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Adding a matting agent can reduce the gloss of the coating, but the matting agent is prone to sedimentation, which reduces the stability of the lotion, and if the mixing is uneven, there are problems such as the difference in the gloss of the coating. Therefore, in order to solve the adverse effects caused by the addition of matting agents, people began to pay attention to the research of waterborne polyurethane self matting resin and microsphere waterborne polyurethane matting resin without adding matting agents.

1. Self Extinction Waterborne Polyurethane Resin

Self matting resin refers to a coating resin that has surface matting effect after film formation without adding additional matting powder or wax to the coating resin. The self matting resin has good compatibility with other resins and similar refractive index after film formation because its components have similar physical and chemical properties and optical energy group structure with matting agent particles, which effectively solves the problems caused by adding matting agent. At the same time, due to the fact that the refractive index of the added matting agent and the coating molecule are not used, the properties of both matting and transparency cannot be considered, and the application requirements of some coatings cannot be met. Therefore, the self matting coating resin that does not use an external matting agent has attracted much attention. The waterborne polyurethane self extinction resin without any matting agent was synthesized by hydrazine hydrate post chain extension method. In the process of and, particles similar to matting agent are generated, and the particles float evenly on the surface of the adhesive film, making the surface micro rough. This method not only solves the defects caused by the use of matting agent, but also has excellent lotion stability, and can also improve the rubbing resistance, folding fastness and rubbing fastness of the coating film. It can be widely applied to the surface coating of leather, polyvinyl chloride (PVC) leather, polyurethane artificial leather, etc. The Chinese patent cn106432667b discloses a preparation method of a self matting soft and sensitive waterborne polyurethane leather finishing agent. The modified patent uses hmdi, HDI Trimer, propylene carbonate glycol and dimethylbutyric acid (DMBA) as main raw materials and hydrazine hydrate as the chain extender after emulsification to prepare a matting waterborne polyurethane. The HDI Trimer in the raw material has a ring structure of three functional groups. The ring structure is stable during the synthesis process, which can form a cross-linked network structure for some polyurethane products. The compatibility of the generated micro gel with other polyurethane resins is decreased during the film formation process. In addition, there is a certain degree of crystallinity in the polyurethane, which leads to a decrease in the transparency of the film formation, achieving the extinction effect of the mask, and greatly improving the elasticity, water resistance, solubility resistance and wear resistance of the polyurethane film.

2. Modification Of Waterborne Polyurethane Matting Resin

Since the addition of matting agent may affect the physical properties of the coating film, and the hydrophilic groups contained in the self matting waterborne polyurethane resin will cause poor water resistance of the coating film after the formation of the lotion film, especially when it is used for the top coating of leather or paper, many companies prepare matting resins through modification, such as silicone modification and cross-linking modification. In the process of film formation of organosilicon modified waterborne polyurethane matting resin, the hydrophobic organosilicon segments migrate to the surface of lotion coating film to form a micro rough surface, which makes the polyurethane have both organic and inorganic properties, and the water resistance, thermal stability and mechanical properties are effectively improved. Silicone modified waterborne polyurethane matting resin was prepared by using PDMS modified PTMG, diisocyanate (IPDI) and dimethylol propionic acid (DMPA) as raw materials. The crosslinking modification changes the structure of linear polyurethane, which is the result of its crosslinking to form dense network polyurethane macromolecules. The particle size of polyurethane lotion increases, and the water evaporates during the drying process of lotion. The examples with larger diameter form a rough surface and low gloss after stacking each other. At the same time, the heat resistance, water resistance and chemical resistance of the prepared waterborne polyurethane were also improved due to the dense cross-linking network structure. The self extinction lotion of waterborne polyurethane modified by internal crosslinking was prepared by post chain extension method. The film surface was rough.

Concluding Remarks

As an important aspect of the application of waterborne polyurethane resin, matting coating resin has been paid attention by the coating industry. However, some products have poor stability. Since there is no need to add matting agent in the coating, the self matting coating resin has strong stability and excellent coating performance, which will become the development trend in the future.