JP6743698B2 - Film for solar cell back sheet, solar cell back sheet using the same, and solar cell - Google Patents

Description

The present invention relates to a film for a solar cell backsheet, a solar cell backsheet and a solar cell using the film.

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 becoming popular.

A typical configuration of a general solar cell is shown in FIG. The solar cell includes a power generation element 3 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 composed by sticking together. Sunlight is introduced into the solar cell through the transparent substrate 4. The 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 generating element 3 and used for various electric devices. Here, the solar cell backsheet 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. Although various proposals have been made for the solar cell system and each member, for the solar cell backsheet 1, polyethylene, polyester, or fluorine resin films are mainly used. (See Patent Documents 1 to 3)
In the conventional solar battery backsheet, a technique has been developed to improve the efficiency of the solar battery module by reflecting the light passing between the solar battery cells by the solar battery backsheet and taking it into the cells. Specifically, a technology for forming a reflective layer with white beads and a white binder on the surface of a base material to improve module efficiency, and a technology for providing a highly reflective solar cell backsheet by forming a layer containing cavities (Patent References 4 and 5) have been proposed.

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

However, as in Patent Document 4, in the proposal of forming a reflective layer with white beads and a white binder on the surface of a base material, by using white beads, the bonding material is applied when manufacturing EVA or a back sheet, which is a sealing material for solar cells. However, there is a problem that the adhesiveness with other member films deteriorates. Further, as in Patent Document 5, the proposal for forming a highly reflective backsheet by forming a layer containing cavities has a certain effect of improving the power generation efficiency, but is still insufficient for improving the power generation efficiency of the solar cell module. There was a problem that was.

Therefore, in view of such background of the prior art, the present invention provides a film for a solar cell backsheet that achieves both excellent output improving effect and adhesion, and a solar cell backsheet and a solar cell using the film. It is a thing.

That is, the present invention is a void-containing polyester film having a porosity of 10% or more as a whole, and in a 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. And a line connecting the one surface to the other surface is equally divided into four points in the thickness direction (a film thickness direction center point (C1 point), a midpoint between the film thickness direction center point and the film surface (C2- 1) and (C2-2 point)), the average area per cavity existing on the dividing 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), the average area per cavity present on dividing the horizontal line passing through the C2-2 points Is Scs′ (μm ² ), 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 It is a film for a solar cell backsheet having an amount of 35 equivalents/ton or less.

ADVANTAGE OF THE INVENTION According to this invention, as compared with the conventional film for solar cell backsheets and solar cell backsheets, the adhesion retention property with EVA resin which is a sealing material of a solar cell, or another member film bonded at the time of processing a backsheet ( A solar cell having excellent power generation efficiency (hereinafter referred to as output improvement) can be provided by being excellent in adhesion (hereinafter referred to as “adhesion”) and further equipped with the solar cell backsheet of the present invention.

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. 1 is a schematic view showing a cross section in the thickness direction of a film for solar cell backsheet. 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 uses the film for solar cell backsheets of this invention, and has a functional layer on one side through an adhesive layer. It is sectional drawing which shows typically an example of a structure of the solar cell backsheet which uses the film for solar cell backsheets of this invention, and has a functional layer on both sides through the adhesive layer.

The film for a solar cell backsheet of the present invention is a void-containing polyester film having a porosity of 10% or more in the entire film, and in the cross section in the thickness direction of the polyester film, a surface from one surface of the film to the other surface A line perpendicular to the direction is drawn, and the line connecting the other surface to the other surface is equally divided into four points in the thickness direction (film thickness direction center point (C1 point), film thickness direction center point and film surface 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)), one cavity existing on the divided horizontal line passing through C1 point The average area per unit is Sc (μm ² ), the cavity existing on the dividing horizontal line passing through the point C2-1 is Scs (μm ² ), the average area per unit is the cavity existing on the dividing horizontal line passing through the point C2-2 When the average area per piece is Scs' (μm ² ), at least one of (Sc/Scs) and (Sc/Scs') is 1.1 or more and 35 or less, and a polyester resin constituting the polyester film. It is characterized by satisfying that the amount of terminal carboxyl groups of is not more than 35 equivalents/ton.
The film for a solar cell backsheet of the present invention will be described below.

The film for a solar cell backsheet of the present invention is a void-containing polyester film having a porosity of 10% or more as a whole, and contains a polyester resin as a main component. Here, having the polyester resin as a main component means that the polyester resin is contained in an amount of more than 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 a dicarboxylic acid or its ester-forming derivative (hereinafter collectively referred to as "dicarboxylic acid component") and a diol component, 2) a carboxylic acid or a carboxylic acid derivative in one molecule. It can be obtained by polycondensation of a compound having a hydroxyl group with a compound of 1) and 2). The polyester resin can be polymerized 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, adamantane dicarboxylic acid, norbornene dicarboxylic acid, cyclohexanedicarboxylic acid, alicyclic dicarboxylic acids such as 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 Aromatic dicarboxylic acids such as acids, 5-sodium sulfoisophthalic acid, phenylendanedicarboxylic acid, anthracene dicarboxylic acid, phenanthrene dicarboxylic acid, and 9,9'-bis(4-carboxyphenyl)fluorenic acid, or ester derivatives thereof are typical. Take as an example. In addition, these may be used alone or in combination of a plurality of types.

A dicarboxy compound obtained by condensing at least one carboxy terminal of the above-mentioned dicarboxylic acid component, oxyacids such as 1-lactide, d-lactide, and hydroxybenzoic acid and derivatives thereof, and a series of a plurality of such oxyacids. 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, and 1,3-butanediol, Cyclohexanedimethanol, spiroglycol, alicyclic diol such as isosorbide, bisphenol A, 1,3-benzenedimethanol, 1,4-benzenedimethanol, fragrance such as 9,9'-bis(4-hydroxyphenyl)fluorene Group diols are typical examples. In addition, these may be used alone or in combination of a plurality of types as necessary. Further, a dihydroxy compound formed by condensing a diol with the hydroxy terminal of at least one of the above-mentioned diol components can also be used.

In 2), examples of the compound 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 their derivatives, oligomers of oxyacids, and dicarboxylic acids. Examples thereof include those in which an oxy acid is condensed with one carboxyl group of an acid.

The polyester resin obtained from the above two components comprises polyethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, polypropylene terephthalate, polybutylene terephthalate, poly-1,4-cyclohexylene dimethylene terephthalate and mixtures thereof. Is preferably used, and more preferably polyethylene terephthalate and polyethylene-2,6-naphthalene dicarboxylate are preferable from the viewpoint of good film-forming property, and polyethylene is preferable from the viewpoint that a film for a solar cell backsheet having more excellent adhesion can be obtained. Most preferred is terephthalate.

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

Conventionally, in applications where adhesion with an adherend such as an adhesive is required, it is known that by increasing the polarity of the adhered surface, the energy affinity with the adherend such as an adhesive can be further increased. ing. That is, in the film for a solar cell backsheet, when the amount of terminal carboxyl groups of the polyester resin forming the film is increased, the polarity of the polyester resin forming the film is increased and the adhesiveness with a sealing agent such as EVA tends to be increased. There was However, as a result of diligent studies by the present inventors, when the amount of the terminal carboxyl group exceeds 35 equivalents/ton, although the initial adhesiveness is excellent, the resistance to moist heat of the polyester film is lowered, so that the film is left outdoors for a long period of time. It was found that, when it is peeled, the film becomes brittle and the adhesion surface is destroyed, resulting in a decrease in the adhesion to EVA and other member films. It has also been found that the film may be discolored due to wet heat deterioration and the reflectivity may be impaired, resulting in a decrease in output improvement. The film for a solar cell backsheet of the present invention controls the size of the cavity contained in the film to a specific size as described below, so that the amount of terminal carboxyl groups of the polyester resin constituting the polyester film is 35 equivalents. It is possible to improve the adhesiveness even if it is less than or equal to /ton, and it is possible to achieve both excellent adhesiveness and wet heat resistance, which are difficult to achieve in the past, and also output improvement characteristics.

The lower limit of the amount of terminal carboxyl group is not particularly limited as long as it does not impair the effects of the present invention, but 7 equivalents/ton or more is more preferable, and 11 amounts/ton or more is further preferable. If the amount of terminal carboxyl groups is less than 7 equivalents/ton, the polar end groups on the surface become 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 still more preferably 0.67 dl/g or more. When the intrinsic viscosity IV is less than 0.63 dl/g, the dispersibility of the nucleating agent forming the cavities may be reduced, and as a result, the adhesion may be reduced. In addition, the resistance to moist heat of the polyester film may be lowered. 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 be 0.63 dl/g or more and 0.80 dl/g or less, a film for a solar cell backsheet that has both adhesion, wet heat resistance, and processability can be obtained. You can

Further, the number average molecular weight Mn of the polyester resin is preferably 8,000 to 40,000, more preferably the number average molecular weight Mn is 9000 to 30,000, and further preferably 10,000 to 20,000. When the number average molecular weight Mn is less than 8000, durability such as moist heat resistance and heat resistance may decrease. On the other hand, when the number average molecular weight Mn exceeds 40,000, the polymerization is difficult, and even if the polymerization is possible, the extrudability of the polyester resin may deteriorate.

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. More preferably, Mn and Na are contained in the above range. When Mn or Na is contained in the polyester resin in the above range, hydrolysis of the film is suppressed, and a film for a solar cell backsheet that has excellent wet heat resistance, adhesion, and output improvement can be obtained. ..

The polyester film of the present invention has a cavity inside. In the present invention, “cavity” is obtained when a microtome is used, the film is cut perpendicularly to the film surface direction without being crushed in the thickness direction, and the cut surface of the film is observed using an electron microscope. Represents voids having a cross-sectional area of 0.1 μm ² or more observed in the observed image. The polyester film of the present invention needs to have a porosity (a ratio of cavities in the film cross section) of 10% or more. The porosity is more preferably 15% or more, further preferably 20% or more. The porosity of the entire film can be obtained from the area of the hollow portion in the observed 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. On the other hand, if the voids are too small, stress concentrates at the contact interface with another member film, and the adhesion of the film for solar cell backsheet decreases.

