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Laboratory Remarks
Gel inks are water based
products; water has a boiling point lower than the solvents used into a ball
pen ink. For this reason refills need a rubber cap to protect them from the
air, and a silicon follower to protect their back from the drying. Moreover the
high temperatures of the storage may cause the formation of air bubbles which
may cause inconsistency on writing performances. This formation of
bubbles follows Henry law: “ the solubility of a gas into water is inversely
proportional to the temperature and directly proportional to the pressure”. When
water comes out of the bottle or from the water tap, the pressure on it
decrease, while the temperature increase.
Viscosity: Gel inks arefluids with a peculiar rheology so that they can work also at a very low
viscosity. For this reason if the tip is not sealed all the ink will flow back
from the refills; the silicon follower infact act only has a non drying agent
and has no resistence to the ink flow.
Another
problem due to this peculiar rheology is the “push back effect”. In this case
the cap is producing an air tight force against the wall of the tube and push
the air through the tip causing irregular writing. Due to this pressure the ink
englobe the air which block the flow. Very important is to design the cap so
that the tip enter into the rubber stopper before clicking into the body. In
this case the air exit from the cap and in not pushed into the tip.
Centrifugation: Is necessary
to remove the little air bubbles englobed into the ink during the manufacturing
and, to push the silicon paste, injected on the back of the refill, directly
against the gel ink in order to avoid its evaporation. Due to the
different types of inks, the centrifuging has to be done with the maximum care.
Dye base: can be centrifuged without problems
for a long period of time and at high speed, provided that the seal between the
adapter and the tube, point and adapter and, point and plug are suitable to
block ink leaking under pressure (in the tube by the centrifugal force).
Pigment base: made with non soluble pigments, well dispersed in the ink, but with
a specific gravity higher than the base in which they are dispersed,
therefore, under the action of a centrifugal force they have the tendency to
separate forming a solid layer on the tips; this will block the ink feeding
causing inconsistency in writing. It will be very important not to exceed the
threshold of the centrifugal force which will cause the separation of the
pigment. The suggested centrifugation
speeds are depending from Ball diamter and are the following
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Ø mm
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rpm
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Time
(min)
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0,50
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900
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2
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0,60
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800
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2
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1,00
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600
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2
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Glitter, Pastel and Metallic Inks: the difference of specific
gravity between the pigment and the ink base is higher that the standard
pigmented inks, therefore more unstable. Consequently, the speeds and
times of centrifugation have to be reduced and the second centrifugation
after 48 hours it absolutely necessary for getting a good de-aeration
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Ø mm
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rpm
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Time
(min)
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0,50
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500
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1
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0,60
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450
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1
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1,00
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350
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1
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After First centrifugation, for the best possible performance, refills should be left to rest tip down and by one of the following methods:
a) for at least 48 hours at a temperature of about 60°C (recommended for refills with the protection wax drop on tip).
b) for at least 72 hours at a temperature of 30-40°C (recommended for refills with tip protection different than above).
Allow refills to cool at room temperature then carry out a second centrifugation at a temperature not higher than 40°C and not lower at 20°C.
Refills and pens should never be kept for a long time a temperatures over 50°C to avoid air entering in solution again.
At
the end, we suggest to put
the refills in horizontal position and temperature should never exceed 45°C.
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