Talking about the Influence of Printing Speed on Printing Pressure
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Offset printing is indirect printing. Using the intermediate rubber of the blanket cylinder, the graphic on the plate cylinder is transferred onto the printed paper under the pressure of the impression cylinder. The printing speed of the offset printing machine is for the printing pressure. The impact is large, and many printing examples show that as the printing speed increases, the printing pressure increases. This is because the increase in the printing speed inevitably reduces the time during which the printing plate contacts the point at which the blanket, the blanket, and the sheet of the substrate are in contact with each other. This reduction in time means that the degree of incomplete contact between the printed surfaces is increased, which is very dangerous.
In order to effectively avoid the incomplete image transfer caused by incomplete contact between the printed surfaces during offset printing, the dots and graphics are not strong, the plate is missing, and the ink is gray and gray, so it is necessary to use a large printing pressure. . In this way, the ink can be transferred from the ink supply surface to the ink receiving surface faster, and the ink can complete its ideal transfer process in a shorter time.
The ideal pressure is not static, so when deciding on many factors that affect stress, it must be carefully analyzed according to the actual situation in the printing process.
In recent years, the printing speed of offset printing machines has increased rapidly. The highest speed sheetfed offset printing press has reached 12,000 to 15,000 sheets per hour. The machine speed is high and its printing pressure must be increased accordingly. The reasons are as follows:
(1) To increase the printing pressure to compensate for the incompleteness of the transfer of graphic and text points caused by incomplete contact between the printing surfaces due to the short imprinting time, the incompleteness of the graphic dot dot imprint, and the elimination of the version.
(2) As the printing speed of the offset printing press continues to increase, the diameter of the drum is small, and the compression width during the rolling process is also reduced accordingly. If you do not increase the printing pressure, it will also affect the transfer of ink and graphics.
If the printing pressure is too large or too small, the quality of the printed product will be reduced, and the excessive printing pressure will bring about the following shortcomings:
(1) The graphic distortion, the print becomes coarse, and the dot is enlarged.
(2) The ink is partially "overfilled", resulting in uncoordinated print tones.
(3) The paper is pulled up and powdered.
(4) The main pressure-bearing parts and rotating parts of the printing press are greatly deformed, thereby affecting the working life of the parts.
(5) Accelerated plate wear compared to normal pressure and friction conditions.
(6) The imprinted dots are enlarged, the printed matter is unclear, and the print durability of the blanket is affected.
(7) Since the load of the machine increases, the power consumption is also large.
When the printing pressure is too small, it will cause:
(1) The transfer of printed graphics is not complete.
(2) The outlets are not real and the colors are gray.
(3) Make the original defects and problems such as plates, linings, papers and printing presses more obvious.
The ideal pressure should be based on the deformation of a certain printing surface, the minimum pressure is uniformly used on the basis of sufficient printing, and it is recognized by most people as the amount of ink that most people are satisfied with. Print pressure that is properly transferred.
Under normal circumstances, the appropriateness of printing pressure is often expressed by the printing quality of printed products. The pressure should be based on the premise that the printed products have strong dot, clear text, bright colors and shades, and the more they are applied. Small is better.