Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Patent
1998-08-04
2000-12-05
Padgett, Marianne
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
427536, 427539, 427560, 427562, 427565, 427569, 427575, 427218, 427212, 106493, 106499, 106 19R, C23C 1602, C23C 1650, C09D 1700, C09D 500, B05D 306
Patent
active
061561142
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention concerns the atmospheric and subatmospheric treatment of particulate materials by a plasma-activated gas species to modify the particle surfaces. U.S. Pat. No. 4,478,643 discloses a pigment treated with a low temperature plasma wherein the pigment is maintained in a commercially available plasma asher for a time that is excessive and will cause pigment degradation. U.S. Pat. No. 5,234,723 discloses a process for treating particulates with a plasma-activated species at subatmospheric pressure by dropping a particulate through said treatment zone homogeneously. U.S. Pat. No. 5,176,938 discloses a process for treating particulates by passing them through a plasma flame. U.S. Pat. No. 5,340,618 discloses a method of treating a powder with an atmospheric pressure plasma by dispersing the powder within the reaction chamber using what appears to be a fluidized bed arrangement without addressing the problem of deagglomeration.
The process of the instant invention avoids the harsh treatment conditions of the '643 and '938 processes and the agglomeration of the '723 and '618 processes.
The organic particles contemplated for surface modification by the method of this invention have varying affinities for clumping together as agglomerates and/or aggregates by virtue of physical and/or chemical attractions among particles. It is believed that plasma activated species essentially will only interact with, and thereby treat, the surfaces of the clumps. When clumps or agglomerates are treated, only primary particles that are at or near the surface of the clump will be treated by the plasma activated species. It therefore follows that the larger the size of the clump, the smaller the proportion of the primary particles within the clump that can be treated by the gas species and hence the less effective the treatment process will be.
There is almost nothing in the prior art to guide one in the successful implementation of a modification process for materials that readily agglomerate. In this regard, it has now been discovered that successful surface modification of particles requires an integrated process for deagglomerating clumps of particles and treating them while in their deagglomerated state and before they have an opportunity to reagglomerate. It has been found necessary, for readily clumping particulate materials, to treat the particles while they are in a subdivided state, in order to achieve effective treatment at commercial production rates. The degree to which the clumps are subdivided must be no greater than a certain multiple of the mean dimension of the primary particles. The required conditions for the successful modification of normally clumping particulate organic materials by the process of this invention are as described in more detail hereafter.
SUMMARY OF THE INVENTION
This invention concerns a method for treating the surface of particulate materials that exhibit irreversible degradation when heated above a threshold temperature not exceeding about 500 degrees C. with at least one species of plasma-activated process gas in a treatment chamber that contains the plasma source or is downstream of the plasma source, comprising the steps of: portion of the surface of substantially each fraction of deagglomerated particles, process gas in the reaction chamber before reagglomeration can occur to any substantial degree, deagglomerated particle fraction with the activated process gas, and they do not thermally degrade.
This invention also concerns a method for grinding agglomerated pigment particles comprising the steps: surface-modified by the method of this invention, and deagglomeration is effected at less than about 85% of the time it would take under identical conditions to deagglomerate pigment particles not surface-modified by the method of this invention.
This process will effect size reduction of the agglomerated particles. Wet-milling and high-shear mixing can also be employed in deagglomeration.
This invention also concerns a color composition (color conc
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Bell Timothy Allan
Best Wronald Scott
Chouinard Michael Patrick
Harding Thomas William
Herman Paul Francis
Costello James A.
Deshmukh Sudhir G.
E. I. Du Pont de Nemours and Company
Padgett Marianne
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