Managing variables associated with the substrates you use is critical to quality. Find out how to work with some popular, but picky, materials.
Thermoplastic (TP) inks, also called hot-melt inks, are solid at room temperature and require heat to become printable. The inks are pre-heated from 149-167°F, and the molten enamel is then poured into a metal screen that is heated via an electric current. The molten ink acts like conventional ink as it passes through the screen, but once it strikes the colder glass, it solidifies and returns to a waxy state. TP inks are nicely suited for use on automatic, multicolor presses. Once printed, however, the multicolor image is somewhat fragile and still requires the organic pigments and resins to be fired at 392°F in a lehr.
The big advantage of fired inks is that they fuse to, and become part of, the substrate. Metals such as gold, silver, palladium, and platinum can also be used as pigments and applied to glass and ceramics for decorative or industrial applications. The major disadvantage is the complexity and cost of operating gas-fired lehrs.
The method of printing UV inks is the same as printing onto plastics and board. Organic pigments and resins are cured by UV radiation. UV curing uses far less energy than a lehr and the ink cures instantly. Adhesion is excellent on pre-treated glass and
good on untreated glass. UV ink is not as tough as fired enamels, but it is an acceptable alternative for many applications.
The most effective method of applying complex, multicolor designs is to print onto transfer paper and apply the graphic either as a water-slide or heat-applied transfer. Image quality is second to none, and you can use many colors. Four-color process requires a white background, which may be printed.
Automotive applications are significant in glass printing. Shades and filters are printed on the windshield edges, as are electrical circuits (defrosters) and antennae. Architectural glass is another area where printing is popular. Screen-printed effects can generate significant added value to buildings. Even internal partitions imaged with exotic designs can transform the working environment.
Johnny Shell, SGIA’s vice president of technical services, directs and coordinates the activities for the Association’s Technical Services department. He also teaches SGIA workshops, writes technical articles for the SGIA Journal, and conducts seminars.
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