First, technology sources and technical level
The nanometer is a unit of measurement of length, which is 1 x 10-9 m. Although artificially manufactured nanomaterials can be counted from the manufacture of carbon black pigments thousands of years ago in China, nanoparticles were first developed in Germany in 1984, pioneering the use of nanotechnology by humans. Nanoparticles are a new state of matter, and are aggregates of particles with a diameter of less than 100 nm. The morphology of particles can only be observed under an electron microscope.
In 1992, the International Conference on Nanostructure Materials defined nanomaterials as “aggregates of any dimension of 1 phase to 100 nm in one phase of a two-phase material.†In the 1980s, due to the application of electron energy spectrum and scanning tunneling microscopes, Many anomalous properties of micro-particles have been discovered. This has become a hot area for the global scientific and technological community and national governments to pay close attention to. Nano-particles have more specific physical and chemical properties than conventional micro-particle materials, and it has been widely used in many fields such as machinery, electronics, energy, chemicals, biology, building materials, and national defense.
Nanotechnology is a research and development hotspot in the world today. However, nanotechnology and materials are still in their infancy in China. Most of the results are still in the laboratory. Only a few species have entered the industrialization. Nano-scale calcium carbonate is one of them. One. Calcium carbonate is one of the most light-colored fillers used in the processing of rubber products due to its easy availability of materials, low price, low toxicity, low pollution, high whiteness, large amount of filling, and good mixing and processing performance. However, due to the limitations of its own hydrophilicity and traditional production processes, calcium carbonate products are usually coarse particles, surface area is small, and the surface is lack of activity. Compounding with polymers often only plays a role in filling increments and lacks reinforcing effect. Can not fully play its due role.
Nano-scale calcium carbonate is a new type of ultra-fine solid material developed in the 1980s, with a particle size of 1 nm to 100 nm. Due to the ultra-fine refinement of nanoscale calcium carbonate particles, their crystal structure and surface electronic structure are changed, resulting in quantum size effect, small size effect, surface effect and macroscopic quantum effect that ordinary calcium carbonate does not have, in magnetic and catalytic properties. The photothermal resistance and melting point show superior performance compared with conventional materials. It is filled with rubber and plastic to make the surface of the product bright, good elongation, high tensile resistance, strong tear resistance, bending resistance, crack resistance, and is an excellent white reinforcing material in advanced inks and coatings. Has good gloss, transparency, stability, quick drying and other characteristics.
Nano-sized calcium carbonate can not only increase the capacity and reduce the cost, but also can be used in plastic, rubber and paper, and it also has reinforcing effect. The calcium carbonate product with a particle size of less than 20 nm has a reinforcing effect comparable to that of white carbon black, and a calcium carbonate product with a particle size of less than 80 nm can be used for anti-rock hitting paints for automobile chassis. Therefore, research and development and application of nano-scale calcium carbonate have attracted attention at home and abroad.
Nano-scale calcium carbonate is light calcium carbonate in the range of 0.1 nm to 100 nm on average, including ultra-fine calcium carbonate and ultra-fine calcium carbonate, and is a nano-powder material.
二ã€Overview of Application of Micro-Calcium Carbonate (PCC) and Nano-CaCO3 at Home and Abroad
In the United States, Japan, Western Europe and other developed countries, paper-making consumption PCC accounted for the first place in all industries, while China is currently in the third place. In the paper industry, as the sizing technology in the papermaking process changes from acidic sizing to medium-alkaline sizing, it provides a huge potential market for the application of calcium carbonate. Calcium carbonate is used for papermaking fillers with high whiteness, good light scattering, high bulkiness after adding paper, good plasticity and softness, fine paper surface, which can greatly improve the performance of paper and make paper mills get a clear economy. benefit. Therefore, most of the paper mills in Europe, America, and Japan changed from acid sizing to medium-alkaline sizing. In recent years, China's papermaking industry has also started to change from acidic sizing to neutral sizing technology in papermaking technology, and the former Ministry of Light Industry has included medium-alkaline sizing technology as one of the national “8th Five-Year†key promotion projects. This requires that we only continue to develop new calcium carbonate products to meet the needs of the paper industry.
