JP2016143746A - Encapsulant sheet for solar cell module and solar cell module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an encapsulant sheet for solar cell module capable of suppressing occurrence of crack in a solar cell element caused by a bus bar, while having sufficient heat resistance.SOLUTION: In a TMA curve showing a relationship of a predetermined temperature range (°C) and the depth (μm) of a needle pushed into an encapsulant sheet, obtained by thermomechanical analysis (TMA) test, the slope P(push-in depth (μm) of the TMA curve/temperature (°C)) is obtained in the predetermined temperature range (°C), and the value P(P=100×(P/P)) of the ratio of P, i.e., the gradient at 80% of the thickness of the encapsulant sheet to P, i.e., the maximum value of the absolute value of the gradient P is 30% or less.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a sealing material sheet for a solar cell module and a solar cell module.

  In recent years, solar cells as a clean energy source have attracted attention due to the growing awareness of environmental issues. Currently, various types of solar cell modules have been developed and proposed. Generally, a solar cell module has a configuration in which a transparent front substrate made of glass or the like, a solar cell element, and a back surface protection sheet are laminated via a sealing material sheet.

  The sealing material sheet is required to have adhesion and durability with the transparent front substrate, the solar cell element, and the back surface protection sheet, embedding property of the solar cell element, heat resistance, and the like.

  The sealing material sheet is improved in heat resistance of the sealing material sheet by crosslinking the resin composition. However, when the encapsulant sheet is excessively crosslinked, the embedding property of the solar cell element is deteriorated.

  Then, as what combines the embedding property and heat resistance of a solar cell element when manufacturing a solar cell module, an ionizing radiation cross-linking resin is included in the resin constituting the encapsulant sheet, A sealing material sheet having a structure in which the gel fraction is changed along the sheet thickness direction by irradiating ionizing radiation from one surface has been proposed (Patent Document 1).

JP 2011-74261 A

  Although patent document 1 describes the sealing material sheet excellent in the embedding property of a solar cell element, it does not consider about the wiring which connects a photovoltaic cell. On the other hand, when stacking as a solar cell module, a wiring for extracting electricity from the solar cell element called a bus bar is arranged between the solar cell element and the sealing material sheet. Here, when manufacturing a solar cell module, it generally includes a laminating step for laminating the solar cell modules, and in the laminating step, the solar cell element and the sealing material sheet are heated and laminated with a pressing pressure. . However, since the bus bar has a certain thickness, the stress due to press working concentrates on the portion of the solar cell element where the bus bar overlaps. Therefore, there is a problem that cracks occur in the solar cell element portion where the bus bars overlap.

  This invention is made | formed in view of the above condition, and suppresses generation | occurrence | production of the crack of the solar cell element resulting from a bus bar, although it is a sealing material sheet for solar cell modules which has heat resistance enough. It is an object of the present invention to provide a possible solar cell module sealing material sheet and solar cell module.

As a result of sincerity studies to solve the above problems, the present inventors have focused on a thermomechanical analysis (TMA) test of the sealing material sheet, and have a gradient P (indentation depth (μm) / temperature of the TMA curve. (.Degree. C.)) It has been found that the above problem can be solved if the sealing material sheet specifies a gradient ratio at a predetermined film thickness with respect to the maximum value P _max of the absolute value, and the present invention has been completed. . More specifically, the present invention provides the following.

(1) A sealing material sheet for a solar cell module, which is obtained in a thermomechanical analysis (TMA) test under the following conditions, and has a predetermined temperature range (° C.) and the pushing depth of the needle into the sealing material sheet In the TMA curve showing the relationship with (μm), the gradient P (indentation depth (μm) / temperature (° C.)) of the TMA curve in the predetermined temperature range (° C.) is obtained, and the absolute value of the gradient P The value of P ₁ (P ₁ = 100 × (P ₈₀ / P _MAX )), which is the ratio of P ₈₀ that is the gradient at 80% of the film thickness of the sealing material sheet, to P _MAX that is the maximum value of 30 is 30 % Encapsulant sheet.
(TMA test: A φ10 mm encapsulant sheet was set in a TMA apparatus, pressed into a φ1 mm needle to a constant pressure of 20 kPa, and the temperature was raised from room temperature to 150 ° C. at a heating rate of 5 ° C./min. indentation depth is measured. _{However, P 80} is, when the indentation depth of the needle at 0.99 ° C. of less than 80% more than 50% of the thickness of the encapsulant sheet, _{P 0.99 ° C.} is the slope at 0.99 ° C. Is used.)

(2) The sealing material sheet according to (1), wherein the P _MAX (indentation depth (μm) / temperature (° C.)) is 10 μm / ° C. or more and 50 μm / ° C. or less.

(3) The encapsulant sheet according to (1) or (2), wherein the P ₈₀ (indentation depth (μm) / temperature (° C.)) is 1 μm / ° C. or more and 10 μm / ° C. or less.

