Ink is the basic element for expressing printed images. The thickness of the ink directly affects the gradation, color, and clarity of the image. Therefore, it is very important to control the transfer of ink. Generally speaking, the total ink transfer rate of offset printing is relatively low, about 38%. Factors such as the suitability of paper and ink, the suitability of printing plates and blankets, the balance of water and ink, printing plates, and printing pressure all affect the amount and uniformity of ink transfer. From the point of view of the performance of the printing press, the printing speed can be easily adjusted within a relatively large range, but the printing pressure cannot automatically follow the change according to a certain functional relationship with the speed change. Therefore, in actual production, it is always used to fix the printing pressure first, and then adjust the amount of ink to adapt to the change of printing speed. Studying the effect of printing speed on ink transfer has certain guiding significance for the adjustment of water ink volume, printing speed, printing pressure, etc. in production. 1. Experiment In order to study the effect of printing speed on ink transfer volume and ink uniformity, the following test strips were designed: a 40cm × 1cm field, placed at the grip area, used to measure the density of the field and the uniformity of the ink distribution in the axis . Two 20-step ladders with an increment of 5% are placed on both sides of the image to measure the increase of the dots at all levels and calculate the relative contrast. The dots used are circular amplitude modulation dots, and the number of screen lines is l75LPl. In the experiment, the SBK-B iodine gallium lamp plate-making machine is used for plate printing. The lamp power is 3500 (TH4200) W. Manual development. The levels on the scale are clear. Measured with DigiDens T6CR color reflection densitometer, the level errors at all levels are controlled within ± 1%. The paper is 80g / m2 double-sided coated paper, printed by WIN500 monochrome offset printing machine, the inking system is a ten-roller zigzag arrangement, and the inking parameters are: accumulation coefficient Kj = 3.41; uniform ink coefficient Ky = 2.49; inking coefficient Kg = 0.92. Observe the reflection of the printing plate during printing, and control the amount of water based on the dark gray. The control of printing pressure is to judge the pressure between the three cylinders by adjusting the wheelbase of the cylinder and observing the width of the ink mark on the rubber cylinder. When the pressure is normal, the width of the ink mark of the rubber cylinder should be 4 ± 0.5mm, and stabilize the pressure during the printing process . To measure the effect of printing speed on ink transfer, print at 1, 5, 9 (× 1000RPH) respectively. Experiment l Ink supply control: ①Adjust the ink fountain key to control the ink output, set the number of teeth of the ink fountain roller to l, start the printing with 1000RPH to the solid density of 1.75, print 100 sheets after stabilizing, from 100 samples Randomly select 10 for location analysis. ② Print at 5000RPH for 10 minutes, take samples every 2 minutes, a total of 10 sheets. ③ Print at 9000RPH for 10 minutes, take samples every 2 minutes, and take a total of 10 sheets. Experiment 2 Ink supply control: ①Adjust the ink fountain keys to control the ink output, set the number of teeth of the ink fountain roller to 5, start the printing with 9000RPH to the solid density of l.7, print 100 sheets after stabilizing, from 100 samples Randomly select 10 pieces for measurement and analysis. ②Print at 5000RPH for 10 minutes, take samples every 2 minutes, take a total of 10 sheets. ③ Print at 1000RPH for 10 minutes, take samples every 2 minutes, a total of 10 sheets. The taken samples were measured with the DigiDens T6CR color reflection densitometer to measure the corresponding solid density and dot value, and the printing relative contrast K value was calculated. When calculating the K value, the average solid density and the average density value of the dots of 75% were used. 2. Experimental analysis 1. Field density analysis The solid color patch is actually a layer of ink film with a certain thickness. The solid density is determined by the nature of the ink pigments and binders to absorb light. It is also affected by the thickness of the ink layer and the state of the ink film. In printing, once the type of ink is determined, the factors that affect the solid density of the ink are the thickness of the ink film and the state of the conjunctiva. By controlling the thickness of the ink film during printing, the reproduction quality of the printed matter is controlled. Measure the density value of the 40cm × lcm field test strip at the mouth of the sample, take a test point every 2cm, measure 10 samples and take the average value in Table 1. In the experiment, the pressure between the rollers of the inking system of the printing press was generated by the weight of the rollers. The pressure between the rollers could not be adjusted with the change of printing speed. When the printing speed is increased, the pressure between the rollers is basically constant, and the time between the rollers and the rollers is reduced, which leads to a reduction in the ink transfer rate and a decrease in ink leveling performance. According to Table 1, the solid density values ​​at three printing speeds of 1000 RPH, 5000 RPH, and 9000 RPH are compared. The dispersion is different, and the standard deviations are 0.018, 0.032, and 0.045, respectively. It shows that printing speed not only affects the transfer rate of ink, but also significantly affects the performance of ink distribution. The higher the printing speed, the worse the ink leveling performance. The inking system of this experimental printer