Selective dispersing agent

Dispersing agent Gu name incredible, is to all kinds of powder reasonably dispersed in a solvent, through a certain amount of charge exclusion principle or polymer steric effect, make all kinds of solid stably suspended in the solvent (or dispersion).

Pigment dispersion is a very important part in the production of coatings. It is directly related to the storage, construction, appearance and properties of the coatings, so it is a very important production process. However, the dispersion of the slurry is not only related to the dispersion of the material, but also the formulation of the coating formulation and the choice of raw materials.

Double layer theory

Water - based coatings are used as dispersing agents that must be dissolved in water, and they are selected to be adsorbed onto the interface of the powder and water. Commonly used is the anionic type, they are formed in the water to form a anion, and has a certain surface activity, surface adsorption of powder. After the powder particle surface is adsorbed on the surface of the particles, a double layer is formed. The anion is adsorbed on the surface of the particles. In the medium with the opposite charge of the ion is called the reverse ion. They are adsorbed on the surface of ions by electrostatic adsorption, and a part of the reaction is closely related to the binding of the particles and the surface ions. They are in the medium as a whole, with a negative charge, while the other part of the anti - ion is surrounded by the surrounding, they are known as the free and anti - ion, forming a diffusion layer. Such as the formation of a double layer between the surface ion and the counter ion.

The zeta potential of particles: negatively charged and diffusion layer of positively charged form electric double layer, called the electric potential. Thermal potential: the formation of a double layer of electrical double layer, the corresponding potential.

The action of the electric potential is not the thermal potential, the electric potential and the electric potential, but the charge repulsion. If the medium increases the concentration of the counter ions, the free counter ions in the diffusion layer are forced into the bound counter ion layer, so that the double layer is compressed and the action potential decreases. Without charge repulsion, the system has no stability and flocculation.

Steric effect

A stable dispersion system formed, in addition to the use of electrostatic repulsion, i.e., the adsorption on particle surface negative charge repel each other, to stop between the particle and the adsorption / aggregation and final form of large particles and hierarchical / settlement outside, but also the use of the steric hindrance effect of the theory, namely on the adsorption of negatively charged particles close to each other, making them slide mutually staggered, the steric hindrance effect of the surface active agent is non-ionic surface active agent. The theory of electrostatic repulsion and steric hindrance is flexible and can form a highly stable dispersion system.

The polymer adsorption layer has a certain thickness, which can effectively prevent the particles from the mutual adsorption, mainly depends on the polymer solvent layer, when the powder surface adsorption layer reaches 8-9nm, the repulsive force between them can protect the particles without flocculation. So the polymer dispersing agent is better than the ordinary surface active agent.

Edit this paragraph determination method

Dispersant dosage

(1) Daniel flowing point assay: with a dropper to a certain amount of pigment and pigment mixture droplets gradually into the dispersing agent of water solvent, and with a small scraper carefully lapping uniform, until after grinding pigment paste can scraper shed from the end, the calculation pigment fraction agent and the ratio of pigment. [2]

(2) plus the amount of curve method: to a certain amount of pigment and pigment mixtures made of thick slurry, under stirring droplets gradually into the darker pigment fraction agent solution, each with a measured a viscosity. The amount of pigment dispersing agent, the lowest point is the optimum dosage of dispersant.

(3) concentration / flocculation: a certain amount of pigment and pigment mixtures made of thick slurry, successive addition of the pigment dispersant solution, and mixing uniformly until from the scraper can be completely through. 2 U1 N0 N2 ^6 O- Z1 T9 T 1ml R9 in a black background on the glass plate with a drop of a drop of a drop of pigment slurry. Then gently mix evenly. If flocculation occurs, then in the pigment slurry to increase pigment dispersing agent, until no flocculation occurs, according to the pigment of the pigment dispersant dosage, called C-A value (concentration - flocculation value).

Note: the Daniel flow point is suitable for solvent based coatings, which is not suitable for latex paint. Dosage curve method is only suitable for the slurry itself. In latex paint often dispersant shortage phenomenon, the application must be more (up to double). C-A more comprehensive.

The optimum dispersant concentration (ODC) is usually expressed by the amount of dispersant required per unit of mass per unit of mass. The larger the surface area of the unit volume of the pigment, the higher the ODC.