In recent years, paper manufacturers and users have paid more and more attention to the bulk of the paper, because the bulk has a significant impact on the cost and performance of the product. High bulk means that at the same thickness, the basis weight can be reduced, and the amount of fiber used can be reduced to achieve cost savings; high bulk can increase paper stiffness, allowing book publishers to maintain full book thickness with fewer pages, and can also increase paper opacity, printability, and reduce printing ink bleed-through. Therefore, the high-bulk is of great significance to the cost control of paper, product performance and added value of products.
What is high-bulk? This is an important indicator of paper, which is the ratio of basis weight to thickness. Bulk indicates the density of the paper, that is, the size of the porosity of the paper.
The main factors affecting the bulk of paper include papermaking fiber raw materials, pulp type, beating operation, fillers, chemicals, pressing, drying, calendering, etc.
The fiber morphology of the papermaking fiber raw material has an important influence on the bulk of the paper. Thicker fibers have higher porosity and higher bulk of paper, but the bulk is not only related to fiber thickness, but also has a very important relationship with the crushing of fibers during the paper-making process. It ultimately depends on the degree of crushing and deformation of the fibers. Therefore, the fibers with a small diameter and thick walls are stiffer, not easy to be crushed, and easy to form high bulk paper.
The type of pulp also has a great influence on the bulk of the paper. Generally speaking, high-yield pulp>thermomechanical pulp>kraft pulp>waste pulp. Different raw materials have different bulk in the same pulp, hardwood > softwood. The high bulk of high-yield pulp itself is incomparable with other pulps, so high-yield pulp is widely used to partially replace bleached kraft hardwood pulp in high-grade paper. The selection and ratio of pulp types are the key to the current high bulk paper production process. Adding high yield pulp to improve paper bulk is currently the most effective method widely used by paper mills.
Bulk is a very important property of paper. High-bulk paper can maintain the necessary stiffness, reduce fiber consumption, save pulp costs, and improve bulk. The most feasible methods at present include adding high-yield pulp, pulp selection and process systems. Optimization and development of new bulk additives are also an important research direction.
Post time: Aug-01-2022