  (4) The pressing depth of the needle at a temperature of the melting point of the encapsulant sheet + 40 ° C. is within 85% of the film thickness of the encapsulant sheet, according to any one of (1) to (3) Sealing material sheet.

(5) The sealing material sheet according to any one of (1) to (4), wherein polyethylene having a density of 0.860 g / cm ³ or more and 0.970 g / cm ³ or less is 85% or more in the total sealing material composition. The sealing material sheet of description.

  (6) The encapsulant sheet is a multilayer sheet comprising an intermediate layer and outermost layers disposed on both sides thereof, and the outermost layer further contains a silane-modified polyethylene resin (5) The encapsulant sheet described in 1.

  (7) The encapsulant sheet according to any one of (1) to (6), wherein the encapsulant sheet has a thickness of 300 μm or more and 600 μm or less.

  (8) A solar cell module comprising: the encapsulant sheet according to any one of (1) to (7); a solar cell element; and a bus bar that is a wiring for taking out electricity from the solar cell element, The solar cell module, wherein the bus bar is disposed between the sealing material sheet and the solar cell element, and the thickness of the bus bar is 150 μm or more and 300 μm or less.

  (9) The solar cell module according to (8), wherein the thickness of the solar cell element is 150 μm or more and 300 μm or less.

According to the present invention, in the thermomechanical analysis test (TMA) test of the encapsulant sheet, a predetermined value with respect to the maximum value P _max of the absolute value of the gradient P (indentation depth (μm) / temperature (° C.)) of the TMA curve. The encapsulant sheet that specifies the gradient ratio in film thickness is an encapsulant sheet for solar cell modules that has sufficient heat resistance, but can prevent the occurrence of cracks in the solar cell elements due to the bus bars. It is a stopping material sheet.

It is a cross-sectional schematic diagram which shows an example of the layer structure of the sealing material sheet of this invention, and a solar cell module using the same. In the thermomechanical analysis test (TMA) test which concerns on the sealing material sheet | seat of an Example and a comparative example, it is the graph which showed the relationship between temperature (degreeC) and the pushing depth of the needle | hook to a sealing material sheet. In the thermomechanical analysis test (TMA) test concerning the sealing material sheets of Examples and Comparative Examples, the relationship between the temperature (° C.) and the absolute value of the gradient of the TMA curve (indentation depth (μm) / temperature (° C.)). It is the graph which showed.

  Hereinafter, the sealing material sheet and solar cell module for solar cell modules of this invention are demonstrated in detail. The present invention is not limited to the embodiments described below.

<Sealing material sheet>
The sealing material sheet of the present invention may be expressed as a thermomechanical analysis test (hereinafter referred to as a TMA test) showing a relationship between a predetermined temperature range (° C.) and a needle pressing depth (μm) into the sealing material sheet. The gradient P (indentation depth (μm) / temperature (° C.)) of the TMA curve in a predetermined temperature range (° C.) is obtained, and the seal against P _MAX that is the maximum absolute value of the gradient P is obtained. The sealing material sheet has a value of P ₁ (P ₁ = 100 × (P ₈₀ / P _MAX )), which is a ratio of P ₈₀ , which is a gradient at 80% of the film thickness of the stopping material sheet, of 30% or less. By optimizing the value of P ₁ (P ₁ = 100 × (P ₈₀ / P _MAX )), the generation of cracks in the solar cell element due to the bus bar is achieved while the sealing material sheet has sufficient heat resistance. It can be set as the sealing material sheet which can be suppressed.

  Here, the TMA test in the present invention means that a sealing material sheet of φ10 mm is set in a TMA apparatus, a pressure of 20 kPa is applied to a φ1 mm needle, a predetermined temperature range (° C.) at a temperature rising rate of 5 ° C./min, For example, it refers to a test in which the temperature is raised from room temperature to 150 ° C., and the indentation depth of the needle is measured. As a thermomechanical analysis (TMA) apparatus, for example, TMA / SS7100 manufactured by SII Nanotechnology can be used.

