Photovoltaic module backsheet comprising polyolefin layers

Abstract

The present invention relates to a photovoltaic module backsheet, comprising photovoltaic module backsheet comprising, in order: a functional layer; a connecting layer; and a weather-resistant layer, wherein each layer of the backsheet comprises at least 50 wt. % polyolefin and the backsheet is free of fluorinated polymers, characterized in that: i) the functional layer comprises a blend of polyethylene and a polyethylene copolymer; and ii) the weather-resistant layer comprises polypropylene; a UV stabilizer; a primary antioxidant, which primary antioxidant is a phenolic antioxidant or an aromatic amine antioxidant; and secondary antioxidant, which secondary antioxidant is a trivalent phosphorus containing antioxidant or a thioether containing antioxidant. The present invention also relates to a process for producing the backsheet and a photovoltaic module comprising the backsheet according to the present invention.

Claims

1. A photovoltaic module backsheet comprising: a functional layer located at a first face of the backsheet and adapted to being positioned adjacent photovoltaic cells of a photovoltaic module; a weather-resistant layer located at a second face of the backsheet opposite the first face and adapted to being exposed to air; and a connecting layer which connects the functional layer to the weather-resistant layer, wherein (i) the functional layer comprises a ternary blend which comprises, based on the weight of the functional layer: (ia) 5 to 30 wt. % of polypropylene, (ib) at least 50 wt. % of polyethylene, and (ic) 20 to 40 wt. % of an ethylene methacrylate copolymer; and wherein (ii) the weather-resistant layer comprises, based on the weight of the weather-resistant layer: (iia) at least 50 to at most 95 wt. % of polypropylene; (iib) a UV stabilizer; (iic) a primary antioxidant which is selected from the group consisting of phenolic antioxidants and aromatic amine antioxidants; and (iid) a secondary antioxidant which is selected from the group consisting of trivalent phosphorus containing antioxidants and thioether containing antioxidants, wherein the primary and secondary antioxidants are each present in a wt. % amount such that a ratio of the wt. % of the primary antioxidant to the wt. % of the secondary antioxidant is from 0.1 to 1.0, and wherein (iii) the connecting layer comprises: (iiia) at least 50 wt. % to at most 95 wt. % of polyethylene, and (iiib) a maleic anhydride grafted polyolefin, wherein the backsheet is free of fluorinated polymers.

2. The photovoltaic module backsheet according to claim 1, wherein the photovoltaic module backsheet consists of the functional layer, the connecting layer and the weather-resistant layer.

3. The photovoltaic module backsheet according to claim 1, wherein the weather-resistant layer comprises a polypropylene-polyethylene copolymer.

4. The photovoltaic module backsheet according to claim 3, wherein the weather-resistant layer comprises from 75 to 90 wt. % of the polypropylene-polyethylene copolymer.

5. The photovoltaic module backsheet according to claim 1, wherein the weather-resistant layer comprises an outer sub-layer comprising an inorganic filler and an inner sub-layer comprising an inorganic filler, wherein the outer sub-layer comprises a lower wt. % of inorganic filler than the inner sub-layer.

6. The photovoltaic module backsheet according to claim 5, wherein the outer sub-layer and inner sub-layer each comprise titanium dioxide, and the outer sub-layer comprises a higher wt. % titanium dioxide than the inner sub-layer.

