JP5052714B2 - Adhesive sheet, solar cell filler sheet and solar cell using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an adhesive sheet excellent in durability, and more particularly to an adhesive sheet suitable for a solar cell filler used for fixing a cell in a solar cell module or joining to a back sheet, and a solar cell using the same. .
[0002]
[Prior art]
In recent years, solar cells have become widespread as power supply sources. Accordingly, diversity of installation environments and long-term durability are required, and various members used for solar cells are required to have long-term reliability in harsh environments.
[0003]
The solar cell filler is one of such members, and is required to have a function as an adhesive and a function of protecting a photovoltaic element (cell) from an external impact. Resins such as vinyl acetate copolymer), PVB (polyvinyl butyral), and silicone have been proposed.
[0004]
Conventionally, as a practical filler, an EVA-based resin is most often used from the viewpoint of price, workability, moisture resistance, and the like. However, when the EVA type is used over a long period of time, deterioration / degeneration such as yellowing, cracking, foaming, etc. occurs, which is considered to be one factor leading to a decrease in power generation due to cell corrosion and the like. It was. In addition, the same deterioration / degeneration phenomenon is easily generated when the environmental conditions become a little severe or newly added, and therefore, its use is limited.
These EVA-based resins cause such deterioration and deterioration as a problem in composition, such as highly hydrolyzable ester structures and organic peroxides and polyfunctional vinyl compounds added for thermal crosslinking. Cross-linking agents such as, cross-linking agent residues and reaction products, active carbon such as EVA cross-linking points and reactive ends, gradually overcoming the suppression effect of pre-added UV absorbers, antioxidants, etc. Presumed to cause deterioration and alteration.
[0005]
[Problems to be solved by the invention]
The purpose of this patent is to provide an adhesive sheet made of an ethylene-based resin that has excellent performance equivalent to that of an EVA-based resin and solves the deterioration and alteration problems, and a sheet for solar cell filler. .
[0006]
[Means for Solving the Problems]
That is, the present invention provides the following inventions.
[0007]
[1] Modification containing at least 0.01% by mass or more of alkoxysilane as a copolymerization component, having a melting point of 80 ° C. or higher and 120 ° C. or lower and a shear elastic modulus at 80 ° C. of 3 × 10 ⁵ Pa or higher. Adhesive sheet made of an ethylene-based resin and containing no organic peroxide (however, the gel fraction of the sheet after being laminated and bonded and modularized (weight% of insoluble content after Soxhlet extraction at the xylene boiling point) ) Except 60% or more) .
[0009]
[2] The modified ethylene-based resin is one or more ethylenes selected from the group consisting of polyethylene, ethylene-α olefin copolymers, ethylene-vinyl acetate copolymers, and ethylene-acrylic acid ester copolymers. The resin according to [1], which is a resin in which an alkoxysilane is graft -copolymerized to a resin, or a mixture of the resin that has been graft-copolymerized and an ethylene-based resin other than the resin that has been graft-copolymerized . Adhesive sheet.
[0010]
[3] It contains at least 0.01% by mass and less than 10% by mass of alkoxysilane as a copolymer component, has a melting point of 80 ° C. or higher and 120 ° C. or lower, and has a shear elastic modulus at 80 ° C. of 3 × 10 ⁵ Pa. It is made of the above modified ethylene-based resin and does not contain an organic peroxide. The sheet for solar cell filler (however, the gel fraction of the sheet after being laminated and bonded to be modularized (Soxhlet extracted at the xylene boiling point) Excluding those having a weight% of insoluble matter later) of 60% or more) .
[0012]
[4] The modified ethylene-based resin is one or more ethylene selected from the group consisting of polyethylene, ethylene-α olefin copolymer, ethylene-vinyl acetate copolymer, and ethylene-acrylic acid ester copolymer. The resin according to [3], which is a resin in which an alkoxysilane is graft -copolymerized to a resin, or a mixture of the resin that has been graft-copolymerized and an ethylene-based resin other than the resin that has been graft-copolymerized . Sheet for solar cell filler.
[0013]
[5] [3] or [4] photovoltaic filler sheet according to the at least be laminated and adhered to the non-light-receiving surface modularized ing in solar cells of the solar cell. Here, the non-light-receiving surface means a surface opposite to the light-receiving surface of the solar battery cell.
[0014]
Hereinafter, the present invention will be described in detail.
