JPWO2016190146A1 - Solar cell backsheet film, solar cell backsheet and solar cell using the same - Google Patents

Abstract

A void-containing polyester film having a porosity of 10% or more of the whole film, and in the cross section in the thickness direction of the polyester film, a line perpendicular to the surface direction is drawn from one surface of the film to the other surface, Three points (the film thickness direction center point (C1 point), the intermediate point between the film thickness direction center point and the film surface (C2-1 point), In each of the lines (divided horizontal lines) parallel to the surface direction of the film passing through each of C2-2 points)), the average area per cavity existing on the divided horizontal lines passing through the C1 points is Sc (μm2), C2 Scs (μm 2) represents the average area per cavity existing on the divided horizontal line passing through the point −1, and Scs ′ represents the average area per cavity existing on the divided horizontal line passing through the point C2-2. When (μm2), at least one of (Sc / Scs) and (Sc / Scs ′) is 1.1 or more and 35 or less, and the amount of terminal carboxyl groups of the polyester resin constituting the polyester film is 35 equivalents / ton. The film for solar battery back sheets which is the following. Provided are a film for a solar battery back sheet that achieves both excellent output improvement effects and adhesion, a solar battery back sheet and a solar battery using the film. [Selection figure] None

Description

  The present invention relates to a film for a solar battery back sheet, a solar battery back sheet using the film, and a solar battery.

  In recent years, photovoltaic power generation, which is clean energy, has attracted attention as a semi-permanent and pollution-free next-generation energy source, and solar cells are rapidly spreading.

A typical configuration of a general solar cell is shown in FIG. In the solar cell, a power generation element 3 is sealed with a transparent sealing material 2 such as EVA (ethylene-vinyl acetate copolymer), a transparent substrate 4 such as glass, and a resin sheet called a solar cell backsheet 1. It is configured by sticking together. Sunlight is introduced into the solar cell through the transparent substrate 4. Sunlight introduced into the solar cell is absorbed by the power generation element 3, and the absorbed light energy is converted into electric energy. The converted electric energy is taken out by a lead wire (not shown in FIG. 1) connected to the power generation element 3 and used for various electric devices. Here, the solar battery back sheet 1 is a sheet member that is installed on the back side of the power generation element 3 with respect to the sun and is not in direct contact with the power generation element 3. Various proposals have been made for the solar cell system and each member. For the solar cell backsheet 1, polyethylene-based, polyester-based, and fluorine-based resin films are mainly used. (See Patent Documents 1 to 3)
In the conventional solar battery backsheet, a technique has been developed that improves the efficiency of the solar battery module by reflecting the light that has passed between the solar battery cells with the solar battery backsheet and taking it into the cells. Specifically, a technology that improves the module efficiency by forming a reflective layer with white beads and a white binder on the surface of the substrate, and a technology that provides a highly reflective solar cell backsheet by forming a layer containing cavities (patent) Documents 4 and 5) have been proposed.

JP-A-11-261085 JP-A-11-186575 JP 2006-270025 A JP 2012-84670 A Japanese Patent No. 4766192

  However, as proposed in Patent Document 4, in the proposal of forming a reflective layer with white beads and white binder on the surface of the substrate, by using white beads, bonding is performed at the time of EVA or solar cell sealing material production. There exists a subject that adhesiveness with the other member film which falls. Further, as proposed in Patent Document 5, a proposal for forming a highly reflective backsheet by forming a layer including a cavity can achieve a certain power generation efficiency improvement effect, but is still insufficient for improving the power generation efficiency of the solar cell module. There was a problem of being.

  Therefore, in view of the background of such conventional technology, the present invention provides a film for a solar battery back sheet that achieves both excellent output improvement effect and adhesion, a solar battery back sheet and a solar battery using the same. Is.

That is, the present invention is a void-containing polyester film having a porosity of 10% or more of the entire film, and in the cross section in the thickness direction of the polyester film, a line perpendicular to the surface direction is formed from one surface of the film to the other surface. The line connecting the one surface to the other surface is divided into four equal parts in the thickness direction (film thickness direction center point (C1 point), intermediate point between the film thickness direction center point and the film surface (C2- In each of the lines parallel to the plane direction of the film passing through each of (1 point) and (C2-2 point)) (divided horizontal line), the average area per cavity existing on the divided horizontal line passing through C1 is Sc. (μm ^2), Scs an average area per cavity present on dividing the horizontal line passing through the C2-1 points (μm ^2), per one cavity present on dividing the horizontal line passing through the C2-2 points Average area 'when a ^{(μm 2), (Sc /} Scs), (Sc / Scs' Scs a) is at least one of 1.1 to 35 or less of, the polyester resin constituting the polyester film of terminal carboxyl It is a film for solar battery back sheets having a base amount of 35 equivalents / ton or less.

According to the present invention, compared to the conventional solar battery backsheet film and solar battery backsheet, the adhesiveness retention between the EVA resin which is a sealing material for solar battery cells and other member films to be bonded during backsheet processing ( Hereinafter, it is excellent in adhesion), and further, by mounting the solar cell back sheet of the present invention, a solar cell having higher power generation efficiency (hereinafter referred to as output improvement) than the conventional one can be provided.

It is sectional drawing which shows typically an example of a structure of the solar cell using the film for solar cell backsheets of this invention. The thickness direction cross section of the film for solar cell backsheets is shown typically. It is sectional drawing which shows typically an example of a structure of the film for solar cell backsheets of this invention which has a functional layer on both surfaces. It is sectional drawing which shows typically an example of a structure of the solar cell backsheet which has a functional layer through the contact bonding layer on the single side | surface using the film for solar cell backsheets of this invention. It is sectional drawing which shows typically an example of a structure of the solar cell backsheet which has a functional layer through the contact bonding layer on both surfaces using the film for solar cell backsheets of this invention.

The film for solar battery backsheet of the present invention is a void-containing polyester film having a porosity of 10% or more of the entire film, and faces from one surface of the film to the other surface in a cross section in the thickness direction of the polyester film. A line perpendicular to the direction is drawn, and a line connecting the one surface to the other surface is divided into four equal parts in the thickness direction (film thickness direction center point (C1 point), film thickness direction center point and film surface One of the cavities existing on the divided horizontal line passing through the point C1 in each of the lines (divided horizontal lines) parallel to the plane direction of the film passing through each of the intermediate points (C2-1 point) and (C2-2 point) the average area per Sc (μm ^2), Scs an average area per cavity present on dividing the horizontal line passing through the C2-1 points (μm ^2), dividing the horizontal line passing through the C2-2 points 'When the ^{(μm 2), (Sc /} Scs), (Sc / Scs' Scs the average area per cavity that exists is 35 or less, at least one of 1.1 or more of) the polyester film It is characterized by satisfy | filling that the amount of terminal carboxyl groups of the polyester resin to comprise is 35 equivalent / tons or less.
The solar cell backsheet film of the present invention will be described below.

  The film for solar battery backsheet of the present invention is a void-containing polyester film having a porosity of 10% or more of the whole film, and has a polyester resin as a main component. Here, the polyester resin as a main component means that the polyester resin is contained in an amount exceeding 50% by mass with respect to the resin constituting the polyester film of the present invention.

  The polyester resin used in the present invention is: 1) polycondensation of dicarboxylic acid or its ester-forming derivative (hereinafter collectively referred to as “dicarboxylic acid component”) and diol component, 2) carboxylic acid or carboxylic acid derivative in one molecule And a polycondensation of a compound having a hydroxyl group and 1) 2). The polymerization of the polyester resin can be performed by a conventional method.

  In 1), as the dicarboxylic acid component, malonic acid, succinic acid, glutaric acid, adipic acid, suberic acid, sebacic acid, dodecanedioic acid, dimer acid, eicosandioic acid, pimelic acid, azelaic acid, methylmalonic acid, Aliphatic dicarboxylic acids such as ethylmalonic acid, alicyclic dicarboxylic acids such as adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexane dicarboxylic acid, decalin dicarboxylic acid, terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4′-diphenyldicarboxylic acid, 4,4′-diphenyletherdicarboxylic acid, 4,4′-diphenylsulfonedicarboxylic acid Acid, 5-sodium Hoisofutaru acid, phenyl ene boys carboxylic acid, anthracene dicarboxylic acid, phenanthrene carboxylic acid, 9,9'-bis (4-carboxyphenyl) aromatic dicarboxylic acids such as fluorene acid, or the like its ester derivatives and the like as a typical example. These may be used alone or in combination.

  Further, a dicarboxy compound obtained by condensing oxyacids such as l-lactide, d-lactide, hydroxybenzoic acid and the like, or a combination of a plurality of such oxyacids, at least one carboxy terminus of the dicarboxylic acid component described above Can also be used.

  Next, as the diol component, aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, Fragrances such as cycloaliphatic diols such as cyclohexanedimethanol, spiroglycol and isosorbide, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, 9,9'-bis (4-hydroxyphenyl) fluorene Group diols are typical examples. Moreover, these may be used independently or may be used in multiple types as needed. In addition, a dihydroxy compound formed by condensing a diol with at least one hydroxy terminal of the diol component described above can also be used.

  In 2), examples of compounds having a carboxylic acid or a carboxylic acid derivative and a hydroxyl group in one molecule include oxyacids such as l-lactide, d-lactide and hydroxybenzoic acid, and derivatives thereof, oligomers of oxyacids, dicarboxylic acids Examples thereof include those obtained by condensing an oxyacid with one carboxyl group of the acid.

  Polyester resins obtained from the above two components include polyethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, polypropylene terephthalate, polybutylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate, and mixtures thereof. Polyethylene terephthalate and polyethylene-2,6-naphthalenedicarboxylate are preferred from the viewpoint that the film-forming property is good, more preferably polyethylene from the point that a film for a solar battery backsheet having better adhesion can be obtained. Most preferred is terephthalate.

  In the solar battery backsheet film of the present invention, the polyester resin constituting the polyester film needs to have a terminal carboxyl group content of 35 equivalents / ton or less. It is preferably 30 equivalent / ton or less, more preferably 25 equivalent / ton or less, still more preferably 20 equivalent / ton or less, and particularly preferably 17 equivalent / ton or less.

  Conventionally, in applications that require adhesion to an adherend such as an adhesive, it is known that energy affinity with an adherend such as an adhesive can be further increased by increasing the polarity of the adhesion surface. ing. That is, in the solar cell backsheet film, when the terminal carboxyl group amount of the polyester resin constituting the film is increased, the polarity of the polyester resin constituting the film is increased, and the adhesiveness with a sealing agent such as EVA tends to be increased. It was in. However, as a result of intensive studies by the present inventors, when the amount of the terminal carboxyl group exceeds 35 equivalents / ton, the initial film adhesion is excellent, but the moisture and heat resistance of the polyester film is reduced. It was found that the film became brittle and the adhesion surface was broken, resulting in a decrease in adhesion with EVA and other member films. In addition, the present inventors have found that the film may be discolored due to wet heat deterioration, and the output improvement may be reduced due to the loss of reflectivity. The film for solar cell backsheet of the present invention has 35 equivalents of the terminal carboxyl group amount of the polyester resin constituting the polyester film by controlling the size of the cavity contained in the film to a specific size as described later. It is possible to improve the adhesiveness even if it is less than / ton, and it is possible to achieve both excellent adhesiveness and heat-and-moisture resistance, and output improvement characteristics, which were difficult to achieve in the past.

  The lower limit of the terminal carboxyl group amount is not particularly limited as long as the effect of the present invention is not impaired, but is preferably 7 equivalents / ton or more, more preferably 11 amounts / ton or more. When the amount of the terminal carboxyl group is less than 7 equivalents / ton, the polar end groups on the surface are insufficient, the absolute value of the adhesion strength becomes small, and the adhesion improving effect of the present invention may be insufficient.

  The intrinsic viscosity IV of the polyester resin constituting the polyester film is preferably 0.63 dl / g or more and 0.80 dl / g or less, more preferably 0.65 dl / g or more, and further preferably 0.67 dl / g or more. When the intrinsic viscosity IV is less than 0.63 dl / g, the adhesiveness may decrease as a result of a decrease in the dispersibility of the nucleating agent that forms cavities. Moreover, the heat-and-moisture resistance of a polyester film may also fall. On the other hand, when the intrinsic viscosity IV exceeds 0.80 dl / g, the extrudability of the polyester resin may deteriorate. Therefore, by setting the intrinsic viscosity IV of the polyester resin constituting the polyester film to 0.63 dl / g or more and 0.80 dl / g or less, a film for a solar battery back sheet having both adhesiveness, heat-and-moisture resistance, and workability is obtained. Can do.

  Furthermore, the number average molecular weight Mn of the polyester resin is preferably from 8000 to 40000, more preferably from 9000 to 30000, still more preferably from 10000 to 20000. When the number average molecular weight Mn is less than 8000, durability such as heat and moisture resistance and heat resistance may be lowered. On the other hand, when the number average molecular weight Mn exceeds 40,000, the polymerization is difficult and the extrudability of the polyester resin may be deteriorated even if the polymerization is possible.

