Introduction to gravure printing technology
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First, the main difference between engraving gravure and corrosion intaglio
According to the manufacturing process of the gravure printing plate, the printing plate can be divided into a corroded gravure of the engraved gravure.
1. Processing of engraved gravure and corrosion intaglio
The engraving gravure is processed by an electric engraving machine. The needles of different angles are used to form V-shaped grooves of different depths after being punched on the copper-plated gravure cylinder, and the surface of the gravure cylinder is plated with a wear-resistant chrome layer. , you can make a printed version on the machine. During the printing process, the ink is transferred to the printing material by these V-shaped grooves.
Corrosion intaglio is an image-forming technique that produces an image on the surface of a copper-plated gravure cylinder that is etched to form a U-shaped groove on the surface of the cylinder, which is then chrome-plated and surface-polished.
2. Comparison of engraved gravure and corrosion intaglio
The performance of the engraved gravure and the corrosion intaglio is not much different, but the service life of the two is quite different.
After the V-shaped groove on the surface of the engraved plate is worn, the depth of the groove becomes shallow. As the width of the bottom of the V-shaped groove becomes narrower, the area of the dot becomes smaller, the amount of ink in the groove gradually decreases, and the color of the ink rapidly becomes shallow, causing the plate to be scrapped. . Engraving gravure in the engraving process if the depth control is not good, it will also affect the printing quality, too deep in the printing process is likely to cause ghosting; too shallow will affect the life of the printing plate.
The surface of the corroded plate is a U-shaped groove. As the plate wears, the depth of the groove becomes shallow, but the area of the dot does not change, and the amount of ink reduction is relatively slow, and the printing color does not change much, so Its service life is relatively long.
At present, domestic gravure manufacturers use electro-engraving plates, corrosion gravure is mainly produced by foreign manufacturers, and the price is relatively high.
Second, the composition of the gravure printing machine
The gravure printing machine is mainly composed of an uncoiler, a guiding group, a printing group, a cutting group and a control group. The uncoiler mainly completes the unfolding of the web under certain speed and tension conditions, and maintains a corresponding stable state, and at the same time completes the automatic or manual splicing of the web. The main function of the guiding group is to ensure that the paper web is not laterally offset during the printing process, and that the tension of the paper is stable. The printing group is the main component of the gravure printing machine, and the main processes of printing are completed, including ink supply, printing, drying and the like. The slitting group divides the printed whole printed semi-finished product into small pieces of molded products. The control group mainly sets the operating parameters and working state of the gravure press, including speed, tension, temperature, and working status of the pressure roller, the doctor blade and the ink pump.
Third, the principle and operation of the machine
The uncoiler is mainly composed of a clutch, a tension roller and a tension controller. The three components form a closed-loop automatic control system that automatically adjusts the speed and tension of the web unwinding.
1, working principle
The uncoiler is a non-powered driven device, which adjusts the supply of paper mainly according to the need of the printing unit to feed the paper (the paper pulls the web rotation speed). The control of the web rotation speed is achieved by a clutch and a paper reel. In the past, electromagnetic clutches were mostly used, and currently large and colorful pneumatic clutches are used.
In the printing process, the printing speed is not a constant value, sometimes it is gradually increased, and sometimes it is gradually decreasing, so it is necessary to use a tension roller to control the supply amount and tension of the paper.
The tension roller swings up and down around the fixed point, and the thrust of the cylinder is balanced with the pulling force of the paper to ensure that the tension roller is in equilibrium. The position where the tension roller is located indicates the tension of the paper and the amount of paper supply, and the information of the position is input to the tension and the paper supply speed. During the printing process, the smaller the distance the tension roller floats up and down, the more favorable the stability of the paper tension.
The tension controller is a key component in the uncoiler tension control system. It mainly completes the processing, analysis and execution of the detection signal. At present, the MCS-202E controller is mainly used in China. The controller can indicate the working state of the brake pads with the clutch paper reel, and set or correct the position of the tension roller at any time.
2, the operation of the unwinder
According to the requirements of border printing, gravure printing machines generally use ordering webs. Due to the different machine models, the outer diameter of the uncoiler's paper core shaft is quite different, generally 3, 6 or 12 inches. Therefore, when ordering the web, the outer diameter of the core of the paper roll should be considered first. Generally, the inner diameter of the core of the web is required to be 2~5 mm larger than the core of the paper. Secondly, the maximum web that can be used by the unwinder should be noted. The outer diameter should be checked for deformation of the paper core during installation. If the deformation is too large, it should be repaired first. After the paper is unfolded and squared, insert the core into the core of the web, then check the distance between the ends of the core, and try to center the web.
After the web is on the machine, make sure that it is in the same position as the top roll. If the uncoiler is to automatically take the paper, it should be docked or lapped according to the requirements of the uncoiler. When splicing, first scribe at the splicing position, and then paste it with double-sided, single-sided tape. During the splicing process, it is necessary to ensure that the outer diameters of the two rolls of paper are consistent.
If the uncoiler is manually picking up the paper, the roll paper is cut off after the machine is stopped, and the lateral position of the paper is adjusted, and it is directly attached to the beginning of the new web.
Fourth, the adjustment of the horizontal position of the paper during the printing process
The so-called lateral adjustment is to adjust the position of the paper along the axial direction of the printing plate. This is quite different from the lateral registration of the pattern at the time of printing. Generally divided into three parts: uncoiler adjustment, pre-printing and pre-cutting adjustment.
Unwinder adjustment
The installation of the web on the uncoiler is generally centered, but sometimes the plate pattern must be adjusted to the side, and the lateral position of the web must be adjusted. This adjustment is generally a one-time manual adjustment.
2. Pre-printing adjustment
This is the main work in the horizontal adjustment and is done automatically by the steering group. The cylinder pushes the drive roller to swing around a fixed point, thereby adjusting the relative position of the drive roller, the dotted 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 detecting switches on both sides is first set according to the requirements of the position of the printing plate on the lateral position of the paper. This forms a closed loop control system that controls the lateral position of the paper. The system has high control accuracy and can reach (+-) 0.15 mm. In addition, it can be controlled on one side or two sides.
3. Adjust before cutting
In order to ensure that the slitting knife is cut to the transverse tangent position, the lateral 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 preset.
Fifth, tension control method and principle of gravure printing machine
Division of tension zone
The tension zone of the gravure printing machine can be divided into three zones: an unwinding tension zone, a printing tension zone and a slitting tension zone. The unwinding tension zone includes tension control between the web core of the web and the sheet feeding roller in the guiding group; the printing tension zone includes tension control between the sheet feeding roller in the guiding group and the sheeting roller in the printing group; The printing group takes out the paper roll to the slitting tension roller as a slitting tension zone. For gravure presses that do not have a slitting group and only a rewinding group, the slitting tension zone includes the area from the paper force roller to the multiple spool.
2. The control principle of the tension zone
The tension control of the unwinding tension zone is mainly done by the uncoiler. Tension control is a main function of the uncoiler, so the control principle of the tension zone is consistent with the working principle of the uncoiler. The clutch, tension roller and tension controller form a closed-loop control system.
The printing tension zone is an important part of the gravure press tension control system and is the key to ensuring the accuracy of printing registration. The tension control of the tension zone adopts the differential principle, and 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 feed roller of most gravure printing machines is synchronized with the running speed of the printing machine, and the paper roller end of the paper is connected with the stepping motor to realize differential control.
The tension control in the slitting tension zone is also important. If the slitting accuracy is not achieved due to the instability of the tension, waste 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 force roller, and the shaft end of the paper roll of the slitting group is connected with the stepping motor to realize the differential control.