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US-12622069-B2 - Photovoltaic element and polymer composition for front sheet thereof

US12622069B2US 12622069 B2US12622069 B2US 12622069B2US-12622069-B2

Abstract

The present invention relates to a photovoltaic element, comprising a front layer, a back layer, and a plurality of photovoltaic cells, which photovoltaic cells are present between the front layer and back layer, wherein the front layer consists of a polypropylene composition, comprising: a) a random polypropylene resin; b) a mixture of light stabilizing additives; said mixture comprising: i) a high molecular weight hindered tertiary amine light stabilizer (t-HM-HAL S) having a weight average molecular weight of at least 1600 g/mol; ii) a low molecular weight hindered secondary amine light stabilizer (s-LM-HALS) having a weight average molecular weight of below 1000 g/mol; iii) an ultraviolet synergist, being a n-alkyl-3,5-dialkylated 4-hydroxybenzoate; iv) an ultraviolet absorber, being a hydroxybenzotriazole compound or a hydroxyl benzophenone compound or a mixture thereof; c) a mixture of antioxidant additives; said mixture comprising: i) a phenolic antioxidant; and ii) a phosphite additive. The invention also relates to a polypropylene composition and to the use thereof as front layer.

Inventors

  • Sarah Van Mierloo
  • Maud Corrina Willie van der Ven
  • Henrica Norberta Alberta Maria Steenbakkers-Menting
  • Roland VAN GIESEN

Assignees

  • SABIC GLOBAL TECHNOLOGIES B.V.

Dates

Publication Date
20260505
Application Date
20190711
Priority Date
20180712

Claims (20)

