The role of water in printing

Back in 1798, Aloys Senefelder accidentally splashed water on Mom's list of details, and the list was just written on a stone. He could not think that 200 years later, lithography used water as the printing process. The main ingredient.

It is undeniable that many things have changed. Today, the alumina version has replaced stone, and the application of water is controlled by a complex dampening system. However, the ink cannot be transferred to the water-coated surface, but the principle of adhesion to the oleophilic image material is still based on lithography.

Yes, waterless printing advocates have made great progress. It is also the subject of future research. However, the dampening system is still indispensable for lithography. Let us briefly discuss how it works.

The non-image area of ​​the aluminum plate was treated as a hydrophilic surface. The material of the plate with the image area is drained and oleophilic, such as copper or photopolymer. During the printing process, the printing plate is first moistened by the roller or wetted by the dampening system's spraying device, so that the non-image area on the plate cannot absorb the ink.

Next, the plate is rotated and brought into contact with the ink cylinder, and the ink is only transferred to the imaged area. The printable area of ​​the lithographic plate has no protrusions, and the lithographic printing method is also referred to as lithography - the inked portion and the non-inked portion are on a horizontal plane. The inked part of the letterpress printing is raised, and the inked part of the gravure printing is recessed.

As water wets the entire layout, water has become a hidden cause. Because ink and water are incompatible, the relationship between them can only rely on a fine chemical balance. To achieve this balance, it should be noted that the fountain solution cannot consist only of water—in fact, it is a mixture of several chemical agents called fountain solutions.

An example of a component that forms a fountain solution includes a film protective adhesive such as gum arabic or a synthetic substitute; various salts such as magnesium nitrate; and organic acids such as phosphorous acids Or citric acid. Each of these components plays an important role in ensuring that the no-image area is completely invisible and accepts only water.

Ideally, one printing plate should be sufficiently wetted to prevent ink transfer to the imageless area. If the plate is applied with too much dampening fluid, problems will arise. The paper absorbs part of the excess fountain solution, and the rest goes to the area of ​​the ink, creating a mixture of ink and water – this is the starting point of the problem.

Under the action of the ink roller, a small part of the fountain solution is grinded into the ink. Generally, the ink can contain a certain amount of fountain solution; in fact, they form an emulsion that can be controlled. Emulsions are defined as the state in which fine particles of an incompatible liquid are dispersed in another liquid. (Mayonnaise is an excellent example)

If the emulsified fountain solution remains stable and within the limits that the ink can contain, everything will be perfectly normal and the ink will be transferred to the plate in the normal way. Workers on the press claimed that this condition was to achieve "water-ink balance." At this time, we already know what is the water-oil emulsion.

On the other hand, if there is too much water at the time of printing, it will exceed the limit of ink containing water. At this time the state of the emulsion is broken, forming an oil-water emulsion, which is characterized by the fine particles of oil floating in the fountain solution. The small particles of these inks will transfer to the non-image area on the plate as the fountain solution forms a dirty spot, and the plates of the non-image area that should not be inked become very sensitive.

The ink's ability to hold water can be determined by several instruments, that is, its ability to accept water. This is very important, and the accommodation capacity differs depending on the chemical composition of the fountain solution and the composition of the ink. Even different water treatment devices can affect the ink and water interactions.

In order to maintain the best working relationship between the ink and the fountain solution, it is recommended that when the product used changes, or the supplier of the material changes, a sample of the new product should be found. Before the formal printing, the ink is tested. Ability to hold water.

The depth of the particles on the plate may even affect the amount of fountain solution needed, which is easily overlooked. Plates with deeper particles will absorb more fountain solution than normal plates. If the ability of an ink to contain water is appropriate to the minimum of a normal particle plate, then when using a deep-grain printing plate, the relationship between the ink and the water will be greatly increased due to the more adsorbed fountain solution. influences.

Since most inks have a wide range of water holding capacity, if the supplier of the printing plate changes, the best advice is to promptly notify the ink producer. It is very likely that a new fountain solution is needed for the new printing plate.

Only by making the channels of communication unimpeded can printers ensure that their work is carried out smoothly and that the problems that arise in water and ink problems are minimized.

Source: Fujian Printing Network