Nano calcium carbonate is also called superfine calcium carbonate. The name of the standard is superfine calcium carbonate. The most mature industry of nano calcium carbonate is plastic industry, which is mainly used in high-grade plastic products. It can improve the rheological property of plastic masterbatch and improve its formability. As a plastic filler, it has the function of toughening and reinforcing, improving the bending strength and flexural elastic modulus of the plastic, thermal deformation temperature and dimensional stability of the plastic, and also endowing the plastic with thermal hysteresis. Nano calcium carbonate used in ink products shows excellent dispersion and transparency, excellent gloss, and excellent ink absorption and high dryness. Nano calcium carbonate as ink filler in resin based ink has the advantages of good stability, high gloss, no influence on the drying performance of printing ink and strong adaptability.
Nano calcium carbonate is a kind of functional inorganic filler with particle size of 1-100nm. It is widely used in rubber, plastics, papermaking, ink, paint, sealant and adhesive, medicine, toothpaste, food and other fields. However, different applications have different requirements on the particle size, crystal shape, oil absorption value and dispersion of nano calcium carbonate.
1、Application of nano calcium carbonate in plastics
In the processing and production of plastics, ordinary calcium carbonate products can only be used as general fillers. In addition to being used as fillers, modified nano calcium carbonate can also play the role of activator and reinforcing agent, which can increase the volume of plastic products, enhance the hardness and strength of products, improve the processing performance of plastics, and enhance the heat resistance, bending strength and elastic modulus of plastic products And other performance indicators.
Nano calcium carbonate has been widely used in the processing of PVC, PS, PP and other plastics. Among them, the amount of PVC is the largest, especially for wire and cable, pipe and other products. Nano calcium carbonate has a good reinforcement and toughening effect on PVC plastics. Its main nano characteristics make the processed PVC plastics have good mechanical properties such as strength, barrier, flame retardant and thermal stability.
The technical requirements of nano calcium carbonate in plastic industry are as follows：
Oil absorption value: the plastic industry generally requires very low oil absorption value of nano calcium carbonate, because the particle size of nano calcium carbonate is small and the specific surface area is large. If the oil absorption value is large, more plasticizer will be consumed during mixing, which will increase the viscosity of the system, not only affecting the processing performance, but also increasing the production cost.
Crystal shape: mainly cubic, spherical, these crystal products show less flow resistance, easy to produce and process, and do not affect the surface gloss of plastic products.
Particle size: the particle size of nano calcium carbonate used in plastics is generally controlled at about 100nm. If the particle size is too large, it can not reflect the effect of nano calcium carbonate, and will affect the appearance of products; if the particle size is too small, the surface energy will be increased, and the particles will agglomerate seriously, which is difficult to be completely dispersed during processing, resulting in particles on the surface of products.
Dispersibility: nano calcium carbonate with high dispersion should be selected. If nano calcium carbonate agglomerates seriously, the secondary particle size will be much larger than the primary particle size, while the shear force of plastic processing and mixing is not too strong. Some nano calcium carbonate with serious agglomeration is not easy to disperse, which will cause local defects in application and lead to product quality problems.
Moisture: the moisture control should not be higher than 0.5%. If the moisture content is too high, the plastic surface will produce bubbles or hollows.
PH value: the pH value of nano calcium carbonate should be controlled below 10. If the pH value is too high, it will affect the whiteness and surface gloss of the products, and make the appearance worse. At the same time, high pH will also increase the viscosity of the system and affect the processing process.
Among all kinds of non-metallic mineral powder materials used in the plastic industry, the amount of calcium carbonate is the largest, accounting for 60-70% of the total amount of plastic additives. However, there are still many problems in high-performance application research, especially how to solve the agglomeration of nano calcium carbonate, how to improve the dispersion effect of nano calcium carbonate, and how to improve the bonding strength of composite materials have not been effectively solved.
