JP6255669B2 - Sealing material sheet - Google Patents

Description

  The present invention relates to an encapsulant sheet made of polyethylene resin for a solar cell module, and more particularly to an encapsulant sheet that is colored white to improve power generation efficiency.

  Conventionally, a combination of an ethylene-vinyl acetate copolymer resin (EVA) and a crosslinking agent typified by an organic peroxide has been used as a sealing material sheet for a solar cell module. In recent years, polyethylene resins have been studied in place of EVA taking advantage of excellent water vapor barrier properties.

  Although these sealing material sheets may be used as they are without being colored, the solar cell element 4 in the solar cell module 1 of FIG. 1 (hereinafter also simply referred to as a cell) is usually colored in plan view, For this reason, as described in Patent Document 1 below, as a design improvement, only the back sealing material sheet layer 5 of FIG. 1 is colored black or the like.

  In addition, as described in Patent Document 2 below, in order to improve power generation efficiency, only the EVA-based back sealing material sheet layer 5 is colored white.

JP 2009-256459 A JP 2006-036874 A

  As the white pigment for coloring the resin white, titanium oxide particles are usually used. However, since these particles usually have water absorption, there is a problem that the resistance to PID (POTENTIAL INDUCED DEGRADATION) decreases due to water absorption. In the configuration of Patent Document 2, since titanium oxide is contained in an EVA resin having high water absorption, the PID resistance is inferior.

  The present invention has been made in order to solve the above problems, and the object thereof is for a solar cell module having a low water absorption and excellent PID resistance and corrosion resistance while being a white colored sealing material sheet. It is providing the sealing material sheet | seat.

  The inventors have found that the water absorption can be lowered while increasing the spectral reflectance by multilayering the encapsulant sheet and adjusting the content of the white pigment by the layer, and the present invention has been completed. It is a thing. More specifically, the present invention provides the following.

(1) In the solar cell module, a sealing material sheet made of polyethylene resin disposed on the non-light-receiving surface side of the solar cell,
The encapsulant sheet contains 4% by weight or more and 10% by weight or less of a white pigment,
The encapsulant sheet has a multilayer structure composed of layers having different contents of the white pigment,
A sealing material sheet having a water absorption rate of 0.2% or less according to JIS-K7209.

  (2) The encapsulant sheet according to (1), wherein the multilayer structure has a skin layer disposed on the side in close contact with the solar battery cell, and the content of the white pigment in the skin layer is 4% or less. .

  (3) The encapsulant sheet has a two-layer / three-layer structure of skin layer / inner layer / skin layer, the content of the white pigment in the skin layer is 4% or less, and the white pigment in the inner layer The sealing material sheet according to (1) or (2), wherein the content is 4% or more.

  (4) The encapsulant sheet according to any one of (1) to (3), wherein spectral reflectances at a wavelength of 400 nm and 900 nm of the encapsulant sheet 300 μm are both 80% or more.

  ADVANTAGE OF THE INVENTION According to this invention, the sealing material sheet for solar cell modules which raises spectral reflectance, raises electric power generation efficiency, and can prevent the fall of PID tolerance by the water absorption of a sealing material sheet, and prevention of inhibition can be provided.

It is sectional drawing which shows typically an example of the laminated constitution of the solar cell module of this invention.

<Solar cell module>
Hereinafter, an example of the solar cell module of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of the layer structure of the solar cell module of the present invention. In the solar cell module 1 of the present invention, the transparent front substrate 2, the front sealing material sheet layer 3, the solar cell element 4, the back sealing material sheet layer 5, and the back surface protection sheet 6 are sequentially arranged from the incident light receiving surface side. Are stacked.

  In the solar cell module 1, for example, the transparent front substrate 2, the front sealing material sheet layer 3, the solar cell element 4, the back sealing material sheet layer 5, and the back surface protection sheet 6 are sequentially laminated. It can be manufactured by integration by vacuum suction or the like, and then thermocompression-molding the above-mentioned member as an integral molded body by a molding method such as a lamination method. Here, the sealing material sheet of the present invention is applied to the back sealing material sheet layer 5.

