Polypropylene-based layer element having balanced mechanical and stress-whitening properties

Abstract

A layer element (LE) comprising one or more layers, wherein at least one layer (L) comprises a polypropylene composition (PC) comprising: a) from 50.0 to 97.0 wt.-%, of a HECO comprising: wherein the HECO has an MFR2 of 0.5 to 20.0 g / 10 min and a C2(SF) of 10.0 to 45.0 wt.-%; b) from 1.0 to 12.0 wt.-% of talc (T); c) from 2.0 to 20.0 wt.-% of an ethylene / C4-C10 alpha olefin copolymer (EC); d) optionally, from 0.0 to 25.0 wt.-% of a propylene homopolymer (h-PP) having an MFR2 of 0.1 to 5.0 g / 10 min; e) optionally, from 0.00 to 0.06 wt.-% of one or more white pigments (P); and f) optionally, from 0.0 to 5.0 wt.-% of one or more further additives (A).

Description

[0001] Polypropylene-based layer element having balanced mechanical and stresswhitening properties

[0002] Field of the Invention

[0003] The present invention is directed to a layer element comprising one or more layers, wherein at least one layer comprises a polypropylene composition comprising a heterophasic propylene-ethylene copolymer, talc, an ethylene / C4-Cio alpha olefin copolymer, optionally a propylene homopolymer, optionally one or more white pigments, and optionally one or more further additives, as well as to a photovoltaic module comprising said layer element as the protective back layer element.

[0004] Background to the Invention

[0005] Photovoltaic modules, also known as solar cell modules, produce electricity from light and are used in various kind of applications as well known in the field. The type of the photovoltaic module can vary. The modules have typically a multilayer structure, i.e. several different layer elements which have different functions. The layer elements of the photovoltaic module can vary with respect to layer materials and layer structure. The final photovoltaic module can be rigid or flexible.

[0006] The rigid photovoltaic module can for example contain a rigid protective front layer element, such as a glass element, front encapsulation layer element, a photovoltaic element, rear encapsulation layer element, a protective back layer element, which is also called a backsheet layer element and which can be rigid or flexible, as well as, optionally, e.g. an aluminium frame. In flexible modules all the above elements are flexible, whereby the protective front layer element can be e.g. a fluorinated layer made from polyvinylfluoride (PVF) or polyvinylidenefluoride (PVDF) polymer, and the backsheet layer element is typically a polymeric layer element. The above exemplified layer elements can be monolayer or multilayer elements, with multilayer elements containing individual layers of PVF, PVDF, PET, PA, PP all routinely employed. Moreover, there may be adhesive layer(s) between the layers of an element or between the different layer elements, as well as coatings on individual layers. It is common to have multilayer elements that combined individual layers having different types of polymer (e.g. a PET layer combined with a PV(D)F layer). The backsheet layer element may contain one or more pigmented layers. The backsheet layer element functions typically as an insulation element. However, also photovoltaic modules with conductive backsheet layer element exist, depending on the type of the photovoltaic module. All said terms have a well-known meaning in the art.

[0007] WO 2017 / 071847 Al describes polypropylene compositions suitable for white three-layer backsheet layer elements. Whilst these backsheet layer elements have excellent stress cracking resistance and dimensional stability (especially co-efficient of linear thermal expansion, CLTE), improvements can be made in terms of stress whitening properties. Furthermore, the high amounts of filler / pigment in the backsheet layer elements of WO 2017 / 071847 make said backsheet layer elements unsuitable for use in bifacial photovoltaic modules, wherein light enters the module from both the front and rear face.

[0008] As such, there remains a need for backsheet layer elements having well balanced mechanical and optical properties (enabling transmission of light from the rear side of the module), and additionally good visual appearance, especially a low sensitivity to the appearance of visual defects, such as stress whitening during transport and handling, which is suitable for use in bifacial photovoltaic modules. When compared with typical backsheet layers that comprise layers formed from very different polymers (e.g. PA layer with PP layer), it is a further target to achieve these well balance properties without having to combine layers having different polymer types, i.e. the layers would all be predominantly the same polymer type, for example polypropylene or polypropylene-based compositions. It is also desirable that a multilayer element can be produced in a single processing (e.g. co-extrusion) step.

[0009] Summary of the Invention

[0010] The present invention is thus based on the finding that by blending a heterophasic propyleneethylene copolymer with talc, an ethylene / C4-Cio alpha olefin copolymer, optionally a propylene homopolymer, optionally one or more white pigments, and optionally one or more further additives, polypropylene compositions having particularly beneficial balance of mechanical properties and stress whitening resistance. In a first aspect, the present invention is directed to a layer element (LE) comprising one or more layers, wherein at least one layer (L) comprises a polypropylene composition (PC) comprising: a) from 50.0 to 97.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of a heterophasic propylene-ethylene copolymer (HECO), comprising: i) a crystalline matrix (M) being a propylene homopolymer; and ii) an amorphous propylene-ethylene elastomer (E) that is dispersed in said crystalline matrix (M), wherein the heterophasic propylene-ethylene copolymer (HECO) has a melt flow rate (MFR2), determined according to ISO 1133 at 230 °C and 2.16 kg, in the range from 0.5 to 20.0 g / 10 min and a soluble fraction that has an ethylene content (C2(SF)), determined by CRYSTEX QC analysis, in the range from 10.0 to 45.0 wt.- 0 / / o, . b) from 1.0 to 12.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of talc (T); c) from 2.0 to 20.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of an ethylene / C4-Cio alpha olefin copolymer (EC); d) optionally, from 0.0 to 25.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of a propylene homopolymer (h-PP) having a melt flow rate (MFR2), determined according to ISO 1133 at 230 °C and 2. 16 kg, in the range from 0.1 to 5.0 g / 10 min; e) optionally, from 0.00 to 0.06 wt.-%, relative to the total weight of the polypropylene composition (PC), of one or more white pigments (P); and f) optionally, from 0.0 to 5.0 wt.-% of one or more further additives (A).

[0011] In a second aspect, the present invention is directed to a photovoltaic (PV) module comprising, in the given order, a protective front layer element (1), a front encapsulation layer element (2), a photovoltaic element (3), a rear encapsulation layer element (4) and a protective back layer element (5), wherein the protective back layer element (5) consists of the layer element (LE) of the first aspect, wherein the protective back layer element (5) has a total luminous transmittance, determined according to ASTM D1003, in the range from 73 to 100%.

[0012] Definitions

[0013] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the invention pertains. Although, any methods and materials similar or equivalent to those described herein can be used in practice for testing of the present invention, the preferred materials and methods are described herein. In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below.

[0014] Unless clearly indicated otherwise, use of the terms “a”, “an”, and the like refers to one or more.

[0015] In the following amounts are given in % by weight (wt.-%) unless it is stated otherwise.

[0016] A propylene homopolymer is a polymer that essentially consists of propylene monomer units. Due to impurities especially during commercial polymerization processes, a propylene homopolymer can comprise up to 0.1 mol% comonomer units, preferably up to 0.05 mol% comonomer units and most preferably up to 0.01 mol% comonomer units.

[0017] A propylene random copolymer is a copolymer of propylene monomer units and comonomer units, preferably selected from ethylene and C4-C8 alpha-olefins, in which the comonomer units are distributed randomly over the polymeric chain. The propylene random copolymer can comprise comonomer units from one or more comonomers different in their amounts of carbon atoms.

[0018] Heterophasic propylene copolymers typically comprise: a) a crystalline propylene homopolymer or copolymer matrix (M); and b) an elastomeric rubber, preferably a propylene-ethylene copolymer (E). In case of a random heterophasic propylene copolymer, said crystalline matrix phase is a random copolymer of propylene and at least one alpha-olefin comonomer.

[0019] The elastomeric phase can be a propylene copolymer with a high amount of comonomer that is not randomly distributed in the polymer chain but is distributed in a comonomer-rich block structure and a propylene-rich block structure. A heterophasic polypropylene usually differentiates from a monophasic propylene copolymer in that it shows two distinct glass transition temperatures Tg which are attributed to the matrix phase and the elastomeric phase.

[0020] The present invention will now be described in more detail.

[0021] Detailed Description

[0022] In a first aspect, the present invention is directed to a layer element (LE) comprising one or more layers, wherein at least one layer (L) comprises a polypropylene composition (PC) comprising: a) a heterophasic propylene-ethylene copolymer (HECO); b) talc (T); c) an ethylene / C4-Cio alpha olefin copolymer (EC); d) optionally, a propylene homopolymer (h-PP); e) optionally, one or more white pigments (P); and f) optionally, one or more further additives (A).

[0023] Heterophasic propylene-ethylene copolymer (HECO)

[0024] One essential component of the polypropylene composition (PC) is the heterophasic propylene-ethylene copolymer (HECO).

[0025] The heterophasic propylene-ethylene copolymer (HECO) is provided in an amount in the range from 50.0 to 97.0 wt.-%, more preferably in the range from 55.0 to 96.5 wt.-%, most preferably in the range from 60.0 to 95.0 wt.-%, relative to the total weight of the polypropylene composition (PC).

[0026] The heterophasic propylene-ethylene copolymer (HECO) has a melt flow rate (MFR2), determined according to ISO 1133 at 230 °C and 2. 16 kg, in the range from 0.5 to 20.0 g / 10 min, more preferably in the range from 1.0 to 10.0 g / 10 min, most preferably in the range from 2.0 to 5.0 g / 10 min.

[0027] The heterophasic propylene-ethylene copolymer (HECO) may be characterized according to the CRYSTEX QC method using trichlorobenzene (TCB) as a solvent. This method is described below in the determination methods section. The crystalline fraction (CF) contains for the most part the matrix phase and only a small part of the elastomeric phase and the soluble fraction (SF) contains for the most part the elastomeric phase and only a small part of the matrix phase. In some cases, this method results in more useful data (than for example xylene cold soluble-based methods), since the crystalline fraction (CF) and the soluble fraction (SF) more accurately correspond to the matrix and elastomeric phases respectively. Due to the differences in the separation methods of xylene extraction and CRYSTEX QC method the properties of XCS / XCI fractions on the one hand and crystalline / soluble (CF / SF) fractions on the other hand are not exactly the same, meaning that the amounts of matrix phase and elastomeric phase can differ as well as the properties.

[0028] The heterophasic propylene-ethylene copolymer (HECO) preferably has an ethylene content (C2(total)), determined by CRYSTEX QC analysis, in the range from 0.5 to 20.0 wt.-%, more preferably in the range from 1.0 to 14.0 wt.-%, most preferably in the range from 2.0 to 9.0 wt.-%.

[0029] The heterophasic propylene-ethylene copolymer (HECO) preferably has a soluble fraction (SF) content, determined by CRYSTEX QC analysis, in the range from 5.0 to 35.0 wt.-%, more preferably in the range from 7.0 to 30.0 wt.-%, most preferably in the range from 9.0 to 20.0 wt.-%. The heterophasic propylene-ethylene copolymer (HECO) preferably has an ethylene content of the soluble fraction (C2(SF)), determined by CRYSTEX QC analysis, in the range from 10.0 to

[0030] 45.0 wt.-%, more preferably in the range from 15.0 to 40.0 wt.-%, most preferably in the range from 20.0 to 35.0 wt.-%.

[0031] The heterophasic propylene-ethylene copolymer (HECO) preferably has an intrinsic viscosity of the soluble fraction (iV(SF)), determined by CRYSTEX QC analysis, in the range from 1.00 to 4.00 dL / g, more preferably in the range from 1.20 to 3.00 dL / g, most preferably in the range from 1.50 to 2.50 dL / g.

