Inkjet printing technology lends itself to many industrial applications because a droplet of ink can be placed on a substrate without the printing device having to make contact with the surface of the receiving material. With current inkjet print head technology, many materials can be jetted at high frequencies allowing both high resolution and high productivity printing on a variety of surfaces. 

 

Over the last few years this has been especially important to the production of decorated ceramic tiles. The conversion from printing the design on tiles using the traditional laser etched silicon drum analog printing technology to inkjet array printing technology has been very rapid because inkjet printing offers enormous economic advantages. The evolution of the processes used to print ceramic tiles started with dye-sublimation transfer printing, then advanced to direct printing with solvent and UV inks, to the incorporation of inkjet printing into the production lines of the world’s ceramic tile manufacturers. 

 

Digitally printing ceramic tiles with inkjet technology has come a long way. This example, printed using Durst Random Design Printing Technology, uses a different design on each panel, creating a more organic look. (Image courtesy of Durst US. Source: durst-online.com)

DYE-SUB PRINTING

Soon after the development and widespread deployment of piezo inkjet technology on the desktop by companies like Epson in the mid 1990s, companies like Sawgrass Technologies began introducing water-based dye-sublimation inks for transfer printing to ceramic tiles as well as other substrates that were prepared to receive the dyes. With this approach, the inks are printed on transfer paper and heat transferred to the tiles. The tiles have to be specially prepared with a coating in order to receive the dyes. The coating allows the dyes, when heated, to penetrate the surface of the tile and to remain fixed. 

 

Since the dyes are then inside a clear surface coating on the tiles the physical durability is only dependent on the durability of the coating on the tile and not the durability of the ink. The process results in extremely vivid colors and a very wide color gamut. These dyes are organic in nature and are transferred only after the tile is fired. Firing after printing would destroy the organic dyes. 

 

Up to five printhead arrays can be used to provide the desired color. With the grayscale capability of the printheads, large amounts of pigment can be placed on the tile. When printing onto black tiles, white ink along with numerous colored mineral inks can be included to provide the desired simulated stone coloration. (Image courtesy of Durst US. Source: durst-online.com)

A major deficiency with this approach is very limited image permanence. UV light stability is very poor and not at all competitive with analog pigment printing of the tiles. It is inadequate for permanent tile applications. Since the printers are scanning printers and the process requires both printing and transfer; the process is slow and suitable only for on-demand type short-run applications. This approach provides beautiful printed tiles but cannot meet the productivity and durability requirements of the production printing of tiles.

 

DIRECT PRINTING 

With the development of UV pigment ink technology—particularly in flatbed printer configurations—a new option for ceramic tile decoration becomes available. UV curable inks contain durable organic pigments in an organic binder which bond the inks to the tiles. These inks are on the surface of the tile and not inside as with the dye sublimation technology. 

 

This decorative tile molding trim features a raised bass-relief design. Irregular and contoured tile surfaces are not problematic with the right printhead configuration. (Produced by T.S.C. SpA, image courtesy of FUJIFILM Dimatix)

The Durst Gamma 75 HDS is high-performance inkjet printer for printing onto ceramic tiles. It is designed for glaze lines running at linear speeds up to 35m/min., and features the unique capability of jetting high ink quantities. (Image courtesy of Durst US. Source: durst-online.com)

While the inks are reasonably durable to UV light and the binders can be reasonably durable, they do not come close to the durability requirements of commercially produced ceramic tiles. In addition, the individually printed drops provide a Braille-like relief on the surface of the tiles. If the inks are printed prior to firing of the tiles the temperatures required will completely incinerate the pigments as well as the binder so the color would be lost. 

 

So, while they provide some advantages over dye sublimation, they fall short of the performance of commercial tile printing technology. Similar results can be seen when using traditional solvent or resin type pigmented inks, like Sepiax or Latex. In any case these printers are scanning printers and print far too slowly to be viable alternatives to analog silicone drum printing used for commercial tile production.

 

COMMERCIAL CERAMIC TILE INKJET PRESSES

In the early 2000s it became apparent to ceramic tile manufacturers that inkjet technology may offer a viable option to improve their process of producing printed tiles. It gave promise of more flexibility in design while reducing the need for the long production runs required to amortize the very expensive and time consuming setup and clean up processes with analog printing. 

