It can slow down the reaction, maintain chemical balance, reduce surface tension, prevent light, thermal decomposition or oxidative decomposition. it mainly includes lead salts, metal soaps, organic tin, organic antimony, organic rare earths, pure organic compounds. Thermal stabilizers commonly used in industry mainly include lead salts, metal soaps, organic tin, organic antimony, organic rare earths, pure organic compounds, etc.
1.1 Organotin
(1) Excellent transparency The biggest advantage of organotin stabilizers is that they have excellent transparency. The use of organotin stabilizers in PVC formulations can produce crystalline products. Because of this, organic tin can be used in bottles, containers, corrugated boards, various types of rigid packaging containers, hoses, profiles, films, etc.
(2) Extraordinary thermal stability In terms of thermal stability, there is no other type of thermal Stabilizer that can surpass it. Therefore, it is the preferred stabilizer for rigid PVC, and some varieties have better performance in soft products. Suitable for all PVC homopolymers, such as emulsion, suspension and bulk PVC, as well as vinyl chloride copolymers, graft polymers and polymer blends.
(3) The product is non-toxic. Most organotin stabilizers are non-toxic, and the migration of organotin stabilizers in rigid PVC is minimal. Therefore, organotin stabilizers are the preferred heat stabilizers for PVC for food contact.
(4) Good compatibility. Organotin stabilizers have good compatibility with PVC, so there is generally no precipitation on the metal surface, such as lead salt stabilizers and metal soap stabilizer systems.
(5) Poor lubricity Sulfur-containing tin stabilizers have poor self-lubricity. Therefore, many commercially available sulfur-containing organotins are equipped with lubricants to prevent hot melt from adhering to processing equipment during processing.
(6) High cost Compared with other types of stabilizers, the overall performance of organotin stabilizers is closer to the ideal stabilizer. However, all organotin stabilizers, regardless of their structure, have the main disadvantage that their manufacturing cost is much higher than that of lead stabilizers or metal soap compounds. In recent years, by adopting new synthetic technology, or reducing its usage in formulas, its formula cost has been reduced. In the 1970s, foreign countries developed low-priced tin products, which reduced the tin content, which also reduced the price to a certain extent.
1.2 Lead salt
(1) l Excellent stability experiments proved that among the commonly used basic lead salts, the heat resistance of sulfite is better than that of sulfate, and the heat resistance of sulfate is better than that of phosphite. The tribasic lead sulfate, which is widely used in the PVC industry, has a higher effective lead content and shows better thermal stability than other products.
(2) Excellent insulation. Because lead salt is non-ionic and non-conductive, it is inert, which makes lead salt stabilizers widely used in wire and cable industries.
(3) Excellent weather resistance. Many salt compounds can act as white pigments and can show strong covering power, so they have strong weather resistance.
(4) Poor transparency Transparency is a problem related to weather resistance. When used in wires, cables and record materials, there is no need to care about transparency, because most of these products are white or very dark black.
(5) Inexpensive Lead Salt Stabilizer is the lowest price among all stabilizers. Therefore, despite the continuous introduction of new stabilizers, lead salt stabilizers still dominate the stabilizer market after half a century. The composite lead salt introduced to solve the dust and dispersion problem has increased in price, but still maintains a competitive advantage with other types of stabilizers.
(6) The toxicity of the toxic lead salt stabilizer limits its application in many occasions with strict hygiene requirements. For example, many countries have revised the lead content standards in drinking water, and it is no longer possible to use lead salt in PVC water pipes.
(7) Poor dispersibility The dispersibility of salt lead is poor, but the newly launched one-package product is equipped with lubricants, which solves the dispersibility problem to a certain extent. Because of the above characteristics of lead salt stabilizers, they are especially suitable for high-temperature processing. They are widely used in various opaque hard and soft products and cable materials, such as various pipes, plates, indoor and outdoor profiles, foam plastics, artificial leather, and wires. Cables, records, welding rods, etc. The most important lead salt stabilizers are tribasic lead sulfate, dibasic lead phosphite, and dibasic lead stearate.
