Exchange of experience: factors affecting the dryness of the blot
1. Environmental temperature effect
When the temperature rises, the molecular motion speed increases, the intramolecular energy increases, and more peroxides are easily formed with the activated gene, thereby accelerating the polymerization of the oil molecules. Therefore, as the temperature increases, the oxidative polymerization of the ink increases, thereby accelerating the drying of the ink.
The drying process of the ink film is an exothermic reaction, and the heat released when the sheet is dried also accelerates the drying speed of the blot. The effect of temperature on the speed of blotting is obvious. When the temperature of the environment rises, the ink dries quickly, and vice versa. For example, in summer, the weather is hot, and the light-drying and quick-drying ink can be dried quickly without adding dry oil. However, in the cold winter, it is necessary to add dry oil.
2. Environmental humidity
During the offset printing process, the plate layout needs to be wetted with water. The water is a polar molecule, and the oil is a non-polar molecule. Since the printing plate is wetted with water, ink emulsification occurs, and the ink emulsification is controlled between 10 and 30%. Within the range, the rate of water condensation and evaporation is closely related to the drying of the blot. Since water molecules are highly polar substances, the presence of moisture can hinder the oxidative polymerization of oil molecules into a film, which will affect the drying speed of the imprint. The level of environmental humidity will play a role in the evaporation rate of water. When the ambient humidity is increased, the activity of oxygen in the air is also weakened, which reduces the absorption of oxygen by the ink, and the moisture emulsified in the inner layer of the ink film also softens the ink film, thereby slowing the drying speed of the ink. Therefore, in the offset printing process, the ink and water balance should be controlled. Under the premise of not being dirty, use as little moisture as possible to reduce the emulsification of the ink. The water content in the ink is very close to the dryness of the blot.
Second, the impact of ink auxiliary materials
Transparent thinners, white oils, debonding agents, etc. all have the property of inhibiting the drying of the ink, and the drying of the blot is slowed down. The main components of the thinner, weili oil, white ink, white oil, etc. are the presence of aluminum oxide in the binder and aluminum hydroxide, which is insoluble in water. Since aluminum hydroxide is easily dissociated by water, the degree of emulsification of the ink is increased during printing, so that the blotting is dried slowly. Weili oil is generally used as a thinner for multi-color overprinting inks of ordinary products. The color of diluted inks has basically no effect, but the brightness is generally low and the drying is slow. White oil is a white translucent emulsion. It can reduce the viscosity of the ink by using the ink color. The color is uniform, the white oil has no dryness, the loose color contains moisture, and the ink accelerates the emulsification. After the moisture is absorbed into the ink layer, it gradually Evaporation, blocking the oxidative polymerization process of the ink, will seriously affect the speed of blotting.
In the offset printing process, in order to change the printing suitability of the ink, or to reduce the viscosity of the ink, a non-drying excipient such as a detacking agent is often added, and the gloss and fluidity of the ink color are not substantially affected. However, it is not possible to use too much, because of its dryness and permeability, it is easy to cause the drawback of slow drying of the print, and the content in the ink is less than 5%.
In general, if the ink needs to be diluted and de-bonded, the amount of drier should be increased in the ink accordingly. Such as: red, white dry oil.
Third, the impact of the water bucket solution
The water bucket solution can not be separated from acidic substances, such as: phosphoric acid, citric acid, etc. First, the flat concave plate needs to supplement the inorganic salt layer lost during the printing process. Phosphoric acid and other acidic substances have the function of cleaning the dirty ink, and the acidity will make The drying of the ink is destroyed. The stronger the acidity of the water hopper solution, the slower the drying time of the ink. Therefore, it is necessary to control the pH value of the water hopper solution. When formulating the water hopper solution, operate according to the instructions of the wetting powder. Add some gum arabic to the dampening solution to enhance the ability of hydrophilic to remove dirt and reduce the emulsification of the ink to affect the drying.
Fourth, the impact of paper
Paper is very influential on blotting.
The effect of the pH of the paper on the pH. The paper Zui is neutral, that is, the PH value is 7. However, most of the paper is weakly alkaline. The paper is acidic, and the drying effect of the imprint is very large. The acidity of the paper is large, so that the ink layer can not be used for several days. Dry, affecting timely delivery,
The fiber structure of the paper affects the drying of the print. The surface is rough, the structure is loose, the permeability is large, and the paper with less sizing is quick to dry; on the contrary, the surface smoothness is high, and the fiber-bonded tough coated paper and card paper are dried slowly.
Fifth, the distribution of graphics and the influence of the thickness of the ink layer
In the offset printing process, the image has a large area and a uniform distribution, and the water consumption on the surface of the printing plate is large. Because the water consumption is uniform, the emulsified value of the ink on each surface of the ink roller is relatively average. In general, the prints with the ends close to the edge of the blank portion are not easy to dry due to the large amount of emulsification. The smaller the area of ​​the layout image, the greater the ink emulsification value. To prevent the occurrence of dryness. In addition to adding a drier, it is more important to strictly control the moisture of the plate, reduce the lead of the ink, and ensure that the blot is dry at the right time.
Excessive thickness of the imprinted ink layer reduces the contact of the ink layer with the air, and when the surface of the ink layer forms a film, the velocity of oxygen in the air into the interior of the ink film is slowed down. The ink layer is thick, the contact chance of the printing ink and the paper is reduced, and the osmosis is correspondingly reduced. Therefore, the drying speed of the excessively thick ink layer can only be very slow, and the thickness of the ink layer is adjusted according to the thickness of the different ink layers. It is necessary to control the thickness of the imprinted ink layer to avoid the appearance of large ink and large water on the offset printing, the thick and vivid color of the one-sided surface, and the excessive thickness of the ink layer caused by excessively increasing the amount of ink.
Sixth, the impact of receiving paper stacking
The stacking of the printed sheets and the drying speed of the blotting have a great influence. The offset printing ink is on the oxidized paper. The drying of the ink film depends on the oxidation of oxygen in the air and the reaction of the exothermic heat. If the surface of the paper is smooth, the stacking is high. The air is difficult to contact with the imprint, and it is inevitable that a middle portion of a sheet of paper will be thick and the sheet will dry slowly.
In order to speed up the drying of the imprinted ink film, it is often adopted to separate the printed sheets by multiple layers on the delivery table by using wood splints, to reduce stacking too thick, to speed up drying, or to end printing for a certain period of time, and to pass through the printed semi-finished products. The aim is to increase the contact of the blot with air and speed up the blotting.
After the ink is transferred from the printing plate to the surface of the printed matter, a part of the connecting material in the ink is infiltrated; at the same time, the solvent in the connecting material starts to volatilize, and the main part of the connecting material generates a chemical reaction and a physical reaction, thereby making the surface of the printed matter The ink film gradually increases its viscosity and hardness, and finally forms a solid film layer after the Zui.
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