echemi logo
Product
  • Product
  • Supplier
  • Inquiry
    Home > Coatings News > Paints and Coatings Market > Study on the production technology of wet calcium carbonate and its application in powder coatings

    Study on the production technology of wet calcium carbonate and its application in powder coatings

    • Last Update: 2021-04-19
    • Source: Internet
    • Author: User
    Search more information of high quality chemicals, good prices and reliable suppliers, visit www.echemi.com

    Abstract: This article introduces the dry and wet production process of heavy calcium carbonate, and compares it with light calcium carbonate.

    The application of wet-process ultrafine heavy calcium and lightweight nano-calcium carbonate in the field of powder coatings has been studied.


    The results show that wet-grinding calcium carbonate is used in powder coatings, and its coating film gloss and impact resistance are better than lightweight Calcium carbonate.


    Calcium carbonate is an important and widely used inorganic salt.


    According to different processing methods, it is usually divided into heavy calcium carbonate and light calcium carbonate com" href="">coating.


    Heavy calcium carbonate, also known as ground calcium carbonate, or heavy calcium for short, is made by physical processing with natural calcite, limestone, dolomite, chalk, shells, etc.


    as raw materials; light calcium carbonate is also called precipitated calcium carbonate, or light calcium for short , Is processed by chemical methods.


    At present, the filler used in powder coatings is mainly barium sulfate, including precipitated barium sulfate and ultrafine barium sulfate.


    With the EU and the United States listing barium in barium sulfate as a heavy metal, the practical use of barium sulfate in some export products has been restricted.


    In addition, the price of barium sulfate is higher than that of calcium carbonate, and calcium carbonate is a white filler that is cheap and does not contain heavy metal elements.


    With the advancement of production technology, calcium carbonate shows the development of functionalization and ultra-fineness, and its performance has been able to reach The requirements of powder coatings, and its application in powder coatings can reduce costs.


    Wet grinding ultra-fine heavy calcium carbonate is a deep-processed product of ultra-fine calcium carbonate developed by our company in recent years.


    Compared with ordinary heavy calcium carbonate produced by traditional technology and light calcium carbonate produced by chemical precipitation method, its It has a series of advantages such as finer fineness, larger specific surface area, and higher chemical stability.


    In this experiment, dry-grind ultra-fine calcium carbonate, wet-grind ultra-fine heavy calcium carbonate, and lightweight nano-calcium were selected to be used in powder coatings, and their performance was compared.

    1.


    Heavy calcium production process

    The production methods of heavy calcium carbonate are mainly dry and wet.


    The dry method generally produces heavy calcium below 2500 mesh.


    The production of ultra-fine heavy calcium carbonate above 2500 mesh mainly uses wet grinding, and dry grinding is used as the first step of wet grinding.

    1.


    1 Dry process

    Dry production of heavy calcium is currently a more common method in China, and the technology is relatively mature.
    Generally, products of various particle sizes can be obtained by using a processing technology system composed of grinding equipment and grading equipment.

    The main equipment used is Raymond mill, ring roller mill, ball mill, high-pressure roller mill, vertical mixing mill, jet mill, etc.
    The classification equipment mainly adopts impeller-type superfine classifier.

    The dry production process has the characteristics of low equipment investment, mature technology, simple process, low energy consumption, and high single-machine output.
    The general dry process for producing heavy calcium is shown in Figure 1.

    1.
    2 Wet process

    With the development of heavy calcium carbonate becoming more and more refined, the traditional dry production process cannot meet the requirements in terms of equipment itself or economic benefits, and the wet grinding process has emerged as the times require.

    The biggest difference between wet grinding and dry grinding is the difference in the dispersion medium.
    Dry grinding uses air as the dispersion medium, while wet grinding uses water as the dispersion medium and is equipped with grinding aids to make the particles more dispersed.
    The grinding efficiency is higher and the particle size is finer.

    The general wet grinding process is shown in Figure 2.
    After washing, the raw ore is crushed to about 400 mesh in two stages, prepared into a certain concentration of slurry, added with grinding aids, and fed to the vertical grinder, using zirconia beads as the grinding medium ;

    The fineness of the discharge is controlled by adjusting the various parameters of the mill.
    The material is discharged in the form of slurry after being ground, and collected and bagged after drying and dust removal.

    2.
    The characteristics of wet grinding superfine heavy calcium

    Because the production process and grinding environment of wet grinding heavy calcium are obviously different from dry grinding heavy calcium and light calcium, the physical properties of its products are also purely different.

    2.
    1 Comparison of the performance of wet and dry heavy calcium

    1) Granularity.
    Wet-grinding ultra-fine heavy calcium has a fine particle size.
    It mainly produces products above 3000 mesh, and the content of -2μm can generally reach 90%, while the particle size of dry products is relatively coarse, mainly producing products below 2500 mesh.

    2) Particle size distribution.
    The wet-process production of heavy calcium has a narrow particle size distribution, showing a unimodal or bimodal distribution; while the dry production of heavy calcium has a wide particle size distribution, with a bimodal or multimodal distribution.

    3) Particle shape.
    Due to the difference in the grinding environment and force mode of the particles during grinding, the particles of wet grinding heavy calcium products are generally spherical or quasi-spherical, while the dry products are mostly indeterminate and have obvious edges and corners.

