Gravure printing referred to as "gravure". The printing method in which the printing plate is indented partially. In the earliest European countries in the 15th century, hand-painted depressions on metal plates were printed with ink. The ink on the surface of the layout was decontaminated, leaving only the ink remaining in the recesses to be transferred to the paper. Later developed photo etching gravure (formerly known as shadow edition) and mechanical engraving gravure (including engraving with an electronic engraving machine), laser engraving gravure, electron beam engraving gravure and so on. The gravure shape also develops from flat to arc. Modern gravure is mostly rotary printing. Plate material to the metal (auxiliary chrome, nickel, etc.), the development of plastic sleeve method. It is mostly used for color images, advertisements, packaging and decorating, and printing of professional banknotes. The finished product has delicate and thick features.
working principle:
The gravure printing machine is mainly composed of the uncoiler, guide group, printing group, slitting group and control group. The unwinding machine mainly completes the unwinding of the web under a certain speed and tension, and maintains a corresponding stable state, and simultaneously completes automatic or manual splicing of the web. The main function of the guide group is to ensure that the paper web is not offset laterally during the printing process, and at the same time, the paper tension is stable. The printing group is the main component of the gravure printing machine. The main processes for printing are ink supply, printing and drying. The slitting group will print the entire printed semi-finished product and cut it into a molded sheet product. The control group mainly sets the operating parameters and working conditions of the gravure printing machine, including the speed, tension, temperature, and the working status of the pressure roller, the squeegee, and the ink pump.
The principle and operation of the uncoiler
Uncoiler consists of clutch, tension roller and tension controller. The three form a closed-loop automatic control system for automatically adjusting the speed and tension of web unrolling.
1, working principle
The unwinding machine is a passive device that does not have power. It mainly adjusts the paper supply according to the need of the printing unit to feed the paper (paper pulls the rotation speed of the web). The control of the web rotation speed is achieved through the clutch and the paper spool. Most of the previous use of electromagnetic clutch, the current use of large and colorful pneumatic clutch.
In the printing process, the printing speed is not a constant value, sometimes gradually increasing, sometimes decreasing gradually, so the tension roller is needed to control the paper supply and tension.
The tension roller swings up and down around a fixed point. The thrust of the cylinder and the tension of the paper are balanced to ensure that the tension roller is in equilibrium. The position of the tension roller indicates the tension of the paper and the amount of paper supply, and the position information is input to the tension and the paper supply speed. During the printing process, the smaller the distance between the tension roller and the floating roller, the more conducive to the stability of the paper tension.
The tension controller is a key component in the tension control system of the uncoiler. It mainly completes the processing and analysis of detection signals and issues execution commands. At present, MCS-202E controllers are mainly used in the country. The controller can indicate the working state of the brake pad using the clutch paper reel and set or correct the position of the tension roller at any time.
2. Operation of uncoiler
According to the requirements of frontier printing, gravure printing machines generally use to order webs. Due to the different machine models, the outer diameter of the uncoiler paper mandrel is relatively different, typically 3, 6 or 12 inches. Therefore, when ordering a web, the outer diameter of the mandrel must first be considered. Generally, the inner diameter of the paper core is required to be 2 to 5 mm larger than the axis of the paper mandrel. Secondly, it should also be noted that the most suitable web can be used for the unwinding machine. Outside diameter, during installation, check whether there is any deformation of the paper core. If the deformation is too large, repair it first. After the paper is unfolded and straightened, insert the paper core into the paper roll core, and then check the distance between the two ends of the paper core shaft to center the roll paper as far as possible.
After the roll paper machine, make sure that the horizontal position is in the same position as the roll paper. If the uncoiler is automatically tying paper, it should be docked or overlapped according to the requirements of the uncoiler. When splicing, first scribe at the splicing position, and then use double-sided and single-sided adhesive tape for pasting. During the splicing process, it must be ensured that the outer diametral line speeds of the two rolls are consistent.
If the uncoiler is manually picking up the paper, the roll-up web will be cut after stopping, and the horizontal position of the paper will be adjusted and it will be directly attached to the beginning of the new web.
Adjustment of horizontal position of paper during printing
The so-called lateral adjustment is to adjust the position of the paper along the axial direction of the printing plate. This is very different from the lateral registration of the pattern at the time of printing. It is generally divided into three parts: unwinding machine adjustment, printing before printing and before slitting.
1. Unwinder adjustment
The installation of the web on the decoiler is generally centered, but when the plate pattern is biased to one side, the lateral position of the web must be adjusted. This adjustment is generally a one-time manual adjustment.
2. Pre-print adjustment
This is the main work in horizontal adjustment, which is done automatically by the guidance group. The cylinder pushes the drive roller to swing around a fixed point to adjust the relative position of the drive roller. The dashed line is the width of the paper and the arrow is the direction of paper movement. In the process of use, the lateral position of the photoelectric detection switches on both sides is first set according to the position of the position of the printing plate pattern on the lateral position of the paper. This forms a closed-loop control system that guides the controller to control the lateral position of the paper. The system is highly precise and can reach +/- 0.15 mm. In addition, it can perform single-sided or double-sided control.
3. Adjust before cutting
In order to ensure that the slitter knife cuts to the horizontal cutting position, the lateral position of the paper needs to be adjusted. This position generally adopts the same closed-loop control system as before printing, and also needs to set the position of the photodetector in advance.
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