Relationship between exposure time and light source in rotary screen printing

1. Exposure time

The rotary screen exposure time involves the problem of exposure sensitization. In the process of plate making, overexposure will make the photosensitized film excessively sensitized, and the film will harden. The formed unexposured area will have poor expansibility and will not be easy to wash. It will cause the pattern to be difficult to appear. The lack of exposure will result in insufficient photosensitivity of the photopolymer. The film is tender and easy to wash out, resulting in the appearance of trachoma, zigzag patterns, in severe cases, the film will fall off. In short, mastering the correct exposure time is a very important process for the photographic process, which is associated with the exposure light source and the photosensitizer.

2. Exposure light source

Exposure light source refers to a light source that can cause chemical and physical changes in the photo-resist layer in a relatively short time during the exposure process. Choosing the right light source can reduce the exposure time, speed up plate making and improve plate quality. The cross-linking reaction of the rotary screen photoresist mainly takes place after absorbing ultraviolet light. The exposure light sources used are all ultraviolet light sources, and their spectral characteristics and intensity have a direct relationship with the plate making effect. Therefore, when selecting the light source, it is necessary to consider matching with the absorption wavelength of the photosensitive material used in order to obtain good results. The rotary screen photosensitive material is sensitive to ultraviolet light in the wavelength range of 300-400 nm, and the types of light sources outputting relatively abundant light in this wavelength range include high-pressure mercury lamps and iodine-neon lamps. The wavelengths generated by these two types of light sources are more consistent with the absorption wavelength of the photosensitive material of the rotary screen, and can exert a higher light-sensing efficiency in the plate-making exposure, so that the photosensitive adhesive produces light-curing in a short time under light irradiation.

Source of information: Shanghai Academy of Textile Science