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Get a Feel for Flocking

(December 1999) posted on Sun Dec 19, 1999

Increasing competition among garment printers creates renewed interest in this decorating method


By Bob Borowski

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It's no secret that consumer tastes in casual clothing are becoming more sophisticated. If you need proof, consider the growing number of garment screen printers who are turning to new decorating techniques and materials to enhance the appeal of the T-shirts and sportswear they offer. Specialty inks, embroidery, embossing, and other alternatives to traditional plastisol garment graphics have all attracted interest from shops that want to bring their products into the fashion mainstream. And this search for alternatives is leading some printers back to a decorating option that's enjoyed several periods of popularity over the past two decades: flocking technology.

First introduced in the mid 1970s, the flocking process is not new, but it sank into relative obscurity during the heyday of licensed screen-printed sportswear in the late '80s and early '90s. Now, however, unique design characteristics and increasing competition among garment printers are creating renewed interest in this decorating method.

What is flocking?

Flocking is the process of applying nylon or rayon fibers directly onto garments and other surfaces. Using special equipment, the fibers are propelled into an adhesive that has been screen printed on the garment in the shape of the desired design. (For more details about how to properly apply adhesive for flocking applications, see "Printing Adhesives for Flocking" below.) Under ideal conditions, the fibers are anchored in the adhesive at right angles to the garment surface. The resulting design has a plush, even, velour-like finish with bright color and a soft hand (Figure 1). When correctly applied, the flocked design is durable and permanent.

In the early '80s, printers saw the appearance of the first automated systems for applying multicolor flock designs. At that time, all flocking systems relied on water-based adhesives to affix the fibers to the item being decorated. The process required a high degree of technical knowledge by the user and was often complicated by the tendency for the adhesives to dry on screen.

This time around, a lot has changed, especially in the North American market. To improve the flexibility of flocking systems, plastisol flocking adhesives are now available. After the flock fibers are applied, these adhesives can be carefully cured on conventional conveyor dryers and provide a durable bond between the garment and fibers.

Rather than focusing on multicolor flock designs, most screen printers today use flocking in conjunction with multicolor screen-printed graphics. In this scenario, a single flock color is applied over one or more graphic elements screen-printed with traditional plastisol or water-based inks. Using only one flock color allows you to generate flocked products at a much higher production rate than with multicolor flocking.

Flocking Fundamentals

As I mentioned before, the key to successful flocking is to apply an even and continuous coating of flock fibers. With early mechanical flocking systems, sometimes referred to as beater bar or gravity flocking systems, the process consisted of shaking flock fibers onto the garment surface and rapidly vibrating the garment to move fibers into the desired position and shake off excess fibers.

As you might expect, this method could not guarantee the orientation of flock fibers, so the flocked surface tended to be irregular. Additionally, fibers applied in his manner frequently didn't penetrate the adhesive sufficiently to ensure that they would remain affixed to the garment.

But in the early '80s, DC-electric flocking units made their appearance and vastly improved the flocking process. These systems generate electrostatic charges to propel fibers at a high velocity onto the adhesive-coated substrate. The key benefit to the electrostatic approach is that the fibers go into the adhesive film standing up (perpendicular to the surface) and form a high-density flocked pile. To understand how this process works, let's consider the materials and mechanics of electrostatic flocking.

The rayon (or nylon) fibers used in flocking are manufactured at a uniform thickness (dtex) and cut to a specific length, commonly 0.03 in. (0.76 mm). After cutting, the fibers are usually vat dyed to achieve a particular color, and chemicals are added that enable the fibers to accept an electrical charge in an electrostatic field. When processing is complete, the flock fibers are carefully dried to maintain a specific moisture content and electrical resistivity.

The other half of the flocking equation is the flocking equipment itself. Today, three general flocking-system configurations are available. These include automatic carousel systems for multicolor flocking, standalone flocking units designed to take up one station on automatic garment presses (similar to a flash-curing unit), and portable handheld models for lower-volume applications.

Costs for these systems vary dramatically, from about $3200 for a handheld unit to roughly $12,000 for a single-color standalone unit. Multicolor flocking carousels start at roughly $130,000 and may lead to additional expenses, such as climate-control and drying systems.

All these systems use the same basic approach, but for simplicity's sake, we'll focus on the single-color standalone unit (Figure 2). In this system, flock fibers of the desired color are fed into a flock compartment at the top of the unit. During operation, these fibers are brushed through a perforated steel plate below the compartment at a consistent rate. As the fibers contact the plate, the unit imparts a charge onto each fiber. At the same time, a metal platen below the garment acts as a ground and attracts the fibers as they fall through the mesh. The charge on each fiber is polar, and as a result, the fibers orient themselves so that they travel toward the platen lengthwise. Consequently, when they strike the printed adhesive on the garment, they bond at a right angle to the surface.

Throughout this process, the flock acts as a dipole and is able to oscillate between the flock container and the garment until the adhesive on the garment is completely covered with fibers. The remaining free fibers return to the flock container for later use, and the garment is left with a thick, even flock coating in the desired areas.

Automated flocking systems (standalone and multicolor carousels) can be set to apply fibers automatically when the platen is indexed. They also allow the user to control several other characteristics of the flocking process, such as brush speed, electrostatic field strength, and garment dwell time in the electrostatic field.

When applying multicolor flock designs, the configuration and function of the equipment is similar to that of standalone units, but the technique is different. Multicolor flocking units feature one screen-printing station for applying the adhesive and multiple flocking stations--one for each flock color. Rather than a perforated steel plate, however, the flocking units feature metallized mesh below the flock containers.

