Application of sodium polyacrylate in paper coating
With the advent of high-speed coated paper machines and high-concentration coatings, the demand for dispersants used in the preparation of coatings is increasing, and the quality requirements for dispersants are also increasing. Polyphosphate has historically been the primary dispersant for paper coatings, and the dispersant sodium polyacrylate is a special type of polymeric surfactant due to its better long-term stability, especially in high temperature environments. The stability exhibited, so it is more and more widely used in the preparation of paints.
The action of a dispersant on pigment particles is a chemical process. First, the dispersant is dissolved in water, ionized in water, and has a large degree of ionization, forming large anions and small cations of equal charge, and positive and negative ions are firmly adsorbed on the surface of the pigment particles, so that the ions have the same electric charge; The oppositely charged ions are freely diffused into the surrounding liquid medium to form a diffusion layer of charged ions, ie, an electric double layer; since the ions with the same charge mutually repel each other, an electrostatic repulsion is formed, which prevents the pigment from flocculation in the aqueous medium, thereby achieving The purpose of dispersion. The dispersant sodium polyacrylate is a polyelectrolyte characterized by a skeleton having a large ion and a counter ion having a small equivalent number and independent charge. Under the action of electrostatic repulsion, the dispersant sodium polyacrylate has strong ionization performance, and the more complete the ionization degree, the more the affinity of the pigment particles on the surface to adsorb ions, the more effective the dispersion is. Therefore, sodium polyacrylate is the most ideal coating pigment dispersant from the perspective of dispersion mechanism.
In the preparation of paints, there are many factors that affect the pigment dispersion effect, such as the dispersion method, the rotational speed and dispersion time of the dispersion disk, the mixing strength, the concentration of the dispersion (solid content), the electrolyte and the metal ion valence in the dispersion. Among them, the role of the dispersant is the most critical. In the preparation of the paint, the basic purpose of the pigment dispersion process is to thoroughly mix the fluid medium and the pigment so that each pigment particle becomes a dispersed monomer surrounded by a fluid medium in a stable environment, neither flocculation nor precipitation. For paper coatings, there is another purpose, which is to obtain the highest pigment volume concentration by dispersion; to prepare a rheologically good coating mixture; to reduce the amount of adhesive; and to have good directional properties of the pigment particles on the surface of the coating.
Sodium polyacrylate can be used as a dispersant, a detergent builder, a flocculant, etc., depending on the relative molecular mass. Since low molecular weight sodium polyacrylate has relative molecular mass adjustability, it can adapt to different needs.
The relative molecular mass is low, and the surface of a single particle can stay a plurality of molecules, so that the polymer adsorbed on the surface of the particle has many dispersion effects and low viscosity. If the relative molecular mass is multiplied, a plurality of particles are surrounded by one polymer molecule to form a particle bridge and it is difficult to achieve a dispersion effect. Therefore, the preparation of the coating uses sodium polyacrylate having a low molecular weight of 500 to 5000 as a dispersing agent. Low molecular weight sodium polyacrylate and most pigments can produce low viscosity and high solid content coatings, can improve pigment fineness and dispersion stability, and are soluble in water, difficult to hydrolyze, non-flammable, non-toxic It has no characteristics such as corrosion. Therefore, the use of low molecular weight sodium polyacrylate as a dispersing agent for paper coatings has received more and more attention.
XQ-5040 dispersant is a high-efficiency and low-cost dispersant. It is used in a small amount and does not require additional auxiliary dispersant during the grinding process. The results of the dispersant dosage test for various pigments show that the optimum amount of XQ-5040 is low and the viscosity of the grinding is also low. Its flat L-shaped dispersion curve indicates that too much dosage will not cause adverse effects. Therefore, an appropriate amount of XQ-5040 can be selected, and the optical and physical properties of the coating remain stable even if the amount of the pigment is changed.