JP2012033967A - Polyester resin sheet for solar cell, laminate using the same, solar cell backside protecting sheet, and module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin sheet inexpensive and excellent in hydrolysis resistance and heat resistance for a solar cell, that improves electricity conversion efficiency of the solar cell by improving hydrolysis resistance and heat resistance and also improving concealing properties, and a solar cell using the same.SOLUTION: This polyester resin sheet for the solar cell has a polyester resin layer formed by using one or more layers each having number average molecular weight of 18,500-40,000, and has one or more layers having 5-40 wt.% of titanium oxide in the polyester resin layer. In this polyester resin sheet for the solar cell, a light transmittance of a wavelength of 300-350 nm is 0.005-10%, a relative reflectance is not less than 80% and not more than 105%, apparent density is 1.37-1.65 g/cm, optical concentration is 0.55-3.50, and the optical density varies within 20% from a center value.

Description

  INDUSTRIAL APPLICABILITY The present invention is a solar cell backsheet that is inexpensive and excellent in environmental resistance (hydrolysis resistance, weather resistance, etc.) and that is optimal for a field that requires the reflectance on the back side of sunlight incident light, and the same. It relates to solar cells.

  In recent years, solar cells, which are clean energy, have attracted attention as the next-generation energy source, and development is progressing from the construction field to electrical and electronic parts. The configuration of the solar cell unit is basically composed of a high light-transmitting material, a solar cell module, a filling resin layer, and a back surface sealing sheet, and is used for a built-in roof of a house, an electric, an electronic component, or the like. Is. The thermoplastic resin sheet used as the backside sealing sheet used for some of the components of solar cells is used, but this (for solar cells) thermoplastic resin sheet is also resistant to the natural environment (hydrolysis and weather resistance). Sex) is strongly required. Furthermore, since the improvement of the solar cell conversion efficiency of a solar cell is also requested | required, it is converted into electricity using the reflected light of the back surface sealing film of a solar cell. There is also a demand for lightness, strength, and battery processability. Patent Document 1 discloses that a base polymer having a high number average molecular weight is used as a low specific gravity solar cell backsheet. However, UV resistance and hiding properties are inferior, and further improvement is required.

  In the case of a solar cell module used outdoors, the solar cell is encapsulated with a synthetic resin on a tempered glass plate or metal substrate in order to enhance the mechanical resistance and environmental resistance that is unlikely to deteriorate in an environmental atmosphere to ensure reliability. Such a structure is generally used. More specifically, the module structure by the laminating method will be described. An ethylene-vinyl acetate copolymer (hereinafter referred to as "EVA") sheet / solar cell / EVA sheet / aluminum foil is sandwiched between reinforced glass plates with a vinyl fluoride sheet. A structured sheet (hereinafter, referred to as “aluminum-fluorine composite sheet”) is laminated in this order and heat-pressed is used.

Further, when the solar cell is a thin film solar cell such as amorphous silicon, a solar cell is directly formed on a tempered glass plate, and an EVA sheet and an aluminum-fluorine composite sheet are laminated and heat-pressed. Yes. As the solar cell back surface sealing film, it is known to use a polyethylene-based resin or a polyester-based resin, or a fluorine-based film. (See Patent Documents 2-3)
Moreover, although the polyester film which has a bubble (refer patent document 4) is known, these films are not utilized as an object for the back sheets for solar cells.

JP 2002-26354 A (page 2, column 1, lines 32 to 39) Japanese Patent Laid-Open No. 11-261085 (page 2, column 1, column 36-2, line 4) JP-A-11-186575 (page 2, column 1, column 36 to page 3, column 1, line 22) Japanese Examined Patent Publication No. 7-37098 (first page, first column, first to third page, second column, 23rd line)

  The conventional sheet described above has the following problems. Conventionally, the biaxially stretched polyester sheet used in this field has been limited in use in this field because it is poor in hydrolysis resistance, which is most required for environmental resistance. In addition, the biaxially stretched polyester sheet colored in white has improved reflectance, but its use in this field has been limited because of its poor hydrolysis resistance.

  In addition, the fluorine-based sheet is excellent in hydrolysis resistance and weather resistance, but has a drawback in that it has poor gas barrier properties and the sheet is weak. Therefore, such a sheet has been used by laminating a metal foil or the like such as aluminum in order to improve the barrier property and provide the strength of the sealing material on the back surface. Even when the film of Patent Document 1 invented to solve these problems is used, peeling from the laminated interface becomes a problem, which is a problem when manufacturing solar cells or when constructing on a roof or the like.

  Moreover, although the polyester sheet is relatively inexpensive, it has difficulty in heat resistance when exposed to high temperatures (100 to 120 ° C.).

  In view of the background of such prior art, the present invention improves the conversion efficiency of a solar cell by improving the hydrolysis resistance and interface peeling prevention property at low cost and further improving the concealability. An object of the present invention is to provide a polyester resin sheet and a solar cell using the same.

  In view of the background of such prior art, the present invention has been intensively studied to improve hydrolysis efficiency, heat resistance, and further improve the conversion efficiency of solar cells by improving concealment. We have developed and applied a polyester resin sheet for solar cells that satisfies high UV transmittance, relative reflectance, apparent density, optical density, variation in optical density, and number average molecular weight. It has been investigated.

The present invention employs the following means in order to solve such problems.
That is,
(1) having a polyester resin layer using one or more layers having a number average molecular weight of 18500 to 40,000, and having at least one layer having 5 to 40 wt% titanium dioxide in the polyester resin layer A polyester resin sheet having a light transmittance of 0.005 to 10% at a wavelength of 300 to 350 nm, a relative reflectance of 80% to 105%, an apparent density of 1.37 to 1.65 g / cm ³ , and an optical density 0.55 to 3.50, and the optical density variation is within 20% of the center value, a polyester resin sheet for solar cells,
(2) The polyester resin sheet for solar cells according to (1), wherein the optical density variation is within 15% of the center value,
(3) The polyester resin sheet for solar cells according to (1), wherein the thermoplastic resin sheet has a total light transmittance of 0.005 to 25%,
(4) The thermoplastic resin sheet for solar cells according to claim 1, wherein the thickness of the layer having 5 to 40 wt% titanium dioxide is 7 to 100% of the thickness of the entire polyester resin layer.
(5) The polyester resin sheet for solar cells according to any one of (1) to (4), wherein the elongation retention before and after aging for 3000 hours is 40 to 100% in an environment of a temperature of 85 ° C. and a humidity of 85% RH. ,
(6) The polyester resin sheet for solar cells according to any one of (1) to (5), wherein the elongation retention before and after aging for 15 hours is 40 to 100% under an environment of a temperature of 140 ° C.
(7) The polyester resin sheet for solar cells according to (1) to (6), which has a gas and water vapor barrier layer,
(8) A polyester resin sheet laminate for solar cells in which at least the polyester resin sheet according to (1) to (7) and a gas and water vapor barrier layer are laminated,
(9) In the measurement of water vapor transmission rate according to JIS-K-7129, at a temperature of 40 ° C. and a humidity of 90% RH, the water vapor transmission rate in terms of 100 μm is 0.5 g / (m ² · 24 hr) or less (1) To (7) a polyester resin sheet laminate for solar cells,
(10) The solar cell polyester resin sheet or solar cell polyester resin sheet laminate according to (1) to (9), wherein the solar cell back surface protective sheet is used as a solar cell back surface sealing material,
(11) A solar cell module using the solar cell back surface protective sheet according to (10),
It is.

  According to the present invention, a thermoplastic resin sheet and a laminate for a solar cell that improve the conversion efficiency of the solar cell by improving inexpensive and excellent hydrolysis resistance and heat resistance, and further improving the concealing property. Can be provided. This sheet and laminate can be suitably used not only for solar cells used as roofing materials, but also for flexible solar cells and electronic components.

1 is a cross-sectional view of a solar cell using the polyester resin sheet for solar cells of the present invention. It is sectional drawing which shows an example of the structure of the polyester resin sheet laminated product for solar cells which has a gas barrier layer in the single side | surface of a film. It is sectional drawing of another example which shows the structure of the polyester resin sheet laminated product for solar cells which has a gas barrier layer between two layers of films. It is sectional drawing which shows an example of the structure of the polyester resin sheet laminated product for solar cells which has a gas barrier layer (base material sheet + metal or an inorganic oxide layer) on the single side | surface of a film.

