A digital sublimation printer is use to print polyester fabrics with sublimation inks. Sublimation printing is born for the market of flags and banners but now has spread in the fashion industry.
The technology of digital large format printing are over thirty years to the service markets. They were born for the graphics and visual communication industry. Over time, thanks to the evolution of inks and performance, they have also reach the textile industry. The large-format plotters were soon made inroads into the market flags and fabric banners, before reaching fashion and fashion more stringent.
This was possible thanks to two technologies:
- print heads with piezoelectric technology
- sublimation inks with special formulations, with nanodisperse dyes.
Sublimation printing is now especially popular because they are now on the market polyester rich fabrics but very similar to the touch of natural fibers, more complex to print. The sublimation ink, in fact, binds well to the polyester fabric, pure or with percentages not lower than 40% (mix-polyester).
Why is it call “sublimation printing” or “sublimation printing”? Definition
Let’s start with the basics. It is call ” sublimation printing ” or ” sublimation printing ” because the inks are fix to the polyester fabric through a sublimation process. Sublimation is the passage of a solid material directly to the gaseous state, without passing from the liquid state.
How do sublimation inks work?
The sublimation inks , or sublimating inks , are a type of inks “missing”. It means that they chemically bind to the polyester. They are use in sublimation inkjet printers.
Through the application of heat and pressure, they pass from the solid to the gaseous state and then return to the solid state on the polyester fabric. This particular process serves to keep the sublimation dye inside the fabric fiber, where it is fix by heat and pressure. Heat and pressure are exerted by a calendar or a heat press (heat press).
Sublimation inks are “live” inks, in the sense that they contain components that tend to oxidize and “degrade” rapidly if expose to light, air and thermal changes. This can cause fungal growth in printer hydraulics. These features have made this technology the prerogative only of plotters equip with piezoelectric inkjet heads. In fact, thermal heads as they are conceive today would cause the ink to “self-sublimate” before it is even spray.
How does thermal sublimation printing work?
The sublimation printing on polyester fabric can take place in two modes:
- direct sublimation printing on the fabric , with subsequent heat setting of the ink in a calender or heat press
- indirect sublimation printing, by printing on a special paper design for transferring the ink onto the fabric through a calendar or heat press ( transfer paper ).
As you can see, all these processes take place hot. In fact, printing with digital sublimation ink requires the aid of heat and pressure in order to be transferred and maintain in the fiber of the fabric. Pressure and heat are generate by the calendar or heat press.
Each of the two production methods has pros and cons. In general, sublimation of digital textile printing applies well to both cases.
Direct sublimation printing
Direct is the simplest type of sublimation printing from a process point of view. The large format sublimation digital printer prints the graphics directly onto the polyester or polyester-blend fabric. At the end of printing, the reel of fabric is pass through a calender or heat press to heat- fix the sublimation ink to the fabric fiber.
Indirect sublimation printing with transfer paper
The indirect sublimation inkjet printing process requires the plotter not to print the fabric directly, but a specific paper. This is call ” transfer paper “.
The graphics are print on the paper in a mirror image. In this way, once that the paper will be coupled to the fabric, the ink will move from one to another by returning a readable image, straight. The ink is transfer from the paper to the fabric thanks to the heat and pressure generate by the calendar or heat press.
From plotter to transfer paper, the ink solidifies and dries quickly. Once the paper is couple to the fabric, the ink held up there by the paper sublimates, transferring onto the fabric.
How is a sublimation printer made and how does it work?
A textile sublimation printer is, of course, a roll-to-roll. There are printers of various sizes, from 1.6 to 5 meters. All sublimation printers work with rolls of polyester or polyester blend fabric.
Some sublimation printers have an in-line or even integrated calender . Most sublimation printing systems have a separate ink fixing system: a calendar or even a flat heat press.
Press or calendar for direct or indirect sublimation
As we said, there are two possibilities to actually accomplish ink sublimation:
- the thermal calender
- the heat press (or heat press ).
The rotary type thermal calendar for sublimation
The rotary-type thermal calendars allow the thermal transfer of the ink from the paper to the fabric. This process is called calendaring. Current machines allow direct control of temperature and pressure, in order to guarantee the best possible result. They are obviously ideal for roll processing. The size of the operating light must be, for obvious production reasons, equal to or greater than the print reel.
The rotary-type thermal calendars also allow the fixing of the sublimated ink directly on the fabric (instead of passing through transfer paper). In this way, a better hold overtime is guaranteed, in the case of roll-to-roll printing.
There are different types of rotary type calenders, with different types of options, to best adapt to the type of application produce:
- visual communication
- flags
- sports products and sportswear
- fashion industry.
