The so-called difficult faults of offset printing refer to the unconventional problems that occur in printing practice, and some have become the difficulties of printing quality. Difficult problems of offset printing are various and can happen at any time. How to eliminate the difficult problems of offset printing has become a major problem in the actual production of printing.
1. Troubleshooting is a manifestation of the ability of the printing operator
In the process of printing production, it is inevitable that difficult faults occur in the year, and finding and eliminating faults is a manifestation of the ability of the printing operator. To effectively eliminate the difficult problems of offset printing, the operator should have the following technical qualities.
1. Master the basic knowledge of printing machinery
First of all, to master the basic knowledge of printing machinery, to be able to understand the structure of various types of offset printing machines, and to master the adjustment methods of its key parts, and to judge the mechanical failure is basically accurate.
Whether it is a domestic offset press or an imported high-end offset press, the basic principles are the same, but there are some differences in the specific operating methods. In general, for single-sheet offset presses, the adjustment focus should be on the roller gripper , The paper gripper, the front rule, the side rule and other components themselves and their handover relationship, at the same time, we must pay special attention to the adjustment of the three major pressures (roller pressure, plate pressure, printing pressure), for the web offset press, except for the roller In addition to the adjustment of ink roller pressure and printing pressure, it is also important to focus on tension control and adjustment of the folding structure.
2. To understand the performance of printing materials and master the main points of printing process
Paper, ink, Fountain solution, printing plate, blanket, water roller, ink roller, etc. These printing materials are called the original materials of the offset printing process. During production, you must be familiar with the basic composition, performance, and changes in the printing process of these printed materials.
In the printing process, it is necessary to grasp the variables in offset printing, that is, the environmental temperature and humidity, the thickness of the ink layer, the amount of fountain solution, the accumulation of paper wool and ink residue on the blanket, and so on. Ink and ink balance and reasonable lining run through the practice of modern offset printing. Whether it can be mastered and put into practice is a criterion for judging the level of senior technicians, and it is also a key element for improving the quality of printing. In addition, the printing process failures mostly originate from the process operation of the use of printed materials. Therefore, the safe and standardized operation method can also reflect the technical quality of senior technicians, and has a demonstration role for novices who are new to the offset press.
3. Familiar with the application of offset digital technology
While tracking new technologies, new materials, and new processes, printing operators must be particularly familiar with the application of computers in printing machines, as well as advanced digital technologies such as CIP3 / CIP4, PPF / JDF workflows and job formats, to further adapt and support Lay the foundation for the integration of printing.
2. Trouble shooting steps and methods
If there are any difficult faults in the offset production process, senior technicians are duty-bound and should actively face them to help the machine staff solve them as soon as possible. Generally, the steps and methods to eliminate the faults of offset printing are: observation, questioning, judgment and elimination.
1. Observed
Observation is a comprehensive and accurate understanding of the time, location and manifestation of difficult faults. For example, once irregular registration is not allowed, for sheet-fed offset printing presses, you should observe the paper feeding, side rules, front rules, paper gripper movement and machine parts wear, and observe the quality of the substrate. For web offset presses, the focus should be on observing the tension of the tape and the operating conditions of the floating roller.
2. question
Questioning is a very valuable quality of thinking, which is the basis for analyzing failures. When some failures occur, do not rush to make conclusions. Carefully analyze whether these failures belong to pre-press platemaking or printing processes, whether they are process failures or machinery. The fault, whether it is a common fault or a difficult mine barrier, and why such a fault occurs, etc. This questioning power should be possessed by every printing operator.
3. Judgment
Observation can inspire thinking, and judgment is the determination of thinking, and there are only two possibilities for determination, and it is negative if it is not certain. In the process of offset printing, there may be some kind of difficult problems, after observation, questioning, judgment is very important. First of all, the judgment must be true. Only on the basis of truth, the judgment is meaningful. Second, the judgment must be timely and accurate, so as to reduce unnecessary auxiliary time. Of course, these are based on observation and related knowledge and operating experience. .
