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In the more advanced management abroad, there is a very important link in the control of production costs, which is the control of the so-called press Make-ready time. The three main parts of this so-called preparation time for printing are the settings of the printing press, the correction of the ink color of the printed product, and the time of the position correction. The speed of the work of position correction will directly affect the entire preparation time. The extension of the preparation time will mean the idle of expensive printing equipment, which also means the increase of printing costs. Therefore, it is necessary to discuss how to adjust the plate registration quickly and accurately. In the following we will discuss some of the printing plate position correction operations (hereinafter referred to as proofreading) in preparation for printing and how to effectively improve this work efficiency.
In the proofreading work, two factors are generally considered, one is the positioning of the edition center (graphic part) on the substrate, and the other is the registration between the editions (including the registration between the front and back of the printed product) ). Let's introduce them separately.
The positioning of the printing plate heart on the substrate is the first step in correct proofreading.
The so-called positioning of the plate core is actually positioning the graphics on the printing plate accurately on the substrate, and then meeting the requirements of overprinting and post-press processing. For our more common printed matter, it is to print the part of the graphics and text we need to print on the surface of the substrate, and to have a margin to meet the requirements of the finished product, but also to meet certain special requirements of post-press processing.
· For different printing plates and substrates, the positioning of the plate center should follow the following principles:
2. If the plate core is small and the substrate is large, the plate core should be centered up, down, left and right on the substrate.
3. When the plate center is large, and the area of ​​the substrate appears compact, at least the cutting distance of the edge of the image and text must be ensured (the red arrow in Figure 1 indicates the cutting distance).
4. For the printing plate with corner lines, generally print all four corner lines, and ensure that the size of the mouth is the same. When it is impossible to ensure that all four corner lines are printed, the size of the mouth opening can be appropriately reduced so that all the slightly delayed corner lines are printed without affecting the clearness of the mouth graphics.
5. According to the graphic features of the printed matter and the characteristics of the offset printing process, the head of the printed piece or the positioning edge of the printed sheet should be kept as large as possible, and the foot or the non-positioned edge of the printed sheet should be kept small.
6. Under the premise of ensuring the correct position of the center of the plate, for multi-color prints, it is necessary to ensure that the error between colors and colors does not exceed 0.1 ?, and the front and back overprint generally cannot exceed 0.5 ?.
· In the actual production operation, in addition to strictly working on the work order, we also have the following considerations:
1. Due to cutting reasons, the actual printed paper cannot completely guarantee that the paper edges are neatly trimmed (that is, there is a deviation in the cutting size). Therefore, when correcting the position of the plate, we should move the plate center to the ruled edge according to the degree of error of the paper size.
2. When there is a picture and text at the position of the heart of the printing letterpress, especially the printing of "bleeding", try to move the printing sheet slightly towards the center. This has two advantages. First, it can ensure that the graphics of the mouth part can be printed as much as possible; second, it can reduce the damage to the graphics part of the mouth part due to the serious versioning.
3. For some products with special binding requirements, we must carefully analyze, for example, as shown in Figure 2, the illustration requires that the initial steps of binding be completed after 1 and 2 folding, so that we must put the distance a and the distance b in When the plate is corrected, the consistency is reached, or a is slightly less than b (if a is greater than b, it will cause the left edge to be folded at B when folding twice, which will cause difficulty in binding).
There are many other issues that should be paid attention to in actual printing work, which are not listed here. Above we have briefly introduced a few points that need to be paid attention to when calibrating the printing plate. The position of the plate center on the substrate should be known.
Regarding the overprint between the color of the printing plate and the color, between the front and back, it is actually the same as the positioning operation method of the printing plate on the substrate, only need to drag each color printing plate to the predetermined printing plate positioning position (or use Other methods, as described below) are sufficient.
The operation of the school version seems to be a very simple problem. Many people think that it is only a proficient process. Most operators tend to think from the master. Few people have received more formal training in this area. As a result, there are many ways to operate the position correction. Many people think that no matter what method is used, as long as the position is corrected, in fact, the author believes that there is only one correct correction idea, and the correct idea can be used to achieve fast and accurate To correct the layout, and wrong or irregular calibration methods will often be different in work, affecting work efficiency and even causing unnecessary quality problems. Let's talk about the operation method of plate correction.
