ISO/TC 35/SC 9/WG 16 - Coating powders

This document specifies a method for determining the time for a thermosetting coating powder to gel at a specified temperature. A method is described for checking batch to batch variation and for the quality control of a given coating powder. The method is not applicable to coating powders with ultra-short gel times (less than 15Â s).

This document establishes a method for the estimation of the storage stability of thermosetting coating powders. It provides the procedures for determining the changes both in the physical state of a thermosetting coating powder and in its chemical reactivity, together with its capacity to form a satisfactory final coating.

This document specifies a liquid displacement pycnometer method for the determination of the density of coating powders. The method is based on a determination of the mass and the volume of a test portion. Coating powders with density 3, can be measured in accordance with ISO 1183-1 and the appropriate method, by agreement.

This document specifies a method for the determination of density for all types of coating powders using a gas comparison pycnometer.

This document specifies a method for determining the mass fraction in per cent (%) of a sprayed coating powder which is deposited on a test item under known spray gun and environmental conditions. The method is applicable to powders applied by corona or tribo charging and can be used to compare the deposition efficiency of different powders with the same or different gun with the same powder. This method is only used for comparison when powders or guns are evaluated consecutively, as the influence of the environment and the equipment can vary significantly with time and location.

This document specifies a method for estimating the flow properties of a mixture of coating powder and air. The results obtained are influenced by the composition of the coating powder, its density, particle size distribution and particle shape, together with the tendency of the particles to agglomerate and to accept a charge.

This document specifies a method for the determination of loss of mass on stoving of coating powders that are to be applied by electrostatic spraying or flock spraying or fluidized bed. The method described in this document is a simple, practical test which provides sufficiently accurate results for coating powders that lose approximately 2 % (by mass) on stoving (heating). Above 2 %, accuracy decreases with an increasing loss in mass. This method determines the amount of all volatile matter, including water. Thermogravimetric testing as described in the ISO 11358 series can be used as a comparative method.

This document specifies a comparative method for determining the flow characteristic of a fused thermosetting coating powder down a plane inclined at a set angle to the horizontal. The aim of the test method described in this document gives an indication of the degree of melt flow that can occur during the curing of the coating powder. This characteristic contributes to the surface appearance and to the degree of coverage over sharp edges. The test is a comparative method for checking for batch to batch variation in the behaviour of a given coating powder. Correlation between the results from coating powders of differing composition is not to be expected. This method is not suitable for coating powders which have gel times of less than 1 min at the test temperature when characterised according to ISO 8130‑6. This method is also not suitable for textured powders.

This document defines special terms used in the field of coating powders. Other terms and definitions related to paints and varnishes are given in ISO 4618.

This document specifies a visual method to determine the deterioration of surface quality of the final coating when mixing two different coating powders. The surface quality will depend on the following characteristics of the coating powders: a) the chemical reactivity; b) the chemical composition; c) the melt properties. The onset of the incompatibility in appearance, its nature and its extent will depend greatly on the ratio in which the powders are mixed. The nature of the incompatibility in surface appearance can manifest itself in various ways, described in Clause 8. This test is useful in predicting the possibility of incompatibility arising from mixing different powders both during the manufacturing process and during the application of the coating powder. This document concerns only changes in visual aspects of the coating. The mixture series can also be used for testing properties such as mechanical properties, chemical properties, corrosive properties and resistance against UV radiation. Further properties can be agreed between interested parties.

This document specifies a method for the determination of the particle size distribution of coating powders by sieve analysis. Particle size distributions with a maximum of less than 100 µm is determined by laser diffraction, ISO 8130‑13. This method is used especially for determining the oversize material or for the presence of contamination and can be used as a quality control procedure ("go"/"no go" test) by checking the amount retained on a single sieve. The following particle sizes are typical for coating powders, however the particle size can deviate depending on the application: — thin-film technology: 1 µm to 63 µm; — electrostatic coating: 10 µm to 200 µm; — fluidizing-bed method: 100 µm and above. NOTE Sieves with a mesh size smaller than 32 µm are not practical and are likely to become blind during use.

This document specifies a method for the determination of the equivalent-sphere particle size distribution of coating powders by laser diffraction, for particles of the size range from 1 µm to 300 µm. NOTE There is a possibility that particle sizes >300 µm need the use of a different optical model. This document is specific for the measurement of coating powders and also draws attention to ISO 13320, which provides guidance on instrument qualification and particle size distribution. Laser diffraction is not suitable for determining oversize material, which can be verified by sieve analysis as described in ISO 8130‑1 or by dynamic image analysis as described in ISO 13322‑2.