EP4701858A1

EP4701858A1 - Layer element suitable as integrated backsheet for a bifacial photovoltaic module

Info

Publication number: EP4701858A1
Application number: EP24722230.0A
Authority: EP
Inventors: Qizheng Dou; Minna Kaarina AARNIO-WINTERHOF; Francis Reny COSTA; Dietrich Gloger; Jeroen Oderkerk; Jessica HESSELGREN
Original assignee: Borealis GmbH
Current assignee: Borealis GmbH
Priority date: 2023-04-26
Filing date: 2024-04-25
Publication date: 2026-03-04
Also published as: WO2024223775A1

Abstract

The present invention relates to a layer element comprising a polyethylene based layer (A) and a polypropylene based layer (C) sandwiching a polyolefin based layer (B) comprising a copolymer of propylene and ethylene (B- 1) having a melting temperature Tm of from 130 to 175 °C and a copolymer of ethylene and one or more comonomers selected from 4 to 12 carbon atoms (B-2) having a melting temperature Tm of from 100 to 140°C, in a structure A- B-C, an article, preferably a photovoltaic module, such as a bifacial photovoltaic module, comprising said layer element as integrated backsheet element, a process for producing said layer element, a process for producing said photovoltaic module and the use of said layer element as integrated backsheet element of a bifacial photovoltaic module.

Description

Layer element suitable as integrated backsheet for a bifacial photovoltaic module

Technical background

In certain end use applications, like outdoor end use wherein temperature may vary within wide range and articles may be exposed to sunlight, the polymeric articles have special requirements for instance with respect to mechanical properties, long-term thermal stability, especially at high temperatures, barrier properties and UV stability.

For instance photovoltaic (PV) modules, also known as solar cell modules, produce electricity from light and are used in various kinds of applications, i.a. in outdoor 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. The above exemplified layer elements can be monolayer or multilayer elements. Typically the layer elements of PV module are assembled in order of their functionality and then laminated together to form the integrated PV module. Moreover, there may be adhesive layer(s) between the layers of an element or between the different layer elements. The photovoltaic (PV) module can for example contain, in a given order, a protective front layer element which can be flexible or rigid (such as a glass layer 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; and optionally e.g. an aluminium frame. Accordingly, part or all of the layer elements of a PV module, e.g. the front and rear encapsulation layer elements, and often the backsheet layer, are typically of a polymeric material, like ethylene vinyl acetate (EVA) based material, polyester based material or polyamide based material and fluoropolymer based materials.

Bifacial PV modules produce solar power from both sides of the panel. Whereas traditional opaque-backsheeted panels are monofacial, bifacial modules expose both the front and rear side of the solar cells. By producing solar power also from the rear side an increase of power output from bifacial PV modules of up to 30% compared to monofacial PV modules can be expected. Bifacial modules come in many designs. Some are framed while others are frameless. Some are dual -glass, and others use light transmitting backsheets. Most use monocrystalline cells, but there are polycrystalline designs. The one thing that is constant is that power is produced from both sides. There are frameless, dual -glass modules that expose the rear side of cells but are not bifacial. True bifacial modules have contacts/busbars on both the front and rear sides of their cells. Prerequisite for using a PV module as a bifacial PV module is a high transparency of the layer elements on the rear side of the solar cells for increasing the power output from the rear side of the solar cells. Nevertheless, the backsheet layer element also needs to show good mechanical stability in its function as protective back layer element. Therefore, most bifacial PV modules are dual glass modules with both protective elements on front and rear side being glass elements.

The main drawback of glass-glass modules with bifacial solar cells is the weight, which makes the handling and installation tedious, also the logistic costs might be negatively affected.

Glass being a great source of Na⁺ ion and bifacial solar cells (especially the rear side) being sensitive to potential induced degradation (PID), the bi facial modules have tendency to show high PID degradation. Currently, industry is solving it by having PID resistant encapsulant and/or Na free glass. One alternative and cheaper solution will be replacement of rear glass by a PP based transparent backsheet.

Another problem with glass-glass module is the lamination process takes longer time and also process optimization is very tedious with conventional membrane based laminators. Therefore, plate-plate laminator or autoclave based lamination are ideal to produce good quality glass-glass module. However, more than 95% of solar laminators are based on membrane based laminator and hence many module producers just cannot simply switch to bi-facial module due to this limitation. A transparent polymeric backsheet will solve this problem fully.

The problems with competitive polymeric transparent backsheet are also manifold, like high cost, week interlayer adhesion, non compatibility with different types of encapsulant and limited hydrolytic stability (especially for PET based backsheets), and environmental aspects (presence of fluorinated polymers).

WO 2021/239446 discloses layer elements suitable for integrated backsheets for bifacial photovoltaic modules, which show high transparency but tend to show poorer adhesion between the encapsulant and the backsheet layers, when using specific materials for the encapsulant and backsheet layers. Thus, the structure of the layer elements is rather unflexible when choosing materials for the encapsulant and the backsheet layers.

There is still room for improvement in regard of a balance of properties for the layer elements on the rear side of the solar cells for a bifacial PV module. The layer elements on the rear side of the solar cells should show good adhesion between the backsheet layer and the rear encapsulation layer together with good optical properties.

In the present invention a layer element is provided which comprises a polyethylene based layer A, a polyolefin based layer B and a polypropylene based layer C in adherent contact to each other with the layer structure A-B-C. Said layer element can be used as an integrated backsheet element for a PV module. When using said integrated backsheet element in a bifacial PV module a good adhesion between the layers together with good optical properties are obtained.

Summary of the invention

The present invention relates to a layer element comprising at least three layers (A), (B) and (C), wherein layer (A) comprises a polyethylene composition (PE-A); layer (B) comprises a polyolefin composition (PO-B) comprising

(B- 1) a copolymer of propylene and ethylene having a melting temperature Tm of from 130 to 175°C, preferably from 135 to 172°C, more preferably from 140 to 170°C, determined by differential scanning calorimetry according to ISO 11357 / part 3 / method C2; and

(B-2) a copolymer of ethylene and one or more comonomers selected from alpha-olefins having 4 to 12 carbon atoms having a melting temperature Tm of from 100 to 140°C, preferably from 105 to 130°C, more preferably from 110 to 125 °C, determined by differential scanning calorimetry according to ISO 11357 / part 3 / method C2; and layer (C) comprises a polypropylene composition (PP-C); wherein layer (B) has a first surface and a second surface located opposite to the first surface; the first surface of layer (B) is in adherent contact with a surface of layer (A) and the second surface of layer (B) is in adherent contact with a surface of layer (C), resulting in a layer structure A-B-C having the layer (B) sandwiched between the layer (A) and the layer (C).

Further, the present invention relates to an article comprising the layer element as described above or below. Said article is preferably a photovoltaic module, most preferably a bifacial photovoltaic module.

Still further, the invention relates to a process for producing the layer element as described above or below comprising the steps of: adhering the layers (A), (B) and (C) of the layer element together by extrusion and/or lamination in the configuration A-B-C; and recovering the formed layer element.

Additionally, the invention relates to a process for producing a photovoltaic (PV) module as described above or below comprising the steps of: assembling the photovoltaic element, the layer element and optional further layer elements to a photovoltaic (PV) module assembly; laminating the layer elements of the photovoltaic (PV) module assembly in elevated temperature to adhere the elements together; and recovering the obtained photovoltaic (PV) module. Finally, the invention relates to the use of the layer element as described above or below as an integrated backsheet element of a bifacial photovoltaic module comprising a photovoltaic element and said layer element, wherein the photovoltaic element is in adhering contact with layer (A) of the layer element.

Definitions

An olefin homopolymer is a polymer, which essentially consists of olefin monomer units of one sort. Due to impurities especially during commercial polymerization processes an olefin 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.

In this sense a propylene homopolymer is a polymer which essentially consists of propylene monomer units and an ethylene homopolymer is a polymer which essentially consists of ethylene monomer units.

An olefin copolymer is a polymer which in addition to olefin monomer units also comprise one or more comonomer units in a minor molar amount.

Thereby, a copolymer of propylene comprises a molar majority of propylene monomer units and a copolymer of ethylene comprises a molar majority of ethylene monomer units.

An olefin random copolymer is a copolymer with a molar majority of said olefin monomer units, in which the comonomer units are randomly distributed in the polymeric chain.

A heterophasic polypropylene is a propylene-based copolymer with a crystalline matrix phase, which can be a propylene homopolymer or a random copolymer of propylene and at least one alpha-olefin comonomer, and an elastomeric phase dispersed therein. The elastomeric phase can be a propylene copolymer with a high amount of comonomer which is not randomly distributed in the polymer chain but are distributed in a comonomer-rich block structure and a propylene -rich block structure.

A heterophasic polypropylene usually differentiates from a one-phasic propylene copolymer in that it shows two distinct glass transition temperatures Tg which are attributed to the matrix phase and the elastomeric phase.

A plastomer is a polymer which combines the qualities of elastomers and plastics, such as rubber-like properties with the processing abilities of plastic. An ethylene-based plastomer is a plastomer with a molar majority of ethylene monomer units.

A layer element in the sense of the present invention is a structure of one or more layers with a defined functionality which serves a certain purpose in an article comprising said layer element. In the field of PV modules a layer element is a structure of one or more layers which serves one of several functionalities such as outer protection (i.e. a protective front layer element or protective back layer element), encapsulation of the photovoltaic element (i.e. the front encapsulation layer element or rear encapsulation layer element) and the energy conversion (i.e. the photovoltaic element). A layer element can comprise other components, which are not layers, such as e.g. braces, spacers, frames etc.

An integrated backsheet element of a PV module is a structure of more than one layers which encompasses more than one functionality of the PV module. It is preferred that the integrated backsheet element encompasses the outer protection functionality of the protective back layer element and the encapsulation of the photovoltaic element function of the rear encapsulation layer element. These functionalities are usually encompassed by different layers of the integrated backsheet element.

A bifacial photovoltaic module is a photovoltaic module which produces solar power from the front and the rear side of the solar cells of the photovoltaic element.

Two layers being in adhering contact means that the surface of one layer is in direct contact with the surface of the other layer without any layers or any spacers between these layers.

Different in the context of the present invention means that two polymers differ in at least one property or structural element.

Detailed description

Layer element

The layer element of the present invention comprises three layers (A), (B) and (C). The first surface of layer (B) is in adherent contact with one surface of layer (A) and the second surface of layer (B) is in adherent contact with one surface of layer (C), resulting in the layer structure A-B-C. Thereby, layer (B) is sandwiched between layers (A) and (C).

The layer element can consist of layers (A), (B) and (C) in the configuration A-B-C. Then the layer element is a three-layer element.

The layer element alternatively can comprise one or more layer(s) in addition to the layers (A), (B) and (C). These additional layers can either be added to the surface of layer (A), which is not in adherent contact with layer (B) (i.e. layer(s) (X)), or to the surface of layer (C), which is not in adherent contact with layer (B) (i.e. layer(s) (Y)), or both (layers (X) and (Y)).

Possible configurations are X-A-B-C, A-B-C-Y and X-A-B-C-Y.

Layer(s) (X) can be one or more additional layers, such as 1, 2, 3 or 4 additional layer(s) (X), preferably one additional layer (X). Layer(s) (X) can be the same as layer (A) or different from layer (A).

Layer(s) (Y) can be one or more additional layers, such as 1, 2, 3 or 4 additional layer(s) (Y), preferably one additional layer (Y). Layer(s) (Y) can be the same as layer (C) or different from layer (C).

Usually, the layers (A) and (C) have the same or a greater thickness than layer (B).

In a three-layer element the thickness of layer (A) is preferably from 40 to 65 % of the total thickness of the three-layer element.

In a three-layer element the thickness of layer (B) is preferably from 2.0 to 20 % of the total thickness of the three-layer element.

In a three-layer element the thickness of layer (C) is preferably from 25 to 50 % of the total thickness of the three-layer element.

Layer (A) preferably has a thickness of from 100 pm to 750 pm, preferably from 150 pm to 650 pm, most preferably from 200 pm to 550 pm. Layer (A) can be mono-layer film consisting of one layer A or coextruded with X layer(s), typically having a layer thickness distribution of 10%/80%/10% up to 33.3%/33.3%/33.3%.

Layer (B) preferably has a thickness of from 10 pm to 100 pm, preferably from 20 pm to 80 pm, most preferably from 25 pm to 70 pm.

Layer (C) preferably has a thickness of from 125 pm to 750 pm, more preferably from 150 pm to 650 pm, most preferably from 200 pm to 550 pm. The total thickness of combined layers (C) and (Y) is preferably in the range of from 150 to 800 pm, preferably from 175 to 700 pm, most preferably from 200 to 600 pm.

Layer (B) and (C) are preferably coextruded as two layer element B/C, or 3 layer element B/C/Y, such as B/C/C, or alternatively B/C/(Y)x, with x being the number of multiple layers (Y) as discussed above.

The thickness distribution of such 3-layer concept varies between 10%/80%/l 0% up to 30%/40%/30%.

In a 5-layer concept with multiple (Y) layers, e.g. three (Y) layers, the relative thickness distribution of B/C7Y/Y/Y or B/C/C/C/Y can be further varied between 5%/15%/60%/15%/5% and 20%/20%/20%/20%/20%.

The layer element usually has a total thickness of from 250 pm to 2000 pm, preferably from 400 pm to 1750 pm and most preferably from 600 pm to 1500 pm.

In one embodiment it is preferred that none of the layers of the layer element comprises titanium dioxide, preferably a pigment as defined below. This means that preferably the layer element is free of titanium dioxide, preferably free of pigment. In said embodiment the layer element is especially suitable as integrated backsheet of a bifacial photovoltaic module. In another embodiment it is preferred that layer (B) does not comprise titanium dioxide, preferably a pigment as defined below. This means that preferably only layer (B) of the layer element is free of titanium dioxide, preferably free of pigment, whereas one or more of layers (A) and (C), and optionally layers X and Y comprise titanium dioxide, preferably a pigment as defined below. In said embodiment it is especially preferred that layer (C) and optionally layer(s) Y comprise titanium dioxide, preferably a pigment as defined below, whereas layers (B), (A) and optionally (X) ) does not comprise titanium dioxide, preferably a pigment as defined below. In said embodiment the layer element is especially suitable as integrated backsheet of a monofacial photovoltaic module.

In some embodiments none of the layers of the layer element comprises a flame retardant as defined below. Pigments in the sense of this application preferably are selected from mica, titanium dioxide, CaCCh, dolomite, carbon black or any kind of coloured pigment (such as yellow, green, red, blue and so on), which could be included due to aesthetic reasons.

If present, the amount of titanium dioxide or pigment in the accordant layer is preferably up to 25 wt%, like from 2.0 to 25 wt%, preferably from 3.0 to 20 wt%, based on the total weight of the composition of the accordant layer.

In regard of the optical properties has been found that the layer element shows a relatively high clarity and low haze considering the thickness of the layer element, when measured on the combined layers (B) and (C) prepared as described in the example section:

In the example section the combined layers (B) and (C) have a haze, determined according to ASTM D1003-13, of from not more than 50 %, such as from 30 to 50 %, preferably from 33 to 48 %, more preferably from 35 to 46 %.

Further, in the example section the combined layers (B) and (C) have a clarity, determined according to ASTM D1003-13, of at least 88%, such as from 88 to 99 %, preferably from 90 to 99 %, more preferably from 92 to 99 %.

The layer element according to the invention preferably has the following transmittance properties, when measured on the combined layers (B) and (C) prepared as described in the example section:

The combined layers (B) and (C) have a total luminous transmittance, determined according to ASTM D1003-13, of at least 84%, more preferably at least 86%, most preferably at least 87%.

