Analysis of the most popular lithographic offset p

2022-08-09
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Analysis of the medium fountain solution for offset lithography printing (Part 1)

as the saying goes, "if you master water, you will master offset printing". Offset printing is based on the basic principle that oil and water are immiscible. The printing image and text part is lipophilic and water repellent, and the blank part is hydrophilic and ink repellent. In the process of offset printing, too much moisture in the layout will cause empty printing points, ink roller deinking, matte color, fuzzy layers, poor texture, slow drying speed of imprinting, etc. If the moisture content of the page is too small, there will be some unclear, paste, dirty and other phenomena. Therefore, the key problem of offset printing technology is how to ensure that sufficient and uniform water is given to minimize the water supply under the premise of achieving the best printing quality, so as to achieve the balance of water and ink. This paper discusses the fountain solution in offset lithography

analysis of lithography fountain solution

the main feature of offset printing is that the printing can be completed only with the participation of fountain solution, which is not available in any other printing method. Because of this, the whole printing process of offset printing is related to fountain solution. The printing quality of plastic bags must be uniform in two aspects: on the one hand, the interaction between fountain solution and ink, paper, printing and other related parts, which is expressed through the printing process; On the other hand, it is the wetting effect of the nature of the fountain solution on the relevant parts above. This wetting effect is mainly manifested in the printing process based on the nature of the fountain solution itself. These two aspects are both related and different. Therefore, one of the keys of offset printing technology is to master the nature of fountain solution, the role of fountain solution and related parts, and the correct use in actual operation. This largely determines the quality of offset printing products

I. function and property of fountain solution

offset printing cannot be separated from water, and this "water" plays a decisive role in offset printing production. But why is this kind of phenomenon called deformation strengthening or work hardening? Do not use pure tap water as the fountain solution for offset printing. Although tap water can also wet the printing plate layout and adsorb on the non image blank part. However, the wettability of tap water can not meet the requirements of printing production, and the adsorption is poor and not lasting. Therefore, there must be an offset fountain solution suitable for the requirements of printing production. This fountain solution must have strong wettability and lasting adsorption performance, and can meet the requirements of printing process. Therefore, there are not only tap water, but also some other substances in offset printing fountain solution

1 ﹐ type of fountain solution: add certain chemical components to the water, that is, configure the original solution with high concentration. When using, dilute the original solution with water, that is, prepare the fountain solution. According to the chemical composition of fountain solution, it can be divided into ordinary fountain solution, alcohol fountain solution and surfactant fountain solution

① common fountain solution the main chemical components of common fountain solution are: water (CH2O), phosphoric acid (H3PO4), ammonium nitrate (NH4NO3) and ammonium dihydrogen phosphate cnh4h2po4). This kind of fountain solution has high surface tension and poor spreading performance. In order to resist the infiltration of ink, a thick water film must be formed in the blank part of the printing plate. Generally used in monochrome and two-color offset press

② alcohol fountain solution alcohol fountain solution is prepared by adding 10~25% isopropanol or ethanol to ordinary fountain solution. The surface tension of this fountain solution is low, and less liquid supply can form a water film that resists ink infiltration in the blank part of the printing plate. It is suitable for multicolor offset printing machines with cooling and water supply devices

③ surfactant fountain solution surfactant fountain solution is prepared by adding surfactant to ordinary fountain solution. Surfactant fountain solution has the advantages of low surface tension and good spreading performance of alcohol fountain solution, and has the characteristics of non-toxic, non-volatile and non explosion. It is an ideal fountain solution for multi-color printing machines

2. Wetting principle of fountain solution:

① first look at the situation shown in Figure a. Figure a wetting and contact angle diagram shows the wetting state of water droplets on different material surfaces. Figure (a) the water drop is round, indicating that the interaction between the water drop and the solid surface is very small, or the wettability is poor. Make all lines of, and its included angle θ It means that the contact angle between the water drop and the solid surface is greater than 90 °; Figure (b) the water drop is semicircular, indicating that the interaction between the water drop and the solid surface is large and the wettability is good. Similarly, it is made as all lines of, and the contact angle is obvious θ Is less than 90 °. contact angle θ It's better to be big or small, of course, it's better to be small. The contact angle novel shows that its wettability is good. The spreading covers a large solid surface area, and the coverage area is also uniform. Relatively speaking, the less water is used on the same surface area. Such a property is exactly what our offset printing technology needs

② as shown in Figure B, the change of surface tension after adding alcohol to pure water. Figure B tension change of pure water and alcohol (a) shows pure 2. The iron filings in the jaw and chuck are regularly cleaned with water droplets due to the effect of surface tension, with an included angle of 120 °. Figure (b) shows that when 20% alcohol is added, its surface tension decreases, and the same water droplet area expands, with an included angle of 50 °. Figure (c) shows that when 25% alcohol is added, its surface tension is smaller, and the wetted area of the same water droplets extends to pure water. What are the problems that should be paid attention to when installing the tensile testing machine? Twice the wet area, with an included angle of 10 °

3. Performance of fountain solution:

generally speaking, fountain solution should have the following main properties from the perspective of factors related to printing technology and printing:

① it should have sufficient wettability and be able to form a thin and uniform water film on the blank part of the printing plate surface that is not graphic

② it should have water absorption to protect the non image blank part of the printing plate and repair the hydrophilic layer worn during the printing process

③ it should have the function of cleaning the non image blank part of the printing plate

④ stable and adjustable acidity should be maintained in the production process

⑤ the influence on the ink performance and the emulsification degree with the ink in the production process should meet the requirements of printing technology. ⑥ It has no impact on the appearance quality of products and no damage to production operators

4. Function of fountain solution:

the composition of fountain solution, no matter which form or method, is determined by the function of fountain solution in printing production. From the perspective of printing production process, its main functions should be:

① it should have the function of hydrophilic and oil repellent (ink)

② it should have the function of protecting the water absorbing layer of the non image blank part of the printing plate

③ it should have good wetting effect

④ it should have certain adjustment effect on some performance

⑤ it should have a certain anti-corrosion effect

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