Weathering resistance and mechanical properties of...

1、Weathering resistance The weathering resistance is one of the main characteristics of the silicone resin, which is widely used as a weather-resistant coating base material. Film durability test is the most simple method is to be coated with the silicone resin test piece, exposed to the outdoor, and to observe the coating gloss or color change and cracks, etc.. However, due to the amount of sunlight received by the specimen in the outdoor temperature changes, rain, snow, wind, frost attacks, air free of dust and various chemical substances pollution are not the same, it is difficult to strict standards. Appraisal and analysis more difficult. Combined with the outcome of the longer period (in years), thus making this method gradually less now with the accelerated aging test machine strike weather data.   In the acceleration test conditions, the coating gloss is maintained at 60%, alkyd resin coatings 250h and 750h, containing 50% (mass fraction) siloxane, containing 30% (mass fraction) of silicone alkyd resin coatingalkyd resin coating 2000h, the silicone coating gloss retention rate is still higher than 80% after 3000h after.   In a number of factors that can cause degradation of coatings, sunlight, especially ultraviolet radiation is the main reason to cause the coating reduced gloss and surface chalking. Is known, the sunlight spectrum distribution of the Earth's surface, the light sensitive wavelength region, is the root cause of the poor weather resistance of the organic resin. Known, the methyl silicone almost no absorption of UV light of 280nm or less (including a small amount of ultraviolet light) containing PhSiO1.5 or Ph2SiO link silicone absorbs only sunlight silicone smaller, which is the main cause of a silicone resin coating excellent weatherability. 2、Mechanical behavior Purposes, depending on the requirements of the mechanical properties of silicone resin. As the electrically insulating paint, coatings and adhesives, silicone resin, people are more concerned about its hardness, elastic, thermoplastic and adhesiveness. The silicone resin film hardness and elasticity, can be varied within a wide range by adjusting the resin molecular structure. When the higher the content of trifunctional or tetrafunctional chain, i.e. the greater the crosslink density, high hardness and low elastic film can be obtained; introduction of sterically hindered substituent, and can improve the flexibility and thermal elastic positive is a methyl phenyl silicone resin is flexible methyl silicone resin and thermoplastic than reason. Thus, the silicone resin without the use of special plasticizer, but by an appropriate mix of hard and soft silicone to meet the requirements of plastic.   When used for certain coatings, the hardness of pure silicon resin coating film is insufficient, and more than the thermoplastic; organic modified silicone resin, it is easy to resolve this conflict.   Pigments and catalysts can also affect the hardness and elasticity of the silicone resin. Pigments Haste silicone resin film oxidation, and to convert it into a more rigid silicon glass. Use a low activity catalyst, the condensation reaction is not complete, only soft coating; Conversely, the use of high-activity catalyst compound (such as Pb, Al, etc.), to obtain a hard and brittle coating, but some titanium catalyst (e.g., esters) no longer able to seriously reduce the elasticity of the premise, and effectively improve the hardness of the coating.   Silicone resin, but poor adhesiveness to copper, iron, aluminum, silver, tin, glass and ceramics, good adhesiveness, especially in high temperature and long time after the heat aging, may make a surface oxide film of copper do notaccelerate silicon resin by pyrolysis reaction so. The grease of organic material such as plastic, silicone rubber such (gb.szrl.net), an adhesive, depending on the surface of the latter and the compatibility with the silicone resin. The lower surface and bonding compatibility worse the harder material. Through processing (including scrubs and primer) on the surface of the substrate, especially the introduction of a tackifying component in the silicone resin, a silicone resin can be improved to some extent the adhesion to difficult substrates.