Product Grades of Coated Duplex Board With Grey Back

White board paper is made by blending the surface pulp with each layer of base pulp on a multi-circular screen multi-drying cylinder paper machine or a long circular screen mixed paperboard machine. Pulp is generally classified into face pulp (surface layer), second layer, third layer, and fourth layer. The fiber ratio of each layer of pulp is different, and the fiber ratio of each layer of pulp also varies according to the quality of the paper being made. The first layer is the surface layer pulp, which requires high whiteness and certain strength. It is usually made of bleached sulfate wood pulp or mixed with partially bleached chemical grass pulp and waste paper pulp from white paper edges. The second layer is the liner, which serves to isolate the surface layer from the core layer and is also required to have a certain degree of whiteness. Usually, 100% mechanical wood pulp or light-colored waste paper pulp is used. The third layer is the core layer, mainly serving as a filler to increase the thickness of the cardboard and enhance its stiffness. It is typically made from a mixture of waste paper pulp or grass pulp. This layer is the thickest, and for cardboard with a high basis weight, it is often used to hang the pulp in several mesh slots in several layers. The last layer is the bottom layer, which has the functions of improving the appearance of the cardboard, enhancing its strength and preventing curling. It is usually made from high-yield pulp or better waste paper pulp as raw materials. The bottom color of the cardboard is mostly gray, but other bottom colors can also be produced as required.