Coextruded, crosslinked multilayer polyolefin foam structures and methods of making the same

Patent metadata

Field	Value
Publication number	US-2016185025-A1
Application number	US-201414586781-A
Country	US
Kind code	A1
Filing date	Dec 30, 2014
Priority date	Dec 30, 2014
Publication date	Jun 30, 2016
Grant date	—

Abstract

A physically crosslinked, closed cell continuous multilayer foam structure comprising at least one polypropylene/polyethylene coextruded foam layer is obtained. The multilayer foam structure is obtained by coextruding a multilayer structure comprising at least one foam composition layer, irradiating the coextruded structure with ionizing radiation, and continuously foaming the irradiated structure.

First claim

1 . A method of forming a multilayer structure comprising:
coextruding:
a foam layer comprising:
polypropylene or polyethylene; and
a chemical foaming agent; and

a film layer on a side of the foam layer, the film layer comprising polypropylene or polyethylene.

2 . The method of claim 1 , wherein the foam layer comprises polypropylene with a melt flow index of 0.1-25 grams per 10 minutes at 230° C.

3 . The method of claim 1 , wherein the foam layer comprises polyethylene with a melt flow index of 0.1-25 grams per 10 minutes at 190° C.

4 . The method of claim 1 , wherein the foam layer comprises a crosslinking agent.

5 . The method of claim 1 , wherein the chemical foaming agent comprises azodicarbonamide.

6 . The method of claim 1 , wherein the foam layer comprises polypropylene and polyethylene.

7 . A method of forming a multilayer foam structure comprising:
coextruding:
a foam layer comprising:
polypropylene or polyethylene; and
a chemical foaming agent; and

a film layer on a side of the foam layer, the film layer comprising polypropylene or polyethylene;
irradiating the coextruded layers with ionizing radiation; and foaming the irradiated, coextruded layers.

8 . The method of claim 7 , wherein the ionizing radiation is selected from the group consisting of alpha rays, beta rays, gamma rays, or electron beams.

9 . The method of claim 7 , wherein the coextruded structure is irradiated up to 4 separate times.

10 . The method of claim 8 , wherein the ionizing radiation is an electron beam with an acceleration voltage of 200-1500 kV.

11 . The method of claim 10 , wherein an absorbed electron beam dosage is 10-500 kGy.

12 . The method of claim 7 , wherein the ionizing radiation crosslinks the extruded structure to a crosslinking degree of 20-75%.

13 . The method of claim 7 , wherein foaming comprises heating the irradiated structure with molten salt.

14 . The method of claim 7 , wherein the multilayer foam structure has a density of 20-250 kg/m 3 .

15 . The method of claim 7 , wherein the multilayer foam structure has an average closed cell size of 0.05-1.0 mm.

16 . The method of claim 7 , wherein the multilayer foam structure has a thickness of 0.2-50 mm.

17 . The method of claim 7 , wherein a mean surface roughness for the foam layer is less than 80 μm.

18 . The method of claim 7 , wherein the foam layer comprises polypropylene and polyethylene.

19 . A method of forming a multilayer structure comprising:
coextruding:
a first foam layer comprising:
polypropylene or polyethylene; and
a first chemical foaming agent; and

a second foam layer on a side of the first foam layer, the second foam layer comprising:
polypropylene or polyethylene; and
a second chemical foaming agent.

20 . The method of claim 19 , wherein the first and second layers comprise polypropylene with a melt flow index of 0.1-25 grams per 10 minutes at 230° C.

21 . The method of claim 19 , wherein the first and second layers comprise polyethylene with a melt flow index of 0.1-25 grams per 10 minutes at 190° C.

22 . The method of claim 19 , wherein the first and second layers comprise a crosslinking agent.

23 . The method of claim 19 , wherein the first and second chemical foaming agents comprise azodicarbonamide.

24 . The method of claim 19 , wherein the first and second layers comprise polypropylene and polyethylene.

25 . A method of forming a multilayer foam structure comprising:
coextruding:
a first foam layer comprising:
polypropylene or polyethylene; and
a first chemical foaming agent; and

a second foam layer on a side of the first foam layer, the second foam layer comprising:
polypropylene or polyethylene; and
a second chemical foaming agent;

irradiating the coextruded layers with ionizing radiation; and foaming the irradiated, coextruded layers.

26 . The method of claim 25 , wherein the ionizing radiation is selected from the group consisting of alpha rays, beta rays, gamma rays, or electron beams.

27 . The method of claim 25 , wherein the coextruded structure is irradiated up to 4 separate times.

28 . The method of claim 26 , wherein the ionizing radiation is an electron beam with an acceleration voltage of 200-1500 kV.

29 . The method of claim 28 , wherein an absorbed electron beam dosage is 10-500 kGy.

30 . The method of claim 25 , wherein the ionizing radiation crosslinks the extruded structure to a crosslinking degree of 20-75%.

31 . The method of claim 25 , wherein foaming comprises heating the irradiated structure with molten salt.

32 . The method of claim 25 , wherein the multilayer foam structure has a density of 20-250 kg/m 3 .

33 . The method of claim 25 , wherein the multilayer foam structure has an average closed cell size of 0.05-1.0 mm.

34 . The method of claim 25 , wherein the multilayer foam structure has a thickness of 0.2-50 mm.

35 . The method of claim 25 , wherein a mean surface roughness for the first foam layer is less than 80 μm.

36 . The method of claim 25 , wherein the first and second layers comprise polypropylene and polyethylene.

Assignees

• Toray Plastics America Inc

Inventors

• Baldwin Jesse
• Bock Kaitlyn M
• Sieradzki Pawel

Classifications

• B29C48/21

  the layers being joined at their surfaces · CPC title

• B29L2031/712

  Containers; Packaging elements or accessories, Packages (closures therefor B29L2031/56; ink or toner cartridges B29L2031/7678; squeeze tubes B29L2023/20; suitcases B29L2031/7418) · CPC title

• B29C2035/0872

  using ion-radiation, e.g. alpha-rays · CPC title

• B29K2105/04

  cellular or porous · CPC title

• B29C44/505

  extruding the compound through a flat die (in general B29C48/03) · CPC title