Polyamide fluidized-bed-coating powder for thin-layer fluidized-bed coating

Abstract

One embodiment of the present invention provides a polyamide powder, which includes polyamide particles having a median grain size d 50 of from 20 to 90 μm, a content of fines <5 μm of below 1% by weight, and at least 75% by weight of spherical particles in which all three spatial axes x, y and z of the individual particles have the same dimension to within ±10%. Other embodiments of the invention provide a process for making and using the powder, and articles coated articles obtained thereby.

1 - 9 . (canceled)  
     
     
         10 . A process for obtaining a polyamide powder, comprising: 
 screening a polyamide powder to remove particles having a size of ≧125 μm to obtain a screened powder;    mechanically post-treating the screened powder to round off corners and edges, to obtain a post-treated powder; and    removing a portion of fines having a size of <5 μm from the post-treated powder, to obtain a polyamide powder product, comprising 
 polyamide particles having a median grain size d 50 of from 20 to 90 μm,  
 a content of fines <5 μm of below 1% by weight, and  
 at least 75% by weight of spherical particles in which all three spatial axes x, v and z of the individual particles have the same dimension to within ±10%.  
   
     
     
         11 . The process as claimed in  claim 10 , wherein said post-treating comprises rounding off the corners and edges in a mill, an impact device, or both.  
     
     
         12 . The process as claimed in  claim 10 , wherein the portion of fines are removed in a pneumatic classifier.  
     
     
         13 . The process as claimed in  claim 10 , further comprising, in a fluidized-bed coating process, fluidizing said polyamide powder product, and contacting the fluidized powder with a metal surface.  
     
     
         14 . A coated surface, prepared by a process comprising, in a fluidized-bed coating process, fluidizing said polyamide powder product, contacting the fluidized powder with a metal surface, and forming a polyamide coating on said metal surface.  
     
     
         15 . The coated surface as claimed in  claim 14 , wherein said coating comprises a polyamide layer having a thickness of 50 to 200 μm.  
     
     
         16 . A process for coating a surface, comprising: 
 in a fluidized-bed coating process, fluidizing a polyamide powder to obtain a fluidized polyamide powder;    contacting the fluidized powder with a metal surface and    forming a polyamide coating on said metal surface;    wherein said coating has a thickness of 50 to 200 μm,    wherein said polyamide powder comprises 
 polyamide particles having a median grain size d 50 of from 20 to 90 μm,  
 a content of fines <5 μm of below 1% by weight, and  
 at least 75% by weight of spherical particles in which all three spatial axes x, y and z of the individual particles have the same dimension to within ±10%.  
   
     
     
         17 . (canceled)  
     
     
         18 . The process according to  claim 16 , wherein in said polyamide powder, at least 80% by weight of spherical particles in which all three spatial axes x, y and z of the individual particles have the same dimension to within ±10%.  
     
     
         19 . The process according to  claim 16 , wherein said polyamide is selected from the group consisting of nylon-11 and nylon-12.  
     
     
         20 . The process according to  claim 16 , wherein said polyamide powder has an η rel  of from 1.30 to 1.65.  
     
     
         21 . The process according to  claim 16 , wherein said polyamide powder has an η rel  of from 1.40 to 1.63.  
     
     
         22 . The process according to  claim 16 , wherein the polyamide powder further comprises one or more regulators having amino end groups and carboxy end groups, and wherein a ratio of the amino end groups to the carboxy end groups is ≧3:1 or ≦1 :3.  
     
     
         23 . The process according to  claim 22 , wherein the regulators are selected from the group consisting of dicarboxylic acid, diamine, and combinations thereof.  
     
     
         24 . The process according to  claim 16 , wherein said polyamide powder further comprises at least one member selected from the group consisting of titanium dioxide, aluminum oxide, and silica.  
     
     
         25 . The process according to  claim 16 , wherein said polyamide powder has an upper grain size limit of 125 μm.  
     
     
         26 . A coating prepared according to the process of  claim 16.