The effects of high solids content on coating color rheology and runnability
Nick, Tapani (2021)
Nick, Tapani
2021
All rights reserved. This publication is copyrighted. You may download, display and print it for Your own personal use. Commercial use is prohibited.
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi-fe202101242546
https://urn.fi/URN:NBN:fi-fe202101242546
Tiivistelmä
The rheology and water release behavior of talc containing paper coating colors was studied, focusing on the effects of high solids content. Increasing the solids contents of coating colors is among the best ways to cut costs in the production of coated paper. However, runnability problems, such as coating defects, become more likely with increasing solids contents, especially when pigments with high aspect ratios are used.
Four experimental coating color blends and a reference coating color were used in the study. The experimental blends varied in their dispersing chemistry, and samples were prepared at three solids contents, namely 55 wt%, 58.5 wt% and 62 wt%. Additional studies were made by adjusting the pigment/-binder-ratio. Three experimental blends were produced containing 10 parts of small spherical precipitated calcium carbonate (PCC). The parameters of the coating colors were thus solids content, dispersing chemistry, pigment/binder-ratio and PCC addition.
Of all the parameters, solids content had the highest impact on high shear viscosity. All experimental blends had good performance during rotational high shear measurements, but the measurements with the capillary viscometer showed much higher viscosities for the samples with the highest solids contents. The results from the two high shear measurement methods correlated well at lower solids contents. There was no significant difference in the high shear viscosity among the blends with different dispersing chemistries.
The addition of PCC did reduce high shear viscosity slightly, but similar change was gained when the pigment/binder-ratio was increased with talc. The low shear viscosity of the samples containing PCC was noticeably higher compared to the other samples.
The solids contents did not determine water retention of the samples, largely due to differing thickener concentrations. Although there were differences in water retention between the samples, all studied samples performed at a satisfactory level.
Four experimental coating color blends and a reference coating color were used in the study. The experimental blends varied in their dispersing chemistry, and samples were prepared at three solids contents, namely 55 wt%, 58.5 wt% and 62 wt%. Additional studies were made by adjusting the pigment/-binder-ratio. Three experimental blends were produced containing 10 parts of small spherical precipitated calcium carbonate (PCC). The parameters of the coating colors were thus solids content, dispersing chemistry, pigment/binder-ratio and PCC addition.
Of all the parameters, solids content had the highest impact on high shear viscosity. All experimental blends had good performance during rotational high shear measurements, but the measurements with the capillary viscometer showed much higher viscosities for the samples with the highest solids contents. The results from the two high shear measurement methods correlated well at lower solids contents. There was no significant difference in the high shear viscosity among the blends with different dispersing chemistries.
The addition of PCC did reduce high shear viscosity slightly, but similar change was gained when the pigment/binder-ratio was increased with talc. The low shear viscosity of the samples containing PCC was noticeably higher compared to the other samples.
The solids contents did not determine water retention of the samples, largely due to differing thickener concentrations. Although there were differences in water retention between the samples, all studied samples performed at a satisfactory level.