An Analysis of the Fountain Solution in Lithographic Offset Printing (I)

As the saying goes: "If you have mastered the water, you will master the offset printing." Offset printing is based on the basic principle of immiscibility of oil and water. The printing and graphic part is hydrophobic and water-repellent, and the blank part is hydrophilic and ink-repellent. In the offset printing process, the layout of water over the General Assembly caused the printing outlets to be empty, the ink roller deinking, the color is no light, the level of fuzzy, poor texture, slow drying and so on. Moisture in the layout is too small, and dots, stencils, and dirty prints will appear. Therefore, it is a key issue for offset printing technology how to ensure that a sufficient and uniform amount of water is provided, and the amount of water supply is controlled to the minimum under the premise of achieving the best printing quality so as to achieve ink-water balance. This article discusses the analysis of fountain solution in lithographic offset printing.

Analysis of lithographic fountain solution

The main feature of offset printing is that printing must involve the participation of fountain solution to complete the printing. This is not the case with any other printing method. Because of this, the entire printing process of offset printing is related to the fountain solution. This is mainly manifested in two aspects: on the one hand, the interaction between the fountain solution and ink, paper, and related parts of the printing, these interactions are expressed through the printing process; on the other hand, the nature of the fountain solution itself is related to the above Part of the wetting effect, this wetting effect is based on the nature of the fountain solution itself, mainly manifested in the printing process. These two aspects are both related and different. Therefore, one of the keys to the offset printing technology is to grasp the nature of the fountain solution, the effects of the fountain solution and related parts, and the correct use in the actual operation. This largely determines the quality of offset products.

First, the role and nature of fountain solution

Offset printing can not be separated from water, and this "water" has a pivotal role in offset printing production. But why not use a simple tap water to make offset fountain solution? Although tap water can also wet the plate layout, it adsorbs on the non-image blanks. However, the wettability of tap water cannot be adapted to the printing production requirements, and the adsorptivity is poor and does not last long. Therefore, there must be an offset fountain solution suitable for printing production requirements. This fountain solution must have strong wettability and long-lasting adsorption performance, and can meet the printing process requirements. Therefore, there are not only tap water, but also some other substances in the offset fountain solution.

1. Kind of fountain solution:
Add certain chemical components to the water, that is, configure the original solution with higher concentration. When using, dilute the original solution with water, that is, prepare a fountain solution. According to the chemical composition of the fountain solution can be divided into ordinary fountain solution, alcohol fountain solution and surfactant fountain solution 3 kinds.

1 Ordinary fountain solution The main chemical components of ordinary fountain solution are: water (CH2O), phosphoric acid (H3PO4), ammonium nitrate (NH4NO3) and ammonium dihydrogen phosphate CNH4H2PO4). Such fountain solution has higher surface tension and poor spreading performance. A thicker water film must be formed on the blank portion of the printing plate to resist ink infiltration. Generally used for monochrome and two-color offset presses.

2 Alcohol fountain solution Alcohol fountain solution is prepared by adding 10~25% isopropyl alcohol or ethanol to ordinary fountain solution. The fountain solution has a lower surface tension, and a smaller amount of liquid can form a water film that resists ink infiltration in the blank portion of the printing plate, and is suitable for a multicolor offset printing machine with a cooling water supply device.

3 Surfactant fountain solution Surfactant fountain solution is prepared by adding surfactant to common fountain solution. Surfactant fountain solution has the advantages of low surface tension, good spreadability, non-toxicity, no volatility, and no explosive hazard. It is an ideal fountain solution for multi-color printing presses.

2. Wetting principle of fountain solution:

1 First look at the situation shown in Figure A.

The figure shows the wetting state of water droplets on the surfaces of different substances. Figure (a) Water droplets are round, indicating that the water droplets have little interaction with the surface of the solid, or that the wetting performance is not good. For all lines, the angle θ indicates that the contact angle between the water droplet and the solid surface contacted is greater than 90°. Figure (b) The water droplets are semicircular, indicating that the water droplets interact with the surface of the solid with a large amount of wettability, and all the lines OF are also used. Obviously, the contact angle θ is less than 90°. The contact angle θ is good or good, of course, it is small, and the small contact angle indicates good wettability, covering the solid surface area, covering the area is even, relatively speaking, the water used in the same surface area is less The nature like this is exactly what our offset printing technology needs.

2 As shown in Figure B, the surface tension changes after adding alcohol in pure water.

Fig. (a) shows pure water. As a result of the surface tension, water droplets appear and the included angle is 120°. Figure (b) shows the addition of 20% alcohol. The surface tension is reduced, and the same water droplet area is enlarged with an included angle of 50°. Figure (c) shows the addition of 25% alcohol. The surface tension is even smaller. The same wetting area of ​​the bead extends to twice the wetting area of ​​the pure water and the included angle is 10°.

3 fountain solution performance:

From the point of view of the printing process technology and printing related factors, in general, the fountain solution should have the following main properties:

1 It should have enough wettability to form a thin, uniform film of water on the non-graphically blank part of the plate surface.

2 It should have water-absorbing properties to protect the non-image blank areas of the printing plate, and it can repair the hydrophilic layer that is worn during the printing process.

3 should have the function to clean the non-image blank part of the plate layout.

4 During the production process, stable and adjustable acidity should be maintained within a certain range.

5 The influence on the ink performance and the degree of emulsification with the ink in the production process should meet the requirements of the printing technology. 6 No effect on the appearance of the product, no harm to the production operator.

4. The role of fountain solution:

The composition of the fountain solution, whatever form it takes, and regardless of the method used, is determined by the role of the fountain solution in print production. From the print production process, its main role should be:

1 should have the role of hydrophilic oleophobic (ink);

2 It should have the function of protecting the water absorption layer of the non-image blank part of the printing plate;

3 should have a good wetting effect;

4 should have some adjustment of certain properties;

5 should have a certain degree of antiseptic effect.