JP2020013864A - Solar cell module of multiple wire connection system - Google Patents

Abstract

To provide a "solar cell module" in which the entire configuration is optimized so that interlayer adhesion and light transmittance of a boundary surface between a collector wire fixing film and a sealing material can be improved sufficiently, with special consideration given to the constitution of the boundary surface.SOLUTION: A solar cell module 1 includes a collector wire fixing film 6 laminated on the surface of a solar cell element 4 while coating multiple collector wires 64 placed on the surface of the solar cell element 4, and a sealing material 3 sealing the solar cell element 4. In one surface of the collector wire fixing film 6, the multiple collector wires 64 are embedded, the other surface of the collector wire fixing film 6 is adhering to the sealing material 3, and the sealing material 3 and the collector wire fixing film 6 are a resin film where polyethylene-based resin having density of 0.870-0.930 g/cmis the base resin.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a solar cell module of a multi-wire connection type, that is, a solar cell module in which a solar cell element is mounted in a multi-wire type in which a plurality of fine wires are electrically connected between solar cell elements.

  Conventionally, the layer configuration of a solar cell module is generally the same as the layer configuration of the solar cell module 1 shown in FIG. That is, the transparent front substrate 2, the light-receiving surface sealing material 31, the plurality of solar cell elements 4, the non-light-receiving surface-side sealing material 32, and the back surface protection sheet 5 are sequentially stacked from the light receiving surface side. In addition, for a plurality of solar cell elements, usually, on the front or back surface of each element, a plurality of adjacent solar cell elements are connected, and a lead wire for collecting electricity generated in each of these elements is connected. I have. Conventionally, as such a conductor arranged to electrically connect solar cell elements to each other, a band-shaped conductor having a width of about 2 mm to 5 mm called a "bus bar" has been generally used. .

  A conducting wire for electrically connecting a plurality of solar cell elements is an essential component for constituting a solar cell module. However, on the other hand, in the light-receiving surface of the solar cell element, the sunlight that enters the solar cell element is physically blocked at a portion covered by these conductive wires. Minimizing the decrease in light use efficiency due to this has been recognized as a pressing issue in the competition for the development of solar cells, which requires strict improvement in power generation efficiency per unit area.

  In order to solve such a problem, instead of the above-mentioned strip-shaped conductive wire (bus bar), a current collecting wire composed of a large number of fine wires having a diameter of about 100 μm to 200 μm having a substantially perfect circular cross section is connected to the solar cell elements. A connection configuration between solar cell elements called "multi-wire connection" used as a conductive wire for electrical connection has begun to be adopted. The demand for the “multi-wire connection” is expected to increase in the future as a technology for improving the power generation efficiency of the solar cell module (see Patent Documents 1 and 2).

  When the solar cell elements are electrically joined by “multi-wire connection” using a large number of thin wires, each thin wire can be fixed to the solar cell element by soldering or the like, but as shown in FIG. A large number of current collecting wires 64 are embedded in a resin film (“current collecting wire fixing film” 6A, 6B), and the adjacent solar cell element 4A is formed by the resin film in which the current collecting wires are embedded (“current collecting wire fixing film”). It is anticipated that the structure for electrically connecting 4B and 4B will become the mainstream connection structure in “multi-wire connection” in the future as a more preferable connection structure.

  The solar cell module is expected to be used for a long period of time in a harsh wet heat environment. Therefore, the above-mentioned resin film (“collector wire fixing film”) used for performing “multi-wire connection” in the above-described embodiment has “heat resistance” that can withstand a severe use environment and a large number of fine wires by heat compression. It is necessary to achieve both “molding properties” for stably embedding and supporting physical properties that are generally considered to be mutually contradictory. In the present specification, the resin component of the current-collecting wire fixing film has no gap around the individual thin wires (current-collecting wires) each having a substantially circular cross section when the current-collecting wire fixing film is heat-pressed to the current collecting wire portion. The wraparound property is referred to as “molding property” of the film. This “molding property” is an essential property for the “collecting wire fixing film” to stably support the collecting wire portion.

  At the time of filing the present application, as a resin film having a configuration capable of simultaneously satisfying the two contradictory requirements, a base layer made of a polyester-based resin such as polyethylene terephthalate (PET) having excellent heat resistance and a molding property are generally excellent. 2. Description of the Related Art A resin film having a multilayer structure in which a sealing layer made of a polyethylene resin is joined with an adhesive or the like has been widely used as a resin film for performing “multi-wire connection”.

  In addition, Patent Documents 1 and 2 disclose that the above-mentioned resin film (“current collecting wire fixing film”) used for performing “multi-wire connection” has a difference in the degree of crosslinking in the film thickness direction in the polymer forming the film. There is a description that it is possible to secure the adhesiveness and the heat resistance of the entire film by adding.

  As described above, in the current-collecting wire fixing film used in the multi-wire connection type solar cell module, various types of moldings for improving the molding property for embedding the current-collecting wire while maintaining compatibility with the heat resistance of the entire film. Attempts have been made to improve.

  However, in the solar cell module 1 performing “multi-wire connection”, the adhesion between the two layers at the interface (see FIGS. 1 to 3) between the current collecting wire fixing film and the sealing material, which occupies a large area in structure. In addition, no particular consideration has been given to issues such as maximizing the light transmittance of the entire solar cell module affected by the configuration of the interface.

International Publication No. 2004/021455 International Publication No. WO 2017/076735

  The present invention has been completed in the above situation, and in the "multi-wire connection type solar cell module" where demand is expected to expand in the future, the heat resistance and molding required for the "current collector wire fixing film" While responding to the basic requirement of having a good balance of properties, special consideration is also given to the configuration of the interface between the "current collector wire fixing film" and the sealing material, and the interlayer adhesion at this interface and the It is an object to provide a “solar cell module” whose overall configuration is optimized so that the light transmittance affected by the configuration can be sufficiently improved.

  The present inventors have formed a low-density polyethylene base resin for all layers of a “current collector wire fixing film for a solar cell module” that requires both heat resistance and molding properties. The sealing material to be disposed opposite to the surface opposite to the embedded surface of the multi-wire in the `` current collecting wire fixing film for the battery module '' is also formed by low-density polyethylene. The inventors have found that the above problems can be solved, and have completed the present invention. Specifically, the present invention provides the following.