  1. 1 . A photovoltaic element, comprising: a transparent to light front layer, a back layer, and a plurality of photovoltaic cells, which photovoltaic cells are present between the transparent to light front layer and back layer, wherein the transparent to light front layer consists of a polypropylene composition, comprising: a) 97.5 to 99.5 wt. % of a random polypropylene resin, based on the total weight of the polypropylene composition, wherein the random polypropylene resin has a C2 content of between 1.0 and 5.0 wt. %, based on the weight of the random polypropylene resin; b) a mixture of light stabilizing additives; said mixture comprising: i) a high molecular weight hindered tertiary amine light stabilizer (t-HM-HALS) having a weight average molecular weight of at least 1600 g/mol; ii) a low molecular weight hindered secondary amine light stabilizer (s-LM-HALS) having a weight average molecular weight of below 1000 g/mol; iii) an ultraviolet synergist, being a n-alkyl-3,5-dialkylated 4-hydroxybenzoate; and iv) an ultraviolet absorber, being a hydroxybenzotriazole compound or a hydroxyl benzophenone compound or a mixture thereof; c) a mixture of antioxidant additives; said mixture comprising: i) a phenolic antioxidant; and ii) a phosphite additive; and d) 0 to 5 wt. % of one or more additional additives, based on the total weight of the polypropylene composition.
  2. 2 . The photovoltaic element according to claim 1 , wherein the phenolic antioxidant c)i) is 1,3,5-tris(4-t-butyl-2,6-dimethyl-3-hydroxy-benzyl)-iso-cyanurate, tetrakis[methylene-3(3′,5′-di-t-butyl-4-hydroxyphenyl)propionate]methane, or 1,3,5-trimethyl-2,4,6-tris-(3,5-di-t-butyl-4-hydroxybenzyl)benzene.
  3. 3 . The photovoltaic element according to claim 1 , wherein the high molecular weight hindered tertiary amine light stabilizer has a molecular weight (Mw) of between 1800 and 5000 g/mol.
  4. 4 . The photovoltaic element according to claim 1 , wherein the polypropylene composition further comprises the d) one or more additional additives in an amount of at most 3 wt. %, based on the total weight of the polypropylene composition.
  5. 5 . The photovoltaic element according to claim 1 , wherein the mixture of light stabilizing additives comprises as the ultraviolet synergist b)iii) n-hexadecyl 3,5-di-t-butyl-4-hydroxybenzoate and/or wherein the mixture of light stabilizing additives comprises as the ultraviolet absorber b)iv) a compound selected from the group consisting of 2-(2′-hydroxy-3′-t-butyl-5′-methylphenyl)-5-chlorobenzotriazole and 2-hydroxy-4-n-octyloxy-benzophenone.
  6. 6 . The photovoltaic element according to claim 1 , wherein the amount of said high molecular weight hindered tertiary amine light stabilizer b)i) is between 0.1 to 0.4 wt. %, based on the total weight of the polypropylene composition and/or wherein the amount of said low molecular weight hindered secondary amine light stabilizer b)ii) is between 0.1 and 1.0 wt. %, based on the total weight of the polypropylene composition and/or wherein the amount of said ultraviolet synergist b)iii) is between 0.1 and 0.5 wt. %, based on the total weight of the polypropylene composition and/or wherein the amount of said ultraviolet absorber b)iv) is between 0.1 and 0.5 wt. %, based on the total weight of the polypropylene composition.
  7. 7 . The photovoltaic element according to claim 1 , wherein the random polypropylene resin has a C2 content of 3.8 and 4.2 wt. %, based on the weight of the random polypropylene resin.
  8. 8 . The photovoltaic element according to claim 1 , wherein the random polypropylene resin has a melt flow rate measured according to ISO 1133:2005 at 230° C./2.16 kg of between 0.3 and 10.0 dg/min.
  9. 9 . The photovoltaic element according to claim 1 , wherein the high molecular weight hindered tertiary amine light stabilizer b)i) is 1,3,5-triazine-2,4,6-triamine, N,N′″-11,2-ethanediylbis [[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]imino]-3,1-propanediyl]]-bis[N′,N″-dibutyl-N′,N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl), the low molecular weight hindered secondary amine light stabilizer b)ii) is a mixture of esters of 2,2,6,6-tetra-methyl-4-piperidinol and one or more fatty acids, the ultraviolet synergist b)iii) is n-hexadecyl 3,5-di-t-butyl-4-hydroxybenzoate, the ultraviolet absorber b)iv) is 2-(2′-hydroxy-3′-t-butyl-5′-methylphenyl)-5-chlorobenzotriazole, the phenolic antioxidant c)i) is tetrakis[methylene-3(3′,5′-di-t-butyl-4-hydroxyphenyl)propionate] methane, and the phosphite additive c)ii) is tris (2,4-di-t-butylphenyl) phosphite; and wherein the polypropylene composition further comprises calcium stearate.
  10. 10 . The photovoltaic element according to claim 1 , wherein: the mixture of light stabilizing additives b) is present in an amount of 0.35 to 2.2 wt. %, based on the total weight of the polypropylene composition; and the mixture of antioxidant additives c) is present in an amount of between 0.05 and 1.0 wt. %, based on the total weight of the polypropylene composition.
