Influence of different nonmineral powders on the rheological properties of fluids
Rheological properties
As one of the important indicators of fluids, rheological properties directly affect the storage stability and construction performance of adhesives, coatings and inks. Rheological properties are expressed as the relationship between shear force and viscosity, of which viscosity is a key indicator of fluid flow characteristics. By measuring the change of fluid under different shear forces, the rheological properties of adhesives, coatings and inks can be accurately analyzed. Powder filler as an important component of adhesives, coatings and inks is one of the factors affecting the rheological properties, and at the same time, the properties are closely related to the type of powder filler, processing technology, particle size and mineral morphology.
In the actual production of adhesives, coatings and inks, such as viscosity is one of the main control indicators, viscosity is defined as a certain shear rate, the ratio of shear stress and shear rate, the apparent shear viscosity at the shear rate, referred to as viscosity.
Common viscosity testing instruments include: rheometer, rotational viscometer, Stormer viscometer, Coat #4 Cup Viscometer, etc. Viscosity and rheological properties of the application, such as: coatings in the storage process hope that the system has a higher viscosity, to prevent the precipitation of pigment fillers; in the construction of the system needs a lower viscosity, conducive to the coating film leveling, this time, if there is a certain degree of rheological properties of the fluid, such as high reduction of low viscosity, high viscosity low shear, it can be a good solution to the problem.
Experimental Tests
In order to illustrate more clearly the influence of powders on the rheological properties of fluids, the following are the rheological properties of adhesives with different kinds of powders, as shown by the rheometer. The following is a comparison of the rheological properties of 800 mesh talcum powder, calcium carbonate and barium sulfate:
Test results show that: viscosity comparison under the same mesh number, talc＞calcium carbonate＞barium sulfate.
1, talcum powder thickening is better, while having shear viscosity characteristics, that is, in the production and storage process is not easy to delamination and precipitation, but also can improve the coating effect, but talcum powder oil absorption value is higher to add too much will lead to the system viscosity is too high, is not conducive to the production and construction;
2, heavy calcium carbonate rheological properties in general, viscosity effect is weaker than talcum powder, but has a low value of oil absorption, high whiteness, dry covering good characteristics, such as adhesives, coatings and printing ink in a wide range of applications;
3, barium sulfate oil absorption value is very low, relative to other powders on the system viscosity impact is very small, the theory can improve the amount of powder filling, but the ratio of significant stability is weak, usually need to be used with additives or thickening type powder.
Another for the application characteristics of calcium carbonate, will also carry out different processes to improve the application characteristics of its products, processes such as additives modification and ultrafine processing.
Test results show that: viscosity comparison, nano-calcium > heavy calcium carbonate > low oil-absorbing activated calcium.
1, generally the finer the powder, the higher the oil-absorbing value, the higher the viscosity, by the nano-calcium particle size between 60-100nm, has an excellent thickening effect, can effectively improve the stability of the fluid;
2, at the same time, as can be seen above, low oil-absorbing active calcium viscosity rate slower than the heavy calcium carbonate, that is, in the same proportion of its viscosity is smaller, and the other by the right figure can be seen in the high proportion of low oil-absorbing active calcium in the addition of a certain amount of shear viscosity effect, similar to the rheological properties of talcum powder, with the production and construction of a friendly features;
3、At the same time, generally with the different additive ratio of the powder filler, the system viscosity will also appear different changes, the follow-up Division I will start a new share for this.
