One, overprint system optimization settings
With the rapid development of electronic technology and computer technology, the combination of modern gravure printing machine and computer technology has become increasingly closer. Especially the modern advanced high-speed gravure printing machine, its overprinting system mostly adopts the microcomputer to carry on the control processing, through the signal feedback to adjust the overprint deviation of the printing image.
1. According to the shape of the printing pattern to set the position of the color registration
Overprinting identification color code is generally used a trapezoidal pattern, in order to register the system can be more effective to identify, when setting the position of the color code, should try to avoid similar patterns in the printing pattern, that is: Do not let the printing pattern Similar shapes and color patches appear adjacent to the same scanning area. Otherwise, the operator may easily cause misidentification of the waveform on the display screen, causing a series of unnecessary troubles to the register adjustment, resulting in unnecessary Waste, when the situation is serious, can also cause the overprint system to be unable to work stably.
2. According to different types of manuscripts for overprinting reference selection optimization
Two representative manuscripts are discussed separately below.
The first type of manuscript: the main body of the printing is lines and solids. The feature of this type of manuscript lies in the fact that its graphics and texts are mainly based on the field and lines. The overprint relationship between images and images is simple and the requirements are not high. This type of manuscript can be divided into two categories:
1 There is an overprint relationship between each spot color pattern and a certain color plate pattern. The color code setting of this printing piece can be that each color plate is only overprinted with a key color plate, that is, the reference color code of each color plateset is Key version color standard.
2 There are higher requirements for overprinting between the two field editions (A and B) and overprinting with the key color version (C edition), while other color editions (D edition and E edition) are only related to key color editions. (C version) There is an overprint relationship, and there is no overprint relationship with the first two field versions, then the overprint relationship for such manuscripts can be set as: A → B → C; D → C; F → C (“A → B "On behalf of "A" with reference to "B" overprint, and so on).
The second type of manuscript: originals where images, lines, and solids coexist. The feature of this kind of manuscript is that the image part is rich in levels, and the color reproduction is formed by superimposing the colors of a plurality of color groups. There is a high-precision overprint relationship between the images and the images. If the overlay accuracy is not enough, the image part will be There are a series of overprint issues such as unclear and ghosting. Suppose that the image part is formed by superimposing the patterns printed on the spot colors A, B, C, and D. E is the line text version, and there is no obvious overprint relationship with the image part. The F version is the field reference version. There are overprint relations between other editions, then the overprint relationship between them can be set to A→B→C→D→F; E→F. The color sequence of A, B, C, D four-color version can be interchanged according to the specific situation.
Second, the gravure tension control
Paper or film in the pre-press unwinding process, multi-color printing process or post-press collection process need to maintain a certain tension, tension is too easy to produce longitudinal wrinkles, tension is too small and easy to produce lateral wrinkles. In short, the tension fluctuations will affect the accuracy of overprinting, thus affecting the stability of the quality of printed products, so the tension must be controlled.
1. Printing machine tension control
(1) Tension control from the feed shaft to the feed pulling roller
Due to the action of the pulling roller, the printing material is pulled out of the feeding shaft at a certain speed and tension and sent to the printing section. The tension of this part is greater than the tension of the printing section. The tension is usually controlled by a brake attached to the feeding shaft. . As we all know, the winding diameter of the work gradually becomes smaller. In recent years, due to the increase in speed and the use of diversified materials, the coil diameter has changed greatly.
Therefore, manual mechanical brakes used in the past have not been able to obtain high quality prints. Therefore, the use of automatic control methods, especially the use of tension measurement data management becomes a necessary practice. Its detection methods are spring-rolled roller type and micro-displacement type detection. Mechanical brakes have been used since very early, and they are inexpensive, but they are inaccurate. So gradually there are other forms. Magnetic powder brakes use magnetic powder as a friction medium to generate a braking force through an electric current. Because of its good linearity in torque-current characteristics, they are widely used. Although pneumatic brakes are used in many printing machines, they are gradually replaced by large-capacity magnetic powder brakes because of the non-linear torque characteristics and large wear factors. The tension of the feed is determined by the following factors: 1 Stretch change due to uneven thickness; 2 Material slipping and even being caught slow; 3 Roll not installed, material and shaft eccentric; 4 Turning device in rotation The resulting change in peripheral speed; 5 the reaction force of the press roller and knife when the paper is fed; 6 The roundness of each roller is not enough.
Most of these changes took place within a short period of time and were transmitted to the printing department as tension changes. From the mechanical structure point of view, it must be noted that the inertia of the guide roller and the manufacturing error between the feed shaft and the traction roller are the causes of the increase in tension, and in particular, the low tension of several kilograms or less must not be ignored.
(2) Tension change and control between traction roller and plate roller (traction part)
In the gravure printing machine, the traction roller and the first plate roller are usually provided with a peripheral speed synchronization mechanism. This is different from the feed situation, the diameter does not change, so use other principles to control the tension.
The printed material has the same elasticity and plasticity as a general object, and the printing process is performed within the elastic limit. Therefore, the tension must be controlled according to the law of elasticity. This is to understand the characteristics of different materials. In order to obtain the same elongation in use, the tension can be determined by various ratios of the width and thickness of the material.
There are two ways to get the proper tension:
a. Change the diameter of the pressure roller slightly; correct the number of revolutions of the pressure roller. The time required for the printed material to reach the set tension from the tension-free state is a one-time delay response of the distance between the press rolls and the speed reduction value as a time constant. This type is usually called a stretch control. For the basic form of the gravure printing machine, tension is applied between the feeding roller and the printing roller, between each printing roller, between the printing roller and the receiving drawing roller, based on this principle.
b. There is also a method of controlling the tension by roll-type roller. The principle is that the tension changes with the change of the weight and the change of the position of the weight. No matter under what circumstances, the pendulum roller has the effect of absorbing the tension change, and the pendulum roller generally adopts manufacturing error. Small, low-inertia, light-weight, and large-diameter rollers (such as hollow aluminum tubes) are usually used to remove the short-period tension variations between the feed and the take-up roll, which stabilizes small changes in tension. This method can also reduce the damage of the paper.