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

Water-based two-part polyurethane coating with water as the dispersion medium, minimize the emission of VOCs, while maintaining the solvent-based two-group polyurethane coating excellent construction process, decorative appearance, physical and aesthetic properties and chemical resistance performance, has become the current hot spot and development direction of coating research.
components of water-based two-component polyurethane coatings
two-component cross-linked water-based polyurethane coatings, i.e. coatings are divided into two components: one is water-based polyol components;
1, water-based polyols
according to the colloidal structure of water-based polymers, it can be divided into two categories: one is water-dispersed polyols, the other is emulsion-based polyols

. The preparation of water-based polyurethane polyols can be prepared using traditional water-based polyurethane dispersion methods, but there should be more hydroxyl in the hydrophosphate group of polymers, and the reaction requirements of two-part coatings should be met in chemical structure. Common methods are prejudge and acetone.
two-part water-based polyurethane coating and two-group solvent-based polyurethane coating, its polyol has a good dispersion, can promote the unmodified, water-repugnant polycyanate curing agent in water stable dispersion. According to the preparation method, the water-based polyol system can be divided into emulsion-type polyols and dispersive polyols.
2, emulsion-type polyol
the earliest use of polyols for emulsion-type polyols, it is through emulsion polymerization of acrylic polyol latex with a variety of structures. The advantage of its dual-part system is that the relative molecular mass of the polymer is large, the coating film is drying at room temperature fast, the defect is that it is less dispersed to the unmodified polychyanate curing agent, resulting in a poor appearance of the coating film, and a short application period.
3, dispersive polyols
In order to improve the water dispersion of polyol system to polycyanate curing agent, improve the performance of two-group water-based polyurethane coatings, can be used dispersed polyols, also known as second-generation hydroxyhydroxy resins, there is more research in this area. The polyol resin is first synthesized in an organic solvent, its molecular structure contains hydroelectonic ionized groups or hydro-hydro-ionized chain segments, and then the resin or solution is dispersed in water to obtain dispersed polyols. It is characterized by low relative molecular mass, small dispersion particle size (Dn s 10 to 200nm), superior dispersion of curing agents, good appearance of the formation of coating film, excellent comprehensive performance. Depending on the chemical structure, it can be divided into acrylic polyol dispersion, polyurethane polyol dispersion and polyester polyol dispersion.
4, acrylic polyol dispersion
compared with acrylic polyol latex, acrylic polyol dispersion has a lower relative molecular mass (Mw - 2000 to 10000), higher hydroxyl energy, smaller particle size, good dispersion of curing agents, high film crosslinking, with excellent comprehensive properties, but the film drying speed is slower than the former.
5, polyurethane polyol dispersants
polyurethane dispersants themselves are a class of high-performance adhesives. It is used to make two-component water-based coatings, coating appearance is good, with excellent mechanical properties, chemical resistance and wear resistance. And according to the actual needs, by adjusting the concentration of amino acid to determine the film performance. The preparation of polyurethane dispersions mostly uses adipose isocyanate, its color preservation and weather resistance is better than aromatic isocyanate, and the reaction activity with water is also much smaller than aromatic isocyanate. 1,6-heterocyanate (HDI), isofone diocyanate (IPDI) and hydrogenated diphenyl methane diocyanate (H12MDI) are the three most used classes of fatty isocyanates by researchers.
6, polyester polyol dispersion
polyester polyol dispersion preparation of two-part coating has good mobility, strong wetting of pigments, coating film gloss and high advantages. However, the biggest defect of coating film made with such dispersions is poor hydrolysis resistance. This is because polyester polyols tend to hydrolysis, which can cause the polymer chain to break, which in turn affects coating properties. Consideration may be given to bridging acrylic polymers to polyester molecular chains and preparing polyester-acrylic compound polyol dispersions to improve the hydrolytic resistance of polyester chains. The two-component coating of the polyol composite system 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.
Water-based two-component polyurethane coatings the latest development direction
1, nano-hybridization technology
nanoparticles (such as graphene, silver, phosphorus, sodium, silicon, zinc, titanium, etc.) into the water-based two-component polyurethane coating system, can significantly enhance the coating of certain functions, such as heat resistance, corrosion resistance, bacteria resistance, combustion resistance, chemical resistance, corrosion resistance, mechanical strength.
2, resin overspending technology
overspending resin presents a three-dimensional molecular structure, compared with the traditional linear structure resin, with super-high-level energy, molecular structure compact, less chain winding and so on, its very high reactivity and good fluidization is very suitable for low temperature baking or normal temperature self-drying water-based two-group polyurethane coating system.
3, resin hybridization technology
resin hybridization technology is to hybridize different types of resins to produce a new resin with the advantages of the original resin, to meet a wider range of application needs.
Water-based two-component polyurethane coatings have both environmental protection and high-performance characteristics, as the most important environmentally friendly coatings, in the past ten years, whether it is the raw materials update and formulation involved, or the production and construction of coatings, have made great progress, has been widely recognized by the market, has become the development trend of environmental protection coatings.
Because of the complex design of water-based coating formula, water-based coating construction is difficult, water-based market size is not yet mature, industry standards have yet to be standardized and other objective reasons, decided that water-based two-group polyurethane coatings still have a long way to go.
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