Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1991-07-25
1994-06-07
Michl, Paul R.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
523204, 523206, 523207, 523220, 428407, C09C 310, C09D 503, C08J 320
Patent
active
053190017
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to coloured powder coatings. Powder coating compositions generally comorise a solid film-forming resin, usually with one or more pigments. They can be thermoplastic but are more usually thermosetting, incorporating two co-reactive film-forming resins or incorporating a curing agent for the film-forming resin in the powder particles. Powder coating compositions are generally prepared by intimately mixing the ingredients, for example in an extruder at a temperature above the softening point of the film-forming resin but below the curing temperature, and comminuting the mixture to the desires particle size. The powder coating is usually apelied by electrostatic spray, and the particle size required for most commercial electrostatic spray apparatus is a mean particle size of 15-75 microns. preferably 25-50 microns. In the electrostatic spray process the powder coating particles are electrostatically chargea by the spray gun and the substrate is earthed or oppositely charged. The powder coating particles which do not adhere to the substrate can be recovered for re-use so that powder coatings are economical in use of ingredients as well as non-polluting.
Powder coatings form a rapidly growing sector of the coatings market. One disadvantage of powder coating compositions is that it is difficult to produce small batches of any particular shade rapidly. Improvements in pigment dispersion techniques have made available fluid concentrated colour dispersions which can be added to a range of colourless or white paint bases to rapidly prepare liquid paint in any shade desired, avoiding the need for a paint store to keep several different types of paint each in a wide variety of shades. Such concentrated colour dispersions cannot readily be mixed into powder coatings. There is a need for a process whereby powcer coatings can be rapidly supplied in a wide variety of shades without tne need to store all the different shades.
PRIOR ART
U.S. Pat. No. 3,843,571 relates to a "metallic glamour" finish applied as a powder coating comprising particles of size 1 to 75 microns, that is passing 200-mesh U.S. Sieve. The powder coating compositions comprise 95.0 to 99.9% by weight powder particles of at least two different colours capable of adhering to one another to form a continuous film when heated to their melt temperature, and 0.1 to 5.0% by weight reflective flakes. The coloured particles consist of 70 to 99.9% by weight film-forming binder and 0.1 to 30% by weight colorant particles.
SUMMARY OF THE INVENTION
A coloured powder coating composition according to the invention consists of solid particles, each of which comprises a solid polymeric binder system and at least the majority of which contain at least one colouring agent, the composition being a mixture of particles of at least two different colours, and the size of the particles being sufficiently low that when the powder coating is applied to a substrate and heated to form a continuous coating the differences in colour in the cured powder coating arising from the different coloured particles cannot be discerned by the human eye.
A process according to the invention for the preparation of a coloured powder coating composition in a desired colour comprises providing powder coating compositions in at least two basic colours, optionally together with an uncoloured powder coating composition, each composition consisting of solid particles and each particle comprising a solid polymeric binder system, the particles of the basic colour compositions also containing a colouring agent, and the compositions having a particle size such that substantially all the particles have their largest dimension below 10 microns, and mixing the powder coating compositions in proportions selected to give a coloured powder coating composition which when applied to a substrate and heated to form a continuous coating forms a film of the desired colour. In a modification of such a procedure, an alternative process according to the invention for th
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Handyside Timothy M.
Morgan Andrew R.
Sinclair-Day John D.
Courtaulds Coating (Holdings) United
Merriam Andrew E. C.
Michl Paul R.
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