P _MAX in the TMA test is the maximum absolute value of the gradient P (indentation depth (μm) / temperature (° C)) obtained by differentiating the indentation depth (μm) in the TMA curve with temperature (° C). is there. P _MAX is the maximum value of the pushing speed of the needle in the TMA test, and is a parameter indicating the flexibility of the sealing material sheet. An encapsulant sheet having a large P _MAX indicates that the encapsulant sheet has high flexibility in press processing of the laminate. Therefore, in the case of a sealing material sheet having a large P _MAX , the bus bar can be easily embedded in the pressing process of the laminate, and the stress of the pressing process applied to the place where the bus bar and the solar cell element overlap is reduced. Can do. Therefore, the generation | occurrence | production of the crack of the solar cell element resulting from the overlap of a bus bar can be suppressed. Lamination in the laminating process is divided into a vacuuming process and a pressing process, and is performed at a set temperature of about 110 ° C to 150 ° C. The temperature reaches 70 ° C. to 90 ° C. in the evacuation step, and the temperature is raised to the set temperature in the pressing step. Thus general burden on the solar cell element is preferably a temperature at P _MAX for at pressing process starts becomes highest is 70 ° C. to 90 ° C.. The value of P _MAX (indentation depth (μm) / temperature (° C.)) is preferably 10 μm / ° C. to 50 μm / ° C., more preferably 12 μm / ° C. to 35 μm / ° C., and more preferably 15 μm / ° C. More preferably, the temperature is set to 30 ° C./° C. By setting the value of P _MAX (indentation depth (μm) / temperature (° C.)) to 10 μm / ° C. or more, the generation of cracks in the solar cell element due to the overlapping of the bus bars can be more effectively suppressed. . By setting the value of P _MAX (indentation depth (μm) / temperature (° C.)) to 50 μm / ° C. or less, a sealing material sheet having sufficient heat resistance can be obtained.

The _{P 80} of TMA test, a gradient at 80% of the thickness of the sealing material sheet (indentation depth ([mu] m) / Temperature (° C.)). Here, the gradient at 80% of the film thickness of the encapsulant sheet refers to the gradient (indentation depth (μm) / temperature) when the needle indentation depth is 80% of the film thickness of the encapsulant sheet. ° C)). P ₈₀ is a parameter indicating the heat resistance of the sealing material sheet. Higher P ₈₀ is smaller sealing material sheet, which means to include many areas highly crosslinked during sealing material sheet. Therefore, it has a high heat resistance as small encapsulant sheet P _80. If less sealing material sheet P ₈₀ is the heat resistance of the sealing material sheet is further improved. The value of P ₈₀ (indentation depth (μm) / temperature (° C.)) is preferably from 1 μm / ° C. to 10 μm / ° C., more preferably from 2 μm / ° C. to 6 μm / ° C. By setting the value of P ₈₀ (indentation depth (μm) / temperature (° C.)) to 10 μm / ° C. or less, a sealing material sheet having sufficient heat resistance can be obtained. By setting the value of P ₈₀ (indentation depth (μm) / temperature (° C.) to 1 μm / ° C. or more, the generation of cracks in the solar cell element due to the overlapping of the bus bars can be more effectively suppressed. . In addition, when P ₈₀ has a pressing depth of the needle at 150 ° C. of 50% or more and less than 80% of the film thickness of the encapsulant sheet, P _{150 ° C.} which is a gradient at _{150 ° C.} is used.

In the TMA test, P ₁ (P ₁ = 100 × (P ₈₀ / P _MAX )) is P _MAX which is the maximum absolute value of the gradient P (indentation depth (μm) / temperature (° C.)) of the TMA curve. for, the ratio of the P ₈₀ is the slope at 80% of the thickness of the sealing material sheet. Sealing material sheet of the present invention, the machining conditions by ionizing radiation suitably adjusted, and a flexible region which is excellent in laminate suitability, P ₁ so as to have both a region with a high degree of crosslinking with excellent heat resistance ( By setting P ₁ = 100 × (P ₈₀ / P _MAX )) to 30% or less, more preferably 20% or less, cracks of the solar cell element due to the bus bar are generated while having high heat resistance. Can be suppressed.

  The melting point of the sealing material sheet in the TMA test + the needle indentation depth at a temperature of 40 ° C. is preferably within 85% of the film thickness of the sealing material sheet, more preferably within 80%, more preferably 75%. More preferably, it is within. The heat resistance of a sealing material sheet | seat can be made more preferable by making the indentation depth of the needle | hook in a TMA test into such a range.

  The thickness of the encapsulant sheet is more preferably 300 μm or more and 600 μm or less. By setting it as such a range, an impact can fully be relieved and it can be set as a highly productive sealing material sheet.

[Encapsulant composition]
The sealing material sheet of the present invention preferably contains, for example, 85% or more of a polyethylene resin having a density of 0.860 g / cm ³ or more and 0.970 g / cm ³ or less in the total sealing material composition. By including the polyethylene-based resin in such a range, it is possible to reduce decomposition due to long-term use of the encapsulant sheet and to have transparency of the encapsulant sheet. As the polyethylene resin, low density polyethylene (LDPE) can be more preferably used, and linear low density polyethylene (LLDPE) or metallocene linear low density polyethylene (M-LLDPE) can be particularly preferably used.

The density of the polyethylene resin is preferably 0.860 g / cm ³ or more and 0.970 g / cm ³ or less, and particularly preferably 0.865 g / cm ³ or more and 0.930 g / cm ³ or less. By setting the density of the polyethylene resin within the above range, the transparency of the sealing material can be further improved.

  The polyethylene resin preferably has a melting point of 40 ° C. or higher and 90 ° C. or lower, and more preferably a melting point of 55 ° C. or higher and 80 ° C. or lower.

