Dielectric heating of foamable compositions

Abstract

A method for dielectrically heating foamable composition to foam and set the composition is described. In particular, radio frequency (RF) heating is used to heat the foamable composition to provide insulation in the manufacture of an article.

1 . A method for foaming a composition comprising:
 (a) preparing the composition comprising (i) a water-based polymer, (ii) a plurality of expandable microspheres having an initial expandable temperature range of from about 80° C. to about 110° C., and a maximum expandable temperature range of from about 50° C. to about 150° C.; and (iii) optionally, an additive; and   (b) exposing the composition to a dielectric heating;   
       whereby the plurality of expandable microspheres in the composition expands. 
     
     
         2 . The method of  claim 1 , wherein the water-based polymer is selected from the group consisting of emulsion-based polymer selected from the group consisting of starch, vinyl acetate ethylene dispersion, polyvinyl acetate, polyvinyl acetate polyvinyl alcohol, dextrin stabilized polyvinyl acetate, polyvinyl acetate copolymers, vinyl acetate-ethylene copolymers, vinylacrylic, styrene acrylic, acrylic, styrene butyl rubber, polyurethane and mixtures thereof. 
     
     
         3 . The method of  claim 1 , wherein the expandable microspheres have a hydrocarbon core and a polyacrylonitrile shell. 
     
     
         4 . The method of  claim 1 , wherein the additive is selected from the group consisting of plasticizer, tackifiers, humectants, preservatives, e.g., antioxidant, biocide; filler, pigment, dye, stabilizer, rheology modifier, polyvinyl alcohol, and mixtures thereof. 
     
     
         5 . The method of  claim 1 , further comprising defoamer, preservative, surfactant, rheology modifier, filler, pigment, dye, stabilizer, polyvinyl alcohol, humectant, and mixtures thereof. 
     
     
         6 . The method of  claim 1 , wherein the composition further comprises an accelerator that is a multivalent water-soluble salt. 
     
     
         7 . The method of  claim 6 , wherein the accelerator is selected from the group consisting of aluminum nitrate, zirconium acetate, ammonium zirconyl carbonate and mixtures thereof. 
     
     
         8 . The method of  claim 1 , wherein the dielectric heating is radio frequency heating. 
     
     
         9 . The method of  claim 9 , wherein the radio frequency heating is conducted at ranges of less than about 300 MHz. 
     
     
         10 . The method of  claim 10 , wherein the radio frequency heating is conducted at ranges of about 13, 27 or 40 MHz. 
     
     
         11 . A process for forming an article comprising the steps of:
 (a) preparing the composition comprising (i) a water-based polymer, (ii) a plurality of expandable microspheres having an initial expandable temperature range of from about 80° C. to about 110° C., and a maximum expandable temperature range of from about 50° C. to about 150° C.; and (iii) optionally, an additive;   (b) applying the composition onto a first substrate;   (c) applying a second substrate onto the composition, thereby forming the article wherein the composition is sandwiched between the two substrates;   (d) applying a dielectric heating to the article;   
       whereby the plurality of expandable microspheres in the composition expands. 
     
     
         12 . The process of  claim 11 , wherein the water-based polymer is selected from the group consisting of emulsion-based polymer selected from the group consisting of starch, vinyl acetate ethylene dispersion, polyvinyl acetate, polyvinyl acetate polyvinyl alcohol, dextrin stabilized polyvinyl acetate, polyvinyl acetate copolymers, vinyl acetate-ethylene copolymers, vinylacrylic, styrene acrylic, acrylic, styrene butyl rubber, polyurethane and mixtures thereof. 
     
     
         13 . The process of  claim 11 , wherein the first substrate and the second substrate, independently are selected from a cellulosic substrate, wood or plastic having a melting point greater than about 100° C. 
     
     
         14 . The process of  claim 11 , wherein the cellulosic substrate is a fiberboard, corrugated board, solid bleached boards, kraft paper or coated paper. 
     
     
         15 . The process of  claim 11 , wherein the composition is applied in a pattern that is a series of dots, stripes, waves, checkerboards, or a polyhedron shape that have substantially a flat base. 
     
     
         16 . The process of  claim 11 , further comprising the steps of applying an adhesive, in between the first substrate and a second substrate, which is a hot melt adhesive. 
     
     
         17 . The process of  claim 11 , wherein the dielectric heating is radio frequency heating. 
     
     
         18 . The process of  claim 17 , wherein the radio frequency heating is conducted at ranges of less than about 300 MHz. 
     
     
         19 . The process of  claim 18 , wherein the radio frequency heating is conducted at ranges of about 13, 27 or 40 MHz. 
     
     
         20 . The process of  claim 11 , wherein the article is a cup, food container, case, carton, bag, box, lids, envelope, wrap or clamshell.