<Sealing material sheet>
In the present invention, a polyethylene-based resin multilayer sealing material sheet is used as the sealing material sheet, and the water absorption rate of each layer is adjusted to achieve predetermined spectral reflectance and water absorption rate. .

As the encapsulant sheet composition constituting the encapsulant sheet, low density polyethylene having the following density of 0.920 g / cm ³ or less is preferably used.

[Low density polyethylene]
In the present invention, general polyethylene can be used. Preferably, low density polyethylene (LDPE) having a density of 0.920 g / cm ³ or less, more preferably 0.900 to 0.880 g / cm ³ linear low density polyethylene (LLDPE) is used. If it is this range, favorable softness | flexibility and heat resistance can be provided, maintaining sheet workability.

  In the present invention, it is preferable to use a metallocene linear low density polyethylene. Metallocene linear low density polyethylene is synthesized using a metallocene catalyst which is a single site catalyst. Such polyethylene has few side chain branches and a uniform comonomer distribution. For this reason, molecular weight distribution is narrow, it is possible to make it the above ultra-low density, and a softness | flexibility can be provided with respect to a sealing material. As a result of imparting flexibility, the adhesion between the sealing material and the substrate, such as the adhesion between the sealing material and the solar cell element and the adhesion between the sealing material and the back surface protective sheet, is increased.

  As the α-olefin of the linear low density polyethylene, an α-olefin having no branch is preferably used. Among these, 1-hexene and 1-heptene which are α-olefins having 6 to 8 carbon atoms are preferable. Or 1-octene is particularly preferably used. When the number of carbon atoms of the α-olefin is 6 or more and 8 or less, the sealing material can be given good flexibility and good strength. As a result, the adhesion between the sealing material and the substrate is further increased.

  The melt mass flow rate (MFR) of low density polyethylene is MFR at 190 ° C. and a load of 2.16 kg measured in accordance with JIS-K6922-2 (hereinafter, the measurement value under this measurement condition is referred to as MFR). It is preferably 0.5 g / 10 min or more and 40 g / 10 min or less, and more preferably 1 g / 10 min or more and 40 g / 10 min or less.

  The sealing material composition of the present invention may further contain a silane-modified polyethylene resin. The silane-modified polyethylene resin is obtained by graft-polymerizing an ethylenically unsaturated silane compound as a side chain to linear low-density polyethylene (LLDPE) or the like as a main chain. Since such a graft copolymer has a high degree of freedom of silanol groups that contribute to the adhesive force, the adhesion of the sealing material to other members in the solar cell module can be improved.

  The silane-modified polyethylene resin can be produced, for example, by the method described in JP-A-2003-46105. By using the resin as a component of the sealing material composition of the solar cell module, strength and durability can be obtained. In addition, it has excellent weather resistance, heat resistance, water resistance, light resistance, wind pressure resistance, yield resistance, and other characteristics, and is also affected by manufacturing conditions such as thermocompression bonding for manufacturing solar cell modules. Therefore, it is possible to manufacture solar cell modules having extremely excellent heat-fusibility, stably and at low cost, and suitable for various applications.

  Examples of ethylenically unsaturated silane compounds to be graft polymerized with linear low density polyethylene include, for example, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltripropoxysilane, vinyltriisopropoxysilane, vinyltributoxysilane, vinyltripentyloxysilane , One or more selected from vinyltriphenoxysilane, vinyltribenzyloxysilane, vinyltrimethylenedioxysilane, vinyltriethylenedioxysilane, vinylpropionyloxysilane, vinyltriacetoxysilane, and vinyltricarboxysilane be able to.