is a typical short ink path, and the ink leveling coefficient Ky = 2.49. Compared with large offset presses, due to the short ink path, the ink leveling performance is not ideal, and it is not suitable to use a higher printing speed . From the data in Table 1, the situation is similar in the case of large ink supply. Some studies also show that even if the flat printing machine is in a stable state, there will be a density change of about 0.02; the difference in the structure of the ink transfer device will cause a density change of up to about 0.12 between the gripper and the trailing tip. By comparing the density values ​​at all levels of the three printing speeds in Figure 1, under the same ink supply, the faster the printing speed, the lower the actual density of the printed product. As the printing speed increases, the contact time between the printing plate and the blanket, and the blanket and the paper decreases accordingly. The amount of ink transferred to the surface of the substrate will also decrease, and the density will decrease, resulting in the ink color of the imprint. shallow. Figure 2 shows that the normal ink supply at 9000 RPH printing speed is significantly larger for the 1000 RPH printing speed. The ink supply amount set to obtain a density value of 1.68 at the printing speed of 9000RPH. At the low printing speed of 1000RPH, the corresponding solid density reached 2.13, which resulted in the merge of the medium and dark tone levels. At the beginning, when printing speed is 1000RPH, the merger starts at 40% of the dots. It is obvious that the printing speed has a huge influence on the ink transfer. 2. Network analysis Offset printing is based on dots as the basic elements that constitute an image, and changes in dots will inevitably affect changes in tone, color, and image clarity on the printed matter. The dot increase value refers to the difference between the dot area of ​​a certain part of the printed matter and the dot area on the corresponding color separation sheet. Due to the double-reflection effect and the ink squeeze spreading caused by the pressure, the dot increase is inevitable. However, the dot increase value should be controlled within a certain range. Once this range is exceeded, there will be a serious decline in print quality, such as tone loss, density increase, color change, etc. This increase is abnormal. According to the 50% network expansion value specified in GB7705-87, fine products should be in the range of 8% to 20%, and general products should be in the range of 10% to 25%. From Figure 3 and Figure 4, the printing speed has a significant effect on the increase of the dot value. Under high-speed printing, the amount of ink transfer is small, and the contact time between the inking roller and the printing plate, the printing plate and the blanket, and the blanket and the paper are also reduced, and the degree of ink spreading is also small. The overall result is an increase in dots The value is small, especially in the mid-high light area, very obvious. The dot increase value at high printing speed and low printing speed shown in Figure 4 is as high as 50% at 50%, which obviously does not meet the print quality requirements. Because the level range of the original is generally larger than the range that can be copied by printing, in theory, the larger the ink transfer amount, the thicker the ink layer, and the greater the density, the printed matter can also obtain a larger level range. However, the increased ink transfer volume will inevitably cause the dot increase value to be too large, the gradation merge, the tone, color and image clarity will change. In severe cases, the back will be dirty, through-printing, paste, high-printing The situation of flying ink at high speed seriously affects the printing quality. In production, by controlling the printing contrast K value, the field density and dot increase value can be controlled more reasonably. Table 2 shows the printing contrast K value in six cases in two experiments. It can be seen that the printing speed affects the printing contrast K value by affecting the amount of ink transfer. The data of experiment 1 shows that as the printing speed increases, the amount of ink transfer decreases and the printing contrast decreases. In this case, the ink supply can be increased to increase the printing contrast, but the ink leveling performance of the machine should be paid close attention to to avoid poor ink leveling at high speeds. The data of Experiment 2 shows that under the condition of large ink volume and low printing speed, the dark tone levels in the printed matter have been seriously merged. 3. Conclusion Printing speed has a significant effect on ink transfer. In actual production, the ink supply and printing speed should be reasonably determined according to the ink delivery performance of the printing press. During the printing process, it is not appropriate to frequently change the printing speed, nor to adjust other printing conditions randomly, such as ink supply, water supply, printing pressure, etc. Higher printing speed can greatly improve the production efficiency, but it will also reduce the quality uniformity of the printed products, and will also introduce some unstable factors, such as paper feeding faults, positioning faults, reduced overprint accuracy, flying ink, and paper pulling Wait. At the same time, we should pay attention to the ink delivery parameters of the printer. Although the ink distribution parameters obtained by various models are very similar, due to the large difference in the length of the ink path, the ink distribution effect is not the same. In order to obtain stable ink transfer, the supply Ink volume, printing speed and printing machine ink infusion performance parameters are organically combined. 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