A Brief Analysis of the Chinese Fountain Solution for Lithographic Offset Printing (Part 2)

Second, fountain solution printing balance

The balance of the fountain solution mainly includes the balance between the fountain solution and the ink in the printing state, the balance with the printing plate in the working state, and the balance with the paper under the printing effect.

1 balance of fountain solution and ink:

In the balancing problem of the fountain solution, the balance between the fountain solution and the ink is the main problem, and it is also the most representative. Because in the entire printing process, this equilibrium state is directly related to other aspects of the balance. Both the ink and the fountain solution are liquids, which are mixed by mechanical or physical action in the printing state. The mixing performance depends on the interaction of the surface tension of the two liquids, the fountain solution and the ink. Because some of the printing properties of the inks have already been formed during the manufacturing process, an auxiliary agent may be used to adjust the viscosity and fluidity of the inks, but it is not obvious for changing the surface tension. Therefore, the actual production is often to change the surface tension of the fountain solution to adjust its mixing performance. The basic principle of offset printing is to use the principle of oil and water mixing. This basic principle is correct, but it is only basic. In fact, it is impossible to not mix. If it is absolutely required not to mix, printing cannot be performed normally. In the printing process, the ink and the fountain solution are finally mixed in a milky form due to the presence of pressure, the presence of mechanical friction, the properties of the printing plate, the performance of the ink, the influence of the printing environment, and the like. This is the emulsification of the ink. . The emulsification of the ink is present. A proper amount of emulsification and stable emulsification are beneficial to the printing process and are also necessary. As long as this emulsification is no longer extended, the fountain solution and the ink are generally balanced.

2 balance between fountain solution and paper:

In the actual printing, about 10% of the fountain solution will be transferred to the paper through the plate, blanket. The balance of fountain solution and paper can be understood from the following four aspects.

1 The balance of paper and fountain solution is a state. When the balance is reached, the moisture content of the paper should not affect the accuracy of overprinting, does not affect the drying and color of the print, and does not affect the printing performance of the paper. At the same time, the moisture contact process of the printed sheet should be normal after printing.

2 There are certain conditions for the balance between paper and fountain solution. The amount of fountain solution is determined by the amount of ink and printing plate required. It is not determined by the moisture content of the paper. While meeting the requirements of the ink and the printing plate, the water content of the paper should not exceed the allowable amount as much as possible.

3 The balance between paper and fountain solution is temporary and dynamic.

4 The balance between paper and fountain solution is affected by the environment. In addition to some technical factors affecting the moisture content of the paper, the paper itself hydrophilicity, ambient temperature and relative humidity affect the moisture content of the paper at any time. The general printing shop temperature should be maintained at about 24° and the relative humidity should be around 65%.

Third, the main factors causing fountain solution consumption

1 print surface coating consumption:

The amount of fountain solution required on the surface of the printing plate is the main aspect of fountain solution consumption. Regardless of the type of plate used in the printing plate, the output of the fountain solution should be sufficient to meet the water film formed on the surface of the printing plate.

2  Consumption of paper surface absorption:

Paper is a highly hydrophilic substance. The fountain solution coated on the surface of the printing plate is partially absorbed by the ink roller and transferred to the surface of the blanket. The fountain solution on the surface of the blanket is almost completely absorbed by the surface of the paper.

3. The effect of indoor temperature and humidity on the volatilization of fountain solution:

According to the technical requirements of the offset printing process, the printing shop temperature is generally around 24° and the relative humidity is around 65%. Extreme humidity and low relative humidity all contribute to the evaporation of fountain solution.

Fourth, improper use of fountain solution on the quality of printed products

1 fountain solution used too much:

Excessive fountain solution will accelerate the "oil-in-water" emulsification and change to the "oil-in-water" type, destroying the balance between ink and fountain solution. Caused dark prints, deinking, floral version and other faults.

