Method and apparatus for extrusion coating of fluorescent light tubes

Abstract

A method and apparatus for coating the glass envelope and portions of the end caps of fluorescent light tubes in a continuous and sequential manner with a thermo-plastic material. The coating is applied by a cross head extruder through which the light tubes are sequentially fed. A vacuum applied during the coating process promotes direct and intimate contact between the coating and the light tubes. The end caps may be heated prior to coating to ensure adherence of the coating to the end caps and not to the glass envelope. Post-coating processes include cooling the coating, severing individual light tubes from the chain of sequentially coated light tubes, and readying the coated light tubes for packaging. The method is automatic, with the apparatus being automatically controlled by a control unit.

I claim:  
     
         1 . A method of coating an article having opposing ends, the method comprising the steps: 
 a) loading the article on a coating conveyor system;    b) feeding the article to a coating station, which includes an article coating machine;    c) applying a coating to the article at the coating station; and    d) conveying said article to a stacking and/or packaging station.    
     
     
         2 . A method according to  claim 1  further comprising removing excess coating from the ends of the article.  
     
     
         3 . A method according to  claim 1 , further comprising loading a plurality of articles on the coating conveyor system to form a chain of articles with gaps therebetween.  
     
     
         4 . A method according to  claim 3 , further comprising applying the coating to the chain of articles and gaps.  
     
     
         5 . A method according to  claim 4 , further comprising separating each article from the chain after the coating step.  
     
     
         6 . A method according to  claim 4 , further comprising cooling the chain after the coating step.  
     
     
         7 . A method according to  claim 1 , further comprising applying a vacuum during the coating step.  
     
     
         8 . A method according to  claim 1 , further comprising preheating a portion of said article before the loading step.  
     
     
         9 . A method according to  claim 1  wherein the coating step further comprises extruding a molten thermo-plastic material.  
     
     
         10 . A method for coating fluorescent light tubes having opposing end caps, the method comprising the steps: 
 a) conveying the plurality of light tubes sequentially in longitudinal alignment with one another; and    b) extruding a coating of molten thermo-plastic material about each light tube substantially in direct intimate contact with each light tube.    
     
     
         11 . The method according to  claim 10 , further comprising cooling the coating below the softening temperature of the thermo-plastic material after the coating step.  
     
     
         12 . The method according to  claim 10 , further comprising heating the end caps of the plurality of light tubes before the conveying step.  
     
     
         13 . The method according to  claim 10 , further comprising applying a vacuum during the extruding step.  
     
     
         14 . The method according to  claim 12 , wherein the step of heating the end caps comprises applying an infra-red heater to the end caps.  
     
     
         15 . The method according to  claim 10 , wherein the step of conveying the plurality of light tubes comprises impelling each light tube in advance of the extruding step and impelling each light tube following the cooling step.  
     
     
         16 . The method according to  claim 11 , wherein the cooling step comprises applying a coolant to the light tubes.  
     
     
         17 . The method according to  claim 16 , wherein the cooling step comprises applying a water bath to the light tubes.  
     
     
         18 . The method according to  claim 16 , wherein the cooling step comprises applying air to the light tubes.  
     
     
         19 . The method according to  claim 10 , wherein the extruding step comprising extruding a continuous coating of molten thermo-plastic material thereby connecting sequentially coated light tubes.  
     
     
         20 . The method according to  claim 19  further comprising separating the continuous coating between the end caps of sequential light tubes.  
     
     
         21 . The method according to  claim 20 , wherein the separating step comprises applying a cutting tool to the continuous coating between the end caps of sequential light tubes.  
     
     
         22 . The method according to  claim 20 , further comprising accelerating each light tube to effect separation between sequential light tubes.  
     
     
         23 . The method according to  claim 10 , further comprising trimming excess coating from the end caps of the light tubes and labeling the light tubes.  
     
     
         24 . The method according the  claim 10 , further comprising automatically controlling the conveying and feeding steps via a controller  
     
     
         25 . The method according the  claim 12 , further comprising automatically controlling the heating, conveying, and feeding steps via a controller.  
     
     
         26 . The method according the  claim 11 , further comprising automatically controlling the conveying, feeding, and cooling steps via a controller.  
     
     
         27 . The method according the  claim 20 , further comprises automatically controlling the conveying, feeding, and separating steps via a controller.  
     
