JP2014036076A - Resin composition for solar battery sealing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a resin composition for a solar battery sealing material, improving an initial conversion efficiency of a solar battery module by allowing light that is not received at a power generation element to be reflected at a rear face sealing material and to be re-received at the power generation element, and further having no deterioration in an initial adhesive strength between a sealing material and an adjacent inorganic material member, so that peeling at an adhesive surface with time hardly occurs and a high conversion efficiency can be maintained; and a solar battery sealing material.SOLUTION: A resin composition for a solar battery sealing material includes: titanium dioxide having an average primary particle size of 0.15-0.45 μm; a moisture absorbent and/or a fired product thereof; and an ethylene-based resin.

Description

  The present invention relates to a resin composition for a solar cell encapsulant.

In recent years, the photovoltaic power generation system has been gaining attention all over the world as a clean and sustainable energy system from the viewpoint of global warming countermeasures and replacement of fossil fuels that are feared to be depleted. Therefore, the market size of solar cells is increasing year by year. In addition, the photovoltaic power generation system has been attracting attention from the viewpoints of the recent safety concerns of nuclear power generation and private power generation in an emergency. However, reducing the power generation cost is the biggest challenge for further expansion of the photovoltaic power generation system. In recent years, the power generation cost of photovoltaic power generation has been greatly reduced due to technological innovation. However, the power generation cost of solar power generation at present is still higher than other energy sources, and technical innovations such as higher efficiency and longer life of solar cell modules are required.
Currently, the mainstream photovoltaic power generation is composed of silicon-based solar cell modules such as crystalline silicon and amorphous silicon, and compound semiconductor-based solar cell modules such as CdTe and CIGS and peripheral devices. Moreover, these solar cell modules are of a super straight structure sandwiched between sealing elements from both sides of the power generation element, such as transparent substrate / surface sealing material / power generation element / back surface sealing material / back surface protection member, or transparent substrate / Power generation element / sealing material / back surface protection member A power generation element formed on the surface of the substrate is laminated with a sealing material and a back surface protection member. In general, on the back side of the light receiving surface of a power generation element using a crystalline silicon cell, an aluminum paste is printed on the entire surface of a silicon wafer in order to efficiently extract generated power. In addition, a heat-strengthened white plate glass is usually used for the transparent substrate, and a weather-resistant resin sheet is used for the back surface protection member.
However, in recent years, from the viewpoint of weather resistance, a transparent substrate is often used for the back surface protection member.

  In order to increase the efficiency of the solar cell module, in addition to improving the power generation efficiency of the power generation element itself, it is considered to increase the amount of light received by the power generation element. Therefore, Patent Document 1 discloses that titanium dioxide is added to the back surface protection sheet to reflect incident light and increase the amount of light received by the power generation element. Patent Document 2 discloses that titanium dioxide is blended with a solar cell sealing material to reflect incident light and increase the amount of light received by a power generation element.

JP 2007-208179 A JP 2008-103471 A

  However, in recent years, from the viewpoint of improving the durability of the solar cell module, the use of a glass protective plate without using a resin-made back protective sheet has increased, so that the back protective sheet of Patent Document 1 cannot be used. There is a case.

  Moreover, although a solar cell sealing material seals by closely_contact | adhering with the glass surface of a solar cell module, the sealing material of patent document 2 originates in containing titanium dioxide, and adhesiveness with a glass surface or Adhesiveness with the aluminum back electrode of the power generation element is lowered. This usually involves adding a silane coupling agent having a functional device that reacts with organic materials and inorganic materials in order to increase the adhesion between the transparent substrate and the aluminum back electrode and the sealing material. The compounded titanium oxide also reacts with the functional group of the silane coupling agent. Therefore, there is a problem that not only the initial adhesive strength is lowered but also the sealing material is peeled off from the glass surface when used outdoors for a long time.

  In the present invention, since light can be efficiently reflected, the amount of light received by the power generation element is increased, so that the initial conversion efficiency is improved, and the adhesiveness between the sealing material and the inorganic material member in contact with the sealing material is good. Therefore, it aims at providing the resin composition for solar cell sealing materials which can manufacture the solar cell sealing material which suppresses the fall of initial stage adhesive strength, and also does not produce peeling even if it uses for a long period of time.

  The present invention includes a solar cell encapsulant comprising: titanium dioxide having an average primary particle diameter of 0.15 to 0.45 μm, surface-coated with at least an aluminum oxide, a hygroscopic agent, and an ethylene-based resin. It is a resin composition.

According to the present invention having the above configuration, the use of titanium dioxide having an average primary particle size of 0.15 to 0.45 μm allows reflection of wavelengths in the near-infrared region, which contributes to power generation, so that the initial conversion efficiency is high. Increase. Compared with the case where the titanium dioxide is blended in the back surface protective sheet, this reflection can contribute to the improvement of conversion efficiency because the sealing material has a short distance to the power generation element and the reflected light is not easily attenuated.
Usually, a silane coupling agent is blended in the sealing material in order to improve adhesion with glass or an inorganic material member adjacent to the sealing material such as the power generation element aluminum back electrode. This silane coupling agent is hydrolyzed by moisture in the atmosphere to form silanol, and then moves to the interface with the sealing material by hydrogen bonding with the surface of the inorganic material, and then is subjected to strong chemical reaction by dehydration condensation reaction. By forming the bond, the glass surface and the sealing material are in close contact with each other. However, conventionally, this silane coupling agent has been bonded to the surface functional group of titanium dioxide by hydrogen bonding, contrary to the original intention, and the adhesion to the surface of the inorganic material has been lowered. However, in the present invention, the hydrogen bonds are suppressed by coating the surface of titanium dioxide with aluminum oxide. On the other hand, although the sealing material contains water by the coating treatment, the hygroscopic agent captures water, so the silane coupling agent is not hydrolyzed on the surface of titanium dioxide, and the sealing material and the other member are not hydrolyzed. Since it becomes easy to hydrolyze at an interface, the fall of adhesiveness can be suppressed now.

  According to the present invention, since the amount of light received by the power generation element can be increased, the initial conversion efficiency is improved, and furthermore, the adhesion between the sealing material and the inorganic material member in contact with the sealing material is good. In addition, it was possible to provide a resin composition for a solar cell encapsulant and a solar cell encapsulant that hardly inhibit peeling even when used for a long time.

