Method for preparing composition suitable for electrostatic painting

Abstract

Methods are provided for preparing a composition having a melt viscosity of between 160 Pas and 400 Pas, as determined according to ISO-11443-2014 at 270° C. and a shear rate of 265 1/s, and a volume resistivity of at most 105 Ohm·cm, measured according to ASTM D257 on an injection molded test sample of 3 mm thickness and a diameter of 50 mm and coated with a gold layer on an upper and lower surface and, as well as the composition itself and painted parts comprising the composition.

1 . A method for preparing a composition having a melt viscosity of between 160 Pas and 400 Pas, as determined according to ISO-11443-2014 at 270° C. and a shear rate of 265 1/s, and a volume resistivity of at most 10 5  Ohm·cm, as measured according to ASTM D257 on an injection molded test sample of 3 mm thickness and a diameter of 50 mm and coated with a gold layer on an upper and lower surface, the method comprising the following steps:
 (i) providing a polybutylene terephthalate (PBT) having a relative solution viscosity (RSV) of between 1.6 and 2.4 as measured at 25° C. in meta-cresol according to ISO 1628-5, in an amount of between 40 and 70 wt % with respect to the total weight of the composition; 
 (ii) providing a polyethylene terephthalate (PET) having a relative solution viscosity (RSV) of between 1.1 and 1.5 as measured at 25° C. in dichloro acetic acid according to ISO 1628-5, in an amount of between 10 and 40 wt % with respect to the total weight of the composition; 
 (iii) providing a filler in an amount of between 10 and 30 wt % wherein the filler is chosen from the group consisting of glass fibers, talc, mica, wollastonite, glass beads and milled glass and combinations thereof, wt being with respect to the total weight of the composition; 
 (iv) providing an electrically conductive additive in an amount between 2 and 10 wt % with respect to the total weight of the composition, wherein the electrically conductive additive is chosen from the group consisting of carbon black, carbon fibers, graphite, carbon nanotubes, and graphene and combinations thereof and wherein the electrically conductive additive exhibits a volume resistivity of at most 10 5  Ohm·cm, as measured according to ASTM D257 on an injection molded test sample of 3 mm thickness and a diameter of 50 mm, consisting of 8 wt % of electrically conductive additive and 92 wt % of PBT having a relative solution viscosity of 2.0 in meta cresol, wherein the wt % is with respect to the total weight of the injection molded test sample, which injection molded test sample was coated with a gold layer on an upper and lower surface; and 
 (v) mixing at least the PBT, PET, filler and electrically conductive additive at a temperature of between 240 and 260° C. in order to obtain the composition. 
 
     
     
         2 . The method according to  claim 1 , wherein the electrically conductive additive exhibits a volume resistivity of at most 10 5  Ohm·cm when measured on an injection molded test sample consisting of 7 wt % of electrically conductive additive and 93 wt % of PBT having a relative solution viscosity of 2.0 in meta cresol. 
     
     
         3 . The method according to  claim 1 , wherein the electrically conductive additive exhibits a volume resistivity of at most 10 5  Ohm·cm when measured on an injection molded test sample consisting of 6 wt % of electrically conductive additive and 94 wt % of PBT having a relative solution viscosity of 2.0 in meta cresol. 
     
     
         4 . The method according to  claim 1 , wherein at least part of the mixing is performed in an extruder. 
     
     
         5 . The method according to  claim 4 , wherein the extruder is a twin-screw extruder. 
     
     
         6 . The method according to  claim 4 , wherein the filler and/or the electrically conductive additive is provided to the extruder via a side feeder. 
     
     
         7 . The method according to  claim 1 , wherein the filler is talc. 
     
     
         8 . The method according to  claim 1 , wherein the electrically conductive additive is carbon black. 
     
     
         9 . The method according to  claim 8 , wherein the carbon black has an oil absorption number of at least 300 ml/100 g, as measured according to ASTM D-2414, and wherein the carbon black is provided in an amount of between 3 and 5 wt %. 
     
     
         10 . A method for preparing a painted part, comprising the steps of:
 (a) preparing the composition according to the method of  claim 1 ;   (b) preparing a part comprising the composition;   (c) grounding or charging the part such that the part attracts paint particles;   (d) coating the part with at least one layer of paint either by spraying the paint in such a manner that the paint is charged so as to be attracted to the part or dipping the part into a charged paint reservoir; and   (e) drying and/or curing the paint after application of one or more layers of the paint thereby obtaining a painted part.   
     
     
         11 . A painted part obtained by the method according to  claim 9 .