Thermoplastic injection molding method for capping a tubular filtration medium

Abstract

A method for over-molding a tubular filter element 16 , at least at one end 16 b thereof, with a thermoplastic end cap 12 . The over-molding method can be used to manufacture easily and cost-effectively a filter cartridge, of good durability, from an unprecedented range of polymeric materials and components. The thermoplastic over-molding method does not require pre-lamination of said end 16 b , and can be performed at temperatures and pressures that do not result in undesirable morphological changes in the tubular filtration medium. Exemplary filter cartridges made through the over-molding method comprise a tubular filtration medium interposed between thermoplastic end caps, the thermoplastic material of the end caps infiltrating the tubular filtration medium, thereby creating mechanical interlock zones at the ends thereof.

What is claimed: 
     
         1 . A filter cartridge comprising:
 a pair of thermoplastic end caps; and   a porous tubular filtration medium having an inner surface, an outer surface, a first end having a first outer peripheral leading edge and a second end having a second leading outer edge positioned between the thermoplastic end caps,   wherein the thermoplastic material of the end caps infiltrates the first and second outer peripheral leading edges of the porous tubular filtration medium to form first and second interlock zones, such that the first and second ends of the filtration medium are fixed respectively thereto the pair of thermoplastic end caps at the first and second interlock zones without the use of an edge film or edge seal located between the filtration medium and the pair of end caps,   wherein the materials used for the thermoplastic end cap and the tubular filtration medium are dissimilar.   
     
     
         2 . The filter cartridge of  claim 1 , wherein the filtration medium comprises a polymeric pleated membrane. 
     
     
         3 . The filter cartridge of  claim 2 , wherein the thermoplastic end caps have a thermal melt temperature substantially below the thermal melt temperature of the polymeric material pleated membrane. 
     
     
         4 . The filter cartridge of  claim 1 , further comprising an inner durable element overlapping the inner surface of the filtration medium, and an outer durable element overlapping the outer surface of the filtration medium, the inner and outer durable element configured for the passage of fluid there through. 
     
     
         5 . The filter cartridge of  claim 1 , wherein the filtration medium includes a single unitary filter medium. 
     
     
         6 . The filter cartridge of  claim 1 , wherein the filtration medium includes a unitary composite filter medium comprising more than one layer. 
     
     
         7 . The filter cartridge of  claim 1 , wherein the filtration medium is made from a material selected from the group consisting of nitrocellulose, cellulose acetate, polycarbonate, polypropylene, PES, PVDF, and polysulfone. 
     
     
         8 . The filter cartridge of  claim 1 , wherein the filtration medium is a membrane. 
     
     
         9 . The filter cartridge of  claim 1 , wherein the filtration medium is selected from the group consisting of woven fibers, non-woven fibers, natural fibers, synthetic fibers, and metallic fibers. 
     
     
         10 . A filter cartridge comprising:
 a pair of thermoplastic end caps; and   a porous tubular filtration medium having a first end having a first outer peripheral leading edge and a second end having a second leading outer edge positioned between the thermoplastic end caps,   wherein the thermoplastic material of the end caps infiltrates the first and second outer peripheral leading edges of the porous tubular filtration medium to form first and second interlock zones, such that the first and second ends of the filtration medium are fixed respectively thereto the pair of thermoplastic end caps at the first and second interlock zones without the use of an edge film or edge seal located between the filtration medium and the pair of end caps,   wherein the materials used for the thermoplastic end cap and the tubular filtration medium are dissimilar,   wherein the filter cartridge is manufactured by,
 (a) providing a die mold having an inner mold cavity with an inner mold surface, a supply duct connected to the inner mold cavity, the inner mold cavity having a region thereof shaped to substantially conform to the outer contours of the thermoplastic end cap; 
 (b) inserting the tubular filtration medium into the inner mold cavity, prior to injecting the molten thermoplastic material, such that the first leading edge of the first end does not contact the inner mold surface but is within the region of the mold conforming to the outer contours of the thermoplastic end cap; 
 (c) injecting a sufficient quantity of molten thermoplastic material through the supply duct into the inner mold cavity to fill the region of the mold conforming to the outer contours of the thermoplastic end cap, the molten thermoplastic material coming into direct contact with the first outer peripheral leading edge of the first end of the tubular filtration medium, infiltrating and flowing into and around the first end of the tubular filtration medium; 
 (d) forming the thermoplastic end cap and a first interlock zone in the first end of the tubular filtration medium to mechanically secure together the thermoplastic end cap to the first end of the tubular filtration medium; and 
 (e) removing the end capped tubular filtration medium from the die mold after the molten thermoplastic material has sufficiently cured; 
   wherein the thermoplastic material has a thermal melt temperature substantially below the thermal melt temperature of the tubular filtration medium.