Ink balance control during offset printing

Offset printing is a unique printing method that wets the surface of a printing plate with water. It utilizes the principle of immiscibility of oil and water. The offset printing plate graphic part is hydrophilic and hydrophobic, the blank part is hydrophilic and oleophobic, and the offset printing is correctly controlled. The balance between ink and water is the key to improving the quality of printed products, and it is also a measure of the technical level of operators. Under the current conditions, offset printing machines still lack water, but too little or too much water is used to produce and print quality belts. Adverse factors.

First, the layout of the excessive moisture hazards

1 Imprinted ink should be diluted; 2 Ink emulsification serious; 3 Imprinted ink drying speed is slow; 4 Printed products are not shiny; 5 Paper water will be extended and deformed resulting in overprinting; 6 Paper back stained; 7 Easy Caused by the flower version; 8 due to moisture blocking the ink can not be properly transported; 9 machine parts of the roller is prone to rust; 10 paper delivery parts of the paper is not neat.

Second, the harm of water is too small

1 layout from the dirty; 2 paste version; 3 ink is very dark.

Therefore, it is necessary to prevent the use of too little moisture for the sake of mastery, and to keep the printing plate from being dirty. In fact, how much water is used is one of the important signs of technical proficiency. The principle of water volume: on the premise that the plate layout is not dirty or paste, use the minimum amount of water, use a minimum amount of water, oil to print a good product, it should emphasize the use of the least water, and obtain the amount of water and ink Balance.

Third, the layout of the amount of water and the relationship between the amount of ink

The blank part on the surface of the printing plate surface is in the printing process, because there is a certain water film, and the principle of immiscibility between oil and water is not stained by the ink on the ink roller. If the strength of the blank part of the water layer is not sufficient to block the adsorption of the ink on the blank part, then the stain on the plate surface occurs. Conversely, if the printing plate layout water is too large, it will hinder the normal transport of the printing plate ink volume by the ink transfer member. So the place where offset printing is different from other printing methods. In the offset printing process, the darkness of the blotting ink color, in addition to the need to control the amount of ink under the ink and the transmission process, affecting the depth of the ink blot, there is an important factor that is directly related to the size of the offset printing surface moisture.

When the moisture of the plate increases during the offset printing, the blotting ink immediately fades accordingly. Conversely, if the plate layout is reduced in water content, the amount of ink is reduced accordingly so that the ink color remains dark and consistent.

Changing the amount of ink on the ink fountain or increasing or decreasing the moisture can change the color of the blotting ink. Therefore, in the offset printing process, it should be adjusted according to the direct cause of too deep or too light. Of course, it is impossible to simply rely on reducing moisture to deepen the ink, because too little water will make the blank part of the layout dirty; on the contrary, the amount of water on the printing plate is too much, the printed ink color will be subdued, the ink is too light, and mistaken for This is the cause of the lack of ink. Incorrectly adding ink and increasing the amount of ink destroys the balance between water and ink. If the water supply is increased at this time, such a vicious cycle will eventually lead to the pile of excess ink on the ink roller. It is impossible to gather even printing, and this phenomenon of water, ink, and ink is absolutely forbidden in the offset printing process.

Practice has proved that in addition to the amount of ink depends on the amount of ink in the offset, the increase or decrease in the amount of water will also affect the ink. When the amount of ink changes, at the same time pay attention to whether the amount of water is adapted, often correctly discriminate the size of water and ink, the balance of ink and water, the balance between the two is not rigidly fixed in a numerical value, but in a considerable range balance. However, superb technology should be balanced in the lowest range, using the minimum amount of water, which is a difficult point in the offset printing process.

