EP-4741454-A1 - SUSTAINABLE CROSSLINKING OF FLAME RETARDANT POLYOLEFIN COMPOSITION

EP4741454A1EP 4741454 A1EP4741454 A1EP 4741454A1EP-4741454-A1

Abstract

The present invention provides a flame retardant polyolefin composition comprising at least one crosslinkable polyolefin base resin containing hydrolysable silane groups (A), at least one silanol condensation catalyst (B) being an inorganic tin (II) compound in which a tin atom has no covalent bond to a carbon atom, and at least one flame retardant inorganic filler (C), which can be efficiently crosslinked even at ambient temperature. Moreover, the present invention provides the use of tin (II) oleate, tin (II) neodecanoate or mixtures thereof for crosslinking a polyolefin composition containing at least one crosslinkable polyolefin base resin containing hydrolysable silane groups, under ambient conditions and a process for producing a crosslinked article and a cable or wire.

Inventors

HESSELGREN, Jessica
Gschneidtner, Tina
PIEL, Tanja Maria
SMEDBERG, ANNIKA
PRIETO CONGOST, Oscar

Assignees

Borealis GmbH

Dates

Publication Date: 20260513
Application Date: 20241112

Claims (15)

A flame retardant polyolefin composition comprising (A) at least one crosslinkable polyolefin base resin containing hydrolysable silane groups, wherein the polyolefin base resin is polyethylene or polypropylene, (B) at least one silanol condensation catalyst, and (C) at least one flame retardant inorganic filler, wherein the silanol condensation catalyst is an inorganic tin (II) compound in which the tin atom has no covalent bond to a carbon atom.
The flame retardant polyolefin composition according to claim 1, wherein the at least one flame retardant inorganic filler (C) is selected from calcium carbonate, aluminium hydroxide and magnesium hydroxide or a combination thereof.
The flame retardant polyolefin composition according to claim 1 or 2, wherein the at least one crosslinkable polyolefin base resin containing hydrolysable silane groups (A) is a terpolymer comprising a polar comonomer, which is preferably an alkyl acrylate comonomer.
The flame retardant polyolefin composition according any one of claims 1 to 3, wherein the flame retardant polyolefin composition further comprises at least one scorch retardant.
The flame retardant polyolefin composition according to any one of claims 1 to 4, wherein the at least one crosslinkable polyolefin base resin containing hydrolysable silane groups (A) contains the hydrolysable silane groups in an amount of 0.1 to 3.0 wt.-% based on the total weight of the crosslinkable polyolefin resin, and/or wherein the hydrolysable silane groups are selected from trimethoxy silane groups, triethoxysilane groups and a mixture thereof.
The flame retardant polyolefin composition according to any one of claims 1 to 5, wherein the at least one silanol condensation catalyst (B) is represented by the following formula (II): [R 1 COO]Sn[OOCR 2 ] (II) wherein R 1 and R 2 independently represent a straight or branched, saturated or unsaturated hydrocarbyl group having 2 to 30 carbon atoms, preferably 8 to 20 carbon atoms.
The flame retardant polyolefin composition according to claim 6, wherein the at least one silanol condensation catalyst (B) is selected from tin (II) oleate, tin (II) neodecanoate and a mixture thereof.
The flame retardant polyolefin composition according to any one of claims 1 to 7, which contains, based on the total mass of the flame retardant polyolefin composition, (A) the at least one crosslinkable polyolefin base resin containing hydrolysable silane groups in an amount of 10.0 to 75.0 wt.-%, preferably 15.0 to 70.0 wt.-%, (B) the at least one silanol condensation catalyst in an amount of 0.01 to 2.0 wt.-%, preferably 0.02 to 1.0 wt.-%, and (C) the at least one flame retardant inorganic filler in an amount of 15.0 to 70.0 wt.-%, preferably 20.0 to 65.0 wt.-%.
The flame retardant polyolefin composition according to claim 8, containing, based on the total mass of the flame retardant polyolefin composition, (A) the at least one crosslinkable polyolefin base resin containing hydrolysable silane groups in an amount of 45.0 to 75.0 wt.-%, preferably 50.0 to 70.0 wt.-%, wherein the at least one crosslinkable polyolefin base resin containing hydrolysable silane groups is a terpolymer comprising a butyl acrylate comonomer, such as an ethylene butyl acrylate (EBA)-based copolymer containing hydrolysable silane groups, (B) the at least one silanol condensation catalyst in an amount of 0.05 to 2.0 wt.-%, preferably 0.1 to 1.0 wt.-%, and (C) the at least one flame retardant inorganic filler in an amount of 15.0 to 40.0 wt.-%, preferably 20.0 to 35.0 wt.-%, wherein the at least one flame retardant inorganic filler is a carbonate metal salt, such as calcium carbonate; or containing, based on the total mass of the flame retardant polyolefin composition, (A) the at least one crosslinkable polyolefin base resin containing hydrolysable silane groups in an amount of 10.0 to 35.0 wt.-%, preferably 15.0 to 30.0 wt.-%, wherein the crosslinkable polyolefin base resin containing hydrolysable silane groups is a terpolymer comprising a methyl acrylate comonomer, such as an ethylene methyl acrylate (EMA)-based copolymer containing hydrolysable silane groups, (B) the at least one silanol condensation catalyst in an amount of 0.01 to 1.0 wt.-%, preferably 0.02 to 0.75 wt.-%, and (C) the at least one flame retardant inorganic filler in an amount of 40.0 to 70.0 wt.-%, preferably 45.0 to 65.0 wt.-%, wherein the at least one flame retardant inorganic filler is a hydroxide metal salt, such as aluminum hydroxide or magnesium hydroxide.
Use of tin (II) oleate, tin (II) neo decanoate or mixtures thereof, preferably tin (II) neodecanoate, for crosslinking a polyolefin composition containing at least one crosslinkable polyolefin base resin containing hydrolysable silane groups, at ambient conditions or under application of heat.
The use according to claim 10, wherein the polyolefin composition further contains at least one inorganic basic filler as flame retardant compound and/or at least one scorch retardant.
A process for producing a crosslinked article, comprising the steps of - providing the flame retardant polyolefin composition according to any of claims 1 to 9, - extruding the composition to form an article, - optionally cooling down the article, and - crosslinking the article either under application of heat or at ambient conditions to form a crosslinked article.
Crosslinked article comprising the flame retardant polyolefin composition according to any of claims 1 to 9.
Article according to claim 13 being a wire or cable comprising at least one layer made of the flame retardant polyolefin composition according to any of claims 1 to 9, the article preferably being a low, medium or high voltage power cable.
Article according to claim 14, wherein the article is a cable and the at least one a layer is a jacketing layer or an insulating layer.

