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Yuan Lei's Little Knowledge | Application of Kaolin in Rubber and Plastic Materials and Summary of Common Problems

Release time:

2024-01-31 14:47

Application of Kaolin in Rubber and Plastic

Introduction of 1. Kaolin

Kaolin (clay) is an important non-metallic mineral, and mica, quartz, calcium carbonate and called the four non-metallic minerals. Kaolin is mainly composed of kaolinite cluster minerals (kaolinite, ground stone, perlite, halloysite, etc.) with a small flake, tubular and laminated flake less than 2 microns. The ideal chemical formula is AL2O3-2SiO2-2H2O, its main mineral composition is kaolinite and halloysite, kaolin chemical composition contains a large number of Al2O3、 SiO2and a small amount of Fe2O3、TiO2and trace amounts of K2O its Na2O, CaO and MgO, etc.

2. kaolin physicochemical properties

The Mohs hardness of kaolin is 1-2, some minerals can reach 3-4, the specific gravity is 2.58 - 2.60, and the refractoriness is 1770 - 1790 ℃. Pure kaolin with high whiteness, soft, easy to disperse, good suspension, good plasticity and high adhesion, excellent electrical insulation properties; with good acid solubility, low cation exchange capacity, good fire resistance and other physical and chemical properties. Therefore, kaolin has become a necessary mineral raw material for dozens of industries such as papermaking, ceramics, rubber, chemical industry, paint, medicine and national defense. After calcination of kaolin, the percentage of silica and alumina and all aspects of performance is much better than natural kaolin.

Application of 3. Kaolin in Rubber and Plastic

1. Application of kaolin in plastics

Can improve the glass temperature, improve the tensile strength and modulus, and insulation properties. Kaolin acts as a nucleating agent in polypropylene, which can improve the rigidity and strength of polypropylene. It can block infrared rays in plastic films (such as PE). Adding 5~8 parts of modified calcined kaolin to PVC high-voltage cable plastic sheath material can improve the volume resistivity of the cable. At the same time, kaolin also has anti-sedimentation effect. In the past, antimony trioxide powder was generally used as flame retardant in the production of flame retardant copper clad laminate, due to the high density of antimony trioxide, it is easy to sink in the rubber compound, so a certain amount of kaolin is added to prevent sedimentation, and it can also partially replace antimony trioxide. After a certain proportion of kaolin is added, the flame retardant white extinguishing time of copper clad laminate reaches Fvl level, thus partially replacing and reducing the cost of flame retardant.

2. Application of Kaolin in Rubber

The use of kaolin fine powder instead of light calcium production of rubber tube, tensile strength, elongation at break, tensile deformation rate, Shore A strength and other major technical indicators can meet the requirements of the relevant standards. At the same time, as the particle size of kaolin fine powder decreases, the reinforcement is improved, and the performance is better than light calcium. Adding kaolin compound, mixing is also easy, but also conducive to the dispersion of carbon black in the compound, the surface of the compound is also smooth and soft, the surface of the finished product is fine and smooth.

 

 

Summary of Common Problems of 4. Kaolin

1. Kaolin will be used together with antimony trioxide to make synergistic flame retardant. What is the function of kaolin?

Answer: First of all, kaolin and antimony trioxide are used together. The most important thing is to maintain the original quality inspection. The most important thing is to add kaolin. The most important thing is to reduce costs. The second thing is that kaolin ingredients and attributes (neutral) determine the synergistic flame retardant effect, and the effect of antimony trioxide remains unchanged.

Secondly, kaolin is composed of silica, aluminum oxide, its structure and stability are close to inert, do not react with any acid and alkali, and the pH value is neutral. Kaolin itself comes with flame retardant effect, but the effect is not so obvious, so it is only synergistic flame retardant, in fact, antimony trioxide plays the most important role, kaolin plays a role in reducing costs, and the effect remains unchanged.

2. Customers make rubber and currently use kaolin on the market, but the products they make have yellowing, but there is no problem without kaolin. What is this situation? Do we have any suitable product recommendations?

Answer: Kaolin has a wide range of functions. Whether there is yellowing depends on the rubber species and the designed formula, as well as the amount of kaolin added. Because Jinyang is calcined at normal temperature, its compatibility with some rubber species is not very good. The main yellowing is not the yellowing of kaolin itself. In fact, it stabilizes kaolin, affects the original system, and even affects the functions of some powders. My personal experience and suggestions with low temperature calcined soil, or low temperature surface treatment of soil, the effect will be better.

3. Customers make heat shrinkable sleeves. At present, magnesium hydroxide is mainly used. During flame retardant combustion test, there will be some clay-like viscous feeling, which is not the function of magnesium hydroxide. Customers judge that kaolin may be added. How to solve it?

A: First of all, according to our technical analysis, it is normal that there will be kaolin. First of all, consider the kaolin ingredients, how much impact on this product, if the impact is large, only pure magnesium hydroxide can be considered; if there is no change, you can consider mixed use, after all, cost considerations.

Secondly, it has the characteristics of improving viscosity, but it depends on the medium. Kaolin itself is also called clay and clay. If the medium is the same, the viscosity of kaolin is higher than that of some powder. However, some external forces, such as additives, are needed to improve the viscosity. Kaolin will not change below 1300 degrees. If only kaolin is used for promotion, it will have certain effect, but whether it can meet the requirements needs further verification.

When kaolin is calcined itself, the crystal water is removed, and the water content of the finished product is only 0.1 percent. The same kaolin, when the calcination temperature changes, its performance will also change, which will produce different effects, coupled with surface treatment, there will be more performance. No exact experiment has been done on the decomposition of kaolin, but we have done experiments before. When the calcination temperature is 1800 degrees, there is still no big change, but all the properties almost disappear and become pure mullite.

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