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 . A polyamide powder, 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, y and z of the individual particles have the same dimension to within ±10%.    
   
   
       2 . The polyamide powder as claimed in  claim 1 , wherein 
 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%.    
   
   
       3 . The polyamide powder as claimed in  claim 1 , wherein the polyamide is selected from the group consisting of nylon-11 and nylon-12.  
   
   
       4 . The polyamide powder as claimed in  claim 1 , which has an η re1  of from 1.30 to 1.65.  
   
   
       5 . The polyamide powder as claimed in  claim 1 , which has an η re1  of from 1.40 to 1.63.  
   
   
       6 . The polyamide powder as claimed in  claim 1 , wherein the polyamide 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.  
   
   
       7 . The polyamide powder as claimed in  claim 6 , wherein the regulators are selected from the group consisting of dicarboxylic acid, diamine, and combinations therof.  
   
   
       8 . The polyamide powder as claimed in  claim 1 , wherein the powder further comprises at least one selected from the group consisting of titanium dioxide, aluminum oxide, and silica.  
   
   
       9 . The polyamide powder as claimed in  claim 1 , wherein the powder has an upper grain size limit of 125 μm.  
   
   
       10 . A process, 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 the polyamide powder product as claimed in  claim 1 .    
   
   
       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 the polyamide powder as claimed in  claim 1 , contacting the fluidized powder with a metal surface, and forming a polyamide coating on said metal surface.  
   
   
       17 . The process as claimed in  claim 16 , wherein said coating has a thickness of 50 to 200 μm.