Gravure Impression Roller
2015-06-18 17:42:23


   Impression Roller. The gravure impression cylinder, or impression roller, is a hard cylinder covered with a synthetic rubber lying directly above the gravure cylinder. The purpose of the impression roller is to exert pressure on the substrate passing through the nip between the impression roller and gravure cylinder. This forces the substrate partially into the cells on the gravure cylinder, where capillary action transfers the ink to the substrate. The pressure exerted on the substrate as it passes though the nip can be adjusted. The impression roller typically has a smaller diameter than the gravure cylinder and consequently rotates at a faster rate. However, in the nip between the two cylinders, the rubber is deformed slightly by the pressure of impression roller against the gravure cylinder. Faster press speeds in recent years, however, have resulted in excessive heat buildup in smaller impression rollers. Consequently, many presses now utilize larger-diameter rollers, which also have the added advantage of reducing stress on the web, as the increased size of the nip results in the same total amount of pressure being applied but over a larger surface area. Too large an impression roller, however, can cause printing defects, as the substrate remains in the nip for a longer period of time. As with the gravure cylinder itself, the TIR of an impression roller should be carefully monitored. The excessive friction caused during web gravure printing can also result in high static charge buildup. These charges can exceed 25,000 volts and can cause such printing problems as whiskering, or health hazards such as severe electrocution. A related phenomenon, but one which is induced deliberately and which has positive effects, is known as electrostatic assist, in which the impression roller is given a static charge that attracts the droplets of ink from the gravure cells to the substrate, and helps to more completely transfer ink and reduce the occurrence and severity of such problems as snowflaking. (See Impression Roller.)
  Edited by Better package Co., Ltd

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