Adjusting the ink aid - desiccant
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The desiccant is a material which is only used to accelerate the drying speed of the grease ink having an unsaturated and double bond structure and shorten the drying time. That is, a material that accelerates the drying time of the oxidized conjunctiva drying type ink. Its composition is mainly composed of organic and inorganic compounds containing metal elements such as cobalt, manganese, lead, zinc, iron, calcium, vanadium and zirconium, and ink-like materials and inks.
At present, commonly used red dry oil, which is a liquid dry oil made mainly of purple red cobalt naphthalate. The other is a white dry oil, which is a slurry-like dry oil prepared by dispersing in an ink binder from manganese borate and a small amount of cobalt naphthalate.
The main difference between this improved material is that the strength of the dry-drying ability is different. This is due to the strength of the metal activity.
The more unified view is that cobalt has the highest activity, its main function is to enhance the oxidation of the surface of the ink, and can quickly form a film, known as surface dry oil. Therefore, if it is used more, it will cause surface crusts or wrinkles, and it will also cause crystallization and overprinting.
Followed by manganese, it is also the first to dry the surface of the gold, and from the top to the bottom, the tendency to peel 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 coating is called thick oil or lead oil. It is mild and sensitive to temperature.
Manganese and lead are often mixed and used to complement each other.
In the ink with oxidation, the addition of a desiccant can play the role of:
Shorten the induction period. Since the dry oil contains sterols, the fertility powder, lecithin and the like are antioxidants, causing the oxygen not to be in contact with the unsaturated structure of the oil quickly. Active metals can alter the properties of these materials, counteracting their negative effects, and precipitating the antioxidants, allowing them to combine with oxygen quickly.
Accelerate the oxidation rate. Due to the metal activity, the oxygen uptake increases, and as the properties of the ink material differ, the chance of forming a hydroperoxide increases, thereby accelerating the oxidation rate.
Promote polymerization. They can change the type of volatiles and increase their amount, which accelerates the polymerization and causes the ink to solidify.
Accelerate the condensation of the binder molecules. The oil molecules are strongly aligned, resulting in the early formation of bonding and solidification phenomena.
In the printing process, it is often necessary to adjust the printability, especially the dry adjustment, that is, adding an appropriate amount of dry oil to the ink is also the most difficult to justify. On the one hand, since the ink is not necessarily added with dry oil at the time of manufacture, even if it is added, there is a problem that the adsorption of the components in the ink is degraded, and it has not been satisfactorily solved. On the other hand, the speed, temperature, humidity, paper condition, and thickness of the patterned ink layer vary from place to place, and it is necessary to determine the adjustment or the amount according to the actual situation.
Dryness is too fast and too slow, which is unfavorable for printing. Only by maintaining proper drying speed can the printing be carried out normally and normal drying can be obtained.
If the drying speed is too fast, it will cause partial wrinkles or deformation of the printed matter, which is unfavorable for overprinting, and causes "crystallization" and ink "lifting" and other defects. The drying is too slow, causing "dirty", the writing and pattern are dirty, and the printing cannot be performed normally.
Therefore, the drying speed of the ink is highly related to the quality of the printed product. Careful detection of the drying speed of the ink is beneficial to the amount of dry oil used in the adjustment of the ink and the accurate mastering of the color overprinting time.
Adding an appropriate amount of dry oil to the ink is essential for improving the quality of the print and ensuring normal printing. The amount to be added depends on the ink condition at hand, the temperature and humidity at that time, and the surface condition of the paper, such as ink absorption, thickness of the ink layer, etc., based on a comprehensive experience.
Excessive amount of dry oil is added. This is a problem that people who have insufficient experience in adjusting ink often have problems. The more they add, the better, the faster the printed products are, the better the quality. In fact, it is counterproductive. The more the dry oil is added, the more the ink is diluted and the texture becomes thicker, which promotes the drying and stacking of the ink on the ink roller, the printing plate and the offset printing rubber, and accelerates the emulsification, because the metal salt reacts with the offset printing water to make the syrup into water. Neutral, lost the role of the guarantee, this will cause the paste, the plate; the ink is dried outside the seal without rushing, causing the overprinting is not allowed; it will cause the paper to stick. In fact, the dry oil itself is not dry, which causes more problems, not only affects the surface quality of the printed product, but also makes the printed product tarnished.
The amount of dry oil added is too small, so that the printed product can not be dried in the required time, lengthen the production cycle; the printed product is delayed, causing back contamination; or it is difficult to feed paper, paper and register.
Generally speaking, the amount of red dry oil is small, and the amount of white dry oil is large. The amount of red dry oil should be within 3%, and 0.5~1% is often used; the amount of white dry oil should be within 7%, and 2~5% is often used. Admittedly, this is not a fixed number, but also depends on the specific type of ink. For example, the medium blue of iron blue, the deep blue itself is very fast due to iron ions, so it is not necessary to add dry oil, but to suppress dryness. White dry oil on black ink, gold red ink has the defect that the ink color becomes gray and fades, and it cannot be added. And apply red dry oil. If the paper is acidic, add more dry oil, it will not help.
In summary, the use of dry oil (desiccant) is a relatively complicated matter, we must be careful, we should pay attention to: can not easily increase the proportion of dry oil, it is necessary to increase, but also reasonable, in order to facilitate the printing, do not exceed The maximum amount specified above.