Calcium carbonate is an important and widely used inorganic salt mineral, commonly known as “industrial monosodium glutamate”, is one of the commonly used fillers in all walks of life. Calcium carbonate can not only reduce the raw material cost of rubber and plastic products, but also improve some properties of rubber and plastic materials. Different kinds of calcium carbonate can significantly improve the properties of rubber and plastic materials when used properly. According to the different production process, calcium carbonate can be divided into heavy calcium carbonate and light calcium carbonate.
1. What is the difference between heavy calcium carbonate and light calcium carbonate?
Heavy calcium carbonate and light calcium carbonate have their respective roles in rubber and plastic industry. From an academic point of view, there are many differences between them, such as source, bulk density, pH value, moisture content, crystal shape, oil absorption value, etc. Let’s take a look at the differences between heavy calcium carbonate and light calcium carbonate.
(1) Source:
Heavy calcium carbonate (commonly known as ground calcium carbonate) can be made by directly crushing natural calcite, limestone, chalk and shell by mechanical method (Raymond mill or other high-pressure mill). Because the settling volume of heavy calcium carbonate is smaller than that of light calcium carbonate, it is called heavy calcium carbonate.
Light calcium carbonate, also known as precipitated calcium carbonate, is calcined limestone and other raw materials to produce lime (the main component is calcium oxide) and carbon dioxide, and then water is added to digest lime to produce lime milk (the main component is calcium hydroxide), and then carbon dioxide is added to carbonize lime milk to form calcium carbonate precipitation, and finally dehydration, drying and grinding are carried out. Or it is prepared by the double decomposition reaction of sodium carbonate and calcium chloride to form calcium carbonate precipitate, which is then dehydrated, dried and crushed. Because the settling volume of light calcium carbonate (2.4-2.8 ml / g) is larger than that of heavy calcium carbonate (1.1-1.9 mg / L), it is called light calcium carbonate.
(2) The packing density is different
The most obvious difference between heavy calcium and light calcium lies in the different bulk density of products. The bulk density of heavy calcium products is larger, generally 0.8 ~ 1.3g / cm ~ 3; while the bulk density of light calcium products is small, mostly 0.5 ~ 0.7g/cm ~ 3; the bulk density of some nano calcium carbonate products is even lower, which can reach about 0.28g/cm ~ 3. From the packaging volume of the products, we can roughly distinguish the products of heavy calcium and light calcium. Generally, most of the heavy calcium products are 25kg / package, and the product packaging volume is small, while the light calcium products of the same quality have a larger packaging volume. Some nano calcium carbonate products are also packaged with 15kg / package or 20kg / package.
(3)The whiteness is different
Because there are many impurities in the heavy calcium carbonate product, the whiteness of the product is generally 89% – 93%, and a few products can reach 95%. The light calcium products are made by chemical synthesis, many impurities are removed, and the purity of the products is very high. Therefore, the whiteness of most products is 92% – 95%, and some products can reach 96% – 97%. This is also the main reason why light calcium products are mostly used for filling high-grade or light color products.
(4) The modification function is different
There are slight differences between the modification effects of heavy calcium carbonate and light calcium carbonate. Heavy calcium carbonate is better for tensile strength, while light calcium carbonate is better for impact strength and rigidity. Generally, the surface of plastic with light calcium carbonate is smoother and the density is lower; the processing fluidity of heavy calcium plastic is better, and the properties of plastic filled with small particle size of heavy calcium are also better.
(5) The particle size is different。
The particle size of heavy calcium carbonate is 0.5 ~ 45um, and the particle size of product varies with the grinding equipment. The particle size of ordinary light calcium products is generally 0.5-15um, which is difficult to be accurately measured due to its spindle shape, which is generally within a range; the nano calcium carbonate in light calcium is finer, and the size is generally 20-200nm. The particle size of ordinary light calcium carbonate is generally about 2500 mesh, which can meet the performance requirements of PVC pipes and profiles. Therefore, from the perspective of particle size, light calcium carbonate is traditionally used for PVC pipes and profiles. In the past, due to the limitation of crushing equipment, heavy calcium carbonate could not reach this fineness. Now, the particle size of heavy calcium carbonate can fully meet the needs, even finer than light calcium carbonate. Therefore, both PVC pipes and profiles can be selected.
