Other characteristics of high temperature vulcanization

High-temperature vulcanization system requires fast vulcanization speed, low tendency to burn, and no frosting. Therefore, it is best to use heat-resistant rubber and constant sulfur and high accelerator. In addition, there are high requirements for anti-focus and anti-aging systems.

In order to increase the vulcanization rate, a sufficient amount of stearic acid must be used to increase the solubility of the zinc salt and improve the activation function of the system.

In order to prevent the thermal aging of high temperature vulcanization and ensure the flatness of vulcanization, the anti-aging agent is absolutely necessary in the high-temperature vulcanization system, but it is not necessary. For example, adding 1 part of the antioxidant D to TMTD/Zn0 can effectively maintain the stability of the crosslinking density and the flatness of the vulcanization. To prevent the occurrence of scorch, the scorch retarder PVI can be added to the system.

Principle of high temperature vulcanization system

(1) Selection of heat-resistant rubber type In order to reduce or eliminate the vulcanization reversion phenomenon of vulcanized rubber, a rubber with a low double bond content should be selected. Various rubbers have different thermal stability and different extreme vulcanization temperatures. Suitable for high temperature and rapid vulcanization are EPDM, IIR, NBR, SBR and so on.

(2) Adopting an effective or semi-effective vulcanization system Because CV vulcanization system has a high content of polysulfide cross-linking bonds, it is easy to produce vulcanization and reversion at high temperatures, so CV is not suitable for high-temperature rapid vulcanization systems. The high-temperature fast vulcanization system uses an effective EV with a high content of monosulfur and disulfide bonds and a semi-effective SEV vulcanization system, and the vulcanized rubber has good heat-resistant oxygen aging performance.

Generally, a high-promoting low-sulfur and sulfur-supported vulcanization compound is used, and the latter is preferably DTDM, and has a wide range of scorch time and vulcanization characteristics, and is easy to meet rubber manufacturing requirements. TMTD is limited in application due to short scorch time and severe frosting. Although EV and SEV have better effects on high-temperature vulcanization than CV, they are still not ideal enough to completely solve the disadvantages of vulcanization reversion and poor flexural resistance caused by high-temperature vulcanization. A better method should be found.

(3) Special compounding of vulcanization In order to maintain the crosslink density of the vulcanizate at a high temperature, a method of increasing the amount of sulfur, increasing the amount of the accelerator, or both may be employed. However, increasing the amount of sulfur will reduce the vulcanization efficiency and increase the content of polysulfide crosslinks; while increasing the sulfur and accelerator, the vulcanization efficiency will remain unchanged; while maintaining the amount of sulfur and increasing the amount of accelerator, it can be improved. Vulcanization efficiency, this method is better and has been widely promoted and applied in the tire industry.

The amount of S is constant, and the effect of increasing the amount of accelerator on the crosslink density and strength

Under the condition of keeping the amount of sulfur constant and increasing the amount of accelerator, the crosslinking density and the tensile strength retention rate. If DTDM is used instead of sulfur, the effect is better, and under high-temperature vulcanization conditions, excellent performance like CV vulcanizate can be obtained.

Synthetic rubber vulcanization system is less sensitive to temperature than NR, so the combination of NR and synthetic rubber is particularly important, and the system after use not only maintains the stability of crosslink density at high temperature vulcanization, but also maintains the best vulcanizate. Physical properties are an effective method for rubber products to be vulcanized at a temperature, shortening the curing time, and improving production efficiency.

High temperature rapid vulcanization system

With the automation and linkage of rubber manufacturing, high-temperature rapid vulcanization systems are widely used, such as injection vulcanization and cable vulcanization. The so-called high-temperature vulcanization refers to vulcanization performed at 180 to 240 ° C. Generally, for every 10 ° C increase in vulcanization temperature, the vulcanization time can be shortened by about half, and the production efficiency is greatly improved. However, an increase in the vulcanization temperature causes a decrease in the physical and mechanical properties of the vulcanizate, which is related to a decrease in the crosslink density at high temperature vulcanization. When the temperature is higher than 160 °C, the crosslink density decreases most obviously. Therefore, the higher the vulcanization temperature, the better. The high vulcanization temperature should be considered comprehensively.

Semi-effective vulcanization system

In order to improve the anti-thermal aging and dynamic fatigue properties of vulcanizates in rubber manufacture, a vulcanization system with a promoter and sulfur in between CV and EV was developed. The obtained vulcanizate has both proper amount of polysulfide. The bond has an appropriate amount of single and disulfide cross-linking bonds, so that it has both good dynamic performance and moderate heat-resistant oxygen aging properties. Such a vulcanization system is called a semi-effective vulcanization system (SEV). For static and dynamic products with certain temperature requirements, there are two ways to cooperate:

1 accelerator dosage / sulfur dosage ≈ 1.0 / 1.0 = 1 (or slightly larger than 1);

2 Sulfur and sulfur carrier are used together, and the amount of accelerator is the same as that in SEV.

Effective vulcanization system

Since the number of the vulcanizate network obtained by the ordinary sulfur vulcanization system is a polysulfide crosslink, the crosslinking efficiency of sulfur in the vulcanization reaction is low. Experiments have shown that changing the proportion of accelerator can effectively improve the crosslinking efficiency of sulfur in the vulcanization reaction and improve the structure and product properties of vulcanizate in rubber manufacture.

When the ratio of accelerator to vulcanizing agent rises, the network structure of vulcanizate changes, the content of monosulfide crosslinks increases, and the degree of effective cross-linking of sulfur increases, but the fatigue life first rises and then decreases to increase sulfur during vulcanization. Crosslinking efficiency, there are two commonly used methods of coordination.

(1) High-promoting, low-sulfur blending to increase the amount of accelerator (3~5 parts) and reduce the amount of sulfur (0.3~0.5 parts).

(2) Sulfur-free coordination is the combination of sulfur carrier, such as TMTD or DTDM (1.5~2 parts).

In the vulcanized rubber network obtained by the above two combinations, the content of single bond and double bond accounts for more than 90%, and the network has little main chain modification. The utilization rate of sulfur in the vulcanization system is high, and it is called effective vulcanization system (EV). The vulcanizate of O EV vulcanization system has high resistance to thermal aging, but the initial dynamic fatigue performance is poor. Commonly used in high temperature static products such as sealing products, high temperature rapid vulcanization system.