NIR-REFLECTIVE MULTI-LAYER MATERIAL SHEET

Abstract

The present invention relates to a multi-layer material sheet comprising an NIR-reflective, translucent polymeric layer having a reflectance of more than 20% of all light with a wavelength from 750 nm to 1000 nm and a transmission of more than 50% of all light with a wavelength from 380 nm to 750 nm and an NIR-reflective, colored polymeric layer having a reflectance of more than 25% of all light with a wavelength from 1000 nm to 2100 nm. The present invention also relates to a backsheet suitable for use in a photovoltaic module, said backsheet comprising said multi-layer material sheet; and to a photovoltaic module comprising said backsheet.

Claims

1. A multi-layer material sheet comprising an NIR-reflective, translucent polymeric layer having a reflectance of more than 20% of all light with a wavelength from 750 nm to 1000 nm and a transmission of more than 50% of all light with a wavelength from 380 nm to 750 nm; and an NIR-reflective, colored polymeric layer having a reflectance of more than 25% of all light with a wavelength from 1000 nm to 2100 nm.

2. A multi-layer material sheet according to claim 1, whereby the NIR-reflective, colored polymeric layer has a reflectance of less than 35% of all light with a wavelength from 380 nm to 750 nm.

3. A multi-layer material sheet according to claim 1, wherein the NIR-reflective, translucent polymeric layer and the NIR-reflective, colored polymeric layer are adjacent to each other or are separated by an adhesive layer.

4. A multi-layer material sheet according to claim 1, wherein the NIR-reflective, translucent polymeric layer comprises an inorganic near infra-red-reflective pigment.

5. A multi-layer material sheet according to claim 4, wherein the inorganic near infra-red-reflective pigment is selected from the group consisting of mica, SiO.sub.2, TiO.sub.2, tin oxide, ZnO, ZnSnO, aluminium-doped ZnO, indium tin oxide, antimony tin oxide, ZrO.sub.2 and mixtures thereof.

6. A multi-layer material sheet according to claim 4, wherein the NIR-reflective, translucent polymeric layer comprises from 0.1 wt. % to 8 wt. % of the inorganic near infra-red-reflective pigment, based on the total weight of the NIR-reflective, translucent polymeric layer.

7. A multi-layer material sheet according to claim 1, 6, wherein the NIR-reflective, translucent polymeric layer has a total transmittance ≥50% as measured according to ISO13468-2.

8. A multi-layer material sheet according to claim 1, wherein the NIR-reflective, translucent polymeric layer comprises a thermoplastic polymer.

9. A multi-layer material sheet according to claim 8, wherein the thermoplastic polymer is a polyolefin or a mixture of polyolefins.

10. A multi-layer material sheet according to claim 1, wherein the NIR-reflective, colored polymeric layer comprises a thermoplastic polymer.

11. A multi-layer material sheet according to claim 10, wherein the thermoplastic polymer of the NIR-reflective, colored polymeric layer is selected from the group consisting of polyamide, polyester, rubber modified polyester, polyolefin and combinations thereof.

12. A multi-layer material sheet according to claim 1, wherein the NIR-reflective, translucent polymeric layer has a thickness of from 10 μm to 150 μm.

13. A multi-layer material sheet according to claim 1, wherein the NIR-reflective, colored polymeric layer has a thickness of from 100 μm to 400 μm.

14. A multi-layer material sheet according to claim 1, further comprising a weather-resistant layer.

15. A multi-layer material sheet comprising a NIR-reflective, translucent polymeric layer having a reflectance of more than 20% of all light with a wavelength from 750 nm to 1000 nm and a transmission of more than 50% of all light with a wavelength from 380 nm to 750 nm; and a colored polymeric layer having a reflectance of less than 35% of all light with a wavelength from 380 nm to 2100 nm.

