Waterborne PU resin is a kind of polyurethane system which uses water instead of organic solvent as dispersion medium.Water-based polyurethane resin is widely used as adhesive, coating and coating products due to its excellent environmental protection, excellent mechanical properties and good compatibility with other waterborne resins
Synthesis of water-based polyurethane generally, the synthesis of waterborne PU resin is prepolymerization of diisocyanate, oligomer polyols and chain extender. The reaction mechanism of this step is a step by step polymerization.After the reaction to produce a certain molecular weight prepolymer or high molecular weight PU resin, and then emulsified in water by phase transfer method, waterborne PU resin can be synthesized.
Synthetic raw materials of waterborne PU resin:
Polyisocyanate, common varieties are aromatic diisocyanate, including TDI, MDI;Aliphatic diisocyanates HDI and aliphatic diisocyanates IPDI, HMDI, etc.Aromatic PU has good mechanical properties, but its application is limited by the presence of benzene ring, its resistance to yellowing and its high thermal activation temperature.Aliphatic or aliphatic PU has better hydrolysis resistance, better storage temperature than aromatic polyurethane, and better resistance to yellowing.High quality waterborne PU resin is generally synthesized by aliphatic or aliphatic isocyanates.
Macromolecular polyols: the macromolecular polyols used in the synthesis of waterborne PU resin are mainly polyether polyols, polyester polyols, polyethylene glycol, polytetrahydrofuran ether, polyester amide, polyols of acrylic acid and so on.The ether group in polyether polyurethane is easy to rotate, has better flexibility, better low temperature performance, and the ether group is not easy to hydrolysis, better water resistance than polyester polyurethane.However, due to the poor hydrolysis resistance of polyester itself, the storage period of polyester waterborne polyurethane made from common raw materials is relatively short.
Chain extender: small molecule chain extender with 1, 4 - butanediol glycol, ethylene glycol, has two acid and ethylenediamine, hydrophilic chain extender is to the end of isocyanate and polyurethane pre polymers of extender chain at the same time the introduction of hydrophilic groups of substances, divided into anionic, cationic and nonionic, three kinds of commonly used have dihydroxy methyl propionic acid (DMPA), sodium oxalic taurine, divinyl three amine, methyl diethanolamine, etc.These structures usually contain carboxyl, sulfonic acid or secondary amino groups. When their side chains are attached to the polyurethane molecular chains, functional groups that can be ionized can be found on the PU chain segments.
Neutralizer: also known as a salting agent, a reagent that reacts groups such as carboxylic acid or sulfonic acid to form polymer salts or ionic groups.The neutralizer for anionic waterborne PU mainly includes triethylamine, ammonia, sodium hydroxide, etc., while the neutralizer for cationic waterborne PU mainly includes acetic acid, CH3I, epichlorohydrin, etc.
Solvent: acetone is commonly used as the solvent, because the viscosity of waterborne PU will increase in the reaction process, leading to difficult stirring and inadequate reaction. Acetone is added to reduce the viscosity, which is conducive to stirring the reaction.Acetone has a low boiling point. After synthesis, acetone in waterborne PU can be removed.
Performance advantages of waterborne PU resin:
1. Because the dispersion medium is water, it is non-toxic, not easy to burn, not polluting the environment, safe and reliable for energy saving.Safe transportation and good working environment.There is no toxic -nco group in the system, and the product is safe and environmentally friendly without residual toxic solvent.
2. The moisture and air permeability of waterborne PU resin is far better than that of similar solvent PU products. Due to its strong hydrophilicity, it has a strong ability to combine with water and thus has good moisture and air permeability.
3. As water is a continuous phase, the viscosity of the waterborne polyurethane system is independent of the molecular weight of the polyurethane resin, and is lower than that of the solvent PU with the same solid content, so it is convenient for processing and easy to operate.
4. The waterborne PU resin system can be blended or copolymerized with other waterborne emulsions, which can reduce the cost or produce more diversified and excellent PU emulsions.
5. Water-borne PU resin has good film-forming performance, firm bonding, cold resistance, water resistance, solvent resistance and abrasion resistance.Due to its adjustable hardness, the application field of waterborne PU resin has been greatly broadened. The hard waterborne PU resin can be used as waterborne floor paint and waterborne wood paint, while the soft waterborne PU resin can be used as soft coating finish for fabrics, etc.
Application fields of waterborne PU resin:
Material composite: PVC, PP, ABS, XPE, PU, PET, wood, cloth, paper and other materials bonding composite;
Automotive interior adhesive: automotive interior adhesive (door interior panel, instrument panel, handrail, etc.), automotive interior flocking adhesive (storage box, sealing strip, spare tire cover panel, etc. Flocking).
Flocking glue: suitable for all kinds of plastic parts (PVC, ABS, PU...)Electrostatic flocking on materials such as sponges and metal parts.
Vacuum absorbing plastic: PVC (PVC) and other soft materials and density board, particle board, wood and other vacuum forming, used in the door without paint, cabinets, computer table, speaker board.
The coating (coating) of metal, glass, stone, wood, rubber, plastic, fabric and other materials, as the coating of metal, glass, stone and other materials, plays an excellent performance of surface enhancement and brightening, wear resistance and aging resistance, solvent resistance and corrosion resistance, high and low temperature and acid and alkali resistance.As a fabric finishing, can play a soft and comfortable feel, waterproof breathable and wet, bright and beautiful color, anti-wrinkle anti-shrink anti-ball effect.
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