2、Application of nano calcium carbonate in rubber
Nano calcium carbonate is mainly used in tire, wire, cable and rubber products in rubber industry. It can increase volume, reduce cost and improve rubber processing performance. At present, the main calcium carbonate used in rubber is heavy calcium carbonate and ordinary light calcium carbonate. The application field and scope of nano calcium carbonate are also expanding. The rubber products with nano calcium carbonate are much better than ordinary calcium carbonate in elongation, compression deformation, yield resistance and tear resistance. The nano calcium carbonate treated by special technology has high surface activity. Under ultraviolet irradiation, it can release free moving electrons and easily react with oxygen or organic substances to kill viruses and bacteria. Therefore, nano calcium carbonate also has the effect of sterilization and disinfection.
Tire: nano calcium carbonate can partly replace carbon black and white carbon black in the production of automobile tires, but there is still a gap in reinforcement effect. Therefore, it is mainly applied in the parts with less stress, such as sidewall, cord compound, inner layer rubber, buffer rubber, etc. In production, nano calcium carbonate and active zinc oxide can greatly improve the strength of tire tread compound.
Rubber tube and tape: nano calcium carbonate is mainly used to strengthen and whiten the rubber tube and tape, and improve the dispersibility of the rubber compound at the same time.
Wire and cable: nano calcium carbonate is generally used in the protective cover of mine wire and cable, high voltage wire and cable, marine wire and cable, and electrical wire and cable glue.
The technical requirements of nano calcium carbonate in rubber industry are as follows ：
Oil absorption value: the rubber industry has higher requirements for the oil absorption value of nano calcium carbonate. The higher the oil absorption value, the better the wettability and reinforcement of rubber.
Crystal form: due to the high reinforcement performance of rubber, the crystal form of nano calcium carbonate should be mainly chain or chain like, and the chain segments will entangle each other during processing, which can enhance the strength of the system
Particle size: the particle size of nano calcium carbonate used in rubber is generally 80-120nm. If the particle size is too large, the reinforcement effect cannot be achieved. However, if the particle size is too small, the contact area between the particle size and the rubber infiltration increases, which makes the dispersion difficult and affects the rubber mixing.
Moisture: the moisture content should not be higher than 0.5%. If the moisture content is too high, the scorching time of vulcanization will be prolonged, which is not conducive to the increase of vulcanization rate.
PH value: the pH value of nano calcium carbonate mainly affects its vulcanization rate, which should be controlled at 9.5-10.5. If the pH value is low, the vulcanization rate will slow down, the efficiency will be reduced and the energy consumption will be increased.
Adding nano calcium carbonate to the rubber can enhance the reinforcing effect of the rubber, and also improve the aging resistance, oil resistance and dispersibility of the material. Compared with ordinary light calcium products, the reinforcing effect of nano calcium carbonate is better, but worse than carbon black and silica. If carbon black and silica are replaced by nano calcium carbonate, the strength of the material will be reduced. If the use amount is too large, the roller sticking phenomenon will occur. Therefore, the technical formula needs reasonable debugging and continuous optimization.
3、Application of nano calcium carbonate in adhesives
The adhesive is mainly composed of base glue, curing agent, filler, coupling agent and catalyst. With the rapid development of China’s real estate, packaging materials, building materials and other fields, the amount of adhesives increases rapidly. As one of the important fillers of adhesives, nano calcium carbonate not only has low price, but also has good compatibility with adhesives. It can accelerate the crosslinking process of adhesives, improve thixotropy, improve the adhesion, tensile strength and reinforcement effect. At present, the application technology of nano calcium carbonate in polysiloxane sealant has been relatively mature, but the application in polyurethane adhesive is still in its infancy. Polyurethane adhesive has excellent adhesion and aging resistance, and has the surface coating property that silicone does not have. In the application field of pollution-free, good adhesion and weather resistance, polyurethane adhesive has obvious advantages.
The main technical requirements of nano calcium carbonate used in adhesives are as follows:
Oil absorption value: oil absorption value is an index that silicone rubber manufacturers pay close attention to, which directly affects the wettability of nano calcium carbonate in the rubber. Higher nano calcium carbonate has advantages in mechanical properties and thixotropy, but it will lead to viscous colloid, consume more additives and increase production cost. The oil absorption value requirements of nano calcium carbonate in formulation systems of different manufacturers are different, which should be determined by It depends on the circumstances.
