Shape Memory Products and Method For Making Them

Abstract

A method for producing a heat-shrinkable product is provided. First, a polymer composition containing a polymer, a crosslinking agent and a micro-encapsulated foaming agent uniformly dispensed therein is melt mixed. The foaming agent has a peak activation temperature which is higher than a temperature of the melt mixing. Next, the polymer composition is injection molded into a molded product. This carried out at the peak activation temperature to activate the foaming agent. Then, the molded product is crosslinked within the mold.

What is claimed is: 
     
         1 . A method for producing a shape memory product comprising the steps of:
 (i) melt mixing a polymer composition containing a polymer, a crosslinking agent and a micro-encapsulated foaming agent uniformly dispensed therein, the micro-encapsulated foaming agent having a peak activation temperature which is higher than a temperature of the melt mixing,   (ii) injection molding the polymer composition into a molded product, the injection molding carried out at the peak activation temperature to activate the micro-encapsulated foaming agent; and   (iii) crosslinking the molded product within a mold.   
     
     
         2 . The method according to  claim 1 , wherein the micro-encapsulated foaming agent is a blowing agent. 
     
     
         3 . The method according to  claim 2 , wherein the polymer composition includes a polyolefin. 
     
     
         4 . The method according to  claim 3 , wherein the polymer composition further includes polyethylene. 
     
     
         5 . The method according to  claim 4 , wherein the polymer composition further includes ethylene-vinyl acetate copolymer (EVA). 
     
     
         6 . The method according to  claim 1 , wherein the polymer composition includes 40 to 60% by weight of polyethylene and 10 to 20% by weight of EVA. 
     
     
         7 . The method according to  claim 1 , wherein injection molding is carried out at a temperature in a range of 120 to 160° C. 
     
     
         8 . The method according to  claim 7 , wherein the mold is heated to a temperature in a range of 170 to 210° C. 
     
     
         9 . The method according to  claim 8 , wherein the injection molding is carried out at a pressure in a range of 10 to 20 MPa. 
     
     
         10 . The method according to  claim 1 , wherein the crosslinking agent includes an organic peroxide compound. 
     
     
         11 . The method according to  claim 10 , wherein the polymer composition includes a radiation crosslinking promoter. 
     
     
         12 . The method according to  claim 11 , wherein molded product is crosslinked using radiation. 
     
     
         13 . The method according to  claim 12 , wherein the polymer composition further includes a flame retardant. 
     
     
         14 . A shape memory product comprising:
 a base polymer in an amount of 50-90 wt %;   a micro encapsulated foaming agent in an amount of 0.5 to 3 wt %;   an organic peroxide crosslinking agent in an amount of 0.1 to 1 wt %; and   a flame retardant in an amount of 15 to 30 wt %.   
     
     
         15 . The shape memory product according to  claim 14 , wherein the base polymer includes polyethylene in an amount of 30 to 70wt %. 
     
     
         16 . The shape memory product according to  claim 15 , wherein the base polymer includes polyethylene in an amount of 40 to 60wt %. 
     
     
         17 . The shape memory product according to  claim 15 , wherein the base polymer further includes ethylene/vinyl acetate copolymer (EVA) in an amount of 10 to 25wt %. 
     
     
         18 . The shape memory product according to  claim 17 , wherein the base polymer further includes ethylene/vinyl acetate copolymer (EVA) in an amount of 10 to 20wt %. 
     
     
         19 . The shape memory product according to  claim 14 , wherein the micro encapsulated foaming agent is a blowing agent. 
     
     
         20 . The shape memory product according to  claim 19 , wherein the blowing agent includes a plurality of polymeric shells encapsulating a heat-activated chemical compound. 
     
     
         21 . The shape memory product according to  claim 20 , wherein the plurality of polymeric shells have an unexpanded diameter between 6 μm to 40 μm, and an expanded diameter between 20 μm to 150 μm. 
     
     
         22 . The shape memory product according to  claim 14 , wherein the organic peroxide crosslinking agent is 2,5-bis (t-butylperoxy)-2,5-dimethylhexane. 
     
     
         23 . The shape memory product according to  claim 14 , further comprising a radiation crosslinking promoter in an amount of 0.2 to 1.5 wt %. 
     
     
         24 . The shape memory product according to  claim 14 , wherein the flame retardant is selected from a group consisting of polybrominated aromatics, alumina trihydrate, and phosphorus-based retardants. 
     
     
         25 . A method for producing a heat-shrinkable product comprising the steps of:
 (i) melt mixing a polymer composition having:
 a base polymer in an amount of 50-90 wt %; 
 a micro encapsulated foaming agent in an amount of 0.5 to 3 wt %; and 
   an organic peroxide crosslinking agent in an amount of 0.1 to 1 wt %;   (ii) injection molding the polymer composition into a molded product, the injection molding carried out at a peak activation temperature to activate the micro-encapsulated foaming agent; and   (iii) crosslinking the molded product.   
     
     
         26 . The method according to  claim 25 , wherein the base polymer includes polyethylene in an amount of 40 to 60wt %. 
     
     
         27 . The method according to  claim 26 , wherein the base polymer further includes ethylene/vinyl acetate copolymer (EVA) in an amount 10 to 20wt %. 
     
     
         28 . The method according to  claim 27 , wherein the blowing agent includes a plurality of polymeric shells encapsulating a heat-activated chemical compound. 
     
     
         29 . The method according to  claim 28 , wherein the plurality of polymeric shells have an unexpanded diameter between 6 μm to 40 and an expanded diameter between 20 μm to 150 μm. 
     
     
         30 . The method according to  claim 29 , wherein the polymer composition further includes a crosslinking agent in an amount of 0.2 to 1.5 wt %. 
     
     
         31 . The method according to  claim 30 , wherein the polymer composition further includes a flame retardant in an amount of 15 to 30 wt %. 
     
     
         32 . The method according to  claim 24 , wherein injection molding is carried out at a temperature in a range from 120 to 160° C. 
     
     
         33 . The method according to  claim 32 , wherein the molded product is heated in a mold at a temperature in a range from 170 to 210° C. 
     
     
         34 . The method according to  claim 33 , wherein the injection molding is carried out at a pressure in a range from 10 to 20 MPa.