Abstract:
A dip coating apparatus and method of dip coating. The apparatus includes a guide surface, a bendable tube, a carriage, and a support assembly. The bendable tube redirectionally engages the guide surface intermediate the first and second longitudinal ends of the tube. The carriage is vertically repositionable and cooperatively engages the tube proximate the first longitudinal end of the tube, whereby vertical repositioning of the carriage effects a change in the vertical distance between the first and second longitudinal ends of the tube. The support assembly releasably suspends an elongate workpiece for introduction of at least a portion of the workpiece into the tube through the first longitudinal end of the coating tube as the carriage is vertically repositioned upwards towards the support assembly.

Description:
BACKGROUND OF THE INVENTION 
     Elongate flexible workpieces, such as guidewires and catheters, are often coated to provide a desired property or characteristic, such as enhanced lubricity, improved biological compatibility or rust resistance. The coating is commonly applied by dipping the workpiece into a coating solution, removing the workpiece from the coating solution, and curing the coating. 
     Typical dip coating equipment employs coating tubes to retain the coating solution and guide the flexible workpieces as they are dipped into the solution. The top of each coating tube is usually equipped with a funnel for facilitating introduction of a workpiece into the coating tube. The coating tubes are commonly straight vertical tubes having a length sufficient to accommodate the longest workpiece to be coated. 
     While generally effective for coating elongate flexible workpieces, such equipment is rather bulky, arduous to use as the operator must repeatedly reach up, often above his/her head, to mount and dismount the workpieces, and requires substantial quantities of often expensive coating solution to “prime” the system, resulting in considerable waste. 
     In an effort to overcome these drawbacks, dip coating equipment has been designed with spiral or helical coating tubes submerged in a common reservoir of coating solution. One such coating apparatus is disclosed in United States Published Patent Application 20060210699. 
     While overcoming many of the drawbacks associated with straight-tube dip coating equipment, it has been discovered that coiled-tube dip coating equipment does not work well with certain types of elongate flexible workpieces as such workpieces are not susceptible to being pushed or threaded along the length of a coiled coating tube, resulting in incomplete coating and/or a kinked workpiece. 
     Accordingly, a continuing need exists for dip coating equipment capable of consistently and efficiently coating a wide variety of elongate flexible workpieces while using minimal coating solution to prime the system and permitting an operator to mount and dismount workpieces at a comfortable height. 
     SUMMARY OF THE INVENTION 
     A first aspect of the invention is a dip coating apparatus having a guide surface, a bendable tube, a carriage, and a support assembly. The bendable tube redirectionally engages the guide surface intermediate the first and second longitudinal ends of the tube. The carriage is vertically repositionable and cooperatively engages the tube proximate the first longitudinal end of the tube, whereby vertical repositioning of the carriage effects a change in the vertical distance between the first and second longitudinal ends of the tube. The support assembly releasably suspends an elongate workpiece for introduction of at least a portion of the workpiece into the tube through the first longitudinal end of the coating tube as the carriage is vertically repositioned upwards towards the support assembly. 
     A second aspect of the invention is a dip coating apparatus having a tube, a carriage and a support assembly. The carriage is vertically repositionable and comprises a basin defining a fluid retention cavity in fluid communication with the tube for supplying fluid to the tube when the carriage is moved upward, and receiving overflow fluid from the tube when the carriage is moved downward. The support assembly releasably suspends an elongate workpiece for introduction of at least a portion of the workpiece into the tube through the first longitudinal end of the coating tube as the carriage is vertically repositioned upwards towards the support assembly. 
     A third aspect of the invention is a method of dip coating an elongate workpiece. The method includes the steps of (i) moving the first longitudinal end of a tube defining a lumen upwards away from the second longitudinal end of the tube and towards a workpiece so as to introduce a length of the workpiece into the lumen and into contact with coating solution retained within the lumen, and (ii) moving the first longitudinal end of the tube downward towards the second longitudinal end of the tube and away from the partially coated workpiece until the partially coated workpiece is removed from the lumen defined by the tube. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front view of one embodiment of the invention. 
         FIG. 2  is a front view of the workpiece support assembly portion of the dip coating apparatus shown in  FIG. 1  depicting a single workpiece. 
         FIG. 3A  is a front view of the coating tube assembly portion of the dip coating apparatus shown in  FIG. 1  in the retracted position and depicting every other tube. 
         FIG. 3B  is a front view of the coating tube assembly portion of the dip coating apparatus shown in  FIG. 1  in the extended position and depicting every other tube. 
