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In the actual printing production, the viscoelastic effect of rubber will have a direct impact on the dynamic hardness of the rubber roller, the printing pressure and the heat accumulation in the rubber roller.
The heat accumulation in lithographic offset printing is relatively easy to occur, so the rubber material used in lithographic printing should be selected from rubber materials with relatively lagging viscoelasticity. very important.
Also for 25 ℃ rubber, the dynamic pressure and dynamic hardness of the rubber material with larger internal friction during the printing process are larger, and it is easier to accumulate heat under the same printing conditions.
Higher temperature and wider indentation will lead to a non-linear increase in the actual pressure during the printing process, resulting in a sharp increase in heat accumulation in the rubber roller body, which directly leads to damage to the rubber roller. In addition, in different printing methods, the heat accumulation of the rubber roller is also different, such as offset printing, sheet paper offset printing is higher than the roll paper offset printing heat accumulation.
Therefore, even if the glue type that can be used normally at a certain temperature has been selected, the correct indentation width should be used in actual printing (manufacturers generally provide the appropriate indentation requirements for their original rubber rollers in the manual) And take measures to stop the temperature rise. Especially when the machine is idling. Using a special empty car protection paste can get the effect of lowering the temperature.
Selection of rubber roller hardness
Glue type and hardness are very important for different printing methods. Different printing requires rubber rollers to have different mechanical and chemical standards. Taking offset printing as an example, the hardness of the printing rubber roller can reflect the quality of the rubber to a certain extent. Excessive hardness may increase the corrosion resistance, but the ability to carry water and ink decreases, and the loss of the printing machine and the The wear of the PS version of the graphics and text has increased. If the hardness is too low, the service life of the rubber roller may be too short due to poor resistance to compression and corrosion.
The principle of determining the hardness of the printing rubber roller is: on the premise of ensuring good water and ink filling ability, and having sufficient resistance to chemical corrosion and physical action, the hardness of the printing rubber roller should be appropriately reduced.
In actual printing applications, choosing the appropriate glue type can avoid the printing quality failure caused by the rubber roller, so as to ensure that the printing is relatively stable and smooth.
In addition, the rubber rollers used in different places have different performances. The rubber type of the rubber roller used in the automatic cleaning device of the printing machine has a good ability to transfer and self-clean the cleaning agent, and has good corrosion resistance; in addition, there are now decontaminations that specifically solve the problem of paper wool and paper powder glue roll. [next]
Effect of rubber roller pressure on printing
The printing pressure is a comprehensive reflection of the various technical indicators of the rubber roller in the printing process. The printing pressure of the rubber roller is affected by the properties of the rubber roller's hardness, elasticity and surface roughness. For the rubber rollers at different positions on the printing press, the pressure standard It is also established. The pressure adjustment of the rubber roller directly affects the quality of the printed product during printing, and also directly affects other aspects, such as: the life of the rubber roller, the depreciation of the machine and the power consumption.
When the indentation width is 4mm, the rubber roller pressure reaches 18N, and when the width is 6mm, the pressure can reach 63.5N, when the width is 8mm, the pressure reaches 149N. From this we can draw the following conclusions:
1) The indentation width is increased by 50% and the rubber roller pressure is increased by 250%;
2) The indentation width is increased by 100% and the rubber roller pressure is increased by 725%.
Therefore, under the premise of not affecting the printing quality, the rubber roller pressure should be as small as possible. Because in actual operation, the indentation width is the performance of the printing pressure, and the indentation width requirement provided by the manufacturer is the printing pressure standard of the original rubber roller that has been tested. It is best not to change it at will.
For controlling printing costs, the impact of printing pressure is also great. The author has done the following tests:
Offset press: Heidelberg CD102 five-color printing press
Ink: Hanghua standard four-color offset printing ink
Fountain solution: BottcherFount3010
Printing pressure test roller: 60mm diameter inking roller
Printing speed: 10,000 sheets / hour;
Working hours: 24 hours / day
Original ink roller hardness: SH25
Original water roller hardness: SH25
After 2 months, adjust the printing pressure to 50% of the first month. From the results, it can be seen that the printing pressure has a considerable influence on the printing cost during the printing process. [next]
Control range of rubber roller technical indicators
The technical index of the rubber roller must be consistent with the actual production requirements. For this reason, the author conducted a survey on the changes in the technical index of the printing rubber roller in production, and summarized how to adjust the technical parameters of the rubber roller during high-speed printing The operation process of the machine is controlled.
Equipment: Heidelberg CD102
Year of manufacture: 1992
Printing medium: ordinary ink, coated paper
Printed products: beautiful pictures
Machine speed: average 11,000 sheets / hour
Rubber roller: original Boxing rubber roller
Working status: two shifts / day, working 24 hours, the actual normal operating time is about 18 hours / day
Through the technical tracking of the first color group of the machine for 3 months, the hardness, diameter and surface condition of the rubber roller are regularly tested. Under standard cleaning conditions, the surface hardness of the ink roller changes within SH2, the diameter The change is within 2%, and the loss of surface structure is within 10%. In this case, the printing is still relatively smooth, and the original performance can be restored after normal maintenance. [next]
The test results of the actual operation show that, for printing fine products, the acceptable variation range of the technical specifications of the rubber roller is as follows:
1) Hardness index
Standard hardness: SH25 (Heidelberg CD102)
Acceptable hardness change: SH5
If it exceeds this range of hardness change, it may cause printing failure, and the rubber roller is also difficult to maintain and recover.
2) Diameter index
Acceptable diameter change: 5%
If this diameter change is exceeded, it needs to be replaced as soon as possible.
3) Surface roughness
If the wear condition is not considered, the surface roughness of the rubber roller is evaluated only by the degree of glaze on the surface of the rubber roller. When glaze causes a loss of surface area of ​​more than 30%, it will cause serious printing problems. For rubber rollers of good quality, corresponding measures can be taken to recover; when glazing causes the loss of surface area to reach more than 50%, even if the measures are temporarily restored, the rubber roller should be replaced. Pay attention to timely cleaning and maintenance of the rubber roller, which can reduce the change of surface roughness.
During the operation, the characteristics of the printed matter and the changes of the rubber roller should be foreseeable. If there is a change that exceeds the allowable range within 3 months, you should first check whether an inappropriate rubber roller is used (such as ordinary printing for UV printing) Ink roller and water roller), followed by the use of inappropriate ink, fountain solution or cleaning agent.
In the printing process, the causes of rubber roller failure are often multi-faceted, and the factors that affect the normal use and life of the rubber roller are also closely related to the other printing auxiliary equipment used. For example, the use of high-quality printing rubber rollers, but the use of improper paper will exacerbate the generation of crystals on the surface of the rubber rollers, leading to quality problems; long-term use of inks containing aromatic polymers for printing or cleaning with aromatic detergents The roller will damage the rubber roller, which will affect the printing quality. For printing problems caused by chemicals in the printing process, you can seek the help of technical personnel, and experts recommend that printing companies choose the printing equipment that is harmless to the printing rubber roller and has a balance of printability, so that the most resources can be achieved. Optimization.
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