(1) A solar cell module of a multi-wire connection system, wherein a plurality of solar cell elements, a plurality of current collection wires arranged on a surface of the solar cell element, and the plurality of current collection wires are covered. A current-collecting wire fixing film laminated on the surface of the solar cell element, and a sealing material for sealing the solar cell element, comprising, on one surface of the current-collecting wire fixing film, a plurality of The current collecting wire is embedded therein, and the other surface of the current collecting wire fixing film is in close contact with the sealing material, and the sealing material and the current collecting wire fixing film each have a density of 0. 870 g / cm ³ or more 0.930 g / cm ³ or less of the polyethylene resin is a resin film containing as a base resin, the solar cell module of the multi-wire connection method.

(2) The current-collecting wire fixing film is a resin film having a melting point of 90 ° C. or more and 110 ° C. or less and a polyethylene resin as a base resin, and has a TMA curve defined by the following definition between 90 ° C. and 100 ° C. The solar cell module according to (1), wherein the inclination is −3.0 or more and −1.3 or less.
“Slope of TMA curve”: In the “TMA curve” obtained by the following “thermomechanical analysis (TMA) test”, the indentation depth is Y ₁ (μm) at the temperature X ₁ (° C.), and the temperature X _{When the} indentation depth is Y ₂ (μm) at ₂ (° C.) (> X ₁ (° C.)), the “slope (a) of the TMA curve” between X ₁ and X ₂ is (a) = (Y ₂ −Y ₁ ) / (X ₂ −X ₁ ). Time, however, penetration depth before the temperature reaches X ₂ is a case has been reached -150Myuemu (when the needle penetrates the film to be measured), the temperature X _2, indentation depth reached -150Myuemu Replace with temperature.
“Thermo-mechanical analysis (TMA) test”: A 150 μm-thick current-collecting wire-fixed film sheet was set on a thermo-mechanical analysis (TMA) test apparatus, and was pushed into a φ1 mm needle to a constant pressure of 100 kPa, and the temperature was raised at a rate of 5 ° C. The temperature is raised from room temperature to 150 ° C./min, and the depth of the needle being pushed at that time is measured. However, when the film to be measured has an MFR (g / min) at 190 ° C. and a load of 2.16 kg measured in accordance with JIS-K6922-2 which changes along the thickness direction, the needle is pushed into the MFR. (G / min) is performed from the surface with the larger side. The “TMA curve” that can be obtained by the thermomechanical analysis (TMA) test means that the temperature is X in the thermomechanical analysis (TMA) test and the needle indentation depth at the temperature is Y. In the XY coordinates, it refers to a curve indicating the correlation between the temperature and the depth of the needle pressing.

  (3) The current collecting wire fixing film is a multilayer resin film including a sealing layer having a melting point of the base resin of less than 100 ° and a base layer having a melting point of the base resin of 100 ° or more, The solar cell module according to (1) or (2), wherein a plurality of the current collection wires are embedded in the sealing layer.

  (4) The solar cell module according to (3), wherein the sealing layer contains a silane-modified polyethylene-based resin.

  According to the present invention, in a “multi-wire connection type solar cell module”, for which demand is expected to increase in the future, a basic requirement that a good balance between heat resistance and molding properties required for a “current collector wire fixing film” is provided. In addition, the structure of the interface between the "collecting wire fixing film" and the encapsulant should be taken into account in particular, and the interlayer adhesion at this interface and the light transmittance affected by the structure of this interface should be sufficient. It is possible to provide a “solar cell module” whose overall configuration is optimized so that it can be improved.

It is sectional drawing which shows an example of the layer structure of the solar cell module of this invention typically. It is a perspective view used for description of "multi-wire connection" in the solar cell module of the present invention. FIG. 3 is a side view of the connection structure of “multi-wire connection” in FIG. 2. FIG. 2 is a partially enlarged cross-sectional view of the solar cell module schematically showing a mode of embedding a current collecting wire into a current collecting wire fixing film in the solar cell module of FIG. 1. It is sectional drawing which shows typically the aspect of the change of the crosslinking degree in the film thickness direction of the collector wire fixing film which concerns on this invention. It is a graph which shows the TMA curve of the current collection wire fixing film which concerns on this invention, and the conventional current collection wire fixing film.

  Hereinafter, the multi-wire connection type solar cell module of the present invention will be described. The present invention is not limited to the embodiments described below.

<Multi-wire connection type solar cell module>
As shown in FIG. 1, a solar cell module 1 of the present invention, which is a multi-wire connection type solar cell module, includes a transparent front substrate 2, a light receiving surface side sealing material 31, and a non-light receiving surface side sealing material 32. The solar cell element 4 has a basic structure in which the material 3 and the back surface protection sheet 6 are laminated, and a plurality of solar cell elements 4 are provided inside the basic structure with a light receiving surface side sealing material 31 and a non-light receiving surface side sealing material 32. It is sealed by the sealing material 3 in a sandwiched manner. The plurality of solar cell elements 4 are electrically connected to each other by a plurality of current collecting wires 64 (see FIG. 2), and the plurality of current collecting wires 64 are embedded in the current collecting wire fixing film 6. In FIG. 4, the surface of the solar cell element 4 is covered with a current collecting wire fixing film 6 and fixed on the same surface. The surface of the current-collecting wire fixing film 6 opposite to the surface on which the current-collecting wires 64 are embedded is in close contact with the sealing material 3.

  The current collecting wire fixing film 6 constituting the solar cell module 1 is a resin film in which all layers are formed of a resin composition containing a polyethylene resin as a base resin. Details of the composition, layer configuration, and manufacturing method of the current-collecting wire fixing film 6 will be described later. In addition, in this specification, "base resin" means the resin whose content ratio is the largest in all the resin components in the said resin molding, When the content ratio in a resin component is 50 mass% or more, And preferably 90% by mass or more.

The sealing material 3 (light receiving surface side sealing material 31 and non-light receiving surface side sealing material 32) constituting the solar cell module 1 is a resin sheet mainly exhibiting a function of protecting the solar cell element 4 from external impact. . In particular, the light-receiving-surface-side sealing material 31 is required to be a transparent sheet in order to transmit sunlight with a high transmittance. Conventionally, as the sealing material 3 (31, 32), a sealing material sheet made of an ethylene-vinyl acetate copolymer (EVA) has been widely used. 3, or at least the light-receiving-side sealing member 31, with limited density 0.870 g / cm ³ or more 0.930 g / cm ³ or less of the polyethylene resin to the resin film based resin.

