JP2013016864A - Film for backside sealing of solar cell and solar cell using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the environmental resistance, e.g., hydrolysis resistance or weather resistance, by using an inexpensive PET-BO having excellent mechanical characteristics and heat resistance, and to provide a film for backside sealing of a solar cell which ensures a high reflectance advantageous for conversion efficiency of sunlight, reduction of leakage current and lightweight, and a solar cell using the same.SOLUTION: The film for backside sealing of a solar cell has a gas barrier layer combining a polyethylene terephthalate film. The polyethylene terephthalate film is composed of a polymer having a number-average molecular weight in the range of 18500-40000, and has a thickness of 7% or more of the total film thickness. The solar cell uses the film for backside sealing of a solar cell in a solar cell system.

Description

  INDUSTRIAL APPLICABILITY The present invention is a solar cell back surface sealing film that is inexpensive and excellent in environmental resistance (hydrolysis resistance, weather resistance, etc.), and that is optimal for fields where reflection efficiency and light weight on the back side are required, and the same. It relates to solar cells.

  In recent years, solar cells have attracted attention as the next-generation energy source, and development is progressing from the construction field to electrical and electronic parts. The solar cell back surface sealing film used for a part of the components of the electrical ground is also strongly required to have durability (hydrolysis resistance and weather resistance) against the natural environment. Furthermore, the improvement of the solar light conversion efficiency of a battery is also requested | required and it converts even the reflected light of the back surface sealing film of a solar cell. There is also a demand for lightness, strength, and battery processability.

  As a solar cell back surface sealing film, it is known to use a polyethylene-based resin or a polyester-based resin sheet, or to use a fluorine-based film (Patent Documents 1 and 2).

  In addition, bi-axially stretched polyethylene terephthalate film (hereinafter referred to as PET-BO) colored in white for the purpose of converting reflected light by each manufacturer to improve the conversion efficiency, and PET-BO or fluorine-based in black for decoration purposes. Solar cells using the film as a backside sealing film are on the market.

  Moreover, a heat-resistant polyester film is known as an electrical insulation film, and is known for its low oligomerization and improved heat resistance (Patent Documents 3 and 4). Moreover, the polyester film which has a bubble is known (patent document 5). However, these films are not used as back surface sealing films for solar cells.

JP-A-11-261085 JP-A-11-186575 JP 58-209530 A JP 58-36573 A Japanese Patent Publication No. 7-37098

  That is, these conventional film base materials have the following problems.

  Conventionally, PET-BO 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. Also, white-colored PET-BO has improved reflection efficiency but has poor hydrolysis resistance.

  In addition, the fluorine-based film is excellent in hydrolysis resistance and weather resistance, but has a drawback that it has poor gas barrier properties (particularly water vapor barrier properties) and the film is weak. Therefore, such a film 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 back surface sealing film layer.

  However, this is contrary to the purpose of this field where weight reduction is required, and it is disadvantageous in terms of cost.

  Moreover, although the thing using a polyethylene sheet is comparatively cheap, there existed difficulty in the heat resistance when exposed to high temperature (100-120 degreeC).

  In view of the background of such prior art, the present invention improves the environmental resistance such as hydrolysis resistance and weather resistance using PET-BO having inexpensive and excellent mechanical properties and heat resistance, It is an object of the present invention to provide a solar cell back surface sealing film that imparts a high reflectivity advantageous in conversion efficiency, a reduction in leakage current, and lightweight, and a solar cell using the same.

  The present invention employs the following means in order to solve such problems. That is, the solar cell back surface sealing film of the present invention is a film having a gas barrier layer combined with a polyethylene terephthalate film, and the polyethylene terephthalate film is composed of a polymer having a number average molecular weight of 18500 to 40,000. And having a thickness of 7% or more of the total film thickness. Moreover, the solar cell of the present invention is characterized by using such a solar cell back surface sealing film in a solar cell system.

  According to the present invention, despite the use of a relatively inexpensive PET film, hydrolysis resistance and weather resistance are improved, and the conversion efficiency of the solar cell is further improved due to high reflectivity and reduced leakage current. In addition, the weight can be reduced.

This figure shows sectional drawing of the solar cell which uses the solar cell backside sealing film of this invention. This figure is sectional drawing which shows an example of the structure of the solar cell backside sealing film which has a gas barrier layer in the single side | surface of a film. This figure is sectional drawing of another example which shows the structure of the solar cell backside sealing film which has a gas barrier layer between two layers of films.

  The present invention is advantageous in improving the environmental resistance such as hydrolysis resistance and weather resistance using PET-BO having the above-mentioned problems, that is, inexpensive and excellent mechanical properties and heat resistance, and solar conversion efficiency. Surprisingly about the solar cell backside sealing film that gives high reflectivity, reduced leakage current and light weight, I tried to compose a gas barrier film with a specific polyethylene terephthalate film. It has also been clarified that such problems can be solved at once.

  The solar cell referred to in the present invention refers to a system that converts sunlight into electricity and stores the electricity, and preferably has a high light transmission material, a solar cell module, a filling resin layer, and a back surface sealing film as a basic configuration. There are, for example, the structure shown in FIG. 1, which is incorporated in the roof of a house, and is used for electricity, electronic parts, etc. and has a flexible property.

