Syntactic foam plugs

Abstract

The present invention provides an improved syntactic foam plug for plug assist thermoforming wherein such plug is composed of a thermoplastic material having a relatively high melting and/or glass transition temperature. Accordingly, the subject invention encompasses diminishing or removing the undesirable characteristics of thermoset syntactic plugs while increasing the ease by which these articles may be constructed for a given use, by forming such plugs from syntactic foams containing thermoplastics.

1 . A plug for thermoforming operations composed of a syntactic foam comprising:
 a thermoplastic resin having a melting point and/or Tg at least 5° C. higher than the design operating temperature of said thermoforming operation, and   a hollow filler having a lower density than said resin.   
   
   
       2 . The plug according to  claim 1 , wherein said thermoplastic resin has a melting point and/or Tg of greater than 180° C. 
   
   
       3 . The plug according to  claim 1 , wherein said thermoplastic resin has a melting point/and or Tg of greater than 200° C. 
   
   
       4 . The plug according to  claim 1 , wherein said thermoplastic resin comprises a polyamide, polycarbonate, polyurethane, polyester, polyacrylate, and/or copolymers and/or mixtures thereof. 
   
   
       5 . The plug according to  claim 4 , wherein said thermoplastic resin comprises a polyamide formed from a lactam monomer having at least 6 carbon atoms. 
   
   
       6 . The plug according to  claim 5 , wherein said thermoplastic resin comprises nylon 6, nylon 6.6 or mixtures thereof. 
   
   
       7 . The plug according to  claim 1 , wherein said syntactic foam comprise less than 70 vol. % of said hollow filler. 
   
   
       8 . The plug according to  claim 1 , wherein said hollow filler includes glass microspheres, hollow polymeric microspheres, hollow ceramic microspheres, microspheres of urea-formaldehyde resin and/or phenol-formaldehyde resin. 
   
   
       9 . A process for forming the plug according to  claim 1 , wherein said plug is formed in-situ from a mixture comprising said filler and a monomer which is polymerized in a mold that at least approximates the shape of the desired plug. 
   
   
       10 . The process according to  claim 9 , wherein a lactam monomer is polymerized to polyamide. 
   
   
       11 . The process according to  claim 10 , wherein said in-situ polymerization to polyamide is assisted with an alkali earth metal and/or alkaline earth metal catalyst. 
   
   
       12 . The process according to  claim 11 , wherein said in-situ polymerization is assisted by an organic isocyanate, ketene, acid chloride, acid anhydride, or N-substituted imide polymerization promoter. 
   
   
       13 . A process of thermoforming at least one article using the plug according to  claims 1  or the plug prepared by the process of  claims 9 . 
   
   
       14 . An article formed by the process of  claim 13 .