Reduce ink fading for more stable printing
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Regardless of the quality of the print now, ink fading is sometimes a problem. Our R&D engineers have considered how to further improve the quality and they have found a solution.
Prior to this, the Roland 700 Ink Supply Unit already had the ability to ensure stable printing. These include the stepless adjustable lateral stroke of the squeezing roller, the squeezing of the offset on the plate roller, and the most important thing is to be able to control the center of the PECOM press to change the ink at an angular increment of 30. The starting angle of the ink of the roller.
A number of tests were performed to determine the influence parameters that minimize ink fading. As a result, it was found that only the inking roller directly contacting the plate roller had a significant influence on the fading of the ink. The improvements made here halve the change in ink density on the sheet, which is very light and almost invisible to the naked eye.
Modern presses, such as the Roland 700, are built for reliable engineering and advanced control and adjustment technology to meet the highest demands. However, the problem of density change on the sheet will occasionally occur in some special cases. To this end, Manroland's R&D engineers were asked to check the parameters that affected the fading of the ink. We have been able to reduce the ink fading from the PECOM press center by changing the starting angle of the ink jet roller, but the purpose of the task is to determine the cause and related factors to provide improved printing results New possibilities.
What is ink fading？
"Ink fading" is an industry term for the variation of ink on the sheet. The term "fading" is used because it usually happens that the ink at the end of the image is less dense than the front end.
What causes the ink to fade?
In the circumferential direction of the plate cylinder, the graphic and non-graphic parts are irregularly distributed. At the same time, the non-printing roller gap also has an effect. Cross-talking affects ink fading.
How the irregularly distributed graphic and non-image portions cause ink fading can be explained as follows: The ink roller of the ink supply device forms an ink reservoir, which is continuously replenished from the ink fountain by the metering member and the inked roller. The relatively high ink storage amount on the ink roller in the ink supply device compensates for the above irregular effect by the ink stroke and the ink width of a certain width.
The ink is transferred to the graphic portion of the plate by the plate roller. Depending on how much the ink reservoir "ink reservoir" is different, more or less ink is transferred to the plate and transferred from the plate to the substrate through the blanket.
Therefore, the following effect is produced: the amount of ink on the ink roller increases each time the non-image area does not acquire ink from the "ink library". When the printing area is colored with ink, the amount of ink on the ink roller is reduced. The plate cylinder gap forms a relatively large non-image area. This results in a "sawtooth" shape in the ink: the ink layer at the beginning of the print is slightly higher and the ink layer at the end of the print is slightly lower.
The design of the cross-talking ink in the ink supply device can smooth the ink distribution characteristics on the ink roller, thereby helping to prevent ghosting. But this necessary and popular feature also has side effects - the ink on the ink affects the fading of the ink. The printer knows this, because adjusting the starting angle of the ink will cause a big change in the degree and development of the ink fading, but the exact cause of this effect has never been clarified before, at least we are fading the ink on the ink. The explanation of the impact is not known.
The influence variables of ink fading include:
The distribution of prints and blanks on the circumference of the drum, the image is another
The quality of the ink used
The range of ink. For example, the ink roller rolls the entire distance of the series
The starting angle of the ink, such as the position of the ink roller relative to the printing cylinder when the lateral movement is started
To prevent or minimize ink fading. Of course we can only change the variable that can be changed and will not cause the quality of other important areas.
What influence variables can be changed?
The image cannot be changed. After all, the press can print difficult jobs without problems.
The possibility of changing the properties of the ink is often limited. Ink characteristics are usually primarily determined by characteristics such as gloss or printing characteristics. It is rarely preferred to choose an ink that has no tendency to fade ink.
The range of ink amplitude is very limited. This is because the ink is implemented in many essential tasks. One of the points is that the metering elements, such as the ink spoon, make the different ink areas laterally uniform (30mm on the Manroland sheetfed offset press width). However, the main task of the ink is to eliminate the fluctuation of the ink supply on the offset roller generated by the image, that is, to produce ghosts. This is the most important task, requiring a certain length of ink stroke, so there is only a small change here.
The biggest possibility of producing effective changes is provided by the starting angle of the ink, which is the best way to eliminate ink fading in the past, and the advantage is that there is no "side effect" worth mentioning here.
Printing test produces new discoveries
Manroland R&D engineers conducted extensive testing to determine the effects of variables that have different effects on ink fading. Evaluation of these printing tests resulted in measurements that minimize ink fading problems.
Related to images, the purpose of the test is to find out the answers to the following questions: To what extent does the ink fade without the roller gap? How much is the image structure detected? The important question about all the squeezing rollers is: How does the cross-inking amplitude affect the fading of the ink? How does the initial angle of the ink affect the fading of the ink?
During the printing test, the following influence parameters were systematically changed:
Plate
Ink
Printing speed
Ink supply device structure
Ink amplitude
Ink start angle
What results can be derived from the print test?
The graphic and non-image parts of the plate and the gap between the rollers can cause the ink density of the ink to be measured to 3% between the front end and the end of the print to fade.
Cross-talking has an effect on ink density changes. The qualitative results of these changes depend only on the starting angle of the ink jet and the structure of the ink supply device. Only two inking rollers that are in contact with the platen roller affect the density due to the respective ink density characteristics, the quality of which depends on the starting angle of the ink. The fading of ink reduced by ink is the sum of these two characteristics. The structure of the printing ink and the inking device is of great significance for the degree of fading of the ink reduced by the cross-inking. On the other hand, the plate and printing speed have only a slight effect on the degree of fading of the ink reduced by the cross-inking.
Improvements in ink supply devices have brought breakthroughs
After thorough research on the variables affecting ink fading, Manroland's R&D engineers successfully reduced the problem of ink fading by simply improving the ink supply.
The FOGRA Institute conducted a formal acceptance test. On October 28 and 29, 1999, the improvement was officially accepted at the FOGRA Institute at the Offenbach plant.
Press: The printing test was carried out on a five-color Roland 700 with a set of glazing units and a lengthening of the delivery table with an improved ink supply. For comparison, the same test was performed on another six-color Roland 700, which was also glazed and had a lengthening tray but no improvement to the ink supply. The beta for testing ink fading is a new beta developed by FOGRA for this purpose.
Substrate: Tested using 135 gsm of coated paper.
Ink: Two inks, black ink, were used with a print density of 2.05-2.2, which is much higher than the 1.80 ± 0.08 given in the FOGRA Guide. Also use a spot color - Blue Reflex Blue, printed at a density of 1.8-1.9, to check for ink fading.
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 was carried out at a speed of 87% of the maximum speed of the Roland 700, for example 13,000 sheets/hour.
Plate: This test uses FOGRA's newly designed plate, which is designed to test ink fading. This is a very demanding printed test version consisting of mesh patches and solid patches. Its content not only detects ink fading, but also detects ghosting.
Ink fading is less than 85% of the calibration error
When the starting angle of the ink is 270, the ink is not struck by the plate or the three ink rollers are strung, and the ink fading is only 1.4% and 1.7%, respectively. The ink fading was reduced by more than 50% compared to the case where the same method was used but the ink supply device was not improved. This means that these values are about 85% lower than the 10% ink fading value specified by FOGRA/BVD.
From all of these experiments, printer inks that improved the ink supply device faded by 30% compared to presses that did not improve the ink supply.
Ghost reduction: This beta also detects ghosts. The improved device will soon become a standard part.