1.3 Organic antimony
(1) Better stability. The organic antimony stabilizer has basically the same color stability and lower melt viscosity as organotin at the same temperature. In the twin-screw extrusion process, the effect is particularly outstanding when used in combination with calcium stearate. .
(2) The price of organic antimony stabilizer is much lower than that of methyl tin or butyl tin. In addition, the amount of organic antimony used is relatively low, so the use of organic antimony can achieve a 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, the PVC water supply pipe manufactured with a formula composed of antimony stabilizers, calcium stearate and other lubricants conforms to the U.S. NSF (National Sanitation Foundation) )Regulation.
(4) Poor transparency and light stability. The transparency of organic antimony compounds is not as good as organotin stabilizers, and it is also lower than the barium/fu and calcium/zinc metal soap system. It is close to lead salts and has poor light stability, so antimony is stable. The agent is mostly used for indoor products without color requirements. The antimony stabilizer itself is also required to be stored in an opaque container.
(5) Poor lubricity. Antimony stabilizers have poor lubricity. Therefore, its use must be combined with a large amount of lubricant without exception.
1.4 Metal soap
(1) The tin soap stabilizer Fu soap is the best type of metal soap. Its advantages are also reflected in the absence of initial coloring, and can produce colorless and transparent products; excellent light stability; it has the effect of preventing precipitation and adhesion. . However, because tin salt is toxic, there are strict regulations on its manufacture and use in the Labor Safety and Health Law. In recent years, the use of Fuzao has shown a downward trend.
(2) Zinc soap stabilizerThe thermal stability of zinc-based stabilizer to PVC is extremely poor. The sample with zinc soap suddenly turns black when heated, that is, the so-called "Zine burning" phenomenon occurs, but it has the following advantages: The initial coloring is excellent; the effect of preventing fouling is good; it can improve the weather resistance; many zinc soaps are recognized as non-toxic stabilizers, so they can be used in non-toxic formulations with calcium soaps.
(3) Barium soap stabilizer Barium compounds have good thermal stability and good lubricity, but the red initial coloration occurs during processing, and it is easy to cause sticking to the roller.
(4) The stability of calcium soap stabilizer is poor, but it is recognized as a non-toxic additive in the world and has excellent lubricity.
(5) Other metal soap stabilizers used in the industry include magnesium stearate, file stearate, 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 is approved by the U.S. FDA and the Japanese Vinyl Chloride Food Hygiene Association for food packaging; Stearic Acid files and potassium stearate are also non-toxic products and belong to lead salts , Tin soap and barium soap substitute.
(6) The performance requirements of the composite metal soap stabilizer processing industry for stabilizers are various, and a single metal soap often cannot meet the use requirements, so the use of composite stabilizers has become a trend. A single metal soap compound is rarely used in the PVC industry, and it is usually a compound of several metal soaps. This compound is not a simple addition of properties, but takes advantage of the synergy between the components. The composite metal soap stabilizer generally includes the stabilizer main body (i.e. metal soap), solvent (organic solvent, plasticizer, liquid non-metal stabilizer, etc.), functional additives (auxiliary stabilizer, transparency modifier, light stabilizer, Lubricants, etc.). According to the form, it is divided into solid compound and liquid compound. According to the main component, it can be divided into calcium/zinc Compound Stabilizer, barium/fu compound stabilizer, barium/zinc compound stabilizer, etc. Among them, the calcium/zinc composite stabilizer has a pivotal role in replacing toxic metals because it is non-toxic.
1.5 Rare earth stabilizer
(1) Excellent thermal stability The thermal stability of rare earth stabilizers is better than traditional lead salt series and barium/zinc, barium/ho/zinc stabilizers. In some applications, rare earth stabilizers can partially or completely replace organotin.
(2) Good transparency. The refractive index of rare earth stabilizers is very close to that of PVC Resin, which can replace traditional 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, rare earth stabilizers have anti-photoaging effects and are 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 to replace lead salt stabilizers in cable material formulations, and their electrical insulation properties are comparable to lead salts.
(5) Non-toxic, safe and hygienic. Rare earth elements are low-toxic elements and have no toxic hazards to the human body in their production, processing, transportation and storage. Rare earth stabilizers are non-toxic products and can be used in food packaging and medical packaging products.