  In the solar cell module 1, as described above, the sealing material 3 (31) is a resin film having a polyethylene resin as a base resin, and is fixed to a current collecting wire facing the sealing material over a wide area. All layers of the film 6 are also formed using a polyethylene resin as a base resin. Therefore, when a current collecting wire fixing film using a polyester resin as a base resin, which has been widely used in the past, is used, or a sealing material using EVA as a base resin, which is a general-purpose sealing material resin, is used. As compared with the case where the sealing material 3 is provided, the adhesion at the interface between the sealing material 3 and the current collecting wire fixing film 6 is extremely excellent. In addition, since the resin in contact with the wide interface is the same kind of resin, the interface can be formed with a resin having a close refractive index without using an adhesive or the like, so that the entire upper and lower resin layers including this interface can be formed. By improving the transparency and reducing the refraction of the incident light at this interface, the arrival rate of the incident light to the solar cell module to the solar cell element can be improved.

  As the solar cell element 4, any solar cell element to which “multi-wire connection” can be applied, such as an amorphous silicon type or a crystalline silicon type, can be used without particular limitation. As the transparent front substrate 2 and the back surface protection sheet 5, conventionally known members can be used without particular limitation as respective members for use in a solar cell module. Moreover, the solar cell module of the present invention may further include a member other than the above members as necessary.

  Here, the current-collecting wire fixing film 6 incorporated in the solar cell module 1 having the above configuration is different from, for example, a conventional multilayer film in which heat resistance is formed of a polyester resin, and has a sufficient light resistance. (UV resistance). Therefore, in the solar cell module, it is unnecessary to add the ultraviolet absorber to the light-receiving-surface-side sealing material 31, which has been required in the related art. Thereby, in the solar cell module 1, in the multi-wire connection type solar cell module which was conventionally considered to be difficult to sufficiently contribute light in the UVA region to power generation, light in the UVA region is sufficiently generated for power generation. Can be contributed.

[Method of manufacturing solar cell module]
In general, a solar cell module can be manufactured by a manufacturing method in which a stacked body formed by stacking solar cell elements, a sealing material, and other members constituting the solar cell module is heat-pressed and integrated. In the case of manufacturing the solar cell module 1 including a “multi-wire connection” structure in which each solar cell element is connected by the current collecting wire 64 embedded in the current collecting wire fixing film 6, After the current collecting wire 64 is embedded and the current collecting wire fixing film 6 in which the current collecting wire 64 is embedded is temporarily press-bonded to the solar cell element 4, the transparent front substrate 2, the light receiving surface side sealing material 31, the solar cell element 4. A vacuum heat laminating process is performed in which a laminate formed by sequentially laminating the members including the non-light receiving surface side sealing material 32 and the back surface protection sheet 5 is integrated by vacuum suction or the like. In the case of vacuum heat lamination, the lamination temperature is preferably in the range of 130 ° C. or more and 170 ° C. or less. Further, the lamination time is preferably in the range of 5 minutes to 30 minutes, and particularly preferably in the range of 8 minutes to 15 minutes. In this way, when the above-described layers are formed into an integrally molded body by thermocompression bonding, a portion of the resin on the sealing surface side wraps around the current collecting wire 64 having a substantially circular cross section by heating without gaps, thereby forming an integrated body. In the solar cell module after the formation, a high adhesiveness is developed between the current collecting wire fixing film 6 and the current collecting wire 64, and the current collecting wire 64 is extremely stably supported.

[Fixing wire fixing film]
Hereinafter, the composition, layer configuration, and manufacturing method of the current-collecting wire fixing film 6 that constitutes the solar cell module 1 will be described in detail. As shown in FIG. 1, when the plurality of solar cell elements 4 are electrically connected to each other by “multi-wire connection” in the solar cell module 1, the current collecting wire fixing film 6 includes a large number of collectors constituting this connection structure. This is a resin film used for stably fixing the electric wire 64 to each solar cell element 4.

  As shown in FIGS. 2 and 3, the connection between the solar cell elements 4 in the multi-wire connection type solar cell module 1 is performed by connecting the current collecting wire fixing films 6 </ b> A and 6 </ b> B in which a large number of current collecting wires 64 are embedded. This is performed by bonding to the front surface or back surface of 4A, 4B.

  Further, as shown in FIG. 4, in the “multi-wire connection” using the current collecting wire fixing film 6, the current collecting wire 64 bonded to the solar cell element 4 </ b> B is embedded in the current collecting wire fixing film 6. At the same time, a part thereof is exposed from the surface of the current collecting wire fixing film 6 so as to be able to conduct to the solar cell element 4B, and the individual current collecting wires 64 are exposed on the surface of the solar cell element 4B or It is joined to the back electrode part.

The current-collecting wire fixing film 6 used in the above-described embodiment may be a single-layer film or a multilayer film. Then, even in the case of a one layer configuration, the current collector wire fixing film 6, all of the layers, and the density of 0.870 g / cm ³ or more 0.930 g / cm ³ or less of the polyethylene resin base resin resin One of the features of the present invention is that it is formed of a composition.

  The current collector wire fixing film 6 in which all layers are formed of a resin composition containing a polyethylene-based resin as a base resin has a “slope of a TMA curve” defined below between a temperature of 90 ° C. and 100 ° C. , -3.0 or more and -1.3 or less, the behavior of the material resin at the time of thermal lamination processing at the time of integration as a solar cell module is optimized, as will be described later in Examples, The compatibility between heat resistance and molding properties can be more stably exhibited in a general solar cell module manufacturing process.

Here, the “slope of the TMA curve” in the present specification is based on the following definition.
"Slope of TMA curve"
: In the “TMA curve” obtained by the following “thermomechanical analysis (TMA) test”, the indentation depth is Y ₁ (μm) at the temperature X ₁ (° C.), and the temperature X ₂ (° C.) (> (X ₁ (° C.)), when the indentation depth is Y ₂ (μm), “the slope (a) of the TMA curve” between X ₁ and X ₂ is (a) = (Y ₂ −Y ₁ ) / (X ₂ −X ₁ ). Time, however, penetration depth before the temperature reaches X ₂ is a case has been reached -150Myuemu (when the needle penetrates the film to be measured), the temperature X _2, indentation depth reached -150Myuemu Replace with temperature.