Description

Field of the invention The present invention relates to a flame retardant polyolefin composition (FRPC) comprising at least one crosslinkable polyolefin base resin containing hydrolysable silane groups (A), wherein the polyolefin base resin is polyethylene or polypropylene, at least one silanol condensation catalyst (B) being an inorganic tin (II) compound in which a tin atom has no covalent bond to a carbon atom, and at least one flame retardant inorganic filler (C). Technical background Crosslinking is a known method to impart improved mechanical and chemical heat resistance properties to polyolefin compositions used in the production of wires or cables. Crosslinking may be performed by condensation of silanol groups contained in the polyolefin composition, which can be obtained by hydrolysis of silane groups. Another desirable feature of polyolefin compositions is flame retardancy. However, flame retardants typically suffer from either limitations in mechanical properties, such as tensile properties and tear strength, or in flame retardant (FR) properties. As such, there is a growing demand for flame retardant polyolefin compositions that can fulfil both mechanical and FR properties. At present, a commonly used catalyst for crosslinking flame retardant polyolefin compositions is dioctyltin dilaurate (DOTL), which, owing to its health and environmental hazardousness, is facing increasing regulatory pressure and may be phased out in the near future. Therefore, although the catalytic performance of organic tin catalysts such as dioctyltin dilaurate (DOTL) is good, those catalyst needs replacement for environmental and toxicity reasons. An environmental friendly catalyst for crosslinking condensation of silanol groups contained in the crosslinkable polyolefin compositions include organic acid-based catalysts, such as sulfonic acid-based catalysts. However, flame retardants, as well as other additives, commonly used in the field of flame retardant polyolefin compositions include basic compounds, that is, compounds that tend to react with acidic compounds by accepting protons, which can interfere with the crosslinking reactivity of the silanol crosslinking catalyst. Hence, organic acid-based catalysts, can be neutralized under such conditions, which impairs with the desired catalytic crosslinking activity. EP2876132 A1 relates to a crosslinkable polyethylene composition comprising inorganic tin(II) compounds in which a tin atom has no covalent bond to a carbon atom. The Examples therein disclosed however do not include flame retardant polyethylene compositions and polyethylene compositions crosslinked at ambient temperature. EP2752243 A1 relates to the use of tin salt of neodecanoic acid and its solutions in coatings and paints, adhesives, sealants and elastomers and in the production of polyurethane systems (PUR systems). EP2562209 relates to a cable comprising a polymer composition comprising a LDPE bearing hydrolysable silane groups and a silanol condensation catalyst, the silanol condensation catalyst being metal acetylacetonate (acac) complexes. EP2562768 A1 relates to a cable comprising a polymer composition comprising a polyolefin bearing hydrolysable silane groups and a silanol condensation catalyst, the silanol condensation catalyst being a sterically hindered amine. WO2011/160964 A1 relates to a cable comprising a polymer composition comprising a polyolefin bearing hydrolysable silane groups and a silanol condensation catalyst, the silanol condensation catalyst being a zirconium, titanium or other lewis acid complexes. However, none of the aforementioned inventions was tested with flame retardant polyolefins composition containing flame retardant inorganic filler and thus, owing to the possible impediment to the catalytic activity represented by the flame retardant inorganic filler, there is a need for a robust silanol condensation catalyst which is both environmentally friendly and capable of crosslinking polyolefin compositions in the presence of basic compounds such as flame retardant inorganic filler. Furthermore, there is also a need for such robust catalyst to be able to operate at lower temperatures and even ambient conditions, so as to simplify the crosslinking process and reduce costs and environmental impact. Summary of the invention It is the object of the present invention to provide a flame retardant polyolefin composition (FRPC) which can be efficiently crosslinked in the presence of flame retardant inorganic filler, and that can be crosslinked at lower temperate or even ambient conditions, whilst retaining desirable properties such as hot set properties. The inventors of the present invention surprisingly found that the object can be solved by providing a polyolefin composition comprising at least one crosslinkable polyolefin base resin containing hydrolysable silane groups (A), wherein the polyolefin base resin is polyethylene or polypropylene, at least one silanol condensation cataly