1.Introduction to silicone acrylic emulsion
Silicon-acrylic emulsion is a kind of composite emulsion. It is a copolymer emulsion of organosilicone and acrylate.Acrylic resin has many excellent characteristics, such as weather resistance and light resistance, long time under ultraviolet irradiation is not easy to yellow. In addition, it also has flexibility, so it is often used as a leather finishing agent. However, as acrylic resin belongs to thermoplastic materials, it is a linear molecular structure, lack of crosslink points, not easy to form a network structure, sensitive to temperature changes, high temperature return viscosity, low temperature lack of elastic, that is, easy to appear hot viscosity cold brittle phenomenon.
The main chain of organosilicon resin is si-o bond, and its bond energy is 450k J/mol, which is much higher than the bond energy of 345kJ/mol of c-c bond and bond energy of 351kJ/mol of c-o bond. Therefore, organosilicon resin has good resistance to high temperature, infrared radiation and ultraviolet light, chemical resistance；In addition, the surface energy of organosilicon resin and low vitrification temperature are low.With good hydrophobic wear resistance and anti - pollution.
In summary, the modification of acrylic resin with an appropriate amount of silicone resin can not only make up for the defects of acrylate, but also improve its mechanical properties.
2.Modification method of silicon - acrylic emulsion
Silicone acrylic emulsion modified method there are two ways: the physical method is to a certain amount of siloxane and acrylate mechanical mixing, this method is simple, but due to both the surface and the difference of molecular structure, poor compatibility with polysiloxane acrylate, because the former is migration, caused by composite emulsion stability is poor, prone to phase separation phenomenon, the result is not ideal.Chemical method is the use of emulsion polymerization, in addition to the siloxane and acrylate have a simple physical cross-linking, but also the existence of chemical bonds, so that the two components of the polarity of the material with a large difference in the combination, in the micro to achieve uniform dispersion, improve the stability of the emulsion.
The silicon-propylene composite emulsion was prepared by chemical method, and then the silicon-propylene composite emulsion was used to replace the water-borne polyurethane emulsion.The modified waterborne polyurethane emulsion has the advantages of three, and the water resistance is improved.
According to the preparation method of si-acrylic emulsion, si-acrylic emulsion was prepared by seed emulsion polymerization with methyl methacrylate acrylic vinyl silicone oil as raw material.Then the prepared silicon-acrylic emulsion was modified to the prepared waterborne polyurethane, the composite emulsion was configured by blending method, the film was formed on different substrates, and the mechanical properties of the film such as adhesion contact Angle water absorption were tested,The film surface of the modified si-acrylic emulsion /WPU composite was observed by scanning electron microscope.The structure was analyzed by ir spectra.The experimental results show that the water absorption rate is the lowest when the content of si-propylene emulsion is 2%, which is 18.19%.The adhesion reaches a level when the content is 4% and 5%.Viscosity is also lower than before modification.
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