High-density printing has drawn a lot of interest the past few months.  But one of the applications that holds the most potential has gotten little, if any, attention - caps.   High-density printing on caps can provide a wide range of cool looks and set your company apart.  It also can reduce or eliminate some of the challenges typically associated with direct cap printing.

        In a number of ways, high-density screen printing and caps are a perfect combination.  There's a big push for fashion in caps, and 3-D printing makes a fashion statement.  Textured prints, brushed-leather looks, multiple color levels, changing 3-D images, and many other unique effects are possible with a little imagination and effort.

           Because of the hand of the finished print and the cost of producing it (e.g. stencils, labor, time), high-density is better used for smaller prints.   And high-density ink formulas easily cover and fill in substrate irregularities, helping to render substrate inconsistencies a non-issue when printing volume cap orders.

        High-density inks also are easy to print, if you know how.  On the following pages are specific recommendations to make your trip into this new world of printing easier.

        The primary differences between printing standard and high-density plastisol inks relate to the stencil thickness and the ink.  Standard plastisols typically are printed through 20-50 micron stencils.  High-density inks is printed through stencils 90, 150, 200, 350, 400, 700, or 1000 microns thick.

        Printed high-density ink looks like it was die cut from a solid sheet with sharp corners (Figure 1).  High-density inks do not rise like puff inks and do not have rounded edges.

        * Mesh for high-density printing is coarse - a 60 or 80 monofilament.  Use white mesh with dyed emulsion or film.  With clear film, use dyed mesh to reduce light scatter and image under-cutting.

        * Screens for high-density printing should be retensionable.  Coarse (60 or 80 monofilament) mesh can hold tensions as high as 60 N/cm2.  High tension is critical to printing a uniform thickness and maintaining a square edge on the ink deposit.

Figure 1. Stencils for high-density printing are
extremely thick and may be created using
direct emulsions, by layering capillary films, or
by using thick stencil materials.

        * Capillary film is my recommendation for high-density stencils.  Start with 150, 200, or 250 microns, pure polymer film.   Pure polymer exposes in about one-seventh of the time traditional emulsions do.  Exposing these thick emulsions, however, also is different.

        Capillary film 200 microns or thicker should be applied to a screen using the direct/indirect method with polymer liquid emulsion.  In my experience, a better alternative is to expose and wash out the 50 micron film first, then apply sheets of 200 micron film.  (Hint: It's easier to wash out the image if you lay a wet paper towel over it a minute or two before removing the emulsion.)

        Images can be printed thicker than the stencil by repeatedly printing, then flashing.

        * Exposure time is important.  Use an exposure calculator for the first exposure.  If there is a lot of white foam, the capillary film peels off the mesh, or the emulsion feels greasy during washout, increase the exposure time.

        A dyed capillary film cannot be overexposed; however, the positive must be dense enough so the image will wash out.  Clear film can be overexposed, though.  This results in images that are ragged and collapse at the edges instead of having hard, sharp, 90 degree edges.

        With clear film, it's particularly important to use an exposure calculator to avoid underexposure or overexposure.  Figure 2 shows typical exposure times for dyed film using a homemade, 500 watt halogen light exposure unit vs. a 1000 watt mercury vapor commercial unit.   In both cases, the light is 22 inches from the glass of the exposure unit.

Click on Photo to Enlarge

        * High-density inks are offered pre-mixed by several major manufacturers.  The ink can be printed straight from the container.  High-tension mesh and a sharp squeegee blade are important for shearing these inks.

        * Parallel screens are critical.  If there is any screen pitch, the ink deposit will be wedge-shaped.  For example, the halftone dots on the Hoyas basketball print (Figure 3) would be higher on one side of the image than the other.

Figure 3  This Hoyas print was done using Newman
M-1 frames, with 61M mesh stretched to 55 N/cm2;
six sheets (900 microns) of Ulano CDF-QT-150 pure-
polymer capillary film (one sheet was exposed and
washed out and a second rolled on while the first
was still wet); Union Ink's Hi-Square plastisol (3DSQ)
PI 66C; and a Serilor 70--90-70, square-edge, sharp
squeegee.  The squeegee angles were 30 degrees
for the flood stroke and 55 degrees for the print stroke,                                                          Click on Photo to Enlarge
with very light to medium pressure, slow for the flood
stroke, normal for the print stroke.  The six-panel cap
was provided by Alternative Headwear.  Printing was
on an R Jennings Caprinter set up with Quick Print for
minimal off-contact.

