ween two layers of lamination film and glass.
Screen printing has the ability and versatility to give a monolithic flood coat, tints/transparencies from 10 to 90 per ...
ween two layers of lamination film and glass.
Screen printing has the ability and versatility to give a monolithic flood coat, tints/transparencies from 10 to 90 per cent, selective patterns with texture and multiple colours through sequential printing. When printing large format glass, the robustness of the machine and the flatness of the print table are important to ensure complete and uniform coverage. The mechanical stress and desired quality demand from processing larger and heavier sheets of glass are significantly greater than those experienced in other flat glass printing applications. The mechanical stability of the screen printing process leads to predictable, repeatable results for high volume printing. Screens are required for each image to be printed. Typically the glass is washed and dried directly before printing. For quality print production, there are three general types of printers.
A semi-automatic printer requires the operator to position the glass manually against adjustable stops, with the glass either on retractable ball rolls or an air floatation table. Once locked into position by vacuum on the table, the print cycle is automatic. A three-quarter automatic printer adds a conveyor thru the printer, allowing glass to enter and exit with-
out operator intervention while maintaining the manual registration process.
A fully-automatic printer adds registration (squaring) for the glass to automatically align the glass with the pattern to be printed.
Most systems are controlled via a PLC so that the operator can store recipes for quick recall and machine setup. A robust print head and bridge hold the squeegee in proper position for a uniform print. Anti-drip systems are important to prevent ink, particularly tints/transparencies, from dripping onto the image area during the flood stroke which applies the ink to the screen prior to the next print. High speed printers are capable of providing 120 and more prints per hour. Added features such as laser screen alignment, pneumatic screen clamping, and other options help to shorten setup
times. After printing the glass moves into a dryer, which for water miscible ceramic inks brings the ink to about 160°C. A cooling section may follow if the glass is to be offloaded or the glass can directly enter the tempering operation to fire the ink into the glass.
Digital printers can reproduce images, photos, art renditions, patterns, and textures in multicolor, providing excellent results when making short runs or when one-of-a-kind prints are desired. Print cycle time is significantly longer than a screen printer, although it can deliver solid colours to four-
colour processing in a single pass.
Digital printing is beginning to provide products for light diffusion, light transmission, energy efficiency, conductive surfaces, anti-skid surfaces, and sun control. Digital printers use special formulations of ceramic inks that are suitable for both interior and exterior projects with glass sizes up to jumbo. Print resolution is up to 720 dpi with edge-to-edge printing in a full selection of colours.
A reverse roll coater applies a full flood coating directly onto an uncoated or pre-printed image. Power in-feed and out-feed conveyors allow for easy interface with up- and downstream components.
A reverse roll coater typically has three rolls: the bottom or backup roll, the coating roll which has a rubber surface that may or may not be grooved depending on the wet thickness to be applied, and the metering (doctor) roll, to control the thickness of the coating applied to the coating roll. Roll coaters can also be equipped with pattern print rolls to apply continuous repeating patterns, dots, lines, and grids. Roll coaters are easy to maintain and clean. The most common application is spandrel glass used for obscuration panels, wall coverings and privacy partitions. Common inks include ceramic inks and silicone based inks.
Laminated glass, which originated for safety purposes, can create effects not possible with other techniques. Printed film, fabrics, metal mesh, and other objects that are open to the imagination can be laminated between layers of materials such as EVA or PVB. The thickness of the interlayer can be selected to mould around the thickness of the material being laminated. The interlayer material may also be direct printed and is available in a large selection of colours. One of the glass sheets can also be tempered to provide further strength to the product, so a combination of unique decorations and safety are characteristics of this product. Multiple layers of glass and decorative interlayers are also possible.
Acid etched glass, either alone or with colour decorations, can provide spectacular wall and partition effects. Ceramic ink can create etch-like and colour effects. Spot etching can be complimented with colour applied either digitally or with a screen printer, producing unique and spectacular effects.
The dryer/curing oven consists of a conveyor system combined with medium wavelength infrared and convection for efficiency and flexibility of paint types. The dryer/curing oven should be suitable for water-miscible, pine oil, terpinol, and silicone inks as well as speciality inks like enamels, epoxy, and many others. The dryer/curing system is generally located outside a print/coating room so as not to generate heat back into these rooms. The dryer/curing oven may utilize flat panel or tubular quartz medium heaters, with or without a combination of heated air. Zones are provided in direction of travel to allow the creation of ramp/soak processing. Edge zones provide extra energy for product edge losses, providing a uniformly heated product. For production requirements that have many widths of glass, cutoff zones can turn off unneeded heaters. The oven is fully insulated to retain the energy within with removable side panels and bottom panels for maintenance and cleaning. Common conveyors included driven rolls spiral-wrapped with stainless steel rope, open weave Teflon coated fiberglass/Nomex (TM-DuPont) belts, wire mesh belts, and cross bar conveyors. The roll system with the spiral-wrap stainless steel rope is the most robust and requires the least amount of maintenance. The stainless steel rope provides a cushion for the glass as well as thermally isolating the glass from the conveyor roll. Many belt materials wear over time and create residue that can end up in the coating on the glass. Exhaust is provided to remove the by-products evaporated during the process. A PLC controls the system allowing the operator to setup a recipe for later recall, to automatically setup the heater temperature zones, exhaust flow and conveyor speed.