Analysis of the important factors affecting the performance of the inking unit - ink roller arrangement
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The inking unit, as an important mechanism of the printing press, together with the other three printing elements (printing plates, originals, and printing materials) determines the quality of the printed matter. There is no reasonable inking device to ensure that it is impossible to print beautiful prints. The arrangement of the ink rollers is an important factor affecting the performance of the inking unit. Therefore, we analyze and study the ink roller arrangement of the offset printing machine, and provide a good foundation for printing the ideal printed matter by understanding and mastering the ink conveying performance of the printing machine.
First, the role and composition of the inking unit
The inking device quickly smoothes the strip ink output from the ink fountain roller from both the circumferential direction and the axial direction, so that the ink transmitted to the printing plate is uniform and appropriate. Therefore, whether the ink color of the printed matter is uniform and the level is clear has an important relationship. Generally, the inking unit of the offset printing machine is divided into three parts: the ink supply part, the ink distribution part, and the ink application part. As shown in Figure 1.
Figure 1 Composition of the inking unit
The ink supply portion functions to store ink and supply ink to the ink-dispensing portion, and the main components include an ink fountain roller (also referred to as an ink discharge roller), an ink fountain, and an ink transfer roller. The ink fountain roller rotates intermittently or continuously at a slow speed, and the ink transfer roller swings back and forth, and the strip-shaped ink layer is transmitted to the high-speed rotating ink-distributing roller to quickly smooth the strip-shaped ink layer. The amount of ink supplied can be adjusted according to the requirements of the printing process. Adjusting the height or the rotation speed of the ink fountain roller can change the total ink supply amount, adjusting the ink fountain adjusting screw to change the gap between the ink fountain blade and the ink fountain roller, and supplying ink layers of different thicknesses to complete the normal ink supply to the printing plate.
The function of the ink-dispensing portion is to quickly smooth the strip ink, transfer it to the ink portion and store a portion of the ink. The main components of the ink-dispensing section include the leveling roller, the heavy roller, and the tandem roller, which include the most ink rollers. A group of ink rollers with the squeezing roller 2 as the core is mainly used for the ink layer, and also has the function of storing ink. A group of ink rollers with the squeezing roller 3 as the core further smooth the ink, and finally the ink is supplied to the four priming rollers. In addition, this group of ink rollers can not only smooth the ink, but also store and recover excess ink. The rotation of the squeezing roller is driven by the shaft end gear, and there is also an axial movement driven by the oscillating rod mechanism; the squeezing roller and the heavy roller are driven by the surface friction force.
The effect of the inking portion is to apply ink to the portion of the printing plate. The inking portion is composed of an inking roller (also referred to as a plate roller), and the inking roller has 3-6, generally four. The inking portion transfers a very thin ink layer (about 6-10 microns) that has been evenly distributed to the printing plate. The circumferential speed of the inking roller during the transfer is equal to the circumferential linear velocity of the plate cylinder. Since the inking roller directly contacts the printing plate, the accuracy requirement is the highest compared to other ink rollers.
The ink roller should be in contact with the acidic dampening liquid and ink during printing. Therefore, the ink roller material should have corrosion resistance, oil resistance and good lipophilicity to ensure that the surface can uniformly adsorb the ink. In order to achieve such an effect, rubber is generally applied to the surface of the soft roller, and the surface of the hard roller is chrome-plated or sprayed with a hard plastic, nylon.
Second, the performance evaluation indicators of the inking unit
The performance evaluation indicators of the inking unit include static indicators and dynamic indicators. The static indicators include: ink coefficient, ink uniform coefficient, accumulation coefficient, ink coefficient, ink rate and so on.
The inking coefficient Kg indicates the degree of uniformity of the ink on the printing plate. It is measured by the ratio of the sum of the areas of all the inking rollers to the area of the printing plate. The ink coefficient Kg value depends on the machine type, use and process requirements, etc., and should generally be greater than 1. The larger the Kg value is, the better the ink effect is in a certain range. Sheet-fed offset presses typically have a Kg value of 1-1.5. Book and newspaper web offset presses have Kg values between 0.65-1.2. In order to increase the Kg value generally increases the number of inking rollers or increases the diameter of the inking roller, first consider increasing the number of inking rollers. The sheet-fed offset presses have a total of 4 inking rollers and 5 indentations, while commercial web-fed offset printing rollers have a maximum of 3 inking rollers.
The uniform ink coefficient Ky represents the degree to which the ink is evenly distributed in the ink-dispensing portion, and is expressed by the ratio of the sum of the area of all the leveling rollers to the area of the printing plate. In general, the larger the uniform ink coefficient, the better, depending on the performance and use of the machine. The sheet-fed offset printing machine has a uniform ink coefficient of 4-5.5, the number of ink rollers is 15-25, and the number of ink rollers of the web offset printing machine is 7-15.
