Powder Coatings Extruder Twin-Screw
Powder coating compositions are solid compositions that generally comprise a solid film-forming resin, usually with one or more pigments and, optionally, one or more performance additives such as plasticizers, stabilizers, flow aids and extenders. The resins are usually thermosetting, incorporating, for example, a film-forming polymer and a corresponding crosslinking agent (which may itself be another film-forming polymer). Generally, the resins have a T9, softening point or melting point above 300C.
The demand for Powder Coatings has shown consistent growth over the last 20 years as this environmentally friendly process has replaced wet paint in many traditional applications.
As products are developed for new applications, including wood and glass coatings, and the use in automobile finishing becomes established, it will be important for the powder coating producer to stay at the forefront of this technology. Use of small and flexible process equipment to support these developments will continue to be a key element in a company’s research, development and quality control.
Conventionally, the powder coating is produced by dry-blending the components of the composition together, and then extruding the blend at a temperature above the softening point of the resin but below the curing temperature thereof to produce a melt-mix of the formulated ingredients.
The extrudate is immediately cooled and pressed into a solid sheet, where the formulated coating material is progressively kibbled and ground to a well- defined particle distribution for spraying by an applicator.
For those powder coating compositions that are to contain pigments and additives, thorough dry blending of the film-forming resin with these components is typically achieved using a line of two high-intensity pre-blending mixers and a low-intensity final mixer.
High-speed, revolving blades in the pre-blending mixers evenly distribute small amounts of pigments and additives and aid in the dispersion of resin. The final mixer - typically containing tumble and chopper blades - accepts product from the pre-blending mixers along with raw materials that have not passed through pre-blending.
Dry-mixed material from the final mixer or from an intermediate weigh hopper then enters the feed port on the extruder.