  Further, the polyester resin preferably contains Mn or Na as a metal element. It is preferable that Mn is contained in the range of 50 to 200 ppm and Na is contained in the range of 10 to 80 ppm. It is more preferable that Mn and Na are included in the above range. When Mn or Na is contained in the above range in the polyester resin, hydrolysis of the film is suppressed, and a film for a solar battery back sheet that has both excellent heat and moisture resistance, adhesion, and output improvement can be obtained. .

The polyester film of the present invention has a cavity inside. In the present invention, the “cavity” was obtained when the film was cut perpendicularly to the film surface direction without crushing the film in the thickness direction using a microtome, and the cut surface of the film was observed using an electron microscope. A cross-sectional area observed in the observation image represents a void having a size of 0.1 μm ² or more. The polyester film of the present invention needs to have a porosity (a ratio of voids in the film cross section) of 10% or more. More preferably, the porosity is 15% or more, and further preferably 20% or more. The porosity of the entire film can be obtained from the area of the hollow portion in the observation image. Details of the method for measuring the porosity will be described later. If the porosity is less than 10%, the reflectivity is insufficient and the output improvement is reduced. Moreover, when there are too few voids, stress concentrates at the adhesion interface with other member films, and the adhesion of the film for solar cell backsheet is reduced.

  The method for forming the cavities inside the polyester film is not particularly limited, but a method in which a cavity nucleating agent is contained in the polyester film and then stretched is preferable. It is difficult to control the structure of the cavity formed by the foaming agent or the like, and the adhesiveness of the solar battery backsheet film may be lowered.

  Examples of the cavity nucleating agent include organic nucleating agents such as olefin resins that are incompatible with polyester resins, and inorganic nucleating agents such as inorganic particles and glass beads. An organic nucleating agent is preferable as the cavity nucleating agent from the viewpoint that it is easy to incline the shape of the cavity in the thickness direction by a manufacturing method described later. By providing the hollow shape with an inclination in the thickness direction, the adhesion of the solar battery backsheet film can be enhanced.

  Organic nucleating agents include olefin resins, nylon 6, nylon 66, nylon 610, nylon 11, nylon 12, nylon 46, nylon MXD6, nylon 6T, and other polyamide resins, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene- Styrene resins such as styrene copolymers, acrylic resins such as polymethyl methacrylate and polybutyl methacrylate, fluorine resins such as polytetrafluoroethylene and polyvinylidene fluoride, polyphenylene sulfide, polysulfone, polyethersulfone, polyarylate, poly Super engineering plastics such as ether imide, or different types of polyester resins that are incompatible with the polyester resin of the polyester film of the present invention are also used. It is possible. Examples of the olefin resin include aliphatic polyolefin resins such as polypropylene, polyethylene, high density polyethylene, low density polypropylene, ethylene-propylene copolymer, polymethylpentene, and cyclic polyolefin resins such as cycloolefin polymer and cycloolefin copolymer. Among them, an olefin-based resin having a Vicat softening point of 140 ° C. or higher is preferable as the organic nucleating agent from the viewpoint of excellent output improvement of the film for a solar battery backsheet by forming a fine cavity and improving the reflectivity. An olefin resin having a temperature of at least ° C is more preferable. When an olefin resin having a Vicat softening point of less than 140 ° C. is used as the organic nucleating agent, the shape of the cavities may become too coarse, and the film adhesion for a solar battery backsheet and the output improvement may be reduced.

  The amount of the organic nucleating agent contained in the polyester film is preferably 1% by mass or more and 30% by mass or less, more preferably 4% by mass or more and 15% by mass or less, and still more preferably, with respect to the total mass of the polyester film. Is 8 mass% or more and 13 mass% or less. Here, when the amount of the organic nucleating agent contained in the polyester film is less than 1% by mass, the film for solar battery backsheet is excellent in adhesion, but may be inferior in output improvement due to decrease in reflectivity. . On the other hand, when the amount of the organic nucleating agent exceeds 30% by mass, although the output improvement is excellent, there are cases where there are too many cavities and the adhesion is poor.

  Further, when an organic nucleating agent is used, it is preferable to use a dispersion aid at the same time. As the dispersion aid, a polyester elastomer or an amorphous polyester resin in which a polyether structure, a bent skeleton structure, a bulky cyclohexane skeleton structure, or the like is copolymerized is preferably used. From the viewpoint of further improving dispersibility, a form in which two or more kinds of dispersion aids are used in combination is also preferably used. Further, the amount of the dispersion aid contained in the polyester film is preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 8% by mass or less, and still more preferably with respect to the total mass of the polyester film. It is 3 mass% or more and 6 mass% or less. Here, when the amount of the dispersion aid contained in the polyester film is less than 1% by mass, the effect as the dispersion aid is insufficient, and the adhesion may be lowered. On the other hand, when the amount of the dispersion aid exceeds 10% by mass, the dispersibility may be excessively improved, and the adhesion may be lowered. Furthermore, there is a risk that the heat and humidity resistance of the polyester film may be lowered due to the decrease in crystallinity.

In the film for solar cell backsheet of the present invention, the cavity in the observation image of the cross section in the thickness direction of the polyester film draws a line perpendicular to the surface direction from one surface of the film to the other surface, Three points (the film thickness direction center point (C1 point), the intermediate point between the film thickness direction center point and the film surface (C2-1 point), (C2-2) In the line parallel to the plane direction of the film passing through the point)) (divided horizontal line), the average area per cavity existing on the divided horizontal line passing through the point C1 is Sc (μm ² ), and the dividing through the point C2-1 When the average area per cavity existing on the horizontal line is Scs (μm ² ) and the average area per cavity existing on the divided horizontal line passing through the point C2-2 is Scs ′ (μm ² ), Sc / Scs), At least one of (Sc / Scs ′) is a polyester film of 1.1 to 35. Preferably they are 1.5 or more and 20 or less, More preferably, they are 2.0 or more and 15 or less, More preferably, they are 2.5 or more and 10 or less. Details of how to obtain Sc (μm ² ), Scs (μm ² ), and Scs ′ (μm ² ) will be described later.

  As a result of intensive studies by the present inventors, in the void-containing polyester film, the size of the void contained in the film is at least one of (Sc / Scs) and (Sc / Scs ′) of 1.1 or more and 35 or less. It has been surprisingly found that the adhesion improves when the thickness direction is inclined so that It is not completely clear why this effect occurs, but the inventors presume as follows. If both (Sc / Scs) and (Sc / Scs') are less than 1.1 (the inclination of the size of the cavities contained in the film is small in the thickness direction), fine cavities are formed inside the polyester film. Even if it has done, when the film for solar battery back sheets of this invention is closely_contact | adhered with EVA which is the sealing material of a photovoltaic cell, or the other member film pasted at the time of backsheet preparation, it will try to peel an adhesion surface Since the force is applied uniformly in the film plane, the adhesiveness of the solar battery backsheet film is lowered. On the other hand, if both (Sc / Scs) and (Sc / Scs') exceed 35 (the inclination in the thickness direction of the size of the cavity contained in the film is large), the deviation of the cavity area in the thickness section becomes large. As a result, the peeling easily proceeds from the coarse cavity portion, and as a result, the adhesiveness is lowered. Moreover, since the light reflectivity by a cavity falls, the output improvement property of the film for solar cell backsheets of this invention also falls, and the electric power generation output of the mounted solar cell cannot be raised.

  In the present invention, (Sc / Scs) and (Sc / Scs') indicate the shape of the cavity, the type of the cavity nucleating agent, the amount of the cavity nucleating agent, the amount of the dispersing agent, or the polyester resin after melt extrusion at the time of film production. It can be adjusted by the cooling rate. For example, by using an olefin resin having a Vicat softening point of 140 ° C. or higher as an organic nucleating agent, and increasing the amount of the cavity nucleating agent and the amount of the dispersion aid within a preferable range, the cavities can be uniformly refined and the The amount of cavities increases and (Sc / Scs) and (Sc / Scs') decrease. On the other hand, by reducing the amount of the cavity nucleating agent and the amount of the dispersion aid within a preferable range, the deviation of the cavity area in the thickness section increases, and (Sc / Scs) and (Sc / Scs') increase. Further, when the cooling rate of the polyester resin after melt extrusion at the time of film production is high, the inclination in the thickness direction of the size of the cavity contained in the film tends to be small, and (Sc / Scs) and (Sc / Scs' ) Becomes smaller. In addition, when the cooling rate is low, the inclination of the size of the cavity contained in the film tends to be small, and (Sc / Scs) and (Sc / Scs') increase.

  That is, the film for solar cell backsheet of the present invention adjusts the type of the inner cavity nucleating agent, the amount of the cavity nucleating agent, the amount of the dispersing agent, or the cooling rate of the polyester resin after melt extrusion at the time of film production within a preferable range. By doing so, at least one of the hollow (Sc / Scs) and (Sc / Scs') inside the polyester film is 1.1 to 35, and the solar cell back sheet has both excellent adhesion and improved output. It can be a film.

When the values of (Sc / Scs) and (Sc / Scs') are different and only one of them is in the range of 1.1 to 35, the (Sc / Scs) or By positioning the surface in which (Sc / Scs ′) is in a preferable range, adhesion and output improvement can be further improved. For example, when only (Sc / Scs) is 1.1 or more and 35 or less, the solar battery back sheet film arranged so that the sealing material is located on the film surface side close to Scs is improved in adhesion and output. Can be made compatible.
Here, when both (Sc / Scs) and (Sc / Scs ′) are in the range of 1.1 to 35, the adhesion on both surfaces of the solar battery backsheet film is excellent. Even in a configuration in which one side of the film for solar battery backsheet is bonded to another member film and the other side is directly bonded to the solar battery cell, it is more preferable because excellent adhesion can be obtained on both surfaces of the film. .

The film for solar battery backsheet of the present invention can increase the power generation output by reusing light by reflecting the light that has passed between the solar battery cells while diffusing with the solar battery backsheet. Here, from the viewpoint of increasing the light diffusibility, a form in which inorganic particles are contained in the polyester resin composition constituting the polyester film is preferable.
Examples of the inorganic particles used here include calcium carbonate, magnesium carbonate, zinc carbonate, titanium oxide, zinc oxide, cerium oxide, magnesium oxide, barium sulfate, zinc sulfide, calcium phosphate, alumina, mica, mica, talc, clay, and kaolin. , Lithium fluoride, calcium fluoride, and the like. Further, among these, calcium carbonate, magnesium carbonate, titanium oxide, zinc oxide, and barium sulfate are preferable from the viewpoint of easy processing with a polyester resin, and titanium oxide from the viewpoint of simultaneously improving the ultraviolet resistance of the film for solar battery backsheet. Is more preferable. Examples of titanium oxide include crystalline titanium oxide such as anatase type titanium oxide and rutile type titanium oxide. From the viewpoint of increasing the difference in refractive index from the polyester used, titanium oxide having a refractive index of 2.7 or more is preferable, and at the same time, rutile type titanium oxide is used from the viewpoint of superior ultraviolet resistance. Further preferred.
That is, the film for solar cell backsheets of this invention can improve output improvement more by making an inorganic particle be included in the polyester resin composition which comprises the polyester film which has the said cavity.

  Although it does not restrict | limit especially as a form which makes the resin composition which comprises a polyester film contain an inorganic particle here, it has a laminated structure of 3 layers or more, and both surface layers (one surface layer is P2 layer) And the other surface layer is a P2 ′ layer) at least one resin composition contains inorganic particles and does not have a surface layer (this layer is a P1 layer) Is preferably a structure containing the above-described cavity nucleating agent, and more preferably a three-layer structure including P2 layer / P1 layer / P2 ′ layer.

In addition, when inorganic particles are contained in the P2 layer and the P2 ′ layer, they may become a cavity nucleating agent and the surface layer may contain a small amount of cavities. At this time, the porosity (Ps) of the P2 layer and the porosity (Ps ′) of the P2 ′ layer are preferably 5.0% or less, more preferably 4.0% or less, and still more preferably 3.5%. It is as follows. When either of the porosity (Ps) and (Ps ′) of the P2 layer and the P2 ′ layer exceeds 5.0%, the surface layer side may become unstable in the cavity area and the adhesion may be lowered. . In the film for solar cell backsheet of the present invention, the porosity (Ps) of the P2 layer and the porosity (Ps ′) of the P2 ′ layer are 5.0% or less, without reducing the adhesion, The reflectivity of the P1 layer and the diffusibility of the P2 layer or the P2 ′ layer can be utilized without canceling each other, and the output improvement can be further improved. Furthermore, process contamination by the cavity nucleating agent can be prevented during the production of the polyester film.
In addition, when only one of the porosity (Ps) of the P2 layer and the porosity (Ps ′) of the P2 ′ layer is a film that satisfies 5.0% or less, the solar battery cell that expects the effect of the present invention Adhesion can be further improved by positioning the P2 layer or the P2 ′ layer that satisfies the above range on the side.
The structure having the P2 layer or the P2 ′ layer containing the inorganic particles having ultraviolet resistance in the surface layer of the film for the solar battery backsheet of the present invention is effective for improving the output and for the solar battery backsheet by the ultraviolet rays hitting the solar battery cell. It can be said to be a more preferable form because it can achieve both UV resistance such as suppressing discoloration of the film. Moreover, the laminated structure which has an inorganic particle in both the resin composition which comprises a P2 layer and a P2 'layer has the effect of the ultraviolet-ray resistance by the side of the said photovoltaic cell with respect to the reflected light of the ultraviolet ray which hits the back surface of a solar cell. It can also be demonstrated, and it can be said that it is a more preferable form.