        Register the screens on-contact using Plexiglas or another material about 3/32 inch thick.  After registering the screens, remove the Plexiglas so the screen is off-contact, but parallel to the platen.

        * Off-contact should be minimal.  It's tempting to use 1/16 inch, or even greater off-contact with a thick ink deposit.  There should be only enough space between the bottom of the screen and the top of the cap (print surface) to slide in a piece of paper.

        * A squeegee with an aluminum handle and a 70-90-70 or similar durometer blade is preferable.  The blade edge should be square and sharp.  The bolts in the handle should be within 1 inch of each end to support the corner of the blade.

        If the blade corner deflects during the print stroke, it causes the ink deposit to be inconsistent across the image.  Aluminum handles have a compression-fit blade; the bolts go through the handle, not the blade.  Bolts that go through a blade warp it in time.

        * Curing takes longer than in conventional applications.  The thick ink deposit requires more dwell time, but not more heat.  In fact, the temperature can be reduced to conserve energy while the heat penetrates the ink.  Like other plastisols, high-density ink does not crack or pick off if properly cured.

        * Six-panel caps require special treatment.  Pads made of Neoprene or similar material the same thickness as the seam can be placed on either side of it to eliminate "speed bumps" or "pot holes" on the print surface.

        Figure 4 makes it easier to comprehend the dimension of the image.  It shows, for example, that a thickness of 1/64 inch is equivalent to 400 microns.  A 200 micron thick image is 1/128 inch high.

Click on Photo to Enlarge

        The 50 microns printers use for puff inks and white ink on dark shirts are 1/512 inch.   High-density inks create very thick deposits compared to standard plastisols, but the prints do not look particularly heavy.

Figure 5.  The same specs for printing this fused-
buckram corduroy cap from Universal were the
same as for the Hoyas six-panel print in Figure 3.

        The Hoyas image is a simple print requiring only two screens.  The first covers the substrate and creates a smooth top surface, even on panel seams (Figure 3) and corduroy (Figure 5).   One of the great features of high-density ink is its forgiving quality in terms of the print and substrate.  Part of the image was missed at the bottom of the print in Figure 6.  The image in Figure 7 was printed again without losing the image's sharp definition.

Figure 6.  High-density ink is forgiving in terms of the print and substrate.  Above, part of the image was missed at the bottom of the print.

Figure 7.  Here, the image was printed again without
losing its sharp definition.

        Printing with high-density inks requires flooding the image using a low squeegee angle (30 degrees between the mesh and blade) and using slow strokes with light pressure so the ink can deflect downward and fill the stencil.  If the screen is held on-contact during the flood stroke and releases so it's slightly off-contact for the print stroke, the image prints sharper.  The print stroke, by contrast, should be closer to a 75 degree angle or greater, at normal speed, with light pressure to shear off the back side of the image that could hold the ink in the mesh.

        Avoid excessive pressure during the print stroke, or the ink will spread laterally between the mesh and cap.  If the ink side of the mesh is clear, the mesh peels off easier and cleaner, avoiding problems like those in Figure 6.  Mesh peel-off can be further promoted by picking the screen up slowly from the cap-bill side of the frame.

        After the first screen was printed, the first Hoyas image (Figure 3) was flash cured on medium heat for 15 seconds using an infrared cap dryer wit forced air.  A second screen with the same color ink was used to print only large halftone dots.  This approximates the texture of a basketball.

        A single, thicker film saves time in screen making and avoids the risk of mounting positives out of register when exposing multiple layers of film.  However, layers of film make it possible to use positives that are not as dense as they'd have to be otherwise and to prepare thick stencils with a weak light source.  Dense, black images are critical with the longer exposure times thick films require.

        The screen for the Hoyas image was made with 61 white monofilament mesh tensioned to 55 N/cm2.   Six sheets of 150 micron capillary film were used for the first screen and one for the second.  The first sheet on the first screen was exposed using a pin-registration system, washed out, and coated with a second sheet of film using plain water while the sheet was flat and horizontal.  This process was necessary because thicker film was not available.  Although time-consuming, it works.

        The film is coiled with the emulsion side (as opposed to the film-backing side) out to provide for even pressure when rolling the film onto the wet surface (Figure 8).  The film overlaps the edge of the frame to give uniform stencil thickness and prevent emulsion breakdown during printing.

Figure 8.  Although time-consuming, stencils built
using layers of film can produce very successful results.
In creating the Hoyas print (Figures 3 and 5), the film                                                      Click on Photo to Enlarge
was coiled with the emulsion side (as opposed to the
film-backing side) out to provide for even pressure when
rolling the film onto the wet surface.  The film overlaps
the edge of the frame to ensure uniform thickness and
guard against breakdown.

