How to choose the right pigment when making water-based ink

When making water-based inks, it is very important to choose the right pigments.

Hue is the primary consideration in the selection of pigments, followed by gloss, chemical resistance, easy dispersibility and compatibility with other components, and finally the choice of dispersion equipment.

So how to choose dry pigments in water-based inks?

The use of dry pigments has both advantages and disadvantages.

Pigment selection

When formulating an ink system, the form of the pigment used and the long-term storage stability should first be considered.

One advantage of choosing a dry pigment is that the dry pigment is a 100% dry product, so there is no need to test the concentration of the pigment in the ink; for filter cakes or dispersed pigments, experiments must be performed to determine the concentration of the pigment in the ink.

Moreover, dry pigments are easier to handle than the other two types of pigments.

01, opaque pigment

Opaque pigments can be used in some water-based inks with low transparency requirements.

The opacity of the pigment provides a good hiding power for the pigment, so the ink formulated with the opaque pigment is often used in the printing of corrugated paper and packaging paper.

02, transparent pigment

Printing high-quality printed products, such as metal foils, labels and paper, requires transparent and glossy printing inks, and often uses particle school pigments as colorants.

In many packaging areas, transparent pigments can provide better gloss, high printing strength and dyeing strength.

Resinization

When formulating water-based inks, it is very important to resinize the pigments.

Adding resin during or after the pigment coupling process can prevent crystal growth, thereby contributing to the dispersion and transparency of the pigment.

The resin can also encapsulate the pigment particles, making the pigment easier to disperse during the pre-dispersion process.
Compared with non-resinized pigments, resinized pigments can produce more transparent inks.

Pigments developed in water-based ink systems can give excellent transparency, gloss and low rheology, but these pigments are not suitable for solvent inks.

Compatibility and stability of pigment/vehicle

The use of highly resinous pigments in water-based ink systems is prone to unstable rheology, which is mainly caused by the incompatibility of the resin added in the pigment manufacturing process with the ink grinding and the acrylic resin in the formulation.
Highly resinous pigments, such as CI Pigment Yellow 83, should be carefully selected to avoid the above problems.

In the water-based ink system, the instability of the metallic azo red calcium salt pigment can also be observed.
Such as CI Pigment Red 48:2 or CI Pigment Red 57:1.
In these pigments, the amine protons in the molecule are attached to the benzene molecule.
When the crystal water is removed from the molecule, discoloration can be observed.
When these pigments absorb water, the color shifts to the yellow phase, and when the water is dried, it shifts to the blue phase.

If the pigment is stable, the hue should return to the original color.
For example, CI Pigment Red 49:2, its calcium salt, barium salt and strontium salt are all hue stable pigments in aqueous solution.