Calcined kaolin surface modification process and precautions!

Calcined kaolin is a mineral material with high whiteness, large specific surface area, good insulation and thermal stability prepared by calcination and dehydration of natural kaolin. Calcined kaolin has excellent chemical resistance, solvent resistance, acid and alkali resistance and good reinforcement and processing properties. It is widely used in paints, coatings, paper, rubber and plastic products, cables, ceramics and other industries.

1.Calcination process of calcined kaolin

Due to the different calcination temperatures of the kaolin in the calcination process, the phases of the calcined products are different and the properties are different, resulting in different application directions and application fields. Therefore, the calcination temperature is a key factor in producing different kaolin products.

Low-temperature calcination (600-1000 ° C), its kaolin products have high activity and are used for the synthesis of functional materials such as molecular sieves, aluminum salt chemicals and plastics and rubber.

At medium temperature calcination (1000°C-1200°C), the kaolin product has high whiteness and good opacity. It can be used in the papermaking and coating industries to replace titanium dioxide as a structural pigment. Used in papermaking can increase the pore volume and bulk of the paper coating, and reduce the loss of brightness and opacity during calendering.

High-temperature calcination (above 1200 °C), its kaolin products are mullite, cordierite, used to produce mullite grain-molded sand, advanced refractory materials and special ceramics.

The calcined kaolin can be classified into incompletely calcined kaolin and fully calcined kaolin depending on the calcination temperature.

Incomplete calcination of kaolin: calcination temperature of 650-750 ° C, dehydroxylation, density of 2.4-2.5 g / cm3, can be used for papermaking fillers and coating.

Completely calcined kaolin: The calcination temperature is 1000-1050 ° C, and a small amount of mullite crystals have appeared under an electron microscope, the density is about 2.7 g/cm 3 , and the whiteness is above 90%. The good performance of fully calcined kaolin is important for the production of coated papers, especially for low-quantity coated papers, and in high-grade paperboard coatings.

2.Surface modification of calcined kaolin

The surface modification of calcined kaolin is to purposefully change the physical and chemical properties of the surface according to the needs of the application.

Surface modification mechanism: The surface chemical method is to adsorb or chemically react the functional groups in the organic molecules on the surface of the kaolin particles, and coat the surface of the particles to organicize the surface of the kaolin.

Surface modification purposes:

It is necessary to change the properties of the kaolin powder interface and improve the affinity of the calcined kaolin and the organic polymer material;

Improve the dispersibility in organic polymer materials, enhance the various properties of the product, and play a functional role;

Increasing the amount of calcined kaolin to increase the grade of the product and reducing the cost of the product.

The surface modification of calcined kaolin is a very important deep processing method, and it is also a very effective way to expand the application field of calcined kaolin and improve the quality of organic polymer products.

The selection and application of surface modifiers is the key technology for surface modification of kaolin, and the process and equipment for surface modification are also important parts of surface modification technology.

(1) Selection of calcined kaolin surface modifier

When selecting the surface modifier, different modifiers and additives should be selected according to the technical performance requirements of the formulation and processing technology of adding organic polymer materials and products according to the requirements of kaolin.

For the surface modification of calcined kaolin, a silane coupling agent is generally selected mainly. For special requirements of polymer products, two or more modifiers should be selected to form a composite surface modifier.

According to the performance and technical requirements of the materials, a certain amount of additives or other modifiers may be added respectively, and the calcined kaolin is effectively surface-modified with the silane coupling agent, so that the performance and quality of the calcined kaolin can be higher. Requirements.

The amount of the surface modification machine can be calculated according to the modification amount, specific surface area and minimum coating area of the calcined kaolin. The general empirical addition amount is about 0.3% - 1.2%.

(2) Surface modification process of calcined kaolin

The calcined kaolin is first heated to react with the silane coupling agent and requires a certain temperature to be maintained for the kaolin under dynamic conditions. Only in this way can the excess water in the reaction process and after the reaction be removed to achieve a stable and strong covalent bond between the coupling agent and the kaolin. Therefore, the surface modification process must be determined according to the mechanism of surface modification.

Calcined kaolin is reacted at a certain temperature during the surface modification process.

