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The latest development in the application of light calcium carbonate in PCC of papermaking industry refers to a product prepared by chemical synthesis, which is formed by introducing carbon dioxide into lime water or directly precipitating under the action of sodium carbonate solution and lime water. The quality of light calcium carbonate is superior to heavy calcium carbonate. Its particle size is small, porous and narrow. It has the advantages of fine particle size, high whiteness, low price, low foaming and good printing adaptability. Very suitable for paper packing, basically meet the requirements of paper printing and optical properties. Therefore, light calcium carbonate is used as a filler for some high-grade paper. By comparing the effects of adding light calcium carbonate and kaolin on the quality performance of the base paper, Li Dan found that the super glazed paper with light calcium carbonate had higher whiteness and opacity, while the printing parameters such as smoothness, paper gloss, printing gloss and fluidity were similar to those of kaolin. A possible issue is the potential impact of the high voidage of light calcium carbonate on printing concentration, ink requirements, and printing uniformity. Jia Tian Xiang research found that light calcium carbonate can improve and improve coated board whiteness, smoothness, surface strength and ink absorption.
The whiteness, opacity, looseness, evenness and smoothness of the electrostatic carbon paper filled with light calcium carbonate have been greatly improved, the printing suitability of the paper has been improved, the ash content of the paper has been increased, and the shape stability of the paper has been improved. Yong-shun liu and other researchers found that adding light calcium carbonate light weight printing paper has high volume of paper and opacity, good printing performance, good paper evenness and fineness, to reduce the glare of paper, increase paper ash, smoothness and shape stability, but unfavorable to the sizing, the tensile strength and surface strength of paper. Zhang Yang's research found that light calcium carbonate can partially replace calcined kaolin for carbon-free carbon paper, which is beneficial to save the cost of papermaking. There is no binding force between light calcium carbonate and pulp fibers, resulting in low retention rates. Therefore, light calcium carbonate usually needs modification before use. The modification of light calcium carbonate can be divided into two processes: dry process and wet process. Wet - modified product quality is good, the amount of surfactant is low. However, when using modifiers that are easily hydrolyzed or insoluble in water, a dry modification process is required. Dry surface modification is a widely used method, which is simple and easy to be used in industrial production.
Now, the market has mainly heavy, light, activated, and nano calcium carbonate. Heavy and light are the most used.
Many users often have questions. They are all calcium carbonate. So, what is the difference between heavy and light forms?
Calcium-carbonate-powder-for-ceramicsWe make heavy calcium carbonate by crushing natural minerals. These include calcite, limestone, chalk, and shells. They are crushed into the right sizes. Light calcium carbonate is mainly a powder made from limestone. It is made through several steps: calcination, digestion, carbonization, dehydration, drying, and grading.
In fact, heavy and light calcium have similar density. Heavy calcium is 2.6~2.9g/cm3 and light calcium is 2.4~2.6g/cm3. The main difference lies in the bulk density.
The bulk density of heavy calcium is relatively large, generally 0.8~1.3g/cm3;
The bulk density of light calcium is relatively small, generally 0.5~0.7g/cm3.
Making light calcium involves complex processes like calcination and carbonization. So, its price is usually about 30% higher than that of heavy calcium of the same size.
Heavy calcium is mainly made by grinding. So, its particles are mainly cube, polygon, or cuboid. Light calcium can take many shapes. These include spindle, cube, needle, chain, sphere, flake, and rhombus. This variety comes from the crystal-form control agent.
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Heavy calcium has a lower oil absorption value. It&#;s generally 40-60 mL/100 g. This is due to its large particles, smooth surface, and small specific area.
Light calcium has fine particles. Its surface is rough and has a large area. So, its oil absorption is higher, usually 60-90 mL/100 g.
Heavy calcium products are usually 89-93% white due to impurities. Few reach 95% whiteness. Light calcium products are purer. They are typically 92-95% white. Some reach 96-97% whiteness.
The surface area of ordinary heavy calcium carbonate is about 1m2/g. The area of heavy fine calcium carbonate is 1.45~2.1m2/g.
Ordinary light calcium carbonate has a specific surface area of about 5m2/g. Light fine calcium carbonate has a specific surface area of 27~87m2/g.
From a flow perspective, the microstructure of light calcium is spindle-shaped. Its oil absorption value is relatively large. So, its dry flow is not as good as that of heavy calcium. Generally, adding more than 25 parts in the formula will affect the fluidity of the mixture. In comparison, heavy calcium is lumpy. It makes the mixture flow better. Relaxing some physical properties of the product can add much more heavy calcium.
The moisture content of heavy calcium products is low and stable, generally 0.2%~0.3%;
The moisture content of light calcium ranges from 0.3% to 0.8%.
Different application fields have different quality requirements for calcium carbonate, for example:
Sealants are filled with light calcium. They have good fluidity and high hardness. Heavy calcium has slightly lower hardness.
Light calcium has more advantages for making paper whiter. High-end cigarette paper, thermal paper, and lightweight paper prefer light calcium.
Plastics flow better. This is true for stretch products. These include polypropylene woven bags, cloth, and packaging tapes. The flow is improved due to heavy calcium. It is also much cheaper than light calcium. So, heavy calcium is much better for these stretch products.
Rubber: Light calcium half-reinforces. It makes vulcanized rubber it fills a bit better than heavy calcium .
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