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Calcium carbonate powder surface modification2019-01-16 09:11:51
Calcium carbonate as a powder material commonly used in plastics has many advantages that other powder materials do not have, such as high whiteness, easy surface organic treatment, light wear on processing equipment and molds, good fluidity in molding processing, etc., plus resources Rich in quality and low in price, and it has become the first choice of inorganic mineral powder materials in the plastics processing industry.
The untreated surface of calcium carbonate has poor compatibility with the resin, which tends to cause uneven dispersion in the polymer matrix, thereby causing interface defects of the composite material, reducing the mechanical strength of the material, and as the amount is increased, these disadvantages are more obvious. Therefore, it is necessary to carry out surface modification, and the surface modification can increase the interfacial compatibility and affinity of calcium carbonate with the organism, thereby improving the physical properties of the composite material with rubber or plastic.
1. Surface modifier
There are many kinds of surface treatment agents, but the commercially available surface treatment agents which are used in a large amount mainly include stearic acid, titanate coupling agent and aluminate coupling agent, in addition to silane coupling agent and phosphoric acid. Ester coupling agent and the like.
Stearic acid is the cheapest modifier for surface treatment of calcium carbonate and is suitable for polyvinyl chloride plastics. Since stearic acid can be used to make the surface of calcium carbonate organic, it can also be used as an external lubricant for polyvinyl chloride. For polyolefin plastics, stearic acid can also be used to treat calcium carbonate, but it is used in larger amounts and only serves as a coating because it has no chemical reaction, so the overall effect is not as good as that of the coupling agent. Several coupling agents can be used for the surface treatment of calcium carbonate, but each has its own characteristics.
Titanate coupling agents are mostly liquid and easy to distribute, but usually have a darker color and are not suitable for products requiring high whiteness;
Aluminate is cheaper than titanate, white or light yellow in color, which is good for white products, but usually solid waxy, requiring sufficient time for melting and distribution;
The silane coupling agent is very expensive, and because of the small and short flexible carbon chain in the molecular structure, it has an influence on the processing fluidity of the filled plastic. When selecting a surface treatment agent, both price and effect should be considered, especially considering which plastic and product to be used for the treated calcium carbonate.
The most critical problem in using a coupling agent is to allow it to reach and react with each particle of calcium carbonate at the fastest rate to form a chemical bond. This requires that one should be distributed under high-speed motion, and the other is to have a suitable temperature to facilitate the chemical reaction. If the moisture content of the calcium carbonate is high, the coupling agent may react with water first (H+ is provided by H2O), rather than reacting with the hydroxyl groups on the surface of the calcium carbonate, the surface treatment purpose cannot be achieved.
Therefore, it is necessary to ensure the three conditions of rapid distribution, suitable temperature and no moisture, in order to play the role of the coupling agent.
2. Powder modification equipment
The high-speed mixer currently in use is not originally designed for the surface treatment of powder materials, but is designed and manufactured for the pre-plasticization of polyvinyl chloride resin, so it is not a device that is naturally suitable for powder surface treatment. It is even less suitable for powder materials with a smaller particle size including calcium carbonate.
For modified plastics processing enterprises, the surface treatment of calcium carbonate is often carried out by themselves. First, the formula can be flexibly mastered. Secondly, the surface treatment of calcium carbonate can be connected in series with the downstream process. Therefore, their focus is on transforming the existing high-speed mixer. To make it more suitable for your own process requirements.
For the production of large quantities of active calcium carbonate, it is necessary to consider the use of surface treatment equipment with large processing capacity and continuous production.
CLG powder surface coating machine is the main equipment of our company.
The powder surface treatment is completed mainly by means of three modifying rollers. The dry powder and dosed agent are put into modifying rollers simultaneously. With high speed rotation, the materials and agent is running in the form of fluidizing vortex. The modification is completed with the heat generated by high speed shearing, colliding and friction among the rotor, stator and the powder.
