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Broadly speaking, chemicals that increase the stability of solutions, colloids, solids, and mixtures are called stabilizers. It can slow down the reaction, maintain chemical equilibrium, reduce surface tension, and prevent light, thermal or oxidative decomposition. The broad source of chemical stabilizers is very wide, mainly based on the design purpose of the formula designer, any chemical can be flexibly used to achieve the purpose of stable product quality.

In a narrow sense, it mainly refers to reagents that maintain the stability of high-polymer plastics, rubber, and synthetic fibers, and prevent their decomposition and aging.


1 Introduction

Industrially used heat stabilizers mainly include lead salts, metal soaps, organic tin, organic antimony, organic rare earths, and pure organic compounds. It is estimated that China currently has a heat stabilizer production capacity of 70,000 ta /, and its consumption in 2000 was about 80,000 t / a. The development of lead salts in China is focused on eliminating dust pollution, and relevant measures have been taken; organic tin consumption in the Chinese market is relatively low; due to poor promotion of high-performance auxiliary stabilizers, there is still a lack of a cost-effective composite metal soap system on the market ; Rare earth stabilizers are a new force in the development of thermal stabilizers in China. The global consumption of thermal stabilizers has exceeded 300,000 t / a.The United States represents a new level of development of the world's thermal stabilizers and is at the forefront of the world in terms of lead-free; Japan's thermal stabilizer output is about 61.7 million tons. / a, still dominated by lead salts; the consumption of heat stabilizers in Western Europe is about 110,000 t / a.

2 performance characteristics and application of thermal stabilizer

In actual blending, in addition to the requirements of the stabilizer to meet the needs of thermal stability, it is often required to have excellent processability, weather resistance, initial coloring, and light stability, and strict requirements on its odor and viscosity.At the same time, polychloride Vinyl products are also ever-changing, including pipes, sheets, blow-molded parts, injection molded parts, foam products, paste resins, etc. Therefore, the selection of heat stabilizers in PVC processing is very important, and most of the processing formulas need to be developed by processing manufacturers.

1.1 organotin

(1) The transparent organotin stabilizer has the great advantage of having transparency. The PVC formula using the organotin stabilizer can obtain crystalline products. Because of this, organotin can be used in bottles, containers, corrugated boards, various types of rigid packaging containers, hoses, profiles, films, etc.

(2) Extraordinary thermal stability No other type of thermal stabilizer can surpass it in terms of thermal stability. Therefore, it is a stabilizer for rigid PVC, and some varieties also perform better in soft products. Suitable for all PVC homopolymers, such as emulsions, suspensions and bulk PVC, as well as copolymers, graft polymers and blended polymers of vinyl chloride.

(3) Non-toxic products Most organotin stabilizers are non-toxic. In addition, the migration of organotin stabilizers in rigid PVC is minimal. Therefore, organotin stabilizers are heat stabilizers for food contact PVC.

(4) Good Compatibility Organotin stabilizers have good compatibility with PVC, so the phenomenon of precipitation on the metal surface, which is common in lead salt stabilizers and metal soap stabilizer systems, generally does not occur.

(5) Poor lubricity. Sulfur-containing tin stabilizers are slightly less self-lubricating. Therefore, many commercially available sulfur-containing organic tins are formulated with a lubricant to prevent hot melt from sticking to processing equipment during processing.

(6) Expensive compared with other types of stabilizers, the overall performance of organotin stabilizers is closer to the ideal stabilizer. However, the main disadvantage of all organotin stabilizers, regardless of their structure, is that the manufacturing cost is much higher than that of lead stabilizers or metal soap compounds. In recent years, the cost of formula has been reduced by adopting new synthetic technology, or reducing its use in the formula. In the 1970s, low-priced tin products were developed abroad, which lowered the tin content and lowered the price to a certain extent.

1.2 Lead salt

(1) Excellent stability experiments prove that in commonly used basic lead salts, the heat resistance of sulfite is better than sulfate, and the heat resistance of sulfate is better than phosphite. The widely used tribasic lead sulfate in the PVC industry has a higher effective lead content and exhibits better thermal stability than other products.

(2) Excellent insulation Since lead salts are non-ionic and non-conductive, they are inert, which makes lead salt stabilizers widely used in the wire and cable industry.

(3) Excellent weather resistance Many salt compounds can play the role of white pigments, can show strong covering power, and therefore have strong weather resistance.

(4) Poor transparency. Transparency is an issue related to weather resistance. When used in wires, cables, and recording materials, there is no need to care about transparency, because these products are mostly white or deep black.

(5) Low-priced lead salt stabilizers are among the lowest in all stabilizer varieties. Therefore, despite the continuous introduction of new stabilizers, lead salt stabilizers still dominate the market after half a century. The compound lead salt introduced to solve the problem of dust and dispersion has increased in price, but still maintains a competitive advantage with other types of stabilizers.

(6) The toxicity of toxic lead salt stabilizers has limited its application in many places with strict health requirements. For example, many countries have revised the lead content standards in drinking water, and the use of lead salts in PVC water pipes is no longer possible.

