Talking about the application of viscoelasticity of rubber roller

In the actual printing production, the viscoelastic effect of rubber has 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. Therefore, the rubber roller material used in lithographic printing should use a rubber material with a relatively laggy viscoelasticity. This controls the dimensional stability of the rubber roller and the aging of the rubber and prevents excessive printing pressure. very important.

The same 25 °C rubber, the internal friction of a large rubber material in the printing process of dynamic pressure and dynamic hardness are relatively large, and under the same printing conditions is relatively easy to accumulate heat.

Higher temperatures and wider indentations 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 roller body, directly leading to damage to the rubber roller. In addition, there are differences in the thermal accumulation of the rubber roller in different printing methods. For example, offset printing, sheet-fed offset printing has a higher heat accumulation than that of web offset printing.

Therefore, even if a gel type that can be used normally at a certain temperature has been selected, the correct indentation width should be used in actual printing (manufacturers will generally provide the appropriate indentation requirements of their original rubber rollers in the instructions). And take measures to prevent warming. Especially when the machine is idle. Use a special empty car protection cream to reduce the temperature.

Rubber roller hardness selection

Gel type and hardness are very important for different printing methods. Different printing requirements have different mechanical standards and chemical standards. Taking offset printing as an example, the hardness of the printing roller can reflect the quality of the rubber to a certain extent. If the hardness is too high, the anti-corrosion capability may be enhanced, but the ability to carry water and ink is reduced, and the loss of the printing machine and The wear of PS version graphics increases. If the hardness is too low, the life of the rubber roller may be too short due to poor compressive and corrosion resistance.

The principle of determining the hardness of the printing roller is: under the premise of ensuring good watering and inking ability and sufficient resistance to chemical corrosion and physical action, the hardness of the printing roller should be appropriately reduced.

In practical printing applications, the use of an 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 properties. The rubber type of the rubber roller used in the automatic cleaning device of the printing press has good cleaning agent transmission and self-cleaning ability, and has good anti-corrosion performance; in addition, there is now a special solution to the problem of paper dust and paper powder. glue roll.

The effect of rubber roller pressure on printing

Rubber roller technical indicator control range

The technical indicators of the rubber roller must be consistent with the requirements of actual production. For this reason, the author specifically conducted research on changes in the technical indicators of the printing roller in production, and summarized how to adjust the technical parameters of the roller in the high-speed printing process. The operation of the machine is controlled.

Equipment: Heidelberg CD102

Year of manufacture: 1992

Print media: ordinary ink, coated paper

Printed products: exquisite album

Machine speed: an average of 11,000 sheets/hour

Cots: Original Star Rubber Roller

Work status: two shifts/day, work 24 hours, actual normal operation time is about 18 hours/day

Through the 3-month technical tracking of the first color group of the machine, the hardness, diameter, and surface state of the rubber roller are periodically tested. Under the condition of standard cleaning, the surface hardness of the roller is within SH2, and the diameter Within 2%, the loss of the surface structure is within 10%. In this case, the printing is still carried out smoothly, and the original performance can be restored after normal maintenance.

The actual operating test results show that the range of acceptable changes of technical indicators for printing fine products and rubber rollers 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 it exceeds this diameter change, it needs to be replaced as soon as possible.

3) Surface roughness

If the wear is not considered, the surface roughness of the rubber roller is only evaluated by the degree of glaze on the surface of the rubber roller. When the surface area is lost by more than 30% due to glaze, severe printing problems may occur. For a good quality rubber roller, appropriate measures can be taken to restore it; when the surface loss is more than 50% due to glaze, even if measures are taken to recover temporarily, you should consider replacing the rubber roller. Pay attention to cleaning and maintaining the roller in time to reduce the change of surface roughness.

During the operation, the characteristics of the printed matter and the change of the rubber roller must be foreseen. If the change beyond the permissible range occurs within 3 months, it should first be checked whether an inappropriate roller is used (such as the use of UV printing Ink roller and water roller, and secondly if inappropriate ink, fountain solution or cleaner is used.

In the printing process, the cause of the failure of the roller is often many, and the factors that affect the normal use and life of the roller are also closely related to other printing aids used. For example, the use of high-quality printing rollers, but the use of improper paper will exacerbate the crystallization of the roller surface, resulting in quality problems; long-term use of inks containing aromatic polymers for printing or use aromatic detergent cleaning glue The rollers will hurt the rollers and affect the quality of the printing. For printing problems caused by chemicals in the printing process, technical personnel can be sought for help, and experts recommend that printing companies choose the printing equipment that does not harm the printing roller and have a balance between printing properties so as to achieve the best resources. Optimization.

The printing pressure is a comprehensive manifestation of 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 roller hardness, elasticity and surface roughness, and the pressure standard of the rubber roller at different positions on the printing machine. 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, depreciation of the machine and power consumption, and the like.

When the indentation width is 4mm, the pressure of the rubber roller reaches 18N, and when the width is 6mm, the pressure can reach 63.5N, and when the width is 8mm, the pressure reaches 149N. From this we can draw the following conclusion:

1) Increase the width of the indentation by 50% and increase the pressure of the roller by 250%;

2) Increase the width of the indentation by 100% and increase the pressure of the roller by 725%.

Therefore, the pressure of the roller should be as small as possible without affecting the printing quality. Because in practice, the width of the indentation is the performance of the printing pressure, the width of the indentation provided by the manufacturer is the printing pressure standard of the original rubber roller that has been tested, and it is best not to arbitrarily change it.

For controlling printing costs, the influence of printing pressure is also great. I have done the following tests:

Offset press: Heidelberg CD102 five-color printing machine

Ink: Hanghua standard four-color offset ink

Fountain solution: BottcherFount3010

Printed pressure test roller: 60mm diameter inking roller

Printing speed: 10000 sheets/hour;

Working time: 24 hours/day

Original ink roller hardness: SH25

Original water roller hardness: SH25

After 2 months, the printing pressure was adjusted to 50% of the first month. From the results, it was found that the printing pressure had a significant influence on the printing cost during the printing process.