[article]
| Titre : |
Modern measurement of effect pigments - useful and useless geometries |
| Type de document : |
texte imprimé |
| Auteurs : |
Werner Rudolf Cramer, Auteur |
| Année de publication : |
2019 |
| Article en page(s) : |
p. 27-29 |
| Langues : |
Anglais (eng) |
| Catégories : |
Mesure
Pigments -- Propriétés optiques
Pigments à effets spéciaux
|
| Index. décimale : |
667.2 Colorants et pigments |
| Résumé : |
The selection of necessary measurement geometries is based on the optical-physical properties of the pigments. As a rule, one geometry is sufficient to read colour pigments in a car colour. Usually, this is illuminated at 45° and measured at 0° (from the normal). Alternatively, sphere geometry is used. To measure aluminium pigments with their varying brightnesses, several geometries are needed to detect these brightness changes. Measurements at a fixed illumination and aspecular angles show the increase in brightness the Gloser to gloss is measured. Due to the Fresnel law, these changes in brightness are not linear.
Particular attention is paid to the interference pigments found in most car colours. The colourful interference pigments change their brightness and their colour, while white interference pigments show no colour changes.
The optical properties of the interference pigments are described by the interference law. This law shows the dependence of the resulting colour on the angle of the incident light. The flatter the illumination, the more the reflection maximum shifts to shorter wavelengths, ie red interference pigment turns yellow, a green one gets bluer and it
increases non-linearly. If these properties are not met, the colour measurement is not plausible.
Due to these optical-physical properties, interference pigments can be optimally described with three illumination angles: a steep (eg 15°), the classic at 45° and a flat angle (eg 65°) with the same difference angle of 15°. Illumination angles that lie between these geometries result in no additional information.
The Gloser to the gloss angle, the larger the differences in the reflection peaks (maxima) become. Mostly, this series "breaks off" at 5° from gloss. Often the measurements at 10° off gloss appear critical. The usual 15° of gloss (aspecular) is "stable" at all illumination angles.
If a colourful, transparent interference pigment is applied to a white background as described above, the measurements at a fixed illumination of 45° produce a colour change between the reflection and the transmission colour in the range of 20° and 30° from the gloss angle. |
| Note de contenu : |
- Fig. 1 : Below : With flatter illumination of interference pigments, their maxima shift to shorter wavelength. At the same Lime their maxima increase
- Fig. 2 : a*b*-values of many geometries show a pattern which can be reduced on a few geometries. These geometries characterise any interference pigment
- Fig. 3 : Readings at 5° off gloss are not plausible because the difference between maxima must increase
- Fig. 4 : Colour interference pigments change their reflection colour to the complementary transmission colour if applied on a white ground. The transition area is between 20° and 30° off gloss. With portable instruments you find the change mostly between 45°/as25° and 45°/as45°
- Fig. 5 : Typical description of an interference pigment: Interference fines are based on values measured near gloss. And aspecular Unes are going off gloss. At 45°/as75° and 45°/as110° there are strange behaviours on a white ground
- Fig. 6 : Except 15°/a515°, aspecular geometries at 15°-illumination show no additional information to describe an interference pigment
|
| En ligne : |
https://drive.google.com/file/d/1RHgjCIJfOzesKgKmvRbhEV6XFCBb1VJB/view?usp=drive [...] |
| Format de la ressource électronique : |
Pdf |
| Permalink : |
https://e-campus.itech.fr/pmb/opac_css/index.php?lvl=notice_display&id=32882 |
in POLYMERS PAINT COLOUR JOURNAL - PPCJ > Vol. 209, N° 4653 (08/2019) . - p. 27-29
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Modern measurement of effect pigments - useful and useless geometries in POLYMERS PAINT COLOUR JOURNAL - PPCJ, Vol. 209, N° 4653 (08/2019)
