Main trend of paper sizing development: neutral sizing
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With the development of the global economy and culture, the position of the paper industry in the industry has become increasingly prominent. After China's paper output exceeded 10 million tons, it has ranked third in the world for eight consecutive years, second only to the United States and Japan.
However, we cannot fail to notice the fact that imported paper products and their raw materials are rising sharply every year in the case of a sharp increase in production. What is the reason? Experts analyzed that in addition to the growth of per capita consumption factors, the backwardness of China's paper chemical industry is an important reason.
From the current situation, China's paper products are low in technical content, and the product structure is mainly in the middle and low grades. The development of society has brought about the continuous upgrading of paper demand. Domestic users have begun to further improve the water resistance, oil resistance, wet strength, smoothness, printability and softness of paper products, which has caused the old China. The production mode has produced a surplus of medium and low-grade paper products, while high-end products are in short supply, which has led to a large increase in the consumption of imported high-grade paper and its raw materials. Therefore, it is an urgent task for China's paper industry to improve the quality of paper products in China as soon as possible.
Rapid development of China's paper chemical industry, and the application of as soon as possible in production, as soon as possible, is the key to solving the problem. Paper sizing agents are critical in many papermaking chemicals.
Gluing is an important part of papermaking. The quality of sizing is directly related to the quality of paper. The development of sizing is inseparable from the development of sizing. From papermaking to today's paper sizing has experienced no from rice paper. Sizing from acid sizing of rosin to neutral sizing of synthetic sizing agent, neutral sizing of anion dispersing rosin, cationic dispersing rosin, medium and alkaline sizing of neutral polyester, each application Advances in the glue process are closely related to the sizing agent invention. Historically, saponified rosin gum has been used for sizing, but the free rosin which acts as a sizing agent in saponified rosin gum accounts for only about 20% of the total rosin gum. The glue effect is very poor, and it can only make up for this deficiency by increasing the amount of paper auxiliaries such as rosin gum, aluminum sulfate and fluorescent whitening agent. However, it directly caused a waste of a large amount of resources, a large amount of papermaking wastewater discharge and greatly increased papermaking costs and poor paper quality. However, there are still a few companies in China that use saponified rosin. In the 1970s, anionic rosin gum was used as a paper sizing agent. The papermaking industry in China has been promoted since the 1990s. Using anionic rosin as a sizing agent can greatly reduce the amount of papermaking auxiliaries and make paper. The quality has been significantly improved, but since the anionic rosin has to be sized under acidic conditions, it causes a large amount of acidic sewage discharge, increases the degree of environmental pollution and sewage treatment costs, and it cannot be sizing at high temperatures (45 ° C) in summer. Affect the normal production of the enterprise. Foreign countries have used neutral sizing agents as paper sizing agents since the early 1980s. Its advantages are:
Excellent performance and wide application range: applicable to all kinds of cultural paper, board paper, news paper, fruit bag paper and packaging paper requiring sizing for wood pulp, syrup, US waste pulp and other pulp production, etc. For applications within the range of values (7-9), the most suitable conditions for papermaking are pH (7.5-8.5). Calcium carbonate fillers can be used to replace traditional rosin acid sizing and AKD neutral sizing.
Features:
1 A sufficient sizing effect is obtained in the dryer section of the paper machine, and the wet paper has achieved good performance in the size press.
2 There is no problem of paper slippage after AKD sizing and sizing water solution
3 The control of sizing is relatively improved, and the use of calcium carbonate does not hinder the sizing.
4 The emulsion has good stability, is not easy to undergo hydrolysis reaction, and reduces the sizing effect.
5 The sizing agent is directly added to the pulp, and the sizing effect can be achieved without the retention of other retention systems.
The 6 papers are elastic, and the hand feels smooth and delicate, which changes the coarse, hard and brittle characteristics of the straw.
7 paper has good ink absorption performance and high printing resolution
8 paper has good durability, and it is not easy to return to yellow after long-term storage, which overcomes the characteristics of easy return to yellow of acid paper.
Paper sizing is rapidly developing in the direction of neutral sizing, while neutral sizing is divided into two directions. One is its own neutral sizing agent, such as AKD, ASA, cationic dispersed rosin, medium Polyester, the other is non-self-aligning neutral sizing agent, such as anionic neutral dispersion rosin, anionic petroleum resin, neutral polyester, etc., and the latest research direction is to unify the two, to prepare both A sizing agent that retains itself and rosin sizing properties, such as neutral polyester, epoxidized rosin, and the like.
The self-retaining sizing agent is mainly a reactive sizing agent and a self-cationizing sizing agent, and the reactive sizing agent AKD and ASA can realize self-setting by using a self-functional group and a hydroxyl group on a fiber or a semi-fiber, without resorting to Aluminum sulfate does not need to be added with aluminum sulfate in use, and its use is less affected by pH value. Therefore, it has been popular in Europe and America in recent years, but its molecular structure active group is easily hydrolyzed, and the water-contaminated pollution papermaking system is used. The conditions are extremely harsh, and recently there has been a tendency to be replaced by a rosin-based sizing agent, especially in Japan, where about 2/3 of the sizing agent is used and an anionic neutral dispersion rosin is reused.
Rosin sizing agent is a traditional sizing agent. Due to its continuous innovation and improvement, it has reached near-neutral, neutral and weakly alkaline sizing. In addition, it is easy to prepare, low in cost, non-hydrolyzed, and fast in sizing. It is strong in nature and renewable in raw materials. It is gradually replacing synthetic sizing agents.
The rosin-based sizing agent is mainly cationic dispersing rosin and anionic dispersing rosin. The traditional anionic dispersing rosin cannot achieve true neutral sizing. The cationic dispersing rosin must be prepared with more expensive cationic emulsifiers and cations. Surfactant, complicated equipment, strict preparation process, so the manufacturing cost is high, so the use of low molecular surfactant as an emulsifier, with the aid of other cation retention agents, reduce dependence on aluminum sulfate, to achieve anion-dispersed rosin It is completely neutral, and even weakly alkaline, it becomes the darling of rosin neutral sizing agent.
The introduction of the neutral polyester SPK has eclipsed both the neutral sizing agent and the rosin sizing agent. Since the neutral polyester molecule has two terminal carboxyl groups, it can be retained on the fiber by means of sulphate with the aid of aluminum sulfate or other cationic groups, but the amount is much less than rosin, and the rosin sizing is retained. The advantage of speed. At the same time, its polar oxygen can form a covalent coordinate bond with the hydroxyl group of the fiber, so that it can retain its own shape and thus has the characteristics of a synthetic sizing agent. At the same time, the sizing agent is not easy to be hydrolyzed, the sizing is rapid, and the quick release property is strong Therefore, it has the advantages of both, overcomes its shortcomings, and will become the new master of neutral sizing agent.