The accumulation factor Kj represents the ability to accumulate ink in the inking system. The ratio of the sum of the area of the entire leveling roller and the inking roller to the area of the printing plate is measured. The larger the accumulation coefficient Kj is, the larger the ink accumulation amount of the inking system is, and the ink color stability is good. However, as the value of Kj increases, the inking system becomes less and less sensitive to changes in the amount of ink supplied. The process of adjusting the transition of the ink color is lengthened, and the transient response becomes slower. Therefore, using a computer to control the ink color system, the Kj value should not be too large.
The number of ink lines N reflects the number of times the ink rolls and rolls between the ink rollers during the transfer and thinning process, also called the number of contact lines. It is indicated by N that the larger the value of N, the better the ink leveling effect.
The inking rate of the inking roller represents the percentage of the amount of ink supplied to the printing plate by the inking roller to the total amount of ink on the printing plate. The performance of the inking performance is ultimately determined by the uniformity of the ink applied on the printing plate, and the amount of ink per inking roller directly affects the uniformity of the ink layer on the printing plate. According to the direction in which the plate cylinder rotates, the inking rate of the first two inking rollers is generally about 80%, and the inking rate of the latter two inking rollers is about 20%.
Dynamic indicators include system response time, system settling time, and ink layer thickness uniformity. The system response time is the time elapsed from the change in the amount of ink delivered from the input section of the inking system to the change in the thickness of the ink layer of the substrate at the output of the system. In general, the ink system of Changmo Road has a long response time, and the response time of the ink system of the short ink path is short. In the printing process, it is always desirable that the stabilization time is as short as possible, because the shorter the transition time, the more time is saved, the resources are saved, and the waste of the paper is reduced. The consistency of the thickness of the ink layer refers to the closeness of the thickness of the ink layer on the substrate to the thickness of the target ink layer, and is expressed by the standard deviation of the two. The smaller the standard deviation, the smaller the deviation between the thickness of the ink layer and the thickness of the target ink layer, and the better the consistency.
Third, the arrangement of the ink roller
According to the arrangement of the ink rollers before the lower ink rollers, single, double, and multi-channel ink transfer is performed. Figure 2 shows the arrangement of the ink rollers of the German Kenigbauer offset press. It adopts the method of single-pass ink transfer, and the ink is transferred to the lower ink-distributing roller through the intermediate ink roller and the uniform roller. The two-way ink transfer is divided into left and right passes to the lower ink roller after the ink reaches the middle ink roller. Figure 3 shows the Roland ROLAD 700 series press. The multi-pass ink transfer is carried out after the ink passes through the intermediate ink roller, and then passes through a plurality of ink transfer rollers to the lower ink roller. In Figure 4, the Heidelberg S series and other printing machines, Komori L-432 offset printing machine, and Mitsubishi F series printing all adopt multi-channel ink transmission.
Figure 2 single-channel ink transfer Figure 3 two-way ink transfer
(a) (b) (c)
Figure 4 multi-channel ink transmission
According to the arrangement position of the ink roller, it is divided into a symmetric type and an asymmetric type. The ink roller of a lithographic printing machine belongs to a symmetrical arrangement. As shown in FIG. 5, the ink is divided into two symmetrical paths by a middle squeezing roller, and then supplied to the ink roller by a squeezing roller. Most presses use an asymmetric ink roller arrangement, such as the ink path system of the printer shown in Figures 2, 3, and 4. In Figure 4 (a), on the Heidelberg S series printing press, the ink is divided into two ink supply by the intermediate ink roller and then passes through a plurality of ink distribution rollers, and the right channel is supplied to a lower ink roller, and the left channel is supplied with two ink rollers. Ink roller.
Figure 5 symmetric
According to the characteristics of ink transfer and uniform ink, it is divided into multi-roll type and ink storage roller type. The multi-roll type inking unit is characterized in that before the ink reaches the inking roller, it is uniformly inked by a series of soft and hard ink rollers of different diameters. The ink storage roller type inking unit uses a large metal roller in the middle of the inking system, surrounded by a series of soft ink rollers to store, transfer and level the ink. The data of the typical offset printing machine ink roller at home and abroad (Table 1-4) and the ink roller arrangement diagram of the typical offset printing machine inking system at home and abroad (Fig. 6-11) are shown below.
