figure1.jpg

Prepress for Special-Effect Garment Printing

Decorating garments with special-effect inks can be a daunting task when you don’t have everything in place in prepress. These tips will assist you in building reliable and repeatable processes and procedures.

Becoming familiar with how special-effect inks work is critical to printing them successfully, no matter how long the job run. Experimentation aids in determining how special-effect inks will appear on finished garments, given your shop’s equipment and practices.

An ink’s features play a big part in how much it should be incorporated into a design. A high-density ink might work best when used to accentuate smaller or finer design elements, while specialized decorating materials—caviar beads and flock, for example—might not work as effective on smaller designs or graphics that feature very fine lines. Decorative products such as these don’t provide enough surface area to create a visible effect.

Design elements to which special-effect inks are applied must be sized appropriately to take full advantage of the refractive, textural, or other quality the inks impart. Similarly, design considerations come into play when using inks that change dimensionally.

Let’s use puff ink as an example of such an ink. The artist may need to build open space into a design to accommodate the desired expansion of the puff. In addition, when puff is overprinted, its expansion will raise, texture, and lighten the overprinted colors. Large areas of puff can bend or curl, while thick layers of the ink can expand unpredictably and inconsistently, particularly when lots of puff additive is used.

In general, the best way to create artwork for special-effect printing is to think about the printing process in reverse order: curing, printing, prepress, and design creation. Examining the workflow in reverse will allow you to identify your limitations in each step and then make adjustments in preceding steps to make up for those limitations.

Colors and print order
Specialty inks are often printed last in the sequence, particularly those that rise beyond the substrate surface. They are up last because they can interfere with the printing of other colors that may be printed close to the raised edges. However, overprinting raised areas can sometime yield interesting and unique effects in finished prints. Print order can influence many aspects of a design, including the actual number of colors available on press.

Some special effects require that the garments undergo additional processing steps after printing—some of which necessitate the removal of garments from the press before the specialty ink or coating is applied. Caviar beads, flocking, metallic flakes, and large glitter are often applied off-press to printed adhesives or on one of the last print positions on press. Specialized press attachments are available for some of these products, but most shops rely on labor-intensive, off-press methods, at least at first, to become familiar with adhesive-locked materials.

Ink color and opacity
You can generate creative effects when using some types of specialty inks as underlay colors that are then overprinted with conventional formulations. Communicate the desired effect to the production staff, and choose the appropriate combination of underlay and overprint colors.

Using flake-bearing or reflective inks as an underlay, for example, can lead to attractive designs with a deep, layered look. However, the overprinted color must be translucent so that light can penetrate the ink and reflect light from the metallic particles. Dense, opaque colors are typically needed for prints in which high-density inks are layered.

Screenmaking
Print quality begins in prepress. Design creation is an important part of it, but screenmaking is equally critical. High-quality positives are required, given the extended exposure times and tight registration associated with many types of special-effect inks. You need to produce the greatest degree of contrast in the dark, imaged areas of the film relative to the clear areas of the positive (high Dmax, low Dmin) to prevent light transmission into image areas and to provide maximum exposure in non-image areas.
With low-quality positives, the extended exposure times required for thick stencils used with special-effect inks are bound to cause problems. If you can’t generate top-quality positives, then you won’t be able to hold the registration needed for tight-tolerance applications such as lenticular garment prints.

Mesh selection and ink-particle size
The primary consideration when it comes to mesh selection is to ensure that mesh openings are large enough to accommodate specialty pigments or particles borne by the ink (Figure 1). Metallic flakes, glitter, solid particles, and even thicker ink formulations all require mesh that has larger openings and, possibly, a larger thread diameter.

As a general rule, you should select mesh with openings at least double the width of the largest particles in the ink. Ideally, you would use mesh with openings that are triple the width of the largest particles. Doing so would prevent multiple particles from wedging into openings and creating blockages in the mesh.

Mesh selection and stencil thickness are also important when you print an adhesive to which flock, glitter, or other particles with be affixed. Adhesive products must be printed thick enough on the substrate to hold the particles firmly in place, even during washing. For caviar beads, as an example, optimum adhesion occurs when at least half of each beads is embedded into the adhesive (Figure 2). Check with the manufacturers of the inks and coatings you use to find out about specifications for the adhesive thickness that best works with their specialty particles.

Mesh tension
Proper mesh tension is required for quality in any screen-printing job, but it takes on even greater importance when special-effects inks are concern. For example, high mesh tension is a must when working with high-density inks. High-density inks depend on thick layers of ink produced by thick stencils.

The combination of mesh and stencil is dynamic. Squeegee pressure causes flexing and stretching on press, and the greater the span from the edge of an opening in a thick stencil to the other, the greater the deflection of the mesh as it is brought into contact with the substrate. Deflection in large, open space leads to concave prints that have thick in deposits on the edges and thin areas in the centers (Figure 3). Highly tensioned mesh allows for lower off-contact and minimizes the deflection that causes concave prints.

Additional considerations
Thorough testing is the best way to determine compatibility between specialty inks, coatings, and additives. For example, your experiments may indicate that puff additives and metallic inks don’t play well together. Ink manufacturers can give you valuable insight about using special-effect inks properly, but trial and error will demonstrate how the inks behave with the artwork and equipment you use in your shop.

Generally speaking, less is more when it comes to special-effect inks. Sure, you can master the techniques necessary to put several types of specialty formulations to good use in a single design, but that doesn’t mean you should go crazy with lots of ink types in a single garment decoration. Using more than one specialty ink in a design can distract the consumer by creating a confusing field of visual and tactile effects that diminishes the overall impact of the design.

Finally, keep in mind that garments are washed and dried. Test your special-effect prints for washfastness and overall longevity after several wash/dry cycles. Be prepared to communicate the limitations of the special-effect designs to your customers, give them instructions about care and durability, and always focus on creative work and careful testing throughout your garment-printing workflow.

Excerpted from an article by Douglas Grigar, originally published in the June, 2004 edition of Screen Printing magazine. Images courtesy of Douglas Grigar.

View more from this Screen Printing issue