Resins are film forming materials used in the production of paints and coatings. It binds the pigment particles into a coherent film that adheres to the substrate. The quality of the resin used in the production of paints and coating decides the durability of the paint. Resins are used depending upon the functional properties of the paint.
Functions of Resin
To provide gloss and elasticity.
For the suspension of pigments.
To provide resistance to water, chemicals and abrasion.
Makes coating adhere to the surface.
Acts as a dispersant.
For drying properties.
Alkyd resins from the largest group of synthetic resins are used in paint industry. Most air drying enamels are based on long or medium oil alkyd resins. These resins dry at room temperature and have excellent flow and leveling properties, good exterior durability and can be thinned with mineral turpentine. Oils used for producing alkyd resins are linseed oil, soybean oil and Dehydrated Castor Oil (DCO).
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Vinayak solvent based plant produces paints, coatings, stains, and surface treating products at a rate of about 1.1 million gal/yr. These paint manufacturing plants operations primarily involve blending and mixing of raw materials, product testing and packaging and cleaning of vessels and lines. Color separation of the product is done to befit customer specifications.
Water-based and solvent-based paints are mixed in different tanks from 200- to 1000-gal capacity. The material used in water-based paints includes water, latex, resins, extenders, and dispersed pigments. For solvent-based paints, the materials are generally similar in type, but solvent replaces water and latex. Other ingredients used in this base include plasticizers, tints, and thinners.
After batches are made up, they are transferred to the let-down tanks. Additional water (or solvent), resins, preservatives, anti-foaming agents, thinners, and bactericides are added thereafter in the tanks. Batch testing encompasses checking color, viscosity and gloss. The material are then filtered and charged to cans for labeling, packaging, and shipping.
The principal waste streams are the result of equipment cleaning, especially from water-based paints. For example, rinsing the let-down tanks ordinarily requires about 35 gal of rinse water, but that amount increases to 53 gal if light paint is to be blended after dark paint. The hazardous nature of water rinses results from the mercury used as a bactericide in the paint.
The rinses are separated from the paints according to the color intensity. Waste rinses that are not reused are piped to holding and flocculation tanks, after that alum is added to lower the pH and flocculent is added to precipitate some solids. Finally, the supernatant liquid is removed for reuse in other paint formulations.
The tanks are rinsed with mineral spirits at a rate of about 5 gal/400-gal tank. Thereafter, the washings are sent off-site for recovery, followed by recycling or sale as fuel.
In addition to reusing rinse water and recovering solvent, following measures to reduce waste generation are specified below : Cleaning of the equipment before paint dries and hardens.
Eliminating hazardous materials.
Avoiding hazardous container waste by collecting the bactericide in water-soluble bags.
Scheduling batch formulations so that light colored paints precede dark ones.
Reducing the inventory of raw materials to avoid degradation and spoilage and to ensure a high-quality product.
Using bag filters for collecting dust.