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Screen Printing



The age-old process has become easier to incorporate, allowing more converters to enter new and different markets.



By Steve Katz, Editor



Published September 1, 2012
Related Searches: Label printing Platemaking Label industry Rotary screen
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A wine label printed with Kocher + Beck’s TecScreen
The general public associates screen printing, or “silkscreening,” with the garment industry, not so much packaging and label printing. An internet search of the terms will return businesses that specialize in T-shirts, embroidery, custom clothing and the like. However, it is also now commonplace to see screen printing applications used in fine art, commercial and package printing.

In order for brand owners to compete in certain highly competitive markets – wine, beauty, specialty foods – image is everything. And the screen printing process provides effects that can bring a label to another level. 

The printing technique is old, versatile and offers a range of graphic advantages over other print methods. 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.

Screen printing allows for printing on substrates of any shape, thickness and size. It allows for printing front and backside of a clear label to ensure that lettering shines through, and clear labels on dark-colored bottles or tubes are often printed with screen white. 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. Also, gold and silver screen inks are often used in lieu of foil.

Most recently, the technology has been adapted for more advanced applications, like printed electronics, where it is being used in laying down conductors and resistors in multi-layer circuits using very thin materials as the substrate.

The process continues to evolve, and  its become a mainstream form of advanced product decoration. Screen machinery and equipment suppliers are doing their due diligence to not only improve upon the technology, but also make it more affordable.

Gallus Rotascreen and Screeny

A Gallus Rotascreen unit in an RCS 330 press

Heinz Brocker, Gallus’ vice president, Screen Printing Business, has been responsible for all global screen activities for St. Gallen, Switzerland-based Gallus Group since the 1980s, and was a member of the team that invented the company’s well-known Screeny printing plates. He points out that in today’s label market, replacing an existing print station with screening is a growing
trend. “Screen units can easily replace a printing unit of another process, for example, the plug-and-print concept on the Gallus EM280 or Gallus RCS, where a flexo or offset unit can be replaced by a screen unit,” Brocker explains. “The operation is on the same level as the other main processes, and is not on top of other printing units where the operator needs to go up a ladder to set in the screens, make adjustments and monitor the quality.

“These screen units have the same MMI operation procedures (with touch screen) like the other processes for easy operation, there’s just a little difference in operating between the various printing processes,” he adds.

Brocker emphasizes that adding screen printing capability is a great way for a label printer to enter markets that otherwise would not be accessible. “By combining the different processes, you can make really attractive effects, and give a printer the opportunity to go into new, high demand market segments.”

Screen printing applies more ink then all other processes. Brocker says, “From 5 – 300 micron (offset, digital), less than 1 micron, digital inkjet with special jet nozzles up to 3 microns, or even more if using an additional head with a special high volume jet nozzle for varnishing. Transparent labels very often need a high coverage backing. Consumers like the relief effect that screen provides, the gloss effect, and the deep color intensity. Security features or color-shifting effects can be achieved by applying ink with very large size pigments. And the relief effects by thick film of transparent varnish are ideal for printing Braille characters.”

Gallus offers label converters Rotascreen, a comprehensive rotary screen system. The system consists of its own screen printing units which can be easily integrated into modular Gallus printing presses.

Screeny printing plates, developed specifically for the label industry and manufactured by Gallus, offer a wide range of products for every need. For printing of very fine images to coarse Braille characters, the company has different product lines for both conventional plates and digital plates. The Screeny Standard line is designed for conventional short runs. The Screeny S-Line is for robust, long lasting and high speed printing and is ideal for long runs and multiple re-use for repeat orders. Screeny Digital Plates are coated with an ablation layer which is laminated onto the photopolymer. The ablation layer is applied digitally by a point laser. The screen is then exposed, washed out and assembled in the conventional manner.

“The demand for screen printed products is increasing. Screen technology offers huge potential for creative label solutions and gives marketers lots of possibilities for differentiation. Emphasis on branding is very important in markets with a lot of the similar products,” Brocker says. “To make screen technology more competitive, the main producers of screen plates are offering better products for longer runs and more re-use. Gallus as a system supplier offers one-stop shopping and develops continuous improvements on all system elements.” 

Kocher + Beck’s TecScreen
Kocher + Beck, headquartered in Pliezhausen, Germany, focuses on allowing screen printed labels to become a more cost-effective option by implementing TecScreen, the company’s high quality screen printing plates.

John Fehrenbacher, product manager, TecScreen, says costs are always a major issue in the label market, and it’s also an issue when it comes to screen printing plates. “Kocher + Beck gives label printers the opportunity to produce the screen printing plates on a price level without blowing up the frame. In this case, our customers are able to use the advantages of screen printing at an affordable price.”

TecSreen has a number of design characteristics that make it, literally, stand apart. Available in most common roll widths, it features a high-contrast red coating that facilitates visual inspection and increases reliability. Special roll dimensions and sheets are cut to size at the request of the customer. A special processing technique is used for the formatting of sheets, which is based on the high precision production of K+B flexible dies and permits tolerances of less than 1/100 mm. “The register accuracy achieved by this is highly valued by the customers during welding of the screens and subsequent assembly,” Fehrenbacher says.

