Pick resistance

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The pick resistance of the paper describes the characteristic of the paper not to tear. This property is very important in the printing process , since high tensile forces act on the surface of the printing material while the ink is being applied. These can lead to the paper being plucked .

causes

Picking occurs when the adhesive forces of the printing ink are greater than the internal binding forces of the printing material. The strength compression is stronger at the edge than in the core. These injuries can consist of a loosening of paper fibers , fillers or streak particles. It can be a lifting of surface particles or even the complete tearing of the paper. Such injuries are caused by the tensile forces that occur during the printing process between the printing ink and the paper at the moment the color splits. The pick resistance of a paper or other printing material is the resistance that the paper opposes tensile forces that are effective perpendicular to the plane of the sheet. This resistance is determined by the freeness of the paper fibers, the type of felting, the sizing and the fillers, but also the temperature and humidity conditions. It also provides information as to whether one paper is suitable for a stricter color or for a higher run speed and higher pressure compared to another and whether the wire or felt side has different properties.

Manifestations

Injuries to the surfaces appear in two forms. When pelting , fiber particles are released from the surface. This brush-like surface can be seen with a magnifying glass. Plucking is the tearing of individual particles from the surface of the paper or the tearing of the structure of the paper. This can be done by pulling the printing ink when it is transferred to the printing material. The causes are either too quick a color or a bad, non-pick-free paper. The result is so-called plucking points. These are small depressions in the printed image. In turn, they cause misprints.

Detection methods

There are various pick tests that the paper can be subjected to for safety. With the wax test a vertical tensile load is exerted exclusively on one paper sheet plane. Such plucking tests are similar to the stresses on paper, such as those that occur when printing a rubber stamp or in a platen press . This method makes use of suitable waxes that are placed on the paper surface in the melted state and are intended to reproduce those tensile forces when peeled off.

On the other hand, test printing devices can also be used, which make it possible to imitate the actual printing process. In this case, when using a test printing ink, the unwinding speed and the pressure can be changed as a function of the viscosity as parameters.

literature

  • Wolfgang Walenski: Dictionary of printing and paper . Klostermann publishing house, Frankfurt / M. 1994, ISBN 3-465-02619-5 .