REFRIGERATOR APPLIANCE HAVING AT LEAST ONE INNER PLASTIC LINER AND METHOD FOR MANUFACTURING THE LINER

Abstract

A refrigerator appliance having at least one internal liner, in particular a cabinet liner or a door liner, defining an inner compartment and made of a blend material comprising a mixture of a propylene-ethylene copolymer and a polymer selected in the group consisting of PE and EVA.

Claims

1. A refrigerator appliance having at least one internal liner, in particular a cabinet liner or a door liner, defining an inner compartment; wherein the liner is made of a blend material comprising a mixture of: a propylene-ethylene copolymer, and a polymer selected in the group consisting of PE and EVA.

2. The refrigerator appliance according to claim 1, wherein the blend material is a physical mixture of the polymer and the propylene-ethylene copolymer.

3. The refrigerator appliance according to claim 1, wherein the polymer blended with the propylene-ethylene copolymer is mixed with the propylene-ethylene copolymer in an amount ranging from 23 to 50 phr (parts per hundred resin).

4. The refrigerator appliance according to claim 1, wherein the ethylene-propylene copolymer has propylene as a main component and is either a random copolymer or a block copolymer.

5. The refrigerator appliance according to claim 1, wherein the propylene-ethylene copolymer is a random copolymer and has a content of ethylene units ranging between about 1% and about 8% w/w.

6. The refrigerator appliance according to claim 5, wherein the propylene-ethylene copolymer is a random copolymer and has a content of ethylene units ranging between about 2% and about 6% w/w.

7. The refrigerator appliance according to claim 1, wherein the propylene-ethylene copolymer is a block copolymer and has a content of ethylene units ranging between about 5% and about 25% w/w.

8. The refrigerator appliance according to claim 7, wherein the propylene-ethylene copolymer is a block copolymer and has a content of ethylene units ranging between about 5% and about 12% w/w.

9. The refrigerator appliance according to claim 1, wherein the polymer blended with the ethylene-propylene copolymer is a high density polyethylene (HDPE).

10. The refrigerator appliance according to claim 9, wherein the content of HDPE in the blend material polymer portion ranges from 23 to 50 phr.

11. The refrigerator appliance according to claim 1, wherein the blend material comprises at least one filler, in particular a mineral filler, in an amount ranging from 5 to 50 phc (parts per hundred compound).

12. The refrigerator appliance according to claim 11, wherein the filler is a lamellar or fibrolamellar filler.

13. The refrigerator appliance according to claim 11, wherein the filler is talc, calcium carbonate or kaolin clay.

14. The refrigerator appliance according to claim 1, wherein the blend material comprises also polypropylene homo-polymer in an amount ranging between about 0% and about 25% w/w.

15. A method for manufacturing a liner, in particular a cabinet liner or a door liner, of a refrigerator appliance; the method comprising: preparing a blend material comprising a mixture of a propylene-ethylene copolymer and a polymer selected in the group consisting of: PE and EVA; extruding the blend material into sheets; and thermoforming a sheet of the blend material to shape the liner.

16. The method according to claim 15, wherein the blend material is a physical mixture of the polymer and the propylene-ethylene copolymer.

17. The method according to claim 15, wherein the polymer blended with the ethylene-propylene copolymer is mixed with the propylene-ethylene copolymer in an amount ranging from 23 to 50 phr.

18. The method according to claim 15, wherein the ethylene-propylene copolymer has propylene as a main component and is either a random copolymer or a block copolymer.

19. The method according to claim 15, wherein the propylene-ethylene copolymer is a random copolymer and has a content of ethylene units ranging between about 1% and about 8% w/w.

20. The method according to claim 18, wherein the propylene-ethylene copolymer is a random copolymer and has a content of ethylene units ranging between about 2% and about 6% w/w.

21. The method according to claim 15, wherein the propylene-ethylene copolymer is a block copolymer and has a content of ethylene units ranging between about 2% and about 25% w/w.