[0032] The heterophasic propylene-ethylene copolymer (HECO) preferably has a crystalline fraction (CF) content, determined by CRYSTEX QC analysis, in the range from 65.0 to 95.0 wt.-%, more preferably in the range from 70.0 to 93.0 wt.-%, most preferably in the range from 80.0 to 91.0 wt.-%.

[0033] The heterophasic propylene-ethylene copolymer (HECO) preferably has an ethylene content of the crystalline fraction (C2(CF)), determined by CRYSTEX QC analysis, in the range from 0.5 to 15.0 wt.-%, more preferably in the range from 0.7 to 7.0 wt.-%, most preferably in the range from 1.0 to 4.0 wt.-%.

[0034] The heterophasic propylene-ethylene copolymer (HECO) preferably has an intrinsic viscosity of the crystalline fraction (iV(CF)), determined by CRYSTEX QC analysis, in the range from 1.20 to 5.00 dL / g, more preferably in the range from 1.50 to 3.50 dL / g, most preferably in the range from 2.00 to 3.00 dL / g.

[0035] The heterophasic propylene-ethylene copolymer (HECO) preferably has an intrinsic viscosity (iV(total)), determined by CRYSTEX QC analysis, in the range from 1.20 to 5.00 dL / g, more preferably in the range from 1.50 to 3.50 dL / g, most preferably in the range from 2.00 to 3.00 dL / g. The heterophasic propylene-ethylene copolymer (HECO) preferably has a melting temperature (Tm), determined by differential scanning calorimetry (DSC), in the range from 160 to 172 °C, more preferably in the range from 163 to 171 °C, most preferably in the range from 165 to 170 °C.

[0036] The heterophasic propylene-ethylene copolymer (HECO) comprises: i) a crystalline matrix (M) being a propylene homopolymer; and ii) an amorphous propylene-ethylene elastomer (E);

[0037] The crystalline matrix component (M) preferably is free from 2,1 -regiodefects as determined by quantitative13C-NMR spectroscopy. The absence of 2,1 -regiodefects is typical for polypropylenes polymerized using Ziegler-Natta catalysts.

[0038] Preferably, the heterophasic propylene-ethylene copolymer (HECO) has been polymerized in the presence of a Ziegler-Natta catalyst.

[0039] Talc

[0040] Another essential component of the polypropylene composition (PC) is the talc (T).

[0041] The talc (T) is provided in an amount in the range from 1.0 to 12.0 wt.-%, more preferably in the range from 1.5 to 10.0 wt.-%, most preferably in the range from 2.0 to 8.0 wt.-%, relative to the total weight of the polypropylene composition (PC).

[0042] The talc (T) preferably has a median diameter (dso), determined according to ISO 13320-1 (laser), in the range from 1.5 to 10.0 pm, more preferably in the range from 2.0 to 9.0 pm, most preferably in the range from 3.0 to 8.0 pm.

[0043] The talc (T) preferably has a top cut diameter (d^). determined according to ISO 13320-1 (laser), in the range from 4.0 to 25.0 pm, more preferably in the range from 6.0 to 20.0 pm, most preferably in the range from 8.0 to 18.0 pm. The talc (T) preferably has a median diameter (dso), determined according to ISO 13317-3 (sedigraph), in the range from 1.0 to 5.0 pm, more preferably in the range from 1.1 to 4.5 pm, most preferably in the range from 1.2 to 4.0 pm.

[0044] The talc (T) preferably has a top cut diameter (do ). determined according to ISO 13317-3 (sedigraph), in the range from 2.0 to 15.0 pm, more preferably in the range from 2.5 to 12.0 pm, most preferably in the range from 3.0 to 10.0 pm.

[0045] The talc (T) preferably has a loss on ignition at 1050 °C, determined according to DIN 51081, of 8.0% or less, more preferably of 7.0% or less.

[0046] The talc (T) preferably has a whiteness, defined by the CIELAB L* value, of greater than or equal to 95.0, more preferably greater than or equal to 96.0, most preferably greater than or equal to 97.0.

[0047] Ethylene / C4-Cio alpha olefin copolymer (EC)

[0048] Another essential component of the polypropylene composition (PC) is the ethylene / C4-Cio alpha olefin copolymer (EC).

[0049] The ethylene / C4-Cio alpha olefin copolymer (EC) is an elastomeric copolymer containing ethylene monomers and comonomers selected from C4 to C10 alpha olefins.

[0050] Preferably, the ethylene / C4-Cio alpha olefin copolymer (EC) is a copolymer of ethylene and a comonomer selected from C4-C8 alpha olefins, more preferably selected from Ce-Cs alpha olefins, yet more preferably selected from 1 -hexene and 1 -octene, most preferably the ethylene / C4-Cio alpha olefin copolymer (EC) is a copolymer of ethylene and 1-octene.

[0051] The ethylene / C4-Cio alpha olefin copolymer (EC) is provided in an amount in the range from 2.0 to 20.0 wt.-%, more preferably in the range from 2.0 to 18.0 wt.-%, most preferably in the range from 3.0 to 15.0 wt.-%, relative to the total weight of the polypropylene composition (PC).

[0052] The ethylene / C4-Cio alpha olefin copolymer (EC) preferably has a melt flow rate (MFR2), determined according to ISO 1133 at 190 °C and 2.16 kg, in the range from 0.1 to 20 g / 10 min, more preferably in the range from 0.3 to 15 g / 10 min, most preferably in the range from 0.5 to 10 g / 10 min.

[0053] The ethylene / C4-Cio alpha olefin copolymer (EC) preferably has a density, determined according to ISO 1183-187, in the range from 850 to 900 kg / m3, more preferably in the range from 855 to 890 kg / m3, most preferably in the range from 858 to 885 kg / m3.

[0054] Suitable commercially available ethylene / C4-Cio alpha olefin copolymers (EC) include plastomer products under tradename QUEO™, supplied by Borealis, or Engage™ supplied by ExxonMobil, Lucene supplied by LG, or Tafimer supplied by Mitsui.

[0055] Propylene homopolymer (h-PP)

[0056] An optional component of the polypropylene composition (PC) is the propylene homopolymer (h-PP).

[0057] If present, the propylene homopolymer (h-PP) is provided in an amount in the range from 0.0 to 25.0 wt.-%, more preferably in the range from 5.0 to 20.0 wt.-%, most preferably in the range from 10.0 to 17.0 wt.-%, relative to the total weight of the polypropylene composition (PC).

[0058] The propylene homopolymer (h-PP) has a melt flow rate (MFR2), determined according to ISO 1133 at 230 °C and 2.16 kg, in the range from 0. 1 to 5.0 g / 10 min, more preferably in the range from 0.3 to 3.0 g / 10 min, most preferably in the range from 0.4 to 1.0 g / 10 min. The propylene homopolymer (h-PP) preferably has a melting temperature (Tm), determined by differential scanning calorimetry (DSC), in the range from 156 to 170 °C, more preferably in the range from 157 to 168 °C, most preferably in the range from 158 to 164 °C.

[0059] The propylene homopolymer (h-PP) preferably has a pentad isotacticity (mmmm) as determined by quantitative13C-NMR spectroscopy, in the range from 70 to 99%, more preferably in the range from 85 to 95%.

[0060] The propylene homopolymer (h-PP) preferably is free from 2,1 -regiodefects as determined by quantitative13C-NMR spectroscopy. The absence of 2,1 -regiodefects is typical for polypropylenes polymerized using Ziegler-Natta catalysts.

[0061] Preferably, the propylene homopolymer (h-PP) has been polymerized in the presence of a Ziegler-Natta catalyst.

[0062] One or more white pigments (P)

[0063] A further optional component of the polypropylene composition (PC) is one or more white pigments (P).

[0064] If present, the one or more white pigments (P) are provided in an amount in the range from 0.00 to 0.06 wt.-%, relative to the total weight of the polypropylene composition (PC).

[0065] In the broadest sense, the one or more white pigments may be any white pigments known in the art.

[0066] It is preferred that the one or more white pigments (P) are selected from inorganic white pigments.

[0067] Even more preferably, at least one of the one or more white pigments (P) is titanium dioxide. It is particularly preferred that only one white pigment is present, wherein this white pigment is titanium dioxide.

[0068] The titanium dioxide is preferably in a form of rutile. Rutile is a mineral that is primarily based on titanium dioxide and has a tetragonal unit cell structure as well known in the art.

[0069] Since very small amounts of the one or more white pigments (P) are present in the polypropylene composition (PC), it is generally advisable to add the one or more white pigments (P) via a pigment-containing masterbatch. Such a pigment-containing masterbatch comprises a carrier polymer, such as a propylene homopolymer or a propylene copolymer, the one or more white pigments (P) and optional further additives, such as the further additives (A) discussed above. If the one or more white pigments (P) is added via the use of a pigment-containing masterbatch, the amount of the masterbatch carrier polymer is not counted towards the total amount of one or more white pigments (P). In the embodiment provided above wherein the polypropylene composition (PC) consists of the heterophasic propylene-ethylene copolymer (HECO), talc (T), the ethylene / C4-Cio alpha olefin copolymer (EC), the optional propylene homopolymer (h-PP), one or more white pigments (P) and one or more further additives (A), the masterbatch carrier polymer is counted as part of the one or more further additives (A).

[0070] One or more further additives (A)

[0071] Another optional component of the polypropylene composition (PC) is one or more further additives (A).

[0072] If present, the one or more further additives (A) are provided in an amount in the range from 0.0 to 5.0 wt.-%, relative to the total weight of the polypropylene composition (PC).

[0073] The selection of suitable additives for the polypropylene composition (PC) is within the general knowledge of the person skilled in the art. For example, the one or more further additives (A) may be selected from the group consisting of antioxidants, stabilizers, fdlers, nucleating agents, and antistatic agents.

[0074] Such additives are generally commercially available and are described, for example, in "Plastic Additives Handbook", pages 871 to 873, 5th edition, 2001 of Hans Zweifel.

[0075] It is understood that the content of additives (A), given with respect to the total weight of the polypropylene composition (PC), includes any carrier polymers used to introduce the additives to said polypropylene composition (PC), i.e. masterbatch carrier polymers. An example of such a carrier polymer would be a polypropylene homopolymer in the form of powder.

[0076] Any white pigments present in the polypropylene composition do not count towards the content of one or more further additives, rather these are present as the one or more white pigments (P), as described above.

[0077] Polypropylene composition (PC)

[0078] The polypropylene composition (PC) of the first aspect comprises, more preferably consists of: a) from 50.0 to 97.0 wt.-%, more preferably 55.0 to 96.5 wt.-%, most preferably 60.0 to 95.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 1.0 to 12.0 wt.-%, more preferably 1.5 to 10.0 wt.-%, most preferably 2.0 to 8.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); c) from 2.0 to 20.0 wt.-%, more preferably 2.0 to 18.0 wt.-%, most preferably 3.0 to 15.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC); d) optionally, from 0.0 to 25.0 wt.-%, more preferably 5.0 to 20.0 wt.-%, most preferably 10.0 to 17.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the propylene homopolymer (h-PP); e) optionally, from 0.00 to 0.06 wt.-%, relative to the total weight of the polypropylene composition (PC), of the one or more white pigments (P); and f) optionally, from 0.0 to 5.0 wt.-% of the one or more further additives (A).

[0079] In the broadest sense, the polypropylene composition (PC) comprises: a) from 50.0 to 97.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 1.0 to 12.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); c) from 2.0 to 20.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC); d) optionally, from 0.0 to 25.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the propylene homopolymer (h-PP); e) optionally, from 0.00 to 0.06 wt.-%, relative to the total weight of the polypropylene composition (PC), of the one or more white pigments (P); and f) optionally, from 0.0 to 5.0 wt.-% of the one or more further additives (A).

