Silicone resin coating has been widely used in many fields because of its excellent high temperature resistance, weather resistance and other properties. However, at present, silicone resin is mainly methyl silicone resin and methyl phenyl silicone resin, or its flexibility is poor, or it needs to be cured at high temperature for a long time, which limits its application.
In this paper, through the hydrolysis co polycondensation reaction of methyl trimethoxysilane (MTMS) and propyl trimethoxysilane (PTMs), PTMs is introduced into methyl silicone resin, and the flexible organic groups contained in PTMs are used to improve the flexibility of the coating, so as to prepare silicone resin coatings with low curing temperature, fast curing speed and good flexibility. The main contents and results are as follows:
1. The hydrolysis processes of MTMS and PTMs were investigated by conductivity meter. The effects of the type of alkoxysilane, solvent, amount of water added, type and content of catalyst, hydrolysis temperature and time on the hydrolysis of alkoxysilane were studied; The effects of MTMS / PTMs ratio, water addition, distillation reaction temperature and distillation time on the storage stability and coating properties of modified methyl silicone resin coatings were studied; The curing characteristics of self-made silicone resin coatings were studied by thermogravimetric analysis (TG) and infrared spectroscopy (FTIR).
The results show that when the mass ratio of MTMS / PTMs is 3:1 and the mass ratio of H2O / alkoxysilane is 4:1, PTMs is pre hydrolyzed at 60 ℃ for 15min and then added to MTMS for hydrolysis and polycondensation at one time. The modified methyl silicone resin coating has good comprehensive properties. After curing, the pencil hardness is 4h, the adhesion is grade 1 and the flexibility is 2mm. The initial thermal decomposition temperature of the coating in nitrogen and air is basically the same (240 ℃), but with the increase of temperature, the thermal stability of the coating in air is significantly worse than that in nitrogen.
2. The effects of curing catalysts such as dibutyltin dilaurate, triethylenetetramine and KH-550 on the curing, physical and mechanical properties and thermal stability of modified methyl silicone resin coatings were studied.
The results show that after adding 0.3% (mass fraction) curing catalyst KH-550, the modified methyl silicone resin cured at room temperature has good comprehensive properties, the surface drying time is about 35min, the pencil hardness of the cured coating is 3h, the adhesion is grade 1, the flexibility is 2mm, and the initial thermal degradation temperature in nitrogen atmosphere is 251.7 ℃.
3. The effects of difunctional siloxane dimethyl dimethoxysilane (DDS) and Diphenyldimethoxysilane (DPDS) on the preparation process, curing conditions, physical and mechanical properties, thermal stability, glass transition temperature and storage stability of silicone resin coatings were studied.
The results showed that: the introduction of two functional siloxane greatly enhanced the gel time of modified silicone coatings while improving the flexibility, impact resistance and adhesion of the coatings, but also resulted in the decrease of hardness of the coatings. The introduction of DDS decreased the initial thermal degradation temperature of the modified silicone coating, while the introduction of DPDS increased the initial degradation temperature of the coating. The modified methyl silicone coating containing difunctional siloxane has good damping characteristics near room temperature, so it is specul