The present invention has a polyester resin layer using one or more layers having a number average molecular weight of 18500 to 40,000, and at least one layer having 5 to 40 wt% titanium dioxide in the polyester resin layer. A polyester resin sheet having a transmittance of light having a wavelength of 300 to 350 nm of 0.005 to 10%, a relative reflectance of 80% to 105%, and an apparent density of 1.37 to 1.65 g / cm ³ , This is a polyester resin sheet for solar cells having an optical density of 0.55 to 3.50 and an optical density variation of 20% or less with respect to the center value.

  The solar cell referred to in the present invention refers to a system for converting sunlight into electricity (hereinafter referred to as “conversion”), and preferably a high light transmission material, a solar cell module, a filling resin layer, and a back surface sealing sheet. For example, in the structure shown in FIG. 1, the structure is incorporated into a roof of a house, or is used for electrical or electronic components.

  Here, the high light-transmitting material is a material that efficiently allows sunlight to enter and protects the internal solar cell module. Preferably, glass, a high light-transmitting plastic, a film, or the like is used. The solar cell module converts sunlight into electricity and is the heart of the solar cell. The module is made of a semiconductor such as silicon, cadmium-tellurium, germanium-arsenic. There are single crystal silicon, polycrystalline silicon, amorphous silicon and the like that are widely used at present.

  Moreover, the said filling resin layer is used for the purpose of fixation and protection of the solar cell module in a solar cell, and an electrical insulation, and an ethylene vinyl acetate resin (EVA) is especially preferably used in terms of performance and price.

  The present invention is suitably used as a back surface sealing sheet for solar cell modules. This sheet contributes to increasing the conversion efficiency of the solar cell by increasing the reflectivity by increasing the function of blocking the water vapor that the solar cell module dislikes and the concealability inside the solar cell. Moreover, it becomes a solar cell excellent in durability by shielding UV region wavelength 300-350 nm which injects from a back surface.

  The polyester resin in the present invention is a polycondensate of a dicarboxylic acid derivative and a diol derivative, for example, polyethylene terephthalate, polypropylene terephthalate, polybutylene terephthalate, polyethylene-2,6-naphthalate, poly 1,4-cyclohexanedimethylene terephthalate. 1,4-cyclohexanedimethanol copolymerized polyethylene terephthalate can be used. In particular, since polyethylene terephthalate is inexpensive, it can be used for a wide variety of applications. In addition, these resins may be homo resins, and may be copolymers or blends. The melting point of the polyester preferably used is preferably 250 ° C. or higher in view of heat resistance, and preferably 300 ° C. or lower in terms of productivity. If it is in this range, other components may be copolymerized or blended. In addition, additives such as a slip agent, a colorant, an antistatic agent, and a low-density agent are added within a range of, for example, 60% by weight or less as long as they are within the range where there is no problem in terms of mechanical properties and productivity. Also good.

  The polyester resin sheet for solar cells of the present invention refers to a sheet formed by biaxially stretching an unstretched and non-oriented sheet obtained by melt-molding the above polymer. The thickness of the sheet is preferably in the range of 20 to 350 microns from the viewpoints of appropriate waist strength, processability, and light weight of the solar cell as a solar cell backside sealing sheet.

  The thickness of the polyester resin sheet for solar cells is important for improving the withstand voltage of the partial discharge voltage, and a method of increasing the thickness to the target withstand voltage by a method such as lamination or bonding by coextrusion is preferably used.

  The polyester resin layer in the present invention is a layer composed of a polyester resin having a number average molecular weight of 18500 to 40000, and may be a single layer or a plurality of layers. The polyester resin sheet of the present invention refers to a multilayer or a single layer having the above-described polyester resin layer and having other polyester layers as necessary.

  In the present invention, the light transmittance of the polyester resin sheet at a wavelength of 300 nm to 350 nm needs to be 0.005 to 10%. The light transmittance at a wavelength of 300 nm to 350 nm in the present invention refers to the ratio of incident light having the wavelength incident on the sheet and transmitted light on the opposite surface. In order to reduce UV deterioration, the transmittance (hereinafter also referred to as UV transmittance) of the wavelength (300 to 350 nm) in the UV region of the thermoplastic resin sheet for solar cells is preferably in the range of 0.005 to 10%, preferably It is necessary to be in the range of 0.01-7%, more preferably 0.05-5%. In the wavelength of the incident light, light in the UV region that deteriorates the polyester resin sheet for solar cells is also included. When the light can be shut out near the surface layer, penetration of the wavelength in the UV region into the inner layer There is little, UV degradation of an inner layer part is few, and it is excellent in a weather resistance. When the UV transmittance exceeds 10%, the molecular chain is broken by the energy of the UV wavelength over time, and the mechanical properties are deteriorated. Moreover, it turns out that the color tone also changes to yellow and it has deteriorated from the appearance.

  As a method for controlling the light transmittance (UV transmittance) at a wavelength of 300 nm to 350 nm, it is possible to control by controlling the mixing ratio of the following titanium dioxide.

  Increasing the mixing ratio of titanium dioxide increases the concealability and at the same time significantly lowers the transmittance at a wavelength of 300 to 350 nm. The UV transmittance of the thermoplastic resin sheet is preferably 0.005 to 10%, and this effect is manifested when the mixing ratio of titanium dioxide (content of titanium dioxide with respect to the layer containing titanium dioxide) is 5%. It is from the area exceeding%. Preferably, it is 7% by weight or more, more preferably 10% or more. As for the upper limit, the concentration of titanium dioxide is desirably 40% by weight or less from the viewpoint of productivity and sheet strength. By having the layer having the titanium dioxide content in the polyester resin layer, the light transmittance range of the wavelength of 300 to 350 nm of the present invention can be obtained.

  In the present invention, the relative reflectance of the thermoplastic resin sheet needs to be 80% to 105%, more preferably 83% to 105%, and still more preferably 85% to 105%. If it is less than 80%, the optical loss is large and hardly contributes to the conversion efficiency.

  Here, the relative reflectance referred to in the present invention is 100% reflectance (base value) when the reflectance is measured at a wavelength of 560 nm using alumina oxide as a standard white plate, and the measured value in the sample is It is converted as a numerical value for the base value. When the relative reflectance is within the range of the present invention, the light leaking from the gap between the solar battery modules can be diffusely reflected with respect to the incident light and delivered again to the solar battery cell. Since the illuminance can be improved, the conversion efficiency of the solar cell is improved.

In the present invention, the apparent density of the polyester resin sheet is required to be 1.37 to 1.65 g / cm ³ .

Here, the apparent density refers to a numerical value calculated from the thickness, area, and weight of the entire sheet laminated in a multilayer or single layer. By adding inorganic particles having a high specific gravity, the refractive index difference is increased at the interface, contributing to the reflection performance. The lower limit of the apparent density contributing to the reflectance is from 1.37 g / cm ³ , and the upper limit is 1.65 g / cm ^{3 in} consideration of the lightness of the solar cell. The method for controlling the apparent density to 1.37 to 1.65 g / cm ³ can be achieved by controlling the type of polyester resin, the type of inorganic particles, and the mixing ratio of inorganic particles. As the inorganic particles, talc, magnesium oxide, titanium dioxide, zinc dioxide, calcium carbonate, barium sulfate, gypsum and the like are preferably used. In particular, when titanium dioxide is used, the wavelength in the UV region is diffusely reflected, and thus has a remarkable effect on UV resistance.

  In addition, it is effective to use a fluorescent brightening agent such as 4,4'-bis (2-benzoxazolyl) stilbene to increase the whiteness.