16. A multi-layer material sheet according to claim 15 wherein the colored polymeric layer comprises carbon black.

17. A multi-layer material sheet comprising: a) an NIR-reflective, translucent polymeric layer, which layer comprises functionalized polyethylene, polyethylene and optionally polypropylene and an NIR-reflective pigment; b) an NIR-reflective, colored layer, which layer comprises a polyolefin, an NIR reflective pigment and a colored pigment; and c) a weather-resistant layer.

18. A multi-layer material sheet according to claim 17, wherein: a) the NIR-reflective, translucent polymeric layer has a thickness of from 10 to 150 μm and comprises ethylene copolymerized with methacrylate and from 0.1 to 8 wt. % of an NIR-reflective pigment comprising mica and SiO.sub.2; b) the NIR-reflective, colored layer has a thickness of from 100 to 400 μm and comprises polypropylene or propylene copolymerized with maleic anhydride and from 0.1 to 8 wt. % of NIR-reflective pigment which is also a colored pigment; and c) the weather-resistant layer comprises polyamide 12 or polypropylene.

19. A backsheet suitable for use in a photovoltaic module, said backsheet comprising a multi-layer material sheet as defined in claim 1,

20. A photovoltaic module comprising a backsheet as defined in claim 19.

21. A photovoltaic module according to claim 20, comprising, in order of position from the front, sun-facing, side to the back, non-sun-facing side: a transparent top layer; optionally a front encapsulant layer; a solar cell layer comprising one or more electrically interconnected solar cells; optionally, a back encapsulant layer; and a backsheet.

Description

[0112] The invention will be further explained with the help of figures and examples without being however limited thereto.

[0113] FIG. 1 is a plot of reflectivity against wavelength for the film of Example 3, an NIR-reflective, translucent polymeric layer.

[0114] FIG. 2 is a plot of transmittance against wavelength for the film of Example 3, an NIR-reflective, translucent polymeric layer.

[0115] FIG. 3 is a plot of reflectivity against wavelength for the film of Example 4, an NIR-reflective, colored polymeric layer.

[0116] FIG. 4 is a plot of reflectivity against wavelength for the co-extruded film of Example 5, a multi-layer material sheet.

[0117] FIG. 5 is a plot of reflectivity against wavelength for the co-extruded film of Examples 6, 7, 8, multi-layer material sheets, and Comparative Experiment 1.

[0118] FIG. 6 is a plot of reflectivity against wavelength for the film of Example 4, an NIR-reflective, colored polymeric layer.

[0119] FIG. 7 is a plot of reflectivity against wavelength for the film of Example 4, an NIR-reflective, colored polymeric layer.

[0120] FIG. 8 shows an example multi-layer material sheet according to the present invention. A functional layer (1) is connected to a structure-reinforcing layer (3) through a tie-layer (2). A weather resistant layer (5) is connected to the other side of the structure-reinforcing layer (3) via a second tie layer (4).

[0121] The present invention will now be described in detail with reference to the following non-limiting examples which are by way of illustration.

EXAMPLES

Example 1

Preparation of NIR-Reflective Translucent Granulate 1

[0122] Granulate of NIR-reflective translucent polymeric material was produced by addition of Iriotec® 9870 powder to a powder of a polymeric mixture of 70 wt % polyethylene and a 30 wt % polyethylene copolymer including additives into a twin-screw extruder equipped with feeders, an 18 mm screw containing elements for mixing, melting and transport of the melt, vacuum dome, atmospheric degassing and a die-plate of 1×4 mm. After the die in consecutive order a 1.5 m long water bath, an air knife and pelletizer was installed. Total concentration of Iriotec® 9870 in the compound was 3 wt % in relation to the total weight of the polymeric material. All materials were dosed on the throat. Temperatures of zone 1 is set to 200° C., the other zones were set to 230° C. Temperature of the melt measured upon exiting the die is 270° C. Extruder was set to 300 RPM and the throughput is 5 kg/hr. Vacuum was set to −0.7 bar.

