Injection moulding process for the preparation of a foamed article with improved surface quality

1 . An injection moulding process for preparing a foamed article in a mould comprising the following sequential steps:

a) Closing the mould to form a mould cavity having a volume V1;

b) Injecting a foamable polymer composition into the mould cavity to form a filled mold cavity in which at least 90% of the volume V1 is filled;

c) Applying a pressure P to the foamable polymer composition in the filled mold cavity for a duration t, wherein P is in the range from 21.6 to 2160 bar, and t is in the range from 1.3 to 10.2 s;

d) Increasing the volume of the filled mould cavity to a volume V2 to allow expansion of the foamable polymer into a pre-foamed article;

e) Allowing the pre-foamed article to solidify to form the foamed article; and

f) Ejecting the foamed article from the mould.

2 . An injection moulding process for preparing a foamed article in a mould comprising the following sequential steps:

a) Closing the mould to form a mould cavity having a volume V1;

b) Injecting a foamable polymer composition into the mould cavity to form a filled mold cavity in which at least 90% of the volume V1 is filled;

c) Applying a pressure P to the foamable polymer composition in the filled mold cavity for a duration t, wherein P is in the range from 21.6 to 2160 bar, and t is in the range from 5.1 to 10.2 s;

d) Increasing the volume of the filled mould cavity to a volume V2 to allow expansion of the foamable polymer into a pre-foamed article;

e) Allowing the pre-foamed article to solidify to form the foamed article; and

f) Ejecting the foamed article from the mould.

3 . The injection moulding process according to claim 1 , wherein P is in the range from 46.4 to 123821.6 to 2160 bar.

4 . The injection moulding process according to claim 1 , wherein t is in the range from 2.1 to 9.6 s.

5 . The injection moulding process according to claim 1 , wherein the foamed article has an expansion ratio in the range from 1.05 to 3.14, wherein the expansion ratio is the ratio between the density of the foamable polymer composition before foaming and that of the foamed article and wherein the density is measured according to ISO 1183-1:2012.

6 . The injection moulding process according to claim 1 , wherein the mould cavity is opened by at most 11.2 cm.

7 . The injection molding process according to claim 1 , wherein the foamable polymer composition comprises a thermoplastic composition and at least a foaming agent.

8 . The injection molding process according to claim 7 , wherein the thermoplastic composition has a melt flow index (MFI) in the range from 5-120 dg/min, as measured according to ISO1133-1:2011 at 230° C. with a 2.16 kg load.

9 . The injection molding process according to claim 7 , wherein the amount of the thermoplastic composition is at least 92 wt %, based on the total amount of the foamable polymer composition.

10 . The injection molding process according to claim 7 , wherein the thermoplastic composition comprise an inorganic filler.

11 . The injection molding process according to claim 7 , wherein amount of the inorganic filler is in the range from 5 to 30 wt %, based on the total amount of the thermoplastic composition.

12 . The injection molding process according to claim 7 , wherein the thermoplastic composition comprises a thermoplastic polymer, wherein the thermoplastic polymer is a polypropylene.

13 . The injection moulding process according to claim 1 , wherein P is in the range from 110 to 791 bar.

14 . The injection moulding process according to claim 2 , wherein P is in the range from 46.4 to 1238 bar.

15 . The injection moulding process according to claim 2 , wherein P is in the range from 110 to 791 bar.

16 . The injection moulding process according to claim 1 , wherein P is equal to 400 bar; and t is in the range from 1.3 to less than 5 s or from greater than 5 to 10.2 s.

17 . The injection moulding process according to claim 1 ,

wherein P is in the range from 21.6 to less than 400 bar or from greater than 400 to 2160 bar;

t is in the range from 1.3 to less than 5 s or from greater than 5 to 10.2 s;

step (b) has a duration of greater or less than 0.21 s, and is injected with an injection speed of greater or less than 250 cm 3 /s; and

step (e) has a duration of greater or less than 40 s.

18 . The injection moulding process according to claim 1 , wherein P is in the range from 21.6 to less than 400 bar or greater than 400 to 2160 bar.

19 . The injection moulding process according to claim 1 , wherein t is in the range from 1.3 to less than 5 s or greater than 5 to 10.2 s.

20 . The injection moulding process according to claim 1 , wherein P is in the range from 21.6 to less than 400 bar or greater than 400 to 2160 bar and t is in the range from 1.3 to less than 5 s or greater than 5 to 10.2 s.