Method for powder coating the surface of heat sensitive objects

Method for powder coating the surfaces of heat sensitive objects having properties to absorb humidity with polymeric powder having a melting temperature less than about 100° C., said polymeric powder including a polymer curable under the influence of ultraviolet radiation, said method comprising:

• conditioning said objects by storing said objects in an atmosphere having a predetermined relative humidity;
• pre-heating said objects by infrared radiation until the temperature measured at the surface of said objects has reached about 40° C. to 85° C. while retaining moisture thereon;
• spraying said objects in an atmosphere having an air temperature of about 10° C. to 40° C. with said polymeric powder which is charged with static electricity, wherein said objects are grounded so that said polymeric powder will be retained at the surface of said objects by means of electrostatic forces, the grounded objects having electrical conducting properties resulting from said moisture produced on the surface of said objects during the pre-heating;
• heating said polymeric powder coated objects to a temperature at which said polymeric powder melts and sticks to said objects, said heating performed by simultaneously using infrared radiation and blowing air heated to a pre-determined temperature to maintain the surface temperature of said polymeric powder coated objects at no greater than about 100° C.;
• and
• curing said polymeric powder by exposing said objects coated with the melted polymeric powder to UV radiation while simultaneously blowing air against the surface of said objects exposed to said radiation, said air having a temperature of about 5° C. to 40° C., whereby the temperature of the polymeric powder during said curing is maintained at a temperature not substantially exceeding the melting temperature of said polymeric powder.

Method for powder coating the surfaces of objects with polymeric powder having a melting temperature less than about 100° C., said polymeric powder including a polymer curable under the influence of electromagnetic radiation, said method comprising:

• preparing said objects to be coated for retaining said polymeric powder;
• spraying said objects with said polymeric powder having an electrostatic charge in a first conditioned atmosphere;
• melting said polymer powder retained on said objects by heating said polymer powder by exposure to infrared radiation and by simultaneously directing heated air towards said objects, said heated air and said infrared radiation having a temperature adapted to maintain the temperature of said objects less than about 100° C.;
• irradiating said objects with electromagnetic radiation for initiating the curing of the heated polymeric powder and simultaneous cooling said objects by flowing conditioned air over said objects, whereby said objects are maintained at a temperature below the melting temperature of said polymer powder thereby compensating for the heating of said objects from said electromagnetic radiation.

Method for powder coating the surfaces of heat sensitive objects having the property to absorb humidity with polymeric powder having a melting temperature less than about 100° C., said polymeric powder including a polymer curable under the influence of electromagnetic radiation, said method comprising:

• storing said objects having a surface in an atmosphere having a predetermined relative humidity, whereby said objects absorb moisture from said atmosphere;
• pre-heating said objects by infrared radiation until the temperature at the surface of said objects has reached about 40° C. to 85° C. while retaining moisture thereon;
• grounding said objects so that said polymeric powder will be retained at the surface of said objects by means of electrostatic forces, the grounded objects having electrical conducting properties resulting from the moisture produced on the surface of said objects during said pre-heating;
• spraying said grounded objects in an atmosphere having an air temperature of about 10° C. to 40° C. with said polymeric powder having an electrostatic charge;
• heating said polymeric powder coated objects to a temperature at which said polymeric powder melts by simultaneously using infrared radiation and blowing air having a pre-determined temperature to maintain the temperature of said objects at less than about 100° C.;
• and
• curing said polymeric powder by exposing said polymeric powder coated objects to electromagnetic radiation while simultaneously blowing air against the surface of said objects, whereby the temperature of the polymeric powder during said curing is maintained at a temperature not substantially exceeding the melting temperature of said polymeric powder.