The upper limit of the total luminous transmittance, determined according to ASTM D1003- 13, is usually not more than 99%, preferably not more than 97%, more preferably not more than 95%.

The combined layers (B) and (C) have a diffuse luminous transmittance, determined according to ASTM D1003-13, of at least 30%, more preferably at least 32%, most preferably at least 34%.

The upper limit of the diffuse luminous transmittance, determined according to ASTM

DI 003-13, is usually not more than 50%, preferably not more than 45%, more preferably not more than 43%. Despite a rather high overall thickness, the layer element shows surprisingly good optical properties in regard of high transmittance properties, low haze and high clarity, when measured on the combined layers (B) and (C) prepared as described in the example section.

Further, the layer element preferably has an adhesion before ageing between layers (A) and (B), determined according to method (a) given in the determination methods, of more than 7.0 N/mm, more preferably at least 8.0 N/mm.

The upper limit is usually not higher than 18 N/mm, such as not higher than 16 N/mm.

Still further, the layer element preferably has an adhesion after ageing for 1000 h at 80°C and 85 % RH between layers (A) and (B), determined according to method (a) given in the determination methods, of more than 4.0 N/mm, more preferably at least 4.2 N/mm.

Furthermore, the layer element preferably has an adhesion after ageing for 2000 h at 80°C and 85 % RH, determined according to method (a) given in the determination methods, of more than 4.0 N/mm, more preferably at least 4.2 N/mm.

Further, the layer element preferably has an adhesion before ageing between layers (A) and (B), determined according to method (b) given in the determination methods, of more than 7.0 N/mm, more preferably at least 8.0 N/mm.

Still further, the layer element preferably has an adhesion after ageing for 1000 h at 80°C and 85 % RH between layers (A) and (B), determined according to method (b) given in the determination methods, of more than 4.0 N/mm, more preferably at least 4.2 N/mm.

The upper limit is usually not higher than 18 N/mm, such as not higher than 16 N/mm. Furthermore, the layer element preferably has an adhesion after ageing for 2000 h at 80°C and 85 % RH, determined according to method (b) given in the determination methods, of more than 4.0 N/mm, more preferably at least 4.2 N/mm.

Layer A

Layer A comprises, preferably consists of the polyethylene composition (PE-A).

The polyethylene composition (PE-A) comprises a copolymer of ethylene, which is selected from

(PE-A-a) a copolymer of ethylene, which bears silane group(s) containing units; or

(PE-A-b) a copolymer of ethylene with polar comonomer units selected from one or more of (Ci-Ce)-alkyl acrylate or (Ci-Ce)-alkyl (Ci-C6)-alkylacrylate comonomer units, which additionally bears silane group(s) containing units, whereby the copolymer of ethylene (PE-A-a) is different from the copolymer of ethylene (PE-A-b); or

(PE-A-c) a copolymer of ethylene with vinyl acetate comonomer units or

(PE-A-d) a copolymer of ethylene with one or more alpha-olefin comonomer units having from 3 to 10 carbon atoms, wherein the copolymer of ethylene (PE-A-d) has a density of from 850 to less than 900 kg/m³, preferably from 860 to 890 kg/m³, more preferably from 865 to 885 kg/m³, determined according to ISO 1183.

The copolymers of ethylene (PE-A-a) and (PE-A-b) bear silane group(s) containing units. The silane group(s) containing units can be present as comonomer units of the copolymer of ethylene or as a compound grafted chemically to the copolymer of ethylene. “Silane group(s) containing comonomer units” means herein above, below or in claims that the silane group(s) containing units are present in the copolymer of ethylene as a comonomer units.

In the case of silane group(s) containing units being incorporated into the copolymer of ethylene as a comonomer units, the silane group(s) containing units are copolymerized as comonomer units with ethylene monomer units during the polymerization process of copolymer of ethylene. In the case that the silane group(s) containing units are incorporated into the copolymer of ethylene by grafting, the silane group(s) containing units are reacted chemically (also called as grafting), with the copolymer of ethylene after the polymerization of the copolymer of ethylene. The chemical reaction, i.e. grafting, is performed typically using a radical forming agent such as peroxide. Such chemical reaction may take place before or during the lamination process of the invention. In general, copolymerisation and grafting of the silane group(s) containing units to ethylene are well known techniques and well documented in the polymer field and within the skills of a skilled person.

It is also well known that the use of peroxide in the grafting embodiment decreases the melt flow rate (MFR) of an ethylene polymer due to a simultaneous crosslinking reaction. As a result, the grafting embodiment can bring limitation to the choice of the MFR of the copolymer of ethylene as a starting polymer, which choice of MFR can have an adverse impact on the quality of the polymer at the end use application. Furthermore, the by-products formed from peroxide during the grafting process can have an adverse impact on the use of the polyethylene composition (PE-A) at end use application.

The copolymerisation of the silane group(s) containing comonomer units into the polymer backbone provides more uniform incorporation of the units compared to grafting of the units. Moreover, compared to grafting, the copolymerisation does not require the addition of peroxide after the polymer is produced.

Thus, it is preferred that the silane group(s) containing units are present in copolymer of ethylene as a comonomer units.

I.e. in case of copolymer of ethylene (PE-A-a) the silane group(s) containing units are copolymerised as comonomer units together with the ethylene monomer units during the polymerisation process of the copolymer of ethylene (PE-A-a).

In the case of the copolymer of ethylene (PE-A-b) the silane group(s) containing units are copolymerised as a comonomer units together with the polar comonomer units and ethylene monomer units during the polymerisation process of the copolymer of ethylene (PE-A-b).

The silane group(s) containing units, preferably the silane group(s) containing comonomer units, of the copolymer of ethylene (PE-A-a) or the copolymer of ethylene (PE-A-b) are preferably a hydrolysable unsaturated silane compound represented by the formula (I): RJSll qYs-q (I) wherein

R¹ is an ethylenically unsaturated hydrocarbyl, hydrocarbyloxy or (meth)acryloxy hydrocarbyl group, each R² is independently an aliphatic saturated hydrocarbyl group,

Y which may be the same or different, is a hydrolysable organic group and q is 0, 1 or 2;

Further suitable silane group(s) containing comonomer is e.g. gamma-(meth)acryl-oxypropyl trimethoxysilane, gamma(meth)acryloxypropyl triethoxy silane, and vinyl triacetoxysilane, or combinations of two or more thereof.

One suitable subgroup of compound of formula (I) is an unsaturated silane compound or, preferably, comonomer of formula (II)

CH₂=CHSi(OA)₃ (II) wherein each A is independently a hydrocarbyl group having 1-8 carbon atoms, suitably 1-4 carbon atoms.

The silane group(s) containing unit, or preferably, the comonomer, of the invention, is preferably the compound of formula (II) which is vinyl trimethoxysilane, vinyl bismethoxyethoxy silane, vinyl triethoxy silane, more preferably vinyl trimethoxy silane or vinyl triethoxy silane.

The amount of the silane group(s) containing units present in the based on the total amount of monomer units in the the copolymer of ethylene (PE-A-a) or the copolymer of ethylene (PE-A-b), preferably as comonomer units, is preferably in the range of from 0.01 to 1.5 mol%, more preferably from 0.01 to 1.00 mol%, still more from 0.05 to 0.80 mol%, even more preferably from 0.10 to 0.60 mol%, most preferably from 0.10 to 0.50 mol%, based on the total amount of monomer units in the the copolymer of ethylene (PE-A-a) or the copolymer of ethylene (PE-A-b).

In one preferred embodiment the copolymer of ethylene is the copolymer of ethylene, which bears silane group(s) containing units (PE-A-a), preferably with silane group(s) containing comonomer units. In this embodiment the copolymer of ethylene (PE-A-a) does not contain, i.e. is without, a polar comonomer as defined for the copolymer of ethylene (PE-A-b). Preferably, the silane group(s) containing comonomer units are the sole comonomer units present in the copolymer of ethylene (PE-A-a). Accordingly, the copolymer of ethylene (PE- A-a) is preferably produced by copolymerising ethylene monomer units in a high pressure polymerization process in the presence of silane group(s) containing comonomer units using a radical initiator.

In said preferred embodiment the copolymer of ethylene (PE-A-a) is preferably a copolymer of ethylene with silane group(s) containing comonomer units according to formula (I), more preferably with silane group(s) containing comonomer units according to formula (II), still more preferably with silane group(s) containing comonomer units selected from vinyl trimethoxysilane, vinyl bismethoxyethoxysilane, vinyl triethoxysilane or vinyl trimethoxysilane comonomer. It is especially preferred that the copolymer of ethylene (PE- A-a) is a copolymer of ethylene with vinyl trimethoxysilane or vinyl triethoxysilane comonomer, most preferably a copolymer of ethylene with vinyl trimethoxy silane.

In another preferred embodiment the copolymer of ethylene is copolymer of ethylene with polar comonomer unit(s) selected from one or more, preferably one, of (Ci-Ce)-alkyl acrylate or (Ci-Ce)-alkyl (Ci-C6)-alkylacrylate comonomer unit(s), which additionally bears silane group(s) containing units (PE-A-b). Preferably, the silane group(s) containing units are present as comonomer units. In this embodiment the copolymer of ethylene (PE-A-b) is thus preferably a copolymer of ethylene with polar comonomer(s) units selected from one or more, preferably one, of (Ci-Ce)-alkyl acrylate or (Ci-Ce)-alkyl (Ci-C6)-alkylacrylate; and with silane group(s) containing comonomer units. Preferably, the polar comonomer units and the silane group(s) containing comonomer units are the sole comonomer units present in the copolymer of ethylene (PE-A-b). Accordingly, the copolymer of ethylene (PE-A-b) is preferably produced by copolymerising ethylene monomer units in a high pressure polymerization process in the presence of polar comonomer units and silane group(s) containing comonomer units using a radical initiator. Preferably, the polar comonomer units of the copolymer of ethylene (PE-A-b) are selected from (Ci-Ce)-alkyl acrylate comonomer units, more preferably from methyl acrylate (MA), ethyl acrylate (EA) or butyl acrylate (BA) comonomer units, most preferably from methyl acrylate comonomer units.

Without binding to any theory, for instance, methyl acrylate (MA) is the only acrylate which cannot go through the ester pyrolysis reaction, since does not have this reaction path. Therefore, the copolymer of ethylene (PE-A-b) with MA comonomer units does not form any harmful free acid (acrylic acid) degradation products at high temperatures, whereby the copolymer of ethylene (PE-A-b) comprising methyl acrylate comonomer units contributes to good quality and life cycle of the end article thereof. This is not the case e.g. with vinyl acetate units of EVA, since EVA forms harmful acetic acid degradation products at high temperatures. Moreover, the other acrylates like ethyl acrylate (EA) or butyl acrylate (BA) can go through the ester pyrolysis reaction, and if degrade, would form volatile olefinic byproducts.

The amount of the polar comonomer units present in the copolymer of ethylene (PE-A-b) is preferably in the range of from 0.5 to 30.0 mol%, preferably from 2.5 to 20.0 mol%, still more preferably from 5.0 to 15.0 mol%, most preferably from 7.5 to 12.5 mol%, based on the total amount of monomer units in the copolymer of ethylene (PE-A-b).

It is preferred that the copolymer of ethylene (PE-A-b) is a copolymer of ethylene with methyl acrylate, ethyl acrylate or butyl acrylate comonomer units and with vinyl trimethoxysilane, vinyl bismethoxyethoxysilane, vinyl triethoxysilane or vinyl trimethoxysilane comonomer units, more preferably with vinyl trimethoxysilane or vinyl triethoxysilane comonomer units.

More preferably the copolymer of ethylene (PE-A-b) is a copolymer of ethylene with methyl acrylate comonomer units and with vinyl trimethoxysilane, vinyl bismethoxyethoxysilane, vinyl triethoxysilane or vinyl trimethoxysilane comonomer, still more preferably a copolymer of ethylene with methyl acrylate comonomer units and with vinyl trimethoxysilane or vinyl triethoxysilane comonomer units, most preferably a copolymer of ethylene with methyl acrylate comonomer units with vinyl trimethoxysilane. The polyethylene composition (PE-A) enables, if desired, to decrease the melt flow rate (MFR) of the copolymer of ethylene (PE-A-a) or copolymer of ethylene (PE-A-b) compared to prior art and thus offers higher resistance to flow during the production of the layer (A) and the layer element of the invention. As a result, the preferable MFR can further contribute, if desired, to the quality of the layer element, and to article, preferably the PV module, comprising the layer element.

The melt flow rate, MFR2, of the copolymer of ethylene (PE-A-a) or copolymer of ethylene (PE-A-b) is preferably less than 20 g/10 min, preferably less than 15 g/10 min, more preferably from 0.1 to 13 g/10 min, still more preferably from 0.5 to 10 g/10 min, even more preferably from 1.0 to 8.0 g/10 min, more preferably from 1.5 to 6.0 g/10 min.

The copolymer of ethylene (PE-A-a) or copolymer of ethylene (PE-A-b) preferably has a melting temperature of from 70 to 120°C, more preferably from 75 °C to 110°C, still more preferably from 80°C to 100°C and most preferably from 85°C to 95°C. The preferable melting temperature is beneficial for instance for a lamination process, since the time of the melting/softening step can be reduced.

Preferably the density of the copolymer of ethylene (PE-A-a) or copolymer of ethylene (PE- A-b) is from 920 to 960 kg/m³, preferably from 925 to 955 kg/m³ and most preferably from 930 to 950 kg/m³.

The copolymer of ethylene (PE-A-a) or copolymer of ethylene (PE-A-b) can be e.g. commercially available or can be prepared according to or analogously to known polymerization processes described in the chemical literature.

In a preferred embodiment the copolymer of ethylene (PE-A-a) or copolymer of ethylene (PE-A-b) is produced by polymerising ethylene suitably with silane group(s) containing comonomer units as defined above, and in case of the copolymer of ethylene (PE-A-b) also with the polar comonomer units as described above, in a high pressure (HP) process using free radical polymerization in the presence of one or more initiator(s) and optionally using a chain transfer agent (CTA) to control the MFR of the polymer.

A suitable high pressure (HP) process with suitable polymerization conditions is described in WO 2018/141672.

Such HP polymerisation results in a so called low density polymer of ethylene (LDPE), herein to copolymer of ethylene (PE-A-a) or copolymer of ethylene (PE-A-b). The term LDPE has a well-known meaning in the polymer field and describes the nature of polyethylene produced in HP, i.e. the typical features, such as different branching architecture, to distinguish the LDPE from PE produced in the presence of an olefin polymerisation catalyst (also known as a coordination catalyst). Although the term LDPE is an abbreviation for low density polyethylene, the term is understood not to limit the density range, but covers the LDPE-like HP polyethylenes with low, medium and higher densities.

In another preferred embodiment the polyethylene composition (PE-A) comprises a copolymer of ethylene monomer units and vinyl acetate comonomer units (EVA) (PE-A-c).

The amount of the vinyl acetate (VA) comonomer units present in the copolymer of ethylene (PE-A-c) is preferably in the range of from 0.5 to 30.0 mol%, preferably from 2.5 to 20.0 mol%, still more preferably from 5.0 to 15.0 mol%, most preferably from 7.5 to 12.5 mol%, based on the total amount of monomer units in the copolymer of ethylene (PE-A-c).

The melt flow rate, MFR2, of the copolymer of ethylene (PE-A-c) is preferably from 0. 1 to 13 g/10 min, still more preferably from 1.0 to 50 g/10 min, more preferably from 5.0 to 45.0 g/10 min, more preferably from 7.5 to 40.0 g/10 min, most preferably from 10.0 to 35.0 g/10 min, when determined according to ISO 1133 at 190 °C and at a load of 2. 16 kg.

