In offset printing, the plate water roller wets the water on the plate first, the blank part of the plate is hydrophilic and absorbs a certain amount of water, and the graphic part is oleophilic but does not absorb water; At this time, the graphic part will absorb a certain amount of ink. Then through imprinting, moisture and ink are transferred to the paper through the plate cylinder and rubber cylinder. The difficulty of this process is the balance of water and ink, and fountain solution is the key.

Composition and function of fountain solution

The choice of fountain solution should be very cautious, to check whether it has the following ingredients: buffer, printing plate protection agent, wetting agent, preservative, desiccant. Biocides and anti-foaming agents. The buffering agent mainly plays a role in stabilizing the pH value of the fountain solution. Because the stock solution of the fountain solution is generally acidic, with slowness; the pH of the fountain solution will fluctuate greatly due to the change in the amount of the intermediate agent added, and the addition amount is not suitable Will affect the service life of the printing plate (corrosion to the printing plate). In addition, the ink will be difficult to dry, especially the ink containing metal pigments.

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

In the printing process, the less dampening solution is used, the better the wetting agent is. The wetting agent is very important. The wetting agent can reduce the surface tension of the fountain solution, so that the moisture is evenly distributed on the printing plate, and a good dampening effect can be achieved with less fountain solution. Generally, the amount of alcohol added in the traditional fountain solution is more than 15%, while the modern new fountain solution contains a wetting agent, which can greatly reduce the amount of alcohol.
Preservatives can protect metal parts, because the fountain solution is weakly acidic and corrosive to the metal parts of the printing press; desiccants can promote the drying of the ink; biocides can prevent the growth of algae and microorganisms in the water circulation system, Avoid blockage of pipelines; anti-foaming agent can prevent the formation of foam, because a large amount of foam in the water tank is not conducive to wetting the printing plate.

Modern new fountain solution should contain the above-mentioned components. In addition, the user should also choose the water quality and other conditions of the printing factory to test the hardness, conductivity and pH of the water used in the factory. The fountain solution manufacturer should also provide suitable fountain solution and related parameters according to the user's water quality conditions. These control parameters mainly include the amount of the fountain solution added, the amount of isopropyl alcohol (alcohol), the pH value of the fountain solution and Conductivity, etc.

Use of fountain solution

The amount of fountain solution stock is generally controlled at 2% to 3%, but if the necessary measuring tools are missing, or the automatic extraction equipment fails, the operator often can only add based on experience, which triggers the Many problems in the control of the amount of plate fluid.

If the addition amount of fountain solution is too small, it will be easy to get dirty during printing, and it will take a long time to adjust the machine; it is not easy to achieve water-ink balance, it is difficult to obtain a satisfactory ink color effect, and increase the risk of machine corrosion. If the amount of fountain solution is too large, the ink is easily over-emulsified and the ink color is not easy to control; the phenomenon of flicking and flying ink will pollute the water bucket and the water roller; the ink roller does not apply ink, and the ink is easy to accumulate on the blanket.

In order to solve these problems, when adding fountain solution manually, a standard measuring tool should be equipped to ensure quantitative addition; if there is an automatic addition 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%. The general operator will think that the larger the amount of alcohol added, the less likely to be dirty, so the amount of alcohol is always too large. In fact, when the amount of alcohol is too high, it will make the surface of the paper more soluble, and the printed products are prone to paper dust; the ink is easy to over emulsify, which affects the quality of the print.

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

In short, controlling the fountain solution in the printing process will often have twice the result with half the effort.

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