Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-03-16
2001-05-15
Sanders, Kriellion (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S514000, C524S520000, C428S421000
Reexamination Certificate
active
06232372
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the field of compositions containing fluoropolymer and high temperature resistant polymer binder. Such compositions are useful for coating metal surfaces, including use as a primer in multi-layer coating systems.
BACKGROUND OF THE INVENTION
Fluoropolymer resins, and especially perfluoropolymer resins, are known for their low surface energy and antistick properties, and thermal and chemical resistance. These fluoropolymer compositions do not stick to other materials, especially dissimilar materials, with any practical degree of bond strength.
Some high temperature resistant thermoplastics, such as polyamide imide, polyarylene sulfide and polyether sulfone, have found use as polymer binders in fluoropolymer coating formulations. See, for example U.S. Pat. No. 5,230,961 (Tannenbaum) and U.S. Pat. No. 5,093,403 (Rau et al.). However, for dry powder coating such as discussed in the '403 patent, particle dimensions of the formulation components are determined by grinding or milling capabilities and limit the homogeneity of coatings fabricated from the blend. Such blends also exhibit segregation in shipping, processing and recovery of scrap powder. When using a powder mixture for electrostatic spraying, the components of the mixture tend to segregate. The segregation can produce a variable powder coating composition when the powder is sprayed on a substrate. Another notable problem occurs in electrostatic spray coating in conjunction with the sprayed powder that does not adhere to the target substrate, known as “overspray”. Segregation in the overspray prevents direct recycle to the spraying operation.
There remains a need for compositions of melt-fabricable fluoropolymer with high temperature resistant polymer binder in which the components provide a more homogeneous blend, and one resistant to segregation during shipping or processing.
SUMMARY OF THE INVENTION
This invention provides a composition comprising a plurality of multicomponent particles, one component of each of the particles being melt fabricable fluoropolymer and another component of each of the particles being a high temperature resistant non-dispersed polymer binder. The components of the particles are bound together by mechanical engagement, or alternatively, by chemical interaction. The composition is preferably in the form of a free-flowing powder which, because of the components being bound together, is not subject to segregation of component resins during shipping or processing.
In one embodiment, the invention provides a composition comprising a plurality of multicomponent particles wherein the melt fabricable fluoropolymer component of each particle is dispersed in a high temperature resistant polymer binder matrix.
In a second embodiment, the invention provides a composition comprising a plurality of multicomponent particles wherein the melt fabricable fluoropolymer component of each particle is present as a core coated with high temperature resistant polymer binder.
In a third embodiment, the invention provides a composition comprising a plurality of multicomponent particles wherein the melt fabricable fluoropolymer and the high temperature resistant non-dispersed polymer binder components of each particle are bound to one another by chemical interaction, preferably with the polymer binder being in the form of a coating around a core of the fluoropolymer. The melt fabricable fluoropolymer component of the third embodiment has polar functionality.
The invention also provides a general process for making a composition comprising multicomponent particles, one component of each of the particles being melt fabricable fluoropolymer and another component of each of the particles being a high temperature resistant polymer binder, by combining melt-fabricable fluoropolymer particles and a solution of high temperature resistant polymer binder, mixing the fluoropolymer with the solution of polymer binder and isolating a composition of multicomponent particles. The melt-fabricable fluoropolymer may be added in the form of fundamental particles of aqueous fluoropolymer dispersion or in the form of particles of fluoropolymer powder. This general process prevents the polymer binder from combining with a fluoropolymer particle as a dispersion of the polymer binder in the particle.
To make the first embodiment of multicomponent particles, the melt-fabricable fluoropolymer is in the form of an aqueous dispersion of fundamental fluoropolymer particles when combined with a solvent solution of polymer binder wherein the solvent is miscible with the water of the aqueous dispersion, and these ingredients are mixed under conditions of high shear followed by isolating a composition of multicomponent particles of fundamental melt-fabricable fluoropolymer particles dispersed in polymer binder matrix.
To make the second embodiment of multicomponent particles, the melt-fabricable fluoropolymer is in the form of fluoropolymer powder when combined with the solution of polymer binder, and this combining step is followed by mixing the ingredients and isolating a composition of multicomponent particles of the melt fabricable fluoropolymer resin coated with polymer binder resin. Isolation may be by filtration, evaporation or aqueous treatment.
To make the third embodiment of multicomponent particles, the melt-fabricable fluoropolymer is in the form of an aqueous dispersion of fundamental particles of fluoropolymer which contain units of polar functional groups when combined with a solvent solution of polymer binder wherein the solvent is miscible with water, and this combination step is followed by mixing and isolating a composition of multicomponent particles in the form of polymer binder coating bound to a core of melt-fabricable fluoropolymer by chemical interaction.
REFERENCES:
patent: 3635926 (1972-01-01), Gresham et al.
patent: 5093403 (1992-03-01), Rau et al.
patent: 5230961 (1993-07-01), Tannenbaum
patent: 0 124 085 (1984-11-01), None
patent: 0 222 945 B1 (1987-05-01), None
patent: 0 226 668 B1 (1987-07-01), None
patent: 0 373 588 (1990-06-01), None
patent: 95/21216 (1995-08-01), None
Brothers Paul Douglas
Kerbow Dewey Lynn
McKeen Laurence W.
E. I. Du Pont de Nemours and Company
Sanders Kriellion
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