The copolymer of ethylene (PE-A-c) preferably has a melting temperature of from 25 to 95°C, more preferably from 30°C to 90°C, still more preferably from 35°C to 85°C and most preferably from 40°C to 80°C. The preferable melting temperature is beneficial for instance for a lamination process, since the time of the melting/softening step can be reduced. Preferably the density of the copolymer of ethylene (PE-A-c) is from 940 to 975 kg/m³, preferably from 945 to 970 kg/m³ and most preferably from 950 to 965 kg/m³.

The copolymer of ethylene (PE-A-c) is preferably crosslinkable.

The copolymer of ethylene (PE-A-c) usually is commercially available but can be prepared according to or analogously to known polymerization processes described in the chemical literature.

Suitable commercially available copolymers of ethylene (PE-A-c) can be purchased e.g. from Hangzhou First Applied Material Co., Ltd (PR China).

In yet another preferred embodiment the polyethylene composition (PE-A) comprises a copolymer of ethylene with one or more alpha-olefin comonomer units having from 3 to 12 carbon atoms (PE-A-d), which has a density of from 850 to less than 900 kg/m³, preferably from 860 to 890 kg/m³, more preferably from 865 to 885 kg/m³, determined according to ISO 1183.

Said copolymer of ethylene (PE-A-d) qualifies as very low-density polyethylene (VLDPE). The very low-density polyethylene (VLDPE) can be identified as polyolefin elastomer (POE). According to the IUPAC definition an elastomer is a polymer that displays rubberlike elasticity.

Polyethylene based elastomers are commercially available under the tradenames Queo™, Exact™, Engage™, F RST® TF series and others.

The copolymer of ethylene (PE-A-d) preferably has a melt flow rate (ISO 1133, 2. 16 kg, 190°C) of from 0.5 to 25.0 g/10 min, more preferably from 1.0 to 22.5 g/10 min, still more preferably from 2.5 to 20.0 g/10 min.

The copolymer of ethylene (PE-A-d) preferably has a melting temperature of from 25 to 95°C, more preferably from 30°C to 90°C, still more preferably from 35°C to 85°C and most preferably from 40°C to 80°C. The preferable melting temperature is beneficial for instance for a lamination process, since the time of the melting/softening step can be reduced. The copolymer of ethylene (PE-A-d) is copolymer of ethylene and one or more comonomer units, preferably one comonomer, selected from alpha-olefins having from 3 to 12 carbon atoms, preferably from alpha-olefins having from 4 to 8 carbon atoms. It is preferred that the polymeric component is a copolymer of ethylene and 1 -butene or a copolymer of ethylene and 1 -octene.

It is preferred that component (PE-A-d) does not include any other monomers than ethylene and one or more comonomer units selected from alpha-olefins having from 3 to 12 carbon atoms, i.e. consists of monomer units selected from ethylene and one or more comonomer units, preferably one comonomer, selected from alpha-olefins having from 3 to 12 carbon atoms.

The copolymer of ethylene (PE-A-d) is preferably produced in a solution polymerization process using a metallocene catalyst, as known in the art.

The copolymer of ethylene (PE-A-d) is preferably crosslinkable.

The polyethylene composition (PE-A) preferably comprises the copolymer of ethylene (PE- A-a), (PE-A-b), (PE-A-c) or (PE-A-d) in an amount of from 20.0 wt% to 100 wt%, more preferably from 20.0 wt% to 99.9999 wt%, still more preferably from 65.0 to 99.999 and most preferably from 87.5 wt% to 99.99 wt%, based on the total weight amount of the polyethylene composition (PE-A).

The amount of the copolymer of ethylene (PE-A-a), (PE-A-b), (PE-A-c) or (PE-A-d) in the polyethylene composition (PE-A) depends on the presence of additional components in the polyethylene composition (PE-A).

The polyethylene composition (PE-A) suitably comprises additive(s) which are other than filler, pigment, carbon black or flame retardant which terms have a well-known meaning in the prior art.

The optional additives are e.g. conventional additives suitable for the desired end application and within the skills of a skilled person, including without limiting to, preferably at least antioxidant(s), UV light stabilizer(s) and/or UV light absorbers, and may also include metal deactivator(s), clarifier(s), brightener(s), acid scavenger(s), as well as slip agent(s) etc. Each additive can be used e.g. in conventional amounts, the total amount of additives present in the PE composition (PE-A) being preferably as defined below. Such additives are generally commercially available and are described, for example, in "Plastic Additives Handbook", 5th edition, 2001 of Hans Zweifel.

The amount of additives is preferably in the range of from up to 10.0 wt%, such as 0.0001 to 10.0 wt%, more preferably 0.001 and 5.0 wt%, most preferably 0.01 to 2.5 wt%, based on the total weight amount of the polyethylene composition (PE-A).

The polyethylene composition (PE-A) can further comprise flame retardants.

Optional flame retardants are typically conventional and commercially available. Suitable optional flame retardants are as defined herein in context of the layer C to fillers.

The amount of flame retardants is preferably in the range of from up to 20.0 wt%, such as 0.1 to 20.0 wt%, preferably 0.5 to 15.0 wt%, most preferably 1.0 to 10.0 wt%, based on the total weight amount of the polyethylene composition (PE-A).

The polyethylene composition (PE-A) can further comprise a pigment as defined above, preferably titanium dioxide.

It is, however, preferred that the polyethylene composition (PE-A) does not comprise titanium dioxide, preferably a pigment as defined above.

The polyethylene composition (PE-A) can further comprise polymers which are different from the copolymer of ethylene (PE-A-a), (PE-A-b), (PE-A-c) or (PE-A-d).

It is however preferred that the polyethylene composition (PE-A) comprises the copolymer of ethylene (PE-A-a), (PE-A-b), (PE-A-c) or (PE-A-d) as the only polymeric component(s).

“Polymeric component(s)” exclude herein any carrier polymer(s) of optional additive or filler, e.g. carrier polymer(s) used in master batch(es) of additive or, respectively, filler optionally present in the polyethylene composition (PE-A). Such optional carrier polymer(s) are calculated to the amount of the respective additive or, respectively filler based on the amount (100 wt%) of the polyethylene composition (PE-A). In an especially preferred embodiment, the polyethylene composition (PE-A) is free of fdlers, pigments and/or carbon black.

The absence of fdlers, pigments and/or carbon black has been found to increase the transparency of layer (A) which helps to improve the power output of a bifacial photovoltaic module.

It is further preferred that the polyethylene composition (PE-A) is additionally free of flame retardants as defined above. In said embodiment the polyethylene composition (PE-A) is preferably free of fillers, pigments, carbon black and/or flame retardants.

In one embodiment the polyethylene composition (PE-A) comprises, preferably consists of, 70.0 to 99.9999 wt%, preferably 80.0 to 99.499 wt%, most preferably 87.5 to 98.99 wt% of the copolymer of ethylene;

0.0001 to 10.0 wt%, preferably 0.001 and 5.0 wt%, most preferably 0.01 and 2.5 wt% of additives and

0 to 20.0 wt%, preferably 0.5 to 15.0 wt%, most preferably 1.0 to 10.0 wt% of flame retardant.

In said embodiment the polyethylene composition (PE-A) usually has the same ranges of the properties of melt flow rate MFR2 and shear thinning index SHI0.05/300 as defined for the copolymer of ethylene (PE-A-a), copolymer of ethylene (PE-A-b), copolymer of ethylene (PE-A-c) or copolymer of ethylene (PE-A-d) above.

In another embodiment the polyethylene composition (PE-A) comprises additives but no flame retardant as defined above. Then, the polyethylene composition (PE-A), comprises, preferably consists of, based on the amount (100 wt%) of the polyethylene composition (PEAK

90.0 to 99.9999 wt%, preferably 95.0 to 99.999 wt%, most preferably 97.5 to 99.99 of the copolymer of ethylene; and

0.0001 to 10.0 wt%, preferably 0.001 and 5.0 wt%, most preferably 0.01 and 2.5 wt%, of the additives. In said embodiment the polyethylene composition (PE-A) usually has the same ranges of the properties of melt flow rate MFR2, density and melting temperature Tm as defined for the copolymer of ethylene (PE-A-a), copolymer of ethylene (PE-A-b), copolymer of ethylene (PE-A-c) or copolymer of ethylene (PE-A-d) above.

This embodiment is especially preferred for the polyethylene composition (PE-A) of the layer element of the present invention.

Preferably the layer A of the layer element consists of the polyethylene composition (PE-A) comprising the copolymer of ethylene as defined above, below or in claims.

The layer (A), preferably the polyethylene composition (PE-A), most preferably the copolymer of ethylene (PE-A-a) or (PE-A-b), is preferably not crosslinked using peroxide. When using the copolymer of ethylene (PE-A-c) or (PE-A-d), the layer (A), preferably the polyethylene composition (PE-A), most preferably the copolymer of ethylene (PE-A-c) or (PE-A-d), can be crosslinked using peroxide, preferably in the presence of an organic peroxide. The crosslinking process and conditions are well known in the art and depend on the nature of the used peroxide.

It is preferred that the layer (A), preferably the polyethylene composition (PE-A), most preferably the copolymer of ethylene (PE-A-a) or (PE-A-b), is not crosslinked via the silane group(s), especially in the presence of a silanol condensation catalyst.

Thus, the layer (A), preferably the polyethylene composition (PE-A) does not comprise a silanol condensation catalyst. Such silanol condensation catalysts are known in the art.

Layer (A) preferably has a thickness of from 100 pm to 750 pm, preferably from 150 pm to 650 pm, most preferably from 200 pm to 550 pm.

Layer (B)

The layer element comprises layer (B), which is sandwiched and in adherent contact with layers (A) and (C).

Layer (B) comprises, preferably consists of the polyolefin composition (PO-B). The polyolefin composition comprises

(B-2) a copolymer of ethylene and one or more comonomers selected from alpha-olefins having 4 to 12 carbon atoms having a melting temperature Tm of from 100 to 140°C, preferably from 105 to 130°C, more preferably from 110 to 125 °C, determined by differential scanning calorimetry according to ISO 11357 / part 3 / method C2.

The copolymer of propylene and ethylene (B- 1 ) preferably has a total ethylene content of from 1.5 to 12.5 wt.-%, more preferably from 2.0 to 11.0 wt.-%, still more preferably from 3.0 to 10.0 wt.-%, based on the total weight of the copolymer of propylene and ethylene (B- 1) and determined by FTIR after basic assignment calibrated via quantitative ¹³C NMR spectroscopy.

It is preferred that ethylene is the only comonomer in the copolymer of propylene and ethylene (B-l), i.e. the copolymer of propylene and ethylene (B- 1) consists to propylene and ethylene monomer units.

Further, the copolymer of propylene and ethylene (B-l) preferably has a melt flow rate MFR2 of from 0.5 to 7.5 g/10 min, more preferably from 1.0 to 6.0 g/ 10 min, still more preferably from 1.5 to 5.0 g/10 min, determined according to ISO 1133 at a temperature of 230°C and load of 2.16 kg.

Still further, the copolymer of propylene and ethylene (B-l) preferably has a Vicat A softening temperature of from 100 to 165 °C, more preferably from 110 to 160°C, still more preferably from 115 to 155°C.

The mechanical and impact properties depend on the nature of the copolymer of propylene and ethylene (B-l) and therefore can have a rather broad range. The copolymer of propylene and ethylene (B- 1) can have a flexural modulus in the range of from 400 to 2000 MPa, preferably from 450 to 1750 MPa, more preferably from 500 to 1500 MPa.

Further, the copolymer of propylene and ethylene (B- 1) can have a Charpy notched impact strength at 23°C of from 5.0 to 75 kJ/m², preferably from 7.5 to 60 kJ/m², more preferably from 10 to 50 kJ/m².

The copolymer of propylene and ethylene (B- 1 ) preferably is a heterophasic copolymer of propylene, which comprises, a polypropylene matrix component and an elastomeric propylene-ethylene copolymer component which is dispersed in said polypropylene matrix.

The matrix component of the heterophasic copolymer of propylene can be a propylene homopolymer component or a propylene random copolymer component.

When being a propylene random copolymer component, the matrix component is preferably a propylene-ethylene random copolymer.

The XCS fraction of the heterophasic copolymer of propylene is regarded herein as the elastomeric component, since the amount of XCS fraction in the matrix component is conventionally markedly lower. For instance, in case the matrix component is a homopolymer of propylene, then the weight amount of the xylene cold soluble (XCS) fraction of the heterophasic copolymer of propylene is understood in this application also as the amount of the elastomeric propylene copolymer component present in the heterophasic copolymer of propylene.

The heterophasic copolymer of propylene preferably has a xylene cold soluble (XCS) fraction in amount of from 5 to 40 wt%, more preferably from 10 to 35 wt%, based on the total amount of the heterophasic copolymer of propylene. The xylene cold soluble (XCS) fraction preferably has an ethylene content of from 20 to 45 wt%, more preferably from 24 to 40 wt%, based on the total weight of the XCS fraction.

Further, the heterophasic copolymer of propylene preferably has a density of 900 to 910 kg/m³.

In one embodiment the copolymer of propylene and ethylene (B- 1) is a heterophasic copolymer of propylene and ethylene (B-l-a), which comprises a random copolymer of propylene and ethylene as matrix component and a elastomeric propylene -ethylene copolymer component which is dispersed in said matrix component.

In said embodiment the matrix phase, being measured as the phase insoluble in cold xylene (XCI fraction), preferably has an ethylene content of from 1.0 to 6.0 wt%, preferably from 1.5 to 5.5 wt%, more preferably from 2.0 to 5.0 wt%, based on the total weight of the XCI fraction.

The XCI fraction further preferably has a melt flow rate of from 1.5 to 10 g/10 min, more preferably from 2.0 to 7.5 g/10 min, still more preferably from 2.5 to 5.0 g/10 min.

The heterophasic copolymer of propylene and ethylene (B-l-a) preferably an amount of XCS fraction of from 10 to 40 wt%, more preferably from 15 to 35 wt%, based on the total amount of the heterophasic copolymer of propylene (B-l-a).

The XCS fraction preferably has an ethylene content of from 20 to 45 wt%, more preferably from 25 to 40 wt%, based on the total weight of the XCS fraction.

The heterophasic copolymer of propylene and ethylene (B-l-a) preferably has a melt flow rate of from 0.5 to 7.5 g/10 min, more preferably from 1.0 to 6.0 g/10 min, still more preferably from 1.5 to 5.0 g/10 min.

Further, the heterophasic copolymer of propylene and ethylene (B-l-a) preferably has a total ethylene content of from 5.0 to 12.5 wt.-%, more preferably from 6.5 to 11.0 wt.-%, still more preferably from 7.5 to 10.0 wt.-%, based on the total weight of the copolymer of propylene and ethylene (B-l-a).

It is preferred that the heterophasic copolymer of propylene and ethylene (B-l-a) has a melting temperature Tm of from 130 to 155°C, preferably from 135 to 152°C, more preferably from 140 to 150°C.

Still further, the heterophasic copolymer of propylene and ethylene (B-l-a) preferably has a Vicat A softening temperature of from 100 to 135°C, more preferably from 110 to 130°C, still more preferably from 115 to 125 °C.

The heterophasic copolymer of propylene and ethylene (B-l-a) preferably has a flexural modulus in the range of from 400 to 1000 MPa, preferably from 450 to 800 MPa, more preferably from 500 to 750 MPa.