(6) Price difference:
The processing of heavy calcium carbonate is mainly realized by mechanical crushing and grinding; the production of light calcium carbonate is made by chemical reaction precipitation, which is much more complex than heavy calcium carbonate, and the requirements are correspondingly more strict. Therefore, the heavy calcium carbonate with the same particle size is about 30% cheaper than the light calcium carbonate. If the performance allows, the heavy calcium carbonate can be selected, which is more economical and cheaper 。
2. How to choose calcium carbonate in rubber and plastic industry?
Some people think that the use of foreign plastic products in the filler of calcium is the main position, the classic saying is 14-18:1, so the plastic industry should try to use calcium, instead of light calcium.
The use of heavy calcium and light calcium in plastic products is similar to rubber products. Some manufacturers have reported that under the same conditions, the use of – 400 mesh of heavy calcium instead of light calcium has obvious advantages for products sold by weight, but if the products are sold according to length, area or number, the heavy calcium does not have an advantage over light calcium.
For example, if the same weight of material is filled with the same amount of material, the length of the product obtained will be different. If the tube is filled with heavy calcium, it will be a few thousandths shorter than that filled with light calcium. For artificial leather or synthetic leather measured by area, the difference in area can also be felt. Therefore, plastic product processing plants should not give up the use of light calcium easily.
From an academic point of view, there are many differences between the two, such as different crystal forms, different specific surface areas, different oil absorption values, and so on. In the plastic matrix, the form of the particles of heavy calcium or light calcium is distributed in the matrix macromolecules one by one, or in groups, in the form of loose aggregates in the matrix resin, and the interface state between these particles and resin macromolecules is directly related to the mechanical properties of materials.
It is not the same to use the heavy calcium or the light calcium in the plastic products. We should give full play to their respective advantages and combine the technical and economic factors to make a comprehensive consideration.
For example, in the production of PVC artificial leather, it can be divided into scraping method, calendering method and extrusion method according to the manufacturing process, while the scraping method uses PVC paste resin, which needs to add a lot of plasticizer. The oil absorption value of light calcium is 4-5 times higher than that of heavy calcium. Therefore, the use of light calcium requires more plasticizer to achieve the same flexibility than the use of heavy calcium. If the amount of plasticizer can be reduced, the use of heavy calcium may be more economical.
For example, polypropylene woven bags, woven cloth, packing belt and other unidirectional tensile products, using heavy calcium carbonate and light calcium carbonate as fillers did not find any difference in length. It is found that most of the filler particles are located in the space between the macromolecules formed by stretching. After several times stretching and rapid cooling, the morphology of the macromolecules is rapidly frozen, while the true density of the light calcium and the heavy calcium is almost the same, so the effect on the final length of the product is not obvious. On the other hand, compared with light calcium, the processing fluidity of heavy calcium is better, and the price is much lower. Therefore, in this kind of unidirectional tensile products, it is absolutely dominant.
In addition, in the molding processing technology of plastic door and window profiles, the filler is light calcium, and the dosage is 8-10phr. It should be pointed out that the formula provided by foreign countries is scientific. The starting point of adding calcium carbonate is to improve the overall performance of profile, not to use cheap raw materials to reduce cost.
3. Application of calcium carbonate in degradable plastics
PLA is one of the fastest developing degradable plastics in the market. Calcium carbonate is used as powder filler in raw material processing to provide the performance and price composition of PLA. This method is also widely used in traditional plastics, which can not only improve some properties, but also reduce the cost of plastic raw materials. Compared with other non-metallic mineral powder, calcium carbonate has great advantages: low price, easy coloring, low hardness, less wear for screw and die, good thermal and chemical stability, easy drying, non-toxic and tasteless.
