Currently, in the papermaking process, the amount of fillers and pigments used is second only to fiber, making them the second most important raw material. Commonly used paper fillers include calcium carbonate, talc, kaolin, wollastonite, bentonite, etc. With the gradual shift from acidic papermaking processes to neutral and alkaline papermaking processes, Guangxi Longhua calcium carbonate, as an important papermaking raw material, is being used more and more in the papermaking industry.

Currently, in the papermaking process, the amount of fillers and pigments used is second only to fiber, making them the second most important raw material. Commonly used paper fillers include calcium carbonate, talc, kaolin, wollastonite, bentonite, etc. As acidic papermaking processes gradually shift towards neutral and alkaline papermaking processes, Guangxi Longhua Calcium carbonate, as an important raw material for papermaking, is increasingly used in the papermaking industry.

　　I. Guangxi Longhua The Role of Calcium Carbonate in the Papermaking Industry

　　 Guangxi Longhua The application of calcium carbonate in papermaking mainly involves two aspects: firstly, as a paper filler, and secondly, as a coating pigment.

　　1. Filler

　　As a paper filler, paper fillers are fine, white mineral powders that are generally insoluble or slightly soluble in water. The main purposes of adding fillers to paper include: fillers dispersed between pulp fibers fill the gaps, improving the opacity and whiteness of the paper; improving the ink absorbency of the paper, making the paper more suitable for printing; meeting certain special performance requirements of the paper, such as improving the conductivity and heat resistance of the paper; reducing the use of fiber raw materials and lowering production costs; fillers have a large specific surface area, which helps to overcome resin barriers.

　　 Guangxi Longhua The advantages of using calcium carbonate as a paper filler are: abundant sources, low price; fine particles, high whiteness, significantly improving the opacity of the paper; fast ink absorption speed, increasing the ink absorbency of the paper; making the paper relatively soft, dense, and glossy; having a relatively small impact on the physical strength of the paper. The amount of filler added is mainly determined by factors such as the type of paper, the type of pulp, the properties of the filler itself, and the paper machine's papermaking conditions. In order to save plant fibers and reduce production costs, the amount of filler added should be appropriately increased on the premise of ensuring the papermaking and use requirements.

　　2. Coating

　　The purpose of coating is to improve the quality and uniformity of the final printed products of paper or paperboard. The main goal of pigment coating is to obtain better optical properties, smoothness, and gloss. Most importantly, it is to obtain better printing visual effects. Paper coatings usually consist mainly of pigments, adhesives, additives, and water. Among these components, the most important is the pigment, and many characteristics of coated paper depend on the choice of pigment.

　　Because Guangxi Longhua Calcium carbonate has high whiteness and good fluidity, making it suitable for preparing high-solid-content coatings; it requires less adhesive and can improve the ink absorbency of the coating; it provides good whiteness and tone and improves breathability; it is one of the most commonly used coating pigments.

　　II. Application Differences between Heavy Calcium and Light Calcium in the Papermaking Industry

　　 Guangxi Longhua Heavy calcium carbonate, as a filler, is mainly used in printing paper, writing paper, office paper, and advertising paper, except for cigarette paper, filter paper, and special low-grammage information paper. Guangxi Longhua Light calcium carbonate can be used in principle in all types of paper, and is currently mainly used as a filler for high-grade paper. For example: cigarette paper, office information paper (such as fax paper, instrument recording paper, inkjet printing paper), low-grammage newsprint, low-grammage coated paper, etc. Heavy calcium carbonate and light calcium carbonate have their own advantages as paper fillers, and the choice of calcium carbonate should depend on the actual paper production process requirements.

　　 Guangxi Longhua Heavy calcium carbonate has better fluidity than light calcium carbonate and saves the amount of adhesive in the coating, making it suitable for high-solid-content paper coatings and increasingly high-proportion applications. Due to the higher production cost of light calcium carbonate and its relatively poor rheology, its application in coating pigments cannot yet compete with heavy calcium carbonate.

　　However, the functional application of modified light calcium or finer nano-calcium in the papermaking industry has been widely recognized, which can enable paper to obtain specific properties and reduce costs. Its impact on paper quality is mainly reflected in the following aspects.

　　1. Stiffness

　　The stiffness of paper is a function of the thickness and elastic modulus of the paper. The influence of filler on stiffness should consider the combined influence of filler on bulk and tensile strength.

　　When the amount of filler added is small, the addition of filler basically does not affect the stiffness of the paper. When the amount of filler added is further increased, the stiffness decreases significantly with the increase in the amount of filler.

　　2. Density (Bulk)

　　The density of paper fibers is 1 g/cm³, while the density of fillers is mostly 2.5-3.0 g/cm³, so the addition of fillers will change the bulk of the paper.

　　3. Paper Strength

　　The bonding between fibers is the basis of paper strength. The addition of fillers reduces the bonding between fibers, so adding a large amount of fillers will significantly reduce the strength of the paper.

　　Among them, tensile strength, folding endurance, and bursting strength decrease significantly, while tearing strength decreases slightly, and the amount of filler used is limited. At the same time, the application of certain papermaking aids can significantly reduce this strength reduction phenomenon.

　　4. Conducive to Improving Opacity

　　Paper without filler is composed of fibers and air. Air exists in the pores between fibers. Due to the different refractive indices of fibers and air, when a light beam irradiates the surface of the paper, part of the light is scattered at the interface between the fibers and air, giving the paper a certain (relatively low) opacity. In printing, this mainly manifests as easy show-through.

　　After adding light calcium with a refractive index greater than cellulose to the paper, the number of light scattering interfaces inside the paper is increased, that is, there are three different types of interfaces: between fibers and air, between filler and fibers, and between filler and air. Among these three interfaces, the difference in refractive index between filler and air is larger.

　　Therefore, light is maximally scattered at the interface between the filler and air, increasing the opacity of the paper.

　　5. Influence on the Properties of Printing Paper

　　Adding calcium carbonate to printing paper can improve the printability of the paper, such as increasing the whiteness, smoothness, opacity, and stiffness of the paper. Improving the affinity, softness, and stability of the paper to ink, thus contributing to the improvement of the quality of printed matter.

　　Of course, adding too much filler to paper also brings some negative effects, mainly manifested in the reduction of paper strength and the decline of sizing effect. During printing, powder shedding and hair shedding are prone to occur. Filler particles transferred to the printing plate and rubber blanket will cause blurring, etc. Due to the friction of the filler, it will also wear the printing plate, but adding light calcium carbonate can reduce the wear of the printing plate to the minimum.

　　6. Impact on the special properties of paper

　　To Guangxi Longhua Studies on nano calcium carbonate have shown that after adding nano calcium carbonate filler in the papermaking process, the paper has the following characteristics: it can slow down the aging of the paper, allowing the paper to be preserved for a longer time; it allows the paper to absorb a certain amount of ultraviolet light; it makes the paper not easy to yellow or brittle, and has good insulation performance, etc.

　　 Guangxi Longhua Nano calcium carbonate is used as a coating pigment for papermaking, which is beneficial to improve the gloss, whiteness and hue of the coated paper; it can ensure the purity of the white pigment color; it is beneficial to improve the opacity, gloss and printing gloss of the paper; it can change the rheological properties of the coating preparation liquid; and realize the functionalization of the coating processing paper, such as insulation, conductivity, and antibacterial properties. Nano calcium carbonate, as a papermaking filler, is generally used in the production of special paper products, such as diapers, sanitary napkins, color spray printing paper, paper towels, and breathable membranes.