Further, the heterophasic copolymer of propylene and ethylene (B-l-a) preferably has a Charpy notched impact strength at 23°C of from 5.0 to 35 kJ/m², preferably from 7.5 to 30 kJ/m², more preferably from 10 to 25 kJ/m².

In another embodiment the copolymer of propylene and ethylene (B-l) is a heterophasic copolymer of propylene and ethylene (B-l-b), which comprises a propylene homopolymer as matrix component and a elastomeric propylene-ethylene copolymer component which is dispersed in said matrix component.

In said embodiment the matrix phase, being measured as the phase insoluble in cold xylene (XCI fraction), preferably has an ethylene content of less than 1.0 wt%, preferably from 0 to 0.7 wt%, more preferably from 0 to 0.5 wt%, based on the total weight of the XCI fraction.

The XCI fraction further preferably has a melt flow rate of from 1.0 to 10 g/10 min, more preferably from 1.5 to 7.5 g/10 min, still more preferably from 2.0 to 5.0 g/10 min. The heterophasic copolymer of propylene and ethylene (B-l-b) preferably an amount of XCS fraction of from 5 to 25 wt%, more preferably from 10 to 20 wt%, based on the total amount of the heterophasic copolymer of propylene (B-l-b).

The heterophasic copolymer of propylene and ethylene (B-l-b) preferably has a melt flow rate of from 0.5 to 7.5 g/10 min, more preferably from 1.0 to 6.0 g/10 min, still more preferably from 1.5 to 5.0 g/10 min.

Further, the heterophasic copolymer of propylene and ethylene (B-l-b) preferably has a total ethylene content of from 1.5 to 7.5 wt.-%, more preferably from 2.5 to 6.0 wt.-%, still more preferably from 3.5 to 5.0 wt.-%, based on the total weight of the copolymer of propylene and ethylene (B-l-b).

It is preferred that the heterophasic copolymer of propylene and ethylene (B-l-b) has a melting temperature Tm of from 150 to 175 °C, preferably from 155 to 172°C, more preferably from 160 to 170°C.

Still further, the heterophasic copolymer of propylene and ethylene (B-l-b) preferably has a Vicat A softening temperature of from 130 to 165°C, more preferably from 140 to 160°C, still more preferably from 145 to 155°C.

The heterophasic copolymer of propylene and ethylene (B-l-b) preferably has a flexural modulus in the range of from 1000 to 2000 MPa, preferably from 1100 to 1750 MPa, more preferably from 1200 to 1500 MPa.

Further, the heterophasic copolymer of propylene and ethylene (B-l-b) preferably has a Charpy notched impact strength at 23°C of from 25 to 75 kJ/m², preferably from 30 to 60 kJ/m², more preferably from 35 to 50 kJ/m². The copolymer of propylene and ethylene (B-l), preferably the heterophasic copolymer of propylene can be a commercially available grade or can be produced e.g. by conventional polymerisation processes and process conditions using e.g. the conventional catalyst system known in the literature.

The copolymer of propylene and ethylene (B-l), preferably the heterophasic copolymer of propylene as described herein, can be polymerized in a sequential polymerization process, such as a multistage process.

A suitable process is described in WO 2018/141672.

A preferred multistage process is a “loop-gas phase”-process, such as developed by Borealis A/S, Denmark (known as BORSTAR® technology) described e.g. in patent literature, such as in EP 0 887 379, WO 92/12182 WO 2004/000899, WO 2004/111095, WO 99/24478, WO 99/24479 or in WO 00/68315.

A further suitable slurry-gas phase process is the Spheripol® process of LyondellBasell.

After the copolymer of propylene and ethylene (B-l), preferably the heterophasic copolymer of propylene has been removed from the last polymerisation stage, it is preferably subjected to process steps for removing the residual hydrocarbons from the polymer. Such processes are well known in the art and can include pressure reduction steps, purging steps, stripping steps, extraction steps and so on. Also combinations of different steps are possible. After the removal of residual hydrocarbons the heterophasic copolymer of propylene is preferably mixed with additives as it is well known in the art. Such additives are described above for the polyethylene composition (PE-A). The polymer particles are then extruded to pellets as it is known in the art. Preferably co-rotating twin screw extruder is used for the extrusion step. Such extruders are manufactured, for instance, by Coperion (Werner & Pfleiderer) and Japan Steel Works.

The copolymer of propylene and ethylene (B-l), preferably the heterophasic copolymer of propylene is preferably produced by polymerisation using any suitable Ziegler-Natta type. Typical suitable Ziegler-Natta type catalyst is stereospecific, solid high yield Ziegler-Natta catalyst component comprising as essential components Mg, Ti and Cl. In addition to the solid catalyst a cocatalyst(s) as well external donor(s) are typically used in polymerisation process.

Components of catalyst may be supported on a particulate support, such as inorganic oxide, like silica or alumina, or, usually, the magnesium halide may form the solid support. It is also possible that catalysts components are not supported on an external support, but catalyst is prepared by emulsion-solidification method or by precipitation method.

Alternatively the copolymer of propylene and ethylene (B-l), preferably the heterophasic copolymer of propylene of the invention can be produced using a modified catalyst system as described below.

More preferably, a vinyl compound of the formula (I) is used for the modification of the catalyst:

CH₂=CH-CHR¹R² (IV) wherein R¹ and R² together form a 5- or 6-membered saturated, unsaturated or aromatic ring, optionally containing substituents, or independently represent an alkyl group comprising 1 to 4 carbon atoms, whereby in case R¹ and R² form an aromatic ring, the hydrogen atom of the -CHR ¹ R² moiety is not present.

More preferably, the vinyl compound (IV) is selected from: vinyl cycloalkane, preferably vinyl cyclohexane (VCH), vinyl cyclopentane, 3 -methyl- 1 -butene polymer and vinyl-2- methyl cyclohexane polymer. Most preferably the vinyl compound (IV) is vinyl cyclohexane (VCH) polymer.

The solid catalyst usually also comprises an electron donor (internal electron donor) and optionally aluminium. Suitable internal electron donors are, among others, esters of carboxylic acids or dicarboxylic acids, like phthalates, maleates, benzoates, citraconates, and succinates, 1,3 -di ethers or oxygen or nitrogen containing silicon compounds. In addition mixtures of donors can be used.

The cocatalyst typically comprises an aluminium alkyl compound. The aluminium alkyl compound is preferably trialkyl aluminium such as trimethylaluminium, triethylaluminium, tri-isobutylaluminium or tri-n-octylaluminium. However, it may also be an alkylaluminium halide, such as diethylaluminium chloride, dimethylaluminium chloride and ethylaluminium sesquichloride. Suitable external electron donors used in polymerisation are well known in the art and include ethers, ketones, amines, alcohols, phenols, phosphines and silanes. Silane type external donors are typically organosilane compounds containing Si-OCOR, Si-OR, or Si- NR2 bonds, having silicon as the central atom, and R is an alkyl, alkenyl, aryl, arylalkyl or cycloalkyl with 1 -20 carbon atoms are known in the art.

Examples of suitable catalysts and compounds in catalysts are shown in among others, in WO 87/07620, WO 92/21705, WO 93/11165, WO 93/11166, WO 93/19100, WO 97/36939, WO 98/12234, WO 99/33842, WO 03/000756, WO 03/000757, WO 03/000754, WO 03/000755, WO 2004/029112, EP 2610271, WO 2012/007430. WO 92/19659, WO 92/19653, WO 92/19658, US 4382019, US 4435550, US 4465782, US 4473660, US 4560671 , US 5539067, US5618771, EP45975, EP45976, EP45977, WO 95/32994, US 4107414, US 4186107, US 4226963, US 4347160, US 4472524, US 4522930, US 4530912, US 4532313, US 4657882, US 4581342, US 4657882.

Alternatively, the copolymer of propylene and ethylene (B-l), preferably the heterophasic copolymer of propylene can be produced in the presence of a single-site catalyst such as a single site solid particulate catalyst free from an external carrier, preferably a catalyst comprising (i) a complex of formula (I): wherein

M is zirconium or hafnium; each X is a sigma ligand; L is a divalent bridge selected from - 2C-, -R'zC-CR'z-, -R'zSi-, -R'2Si-SiR'2-, -R'zGe-, wherein each R is independently a hydrogen atom, Ci-C2o-hydrocarbyl, tri(Ci-C2o- alkyl)silyl, Ce-C2o-aryl, C7-C2o-arylalkyl or C7-C2o-alkylaryl;

R² and R²' are each independently a C1-C20 hydrocarbyl radical optionally containing one or more heteroatoms from groups 14-16;

R⁵' is a C1-20 hydrocarbyl group containing one or more heteroatoms from groups 14-16 optionally substituted by one or more halo atoms;

R⁶ and R⁶' are each independently hydrogen or a C1-20 hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16;

R⁷ and R⁷ are each independently hydrogen or C1-20 hydrocarbyl group optionally containing one or more heteroatoms from groups 14-16;

Ar is independently an aryl or heteroaryl group having up to 20 carbon atoms optionally substituted by one or more groups R¹;

Ar' is independently an aryl or heteroaryl group having up to 20 carbon atoms optionally substituted by one or more groups R¹; each R¹ is a C1-20 hydrocarbyl group or two R¹ groups on adjacent carbon atoms taken together can form a fused 5 or 6 membered non aromatic ring with the Ar group, said ring being itself optionally substituted with one or more groups R⁴; each R⁴ is a C1-20 hydrocarbyl group; and (ii) a cocatalyst comprising a compound of a group 13 metal, e.g. Al or boron compound.

Such catalysts are described in W02013/007650 which is incorporated herein by reference.

The copolymer of ethylene (B-2) comprises one or more comonomers selected from alphaolefins having 4 to 12 carbon atoms, preferably 4 to 8 carbon atoms. Preferably, the copolymer of ethylene (B-2) is a terpolymer of ethylene and two comonomers differing in their amount of carbon atoms

It is preferred that the copolymer of ethylene (B-2) is a copolymer of ethylene with comonomer units derived from 1 -butene and/or 1 -hexene. Preferably the copolymer of ethylene (B-2) is a terpolymer of ethylene with comonomer units derived from 1 -butene and 1 -hexene. The term ‘a copolymer of ethylene with comonomer units derived from 1 -butene’ indicates that the copolymer of ethylene (B-2) contains only units derivable from ethylene and 1- butene.

The term ‘a copolymer of ethylene with comonomer units derived from 1 -hexene’ indicates that the copolymer of ethylene (B-2) contains only units derivable from ethylene and 1- hexene.

The term ‘a terpolymer of ethylene with comonomer units derived from 1 -butene and 1- hexene’ indicates that the copolymer of ethylene (B-2) contains only units derivable from ethylene, 1 -butene and 1 -hexene.

The copolymer of ethylene (B-2) has a total comonomer content, i.e. the content of comonomer units derived from 1-butene and/or 1-hexene, of from 1.0 to 25.0 wt.-%, preferably from 1.5 to 22.5 wt.-%, still more preferably from 2.0 to 20.0 wt.-%.

The copolymer of ethylene (B-2) preferably has a 1-butene content of from 0. 1 to 5.0 wt.-%, more preferably from 0.2 to 3.5 wt.-%, still more preferably from 0.3 to 2.0 wt.-%, based on the total weight of the copolymer of ethylene (B-2).

The copolymer of ethylene (B-2) preferably has a 1-hexene content of from 4.0 to 20.0 wt.- %, more preferably from 5.0 to 18.0 wt.-%, still more preferably from 6.0 to 15.0 wt.-%, based on the total weight of the copolymer of ethylene (B-2).

The copolymer of ethylene (B-2) can be unimodal in regard to the comonomer distribution. This means that the comonomer units derived from 1-butene and/or 1-hexene are uniformly distributed in the copolymer of ethylene (B).

The copolymer of ethylene (B-2) can be multimodal in regard to the comonomer distribution.

This means that the copolymer of ethylene (B-2) comprises components with different When being a copolymer of ethylene and the comonomer units derived from 1-butene or 1- hexene the copolymer of ethylene (B-2) in one embodiment can comprise an ethylene homopolymer component and a copolymer of ethylene and 1-butene or 1-hexene component. When being a copolymer of ethylene and the comonomer units derived from 1 -butene or 1- hexene the copolymer of ethylene (B-2) in another embodiment can comprise two copolymer of ethylene and 1 -butene or 1 -hexene components with different comonomer content.

When being a terpolymer of ethylene and the comonomer units derived from 1 -butene and 1- hexene the copolymer of ethylene (B-2) in one embodiment can comprise an ethylene homopolymer component, a copolymer of ethylene and 1 -butene component and a copolymer of ethylene and 1 -hexene component.

When being a terpolymer of ethylene and the comonomer units derived from 1 -butene and 1- hexene the copolymer of ethylene (B-2) in another embodiment can comprise an ethylene homopolymer component and a terpolymer of ethylene, 1 -butene and 1 -hexene component. When being a terpolymer of ethylene and the comonomer units derived from 1 -butene and 1- hexene the copolymer of ethylene (B-2) in yet another embodiment can comprise a copolymer of ethylene and 1 -butene component and a copolymer of ethylene and 1 -hexene component.

In a preferred embodiment, the copolymer of ethylene (B-2) is a terpolymer of ethylene with comonomer units selected from 1 -butene and 1 -hexene having a 1 -butene content of from 0.1 to 5.0 wt.-%, preferably from 0.2 to 3.5 wt.-%, still more preferably from 0.3 to 2.0 wt.- % and a 1-hexene content of from 4.0 to 20.0 wt,-%, more preferably from 5.0 to 18.0 wt.-%, still more preferably from 6.0 to 15.0 wt.-%, based on the total weight of the copolymer of ethylene (B-2).

The copolymer of ethylene (B-2) has a density of from 900 to 930 kg/m², preferably from 905 to 925 kg/m², more preferably from 910 to 920 kg/m², determined according to ISO 1183.

The copolymer of ethylene (B-2) preferably is a linear low density polyethylene (LLDPE).

The copolymer of ethylene (B-2) has a melt flow rate MFR2 of from 0.1 to 5.0 g/10 min, preferably from 0.5 to 4.0 g/10 min, more preferably from 1.0 to 3.0 g/10 min, determined according to ISO 1133 at a load of 2.16 kg and a temperature of 190°C The copolymer of ethylene (B-2) preferably has an intrinsic viscosity iV of from 1.5 to 2.5 dl/g, more preferably from 1.7 to 2.2 dl/g, determined according to DIN ISO 1628/1, October 1999 (in Decalin at 135 °C).

Further, the copolymer of ethylene (B-2) preferably has a ratio of weight average molecular weight to number average molecular weight Mw/Mn of from 2.0 to 5.0, preferably from 2.5 to 4.5, more preferably from 3.0 to 4.0, determined by Gel Permeation Chromatography (GPC) according to ISO 16014-4:2003 and ASTM D 6474-99.

The copolymer of ethylene (B-2) preferably has a Vicat A softening temperature of from 80 to 120°C, preferably from 85 to 110°C, more preferably from 90 to 105°C.

The copolymer of ethylene (B-2) is characterized by a melting temperature of from 100 to 140°C, preferably from 105 to 130°C, more preferably from 110 to 125°C.

The presence of a copolymer of ethylene having a melting temperature of less than 100°C has been shown in the example section to have a rather poor adhesion, especially after ageing.

The copolymer of ethylene (B-2) is preferably obtainable by polymerization in the presence of a single site catalyst system. The single site catalyst system preferably comprises catalytically active metallocene compound or complex combined with a cocatalyst. The metallocene compound or complex is referred herein also as organometallic compound (C).

The organometallic compound (C) comprises a transition metal (M) of Group 3 to 10 of the Periodic Table (IUPAC 2007) or of an actinide or lanthanide.

