Why Is The Surface Modification Effect Of Calcium Carbonate Poor?You Need To Pay Attention To ThesePosted: 2018-10-08

  • Surface modification is one of the most important and necessary deep processing technologies for the production of calcium carbonate (including light calcium carbonate and heavy calcium carbonate). It is an important means to improve the application performance, improve applicability, expand market and dosage of calcium carbonate.

     

    calcium carbonate

    The surface modification of calcium carbonate powder must be based on the mechanism of surface modification. At the same time, consider the substrate, main formula and technical requirements of organic polymer products in downstream products. After comprehensive consideration, choose a reasonable surface modifier. To determine the surface modification process and equipment, in order to produce qualified active calcium carbonate products on this basis. The modifier, modification process and modification equipment are the three key points in the process of realizing the modification effect.

    Point 1: Select the surface modifier

    The surface modification of calcium carbonate powder is mainly to solve three problems:

    1. The problem of dispersion of calcium carbonate;

    2. The problem of interface with organic polymer materials;

    3. The problem of functionalization and specialization after surface modification.

    Therefore, the above points should be considered comprehensively when selecting the surface modifier, and according to the structure and properties of the surface modifier and its mechanism of action with calcium carbonate powder, the base of the downstream organic polymer products should also be considered. The nature, formulation, technical requirements and physical and chemical properties of calcium carbonate are selected for correct and targeted selection.

    Common surface modifiers for calcium carbonate include stearic acid (salt), titanate coupling agents, aluminate coupling agents, and the like.

    (1) Stearic acid (salt)

    Stearic acid (salt) is the most commonly used surface modifier for calcium carbonate. The dry process can be directly added with stearic acid. In the wet process, stearic acid is first saponified or stearate, such as sodium stearate.

    In order to make the stearic acid better disperse and uniformly react with the calcium carbonate particles, stearic acid may be diluted with a solvent (such as anhydrous ethanol) in advance, and other additives may be added in an appropriate amount during the modification.

    Active calcium carbonate modified with stearic acid (salt) is mainly used for filling polyvinyl chloride plastics, cable materials, adhesives, inks, coatings, and the like.

    (2) Titanate coupling agent

    The molecular structure of the titanate coupling agent is divided into six functional zones, each of which has its own characteristics. After understanding the characteristics, it is possible to flexibly select a titanate coupling agent that can meet various requirements according to the characteristics of the powder to be treated and the application field.

    Titanate coupling agents are classified into monoalkoxy, chelated, and coordinated types:

    The monoalkoxy type is characterized by its versatility and wide adaptability, and is mainly suitable for the treatment of dry calcium carbonate powder.
    The chelating type is a surface modification of a calcium carbonate powder containing a glycol chelating group and suitable for a certain water content.
    The coordination type is good in water resistance, most of which does not dissolve in water, does not undergo transesterification reaction, and is suitable for surface modification of various powders.
    Calcium carbonate treated with a titanate coupling agent has good compatibility with polymer molecules. At the same time, since the titanate coupling agent can form a molecular bridge between the calcium carbonate molecule and the polymer molecule, the interaction between the organic polymer or the resin and the calcium carbonate is enhanced, and the thermoplastic filled composite material can be improved. Mechanical properties such as impact strength, tensile strength, flexural strength and elongation. Compared with the untreated calcium carbonate filler or the stearic acid (salt) treated calcium carbonate, the properties of the modified calcium carbonate surface coated with the titanate coupling agent are significantly improved.

    (3) Aluminate coupling agent

    Aluminate coupling agents have previously been rarely used due to ease of hydrolysis. In recent years, the aluminate produced by the manufacturer has adopted a special structure that partially satisfies the coordination number of the central aluminum atom, so that the product quality is greatly improved. The aluminate coupling agent has a light color, a high thermal stability coordination effect and a lubricating plasticization effect, and has a wide application range.

    Other types of surface modifiers are also available, such as surfactants, dispersants, grafting agents, and the like.

    (4) Composite modification system

    In the choice of modifiers, it is not necessary to use only the coupling agent for surface modification. Instead, a certain amount of other substances should be added according to the properties of the calcium carbonate powder and the formulation and process technical requirements of the organic polymer product. Helping modifiers and auxiliaries, combined with coupling agents for more effective surface modification, to achieve higher performance and quality of modified calcium carbonate powder products, so that the cost of the products is lower.

    Point 2: Selecting the surface modification process

    The surface modification process of calcium carbonate powder should be determined according to the reaction mechanism of the selected surface modifier and calcium carbonate powder.

    1. Dynamically heating the calcium carbonate powder to remove the adsorbed water;

    2. When heating to 100-110 ° C, the surface modifier is added by atomization, and when two modifiers are used, it is best to add separately;

    3. Maintain a certain temperature and time under dynamic conditions, and the effect of modification is different due to different reaction time.

    For example, the process of dry treatment of calcium carbonate with stearic acid is to first dry the calcium carbonate to remove water (if the moisture content of the calcium carbonate is less than 1%, it can be dried), and then add the stoichiometrically configured stearic acid. The surface modification of the calcium carbonate powder is completed in a surface modification machine.