An example of the cross section of the structure of a solar cell module is shown. An example of the cross section of the structure of a solar cell module is shown. It is sectional drawing which shows the layer structure of the sample for adhesive evaluation. It is sectional drawing which shows the sample for adhesive evaluation.

  First, the present invention will be described in detail. In the present specification, the description of “any number A or more and any number B or less” and “any number A to any number B” is a range larger than the number A and the number A, and the number B And a range smaller than the number B.

  Titanium dioxide blended in the resin composition for solar cell encapsulant of the present invention has a property of reflecting visible light and infrared light contained in sunlight. Although the spectral sensitivity differs depending on the type, the solar cell has a sensitivity peak from the visible light to the near-infrared light region. Spectral sensitivity refers to a characteristic that expresses the efficiency of power generation in a solar cell for each wavelength. Therefore, the light that has not been received by the power generation element is reflected by the titanium dioxide mixed in the sealing material, so that the light reception to the power generation element becomes possible and the conversion efficiency is improved. This effect contributes more to power generation because the amount of light is less attenuated than when reflected by the back surface protection sheet. Moreover, by mix | blending a hygroscopic agent, the fall of the adhesiveness of a sealing material and the inorganic material member which a sealing material contacts can be suppressed. In order to increase the adhesion between the inorganic material and the sealing material, a silane coupling agent is usually used. This is because the silane coupling agent has a functional group that binds to an organic material and an inorganic material in the molecule, and acts as an intermediary between the organic material and the inorganic material. This silane coupling agent is hydrolyzed by moisture to become silanol, and subsequently moves to the substrate surface by hydrogen bonding with the inorganic surface, and then forms a strong chemical bond by dehydration condensation reaction. In parallel with this reaction, silanol groups are condensed with each other to produce a siloxane oligomer. In general, chemical bonding with a silane coupling agent is very likely to occur on the glass surface or aluminum back electrode, which is an inorganic material member, and titanium dioxide is known to be less reactive than the inorganic material. ing. However, in ethylene resin, the reactivity of the silane coupling agent is greatly increased. In addition, when titanium dioxide is surface-coated with a metal oxide such as an oxide of aluminum, the water of crystallization present in the crystal lattice of the metal oxide promotes hydrolysis of the silane coupling agent, Since the reaction occurs not only on the glass surface of the transparent substrate and the aluminum back electrode, but also on the titanium dioxide surface, the adhesive strength between the glass or aluminum back electrode and the sealing material is lowered. In the present invention, it has been found that a surprising effect of suppressing a decrease in adhesive strength with an inorganic material member by blending a hygroscopic agent. This is because the hygroscopic agent adsorbs titanium dioxide to capture metal oxide-derived water, suppresses hydrolysis of the silane coupling agent on the titanium dioxide surface, and suppresses migration of the silane coupling agent. I guess it is because. As a result, the silane coupling agent preferentially shifts to inorganic material members such as transparent substrates and aluminum back electrodes, suppresses the decrease in the initial adhesive strength, prevents the adhesion surface from peeling off over time, and provides high conversion. Efficiency can be maintained.

In the present invention, it is important to include a hygroscopic agent. The hygroscopic agent is preferably an inorganic compound particle. Specific examples include porous materials such as zeolite, activated carbon and silica gel, composite metal compounds such as kaolinite, bentonite, hydrotalcite, smectite, montmorillonite and vermiculite, calcium carbonate, sodium sulfate and potassium oxide.
In the present invention, the hygroscopic agent is preferably a composite metal compound in which a part of metal ions constituting the inorganic compound containing metal is replaced with another metal ion. The composite metal compound is a compound in which atoms in the crystal are replaced with other atoms without changing the crystal structure, and since the atom to be replaced usually occurs between ions having the same radius, the crystal structure is greatly changed. There is no. However, since the atom is replaced with an atom having a different charge, a shortage or surplus of the charge is generated, and a counter ion can be positioned between the crystal layers or the crystal surface to compensate for the charge. Because of this characteristic, it is presumed that it forms a pair with the charge on the surface of titanium dioxide and is easily adsorbed. Therefore, water derived from the surface coating of titanium dioxide is captured, and the hydrolysis of the silane coupling agent is suppressed on the surface of titanium dioxide, so that a decrease in adhesive strength with glass can be suppressed. As the composite metal compound, montmorillonite and hydrotalcite are particularly preferable. The general formula of montmorillonite is (M ⁺ , M _1/2 ²⁺ ) _y · (Al _{2 -y} Mg _y ) · Si ₄ O ₁₀ · (OH) ₂ · nH ₂ O
(M = n-valent metal such as Na, K, Ca, Mg, etc., y = 0.2 to 0.6).
The general formula of hydrotalcite is Mg _1-a · Al _a (OH) ₂ · An ⁿ _{a / n} · cH ₂ O
(0.2 ≦ a ≦ 0.35, 0 ≦ c ≦ 1, An: n-valent anion).

  The average primary particle size of the hygroscopic agent is preferably 0.01 to 0.9 μm, and more preferably 0.01 to 0.7 μm. When the average primary particle diameter is in the range of 0.01 to 0.9 μm, the hygroscopicity can be further improved.

  The hygroscopic agent preferably has a hygroscopic amount of 0.005 to 0.5 g per g. When the amount of moisture absorption is within the above range, it becomes easy to achieve both water capture and adhesion.

It is also preferable to use a fired product (hydrotalcite fired product) obtained by heating and firing hydrotalcite as a moisture absorbent. The firing temperature of the fired product is preferably about 300 to 850 hours. The firing time is preferably about 1 to 24 hours.
The fired product preferably has a BET specific surface area of 50 to 220 m ² / g. From the viewpoint of adsorption, 80 to 200 m ² / g is more preferable. If it is less than 50 m ² / g, the adsorptive power to titanium dioxide may be insufficient. When exceeding 220 m < ² > / g, there exists a possibility of adsorb | sucking with compounds other than titanium dioxide.

  A method for producing hydrotalcite will be described.