        When dyed capillary film is layered like this or clear emulsion is used, a drying cabinet is helpful in speeding the drying process.  If the emulsion is not dry, it is difficult or impossible to remove the plastic backing sheet, and clear emulsion will blister.  A 10 inch fan with a heating coil can suffice as a drying cabinet.

        A leather patch is the easiest printing example.  Again, 61 monofilament mesh was used with 250 micron film.  The flood stroke is low and slow.  The print stroke was about 55 degrees at normal speed with only enough pressure to make contact with the cap.

        A simple rectangle with stitch marks around the edges is printed.  The high-density suede ink is flashed 10 seconds with medium heat and forced air.  Then athletic blue ink is printed through 40 micron capillary film on 110 monofilament.  The blue ink is printed with light pressure at 55 degrees using only one stroke to preserve the image detail.  The 250 micron patch is printed over a six panel seam; it doesn't get any easier than this.

        The 250 micron film used is clear.  This film does not adhere to the mesh with water alone like dyed capillary film.  First, the screen is coated on both sides with liquid pure polymer emulsion to serve as an adhesive.  Then the dry clear film is laid over the wet liquid emulsion.

        Leather patches are an example of how fine detail can be printed on six-panel caps.  Screen printers tend to avoid printing over seams with standard plastisols because it's easy to lose fine detail in the crack or seam stitching.  With high-density inks, these surface inconsistencies are covered by the underbase.

        Lenticular printing on shirts is catching on with screen printers who want to add new, interesting effects to their prints.  Such images are composed of vertical lines printed with high-density ink.  When applying this technique to caps, the print stroke is toward the bill of the cap rather then parallel to the bill, across the cap, as is typically the case.

        A short, wide image is required for a lenticular cap print to avoid interference from the cap bill.   However, six-panel caps should have images even smaller than the 2 1/4 inch diameter Hoyas to be cool with younger customers.  The five-panel golf caps typically popular with the age 30 to 55 crowd are better for larger images.

        High density looks particularly good in small images like corporate logos (Figure 9), sports images, and the like.  Not all artwork is appropriate for high-density printing.  Fine lines and small details are an example.  The stencil thickness limits the detail that can be exposed and printed.

Figure 9.  The Solo sports logo was designed as a new
corporate logo for a ski apparel company and printed
by Seri-Graphics, Glens Falls, N.Y.  A Newman M-1 cap                                                 Click on Photo to Enlarge
frame with 60 M mesh at a high tension was used for the
screen.  The stencil was made using a single sheet of
400 micron Murakami capillary film.  The Luna Pier cap
from Broder Bros. was printed on an R Jennings Caprinter
using Union Hi-Square high-density ink with the white
tinted by the printer.  Cap courtesy of Seri-Graphics,
Glens Falls, N.Y.

        The sharp, new look of high density is sure to catch your customers' attention and generate new interest in screen printed products.  Your success with high density will depend on your creativity and willingness to experiment. 

        The author welcomes questions concerning this article or other points concerning high-density printing.

*   *   *

              (Editor's Note)   (Below the Editor's Note is a photo of a printed image, but it may load slowly.  Click on the Jeep photo.)

        Roger Jennings is President of
R Jennings Mfg.  His company manufactures
cap printing equipment using
the latest technology.  Jennings is
considered one of the foremost experts
on cap printing in the industry and is
a regular contributor to IMPRESSIONS.
He also is a regular speaker at The
Imprinted Sportswear Shows where he
does seminars on cap printing,
technical screen printing, and business
topics.  Jennings has 20 screen printing
patents, including all existing cap printing
patents.  You may contact him by fax at
(518) 798-3172 or by phone at (518) 798-
2277.

The copy on the CJ-7 cap photo reads:

A lenticular image actually is two images,
but only one can be seen at a time.  When
viewed directly from the front, the "CJ-7"
is seen with thin, black lines through the
image.  From a side angle, the high-density
ink printed through a 250 micron stencil
prevents the red and white from being seen.
"Jeep" has been knocked out of the high-
density black lines to view the Jeep image in
red and white.  The high-density ink is
printed over the black lines that were printed
previously through a 40 micron stencil so that
the black lines run the length of the image
when the cap is viewed from the front.

Sharp stencil edges and very high-tension, flat
screens that are parallel to the platen are
required to hold the resolution of the high-
density ink image.

(C) R Jennings Manufacturing Company, Inc.  2002