral orientation balance by appropriately controlling the longitudinal and lateral stretching ratios.

  When high thermal dimensional stability is required, it is desirable to subject the film to a longitudinal relaxation treatment. As a method of the longitudinal relaxation treatment, a known method, for example, a method of performing longitudinal relaxation treatment by gradually narrowing the clip interval of the tenter (Japanese Patent Publication No. 4-0221818), a razor in the tenter, and the end of the film For example, a method of cutting the portion to avoid the influence of the clip and performing the longitudinal relaxation treatment (Japanese Patent Publication No. 57-54290) can be exemplified. Further, a method of relaxing by applying heat off-line may be used. Furthermore, in the said extending process, high thermal dimensional stability can also be provided to a film by controlling extending | stretching conditions suitably.

  In order to impart various functions to the film, the surface of the film may be coated with a polymer resin by coating or the like, or inorganic and / or organic particles may be contained in the coating layer. The method of providing is not particularly limited. For example, when forming a coating layer for imparting easy adhesion, the coating layer may be provided after film formation (off-line coating method), or film formation It may be provided inside (in-line coating method). From the viewpoint of productivity, it is preferably provided during film formation.

<Characteristics of white polyester film for solar cell>
The thickness of the white polyester film for solar cells of the present invention is 30 to 380 μm. 35 μm or more is preferable, 40 μm or more is more preferable, 250 μm or less is preferable, and 230 μm or less is more preferable. By making the thickness of the film within the above range, it is excellent in electrical insulation, and is easily reduced in weight and thickness. On the other hand, when the thickness of the film is larger than 380 μm, it is difficult to cope with the reduction in weight and thickness. Moreover, when smaller than 30 micrometers, an electrical insulation effect is hard to show | play.

  The whiteness degree of the white polyester film for solar cells of this invention is 50 or more, Preferably it is 60 or more. When the whiteness is less than 50, the concealability is inferior, and it is difficult to visually check the film when processing the solar cell module, which may reduce the processing efficiency.

  The average reflectance in the wavelength range of 400-800 nm of the white polyester film for solar cells of this invention is 50% or more, Preferably it is 60% or more. Further, the higher the average reflectance, the better. However, in reality, the upper limit is about 95%. When the reflectance is less than 50%, the film itself and the solar cell internal member are deteriorated by light, which is not preferable.

  The thermal shrinkage rate at 150 ° C. of the white polyester film for solar cell of the present invention is preferably 0.2% or more, more preferably 0.4% or more, and preferably 3.0% or less in the longitudinal direction, 1.8 % Or less is more preferable. This suppresses the occurrence of curling during heat processing or in a laminated state. On the other hand, if the heat shrinkage rate is less than 0.2%, the film may bend during processing. Moreover, when larger than 3.0%, the shrinkage | contraction at the time of a process is large, and a washboard-like wrinkle may generate | occur | produce. As a method of setting the heat shrinkage rate at 150 ° C. within the above range, it can be carried out by controlling stretching conditions or by applying longitudinal relaxation treatment and transverse relaxation treatment in the heat setting step.

  The white polyester film for solar cells of the present invention preferably has a vertical and horizontal orientation balance. That is, the MOR value (MOR-C) when the film thickness is converted to 50 μm is preferably 1.0 or more, more preferably 1.3 or more, preferably 2.0 or less, and more preferably 1.8 or less. Thereby, the vertical and horizontal orientation balance of the film is adjusted, and the mechanical strength and durability are easily maintained. Further, curling during the lamination is suppressed, and adhesion is improved. As a method for bringing MOR-C into the above range, it can be carried out by controlling the ratio of the longitudinal and lateral stretching ratios in the stretching step.

  The white polyester film for solar cells of the present invention can exhibit high hydrolysis resistance that can withstand long-term use outdoors. Specifically, as an evaluation index for hydrolysis resistance, the breaking elongation retention of the film after accelerated hydrolysis test (105 ° C., 100% RH, 0.03 MPa, treatment for 200 hours) is preferably 60% or more, preferably It can be maintained at 70% or more and 100% or less.

