Yuan Lei's Little Knowledge | What kind of nano calcium carbonate should the paper industry use
In the field of papermaking, nano calcium carbonate is mainly used for special paper products, such as diapers, sanitary napkins, etc.
(1) The particle size of nano calcium carbonate is small and uniform, and the wear on the paper machine is small, and the paper products produced are more uniform and smooth;
(2) high light, high brightness can improve the paper whiteness and light;
(3) The high expansion performance enables the paper mill to use more fillers and less pulp, which greatly reduces the cost of raw materials;
(4) High oil absorption value can improve the pigment fastness of colored paper, and also give the paper good bending, flexibility, and good absorption of ink and water.
In the paper coating, nano calcium carbonate is generally only used in quantitative coated paper, matte copper paper and other special products, the amount can even be as high as 80%. Because of its high whiteness, large specific surface area, high surface activity, high strength and hardness, nano calcium carbonate can help to improve the quality of coated paper. By adding nano-calcium carbonate to the coating, coated paper with high gloss, high whiteness, high surface strength and high ink absorption can be obtained, and the smoothness of the paper can be improved.
■ Technical requirements of nano calcium carbonate for papermaking
(1) Crystal morphology
The crystal morphology of PCC is one of the most important factors affecting the operation of papermaking, coating performance and paper quality. Various forms of PCC can be roughly divided into two forms of existence: single crystal particles and polymers. The former affects papermaking mainly from the morphology and aspect ratio, while the latter mainly comes from the pore structure characteristics in the complexing body.
(2) Aspect ratio
The aspect ratio refers to the ratio of the length to the diameter of a single particle. Spindle, columnar and needle are all crystal forms with large aspect ratio, and their aspect ratio is generally (4~7):1. PCC with large aspect ratio is used as paper filler. When calcium carbonate single crystal is combined with paper fibers, it is easy to produce bridging effect, which makes the fibers bulge and form uniform pores, thus improving the air permeability, thickness, opacity, stiffness and reducing the difference between the two sides of the paper, it is advantageous to obtain a higher filler retention rate.
Rice granular and rhombic cubes belong to the small aspect ratio, and the aspect ratio of the two are:(2~3):1,(1~2):1; and the sheet body is usually described by the aspect ratio, generally (6~14):1, small aspect ratio PCC, only suitable for paper coatings, showing good coating gloss.
(3) Multimeric PCC
Also known as complex body PCC, generally by the needle, very fine spherical, cube, rice and other monomer polymerization, such as chrysanthemum. Its main physical characteristics are: high porosity, high dispersion coefficient, high oil absorption value (adsorption) and low bulk density value. At the same filler retention rate, it is beneficial to improve the opacity, bulk, stiffness, calendered paper smoothness, air permeability and ink absorption of the filled paper.
The main negative effect is that the strength and sizing of the paper are slightly lower, followed by the higher viscosity and lower surface strength when used in coatings. Therefore, the complex PCC is rarely used alone in papermaking coatings, often mixed with other small aspect ratio PCC.
(4) particle apparent shape
Any form of PCC requires that the crystal form is regular, complete, consistent, with smooth edges and no defects. There is no adhesion between aggregate particles. The number of chrysanthemum-shaped single crystal particles is similar, the opening degree is similar, and the end of the single crystal is peaked. Spindle-shaped and needle-shaped peaks.
(5) Apparent pore and porosity
The surface of PCC has fine pores, and the microscopic pores of PCC with good quality are fine and uniform, so that PCC with the same morphology and particle size has a larger specific surface area, and high oil absorption value and astigmatism coefficient.
Calcium carbonate, pcc, long diameter, paper, nano, coating, morphology, particle, paper making
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