Example 2

Preparation of NIR-Reflective Black Granulate 2

[0123] Granulate of NIR-reflective black polymeric material was produced by addition of Shepherd Black BK10G966 powder to polypropylene including additives as a powder into a twin-screw extruder equipped with feeders, an 18 mm screw containing elements for mixing, melting and transport of the melt, vacuum dome, atmospheric degassing and a die-plate of 1×4 mm. After the die in consecutive order a 1.5 m long water bath, an air knife and pelletizer was installed. Total concentration of Shepherd Black BK10G966 in the compound is 8 wt % in relation to the total weight of the polymeric material. All materials were dosed on the throat. Temperature of zone 1 was set to 200° C. the other zones were set to 230° C. Temperature of the melt measured upon exiting the die was 270° C. Extruder was set to 300RPM and the throughput was 5 kg/hr. Vacuum was set to −0.7 bar.

Example 3

Film Processing of the NIR-Reflective, Translucent Granulate 1

[0124] Granulate 1 (Example 1) was processed into a cast film of approximately 20 μm thickness by using a Collin flat line set-up equipped with a single screw extruder 30/25D with a 3-stage screw, feed block, flat coat die of 300×0.4 mm and a take-off device. Cylinder temperatures went from water cooled at the intake till 225° C. at the end. Connector, feed block and die temperatures were set till 225° C. Take off speed was 5 m/min. Screw speed was 15 RPM.

[0125] Total reflectivity and total transmittance of this film was measured using integrating sphere apparatus and based on ISO 13468-2 at 20 μm thickness and is shown in FIG. 1 and FIG. 2.

Example 4

Film Processing of the NIR-Reflective, Black Granulate 2

[0126] Granulate 2 (example 2) was processed into a cast film of approximately 150 μm thickness by using a Collin flat line set-up equipped with a single screw extruder 30/25D with a 3-stage screw, feed block, flat coat die of 300×0.4 mm and a take-off device. Cylinder temperatures went from water cooled at the intake till 225° C. at the end. Connector, feed block and die temperatures were set till 225° C. Take off speed was 3 m/min. Screw speed was 60 RPM. Total reflectivity of this film was measured using integrating sphere apparatus and based on ISO 13468-2 at 150 μm thickness and is shown in FIG. 3.

Example 5

NIR-Reflective Multi-Layer Backsheets

[0127] Granulates 1 and 2 were coextruded into a multi-layer cast film of 170 μm thickness by using a Collin flat film line with a multi-layer set up with 2 extruders. Extruder A was a single screw extruder 30/25D with a 3-stage screw. Extruder B was a single screw extruder 25/25D also with a 3-stage screw. It was further equipped with a feed block 2-layer set-up, a flat coat die 300×0.4 mm and a take-off device. Cylinder temperatures change from water cooled at the intake till 225° C. at the end. Connector, feed block and die temperatures were set till 225° C. Take off speed was 3 m/min. Granulate 2 was fed onto extruder A and screw speed was 60 RPM which gives a thickness of 150 μm. Granulate 1 was fed on extruder B and screw speed was 16 RPM which gives a thickness of 20 μm. Total reflectivity of this film is measured with the NIR-reflective translucent layer towards the light source using integrating sphere apparatus and based on ISO 13468-2 at 170 μm thickness and is shown in FIG. 4.

Examples 6 to 8

[0128] The ingredients listed for each layer of each example in Table 1, below were respectively melt mixed in an extruder together with standard additives and pelletized to obtain pellets for use in the respective layers. Parts given are parts by weight, the total weight of each component being 100.

