Static electricity on sheetfed presses

What is static electricity?

All substances consist of a single atom. Each of these atoms also consists of a positively charged nuclei and an anion electron orbiting. Any one nucleus has the same number of negative electrons (protons) expressed by its atomic number. Therefore, in general, the charges cancel each other, so that all the substances are in their original electrically neutral natural state - we can call them "uncharged" substances.

However, if the objects are brought into contact with each other, pressed together or rubbed against each other, and then separated again, the natural balance of positive charges and negative charges will be disrupted. Negative particles (electrons) are mechanically pulled out of the surface of an object and transferred from this friction to the surface of another object. In the resulting charge imbalance, an object now has too few electrons to cancel out all the positive charges of its protons, and therefore "positively charged." At the same time, another object now possesses too many electrons and thus “charges negatively”. Objects with the same charge—whether positive or negative—are mutually exclusive and objects with different charges attract each other.

Static electricity on sheetfed presses

This phenomenon also affects the printing press in various ways. The attractiveness between properly charged papers can even result in a suspension of the entire production process. For example, on feeders, this phenomenon can be manifested as sticking of paper stacks, poor paper separation, double sheets, and undulations on the transport table and bending when reaching the front gauge. In the delivery device, when dropped from the gripper bracket, the paper does not straighten out properly, creating a messy paper stack. This in turn limits the subsequent processing of postpress paper. If it is a very sensitive material, the application of ink can also be weakened.

The tendency of a material to accumulate static charges depends not only on its physical properties but also on its operation and the environmental conditions of the press room. Although the paper is easily charged during the hours of humidity, the friction of the plastic film is mainly responsible for the charging. Anti-Static Systems Installed at the Factory In order to solve the problem of static electricity generation, KBA's sheet offset presses can already be equipped with various structures of anti-static devices manufactured by KERSTENE lektrostatik GmbH in Freigurg im Breisgau prior to shipment. The basic requirements for thin paper or coated paper and board will be handled by a relatively simple set of basic components. Higher-level components expand the range of potential applications and satisfy the significantly increased requirements for plastic substrates.

The printable all-plastic assembly equipment installed on the Rapida 106 press at KBA's Print Testing Centre allowed us to identify individual components and to briefly describe their use.

Anti-Static System on Feida

All anti-static systems at the edge of the pile are used to support the separation of the paper, as it is crucial for feeders to achieve trouble-free operation. Six anti-static heads will be installed in the width of the rear of the feeder. The middle two components are the DK106 Electrostatic Discharge Heads, which are mounted on KBA's paper-dispensing mouthpiece (1.1) so that static electricity can be eliminated with a sudden split paper blow. The four DD406 ESD blow nozzles on the side are used to blow air with variable volume of static electricity as loose paper into the top of the stack (1.2 and 1.3). Two other static eliminators are mounted on the side edges of the stack. Here, the static elimination head will also be installed on KBA's nozzle.