  The graft amount, which is the content of the ethylenically unsaturated silane compound, is, for example, 0.001 to 15 masses with respect to a total of 100 mass parts of all the resin components in the sealing material composition containing other polyethylene-based resins described later. What is necessary is just to adjust suitably so that it may become a% grade, Preferably, it is about 0.01-5 mass%, Most preferably, it may be about 0.05-2 mass%. In the present invention, when the content of the ethylenically unsaturated silane compound is large, the mechanical strength and heat resistance are excellent. However, when the content is excessive, the tensile elongation and heat-fusibility tend to be inferior.

  The sealing material composition of the present invention may further contain an acid-modified polyethylene resin typified by maleic anhydride modification. The acid-modified polyethylene resin is obtained, for example, by graft polymerization using, for example, maleic anhydride or the like as a side chain on linear low density polyethylene (LLDPE) or the like as a main chain. Such a graft polymer has a high polarity of the acid part which contributes to adhesive force, and can improve the adhesiveness of the sealing material sheet to the metal member in the solar cell module.

  The content of the acid-modified polyethylene resin is preferably 15% by mass or more and 40% by mass or less in all resin components. By setting it as this range, generation | occurrence | production of blocking and acidic gas can be suppressed, and heat resistance and the adhesiveness to a metal can be made favorable.

Specific examples of the acid-modified polyethylene resin include maleic anhydride-modified resin. Specific examples include Admer SF731 (manufactured by Mitsui Chemicals, Inc., density 0.880 g / cm ³ ), Admer SF730 (manufactured by Mitsui Chemicals, Inc., density 0.880 g / cm ³ ), and the like.

The content of the polyethylene resin having a density of 0.920 g / cm ³ or less contained in the encapsulant composition is preferably 10% by mass or more and 99% by mass or less, more preferably 50% by mass or more in the composition. It is 99% by mass or less, more preferably 90% by mass or more and 99% by mass or less. That is, other resins may be included as long as the effects of the present invention are not impaired. These may be used, for example, as an additive resin, or may be used for masterbatching other components described later.

[Multilayer structure and white pigment]
The sealing material sheet of the present invention has a multilayer structure. The multilayer configuration is not particularly limited, but two types, two layers, two types, three layers, and the like are preferably used, and among them, the two types, three layers configuration of skin layer / inner layer / skin layer is preferable. The skin layer here means a layer having a thickness smaller than that of the inner layer, and the skin layer is disposed at least on the side in close contact with the solar battery cell. As a preferred layer ratio, the layer thickness ratio of the skin layer to the inner layer is preferably 1: 1.2 to 1:10, more preferably 1: 2 to 1: 7, and particularly preferably 1: 3 to 1: 1. 6. These films can be formed by a conventionally known multilayer coextrusion method or the like.

  The encapsulant sheet contains a white pigment, and by adjusting the content in each layer, the spectral reflectance of the entire encapsulant sheet and the water absorption rate are adjusted to improve power generation efficiency, Improves element corrosion resistance. The white pigment is not particularly limited. For example, titanium oxide, calcium carbonate, zinc white, lead white, lithopone, barite, precipitated barium sulfate, gypsum, and the like can be used. It is preferable to use about a certain amount of titanium oxide from the viewpoint of power generation efficiency.

  The content of the white pigment in the encapsulant sheet is 4% by mass or more and 10% by mass or less as a whole, that is, the average white content of all layers. If it is less than 4% by mass, the spectral reflectance is low and the power generation efficiency is not improved. If it exceeds 10% by mass, the water absorption rate becomes high and the PID resistance and the element corrosion resistance are inferior. On the other hand, if it exceeds 10% by mass, the resin becomes brittle, the sheet is cut during film formation, and the film forming property is lowered, which is not preferable.

  The content of the white pigment in each layer of the encapsulant sheet is preferably skin layer <inner layer and more in the inner layer, specifically, 4% by mass or less for the skin layer and 4% by mass or more for the inner layer. The content of the skin layer is preferably zero, and the content of the inner layer is preferably 6% by mass to 8% by mass.