  The sealing material sheet of the present invention is preferably a multilayer sheet comprising an intermediate layer and outermost layers disposed on both sides thereof, and the outermost layer further contains a silane-modified polyethylene resin. It is preferable to do. The silane-modified polyethylene resin is a resin obtained by graft polymerizing low-density polyethylene (LDPE) serving as a main chain, preferably linear low-density polyethylene (LLDPE) with an ethylenically unsaturated silane compound as a side chain. Since such a graft copolymer has a high degree of freedom of silanol groups that contribute to the adhesive force, it can improve the adhesion of the sealing material sheet to other members in the solar cell module.

  The encapsulant composition for forming the encapsulant sheet may contain a necessary minimum amount of a crosslinking agent, but it is more preferable not to add a crosslinking agent. While the addition of a crosslinking aid allows adequate crosslinking to proceed sufficiently, the addition of a crosslinking agent such as an organic peroxide during the heat laminating process for integration with the solar cell module This is because the risk of problems such as foaming due to degas is increased. When adding a crosslinking agent, a well-known thing can be used and it does not specifically limit, For example, a well-known radical polymerization initiator can be used.

  In addition, the sealing material composition for molding the sealing material sheet may contain other components such as a crosslinking aid, a light stabilizer, an ultraviolet absorber, and a heat stabilizer as necessary. . The other components are preferably in the range of 0.001% by mass to 5% by mass with respect to the total amount of the sealing material composition.

<Method for producing sealing material sheet>
[Sheet making process]
The sealing material sheet of this invention can be manufactured by passing through the sheet-forming process which melt-molds each composition and obtains a sealing material sheet, for example. Molding is performed by various molding methods such as injection molding, extrusion molding, hollow molding, compression molding, and rotational molding, which are usually used in ordinary thermoplastic resins. As an example of the method for forming the encapsulant sheet as the multilayer sheet, a method of forming by co-extrusion using two or more melt-kneading extruders can be given.

[Crosslinking process]
The sealing material sheet of this invention can be manufactured by passing through the bridge | crosslinking process which performs the bridge | crosslinking process by ionizing radiation with respect to the non-crosslinked sealing material sheet | seat after forming into a sheet, for example. A cross-linking step of performing a cross-linking treatment with ionizing radiation on an uncross-linked encapsulant sheet is a solar cell module integration step in which the encapsulant sheet is integrated with other members after completion of the sheeting step. Do before you start. It is set as the sealing material sheet from which the crosslinking degree of the sealing material sheet changed along the thickness direction of the sealing material sheet by this crosslinking process. The cross-linking treatment may be performed continuously in-line following the sheet forming step, or may be performed off-line.

  Here, the degree of cross-linking of the encapsulant sheet refers to the rate of cross-linking of the encapsulant sheet as specified by parameters such as gel fraction and MFR, and the lower the degree of cross-linking, the less cross-linking reaction has occurred. It means that there are many resin component regions. The gel fraction (%) means that 0.1 g of the sealing material is put in a resin mesh, extracted with 60 ° C. toluene for 4 hours, taken out together with the resin mesh, weighed after drying, and compared before and after extraction. The mass% of residual insoluble matter was measured and this was used as the gel fraction. Moreover, MFR (g / 10min) can be calculated | required by measuring by 190 degreeC and load 2.16kg measured by JIS-K6922-2.

  Regarding the crosslinking treatment by irradiation with ionizing radiation, the individual crosslinking conditions are not particularly limited. Although it can carry out by ionizing radiations, such as an electron beam (EB), an alpha ray, a beta ray, a gamma ray, a neutron beam, it is preferable to use an electron beam especially.

Moreover, the ionizing radiation can mention the method of irradiating the ionizing radiation of different intensity | strength from only one surface side or front and back of a sealing material sheet. By irradiating ionizing radiation having different intensity from only one side or front and back surfaces of the encapsulant sheet, the degree of crosslinking of the encapsulant composition can be changed along the thickness direction of the encapsulant sheet. . By doing _so, it is possible to manufacture the sealing material sheet value of _{P 1 (P 1 = 100 ×} (P 80 / P MAX)) is 30% or less.

When ionizing radiation is irradiated by single-sided irradiation, the acceleration voltage is determined by the thickness of the sheet that is the object to be irradiated, and a thicker sheet requires a larger acceleration voltage. For example, in a sealing material sheet having a thickness of 550 μm, irradiation is performed at 100 kV to 250 kV. When the acceleration voltage is less than 100 kV, crosslinking is insufficient, and the heat resistance of the encapsulant sheet is insufficient. On the other hand, when the acceleration voltage exceeds 250 kV, the peak inside the surface is the peak of the maximum dose, and P ₁ (P ₁ = 100 × (P ₈₀ / P _MAX )) in the TMA test, which is a characteristic parameter of the present invention. It becomes difficult to produce a sealing material sheet having a preferable value. The irradiation dose ranges from 30 kGy to 50 kGy, preferably from 35 kGy to 45 kGy. Irradiation may be in an air atmosphere or a nitrogen atmosphere.

