The Advantages of Printing with Capillary Film

Capillary Film

Consumers demand choice.  Decorated golf shirts and collared shirts
have replaced ties and jackets at work.  Tote bags, sport bags, and computer
bags have replaced brief cases.  These changes in demand create opportunities
for decorators to earn the highest profits before the new technology becomes
commonplace.

The market
has broadened from decorating smooth T-shirts to a wide range of weaves, plus
over seams of caps.  At first, decorators responded with embroidery, but
today progress allows better looking, more profitable options for decorators.  As
market demand shifts, the decorating technology must change to supply what
consumers want.

Capillary
film replaces liquid emulsion as the technology necessary to meet a wide range
of decorator demands, including:

1. textured garments
2. textured prints
3. higher resolution images
4. lower cost production

Textured Garments  Capillary film used with a
3-D ink lets a decorator lay an ink film over a texture sufficient to compensate
for the depth of the texture.  Pique, corduroy and seams can all be covered
with ink that has a smooth top surface and uniform opacity.  Screen printers
can now decorate golf shirts, bags and 6-panel caps that were the domain only
of embroidery.
Textured Prints  Ink can be laid down in layers
of different ink film thickness.  This allows printing raised seams
of a baseball or raised half tone dots on footballs and basketballs.  A
wildlife mascot can be printed with deep socket eyes, and nose and hair that
stand off the printed surface.  A corporate logo can be printed like
the raised surface of a sign (Exhibit – Sierra Nevada Brewing Company).
Higher Resolution Images  Ink follows the texture
of the garment producing ragged edges on textured garments.  Capillary
film allows printing photographic quality, high resolution images on textures.  Corporate
customers want their logo or brand image to appear on apparel exactly as
it appears in advertising, on packaging and other forms of print media.  Here
is a screen printer’s opportunity to offer a better product than embroidery
(Exhibit – Adobe embroidered vs. Adobe printed).
Lower Cost Production  The bottom line is profit
per hour.  Once a reasonable objective for your profit per hour is determined,
any operating problem that prevents meeting that objective must be addressed.  For
example, pin holes in stencils must be fixed requiring costly downtime.  Capillary
film eliminates pin holes.  A simple job of white ink on a black shirt
would be flash cured in most shops, and printed a second time to produce
a bright image.  The time devoted to flash curing limits manual printing
production to 30-40 shirts per hour compared to 100-120 per hour when flashing
is replaced with capillary film.
What is Capillary Film?  Capillary film is fundamentally
different from liquid emulsion.  The film is liquid emulsion coated
to a polyester sheet which is later applied with plain water to screen mesh.  This
produces a 2-ply structure.  Ink passes around the threads of the mesh,
and the image is defined by stencil material without the influence of mesh.  The
mesh count is no longer used to meter the amount of ink being deposited.  The
film thickness determines the ink thickness.  As a result of the 2-ply
structure, higher resolution images are produced than with screens coated
with liquid emulsion.  The difference is particularly obvious when printing
fine lines and details.

All images are printed in three dimensions.  The x-y dimension is the
image size, but the thickness determines opacity.  A screen printer’s
requirements can range from the thinnest deposits of ink for process and CD
prints to the thickest for high density ink or textured prints.  The following
is a guideline to selecting the optimal film thickness for your application.

Advantages for Small Shops  Capillary film is
not messy like liquid emulsion, does not require mixing ingredients, does not
require storage in the refrigerator, and has a longer shelf life.  There
is no waste, since you cut off and use just what you want. 

Film eliminates the inconsistencies of liquid emulsion.  How many times
did you pull the scoop coater up the screen, on each side?  At what angle?  At
what speed, and pressure?  The number of coatings and how liquid is coated
on a screen determines the coating thickness and therefore exposure time.  An
unknown thickness often in many shops means screens are made a second time,
and that reduces profit per hour.

Many small shops still use wooden screens.  Have you wooden screen users
ever noticed the stencil is darker, and thicker, in the middle of the screen
compared to the outside edges near the frame?  An uneven emulsion thickness
deposits an uneven amount of ink, may be difficult to expose fully, and may
limit your ability to produce halftone colors.  Film is your solution.

Consistency for All shops  Each time a screen
printer changes the thickness of the capillary film being used, the chemistry,
or brand, the exposure time required should be measured with an exposure calculator
(cost $5-45).  Then every time that product is used again there is no
guessing what time is optimal.  After several months of screen making,
the exposure time that produced fully exposed screens may be slightly under
exposed and require extending the exposure time 10% to compensate for the wear
on the bulb.

An exposure calculator is particularly important with the use of vellum.  Vellum
produces gray rather than dense black images.  Light passes through gray
positives.  Over exposed images expose the stencil material in the image
area making washout difficult.

There are capillary films made from the older diazo formulas, the new photopolymer
emulsions and dual cure emulsions.  Generally speaking, photopolymers
require about 25% of the exposure time of a diazo formula of the same thickness.  So
a photopolymer speeds up screen making, and that goes to the bottom line.

There can be significant differences in exposure times between different brands.  Two
film brands each 50 microns of photopolymer were exposed, and one was fully
exposed in 21 seconds and the other in 3 minutes 40 seconds.

Doubling the thickness of a dyed capillary film more than doubles exposure
time.  Film can be purchased without dyes, but that does not provide
protection against light halation and undercutting.  So fine lines, accurate
reproduction of half tone dots and films thicker than 200 microns require dye
to reproduce accurate dimensions.

