Coating Viscosity Determination
The viscosity of the coating, also known as the consistency of the coating, refers to the property that the fluid itself has an adhesive surface, causing the internal flow of the fluid to hinder its relative flow. As with any fluid, the viscosity of the system is a fundamental property of the fluid.
This index directly affects the construction performance, leveling and sagging of the sample film. By measuring viscosity, we can observe the degree of polymerization of the coating after storage for a period of time. According to different construction requirements, we can adjust the viscosity with suitable diluents to achieve different viscosity indexes caused by brushing and airless spraying.
Paint viscosity during the painting process. It can be divided into original viscosity and construction viscosity. The original viscosity is the viscosity of the original paint when it enters the factory, and the construction viscosity is also called the working viscosity, that is, the viscosity suitable for a certain coating method.
The viscosity of coatings can be measured by methods such as capillary rheometer and Rotational Viscometer. The national standard CB/T 1723- -93 stipulates 3 methods of measuring viscosity, including the method of measuring the viscosity of paint by Tu-1. Xu-4 Viscosity Cup and falling ball viscometer. Among them in the coating process is Tu-4 Viscosity Cup method was used. This method is simple and easy, that is, the time for 100mL paint liquid to flow out from the aperture with a diameter of φ4mm at a specified temperature is recorded, expressed . This method is suitable for all kinds of low viscosity coatings.
Factors Influencing Viscosity
There are many factors affecting the viscosity of coatings. In summary, there are mainly the following points:
(1) The composition of the coating and the type of additives The greater the resin content, the higher the viscosity.
(2) The relative molecular mass and distribution of the polymer chain of the film-forming material The higher the relative molecular mass, the greater the viscosity;
The more flexible, the more non-Newtonian the coating, ie the greater the dependence of viscosity on shear.
(3) Filler fineness The higher the fineness of the filler, the better the dispersion and the higher the viscosity.
(4) Solubility of the solvent The better the solubility, the greater the viscosity, the higher the density of the formed film and the more uniform the structure . Be sure to pay attention to the choice of thinner during construction.
(5) Construction temperature The higher the construction temperature, the smaller the viscosity and the better the bonding performance with the base material.