Backsheet comprising a polyolefine based functional layer facing the back encapsulant

Abstract

The present invention relates to a solar cell backsheet, comprising a functional layer wherein the functional layer comprises a polyethylene alloy and a semi-crystalline polymer such as polypropylene, preferably at least 10 wt % of polypropylenes based on the total weight of the polymers in the functional layer. The polypropylene is selected from a polypropylene homo- or copolymer, the copolymer is a random or block copolymer. The polyethylene alloy comprises a copolymer containing an ethylene segment (—CH2-CH2-) which is selected from one or more of ethylene acrylate copolymer, ethylene-hexene copolymer, ethylene-octene copolymer, ethylene-vinyl acetate copolymer. The functional layer further comprises an inorganic filler selected from one of calcium carbonate, titanium dioxide, barium sulfate, mica, talc, kaolin, glass microbeads and glass fibers. The present invention also relates to a photovoltaic module comprising the backsheet according to the present invention.

Claims

1. A solar cell backsheet comprising: a functional layer facing a back encapsulant, and a structural reinforcement layer adhered to the functional layer, wherein the functional layer comprises a blend of: (i) a polyethylene alloy comprising a polyethylene and an ethylene-vinyl acetate (EVA) copolymer and/or an ethylene-methacrylate (EMA) copolymer, and (ii) a semi-crystalline polypropylene polymer with a melting point above 140° C. selected from the group consisting of polypropylene homopolymer, polypropylene copolymer and maleic anhydride grafted polypropylene, and wherein the structural reinforcement layer comprises a layer selected from the group consisting of polypropylene, modified polypropylene, maleic anhydride grafted polypropylene and blends thereof, and wherein the semi-crystalline polypropylene polymer is present in the functional layer in an amount of 5-15 wt. %, based on total weight of polymers in the functional layer, sufficient to achieve a peel strength between the functional layer and the structural reinforcement layer of greater than 40 N/cm.

2. The solar cell backsheet according to claim 1, wherein the functional layer further comprises an inorganic filler.

3. The solar cell backsheet according to claim 2, wherein the inorganic filler is at least one selected from the group consisting of calcium carbonate, titanium dioxide, barium sulfate, mica, talc, kaolin, glass microbeads and glass fibers.

4. The solar cell backsheet according to claim 1, further comprising a weather-resistant layer and/or an adhesive layer.

5. The solar cell backsheet according to claim 4, wherein the weather-resistant layer comprises a fluoro-resin or a polyamide.

6. The solar cell backsheet according to claim 4, wherein the adhesive layer comprises a maleic anhydride grafted polyolefin.

7. The solar cell backsheet according to claim 4, wherein the weather-resistant layer and/or the adhesive layer further comprise an inorganic filler.

8. The solar cell backsheet according to claim 1, wherein the polyethylene of the polyethylene alloy comprises linear low density polyethylene (LLDPE).

9. The solar cell backsheet according to claim 1, further comprising an adhesive layer between the functional layer and the structural reinforcement layer.

10. The solar cell backsheet according to claim 9, wherein the adhesive layer comprises maleic anhydride grafted polyethylene or maleic anhydride grafted polypropylene.

11. A photovoltaic module comprising the backsheet according to claim 1.

Description

EXAMPLES

(1) Method for Manufacturing a Lower Solar Backplate Comprises the Following Steps:

(2) Material of a weathering-resistant layer, an adhesive layer, a structure reinforcing layer and a functional layer are respectively pelletized by an extruder to obtain plastic pellets of respective layers.

(3) A back sheet is prepared by a multilayer co-extrusion process whereby the pellets of the respective layers are added to multiple extruders, melt-extruded at a high temperature, flow through an adapter and a die, cooled by a cooling roller and shaped to manufacture the multi-layer back sheet. Composition of the different layers in the multilayer backsheets are given in table 1.

(4) Measurements

(5) Peel strength is measured between the functional layer and the structure reinforcing layer and between the functional layer and EVA as encapsulant

(6) Aging is measured: Appearance after ageing (121° C., 100% humidity) in an HAST high pressure accelerated ageing test machine for 48 hours.

(7) Appearance and yellowing are measured after ageing by 120 KWH ultraviolet radiation.

(8) Results of these measurements for the multilayer backsheets of comparative examples I and II and for examples 1-5 are given in table 2.

Comparative Example I (CE-I)

(9) A PVDF fluorine polymer is used as a weathering-resistant layer, a blend of polymers of maleic anhydride grafted polypropylene and EMA ethylene methyl acrylate is used as an adhesive layer which can adhere both the fluorine polymer and the maleic anhydride grafted polypropylene. No semi-crystalline polymer is added to the functional layer.

Comparative Example II (CE-II)

(10) A nylon 12 (PA12) polymer is used as a weathering-resistant layer, maleic anhydride grafted polypropylene is used as an adhesive layer. No semi-crystalline polymer is added to the functional layer.

Examples 1-4

(11) A semi-crystalline polymer such as polypropylene or maleic anhydride grafted polypropylene is added to the functional layer in Examples 1-4, respectively.