TecScreen grades offered cover all common printing tasks and are available for all machine types on the market. The product range includes wire cloth grades for fine line and text work, for example, those found in pharmaceutical labels. There are several grades with differing resolution and color application quantity to choose from for the classic screen printing applications such as a white background or the printing of decorative elements. “Spot coating and the printing of relief varnishes are enabled with coarser grades. The TecScreen product range is also an appropriate solution for printing Braille and hazard symbols,” Fehrenbacher adds.

TecScreen can be processed conventionally with films in a continuous printer, while digital UV imagesetters can be used for imaging. Kocher + Beck offers exposure tests to determine the exact exposure time in conventional imagesetters. In addition, it is possible to determine the amount of exposure with the aid of a UV measuring device in order to establish the exposure times under standardized conditions.

“Another important aspect of TecScreen is our offering of complete peripheral screen equipment. This includes the consumables such as adhesive, adhesive tape, screen filler and welding threads and the necessary devices for the screen production such as the dryer, washout box, welder terminal and assembly tower,” Fehrenbacher says.

Kocher + Beck offers customers the option of manufacturing the screens in-house to those customers who up to now have had to buy incomplete screen cylinders. This increases the productivity on the printing machine, as the platemaking only takes, on average, about 30 minutes to produce.

Stork Prints
Using Stork Prints’ Rotary Screen Integration (RSI) technology, rotary screen printing can be combined with other printing techniques, including flexo, offset, gravure and letterpress. “Rotary screen printing offers the opportunity to add a new dimension to your label printing capabilities,” states Rieks Reyers, marketing and sales manager for Stork Prints, Boxmeer, the Netherlands.

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. Reyers emphasizes that Stork can accommodate most label press sizes and scope of operation. “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,” he 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 Stork Prints’ Flexible Positioning System. The system allows converters to move the RSI module to any print station on press.

Reyers notes that while the types of screen applications have evolve to include RFID, solar cells, mirror heating, bank notes, brand protection and scratch offs, the overall trend points to shorter runs. “Clearly, the runs are getting shorter. And we have responded by introducing RSI units for semi-rotary and RSI units for Rotaplate (on roll),” Reyers says.

Stork’s RSI units are easily shifted to the position where screen printing is needed using an optional sliding rail. The print units reach speeds of up to 100 m/min, and can be controlled through the main panel of the press. This provides simultaneous, centralized monitoring of all rotary screen positions alongside other printing and converting operations.

In addition to the units, Stork also offers its RotaMesh and RotaPlate screens. The RotaMesh screens are for RSI systems, and the re-usable RotaPlate screens are for non-Stork Prints systems. Both screen systems feature the ultra-stable, electroformed pure-nickel construction, offering easy handling, high stability and longevity at relatively high speeds. RotaMesh and RotaPlate applications include tactile, glitter, holograms, opaque whites, adhesives, glow in the dark, UV-active, thermo-sensitive, iridescent, security and brand protection.



Telstar’s custom retrofit units
Twenty years ago when Tom Kirtz started Telstar Engineering, one of his first press retrofit projects was building a rotary screen add-on to a customer’s existing Mark Andy 2200 press. Over the ensuing years, rotary screen has been an important and steady part of the Burnsville, MN-based company’s wide range of retrofit decorating and converting unit options. Three screen systems have been shipped and installed this year with another soon going into production. “These are no longer just for narrow web label production. We are getting orders for rotary screen sizes up to 28” from customers who want to improve the performance and capabilities of their existing equipment,” Kirtz says.


Custom designed for 22" wide screens, this retrofit unit shown
prior to shipping, operates right-to-left operation, a Telstar
exclusive.
While rotary screen came into it’s own as a way of providing a heavy, opaque background for other decorating techniques, Kirtz says it remains the standard for this application even on the newer clear and “no-label” look products popular today. It is also used for specialized applications such as conductive inks for electronic patterns, thermochromatic and metalized inks, heavy deposits for special effects, tactile deposits of UV curable inks, specialty chemical applications; varnish over hot foil, medical salves and ointments for “patch” products, Braille inks along with other raised tactile surfaces and thixotropic inks.

Telstar points to its CadToGo on-site engineering service as a major factor in the continuing strength of its rotary screen retrofit units. “Virtually any brand of existing or new press can be outfitted with a retrofit machine from Telstar and can be bridge- or rail-mounted, placed within a stretched press path, or can be installed for first-down application. The retrofits accommodate woven mesh screens from suppliers like Stork, Kocher-Beck, Gallus and more,” he says.
Kirtz points to an industry exclusive feature of Telstar rotary screen units: they are available in both left-to-right and right-to-left operation. “Pre-engineering a custom-designed unit also means there is very little downtime at installation,” he says.
 

A Mark Andy LP3000 with three
Telstar rotary screen print heads

In continuing support of its rotary screen unit customers, Telstar also offers a complete line of peripheral equipme=nt necessary for quality performance and production including seamers, shear punches, squeegees, rings and gears. Its ink pumps can be both standalone single units or stackable. The pumps are reversible for easy cleanup.

“We see rotary screen as a staple product in the label industry, especially now that retrofit equipment has become widely recognized as a way to get more out of existing press equipment. It allows many printers the chance to compete in markets they were not able to reach,” Kirtz adds. 


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