When the ionizing radiation is irradiated by single-sided irradiation, the irradiation direction of the ionizing radiation may be applied from the solar cell side where the bus bar is disposed or from the opposite direction of the solar cell side. That is, the maximum value of the degree of crosslinking may be on the solar cell side of the encapsulant sheet or in the opposite direction to the solar cell side. Manufacturing a sealing material sheet having a preferable value of P ₁ (P ₁ = 100 × (P ₈₀ / P _MAX )) in a TMA test by irradiating ionizing radiation with a predetermined acceleration voltage and dose. Can do.

In addition to performing irradiation with ionizing radiation by single-sided irradiation, ionizing radiation with different intensities may be irradiated from the front and back surfaces. A sealing material in which the value of P ₁ (P ₁ = 100 × (P ₈₀ / P _MAX )) in the TMA test is preferable also by irradiating ionizing radiation with different intensities from the front and back surfaces as in the case of single-side irradiation. Sheets can be manufactured.

  This crosslinking treatment may be performed continuously in-line following the sheet forming step, or may be performed off-line. Further, when the crosslinking treatment is a general heat treatment, generally, the content of the crosslinking agent is 0.5 parts by mass or more and 1.5 parts by mass or less with respect to 100 parts by mass of all components of the sealing material sheet. However, in the sealing material sheet of the present invention, the content of the crosslinking agent may be 0, and even if it is contained, it is preferably less than 0.5 parts by mass. Thereby, the risk of the productivity fall by gelatinization of the sealing material composition in the sheeting process of a sealing material composition can be reduced.

<Solar cell module>
An embodiment of a solar cell module using the sealing material sheet of the present invention will be described. FIG. 1 is a cross-sectional view showing a layer structure of a solar cell module 10 using the sealing material sheet of the present invention. In the solar cell module 10 of the present invention, the transparent front substrate 2, the front sealing material layer 3, the solar cell element 4, the back sealing material layer 5, and the back surface protection sheet 6 are laminated in order from the incident light receiving surface side. ing. Between the solar cell element 4 and the front sealing material layer 3, a bus bar 7 that is a wiring for taking out electricity from the solar cell element is disposed. The solar cell module 10 of the present invention can use the sealing material sheet of the present invention for at least one of the front sealing material layer 3 and the back sealing material layer 5. It is preferable that the bus bar is disposed between the sealing material sheet of the present invention and the solar cell element. Although it is a sealing material sheet having sufficient heat resistance, the occurrence of cracks in the solar cell element due to the bus bar can be suppressed. In the solar cell module shown in FIG. 1, it is preferable to use the sealing material sheet of this invention for the front sealing material layer 3 which is the side by which the bus-bar 7 is arrange | positioned.

  Moreover, when the bus bar is arrange | positioned at the back surface sealing material layer side of a photovoltaic cell, it is preferable to use the sealing material sheet of this invention for a back surface sealing material layer (not shown). Although it is a sealing material sheet having sufficient heat resistance, the occurrence of cracks in the solar cell element due to the bus bar can be suppressed.

  The thickness of the bus bar is preferably 150 μm or more and 300 μm or less. By setting it as such a range, it can have favorable electroconductivity as wiring which takes out electricity from a solar cell element.

  The thickness of the solar cell element is preferably 150 μm or more and 300 μm or less. By setting it as 150 micrometers or more, the risk of the crack generation of a solar cell element can be suppressed. Productivity can be made favorable by setting it as 300 micrometers or less.

<Method for manufacturing solar cell module>
The solar cell module 10 is formed by sequentially laminating a member composed of the transparent front substrate 2, the front sealing material layer 3, the solar cell element 4 including the bus bar 7, the back sealing material layer 5, and the back surface protection sheet 6, for example. Then, they can be integrated by vacuum suction or the like, and then manufactured by thermocompression-bonding the above-mentioned member as an integral molded body by a molding method such as a lamination method.

  In addition, in the solar cell module 10, the transparent front substrate 2, the solar cell element 4, and the back surface protection sheet 6 can use a conventionally well-known material without a restriction | limiting in particular. Moreover, the solar cell module 10 of this invention may also contain members other than the said members, such as a heat dissipation sheet, for example.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example.

[Sealing material composition for intermediate layer]
Metallocene-based linear low density polyethylene (M-LLDPE): Metallocene linear low-density polyethylene 96.5 mass with a density of 0.880 g / cm ³ , a melting point of 60 ° C. and an MFR of 3.5 g / 10 min at 190 ° C. %, Density 0.884 g / cm ³ , MFR at 190 ° C. 1.8 g / 10 min silane-modified polyethylene resin 2.73% by mass, light stabilizer (KEMISTAB 62) 0.0545% by mass, ultraviolet absorber (KEMISORB 12 ) 0.318% by mass, UV absorber (KEMISORB 79) 0.0545% by mass, UV absorber (KEMISORB 202) 0.00636% by mass, crosslinking aid (tricyclodecane dimethanol diacrylate) 0.382% by mass. In order to create a sealing material sheet for the inner layer of the sealing material sheets of Examples and Comparative Examples It was set as the sealing material composition of this.

