Calcium carbonate manufacturer: Popular science on the most basic application of calcium carbonate for papermaking; Paper is composed of fibers, but for some papers, it is difficult to achieve the purpose of paper use with only fibers. Therefore, 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 paper use.

Calcium carbonate manufacturer: Popular science on the most basic application of calcium carbonate for papermaking; Paper is composed of fibers, but for some papers, it is difficult to achieve the purpose of paper use with only fibers. Therefore, 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 paper use.

　　The main functions of adding fillers

　　1) Improve the whiteness of the paper, because the whiteness of the filler is higher than that of the pulp;

　　2) Improve the opacity of the paper;

　　3) Improve the smoothness of the paper;

　　4) Improve the softness of the paper;

　　5) Improve the printing performance of the paper;

　　6) Reduce the degree of deformation of the paper, that is, improve the flatness and dimensional stability of the paper;

　　7) Reduce resin obstacles;

　　8) Meet the special requirements of certain papers;

　　Types and properties of fillers

　　The main types of fillers used for papermaking in China include Guangdong calcium carbonate, talc, kaolin, titanium dioxide, and iron oxide yellow pigment.

　　1. Guangxi Longhua Calcium Carbonate

　　Guangxi Longhua calcium carbonate is divided into light (PCC) and heavy (GCC) (grinding). Generally, the calcium carbonate used for paper production is Guangdong light calcium carbonate (also known as precipitated calcium carbonate), and GCC is used as a coating pigment calcium carbonate.

　　Guangxi Longhua light calcium carbonate: The light calcium carbonate used for papermaking is mainly made from limestone, which is calcined and digested in a lime kiln. Under specific conditions, it is formed by carbonation reaction.

　　Advantages of Guangxi Longhua light calcium carbonate:

　　Because the Chinese papermaking industry has long used acidic sizing methods, calcium carbonate cannot be used as a papermaking filler (cigarette paper has been using calcium carbonate as a filler for a long time because it is not sized).

　　Due to the disadvantages of acidic sizing and the emphasis on environmental protection, and due to the research and development of neutral sizing agents, the paper sizing process worldwide is gradually shifting from acidic sizing to slightly acidic, neutral (alkaline) sizing, which allows Guangxi Longhua calcium carbonate to be used and developed as a papermaking filler.

　　The advantages of using it as a papermaking filler are:

　　1) It can give the paper higher whiteness;

　　2) It can give the paper higher opacity;

　　3) Good coverage;

　　4) High bulk density;

　　5) Good printing adaptability and ink absorbency;

　　6) Excellent breathability;

　　7) Good combustion-supporting properties;

　　Guangxi Longhua light calcium carbonate is an excellent filler for cigarette paper, but in the production process of Guangdong light calcium carbonate, due to different process conditions, the crystal structure, particle size, and distribution of Guangdong calcium carbonate are different, which has a significant impact on the strength and air permeability of cigarette paper.

　　For a long time, we haven't paid enough attention to this. With the in-depth development of the market economy and the impact of foreign high-grade cigarette paper (high strength, high air permeability) on the Chinese market, enterprises producing high-grade cigarette paper have reached a consensus on the quality requirements of light calcium carbonate used for producing high-grade cigarette paper. Currently, attention has been paid to the production process of light calcium carbonate used for high-grade cigarette paper, and research and development are underway. This is a welcome progress.

　　In the near future, China will be able to produce light calcium carbonate suitable for high-grade cigarette paper.

　　Among the above quality indicators, the main ones are sedimentation volume and iron content, and there are also strict requirements for the content of free alkali. Generally, the content of free alkali (calculated as CaO) is required to be less than 0.1%.

　　Heavy calcium carbonate: Heavy calcium carbonate is generally not used as a papermaking filler, but only as a coating pigment. Because heavy calcium carbonate is produced by grinding, its shape is irregular, in the form of prisms, flakes, rhombuses, and partial triangular pyramids, etc. When printing, its ink absorbency is better than PCC, and its viscosity is lower than PCC.

