Application of decoration: Growth of digital printing on glass

Application of decoration
Skara KG in Würzburg has been specializing in digital printing on decorating materials and has since 2007 set up a new business segment: finishing of glass. Next to the application of decoration for interiors they have ordered and installed an industrial production line Virtu RS35 from Polytype for printing on glass, which enables professional growth.

Skara KG has been established in 1997 as digital printing shop and is today directed by Carl-Robert Kümpers and Martin Hack as managing stockholders. The company with 18 employees prints on decorating materials of up to a width of 250 cm on a dye-sublimation printer as well as on 3 latex printers in widths up to 165 and 260 cm. They produce typical posters for impinging light or transparency on photographic paper for brilliant colors and good contrasts or backlit films for display cases. Latex printers are used to print on wallpapers for internal and external use or for company name plates, car decorations and exhibition boards.

When the first Virtu RS25 flatbed printer for rigid materials was installed one could also produce large size posters up to 18/1 placards and twin-wall sheet  as a rigid alternative for printing on paper or expanded plastic slabs. Since UV-curable inks adhere extremely well to non-absorbing substrates it became possible to print on all kinds of plastics as well as on wood, glass and acryl.

Arbucomp: Facades and glass roofs
Arbucomp GmbH was established by Carl-Robert Kümpers as a company for the design of facades and roofs using special glass materials. The company merged with Skarpa KG in 2010.

Originally Mr. Kümper had studied law and became a lawyer, however, instead of joining a law firm he joined Okalux GmbH, a company established by his father and specializing in the production of special insulation glass for external applications. He has arranged for Okalux to realize, among other projects, the impressive glass roof of the Great Court of the British Museum, the glass shell of the Seattle Central Library and the glass façades of the Rathauspassage in Innsbruck.

After his father’s death he headed the company as Managing Director until 2005 and became afterwards independent with Arbucomp.  During the execution of his projects he has among others also worked with Skara because imaging on glass was very brilliant.  Carl-Robert Kümper compliments the concept of the Virtu design: “…the print quality of Virtu is outstanding”. However, the manual preparation of the glass  panels for printing turned out to be difficult  and error-prone. Therefore, he planned for the merger of the two companies the installation of an automatic industrial production line Virtu RS35 with a width of 350 cm and the sole possibility to comply with the high quality demands on printing on glass.

Security glass
The industrial printing on glass is realized on rear window heaters, thin layer solar panels and ceramic stove tops, however, they are only manufactured by specialized companies.
 Digital print shops use ink jet systems for imaging on float glass, tampered and laminated safety glass. The latter two are derived from float glass which is today’s most used structural glass for windows and facades.
 Toughened safety glass is a tempered glass which is heated up to 650°C and then evenly quenched with chilled air. When broken by external action it will crack into tiny fragments without sharp edges. Skarpa mainly use tempered safety glass which they purchase from a glass supplier.

The Virtu RS35 production line
Bernd Würth, the responsible product and sales manager at Polytype for Virtu printing systems for industrial digital printing explains the production line. He has composed the installation at Skara and developed the individual modules.

The entire production line comprises the following components: cleaning, flame treatment, primer application and printing unit plus the respective conveyors between the stations. Skara already owned a vertical cleaning unit for glass panels of up to 250 x 600 cm. After the cleaning the panels are placed on a mobile table which the operator will move to the loading conveyor from where the glass panels are transferred to the in-feed conveyor of the production line.  Bernd Würth explained the computer terminal where the print jobs are received from the pre-print department and conveyed to control the transport through the flame treating and primer stations.

In the pre-treating station the glass panel is treated by a gas fired open flame. This improves the evenness of the glass surface tension, it burns off residue or dirt which had not been removed in the washing station and the silane gas enhances the adhesion of the primer.

An accumulator or buffer conveyor transfers the panels into the primer station where 4 nozzles spray the primer at high speed onto the glass. Afterwards the glass is moved to a long positioning conveyor which serves as buffer and to put the panels at exact right angle XY position for the printer. A take-off conveyor takes the panels out of the Virtu RS35 from where they will be handled manually. The electronic control of the 20 m production line accounts for the dimensions of the various panel sizes for pre-treating and priming and sensors control the conveying speed. The high printing speed of the Virtu RS35 can thus be adapted to the in-time arrival of the glass panel for the following job order.
The Virtu RS printer
Real XY-printing! The printing table is covered with a blanket with reticular structure for the vacuum which transports the substrate through the machine. The entire print table is subdivided in square segments and in turn the strong vacuum will only develop under the actual substrate.

The print head is moved by very precisely working linear motors in both directions across the entire print width on the crossbar which in turn can also cover the entire length of the print table. This XY-technology enables to print one large or several small panels on the print table with the head approaching the panels at high speed.

An encoder-wheel takes the measurement of the movements of both the print head and the print table with a precision of one thousandth of a millimeter. On other machines this encoder-wheel is geared to the conveyor rolls and can, therefore, not detect slippage of the material.

Sparing consumption
Next to high precision the components of Virtu printers operate with sparing consumption. Only a few centimeters of the roll-material are drawn onto the print table and fixed by vacuum and, therefore, only a few centimeters of material are wasted at substrate changes. An ideal type of ink is offered for each application:
for roll-to-roll applications on flexible substrates Polytype Flex Ink; for combined roll-to-roll and flatbed applications Polytype Multi Purpose Ink and for printing on glass Polytype Vetro Ink. In order to reduce ink consumption for process printing the server converts all image data to RGB technology. Cleaning of UV-printing heads is only required at the beginning or ending of the shift or after several hours of production interruption and not as on other printing machines at the start of every new print job.

DRUPA news: Quantum printer
Virtu models print at high speeds with 6 colors plus white and a resolution of 1200 dpi resulting in very high picture quality with an ink consumption of 80 or 30 picoliter. With the development of new ink jet nozzles it is now possible to achieve the same picture quality with smaller jets at higher frequency resulting in two to four times higher productivity. The new “Quantum Printer” will be introduced at DRUPA 2012 and is for users who want a particularly high print capacity.

Printing on glass will grow
After our final discussion Carl-Robert Kümpers is convinced of the growth of digital printing on glass. “Photographic reproduction on glass already results in more brilliant images than on paper or at least we can match the quality”. Printed glass panels in the entry of his print shop confirm this statement. Nevertheless many customers still shy away from printing on glass and use acryl instead. However, it is not true that acryl is cheaper than glass. First of all glass is cheaper than acryl; second, larger size acryl panels need to be reinforced with aluminum to avoid fluttering.

Admittedly printing on glass can represent a lot of problems for many print shops because the manual cleaning, flame treating and priming cannot be done cleanly and efficiently enough and thus resulting in expensive waste. Skara has solved these problems with the installation of an industrial production line.

The two salesmen in Germany and Mr. Kümpers for the international market are booked to capacity – but growth can still be enhanced. The Web site of Skara AG is in particular very helpful by presenting the entire Skara production range with impressive pictures. Also see the Webshop  www.pretty-impressive.de.

 Mr. Kümpers states: “Digital printing on glass will make inroads in the sector decoration, because it is possible to realize individual concepts, production is more flexible than with silk screen printing, production is cheaper when many different colors and motifs must be printed because there are no costs for printing plates and in comparison with silk screen printing smaller lot sizes can be printed more economically”.