General knowledge of coating: wetting and dispersing mechanism of wetting and dispersing agent

It is suggested that the emulsion paint is a mixture of water dispersion of polymer and pigment and filler In order to mix the pigments and fillers evenly with the emulsion, there must be 3 synergistic processes: wetting, dispersing and stabilizing Wetting: the gas-solid interface of pigments and fillers is transformed by wetting agent and dispersant Dispersion: the pigment particles are sheared by mechanical equipment such as high-speed disperser and sanding machine, so that the particles are dispersed from agglomerates and adherents into primary particles Stability: the surface of primary particles is adsorbed by wetting agent and dispersant, and the surface of primary particles is banded by double electric layer and potential resistance Paint knowledge how about Akzo Nobel Powder Coating Recommended introduction: powder coating is a kind of coating with different form from general coating, which is in powder form It is a new type of coating, because of its own advantages and more 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primary particles Stability: the surface of the primary particles is adsorbed on it by wetting agent and dispersant, and the surface of the primary particles is repelled by the same charge and stabilized by the action of double electric layer and potential resistance Types and characteristics of dispersants used at present are mainly divided into: inorganic, organic and polymer Due to the lack of charge, dispersants such as sodium hexametaphosphate and sodium tripolyphosphate are gradually fading out Organic surfactants are mainly non-ionic surfactants, such as polyoxyethylene alkylbenzene ether Polymers include poly (methyl) acrylic acid sodium (ammonium) salt, maleic anhydride and diisobutylene copolymer sodium (ammonium) salt solution In addition to electrostatic repulsion force, polymer dispersant can also provide effective potential repulsion force This is the main reason why it is widely used in the manufacture of emulsion paint The factors that affect the dispersing property are as follows: 1 The structure polymer dispersant is composed of lipophilic group (hydrophobic group) and hydrophilic dissociative group The lipophilic group is adsorbed on the lipophilic surface of the pigments and fillers, and the dissociated group provides charge The hydrophilicity of dispersant should not be too strong, otherwise it can not be adsorbed on the surface of pigment and filler particles After shearing, the pigments and fillers are gathered again with van der Waals force, which becomes larger and settles It is generally believed that the dispersant can be dissolved when it is fully stirred in water On the contrary, when entering into the water phase, it will dissolve into a whole soon, which will cause problems in future storage 2 The relative molecular weight distribution is an important index for testing dispersants A good dispersant should be a polymer with appropriate molecular weight and narrow distribution, because only a very narrow segment of polymer with relative molecular weight plays a role 3 Neutralizing agent and pH value use sodium hydroxide and ammonia water as neutralizing agent to make polymer dispersant water-soluble Due to the variety of alkali, it can be divided into sodium salt and ammonium salt From the perspective of dispersion efficiency, sodium salt is higher than ammonium salt, and ammonium salt will release ammonia slowly after the emulsion paint film is formed, which improves the miscibility of the dispersant and the main resin and improves the water resistance of the paint film, so it is widely used in exterior wall paint The pH value of the system has a great relationship with the dispersion stability The charge on the surface of pigments and fillers will attract the opposite charge to form a double electric layer, and form the stabilization of charge repulsion The surface charge of each pigment and filler is zero or neutral at a certain pH value, which is called the isoelectric point When the isoelectric point, it can not attract the heteroelectric charge and form a double electric layer, so the pH value of the dispersion system should be deviated from the isoelectric point of the pigment and filler to obtain a good dispersion and stability effect 4 The selection of dispersant ① in the manufacture of latex paint, organic wetting agent and polymer dispersant are generally used to solve the problem of stable wetting and dispersion The key to selection is strong dispersion, good effect and high stability White pulp can be prepared for comparative test of heat storage, and determined with the same formula and different dispersants (taking the same solid content) Test steps: accurately weigh dispersant, wetting agent, defoaming agent, bactericide, propylene glycol and deionized water into enamel beaker, mix them with high-speed disperser in laboratory at low speed, and then put them to weigh all kinds of accurate powder After mixing evenly, disperse them with high-speed (1400 R / min) for 45min, put them into glass bottle and seal the bottle mouth Put value = "60" TCSC = "0" unitname = "℃" W: St = "on" style = "margin top: 0px; margin right: 0px; margin bottom: 0px; margin left: 0px; padding top: 0px; padding right: 0px; padding bottom: 0px; padding left: 0px; word wrap: break word; "> 7 days after drying at 60 ℃, it is the best to stir with a glass rod, which can easily touch the bottom; it is the second best if it is slightly hard, but it can be stirred evenly; if there is a hard block, it is not bad if it can not be stirred This method can be used to judge the quality of dispersants, and it can also be used as the basis for selecting dispersants The same effect can be obtained after heat storage for two weeks with the same quantity and different kinds of dispersant ② According to the theory of adding curve of pigment dispersant, the amount of pigment used is tested Different dosage of the same dispersant is used for pulping Measure the viscosity, find out the lowest point of viscosity and the corresponding amount of dispersant X The actual dosage is slightly enlarged, i.e x = 1.2 • x (x is the actual dosage of dispersant in emulsion paint formula) Of course, the fineness must be checked at each viscosity point as a reference ③ in the compatibility test with the color paste, the same formula, the same number of dispersants of different brands are used to make the exterior wall emulsion paint, and then the same color paste is mixed Observe the compatibility of emulsion paint and color paste after heat storage for a period of time To evaluate the applicability of dispersant, the uniformity of film was observed ④ According to GB / T 9755-2001 water resistance project, the water resistance of paint film can be observed If there is no change in 96h, the time can be prolonged Observe the water resistance of paint film to judge and select dispersant Dispersants are expected to be applied to styrene, propylene, acetic acid and acetic acid emulsions With the development of science and technology, waterborne epoxy, polyurethane and fluorocarbon paints will be produced continuously This is a challenge to the applicability of dispersants and also an opportunity for the dispersant industry In order to adapt to the development of waterborne epoxy, polyurethane and fluorocarbon paint, polyacrylic acid grafted amines, esters and ethers dispersants will have great development and better commercial prospects It will be hydrophobic and non-ionic to stabilize the dispersion of pigment with steric hindrance and effective anchoring group Its HLB value is low, and it can provide suitable shearing force when making all kinds of pigment slurry It can disperse not only inorganic pigment, but also organic pigment and carbon black It is the development direction of water-based dispersant Home of coatings is specialized in coatings, diatom mud, paint coating, coating technology, fire retardant coating news and coating, diatom mud, paint coating, coating 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