  The method for synthesizing hydrotalcite is not particularly limited, and any known method can be used. For example, an alkaline aqueous solution containing an anion, a magnesium salt aqueous solution, and an aluminum salt aqueous solution are mixed to obtain a mixed solution having a pH in the range of 10 to 14, and then the mixed solution is heated at a temperature in the range of 80 to 100 ° C. for 2 to 24. It can be obtained after aging for about an hour.

  The alkaline aqueous solution containing the anion is preferably a mixed alkaline aqueous solution of an aqueous solution containing an anion and an aqueous alkali hydroxide solution.

  As an aqueous solution containing an anion, aqueous solutions such as sodium carbonate, potassium carbonate, sodium phosphate, sodium silicate, organic carboxylate, organic sulfonate, and organic phosphate are preferable.

  As the alkali hydroxide aqueous solution, sodium hydroxide, potassium hydroxide, ammonia, urea aqueous solution and the like are preferable.

  As magnesium salt aqueous solution, magnesium sulfate aqueous solution, magnesium chloride aqueous solution, magnesium nitrate aqueous solution, etc. can be used, Preferably they are magnesium sulfate aqueous solution and magnesium chloride aqueous solution. A slurry of magnesium oxide powder or magnesium hydroxide powder may be substituted.

  As the aluminum salt aqueous solution, an aluminum sulfate aqueous solution, an aluminum chloride aqueous solution, an aluminum nitrate aqueous solution, or the like can be used, and preferably an aluminum sulfate aqueous solution or an aluminum chloride aqueous solution. A slurry of aluminum oxide powder or aluminum hydroxide powder may be substituted.

  The mixing order of the alkaline aqueous solution containing anions, magnesium and aluminum is not particularly limited, and each aqueous solution or slurry may be mixed simultaneously. Preferably, an aqueous solution or slurry in which magnesium and aluminum are mixed in advance is added to an aqueous alkali solution containing anions.

  Moreover, when adding each aqueous solution, you may carry out either when adding this aqueous solution at once, or when dripping continuously.

  The calcined product of hydrotalcite is preferably a calcined product heat-treated at 200 to 850 ° C. for 1 to 24 hours. And it is more preferable to heat-process at 300 to 800 degreeC. The heat treatment time may be adjusted according to the heat treatment temperature, and the atmosphere during the heat treatment may be either an oxidizing atmosphere or a non-oxidizing atmosphere, but it is better not to use a gas having a strong reducing action such as hydrogen.

  Some zeolites have various crystal structures and chemical compositions, and the adsorption characteristics differ depending on the difference, but various zeolites can be used in the present invention.

  A method for producing zeolite will be described.

  The method for synthesizing the zeolite is not particularly limited, and any known method can be used. For example, it can be obtained by reacting an alkali metal silicate aqueous solution and an aluminum-containing aqueous solution while maintaining a certain ratio.

  The alkali metal silicate aqueous solution is an aqueous solution of lithium silicate, sodium silicate, potassium silicate or the like. The aqueous solution containing aluminum is an aqueous solution of aluminum sulfate, aluminum nitrate, aluminum chloride, sodium aluminate, potassium aluminate or the like.

  The supply ratio of both aqueous solutions is set by the molar ratio of silica and alumina and can be arbitrarily determined. At that time, the reaction solution becomes a slurry, and the pH of the slurry is adjusted by the amount of alkali or acid added to both aqueous solutions, and is preferably 5-9.

  In the present invention, it is important that the titanium dioxide has an average primary particle diameter of 0.15 to 0.45 μm. And from a viewpoint of light scattering, 0.15-0.35 micrometer is more preferable. When the average primary particle diameter is less than 0.15 μm or exceeds 0.45 μm, the light scattering efficiency in the spectral sensitivity region of the solar cell power generation element is lowered, and the contribution to the conversion efficiency may be lowered. Further, as the crystal form of titanium dioxide, rutile type, anatase type and brookite type can be used, but rutile type is preferable. Since the rutile type has a higher refractive index and higher light scattering efficiency than other types, it can further contribute to the conversion efficiency. The average primary particle diameter of titanium dioxide is an average of particle diameters (for example, 20 to 50 particles) that can be observed from an enlarged image of a scanning electron microscope.

  It is important that titanium dioxide is surface-coated with an oxide of aluminum. By covering the surface with aluminum oxide, the dispersibility of titanium dioxide increases and the contribution to the conversion efficiency increases. Furthermore, since aggregation is suppressed, the amount of surface coating over time is preferably 0.5 to 5 parts by weight of aluminum oxide with respect to 100 parts by weight of titanium dioxide before surface coating. By covering in the above range, the dispersibility and adhesion of titanium dioxide are further improved.

Titanium dioxide can be surface coated with two or more metal oxides. In this case, it is preferable to use a total of 0.5 to 8 parts by weight of the metal oxide based on 100 parts by weight of titanium dioxide before surface coating. The metal oxide is preferably an oxide of aluminum, silicon, or zirconium. Due to the presence of this surface coating layer, adsorption of titanium dioxide and the hygroscopic agent occurs, and the crystal water is more easily captured. Therefore, hydrolysis of the silane coupling agent on the titanium dioxide surface is difficult to occur. Thereby, a silane coupling agent becomes easy to transfer to an inorganic material like glass and a sealing material interface. As a result, the adhesion between the sealing material and the inorganic material member in contact with the sealing material is improved. Examples of metal oxides include alumina that is an oxide of aluminum, hydrous alumina that is a hydrous oxide (Al ₂ O ₃ .nH ₂ O), silica that is an oxide of silicon, and hydrous silica that is a hydrous oxide. (SiO ₂ .nH ₂ O) and zirconium oxide which is an oxide of zirconium are preferable.

  A method for forming a surface coating layer using an inorganic oxide for titanium dioxide will be described.

