Performance characteristics and applications of heat stabilizers

In the actual cooperation, in addition to meeting the needs of thermal stability, stabilizers are often required to have excellent processability, weather resistance, initial coloration, light stability, and strict requirements on its smell and viscosity. At the same time, PVC 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 during PVC processing is very important, and most processing formulas need to be developed by the processing manufacturers themselves.
1.1 Organic Tin
(1) The greatest advantage of excellent transparency of organotin stabilizers is their outstanding transparency. By using organotin stabilizers in PVC formulations, crystalline products can be obtained. Because of this, organotin can be used in bottles, containers, corrugated boards, various types of hard packaging containers, hoses, profiles, films, etc.
(2) There is currently no other type of thermal stabilizer that can surpass its extraordinary thermal stability. Therefore, it is the preferred stabilizer for hard PVC, and some varieties also have good performance in soft products. It is applicable to all PVC homopolymers, such as lotion, suspension and bulk PVC, as well as copolymer, graft polymer and blend polymer of vinyl chloride.
(3) Most organic tin stabilizers are non-toxic, and their migration in hard PVC is minimal. Therefore, organic tin stabilizers are the preferred heat stabilizers for PVC used in contact with food.
(4) Good compatibility: Organic tin stabilizers have good compatibility with PVC, so the phenomenon of precipitation on metal surfaces, which is common in lead salt stabilizers and metal soap stabilizer systems, generally does not occur.
(5) The self-lubricating properties of sulfur-containing tin stabilizers are slightly poor. Therefore, many commercially available sulfur-containing organotin compounds are equipped with lubricants to prevent hot melt from adhering to processing equipment during processing.
(6) Compared with other types of stabilizers, the comprehensive performance of organotin stabilizers is closer to the ideal stabilizer due to their high cost. But the main disadvantage of all organotin stabilizers, regardless of their structure, is that their manufacturing cost is much higher than that of lead stabilizers or metal soap composites. In recent years, the use of new synthesis techniques or reducing their usage in formulations has led to a decrease in formulation costs. In the 1970s, low-priced tin products were developed abroad, reducing the tin content and to some extent lowering prices.
1.2 Lead salts
(1) Excellent stability experiments have shown that in commonly used salt based lead salts, sulfite has better heat resistance than sulfate, while sulfate has better heat resistance than hypophosphite. Tribasic lead sulfate, which is widely used in the PVC industry, has a higher effective lead content and exhibits better thermal stability than other products.
(2) Due to its non-ionic and non-conductive nature, lead salts have excellent insulation properties and are therefore inert. This makes lead salt stabilizers widely used in the wire and cable industry.
(3) Many salt compounds have excellent weather resistance and can act as white pigments, exhibiting strong coverage and thus possessing strong weather resistance.
(4) Poor transparency is an issue related to weather resistance. When used in wires, cables, and record materials, transparency is not a concern as most of these products are white or very dark black.
(5) Low cost lead salt stabilizers are the lowest priced among all stabilizer varieties. Therefore, despite the continuous introduction of new stabilizers, lead salt stabilizers still dominate the stabilizer market half a century later. The composite lead salt introduced to solve dust and dispersion problems has increased in price, but still maintains a competitive advantage over other types of stabilizers.
(6) The toxicity of toxic lead salt stabilizers limits their application in many situations with strict hygiene requirements. For example, many countries have revised their standards for lead content in drinking water, making it impossible to use lead salts in PVC water pipes.
(7) The dispersibility of salt lead is poor, but the newly launched packaging product is equipped with a lubricant, which to some extent solves the dispersibility problem. Because of the above characteristics, lead salt stabilizers are particularly suitable for high-temperature processing, and are widely used in various opaque hard and soft products and cable materials, such as various pipes, plates, indoor and outdoor profiled materials, foam plastics, artificial leather, wires, cables, records, welding rods, etc. The most important lead salt stabilizers are tribasic lead sulfate, dibasic lead phosphite, dibasic lead stearate, etc.
1.3 Organic antimony
(1) Organic antimony stabilizers have good stability and similar color stability to organotin at the same temperature, as well as lower melt viscosity. In the twin-screw extrusion process, the effect is particularly prominent when used in combination with calcium stearate.
(2) Organic antimony stabilizers have much lower prices than methyl tin or butyl tin. In addition, the usage of organic antimony is relatively low, so using organic antimony can achieve a good balance between performance and price.
(3) The product is non-toxic. When using a twin-screw extruder to manufacture PVC pipes in the United States, PVC water pipes made with a formula composed of antimony stabilizers, calcium stearate, and other lubricants comply with the National Sanitation Foundation (NSF) regulations.
(4) Organic antimony compounds have poor transparency and photostability compared to organotin stabilizers, as well as lower transparency than barium/fluorine and calcium/zinc metal soap systems. They are similar to lead salts and have poor photostability. Therefore, antimony stabilizers are mostly used for indoor products without color requirements. Antimony stabilizers themselves also require storage in opaque containers.