Crystal form: generally cubic or rhombic hexahedron, and also need to adapt to the technical requirements and production equipment of the product.
If the particle size of CaCO 3 is too small to be controlled, the colloid will be easy to agglomerate; if the particle size is too small, the colloid will be easily agglomerated
Moisture: the lower the moisture content is, the better the nano calcium carbonate is used for adhesives, generally less than 0.5%. If the water content of nano calcium carbonate is higher, the hydroxyl groups on the surface increase, and the aggregates tend to agglomerate with each other, forming a three-dimensional network under the action of the base rubber, which increases the viscosity of the rubber, prolongs the mixing time, reduces the output and increases the energy consumption; too much water also causes the increase of energy consumption It reacts with the additives to produce particles, resulting in poor dispersion of the products and the appearance of particles. In the polyurethane adhesive, there are many isocyanate radicals, which are easy to hydrolyze. The formation of CO2 is the foaming phenomenon on the surface of the product.
PH value: calcium carbonate is a kind of weak alkali salt with pH value of 8-10. The surface coating agent of nano active calcium carbonate is generally weak organic acid or organic acid salt, which has a certain neutralization effect on its surface. In the production process, the phenomenon of calcium carbonate returning to alkali is very common. If the alkali is not properly treated, it will generate water with the acid component in the rubber material, which will hydrolyze siloxane to produce inorganic particles The poor appearance of the product will also affect its mechanical properties.
Specific surface area: as the particle size is controlled at 60 ~ 100nm, the corresponding specific surface area should be controlled at 20 ~ 25m2 / g. if the specific surface area is too large, the reinforcement effect will be enhanced, but at the same time, the extrusion performance of the adhesive will be deteriorated, and the dispersion effect of the product will also be affected.
At present, with the further research of nano calcium carbonate system, it will not play the same role in the field of nano adhesive, such as nano calcium carbonate.
4、Application of nano calcium carbonate in coatings
Heavy calcium carbonate, light calcium carbonate and nano calcium carbonate are widely used in coatings. Compared with heavy calcium carbonate or ordinary light calcium, nano calcium carbonate not only has better reinforcement effect, but also can improve the covering power, gloss, transparency, fast drying property and stability of coatings. In some industries, such as automobile coatings and architectural coatings, nano calcium carbonate can partly or completely replace the expensive titanium dioxide to reduce the cost of enterprises.
The main technology of nano calcium carbonate used in PVC plastisol system is marked with：
Oil absorption value: generally, the requirements are low. If the oil absorption value is high, the viscosity of the system will increase, and more plasticizers will be needed, which will increase the production cost. However, the oil absorption value requirements of nano calcium carbonate for different products are not completely the same, which depends on the specific situation. For example, some customers need products with high oil absorption value, high viscosity and high yield value.
Crystal form: generally cubic
Particle size: generally controlled at 60-100nm. If the particle size is too large, the viscosity of the system will be reduced, the mechanical properties will be affected, and the thixotropy of the system will become worse; if the particle size is too small, nano calcium carbonate will agglomerate seriously, which will easily lead to poor dispersion and pitting on the surface of colloid. At the same time, viscosity and yield value will be increased.
In addition to the above conventional detection indexes, the nano calcium carbonate used in PVC plastisol system also has special requirements for some application properties
It has good thixotropy, i.e. high shear thinning and low shear thickening. When nano calcium carbonate is applied in PVC plastisol system, the viscosity decreases at high shear rate, which is conducive to the flow of coating. However, under the condition of low shear rate before and after construction, the viscosity becomes higher, which can effectively prevent the coating from sagging;
With high yield value, the coating has good strength and can prevent small disturbance and external force impact;
Good quality stability.
At present, there is a big gap in the quality stability of domestic nano calcium carbonate compared with imported products, and some good indicators are difficult to appear and maintain.
5、Application of nano calcium carbonate in ink
The ink is mainly composed of pigments, binders, fillers, additives, etc. the modified nano calcium carbonate has good compatibility with the binder, and has the advantages of high gloss, strong stability, strong adaptability, and does not affect the ink factor and drying performance. It can comprehensively improve the quality of the ink and reduce the production cost.
