Waterborne paints polyester resins

Polyester resins possess premium performance properties such as exterior durability, gloss, flexibility hardness, color stability, and versatility of cure. Polyesters are used in product finishes for household appliances, food and beverage containers, aircraft and equipment, automotive primers and bake coats, metal furniture, and fixtures. For example, water-soluble saturated polyesters are used in industrial baking paints, and in combination with melamine resin. Polyesters can be formulated in high solids and waterborne formulations to meet the requirements for the low VOC coatings being mandated by the EPA. 

Polyester resins for waterborne paints mostly contain anionic groups (e.g., carboxyl groups) and become water soluble after amine neutralization. Waterborne paints based on polyesters also contain cosolvents, preferably glycol ethers. Powder coatings based on low molecular mass resins are solvent-free, like radiation-curable polyester paints. 

Conventional grinding methods are used to incorporate pigments into solvent-borne and waterborne polyester resins as well as into radiation-curable polyester paints containing reactive diluents. Pigmented powders are produced by coextrusion of polyester granulate with pigments, followed by grinding. 

Polyester paints with high solids contents (65-75 wt% at application viscosity) can be produced from very low molecular mass resins [2.95]. Low-pollution paints can also be produced from water-soluble polyester resins [2.85]. On account of their good water solubility, HMMM resins are particularly suitable for cross-linking these resins. Organic cosolvents (mostly glycol ethers) must be added to waterborne polyester paints to control their viscosity and applicability (leveling, substrate wetting). 

Paint consists of a mixture of pigments which gives body and colour, and a resin or binder which is the actual film-forming component and acts as a glue to hold the pigment together and stick them to the surface. Binders include synthetic resins such as acrylics, polyurethanes, polyesters and epoxies and can be a combination of resins, e.g. epoxy/ acrylic and polyurethane/acrylic. To adjust the curing properties and reduce the viscosity so that the paint can be easily applied, a solvent or carrier is used. These evaporate after application and do not form part of the paint film. In waterborne paints, the carrier is water. With solvent-borne paints, also called oil-based paints, the carrier is a solvent such as acetone, turpentine, naphtha, toluene, xylene and white spirit. 

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