Efficient dispersion technology and equipment of t

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Efficient dispersion technology and equipment of environmental friendly water-based coatings

efficient dispersion technology and equipment of environmental friendly water-based coatings

June 5, 2019

coatings are actually the product of modern industrial development, but they have a long history of development. With the emergence of polymer materials, people's daily life and industrial development have undergone significant changes. Under the guidance of fine chemical products, the quality of the original paint has been significantly improved. In recent years, the sales volume of coatings has exceeded 5% of the output value of the chemical industry, and shows a steady growth trend, which also shows the important role of coatings in the development and construction of the national economy

1 composition and category of coating

1.1 film forming material

film forming material is mainly composed of two parts, which are polymer materials and grease, which are important components of coating covering the surface of coating. As the basis of coating composition, the physical and chemical properties of the film-forming material have a direct impact on the coating. The primer must have good adhesion and rust resistance, so that it can be closely combined with the topcoat; The finish coat needs to have good insulation and decoration. According to economic factors and practical requirements, the film-forming materials should be selected first, and then other components should be analyzed

1.2 dispersion diluent

under normal circumstances, the viscosity of film-forming materials is relatively large, belonging to high molecular polymers. Organic solvent as a dispersion medium, with coordinated paint viscosity 2 The experimental record requires that the degree can be achieved through the display screen in the form of data and curves, so that the film-forming material can be dispersed into liquid, so as to ensure that the coating can be applied directly. After the coating construction and film forming, the organic solvent will volatilize into the atmosphere, and the film-forming substances will form a protective film on the surface of the object. The volatile matter in the paint is mainly water and organic solvent, but the organic solvent will cause environmental pollution after volatilization, so the use quantity should be strictly controlled

1.3 pigments and fillers

pigments and fillers cannot form a film alone in the process of practical application. They need to be fused with film-forming substances with the help of relevant means to form a film after the coating is cured. In other words, the application of film in pigments and coatings acts as an auxiliary material

pigments can provide various colors for coatings and have good decorative effects. In addition, pigments also play a good role in improving the acid-base and chemical resistance of the material film. Filler, also known as physical pigment, although the coloring effect is not obvious, it can effectively improve the performance of the coating and reduce the production cost of the coating

2 dispersion technology and equipment of environmental friendly waterborne coatings

2.1 dispersion mechanism of pigments and fillers

coatings have many categories, but the production principle is basically the same. On the whole, the coating belongs to the system after the mixing of pigment, solvent and paint. Under the effect of coating, it is evenly applied on the surface of the object and forms a film after curing. Although it is relatively simple to say, it is not easy in fact. Color paint belongs to viscous paint, which is mainly composed of solvents and additives. The whole system contains a variety of phase interfaces, and different components are always in the state of interaction. Therefore, the stability of the system is low, and the problem of phase interface separation is very easy to occur. However, the color paint production needs to be in a relatively stable state. Once there is a separation problem, the viscosity of the color paint will be significantly affected, and the effect of this paint after construction is not ideal. Therefore, the color paint is not just a simple mixing of different components, but should be dispersed into the paint structure with the help of effective dispersion means

in a broad sense, solid matter is distributed in liquid or gas state, which is called dispersion. For coatings, dispersion mainly means that the pigment is evenly distributed in the resin solution and is in a relatively stable system. The dispersion of pigments in the paint is relatively cumbersome, which can be basically divided into three stages: wetting stage, depolymerization stage and stabilization stage

2.1.1 wetting stage

when the surface of pigment particles is applied in paint production, the top layer will definitely contact with water and air, and the gap between different particles will also be filled with air. If the pigment wants to be evenly dispersed into the paint, the prerequisite is to use the paint to replace water and air, and at the same time, form a coating on the surface of the pigment particles. The process of paint replacing moisture and air and forming a coating film on the surface of pigment is the wetting stage of pigment

2.1.2 depolymerization stage

the pigment is dispersed in the paint. It is far from enough for the paint to only get a guiding contact with the test bench on the surface of the pigment particles. The main reason is that the pigment cannot be in a stable dispersion state. Therefore, it is necessary to apply external force to decompose the pigment particles, change their volume into primary particles, and increase the basic area of pigment particles and coatings. With the help of external force, the process of restoring the pigment to the original particles is called the depolymerization stage

2.1.3 stabilization stage

pigments want to be stably distributed in the paint system, mainly through two mechanisms, which are steric resistance stabilization and charge stabilization. Under normal circumstances, in the environment of aqueous solution, the dielectric constant of pigment particles is relatively high, and the stabilizing effect of charge is very significant

after adsorption, the positive and negative ions of pigment particles will gradually transfer to the opposite solution, and then form a charged particle film on the surface of the solution. When opposite particle charges are accumulated on the particle surface, a double charge layer will be formed. This particle distribution is also known as equilibrium particles. The number of double charge layers decreases with the increase of solution depth. In the process of contact between two particles, there is no charge repulsion, which will inevitably cause the charge redistribution of pigment particles, increase the repulsion between particles, and the dispersion system can be in a stable state. This stage is also called the stabilization stage

2.2 environmental friendly water-based coating dispersion equipment

2.2.1 high speed dispersing machine

high speed dispersing machine is one of the most simple coating dispersion equipment. In the operation process, it is combined with the sand mill to act as the pigment pre mixing equipment. In some cases, the high-speed disperser can also become a separate pigment dispersion equipment. The most critical part of the high-speed dispersing machine is the dispersing impeller. The edge of the dispersing impeller presents a curved tooth shape, which is called the yield point or yield strength, and the inclination angle is about 30 °. Each tooth surface will produce impact during operation. The reason for this kind of failure is that there is air in the oil pump of the hydraulic universal testing machine, and the strike force is not completely eliminated. In fact, the material moves from the inside of the tooth surface to the edge, which belongs to shear action. When the paint goes back and forth between the tooth surface and the edge and is in the state of acceleration and deceleration, the viscosity will gradually decrease

the advantages of high-speed disperser are: simple structure, convenient actual operation and later maintenance, high production efficiency. With the continuous increase of equipment categories of high-speed disperser, the scope of application has become more and more extensive

2.2.2 sanding mill

sanding mill was produced in the late 1950s and was first applied in China in the 1960s. The sand mill itself is relatively small, can carry out continuous decentralized operation, and has high operation efficiency, which has been widely used. At the same time, it gradually replaces the role of ball mill in coating

the sanding mill is mainly composed of five parts, including grinding cylinder, dispersion disk assembly, motor, frame and spindle

3 conclusion environmental friendly water-based coatings will not pollute the ecosystem in application, and have good development prospects, accounting for an increasing proportion in the coating industry. However, in the actual production of environment-friendly waterborne coatings, the traditional dispersion technology and equipment are still adopted for pigment dispersion, and the production efficiency is relatively low. This paper analyzes and studies the dispersion technology and equipment of environmental friendly waterborne coatings, understands the application advantages of different dispersion technologies and equipment, and hopes to provide high-quality technology and equipment guarantee for pigment dispersion in environmental friendly waterborne coatings

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