Since the white polyester film for solar cells of the present invention is suppressed from photolysis and deterioration even under light irradiation, it can exhibit excellent light resistance that can withstand long-term use outdoors. Specifically, as an evaluation index of the light resistance, the breaking elongation retention of the film after the accelerated light deterioration test (63 ° C., 50% RH, UV irradiation intensity 100 mW / cm ² , irradiation for 100 hours) is 35% or more, Preferably, it can be maintained at 40% or more.

  The change in the color b * value after the accelerated light deterioration test of the white polyester film for solar cell of the present invention is preferably 12 or less, and more preferably 10 or less. When the change in the color b * value is greater than 12, the appearance deteriorates due to secular change, which is not preferable.

  Since the white polyester film for solar cells of the present invention is further laminated with another layer and used as a solar cell back surface sealing sheet, the film surface is preferably smooth. 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 both environmental durability represented by light resistance and hydrolysis resistance, whiteness and light reflectivity, and excellent electrical insulation. Therefore, the conventional durable layer (hydrolysis-resistant layer), white layer and insulating layer can be integrated. Therefore, it can respond to weight reduction and thin film by using the white polyester film for solar cells of this invention for a solar cell backside sealing sheet.

<Solar cell backside sealing sheet>
The white polyester film for solar cells of the present invention can be used as a base film (base film) for a solar cell backside sealing sheet or a bonding material for flexible electronic members. In particular, it is suitable as a base film for a solar cell backside sealing sheet that requires high environmental durability.

  The solar cell backside sealing sheet referred to in the present invention is a sheet that protects the solar cell module on the back side of the solar cell by being used on the surface 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 as a solar cell back surface sealing sheet alone or in combination of two or more. For the purpose of imparting water vapor barrier properties, a water vapor barrier layer such as a water vapor barrier film or an aluminum foil can be laminated on the white polyester film for solar cells of the present invention. As a lamination | stacking form of the said water vapor | steam barrier layer, it can laminate | stack via an adhesive layer, can be laminated | stacked directly, or can be made into a sandwich structure.

  As said water vapor | steam barrier film, a polyvinylidene fluoride coating film, a silicon oxide vapor deposition film, an aluminum oxide vapor deposition film, an aluminum vapor deposition film, etc. can be used.

<Solar cell module>
The solar cell module in the present invention refers to a system that takes in incident light such as sunlight and room light, converts it into electricity, and stores the electricity. The solar cell back surface sealing sheet and the solar cell back surface sealing sheet And a solar cell element embedded in the filler layer.

  Resin used for a filler layer is not specifically limited, Olefin resin, such as EVA and PVB, can be illustrated.

  In addition, the solar cell module of the present invention may include a surface protective sheet, a high light transmissive material, and the like, and may have a flexible property depending on the application.

  This application claims the benefit of priority 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 October 7, 2011 are incorporated herein by reference.

  Next, the present invention will be described in detail with reference to examples and comparative examples. However, the present invention is not limited to these examples, and all modifications may be made without departing from the spirit described above and below. It is included in the technical scope of the present invention. The measurement / evaluation method used in the present invention is as follows.

<Average particle size of inorganic fine particles>
The inorganic fine particles were observed with a scanning electron microscope, and the magnification was appropriately changed according to the size of the particles, and photographs were taken. An enlarged copy of the photograph was taken, and the circumference of each particle was traced for at least 100 fine particles selected at random, and the equivalent circle diameters of the particles were measured from these trace images with an image analysis device. The average value was defined as the average particle size.

<Intrinsic viscosity of polyester (IV)>
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 master batch and a film containing fine particles, the solid content was removed by centrifugation, and then the measurement was performed.

<Content of diethylene glycol (DEG)>
After 0.1 g of polyester was thermally decomposed in 2 ml of methanol at 250 ° C., it was quantitatively determined by gas chromatography.

