The role of fountain solution in the printing process (4)

Ten, corrosion

If water and metal come into contact, corrosion can occur. There are metal rollers, bearing rings, and plates in the press. There are two types of corrosion:

1. Contact corrosion occurs on the metal plate. When there is a water containing electrolyte, the degree of corrosion depends on the difference in the potential energy of the conductivity of the electrolyte, the size of the contact surface, and the degree of polarization:

- At the beginning of the roller coating, the splices

- between aluminum plate and plate roller

- Contact surface of roller body and bearing

2. The corrosive flow is caused by static electricity on the paper path, the blanket, and the liner. As a result, marks and flaking are generated on the joint surface and seams of the blanket roller.

In order to reduce or eliminate this corrosion, it is necessary to reduce the corrosive effect of water (the pH should not be lower than 4.4/lower halide content/lower - conductivity/polarization resistance, such as corrosion inhibitors).

Eleven, isopropyl alcohol

The use of isopropyl alcohol (IPA) in offset printing is regarded as the right thing to do. Despite the disadvantages (unfavorable to the environment and health), especially the special storage methods are expensive, it is difficult to imagine the printing without IPA.

To be ideal, why isopropyl alcohol is so important in offset printing, we must first understand its role in offset printing.

1. Reduce static and dynamic surface tension

Better and faster wetting of the parts of the plate that require wetting

Reach ink and water balance quickly

Adjust the state of the emulsion

2. Increase the viscosity of the wetting fluid

Large adjustment space (ink and water volume)

Wet roller speed is lower.

3. Volatile

- Volatile cold

- Good ink drying effect

4. Prevent bacteria from producing

A reduction in the growth of algae in a wet device

IPA was added to the already prepared wetting fluid. According to experience, the ideal addition amount is from 7% to 8%. The measurement of IPA is controlled by measuring the density and humidity of the wetting fluid. The practical amount of isopropyl alcohol in the wetting fluid can only be determined by using the specific gravity. The parameters can be accurately determined.

12. Decrease Isopropanol Consumption According to VOC Guidelines

When using isopropyl alcohol to obtain benefits, it also brings disadvantages to the environment and users. When printing, the use of less or no IPA at the same time as maintaining the same print quality standards has become a requirement for the printing industry and the printing industry for the material industry in recent years. The faster the printing press, the smaller the printing format and the simpler the printing surface, the easier it is to reduce the amount of IPA. If the press speed is too low, the ink and water balance is difficult to reach. If the printed surface is too large, the wetting of the printing plate becomes a problem, and the varied printing patterns and the different contour requirements may cause the wetting fluid-related problems (dirty/dirty).

According to the different printing presses, reducing the content of IPA will automatically destroy the water transfer. Only the roller speed of the fountain roller can handle it, which will naturally reduce the adjustment space of ink and water. If several factors are added together, ideal printing is not possible, but printing without isopropyl alcohol is possible. The wetting fluid additives used must minimize the surface tension of water. At the same time increase the viscosity. This will ensure that the ink and water have enough room for adjustment. According to experience, the amount of water reaching the ink is still reduced. As a result, the dot gain is reduced and the drying effect of the ink is improved. However, the amount of ink transferred must be carefully considered.

The same principle applies here: the amount of ink and water is as small as possible.

Sometimes ink and paper powder can quickly accumulate on the blanket. If it cannot be solved by the usual methods, the ink must be changed (reducing the viscosity). The contact pressure between the wetting rollers should be as small as possible. Soft wetting and fountain rolls are recommended.

Thirteen, the temperature of the wetting medium

The adjustment of the wetting fluid temperature is important for stable printing. It has an influence on the viscosity of the wetting fluid and the stable formation of the ink and the water emulsion in the inking device. In addition, cooling the water tank can prevent the printing press from long-term. Hot during operation. While reducing the amount of alcohol added, cooling the dampening solution helps to reduce the volatilization of alcohol in the dampening solution.

advantage:

- higher wetting fluid viscosity

- Better water transfer when the roller speed is low
- The temperature of each element remains stable

- Improve the stability of inks and water emulsions

- Isopropyl alcohol contained in the wetting fluid is more slowly evaporated.