  As a method of coating the titanium dioxide particles with an inorganic oxide, a known method can be used. For example, when coating with aluminum oxide, an aqueous solution of aluminum oxide is added to an aqueous slurry in which titanium dioxide particles are dispersed, and the pH is adjusted to 4 to 9 using an aqueous solution of an acidic compound or a basic compound. A surface coating layer can be formed. Then, you may perform filtration, washing | cleaning, and drying as needed. As the acidic oxide used for adjusting the pH, inorganic acids such as sulfuric acid and hydrochloric acid, or organic acids such as acetic acid and formic acid can be used. Moreover, as a basic compound, well-known compounds, such as sodium hydroxide, potassium hydroxide, and ammonia, can be used. The non-volatile content of titanium dioxide particles in the aqueous slurry is preferably 50 to 800 g / l, more preferably 100 to 600 g / l. A coating layer having a uniform thickness can be easily obtained by setting the concentration to a predetermined nonvolatile content.

  Examples of the aluminum oxide include sodium aluminate, aluminum sulfate, and aluminum nitrate, aluminum chloride, alumina, hydrous alumina, and the like.

  When coating with silicon oxide or zirconium oxide, the same method as for coating with aluminum oxide can be used. The coating using these metal oxides may be coated with a mixture with aluminum oxide, or may be laminated and coated with a plurality of layers. The order of these coatings is not limited, but it is preferable to coat so that the aluminum oxide is the outermost layer. Furthermore, in the manufacturing process of titanium dioxide, operations such as dehydration, drying, and pulverization are easy, which is preferable.

  Examples of the silicon oxide include water-soluble alkali metal silicate salts such as sodium silicate. Examples of the zirconium oxide include zirconium sulfate, zirconium nitrate, and zirconium chloride.

Titanium dioxide preferably forms a coating layer using an organic substance after forming a surface coating layer containing an inorganic oxide.
Examples of organic substances include polyhydric alcohols, organosilicon compounds, amines, amino acids, fatty acids, carboxylates, metal soaps, and waxes. Of these, polyhydric alcohols and organosilicon compounds are preferred. The organic substance can be used alone or in combination of two or more. The surface coating amount using an organic substance is preferably 0.1 to 3 parts by weight, and more preferably 0.1 to 1.5 parts by weight with respect to 100 parts by weight of titanium dioxide before treatment.

  Specific examples of the polyhydric alcohol that can be used in the present invention include trimethylol ethane, trimethylol propane, ditrimethylol propane, trimethylol propane ethoxylate, pentaerythritol, and the like, and trimethylol propane, trimethylol ethane preferable.

  Examples of the organosilicon compound that can be used in the present invention include organosilane, organopolysiloxane, and organosilazane.

  Specifically, as the organosilane, aminopropyltriethoxysilane, N-β (aminoethyl) γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxy Silane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, γ- (methacryloyloxypropyl) trimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-chloropropyl Triethoxysilane, n-butyltriethoxysilane, isobutyltrimethoxysilane, hexyltrimethoxysilane, hexyltriethoxysilane, hexylmethyldimethoxysilane, hexylmethyldiethoxysilane, cyclohexane Xylmethyldiethoxysilane, octyltrimethoxysilane, octyltriethoxysilane, decyltrimethoxysilane, phenyltriethoxysilane, trifluoropropyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, or their hydrolysis products It is done.

  Organopolysiloxanes include dimethylpolysiloxane, methylhydrogen polysiloxane, methylmethoxypolysiloxane, methylphenylpolysiloxane, dimethylpolysiloxanediol, dimethylpolysiloxane dihydrogen, side chain or both-end amino-modified polysiloxane, side chain or both. End- or single-end epoxy-modified polysiloxane, double-end or single-end methacryl-modified polysiloxane, side-chain or double-end carboxyl-modified polysiloxane, side-chain or double-end or single-end carbinol-modified polysiloxane, double-end phenol-modified polysiloxane, Side-chain or both-end mercapto-modified polysiloxane, both-end or side-chain polyether-modified polysiloxane, side-chain alkyl-modified polysiloxane, side-chain methylstyryl-modified polysiloxane, Chain higher carboxylic acid ester-modified polysiloxane, a side-chain fluoroalkyl-modified polysiloxanes, side-chain alkyl-carbinol-modified polysiloxane, the side chain amino both end carbinol-modified polysiloxanes or copolymers thereof, and the like.

  Examples of organosilazanes include hexamethylsilazane and hexamethylcyclotrisilazane.

  Formation of the coating layer using an organic substance is carried out by solid-liquid separation of titanium dioxide whose surface is coated with a metal oxide from an aqueous slurry, drying it, and then bringing the organic compound into contact with the organic compound in the gas phase. Or a method of contacting the titanium dioxide and the organic compound in an aqueous slurry.

  A method for forming a coating layer of an organic compound by contacting with the organic compound in a gas phase includes a dry pulverizer such as a fluid energy pulverizer and an impact pulverizer, a high-speed stirrer such as a Henschel mixer and a super mixer, and the like. It can be carried out by stirring and mixing the titanium dioxide and the organic compound.

  The method of forming a coating layer of an organic compound by bringing it into contact with the aqueous slurry is performed by adding the organic compound to the aqueous slurry, followed by stirring and mixing after coating with a metal oxide. Can do.

Examples of ethylene resins include polyvinyl butyral resins, ionomer resins, polyacrylic resins, polymethacrylic resins, polyvinyl alcohol resins, copolymer resins using at least ethylene, polyvinyl acetate resins, and modified resins thereof. Is preferred. Among these, a copolymer resin using at least ethylene is more preferable. The copolymer resin using at least ethylene is a copolymer of two or more types of monomers, and is not particularly limited as long as at least one of the monomers is an ethylene monomer. Specifically, ethylene vinyl acetate copolymer, ethylene methyl acrylate copolymer, ethylene ethyl acrylate copolymer, ethylene methyl methacrylate copolymer, ethylene ethyl methacrylate copolymer, ethylene ionomer, ethylene acetate Examples include vinyl multi-component copolymers, ethylene methyl acrylate multi-component copolymers, ethylene ethyl acrylate multi-component copolymers, ethylene methyl methacrylate multi-component copolymers, and ethylene ethyl methacrylate multi-component copolymers. It is done. Among these, an ethylene vinyl acetate copolymer is preferable. Furthermore, in the lamination process when manufacturing a solar cell module, the power generation element is not easily damaged, and from the viewpoint of improving the transparency and productivity of the solar cell encapsulant, synthesis of ethylene vinyl acetate copolymer is performed using vinyl acetate. Is preferably used in an amount of 15 to 40% by weight, more preferably 25 to 35% by weight.
In the present invention, the ethylene resin preferably has a melt flow rate (hereinafter simply referred to as MFR) of 0.1 to 60 g / 10 min, and more preferably 0.5 to 45 g / 10 min. By setting the MFR within a predetermined range, the moldability, mechanical strength, and the like can be improved. The melt flow rate is a numerical value measured according to JIS K7210.