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

(1) Preparation of sample The film or the raw material polyester resin is pulverized and vacuum-dried at 70 ° C. for 24 hours, and then weighed in a range of 0.20 ± 0.0005 g using a balance. (G). A sample weighed with 10 ml of benzyl alcohol is added to a test tube, the test tube is immersed in a benzyl alcohol bath heated to 205 ° C., and the sample is dissolved while stirring with a glass rod. The dissolution time is 3 minutes, 5 minutes, and 7 minutes. The samples at that time were designated as A, B, and C, respectively. Next, a new test tube was prepared, and only benzyl alcohol was added, and the same procedure was followed. Samples when the dissolution time was 3, 5, and 7 minutes were designated as a, b, and c, respectively.

(2) Titration Titration was performed using a 0.04 mol / L potassium hydroxide solution (ethanol solution) whose factor (NF) was previously known. The titration of the potassium hydroxide solution was determined with the point where the indicator phenol red changed from yellowish green to light red. Samples A, B, and C were titrated as XA, XB, and XC (ml), and samples a, b, and c were titrated as Xa, Xb, and Xc (ml).

(3) Calculation of acid value From the titration amounts XA, XB, and XC for each dissolution time, the titration amount V (ml) at a dissolution time of 0 minutes was determined by the least square method. Similarly, a titration amount V0 (ml) at a dissolution time of 0 minutes was determined from Xa, Xb, and Xc. Next, the acid value (eq / ton) was determined according to the following formula.
Acid value (eq / ton) = [(V−V0) × 0.04 × NF × 1000] / W

<Apparent density of film>
The apparent density of the film was measured according to JIS K 7222 “Foamed Plastics and Rubber—Measurement of Apparent Density”. However, in order to simplify the notation, the unit was converted to g / cm ³ .

<Whiteness of film>
The whiteness of the film was measured using Z-1001DP manufactured by Nippon Denshoku Industries Co., Ltd. according to JIS L 1015-1981 method.

<Average reflectance of film>
An integrating sphere is attached to a spectrophotometer (manufactured by Shimadzu Corporation, self-recording spectrophotometer “UV-3150”), and the reflectance of a standard white plate (manufactured by SphereOptics, white standard plate “ZRS-99-010-W”). Was calibrated as 100%, and the spectral reflectance was measured. The measurement was performed in 1 nm increments in the wavelength range of 400 to 800 nm, and the average value was obtained. In the case of a single film, measurement was performed by placing a non-reflective black mount on the back of the sample film. Measurement was performed by applying light from the concentrated inorganic fine particle containing layer side.

<Light reflection fluctuation rate of film>
With respect to the obtained film roll, when the roll winding start is 0% and the winding end is 100%, a 1 m × 1.8 m film piece is cut out from the center of the length position of 10%, 50%, 90%. It was. Five film samples having a square of 20 cm square from the four corners and the center of each film piece were sampled, and each average reflectance was measured by the above-described “average reflectance of film”. The average value of the average reflectance of each film sample was set as the center value, and the difference between the maximum value and the minimum value of the average reflectance divided by the center value was set as the light reflection variation rate.

<Accelerated light degradation test>
Using an eye super UV tester (SUV-W151, manufactured by Iwasaki Electric Co., Ltd.), continuous UV irradiation treatment was performed for 100 hours at 63 ° C., 50% RH, irradiation intensity of 100 mW / cm ² on the inorganic fine particle concentration containing layer side of the film. .

<Accelerated hydrolysis test>
HAST (Highly Accelerated Temperature and Humidity Stress Test) standardized in JIS C 60068-2-66 was performed. The sample film was cut into a size of 70 mm × 190 mm, and a jig was used to keep the distance where they did not contact each other. Using EHS-221 manufactured by ESPEC CORP., Treatment was performed at 105 ° C., 100% RH, 0.03 MPa, 200 hours.

<Break elongation retention>
Evaluation of light resistance and hydrolysis resistance was carried out based on the elongation at break. The elongation at break before and after the accelerated light degradation test and accelerated hydrolysis test was measured according to JIS C 2318-1997 5.3.31 (tensile strength and elongation), and the elongation at break according to the following formula: Retention rate (%) was calculated.
Breaking elongation retention ratio (%) = [(breaking elongation after treatment) × 100] / (breaking elongation before treatment)
With respect to the elongation retention after the accelerated light deterioration test, the case of less than 35% was evaluated as x, the case of 35% or more and less than 60% as ◯, and the case of 60% or more as ◎.

