The desiccant is a material that is used only to accelerate the drying speed of a grease ink having an unsaturated and double bond structure and shorten the drying time. That is, the material that accelerates the drying time of the oxidized conjunctiva drying ink. Its composition is mainly composed of organic and inorganic compounds containing cobalt, manganese, lead, zinc, iron, calcium, vanadium, zirconium and other metal elements, ink binders, inks, and other slurries and liquid materials.
At present, red dry oil is commonly used, and it is a liquid dry oil made from purple-red cobalt naphthalate. The other is dry white oil, which is made of manganese borate and a small amount of cobalt naphthalate, dispersed in the ink binder, made of slurry dry oil.
The main difference of this kind of material is that the strength of the drying ability is different. This is due to the strength of the metal activity.
The more unified view is that cobalt has the greatest activity. Its main function is to promote the oxidation of the ink surface, and can quickly form a film, known as the surface of dry oil. Therefore, the use of multiple surfaces results in surface crusting or wrinkling, as well as crystallization and overprinting.
Followed by manganese, it is also the first gold surface dry, and from top to bottom, the tendency to peeling is not obvious.
The weakest is lead, but it is much stronger than calcium. It can make the ink film dry and thick together. Therefore, the paint is called thick oil or lead oil. It is mild and sensitive to temperature.
Manganese and lead are often used in combination to complement each other.
In the ink with oxidation effect, adding desiccant can play the role of:
Reduce the induction period. Because dry oil contains sterols, fertility powders, lecithin, etc. are antioxidants, resulting in oxygen can not quickly come into contact with unsaturated structures. Active metals can change the properties of these materials, counteract their negative effects, precipitate the antioxidants, and thus quickly combine with oxygen.
Accelerate oxidation rate. Due to the activity of the metal, the oxygen uptake is increased, and with the occurrence of differences in the properties of the ink material, the chance of forming hydroperoxides increases, thereby accelerating the oxidation rate.
Promotes polymerization. They can change the type of volatiles and increase their amount, thereby speeding up the polymerization and leading to the solidification of the ink.
Accelerate the condensation of the linker molecules. The oil molecules are strongly oriented, leading to the early formation of bonding and curing phenomena.
In the printing process, it is often necessary to adjust the printability, especially the dryness adjustment, that is, to add the appropriate amount of dry oil in the ink, which is also the most difficult to justify. On the one hand, the ink is not necessarily added with a drying oil at the time of its manufacture. Even if it is added, there is a problem of “old difficulty†that causes the components to be soaked in the ink, which has not yet been satisfactorily solved. On the other hand, the speed, temperature, humidity, paper condition, and the thickness of the pattern ink layer are all different in different places. It is necessary to decide whether or not to adjust the amount and amount according to the actual situation.
Drying is too fast and too slow, which is unfavorable for printing. Only when proper drying speed is maintained can printing be performed normally and normal drying can be ensured.
Drying speed is too fast, it often causes partial wrinkling of printed materials, or handwriting deformation, which is unfavorable for overprinting, and causes "crystallizing", ink "thickness" and other ills. Drying is too slow, resulting in "dirty", dirty writing, patterns, printing can not be normal.
Therefore, the ink drying speed has a great relationship with the quality of printed products. It is very beneficial to carefully measure the drying speed of the ink.
Adding the right amount of dry oil to the ink is critical for improving the quality of the print and ensuring normal printing. The amount added depends on the condition of the ink at hand, the temperature and humidity at that time, and the surface conditions of the paper, such as the ink absorption and the thickness of the ink layer, etc., for comprehensive analysis and application of rich experience.
Too much dry oil is added. This is a problem frequently experienced by people with insufficient ink transfer experience. The more they add, the better, and the faster the print, the better the quality. In fact, it is counterproductive. The more dry oil is added, the ink is diluted and the texture becomes thicker, which causes the ink to dry and deposit ink on the ink roller, printing plate and offset rubber, and accelerates emulsification. The reaction of the metal salt and the offset ink makes the syrup become Neutral, lost the role of Paul, this will cause paste version, flower version; ink outside the dry seal without overdue, causing overprinting is not allowed; will cause paper adhesions. In fact, the dry oil itself is not dry, this will cause more problems, not only affect the surface quality of printed products, but also make the print products lose their luster.
Too little dry oil is added, so that the printed product cannot be dried within the required time and the production cycle is lengthened; the printed product is not dry, causing back stains; or the paper feeding, paper feeding and registering are difficult.
In general, there is less red dry oil and more dry white oil. The amount of red dry oil should be within 3%, and 0.5 to 1% should be used regularly. The amount of dry white oil should be within 7%, and 2 to 5% should be used as well. It is true that this is not a definite number, but also depends on the specific type of ink. For example, iron blue is the medium blue, and dark blue itself is quickly dried due to iron ions. Therefore, it is not necessary to add dry oil, but to suppress dryness. White dry oil on the black ink, gold and red ink will cause the ink to gray, fade defects, they can not join. The application of red dry oil. If the paper is acidic, adding more dry oil will not help.
In summary, the use of dry oil (desiccant) is a relatively complicated matter, it must be treated with caution, it should be noted: Do not easily increase the proportion of dry oil, really need to increase, but also reasonable, in order to facilitate the normal printing, do not exceed The maximum amount specified above.