ISO/TC 107/JWG 4 - Joint ISO/TC 107 - ISO/TC 35/SC 9 WG: Thickness measurement methods for coatings, paints and varnishes

This document specifies spectroscopic ellipsometry for the determination of optical properties (refractive index n and extinction coefficient k) and the optical classification of different types of amorphous carbon films within the n-k plane. It is applicable to amorphous carbon films deposited by ionized evaporation, sputtering, arc deposition, plasma-assisted chemical vapour deposition, hot filament techniques and others. It does not apply to carbon films modified with metals or silicon, amorphous carbon films that have a gradient of composition/property in the thickness, paints and varnishes.

This document specifies a method for determining optical and dielectric constants in the UV-VIS-NIR spectral range as well as layer thicknesses in the field of at-line production control, quality assurance and material development through accredited test laboratories. It is applicable to stand-alone measuring systems. The presentation of the uncertainty of results conforms to ISO/IEC Guide 98-3.

This document specifies a method for using phase-sensitive eddy-current instruments for non-destructive measurements of the thickness of non-magnetic metallic coatings on metallic and non-metallic basis materials such as: a) zinc, cadmium, copper, tin or chromium on steel; b) copper or silver on composite materials. The phase-sensitive method can be applied without thickness errors to smaller surface areas and to stronger surface curvatures than the amplitude-sensitive eddy-current method specified in ISO 2360, and is less affected by the magnetic properties of the basis material. However, the phase-sensitive method is more affected by the electrical properties of the coating materials. In this document, the term "coating" is used for materials such as, for example, paints and varnishes, electroplated coatings, enamel coatings, plastic coatings, claddings and powder coatings. This method is particularly applicable to measurements of the thickness of metallic coatings. These coatings can be non-magnetic metallic coatings on non-conductive, conductive or magnetic base materials, but also magnetic coatings on non-conductive or conductive base materials. The measurement of metallic coatings on metallic basis material works only when the product of conductivity and permeability (σ, μ) of one of the materials is at least a factor of two times the product of conductivity and permeability for the other material. Non-ferromagnetic materials have a relative permeability of one.

This document gives guidelines for determining the average surface density over a measured area of anodic oxide or of a coating deposited autocatalytically, mechanically, by chemical conversion, by electrodeposition, by hot dip galvanizing and by chemical or physical vapour deposition using gravimetric and other chemical analysis procedures that have attained some degree of national or international standardization. A variety of procedures are described and include: — gravimetric procedures for chemical or electrochemical dissolution of the coating or the substrate to determine the coating surface density; — gravimetric procedures for weighing the uncoated substrate and the coated (finished) specimen to determine the coating surface density; — analytical procedures that utilize dissolution of the coating for determination of the coating surface density by instrumental chemical analysis methods. With the exception of the gravimetric method as described in ISO 3892, this document does not give the measurement uncertainties of the methods cited.

ISO 2360:2017 specifies a method for non-destructive measurements of the thickness of non-conductive coatings on non-magnetic electrically conductive base metals, using amplitude-sensitive eddy-current instruments. In ISO 2360:2017, the term "coating" is used for materials such as, for example, paints and varnishes, electroplated coatings, enamel coatings, plastic coatings, claddings and powder coatings. This method is particularly applicable to measurements of the thickness of most oxide coatings produced by anodizing, but is not applicable to all conversion coatings, some of which are too thin to be measured by this method (see Clause 6). This method can also be used to measure non-magnetic metallic coatings on non-conductive base materials. However, the phase-sensitive eddy-current method specified in ISO 21968 is particularly usable to this application and can provide thickness results with a higher accuracy (see Annex A). This method is not applicable to measure non-magnetic metallic coatings on conductive base metals. The phase-sensitive eddy-current method specified in ISO 21968 is particularly useful for this application. However, in the special case of very thin coatings with a very small conductivity, the amplitude-sensitive eddy-current method can also be used for this application (see Annex A). Although the method can be used for measurements of the thickness of coatings on magnetic base metals, its use for this application is not recommended. In such cases, the magnetic method specified in ISO 2178 can be used. Only in case of very thick coatings above approximately 1 mm, the amplitude-sensitive eddy-current method can also be used for this application (see Annex A).

ISO 2178:2016 specifies a method for non-destructive measurements of the thickness of non-magnetizable coatings on magnetizable base metals. The measurements are tactile and non-destructive on typical coatings. The probe or an instrument with integrated probe is placed directly on the coating to be measured. The coating thickness is displayed on the instrument. In ISO 2178:2016 the term "coating" is used for material such as, for example, paints and varnishes, electroplated coatings, enamel coatings, plastic coatings, powder coatings, claddings. NOTE This method can also be applied to the measurement of magnetizable coatings on non-magnetizable base metals or other materials (see ISO 2361).