Further, the above-mentioned “thermomechanical analysis (TMA) test” refers to a test performed under the following conditions.
"Thermo-mechanical analysis (TMA) test"
: A 150 μm-thick current-collecting wire fixed film sheet was set on a thermomechanical analysis (TMA) test apparatus, pushed into a needle of φ1 mm to a constant pressure of 100 kPa, and was heated from room temperature to 150 ° C. at a heating rate of 5 ° C./min. Warm and measure the depth of needle penetration at that time. However, when the film to be measured has an MFR (g / min) at 190 ° C. and a load of 2.16 kg measured in accordance with JIS-K6922-2 which changes along the thickness direction, the needle is pushed into the MFR. (G / min) is performed from the surface with the larger side. The "MFR" of the current-collecting wire fixing film in the present specification refers to 190 ° C. of the MFR at the stage when the current-collecting wire fixing film including the cross-linking treatment and the like was completed, measured according to JIS-K692-2-2. , 2.16 kg. The “TMA curve” that can be obtained by the thermomechanical analysis (TMA) test means that the temperature is X in the thermomechanical analysis (TMA) test and the needle indentation depth at the temperature is Y. In the XY coordinates, it refers to a curve indicating the correlation between the temperature and the depth of the needle pressing. As the thermomechanical analysis (TMA) device, for example, TMA / SS7100 manufactured by SII Nanotechnology or the like can be used.

  By setting the slope of the TMA curve according to the above definition to be −3.0 or more, a surface on which the current collecting wire 64 is embedded (hereinafter, referred to as a “sealing surface”) during thermal lamination processing for integration as a solar cell module. "), The current collecting wire fixing film 6 adheres to the solar cell element 4B while following the outer peripheral shape of the current collecting wire 64 on the same side, thereby exhibiting a sufficient molding property.

  On the other hand, by setting the slope of the TMA curve to be -1.3 or less, excessive flow of the resin is suppressed as a whole in the current-collecting wire fixing film during the above-described thermal lamination processing, whereby the current-collecting wires 64 are collected. It can be prevented from penetrating the electric wire fixing film and being exposed from the surface opposite to the sealing surface.

  The current-collecting wire fixing film 6 in which the slope of the TMA curve according to the above definition is −3.0 or more and −1.3 or less has, for example, a melting point in the range of 90 ° C. or more and 110 ° C. or less, and has an MFR of A plurality of different polyethylene resin films can be constituted by a multilayer film appropriately laminated and arranged. As a specific example, a resin layer having a thickness of 100 μm and having a melting point of 100 ° or more as a base resin is used as a base layer for securing heat resistance. A resin layer having a thickness of 25 μm as a resin is laminated on both surfaces thereof to form a multilayer resin film, and the latter resin layer composed of a resin having a relatively low melting point is disposed on the outermost surface on the side of the embedded surface. This can be realized by forming a sealing layer. In this case, the MFR of the base layer is preferably less than 1.0 g / min, and the MFR of the sealing layer is larger than the MFR of the base layer, and is 1.0 g / min. It is preferably at least 30.0 g / min.

  Alternatively, as shown in FIG. 5, for example, a resin film having a TMA curve with a slope of −3.0 or more and −1.3 or less as defined above has a melting point in the range of 90 ° C. or more and 110 ° C. or less. It is also manufactured by subjecting a single-layer resin film made of one polyethylene resin to a cross-linking treatment of irradiating ionizing radiation E only from one side under a condition such that the degree of cross-linking gradually decreases in the film thickness direction. be able to. In this case, the portion on the upper surface side in FIG. 5 where the crosslinking has sufficiently proceeded functions as the base material layer 61, and the lower surface side functions as the sealing layer 62.

  Here, the current-collecting wire fixing film 6 in which the slope of the TMA curve according to the above definition is −3.0 or more and −1.3 or less has a load of 190 ° C. measured according to JIS-K692-2-2 regardless of the layer configuration. The MFR at 2.16 kg gradually decreases from the sealing surface side to the opposite surface along the film thickness direction. However, the phrase “MFR gradually decreases along the thickness direction of the film” does not necessarily mean that the MFR always decreases in the entire region in the thickness direction of the film. . In the present specification, the test piece of the film is uniformly divided into three layers at a ratio of 1: 4: 1 in the thickness direction regardless of the layer configuration, and each of these three layers is referred to as a surface layer 1. Assuming that “intermediate layer—surface layer 2”, the magnitude relationship between the MFRs of these three layers is such that MFR of surface layer 1 ≦ MFR of intermediate layer <MFR of surface layer 2, or If the relationship of MFR of 1 <MFR of the intermediate layer ≦ MFR of the surface layer 2 is satisfied, it is considered that the requirement that “the MFR gradually decreases along the film thickness direction” is satisfied. And That is, for example, in the case of a film of -150 μm, the MFR of each surface layer is the MFR measured by scraping a test piece from each surface to a depth of 25 μm, and the MFR of the other portion near the center is the intermediate layer. If the MFR values of these three layers decrease gradually in light of the above definition, it is considered that the MFR is decreasing along the film thickness direction.

  The total thickness of the current-collecting wire fixing film 6 is preferably 75 μm or more and 200 μm or less. In the case of a multilayer film, for example, the thickness of a layer assumed to function as the sealing layer 62 is preferably 65 μm or more and 170 μm or less. However, these thickness ranges are based on the premise that the diameter of the current collecting wire 64 in a general “multi-wire connection” structure is approximately 100 μm to 200 μm. However, the present invention is not limited to this. In particular, the thickness of the sealing layer 62 may be appropriately adjusted according to the diameter of the current collecting wire to be embedded.