 

Spanish and Italian tile manufacturers were the first to begin to incorporate inkjet in their processes. They commissioned the fabrication of early equipment that used arrays of printheads to print mineral pigments onto “biscuits” prior to firing. The same mineral pigments used in analog tile printing were prepared into inkjet inks that would perform in industrial inkjet printheads. The challenges were many but the equipment and ink developers prevailed.

 

 

The TeckVersa by Teckwin offers high-speed inkjet printing of ceramic tiles and is designed for commercial ceramic tile decoration. (Image courtesy of Teckwin)

CERAMIC INKJET INK CHALLENGES

For the ink the challenges include the grinding of the pigments used in analog printing that are typically much too large for inkjet printing down to those small enough to allow for reliable printing. To achieve the solids required to impart the desired color large drops and highly concentrated inks are needed. The choice of solvent was easy. Organic oil which does not evaporate but rather burns off during firing made nozzle maintenance feasible with arrays of nozzles. There are still big problems with pigment settling. The density of the mineral pigments are several times higher than the fluid, and with solids concentrations as much as 10-20 percent even the small submicron particles settle rapidly. 

 

Printheads with ink recycling capability are required to keep the printheads functional. Organic binders are incorporated to keep the pigments dispersed in the ink and to provide control of dot spread on the “biscuit”. The most frequently used printheads with this capability are provided by Fujifilm Dimatix and Xaar. Ink manufacturers include Ferro and Chimigraf.

 

In graphics printing process color is used to create the colors required in the final print. These colorants are transparent and in combination provide a wide color gamut. With mineral pigments this is not the case. Instead of cyan, magenta, yellow and black (and maybe orange and green), ceramic inks mineral pigments include colors like brown, blue, pink, yellow, red brown, black, beige and green. If you want a magenta ink the pigment must contain gold and the inks would sell for more than $3,000 per liter. The mineral colors are not transparent so they are printed essentially as spot colors. 

 

Tiles in this showroom were printed using Teckwin’s TeckVersa inkjet ceramic tile printer. (Image courtesy of Teckwin)

The colors are appropriate since most ceramic tiles are printed to simulate earthen tones found in stone or marble. Clearly this presents a different set of problems for the software. The typical process color management software would be inappropriate. Color calibration is also a challenge. The color of the ink before firing is completely different than after firing. The minerals oxidize and melt into the ceramic during the firing. The resulting colors and color density are dependent on the glaze as well as the firing conditions. Firing at too high of a temperature for too long a time will result in a decrease in color and each color is affected differently so these parameters must be included in the color calibration of the printer. 

 

TILE INDUSTRY MOVING TOWARD INKJET

Even with all these differences the financial incentives are so great that the entire industry is converting rapidly to inkjet. The ceramic tile manufacturer can pay back their investment in an inkjet digital press for ceramic tiles in as little as six months. 

 

Now that many tile manufacturers have purchased digital printers they have changed the marketing dynamics of designs, response to customers, etc; their competitors must do the same or suffer the same consequences the large sign screen printers that did not buy wide format flatbed printers. Typical resolutions (across the print path) is 200 dpi for low resolution tiles up to 360/400 for high resolution tiles. In the process direction the resolution required is job dependent (along with drop volume to get appropriate color fill) from 100 dpi to 600 dpi. 

 

Floor tiles are often printed in the lower to middle resolution range whereas decorative or wall tiles almost always require higher resolution. Hundreds of ceramic inkjet presses have been put into production and this year more than 500 printers will be added. The typical four color printer is around $700,000 with some of the larger printers priced up to $1.1 million. The four color low resolution printers printing 0.7 meter wide would have over 22,000 jets and the high resolution printer one meter wide would have over 60,000 jets.

 

SUMMARY

Ceramic tile decoration has changed for the better. With much wider design freedom, much shorter economical manufacturing runs inkjet has changed the game. Howard Baldwin, VP, of Dimatix FujiFilm (previously Spectra) says “the economic advantages of digitally printing ceramics, using inkjet presses, is so great compared to traditional analog decoration methods that it has created a dramatic change in how tiles are manufactured. In addition; it is probable that it will evolve to be used in other related applications. In the opinion of Dimatix; the future is bright for users and developers of inkjet systems and consumables in this fast growing digital application.”