Over the years, the textile printing industry has come to rely on various types of ink for decorative and promotional applications. Based on the media to print on, an inkset and a process are chosen to give the best quality and economical value. This includes offerings in acid, reactive, pigment, disperse direct and dye-sublimation, to name but a few.

With the ever-increasing amount of new technology and solutions, print shops now have a multitude of options to choose from, be it for traditional screen, digital inkjet or hybrid print systems. And while this variety allows for the selection of a dedicated or made-to-measure workflow, it also imposes the need to understand these varieties before a process can be labeled as a “best fit”.

Understanding the process

To understand the process is to understand the choice. The many different application fields translate into a complexity that many still underestimate. As we wrote before, there is still no one ink for every printing need, nor one type of technology to cover all segments.

Firstly, the print process needs to fit requirements of the application: visual communication, soft signage and graphics often use polyester fabrics, where disperse direct, dye-sub, but also latex, solvent and UV-curable inks can be used. Fast fashion and haute couture often involves cotton and blends, where traditionally reactive and pigment inks are employed. Sportswear and swimwear are largely made of polyamide, polyester and blends: here, acid and dye-sub are the predominantly chosen ink types. The simple fact of media-ink compatibility requirements is the main reason we are faced with so many options.

Secondly, the post-processing involves different types of set-ups, and all are based on the primary media and ink combination. This adds a layer of complexity as well. Infra-red fixation can be used for disperse direct; heat-presses and calandering systems are the go-for choices in dye-sublimation transfer solutions, while steaming and washing are needed for acid and reactive inks. This, subsequently, translates to vastly different print production workflows.

Last but not least, the qualities of the printed end-product should fit the needs of the application. Longevity, fastness and hand properties are important. Post-processing is something to think about: is the printed material easily processed, applied or handled? Should it be washed, or does it need a finish (e.g. fire retardant, water repellent)?

Choice of ink

Ink types are developed to achieve best results on a particular media and are often a direct adaptation of the ink used in traditional systems. The digital variants are often limited by the mechanical limitations of the print engine. Temperature, firing rate, nozzle size and other physical constraints are compensated for with changes in viscosity, surface tension and chemical composition. This applies to all ink types for digital inkjet.

Pigmented ink, for the most part, is a water-based solution that has insoluble color particles that adhere to a substrate by means of a binder. Its predominant use is found with cotton and polyester-cotton blends. Since a pigment particle itself has no binding capabilities, an intermediate substance is needed to ‘glue’ the colors to the textile. Properties such as hand, rub fastness, wash fastness and color gamut are, at least for digital inkjet printing, still considered to be of insufficient quality.

The production process involving acid ink is different than the relatively easy process of using pigment or disperse/dye-sub ink. Fixation of the colors is achieved through normal temperature steaming. A washing cycle follows the fixation process. An important consideration is the long fixation time, involving expensive high-volume steamers. In addition, a pre-treatment of the fabric is necessary. Acid inks are used for fabrics made from polyamide, silk and wool.

Similar to acid inks, the production process with reactive inks is based on steaming and washing. Here too, the traditional process has been transformed into a digital variant that has proven effective for many years already. For both acid and reactive inks, the quality requirements are more than sufficient in today’s digital production process. Reactive inks are used for cotton and linen, silk, wool and viscose products.

Why dye-sublimation?

Out of all of this, dye sublimation seems to be the most versatile option. That is: when printing on polyester or polymer coated items. In addition to the simpler workflow (“print, transfer, done”), dye-sublimation workflows allow for application of both flexible and rigid materials of various sorts. It is, in fact, one of the defining questions to answer: does one need to decorate various types of material that cannot be printed onto directly otherwise?

Examples of when the media characteristics prevent other than dye-sub systems to be used are plenty: when, for instance, the substrate is stretchy or prone to deformation during the printing stage, a calander can keep the media stable and in place. Or when the media is curved and comes as a single item, instead of being on a roll, dye-sub may also be the best option.

The list of substrates and surfaces that can be printed on with dye-sublimation is virtually endless: banners, lamp shades, shirts, curtains, backdrops, but also rigid materials such as mugs, license plates, snow boards and pens.