From a technical point of view, it is a long-term process for environmental protection materials to replace non degradable plastics, and the improvement space of degradable plastics in terms of fall resistance, heat resistance and corrosion resistance is another problem. This also means that China’s degradable plastics will usher in development opportunities. By 2030, the demand for degradable plastics in China is expected to reach 4.28 million tons, and the market scale can reach 85.5 billion yuan. Due to the relatively low price, the superfine ground calcium carbonate, light calcium carbonate and nano calcium carbonate can promote the degradation of plastics and are relatively friendly to the environment. In the future, the proportion of the additives in the degradable plastics will be larger and larger, and the market prospect will be more and more broad.
4. Recent situation of calcium carbonate industry in China
There is no doubt that China is rich in calcium carbonate mineral resources. In August, new calcium carbonate deposits were discovered in Guangxi and Hunan, with a total reserve of 607.5 million tons, providing sufficient resources for the development of local calcium carbonate industry.
In recent years, China’s calcium carbonate industry has been in a steady growth trend. In 2019, the output of China’s calcium carbonate industry is 35.95 million tons, including 13.5 million tons of light calcium carbonate and 22.45 million tons of heavy calcium carbonate; the import volume is 49000 tons, the export volume is 122000 tons, and the apparent consumption is 35.877 million tons.
The price of products also shows an increasing trend. Heavy calcium carbonate products increase from 535 yuan / ton in 2014 to 572 yuan / ton in 2019, and light calcium carbonate products increase from 640 yuan / ton in 2014 to 822 yuan / ton in 2019. The output value also maintained a rapid growth, from 16.696 billion yuan in 2014 to 24.178 billion yuan in 2019, with a compound growth rate of 7.69%. In 2019, China’s output value of calcium carbonate is 24.178 billion yuan, including 11.208 billion yuan of light calcium carbonate and 12.97 billion yuan of heavy calcium carbonate.
5. ALPA x Outstanding technology in calcium carbonate industry (Non-metallic minerals)
In the field of non-metallic mineral processing, ALPA can provide the following core technologies:
（1）Large scale and low-cost production can be realized by using ball milling classification process. Taking calcium carbonate as an example, a single production line D97: 10 μm can produce 100000 tons of products annually, and the power consumption per ton of products can reach 150 degrees.Suitable minerals include calcite, marble, limestone, quartz, zircon sand, feldspar, coal gangue, dolomite, magnesite, etc.
（2）The ultra-fine and low-cost production can be realized by using steam mill technology. Taking talc as an example, the particle size of talc can reach 1 μm and the thickness of talc is 300nm. Suitable minerals include talc, graphite, mica, wollastonite, fibrous brucite, attapulgite, kaolin, etc.
（3）The ultra-fine and ultra-pure production can be realized by using Jet mill technology, which is suitable for processing high value-added minerals. Taking quartz as an example, the particle size of the product can reach 2 μm, and the increment of metal impurities in the product is less than 10ppm. Suitable minerals include talc, quartz, barite, graphite, tourmaline, maifanite, etc.
（4）Surface modification technology can meet the application of minerals in rubber and plastic industry, such as Three-roller Mill modification process, Turbo Mill modification process, Pin Mill modification process, High-speed Mixer intermittent modification process, etc. different modification processes and modifiers can be used according to different materials, and the highest coating rate can be achieved with the least modifier. The amount of modifier is about 0.8-1.2%, and the coating rate is about 98%.
Green high value processing concept of non-mineral powder:
（1）The meaning of green ：Dry process, no emissions of three wastes; airtight negative pressure, no dust leakage and noise pollution; automation, intelligence and networking; it can realize high-value utilization of solid waste and tailings, recommending with the matched equipment according to requirements. Responding to changes in environmental protection and labor.
（2）The meaning of high value：Keep up with the needs of users for transformation and upgrading, providing with high value-added products based on material science. The research direction focuses on the particle size and its distribution, shape, purity, dispersion and surface modification, determines the processing technology based on its mineralogical composition and structural characteristics, and provides customized solutions combined with environmental protection requirements.