Sensing Thickness – Improving The Accuracy of Contrast Ratio Assessment Using a Specially Developed Laser Unit

• Type: Article in International Scientific Journal
• Date: 2004

Authors

Afonso Leite (Author) FEUP; Ana Pereira (Author) FEUP; Fernanda Oliveira (Author) FEUP; José Nogueira (Author) FEUP; Joaquim Mendes (Author) FEUP; Adélio Mendes (Author) FEUP

Journal

Title: Journal of Coating Technology

No. 7

Pages: 44-48

Publisher: Springer

Scientific classification

FOS: Engineering and technology > Mechanical engineering

CORDIS: Technological sciences > Engineering > Control engineering

Other information

Abstract (EN): The contrast ratio (CR) is an important characteristic of a paint, which is determined experimentally using a spectrophotometric method. The CR is highly dependent on the paint film thickness, among other factors. The draw down bars normally used for spreading the paint over the paper cards, produce films with a large thickness standard deviation due to various reasons, among them the paint rheology and normal pressure and speed at which the draw down bar is moved. Also, the paint film thickness is normally assumed to be equal to the gap depth of the draw down bar what, as it will shown, is far to be correct. This work describes an automatic unit, which was developed to determine accurately the thickness of wet paint films based on a laser sensor. Tests were performed to assess its accuracy and reproducibility. Finally, mathematical relationships between the wet thickness and the CR were obtained for three different paints, which agree very well with the experimental results. The developed unit allows the determination of the CR with a far better accuracy: it is possible, using the proposed mathematical relations, to obtain the CR for a given thickness (e.g. 100 m), even when the CR is experimentally obtained for other film thicknesses. This work is the first step on the development of methods to measure the CR and the colour strength of white bases with an improved accuracy and more quickly, allowing for speeding up the quality control normally performed before the approval of any paint batch.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 5