The main components of the P2 layer and the P2 ′ layer (hereinafter sometimes expressed as the P2 layer in a unified manner) can be freely selected as long as the effects of the present invention are not impaired. For example, by using the same polyester resin as the P1 layer as the main component of the P2 layer, a film for a solar battery back sheet having excellent adhesion between the P1 layer and the P2 layer interface can be obtained. Further, by using an acrylic resin or the like as the main component of the P2 layer, it becomes possible to provide a P2 layer with a higher filling of inorganic particles on the P1 layer by a coating method, and to achieve both excellent adhesion and improved output. It can be set as the film for battery back sheets.
When the film for solar battery backsheet of the present invention has the above-described P2 layer and / or P2 ′ layer, the thickness of the P1 layer is T1 (μm), the thickness of the P2 layer is T2 (μm), and the P2 ′ layer. Is T2 ′ (μm), the inorganic particle concentration contained in the resin composition constituting the P2 layer is W2 (mass%), and the inorganic particle concentration contained in the resin composition constituting the P2 ′ layer is W2 ′ (mass). %), At least one of (T2 / T1) × W2 and (T2 ′ / T1) × W2 ′ preferably satisfies 0.35 or more and 1.50 or less. More preferably, they are 0.75 or more and 1.40 or less, More preferably, they are 0.90 or more and 1.20 or less.

  Here, if both (T2 / T1) × W2 and (T2 ′ / T1) × W2 ′ are less than 0.35, the diffusibility of the P2 layer and the P2 ′ layer is insufficient, and either layer is a solar cell. Even if it installs in the side, the output improvement property of the film for solar cell backsheets may fall. On the other hand, when both (T2 / T1) × W2 and (T2 ′ / T1) × W2 ′ exceed 1.50, the diffusibility of the P2 layer and the P2 ′ layer becomes too strong, and the light reaches the P1 layer. However, the output improvement performance may be reduced.

  In addition, when only one of (T2 / T1) × W2 and (T2 ′ / T1) × W2 ′ is a film satisfying 0.35 or more and 1.50 or less, a solar cell that expects the effect of the present invention By positioning the P2 layer or the P2 ′ layer that satisfies the above range on the cell side, the output improvement can be further improved. For example, when only (T2 / T1) × W2 is 0.35 or more and 1.50 or less, the solar battery backsheet film arranged so that the sealing material of the power generation cell is located on the P2 layer side is adhesive. , Output improvement can be made compatible. It is preferable for both (T2 / T1) × W2 and (T2 ′ / T1) × W2 ′ to be 0.35 or more and 1.50 or less because the output improvement property is particularly excellent.

  When the P1 layer also contains inorganic particles, the inorganic particle concentration is preferably 10% by mass or less with respect to the total mass of the P1 layer, from the viewpoint of maintaining the excellent adhesion of the solar cell backsheet film. More preferably, it is more preferably 3% by weight or less. When the inorganic particle content of the P1 layer exceeds 10% by mass, (Sc / Scs) or (Sc / Scs') of the polyester film becomes small, and the adhesion of the film for solar battery backsheet may be lowered.

  Further, T1 / (T1 + T2 + T2 ′) indicating the ratio of the P1 layer to the total film thickness is preferably in the range of 0.6 or more and 0.99 or less, and the P2 layer and P2 ′ with respect to the total film thickness. T2 / (T1 + T2 + T2 ′) and T2 ′ / (T1 + T2 + T2 ′), which indicate the proportion of the layer, are preferably 0.01 or more and 0.2 or less. By satisfying the above range, both excellent adhesion and improved output can be achieved.

  The film for solar cell backsheet of the present invention, if necessary, other than the above-described hollow nucleating agent and inorganic particles, as long as the effect of the present invention is not impaired, a heat-resistant stabilizer, an oxidation-resistant stabilizer, an ultraviolet absorption Additives such as an agent, an ultraviolet stabilizer, an organic / inorganic lubricant, an organic / inorganic fine particle, a filler, a nucleating agent, a dye, and a coupling agent may be blended. For example, when an ultraviolet absorber is selected as an additive, the ultraviolet resistance of the solar cell backsheet film of the present invention can be further enhanced. In addition, the electrical insulation can be improved by adding an antistatic agent or the like.

  The total thickness of the solar cell backsheet film of the present invention is preferably 25 μm or more and 350 μm or less, more preferably 30 μm or more and 300 μm or less, and further preferably 50 μm or more and 260 μm or less. When the film for solar battery backsheet of the present invention has a thickness of less than 25 μm, wrinkles may occur during bonding with other member films. On the other hand, if the thickness is greater than 350 μm, the winding property may deteriorate. In addition, if the thickness of the entire film is 45 μm or more, the effect of improving the adhesion due to the above-described deviation of the cavity area in the thickness direction can be remarkably obtained, and the output improvement effect can be obtained because the light reflectivity is good. preferable. More preferably, it is 48 micrometers, More preferably, it is 50 micrometers or more.

  Furthermore, the film for solar battery backsheet of the present invention preferably has a thermal conductivity of 0.9 W / m · K or less, and more preferably 0.75 W / m · K or less. When the solar cell backsheet film of the present invention is used as a solar cell backsheet, another film may be laminated on the surface opposite to the surface in close contact with the sealing material (hereinafter referred to as the air side surface). By setting the rate to 0.9 W / m · K or less, it is possible to block the heat generation of the cells and suppress the deterioration of the adhesion with the film laminated on the air side surface. The thermal conductivity of the solar cell backsheet film can be lowered by increasing the porosity of the solar cell backsheet film.

(Method for producing film for solar battery back sheet)
Next, an example is given and demonstrated about the manufacturing method of the film for solar cell backsheets of this invention. This is an example, and the present invention should not be construed as being limited to the product obtained by such an example.

  First, the polyester resin used as the raw material of the solar cell backsheet film of the present invention can be obtained by subjecting a dicarboxylic acid or its ester derivative and a diol to a transesterification or esterification reaction by a known method. Examples of conventionally known reaction catalysts include alkali metal compounds, alkaline earth metal compounds, zinc compounds, lead compounds, manganese compounds, cobalt compounds, aluminum compounds, antimony compounds, titanium compounds, and phosphorus compounds. Preferably, an alkali metal compound, a manganese compound, an antimony compound or a germanium compound, or a titanium compound is preferably added as a polymerization catalyst at any stage before the normal production method is completed, and the solar battery backsheet film is adhered. It is more preferable to add a sodium compound or a manganese compound from the viewpoint of further improving the properties. As such a method, for example, when a manganese compound is taken as an example, it is preferable to add the manganese compound powder as it is.

  The amount of terminal carboxyl groups of the polyester resin is determined by heating at a polymerization temperature or after polymerization of the polyester resin at a temperature of 190 ° C. to less than the melting point of the polyester resin under reduced pressure or an inert gas such as nitrogen gas. The so-called solid-state polymerization time can be controlled. Specifically, the amount of terminal carboxyl groups increases as the polymerization temperature increases, and the amount of terminal carboxyl groups decreases as the time of solid phase polymerization increases.

  The method for incorporating a cavity nucleating agent, inorganic particles, etc. into the film for solar cell backsheet of the present invention is to prepare master pellets prepared by melting and kneading raw materials in advance using a vent type biaxial kneading extruder or tandem type extruder. A blending method is preferred. At this time, since the master pellet receives a heat history, there is a concern that the heat deterioration is not a little progressed. Therefore, it is more preferable to prepare a master pellet containing the cavity nucleating agent and inorganic particles at a higher concentration, and mix and dilute them. Specifically, when adding the cavity nucleating agent to the solar cell backsheet film of the present invention, a master pellet having a larger content than the content of the cavity nucleating agent to be contained in the polyester film is prepared in advance. It mixes with the polyester resin which is the main component of a polyester film, and adjusts to the target content.

Next, the method for producing a film for a solar battery backsheet according to the present invention is a method in which a raw material adjusted to have a polyester film composition is heated and melted in an extruder and extruded from a die cooled onto a cast drum to be processed into a sheet shape. The method (melt cast method) can be used.
Here, the film for solar battery backsheet of the present invention is preferably cooled at a cast drum temperature of 30 to 80 ° C., more preferably 40 to 70 ° C., and further preferably 45 to 60 ° C. When the temperature of the cast drum is less than 30 ° C., the cooling rate of the melt-extruded film is too fast, and the (Sc / Scs) or (Sc / Scs ′) of the polyester film may become small and deviate from the preferred range. On the other hand, when the temperature of the cast drum exceeds 80 ° C., crystallization of the polyester resin proceeds too much, and tearing may occur during stretching.

  Subsequently, the obtained sheet is led to a roll group heated to a temperature of 70 to 140 ° C., stretched in the longitudinal direction (longitudinal direction, that is, the traveling direction of the sheet), and cooled with a roll group having a temperature of 20 to 50 ° C. . Subsequently, the both ends of the sheet are guided to a tenter while being gripped by clips, and are stretched in a direction (width direction) perpendicular to the longitudinal direction in an atmosphere heated to a temperature of 80 to 150 ° C. In this case, the draw ratio is preferably 2 to 30 times in terms of surface magnification, more preferably 4 to 25 times, and still more preferably 6 to 20 times. By stretching at the above magnification, a cavity having an appropriate size can be formed in the polyester film of the present invention. If the surface magnification is less than twice, the cavity may be small and output improvement may be reduced. On the other hand, when the surface magnification exceeds 30 times, the cavity may become too large and the adhesion may be lowered. Also, it is not preferable from the viewpoint of excessive load on the film forming machine.

  Furthermore, the difference in the draw ratio between the longitudinal direction (running direction during film formation) and the width direction of the film is preferably 4 times or less, more preferably 2 times or less, and still more preferably 1 time or less. When the difference in the draw ratio exceeds 4 times, the shape of the cavity inside the polyester film is biased in one direction, and the adhesion may be lowered.

  That is, the film for the solar battery backsheet of the present invention is a polyester film in which the difference in the draw ratio between the longitudinal direction (running direction during film formation) and the width direction of the film is 4 times or less, and the surface magnification is 2 times or more and 30 times. By stretching at the following magnification, it is possible to obtain a film for a solar battery back sheet that has both excellent adhesion, improved output and wet heat resistance, and excellent workability.

  Subsequently, heat setting is performed in the tenter after stretching. The set temperature at this time is preferably 150 ° C. or higher and 250 ° C. or lower, more preferably 170 ° C. or higher and 230 ° C. or lower, and further preferably 180 ° C. or higher and 220 ° C. or lower. When heat setting is performed at less than 150 ° C., the thermal dimensional stability of the solar cell backsheet film is lowered, and there is a risk of problems such as curling during backsheet processing. On the other hand, when heat setting is performed at a temperature exceeding 250 ° C., the hollow nucleating agent inside the film may flow and the desired reflection performance may not be obtained.

  Moreover, when the film for solar cell backsheets of the present invention has a P2 layer, for example, the raw material constituting the P1 layer and the raw material constituting the P2 layer are put into two different extruders, melted, and then merged, A method of co-extrusion on a cast drum cooled from a die and processing it into a sheet (co-extrusion method), or a raw material constituting the P2 layer dissolved in a solvent after forming a polyester film having a P1 layer alone A method (coating method) in which the P2 layer is formed by applying a roll coating method, a dip coating method, a bar coating method, a die coating method, a gravure roll coating method and the like and then drying the solvent is preferably used.

  The solar cell backsheet film obtained by the above production method is excellent while maintaining the heat and moisture resistance, heat resistance, ultraviolet resistance, thermal dimensional stability, and workability of the conventional solar cell backsheet film. It is possible to achieve both adhesion and output improvement.

(Solar cell back sheet)
Next, the solar cell backsheet of this invention is demonstrated. It is important that the solar cell backsheet of the present invention is a solar cell backsheet having the film for solar cell backsheet of the present invention and at least one functional layer. Especially, it is preferable that the curl height of the solar cell backsheet calculated | required by the measuring method mentioned later is 10 mm or less, and it is more preferable that it is 5 mm or less. By setting the curl height of the solar battery back sheet to 10 mm or less, it is possible to reduce the occurrence rate of misalignment and cell cracks caused by curling, and to improve the productivity of the solar battery.

  In order to make the curl height of the solar battery back sheet 10 mm or less, the Young's modulus of the solar battery back sheet film is 4.0 GPa or less, and the Young's modulus of the solar battery back sheet is 4.0 GPa or less. Is preferred. More preferably, the Young's modulus of the solar cell backsheet film is 4.0 GPa or less, and the Young's modulus of the solar cell backsheet is more preferably 3.0 GPa or less. The lower limit of the Young's modulus of the solar cell backsheet film and the solar cell backsheet is not particularly limited as long as the function of the present invention is not impaired, but 0.5 GPa or more is sufficient.