(5) Antimony stabilizers have poor lubricity, so their use invariably requires the use of a large amount of lubricant.
1.4 Metal soap
(1) Tin soap stabilizer Fu soap is the best performing type of metal soap, and its advantages are also reflected in the absence of initial coloring, which can produce colorless and transparent products; Excellent photostability; It has the effect of preventing precipitation and adhesion. However, due to the toxicity of tin salts, there are strict regulations on their manufacturing and use in the Labor Safety and Health Law. In recent years, the use of soap has shown a downward trend.
(2) Zinc soap stabilizers have extremely poor thermal stability for PVC, and the samples added with zinc soap quickly turn black when heated, resulting in the so-called "Zine burning" phenomenon. However, they have the following advantages: excellent initial coloring properties; Good anti fouling effect; Can improve weather resistance; Many zinc soaps are recognized as non-toxic stabilizers, so they can be used in conjunction with calcium soaps in non-toxic formulations.
(3) Barium soap stabilizers have good thermal stability and good lubricity, but they produce initial red coloring during processing and are prone to sticking to rollers.
(4) Calcium soap stabilizers have poor stability, but are recognized by countries around the world as non-toxic additives with excellent lubricity.
(5) Other metal soap stabilizers used in the industry include magnesium stearate, stearic acid file, aluminum stearate, potassium stearate, etc. Among them, magnesium stearate is similar to calcium stearate and can be used as a material in contact with food; Aluminum stearate is similar to zinc stearate and is approved for use in food packaging by the US FDA and the Japan Chloroethylene Food Hygiene Association; Stearic acid files and potassium stearate are also non-toxic products, which are substitutes for lead salts, tin soaps, and barium soaps.
(6) The processing industry of composite metal soap stabilizers has various performance requirements for stabilizers, and a single metal soap often cannot meet the usage requirements. Therefore, the use of composite stabilizers has become a trend. In the PVC industry, a single metal soap compound is rarely used, and usually a composite of several metal soaps is used. This composite is not a simple addition of properties, but rather utilizes the synergistic effects between components. Composite metal soap stabilizers generally include the stabilizer body (i.e. metal soap), solvents (organic solvents, plasticizers, liquid non-metallic stabilizers, etc.), and functional additives (auxiliary stabilizers, transparency modifiers, light stabilizers, lubricants, etc.). According to their morphology, they can be divided into solid complexes and liquid complexes, and according to their main components, they can be divided into calcium/zinc composite stabilizers, barium/fluorine composite stabilizers, barium/zinc composite stabilizers, etc. Calcium/zinc composite stabilizers play a crucial role in replacing toxic metals due to their non toxicity.
1.5 Rare earth stabilizer
(1) The excellent thermal stability of rare earth stabilizers is superior to traditional lead salt series and barium/zinc, barium/pickaxe/zinc stabilizers. In some applications, rare earth stabilizers can partially or completely replace organotin.
(2) The refractive index of rare earth stabilizers with good transparency is very close to that of PVC resin, which can replace the traditional use of organotin and be used in the field of products with high transparency requirements.
(3) Rare earth elements have excellent weather resistance and can absorb ultraviolet light at 230-320nm. Therefore, rare earth stabilizers have anti-aging properties and are suitable for outdoor products such as PVC corrugated boards and window materials.
(4) Excellent electrical insulation performance. Some rare earth multifunctional stabilizers can be used to replace lead salt stabilizers in cable material formulations, and their electrical insulation performance can be comparable to that of lead salts.
(5) Non toxic, safe, and hygienic rare earth elements are low toxicity elements that pose no toxic hazards to human health during their production, processing, transportation, and storage. Rare earth stabilizers are non-toxic products that can be used in food packaging and pharmaceutical packaging products.
(6) When the processing performance is slightly poor and the amount of rare earth stabilizer used is large, the material's roll separation is not ideal and there is a tendency for pressure separation. Generally, good results can be achieved by using stearic acid or calcium stearate in combination.
In summary, rare earth stabilizers can be used for upper and lower water pipes, injection molded pipe fittings, window frame profiles, door and wall panels, wire conduit, foam products, artificial leather, cable materials, soft and hard transparent products, food packaging materials, etc.
1.6 Auxiliary Stabilizers Auxiliary stabilizers include acetic acid phosphite, epoxidized soybean oil, hindered phenols, etc. They mainly rely on the synergistic effect with metal stabilizers to improve stability, and are generally referred to as co stabilizers. And compounds such as amino acid crotonate vinegar, 2-phenylene derivatives, pulse derivatives, and ketones can not only be used in combination with metal stabilizers to improve their effectiveness, but also have a certain degree of stability. These compounds are usually called pure organic stabilizers. The development of PVC stabilizers has been relatively slow to this day, while the research and development of auxiliary stabilizers have been unprecedentedly active, forming a major trend in the field of PVC stabilizers. Auxiliary stabilizers are rarely used alone and are often used in combination with the main stabilizer to improve initial coloring or long-term stability performance.