[0080] In a preferred embodiment, the polypropylene composition (PC) comprises, more preferably consists of: a) from 55.0 to 96.5 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 1.5 to 10.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); c) from 2.0 to 18.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC); d) optionally, from 5.0 to 20.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the propylene homopolymer (h-PP); e) optionally, from 0.00 to 0.06 wt.-%, relative to the total weight of the polypropylene composition (PC), of the one or more white pigments (P); and f) optionally, from 0.0 to 5.0 wt.-% of the one or more further additives (A). In a further preferred embodiment, the polypropylene composition (PC) comprises, more preferably consists of: a) from 60.0 to 95.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 2.0 to 8.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); c) from 3.0 to 15.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC); d) optionally, from 10.0 to 17.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the propylene homopolymer (h-PP); e) optionally, from 0.00 to 0.06 wt.-%, relative to the total weight of the polypropylene composition (PC), of the one or more white pigments (P); and f) optionally, from 0.0 to 5.0 wt.-% of the one or more further additives (A).

[0081] In one embodiment, the polypropylene composition (PC) comprises, more preferably consists of: a) from 68.0 to 97.0 wt.-%, more preferably 72.0 to 96.50 wt.-%, most preferably 77.0 to 95.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 1.0 to 12.0 wt.-%, more preferably 1.5 to 10.0 wt.-%, most preferably 2.0 to 8.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); and c) from 2.0 to 20.0 wt.-%, more preferably 2.0 to 18.0 wt.-%, most preferably 3.0 to 15.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC).

[0082] In another embodiment, the polypropylene composition (PC) comprises, more preferably consists of: a) from 50.0 to 97.0 wt.-%, more preferably 55.0 to 91.5 wt.-%, most preferably 60.0 to 85.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 1.0 to 12.0 wt.-%, more preferably 1.5 to 10.0 wt.-%, most preferably 2.0 to 8.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); c) from 2.0 to 20.0 wt.-%, more preferably 2.0 to 18.0 wt.-%, most preferably 3.0 to 15.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC); and d) from 0.0 to 25.0 wt.-%, more preferably 5.0 to 20.0 wt.-%, most preferably 10.0 to 17.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the propylene homopolymer (h-PP).

[0083] In yet another embodiment, the polypropylene composition (PC) comprises, more preferably consists of: a) from 68.0 to 97.0 wt.-%, more preferably 72.0 to 96.5 wt.-%, most preferably 77.0 to 95.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 1.0 to 12.0 wt.-%, more preferably 1.5 to 10.0 wt.-%, most preferably 2.0 to 8.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); c) from 2.0 to 20.0 wt.-%, more preferably 2.0 to 18.0 wt.-%, most preferably 3.0 to 15.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC); and d) from 0.00 to 0.06 wt.-%, relative to the total weight of the polypropylene composition (PC), of the one or more white pigments (P).

[0084] In a further embodiment, the polypropylene composition (PC) comprises, more preferably consists of: a) from 63.0 to 97.0 wt.-%, more preferably 67.0 to 96.5 wt.-%, most preferably 72.0 to 95.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 1.0 to 12.0 wt.-%, more preferably 1.5 to 10.0 wt.-%, most preferably 2.0 to 8.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); c) from 2.0 to 20.0 wt.-%, more preferably 2.0 to 18.0 wt.-%, most preferably 3.0 to 15.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC); and d) from 0.0 to 5.0 wt.-% of the one or more further additives (A).

[0085] In yet a further embodiment, the polypropylene composition (PC) comprises, more preferably consists of: a) from 50.0 to 97.0 wt.-%, more preferably 55.0 to 91.5 wt.-%, most preferably 60.0 to 85.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 1.0 to 12.0 wt.-%, more preferably 1.5 to 10.0 wt.-%, most preferably 2.0 to 8.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); c) from 2.0 to 20.0 wt.-%, more preferably 2.0 to 18.0 wt.-%, most preferably 3.0 to 15.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC); d) from 0.0 to 25.0 wt.-%, more preferably 5.0 to 20.0 wt.-%, most preferably 10.0 to 17.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the propylene homopolymer (h-PP); and e) from 0.00 to 0.06 wt.-%, relative to the total weight of the polypropylene composition (PC), of the one or more white pigments (P).

[0086] In another embodiment, the polypropylene composition (PC) comprises, more preferably consists of: a) from 50.0 to 97.0 wt.-%, more preferably 55.0 to 91.5 wt.-%, most preferably 60.0 to 85.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 1.0 to 12.0 wt.-%, more preferably 1.5 to 10.0 wt.-%, most preferably 2.0 to 8.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); c) from 2.0 to 20.0 wt.-%, more preferably 2.0 to 18.0 wt.-%, most preferably 3.0 to 15.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC); d) from 0.0 to 25.0 wt.-%, more preferably 5.0 to 20.0 wt.-%, most preferably 10.0 to 17.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the propylene homopolymer (h-PP); and e) from 0.0 to 5.0 wt.-% of the one or more further additives (A).

[0087] In yet another embodiment, the polypropylene composition (PC) comprises, more preferably consists of: a) from 63.0 to 97.0 wt.-%, more preferably 70.0 to 96.5 wt.-%, most preferably 74.0 to 95.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 1.0 to 12.0 wt.-%, more preferably 1.5 to 10.0 wt.-%, most preferably 2.0 to 8.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); c) from 2.0 to 20.0 wt.-%, more preferably 2.0 to 18.0 wt.-%, most preferably 3.0 to 15.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC); d) from 0.00 to 0.06 wt.-%, relative to the total weight of the polypropylene composition (PC), of the one or more white pigments (P); and e) from 0.0 to 5.0 wt.-% of the one or more further additives (A).

[0088] In a final embodiment, the polypropylene composition (PC) comprises, more preferably consists of: a) from 50.0 to 97.0 wt.-%, more preferably 55.0 to 91.5 wt.-%, most preferably 60.0 to 85.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 1.0 to 12.0 wt.-%, more preferably 1.5 to 10.0 wt.-%, most preferably 2.0 to 8.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); c) from 2.0 to 20.0 wt.-%, more preferably 2.0 to 18.0 wt.-%, most preferably 3.0 to 15.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC); d) from 0.0 to 25.0 wt.-%, more preferably 5.0 to 20.0 wt.-%, most preferably 10.0 to 17.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the propylene homopolymer (h-PP); e) from 0.00 to 0.06 wt.-%, relative to the total weight of the polypropylene composition (PC), of the one or more white pigments (P); and f) from 0.0 to 5.0 wt.-% of the one or more further additives (A).

[0089] In all of the above embodiments, the sum of the individual contents of the heterophasic propylene-ethylene copolymer (HECO), the talc (T), the ethylene / C4-Cio alpha olefin copolymer (EC), the optional propylene homopolymer (h-PP), the optional one or more white pigments (P), the optional one or more further additives (A) preferably add up to at least 90 wt.-%, more preferably at least 95 wt.-%, yet more preferably at least 98 wt.-%. Most preferably, the polypropylene composition (PC) consists of the heterophasic propyleneethylene copolymer (HECO), the talc (T), the ethylene / C4-Cio alpha olefin copolymer (EC), the optional propylene homopolymer (h-PP), the optional one or more white pigments (P), and the optional one or more further additives (A).

[0090] The polypropylene composition (PC) preferably has a melt flow rate (MFR2), determined according to ISO 1133 at 230 °C and 2.16 kg, in the range from 0.5 to 20 g / 10 min, more preferably in the range from 1.0 to 10 g / 10 min, most preferably in the range from 2.0 to 5.0 g / 10 min.

[0091] The polypropylene composition (PC) preferably has a soluble fraction (SF) content, determined by CRYSTEX QC analysis, in the range from 10.0 to 40.0 wt.-%, more preferably in the range from 10.5 to 35.0 wt.-%, most preferably in the range from 11.0 to 30.0 wt.-%, based on the total weight of the polypropylene composition (PC).

[0092] The polypropylene composition (PC) preferably has a crystalline fraction (CF) content, determined by CRYSTEX QC analysis, in the range from 60.0 to 90.0 wt.-%, more preferably in the range from 65.0 to 89.5 wt.-%, most preferably in the range from 70.0 to 89.0 wt.-%, based on the total weight of the polypropylene composition (PC).

[0093] The polypropylene composition (PC) preferably has an ethylene content (C2(total)), determined by CRYSTEX QC analysis, in the range from 5.0 to 30.0 wt.-%, more preferably in the range from 5.0 to 25.0 wt.-%, most preferably in the range from 5.0 to 20.0 wt.-%.

[0094] The polypropylene composition (PC) preferably has an ethylene content of the soluble fraction (C2(SF)), determined by CRYSTEX QC analysis, in the range from 30.0 to 68.0 wt.-%, more preferably in the range from 32.0 to 66.0 wt.-%, most preferably in the range from 34.0 to 64.0 wt.-%.

[0095] The polypropylene composition (PC) preferably has an ethylene content of the crystalline fraction (C2(CF)), determined by CRYSTEX QC analysis, in the range from 0.6 to 8.0 wt.- %, more preferably in the range from 0.7 to 6.5 wt.-%, most preferably in the range from 0.8 to 5.5 wt.-%.

[0096] The polypropylene composition (PC) preferably has an intrinsic viscosity of the soluble fraction (iV(SF)), determined by CRYSTEX QC analysis, in the range from 1.20 to 2.60 dL / g, more preferably in the range from 1.30 to 2.40 dL / g, most preferably in the range from 1.40 to 2.20 dL / g.

[0097] The polypropylene composition (PC) preferably has an intrinsic viscosity of the crystalline fraction (iV(CF)), determined by CRYSTEX QC analysis, in the range from 1.80 to 3.20 dL / g, more preferably in the range from 2.00 to 3.00 dL / g, most preferably in the range from 2. 10 to 2.80 dL / g.

[0098] The polypropylene composition (PC) preferably has an intrinsic viscosity (iV(total)), determined by CRYSTEX QC analysis, in the range from 1.60 to 3.00 dL / g, more preferably in the range from 1.90 to 2.70 dL / g, most preferably in the range from 2.00 to 2.60 dL / g. The polypropylene composition (PC) preferably has a coefficient of linear thermal expansion (CLTE) in the machine direction, determined between +23 and +80 °C, according to ISO 11359-2 on 80* 10x4 mm3injection-moulded specimens prepared according to ISO 19069-2, of less than 120 * 10'6K-1, more preferably of less than 117 * 10'6K-1, most preferably of less than 114 * 10’6K1.

[0099] The polypropylene composition (PC) preferably has a coefficient of linear thermal expansion (CLTE) in the machine direction, determined between -30 and +80 °C, according to ISO 11359-2 on 80x 10x4 mm3injection-moulded specimens prepared according to ISO 19069-2, of less than 95 * 10'6K-1, more preferably of less than 92 * 10'6K-1, most preferably of less than 89 * 10’6K1.

[0100] The polypropylene composition (PC) preferably has a flexural modulus, determined according to ISO 178 on 80x 10x4 mm3injection-moulded specimens prepared according to ISO 19069-2, in the range from 800 to 2200 MPa, more preferably in the range from 900 to 2000 MPa, most preferably in the range from 1000 to 1900 MPa.

[0101] The polypropylene composition (PC) preferably has a tensile modulus, determined according to ISO 527-3 on a 400 pm monolayer cast film specimen in the machine direction, in the range from 800 to 2000 MPa, more preferably in the range from 900 to 1700 MPa, most preferably in the range from 1000 to 1500 MPa.

[0102] The polypropylene composition (PC) preferably has a tensile modulus, determined according to ISO 527-3 on a 400 pm monolayer cast film specimen in the transverse direction, in the range from 700 to 2000 MPa, more preferably in the range from 800 to 1700 MPa, most preferably in the range from 900 to 1400 MPa.

