Wide-format Graphics: Transfer vs. direct dye sublimation

by all | 9 February 2015 12:34 pm

By John Selfhout
The mix of attendees and exhibitors at the recent 2014 Specialty Graphic Imaging Association (SGIA) Expo clearly showed there is widespread interest in—and creative possibilities for—printing graphics on textiles. Transfer-based and direct disperse options for dye sublimation are now well-developed processes for printing fabric graphics in brilliant colours and high resolution that are durable and washable and will drape and handle well. Both of these processes are very similar, but the differences between them are nevertheless significant and, given they call for their own dedicated equipment, signmakers will generally have to choose which of the two is best for their purposes. In this respect, there are many aspects to consider before a well-balanced decision can be made.

Transfer
Transfer-based dye sublimation is an older method, originally developed before digital printers were available. Today, it is accomplished with digital printing technologies, yet the basic process has not changed significantly.

First, the graphics are printed onto a specially coated paper. Then, the printed images are transferred to a polyester-based material—which may be a woven or knitted fabric or a non-woven substrate—under pressure and high temperature for a specified period, using a heat press or rotary calender and special protective paper. The better the degree of control over these parameters is, the better, more consistent and more reproducible the results will be.

This technique works due to the specific characteristics of both the dye sublimation ink and the fibres of the uncoated substrate. The dye sublimation ink comprises solid particles dispersed in water, oil or a solvent, which acts as a carrier for the ink particles. The four basic ink colours of cyan, magenta, yellow and key/black are sufficient for creating any combination of colours in the graphic.

One key characteristic of dye sublimation ink particles is how they transition from a solid to a gaseous state when they are heated. Most materials can exist in three states, including solid, aqueous and gaseous, but these inks never become aqueous, which makes it easier to control the process of transferring them from the paper into the textile.

As mentioned, the nature of the fibres plays an equally important role. Unlike natural fibres, these manmade fibres are created by melting polymers and using pressure to force them through nozzles in their liquid state. High-
quality fibres can be achieved with this well-established process, but they will include amorphous areas, including micro-pits and holes.

The amorphous areas are where the dye sublimation ink molecules can find sufficient surface area to connect to the polymers. The result is a permanent, irreversible connection between the inks and the polymers, since the substrate is dyed deep within its fibres, rather than simply adhering graphics to its surface. In this way, brilliant colours can be achieved without changing the feel or handle of the textile—and the material can be washed without threatening the integrity of the graphics.

With today’s digital technology, the transfer-based dye sublimation printing process also relies on a raster image processor (RIP) software package to prepare the images at the beginning. And then, following the printer, transfer paper and heat press or rotary calender, the process may also require a cutter or a sewing machine, depending on the intended final product.

Direct
The more recently established direct disperse process for dye sublimation benefits from many of the same material characteristics, including the amorphous areas of the polymers and the lack of aqueous state for the ink particles, but as the name suggests, dispersed inks are directly placed onto the fabric or non-woven substrate. In this sense, it is a one-step process, rather than the two-step transfer process.

One of the main differences is the use of a coated substrate. The coating is essential in preventing the dispersed inks from spreading across the material in an uncontrollable manner, which would ruin the sharpness of the printed graphics.

Transfer-based dye sublimation still achieves better edge sharpness in images, but today’s direct disperse dye sublimation printers have been engineered to a high standard and are certainly adequate for many common applications. By applying large amounts of ink onto the face side of an open and lightweight material, an almost complete print-through effect can be achieved.

This type of printing requires a raster image processor (RIP) software package to prepare the images, a printer designed specifically to work with textile-based substrates (i.e. with tension control, web guiding under the printheads and a tray to collect any ink that passes right through the substrate), the aforementioned coated substrates. The printer may also need to facilitate temperature and time control with an on-board unit, if there is no separate heat press.

Comparison points
Given these differences, there are many factors to consider and ‘homework’ to do before investing in either transfer-based or direct disperse dye sublimation systems, but the best choice is often dictated by the sign shop’s desired applications.

Flags and banners, for example, may require the ink penetration of direct disperse printing to create a two-sided graphic product. The most common method for producing sportswear, on the other hand, is to work with precut garment sections and undertake transfer-based printing with a hand press or a suitable singe-piece transfer calender.

