Method of making coextruded crosslinked polyolefin foam with polyamide cap layers

Patent metadata

Field	Value
Publication number	US-11628648-B2
Application number	US-202016836389-A
Country	US
Kind code	B2
Filing date	Mar 31, 2020
Priority date	Mar 31, 2020
Publication date	Apr 18, 2023
Grant date	Apr 18, 2023

Abstract

Described herein are physically crosslinked, closed cell continuous multilayer foam structures that includes a foam layer comprising polypropylene, polyethylene, or a combination of polypropylene and polyethylene and a polyamide cap layer. The multilayer foam structure can be obtained by coextruding a multilayer structure comprising at least one foam composition layer and at least one cap composition layer, irradiating the coextruded structure with ionizing radiation, and continuously foaming the irradiated structure.

First claim

The invention claimed is:

1. A method of forming a multilayer foam structure comprising:
coextruding:
a first layer comprising:
a first polypropylene, a first polyethylene, or a first combination of polypropylene and polyethylene;
a chemical foaming agent; and
a crosslinking promoter in an amount of 0.5-5 wt. %; and

a second layer on a side of the first layer, the second layer comprising:
60-85 wt. % polyamide; and
10-40 wt. % of a second polypropylene, a second polyethylene, or a second combination of polypropylene and polyethylene;

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

2. The method of claim 1 , wherein the first layer comprises at least 70 wt. % of the first polypropylene, the first polyethylene, or the first combination of polypropylene and polyethylene.

3. The method of claim 1 , wherein a thickness of the second layer is less than 1 mm.

4. The method of claim 1 , wherein the first layer comprises additives in an amount of 1-20 wt. %.

5. The method of claim 1 , wherein the second layer comprises additives in an amount of 1-10 wt. %.

6. The method of claim 1 , wherein the first or second polypropylene has a melt flow index of 0.1-25 grams per 10 minutes at 230° C.

7. The method of claim 1 , wherein the first or second polyethylene has a melt flow index of 0.1-25 grams per 10 minutes at 190° C.

8. The method of claim 1 , wherein an amount of the chemical foaming agent in the first layer is 3-15 wt. %.

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

10. The method of claim 1 , wherein the ionizing radiation is selected from the group consisting of alpha, beta (electron), x-ray, gamma, and neutron.

11. The method of claim 1 , wherein the coextruded structure is irradiated up to four separate times.

12. The method of claim 1 , wherein the ionizing radiation is an electron beam with an acceleration voltage of 200-1500 kV.

13. The method of claim 12 , wherein an absorbed electron beam dosage is 10-500 kGy.

14. The method of claim 1 , wherein the ionizing radiation crosslinks the extruded structure to a crosslinking degree of 20-75%.

15. The method of claim 1 , wherein foaming comprises heating the irradiated structure with molten salt and radiant heaters or a hot air oven.

16. The method of claim 1 , wherein the density of the multilayer foam structure is 20-250 kg/m 3 .

17. The method of claim 1 , wherein the first layer of the multilayer foam structure has an average closed cell size of 0.05-1.0 mm.

18. The method of claim 1 , wherein the multilayer foam structure has a thickness of 0.2-50 mm.

Assignees

• Toray Plastics America Inc

Inventors

• Sieradzki Pawel
• Baldwin Jesse Jude
• Ben-Daat Dan
• Bock Kaitlyn Michelle

Classifications

• B32B2262/0276

  Polyester fibres · CPC title

• B32B2266/08

  Closed cell foam · CPC title

• B32B9/025

  comprising leather · CPC title

• B29C48/21

  the layers being joined at their surfaces · CPC title

• B32B7/12

  using interposed adhesives or interposed materials with bonding properties · CPC title