Screen printing is one of the oldest forms of the print process. Historians date its first usage to China’s Song Dynasty, which lasted from 960 to 1279 CE. Centuries later, the process was given its first patent, in 1907, to Englishman Samuel Simon. Originally a profitable industrial technology, screen printing was eventually adopted by graphic artists as a convenient method for duplicating work, and over the years, it has only gained in popularity.
The process consists of three elements: the screen, which is the image carrier; the squeegee; and ink. Flat screen printing uses a porous mesh stretched tightly over a frame. The screen is placed over the substrate and the ink is deposited at one end of the frame. The squeegee moves over the course of the screen, forcing the ink through the fine mesh openings and onto the substrate. In rotary screen printing, the screen is formed into a cylinder. The squeegee is mounted in a fixed position inside the screen cylinder. As ink is introduced onto the squeegee, the cylinder rotates and the ink is pushed out of the screen onto the moving substrate.
The printable image is created on the screen through exposure of the image in prepress. Unexposed screens contain a coating through which ink will not pass. Exposure and subsequent washout removes the coating from the image area, through which the ink will pass. The diameter of the threads and the thread count of the mesh will determine how much ink is deposited onto the substrates.
Today it’s common to see screen applications used in both fine arts and in commercial printing. Screen printing’s versatility is evident in how it allows for printing on substrates of any shape, thickness and size. Also, a greater thickness of the ink can be applied to the substrate than is possible with other printing techniques, allowing for the creation of effects such as tactile and Braille, glitter, scratch offs, and raised text. Gold and silver screen inks are also used in lieu of foil.
While perhaps the general public thinks of garments when it comes to screen printing, the technique is used in a wide range of markets, the label industry included. In recent years, it has even been adapted for more advanced applications, like printed electronics, where it is used in laying down conductors and resistors in multi-layer circuits using very thin materials as the substrate.
In the label industry, converters can incorporate screen print units into existing presses. They can also buy standalone screen printers. What follows describes just some of label industry suppliers’ screen printing products and services.
“Rotary screen printing offers the opportunity to add a new dimension to your label printing capabilities,” says Rieks Reyers, marketing and sales manager for Stork Prints, Boxmeer, the Netherlands. Reyers notes that rotary screen printing can be combined with other printing techniques, including flexo, offset, gravure and letterpress using Stork Prints’ Rotary Screen Integration (RSI) technology.
The Stork Prints RSI module is a self-contained, single-color printing unit designed for easy integration onto an existing press, and the units are compatible with most any press maker’s machinery. “We have dedicated screen units for many OEM partners, including Mark Andy, Nilpeter, Omet, MPS, Codimag, just to name a few. These units are mechanically driven. We also have universal screen units that can be mounted on any reel-to-reel press,” Reyers says.
All of Stork’s universal units have their own servo drive. RSI standard units have a repeat of 12" to 25¼", and RSI compact units have a repeat of 12-18". “This allows slow rotation when the press has stopped, a great advantage for operators,” notes Reyers. “The servo drive, in combination with the optional automatic register control, is another great feature for operators. The equipment is versatile – just replace the screen for another application.” UV, water-based and solvent-based units are all available.
Depending on the press, RSI units may be fitted in a fixed position or on a cassette frame. For optimal flexibility, the RSI can be mounted on a Stork Prints’ Flexible Positioning System. This patented system allows converters to move the RSI module to any print station on press.
Reyers says that while, traditionally, screen printing was used for opaque white – and that is still an important application – the number of applications has increased. Today, he says, screen printing is being used in the manufacture of RFID antennae, solar cells, glitter effects, mirror heating, bank notes, brand protection, scratch offs, and gift vouchers.
While the types of applications have evolved, the length of the runs is also changing. “Clearly, the runs are getting shorter. And we have responded by introducing RSI units for semi rotary and RSI units for Rotaplate (on roll). Here, we are able to reach 80 micron lines or text,” says Reyers, urging converters: “Don’t be afraid of this great, versatile technology. Let us help you use it.”
Gallus, St. Gallen, Switzerland, is a company that is immersed in the screen printing market, counting both consumables and machinery among its offerings.
The Gallus’ Rotascreen is a modular system, where the screen printer is platform mounted and fully integrated into Gallus machinery. “The RCS 330/430 screen unit is exchangeable with flexo, offset, and hot foil embossing, at the touch of a button without breaking the web,” says Brian Bishop, president of Philadelphia-based Gallus Inc. “The presses computerized touch screen control system automatically recognizes the unit when slid into position, sets the squeegee pressure, and sets both lineal and lateral register without running material through the press for optimum waste management.
Gallus RCS 330 Rotascreen
In addition to its screen printer, Gallus long ago developed the technology to produce the screens themselves – Gallus Screeny – and offers a complete system designed to help printers cut their operating costs. Based on a customized needs analysis and with the help of a cost-benefit analysis, the company says it will help converters use rotary screen printing to optimize efficiency throughout the value added chain. “In view of the ever fiercer competition within the label printing industry, label printers are under constant pressure to improve their production strategies. Efficient processes, effective cost control, a high level of innovation, consistent high quality, excellent reliability and minimal waste are now more than ever the cornerstones of business success for today’s label printers,” Bishop says.
“Less than 30 minutes is required to get from the reprofilm to the ready-to-use screen,” says Bishop. Screeny Digital, also offered by Gallus, creates the image on the screen using digital ablation, and does not require film to create the image.