[0103] The polypropylene composition (PC) preferably has a stress whitening onset force in the transverse direction, determined according to the method described in the determination methods on a 400 pm monolayer cast film specimen, in the range from 35 to 100 N, more preferably in the range from 38 to 85 N, most preferably in the range from 40 to 70 N. The polypropylene composition (PC) preferably has a stress whitening onset displacement in the transverse direction, determined according to the method described in the determination methods on a 400 pm monolayer cast fdm specimen, in the range from 0.60 to 2.00 mm, more preferably in the range from 0.70 to 1.70 mm, most preferably in the range from 0.80 to 1.40 mm.

[0104] The polypropylene composition (PC) preferably has a slope of the stress whitening light curve in the transverse direction, determined according to the method described in the determination methods on a 400 pm monolayer cast fdm specimen, in the range from -7000 to -500 mV / mm, more preferably in the range from -6000 to -1000 mV / mm, most preferably in the range from -5000 to -2000 mV / mm.

[0105] The polypropylene composition (PC) preferably has a total luminous transmittance, determined according to ASTM DI 003 on a 400 pm monolayer cast fdm specimen, in the range from 73 to 100%, more preferably in the range from 75 to 100%, most preferably in the range from 77 to 100%.

[0106] The polypropylene composition (PC) preferably has a diffuse luminous transmittance, determined according to ASTM DI 003 on a 400 pm monolayer cast fdm specimen, in the range from 45 to 100%, more preferably in the range from 51 to 90%, most preferably in the range from 55 to 80%.

[0107] Layer element (LE)

[0108] In the first aspect, the present invention is directed to a layer element (LE) comprising one or more layers, wherein at least one layer (L) comprises the polypropylene composition (PC) described above.

[0109] More preferably, at least one layer (L) consists of the polypropylene composition (PC).

[0110] In the case that the layer element (LE) is a monolayer element, then this monolayer element consists of the polypropylene composition (PC). In the case that the layer element (LE) is a two-layer element, then it is preferred that one layer (L) consisting of the polypropylene composition (PC) and the other layer is different to layer (L). In this embodiment, layer (L) preferably has a thickness in the range from 70 to 99% of the total thickness of the two-layer element.

[0111] It is particularly preferred that the layer element (LE) is a three-layer element having a structure ABC, wherein preferably layer B is the layer (L) consisting of the polypropylene composition (PC). Layers A and C may also comprises or consist of polypropylene compositions having the properties given above for the polypropylene composition (PC), being either the same or different from the polypropylene composition (PC) of layer B. If layers A and C both comprises or consist of polypropylene compositions having the properties given above for the polypropylene composition (PC), then it is preferred that the polypropylene composition (PC) of layer B has at least as high, preferably higher, content of talc (T) than the polypropylene compositions of layers A and C.

[0112] In the three-layer embodiments, the thicknesses of layers A and C are independently in the range from 1 / 10 to 1 / 3 of the total thickness of the three-layer element and the thickness of layer B is in the range from 1 / 3 to 4 / 5 of the total thickness of the three-layer element.

[0113] Alternatively, the layer element (LE) may be a five-layer element having, for example, structure A / X / B / X / C or A / B1 / B2 / B3 / C, wherein A, B, and C are as defined for the three- layer element and layers Bl, B2, and B3 are each individually as defined for layer B of the three-layer element and may be the same or different. The identity of layer X is not particularly limited.

[0114] In each of the multilayer element embodiments discussed above, it is preferred that at least 50% of the thickness of the multilayer film is formed of layers consisting of polypropylene compositions (PC), wherein each instance of the polypropylene composition (PC) may be the same or different. Furthermore, if the layer element (LE) is a multilayer element, then it is preferred that the multilayer element is a co-extruded multilayer element (in contrast to a laminated multilayer element). The co-extrusion method may be any co-extrusion method known to the person skilled in the art, but is more preferably blown fdm co-extrusion or cast fdm co-extrusion, most preferably cast fdm co-extrusion.

[0115] The layer element (LE) preferably has a thickness in the range from 100 to 2000 pm, more preferably in the range from 125 to 1500 pm, most preferably in the range from 150 to 1000 pm.

[0116] The layer element (LE) preferably has a total luminous transmittance, determined according to ASTM D1003, in the range from 73 to 100%, more preferably in the range from 75 to 100%, most preferably in the range from 77 to 100%.

[0117] The layer element (LE) preferably has a diffuse luminous transmittance, determined according to ASTM D1003, in the range from 45 to 100%, more preferably in the range from 51 to 90%, most preferably in the range from 55 to 80%.

[0118] The layer element (LE) preferably has a stress whitening onset force in the transverse direction, determined according to the method described in the determination methods, in the range from 35 to 100 N, more preferably in the range from 38 to 85 N, most preferably in the range from 40 to 70 N.

[0119] The layer element (LE) preferably has a stress whitening onset displacement in the transverse direction, determined according to the method described in the determination methods, in the range from 0.60 to 2.00 mm, more preferably in the range from 0.70 to 1.70 mm, most preferably in the range from 0.80 to 1.40 mm.

[0120] The layer element (LE) preferably has a slope of the stress whitening light curve in the transverse direction, determined according to the method described in the determination methods , in the range from -7000 to -500 mV / mm, more preferably in the range from -6000 to -1000 mV / mm, most preferably in the range from -5000 to -2000 mV / mm. The layer element (LE) preferably has a tensile modulus in the machine direction, determined according to ISO 527-3, in the range from 800 to 2000 MPa, more preferably in the range from 900 to 1700 MPa, most preferably in the range from 1000 to 1500 MPa.

[0121] The layer element (LE) preferably has a tensile modulus in the transverse direction, determined according to ISO 527-3, in the range from 700 to 2000 MPa, more preferably in the range from 800 to 1700 MPa, most preferably in the range from 900 to 1400 MPa.

[0122] The skilled person would be aware that the machine direction and transverse direction refer to the orientation during production of the fdm. The skilled person would also be aware that, in the context of the present invention, the transverse direction is also the direction with the lowest tensile modulus, allowing a measurement to be taken in the transverse direction, even if the production conditions are unknown.

[0123] In one particularly preferred embodiment, the layer element (LE) is a three-layer element, consisting of the following layers, in the given order: i) an adhesive layer; ii) a core layer, comprising, more preferably consisting of, the polypropylene composition (PC); and iii) a skin layer, comprising, more preferably consisting of, a further polypropylene composition (PC’) having the properties as defined for the polypropylene composition (PC) above.

[0124] Both the polypropylene composition (PC) of the core layer and the further polypropylene composition (PC’) of the skin layer have the properties / component as described for the polypropylene composition (PC), although the polypropylene composition (PC) of the core layer may be the same as or different from the polypropylene composition (PC’) of the skin layer. It is particularly preferred that the polypropylene composition (PC’) of the skin layer has a content of talc that is equal to or lower than, more preferably lower than, the polypropylene composition (PC) of the core layer.

[0125] The polypropylene compositions of the first aspect achieves a balance of mechanical properties and stress whitening resistance; however, compositions having higher amounts of talc generally have worse stress whitening resistance (although superior mechanical properties). By having an arrangement wherein the skin layer has lower levels of talc than the core layer, a higher surface stress whitening resistance can be achieved without compromising the mechanical properties of the core layer, said core layer being primarily responsible for the mechanical properties of the three-layer layer element (LE).

[0126] Additionally or alternatively, it is preferred that the adhesive layer comprises talc and optionally titanium dioxide.

[0127] The adhesive layer preferably comprises talc in an amount in the range from 0.5 to 5.0 wt.- %, more preferably in the range from 1.0 to 4.0 wt.-%, most preferably in the range from 1.5 to 3.0 wt.-%, relative to the total weight of the adhesive layer.

[0128] If the adhesive layer comprises titanium dioxide, it is preferably present in an amount in the range from 0.005 to 0.065 wt.-%, more preferably in the range from 0.010 to 0.060 wt.-%, yet more preferably in the range from 0.015 to 0.055 wt.-%, most preferably in the range from 0.020 to 0.050 wt.-%, relative to the total weight of the adhesive layer.

[0129] In the broadest sense, the polymers used for the adhesive layer may be any polymers known by the person skilled in the art to be used for this purpose.

[0130] It is preferred that the adhesive layer comprises: a) a propylene-ethylene copolymer having a melting temperature (Tm), determined by differential scanning calorimetry (DSC), in the range from 130 to 175 °C, more preferably in the range from 135 to 172 °C, most preferably in the range from 140 to 170 °C; and bl) a copolymer of ethylene and one or more C4-12 alpha olefin comonomers having a melting temperature (Tm), determined by differential scanning calorimetry (DSC), in the range from 100 to 140 °C, more preferably in the range from 105 to 130 °C, most preferably in the range from 110 to 125 °C; and / or b2) a copolymer of ethylene and one or more C4-12 alpha olefin comonomers having a melting temperature (Tm), determined by differential scanning calorimetry (DSC), in the range from 30 to 60 °C, more preferably in the range from 32 to 58 °C, most preferably in the range from 35 to 56 °C.

[0131] In this embodiment, component a) must be present and at least one of components bl) and b2) must also be present.

[0132] The propylene-ethylene copolymer of component a) is preferably a heterophasic propyleneethylene copolymer, more preferably a random-heterophasic propylene-ethylene copolymer.

[0133] Furthermore, the adhesive layer may optionally comprise a polar modified polypropylene (PMP), which is preferably a maleic anhydride-grafted polypropylene. This polar modifier polypropylene may be present in amounts of from 0.5 to 10 wt.-%, more preferably in the range from 1.0 to 8.0 wt.-%, most preferably in the range from 3.0 to 6.0 wt.-%, relative to the total weight of the adhesive layer.

[0134] Suitable compositions for the adhesive layer are described in EP 23 170 084.0 and EP 23170 090.7, which provide further details of the individual components a), bl) and b2).

[0135] Photovoltaic (PV) module

[0136] In a second aspect, the present invention is directed to a photovoltaic (PV) module comprising, in the given order, a protective front layer element (1), a front encapsulation layer element (2), a photovoltaic element (3), a rear encapsulation layer element (4) and a protective back layer element (5), wherein the protective back layer element (5) consists of the layer element (LE) of the first aspect, wherein the protective back layer element (5) has a total luminous transmittance, determined according to ASTM D1003, in the range from 73 to 100%, more preferably in the range from 75 to 100%, most preferably in the range from 77 to 100%.

[0137] The “photovoltaic element” means that the element has photovoltaic activity. The photovoltaic element can be e.g. an element of photovoltaic cell(s), which has a well-known meaning in the art. Silicon based material, e.g. crystalline silicon, is a non-limiting example of materials used in photovoltaic cell(s). Crystalline silicon material can vary with respect to crystallinity and crystal size, as well known to a skilled person. Alternatively, the photovoltaic element can be a substrate layer on one surface of which a further layer or deposit with photovoltaic activity is subjected, for example a glass layer, wherein on one side thereof an ink material with photovoltaic activity is printed, or a substrate layer on one side thereof a material with photovoltaic activity is deposited. For instance, in well-known thin fdm solutions of photovoltaic elements e.g. an ink with photovoltaic activity is printed on one side of a substrate, which is typically a glass substrate.

[0138] The photovoltaic element is most preferably an element of photovoltaic cell(s).

[0139] “Photovoltaic cell(s)” means herein a layer element(s) of photovoltaic cells, as explained above, together with connectors.

[0140] The materials of the above elements other than the protective back layer element (5) are well known in the prior art and can be chosen by a skilled person depending on the desired PV module.

[0141] The front and rear encapsulation layers (2 and 4) may be selected from any known encapsulation layers known in the art. Suitable materials for encapsulation layers include ethylene vinyl acetate (EVA) and silane-functionalized polyethylenes, such as those disclosed in WO 2017 / 076629 Al.

