Kraft paper has a high tensile force, such as single light, double light, stripes, no grain, and the like. Mainly used for wrapping paper, envelopes, paper bags, etc. and printing machine drum lining. Used as packaging material. High intensity. Usually yellowish brown. The semi-bleached or fully bleached kraft pulp is light brown, cream or white. Quantitative 80 ~ 120g / m2. The crack length is generally above 6000m. Tear strength, breaking work and dynamic strength are high. Mostly web and flat paper. The sulphate softwood pulp is used as raw material, and it is beaten and made on a long net paper machine. Can be used as cement bag paper, envelope paper, rubber seal paper, asphalt paper, cable protective paper, insulation paper, etc.
A long time ago, "kraft paper" was really made from the calf's skin. Of course, this kind of "kraft paper" is only used when it is used to make the drum skin. The kraft paper used for your book is that after people learn the papermaking technology, the wood fiber of the conifer is chemically pulped. Then, put it into the beater for beating, then add rubber, dye, etc., and finally copy it into paper in the paper machine. Because the color of this paper is yellowish brown, the paper is tough, much like cowhide, so people call it kraft paper.
In fact, the manufacturing methods of kraft paper and plain paper are not much different. Why is kraft paper stronger than plain paper? This is mainly because the wood fiber used for making kraft paper is relatively long, and when cooking wood, it is treated with caustic soda and alkali sulfide chemicals, so that their chemical action is relatively mild, and the original strength of the wood fiber is damaged. It is relatively small, so the paper made from this pulp, the fiber and the fiber are closely interdependent, so the kraft paper is very strong.