Drying and printing of ink in the hottest offset p

Ink drying and printing in offset printing (Part 2)

4 The influence of paper

paper has a great influence on ink drying, which is mainly reflected in:

(1) the pH of paper. The acidic substances on the surface of paper can react with the metal salts in the desiccant, making the desiccant ineffective, preventing or destroying the oxidative polymerization reaction, and slowing down the drying of imprints on the paper. The smaller the pH value of paper, the slower the drying speed

(2) the structural surface of paper is rough, the structure is loose, and the paper with high permeability and low sizing degree will promote drying, on the contrary, it will dry slowly, which is reflected in the penetration drying method. The ink accumulates thicker on the paper with smooth and tough surface than on the paper with rough and loose surface, and its contact with air is less, and the oxidation conjunctiva is slow, so the paper with smooth and tough surface prints slowly dry

(3) water content of paper the water content of paper has a certain impact on the penetration of ink and oxidation conjunctiva. The water content of paper is high, the penetration of ink into paper is reduced, and the sample breakpoint is good. At the same time, water can also block the oxidation conjunctiva of ink

5. The stronger the acidity of the fountain solution is, the longer the drying time of the ink is. This is because in the offset printing process, ink emulsification is inevitable. The acid in the fountain solution reacts with the desiccant, and the desiccant fails, which destroys the drying of the ink. Generally speaking, the pH value of the fountain solution should be kept at 4 Between, the lamination has little effect on the drying of ink

6. Influence of additives

in the printing process, sometimes in order to make the ink have good printing adaptability, various additives need to be added to the ink. In fact, additives have a certain impact on the drying of the ink. For example, both Willy oil and white oil have the property of inhibiting the drying of ink, making the imprint dry slowly. The main component of Willy oil is aluminum hydroxide, which will adsorb the desiccant and make it ineffective. At the same time, aluminum hydroxide will increase the emulsification of ink, and white oil is also very easy to cause the emulsification of ink, affecting the oxidation film of ink

in order to reduce the viscosity of the ink in the printing process, non dry excipients such as de adhesion agent are added. These excipients themselves dry very slowly, and a small amount of addition does not significantly affect the drying of the ink. If used excessively, the wax in the de adhesion agent floats on the imprinted surface due to its small proportion, blocking the oxidative polymerization conjunctiva of the binder

7. Other factors

the smaller the area of the layout, the greater the emulsification of the ink, and the ink is not easy to dry. At this time, it is necessary to control the moisture of the layout and appropriately increase the amount of desiccant to ensure the 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 be reduced, and the oxidation conjunctiva and penetration will be affected

the stacking of prints has a lot to do with drying. If the area of the print is large, the paper surface is smooth, the stacking is high, the air is difficult to contact with the ink, and the oxygen is not supplemented in time, the drying will be slow, especially in the middle of the print

whether the printing sheet is exposed or not also affects the drying speed of the ink

III. harm of inappropriate ink drying speed

1 Harm caused by too fast drying of ink:

(1) too fast drying of ink increases the viscosity of ink, poor fluidity, paper roughening, and even paper tearing in serious cases

(2) the ink accumulates in the graphic part of the printing plate and rubber, making the graphic and text of the layout dirty

(3) the ink conjunctiva on the surface of the printing plate and the ink roller is dry and solid, changing the original wetting property so that the lipophilicity is weakened, the printing plate is not inked, the ink roller is not inked, and the graphics and texts are white and pale

(4) the ink film is dry and the surface is very smooth, losing adsorption and crystallization, making the subsequent color overprint impossible

6. Oxygen index tester: combustion performance of polymer under specified experimental conditions 2 Harm caused by ink not drying or slow drying:

(1) the next color overprint cannot be completed, and the next process such as cutting cannot be carried out

(2) the back of the print is sticky

(3) the ink penetration increases, resulting in chalking, blurred edges of graphics and texts, and the graphics and texts themselves are dim

IV. control of ink drying

1 can still keep in touch and confirm the location of the child The correct use of dry oil

the correct addition of dry oil is one of the important means to control ink drying. The type and amount of dry oil should be determined according to the nature of dry oil itself, the temperature and humidity of the environment, the structural performance of paper, the type of oil, the thickness of ink layer, the amount of additives, the number of prints and other factors. Adding too much dry oil will lead to the thickening of ink texture, the drying of ink roller, and the dilution of ink, Problems such as increased ink emulsification make it difficult to print. In fact, adding too much dry oil will lead to the situation that speed is not achieved. In the case of excessive dry oil, the surface of the ink layer will soon dry and form a closed state, and the internal drying will be extremely slow. However, if the dry oil is added less, the printed matter cannot be dried within the required time, delaying the production speed, and the printed matter is easy to stick and dirty, which seriously affects 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. We should test the printing performance of ink and paper, especially the drying performance, estimate the amount of dry oil, and do not change the viscosity and fluidity of ink for the convenience of operation in the production process

3. Observe various signs in printing

various signs of ink drying can be shown in the printing process, and some adverse factors also have omens. If it can be found in time and measures can be taken, the disadvantages of too fast or too slow drying can be prevented to ensure the smooth progress of production

4. Control the pH value and layout of the fountain solution and formulate investment guidelines for key areas moisture

the impact of the pH value of the fountain solution on drying is as described above. Excessive moisture in the layout will increase the emulsification of the ink and slow down the drying. Printing with minimum moisture is one of the technical measures to ensure the timely drying of the product

source: printing chemicals