    Figure 3 is the particle size distribution diagram of the wet grinding ultrafine CaCO3 produced by our company.
    It can be seen from Fig.
    3 that the particle size of ultra-fine wet-grinding CaCO3 has a bimodal distribution, with peaks at 0.
    75-0.
    82 um and 1.
    58-1.
    74 um respectively, and most of the CaCO3 particle diameters are below 2 um.
    Micron-level materials.

    2.
    2 Performance comparison of wet superfine heavy calcium and light calcium

    1) Light calcium is produced by chemical precipitation method, with small particle size, generally spindle-shaped or chain-shaped particles.
    The oil absorption value is higher than that of heavy calcium.
    Even the surface-treated light calcium has a higher oil absorption value than ordinary wet-grinding heavy calcium.
    , Which leads to the increase in the amount of light calcium used as a filler as an auxiliary agent.

    2) The application field of wet grinding heavy calcium is wider than that of light calcium.
    In some fields (such as plastics), because the fluidity of wet grinding superfine heavy calcium is better than that of light calcium, its addition amount is higher than that of light calcium.
    Big.

    3) Wet grinding uses physical methods to process and produce calcium carbonate, and only water is added during the production process, without the influence of any impurities or chemical substances, and the chemical stability of the product is relatively high;

    The production of light calcium carbonate is produced by a chemical synthesis method, which is prone to supersaturation reaction during the carbonization reaction, which easily causes the free acid-base value of the product surface to be unstable, and at the same time, it is easy to bring impurities such as coal ash into the product.

    3.
    The application of wet superfine ground calcium carbonate in powder coatings

    In the production of powder coatings, due to cost considerations, some fillers are usually added to the formulation design to reduce costs.

    The commonly used filler in powder coatings is barium sulfate, but barium sulfate deposits generally contain a certain amount of heavy metal elements, which are difficult to separate during the production process, and barium itself has been defined as a heavy metal element by the European Union and the United States.

    These factors have affected the application of barium sulfate in powder coatings.
    The heavy calcium carbonate is directly processed from natural calcite, dolomite and other ores, does not contain heavy metals, and has abundant raw ore resources and low prices.
    Therefore, it has been widely used in powder coatings.

    3.
    1 The role of calcium carbonate in powder coatings

    It acts as a skeleton in the powder coating, increases the thickness of the paint film, and improves the wear resistance and durability of the coating.
    It can reduce the cost of coatings and increase the powder coating rate and spray area of ​​powder coatings.
    In addition, it does not contain heavy metals and is the first choice for heavy metal-free powder coatings.

    3.
    2 Experimental part

    3.
    2.
    1 Raw materials and formula

    In order to fully verify the application performance of different fineness wet-process heavy calcium carbonate in powder coatings, we selected dry-process heavy calcium, light calcium carbonate and other fillers for comparative experiments.
    The experimental formula is shown in Table 1.

    3.
    2.
    2 Test results of physical properties of different fillers

    The CC-2500, CC-3000, CC-6000 were tested according to the HG/T3249.
    2-2008 standard, and the lightweight nano-calcium was tested according to the HG/T2226-2010 standard.
    The test results are shown in Table 2.

    Among them, CC-2500 is the 2500 mesh product produced by the company by dry grinding; CC-3000 and CC-6000 are the products produced by the company by wet grinding; the lightweight nano-calcium is the lightweight nanometer produced by a large-scale light calcium manufacturer in China calcium.

    From the results in Table 2, it can be seen that the fineness of CC-6000 product is the finest, and its specific surface area is also the largest.

    Since the finer the powder is easier to exert the effect of each particle, it will have higher light transmittance and mechanical properties.
    Because CC-6000 is a wet-grinding ultrafine calcium carbonate, The particle shape is uniform and regular, and it should have higher gloss when used in powder coatings.

    3.
    2.
    3 Performance test of different fillers used in powder coatings

    According to the experimental formula in Table 1, different fillers were added to prepare powder coatings.
    The test results are shown in Table 3.

    Table 3 Measurement results of different fillers used in powder coatings

    It can be seen from the results in Table 3 that when wet-process calcium carbonate is used in powder coatings, as the fineness increases, its gloss shows an upward trend; while lightweight nano-calcium is not suitable for its high oil absorption capacity.
    High-gloss products; and its impact resistance is not as good as wet calcium carbonate.

    4.
    Conclusion

    Wet grinding ultrafine heavy calcium carbonate is spherical or nearly spherical due to its fine particle size and uniform particle morphology, which can be widely used in coatings, plastics, rubber, ink and other industries;

    Used in powder coatings, wet grinding of ultra-fine heavy calcium carbonate can prepare high-gloss powder coatings.
    Its comprehensive performance is better than that of light calcium carbonate.
    In some fields that require no heavy metal content, calcium carbonate can be used instead of barium sulfate.
    It is mainly used in the coating of indoor home appliances, baby toys and other fields.

    This article is an English version of an article which is originally in the Chinese language on echemi.com and is provided for information purposes only. This website makes no representation or warranty of any kind, either expressed or implied, as to the accuracy, completeness ownership or reliability of the article or any translations thereof. If you have any concerns or complaints relating to the article, please send an email, providing a detailed description of the concern or complaint, to service@echemi.com. A staff member will contact you within 5 working days. Once verified, infringing content will be removed immediately.

    Contact Us

    The source of this page with content of products and services is from Internet, which doesn't represent ECHEMI's opinion. If you have any queries, please write to service@echemi.com. It will be replied within 5 days.

    Moreover, if you find any instances of plagiarism from the page, please send email to service@echemi.com with relevant evidence.