Paper is made of fiber, but for some paper, it is difficult to achieve the purpose of using paper only by fiber. For cultural paper, printing paper, decorative base paper, white cardboard, cigarette paper, etc. Some fillers must be added to the pulp to meet the requirements of the paper.
The main types of fillers used in papermaking in China are talcum powder, porcelain clay, calcium carbonate, titanium dioxide and iron oxide yellow pigments.
Talc powder in nature is a non-metallic mineral substance in the form of hydrated silicate. It has large reserves in our country, abundant resources, easy to mine and process, and low price. Talc powder has the characteristics of fine texture, smoothness, high whiteness, strong covering power and low abrasion. The industrial talc used in paper mills is different from pure talc, which is based on straight amphibole and tremolite. The current use of talcum powder in each paper mill isZZ-special grade, its Fe2O3 content is preferably less than 0.1, because the high content will affect the whiteness of the paper; Its CaCO content is preferably less than 1.5, which can reduce the influence of foam in the system, improve the quality of the paper, reduce the breakage, and improve the copy rate and finished product rate of the paper machine.
Sometimes in the production process of paper in order to improve the opacity of the paper and improve the printing performance of the paper, in the addition of the filler also want to use part of the calcined clay. Calcined porcelain clay has a large specific surface area and a porous and loose structure, which improves the covering ability of the paper, and is also conducive to the absorption of printing ink, which effectively improves the printing effect of the paper.
Calcined kaolin used as paper filler, its advantages are:
1) improve paper whiteness;
2) Improve the opacity of the paper and increase the covering ability of the paper;
3) Reduce the print-through phenomenon in the printing process
4) improve the printing performance of paper;
5) than other fillers, reduce the impact on the tensile strength of the paper;
Calcium carbonate (CaCO3）
Light calcium carbonate: used as light calcium carbonate for papermaking, mainly limestone as raw material, calcined and digested by lime kiln. Under specific conditions, carbonization reaction.
The advantages of light calcium carbonate:
As China's paper industry has long been using acid sizing methods, for this reason can not be used.
Calcium acid is used as a filler for paper (cigarette paper has long used calcium carbonate as a filler due to non-sizing).
The advantages of using as a papermaking filler are:
1) can make the paper has a higher whiteness;
2) can make the paper has a higher opacity;
3) Good coverage;
4) High bulk thickness;
5) Good printing adaptability and ink absorption;
6) Excellent air permeability;
7) Good combustion-supporting property;
Light calcium carbonate is an excellent filler of cigarette paper, but in the production process of light calcium carbonate, due to different process conditions, the crystal structure, particle size, and distribution of calcium carbonate are different, the strength of cigarette paper, breathability has a significant impact.
Papermaking is a complex process, different paper varieties have different quality requirements, in order to achieve a certain requirement of paper it is necessary to join the filler; filler more types, each with different properties, different paper varieties and process conditions, it is necessary to choose different filler or filler combination, in order to obtain the best effect.