Fabric Printing: Of Heat Presses and Papers

In the two previous installments of our “Fabric Expert” series, we looked at the printing process, with an emphasis on dye-sublimation. In fabric printing, however, the printer is only half of the imaging equation. Depending on the ink you’re using, you will also need some kind of post-printing equipment to complement or complete the printing process.

For dye-sublimation, says Andy Arkin, director of integration for Next Wave Sublimation Solutions, “a printer does you no good unless you have a heat press.” Next Wave offers all the pieces of a complete digital textile printing workflow, including software, printer, ink, paper, fabrics, heat presses, and finishing equipment. They distribute transfer-based dye-sublimation printers, and are also a distributor of EFI Reggiani fabric printing equipment.

Before we look at heat presses, let’s back up a second and talk for a moment about transfer paper, an often overlooked but vitally important component of the dye-sublimation process.

Paper view

Dye-sublimation transfer paper contains a special coating that holds the ink laid down during printing. During the transfer stage, under exposure to heat and pressure, the paper releases that ink onto the fabric. Dye-sublimation can be used on substrates other than textiles, so you need to choose your transfer paper accordingly.

“You should be conscious of the type of paper you’re using,” says Rob Repasi, VP of Global Sales for Beaver Paper & Graphic Media. “There are papers that are more desirable for textiles as opposed to hard surfaces such as ceramics, coffee mugs, or metal."

There are premium multipurpose papers—like Beaver Paper TexPrintXPHR—that are compatible with both hard and soft substrates, which is convenient if you’re offering a variety of dye-sub-printed products.

The quality of the paper will largely determine how much of ink gets released, but ink dye load is an important consideration. “Dye load” refers to how much colorant (dye) the ink contains relative to the liquid vehicle. The higher the dye load, the less ink you need to lay down to get a given level of color. Different transfer papers are thus formulated to be compatible with the dye load of the ink, which is usually a function of the make and model of the printer you are using—or, that is, the printer manufacturer’s ink set.

Ideally, a transfer paper will release 90 percent of the ink “stored” in it. There is no quantitative way to measure this, but if you find you’re not getting as much ink out as you think you should be, you may need to switch papers or adjust your color profiles. Alternatively, you may be releasing too much ink onto the fabric, which means that you may be putting too much ink onto the paper to begin with.

“There is a misconception of how much ink is really needed,” says Repasi. “More ink doesn’t necessarily mean more color. You’ll end up with a very poor image by applying more ink than the paper can handle.” It’s all a question of balance. “The right amount of ink with the right color management with the right paper will generate the best possible output of color.”

Printed transfer paper doesn’t have to be sublimated immediately. Beaver Paper’s own internal experiments have found that printed transfer paper can last for years. “We’ve transferred literally a year or two later and it’s remarkably close to the original prints,” says Repasi. It will of course depend on the conditions under which the paper is stored. Still, in today’s fast-turnaround world of digital printing, you’ll probably never need to store transfer paper for even a few hours, but if you need to, you can.

Pressing matters

Once you have your transfer paper printed, it’s time to fire up the heat press.

First a terminological note. We often see the term calender – not to be confused spelling-wise with calendar (despite Autocorrect’s best efforts) – used in conjunction with dye-sublimation printing. What’s the difference between a calender and a heat press?

“A calender press is a rotating heated drum intended for feeding continuous materials for sublimating items like banners or other long stretches or bulk fabric,” says Aaron Knight, VP of Geo Knight and Co., a manufacturer of a wide variety of flatbed and specialty heat presses. “It’s not capable of pressing rigid materials, nor is it appropriate for doing smaller piece goods.” A calender, then, is a roll-to-roll heat press.

In a calender, heat is produced in a central drum against which the fabric and paper are pressed. The highest-quality calenders have a central drum filled with oil that is heated to the desired temperature required for sublimation, typically in the neighborhood of 400°F. The transfer paper/fabric sandwich is rolled around this drum at a set rate that is, again, optimal for sublimation. A top-notch oil-filled calender will run you about $30,000 to $60,000, but can last for more than 25 years.

There are other kinds of less expensive calenders that use electric heating elements rather than oil, but a common problem with them is inconsistent heat around the circumference or across the width of the drum. This can cause imaging problems or discoloration during sublimation which, after all, is a careful balance of time, temperature, and pressure. “If any one of those three changes, you will not have a consistent result,” said Arkin. “Color will not come out the way it is supposed to. If you have inconsistent heat on the press, the sublimation process will not be consistent across the entire piece of fabric.”

Calenders have different width drums, which affect the press’s throughput. The larger the diameter of the drum, the more fabric can be wrapped around it, and thus the faster the process will be.

Calenders transfer the fabric and transfer paper on a belt often made of Nomex. “The belt is a critical part of the nice tight sandwich you need around the circumference of the drum,” says Arkin. “Cheaper machines have very thin belts, while good machines have belts that are one-half to inch to three-quarters of an inch thick. If it doesn’t stay nice and flat, sublimation gases can escape.” A high-quality belt can last up to five or six years. There are beltless calenders that are suitable for direct-to-fabric dye-sublimation, where you don’t have to worry about transfer paper.