The current-collecting wire fixing film 6 is a resin formed using a resin composition based on a polyethylene-based resin such as low-density polyethylene (LD) in order to maintain a good balance between molding properties and heat resistance. It is preferable to form the film by further performing a crosslinking treatment for ensuring heat resistance. As the polyethylene resin, those having a melting point of 90 ° C. or more and 110 ° C. or less can be appropriately selected and used. Further, the density of the polyethylene resin, as long 0.870 g / cm ³ or more 0.930 g / cm ³ or less, preferably, density 0.900 g / cm ³ or more 0.920 g / cm ³ or less. Here, the base resin refers to a resin having the largest content ratio among all resin components in the resin layer, and the content ratio in the resin component is 50% by mass or more, and 90% by mass or more. It is preferred that

As a polyethylene resin having excellent flexibility, which is more preferable as the base resin of the resin composition forming the current collecting wire fixing film 6, for example, a polyethylene α-olefin copolymer can be mentioned. The polyethylene-based α- olefin copolymer is preferably a density 0.870 g / cm ³ or more 0.910 g / cm ³ or less of low density polyethylene of α- olefin copolymer.

  Specific examples of commercially available polyethylene-based α-olefin copolymers that can be preferably used as a base resin for forming the current-collecting wire fixing film 6 include “Tuffmer DF-710 (trade name) ) / (Mitsui Chemicals) "," Tuffmer DF-119 (trade name) / (Mitsui Chemicals) "," Tuffmer A-1085S (trade name) / (Mitsui Chemicals) "," Tuffmer A- 4070S (trade name) / (Mitsui Chemicals) "," Tuffmer A-4085S (trade name) / (Mitsui Chemicals) "," Tuffmer A-4090S (trade name) / (Mitsui Chemicals) ", “Kernel KF260T (trade name) / (Nippon Polyethylene)”, “Kernel KF270 (trade name) / (Nippon Polyethylene)”, “Kernel KF370 (trade name) / (Nippon Polyethylene) Ethylene), "Kernel KF360T (trade name) / (Nippon Polyethylene)", "Kernel KS240T (trade name) / (Nippon Polyethylene)", "Kernel KS340T (trade name) / (Nippon Polyethylene) ), "Kernel KS260 (trade name) / (Nippon Polyethylene Corporation)", "Exelen VL100 (trade name) / (Sumitomo Chemical Co., Ltd.)", "Exelen VL102 (trade name) / (Sumitomo Chemical Co., Ltd.) "Exelen VL200 (trade name) / (Sumitomo Chemical Co., Ltd.)", "Exelen FX201 (trade name) / (Sumitomo Chemical Co., Ltd.)", "Exelen FX301 (trade name) / (Sumitomo Chemical Co., Ltd.)", "Exelen FX307 (trade name) / (Sumitomo Chemical Co., Ltd.)", "Exelen FX352 (trade name) / (Sumitomo Chemical Co., Ltd.)", "Exelen FX351 ( Commercially available products such as "(trade name) / (Sumitomo Chemical Co., Ltd.)" and "Exelen FX357 (trade name) / (Sumitomo Chemical Co., Ltd.)" can be mentioned.

  It is preferable that the resin composition forming the current-collecting wire fixing film 6 further contains a light-resistant stabilizer in addition to the base resin. As the light stabilizer, various hindered amine-based light stabilizers obtained by polymerizing ethylene and a monomer having a specific chemical structure can be preferably used. As the hindered amine light stabilizer, a light stabilizer composed of a copolymer of a cyclic aminovinyl compound and ethylene and having a huge molecular structure having a molecular weight of 30,000 or more can be particularly preferably used. The content of the light resistance stabilizer may be 3% by mass or more and 10% by mass or less, and is more preferably 3.5% by mass or more and 4.5% by mass or less. As the above-mentioned hindered amine light stabilizer which can be preferably used as a light stabilizer added to the base material layer of the current collector wire fixing film of the present invention, specific examples which are commercially available include, for example, "XJ-100H" (Molecular weight: 35,000, manufactured by Nippon Polyethylene Co., Ltd.), and a high molecular weight type hindered amine-based light stabilizer.

  A silane copolymer (hereinafter, also referred to as “silane-modified polyethylene resin”) obtained by copolymerizing an α-olefin and an ethylenically unsaturated silane compound as a comonomer is fixed to the current collecting wire fixing film 6. More preferably, it is contained in the amount range. By incorporating an appropriate amount of the silane-modified polyethylene-based resin, it is possible to further enhance the adhesiveness with each of the members vertically stacked upon integration as a solar cell module such as a solar cell element or a sealing material sheet. In particular, when the current-collecting wire fixing film is a multilayer film, the sealing layer 62 disposed on the outermost surface side preferably contains the silane-modified polyethylene-based resin.

  The silane-modified polyethylene-based resin is obtained by graft-polymerizing a linear low-density polyethylene (LLDPE) serving as a main chain with an ethylenically unsaturated silane compound as a side chain. Such a graft copolymer has a high degree of freedom of silanol groups contributing to the adhesive force, and therefore improves the adhesion of the current-collecting wire fixing film 6 to other laminated members constituting the solar cell module 1. Can be. The content of the silane-modified polyethylene resin in the resin component of the adhesive layer 622 is preferably 5% by mass or more and 25% by mass or less. The silane-modified polyethylene-based resin can be produced, for example, by the method described in JP-A-2003-46105.

  As an ethylenically unsaturated silane compound to be graft-polymerized with a linear low-density polyethylene, for example, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinyltripentyloxysilane Use one or more selected from vinyltriphenoxysilane, vinyltribenzyloxysilane, vinyltrimethylenedioxysilane, vinyltriethylenedioxysilane, vinylpropionyloxysilane, vinyltriacetoxysilane, and vinyltricarboxysilane be able to.

  The content ratio of each resin contained in each layer of the current-collecting wire fixing film 6 is detected by, for example, DSC (differential scanning calorimetry), IR (infrared spectroscopy), and NMR (nuclear magnetic resonance). It can be analyzed from the peak ratio and the like.

[Method of manufacturing current collector wire fixing film]
The method for manufacturing the current-collecting wire fixing film is not limited to a specific method. As an example, a resin film satisfying the requirements for the above-described ATM curve can be obtained by the manufacturing method described below. That is, the current-collecting wire fixing film of the present invention is a film-forming step of forming an uncrosslinked resin film by forming a resin composition based on the above-mentioned polyethylene-based resin forming the base resin by melt extrusion, and A cross-linking treatment step of irradiating ionizing radiation only from one side of the uncross-linked resin film and performing a cross-linking treatment so that the degree of cross-linking is different between the one side and the opposite side. can do.