[Sealant composition for outermost layer]
Metallocene linear low density polyethylene (M-LLDPE): density 0.885 g / cm ³ , melting point 66 ° C., MFR at 190 ° C. of 18 g / 10 min. Metallocene linear low density polyethylene 86.0% by mass, Silane modification with a metallocene linear low density polyethylene of 96.5% by mass at 190 ° C. of 3.5 g / 10 min, a density of 0.884 g / cm ³ , and an MFR at 190 ° C. of 1.8 g / 10 min. Polyethylene resin 13.6% by mass, light stabilizer (KEMISTAB62) 0.0545% by mass, UV absorber (KEMISORB12) 0.318% by mass, UV absorber (KEMISORB79) 0.0545% by mass, UV absorber (KEMISORB202) It mixes so that it may become 0.00636 mass%, the sealing material sheet | seat for inner layers of the sealing material sheet of an Example and a comparative example It was set as the sealing material composition for producing a process.

<Manufacture of encapsulant sheet for solar cell module>
Each sealing material composition was produced using a 30 mm extruder and a film molding machine having a 200 mm wide T-die to produce an inner layer and an outer layer sealing material sheet at an extrusion temperature of 210 ° C. and a take-off speed of 1.1 m / min. These inner-layer and outer-layer sealing material sheets were laminated to obtain a three-layer solar cell module sealing material sheet (Example and Comparative Example). All of these encapsulant sheets had a thickness of 550 μm, and the outer layer: inner layer: outer layer thickness ratio was 1: 5: 1. Moreover, about the sealing material sheet | seat which concerns on an Example and a comparative example, a sheet | seat is laminated | stacked on the conditions of Table 1 using an electron beam irradiation apparatus (Iwasaki Electric Co., Ltd. product name EC250 / 15 / 180L), respectively. Irradiated to produce a crosslinked encapsulant sheet. In addition, melting | fusing point of the sealing material sheet was 60 degreeC.

  In Table 1, the acceleration voltage (kV) means an acceleration voltage (kV) for electron beam irradiation. Illuminance (kGy) means the illuminance (kGy) of electron beam irradiation.

  In addition, when the gel fraction of the encapsulant sheet 1 was measured by the following method, the gel fraction of the encapsulant sheet obtained by collecting portions from the surface on the electron beam irradiation side of the encapsulant sheet to a depth of 100 μm was It was 20%, and the gel fraction of the encapsulant sheet obtained by collecting a portion from the surface opposite to the electron beam irradiation surface of the encapsulant sheet to a depth of 100 μm was 0%. From this result, it was confirmed that the cross-linking degree of the encapsulant sheet 1 changed along the thickness direction of the encapsulant sheet, and the surface on the electron beam irradiation side was a surface having a high degree of crosslinking.

  The gel fraction is measured by collecting 0.1 g of each part from the both sides of the encapsulant sheet 1 to a depth of 100 μm, putting it in a resin mesh, extracting it with toluene at 60 ° C. for 4 hours, taking out the resin mesh and drying it. After weighing, it was measured by comparing the mass before and after extraction and measuring the mass% of the remaining insoluble matter.

  Moreover, the sealing material sheet 3 was produced similarly to the sealing material sheet 1 except not irradiating an electron beam. When the gel fraction on both sides of the encapsulant sheet 3 was measured in the same manner as the encapsulant sheet 1, the gel fraction of the part from the surface to 100 μm on both sides was 0%, and in the thickness direction of the encapsulant sheet It was confirmed that the degree of cross-linking did not change.

  Furthermore, it produced similarly to the sealing material sheet 1 except having irradiated the electron beam on both surfaces of the sealing material sheet 4 as the sealing material sheet 4. FIG. When the gel fraction on both sides of the encapsulant sheet 4 was measured in the same manner as the encapsulant sheet 1, the gel fraction of the part from the surface to 100 μm on both sides was 20%, and in the thickness direction of the encapsulant sheet It was confirmed that the degree of cross-linking did not change.