The method for forming cavities inside the polyester film is not particularly limited, but a method in which the polyester film contains a cavity nucleating agent and is 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 cell backsheet film may be reduced.

Examples of the cavity nucleating agent include organic nucleating agents such as olefinic resins which are incompatible with polyester resin, and inorganic nucleating agents such as inorganic particles and glass beads. As the cavity nucleating agent, an organic nucleating agent is preferable because it is easy to make the shape of the cavity inclined in the thickness direction by the manufacturing method described later. By making the shape of the cavity inclined in the thickness direction, the adhesion of the film for a solar cell backsheet can be enhanced.

As the organic nucleating agent, an olefin resin, nylon 6, nylon 66, nylon 610, nylon 11, nylon 12, nylon 46, nylon MXD6, nylon 6T or other polyamide resin, polystyrene, acrylonitrile-styrene copolymer, acrylonitrile-butadiene- Styrene resin such as styrene copolymer, acrylic resin such as polymethylmethacrylate and polybutylmethacrylate, fluorine resin such as polytetrafluoroethylene and polyvinylidene fluoride, polyphenylene sulfide, polysulfone, polyether sulfone, polyarylate, poly It is also possible to use super engineering plastics such as ether imide, or different types of polyester resins that are incompatible with the polyester resin constituting the polyester film of the present invention. Examples of the olefin-based resin include polypropylene, polyethylene, high-density polyethylene, low-density polypropylene, ethylene-propylene copolymer, aliphatic polyolefin resin such as polymethylpentene, cyclic polyolefin resin such as cycloolefin polymer and cycloolefin copolymer, and the like. Among them, an olefinic resin having a Vicat softening point of 140° C. or higher is preferable as the organic nucleating agent, since an organic nucleating agent has an excellent output improving property of a film for a solar cell backsheet by forming fine voids and further improving reflectivity. An olefin resin having a temperature of 0° C. or higher is more preferable. When an olefinic resin having a Vicat softening point of less than 140° C. is used as the organic nucleating agent, the shape of the cavity may be excessively coarsened, and the film adhesion for a solar cell backsheet and 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 further preferably, based on the total mass of the polyester film. Is 8% by mass or more and 13% by 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 a solar cell backsheet has excellent adhesion but may have poor output improvement due to reduced reflectivity. .. On the other hand, when the amount of the organic nucleating agent exceeds 30% by mass, the output improving property is excellent, but the number of cavities is too large and the adhesiveness may be poor.

Further, when an organic nucleating agent is used, it is preferable to use a dispersion auxiliary together. 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 the dispersibility, a form in which two or more 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 further preferably, the total mass of the polyester film. It is 3% by mass or more and 6% by mass or less. If the amount of the dispersion aid contained in the polyester film is less than 1% by mass, the effect as the dispersion aid may be insufficient and the adhesion may decrease. On the other hand, when the amount of the dispersion aid exceeds 10% by mass, the dispersibility is excessively improved, which may rather reduce the adhesion. Furthermore, the decrease in crystallinity may decrease the wet heat resistance of the polyester film.

The film for a solar cell backsheet of the present invention has a cavity in an observed image of a cross section in the thickness direction of a polyester film, and draws a line perpendicular to the surface direction from one surface of the film to the other surface, and from one surface to another. Three points that divide the line connecting one surface into four equal parts in the thickness direction (the center point in the film thickness direction (C1 point), the midpoint between the center point in the film thickness direction and the film surface (C2-1 point), (C2-2) Sc (μm ² ), the average area per cavity existing on the dividing horizontal line passing through the point C1 in a line (dividing horizontal line) parallel to the plane direction of the film passing through the point C), and 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 ), ( At least one of Sc/Scs) and (Sc/Scs') is a polyester film of 1.1 or more and 35 or less. It is preferably 1.5 or more and 20 or less, more preferably 2.0 or more and 15 or less, and further preferably 2.5 or more and 10 or less. The 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 voids contained in the film is 1.1 or more and 35 or less in at least one of (Sc/Scs) and (Sc/Scs'). It was surprisingly found that the adhesion is improved by providing a gradient in the thickness direction so that It is not completely clear why this effect occurs, but the inventors presume as follows. When both (Sc/Scs) and (Sc/Scs') are less than 1.1 (the inclination of the size of the cavity contained in the film in the thickness direction is small), a fine cavity is formed inside the polyester film. Even if it is done, when the film for solar battery backsheet of the present invention is brought into close contact with EVA which is a sealing material for solar battery cells and other member films which are stuck together at the time of manufacturing the backsheet, the film tends to peel off the contact surface. Since the force is applied to the surface of the film too uniformly, the adhesion of the film for solar cell backsheet decreases. On the other hand, when both (Sc/Scs) and (Sc/Scs') exceed 35 (the size of the cavity contained in the film has a large inclination in the thickness direction), the deviation of the cavity area in the thickness cross section is large. As a result, the peeling progresses easily from the coarse cavity, resulting in a decrease in adhesion. Further, since the light reflectivity due to the cavity is lowered, the output improving property of the film for a solar cell backsheet of the present invention is also lowered, and the power generation output of the mounted solar cell cannot be increased.

In the present invention, (Sc/Scs) and (Sc/Scs′) are the shapes of cavities such as the kind of cavity nucleating agent, the amount of cavity nucleating agent, the amount of dispersant, or the polyester resin after melt extrusion during film production. It can be adjusted by the cooling rate. For example, by using an olefinic resin having a Vicat softening point of 140° C. or higher as an organic nucleating agent and increasing the amount of the void nucleating agent and the amount of the dispersion aid within the preferable ranges, the voids are further miniaturized more uniformly and 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 the preferable ranges, the deviation of the cavity area in the thickness cross section increases, and (Sc/Scs) and (Sc/Scs') increase. Further, when the cooling rate of the polyester resin after melt extrusion during film production is high, the inclination of the size of the cavity contained in the film in the thickness direction tends to be small, and (Sc/Scs) and (Sc/Scs'). ) Becomes smaller. Further, when the cooling rate is slow, the inclination of the size of the cavities contained in the film in the thickness direction tends to be small, and (Sc/Scs) and (Sc/Scs') are large.

That is, the film for a solar cell backsheet of the present invention adjusts the type of the cavity nucleating agent inside, the cavity nucleating agent amount, the dispersant amount, or the cooling rate of the polyester resin after melt extrusion during film production within a preferable range. By doing so, at least one of the voids (Sc/Scs) and (Sc/Scs') inside the polyester film is 1.1 or more and 35 or less, and for a solar battery backsheet that 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 is in the range of 1.1 or more and 35 or less, (Sc/Scs) or By arranging the surface where (Sc/Scs') is in the preferable range, the adhesiveness and the output improving property can be further enhanced. For example, when only (Sc/Scs) is 1.1 or more and 35 or less, the solar cell backsheet film arranged so that the sealing material is located on the film surface side close to Scs has good adhesion and output improvement. Can be achieved at the same time.
Here, when both (Sc/Scs) and (Sc/Scs') are in the range of 1.1 or more and 35 or less, the adhesiveness on both surfaces of the film for solar cell backsheet is excellent, and therefore, for example, the present invention It is more preferable that one side of the film for a solar battery backsheet is laminated with another member film, and the other side is directly laminated to the solar cell, because excellent adhesion can be obtained on both surfaces of the film. ..

INDUSTRIAL APPLICABILITY The film for a solar battery backsheet of the present invention can reuse the light and increase the power generation output by reflecting the light passing between the solar cells while diffusing the light on the solar battery backsheet. From the viewpoint of enhancing the light diffusibility, it is preferable that the polyester resin composition forming the polyester film contains inorganic particles.
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, kaolin. , Lithium fluoride, and calcium fluoride. 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 is preferable from the viewpoint of simultaneously increasing the ultraviolet resistance of the film for solar cell 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 being superior in ultraviolet resistance. More preferable.
That is, in the film for a solar cell backsheet of the present invention, the output improving property can be further enhanced by incorporating inorganic particles into the polyester resin composition forming the polyester film having the voids.

The form in which the resin composition forming the polyester film contains the inorganic particles is not particularly limited, but has a laminated structure of three or more layers, and both surface layers (one surface layer is a P2 layer). , The other surface layer is a P2′ layer), and at least one of the resin compositions constituting the P2′ layer contains inorganic particles and does not have a surface layer (the layer is a P1 layer). Preferably contains the above-mentioned cavity nucleating agent, and more preferably has a three-layered laminated structure of P2 layer/P1 layer/P2′ layer.

When inorganic particles are contained in the P2 layer and the P2′ layer, they may serve as void nucleating agents and may also contain a small amount of voids in the surface layer. 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 further preferably 3.5%. It is the following. If any of the porosities (Ps) and (Ps′) of the P2 layer and the P2′ layer exceeds 5.0%, the deviation of the void area on the surface side may become unstable and the adhesiveness may deteriorate. .. In the film for a 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 lowering the adhesiveness, The reflectivity of the P1 layer and the diffusivity of the P2 layer or the P2' layer can be utilized without canceling each other, and the output improvement can be further enhanced. Further, it is possible to prevent process contamination by the cavity nucleating agent during the production of the polyester film.
When only one of the porosity (Ps) of the P2 layer and the porosity (Ps′) of the P2′ layer is 5.0% or less, a solar cell expected to have the effect of the present invention By arranging the P2 layer or P2′ layer satisfying the above range on the side, the adhesion can be further improved.
The structure having a P2 layer or a P2' layer containing the above-mentioned inorganic particles having ultraviolet resistance in the surface layer of the film for a solar battery backsheet of the present invention has an output improving effect and a solar battery backsheet for ultraviolet light hitting a solar battery cell. It can be said to be a more preferable form because it is possible to achieve both UV resistance such as suppressing discoloration of the film. In addition, the laminated structure having inorganic particles in both the resin composition forming the P2 layer and the P2′ layer has the above-mentioned effect of the ultraviolet resistance on the side of the solar battery cell against the reflected light of the ultraviolet light hitting the back surface of the solar battery. Can also be exhibited, which is a more preferable form.