(Film forming process)
The film forming step of performing the melt molding of the resin composition can be performed by a known molding method, that is, various molding methods such as injection molding, extrusion molding, hollow molding, compression molding, and rotational molding. The lower limit of the molding temperature during molding may be any temperature that exceeds the melting point of the resin composition.

  When the current-collecting wire fixing film is formed of a multilayer film, the film formed in advance for each layer by the above-described melt forming method can be formed into a multilayer film by bonding them together via an adhesive. By forming a multilayer film by a process of co-extruding a resin composition forming each layer, a current collector wire fixing film can be manufactured with higher productivity.

(Crosslinking step)
In the cross-linking step, ionizing radiation is irradiated only from one side of the uncrosslinked resin film obtained in the film forming step, and the degree of cross-linking is different between this one side (the surface irradiated with ionizing radiation) and the opposite side. More specifically, the cross-linking treatment is performed under irradiation conditions such that the degree of cross-linking gradually decreases from the irradiation surface side of the ionizing radiation to the opposite surface.

  The individual crosslinking conditions in the crosslinking treatment by irradiation with ionizing radiation are not limited within a specific numerical range. However, it is preferable to appropriately adjust the slope of the TMA curve according to the above definition of the current-collecting wire fixing film after the crosslinking treatment to be −3.0 or more and −1.3 or less. For example, by adjusting and determining the above irradiation conditions based on the results of a TMA test of a resin film that has been manufactured by test in advance, the heat resistance and the moldability can be improved based on a single versatile index. A current collector fixing film compatible at a high level can be manufactured with high quality stability.

  As ionizing radiation used for the crosslinking treatment, ionizing radiation such as electron beam (EB), α-ray, β-ray, γ-ray, and neutron beam can be selected, but it is preferable to use an electron beam.

  The optimum value of the accelerating voltage in the electron beam irradiation mainly varies depending on the thickness of the resin film as the object to be irradiated, and a thicker film requires a higher accelerating voltage. For example, in the case of a polyethylene film having a thickness of 150 μm, the optimum value slightly varies depending on the composition of the material resin composition as a whole, such as the density and melting point of the base resin, and the types and amounts of other additives, but as a rough guide. It is preferable to irradiate at a voltage of 90 kV or more and 110 kV or less. If the acceleration voltage is lower than this, crosslinking does not proceed sufficiently even on the irradiation surface side, and the slope of the TMA curve defined above tends to be smaller than -3.0. Crosslinking also proceeds excessively on the side of the sealing surface opposite to the side, and the slope of the TMA curve defined above tends to exceed -1.3.

  Also, the irradiation dose in the electron beam irradiation is preferably approximately 100 kGy or more and 250 kGy or less as a rough guide as in the above. If the irradiation dose is less than 100 kGy, crosslinking does not proceed sufficiently even on the irradiation surface side, and the slope of the TMA curve defined above tends to be smaller than -3.0. Crosslinking also proceeds excessively on the side of the sealing surface opposite to the side, and the slope of the TMA curve defined above tends to exceed -1.3.

  In addition, Patent Documents 1 and 2 disclose a technical idea of providing a difference in the degree of crosslinking as an abstract idea, but it is not easy to actually appropriately incline the degree of crosslinking in the film thickness direction. Absent. In addition, as long as the components are incorporated into the solar cell module, those that show the optimal behavior under the temperature conditions at the time of thermal lamination processing for integration as an actual solar cell module are practically “appropriate”. It can be said, however, that there is no standard on how to identify films that are optimized based on objective indicators. In reality, it has been found that the optimum cross-linking conditions are individually found each time through complicated trial and error.

  Thus, the adjustment of the degree of cross-linking in the “current collector wire fixing film” is not easy in practice, and can be stably manufactured based on a general-purpose index. The development of "fixed film" was required. The above-described manufacturing method is a new manufacturing method that has advantageous effects over the conventional technology as a manufacturing method that can meet such demands.

  It is a well-known technical matter at the time of filing the present application that a sealing material using a polyethylene resin as a base resin can be used instead of EVA as a sealing material for a multi-wire connection type solar cell module. Therefore, in order to verify the effects of the present invention, when a polyethylene-based resin film is selected as a sealing material, the film is configured with a current-collecting wire fixing film that exhibits the effects of the present invention in combination with the resin film. Even if the resin film to be formed is a resin film formed of a resin composition using a polyethylene resin as a base resin, to confirm that the required performance as a current collecting wire fixing film can be satisfied at a preferable level. Then, the following tests were performed.

<Preparation of current collector wire fixing film>
Using the following amounts of each resin material and each additive, current collector wire fixing films of Examples and Comparative Examples were produced.

(Film forming process)
For Examples 1 to 3, first, a resin composition having the following polyethylene-based α-olefin copolymer as a base resin was melt-extruded at 190 ° C. by an extruder equipped with a T-die to obtain a thick resin. A single-layer resin film having a thickness of 150 μm was obtained.
In Example 4, a resin composition using the following low-density polyethylene (LDPE) as a base resin as a base resin, and a resin composition using the following polyethylene-based α-olefin copolymer (α-olefin) as a base resin The product was used as a sealing layer, and these were formed into a multilayer film by co-extrusion to obtain a multilayer resin film. This multilayer resin film also had a total thickness of 150 μm, and the thickness of each layer was 75 μm for the sealing layer (α-olefin) and 75 μm for the base layer (LDPE).
For the comparative example, the following polyethylene terephthalate (PET) resin film was used as a base layer, and a separately formed resin film using low density polyethylene (LDPE) as a base resin was used as a sealing layer, and an acrylic adhesive was used. The two resin films were joined by a dry lamination method to obtain a multilayer resin film. The total thickness of this multilayer resin film was 155 μm, and the thickness of each layer was 75 μm for the sealing layer (LDPE) and 75 μm for the base layer (PET). The thickness of the adhesive layer between both layers was 5 μm.
Further, the following hindered amine light stabilizer (HALS) was added to the sealing layers of Examples 1 to 4 and Comparative Example at a content ratio of 1.0% by mass in the resin component of each layer. .