  With respect to the elongation retention after the accelerated hydrolysis test, x is less than 60%, o is 60% or more and less than 80%, and o is 80% or more.

<Change in color b * value>
The sample film was cut into 40 mm × 40 mm and a color white * color difference meter (ZE-2000, manufactured by Nippon Denshoku Co., Ltd.) was used using a standard white plate with X = 94.19, Y = 92.22 and Z = 110.58. ), The color b * value of the sample film before and after the accelerated light degradation test was measured according to JIS K 7105-1981 5.3.5 (a). The change in color b * value was determined according to the following formula.
Change in color b * value = (color b * value after accelerated light degradation test) − (color b * value before accelerated light degradation test)
Regarding the change in the color b * value, a value higher than 12 was indicated as x, a value of 5-12 as ◯, and a value of less than 5 as 、 ５.

<Heat shrinkage at 150 ° C. in the longitudinal direction (HS150)>
The sample film was cut into 10 mm × 250 mm, and the long side was aligned in the direction in which measurement was desired, and marks were made at intervals of 200 mm, and the mark interval A was measured under a constant tension of 5 g. Subsequently, the sample film was allowed to stand in an oven at 150 ° C. under no load for 30 minutes, and then removed from the oven and cooled to room temperature. Thereafter, the mark interval B was determined under a constant tension of 5 g, and the thermal shrinkage (%) was determined by the following formula. The heat shrinkage rate was measured at a position equally divided into three in the width direction of the sample film, the average value of the three points was rounded off to the third decimal place, and the second decimal place was rounded.
Thermal contraction rate (%) = [(A−B) × 100] / A

<MOR-C>
The obtained film was divided into 5 equal parts in the width direction, 100 mm square samples were taken in the longitudinal direction and the width direction at each position, and a microwave transmission type molecular orientation meter (manufactured by Oji Scientific Instruments, MOA-6004) was used. And measured. The thickness correction was 50 μm, MOR-C was determined, and an average value of 5 points was used.

<Surface strength>
The sample film cut out to 5 cm × 20 cm was adhered to the flat glass using the polyester double-sided pressure-sensitive adhesive tape A so that the inorganic fine particle concentration containing layer side was the outside. A 24 mm wide adhesive tape B (manufactured by Nichiban Co., Ltd., cello tape (registered trademark)) was applied to the surface of the sample film over a length of 35 mm and left for 1 minute. Thereafter, the adhesive tape B was peeled off in a direction perpendicular to the glass surface, and the surface on the inorganic fine particle concentration containing layer side was observed.

  When the surface of the sample film is peeled off at 50% or more of the peeled area of the adhesive tape B, it is defined as “peeling”. When the frequency of “peeling” is less than half after 5 or more repetitions, “◯” (excellent surface strength) The case of more than half was evaluated as “×” (poor surface strength).

<Adhesiveness>
Prepare the film obtained in Example 13 to 100 mm × 100 mm and the following EVA sheet cut out to 70 mm × 90 mm, and prepare a film / EVA sheet / film (all films have the coating layer surface facing the EVA sheet) The sample was prepared by stacking with the structure of 2) and thermocompression bonding under the following adhesion conditions. The produced sample was cut out to 20 mm × 100 mm, and then attached to a SUS plate, and the peel strength between the film layer and the EVA sheet layer was measured using a tensile tester under the following conditions. The peel strength was determined as the average value of the parts that were stably peeled after exceeding the maximum point. The ranking was based on the following criteria.
A: 100 N / 20 mm or more, or material destruction of film ○: 75 N / 20 mm or more, less than 100 N / 20 mm Δ: 50 N / 20 mm or more, less than 75 N / 20 mm ×: less than 50 N / 20 mm

