Abstract
Most performance properties of coatings, such as rheology, colour strength, UV radiation resistance, and gloss, can be related to the degree (or lack) of dispersion [1,2]. When evaluating the presence of agglomerates in coatings or mill bases, the industry generally applies the maximum particle size as the critical parameter. However, the entire particle size distribution (PSD) plays a role in the performance [3]. Over the years, a range of instruments, based on new principles, has been introduced beyond the Hegman gauge [4-6]. However, obstacles are also evident, because these methods are highly influenced by the complex composition and the high solids contents of coatings or mill bases. The aim of the present work was to develop an analysis procedure, based on laser diffraction, for PSD measurements of coating products.
In the four series experiments, acrylic based TiO2 or Cu2O mill bases were used, and perturbations in composition and production parameters were investigated. To estimate the PSD of withdrawn samples, a laser diffraction instrument (Malvern MasterSizer 3000, MV chamber) was employed. Sampling from the same batch was done at different dispersion times (i.e. from 15 seconds and up to 40 minutes).
The PSD measurements were influenced by the obscuration value of the sample, the refractive index input values, and the shape of the pigment. Furthermore, prior to a measurement, the mill base (or coating) sample had to be diluted, which affects the stability of particles and agglomerates.
When using pure xylene as the measurement medium, a solvent shock, which resulted in non-representative PSDs, was observed. However, when using a binder-solvent mixture, taking rheological considerations into account, solvent shock was avoided and reliable PSDs could be obtained. Furthermore, to detect the transient PSD and volume-moment mean diameter, associated with variations in coating formulations and operation parameters, the analytical range of the instrument was sufficient.
In summary, the principle of laser diffraction was demonstrated to be a reliable tool for PSD estimations for mill bases and coatings, as long as the dilution process is properly analyzed and controlled.
In the four series experiments, acrylic based TiO2 or Cu2O mill bases were used, and perturbations in composition and production parameters were investigated. To estimate the PSD of withdrawn samples, a laser diffraction instrument (Malvern MasterSizer 3000, MV chamber) was employed. Sampling from the same batch was done at different dispersion times (i.e. from 15 seconds and up to 40 minutes).
The PSD measurements were influenced by the obscuration value of the sample, the refractive index input values, and the shape of the pigment. Furthermore, prior to a measurement, the mill base (or coating) sample had to be diluted, which affects the stability of particles and agglomerates.
When using pure xylene as the measurement medium, a solvent shock, which resulted in non-representative PSDs, was observed. However, when using a binder-solvent mixture, taking rheological considerations into account, solvent shock was avoided and reliable PSDs could be obtained. Furthermore, to detect the transient PSD and volume-moment mean diameter, associated with variations in coating formulations and operation parameters, the analytical range of the instrument was sufficient.
In summary, the principle of laser diffraction was demonstrated to be a reliable tool for PSD estimations for mill bases and coatings, as long as the dilution process is properly analyzed and controlled.
| Original language | English |
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| Publication date | 2022 |
| Number of pages | 1 |
| Publication status | Published - 2022 |
| Event | 2022 European Technical Coatings Congress - Auditorium Maximum, Krakow, Poland Duration: 12 Jul 2022 → 14 Jul 2022 https://etcc2022.org/ |
Conference
| Conference | 2022 European Technical Coatings Congress |
|---|---|
| Location | Auditorium Maximum |
| Country/Territory | Poland |
| City | Krakow |
| Period | 12/07/2022 → 14/07/2022 |
| Internet address |