Light calcium carbonate is mainly used as a filler in alkaline papermaking, and a small part is used as a pigment. Widely used in pulp market without wood pulp, it has excellent physical properties such as high transparency, high density, high swelling capacity, uniform particle size, solid pigment, etc. compared with kaolin and heavy calcium. Taking the current world's largest paper-producing country and paper-consuming country U.S. as an example, in 2005, the ratio of light-weight calcium carbonate used in paper-making fillers reached 65%, with a growth rate of 4%. US ultra-fine calcium carbonate is mainly used in paper and coatings, including a variety of crystalline nano calcium carbonate products. Japan produced an ultra-fine calcium carbonate with a mean grain activity of 0.04 μm in 1952 and an ultra-fine calcium carbonate with a mean grain activity of 0.005 μm in 1983.
The papermaking process is PCC's largest user, accounting for 73% of the world's PCC usage. PCC's two different process uses in papermaking are paper fillers and paper coatings. It is mainly used for filling non-abrasive wood coated paper (WFO), the maximum filling amount can reach 25%, and the amount is expected to increase.
Nano-calcium carbonate as a paper-making filler has a high degree of light-shielding and high brightness, improves the whiteness and light-shielding properties of paper products, and also has a high expansion, which enables paper mills to use more fillers, while using less paper pulp, and The raw material cost is reduced, the granularity is small and uniform, the wear on the paper machine is small, and the paper products produced are more uniform and smooth; the oil absorption value is high, and the pigment solidity of the color paper can be improved. At present, the application of nano-scale calcium carbonate in the paper industry is mainly in high-end sanitary napkins, paper diapers and adult nursing incontinence pads, cigarette papers and paper-making coatings.
Third, the application of nano calcium carbonate in papermaking
Compared with the corresponding normal materials, nanomaterials exhibit many exotic characteristics in terms of optical, thermal, magnetic, mechanical and chemical properties, such as reduced density, increased strength and hardness, improved toughness, improved diffusion capacity, and thermal expansion coefficient. Improve etc. At present, there are not many experiments on the research and application of nanotechnology in the field of papermaking, so it is necessary to carry out this research. In the area of ​​papermaking coatings, nano-scale calcium carbonate may help improve the quality of coated paper because of its high whiteness and its characteristics as nano-scale materials—large surface area, high surface activity, and high strength and hardness. By adding nanoscale calcium carbonate to the paint, it is hoped that a high gloss and high ink absorbency coated paper can be obtained and the smoothness of the paper can be improved. However, due to the existence of defects such as high surface energy of particles, easily agglomerating on the surface, non-cohesiveness between the surface of the nanometer calcium carbonate, and lack of binding force with organic substances, the nano-scale calcium carbonate increases the difficulty of its practical application and requires continuous research and breakthroughs. .
When 5% nano calcium carbonate is added to the original formula of papermaking coating, the strength and smoothness of the coating can be improved with the same amount of adhesive and dispersant, and the ink absorption performance is also improved. After adding nano-scale calcium carbonate, several important physical and chemical indicators of the coating have been greatly improved:
(1) Increased IGT stretched grain strength. When the formula contains 5% nano-calcium carbonate, the IGT value is significantly increased, which is nearly 80% higher than that without nano-calcium carbonate. If the problem of nano-calcium carbonate dispersion technology can be solved, the value of IGT tensile strength may be greatly improved.
(2) Roughness is greatly affected by nano-CaCO3. The main reason is that the particles of nano-particles are small. Therefore, the dents and small bumps on the paper surface are relatively reduced, so that the paper surface tends to be smoother and smoother. When the nano-calcium carbonate accounted for 5%, the roughness was low, and the paper was relatively smooth; as reflected in the measured value of the IGT tensile pull strength, high-content nanoparticles require a high level of dispersion technology. When the amount of nano-calcium carbonate is well-dispersed, it contributes to the reduction of the roughness and the increase of the smoothness.
