screen printing

 

 

 

Screen printing starts with just that ... A Screen (Mesh stretched tightly across a rigid frame)

What is mesh? Is a fabric manufactured to have thousands of wide spaces between the threads, this spacing allows ink to squeeze through.

 

Problems and possible solutions..

Problems Solutions
When coating screens emulsion is too
thick, chunky and drips.
Coat in thinner applications, use sharper blade on coater. Coat
thin, dry, coat again for a stronger stencil. Make good positive
contact with the scoop coater and the screen.
When washing out a screen the squeegee
side feels very slimy, the emulsion puckers
then peels.
Increase the exposure time, the stronger side of the screen is
where the light contacts first. A good exposure will eliminate the
“slime” and yield a stronger screen.
After washing the screen there are holes in
the emulsion surrounding the design?
Always clean the glass to the exposure unit prior to burning a
screen, check for scratches on glass. Make sure your darkroom is
clean, as dust in the mesh during coating may cause pinholes.
The screen breaks down and/or pinholes
develop mid-production.
After the screen has been washed, touched-up
and dried it's highly recommended to expose the
screen again or place in the sun for 5 minutes.
The screen has “halos” or spots in the
emulsion that are lighter in color and
usually circular, interfering with art or
breaking down.
Oil from fingers, dirt and contaminants can leave “rings or halos”
in your coating. These will lead to bad edge definition, premature
breakdowns.
When making the first print with new
screens there are streaks in design that
won't print although the design appeared
completely open.
After exposing and washing if the exposure time wasn't correct
and the emulsion feels “slimy” when the screen
is set on end the slime drips into the design and blocks the open
areas.
Screens take a long time to dry and/or
sticky.
Humidity affects screens greatly; a de-humidifier will dry screens
quickly and completely.
After exposing screen and processing the
image appears but doesn't wash out
completely or at all. Even with high
pressure.
The film positive may not be dark enough, double your films,
check your printer settings, use a RIP or the screen may have
been exposed to excessive room light.
When reclaiming, even with proper
chemicals the design will not wash out,
even using a pressure washer.
Improper exposure times (underexposing) will lock in the
emulsion. Using a higher power pressure washer will damage the
mesh. The screen will need to be re-stretched.
When lining up a multicolor job the designs
colours are burnt in odd locations, some fit
while others won't.
Make sure when burning multi-color films to use
“Pre-registration” system and all film colours are in alignment.
When making a test print the ink leaks
from the sides of the screen.
Always tape the inside perimeter of the screen, tape along the
outside of the screen as an added precaution.
Incomplete print image. Streaks in print or
middle fading out, rough finish.
Turn blade around, sharpen or renew blade. Squeegee not
parallel with screen. Squeegee edge is not flat.
Incomplete print image. One side keeps
hanging in the screen, deposits uneven.
Minimum squeegee width is 10 mm or 1½ to 2” extra on each side
of screen image. Make sure to have even pressure on both sides
of the squeegee.
Incomplete print image. Stencil emulsion
too thick for type of image and/or viscosity
of printing inks.
Use recommended screen mesh with thinner coating or
change to less viscous ink (see below).
Incomplete print image. Ink too thick to be
completely drawn out of screen image as
screen lifts off substrate behind squeegee
on print stroke.
Adjust off-contact and slow your print speed down or adding
curable reducer in small quantity, until suitable consistency is
obtained. Change mesh count as last resort.
Incomplete print image. Ink has dried in
screen and is blocking flow through part of
image (Common with solvent and waterbase
inks).
Use recommended drying retarder instead of thinner, after
removing screen and cleaning it. Keep screen flooded in both
cases.
Image was not washed out correctly when
screen was made.
Rub with damp cloth or remake screen using fine spray to wash
out image area thoroughly. Blot dry to remove water.
Screen is breaking down, film used to
make screen was not dense enough to
prevent light getting through, weakening
image in stencil.
Create new artwork with clean-edged solid lines and areas to
block off light COMPLETELY.
Lines of artwork too fine for type of screen
used.
Make new screen using recommended mesh for fine details.
Print area incorrectly positioned, has
overrun edge or won't line up properly.
If screen positioning controls will not correct (Joystick/mico), the
image is wrongly placed on screen: correct position is central and
equal distance from sides of frame.
Incomplete print image, perhaps with a
heavy deposit of ink in places.
Increase pressure in small steps until good impression is
obtained.
Incomplete print image with very light
deposit.
Off contact (print gap) is too large. Set screen-to-substrate gap
correctly. Ink may be too thick or change the angle on your
squeegee.
Print image becomes incomplete, after
starting of print run it was satisfactory.
If the is blade not properly in contact with screen during flood
stroke, poor distribution of ink supply lessens coverage and
consistency.
Print image missing at one end (or the
other) but print quality is satisfactory.
Length of print stroke too short. Print the entire image so that
squeegee is not lifted off screen until a minimum of 5cm past end of
image area.
Print image missing both sides. Squeegee too narrow. Minimum squeegee width 1cm to 2cm past
end of image area.
Missing parts of print or nick in successive
prints, after satisfactory start to print run.
Lint, dust and particles. Raise the screen and wipe underside of
screen before continuing; make sure to snap (shake) shirts clean
before loading.
Print image out of register. Screen not accurately aligned over shirt Screen isn't properly
locked in registration guide or mesh may be too loose, replace.
Print smudged or ink spreads at bottom of
design. Off contact is too close or the
squeegee is resting on open image
allowing ink to gather there.
Squeegee-to-screen gap too small. Increase off contact until
screen peels away from substrate immediately behind squeegee.
Print smudged or ink spreads at bottom of
design (Continued:)
Strands of mesh from damaged screen are hanging down from
the frame and dragging across the print area. Check and remove.
Print image has serrated edges. Screen mesh too coarse or stencil emulsion is too thin. Change to
screen with finer mesh or change to a thicker emulsion coating.
Poor definition at edges of image
particularly at rear edge of each deposit
with ink deposit thin.
Squeegee pressure too heavy. Reduce squeegee pressure in
small steps until good print is obtained, then increase pressure
slightly.
Poor definition at edges of image with
heavy ink deposit.
Off contact too high, reduce screen-to-substrate gap until problem
clears.
Printing ink does not take properly to
substrates or washes off, cracks, etc.
Proper inks, check for total cure.
(166 Degrees C) Goods might have contaminated printing surface
(waterproofing, starches).
Ink spreads and/or bleeds after printing. Screen mesh too coarse for type of printing ink and type of image
(example: some gold inks for fine-line conductor work) and/or
improper cure.
Shirt sticks to screen / Flat stock sticks to
screen.
Shirt is not held down by table adhesive (Board Glue). Increase Snap off.
   
   
   
   
   
   

 

 

 

 
Designed by PeasySqueegee  - 2016