If you’re not sublimating rolls of fabric but rather cut pieces, the alternative to a calender is a flatbed heat press. Flatbeds also come in several varieties:

• A clamshell opens and closes like its namesake, squeezing the paper and fabric together.
• On a swing-away press, the upper platen, which holds the heating element, slides away to the left or right, making it more suitable than a clamshell for thicker substrates.
• A drawer press has a front-loading lower platen that, when the fabric and paper are loaded, slides back in place and the heating element is brought down on top of it. There are also specialty heat presses that can accommodate things like mugs, plates, caps, and other three-dimensional objects.

In most cases, an automatic timer can pop the press open after a desired transfer time to prevent overheating, especially if an operator is attending to multiple presses.

There are newer “all over sublimation” flatbed heat presses with heating elements on both the top and bottom that essentially “duplex” dye-sub transfer, which is useful for applying continuous graphics to both sides of, say, a T-shirt.

When it comes to choosing a flatbed press, says Knight, “the product the user is printing, and the volume they are doing, will dictate which of these choices is appropriate. Also, the size of the item they are printing will direct them towards a few narrowed-down choices for heat presses.”

If you are using a flatbed heat press, you may need to use “tack” transfer paper, which has an adhesive applied that, when activated by heat, keeps the paper in contact with the fabric so there is no shifting during the sublimation process, which can cause blurring or ghosting. Tack paper isn’t usually required when you are using a roll-to-roll heat press, except if you’re sublimating onto a very elastic fabric which can stretch as it moves through the calender, resulting in a distorted image when it relaxes after cooling.

If you are sublimating to highly stretchy fabric, you may need to compensate for stretch even before printing. “You establish what the shrink or stretch is for a given material, and you build those distortions into your files when you print them,” says Arkin. “Every time you handle that particular fabric type, you print it the exact same way so you get a consistent result.” It’s kind of like color profiling, in a way.

Even if you are doing direct-to-fabric rather than transfer-based dye-sublimation, you still need to run the printed fabric through a calender to fix the ink onto the fibers of the polyester, and the same quality and consistency concerns apply.

Even if you’re printing with other kinds of dye or pigment inks – not sublimation –you still need some kind of pre- and/or post-treatment of the fabric. Reactive and acid dye inks require steaming after printing, then washing to remove excess ink. This is one reason that dye-sublimation is so attractive for fabric printing; these other ink types can require a lot of water.

Sewing it up

Regardless of the specific configuration of heat press, you don’t want to skimp on quality. “Look for same-day support and longevity; in a word, quality,” says Knight. “In the equipment world, especially with heat presses that reach high temperatures and high pressures, you need one that will last decades, not just months or a few years. A good heat press gives you quality results and builds your business – a bad press puts you out of business.”

“The right heat press is what separates you from being able to produce an okay graphic vs. a fantastic graphic,” says Arkin.

Next month, in the fourth installment of this series, we will look at the finishing process: sewing, welding, and a fast-growing form of fabric finishing, especially for signage, silicone-edge graphics. 

Demonstrating the MAGIC of a Complete Fast-Fashion Workflow

This past February, EFI showcased its end-to-end workflow for a design-to-finished-garment process at the MAGIC Marketplace event, at the Las Vegas Convention Center. Held twice a year, the MAGIC events bring together the fashion retail industry to promote the latest in apparel, footwear, accessories, and manufacturing – from contemporary luxury brands to the latest in “fast fashion.”

A complete ecosystem for digital textile production, EFI’s Digital Textile Apparel workflow comprised the following components:

Design: EFI Optitex 2D and 3D solutions enabled selection and preparation of designs, including patternmaking and avatar draping.

Print preparation: EFI Fiery DFE systems quickly and accurately converted designs into printing data, with fast data transfer to digital inkjet printers and to dedicated cutting systems.

Printing: EFI Reggiani printing solutions offered a digital printing process with water-based dye-sublimation inks. The eco-friendly, green production technology with water-based inks delivered stunning colors and color fidelity for striking fashion designs.

Image transfer: A heat press from EFI partner Klieverik was used to transfer printed designs from paper onto fabric.

Cutting: Technologies from EFI partner Zünd automated the cutting process compatible for almost any material to prepare fabrics for sewing.

Sewing: Automated sewing solutions created finished garments from printed pieces.

“EFI has assembled a unique solution for the fast fashion market, and we were excited to bring it to MAGIC,” says EFI Reggiani VP and general manager Adele Genoni. “From design to print to cut-and-sew, to the finished garment, visitors to our booth [experienced] the complete workflow and gained an understanding of the huge potential that on-demand digital printing can bring to the fashion industry.”

“This workflow makes it easy to collaborate globally and reduces the cost of both sample making and the manufacture of small-lot apparel. It’s already revolutionizing the fast fashion market by reducing the need to ship expensive samples around the globe, speeding up the design and manufacturing process.”