Gloss meter
A gloss meter (also called a reflectometer or gloss meter ) is a measuring device with which the gloss of a flat surface , for example of plastic, paper or paint, is measured. In this context, gloss is understood to be a ratio between the incident light and the light reflected from the surface at the angle of the specular reflection. Gloss meters are widely used in process monitoring in the production of paper and in quality assurance in the automotive industry .
Structure of a gloss meter
A gloss meter consists of a light source and a lens , which radiates parallel light onto a sample surface, and a receiver with a lens, diaphragm and photo receiver, which records the reflected light and measures it quantitatively. With a gloss meter, directed light is irradiated onto the sample surface at a defined angle. At the same angle, a detector records the light radiation reflected from the sample surface. In the physical sense, the measured value represents the integral over the reflection indicator of the test body surface for a solid angle range determined by the apertures of the illumination and detector optics.
Unit of measurement
Is the unit of a gloss meter GU ( English gloss units or gloss unit ). The scale for the gloss unit is based on the reference value that is achieved with a polished, black glass standard with a defined refractive index. During calibration, this reference value is set as 100 GU. The second reference point on the scale is 0 GU, the measured value that is achieved with a perfectly matt surface. The gloss of most non-metallic surfaces (paint, paper, ...) is in the range between 0 and 100. However, much higher values of up to 2000 GU can be achieved for polished metal surfaces and mirrors. In the case of transparent materials, however, the reflectometer values can be very low. In these cases, however, a gloss meter is usually not used, but the degree of reflection, i.e. the quotient of reflected light to radiated light, is given for a certain angle.
Performing the measurement
The angle at which measurements are taken is specified in the relevant standards, depending on the material and the expected gloss. It is chosen so that the sensitivity of the detector is used as well as possible. The three angles 20 °, 60 ° and 85 ° are specified in several standards. According to ISO 2813, the gloss is first measured at an angle of 60 °. If the measured value in this first measurement is above 70 GU, the measuring angle is reduced to 20 °. If it is below 10 GU, it is increased to 85 °. Otherwise the measured value can be accepted. Modern glossmeters carry out this angle adjustment automatically.
| Gloss area | 60 ° value | Measuring angle |
|---|---|---|
| gloss | > 70 GU | 20 ° |
| medium gloss | 10-70 GU | 60 ° |
| low gloss | <10 GU | 85 ° |
In addition to 20 °, 60 ° and 85 °, an angle of 45 ° is specified for ceramics, plastic films, textiles and anodized aluminum and an angle of 75 ° for paper.
In practice, measurements are not always made according to this procedure prescribed in the standard. In the absence of a 20 ° measuring device, some users also deliberately measure high gloss with the 60 ° measuring angle or evaluate measured values with decimal places, although in the standard the characteristic values for the measuring system analysis are a repeatability of 1 GU (at 60 ° and 85 °) or 2 GU (at 20 °) must be achieved with a confidence interval of 95%.
Explanation of the benefits
To ensure a homogeneous overall impression with a product that consists of several components, knowledge of the gloss value of the individual parts is very relevant. Product examples can be found, for example, in automobile construction, where the components of the vehicle interior are manufactured in different production steps and then assembled. In the end product, there should be no difference between the individual components in terms of their visual appearance (in addition to gloss, color and texture).
“Just a few decades ago, this was done [to measure the gloss], a visual comparison with a set of glossy tables (e.g. according to Boller). The gloss value was given here in “gloss percentage”. ”This determination of a gloss value is obviously very subjective and the meaningfulness is shaped by the experience and ability of the user. A gloss meter, on the other hand, provides a measured value with which the gloss level of a surface can be determined in a quantifiable and reproducible manner.
Norms
| angle | 20 ° | 60 ° | 85 ° | 45 ° | 75 ° | 20 ° Tappi | 45 ° DIN | 75 ° DIN | 75 ° |
|---|---|---|---|---|---|---|---|---|---|
| scope of application | Automotive, paint, varnish, plastics and processing industries |
Auto, ceramic, foil and textile industries |
Foil and paper industry | Leather, grained and porous surfaces |
|||||
| Gloss area | gloss | Medium gloss | Matt finish | Medium gloss | gloss | Medium gloss | Matt finish | Matt to high gloss | Matt finish |
| ASTM C346 | X | ||||||||
| ASTM D523 | X | X | X | ||||||
| ASTM D2457 | X | X | X | X | |||||
| BS3900 D5 | X | X | X | ||||||
| DIN 67530 | X | X | X | ||||||
| DIN EN ISO 2813 | X | X | X | ||||||
| EN ISO 7668 | X | X | X | X | |||||
| EN ISO 8254-1 | X | ||||||||
| EN ISO 8254-2 | X | ||||||||
| EN ISO 8254-3 | X | ||||||||
| EN 14086 | X | ||||||||
| DIN 54502 | X | X | |||||||
| TAPPI T480 | X | ||||||||
| TAPPI T 653 | X | ||||||||
| JI Z 8741 | X | X | X | X | X | ||||
Individual evidence
- ^ A b Zehntner GmbH Testing Instruments (Ed.): Gloss measurement . Introduction ( zehntner.com [PDF; accessed on September 3, 2012] company publication).
- ↑ a b c DIN EN ISO 2813: 2015-06: Coating materials - Determination of the gloss value below 20 °, 60 ° and 85 °.
- ↑ a b c Günter Kalinna: Gloss measurement. Shiny quality? In: Journal for surface technology . No. 6 , 2012, p. 64–66 ( erichsen.de [accessed September 4, 2012]).
- ↑ C. Boller: A gloss scale . In: Fat soaps, paints . tape 57 , no. 12 , 1955, pp. 1018-1020 .