22. The method according to claim 21, wherein the propylene-ethylene copolymer is a block copolymer and has a content of ethylene units ranging between about 5% and about 12% w/w.

23. The method according to claim 15, wherein the polymer blended with the ethylene-propylene copolymer is a high density polyethylene (HDPE).

24. The method according to claim 23, wherein the content of HDPE in the blend material polymer portion ranges from 23 to 50 phr.

25. The method according to claim 15, wherein the blend material comprises at least one filler, in particular a mineral filler, in an amount ranging from 5 to 50 phc (parts per hundred compound).

26. The method according to claim 25, wherein the filler is a lamellar or fibrolamellar filler.

27. The method according to claim 25, wherein the filler is talc, calcium carbonate or kaolin clay.

28. The method according to claim 15, wherein the blend material comprises also polypropylene homo-polymer in an amount ranging between about 0% and about 25% w/w.

29. The method according to claim 15, wherein the step of thermoforming the sheet of blend material is performed onto a male mold.

Description

[0054] The invention is further described by way of example in the following non-limiting embodiments, with reference to the accompanying drawings in which:

[0055] FIGS. 1 to 9 are diagrams showing different characteristics of materials used according to the invention with respect to prior art materials (as previously discussed);

[0056] FIG. 10 is a simplified, schematic perspective view of a refrigerator appliance according to the invention;

[0057] FIG. 11 is a schematic perspective view of a liner, in particular a cabinet liner, of the refrigerator appliance of FIG. 10;

[0058] FIG. 12 is a schematic representation of the main steps of a method according to the invention for manufacturing the liner of FIG. 11, as well as other plastic liners of refrigerator appliances;

[0059] FIGS. 13 and 14 show in greater details some steps of the method according to the invention, in particular of an extrusion process and a thermoforming process which are part of the method of FIG. 12.

[0060] In FIG. 10, it is indicated as a whole with reference numeral 1 a refrigerator appliance 1 having at least one inner plastic liner 2 defining at least one inner hollow compartment 3.

[0061] The appliance 1 comprises a hollow cabinet 4 internally provided with at least one cell 5, and having a front opening 6 closed by a door 7.

[0062] In the exemplary embodiment of FIG. 10, the appliance 1 is a combined fridge/freezer appliance and comprises a single cabinet 4 housing a refrigerator cell 5a and a freezer cell 5b, closed by respective doors 7.

[0063] With reference also to FIG. 11, the cells 5 are advantageously defined by respective compartments 3 of the liner 2, which in this case is advantageously a monolithic cabinet liner.

[0064] Hereinbelow, reference is made by way of example to a cabinet liner, but it is clear that the following description applies to any other liner, for example a single cell liner or a door liner, of a refrigerator appliance.

[0065] The liner 2 comprises a monolithic hollow body 8 shaped to define one or more (two, in the example of FIG. 11) compartments 3; each compartment 3 is advantageously delimited by lateral walls 9 projecting from a back wall 10 and has a front opening 11 opposite to the bottom wall 10.

[0066] The liner 2, i.e. the body 8, is made of a plastic (polymeric) material, in particular a polypropylene-based blend material.

[0067] The blend material and its components have been previously described.

[0068] As previously described, the liner 2 is made of a blend material comprising a physical mixture of a propylene-ethylene copolymer; a polymer selected in the group consisting of PE and EVA; and optionally at least one filler, for example talc or calcium carbonate or kaolin clay.

[0069] In particular, the polymer blended with the propylene-ethylene copolymer is mixed with the propylene-ethylene copolymer in an amount ranging from 23 to 50 phr (parts per hundred resin).

[0070] Preferably, the polymer blended with the ethylene-propylene copolymer is a high density polyethylene (HDPE).

[0071] As already mentioned, the propylene-ethylene copolymer of the invention can be either a random copolymer or a block copolymer.