The main components of the P2 layer and the P2′ layer (hereinafter, may be collectively referred to as the P2 layer) 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 that of the P1 layer as the main component of the P2 layer, a solar cell backsheet film having excellent adhesiveness at the interface between the P1 layer and the P2 layer can be obtained. In addition, by using an acrylic resin or the like as the main component of the P2 layer, it becomes possible to provide the P2 layer in which the inorganic particles are more highly filled on the P1 layer by a coating method, and it is possible to achieve excellent adhesion and improved output. It can be used as a film for a battery back sheet.
When the film for a solar cell backsheet of the present invention has the above-mentioned 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 concentration of inorganic particles contained in the resin composition forming the P2 layer is W2 (mass %), and the concentration of inorganic particles contained in the resin composition forming 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. It is more preferably 0.75 or more and 1.40 or less, and even more preferably 0.90 or more and 1.20 or less.

Here, when both of (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 which layer is the solar cell Even if it is installed on the side, the output improvement of the film for solar cell backsheet may be reduced. On the other hand, when both (T2/T1)×W2 and (T2′/T1)×W2′ exceed 1.50, the light reaching the P1 layer becomes too strong because the diffusivity of the P2 layer and the P2′ layer becomes too strong. Since the amount of the power is reduced, the output improvement may be rather deteriorated.

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 expected to have the effect of the present invention By arranging the P2 layer or the P2′ layer satisfying the above range on the cell side, it is possible to further improve the output improvement property. For example, when only (T2/T1)×W2 is 0.35 or more and 1.50 or less, the solar cell backsheet film arranged so that the sealing material of the power generation cell is located on the P2 layer side has an adhesiveness. It is possible to achieve both output improvement. It is preferable that both (T2/T1)×W2 and (T2′/T1)×W2′ be 0.35 or more and 1.50 or less, because the output improvement is particularly excellent.

When the P1 layer also contains inorganic particles, the inorganic particle concentration is preferably 10% by mass or less based on the total mass of the P1 layer from the viewpoint of maintaining excellent adhesion of the film for solar cell backsheet. Mass% or less is more preferable, and 3 mass% or less is further preferable. When the content of the inorganic particles in 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 a solar cell backsheet may deteriorate.

Furthermore, T1/(T1+T2+T2′), which represents 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′ relative to the entire film thickness. It is preferable that T2/(T1+T2+T2′) and T2′/(T1+T2+T2′), which represent the ratio occupied by the layers, are 0.01 or more and 0.2 or less. By satisfying the above range, both excellent adhesion and improved output can be achieved.

In the film for a solar cell backsheet of the present invention, in addition to the above-mentioned cavity nucleating agent and inorganic particles, if necessary, within a range that does not impair the effects of the present invention, a heat resistance stabilizer, an oxidation resistance stabilizer, and ultraviolet absorption. Additives such as agents, ultraviolet stabilizers, organic/inorganic lubricants, organic/inorganic fine particles, fillers, nucleating agents, dyes, coupling agents and the like may be added. For example, when an ultraviolet absorber is selected as the additive, it becomes possible to further enhance the ultraviolet resistance of the film for a solar cell backsheet of the present invention. Also, an antistatic agent or the like can be added to improve the electric insulation.

The thickness of the entire film for a solar cell backsheet 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 thickness of the solar cell backsheet film of the present invention is less than 25 μm, wrinkles may occur during the laminating process with other member films. On the other hand, if the thickness is thicker than 350 μm, the windability may deteriorate. When the thickness of the entire film is 45 μm or more, the effect of improving the adhesiveness due to the unevenness of the cavity area in the thickness direction described above is remarkably obtained, and the output improving effect is obtained because the light reflectivity is good. preferable. The thickness is more preferably 48 μm, further preferably 50 μm or more.

Furthermore, the film for a solar cell 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 film for a solar cell backsheet of the present invention is used as a solar cell backsheet, another film may be laminated on the surface opposite to the surface in contact with the encapsulant (hereinafter referred to as the air side surface). By setting the rate to 0.9 W/m·K or less, heat generation of the cell can be blocked, and a decrease in adhesion with the film laminated on the air side surface can be suppressed. 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 cell back sheet)
Next, the method for producing the film for a solar cell backsheet of the present invention will be described with reference to examples. This is an example, and the present invention should not be construed as being limited to the products obtained by such an example.

First, the polyester resin used as the raw material for the film for a solar cell backsheet of the present invention can be obtained by subjecting a dicarboxylic acid or an ester derivative thereof and a diol to a transesterification reaction or an 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, at any stage before the completion of the usual production method, it is preferable to add an alkali metal compound, a manganese compound, an antimony compound or a germanium compound, a titanium compound as a polymerization catalyst, and the adhesion of the solar cell backsheet film. It is more preferable to add a sodium compound and 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 the temperature at the time of polymerization, or after the polyester resin is polymerized, heated at 190°C to a temperature lower than the melting point of the polyester resin under reduced pressure or under the flow of an inert gas such as nitrogen gas. It can be controlled by the so-called solid-state polymerization time. Specifically, the amount of terminal carboxyl groups increases as the temperature during polymerization increases, and the amount of terminal carboxyl groups decreases as the solid phase polymerization time increases.

The method for incorporating a cavity nucleating agent or inorganic particles into the film for a solar cell backsheet of the present invention is a master pellet prepared by melt-kneading a raw material in advance using a vent-type twin-screw kneading extruder or a tandem type extruder. The method of blending is preferred. At this time, the master pellet is subjected to a heat history, so that there is a concern that thermal deterioration will progress to some extent. Therefore, it is more preferable to prepare a master pellet containing a cavity nucleating agent or inorganic particles at a higher concentration and mix and dilute them to use. Specifically, when adding a cavity nucleating agent to the film for a solar cell backsheet of the present invention, a master pellet having a larger content than the cavity nucleating agent content to be contained in the polyester film is prepared in advance, and It is mixed with the polyester resin, which is the main component of the polyester film, to adjust the content to the target.

Next, the method for forming a film for a solar cell backsheet of the present invention is a raw material adjusted to have a composition of a polyester film, heated and melted in an extruder, and extruded from a die onto a cast drum to be processed into a sheet. The method (melt casting method) can be used.
The film for a solar cell backsheet of the present invention is preferably cooled at a cast drum temperature of 30 to 80°C, more preferably 40 to 70°C, still more preferably 45 to 60°C. If the temperature of the cast drum is lower than 30° C., the cooling rate of the melt-extruded film is too high, and the (Sc/Scs) or (Sc/Scs′) of the polyester film becomes small, which may deviate from the preferable range. On the other hand, if the temperature of the cast drum exceeds 80° C., the crystallization of the polyester resin may proceed too much, causing breakage during stretching.

Subsequently, the obtained sheet is guided 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 by a roll group having a temperature of 20 to 50° C. .. Subsequently, the sheet is guided to a tenter while holding both ends with clips, and stretched in a direction (width direction) perpendicular to the longitudinal direction in an atmosphere heated to a temperature of 80 to 150°C. At this time, the stretching ratio is preferably a surface magnification of 2 times or more and 30 times or less, more preferably 4 times or more and 25 times or less, and further preferably 6 times or more and 20 times or less. Cavities having an appropriate size can be formed in the polyester film of the present invention by stretching at the above-mentioned ratio. If the surface magnification is less than 2 times, the cavities become small and the output improvement may deteriorate. On the other hand, if the surface magnification exceeds 30 times, the voids may become too large and the adhesion may deteriorate. Further, it is not preferable from the viewpoint that the load on the film forming machine becomes too large.

Further, the difference between the stretching ratios in 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, still more preferably 1 time or less. If the difference in the draw ratio exceeds 4 times, the shape of the cavities inside the polyester film may be biased in one direction, and the adhesion may deteriorate.

That is, in the film for a solar cell backsheet of the present invention, the polyester film has a stretching ratio difference of 4 times or less in the longitudinal direction (running direction during film formation) and the width direction of the film, and an area magnification of 2 times or more and 30 times. By stretching at the following ratios, it is possible to obtain a film for a solar cell backsheet that has excellent adhesion, output improvement, and moist heat resistance, and is excellent in processability.

Then, after stretching, heat setting is performed in a tenter. 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 the heat setting is performed at less than 150° C., the thermal dimensional stability of the film for solar cell backsheet is lowered, and problems such as curling may occur during backsheet processing. On the other hand, when heat setting is performed at a temperature of more than 250° C., the void nucleating agent inside the film may flow and the desired reflection performance may not be obtained.

Further, when the film for a solar cell backsheet of the present invention has a P2 layer, for example, the raw materials forming the P1 layer and the raw materials forming the P2 layer are charged into two different extruders, respectively, melted and then joined together, A method of coextruding on a cast drum cooled from a die and processing into a sheet (coextrusion method), or a method of forming a polyester film having a P1 layer by itself and then forming a raw material for a P2 layer dissolved in a solvent. A method (coating method) of forming a P2 layer by drying the solvent after coating by a roll coating method, a dip coating method, a bar coating method, a die coating method, a gravure roll coating method, or the like is preferably used.

The film for solar cell backsheet obtained by the above-mentioned production method is excellent in moisture resistance and heat resistance of conventional solar cell backsheet films, heat resistance, ultraviolet resistance, thermal dimensional stability, while maintaining processability. It is possible to achieve both good adhesion and improved output.

(Solar cell back sheet)
Next, the solar cell backsheet of the present invention will be described. It is important that the solar cell backsheet of the present invention is a solar cell backsheet having the film for a solar cell backsheet of the present invention and at least one or more functional layers. Among them, the curl height of the solar cell backsheet, which is determined by the measuring method described below, is preferably 10 mm or less, and more preferably 5 mm or less. By setting the curl height of the solar cell backsheet to 10 mm or less, the occurrence rate of misalignment and cell cracking caused by curl is reduced, and the productivity of solar cells can be improved.