The term "an organometallic compound (C)" in accordance With the present invention includes any metallocene compound of a transition metal which bears at least one organic (coordination) ligand and exhibits the catalytic activity alone or together with a cocatalyst. The transition metal compounds are well known in the art and preferably covers compounds of metals from Group 3 to 10, e.g. Group 3 to 7, or 3 to 6, such as Group 4 to 6 of the Periodic Table, (IUPAC 2007), as well lanthanides or actinides. In an embodiment the organometallic compound (C) has the following formula (1): (L)_mR_nMX_q (I) wherein

“M” is a transition metal (M) transition metal (M) of Group 3 to 10 of the Periodic Table (IUPAC 2007), each “X” is independently a monoanionic ligand, such as a o -ligand, each “L” is independently an organic ligand which coordinates to the transition metal “M”, “R” is a bridging group linking said organic ligands (L), “m” is 1, 2 or 3, preferably 2, “n” is 0, 1 or 2, preferably 1, “q” is 1, 2 or 3, preferably 2 and m+q is equal to the valency of the transition metal (M).

“M” is preferably selected from the group consisting of zirconium (Zr), hafnium (Hf), or titanium (Ti), more preferably selected from the group consisting of zirconium (Zr) and hafnium (Hf).

“X” is preferably a halogen, most preferably Cl.

Most preferably the organometallic compound (C) is a metallocene complex which comprises a transition metal compound, as defined above, which contains a cyclopentadienyl, indenyl or fluorenyl ligand as the substituent “L” Further, the ligands “L” may have substituents, such as alkyl groups, aryl groups, arylalkyl groups, alkylaryl groups, silyl groups, siloxy groups, alkoxy groups or other heteroatom groups or the like. Suitable metallocene catalysts are known in the art and are disclosed, among others, in WO-A- 95/12622, WO-A -96/32423, WO-A-97/28170, WO-A-98/32776, WO-A-99/61489, WO-A- 03/010208, WO-A -03/051934, WO-A-03/051514, WO-A-2004/085499, EP-A-1752462 and EP-A-1739103.

Most preferred the metallocene catalyst, which means the catalytically active metallocene complex, as defined above, is used together With a cocatalyst, which is also known as an activator. Suitable activators are metal alkyl compounds and especially aluminium alkyl compounds known in the art. Especially suitable activators used with metallocene catalysts are alkylaluminium oxy-compounds, such as methylaluminoxane (MAO), tetraisobutylalumoxane (TIB AO) or hexaisobutylalumoxane (HIBAO).

The polyolefin composition (PO-B) preferably comprises additives.

Herein the term additives exclude the optional filler(s), optional pigment(s) and optional flame retardant(s). Such additives are preferably conventional and commercially available, including without limiting to, UV absorbers, UV stabilisers, antioxidants, nucleating agents, clarifiers, brighteners, acid scavengers, as well as slip agents, processing aids etc. Such additives are generally commercially available and are described, for example, in "Plastic Additives Handbook", 5th edition, 2001 of Hans Zweifel.

Each additive can be used e.g. in conventional amounts. The suitable additives and the amounts thereof for layer (B) can be chosen by a skilled person depending on the desired article and the end use thereof.

Preferably, the additives are selected at least from alpha-nucleating agents, UV absorbers and UV stabilisers) comprising hindered amine compound and antioxidant(s) comprising a dialkyl amine compound. More preferably the additives are selected at least from alphanucleating agent(s), UV absorber(s), UV stabiliser(s) comprising hindered amine compound and antioxidant(s) comprising a dialkyl amine compound, and wherein the additives are without phenolic unit(s). The expression “the additives are without phenolic unit(s)” means herein that any additive compound including UV stabiliser(s) and antioxidant(s) present in the polyolefin composition (PO-B) bears no phenolic units. Preferably the composition does not comprise any components, like additives, with phenolic units.

Accordingly, herein the filler(s), pigment(s) and flame retardant(s) are not understood nor defined as the additives.

It is preferred that the polyolefin composition (PO-B) is free of pigments, and/or flame retardants.

The polyolefin composition (PO-B) is preferably free of fillers. It is especially preferred that the polyolefin composition (PO-B) is free of fillers, pigments and/or flame retardants.

The polyolefin composition (PO-B) can further comprise polymers, which are different from the copolymer of propylene and ethylene (B- 1) and the copolymer of ethylene (B-2).

The optional further polymer component(s) can be any polymer other than the copolymer of propylene and ethylene (B- 1 ) and the copolymer of ethylene (B-2), preferably a polyolefin based polymer.

Typical examples of further polymer component(s) are one or both of a plastomer or functionalised polymer, which both have a well-known meaning.

The optional plastomer, if present, is preferably a copolymer of ethylene with at least one C3 to CIO alpha-olefin. The plastomer, if present, has preferably one or all, preferably all, of the below properties a density of 850 to 915, preferably 860 to 910, kg/m³, MFR2 of 0. 1 to 50, preferably 0.2 to 40 g/lOmin (190°C, 2. 16kg), and/or the alpha-olefin comonomer is 1 -octene.

The optional plastomer, if present, has a density, which is lower than the density of the copolymer of ethylene (B-2).

The optional plastomer, if present, is preferably produced using a metallocene catalyst, which term has a well-known meaning in the prior art. The suitable plastomers are commercially available, e.g. plastomer products under tradename QUEO™, supplied by Borealis, or Engage™ supplied by ExxonMobil, Lucene supplied by LG, or Tafmer supplied by Mitsui. The amount of the optional plastomer, if present, is preferably of 3 to 45 wt%, preferably 3 to 30 wt%, more preferably 3 to 15 wt, based on the amount of the polypolefin composition (PO-B). If present, then the amount of the optional plastomer is less than the combined amount of the copolymer of propylene and ethylene (B- 1) and the copolymer of ethylene (B-2).

The optional functionalised polymer, if present, is a polymer which is functionalised e.g. by grafting. For instance, polar functional groups, such as maleic anhydride (MAH), can be grafted to a polyolefin to form functional polymers thereof. The copolymer of propylene and ethylene (B- 1) and the copolymer of ethylene (B-2), is/are different from optional functionalised polymer. The copolymer of propylene and ethylene (B-l) is without grafted functional units. I.e. the term copolymer of propylene and ethylene (B-l) excludes the polymers of propylene grafted with functional groups. The amount of the optional functionalised polymer, if present, is preferably of 3 to 30 wt%, preferably 3 to 20 wt%, preferably 3 to 15 wt%, more preferably 4 to 12 wt%, based on the amount of the polyolefin composition (PO-B). If present, then the amount of the optional functionalised polymer(s) is less than the combined amount of the copolymer of propylene and ethylene (B-l) and the copolymer of ethylene (B-2).

The polyolefin composition (PO-B) preferably comprises, preferably consists of: more than 15.0 wt%, preferably 17.5 to 98.8 wt%, preferably 50.0 to 97.0 wt%, of the copolymer of propylene and ethylene (B-l), up to 50 wt%, preferably 1.0 to 45.0 wt%, preferably 2.5 to 42.5 wt%, of the copolymer of ethylene (B-2), 0.2 to 5.0 wt%, preferably of 0.5 to 5.0 wt%, of additives, 0 to 45 wt%, preferably 0 to 30 wt%, preferably 0 to 15 wt%, more preferably 0 to 10 wt%, of plastomer;

0 to 30 wt%, preferably 0 to 20 wt%, preferably 0 to 15 wt%, more preferably 0 to 12 wt% of functionalised polymer(s), based on the total amount of the polyolefin composition (PO-B).

The copolymer of propylene and ethylene (B-l) and the copolymer of ethylene (B-2) are then compounded together with the additives and optionally one or more of optional components as described above in a known manner. The compounding can be effected in a conventional extruder e.g. as described above and the obtained melt mix is produced to an article or, preferably, pelletised before used for the end application. Part or all of the additives or optional components may be added during the compounding step.

Layer (C)

Layer (C) comprises a polypropylene composition (PP-C)

It is preferred that the polypropylene composition (PP-C) comprises

(PP-C-a) a random copolymer of propylene monomer units with alpha olefin comonomer units selected from ethylene and alpha-olefins having from 4 to 12 carbon atoms; or

(PP-C-b) a heterophasic copolymer of propylene which comprises, a polypropylene matrix component and an elastomeric propylene copolymer component which is dispersed in said polypropylene matrix.

In one embodiment the polypropylene composition (PP-C) comprises a random copolymer of propylene monomer units with alpha olefin comonomer units selected from ethylene and alpha-olefins having from 4 to 12 carbon atoms (PP-C-a).

The comonomer units are selected from ethylene and alpha-olefins having from 4 to 12 carbon atoms, preferably from ethylene and alpha-olefins having from 4 to 8 carbon atoms, more preferably from ethylene, 1 -butene and 1 -hexene, still more preferably from ethylene and 1 -butene and most preferably from ethylene.

Preferably, the random copolymer (PP-C-a) only includes one sort of comonomer units as described above. In this case the random copolymer is a random copolymer of propylene monomer units with alpha olefin comonomer units selected from one of ethylene and alphaolefins having from 4 to 12 carbon atoms. Alternatively, the random copolymer (PP-C-a) includes more than one sort of comonomer units as described above, such as two or three. In this case the random copolymer is a random copolymer of propylene monomer units with two or more, such as two or three, alpha olefin comonomer units selected from one of ethylene and alpha-olefins having from 4 to 12 carbon atoms.

The comonomer content in the random copolymer (PP-C-a) in preferably the range of from 0.5 to 15.0 wt%, more preferably in the range of from more than 1.0 wt% to 12.5 wt%, even more preferably in the range of from 1.5 to 10.0 wt%, still most preferably in the range of from 2.0 to 8.0 wt.

The random copolymer (PP-C-a) preferably has a melt flow rate MFR2 (230°C) measured according to ISO 1133 in the range of from 0.5 to 20.0 g/lOmin, more preferably in the range of from 1.0 to 15.0 g/ 10 min, even more preferably in the range of from 1.5 to 12.0 g/ 10 min, still more preferably in range of from 1.8 to 10.0 g/10.

Further, the random copolymer (PP-C-a) can be defined by the xylene cold soluble (XCS) content measured according to ISO 6427. Accordingly the propylene polymer is preferably featured by a xylene cold soluble (XCS) content of below 25.0 wt%, more preferably of below 20.0 wt%.

Thus it is in particular appreciated that the random copolymer (PP-C-a) has a xylene cold soluble (XCS) content in the range of 2.0 to below 20.0 wt %, most preferably in the range of 3.0 to 18.0 wt%.

Still further, the random copolymer (PP-C-a) can be defined by the melting temperature (Tm). Accordingly the propylene polymer preferably has a melting temperature Tm of equal to or higher than 120°C. Even more preferable the melting temperature Tm is in the range of 125°C to 160°C, most preferably in the range of 125°C to 155°C.

The random copolymer (PP-C-a) preferably has a density in the range of from 900 to 910 kg/m³. The crystallisation temperature measured via DSC according to ISO 11357 of the random copolymer (PP-C-a) can be equal or higher than 85°C, preferably in the range of 85°C to 150°C, and even more preferably in the range of 90°C to 130°C.

The random copolymer (PP-C-a) can be further unimodal or multimodal, like bimodal in view of the molecular weight distribution and/or the comonomer content distribution; both unimodal and bimodal propylene polymers are equally preferred.

If the random copolymer (PP-C-a) is unimodal, it is preferably produced in a single polymerization step in one polymerization reactor (Rl). Alternatively a unimodal propylene polymer can be produced in a sequential polymerization process using the same polymerization conditions in all reactors.

If the propylene polymer is multimodal, it is preferably produced in a sequential polymerization process using different polymerization conditions (amount of comonomer, hydrogen amount, etc.) in the reactors. In some embodiments, a propylene homopolymer fraction is polymerized in one reaction step and a propylene copolymer fraction is polymerized in a second reaction step of a sequential polymerization process.

The random copolymer (PP-C-a) is preferably the propylene polymer is produced in the presence of a Ziegler-Natta catalyst system or a single site catalyst system, such as a metallocene catalyst system. Suitable catalyst systems are the same as discussed below for the heterophasic copolymer of propylene (PP-C-b).

The random copolymer (PP-C-a) can be produced in a single polymerization step comprising a single polymerization reactor (Rl) or in a sequential polymerization process comprising at least two polymerization reactors (Rl) and (R2), whereby in the first polymerization reactor (Rl) a first propylene polymer fraction is produced, which is subsequently transferred into the second polymerization reactor (R2). In the second polymerization reactor (R2) a second propylene polymer fraction is then produced in the presence of the first propylene polymer fraction.

Polymerization processes which are suitable for producing the random copolymer (PP-C-a) generally comprises one or two polymerization stages and each stage can be carried out in solution, slurry, fluidized bed, bulk or gas phase. The term “polymerization reactor” shall indicate that the main polymerization takes place. Thus in case the process consists of one or two polymerization reactors, this definition does not exclude the option that the overall system comprises for instance a pre -polymerization step in a pre-polymerization reactor. The term “consist of’ is only a closing formulation in view of the main polymerization reactors.

The term “sequential polymerization process” indicates that the random copolymer (PP-C-a) is produced in at least two reactors connected in series. Accordingly such a polymerization system comprises at least a first polymerization reactor (Rl) and a second polymerization reactor (R2), and optionally a third polymerization reactor (R3).

The first, respectively the single, polymerization reactor (Rl) is preferably a slurry reactor and can be any continuous or simple stirred batch tank reactor or loop reactor operating in bulk or slurry. Bulk means a polymerization in a reaction medium that comprises of at least 60 % (w/w) monomer. According to the present invention the slurry reactor is preferably a (bulk) loop reactor.

In case a “sequential polymerization process” is applied the second polymerization reactor (R2) and the optional third polymerization reactor (R3) are gas phase reactors (GPRs), i.e. a first gas phase reactor (GPR1) and a second gas phase reactor (GPR2). A gas phase reactor (GPR) according to this invention is preferably a fluidized bed reactor, a fast fluidized bed reactor or a settled bed reactor or any combination thereof.

A preferred multistage process is a “loop-gas phase”-process, such as developed by Borealis (known as BORSTAR® technology) described e.g. in patent literature, such as in EP 0 887 379, WO 92/12182, WO 2004/000899, WO 2004/111095, WO 99/24478, WO 99/24479 or in WO 00/68315.

A further suitable slurry-gas phase process is the Spheripol® process of Basell.

Suitable polymerization conditions are the same as discussed below for the polypropylene matrix component of the heterophasic copolymer of propylene (PP-C-b). In another embodiment, the polypropylene composition (PP-C) comprises a heterophasic copolymer of propylene which comprises a polypropylene matrix component and an elastomeric propylene copolymer component which is dispersed in said polypropylene matrix (PP-C-b).

The matrix component of the heterophasic copolymer of propylene (PP-C-b) can be a propylene homopolymer component or a propylene random copolymer component.

When being a propylene random copolymer component, the matrix component is preferably a random copolymer of propylene with one or more of ethylene and/or C-rCs alpha olefin comonomers. It is preferred that said propylene random copolymer component is a propylene -ethylene random copolymer.

Preferably, the polypropylene matrix component of the heterophasic copolymer of propylene (PP-C-b) is a homopolymer of propylene.

The XCS fraction of the heterophasic copolymer of propylene (PP-C-b) is regarded herein as the elastomeric component, since the amount of XCS fraction in the matrix component is conventionally markedly lower. For instance, in case the matrix component is a homopolymer of propylene, then the weight amount of the xylene cold soluble (XCS) fraction of the heterophasic copolymer of propylene (PP-C-b) is understood in this application also as the amount of the elastomeric propylene copolymer component present in the heterophasic copolymer of propylene (PP-C-b).