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

  The filled resin layer is used for the purpose of fixing and protecting the solar cell module in the solar cell and for electrical insulation, and among them, ethylene vinyl acetate resin is preferably used in terms of performance and price.

  In addition, the solar cell back surface sealing film referred to in the present invention is an important role in protecting the solar cell module on the back side of the solar cell, and the film is most disliked by the solar cell module. In order to cut off, a layer provided with a water vapor barrier layer (water vapor barrier layer) is used as shown in FIGS.

Here, the gas barrier layer referred to in the present invention means a layer having a water vapor barrier property, for example, a metal or a metal oxide provided as a layer between the surface layer or two layers of the film. , transmission values of water vapor measured according to the standard of JIS Z0208-73 is preferably refers to a layer that can achieve the following 2.0g ^/ m 2 /24Hr/0.1mm. As such a metal, aluminum is preferably used, and as a metal oxide, a silicon oxide is preferably used. Further, such a gas barrier layer has a function of reflecting the sunlight leaking from the electric ground portion and also converting the reflected light to improve the conversion efficiency.

  As the solar cell back surface sealing film of the present invention, a polyethylene terephthalate biaxially stretched film (PET-BO) provided with the above water vapor barrier layer is preferably used.

  Here, polyethylene terephthalate is a crystalline thermoplastic resin obtained by using terephthalic acid and its derivative as a dicarboxylic acid component and ethylene glycol as a glycol component, and polymerizing them by an esterification reaction. The melting point of such polyethylene terephthalate is preferably 250 ° C. or higher in view of heat resistance, and preferably 300 ° C. or lower in view of productivity. Within this range, other components may be copolymerized or blended. Further, if there is no problem in terms of mechanical properties and productivity, additives such as a slip agent, a colorant, an antistatic agent, a low density agent and the like may be added in a range of, for example, 50% by weight or less. Good.

  The biaxially stretched film refers to a film obtained by subjecting an unstretched and non-oriented sheet obtained by melt molding the above polymer to biaxial stretching and heat treatment. The thickness of the film is preferably in the range of 20 to 200 μm from the viewpoint of appropriate waist strength, processability, and light weight of the solar cell as a solar cell back surface sealing film.

  Here, the PET-BO layer of the solar cell backside sealing film of the present invention is present as a layer having a thickness of 7% or more, more preferably 10% or more of the total thickness of the sealing film, and Such a PET-BO layer is composed of a high molecular weight polyethylene terephthalate having a number average molecular weight of 18500 to 40000, preferably in the range of 1900 to 35000, in order to impart hydrolysis resistance.

  Here, the number average molecular weight is measured by a sol permeation chromatography method (GPC method) described later. When the thickness of the high molecular weight layer is less than 7%, the hydrolysis resistance of ordinary PET-BO is improved. The film for sealing the back surface of the solar cell is rapidly deteriorated. In addition, when the molecular weight exceeds 40,000, it is substantially impossible to polymerize, and those having a molecular weight of 35,000 or less are preferable in view of melt moldability and biaxial stretchability.

  Moreover, this PET-BO layer may be laminated | stacked in any form of the front-back surface or this single side | surface of this sealing film, and even if it is any form, with respect to the total thickness of this sealing film In other words, it is sufficient that the layers are laminated with a thickness of 7% or more.

  In order to effectively prevent hydrolysis degradation of the solar cell back surface sealing film of the present invention, it is preferable that the film is laminated on both surfaces. Moreover, it is preferable that the PET-BO layer of the present invention contains an ultraviolet absorber by a method such as blending or surface coating. In addition, dyes, colorants, fluorescent brighteners, and the like may be colored in each color by blending, coating, dyeing, and the like. Especially, it is especially preferable that it is colored white from the surface of the improvement of a surface reflectance, and a weather resistance. The whiteness in that case is preferably 75% or more as measured by a color difference hunter method. When the whiteness is less than 75%, the reflectance is low, and the effect of improving the conversion efficiency of the solar cell tends to be lost. In addition, the 100 μm-thickness optical density (F) measured by an optical densitometer is preferably 0.8 or more (particularly preferably 1.0 or more) from the concealability inside the solar cell.

As PET-BO of the present invention, bubbles are provided in the film, and an apparent density of 1.37 to 0.85 g / cm ³ , preferably 1.35 to 0.9, improves the conversion efficiency of the solar cell. It is particularly preferably used in terms of reducing leakage current (an effect of lowering the dielectric constant of the base material) and reducing the weight. Here, the apparent density is a value measured with an electromagnetic scale. When the density of the low apparent density layer exceeds 1.37 g / cm ³ , there is no effect of reducing the dielectric constant, and the light weight effect is lost. If the density is less than 0.85 g / m ³ , the mechanical strength, electrical insulation and gas barrier properties are lowered, and the use as the solar cell back surface sealing film of the present invention tends to be difficult.

  In addition, the film having a relatively low apparent density is particularly a composite of a film layer having no air bubbles on at least one side of the film having the above apparent density, considering the mechanical strength and protecting the surface layer of the film (preventing scratches, etc.). Preferably used. In this case, the surface layer of the film is particularly preferably one using PET-BO having a number average molecular weight of 18500 to 40,000 in a thickness direction of 7% or more in the present invention. Of course, the high molecular weight PET layer alone having the above apparent density may be used. In the solar cell back surface sealing film of the present invention, two or more such films may be stacked and used.