By setting the Young's modulus of the solar battery back sheet to 4.0 GPa or less, when stacking the curl generated when the solar battery back sheet is stored in a roll state on the solar battery, the solar battery back sheet is caused by its own weight. Can be flattened.
The method for setting the Young's modulus of the solar cell backsheet film in the above range is not particularly limited, but can be adjusted by the following method. For example, when the porosity in the polyester film for solar battery backsheet is increased or the draw ratio during film formation is decreased, the Young's modulus of the film for solar battery backsheet tends to be lowered. Moreover, when the porosity in the polyester film for solar battery back sheets is lowered or the stretching ratio at the time of film formation is increased, the Young's modulus of the film for solar battery back sheets tends to increase. Further, the Young's modulus of the solar battery backsheet tends to be high when the Young's modulus of the film for solar battery backsheet used for the solar battery backsheet is high, and low when it is low. In addition, it can adjust with the Young's modulus of the layer laminated | stacked on the film for solar cell backsheets.

The functional layer of the solar battery backsheet of the present invention is preferably a layer containing at least one of polyethylene, polypropylene, and ethylene vinyl acetate copolymer, or a combination of a plurality of combinations, because the adhesion becomes good. In particular, in the solar cell backsheet of the present invention, by having the functional layer between the solar cell backsheet film and the encapsulant, it becomes possible to have good adhesion to the encapsulant. Among these, it is particularly preferable to use polyethylene from the viewpoint of weather resistance and water vapor barrier properties. When a layer including at least one of polyethylene, polypropylene, and ethylene vinyl acetate copolymer or a combination thereof is used as a functional layer, the thickness of the functional layer is preferably 30 μm or more and 300 μm or less, and 50 μm or more and 200 μm or less. It is more preferable that By setting the thickness of the layer to 30 μm or more, water vapor barrier properties and insulating properties are improved, and by setting the thickness to 300 μm or less, it is possible to suppress process contamination due to the protrusion of the functional layer B at the time of manufacturing a solar cell.
The method of laminating the layer containing at least one of polyethylene, polypropylene, and ethylene vinyl acetate copolymer or a combination thereof with the film for solar cell backsheet of the present invention as a functional layer is not particularly limited. , A method of directly laminating the film for solar cell backsheet of the present invention, and a method of laminating the film for solar cell backsheet of the present invention and a functional layer via an adhesive or the like within a range not inhibiting the effects of the present invention. Can be mentioned.

The functional layer of the backsheet of the present invention is made of polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropolypropylene copolymer. A layer containing at least one of (FEP) or a combination thereof is preferable because the weather resistance of the backsheet can be improved. In particular, it is preferable that the functional layer is laminated on the air side surface of the film for solar battery backsheet of the present invention because deterioration due to ultraviolet rays can be suppressed. From the viewpoint of weather resistance, the functional layer preferably contains at least one of PVF and PVDF.
When a layer including at least one of PVF, PVDF, ETFE, and FEP or a combination thereof is used as a functional layer, the thickness of the functional layer is preferably 25 μm or more and 125 μm or less, and is 25 μm or more and 75 μm or less. It is more preferable. When the thickness of the layer is 25 μm or more, the weather resistance is improved, and when it is 125 μm or less, the workability of the solar battery back sheet is improved.

  The method of laminating the layer containing at least one of PVF, PVDF, PTFE, and ETFE as a functional layer on the film for solar cell backsheet of the present invention is not particularly limited. And a method of laminating the solar cell backsheet film of the present invention and a functional layer via an adhesive or the like within a range not impairing the effects of the present invention.

The functional layer of the solar cell backsheet of the present invention is preferably a layer containing polyurethane, since the adhesion becomes good. In particular, when the functional layer is located between the film for solar battery backsheet of the present invention and the sealing material, the adhesion with the sealing material is improved. The polyurethane here is a general term for polymers obtained from a compound having an isocyanate group and a compound having a hydroxyl group. Examples of the compound having an isocyanate group include trimethylene diisocyanate (TDI), hexamethylene diisocyanate (HDI), methylenebis (4,1-phenylene) = diisocyanate (MDI), 3-isocyanate methyl-3,5,5-trimethylcyclohexyl isocyanate. (IPDI), xylylene diisocyanate (XDI) and other diisocyanates, trimethylolpropane adducts of these diisocyanates, isocyanurates that are trimers of these diisocyanates, burette conjugates of these diisocyanates, polymeric diisocyanates, etc. Of these, HDI is preferred from the viewpoint of color tone. Examples of the compound having a hydroxyl group include polyester polyols, polyether polyols, polyacrylic polyols, and fluorine-based polyols, and polyacrylic polyols and fluorine-based polyols are preferable from the viewpoint of heat and moisture resistance and weather resistance.
When a layer containing polyurethane is used as the functional layer, the thickness of the functional layer is preferably 1 μm or more and 20 μm or less, and more preferably 2 μm or more and 10 μm or less. When the layer containing polyurethane is a functional layer, the weather resistance is improved by setting the thickness of the functional layer to 1 μm or more, and the workability of the backsheet is improved by setting the thickness to 20 μm or less.
The method of laminating a layer containing polyurethane as a functional layer with the film for solar battery backsheet of the present invention is not particularly limited, but roll coating, gravure roll coating, kiss coating, and other coating methods, or The method of laminating by a printing method etc. is mentioned.
Moreover, it is preferable that the functional layer of the solar cell backsheet of this invention contains an inorganic compound. When the functional layer of the solar cell backsheet contains an inorganic compound, the water vapor barrier property of the solar cell backsheet is improved. As the inorganic compound contained in the functional layer, silica and alumina are preferable, and silica is particularly preferable in terms of water vapor barrier property and heat and moisture resistance.
The method for laminating the layer containing the inorganic compound as a functional layer with the film for solar cell backsheet of the present invention is not particularly limited, but the method for directly laminating the film for solar cell backsheet of the present invention or the present invention. Layers other than the polyester film obtained by laminating the film for solar cell backsheet of the present invention and the inorganic compound as long as the inorganic compound is laminated on the polyester film different from the film for solar cell backsheet of the present invention and the effect of the present invention is not impaired. And a method of laminating the layer via an adhesive or the like.

  In addition, the solar cell backsheet of the present invention is excellent in weather resistance and workability when a functional layer containing polyester is laminated with the film for solar cell backsheet of the present invention via an adhesive layer to form a solar cell backsheet. preferable.

  When the functional layer is a layer containing polyester, the thickness of the functional layer is preferably 25 μm or more and 188 μm or less, and more preferably 38 μm or more and 125 μm or less. It is possible to improve the weather resistance by increasing the thickness of the layer to 25 μm or more, and to improve the workability of the backsheet by reducing the thickness to 188 μm or less.

  In addition, in this invention, when the film for solar cell backsheets of this invention has a functional layer laminated | stacked through the contact bonding layer, porosity, (Sc / Scs), (Sc / Scs') are adhesive layers. And not including the functional layer. For example, in the case of a laminated film having the structure of polyester-containing functional layer / adhesive layer / void-containing polyester film, the center point in the direction of the thickness of the void-containing polyester film is C1, and C1 and the void-containing polyester film The midpoint with the surface is defined as (C2-1 point) and (C2-2 point).

(Solar cell)
Next, the solar cell of the present invention will be described. The solar cell of this invention mounts the said film for solar cell backsheets as it is. Alternatively, the solar battery back sheet is mounted.
A structural example of the solar cell of the present invention is shown in FIG. As a transparent substrate 4 such as glass and a solar cell back sheet 1, a power generating element connected with a lead wire (not shown in FIG. 1) for taking out electricity is sealed with a transparent sealing material 2 such as EVA resin. However, the present invention is not limited to this and can be used for any configuration.

  Here, in the solar battery of the present invention, the solar battery backsheet 1 plays a role of protecting the power generation cell installed on the back surface of the sealing material 2 that seals the power generation element. Here, it is preferable that the solar battery backsheet is disposed so that the P2 layer is in contact with the sealing material 2 in terms of increasing the power generation efficiency of the solar battery. By setting it as this structure, it can be set as the solar cell which made the outstanding adhesiveness and power generation efficiency of the film for solar cell backsheets of this invention compatible.

  The power generating element 3 converts light energy of sunlight into electric energy, and is based on crystalline silicon, polycrystalline silicon, microcrystalline silicon, amorphous silicon, copper indium selenide, compound semiconductor, dye enhancement Arbitrary elements such as a sensitive system can be used in series or in parallel according to the desired voltage or current depending on the purpose. Since the transparent substrate 4 having translucency is located on the outermost surface layer of the solar cell, a transparent material having high weather resistance, high contamination resistance, and high mechanical strength characteristics in addition to high transmittance is used. In the solar cell of the present invention, the transparent substrate 4 having translucency can be made of any material as long as the above characteristics are satisfied. Examples thereof include glass, tetrafluoroethylene-ethylene copolymer (ETFE), polyfluoride. Vinyl fluoride resin (PVF), polyvinylidene fluoride resin (PVDF), polytetrafluoroethylene resin (TFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polytrifluoroethylene chloride resin (CTFE) ), Fluorinated resins such as polyvinylidene fluoride resin, olefinic resins, acrylic resins, and mixtures thereof. In the case of glass, it is more preferable to use a tempered glass. Moreover, when using the resin-made translucent base material, what extended | stretched the said resin uniaxially or biaxially from a viewpoint of mechanical strength is used preferably. Moreover, in order to give these substrates the adhesiveness with EVA resin etc. which are the sealing materials of an electric power generation element, it is also preferably performed to give the surface a corona treatment, a plasma treatment, an ozone treatment, and an easy adhesion treatment. .

  The sealing material 2 for sealing the power generating element covers the surface of the power generating element with resin and fixes it, protects the power generating element from the external environment, and has a light-transmitting base material for the purpose of electrical insulation. In addition, a material having high transparency, high weather resistance, high adhesion, and high heat resistance is used to adhere to the backsheet and the power generation element. Examples thereof include ethylene-vinyl acetate copolymer (EVA), ethylene-methyl acrylate copolymer (EMA), ethylene-ethyl acrylate copolymer (EEA) resin, ethylene-methacrylic acid copolymer (EMAA), Ionomer resins, polyvinyl butyral resins, and mixtures thereof are preferably used.

  As described above, by mounting the film for solar cell backsheet of the present invention on a solar cell as a solar cell backsheet, even when placed outdoors for a long period of time compared to conventional solar cells, Adhesiveness is maintained, and further, power generation efficiency can be increased. The solar cell of the present invention can be suitably used for various applications without being limited to outdoor use and indoor use such as a solar power generation system and a power source for small electronic components.

[Measurement method and evaluation method of characteristics]
(1) Polymer characteristics (1-1) Amount of terminal carboxyl groups (in the table, described as COOH amount)
The terminal carboxyl group amount was measured by the following method according to the method of Malice. (Reference: M. J. Malice, F. Huizinga, Anal. Chim. Acta, 22 363 (1960))
2 g of a measurement sample was dissolved in 50 mL of o-cresol / chloroform (mass ratio 7/3) at a temperature of 80 ° C., titrated with a 0.05 N KOH / methanol solution, and the terminal carboxyl group concentration was measured. The value of In addition, the indicator at the time of titration used phenol red, and the place where it changed from yellowish green to light red was set as the end point of titration. If there is an insoluble matter such as inorganic particles in the solution in which the measurement sample is dissolved, the solution is filtered to measure the mass of the insoluble matter, and the value obtained by subtracting the mass of the insoluble matter from the measurement sample mass is measured. The following correction was made.

(1-2) Intrinsic viscosity IV
The measurement sample was dissolved in 100 ml of orthochlorophenol (solution concentration C (measurement sample mass / solution volume) = 1.2 g / ml), and the viscosity of the solution at 25 ° C. was measured using an Ostwald viscometer. Similarly, the viscosity of the solvent was measured. [Η] was calculated by the following formula (4) using the obtained solution viscosity and solvent viscosity, and the obtained value was defined as the intrinsic viscosity (IV).
ηsp / C = [η] + K [η] ² · C (4)
(Where ηsp = (solution viscosity / solvent viscosity) −1, K is the Huggins constant (assuming 0.343))
In addition, when there existed insoluble matters, such as inorganic particles, in the solution in which the measurement sample was dissolved, the measurement was performed using the following method.
(I) A measurement sample is dissolved in 100 mL of orthochlorophenol to prepare a solution having a solution concentration higher than 1.2 g / mL. Here, let the mass of the measurement sample used for orthochlorophenol be the measurement sample mass.
(Ii) Next, the solution containing insoluble matter is filtered, and the mass of the insoluble matter is measured, and the volume of the filtrate after filtration is measured.
(Iii) Orthochlorophenol was added to the filtrate after filtration, and (measurement sample mass (g) -insoluble matter mass (g)) / (volume of filtrate after filtration (mL) + added orthochlorophenol The volume (mL) is adjusted to 1.2 g / 100 mL.
(For example, when a concentrated solution having a measurement sample mass of 2.0 g / solution volume of 100 mL was prepared, the mass of insoluble matter when the solution was filtered was 0.2 g, and the filtrate volume after filtration was 99 mL Adjust to add 51 mL of orthochlorophenol ((2.0 g-0.2 g) / (99 mL + 51 mL) = 1.2 g / mL))
(Iv) Using the solution obtained in (iii), the viscosity at 25 ° C. is measured using an Ostwald viscometer, and using the obtained solution viscosity and solvent viscosity, η] is calculated, and the obtained value is defined as intrinsic viscosity (IV).

