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Cleaning
the Screen |
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Proper
fabric treatment and adequate
degreasing are very important
for good result. Therefore,
wash the screen with clean
water and dry it. |
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Mixing |
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Take
1 kg of BLUECOAT emulsion
in a clean vessel. Also take
a glass of distilled water
sufficient to mix 5 to 7 grams
of Ammonium Bicromate and
stir the solution till it
is completely dissolved. Mix
this solution of Ammonium
Bicromate with the BLUECOAT
solution of 1 kg. and stir
until the colour of the solution
is changed to light uniform
green. Viscosity of the emulsion
can be adjusted with distilled
water Filter the emulsion
with bolting cloth and close
the container at least for
1/2 hour so that all the air-bubbles
are disappeared. |
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Processing
and Coating Techniques |
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It
is always desirable that light
in the Photography department
is subdued light and if possible,
yellow light.
Direct emulsion coating requires
skill to produce uniform pinhole
free stencils. Important factors
are the fabric mesh number,
thread diameter, colour of
the fabric the tension and
the solid contents, the thickness
of the coating blade, angle
and speed of the coating blade
across the screens etc. If
you change the supplier of
the bolting cloth, check and
see that you are receiving
the same type of material
as before. Thus it is very
important that print quality
is dependent upon the correct
coating technique. If the
coating is made to the satisfaction
then one coating is sufficient
from outside otherwise repeat
the procedure. |
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Drying |
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After
the coating is over, it is
important to thoroughly dry
the coated screen before it
is exposed otherwise stencil
quality will be poor. Moisture
remain present in the coated
screen even when the screen
feels dry to touch if you
are coating the screen for
second time. It is important
that the first coat be thoroughly
dry before the second coat
is applied. Dry the coated
screens in horizontal position
at room temperature with fans,
to get best result and sharpness. |
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Exposure |
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Exposing
is one of the most important
factors in achieving fine
image and sharpness and maximum
mechanical screen resistance.
The only way of achieving
the correct exposing is through
adjusting exposing time using
fixed factors such as no of
tubelight, the quality of
the light, set distance and
set coating techniques and
accordingly photography time
is adjusted. Time of photography
varies between 30 seconds
to 120 seconds under standard
conditions. |
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Washing |
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Immediately
after the exposure of screen
wash the screen With gentle
spray of water from the squeeze
side i.e. inside until the
image comes up if required
use rubber foam gently. |
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Blocking
out and touch up |
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The
most common method is to use
the excess emulsion for filling
the entire screen with a piece
of cardboard it touching is
required use the same material. |
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Drying
with sensitizer |
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After
the screen is washed out.
dry the screen and apply with
piece of cloth liquid solution
of ammonium bicromate. Before
sending it to printing department,
wash the screen with a sprayer
to remove the excess bircromate.
Your screen is ready for printing. |
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Advantages |
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Time
saving |
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Considerable
time is saved in preparing
one complete screen with Blue
Coat photo emulsion. The screen
is ready to use within 30
to 45 minutes depending upon
the repeat and urgency which
otherwise take on day with
lacquer. |
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Cheaper |
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Cost
wise Bluecoat emulsion is
cheaper than the traditional
lacquer which is very costly. |
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No
disruption |
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Printing
programme is not disturbed
if screen is torn out on the
table or machine. With BLUECOAT
emulsion, Screens can be prepared
immediately. |
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Sharpness
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Sharpness
of the design is the hallmark
of the BLUECOAT photo emulsion
and sharpness of the design
improves to a great extent. |
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Cleanliness
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Cleanliness
in the photography department
and avoidance of bad smell
is possible with the use of
BLUECOAT photo emulsion. |
