The role of calcium carbonate in grey background white paper

The demand for grey-backed whiteboard paper is increasing. After its development in recent years, grey-backed whiteboard paper has now made great progress from the past in terms of paper appearance, physical strength, and printability. Improving production costs while ensuring product quality is a matter of survival and development for grey-backed whiteboard paper companies. This article focuses on the application of precipitated calcium carbonate, i.e. light calcium, in the coating of grey-backed whiteboard paper, which further improves the quality of the finished paper while reducing production costs, significantly enhancing the enterprise's profitability and the market competitiveness of the product.

Precipitated calcium carbonate, or light calcium, is an inorganic non-metallic mineral pigment commonly used in the paper industry. Precipitated calcium carbonate is produced by forging calcium carbonate ore to produce quicklime, which is then dissolved in water to produce slaked lime, to which carbon dioxide gas is introduced under controlled conditions to produce calcium carbonate precipitate, which is separated by centrifugation to obtain liquid precipitated calcium carbonate, or further dried to obtain dry precipitated calcium carbonate. Light calcium is the name of the classification in relation to heavy calcium, which is mainly the wet grinding of calcium carbonate ore into small particles of calcium carbonate with a special grinding ball mill, or, depending on the situation and requirements, liquid or dry bicarbonate. The properties of light calcium and heavy calcium vary considerably depending on the processing method. In a wide range of applications in the paper industry, these differences are mainly reflected in the particle size and size distribution, the abrasion value, the purity of the calcium carbonate as well as the morphology of the particles and their influence on the quality of the paper. Of course, in addition to being used in coatings, popular use in factories nowadays is to mix light calcium with heavy calcium in a certain proportion and apply it to the filling of paper, thus making use of the cost advantages of heavy calcium and the high paper thickness and opacity of light calcium.

As the particle form of light calcium is approximate rod shape, compared with the approximate spherical, square, and irregular form of heavy calcium, it has a relatively high specific surface area, thus the application of light calcium in the coating can improve the thickness of the coating, increase the porosity of the coating, which can improve the ink absorption of the coating, the ink absorption speed and the printing suitability of the paper, and the elasticity and compressibility of the coating is better, which is conducive to improving The gloss of the finished paper and the print gloss. Usually, to obtain these properties in the paper, higher-priced wrought clay and imported china clay are added to the coating. Among them, wrought clay is not only expensive but if too much is used in the coating, it may also cause difficulties in the dispersion of the coating and affect the rheology and leveling of the coating, sometimes causing some difficulties in production.

The main performance index of the coating does not change much when replacing the forged clay and a certain amount of imported china clay with light calcium; the brightness of the paper is more stable, the color phase does not change much, the gloss is slightly improved and the roughness is increased; the printing index of the paper meets the requirements, and the ink absorption speed is improved.

In general, using coated light calcium in the surface coating instead of the more expensive wrought clay and imported china clay can achieve the finished paper's relevant physical indicators and printing performance requirements. Customers have well received the paper samples coated with light calcium in practice.