Hardness unit: Shore degree; Diameter unit: mm
Table 1 PD4880-01 four-color offset printing machine wet mixing system each roller data
Table 2 Data of each roller of the wetting and leveling system on the JS2102 double-sided offset printing machine
Table 3 Data of each roller of the wetting and leveling system of JS2102 type double-sided offset printing machine
Table 4 Data of each roller of Heidelberg S series wetting and leveling system
Arrangement of ink roller arrangement of inking system of typical offset printing machine at home and abroad
6 Heidelberg Speedmaster offset roller arrangement 7 J2101 offset printer roller arrangement
8 J4102 offset printing machine ink roller arrangement 9 JS2102 double-sided offset printing machine ink roller arrangement
10 PZ4880 type four-color offset printing machine ink roller arrangement 11 Roland 700 offset printing machine ink roller arrangement
In order to better transfer ink and evenly ink, the ink roller of the inking unit should be used in combination with a soft leveling roller and a hard ink roller so that the ink rollers are in good contact with each other under a certain pressure. The arrangement of the ink roller is advantageous for the reasonable distribution of the amount of ink in the ink roller. Most presses supply the printing ink from the first set of inking rollers, and the second group acts as a leveling ink in addition to supplying a small amount of ink to the printing plate. That is to say, when arranging the arrangement of the ink rollers, it is necessary to satisfy the principle of light weight before and after the ink supply amount. Modern printers do not use a symmetrical ink roller arrangement. In some printers in which the ink rollers are arranged symmetrically, in order to improve the ink supply distribution of the inking roller, a heavy roller is added after the intermediate ink roller, that is, when the flow is split, to increase the pressure between the ink rollers, thereby injecting the ink into the heavy roller. The roller increases the amount of ink that is split. At the same time, when the contact pressure between the ink roller and the printing plate is adjusted, the contact pressure between the inking roller of the weighted roller and the printing plate is greater than the pressure between the inking roller of the unweighting roller and the printing plate, and thus The inking rate of the inking roller with heavy rollers is increased. The arrangement of the ink roller should also consider the overall layout of the printing machine and the number of ink rollers. The overall layout can make reasonable use of space, make the machine compact, and facilitate the installation and disassembly of the ink roller. The more the number of ink rollers, the better the ink distribution performance, but at the same time, the response time of the system becomes longer and the dynamic performance deteriorates. Therefore, static performance and dynamic performance should be considered together to determine the number of ink rollers required.
Fourth, the influence of ink roller arrangement on the performance of ink transmission
(a) (b)
Figure 12 Effect of the arrangement of the ink rollers on the ink distribution
In the inking system, the arrangement of the ink rollers is slightly changed, the transfer route of the ink between the ink rollers will change, the amount of ink on each ink roller changes, and the ink transfer rate of each ink roller to the printing plate also changes. . Figure 12 is a two ink delivery system in which the number of ink rollers is the same and the arrangement is slightly different. Both inking systems are ideal ink delivery systems, that is, all the ink rollers in the ink delivery system can be well wetted by the ink and have no absorption to the ink; in the process of inking, the ink removing roller and the transfer roller In addition, the surface speed of all the ink rollers is equal to the surface speed of the plate cylinder surface. The ink is separately attached to the two ink rollers by the gap between the ink rollers in the case of forced compression, and the ink is transferred and distributed. In this ideal case, in (a), the ink transfer rates of the inkjet rollers are both 41.67%. The inking rate of the 3, 4 inking rollers is 8.33%. In (b), the amount of ink delivered to the printing plates by the four inking rollers is equal, and the inking rate is 25%. Therefore, it can be known that the distribution of the ink conveyed from the ink fountain on the respective ink rollers in the transport system and the ink transport rate of each of the ink jet rollers have a certain relationship with the arrangement pattern of the ink rollers. In the inking system of Fig. 12(a), the first two inking rollers have a high ink transfer rate of 83.34%, which mainly serves to supply ink to the printing plate; the latter two inking rollers have a low ink filling rate of only 16.66%, mainly The role of playing the ink layer on the plate. In the (b) inking system, the four inking rollers have the same inking rate, which supplies both the printing plate and the ink layer on the printing plate. The two functions are equally important. Obviously, using (b) the ink roller arrangement of the inking system, the ink is transferred to the printing plate, the ink marks on the printing plate, and the ink layer is uneven. Such an arrangement of the ink rollers is not in the design of the offset printing machine. Take it.
The arrangement of the ink rollers also affects the inking performance by affecting the length of the ink path. In the case of ensuring various performance indexes of the inking unit, a certain number of ink rollers adopt different arrangement forms, which directly affects the ink path and the ink injecting rate, and relates to the uniformity of printing to the printing plate and the quality of the printing. In the printing process, the ink path is too long, the difference in the thickness of the ink layer on the ink roller between the transfer roller and the inking roller is large, the ink is slowed down, and an excessive amount of ink is accumulated on the upper ink roller. When the paper feeding fails or other reasons require the roller to be pressed off, the ink roller is idling away from the printing plate, the ink roller thickness difference is reduced and tends to be uniform, and the thickness of the ink roller is increased compared with the normal printing; when the printing is performed again If the printing and printing part of the printing plate is too much ink, it will cause the paste or the ink to be too dark. The ink path is too short, the ink speed is fast, and the ink roller can not evenly mix the ink axially in time, which inevitably causes the ink color transmitted to the image to be uneven. However, the speed of the ink is fast, which can reduce the undesirable phenomenon caused by the long ink retention time. Therefore, the arrangement of the ink rollers affects the length of the ink path and further affects the inking performance.