[Crosslinking agent]
In the sealing material sheet, a crosslinking agent can be appropriately contained as an optional component. A well-known thing can be used for a crosslinking agent, It does not specifically limit, For example, a well-known radical polymerization initiator can be used. Examples of radical polymerization initiators include hydroperoxides such as diisopropylbenzene hydroperoxide and 2,5-dimethyl-2,5-di (hydroperoxy) hexane; di-t-butyl peroxide, t-butyl Cumyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, 2,5-dimethyl-2,5-di (t-peroxy) hexyne-3, etc. Dialkyl peroxides; diacyl peroxides such as bis-3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, benzoyl peroxide, o-methylbenzoyl peroxide, 2,4-dichlorobenzoyl peroxide; t-butyl peroxyacetate, t-butyl pero Ci-2-ethylhexanoate, t-butyl peroxypivalate, t-butyl peroxyoctoate, t-butyl peroxyisopropyl carbonate, t-butyl peroxybenzoate, di-t-butyl peroxyphthalate, 2 , 5-dimethyl-2,5-di (benzoylperoxy) hexane, 2,5-dimethyl-2,5-di (benzoylperoxy) hexyne-3, t-butylperoxy-2-ethylhexyl carbonate Oxyesters; organic peroxides such as methyl peroxides such as methyl ethyl ketone peroxide and cyclohexanone peroxide, or azo compounds such as azobisisobutyronitrile and azobis (2,4-dimethylvaleronitrile), dibutyltin Diacetate, Dibutyltin dilaurate , It may be mentioned dibutyltin dioctoate, dioctyltin dilaurate, dicumyl peroxide, such a silanol condensation catalyst. As content of a crosslinking agent, it is preferable that 0.01 mass%-2 mass% are contained in a composition, More preferably, it is the range of 0.05 mass%-1.5 mass%.

[Crosslinking aid]
In the present invention, a polyfunctional monomer having a carbon-carbon double bond and / or an epoxy group may be used as a crosslinking aid. More preferably, the functional group of the polyfunctional monomer is an allyl group, a (meth) acrylate group, or a vinyl group. As a result, heat resistance is imparted in order to promote an appropriate crosslinking reaction, and in the present invention, the crosslinking aid reduces crystallinity of the low density polyethylene and imparts flexibility.

  Specifically, polyallyl compounds such as triallyl isocyanurate (TAIC), triallyl cyanurate, diallyl phthalate, diallyl fumarate, diallyl maleate, trimethylolpropane trimethacrylate (TMPT), trimethylolpropane triacrylate (TMPTA) Poly (meth) acryloxy compounds such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, 1,9-nonanediol diacrylate, Glycidyl methacrylate containing epoxy groups, 4-hydroxybutyl acrylate glycidyl ether and 1,6-hexanediol diglycidyl ether containing two or more epoxy groups, 1 4-butanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, and epoxy compounds such as trimethylolpropane polyglycidyl ether. These may be used alone or in combination of two or more.

  Of these, TAIC is preferably used from the viewpoint of good compatibility with low density polyethylene, lowering crystallinity by crosslinking, imparting heat resistance, and imparting flexibility at low temperatures.

  The amount of the crosslinking aid used is preferably 0.01 to 3% by mass, more preferably 0.05 to 2.0 parts by mass in the composition. Within this range, an appropriate crosslinking reaction can be promoted to make the gel fraction 80% or less.

[Radical absorbent]
In the present invention, the gel fraction can be adjusted more finely by adjusting the degree of cross-linking by using the above-mentioned cross-linking auxiliary agent serving as a radical polymerization initiator in combination with the radical absorbent for quenching it. . Examples of such radical absorbents include hindered phenol-based antioxidants, hindered amine-based weather resistance stabilization, and the like. A hindered phenol-based radical absorbent having a high radical absorbing ability near the crosslinking temperature is preferred. It is preferable that the usage-amount of a radical absorber is contained in 0.01 to 3 mass% in a composition, More preferably, it is the range of 0.05 mass part-2.0 mass parts. Within this range, the gel fraction can be adjusted by appropriately suppressing the crosslinking reaction.

