1. The main difference between engraved gravure and corroded gravure
According to the production process of gravure printing plate, the printing plate can be divided into engraved gravure etching gravure.
1. Processing of engraved gravure and corroded gravure
The engraving gravure is processed by an electric engraving machine, using needles of different angles to form a V-shaped groove of different depths after being hit on the copper-plated intaglio cylinder, and then the surface of the intaglio cylinder is plated with a wear-resistant chromium layer, after polishing , You can make a printed version on the machine. During the printing process, these V-shaped grooves are used to transfer the ink to the printing material.
Etching gravure uses imaging technology to create an image on the surface of a copper-plated intaglio cylinder. After etching, a U-shaped groove is formed on the cylinder surface, and then chrome plating and surface polishing are performed.
2. Comparison of engraved gravure and corroded gravure
The use performance of engraved gravure and corroded gravure is not much different, but the service life of the two is quite different.
After the V-groove on the surface of the engraved gravure is worn, the depth of the groove becomes shallow. As the width of the bottom of the V-groove becomes narrower, the area of ​​the dots becomes smaller, the amount of ink in the groove gradually decreases, and the ink color quickly becomes lighter, resulting in scrapping . If the depth control of the engraved gravure is not good during the engraving process, it will also affect the printing quality. Too deep is easy to cause ghosting during the printing process; too shallow will affect the service life of the printing plate.
The surface of the etched layout is a U-shaped groove. As the printing plate wears, the depth of the groove becomes shallow, but the area of ​​the dots does not change, and the amount of inking decreases slowly, and the printing color does not change much, so Its service life is relatively long.
At present, domestic gravure manufacturers all use electro-engraving to make plates, and corrosion gravure is mainly produced by foreign manufacturers, and the price is relatively high.
2. Composition of gravure printing machine
The gravure printing machine is mainly composed of decoiler, guide group, printing group, slitting group and control group. The unwinder is mainly to complete the unwinding of the roll paper under a certain speed and tension, and maintain the corresponding stable state, and at the same time complete the automatic or manual splicing of the roll paper. The main function of the guide group is to ensure that the paper web does not shift laterally during the printing process, and at the same time ensure that the paper tension is stable. The printing group is the main component of the gravure printing machine, and completes the main printing process, including ink supply, printing, drying and so on. The slitting group divides the printed whole printed semi-finished product into slit shaped products. The control group mainly sets the operating parameters and working status of the gravure printing machine, including speed, tension, temperature, and working status of the pressure roller, doctor blade and ink pump.
3. The principle and operation of the winding machine
Uncoiler is mainly composed of clutch, tension roller and tension controller. The three constitute a closed-loop automatic control system, which is used to automatically adjust the speed and tension of the web unwinding.
1. Working principle
Uncoiler is a driven device without power. It mainly adjusts the paper supply according to the needs of the printing unit's paper output (the speed of the paper pulling the roll). The control process of the rotating speed of the roll paper is realized by the clutch and the paper reel. In the past, most of the electromagnetic clutches were used, and currently Dahuachuang uses pneumatic clutches.
In the printing process, the printing speed is not a constant value, sometimes it gradually increases, and sometimes it gradually decreases, so it is necessary to use tension rollers to control the paper supply and tension.
The tension roller swings up and down around a fixed point, and the thrust of the air cylinder is balanced with the tension of the paper to ensure that the tension roller is in a balanced state. The position of the tension roller indicates the tension of the paper and the size of the paper supply. Enter the information of this position into the tension and the paper supply speed. In the printing process, the smaller the distance that the tension roller floats up and down, the more conducive to the stability of the paper tension.
The tension controller is a key component in the tension control system of the decoiler. It mainly completes the processing and analysis of the detection signal and issues the execution command. At present, the MCS-202E controller is mainly used in China, which can indicate the working state of the brake pads used with the clutch paper reel, and set or correct the rubbing position of the tension roller at any time.