  11. 11 . The photovoltaic element according to claim 1 , wherein the amount of said high molecular weight hindered tertiary amine light stabilizer b)i) is between 0.15 to 0.3 wt. %, based on the total weight of the polypropylene composition and/or wherein the amount of said low molecular weight hindered secondary amine light stabilizer b)ii) is between 0.2 and 0.6 wt. %, based on the total weight of the polypropylene composition and/or wherein the amount of said UV synergist b)iii) is between 0.2 and 0.4 wt. %, based on the total weight of the polypropylene composition and/or wherein the amount of said UV absorber b)iv) is between 0.1 and 0.2 wt. %, based on the total weight of the polypropylene composition.
  12. 12 . The photovoltaic element of claim 1 , wherein the random polypropylene resin has a C2 content of between 2.0 and 5.0 wt. %, based on the weight of the random polypropylene resin, and a melt flow rate measured according to ISO 1133:2005 at 230° C./2.16 kg of between 1.0 and 2.0 dg/min.
  13. 13 . The photovoltaic element of claim 1 , wherein the random polypropylene resin has a C2 content between 3.8 and 5.0 wt. %, based on the weight of the random polypropylene resin, and a melt flow rate measured according to ISO 1133:2005 at 230° C./2.16 kg of between 1.0 and 2.0 dg/min.
  14. 14 . A photovoltaic element, comprising: a transparent to light front layer, a back layer, and a plurality of photovoltaic cells, which photovoltaic cells are present between the transparent to light front layer and back layer, wherein the transparent to light front layer consists of a polypropylene composition, comprising: a) 97.5 to 99.5 wt. % of a random polypropylene resin, based on the total weight of the polypropylene composition, wherein the random polypropylene resin has a C2 content of between 2.0 and 5.0 wt. %, based on the weight of the random polypropylene resin, and a melt flow rate measured according to ISO 1133:2005 at 230° C./2.16 kg of between 1.0 and 2.0 dg/min; b) a mixture of light stabilizing additives; said mixture comprising, based on a total weight of the polypropylene composition: i) 0.1 to 0.4 wt. % of a high molecular weight hindered tertiary amine light stabilizer (t-HM-HALS) having a weight average molecular weight of at least 1600 g/mol; ii) 0.1 to 1.0 wt. % of a low molecular weight hindered secondary amine light stabilizer (s-LM-HALS) having a weight average molecular weight of below 1000 g/mol; iii) 0.1 to 0.5 wt. % of an ultraviolet synergist, being n-hexadecyl 3,5-di-t-butyl-4-hydroxybenzoate; and iv) 0.1 to 0.5 wt. % of an ultraviolet absorber, being 2-(2′-hydroxy-3′-t-butyl-5′-methylphenyl)-5-chlorobenzotriazole, 2-hydroxy-4-n-octyloxy-benzophenone, or a combination thereof; c) a mixture of antioxidant additives; said mixture comprising: i) a phenolic antioxidant, which is 1,3,5-tris(4-t-butyl-2,6-dimethyl-3-hydroxy-benzyl)-iso-cyanurate, tetrakis[methylene-3(3′,5′-di-t-butyl-4-hydroxyphenyl)propionate]methane, or 1,3,5-trimethyl-2,4,6-tris-(3,5-di-t-butyl-4-hydroxybenzyl)benzene; and ii) a phosphite additive; and d) 0 to 5 wt. % of one or more additional additives, based on the total weight of the polypropylene composition.
  15. 15 . The photovoltaic element according to claim 14 , wherein the high molecular weight hindered tertiary amine light stabilizer b)i) is 1,3,5-triazine-2,4,6-triamine, N,N′″-11,2-ethanediylbis [[[4,6-bis[butyl(1,2,2,6,6-pentamethyl-4-piperidinyl)amino]-1,3,5-triazine-2-yl]imino]-3,1-propanediyl]]-bis[N′,N″-dibutyl-N′,N″-bis(1,2,2,6,6-pentamethyl-4-piperidinyl), the low molecular weight hindered secondary amine light stabilizer b)ii) is a mixture of esters of 2,2,6,6-tetra-methyl-4-piperidinol and one or more fatty acids, the ultraviolet synergist b)iii) is n-hexadecyl 3,5-di-t-butyl-4-hydroxybenzoate, the ultraviolet absorber b)iv) is 2-(2′-hydroxy-3′-t-butyl-5′-methylphenyl)-5-chlorobenzotriazole, the phenolic antioxidant c)i) is tetrakis[methylene-3(3′,5′-di-t-butyl-4-hydroxyphenyl)propionate] methane, and the phosphite additive c)ii) is tris (2,4-di-t-butylphenyl) phosphite.
  16. 16 . The photovoltaic element of claim 15 , wherein the polypropylene composition further comprises calcium stearate.
  17. 17 . The photovoltaic element of claim 14 , wherein the amount of said high molecular weight hindered tertiary amine light stabilizer b)i) is between 0.15 to 0.3 wt. %, based on the total weight of the polypropylene composition, the amount of said low molecular weight hindered secondary amine light stabilizer b)ii) is between 0.2 and 0.6 wt. %, based on the total weight of the polypropylene composition, the amount of said UV synergist b)iii) is between 0.2 and 0.4 wt. %, based on the total weight of the polypropylene composition, and the amount of said UV absorber b)iv) is between 0.1 and 0.2 wt. %, based on the total weight of the polypropylene composition.
  18. 18 . The photovoltaic element of claim 14 , wherein the mixture of antioxidant additives c) is present in an amount of between 0.05 and 1.0 wt. %, based on the total weight of the polypropylene composition.
  19. 19 . The photovoltaic element of claim 14 , wherein a weight ratio of b)i) to b)ii) to b)iii) to b)iv) is about 2:4:2:1.
