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Causes And Elimination Of Printing Ink Deinking

         In packaging printing, there are occasional streaks or light colors, that is, no inking and deinking failure. This is due to the swelling of pigments and fillers in the ink system, resulting in the overall gelatinization of the ink.Causes And Elimination Of Printing Ink Deinking

Causes And Elimination Of Printing Ink Deinking

       The theoretical explanation is that the yield value of ink is too high to form cheese. In fact, there are too many pigments and fillers in the ink, which makes the ink gel or water in storage. Causes And Elimination Of Printing Ink Deinking

        The author makes a rough discussion on this problem and communicates with colleagues in the packaging and printing industry on the troubleshooting methods.Causes And Elimination Of Printing Ink Deinking

1、 Concept of gelatinization and acid-base of ink

        In the early use of oxidation drying and penetration drying inks, we often encounter the gelation problem of inks, and occasionally in solvent (volatile drying) and water-based inks. Causes And Elimination Of Printing Ink Deinking

       The causes of gelation are very complex (including the process flow of ink manufacturing, such as the first addition and later addition of drying agent, etc.). The author believes that there are several reasons for gelation:Causes And Elimination Of Printing Ink Deinking

1. The resin molecular weight of the ink system is too large (viscosity is too high);Causes And Elimination Of Printing Ink Deinking

2. Too many solid components (even resin binders with low viscosity are no exception);Causes And Elimination Of Printing Ink Deinking

3. The acid value of the ink system is too high;Causes And Elimination Of Printing Ink Deinking

4. Pigments and fillers are alkaline;Causes And Elimination Of Printing Ink Deinking

5. Too much desiccant content or improper order of putting additives (for example, there will be two results before and after ink production);

6. There are too many solvents in the ink system, especially fast drying solvents.Causes And Elimination Of Printing Ink Deinking

      The first two reasons mentioned above belong to the field of physics, which can be easily avoided and eliminated by experienced ink manufacturers or packaging and printing operators. The latter four reasons belong to the category of chemical reaction.Causes And Elimination Of Printing Ink Deinking

       In this regard, the author has described the proton donor and proton acceptor around the relationship between acid and alkali in “talking about the application of coupling agent in water washable ink”, China packaging daily on September 20, 1997, foreign packaging abstract in the first issue of 1998 and Guangdong packaging.Causes And Elimination Of Printing Ink Deinking

        In 1998, the fifth issue of Guangdong packaging and China Packaging magazine published the author’s research on green packaging printing ink. When the rosin resin with molecular weight of 330 used high pigment carbon black to produce solvent based flexible quick drying ink has gelatinization and plate stacking failure,Causes And Elimination Of Printing Ink Deinking

       it expounds the advantages and disadvantages of its strong acid pigment carbon black pigment and rosin acid value.Causes And Elimination Of Printing Ink Deinking

       When the acid-base characteristics of pigments do not match the acid-base characteristics of binders, a variety of resin, pigment and filler combination schemes can be adopted, or appropriate solvents can be selected to make up or improve, which is a common remedial measure.Causes And Elimination Of Printing Ink Deinking

        In chemical reaction, when the stoichiometric concentration is large to a certain value (strictly speaking, it is a very narrow concentration range), its macro properties will change suddenly. At this time, the active molecules of the ink system began to associate to form colloidal aggregates of different sizes.Causes And Elimination Of Printing Ink Deinking

        Such aggregates are called micelles or micelles, also known as associated colloids. The important characteristic of micelles is solubilization, which greatly increases the solubility of insoluble or slightly soluble substances (commonly known as swelling), thus accelerating the chemical reaction. The reaction mechanism may be closely related to the dispersion process of binder, especially pigment.Causes And Elimination Of Printing Ink Deinking

2、 It is an effective way to eliminate swelling and avoid gelation

      In addition to the above reasons, the drying agent of the ink system can also directly affect the viscosity of the ink and the precipitation of pigments and fillers during storage. For example, high viscosity alkyd resin and alkaline pigment zinc oxide are ground together in the presence of desiccant, Causes And Elimination Of Printing Ink Deinking

      which will promote the gelation and swelling of ink during storage. This is due to the reaction between free fatty acids and alkaline pigments during thermal processing.Causes And Elimination Of Printing Ink Deinking

       Therefore, when manufacturing ink with high viscosity ink raw materials, lead, cobalt and manganese driers should not be added in the grinding process. However, the swelling tendency can be reduced by adding 1% benzoic acid.Causes And Elimination Of Printing Ink Deinking

       Another disadvantage of desiccant is that it can accelerate the deposition of pigment in the storage process of ink. Causes And Elimination Of Printing Ink Deinking

       For example, when titanium dioxide is used to make ink, zinc naphthenate is added during grinding, and the pigment is easy to precipitate and form hard blocks. Therefore, adding desiccant before pigment grinding will lead to poor storage of ink, easy swelling, gelation and precipitation agglomeration.Causes And Elimination Of Printing Ink Deinking

      In recent years, people have put forward some remedial measures around the swelling, gelatinization, precipitation and caking of packaging and printing ink. This passive operation not only increases the production cost of packaging and printing manufacturers, delays time, but also increases the difficulty of processing. Causes And Elimination Of Printing Ink Deinking

        The reasons for the gelatinization, thickening and agglomeration of the ink system are: the saponification of the base pigment and the binder with high acid value or containing free fatty acids, which makes the binder agglomerate and gelatinize, the water absorbed by the ink system, the pigment content is too high, and the miscibility of the binder and oil additives is poor. There are generally four remedies:

1. When it is too thick or gelled due to the high degree of polymerization of the binder, add aliphatic hydrocarbons, esters, ketones, etc. for dilution.Causes And Elimination Of Printing Ink Deinking

2. Saponification ink plus rosin uses its high acid value substances to remove.Causes And Elimination Of Printing Ink Deinking

3. In the past, naphthoic acid metal salt was added to the ink.Causes And Elimination Of Printing Ink Deinking

4. The ink needs to be controlled by adding inorganic salt.Causes And Elimination Of Printing Ink Deinking

       In view of the above faults, the author analyzes and selects a new commercially available anti swelling and gel breaking material – the improved phosphoester titanate coupling agent of Yizheng Tianyang chemical plant (national inspection free product), which not only has excellent dispersion performance for pigments, but also can bring the swollen and gelled packaging and printing ink back to life. In the printing process, the above faults can be suppressed by adding 3-5% anti swelling and gel breaker to the swollen ink.Causes And Elimination Of Printing Ink Deinking

        In the ink formula, only 1.5-2.5% anti swelling gel breaker with pigment and filler can avoid the swelling and gelation of the ink. Toluene or xylene can also be diluted with the product in the ratio of 1:1 and ground with oil added ink, which can greatly improve the dispersion of pigment, and prevent the stripe or light color fault caused by swelling, Causes And Elimination Of Printing Ink Deinking

       gelation and precipitation of packaging printing ink in the process of production, storage and printing. It can also greatly improve the branching degree of ink, increase the adhesion fastness of ink film, reduce the baking temperature and blowing amount of solvent ink, and effectively maintain the fluidity of printing ink.Causes And Elimination Of Printing Ink Deinking