** We often use to adjust the position of the printing plate (actually the relative position between the printing plate and the substrate):
1. Top page operation. That is to adjust the axial position of the printing plate through the top plate screws at both ends of the printing plate clamp.
2. Pull version operation. Adjust the circumferential position of the printing plate through the plate-pulling screw (also called the plate screw) on the plate holder.
4. Front regulation. By changing the front and rear position of the front gauge block, the circumferential position (relative to the substrate) of all the color group plates on the printing press can be adjusted. The range of this adjustment is generally very small, should not exceed 0.3 ?, and the author's experience in the work does not advocate adjusting the relative position of the printing plate by adjusting the front rule.
5. Adjustment of adjusting mechanism. This type of adjustment mechanism is generally available on printing machines with more than two colors. It has the characteristics of simple, rapid, accurate and intuitive adjustment, but in general, the adjustment range is small (the axial direction is generally ± 0.4; the circumferential direction is ± 0.2) When the plate error is large, the top plate and the pull plate must be adjusted. The plate adjustment mechanism has axial and circumferential adjustment mechanisms, and modern high-speed multi-color machines will also have plate skew adjustment mechanisms (however, the adjustment range of this type of adjustment mechanism is very small, which can only reach 0.1?). The above operations are mainly carried out by manual wheel or console.
6. Borrow the roller. By changing the relative positions of the printing plate cylinder and the transmission gear at the cylinder end, the circumferential position of the printing plate is adjusted in parallel. When the circumferential position of the printing plate needs to change a lot, and the plate pulling mechanism is helpless, or the adjustment by the plate pulling mechanism is more time-consuming and troublesome, the roller is usually used.
For general printed products, the top plate and the plate screws on the plate cylinder are usually adjusted first (coarse adjustment) during the trial printing. When the plate is within the range that can be controlled by the plate adjustment device, the adjustment is used. Fine adjustment (fine adjustment) of the version device.
** Generally there are the following steps for proofreading work:
1. First, adjust the circumferential position of the graphics on the substrate through the side rule. Generally, this work is adjusted according to the size of the substrate after the previous batch of printing is finished, and before the next batch of printing is started. Yes, there is no need to move in the process of proofreading, but if it involves simultaneous translation of the axial positions of all printing plates on the printing press, it is also very convenient and quick to use the side gauge to adjust.
2. Trial printing operation.
3. For printing plates with relatively different circumferential positions, perform the operation of borrowing the cylinder (the scale on the surface of the cylinder). According to the results of the trial printing, according to the rule line on the printing job, the first proofreading adjustment is performed on the printing plate. This adjustment is generally done by means of pulling and topping. Of course, the error is relatively small and can be adjusted directly through the adjustment mechanism.
4. Repeat the trial printing, if the position is still very different, repeat the third step.
5. Until when the error between the printing plates is relatively small (reaching the adjustment range of the adjustment mechanism), the printing plate is accurately adjusted by the adjustment mechanism.
6. When the positioning of the printing plate on the printed product and the positioning between the plates reach the overprinting precision required for printing, you can perform color correction, or start printing after color correction.
** In the proofing operation mentioned above, the time-consuming coarse adjustment of the position of the printing plate in steps 3 and 4 is as follows. We will use two-color overprinting as an example to illustrate this process:
The following three figures are some typical examples in the layout calibration (the red and black borders in the figure are for the analysis of the imaginary lines drawn):
(The above three pictures are all below the image, and the black version is set to the correct position for the convenience of discussion)
The characteristic of Figure A is that the red printing plate and the black printing plate are parallel and misaligned. This situation is the simplest to correct. The difference between the printing plate seen on the gauge line and the actual length of the required plate is the same. Only need to loosen the plate screw at the trailing edge of the red printing plate, and pull the printing plate to the gripper length by the corresponding length. Finally, re-tighten all the tensioning screws at the drag, and then tighten the screw in the middle of the gripper. (Another situation is that the printing plates are axially and parallelly misaligned. As in the case of A, as long as the top plate screws at the corresponding positions are loosened, the top plate screws can be pushed up according to the distance seen on the plate).