Due to the high surface energy of nanoparticles, they are in a thermodynamically unstable state and can easily aggregate into clumps, thus affecting the dispersion of nano-CaCO3. Use only ordinary mechanical dispersion and dispersants to achieve the desired dispersion. The dispersant used is sodium polyacrylate. When it is selected, considering its good dispersion effect on porcelain clay and calcium carbonate, and having certain advantages in the dispersion principle, it is a better choice. However, it must be taken into consideration that on the one hand, the surface of nano-calcium carbonate is hydrophilic and oleophobic, showing strong polarity, and it is difficult for the organic dispersant to disperse it uniformly, and there is no binding force with the organic matter, which can easily cause interface defects, resulting in degraded material properties. However, the selected sodium polyacrylate is just another organic dispersant; on the other hand, the dispersant used is a dispersant used in conventional large-particle coatings. It is possible that this dispersion mechanism is not suitable for the dispersion of nanoparticles. Therefore, whether or not nano calcium carbonate can be uniformly dispersed will greatly affect the coating performance of the coating. In addition, from a theoretical point of view, the surface area of ​​nano-calcium carbonate is large, and the amount of adhesive to be used should be increased accordingly, and the proportion of these needs to be experimentally demonstrated.
However, different industries have different requirements for nano-scale calcium carbonate, and different types of products in the same industry have different requirements for nano-calcium carbonate. Therefore, on the one hand, it is necessary to understand the requirements of nano-CaCO3 for downstream products of different varieties in different industries; on the other hand, it is also necessary to study how nano-CaCO3 is applied, and it is best to provide formulas that can be adapted to the application of a certain industry or a certain species.
Fourth, nano ultra-low quantitative corrugated paper
Nano-ultra-low-rate corrugated paper is produced by adding special nano-technology auxiliary materials to the production process of ordinary corrugated paper. The product has higher strength, smoother surface, better dewatering performance and lower production cost than ordinary products. At the same time, the product can not fall off the powder during use, the amount of adhesive is low, the shape of the corrugated is uniform, and the shape is stable.
In the production process of ordinary corrugated paper, the company where the author was in 2005 after the comprehensive upgrading of the pulping equipment, through the introduction of high-tech nano-calcium carbonate materials, and with other high-tech, superior performance The French import chemical additives - PG2, KB156 retention aids, after special equipment processing, manufacturing a new paper additive with nanotechnology, directly added to the concentration of only 0.8% of the slurry. After being fully mixed, it is sprayed onto a sheet forming net to form a wet paper sheet containing nano-calcium carbonate through a paper-making machine cluster tube headbox. Since nano-CaCO 3 contains positive and tight fibers, 80% of the nano-calcium carbonate is retained in the paper sheet with the aid of PG 2 and KB 156 additives. After the wet paper sheet is dehydrated by the high-vacuum roll, the two-line pressure of 100N/mm or more is further processed, and a set of 40 high-pressure high-temperature drying cylinders are dried to form a 8% moisture-containing nano-calcium carbonate corrugated sheet. Base paper. Due to the addition of nano-calcium carbonate and chemical additives, the product can be quantified from corrugated base paper with the original specification of 110g/m3 with low basis weight of 850mm to 2500mm, and further reduced to ultra-low basis weight corrugated paper with the weight of only 90g/m2 to 100g/m2. The main raw materials and ratio: # 11 ACC 40%; semi-chemical wheat straw pulp 30%; domestic waste paper 15%; carton waste 15%.
Five, nano-calcium carbonate and additives system operating procedures
(1) Name of accessories:
Nano-calcium carbonate, PG2 retention aids, KB156 retention aids, cationic dispersions, aluminum sulfate. (B) Nano-scale calcium carbonate performance indicators:
Nano calcium carbonate DD products.
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