MODELLING OF PERCEPTUAL GLOSS BY PHYSICAL MEASUREMENT OF FLAT SURFACE

While ‘physical gloss’ exists as a physically measurable index, people perceive a ‘perceptual gloss’ as gloss on object surfaces. However, the physical gloss does not always match the perceptual gloss. Thus, we analysed the relationship between physical features and perceptual gloss by measuring the physical properties of object surfaces, including physical gloss. For the experiment, we prepared 127 samples of flat objects that consisted of three materials: paper, resin, and metal plating. Perceptual gloss was visually evaluated using a magnitude estimation method. Plural measurements were conducted to obtain physical features such as gloss unit, haze, distinctness of image (DOI), luminance image features, and transmittance of the samples. Then, we constructed a prediction model of perceptual gloss using these physical features and perceptual gloss through multiple regression analysis. As a result, the prediction accuracy was improved by combining multiple physical quantities with simple regression, using only a gloss unit.

Investigation of the Performance of Fumed Silica as Flow Additive in Polyester Powder Coatings

Fumed silica is one of the most commonly used flow additives in the powder coating industry. To investigate the influence of the properties of fumed silica on powder coatings, three different types of fumed silica, Aerosil R812, R972, and R8200, were selected and introduced to an ultra-high-gloss powder paint by the dry-blending method with preset mixing conditions and times. Their effect on the powder flowability, coating application related properties and film properties were carefully studied. The angle of repose (AOR) and bed expansion height data, which represent the semi-dynamic and dynamic flowability of powders respectively, show a strong flowability enhancement for the powders with additives, and R812 exhibits the best performance compared to 8200 and R972, mainly due to its high hydrophobicity and specific surface area. For the ultra-high-gloss powder paint, all the flow additives cause slight gloss reductions, surface roughness increase and a significant effect on the distinctness of image (DOI). The addition of R972 is beneficial to the transfer efficiency of powders compared with the other two, while the additives impose only a minor influence in the Faraday cage effect. The melting and curing dynamics, i.e., gel time, and inclined plate flow, are not affected by the flow additives.