Polyamide fluidized-bed-coating powder for thin-layer fluidized-bed coating
View Patent ↗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 dimensions 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 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, y and z of the individual particles have the same dimension to within ±10%.
2. The process as claimed in claim 1 , wherein said post-treating comprises rounding off the corners and edges in a mill, an impact device, or both.
3. The process as claimed in claim 1 , wherein the portion of fines are removed in a pneumatic classifier.
4. The process as claimed in claim 1 , further comprising, in a fluidized-bed coating process, fluidizing said polyamide powder product, and contacting the fluidized powder with a metal surface.
5. 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%.
6. The process according to claim 5 , 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%.
7. The process according to claim 5 , wherein said polyamide is selected from the group consisting of nylon-11 and nylon-12.
8. The process according to claim 5 , wherein said polyamide powder has an η rel of from 1.30 to 1.65.
9. The process according to claim 5 , wherein said polyamide powder has an η rel of from 1.40 to 1.63.
10. The process according to claim 5 , 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.
11. The process according to claim 10 , wherein the regulators are selected from the group consisting of dicarboxylic acid, diamine, and combinations thereof.
12. The process according to claim 5 , wherein said polyamide powder further comprises at least one member selected from the group consisting of titanium dioxide, aluminum oxide, and silica.
13. The process according to claim 5 , wherein said polyamide powder has an upper grain size limit of 125 μm.