Excluding the New Process of Gelling and Swelling of Packaging Printing Inks

In the packaging printing process, occasionally the phenomenon of streaks or light colors appear in the printing. This failure of the packaged printing industry as ink-removing and ink-dropping rollers is caused by the swelling of pigments and fillers in the ink system before printing. Ink is caused by the overall gelation.

Theoretic explanation is that the ink's yield value is too high to be cheese-like. From a practical point of view, there are too many pigments and fillers in the ink, which causes the ink to gel or cause water in the ink system during storage to cause partial flocculation.

For a long time, people used the method of installing stirrers or other inks in the ink fountain to fight the problem of ink swell or gelation, and some put an iron bar in the ink fountain to push the ink to the ink fountain roller to ensure Printing ink fluidity. Most of the operation uses high viscosity varnish or thinner to adjust the ink (but must be used with the adjustment, otherwise it will continue to swell). At present, some manufacturers will drop the ink and replace the ink with strong flow and water resistance. The author discusses this issue and excludes the failure of the new process and printing colleagues.

First, the bulge of the ink and the concept of acid and alkali

The problem of gelation of printing inks is encountered in the early use of oxidative drying and osmotic drying inks, and occasionally in solvent-based and water-based inks. We know that the cause of gelation is very complicated, including the process flow of ink manufacturing, such as the addition and subsequent addition of desiccants. Usually after the fault occurs, operators often do nothing. The cause of gelation, the author thinks there are the following six kinds:

(1) The resin molecular weight of the ink system is too large (the viscosity is too high);
(2) There are too many solid components (even small viscosity resin binders are no exception);
(3) The acid value of the ink system is too high;
(4) pigments, fillers with alkaline;
(5) The desiccant content is too much or the order of the additives is improper (such as two results before and after ink production);
(6) There are too many solvents for the ink system, especially fast drying agents.

From the above reasons, it can be found that the first two belong to the category of physics, which is very easy to avoid and eliminate for an experienced ink manufacturing practitioner or printing operator. The latter four reasons belong to the category of chemistry. When we explored around the latter four reasons, it was found that excessive humidity, volatile solvents, and improper use of auxiliary additives may cause gelation of the ink. The various phenomena that occur indicate that acid, alkali, and so-called amphoteric solvents, resins, and neutral pigments and amphoteric pigments that do not form hydrogen-bonded aliphatic hydrocarbon solvents are involved in the gelation, that is to say: The acid-base characteristics are not compatible with the acid-base characteristics of the binder. We can use various resins and pigments, and the acidity and alkalinity of the fillers are suitable to balance or select the appropriate solvent to make up for or improve. This is a routine and effective remedy. .

When the stoichiometric concentration reaches a certain level, various macroscopic properties will suddenly change. From a microscopic point of view, the active molecules exhibited by the inks at this time begin to form aggregates of unequal size. This aggregate becomes a clump or micelle and also becomes an associated colloid. An important characteristic of micelles is solubilization, which greatly increases the solubility of otherwise insoluble or sparingly soluble substances, commonly known as bloating, thereby accelerating the chemical reaction.

Second, eliminate the swelling, to avoid the effective way of gelatinization

In addition to the above-mentioned reasons, the driers in the ink system can also directly affect the viscosity during storage, increase and the bottom of the pigment filler. Another disadvantage of driers is that they accelerate the settling of the pigment during storage and form a hard mass. Therefore, adding the driers before the pigments are grinded will result in poor ink storage, swell, gelation, and agglomeration of the bottom.

Over the years, based on the phenomenon of gelation, thickening, and clumping of the ink system, the chemical reaction relationships between hydrochloric acid pigments and linking materials containing higher acid values ​​or containing free fatty acids have been identified and the following four commonly used remedial measures have been summarized: (1) When it is too thick or when the degree of polymerization of the linking material is too high to form a gel, dilute by adding aliphatic hydrocarbons, esters, ketones, etc.; (2) Gelatinizing ink that reacts into soap Adds rosin to dissolve in linoleum and utilizes its high acid content (3) The addition of metal salts of folate to the printing ink is a common method used in the past; (4) The addition of inorganic salts to the ink can be controlled.

Based on many years of practice, the authors aimed at the above-mentioned failures, analyzed the structure of the ink-adjusting formula, and screened new materials for anti-expansion breakers sold in the market. After that, the authors believe that the improved phosphate ester phthalate coupling agent has excellent dispersion of pigments. Besides the performance, there are special functions that can make the swelled and gelled printing inks rejuvenate. For example, in the printing process, only 3% to 5% anti-expansion gel breakers need to be added to the swelled ink. It was controlled to restore the original structure of the ink and the viscosity returned. Therefore, we only need to directly add pigments, fillers 1.5% to 2.5% anti-expansion breaker to avoid printing bloated and gelation, can also use toluene and the product diluted with ink after grinding and dispersing, can not only greatly improve the pigment The dispersibility can also prevent the occurrence of streaks or color fading caused by swelling, gelation, and precipitation during the production, storage, and printing of the printing ink, and at the same time, the ink curing degree can be greatly increased and the ink can be increased. The fastness of the film is attached, thereby effectively improving the fluidity of the printing ink during normal printing.

Source: PACK.CN