In many large Chinese printing factories, offset printing machines are the main printing machine. Many printing examples show that when the printing speed increases greatly, the printing pressure will also increase. The appropriateness of printing pressure often affects the quality of book printing.
The Influence of Offset Printing Speed on Printing Pressure
Offset printing is an indirect printing method. Which uses the elastic body in the middle of the rubber cylinder to transfer the images and texts on the printing plate cylinder. To the printed paper under the effect of the printing pressure of the printing cylinder. The printing speed of the offset press has a great impact on the printing pressure. Many examples of printing brush show that when the printing speed increases greatly. The printing pressure will also increase. This is because the increase of printing speed will inevitably reduce the time of contact between the printing plate and the blanket. The blanket and the corresponding points of the paper are to be printed. This reduction in time means that the degree of incomplete contact between printed surfaces increases, which is very dangerous.
To effectively avoid the incomplete transfer of graphic and text dots caused by the incomplete contact between the printing surfaces during offset printing. The dot and graphic and text are not solid, the plate is lost, and the ink is gray, etc., a larger printing pressure must be used. In this way, the ink can be transferred from the ink supply surface to the ink receiving surface quickly. And the ink can complete its ideal transfer process in a short time.
The ideal pressure is not unchangeable, so when determining many factors that affect the pressure. It must be carefully analyzed according to the actual situation in the printing process.
In recent years, the printing speed of the offset press has increased relatively fast. The single-sheet offset press with the highest speed per hour has reached 12000~15000 sheets/hour. With the high speed of the machine, its printing pressure must increase accordingly. The reasons are as follows:
First of all, we should increase the printing pressure to make up for a series of disadvantages. Such as incomplete transfer of graphic and text dots, weak printing of graphic and text dots. And plate loss caused by incomplete contact between printing surfaces caused by the short printing time.
Because of with the continuous improvement of the printing speed of the offset press. The diameter of the drum is smaller, and the compression width in the rolling process is also correspondingly reduced. If the printing pressure is not increased, the image and text transfer of the ink will also be affected.
Too much or too little printing pressure will lead to the reduction of print quality. While too much printing pressure will bring the following drawbacks:
A. The graphics and text are distorted, the imprint becomes thicker, and the dot is enlarged greatly.
B. The ink is partially “too full”, resulting in inconsistent color tone of printing.
C. The paper is pulled up and peeled.
D. The main pressure-bearing parts and rotating parts of the printing machine are greatly deformed. Thus affecting the service life of the parts.
E. Compared with normal pressure and friction conditions, it accelerates the wear of printing plate.
F. The printing dot is enlarged, the printing level is unclear, and the printing resistance of the blanket is affected.
G. Due to the increased load of the machine, the power consumption is also high.
When the printing pressure is too small. It will cause: the transfer of printed graphics and text is not complete. The dot is not solid and the color is gray. Make the original defects and defects of printing plate, lining, paper and printing machine more obvious.
The ideal pressure should be the printing pressure. That can be reasonably transferred by using the smallest pressure uniformly. On the basis of the sufficient strength of the print under the condition of certain printing surface deformation. And is recognized by most people as the ink volume that most people are satisfied with.
In general, the appropriateness of printing pressure is often reflected by the quality of the book printing. The pressure should be based on the premise that the printed matter has solid mesh, clear graphics and text. Bright colors and appropriate shades, and the smaller the pressure is, the better.