Nip Impression Paper
Nip or pinch rolls are powered rolls that are used to press two or more sheets together during lamination or embossing. High pressure is created at the nip point as the rolls pull the material through the process equipment. As a result, stresses are created within these materials. Therefore, it is important that such stresses are uniform to prevent wrinkling or distortion of product.
Nip Impression Paper is a generic term for a film that can be run through the nip to characterize the pressure profile between the rolls. Fujifilm Prescale®, pressure indicating film, is a nip impression paper that is distributed by Sensor Products. Fujifilm Prescale® works by virtue of microcapsules, coated onto the film substrate, that rupture at various predetermined stress levels. On the application of force, the film develops a permanent and irreversible color. The color intensity of the exposed film is directly proportional to the amount of pressure.
By visually comparing the resultant film with a set of color standards, manufacturing personnel can measure actual roll contact pressure and pressure distribution across the rolls. For users who require greater accuracy than can be obtained by a simple visual comparison, a sophisticated Topaq®, a Windows®-based analysis system, may be used to read and evaluate the pressure film samples. Figures 1 through 3 illustrate the use of Fujifilm Prescale® and Topaq®.
Fig 1: Insert Film between Nip Rolls
Fig 2: Color on Fujifilm Prescale is Proportional to the Pressure.
Fig 3: Topaq Analysis of Pressure