  20. 20 . The photovoltaic element of claim 14 , wherein a weight ratio of c)i) to c)ii) is about 1:2.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a National Stage application of PCT/EP2019/068673, filed Jul. 11, 2019, which claims the benefit of European Application No. 18183191.8, filed Jul. 12, 2018, both of which are incorporated by reference in their entirety herein. TECHNICAL FIELD The present invention relates to a photovoltaic element, comprising a front layer, a back layer, and a plurality of photovoltaic cells, which photovoltaic cells are present between the front layer and back layer, wherein the front layer consists of a polypropylene composition. The invention also relates to a polypropylene composition and to the use thereof as front layer. BACKGROUND The present teachings relate to a photovoltaic element having a plurality of electrically interconnected photovoltaic, or, solar, cells placed in between a front layer and a back layer. Polypropylene resins can deteriorate by heath, light and/or oxygen. UV degradation of polypropylene leads to a decline in mechanical properties concomitant with appearance changes (e.g. color, gloss) as well as transmittance. In particular the mechanical strength can be decreased and the polypropylene material can become coloured. In order to prevent such deterioration of a polypropylene composition, there have been proposed a number of additives, used either alone or in various combinations. For polypropylene random (PP random) building and construction applications visual and mechanical changes are playing an important role. Additionally it is important not to have a significant loss in transmittance due to degradation of the material. Phenolic antioxidant (PAO) additives are widely employed to protect polypropylene random (PP random) against thermo-oxidative degradation during processing and in service conditions. Even though phenolic antioxidants offer good stabilisation of polypropylene, most phenolic antioxidants exhibit the disadvantage of yellowing due to their oxidation to coloured quinonoid compounds by air or NOx gases. Furthermore, the phenolic antioxidants often exert only a limited effect when employed alone. Therefore phenolic antioxidants have been used in combination with other compounds. For example, phenolic antioxidants have been used in combination with phosphites which are known to enhance the effectiveness of the phenolic antioxidants due to complementary and synergistic mechanisms of action (e.g. decomposition of hydroperoxides formed in the polymer at high temperature and in the presence of oxygen). Phenolic antioxidants have also been combined with various light stabilisers in order to achieve a high weather resistance. Examples of light stabilisers include benzophenone, benzotriazole and triazine type ultraviolet radiation absorbers, hindered hydroxy-benzoates and hindered amine compounds. In particular, the application of hindered amine light stabilisers (HALS) has been more and more increased since they are non-colouring, exert a high photostabilising effect and also can improve the heat resistance. However, providing adequate protection to polymer systems exposed to both severe ultraviolet (UV) radiation and high heat in service conditions still remains a challenge. For instance, applications such as building and construction, are particularly demanding and require high performing stabilising formulations to fulfil increased requirements in these applications. SUMMARY It is an object of the present invention to provide an improved polypropylene material for use as front layer in a photovoltaic module. A further object of the invention is to provide a photovoltaic element which can be manufactured in an efficient manner at low costs, and which can be recycled in an efficient manner, to a large degree. It is a further object of the present invention to provide a polypropylene composition having increased UV stability and good transparency. In a first aspect, the teaching relates to a photovoltaic element, comprising a front layer, a back layer, and a plurality of photovoltaic cells, which photovoltaic cells are present between the front layer and back layer, wherein the front layer consists of a polypropylene composition, comprising: a) a random polypropylene resin;b) a mixture of light stabilizing additives; said mixture comprising: i) a high molecular weight hindered tertiary amine light stabilizer (t-HM-HALS) having a weight average molecular weight of at least 1600 g/mol;ii) a low molecular weight hindered secondary amine light stabilizer (s-LM-HALS) having a weight average molecular weight of below 1000 g/mol;iii) an ultraviolet synergist, being a n-alkyl-3,5-dialkylated 4-hydroxybenzoate;iv) an ultraviolet absorber, being a hydroxybenzotriazole compound or a hydroxyl benzophenone compound or a mixture thereof; c) a mixture of antioxidant additives; said mixture comprising: i) a phenolic antioxidant; and ii) a phosphite additive. The invention also relates to a composition comprising, a) a ra