         FIG. 4  is a side view of the coating tube assembly portion of the dip coating apparatus shown in  FIG. 1  in the refracted position. 
         FIG. 5  is a top view of the carriage portion of the coating tube assembly shown in  FIG. 1 . 
         FIG. 6  is an enlarged cross-sectional side view of the carriage shown in  FIG. 4  taken along line  6 - 6  with the tubes removed. 
         FIG. 7  is a top view of the take-up spool system shown in  FIG. 1  with the tubes removed. 
         FIG. 8  is a schematic of the fluid flow between the carriage and a separate reservoir. 
         FIG. 9  is an electrical schematic of the dip coating apparatus shown in  FIG. 1 . 
         FIG. 10A  is a front view of an alternative take-up system in the retracted position with a single tube attached. 
         FIG. 10B  is a side view of the alternative take-up system shown in  FIG. 10A  in the extended position. 
         FIG. 11A  is a front view of one tube filled with coating solution from an alternative coating tube assembly in the retracted position. 
         FIG. 11B  is a front view of the alternative coating tube assembly shown in  FIG. 11A  in the extended position. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Nomenclature 
     
         
           10  Dip Coating Apparatus 
           20  Workpiece Support Assembly 
           30  Coating Tube Assembly 
           40  Frame 
           45  Carriage Support Stanchions 
           50  Tube (Collapsible) 
           51  First Longitudinal End of Tube 
           52  Second Longitudinal End of Tube 
           59  Lumen Defined by Tube 
           60  Carriage 
           60   a  Base 
           60   b  Sidewalls 
           61  Coupling 
           62  Funnel 
           65  Drive Mechanism for Carriage 
           65   b  Belt 
           65   m  Motor 
           69  Fluid Retention Cavity 
           70  Take-Up Spools 
           75  Drive Mechanism for Take-Up Spool 
           75   b  Belt 
           75   m  Motor 
           79  Nip Point 
           80  Reservoir 
           90  Pump 
           100  Controller 
           145  Traveler Support Stanchions 
           170  Traveler Board 
           171  Nip Roller 
           172  Pulley 
           179  Nip Point 
           250  Tube (Bendable) 
           251  First Longitudinal End of Tube 
           252  Second Longitudinal End of Tube 
           259  Lumen Defined by Tube 
           260  Carriage 
           262  Funnel 
           270  Guide 
         S Coating Solution 
         W Workpiece 
         x Horizontal Direction 
         y Transverse Direction 
         z Vertical Direction 
         z 1  Upward Direction 
         z 2  Downward Direction
 
Construction
 
       
    
     First Embodiment 
     Referring to  FIG. 1 , the dip coating apparatus  10  includes a frame  40  supporting a workpiece support assembly  20  over a coating tube assembly  30 . The workpiece support assembly  20  includes clips (unnumbered) or other fastening mechanisms for releasably suspending elongate workpieces W in vertical z alignment above tubes  50  or  250  in the coating tube assembly  30 . 
     Typical workpiece support assemblies  20  suitable for use include those shown and described in United States Patent Application Publications 2001/0026834 and 2006/0210699. 
     Referring to  FIGS. 1 ,  3 A and  3 B, one embodiment of the coating tube assembly  30  includes tubes  50  attached at the first longitudinal end  51  to a carriage  60  and attached at the second longitudinal end  52  to a take-up spool  70 . 
     The tubes  50  used in the embodiment depicted in  FIGS. 1 ,  3 A,  3 B,  4 - 7 ,  10 A and  10 B are collapsible, permitting the tubes  50  to be flattened for winding onto the take-up spools  70  and for permitting the sidewalls (unnumbered) of the tube  50  to be pinched together anywhere along the longitudinal length of the tube  50  to seal the lumen  59  defined by the tube  50 . Suitable tubes  50  include those manufactured from plastic film having a thickness of up to about 20 mil. 
     The carriage  60  used in the embodiment depicted in  FIGS. 1 ,  3 A,  3 B and  4 - 7  and the embodiment depicted in  FIGS. 10A and 10B  includes a base  60   a , and sidewalls  60   b  defining a fluid retention cavity  69  capable of holding a supply of coating solution S. The carriage  60  is driven by any suitable drive mechanism  65 , such as a belt  65   b  and electric motor  65   m , to reciprocate along a vertical stanchion  45  as between a retracted position, shown in  FIGS. 3A and 10A , and an expanded position, shown in  FIGS. 3B and 10B . 
