Reduce ink fading for more stable printing 0

Reduce ink fading and achieve more stable printing

no matter how high the printing quality is now, ink fading is sometimes still a problem. Our R & D engineers have considered how to further improve the quality, and they have also found a solution

before that, the Roland 700 ink supply device had the performance to ensure stable printing. It includes the stepless adjustable transverse stroke of the inking roller and the adjustable inking on the "living part" of the plate roller. The most important thing is to change the inking starting angle of the inking roller in an angle increment of 30 from the center of the pecom printer

a large number of tests were carried out to determine the influence parameters to minimize ink fading. The results showed that only the inking roller in direct contact with the plate roller had a significant effect on the ink fading. The improvement made here will halve the change of ink density on the printing sheet, which is very light and almost invisible to the naked eye

modern printing presses, such as Roland 700, have reliable engineering and advanced control and adjustment technology to meet the highest requirements. However, the problem of density change on the printing sheet still occasionally occurs in some special cases. To this end, Manroland's R & D engineers were ordered to check the parameters affecting ink fading. We can reduce this ink fading phenomenon by changing the ink stringing starting point of pecom printing press center, which promises to provide lifelong consulting service and equipment maintenance service for customers. However, the purpose of the task is to determine the causes and related factors, so as to provide

new possibilities for improving printing effect

what is ink fading

"ink fading" is an industry term for the fluctuation of ink on a printing sheet. The word "fade" is used because it usually happens that the ink at the end of the image is less dense than at the front

in the circumferential direction of the plate cylinder, the graphic and non graphic parts are irregularly distributed. At the same time, the non printing drum clearance also has an impact. Horizontal ink string affects ink fading

how the irregularly distributed graphic and non graphic parts cause ink fading can be explained as follows: the ink roller of the ink supply device forms an ink storage, which is continuously supplemented from the ink bucket through the metering parts and the ink roller. In the ink supply device, the relatively high ink storage on the ink roller compensates the above irregular effect through the ink string stroke and a certain width of ink string bandwidth

transfer the ink to the graphic part of the printing plate by the plate ink roller. According to the number of "ink storage" of the ink roller, more or less ink is transferred to the printing plate and transferred from the printing plate to the substrate through blanket

therefore, the following effect occurs: whenever the non graphic area does not obtain ink from the "ink library", the amount of ink on the ink roller increases. When ink is applied to the printing area, the amount of ink on the ink roller decreases. The plate cylinder gap forms a relatively large non graphic area. Therefore, it leads to the "sawtooth" shape in inking: the ink layer at the beginning of the print is slightly higher, while the ink layer at the end of the print is slightly lower

the design of transverse ink string in the ink supply device can make the ink distribution characteristics on the ink roller smooth, so it is helpful to prevent ghosts. But this necessary and popular function also has a side effect - ink string affects ink fading. The printer knows this because adjusting the starting angle of ink string will greatly change the degree and development of ink fading, but the exact reason for this effect has never been clarified before, at least we don't know the explanation of the impact of ink string on ink fading

the influencing variables of ink fading include:

the distribution of printing and blank parts around the drum, the quality of the ink used and the ink range. For example, the entire distance of the ink string movement of the ink string roller to the ink string starting angle. For example, when starting the lateral movement, the position of the ink string roller relative to the pressure printing cylinder is to prevent or minimize the fading of the ink. Of course, we can only change the influencing variables that can be changed, and will not cause the quality of other important areas

which influence variables can be changed

the image cannot be changed. In the final analysis, the printing press can print hard to print live parts without any problem

the possibility of changing ink properties is usually limited. Ink characteristics are usually mainly determined by some characteristics, such as gloss or printing characteristics. Rarely give priority to the choice of ink without ink fading tendency

the range of inking range is very limited. This is because ink string performs many essential tasks. One of them is that the metering elements, such as ink spoon, make different ink areas horizontally uniform (30mm wide on Manroland sheet offset press). However, the main task of inking is to eliminate the ink supply fluctuation on the plate roller generated by the image, that is, ghost. This is the most important task. It requires a certain length of ink string stroke, so there is only a small change here

the greatest possibility of effective change is provided by the starting angle of ink string, which is the best method to eliminate ink fading that has been adopted in the past, and its advantage is that there are no "side effects" worth mentioning here.

printing test has produced new findings

Manroland R & D engineers have conducted a large number of tests to determine the effects of variables that have different effects on ink fading. Evaluation of these printing tests resulted in measurements that minimized ink fading problems

it is related to the image. The purpose of the test is to find out the answers to the following questions: to what extent does the ink fade without roller gap? To what extent is the image structure detected? The important question about all inking rollers is: how does the inking range affect the ink fading? How does the starting angle of ink string affect the fading of ink

during the printing test, the following influencing parameters are systematically changed:

printing plate

ink

printing speed

structure of ink supply device

ink range

ink initial angle

what results can be deduced from the printing test

the graphic and non graphic parts on the printing plate and the roller gap can cause the ink with the measured ink density of 3% from the front end to the end of the printed product to fade

transverse ink string has an effect on the change of ink density. The qualitative results of these changes only depend on the starting angle of ink string and the structure of ink supply device. Only two inking rollers in contact with the plate inking roller affect the density due to their respective ink density characteristics, and their quality depends on the initial angle of inking. Ink fading caused by ink string reduction is the sum of these two characteristics. The structure of printing ink and inking device is of great significance to the degree of ink fading reduced by ink string. On the other hand, the printing plate and printing speed have only a slight effect on the degree of ink fading reduced by ink string

the improvement of ink supply device has brought a breakthrough

after a thorough study of the variables affecting ink fading, Manroland's R & D engineers have successfully reduced the problem of ink fading by simply improving the ink supply device

the Fogra Institute conducted a formal acceptance test. On October 28 and 29, 1999, the improvement was formally accepted by the Fogra Research Institute of Offenbach factory

printing machine: the printing test is carried out on a five-color Roland 700 with a set of polishing unit and an extended paper receiving table. The machine is equipped with an improved ink supply device. For comparison, the same test was carried out on another six color Roland 700, which also has glazing and an extended paper receiving table, but does not improve the ink supply device. The test version for testing ink fading is a new test version specially developed by Fogra for this purpose. It is necessary to protect, debug, maintain and clean these curve instruments and load curve instruments

substrate: test with 135gsm coated paper

ink: use two kinds of ink - black ink, printing density 2 2, much higher than the 1.80 ± 0.08 given in the Fogra guidelines. A spot color, blue reflex blue, is also used, and the printing density is 1 9. To check the fading of ink

production speed: Fogra stipulates that the production speed is 70% of the maximum output speed of the printing press. However, in order to simulate more actual production conditions, the comparative test is carried out at 87% of the maximum speed of Roland 700, such as 13000 sheets/hour

printing plate: this test uses the printing plate newly designed by Fogra, and its design theme is specifically to test the fading of ink. This is a very strict printing test version, which is composed of target color blocks and field color blocks. Its content not only detects ink fading, but also detects ghosting

the ink fading is lower than 85% of the calibration error value

when the starting angle of inking is 270, the ink fading is only 1.4% and 1.7% when the inking rollers do not move in series or the three inking rollers move in series. Compared with the case where the same method is used but the ink supply device is not improved, the ink fading is reduced by more than 50%. This shows that these values are 85% lower than the 10% ink fading value specified in Fogra/BVD, which is on the left and right of the existing land in China

from all these experiments, the ink fading of the printer with improved ink supply device is 30% lower than that of the printer without improved ink supply device

ghost reduction: this beta also detects ghosts. The improved device will soon become a standard part