(6) The processing performance is slightly worse. In the case of a large amount of rare earth stabilizer, the roll release of the material is not ideal, and there is a tendency to press out. Generally, better results can be achieved by using stearic acid or calcium stearate in combination.
In summary, rare earth stabilizers can be used for water pipes, injection pipe fittings, window frame profiles, door panels, wire ducts, foam products, artificial leather, cable materials, soft and hard transparent products, food packaging materials, etc.
1.6 Auxiliary stabilizers Auxiliary stabilizers include phosphite, epoxy soybean oil, hindered phenols, etc., which mainly rely on the synergistic effect between metal stabilizers to improve the stabilizing effect, and are generally called co-stabilizers. In addition to compounds such as mesaminocrotonic acid ester, 2-phenyl saccharin, vein derivatives, and diketone can be used in combination with metal stabilizers to improve the effect of metal stabilizers, they also have a certain stabilizing effect. Such compounds are usually called pure organic stabilizers. With the development of PVC stabilizers today, the progress of metal stabilizers is relatively slow, and the research and development of auxiliary stabilizers are unprecedentedly active, which has constituted a major trend in the field of PvC stabilizers. Auxiliary stabilizers are rarely used alone, and are often used in conjunction with primary stabilizers to improve initial coloration or improve long-term stability.
Heat stabilizer is one of the indispensable main auxiliaries for PVC processing. The number of parts used for PVC heat stabilizer is small, but its role is huge. The use of heat stabilizer in PVC processing can ensure that PVC is not easy to degrade and relatively stable. The commonly used heat stabilizers in PVC processing include basic lead salt stabilizer, metal soap stabilizer, organotin stabilizer, rare earth stabilizer, epoxy compound, etc. The degradation mechanism of PVC is complex, the action mechanism of different stabilizers is different, and the stabilization effect is also different.PVC stabilizer, action mechanism and application
1 Lead salt stabilizer
Lead salt stabilizers can be divided into three categories:
(1) Pure lead salt stabilizer is mostly a basic salt containing PbO;(2) The heat stabilizer with lubricating effect is mainly the neutral and basic salt of fatty acid;
(3) Composite lead salt stabilizer, and solid and liquid composite stabilizer containing a synergistic mixture of lead salt and other stabilizers and components.
Lead salt stabilizer has strong thermal stability, good dielectric properties, and low price. The reasonable ratio of lead salt stabilizer and lubricant can widen the processing temperature range of PVC resin, and the quality of processed and post-processed products is stable. It is the most commonly used stabilizer at present. Lead salt stabilizer is mainly used in hard products. Lead salt stabilizer has the characteristics of good heat stabilizer, excellent electrical performance and low price. However, lead salt is toxic and can not be used in products that contact with food, nor can it make transparent products, and it is easy to be contaminated by sulfide to generate black lead sulfide.
2 Metal soap stabilizer
Stearic acid soap heat stabilizers are generally prepared by saponification of alkaline earth metals (calcium, cadmium, zinc, barium, etc.) with stearic acid, lauric acid, etc. There are many kinds of products, each with its own characteristics. Generally speaking, lubricating stearic acid is better than lauric acid, and the compatibility with PVC lauric acid is better than stearic acid.
Metal soaps can absorb HCl, and some varieties can replace the Cl atom of the active site with fatty acid radical through the catalysis of metal ions, so they can play a different degree of thermal stability on PVC. In PVC industry, there is rarely a single metal soap compound, but usually a compound of several metal soaps. The common stabilizer is calcium zinc soap. According to Frye-horst mechanism, the stability mechanism of calcium/zinc composite stabilizer can be considered as follows: first, zinc soap reacts with allyl chloride on the PVC chain, and then calcium soap, zinc soap and chlorine chloride react to form unstable metal chlorides. At this time, the auxiliary stabilizer, as the intermediate medium, transfers the chlorine atoms to the calcium soap to regenerate the zinc soap, delaying the formation of zinc chloride which can promote the dehydrochlorination.