(12) TABLE-US-00001 TABLE 1 Weather- Structure resistant Adhesive reinforcing Adhesive Functional Multilayer layer layer layer layer layer backsheet (thickness) (thickness) (thickness) (thickness) (thickness) CE-I 80 parts of 50 parts of 90 parts of 50 parts of 70 parts of PVDF, 15 maleic copolymerized maleic LLDPE, 20 parts of anhydride PP, 10 parts anhydride parts of EVA, PMMA and grafted of TiO.sub.2 and grafted 10 parts of 5 parts of polypropylene 0.3 parts of polypropylene TiO.sub.2 and 0.5 TiO.sub.2, and 50 parts Irganox 1010, and 50 parts parts of an blended of blended (250 μm) of ultraviolet (25 μm) ElvaloyAC1224 ElvaloyAC1224 stabilizer, (25 μm) (25 μm) blended (50 μm) CE-II 100 parts 100 parts of 90 parts of 100 parts of 70 parts of of PA12, maleic copolymerized maleic LLDPE, 20 0.5 parts of anhydride PP, 10 parts anhydride parts of EVA, Tinuvin770, grafted of TiO.sub.2 and grafted 10 parts of 0.3 parts of polypropylene 0.3 parts of polypropylene TiO.sub.2 and 0.5 Irganox (25 μm) Irganox 1010, (25 μm) parts of an B225 and blended ultraviolet 10 parts of (250 μm) stabilizer, TiO.sub.2, blended blended (50 μm) (25 μm) Example 1 100 parts 100 parts of 90 parts of 100 parts of 65 parts of of PA12, maleic copolymerized maleic LLDPE, 20 0.5 parts of anhydride PP, 10 parts anhydride parts of EVA, Tinuvin770, grafted of TiO.sub.2 and grafted 5 parts of 0.3 parts of polypropylene 0.3 parts of polypropylene copolymerized Irganox (25 μm) Irganox 1010, (25 μm) PP, 10 parts B225 and blended of TiO.sub.2 and 10 parts of (250 μm) 0.5 parts of TiO.sub.2, an ultraviolet blended stabilizer, (25 μm) blended (50 μm) Example 2 100 parts 100 parts of 90 parts of 100 parts of 60 parts of of PA12, maleic copolymerized maleic LLDPE, 20 0.5 parts of anhydride PP, 10 parts anhydride parts of EVA, Tinuvin770, grafted of TiO.sub.2 and grafted 10 parts of 0.3 parts of polypropylene 0.3 parts of polypropylene copolymerized Irganox (25 μm) Irganox 1010, (25 μm) PP, 10 parts B225 and blended of TiO.sub.2 and 10 parts of (250 μm) 0.5 parts of TiO.sub.2, an ultraviolet blended stabilizer, (25 μm) blended (50 μm) Example 3 100 parts 100 parts of 90 parts of 100 parts of 55 parts of of PA12, maleic copolymerized maleic LLDPE, 20 0.5 parts of anhydride PP, 10 parts anhydride parts of EVA, Tinuvin770, grafted of TiO.sub.2 and grafted 15 parts of 0.3 parts of polypropylene 0.3 parts of polypropylene copolymerized Irganox (25 μm) Irganox 1010, (25 μm) PP, 10 parts B225 and blended of TiO.sub.2 and 10 parts of (250 μm) 0.5 parts of TiO.sub.2, an ultraviolet blended stabilizer, (25 μm) blended (50 μm) Example 4 100 parts 100 parts of 90 parts of 100 parts of 55 parts of of PA12, maleic copolymerized maleic LLDPE, 20 0.5 parts of anhydride PP, 10 parts anhydride parts of EVA, Tinuvin770, grafted of TiO.sub.2 and grafted 15 parts of 0.3 parts of polypropylene 0.3 parts of polypropylene maleic Irganox (25 μm) Irganox 1010, (25 μm) anhydride B225 and blended (250 μm) grafted PP, 10 10 parts of parts of TiO.sub.2 TiO.sub.2, and 0.5 parts blended of an (25 μm) ultraviolet stabilizer, blended (50 μm)
In Table 1, the respective layers are multi-component layers and the proportion of each component is in parts by weight.

(13) Elvaloy AC1224 is a copolymer of ethylene and methyl acrylate from DuPont;

(14) TABLE-US-00002 TABLE 2 Ultraviolet Peeling strength Peeling strength ageing between between Peeling strength resistance of functional layer functional layer after ageing functional layer and structure and encapsulation (120° C., 100% (yellowing after reinforcing layer layer hμmidity) of 48 120 KWH RESULTS (N/cm) (N/cm) hours in HAST radiation) Comparative 34 74.5 No layering or 0.5 Example I cracking is seen Comparative 36 72.6 No layering or 0.4 Example II cracking is seen Example 1 >40 65.3 No layering or 0.3 (Unpeelable) cracking is seen Example 2 >40 68.8 No layering or 0.5 (Unpeelable) cracking is seen Example 3 >40 66.8 No layering or 0.5 (Unpeelable) cracking is seen Example 4 >40 68.8 No layering or 0.7 (Unpeelable) cracking is seen

(15) It can be seen from the data in Table 2 that the addition of 5-15 parts of polypropylene (PP) to the functional layer, results in remarkably improved adhesion force between the functional layer and the structural reinforcing layer, while the adhesion force between the functional layer and the EVA encapsulation layer is reduced slightly. The adhesion force between the functional layer and the structural reinforcing layer increases by the addition of 10 parts by weight of polypropylene PP and 15 parts by weight of maleic anhydride grafted polypropylene (MPP). It can be seen from the test results of HAST and ultraviolet ageing resistance that the addition of polypropylene or maleic anhydride grafted polypropylene in the functional layer has little effect on the hydrolysis resistance and ultraviolet ageing resistance.

(16) As can be seen from Tables 1 and 2, the adhesion forces between the functional layers and the structural reinforcing layers in the backsheets of Examples 1-4 are remarkably improved with respect to that of the backsheets of Comparative Examples I and II. Furthermore, the peeling strengths to the encapsulation layers can also be maintained at a good level, there is no weak point in terms of the adhesion forces between the backsheet layers and the adhesion forces to the encapsulation layers which means that the overall durability of the backsheets is improved.