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7 Practical Guidelines for Paint Workers
Article 5: Precautions When Mixing Paint
Key Points
Maintaining the accurate mixing ratio of the base component and hardener is crucial for ensuring the quality of the paint film.
Mixing only the necessary amount and prompt cleaning of equipment after painting are essential for the proper use and safety of the paint.
Using thinners with appropriate solvent design is essential to maximize the performance of the paint and prevent poor curing.
Precautions When Mixing Paint
When mixing paint, especially pay attention to the following three points:
1. (For two-component paints) Adhere to the mixing ratio of the base component and the hardener.
Just before painting, mix the base component and the hardener in the weight ratio specified by the manufacturer. The curing reaction between the base component and the hardener of a two-component paint can be likened to a jungle gym. The base component is like the pipes of the jungle gym, and the hardener is like the fittings that connect the pipes. If there are not enough fittings to connect the pipes, the assembly of the jungle gym will be incomplete and wobbly, resulting in poor curing. Conversely, if the main component, the pipe, is insufficient, the expected paint film performance will not be fully achieved.
2. (For two-component paints) Mix only the amount needed for painting and do not store the mixture after painting.
Once the base component and the hardener are mixed, a chemical reaction begins to form the paint film, and over time, the paint thickens and eventually hardens (gelation). This gelation can lead to painting defects such as stringiness during spraying, deterioration of smoothness, pinholes, and orange peel. This appropriate time range for the reaction to proceed is called the “pot life,” which varies depending on the type of paint and environmental conditions. Generally, at about 20°C, polyurethane resin paint has a pot life of approximately 3 hours, epoxy resin paint about 4 hours, and unsaturated polyester resin about 30 minutes. Especially for unsaturated polyester resin, due to its short pot life, it is necessary to clean the equipment promptly after painting.
3. Use the manufacturer’s specified products or thinners with appropriate solvent
Using products other than those specified by the manufacturer or thinners without appropriate solvent design can cause poor curing. For example, diluting a two-component polyurethane resin paint with lacquer thinner can lead to a reaction with the alcohol in the hardener, forming a brittle paint film with low alcohol resistance. Furthermore, polyurethane resin paints vary in resin composition according to their application for metal, woodworking, and plastics, so the solvent composition of the suitable thinner also varies.