[0142] The photovoltaic (PV) module of the second aspect is a bifacial photovoltaic module, meaning that light may enter from either the front side or the rear (back) side, as indicated by the total luminous transmittance of the protective back layer element (5), determined according to ASTM D1003, in the range from 73 to 100%, more preferably in the range from 75 to 100%, most preferably in the range from 77 to 100%.

[0143] The layer element (LE) of the protective back layer element (5) preferably has a diffuse luminous transmittance, determined according to ASTM D1003, in the range from 45 to 100%, more preferably in the range from 51 to 90%, most preferably in the range from 55 to 80%.

[0144] The layer element (LE) of the protective back layer element (5) preferably has a stress whitening onset force in the transverse direction, determined according to the method described in the determination methods, in the range from 35 to 100 N, more preferably in the range from 38 to 85 N, most preferably in the range from 40 to 70 N.

[0145] The layer element (LE) of the protective back layer element (5) preferably has a stress whitening onset displacement in the transverse direction, determined according to the method described in the determination methods, in the range from 0.60 to 2.00 mm, more preferably in the range from 0.70 to 1.70 mm, most preferably in the range from 0.80 to 1.40 mm.

[0146] The layer element (LE) of the protective back layer element (5) preferably has a slope of the stress whitening light curve in the transverse direction, determined according to the method described in the determination methods , in the range from -7000 to -500 mV / mm, more preferably in the range from -6000 to -1000 mV / mm, most preferably in the range from - 5000 to -2000 mV / mm.

[0147] The layer element (LE) of the protective back layer element (5) preferably has a tensile modulus in the machine direction, determined according to ISO 527-3, in the range from 800 to 2000 MPa, more preferably in the range from 900 to 1700 MPa, most preferably in the range from 1000 to 1500 MPa.

[0148] The layer element (LE) of the protective back layer element (5) preferably has a tensile modulus in the transverse direction, determined according to ISO 527-3, in the range from 700 to 2000 MPa, more preferably in the range from 800 to 1700 MPa, most preferably in the range from 900 to 1400 MPa.

[0149] The protective front layer element (1) and the protective back layer element (5) may be rigid or flexible. Preferably, the protective front layer element (1) and the protective back layer element (5) are both flexible. Alternatively, the protective front layer element (1) is rigid, more preferably is glass.

[0150] In the context of the second aspect, it is particularly preferred that the layer element (LE) of the protective back layer element (5) is a multilayer element, wherein at least one layer (L) comprises, more preferably consists of, the polypropylene composition (PC).

[0151] It is particularly preferred that the layer element (LE) of the protective back layer element (5) is a three-layer element, wherein at least one layer (L) comprises, more preferably consists of, the polypropylene composition (PC).

[0152] In one particularly preferred embodiment, the layer element (LE) of the protective back layer element (5) is a three-layer element, consisting of the following layers, in the given order: i) an adhesive layer in adherent contact with the rear encapsulation layer element (4); ii) a core layer, comprising, more preferably consisting of, the polypropylene composition (PC); and iii) a skin layer, comprising, more preferably consisting of, a further polypropylene composition (PC’) having the properties as defined for the polypropylene composition (PC) above.

[0153] Both the polypropylene composition (PC) of the core layer and the further polypropylene composition (PC’) of the skin layer have the properties / component as described for the polypropylene composition (PC) of the first aspect, although the polypropylene composition (PC) of the core layer may be the same as or different from the polypropylene composition (PC’) of the skin layer. It is particularly preferred that the polypropylene composition (PC’) of the skin layer has a content of talc that is equal to or lower than, more preferably lower than, the polypropylene composition (PC) of the core layer.

[0154] The polypropylene compositions of the first and second aspects achieve a balance of mechanical properties and stress whitening resistance; however, compositions having higher amounts of talc generally have worse stress whitening resistance (although superior mechanical properties). By having an arrangement wherein the skin layer has lower levels of talc than the core layer, a higher surface stress whitening resistance can be achieved without compromising the mechanical properties of the core layer, said core layer being primarily responsible for the mechanical properties of the three-layer back layer element (5).

[0155] Additionally or alternatively, it is preferred that the adhesive layer comprises talc and optionally titanium dioxide.

[0156] The adhesive layer preferably comprises talc in an amount in the range from 0.5 to 5.0 wt.- %, more preferably in the range from 1.0 to 4.0 wt.-%, most preferably in the range from 1.5 to 3.0 wt.-%, relative to the total weight of the adhesive layer.

[0157] If the adhesive layer comprises titanium dioxide, it is preferably present in an amount in the range from 0.005 to 0.065 wt.-%, more preferably in the range from 0.010 to 0.060 wt.-%, yet more preferably in the range from 0.015 to 0.055 wt.-%, most preferably in the range from 0.020 to 0.050 wt.-%, relative to the total weight of the adhesive layer.

[0158] In the broadest sense, the polymers used for the adhesive layer may be any polymers known by the person skilled in the art to be used for this purpose.

[0159] It is preferred that the adhesive layer comprises: a) a propylene-ethylene copolymer having a melting temperature (Tm), determined by differential scanning calorimetry (DSC), in the range from 130 to 175 °C, more preferably in the range from 135 to 172 °C, most preferably in the range from 140 to 170 °C; and bl) a copolymer of ethylene and one or more C4-12 alpha olefin comonomers having a melting temperature (Tm), determined by differential scanning calorimetry (DSC), in the range from 100 to 140 °C, more preferably in the range from 105 to 130 °C, most preferably in the range from 110 to 125 °C; and / or b2) a copolymer of ethylene and one or more C4-12 alpha olefin comonomers having a melting temperature (Tm), determined by differential scanning calorimetry (DSC), in the range from 30 to 60 °C, more preferably in the range from 32 to 58 °C, most preferably in the range from 35 to 56 °C.

[0160] In this embodiment, component a) must be present and at least one of components bl) and b2) must also be present.

[0161] The propylene-ethylene copolymer of component a) is preferably a heterophasic propyleneethylene copolymer, more preferably a random-heterophasic propylene-ethylene copolymer.

[0162] Furthermore, the adhesive layer may optionally comprise a polar modified polypropylene (PMP), which is preferably a maleic anhydride-grafted polypropylene. This polar modifier polypropylene may be present in amounts of from 0.5 to 10 wt.-%, more preferably in the range from 1.0 to 8.0 wt.-%, most preferably in the range from 3.0 to 6.0 wt.-%, relative to the total weight of the adhesive layer.

[0163] Suitable compositions for the adhesive layer are described in EP 23 170 084.0 and EP 23170 090.7, which provide further details of the individual components a), bl) and b2).

[0164] All fallback positions and preferred embodiments of the layer element (LE) and the polypropylene composition (PC) of the first aspect apply mutatis mutandis to the layer element (LE) of the protective back layer (5) of the second aspect. E X A M P L E S

[0165] 1. Determination methods

[0166] The following definitions of terms and determination methods apply for the above general description of the invention including the claims as well as to the below examples unless otherwise defined.

[0167] Quantification of microstructure by NMR spectroscopy

[0168] Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used to quantify the isotacticity of the polymers.

[0169] Quantitative13C{’H} NMR spectra recorded in the solution-state using a Bruker Avance III 400 NMR spectrometer operating at 400. 15 and 100.62 MHz for 'H and13C respectively. All spectra were recorded using a13C optimised 10 mm selective excitation probehead at 125°C using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in approximately 3 ml of l,2-tetrachloroethane-d2 (TCE-d2) along with approximately 3 mg BHT (2,6-di-tert-butyl-4-methylphenol CAS 128-37-0). To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatory oven for at least 1 hour. Upon insertion into the magnet the tube was spun at 10 Hz. This setup was chosen primarily for the high resolution needed for tacticity distribution quantification {busicoOl, busico97}. Standard single-pulse excitation was employed utilising the NOE, 3 s recycle delay and bi-level WALTZ16 decoupling scheme {zhou07,busico07}. A total of 8192 (8k) transients were acquired per spectra.

[0170] 13C{’H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals using proprietary computer programs. All chemical shifts were internally referenced to the methyl signal of the isotactic pentad mmmm at 21.85 ppm.

[0171] The tacticity distribution was quantified through integration of the methyl region between 23.6 and 19.7 ppm correcting for any sites not related to the stereo sequences of interest {busicoOl, busico97}. Characteristic signals corresponding to the presence of regio defects {resconiOO} were not observed.

[0172] The pentad tacticity distribution was determined through direct separate integration of each methyl signal from a given steric pentad followed by normalisation to the sum of methyl signals from all steric pentads. The relative content of a specific steric pentad was reported as the mole fraction or percentage of a given steric pentad xxxx with respect to all steric pentads:

[0173] [xxxx] = xxxx / (mmmm + mmmr + rmmr + mmrr + xmrx + mrmr + rrrr + mrrr + mrrm) where xmrx represents the combined integral of both mmrm and rmrr as signal from these steric pentads are not commonly resolved. The pentad isotacticity was thus given by:

[0174] [mmmm] = mmmm / (mmmm + mmmr + rmmr + mmrr + xmrx + mrmr + rrrr + mrrr + mrrm) busicoOl Busico, V., Cipullo, R., Prog. Polym. Sci. 26 (2001) 443 busico97 Busico, V., Cipullo, R., Monaco, G., Vacatello, M., Segre, A.L.,

[0175] Macromoleucles 30 (1997) 6251 zhou07 Zhou, Z., Kuemmerle, R., Qiu, X., Redwine, D., Cong, R., Taha, A., Baugh, D. Winniford, B„ J. Mag. Reson. 187 (2007) 225 busico07 Busico, V., Carbonniere, P., Cipullo, R., Pellecchia, R., Severn, J., Talarico, G., Macromol. Rapid Commun. 2007, 28, 1128 resconiOO Resconi, L., Cavallo, L., Fait, A., Piemontesi, F., Chem. Rev. 2000, 100, 1253

[0176] CRYSTEX QC analysis

[0177] Crystalline and soluble fractions method

[0178] The crystalline (CF) and soluble fractions (SF) of the polypropylene (PP) compositions as well as the comonomer content and intrinsic viscosities of the respective fractions were analyzed by use of the CRYSTEX instrument, Polymer Char (Valencia, Spain). Details of the technique and the method can be found in literature (Ljiljana Jeremie, Andreas Albrecht, Martina Sandholzer & Markus Gahleitner (2020) Rapid characterization of high-impact ethylenepropylene copolymer composition by crystallization extraction separation: comparability to standard separation methods, International Journal of Polymer Analysis and Characterization, 25:8, 581-596)

[0179] The crystalline and amorphous fractions are separated through temperature cycles of dissolution at 160 °C, crystallization at 40 °C and re-dissolution in 1,2,4-trichlorobenzene at 160 °C. Quantification of SF and CF and determination of ethylene content (C2) are achieved by means of an integrated infrared detector (IR4) and for the determination of the intrinsic viscosity (IV) an online 2-capillary viscometer is used.

[0180] The IR4 detector is a multiple wavelength detector measuring IR absorbance at two different bands (CH3 stretching vibration (centred at app. 2960 cm1) and the CH stretching vibration (2700-3000 cm1) that are serving for the determination of the concentration and the Ethylene content in Ethylene-Propylene copolymers. The IR4 detector is calibrated with series of 8 EP copolymers with known Ethylene content in the range of 2 wt.-% to 69 wt.-% (determined by13C-NMR) and each at various concentrations, in the range of 2 and 13 mg / ml. To encounter for both features, concentration and ethylene content at the same time for various polymer concentrations expected during Crystex analyses the following calibration equations were applied:

[0181] Cone = a + b*Abs(CH) + c*(Abs(CH))2+ d*Abs(CH3) + e*(Abs(CH3)2+ f*Abs(CH)*Abs(CH3) (Equation 1)

[0182] CH3 / IOOOC = a + b*Abs(CH) + c* Abs(CH3) + d * (Abs(CH3) / Abs(CH)) + e * (Abs(CH3) / Abs(CH))2(Equation 2)

[0183] The constants a to e for equation 1 and a to f for equation 2 were determined by using least square regression analysis.

