Talk about the three flats, three small and five Qin in the offset printing
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Offset printing is not really difficult, as long as it can do three, three, and five.
Sanping is: flat roller, flat ink roller, flat water roller; three small is small pressure, small water volume, small amount of ink; five diligence refers to diligently looking at the layout of water, diligently mixing ink, diligent ink, washing rubber , printing plates, diligence on proofs.
With the increase in the experience of operating machines, it has become very important to gradually discover these three "essentials". For the operation of analog control printing quality (human eyes) until now, it is still very important!
Below I will discuss some of the "essentials" of these three offsets in combination with their own views.
First, the so-called three flat: refers to the flat roller, the ink roller is flat, the water roller is flat. According to the requirements, according to the data, the roller lining and the surface of the water roller are flat and the pressure between them is uniform. The center distance of the three rollers meets the standard and remains relatively constant during the production process.
·The flattening of the drum: The flattening of the drum means that the blanket is flat, the printing plate is flat, and the stamping is flat. The three flats seem to be simple, and the actual production is really complete, which is really not easy.
A. The surface of the drum. Due to the long-term normal and abnormal use of the machine, wear and corrosion will inevitably occur on the surface of the three rollers, so that the surface of the roller is naturally difficult to ensure "flat". This phenomenon is particularly prone to occur in early cast iron drums. On the surface, or long-term printing of small-format paper, suddenly changed to large-format printing. This requires our operators to have a good grasp of the situation of the equipment, and can take timely measures when the situation (paper format, etc.) changes, this measure is mainly to remedy the drum depression (such as glue, stickers The more accurate this offset, the flatter the drum, and the flatter the ink that is transferred to the substrate during printing (only relative to the transfer of the three rollers).
B. Blankets and plates and their pads. When installing plates, blankets and their liners, be sure to operate them in strict accordance with the operation requirements to prevent the blankets from being slightly parallel, not parallel to the body and facing outwards, and more preventive. Foreign objects and pads are wrinkled. For the old used blanket, the surface is inevitably uneven, the older generation of printing workers summed up a whole set of rubber pad method: 1. full version; 2. test pressure; 3. draw map; 4. pad rubber. These methods seem to be a bit outdated, but today it seems to be worthwhile to save on production costs while ensuring print quality.
C. Ensure that the machine's inspection mechanism is working properly and safely. This is an important premise to prevent the occurrence of rolling blankets or rollers. In the normal production process, it is necessary to check whether the double-sheet detection, empty sheet and paper advance detection are normal. For the photoelectric detection head, always wipe the photoelectric head. Paper wool and dust and so on. The ink path is thoroughly cleaned regularly and on time to prevent the dry ink stick from falling into the drum area and crushing the rubber. Operate the equipment in strict accordance with the safe operation of the equipment to prevent foreign matter from entering the drum. Avoid using strong alkali and strong acid when cleaning the rollers and machines to avoid corrosion of the drum surface.
The three points mentioned above are actually some extensions to the flattening of the rollers. These are the preconditions for ensuring normal and reasonable imprinting, especially for the uniform and reasonable transfer of the ink film on the surface of the drum.
·Ink roller flat, water roller flat: mainly refers to water, ink roller and roller, the pressure between the roller and the plate is moderate and uniform, so as to ensure uniform and stable water and ink transport to the layout, in order to Achieve a good ink and water balance. The water roller flat and the ink roller have the following necessity.
A. Protect the plate. When the pressure is too large, the sand on the surface of the printing plate is greatly worn, resulting in a decrease in the printing durability of the printing plate.
B. Reasonable transfer of ink. The pressure between the water roller and the ink roller and between the printing plates are uniform and reasonable, which is an important prerequisite for ensuring ink balance and uniformity of the ink film. This seems to be simple. In fact, it requires a lot of experience to achieve it. However, when the process of "flat" of the ink roller is mastered, it is a solid step for printing a good printed product.
Second, the realization of three small: the minimum pressure, the smallest amount of water, the smallest amount of ink, these three are the experience of the printing workers in the years of practice. Let me talk about my own opinion below.
• Minimal pressure: refers to the use of minimal printing pressure while ensuring proper ink transfer, which is somewhat close to the concept of ideal pressure advocated in many printed textbooks. The direct benefit of this is that the line speed difference between the rollers is reduced. Since the pressure uses the minimum printing pressure, the deformation of the dots due to the pressure is also controlled to a minimum. The indirect benefit is to reduce the wear of the printing plate, improve the printing durability of the printing plate, and also reduce the wear of the printing mechanism and improve the service life of the printing machine.