The evolutions of calenders for the thermal transfer of sublimation ink have been seen during the years 2000 and 2010. Today it is difficult to find true innovation or to witness a revolution in this market. Few manufacturers have been able to successfully meet the growing demand for sublimation printers equip with 3.2m and 5m superwide format inkjet printers. Currently the market leader in the field of calenders for superwide format digital textile sublimation is Monti Antonio, a historic producer from Vicenza.
The heat press for direct and indirect sublimation
The thermal transfer presses are of two different types:
- without vacuum plane for the vacuum effect; presses in format for T-shirts or in larger sizes for the fashion and soft signage sector are usually of this type
- with the vacuum plane : these guarantee the best possible result in any condition. They are mainly use for applications in the fashion and soft signage sectors.
For the fashion sector, some manufacturers have introduce specific options to reduce manual interaction when handling transfer paper from reel to piece of fabric.
As with calenders, there was also an evolution in the world of thermal presses with fix platens in the early 2000s . Here the advent of the vacuum has considerably increase the possibilities of working in the piece. And bifaciality has had interesting application developments in sport and textile graphics for communication.
Double-side sublimation printing: myth or reality?
The ink penetration on the back of the fabric is absolutely possible. It is control by several variables:
- specific pre-treatments
- amount of ink deposits on the substrate. In this case, you need a good “thrust” deriving from the pressure exerted by the calendar, which must be of the vacuum type. That is, it must be able to generate the vacuum effect to allow the ink to pass very quickly to the back of the substrate.
Obviously, the back will never be as perfect from an aesthetic point of view as the front, but very similar. Observe from a distance of a couple of meters, it will be difficult to see the difference. The thicker the fabric, the lower the quality of the double-side effect.
The transfer paper for indirect sublimation printers
Transfer paper is a special type of paper use in digital printing indirect sublimation. It is superficially treat to accept the water-base sublimation ink without altering its characteristics up to the transfer onto fabric.
In the past years, all the main paper mills specializing in coat papers for inkjet printing have been able to produce and offer the market better and better substrates. Transfer papers capable of maintaining dimensional stability at any speed and ink load and capable of maintaining the writing quality intact at the end of the sublimation on fabric.
The weights of the transfer paper vary greatly. Must be select:
- depending on the final result or the application to be carried out
- depending on the type of fabric on which the ink will be transfer
- in relation to the quality and type of calender present in the company.
The polyester or polyester blend fabric for a direct and indirect sublimation printer
A small introduction to the world of fabrics. We can divide them base on the fiber they are made of, but also on the type of weaving . The most common are precisely the “fabrics”, produce by intertwining perpendicular threads. They can have a simple weft, but also more complex weaves, so as to produce particular designs or figures with yarns: there are a practically infinite number of ways to weave the warp and the weft.
The weaving determines not only the appearance of the fabric (such as the shine) but also its hand (the sensation when you touch a fabric), the permeability, the drape, the dimensional stability, the elasticity, the resistance and the resistance to ‘abrasion. This is why it is so important to know how to choose the right fabric for the right end use . In particular, the last five characteristics (drape, dimensional stability, elasticity, strength and abrasion resistance) are very important when it comes to digital textile printing and media handling during the entire printing process, especially if industrial.
The polyester is a polymeric synthetic fiber. It can also be use mixe with other natural fibers (cotton) or synthetic (nylon, polypropylene, Lycra).
The choice of the best polyester or mix polyester fabric for sublimation is crucial. From this choice derive:
- print speed
- resolution.
Not only. Each sector of use of finish products has different characteristics. For example, a polyester backing use in the soft signage industry needs to be lightweight and wrinkle-proof, so it can be easily fold and unfolded, saving you money on shipping.
What is a possible alternative to the sublimation printer?
To date, the only non-piezo inkjet head technology that has managed to partially replace direct sublimation printing on fabric is HP Latex Thermal Technology . The alternative is only possible for some specific applications in the graphics and visual communication market. There are still no known evolutions regarding the application of sublimation with its own thermal inkjet technology. This is because the thermal shock necessary for the formulation of the drop would damage the ink itself directly in the print head.
What are the evolutions of sublimation printing today?
To date, sublimation printing has reach everywhere. It is difficult to find a digital textile printing market where it has not to establish itself. In the same way, the sublimation thermal transfer of the ink has also been using in other industrial markets, where the surface to be decorate is cover with a polyester coating.
The evolutions concern its application in single pass printing on transfer paper, up to the superwide format from 3.2 m to 5 m for typical applications of visual communication or for the decoration of exhibition stands or interior furnishings for temporary shops. In the case of the smaller formats of 1.60 and 2.5 m of print light, the applications range from fast fashion to graphics, up to sportswear.