Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2001-06-13
2004-10-19
Shosho, Callie (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
Reexamination Certificate
active
06806302
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the production of liquid, pigmented coating compositions containing organic solvents or water.
DESCRIPTION OF RELATED ART
Processes for the production of pigmented, liquid coatings are generally known. Such coatings consist of binders, optionally curing agents, pigments, optionally fillers and additional additives necessary in coatings, such as, dispersants, levelling agents, anticratering agents, catalysts, and aqueous or organic solvents. Such coatings are generally produced in such a manner that a pigment paste is produced from proportions of the binders, optionally from specially selected paste binders together with pigments and various additives and said paste is ground in known mills, for example, bead mills, to a suitable particle size and the pigments are wetted. Additional coating binders, additives, solvents and optionally curing agents are then added to this pigment paste and homogenized in suitable mixing units, for example, dissolvers. The process is generally a batch process. Such production processes are described, for example, in EP-A 260 447, EP-A 391 271, EP-A 586 986.
Powder coatings are produced by introducing generally solvent-free, solid binders in pellet form into an extruder together with suitable pigments, fillers, additives and this mixture is heated in the extruder such that the binders melt and the pigments are dispersed in a suitable particle size when processed by the extruder. In the case of externally cross-linking binders, curing agents and additional additives may optionally be added after dispersion. These components are homogeneously mixed and the melt is then discharged from the extruder, cooled and processed, such that relatively large pieces of powder coating are obtained. In a subsequent processing step, these pieces are then ground using suitable mills to a particle size suitable for application. Such processes are described, for example, in EP-A 0 826 018 or EP-A 0 560 792.
Processes are also known, for example, from EP-A 0 887 390 or EPA 0 720 999, for the production of powder coatings in which suitable binders are processed together with pigments and additional additives in an extruder, wherein supercritical processing media, for example, supercritical gases, such as, supercritical CO
2
, are added to reduce viscosity in the extruder and, after discharge from the extruder, the supercritical medium is removed and a dispersed material is obtained that is converted into a powder coating in further processing steps, for example, grinding.
Disadvantages of the above-mentioned procedure for liquid coatings are that the coatings are produced in individual batches, each of which must be adjusted individually to the desired properties to allow for variations in the production process and then further processed. A batch operation also is conventional for the production of powder coatings. Elevated energy input is required in the grinding process for pigment pastes or powder coatings and the corresponding processing conditions must be precisely controlled if the binders are not to be destroyed during this process step. The grinding step is time-consuming and demanding with regard to machinery. The present invention provides a process for the production of liquid coatings, in which an elaborate precursor grinding step is avoided, and that permits continuous operation and uniform conditions during coating production.
SUMMARY OF THE INVENTION
It has surprisingly been found that a production process for the continuous production of liquid coating compositions is possible by introducing solvent-free or low-solvent solid binders into an extruder together with pigments, fillers and optionally additives, mixing and dispersing the constituents, optionally introducing and homogenizing additional binders, curing agents and additives into the process mixture, feeding organic solvents and/or water in one or more stages and reducing the viscosity and processing temperature of the process mixture, discharging the process mixture from the extruder, wherein the process mixture is homogenized by a rotor/stator mixer after addition of further organic solvents and/or water and optionally further constituents and is adjusted to the coating parameters.
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Domke Friedrich
Kramer Evert
Benjamin Steven C.
E. I. du Pont de Nemours and Company
Shosho Callie
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