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

I. Offset Wetting Media

In offset printing, water is one of the most important factors. It affects inks, offset plates, paper, and printing presses, and the result is the printing itself.

Herein we not only introduce the influence of water on the above parameters, but also describe in detail the role of the wetting agent additive, and cite examples to illustrate.

Wetting agent additives control the water and at the same time improve the quality of the water, thereby promoting the idealization of the printing process.

In recent years, wetting fluid additives have been continuously improved to adapt to new requirements, and at the same time, alcohol is gradually removed from the ideal. Therefore, the factors that need to be taken into account when choosing a wetting agent additive are very different from a few years ago.

Here are a few key points:

* Reduce the amount of IPA

* Chlorine-free paper

* Ink that does not dry on the ink roller

* Digital Printing

* harmless to the environment

*Plant type

Second, the role of wetting media in offset printing

Regional role

Offset Printing * Quickly balance ink and water

* Well wet the place where you walk

* Protect pS plate from corrosion

* Protection from downtime

* Resist Print Force

*Applicable to various printing plates

Ink

* Stabilize the emulsification of ink and water

*Achieve ideal drying process

* Quickly reach the balance between ink and water

* Does not precipitate pigment

Printing machine

* Protect the printing press from corrosion, pH value is controlled between 4.5~5.5

* Prevent ink flooding due to excessive wetting

*Applicable to various wetting devices

* Prevents the accumulation of paper powder in various parts of the printing press

* Prevent water and grease accumulation

* Prevent salt deposits

water

* Stable adjustment of pH

* Reduce or eliminate isopropyl alcohol

* Elimination of algae and bacteria

* The ideal surface and interfacial tension (adjust the surface tension according to the ink thickness)

* Adjust the properties of the wetting fluid to achieve the desired

* Increase viscosity and water

paper

* Stay in suspension and take it away

* Prevents the precipitation of fibers of the filler

surroundings

* Reduce solvent evaporation

* Harmless to the environment, decomposable

* Minimize IPA additives

Third, water / water hardness and conductivity

Water is composed of hydrogen and oxygen (H2O) and is dissolved in water in various salts. These salts determine the hardness and neutrality of water (pH=7). The difference in salt dissolved in water is determined by the type of salt, the temperature of the water, and the quality of the soil. The salt concentration is determined by the total hardness, the carbonate hardness, and the conductivity of water.

The total hardness (dH) represents the constant hardness, which is determined by the content of cations (calcium, magnesium).

The carbonate hardness (KH) represents a temporary, momentary hardness determined by the content of negative ions (hydrogen carbonate, carbonic acid).

Moisture is a very important factor because it affects the water's ability to dissolve (the lower the water temperature, the harder it is to dissolve the salt in the water).

Fluctuations in temperature can lead to precipitation of salt crystals during printing, and these salt crystals can accumulate on rollers, printing plates or blankets. the result is:

* Over-wetness causes poor inking

*Dirty version

* Salt accumulates in the wetted part of the printing plate.

The harder the water, the more important it is to add wetting additives. The wetting additive is a special compounding component that can prevent the precipitation of salt crystals.

Carbonate affects the pH of the water. The pH required for printing is 5, in order to achieve this value, the acid needs to be added to the wetting fluid, the acid is neutralized very quickly, the pH is increased, and the corrosive carbonic acid is released. The pH buffer prevents the pH from rising and maintains the pH of the water at a stable level, which can extend the use time of the PS plate. If the pH is higher than 5.5 or lower than 4.5, the PS will be destroyed. Version of photosensitive layer, reduce the use of time. These buffers have different resistance to carbonate depending on the quality, and the amount of buffer is determined by the amount of each hardness component.

Even with ideal wetting media adjustments, there are still problems such as pH fluctuations, or excessive wetting and insufficient ink. One of the reasons for these phenomena is usually due to water instability (different, severely fluctuating Hardness) caused.

Example: The wetting fluid additive is adjusted according to the water's carbonate hardness of 8°KH. The pH value is constant at 5 levels. Now, the salt concentration in the water is increased to 20°KH. The result is that the pH value is increased to 6 . In this case, after the tap water treatment is completed (standardization → softening → desalination), since the corrosive power of chlorine is very strong, this treatment method is also recommended for situations where the chlorine content in the water is too high. The hardness of water does not account for the amount of salt dissolved in water. Salts that have no effect on the hardness of water are not taken into account here, but the conductivity value of water here can provide more detailed information on the salts in water because the amount of all electric carriers in the water can be inferred from the conductance value (Electrical The carrier is the salt ion dissolved in water. There is no direct connection between the conductivity and hardness of the water.

Isopropanol, cleaning agents, ink and paper, and temperature fluctuations are all factors that affect the conductance value of water. The increase in the temperature of salt and water precipitated from paper and ink will increase the conductance. In contrast, isopropyl alcohol and cleaning agents It will reduce the conductivity of water.

The amount of wetting fluid additive dispensed based on the measurement of the conductance value is very inaccurate. This method is only suitable for fresh wetting fluids.