(Resin materials, additives)
Polyethylene-based α-olefin copolymer (described as “α-olefin” in Table 1)
: Density 0.893 g / cm ³ , melting point 77 ° C., trade name “Toughmer A-4090S” (manufactured by Mitsui Chemicals, Inc.)
Polyethylene terephthalate resin film (described as “PET” in Table 1)
: Thickness 75 μm, melting point 260 ° C., trade name “Lumirror (registered trademark) T60 (manufactured by Toray Industries, Inc.)” (referred to as “PET film” in Table 1)
Polyethylene resin (described as "LDPE" in Table 1)
: Density 0.920 g / cm ³ , melting point 106 ° C, trade name “Sumikasen (registered trademark) L420” (manufactured by Sumitomo Chemical Co., Ltd.)
Hindered amine light stabilizer (HALS)
: Molecular weight 35,000, trade name “XJ-100H” (manufactured by Nippon Polyethylene Corporation)

(Crosslinking step)
Of the uncrosslinked resin films obtained in the above-described film forming process and in each of the Examples and Comparative Examples, ionizing radiation was performed under the conditions indicated by numerals 1 to 4 in the column of “EB irradiation conditions” in Table 1 below. For the crosslinking treatment. As an electron beam irradiation apparatus, "Iwasaki Electric Co., Ltd., product name EC250 / 15 / 180L" was used. The accelerating voltage and the illuminance under each of the processing conditions 1 to 4 are as follows, and the irradiation of ionizing radiation was performed only from one side of each resin film (the substrate layer side in Example 4). In addition, about the film described with the number 0 in the same column, the crosslinking process was not performed (comparative example).

(Cross-linking treatment conditions)
EB irradiation condition 1
: Acceleration voltage 125 kV, illuminance 80 kGy
EB irradiation condition 2
: Acceleration voltage 125 kV, illuminance 90 kGy
EB irradiation condition 3
: Acceleration voltage 125 kV, illuminance 100 kGy
EB irradiation condition 4
: Acceleration voltage 125 kV, illuminance 110 kGy

<TMA test>
A TMA test was performed on the current-collecting wire fixing films of each of the examples and comparative examples, and the “slope of the TMA curve” of each film was determined based on the above definition. The results were as shown in Tables 1 and 2. In Examples 1 to 4 in which the cross-linking treatment was performed by EB irradiation from one side, the needle was pushed in from the side opposite to the irradiation side. In the comparative example, the needle was pushed from the surface on the side of the sealing layer (LDPE). For Examples 1 to 4 and Comparative Example, FIG. 6 also shows a graph of the transition of the indentation depth for each temperature.

<Evaluation Example 1: Moldability>
The molding properties of the current-collecting wire fixing films of Examples and Comparative Examples were evaluated by the following test methods.
[Molding evaluation test]
The molding properties of the current-collecting wire fixing films of Examples and Comparative Examples were evaluated by the following test methods.

[Molding evaluation test]
On a glass substrate (white plate float semi-tempered glass JPT3.2 180 mm × 180 mm × 3.2 mm), an aluminum plate of 200 μm in thickness and 150 mm × 150 mm assuming a simulated solar cell element is allowed to stand, and the aluminum Example in which 20 pieces of copper wire having a length of 150 mm and a diameter of 200 μm are arranged in parallel at a pitch of 1.0 mm on a plate, and further cover all these aluminum plates and copper wires, and cut into a size of 100 mm × 100 mm, A laminate of the respective collector wire fixing films of the comparative example was subjected to a vacuum heating laminator treatment at a set temperature of 165 ° C., evacuation for 3 minutes, and atmospheric pressure pressurization for 7 minutes, to fix the collector wires of the respective examples and comparative examples. For the film for use, a “sample for evaluation of molding properties and heat resistance” was obtained. For each of these molding evaluation samples, the state of each sample after lamination was visually observed, and the molding properties were evaluated according to the following evaluation criteria. Table 2 shows the evaluation results as “molding properties”.
(Evaluation Criteria) A: The current-collecting wire fixing film completely follows the concavo-convex surface made of the facing aluminum plate and copper wire. No void formation was observed.
C: A part of the current-collecting wire fixing film did not completely follow the uneven surface formed of the aluminum plate and the copper wire facing each other, and a partially defective portion (void) was formed near the copper wire.

<Evaluation Example 2: Heat resistance>
The heat resistance of the “sample for evaluation of molding property and heat resistance” of Examples and Comparative Examples prepared and used in <Evaluation Example 1> was evaluated by the following test methods.
[Heat resistance evaluation test]
With respect to the current collecting wire fixing films of the above Examples and Comparative Examples, the state of each sample after lamination was visually observed, and the molding property was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2 as "heat resistance". The heat resistance was evaluated by the following method. The state after lamination of each sample of the durable battery module was visually observed, and the molding property was evaluated according to the following evaluation criteria. The evaluation results are shown in Table 2 as "heat resistance".
(Evaluation Criteria) A: The current-collecting wire fixing film completely covered the concavo-convex surface made of the facing aluminum plate and copper wire, and no wire exposure was observed on the film surface.
C: The current-collecting wire fixing film covered the concavo-convex surface made of the facing aluminum plate and copper wire, but a part of the wire was exposed on the film surface.

  From the test and evaluation results of Evaluation Example 1 (molding property) and Evaluation Example 2 (heat resistance), the current-collecting wire fixing film in which all layers are formed of a resin composition containing a polyethylene resin as a base resin has a molding property. It can be seen that both the heat resistance and the heat resistance can be achieved at a preferable level. In particular, when the slope of the TMA curve in the specific temperature range is controlled in the range of −3.0 or more and −1.3 or less, it can be seen that both the molding property and the heat resistance can be achieved at a higher level. .

<Evaluation Example 3: Light fastness>
For each of the current-collecting wire fixing films of the examples and the comparative examples, the light resistance was evaluated by the following test method.
[Light fastness test]
Each test piece of the current-collecting wire fixing film of each of the examples and the comparative examples cut into a size of 50 mm × 50 mm was put into a super UV tester (“I-Super UV tester (manufactured by Iwasaki Electric Co., Ltd.)”) and 100 mW / cm ^2. A deterioration promotion test was performed for 168 hours under the irradiation conditions described above. After 168 hours, the test piece was taken out of the tester, and the appearance was visually observed to evaluate the light resistance. The evaluation criteria were as follows. The evaluation results are shown in Table 2 as "light fastness".
(Evaluation criteria)
A: No change in appearance B: Fine cracks not exceeding 10 mm in maximum length and not penetrating in the depth direction are within a very small part of the film surface (within the area ratio, within 1/5 of the entire surface). Only occur in
C: A crack (crack) or breakage penetrating the film in the depth direction has occurred.