  In the present invention, the optical density when measured with a Macbeth optical densitometer needs to be 0.55 or more, more preferably 0.60 or more. The upper limit is theoretically as high as possible, but is 3.5 or less, preferably 3.0 or less, and more preferably 2.5 or less from the viewpoint of productivity and sheet strength. Here, the optical density referred to in the present invention indicates that the higher the numerical value as a concealing index, the higher the concealing property. In the present invention, an optical densitometer (manufactured by Macbeth: TR-524). The value measured under the conditions described below. The solar cell thermoplastic resin sheet needs to be concealed in order to reflect sunlight that leaks from the gap above the solar cell and to convert the reflected light into electricity, thereby improving the conversion efficiency. It is. In particular, the solar cell thermoplastic resin sheet disposed below the solar cell module needs to prevent incident light leaking from the gap from leaking out of the solar cell. If the optical density is less than 0.55, the incident light is emitted outside the solar cell. In this case, since it cannot be used again for electrical conversion in a solar battery cell, an improvement in conversion efficiency cannot be expected, which is not preferable. Increasing the mixing ratio of inorganic particles such as titanium dioxide increases the concealability and at the same time significantly lowers the transmittance. As described above, the optical density, which is an index of hiding properties, is preferably 0.55 to 3.5, and this effect is exhibited from a region where the mixing ratio of titanium dioxide exceeds 5% by weight. The titanium dioxide concentration is preferably 7% by weight or more, more preferably 10% by weight or more. As for the upper limit, the concentration of titanium dioxide is desirably 40% by weight or less from the viewpoint of productivity and sheet strength. The range of the optical density of the present invention can be obtained by providing the polyester resin layer with a layer having the titanium dioxide content relative to the layer containing titanium dioxide.

In the present invention, the optical density variation when measured with a Macbeth optical densitometer needs to be within 20% of the center value. The variation in optical density is expressed as (maximum value−minimum value) / center value. For example, when the center value of the optical density is 1.0, the variation of the optical density is in the range of 0.2, and the optical density needs to be in the range of 0.9 to 1.1. The optical density variation is preferably within 15% with respect to the center value, and more preferably within 10% with respect to the center value. Since the optical density variation is required to be uniform in the plane of the solar cell module, it is necessary to satisfy the present general-purpose size within a range of 1.5 m length × 1 m width. Optical density variation is sampled into a size of 1.5 m in the longitudinal direction and 1 m in the width direction every 100 m in the longitudinal direction from the center of the product roll, and further, the four corners of the cut sample of 1.5 m × 1.0 m are changed to 10 cm × 10 cm. Sampling was performed, and the optical density was measured three times using the 10 cm × 10 cm sample to obtain the optical density. For each product roll, the optical density variation was calculated from the maximum value, minimum value, and center value (the number of data was 20) of the optical density when measured 5 times, and was used as the optical density variation. If the optical density variation is out of the range of 20%, it will affect the variation in UV transmittance, the variation in total light transmittance, and the variation in relative reflectance, which is not preferable in terms of performance and quality. In order to make the optical density variation within 20%, it is necessary to reduce the classification of the raw material chips. For example, when using raw material chips having different specific gravities, this can be achieved by changing the size of the chip. The specific gravity of titanium dioxide is 3.9 to 4.2 g / cm ³ , and the specific gravity of polyester is 1.2 to 1.4 g / cm ³ . The specific gravity of the master chip containing 50% by weight of titanium dioxide is 2.5 to 2.8 g / cm ³ . Conventionally, the shape of the master chip has been a cylindrical shape having a length of 5.95 to 8.05 mm, a width of 3.20 to 4.80 mm, and a height of 1.70 to 2.30 mm. In the above chip shape, when diluting the titanium dioxide concentration to 5 to 40% by weight, the master chip of titanium dioxide and the polyester chip are classified in the hopper at the top of the extruder, and the master chip having a high specific gravity is discharged first. There was a problem. Therefore, the sheet discharged earlier contains a large amount of titanium dioxide, so that the optical density is high. In the sheet discharged later, the titanium dioxide density is low, the optical density is low, and the optical density variation is large. Therefore, by changing the shape of the titanium dioxide master chip into a cylindrical shape having the following length: 2.40 to 4.60 mm, width: 3.20 to 4.80 mm, and height: 1.70 to 2.30 mm, It becomes possible to make it the range of the optical density variation of the present invention.

  In the present invention, in order to satisfy hydrolysis resistance, the polyester resin sheet needs to have a polyester resin layer having a number average molecular weight of 18500 or more. The upper limit is preferably as high as possible. However, when the number average molecular weight exceeds 40,000, extrusion is practically impossible, and in view of melt moldability and biaxial stretchability, a molecular weight of 35,000 or less is more preferable. That is, the number average molecular weight is 18500 to 40000, more preferably 19000 to 35000, and still more preferably 20000 to 30000. Here, the number average molecular weight referred to in the present invention is measured by sol permeation chromatography (GPC) described later, and the number average molecular weight is an index of the degree of polymerization. When the number average molecular weight is within the range of the present invention, even when the hydrolysis reaction of the polyester resin proceeds, the degree of polymerization at the reaction start point is high, so that deterioration over time is superior to the number average molecular weight lower than 18500. Can be reduced.

  In order to adjust the number average molecular weight within the scope of the present invention, in the polymerization of the thermoplastic resin, the temperature for high polymerization is changed, for example, 190 to 230 ° C., the polymerization time is changed for 10 to 23 hours, and different number average molecular weights are obtained. A polymer can be obtained.

  In the present invention, the total light transmittance of the polyester resin sheet is preferably 0.005 to 25%. Here, a total light transmittance means the value measured according to JIS-K-7105 using Suga Test Instruments haze meter HGM-2DP. Total light transmittance is an index of concealment, especially by reducing the total light transmittance of wavelengths in the visible light region, the sunlight that has entered the wavelength that contributes to power generation is transmitted outside the solar cell It can be prevented from running away. The effect of increasing the concealment is remarkable when 5 to 40% by weight of titanium dioxide is added. If it is less than 5% by weight, the concealability is lowered, and the target total light transmittance cannot be reduced. If it exceeds 40% by weight, it is not preferable because it causes clogging of the membrane-forming filter and the sheet itself is liable to break, resulting in deterioration of productivity. The titanium dioxide concentration is preferably 7% by weight or more, more preferably 10% or more. The range of the total light transmittance of this invention can be obtained by having in the polyester resin layer the layer which is content of the said titanium dioxide with respect to the layer containing titanium dioxide. As long as the titanium dioxide concentration satisfies the above range, it may have a plurality of layers and a high concentration layer.

  In the present invention, the thickness of the polyester resin layer having a number average molecular weight of 18500 or more is preferably 7 to 100% of the thickness of the entire polyester resin sheet. Preferably, it is 10% or more. More preferably, it is 15% or more. That is, the entire sheet need not have a number average molecular weight of 18500 to 40,000, and a high molecular weight polyester resin having a thickness of 7% or more in the thickness direction of the film and having a number average molecular weight of 18500 to 40,000 may be formed. It is a polyester resin layer having a thickness of 7% or more, more preferably 10% or more of the thickness of all layers, and having a number average molecular weight in the range of 18500 to 40,000. It is preferable to form the surface layer most in order to impart hydrolysis resistance. Even if it is a high molecular weight polyester resin layer having a number average molecular weight of 18500-40000 with a thickness of less than 7% in the layer thickness direction, it is inferior in hydrolysis resistance, resulting in a decrease in strong elongation retention and rapid deterioration. If it is laminated with a thickness of 7% or more, it is advantageous for delamination from the lamination interface.

  Moreover, in this invention, the polyester resin layer whose number average molecular weight is 18500 or more consists of several layers, and the layer containing 5 to 40 weight% of titanium dioxide is 7 to 100% of the thickness of the whole polyester resin layer. Is preferred. Preferably, it is 10% or more of the total thickness of the polyester resin layer. More preferably, it is 15% or more of the total thickness of the polyester resin layer. The content of titanium dioxide is more preferably 7 to 30% by weight, and still more preferably 10 to 20% by weight. In this polyester resin layer, by separating the layer having a high concentration of titanium dioxide from the other layers, both the film-forming property and the optical properties can be improved.

  Moreover, in order to effectively express the hydrolysis degradation prevention of the polyester resin sheet for solar cells of the present invention, it is more preferable that the polyester resin layers having an average molecular weight of 18500 to 40,000 are laminated on both sides.

