1. The influence of ambient temperature and humidity
1. Influence of ambient temperature
When the temperature rises, the movement speed of the molecules is accelerated, the internal energy of the molecules is increased, and it is easy to generate more peroxides with the activated genes, thereby accelerating the polymerization of oil molecules. Therefore, as the temperature increases, the oxidative polymerization of the ink will increase faster, thereby speeding up the drying of the ink.
The drying process of the ink film is an exothermic reaction, and the heat released when the printed sheet is dried will also speed up the drying of the blot. The effect of temperature on the speed of blot drying is obvious. The temperature of the environment increases, the ink dries faster, and vice versa. For example, in the summer when the weather is hot, the bright and quick-drying ink can dry quickly without adding dry oil, but in the cold winter, you need to add dry oil.
2. Influence of environmental humidity
In the offset printing process, we need to wet the plate surface with water, water is a polar molecule, oil is a non-polar molecule, because wetting the plate with water, there will be ink emulsification phenomenon, the ink emulsification is controlled between 10-30% Within the scope, the moisture precipitation and evaporation rate are closely related to the drying of the blot. Because water molecules are very polar substances, the presence of water can hinder the oxidation and polymerization of oil molecules to form a film, which will affect the drying speed of the blot. The level of environmental humidity will play a role in the rate of water evaporation. As the environmental humidity increases, the activity of oxygen in the air will also decrease, reducing the absorption of oxygen by the ink. At the same time, the emulsified moisture in the inner layer of the ink film also softens the ink film, thereby slowing the drying speed of the ink. Therefore, it is necessary to control the water and ink balance during the offset printing process. On the premise of not dirtying the plate, use as little water as possible to reduce the emulsification of the ink. The amount of water in the ink is very closely related to the drying of the blot.
Second, the impact of ink auxiliary materials
The transparent diluent, white oil, detackifier, etc. all have the property of inhibiting the drying of the ink, which slows the drying of the blot. The main components of diluent, velvet oil, white ink, white oil, etc. are that there is often aluminum oxide in the binder and aluminum hydroxide, which is insoluble in water. Since aluminum hydroxide easily dissociates when it meets water, it will increase the degree of emulsification of the ink during printing, so the blot will dry more slowly. Weili oil is generally used as a diluent for multi-color overprinting inks of ordinary products. The color of the diluted ink has basically no effect, but the brightness is average and the drying is slow. White oil is a white translucent emulsified product. It can reduce the viscosity of the ink by diluting the ink color. The color matching is uniform. The white oil is non-drying. The loose quality contains water, which accelerates the emulsification of the ink. Evaporation blocks the oxidative polymerization process of the ink, which will seriously affect the speed of blot drying.
In the offset printing process, in order to change the printing suitability of the ink, or reduce the viscosity of the ink, often add non-drying auxiliary materials such as debonding agent, basically does not affect the gloss and fluidity of the ink color. However, do not use too much, because of its non-drying and penetrating substances, it is easy to cause the drawback of slow drying of the blot, and the content in the ink is less than about 5%.
In general, if the ink needs to be diluted and desticked, the amount of drier should be increased in the ink accordingly. Such as: red and white dry oil.
Third, the impact of the water bucket solution
Acidic substances, such as phosphoric acid and citric acid, are indispensable in the hopper solution. First, the gravure 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. The drying of the ink is damaged. The stronger the acidity of the water bucket solution, the slower the drying time of the ink, so it is necessary to control the PH value of the water bucket solution. When formulating the water bucket solution, follow the instructions of the wetting powder. Add some gum arabic to the wetting liquid to enhance the ability of hydrophilic to remove dirt, reduce the emulsification of the ink and affect the drying.
Four, the impact of paper
Paper is very influential on the drying of blots.
The effect of the pH value of the paper. The paper is preferably neutral, that is, the PH value is 7, but most of the paper is weakly alkaline. The acidity of the paper often has a great influence on the drying of the blot. The acidity of the paper is large, which can make the ink layer not work for a few days. Drying affects timely delivery, and the fiber structure of the paper affects the drying of the print. The surface of the paper with rough surface, loose structure, high permeability and less sizing dries quickly. On the contrary, the surface smoothness is high, and the fibrous dense and tough coated paper and card paper are slow to dry.
5. The influence of graphic distribution and ink layer thickness
In the offset printing process, the area of ​​the picture and text is large and the distribution is even. The water consumption on the surface of the printing plate is large. Because the water consumption is uniform, the emulsification value of each part of the ink on the surface of the ink roller is relatively average. Under normal circumstances, the marks close to the edge of the blank part at both ends are not easy to dry due to the large amount of emulsification. The smaller the graphic area of ​​the layout, the greater the ink emulsification value. To prevent non-drying. In addition to adding a drier, it is more important to strictly control the moisture of the plate surface, reduce the induction of the ink, and ensure the timely drying of the blot.
If the ink layer is too thick, it will reduce the contact between the ink layer and the air. When a thin film is formed on the surface of the ink layer, the speed of oxygen in the air entering the ink film will be slowed down. The ink layer is thick, and the chance of contact between the blotting ink and the paper is reduced, and the penetration effect is reduced accordingly. Therefore, the drying speed of the excessively thick ink layer can only be very slow, and the amount of desiccant can be adjusted according to the thickness of the ink layer. It is necessary to control the thickness of the imprinted ink layer to avoid the large ink and water on the offset printing, the one-sided emphasis on thickness and bright colors, and the disadvantages of excessive thickness of the ink layer caused by excessively increasing the amount of ink.
6. Impact of stacking
The stacking of printed sheets and the drying speed of the imprint have a great influence. The offset ink is oxidized on the paper, and the ink film is dried by the reaction with oxygen in the air to generate oxidation and polymerization exotherm. If the surface of the paper is smooth, the stacking is high It is difficult for the air to come into contact with the imprint, and there will inevitably be a thick stack in the middle of a piece of paper, and the printed sheet will dry slowly.
In order to speed up the drying of the blotting ink film, it is often used to divide the printed sheets in multiple layers on the paper receiving table with a wooden plywood to reduce the excessive stacking, speed up the drying, or wait for a certain time after the printing of the printed sheet is over, and ventilate the semi-finished printed products The purpose is to increase the contact between the blot and the air and accelerate the drying of the blot.
After the ink is transferred from the printing plate to the surface of the printed matter, part of the connecting material in the ink penetrates; at the same time, the solvent in the connecting material begins to volatilize, and the main part of the connecting material produces chemical reactions and physical reactions, etc., so that the surface of the printed material The ink film gradually increased its viscosity and hardness, and finally formed a solid film.
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