TABLE-US-00002 TABLE 1 Weather- Example resistant Structure Functional no. layer Tie layer reinforcing layer Layer Ex. 6 100 parts 90 parts maleic 92 parts 59 parts of TiO.sub.2 - anhydride grafted copolymerized polyethylene; 27 filled polypropylene; 10 polypropylene; 8 parts ethylene stabilized parts α-olefin parts Sicopal black copolymer; 11 parts PA12 block copolymer K0095; copolymerized polypropylene; 3 parts Iriotec ® 9870; Ex. 7 100 parts 90 parts of maleic 92 parts 59 parts carbon anhydride grafted copolymerized polyethylene; 27 black- polypropylene; 10 polypropylene; 8 parts ethylene filled parts α-olefin parts Sicopal black copolymer; 11 parts stabilized block copolymer K0095 copolymerized PA12 polypropylene; 3 parts Iriotec ® 9870; Ex. 8 100 parts 87 parts of maleic 92 parts 59 parts carbon anhydride grafted copolymerized polyethylene; 27 black- polypropylene; 10 polypropylene; 8 parts ethylene filled parts α-olefin parts Sicopal black copolymer; 11 parts stabilized block copolymer; K0095 copolymerized PA12 3 parts Iriotec ® polypropylene; 3 9870 parts Iriotec ® 9870;

[0129] For each example, the pellets were fed to one of multiple extruders, melt-extruded at a high temperature, passed through an adapter and a die, cooled by a cooling roller and shaped into a multi-layer film having a total thickness of 300 μm. Each example had, in order, the following composition: [0130] 30 μm weather-resistant layer; [0131] 25 μm tie layer; [0132] 190 μm structure-reinforcing layer; [0133] 25 μm tie layer; [0134] 30 μm functional layer.

Comparative Experiment 1

High Reflective Black Backsheet

[0135] A high reflective black backsheet produced according to embodiment (3) of Examples 1 and 2 of US 2013/276876.

[0136] The total reflectivity of each of Examples 6, 7, 8 and Comparative Example 1 was measured using integrating sphere apparatus and based on ISO 13468-2, with the functional polymeric layer towards the light source. The results are shown in FIG. 5. Examples 6, 7 and especially 8 give higher total reflectance in the NIR region from 750 nm till 1000 nm. Examples 6, 7 and especially 8 give higher total reflectance in the NIR region from 750 nm till 1000 nm. This wavelength range is most relevant, since this range is above the visible spectral range for the human eye (approximately 380-740 nm) and in this range the (external) quantum efficiency for a typical silicon solar cell is relatively high (>90%).

Example 9

NIR-Reflective Green-Colored Polymeric Layer

[0137] A strand of NIR-reflective polymeric material was produced by addition of Shepherd Green 100650 powder to a powder of a polymeric mixture of 70 wt. % polyethylene and a 30 wt. % polyethylene copolymer including additives. The mixture was introduced into a small-scale twin-screw extruder. The total concentration of Shepherd Green 100650 in the compound was 8 wt. % in relation to the total weight of the polymeric material. The mixture was melt extruded at 175° C. and 200 rpm over 2 minutes, wherein the material is collected as a strand. A film was pressed from this strand by placing approximately 1 gram into a precut aluminum mold with dimensions 100 mm×100 mm×65 μm. Pressing was carried out using a THB400 handheld press at 175° C. for 3 minutes. Pressure was increased stepwise from 100 to 200 and finally 300 kN. Each step lasted 1 minute. After 3 minutes, the sample was cooled under pressure to room temperature. A film having a thickness of 100 μm was obtained. The total reflectivity of the film was measured using integrating sphere apparatus and based on ISO 13468-2 and is shown in the FIG. 6. A green-coloured film showing significant reflectivity above 750 nm wavelength was produced.

Example 10

NIR-Reflective Orange-Colored Polymeric Layer

[0138] Example 9 was repeated except that 8 wt. % Shepherd Orange 10P340 powder was used in place of 8 wt. % Shepherd Green 100650. Total reflectivity of the film was measured using integrating sphere apparatus and based on ISO 13468-2 and is shown in the FIG. 7. An orange-coloured film showing significant reflectivity above 600 nm wavelength was produced.