  In the present invention, the elongation retention after aging for 3000 hours in an environment of a temperature of 85 ° C. and a humidity of 85% is preferably 40 to 100%. Aging for 3000 hours in an environment of temperature 85 ° C. and humidity 85% is one of the tests for examining the hydrolyzability equivalent to 25 years in the outdoor exposure state as a thermoplastic resin sheet for solar cells. In order to satisfy the ratio, it is preferable to have a polyester resin layer having a number average molecular weight in the range of 18500 to 40,000, dispose this layer as the outermost layer, and make the layer thickness 7% or more of the total thickness of the sheet. When the film layer is less than 7%, deterioration proceeds from the outermost layer, and the elongation retention may be less than 40%.

  In the present invention, the elongation retention after aging for 15 hours in an environment of 140 ° C. is preferably 40 to 100%. Solar cells are used outdoors and can be exposed to high temperatures such as in the desert or the tropics. Moreover, in the sealed area | region, it rises more than atmospheric temperature. Furthermore, since the solar cell module itself generates heat when generating electric power, heat resistance in an environment where the backsheet is used is also an important item. The accelerated test for heat resistance can be replaced by the above evaluation. In order to set the elongation retention after aging for 15 hours in an environment of a temperature of 140 ° C. to 40 to 100%, it has a polyester resin layer having a number average molecular weight in the range of 18500 to 40,000, and this layer is the outermost layer. It is preferable to arrange and make the layer thickness 7% or more of the total thickness of the sheet. If the polyester resin layer is less than 7%, the deterioration progresses from the outermost layer and the elongation retention may be less than 40%.

  The polyester resin sheet laminate for solar cells of the present invention is formed by laminating a polyester resin sheet and a gas and water vapor barrier layer. Here, the gas barrier layer referred to in the present invention refers to a layer having a water vapor barrier property, for example, a metal or metal oxide provided as a layer between the surface layer or two sheets of the sheet. . The polyester resin sheet for solar cells of the present invention is provided with a water vapor barrier layer (water vapor barrier layer) as shown in FIGS. 2 and 3 in order to block the entry of water vapor from the outside, which is most hated by solar cell modules. Are preferably used. In a laminate having no gas and water vapor barrier layer in the outermost layer, the water vapor barrier property is inferior, and there may be problems such as entering into the circuit in the solar cell module and shorting the circuit.

The polyester resin sheet laminate of the present invention has a water vapor transmission rate of 0.5 g / (m in terms of 100 μm at a temperature of 40 ° C. and a humidity of 90% RH in the measurement of water vapor transmission rate according to JIS-K-7129. ² · 24 hr) or less. The water vapor transmission value measured according to the standard of JIS K7129 is 0.5 g / (m ² · 24 hr) (100 μm thickness conversion) or less, preferably 0.25 g / (m ² · 24 hr) (100 μm thickness conversion) ) Or less, and more preferably, a metal or metal oxide layer is preferably used in order to achieve 0.10 g / (m ² · 24 hr) (in terms of thickness 100 μm) or less. As such a metal, aluminum is preferably used, and as a metal oxide, an oxide of silicon or aluminum is preferably used. Passing more water vapor than 0.5 g / (m ² · 24 hr) (converted to 100 μm thickness) promotes hydrolysis of the polyester resin sheet for solar cells, and deteriorates both strength and elongation and becomes brittle. It becomes a trouble of the said solar cell module.

  The solar cell back surface protective sheet of the present invention is a solar cell polyester resin sheet or a solar cell polyester resin sheet laminate, and is a solar cell back surface protective sheet used for a solar cell back surface sealing material. The polyester resin sheet for solar cells of the present invention has a role as a back surface protection sheet and can protect the solar cell module from dirt, water vapor, and the like, and therefore can be suitably used as a solar cell back surface sealing material. .

  The solar cell module of this invention is a solar cell module using the said solar cell back surface protection sheet. A solar cell module using a polyester resin sheet for solar cells that satisfies the above characteristics as a back surface protective sheet can be suitably used as a solar cell. Next, an example is demonstrated about the manufacturing method of the polyester resin sheet for solar cells of this invention.

  For example, terephthalic acid or a derivative thereof and ethylene glycol are transesterified by a known method. Examples of the reaction catalyst include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, and titanium compounds, and examples of the colorant include phosphorus compounds. As a polymerization catalyst, it is preferable to add an antimony compound, a germanium compound, or a titanium compound. As such a method, for example, when a germanium compound is taken as an example, it is preferable to add the germanium compound powder as it is.

  The method for controlling the number average molecular weight of the polyester resin of the present invention to 18500 to 40,000 is the above method, after polymerizing a normal polyester resin having a number average molecular weight of 18000 level, a temperature of 190 ° C. to less than the melting point of the polyester resin. Thus, a so-called solid-phase polymerization method in which heating is performed under reduced pressure or a flow of an inert gas such as nitrogen gas is preferable. This method can increase the number average molecular weight without increasing the terminal carboxyl group amount of the polyester resin.

  Next, in order to convert the polymer into a polyester resin sheet for a solar cell, the polymer is dried as necessary, and the polyester resin fed from different flow paths using two or more extruders is converted into a multi-manifold die. Alternatively, a method of laminating in multiple layers using a field block, a static mixer, pinol, or the like can also be used. Moreover, you may combine these arbitrarily.

  Sheets stacked in multiple layers discharged from a die are extruded onto a cooling body such as a casting drum, and cooled and solidified to obtain a casting sheet. At this time, it is preferable to use a wire-like, tape-like, needle-like, or knife-like electrode, which is brought into close contact with a cooling body such as a casting drum by electrostatic force and rapidly solidified.

  The casting sheet thus obtained may be biaxially stretched as necessary. Biaxial stretching refers to stretching in the longitudinal direction and the transverse direction. Stretching may be sequentially biaxially stretched or simultaneously stretched in two directions. Further, re-stretching may be performed in the longitudinal and / or transverse direction.

  Here, the stretching in the longitudinal direction refers to stretching for imparting molecular orientation in the longitudinal direction to the film, and is usually performed by a difference in peripheral speed between rolls. This stretching may be performed in one stage, or may be performed in multiple stages using a plurality of roll pairs. The stretching ratio varies depending on the type of resin, but usually the area ratio is preferably 2 to 15 times. For example, when polyethylene terephthalate is used, the longitudinal direction stretching ratio is particularly preferably 2 to 4 times. Used.

  Thereafter, in order to stretch in the transverse direction, the film is passed through in the transverse direction (machine width direction) through the film in a state where the clip holding the end portion is set on the condition of 2 to 4 times and held by the clip. The ambient temperature is set in such a way that the stretching temperature of the film is 85 to 110 ° C. and stretched in the transverse direction. In order to obtain dimensional stability in the subsequent steps, heat treatment is performed at 180 to 240 ° C. to obtain the polyester resin sheet for solar cells of the present invention.

  Here, the method for improving the reflectance is a method in which a large amount of fine particles having a number average particle diameter of 0.1 to 1 μm are added to the polyester in the polyester resin sheet and uniformly dispersed in a sheet form. The diffuse reflectance of the fine particles improves the relative reflectance. The method of adding fine particles is preferably a compound method. In the present invention, titanium dioxide is used as the fine particles. Specifically, a method of adding 50% by weight of titanium dioxide particles to polyester to prepare a master chip and diluting to a target concentration is preferable. As the dispersion aid, for example, polyalkylene glycol or a copolymer thereof can be used, and specifically, polyethylene glycol, polypropylene glycol, polybutylene terephthalate-polytetramethylene glycol copolymer and the like are preferable. used.

  Next, in order to impart gas and water vapor barrier properties to the sheet constituting the polyester resin sheet for solar cells of the present invention, as a method of laminating the gas and water vapor barrier layers, as shown in FIG. There is a method of providing directly on the surface of the polyester resin sheet for solar cell of the present invention by a known method. The thickness is usually preferably in the range of 100 to 700 angstroms. Note that the barrier layer does not have to be a single layer, and may be provided on both sides of the sheet as shown in FIG.