     As shown in  FIG. 4 , the first longitudinal end  51  of each tube  50  is secured to the base  60   a  and placed in fluid communication with the fluid retention cavity  69  by a suitable coupling  61 . A guide funnel  62  extends upward z 1  from each coupling  61  for guiding a workpiece W suspended from the workpiece support assembly  20  into the lumen  59  of the corresponding tube  50 . An annual gap (not shown) is preferably provided between each coupling  61  and guide funnel  62  for permitting fluid to flow between the fluid retention cavity  69  and the lumen  59  of the tube  50 . 
     A separate reservoir  80  containing additional coating solution S may be placed in fluid communication with the fluid retention cavity  69  via suitable inlet/outlet orifices (not shown) in the carriage  60  and the reservoir  80 , for supplying additional coating solution S to the fluid retention cavity  69  when necessary and receiving any overflow of coating solution S from the fluid retention cavity  69 . The reservoir  80  may be entirely separate from the coating apparatus  10  connected only by suitable hosing (not shown), may be attached to the frame  40 , or even attached to the carriage  60  for movement along the stanchion  45  in conjunction with the carriage  60 . Fluid flow may be effected solely by gravity, or with the aid of a pump  90 . 
     As shown in  FIGS. 1 ,  3 A,  3 B,  4 ,  7 ,  10 A and  10 B, the second longitudinal end  52  of each tube  50  is secured to a slack control and tensioning system. One suitable slack control and tensioning system, shown in  FIGS. 1 ,  3 A,  3 B,  4  and  7  is a take-up spool  70 . The take-up spools  70  keep the tubes  50  taut by “reeling-in” and “reeling-out” the tubes  50  as the carriage  60  moves between the retracted and expanded positions, and neatly winding any slack in the tubes  50  around the spool  70 . The take-up spools  70  place sufficient tension on the tubes  50  to cause the tubes  50  to collapse as they come into contact with the take-up spools  70 , or alternatively into contact with a nip roller (not shown), so as to create a nip point  79  at which the lumen  59  of the tube  50  is sealed. The take-up spools  70  are driven by any suitable drive mechanism  75 , such as a belt  75   b  and electric motor  75   m.    
     Another suitable slack control and tensioning system, shown in  FIGS. 10A and 10B  is a traveler board  170  driven by any suitable drive mechanism (not shown), such as a belt (not shown) and electric motor (not shown), to reciprocate along a vertical stanchion  145  as between a retracted position, shown in  FIG. 10A , and an expanded position shown in  FIG. 10B . The traveler board  170  keeps the tubes  50  taut by moving a distance along the vertical stanchion  145  equal and opposite to the distance traveled by the carriage  60  along the vertical stanchion  45 . The tubes  50  are guided from the carriage  60  to the travel board  170  by a nip roller  171  positioned immediately underneath each corresponding coupling  62 , and a pulley  172 . As with the take-up spools  70 , the traveler board  170  places sufficient tension on the tubes  50  to cause the tubes  50  to collapse as they come into contact with the nip rollers  171  so as to create a nip point  179  at which the lumen  59  of the tube  50  is sealed. 
     In order to coordinate movement of the carriage  60  and the slack control and tensioning system, the drive mechanisms for each must be coordinated by a suitable controller  100 , such as depicted schematically in  FIG. 9 , to ensure that the length of tubing  50  “reeled-out” from the take-up spools  70  or the distance traveled by the traveler board  170  corresponds to the distance traveled by the carriage  60 . Alternatively, the carriage  60  and slack control and tensioning system can be driven by the same motor. 
     Second Embodiment 
     Referring to  FIGS. 11A and 11B , a second embodiment of the coating tube assembly  30  includes tubes  250  attached at the first longitudinal end  251  to a carriage  260 , sealed at the second longitudinal end  252  and filled with a coating solution S. 
     The tubes  250  used in this embodiment can be bent without collapsing so as to permit the tubes  50  to be curved back upon themselves about a fairly tight turning radius of less than about  20  cm, preferably less than about 10 cm and most preferably less than about 5 cm, without collapsing the lumen  259  of the tube  250 . Suitable tubes  50  include those manufactured from rubber or polyethylene. 
