Page 24 - PITTURE E VERNICI EUROPEAN COATINGS Issue 3/May-June 2017

RAW MATERIALS
RESINS
RESINE
fillers, which cause surface roughness in the dried coating film thus reducing gloss[1]. In printing and packaging as well as wood finishing it is highly desired to provide matted transparent coatings which enhance the color depth of the underlying substrate. High visual transparency is a key requirement in these markets. This can be difficult when using micron sized fillers, partly due to refractive index mismatching. The alternative approach is to design a polymer, which forms a low gloss rough surface on its own. Such polymers can be cast in thin films, and have high transparency due index mismatching.
Fig. 3 Finger friction measurement in progress using triaxial force measurement apparatus Misure dell’attrito del dito in avanzamento con l’apparato di misura a carico triassiale
retaniche mostrano una sufficiente coalescenza durante la fase filmo- gena così da dare un film uniforme, conservando solitamente la loro forma originale e dando luogo ad una rugosità superficiale definita. Sebbene queste particelle rientrino nel range dimensionale dei micron, questo effetto può già essere ottenuto nei rivestimenti con uno spessore di pochi micron.
PROPRIETÀ OTTICHE: COME APPARE?
Da sempre nell’industria produttrice di rivestimenti la brillantezza è tenuta sotto controllo con i riem-
In order to obtain quantitative data on surface topography, roughness profiles can be analysed by means of white light interferometry.
From the obtained 3D profiles (Fig. 2), many different surface parameters can be calculated, such as the root mean squared roughness (Rq), representing the height differences between valleys and peaks, and the average spacing between the peaks (L).
HAPTIC PROPERTIES: HOW DOES IT FEEL?
Haptic perception is the outcome of a tribology experiment we perform with our skin: as we move our finger over a surface, the forces and vibrations generated in this frictional contact are detected by several types of neural mechanoreceptors embedded in the skin, whose signals are processed by our brains into our sensory experience of “feel”[2].
The contact mechanics and frictional forces between skin and surface therefore play a key role in haptic perception[3].
During touch, the surface roughness of both skin and surface prevents perfect contact in the entire apparent contact area. Generally, a softer surface deforms more easily, leading to more contact area and thus higher friction[4].
We constructed a finger friction measurement apparatus enabling us to study frictional forces generated on our materials during touch. Inspired by examples in literature[5,6], the apparatus consists of a triaxial force cell on which the sample surface of interest can be mounted:
no internal refractive
pitivi organici ed inorganici, che causano la rugosità superficiale nel film di rivestimento essiccati riducendone la brillantezza[1].
Sia nel settore della stampa che in quello dell’imballaggio, ma anche in quello delle finiture del legno sono molto apprezzati i rivestimenti trasparenti opacizzati che apportano migliorie all’intensità della tinta del substrato sottostante. L’alta trasparenza visiva è un requisito chiave di questi mercati.
Questo può essere difficilmente ottenibile quando si usano riempitivi nell’ordine dei micron, in parte per la
Fig. 4 Force deformation curve of the PUD coatings studied in this work
Curva di deformazione di una forza dei rivestimenti PUD studiati in questa attività
MATERIE PRIME
20 Pitture e Vernici - European Coatings - Formulation 3 / 2017