How long does the three-proof paint dry? Key factors affecting curing speed

Three-proof paint (also known as conformal coating or PCB three-proof paint) is the key material to protect printed circuit board from moisture, dust, chemical corrosion and extreme temperature. Its drying and curing time directly affects the production efficiency and product quality. Let's learn more about the drying time of the three-proof paint and the key factors affecting the curing speed.

Drying and curing process of three-proof paint
The drying of three-proof paint is usually divided into two stages: surface drying (the surface does not stick to hands, forming a preliminary protective film) and hard work/complete curing (internal cross-linking is completed, achieving the best protective performance).

• Ordinary solvent-based acrylic or silicone three-proof paint: under the condition of 25℃ and relative humidity of about 50%, the surface drying time is generally 10-30 minutes, and it takes 24-72 hours to completely cure.
• Polyurethane three-proof paint: the surface is dry for about 30 minutes, and it takes 24-48 hours to completely cure.
• UV-curable three-proof paint: After being irradiated by ultraviolet light with appropriate intensity, the surface can be dried in a few seconds to ten seconds (local shadow areas still need moisture-assisted curing). These data come from the measured reference of many mainstream electronic chemical manufacturers, and it is suggested that the specific product TDS (technical data sheet) shall prevail in actual production.

Influence of ambient temperature
Temperature is one of the most important factors to determine the curing speed. For every 10℃ increase in temperature, the chemical reaction rate can usually be increased by 1-2 times. If the product dried at room temperature (25℃) for 10-30 minutes is baked at 60-80℃, the surface drying can be shortened to several minutes, and the complete curing time can be compressed to 2-4 hours. On the contrary, low temperature (such as below 15℃) will significantly prolong the drying cycle and even lead to incomplete curing.

The role of environmental humidity
The influence of humidity on different types of three-proof paints is obvious. In the high humidity (> 75%) environment, solvent volatilization is slow, whitening or orange peel defects are easy to appear, and drying time is prolonged. However, the moisture curing type (such as some polyurethane or silicone modified products) needs moderate humidity (40-60%) to promote crosslinking, and too low humidity will delay curing.

The decisive role of coating thickness
The recommended dry film thickness of three-proof paint is usually 25-150μm m.. Every time the thickness is doubled, the solvent volatilization and heat conduction path are prolonged, and the curing time can be increased by 2-4 times. Too thick coating (> 200μm) is not only slow to dry, but also prone to problems such as incomplete internal curing and cracking. The coating amount should be strictly controlled in production to avoid one-time thick coating.

Core differences between types and formulations of three-proof paints
The curing mechanism of different chemical systems is different, and the drying speed varies greatly:

UV curing type: the fastest, several seconds dry, suitable for high-efficiency production line.
Solvent evaporation+room temperature curing type (acrylic acid is the most common): medium speed, low cost and easy to repair.
Thermosetting/moisture curing type (some silicone, polyurethane): longer time, but better high and low temperature resistance. In addition, the content of catalyst and the type of solvent in the product formula will also directly affect the curing curve.

Mastering these factors can help engineers optimize process parameters and significantly improve production efficiency on the premise of ensuring protective performance.

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