Talking about the factors that affect the ink drying speed

Several batches of products of our factory had been slow to dry due to the ink. After the machine was placed for 5 to 6 days, the folding was still dirty, especially in the field. To this end, we have considered and reformed in many ways so that the situation can be controlled. Here, the author discusses the factors that affect the ink drying speed in combination with practice.

The nature of the ink itself

We mainly talk about the main part of the ink - the link material. The ink is dried on paper in two stages, namely fixing and drying the conjunctiva. The ink changes from a liquid to a semi-solid state and cannot be re-transferred. This is the fixing phase of the ink and the initial drying of the ink. The physical and chemical reactions occur in the main part of the binder in the semi-solid ink, and the film is completely dried and solidified. This is the ink. The thorough drying phase.

Ink drying is generally divided into three types: penetrating, oxidized conjunctiva, and volatile. The ink using mineral oil as the linking material is a penetrating dry, the ink using the dry vegetable oil as the linking material is an oxidative conjunctiva-type drying, and the ink using the volatile solvent as a linking material is a volatile drying. Now commonly used fast-drying bright offset inks account for 35% to 40% of resin, dry vegetable oil accounts for about 30%, and high-boiling kerosene accounts for 15% to 25%. This miscibility state determines the dry form of the ink is penetration and Oxidation conjunctiva combined dry form.

It can be seen that the nature of the binder in the ink plays an important role in ink drying. Based on the above theory, combined with the production practice and communication with the ink manufacturers, we replaced the Tiens TOW-729, which was originally used for printing paper of more than 60g/m2, with TOW-779 to speed up the drying of the ink.

Paper pH

If the paper is acidic, the acidic substance reacts with the polyvalent metal in the desiccant to produce a product that is soluble in the oil and prevents the oxidative conjunctiva of the ink and inhibits drying of the ink. In general, the greater the acidity, the more severe the degree of inhibition or destruction of the oxidative polymerization of the ink. We measured the pH of the paper and contacted the paper mill and asked the mill to give feedback on the pH of the paper. As a result, the paper mill concluded that when the paper was produced, the pH was lowered, ie, the pH was increased. Big acidity. Thus, we have found a reason for the slow drying of the ink.

Fountain solution pH

When the pH of the general fountain solution is lower than 3.8, the hydrogen ions in the fountain solution will react with the metal driers to destroy the original molecular structure of the driers and affect the drying speed of the ink on the paper. To this end, through repeated measurement and practice, we regulate the pH value of the fountain solution for sheetfed printing; when it is hot, the pH value is controlled between 4.8 and 5.5. At this time, the amount of fountain solution added is 2%. 3%; In cold weather, the pH is controlled between 5.5 and 6.0. The pH of the fountain solution is controlled within a certain range, which is helpful for accelerating the drying of the ink on the paper.

Water supply

According to the principle of water-ink balance, if the layout volume is too large, the layout ink volume will also increase. In this way, the amount of blotting ink will be too large, and the ink drying speed will slow down. Therefore, the amount of water supply should be reduced as much as possible, and the least amount of water should be balanced with the ink on the printing plate to facilitate the ink drying. At the same time, if the layout is large and the ink is large, problems such as ink emulsification are easily caused, which is not conducive to ink drying. Therefore, reducing the amount of water can also speed up the drying of the ink on the paper.

Environmental temperature and humidity

If the relative humidity of the environment is relatively high, the water content of the paper will increase. This water can directly participate in the hydrolysis of cellulose and hemicellulose, increase the acidic content of the paper, prevent the oxidation and conjunctiva of the ink, and then affect the drying speed of the ink. On the contrary, the ink is relatively dry. If the ambient temperature increases, the speed of molecular motion is accelerated, which is beneficial to accelerating the oxidation and conjunctiva of the ink, thereby accelerating the ink drying speed. On the contrary, it will slow down.

Practice has proved that the best relative humidity of the environment is 50% to 75%, and the air circulation in the workshop is maintained so that the printed matter can be stored in a well-circulated environment. The ambient temperature will vary from season to season, and it is best kept at 18-28°C.