Method of Making a Polymer Foam
In general, the present invention is directed to a continuous method of making a polymer foam by using a polymer having a first monomeric component and a second monomeric component. The method employs a tandem type extruder having a first extruder and a second extruder. The method disclosed herein can provide a foam having a desired cell size, cell density, porosity, foam density, and/or thermal conductivity, etc. In turn, the polymer foams produced according to the present method can have numerous applications, such as thermal insulation applications for appliances including ovens, freezers, refrigerators, etc.
1 . A continuous method for making a polymer foam, the method comprising
extruding a polymer in an extruder system comprising a tandem-type extruder comprising a first extruder and a second extruder,
contacting the polymer with a blowing agent after melting the polymer,
wherein the polymer comprises a first monomeric component characterized by a glass transition temperature of 80° C. or greater and a second monomeric component characterized by a glass transition temperature of −45° C. or less, and
wherein the blowing agent is provided in an amount of less than 15 wt. % based on the weight of the polymer.
2 . The method according to claim 1 , wherein the first monomeric component is characterized by a glass transition temperature of 90° C. or greater.
3 . The method according to claim 1 , wherein the second monomeric component is characterized by a glass transition temperature of −80° C. or less.
4 . The method according to claim 1 , wherein the first monomeric component is characterized by a glass transition temperature of from 80° C. to 250° C. and the second monomeric component is characterized by a glass transition temperature of from −45° C. to −150° C.
5 . The method according to claim 1 , wherein the first monomeric component is characterized by a glass transition temperature and the second monomeric component is characterized by a glass transition temperature, wherein the difference in the glass transition temperature is from about 125° C. to about 350° C.
6 . The method according to claim 1 , wherein the first monomeric component comprises styrene and acrylonitrile.
7 . The method according to claim 1 , wherein the second monomeric component comprises butadiene.
8 . The method according to claim 1 , wherein the first monomeric component comprises a carbonate, a methyl methacrylate, or an etherimide.
9 . The method according to claim 1 , wherein the second monomeric component comprises a siloxane or a butyl acrylate.
10 . The method according to claim 1 , wherein the polymer comprises an acrylonitrile/butadiene/styrene copolymer.
11 . The method according to claim 1 , wherein the polymer comprises a poly(methyl methacrylate)/poly(butyl acrylate) copolymer, a polycarbonate/polysiloxane copolymer, or a polyetherimide/polysiloxane copolymer.
12 . The method according to claim 1 , wherein the blowing agent comprises carbon dioxide.
13 . The method according to claim 12 , wherein the carbon dioxide is supercritical carbon dioxide.
14 . The method according to claim 1 , wherein the blowing agent is provided in an amount of 12 wt. % or less based on the weight of the polymer.
15 . The method according to claim 1 , wherein the pressure in the second extruder is increased by at least a factor of 2.
16 . The method according to claim 1 , wherein the blowing agent is injected to the first extruder at an injection point and the pressure in the second extruder is greater than the pressure at the injection point.
17 . A polymer foam made according to the method of claim 1 , wherein the foam has a porosity of 75% or higher.
18 . A polymer foam made according to the method of claim 1 , wherein the foam comprises cells having an average cell size of 10 microns or less.
19 . A polymer foam made according to the method of claim 1 , wherein the foam has a cell density of 10 9 cells/cm 3 or more.