     
         28 . The method according the  claim 22 , further comprises automatically controlling the conveying, feeding, separating, and accelerating steps via a controller.  
     
     
         29 . The method according the  claim 23 , further comprises automatically controlling the conveying, feeding, trimming and labeling steps via a controller.  
     
     
         30 . The method according to  claim 10 , wherein the coating step further comprises maintaining a uniform thickness of the molten thermo-plastic material encircling the light tubes to between about 10 mil and about 22 mil.  
     
     
         31 . The method according to  claim 30 , wherein the coating step further comprises maintaining a uniform thickness of the molten thermo-plastic material encircling the light tubes to between about 14 mil and about 20 mil.  
     
     
         32 . The method according to  claim 30 , wherein the coating step further comprises maintaining a uniform thickness of the molten thermo-plastic material encircling the light tubes to between about 16 mil and about 18 mil.  
     
     
         33 . The method according to  claim 10 , wherein the conveying step comprises maintaining the end caps of sequential light tubes at a spaced interval between about 0.5 inch and about 2.5 inches.  
     
     
         34 . The method according to  claim 33 , wherein the conveying step comprises maintaining the end caps of sequential light tubes at a spaced interval between about 1.0 inch and about 2.0 inches.  
     
     
         35 . The method according to  claim 33 , wherein the conveying step comprises maintaining the end caps of sequential light tubes at a spaced interval of about 1.5 inch.  
     
     
         36 . The method according to  claim 10 , further comprising the step of adjusting a rate of travel of the light tubes by regulating the conveying step.  
     
     
         37 . The method according to  claim 36 , wherein the adjusting step comprises maintaining the travel rate at between about 16 ft/min and about 60 ft/min.  
     
     
         38 . A method for coating fluorescent light tubes having opposing end caps, the method comprising the steps: 
 a) heating the end caps of a plurality of light tubes;    b) conveying the plurality of light tubes sequentially in longitudinal alignment with one another;    c) extruding a coating of molten thermo-plastic material about each light tube while applying a vacuum to evacuate air from between each light tube and the coating to promote direct intimate contact of the coating with each light tube;    d) cooling the coating below the softening temperature of the thermo-plastic material; and    e) separating each light tube from the plurality of light tubes.    
     
     
         39 . The method according to  claim 38 , further comprising automatically controlling the heating, conveying, extruding, cooling and separating steps via a controller.  
     
     
         40 . The method according to  claim 38 , further comprising accelerating each light tube after the separating step.  
     
     
         41 . The method according to  claim 38 , further comprising trimming excess coating from each light tube after the separating step.  
     
     
         42 . The method according to  claim 39 , further comprising labeling each light tube.  
     
     
         43 . A machine for coating a plurality of fluorescent light tubes comprising: 
 a) a heating table; and    b) a cross head extruder    wherein the plurality of light tubes is preheated on the heating table before being fed to the cross head extruder.    
     
     
         44 . The machine according to  claim 43 , further comprising a vacuum assembly attached to the cross head extruder to apply a vacuum therein to promote a direct and intimate contact between the plurality of light tubes and the coating of a molten thermo-plastic material extruded by the cross head extruder.  
     
     
         45 . The machine according to  claim 43 , wherein the heating table comprises a plurality of infra-red panels.  
     
     
         46 . The machine according to  claim 43 , further comprising a cooling station disposed adjacent to the cross head extruder for cooling the plurality of light tubes therein.  
     
     
         47 . The machine according to  claim 46 , wherein the cooling station comprises a chilled water bath.  
     
     
         48 . The machine according to  claim 46 , wherein the cooling station comprises an air supply.  
     
     
         49 . The machine according to  claim 46 , further comprising a cutting station for separating the plurality of light tubes, the cutting station disposed adjacent the cooling station.  
     
     
         50 . The machine according to  claim 49 , wherein the cutting station comprises a cutting tool.  
     
     
         51 . The machine according to  claim 50 , wherein the cutting station comprises a heated shearing system.  
     
     
         52 . The machine according to  claim 43 , further comprising an acceleration system to effect separation of the plurality of light tubes.  
     
     
         53 . The machine according to  claim 43 , further comprising a trimming station for removing excess coating from the plurality of light tubes.  
     
     
         54 . The machine according to  claim 43 , further comprising a labeling station for labeling the plurality of light tubes.  
     
     
         55 . The machine according to  claim 43 , further comprising a control unit connected thereto for automatic control thereof.