[Other ingredients]
The sealing material composition may further contain other components. For example, a weathering master batch for imparting weather resistance to a sealing material produced from the sealing material composition of the present invention, various fillers, a light stabilizer, an ultraviolet absorber, a heat stabilizer, a silane coupling agent Etc. are exemplified. These contents vary depending on the particle shape, density, and the like, but are preferably in the range of 0.001 to 5 mass% in the encapsulant composition. By including these additives, it is possible to impart a mechanical strength that is stable over a long period of time, an effect of preventing yellowing, cracking, and the like to the encapsulant composition.

  A weatherproof masterbatch is obtained by dispersing a light stabilizer, an ultraviolet absorber, a heat stabilizer and the above-mentioned antioxidant in a resin such as polyethylene, and adding this to a sealing material composition. Thus, good weather resistance can be imparted to the encapsulant. The weatherproof masterbatch may be prepared and used as appropriate, or a commercially available product may be used. The resin used for the weatherproof masterbatch may be the low density polyethylene used in the present invention, or the other resins described above.

  These light stabilizers, ultraviolet absorbers, heat stabilizers and antioxidants can be used alone or in combination of two or more.

  In addition to the above, other components used in the sealing material composition of the present invention include adhesion improvers, nucleating agents, dispersants, leveling agents, plasticizers, antifoaming agents, flame retardants, and the like. it can.

<Physical properties of encapsulant sheet>
The sealing material sheet of the present invention obtained by film-forming the above composition has a water absorption rate of 0.2% or less according to JIS-K7209. The spectral reflectance at a wavelength of 400 nm and 900 nm with a thickness of 300 μm is both 80% or more, and the spectral reflectance at a wavelength of 400 nm is preferably 90% or more, more preferably 95% or more.

Here, the water absorption rate (%) according to JIS-K7209 means that a sample is cut into a 100 mm square and placed in an oven at 40 ° C. for 1 day or more (mass W ₀ ). A sufficiently dried sample was immersed in distilled water at 23 ° C. for 24 hours (mass W ₁ ), and calculated from the change in weight before and after the addition (water absorption (%) = 100 × (W ₁ −W ₀ ) / W ₀ ).

  Moreover, the spectral reflectance in wavelength 400nm and 900nm is a value measured by the method and conditions prescribed | regulated by JIS-K0115 using a spectrophotometer. Here, the spectral reflectance is the reflectance at the surface of the encapsulant sheet, and when the skin layer is provided in a multilayer configuration, the spectral reflectance is measured from the skin layer side.

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

[ Reference Example 1]
First, the following master batch and compound pellets were prepared.
Silane modified transparent resin: vinyl trimethoxy with respect to 98 parts by mass of metallocene linear low density polyethylene (M-LLDPE) having a density of 0.881 g / cm ³ and an MFR at 190 ° C. of 2 g / 10 min. 2 parts by mass of silane and 0.1 part by mass of dicumyl peroxide as a radical generator (reaction catalyst) are mixed, melted and kneaded at 200 ° C., density 0.884 g / cm ³ , MFR at 190 ° C. A silane-modified transparent resin having a weight of 1.8 g / 10 min was obtained.
Weatherproof masterbatch: 3.8 parts by mass of benzophenol UV absorber and hindered amine light stabilizer 5 with respect to 100 parts by mass of powder obtained by pulverizing Ziegler linear low density polyethylene having a density of 0.880 g / cm ³ Mass parts and 0.5 parts by mass of a phosphorous heat stabilizer were mixed, melted, processed, and pelletized to obtain a master batch.
Crosslinking agent compound resin: 2,5-dimethyl-2,5- as a crosslinking agent with respect to 100 parts by mass of M-LLDPE pellets having a density of 0.880 g / cm ³ and MFR at 190 ° C. of 3.1 g / 10 min. Compound pellets were obtained by impregnating 0.5 parts by mass of di (t-butylperoxy) hexane.
White pigment masterbatch: 60 parts by mass of titanium oxide having an average particle size of 0.3 μm per 100 parts by mass of M-LLDPE pellets having a density of 0.900 g / cm ³ and MFR at 190 ° C. of 3.1 g / 10 min. A master batch was obtained by mixing and pelletizing.

