Exclude the process of ink gelation and swell in the printing process (I)

In the process of packaging and printing, streaks or shades of color may sometimes appear on the printed matter. The failure of the ink-jet and ink-drop rollers is caused by the ink gelation caused by the swelling of the pigments and fillers in the ink. The gelation of the ink is due to its high yield value and the ink is too sticky to form a cheese. From an application point of view, there are too many pigments and fillers in the ink, which causes the ink to gel, or water enters the ink during the storage process and causes partial flocculation.

For a long time, various measures have been taken against bloating and gelatinization, including constantly stirring the ink in the ink fountain, installing a stirrer in the ink fountain, or placing an iron bar on the ink of the ink fountain to push the ink to the ink fountain roller. To maintain the fluidity of the ink. The use of medium and high viscosity varnish or thinner to adjust the ink (must follow the tone, otherwise the ink will continue to swell or gel). Some manufacturers replace the ink with a good fluidity and strong ink resistance.

1 Causes the gel to swell

The problem of gelation of packaging printing inks is occasionally encountered in early oily (oxidative drying and osmotic drying) and water-based inks. The cause of gelation is very complicated, including the process flow of ink manufacturing, such as the first and second addition of driers, and the type and quality of ink components. When the ink composition changes, various problems will follow.

The reasons for gelation are:

(1) Large ink viscosity

    Because the molecular weight of the resin in the ink system is too large, the viscosity of the ink is too high, and therefore it is easy to gel.

(2) More solid components

There are too many solid components, even resin binders with low viscosity.

(3) High ink acidity

Research data and experiments on packaging printing inks show that ink composition ingredients such as pH, amphoteric solvents, resins, aliphatic hydrocarbon solvents that do not form hydrogen bonds, and neutral pigments are related to the gelation of inks. When the pH of the pigment is not compatible with the acid-base characteristics of the binder, a variety of resins and pigments, fillers can be used to debug the acid-base characteristics, or choose the appropriate solvent to make up for the improvement.

(4) Performance of pigments and fillers

When studying the chemical reaction of ink, it was found that when the concentration is large enough, some substances will mutate. At this time, the active molecules in the ink begin to associate and form aggregates of unequal size of micelles. Such aggregates are called micelles or micelles, also known as associative colloids. An important feature of micelles is their solubilizing effect, which increases the solubility of the originally insoluble or slightly soluble substance, resulting in swelling, which accelerates the chemical reaction. This is highly likely to have a close relationship with the binder, especially the pigment dispersion process.