[0015]
Examples of the modified ethylene resin containing an alkoxysilane as a copolymer component used in the present invention include ethylene, ethylene-α olefin copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, and other ethylene-based resins. Examples include those obtained by grafting alkoxysilane to the resin, or those obtained by copolymerizing alkoxysilane in the course of polymerizing the ethylene resin. Preferably, any one of polyethylene, ethylene-α olefin copolymer, ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymer, or a mixture of two or more thereof, or these and alkoxysilanes thereof. Is a mixture with an ethylene resin other than the grafted modified ethylene resin.
[0016]
In the present invention, the use of polyethylene or an ethylene-α-olefin copolymer as an ethylene resin as the base of such a copolymer component is one of the compositional problems in conventional EVA resins. The contribution of hydrolyzability can be virtually eliminated and favorable results in durability can be obtained. In addition, when an ethylene-acrylic acid ester copolymer is used, the hydrolyzability can be lowered and the durability can be greatly improved as well. On the other hand, in the case of ethylene-vinyl acetate copolymer, deterioration caused by crosslinking agents and crosslinking points added for crosslinking in conventional EVA resins can be suppressed, so that a considerable improvement in durability can be achieved. Can play.
[0017]
In the present invention, various additives such as a light stabilizer, an ultraviolet absorber, an antioxidant, a processing aid, and a crystal nucleating agent are added to the modified ethylene resin within a range not to impair the purpose of the present invention. Can do. In particular, when this modified ethylene resin does not substantially contain an ethylene-vinyl acetate copolymer, it does not contain a highly hydrolyzable ester structure. Can be added.
[0018]
In the present invention, as the ethylene-based resin containing alkoxysilane as a copolymerization component, one having a melting point of 80 ° C. or higher and 120 ° C. or lower is used. When the melting point exceeds 120 ° C., the temperature required for adhesion increases, and for example, in the process of assembling a solar cell module, the module cannot be heated sufficiently due to restrictions imposed by equipment and other materials. It is not preferred because it does not soften or melt and does not sufficiently adhere to the cell, the light-receiving glass, and the back sheet. In addition, when the melting point is less than 80 ° C., there is no heat resistance as an adhesive sheet. Therefore, when used as a solar cell filler, for example, in the environment where the solar cell module is installed, displacement and peeling occur due to a decrease in adhesive strength. This is not preferable because of fear.
[0019]
The melting point of the modified ethylene-based resin is the type, amount, and other components of the copolymerization component. The ethylene-based resin containing the alkoxysilane used as a copolymerization component and the ethylene-based resin containing the alkoxysilane as the copolymerization component. It can be controlled within a desired range by the melting point of the other ethylene-based resin, the mixing ratio, and the like. The melting point is a value measured according to JIS K7121 (the highest value in the case of a plurality of values).
[0020]
In the present invention, as the silane-modified ethylene resin containing alkoxysilane as a copolymerization component, one having a shear elastic modulus at 80 ° C. of 3 × 10 ⁵ Pa or more is used. When the shear modulus is less than 3 × 10 ⁵ Pa, there is no heat resistance as an adhesive sheet. For example, when it is used as a solar cell filler, displacement / peeling due to a decrease in adhesive strength in the environment where the solar cell module is installed. This is not preferable. The shear modulus can be controlled by the melting point of the modified ethylene resin and additives. In the present invention, the shear modulus is a value measured by a normal viscoelasticity measuring device (for example, a dynamic viscoelasticity measuring device manufactured by Iwamoto Seisakusho) under the conditions of a period of 2π rad and an amplitude distortion of 0.5%.
[0021]
Since the adhesive sheet of the present invention contains alkoxysilane as a copolymerization component, it reacts with moisture in the air or resin to generate silanol groups, and these silanol groups react with the adherend. It is thought that excellent adhesive force is exhibited by forming a bond.
[0022]
In the present invention, the alkoxysilane grafted or copolymerized on the ethylene-based resin is preferably an alkenylalkoxysilane having a radical polymerizable functional group (alkenyl group) such as vinylalkoxysilane, isopropenylalkoxysilane, and allylalkoxysilane. used. For example, vinyl alkoxysilanes such as vinylmethoxysilane, vinylethoxysilane, vinylpropoxysilane, and vinylbutoxysilane are preferably used, and added to the target ethylene resin by graft reaction using functional groups such as vinyl groups. Is done. The graft amount is 0.01% by mass or more, preferably 0.1% by mass or more, and if it is less than that, for example, when used as a filler for solar cells, adhesion to the light-receiving glass and the cell is impaired. Therefore, it is not preferable. The amount of grafting can be controlled by the grafting reaction conditions such as the amount and type of alkoxysilane, reaction temperature, time, and additives such as catalyst and swelling agent.
