Coating classification: associated thickener

Core tip: Introduction: Thickener is a kind of rheological agent, which plays a very important role in controlling the rheological properties of the system, especially in latex paint or adhesive, it can give the product excellent performance and physical and chemical stability For example, adding a proper amount of thickener in the water-based coating can improve the workability, thixotropy, anti sagging, pigment dispersion and storage stability of the emulsion paint At first, cellulose (hydroxyethyl cellulose and hydroxypropyl methylcellulose) was used as thickener for coatings, but it could not meet the requirements of rheological properties of coatings and was easily damaged by microorganisms, so its use was limited Then people 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 and more known by people Let's introduce Akzo Nobel Powder coating Akzo Nobel Powder coating is a cost-effective coating solution, which can be applied to different kinds of products After the treatment of static electricity and fire baking, a tough and durable coating surface will be formed, with the least impact on the environment Since the introduction of this technology, powder coating has been able to continue to maintain the Paint Home News: Introduction: thickener is a kind of rheological agent, which plays a very important role in controlling the rheological properties of the system, especially in latex paint or adhesives, it can give products excellent performance and physical and chemical stability For example, adding a proper amount of thickener in the water-based coating can improve the workability, thixotropy, anti sagging, pigment dispersion and storage stability of the emulsion paint At first, cellulose (hydroxyethyl cellulose and hydroxypropyl methylcellulose) was used as thickener for coatings, but it could not meet the requirements of rheological properties of coatings and was easily damaged by microorganisms, so its use was limited Later, alkali soluble thickeners were developed The molecular chain of these thickeners contains a certain amount of carboxyl group When neutralized with alkali, they can quickly change from a low viscosity dispersion system to a water-soluble transparent viscous body, and the viscosity of the whole system suddenly increases They are characterized by high molecular weight, low viscosity, good compatibility with various emulsions and water-soluble systems, no biodegradation, and obvious thickening effect Its disadvantage is that its rheological property is not ideal, it is sensitive to electrolyte and its viscosity is not stable Associating thickener is a kind of hydrophobic modified polymer, which can adjust the viscosity at high and low shear rates respectively It overcomes the disadvantages of high viscosity of colloidal dispersion at low shear rate, which leads to the deterioration of the fluidity and leveling of the coating, and low viscosity at high shear rate, which makes the coating unable to transfer smoothly from roller coater to the coating Thickening mechanism: association thickener is a water-soluble polymer of hydrophobic association type, which generally refers to a water-soluble polymer with a small amount of hydrophobic groups on the hydrophilic macromolecular chain In polymer aqueous solution, hydrophobic groups aggregate due to hydrophobic action, which makes macromolecular chains associate with each other in and between molecules, which greatly affects the rheological properties of aqueous solution Above the critical associating concentration, a supramolecular structure dominated by intermolecular association is formed, which increases the volume of fluid mechanics, so it has better thickening property and is a new generation of thickener Because there are two or more lipophilic groups in the water-soluble chain with low molecular weight of the associated thickener, there is surfactant behavior in water, which can form micelles However, the two lipophilic groups in the molecule are not necessarily in the same micelle, so they are linked to form a structure The affinity groups of the associating thickeners can adsorb emulsion particles and pigment particles, which enhance the structure Moreover, the particles bridged by the thickener macromolecules form a physical network structure, which can be destroyed gradually in the shear field, so the flow properties of the system can be controlled Such association breaks off at high shear rate, reduces viscosity, forms again after shear removal, and recovers viscosity However, the formation of association takes time, so the recovery of viscosity is not as fast as that of cellulose, so a certain flow time is given, which is conducive to leveling and improving luster Species: associative thickeners mainly include non-ionic hydrophobic modified ethylene oxide polyurethane