(Sample preparation conditions)
Apparatus: Vacuum laminator (manufactured by NPC, LM-30 × 30 type)
Pressurization: 1 atm EVA sheet:
A. Standard cure type Sunvik, Ultra Pearl (registered trademark) PV (0.4 μm)
Lamination process: 100 ° C. (vacuum 5 minutes, vacuum pressurization 5 minutes)
Cure process: Heat treatment 150 ° C (normal pressure 45 minutes)
II. Solar Eva (registered trademark) SC4 (0.4 μm), manufactured by Mitsui Fabro
Lamination process: 130 ° C (vacuum 5 minutes, vacuum pressurization 5 minutes)
Cure process: Heat treatment 150 ° C (normal pressure 45 minutes)
B. Fast cure type Ultravial (registered trademark) PV (0.45 μm) manufactured by Sanvic
Lamination process: 135 ° C (vacuum 5 minutes, vacuum pressure 15 minutes)
II. Solar Eva (registered trademark) RC02B (0.45 μm) manufactured by Mitsui Fabro
Lamination process: 150 ° C. (vacuum 5 minutes, vacuum pressure 15 minutes)

<Manufacture of polyester resin pellets>
(1) Production of PET resin pellet I (PET-I) When the temperature of the esterification reaction can was reached and reached 200 ° C., a slurry composed of 86.4 parts by mass of terephthalic acid and 64.4 parts by mass of ethylene glycol was prepared. While charging and stirring, 0.017 parts by mass of antimony trioxide and 0.16 parts by mass of triethylamine were added as catalysts. Next, the pressure was increased and the pressure esterification reaction was performed under the conditions of a gauge pressure of 3.5 kgf / cm ² (343 kPa) and 240 ° C. Thereafter, the inside of the esterification reaction vessel was returned to normal pressure, and 0.071 part by mass of magnesium acetate tetrahydrate and then 0.014 part by mass of trimethyl phosphate were added. Furthermore, the temperature was raised to 260 ° C. over 15 minutes, and 0.012 part by mass of trimethyl phosphate and then 0.0036 part by mass of sodium acetate were added. After 15 minutes, the resulting esterification reaction product was transferred to a polycondensation reaction can, gradually heated from 260 ° C. to 280 ° C. under reduced pressure, and subjected to a polycondensation reaction at 285 ° C.

  After completion of the polycondensation reaction, filtration is performed with a filter made of NASRON (registered trademark) with a 95% cut diameter of 5 μm, extruded into a strand form from a nozzle, and using cooling water that has been previously filtered (pore diameter: 1 μm or less). It was cooled and solidified 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 contained substantially no inert particles and internally precipitated particles.

(2) Production of PET resin pellet II (PET-II) After pre-crystallizing PET resin pellet I (PET-I) at 160 ° C in advance, it was subjected to solid phase polymerization in a nitrogen atmosphere at 220 ° C, and intrinsic viscosity was obtained. A PET resin pellet II (PET-II) having 0.71 dl / g and an acid value of 11 eq / ton was obtained.

(3) Production of PET resin pellet III (PET-III) Except for changing the polycondensation reaction time, the same method as PET resin pellet I (PET-I) was used, with an intrinsic viscosity of 0.51 dl / g and an acid value of 39 eq. / Ton PET resin pellet III (PET-III) was obtained.

(4) Production of PET resin pellet IV (PET-IV) (Preparation of polycondensation catalyst solution)
A) Preparation of ethylene glycol solution of phosphorus compound To a flask equipped with a nitrogen inlet tube and a cooling tube, 2.0 liters of ethylene glycol was added at room temperature and normal pressure, and then stirred at 200 rpm in a nitrogen atmosphere as a phosphorus compound. 200 g of Irganox (registered trademark) 1222 (manufactured by Ciba Specialty Chemicals (currently BASF)) was added. Further, 2.0 liters of ethylene glycol was added, the temperature was raised by changing the jacket temperature setting to 196 ° C., and the mixture was stirred under reflux for 60 minutes from the time when the internal temperature reached 185 ° C. or higher. Thereafter, the heating was stopped, the solution was immediately removed from the heat source, and the solution was cooled to 120 ° C. or less within 30 minutes while maintaining the nitrogen atmosphere. The mole fraction of Irganox 1222 in the obtained solution was 40%, and the mole fraction of the compound whose structure changed from Irganox 1222 was 60%.