The mesh is coated with emulsion and exposed with each design element that will be applied in that particular flock color. This way, a flock color is only applied to the adhesive where the design calls for it. Subsequent flock screens block out this portion of the design and allow their colors to be applied to other areas, just like screens for multicolor printing. In this process, tight registration between the flock screens and the screen used to print the adhesive is a must.

Multicolor effects can also be achieved with single-color standalone units, but they are more difficult to control. In such situations, the printer uses tape to block out areas of the perforated plate where no flock fibers of a particular color should go through. After this flock color is applied, the unit is reloaded with a flock fibers of a new color and a different area of the plate is masked off. The process is repeated until all colors have been applied. This method is used infrequently, primarily because of potential color-registration problems and the time-consuming process of changing flock colors.

Handheld units are simple, scaled back versions of the automatic systems (Figure 3). They comprise an electrostatic generator that works in conjunction with a grounded substrate or metal platen. A handheld flock fiber compartment is attached to the generator. When the unit is operating, the user simply moves the flocking head over the surface to be decorated.

Handheld units require good technique on the part of the user. For example, if the flocking head is held too far from the garment surface, poor coverage by the flock fibers may result. And if the user doesn't keep the head parallel with the garment, the fibers may imbed in the adhesive at an angle rather than perpendicular to the surface. Finally, regardless of application technique, handheld units tend to be more messy than automated models and leave more loose flock fibers on the garment, resulting in excessive waste.

Speaking of loose fibers, even automated systems leave a small amount of loose fiber on decorated garments. So most high-volume flock users install cleaning units designed to rapidly remove excess flock fibers from a garment after the image is cured. These self-contained devices create a vacuum that draws in the garment and remove loose fibers from both sides of the garment. Other flocking concerns

Managing climate and curing with flocked items

As with screen-printing technologies, several variables can influence your success with flocking. One of the major variables relates to the climate (temp-erature and humidity) in the shop area where flock fibers are applied. The problem is that flock fibers are moisture sensitive, and temperature and humidity affect how the fibers react in the electrostatic field. Flock fibers like an environment with approximately 55% humidity at about 68°F (20°C).

When any new supply of flock fibers is opened, the fibers will give off or accept moisture based on the environment of the immediate surroundings. If the moisture content of the fibers changes from the level present immediately after manufacturing, it can alter the fibers' electrical resistivity, and consequently, the density and adhesion of the final flock coating. Less than 30% relative humidity in your shop will lead to fibers that probably won't accept a charge, and levels of more than 65% will cause the flock to stick together and flow poorly through the metallized screen or plate. For best results, flocking should be performed in a climate controlled room--especially if you're doing multicolor flocking work.

Another consideration to bear in mind involves curing the flocked graphic. Since most screen printers do not use water-based adhesives, their dryers generally do not feature multiple, independent heat zones with changeable rates of airflow, which can improve drying time. Even with plastisol adhesives, flocked prints can require additional drying time over conventional screen-printed graphics. In fact, with some conveyor dryers, flocked garments must be passed through the dryer two or more times to cure fully. To ensure that your flocked designs have been exposed to proper drying conditions, make sure to wash test samples from each run you produce.

Conclusion

For years, flocking has been a valuable decorating alternative with a unique appeal. Although it costs a little more than producing a plastisol screen print, it's far less expensive than embroidery. Flocking is an economical option for producing images with a soft texture, bright color, and dimensional quality, which can add value to the garments you offer and potentially earn new business for your company.

And garments aren't the only products suitable for flocking. You can branch out into new areas with flocking, such as doormats, coasters, ad-specialty items, and similar novelty goods. Additionally, for those with a firm understanding of flocking materials and application techniques, flock fibers can also be used to produce flock transfers.

Flocking remains a relatively obscure decorating option, but as more printers look for alternative methods to differentiate their products, it is sure to gain popularity. Now may be the best time for your company to adopt flocking technology and offer a high-quality product few of your competitors can match.

Printing Adhesives for Flocking

Mesh: In general, use 60-110 thread/in. (24-43 thread/cm) monofilament mesh or 8xx or 10xx multifilament mesh.

Frame: Use retensionable aluminum frames, stabilized at a minimum of 20 N/cm.

Stencil: Standard emulsions are fine for use with plastisol adhesives. For meshes above 110 thread/in., create a stencil "well" by using only one emulsion coat on the squeegee side and up to eight coats on the print side. Increased exposure time may be required. Indirect stencil films may also be used.

Artwork: Produce artwork in a similar fashion to graphics used for printing puff inks, with lines no smaller than 1/16 in. (1.6 mm). Avoid large, solid areas, which can increase curing times on decorated garments.

Adhesive: Use a two-part plastisol adhesive formulated expressly for flock fibers. Prepare the adhesive in small batches using a tightly resealable container. Prolonged exposure to air can reduce the material's adhesion properties. You can also add compatible pigments (up to 10% by weight) to the adhesive, but this may increase curing times.

Printing: Print with off-contact that allows the mesh to separate from the print surface after light to moderate squeegee pressure. Make sure that the adhesive is printed on top of the fabric, not driven into it.

Curing: Adjust curing parameters until the flocked garments pass a wash test. This is the only safe way to ensure sufficient curing.

Testing for adhesion: Allow finished garments to set for 24 hours before wash testing. Flock fibers coming loose from garments indicates improper application or insufficient curing.

About the author

Bob Borowski has been involved in the flocking industry since 1971. In 1973, he founded Creative Coatings Corp., a sales and marketing group for flocked materials and flocking equipment that represents numerous German equipment manufacturers in North America and a number of US manufacturers of flocked products. Borowski can be reached via e-mail at Flocking@aol.com.


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