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Paper has a great influence on the ink drying, mainly in:
(1) Acidity of the paper The acidity of the paper surface reacts with the metal salt in the desiccant to disable the desiccant, prevent or destroy the oxidative polymerization reaction, slow the drying of the blot on the paper surface, the smaller the PH value of the paper, The slower the drying speed.
(2) The structure of the paper surface is rough, the structure is loose, and the paper with a high permeability and a small degree of sizing promotes drying, and vice versa. This is reflected in the osmotic drying method. The ink on the smooth and tough paper surface is thicker than the surface rough and loose paper, it has less contact with the air, the oxidized conjunctiva is slow, so the surface smooth and tough paper imprint slow drying.
(3) Water content of paper The moisture content of the paper has a certain degree of influence on the penetration of the ink and on the oxidized conjunctiva. The moisture content of the paper is high and the penetration of the ink into the paper is reduced. At the same time, the moisture can also cause the oxidized conjunctiva of the ink to be blocked.
5. Effect of fountain solution
The stronger the acidity of the fountain solution, the longer the drying time of the ink. This is because during the offset printing process, the ink emulsification inevitably exists. The acid substances in the fountain solution chemically react with the desiccant and the desiccant fails. The ink drying is damaged. Generally, the pH of the fountain solution should be maintained between 4.5-6. The stacking has little effect on the drying of the ink.
6. Influence of additives
In the printing process, in order to make the ink have good printing adaptability, it is necessary to add various additives in the ink. In fact, the additive has a certain influence on the drying of the ink. For example, both Weili oil and white oil have the property of inhibiting ink drying and slow drying of the imprint. The main component of Willi oil is aluminum hydroxide. Aluminum hydroxide will absorb the desiccant and make it lose its function. At the same time, the aluminum hydroxide will increase. Ink emulsification, white oil is also very easy to cause the emulsification of the ink, affecting the oxidation of the ink conjunctiva.
In the printing process, in order to reduce the viscosity of the ink, non-drying auxiliary materials such as de-bonding agents are added. The auxiliary materials themselves are dried very slowly. A small amount of the additives does not significantly affect the drying of the ink. If the ink is used excessively, the wax in the de-bonding agent is used. The substance has a small specific gravity and floats on the surface of the imprint and blocks the oxidized polymeric conjunctiva of the binder.
7. Influence of other factors
The smaller the area occupied by layout images, the greater the emulsification of the ink and the less drying of the ink. At this time, it is necessary to control the moisture of the layout, and appropriately increase the amount of desiccant to ensure timely drying of the ink. If the ink layer is too thick, the contact area between the ink layer and the air will be reduced, and the contact between the ink and the paper will also be reduced, and the oxidized conjunctiva and infiltration will be affected.
The stacking of printing products has a lot to do with drying. If the area of ​​the printed sheets is large, the paper surface is smooth, and the stacking height is high, the air is difficult to contact with the ink. If the oxygen is not added in time, the drying will be slow, and the middle of the printed sheets will be even worse.
Whether the printed sheet is exposed or not has an effect on the drying speed of the ink.
Third, the ink drying speed unfavorable degree of harm
1.Hazards caused by ink drying too quickly:
(1) The ink is dried too fast and the viscosity of the ink is increased, the flowability is poor, the paper is pulled, and even when the paper is severe, the paper is torn;
(2) The ink accumulates in the graphic part of the printing plate and the eraser, making the plate graphic dirty;
(3) The ink conjunctiva on the surface of the printing plate and the ink roller is dry and solid, changing the original wetting properties to weaken the lipophilicity, the printing plate is not inked, the ink roller is not under ink, and the graphic is white and pale;
(4) The ink film is dry and the surface is very smooth, loses the adsorption force, and the phenomenon of crystallization occurs, so that the back color is not overprinted.
2. Damage caused by ink dripping or slow drying:
(1) The next color overprint cannot be completed, and the next process such as cutting cannot be performed;
(2) The back of the printed product is dirty;
(3) The amount of ink permeation increases, resulting in powdering, the edges of the picture are blurred, and the picture text is dull.
Fourth, the ink drying control
1. The correct use of dry oil
The correct addition and placement of dry oil is one of the important means to control ink drying. It depends on the nature of the oil itself, the temperature and humidity of the environment, the structural properties of the paper, the type of oil, the thickness of the ink layer, and the amount of additives added. The number of prints and other factors to determine the type and amount of dry oil, add too much dry oil, will lead to thicker ink texture, ink roller drying, ink is diluted, ink emulsification and other issues, making it difficult to print In practice, adding too much dry oil to the actual situation will cause the situation where the desire is not reached. In the case of excessive dry oil, the surface of the ink layer will soon dry and form a closed state, and internal drying will be extremely slow. However, when the amount of dry oil is low, the printed products cannot be dried within the required time, which will delay the production speed. The printed products are likely to be dirty and seriously affect the printing quality.
2. Strengthen the inspection and management of raw materials
The inspection of raw materials is one of the important ways to improve product quality. It should be tested on the printing performance of inks and papers. In particular, the drying performance is estimated to be dry and heavy. In the production process, it is not necessary to change the ink freely for the convenience of operation. Viscosity and fluidity.
3. Observe various signs in printing
Ink drying conditions can show various signs in the printing process. Some unfavorable factors also have warning signs. If you can find and take measures in time, you can prevent the problems of drying too quickly or too slowly and ensure the smooth production.
4. Control the pH of the fountain solution and the layout moisture
The effect of the pH of the fountain solution on drying was as previously described. Moisture in the layout will increase the emulsification of the ink, slow the drying, and print with the minimum moisture, which is one of the technical measures to ensure the product is dried in time.
Source: Print Chemicals Network
4. Effect of paper