[0072] In particular, if the propylene-ethylene copolymer is a random copolymer, then the copolymer advantageously has a content of ethylene units ranging between about 1% and about 8% w/w, more advantageously between about 2% and about 6% w/w; if the propylene-ethylene copolymer is a block copolymer, then the copolymer advantageously has a content of ethylene units ranging between about 5% and about 25% w/w, more advantageously between about 5% and about 12% w/w.

[0073] The material optionally comprises the polypropylene-ethylene copolymer as a main component, and also homo-polypropylene (polypropylene homo-polymer), preferably in an amount ranging between about 0% and about 25% w/w with respect to the PP copolymer and more preferably in an amount ranging between about 0% and about 15% w/w.

[0074] Optionally, the blend material comprises at least one filler, in particular a mineral filler, preferably in an amount ranging from 5 to 50 phc (parts per hundred compound).

[0075] Advantageously, the filler is a lamellar or fibrolamellar filler such as talc or kaolin clay; or a granular filler such as calcium carbonate.

[0076] Optionally, the material comprises additives, like antioxidant chemicals, lubricants, processing agents, and small percentages of other fillers; and/or titanium dioxide.

[0077] The liner 2 is advantageously manufactured by the method described hereinbelow with reference to FIGS. 12 to 14.

[0078] The manufacturing method of the invention advantageously comprises (FIG. 12) the steps of: [0079] preparing the blend material of the liner 2, advantageously by compounding the propylene-ethylene copolymer with the polymer selected in the group of PE and EVA and optionally with the filler(s); [0080] extruding the material into sheets 12, by using an extruder 13; [0081] thermoforming a sheet 12 by means of a male mold 14 to shape the liner 2.

[0082] In a preferred embodiment, the material is prepared directly in the extruding step: all the components, in particular the filler(s) and the PP copolymer (polypropylene-ethylene copolymer), are preferably compounded in the extruder 13. A twin-screw co-rotating extruder may be advantageously used.

[0083] However, some (or even all) components can also be pre-mixed in a mixing step before the extrusion step.

[0084] As shown in FIG. 13, the extruder 13 preferably has a plane dye 15 to produce a thin, flat planar flow.

[0085] Since the extruding process can generate, inside the material, internal stresses that can then be released at high temperature, during the following thermoforming process, it is advantageous to control the extruding process in order to obtain a nearly unoriented sheet; controlling of the extruding process is well known in the art, so it will not be described in more details.

[0086] The extruded material which exit from the dye 15 is preferably pulled through a rolling unit 16, comprising a set of cooling rolls and a calender, where the material is cut into sheets 12, the sheets 12 are cooled and the final thickness of each sheet 12 is determined precisely. The sheets 12 are then preferably stacked.

[0087] Each sheet 12 comprises, and preferably consists of, a single, substantially uniform layer of the polypropylene-based material. In another advantageous embodiment, in order to improve the final product surface appearance, each sheet 12 comprises, and preferably consists of, a main layer, made of the above described polypropylene-based material, and a glossy or semiglossy covering layer, covering a face of the main layer and made of neat polypropylene or a PP compound with glossy appearance. Advantageously, the covering layer is co-extruded or laminated with the main layer.

[0088] Each individual sheet 12 is then supplied to a thermoforming section 17 (FIG. 12), comprising a heating unit 18 and a forming unit 19.

[0089] In the thermoforming section 17, the sheet 12 is first heated, for example by passing through the heating unit 18; and then shaped by thermoforming in the forming unit 19 to form the liner 2.

[0090] With reference also to FIG. 14, in the heating unit 18, the sheet 12 is heated to a predetermined operating temperature (forming temperature) at which the material is softened to a substantially rubbery state.

[0091] Advantageously, the operating temperature is between about 125 C. and about 155 C.

[0092] The sheet 12 is preferably advanced through the heating unit 18, having upper and lower heaters 20. The heaters 20 preferably (ma not necessarily) comprise infrared (IR) heating sources.

[0093] In order to reach a high efficiency, the heaters 20 have preferably an emission wavelength ranging between 2.9 and 4.2 microns (34502380 cm-1), with the highest emission in the range 3.23.8 microns (31252630 cm-1), corresponding to the absorbing range for PP polymers.