     The tubes  250  are directed by a guide  270  which slidably engages the tubes  250 . The tubes  250  can be guided along any desired path ranging from a 180° bend, a 90° bend, two separate 90° bends, a spiral, a helix, etc. Generally, the path should be selected to minimize the overall size of the entire coating tube assembly  30  while avoiding sharp turns and providing a straight vertical section in contact with a workpiece W being coated. 
     As with the first embodiment, the carriage  260  is driven by any suitable drive mechanism (not shown), such as an electric motor (not shown) and a belt (not shown), to reciprocate along a vertical stanchion (not shown) as between a lower start position, shown in  FIG. 11A , and an upper coating position, shown in  FIG. 11B . 
     A guide funnel  262  engages the first longitudinal end  251  of each tube  250  for guiding a workpiece W suspended from the workpiece support assembly  20  into the lumen  259  of the corresponding tube  250 . 
     Use 
     First Embodiment 
     The first embodiment of the coating apparatus  10  of the present invention provides consistent and efficient coating of a wide variety of elongate flexible workpieces W while using minimal coating solution S to prime the system and permitting an operator (not shown) to mount and dismount workpieces W at a comfortable height. Use involves the steps of (i) positioning the carriage  60  into the retracted position as shown in  FIG. 3A , (ii) filling the fluid retention cavity  69  of the carriage  60  and the lumen  59  of each tube  50  down to the nip point  79  with coating solution S, (iii) clipping workpieces W onto the workpiece support assembly  20 , and (iv) activating the coating apparatus  10  to perform a coating cycle. 
     When the slack control and tensioning system is take-up spools  70 , the coating cycle involves (a) immersing a lowermost length of each workpiece W suspended from the workpiece support assembly  20  into coating solution S contained within the lumen  59  of a vertically z aligned tube  50  by simultaneously driving the carriage  60  upwards z 1  towards the workpieces W while unreeling a corresponding length of tubing  50  from the take-up spool  70 , causing coating solution S to flow from the fluid retention cavity  69  defined by the carriage  60  into the lumen  59  of each tube  50  as the length of the lumen  59  above the nip point  79  increases, followed by (b) withdrawing the now coated lowermost length of each workpiece W from the corresponding tube  50  by driving the carriage  60  downward z 2  away from the workpieces W while winding a corresponding length of tubing  50  onto the take-up spool  70 , causing coating solution S to flow from the lumen  59  of each tube  50  back into the fluid retention cavity  69  defined by the carriage  60  as the length of the lumen  59  above the nip point  79  decreases. 
     When the slack control and tensioning system is a traveler board  170 , the coating cycle involves (a) immersing a lowermost length of each workpiece W suspended from the workpiece support assembly  20  into coating solution S contained within the lumen  59  of a vertically aligned tube  50  by simultaneously driving the carriage  60  upwards z 1  towards the workpieces W while driving the traveler board  170  an equal distance downward z 2 , causing coating solution S to flow from the fluid retention cavity  69  defined by the carriage  60  into the lumen  59  of each tube  50  as the length of the lumen  59  above the nip point  179  increases, followed by (b) withdrawing the now coated lowermost length of each workpiece W from the corresponding tube  50  by driving the carriage  60  downward z 2  away from the workpieces W while driving the traveler board  170  an equal distance upward z 1 , causing coating solution S to flow from the lumen  59  of each tube  50  back into the fluid retention cavity  69  defined by the carriage  60  as the length of the lumen  59  above the nip point  79  decreases. 
     Second Embodiment 
     The second embodiment of the coating apparatus  10  of the present invention also provides consistent and efficient coating of a wide variety of elongate flexible workpieces W while using minimal coating solution S to prime the system and permitting an operator (not shown) to mount and dismount workpieces W at a comfortable height. Use involves the steps of (i) positioning the carriage  260  into the upper coating position as shown in  FIG. 10B  (ii) filling the lumen  259  of each tube  250  with coating solution S, (iii) repositioning the carriage  260  into the lower start position as shown in  FIG. 10A , (iv) clipping workpieces W onto the workpiece support assembly  20 , and (v) activating the coating apparatus  10  to perform a coating cycle. 
     The coating cycle involves (a) immersing a lowermost length of each workpiece W suspended from the workpiece support assembly  20  into coating solution S contained within the lumen  259  of a vertically aligned tube  250  by driving the carriage  260  from the lower start position upwards towards the workpieces W into the upper coating position, followed by (b) withdrawing the now coated lowermost length of each workpiece W from the corresponding tube  250  by driving the carriage  260  downward z 2  from the upper coating position away from the workpieces W towards the lower start position.