Unique Processing Differences  Capillary films
can take longer to expose compared to liquid emulsion when the stencil coating
is thicker.  Therefore, the image may have to be washed out differently.  This
is particularly obvious with thicker films.

The method recommended is to wet both sides of the screen.  No water
pressure is necessary or desired.  As water is absorbed into the image
area, the image swells and the image becomes visible.  The image area
becomes rough to the touch as the  image becomes laden with water.  This
process can be accelerated and be more consistent by laying a paper towel over
the image and wetting the paper towel to keep the water in contact with the
image while the water is being absorbed into the stencil.

Now spray tap water at the image, but do not use a power washer.  Tap
water pressure will wash out a stencil that is softened with absorbed water
and not over exposed.  High water pressure should be avoided, because,
like sand blasting, the hard, sharp edges will be removed.  The hard edges
are key to producing high resolution images.

When capillary film is thick, such as 200 microns and more, the stencil will
probably have to be washed out in layers.  After the first attempt to
wash out the image the image will not wash out all the way through the image.  The
image appears like an engraving.  The wet paper should be applied to the
image a second time, or third time, or as many times as required, each time
for 1-2 minutes for water to absorb deeper into the stencil so the stencil
can be sprayed out.

If too much water is used, the edges of the image may absorb water and lift
up.  Stop attempting to wash out the screen.  Allow the screen to
dry, and the stencil will flatten out.  Similarly, when washing out fine
lines in thick stencils, drying a screen during the process may be necessary
to shrink the stencil to open up the image.

Exposure Time and Laminating Films  Many shops
have fluorescent, quartz, halogen and other poor exposure light sources.  Thick
capillary films requiring long exposure times will not be a problem, if thinner
films are laminated.  Each film is exposed and washed out before applying
another piece of film that even a weak exposure unit can expose.

A 50 micron photopolymer capillary film exposes in a time similar to what
most shops experience with liquid emulsion.  If the 50 microns are exposed
and washed out, and then another capillary film, say 200 microns, is laid over
the 50 microns, the 50 acts like a gasket keeping the 200 separated from the
support of the mesh during the later wash out of the 200 microns.  This
produces a stencil 250 microns thick.  If another 200 microns is laid
over the image, a printed image 450 microns thick is created.

How to Apply Film  Capillary film needs lots
of water to stick to the screen.  “The wetter, the better.”  Insufficient
water leaves air bubbles trapped between the mesh and capillary film that look
like white spots.

The easiest way to apply capillary film is to get a length of ½” I.D.
(3/4” O.D.) P.V.C. water pipe 14” or so long.  Roll the film
around the pipe with the emulsion (dull) side exposed on the outside so film
can be rolled down a wet screen on the print side (bottom) with one hand.  The
technique is first to spray the degreasing agent off the screen.  Then
hold the water nozzle in contact with the bottom of the screen.  The screen
should be angled upright to hold water in the mesh while spraying the water
up the screen.  The water should be panned back and forth in windshield
wiper fashion to create a film of water sheeting down the screen.  Simultaneously,
place the roll of capillary film with the P.V.C. pipe at the top of the screen
and roll the film down in the water being sprayed before the roll of capillary
film

Contrary to instructions from the emulsion manufacturers, do not squeegee
wet capillary film into the mesh.  The coarse mesh will push through the
wet stencil material reducing the film thickness and possibly weakening the
film.  Squeeging soft stencil material may cause pin holes, unless the
film is 200 microns or thicker.  If capillary film is 200 microns or thicker,
a light squeegee stroke can be used to improve adhesion.

If air is trapped between the film and mesh, hold the screen in a horizontal
position looking into the ink side of the screen, and gently nudge the trapped
air from the side of the air bubble off the edge of the sheet of film.  Spraying
water into the screen using a bottle like spraying flowers also helps to draw
the film to the mesh and eliminate the air.

Cost  Cost is not just the price of the stencil
material, but also your time and overhead (typically 3-4 times direct labor
cost) to  apply emulsion and handle the product.  Other costs, like
the value of production lost fixing pin holes, should be added to the cost
of liquid emulsion.  Since capillary film is applied to the wet screen
that was just degreased, the additional time required to dry a screen before
applying liquid emulsion and multiple coatings of liquid emulsion are eliminated.  So
total cost should be compared rather than component costs.

Capillary film 20-50 microns costs in the range of 1.0-1.5 cents per square
inch.  So a 12” x 12” sheet would cost between $1.44 and
$2.16, depending on the capillary film thickness.  The cost per garment,
if printing 100 garments, would be $ .01 to $ .02 per garment.   So
the cost is negligible compared to the production value lost to pin holes,
labor, overhead and so forth.  Also, unlike liquid emulsion, the entire
screen is not covered with capillary film, but only the image area.  So
a lot less capillary film is used compared to liquid emulsion.  The rest
of the screen is covered with packing tape or the clear plastic sheets that
come off the capillary film taped onto the screen.  Plastic sheets and
tape make reclaiming screens faster and easier, and that saves money.

Conclusion  Capillary film allows printing the
highly profitable textured materials, and creating three dimensional textured
prints that customers are sure to love.  Corporate customers will appreciate
the superior image resolution, and you will welcome the lower production costs
that also make you more money.  If you have not tried capillary film,
you will want to get a sample to see how it can help your business.