[0184] The CH3 / IOOOC is converted to the ethylene content in wt.-% using following relationship:

[0185] Wt.-% (Ethylene in EP Copolymers) = 100 - CH3 / IOOOTC * 0.3 (Equation 3) Amounts of Soluble Fraction (SF) and Crystalline Fraction (CF) are correlated through the XS calibration to the “Xylene Cold Soluble” (XCS) quantity and respectively Xylene Cold Insoluble (XCI) fractions, determined according to standard gravimetric method as per ISO16152. XS calibration is achieved by testing various EP copolymers with XS content in the range 2-31 wt.-%. The determined XS calibration is linear:

[0186] Wt.-% XS = 1,01* Wt.-% SF (Equation 4)

[0187] Intrinsic viscosity (IV) of the parent EP copolymer and its soluble and crystalline fractions are determined with a use of an online 2-capillary viscometer and are correlated to corresponding IV’s determined by standard method in decalin according to ISO 1628-3. Calibration is achieved with various EP PP copolymers with IV = 2-4 dL / g. The determined calibration curve is linear:

[0188] IV (dL / g) = a* Vsp / c (equation 5)

[0189] The samples to be analyzed are weighed out in concentrations of lOmg / ml to 20mg / ml. To avoid injecting possible gels and / or polymers which do not dissolve in TCB at 160 °C, like PET and PA, the weighed out sample was packed into a stainless steel mesh MW 0, 077 / D 0,05mmm.

[0190] After automated filling of the vial with 1,2,4-TCB containing 250 mg / 1 2,6-tert-butyl-4- methylphenol (BHT) as antioxidant, the sample is dissolved at 160 °C until complete dissolution is achieved, usually for 60 min, with constant stirring of 400rpm. To avoid sample degradation, the polymer solution is blanketed with the N2 atmosphere during dissolution.

[0191] A defined volume of the sample solution is injected into the column filled with inert support where the crystallization of the sample and separation of the soluble fraction from the crystalline part is taking place. This process is repeated two times. During the first injection the whole sample is measured at high temperature, determining the IV[dl / g] and the C2[wt.%] of the PP composition. During the second injection the soluble fraction (at low temperature) and the crystalline fraction (at high temperature) with the crystallization cycle are measured (wt.-% SF, wt.-% C2, IV). Quantification of microstructure by NMR spectroscopy (for CRYSTEX calibration) Quantitative nuclear-magnetic resonance (NMR) spectroscopy was used for calibration.

[0192] Quantitative13C{’H} NMR spectra were recorded in the solution-state using a Broker Avance Neo 400 NMR spectrometer operating at 400.15 and 100.62 MHz for 'H and13C respectively. All spectra were recorded using a13C optimized 10 mm extended temperature probe head at 125 °C using nitrogen gas for all pneumatics. Approximately 200 mg of material was dissolved in approximately 3 ml of l,l,2,2-tetrachloroethane-d2 (TCE-d2) along with approximately 3 mg BHT (2,6-di-tert-butyl-4-methylphenol CAS 128-37-0) and chromium-(III)- acetylacetonate (Cr(acac)s) resulting in a 60 mM solution of relaxation agent in solvent as described in G. Singh, A. Kothari, V. Gupta, Polymer Testing 2009, 28(5), 475.

[0193] To ensure a homogenous solution, after initial sample preparation in a heat block, the NMR tube was further heated in a rotatory oven for at least 1 hour. Upon insertion into the magnet the tube was spun at 10 Hz. This setup was chosen primarily for the high resolution and quantitatively needed for accurate ethylene content quantification. Standard single-pulse excitation was employed without NOE, using an optimised tip angle, 1 s recycle delay and a bi-level WALTZ16 decoupling scheme as described in Z. Zhou, R. Kuemmerle, X. Qiu, D. Redwine, R. Cong, A. Taha, D. Baugh, B. Winniford, J. Mag. Reson. 187 (2007) 225 and V. Busico, P. Carbonniere, R. Cipullo, C. Pellecchia, J. Severn, G. Talarico, Macromol. Rapid Commun. 2007, 28, 1128. A total of 6144 (6k) transients were acquired per spectra.

[0194] Quantitative13C{’H} NMR spectra were processed, integrated and relevant quantitative properties determined from the integrals. All chemical shifts were indirectly referenced to the central methylene group of the ethylene block (EEE) at 30.00 ppm using the chemical shift of the solvent. This approach allowed comparable referencing even when this structural unit was not present.

[0195] Characteristic signals corresponding to the incorporation of ethylene were observed (as described in Cheng, H. N., Macromolecules 1984, 17, 1950) and the comonomer fraction calculated as the fraction of ethylene in the polymer with respect to all monomer in the polymer: fE = ( E / ( P + E )

[0196] The comonomer fraction was quantified using the method of W-J. Wang and S. Zhu, Macromolecules 2000, 33 1157, through integration of multiple signals across the whole spectral region in the13C{’H} spectra. Integral regions were slightly adjusted to increase applicability across the whole range of encountered comonomer contents.

[0197] The mole percent comonomer incorporation was calculated from the mole fraction:

[0198] E [mol%] = 100 * fE

[0199] The weight percent comonomer incorporation was calculated from the mole fraction: E [wt%] = 100 * ( fE * 28.06 ) / ( (fE * 28.06) + ((1-fE) * 42.08) ).

[0200] Melt Flow Rate

[0201] The melt flow rate (MFR) is determined according to ISO 1133 and is indicated in g / 10 min. The MFR is an indication of the flowability, and hence the processability, of the polymer. The higher the melt flow rate, the lower the viscosity of the polymer. The MFR2 of polypropylene is determined at a temperature of 230 °C and a load of 2.16 kg. The MFR2 of polyethylene is determined at a temperature of 190 °C and a load of 2.16 kg.

[0202] Density

[0203] The density is measured according to ISO 1183-187. Sample preparation is done by compression moulding in accordance with ISO 1872-2:2007.

[0204] The xylene soluble fraction at room temperature (XCS, wt.-%): The amount of the polymer soluble in xylene is determined at 25 °C according to ISO 16152; 5thedition; 2005- 07-01.

[0205] DSC analysis, melting temperature (Tm) and heat of fusion (Hf), crystallization temperature (Tc) and heat of crystallization (Hc): measured with a TA Instrument Q200 differential scanning calorimetry (DSC) on 5 to 7 mg samples. DSC is run according to ISO 11357 / part 3 / method C2 in a heat / cool / heat cycle with a scan rate of 10 °C / min in the temperature range of -30 to +225 °C. Crystallization temperature (Tc) and crystallization enthalpy (Hc) are determined from the cooling step, while melting temperature (Tm) and melting enthalpy (Hm) are determined from the second heating step. Average particle size (diameter) t / so and top cut 95

[0206] The particle size definitions are calculated from the particle size distribution [mass percent] as determined by two different methods:

[0207] Laser diffraction method, using Laser Mastersizer, according to ISO 13320-1.

[0208] Sedigraph method, i.e. gravitational liquid sedimentation, according to ISO 13317-3.

[0209] The dso is defined as the median diameter (by mass), whilst <L is the diameter at the 95thpercentile (by mass), as observed from the particle size distribution.

[0210] Loss on ignition

[0211] Loss on ignition at a temperature of 1050 °C was determined according to DIN 51081.

[0212] CIELAB

[0213] The method was used for measurement of colour and complies with ISO 11664-4. With a spectrophotometer, the 3 standard colour value values X, Y and Z are measured, which are used to calculate the CIE L*, a*, b* and its colour distances.

[0214] The Flexural Modulus is determined according to ISO 178 method A (3-point bending test) on 80 mm x 10 mm x 4 mm specimens. Following the standard, a test speed of 2 mm / min and a span length of 16 times the thickness was used. The testing temperature was 23±20C. Injection moulding was carried out according to ISO 19069-2 using a melt temperature of 230 °C for all materials irrespective of material melt flow rate.

[0215] Tensile properties in machine and transverse direction were determined according to ISO 527-1 / -3 at 23°C on monolayer cast films with a thickness of 400 pm produced as indicated below. In addition, the tensile modulus (secant modulus between 0.05% and 0.25% elongation) was also determined. Testing was performed at a cross head speed of 1 mm / min to determine the tensile modulus, then the test speed was increased to 200 mm / min until the film broke.

[0216] Optical properties

[0217] The total luminous transmittance, diffuse luminous transmittance and haze were measured according to ASTM DI 003 -21 (Method A-Hazemeter). The clarity is measured using the same machine and principle as haze but for angle less than 2.5° from normal. For clarity measurements, the specimens are positioned in the “clarity-port“. The measurement was performed as follows:

[0218] • Device: Haze gard plus

[0219] • Manufacturer: BYK-Gardner GmbH

[0220] • Type: 4725

[0221] • Illuminant C

[0222] Conditions:

[0223] • Conditioning time: > 96 h

[0224] • Temperature: 23 °C

[0225] • Test procedure: A - Hazemeter

[0226] Coefficient of linear thermal expansion CLTE

[0227] The coefficient of linear thermal expansion (CLTE) was determined in accordance with ISO 11359-2: 1999 on 10 mm long pieces cut from the same injection molded specimens as used for the flexural modulus determination. The measurement was performed in a temperature range from -30 to +80 °C at a heating rate of 1 °C / min and a temperature range from 23 to +80 °C at a heating rate of 1 °C / min in the machine direction.

[0228] Stress whitening

[0229] Stress whitening is determined on dog-bone-shaped specimens of ISO 527-2 type IB (Figure 3). The specimens are milled from cast films of 400 pm thickness. The specimens have an additional parallel narrowed area with a length of 6 mm and a width of 7 mm in the centre to concentrate the stresses. The optical transparency measurement device is positioned in the centre of this area.

[0230] The specimen is mounted in a Zwick Z010 with a 500 N load cell and a clamping distance of 105 mm. The displacement is measured using a mechanical extensometer with an initial clamping distance of 70 mm. The tensile test is conducted at a constant cross-head speed of 5 mm / min and at least up to the yielding of the specimen.

[0231] The optical transparency measurements device is made in-house and comprises a warm white LED Nichita NSPL510DS and a photodiode Hamatsutsu S13948-01SB. The distance between the LED and the photodiode is 5.25 mm. In front of the photodiode is a mask with a pinhole of 1.5 mm in diameter to restrict light passing from the side.

[0232] The comparison of the transparency measurements of the in-house-made device against the total transmittance measurement according to ASTM DI 003 with a Haze-gard plus from BYK-Gardnerare is shown in Figure 2. It can be seen that there is a good correlation between the two measurements.

[0233] The optical response (light transmission through the sample) and the tensile load along the deflection are recorded. The initial Transparency (i), the onset Transparency (ii) and the slope of the transparency vs displacement (iii) are used to characterise the materials (Figure 3).

[0234] Adhesion tests

[0235] The adhesion test is performed on laminated strips, the backsheet is peeled in a tensile testing equipment while measuring the force required.

[0236] A laminate consisting of glass, 2 encapsulants fdms and the multilayer films produced as described in the experimental section is first laminated. Between the encapsulant and backsheet a small sheet of Teflon is inserted at one end of the laminate. This will generate a small part of the backsheet that is not adhered to the encapsulant. This part will be used as the anchoring point for the tensile testing device. All vacuum laminations were performed at 150°C, using 5 minutes of evacuation time and 10 minutes holding time with membrane down at a pressure at 800 mbar.