<TMA test>
A TMA test was performed on the sealing material sheets 1 to 5. Specifically, the sealing material sheet is cut out to φ10 mm, set in a TMA apparatus (TMA / SS7100 manufactured by SII Nanotechnology), the temperature of the sealing material sheet is increased, and the pressure of 20 kPa is applied from the surface of the sealing material sheet. A needle having a diameter of 1 mm was pushed in and the depth of pushing was measured. The heating rate was 5 ° C./min, and the temperature was raised from room temperature to 150 ° C. Table 2 shows P ₈₀ which is the gradient of the TMA curve at 80% of the film thickness of the encapsulant sheet (indicated as P _{80 in} Table 2) and P _MAX which is the maximum absolute value of the gradient P of the TMA curve ( In Table 2, P _MAX (denoted as P _MAX ), 100 × (P ₈₀ / P _MAX ), P ₁ (denoted as P _{1 in} Table 2), resin melting point + the sealing material film thickness at 100 ° C., which is 40 ° C. The ratio of the indentation depth of the needle with respect to (indicated as the indentation depth in Table 2) is shown. Table 2 shows the direction of pushing the needle in the TMA test (in Table 2, indicated as the measurement direction), and “EB irradiation surface” means that measurement was performed by pushing the needle from the electron beam irradiation surface. The “opposite surface” means that the measurement was performed by pushing the needle from the opposite surface as viewed from the electron beam irradiation surface. In addition, since the sealing material sheet 3 is unirradiated and the sealing material sheet 4 is double-sided irradiation, the special measurement direction is not described.

  FIG. 2 shows a graph showing the relationship between the temperature (° C.) in the TMA test of the sealing material sheets 1 to 5 and the depth (μm) of pushing the needle into the sealing material sheet. FIG. 3 is a graph showing the relationship between the temperature (° C.) and the gradient of the TMA curve (indentation depth (μm) / temperature (° C.)) of the sealing material sheets 1 to 5.

From Table 2, the electron beam irradiation surface of the sealing material sheet 1 (Example 1), the surface opposite to the electron beam irradiation surface of the sealing material sheet 1 (Example 1), the sealing material sheet 2 (Example 2) electron beam irradiation surface, _{P 1} showed 30% or less. On the other hand, the surface of the sealing material sheet 3 (Comparative Example 1), the surface of the sealing material sheet 4 (Comparative Example 2), the electron beam irradiation surface of the sealing material sheet 5 (Comparative Example 3), _{P 1} 30% It became super.

<Cell crack test>
Using the sealing material sheets 1 to 5 (Examples 1 and 2 and Comparative Examples 1 to 3), solar cell modules (indicated as modules 1 to 6 in Table 3) were prepared, and a cell crack test was performed. Specifically, 180 mm, 3.2 mm thick white plate semi-tempered glass (manufactured by AGC Fabricec Co., Ltd .: 3KWE33), each sealing material sheet as a light receiving surface side sealing material, 1.5 mm wide bus bar (thickness) 5-inch single crystal solar cell element (thickness: 200 μm), three sealing material sheets as non-light-receiving surface side sealing material, and back surface protection sheet (polyethylene terephthalate (PET): thickness 188 μm) Were laminated in this order, vacuum heating was performed for 5 minutes at a heating temperature of 150 ° C. (pressure: 0 kPa), and then lamination was performed for 7 minutes at atmospheric pressure (pressure: 100 kPa) to prepare a solar cell module. . In addition, the bus bar connected to the solar battery cell is disposed on the light receiving surface side. In Table 3, the “sealing material sheet surface in contact with the bus bar” represents the surface of the light receiving surface side sealing material in contact with the bus bar, and the “EB irradiation surface” represents the electron beam irradiation surface. The “opposite surface” means that the opposite surface as viewed from the electron beam irradiation surface is laminated so as to contact the bus bar. And the presence or absence of the crack generation | occurrence | production of the solar cell element of a solar cell module was confirmed by the EL (Electroluminescence) test | inspection. Cracks were confirmed by attaching an electrode to the cell, applying a voltage, and photographing the light emitted at infrared wavelengths with a camera. The evaluation results are shown in Table 3 (indicated as cell cracks in Table 3). The evaluation criteria are as follows.

[Evaluation criteria]
○: No crack was confirmed in the solar cell element.
X: A crack was confirmed in the solar cell element.

From Table 3, the electron beam irradiation surface of the sealing material sheet 1 P ₁ showed less than 30% (Example 1), the opposite surface of the electron beam irradiation surface of the sealing material sheet 1 (Example 1), sealing In the cell crack test, modules 1 to 3 laminated so that the electron beam irradiated surface of the material sheet 2 (Example 2) was in contact with the bus bar were not confirmed to have cracks in the solar cell element. On the other hand, the module 5 by laminating a sealing material sheet 4 P ₁ showed more than 30% (Comparative Example 2), the crack of the solar cell element was confirmed.

<Heat resistance test>
About the sealing material sheets 1-5 (Examples 1, 2 and Comparative Examples 1-3), the heat resistance test was done. Specifically, a sealing material sheet cut out to 5 × 7.5 cm is placed vertically on a large-sized glass plate on a large-sized glass plate that has been subjected to graining, and left at 80 ° C. for 12 hours. The moving distance of 5 × 7.5 grain glass after being left was measured and evaluated. The measured values were evaluated according to the following evaluation criteria. The evaluation results (shown as heat resistance in Table 4) are shown in Table 4. In Table 4, “EB irradiated surface” means that the electron beam irradiated surface was tested so as to come into contact with the textured glass, and “opposite surface” means that the opposite surface is in contact with the textured glass as viewed from the electron beam irradiated surface. It means that it was tested. The evaluation criteria are as follows.

