In the rubber industry, calcium carbonate is the third largest inorganic filler and reinforcing agent after carbon black and silica. In the past two years, in order to reduce carbon emissions and environmental problems caused by excessive carbon black release, the application of calcium carbonate in rubber has received more attention.
As a filler, calcium carbonate can increase the volume of rubber, reduce the cost of products, and improve processing performance without significantly affecting the performance of rubber products. As a reinforcing agent, calcium carbonate can greatly improve the wear resistance, tear strength, tensile strength, modulus, swelling resistance and other properties of the vulcanizate.
So what kind of calcium carbonate is a filler for rubber, and what kind of calcium carbonate is a reinforcing agent for rubber? Among them, there is no strict or standard division.
Light calcium is a commonly used filler and extender in the rubber industry. It has large filling amount, easy extrusion, good gloss, low hardness and high elongation. Its mechanical properties can exceed the level of clay and semi-soft carbon black. Active nano-calcium can not only be used as a filler for rubber compounds, but also has high reinforcing properties, which can improve the wear resistance, tear strength, modulus and other properties of rubber, and can also reduce production costs. Heavy calcium has outstanding filling performance in rubber, easy to mix and disperse, and the compounding amount can reach 100% to 250% of the rubber amount.
How to modify calcium carbonate for rubber?
In recent years, powder surface modification technology has become one of the hot technologies that people pay attention to. Among them, surface coating modification is an important one in surface modification technology. Coating, also known as coating or coating, is a method of coating the surface of mineral particles with inorganic or organic matter to achieve modification.
The surface coating of calcium carbonate powder is also to introduce a coating layer on its surface as required, so that the modified calcium carbonate can be regarded as a composite powder composed of a “core layer” and a “shell layer”. By coating the surface of calcium carbonate with a covering layer with different chemical composition (such as carbon black), it can make it have good dispersibility and compatibility with rubber. Different powder coating modification processes can specifically improve its thermal, mechanical and chemical stability, change its optical, magnetic, electrical, catalytic, hydrophilic, hydrophobic and sintering properties, and improve its corrosion resistance, durability and use. life, etc.
Hebei Lixin New Material Technology Co., Ltd. has announced a preparation method of light calcium carbonate for rubber. By controlling the preparation process of nano calcium carbonate, the technology obtains calcium carbonate with a chain-like crystal structure, and forms a carbon black layer on the surface of calcium carbonate to obtain an active surface layer with good compatibility with rubber. The surface energy of the coated calcium carbonate is reduced, and it is not easy to agglomerate, the specific surface area is significantly increased, and the dispersibility is good.
Research results of calcium carbonate technology for rubber
In the rubber production process, the role of calcium carbonate is also a relatively complex process. On the whole, under the control of many processes, it mainly achieves reinforcement, filling, color matching, process improvement, product performance improvement, reduction of glue content or replacement of parts. Silica, titanium dioxide and other purposes.
Li Guantao et al. provide a preparation method of light calcium carbonate special for rubber. By controlling the preparation process of nano-calcium carbonate, calcium carbonate with chain-like crystal structure is obtained, and a carbon black layer is formed on the surface of calcium carbonate to obtain an active surface layer with good compatibility with rubber. At the same time, the surface energy of the chain calcium carbonate with carbon black layer is reduced, the agglomeration is not easy to occur, the specific surface area is obviously increased, and the dispersibility is good.
Tan Shulong et al. provided a preparation method of acrylate rubber-coated ultrafine calcium carbonate particles. A silane coupling agent containing carbon-carbon double bonds is used to introduce active double bonds on the surface of the calcium carbonate particles, and then the modified calcium carbonate particles are copolymerized with acrylate monomers to achieve the purpose of rubber grafting and coating the calcium carbonate particles. The rubber synthesis and subsequent vulcanization are combined into one, which avoids the complicated vulcanization process required in the existing rubber production technology, and simplifies the technological process. Technically, the rubber is grafted on the surface of the calcium carbonate particles to solve the problems of unsatisfactory compatibility between the calcium carbonate filler and the base rubber and weak interfacial force during the existing rubber vulcanization process.
Tang Wen et al. provide an application technology of modified calcium carbonate in cable rubber sheath, which can prepare cable rubber sheath with flame retardant effect and anti-aging properties. The cable is made by mixing, thinning, calendering, and sheathing of raw materials such as rubber, carbon black, modified calcium carbonate, stearic acid, hexamethylenetetramine, polymethacrylate, and ultraviolet absorber. Rubber sheath, with good dispersion, tensile strength, tensile elongation and other properties. In addition, Tang Wen et al. mixed heavy calcium carbonate with other raw materials at high speed, and then dried and pulverized it for use in rubber products. Calcium carbonate also has high dispersibility and obvious reinforcing effect.
Xiao Yuxiu et al. provided a preparation method of superfine heavy calcium carbonate for wear-resistant rubber. Adding the pre-dispersant in two portions can avoid the agglomeration of the coarse calcium carbonate powder during mixing and grinding. Calcium carbonate adopts wet grinding method, adding inorganic silicon source to the grinding slurry, which can carry out in-situ inorganic coating on the surface of calcium carbonate, and can also be used as a dispersant, which further reduces the occurrence of calcium carbonate in the grinding process. agglomeration phenomenon. After the coating treatment, the dispersibility of the product is improved, and the mechanical properties and wear resistance of the rubber are ensured.
Epilogue
Calcium carbonate for rubber is rich in varieties and has a wide range of application scenarios. Compared with carbon black, graphene, carbon nanotubes, etc., it has obvious price advantages, and the application technology of downstream enterprises is mature. At present, the domestic production of nano-calcium carbonate is gradually increasing, and various special-purpose calcium carbonates are developing rapidly.