  On the other hand, instead of directly providing a barrier layer on the sheet, a gas barrier sheet provided with a metal or inorganic oxide layer on another base sheet as shown in FIG. 4 is bonded to the surface of the polyester resin sheet for solar cells of the present invention. There is also a method of making a laminated product using an agent layer or the like. Moreover, the method of laminating | stacking metal foil (for example, aluminum foil) on the film surface can also be used. In this case, the thickness of the metal foil is preferably in the range of 10 to 50 μm from the viewpoint of workability and gas barrier properties. Further, the gas barrier layer is not necessarily arranged on the surface of the sheet, and may be sandwiched between, for example, two layers of films.

  Moreover, the structure of the solar cell back surface protection sheet which uses the polyester resin sheet for solar cells of this invention is not limited to lamination | stacking with the said gas and a water vapor | steam barrier sheet. As a laminate with the polyester resin sheet for solar cells of the present invention, in addition to the barrier sheet, for example, a reflective sheet having a further excellent light reflectivity, and a thick plastic sheet of 100 μm or more in order to enhance electrical insulation Further, it may be laminated with one or more sheets selected from a black-colored or heat-conductive sheet having high heat conductivity for enhancing heat dissipation and a fluororesin sheet for further improving weather resistance. Further, the order of lamination is not particularly limited, but it is preferable that the sheet having the function of reflecting light is disposed as close to the solar cell as possible, and the sheet having weather resistance is disposed on the outermost side. In this invention, what was laminated | stacked via the adhesive agent etc. is used as a laminated product, and what was laminated | stacked without using an adhesive agent etc. is used as a sheet | seat.

The solar cell module of the present invention has, for example, the configuration shown in FIG. That is, a base material (glass, film, etc.) having a high light transmittance is placed on the surface, a solar cell module such as a silicon system is provided with a lead wire that can take out electricity, and fixed with a filling resin such as EVA resin, Thereafter, the polyester resin sheet for solar cell of the present invention is fixed to the back side with a solar cell back surface protective sheet for back surface sealing.
The physical properties used in the present invention, the evaluation method thereof, and the evaluation criteria will be described below.
<Physical properties and evaluation methods, evaluation criteria>
(1) Number average molecular weight (Mn)
Using a 244 type gel permeation chromatograph GCP-244 (manufactured by WATERS) at room temperature (23 ° C.), two Shodex K 80M (manufactured by Showa Denko KK) in the column, TSK-GEL-G2000Hxl (Tosoh Corporation) 1) was used, and molecular weight calibration was performed using polystyrene (PS) (standard product) before measuring the polyester resin sheet for solar cells. Using the elution volume (V) and the molecular weight (M), the coefficient (A ₁ ) of the third-order approximation (i) is calculated and plotted.
Log (M) = A ₀ + A ₁ V + A ₂ V ² + A ₃ V ³ ... (I)
After completion of the calibration and drawing, the sample of the polyester resin sheet for solar cells was dissolved in 0.2% (wt / vol) of orthochlorophenol / chloroform (1/4 volume ratio) in a solvent. The injection amount into the chromatograph was 0.400 ml, and the flow rate was 0.8 ml / min. The detector used was an R-401 differential refractive index (WATERS), and the number average molecular weight was calculated according to the following formula.
Number average molecular weight (Mn) = ΣNiMi / ΣNi
Molar fraction; Ni, molecular weight corresponding to each holding capacity (Vi) (Mi)
A composite or single film was sampled and measured. The composite film was sampled by polishing the film while observing under a microscope.

(2) Content of titanium dioxide Using the sheet as a sample, the elemental amount of titanium, which is an element peculiar to titanium dioxide, was determined by a fluorescent X-ray elemental analyzer (manufactured by Horiba, Ltd., MESA-500W type). The titanium dioxide content was converted from the titanium element amount.

(3) Optical Density The transmitted light flux was measured with an optical densitometer (Macbeth: TR-524) and calculated by the following formula.
Light source: Visible light spectral composition: Color temperature 3006 ° K tungsten bulb Measurement environment: Temperature 23 ° C ± 3 ° C, Humidity 65 ± 10% RH
Calculation formula: optical density = log ₁₀ (F ₀ / F)
F: Transmitted light flux of sample, F ₀ : Transmitted light flux without sample.

(4) Optical density variation (%)
The variation in optical density was expressed as [(Fmax−Fmin) / Fave] × 100.
Fmax: Maximum value of 20 data, Fmin: Minimum value of 20 data, Fave: Average value of 20 data
The optical density measurement method was measured by the same method as in (3) above.
Optical density variation was sampled from the product roll at a central portion of 100 m in the longitudinal direction at a size of 1.5 m in the longitudinal direction and 1 m in the width direction, and four squares of 1.5 m × 1.0 m were cut into 10 cm × 10 cm. The optical density was measured three times using the sample, and the average value of the three times was defined as the optical density. For each product roll, the optical density variation was calculated from the maximum value, the minimum value, and the central value (the number of data is 20 at 5 locations × 4 samples) of the optical density when measured 5 times.

(5) Apparent density
The measurement was made with an electromagnetic balance (SD-120L manufactured by Kensei Kogyo Co., Ltd.).

  N = 3 measurements were made and an average value was adopted.

(6) Aging of the film in an atmosphere of hydrolysis resistance at 85 ° C. and 85% RH, measuring the breaking elongation of the sheet by ASTM-D61T, and the ratio when the breaking elongation without aging is 100% (retention ratio ) And judged according to the following criteria.
Aging time: 0 hr (100%), 3000 hr
A: Retention rate is 50 to 60% or more B: Retention rate is less than 50 to 60% B: Retention rate is 40 to less than 50% X: Retention rate is less than 40%

(7) The weather resistance promotion tester iSuper UW tester was used to perform the following cycle for 5 cycles, and the elongation retention was obtained in the same manner as described above, and evaluated according to the same criteria as above.
1 cycle: UV irradiation for 8 hours in an atmosphere at a temperature of 60 ° C. and a humidity of 50% RH, and then aging for 4 hours in a condensation state (temperature of 35 ° C., humidity of 100 RH). UV irradiation intensity: 100 mW / cm ²
○: b value increase rate (5 or less)
Δ: Increase in b value (5-25)
X: B value increase rate (25 or more).

(8) Total light transmittance It measured according to JIS-K-7105 (1981) using Suga Test Instruments haze meter HGM-2DP.

(9) Relative reflectance Using a Hitachi spectrophotometer U-3310, both the standard white plate opening and the test piece opening were 560 nm using alumina oxide as the standard white plate, and the inclination angle of the test piece opening was 10 °. In addition, the diffuse reflectance was measured (T ₀ ), and the reflectance at that time was 100%. Thereafter, the opening of the test piece was replaced with a test piece, and the diffuse reflectance was measured at 560 nm. Then, it converted into relative reflectance (R) by the following formula.

R (%) = T ₁ / T ₀ × 100
T ₀ : reflectance of standard white plate
T ₁ : reflectance of the test piece.

(10) UV (300 to 350 nm) light transmittance Using a Hitachi spectrophotometer U-3310, both the standard white plate opening and the test piece opening are 300 to 350 nm using alumina oxide as the standard white plate. The transmittance in the absence of the sample was measured with an inclination angle of the opening of 10 ° (A ₀ ), and the transmittance at that time was 100%. Then, this sample was arrange | positioned in front of incident light, the measured value of the transmittance | permeability (A1) of 300-350 nm was taken for every 5 nm wavelength, and the average value of the measured value was made into UV transmittance T (%).

T (%) = A ₁ / A ₀ × 100
A ₀ : Transmittance without sample
A ₁ : Transmittance of the test piece.

(11) Water vapor transmission rate
The water vapor transmission rate was measured according to JIS K7129 (1992). The measurement conditions were 24 hours, temperature 40 ° C., humidity 90% RH, and converted to m ² . (Thickness is converted to 100 μm).

(12) Heat resistance The film was aged in an atmosphere of 140 ° C. for 15 hours, the elongation at break of the film was measured by ASTM-D61T, the elongation at break without aging was taken as 100%, and the ratio to the elongation after aging ( Retention rate) was calculated. And it determined on the following reference | standard.

