Reasons and elimination of deinking of the hottest

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Printing ink deinking causes and troubleshooting

release date: Source: China paper

in packaging and printing, there are occasional streaks or light colors, that is, no inking and deinking faults. This is due to the swelling of pigments and fillers in the ink system, resulting in the overall gelatinization of the ink. Today, China paper industry takes you into printing ink and introduces the causes of relevant failures in detail

the theoretical explanation is that the yield value of ink is too high, forming cheese. In fact, there are too many pigments and fillers in the ink, which cause the ink to gelatinize or water to enter the ink during storage. The author makes a rough discussion on this issue and communicates with colleagues in the packaging and printing industry on the troubleshooting methods

first, the concept of gelation and acid-base of ink

in the early use of oxidation drying and penetration drying inks, we often encounter the problem of gelation of ink, and occasionally in solvent (volatile drying) and water-based inks. The causes of gelation are very complex (including the technological process of ink manufacturing, such as adding driers first and then adding driers, etc.). The author believes that there are several reasons for gelation:

1, the molecular weight of the resin in the ink system is too large (the viscosity is too high)

2. Too many solid components (even resin binders with low viscosity are 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 putting additives (for example, there will be two results when putting ink before and after production)

6. There are too many solvents in the ink system, especially fast drying solvents

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 last four reasons belong to the category of chemical reaction. In this regard, the author has made material quality problems around the relationship between acid and alkali in "talking about the application of coupling agents in water washable inks", the "basic principles of attachment design of electronic universal testing machine of China Packaging News" on September 20, 1997, the first issue of "foreign packaging Abstracts" in 1998, and "Guangdong packaging": different materials in different industries have different compressive strength, proton donors and proton acceptors. In 1998, the author's "Research on green packaging printing ink" published in the fifth issue of Guangdong packaging and China Packaging magazine described the advantages and disadvantages of its strong acid pigment carbon black pigment and rosin acid value when the rosin resin with molecular weight of 330 used high pigment carbon black to produce solvent based flexible quick drying ink had gelatinization and stacking failures. When the acid-base characteristics of pigments do not match the acid-base characteristics of binders, a variety of combinations of resins, pigments and fillers can be used, or appropriate solvents can be selected to make up or improve, which is a commonly used remedial measure

in chemical reactions, when the stoichiometric concentration reaches a certain value (strictly speaking, a very narrow concentration range), its macro properties will change abruptly. At this time, the active molecules of the ink system began to associate, forming colloidal aggregates of different sizes. 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 is probably closely related to the dispersion process of binders, especially pigments

second, an effective way to eliminate swelling and avoid gelatinization with poor screw replacement accuracy

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 in storage. For example, high viscosity alkyd resin and alkaline pigment zinc oxide are ground together in the presence of driers, which will promote the gelatinization and swelling of ink during storage. This is due to the reaction between free fatty acids and alkaline pigments during thermal processing. Therefore, when making ink with high viscosity ink raw materials, lead, cobalt and manganese driers should not be added in the grinding process. But after adding 1% benzoic acid, the swelling tendency can be reduced. Another disadvantage of driers is that they can accelerate the deposition of pigments during the storage of inks. 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 a drying agent before grinding the pigment will lead to poor storage of the ink, easy swelling, gelatinization, precipitation and caking

in recent years, people have put forward various remedial measures around the swelling, gelatinization, precipitation and caking of packaging and printing inks. This passive operation not only increases the production cost of packaging and printing manufacturers, delays time, but also increases the difficulty of processing. The reasons for the gelatinization, thickening and caking of the ink system are: Saponification of the base pigment with the binder with high acid value or containing free fatty acids, which condenses and gelatinizes the binder itself, the ink system absorbs water, the pigment content is too high, and the miscibility of the binder and oil additives is poor. Generally, there are four remedies as follows:

1. When it is too thick or gelatinized due to the high polymerization degree of the binder, add aliphatic hydrocarbons, esters, ketones, etc. to dilute it

2. Saponified ink plus rosin is relieved by its high acid value substance

3. In the past, the metal salt of naphthoic acid was added to the ink

4. Ink painting needs to be controlled by adding inorganic salts

in view of the above failures, the author analyzed and screened out the new anti swelling and gel breaking materials on the market -- 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 make the swollen and gelatinized packaging and printing inks come back to life -. In the printing process, the above faults can be suppressed by adding% anti swelling and gel breaker to the swollen ink. In the ink formula, only pigments and fillers need to be directly added 1 5% anti swelling gel breaker can avoid ink swelling and gelation. Toluene or xylene can also be used to grind the diluted oil with the product in the ratio of 1:1, which can greatly improve the pigment content. The main reason is that the viscosity of the oil used in the reducer is too small or too dispersive. At the same time, it can prevent the streaks or light color faults caused by swelling, gelatinization and sedimentation in the production, storage and printing process of the packaging printing ink. It can also greatly improve the branching degree of ink, increase the adhesion fastness of ink film, reduce the baking temperature and blowing volume of solvent based ink, and effectively maintain the fluidity of printing ink

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