2. Operation of the decoiler
According to the requirements of frontier printing, gravure presses generally use ordered roll paper. Due to the different machine models, the outer diameter of the uncoiler paper mandrel varies considerably, generally 3, 6 or 12 inches. Therefore, when ordering roll paper, first consider the outer diameter of the paper roll mandrel. Generally, the inner diameter of the roll paper core is 2 to 5 mm larger than the paper mandrel; second, you should also pay attention to the largest roll paper that can be used by the unwinder. For the outer diameter, check the paper core for deformation during installation. If the deformation is too large, it should be repaired first. After the paper is unfolded and straightened, insert the paper core into the roll paper core, and then check the distance between the ends of the paper core shaft, and try to install the roll paper in the center.
After the roll paper is loaded on the machine, make sure that the horizontal direction is at the same position as the roll paper. If the decoiler is to pick up paper automatically, it should be connected or overlapped according to the requirements of the decoiler. At the time of splicing, the line should be marked at the splicing position first, and then pasted with double-sided and single-sided tape. During the splicing process, it is necessary to ensure that the linear speed of the outer diameter of the two rolls of paper is the same.
If the unwinder is receiving paper manually, cut the upper roll paper after shutdown, adjust the horizontal position of the paper, and stick it directly to the beginning of the new roll paper.
Fourth, the adjustment of the horizontal position of the paper during the printing process
The so-called horizontal adjustment is to adjust the position of the paper along the axial direction of the printing plate. This is very different from the horizontal registration of the pattern during printing. Generally divided into three parts: uncoiler adjustment, adjustment before printing and before slitting.
1. Unwinder adjustment
The installation of the roll paper on the unwinder is generally centered, but sometimes when the printing plate pattern is biased to one side, the horizontal position of the roll paper must be adjusted.
2. Adjustment before printing
This is the main task in horizontal adjustment and is automatically completed by the guidance group. The cylinder drives the transmission roller to swing around a fixed point, so as to adjust the relative position of the transmission roller. The dotted line is the paper width and the arrow is the paper movement direction. In use, first set the lateral position of the photoelectric detection switches on both sides according to the requirements of the printing plate pattern position on the lateral position of the paper. In this way, a closed-loop control system is formed, and the guide controller version controls the lateral position of the paper. The control precision of this system is very high, which can reach (+-) 0.15mm, in addition, it can also be controlled on one side or both sides.
3. Adjust before slitting
In order to ensure that the slitting knife cuts to the horizontal cutting position, the horizontal position of the paper needs to be adjusted. This position generally uses the same closed-loop control system as before printing, and the position of the photodetector needs to be set in advance.
5. Tension control method and principle of gravure printing machine
1. Division of the tension zone
The tension zone of the gravure printing machine can be divided into three zones: unwinding tension zone, printing tension zone and slitting tension zone. The unwinding tension zone includes the tension control between the roll paper mandrel and the paper feed roller in the guide group; the printing tension zone includes the tension control between the paper feed roller in the guide group and the paper output roller in the printing group; The cutting tension zone is between the printing paper exit roller and the slitting tension roller. For a gravure printing machine without a slitting group and only a rewinding group, the slitting tension zone includes the area from the paper force roller to the rewinding shaft.
2. The control principle of the tension zone
The tension control in the unwinding tension zone is mainly performed by the unwinding machine. Tension control is a main function of the decoiler, so the control principle of the tension zone is consistent with the working principle of the decoiler. The closed loop control system consists of a clutch, a tension roller and a tension controller.
The printing tension zone is an important part of the tension control system of the gravure printing machine and the key to ensuring the accuracy of the printing register. The tension control in this tension zone adopts the principle of differential speed. The system adjusts the tension of the paper by controlling the running speed of the paper feed roller and the paper output roller. At present, the paper feeding roller of most gravure printing machines is synchronized with the running speed of the printing press, and the shaft end of the paper output roller is connected to a stepping motor to achieve differential speed control.
Tension control in the slitting tension zone is also very important. If the slitting accuracy cannot be achieved due to unstable tension, waste products will be produced. For this reason, the tension zone generally adopts the same control method as the printing tension zone. The basic speed is the running speed of the printing group and the paper power roller, and the shaft end of the paper roller of the cutting group is connected to the stepping motor to realize differential speed control.
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