In order to set the curl height of the solar cell backsheet to 10 mm or less, the Young's modulus of the film for solar cell backsheet is set to 4.0 GPa or less and the Young's modulus of the solar cell backsheet is set to 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 cell backsheet to 4.0 GPa or less, the curl that occurs when the solar cell backsheet is stored in a roll state is caused by the weight of the solar cell backsheet when it is stacked on the solar cell. Can be flat.
The method for setting the Young's modulus of the solar cell backsheet film in the above range is not particularly limited, but it can be adjusted by the following method. For example, if the porosity in the polyester film for solar cell backsheet is increased or the stretching ratio during film formation is decreased, the Young's modulus of the film for solar cell backsheet tends to decrease. Further, when the porosity in the polyester film for solar cell backsheet is lowered or the stretching ratio during film formation is increased, the Young's modulus of the film for solar cell backsheet tends to increase. The Young's modulus of the solar cell backsheet tends to increase when the Young's modulus of the solar cell backsheet film used for the solar cell backsheet is high, and tends to be low when the Young's modulus is low. Other than that, it can be adjusted by the Young's modulus of the layer laminated on the film for solar cell backsheet.

The functional layer of the solar cell backsheet of the present invention is preferably a layer containing at least one of polyethylene, polypropylene, and an ethylene vinyl acetate copolymer, or a layer containing a combination of two or more thereof, because the adhesion is 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 sealing material, it becomes possible to have good adhesion with the sealing material. Among them, polyethylene is preferably used from the viewpoint of weather resistance and water vapor barrier property. When the layer containing at least one of polyethylene, polypropylene, and ethylene vinyl acetate copolymer, or a combination of a plurality of layers is used as the 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. Is more preferable. When the thickness of the layer is 30 μm or more, the water vapor barrier property and the insulating property are improved, and when the thickness is 300 μm or less, it is possible to suppress the process contamination due to the protrusion of the functional layer B during the production of the solar cell.
The method of laminating at least one of polyethylene, polypropylene, an ethylene vinyl acetate copolymer, or a layer containing a combination of a plurality of layers as a functional layer with the film for a solar cell backsheet of the present invention is not particularly limited. The method for directly laminating the film for a solar cell backsheet of the present invention or a method for laminating the film for a solar cell backsheet of the present invention and a functional layer via an adhesive or the like within a range that does not impair the effects of the present invention. Can be mentioned.

Further, the functional layer of the backsheet of the present invention has polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropolypropylene copolymer. A layer containing at least one of (FEP) or a combination of a plurality of (FEP) 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 a solar cell 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 the layer containing at least one of PVF, PVDF, ETFE, and FEP, or a combination of a plurality of layers is used as the functional layer, the thickness of the functional layer is preferably 25 μm or more and 125 μm or less, and 25 μm or more and 75 μm or less. 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 cell backsheet is improved.

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

It is preferable that the functional layer of the solar cell backsheet of the present invention is a layer containing polyurethane because the adhesion is good. In particular, when the functional layer is located between the film for a solar cell backsheet of the present invention and the encapsulant, the adhesion with the encapsulant is improved. The polyurethane referred to 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. There are diisocyanates such as (IPDI) and xylylene diisocyanate (XDI), trimethylolpropane adducts of these diisocyanates, isocyanurate bodies which are trimers of these diisocyanates, buret-bonded bodies of these diisocyanates, and polymeric diisocyanates. Of these, HDI is preferable from the viewpoint of color tone. Examples of the compound having a hydroxyl group include polyester polyols, polyether polyols, polyacrylic polyols, fluorine-based polyols and the like, and polyacrylic polyols and fluorine-based polyols are preferable from the viewpoint of wet heat resistance and weather resistance.
When the 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 used as the functional layer, the weather resistance is improved by setting the thickness of the functional layer to 1 μm or more, and the processability of the backsheet is improved by setting the thickness to 20 μm or less.
The method for laminating a layer containing polyurethane as a functional layer with the film for a solar cell backsheet of the present invention is not particularly limited, but a roll coating method, a gravure roll coating method, a kiss coating method, and another coating method, or The method of laminating by a printing method etc. is mentioned.
Further, the functional layer of the solar cell backsheet of the present invention preferably 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 wet heat resistance.
The method for laminating the layer containing an inorganic compound as a functional layer on the film for a solar cell backsheet of the present invention is not particularly limited, but a method for laminating directly on the film for a solar cell backsheet of the present invention, or the present invention Of the solar cell backsheet film is laminated with an inorganic compound on a different polyester film, within the range that does not impair the effects of the present invention, a layer other than the polyester film obtained by laminating the solar cell backsheet film of the present invention and the inorganic compound (function A method of laminating the layers) via an adhesive or the like can be mentioned.

Further, the solar cell backsheet of the present invention, a functional layer containing a polyester is laminated with the film for a solar cell backsheet of the present invention via an adhesive layer, and a solar cell backsheet has excellent weather resistance and processability. preferable.

When the layer containing polyester is used as the functional layer, 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 processability of the backsheet by decreasing 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 via an adhesive layer, porosity and (Sc/Scs), (Sc/Scs') are adhesive layers. It does not include the or functional layer. For example, in the case of a laminated film having a structure of functional layer containing polyester/adhesive layer/void-containing polyester film, the center point in the thickness direction of the void-containing polyester film is C1 point, and the film of C1 point and the void-containing polyester film Intermediate points with the surface are (C2-1 point) and (C2-2 point).

(Solar cell)
Next, the solar cell of the present invention will be described. In the solar cell of the present invention, the above-mentioned film for solar cell backsheet is mounted as it is. Alternatively, the above-mentioned solar battery back sheet is mounted.
A structural example of the solar cell of the present invention is shown in FIG. A power generation element to which a lead wire (not shown in FIG. 1) for taking out electricity is connected is sealed with a transparent sealing material 2 such as EVA resin, and a transparent substrate 4 such as glass and a solar cell backsheet 1 are used. Although it is configured by bonding, it is not limited to this and can be used in any configuration.

Here, in the solar cell of the present invention, the solar cell backsheet 1 plays a role of protecting the power generation cell installed on the back surface of the encapsulant 2 that seals the power generation element. Here, it is preferable to arrange the solar cell backsheet so that the P2 layer is in contact with the sealing material 2 in order to increase the power generation efficiency of the solar cell. With this configuration, it is possible to obtain a solar cell that has both excellent adhesiveness and power generation efficiency of the film for a solar cell backsheet of the present invention.

The power generation element 3 converts light energy of sunlight into electric energy, and includes crystalline silicon type, polycrystalline silicon type, microcrystalline silicon type, amorphous silicon type, copper indium selenide type, compound semiconductor type, dye increasing type. Depending on the purpose such as a sensitive system, a plurality of arbitrary elements can be used by connecting them in series or in parallel according to a desired voltage or current. Since the transparent substrate 4 having a light-transmitting property is located in the outermost layer of the solar cell, a transparent material having high weather resistance, high stain resistance and high mechanical strength in addition to high transmittance is used. In the solar cell of the present invention, the transparent substrate 4 having a light-transmitting property may be made of any material as long as it satisfies the above characteristics, and examples thereof include glass, tetrafluoroethylene-ethylene copolymer (ETFE), and polyfluoride. Vinyl chloride resin (PVF), polyvinylidene fluoride resin (PVDF), polytetrafluoroethylene resin (TFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polytrifluorochloroethylene resin (CTFE) ), a fluorine-based resin such as polyvinylidene fluoride resin, an olefin-based resin, an acrylic-based resin, and a mixture thereof. In the case of glass, it is more preferable to use one that is reinforced. When a resin-made light-transmitting substrate is used, a uniaxially or biaxially stretched resin is preferably used from the viewpoint of mechanical strength. Moreover, in order to impart adhesiveness to these base materials such as EVA resin which is a sealing material for the power generation element, it is also preferable to subject the surface to corona treatment, plasma treatment, ozone treatment, and easy adhesion treatment. ..

The sealing material 2 for sealing the power generating element is a base material having a translucent property in addition to the purpose of protecting the power generating element from the external environment by fixing irregularities on the surface of the power generating element with resin to protect the power generating element. A material having high transparency, high weather resistance, high adhesiveness, and high heat resistance is used for adhesion to the back sheet 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 a solar cell backsheet of the present invention on a solar cell as a solar cell backsheet, the solar cell backsheet with a solar cell backsheet even when placed outdoors for a long period of time as compared with a conventional solar cell. Adhesion is maintained, and power generation efficiency can be further improved. INDUSTRIAL APPLICABILITY The solar cell of the present invention is not limited to outdoor applications and indoor applications such as a solar power generation system and a power source for small electronic components, but can be suitably used for various applications.

[Characteristic measuring method and evaluation method]
(1) Polymer characteristics (1-1) Amount of terminal carboxyl group (described as COOH amount in the table)
The amount of terminal carboxyl groups was measured by the following method according to the method of Maurice. (Reference: MJ Maurice, 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. and titrated with a 0.05 N KOH/methanol solution to measure the terminal carboxyl group concentration, and equivalent weight/polyester 1 t It was shown by the value of. In addition, phenol red was used as an indicator at the time of titration, and the point where the color changed from yellow-green to pink was taken as the end point of titration. When the solution in which the measurement sample is dissolved has insoluble matter such as inorganic particles, 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 sample mass. Was corrected.

(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. Also, the viscosity of the solvent was measured in the same manner. [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)
(Here, ηsp=(solution viscosity/solvent viscosity)−1, and K is the Huggins constant (assumed to be 0.343).)
When the solution in which the measurement sample is dissolved contains insoluble matter such as inorganic particles, 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, the mass of the measurement sample used for orthochlorophenol is defined as the mass of the measurement sample.
(Ii) Next, the solution containing the insoluble matter is filtered to measure the mass of the insoluble matter and the volume of the filtrate after filtration.
(Iii) Orthochlorophenol was added to the filtrate after filtration to obtain (measured sample mass (g)-insoluble matter mass (g))/(volume of filtrate after filtration (mL)+added orthochlorophenol The volume (mL) is adjusted to be 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 volume of the filtrate after filtration was 99 mL. Adjusts the addition of 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. was measured using an Ostwald viscometer, and using the obtained solution viscosity and solvent viscosity, according to the above formula (C), [ [η] is calculated, and the obtained value is taken as the intrinsic viscosity (IV).

