Requirements of rubber products for fillers and functions of various carbon black in rubber (1)


Requirements of rubber products for fillers






1. General requirements






(1) the surface of reinforcing filler particles should have strong chemical activity, can produce good combination with rubber, and can improve the mechanical properties, aging resistance and adhesive properties of vulcanizate. The surface of the non reinforcing filler particles is chemically inert and does not combine with the rubber, which does not affect the mechanical properties, weather resistance, acid and alkali resistance and water resistance of the vulcanizate.


(2) it has high chemical purity, uniform fineness, good wettability and dispersibility for rubber.


(3) it is not volatile, odorless, tasteless, non-toxic and has good storage stability.


(4) fillers for white, light and color rubber products shall not be polluted or discolored.


(5) low price and easy access.






2. Performance requirements






(1) fineness: Generally speaking, the finer the filler particles, the larger the specific surface area, the larger the contact area with rubber, and the better the reinforcement effect. The finer the non reinforcing filler particles are, the better the mixing effect is. But it must be evenly dispersed. If the dispersion is not uniform, even if the particles are very fine, the mixing effect is not good.






(2) particle shape and crystal form: the particle shape of the filler is better in spherical shape, and the sheet or needle shaped filler is easy to produce directional arrangement when the vulcanizate is stretched, resulting in the increase of permanent deformation and the decrease of tear resistance. Carbon black and white carbon black are amorphous in reinforcing filler, and other fillers also have crystalline type. For example, although the chemical composition of silica and silica is silica, the former is crystalline and the latter is amorphous. There are two kinds of crystalline fillers, one is heteroaxial crystallization, the other is equiaxial crystallization. The triaxial x, y and Z of coaxial crystal are similar and isotropic. There are significant differences in X, y, Z triaxial crystallization. Among the common non-metallic mineral fillers, ceramsite, graphite and diatomite belong to the triaxial crystallization system. Calcium carbonate is an equiaxed crystal system. For rubber products with good wear resistance and tear resistance, it is not suitable to use off-axis crystal system as reinforcing filler.






(3) surface properties: when the powder filler is mixed with rubber, its particles are surrounded by rubber molecules, and the extent to which the particle surface is wetted by rubber has a great influence on the reinforcement efficiency. The particles that are not easy to be wetted are not easy to disperse and agglomerate in the rubber, thus reducing the reinforcing effect. This can be improved by the addition of certain substances that contribute to increased wetting. For example, the addition of fatty acids to calcium carbonate, which has little reinforcement effect, reduces the surface tension, increases the wetting degree and improves the reinforcement effect.






The role of carbon black in rubber






Carbon black is the main reinforcing filler of rubber, 90% - 99% of which is element carbon, and the rest is a little volatile and moisture. In the production process of carbon black, a small amount of carboxyl, quinone, phenol, lactone and other chemical groups are adsorbed or combined on its surface. In the past, it was thought that the reinforcing effect of carbon black only depended on its particle size (specific surface area) and structure, but not on its surface chemical properties. In recent years, a large number of research results show that the chemical groups on the surface of carbon black particles can react with rubber in the mixing process, which increases the binding rubber, and then improves the mechanical properties and aging resistance of vulcanizate.


Carbon black is a kind of amorphous carbon. Light, loose and very fine black powder, with a very large surface area and a range of 10-3000m2 / g, is the product of incomplete combustion or thermal decomposition of carbon containing substances (coal, natural gas, heavy oil, fuel oil, etc.) under the condition of insufficient air.






Carbon black can be divided into "reinforcing carbon black", "conducting carbon black" and "wear-resistant carbon black" according to its performance. Carbon black can be used as black dye, for making Chinese ink, ink, paint, etc., and is often used as reinforcing agent in rubber production. According to different purposes, carbon black is usually divided into carbon black for pigment, carbon black for rubber, conductive carbon black and special carbon black.






China is one of the first countries in the world to produce carbon black. In ancient times, people burned animal and vegetable oils and pine branches to collect black ash from fire smoke, which was used to make ink and black pigments. This kind of black ash called "soot" is the earliest carbon black.






In 1912, it was found that carbon black had a reinforcing effect on rubber. Since then, carbon black has gradually become an indispensable raw material for rubber industry.


From rubber technical net