[0237] Encapsulant film was EVA Hangzhou First F406P with 28% vinylacetate and MFR2 = ca. 35 g / 10 min (all information provided from Technical Data Sheet), commercially available from Hangzhou First Applied Material Co., Ltd (PR China).

[0238] The laminate is then cut along the laminate to form a 13 mm wide stripe, the cut goes through the backsheet and the encapsulant film all the way down to the glass surface.

[0239] The laminate is mounted in the tensile testing equipment and the clamp of the tensile testing device is attached to the end of the strip.

[0240] The pulling angle is 90° in relation to the laminate and the pulling speed is 50mm / min. The adhesion force is the average force per 50mm of peeling starting 25mm into the strip and ending at 75mm.

[0241] The average force over the 50 mm is divided by 13, as the width of the strip is 13 mm and presented as the adhesion strength (N / mm).

[0242] 2. Examples

[0243] 2.1 Synthesis of the heterophasic propylene-ethylene copolymers (HECO)

[0244] HECO1 and HECO2 are (respectively) HECOA and HECOB of WO 2017 / 071847 Al. HECO1 contains 1500 ppm ADK-STAB A-612 (supplied by Adeka Corporation) and 300 ppm Synthetic hydrotalcite (ADK STAB HT supplied by Adeka Corporation), whilst HECO2 contains 1000 ppm ADK 25 STAB AO-60 (supplied by Adeka Corporation), 1000 ppm ADK- STAB 2112 RG (supplied by Adeka Corporation) and calcium stearate 500 ppm (CEASIT- AV / T, supplied by Baerlocher).

[0245] HECO3 as used in the examples was produced using a Ziegler-Natta catalyst as used in the inventive examples of WO 2016 / 066446 Al and pre-polymerized with vinylcyclohexene to achieve nucleation with poly(vinylcyclohexene). Nucleation by prepolymerization with vinylcyclohexane is described in EP 2 960 256 Bl and EP 2 960 279 Bl in detail. Dicyclopentyl dimethoxy silane (donor D) was used as external donor and triethyl aluminium (TEAL) was used as co-catalyst. The polymerization conditions are presented in Table 1 below.

[0246] Table 1 Polymerization conditions for HEC03

[0247] The resultant polymer powder was compounded with 1500 ppm ADK-STAB A-612 (supplied by Adeka Corporation) and 300 ppm Synthetic hydrotalcite (ADK STAB HT supplied by Adeka Corporation) on a ZSK 58 twin screw extruder, with melt temperature of 205 °C, production rate 200 kg / h.

[0248] Properties of HECO 1 to HECO3 are given in Table 2.

[0249] Table 2 Properties of the heterophasic propylene-ethylene copolymers (HECO)

[0250] 2.2 Compounding of polypropylene compositions

[0251] The inventive and comparative compositions were prepared in a co-rotating twin-screw extruder (Coperion ZSK 40) at 220 °C according to the recipes in Table 2. The properties (MFR2 and CRYSTEX QC data) of the resultant pellets are given also in Table 2. Table 2 Recipes and pellet properties of Comparative and Inventive Examples

[0252] The following components were employed in Table 2 and Table 5 (see section 2.4):

[0253] T1 talc with median diameter dso of 1.3 pm and a top cut d^ diameter of 3.9 pm, both determined by Sedigraph analysis (ISO 13317-3), a median diameter dso of 4.4 pm and a top cut d ^ diameter of 9.9 pm, both determined by laser diffraction (ISO 13320-1), a loss on ignition (LOI) at 1050 °C of 6.0%, and a CIELAB L* value of 98.0.

[0254] T2 talc with median diameter dso of 2.4 pm and a top cut d^ diameter of 8.7 pm, both determined by Sedigraph analysis (ISO 13317-3), a median diameter dso of 5.7 pm and a top cut d ^ diameter of 15.5 pm, both determined by laser diffraction (ISO 13320-1), a loss on ignition (LOI) at 1050 °C of 6.0%, and a CIELAB L* value of 97.5.

[0255] EC 1 an elastomeric ethylene-octene copolymer with a trade name of Queo

[0256] 8201, commercially available from Borealis AG, having an MFR2 (190 °C) of 1. 1 g / 10 min and a density of 882 kg / m3.

[0257] EC2 an elastomeric ethylene-octene copolymer with a trade name of Queo

[0258] 8203, commercially available from Borealis AG, having an MFR2 (190 °C) of 3.0 g / 10 min and a density of 882 kg / m3.

[0259] EC3 an elastomeric ethylene-octene copolymer with a trade name of Queo

[0260] 8210, commercially available from Borealis AG, having an MFR2 (190 °C) of 10 g / 10 min and a density of 882 kg / m3.

[0261] EC4 an elastomeric ethylene-octene copolymer with a trade name of Queo

[0262] 6800LA, commercially available from Borealis AG, having an MFR2 (190 °C) of 0.5 g / 10 min and a density of 868 kg / m3.

[0263] EC5 an elastomeric ethylene-octene copolymer with a trade name of Queo

[0264] 700 ILA, commercially available from Borealis AG, having an MFR2 (190 °C) of 1.0 g / 10 min and a density of 870 kg / m3. EC6 an elastomeric ethylene-octene copolymer with a trade name of Queo

[0265] 7007LA, commercially available from Borealis AG, having an MFR2 (190 °C) of 6.5 g / 10 min and a density of 870 kg / m3.

[0266] RAHECO a Ziegler-Natta catalyzed random heterophasic propylene-ethylene copolymer having a propylene-ethylene copolymer matrix with an MFR2 of 4.0 g / 10 min and a C2(matrix) content of 4. 1 wt.-% and an ethylenepropylene elastomeric phase in an amount of 21 wt.-% (measured as XCS content), and an ethylene content in the elastomeric phase of 35 wt%. The random heterophasic propylene-ethylene copolymer composition has an MFR2 of 4.9 g / 10 min, a total ethylene content of 9.2 wt%, a melting temperature of 142°C, a Vicat A softening temperature of 120°C, a flexural modulus of 550 MPa and a Charpy notched impact strength at 23°C of 12 kJ / m2and has been produced using the process as described for the heterophasic propylene copolymer IE2 in the example section ofWO 2015 / 117948 Al.

[0267] LLDPE a metallocene-catalyzed linear low density polyethylene of example IE1 of EP 3 257 895 Al having a 1-butene content of 0.3 mol-% (0.6 wt%), a 1-hexene content of 2.6 mol-% (8.1 wt%), density of 918 kg / m3, a melt flow rate MFR2 of 1.5 g / 10 min, a melting temperature of 122°C and a Vicat A temperature of 102°C.

[0268] PMP a maleic anhydride-grafted polypropylene with a trade name of Epolene

[0269] E-43, commercially available from Westlake Polymers LLC (US). h-PP propylene homopolymer having an MFR2 (230 °C) of 0.6 g / 10 min, an isotactic pentad concentration of 91%, and a melting temperature of 160 °C. h-PP is prepared using a Ziegler-Natta catalyst and is thus free of 2,1- regiodefects. The propylene homopolymer (h-PP) was produced in general agreement with EP2543684B1, which describes the diluent- slurry polymerization of high-isotactic polypropylene in five stirred-tank reactors using kerosene as the diluent.

[0270] TiCf MB a titanium dioxide masterbatch composition, containing 7.0 wt.-% of titanium dioxide, produced by blending 10 wt.-% of Polywhite P 8377 CL (a titanium dioxide masterbatch containing 70 wt.-% of titanium dioxide, commercially available from LyondellBasell (Italy)) with 90 wt.-% of a propylene-ethylene random copolymer having an MFR2 of 2.0 g / 10 min, a total ethylene content of 1.5 wt%, a xylene cold solubles (XCS) content of 0.7 wt.-%, a melting temperature of 142°C, a Vicat A softening temperature of 133°C, a flexural modulus of 1050 MPa and a Charpy notched impact strength at 23°C of 4.7 kJ / m2, which has been produced using the process as described for the random polypropylene copolymer Poly 1 in PCT7EP2023 / 058435.

[0271] * CE1 corresponds to IE6 of WO 2017 / 071847 Al and consists of 27.2 wt.-% of HECO1, 40.7 wt.-% ofHECO2, 23 wt.-% of talc, 8 wt.-% ofplastomer (Queo 8230), and 1.1 wt.-% of additives (see WO 2017 / 071847 Al for full details).

[0272] 2.3 Mechanical, optical and stress whitening properties of the inventive and comparative compositions

[0273] The mechanical, optical, and stress whitening properties of the resultant compositions, either measured on injection moulded specimens or on 400 pm monolayer films (produced on Dr.

[0274] Collin cast film line, with extruder with 30 mm screw and LD of 30, calendaring unit with two cooling rolls (25°C), and melt temperature 220°C), are given in Tables 3a to 4b. Table 3a Mechanical / optical properties of inventive HEC01 -based compositions

[0275] Table 3b Mechanical / optical properties of inventive HECO3-based compositions

[0276] Table 4a Stress whitening properties of inventive HEC01 -based compositions

[0277] Table 4b Stress whitening properties of inventive HEC03-based compositions

[0278] The inventive compositions have an improved balance of mechanical, optical and stress whitening properties, compared to the state of the art composition CE1 and the individual HECOs (HECO1 and HECO3).

[0279] The inventive compositions have slightly worse CLTE than CE1, but drastically improved total luminous transmittance (which allows for greater power generation in a PV module) and tensile modulus. In comparison to their respective base HECO, the inventive examples have slightly worse total luminous transmittance, but generally improved tensile modulus, as well as improved CLTE.

[0280] Furthermore, the stress whitening effects are even more pronounced. In such fdms, it is generally the transverse direction (TD) in which potential weaknesses are to be found. HECO3 has a relatively late onset of stress whitening (see onset force (TD) and onset brightness (TD)); however, once the stress whitening has begun, the slope of -9930 mV / mm indicates that the stress whitening effect rapidly deteriorates the fdm. On the other hand, CE1 has an early onset of stress whitening (which is not desirable), though the slope is much less steep. The inventive examples achieve an improved balance of late onset (see onset force (TD) and onset displacement (TD)) and a less steep slope (slope (TD)), indicating that stress whitening does not occur readily and, when it does occur, it is less severe.

[0281] 2.4 Multilayer films comprising the inventive compositions

[0282] Multilayer fdms were also prepared from some of the inventive compositions.

[0283] 3-layer coextruded fdm samples of the composition A-B-C were prepared on a Dr. Collin cast fdm line consisting of 3 automatically controlled extruders, a calendar unit with two chill rolls, a take-off unit.

[0284] Each layer was extruded with an individual extruder: Two outer layers (layer A and layer C) were extruded with extruders equipped with 25 mm screw with LD of 30. The core layer (layer B) was extruded with extruder equipped with 30 mm screw with LD of 30. The thickness of each core layer B was 300 pm, for each layer A was 50 pm and for each layer C was 50 pm resulting in a fdm thickness of the 3-layer coextruded fdm of 400 pm. The melt temperature ranged 220-245°C. The chill roll was cooled to 30 °C. The die width was 0.5- 1.5 mm adjustable flex-lip.

[0285] The individual layers (A-B-C) of the resultant multilayer films are given in Table 5, as well as optical properties and adhesion (measured according to the process given in the determination methods, wherein layer A is the layer in contact with the EVA layer)

[0286] Table 5 Multilayer films

[0287] The compositions used for the adhesive layers (A) are:

[0288] El 75 wt.-% of RAHECO, 10 wt.-% of EC6, 10 wt.-% of LLDPE, and 5 wt.-% of PMP.

