The analysis of the mutual "permeation" of dark printing colors with reactive dyes is generally believed that the printing paste of reactive dyes (especially dark colors) has high dye concentration, strong alkalinity, and a large amount of urea and inorganic salts. Therefore, it is required that the photosensitive adhesive film be alkali resistant to avoid the occurrence of sand holes and improve the printing resistance.
However, according to extensive theoretical and applied research, the above viewpoint is not comprehensive enough. We believe that the main reason for the above-mentioned problems in the application of diazo photosensitive adhesive screen in active dark printing is that the active groups in the active dye contain monochlorotriazine (X and K types), vinyl sulfone sulfate (KN type), and double reactive groups (M type). When these reactive groups react chemically with the hydroxyl groups in PVA on the surface of the diazo photosensitive adhesive screen that has not been fully cured by light, and adhere to the screen, they are easily prone to printing defects when squeezed by a scraper or magnetic rod. The basic principle can be expressed by the chemical reaction equation of the diazo photosensitive resin system as follows:
If the photopolymerization is not complete or the high-pressure water gun cannot rinse thoroughly after development, the hydroxyl groups in the remaining PVA on the screen will react chemically with the active groups on the reactive dye, forming ether bonds and binding to the surface of the screen. Repeated squeezing by scrapers or magnetic bars during printing can cause slight loosening of the adhesive film, resulting in the active paste on the screen surface gradually seeping from the scraping surface to the printing surface, and can easily cause a large number of sand holes, leading to poor printing durability and fastness.
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