Pigment selection and dispersion in water-based ink

When making water-based inks, it is very important to choose the right pigments.
Most manufacturers will provide several pigments with different properties so that you can choose pigments for your particular system
.

Hue is the first consideration in the selection of pigments, followed by gloss, chemical resistance, easy dispersibility and compatibility with other components, and finally the selection of dispersion equipment.
If the most effective dispersion equipment can not achieve a suitable dispersion ink, You can consider choosing filter cake or dispersed pigments as colorants

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

.

②Transparent pigments print good quality printed products, such as metal foils, labels and paper, which require transparent and glossy printing inks, and often use particle school pigments as colorants

.
In many packaging fields, transparent pigments can provide excellent gloss, high printing strength and dyeing strength

(2) Resinization

When preparing 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

(3) Compatibility and stability of pigments/vehicles

.
The use of highly resinous pigments in water-based ink systems is prone to unstable rheology, mainly due to the resin and ink added during the pigment manufacturing process.
Caused by incompatibility of acrylic resins

In most cases, the pigments used in water-based flexographic inks and water-based gravure inks use acrylic resin as the binder.
According to the type and concentration of the pigment, some anionic, non-ionic or zwitterionic surfactants or their combinations are added to help dispersion
.

Pigments with the same CI number from different suppliers have the same performance, but because most pigments are resin-treated, pigments that are stable in one water dispersion system may be incompatible in another system.

.
In addition to acrylic resins, other resins such as polyester resins, epoxy resins, urethane resins, etc.
can also be used to make water-reducing dispersants
.
Depending on the resin system, certain non-ammonia solvents can be added to prepare inks to avoid unhelpful taste and high volatile content
.
It should also be noted that the pigments suitable for one resin system are not necessarily suitable for another system
.

The equipment used for pigment dispersion includes high-speed dispersers, mixers with different blades, power dispersing mills, ball mills or media mills
.

The current modern equipment is the use of stainless steel or ceramic media grinders
.
The dispersion quality depends on the size of the medium and the proportion of the medium in the dispersing material.
If a small particle medium and a high medium ratio are used, a good quality dispersion can be achieved
.

Other factors that determine the final dispersion quality are the percentage of pigments, resins and dispersants
.
The proportion of various substances is finally determined through formula experiment.
Ammonia, caustic soda, monoethanolamine or other amine additives can be used to increase the solubility of the resin.
The pH value of the aqueous solution is between 8.
5 and 9.
5
.
When it is lower than 8.
2, the dispersion system will become thicker, and the disadvantage of blocking the nozzle by the vehicle will occur
.
When it is higher than 9.
5, a lot of bubbles will be produced
.