Nano calcium carbonate used in ink requires high performance. After use, the ink should show good dispersion, absorption, transparency, gloss, good covering power and printing adaptability. The dispersion determines the glossiness, fluidity and transparency of the ink. The crystal shape of nano calcium carbonate is mainly cubic, and the nano calcium carbonate of cube has low oil absorption value, It is characterized by good fluidity and easy dispersion; the particle size is generally between 20 nm and 100 nm; the fluidity is related to the crystal shape and particle size, and the cubic and spherical crystal forms show greater fluidity, while the chain type shows a smaller fluidity. The manufacturers need to select the appropriate nano calcium carbonate according to the type of ink produced; an important index of glossiness ink is the crystal of calcium carbonate The shape is related to the particle size distribution. The nano calcium carbonate of the cube has a narrow particle size distribution, which is arranged orderly in the ink coating, making the printed surface smooth and showing good luster; the whiteness requirement is low, because other pigments need to be added, too high whiteness will cause difficult coloring.
In the ink industry, nano calcium carbonate plays an important role. The quality of the ink determines the quality of the printed matter. The ink prepared with nano calcium carbonate is smooth, stable, good printability and strong covering power.
In the printing process, it also shows good ink absorption, which is conducive to the quick drying of the ink.
6、Application of nano calcium carbonate in Papermaking
In the paper industry, the application of nano calcium carbonate is mainly in the following aspects:
As paper filler, nano calcium carbonate has small and uniform particle size, small wear on equipment, fine and uniform paper products, small particle size, large oil absorption value and specific surface area, which is conducive to the firmness of pigments; good whiteness, high brightness and good light shielding property can improve the whiteness and shading of paper; it can save the amount of pulp used, reduce the cost, and be conducive to environmental protection.
In cigarette paper, the addition of nano calcium carbonate is about 45% – 50%, because of its high refractive index and good opacity, the cut tobacco inside the cigarette paper can not be seen from the outside; when the cigarette is burning, the CO2 released from calcium carbonate can control the burning speed to a certain extent, but not make the smoke extinguish. At the same time, calcium carbonate can keep the ash content after combustion very well It can increase the air permeability of paper and reduce the tar content in cigarette.
In high-grade toilet paper, especially in women’s products, baby products such as sanitary napkins, diapers, diapers and other products, nano calcium carbonate is widely used to produce polyethylene film with good air permeability and water resistance. In addition, due to the small particle size of nano calcium carbonate, the products are delicate, do not hurt the skin, and will not cause sensory discomfort to the human body.
Its application in paper coating. Different from papermaking filler, nano calcium carbonate for coating is mainly transported in the form of slurry. The advantages are saving production energy consumption, reducing cost, no dust and environmental protection. It can be directly pumped into use and simplify the production process. Nano calcium carbonate can improve the glossiness, whiteness, smoothness, surface strength and ink absorption of coated paper due to its high whiteness, large specific surface area, high activity and good reinforcement.
In different products, the requirements of nano calcium carbonate crystal shape are also different. When used in paper-making fillers, they are mainly spindle shaped, chain shaped and spherical; when used in cigarette paper, they are mainly spindle shaped and needle shaped; when used in paper coating, they are mainly spindle shaped, sheet-shaped and cubic.
The application of nano calcium carbonate in papermaking industry still has great development potential. Because there are still many technical bottlenecks and application problems to be solved in the use process, the high-grade nano calcium carbonate products for papermaking still rely on import. However, with the continuous development of papermaking technology, the paper-making process has changed from acid sizing to neutral and alkaline sizing, which provides a good opportunity for the development of calcium carbonate in papermaking, and the application of nano calcium carbonate will become more extensive.
There are many enterprises involved in raw materials, production and application industries in the industrial chain of nano calcium carbonate. In order to realize the integration of the industrial chain, the technical exchange and innovation between relevant enterprises is very important. Only by meeting the demand of supply and demand among various industries and expanding the market can we achieve win-win results.
Source: Fan tiguo. Preparation and application of nano calcium carbonate [D]. Hubei University of technology, 2018