Study on Properties of Water-Resistant Screen Printing Photopolymers (II)

Fig.1 and Fig.2 are the UV spectra of the diazo-resin and the UV spectra of the diazo-resin of PVA and PVAC, respectively. From Fig. 1, it can be seen that the diazo resin has a high intensity absorption peak at 373 nm, but as the exposure time increases, the intensity of the absorption peak decreases.

The exposure times of the three spectral lines in Fig. 2 are 30 s, 1 min, and 3 min, respectively. It can be seen from the figure that the latter two lines overlap, that is, as the exposure time is longer, the absorption peak of the photoactive group weakens. The photoreactive peak of the photosensitive polymer was 367.2 nm and matched with the wavelength of the emitted light of the high-pressure mercury lamp used.

2.2 Study of Photosensitivity

The PVA was formulated into a 20% aqueous solution, and the PVAC was formulated into a 25% emulsion. The thickness of the film was 11 μm. The photosensitivity characteristics of the photosensitive polymer materials with different ratios of PVA and PVAC as film formers are shown in Fig. 3~Fig. .8. The relationship between composition and sensitivity of film formers is shown in Tab.1. From Tab.1, it can be seen that when the PVA solution:PVAC emulsion is 4:6, the sensitivity of the photoresist is highest, and when the PVA solution content is higher than 40% or lower than 40%, the best sensitivity cannot be achieved. This is because when the PVA solution content is less than 40%, the content of the hydroxyl group in the system is small; and when the PVA solution is higher than 40%, the excess hydroxyl group is not deprived of hydrogen by Cl and no oxygen radical is formed on the PVA chain. Therefore, this part of the excess PVA does not participate in the photochemical reaction and is still water-soluble and is dissolved during the development process, resulting in a decrease in the residual film yield, and thus the sensitivity is not high.