Study on Application of High-speed Rotary Offset Fountain Solution (Part One)

[Abstract] This paper expounds the composition of the high-speed web offset fountain solution, maintains the relative stability of the fountain solution and the ink, and achieves the ink balance required by the printing, and proposes that in the high-speed web transfer printing, a good reproduction of the graphic and text information is proposed. The correct application of the fountain solution and related control elements have practical application value.

Keywords: fountain solution; high speed printing; control method; printing quality

With the rapid development of packaging and printing technology and the acceleration and improvement of informationization, the modern EI]~U direction is developing in the direction of high-speed, multi-color, lightweight paper, and intelligent computer control. The print speed of today's commercial web offset presses has grown from the previous 300 print sheets/min to the current 1000 print sheets/min or more, resulting in high-quality, high-capacity production at high-speed printing and low-cost operation. The expectations and requirements of printing companies for improving printing quality and production efficiency. However, in the field of creating high-speed printing production, how to maintain stable operation and printing quality, ensure that the transfer of graphic and text information in high-speed printing can be reproduced with good graphic reproduction, application and control of fountain solution in printing, It is one of the key factors influencing the ink-water balance, printing quality and efficiency in the printing process.

I Effect and composition of high speed web offset fountain solution

I. I Effect of fountain solution

One of the characteristics of offset printing is the use of the principle of repulsion of oil and water, selective adsorption of ink and fountain solution on the printing plate, the formation of graphic parts and blank parts to achieve graphic reproduction. In the high-speed rotation EI] ~ U process, according to the printing speed 40,000-80000 print / h to calculate, the printing cycle is 0.08 ~ 0.045s, the imprinting transfer time is 0.0008054-0.0004530s. In such a short EI]~U, to obtain graphic inks with clear graphics, rich gradations, and vivid colors, the fountain solution is well-wet in the blank area, preventing the ink from adhering and spreading in the non-inked areas. It is particularly important. For this reason, as a fountain solution for high-speed web offset printing, it should have the following effects:

I) Rapidly spreading and forming a uniform layer of water on the non-graphic surface of the plate to prevent the ink on the surface of the graphic from penetrating the non-graphic surface, ensuring the clarity and stability of the graphic.

2) The acid and hydrophilic colloids in the fountain solution can react chemically and physically with the non-image site base metal exposed due to abrasion, forming a new hydrophilic layer to maintain the non-graphical portion of the plate. Stable hydrophilicity.

3) Control and reduce the temperature of the plate surface. Under high-speed printing conditions, the friction between the printing plate and the blanket cylinder causes high temperatures, which changes the viscosity and fluidity of the printing ink and affects the printing quality. The fountain solution is volatile and removes heat during evaporation to effectively control and reduce the plate surface temperature.

4) Under the effect of printing pressure and high-speed operation, maintain the relative stability of the fountain solution and the ink, and make the emulsification of the ink to a minimum, so as to accelerate the ink-water balance required for high-speed printing.

5) The dampening solution cannot use any chemical reaction with the graphics part of the surface of the printing plate, but has the cleaning function for the ink adhered to the non-graphic part of the plate.

1.2 The composition of fountain solution

High-speed web offset press (M-6OO type) The commonly used fountain solution is isopropyl alcohol fountain solution, also known as the industry's popular alcohol fountain solution. The isopropyl alcohol fountain solution is used because isopropanol is a kind of surfactant that has polarity and can bind with water molecules, which can significantly reduce the surface tension of the fountain solution and increase the non-textured surface of the fountain solution. The affinity isopropyl alcohol fountain solution consists of water, isopropyl alcohol and hydrophilic colloids, phosphoric acid and buffers.

1.2.1 Water

Water is the main component of the fountain solution and is the carrier of various chemicals in the fountain solution. Due to the difference in water quality, the content and composition of impurities in the water are different, and it will affect the acidity and alkalinity of the water, the surface tension of the water, and the printability and printing quality of the fountain solution. For this reason, understanding and mastering the relevant knowledge of water quality is crucial for the configuration of excellent fountain solution.

The difference in water quality is mainly determined by the amount of magnesium and calcium ions contained in the water. Usually 1L water containing lOmg calcium oxide is called 1 degree, the water of calcium oxide is less than 80mg (less than 8 degrees of water) is called soft water, higher than 8 degrees of water is called hard water. The higher the calcium oxide content per unit volume of water, the greater the hardness of the water. In the printing practice, it was found that the hardness of the water is large, and insoluble, greasy calcium soap is generated in the fountain solution, resulting in the occurrence of deposits on the surface of the printing plate, the transfer blanket, the impression cylinder, and the water roller, which affects the high speed Transfer and spreading of printing ink and fountain solution. Serious stain failure. Therefore, the ideal configuration of the dampening solution for high-speed web offset presses should have a hardness in the range of 5 to 10 degrees. If it does not meet this requirement, it can be achieved through water softening treatment. Water softening methods include:

Ion exchange method. Use sodium ions to replace magnesium and calcium ions in hard water; chemical removal. Use bicarbonate to remove magnesium, calcium, etc. in hard water.
(to be continued)