The new Rhopoint ID Inline from Rhopoint Instruments provides continuous, non-contact, inline measurement of the appearance properties of transparent plastic film and sheet. The camera-based system fully quantifies transparency with parameters that are highly correlated to human perception. The robust technology can handle a wide range of line speeds and stabilities and is easy to install and maintain.

Transparent film and sheet are used in applications such as packaging, where it is important that the material has low haze and high transmission so that the packaged product can be viewed clearly. These appearance properties can be affected by the material and by the extrusion process. Inline measurement provides instant feedback that allows a process to be fine-tuned, ultimately achieving a better-quality product, with measured consistency throughout every production run.

Measurements made with the Rhopoint ID-Inline are equivalent to those from Rhopoint’s established, laboratory instrument, the Rhopoint ID Imaging Transmission Appearance Meter, allowing users to directly compare inline measurements to lab data. Both instruments use a proprietary technique developed in partnership with the Materials Department of ETH University in Zurich. 

This technique uses a camera-based device and digital image analysis to characterize changes in transmission. The instrument measures the conventional parameters of haze, clarity and transmission, as well as a new parameter of sharpness that quantifies the loss of perceived detail for objects viewed through a material. The Rhopoint ID instrument separately characterizes sharpness in the vertical and horizontal directions, which is important because optical defects that reduce see-through quality are often caused by processing faults that are directional in nature. The instrument also measures visible transmission, which describes the brightness or luminosity of an object viewed through the material. The digital imaging technology used in the Rhopoint ID overcomes the limitation of a conventional, direct-contact transmission haze meter in characterizing distance-related haze, which is the loss of contrast related to the size of the gap between a material and a viewed object. While traditional instruments quantify haze at a fixed distance, the Rhopoint ID can measure haze at any distance from 0 to 30 mm, to better evaluate materials used for specific applications and viewing distances.   

In addition to non-contact, inline measurement of glass or transparent plastic film and sheet, the system can be set up to measure tubes. Multiple sensors can be distributed to independently measure multiple points across a web, or a sensor can be mounted to be movable. The system has a sampling rate of 10 measurements per second and is unaffected by line speed. Data can be monitored using Rhopoint’s software or can be integrated into a user’s statistical process control system and used for closed-loop feedback control.