[0289] E2 73 wt.-% of RAHECO, 10 wt.-% of EC6, 10 wt.-% of LLDPE, 5 wt.-% of PMP, and

[0290] 2 wt.-% ofTl.

[0291] E3 72.25 wt.-% of RAHECO, 10 wt.-% of EC6, 10 wt.-% of LLDPE, 5 wt.-% of PMP,

[0292] 2 wt.-% of Tl, and 0.75 wt.-% of TiO2 MB.

[0293] The multilayer films of Table 5 all have good adhesion to EVA encapsulants, despite the presence of talc and / or TiO? in the E2 and E3 adhesive layers. Furthermore, core layers having higher amounts of talc and thus worse stress whitening resistance can be covered by a skin layer having lower amounts of talc and thus improved stress whitening resistance (i.e. F2, F3, and F5), resulting in a multilayer film that has improved mechanical properties as a result of the core layer composition and improved stress whitening performance as a result of the skin layer composition, whilst also avoiding any reduction in total luminous transmittance that would be caused by TiCh in the core layer (c.f. total luminous transmittance of F2, F3 and F5 vs, IE14),

Claims

C L A I M S1. A layer element (LE) comprising one or more layers, wherein at least one layer (L) comprises a polypropylene composition (PC) comprising: a) from 50.0 to 97.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of a heterophasic propylene-ethylene copolymer (HECO), comprising: i) a crystalline matrix (M) being a propylene homopolymer; and ii) an amorphous propylene-ethylene elastomer (E) that is dispersed in said crystalline matrix (M), wherein the heterophasic propylene-ethylene copolymer (HECO) has a melt flow rate (MFR2), determined according to ISO 1133 at 230 °C and 2. 16 kg, in the range from 0.5 to 20.0 g / 10 min and a soluble fraction that has an ethylene content (C2(SF)), determined by CRYSTEX QC analysis, in the range from 10.0 to 45.0 wt.-%; b) from 1.0 to 12.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of talc (T); c) from 2.0 to 20.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of an ethylene / C4-Cio alpha olefin copolymer (EC); d) optionally, from 0.0 to 25.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of a propylene homopolymer (h-PP) having a melt flow rate (MFR2), determined according to ISO 1133 at 230 °C and 2.16 kg, in the range from 0.1 to 5.0 g / 10 min; e) optionally, from 0.00 to 0.06 wt.-%, relative to the total weight of the polypropylene composition (PC), of one or more white pigments (P); and f) optionally, from 0.0 to 5.0 wt.-% of one or more further additives (A).

2. The layer element (LE) according to claim 1, wherein the heterophasic propylene- ethylene copolymer (HECO) has one or more, preferably all, of the following features: i) a soluble fraction (SF) content, determined by CRYSTEX QC analysis, in the range from 5.0 to 35.0 wt.-%, based on the total weight of theheterophasic propylene-ethylene copolymer (HECO), and a crystalline fraction (CF) content, determined by CRYSTEX QC analysis, in the range from 65.0 to 95.0 wt.-%, based on the total weight of the heterophasic propylene-ethylene copolymer (HECO); ii) an ethylene content (C2(total)), determined by CRYSTEX QC analysis, in the range from 0.5 to 20.0 wt.-%; iii) an ethylene content of the crystalline fraction (C2(CF)), determined by CRYSTEX QC analysis, in the range from 0.5 to 15.0 wt.-%; iv) an intrinsic viscosity (iV(total)), determined by CRYSTEX QC analysis, in the range from 1.20 to 5.00 dL / g; v) an intrinsic viscosity of the soluble fraction (iV(SF)), determined by CRYSTEX QC analysis, in the range from 1.00 to 4.00 dL / g; vi) an intrinsic viscosity of the crystalline fraction (iV(CF)), determined by CRYSTEX QC analysis, in the range from 1.20 to 5.00 dL / g; and vii) a melting temperature (Tm), determined by differential scanning calorimetry (DSC), in the range from 160 to 172 °C.

3. The layer element (LE) according to any one of the preceding claims, wherein the crystalline matrix (M) of the heterophasic propylene-ethylene copolymer (HECO) is free from 2,1 -regiodefects, as determined by quantitative13C-NMR spectroscopy.

4. The layer element (LE) according to any one of the preceding claims, wherein the ethylene / C4-Cio alpha olefin copolymer (EC) has one or more, preferably all, of the following properties: i) a melt flow rate (MFR2), determined according to ISO 1133 at 190 °C and 2.16 kg, in the range from 0.1 to 20 g / 10 min; ii) a density, determined according to ISO 1183-187, in the range from 850 to 900 kg / m3; and iii) the ethylene / C4-Cio alpha olefin copolymer (EC) is a copolymer of ethylene and a comonomer selected from C4-C8 alpha olefins, more preferably selected from Ce-Cs alpha olefins, yet more preferably selected from 1-hexene and 1-octene, most preferably the ethylene / C4-Cio alpha olefin copolymer (EC) is a copolymer of ethylene and 1-octene.

5. The layer element (LE) according to any one of the preceding claims, wherein the talc (T) has a median diameter (dso), determined according to ISO 13320-1 (laser), in the range from 1.5 to 10.0 pm, and / or a median diameter (dso), determined according to ISO 13317-3 (sedigraph), in the range from l.O to 5.0 pm.

6. The layer element (LE) according to any one of the preceding claims, wherein the propylene homopolymer (h-PP) is free from 2,1 -regiodefects, as determined by quantitative13C-NMR spectroscopy, and preferably has a melting temperature (Tm), determined by differential scanning calorimetry (DSC), in the range from 156 to 170 °C.

7. The layer element (LE) according to any one of the preceding claims, wherein the polypropylene composition (PC) consists of: a) from 50.0 to 97.0 wt.-%, more preferably 55.0 to 96.5 wt.-%, most preferably 60.0 to 95.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the heterophasic propylene-ethylene copolymer (HECO); b) from 1.0 to 12.0 wt.-%, more preferably 1.5 to 10.0 wt.-%, most preferably 2.0 to 8.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the talc (T); c) from 2.0 to 20.0 wt.-%, more preferably 2.0 to 18.0 wt.-%, most preferably 3.0 to 15.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the ethylene / C4-Cio alpha olefin copolymer (EC); d) optionally, from 0.0 to 25.0 wt.-%, more preferably 5.0 to 20.0 wt.-%, most preferably 10.0 to 17.0 wt.-%, relative to the total weight of the polypropylene composition (PC), of the propylene homopolymer (h-PP); e) optionally, from 0.00 to 0.06 wt.-%, relative to the total weight of the polypropylene composition (PC), of the one or more white pigments (P); and f) optionally, from 0.0 to 5.0 wt.-% of the one or more further additives (A).

8. The layer element (LE) according to any one of the preceding claims, wherein the polypropylene composition (PC) has one or more, preferably all, of the following properties: i) a melt flow rate (MFR2), determined according to ISO 1133 at 230 °C and 2.16 kg, in the range from 0.5 to 20 g / 10 min; ii) a soluble fraction (SF) content, determined by CRYSTEX QC analysis, in the range from 10.0 to 40.0 wt.-%, based on the total weight of the polypropylene composition (PC), and a crystalline fraction (CF) content, determined by CRYSTEX QC analysis, in the range from 60.0 to 90.0 wt.- %, based on the total weight of the polypropylene composition (PC); iii) an ethylene content (C2(total)), determined by CRYSTEX QC analysis, in the range from 5.0 to 30.0 wt.-%; iv) an ethylene content of the soluble fraction (C2(SF)), determined by CRYSTEX QC analysis, in the range from 30.0 to 68.0 wt.-%; v) an ethylene content of the crystalline fraction (C2(CF)), determined by CRYSTEX QC analysis, in the range from 0.6 to 8.0 wt.-%; vi) an intrinsic viscosity of the soluble fraction (iV(SF)), determined by CRYSTEX QC analysis, in the range from 1.20 to 2.60 dL / g; and vii) an intrinsic viscosity of the crystalline fraction (iV(CF)), determined by CRYSTEX QC analysis, in the range from 1.80 to 3.20 dL / g.

9. The layer element (LE) according to any one of the preceding claims, wherein the polypropylene composition (PC) has one or more, preferably all, of the following properties: i) a coefficient of linear thermal expansion (CLTE) in the machine direction, determined between +23 and +80 °C, according to ISO 11359-2 on 80* 10x4 mm3injection-moulded specimens prepared according to ISO 19069-2, of less than 120 * 10'6K-1; ii) a coefficient of linear thermal expansion (CLTE) in the machine direction, determined between -30 and +80 °C, according to ISO 11359-2 on 80x 10x4mm3injection-moulded specimens prepared according to ISO 19069-2, of less than 95 * 10'6K-1; iii) a flexural modulus, determined according to ISO 178 on 80x 10x4 mm3injection-moulded specimens prepared according to ISO 19069-2, in the range from 800 to 2200 MPa; iv) a tensile modulus, determined according to ISO 527-3 on a 400 pm monolayer cast fdm specimen in the machine direction, in the range from 800 to 2000 MPa; v) a tensile modulus, determined according to ISO 527-3 on a 400 pm monolayer cast fdm specimen in the transverse direction, in the range from 700 to 2000 MPa; vi) a stress whitening onset force in the transverse direction, determined according to the method described in the determination methods on a 400 pm monolayer cast fdm specimen, in the range from 35 to 100 N; vii) a stress whitening onset displacement in the transverse direction, determined according to the method described in the determination methods on a 400 pm monolayer cast fdm specimen, in the range from 0.60 to 2.00 mm; viii) a slope of the stress whitening light curve in the transverse direction, determined according to the method described in the determination methods on a 400 pm monolayer cast fdm specimen, in the range from -7000 to -500 mV / mm; ix) a total luminous transmittance, determined according to ASTM D1003, in the range from 73 to 100%; and x) a diffuse luminous transmittance, determined according to ASTM D1003 on a 400 pm monolayer cast fdm specimen, in the range from 45 to 100%.

10. The layer element (LE) according to any one of the preceding claims, having a thickness in the range from 100 to 2000 pm, more preferably in the range from 125 to 1500 pm, most preferably in the range from 150 to 1000 pm.

11. A photovoltaic (PV) module, comprising, in the given order, a protective front layer element (1), a front encapsulation layer element (2), a photovoltaic element (3), arear encapsulation layer element (4) and a protective back layer element (5), wherein the protective back layer element (5) consists of the layer element (LE) of any one of the preceding claims, wherein the protective back layer element (5) has a total luminous transmittance, determined according to ASTM D1003, in the range from 73 to 100%.

12. The photovoltaic (PV) module according to claim 11, wherein the layer element (LE) of the protective back layer element (5) is a multilayer element, wherein at least one layer (L) comprises, more preferably consists of, the polypropylene composition (PC).

13. The photovoltaic (PV) module according to claim 12, wherein the layer element (LE) of the protective back layer element (5) is a three-layer element, consisting of the following layers, in the given order: i) an adhesive layer in adherent contact with the rear encapsulation layer element (4); ii) a core layer, comprising, more preferably consisting of, the polypropylene composition (PC); and iii) a skin layer, comprising, more preferably consisting of, a further polypropylene composition (PC’) having the properties as defined in any one of claims 1 to 9, wherein the polypropylene composition (PC) of the core layer may be the same as or different from the polypropylene composition (PC’) of the skin layer.

14. The photovoltaic (PV) module according to claim 13, wherein the adhesive layer comprises talc and optionally titanium dioxide.

15. The photovoltaic (PV) module according to claim 13 or claim 14, wherein the polypropylene composition (PC’) of the skin layer has a content of talc that is equal to or lower than, more preferably lower than, the polypropylene composition (PC) of the core layer.

Images