by Industrial Print Magazine staff
Digital printing’s influence on the decoration of ceramic tiles continues to grow as more tile manufacturers realize its benefits. Advantages include expanding beyond the limitations of pattern repeats—a challenge when working with analog printers, decorating textured surfaces—something a printhead is able to achieve because it does not physically touch a tile, and providing an extended array of options when it comes to colors, finishes, and special effects.
Above: Durst offers the Gamma XD Series, a digital single-pass ceramic printer for inline decoration of ceramic tiles using pigmented ceramic ink.
The ink used—commonly oil-based pigment—endures the high firing temperatures it is subjected to during manufacturing. Printheads designed to jet pigment ink and recirculation systems are other important components.
One Step of Many
Inkjet ink designed to jet directly onto a tile via production printing is one step in a complicated process. The manufacturing of a ceramic tile is multifaceted. Press, glazing, decorating, and firing are four basic steps.
“Inkjet printing in ceramics takes place in the middle of a long and complex process. Since the substrate is printed after being formed and before firing, the most important aspect is the integration with the rest of the applications during the production process,” explains Ramon Bono Palomar, GM, Sun Inkjet Ceramics S.L., a joint venture of Sun Chemical and Vidres S.A.
Norbert von Aufschnaiter, segment manager ceramics printing division, Durst Photoechnik AG, describes the ceramic tile manufacturing process as one that consists of a series of successive stages. This includes raw materials preparation, pressing and drying of weakly bound clay material—referred to as a green body, applying optional layers such as engobe or glaze, and then decoration. Decoration occurs using screen, flexographic, or digital printing methods.
After decoration, additional layers like hepatic effects, wear resistance, or anti-slip are applied; the tile is then dried, fired, and finished—polished or ground. Drying reduces the water content in the tile before it undergoes firing, according to von Aufschnaiter.
These firing temperatures dictate the type of ink used in the decorating process. “Opposite to other inkjet applications, the inks used in ceramic decoration must withstand the high firing temperatures of up to 2,280 degrees Fahrenheit. Therefore, for the pigments, special metal oxides are used,” notes von Aufschnaiter.
The chemical nature of the metal oxides prohibits a large color gamut. Traditional CMYK is not found in this printing scenario, instead colors like blue, beige, brown, orange, yellow, and light pink are used as their color does not degrade at the high temperatures subjected to during firing.
“Another important advantage of these inorganic pigments—metal oxides—is that the colors are 100 percent light proof and will never fade,” adds von Aufschnaiter.
Oil-based pigment inks are preferred. “This is due to the difficult printing conditions with very hot tiles,” explains von Aufschnaiter. When passing through the printer, sometimes the tiles reach 120 to 160 degrees Fahrenheit, and vapor is emitted as well. The oil-based pigment ink can handle these temperatures well.
Water-based pigment inks are unsuccessful, von Aufschnaiter points out, due to the drying behavior clogging the nozzles.
Beyond tolerating the high temperatures subjected to during firing, inks used in the ceramic tile decoration process must be compatible with after-printing applications, such as protective or effect glaze coatings, shares Bono Palomar.
While pigment-based inks are beneficial for many reasons, they do offer one challenge—they contain heavy particles that if not circulated well and regularly can clog print nozzles.
“The sedimentation behavior of ceramic inks is a challenge, due to the very heavy particles,” admits von Aufschnaiter. Metal oxides found in pigment ink carry a weight of approximately five grams/cm3. This requires special continuous recirculation to avoid blocked nozzles.
“All ceramic inks are highly loaded, high-density, hard particle dispersions, and sedimentation cannot be avoided,” agrees Bono Palomar. Any machine must include recirculation and good shaking re-dispersion.
Influenced by Digital
With advancements in digital printing, the decoration of tiles via digital remains dominant in manufacturing facilities. Ink is just one part of the story.
For Bono Palomar, the advancements of the ink and printhead are joined. “There are still sound developmental benefits in the printhead. For starters, it is faster and there is a bigger drop volume and higher particle size. Additionally, the inks provide more tonalities and effects, and offer better process performance.”
Durst began developing a single-pass printer with pigmented ceramic inks in 2003. This was three years after digital printing entered the tile world with a salt-soluble ceramic ink printer. The printer was not developed without its challenges. “For Durst, this development was a big challenge, as the piezo printheads were not classified as suitable for this application. The problems were the strong sedimentation behavior of these pigmented ceramic inks with very heavy metal oxide particles and the hot and steaming tiles,” explains von Aufschnaiter.