(1-3) Metal element content Mg, Mn, and Sb The metal element content was measured by a fluorescent X-ray analysis method (Rigaku Denki Co., Ltd. fluorescent X-ray analyzer (model number: 3270)). Quantification was carried out by an atomic absorption spectrometry (manufactured by Sodachi Seisakusho: Polarized Zeeman atomic absorption spectrophotometer 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 was crushed in the film thickness direction without being crushed in the thickness direction. On the other hand, it was cut vertically and its cross section was obtained. Next, an image obtained by observing the cut surface of the sample was obtained using a scanning electron microscope (SEM) (JEOL Ltd. field emission scanning electron microscope "JSM-6700F").
(2-2) Measurement of the porosity of the whole film The method of (2-1) is arbitrarily selected in the film sample, and a total of 5 different places are selected, and a cross section of the film is cut in the longitudinal direction and the width direction of the film. An image obtained by observing the 10 locations at the maximum magnification capable of observing the entire thickness direction of the film is prepared. Then, only the respective cavity portions were traced on a transparent film, and the ratio of the cavity area measured by using an image analyzer (manufactured by Nireco Corporation: Luzex IID) and the entire film cross-sectional area in the observed image was calculated. The average value at 10 points 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, with respect to a total of 10 observation cross sections produced in the same manner as (2-2), an image obtained by observing the entire surface layer of the film surface layer (P2 layer and P2′ layer) at the maximum magnification that can be observed in the field of view was prepared, and The area ratio was calculated using an image analyzer, and the average value at 10 points was taken as the porosity of the film surface layer.
(2-4) Measurement of cavity area of cavities existing on each horizontal line Images obtained by observing a total of 10 observation cross-sections prepared in the same manner as (2-2) at the maximum magnification at which the entire film thickness direction can be observed. To prepare. Next, a line perpendicular to the thickness direction of the film is drawn for each observed image, and the line is divided into four points (the film thickness direction center point (C1 point), the midpoint between the film thickness direction center point and the film surface). A line (divided horizontal line) parallel to the thickness direction is drawn on the film passing through (C2-1 point) and (C2-2 point). Then, only the cavity portion existing on the dividing horizontal line was traced on a transparent film, and the average area of the cavity existing on each horizontal line was obtained using an image analyzer.
Regarding the number of cavities to be traced, if there are less than 20 cavities on the division horizontal line in the observed image, all the cavities are traced, and if 20 or more cavities exist, the center of gravity of the cavities is It is assumed that 20 cavities near points C1, C2-1 and C2-2 are selected and traced.
(2-5) Calculation of Average Cavity Area Ratio (Sc/Scs), (Sc/Scs') Regarding the average area obtained by (2-4), per cavity existing on the dividing horizontal line passing through the point C1. Sc (μm ² ), the average area per cavity existing on the dividing horizontal line passing through the point C2-1 is Scs (μm ² ), and cavity 1 existing on the dividing horizontal line passing through the point C2-2 The cavity area ratio (Sc/Scs) or (Sc/Scs') is calculated with the average area per piece being Scs' (μm ² ), and the average value of 10 locations in total is calculated as the average cavity area ratio (Sc/ Scs) and (Sc/Scs').

(3) Adhesion Evaluation (3-1) Preparation of Laminated Sample A film for solar cell backsheet of the present invention, a solar cell backsheet, a 125 μm thick biaxially stretched polyester film “Lumirror” (registered trademark) X10S (Toray). 90 parts by mass of "Takelac" (registered trademark) A310 (manufactured by Mitsui Takeda Chemical Co., Ltd.) and 10 parts by mass of "Takenate" (registered trademark) A3 (manufactured by Mitsui Takeda Chemical Co., Ltd.) Were mixed together) and then aged for 48 hours in a thermostat whose temperature was adjusted to 40°C.
(3-2) Adhesion Evaluation Regarding the sample obtained in (3-1), under a condition of a temperature of 120° C. and a relative humidity of 100% with an advanced accelerated life test device Pressure Cooker (manufactured by ESPEC Corp.). Peel strength when the film side for the solar cell backsheet of the present invention is fixed horizontally after the treatment for 48 hours and the bonded portion is subjected to a peel test by peeling at 180° at a speed of 200 mm/min. Was measured, and the adhesiveness of the film for solar cell backsheet was determined as follows.
When peel strength is 6N/15mm or more: A
When the peel strength is 4 N/15 mm or more and less than 6 N/15 mm: B
When peel strength is 2N/15mm or more and less than 4N/15mm: C
When the peel strength is 1 N/15 mm or more and less than 2 N/15 mm: D
If the peel strength is less than 1 N/15 mm: E
Adhesion is good in A to D, and A is the best among them.

(4) Moisture and heat resistance evaluation After cutting out the film for a solar cell backsheet and the solar cell backsheet of the present invention into a shape of a measurement piece of 10 mm x 200 mm, an advanced accelerated life test device Pressure Cooker (manufactured by ESPEC Corp.) was used. 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). The measurement was performed with a chuck distance of 50 mm, a pulling speed of 300 mm/min, and the number of times of measurement n=5. Further, after measuring in each of the longitudinal direction and the width direction of the sheet, the average value thereof was taken as the breaking elongation after the wet heat test. .. From the obtained breaking elongation after the 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
Moisture and heat resistance is good in A to D, and A is the best among them.

(5) UV resistance (change in color tone during UV treatment test)
(5-1) Color tone (b value) measurement Based on JIS-Z-8722 (2000), 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 a solar cell backsheet and the solar cell backsheet was measured at n=3 by the reflection method using the post-spectral method), and the average value was obtained.

(5-2) Color tone change Δb
The film for a solar cell backsheet of the present invention, the solar cell backsheet, with an 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 calculated from the following formula (α). The change in color tone (Δb) after irradiation was calculated. When the film for a solar cell backsheet of the present invention had a P2 layer on one side, the test was conducted so that the surface of the P2 layer side was exposed to the ultraviolet test light. Further, in the case of a solar cell backsheet, in Examples 32 to 37, 45 to 46, 50 to 53, the functional layer B is provided on the opposite surface to the surface having the functional layer B, and in Examples 38 to 44 and 47 to 49, the functional layer B is provided. The test was carried out so that the surface having the functional layer B′ at 54 to 56 was exposed to the ultraviolet test light.
Change in color tone after ultraviolet irradiation (Δb) = b1-b0 (α)
b0: Color tone before UV irradiation (b value)
b1: Color tone after UV irradiation (b value)
From the obtained color tone change (Δb) before and after the ultraviolet treatment test, the ultraviolet resistance was judged as follows.
When the color tone change (Δb) before and after the UV irradiation treatment test is less than 3: A
When the color tone change (Δb) before and after the UV irradiation treatment test is 3 or more and less than 6: B
When the color tone change (Δb) before and after the UV 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 tone change (Δb) before and after the UV irradiation treatment test is 20 or more: E
The UV resistance is good in A to D, and A is the most excellent.

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

(7) Solar cell characteristic evaluation (7-1) Solar cell output improvement evaluation Flux "HOZAN H722" was applied to the front and back silver electrode portions of the polycrystalline silicon solar cell "Gintec G156M3". A wiring material “copper foil SSA-SPS 0.2×1.5 (20) manufactured by Hitachi Cable, Ltd.”, which was applied by a dispenser and cut to a length of 155 mm on the silver electrodes on the front surface and the back surface, was placed on the cell on the front surface side. Place 10 mm away from one end of the wiring material on the end of the wiring material, and the back side so that it is symmetrical with the front side, and use a soldering iron to bring the soldering iron into contact with the back side of the cell at the same time. 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 The strings were placed vertically, and the flux was applied to the portion where the wiring member and the lead-out electrode overlap each other and solder welding was performed to produce a string with a lead-out electrode. At this point, the short-circuit current was measured according to the standard state of JIS C8914:2005, and it was defined as the power generation performance of the cell alone.

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 (Sanvic Co., Ltd. sealing material 0.5 mm) as a front side sealing material. (Thickness), strings with extraction electrodes that have been used to evaluate the power generation performance of the cell alone, 190 mm x 190 mm ethylene vinyl acetate (Sanvic Co., Ltd. sealing material 0.5 mm thick) as the back side sealing material, and cut into 190 mm x 190 mm The film for a solar cell backsheet of the present invention was stacked and fixed in this order, and the glass was set so as to be in contact with a hot plate of a vacuum laminator, and the hot plate temperature was 145° C., vacuum drawing was 4 minutes, press 1 minute, and holding time. Vacuum lamination was performed under the condition of 10 minutes 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. When the film for a solar cell backsheet of the present invention has a P2 layer on one surface, the film was placed so that the P2 layer side faces the power generation cell side.
The obtained solar cell module was subjected to measurement of short-circuit current measured according to the standard state of JIS C8914:2005, and the result was used as the power generation performance of a solar cell equipped with the solar cell backsheet of the present invention.
From the power generation performance of the single cell thus obtained and the power generation performance of the solar cell equipped with the solar cell backsheet of the present invention, a solar cell equipped with the solar cell backsheet of the present invention according to the following formula (β): The power generation improvement rate was calculated.
Power generation improvement rate by modularization (%) = (power generation performance after modularization / power generation performance of cell alone-1) x 100 (%) (β)
From the obtained power generation improvement rate, 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
Regarding the output improvement of the solar cell, A to D are good, and A is the most excellent.
(7-2) Adhesion evaluation of solar cell Ten solar cells prepared in the paragraph (7-1) were prepared and treated for 4000 hr in a constant temperature and humidity chamber (manufactured by ESPEC Corp.) adjusted to 85° C. and 85% RH. After that, it was visually confirmed whether or not peeling occurred in the laminated film for solar cell backsheet. The adhesiveness of the solar cell was confirmed by visually observing how many of the 10 solar cells had the sheet peeled off, and determined as follows.
When peeling has not occurred in all solar cells: A
When the sheet is peeled from one or more and less than four solar cells among the manufactured solar cells: B
When the sheet is peeled off from 4 to 8 solar cells among the manufactured solar cells: C
When eight or more sheets of the manufactured solar cells were peeled from the solar cells: D
When peeling occurs in all solar cells: E
Regarding the adhesion of the solar cell, A to D are good, and A is the most excellent.

