[ankitgangwani]

I am developing Dot Matrix printer ribbon inks. I need help with the formulation.

This is how dot matrix printing works:

A nylon ribbon is inked and put into a cartridge which is put in the printer. The print head strikes the ribbon (just like a typewriter) and the character is printed on the paper which is underneath the ribbon. Since the ink from that area is exhausted after the strike of the ribbon, the ink has to replenish from the surrounding areas so that when an impact is made at the same area again, the printing happens.


A dot matrix ink essentially contains the following –

1.   Vehicle – It carries the dye and the pigment. Vehicles could be non drying oil or glycerine.
2.   Dye – They are mainly oil soluble or spirit soluble dyes. Even though the dyes are soluble in various oils directly (since they already contain oleic and stearic acid), best results are observed in dissolving them in soluble in crude oleic acid and solvents like alcohols and glycols. Examples of dyes that we are using is induline and nigrosine.
3.   Pigment –It gives opacity to the printed character. The difference between a dye and a pigment is that a dye dissolves in the vehicle (a chemical reaction takes place), where as the pigment is just suspended in the vehicle. In our experience, it may not be used also or used in very less quantities (maximum upto 3-5% of the ink) as using more of it tends to increase the viscosity of the inks.
4.   Solvent –Its job is mainly to dissolve the dyes. As per our observation, the dyes are better soluble in a solvent (better color strength) as compared to dissolving them in oils directly. It may or may not be added but I add them to get better color strength

The ingredients are mixed together and grinded in a three roll mill to make the particle size less than 5-6 microns.


Following are the characteristics of a good ink –

1.   Right viscosity – The viscosity of the ink is of supreme importance. The most important characteristic of the ink is spreading of the ink which allows the ink to flow from the surrounding areas to the impacted area from where the ink is exhausted after the impact takes place.
2.   Good light fastness – The ink should produce dark printouts.
3.   Non drying – The inks should not dry from the fabric for a good 1 year as the fabric is placed in the cassette and the cassettes lie on the counter for this amount of time for sale.
4.   Life – Once installed it should produce maximum characters. This is only possible when the ink is of the right viscosity which allows the flow of the ink while absorbed within the ribbon.

We have tried various permutations and combinations of the above ingredients to develop the ink. The observations are summarized as below.

We have tried various vehicles like castor oil, Linseed oil, Soyabean oil, Mobil oil, Oleic Acid and Glycerine and combinations of the above.

The best vehicle is observed to be Castor oil. It mixes the dye properly but the maximum concentration of dye it can take is 5-7% as after that the oil becomes too viscos and stops spreading on the fabric.

All other oils do dissolve the dyes but there is a strange observation about them. When the dyes are dissolved in them and the compound is put on the fabric the only oil spreads leaving the dye at one place which impacts the output.

Oleic acid is temperature sensitive. Even though it dissolves the dye properly but since it is a saturated fat it is not suitable to be used in low temperatures, even of 18-20 degrees Celsius which is normal.

Pigments when added, even though they improve the opacity and darkness of the initial printouts, makes the ink more viscos restricting its flow.

We have also tried to use Dipropylene glycol. It is a compound which is miscible with oils, dissolves the dyes very well. The ink produced in DPG with a 15% dye concentration did produce a good result. Mixture of castor oil and DPG may also be used. But since DPG evaporates, even though at a slow rate the output begins to become less as the flow of the ink within the fabric is affected. The evaporation of DPG is not witnessed in the ink that is lying idle but it evaporates fast when applied on a fabric.

Now we need help in the following –

We need a vehicle which can properly absorb 20-25% of dye within it to get the desired output maintaining the right viscosity and flow of ink within the fabric. If castor oil is to be used as the vehicle then we believe it has to be diluted. What shall be used to dilute castor oil to improve the dye concentration in the ink also ensuring that the ink spreads evenly on the fabric.
Or please suggest any other way by which we can arrive at the right formulation of the ink.

[dolphin42]

I'm experiminting with a combination of about 5% light machine oil, 60% heptane, 35% VanSon VS105 rubber based (non drying) offset printer ink.
the oil is to protect the print head, the heptane is to make the ink so that it will soak into the ribbon, before evaporating.
I'll post about the results. I might also add more of the machine oil (WD-40 looks promising, even) to keep the ink more liquid.

I'd certainly love to know the secrets but I think this formulation might work reasonably well.