Promoters play a very important role in rubber vulcanization. Since the early 20th century, the successful development of organic accelerators has been more than 100 years old. The organic accelerator has rapid development due to its high efficiency, good vulcanization characteristics, and excellent physical and mechanical properties and aging properties of the vulcanizate. At present, there are more than 100 commercialized ones, and there are also 50-60 commonly used. According to the chemical structure, it can be divided into the following 8 categories:
1. Thiazoles [Representatives: MBT (M)]
Acid promoter. The thiazole accelerator is characterized by fast vulcanization speed, flat vulcanization curve, good comprehensive performance of vulcanized rubber, good aging resistance, wide application range, suitable for natural rubber and various synthetic rubbers, and should be combined with acid carbon black. Furnace carbon black should pay attention to the danger of scorching, no pollution, can be used as light-colored rubber products, has bitter taste, and should not be used in the food industry.
2. Subsulphonamides [Representatives: CBS (CZ)]
The same as the thiazoles, the same promoter groups, but one more anti-focus group and an activation group than the thiazoles. The promoting group is acidic and the activating group is alkaline. Therefore, the sulfenamide accelerator is an acid-base self-use accelerator, which combines the advantages of the thiazole accelerator and overcomes the shortcomings of short scorch time. . Its characteristics are as follows: (1) long induction period, fast vulcanization speed, flat vulcanization curve, good comprehensive performance of vulcanized rubber; (2) suitable for combination with furnace carbon black, sufficient safety, favorable for extrusion, calendering and compression molding Adequate fluidity of the material; (3) suitable for high temperature rapid vulcanization and thick product vulcanization;
3. Thiuram [Representative: TMTD (TT)]
It is also one of the more widely used categories in the rubber industry. The commonly used varieties are as follows: TMTM, TMTD, TETD, TRA. As can be seen from the structural formula, the general thiuram contains two active groups and two promoting groups. Therefore, the vulcanization rate is fast and the scorch time is short, which is an ultra-speed grade acid promoter. Pay special attention to the tendency to burn when applying.
4. Dithiocarbamates [Representatives: ZDEC (EZ)]
It can be seen from the structural formula that it is more active than the thiuram. In addition to the same active group and promoting group, it contains a transition metal ion, which makes the rubber unsaturated double bond easier to polarize than the thiuram. Faster, it is an ultra-fast grade acid accelerator. It has a very short induction period for room temperature vulcanization and vulcanization of latex products, as well as vulcanization of low unsaturation rubbers such as butyl rubber and EPDM, which impart excellent aging resistance to vulcanizates.
5. Guanidine class [Representative: DPG (D)]
It is a moderately slow alkaline accelerator and is the most widely used alkaline accelerator. It is widely used in natural rubber and various synthetic rubbers. The most commonly used ones are DPG and DOTG, which are structurally active, have no promoting groups and other functional groups, are slow, and have good operational safety, but have a slower vulcanization rate. It is suitable for vulcanization of thick products such as rubber rollers to improve the tensile stress of the sponge. However, the quinone accelerators tend to crack the product and cause discoloration and contamination. Its greatest advantage is that it can be used in combination with an acid promoter (such as with a thiazole) to activate the vulcanization system and overcome its own shortcomings.
6. Thiourea [Representative: ETU (NA-22)]
Such accelerators have low promotion efficiency and poor scorch resistance. In addition to the use of chloroprene rubber and chlorinated polyethylene for promoting and crosslinking, other diene rubbers are rarely used. ETU and DETU are commonly used accelerators for neoprene.
7. Aldehyde amines [Representatives: H]
It is a condensate of aldehyde and ammonia. It is a weak alkaline accelerator with 4/closed active amine groups. It is a slow accelerator and has no scorch hazard. It is generally used as a second accelerator. Other accelerators are used in combination. In addition, acetaldehyde, also known as AA or AC, is a slow accelerator.
8. Xanthan acid [Representative: ZIX]
It is an acidic ultra-super-speed accelerator with faster vulcanization rate than dithiocarbamate. It is generally not used except for low-temperature glue and latex industry. Its representative product is ZIX, isopropyl. Zinc xanthate.