Composition and latest development direction of th

Composition and latest development direction of water-based two-component polyurethane coating

composition and latest development direction of water-based two-component polyurethane coating

June 9, 2020

water-based two-component polyurethane coating uses water as the dispersion medium to minimize the emission of VOCs, while maintaining the excellent construction process, decorative appearance, physical and mechanical properties and chemical resistance of solvent based two-component polyurethane coating, It has become the hotspot and development direction of current paint research

composition of water-based two-component polyurethane coating

two-component crosslinked water-based polyurethane coating, that is, the coating is divided into two components: one is water-based polyol component; The other is water dispersed isocyanate component

1. Water based polyol components

according to the colloidal structure of water-based polymers, the cooling method is water-cooled, which can be divided into two categories: one is water dispersed polyols, and the other is lotion polyol coatings. The preparation of waterborne polyurethane polyol can adopt the traditional preparation method of waterborne polyurethane dispersion, but there should be more hydroxyl groups in the hydrophilic group of the polymer, which can meet the reaction requirements of two-component coating in terms of chemical structure. The commonly used methods are prepolymer method and acetone method

compared with the two-component solvent based polyurethane coating, the polyol of the two-component waterborne polyurethane coating has good dispersibility, which can promote the stable dispersion of unmodified and hydrophobic polyisocyanate curing agent in water. According to different preparation methods, aqueous polyols can be divided into lotion polyols and dispersed polyols

2. Lotion polyol

the earliest polyol used is lotion polyol, which is an acrylic polyol emulsion with multiple structures obtained by lotion polymerization. The advantage of its application in two-component system is that the relative molecular weight of the polymer is large, and the drying speed of the film at room temperature is fast; The defect is that it has poor dispersibility to unmodified polyisocyanate curing agent, resulting in poor appearance of the film and short application period

3. Dispersed polyols

in order to improve the water dispersibility of polyol system to polyisocyanate curing agent and improve the performance of two-component waterborne polyurethane coating, dispersed polyols, also known as the second generation of waterborne hydroxyl resin, can be used. At present, there are many studies in this field. The polyol resin is first synthesized in an organic solvent, and its molecular structure contains hydrophilic ionizable groups or hydrophilic non-ionic segments, and then the resin or solution is dispersed in water to obtain a dispersed polyol. It is characterized by low relative molecular weight, small particle size of dispersion (dn=10 ~ 200nm), excellent dispersion of curing agent, good appearance of formed film and excellent comprehensive performance. According to different chemical structures, it can be divided into acrylic polyol dispersion, polyurethane polyol dispersion and polyester polyol dispersion

4. The evaluation results of acrylic polyol dispersion

compared with acrylic polyol emulsion, acrylic polyol dispersion has lower relative molecular weight (mw=2000 ~ 10000), higher hydroxyl functionality, smaller particle size, good dispersion of curing agent, high crosslinking degree of film, excellent comprehensive performance, but the drying speed of film is slower than the former

5. Polyurethane polyol dispersion

polyurethane dispersion itself is a kind of high-performance adhesive. The two-component water-based coating prepared with it has good appearance, excellent mechanical properties, chemical resistance and wear resistance. And the film performance can be determined by adjusting the concentration of carbamate according to actual needs. Aliphatic isocyanates are mostly used to prepare polyurethane dispersions. Their color retention and weather resistance are better than aromatic isocyanates, and their reactivity with water is far less than aromatic isocyanates. 1,6-hexamethylene diisocyanate (HDI), isophordione diisocyanate (IPDI) and hydrogenated diphenylmethane diisocyanate (H12MDI) are the three types of aliphatic isocyanates most used by researchers at present

6. Polyester polyol dispersion

the two-component coating prepared by polyester polyol dispersion has the advantages of good fluidity, strong wettability to pigments, and high gloss of film. However, the biggest defect of the coating prepared by this kind of dispersion is poor hydrolysis resistance. This is because the ester bond of polyester polyol is easy to hydrolyze, which will lead to the fracture of polymer chain, and then affect the film performance. Acrylic polymer can be grafted onto polyester molecular chain to prepare polyester acrylic composite polyol dispersion to improve the hydrolysis resistance of polyester chain. The two-component coating prepared by the polyol composite system organically combines the soft chain segment of polyester with the hard chain segment of acrylic resin, which is conducive to the improvement of film hardness and flexibility

the latest development direction of waterborne two-component polyurethane coatings

1. Nano hybrid technology

introducing nanoparticles (such as graphene, silver, phosphorus, sodium, silicon, zinc, titanium, etc.) into the waterborne two-component polyurethane coating system can significantly improve certain functions of the film, such as heat resistance, corrosion resistance, antibacterial property, combustion supporting property, chemical resistance, corrosion resistance, mechanical strength, etc

2. Resin hyperbranched technology

hyperbranched resin presents a three-dimensional molecular structure. Compared with the traditional linear structure resin, it has the characteristics of ultra-high functionality, compact molecular structure, less chain winding, etc. its high reactivity and good rheology are very suitable for low-temperature baking or room temperature self drying aqueous two-component polyurethane coating system

3. Resin hybrid technology

resin hybrid technology is to hybridize different types of resins to produce new resins that have the advantages of the original resin and meet the needs of a wider range of applications

waterborne two-component polyurethane coating has the characteristics of environmental protection and high performance. As the most important environmental protection coating, in recent ten years, great progress has been made in the renewal of raw materials and the involvement of formulas, as well as the production and construction process of coatings. 2. Poor activity has been widely recognized by the market, and has become the development trend of environmental protection coatings

due to the complex formulation design of water-based coatings and the great difficulty of water-based coating construction, more and more plastic processing enterprises are now buying the so-called universal experimental machine. The market scale of "universal" experimental machine is not yet mature, and the industry standards have yet to be standardized, which determines that water-based two-component polyurethane coatings still have a long way to go