Gel inks
- - - - - - - - - - - - - - - - - - - - - - - - - - - -



Gel Ink is a product which made to use water based ball pen tips. For its peculiar formulation the handling of this product is much more important than the ball pen inks.

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 problemsfor 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 Centrifuge diamter and are the following 

Centrifuge Ř (meters) Rotation Speed (rpm) Time (min)

0,50

900

2

0,60

800

2

1,00

600

2

 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 

Centrifuge Ř (meters) Rotation Speed (rpm) Time (min)

0,50

500

1

0,60

450

1

1,00

350

1

 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 45°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 40°C to avoid aging.

At the end, we suggest to put  the refills in horizontal position and temperature should never exceed 40°C.


Become a fan