• Minimal water volume: As mentioned in previous articles, water is actually undesirable in printing, but due to the nature of lithographic printing, water must be relied upon as a medium for selective adsorption of the surface of the printing plate. Due to the presence of water, a certain degree of ink emulsification is inevitable, which leads to problems such as a decrease in ink color saturation and a slow drying of the ink. The presence of water inevitably causes deformation of the substrate, and the substrate surface is resistant. The decrease in the strength of the sheet causes the overprinting problem and the surface of the paper to be detached. Therefore, in printing, we advocate the use of as little water as possible while ensuring that the blanks are clean and the dots are clean.
• Minimum ink volume: This is the experience of the older generation of press operators, but it is only considered for the operation itself. As the amount of ink is reduced, the operation will be made easier, which will be directly from The ink is dried and the amount of water is controlled. However, as a result of the new problem, and the amount of ink is reduced, the thickness of the ink film is also thinned at the same time, that is, the density range on the printed matter is also limited. With the continuous improvement of the ink path on the printing equipment and the continuous improvement of the ink printing adaptability, the author believes that this article should be changed to the maximum amount of ink. The maximum amount of ink should of course be based on the correct ink color. When you increase it, it will make the dot more full, and the density of the ink will also increase at the same time. Of course, this cannot be done at the expense of drying the ink and spreading the dots.
Third, to the five Qin: diligently look at the layout of the water; diligently stir the ink; diligent ink bucket; diligently wash the rubber, printing plate; diligent on the proofs. The five-division operation should be carried out as a standardized operation throughout the entire production process. Below we specifically talk about the importance and necessity of Wuqin for offset printing.
· Look at the moisture of the layout: After the test, there is a better adjustment to the moisture of the plate. It does not mean that the moisture on the plate will be stable. This is because the amount of water on the plate will be directly affected by many factors, such as the degree of printing plate (the printing plate is in the process of printing, the sand on the surface is worn, the water storage capacity is decreasing), printing The speed of the machine; in addition, sometimes when some conditions change, we must make some necessary adjustments to the amount of water, such as when the viscosity of the ink, the fluidity changes; when the temperature of the shop changes; and so many conditions like this occur Changes must constantly adjust the amount of water accordingly. Therefore, in the printing process, do not think that the water volume is set once and for all, and the amount of water in the layout is necessary.
·Stirring ink: Offset ink is a kind of colloid, which also has some characteristics of colloid. Among them, thixotropic is one of the more important characteristics of ink. The specific meaning is that the ink is under the action of external force stirring and shearing. Will increase, when the external force disappears, its fluidity will decrease until it reaches a certain value. Knowing the nature of the ink, it is not difficult to understand why the ink is required to be stirred during the printing process. It is required that the ink in the ink fountain always guarantees a certain degree of fluidity during the printing process. When the flow is increased, the ink transfer effect in the printing process is improved, and no more flow aid is added to the ink. In addition to improving the fluidity of the ink, mixing the ink can also prevent the ink from sticking in the ink fountain and prevent more impurities from accumulating in the ink fountain roller and the ink knife gap. A lot of modern printing equipment in modern countries have more perfect considerations for this, such as adding automatic ink-filling and ink-splitting mechanism on the ink fountain .
· Diligent ink fountain: In the printing process, the ink fountain should be cleaned regularly, so that there is no dry matter such as ink and ink in the ink fountain. Otherwise, the ink is crusted during the printing process, and the paper is depilated and lost. Impurities will block the gap of the ink fountain, causing the ink to be out of order and causing ink failure.
· Washing rubber and printing plates frequently: cleaning the surface of the rubber and printing plates frequently, and removing the ink and paper wool from the surface, which not only ensures the good transfer of the ink, but also plays a very important role in producing clear and lustrous dots. It is more important for large areas of flat screen or in the field, and can extend the life of plates and blankets.
· Diligence on the proofs: In the printing process, due to factors such as water and ink pressure are not static, there are many factors that often change, so in the printing, the printing samples should be taken frequently, compared with the printed samples, according to the changes. Find a new ink balance. In this way, the printed matter can be as close as possible to the print.
Sanping, Sanxiao and Wuqin are the concise experience of printing workers for many years. Today, they still have an irreplaceable role and significance in printing production. Next, we will be carefully experienced by our readers in the actual work.