  Next, an example of the method for producing the solar cell back surface sealing film of the present invention will be described.

  The method for producing polyethylene terephthalate (PET) of the present invention can be obtained by transesterification of terephthalic acid or a derivative thereof and ethylene glycol by a known method. Conventionally known reaction catalysts and anti-coloring agents can be used. Examples of reaction catalysts include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, cobalt compounds. Examples of coloring inhibitors such as titanium compounds include phosphorus compounds. Preferably, an antimony compound, a germanium compound, or a titanium compound is preferably added as a polymerization catalyst at an arbitrary stage before the production of PET is completed. As such a method, for example, when a germanium compound is taken as an example, a germanium compound powder is added as it is or in a glycol component which is a starting material of PET as described in Japanese Patent Publication No. 54-22234. Examples thereof include a method of dissolving and adding a germanium compound.

  The method for controlling the number average molecular weight of the present invention to 18500 to 40,000 (preferably 19000 to 35000) is the following method. After polymerizing a normal PET polymer having a number average molecular weight of 18000 at one end, the melting point of 190 ° C. to PET A so-called solid-phase polymerization method in which heating is performed at a temperature lower than that under reduced pressure or a flow of an inert gas such as nitrogen gas is preferable. The method can increase the number average molecular weight without increasing the amount of unterminated carboxyl groups in PET.

  Next, in order to convert the polymer into a biaxially stretched film, the polymer is dried as necessary, supplied to a known melt extruder, the sheet is extruded from a slit-shaped die, and the polymer is adhered to a metal drum. The film is cooled to a temperature below the glass transition point of to obtain an unstretched film. A biaxially stretched film can be obtained by a known method such as a simultaneous biaxial stretching method or a sequential biaxial stretching method. As the conditions in this case, the stretching temperature can be selected from the glass transition point of the polymer (hereinafter sometimes abbreviated as Tg) to Tg + 100 ° C., and the final temperature range is usually from 80 to 170 ° C. It is preferable from the physical properties and productivity of the film obtained. The stretching ratio can be in the range of 1.6 to 5.0 (preferably 1.7 to 4.5) in both the longitudinal direction and the width direction of the film. The stretching speed is preferably 1000 to 200000% / min. Further, the film is heat-treated after stretching. However, the film can be heat-treated continuously in a heat-treating chamber following the tenter that extends in the width direction, heated in another oven, or heat-treated with a heating roll. As heat treatment conditions, a temperature range of 120 to 245 ° C. and a time range of 1 to 60 seconds is usually used. Relaxing treatment may be performed for the purpose of improving thermal dimensional stability in the width direction and the longitudinal direction during heat treatment.

  The PET-BO for solar cell back surface sealing of the present invention has a high molecular weight PET having a thickness of 7% or more in the thickness direction of the film and a number average molecular weight of 18500 to 40,000. The method of combining the normal molecular weight PET-BO layer and the high molecular weight PET-BO layer is to supply each polymer to a separate extruder during the melt extrusion, and melt both the polymers in a composite facility provided in the melt flow path. A method is generally used in which the composite unstretched sheet is prepared and the composite unstretched sheet is prepared and stretched and heat-treated under the above conditions. This method can be a two-layer laminate of normal PET-BO and a high molecular weight PET-BO, or a three-layer laminate of, for example, high molecular weight PET / normal PET-BO / high molecular weight PET-BO.

  The PET-BO of the present invention can color the film in various ways by adding a colorant, a dye or the like during polymerization of the polymer or in a melt extruder. In particular, the PET-BO of the present invention is preferably colored white. When coloring white, a white additive such as titanium oxide, silica, alumina, calcium carbonate, barium sulfate is added. In order to further increase the whiteness, it is effective to use a fluorescent whitening agent such as thiophenediyl.

Then, giving bubbles in the PET-BO, methods apparent density of the film, 1.37~0.85g / cm ^3, preferably to obtain a film of 1.35~0.90g / cm ³ is, PET Incompatible polymers and fine particles (organic particles, inorganic particles) can be added to the PET to produce (stretch) PET-BO.

  The incompatible polymer and fine particles are not particularly limited as long as the apparent density of the present invention can be obtained. Specific examples of such incompatible polymers include polyethylene, polypropylene, polybutene, polymethylpentene and the like. The polymer may be a homopolymer or a copolymer. Among them, polyolefin having a small critical surface tension is preferable, and polypropylene, polymethylpentene, and the like are preferable in terms of density reduction, heat resistance, and dielectric constant reduction.

  These exist in a granular form in PET, and a compatibilizing agent may be added to control the particle size. As such a compatibilizing agent, for example, polyalkylene glycol or a copolymer thereof can be used, and specifically, polyethylene glycol, polypropylene glycol or the like is preferably used. Further, a surfactant or the like can be added to such an incompatible polymer to make it finer, but it can be added within a range that does not affect electrical characteristics, heat resistance, hydrolysis resistance, and the like.