(1-3) Metal Element Content Regarding the Mg, Mn, and Sb metal element amounts, the X-ray fluorescence analysis method (X-ray fluorescence analyzer manufactured by Rigaku Corporation (model number: 3270)) is used. Quantification was carried out by atomic absorption spectrometry (manufactured by Tadate Seisakusho: Polarized Zeeman atomic absorption photometer 180-80. Frame: acetylene-air).

(2) Cavity area ratio (2-1) Observation of film cross section Using a microtome or CP (cross section polisher) cross section processing, the film for solar cell backsheet of the present invention is not crushed in the thickness direction, but in the film surface direction. On the other hand, cutting and sectioning were performed vertically. Subsequently, the image which observed the cut surface of the sample using the scanning electron microscope (SEM) (JEOL Co., Ltd. field emission scanning electron microscope "JSM-6700F") was obtained.
(2-2) Measurement of the porosity of the entire film The method of (2-1) was arbitrarily selected from a total of five locations in the film sample, and the cross section of the film was cut in the longitudinal and width directions of the film. About 10 places, the image observed by the maximum magnification which can observe the whole thickness direction of a film is prepared. Next, only each cavity is traced on a transparent film, and the ratio of the cavity area measured using an image analyzer (manufactured by Nireco Corporation: Luzex IID) and the total film cross-sectional area in the observed image is calculated. The average value at 10 locations was defined as the porosity of the entire film.
(2-3) Measurement of porosity (Ps) and (Ps ′) of film surface layer For three or more laminated films, the porosity (Ps) and (Ps ′) of the film surface layer were measured by the following method. . That is, for a total of 10 observation cross-sections prepared in the same manner as in (2-2), images prepared by observing the entire surface layer of the film surface layer (P2 layer and P2 ′ layer) at the maximum magnification capable of observing in the field of view were prepared. The area ratio was calculated using an image analyzer, and the average value at 10 locations was defined as the porosity of the film surface layer.
(2-4) Measurement of cavity area of cavities existing on each horizontal line Images observed at the maximum magnification at which the entire thickness direction of the film can be observed with respect to a total of 10 observation cross sections produced in the same manner as (2-2) Prepare. Next, a line perpendicular to the film thickness direction is drawn for each observed image, and the line is divided into four equal points (film thickness direction center point (C1 point), intermediate point between the film thickness direction center point and the film surface) A line parallel to the thickness direction (divided horizontal line) is drawn on the film passing through (C2-1 point) and (C2-2 point). Subsequently, only the cavity portions present on the divided horizontal lines were traced on a transparent film, and the average area of the voids present on each horizontal line was determined using an image analyzer.
As for the number of cavities to be traced, if there are less than 20 cavities on the divided horizontal line in the observation image, all cavities are traced, and if there are 20 or more cavities, the center of gravity of the cavities is It is assumed that 20 cavities close to the points C1, C2-1, and C2-2 are selected and traced.
(2-5) For the average area obtained by calculating (2-4) the average cavity area ratio (Sc / Scs), (Sc / Scs ′) per cavity existing on the divided horizontal line passing through the C1 point Sc (μm ² ), the average area per cavity existing on the split horizontal line passing through the point C2-1 Scs (μm ² ), and the cavity 1 existing on the split horizontal line passing through the point C2-2 The cavity area ratio (Sc / Scs) or (Sc / Scs ′) is calculated with the average area per unit being Scs ′ (μm ² ), and the average value of 10 places in total is the average cavity area ratio (Sc / Scs) and (Sc / Scs').

(3) Adhesion evaluation (3-1) Preparation of bonded sample The film for solar cell backsheet of the present invention, the solar cell backsheet, a 125 μm thick biaxially stretched polyester film “Lumirror” (registered trademark) X10S (Toray Industries, Inc.) 90 parts by mass of adhesive ("Takelac" (registered trademark) A310 (manufactured by Mitsui Takeda Chemical)), 10 parts by mass of "Takenate" (registered trademark) A3 (manufactured by Mitsui Takeda Chemical) ) And then aged for 48 hours in a thermostatic chamber adjusted to 40 ° C.
(3-2) Adhesion Evaluation About the sample obtained in (3-1), using a highly accelerated life test apparatus pressure cooker (manufactured by Espec Corp.) under the conditions of a temperature of 120 ° C. and a relative humidity of 100%. After performing the treatment for 48 hours, the film side for the solar battery backsheet of the present invention was horizontally fixed, and the peel strength when the peeled portion was subjected to a peel test at 180 ° peel at a speed of 200 mm / min. Was measured, and the adhesion of the solar cell backsheet film was determined as follows.
When peel strength is 6N / 15mm or more: A
When peel strength is 4N / 15mm or more and less than 6N / 15mm: B
When peel strength is 2N / 15mm or more and less than 4N / 15mm: C
When peel strength is 1N / 15mm or more and less than 2N / 15mm: D
When peel strength is less than 1 N / 15 mm: E
As for adhesion, A to D are good, and among them, A is the best.

(4) Moisture and heat resistance evaluation After cutting out the film for solar cell backsheet of the present invention and the solar cell backsheet into a measurement piece shape of 10 mm × 200 mm, using a highly accelerated life test apparatus pressure cooker (manufactured by ESPEC Corporation), The treatment was performed for 48 hours under the conditions of a temperature of 125 ° C. and a relative humidity of 100% RH, and then the elongation at break was measured based on ASTM-D882 (1997). Note that the measurement was performed between the chuck 50 mm, the pulling speed 300 mm / min, the number of measurements n = 5, and after measuring for each of the longitudinal direction and the width direction of the sheet, the average value was defined as the breaking elongation after the wet heat test. . From the elongation at break after the obtained wet heat test, the wet heat resistance was determined as follows.
When the breaking elongation after the wet heat test is 60% or more of the breaking elongation before the wet heat test: A
When the breaking elongation after the wet heat test is 40% or more and less than 60% of the breaking elongation before the wet heat test: B
When the breaking elongation after the wet heat test is 20% or more and less than 40% of the breaking elongation before the wet heat test: C
When the breaking elongation after the wet heat test is 10% or more and less than 20% of the breaking elongation before the wet heat test: D
When the breaking elongation after the wet heat test is less than 10% of the breaking elongation before the wet heat test: E
As for the heat and moisture resistance, A to D are good, and among them, A is the best.

(5) UV resistance (color change during UV treatment test)
(5-1) Color tone (b value) measurement Based on JIS-Z-8722 (2000), a spectroscopic color difference meter SE-2000 (manufactured by Nippon Denshoku Industries Co., Ltd., light source halogen lamp 12V4A, 0 ° to −45 °) The color tone (b value) of the film for solar battery backsheet and the solar battery backsheet was measured at n = 3 by a reflection method using a post-spectral method, and the average value was obtained.

(5-2) Color tone change Δb
The film for solar cell backsheet of the present invention, the solar cell backsheet, and eye super ultraviolet tester S-W151 (manufactured by Iwasaki Electric Co., Ltd.), temperature 60 ° C., relative humidity 60%, illuminance 100 mW / cm ² (light source: The color tone (b value) before and after irradiation for 48 hours under the conditions of a metal halide lamp (wavelength range: 295 to 450 nm, peak wavelength: 365 nm) was measured according to the above item (5-1), and ultraviolet rays were obtained from the following equation (α). The change in color tone (Δb) after irradiation was calculated. In addition, when the film for solar cell backsheets of this invention was a structure which has P2 layer on the single side | surface, the test was done so that a ultraviolet test light might hit the surface of the P2 layer side. Further, in the case of the solar battery back sheet, in Examples 32 to 37, 45 to 46, and 50 to 53, the functional layer B is provided on the surface opposite to the surface having the functional layer B, and in Examples 38 to 44 and 47 to 49, The test was conducted so that the ultraviolet test light hits the surface having the functional layer B ′ in 54 to 56.
Color tone change after UV irradiation (Δb) = b1−b0 (α)
b0: Color tone before UV irradiation (b value)
b1: Color tone after UV irradiation (b value)
From the color tone change (Δb) before and after the obtained ultraviolet treatment test, ultraviolet resistance was determined as follows.
When the color change (Δb) before and after the ultraviolet irradiation treatment test is less than 3: A
When the color tone change (Δb) before and after the ultraviolet irradiation treatment test is 3 or more and less than 6: B
When the color change (Δb) before and after the ultraviolet irradiation treatment test is 6 or more and less than 10: C
When the color tone change (Δb) before and after the ultraviolet irradiation treatment test is 10 or more and less than 20: D
When the color change (Δb) before and after the ultraviolet irradiation treatment test is 20 or more: E
As for UV resistance, A to D are good, and A is the best among them.

(6) Thermal conductivity evaluation As a thermal conductivity evaluation of the film for solar cell backsheet of the present invention, a test was performed based on ATSM E 1530. The lower heater was set to 30 ° C. and the upper heater was set to 80 ° C., and measurement was carried out at n = 3. The average value was defined as the thermal conductivity, and the obtained thermal conductivity was determined as follows.
Thermal conductivity is 0.08 W / m · K or less: A
Thermal conductivity is over 0.08 W / m · K and 0.12 W / m · K or less: B
Thermal conductivity exceeds 0.12 W / m · K and 0.14 W / m · K or less: C
Thermal conductivity exceeds 0.14 W / m · K: D
As for thermal conductivity, A to B are good, and A is the best among them.

(7) Solar cell characteristic evaluation (7-1) Output improvement evaluation of solar cell Flux “H722 made by HOZAN” is applied to the silver electrode portions on the front and back surfaces of the polycrystalline silicon solar cell “G156M3 made by Gintech”. A wiring material “copper foil SSA-SPS0.2 × 1.5 (20) manufactured by Hitachi Cable, Ltd.” cut to a length of 155 mm on the front and back silver electrodes was applied with a dispenser, and the cell on the front side Place the wire 10 mm away from one end of the wire on the end of the wiring material and the back side to be symmetrical with the front side, and use the soldering iron to bring the soldering iron into contact from the back side of the cell so that the front and back sides are simultaneously Solder welding was performed to produce 1 cell strings.
Next, the longitudinal direction of the wiring material protruding from the cell of the produced 1 cell string and the longitudinal direction of the extraction electrode “copper foil A-SPS 0.23 × 6.0 manufactured by Hitachi Cable, Ltd.” cut into 180 mm are shown. Placed vertically, the flux was applied to the portion where the wiring material and the extraction electrode overlapped, and solder welding was performed, thereby producing strings with extraction electrodes. At this time, the short-circuit current was measured according to the standard state of JIS C8914: 2005, and the power generation performance of the cell alone was obtained.

Next, 190 mm × 190 mm glass (3.2 mm thick white plate heat-treated glass for solar cells manufactured by Asahi Glass Co., Ltd.) as a cover material, and 190 mm × 190 mm ethylene vinyl acetate (Sanvik sealing material 0.5 mm as a front side sealing material) Thickness), strings with extraction electrodes that have been evaluated for power generation performance of a single cell, 190 mm x 190 mm ethylene vinyl acetate (0.5 mm thick sealant manufactured by Sunvic) as the back side sealing material, and 190 mm x 190 mm The film for solar cell backsheet of the present invention was stacked and fixed in order, and the glass was set so as to be in contact with the hot plate of the vacuum laminator, the hot plate temperature was 145 ° C., the vacuum was drawn for 4 minutes, the press was 1 minute, and the holding time. Under the condition of 10 minutes, vacuum lamination was performed to produce a solar cell for evaluation. At this time, the strings with extraction electrodes were set so that the glass surface was on the cell surface side. In addition, when the film for solar battery backsheets of this invention was a structure which has P2 layer on the single side | surface, it installed so that the P2 layer side might face the electric power generation cell side.
The obtained solar cell module was subjected to measurement of a short-circuit current measured according to the standard state of JIS C8914: 2005, and the power generation performance of the solar cell equipped with the solar cell backsheet of the present invention was obtained.
From the power generation performance of the single cell thus obtained and the power generation performance of the solar cell on which the solar cell backsheet of the present invention is mounted, the solar cell on which the solar cell backsheet of the present invention is mounted according to the following equation (β) The power generation improvement rate was calculated.
Power generation improvement rate by modularization (%) = (Power generation performance after modularization / Power generation performance of single cell-1) × 100 (%) (β)
From the power generation improvement rate obtained, the output improvement was determined as follows.
When the power generation improvement rate is 8.0% or more: A
When the power generation improvement rate is 7.5% or more and less than 8.0%: B
When the power generation improvement rate is 7.0% or more and less than 7.5%: C
When the power generation improvement rate is 6.5% or more and less than 7.0%: D
When the power generation improvement rate is less than 6.5%: E
As for the output improvement property of a solar cell, AD is favorable and A is the most excellent among them.
(7-2) Adhesion Evaluation of Solar Cell Ten solar cells prepared in the section (7-1) were prepared and treated for 4000 hr in a thermo-hygrostat (manufactured by Espec Corp.) adjusted to 85 ° C. and 85% RH. Then, it was visually confirmed whether or not peeling occurred on the laminated film for solar battery backsheet. The adhesion of the solar cells was determined as follows by checking how many of the ten solar cells had the sheet peeled off visually.
When peeling does not occur in all solar cells: A
When the sheet is peeled from one or more than four solar cells among the produced solar cells: B
When sheets are peeled from 4 or more and less than 8 solar cells among the produced solar cells: C
When 8 or more sheets of the produced solar cells are peeled from the solar cells: D
When peeling occurs in all solar cells: E
Adhesiveness of the solar cell is good from A to D, and among them, A is the best.