copolymer (HEUR), hydrophobic modified alkali solution or alkali swelling solution (HASE), hydrophobically modified cellulose (HMHEC), acrylic acid (ester) polymer emulsion and ethene Preparation method: hydrophobically modified hydroxyethyl cellulose (HMHEC) is water-insoluble in nature Cellulose can be made water-soluble by chemical reactions with hydrophilic substituents such as hydroxyl groups Water soluble cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose and methylcellulose have been prepared by this method These cellulosic polymers can be used to prepare associating thickeners through hydrophobic reagents, large monomers of surfactants and water-soluble surfactants In addition, the cellulose Association thickener can be prepared by the direct reaction of amphoteric reagent and cellulose ① Many thickeners of cellulose Association compounds can be synthesized by side group reactions of reactive hydrophobic compounds and common water-soluble cellulose derivatives Hydrophobic reagents usually include long-chain alkyl epoxides, alkyl halides, acyl halides, isocyanates, anhydrides, etc In order to solve the problem of compatibility between hydrophobic reagents and water-soluble cellulose, the reaction is usually carried out in the slurry medium The reason for choosing the slurry medium is that the viscosity of the system is low, which is conducive to the side reaction Typical slurry process includes: swelling cellulose derivatives with organic solvent, adding NaOH into water, and then adding reactive hydrophobic compounds ② Some thickeners for cellulose association can also be prepared by graft copolymerization In graft copolymerization, large monomers with hydrophilic and lipophilic groups and water-soluble monomers are widely used Among all kinds of initiation methods of graft copolymerization, chemical initiation is a hot topic because it is relatively simple In graft copolymerization, in order to solve the compatibility between water-soluble cellulose substrate and hydrophobic vinyl monomer, it is usually necessary to add organic solvent or mixture of organic solvent The best way to graft large monomers of surfactants onto cellulose derivatives is UV irradiation Compared with the above chemical initiation, UV irradiation can graft more surfactant monomers into cellulose derivatives HEUR, a non-ionic hydrophobic modified ethylene oxide polyurethane copolymer, contains a hydrophilic polymer main chain, which usually consists of one or more polyethylene glycol chains (PGE) extended with isocyanate and terminated with long chain hydrophobic segments In order to prepare HEUR, polyurethane prepolymer with NCO end group was prepared In fact, the prepolymer forms the substitution reaction of hydrophilic chain segment in the final HEUR, which can be realized by the reaction of alcohol with single functional group and - NCO at the end of prepolymer In general, the chain of diisocyanate (H12MDI) - polyethylene glycol oligomer with narrow relative molecular weight distribution is extended and terminated with long-chain alcohol to produce HEUR with wide relative molecular weight distribution, which is called S-G HEUR There is another type of HEUR, namely uni HEUR, which is prepared by direct modification of polyethylene glycol with low dispersion The common reaction formula for the preparation of S-G HEUR and uni HEUR is as follows: water is easy to react with diisocyanate, so the trace water must be removed from the reactor before polymerization The reaction device is a round bottom flask equipped with a condensing tube, a thermometer, a N2 pipe and a magnetic stirrer, and the heating device is heated by an oil bath N2 was dried and purified by silica gel, and oxygen was absorbed by pyrophenol solution After drying, the reaction solution was cooled, a proper amount of diisocyanate H12MDI containing dibutyltin was added, and it was fully mixed in the mixed solution of tetrahydrofuran and toluene, which resulted in the gradual increase of polymerization The average relative molecular weight and the molar ratio of the starting reactant are increased gradually The reaction of PEG and H12MDI was continued to obtain the theoretical value of NCO content of NCO / Oh ratio in prepolymer The prepolymer containing - NCO end group was prepared, and then the end capping reaction was carried out by adding toluene solution of monofunctional alcohols The reaction generally lasted for 2 hours HEUR associating thickener / toluene solution was precipitated in petroleum ether and filtered The final product is obtained by collecting in the sintering cup and then drying in vacuum Home of coatings is specialized in coatings, diatom mud, paint coating, coating technology, fire retardant coating news and coating, diatom mud, paint coating, coating technology, fire retardant coating decoration knowledge and decoration renderings,