Difficulties in ink balance: control of modern offset fountain solution

In offset printing, the water roller is wetted by the printing plate water, and the blank part of the printing plate is hydrophilic and absorbs a certain amount of water. The graphic part is oleophilic and does not absorb moisture; the printing plate is inked by the printing roller. At this time, the graphic part will absorb a certain amount of ink. Through embossing, the moisture and the ink pass through the plate cylinder, which is transferred to the paper. The difficulty of this process is the balance of ink and water, and fountain solution is the key.

The composition and function of fountain solution:
The choice of fountain solution should be very careful to check whether it has the following components: buffers, plate protectants, wetting agents, preservatives, desiccants, biocides, and anti-foaming agents.

The buffering agent is mainly used to stabilize the pH value of the fountain solution because the fluid of the fountain solution is generally acidic, and the pH of the fountain solution will fluctuate greatly with the change of the amount of the agent added. Will affect the life of the plate (corrosion to the plate). It also makes it difficult to dry the ink, especially inks containing metallic pigments.

During the printing process, the fountain solution is always in contact with the printing plate, and the non-graphical portion (inorganic salt layer) of the printing plate will be continuously dissolved, thereby reducing the hydrophilicity of the printing plate, resulting in a dirty plate phenomenon. The plate protection agent can continuously replenish the dissolved inorganic salt layer, maintain the dynamic balance, and ensure the plate's stable hydrophilicity. The printing plate protector also contains guard plate glue, and there is no need to wipe the plate in case of temporary stoppage.

In the printing process, the less the better the dampening solution is, the better the dampening agent is. Therefore, the wetting agent is very important. The wetting agent can reduce the surface tension of the fountain solution so that the water is evenly distributed on the printing plate, and a good wetting effect can be achieved with less fountain solution. The amount of alcohol added in the traditional fountain solution is above 15%, while the modern new fountain solution contains a wetting agent, which can greatly reduce the amount of alcohol.

Preservatives protect metal parts because the fountain solution is weakly acidic and corrosive to the metal parts of the press; desiccants promote ink drying; biocides prevent algae and microorganisms from growing in the water circulation system. Avoid blockages in the tubing; anti-foaming agents prevent the formation of foam because the bulk of the foam in the tank is detrimental to the wetting of the printing plate.

The modern new fountain solution should contain the above ingredients. In addition, the user should also select the water quality and other conditions of the printing plant to test the water hardness, conductance, and pH of the factory. The fountain solution manufacturer should also provide applicable fountain solution and related parameters according to the user's water quality conditions. These control parameters mainly include the amount of the fountain solution, the amount of isopropyl alcohol (alcohol) added, the pH of the fountain solution, and Conductivity and so on.

The use of fountain solution The amount of fountain solution is generally controlled at 2% to 3%. However, if the necessary measurement tools are not available, or if the automatic extraction equipment fails, operators can only add it by experience. This has caused many problems in the usage of fountain solution.

If the amount of the fountain solution is too small, the printing plate may be dirty and the machine may take a long time to adjust. It is difficult to achieve ink balance, and it is difficult to obtain a satisfactory ink effect, which increases the risk of machine corrosion. If the amount of fountain solution is too large, the ink is easy to over-emulsify, and the ink is not easy to control; ink throwing and ink flying occur, and the water bucket and the water roller are polluted; the ink roller is not inked and the ink is easily accumulated on the blanket.

In order to solve these problems, a standard measuring tool is required to manually add the fountain solution to ensure the quantitative addition; if there is an automatic adding device, it should be regularly checked and maintained to ensure its normal operation.

When using modern new fountain solution, the amount of alcohol added should be controlled within 10%. Generally, the operator will think that the greater the amount of alcohol added, the more difficult it is to contaminate the plate, so the amount of alcohol is always too large. In actual fact, when the amount of alcohol is too high, the dissolution of the surface of the paper will be intensified, and the printed paper is prone to paper powder. The ink is easily over-emulsified and affects the quality of the printed product.

The two parameters of pH and conductance are usually used to reflect the condition of the fountain solution and monitor it. Tests have shown that when the pH value is within the range of 4.8 to 5.3, the printing is the most stable, the longest printing plate life, the best quality of the printing ink, the ink and ink balance are the most easy to control, and the pH value is not only determined by the addition amount of the fountain solution, but also by the paper. Acid and alkali effects. The conductivity should generally be controlled at (1400 ± 200) μs. The conductance value is easily affected by the hardness of the water, the amount of alcohol, dust and ink mixed in, so the conductivity value is allowed in 800 ~ 2000μs, but when the fountain solution looks obvious If it has been contaminated, it must be reconstituted.

In short, controlling the fountain solution during the printing process will often have a multiplier effect.