Transfer vs. Direct Dye-Sub Printing
There are many different ways of printing on textiles and fabrics, but the most popular inkjet printing technology for fabrics — at least at the non-industrial level — at the moment is dye-sublimation. There are two primary varieties of dye-sublimation printing.
In transfer printing, the printer prints on a special paper that has a coating designed to hold and then, under heat and pressure in a heat press or calender, release the printed image. When the transfer paper is brought into contact with the fabric in a heat press, the ink embedded in the paper is converted to a gas (a process called sublimation) and penetrates directly into the fibers of the substrate. Polyester fabrics are required for transfer dye-sub printing because the process works by slightly melting the fibers so that the ink physically becomes part of them. This is why transfer-based dye sub-printed materials are so washfast.
A growing variant of dye-sublimation printing is direct-to-fabric printing, which eliminates the need for transfer paper, although printed fabrics will still need to be run through a calendar — built into the printer or as a separate unit — for the sublimation process to fix the dye to the fabric. Direct-to-fabric dye-sublimation also requires pretreated polyester fabrics.
Other differences between transfer and direct-to-fabric include the nature of the image. The inks used in direct-to-fabric printing penetrate further into the fabric than those used in transfer printing. The result can be more muted colors and softer text. In direct-to-fabric, there is also greater show-through on the reverse side of the fabric, which is why the top application for direct-to-fabric — at least right now — is flags. A lot of development is going into direct-to-fabric dye-sublimation and new inksets and machines are eliminating — or at least reducing — many of its limitations.
Dye-sub works best on polyester-based fabrics, but what about natural or other kinds of synthetic fibers? For physical and chemical reasons, these require other dye-based textile printing inks. Natural cellulose fibers like cotton require reactive dye inks, while natural or synthetic fibers like silk, wool and nylon require acid dye inks.
As you can tell, making a universal textile printing machine that can handle all types of fibers is a substantial challenge. However, don’t underestimate the cleverness of today’s chemists. A hot new area of development is pigment inks, which can print on virtually any fabric, curing via heat or UV radiation. However, pigment inks require a bonding agent, the amount of which — in relation to the colorant — causes a trade-off between color vibrancy and washfastness.
We are starting to see machines hit the market that bridge one or more of these inksets. Durst, for example, has a machine that can use either transfer-based or direct-to-fabric inks. One interesting new device is Mimaki’s new TX300P-1800 Series which features a dual ink capability, which means users have the ability to print onto natural materials using pigment inks or onto polyester materials with direct dye-sublimationinks using only a single printer. The inksets used in the TX300P-1800 do not require steaming and washing, which are common post-printing processes for many kinds of textile inks.
EFI’s acquisition of Italian textile printing equipment manufacturer Reggiani has also led to a broad and growing array of textile printing equipment that includes dyesub as well as pigment inks, both entry-level all the way up to industrial production.