Usually, in the ink printing process, we sometimes encounter the phenomenon of streaks or pale colors in the printing. This phenomenon is called the failure of the ink and the ink off roller in the industry. The reason for this failure is due to the ink During printing, the pigments and fillers in the ink system swell, causing the entire ink to gel.
From a theoretical point of view: the yield value of the ink is too high, the ink is too short and is creamy. From a practical point of view: there are too many pigments and fillers in the ink, so that the ink gels or water enters the ink system during storage and causes partial flocculation.
For a long time, people have been constantly stirring the ink in the ink fountain for swelling or gelation, or installing a stirrer in the ink fountain, and also put a iron stick on the ink of the ink fountain to push the ink to the ink fountain roller to keep the ink printing. fluidity. Most operators like to use medium and high viscosity ink or thinner to adjust the ink (but this must be used with the adjustment, otherwise it will continue to swell or gel). Some printing companies dump the ink, replace the ink with good fluidity and strong water resistance before printing. Looking at the above failures, the author discusses and analyzes this problem and provides insights on how to eliminate the failure.
The relationship between ink gelation and acid-base
The gelation problem of the ink is often encountered in the early oil type (oxidation drying type and penetration drying type) ink, and occasionally encountered in the solvent type (volatile drying type) and water-based ink. It must be known that the cause of gelation is very complicated (including the ink manufacturing process, such as the first and second addition of the driers, etc.). With the development of science and the use of new materials, we have strengthened the research of scientific theory and the quality control of ink component materials. When the composition structure of ink changes today, various disadvantages will appear at any time, but they will be controlled. The reasons for gelation, the industry believes that there are the following six types:
1. The resin molecular weight of the ink system is too large (the viscosity is too high);
2. Too many solid components (even the resin binder with low viscosity is no exception);
3. The acid value of the ink system is too high;
4. Pigments and fillers are alkaline;
5. Too much desiccant content or improper order of addition (for example, two results will appear before and after ink production);
6. There are too many solvents in the ink system, especially fast-drying solvents;
It can be seen from the above six reasons: the first two belong to the category of physics, and are easily avoided and easily ruled out by an experienced ink manufacturer or packaging and printing operator. The last four reasons belong to the category of chemistry (reaction). We will also discover when exploring the last four reasons; the temperature of the dispersion process is too high, the evaporation of the solvent, and the improper application of auxiliary additives may also cause the ink to tend to acidify. For example, when the rosin resin with a molecular weight of only 330 is printed with high-pigment tank ink to produce solvent-based flexible and quick-drying inks, it will gel and pile up, making it difficult to apply ink. In addition, we should pay attention to the pros and cons of the strong acid pigment carbon ink pigment and rosin acid value. This is enough to indicate that the acid [acid is electrophilic, is an electron acceptor (proton donor)] base is nucleophilic, is an electron donor (proton acceptor), and there are so-called amphoteric solvents (existing proton donation Water, alcohol, carboxylic acid, and nitrocellulose, etc.), followed by an aliphatic hydrocarbon solvent that does not form hydrogen, bonds, neutral pigments and amphoteric pigments, etc. are all gelled Relationship is already obvious. In other words, when people often say that the acid-base properties of pigments are not compatible with the acid-base properties of binders, we can use a variety of resins to balance and adjust the acid-base properties of pigments and fillers or choose appropriate solvents to make up or improve , This is a conventional remedy.
When we explore in the chemistry (reaction) category, we will find that when its stoichiometric concentration reaches a certain value (strictly speaking, a very narrow concentration range), various macroscopic properties will suddenly change. From a microscopic perspective, the active molecules of the ink system at this time began to associate, forming aggregates of varying particle sizes. Such aggregates are called micelles or micelles, also known as associated colloids. An important feature of micelles is the result of their solubilization, which greatly increases the solubility of insoluble or slightly soluble substances-commonly known as swelling, which accelerates the role of chemical reactions. The mechanism of the reaction is very likely to be The binder, especially the pigment dispersion process, is closely related.
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