That said, both processes are feasible for most general graphic applications. The choice may come down to more specific points of comparison, including the customer’s quality requirements, the choice of substrate, in-house production logistics, required investments and combined production costs.

Quality
In some cases, quality requirements vary by installation venue. Edge sharpness, for example, is a more significant parameter for point-of-purchase (POP) displays than for large facility signage.

The customer may set the bar for quality, too. Many big organizations have strictly defined levels of quality control for how their branded graphics appear, whereas a small, local client may be more concerned about the cost-to-benefit ratio of a specific graphic application.

Substrate
Textiles offer unique properties that have proven benefits for the sign industry, but they are not the easiest materials to work with. A stable woven or warp knit material can be processed effectively using a roll-to-roll machine that provides a degree of tension; many printers and ‘fixation’ units fit this description. Less stable materials, on the other hand, can suffer from problems like wrinkling, elongation and width reduction as a result of the application of tension during direct disperse dye sublimation. Some signmakers spend a lot of time to make these less stable fabrics work well, but for the most part, printing onto transfer paper first is the only effective process for them.

Even if a type of material seems to work well, similar textile products from different suppliers may behave completely differently. For one thing, the differences in how textiles have been preprocessed—e.g. thermofixed through the application of both temperature and pressure—are not usually obvious at a glance in a sample book, but will become evident when high temperatures are applied in the sign shop’s rotary calender or a printer’s fixation unit.

Infrared radiation (IR) fixation units and beltless calenders offer no adequate measures to prevent less stable fabrics from shrinking or wrinkling, but calenders equipped with belts do, as the belt holds the material against the heating drum and guides it through the machine without adding further tension. Even then, however, the question remains as to whether or not the printer can cope well with the material. Hence, transfer-based dye sublimation remains the go-to option, as it is perceived as the safest route to take.

In any case, it will require some experience with the processing of textiles before signmakers can make a balanced choice between transfer-based and direct disperse dye sublimation.

Production logistics
Digital printing has made it possible for dye sublimation to produce individually designed items in small quantities and in a short time frame. In principle, 
no matter whether the production room is set up for transfer-based or direct printing, digital technology should enable quick production for each job.

With a growing number of possible applications, however, and with the maturation of the textile printing business in general, customers’ demands are starting to become more stringent. Some will require an identical print across a range of textiles, requiring the sign shop to be flexible in working with different substrates.

In other cases, shops will need their printing equipment available for non-repeat single orders, while the calender is dedicated for orders of only the highest priority. Transfer-based dye sublimation allows them to separating the printer from the calender, to ensure the most efficient use of their in-house equipment.

Investment
A wide-format printer that can directly print on textiles will be more expensive than one that cannot, but on the other hand, the additional cost of the built-in fixation unit will be less than the cost of a calender for transfer-based printing. In the final analysis, both types of dye sublimation require a similar level of capital—and even when there is a difference, a lower initial investment needs to be weighed against whether or not the equipment can deliver exactly what the sign shop’s target market requires.

Production costs
Similarly, direct disperse dye sublimation appears less expensive at first glance. Only one operator is needed, since the fixation unit is attached directly to the printer, and there is no outlay required for transfer and protection paper. A shop can also keep less material in stock.

There are also added costs to the direct process, however, including the coating necessary to make textiles compatible with the printer. And while the cost of inks is similar across the two processes, direct disperse dye sublimation requires a higher ink load than transfer printing. Further, if the application calls for 100 per cent ink fixation, the direct-printed material may require an additional production step for washing.

In the final analysis
For all of these reasons, there is no one, general answer to the question, “Is transfer or direct printing better?” Both processes can yield high-quality products, but the best method can only be identified on the basis of a sign shop’s specific situation. As signmakers analyze their customer base and conduct their cost calculations, the best answer will be that which best meets their market’s needs at the lowest price.

John Selfhout is manager of marketing and sales for Klieverik, which develops rotary thermoprocessing equipment for use in the digital printing of textiles. This article is based on a seminar he presented at the 2014 Specialty Graphic Imaging Association (SGIA) Expo in October in Las Vegas, Nev. For more information, visit www.klieverik.com and www.sgia.org.

Source URL: https://www.signmedia.ca/transfer-vs-direct-dye-sublimation/

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