(8) Young's modulus evaluation The Young's modulus of the solar cell backsheet film and solar cell backsheet was measured based on ASTM-D882 (1997). The measurement was performed with the chuck spacing of 50 mm, the pulling speed of 300 mm / min, and the number of measurements n = 5. After measuring in the longitudinal direction and the width direction of the sheet, the average value was defined as the Young's modulus. From the obtained Young's modulus, it was determined as follows.
When Young's modulus is 2.0 GPa or less: A
When Young's modulus exceeds 2.0 GPa and is 3.0 GPa or less: B
When Young's modulus is more than 3.0 GPa and 4.0 GPa or less: C
When Young's modulus exceeds 4.0 GPa: D
As for Young's modulus, A to C are good, and A is the best among them.

(9) Evaluation of curl height As an evaluation of the solar cell backsheet, the curl height (curling property) was evaluated by the following procedure.
1. A solar battery backsheet cut to 200 mm × 200 mm is wrapped around a paper tube having an outer diameter of 84.2 mm, fixed, stored at 40 ° C. and 50% RH for one week, and the resulting film is removed from the paper tube and evaluated for curl height. Get a sheet for.
2. The obtained curl height evaluation sheet is placed on a flat plate in an environment at 25 ° C. so that the central portion of the curl height evaluation sheet contacts the plate.
3. The distance (curl height) from the four corner plates of the curl height evaluation sheet is measured with a caliper.
4.3. The average value of the four curl heights obtained in step 1 was taken, and the curl height evaluation was determined as follows from the average value of the curl heights obtained.
The average curl height is less than 5 mm: A
Average value of curl height is 5 mm or more and less than 10 mm: B
The average curl height is 10 mm or more and less than 15 mm: C
The average curl height is 15 mm or more: D
The curl height is good from A to C, and A is the best among them.

(10) Evaluation of water vapor barrier property As an evaluation of the water vapor barrier property of the solar battery back sheet, the water vapor transmission rate in a measurement area of 50 cm ² and 40 ° C. and 90% RH is measured according to the infrared sensor method of JIS K7129 (2008). did. From the obtained value, the water vapor barrier property was determined as follows.
Water vapor transmission rate is less than 0.5 g / m ² / day: A
Water vapor transmission rate is 0.5 g / m ² / day or more and less than 1.0 g / m ² / day: B
Water vapor transmission rate is 1.0 g / m ² / day or more and less than 2.0 g / m ² / day: C
Water vapor transmission rate is 2.0 g / m ² / day or more and less than 3.0 g / m ² / day: D
Water vapor transmission rate is 3.0 g / m ² / day or more: E
The water vapor barrier properties A to D are good, and A is the best among them.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not necessarily limited to these.

(Polyester resin material used for P1 layer)
1. PET raw material A (PET-a)
100 parts by mass of dimethyl terephthalate, 57.5 parts by mass of ethylene glycol, 0.03 parts by mass of manganese acetate tetrahydrate and 0.03 parts by mass of antimony trioxide were melted at 150 ° C. in a nitrogen atmosphere. While stirring this melt, the temperature was raised to 230 ° C. over 3 hours to distill methanol, and the transesterification reaction was completed. After the transesterification reaction, an ethylene glycol solution (pH 5.0) in which 0.005 parts by mass of phosphoric acid and 0.021 parts by mass of sodium dihydrogen phosphate dihydrate were dissolved in 0.5 parts by mass of ethylene glycol was added. . The intrinsic viscosity of the polyester composition at this time was less than 0.2. Thereafter, the polymerization reaction was performed at a final temperature of 285 ° C. and a degree of vacuum of 0.1 Torr to obtain polyethylene terephthalate having an intrinsic viscosity of 0.52 and a terminal carboxyl group amount of 15 equivalents / ton. The obtained polyethylene terephthalate was dried and crystallized at 160 ° C. for 6 hours. Thereafter, solid-state polymerization was performed at 220 ° C. and a vacuum degree of 0.3 Torr for 8 hours to obtain polyethylene terephthalate (PET-a) having an intrinsic viscosity of 0.82 and a terminal carboxyl group amount of 10 equivalents / ton. The obtained polyethylene terephthalate composition had a glass transition temperature of 82 ° C. and a melting point of 255 ° C.

2. PET raw material B (PET-b)
A polyethylene terephthalate (PET-b) having an intrinsic viscosity of 0.85 and a terminal carboxyl group amount of 6 equivalents / ton was obtained except that the solid-phase polymerization time was 10 hours.

3. PET raw material C (PET-c)
Except for setting the final temperature of the polymerization reaction to 290 ° C., the same procedure as for PET raw material A was performed to obtain polyethylene terephthalate (PET-c) having an intrinsic viscosity of 0.79 and a terminal carboxyl group amount of 15 equivalents / ton.

4). PET raw material D (PET-d)
Except that the final temperature of the polymerization reaction was 295 ° C., the same procedure as in PET raw material A was performed to obtain polyethylene terephthalate (PET-d) having an intrinsic viscosity of 0.77 and a terminal carboxyl group amount of 20 equivalents / ton.

5. PET raw material E (PET-e)
Except for setting the final temperature of the polymerization reaction to 300 ° C., the same procedure as for PET raw material A was performed to obtain polyethylene terephthalate (PET-e) having an intrinsic viscosity of 0.75 and a terminal carboxyl group amount of 28 equivalents / ton.

6). PET raw material F (PET-f)
As the reaction catalyst, 0.03 parts by mass of magnesium acetate dihydrate instead of manganese acetate, and after completion of the transesterification reaction, the same procedure as in PET raw material A was performed except that only 0.005 parts by mass of phosphoric acid was added. Polyethylene terephthalate (PET-f) having a terminal carboxyl group amount of 10 equivalents / ton was obtained.

7). PET raw material G (PET-g)
Except for setting the final temperature of the polymerization reaction to 297 ° C., the same procedure as for PET raw material A was performed to obtain polyethylene terephthalate (PET-g) having an intrinsic viscosity of 0.76 and a terminal carboxyl group amount of 24 equivalents / ton.

8). PET raw material H (PET-h)
Except for setting the final temperature of the polymerization reaction to 305 ° C., the same procedure as for PET raw material A was performed to obtain polyethylene terephthalate (PET-h) having an intrinsic viscosity of 0.65 and a terminal carboxyl group amount of 34 equivalents / ton.

9. Hollow core master pellet A
Above 1. 42 parts by mass of PET resin A (PET-a) obtained by the above section, cycloolefin copolymer (COC) “TOPAS” (registered trademark) 6018 (Vicat softening point = 188 ° C.) manufactured by Polyplastics Co., Ltd., 40 parts by mass Then, 18 parts by mass of polyester elastomer (TPE) “Hytrel” (registered trademark) 7247 manufactured by Toray DuPont Co., Ltd. was melt-kneaded in a vented extruder at 290 ° C. to prepare a hollow core agent master pellet A.

10. Hollow nucleant master pellet B
In place of PET resin A, 2. 6. Except for using the PET resin B obtained in the above section. The hollow nucleating agent master pellet B was produced by the same composition and method as the hollow nucleating agent master pellet A of the item.

11. Hollow nucleant master pellet C
In place of PET resin A, the above 3. 6. Except for using the PET resin C obtained in the above section. The hollow nucleating agent master pellet C was produced by the same composition and method as the hollow nucleating agent master pellet A of the item.

12 Hollow core master pellet D
In place of PET resin A, the above 4. 6. Except for using the PET resin D obtained in the above section. The hollow nucleating agent master pellet D was produced by the same composition and method as the hollow nucleating agent master pellet A of the item.

13. Hollow core master pellet F
In place of PET resin A, 5. 6. Except for using the PET resin F obtained in the above section. The hollow nucleating agent master pellet F was produced by the same composition and method as the hollow nucleating agent master pellet A.

14 Hollow core master pellet G
Above 1. 26.3 parts by mass of the PET resin A (PET-a) obtained according to the paragraph, cycloolefin copolymer “TOPAS” (registered trademark) 6018 (Vicat softening point = 188 ° C.), 40 parts by mass, manufactured by Polyplastics Co., Ltd. 290 ° C. with vented 18 parts by mass of polyester elastomer (TPE) “Hytrel” (registered trademark) 7247 manufactured by Toray DuPont Co., Ltd. and 15.3 parts by mass of amorphous PET resin (PET-G) Copolyester GN071 manufactured by Eastman Chemical Co., Ltd. The mixture was melt-kneaded in an extruder of No. 1 to produce a hollow nucleating agent master pellet G.

15. Hollow nucleant master pellet H
Above 1. 60 parts by mass of PET resin A (PET-a) obtained by the above section, cycloplastic copolymer “TOPAS” (registered trademark) 6018 (Vicat softening point = 188 ° C.) manufactured by Polyplastics Co., Ltd., and 40 parts by mass were vented. Cavity nucleating agent master pellets H were prepared by melt-kneading in an extruder at 290 ° C.

16. Hollow nucleant master pellet I
Above 1. 42 parts by mass of PET resin A (PET-a) obtained according to the above, polymethylpentene (PMP) “TPX” (registered trademark) DX820 (Vicat softening point = 172 ° C.), 40 parts by mass, 18 parts by mass of a polyester-based elastomer (TPE) “Hytrel” (registered trademark) 7247 manufactured by Toray DuPont Co., Ltd. was melt-kneaded in a vented 290 ° C. extruder to prepare a hollow nucleating agent master pellet I.

17. Hollow core master pellet J
Above 1. 56 parts by mass of PET resin A (PET-a) obtained according to the above, polypropylene (PP) “Noblen” (registered trademark) FLX80E4 (Vicat softening point = 135 ° C.), 40 parts by mass, Sanyo Chemical 4 parts by mass of acid-modified polypropylene (acid-modified PP) “Umex” (registered trademark) PP1010 manufactured by Kogyo Co., Ltd. was melt-kneaded in a vented 290 ° C. extruder to prepare a hollow nucleating agent master pellet J.

18. Titanium oxide master pellet 100 parts by mass of PET resin A (PET-a) obtained according to the above and 100 parts by mass of rutile-type titanium oxide particles (TiO ₂ ) having an average particle diameter of 210 nm are melt-kneaded in a vented 290 ° C. extruder and oxidized. A titanium master pellet was prepared.

19. Barium sulfate master pellet 100 parts by mass of PET resin A (PET-a) obtained according to the above and 100 parts by mass of barium sulfate particles (BaSO ₄ ) having an average particle size of 1.5 μm are melt-kneaded in a vented 290 ° C. extruder, and sulfuric acid is added. Barium master pellets were prepared.

(Film and coating agent used for functional layer B)
20. Polyethylene film A white polyethylene film “4807W” manufactured by Toray Film Processing Co., Ltd. was used.

21. Polyethylene vinyl acetate copolymer film Polyethylene in which 50 parts by mass of polyethylene vinyl acetate (vinyl acetate content 5% by mass) and 30% by mass of titanium dioxide having a number average secondary particle size of 0.25 μm are dispersed as inorganic particles. 50 parts by mass of master chips (containing 30% by mass of titanium dioxide with respect to the total amount of master chips) were supplied to an extruder heated to a temperature of 190 ° C., and a polyethylene vinyl acetate film extruded from a T die was used.

22. Polypropylene film White polypropylene film “B011W” manufactured by Toray Film Processing Co., Ltd. was used.

23. PVF film “Tedlar” (registered trademark) manufactured by DuPont was used.
24. PVDF film Arkema “Kyner” (registered trademark) was used. ETFE Film Daikin Industries, Ltd. “Neofluon” (registered trademark) EF series was used.

26. Urethane coating agent (coating agent a, coating agent b)
As a preparation of coating agent a, “Halshybrit” (registered trademark) polymer UV-G301 (solid content concentration: 40), which is an acrylic coating agent manufactured by Nippon Shokubai Co., Ltd., according to the formulation shown in the column of the main agent in Table 9. (Mass%) were mixed together with colored pigment Titanium Co., Ltd. titanium oxide particles JR-709 and a solvent, and these mixtures were dispersed using a bead mill. Thereafter, a polyester plasticizer “Polysizer” (registered trademark) W-220EL manufactured by DIC Corporation is added as a plasticizer to obtain a base material of a coating material a for forming a resin layer having a solid content concentration of 51 mass%. It was.