[0023]
Moreover, even if it is 10 mass% or more as a graft amount, since the effect of improving the shear modulus reaches its peak and the price only increases, it is preferably less than 10 mass%. Practically, it is most preferably 0.1 to 1.5% by mass.
[0024]
The grafting method is a method in which an unsaturated alkoxysilane is added to an ethylene resin in a solvent and heated in the presence of a radical initiator, and a mixture of the ethylene resin, the unsaturated alkoxysilane and the radical initiator is heated in an extruder. It can be produced by a known method such as a method.
[0025]
The modified ethylene-based resin containing alkoxysilane as a copolymerization component can be used as a single sheet as an adhesive sheet and further as a solar cell filler (hereinafter referred to as “single-layer system”). It is good also as another resin sheet (core material) and a lamination sheet. In the case of a solar cell filler, at least the cell, the light-receiving glass (surface protective material), and only the surface side (one side) in contact with the back sheet is a modified ethylene-based resin containing the alkoxysilane as a copolymer component. On the side (in some cases, the core side), a laminated sheet in which an ethylene resin mainly composed of polyethylene or ethylene-α-olefin copolymer is adhesively laminated may be used. It is also possible to form a laminated sheet in which modified ethylene resins are laminated on both surfaces of the core material (hereinafter, these are referred to as “laminated systems”).
[0026]
In addition, the ethylene resin mainly composed of polyethylene or ethylene-α-olefin copolymer to be laminated includes a light stabilizer, an ultraviolet absorber, an antioxidant, a processing aid, a crystal as long as the object of the present invention is not impaired. Nucleating agents can be added, and since it does not substantially contain hydrolysable ester structures, various additives including a crosslinking agent are added to the extent that it does not exceed the degree of deterioration due to its contribution. Also good.
[0027]
The elastic modulus of polyethylene or the like to be laminated has a shear elastic modulus at 80 ° C. of 3 × 10 ⁵ Pa or more for the same reason as that of the modified ethylene resin containing alkoxysilane as a copolymerization component. Control can be performed in the same manner as described.
[0028]
The modified ethylene resin sheet containing alkoxysilane as a copolymerization component can be obtained by a molding method usually performed in thermoplastic resins such as a calendar method and an extrusion method that are generally performed. In this case, the molding process conditions are performed below the reaction temperature of the alkoxysilane grafted on the sheet. Immediately after the sheet molding, the alkoxysilane is present in a substantially unreacted state in the obtained resin sheet. Need to be like that. In this case, it is preferable to further lower the processing temperature particularly when an alkoxysilane reaction catalyst is added to moderate the processing conditions of the solar cell module.
[0029]
Then, the solar cell encapsulant for sheets of the present invention are laminated and adhered to at least the non-light-receiving surface of the solar cell, the light-receiving surface, it may be used other fillers.
[0030]
In the case of a laminated system in which a modified ethylene resin layer is laminated with an ethylene resin layer mainly composed of an ethylene-α olefin copolymer as the adhesive sheet of the present invention, a coextrusion method, extrusion coating A laminated sheet can be obtained by a method such as a hot roll laminating method. The surface of the modified ethylene-based resin sheet can be embossed in order to suppress bubbles remaining between various layers in the process of processing the module.
[0031]
The thickness of the modified ethylene-based resin sheet used in the present invention is not particularly limited, but when used as a solar cell filler, securing of the sheet following the unevenness of the cell, light reception In consideration of the follow-up of the glass / back sheet swell, the monolayer system is usually about 50 to 1000 μm, preferably about 100 to 600 μm. In the case of a laminated system, the total thickness is usually 50 to 1000 μm, preferably about 100 to 600 μm, and the thickness of the ethylene resin sheet grafted with alkoxysilane is preferably 0.1 to 100 μm. Is about 1 to 30 μm.
[0032]
In order to obtain a solar cell module by using the adhesive sheet of the present invention as a filler, in the case of a single layer system or a laminated system, both are bonded as fillers by the same process as that of conventional fillers. A solar cell module can be obtained by a modularization process in which various members including a conductive sheet are set and laminated. Moreover, the adhesive sheet of this invention can be previously laminated | stacked on the light reception glass, and a photovoltaic cell and a back surface sheet | seat can also be laminated | stacked on a post process by this.
[0033]
In the present invention, since the cross-linking step can be omitted, the temperature can be reduced and the time can be reduced in the modularization step, and the production efficiency can be increased. Accordingly, since the laminating conditions are gentle, stresses such as residual stress can be kept low, which is advantageous in terms of durability. Furthermore, the reliability of the solar cell module is greatly improved as a result of suppressing the adverse effects in various environments as compared with the conventional EVA resin filler.