The size of water is the main factor affecting the darkness of ink. The reason why water and oil are immiscible and the imbalance caused by oil and water on the layout are not understood, and the use of less printing plate is less as far as possible under the premise that the printing plate is not stained. Moisture, to achieve the balance of ink and water, and to maintain a relatively stable, you can ensure a consistent color of ink in a batch of printed products, on the contrary, busy busy blindly frequently adjust the water, ink volume, appear for a while to open the ink and water, and later The ink and water are small, and the ink and ink adjustment is disordered. Because the offset printing ink, ink licking, and ink roller are more than 20, the adjustment of the ink volume has a time course from the ink tank groove to the ink roller, and it is impossible to see immediately. To adjust the amount of ink, offset ink machine longer, there is a transfer process, do not suddenly adjust the amount of water and ink, to avoid a vicious circle.

Fourth, the size of offset water and emulsification

Offset printing The use of water to wet the surface of the printing plate determines the necessity of the presence of ink emulsification. Water is a polar molecule and oil is a non-polar molecule. Offset uses the principle of immiscibility between oil and water. However, when two immiscible liquids, under the influence of a certain factor (ie, under the influence of an emulsifier), become an emulsion, this phenomenon is called emulsification.

A mechanical compound formed by a very fine dispersion of a liquid in another liquid that is incompatible with it is called an emulsion.

Emulsifiers are generally amphiphilic molecules, that is, lipophilic and hydrophilic. Under its action, the oil and water become a mixture.

Why emulsification occurs during printing:

1 Water is not pure water, and aqueous solutions contain many lipophilic substances and emulsifiers. Printing plate dampening fluid is composed of various chemical components. 2 Ink binders are not completely non-polar. Some additives are polar, and some are emulsifiers. 3 There are many other factors that influence the condition.

All in all, emulsification is inevitable during the offset printing process, mainly because the amount of emulsification must be controlled within the range of 10% to 30%.

Emulsification hazards:

1 Ink dilute, tinting power is reduced. 2 The color of the blot changes greatly and the sign color error is large. 3 ink cohesion reduced, resulting in floating and other phenomena. 4 The ink roller has the possibility of deinking. 5 Printing products and semi-products slow down. 6 The paper absorbs water.

V. The conditions for determining water consumption

1 The area and distribution of the layout of the layout, the area of ​​the graphic on the printing plate is large, and the amount of water should be increased. 2 The thickness of the imprinted ink layer, the thickness of the ink layer is large, and the amount of water is large; otherwise, it is small. 3 The nature of the printing paper determines the amount of water used. The surface of the coated paper is smooth and clean, and the amount of water used is large, such as letterpress paper, offset paper, newsprint, and other rough paper. 4 ink water resistance and the size of the impact of the emulsification value. The ink has poor water resistance, and emulsification has a large amount of water. 5 machine speed, ambient temperature, humidity and ambient air circulation. The speed is fast, the water consumption is large, the environment is dry, the summer temperature is high, and the amount of water will be large. 6 type of plate. The original used gravure water consumption is large, and the PS version has a small amount of water. The thickness of the 7-plate baffle and the oldness of the printing plate, the blank part of the printing plate is rough and the water consumption is large. Fine sand eyes, water consumption is small. The new version has a small amount of water. Older versions, such as recycled PS, use more water.

Sixth, the layout of the amount of water identification

When the moisture is too large, it can be analyzed and judged by the following methods: 1 When the water droplets are visible in the ink fountain, the moisture is too large. 2 The ink roller and the transfer roller enter the roll point “accumulate into water droplets”. 3 When shoveling ink with a spatula, the ink under the shovel is analyzed by water. 4 The printed blots are pale, and it is not easy for ink to deepen in time. 5 The ink roller and the printing plate are temporarily detached and the ink color is greatly different. 6 When the paper is dithered, it is weak, and it cannot send a crisp sound. 7 The delivery table is not in order and it is a mess. 8 When the machine was shut down for a long time, the water on the layout still did not evaporate. 9 Erasers, plates, and liners in the cylinder are wetted with moisture.

In addition, the size of the printing plate water can use the reflection of the printing plate to see the amount of water, reflecting a large amount of water, and vice versa. The layout is bright and the volume of water is large; the layout is dark, the volume of water is small, the layout is dark gray, and the amount of water is moderate.