  Further, specific examples of such fine particles include organic particles and inorganic particles. Examples of organic particles include silicon particles, polyimide particles, crosslinked styrene-divinylbenzene copolymer particles, crosslinked polyester particles, fluorine-based particles, and the like. Is used. As the inorganic particles, calcium carbonate, silicon dioxide, barium sulfate or the like is used.

  Next, the method of adding such an incompatible polymer or fine particles to PET is not particularly limited, but when an incompatible polymer is used, it is supplied to an extruder, and the extruder is sheared. A method of dispersing using force is advantageous in terms of cost. Moreover, when using microparticles | fine-particles, the method of adding in a superposition | polymerization stage is preferable. Specifically, a method of adding to ethylene glycol is preferable. In addition, it is preferable to add a phosphorus compound to the calcium carbonate particles to prevent yellowing and foaming.

  In addition, the method of laminating low-density PET-BO and normal PET-BO (non-low-density film) is to laminate (composite) both polymers in the molten state as described above, and to add 2 unstretched sheets of the laminated sheet. A method of stretching heat treatment on the shaft is preferably used because the thickness of each laminated layer can be easily controlled.

  Next, a method for imparting gas barrier properties to the film of the present invention will be described.

  In order to impart gas barrier properties, a metal oxide such as silicon oxide or aluminum oxide or a metal such as aluminum is provided on the surface of the film by a known method such as vacuum deposition or sputtering. Its thickness is usually in the range of 100 to 2000 angstroms. In this case, there is a method in which a gas barrier layer is provided on a film different from the case where a gas barrier layer is provided directly on the film, and this film is laminated on the film surface of the present invention. Moreover, the method of laminating | stacking metal foil (for example, a common thing is 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 does not necessarily have to be on the surface of the film, and may be sandwiched between, for example, two layers of films.

  The solar cell of the present invention is systemized with the configuration shown in Table 1, for example. That is, a base material (glass, film, etc.) having high light transmittance is placed on the surface layer, and a silicon-based solar cell module is provided with a lead wire that can take out electricity and fixed with a filling resin such as ethylene vinyl acetate resin. And it is obtained by providing the back side sealing film of the present invention on the back side (back side) and fixing with an exterior material.

  The following examples illustrate the present invention in more detail.

<Physical properties and evaluation methods, evaluation criteria>
(1) Number average molecular weight (Mn)
A composite or single film was sampled and measured by gel permeation chromatography (GPC). The composite film was sampled by polishing the film while observing under a microscope.
(1) Apparatus: Gel permeation chromatograph GCP-244 (manufactured by WATERS)
(2) Data processing: GPC data processing system manufactured by Toray Research Center, Inc. (3) Column: Two Shodex HFIP 80M (manufactured by Showa Denko KK)
(4) Solvent: Hexafluoropropanol (0.005N-sodium trifluoroacetate)
(5) Flow rate: 0.5ml / min
(6) Temperature: 23 ° C
(7) Sample concentration: 0.06%
Solubility: Complete dissolution Filtration: Maisho Disc W-13-5
(8) Injection volume: 0.300ml
(9) Detector: R-401 type differential refractometer (WATERS)
(10) Molecular weight fair: PET-DMT (standard product).

(2) Whiteness (Hunter method)
The following numerical values were measured with a color difference meter (Nippon Denshoku Co., Ltd .: ND-300A) and obtained from the following formula for calculating the whiteness.
Whiteness (W) = 100 − [(100−L) ² + a ² + b ² ] ^1/2
L: Lightness, a: Saturation, b: Hue.

(3) Optical density (100 μm thickness conversion value: F)
The transmitted light flux was measured with an optical densitometer (Macbeth: TR-524) and calculated according to the following formula.
Light source: visible light spectral composition; tungsten temperature measurement environment: color temperature 3006 ° K (second constant of radiation C ₂ = 14380 μ °): temperature 23 ± 3 ° C., humidity 65 ± 10% RH
Calculation formula: Optical density = log ₁₀ (F ₀ / F) 100 / d
F: Sample transmitted light beam F ₀ : Sample-free transmitted beam d: Film thickness.

(4) Apparent density Measured with an electromagnetic balance (SD-120L manufactured by Kensei Kogyo Co., Ltd.).

(5) Hydrolysis resistance A ratio when the film was aged in an atmosphere of 85 ° C. to 93% RH, the breaking elongation of the film was measured by ASTM-D61T, and the breaking elongation without aging was 100% (retained) Rate) and judged according to the following criteria.
○: Retention rate is 50% or more Δ: Retention rate is 30% to 50%
X: Retention rate is less than 30%.

(6) Weather resistance Using an accelerated tester ice par UW tester, the following cycle was repeated 5 times, and the retention rate was determined by the tensile test method of (5) and evaluated according to the following criteria.
1 cycle: UV irradiation for 8 hours in an atmosphere at a temperature of 60 ° C. and a humidity of 50% RH, followed by aging for 4 hours in a dew condensation state (temperature 35 ° C., humidity 100% RH).
UV irradiation intensity: 100 mW / cm ²
○: Retention rate is 50% or more Δ: Retention rate is 30-50%
X: Retention rate is less than 30%.

