Self-adhesive cohesive materials and tapes (pressure-sensitive adhesives, PSA) are often used in the manufacture of medical products such as wound dressings. They are based on non-reactive adhesives that form a bond when pressure is applied to secure the material to a surface. In the medical field, PPEs are most commonly used for wound care or surgical repair procedures, so the quality of the material is of paramount importance. Compared to traditional sealants and adhesives, PPE offers advantages such as ease of application and versatility of bond strength.

A manufacturer of PPE for medical applications was experiencing yield losses on their production line due to wrinkle defects occurring in the gauze-like nonwoven layer of the product. These non-woven PPEs are produced on lightweight PET plastic and paper substrates with a width of around 70 cm and a thickness of 0.025 to 0.075 mm. After the adhesive coating of the backing material, a thick, white non-woven material with a thickness of also around 0.025 to 0.075 mm is laminated onto the backing material at speeds of up to 55 m/min.

Problem of wrinkling

During the lamination process, the nonwoven material can periodically form wrinkles that render the product unusable and rejects. However, the wrinkles that form during production are difficult to see with the human eye, as the gauze-like nonwoven material is very thin and translucent. If the wrinkles are not detected and removed, they can extend over many hundreds of meters - resulting in the loss of raw materials used, unnecessarily consumed labor, increased overhead costs for the order and angry customers if the wrinkles are not detected before shipping.

Unable to find an off-the-shelf vision solution for this application, the manufacturer turned to system integrator Vision Optronix to develop a vision system to help detect, locate and report wrinkle defects during PPE production. The task of the vision system was to alert the PPE manufacturer's operators so that they could immediately remove any wrinkles that occurred and also to automatically mark the position of the wrinkle defects. In addition, a file of detected wrinkle defects should be created and stored together with the defect images, which the cutting machine operators can use to remove the marked wrinkle defects before shipping.

Illustration of the wrinkle defects

Vision Optronix investigated the problem in the laboratory to find the best method for imaging the wrinkle defects. In addition to the size of the defects and the process speed, the lighting requirements proved to be technically challenging.

During an on-site investigation, the system integrator first checked the wrinkle defects and the web coating system that applies the special coatings. It was important to understand how the various components of the image processing system had to be optomechanically designed in order to fit into the available space. On this basis, the system integrator developed, implemented, programmed and tested a preliminary design of the image processing system, including the necessary electronics, the image processing algorithms and the graphical user interface for the customer.