Calcium and zinc stabilizers can be used as non-toxic stabilizers in food packaging, medical devices and drug packaging, but their stability is relatively low. When calcium stabilizers are used in large amounts, their transparency is poor and they are easy to spray frost. Calcium and zinc stabilizers generally use polyols and antioxidants to improve their performance, and transparent calcium and zinc composite stabilizers for hard pipes have appeared in China.
3 Organotin stabilizer
Alkyl tin in organotin is usually methyl, n-butyl and n-octyl. Most of the products produced in Japan are butyl tin, and octyl tin is more common in Europe. This is the standard non-toxic stabilizer approved in Europe, while methyl tin is used more in the United States.
There are three main types of organotin stabilizers commonly used:
(1) Aliphatic acid salts mainly refer to dibutyltin dilaurate, di-n-octyltin dilaurate, etc;
(2) Maleate salts mainly refer to dibutyltin maleate, bis (monobutyl maleate) dibutyltin maleate, di-n-octyltin maleate, etc;
(3) Mercaptans, of which bis (thiocarboxylic acid) ester is the most used.
Organotin heat stabilizer has good performance and is a good variety for PVC hard products and transparent products. In particular, octyltin has almost become an indispensable stabilizer for non-toxic packaging products, but its price is relatively expensive. Organic tin heat stabilizer (tin mercaptoacetate) has a good stabilizing effect on PVC. Especially the liquid organotin stabilizer can be better mixed with PVC resin than the solid heat stabilizer. The organotin stabilizer (tin mercaptoacetate) can replace the unstable Cl atoms on the polymer, making the PVC resin have long-term stability and initial color retention. The stability mechanism of tin mercaptoacetate was proposed:
(1) S atom can replace unstable Cl atom, thus inhibiting the formation of conjugated polyolefins.
(2) As a product of PVC thermal degradation, HCl can also accelerate the formation of conjugated polyolefins. Tin mercaptoacetate can absorb the HCl produced.
4 Rare earth stabilizer
Rare earth heat stabilizers mainly include organic weak acid salts and inorganic salts of light rare earth lanthanum, cerium and neodymium, which are rich in resources. The types of organic weak acid salts include rare earth stearate, rare earth fatty acid, rare earth salicylate, rare earth citrate, rare earth laurate, rare earth octanoate, etc.
The preliminary study on the action mechanism of rare earth stabilizer is as follows:
(1) The special electronic structure of rare earth lanthanide elements (2 electrons in the outermost layer and 8 electrons in the secondary layer, with many empty orbits) determines that the energy difference of their empty orbits is very small. Under the action of external thermal oxygen or polar groups, the outer or secondary outer electrons are excited, which can coordinate with the unstable Cl on the PVC chain, and can form a coordination complex with the hydrogen chloride decomposed during the processing of PVC, At the same time, there is a strong attraction between rare earth elements and chlorine elements, which can control the free chlorine element, thus preventing or delaying the automatic oxidation chain reaction of hydrogen chloride and playing a role of thermal stability.
(2) The rare-earth multifunctional stabilizer can physically absorb the oxygen in PVC processing and the ionic impurities contained in PVC itself, and enter the lattice hole of the rare-earth multifunctional stabilizer to avoid their impact and vibration on the parent C-Cl bond. Therefore, the activation energy of HCl removal from PVC can be increased by the action of rare earth multifunctional stabilizer, thus delaying the thermal degradation of PVC plastics.
(3) Suitable anion groups in rare earth compounds can replace allyl chloride atoms on PVC macromolecules, eliminate this degradation weakness, and achieve stability. There are many studies on rare earth stabilizers in China. In general, the stability effect of rare earth heat stabilizers is better than that of metal soap stabilizers. It has good long-term thermal stability, and has extensive synergistic effects with other stabilizers. It has the advantages of good tolerance, free from sulfur pollution, stable storage, non-toxic and environmental protection.
In addition, rare earth elements have a unique coupling effect with CaCO3 and promote the plasticizing effect of PVC, so the amount of CaCO3 can be increased, the use of processing aid ACR can be reduced, and the cost can be effectively reduced. The stabilizing effect of rare earth on PVC is characterized by its unique synergistic effect. The proper coordination of rare earth with some metals, ligands and co-stabilizers can greatly improve the stability.
