Fabric Printing: Finishing on a High Note

In this fourth installment of our “Fabric Expert” series, we look at fabric finishing. Just as paper, board, and similar materials can be finished in a variety of ways – cut, mounted, grommeted, laminated, etc. – so, too, are there several ways in which printed textiles can be finished.

It’s important to note up front that, as with any kind of finishing process, the equipment and skills you need will be a function of the kinds of textile products that you are printing, whether that be signage or apparel.

Now that’s a knife

The first and most obvious finishing process is cutting. Cutting printed textiles is not remarkably different from cutting paper – it can be done by hand, with machines, or on cutting tables such as those by Esko or Zünd. There are, however, some special considerations.

The most basic cutting tool is scissors, and the step up from that is a rotary blade, a small, handheld electric cutter with a circular or octagonal blade. “This is used for cutting one or several layers at once,” says Tommy Martin, product manager, textile & apparel business development and marketing, Mimaki USA. “It’s not used for cutting very detailed patterns, but mainly for cross-cutting and other fast, gentle curve cutting.”

Other cutting machines include:

• Band knife: This uses a flexible, endless loop blade that remains stationary while the fabric is moved beneath it. 
• Die cutter: This uses a metal die to cut the fabric into specific shapes, like die-cutting used in commercial printing; it can cut one or several layers of material. 
• Straight blade: This is a large (up to 13 feet), straight, reciprocating blade cutter with a half-inch-wide blade. It’s mostly used for cutting several layers of fabric at high speeds. It can also cut sharp corners and fine detail.

Large cutting tables, such as Esko’s Kongsberg line, which cut other types of wide-format and specialty graphics, can also be used for textiles.

Frayed not

One important consideration in textile cutting is that when you cut a fabric, you are exposing the threads that comprise the fabric. If you have ever made your own cut-off denim shorts, you know what can happen: the threads get more and more frayed. So the edges need to be sealed.

“If you’re just doing right-angle cuts, you can cut fabric pretty easily on any X-Y cutting table,” says Greg Stewart, digital finishing product marketing manager for Esko. “When you get into curves, that’s where the fabric starts to fray on the edge of the cut.”

Polyester-based textiles have an advantage in solving this. Since polyester is a plastic, using a heated knife melts and seals the edge of the fabric as it cuts,

Some power users have turned to laser cutters, either as a tool mounted on X-Y cutting tables, or as a standalone tool to seal fabric edges post-cutting. “We have a number of customers today using the roto-cut tool that enables them to cut the fabric and if they have an edge that needs to be sealed, they use a laser-only device,” says Stewart. This can be a more productive solution compared to mounting a laser tool onto a table. 

“When you fix a laser as a tool on the traverse, you get a lot of downtime when you change over from one type of job to another,” says Stewart. “And the weight that the laser adds slows the table speed down.” A laser also requires a reflective surface, so changing the mat on the table also adds downtime when switching to and from a laser tool.

Then there’s the fabric itself. “The limitation of laser cutters is mainly the type of fabric and how the fabric reacts to the laser,” says Martin. “For example, cotton burns, but polyester leaves a clean, melted edge.”

There are also water-jet cutters that use a high-pressure – up to 60,000 psi – jet of water, or a mixture of water and an abrasive material, to cut fabric, as well as leather and plastic materials.

A stitch in time

Another finishing process is sewing, and the specific type of sewing will vary according to the final product you’re making. If the fabric is going to be made into a garment, it will need to be sewn according to the pattern that was drawn up prior to printing.

If it’s going to be a banner or some other kind of display graphics, it will need to be hemmed. Hemming is done to prevent the fabric from fraying (see above), although if you use a heated knife to seal the edges of cut polyesters, you may be able to skip hemming. (If you are printing and finishing natural fabrics, you probably can’t avoid hemming.) Hemming also provides reinforcement and structural support.

Hemming can be performed by hand, just as you would hem a pair of trousers, although that’s not the most efficient process. If you are doing more than the occasional one-off textile banner or sign, you will need to invest in sewing equipment, and equipment that is more compatible with industrial production than the Singer sewing machine you may have at home. Fabrics used for sign and display graphics can be too thick for consumer-grade sewing equipment, which simply doesn’t have the horsepower and lacks the durability that will be required.

By the way, if all you are doing is simple hemming, you may not need sewing equipment at all. The easiest and least expensive way to hem a graphic is with double-sided adhesive tape, aka heavy-duty banner tape. Dedicated banner tape is stronger and more durable than what you would be likely to pick up in Staples. Although tape is more commonly used to hem vinyl banners, it can be used on fabrics, although it’s not always the best option since tape doesn’t stick particularly securely to textiles. If you are doing outdoor applications, for example, even the slightest wind or rain could cause the tape to come off.

Sewing equipment is not just for hemming, but also to tile multiple panels for extremely large signage, as well as form pole pockets or otherwise reinforce whatever mounting mechanism is going to be used.

“There are hundreds of different types of sewing machines, with thousands of different features, from small home machines to large, fully automated robotic sewing operations and process lines,” says Martin. “I would advise finding a sewing machine supplier that understands the industry that you are in.”

Weld done

Remember how we used a hot knife or a laser to cut and melt the edges of polyester fabrics to prevent fraying? The same principle can be applied to hemming. Called welding, the process applies heat and pressure to fuse the fabric to itself. Welding has more nuances than you would think, and there are several different varieties of welding:

• Dielectric welding: The fabric is sandwiched between a die and a base plate; heat is applied and fuses the fabric along the surface of the die. 
• Rotary welding: The fabric is rolled beneath wheels that apply heat and pressure. 
• Wedge welding: A variety of rotary welding that uses metal wedges to apply heat to the fabric just before it passes beneath the drive wheels.
• Hot air welding: Another variety of rotary welding that jets hot air onto the fabric just before it hits the drive wheel.

The specific type of welding equipment you buy will be a function of the kind of material you’re trying to weld and the products you’re trying to make. Also be aware that welding is not useful for natural fibers, since they don’t melt when exposed to heat and pressure.

Finishing up

Keep in mind that if you are new to fabric printing, you can certainly choose to outsource any or all of these finishing processes. Forming alliances with companies that specialize in textile finishing can be a great way to get your feet wet, without a great deal of initial investment. Then, as you get more proficient, you can bring the needed processes in-house.

Next month, in our final fabric-printing installment, we’ll look at the various vertical markets for textile printing.

Gaining an Edge: Silicone Edge Graphics

If you have been in an airport recently, you may have noticed a form of fabric finishing that has been growing in popularity. Called silicone edge graphics (SEG), it’s a quick and simple method to mount fabric-based signage in a metal frame in a way that’s attractive, lightweight, and easily swappable.

Basically, you sew a thin silicone strip – called a welt or a gasket – around the edge of the printed graphic. The gasket then fits into a groove in a thin aluminum frame. The graphic is pulled tight, very closely resembling rigid graphics. It has become popular for busy public locations, like airports, since an added benefit is that it also absorbs sound.

“If a shop is looking to do wall standoffs or backlit, SEG is a must,” says Tommy Martin with Mimaki USA.

The secret to SEG is making sure the graphic precisely fits the frame. Once you have the template down (SEG kits come in standard sizes), it’s very easy to pop the old graphic out and pop the new one in. This simplicity eliminates the need for having professional installers. For an added effect, LED lights can be used around the edge of the frame or placed behind the graphic to create a backlit display.