Note: 1. When pulling the screw at the loose trailing tip, the length of the pulling plate is longer than the actual need, and it should be as loose as possible to avoid the friction between the printing plate and the printing plate cylinder hindering the pulling of the plate, resulting in the printing plate Stretching deformation; 2. When the distance between the two colors is relatively large, after loosening the drag screw, it should be at the left and right ends of the printing plate (for the axial misalignment is the grip and drag) every one millimeter apart Pull the plates alternately (that is, you cannot pull one end and then pull the other end) to avoid large slippage of the printing plate on the plate cylinder. 3. When the axial parallel adjustment and the circumferential parallel adjustment of the printing plate need to be performed simultaneously, the top plate should be pulled first and then the version. This is a principle that the author adheres to in his work. This can effectively avoid making parallel plates There is a skew. 4. The tension of each printing plate must be consistent. 5. In the plate-pulling operations mentioned above and below, the plate-pulling screws are plate tensioning screws on both sides of the plate clamp, not the center tensioning screw.
The characteristic of figure B is that, except for the corner line at the mouth opening on the left is basically registered, the rest of the gauge lines have large or small deviations. We can imagine an axis or a center of circle. When correcting the position, let the printing plate rotate along this axis. Assuming that the screw at the mouth in the lower left corner is this axis, loosen all the pulls at the drag of the red version. For the screw (the rightmost one can be loose), first drag the top screw on the left end to a corresponding distance to the right, then pull the screw on the edge of the gripper the corresponding distance, and finally tighten the dragged screw and the middle of the gripper like A Screws.
Note: 1. Be sure to push the axial position of the corresponding position first, and then adjust the circumferential direction, because the printing plate is slightly clamped and the gripper is clamped by the plate clamp, and it is generally not deformed. When the printing plate is topped and then the drawing operation is performed, the circumferential direction of the printing plate will not be easily deformed. 2. The distance of the top plate cannot be based on the difference between the angles. Because, as we just mentioned, the correction process is like the printing plate is rotating around a center, and the distance between the screw and the corner of the top plate is different from the center of the circle, so the difference in distance on the corner cannot be directly passed The top screws were corrected at the same distance. Coincidentally, the circumferential error of the printing plate at the corresponding position is exactly similar to the length of the required top. Generally, we need to pull as much as we need in the work. 3. The greater the degree of skewness of the printing plate, the length when the printing plate is pulled (top) should be larger than the error shown on the middle (angle) line (generally this increased range should be continuously obtained by accumulating experience ). 4. When the circumferential error of the printing plate is less than 0.5 ?, do not use the top plate, you can directly pull the plate at the relative position and loosen the situation. Pull down the plate, because the degree of skew of the plate is not very large, pull directly You can straighten the skewed printing plate. In this case, the above-mentioned deformation of the printing plate does not occur.
The C picture is slightly more complicated, and all the gauge lines are misaligned, but we can also think of the red version as a misalignment that occurs when rotating counterclockwise. After analysis, we found that in the process of correction, the left end of the red needs to be pulled slightly, and the right end of the red needs to be pulled toward the mouth. According to our analysis in B, when the printing plate is seriously skewed, it should be topped first and then pulled. The specific steps are to loosen all the plate tension screws except the screws that need to be plated (dragging the platen screws at the left end and the right end of the gripper). After the top plate is grabbed and dragged in an appropriate amount, pull the plate. When the plate pulling is finished, all other screws on the printing plate should be tightened in time.
This is a troublesome situation in the registration of the printing plate, especially when the skewness of the printing plate is relatively large. The main reason is that the amount of the top plate is not easy to determine. How much is the mouth? How much is the delay? Let ’s remember one of the following formulas: dragging the top version amount + gripping top version amount = gripping mouth versioning amount + dragging slightly versioning amount Generally, the versioning amount is well determined, as long as the rules of printing The degree of skewness of the online comprehensive printing plate (here you need to have some experience) can be determined. And the top page volume? Although we cannot directly determine the amount of the top page, we can initially estimate the proportion of left and right skew. Relying on this proportional relationship, we can easily calculate the amount of the top version. This process may seem complicated. In fact, after mastering proficiency, all the errors of the four printing plates can be calculated within one or two minutes by mental arithmetic.
