Effect of printing speed on printing pressure

Offset printing is the use of indirect printing, the use of the rubber roller intermediate elastic body, the plate cylinder on the graphics, under the pressure of the impression cylinder printing pressure, transfer to the printed paper above, offset printing speed for the printing pressure The impact is great, and many examples of printing show that when the printing speed increases, the printing pressure increases. This is due to the increase in the printing speed, which inevitably results in a corresponding reduction in the time during which the printing plate and the blanket, the blanket, and the sheet to be printed are in contact with each other. This reduction in time means that there is an increased degree of incomplete contact between printed surfaces, which is very dangerous.

In order to effectively avoid the incomplete transfer of graphic dots due to incomplete contact between the printing surfaces during offset printing, the dots and graphics are not strong, the plates are off, and the ink is grayish, a large printing pressure must be used. . In this way, the ink can be quickly transferred from the ink supply surface to the ink receiving surface, and the ink can be completed in its ideal transfer process in a shorter time.

The ideal pressure is not immutable, so when deciding on many factors that affect stress, it must be carefully analyzed according to the actual conditions in the printing process.

In recent years, the printing speed of offset presses has been increasing faster. The highest speed sheetfed offset press has reached 12,000 to 15,000 sheets/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 incomplete transfer of image and text points due to the incomplete contact between the printing surfaces due to the brief imprinting time .

(2) As the printing speed of the offset press continues to increase, the diameter of the cylinder is smaller, and the compression width during the rolling process is also reduced. If you do not increase the printing pressure, it will also affect the ink transfer.

Too much or too little pressure in the printing will lead to the reduction of the quality of the printed matter, and the excessive printing pressure brings the following disadvantages:

(1) Distortion of picture and picture, enlargement of prints, and sharpening of dots.

(2) The ink is "overfull" partially, causing the print to be incongruous.

(3) The paper is pulled up and dusted.

(4) Major deformation of the main pressure-receiving parts and rotating parts of the printing press affects the working life of the parts.

(5) Accelerates plate wear compared to normal pressure and friction conditions.

(6) The imprinting dots are enlarged, the level of prints is unclear, and the resistance of the blanket is affected.

(7) As the load of the machine increases, the power consumption is also high.

When printing pressure is too low, 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 defects of printing plates, linings, paper and printing machines more obvious.

The ideal pressure should be to use the minimum pressure evenly on the basis of a certain printing surface deformation under the condition that the printing is sufficiently strong, and it is recognized by most people as the kind of ink that most people are satisfied with. The printing pressure is appropriately transferred.

Under normal circumstances, the appropriateness of the printing pressure is often manifested by the print quality of the printed matter. The pressure should be based on the premise that the print has strong dots, clear graphics, vivid colors, and shades of light. Small is better.