In the last few years the ceramic industry has been rapidly evolving thanks to the progressive digitalization of the processes. The digital ink printing system plays for sure a role of primary importance.
Digital inks are very sensitive products that must respect high and strict parameters in order to ensure excellent performances.
Following here a general picture of their features and principles.
What the aspects that affect the digital inks' properties?
First of all it let’s give a definition.
To put it plainly, we could say that inks are dispersions of a solid into a liquid.
Entering more in detail, inks are formed by:
- A solid part of inorganic pigments. Their inorganic nature is important, being it more suitable to withstand the high temperatures of the firing cycle that ranges from 1.100 °C to 1.200 °C. The organic pigments, on the other side, could disappear during that process.
It is important to underline that the chemical nature of pigments changes according to the colour. A blue ink, for example, contains cobalt-aluminate. In the same way, spheres of tin and chrome can lead to rosy shades.
- A liquid part made of medium and additives to be used as dispersant agents. The medium’s quality is essential: they set the most important parameters such as viscosity, surface tension and drying times. It is clear that any vehicle’s formula changes according to the pigments used within the ink.
The particle size is one of the most relevant requirements too. It has been nanometric – about 1 micron – in order to be used with the current print heads available on the market, whose noozles have a size that is about 50 µm. A bigger size could lead to agglomeration phenomena therefore to a subsequent clogging of the print heads.
The particle size can also impact the performance of the colour development as well as on the possible sedimentation of the solid part within the dispersion.
In general, a small size leads to a less colour development and assures the reduction of sedimentation phenomena.
The viscosity has to be within a very strict set of parameters in order to facilitate the ink drop’s dimension and avoid possible printing problems. A correct viscosity actually ranges fro 10 to 30 cP in application.
As well as the viscosity, the surface tension is responsible for a good development of the ink drop. The estimated values for solvent-based inks range from 28 to 35 mN/m.
Even in the formative stages of the project, some producers are developing new print heads that can work at higher level of surface tension.
Digital inks for ceramic industry, both solvent or water based, are designed in order to reach a good balance of all the parameters involved in the product therefore to let it perform at the best.
This is way a previous development within the laboratories is a must to reach the desired target.
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