Factors affecting print quality

The quality of printing depends to a great extent on the temperature and humidity of the offset printing shop. This is a problem that quality inspection personnel should pay attention to. Temperature and humidity have a great influence on the deformation of paper, the flow and transmission of ink, and at the same time, To a certain extent, it also affects the emotions of operators. Therefore, it is theoretically believed that the offset printing shop should be controlled to be constant temperature and humidity. Obviously, this is impossible. Generally, the temperature of the offset printing shop should be controlled at 22°C to 26°C. It is advisable to control the relative humidity at 50% to 55%.

The control of printing quality in terms of process mainly refers to reasonable liner, ink and ink balance, regular ink transfer and transfer, and appropriate control of printed materials. These issues have been described before and are not repeated here. .

With the rapid development of electronic technology and the popularization of computer applications, printing production has begun to get rid of the backward situation that has long depended on people's eyesight and experienced operation.

The use of densitometer measurement technology to detect printing quality and automatically control printing quality has been widely used in offset printing machines. For example, modern high-end offset printing presses are equipped with a computer touch screen to control all printing units. Through humanized design of the touch screen, all important operations can be performed, everything is monitorable, reliable, fast and convenient.

Fully automatic ink supply system. They can ensure that from the beginning of the print job to the end. The amount of ink in the fountain is kept constant, which is a prerequisite for stable print quality. The state of constant ink volume is assisted by an ultrasonic sensor, and a central ink supply system is used to achieve full automatic ink supply.

A speed-compensated alcohol continuous film wetting system with a uniform wetting fluid film that achieves a stable ink-water balance. In addition, the Vario system, which is dependent on the difference in speed between the water roller and the plate cylinder, can avoid spots on the plate, and can always provide constant printing conditions throughout the print job.

The print quality control panel is designed based on the basic data of print quality control and can detect the density, dot gain value, relative contrast and other print quality data of printed sheets in seconds.

As a printed sheet to be detected, a color scale exclusively for detection must be printed in the direction along the width. The color standard includes dot color patches of various colors, gradation values ​​of 80%, 40%, and 20%. During the test, the color patch of the printed sheet is placed under the test head, the test head is rapidly moved along the track, and the field density of each section and the dot density of 80%, 40%, and 20% are measured to obtain signals of various densities and signals to be measured. It is sent to the computer and compared with the computer's stored density value or compared with the input control signal. After judgment, correction, regulation of the ink fountain roller motor and ink fountain blade motor. Adjust ink fountain roller rotation angle, ink fountain blade and ink fountain roller gap, change ink fountain ink output, to achieve the required ink layer thickness.