1. Ordinary sulfur vulcanization system
Conventional vulcanization system (CV for short) refers to the vulcanization system in the usual sulfur dosage range of diene rubber, which can produce soft and highly elastic vulcanizate. The CV systems of various rubbers are shown in the table below.
Different rubbers, due to the difference in unsaturation, composition and structure, the amount of sulfur in the CV system, the type and amount of accelerators are different. Natural rubber is high cis and high unsaturation rubber. It contains a lot of natural softeners and nitrogen bases. It has a certain effect on rubber activation and vulcanization. The vulcanization speed is relatively fast. The dosage of the agent is lower than that of other rubbers. Generally speaking. The unsaturation of synthetic rubber is lower than that of natural rubber, so the corresponding amount of sulfur is also lower, and the residual fatty acid soaps in synthetic rubber can significantly reduce the vulcanization rate. Therefore, it is necessary to appropriately increase the amount of accelerator to increase the vulcanization speed. For rubber with extremely low degree of unsaturation, such as IIR and EPDM, the vulcanization rate is slow, and the amount of sulfur is generally low, generally 1.5-2 parts. And use efficient and fast vulcanization accelerators such as thiuram TMID,
TM and dithiohelium formates are used as main accelerators, and thiophenes are used as secondary accelerators.
The vulcanizate network obtained by the common sulfur vulcanization system mostly contains polysulfide crosslinks and has a high degree of backbone modification: the vulcanizate has good initial fatigue properties. At room temperature, it has excellent dynamic and static properties. Its biggest disadvantage is that it is not resistant to thermal oxidation aging. Vulcanized rubber cannot be used for a long time at higher temperature.
2. Effective vulcanization and semi-vulcanization system
The so-called Efficient Vulcaniztion is referred to as EV, and the Semi-Efficient Vulcaniztion is referred to as Semi-EV (SEV), which actually refers to the degree of cross-linking effectiveness of sulfur in the vulcanization reaction.
Meaning of EV and Semi EV
In order to improve the effectiveness of sulfur in the vulcanization process, the following two methods are generally adopted:
(1) Increase the amount of accelerator and reduce the amount of sulfur. In this high-promoting / low-sulfur coordination system. 0.3~0.5 parts of sulfur.
(2) Use sulfur-free compounding, that is, compounding of sulfur donors. For example, the cooperation of TMTD or DTDM is adopted.
In the vulcanizate network of the above two vulcanization systems, monosulfide crosslinks and disulfide crosslinks are absolutely dominant, that is, more than 90%, and the network has very little main chain modification. This vulcanization system is called EV vulcanization system.
3. High temperature vulcanization system
In order to improve production efficiency, the automation and linkage of the rubber industry has become an inevitable trend, so high-temperature rapid vulcanization is also widely used. For example, injection vulcanization, continuous cable vulcanization and ultra-high frequency vulcanization are all based on high temperature rapid vulcanization. The so-called high temperature vulcanization refers to the vulcanization at a temperature of 180~240℃, which is much higher than the traditional vulcanization temperature of 140~150℃. According to the vulcanization temperature effect, the vulcanization temperature coefficient changes in the range of 1.8~2.5, and the vulcanization time can be shortened by about half for every 10 °C increase in temperature, which greatly improves the production efficiency. However, when the vulcanization temperature increases, the physical and mechanical properties of the vulcanizate, such as tensile strength, elastic modulus, elongation at break, hardness, and resilience will decrease. This is related to the decrease in crosslink density during high temperature vulcanization.
4. Balanced vulcanization system
Unsaturated diene rubber, especially the common sulfur vulcanization system vulcanizate of natural rubber, is not resistant to thermal oxygen aging, which will cause serious vulcanization reversion, resulting in a sharp decline in the dynamic performance of the product and affecting the service life of tires and other products. . Although effective vulcanization systems can overcome some of the shortcomings of ordinary vulcanization systems, they cannot eliminate the reversion of vulcanizates. In 1977, S.woff used Si69[bis(triethoxysilylpropyl)]tetrasulfide to make the crosslinking density of the vulcanizate in a dynamic constant state under the condition of equal molar ratio with sulfamethoxine and accelerator. Reversion is minimized or eliminated. This vulcanization system is called an equilibrium vulcanization system (Equilibrlum Cure, EC for short). The difference between the vulcanizate of EC and CV is that the crosslinking density is constant in the longer vulcanization cycle, so it has excellent heat aging resistance and fatigue resistance.
The compound of the balanced vulcanization system has the advantages of high strength, high tear resistance, thermal oxygen resistance, reversion resistance, dynamic fatigue resistance and low heat generation. It has important applications in product manufacturing and so on.