Next, 20 parts by mass of the silane-modified transparent resin, 5 parts by mass of the weather resistant masterbatch, 80 parts by mass of the crosslinker compound resin, and a predetermined amount of the masterbatch having the white pigment content shown in Table 1 are mixed and melted. Then, using a 30 mm extruder and a film forming machine having a 200-mm width T-die, an extrusion temperature of 210 ° C. and a take-off speed of 1.1 m / min are used as a sealing material composition, and two types and three layers (layer ratio 1: 5: 1) with a total thickness of 300 μm was produced ( Reference Examples 1 to 3, Examples 4 to 6 , Comparative Examples 3 and 4).

[Comparative Example 1]
100 parts by mass of EVA (vinyl acetate content 28%, manufactured by Mitsui DuPont Polychemicals, trade name EVAFLEX / EV250 grade), 1.5 parts by mass of cross-linking agent (Lupersol 101), antioxidant (NAUGARD-P) 0. Film formation conditions similar to those described above except that the composition was blended with 2 parts by weight, UV absorber (0.1 part by weight of Tinuvin 7709 and 0.3 part by weight of Cyasorb UV-531), and the extrusion temperature was 80 ° C. A single-layer encapsulant sheet having a thickness of 300 μm was prepared.

[Comparative Example 2]
Further, a single-layer sealing material sheet having a thickness of 300 μm was prepared in the same manner as in Comparative Example 1 except that the above-described titanium oxide was added so that the white pigment was 3.8%.

<Evaluation Example 1>
Table 1, Table 1 shows the results of measuring the spectral reflectance, the water absorption rate, and the glass adhesion rate (represented by the maintenance rate% when the initial adhesion force is 100) for the sealing material sheets of Examples, Comparative Examples, and Reference Examples. It is shown in 2.

  From Tables 1 and 2, the sealing material sheet of the present invention has high spectral reflectance, high water absorption, and excellent glass adhesion, and can be suitably used as a back sealing material sheet. Understandable.

DESCRIPTION OF SYMBOLS 1 Solar cell module 2 Transparent front substrate 3 Front sealing material sheet layer 4 Solar cell element 5 Back sealing material sheet layer 6 Back surface protection sheet

Claims (3)

In the solar cell module, a sealing material sheet made of polyethylene resin disposed on the non-light-receiving surface side of the solar cell,
The encapsulant sheet contains 4% by mass or more and 10% by mass or less of a white pigment as an average content of all layers in the encapsulant sheet .
The encapsulant sheet has a multilayer structure composed of layers having different contents of the white pigment,
In the multilayer structure, a skin layer is disposed on the side in close contact with the solar battery cell, and the content of the white pigment in the skin layer is 1.5% by mass or more and 4% by mass or less,
A sealing material sheet having a water absorption rate of 0.2% or less according to JIS-K7209.   The encapsulant sheet according to claim 1, wherein the encapsulant sheet has a two-layer / three-layer structure of skin layer / inner layer / skin layer, and the content of the white pigment in the inner layer is 4% by mass or more.   3. The encapsulant sheet according to claim 1, wherein both of the spectral reflectances at a wavelength of 400 nm and 900 nm of the encapsulant sheet 300 μm are 80% or more.