The technical trends of fountain solution

In offset printing, the high speed and automation of printing machinery are very obvious, especially in the water supply mode, which requires easy operation and uniform water supply to maintain the high quality of printing. For this reason, continuous water supply devices have developed into this area. Mainstream. It has been more than 30 years since the continuous water supply device was put into production. The developer, Dagechem, advocates the addition of volatile organic solvents such as alcohol and butanone in the drug solution. Since then, various types of continuous water supply devices have been developed by various machinery manufacturers, but they have been designed on the premise of using alcohols (see Figure 1). In view of this, 5% to 25% isopropyl alcohol (IPA) has been added to fountain solution. However, due to the unfavorable effect of isopropanol on the safety and environmental protection of the production environment, the material manufacturers have developed and replaced the IPA dampening water. This article will talk about the technical composition and technical trends of replacing the IPA dampening syrup.

The function and composition of the fountain solution The fountain solution is composed of a corrosion component (non-lipid) and an IPA displacer (see Figure 2).

1. The function and general composition of the corrosion component. The role of the corrosion component is to repair the non-lipidation of the non-image portion. The PS plate was coated with a hydrophilic protective layer of colloid on the plate during the plate making process, but the protective layer was gradually worn out as the number of prints increased. In addition, in the long live printing process, due to the friction between the rollers, the aluminum hydrophilic treatment layer will be partially damaged. At this point, the corrosion component plays a role in repairing the hydrophilic layer. In addition, cleaning of once-attached inks is also an important function of corrosion components. Materials having these functions include inorganic acids such as phosphoric acid and nitric acid, organic acids such as tannic acid and tartaric acid, and resin components such as gum arabic.
2.1 The function and general composition of the PA substituent composition. The IPA substitution agent component of dampening solution is designed based on the original function of IPA, such as 1 increasing viscosity effect, 2 decreasing surface tension effect, and 3 controlling ink emulsification effect.
(1) Stickiness effect. When IPA is added to the drug solution, the viscosity will gradually decrease after the addition rate reaches 60%. In the continuous water supply mode, this thickening effect plays an active role. According to the principle of elastic fluid lubrication, the amount of dampening solution between the water supply rollers depends on the viscosity (see Figure 3). According to the theoretical formula, the viscosity of the dampening solution increases, and the amount of dampening solution passing between the rollers increases. increase.

(2) Reduce surface tension effects. In the continuous water supply printing machine, the high-speed rotation of the water supply roller enables the dampening solution to spread evenly on the plate surface. For this purpose, the surface tension needs to be reduced. The surface tension referred to here is the dynamic surface tension, which is different from the static surface tension. The surface tension of a liquid generally varies with time after it has been formed from its liquid surface. At the moment when a new liquid surface is formed, the surface tension after about 10 seconds or more is called a static surface tension, and the surface tension below 1 second, for example, 10 to 3 seconds is called a dynamic surface tension.
To reduce the surface tension, the interface active material needs to be oriented at the gas/liquid interface. However, due to the large molecular weight of the general surfactant, the surface orientation takes more time, and the relative speed of the high-speed printing press is too short (only a few Ten milliseconds). In such a short period of time, dynamic surface tension cannot be reduced (see Figure 4). Therefore, as a reducing agent for dynamic surface tension, a component having a small molecular weight and a high surface orientation ability is required.

In view of the above, IPA is used in a large amount because of its small size and easy surface orientation, and it is easy to reduce the dynamic surface tension. This has been achieved by using a water-soluble solvent such as a glycol in the formulation.
(3) Control the emulsification of the ink. In lithography, it is very important to avoid the emulsification of the ink and fountain solution. The ratio of the fountain solution penetrating into the ink, that is, the emulsification rate, varies depending on the ratio of the ink to the syrup.
A combination of ink and ink with a low emulsification rate causes insufficient supply of water on the non-image portion, which causes dirt (see FIG. 5).
On the other hand, for a combination of ink and ink with a high emulsification rate, moisture is caused to float on the image portion, causing an ink transfer failure and causing an ink roller deinking problem (a phenomenon that ink does not adhere to the ink roller during printing). The ink film on the ink roller functions as a retention layer and a buffer layer of the dampening solution. As the printing progresses, the emulsification rate gradually increases, and it becomes an over-emulsified state, resulting in a change in the visco-elasticity of the ink and easily causing poor ink transfer. Therefore, in the long live printing, it is necessary to control the emulsification rate of the ink.

Second, the trend of dampening the development of dampening medicine to replace the IPA's dampening syrup has been more than 20 years since the development of the equipment, where the equipment manufacturers, after many improvements, is currently on the market sales of the third generation, the fourth generation of products There has also been a great improvement in performance, but unfortunately a single liquid cannot satisfy all the printing conditions. IPA can easily adapt to various printing conditions by adding concentrations. In contrast, IPA's replacement dampening potions are constrained by price, and non-volatile substances have the danger of dissolving the image portion of printing plates. Constraints.

At present, the research and development of dampening syrups has made greater breakthroughs in the latest technological trends in recent dampening syrups.
1. A dampening potion that boosts productivity.
(1) Over-emulsion suppression type. This type is to suppress the phenomenon of over-emulsification of the ink, even if the long-lived printing does not cause an accident. It can reduce the frequency of press cleaning inks, and can also reduce the number of maintenance, the current IP series produced by Fujifilm company belongs to this type of product.
(2) Adapt to high-speed type. In order to respond to the high speed of offset printing, in order to maintain the dampening performance under high-speed conditions and to reduce the dynamic surface tension under high-speed conditions, further formulation of the composition of the interface active material (solvent composition, surfactant composition) is being explored.

(3) suppress fault type. With the light weight of printed paper (there is an increase in the paper with weak surface coating strength of reclaimed coated paper and micro coated paper), the dissolution of inorganic pigments is caused by ink roller deinking and heaping caused by accumulation toward the ink roller. Frequent accidents occur. The purpose is to suppress the occurrence of accidents by blocking metal ions derived from inorganic pigments, and technical development studies in this area are underway.
2. Environmentally friendly fountain solution (1) reduces VOC emissions. VOC (Volatail Organic Compounds) is a commanding organic compound, and its reduction is an important issue from the perspective of the earth's environmental protection. However, it is technically very difficult for VOCs in the fountain solution to achieve zero point. There are some VOC zero products recently, but it is still necessary to use practice to determine its reliability.
(2) Decreases the amount of dampening syrup liquid. For the contaminants such as inks and paper powders that are incorporated into the fountain solution, a dampening solution circulation filtration system that uses a step filter (having a higher adsorption and removal efficiency) has been developed. It not only increases the durability of the dampening potion, but also helps to reduce the discharge of waste liquid and reduce the environmental load. Therefore, it is a worthwhile direction.