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Raw materials and research progress of waterborne polyurethane adhesive

polyurethane adhesive has the advantages of bonding strength, high peel strength, impact resistance, ultra-low temperature resistance, good wear resistance and so on. Its application is more and more extensive However, at present, solvent based polyurethane adhesive dosage is still widely used. With the increasing attention to environmental protection, the voice of reducing volatile organic compounds is higher and higher. Waterborne polyurethane adhesive high molecular polymer has the mechanical properties with the widest range of variability among all known materials. It is an inevitable trend for adhesive to replace solvent based polyurethane adhesive In this paper, the effects of reaction raw materials and their dosage on the properties of waterborne polyurethane adhesive lotion are analyzed, and the research progress of the amount of waterborne polyurethane adhesive is reviewed

in recent years, patents and papers related to waterborne polyurethane have emerged in endlessly. New varieties of waterborne polyurethane continue to appear and their properties continue to improve. It has been widely used in coatings, leather making, printing industry and other fields. At the same time, it has also been applied in the packaging field, and is known as the all-purpose adhesive of the 21st century. Its importance is obvious. The main raw materials and components of waterborne polyurethane adhesive include polypolyols, isocyanates, related additives such as catalysts, chain extenders, neutralizers, crosslinkers, solvents, etc

the main raw material of polyurethane adhesive

polypolyols

polypolyols are mainly polyether polyols and polyester polyols. The prepolymer prepared from polyether polyol has good hydrolytic stability, flexibility, extensibility and low temperature resistance. The waterborne polyurethane in China mainly uses polyoxypropylene triol as raw material. Polyester polyol prepolymer has great cohesion and high bonding strength, but its hydrolysis resistance is not as good as that of polyether type. The hydrolysis resistance of waterborne polyurethane adhesive can be improved by using hydrolysis resistant polyester polyol polyurethane prepolymer and then dispersing it in triethanol. At present, polyester type is generally used as waterborne polyurethane abroad

in addition, the relative molecular weight of polyols also has a great impact on the properties of polyurethane. The larger the molecular weight of polyol, the softer the adhesive film of waterborne polyurethane with many compressed components in engineering; On the contrary, the harder the film, the better the water resistance

diisocyanates

diisocyanates are divided into aromatic diisocyanates and aliphatic or alicyclic diisocyanates. Aromatic diisocyanates contain benzene rings, so the synthesized prepolymer has high strength, but poor yellow resistance; Aliphatic diisocyanates have excellent yellowing resistance, solvent resistance and water resistance because they do not contain unsaturated double bonds. Aliphatic or alicyclic diisocyanates are generally used as raw materials for high-quality waterborne polyurethane abroad, while aromatic diisocyanates (TDL) are mostly used in China due to the limitations of raw material varieties and prices

catalyst

commonly used catalysts include tertiary amine catalysts and organotin catalysts. Tertiary amine catalysts are particularly effective in promoting the reaction between isocyanate and water, and are generally used to prepare polyurethane foam; The data of NCO/OH reaction catalyzed by organotin catalyst should be stronger than that catalyzed by NCO/H20 anti sphere. This kind of catalyst is mostly used in the preparation of polyurethane adhesive

chain extender

chain extender is usually a compound with two active hydrogen groups, with a molecular weight between 18 and 200. Chain extenders are mainly divided into amines and alcohols. Commonly used amines include ethylenediamine, diethylenetriamine and triethylenetetramine, which are usually added during emulsification. There are patent reports that the aqueous polyurethane urea dispersion prepared with mixed amines as chain extender has excellent bonding performance, high glass transition temperature and excellent high temperature performance. Alcohol chain extenders include 1,4-butanediol, ethylene glycol, diethylene glycol, etc

hydrophilic chain extender

hydrophilic chain extender can introduce hydrophilic groups, which is a special raw material only used in the preparation of waterborne polyurethane. Hydrophilic chain extenders are cationic, anionic, amphoteric and non-ionic. At present, anionic self emulsification is widely used and has good effect. Anionic self emulsification can be divided into sulfonic acid self emulsification and carboxylic acid self emulsification. Sulfonic acid self emulsification requires strong dispersion or grinding dispersion, and its stability is poor; The share price of carboxylic acid type then fluctuated significantly. The hydrophilic dispersion of emulsion is stronger than that of sulfonic acid type, which only needs mechanical dispersion. Therefore, carboxylic acid type is widely used at present. Among carboxylic acids, DMPA has the best emulsifying effect. It is a hydrophilic chain extender commonly used in the preparation of polyurethane lotion at home and abroad. As early as the 1960s and 1970s, Germany and the United States used it to prepare polyurethane lotion

neutralizer

neutralizer is also called salifying agent. Neutralizers of cationic polyurethane lotion include acids such as HCI and CH3COOH, alkylating reagents such as CH31, (CH3) 2s04 and epichlorohydrin; The commonly used neutralizers of anionic polyurethane lotion include sodium hydroxide, ammonia water, triethylamine, methylamine, ethanolamine and dimethylethanolamine

solvent

in the process of preparing polyurethane lotion, sometimes the viscosity of prepolymer will be very large, which makes it difficult to stir. It is necessary to add organic solvents such as acetone, methyl ethyl ketone, N,, N-dimethylformamide, N-methylpyrrolidone and toluene, among which acetone is the most commonly used. Generally speaking, after the stable lotion is prepared, the acetone with low boiling point can be removed from the lotion by vacuum distillation to reduce the content and odor of organic solvents in the lotion. During the drying of waterborne polyurethane, the evaporation of a small amount of residual low boiling point solvent can accelerate the drying time of the film, while the presence of a small amount of high boiling point solvent such as N-methyl pyrrolidone can reduce the viscosity of the initial reactant and smooth the film

(to be continued)