Thickness of co-extruded films

During the manufacture of co-extruded films, the film thickness is controlled by rolling processes after extrusion. The film thickness is a key parameter for the overall product quality. With multi-layer films, thickness is determined by using two complementary measurement techniques and a measurement roll as reference. Here, it is very important that both sensors measure in the same axis and are not impaired by the different materials. This means that in addition to measuring the distance to the top edge, a reference signal to the roll is also required.

For this application, Micro-Epsilon offers turnkey measurement systems. For thickness measurement systems for flat film, Micro-Epsilon offers its dual-sensor technique. Here, two sensors utilising different measuring principles are combined in order to provide specific advantages.

For example, in the measurement system for co-extruded plastic films, an eddy current sensor is combined with an optical micrometer. The electromagnetic fields of the eddy current sensor penetrates the film and accurately measures the distance to the metal surface of the measurement roll. The top edge of the film is measured by using optical micrometers. The transmitter emits a light curtain in the direction of the receiver. Because the roll with the film is located within the light curtain, part of the emitted light is blocked. This produces a second signal, from which, together with the reference signal from the measurement roll, the thickness of the film can be calculated. This system is suitable for films with a thickness of between 0.05mm and 10mm and can be used for the most varied of material layers.

As an alternative to the optical micrometer, a capacitive sensor can also be integrated into the system. Known as ‘Thickness measurement system for flat film’, the system measures film thickness between 0.01mm and 2.5mm.
By integrating the system into existing SPC networks, an immediate signal or, via the thickness signal, a continuous correction of the production process, takes place when tolerances are exceeded. These systems can also be integrated into existing production lines.

Turnkey measurement systems from Micro-Epsilon are used for process control and quality assurance in production lines, where they ensure optimised processes through high quality standards. The combination of sensors, software and the mechanical system, to fully integrated measurement systems is one of Micro-Epsilon's core capabilities and offers numerous advantages in terms of improved productivity.