Refrigerator appliance having at least one inner plastic liner and method for manufacturing the liner

1. A method for manufacturing an internal liner comprising a cabinet liner or a door liner of a refrigerator appliance, the method comprising the steps of:

preparing a polypropylene-based material comprising a propylene-ethylene random copolymer in an amount ranging between 60 and 90% w/w having a main polypropylene chain with ethylene units arranged along the polypropylene chain in an amount ranging between about 1% to about 8% w/w of the propylene-ethylene random copolymer, and at least one lamellar or fibrolamellar filler, and one or more alpha or beta nucleating agents;

extruding the polypropylene-based material prepared by compounding the propylene-ethylene copolymer and said at least one lamellar or fibrolamellar filler directly in an extruder into sheets; and

thermoforming a sheet of said polypropylene-based material onto a male mold to shape the liner, wherein the thermoforming step comprises the steps of: heating the sheet to reach an operating temperature between 125° C. and 155° C., at which the sheet is thermoformable; and shaping the sheet onto an outer shaping surface of the male mold.

2. The method according to claim 1 , wherein the propylene-ethylene copolymer has a content of ethylene units ranging between about 2% and about 5% w/w.

3. The method according to claim 1 , wherein the at least one lamellar or fibrolamellar filler is selected from the group consisting of: talc, kaolin, mica, glass flakes, nanoclays, montmorillonite and bentonite, graphite, aluminum nitride, and boron nitride.

4. The method according to claim 3 , wherein said at least one lamellar or fibrolamellar filler is talc.

5. The method according to claim 1 , wherein the at least one lamellar or fibrolamellar filler comprises particles having a substantially platelet shape.

6. The method according to claim 1 , wherein the polypropylene-based material contains the at least one lamellar or fibrolamellar filler in an amount ranging between 10% and 40% w/w.

7. The method according to claim 1 , wherein the polypropylene-based material contains the at least one lamellar or fibrolamellar filler in an amount ranging between 20% and 30% w/w.

8. The method according to claim 1 , wherein the polypropylene-based material further comprises polypropylene homo-polymer.

9. The method according to claim 1 , wherein the polypropylene-based material further comprises polypropylene homo-polymer in an amount ranging between 0% and 25% w/w.

10. The method according to claim 1 , wherein each sheet consists of a single, substantially uniform layer of the polypropylene-based material; or consists of a main layer, made of the polypropylene-based material, and of a glossy or semiglossy covering layer, covering a face of the main layer, made of neat polypropylene or a polypropylene compound with glossy appearance, said covering layer being co-extruded or laminated with the main layer.

11. The method according to claim 1 , wherein the thermoforming step comprises, after the sheet has been heated, a pre-stretching step, in which the heated sheet is pre-stretched before being shaped onto the male mold.

12. The method according to claim 1 , wherein the sheet is vacuum formed onto the male mold.

13. The method according to claim 12 , wherein in the thermoforming step, vacuum is applied on the side of a first face of the sheet, facing the shaping surface of the male mold; and a compressed gas stream is injected on the side of a second face of the sheet, opposite to the first face.

14. The method according to claim 1 , wherein in the thermoforming step the shaping surface of the male mold is at a temperature lower than a recrystallization temperature of the polypropylene-ethylene copolymer.

15. The method according to claim 14 , wherein the temperature of the shaping surface is about 90-110° C.

16. The method according to claim 1 , comprising a first cooling step effected on the sheet shaped to define the liner and still contacting the shaping surface of the male mold.

17. The method according to claim 16 , comprising a second cooling step effected after the liner has been removed from the male mold.