(8) Young's modulus evaluation The Young's modulus of the solar cell backsheet film and the solar cell backsheet was measured based on ASTM-D882 (1997). The measurement was performed with a chuck distance of 50 mm, a pulling speed of 300 mm/min, and the number of times of measurement n=5. Further, after the measurement in each of the longitudinal direction and the width direction of the sheet, the average value was taken as the Young's modulus. The Young's modulus thus obtained was evaluated 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 over 3.0 GPa and below 4.0 GPa: C
When Young's modulus exceeds 4.0 GPa: D
Young's modulus is good in A to C, and A is the most excellent.

(9) Curl Height Evaluation As the evaluation of the solar cell backsheet, the curl height (curl property) was evaluated by the following procedure.
1. A solar cell backsheet cut into 200 mm x 200 mm was wrapped around a paper tube with an outer diameter of 84.2 mm and fixed, and stored at 40°C and 50% RH for 1 week. The obtained film was removed from the paper tube and the curl height was evaluated. Get a sheet for.
2. The obtained curl height evaluation sheet is placed on a flat plate in an environment of 25° C. so that the central portion of the curl height evaluation sheet contacts the plate.
3. The distance (curl height) from the plate at the four corners of the curl height evaluation sheet is measured with a caliper.
4.3. The average value of the curl heights obtained at 4 points was taken, and the curl height was evaluated from the average value of the obtained curl heights as follows.
Average curl height is less than 5 mm: A
The average value of curl height is 5 mm or more and less than 10 mm: B
The average value of curl height is 10 mm or more and less than 15 mm: C
Average curl height is 15 mm or more: D
The curl heights A to C are good, and A is the best.

(10) Evaluation of Water Vapor Barrier Property As an evaluation of the water vapor barrier property of the solar cell back sheet, the water vapor transmission rate in a measurement area of 50 cm ² and 40° C. 90% RH environment is measured according to the infrared sensor method of JIS K7129 (2008). did. From the obtained values, the water vapor barrier property was judged 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
Regarding the water vapor barrier properties, A to D are good, and A is the most excellent.

Hereinafter, the present invention will be described with reference to examples, but the present invention is not necessarily limited to these.

(Polyester resin raw 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 part by mass of manganese acetate tetrahydrate and 0.03 part by mass of antimony trioxide were melted at 150° C. under a nitrogen atmosphere. The temperature of this melt was raised to 230° C. over 3 hours with stirring, methanol was distilled off, and the transesterification reaction was completed. After completion of the transesterification reaction, an ethylene glycol solution (pH 5.0) obtained by dissolving 0.005 part by mass of phosphoric acid and 0.021 part by mass of sodium dihydrogen phosphate dihydrate in 0.5 part by mass of ethylene glycol was added. .. The intrinsic viscosity of the polyester composition at this time was less than 0.2. Then, the polymerization reaction was performed at a final temperature of 285° C. and a vacuum degree 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. Then, solid phase 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)
Polyethylene terephthalate (PET-b) having an intrinsic viscosity of 0.85 and a terminal carboxyl group amount of 6 equivalents/ton was obtained in the same manner as in PET raw material A except that the solid phase polymerization time was changed to 10 hours.

3. PET raw material C (PET-c)
Polyethylene terephthalate (PET-c) having an intrinsic viscosity of 0.79 and a terminal carboxyl group amount of 15 equivalents/ton was obtained in the same manner as in PET raw material A except that the final reached temperature of the polymerization reaction was 290°C.

4. PET raw material D (PET-d)
Polyethylene terephthalate (PET-d) having an intrinsic viscosity of 0.77 and a terminal carboxyl group amount of 20 equivalents/ton was obtained in the same manner as in PET raw material A except that the final reached temperature of the polymerization reaction was 295°C.

5. PET raw material E (PET-e)
Polyethylene terephthalate (PET-e) having an intrinsic viscosity of 0.75 and a terminal carboxyl group amount of 28 equivalents/ton was obtained in the same manner as in PET raw material A except that the final temperature of the polymerization reaction was 300°C.

6. PET raw material F (PET-f)
0.03 parts by mass of magnesium acetate dihydrate instead of manganese acetate as a reaction catalyst, and after 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, and the intrinsic viscosity was 0. A polyethylene terephthalate (PET-f) having a terminal carboxyl group content of 0.80 and 10 equivalents/ton was obtained.

7. PET raw material G (PET-g)
Polyethylene terephthalate (PET-g) having an intrinsic viscosity of 0.76 and a terminal carboxyl group amount of 24 equivalents/ton was obtained in the same manner as in PET raw material A except that the final temperature of the polymerization reaction was 297°C.

8. PET raw material H (PET-h)
Polyethylene terephthalate (PET-h) having an intrinsic viscosity of 0.65 and a terminal carboxyl group amount of 34 equivalents/ton was obtained in the same manner as in PET raw material A except that the final reached temperature of the polymerization reaction was 305°C.

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

10. Cavity nucleating agent master pellet B
Instead of the PET resin A, the above 2. 7. Other than using PET resin B obtained in Section 7. The cavity nucleating agent master pellet B was prepared with the same composition and method as the cavity nucleating agent master pellet A in the above section.

11. Cavity nucleating agent master pellet C
In place of the PET resin A, the above 3. 7. Other than using PET resin C obtained in Section 7. The cavity nucleating agent master pellet C was prepared by the same composition and method as the cavity nucleating agent master pellet A.

12. Cavity nucleating agent master pellet D
In place of PET resin A, the above 4. 7. Other than using PET resin D obtained in Section 7. Cavity nucleating agent master pellet D was prepared with the same composition and method as those of Cavity nucleating agent master pellet A.

13. Cavity nucleating agent master pellet F
5. Instead of PET resin A 7. Other than using PET resin F obtained in Section 7. Cavity nucleating agent master pellets F were prepared with the same composition and method as the cavity nucleating agent master pellets A.

14. Cavity nucleating agent master pellet G
Above 1. 26.3 parts by mass of PET resin A (PET-a) obtained by the above item, and cycloolefin copolymer “TOPAS” (registered trademark) 6018 (Vicat softening point=188° C.) manufactured by Polyplastics Co., Ltd., 40 parts by mass, Toray DuPont Co., Ltd. polyester elastomer (TPE) “HYTREL” (registered trademark) 7247 18 parts by mass, Eastman Chemical Co. amorphous PET resin (PET-G) Copolyester GN071 15.3 parts by mass vented at 290° C. Were melt-kneaded in the extruder to prepare hollow nucleating agent master pellets G.

15. Cavity nucleating agent master pellet H
Above 1. 60 parts by mass of the PET resin A (PET-a) obtained by the above item and 40 parts by mass of cycloolefin copolymer “TOPAS” (registered trademark) 6018 (Vicat softening point=188° C.) manufactured by Polyplastics Co., Ltd. were vented. Melt kneading was carried out in an extruder at 290° C. to prepare hollow nucleating agent master pellets H.

16. Cavity nucleating agent master pellet I
Above 1. 42 parts by mass of PET resin A (PET-a) obtained by the above item, polymethylpentene (PMP) “TPX” (registered trademark) DX820 (Vicat softening point=172° C.), 40 parts by mass, manufactured by Mitsui Chemicals, Inc. 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 cavity nucleating agent master pellets I.

17. Cavity nucleating agent master pellet J
Above 1. 56 parts by mass of the PET resin A (PET-a) obtained by the above item and polypropylene (PP) "Nobrene" (registered trademark) FLX80E4 (Vicat softening point=135° C.) manufactured by Sumitomo Chemical Co., Ltd., 40 parts by mass, Sanyo Kasei 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 extruder at 290° C. to prepare cavity nucleating agent master pellets J.

18. Titanium oxide master pellet 1. 100 parts by mass of the PET resin A (PET-a) obtained by the above item 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 extruder at 290° C. and oxidized. Titanium master pellets were produced.

19. Barium Sulfate Master Pellet 1. 100 parts by mass of the PET resin A (PET-a) obtained by the above item and 100 parts by mass of barium sulfate particles (BaSO ₄ ) having an average particle diameter of 1.5 μm are melt-kneaded in a vented extruder at 290° C., and sulfuric acid is added. Barium master pellets were prepared.

(Film and coating agent used for functional layer B)
20. Polyethylene film 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 chips 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. 25. PVDF film “Kiner” (registered trademark) manufactured by Arkema was used. ETFE film "Neoflon" (registered trademark) EF series manufactured by Daikin Industries, Ltd. was used.

26. Urethane coating agent (Coating agent a, Coating agent b)
As the formulation of the coating agent a, by the formulation shown in the column of the main agent in Table 9, “Huls Hybrid” (registered trademark) polymer UV-G301 (solid content concentration: 40, which is an acrylic coating agent manufactured by Nippon Shokubai Co., Ltd.). (% by mass), the titanium oxide particles JR-709 manufactured by Teika Co., Ltd., which is a color pigment, and a solvent were mixed all at once, and the mixture was dispersed using a bead mill. After that, a polyester plasticizer “Polycizer” (registered trademark) W-220EL manufactured by DIC Corporation was added as a plasticizer to obtain a main component 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. Is added in an amount calculated in advance so 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 out and stirred for 15 minutes to obtain coating a having a solid content concentration of 20% by mass.

As the formulation of the 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. Was added in an amount calculated in advance so that the mass ratio with the resin layer-forming main agent was 65/12, and the diluent shown in Table 10 was calculated in advance so that the solid content concentration was 20% by mass: N-butyl acetate was weighed out and stirred for 15 minutes to obtain a coating material b having a solid content concentration of 20% by mass.