The total comonomer content of the heterophasic copolymer of propylene (PP-C-b) is preferably from 2.0 to 25.0 wt%, more preferably from 3.0 to 20.0 wt%.

It is preferred that the comonomer units of the heterophasic copolymer of propylene (PP-C- b) are selected from ethylene and/or C4-C8 alpha olefin comonomers, more preferably from ethylene. The melting temperature, Tm, of the heterophasic copolymer of propylene (PP-C-b) is preferably at least 145°C, more preferably from 150 to 170°C, most preferably from 155 to 170°C.

The Vicat softening temperature (Vicat A) of the heterophasic copolymer of propylene (PP- C-b) is preferably of at least 90°C, preferably from 105 to 160°C, most preferably from 120 to 155°C.

The heterophasic copolymer of propylene (PP-C-b) preferably has a melt flow rate MFR2 (2.16 kg, 230°C) of 1.0 to 20.0 g/10 min, preferably from 2.0 to 17.5 g/10 min, preferably from 3.0 to 15.0 g/10 min.

Further, the heterophasic copolymer of propylene (PP-C-b) preferably has a xylene cold soluble (XCS) fraction in amount of from 5 to 40 wt%, more preferably from 10 to 37 wt%, based on the total amount of the heterophasic copolymer of propylene (PP-C-b).

Still further, the heterophasic copolymer of propylene (PP-C-b) preferably has a flexural modulus of at least 700 MPa, preferably of 750 to 2500 MPa.

Additionally, the heterophasic copolymer of propylene (PP-C-b) preferably has a Chapry notched impact strength at 23 °C of at least 20 kJ/m², preferably of 30 to 75 kJ/m²

Further, the heterophasic copolymer of propylene (PP-C-b) preferably has a density of 900 to 910 kg/m³.

In a preferred embodiment, the heterophasic copolymer of propylene (PP-C-b) meets all of the above described properties of comonomer content, Tm, Vicat A, MFR2, XCS fraction, flexural modulus, Charpy notched impact strength and density.

The polypropylene composition (PP-C) can also comprise a mixture of two or more, e.g. two such heterophasic copolymers of propylene which are different. The heterophasic copolymer of propylene can be a commercially available grade or can be produced e.g. by conventional polymerisation processes and process conditions using e.g. the conventional catalyst system known in the literature.

The heterophasic copolymer of propylene as described herein, can be polymerized in a sequential polymerization process, such as a multistage process.

A suitable process is described in WO 2018/141672.

After the random copolymer of propylene (PP-C-a) or the heterophasic copolymer of propylene (PP-C-b) has been removed from the last polymerisation stage, it is preferably subjected to process steps for removing the residual hydrocarbons from the polymer. Such processes are well known in the art and can include pressure reduction steps, purging steps, stripping steps, extraction steps and so on. Also combinations of different steps are possible. After the removal of residual hydrocarbons the heterophasic copolymer of propylene is preferably mixed with additives as it is well known in the art. Such additives are described below. The polymer particles are then extruded to pellets as it is known in the art. Preferably co-rotating twin screw extruder is used for the extrusion step. Such extruders are manufactured, for instance, by Coperion (Werner & Pfleiderer) and Japan Steel Works.

The random copolymer of propylene (PP-C-a) or the heterophasic copolymer of propylene (PP-C-b) is preferably produced by polymerisation using any suitable Ziegler-Natta type catalyst or single-site type catalyst. Suitable Ziegler-Natta type catalysts and single-site type catalyst are the same as described above for the copolymer of propylene and ethylene (B-l).

The polypropylene composition (PP-C) preferably comprises additives.

Each additive can be used e.g. in conventional amounts. The suitable additives and the amounts thereof for layer (C) can be chosen by a skilled person depending on the desired article and the end use thereof.

Preferably, the additives are selected at least from UV absorbers and UV stabilisers) comprising hindered amine compound and antioxidant(s) comprising a dialkyl amine compound. More preferably the additives are selected at least from UV absorbers, UV stabiliser(s) comprising hindered amine compound and antioxidant(s) comprising a dialkyl amine compound, and wherein the additives are without phenolic unit(s). The expression “the additives are without phenolic unit(s)” means herein that any additive compound including UV stabiliser(s) and antioxidant(s) present in the polypropylene composition (PP- C) bears no phenolic units. Preferably the composition does not comprise any components, like additives, with phenolic units.

Preferably the polypropylene composition (PP-C) comprises additives and/or flame retardant(s).

The optional flame retardant(s), if present, can be e.g. any commercial flame retardant product, preferably a flame retardant comprising inorganic phosphorous. The amount of the flame retardant(s), if present, is preferably of 1 to 20 wt%, preferably 2 to 15 wt%, more preferably 3 to 12 wt%, based on the amount of the polypropylene composition (PP-C).

As a further component an alpha-nucleating agent can be present within the polypropylene composition (PP-C). One type of preferred alpha-nucleating agents are those which are soluble in the random copolymer of propylene (PP-C-a) or the heterophasic copolymer of propylene (PP-C-b). Soluble alpha-nucleating agents are characterized by demonstrating a sequence of dissolution in heating and recrystallization in cooling to improve the degree of dispersion. Methods for determining said dissolution and recrystallization are described for example by Kristiansen et al. in Macromolecules 38 (2005) pages 10461-10465 and by Balzano et al. in Macromolecules 41 (2008) pages 5350-5355. In detail, the dissolution and recrystallization can be monitored by means of melt rheology in dynamic mode as defined by ISO 6271- 10: 1999.

Soluble alpha-nucleating agents can be selected from the group consisting of sorbitol derivatives, nonitol derivatives, benzene derivatives of formula N-I as defined below, like benzene-trisamides, and mixtures thereof.

Suitable sorbitol derivatives are di(alkylbenzylidene)sorbitols, like 1,3:2, 4- dibenzylidene sorbitol or bis-(3,4-dimethylbenzylidene)sorbitol.

Suitable nonitol derivatives include l,2,3-trideoxy-4,6:5,7-bis-O-[(4- propylphenyl)methylene] -nonitol .

Suitable benzene derivatives include N,N’,N”-tris-tert-butyl-l,3,5-benzenetricarboxamide or N,N’,N”-tris-cyclohexyl-l, 3, 5-benzene-tri carboxamide.

Another type of preferred alpha-nucleating agents are polymeric alpha-nucleating agents. The polymeric alpha-nucleating agent is a polymer of a vinyl compound of the formula CH2=CH-CHR⁶R⁷, wherein R⁶ and R⁷ together form a 5- or 6-membered saturated, unsaturated or aromatic ring or independently represent an alkyl group comprising 1 to 4 carbon atoms. Preferably the polymeric alpha-nucleating agent is a homopolymer of the vinyl compound of the formula CH2=CH-CHR⁶R⁷.

One method for incorporating the polymeric a-nucleating agent into the polypropylene composition (PP-C) includes prepolymerising the polymerisation catalyst by contacting the catalyst with the vinyl compound of the formula CH2=CH-CHR⁶R⁷, wherein R⁶ and R⁷ together form a 5- or 6-membered saturated, unsaturated or aromatic ring or independently represent an alkyl group comprising 1 to 4 carbon atoms. Propylene is then polymerised in the presence of such prepolymerised catalyst as discussed above.

In the prepolymerisation the catalyst is prepolymerised so that it contains up to 5 grams of prepolymer per gram of solid catalyst component, preferably from 0. 1 to 4 grams of prepolymer per one gram of the solid catalyst component. Then, the catalyst is contacted at polymerisation conditions with the vinyl compound of the formula CH2=CH-CHR⁶R⁷, wherein R⁶ and R⁷ are as defined above. Especially preferably R⁶ and R⁷ then form a saturated 5- or 6-membered ring. Especially preferably the vinyl compound is vinylcyclohexane. Especially preferably the catalyst then contains from 0.5 to 2 grams of the polymerised vinyl compound, such as poly(vinylcyclohexane), per one gram of solid catalyst component. This allows the preparation of nucleated polypropylene as disclosed in EP-A- 607703, EP-A-1028984, EP-A-1028985 and EP-A-1030878.

The polypropylene composition (PP-C) can optionally comprise up to 5.0 wt%, preferably from 0.0001 to 5.0 wt% of an alpha-nucleating agent, preferably from 0.001 to 1.5 wt%, and especially preferably from 0.01 to 1.0 wt% of an alpha-nucleating agent, based on the total weight of the polypropylene composition (PP-C).

Any optional carrier polymers of additives, of optional filler(s), of optional nucleating agent(s), e.g. master batches of said components, together with the carrier polymer, are calculated to the amount of the respective component, based on the amount (100 %) of the polypropylene composition (PP-C).

In one embodiment, it is preferred that the polypropylene composition (PP-C) is free of pigment(s). The absence of pigments has been found to increase the transparency of layer (C) which helps to improve the power output of a bifacial photovoltaic module.

In another embodiment, it is preferred that the polypropylene composition (PP-C) comprises pigment(s) as described above, preferably a white pigment, such as titanium dioxide.

In said embodiment the layer element is suitable as an integrated backsheet, preferably an integrated white backsheet for monofacial photovoltaic modules.

The polypropylene composition (PP-C) preferably is free of filler(s).

It is especially preferred that the polypropylene composition (PP-C) is free of filler(s) and pigment(s). In some embodiments the polypropylene composition (PP-C) is free of flame retardant(s) as defined above.

The polypropylene composition (PP-C) can further comprise further polymer component(s). The optional further polymer component(s) can be any polymer other than the random copolymer of propylene (PP-C-a) or the heterophasic copolymer of propylene (PP-C-b), preferably a polyolefin based polymer.

“Polymeric component(s)” exclude herein any carrier polymer(s) of optional additive or filler, e.g. carrier polymer(s) used in master batch(es) of additive or, respectively, filler optionally present in the polypropylene composition (PP-C). Such optional carrier polymer(s) are calculated to the amount of the respective additive or, respectively filler based on the amount (100 wt%) of the polypropylene composition (PP-C).

The polypropylene composition (PP-C) preferably comprises, preferably consists of: more than 25.0 wt%, preferably 30.0 to 99.8 wt%, preferably 70.0 to 99.4 wt%, of the random copolymer of propylene (PP-C-a) or the heterophasic copolymer of propylene (PP-B-b),

0.2 to 5.0 wt%, preferably of 0.5 to 5.0 wt%, of additives,

0 to 50.0 wt%, preferably 0 wt% of further polymer component(s) which are different from the random copolymer of propylene (PP-C-a) or the heterophasic copolymer of propylene (PP-C-b),

0 to 5.0 wt%, preferably from 0.0001 to 5.0 wt% of an a-nucleating agent, preferably from 0.001 to 1.5 wt%, and especially preferably from 0.005 to 1.0 wt% of an a- nucleating agent, and

0 to 25.0 wt%, preferably 0 to 20.0 wt% of pigment, based on the total amount of the polypropylene composition (PP-C).

The random copolymer of propylene (PP-C-a) or the heterophasic copolymer of propylene (PP-C-b), is then compounded together with the additives and optionally one or more of optional components as described above in a known manner. The compounding can be effected in a conventional extruder e.g. as described above and the obtained melt mix is produced to an article or, preferably, pelletised before used for the end application. Part or all of the additives or optional components may be added during the compounding step.

It is preferred that the properties of the polypropylene composition (PP-C) are the same as for the random copolymer of propylene (PP-C-a) or the heterophasic copolymer of propylene (PP-C-b) as described above.

Layer (C) preferably has a thickness of from 125 pm to 750 pm, more preferably from 150 pm to 650 pm, most preferably from 200 pm to 550 pm.

Process for producing the layer element

The invention further provides a process for producing the layer element as defined above or below wherein the process comprises the steps of: adhering the layers (A), (B) and (C) of the layer element together by extrusion and/or lamination in the configuration A-B-C; and recovering the formed layer element.

In one embodiment the layers (A), (B) and (C), preferably layer (B) and (C) of layer element are produced by extrusion, preferably by coextrusion.

The term “extrusion” means herein that the at least two layers of the layer element can be extruded in separate steps or in a same extrusion step, as well known in the art. One and preferable embodiment of the “extrusion” process for producing the at least three layers of the layer element is a coextrusion process. The term “coextrusion” means herein that the at least two layers, such as layers (C) and (B), or at least the three layers (A), (B) and (C) of the layer element can be coextruded in a same extrusion step, as well known in the art. The term “coextrusion” means herein that, in addition to said at least two layers (C) and (B) and optionally (A), also all or part of the additional layers of the layer element as described above, if present, can be formed simultaneously using one or more extrusion heads. The extrusion and preferable coextrusion step can be carried out for example using a blown fdm or cast fdm extrusion process. Both processes have a well-known meaning and are well described in the literature of the field of the art.

Moreover, the extrusion step and the preferable coextrusion step, can be effected in any conventional film extruder, preferably in a conventional cast film extruder, e.g. in a single or twin screw extruder. Extruder equipments, like cast film extruder equipments, are well described in the literature and commercially available.

Other suitable extrusion techniques suitable for producing the layer element of the present invention are e.g. blown-film extrusion, such as blow -film coextrusion, and an extrusion process, such as a cast film extrusion process, preferably a cast film coextrusion process, with a subsequent calendaring process. These techniques are well known in the art.

The extrusion conditions are depend on the chosen layer materials and can be chosen by a skilled person.

Preferably the extrusion, preferably the coextrusion, of the layer element, is carried by cast film extrusion, preferably by cast film coextrusion.

Part or all of said optional additional layer(s) of the layer element are preferably extruded, like coextruded, on the side of the layer (A) or the layer (C), or on the side of both the layer

(A) and (C), preferably on the side of layer (C), which is not in adhering contact with layer

(B) as discussed above. The extrusion of said optional additional layer(s) can be carried out during the extrusion, preferably during the coextrusion, step layer (A) and layer (C), preferably layer (C). Alternatively or additionally, part or all of said optional additional layer(s) can be laminated to said opposite side of one or both of layer (A) and layer (C) after the extrusion, preferably coextrusion, step of layers (A), (B) and (C), preferably layers (B) and (C).

In an alternative embodiment, the layer element is produced by laminating at least two of the layers (A), (B) and (C) to an adhering contact. The lamination is carried out in a conventional lamination process using conventional lamination equipment well known in the art. In a typical lamination process, the separately formed layers of the layer element are arranged to form of the layer element assembly; then said layer element assembly is subjected to a heating step typically in a lamination chamber at evacuating conditions; after that said layer element assembly is subjected to a pressing step to build and keep pressure on the layer element assembly at the heated conditions for the lamination of the assembly to occur; and subsequently the layer element is subjected to a recovering step to cool and remove the obtained layer element.

Similarly in the alternative lamination embodiment, in addition to the layer (A), (B) and (C), the layer element may comprise further layer(s) on side opposite to adhering side of one or both of layers (A) and (C). In that case part or all of said optional additional layer(s) of the layer element can be laminated and/or extruded on the side of layer (A) or (C), or on the side of both the layers (A) and (C), which is not in adhering contact with layer (B) as discussed above. Extrusion of optional additional layer(s) can be done before the lamination step of at least two of layers (A), (B) and (C). The lamination of optional additional layer(s) can be carried out in a step preceding the lamination step of at least two of layers (A), (B) and (C), during the lamination step of at least two of layers (A), (B) and (C), or after the lamination step of at least two of layers (A), (B) and (C).

The formed layer element can be further treated, if desired, for instance to improve the adhesion of the layer element or to modify the outer surfaces of the layer element. For example, the outer sides (opposite to “adhering” sides) of the layers (A) and (C), or in case of producing the layer element by lamination, then also the “adhering” sides of the layer which are laminated, can be surface treated using conventional techniques and equipments which are well-known for a skilled person.