(7) Reflection efficiency Visible light (550 nm) was applied to the gold surface (1000 angstroms) on which gold was vapor-deposited on a glass plate having a thickness of 0.5 mm, and the reflected light was passed through a spectrometer to change the reflected light into an electric current. Detect numerical values. This value (T ₀ ) is set to 100. Next, a film was placed on black paper, and the value (T) in which reflected light was changed to current was measured in the same manner as T _0, and the reflection efficiency was calculated by the following equation.
Reflection efficiency = T / T ₀ × 100.

(8) Reflectivity Judging from the value of (7) above, the effect of the conversion rate of reflected light was assumed and the determination was made according to the following criteria.
○: Reflection efficiency is 50% or more Δ: Reflection efficiency is 30-50%
X: Reflection efficiency is less than 30%.

(9) Gas barrier properties The water vapor transmission rate was measured according to JIS Z0208-73. The measurement conditions were a temperature of 40 ° C. and 90% RH.

(10) Workability A 1 m square solar cell back surface sealing film was prepared, and the waist strength in consideration of the ease of incorporation into the solar cell system was determined according to the following criteria.
○: Level of waist strength is appropriate and 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 in which the waist is too weak or too strong and clearly has difficulty in workability.

(11) Electrical insulation The dielectric breakdown strength (dielectric breakdown voltage per 1 mm of film thickness) was measured according to JIS C2151, and the electrical insulation was judged as follows based on the numerical value of 20 kV / mm required in this field.
○: 25 kV / mm or more Δ: 20-25 kV / mm
X: Less than 20 kV / mm.

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

(13) Composite ratio of composite film [PET-2 / (PET-1 + PET-2)]
The cross section of the composite film was observed with an electron microscope and determined from a cross-sectional photograph.

[Examples 1 to 3, Comparative Example 1]
Mixing 100 parts of dimethyl terephthalate (hereinafter, parts by weight) with 64 parts of ethylene glycol, adding 0.1 part of zinc acetate and 0.03 part of antimony trioxide as a catalyst, and performing transesterification at the reflux temperature of ethylene glycol It was.

  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 (PET) was 0.55. The polymer was cut into chips having a length of 4 mm. This polymer is designated as PET-1.

  This PET-1 was placed in a rotary vacuum device (rotary vacuum dryer) having a temperature of 220 ° C. and a degree of vacuum of 0.5 mmHg, and heated with stirring for 20 hours. The intrinsic viscosity of the obtained PET was 0.73. This polymer is designated as PET-2.

  Each of the PET-1 and PET-2 obtained above was vacuum-dried at a temperature of 180 ° C., a vacuum degree of 0.5 mmHg and a time of 2 hours, and a weathering agent (ultraviolet absorber: Tinuvin (registered trademark) P: Ciba Specialty Chemicals) (Made by Co., Ltd.) is blended in 5% by weight, put into separate extruders, and passed through an apparatus (Pinol) capable of combining the two kinds of polymers in the melt flow path. PET-2 / PET-1 / PET- A molten sheet having a composite structure of 2 was extruded from a T die, and was cast by applying electrostatic force to a cooling drum maintained at 25 ° C. The thickness of the obtained sheet was 0.7 mm. The extrusion temperature for both polymers was 270-290 ° C. The diameter of the PET-1 extruder was 90 mm, and the diameter of the PET-2 extruder was 40 mm. The extrusion amount of both extruders was controlled, and the above composite ratio [PET-2 / (PET-1 + PET-2)] was obtained in 4 types of 6%, 7.2%, 11% and 20%.

  This sheet was stretched 3.0 times in the longitudinal direction of the film 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. Furthermore, it heat-processed at 220 degreeC after that, and obtained the film of 4 types of thickness 50 micrometers.

  The composite ratio of 6% was film-1, the 7.2% film was film-2, the 11% film was film-3, and the 20% film was film-4. Aluminum was vacuum deposited on one side of the film to a thickness of 600 angstroms. The vapor deposition is intended for reflectivity when using solar cells.

On the other hand, silicon oxide (SiO ₂ ) was sputtered onto 12 μm PET-BO (Toray Lumirror (registered trademark) P11) to obtain a silicon oxide film-forming film having a thickness of 800 Å. The sputtering film was laminated on one side of the films 1 to 4 (opposite side of the aluminum vapor deposition side) through the following adhesive.
Adhesive; Urethane adhesive (Adcoat (registered trademark) 76P1: manufactured by Toyo Morton Co., Ltd.)
The above adhesive is mixed at a ratio of 1 part by weight of the curing agent with respect to 10 parts by weight of the main agent, adjusted to 30% by weight with ethyl acetate, and the coating thickness after drying the solvent by the gravure roll method is applied to the non-sputtering surface of the sputtering film. It apply | coated so that it might become thickness of 5 micrometers. 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, and the curing condition was 60 ° C. for 3 days. The obtained four types of films were designated as sealing films-1 to 4.

[Comparative Example 2]
PET-5 obtained by the method of Example 1 was obtained by the method of Example 1 to obtain a film-5 having a thickness of 50 μm and consisting of PET-1 alone. A film for sealing the back surface of a solar cell was produced from the film by the method of Example 1 (referred to as sealing film-5).