4. exclude
Troubleshooting is a fairly meticulous job, not only with strong basic skills, but also with meticulousness and patience, and must never be sloppy. If it is a mechanical failure, you must follow the order of disassembly and assembly of the machine, and take the method of touching and checking; if it is a process failure, you must follow the screening method to "hand to illness", if it is a failure caused by raw materials, The raw materials should be replaced decisively.
Three, troubleshooting examples
In the printing process, there are many kinds of difficult faults, there are many very typical difficult faults, it seems very simple, but it is not easy to handle, the following examples of ghost faults show how to solve the difficult faults.
1. Common ghost failure categories
The so-called ghost image is a phantom that appears in continuous printing. It is a vertical stripe or graphic that is perpendicular to the axis of the cylinder and has different shades of ink. Most of them occur on screen-printed products with solid ground, and the ghost image is pressed on the printed product. The performance on the picture is divided into positive ghosts (see Figure 1) and negative ghosts (see Figure 2); according to the cause of production, there are ghost effects caused by technology and ghosts caused by machinery. From this point of view, the positive and negative ghost images are the appearance on the printed matter, and the reason for this appearance is from the process or mechanical problems, which conforms to the general law of offset printing failure.
2. Ghost fault identification
For the identification of faults, flexible use of observation, questioning, and judgment requires high technical skills and operating skills. For example, after taking a printed product and observing it, it is found that the positive image of the printed product itself is behind the circumference, forming a negative shadow that is relatively lighter than the circumference. This is the positive ghost image; for example, the pattern of the printed product itself is on its circumference. , To form a darker image shadow relative to the surrounding, it must be a negative image ghost.
The ghost image is mainly caused by the lower ink rollers. The lower ink rollers in the offset press mainly smooth out and replenish the uneven ink layer remaining on the surface of the ink rollers, but in fact, this ability to replenish the ink It is limited, but the human eye usually cannot recognize the slight unevenness of the ink layer. If the layout of the plate or the process is not adjusted properly, and the ink roller cannot supplement the uneven ink layer on the ink roller, ghosts may occur.
Positive ghosting is due to the inking roller inking the bar, the ink layer in this area is not sufficiently replenished and evenly distributed, so it will appear on the graphics that require a large amount of ink below, while the negative ghost The shadow is because when the inking roller is inking the printing plate, the blank part is not filled with sufficient ink, which increases the amount of ink in the corresponding part of the inking roller, and the inking roller fails to distribute these ink levels to other areas. The relatively thick ink layer on the roller will be transferred to the printing plate in the next inking roller cycle, which will make the printing plate have too much ink, thus causing negative ghost images.
3. Color shadow troubleshooting
When the judgment of ghosts is accurate, it is necessary to take targeted processing solutions to eliminate ghost failures as soon as possible.
(1) If it is determined that the positive or negative ghost is caused by improper design before printing, the troubleshooting method is as follows: â‘ The layout must be designed before printing to ensure that the ink roller has sufficient ink time; â‘¡ Use pictures as much as possible. Try to avoid showing large borders or large real maps and texts on the printing plate; â‘¢ For fine work, balance the density difference between the picture and the real part on the Internet to make the entire layout as uniform as possible.
(2) For the exquisite prints with high quality requirements, the density difference between the online layout and the field part is small, and ghost images will still appear. For this, the troubleshooting methods are as follows: â‘ Use high-end offset printing presses; â‘¡Adjust the string Ink roller tandem momentum, pay attention to make the starting position of the tandem momentum in the cylinder neutral position; â‘¢ fine-tune the inking roller on the offset press.
(3) If the printing layout cannot be changed, resulting in "ink-out ghost", the troubleshooting method should be: â‘ replace the ink roller to process the surface of the ink roller, and adjust the pressure of the ink roller; â‘¡ adjust to increase the ink amount of the ink-lacking part ; â‘¢ Replace the invalid blanket; â‘£ Avoid using transparent ink.
(4) If ghosts appear and disappear, the troubleshooting methods are as follows: ①control the "water and ink balance", and strictly prevent "water and ink"; ② ensure that the paper is conveyed normally during printing, and prevent "beating out"; ③ Tighten the blanket; ④ If printing a spot color patch, increase the color density slightly to reduce the thickness of the ink layer. ⑤Adjust the ink system to control the accumulation coefficient.
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