I) Preparation of ethylene glycol solution of aluminum compound To a flask equipped with a cooling tube, 5.0 liters of pure water was added at room temperature and normal pressure, and then 200 g of basic aluminum acetate was slurried with pure water while stirring at 200 rpm. Added as. Further, pure water was added so as to be 10.0 liters as a whole, and the mixture was stirred at normal temperature and pressure for 12 hours. Thereafter, the jacket temperature was changed to 100.5 ° C., the temperature was raised, and the mixture was stirred under reflux for 3 hours from the time when the internal temperature reached 95 ° C. or higher. Stirring was stopped and the mixture was 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 for 30 minutes at room temperature, the system was controlled to an internal temperature of 80 to 90 ° C., gradually reduced in pressure to reach 27 hPa, and stirred for several hours. Then, water was distilled off to obtain an ethylene glycol solution of an aluminum compound at 20 g / l. The peak integration value ratio of ²⁷ Al-NMR spectrum of the obtained aluminum solution was 2.2.

(Esterification reaction and polycondensation)
An in-line mixer having a high-speed stirrer was installed in the transfer line from the third esterification reaction tank to the first polycondensation reaction tank, comprising three continuous esterification reaction tanks and three polycondensation reaction tanks. In the continuous polyester production apparatus, 0.75 part by mass of ethylene glycol was continuously supplied to the slurry preparation tank with respect to 1 part by mass of high-purity terephthalic acid. The first esterification reaction tank is 250 ° C. and 110 kPa, the second esterification reaction tank is 260 ° C. and 105 kPa, the third esterification reaction tank is 260 ° C. and 105 kPa, and the prepared slurry is continuously supplied to the polyester oligomer. Got. In addition, 0.025 mass part of ethylene glycol was continuously thrown into the 2nd esterification reaction tank. The obtained oligomer was continuously transferred to a continuous polycondensation apparatus consisting of three reaction vessels, and an ethylene glycol solution of an aluminum compound and an ethylene glycol of a phosphorus compound prepared by the above method in an in-line mixer installed in a transfer line. The initial polycondensation reaction was carried out by continuously adding the solution while stirring with a continuous mixer so as to be 0.015 mol% and 0.036 mol% as aluminum atoms and phosphorus atoms, respectively, with respect to the acid component in the polyester. The polycondensation was carried out at 265 ° C. and 9 kPa, the medium-term polycondensation reaction vessel at 265 to 268 ° C. and 0.7 kPa, the final polycondensation reaction vessel at 273 ° C. and 13.3 Pa, an intrinsic viscosity of 0.63 dl / g, and an acid value of 10 PET resin pellet IV (PET-IV) of .5 eq / ton was obtained.

(5) Production of PET resin pellet V (PET-V) Using the obtained PET resin pellet IV (PET-IV), solid-state polymerization was performed at 220 ° C. under a reduced pressure of 0.5 mmHg using a rotary vacuum polymerization apparatus. Then, PET resin pellet V (PET-V) having an intrinsic viscosity of 0.73 dl / g and an acid value of 5.0 eq / ton was obtained.

<Manufacture of master batch pellets containing fine particles>
(6) Production of Master Batch Pellet I (MB-I) As a raw material, PET resin pellet I (PET-I) 50 mass previously dried at 120 ° C. for about 8 hours under 10 ⁻³ torr (about 0.133 Pa) % Is mixed with 50% by mass of rutile-type titanium dioxide having an average particle size of 0.3 μm (value obtained by electron microscopy) while being fed to a vented twin screw extruder, kneaded and deaerated. Extrusion was performed at 275 ° C. to obtain rutile type titanium dioxide fine particle-containing master batch pellet I (MB-I). The pellet had an intrinsic viscosity of 0.45 dl / g and an acid value of 42.2 eq / ton.

