VOC or Compressed Gas Containment Device Made From a Polyoxymethylene Polymer

Abstract

VOC or compressed gas containment devices, such as polymer fuel tanks, are made from a polyoxymethylene polymer composition. The polymer composition contains a polyoxymethylene polymer that is directly or indirectly chemically attached to an impact modifier. In one embodiment, for instance, a coupling agent bonds the impact modifier to the polyoxymethylene polymer. In order to preserve the permeability of the polymer material when combined with the impact modifier, a polyoxymethylene polymer is used that contains a low level of low molecular weight constituents.

1 .- 20 . (canceled) 
     
     
         21 . A containment device having a hollow volume surrounded by a wall, the wall being made from a polymer composition comprising:
 a) a polyoxymethylene polymer having terminal groups and wherein at least 50% of the terminal groups are hydroxyl groups, the polyoxymethylene polymer having a melt index of from about 5 cm 3 /10 min to about 20 cm 3 /10 min measured at 190° C. and at an applied weight of 2.16 kg;   b) an impact modifier comprising a thermoplastic elastomer, the impact modifier being present in an amount of at least about 5% by weight, the impact modifier being chemically attached to the polyoxymethylene polymer;   c) a coupling agent present in an amount of from about 1.5% by weight to about 10% by weight, the coupling agent comprising an isocyanate; and   wherein the polymer composition has a permeation of less than 5 g mm/m 2  per day at 40° C. according to SAE Test J2665 and has a multi axial impact strength at −40° C. of greater than about 15 ftlb-f according to ASTM Test D3763.   
     
     
         22 . A containment device as defined in  claim 21 , wherein at least about 70% of the terminal groups on the polyoxymethylene polymer are hydroxyl groups and wherein the polyoxymethylene polymer has a melt index of from about 7 cm 3 /10 min to about 12 cm 3 /10 min measured at 190° C. and at an applied weight of 2.16 kg. 
     
     
         23 . A containment device as defined in  claim 21 , wherein the polymer composition has a multi axial impact strength at −40° C. of greater than about 18 ftlb-f according to ASTM Test D3763. 
     
     
         24 . A containment device as defined in  claim 21 , wherein the polymer composition has a multi axial impact strength at −40° C. of greater than about 20 ftlb-f according to ASTM Test D3763. 
     
     
         25 . A containment device as defined in  claim 21 , wherein the containment device has been blow molded. 
     
     
         26 . A containment device as defined in  claim 25 , wherein the containment device comprises a fuel tank that has a volumetric capacity of up to  5  gallons. 
     
     
         27 . A containment device as defined in  claim 25 , wherein the polymer composition has a shear viscosity of from about 8000 Pa-s to about 30,000 Pa-s at a shear rate of 0.1 rad/sec and at a temperature of 190° C. 
     
     
         28 . A containment device as defined in  claim 21 , wherein the wall comprises only a monolayer of the polymer composition. 
     
     
         29 . A containment device as defined in  claim 21 , wherein the coupling agent comprises methylenediphenyl 4,4″-diisocyanate. 
     
     
         30 . A method for blow molding hollow articles comprising:
 combining a polyoxymethylene polymer with an impact modifier to produce a polymer composition, the polyoxymethylene polymer including terminal groups wherein at least about 50% of the terminal groups are hydroxyl groups, the polyoxymethylene polymer having a melt index of from about 5 cm 3 /10 min to about 20 cm 3 /10 min measured at 190° C. and at an applied weight of 2.16 kg, the impact modifier comprising a thermoplastic elastomer, the impact modifier being present in the polymer composition in an amount of at least about 5% by weight;   adding a coupling agent to the polymer composition, the coupling agent comprising an isocyanate that couples the impact modifier to the polyoxymethylene polymer, the coupling agent being added to the polymer composition in an amount sufficient for the polymer composition to have a shear viscosity of at least about 8000 Pa-s at a shear rate of 0.1 rad/sec and at a temperature of 190° C., and wherein greater amounts of the coupling agent are added to the polymer composition as the melt index of the polyoxymethylene polymer increases; and   blow molding a hollow article from the polymer composition.   
     
     
         31 . A method as defined in  claim 30 , wherein at least about 70% of the terminal groups on the polyoxymethylene polymer are hydroxyl groups and wherein the polyoxymethylene polymer has a melt index of from about 7 cm 3 /10 min to about 12 cm 3 /10 min measured at 190° C. and at an applied weight of 2.16 kg. 
     
     
         32 . A method as defined in  claim 30 , wherein the polyoxymethylene polymer has a melt index of from about 10 cm 3 /10 min to about 11 cm 3 /10 min measured at 190° C. and at an applied weight of 216 kg. 
     
     
         33 . A method as defined in  claim 30 , wherein the coupling agent is added to the polymer composition in an amount from about 1.5% to about 10% by weight. 
     
     
         34 . A method as defined in  claim 30 , wherein the coupling agent is added to the polymer composition in an amount from about 1.5% to about 5% by weight. 
     
     
         35 . A method as defined in  claim 30 , wherein the polymer composition has a multi-axial impact strength at −40° C. of greater than about 15 ftlb-f according to ASTM Test D3763. 
     
     
         36 . A method as defined in  claim 30 , wherein the polymer composition has a multi-axial impact strength at −40° C. of greater than about 18 ftlb-f according to ASTM Test D3763. 
     
     
         37 . A method as defined in  claim 30 , wherein the coupling agent is added to the polymer composition such that there is from about 0.5 to about 4 mol of the coupling agent per mol of hydroxyl groups on the polyoxymethylene polymer.