(7) Poor dispersibility Poor dispersibility of salt and lead is poor, but a new packaging product is formulated with a lubricant to solve the dispersibility problem to a certain extent. Because of the above characteristics, lead salt stabilizers are particularly suitable for high-temperature processing.They are widely used in various opaque hard and soft products and cable materials, such as various types of pipes, plates, indoor and outdoor profiles, foam plastics, artificial leather, and wires, Cables, records, welding rods, etc. Important lead salt stabilizers are tribasic lead sulfate, dibasic lead phosphite, and dibasic lead stearate.

1.3 Organic antimony

(1) Good stability At the same temperature, the organic antimony stabilizer has the same color stability and lower melt viscosity as organotin. In the twin-screw extrusion process, the effect is particularly outstanding when used with calcium stearate. .

(2) Lower price Organic antimony stabilizer is much lower than methyl tin or butyl tin. In addition, the use of organic antimony is low, so using organic antimony can achieve better performance / price balance.

(3) The product is non-toxic. In the United States, when a twin-screw extruder is used to manufacture PVC pipes, a PVC water pipe manufactured using a formula composed of antimony-based stabilizers and calcium stearate and other lubricants meets the US NSF (National Sanitation Foundation ).

(4) Poor transparency and light stability. The transparency of organic antimony compounds is not as good as that of organotin stabilizers and is lower than that of barium / fu and calcium / zinc metal soap systems. It is close to lead salts and has poor light stability. Agents are mostly used in indoor products without color requirements. The antimony stabilizer itself also requires storage in opaque containers.

(5) Poor lubricity. Antimony stabilizers have poor lubricity. Therefore, it is necessary to use a large amount of lubricants without exception.

1.4 Metal soap

(1) Tin soap stabilizer Fu soap is a class of metal soap with good performance. Its advantages are also reflected in the absence of initial coloring, which can produce colorless and transparent products; excellent light stability; and the effect of preventing precipitation and adhesion. However, due to the toxic nature of tin salts, their production and use are strictly regulated in the Labor Safety and Health Law. In recent years, the use of blessing soap has shown a downward trend.

(2) Zinc soap stabilizer Zinc stabilizers have very poor thermal stability to PVC. The samples added with zinc soap sharply turn black when heated, which results in the so-called "zine burning" phenomenon. Good initial coloring; good anti-fouling effect; can improve weather resistance; many zinc soaps are recognized as non-toxic stabilizers, so they can be used in combination with calcium soaps in non-toxic formulations.

(3) Barium soap stabilizer Barium compounds have good thermal stability and good lubricity. However, red initial coloring occurs during processing, and it is easy to cause sticky rolls.

(4) Calcium soap stabilizer has poor stability, but it is recognized as a non-toxic additive by various countries in the world and has excellent lubricity.

(5) Other metal soap stabilizers The metal soaps used in the industry include magnesium stearate, stearic acid file, aluminum stearate, potassium stearate, etc., among which magnesium stearate is similar to calcium stearate and can be used Materials that are in contact with food; aluminum stearate is similar to zinc stearate, and the US FDA and Japan Vinyl Chloride Food Hygiene Association are approved for food packaging; stearic acid files and potassium stearate are also non-toxic products, which are lead salts , Tin and bar soap alternatives.

(6) The performance requirements of stabilizers in the processing industry of composite metal soaps are various, and single metal soaps often cannot meet the requirements for use, so the use of composite stabilizers has become a trend. In the PVC industry, a single metal soap compound is rarely used, but is usually a composite of several metal soaps. This complex is not a simple addition of properties, but rather takes advantage of the synergy between the components. Composite metal soap stabilizers generally include the main body of the stabilizer (ie metal soap), solvents (organic solvents, plasticizers, liquid non-metal stabilizers, etc.), functional additives (auxiliary stabilizers, transparency improvers, light stabilizers, Lubricant, etc.). According to the morphology, it is divided into solid composite and liquid composite. According to the main component, it can be divided into calcium / zinc composite stabilizer, barium / fu composite stabilizer, barium / zinc composite stabilizer and so on. Among them, calcium / zinc composite stabilizers play an important role in replacing toxic metals because they are non-toxic.

1.5 Rare earth stabilizer

(1) Excellent thermal stability The thermal stability of rare earth stabilizers is superior to traditional lead-salt-based and barium / zinc, barium / pickle / zinc stabilizers. In some applications, rare earth stabilizers can partially or completely replace organotin.

(2) The refractive index of the rare earth stabilizer with good transparency is very close to that of PVC resin, which can replace the traditionally used organotin and be used in the field of products with higher transparency requirements.

(3) Excellent weather resistance. Rare earth elements can absorb 230-320nm ultraviolet light. Therefore, the rare earth stabilizer has anti-light aging effect and is suitable for outdoor products such as PVC corrugated boards and window materials.

(4) Excellent electrical insulation properties Some rare earth multifunctional stabilizers can be used instead of lead salt stabilizers in cable compound formulations, and their electrical insulation properties are comparable to lead salts.