  From the test and evaluation results of Evaluation Example 3 (lightfastness), the current-collecting wire fixing film in which all layers are formed of a polyethylene resin is different from the conventional configuration (comparative example) in which a polyester film is used as a base resin. It can be seen that a current-collecting wire fixing film having sufficient light resistance can be obtained. Therefore, by using this, in the overall configuration of the solar cell module, the addition of the ultraviolet absorber to the light-receiving surface side sealing material, which has been conventionally required, is not essential. This can contribute to an improvement in the power generation efficiency of the solar cell module.

<Evaluation Example 4: Transparency>
For each of the current-collecting wire fixing films of Examples and Comparative Examples, the transparency was evaluated by the following test method.
[Transparency test]
The test piece of the current-collecting wire fixing film of each Example and Comparative Example cut into 50 mm × 50 mm was vacuum-laminated under the following conditions to eliminate fine irregularities on the surface at the film-forming stage, and then transparent. The property (HAZE) was measured according to JIS K7136 using “Haze transmittance meter HM150 (manufactured by Murakami Color Research Laboratory Co., Ltd.)”. The evaluation criteria were as follows. The evaluation results are shown in Table 2 as "transparency".
(Vacuum lamination conditions)
(Constitution) ETFE / test piece / ETFE (ETFE is removed during measurement)
(Conditions) 165 ° C, evacuation 2 minutes, press 2.5 minutes, 100 kPa
(Evaluation criteria)
A: Haze value of less than 5.0% B: Haze value of more than 5.0% and 14.0% or less C: Haze value of more than 14.0%

  According to the test and evaluation results of Evaluation Example 4 (transparency), the current-collecting wire fixing film in which all layers are formed of a resin composition containing a polyethylene-based resin as a base resin has sufficiently good transparency. It turns out that it is. In particular, in the case where the slope of the TMA curve in a specific temperature range is controlled in a range of −3.0 or more and −1.3 or less by performing a cross-linking step by irradiation with ionizing radiation, the transparency is particularly reduced. It also turns out to be advantageous.

  From the above test and evaluation results, the current-collecting wire fixing film according to the above-described embodiment according to the present invention can be used in a multi-wire connection type solar cell module in which demand is expected to increase in the future. Base material that is used to stably fix the current-collecting wire portion made of to the solar cell element. The basic performance of the current-collecting wire fixing film, which is both heat-resistant and molding, is more stable. It is a "current collector wire fixing film for a solar cell module" that can be held by using the current collecting wire fixing film while maintaining good molding properties on the side of the current collecting wire. The overall configuration has been optimized so that the sealing material side surface of the It can be seen that it is possible to construct a that "solar cell module".

REFERENCE SIGNS LIST 1 solar cell module 2 transparent front substrate 3 sealing material 31 light receiving surface side sealing material 32 non-light receiving surface side sealing material 4 solar cell element 5 back surface protection sheet 6 current collecting wire fixing film 61 base layer 62 sealing layer 621 Base layer 622 Adhesive layer 64 Current collecting wire

Claims (4)

A multi-wire connection type solar cell module, and a plurality of solar cell elements,
A plurality of current collecting wires arranged on the surface of the solar cell element,
A current collecting wire fixing film that covers the plurality of current collecting wires and is laminated on the surface of the solar cell element,
And a sealing material for sealing the solar cell element,
On one surface of the current collecting wire fixing film, a plurality of the current collecting wires are embedded,
The other surface of the current-collecting wire fixing film is in close contact with the sealing material,
The sealing material and the current collector wire fixing film is both a density 0.870 g / cm ³ or more 0.930 g / cm ³ or less of the polyethylene resin is a resin film containing as a base resin, the solar cell module. The collecting wire fixing film,
A resin film containing a polyethylene resin having a melting point of 90 ° C or higher and 110 ° C or lower as a base resin,
The slope of a TMA curve defined by the following definition between a temperature of 90 ° C. and 100 ° C. is −3.0 or more and −1.3 or less.
The solar cell module according to claim 1.
“Slope of TMA curve”: In the “TMA curve” obtained by the following “thermomechanical analysis (TMA) test”, the indentation depth is Y ₁ (μm) at the temperature X ₁ (° C.), and the temperature X _{When the} indentation depth is Y ₂ (μm) at ₂ (° C.) (> X ₁ (° C.)), the “slope (a) of the TMA curve” between X ₁ and X ₂ is (a) = (Y ₂ −Y ₁ ) / (X ₂ −X ₁ ). Time, however, penetration depth before the temperature reaches X ₂ is a case has been reached -150Myuemu (when the needle penetrates the film to be measured), the temperature X _2, indentation depth reached -150Myuemu Replace with temperature.
“Thermo-mechanical analysis (TMA) test”: A 150 μm-thick current-collecting wire-fixed film sheet was set on a thermo-mechanical analysis (TMA) test apparatus, and was pushed into a φ1 mm needle to a constant pressure of 100 kPa, and the temperature was raised at a rate of 5 ° C. The temperature is raised from room temperature to 150 ° C./min, and the depth of the needle being pushed at that time is measured. However, when the film to be measured has an MFR (g / min) at 190 ° C. and a load of 2.16 kg measured in accordance with JIS-K6922-2 which changes along the thickness direction, the needle is pushed into the MFR. (G / min) is performed from the surface with the larger side. The “TMA curve” that can be obtained by the thermomechanical analysis (TMA) test means that the temperature is X in the thermomechanical analysis (TMA) test and the needle indentation depth at the temperature is Y. In the XY coordinates, it refers to a curve indicating the correlation between the temperature and the depth of the needle pressing. The current collecting wire fixing film is a multilayer resin film including a sealing layer having a melting point of the base resin of less than 100 ° and a base layer having a melting point of the base resin of 100 ° or more,
In the sealing layer, a plurality of the current collecting wires are embedded.
The solar cell module according to claim 1.   The solar cell module according to claim 3, wherein the sealing layer contains a silane-modified polyethylene-based resin.

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