The pro’s and the con’s

Dye-sublimation ink (or ‘low energy disperse ink’), is, largely, used in a heat transfer process where the colorants are first being printed onto a paper substrate and then, under influence of heat and pressure, the dyes are transferred to a polyester media or polymer coated surface. Typically, this is done in a roll-to-roll calander or a heat-press system as a second, separate production step.

High energy disperse direct ink, on the other hand, is printed directly onto the media, which means it omits the intermediate step of printing onto a transfer paper, and is then either fixated with an in-line or a separate infra-red fixation unit.

In both cases, the biggest benefit is that the colorants will bond with the substrate during sublimation or fixation. The colors are ‘inside’ the media and don’t stay within the coating and on top of the media, as it is the case with many other ink types.

Another benefit of water-based sublimation ink is the absence of hazardous components as found in UV-curable and solvent inks.

Low energy sublimation ink is easy to print with but has the disadvantage of colors fading faster; its UV resistance, or light-fastness, is less resistant than the high energy disperse direct equivalent. This means that that the printed colors will deteriorate, or fade, much faster under the influence of UV light. As a result, dye-sublimation is popular for indoor and short-use visual communication and graphics production, as well as in activewear and T-shirt production, while disperse direct is mostly used for outdoor applications such as for flags and banners.

Contrary to the high energy disperse ink, dye-sub is less prone to migration issues. To counter the possibility of disperse color particles that have not been fixated completely to migrate to other areas of the media, a washing cycle is needed. This, of course, has an impact on the workflow and the investment in the overall print production equipment.

A consideration when choosing an ink type and print process must include a comparison of waste and cost of production. While the direct printing method doesn’t need printing on transfer paper first before calandering (or heat-pressing) it onto the media, and thus have a lower material cost, it may incur a higher cost of production, using more resources such as water and energy. Since waste is both an economical and an ecological factor in print production, this is an important one to consider.

Future success

Excellent adhesion to substrates, good printability and relatively easy application are key drivers for the success of sublimation printing. Sublimation ink is already an immensely popular product.

Moreover, the wide color gamut of dye-sub inks with vibrant colors is by far the biggest appeal. With colors other than the standard CMYK, such as light tones, fluo’s, deeper blacks and additional colors such as red, turquoise, orange, blue and green, it allows print shops to create appealing printed fabric products.

In non-rigid, textile print production, the true success of sublimation is found in the production of polyester based garments and textiles for interior and promotional decoration. The biggest segment, by far, is clothing: swimwear, sportswear, fast fashion and accessories. About three quarters of the digital dye-sub textile industry is found in this area.

An interesting development is a solution where dye-sub inks can be used to print on cotton fabrics. One of the competitive areas in digital textile print production is where cotton and poly-cotton blends are used for clothing and interior decoration. Should comparable results be achieved through the usage of dye-sub inks, this segment will further see an increase of digital printing systems and new application possibilities.

_{This article has been published in SIP Fachmagazin #4.2018 and was written by Roland Biemans, founder/owner of LMNS.}

_{With an international background of research, development and marketing of software, hardware and supplies in the inkjet printing industry, Roland played an important role at different companies adapting and transforming technology for the development of innovative practical solutions. Among these solutions were the first refill sets and bulk ink systems for large format inkjet printers, edible ink, media winding systems, the first ever double-sided digital textile printer, software for controlling engravers, routers and cutters and an award winning contract proofing software. Most of his time was dedicated to the development and sales of software for color correction, color separation, proofing, photo editing and driving inkjet printers in the sign, banner and color reproduction industry.}

_{Roland initiated the digital textile print competence center in Eindhoven, The Netherlands. Early 2013, he became board member of the European Specialist Printing Manufacturers Association (ESMA), and continues to support the association as Technology Partner. The Specialist Graphic Imaging Association (SGIA) awarded Roland with the outstanding service award in recognition of his effort in advancing the industry and its association.}

_{More information about Roland can be found at his LinkedIn page at: linkedin.com/in/rolandbiemans/}