  The resin composition for a solar cell encapsulant of the present invention can be obtained by blending titanium dioxide, a hygroscopic agent, and an ethylene-based resin in a blending amount according to the raw material ratio of the encapsulant. In this case, 2 to 25 parts by weight of titanium dioxide, preferably 5 to 20 parts by weight, and 0.2 to 8 parts by weight, preferably 0.2 to 8 parts by weight of the hygroscopic agent (B) with respect to 100 parts by weight of the ethylene resin. It is preferable to blend 5 parts by weight. By blending 2 to 25 parts by weight of titanium dioxide, light can be reflected more efficiently, and by blending 0.2 to 8 parts by weight of a hygroscopic agent, hydrolysis of the silane coupling agent on the surface of titanium dioxide is suppressed. It becomes easy to do.

  Moreover, it is preferable to manufacture the resin composition for solar cell sealing materials of this invention as what is called a masterbatch which mix | blended titanium dioxide and the hygroscopic agent in high concentration. Once the master batch is manufactured, the main resin of the encapsulant, for example, ethylene master vinyl acetate copolymer, is blended with the master batch to produce the encapsulant. Water capture tends to occur. Specifically, it is preferable to mix 20 to 200 parts by weight of titanium dioxide and 2 to 20 parts by weight of a hygroscopic agent with respect to 100 parts by weight of the ethylene-based resin.

  The resin composition for a solar cell encapsulant of the present invention is optionally added with a crosslinking agent, a crosslinking aid, a silane coupling agent, an ultraviolet absorber, a light stabilizer, an antioxidant, a flame retardant, a dispersant, and the like. It is also possible to mix an agent. As these additives, known compounds can be used for solar cell sealing materials. Furthermore, various additives can be produced by blending together with titanium dioxide, a hygroscopic agent, and an ethylene resin, but when producing a solar cell encapsulant, what is a resin composition for a solar cell encapsulant? It is also possible to add it separately.

  The crosslinking agent is used for imparting cohesive force to the ethylene-based resin, and an organic peroxide is generally used. Although the addition amount is not particularly limited, it is preferable to use 0.05 to 1.5 parts by weight with respect to 100 parts by weight in total of the ethylene-based resin, titanium dioxide, and the hygroscopic agent. Specific examples include tert-butyl peroxyisopropyl carbonate, tert-butyl peroxy-2-ethylhexyl isopropyl carbonate, tert-butyl peroxyacetate, tert-butylcumyl peroxide, 2,5-dimethyl-2,5-di (Tert-butylperoxy) hexane, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di (tert-butylperoxy) hexyne-3, 2,5-dimethyl-2,5-di (Tert-butylperoxy) hexane, 1,1-di (tert-hexylperoxy) -3,3,5-trimethylcyclohexane, 1,1-di (tert-butylperoxy) cyclohexane, 1,1-di (Tert-hexylperoxy) cyclohexane, 1,1-di tert-amylperoxy) cyclohexane, 2,2-di (tert-butylperoxy) butane, methyl ethyl ketone peroxide, 2,5-dimethylhexyl-2,5-diperoxybenzoate, tert-butyl hydroperoxide, p -Mentane hydroperoxide, dibenzoyl peroxide, p-chlorobenzoyl peroxide, tert-butylperoxyisobutyrate, n-butyl-4,4-di (tert-butylperoxy) valerate, ethyl-3,3 -Di (tert-butylperoxy) butyrate, hydroxyheptyl peroxide, dichlorohexanone peroxide, 1,1-di (tert-butylperoxy) 3,3,5-trimethylcyclohexane, n-butyl-4,4- Te t- butyl peroxy) valerate, 2,2-di (tert- butylperoxy) include butane and the like.

  The crosslinking aid is used to improve the reaction efficiency between the ethylene resin and the crosslinking agent. For example, compounds having a plurality of vinyl groups such as polyallyl compounds and polyacryloxy compounds are preferred. The crosslinking aid is preferably used in an amount of 0.05 to 1.5 parts by weight with respect to a total of 100 parts by weight of the ethylene-based resin, titanium dioxide, and the hygroscopic agent. Specific examples include triallyl isocyanurate, triallyl cyanurate, diallyl phthalate, diallyl fumarate, diallyl maleate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, and the like.

  The silane coupling agent is used to improve the adhesion of the molded member. Examples thereof include compounds having a hydrolyzable group such as an unsaturated group such as a vinyl group, an acryloxy group or a methacryloxy group, or an alkoxy group. The silane coupling agent is preferably used in an amount of 0.05 to 1.5 parts by weight with respect to a total of 100 parts by weight of the ethylene-based resin, titanium dioxide, and the hygroscopic agent. Specific examples include vinyltrichlorosilane, vinyltris (βmethoxyethoxy) silane, vinyltriethoxysilane, vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane. , Γ-glycidoxypropylmethyldiethoxysilane, N-β (aminoethyl) γ-aminopropyltrimethoxysilane, N-β (aminoethyl) γ-aminopropylmethyldimethoxysilane, γ-aminopropyltriethoxysilane, Examples thereof include N-phenyl-γ-aminopropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, and γ-chloropropyltrimethoxysilane.

The resin composition for a solar cell encapsulant of the present invention can be produced by, for example, melting and kneading a raw material containing titanium dioxide, a hygroscopic agent, and an ethylene-based resin, and further forming into a pellet shape. This pellet is preferably produced as a master batch in which titanium dioxide is blended at a high concentration. Here, the melt kneading of the raw materials is performed separately after mixing the raw materials in advance using a general high-speed shearing type mixer such as a Henschel mixer, a super mixer, etc. It may be put into a kneader. Or it can manufacture also by mix | blending all the raw materials which can be used for a sealing material.
For the melt-kneading, for example, a two-roll, three-roll, pressure kneader, Banbury mixer, single-screw kneading extruder, or twin-screw kneading extruder is preferably used.

