Spraying device with improved tip and method of manufacture

Abstract

The invention provides a precision spraying device having an improved atomizing end for reproducibly forming droplets from small amounts of liquid with improved operational stability and spray pattern quality as well as a method of manufacturing. The invention further provides a method for reproducibly coating substrates using the spraying device of the present invention.

1 . A device to disintegrate a liquid into fine droplets using an atomizing gas comprising
 a body having at least a liquid conduit extending from a liquid inlet to a liquid orifice   and a tip defining a space for receiving the atomizing gas and having an inner tapered section extending to an orifice   
     wherein
 the tip is essentially coaxial with the body and an annular gap through which the atomizing gas is expelled is formed between the body and the orifice of the tip 
 and at least the orifice of the tip and a portion of the inner tapered section of the tip are machined to minimize the error of concentricity therebetween so that during operation a gas stream with a substantially uniform gas velocity distribution about the perimeter of the annular gap is formed. 
 
   
   
       2 . The device according to  claim 1 , wherein the orifice of the tip has a diameter of less than 1.2 mm and the error of concentricity between the orifice and said portion of the inner tapered section is less than 20 microns. 
   
   
       3 . The device according to  claim 1 , wherein at least said portion of the inner section of the tip is machined in the same setup as the orifice of the tip. 
   
   
       4 . The device according to  claim 1 , wherein the tip is machined by a turning operation. 
   
   
       5 . The device according to  claim 1 , wherein the tip further comprises a centering section to align the tip in relation to the body and the error of concentricity between the orifice of the tip and the centering section is smaller than 20 microns. 
   
   
       6 . The device according to  claim 5 , wherein the centering section is machined in the same setup as the orifice of the tip. 
   
   
       7 . The device according to  claim 1 , wherein the liquid conduit is free of constrictions. 
   
   
       8 . The device according to  claim 7 , wherein the liquid conduit is comprised of a capillary. 
   
   
       9 . The device according to  claim 1 , further comprising a second liquid inlet extending to a second liquid orifice surrounding and being essentially coaxial with the first liquid orifice to separately supply a second liquid, wherein the second liquid is disintegrated by the atomizing gas upon exiting the second liquid orifice and mixed with the first liquid. 
   
   
       10 . The device according to  claim 1 , further comprising electrostatic means to atomize the liquid. 
   
   
       11 . (canceled) 
   
   
       12 . (canceled) 
   
   
       13 . (canceled) 
   
   
       14 . (canceled) 
   
   
       15 . Method to apply a coating to a medical device using a spraying device having a body with a liquid conduit extending from a liquid inlet to a liquid orifice and a tip being essentially coaxial with the body and defining a space for receiving an atomizing gas, the tip having an inner section extending to an orifice with a diameter of less than 1.2 mm for discharging the atomizing gas through an annular gap formed between the body and the orifice of the tip, comprising the following steps:
 feeding a liquid into the liquid conduit and feeding a gas into the gas conduit and forming a gas stream having a substantially uniform gas velocity distribution about the perimeter of the annular gap;   disintegrating the liquid into fine droplets through the momentum of the gas emerging from the annular gap;   directing the droplets within the gas stream to the medical device so that the droplet trajectories are uniformly distributed around the extended longitudinal axis of the spraying device; and   forming a coating on the medical device.   
   
   
       16 . The method of  claim 15 , wherein the error of concentricity between the inner section of the tip and the orifice of the tip is less than 20 microns. 
   
   
       17 . The method of  claim 15 , wherein the volume median diameter of the generated droplets is less than 10 microns. 
   
   
       18 . The method of  claim 15 , wherein the liquid flow is directed at a substantially constant velocity from the liquid inlet to the liquid orifice. 
   
   
       19 . The method of  claim 15 , wherein the droplet size variation is less than 1%. 
   
   
       20 . (canceled) 
   
   
       21 . The method of  claim 15 , wherein the liquid comprises a polymeric component. 
   
   
       22 . The method of  claim 15 , further comprising the step of feeding a second liquid through an additional orifice positioned between the first liquid orifice and the orifice for the atomizing gas and disintegrating and mixing the second liquid with the first liquid through the momentum of the atomizing gas emerging from the annular gap. 
   
   
       23 . Method to form a reproducible coating on multiple stents using multiple spraying devices comprising the following steps:
 providing multiple stents;   providing multiple spraying devices having a body with at least a liquid orifice and a tip being essentially coaxial with the body and defining a space for receiving an atomizing gas, the tip having an inner section extending to an orifice for discharging the atomizing gas through an annular gap formed between the body and the orifice of the tip;   feeding a liquid into each spraying device and feeding a gas into each spraying device and forming a gas stream with a substantially uniform gas velocity distribution about the perimeter of the annular gap;   disintegrating the liquid into fine droplets through the momentum of the gas emerging from the annular gap so that the variation of the volume median diameter of the sprays produced by the separate spraying devices is less than 2%;   directing the droplets within the gas streams to the medical devices so that the droplet trajectories are uniformly distributed around the extended longitudinal axis of the spraying device; and   forming a coating on the stents.   
   
   
       24 . The method of  claim 23 , wherein the orifice of the tip has a diameter of less than 1.2 mm and the error of concentricity between the inner section of the tip and the orifice of the tip is less than 20 microns. 
   
   
       25 . The method of  claim 23 , wherein the error of concentricity between the inner section and the orifice of the tip is less than 1.7% of the orifice diameter of the tip.