Offset water consumption and conditions for determining water consumption

Offset printing and letterpress, gravure and other printing methods differ in that offset printing is a kind of water printing. Utilizing the natural law of oil and water immiscibility, the water is supplied first and then the ink is supplied. Because of the selective adsorption of different parts of the printing plate and the blank part, the ink and water are formed in the graphic part and the ink is not in the blank part. At the time of printing, the ink on the plate at the plate is first transferred to the surface of the elastic rubber roller, and then the platen is transferred to the paper on the surface of the platen roller.

The water used for offset printing is not ordinary clean water, but it is added to various electrolytes. Commonly used hopper solution must be prepared to meet the requirements of the PS version: 1 To fully wet the layout, it is necessary to reduce the surface tension, to add emulsifier, wetting agent, surfactant in the fountain solution. 2 has the ability to clean, can wash away dirty spots. Various types of acid substances have the ability to clean. Such as phosphoric acid. 3 has a good fat-free ability, not fat is not lipophilic performance. Such as adding gum arabic. 4 can adapt to different climate changes, to add moisture absorbent. 5 can stabilize the pH of the water bucket solvent and put it into acid.

The water consumption of the offset printing fountain solution has the following aspects:
1. Ink emulsification consumes water. The fountain solution is a polar molecule and the ink is a nonpolar molecule. When two mutually incompatible liquids, under the influence of a certain factor, become an emulsion, it is called an emulsification phenomenon. The role of certain factors refers to the role of emulsifiers, such as: soap, detergent, it has lipophilicity and hydrophilicity, so as to wash off the oil of clothes. Why does emulsification occur during the printing process? 1 The hopper solution contains many lipophilic substances and emulsifiers. 2 The ink is not completely non-polar. The additives in the ink are polar and some are emulsifiers. 3 There are many other factors. In short, the emulsification of the ink in the printing process is unavoidable, mainly because the amount of emulsification must be effectively controlled.

2. Paper absorbs water consumption. The commonly used papers for printing include coated paper, card stock, offset paper, letterpress paper, and the like. Because the various fiber properties and smoothness, evenness, sizing, moisture content, stretch rate, surface spinning and other indicators are not the same, so the paper when printing the water absorption is different. For example, the absorption of coated paper consumes less water and the flatness of letterpress paper is poor, absorbing more water.

3. Evaporate into space to consume water. The evaporation of water mainly depends on the following points: 1 The chemical composition of the water bucket solution, there is no volatile compound. For example, the volatile matter of alcohol is strong; 2 the temperature of the water bucket solution, the higher the temperature, the faster the evaporation. 3 The surface area of ​​the water container and offset printing plate exposed to the air is large and the evaporation is rapid.

4. Squeeze throws water. Offset printing speed is generally more than 6000 printing/hours, sometimes more than 10000 printing/hours. The printing drum and blanket cylinder are pressed at high speed and rotate at a high speed. The water on the printing plate is large, it is inevitable to run to throw water to form gas. The fog also consumes a certain amount of water.
Offset determines the conditions of water consumption. The area and distribution of the layout text. If there is a large area in the graphic section of the printing plate, it is necessary to increase the water consumption.

2. Printed ink layer thickness. When printing, the ink layer is thick, the water consumption is large, the ink layer is thin, and the water consumption is small; when using a single-color offset press for multi-color overprinting, the first color of the yellow printing ink layer is thick, the water needs to be larger, and the latter is printed. The magenta and cyan imprinted inks are thin and the water consumption is smaller.

3. The nature of printing paper. If the fiber structure of the paper is loose and the surface is rough, the water absorption performance of the paper is strong; the structure of the coated paper, card paper, etc. is dense, the surface is smooth, and the water absorption is small. The amount of water used is also related to the dry humidity of the paper.

4. The ink has good water resistance, low emulsification value and less water consumption.

5. The speed of offset, the ambient temperature and humidity, and the surrounding air circulation can also affect the amount of water used. The higher the speed of the offset press, the greater the amount of water consumed, the higher the ambient temperature, the lower the humidity, and the better the air circulation, the more water will be consumed.

6. The type of printing plate: In the past, an intaglio printing plate was used with a 0.4 mm thick zinc plate. The plate making process was more complicated. The flat and concave plate had a graphic part of the lak, the blank part was an inorganic salt layer, and the fountain solution was to be supplemented. Inorganic salt layer, flat intaglio water consumption is large; now with the PS version of water consumption is small. Since the PS template part is a diazo compound, the blank part is an anodized film.

7. The fineness of the plates on the plates and the oldness of the plates are relevant. The original version of the PS version uses less water, and the recycled PS version uses more water. The printing plates have a large quantity of fine water for the trachoma, and a rough amount of water for the trach eyes.

8. Offset printing pressure is large, the consumption rate of the water bucket solution is high, and the hardness of the blanket and the consumption of the water bucket solution are also in direct proportion.

What is the amount of water bucket solution to use? There is no standard at present. But there is a clear point of view, according to the results of a comprehensive consideration of various factors, the amount of water bucket solution is still less good. Although offset printing is a water-based printing method, the printing plate can be selected to use a small amount of water under the premise of not contaminating the plate, which can reduce the emulsification of the ink, the expansion and contraction of the paper, the diluting of the print, and avoiding the disadvantages of overprinting.