7. The photovoltaic module backsheet according to claim 1, wherein the primary antioxidant is a phenolic antioxidant which is selected from the group consisting of benzenepropanoic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy-octadecyl ester; 2,5,7,8-Tetra-methyl-2-(4,8,12-tri-methyl-tri-decyl)-chroman-6-ol; N,N-Hexamethylene bis (3,5-di-t-butyl-4-hydroxyhydrocinnamamide); ethylenebis (oxyethylene) bis (3-t-butyl-4-hydroxy-5-methylhydrocinnamate); hexamethylenebis (3,5-di-t-butyl-4-hydroxycinnamate); phenol, 4,44-[(2,4,6-trimethyl-1,3,5-benzenetriyl)-tris-(methylene)]-tris-2,6-bis(1,1-dimethylethyl)-; bis-[3,3-bis-(4-hydroxy-3-t-butylphenyl butanoic acid]-glycol ester; tris(3,5-di-t-butyl-4-hydroxy benzyl) isocyanurate; 3,9-bis(2-(3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy-1,1-dimethylethyl)-2,4,8,10-tetraoxaspiro[5.5]undecane; 1,3,5-Tris (4-t-butyl-3-hydroxy-2,6-dimethylbenzyl)-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione; and tetrakis [methylene (3,5-di-t-butyl-4-hydroxyhydrocinnamate)] methane 3-(3,5-di-t-butyl-4-hydroxy-phenyl) propion acid ester with 1,3,5-tris (2-hydroxy-ethyl)-iso-cyanurate.

8. The photovoltaic module backsheet according to claim 1, wherein the secondary antioxidant is a thioether antioxidant which is selected from the group consisting of dilauryl thiodipropionate, distearyl thiodipropionate, dimyristyl thiodipropionate, pentaerythrityl tetrakis (-laurylthiopropionate) and 3,3-thiodipropanoic acid.

9. The photovoltaic module backsheet according to claim 1, wherein the functional layer has a thickness of from 10 to 50 m.

10. The photovoltaic module backsheet according to claim 1, wherein the connecting layer has a thickness of from 10 to 50 m.

11. The photovoltaic module backsheet according to claim 1, wherein the weather-resistant layer has a thickness of from 100 to 400 m.

12. The photovoltaic module backsheet according to claim 1, wherein the maleic anhydride grafted polyolefin is selected from the group consisting of maleic anhydride grafted polyethylene, maleic anhydride grafted polypropylene, an ethylene-acrylic acid copolymer, an ethylene acrylic acid terpolymer and an ethylene-acrylic ester-maleic anhydride terpolymer.

13. The photovoltaic module backsheet according to claim 12, wherein the maleic anhydride grafted polyolefin is ethylene/butyl acrylate/maleic anhydride grafted polypropylene.

14. The photovoltaic module backsheet according to claim 1, wherein the connecting layer comprises a blend of a polyolefin with a polyethylene-polypropylene block copolymer.

15. The photovoltaic module backsheet according to claim 1, wherein the connecting layer further comprises up to 30 wt. % of a polyolefin elastomer.

16. A photovoltaic module comprising the solar module backsheet as defined in claim 1.

17. A process for producing the photovoltaic module backsheet as defined in claim 1 comprising: i) feeding a functional layer composition; a connecting layer composition; and a weather-resistant layer composition independently to a multi-layer film coextrusion apparatus; and ii) melting and coextruding the compositions, in the multi-layer film coextrusion apparatus, into a photovoltaic module backsheet in the order of the functional layer, the connecting layer, and the weather-resistant layer.

18. A process for producing the photovoltaic module backsheet as defined in claim 1, wherein the weather-resistant layer comprises inner and outer weather-resistant sublayers, and wherein the process comprises: i) feeding a functional layer composition; a connecting layer composition; an inner weather-resistant sublayer composition and an outer weather-resistant sublayer composition independently to a multi-layer film coextrusion apparatus; and ii) melting and coextruding the compositions, in the multi-layer film coextrusion apparatus, into a photovoltaic module backsheet in the order of the functional layer, the connecting layer, the inner weather-resistant sublayer and the outer weather-resistant sublayer.

Description

EXAMPLES

(1) Method for Manufacturing a Photovoltaic Backsheet 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) Damp heat ageing was carried out at 85 C. and 85% relative humidity for a period of 200 hours. Elongation of a sample was measured after damp heat ageing and compared to a sample which was not subjected to damp heat ageing. The elongation retention % was calculated. Calculations were made both for the machine direction and for the transverse direction.

(6) Thermal stability was determined by heating samples to 200 C. for 5 hours. Appearance of the sample after heating is described.

