Antiscorching Agent

Primary accelerators are used to promote the initial stages of vulcanization. They have a relatively fast reaction rate and are typically used in combination with secondary accelerators to achieve the desired level of cross-linking. Examples of primary accelerators include thiourea, diethylthiourea (DETU), and ethylene thiourea (ETU).

Secondary accelerators are used to enhance the action of primary accelerators and to fine-tune the vulcanization process. They have a slower reaction rate than primary accelerators and are typically used in combination with them to achieve the desired level of cross-linking. Examples of secondary accelerators include sulfenamides, thiazoles, and guanylureas.

Retarders are used to slow down the vulcanization process and prevent premature scorching. They are typically used in applications where the vulcanization process needs to be carefully controlled, such as in the production of thin or complex rubber parts. Examples of retarders include zinc oxide and stearic acid.

Activators are used to enhance the effectiveness of accelerators and to improve the overall performance of the vulcanized rubber. They can help to reduce the amount of accelerator needed and improve the efficiency of the vulcanization process. Examples of activators include metal oxide activators, such as zinc oxide and magnesium oxide, and sulfur-based activators.

Specialty accelerators are designed for specific applications and can offer unique properties that are not available with other types of accelerators. Examples of specialty accelerators include ultra-accelerators, which are designed to achieve very high levels of cross-linking, and non-sulfur accelerators, which do not contain sulfur and are used in applications where sulfur-free vulcanization is required.

Sulfur and its derivatives have long been used as antiscorching agents due to their effectiveness in preventing premature vulcanization. They are typically used in combination with other accelerators and have the advantage of being relatively inexpensive and compatible with a wide range of rubber types. However, sulfur-based agents can contribute to the formation of volatile byproducts during processing, which can pose environmental and health risks.

Thiourea and its derivatives, such as thiurams and tetrasulfamides, are known for their excellent antiscorching properties, particularly in sulfur-vulcanized systems. They provide good control over the curing process and can enhance the final physical properties of the vulcanized rubber. However, thiourea-based agents can have limited compatibility with certain additives and may require careful handling due to their potential for skin irritation.

Phosphorous-based compounds, including phosphites and phosphonites, offer effective antiscorching performance in a variety of rubber systems. They are known for their broad compatibility and ability to prevent heat buildup during compounding. Phosphorous-based agents generally have lower toxicity compared to sulfur-based agents and can provide additional benefits such as antioxidation and flame retardance. However, they may be more expensive than traditional sulfur-based alternatives.

Amino-based compounds, such as amines and diamines, are effective in preventing premature vulcanization, especially in high-temperature processing environments. They offer good thermal stability and can improve the processability of rubber compounds. Amino-based agents may require specific curing conditions and may not be compatible with all rubber formulations.

Organotin compounds, such as dialkyltin salts and mercapto-organotins, are known for their high efficiency in preventing scorch in a variety of rubber systems. They provide excellent control over the curing process and can enhance the mechanical properties of vulcanized rubber. However, organotin-based agents can be more expensive and may have environmental and health concerns associated with their use.