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1. (WO2018122293) LOW EMISSION POLYPROPYLENE FOAM SHEETS
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CLAIMS

1. A process for production of a foam having low organic compounds emissions, the process comprising the steps of:

a. providing a foam comprising a propylene composition comprising a high melt strength propylene (HMS-PP) homopolymer or copolymer or combinations thereof, said HMS-PP foam having a melt strength of at least 25 cN at a maximum speed of at least 200 mm/s, as measured in a Rheotens apparatus using a capillary die with a diameter of 2 mm and a length of 6 mm and a temperature of 200 °C with an acceleration of the melt strand drawn down of 120 mm/sec2, and a melting temperature of at least 135°C, preferably at least 140°C, measured according to ISO-11357-3 by DSC analysis,

b. subjecting the HMS-PP foam to a thermal treatment at a temperature Tt which is between 5 and 40 °C, preferably between 5 and 30 °C, more preferably between 5 and 20 °C below the melting temperature Tm of the HMS-PP for a duration between 1 min and 2 hours.

2. The process of claim 1 wherein the thermal treatment is done at a treatment temperature Tt between 5 and 15 °C lower than the melting temperature of the HMS-PP and for a duration between 1 and 10 minutes, preferably between 2 and 8 or 3 to 5 minutes.

3. The process of claims 1 - 2 wherein the melting temperature Tm of the HMS-PP foam is at least 150°C and the temperature Tt is between 120 and 145 °C.

4. The process of claim 1 - 3 wherein the HMS-PP has a melt strength as characterised by the strain hardening factor (SHF), measured as described in the description, of at least 1.7, more preferably of at least 2, even more preferably in the range of 2 to 15, still more preferably in the range of 3.5 to 15 measured at a strain rate of 3.0 s-1 and a Hencky strain of 2.5.

5. The process of claims 1 to 4 wherein the foam is formed by extruding a composition comprising HMS-PP, a blowing agent and preferably a foam nucleating agent, then cooling the foamed extrudate to a temperature between 10 and 30°C below the melting temperature Tm of the HMS-PP and subsequently bring the foamed extrudate to the temperature Tt and do the thermal treatment.

6. The process of claims 1 - 5 wherein the HMS-PP is I) a long-chain branched polypropylenes synthesised with a metallocene catalyst or II) produced by modifying polypropylene homopolymer or polypropylene copolymer having less than 6 wt% of comonomer wherein the modification is done a) by e-beam irradiation or b) by reacting with peroxides in the presence of a polyunsaturated compound followed by thermal treatment to reduce volatiles to a VOC below 75 pgTE/g, as determined according to VDA 278: 2011, and a FOG below 150 pgHD/g, as determined according to VDA 278: 2011.

7. The process of claims 1- 6 wherein the foam is in the form of extruded foam having a foam density of 350 g/liter or lower.

8. The process according to claims 1 - 7 wherein the propylene polymer composition comprises at least 50 wt% relative to the total weight of the propylene polymer composition of a) the HMS-PP and preferably up to 50 wt% of b) one or more polypropylene random copolymers or heterophasic copolymers with ethylene and optionally other C4 - CIO alpha-olefins, or polyethylene.

9. The process according to claim 8, wherein the propylene polymer composition is a heterophasic copolymer composition wherein the HMS-PP polymer a) forms the matrix phase together with the random copolymer b) and/or the matrix of the heterophasic copolymer b) while the dispersed phase of the heterophasic copolymer b) forms the dispersed phase of the heterophasic copolymer composition.

10. The process according to claims 1 - 9, wherein the polypropylene foam product obtained has a volatile organic compounds (VOC) emission, determined according to VDA278 : 2011 at 90°C for 0.5 hrs below 300 pgTE/g, preferably below 200, 150 or 100 and most preferably below 50 MgTE/g .

11. The process according to claims 1 - 10, wherein the polypropylene foam product obtained has a FOG emission, determined according to VDA278: 2011 at 120°C for 1.0 hrs, of below 200 pgHD/g, preferably below 150 and most preferably below 100 pgHD/g.

12. The process according to claims 1 - 11, wherein the polypropylene foam product obtained has a VOC and FOG emission level equal or less than 150%, 120% or more preferably less than 100% of the calculated weight average VOC and FOG emission level of the polypropylene constituents before foaming .

13. The process of claims 1-12, wherein the polypropylene composition further comprises antioxidants and wherein the heat treatment is such that the amount of antioxidant reduces by less than 20 wt%, preferably less than 15 wt%, more preferably less than 10 wt%.

14. A polypropylene foam product obtainable by the process of claims 1 -13, preferably in the form of foamed sheet, beads, pipes, preferably sheets or articles made from foamed sheets or beads.

15. A process for the manufacture of articles comprising a foam and having a low VOC and low FOG for use in closed rooms or compartments, in particular in cars or in food packaging, said process comprising the use of a polypropylene foam produced according to the process of claims 1 - 13.