The above-mentioned situations are just a few typical examples of position correction in our daily work. In fact, in daily work, we often encounter the situation where these situations are mixed together. We are working As long as we carefully analyze the amount of parallel misalignment in the printing plate (this amount can be directly seen from the printed product), how much is the amount of skew (the judgment is often important at this time), Then it is enough to combine the amount of the top version and the amount of the pull version, but pay attention to the principle of first pulling and then pulling.
Pay attention to one issue in the adjustment of A, B, and C, that is, do not use brute force when tightening the screws, and the force of tensioning the printing plate should be the same (each screw of a printing plate should be the same, each color printing plate The tension of the screws should be the same as each other).
After the initial adjustment mentioned above is completed, that is to say, after the trial printing, the graphic overprint error on the printed product is already less than the range that can be adjusted by the plate adjustment mechanism, we can use the plate adjustment mechanism to make accurate adjustments. . (Actually, in many domestic old-fashioned printing presses, there is no version adjustment mechanism or it is damaged, so it is further adjusted by manually pulling and topping). This kind of adjustment is generally simple and intuitive, so I won't introduce too much.
3. Some tips for speeding up the proofreading work:
1. If there is no change in the printing life of the printing plant you are in (for example, many manufacturers mainly based on printing books and periodicals, the type of printing is very monotonous throughout the year), you can draw a line on the roller of the plate cylinder as a standard, each time printing Draw an extension line on the corner of the mouth of the printing plate to follow the online version drawn on the roller pillow. In this way, the error of the good version is basically no more than 0.5? If the printing plate is positive, it can be directly corrected by an automatic or manual plate adjustment mechanism and the overprinting work can be completed.
2. When loading the printing plate, pay attention to loosen the tension screw at the mouth of the mouth by two to three wrenches (according to the experience when tightening the plate), fix the printing plate to the plate clamp, and tighten the screw of the printing plate slightly. After that, tighten the screw at the mouth of the printing plate (it happens to tighten the initial loosening back). This can effectively prevent the printing plate from moving to the gripper mouth by about 0.5 to 1 after each edition, and when the printing plate is revised, the printing plate should be pulled back in a slightly dragging direction.
3. Before the operation of the upper plate, pay attention to center the plate clamp at the mouth of the printing plate, and adjust the top plate screw on the side of the mouth of the plate to 0.3? Away from the side inner wall of the drum with a plug (also can be Rotate the way); when printing, center the printing plate on the plate holder at the mouth (the models with positioning pins can be directly positioned, and the models without positioning pins can be drawn by drawing the rule line at the center of the mouth) Reverse the extension line so that the extension line is aligned with the notch on the plate holder or the center line that was found and marked in advance). The above operations can effectively control the error of the initial position of the printing plate when it is on the machine, and can basically ensure that the top plate operation is not performed at the gripper position. When the printing plate is skewed, it is sufficient to perform the top plate at a slight drag.
4. When the printing plates of all color groups on the machine need to be adjusted synchronously, sometimes it can be achieved by adjusting the front and back positions of the front gauge. However, we do not recommend this on old-fashioned old-fashioned printing machines, because the pre-regulation adjustment on old-fashioned domestic-made printing machines is often very troublesome, it seems to save trouble, but it is actually a waste of time. If in some cases it is necessary to use the pre-regulation for adjustment, make a record and adjust it back to the original position in time after the end of this printing to avoid confusion in the working position.
5. When the gripper on the printing plate changes, the gripper screw needs to be pre-adjusted before the release (if this printout needs to be larger than the previous one, just put the gripper on the gripper before the release. The screw shall be adjusted accordingly (that is, the pre-adjustment of the clamping screw shall be performed accordingly)).
6. When encountering the situation that the drag has been registered and the gripper has not been put on (or the gripper has been put on and the trailing tip has not been put on), you can try to set it by appropriately tightening the tension screws at the corresponding position quasi. Another way is to change the thickness of the pad in the printing plate properly. The specific method I mentioned in a previous article "Factors Affecting the Overprint of Printed Products" will not be repeated here.
The above practices are just some small experiences in our work. We often pay attention to thinking and summarizing in our work. We will find it very helpful to improve our work efficiency.
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