The most preferred process for producing the layer element of the invention is said extrusion process, preferably said coextrusion process for producing layers (B) and (C) and optional layer(s) (Y). More preferably, the extrusion process for producing the layers (B) and (C) and optionally (Y) is a cast film extrusion, most preferably a cast film coextrusion process. Layer (A) or coextruded layer(s) (X) and (A) are then preferably laminated to the coextruded layers (B), (C) and optionally (Y) to form the layer element with the layer structure A-B-C or X-A-B-C or A-B-C-Y or X-A-B-C-Y.

Accordingly, the preferred process for producing the layer element of the invention is an extrusion process, preferably a coextrusion process, which comprises the steps of: mixing in separate mixing devices, preferably meltmixing in separate extruders, the polyolefin composition (PO-B) of layer (B) and the polypropylene composition (PP-C) of layer (C); preparing coextruded layers (B) and (C) in the configuration B-C as such that layers (B) and (C) are in adherent contact with each other; mixing in a mixing device the polyethylene composition (PE-A) of layer (A); preparing layer (A); laminating at least separate layer (A) and coextruded layers (B) and (C) in the configuration B-C to form a layer element of at least layers (A), (B) and (C) in the configuration A-B-C, wherein said Layer (A) and (B) and layers (B) and (C) are in adhering contact to each other; recovering the obtained layer element.

As well known a meltmix of the polymer composition or component(s) thereof is applied to form a layer. Meltmixing means herein mixing above the melting or softening point of at least the major polymer component(s) of the obtained mixture and is carried out for example, without limiting to, in a temperature of at least 10-15°C above the melting or softening point of polymer component(s). The mixing step can be carried out in an extruder, like film extruder, e.g. in cast film extruder. The meltmixing step may comprise a separate mixing step in a separate mixer, e.g. kneader, arranged in connection and preceding the extruder of the layer element production line. Mixing in the preceding separate mixer can be carried out by mixing with or without external heating (heating with an external source) of the component(s).

In the above preferable process, the extrusion process is preferably a cast film extrusion, preferably a cast film coextrusion process. The extrusion process can also be a blown film extrusion process, preferably a blown film coextrusion process, or an extrusion process, such as a cast film extrusion process, preferably a cast film coextrusion process, with a subsequent calendaring process.

Article

The article comprising the layer element can be any article wherein the properties of the layer element of the invention are for instance desirable or feasible.

The layer element can be part of an article or form the article, like film.

As non-limiting examples of such articles, extruded articles or moulded articles or combinations thereof can be mentioned. For instance the molded articles can be for packaging (including boxes, cases, containers, bottles etc), for household applications, for parts of vehicles, for construction and for electronic devices of any type. Extruded articles can be e.g. films of different types for any purposes, like plastic bags or packages, e.g. wrappers, shrink films etc.; electronic devices of any type; pipes etc., which comprise the layer element. The combinations of molded and extruded article are e.g. molded containers or bottles comprising an extruded label which comprises the layer element.

In one embodiment the article is a multilayer film comprising, preferably consisting of, the layer element. In this embodiment the layer element of the article is preferably a film for various end applications e.g. for packaging applications without limiting thereto. In this invention the term “film” covers also thicker sheet structures e.g. for thermoforming.

In a second embodiment the article is an assembly comprising two or more layer elements, wherein at least one layer element is the layer element of the invention. The further layer element(s) of the assembly can be different or same as the layer element of the invention. The second embodiment is the preferable embodiment of the invention.

The assembly of the preferable second embodiment is preferably a photovoltaic (PV) module comprising a photovoltaic element and one or more further layer elements, wherein at least one layer element is the layer element of the invention. The preferred photovoltaic (PV) module of the invention comprises, in the given order, a protective front layer element, preferably a glass layer element, a front encapsulation layer element, a photovoltaic element, and the layer element (LE) of the invention.

In this preferable embodiment the layer element of the invention is multifunctional, i.e. the layer element of the invention functions both as a rear encapsulation layer element and as the protective back layer element. More preferably, layer (A) functions as an encapsulation layer element and layer (C) functions as the protective back layer element, which is also called herein as backsheet layer element. When coextruded with layer (C), layer (B) also is attributed as part of the protective back layer element. Layer (B) functions as adhesive layer, preferably, when coextruded with layer (C), as part of the protective back layer element, in order to improve adhesion between the encapsulation layer element and the protective back layer element. Naturally, as said above under “Layer element of the invention”, there may be additional layers attached to the outer surface of Layer (A) to enhance the “encapsulation layer element” functionality, further naturally, there may be additional layers attached to the outer surface of the layer (C) to enhance the “protective back layer element” functionality. Such additional layers can be introduced to layer (A) and, respectively, to layer (C) by extrusion, like coextrusion, or by lamination, or by combination thereof, in any order.

In the preferred photovoltaic (PV) module of the invention, the side of layer (A) opposite to side adhering to layer (C) is preferably in adhering contact with a photovoltaic element of the PV module.

Moreover, the side of layer (C) opposite to side adhering to layer (B) can be in adhering contact with further layers or layer elements, as known in the art of backsheet layer elements of PV module.

The final photovoltaic module can be rigid or flexible.

Moreover, the final PV module of the invention can for instance be arranged to a metal, such as aluminum, frame. All said terms have a well-known meaning in the art.

The materials of the above elements of the above elements other than the layer element of the invention are well known in the prior art and can be chosen by a skilled person depending on the desired PV module.

The above exemplified layer elements other than the layer element of the invention can be monolayer or multilayer elements. Moreover, said other layer elements or part of the layers thereof can be produced by extrusion, e.g. coextrusion, by lamination, or by a combination of extrusion and lamination, in any order, depending on the desired end application, as well known in the art.

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 film 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.

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

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

The detailed description given above for layer element of the invention applies to layer element present in an article, preferable in a photovoltaic module. In some embodiments of the PV module there can also be an adhesive layer between the different layer elements and/or between the layers of a multilayer element, as well known in the art. Such adhesive layers have the function to improve the adhesion between the two elements and have a well-known meaning in the lamination field. The adhesive layers are differentiated from the other functional layer elements of the PV module, e.g. those as specified above, below or in claims, as evident for a skilled person in the art.

Preferably, there is no adhesive layer between the photovoltaic element and the front encapsulation layer element. Alternatively, preferably there is no adhesive layer between the photovoltaic layer element and the layer element of the invention. More preferably, there is no adhesive layer between the photovoltaic element and the front encapsulation layer element and there is no adhesive layer between the photovoltaic layer element and the layer element of the invention.

As well-known in the PV field, the thickness of the above mentioned elements, as well as any additional elements, of an article, preferably of a laminated photovoltaic module, of the invention can vary depending on the desired end use application, like the desired photovoltaic module embodiment, and can be chosen accordingly by a person skilled in the PV field.

As a non-limiting example only, the thickness of a photovoltaic element, e.g. an element of monocrystalline photovoltaic cell(s), is typically between 100 to 500 microns.

The thickness of layer (A) of the layer element of the photovoltaic (PV) module of the invention, which preferably functions as a rear encapsulation layer element, can naturally vary depending on the desired PV module, as evident for a skilled person. Usually, the thickness of layer (A) is as defined above. The thickness of the rear encapsulation layer element which in addition to layer (A) can comprise further layer(s) (X), can typically be up to 2 mm, preferably up to 1 mm, typically 0.15 to 0.6 mm, when layer(s) (X) are present. As said, naturally, the thickness depends on the desired final end application and can be chosen by a skilled person. Similarly, the thickness of the layer (C) of the layer element, which preferably functions as a protective back layer element (backsheet element) or part of such protective back layer element of the photovoltaic (PV) module of the invention, is usually as defined above together. The thickness of the protective back layer element, which in addition to layer (C) can comprise further layer(s) (Y), can naturally vary depending on the desired PV module application, as evident for a skilled person. As an example only, the thickness of protective back layer element of the preferable PV module can typically be up to 2 mm, preferably up to 1 mm, typically 0. 15 to 0.6 mm, when layer(s) (Y) are present. Naturally, as said, the thickness depends on the desired final end application and can be chosen by a skilled person.

The photovoltaic module comprising the layer element of the present invention is preferably a bifacial photovoltaic module. This means that the photovoltaic cells of the photovoltaic element create photovoltaic activity on their front side and their rear side.

It is preferred that in the bifacial photovoltaic module the photovoltaic cells have contacts/busbars on both their front and rear sides. In said embodiments the back layer element of the bifacial PV module shows sufficient transparency, preferably due to the lack of pigments in all layers of the rear encapsulation layer and the protective back layer element, preferably all layers of the multilayer element.

The bifacial photovoltaic modules comprising the layer element of the present invention surprisingly have a lower weight and are faster to laminate compared to bifacial photovoltaic modules having a glass element as rear protective element. The overall handling of the bifacial photovoltaic modules comprising the layer element of the present invention is also less laborious than bifacial photovoltaic modules having a glass element as rear protective element.

Compared to bifacial photovoltaic modules having a different polymeric material as rear protective element, such as PET or fluoropolymers, the bifacial photovoltaic modules comprising the layer element of the present invention shows an improved adhesion of the backsheet layer element (in the present case layer (C)) to the rear encapsulation layer element (in the present case layer (A)) and good recycling potential. In certain embodiments the PV module can also be monofacial, i.e. the photovoltaic cells of the photovoltaic element create photovoltaic activity mainly on their front side. In said embodiments the protective back layer element usually lacks sufficient transparency, such as due to the presence of pigments in the layer(s) of the protective back layer element, such as in layer (C).

The layer element of the article, preferably of the photovoltaic module, can be produced as described above for the layer element of the invention.

The separate further elements of PV module other than the layer element of the invention can be produced in a manner well known in the photovoltaic field or are commercially available.

Process for preparing a photovoltaic module

The invention further provides a process for producing an assembly of the invention wherein the process comprises the steps of: assembling the layer element of the invention and further layer element(s) to an assembly; laminating the elements of the assembly in elevated temperature to adhere the elements together; and recovering the obtained assembly.

The layer elements can be provided separately to the assembling step. Or, alternatively, part of the layer elements or part of the layers of two layer elements can be adhered together, i.e. integrated, already before providing to the assembling step.

The preferred process for producing the assembly is a process for producing a photovoltaic (PV) module by assembling the photovoltaic element, the layer element of the invention and optional further layer elements to a photovoltaic (PV) module assembly; laminating the layer elements of the photovoltaic (PV) module assembly in elevated temperature to adhere the elements together; and recovering the obtained photovoltaic (PV) module. The conventional conditions and conventional equipment are well known and described in the art of the photovoltaic module and can be chosen by a skilled person.

As said part of the layer elements can be in integrated form, i.e. two or more of said PV elements can be integrated together, e.g. by lamination, before subjecting to the lamination process of the invention.

Preferable embodiment of the process for forming the preferable photovoltaic (PV) module of the invention, is a lamination process comprising, an assembling step to arrange a photovoltaic element and the layer element of the invention to form of a multilayer assembly, wherein layer (A) of the layer element is arranged in contact with the photovoltaic element, preferably an assembling step to arrange, in a given order, a front protective layer element, a front encapsulating layer element, a photovoltaic element and the layer element of the invention to form of a multilayer assembly, wherein layer (A) of the layer element is arranged in contact with a photovoltaic element; a heating step to heat up the formed PV module assembly optionally, and preferably, in a chamber at evacuating conditions; a pressing step to build and keep pressure on the PV module assembly at the heated conditions for the lamination of the assembly to occur; and a recovering step to cool and remove the obtained PV module comprising the layer element.

The lamination process is carried out in laminator equipment, which can be e.g. any conventional laminator which is suitable for the multilaminate to be laminated, e.g. laminators conventionally used in the PV module production. The choice of the laminator is within the skills of a skilled person. Typically, the laminator comprises a chamber wherein the heating, optional, and preferable, evacuation, pressing and recovering (including cooling) steps take place.

Use

The use of the layer element according to the invention as defined above or below as an integrated backsheet element of a bifacial photovoltaic module comprising a photovoltaic element and said layer element, wherein the photovoltaic element is in adhering contact with layer (A) of the layer element.

Thereby, the layer element and the photovoltaic module preferably includes as the properties and definitions of the layer element and the photovoltaic module as described above or below.

Examples

Determination Methods

Melt Flow Rate: 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 measured at a temperature 230 °C and a load of 2.16 kg. The MFR2 of polyethylene is measured at a temperature 190 °C and a load of 2. 16 kg.

Density ISO 1183, measured on compression moulded plaques in accordance with ISO

1872-2:2007.

Comonomer contents:

The 1 -octene comonomer content present in copolymer of ethylene (PE-B-b) was determined as described in WO 2019/134904 for the comonomer content quantification of poly(ethylene-co-l -octene) copolymers.

The 1 -butene and 1 -hexene comonomer content present in the copolymer of ethylene (PE-B-a) was determined as described in EP 3 257 895 Al for the comonomer content quantification of poly(ethylene-co-l-butene-co-l-hexene) terpolymers.

The ethylene comonomer content present in propylene polymers (PP-C-1), (PP-B-a) and (PP-B-b) was determined as described in WO 2017/071847 for the comonomer content quantification of poly(propylene-co-ethylene) copolymers. (T_m) was 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. Melting temperature (Tm) is determined from the second heating step.

Xylene cold soluble (XCS) was measured as described in WO 2018/141672.

Flexural modulus was determined according to ISO 178 at a test speed of 2 mm/min and a force of 100 N, whereby the length of the span between the supports was 64 mm, on test specimens having a dimension of 80 x 10 x 4 mm³ (length x width x thickness) prepared by injection moulding according to EN ISO 1873-2.

Charpy Notched Impact Strength was determined according to ISO 179-1 eA at +23 °C on injection moulded specimens of 80 x 10 x 4 mm³ prepared according to EN ISO 1873-2. The measurement was done after 96 h conditioning time at 23 °C of the specimen.

Vicat softening temperature was measured according to ASTM D 1525 method A (50°C/h, 10N).

Multilayer film preparation by coextrusion:

3-layer coextruded film samples of the composition C’-C-B were prepared on a Dr. Collin cast film line consisting of 3 automatically controlled extruders, a chill roll unit, a take-off unit with a cutting station and three winders to wrap the film and edge strips.

Each layer was extruded with an individual extruder: Two outer layers (layer C’ and layer B) were extruded with extruders equipped with 25 mm screw with LD of 30. The core layer (layer C) was extruded with extruder equipped with 30 mm screw with LD of 30. The thickness of each core layer C was 300 pm, for each layer C’ was 50 pm and for each layer B was 50 pm resulting in a film thickness of the 3-layer coextruded film of 400 pm. The melt temperature ranged between 220-245°C. The chill roll was cooled to 25 °C. The die width was 0.5-1.5 mm adjustable flex-lip. Layers C’ and C have the same composition (PP- C), whereas layer B has the composition (PO-B). Optical properties

The total luminous transmittance, diffuse luminous transmittance and haze were measured according to ASTM D1003-13 (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:

• Device: Haze gard plus

• Manufacturer: BYK-Gardner GmbH

• Type: 4725

• Illuminant C

Conditions:

• Conditioning time: > 96 h

• Temperature: 23 °C

• Test procedure: A - Hazemeter

Adhesion

Two different protocols for adhesion measurement have been applied: a) Adhesion measurement (a)

The adhesion test is performed on laminated strips, the encapsulant film and backsheet is peeled in a tensile testing equipment while measuring the force required for this.