○: Retention ratio is 40% or more Δ: Retention ratio is 30 to less than 40% ×: Retention ratio is less than 30%.

(13) Workability A 1 m square solar cell back surface sealing film was produced, and the waist strength in consideration of the incorporation into the solar cell system was determined according to the following criteria.

    ○: The waist strength is appropriate and it can be easily assembled.

    Δ: A level where the waist is weak or too strong, and there are some difficulties in assembly processing.

    X: A level where the waist is too weak or too strong and clearly has difficulty in workability.

(14) Dielectric constant The dielectric constant was measured according to JIS C2151 (1990).

(15) Thickness of each layer The total thickness was measured according to JIS C2151 (1990), and the laminated section was pretreated by cutting the section in the thickness direction with a microtome, and then a field emission scanning electron microscope (FE) manufactured by Hitachi, Ltd. -SEM) Using S-800, the thickness section was imaged at a magnification (x1000) at which the whole image was taken, and the thickness of the section photograph was measured. The titanium dioxide containing layer can be imaged as a white layer.

(16) Composite ratio The composite ratio was calculated from the result of measuring the thickness of each layer from the cross-sectional photograph by the method of (15).
In the case of the A layer / B layer / C layer configuration, when the base polyester has a number average molecular weight of 18500 to 40,000 and the titanium dioxide content is only A layer,

As described above, the calculation was performed. The number average molecular weight of each layer was measured by the above measurement method using samples collected from each layer.

(17) Titanium dioxide-containing layer particle concentration Titanium dioxide concentration is measured by the method of (2) above, and the titanium dioxide particle concentration of the titanium dioxide-containing layer is calculated from the composite ratio to calculate the particle concentration of the titanium dioxide-containing layer. It was.

(18) Titanium dioxide-containing layer ratio (based on the entire polyester resin sheet)
The titanium dioxide-containing layer ratio was calculated from the results of measuring the thickness of each layer from the cross-sectional photograph by the method (15).
In the case of the A layer / B layer / C layer configuration, when the content of titanium dioxide is only A layer,

Calculated above. The number average molecular weight of each layer was measured by the above measurement method using samples collected from each layer.

  Hereinafter, the present invention will be described in more detail with reference to examples.

Examples 1-4
100 parts of dimethyl terephthalate (parts by weight: hereinafter simply referred to as parts) is mixed with 64 parts of ethylene glycol, 0.1 parts of zinc acetate and 0.03 part of antimony trioxide are added as a catalyst, and the reflux temperature of ethylene glycol is increased. Transesterification was performed.

To this was added 0.08 part of trimethyl phosphate, and the temperature was gradually raised and reduced, and polymerization was carried out at a temperature of 271 ° C. for 5 hours. The intrinsic viscosity of the obtained polyethylene terephthalate was 0.55. The polymer was cut into a chip having a length of 4 mm, and the chip shape of PET (polyethylene terephthalate) was a cylindrical shape. Length: 5.95 to 8.05 mm, width: 3.20 to 4.80 mm, high The height was 1.70-2.30 mm, and the specific gravity was 1.3 g / cm ³ . This PET was put into a rotary vacuum apparatus (rotary vacuum dryer) having a high polymerization temperature of 190 to 230 ° C. and a vacuum degree of 0.5 mmHg, and heated with stirring for 10 to 23 hours to obtain a PET polymer.

In the polymerization of PET used for the compound and the base, the temperature for high polymerization was changed from 190 to 230 ° C., the time for high polymerization was changed for 10 to 23 hours, and the intrinsic viscosity of the PET polymer was 0.60 (Example 1). Four types of PET polymers of 0.66 (Example 2), 0.73 (Example 3), and 0.81 (Example 4) were obtained. These four kinds of PET polymers and titanium dioxide fine particles were compounded to obtain a master chip having 50% by weight of titanium dioxide. Since this master chip had a specific gravity of 2.5 g / cm ³ , the chip shape of the master chip was length: 2.40 to 4.60 mm, width: 3.20 to 4.80 mm, and height: 1.70. It was made into the chip | tip shape where classification | category does not occur easily as a cylinder shape of-2.30 mm. A master chip of titanium dioxide was added by 28% by weight, so that the titanium dioxide concentration was 14% by weight with respect to the base polyester. These polymers were laminated through a laminating apparatus so as to be B layer / A layer / B layer, and formed into a sheet form from a T-die. Although the laminated structure is a composite three-layer structure, the same polymer as the B layer was used for the A layer, and a substantially single layer (B layer / A layer / B layer = B layer / B layer / B layer) was used. Therefore, the polymerization degree of each layer (A layer, B layer) is the same. An unstretched sheet obtained by cooling and solidifying the sheet-like molded product discharged from the T die with a cooling drum having a surface temperature of 25 ° C. is led to a roll group heated to 85 to 98 ° C., and stretched 3.3 times in the longitudinal direction. It cooled with the roll group of 25 degreeC. Subsequently, the film was stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 220 ° C. in a tenter, and after uniform cooling, the solution was cooled to room temperature to obtain a sheet having a winding thickness of 50 μm.

The above-mentioned PET polymer passed through the A and B layers has an intrinsic viscosity of 0.60 as Sheet-2, 0.66 as Sheet-3, 0.73 as Sheet-4, This was sheet 5. On the other hand, silicon oxide (SiO ₂ ) was sputtered onto a 12 μm biaxially stretched polyester resin sheet (Lumirror (registered trademark) P11 manufactured by Toray Industries, Inc.) to obtain a silicon oxide film-forming film having a thickness of 400 Å. Laminated products 2-5 are obtained by laminating the sputtering film on sheets 2-5 with the following adhesive.

Adhesive: Urethane adhesive (Adcoat (registered trademark) 76P1: manufactured by Toyo Morton Co., Ltd.)
The above-mentioned adhesive is blended at a ratio of 1 part by weight of the curing agent to 10 parts by weight of the main agent, adjusted to 30% by weight with ethyl acetate, and the coating thickness after solvent drying is applied to the non-sputtering surface of the sputtering film by the gravure roll method. It applied so that it might become a 5 micrometer thickness. The drying temperature was 100 ° C. In addition, the lamination was performed using a roll laminator at a temperature of 60 ° C. and a pressure of 1 kg / cm ² , and the curing condition was 60 ° C. for 3 days.

Comparative Example 1
Titanium dioxide fine particles having a number average particle size of 0.2 μm are 50% by weight of a master chip (the shape of the master chip is a cylinder length: 5.95 to 8.05 mm, width: 3.20 to 4.80 mm, height: 1. Sheet-1 having a PET polymer intrinsic viscosity of 0.55 (Comparative Example 1) obtained in the same manner as in Example 1 except that the thickness was 1.70 to 2.30 mm) was obtained in the same manner as in Example 1. The laminated product is designated as laminated product-1.

  Further, PET having a number average molecular weight of 41000 and a polymer intrinsic viscosity of 0.90 passed through the A and B layers could not be extruded.

  It can be seen that the polyester resin sheet laminates for solar cells of Examples 1 to 4 are superior in hydrolysis resistance as compared with Comparative Example 1, and the higher the degree of polymerization, the higher the hydrolysis resistance.・ It can be seen that the heat resistance is improved. It can be seen that the variation in optical density can be reduced by the smaller type due to the difference in chip shape.

Examples 5-7
In the same manner as in Examples 1 to 4, the same PET polymer as the B layer (number average molecular weight 21000, intrinsic viscosity 0.71, titanium dioxide particle concentration 14% by weight) was extruded into the A layer, and a substantially single layer structure (B layer / A layer / B layer = B layer / B layer / B layer). The amount of titanium oxide added in the single layer of PET is 5% by weight of sheet 7 (Example 5), 14% by weight of sheet 8 (Example 6), and 40% by weight of sheet 9 (implemented). As Example 7), three types of composite films were prepared, and a silicon oxide sputtering film was laminated on one side of each sheet in the same manner as in Examples 1 to 4, and the laminates were designated as laminates 7 to 9. Other parts were the same as those in Examples 1 to 4.

