By Johnny Shell
With the growing popularity of ‘soft signage,’ where images are printed on textiles to create fabric graphics, many signmakers today are looking into dye sublimation, a highly specialized process with which many of them are not yet familiar.
Any ‘dye,’ by definition, impregnates a colour into a material. In many cases, this colour change is permanent. ‘Sublimation,’ meanwhile, refers to a change of matter from solid to gaseous state without it becoming a liquid at any point it the process.
So, during dye sublimation, solid dye particles are changed—using heat and pressure—into a gas. The gaseous particles are then bonded with a polymer, which consists of a linked series of repeated large, simple molecules. Finally, the dye becomes solid again.
The role of heat
The basic dye sublimation process uses special heat-sensitive dyes to print graphics and text onto a special transfer paper. This paper is then placed on a ‘sublimatable’ substrate—i.e. the aforementioned polymer, a polyester or a polymer-coated item—and they are both placed into a heat press together.
Once the press’ heating cycle is complete, the image on the paper has been transferred to the substrate. In fact, unlike some other types of printing, the graphic has actually become a part of the surface. If someone were to run his/her finger along the surface of the sublimated image, he/she would feel nothing apart from the usual surface of that object.
This is thanks to the high temperatures in the heat press. At these temperatures, the solid dye converts into a gas, without ever becoming a liquid, while the ‘pores’ of the polyester or polymer are opened, allowing the gas to enter. Then, when the temperature drops at the end of the heating cycle, the pores close and the gas reverts to a solid state, now part of the polymer.
Dye sublimation cannot be performed on natural materials, such as 100 per cent cotton fabrics. These natural fibres and non-coated materials have no pores to open and close.
Dyes vs. inks
In today’s wide-format graphics industry, dye sublimation is often handled through digital inkjet printers, but this can cause some confusion, as the process does not use an ink per se. Instead, the fluid stored in the inkjet cartridge is simply the carrier of the dye. This carrier remains on the transfer paper and only the dye itself migrates from the paper to the substrate. Also, the dye has little or no visible colour until it is heated, so the image on the transfer paper usually looks nothing like the final graphic.
Dark materials cannot be used successfully, as a dye can only add colour, which will not show up on a dark substrate. Dyes do not behave like inks.
Other forms of dye sublimation are performed with thermal printers, offset printers, laser printers and screenprinters.
The issue of permanence
When fabrics are decorated through dye sublimation transfers, the graphics cannot be removed the way images screenprinted onto shirts can. Unlike an ink that sits on top of a textile, once the dye has penetrated the fabric’s fibres, it is there forever.
As such, it is very important to get each job right. If any spots appear after transferring an image into a 50 to 100 per cent polyester fabric, chances are they cannot be removed. And indeed, if the spots can be removed, with a bleach or other treatment, then it probably means the images are not being transferred correctly and something is going wrong with the process. When sublimated correctly, dyes are permanent, as they become part of the material.
Another area of confusion is how dye sublimation, which is most frequently associated with polyester-based fabrics, can work on very different materials like ceramics, glass and metals. The answer is through the addition of a polymer-based coating to these materials. Once that special layer has been applied, the dyes can bond to it.
The same is true for non-polyester fabrics. The dye particles are designed to bond with polymers and ‘ignore’ everything else, so trying to apply them to cotton or most other natural materials would be like trying to mix oil and water. There are, however, fabric enhancers, preparation sheets and sprays that can be used to add a layer of polyester to a non-polyester fabric. (These options work best on fabrics that contain at least some level of polyester.)
Entering the market
It is not inexpensive to enter the dye sublimation field. While a sign shop may already have appropriate computers and graphics software in place, with plenty of disk space for high-resolution art files and the right tools for colour correction and management, it is not likely to be equipped with the other necessary components.
While there is a broad range of versatile wide-format printers available today for sign shops, not all printers will work with dye sublimation. The chosen model must be compatible with easily accessed consumables. Laser printers can be used for smaller graphics, for example, because dye sublimation cartridges are available for these devices. The choice will depend on the sign shop’s specific needs, in terms of what products it will offer using dye sublimation, which can range from personalized coffee mugs to building-façade-sized soft signage.
Depending on the type of printer, the sign shop will need inks, ribbons or toners for dye sublimation.
The differences between inks are extensive and will therefore need to be considered carefully. Toner cartridges vary much less, but can differ in colour. Some black toners are darker and more opaque than others. And some may ‘overspray,’ affecting areas of the substrate that they shouldn’t. With ribbons, on the other hand, there is usually only one choice of product for a given printer model.
As for transfer papers, it is best to start out using whichever type is recommended by the ink, toner or ribbon manufacturer. Then, once the sign shop has built up sufficient experience in dye sublimation, it can venture out and try other transfer papers.
Blank substrates need to be right for the type of sublimation being performed. This is especially true with ceramic products.
There are several types of heat presses available. As with printers, the choice will depend on the sign shop’s specific needs. A clamshell-style press will be useful for sublimating mouse pads, shirts and other small, thin and flat items. A swinger-style press is well-suited to thicker flat substrates, such as tiles, marble, glass and wood. Specialty presses can accommodate non-flat substrates, including mugs and hats. There are also ‘combo’ presses, which use interchangeable platens to combine the benefits of flat and specialty presses into one device.
The need for research
With all of this in mind, the decision whether or not to enter the dye sublimation business should be based on careful research. A sign shop will need to be able to invest time, money and effort to make it work, so it is important to know there will be a sufficient return on investment (ROI) from the market.
One of the best ways to answer that question, after understanding the equipment and the process, is to talk to people who have been in the dye sublimation business for a while and can share their experiences.
Johnny Shell is vice-president (VP) of technical services for the Specialty Graphic Imaging Association (SGIA). For more information, visit www.sgia.org.