  In the main agent obtained as described above, “Desmodur” (registered trademark) N3300 (solid content concentration: 100 mass%) manufactured by Sumika Bayer Urethane Co., Ltd., which is a nurate-type hexamethylene diisocyanate resin shown in Table 10. Is added in an amount calculated in advance such that the mass ratio with the resin layer forming main agent is 100/4, and is further calculated in advance so that the solid content concentration is 20% by mass. Diluent: n-propyl acetate was weighed and stirred for 15 minutes to obtain a coating agent a having a solid content concentration of 20% by mass.

  As preparation of coating agent b, “Takenate” (registered trademark) D120N manufactured by Mitsui Chemicals, Inc., which is a hydrogenated xylylene diisocyanate shown in Table 11, and “Zeffle” (registered trademark) GK570 manufactured by Daikin Industries, Ltd. The diluent shown in Table 10 was blended in an amount calculated in advance so that the mass ratio to the resin layer forming main agent was 65/12, and further calculated in advance so that the solid content concentration was 20% by mass: N-Butyl acetate was weighed and stirred for 15 minutes to obtain a coating agent b having a solid content concentration of 20% by mass.

27. An inorganic compound film “Tech Barrier” (registered trademark) LX manufactured by Mitsubishi Chemical Corporation was used.

28. Polyester film “Lumirror” (registered trademark) MX11 manufactured by Toray Industries, Inc. was used as a polyester film.

29. Laminating adhesive (Coating c)
As a laminating adhesive, 36 parts by mass of a dry laminating agent “Dick Dry” (registered trademark) TAF-300 manufactured by DIC Corporation, and a TAF hardener manufactured by DIC Corporation containing a hexamethylene diisocyanate resin as a main component as a curing agent. 3 parts by mass of AH-3 and 30 parts by mass of ethyl acetate were weighed and stirred for 15 minutes to obtain a coating agent c which was a laminating adhesive having a solid content concentration of 30% by mass.

Example 1
77.5 parts by mass of PET raw material A (PET-a) vacuum-dried at 180 ° C. for 2 hours as a raw material constituting the P1 layer and 22.5 parts of the cavity nucleant master pellet A so as to have the composition shown in Table 1 On the other hand, 72 parts by mass of PET raw material A (PET-a) vacuum-dried at 180 ° C. for 2 hours as a raw material constituting the P2 layer and 28 parts by mass of titanium oxide master pellets were mixed, Each was melted and discharged in two different extruders heated to 280 ° C., merged so as to be laminated with P2 / P1 / P2 in a feed block, and then co-extruded from a T die. Next, the co-extruded molten sheet was closely cooled and solidified by an electrostatic application method on a drum maintained at a surface temperature of 50 ° C. to obtain an unstretched sheet. Subsequently, after preheating the unstretched sheet with a roll group heated to a temperature of 80 ° C., a three-fold speed difference is created between the roll heated to a temperature of 88 ° C. and the roll adjusted to a temperature of 25 ° C. After stretching 3 times in the longitudinal direction (longitudinal direction), it was cooled with a roll group at a temperature of 25 ° C. to obtain a uniaxially stretched sheet. Next, while holding both ends of the obtained uniaxially stretched sheet with clips, the tenter is guided to a preheating zone at a temperature of 80 ° C. in the tenter, and subsequently in a heating zone maintained at 90 ° C. in a direction perpendicular to the longitudinal direction (width) Direction). Subsequently, heat treatment was carried out at 220 ° C. for 20 seconds in a heat treatment zone in the tenter, and further uniformly cooled while performing relaxation treatment in the 4% width direction to form a polyester film.

  Adjust the discharge rate of the extruder so that the lamination ratio (P2: P1: P2) of the polyester film after film formation by the above method is 1: 13: 1, and further the line speed so that the total thickness becomes 150 μm. Were adjusted to obtain a solar cell backsheet film of Example 1.

  When the porosity of the obtained solar cell backsheet film was confirmed, the overall porosity was 21%, the porosity of the surface layer was 2.5% for both Ps and Ps ′, and the cavity area ratio was confirmed ( Both (Sc / Scs) and (Sc / Scs') were 3.5. When the polymer properties were measured, the intrinsic viscosity IV was 0.70 dl / g, the terminal carboxyl group amount was 14 equivalents / ton, and the metal elements contained 69 ppm of Mn, 241 ppm of Sb, and 29 ppm of Na.

  Moreover, about the obtained film for solar cell backsheets, as a result of performing solar cell backsheet characteristic evaluation, it turned out that it has the very outstanding adhesiveness, heat-and-moisture resistance, ultraviolet resistance, and heat conductivity. Furthermore, as a result of evaluating the characteristics of the solar cell, it was found that it has excellent output improvement and adhesion.

(Examples 2 to 11)
Except for changing the composition of the P1 layer as shown in Table 1 by using the amount of the hollow core master pellet and the hollow core master pellets G to I, or mixing the titanium oxide master pellet used in the P2 layer with the P1 layer. Obtained the film for solar cell backsheets similarly to Example 1.

  When the cavity area ratio of the obtained solar cell backsheet film was confirmed, as shown in Table 2, (Sc / Scs), (Sc / Scs') varied depending on the amount and type of the cavity nucleating agent or the dispersion aid. did. Specifically, in Examples 2, 4 to 6 in which the amount of the cavity nucleating agent is increased and the types of dispersion aids are increased, the cavity area ratio is smaller than that in Example 1. On the other hand, Examples 3 and 7 to 9 using polymethylpentene as the type of cavity nucleating agent or having a small amount of cavity nucleating agent and containing no dispersion aid confirm that the cavity area ratio is larger than that of Example 1. did. Also, in Examples 10 and 11 in which inorganic particles were added to the P1 layer, it was confirmed that the cavity area ratio was slightly smaller than that in Example 1.

About the obtained film for solar cell backsheets, as a result of performing solar cell backsheet characteristic evaluation, as shown in Table 2, it is a good range although it is partially inferior to Example 1 and inferior in thermal conductivity. I understood it.
Furthermore, as a result of evaluating the solar cell characteristics, it was found that although the output improvement was reduced as the cavity area ratio was increased as compared with Example 1, it was within a good range together with the adhesion.

(Examples 12 to 16)
As shown in Table 3, a solar cell backsheet film was obtained in the same manner as in Example 1 except that the PET resin as the main component of the P1 layer and the P2 layer was changed to PET-b to f as shown in Table 3.

  When the cavity area ratio of the obtained solar cell backsheet film was confirmed, as shown in Table 4, both (Sc / Scs) and (Sc / Scs') were the same as in Example 1. Moreover, when the polymer characteristic was measured, Examples 12-15 changed the intrinsic viscosity IV and the amount of terminal carboxyl groups, and Example 16 changed the kind and content of the metal element to contain.

About the obtained film for solar cell backsheets, as a result of performing solar cell backsheet characteristic evaluation, as shown in Table 4, Examples 12 to 15 are in a good range although inferior in adhesion to Example 1. I understood it. The heat and humidity resistance decreased with a decrease in intrinsic viscosity IV and an increase in the amount of terminal carboxyl groups. It was also found that the thermal conductivity was excellent as in Example 1.
Furthermore, as a result of evaluating the characteristics of the solar cell, it was found that although the output improvement was reduced with the increase in the amount of terminal carboxyl groups as compared with Example 1, the adhesion was in a good range. Moreover, although Example 16 is inferior to Example 1 in terms of the intrinsic viscosity and the amount of terminal carboxyl groups, the adhesion of the solar battery backsheet, the output improvement of the solar battery, and the adhesion are inferior, but it is in a good range. I understood.

(Examples 17 to 25)
A solar battery backsheet film was obtained in the same manner as in Example 1 except that the lamination ratio and film configuration of the solar battery backsheet, the amount of inorganic particles in the P2 layer, and the casting temperature were changed as shown in Table 3.

  When the cavity area ratio of the obtained film for solar cell backsheets was confirmed, as shown in Table 4, Example 25 was smaller than Example 1 in both (Sc / Scs) and (Sc / Scs'). The polymer characteristics were the same as in Example 1.

  As a result of performing solar cell back sheet characteristic evaluation about the obtained film for solar cell back sheets, as shown in Table 4, in Examples 17 to 23, the thickness of the P1 layer was T1 (μm), and the thickness of the P2 layer was T2. (Μm), the adhesiveness is inferior to that of Example 1 as (T1 / T2) × W2 increases when the concentration of inorganic particles contained in the resin composition constituting the P2 layer is W2 (mass%). It was found to be in a good range. Further, the ultraviolet resistance was lowered as the concentration of inorganic particles in the P2 layer was lowered. The thermal conductivity was excellent as in Example 1. Further, as a result of evaluating the solar cell characteristics, the smaller the (T1 / T2) × W2, the worse the output improvement as compared to Example 1, and the larger (T1 / T2) × W2, the poorer the adhesion, but the better It turned out to be a range. Moreover, although Example 25 has the adhesion of the solar cell back sheet which is very excellent similarly to Example 1, and the output improvement property and adhesion of a solar cell, a cavity nucleating agent adheres on a process roll at the time of film forming. I found out that

(Example 26)
As shown in Table 3, a solar cell backsheet film was obtained in the same manner as in Example 1 except that a high concentration of inorganic particles was added to the P1 layer in the P1 layer single film configuration.

  When the cavity area ratio of the obtained solar cell backsheet film was confirmed, as shown in Table 4, both (Sc / Scs) and (Sc / Scs') were smaller than in Example 1. As for the polymer properties, the amount of terminal carboxyl groups was larger than that in Example 1.

  About the obtained film for solar cell back sheets, as a result of performing solar cell back sheet characteristic evaluation, it is a good range although it is inferior in adhesiveness compared with Example 1, and heat conductivity is excellent similarly to Example 1. I found out that In the solar cell characteristic evaluation, it was found that the output range and adhesion were inferior, but in a good range. Moreover, it turned out that a cavity nucleus agent adheres on a process roll at the time of film forming like Example 25. FIG.

(Example 27)
Since barium sulfate particles are used as the inorganic particles of the P2 layer, barium sulfate master pellets are used, and the discharge rate of the extruder is adjusted so that the lamination ratio (P2: P1: P2) of the polyester film is 1: 1: 1. Obtained the film for solar cell backsheets similarly to Example 3. When the cavity area ratio of the obtained solar cell backsheet film was confirmed, as shown in Table 4, both (Sc / Scs) and (Sc / Scs') were smaller than Example 3.
About the obtained solar cell backsheet film, as a result of evaluating the solar cell backsheet characteristics, it was found that the film for the solar cell backsheet had good adhesion although it was inferior to Example 3. The thermal conductivity was excellent as in Example 1. Furthermore, as a result of evaluating the solar cell characteristics, it was found that the solar cell characteristics were inferior to those of Example 3 but had good adhesiveness, and there was no problem in terms of output improvement.

(Example 28)
A solar cell backsheet film was obtained in the same manner as in Example 1 except that the PET resin as the main component of the P1 layer and the P2 layer was changed to PET-g as shown in Table 3.

  When the cavity area ratio of the obtained solar cell backsheet film was confirmed, (Sc / Scs) and (Sc / Scs') were similar to those in Example 1. When the polymer characteristics were measured, the intrinsic viscosity IV and the amount of terminal carboxyl groups were changed as shown in the table.

About the obtained film for solar cell back sheets, as a result of performing characteristic evaluation, it turned out that adhesiveness is favorable as shown in a table | surface. Moreover, although the heat-and-moisture resistance slightly decreased with a decrease in intrinsic viscosity IV and an increase in the amount of terminal carboxyl groups, it was in a range without problems. It was also found that the thermal conductivity was excellent as in Example 1.
Furthermore, as a result of evaluating the solar cell characteristics, as shown in the table, it was found that although the output improvement was slightly reduced with the increase in the amount of terminal carboxyl groups as compared with Example 1, the adhesion was in a good range. It was.

(Examples 29 to 31)
A film for a solar battery back sheet was obtained in the same manner as in Example 1 except that the line speed was changed during film formation and the total thickness of the film was changed as shown in Table 3.

When the cavity area ratio of the obtained solar cell backsheet film was confirmed, both (Sc / Scs) and (Sc / Scs ′) were similar to those in Example 1.
As a result of performing solar cell back sheet characteristic evaluation about the obtained film for solar cell back sheets, as shown in Table 4, it was found that the adhesiveness of the film having a small film thickness was slightly lowered. Further, it was found that the thermal conductivity is in a good range although it is slightly lower than that in Example 1.
Furthermore, as a result of performing solar cell characteristic evaluation, as shown in the table, it was found that the adhesiveness of the solar cell slightly decreased as the film thickness decreased. Moreover, although the output improvement property also fell a little compared with Example 1, it turned out that it is a favorable range.

(Examples 32-44)
Using the coating material c prepared as the laminating adhesive on one surface of the P2 layer of the film for solar battery backsheet obtained in Example 1, it was applied using a wire bar and at a temperature of 80 ° C. for 45 seconds. The dried adhesive layer was formed so that the thickness of the coating film after drying was 5.0 μm.
Next, the functional layer B shown in Table 5 was laminated | stacked on the adhesive bond layer, and it aged for 3 days at the temperature of 40 degreeC, and was set as the solar cell backsheet. The obtained solar cell backsheet had good adhesion, heat and humidity resistance, and ultraviolet resistance, and at least one of Young's modulus, curl height, and water vapor barrier property was excellent. Moreover, it was excellent in the solar cell characteristic.

