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Industrial Inkjet Printing on Glass: Part 1, Flat Glass
By Eileen Fritsch, Industry Author
Glass is produced in many different sizes, shapes, textures and thicknesses for decorative and functional use in buildings, home décor, automotive windshields and windows, bottles, jars, tubes, and touchscreens on appliances, computers, tablets, and smartphones. All glass is produced at high temperatures in glass furnaces and cooled at even temperatures in annealing ovens. But different chemistries, firing temperatures, and heating and cooling cycles produce different types of glass for various requirements. The float glass process produces sheet glass, and glassblowing produces hollow glass such as tubes and containers.
Although some UV-curable inks are fine for some décor and bottling applications, specifically those that require primers and topcoats to fix the inks to the surface of the glass, they don't work well for flat-glass applications such as architectural or automotive glass. These applications require specialized inks that can withstand the higher temperatures associated with strengthening and laminating for greater durability.
So, direct printing on glass is primarily an industrial process. In Part 1, we'll highlight some industrial inkjet printing systems for flat glass. In Part 2 we'll look at industrial inkjet printing systems for decorating glass bottles and packaging.
Different Types of Flat Glass
Industrial producers of flat glass use digital printers with ceramic inks, in which inorganic pigments and glass frit are fused directly with the glass at temperatures that would cause organic additives and ink binders to decompose. After bubbles and voids are expelled to give the glass a compact, shatter-resistant structure, the surface is treated to give the flat glass the characteristics the client has specified. A successful firing of the glass and ceramic ink produces a bubble-free layer in which the pigments are properly distributed in a panel that is uniformly thick.
Some ceramic inks add functional properties that multi-substrate UV-curable inks can't deliver. Some digitally printed ceramic inks can make glass floors and staircases more slip-resistant or entire buildings more energy efficient.
Printing images on glass also involves extra design considerations. For example, if the glass will serve as a room divider, the design on the back of the glass should look just as beautiful as the design on the front of the glass. Factors such as the thickness of the glass, greenish or bluish color variations from batch to batch, surface coatings on the glass, and how the glass will be lit can all affect how the design will look after the decorated glass is permanently installed. Planning well in advance and testing the design outcome is an integral part of the design process, because once the glass is installed, it is costly to make changes.
Currently, companies such as Dip-Tech, Durst (SGIA member since 2002) and Tecglass sell inkjet printers for decorating flat glass used in building projects and automotive manufacturing.
The Role of Glass Processors
According to IBIS World analysts, glass manufacturing in the US is a $26 billion-per-year business that employs 86,496 people in 4,652 companies. The IBIS report grouped glass manufacturers and processors in four categories: (1) flat glass; (2) glass containers; (3) pressed or blown glass; and (4) glass purchased for other products (such as mirrors, light fixtures, arcade games, furniture, or touchscreens).
Laminated glass is produced when two or more units of flat glass are permanently bonded together with an inner layer of a strong, clear resin (polyvinyl butryral or ethylene vinyl acetate). The inner layer holds the glass together, even when the glass is shattered. Laminated glass can also be manufactured to improve the sound-insulating properties of office partitions or block UV rays in windows.
Tempered glass undergoes an additional heating and cooling processes that gives it about four times more strength than the basic annealed glass used in home windowpanes. Whereas annealed glass breaks into sharp, irregular shards, tempered glass breaks into many small, safer pieces that aren't jagged.
Architects and interior designers use laminated and tempered flat glass for indoor fixtures such as partitions, doors, curtain walls, backsplashes, shower stalls, floors, staircases, elevators, and decorative art, or exterior elements such as windows, facades, skylights, canopies and balconies.
Designing Beyond Decoration
According to experts at Dip-Tech, digital ceramic in-glass printing allows for the creation of colorful, durable, and functional designs that were previously impossible.
Some glass design techniques can affect durability, which is critical when designing buildings that will last 30 to 40 years. Other designs address issues of sustainability which are essential requirements in new construction.
"Digital ceramic printing is changing the way architects think and plan," explains Niv Raz, head of Dip-Tech's Architecture Division. "Digital ceramic printing not only affects small details, but can the design can impact the whole project."
For example, by changing the density of patterns printed into the glass, architects can control how much natural light enters a specific room and how much solar heat gain typically occurs during the daylight hours in a site-specific location. The ability to make glass more functional is becoming increasingly important as architects are expected to design energy-efficient buildings that will meet LEED certifications.
With Dip-Tech's printed glass performance calculator, architects can evaluate the energy performance of glass printed with Dip-Tech's digital ceramic inks. The calculator enables glass designers to measure the impact various designs will have on the Solar Heat Gain Coefficient and the percentage of visible light of the glass.
Designs can also be used to solve other challenges such as preventing birds from crashing into clear windows or to emulate the look of more costly, less environmentally friendly building materials.
The see-through properties of glass create both technical challenges and creative opportunities. With direct digital print systems and the right software, designers can create unique effects with double-vision printing, where different graphics are printed on top of one another for viewing designs from different sides of the glass.
Multi-layer printing makes it possible to print a sharply focused graphic over a more translucent, soft-focus background that looks opaque from the other side. The creative options are limitless.
Glass design is emerging as a specialty niche for designers and artists who have been trained in what's possible with glass printing technology. Sometimes, the architect may hire a digital glass designer or digital glass engineer to create the design for the glass. In some cases, the glass processor will offer glass design and file preparation as a service to their clients.
Industrial Printing Requires Deep Knowledge
But industrial inkjet systems with specialized ceramic inks are a must for higher-end, large-scale glass-decorating projects that must last for decades under a variety of harsh conditions.
Glass processing is likely to become even more complex as glass becomes more popular for touchscreen panels on computing devices and home appliances. "Intelligent glass" with composite nanocrystal coatings that can selectively block out heat and light is expected to be a popular choice for designing energy-efficient buildings.
Architects are just beginning to experiment with what's possible. In a five-story building in Hamburg, algae grow between the glass panels of the "bio-reactor" glass façade and produces bio mass and heat from the combination of light and carbon dioxide. Heat exchangers feed the heat directly to the 15 apartments in the building and the bio mass is skimmed off and uses to produce bio gas. A fuel cell converts the bio gas into electricity and heat.
As glass becomes more popular as a building material, glass processors with experience with screen printing and other forms of glass decorating may ultimately have an advantage in using direct digital glass printing systems. These companies are already familiar with the variety of ceramic, screen printing, and conductive inks that can make glass more beautiful and more functional.
Stay tuned for Part 2 of this series, where we'll discuss the challenges and technologies for direct printing on glass bottles - and a few of the companies that have already breached the market.
Eileen Fritsch is a Cincinnati-based freelance writer. Contact her at firstname.lastname@example.org.
This article appeared in the SGIA Journal, November / December 2015 Issue and is reprinted with permission. Copyright 2016 Specialty Graphic Imaging Association (www.sgia.org). All Rights Reserved.
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