Table 1 shows the evaluation results of the five types of solar cell back surface sealing films of Examples 1 to 3 and Comparative Examples 1 and 2.
Shown in

  The solar cell back surface sealing films of Examples 1 to 3 are much more resistant to hydrolysis than those of Comparative Examples, and also have various properties such as gas barrier properties, electrical insulation properties, and reflectivity. Is pleased.

  On the other hand, the thing of the comparative example 1 is not enough hydrolysis resistance. In addition, it is understood that the hydrolysis resistance is improved as the number of high molecular weight film layers having a high number average molecular weight is increased, and the lamination ratio is required to be 7% or more (preferably 10%).

[Examples 4 to 6, Comparative Example 3]
In the polymerization of PET-2 obtained by the method of Example 1, the temperature for high polymerization was changed from 190 to 230 ° C. for 10 to 23 hours, and the intrinsic viscosity of the polymer was 0.60, 0.66, 0.70. , 0.81 of four types of PET polymers were obtained. 17% by weight of titanium oxide fine particles with an average particle diameter of 0.5μm and UV brightening agent (UVITEX OB: manufactured by Ciba Specialty Chemicals Co., Ltd.) 0.2 wt%, and the polymerization degree of the surface PET layer is different in the method and composite structure of Example 1, and four types of composite biaxially stretched PET films with a thickness of 50 μm colored in white (composite ratio is As in Example 3). However, unlike the case of Example 1, no weathering agent was added.

  A silicon oxide sputtering film is laminated on the obtained film by the method of Example, and four types of sealing films (in which the intrinsic viscosity of the polymer is 0.60 to 0.81 are sequentially set as sealing films-6 to 9). ) In addition, aluminum vapor deposition was not performed to the opposite surface of the silicon oxide sputtering film lamination surface like Example 1.

[Comparative Example 4]
A biaxially stretched PET film composed of a PET polymer alone with titanium oxide and fluorescent whitening agent added to PET-1 (PET-1 used in Example 4) was prepared by the method of Comparative Example 2, and the method of Example 4 Thus, a solar cell back surface sealing film was produced (referred to as sealing film-10).

  Table 2 shows the evaluation results of the solar cell back surface sealing films of Examples 4 to 6 and Comparative Examples 3 and 4.

  The solar cell back surface sealing films of the present invention of Examples 4 to 6 are whitened, and have a weather resistance despite using no ultraviolet absorber as compared with Examples 1 to 3 in Table 1. It can be seen that the reflectivity of light is increased and the reflectivity is further improved. On the other hand, the sealing film of Comparative Example 3 is the same as in Comparative Example 1, and the thickness ratio of high molecular weight PET (PET-2) is less than 7% in the present invention. The hydrolysis resistance is not improved. The same is true for Comparative Example 4, and the hydrolysis resistance is not improved even when whitened because it does not have a layer of high molecular weight PET (PET-2).

[Examples 7 to 9]
Three types of composite films were prepared by adding the titanium oxide addition amounts of 5% by weight, 8% by weight, and 15% by weight using the method and composite structure of Example 5, and the same manner as in Example 5 was made on one side of each film. A silicon oxide sputtering film was laminated. It is set as the sealing films 11-13 in order from the thing with the addition amount of a titanium oxide of 5 weight%.

  The solar cell backside sealing films of the present invention of Examples 7 to 9 are obtained by changing the whiteness by changing the addition amount of titanium oxide. The sealing film of Example 7 with a small amount of titanium oxide added has low whiteness and tends to have a low reflectance. Moreover, when compared with the reflectance of the sealing films of Examples 1 to 3 in Table 1, it is also found that the whiteness is preferably 75 or more and the optical density (100 μm conversion; F) is preferably 0.8 or more.

Example 10
Transesterification was conducted according to a conventional method using 100 parts by weight of dimethylene terephthalate, 64 parts by weight of ethylene glycol and 0.09 part by weight of calcium acetate as a catalyst, and an ethylene glycol solution containing 0.20% by weight of trimethyl phosphate was added. An ethylene glycol slurry containing 7% by weight of calcium carbonate having a diameter of 1.1 μm was added to obtain 0.03% by weight of antimony trioxide to obtain a PET polymer having an intrinsic viscosity of 0.58. The polymer and highly polymerized PET used in Example 5 were made into a composite biaxially stretched film by the method and composite structure of Example 5. The stretching conditions were such that the stretching temperature was 95 ° C. for both axes, and the stretching ratio was 3.2 times for both axes. The film was laminated with a silicon oxide sputtering film in the same manner as in Example 5 to obtain a sealing film-14.

Example 11
In the method of Example 10, the amount of calcium carbonate added was 12% by weight, the stretching temperature of the film was 92 ° C. on both axes, and the stretching ratio was 2.9 times vertically and 3.0 times horizontally. Other conditions were the same as in Example 10. The solar cell back surface sealing film thus obtained is referred to as sealing film-15.

Example 12
In the method of Example 10, the amount of calcium carbonate added was 30% by weight, the stretching temperature of the film was 85 ° C. on both axes, and the stretching ratio was 3.2 times vertically and 3.1 times horizontally. Other conditions were the same as in Example 10. The solar cell back surface sealing film thus obtained is referred to as sealing film-16.