　　2. Talc

　　Talc is a layered silicate mineral. The functional characteristics of talc mainly come from its structural characteristics: lipophilicity and hydrophobicity and flaky structure. The chemical stability, low hardness, lubricity, flaky structure, lipophilicity, hydrophobicity, and other structural characteristics of talc determine that it is a rare functional papermaking mineral material. In China, more than 50% of talc production is used in the paper industry. It is mainly used as a papermaking filler, and a small amount is used as a papermaking resin (viscous substance) control agent and coating pigment. Talc can make the paper smooth, increase the weight, and enhance the adsorption capacity of printing ink and pigments.

　　Different types of talc have different properties and are suitable for different paper products. Low-grade talc and its compounded processed products will be mainly used for ordinary papermaking fillers; medium-grade talc is mainly used for functional papermaking fillers and base coating materials with high quality requirements; high-quality talc is mainly used for viscous substance control agents and coating-grade products that can better reflect its functional characteristics. Moreover, after ultrafine processing, talc powder has good adsorption and coverage. Currently, new talc products applicable to the paper industry mainly include cationic modified talc, solid paraffin and AKD modified talc, black talc, and hydrotalcite.

　　3. Kaolin (kaolin)

　　Kaolin clay is mainly used as a filler and pigment in paper surface coating in the papermaking industry. Its properties significantly affect the operability of paper production and the quality of the finished paper. According to different processing methods and product characteristics, kaolin clay for paper coating is divided into water-selected kaolin clay and calcined kaolin clay. Among them, calcined kaolin clay is a functional material for papermaking with high whiteness, porosity, and certain adsorption capacity. According to the different calcination temperatures, it can be divided into incompletely calcined kaolin clay (600-800℃) and completely calcined kaolin clay (950-1050℃). The former is mostly used as a paper filler, while the latter is mostly used as a paper coating material. Its functionality mainly comes from the roasting dehydration and de-organic matter process of kaolin (clay). The porosity of the structure after roasting can improve the bulk density, opacity, ink absorbency, etc., of the paper.

　　Kaolin clay is one of the white non-metallic mineral materials with the largest consumption in the papermaking industry. More than 75% of the world's refined kaolin clay is used in papermaking.

　　4. Wollastonite

　　Unlike traditional fillers, wollastonite is not simply filled into paper, but its high aspect ratio interweaves with plant fibers to form a "plant fiber-mineral fiber" network structure, thus partially replacing short plant fibers. Wollastonite used in papermaking has the advantages of improving paper opacity, reducing production costs, improving evenness, and improving printability.

　　Fibrous wollastonite has many special properties that cannot be replaced by traditional fillers, making it suitable for replacing traditional fillers in cultural paper and some special and high-grade papers. The current important research areas in wollastonite processing include chemical modification technology to reduce product abrasion and improve fiber softness, and processing technology to fully dissociate fiber bundles while maintaining fiber length.

　　5. Titanium Dioxide

　　The commercial name is titanium dioxide, which is made from ilmenite (FeO.TiO2) through processing and refining. It has a high refractive index of 2.55~2.70, high whiteness, and the best covering power for paper among all fillers, but it is expensive.

　　Titanium dioxide has rutile and anatase types, and their chemical properties are different. The former has poor water solubility, so the latter is used as a filler in the papermaking industry (especially thin paper).

　　6. Iron Oxide Pigments

　　Iron oxide pigments used as fillers in some special papers are a kind of inorganic pigment. Their application is not yet widespread. They are part of iron-based pigments, and generally only four types are used: iron oxide red, iron oxide yellow, iron oxide black, and iron oxide brown.

　　The common characteristics of iron oxide color pigments are that they are insoluble in water and have no affinity with pulp fibers. Instead, they rely on the action of alum to adhere to the fibers and achieve coloring, while also playing a filling role. Iron oxide pigments have strong light resistance and good hiding power.

　　Iron oxide pigments play a filler role in high-grade decorative base paper (or water-calendered base paper), and can also partially replace expensive titanium dioxide. At the same time, it also plays a dyeing role, which can replace expensive and seriously polluting organic dyes.

　　7. Bentonite

　　Bentonite is a hydrous aluminum silicate mineral containing a small amount of alkali and alkaline earth metals. Its large specific surface area, high dispersion, and thixotropy make it exhibit many advantages in various applications in the papermaking industry. For example, when used as a paper filler, it has high whiteness and purity, and even large additions will not reduce the paper strength and tear strength; when used as a paper coating, it can improve the water retention, suspension, and rheological properties of the coating. After separation, purification, and modification, the various properties of bentonite are greatly improved, and deep-processed products such as sodium-based bentonite, granular bentonite, and organic bentonite can be produced. The modified bentonite has good adsorption and dispersion properties, and compared with talc, it has a higher retention rate and has less impact on the strength of the finished paper.

