Analysis of Ink Drying Speed

The speed of ink drying is affected by many factors, such as ink composition, ink additives, printing materials, and external conditions, among which are the following:

Effect of pigments

Different pigments have different effects on ink drying. Some pigments can promote drying, some slow drying, and others have no obvious effect on ink drying. The pigments that promote drying include iron blue and chrome yellow, which delay the drying of carbon black, lead oxide, etc. Most organic pigments have no significant effect on the drying of the ink. In the same type of ink, the drying speeds of red ink, black ink, blue ink, and yellow ink are accelerated in turn.

Effect of ink additives

1. The effect of desiccant: The drying of the ink layer on the paper surface is mainly the process of physical and chemical changes, especially the process of oxidizing the conjunctiva of the binder material takes a long time and can not meet the production requirements, so the desiccant can be added to the ink. To speed up the drying of the blot. The desiccant enables the binder in the ink to accelerate the absorption of oxygen in the air to promote its molecular polymerization, and at the same time, accelerates the polymerization reaction, thereby greatly promoting the drying of the imprinting.

2. The effect of the fountain solution: The stronger the acidity of the fountain solution, the longer the drying time of the ink. This is because the ink emulsion is inevitably present in the offset printing process, and the acid substances in the fountain solution react chemically with the desiccant. Drying agent failure to make the ink dry to be destroyed, generally speaking, the fountain solution PH value should be maintained between 4.5 to 6, this has little effect on the drying of the ink.

3. Effect of Additives: In the printing process, in order to make the ink have good printability, it is necessary to add various additives to the ink. These additives have a certain influence on the drying of the ink. For example, weili oil and white oil all have the effect of inhibiting ink drying. The main component of Weili oil is aluminum hydroxide. Aluminum hydroxide will lose its effect due to the adsorption of desiccant. At the same time, aluminum hydroxide will increase ink emulsification. Oil also easily causes the emulsification of the ink and affects the oxidized conjunctiva of the ink.

Impact of printing materials

Paper has a great influence on the ink drying, mainly in:

1. pH of the paper: acid on the surface of the paper reacts with the metal salt in the desiccant, causing the desiccant to fail, preventing or destroying the oxidative polymerization reaction, slowing the drying of the blots on the paper, lowering the pH of the paper, and drying speed The slower.

2. Paper structure: rough surface, loose structure, high permeability, small sizing paper will promote drying, otherwise it will affect the drying, which is reflected in the osmotic drying method. The ink is thicker on rough-surfaced and tougher paper than rough and loose paper, it has less contact with air, and the oxidized conjunctiva is slow, so the smooth and tough paper imprints dry very slowly.

3. Water content of paper: The water content of the paper has a certain degree of influence on the penetration of the ink and 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, moisture can also hinder the oxidized conjunctiva of the ink.

External conditions - the influence of temperature and humidity

When the temperature rises, the movement speed of the material molecules increases, the intramolecular energy increases, the reaction rate of the oxidized conjunctiva also accelerates, and the drying speeds up. In general, the drying speed is increased by 1 time for every 10°C increase in temperature. The drying process is an exothermic reaction, and the heat released when the sheet is dried, in turn, also promotes the drying of the ink.

The effect of humidity on drying is related to the pigment in the ink. When the humidity of the pigment ink reaches 95%, the drying of the ink is not affected. The relative humidity of the air is large, the speed of the oxidative conjunctiva is correspondingly slowed, and the drying speed also follows. Slow down.

Influence of other factors

The smaller the area occupied by the layout graphic, the greater the emulsification of the ink, the more difficult it is for the ink 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 also be reduced, and the oxidized conjunctiva and infiltration will be affected.

The stacking of printing products also has a lot to do with drying. If the area of ​​the paper is large, the paper surface is smooth, and the stacking height is high, the air is difficult to contact with the ink, and the oxygen is not added in time. This causes the drying to be slow, and the middle of the printed sheets is particularly slow. In addition, the exposure of the printed sheets also has an effect on the drying speed of the ink.

Source: 21st Century Fine Chemicals Network