High solid content waterborne polyurethane and the coatings with double crosslinking structure and multiple hydrogen bonds

The development of coating and emulsion with excellent scratch resistance, friction resistance, high transparency, and yellowing resistance is of great significance for protecting the substrate, reducing the wear of the material, and improving the curing and. drying speed of the coating. Therefore, a double-crosslinked waterborne polyurethane (DCWPU) was prepared in this paper to make up for the shortcomings of slow drying speed and poor toughness of the coating film in a single cross-linked system. Meanwhile, DCWPU utilizes chemical bonding crosslinking network and high-density hydrogen bonding array to cooperate with each other, which is beneficial to improve the mechanical properties of the double-crosslinking system. Herein, 3 (2-hydroxyethyl) isocyanurate (THEIC) was introduced as the intramolecular crosslinking agent, and isophorone isocyanate trimer (IPDI-3), which has the same keto azocyclic structure as THEIC, was added as the post crosslinking agent to further increase the crosslinking degree of the system. The effects of cross-linked monomer content in waterborne polyurethane on scratch resistance, friction resistance, and corresponding emulsion solid content of the coating were studied in the work. It was found that with the increase of double cross-linked monomer content, the hydrogen bond force could be effectively improved, and the mechanical properties, wear resistance and solid content of the emulsion could be significantly improved. It is worth mentioning that DCWPU-3 showed the best comprehensive properties. The emulsion solid content was 48.9%, the tensile strength of the film was increased to 21.8 MPa, the elongation at break was 627.2%, the hardness was 4 H, and the wear amount was 1.2 mg.