The application of fountain solution in newspaper printing
As the basis of survival of the newspaper industry, advertising, along with the increasingly fierce market competition and the advent of the era of multi-page and colorization, has also put forward more stringent requirements for printing quality. Newspaper printing mostly adopts the rotary offset printing method, and the water-ink balance not only directly affects the printing quality, but also has a close relationship with the production cost. Therefore, how to control and use the fountain solution to ensure the quality of newspaper ink has become a top priority
(A) the special characteristics of newspaper printing fountain solution
Newspaper printing has a fast printing speed, the water absorption of newsprint is very strong and other characteristics. Operators often have the requirements of the water-ink balance is not strict, understanding is not profound and other problems, generally as long as the page is not dirty, the ink is not a serious emulsification phenomenon to get by, the overall printing quality is not too high requirements. Newspaper printing plants often have thicker dots, water and ink, and other operating habits, it is easy to cause the entire layout of the ink expansion serious, slow drying, thus affecting the quality of printing.
Single-round printing in terms of generality, newspaper printing fountain solution and general offset printing fountain solution is not very different, even in terms of printing quality, newspaper printing fountain solution control requirements than high-grade commercial printing is also appropriately lenient some. However, the production characteristics of newspaper printing are more prominent, and the requirements for fountain solution also have their own characteristics. As the quality of newspaper printing requirements become higher and higher, it is increasingly important to pay attention to the special characteristics of newspaper printing. Newspaper printing fountain solution is different from the characteristics of commercial printing fountain solution, the main differences are.
Newspaper printing with newsprint is a typical non-coating paper, its performance is not the same as offset paper and coated paper, the most prominent problem in the printing process is that the paper is serious hair loss, the printing presses have a negative impact on the fountain system. At the same time, the strong water absorption of newsprint, the fountain solution is absorbed by the paper produced by the pumping up of the overprint accuracy.
Newspaper printing equipment has almost all wheel conversion, with the characteristics of fast printing speed, which makes whether in the process of ink transfer or drying, must take into account the "high-speed" factor, along with the printing speed in recent years to further improve the problem more prominent; secondly, newspaper printing is typical of wet press wet printing, and will The word "wet" is expressed to the fullest.
(B) General newspaper printing fountain solution
Newspaper printing is an offset printing process, so the general theory of offset fountain solution is fully applicable to newspaper printing.
The role of fountain solution in newspaper printing is multifaceted.
① fountain solution can be in the blank part of the printing plate to form a water film that repels ink, blocking the expansion of ink to the blank part to prevent dirty plates.
② electrolytes in the fountain solution can be used in the printing process to replenish the hydrophilic layer of the printing plate damaged by wear and tear, and maintain the hydrophilic properties of the blank part of the printing plate.
③Fountain solution can reduce the surface temperature of the printing plate, maintain the necessary viscosity of the ink, to stop the newspaper printing process dot increase.
④ If the water film is too thin, it will not be able to achieve the need to stop the ink in the blank part of the adhesion; if the water film is too thick, it will lead to serious emulsification of the ink film.
The water used in newspaper printing is not pure water, but a dilute solution containing surfactants, a variety of electrolytes and hydrocolloids. Previously, printers prepared their own fountain solution, mainly by adding gum arabic, glycerin, phosphoric acid and other substances to tap water to form a dilute solution to meet printing needs.
Newspaper printing fountain solution in the surfactant (such as alcohol, isopropyl alcohol or substitutes) is to reduce the surface tension of the fountain solution, the general surface tension of tap water is about 7.2 × 10-2N / m, the surface tension of offset ink is about (3.0 ~ 3.6) × 10-2N / m, must control the surface tension of the fountain solution, so that it is close to the surface tension of the ink, so that the two reach a balance. to reduce the degree of ink emulsification. At the same time, the fountain solution also needs to add acidic electrolytes, buffers, hydrocolloids, preservatives, fungicides, defoamers, etc. to meet the needs of newspaper printing. The pH range of offset printing fountain solution is generally controlled at 4.8 to 5.5, when the dot is the clearest. If it is lower than 4.8, it is easy to fall off the plate, and higher than 5.5, it is easy to paste the plate. Adding pH buffer can effectively control the change of pH value during newspaper printing.
Each added component in newspaper printing fountain solution can have a negative impact on printing. For example, the addition of surfactants will reduce the surface tension of water, although to improve the wetting effect of the layout, but also will intensify the ink emulsion. Therefore, the additives added to the fountain solution, need to be controlled within the appropriate range. Newspaper printing wetting can achieve better results, mainly with the printing ink, paper, printing press water supply, water quality and other factors. Different types and colors of ink, its chemical composition, viscosity, fluidity and water absorption are not the same, not easy to emulsify the ink, the need to add a higher concentration of fountain solution. Ink that is easy to emulsify does not require the use of high concentration of fountain solution.