Electrostatic powder coating method and powder coating material

Abstract

An electrostatic powder coating method includes spraying a charged powder coating material including powder particles which contain a thermosetting resin, a thermosetting agent, and titanium oxide particles as a white pigment to electrostatically attach the powder coating material to an object to be coated; and heating the powder coating material which is electrostatically attached to the object to be coated to thereby form a coating film, wherein a titanium oxide particle content Tic in 1 g of the powder particles of the powder coating material which is electrostatically attached to the object to be coated and a titanium oxide particle content Tio in 1 g of the powder particles of the powder coating material before being sprayed satisfy a relationship of Expression: Tio×0.90≦Tic≦Tio×1.10.

What is claimed is: 
     
         1 . An electrostatic powder coating method, comprising:
 spraying a charged powder coating material including powder particles which contain a thermosetting resin, a thermosetting agent, and titanium oxide particles as a white pigment to electrostatically attach the powder coating material to an object to be coated; and   heating the powder coating material which is electrostatically attached to the object to be coated to thereby form a coating film,   wherein a titanium oxide particle content Tic in 1 g of the powder particles of the powder coating material which is electrostatically attached to the object to be coated and a titanium oxide particle content Tio in 1 g of the powder particles of the powder coating material before being sprayed satisfy a relationship of Expression: Tio×0.90≦Tic≦Tio×1.10.   
     
     
         2 . The electrostatic powder coating method according to  claim 1 ,
 wherein the titanium oxide particle content Tic in 1 g of the powder particles of the powder coating material which is electrostatically attached to the object to be coated and the titanium oxide particle content Tio in 1 g of the powder particles of the powder coating material before being sprayed satisfy a relationship of Expression: Tio×0.95≦Tic≦Tio×1.15.   
     
     
         3 . The electrostatic powder coating method according to  claim 1 ,
 wherein the titanium oxide particle content Tic in 1 g of the powder particles of the powder coating material before being sprayed is from 10% by weight to 60% by weight.   
     
     
         4 . The electrostatic powder coating method according to  claim 1 ,
 wherein a volume average particle diameter of the powder particles of the powder coating material before being sprayed is from 3 μm to 10 μm.   
     
     
         5 . The electrostatic powder coating method according to  claim 1 ,
 wherein an average circularity of the powder particles of the powder coating material before being sprayed is greater than or equal to 0.96.   
     
     
         6 . The electrostatic powder coating method according to  claim 1 ,
 wherein the thermosetting resin includes at least one selected from the group consisting of a thermosetting (meth)acrylic resin and a thermosetting polyester resin.   
     
     
         7 . The electrostatic powder coating method according to  claim 6 ,
 wherein a total value of an acid value and a hydroxyl value of the thermosetting polyester resin is from 10 mgKOH/g to 250 mgKOH/g.   
     
     
         8 . The electrostatic powder coating method according to  claim 6 ,
 wherein a number average molecular weight of the thermosetting polyester resin is from 1,000 to 100,000.   
     
     
         9 . The electrostatic powder coating method according to  claim 6 ,
 wherein a number average molecular weight of the thermosetting (meth)acrylic resin is from 1,000 to 20,000.   
     
     
         10 . The electrostatic powder coating method according to  claim 1 ,
 wherein a content of the thermosetting resin is 20% by weight to 99% by weight with respect to a total content of the powder particles.   
     
     
         11 . The electrostatic powder coating method according to  claim 1 ,
 wherein a content of the thermosetting agent is from 1% by weight to 30% by weight with respect to the thermosetting resin.   
     
     
         12 . The electrostatic powder coating method according to  claim 1 ,
 wherein the powder particles of the powder coating material before being sprayed contain 0.002% by weight to 0.2% by weight of a metal ion with respect to a total content of the powder particles.   
     
     
         13 . The electrostatic powder coating method according to  claim 12 ,
 wherein a valence of the metal ion is two or more.   
     
     
         14 . The electrostatic powder coating method according to  claim 1 ,
 wherein the powder particles of the powder coating material before being sprayed are core/shell type particles.   
     
     
         15 . The electrostatic powder coating method according to  claim 14 ,
 wherein a coverage of a shell portion of the core/shell type particle is from 30% to 100%.   
     
     
         16 . The electrostatic powder coating method according to  claim 14 ,
 wherein a thickness of a shell portion of the core/shell type particle is from 0.2 μm to 4 μm.   
     
     
         17 . The electrostatic powder coating method according to  claim 1 ,
 wherein the powder coating material before being sprayed includes silica particles as an external additive.   
     
     
         18 . The electrostatic powder coating method according to  claim 17 ,
 wherein an externally added amount of the external additive is from 0.01% by weight to 5% by weight with respect to the powder particles.   
     
     
         19 . The electrostatic powder coating method according to  claim 17 ,
 wherein a volume average particle diameter of the external additive is from 5 nm to 200 nm.   
     
     
         20 . A powder coating material, comprising:
 powder particles containing a thermosetting resin, a thermosetting agent, and titanium oxide particles as a white pigment,   wherein when the charged powder coating material is sprayed and the powder coating material is electrostatically attached to an object to be coated, a titanium oxide particle content Tic in 1 g of the powder particles of the powder coating material which is electrostatically attached to the object to be coated and a titanium oxide particle content Tio in 1 g of the powder particles of the powder coating material before being sprayed satisfy a relationship of Expression: Tio×0.90≦Tic≦Tio×1.10.