    When using SLG type powder surface modification machine and continuous powder surface equipment such as vortex grinding, the material and surface modifier are continuously fed simultaneously, stearic acid can be directly added as solid powder, and the dosage is based on powder. The particle size or specific surface area is generally from 0.8% to 1.2% of the mass of the calcium carbonate.

    In order to allow the stearic acid to be better dispersed and uniformly reacted with the calcium carbonate particles, stearic acid may be previously diluted with a solvent such as absolute ethanol. Other additives may be added in an appropriate amount during the modification.

    In addition, the calcium carbonate powder modified by the coupling agent will produce a small amount of agglomerated particles, which will have a certain impact on the quality of the product, so it is necessary to carry out effective classification, in order to fully guarantee the quality of the product.

    Point 3: Selecting the surface modification equipment

    Surface modification equipment can be divided into dry and wet methods. The commonly used dry surface modification equipment is CLG type continuous powder surface modification machine, high speed heating mixer, PSC type powder surface modification machine and eddy current grinding.

     

    Stone-Powder-Modification-Machine-Surface-Powder-Coating (5)

    ▲Clirik CLG Series Powder Surface Modification Machine

    Among them, CLG type continuous powder surface modification machine, PSC type powder surface modification machine, eddy current grinding, etc. are continuous type powder surface modification equipment, and high speed heating mixer is intermittent surface modification equipment.

    Commonly used wet surface modification equipment are temperature-controlled reaction tanks and reactors.

    At present, in the industrial dry continuous surface modification of ultrafine calcium carbonate, especially light calcium carbonate, the SLG continuous powder surface modification machine is dominant.

    According to the mechanism and process of surface modification of calcium carbonate powder, the following requirements should be considered when selecting surface modification equipment:

    (1) The surface modification equipment can heat the powder to 120 ° C, and can be insulated between 90-120 ° C. The heating and holding time can be automatically controlled.

    (2) If there is a venting device, the water to be removed when the surface is modified can be discharged by steam.

    (3) Calcium carbonate powder should be in a state of high speed and dynamic in surface modification.

    (4) Surface modification equipment should meet the requirements for the addition of surface modifiers.

    (5) In order to solve the false agglomerates and hard agglomerates generated in the surface modification, effective grading must be carried out, and special grading equipment is used for matching.

    Therefore, when selecting the powder surface modification equipment, we must carefully consider the surface modification mechanism and process of the powder, and based on this, reasonable selection and matching surface modification production line.

    In addition, the powder surface modification equipment manufacturer should also rationally design and manufacture the ideal powder surface modification equipment based on the mechanism and process of powder surface modification.

    ☆ Development trend of surface modification of calcium carbonate

    The surface modification of calcium carbonate is a simple modification of the modifier, but the surface of the powder with large yield is modified. At present, in addition to the surface modification of ultrafine and nanometer calcium carbonate powders for special purposes, most of the calcium carbonate powders filled in polymer materials use stearic acid or sodium stearate as surface modifiers, and a small part. Aluminate, titanate and other surface modifiers are used.

    The main improvement direction of the surface modification technology of calcium carbonate powder is to improve the surface modification effect and reduce the modification cost.

    (1) Improve surface modification effect

    The effect of improving the surface modification is mainly from three aspects: surface modification method, modification equipment and modifier formulation:

    According to the preparation process of the powder and the type of surface modifier selected, the surface modification can be improved to improve the dispersibility of the calcium carbonate powder and the surface modifier during the modification process and the equality of mutual contact or action opportunities. Method and process;
    Selecting an equal surface modification device that enables the powder and surface modifier to be well dispersed and in contact with each other or the opportunity for action during the modification process;
    Surface modifiers and modifiers are selected according to the type of resin base material and application requirements.
    (2) Reduce the cost of surface modification

    Reducing the cost of surface modification mainly starts from the following aspects:

    Reducing the amount of surface modifier, which is related to the dispersibility of the surface modifier and the uniformity of the action on the surface of the calcium carbonate powder. The surface modifier is well dispersed and can be applied to a certain extent with the surface of the calcium carbonate powder. The amount of surface modifier is reduced, and the surface modifier is one of the main cost components of the surface modification operation of calcium carbonate;


    To reduce the energy consumption of the modification process, the surface modification is mostly the operation that needs heating. It consumes electrical energy and heat energy. The energy consumption is related to the process and equipment performance. To this end, one should try to adopt a simple process, and the second is to adopt energy-efficient Surface modification equipment or device;


    To reduce the loss of powder material during the modification process, the loss of powder material in the modification process not only increases the production cost of the modified product, but also pollutes the workshop environment. To this end, it is necessary to adopt a continuous and closed surface modification as much as possible. Sex equipment; the second is to minimize manual feeding and unloading; the third is to minimize the transport of powder materials and shorten the transport distance.


    In the future, functionalization and specialization will become the main trends in the development of calcium carbonate, and the product structure will also undergo great changes. High-grade products such as nano-scale calcium carbonate, ultra-fine calcium carbonate, medical grade and food grade calcium carbonate; various surface-modified special calcium carbonate, such as natural rubber, synthetic rubber, coating-specific lightweight calcium carbonate, these high-addition The market demand for calcium carbonate products will become larger and larger, and the key technologies and product quality will also be the key to the survival of enterprises.

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