(5) Non-toxic, safe and hygienic rare earth element is a low-toxic element, which has no toxicity hazard to human body during its production, processing, transportation and storage. Rare earth stabilizers are non-toxic products and can be used in food packaging and pharmaceutical packaging products.

(6) When the processing performance is slightly worse, when the amount of rare earth stabilizer is larger, the material's roll-off property is not ideal, and there is a tendency for pressure analysis. Generally, better effects can be achieved by using stearic acid or calcium stearate.

In summary, rare earth stabilizers can be used in water pipes, injection pipe fittings, profiled window frames, door panel siding, wire ducts, foamed products, artificial leather, cable materials, soft and hard transparent products, food packaging materials, etc.

1.6 Auxiliary stabilizers Auxiliary stabilizers include phosphorous acid vinegar, epoxy soybean oil, hindered phenol, etc., mainly rely on the synergistic effect with metal stabilizers to improve the stabilizing effect, generally called co-stabilizers. Compounds such as mesaminocrotonic acid vinegar, 2-phenyl squeegee, pulse derivatives, and edione, can be used in combination with metal stabilizers to improve the effect of metal stabilizers. Compounds are often referred to as pure organic stabilizers. The development of PVC stabilizers to this day has been relatively slow, while active research and development of auxiliary stabilizers has constituted a major trend in the field of PvC stabilizers. The auxiliary stabilizer is rarely used alone, and it is often used in combination with the main stabilizer to improve initial coloring or improve long-term stability.

3 Development of thermal stabilizers

Global environmental protection requirements are becoming more stringent, human beings are increasingly demanding for the purification of the environment on which they live, and the pressure on regulations restricting the use of heavy metal thermal stabilizers is increasing, making the development and production of thermal stabilizers non-toxic and versatile. The pace of development has accelerated. Wuxi, low lead, low dust, and alternative lead salts have become the focus of the development of heat stabilizers worldwide. The introduction of new chemicals as stabilizers is relatively rare, and composite stabilizers are overwhelming.

The development of various stabilizers shows the following trends.

(1) Dust free of lead salts is a basic requirement, and low lead is an environmental compulsion. In view of the performance of lead salts in pipes and insulation materials, the lead-free process has been slow in the world. The true withdrawal of lead salts from the historical stage requires the emergence of new products with excellent performance-price ratios and excellent lead-free products. It also requires the strengthening of environmental regulations and time. .

(2) Methyltin products with excellent organotin performance have been greatly developed, especially in China. China already has a number of methyl tin. In recent years, Shenzhen Fansheng and Hubei Nanxing have made effective efforts in the production and promotion of methyl tin. Fansheng started from the raw material tin, adopted its own technology, mastered the key to the production of 6,000 tons of methyl tin per year, and developed a new inverse organotin compound, marking that China's organic tin production has reached a higher level . At present, the development of organic tin stabilizers in China has been vigorously developed to make the structure of thermal stabilizers more reasonable. There are no technical obstacles. What is needed is the guidance of policies and regulations.

(3) Non-toxic calcium / zinc stabilizers for metal soaps have extremely broad development space. Calcium / zinc stabilizers have been used in large diameter pipes and insulation in foreign countries. But the domestic lack of attention to the development of composite metal soap, the lack of high-performance auxiliary stabilizer varieties, compared with foreign countries, the contrast is large. The development of high-performance composite metal soaps relies on high-performance auxiliary stabilizers.

(4) Rare earth stabilizers are thermal stabilizers with Chinese characteristics and have a strong development momentum. At present, there are more than 10 domestic manufacturers and research institutes involved in the development of rare earth stabilizers. Manufacturers in Baotou and other places have seized the opportunity of China's large-scale development of the western region and plan to build large-scale rare earth stabilizer bases. However, most of the currently introduced rare earth stabilizers are complexes of rare earth and lead salts, which can only be used as a transition product of low lead. The widespread use of rare earth stabilizers also needs to better solve the problems of insufficient lubricity and processability.

(5) Pure organic compounds Pure organic stabilizers are valued as substitutes for metal stabilizers. Ciba Refining, Morton, and other companies have successively introduced pure organic compound varieties represented by amine sulfonated diones.Compared with metal stabilizers, pure organic products are environmentally friendly products and are expected to play a huge role in replacing toxic heavy metal stabilizers. Role.

(6) Other products The new compounds used as heat stabilizers in recent years include hydrotalcite series, perchlorate, etc. Ciba Geigy Corporation used perchloric acid and its salts with epoxy compounds and antioxidants in PVC to obtain heat and color resistance; the hydrotalcite series launched by Japan Common Medicine is a magnesium / aluminum compound It is used in combination with fatty acid zinc in PVC to prevent coloration of the batch; Germany Southern Chemical Company has built a production device with an annual output of 5000t of hydrotalcite and has technology. As a completely harmless additive to the environment, hydrotalcite has broad application prospects. [1]

References

蔡宏国. 国内外热稳定剂现状及发展[J]. 精细与专用化学品,2001,09:17-22. 1.Cai Hongguo. Status and Development of Thermal Stabilizers at 彩乐乐网 and Abroad [J]. Fine and Specialty Chemicals, 2001,09: 17-22.



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