[0034]
【Example】
The present invention will be described more specifically with reference to the following examples.
[0035]
Example 1
(1) Melting point 84 ° C., 0.5 mass part of hindered amine light stabilizer and 0.1 mass part of phenolic antioxidant on silane-modified ethylene-ethyl acrylate copolymer grafted with 0.8 mass% of alkoxysilane In addition, a sheet 1 having a thickness of 300 μm is formed by extrusion at 150 ° C., and this is used as a filler made of an ethylene resin for evaluation. The shear modulus of the sheet at 80 ° C. was 5.0 × 10 ⁵ Pa.
[0036]
(2) Assuming a solar cell, an aluminum plate having a thickness of 0.3 mm was used as an alternative, and an evaluation sample was assembled. That is, a float glass (= light-receiving glass) having a thickness of 3 mm, the same sheet 1 having a thickness of 0.3 mm, an aluminum plate having a thickness of 0.3 mm (= cell replacement), the same sheet 1 having a thickness of 0.3 mm, A surface-adhesive treated polyvinyl fluoride / aluminum foil laminate film (= back sheet) with a thickness of 0.08 mm is set in this order, and is heated and pressurized in a heat-resistant rubber bag at 130 ° C. for 20 minutes. The following various durability tests / evaluations were performed using the samples for evaluation.
1) 2000 hours standing treatment with sunshine weather meter
2) Standing treatment for 2000 hours in an atmosphere of 85 ° C. and 85% RH
(According to JIS C8917)
3) Standing treatment in a 10% aqueous solution of sodium hydroxide at 23 ° C. for 200 hours
(According to JIS K7114)
After each treatment in 1) to 3) , (i) presence / absence of yellowing / cracking / foaming of the filler layer,
(Ii) Presence or absence of peeling from the glass / back sheet,
(Iii) The following three-stage evaluation was performed by comparing the total of 18 items with 6 items for each of the three types of presence / absence of corrosion of the aluminum plate as compared to before treatment.
A: A slight change in the comparison of 18 items is within 10 items, and there is no significant change.
◯: 11 items or more have a slight change in comparison of 18 items, and there is no significant change.
X: There was one or more major changes in the comparison of 18 items.
[0040]
As a result, it was found that the evaluation when the adhesive sheet 1 was used as a filler was ○.
[0041]
(Example 2)
(1) A sheet 2 having a thickness of 300 μm was formed by extruding a silane-modified ethylene-α-olefin copolymer grafted with a melting point of 114 ° C. and 1.0% by mass of alkoxysilane at 180 ° C. The sheet 2 had a shear modulus of elasticity of 1.9 × 10 ⁷ Pa at 80 ° C.
[0042]
(2) About this sheet | seat 2, the sample for evaluation equivalent to a solar cell module was created similarly to Example 1, and the durability test was done similarly and evaluated. As a result, it was found that the evaluation when the adhesive sheet 2 was used as a filler was ◎.
[0043]
(Reference Example 1)
(1) Melting point 112 ° C., low-density polyethylene having a shear modulus of 1.3 × 10 ⁷ Pa at 80 ° C. is used as the core side, and the melting point 84 ° C. and alkoxysilane 0.8% by mass used in Example 1 are grafted. A silane-modified ethylene-ethyl acrylate copolymer added with 0.5 parts by weight of a hindered amine light stabilizer and 0.1 parts by weight of a phenolic antioxidant is used as both surface sides of this core, and coextruded at 180 ° C. A laminated sheet 3 of two types and three layers was molded by the method. The thickness of the surface side of the sheet 3 was 25 μm, the core side was 300 μm, and the total thickness was 350 μm.
(2) About this adhesive sheet 3, the sample for evaluation equivalent to a solar cell module was created like Example 1, and the durability test was done similarly and evaluated. As a result, the evaluation when the adhesive sheet 3 was used as a filler was “good”.
[0044]
(Comparative Example 1)
After using a commercially available heat-crosslinkable EVA sheet (thickness: 400 μm) for vacuum heating and pressure processing in a heat-resistant rubber bag at 130 ° C. for 20 minutes, the oven is heated at 150 ° C. for 20 minutes. A sample for evaluation corresponding to a solar cell module was prepared in the same manner as in Example 1 except that the crosslinking was performed, and the durability test was similarly performed and evaluated. As a result, it was found that the evaluation when the thermally crosslinkable EVA sheet was used as a filler was x.