Example 13
In the method of Example 10, the amount of calcium carbonate added was 12 wt%, the stretching temperature of the film was 95 ° C. on both axes, and the stretching ratio was 4.2 times vertically and 4.3 times horizontally. Other conditions were the same as in Example 10. The solar cell back surface sealing film thus obtained is referred to as sealing film-17.

[Comparative Example 5]
As a film, a fluorine-based film Tedlar (registered trademark) TWH20BS3 (50 μm) manufactured by DuPont was used, and a silicon oxide sputtering film was laminated by the method of Example 1. The thus produced solar cell back surface sealing film was sealed. It is set as a stop film-18.

  The evaluation results of the solar cell back surface sealing films of Examples 10 to 13 and Comparative Example 5 are shown in Tables 3 and 4.

  The solar cell backside sealing films of the present invention of Examples 10 to 13 are those in which bubbles are formed in PET-1 (normal molecular weight PET polymer layer), and a highly polymerized PET layer (PET-2) is combined on both surface layers. It is. The apparent density was lowered in order from the sealing film of Example 10. When the density is 1.37 (preferably 1.35 or less) or less, the effect of reducing the dielectric constant necessary for preventing leakage current is exhibited. When the density is reduced, the effects of reducing the dielectric constant and reducing the weight are increased, but the electrical insulation properties, the processability to solar cells are lowered, and the gas barrier properties tend to be lowered. In this respect, the density is preferably 0.8 or more (preferably 0.9 or more).

  The solar cell back surface sealing film of Comparative Example 5 is a fluorine-based film using a polyvinyl fluoride film used in this field, and the evaluation results are shown in Table 4.

  The weather resistance, hydrolysis resistance, light reflectivity, etc. are excellent, but the electrical insulation, gas barrier properties and film stiffness are weak and the processability of solar cells is poor. For application in this field, it is necessary to make the film thicker or provide a relatively thick metal layer as a gas barrier layer. In addition, the film has a high apparent density, and considering this fact, it goes against the recent demand for weight reduction. Further, there is a problem that the dielectric constant for preventing leakage current for improving the conversion efficiency of the solar cell is high.

  The solar cell back surface sealing film of the present invention is not only a solar cell used as a roofing material, but also a flexible solar cell or an electronic component (clock, calculator, computer related, mobile phone), etc. Also, it can be suitably used.

1: High light transmittance material 2: Solar cell module 3: Back surface sealing film 4: Lead wire 5: Filling resin layer 6: Exterior seal 7: Gas barrier layer 8: Film layer

The present invention employs the following means in order to solve such problems. That is, the solar cell back surface sealing film of the present invention is as follows.
(1)
A film for sealing a back surface of a solar cell having a film in which a polyethylene terephthalate film is combined and a gas barrier layer,
The composite film is obtained by supplying each polymer to a separate extruder at the time of melt extrusion, and combining both polymers in a molten state by a composite facility provided in the melt flow path.
The polyethylene terephthalate film composite film has a polyethylene terephthalate film layer composed of a polymer having a number average molecular weight of 18500 to 27000 on the surface of at least one side of the polyethylene terephthalate film composite,
The thickness of the polyethylene terephthalate film layer composed of a polymer having a number average molecular weight in the range of 18500 to 27000 is 7% or more of the total thickness of the film in which the polyethylene terephthalate film is combined,
The whiteness of the solar cell back surface sealing film is 75% or more,
And the film for solar cell backside sealing characterized by 100 micrometers conversion optical density being 0.8 or more.
(2)
The film according to (1), wherein the polyethylene terephthalate film is a biaxially stretched polyethylene terephthalate film having an apparent density in the range of 1.37 to 0.85 g / cm ^3. Battery backside sealing film.
(3)
Wherein said rear surface of a solar cell sealing film, transmittance value of water vapor measured according to the standard of JIS ^Z0208-73, characterized in that not more than 2.0g / m 2 /24Hr/0.1mm (1 ) Or (2) a solar cell back surface sealing film.
(4)
The solar cell ground characterized by using the film for solar cell backside sealing in any one of said (1)-(3) for the solar cell system.

[ Reference Examples 1 to 3, Comparative Example 1]
Mixing 100 parts of dimethyl terephthalate (hereinafter, parts by weight) with 64 parts of ethylene glycol, adding 0.1 part of zinc acetate and 0.03 part of antimony trioxide as a catalyst, and performing transesterification at the reflux temperature of ethylene glycol It was.

[Comparative Example 2]
PET-5 obtained by the method of Reference Example 1 was used to obtain Film-5 having a thickness of 50 μm and comprising PET-1 alone by the method of Reference Example 1. A film for sealing the back surface of a solar cell was produced from the film by the method of Reference Example 1 (referred to as sealing film-5).

Table 1 shows the evaluation results of five types of solar cell back surface sealing films of Reference Examples 1 to 3 and Comparative Examples 1 and 2.
Shown in

The solar cell backside sealing films of Reference Examples 1 to 3 are much more resistant to hydrolysis than those of Comparative Examples, and also have various characteristics such as gas barrier properties, electrical insulation properties, and reflectivity. Is pleased.

