Composition and Cleaning Principles of Ink Cleaners (1)

Printing aids refer to printing equipment that has a small amount of printing, but has a great influence on printing quality and stability, such as printing rollers, blankets, fountain solutions, and ink cleaners. This article will focus on the printability and use of ink cleaners.

General printer manufacturers will strictly test the chemicals used on their machines, and they also have strict regulations for ink cleaners. For example: Heidelberg presses have been rigorously tested and there are three types of car wash water that can be used on the Heidelberg presses: Bottcherin 60, Superdot and Varn. This shows that printer manufacturers pay attention to ink cleaners, and these will be given in detail in the press's engineering manual.

Ordinary offset printing press uses water supply, ink supply device to supply printing plate fountain solution and ink. Although the ink and the fountain solution are not mutually dissolved, when the offset printing machine presses and prints, the water and the ink are sheared at a high speed in the roll gap and are forcibly mixed and emulsified. Therefore, the ink supplied by the offset printing system to the printing plate is an emulsified ink containing a certain amount of fountain solution.

Offset inks are organic substances according to their molecular structure, which can be dissolved by organic solvents. The pigments in inks are neither soluble in water nor soluble in organic solvents and have only a certain affinity for water. The fountain solution is composed of water, inorganic compounds and gum arabic, and its hydrophilicity is very good. It can be seen that, in the composition of the ink cleaning agent, it is necessary to contain both organic solvents and components that have good affinity with inorganic compounds and pigments, so that the process of cleaning the ink can be performed according to the chemical principle of “structural similarity and compatibility”. The use of the principle of emulsification, the formation of "oil-in-water, water-in-oil" emulsion, in order to achieve the purpose of cleaning the ink roller, blanket and printing plate ink.

Gasoline was first used to clean the ink on the offset press. However, gasoline and kerosene can only dissolve the organic substances in the ink, but do not dissolve the inorganic compound components of the fountain solution in the emulsion ink, and have poor affinity for the pigment of the ink and the paper fluff and paper powder attached to the ink roller. Over time, the surface of the rubber roller will be glazed and the surface will be seriously damaged. The ink roller will lose its ink transmission and the size will change, which will seriously affect the printing pressure, resulting in printing failures such as “dark bars” and “flat screen hair”. In addition, the environmental pollution is serious, the harm to the human body is great, and it is also a hidden danger of fire. Therefore, this kind of cleaner has already been on the verge of being eliminated.

At present, many domestic printing companies only consider the absolute cost in front of them and still use gasoline or kerosene to clean the ink. This process has already had a significant impact on the social benefits and production efficiency of the printing industry and must be changed. In addition, in terms of roller maintenance, many manufacturers are currently doing marketing work in this area. Now many printing companies, especially in the coastal areas, have paid more and more attention to the important role of maintenance on printing efficiency, so the quality ink cleaner has a broad Expansion capacity.

(A) The principle of cleaning ink cleaner

As people's requirements for printing quality are increasing, ink cleaners, which are easily overlooked printing aids, have a greater impact on printing. Many of the quality problems that occur in printing are often caused directly or indirectly by ink cleaners. Such as the rubber roller with water or with low ink performance, the deformation of the rubber roller, the lack of density in the field, flat net flowers, etc., mostly due to the improper use of cleaning agents cause problems with the rubber roller, thus affecting the printing quality, so that the printing downtime increase.

Figure 1 shows the impurity components on the surface of the printing roller, which is the object that the ink cleaner needs to clean.

In the process of cleaning the ink, using the principle of emulsification, use a high-quality ink cleaner and water for cleaning. Cleaners can dissolve oil-soluble substances, water can dissolve water-soluble substances, form "oil-in-water", "oil-in-water" form to complete the cleaning of the surface of the printing roller, can clean most of the oil-soluble and Water-soluble substances. However, every cleaning cannot completely remove the impurities on the surface of the rubber roller, there will always be some impurities left on the surface of the roller, and this also needs to be distinguished according to the nature of the ink, if the spot color ink such as gold and silver is printed, clean Work will be more difficult.

Insoluble substances cannot be removed with general ink cleaners and special cleaning chemicals are required to assist in cleaning. (to be continued)