Will the polycarbonate (PC) film turn yellow when using UV photo oxidation resin?

1. What is the relationship between the setting parameters (Watts / inch) on the UV curing lamp and the readings we see on the radiometer (Watts / cm2 or milliwatts / cm2)? Watt / inch is the power unit of curing lamp, which is obtained according to Ohm's law, volt (voltage) x ampere (current) = watt (power); Watts / cm2 or milliwatts / cm2 represents the peak illumination (UV energy) in each unit area when the radiometer passes through the curing lamp. The peak illumination mainly depends on the power of the curing lamp. The reason why we use watt to measure the peak illumination is mainly because it represents the electric energy consumed by the curing lamp. In addition to the power received by the curing unit, other factors affecting the peak illumination include the condition and geometry of the reflector, the service life of the curing lamp, and the distance between the curing lamp and the curing surface.

2. What is the difference between millijoules and milliwatts? The total energy irradiating a specific surface in a certain period of time is usually expressed in joules / horizontal centimeter or millijoules / square centimeter. It is mainly related to the speed of the conveyor belt, the power, quantity, service life, state of the curing lamp, and the shape and condition of the reflector in the curing system. The power of UV active radiant energy irradiating a specific surface is mainly expressed in watts per square centimeter or milliwatts per square centimeter. The higher the UV energy irradiating the substrate surface, the more energy penetrating into the ink film. Whether it is milliwatt or milliJoule, it can be measured only when the wavelength sensitivity of the radiometer meets certain requirements.

3. Why does polycarbonate (PC) film turn yellow when I use UV photo oxidation resin? Polycarbonate is sensitive to ultraviolet light with wavelength less than 320 nm. The yellowing of the film surface is caused by the breakage of molecular chains caused by photooxidation. Plastic molecular bonds absorb ultraviolet light energy and produce free radicals. These free radicals react with oxygen in the air, which will change the appearance and physical properties of plastics.

4. How to avoid or eliminate yellowing on polycarbonate surface? If UV ink is used to print on polycarbonate film, the yellowing on its surface can be reduced, but it cannot be completely eliminated. The use of solidified bulbs added with iron or gallium can effectively reduce this yellowing. These bulbs will reduce the emission of short wavelength ultraviolet rays to avoid damage to polycarbonate. In addition, properly curing each ink color also helps to reduce the exposure time of the substrate under UV light and reduce the possibility of discoloration of polycarbonate film.