  The solar cell sealing material of this invention can be manufactured by melt-kneading the resin composition for solar cell sealing materials, and then shape | molding it. As the forming method, a known sheet forming method such as a T-die extruder or a calendar forming machine can be used. The thickness of the solar cell encapsulant is preferably about 0.1 to 1 mm.

  In addition, when the solar cell encapsulant is produced by using the solar cell encapsulant resin composition as a master batch, the ethylene-based resin for dilution and the master batch are melt-kneaded and then molded in the same manner as described above. It is preferable to manufacture.

An example of the configuration of the solar cell module of the present invention will be described with reference to FIG. 1 and FIG. The solar cell module of FIG. 1 is manufactured by first depositing a compound semiconductor to be the power generating element 13 on the transparent substrate 11, laminating the solar cell sealing material 12 and the back transparent substrate 14, and heating and pressing. can do. The transparent substrates 11 and 14 are preferably heat strengthened white plate glass. Moreover, it is preferable to use a vacuum laminator with a temperature controller for the heating and pressurization.
Moreover, the solar cell module of FIG. 2 which does not vapor-deposit a power generation element can be manufactured by sealing the upper and lower sides of a solar cell element with a solar cell sealing material. For example, the transparent substrate 15, the solar cell sealing material 16 </ b> A, the power generation element 17, the solar cell sealing material 16 </ b> B, and the back transparent substrate 18 can be laminated in this order, and heated and pressurized. The transparent substrates 15 and 18 are preferably heat strengthened white plate glass. In general, a vacuum laminator can be used for heating and pressurization. In addition, it cannot be overemphasized that the structure of the solar cell module which can use the resin composition for solar cell sealing materials of this invention is not limited to FIG. 1 and FIG.

  EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In addition, a part means a weight part and% means weight%, respectively.

  The example of the surface coating method by the metal oxide of titanium dioxide is shown below. The surface coating method is not limited to the following method.

<Titanium dioxide surface coating layer formation 1>
Rutile titanium dioxide particles having an average particle diameter of 0.28 μm were mixed with water to prepare an aqueous slurry having a titanium dioxide weight of 300 g / l. With this slurry held at 60 ° C., 1.5 parts of sodium aluminate in terms of Al ₂ O ₃ was added to 100 parts of titanium dioxide before surface coating with stirring, and then the pH was adjusted to 5 with sulfuric acid. By adjusting the thickness, an aluminum oxide coating layer was formed. Then, it filtered, wash | cleaned, and also it dried at 120 degreeC for 16 hours, and it grind | pulverized with the jet mill and obtained titanium dioxide (A-1) coat | covered with the oxide of aluminum.

<Titanium dioxide surface coating layer formation 2>
Rutile titanium dioxide particles having an average particle size of 0.25 μm were mixed with water to prepare an aqueous slurry having a titanium dioxide weight of 300 g / l. While maintaining this slurry at 60 ° C., 0.5 part of sodium silicate in terms of SiO ₂ was added to 100 parts of titanium dioxide while stirring. Next, the coating layer of silicon oxide was formed by adjusting the pH to about 5 with sulfuric acid. Subsequently, 1.5 parts of sodium aluminate in terms of Al ₂ O ₃ was added to 100 parts of titanium dioxide with stirring, and then the aluminum oxide coating layer was formed by adjusting the pH to 5 with sulfuric acid. . Thereafter, the mixture was filtered, washed, further dried at 120 ° C. for 16 hours, and pulverized with a jet mill to obtain titanium dioxide (A-2) coated with silicon oxide and aluminum oxide. The inorganic treatment amount of titanium dioxide was measured by chemical composition analysis using a fluorescent X-ray apparatus.

<Titanium dioxide surface coating layer formation 3>
Rutile titanium dioxide particles having an average particle diameter of 0.22 μm were mixed with water to prepare an aqueous slurry having a titanium dioxide weight of 300 g / l. With this slurry kept at 60 ° C., 0.3 part of sodium silicate in terms of SiO ₂ was added to 100 parts of titanium dioxide before surface coating while stirring. Next, the coating layer of silicon oxide was formed by adjusting the pH to about 5 with sulfuric acid. Subsequently, 0.2 parts of zirconium sulfate oxide in terms of ZrO ₂ and 1.2 parts of sodium aluminate in terms of Al ₂ O ₃ were added to 100 parts of titanium dioxide before the surface treatment of titanium dioxide with stirring. Then, the aluminum oxide coating layer was formed by adjusting the pH to 5 with sulfuric acid. Thereafter, the mixture was filtered, washed, dried at 120 ° C. for 16 hours, and pulverized with a jet mill to obtain titanium dioxide (A-3) coated with a silicon oxide and an aluminum oxide.

<Titanium dioxide surface coating layer formation 4>
Rutile titanium dioxide particles having an average particle size of 0.30 μm were mixed with water to prepare an aqueous slurry having a titanium dioxide weight of 300 g / l. While maintaining this slurry at 60 ° C., 0.4 part of zirconium sulfate oxide in terms of ZrO ₂ was added to 100 parts of titanium dioxide before surface coating while stirring. Subsequently, the coating layer of zirconium oxide was formed by adjusting the pH to about 5 with sulfuric acid. Subsequently, 2.6 parts of sodium aluminate in terms of Al ₂ O ₃ was added to 100 parts of titanium dioxide before the surface treatment of titanium dioxide with stirring, and then the aluminum oxide was adjusted by adjusting the pH to 5 with sulfuric acid. A coating layer of the product was formed. Thereafter, the mixture was filtered, washed, further dried at 120 ° C. for 16 hours, and pulverized with a jet mill to obtain titanium dioxide (A-4) coated with a silicon oxide and an aluminum oxide.

  As described in Table 1 for (A-5) to (A-12) by the same method as described above, a surface coating layer using a metal oxide for titanium dioxide was formed.

  Further, (A-9) to (A-13) formed a surface coating layer using the organic substances shown in Table 1.

