The printing quality also depends to a large extent on the temperature and humidity of the offset printing workshop. This is a problem that quality inspectors should pay attention to. The temperature and humidity have a great influence on the deformation of the paper, the flow and transmission of ink, and at the same time, to a certain extent It also affects the emotions of the operator, so it is theoretically believed that the offset printing workshop should be controlled to constant temperature and constant humidity, which is obviously impossible. Generally speaking, the temperature of the offset printing workshop should be controlled at 22 ℃ ～ 26 ℃. The relative humidity should be controlled at 50-55%.
The control of printing quality in terms of process mainly refers to reasonable wrapping, water-ink balance, regular ink transmission and transfer, and appropriate control of printed materials. These issues have been described chapter by chapter, and will not be 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 of relying on human vision for a long time and operating with experience.
The device that uses density meter 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 machines are equipped with computer touch screens to control all printing units and operators. Through the user-friendly touch screen, you can perform all important operations, everything is monitorable, reliable, fast and convenient.
Automatic ink supply system. They can be guaranteed from the beginning to the end of the printing job. The amount of ink in the ink fountain remains constant, which is the prerequisite for stable printing quality. Keeping the ink volume constant is assisted by an ultrasonic sensor, and a central ink supply system realizes automatic ink supply.
Alcohol continuous film wetting system with speed compensation, which has a uniform film of wetting liquid, can achieve a stable water-ink balance state. In addition, a differential (Vario) system that relies on the speed difference between the water roller and the plate cylinder can avoid spots on the printing plate, and can always provide constant printing conditions throughout the printing process.
The printing quality console is designed according to the basic data of printing quality control. It can detect the solid density, dot increase value, relative contrast and other printing quality data of printed sheets within seconds.
As the printed sheet to be tested, a color mark specially designed for testing must be printed in the width direction. The color scale includes solid color scales of various colors, and the dot color scales with tone values ​​of 80%, 40%, and 20%. During testing, the color code of the printed sheet is placed under the detection head, and the detection head moves quickly along the track. The solid density of each section and the dot density of 80%, 40%, and 20% are measured to obtain various density signals. It is sent to the electronic computer, compared with the specified density value stored by the computer, or compared with the input control signal, after judging, correcting, regulating the ink fountain roller motor and ink fountain blade motor. Adjust the angle of the ink fountain roller, the gap between the ink fountain blade and the ink fountain roller, and change the ink output of the ink fountain to achieve the required ink layer thickness.
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