With the development of the global economy and culture, the paper industry is becoming more and more prominent in the industry. After China's paper production 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 help but notice the fact that in the case of a sharp increase in output, the annual imports of paper products and their raw materials have also risen sharply. What is the reason? Experts analyze that, in addition to the growth of per capita consumption factors, China's paper chemical industry is lagging behind is an important reason.
Judging from the current situation, China's paper products have low technical content, and the product structure is mainly based on low-end products. The development of society has brought about continuous upgrades in paper demand, and domestic users have begun to further improve the water resistance, oil resistance, wet strength, smoothness, printability and flexibility of paper products, which has caused China's old The production model produced a surplus of low-end paper products, while high-end products are in short supply, resulting in a large increase in the consumption of imported high-end paper and its raw materials. Therefore, improving the quality of China's paper products as soon as possible is the top priority of China's paper industry.
The rapid development of China's paper-making chemical industry, and its application as soon as possible in production, as soon as possible, is the key to solving the problem. Among many papermaking chemicals, papermaking sizing agent is very important.
Sizing is an important part of papermaking. The quality of sizing is directly related to the quality of papermaking. The development of sizing is inseparable from the development of sizing agents. From the invention of papermaking to today's papermaking, sizing has gone through Sizing to acid sizing of rosin, to neutral sizing of synthetic sizing agent, to neutral sizing of anion dispersed rosin, cationic dispersing rosin, to neutral and alkaline sizing of neutral polyester, each time The progress of the sizing technology is closely connected with the invention of the sizing agent. Historically, saponified rosin gum has been used for sizing. However, the free rosin in the saponified rosin gum only accounts for about 20% of the total amount of rosin gum. The effect of the glue is extremely poor, and this can only be compensated by increasing the amount of paper-making aids such as rosin gum, aluminum sulfate, and optical brightener. However, it directly causes a lot of waste of resources, discharge of a large amount of papermaking sewage and greatly increases the cost of papermaking, and the paper quality is poor. However, there are still a few domestic companies using saponified rosin gum. The anionic rosin gum has been used as a papermaking sizing agent in the 1970s abroad. The papermaking industry in China has been promoted since the 1990s. The use of anionic rosin gum as a sizing agent can greatly reduce the amount of papermaking additives and make paper The quality has been significantly improved, but because the anionic rosin gum must be sizing under acidic conditions, it causes a large amount of acidic sewage discharge, increasing the degree of environmental pollution and sewage treatment costs. At the same time, it cannot be sizing at high temperatures in summer (45 ℃). Affect the normal production of enterprises. Foreign countries have adopted neutral sizing agents as papermaking sizing agents since the early 1980s. Its advantages are:
Wide range of excellent performance: suitable for all kinds of cultural paper, board paper, newsprint, fruit bag paper and packaging paper requiring sizing, etc., which can be produced at a wide pH It can be used within the range of value (7-9). The most suitable copying condition is PH value (7.5-8.5). Calcium carbonate filler can be used, which can replace the traditional rosin acid sizing and AKD neutral sizing.
Features:
â‘ Full sizing effect is obtained in the dryer section of the paper machine, and the wet paper has achieved good performance in the sizing press.
â‘¡There is no paper slip problem after AKD sizing and water sizing agent solves the problem â‘¢The control of sizing is relatively improved, and there is no hindrance to the sizing caused by the use of calcium carbonate. â‘£Emulsion stability is good and hydrolysis reaction is not easy To reduce the sizing effect.
⑤The sizing agent is directly added to the pulp, and the sizing effect can be achieved without other retention systems.
⑥The paper copied is elastic, smooth and delicate, and it changes the characteristics of thick, hard and brittle straw pulp. ⑦The paper has good ink absorption performance and high printing clarity. ⑧The paper has good durability and is not easy to return to yellow after long-term storage. Overcome the characteristic of acid paper to return to yellow easily
Papermaking sizing is developing rapidly towards neutral sizing, and neutral sizing agents are divided into two directions. One is self-retaining neutral sizing agents, such as AKD, ASA, cationic dispersion rosin gum, medium Polyester, the other is a non-self-defining neutral sizing agent, such as anionic neutral disperse rosin, anionic petroleum resin, neutral polyester, etc., and the latest research direction is to unify the two and prepare both Sizing agent that retains its own sizing properties, such as neutral polyester, epoxidized rosin, etc.
Self-retaining sizing agents are mainly reactive sizing agents and self-cationizing sizing agents. Reactive sizing agents AKD and ASA can use their own functional groups to react with hydroxyl groups on fibers or semi-fibers to achieve self-setting, without resorting to Aluminum sulfate does not require the addition of aluminum sulfate when it is used, and its use is less affected by the pH value, so it has gradually become popular in Europe and the United States in recent years, but because its molecular structure active group is also very easy to hydrolyze, it will pollute the papermaking system after hydrolysis. The conditions are extremely harsh. Recently, it has been replaced by rosin-based sizing agents. Especially in Japan, about 2/3 of the sizing agents reuse anionic neutral dispersion rosin gum.
The rosin sizing agent is a traditional sizing agent. Due to its continuous innovation and improvement, it can now achieve near-neutral, neutral and weakly alkaline sizing, coupled with its easy preparation, low cost, no hydrolysis, sizing speed It has strong presentity and renewable raw materials. It is gradually replacing synthetic sizing agents.
The rosin-based sizing agent is mainly cationic disperse rosin gum and anion disperse rosin gum. Since traditional anionic disperse rosin gum cannot achieve true neutral sizing, the preparation of cationic disperse rosin gum must use more expensive cationic emulsifier and cation Surfactant has complicated equipment and strict preparation process, so the manufacturing cost is relatively high, so low molecular surfactant is used as emulsifier, with the help of other cationic retention agents, the dependence on aluminum sulfate is reduced to realize anion-dispersed rosin gum The completely neutral copying, even weak alkaline copying, has become the darling of rosin-based neutral sizing agents.
The introduction of neutral polyester SPK makes its own neutral sizing agent and rosin sizing agent eclipsed. Because the neutral polyester molecule has two terminal carboxyl groups, it can be retained on the fiber by using aluminum sulfate or other cationic groups like rosin, but the amount is much less than rosin, and the rosin sizing is retained Quick advantage. At the same time, its polar oxygen can form a covalent coordination bond with the hydroxyl group of the fiber to achieve its own stereotype, so it has the characteristics of a synthetic sizing agent. At the same time, the sizing agent is not easy to hydrolyze, the sizing is rapid, and the rapidity is strong. Therefore, it has both advantages and overcomes its shortcomings, and will surely become the new master of neutral sizing agent.
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