“The development of pigmented oil-based inks and the full recirculating drop on demand printheads are the main advances that drove the inkjet technology innovations in ceramics,” notes Bono Palomar.
With these advancements, in the tile industry, “digital printing has thus taken over from traditional flexographic printing. It has completely replaced traditional flexographic printing due to the decisive advantages in the printing technology and in the production process,” adds von Aufschnaiter.
Tile manufacturers—whether the tile is used for walls or floors—are like any other industry, searching for variety in their offerings so customers have many choices. One way this is achieved is through special effects like gloss, luster, matte, or metallic, which are used for aesthetic purposes. Practical effects are also possible, for example anti-slip.
Traditional printing techniques utilized their own ink sets with special effects, now there are also digital ceramic printing inks with effects. Ferro Corporation is one ink manufacturer in this space. Its INKSnova color series of digital ceramic printing inks offer effects including light contrast in a glossy-opaque interplay and decoration in relief and bas relief.
According to the company, the series provides surfaces with metallic brilliance to embellish decoration. “They are available as transparent matte inks, glossy transparent inks to increase matte-glossy contrast, and opaque matte inks designed to ensure balance between glossiness and opacity on every kind of ceramic surface, from double fast-firing wall tiles to porcelain stoneware floor tiles,” notes the Ferro website.
The Ferro INKSnova Effect Inks include the following categories—glossy, luster effect, sinking/bas relief effect, anti-slip/slip resistant, transparent matte, opaque matter, metallic effect, and hard matte effect.
Sun Inkjet also develops and produces special inks and effects. Bono Palomar notes that “the tile business is like fashion for buildings, just as furniture can be, and the only way to show the effects to the customers is by providing samples of the designs. It’s important to apply the effects the way they expect to be sold in the markets and it helps to put the design proposals in production.”
Advancements in ink drive the move from analog to digital. Leading printhead manufacturers offer printheads specifically designed to support printing to ceramic.
The Fujifilm Dimatix, Inc. StarFire SG1024/MC is an easy to integrate, high-performance, drop on demand piezoelectric printhead for single-color operation at resolutions of 400 dpi. The StarFire SG1024/MC is a compact, self-contained unit built to withstand the harsh environment of ceramics production.
Konica Minolta, Inc.’s KM1024i is an on demand piezoelectric industrial inkjet printhead featuring a system for independent nozzle channel drive. It enables simultaneous emission from all 1,024 nozzles. The high-density structure featuring four lines of 256 nozzles aligned with high precision enhances positioning accuracy to realize high-definition print quality.
Kyocera offers the KJ4C-0360 for ceramic tile decoration. The 360 dpi model comes with an ink recirculation system structured for using high-viscosity oil-based inks with a large drop volume.
The Seiko Instruments GmbH RC1536 Recirculation Series of printheads is designed to create varnish, white, and metallic digital effects. A range of usable viscosities, particle sizes, and drop volumes are available.
The Xaar 2001+ printhead family delivers reliable results with maximum production uptime. According to the company, thanks to its High Laydown Technology, the printhead delivers unprecedented ink discharge rates to create outstanding decoration effects, ideal for use with gloss, adhesive, luster, and metallic.
Several third-party vendors offer various solutions to drive the printheads.
Global Inkjet Systems (GIS) supports a range of printheads when it comes to drive electronics. The company also offers components for ink delivery systems. GIS designs standalone electronics and software for ink supply system control.
Integrity Industrial Inkjet Integration, Inc.’s Universal Print Controller can be configured to drive up to eight printheads from multiple vendors. An ink delivery module is designed to be used with a variety of fluids and is tailored to deliver ink at the proper rate based on usage by the choice of pump.
Meteor Inkjet Ltd. drive electronics and software are capable of producing complex, multi-pulse waveforms to control printhead drop ejection volume, velocity, and timing. It offers products to drive all leading printheads used for ceramic tile decoration.
Ceramic tile creation is an involved procedure. It includes many steps and digital decoration is just one. The advancements made in ink, printheads, and drive electronics allow for digital printing to be used in decorating processes in tile manufacturing today. IPM
Feb2021, Industrial Print Magazine