14 items to consider when using accelerators

The vulcanization accelerator is simply referred to as a promoter. The addition of a small amount of accelerator in the rubber compound can greatly promote the reaction between the rubber and the vulcanizing agent (crosslinking agent), and can accelerate the vulcanization reaction rate, shorten the vulcanization time, lower the vulcanization reaction temperature, and reduce the vulcanization agent dosage capacity. A compounding agent that enhances or improves the physical and mechanical properties of vulcanizates, and is called a vulcanization accelerator.

The four major functions of the accelerator: First, shorten the vulcanization time, reduce the amount of sulfur, reduce the vulcanization temperature, and secondly improve the scorch performance of the rubber; third, improve the flatness of the rubber vulcanization and improve the performance of the rubber product; The appearance quality of the product.

In the process of selecting and using the accelerator, according to the experience of some friends, we have compiled 14 items to consider when selecting the accelerator. Now we share with you:

1. Rubber type

Different rubbers have different performance characteristics, different vulcanization systems, and different vulcanization systems should consider the matching between different types of accelerators.

2. Promoter quality

Quality is one of the key considerations for formulators when using accelerators. In the current market, there are still many phenomena of counterfeiting and sub-priming, so it must be cautious when selecting, otherwise it will directly affect the performance of rubber vulcanization or anti-aging.

3. Effect on the properties of rubber compounds and vulcanizates

The accelerator participates in the formation of the rubber space network during vulcanization, and has a direct relationship with the structure of the vulcanized rubber, that is, the physical and mechanical properties and the aging properties. The accelerator has a softening effect on the rubber compound, which increases the plasticity of the rubber compound and changes the processing property of the rubber compound.

4. Charring performance

The accelerator has a decisive influence on the scorch time of the compound (i.e., the time until the thermal vulcanization of the compound begins). Therefore, the accelerator selected should have a considerable scorch time, which is the operation safety of the rubber compound during mixing, calendering, extrusion or injection, the fluidity of the rubber in the initial vulcanization and the attachment to the fabric. Efforts have a major impact. In particular, in recent years, in order to improve production efficiency, processing conditions are becoming more and more strict, and the requirements for anti-scorch performance of rubber compounds are also increasing. However, the excessive scorch time will lead to an increase in the total vulcanization time, which is not only unfavorable for the improvement of labor efficiency, but also has an adverse effect on the deformation of the moldless vulcanized product during the vulcanization process.

5. Vulcanization flatness

The accelerator should have a broad vulcanization flatness curve during the optimum vulcanization. In other words, the properties of the vulcanizate should not show significant changes during this time, which is especially important for thick rubber products and solid products. Rubber is a poor conductor of heat. The surface and internal heat of the vulcanizate are inconsistent. The broad vulcanization flatness is a guarantee to avoid excessive sulfur and uniform vulcanization of various parts of the product.

6. Dispersibility

Accelerators with poor dispersibility in the rubber compound not only require a long mixing time, but also increase the power consumption of the equipment, and often cause uneven vulcanization of the product due to uneven mixing. For some hard-to-disperse accelerators, it can be used as a masterbatch.

7. Spraying

The blooming of the rubber compound will cause poor bonding to the subsequent process and reduce the appearance quality of the final product, so it should be avoided. Promoter spray and accelerator are related to the compatibility of rubber. Generally, non-polar EPDM rubber is easy to spray, while polar nitrile rubber and neoprene are difficult to spray. Among the accelerators, in particular, the accelerators TMTD and ZDMC are inferior in compatibility with rubber, and there is a possibility of blooming. The compatibility of the large alkyl promoter ZDEC and ZDBC with rubber is better than that of TMTD and ZDMC, and the blooming phenomenon is reduced.

8. Pollution and coloration

Some accelerators color the rubber products because they have different colors, and some of them are chemically or sun-exposed to make the products discolored. These accelerators cannot use white or brilliant products. Some accelerators have obvious odor and bitterness, and some accelerators can also contaminate other substances by contact migration.

9. Environmental protection

Most of the accelerators currently used are not toxic or very toxic, but they are still toxic. These accelerators should not be used in medical products and food-contact rubber products. Use toxic or toxic accelerators to protect them during handling.

The development trend of accelerators tends to be environmentally friendly and functional. In recent years, the international promotion of harmful nitrosamine promoters in the rubber processing process has been paid more and more attention. The environmentally-friendly new accelerators have been developed in developed countries such as Europe and the United States, and China has gradually paid more attention to environmental protection promotion in recent years. The development and production of agents and predispersions, among which environmentally friendly accelerators are represented by: ZBEC, TBzTD, TIBTD, ZBPD, ZDTP, NS, TBSI, MTT, etc.

10. Water solubility

For the production of latex products, it is convenient to use water-soluble accelerators, among which the representative products are: ZDEC, ZDBC, ZMBT, TMTD, MBT, etc.

11. Promoter combination

Each kind of accelerator has its own characteristics. In order to satisfy the good process performance of the rubber during the operation and the excellent physical and chemical properties of the vulcanized rubber, several kinds can be used together and complement each other.

Rubber properties are distinguished by the nature of the accelerator – the accelerator is divided into a primary accelerator and a secondary accelerator. The main accelerator, also known as the first accelerator, generally uses an acid promoter (referred to as type A) or a neutral accelerator (called type N). The most frequent thiazoles and thiurams, the scorch time sequence of thiazoles is: M < DM < MZ < sulfenamides. The thiuram primary accelerator is only used for film products or model products with extremely short curing time. Dithiocarbamate main accelerator, commonly used in latex products, as well as low-unsaturated rubber such as ethylene propylene rubber and butyl rubber.

The secondary accelerator, also known as the second accelerator or the third accelerator, generally employs a basic accelerator (referred to as type B), and uses a hydrazine (such as a promoter DPG, DOTG, etc.). The accelerator H is also used, and the scorch time can be prolonged, and the amount of the secondary accelerator varies depending on the type of the main accelerator. The sulfenamide accelerator itself is a combination accelerator, and at the vulcanization temperature, the promoter M and the amine compound are decomposed to form an AB combined system. Therefore, a secondary accelerator may generally not be used. Of course, depending on the process requirements, a small amount of accelerator DPG or thiuram accelerator may be used in combination.

12. Cooperate

When using the accelerator, factors such as interaction with other rubber additives and rubber raw materials should be considered.

13. Economics

The selection of accelerators should take into account the ease of procurement of the product in the market. Unusual accelerators or difficult to purchase should pay attention to the impact on production when used in large quantities.

The accelerators commonly found in the market must also take into account the purchase price problem. The use cost of the accelerator is one of the key issues for the formulator.

14. Confidentiality

Common rubber products find a recipe easy, but for special or technical rubber products, formula design requires a lot of energy and financial resources. Designing a rubber formula and keeping it secret is very important for the development of the company. The confidentiality of the formula must involve the confidentiality of the accelerator product, which is one of the important issues considered by the formulator and even the person in charge of the company.