[0094] Once the sheet material has reached the predetermined operating (forming) temperature, the material is in a substantially rubbery state and the heated, softened sheet 12 is moved to the forming unit 19, in particular inside a pressure box 21 or bell which houses the male mold 14, having the shape of the liner 2 to form.

[0095] For example, in the preferred embodiments of FIG. 14, the sheet 12 is positioned inside a vacuum chamber 22 of the pressure box 21 and the sheet 12 is advantageously clamped along its peripheral edge 23 in order to hold tightly the sheet 12. The clamped sheet 12 divides the vacuum chamber 22 of the pressure box 21 into two zones delimited by opposite faces of sheet 12: a first (inner) face 24, facing the male mold 14 and intended to define, after thermoforming, an inner surface of the liner 2; and a second (outer) face 25, opposite to the first face 24 and intended to define, after thermoforming, an outer surface of the liner 2.

[0096] Advantageously, in the pressure box 21 the sheet 12 is first subjected to a pre-stretching step, i.e. the sheet 12 is pre-stretched; and then the pre-stretched sheet 12 is vacuum formed onto the male mold 14.

[0097] For pre-stretching the sheet 12, vacuum is applied in the vacuum chamber 22 on the side of the second (outer) face 25 of the sheet 12.

[0098] For multi-cavity liners, such as combined cabinet liners for refrigerator and freezer, a double suction is advantageously performed and the sheet is blown into a so called double bubble (having two adjacent cavities) pre-stretching.

[0099] Once the sheet 12 is suitably pre-stretched, the male mold 14 is moved in the vacuum chamber 22 against the pre-stretched sheet 12, which is draped around an outer shaping surface 26 of the mold 14.

[0100] Advantageously, the mold 14 (in particular the shaping surface 26 thereof) is at a temperature lower than the recrystallization temperature of the PP copolymer. Preferably, the temperature of the mold 14 is about 90-110 C., for example around 100 C.

[0101] Vacuum is then applied on the side of the first face 24 of the sheet 12, for example through suitable inner channels in the mold 14, so as to draw the sheet 12 against the shaping surface 26 of the mold 14.

[0102] The differential pressure against the sheet 12 is amplified if the pressure inside the pressure box 21 is increased: thus, a compressed gas stream (air) can be advantageously injected in the pressure box 21, on the side of the second face 25 of the sheet 12, simultaneously with the vacuum (acting on the first face 24 of the sheet 12); in this way, it is possible to better replicate even small details on the shaping surface 26 of the mold 14. The sheet pre-stretching in combination with the forming pressure give a more uniform material distribution which is favorable to form complex geometries and undercuts.

[0103] Additional draft angles can be provided for very deep parts.

[0104] The sheet 12 adheres to the shaping surface 26 of the male mold 14 and assume the shape thereof.

[0105] The formed sheet 12, still contacting the shaping surface 26 of the mold 14, is then cooled to harden and form the liner 2, for example by blowing air onto the face 25 and/or by circulating a coolant in cooling conduits 27 inside the male mold 14.

[0106] Once sufficiently cooled, the sheet 12, having the shape of the liner 2, is separated from the male mold 14 (for example by blowing air through the inner channels of the male mold 14), and extracted from the pressure box 21.

[0107] The additional energy used in the heating step for softening the material should be removed efficiently in order to keep a pace corresponding to short production cycles. An additional cooling step can be added after extraction of the liner 2 from the thermoforming section 17 and it is very useful for thick thermoformed parts. Preferably, the warm rigid liner 2 is hence supplied to an additional cooling station (not shown) and cooled in order to reach a temperature that doesn't cause any further deformation; then the liner 2 is advantageously moved to a trimming and cutting unit (not shown) for removing edges and other scraps.

[0108] Clearly, further changes may be made to the refrigerator appliance and to the method for manufacturing the liner of the refrigerator appliance described herein without, however, departing from the scope of the present invention as defined by the enclosed Claims.