The Screen Option
While several decorating techniques are employed by glass and ceramic decorators, one of the most popular methods is the process of screen printing. This ancient art (often known as silk screen printing) may evoke visions of T-shirts and athletic wear, but screen printing is actually one of the most versatile, cost-effective and high-quality processes available for the imprinting of ceramics and glass. Objects ranging from small containers and coffee mugs to huge architectural panels-or any other large, thick or irregularly shaped object-can be decorated via screen printing.
Still, few producers have ventured into what they may consider an expensive and technically challenging process. "The fact of the matter is that screen printing, for all the dramatic effects you can create with it, is a fairly simple and surprisingly affordable venture," said Michael Green, president of The A.W.T. World Trade Group. "A glass or ceramic producer can be up and running a screen printing operation in a relatively short period of time and at a comparatively modest capital outlay."
Process BasicsScreen printing uses a stencil that is attached to or embedded in a fabric or metal mesh (the "screen") stretched across a frame. The ink or paste (frit) passes through the portion of the mesh not masked by the stencil and is deposited directly onto the substrate. In addition to the frit regularly used by architectural and large-scale ornamental glass producers, enamel-based inks and satin etching are very popular among ceramic decorators.
Unlike other printing processes, the type of ink and its viscosity is not limited by an intermediate transfer to a printing plate or roller. The stencil controls where the ink will be deposited, and the size of the openings in the mesh determines what type and how much ink or paste will pass through.
The stencil itself is created with a "film positive" of the artwork, usually generated through a digital printer. (Some screen printers employ a relatively new process of creating the screen directly from a computer, but that system can be expensive and is more appropriate for the highest-volume screen producers.)
For the traditional approach, the film positive is placed over a camera-ready screen frame that has been covered with stretched fabric (mesh) and coated with a light-sensitive liquid emulsion. When the frame is exposed to an intense light source, the screen areas not masked by the image on the film positive harden, while the emulsion beneath the image remains soft enough to wash out after exposure. That leaves the fabric or mesh "open" in the image area, creating a stencil where the ink or paste passes through and is applied directly onto the substrate.
Benefits and ApplicationsBecause the stencil and mesh control exactly where and how much ink will be deposited, screen printing is not subject to the limitations of other processes, such as plate, roller, or even digital printing. In addition, screen printing is much faster than some other decoration methods, with throughput of dozens or even hundreds of impressions per hour being quite common. It also allows decorators to combine glazes, precious metal and iridescent inks to create one-of-a-kind effects. Some applications that incorporate screen printing include:
- Glass and ceramic decorating: beer/liqueur glasses, candle jars, coffee mugs and dinnerware
- Automotive: windshields, rear window defoggers and specialty glass for custom cars
- Gaming: arcade games, casino machines and amusement park rides
- Appliances: stove tops, oven doors, range consoles and microwave doors
- Furniture: mirrors, decorative room dividers and rec room furniture
- Industrial: control panels, plasma displays, printed circuits and solar cells
- Architectural glass: exterior glass panels, interior decorative glass, and shower and patio doors
Another factor to consider is the quality of the image. With screen printing, the image is applied directly to the glass, providing a much cleaner look with a lower profile and avoiding the chance of the label being removed or damaged.
Another important market for decorators is candles. To add to the elegance of the container and increase sales, candle producers are increasingly using decorative glass to package their products. Popular candle jar themes, such as snowflakes and other holiday images, are often achieved through a combination of satin etching and screen-printed white enamel, an effect that can be difficult to achieve using other methods.
Flat glass and industrial ceramic manufacturers also turn to screen printing for applications in the appliance, automotive and architectural markets, including microwave and oven doors, stovetops, and washer and dryer doors. In addition, screen printing can provide a mask for etching intricate patterns on glass. Printed circuit boards and other computer components can also be produced or imprinted using specialized, ultra-fine, high-tension meshes (often stainless steel) to print on the delicate and wafer-thin ceramics and composites used in electronics manufacturing. Rear window defoggers also are likely to have been created with a conductive paste applied by the screen printing process.
The flexibility of screen printing may be best illustrated in some of the latest developments in creating solar panels. Nanoparticles combined with dyes are screen printed in colorful designs to yield energy production integrated with facade decoration.
For larger applications, such as exterior glass panels for office buildings, screen printing also presents an ideal solution to the problem of applying decorative or functional coatings. Flat glass screen presses with printing tables as large as 10 x 25 ft can be produced with vacuum-controlled hold-down and blowback for floatation and transportation. In addition to the presses, special transport systems with non-abrasive guides and vacuum-assisted printing surfaces can hold down, lift and move even the heaviest of glass without scratching or other damage. Once the glass has been printed, companion dryers with a variety of quartz, UV and gas heating options offer quick and complete curing.
Automation OptionsWhether producing large architectural panels for commercial buildings, smaller panels for residential use, solar panels, automotive glass, containers or dozens of other applications, screen printing, curing and transport systems can be readily inserted in a glass production line to keep the entire manufacturing process flowing smoothly. "In addition to substantially increasing efficiency, automating the glass decoration process minimizes handling of the product and lessens the chances of breakage, scratching or other damage," says Green.
Automating the screen printing process can entail something as simple as a transport system to move the substrate into and out of the printer, or as elaborate as a full line that transports the glass into a squaring process to facilitate registration, actual printing, transport to an inspection station, and then on to drying (curing) and cooling and the rest of the production process. For multicolor printing, presses and dryers can be daisy-chained for as many colors as required, or imprinting can be accomplished with carousel-type presses that alternate print stations with UV curing units for several colors on the same machine.
"One of the keys to automating glass decoration is the flexibility available in designing the layout for the operation," says Green. "We have built systems for restricted spaces in which the product had to move from one room to another during decoration, and even, in some cases, taking a right-angle turn along the way."
Technological AdvancesRecent improvements in ink chemistry have also dramatically improved adhesion to non-porous and usually high-gloss surfaces such as glass. In recent years, for example, the industry has developed two-part epoxy inks that give the raised effect of leaded glass after baking, as well as polyester-based inks and solid UV inks.
A press and curing combination capable of printing an image as large as 7 x 14 ft was recently developed.* That unit, which was custom-made for a major glass producer, was designed to handle glass slabs weighing 700 lbs and more while minimizing the amount of manual intervention required to move them through the printing and curing process. The quartz dryer was also custom-adapted for handling especially thick glass panels, with an under-glass heat source added to the conventional overhead unit to guard against potential warping or cracking due to uneven heat distribution.
"With such a broad range of equipment available, any glass or ceramic producer should be able to configure and operate automated decoration equipment that will contribute to increased profits, greater efficiency and enhanced customer satisfaction," says Green.
For additional information regarding screen printing, contact A.W.T. World Trade Inc. at 4321 N. Knox Ave., Chicago, IL 60641; (773) 777-7100; fax (773) 777-0909; e-mail firstname.lastname@example.org; or visit www.awt-gpi.com.
*Developed and manufactured by A.W.T. World Trade Inc.