For rubber, calcium carbonate is the third largest inorganic filler after carbon black and silica. It has a certain reinforcing effect in natural and synthetic rubber and can improve or strengthen the tensile strength of rubber vulcanizates. Strength and wear resistance, improve tear resistance, adjust the Mooney viscosity of the rubber compound, increase plasticity, facilitate molding, make product dimensions more stable, and reduce production costs.
Calcium carbonate has the characteristics of wide resources, low toxicity and pollution, high whiteness, large filling volume and low price. It is widely used in the rubber industry and is the main light-colored filler for rubber products.
Calcium carbonate is divided into heavy calcium carbonate, light calcium carbonate, nano calcium carbonate and modified calcium carbonate. Calcium carbonate products play different roles in rubber products, so their application fields differ slightly.
Heavy calcium carbonate + rubber
Heavy calcium carbonate is a commonly used powdered inorganic filler. It has the characteristics of high purity, high inertness, good stability, high whiteness, low oil absorption and refractive index, and good dispersion. It has a poor reinforcing effect on rubber products, mainly as filling. It plays a filling and compatibilizing role in natural rubber, synthetic rubber and latex. It can make the rubber material strong and easily dispersed in the rubber material. It can also be used as an isolation agent or release agent. Those with a whiteness higher than 90% can also be used as a Whitening agent.
The mechanical properties of heavy calcium carbonate vulcanized rubber are not as good as those of light calcium carbonate and modified calcium carbonate vulcanized rubber, and the wear resistance and elongation stress of the vulcanized rubber are not as good as those of carbon black, clay or silicate vulcanized rubber. In addition, excessive particle size of heavy calcium carbonate particles will also significantly decrease the physical and mechanical properties of the vulcanized rubber. However, its production cost is low, and its use with other reinforcing agents or fillers in rubber can adjust the properties of the vulcanized rubber and reduce production costs.
Heavy calcium carbonate is widely used as an inert filler in natural rubber, styrene-butadiene rubber, latex, etc. It is suitable for manufacturing heels, soles, floors, hoses, foam products, molded products, and extruded products.
Light calcium carbonate + rubber
Modified calcium carbonate, also known as activated calcium carbonate, is produced by surface modification of light calcium carbonate and nano-calcium carbonate using surface modifiers. Compared with before modification, calcium carbonate after modification generally has the characteristics of smaller particle size, lower oil absorption value, good dispersion, and good reinforcement.
The reinforcing properties of modified calcium carbonate are far better than those of unmodified calcium carbonate. Its reinforcing properties are mainly because the surface modifier is an organic substance with amphiphilic groups; it has hydrophilic and lipophilic groups. Surface modifiers combine calcium carbonate and rubber closely through two groups, which is beneficial to improving the physical and mechanical properties of rubber, processing performance, elongation, tensile strength, tear strength, and other properties of products.
Nano calcium carbonate + rubber
Compared with ordinary calcium carbonate powder, nanometer calcium carbonate powder has a small size effect and surface effect and can produce excellent properties that ordinary calcium carbonate does not have. It mainly acts as reinforcement, filling and color adjustment in rubber products.
Nano calcium carbonate has high activity, and its reinforcing performance is much greater than that of light calcium carbonate, which is equivalent to precipitation silica. Nano-calcium carbonate has good dispersion and compatibility in rubber, making the rubber easy to mix and disperse, improving the rubber’s processing performance and the product’s mechanical properties. At the same time, nano-calcium carbonate has a spatial three-dimensional structure and various particle shapes. Studies have found that different crystal forms of nano-calcium carbonate have different reinforcing effects on rubber. Among them, interlocking nano-calcium carbonate has the best reinforcing effect on rubber.
It is worth noting that it can be used alone as a reinforcing filler and in conjunction with other fillers according to production needs. It can not only achieve the functions of reinforcing, filling, improving processing technology and improving product performance, but also has the function of whitening. Functions and partially replaces expensive white fillers such as silica and titanium dioxide.
The rubber industry is also one of the main fields of application for nano calcium carbonate. It is mainly used in the inner and outer rubber of car tires, special parts of automobile tire inner tubes and outer tires, tape hoses, rubber shoes, and rubber cloths. Suitable for NR, BR, SBR and other rubber systems.
Nano calcium carbonate products are used in rubber and have low requirements on hydrochloric acid insoluble matter, heavy metal content and pH value.
Modified calcium carbonate + rubber
Modified calcium carbonate, also known as activated calcium carbonate, is produced by surface modification of light calcium carbonate and nano-calcium carbonate using surface modifiers. Compared with before modification, calcium carbonate after modification generally has the characteristics of smaller particle size, lower oil absorption value, good dispersion, and good reinforcement.
The reinforcing properties of modified calcium carbonate are far better than those of unmodified calcium carbonate. Its reinforcing properties are mainly because the surface modifier is an organic substance with amphiphilic groups; it has hydrophilic and lipophilic groups. Surface modifiers combine calcium carbonate and rubber closely through two groups, which is beneficial to improving the physical and mechanical properties of rubber, processing performance, elongation, tensile strength, tear strength, and other properties of products.
Comparison of SEM photos of unmodified calcium carbonate and modified calcium carbonate:
Modified calcium carbonate is mainly used in rubber products such as tires, hoses, tapes, oil seals, and auto parts and is suitable for NR, NBR, SBR, and other rubbers.
