Altana Micro-Haze Plus Manual do Utilizador descarregar pdf (Página 36)

35

The visual impression of gloss is a

multidimensional parameter. For

many years, reflectometers have

been used to measure gloss. For a

full characterisation of surface

reflection, however, additional

measurands are required.

Microscopically small defects in a

high gloss surface will result in

scattered light of low intensity

adjacent to the main reflection (fig.

18). The surface will appear shiny

covered by a milky and dull haze.

This haze is mostly caused by

specific parameters during the

production process, such as

• Pigment type and degree of

dispersion

• Binding agents, additives

• Application and processing

methods

In addition, weathering and

mechanical wear (cleaning, polish-

ing, abrasive wear) can also result

in a hazy appearance.

Measuring Principles 10

Reflectometer for Measuring

Gloss

The principle of a reflectometer is

based on the measurement of the

specular component of the

reflected light (fig. 17). To this end

the intensity of the reflected light is

measured in an angle range limited

by the aperture.

The measurement of the

reflectometer value is a relative

measurement. The measurement

results are related to a polished,

black glass standard with a defined

refractive index (calibration).

In order to obtain a good

differentiation between the

measurement results over the

whole range from high gloss to low

gloss surfaces three different

angles of illumination, i.e. three

measurement ranges, have been

defined:

20° high gloss surfaces

60° semi gloss surfaces

85° low gloss surfaces

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