(Examples 45-49)
In the same manner as in Examples 32 to 44, the functional layer B shown in Table 6 was laminated on the adhesive layer and aged at a temperature of 40 ° C. for 3 days to obtain a solar battery back sheet. The solar cell backsheets obtained in Examples 45 to 49 had good adhesion, moisture and heat resistance, and ultraviolet resistance, and had a large Young's modulus and curl height, but were excellent in water vapor barrier properties. . Moreover, it was excellent in the solar cell characteristic.

(Examples 50 to 53)
Using one of the P2 layers of the solar cell backsheet film obtained in Example 1, the thickness of the functional layer B after drying becomes the thickness shown in Table 6, using a wire bar according to Table 6, and paint a The paint b was applied and dried at a temperature of 100 ° C. for 60 seconds to produce solar cell backsheet films (in Examples 50 to 53, porosity, (Sc / Scs), (Sc / Scs) ') Was determined based on a laminated film including the functional layer B). When the obtained solar cell backsheet film was evaluated as a solar cell backsheet, both the backsheet characteristics and the solar cell characteristics were excellent.

(Examples 54 and 55)
Using the coating material c prepared as the laminating adhesive on one surface of the P2 layer of the film for solar battery backsheet obtained in Example 1, it was applied using a wire bar and at a temperature of 80 ° C. for 45 seconds. The dried adhesive layer was formed so that the thickness of the coating film after drying was 5.0 μm.
Next, the functional layer B ′ shown in Table 6 was laminated on the adhesive layer and aged at a temperature of 40 ° C. for 3 days. Furthermore, using the coating material c prepared as a laminating adhesive on the other P2 layer on which the functional layer B ′ is not laminated, it is applied using a wire bar, dried at a temperature of 80 ° C. for 45 seconds, and after drying The adhesive layer for lamination was formed so that the thickness of the coating film was 5.0 μm. The functional layer B shown in Table 6 was laminated on the laminating adhesive layer and aged at a temperature of 40 ° C. for 3 days to obtain a solar cell backsheet. The obtained solar cell backsheets shown in Examples 54 and 55 had good adhesion, wet heat resistance, and ultraviolet resistance, and were excellent in Young's modulus, curl height, and water vapor barrier properties. Moreover, it was excellent in the solar cell characteristic.

(Example 56)
Using one of the P2 layers of the solar cell backsheet film obtained in Example 1, the thickness of the functional layer B after drying becomes the thickness shown in Table 6, using a wire bar according to Table 6, and paint a Was applied and dried at a temperature of 100 ° C. for 60 seconds to obtain a solar battery backsheet film having a functional layer B. Further, using a coating c prepared as a laminating adhesive on one P2 layer on which the functional layer B is not laminated, it is applied using a wire bar, dried at a temperature of 80 ° C. for 45 seconds, and dried. The adhesive layer for lamination was formed so that the film thickness was 5.0 μm. A functional layer B ′ shown in Table 6 was laminated on the laminating adhesive layer and aged at a temperature of 40 ° C. for 3 days to obtain a solar cell backsheet. The solar cell back sheet shown in Example 56 was excellent in water vapor barrier property, although Young's modulus and curl height were large. Moreover, the solar cell characteristics were also excellent.

(Comparative Example 1)
A solar cell backsheet film was obtained in the same manner as in Example 1 except that the amount of the hollow nucleating agent in the P1 layer was 3% by mass.
When the porosity of the obtained film for solar battery back sheets was confirmed, it was found that the porosity of the entire film was 9%, which was out of the scope of the present invention.
Furthermore, it turned out that the film for solar cell backsheets obtained by the comparative example 1 is a solar cell backsheet inferior in adhesiveness and heat conductivity. Moreover, it turned out that it is a solar cell inferior to an output improvement property and adhesiveness also about a solar cell characteristic.

(Comparative Examples 2-6)
In order to make the composition of the P1 layer as shown in the table, the amount of the hollow nucleating agent master pellets and the hollow nucleating agent master pellets G to J are used, or the barium sulfate master pellets are used in the P1 layer as the hollow nucleating agent. A film for a solar battery back sheet was obtained in the same manner as in Example 1 except that was used.

  When the cavity area ratio of the obtained film for solar cell backsheet was confirmed, it was found that both (Sc / Scs) and (Sc / Scs') were out of the scope of the present invention.

  Furthermore, it turned out that the film for solar cell backsheets obtained by Comparative Examples 1-4 is a solar cell backsheet with inferior adhesiveness. It turned out that the comparative example 6 is a solar cell backsheet with inferior thermal conductivity. Moreover, it turned out that it is a solar cell in which at least any one of output improvement property and adhesiveness is inferior also about the solar cell characteristic.

(Comparative Example 7)
A film for a solar battery back sheet was obtained in the same manner as in Example 1 except that the discharge rate of the extruder was adjusted so that the lamination ratio (P2: P1: P2) of the polyester film was 1: 1: 1.

  When the cavity of the obtained film for solar cell backsheets was confirmed, it turned out that a cavity does not exist on the division | segmentation horizontal line which passes C2-1 point and C2-2 point.

  Furthermore, it turned out that the film for solar cell backsheets is a solar cell backsheet with inferior adhesiveness and thermal conductivity. Moreover, it turned out that it is a solar cell inferior to an output improvement property and adhesiveness also about a solar cell characteristic.

(Comparative Example 8)
A solar cell backsheet film was obtained in the same manner as in Example 1 except that the PET resin as the main component of the P1 layer and the P2 layer was changed to PET-h.

When the cavity area ratio of the obtained solar cell backsheet film was confirmed, both (Sc / Scs) and (Sc / Scs') were the same as in Example 1, but the polymer properties were measured to determine the amount of terminal carboxyl groups. Decreased to 40 equivalents / ton.
Furthermore, it turned out that the film for solar cell backsheets obtained by the comparative example 8 is a solar cell backsheet inferior in adhesiveness and heat-and-moisture resistance. Moreover, it turned out that it is a solar cell in which both an output improvement property and adhesiveness are inferior also about the solar cell characteristic.

(Comparative Example 9)
Pre-heated unstretched sheet obtained by extruding and cooling from a T-die with a P1 layer single-layer structure during film formation with a roll group heated to a temperature of 70 ° C, and then placed at a position 15 mm away from both surfaces of the sheet A solar cell backsheet film was obtained in the same manner as in Comparative Example 2, except that the film was heated for 0.72 seconds at an output of 50 W / cm with the infrared heater and stretched three times in the longitudinal direction (longitudinal direction).
When the cavity area ratio of the obtained solar cell backsheet film was confirmed, unlike Comparative Example 2, the cavity area in the thickness direction was biased. However, in the range from the film surface to a depth of 10 μm, the average area per cavity is only small, and at a depth of 25 to 75% of the total film thickness, the average area per cavity is different. (Sc / Scs) and (Sc / Scs ′) were 1.0.
As in Comparative Example 2, the film for solar battery back sheet obtained in Comparative Example 9 was found to be a solar battery back sheet having poor adhesion. Moreover, it turned out that it is a solar cell in which both an output improvement property and adhesiveness are inferior also about the solar cell characteristic.

(Comparative Example 10)
A solar battery back sheet was laminated in the same manner as in Example 32 except that the film for Comparative Example 6 was used, and the functional layer B shown in Table 9 was laminated and aged at a temperature of 40 ° C. for 3 days. did. The obtained solar cell back sheet was inferior in Young's modulus and curl height. Moreover, about the solar cell characteristic, although adhesiveness was improved from the comparative example 6, it was a solar cell with inferior output improvement.

(Comparative Example 11)
A solar battery back sheet was laminated in the same manner as in Example 42 except that the film of Comparative Example 6 was used, and the functional layer B shown in Table 9 was laminated and aged at a temperature of 40 ° C. for 3 days. did. The obtained solar cell back sheet was inferior in Young's modulus and curl height. Moreover, it was a solar cell inferior to adhesiveness and output improvement about a solar cell characteristic.

By mounting the solar cell backsheet film of the present invention on a solar cell as a solar cell backsheet, adhesion to the solar cell backsheet even when placed outdoors for a long period of time compared to conventional solar cells Can be maintained, and the power generation efficiency can be increased. The solar cell of the present invention can be suitably used for various applications without being limited to outdoor use and indoor use such as a solar power generation system and a power source for small electronic components.

1: Solar cell back sheet 2: Sealing material 3: Power generation element 4: Transparent substrate 5: Surface on the sealing material 2 side of the solar cell back sheet 6: Surface 7 on the opposite side of the sealing material 2 of the solar cell back sheet : Film thickness direction 8: Film surface direction 9: Intermediate point between the film thickness direction center point and the film surface (point C2-1)
10: Film thickness direction center point (point C1)
11: Intermediate point between the film thickness direction center point and the film surface (point C2-2)
12: Divided horizontal line passing through point C2-1 13: Divided horizontal line passing through point C1 14: Divided horizontal line passing through point C2-2 15: Cavity 16: Functional layer B
17: Film for solar cell backsheet 18: Functional layer B ′
19: Adhesive layer

Claims (14)

A void-containing polyester film,
The porosity of the entire film is 10% or more,
In the thickness direction cross section of the polyester film,
A line perpendicular to the surface direction is drawn from one surface of the film to the other surface, and a line connecting the one surface to the other surface is divided into four equal parts in the thickness direction (film thickness direction center point (C1 Point), in each of the lines parallel to the surface direction of the film (divided horizontal lines) passing through the center point between the film thickness direction center point and the film surface (point C2-1), (point C2-2)),
Sc (μm ² ), the average area per cavity existing on the dividing horizontal line passing through the C1 point,
Scs (μm ² ), the average area per cavity existing on the dividing horizontal line passing through the C2-1 point,
When the average area per cavity existing on the divided horizontal line passing through the C2-2 point is Scs ′ (μm ² ), at least one of (Sc / Scs) and (Sc / Scs ′) is 1.1. The film for solar battery back sheets which is 35 or less and the amount of terminal carboxyl groups of the polyester resin constituting the polyester film is 35 equivalents / ton or less.
(Note that (Sc / Scs) and (Sc / Scs ′) are parallel to the film thickness direction cross section and the film width direction at any five locations of the polyester film, the film being cut in parallel to the film longitudinal direction. The average value of the values obtained from the cross-section in the thickness direction of the film obtained by cutting the film. The film for solar battery backsheet according to claim 1, wherein the total thickness of the polyester film is 45 µm or more. The polyester film has a laminated structure of three or more layers, and at least one of the resin compositions constituting both surface layers (one surface layer is a P2 layer and the other surface layer is a P2 ′ layer). The film for solar battery backsheets according to claim 1 or 2, wherein the composition contains inorganic particles, and a layer having no surface layer (the layer is referred to as P1 layer) contains a cavity. The thickness of the P1 layer is T1 (μm), the thickness of the P2 layer is T2 (μm), the thickness of the P2 ′ layer is T2 ′ (μm), and the inorganic particle concentration contained in the resin composition constituting the P2 layer is W2 (mass) %), When the inorganic particle concentration contained in the resin composition constituting the P2 ′ layer is W2 ′ (mass%),
The film for solar battery backsheet according to claim 3, wherein at least one of (T1 / T2) x W2 and (T1 / T2 ') x W2' is 0.35 or more and 1.50 or less.   When the thickness of the P1 layer is T1 (μm), the thickness of the P2 layer is T2 (μm), and the thickness of the P2 ′ layer is T2 ′ (μm), T1 / (T1 + T2 + T2 ′) is 0.6 or more and 0.99 or less The film for solar cell backsheet according to claim 3 or 4, wherein T2 / (T1 + T2 + T2 ') and T2' / (T1 + T2 + T2 ') are 0.01 or more and 0.2 or less. The film for solar battery backsheet according to any one of claims 3 to 5, wherein the porosity (Ps) of the P2 layer and the porosity (Ps ') of the P2' layer are 5.0% or less. The film for solar cell backsheet according to any one of claims 1 to 6, having a thermal conductivity of 0.9 W / m · K or less. It is a solar cell backsheet which has a film for solar cell backsheets in any one of Claims 1-7, and at least 1 or more functional layer, Comprising: The Young's modulus of the film for solar cell backsheets is 4.0 GPa or less The solar cell back sheet, wherein the solar cell back sheet has a Young's modulus of 4.0 GPa or less. The solar cell backsheet according to claim 8, wherein the functional layer includes at least one of the following group 1 or a plurality of combinations.
Group 1: Polyethylene, polypropylene, ethylene vinyl acetate copolymer The solar cell backsheet according to claim 8, wherein the functional layer includes at least one of the following group 2 or a plurality of combinations.
Group 2: Polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) The solar cell backsheet according to claim 8, wherein the functional layer contains polyurethane. The solar cell backsheet according to claim 8, wherein the functional layer contains an inorganic compound. The solar cell backsheet according to claim 8, wherein the functional layer contains polyester, and the film for solar cell backsheet and the functional layer are laminated via an adhesive layer. The solar cell using the film for solar cell backsheets in any one of Claims 1-7, or the solar cell backsheet in any one of Claims 8-13.

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