Comparative Examples 2 and 3
A polyester resin sheet was prepared in the same manner as in Example 5, except that the particle concentration and the master chip shape were changed. Master chip of 50% by weight of titanium dioxide fine particles having a number average particle diameter of 0.2 μm (chip shape is cylindrical, length: 5.95 to 8.05 mm, width: 3.20 to 4.80 mm, height: 1.70-2.30 mm) was used. In Comparative Example 2, the titanium dioxide concentration was 4% by weight, and the resulting sheet was Sheet-6. And the sheet | seat after lamination | stacking with a gas barrier layer was made into the laminated product-6. In Comparative Example 3, the titanium dioxide concentration was 45% by weight, and the resulting sheet was Sheet-10. And the sheet after lamination with the gas barrier layer was made into laminate product-10, but the filter part of the film formation was immediately clogged, the filtration pressure increased, and the filter had to be replaced, resulting in poor productivity. It was.

  It can be seen that the polyester resin sheet laminates for solar cells of Examples 5 to 7 are superior in optical density, optical density variation, total light transmittance, reflectance, and UV resistance as compared with Comparative Example 2. It can be seen that as the particle concentration is increased, the optical density, the optical density variation, the total light transmittance, the reflectance, and the UV resistance are similarly improved. However, it can be seen that if the particle concentration is increased too much, the gas barrier properties deteriorate, and the workability and productivity tend to deteriorate.

Examples 8-10
The number average molecular weight of the B layer PET was 21,000, the intrinsic viscosity was 0.71, the number average molecular weight of the A layer PET was 18300, and the intrinsic viscosity was 0.55 (both PET had a titanium dioxide particle concentration of 14 wt. %). These polymers were laminated through a laminating apparatus so as to be B layer / A layer / B layer, and formed into a sheet form from a T-die. The stacked configuration is a composite three-layer configuration. An unstretched sheet obtained by cooling and solidifying the sheet-like molded product discharged from the T die with a cooling drum having a surface temperature of 25 ° C. is led to a roll group heated to 85 to 98 ° C., and stretched 3.3 times in the longitudinal direction. It cooled with the roll group of 25 degreeC. Subsequently, the film was stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 220 ° C. in a tenter, and after uniform cooling, it was cooled to room temperature to obtain a sheet having a winding thickness of 250 μm.

  B-12 / A layer / B layer composite ratio [B layer / (A layer + B layer)] is 7.2% for sheet-12 (Example 8), 15% for sheet-13 (Example) 9) 20% of the sheet was used as Sheet-14 (Example 10). In the stretching method, aluminum was vacuum-deposited to a thickness of 600 Å on one side of the film. The vapor deposition is intended for gas barrier properties when using solar cells.

Also, silicon oxide (SiO ₂ ) was sputtered onto a 12 μm biaxially stretched polyester resin film (Lumirror (registered trademark) P11 manufactured by Toray Industries, Inc.) to obtain a silicon oxide film-forming film having a thickness of 400 Å. In a dry laminating machine, a polyurethane adhesive (main agent Takelac A515 / curing agent Takenate A50 = 10/1 solution) manufactured by Takeda Pharmaceutical Co., Ltd. having a solid content of 30% by weight as an adhesive on the surface of the deposited thin film layer of the sputtering film. A coating amount of 5 g / m ² (dry state) was applied, dried, and laminated with the sheets 12 to 14. Thus, the laminated body which provided the gas barrier layer on both sides was made into the laminated bodies -12-14, respectively.

Example 11
The number average molecular weight of PET of the A layer and the B layer was 21000, and the intrinsic viscosity was 0.71 (both PET had a titanium dioxide particle concentration of 14% by weight). These polymers were laminated through a laminating apparatus so as to be B layer / A layer / B layer, and formed into a sheet form from a T-die. The stacked configuration is a composite three-layer configuration. An unstretched sheet obtained by cooling and solidifying the sheet-like molded product discharged from the T die with a cooling drum having a surface temperature of 25 ° C. is led to a roll group heated to 85 to 98 ° C., and stretched 3.3 times in the longitudinal direction. It cooled with the roll group of 25 degreeC. Subsequently, the film was stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 220 ° C. in a tenter, and after uniform cooling, it was cooled to room temperature to obtain a sheet having a winding thickness of 250 μm.
The composite ratio of B layer / A layer / B layer [B layer / (A layer + B layer)] is 100%, and the sheet 15 (Example 11) is similarly measured for various physical properties without providing a gas barrier layer. did.

Comparative Examples 4 and 5
The number average molecular weight of PET of layer B is 21000, the intrinsic viscosity is 0.71, the number average molecular weight of PET of layer A is 18300, and the intrinsic viscosity is 0.55 (both PET has a titanium dioxide particle concentration of 14% by weight). Using these materials, these polymers were laminated through a laminating apparatus so as to be B layer / A layer / B layer, and formed into a sheet form from a T-die. The stacked configuration is a composite three-layer configuration.
A sheet having a composite ratio of B layer / A layer / B layer [B layer / (A layer + B layer)] of 6% (Comparative Example 4) was obtained. In Comparative Example 5, a PET having a number average molecular weight of 18300 and an intrinsic viscosity of 0.55 was used for the B layer PET as in the A layer PET. This sheet was successively stretched 3.0 times in the longitudinal direction of the sheet at a temperature of 90 ° C. by successive biaxial stretching methods, and then the film was supplied to the subsequent tenter and stretched 3.0 times in the width direction at a temperature of 95 ° C. Further, heat treatment was then performed at 220 ° C. to obtain 250 μm sheets of two different thicknesses. Furthermore, a laminate was obtained by the same method as in Example 8.

  Laminated products having a composite ratio of 6% as described above and a gas barrier layer laminated by the method of Example 8 are used for sheet 11, and the same number average molecular weight 18300 as for B layer PET is also used for B layer PET. This was Sheet-16.

Comparative Example 6
This sheet was designated as sheet 17 using a DuPont fluorine-based film “Tedlar” TWH20BS3 (50 μm). The sheet 17 was measured for the same items as in other examples.

  The polyester resin sheets for solar cells of Examples 8 to 10 are much more excellent in hydrolysis resistance than those of Comparative Example 4, and also satisfy various characteristics such as gas barrier properties, total light transmittance, and reflectivity. is doing. On the other hand, in Examples 8 to 10, the hydrolysis resistance is improved as the number of high molecular weight layers having a high number average molecular weight is increased, and the lamination ratio is required to be 7% or more (preferably 15% or more). It is found that it is preferable to use the high molecular weight layer as a whole. The polyester resin sheet for solar cell of Comparative Example 6 is a fluorine-based sheet using a polyvinyl fluoride sheet used in this field, and is excellent in weather resistance, hydrolysis resistance, light reflectivity, etc. The gas barrier properties and sheet stiffness are weak and the processability of solar cells is poor. For application in this field, it is necessary to make the sheet thicker or to provide a relatively thick metal layer as a gas barrier layer. Further, the sheet has a high apparent density, and considering this, it goes against the weight reduction that has recently been required.