　　8. Diatomite

　　The domestic paper industry mainly uses the large porosity, strong adsorption, low bulk density, heat insulation, sound absorption, chemical stability, and non-toxicity of diatomite to produce filter paper and paperboard for liquid beverages, sugar, and brewing industries. It is also used in building decoration paperboard, battery separators, highly absorbent daily-use paper, flame-retardant paper, pet pads, wastewater purifiers, flocculants, etc.; after organic modification, it can also be used as a micro-retention and filtration aid.

　　Rational Selection of Fillers

　　1) Guangxi Longhua Calcium Carbonate

　　With the application of new neutral (alkaline) sizing agents such as AKD, calcium carbonate, which is difficult to use in acidic papermaking, has found its use. Calcium carbonate has a refractive index as high as 1.65, which can significantly improve the whiteness and opacity of paper.

　　In the pH range of 7.5~8.5, calcium carbonate has good stability, so calcium carbonate is used as a filler in paper with neutral (alkaline) sizing; for thin paper, such as cigarette paper and printing-type water-calendered base paper, due to the requirement of high opacity, Guangdong calcium carbonate is used as a filler. For paper with high printing performance requirements, calcium carbonate can also be used as a filler.

　　Because calcium carbonate absorbs less ultraviolet light, it is beneficial to improve the aging of paper. Therefore, calcium carbonate is used as a filler for paper that needs long-term preservation (archival storage); paper with acidic sizing cannot use Guangxi Longhua calcium carbonate as a filler; Guangxi Longhua calcium carbonate can be used in large quantities as a color pigment for coated paper; ground Guangdong calcium carbonate is used because it is cheap, has good coating fluidity, and its printing performance is better than PCC, so ground calcium carbonate is mostly used for white coating.

　　2) Talc

　　Because talc has the characteristics of fine texture, high whiteness, good covering power, and low abrasion, and talc has high smoothness and gloss, and is inexpensive, it is generally used as a filler in cultural paper and printing paper; because talc has good chemical stability, it is used with dispersed rosin as a sizing agent for acidic sizing.

　　The calcium carbonate content in talc is generally required to be below 2.5%, and preferably below 1.5%, because a higher calcium carbonate content is detrimental to both sizing and dyeing. For decorative base paper, a high calcium carbonate content has an adverse effect on subsequent processing steps; as a coating white pigment, it has an adverse effect on the whiteness of the coating.

　　Studies have shown that for every 10% increase in its usage, the whiteness value decreases by 1.0%. This is because talc is slightly hydrophobic, resulting in poor dispersibility in the coating system. Fine talc particles easily trap air, thus forming small air bubbles. When agglomeration occurs, the coating becomes uneven. Therefore, talc is used as little as possible as a pigment in coated paper production.

　　3) Titanium dioxide

　　Due to its high refractive index and high whiteness (97%~99%), its hiding power is the highest among pigments (fillers). Therefore, it is used in the production of high-grade thin paper or high-grade coated paper. However, due to its high price, the amount used is relatively small;

　　4) Kaolin

　　Due to kaolin's good chemical stability and its platy structure, it can improve the smoothness and gloss of paper. Therefore, it can be used as a filler for various types of paper. It is only suitable as a filler for acid-sized paper, but due to its relatively high viscosity, the amount added is small, such as being used together with talc; it can be used as a white pigment for coating. The higher the content of platy kaolin, the better the coating performance (coating fluidity), and the better the gloss and smoothness of the coated paper (paperboard).

　　5) Iron oxide pigments

　　Suitable for the production of thin paper, such as high-grade decorative base paper and water-calendered base paper, etc. This is a characteristic reflected by its high coverage.

　　Papermaking is a complex process, and different paper types have different quality requirements. To achieve certain paper requirements, it is necessary to add fillers; there are many types of fillers, each with different properties. For different paper types and process conditions, different fillers or combinations of fillers must be selected to achieve the best results.