Gallus Screeny is supplied in a sensitized, light protected format and can be stored for at least 12 months. “In reel form, Screeny ensures maximum flexibility – in a minimum amount of space and with little stock,” says Bishop.
The Screeny Process Efficiency Package (Screeny PEP) was developed to help label printers improve efficiency and reduce their total operating costs, says Bishop. “It is split into four sections – imaging, developing, assembly and printing, and postpress. For each section, Gallus Rotascreen offers tried-and-tested solutions to lower total operating costs.”
The Screeny PEP comprises a number of core elements and takes into account the specifics of each individual situation. “It takes into account the existing equipment and options available on-site to propose customized solutions, and implements the best solution based on a sound cost-benefit analysis,” Bishop says.
Spartanics , Rolling Meadows, IL, USA, has recently entered the screen printing market following its partnership with Germany-based Systec. Together, the companies have launched the Spartanics-Systec Fineprint Flatbed Screen Printing Line, designed for enhanced throughput in roll-to-roll screen printing. Applications include UV and chemical resistant labels, high-end cosmetics labels, transfers for printing packaging and other label/packaging applications. The system also makes it possible to manufacture flexible photovoltaic materials of higher quality and lower cost.
Mike Bacon, VP sales and marketing for Spartanics-Systec, says that another key feature of the system is the contact dryers, which, he says, provide up to 70 percent more efficient drying times compared to conventional heated air methods. “There are many applications where traditional air drying systems continue to make for a good investment. They are typically 15 percent cheaper than contact dryers, which is a deciding factor for many businesses. However, when you peel back the benefits of the contact dryer over traditional air drying equipment, the initial investment savings quickly go away,” Bacon says.
Conventional air drying ovens blow heat over the surface of a web or sheet of material. Here, the inks harden by drying, or evaporating the solvent out of the ink. “There are three factors that contribute to how fast they will dry using an air dryer; temperature, amount of air flow and air humidity,” Bacon explains. “A contact dryer, however, uses a heated platen to dry the ink from the bottom to the top, therefore capturing heat energy below the surface of the printed substrate. Since many inks require different temperatures and drying times, the more consistent and concentrated the heat the better and more efficient the drying process,” Bacon says.
Bacon emphasizes that a key advantage of contact drying is that it eliminates “skin effect” on the ink, because the drying begins below the surface of the ink and finishes at the top. “Once the heated plate reaches the desired heating temperature, it can be up to 70 percent more efficient because the heat is captured and does not require constant energy to the heating elements. The heated platen usually contains three heating elements within the system. Generally, the third heating element at the end of the dryer requires much less energy because the heat remains constant from beginning to end. A traditional hot air dryer consistently requires the same amount of energy throughout the dryer because of the loss of heat when blowing air across the surface.”
Another benefit of a contact dryer is the time required to dry the ink. Bacon points out that since it can dry inks more efficiently and faster than a traditional air dryer, the floor space required is reduced. “With square footage within a facility at a premium, the ability to shorten the overall footprint of a screen printing line can save businesses a significant amount of money. It is important to recognize that there are alternative technologies in the field that are offering energy efficient alternatives,” says Bacon.
Delta Industrial, Minneapolis, MN, USA, can integrate a variety of process modules into a complete web converting system to meet specific application requirements. And screen printing is one of those processes.
“It expands the printer’s potential market,” Michael Wagner, sales at Delta Industrial, says of screen printing. “It allows a printer to lay down a greater coat weight of ink or adhesive or coating, giving them the ability to print a greater variety of products including beauty products, heavy coatings for scratch-off or raised print, electronic circuits and RFID,” he says.
Delta Industrial integrates screen printing capabilities into its computer-controlled, servo-driven rotary converting equipment. “This allows for continuous web motion, precise registration, and tension control that Delta machines are known for. Our customers like the flexibility of running rotary screen-printing in line with diecutting, laminating, laser cutting, packaging or any other manufacturing processes,” explains Wagner. All of Delta’s systems are custom designed to meet the customer’s specific application requirements.
Wagner points out that there’s been an increase in screen print technology with the evolution of the printed electronics and RFID markets, and the company’s machinery keeps pace with the changing marketplace. He says, “Delta is unique in our flexibility. We have the ability to integrate screen printing with a variety of other converting capabilities. Delta's engineering experts can help customers discover new possibilities and design equipment for their future needs while allowing opportunities for future growth in new markets.”
Telstar screen unit
Recent applications for the Telstar line of servo-driven rotary screen retrofit units, in addition to label printing, include printed electronics, patterned gaskets, patterned adhesives, and magnetic slurries. Telstar’s screen units are available from 7" to 30" wide with repeats from 12" to 32", printing either left to right or right to left. “A unique feature of the Telstar units allows the use of Gallus, Kocher + Beck, and Screen Printing Systems woven mesh screens as well as Stork sleeves,” says Tom Kirtz, Telstar’s president.
“No special fixtures are required for mounting various brands of screens to the Telstar end rings. Whether it’s a bridge mount, rail mount, or press split, Telstar’s on-site Cad-to-Go services assure a proper fit and function from the very beginning of a project, keeping downtime in control,” Kirtz says.
Along with rotary screen retrofits, Telstar also manufactures units for rotary die, Cast & Cure, hot stamp, hot melt, cold foil, pattern print, decoration, couponing, flexo, unwind/rewind, coating, laminating and more. Telstar manufactures all of its full line of retrofit units as well as full frame, custom converting presses in the US in its Burnsville production facility. It also has a test press on site for R&D as well as product and materials testing.