(7) Manufacture of Master Batch Pellet II (MB-II) Using Master Batch Pellet I (MB-I), solid-state polymerization is performed at 220 ° C. under a reduced pressure of 0.5 mmHg in a rotary vacuum polymerization apparatus. Master batch pellets II (MB-II) having a viscosity of 0.71 dl / g and an acid value of 23.5 eq / ton were obtained.

(8) Production of Master Batch Pellet III (MB-III) Master Batch Pellet I (MB-I) except that PET resin pellet IV (PET-IV) was used instead of PET resin pellet I (PET-I) In the same manner, rutile type titanium dioxide fine particle-containing master batch pellets III (MB-III) were obtained. The pellet had an intrinsic viscosity of 0.46 dl / g and an acid value of 36.3 eq / ton.

(9) Manufacture of master batch pellet IV (MB-IV) Using master batch pellet III (MB-III), solid-state polymerization is performed at 220 ° C. under a reduced pressure of 0.5 mmHg in a rotary vacuum polymerization apparatus, and intrinsic viscosity is obtained. A master batch pellet IV (MB-IV) containing rutile-type titanium dioxide fine particles having 0.70 dl / g and an acid value of 19.4 eq / ton was obtained.

<Preparation of coating solution>
4,4-diphenylmethane diisocyanate 43.75 parts by mass, dimethylolbutanoic acid 12.85 parts by mass, number-average molecular weight 2000 polyhexamethylene carbonate diol 153.41 parts by mass, dibutyltin dilaurate 0.03 parts by mass, and acetone as a solvent 84.00 parts by mass was added and stirred at 75 ° C. for 3 hours under a nitrogen atmosphere. After the reaction solution was cooled to 40 ° C., 8.77 parts by mass of triethylamine was added to obtain a polyurethane prepolymer solution. . 450 parts by mass of water was added to the polyurethane prepolymer solution, adjusted to 25 ° C., and stirred and mixed at 2000 min ⁻¹ for water dispersion. Thereafter, a part of acetone and water was removed under reduced pressure to prepare a water-soluble polyurethane resin solution having a solid content of 35%. The glass transition temperature of the obtained polyurethane resin was −30 ° C.

  Next, 55.86% by mass of water, 30.00% by mass of isopropanol, 13.52% by mass of the polyurethane resin solution obtained above, and particles (silica sol having an average particle size of 40 nm, solid content concentration of 40% by mass) 0.59% % And a surfactant (silicone-based, solid content concentration: 100% by mass) to 0.03% by mass to prepare a coating solution.

<Manufacture of white polyester film for solar cells>
Example 1
The raw material of the fine particle concentration layer (A layer) in which 60% by mass of PET-II and 40% by mass of MB-II are mixed, and another layer in which 86% by mass of PET-II and 14% by mass of MB-II are mixed ( The raw materials of layer B) were put into separate extruders, mixed and melted at 285 ° C., and then joined in a molten state to form layer A / layer B using a feed block. At this time, the discharge rate ratio of the A layer and the B layer was controlled using a gear pump. Subsequently, it was extruded onto a cooling drum adjusted to 30 ° C. using a T-die to produce an unstretched sheet.

  The obtained unstretched sheet was uniformly heated to 75 ° C. using a heating roll, and heated to 100 ° C. with a non-contact heater to perform 3.3-fold roll stretching (longitudinal stretching). The resulting uniaxially stretched film is guided to a tenter, heated to 140 ° C, stretched 4.0 times, fixed in width, heat treated at 215 ° C for 5 seconds, and further relaxed 4% in the width direction at 210 ° C. By doing so, a white polyester film roll for solar cells having a thickness of 80 μm was obtained.

Example 2
The white polyester film roll for solar cells was obtained by the same method as Example 1 except having changed the raw material composition of A layer and B layer as shown in Table 1.

Example 3
The white polyester film roll for solar cells was obtained by the same method as Example 1 except having changed the raw material composition of A layer and B layer as shown in Table 1.

Example 4
The white polyester film roll for solar cells was obtained by the same method as Example 1 except having changed the raw material composition of A layer and B layer as shown in Table 1.

