Influence of pH value of the hottest printing mate

2022-09-19
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Influence of pH value of printing materials on the printing process to avoid causing major accidents

in offset printing, the pH value of paper and fountain solution will directly affect the water ink balance, ink drying performance and ink layer quality in the printing process. Therefore, when controlling and adjusting the balance of ink and water, we should understand the acidity and alkalinity of paper and fountain solution and their impact on the printing process

1. PH value of paper

as the market has higher and higher requirements for printing quality, coupled with the progress of printing technology, the influence of paper characteristics and printing suitability on printing quality has begun to receive attention, and the pH value of paper is a factor that should be mainly controlled

if the pH value of printing paper is neutral, the printing quality can be greatly improved. However, due to the influence of raw materials, processing technology and other factors in paper production, there is no absolute neutral paper with pH =7. The surface of printing paper or coating layer often has a certain acidity or alkalinity. When pH is 7, the surface of paper is alkaline. At present, alkaline pulping is mainly used in papermaking in China, and NaOH is used as cooking agent, so most papers are slightly alkaline. If the alkalinity is too large, the acidity of the fountain solution will change significantly, and the acidity of the hydrophilic adhesive layer of the non graphic part of the printing plate will be weakened. If it cannot be adjusted in time, it will inevitably lead to the decline of the hydrophilicity of the non graphic part, the imbalance of water and ink, the decline of ink coloring power, the dim color of the printed text, and even the phenomena of stencil, paste and ink roller deinking. At the same time, those weak alkaline fibers that fall off the paper coating will be transferred to the blanket, and then transferred to the printing plate through the blanket, resulting in dirty printing plates and reduced printing resistance

when the pH value of the paper is too low, the acidity of the fountain solution will be significantly enhanced, thereby inhibiting the oxidation polymerization reaction and drying speed of the ink, resulting in poor drying of the printed matter

2. PH value of fountain solution

traditional offset printing materials rely on the principle of oil-water repulsion to realize ink image transfer. Fountain solution is essential, and its acidity and alkalinity has a significant impact on the balance of printing plate and ink. The aluminum oxide film formed during offset plate base treatment is amphoteric oxide. If the fountain solution is too acidic, it will increase the corrosion of plate sand, destroy the blank part of the plate, and cause dirt on the plate; And the alkalinity is too strong, which can not protect the blank part, and will corrode the ink and paper. Therefore, offset printing fountain solution is generally weak acidic, and the ideal pH value is between 5 and 6, which can ensure that the printing point is clear, and the hydrophilicity of the non graphic part of the printing plate is stable, which helps to prolong the service life of the printing plate, and can also inhibit the fountain solution from being invaded by bacteria and other impurities, so as to better maintain the balance of water and ink

the components of fountain solution are mainly buffers, preservatives, plate protectants, desiccants, algae inhibitors, etc., among which buffers have the greatest impact on the pH value of fountain solution. The function of buffer is to stabilize the acidity of fountain solution, because tap water accelerates the natural anaerobic process of garbage dump nbsp; Aripack introduced new plastic additives, which are usually neutral. In order to reach the pH value (5~6) required for normal printing, it is necessary to add acid to the fountain solution to keep the pH value of the fountain solution weakly acidic, and the carbonate in the water will react with the added acid to increase the pH value. At this time, it is necessary to add buffer to keep the pH value of the fountain solution at a stable level. At the same time, buffer also has a significant effect on relieving the influence of cleaning agents and other factors on fountain solution. However, with the change of the amount of buffer added, the pH value of the fountain solution will fluctuate greatly. Improper addition will also affect the service life of the printing machine and hinder the drying of the ink, especially the ink containing metal pigments

water also has a great influence on the pH value of fountain solution. Tap water quality can be divided into soft and hard water. Water with high content of metal cations is hard water, and water with high content of anions is soft water. High hardness of water will improve the pH value of fountain solution. When preparing fountain solution, the softness and hardness of water should be adjusted according to the actual needs, and 10 DH is appropriate. It should also be noted that the change of water temperature will affect the concentration of ions in the water. Therefore, controlling the hardness and temperature of water can make the fountain solution achieve the best effect

in order to ensure that the pH value of the fountain solution is relatively stable, the advanced method is to monitor the conductivity of the fountain solution while controlling the amount of buffer and the hardness of water

because with the increase of the concentration of fountain solution, the hardness of water and the rise of water temperature, the conductivity of fountain solution will increase and the pH value will decrease; On the contrary, if alcohol is added to the fountain solution, the conductivity of the fountain solution decreases and the pH value increases. The conductivity of the fountain solution should generally be controlled at (1400 200) s/cm. However, due to the influence of dust, ink, CRO milltm method and other mixtures that are easy to inspect cracks, the conductivity within 800 s/cm~2000 s/cm is also allowed, but when the fountain solution looks obviously polluted, it must be reconstituted

to sum up, we can adopt more accurate methods before printing production, such as measuring the pH value of the paper surface with a surface acidity meter, measuring the pH value and conductivity of the fountain solution with a liquid pH meter and conductivity meter, and controlling them within a reasonable range, so as to effectively avoid the occurrence of pH related problems in the printing process, improve the quality of printed matter, and reduce printing consumables. This is very important for the printing factory

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