Examples 12-19
The number average molecular weight of the B layer PET is 21000, the intrinsic viscosity is 0.71 (the titanium dioxide particle concentration of the B layer is 20% by weight), and the PET of the A layer is the number average molecular weight and titanium dioxide content described in Table 4. The number average molecular weight of PET in the C layer was 17450, and the intrinsic viscosity was 0.50 (the concentration of titanium dioxide particles in the C layer was 0% by weight). These polymers were laminated through a laminating apparatus so as to be B layer / A layer / B layer / C layer, and formed into a sheet form from a T-die. The laminated configuration is a composite four-layer configuration. An unstretched sheet obtained by cooling and solidifying the sheet-like molded product discharged from the T die with a cooling drum having a surface temperature of 25 ° C. is led to a roll group heated to 85 to 98 ° C., and stretched 3.3 times in the longitudinal direction. It cooled with the roll group of 25 degreeC. Subsequently, the film was stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 220 ° C. in a tenter, and after uniform cooling, it was cooled to room temperature, and each thickness sheet was obtained for each winding example. In accordance with the composite ratio of B layer / A layer / B layer / C layer, the C layer was discharged while changing the thickness for each example, and the ratio of the titanium dioxide-containing layer was changed. The total thickness of the polyester resin sheet is 325 μm, and the ratio of titanium dioxide-containing layer of [B layer / (A layer + B layer + C layer)] is 5.5% with respect to the entire sheet, and the thickness of the B layer / A layer / B layer Having a composite ratio of [B layer / (A layer + B layer)] of 7.2% was designated as Sheet-19 (Example 12). The total thickness of the polyester resin sheet is 313 μm, the titanium dioxide-containing layer ratio is 9% of the whole sheet, the thickness of B layer / A layer / B layer is 188 μm, [B layer / (A layer + B layer)] composite ratio Is 15% sheet-20 (Example 13), the total thickness of the polyester resin sheet is 238 μm, the titanium dioxide-containing layer ratio is 16% of the entire sheet, and the thickness of the B layer / A layer / B layer is A sheet having a composite ratio of 188 μm and [B layer / (A layer + B layer)] of 20% was designated as Sheet-21 (Example 14). The total thickness of the polyester resin sheet is 175 μm, the titanium dioxide-containing layer ratio is 17% with respect to the entire sheet, the B layer / A layer / B layer thickness is 100 μm, and [B layer / (A layer + B layer)] composite The ratio is 30% for sheet 22 (Example 15), the total thickness of the polyester resin sheet is 263 μm, the titanium dioxide-containing layer ratio is 21% with respect to the entire sheet, and the thickness of B layer / A layer / B layer is A sheet 23 (Example 16) having a composite ratio of 188 μm and [B layer / (A layer + B layer)] of 30% was used. The total thickness of the polyester resin sheet is 300 μm, the titanium dioxide-containing layer ratio is 17% of the whole sheet, and the B layer / A layer / B layer thickness is 50 μm [B layer / (A layer + B layer)] Is 100% of the sheet 24 (Example 17), the total thickness of the polyester resin sheet is 238 μm, the titanium dioxide-containing layer ratio is 21% with respect to the whole sheet, and the thickness of the B layer / A layer / B layer is 50 μm. , [B layer / (A layer + B layer)] A composite ratio of 100% was designated as sheet 25 (Example 18). The total thickness of the polyester resin sheet is 125 μm, the titanium dioxide-containing layer ratio is 40% of the whole sheet, the B layer / A layer / B layer thickness is 50 μm, and the [B layer / (A layer + B layer)] composite ratio Was made into a sheet 26 (Example 19). Subsequently, for all of Examples 12 to 19, aluminum was vacuum-deposited to a thickness of 600 angstroms from the B layer side on one side of the sheet. Each optical characteristic was measured from the B layer side.

Comparative Example 7
Number average molecular weight of layer B PET is 21000, intrinsic viscosity is 0.71, number average molecular weight of layer A PET is 18300, intrinsic viscosity is 0.55, number average molecular weight of layer C PET is 17450, intrinsic viscosity Was 0.50, and the titanium dioxide particle concentration in the B layer was 20% by weight. These polymers were laminated through a laminating apparatus so as to be B layer / A layer / B layer / C layer, and formed into a sheet form from a T-die. The stacked configuration is a composite three-layer configuration. An unstretched sheet obtained by cooling and solidifying the sheet-like molded product discharged from the T die with a cooling drum having a surface temperature of 25 ° C. is led to a roll group heated to 85 to 98 ° C., and stretched 3.3 times in the longitudinal direction. It cooled with the roll group of 25 degreeC. Subsequently, the film was stretched 3.6 times in the direction perpendicular to the longitudinal direction in an atmosphere heated to 130 ° C. while being guided to a tenter while holding both ends of the longitudinally stretched film with clips. Thereafter, heat setting was performed at 220 ° C. in a tenter, and after uniform cooling, it was cooled to room temperature to obtain a sheet having a winding thickness of 313 μm. B layer / A layer / B layer thickness is 188 μm, [B layer / (A layer + B layer)] composite ratio is 6%, and [B layer / (A layer + B layer + C layer)] contains titanium dioxide The layer ratio was 4.8%. Subsequently, in the same manner as in Examples 12 to 19, aluminum was vacuum-deposited to a thickness of 600 angstroms from the B layer side on one side of the sheet. Each optical characteristic was measured from the B layer side.

  The film thickness is important for increasing the breakdown voltage of the partial discharge start voltage. The co-extrusion of the polyester resin layer of the present invention and the other polyester layer is carried out in order to increase the thickness. As can be seen from Table 4, even in the co-extruded polyester resin sheet for solar cells, the polyester resin layer is composed of a plurality of layers, and the layer containing 5 to 40% by weight of titanium dioxide is a polyester resin sheet (B layer / A layer). It can be seen that suitable characteristics can be obtained when the polyester resin sheet is 7% or more of the thickness of the / B layer). In Comparative Example 7, when the titanium dioxide-containing layer is less than 7% with respect to the entire sheet, the weather resistance and optical properties are not satisfied. Since the optical properties improve as the titanium dioxide-containing layer ratio increases, it is desirable to increase the ratio so as to satisfy the above range in the polyester resin sheet for solar cells. However, in order to reduce costs, a method of increasing the thickness by laminating other than the polyester resin sheet for solar cells of the present invention can also be considered.

  The polyester resin sheet for solar cells of the present invention can be suitably used not only for solar cells used as roofing materials, but also for flexible solar cells and electronic components.

DESCRIPTION OF SYMBOLS 1 All light transmissive material 2 Solar cell 3 Filling resin 4 Solar cell back surface protection sheet 5 Lead wire 6 Water vapor | steam and gas barrier layer 7 Polyester resin layer (A layer)
8 Polyester resin layer (B layer)
DESCRIPTION OF SYMBOLS 9 Adhesive layer 10 Solar cell module 20 Thermoplastic resin sheet laminated article 21 for solar cells Base material sheet 22 Metal or inorganic oxide layer 30 Thermoplastic resin sheet for solar cells

Claims (11)

Polyester resin sheet having a polyester resin layer using one or more layers having a number average molecular weight of 18500 to 40,000, and having at least one layer having 5 to 40 wt% titanium dioxide in the polyester resin layer Because
The light transmittance at a wavelength of 300 to 350 nm is 0.005 to 10%,
Relative reflectance is 80% or more and 105% or less,
An apparent density of 1.37 to 1.65 g / cm ³ ,
The optical density is 0.55 to 3.50,
The polyester resin sheet for solar cells whose optical density variation is within 20% of the central value. The polyester resin sheet for a solar cell according to claim 1, wherein the optical density variation is within 15% of the center value. The polyester resin sheet for solar cells according to claim 1, wherein the total light transmittance of the thermoplastic resin sheet is 0.005 to 25%. 2. The thermoplastic resin sheet for solar cells according to claim 1, wherein the thickness of the layer having 5 to 40 wt% titanium dioxide is 7 to 100% of the thickness of the entire polyester resin layer. The polyester resin sheet for solar cells according to claim 1, wherein the elongation retention before and after aging for 3000 hours is 40 to 100% in an environment of a temperature of 85 ° C and a humidity of 85% RH. The polyester resin sheet for solar cells according to claim 1, wherein the elongation retention before and after aging for 15 hours is 40 to 100% in an environment of a temperature of 140 ° C. The polyester resin sheet for solar cells of Claim 1 which has a gas and water vapor | steam barrier layer. A polyester resin sheet laminate for a solar cell in which at least the polyester resin sheet according to claim 1 and a gas and water vapor barrier layer are laminated. The water vapor transmission rate according to JIS-K-7129 is such that the water vapor transmission rate in terms of 100 µm is 0.5 g / (m ² · 24 hr) or less at a temperature of 40 ° C and a humidity of 90% RH. Polyester resin sheet laminate for solar cells. The solar cell back surface protection sheet used for the back surface sealing material of a solar cell, which is a polyester resin sheet for solar cells or a polyester resin sheet laminate for solar cells according to claim 1. The solar cell module using the solar cell back surface protection sheet of Claim 10.

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