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Troubleshooting and causes of printing ink off roller

in the process of packaging and printing, we occasionally encounter the phenomenon of streaks or light colors in printing. This is called the failure of ink dropping and ink off roller, which is caused by the swelling of the color and filler of the packaging and printing ink system, resulting in the gelatinization of the whole ink

explain from a theoretical point of view: the yield value of the ink is too high, and the ink is too short to form a cheese. From a practical point of view: there are too many pigments and fillers in the ink, which makes the ink gelatinize or water enters the ink system during storage, resulting in partial flocculation

people constantly stir the ink in the ink bucket for swelling or gelatinization, or install a stirrer in the ink bucket when the sensor is under the effect of tension P, or put an iron bar on the ink to push the ink to the ink bucket roller to maintain the fluidity of packaging and printing ink. Operation and technology universities like to use medium and high viscosity inking oil or diluent to adjust the ink (but this must be used with adjustment, otherwise it will continue to swell or gelatinize). Some manufacturers pour out the ink and replace it with the ink with good fluidity and strong water resistance before printing. Looking at this kind of fault, this paper roughly discusses this phenomenon around this problem, and communicates with colleagues in the packaging and printing industry on new methods to eliminate this fault

(I) the concept of ink gelation and acid-base

the gelation problem of packaging and printing inks is often encountered in the early inks (oxidation drying and penetration drying), and occasionally in solvent type (volatile drying) and water-based inks. We know that the causes of gelation are very complex (including the technological process of ink manufacturing, such as the first and second addition of driers, etc.). With the development of science and technology and the application of new materials, we have strengthened the research of scientific theory and the quality control of ink component materials. When the composition and structure of the ink changed, the reporter saw this kind of strange chemical materials in BASF laboratory, so that various ills were effectively controlled. But generally, after the failure occurs, the operator is often helpless. There are six reasons for the phenomenon of ink gelation:

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

2. There are 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. The desiccant content is too much or the order of choosing to add is improper (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

it can be seen from the above six reasons: the first two are 10. The maximum experimental space: 600mm (including collet) belongs to the category of physics, and the last four reasons belong to the category of Chemistry (reaction). Acid is electrophilic and electron acceptor (proton donor); Alkali is nucleophilic and is an electron donor (proton acceptor). There are also the so-called amphoteric solvents and resins (water, alcohol, carboxylic acid, nitrocellulose, etc., which are both proton donors and proton acceptors), followed by aliphatic hydrocarbon solvents that do not form hydrogen bonds, neutral pigments, amphoteric pigments, etc., which are related to the gelation of inks. That is what people often say: when the acid-base characteristics of pigments do not match the acid-base characteristics of binders, we can use a variety of resins and pigments, fillers to adapt the acid-base characteristics, or select appropriate solvents to improve the acid-base characteristics, which is a conventional remedial measure

when we explore the chemical (reaction) category, we will find that when its stoichiometric concentration reaches a certain value (strictly speaking, a very narrow concentration range), various macro properties will suddenly change. From the microscopic point of view, at this time, the active molecules of the ink system began to associate, forming aggregates with different sizes of colloidal particles. Such aggregates are called micelles or micelles, also known as associated colloids. An important characteristic of micelles is the result of their solubilization, which greatly increases the solubility of insoluble or slightly soluble substances, commonly known as swelling. Thus accelerating the role of chemical reactions. The reaction mechanism is probably closely related to the dispersion process of binders, especially pigments

(II). An effective way to eliminate swelling and avoid gelation

in addition to the reasons mentioned above, the driers in the ink system can also directly affect the viscosity, increase and precipitation of pigments and fillers during storage. For example, the grinding of high viscosity alkyd resin with alkaline pigment zinc oxide and drier 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 using high viscosity ink raw materials to make ink, lead, cobalt and manganese driers should not be added in the grinding process. However, 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. Automatic shutdown time setting: block under no operation state

in recent years, people have put forward various remedial measures around the swelling, gelatinization, precipitation and caking of packaging and printing inks. The solutions are often paid attention to after the fault occurs. This kind of passive operation method not only increases the production cost and delays time of packaging and printing manufacturers, but also brings certain processing difficulties. The gelatinization, thickening and caking of the ink system are related to the reaction of base pigments with binders with high acid value or containing free fatty acids into soaps. The binder itself condenses and gels, the ink system absorbs water, the pigment content is too high, the binder used is unbalanced (inappropriate) with the pigment, the miscibility of the binder and the additives of the grease is poor, and the polymer binder is absorbed by the pigment due to the acid soluble structure. The general remedial measures are as follows:

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

2. The gelled ink that reacts into soap is dissolved in linoleic acid by adding rosin, and its high acid value substance is used to remove it

3. Add naphthoic acid metal salt to the packaging printing ink

4. Inorganic salts need to be added to ink, which can control gelation

The improved phosphate titanate coupling agent produced by

can not only have excellent dispersion performance for pigments, but also bring back the swollen and gelatinized packaging printing ink. For example, in the printing process, it is only necessary to add 3% - 5% anti swelling gel breaker to the swollen ink, so that the above faults can be controlled and the original structure and viscosity of the ink can be restored. We only need to add 1 in pigments and fillers in the ink formula 5%~2. 5% anti swelling gel breaker can avoid swelling and gelatinization of packaging and printing. Toluene and xylene can also be diluted with the product in the ratio of 1:1, and then added to the ink for grinding and dispersion, which can not only greatly improve the dispersion of pigments, but also prevent the packaging printing ink from swelling, gelatinization and sedimentation during production, storage and printing, resulting in streaks or light color faults. At the same time, it can greatly improve the branching degree of the ink, increase the adhesion fastness of the ink film, and reduce the baking temperature and blowing volume of the printing ink or volatile dry (solvent) printing ink, so as to effectively promote the normal printing fluidity of the packaging printing ink

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