Kaolin surface modification process: firstly, when the calcined kaolin is dynamically heated to a certain temperature (100 ° C), under the condition of high speed dynamics, the hydrolyzed silane coupling agent or composite modifier is added, preferably by fog. The law is added. The temperature during the reaction between the coupling agent and the kaolin should be kept within 120 ° C. In the case of high speed dynamics, the holding time should be about 3-5 minutes.

In addition, during the reaction process between the surface modifier and kaolin, pseudo-knot particles are often generated, which has a very important influence on the quality of the product, so effective classification must be carried out, and only in this way can the quality of the product be completely ensured.

(3) Calcined kaolin surface modification equipment

The equipment for surface modification of calcined kaolin has a high-speed kneading machine, a continuous modification machine and a high-frequency vibration grinding machine.

High-speed kneading machine modification: the calcined kaolin powder is added to the kneading machine. Under the high-speed rotation movement of the stirring blade, the high-speed rotating stream impinges on the baffle plate to change the direction of material flow, and the material can be rotated. Rotating up and down strengthens the mixing and dispersing effect of the material. When the friction is raised, an additive is added to adjust the apparent properties of the calcined kaolin. When the temperature continues to rise, the modifier is added by atomization or dropping, and then subjected to a high-speed stirring process to achieve the purpose of surface modification.

Continuous Modification Machine Modification: SLG three-cylinder continuous modification machine is to add kaolin and composite modifier according to a certain proportion, and enter the modification chamber by screw feeding. The kaolin can be heated in this section. After the material enters the modified cavity, it is rotated in a fluidized state under the rotation of the rotor rotating at high speed, and the material is fully dispersed and forcedly modified.

High-frequency vibrating mill: This equipment relies on the exciter to make the medium in the cylinder produce high-frequency and small-amplitude vibration. Since the vibration acceleration is much larger than the gravitational acceleration, the medium in the grinding tube produces high-intensity impact and rotational motion. And the material can be heated quickly, so that the material can be quickly and effectively dispersed and mixed under strong vibration and a certain temperature.

The method can complete the dispersing and surface modification of the calcined kaolin once, and can perform surface modification during the process of scattering. Before using the machine, first adjust the gradation of the medium. When the material is fed into the mill to vibrate and heat up, the composite modifier can be added in the atomization mode of the grinding tube according to the flow ratio of the material. Adding auxiliaries and modifiers at the filling ports of the upper and lower grinding tubes.

The modification effect of the device is not only good, but also can improve the processing efficiency of the calcined kaolin, simplify the production process, reduce the modification cost of the kaolin, and has a good application value.

The selection of surface modification equipment should be based on the process determined by the surface modification mechanism of calcined kaolin, and the surface modification unit should be selected and matched.

Regardless of the surface modification equipment used, the surface modification mechanism and the surface modification process should be used to meet the technical requirements of the surface modification process of calcined kaolin. Surface modification equipment should be required to be heated to above 100 °C under high-speed dynamic conditions, and can be insulated to eliminate water vapor. The surface modifier can be added separately, and the function of classification can be solved to solve the problem of surface modification agglomeration and ensure the product. the quality of.

3. Precautions of Calcined kaolin surface modification

At present, modified calcined kaolin is mainly used in the organic polymer products industry, and the organic raw materials, formulations, processing techniques and technical performance requirements used in these industries are different, which provides an important point for the surface modification of calcined kaolin. The problem is how to adapt and meet its requirements and to show the functionality of the modified kaolin.

Whether the modified kaolin can play a functional role, first of all, attention should be paid to the technical aspects of the raw and auxiliary materials of various organic polymer products and the production process. Can it complement each other in the processing, and eliminate the quality of the raw and auxiliary materials? Process parameters such as specifications, formula design, and process conditions, etc., all of which can affect the application effect of modified kaolin.

To do a good job in the surface modification of kaolin, it is necessary to carefully understand the main technical requirements of organic polymer products, the main raw materials and processing technology. Based on this, the modifier should be selected in a targeted manner, the formulation of the modifier should be adjusted, and a reasonable processing process should be determined.

The surface modification of kaolin is not only the coupling agent, but also the addition of a certain amount of other functional additives according to the kaolin properties of different calcination temperatures and the technical requirements of the organic polymer products, and the main coupling agent is used. More effective surface modification makes the performance and quality of the modified kaolin higher.