  Next, an example of a surface coating method using an organic substance of titanium dioxide is shown below. The surface coating method is not limited to the following method.

(Titanium dioxide surface coating layer formation 5)
Titanium dioxide on which an aluminum oxide coating layer is formed is filtered from an aqueous slurry, washed, dried at 120 ° C. for 16 hours, and pulverized with a jet mill while hexyltriethoxysilane is added to 100 parts of titanium dioxide before coating. 0.4 part was added, mixed and coated to obtain titanium dioxide (A-9) having a surface coating layer using an organic substance.

(Titanium dioxide surface coating layer formation 6)
Titanium dioxide on which a coating layer of silicon and aluminum oxide is formed is filtered from an aqueous slurry, washed, dried at 120 ° C. for 16 hours, and pulverized with a jet mill while triturating 100 parts of titanium dioxide before coating. Titanium dioxide (A-10) having a surface coating layer using an organic substance was obtained by adding 0.5 part of methylolethane, mixing and coating.

(Titanium dioxide surface coating layer formation 7)
Titanium dioxide with a coating layer of silicon, zirconium, and aluminum oxide is filtered from an aqueous slurry, washed, dried at 120 ° C. for 16 hours, and pulverized with a jet mill to 100 parts of titanium dioxide before coating. Then, 0.3 part of trimethylolethane was added, mixed and coated to obtain titanium dioxide (A-11) having a surface coating layer using an organic substance.

(Formation of surface coating layer of titanium dioxide 8)
Titanium dioxide on which an aluminum / zirconium oxide coating layer is formed is filtered from an aqueous slurry, washed, dried at 120 ° C. for 16 hours, and pulverized with a jet mill while methylating 100 parts of titanium dioxide before coating. 0.8 parts of hydrogen polysiloxane was added, mixed and coated to obtain titanium dioxide (A-12) having a surface coating layer using an organic substance.

(Titanium dioxide surface coating layer formation 9)
Titanium dioxide having a surface coating layer using an organic substance by adding 0.5 part of trimethylolethane to 100 parts of titanium dioxide that is not formed of an inorganic material and mixing and coating (A -13) was obtained.

  Table 1 shows the coating composition and properties of titanium dioxide.

The chemical compositions and properties of (B) the hygroscopic agents (B-3) to (B-9) are shown in Table 2.
(B-1) Zeolite (Zeoram F-9 manufactured by Tosoh Corporation)
(B-2) Montmorillonite (Kunimine Industries Co., Ltd. Kunipia-F)
(B-3) Hydrotalcite (B-4) Hydrotalcite (B-5) Hydrotalcite (B-6) A calcined product obtained by heat-treating hydrotalcite (B-3) at 650 ° C. for 2.5 hours (B -7) Baked product obtained by treating hydrotalcite (B-3) at 350 ° C. for 3 hours and a half (B-8) Baked product obtained by treating hydrotalcite (B-4) at 800 ° C. for 1 hour and a half (B-9) ) Baked product obtained by treating hydrotalcite (B-5) at 500 ° C. for 3 hours

(C) Ethylene resin (C-1) Ultracene 751 (produced by Tosoh Corporation, ethylene vinyl acetate copolymer, vinyl acetate content: 28%, MFR: 5.7)
(C-2) Everflex V523 (Mitsui / Dupont Polychemical Co., Ltd., ethylene vinyl acetate copolymer, vinyl acetate content: 33%, MFR: 14)

[Example 1]
After putting Ultrasen 751 36 parts, titanium dioxide (A-1) 60 parts and hygroscopic agent (B-1) 4 parts into a super mixer (Mitsui Mining Co., Ltd.) and stirring at a temperature of 25 ° C. for 3 minutes. Then, it was put into a twin screw extruder (manufactured by Nippon Placon Co., Ltd.) and melt kneaded at a temperature of 140 ° C. to obtain a master batch of a resin composition for a solar cell encapsulant.
Separately, a crosslinker master batch in which Ultrasen 751 and a crosslinking agent, a crosslinking aid, and a silane coupling agent were blended, and a UV absorber master batch in which Ultrasen 751 and a UV absorber were blended were prepared.
Ultrasen 751 was added so that the blend amount of the obtained resin composition for a solar cell encapsulant resin composition, a crosslinking agent masterbatch, a stabilizer masterbatch, and Table 3, and all these Charged to a T-die extruder. Next, extrusion molding was performed at 90 ° C. to obtain solar cell sealing materials 12 and 19 (thickness 500 μm). The types and amounts of the crosslinking agent, crosslinking aid, silane coupling agent, and UV absorber in the solar cell encapsulant are as follows with respect to a total of 100 parts of Ultrasen 751, titanium dioxide, and a hygroscopic agent. Used to make the amount.
Crosslinking agent: t-butylperoxy-2-ethylhexyl monocarbonate 0.6 parts Crosslinking aid: triallyl isocyanurate 0.6 parts Silane coupling agent: γ-methacryloxypropyltrimethoxysilane 0.4 parts UV absorber : 2-hydroxy-4 octoxybenzophenone 0.2 part

[Examples 2 to 19]
Solar cell encapsulants 12 and 19 were obtained in the same manner as in Example 1 except that the master batch concentration was changed so that the ethylene-based resin and titanium dioxide had the composition shown in Table 2, respectively.

[Comparative Examples 1-3]
In Comparative Examples 1 to 3, 40 parts of an ethylene-based resin and 60 parts of titanium dioxide shown in Table 1 were put into a supermixer (manufactured by Mitsui Mining Co., Ltd.) and stirred at a temperature of 25 ° C. for 3 minutes. The master batch of the resin composition for solar cell sealing materials was obtained by throwing into the shaft extruder (made by Nippon Placon Co., Ltd.), and melt-kneading at the temperature of 140 degreeC. Other than that was carried out similarly to Example 1, and obtained the crosslinking agent masterbatch and the stabilizer masterbatch. The solar cell encapsulant masterbatch obtained, the crosslinking agent masterbatch, the ultraviolet absorber masterbatch, and an ethylene-based resin were further blended, and the blending ratios shown in Table 4 were used. Solar cell sealing materials 12 and 19 were obtained.