(7) Thermal ageing was carried out at 150 C. for a period of 300 hours. Elongation of a sample was measured after thermal ageing and compared to a sample which was not subjected to thermal ageing. The elongation retention % was calculated. Calculations were made both for the machine direction and for the transverse direction.

(8) Results of these measurements are given in Table 2.

(9) TABLE-US-00001 TABLE 1 Example Connecting layer Functional layer no. Weather-resistant layer (thickness) (thickness) (thickness) Ex. 1 71 parts of polypropylene, 5 parts of 50 parts of 50 parts of polyolefin elastomer, 12 parts of polypropylene, 49 polyethylene, 16 titanium dioxide, 10 parts of talcum parts of polyolefin parts of powder, ultraviolet absorbent is 1.0 elastomer, ultraviolet polypropylene, 20 part of Chimassorb 2020, primary absorbent is 1.0 part parts of ethyl antioxidant is 0.25 part of AO-80, the of Chimassorb 2020, copolymer, 12 parts assistant antioxidant is 0.75 part of primary antioxidant is of titanium dioxide, 412S (240 um) 0.25 part of AO-80, the the ultraviolet assistant antioxidant is absorbent is 1.0 part 0.75 part of of Chimassorb 2020, 412S (30 um) primary antioxidant is 0.25 part of AO-80, the assistant antioxidant is 0.75 part of 412S (30 um) Comp 71 parts of polypropylene, 5 parts of 50 parts of 50 parts of Ex. 1 polyolefin elastomer, 12 parts of polypropylene, 49 polyethylene, 16 titanium dioxide, 10 parts of talcum parts of polyolefin parts of powder, ultraviolet absorbent is 1.0 elastomer, ultraviolet polypropylene, 20 part of Chimassorb 2020, antioxidant absorbent is 1.0 part parts of ethyl is 1 part of Irganox 1010 (240 um) of Chimassorb 2020, copolymer, 12 parts antioxidant is 1 part of of titanium dioxide, Irganox the ultraviolet 1010 (30 um) absorbent is 1.0 part of Chimassorb 2020, antioxidant is 1 part of Irganox 1010 (30 um) Ex. 2 Inner sub-layer: 71 parts of 50 parts of 50 parts of polypropylene, 5 parts of polyolefin polypropylene, 49 polyethylene, 16 elastomer, 12 parts of titanium dioxide, parts of polyolefin parts of 10 parts of talcum powder, ultraviolet elastomer, ultraviolet polypropylene, 20 absorbent is 1.0 part of Chimassorb absorbent is 1.0 part parts of ethyl 2020, primary antioxidant is 0.25 part of Chimassorb 2020, copolymer, 12 parts of AO-80, the assistant antioxidant is primary antioxidant is of titanium dioxide, 0.75 part of 412S (200 um); 0.25 part of AO-80, the the ultraviolet Outer sub-layer: assistant antioxidant is absorbent is 1.0 part 71 parts of polypropylene, 5 parts of 0.75 part of of Chimassorb 2020, polyolefin elastomer, 17 parts of 412S (30 um) primary antioxidant is titanium dioxide, 5 parts of talcum 0.25 part of AO-80, powder, ultraviolet absorbent is 2.0 the assistant parts of Chimassorb 2020, antioxidant antioxidant is 0.75 is primary antioxidant is 0.5 part of part of 412S (30 um) AO-80, the assistant antioxidant is 1.5 part of 412S (40 um) Comp Commercially available polyolefin backsheet Ex. 2

(10) TABLE-US-00002 TABLE 2 Method/ Comp Comp. Test standard Ex. 1 Ex. 1 Ex. 2 Ex. 2 Elongation MD 85 C., 73 67 69 39 retention TD 85% RH 71 65 76 76 (%) after damp-heat aging 2000 h Thermal 200 C., Not Cracked Not Cracked stability test 5 h cracked cracked Elongation MD 150 C., 25 20 36 10 retention TD 300 h 29 21 37 13 (%) after thermal aging