(Evaluation criteria)
○: Less than 1.5 mm Δ: 1.5 mm or more and less than 2 mm ×: 2 mm or more

From Table 4, the electron beam irradiation surface of the sealing material sheet 1 P ₁ showed less than 30% (Example 1), the opposite surface of the electron beam irradiation surface of the sealing material sheet 1 (Example 1), sealing Shibogarasu travel distance of the electron beam irradiation surface was measured contact facing the Shibogarasu of wood sheets 2 (example 2), the surface and sealing of the sealing material sheet 3 P ₁ showed more than 30% (Comparative example 1) It can be seen that it is smaller than the movement distance of the textured glass measured by using the textured glass sheet 5 (Comparative Example 3) as the contact surface of the textured glass. Sealing material sheet 1, 2 Therefore P ₁ is 30% or less (Examples 1 and 2) is presumed to be a sealing material sheet having excellent heat resistance as a sealing material sheet for a solar cell module .

From the test results of Table 3 and Table 4, it can be seen that the encapsulant sheet having a P ₁ (%) value of 30% or less of the encapsulant sheet is good in both the cell crack test and the heat resistance test. From this, in the TMA indentation test of the sealing material sheet, the gradient ratio P _{1 at} a predetermined film thickness with respect to the maximum value P _max of the absolute value of the gradient P (indentation depth (μm) / temperature (° C.)) of the TMA curve. The encapsulant sheet that specifies (%) has excellent heat resistance as an encapsulant sheet, and is an excellent solar cell that can suppress the occurrence of cracks in the solar cell element due to the bus bar. It was confirmed that it was a sealing material sheet for modules.

DESCRIPTION OF SYMBOLS 10 Solar cell module 2 Transparent front substrate 3 Front sealing material layer 4 Solar cell element 5 Back surface sealing material layer 6 Back surface protection sheet 7 Bus bar

Claims (9)

A sealing material sheet for a solar cell module,
In a TMA curve obtained in a thermomechanical analysis (TMA) test under the following conditions and showing a relationship between a predetermined temperature range (° C.) and the depth of pressing of the needle into the sealing material sheet (μm),
In the predetermined temperature range (° C.), the gradient P (indentation depth (μm) / temperature (° C.)) of the TMA curve is obtained,
P ₁ (P ₁ = 100 × (P ₈₀ / P _MAX) which is the ratio of P ₈₀ which is the gradient at 80% of the film thickness of the sealing material sheet to P _MAX which is the maximum absolute value of the gradient P )) Value is 30% or less.
(TMA test: A φ10 mm encapsulant sheet was set in a TMA apparatus, pressed into a φ1 mm needle to a constant pressure of 20 kPa, and the temperature was raised from room temperature to 150 ° C. at a heating rate of 5 ° C./min. indentation depth is measured. _{However, P 80} is, when the indentation depth of the needle at 0.99 ° C. of less than 80% more than 50% of the thickness of the encapsulant sheet, _{P 0.99 ° C.} is the slope at 0.99 ° C. Is used.) 2. The encapsulant sheet according to claim 1, wherein the P _MAX (indentation depth (μm) / temperature (° C.)) is 10 μm / ° C. or more and 50 μm / ° C. or less. The encapsulant sheet according to claim 1, wherein the P ₈₀ (indentation depth (μm) / temperature (° C.)) is 1 μm / ° C. or more and 10 μm / ° C. or less.   The sealing material sheet according to any one of claims 1 to 3, wherein a pressing depth of the needle at a temperature of a melting point of the sealing material sheet + 40 ° C is within 85% of a film thickness of the sealing material sheet. 5. The sealing material sheet according to claim 1, wherein the content of polyethylene having a density of 0.860 g / cm ³ or more and 0.970 g / cm ³ or less is 85% or more in the entire sealing material composition. Sealing material sheet. The sealing material sheet is a multilayer sheet comprising an intermediate layer and an outermost layer disposed on both sides thereof,
The encapsulant sheet according to claim 5, wherein the outermost layer further contains a silane-modified polyethylene resin.   The encapsulant sheet according to claim 1, wherein the encapsulant sheet has a thickness of 300 μm or more and 600 μm or less. A solar cell module comprising: the encapsulant sheet according to any one of claims 1 to 7, a solar cell element, and a bus bar that is a wiring for taking out electricity from the solar cell element.
The bus bar is disposed between the encapsulant sheet and the solar cell element;
A solar cell module, wherein the bus bar has a thickness of 150 μm or more and 300 μm or less.   The solar cell module according to claim 8, wherein the solar cell element has a thickness of 150 μm or more and 300 μm or less.

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