A laminate consists on glass, 2 encapsulants films (layers A and A’) and backsheet (layers B/C/C’) is first laminated. Between the encapsulant and backsheet (between layers A and B) a small sheet of Teflon is inserted in the upper middle on the glass, this will generate a small part of the backsheet that is not adhered to the encapsulant. This pat will be used as the cutting and 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.

The laminate is then cut along the laminate to five stripes (13 mm width each), the cut goes through the backsheet and the encapsulant film all the way down to the glass surface.

This test method specifies a floating roller method for determination of peeling resistance and adhesive behaviour. Therefore, a laminated glass-plate is inserted into a horizontal peel test fixture with the flexible adherent gripped in the lower jaw of the test machine. The peeling angle is 90° in relation to the laminate with a constant crosshead separation speed of 50mm/min. The adhesion strength (N/mm) is the average force (N) divided by the width of the flexible adherent (mm). It is determined within the measurement length (>60mm) which starts 10mm after the initial peek and ends 10mm before the test is stopped. b) Adhesion measurement (b)

A laminate consists on glass, 2 encapsulants films (layers A and A’) and backsheet (coextruded layers B-C-C’) is first laminated. Between the encapsulant and backsheet (between layer A and B) a small sheet of Teflon is inserted at one of the ends, 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.

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.

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

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.

The average force over the 50mm is divided by 1,3 as the width of the strip is 13 mm and presented as the adhesion strength (N/mm).

The ageing is performed in damp heat, 85°C and 85% relative humidity and the samples are take out each 500h up to 2000h. Experimental part

Polyethylene compositions (PE-A) for layer A

For layer A the following polyethylene compositions were used:

Polyethylene 1 (PE-A-1) consists of the ethylene vinyl acetate copolymer composition 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).

Polyethylene 2 (PE-A ■2) consists of elastomeric polyethylene having a density of 880 kg/m³, commercially available as TF4 POE from Hangzhu First Applied Material Co., Ltd (PR China).

Polypropylene compositions (PP-C) for layer C and C’

For layers C and C’ the following polypropylene composition was used: consists of a Ziegler-Natta catalysed heterophasic propylene copolymer composition with a propylene homopolymer matrix phase having a MFR2 of 2.5 g/10 min and an ethylene -propylene elastomeric phase in an amount of 14 wt% (measured as XCS content), and an ethylene content in the elastomeric phase of 37 wt%. The heterophasic propylene copolymer composition has a MFR2 of 3.5 g/10 min, a total ethylene content of 4.2 wt%, a melting temperature of 168°C, a Vicat A temperature of 155°C, a flexural modulus of 1400 MPa and a Charpy notched impact strength at 23 °C of 40 kJ/m² and has been produced using the process as described for the heterophasic propylene copolymer Inv. 2 in the example section ofWO 2015/173175 Al.

The following additives were added to the PP-C-1 composition during the melt homogenisation step:

1500 ppm ADK-STAB A-612 (supplied by Adeka Corporation) and 300 ppm Synthetic hydrotalcite (ADK STAB HT supplied by Adeka Corporation). Polyolefin compositions (PO-B) for layer B

For layer B the following polyolefins were used: a (PP-B-a) consists of Ziegler-Natta catalysed heterophasic propylene copolymer composition with a propylene homopolymer matrix phase having a MFR2 of 2.5 g/10 min and an ethylene -propylene elastomeric phase in an amount of 14 wt% (measured as XCS content), and an ethylene content in the elastomeric phase of 37 wt%. The heterophasic propylene copolymer composition has a MFR2 of 3.5 g/10 min, a total ethylene content of

4.2 wt%, a melting temperature of 168°C, a Vicat A temperature of 155°C, a flexural modulus of 1400 MPa and a Charpy notched impact strength at 23°C of 40 kJ/m² and has been produced using the process as described for the heterophasic propylene copolymer Inv.

2 in the example section ofWO 2015/173175 Al. consists of a Ziegler-Natta catalysed heterophasic propylene copolymer composition with a poly(propylene-co-ethylene) random copolymer matrix phase having a MFR2 of 4 g/10 min and an ethylene content in the matrix phase of 4. 1 wt% and an ethylene -propylene elastomeric phase in an amount of 21 wt% (measured as XCS content), and an ethylene content in the elastomeric phase of 35 wt%. The heterophasic propylene copolymer composition has a 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/m² and has been produced using the process as described for the heterophasic propylene copolymer IE2 in the example section of WO 2015/117948 Al. c (PP B ■c) consists of a propylene homopolymer wax grafted with maleic anhydride, commercially available as Epolene E-43 from Westlake.

Polvethvlene a (PE-B ■a) consists of the metallocene catalysed 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. Polyethylene b (PE-B-b) consists of a metallocene catalysed poly(ethylene-l-octene) elastomer having a density of 870 kg/m³, a melt flow rate MFR2 of 6.6 g/10 min, a melting temperature of 48°C and a Vicat A temperature of 35°C, commercially available as Queo™ 7007LA from Borealis AG.

Preparation of the polyolefin compositions for layer B

The polyolefin compositions PO-B-1 to PO-B-9 were prepared by compounding the above mentioned polyolefins together with an additive package ofl500 ppm ADK-STAB A-612 (supplied by Adeka Corporation) and 300 ppm Synthetic hydrotalcite (ADK STAB HT supplied by Adeka Corporation). .

The compositions of the polyolefin compositions PO-B-1 to PO-B-9 are listed in Table 1 below:

Table 1: Compositions of PO-B-1 to PO-B-9 for layer B

Thereby, compositions PO-B-1, PO-B-2, PO-B-4 and PO-B-5 qualify as comparative compositions as they do not include PE-B-a, which reflects the claimed copolymer of ethylene and one or more comonomers selected from 4 to 12 carbon atoms having a melting temperature Tm of from 100 to 140°C (B-2). Optical properties of the multilayer films

The multilayer films of the composition C’-C-B were prepared by coextrusion as described above. Thereby, for layer C’ and C 100 wt% of the polypropylene composition PP-C-1 has been used. For layer B 100 wt% of the polyolefin compositions PO-B-1 to PO-B-9 have been used. 9 multilayer films Film 1-9 have been obtained. From said multilayer films the optical properties have been measured. The composition of the multilayer films and their optical properties are listed in Table 2.

Table 2: Composition and optical properties of multilayer films 1-9

It can be seen that the multilayer films 1-3 - each comprising PP-B-a as polypropylene component in layer B - show comparable optical properties.

Correspondingly, multilayer films 4-9 - each comprising PP-B-b as polypropylene component in layer B - show comparable optical properties, especially in regard of diffuse and total luminous transmittance. Thereby, it can be seen that the addition of PP-B-c and PE- B-b slightly improve the optical properties of the multilayer films in behalf of haze.

Adhesion properties of the multilayer films 1-9 laminated to layer A

Two sets of laminates were produced which were subjected to two different adhesion protocols.

The first set of multilayer films 1-3 were each laminated to a two-layer structure A’ -A consisting of two layers A’ and A each consisting of polyethylene composition PE-A-1 and polyethylene composition PE-A-2 to form layer elements having the layer structure A’-A-B- C-C’. Each layer A and A’ had a thickness of 450 pm and each two-layer structure A’-A consequently a thickness of 900 pm. The total thickness of each layer structure was 1300 pm. Layers A and A’ had the same composition and shall represent the front and rear encapsulation layers of a photovoltaic module without the photovoltaic cell. The lamination conditions were as follows:

5 min evacuation + 10 min pressing, pressure: 800 mbar, temperature: 150°C

The layer elements were subjected to the adhesion measurement protocol (a) as described above. The general composition of the tested layer elements LE1-LE6 and the adhesion between layer A and B are listed in Table 3.

Table 3: Composition of the layer elements LE1-LE6 and adhesion according to protocol (a)

*Yielding, adhesion is higher than the actual value

** Adhesion to glass is measured before the backsheet and encapsulant release from each other n.m. = not measured

It can be seen that for layer elements LE3 and LE6 according to the invention the adhesion between layer A and B was significantly improved also after ageing without negative influence on the optical properties as shown in Table 2.

The second set of multilayer films 4-9 were each laminated to a two-layer A’ -A consisting of two layers A’ and A each consisting of polyethylene composition PE-A-1 to form layer elements having the layer structure A’-A-B-C-C’ . Each layer A and A’ had a thickness of 450 pm and each two-layer structure A’-A consequently a thickness of 900 pm. The total thickness of each layer structure was 1300 pm. Layers A and A’ had the same composition and shall represent the front and rear encapsulation layers of a photovoltaic module without the photovoltaic cell.

The lamination conditions were as follows:

5 min evacuation + 10 min pressing, pressure: 800 mbar, temperature: 150°C The layer elements were subjected to the adhesion measurement protocol (b) as described above. The general composition of the tested layer elements LE7-LE12 and the adhesion between layer A and B, are listed in Table 4. Table 4: Composition of the layer elements LE7-LE12 and adhesion according to protocol

(b)

It can be seen that for layer elements LE9 to LE12 according to the invention the adhesion between layer A and B was significantly improved especially before ageing without negative influence on the optical properties as shown in Table 2.

It can be seen that addition of higher amounts of PP-B-c and/or PE-B-b to the compositions of layer B (see comparative LE8 and inventive LE10 and LEI 2) lead to significant degeneration of the adhesion properties after long ageing (more than 1000 h).

Claims

1. A layer element comprising at least three layers (A), (B) and (C), wherein layer (A) comprises a polyethylene composition (PE-A); layer (B) comprises a polyolefin composition (PO-B) comprising

(B-l) a copolymer of propylene and ethylene having a melting temperature Tm of from 130 to 175°C, preferably from 135 to 172°C, more preferably from 140 to 170°C, determined by differential scanning calorimetry according to ISO 11357 / part 3 / method C2; and

(B-2) a copolymer of ethylene and one or more comonomers selected from alphaolefins having 4 to 12 carbon atoms having a melting temperature Tm of from 100 to 140°C, preferably from 105 to 130°C, more preferably from 110 to 125 °C, determined by differential scanning calorimetry according to ISO 11357 / part 3 / method C2; and layer (C) comprises a polypropylene composition (PP-C); wherein layer (B) has a first surface and a second surface located opposite to the first surface; the first surface of layer (B) is in adherent contact with a surface of layer (A) and the second surface of layer (B) is in adherent contact with a surface of layer (C), resulting in a layer structure A-B-C having the layer (B) sandwiched between the layer (A) and the layer (C).

2. The layer element according to claim 1, wherein the copolymer of propylene and ethylene (B-l) is (i) a heterophasic copolymer of propylene and ethylene (B-l-a), which comprises a random copolymer of propylene and ethylene as matrix component and a elastomeric propylene-ethylene copolymer component which is dispersed in said matrix component or (ii) a heterophasic copolymer of propylene and ethylene (B-l-b), which comprises a propylene homopolymer as matrix component and a elastomeric propyleneethylene copolymer component which is dispersed in said matrix component.

3. The layer element according to any one of the preceding claims, wherein the copolymer of ethylene (B-2) is a terpolymer of ethylene, wherein (i) the terpolymer is a terpolymer of ethylene and two comonomers differing in their amount of carbon atoms and/or (ii) the terpolymer has a density of from 900 to 930 kg/m², preferably from 905 to 925 kg/m², more preferably from 910 to 920 kg/m², determined according to ISO 1183 and/or a melt flow rate MFR2 of from 0.1 to 5.0 g/ 10 min, preferably from 0.5 to 4.0 g/10 min, more preferably from 1.0 to 3.0 g/10 min, determined according to ISO 1133 at a temperature of 190°C and load of 2. 16 kg.

4. The layer element according to any one of the preceding claims, wherein the polyethylene composition (PE-A) comprises

(PE-A-a) a copolymer of ethylene, which bears silane group(s) containing units; or (PE-A-b) a copolymer of ethylene with polar comonomer units selected from one or more of (Ci-Ce)-alkyl acrylate or (Ci-Ce)-alkyl (Ci-C6)-alkylacrylate comonomer units, which additionally bears silane group(s) containing units, whereby the copolymer of ethylene (PE-A-a) is different from the copolymer of ethylene (PE-A-b); or

(PE-A-c) a copolymer of ethylene with vinyl acetate comonomer units; or

(PE-A-d) a copolymer of ethylene with one or more alpha-olefin comonomer units having from 3 to 12 carbon atoms, wherein the copolymer of ethylene (PE- A-d) has a density of from 850 to less than 900 kg/m³, preferably from 860 to 890 kg/m³, more preferably from 865 to 885 kg/m³, determined according to ISO 1183.

5. The layer element according to any one of the preceding claims, wherein the polypropylene composition (PP-C) comprises

6. The layer element according to any one of the preceding claims, wherein all layers are free of titanium dioxide, preferably free of pigment.

7. The layer element according to any one of the preceding claims, having one or more or all of the following properties: layer (A) has a thickness of from 100 pm to 750 pm; layer (B) has a thickness of from 10 pm to 100 pm; layer (C) has a thickness of from 125 pm to 750 pm; the layer element has a total thickness of from 250 pm to 2000 pm.

8. The layer element according to any one of the preceding claims, wherein the combined layers (B) and (C) have one or more or all of the following properties: a total luminous transmittance, determined according to ASTM D1003-13, of at least 84 %, such as from 84 to 99 %, preferably from 86 to 97 %, more preferably from 87 to 95 %; a diffuse luminous transmittance, determined according to ASTM D1003-13, of at least 30 %, such as from 30 to 50 %, preferably from 32 to 45 %, more preferably from 34 to 43 %; a clarity, determined according to ASTM DI 003-13, of at least 88 %, such as from 88 to 99 %, preferably from 90 to 99 %, more preferably from 92 to 99 %; a haze, determined according to ASTM D 1003-13, of not more than 50 %, such as from 30 to 50 %, preferably from 33 to 48 %, more preferably from 35 to 46 %.

9. The layer element according to any one of the preceding claims having an adhesion before ageing between layers (A) and (B) , determined according to method (a) given in the determination methods, of more than 7.0 N/mm, preferably at least 8.0 N/mm and/or an adhesion after ageing for 1000 h at 80°C and 85 % RH between layers (A) and (B) , determined according to method (a) given in the determination methods, of more than 4.0 N/mm, preferably at least 4.2 N/mm and/or an adhesion after ageing for 2000 h at 80°C and 85 % RH, determined according to method (a) given in the determination methods, of more than 4.0 N/mm, preferably at least 4.2 N/mm.

10. An article comprising the layer element according to any one of claims 1 to 9.

11. The article according to claim 10 being a photovoltaic module comprising a photovoltaic element and the layer element wherein the photovoltaic element is in adhering contact with layer (A) of the layer element.

12. The article according to claim 11, which comprises, in the given order, a protective front layer element, a front encapsulation layer element, a photovoltaic element and an integrated backsheet element, wherein the integrated backsheet element comprises, preferably consists of the layer element.

13. A process for producing the layer element according to any one of claims 1 to 9 comprising the steps of: adhering the layers (A), (B) and (C) of the layer element together by extrusion and/or lamination in the configuration A-B-C; and recovering the formed layer element.

14. A process for producing a photovoltaic (PV) module according to claims 11 or 12 comprising the steps of: assembling the photovoltaic element, the layer element and optional further layer elements to a photovoltaic (PV) module assembly; laminating the layer elements of the photovoltaic (PV) module assembly in elevated temperature to adhere the elements together; and recovering the obtained photovoltaic (PV) module.

15. The use of the layer element according to any one of claims 1 to 9 as an integrated backsheet element of a bifacial photovoltaic module comprising a photovoltaic element and said layer element, wherein the photovoltaic element is in adhering contact with layer (A) of the layer element.