27. Inorganic compound film "Tech Barrier" (registered trademark) LX manufactured by Mitsubishi Chemical Corporation was used.

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

29. Laminating adhesive (coating c)
As a laminating adhesive, 36 parts by mass of DIC Dry Co., Ltd. dry laminating agent "Dick Dry" (registered trademark) TAF-300, and DIC Co., Ltd. TAF hardener containing 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 as a laminating adhesive having a solid content concentration of 30% by mass.

Hereinafter, Examples 5, 6, and 26 shall be read as Reference Examples 5, 6, and 26, respectively.
(Example 1)
77.5 parts by mass of PET raw material A (PET-a) vacuum-dried at 180° C. for 2 hours and 22.5 parts of the cavity nucleating agent master pellet A are used as raw materials forming the P1 layer so as to have the composition shown in Table 1. 72 parts by mass of titanium oxide master pellets and 72 parts by mass of PET material A (PET-a) vacuum dried at 180° C. for 2 hours as a material for forming the P2 layer. Each of them 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 coextruded from a T die. Then, the co-extruded molten sheet was contact-cooled and solidified on a drum kept at a surface temperature of 50°C by an electrostatic application method to obtain an unstretched sheet. Subsequently, after preheating the unstretched sheet with a group of rolls heated to a temperature of 80° C., a speed difference of 3 times is provided between the roll heated to a temperature of 88° C. and the roll adjusted to a temperature of 25° C. After being stretched 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. Then, while holding both ends of the obtained uniaxially stretched sheet with clips, the uniaxially stretched sheet was guided to a preheating zone of a temperature of 80° C. in a tenter, and continuously in a heating zone kept at 90° C. in a direction perpendicular to the longitudinal direction (width). Direction) was stretched 3.5 times. Further, subsequently, heat treatment was carried out at 220° C. for 20 seconds in a heat treatment zone in the tenter, and further gradually cooled while performing relaxation treatment in the 4% width direction to form a polyester film.

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

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

In addition, as a result of evaluating the characteristics of the solar cell backsheet of the obtained film for solar cell backsheet, it was found that the film has extremely excellent adhesion, moist heat resistance, ultraviolet resistance, and thermal conductivity. As a result of further evaluation of the characteristics of the solar cell, it was found that it has extremely excellent output improvement and adhesion.

(Examples 2 to 11)
The amount of the cavity nucleating agent master pellets and the cavity nucleating agent master pellets G to I were used, or the titanium oxide master pellets used in the P2 layer were mixed with the P1 layer, and the composition of the P1 layer was changed as shown in Table 1. A solar cell backsheet film was obtained in the same manner as in Example 1.

When the cavity area ratio of the obtained solar cell backsheet film was confirmed, as shown in Table 2, (Sc/Scs) and (Sc/Scs') were changed depending on the amount and type of cavity nucleating agent or the dispersion aid. did. Specifically, in Examples 2, 4 to 6 in which the amount of void nucleating agent is increased and the type of dispersion aid is increased, the void area ratio is smaller than that in Example 1. On the other hand, it was confirmed that in Examples 3 and 7 to 9 in which polymethylpentene was used as the cavity nucleating agent species or the amount of the cavity nucleating agent was small and the dispersion aid was not contained, the cavity area ratio was larger than that in Example 1. did. It was also confirmed that the cavity area ratios of Examples 10 and 11 in which the inorganic particles were added to the P1 layer were slightly smaller than those of Example 1.

The solar cell backsheet properties of the obtained film for solar cell backsheet were evaluated, and as a result, as shown in Table 2, the adhesion was partially inferior to that of Example 1, but the thermal conductivity was in a good range. I understood it.
As a result of further evaluation of the solar cell characteristics, it was found that the output improvement was reduced as the cavity area ratio was increased as compared with Example 1, but the range was good together with the adhesion.

(Examples 12 to 16)
As shown in Table 3, a film for a solar cell backsheet 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.

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

The solar cell backsheet properties of the obtained film for solar cell backsheet were evaluated. As a result, as shown in Table 4, Examples 12 to 15 are in a good range although the adhesion is inferior to that of Example 1. I understood it. Further, the resistance to moist heat decreased as the intrinsic viscosity IV decreased and the amount of terminal carboxyl groups increased. It was also found that the thermal conductivity was excellent as in Example 1.
As a result of further evaluation of the characteristics of the solar cell, it was found that the output improvement property was reduced as the amount of terminal carboxyl groups increased as compared with Example 1, but the adhesion was within a favorable range. In addition, Example 16 is in the good range although it is inferior to the adhesiveness of the solar cell backsheet, the output improvement of the solar cell, and the adhesiveness in spite of the fact that the intrinsic viscosity and the amount of terminal carboxyl groups are the same as those of Example 1. I understood.

(Examples 17 to 25)
A solar cell backsheet film was obtained in the same manner as in Example 1 except that the lamination ratio of the solar cell backsheet, the film configuration, 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 solar cell backsheet film was confirmed, Example 25 was smaller than Example 1 in both (Sc/Scs) and (Sc/Scs') as shown in Table 4. The polymer characteristics were the same as in Example 1.

About the obtained film for solar cell backsheets, as a result of solar cell backsheet characteristic evaluation, 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 larger the value of (T1/T2)×W2 when the concentration of the inorganic particles contained in the resin composition forming the P2 layer is W2 (mass %), the lower the adhesiveness as compared with Example 1. It was found to be in a good range. Further, the UV resistance was lowered as the concentration of inorganic particles in the P2 layer was lowered. The thermal conductivity was excellent as in Example 1. As a result of further evaluation of solar cell characteristics, the smaller (T1/T2)×W2 is, the lower the output improvement is as compared with Example 1, and the larger (T1/T2)×W2 is, the poorer the adhesion is. It turned out to be a range. In addition, although Example 25 has very good adhesion of the solar cell backsheet, and output improvement and adhesion of the solar cell as in Example 1, the cavity nucleating agent adheres to the process roll during film formation. I found out to do.

(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 structure.

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

The film for a solar cell backsheet thus obtained was evaluated for solar cell backsheet properties. As a result, the adhesiveness was inferior to that of Example 1, but was in a good range, and the thermal conductivity was excellent as in Example 1. It turned out to be Also in the solar cell characteristic evaluation, it was found that the output was in a good range although it was inferior in output improvement and adhesion. It was also found that the void nucleating agent adhered to the process roll during film formation as in Example 25.

(Example 27)
Barium sulfate master pellets are used because barium sulfate particles are used as the inorganic particles of the P2 layer, 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. A film for solar cell backsheet was obtained in the same manner as in Example 3. When the cavity area ratio of the obtained film for solar cell backsheet was confirmed, as shown in Table 4, both (Sc/Scs) and (Sc/Scs') were smaller than those in Example 3.
The solar cell backsheet film thus obtained was evaluated for solar cell backsheet properties, and as a result, it was found that the film had good adhesion, although it was inferior to that in Example 3. The thermal conductivity was excellent as in Example 1. As a result of further evaluation of the characteristics of the solar cell, it was found that, although inferior to that in Example 3, it had good adhesion and the output improvement was within the range without any problem.

(Example 28)
A film for a solar cell backsheet 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 film for solar cell backsheet was confirmed, (Sc/Scs) and (Sc/Scs') were about the same as in Example 1. Further, when the polymer characteristics were measured, as shown in the table, the intrinsic viscosity IV and the amount of terminal carboxyl groups changed.

As a result of evaluating the characteristics of the obtained film for solar cell backsheet, it was found that the adhesion was good as shown in the table. The moist-heat resistance was slightly decreased with the decrease of the intrinsic viscosity IV and the increase of the amount of the terminal carboxyl group, but it was within the problem-free range. It was also found that the thermal conductivity was excellent as in Example 1.
As a result of further evaluation of solar cell characteristics, as shown in the table, it was found that the output improvement was slightly decreased as the amount of the terminal carboxyl groups was increased as compared with Example 1, but the adhesion was within a good range. It was

(Examples 29 to 31)
A film for a solar cell backsheet 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 about the same as in Example 1.
As a result of solar cell backsheet characteristic evaluation of the obtained solar cell backsheet film, as shown in Table 4, it was found that the film having a small film thickness had a slightly lower adhesion. Further, it was found that the thermal conductivity was slightly lower than that of Example 1, but was in a good range.
As a result of further evaluation of the characteristics of the solar cell, it was found that the adhesion of the solar cell slightly deteriorated as the film thickness decreased, as shown in the table. Further, it was found that the output improvement property was slightly lower than that of Example 1, but was in a good range.

(Examples 32-44)
The coating c prepared as an adhesive for lamination was applied to one surface of the P2 layer of the film for solar cell backsheet obtained in Example 1 using a wire bar, and the temperature was 80° C. for 45 seconds. After drying, the adhesive layer for lamination 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 on the adhesive layer and aged at a temperature of 40° C. for 3 days to obtain a solar cell backsheet. The obtained solar cell backsheet had good adhesion, resistance to moist heat, and resistance to ultraviolet light, and was excellent in at least Young's modulus, curl height, and water vapor barrier property. Moreover, the solar cell characteristics were excellent.

(Examples 45 to 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 cell backsheet. The obtained solar cell backsheets of Examples 45 to 49 were good in adhesion, resistance to moist heat and ultraviolet rays, and had large Young's modulus and curl height, but were excellent in water vapor barrier property. .. Moreover, the solar cell characteristics were excellent.

(Examples 50 to 53)
On the one surface of the P2 layer of the film for a solar cell backsheet obtained in Example 1, a coating a was formed according to Table 6 using a wire bar so that the thickness of the functional layer B after drying would be the thickness shown in Table 6. , Coating material b, respectively, and dried at a temperature of 100° C. for 60 seconds to produce a film for solar cell backsheet (in Examples 50 to 53, porosity and (Sc/Scs), (Sc/Scs). ') was obtained based on the laminated film including the functional layer B). When the obtained film for solar cell backsheet was used as a solar cell backsheet and evaluated, both backsheet characteristics and solar cell characteristics were excellent.