[Examples 4 to 6, Comparative Example 3]
In the polymerization of PET-2 obtained by the method of Reference Example 1, the temperature for high polymerization was changed from 190 to 230 ° C. for 10 to 23 hours, and the intrinsic viscosity of the polymer was 0.60, 0.66, 0.70. , 0.81 of four types of PET polymers were obtained. 17% by weight of titanium oxide fine particles with an average particle diameter of 0.5μm and UV brightening agent (UVITEX OB: manufactured by Ciba Specialty Chemicals Co., Ltd.) 0.2% by weight, and the polymerization degree of the surface PET layer is different in the method and composite structure of Reference Example 1 and is colored four kinds of composite biaxially stretched PET films having a thickness of 50 μm (composite ratio is reference) As in Example 3). However, unlike the case of Reference Example 1, no weathering agent was added.

A silicon oxide sputtering film is laminated on the obtained film by the method of Reference Example , and four types of sealing films (in which the intrinsic viscosity of the polymer is 0.60 to 0.81 are sequentially set as sealing films-6 to 9). ) In addition, like Example 1, the aluminum vapor deposition was not performed to the opposite surface of the silicon oxide sputtering film lamination surface.

The solar cell back surface sealing films of the present invention in Examples 4 to 6 are whitened, and have a weather resistance when no ultraviolet absorber is used as compared with Reference Examples 1 to 3 in Table 1. It can be seen that the reflectivity of light is increased and the reflectivity is further improved. On the other hand, the sealing film of Comparative Example 3 is the same as in Comparative Example 1, and the thickness ratio of high molecular weight PET (PET-2) is less than 7% in the present invention. The hydrolysis resistance is not improved. The same is true for Comparative Example 4, and the hydrolysis resistance is not improved even when whitened because it does not have a layer of high molecular weight PET (PET-2).

[ Reference Example 7, Examples 8 and 9 ]
Three types of composite films were prepared by adding the titanium oxide addition amounts of 5% by weight, 8% by weight, and 15% by weight using the method and composite structure of Example 5, and the same manner as in Example 5 was made on one side of each film. A silicon oxide sputtering film was laminated. It is set as the sealing films 11-13 in order from the thing with the addition amount of a titanium oxide of 5 weight%.

The solar cell back surface sealing films of Examples 8 and 9 of the present invention are obtained by changing the whiteness by changing the addition amount of titanium oxide. The sealing film of Reference Example 7 with a small amount of titanium oxide added has low whiteness and tends to have a low reflectance. Moreover, when compared with the reflectance of the sealing films of Reference Examples 1 to 3 in Table 1, it is also found that the whiteness is preferably 75 or more and the optical density (100 μm conversion; F) is preferably 0.8 or more.

[ Reference Example 12]
In the method of Example 10, the amount of calcium carbonate added was 30% by weight, the stretching temperature of the film was 85 ° C. on both axes, and the stretching ratio was 3.2 times vertically and 3.1 times horizontally. Other conditions were the same as in Example 10. The solar cell back surface sealing film thus obtained is referred to as sealing film-16.

[Comparative Example 5]
As a film, a fluorine-based film Tedlar (registered trademark) TWH20BS3 (50 μm) manufactured by DuPont was used, and a silicon oxide sputtering film was laminated by the method of Reference Example 1. The thus produced solar cell back surface sealing film was sealed. It is set as a stop film-18.

The evaluation results of the solar cell back surface sealing films of Examples 10, 11, 13, Reference Example 12 and Comparative Example 5 are shown in Tables 3 and 4.

The solar cell back surface sealing films of the present invention of Examples 10 , 11 , and 13 form bubbles in PET-1 (normal molecular weight PET polymer layer), and composite a highly polymerized PET layer (PET-2) on both surface layers. It is a thing. The apparent density was lowered in order from the sealing film of Example 10. When the density is 1.37 (preferably 1.35 or less) or less, the effect of reducing the dielectric constant necessary for preventing leakage current is exhibited. When the density is reduced, the effects of reducing the dielectric constant and reducing the weight are increased, but the electrical insulation properties, the processability to solar cells are lowered, and the gas barrier properties tend to be lowered. In this respect, the density is preferably 0.8 or more (preferably 0.9 or more).

Claims (5)

  A film having a gas barrier layer combined with a polyethylene terephthalate film, wherein the polyethylene terephthalate film is composed of a polymer having a number average molecular weight of 18500 to 40,000 and has a thickness of 7% or more of the total film thickness. A film for sealing a back surface of a solar cell, comprising:   2. The solar cell back surface sealing film according to claim 1, wherein the solar cell back surface sealing film has a whiteness of 75% or more. ^3. The solar cell backside sealing according to claim 1, wherein the polyethylene terephthalate film is a biaxially stretched polyethylene terephthalate film having an apparent density in the range of 1.37 to 0.85 g / cm ³ . the film. The rear surface of a solar cell sealing film according to claim 1 transmission value of water vapor measured according to the standard of JIS ^Z0208-73, characterized in that not more than 2.0g / m 2 /24Hr/0.1mm The film for solar cell backside sealing in any one of -3.   The solar cell ground using the film for solar cell backside sealing in any one of Claims 1-4 for the solar cell system.

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