Method for manufacture of particles for powder coating

Abstract

A method for manufacture of particles for powder coating is disclosed in which the particles are prepared from a suspension obtained from a mixture of a thermosetting resin solution and an aqueous solution containing a water-soluble polymer. The thermosetting resin solution contains A resin, B resin and an organic solvent wherein: (a) 0.5≦{(SP value of the A resin)−(SP value of the B resin)}≦1.5; (b) {(Tg of the A resin)−(Tg of the B resin)}≧10° C.; (C) 40° C.≦(Tg of the A resin)≦100° C., and, 20° C.≦(Tg of the B resin)≦50° C., and (d) 5/95≦(a ratio in solids weight of the A resin to B resin)≦50/50.

What is claimed is:  
     
         1 . A method for manufacture of particles for powder coating in which the particles are prepared from a suspension obtained from a mixture of a thermosetting resin solution and an aqueous solution containing a water-soluble polymer, wherein said thermosetting resin solution contains A resin, B resin and an organic solvent wherein: 
 (a) 0.5≦{(SP value of the A resin)−(SP value of the B resin)}≦1.5;    (b) {(Tg of the A resin)−(Tg of the B resin)}≧10° C.;    (C) 40° C.≦(Tg of the A resin)≦100° C., and, 20° C.≦(Tg of the B resin)≦50° C.; and    (d) 5/95≦(a ratio in solids weight of the A resin to B resin)≦50/50.    
     
     
         2 . The method of  claim 1  wherein said thermosetting resin solution further contains a curing agent.  
     
     
         3 . The method of  claim 1  wherein said water-soluble polymer comprises a mixture of a first type of water-soluble polymer which does not exhibit a cloud point and a second type of water-soluble polymer which exhibits a cloud point within a temperature range of 30-90° C., and wherein said method includes the steps of: 
 (1) preparing said suspension at a first temperature below said cloud point;  
 (2) heating said suspension to a second temperature higher than the first temperature but below the cloud point to form primary particles therein; and  
 (3) heating the primary particle-containing suspension to a third temperature equal to or higher than the cloud point to form secondary particles therein.  
 
     
     
         4 . The method of  claim 3  wherein, in the step (1) and/or (2), said organic solvent is distilled off.  
     
     
         5 . The method of  claim 1  wherein said A and B resins both are essentially consisted of an acrylic resin.  
     
     
         6 . The method of  claim 5  wherein the A resin has a number average molecular weight in the range of 2,000-4,000 and the B resin has a number average molecular weight in the range of 5,000-10,000.  
     
     
         7 . The method of  claim 5  wherein each of the A and B resins has an epoxy group and said curing agent is polycarboxylic acid.  
     
     
         8 . Spherical particles for powder coating manufactured by using the method of  claim 1 .  
     
     
         9 . Spherical particles for powder coating, containing A and B resins wherein: 
 (a) 0.5≦{(SP value of the A resin)−(SP value of the B resin)}≦1.5;    (b) {(Tg of the A resin)−(Tg of the B resin)}≧10° C.;    (C) 40° C.≦(Tg of the A resin)≦100° C., and, 20° C.≦(Tg of the B resin)≦50° C.; and    (d) 5/95≦(a ratio in solids weight of the A resin to B resin)≦50/50.    
     
     
         10 . The spherical particles of  claim 9  having a volume average particle size in the range of 5-30 μm.  
     
     
         11 . The spherical particles of  claim 9  wherein a value of (volume average particle size)/(number average particle size) is not larger than 2.  
     
     
         12 . The spherical particles of  claim 9  further comprising a curing agent.  
     
     
         13 . The spherical particles of  claim 9  wherein said A and B resins are essentially consisted of an acrylic resin.  
     
     
         14 . The spherical particles of  claim 13  wherein the A resin has a number average molecular weight in the range of 2,000-4,000 and the B resin has a number average molecular weight in the range of 5,000-10,000.  
     
     
         15 . The spherical particles of  claim 13  wherein each of the A and B resins has an epoxy group and said curing agent is polycarboxylic acid.  
     
     
         16 . A method for formation of a multilayer film comprising the steps of: 
 applying a basecoat on an undercoated or further intermediate coated substrate;    applying a layer of the spherical particles of  claim 8  on said basecoat overlying the substrate; and    heating the substrate carrying thereon the layer of particles and the basecoat.    
     
     
         17 . A multilayer film manufactured by the method of  claim 16.