NEW WAYS FOR THE CHARACTERIZATION OF APPEARANCE PROPERTIES OF PLASTIC PRODUCTS AND COMPONENTS CLOSE TO HUMAN VISION Dieter P. Gruber 1 *, Gerald R. Berger, Walter Friesenbichler 2 1 Polymer Competence Center Leoben GmbH, Leoben, Austria 2 Montanuniversitaet Leoben, Chair of Injection Molding of Polymers, Leoben, Austria *dieter.gruber@pccl.at 1. Introduction The first impression of a product’s quality is formed by the appearance of its surface and in most cases, strong conditioning has produced expectations on specific surface attributes that a certain product has to show. In this respect, the human eye-apparatus is still considered to be the most sophisticated evaluation tool. However, evaluation of surface appearance performed exclusively through human observation proves insufficient since the judgment depends on individual factors like the observer’s eyesight, experience and mood at the time of the evaluation. Consequently, there is a strong demand for measurement techniques which provide results that are for one unambiguous and reproducible, but also correspond to the visual perception of individual evaluators. Our newly developed surface inspection methods include the quantitative evaluation of a variety of visual surface deficiencies [1-3]. The methods can be translated into practice, e.g. for a better in-depth optimization of injection molding and extrusion processes and for IN-LINE quality inspection of extruded or injection molded parts. 2. Measurement For our investigations, a multifunctional injection mold was used to manufacture examination samples with controlled defect formation. The polymer part includes ribs with varying thickness. The focus of current studies lies in the quantitative evaluation of the visual perceptibility of sink marks caused by ribs at the sample’s back side. The main wall thickness of the test part measures 2.5 mm while ribs are 1.2 mm, 1.6 mm, 2.0 mm and 2.5 mm thick (Figure 1). Sink marks are shrinkage related phenomena that depend on processing parameters like mold and melt temperature and holding pressure. In a test series, the holding pressure was varied within a range of 20 MPa to 80 MPa. Other processing parameters like the barrel and mold temperature, as well as the injection rate were kept constant. The used polymer was black polycarbonate (PC). In order to ensure a stationary process, 10 cycles of each setting were discarded. The machine vision system included CCD-cameras and D6500 standard light sources. The light sources were adjusted that way that surface structure showed maximal contrast. Finally, images are captured which form the raw data for the calculation of the perceptibility of the surface defects. Figure 1: Backside of an injection molded test part (left) and image of sink marks (right) caused by reinforcing rips