[0045]
(Comparative Example 2)
(1) A sheet having a thickness of 300 μm by extrusion at 180 ° C. by adding 0.5 part by weight of a hindered amine light stabilizer and 0.1 part by weight of a phenolic antioxidant to an ethylene-ethyl acrylate copolymer having a melting point of 95 ° C. 4 was formed. The shear modulus of the sheet 4 at 80 ° C. was 1.7 × 10 ⁶ Pa.
(2) About this sheet | seat 4, the sample for evaluation equivalent to a solar cell module was created similarly to Example 1, and the durability test was done similarly and evaluated. As a result, it was found that the evaluation when the sheet 4 was used as a filler was x.
[0046]
(Comparative Example 3)
(1) A 300 μm thick sheet 5 was formed by extruding a silane-modified ethylene-α-olefin copolymer grafted with a melting point of 122 ° C. and 0.6% by mass of alkoxysilane at 180 ° C. The shear elastic modulus of the sheet at 80 ° C. was 4.1 × 10 ⁷ Pa.
(2) About this sheet 5, the sample for evaluation equivalent to a solar cell module was created like Example 1, and the endurance test was done similarly and evaluated. As a result, it was found that the evaluation when the sheet 5 was used as a filler was x.
[0047]
(Comparative Example 4)
(1) Melting point of 75 ° C., 0.5 part by mass of hindered amine light stabilizer and 0.1 part by mass of phenolic antioxidant on silane-modified ethylene-ethyl acrylate copolymer grafted with 1.7% by mass of alkoxysilane In addition, the sheet 6 having a thickness of 300 μm was formed by extrusion at 120 ° C. The shear modulus of the sheet 6 at 80 ° C. was 1.7 × 10 ⁵ Pa.
(2) About this sheet | seat 6, the sample for evaluation equivalent to a solar cell module was created similarly to Example 1, and the durability test was done similarly and evaluated. As a result, it was found that the evaluation when the sheet 6 was used as a filler was x.
[0048]
Since the adhesive sheet of the present invention is excellent in durability and exhibits adhesive force without being crosslinked, for example, in a solar cell filler, it is possible to reduce the temperature and time in a modularization process. Since the production efficiency is increased and the laminating conditions are gentle, stresses such as residual stress can be kept low, which is advantageous in terms of durability. As described above, the adhesive sheet mainly composed of the silane-modified ethylene-based resin of the present invention has less adverse effects in various environments than the conventional EVA-based resin fillers. There is an effect that the property is greatly improved.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing an example of a solar cell of the present invention.
FIG. 2 is a schematic cross-sectional view showing another example of the solar cell of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sheet | seat for solar cell fillers 2 Light reception glass 3 Solar cell 31 Non-light reception surface 32 Light reception surface 4 Back surface sheet

Claims (5)

A modified ethylene-based resin containing at least 0.01% by mass or more of alkoxysilane as a copolymerization component, having a melting point of 80 ° C. or higher and 120 ° C. or lower and a shear modulus of elasticity at 80 ° C. of 3 × 10 ⁵ Pa or higher. An adhesive sheet containing no organic peroxide (however, the gel fraction of the sheet after being laminated and adhered to be modularized (weight% of insoluble matter after Soxhlet extraction at the xylene boiling point)) is 60 % Or more) .   The modified ethylene resin is one or more ethylene resins selected from the group consisting of polyethylene, ethylene-α olefin copolymer, ethylene-vinyl acetate copolymer and ethylene-acrylic acid ester copolymer. The adhesive sheet according to claim 1, which is a resin in which alkoxysilane is graft-copolymerized, or a mixture of the graft-copolymerized resin and an ethylene-based resin other than the graft-copolymerized resin. . A modified ethylene-based resin containing at least 0.01% by mass or more of alkoxysilane as a copolymerization component, having a melting point of 80 ° C. or higher and 120 ° C. or lower and a shear modulus of elasticity at 80 ° C. of 3 × 10 ⁵ Pa or higher. A sheet for solar cell filler containing no organic peroxide (however, the gel fraction of the sheet after being laminated and bonded and modularized (weight% of insoluble matter after Soxhlet extraction at the xylene boiling point) ) Except 60% or more) .   The modified ethylene resin is one or more ethylene resins selected from the group consisting of polyethylene, ethylene-α olefin copolymer, ethylene-vinyl acetate copolymer and ethylene-acrylic acid ester copolymer. The solar cell filling according to claim 3, wherein the alkoxysilane is a resin copolymerized with graft copolymer, or a mixture of the resin copolymerized with graft copolymer and an ethylene resin other than the resin copolymerized with the graft copolymer. Material sheet.   The solar cell formed by laminating and adhering the solar cell filler sheet according to claim 3 or 4 to at least a non-light-receiving surface of the solar cell.

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