Example 5
The white polyester film roll for solar cells was obtained by the same method as Example 4 except having changed the discharge amount and speed so that film roll thickness might be set to 50 micrometers.

Example 6
A white polyester film roll for solar cells 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 solar cells 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 solar cells was obtained in the same manner as in Example 5 except that the longitudinal draw ratio was 3.1 times and the discharge rate and speed were changed so that the film roll thickness was 188 μm.

Example 9
A white color for solar cells was obtained in the same manner as in Example 5 except that the longitudinal draw ratio was 3.0 times, the transverse draw ratio was 3.7 times, and the discharge amount and speed were changed so that the film roll thickness was 350 μm. A polyester film roll was obtained.

Example 10
A white polyester film roll for solar cells 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 passed through an offline coater set to a temperature of 160 ° C., and the relaxation treatment was performed by adjusting the speed and tension to obtain a white polyester film roll for solar cells.

Example 12
A white polyester film roll for solar cells was obtained in the same manner as in Example 1 except that the feed block was changed to have a configuration of A layer / B layer / A layer.

Example 13
Apply the coating solution prepared above on the B layer side of the uniaxially stretched film after longitudinal stretching by the roll coating method so that the final (after biaxial stretching) coating amount after drying is 0.15 g / m ^2. After that, a white polyester film roll for a solar cell was obtained in the same manner as in Example 1 except that it was dried at 80 ° C. for 20 seconds.

  Table 2 shows the physical properties of the film rolls obtained in Examples 1 to 13.

Comparative Examples 1 and 2
The white polyester film roll for solar cells was obtained by the same method as Example 1 except having changed the composition of A layer and B layer as shown in Table 3.

Comparative Examples 3-5
A white polyester film roll for solar cells 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 rate and speed were changed so that the film roll thickness was 50 μm. Got.

  Table 4 shows the physical properties of the film rolls obtained in Comparative Examples 1 to 5.

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

Claims (9)

A white polyester film for solar cells having a whiteness of 50 or more, an average reflectance in the range of wavelengths from 400 to 800 nm of 50 to 95%, an acid value of 1 to 50 eq / ton, and a thickness of 30 to 380 μm.
The inorganic fine particle concentration containing layer containing 10 to 35% by mass of inorganic fine particles has a multilayer structure arranged as at least one outermost layer, and the thickness of the inorganic fine particle concentration containing layer is relative to the total thickness of the polyester film. The white polyester film for solar cells, wherein the content of inorganic fine particles in the entire polyester film is 2 to 10% by mass.   The white polyester film for solar cells according to claim 1, wherein the inorganic fine particles are titanium dioxide mainly composed of a rutile type.   The white polyester film for solar cells according to claim 1 or 2, wherein a heat shrinkage rate at 150 ° C in the longitudinal direction is 0.2 to 3.0%.   The white for solar cells according to any one of claims 1 to 3, wherein the breaking elongation retention after the accelerated hydrolysis test is 60 to 100% under the conditions of 105 ° C, 100% RH, 0.03 MPa and 200 hours. Polyester film. The sun according to any one of claims 1 to 4, wherein the breaking elongation retention after the accelerated light deterioration test is 35% or more under the conditions of 63 ° C, 50% RH, UV irradiation intensity of 100 mW / cm ² and irradiation for 100 hours. White polyester film for batteries. 6. The sun according to claim 1, wherein the change in the color b * value after the accelerated light deterioration test is 12 or less under the conditions of 63 ° C., 50% RH, UV irradiation intensity of 100 mW / cm ² and irradiation for 100 hours. White polyester film for batteries.   The white polyester film for solar cells according to any one of claims 1 to 6, wherein a coating layer containing a polyurethane resin containing an aliphatic polycarbonate polyol as a constituent component is disposed on at least one surface of the polyester film. .   The solar cell backside sealing sheet using the white polyester film for solar cells in any one of Claims 1-7.   A solar cell module comprising the solar cell back surface sealing sheet according to claim 8, a filler layer adjacent to the solar cell back surface sealing sheet, and a solar cell element embedded in the filler layer.