（1） Rubber type
Different rubbers have different performance characteristics. When different vulcanization systems are used and different types of accelerators are selected for different vulcanization systems, their matching should be considered.
（2） Accelerator quality
The quality of accelerator is one of the key considerations for formulation engineers. In the current market, there are still many fake and inferior products, so you must be careful when selecting them, otherwise it will directly affect the vulcanization or anti-aging properties of rubber.
（3） Effect on properties of compound and vulcanizate
Promoters participate in the formation of the rubber space network structure during vulcanization, which is directly related to the structure of the vulcanizate, namely, its physical and mechanical properties and aging properties. The accelerator can soften the compound, increase the plasticity of the compound and change the processability of the compound.
（4） Scorching property
The accelerator has a decisive influence on the scorch time of the rubber compound (that is, the duration before the start of hot vulcanization of the rubber compound). Therefore, the accelerator selected should enable the rubber compound to have a considerable scorching time, which plays an important role in the operation safety of the rubber compound in the process of mixing, calendering, extrusion or injection, the fluidity of the rubber compound in the early curing stage, and the adhesion to the fabric. Especially in recent years, in order to improve the production efficiency, the processing conditions are more and more strict, and the requirements for the scorch resistance of the rubber compound are also higher and higher. However, too long scorching time will lead to an increase in the total curing time, which is not conducive to the improvement of labor efficiency, but also will have a negative impact on the deformation of molded vulcanized products in the curing process.
The scorch resistance of the accelerator is directly related to the critical curing temperature (i.e. the temperature at which the accelerator begins to act on the curing process), at which the activity of the accelerator is not significant; The accelerator is activated above this temperature to give full play to its vulcanization effect. Unfortunately, most accelerators have not yet measured this temperature. When a variety of promoters are used together, the activity of some promoters is inhibited, and some promoters will have greater activity even below their critical temperature.
（5） Vulcanization flatness
The accelerator shall enable the rubber compound to have a broad vulcanization flat curve during the most suitable vulcanization period. In other words, the performance of the vulcanizate shall not show obvious changes during this period, which is particularly important for thick rubber products and solid products. Rubber is a poor conductor of heat. The surface and internal heating conditions of vulcanized rubber are not consistent. The broad vulcanization flatness is the guarantee to avoid over sulfur and ensure the uniform vulcanization of all parts of the product.
（6） Dispersibility
Accelerators with poor dispersion performance in rubber compound not only need longer mixing time, increase equipment power consumption, but also often cause uneven vulcanization of products due to uneven mixing. Generally, the low melting point accelerator is easy to melt and diffuse in the rubber compound, so the dispersion is good; For high melting point accelerator, it is better to use powder products with small particle size; For some accelerators that are difficult to disperse, they can be used as master rubber.
（7） Frost spraying
Frost spraying of the rubber mixture will cause poor bonding in the next process and reduce the appearance quality of the final product, so it should be avoided. The accelerator spray is related to the compatibility of accelerator with rubber. Generally, nonpolar EPDM is easy to spray, while polar nitrile rubber and chloroprene rubber are difficult to spray. Among the accelerants, especially the accelerants TMTD and ZDMC have poor compatibility with rubber, which may cause frost spray. The large alkyl accelerants EZ and BZ have better compatibility with rubber than TMTD and PZ, and the frost phenomenon is reduced.
（8） Contamination and colourability
Some accelerators cause the rubber products to be colored due to their different colors, and some products to be discolored due to chemical action or sunlight exposure. These accelerators cannot be used for white or bright colored products. Some accelerants have obvious odor and bitter taste. In addition, some accelerants can also pollute other substances through contact and migration.
（9） Environmental protection
At present, most of the accelerants used are non-toxic or extremely toxic, but there are still some individuals with toxicity. These accelerators shall not be used in medical and health products and rubber products in contact with food. The use of toxic or highly toxic accelerators shall be protected during operation.
The development trend of accelerator tends to be environment-friendly and functional. In recent years, more and more attention has been paid to the harmful nitrosamine accelerators in rubber processing. Most of the new environment-friendly accelerators have been developed in developed countries such as Europe and the United States. In recent years, China has gradually attached importance to the research, development and production of environment-friendly accelerators and pre dispersions. The representatives of environment-friendly accelerators include ZBEC, TBzTD, TIBTD, ZBPD, ZDTP, NS, TBSI, MTT, etc.
（10） Water solubility
For the production of latex products, it is convenient to select water-soluble accelerants, including EZ, BZ, MZ, TMTD, M, etc.
（11） Combination of accelerants
Each accelerator has its own characteristics. In order to meet the requirements that the rubber compound has good processing performance during operation and make the vulcanizate have excellent physical and chemical properties, several accelerators can be used together to learn from each other. The properties of rubber are different because of the characteristics of accelerants, which include main accelerants and auxiliary accelerants. The main accelerator, also known as the first accelerator, generally uses acidic accelerator (type A) or neutral accelerator (type N). Thiazole and thiuram are the most common, and the burning time sequence of thiazole is M<DM<MZ<subsulfonamide. The main accelerator of thiuram type is only used for film products or model products with very short curing time. Dithiocarbamate is the main accelerator, which is commonly used in latex products, ethylene propylene rubber, butyl rubber and other low unsaturated rubber. The auxiliary accelerator, also known as the second accelerator or the third accelerator, generally uses alkaline accelerator (called Type B), and most of them use guanidine (such as DPG, DOTG, etc.). The scorching time can be prolonged by using accelerator H. The amount of auxiliary accelerator varies with the type of main accelerator. The subsulfonamide accelerator itself is a mixed accelerator. At the curing temperature, accelerator M and amine compounds will be decomposed to form the AB mixed system. Therefore, it is generally not necessary to select the auxiliary accelerator. Of course, according to the needs of the process, a small amount of accelerator DPG or thiuram type accelerator can also be used.
（12） Synergism
When selecting accelerant, factors such as interaction with other rubber additives and rubber raw materials should also be considered.
（13） Economy
When selecting accelerants, the difficulty of purchasing the product in the market shall be taken into account. For uncommon accelerants or those difficult to purchase, the impact on production caused by mass use shall be noted.
The purchase price of accelerants often seen in the market should also be considered, and the use cost of accelerants is one of the key issues for formulation engineers.
（14） Confidentiality
It is easy to find a formula for common rubber products, but for special or technical rubber products, formula design consumes a lot of energy and financial resources. Designing a rubber formula and keeping it secret is crucial for the development of enterprises. The formula confidentiality must involve the confidentiality of accelerator products, which is also one of the important issues considered by the formula engineer and even the person in charge of the company.
Disclaimer: The image materials and articles of this platform are from the network, so the copyright belongs to the original author. If it infringes your copyright and interests, please contact us, and we apologize and delete them quickly. Article source: Rubber additives trading website
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