Process improvements for preparing catheter balllons

Abstract

A method for forming a balloon for a dilatation catheter involving the steps of extruding a tubing preform of a polyester resin and then blowing the tubing into an oriented balloon, wherein the tubing preform is dried prior to blowing into the balloon form. The addition of this drying step to the balloon forming method has been observed to cause a reduction in the frequency of balloons which are rejected because of visible defects in the balloon wall, while producing the same or higher average wall strengths in the non-defective balloons obtained. Balloon cone and waist thicknesses are reduced by varying the axial tension and blowing pressure at several stages as a mold containing the balloon preform is dipped into a heating medium. Specifically, tubing of a thermoplastic material is placed in a mold and blown by pressurizing and tensioning the tubing and gradually dipping the mold into a heated heat transfer media so as to sequentially blow a first waist, a body and a second waist portion. The tubing is subjected to a relatively lower pressure while the body portion is blown than while the first and second waist portions are blown.

What is claimed is:  
     
         1 . An oriented balloon of thermoplastic material prepared by the method of extruding a hollow tube of the balloon material, and subsequently expanding the tube under heat and pressure in a mold to produce an oriented balloon, wherein the tube is dried prior to said expanding step.  
     
     
         2 . An oriented balloon as in  claim 1  wherein said tube is dried to a moisture content of 0.15% or less.  
     
     
         3 . An oriented balloon as in  claim 2  wherein said tube is dried to a moisture content of 0.10% or less.  
     
     
         4 . An oriented balloon as in  claim 3  wherein said tube is dried to a moisture content of 0.075% or less.  
     
     
         5 . An oriented balloon as in  claim 1  wherein the thermoplastic material is a polyethylene terephthalate homopolymer or copolymer.  
     
     
         6 . In a method of preparing an oriented balloon of thermoplastic material comprising the extruding a hollow tube of the balloon material, and subsequently expanding the tube under heat and pressure in a mold to produce an oriented balloon, the improvement wherein the tube is dried prior to said expanding step.  
     
     
         7 . A method of preparing an oriented balloon as in  claim 6  wherein said tube is dried to a moisture content of 0.15% or less.  
     
     
         8 . A method of preparing an oriented balloon as in  claim 7  wherein said tube is dried to a moisture content of 0.10% or less.  
     
     
         9 . A method of preparing an oriented balloon as in  claim 8  wherein said tube is dried to a moisture content of 0.075% or less.  
     
     
         10 . A method as in  claim 6  wherein the extruded tube is subjected to a stretching step before said expanding step and the tube is dried before said stretching step.  
     
     
         11 . A method of preparing an oriented balloon as in  claim 6  wherein the thermoplastic material is a polyethylene terephthalate homopolymer or copolymer.  
     
     
         12 . A method of forming a balloon for a catheter, the balloon having a first waist portion, a body portion and a second waist portion, the method comprising placing tubing of a thermoplastic material in a mold and blowing the balloon by pressurizing and tensioning the tubing and gradually dipping the mold into a heated heat transfer media so as to sequentially blow the first waist, the body and the second waist portions of the balloon, the tubing being subjected to a relatively lower pressure than while the first and second waist portions are blown.  
     
     
         13 . A method as in  claim 12  wherein the tubing is also subjected to a relatively a lower tension while the body portion is blown than while the first and second waist portions are blown.  
     
     
         14 . A balloon made from the method of  claim 12 .  
     
     
         15 . A catheter comprising an elongated flexible tube having a distal end with a balloon mounted thereon wherein the balloon is a balloon as in  claim 14 .  
     
     
         16 . In a process for forming an elongated balloon having a longitudinal body portion, first and second waist portions of reduced diameter relative to the body portion at opposite ends of the balloon and first and second cone portions connecting corresponding waist portions and respective ends of the longitudinal body portion, the process comprising the steps of placing an extruded and stretched tubular preform in a mold having an internal form corresponding to the desired outer configuration of the balloon, and blowing the balloon by applying axial tension and internal pressure to the preform upon dipping of the mold into a heated heat transfer media, the improvement comprising that the blowing step comprises: 
 pressurizing the stretched tubing to a first pressure in the range of 150-320 psi and applying a first tension in the range of 5-150 g;    dipping the mold to a first depth in the range of from the transition (C) from the first waist to the first cone to the transition (D) from the first cone to the body portion of the balloon;    reducing the pressure to a second pressure between 80 and 170 psi and setting a second tension in the range of the first tension;    dipping the mold to a second depth in the range of from the transition (E) from the body portion to the second cone portion to the transition (F) from the second cone to the second waist;    increasing the pressure to a third pressure higher than the second pressure and between 150 and 320 psi and increasing the tension to a third tension, higher than the first tension, and then,    dipping the mold to a third depth (H) beyond the depth of the second waist.    
     
     
         17 . A method as in  claim 16  wherein the third tension is in the range of 50 to 700 g.  
     
     
         18 . A method as in  claim 16  wherein: 
 the mold is held at the first depth for a predetermined first time interval while maintaining said first tension and first pressure before said pressure reducing step;  
 the mold is held at the second depth while maintaining the second tension and the second pressure for a predetermined second time interval before said pressure increasing step; and,  
 the mold is held at the third depth for a predetermined third time interval while maintaining said third tension and third pressure.  
 
     
     
         19 . The method as in  claim 18  wherein said first time interval is between 1 and 40 seconds, the second time interval is between 1 and 40 seconds and the third time interval is between 10 and 100 seconds.  
     
     
         20 . The method of  claim 18  wherein the difference between said second and third pressures is at least 100 psi.  
     
     
         21 . The method of  claim 18  wherein the thermoplastic material is a polyethylene terephthalate homopolymer or copolymer.  
     
     
         22 . The method of  claim 21  wherein said heat transfer media is heated to a temperature of 90° C. to 100° C.  
     
     
         23 . The method of  claim 16  wherein the extruded tubular preform is dried prior to being stretched.  
     
     
         24 . The method of  claim 23  wherein the extruded tubular preform is dried to a moisture content of less than 0.15%.  
     
     
         25 . The method of  claim 16  wherein the second tension is the same as the first tension.  
     
     
         26 . The method of  claim 16  wherein the second tension is less than the first tension.