Rubber formula dry goods: What is the difference between active calcium carbonate and ordinary calcium carbonate?
Calcium carbonate is the most common mainstream filler in the production formula of rubber products. It can not only increase capacity and reduce production costs, but also improve the processing performance of rubber materials to a certain extent.
However, in actual production, many manufacturers face a choice: should they use regular calcium carbonate or slightly more expensive activated calcium carbonate? Although these two have similar names, their performance in rubber systems is vastly different. Today we will delve into their core differences in depth.
1、 The essential differences in surface structure
The fundamental difference between regular calcium carbonate and active calcium carbonate lies in the physical and chemical properties of the powder surface.
The surface of ordinary calcium carbonate powder is hydrophilic, which makes it prone to agglomeration when mixed with polymer rubber. Due to its inability to tightly bond with rubber polymers, it can only be simply and rigidly filled in the gaps of rubber.
And active calcium carbonate is coated with surfactants such as stearic acid. This "coat" changes its surface properties from hydrophilic to oleophilic. This lipophilic property allows it to blend perfectly into rubber compounds and form a good interfacial bond with polymer chains.
2、 Significant differences in reinforcement performance
The difference between the two is particularly evident in terms of mechanical performance.
Ordinary calcium carbonate only has the effect of weight gain and filling, and its reinforcement ability is very weak. If a large amount is added in order to reduce costs, it will cause a significant decrease in the tensile strength and elongation of the rubber, and the product is prone to become brittle and fracture.
Activated calcium carbonate has a solid reinforcing effect. It can effectively improve the tensile strength and tear strength of rubber. Even with increasing the filling amount, the decrease in rubber mechanical properties is much smaller than that of ordinary calcium carbonate, which can better maintain the toughness of the product.
3、 The advantages and disadvantages of mixing processing performance
The smoothness of processing directly affects production efficiency.
Ordinary calcium carbonate is difficult to disperse in rubber, consumes materials slowly during mixing, and is prone to agglomerate particles. This will cause white spots and lumps inside the rubber material, and the surface of the extruded product will be rough, affecting its appearance and performance.
Due to its excellent dispersibility, activated calcium carbonate is highly prone to powder during mixing, resulting in extremely high uniformity of the rubber material. The extruded and rolled products produced with it have a smooth and delicate surface, better processing fluidity, and can effectively improve production efficiency.
4、 The influence of oil absorption value
The oil absorption value is directly related to the formula cost and the hardness of the rubber material.
The oil absorption value of ordinary calcium carbonate is relatively high, and it will absorb a large amount of softened oil in the rubber formula during mixing. This not only increases the cost of oil, but also causes the rubber material to harden, making it difficult to control the final hardness after vulcanization.
Activated calcium carbonate has a lower oil absorption value and does not consume excessive plasticizers. It can help enterprises save oil and auxiliary materials, while making the hardness of vulcanized rubber more stable and easy to control.
5、 Subsequent performance and durability of the product
The long-term performance of rubber products tests the adhesion of fillers.
Rubber filled with ordinary calcium carbonate has poor toughness, poor flexural flexibility, and is prone to cracking after repeated bending. In addition, due to weak bonding, the product is prone to powdering and frosting (white frost) after long-term storage, and its aging resistance is average.
Rubber filled with activated calcium carbonate has better bending rebound and excellent bending fatigue resistance. It is firmly bonded with rubber, not prone to powdering or whitening, and due to its oil affinity, the product has better waterproof properties.
6、 Applicable scenarios and selection suggestions
Based on the above differences, how should selection be made in practical applications?
Ordinary calcium carbonate is mainly used for low-end rubber products or miscellaneous parts with low strength requirements, with the main purpose of purely reducing production costs.
Activated calcium carbonate is widely used in high-end fields such as sealing strips, rubber hoses, shoe soles, conveyor belts, and EPDM products. In these scenarios, it can be used to partially replace expensive reinforcing agents such as carbon black, thereby achieving effective cost control while balancing product strength.
Summary:
If you only pursue extreme cost saving, ordinary calcium carbonate is the first choice; But if you want to balance product strength and processing efficiency, the rubber formula should prioritize the use of active calcium carbonate. Choosing the right filler is the key to finding the optimal balance between cost and performance.