On the performance and application requirements of

2022-08-02
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On the performance and application requirements of offset printing fountain solution (Part 2)

(V) anti microbial effect of fountain solution. Some spores in the fountain solution come from the air (indoor air contains 2000 to 3000 spores per cubic meter), but they will be infected through tap water (drinking water allows a certain spore content to reach 100). Due to the weak acid pH value, the addition of buffer salt and Arabic gum for plate protection, and constant temperature conditions, all these provide an ideal living environment for yeast, algae and bacteria. If these organisms divide every 20 to 30 minutes, it is not difficult to understand that these organisms will spread to the whole water conveyance system after free reproduction in a very short time. In this case, it may even cause downtime. The water supply pipe and valve on the water transmission device are very thin and should be kept unobstructed. The corrosion problem of offset press materials has caused the research on this problem. To this end, the German Printing Association has formulated a memorandum entitled "suggestions on corrosion protection of offset printing machines"

in practice and theoretical research, it is shown that the fountain solution can be input into the printing machine by adding anti-corrosion bioactive substances to the bucket potion. According to the test, the fountain solution added with this preservative has little corrosion to the plate metal. Here, it should also be pointed out that the substances that can promote corrosion are not only tap water and fountain solution, but also the whole offset printing process, including the mechanical manufacturing materials used, should be taken into account when considering this issue

(VI) protective effect and requirements of fountain solution on printing plate

as we all know, printing plate is not a smooth plate, but composed of multi-layer structure. The aluminum plate base does not work for the actual printing process. For the printing state of a printing plate surface, the hydrophilic oxide layer and the ink friendly organic polymer layer are important

the hydrophilic layer of the printing plate is full of cracks (sand mesh), which expands its surface and is easy to be eroded. Both the rubbers after the development of the printing plate and the bucket potions must be able to close the pores and grooves to prevent the intrusion of substances that can react with aluminum

when printing is interrupted, the printing plate cannot be wetted continuously. If the function of the bucket potion to protect the printing plate is not enough, the printing plate will be corroded, which is commonly mistaken for printing plate oxidation. In this case, some substances intrude into the aluminum plate base through capillary tube, where aluminum salt type corrosion products are formed

because the unit volume of salt is larger than that of alumina in the hydrophilic layer, it "blooms" regularly. The "mushroom" produced in this way is not friendly to water and keeps growing from small to large or from large to small, but is ink friendly, so there are many so-called oxidized dirty spots (i.e. corrosion spots) on the printing plate

(VII) wetting function of the fountain solution on the printing plate

the fountain solution must wet the printing plate well, so as to quickly achieve the water ink balance at the beginning of printing and keep the printing plate in a good free state during continuous printing. In this respect, surface tension and interfacial tension are used as measurable values

in order to explain the concepts of these two tensions, we observe the internal conditions of the liquid (see Figure 3). These individual water molecules exert forces on each other. The so-called cohesion to enhance the core competitiveness of enterprises offsets each other when observing the molecules inside the liquid. However, a water molecule on the surface is attracted to one side by a neighboring molecule, which means that the molecule has an inward force. Therefore, this molecule has more energy than those inside the liquid. Any liquid has the characteristic of reducing its surface energy, that is, each liquid tries to occupy a minimum surface space in a large volume. The geometry that meets this requirement is a sphere (see Figure 4 for mercury, water, and alcohol). The surface tension of ordinary tap water is about 72mn/m (millinewton per meter). The fountain solution with this surface tension can not well wet the printing plate surface. As the Chinese plastic machinery enterprises have expanded the development of emerging markets for extruders in recent years, it is necessary to add a substance (wetting agent and alcohol substitute) that can destroy the cohesion to the bucket potion. In this way, the printing plate surface can be better wetted

if we observe two small water droplets on a flat plate, one of which has a large surface tension and the other has a small surface tension, we can clearly see that the volume of droplets required to wet an area of the same size with a liquid with a small surface tension is small

this indicates good wetting. It can be seen that only a small amount of water supply is required in the printing process by using the water bucket potion to reduce the surface tension. Therefore, the following problems can be avoided; Too much moisture absorption of paper causes stretch, too much moisture absorption of ink causes emulsification, and too much moisture in ink delays ink penetration and drying. In addition to the wetting agents mentioned above, isopropanol also has the property of reducing surface tension. Therefore, in offset printing, isopropanol can be added to the bucket solution to reduce the surface tension

in addition, in order to avoid the printing failure of ink roller deinking, the bucket solution should prevent the formation of insoluble calcium salt, because calcium salt is the root cause of ink roller deinking failure

although fountain solution often plays an unwelcome role in offset printing, so the treatment of waste plastic particles will become a hot topic in the future, its positive role can not be ignored. Water has an indispensable cleaning and transmission function, and also plays a certain role in cooling

from the current point of view, water is indispensable to traditional offset printing and cannot survive without it. The technology of water bucket potion has been widely used. However, we certainly have not reached the peak of its development. The development space of horizontal full water technology is still large, which deserves our attention

information source: Journal Author: Yuyong

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