Process for bleaching needlebush and hardwood mixed chemical pulp stewed by using sodium hydroxide anthraquinone method

Abstract

The invention relates to a process for bleaching needlebush and hardwood mixed chemical pulp stewed by using a sodium hydroxide anthraquinone method. The process comprises the steps of: mixing needlebush chemical pulp stewed by using the sodium hydroxide anthraquinone method with hardwood chemical pulp stewed by using the sodium hydroxide anthraquinone method in a mass ratio which ranges from 3:7to 7:3; and then performing high-whiteness bleaching by employing an ECF (elemental chlorine free) bleaching process having a bleaching working procedure of O1-O2-D0-OEP-D1-D2 or O1-O2-D0-OEP-D1. In the invention, the dosage of consumed chemicals in an entire process is equal to or a little lower than that of a process in which paper pulp is respectively stewed and respectively bleached. The two kinds of stewed crude pulp are similar in Kappa number, therefore other conditions of the bleaching process are milder, and the pulp provided by the invention is easier to bleach than the paper pulp with great hardness difference. Both the whiteness stability of the bleached paper pulp and various physical indexes such as burst index, fracture length, tearing index, folding strength and the like of made paper are better.

Description

technical field [0001] The invention relates to a bleaching process and belongs to the technical field of papermaking. Background technique [0002] With the rapid development of my country's paper industry, wood has become the main raw material of my country's pulp and paper industry. Wood raw materials include coniferous wood and hardwood. There are two main methods for producing chemical pulp from softwood and hardwood, one is the sulfate method, and the other is the sodium hydroxide anthraquinone method. In the actual production of paper, according to the physical strength index requirements of the paper and the characteristics of the paper, the blending ratio of the needle broad chemical pulp of the pulp is different. Under the current situation, hardwood and softwood are boiled and bleached separately, and then mixed into pulp in a certain proportion to produce various high-grade papers. If the coniferous wood and broad-leaved wood are cooked separately and cooked ac...

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Problems solved by technology

[0003] Patent CN 102086609A discloses a mixed kraft pulping process of softwood and hardwood, including material preparation, kraft cooking, washing and screening, and bleaching, and the weight ratio of softwood and hardwood is 7-8: 2-3 The wood chips are evenly mixed and sent to the cooking pot for kraft cooking and pulping. The vertical pot cooking is used for mixed cooking of coniferous wood and hardwood wood. Other technological processes are basically the same as the production of masson pine kraft softwood pulp. Leaf wood is more difficult to cook, and the cooking temperature is higher than that of hardwood wood, and the amount of chemicals required is more. If softwood and hardwood are mixed for cooking, there is a cooking process that is biased towards the cooking conditions of softwood or biased. The problem of the cooking conditions of hardwood: if the mass ratio of softwood chips is greater than that of hardwood chips, the cooking conditions must be biased towards the cooking conditions of softwood, otherwise the softwood cannot be completely pulped at the end of cooking, and the softwood will not be fully pulped. In the case of pulping, hardwood will lose yield due to strong cooking conditions, resulting in increased fiber degradation and reduced physical strength of the pulp; if the mixing ratio of softwood and hardwood is such that the mass of hardwood is greater than that of softwood When it comes to quality, the cooking conditions tend to be similar to those of hardwood. In this case, it is difficult for softwood to pulp completely, so the hardness of the pulp is high, which is not conducive to subsequent pulp bleaching; Mixed cooking with a ratio of 1:1, the cooking conditions are determined according to the lower limit of the cooking conditions of coniferous wood and the upper limit of the cooking conditions of hardwood, which can realize the mixed cooking of coniferous wood, but the hardness of pulp after cooking is relatively high, which is not conducive to Subsequent bleaching of pulp

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