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 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 expansion temperature Texp, and a maximum expandable temperature of Tmax; and (iii) optionally, an additive; and   (b) applying the composition onto a first substrate;   (c) applying a second substrate onto the composition, whereby the composition is sandwiched between the two substrates; and   (d) coalescing the composition.   
     
     
         2 . The process 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 process of  claim 1 , wherein the plurality of expandable microspheres have a hydrocarbon core and a polyacrylonitrile shell. 
     
     
         4 . The process of  claim 1 , further comprising defoamer, preservative, surfactant, rheology modifier, filler, pigment, dye, stabilizer, polyvinyl alcohol, humectant, and mixtures thererof. 
     
     
         5 . The process of  claim 1 , wherein the cellulosic substrate is a fiberboard, corrugated board, solid bleached boards, kraft paper or coated paper. 
     
     
         6 . The process of  claim 1 , wherein the composition comprises from about 0.1 to about 70 wt % by weight of the composition of the plurality of expandable microspheres. 
     
     
         7 . The process of  claim 6 , wherein the composition comprises from about 0.5 to about 60 wt % by weight of the composition of the plurality of expandable microspheres. 
     
     
         8 . The process of  claim 7 , wherein the composition comprises from about 0.5 to about 30 wt % by weight of the composition of the plurality of expandable microspheres. 
     
     
         9 . The process of  claim 6 , wherein the composition comprises from about 30 to about 70 wt % by weight of the composition of the plurality of expandable microspheres. 
     
     
         10 . The process of  claim 1 , wherein the plurality of expandable microspheres have the expansion temperature Texp of from about 80 to about 105° C., and the maximum expandable temperature of Tmax of about 90 to about 140° C. 
     
     
         11 . The process of  claim 1 , wherein the composition further comprises a second plurality of expandable microspheres having a second expansion temperature Texp2, and a second maximum expandable temperature of Tmax2. 
     
     
         12 . The process of  claim 1 , wherein the composition further comprises pre-expanded microspheres. 
     
     
         13 . The process of  claim 1 , wherein the additive is a coalescence agent. 
     
     
         14 . The process of  claim 1 , 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. 
     
     
         15 . The process of  claim 1 , further comprising step (e) after step (d):
 (e) applying a dielectric heating to the composition,   
       whereby the plurality of expandable microspheres in the composition expands. 
     
     
         16 . The process of  claim 15 , wherein the dielectric heating is radio frequency heating. 
     
     
         17 . The process of  claim 16 , wherein the radio frequency heating is conducted at ranges of less than about 300 MHz. 
     
     
         18 . The process of  claim 1 , optionally further comprising the steps of applying an adhesive in between the first substrate and a second substrate. 
     
     
         19 . The process of  claim 18 , wherein the adhesive is a hot melt adhesive, pressure sensitive adhesive, waterborne adhesive or solvent-based adhesive. 
     
     
         20 . The process of  claim 15 , wherein the article is a cup, food container, case, carton, bag, box, lids, envelope, wrap or clamshell.