(Examples 54 and 55)
The coating c prepared as an adhesive for lamination was applied to one surface of the P2 layer of the film for solar cell backsheet obtained in Example 1 using a wire bar, and the temperature was 80° C. for 45 seconds. After drying, the adhesive layer for lamination 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. Further, the coating C prepared as an adhesive for lamination is applied to the other P2 layer not laminated with the functional layer B′ using a wire bar, dried at a temperature of 80° C. for 45 seconds, and after drying. The laminating adhesive layer was formed so that the coating film thickness 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 solar cell backsheets obtained in Examples 54 and 55 were good in adhesion, resistance to moist heat and ultraviolet resistance, and were excellent in Young's modulus, curl height and water vapor barrier property. Moreover, the solar cell characteristics were excellent.

(Example 56)
On the one surface of the P2 layer of the film for a solar cell backsheet obtained in Example 1, a coating a was formed according to Table 6 using a wire bar so that the thickness of the functional layer B after drying would be the thickness shown in Table 6. Was applied and dried at a temperature of 100° C. for 60 seconds to obtain a film for a solar cell backsheet having the functional layer B. Further, the coating C prepared as an adhesive for lamination is applied to one P2 layer on which the functional layer B is not laminated using a wire bar, dried at a temperature of 80° C. for 45 seconds, and the coating after drying. The laminating adhesive layer was formed so that the film thickness 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 solar cell back sheet obtained in Example 56 had a large Young's modulus and curl height, but was excellent in water vapor barrier properties. The solar cell characteristics were also excellent.

(Comparative Example 1)
A film for a solar cell backsheet was obtained in the same manner as in Example 1 except that the amount of the cavity nucleating agent in the P1 layer was 3% by mass.
When the porosity of the obtained film for solar cell backsheet was confirmed, it was found that the porosity of the entire film was 9%, which was outside the range of the present invention.
Further, it was found that the film for a solar cell backsheet obtained in Comparative Example 1 was a solar cell backsheet having poor adhesion and thermal conductivity. Moreover, it was found that the solar cell was also inferior in output improvement and adhesion.

(Comparative Examples 2 to 6)
In order to make the composition of the P1 layer as shown in the table, the amount of the cavity nucleating agent master pellets and the cavity nucleating agent master pellets G to J are used, or the barium sulfate master pellets are used because the barium sulfate particles are used as the cavity nucleating agent in the P1 layer. A film for solar cell backsheet 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, both (Sc/Scs) and (Sc/Scs') were found to be outside the scope of the present invention.

Furthermore, it was found that the films for solar cell backsheets obtained in Comparative Examples 1 to 4 were solar cell backsheets having poor adhesion. It was found that Comparative Example 6 was a solar cell backsheet having poor thermal conductivity. It was also found that the solar cell was inferior in at least one of output improvement and adhesion.

(Comparative Example 7)
A film for a solar cell backsheet 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 backsheet was confirmed, it was found that there was no cavity on the divided horizontal line passing through the points C2-1 and C2-2.

Further, it was found that the film for a solar cell backsheet is a solar cell backsheet having poor adhesion and thermal conductivity. Moreover, it was found that the solar cell was also inferior in output improvement and adhesion.

(Comparative Example 8)
A film for a solar cell backsheet 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 film for solar cell backsheet was confirmed, both (Sc/Scs) and (Sc/Scs') were the same as in Example 1, but the polymer properties were measured and the amount of terminal carboxyl groups was measured. Was reduced to 40 equivalents/ton.
Furthermore, it was found that the film for a solar cell backsheet obtained in Comparative Example 8 was a solar cell backsheet having poor adhesion and wet heat resistance. It was also found that the solar cell was inferior in both output improvement and adhesiveness with respect to solar cell characteristics.

(Comparative Example 9)
An unstretched sheet obtained by extruding from a T-die and cooling with a single layer structure of P1 layer during film formation was preheated by 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 film for a solar cell backsheet was obtained in the same manner as in Comparative Example 2 except that the infrared heater was heated at an output of 50 W/cm for 0.72 seconds and stretched 3 times in the longitudinal direction (longitudinal direction).
When the cavity area ratio of the obtained film for solar cell backsheet was confirmed, a bias was observed in the cavity area in the thickness direction, unlike Comparative Example 2. 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. And (Sc/Scs) and (Sc/Scs') were 1.0.
It was found that the film for a solar cell backsheet obtained in Comparative Example 9 was a solar cell backsheet having poor adhesion, as in Comparative Example 2. It was also found that the solar cell was inferior in both output improvement and adhesiveness with respect to solar cell characteristics.

(Comparative Example 10)
In the same manner as in Example 32 except that the film for solar cell backsheet was the film of Comparative Example 6, the functional layer B shown in Table 9 was laminated and aged at a temperature of 40° C. for 3 days to obtain a solar cell backsheet. did. The obtained solar cell backsheet was inferior in Young's modulus and curl height. Regarding the characteristics of the solar cell, the adhesion was improved from Comparative Example 6, but the output improvement was inferior.

(Comparative Example 11)
In the same manner as in Example 42 except that the film for solar cell backsheet was the film of Comparative Example 6, the functional layer B shown in Table 9 was laminated and aged at a temperature of 40° C. for 3 days to obtain a solar cell backsheet. did. The obtained solar cell backsheet was inferior in Young's modulus and curl height. Moreover, regarding the solar cell characteristics, the solar cell was inferior in adhesion and output improvement.

By mounting the film for a solar cell backsheet of the present invention on a solar cell as a solar cell backsheet, the adhesion with the solar cell backsheet even when placed outdoors for a long period of time as compared with a conventional solar cell. Is maintained, and the power generation efficiency can be further improved. INDUSTRIAL APPLICABILITY The solar cell of the present invention is not limited to outdoor applications and indoor applications such as a solar power generation system and a power source for small electronic components, but can be suitably used for various applications.

1: solar cell backsheet 2: encapsulant 3: power generation element 4: transparent substrate 5: solar cell backsheet encapsulant 2 side surface 6: solar cell backsheet encapsulant 2 opposite surface 7 : Film thickness direction 8: film surface direction 9: midpoint between film thickness direction center point and film surface (C2-1 point)
10: Center point in film thickness direction (C1 point)
11: Midpoint between film thickness direction center point and film surface (C2-2 point)
12: Dividing horizontal line passing through C2-1 point 13: Dividing horizontal line passing through C1 point 14: Dividing horizontal line passing through C2-2 point 15: Cavity 16: Functional layer B
17: Film for solar cell backsheet 18: Functional layer B'
19: Adhesive layer

Claims (15)

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 equally divided into four parts in the thickness direction (center point in the film thickness direction (C1 Point), a midpoint (C2-1 point) between the film thickness direction center point and the film surface, and a line parallel to the surface direction of the film (division horizontal line) passing through each of (C2-2 point)).
The average area per cavity existing on the divided horizontal line passing through the point C1 is Sc (μm ² ),
The average area per cavity existing on the divided horizontal line passing through the point C2-1 is Scs (μm ² ),
At least one of (Sc/Scs) and (Sc/Scs') is 1.5 when the average area per cavity existing on the dividing horizontal line passing through the point C2-2 is Scs' (μm ² ). The above film 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, a film for a solar cell backsheet.
(Note, (Sc / Scs), ( Sc / Scs') is Keru your any five points of the polyester film, a cross-section in the thickness direction of the film was cut parallel to the film in the longitudinal direction of the film, in the width direction of the film Obtained as the average value of the values obtained from the cross section in the thickness direction of the film obtained by cutting the film in parallel.) The film for a solar cell backsheet according to claim 1, wherein the polyester film has a total thickness of 45 μm or more. The polyester film has a laminated structure of three or more layers, and at least one resin of 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 a solar cell backsheet according to claim 1 or 2, wherein the composition contains inorganic particles, and the layer having no surface layer (the layer is referred to as a P1 layer) contains voids. 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 forming the P2 layer is W2 (mass). %), when the concentration of inorganic particles contained in the resin composition constituting the P2′ layer is W2′ (mass %),
At least one of (T1/T2)*W2 and (T1/T2')*W2' is 0.35 or more and 1.50 or less, The film for solar cell backsheets of Claim 3 characterized by the above-mentioned. The film for a solar cell backsheet according to claim 3, wherein the inorganic particles are titanium oxide. 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. And T2/(T1+T2+T2') and T2'/(T1+T2+T2') are 0.01 or more and 0.2 or less, The film for solar cell backsheets in any one of Claims 3-5. The film for solar cell backsheet according to any one of claims 3 to 6, wherein the porosity (Ps) of the P2 layer and the porosity (Ps') of the P2' layer are 5.0% or less. The film for a solar cell backsheet according to claim 1, which has a thermal conductivity of 0.9 W/m·K or less. It is a solar cell backsheet which has the film for solar cell backsheets in any one of Claims 1-8, and at least 1 or more functional layer, The Young's modulus of the film for solar cell backsheets is 4.0 GPa or less. A solar cell backsheet in which the Young's modulus of the solar cell backsheet is 4.0 GPa or less. The solar cell backsheet according to claim 9, wherein the functional layer comprises at least one of the following groups 1 or a combination of a plurality of the following groups 1.
Group 1: Polyethylene, polypropylene, ethylene vinyl acetate copolymer The solar cell backsheet according to claim 9, wherein the functional layer includes at least one of the following groups 2 and a combination of a plurality of the following groups 2.
Group 2: polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) The solar cell backsheet according to claim 9, wherein the functional layer contains polyurethane. The solar cell backsheet according to claim 9, wherein the functional layer contains an inorganic compound. The solar cell backsheet according to claim 9, wherein the functional layer contains polyester, and the solar cell backsheet film and the functional layer are laminated via an adhesive layer. A solar cell using the film for a solar cell backsheet according to any one of claims 1 to 8 or the solar cell backsheet according to any one of claims 9 to 14.

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