2. The volume of the fountain solution is too small: the amount of the fountain solution is too small to cause imbalance between the plate and the fountain solution. The surface fluid of the printing plate is too small, and the inorganic salt layer in the blank portion of the printing plate is not stably repaired and protected. The aluminum plate base is exposed and the oleophilicity is increased, resulting in a dirty plate phenomenon. At the same time, the surface of the plate is also damaged.

3) The fountain solution is too acidic or too weak:

Strong and weak dampening solution will cause imbalance between fountain solution and printing plate. Because dampening is composed of acids and salts, it has the function of timely compensating the inorganic salt protective layer on the surface of the printing plate. If the dampening solution is too acidic or too weak, excessive or insufficient supplements will be formed, resulting in an imbalance between the fountain solution and the printing plate. The dampening solution is too acidic, which is manifested as dirty printing plate surface, ink roller deinking, imprinting, dull printing, image-making, etc.; the dampening fluid is too weak in acidity, and the printing plate is dirty. Paste plate, print outlets become larger, and ink emulsification occurs.

Fifth, the use of fountain solution and control

The following configuration parameters of Speedmaster MultiFS FS13 water hopper liquid for the Heidelberg SM-74 machine:
Temperature setting: 10-12 °C
(Isopropyl alcohol) alcohol ratio: 10% -12%
Dosage: 2%-3%
Conductivity: 1450us±100
PH value: 38—45
1  temperature setting:
In the printing process, the surface temperature of the printing plate is relatively high. As the temperature rises, the water in the printing plate evaporates faster, the viscosity of the ink decreases, and the ink transmission is poor. Especially when the ambient temperature is high, it will cause a dirty plate phenomenon. Therefore, reducing the surface temperature of the printing plate is also necessary to maintain the ink balance. Generally, the cooling fountain solution is about 10-12°C so that the surface temperature of the printing plate can be increased.

2  alcohol ratio:
The addition of alcohol reduces the surface tension of the fountain solution, so that the printed version is well wetted by the heavy plate, which greatly reduces the water consumption, improves the drying speed of the printing product, lowers the surface temperature of the printing plate, stabilizes the viscosity of the printing ink and high-speed printing performance. However, adding too much alcohol will also deteriorate the quality of the ink and cause serious environmental pollution. This will make the gum arabic in the fountain solution easy to precipitate and adversely affect the ink-water balance. Lithographic offset printing generally control the amount of alcohol (isodiol) in 10% -20%.

3 Adding amount of water hopper:
The adding amount of the fountain liquid is generally controlled at 2% - 3%. If the adding amount of the fountain liquid is too small, the printing plate is easily dirty, and it is difficult to achieve ink balance, and it is difficult to obtain a satisfactory ink color effect. If the amount of the fountain liquid is too large, the ink may be over-emulsified, the ink color is not easy to control, the ink throwing and the flying ink may occur, and the water fountain and the water roller may be polluted. The ink roller may not be inked, and the ink may easily accumulate on the blanket.

4PH value and conductivity:

The pH and conductivity parameters are often used to reflect the condition of the fountain solution and to monitor it. Tests have shown that when the PH value is in the range of 38—45, the printing is the most stable, the printing plate has the longest service life, and the quality of the printing product is the best. The ink and ink balance is the most easily controlled. Conductivity is generally controlled at 1450us±100. The conductance value is easily affected by water hardness, alcohol consumption, dust and ink mixed in, so the conductive value is also allowed in 1000~1000us, but when the fountain solution is seriously polluted, it must be Reconstitute.

Sixth, the conclusion

For the problem of fountain solution, it is necessary to grasp its basic principles, master its basic methods and grasp the links with it, especially the factors that have a direct connection. In actual use, there should be a lot of change, and you cannot expect an absolute figure to solve the problem. Problems must be analyzed and judged comprehensively. According to the model of the offset press, the type of the fountain liquid, the brand of the ink, and other variable factors, the fountain solution can be reasonably mastered and used.

Source: PACK.CN