[Comparative Examples 4 and 5]
In Comparative Examples 4 and 5, 34 parts of an ethylene-based resin, 60 parts of titanium dioxide and 6 parts of a hygroscopic agent shown in Table 1 were introduced into a supermixer (manufactured by Mitsui Mining Co., Ltd.) at a temperature of 25 ° C. for 3 minutes. After stirring, the mixture was put into a twin screw extruder (manufactured by Nippon Placon Co., Ltd.) and melt kneaded at a temperature of 140 ° C. to obtain a master batch of a resin composition for a solar cell encapsulant. Other than that was carried out similarly to Example 1, and obtained the crosslinking agent masterbatch and the stabilizer masterbatch. The solar cell encapsulant masterbatch obtained, the crosslinking agent masterbatch, the ultraviolet absorber masterbatch, and an ethylene-based resin were further blended, and the blending ratios shown in Table 4 were used. Solar cell sealing materials 12 and 19 were obtained.

[Comparative Example 6]
In Comparative Example 6, titanium dioxide was not blended, and an ethylene-based resin, a crosslinking agent masterbatch, and a stabilizer masterbatch were charged into a T-die extruder, and solar cells were sealed in the same manner as in Example 1. Materials 12 and 19 were obtained.

  The solar cell sealing materials obtained in Examples 1 to 19 and Comparative Examples 1 to 6 were evaluated according to the following criteria, and the evaluation results are shown in Table 5.

[Preparation of test sample 1]
As shown in FIG. 2, the obtained solar cell encapsulant 19 was sandwiched between a 3 mm thick glass plate 20, a 50 μm thick release sheet 21, and a 300 μm thick protective member 22. Then, it heated for 5 minutes at 150 degreeC under vacuum using the vacuum laminator, and was thermocompression bonded for 15 minutes after that, and the sealing material was bridge | crosslinked. The release sheet is inserted only for the half area, and the glass plate 20 and the sealing material 19 are not bonded to each other at the inserted portion. Next, the laminated body of the sealing material and the protective member was cut into a 1 cm wide strip to obtain a test sample 1 having a width of 1 cm shown in FIG. Then, the 180 degree | times glass peeling test was implemented about the sample which left still for 24 hours in temperature 23 degreeC and humidity 50% RH environment, and the sample after an endurance test. The release sheet is treated with silicone. The protective member has a three-layer structure in which a linear low density polyethylene resin layer, an adhesive layer, and a polyethylene terephthalate resin layer are laminated, and the surface in contact with the sealing material is a linear low density polyethylene resin layer.

[Peel strength]
The peel strength between the sealing material and the glass plate was measured using a test sample 1 shown in FIG. A sample for testing is sandwiched between a transparent substrate on one side of a knob of a tensile tester (manufactured by Toyo Seiki Co., Ltd.) and a laminate of a sealing material and a protective member is sandwiched on the other side, and a 180 degree peel test is performed at a tensile speed of 300 mm / min. Went.

  The endurance test was conducted by a pressure cooker test, and the test sample 1 was allowed to stand for 96 hours in an environment of temperature 105 ° C. and humidity 100% RH.

[Preparation of test sample 2 (solar cell module)]
The obtained solar cell encapsulant 12 (thickness 500 μm) is sandwiched between the glass plate 11 (thickness 3 mm) on which the power generating element 13 is deposited and the glass plate (thickness 3 mm) of the back transparent substrate 14, and a vacuum laminator 1 was heated at 150 ° C. for 5 minutes under vacuum, and then thermocompression bonded for 15 minutes to crosslink the sealing material, thereby producing the solar cell module of FIG.

[Conversion efficiency]
Test sample 2 was tested by a dump heat test using a constant temperature and humidity tester at a temperature of 85 ° C. and a humidity of 85% RH for 3500 hours, and the change in conversion efficiency was evaluated for the sample after the test. did. This conversion efficiency was calculated from the incident light energy, the output at the optimum operating point, and the area of the power generation element. In the evaluation method, the conversion efficiency of the power generation element alone was set to 100, and the conversion efficiency before the sample test (initial conversion efficiency) and the conversion efficiency after the test (time-dependent conversion efficiency) were obtained.

  From the result of Table 5, Examples 1-19 improved the initial conversion efficiency, and the outstanding glass adhesiveness and conversion efficiency retention rate which exceeded the comparative example were obtained. In the present invention, by blending a hygroscopic agent, there is no decrease in the initial glass adhesive strength compared to the unblended, and further, in order to achieve high sealing performance, the solar cell is deteriorated over time. Surprising results have been obtained that suppress and enable high conversion efficiency retention.

DESCRIPTION OF SYMBOLS 11 Transparent substrate 12 Solar cell sealing material 13 Power generation element 14 Back surface transparent substrate 15 Transparent substrate 16 Solar cell sealing material 17 Power generation element 18 Back surface transparent substrate 19 Solar cell sealing material 20 Glass plate 21 Release sheet 22 Protection member 23 Glass Adhesive surface 24 Glass non-adhesive surface

Claims (7)

  A resin composition for a solar cell encapsulant, comprising at least titanium dioxide having an average primary particle diameter of 0.15 to 0.45 μm, surface-coated with an oxide of aluminum, a hygroscopic agent, and an ethylene-based resin.   The resin for solar cell sealing material according to claim 1, wherein the titanium dioxide is surface-coated with 0.5 to 5 parts of aluminum oxide with respect to 100 parts of titanium dioxide before surface coating. Composition.   Titanium dioxide is surface-coated with two or more kinds of metal oxides, and is characterized by using 0.5 to 8 parts in total of the metal oxides with respect to 100 parts of titanium dioxide before surface coating. The resin composition for solar cell sealing materials of Claim 1 or 2 to do.   The resin composition for a solar cell encapsulant according to any one of claims 1 to 3, wherein the titanium dioxide further has a surface coating layer formed of an organic material.   5. The resin composition for a solar cell encapsulant according to claim 1, wherein the moisture absorption amount of the moisture absorbent is 0.005 to 0.5 g per 1 g.   The solar cell sealing material formed by shape | molding the resin composition for solar cell sealing materials in any one of Claims 1-5.   The solar cell module provided with the solar cell sealing material of Claim 6.

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