Historically the first known paintings were found approx. 25,000 years ago in caves in France and Spain. The paintings depict humans, animals, and diagrams. The use of paint as a protective coating was applied by Egyptians and Hebrews to protect their ships. During the Middle Ages, artists began to boil resin with oil to obtain highly miscible paints. In the fifteenth century, they were the first to add drying oils to paint to speed up evaporation. The same artists also adopted a new solvent, linseed oil which remained the most commonly used solvent until synthetics replaced it during the twentieth century.
Raw Materials
Paint is composed of
- Pigments: give the paint color.
- Solvent: make it easier to apply.
- Resins or Binders: help it dry.
- Additives: serve as everything from fillers to anti-fungicidal agents.
For instance:
Pigments; titanium dioxide (white), carbon black (black), iron oxide and cadmium sulfide (red), metallic salts (yellow and orange), iron blue (blue), chrome yellows (green).
Solvents; mineral spirits, alcohols, esters, ketones, acetone.
Resins; natural resins such as linseed oil, coconut, soybean oil. Synthetic resins such as alkyds, acrylics, epoxies, polyurethanes.
Additives; calcium carbonate and aluminum silicate are simply fillers that give the paint body and substance without changing its properties.
Manufacturing Process
A paint production process involves four major steps;
- Pre-assembly and Premix
- Pigment grinding/milling
- Product finishing/blending
- Product filling/packaging
Pre-assembly and Premix
In this step, the liquid raw materials (solvents, resins, oils, alcohols and/or water) are assembled and mixed in containers to form a viscous material for which pigments to add in it. The pigment and liquid mixture forms a thicker material which is then sent to the grinding operations.
Pigment Grinding or Milling
This process occurs in three stages; wetting, grinding, and dispersion. To wet the pigment particles, the wetting agent, which is normally a surfactant, displaces all contaminants (air, moisture, and gases) adsorbed on the surface of the pigment particles. Grinding is the mechanical breakup and separation of the pigment clusters into isolated primary particles. Dispersion is the movement of the wetted particles into the body of the liquid vehicle* to produce a permanent particle separation.
*The vehicle is composed of the binder or if it is necessary to thin the binder with a diluent like solvent or water, it is the combination of binder and diluent.
Product Finishing
This step consists of three intermediate stages; thinning, tinting, and blending.
Thinning
Material letdown or thinning is the process by which a completed mill base dispersion is let down or reduced with solvent and/or binder to give a coating which is designed to provide a durable, serviceable film for easy applying to the substrate.
Tinting
Tinting is the process of adjusting the color of completed mill base dispersions. Various combinations of pigments, solvents, resins, and pastes are added to the material to meet the color requirements.
Blending
Blending is the process of incorporating the additions into the material in order to meet the desired product specifications.
Product Filling
The transfer step involves product filtration by a variety of ways. Once the material has been filtered, it can be transferred into pails, drums, tote tanks, or another container for shipment. Filling may be accomplished by either manually or mechanically depending on the number and size of the containers to be filled.
Thank you. See you next blog.
admin – June 5, 2019
Excerpt some contents from “Control of VOC Emissions from Ink and Paint Manufacturing Processes” by Control Technology Center, April 1992.