First, vulcanizing agent
1, sulfur, divided into ordinary sulfur, insoluble sulfur, colloidal sulfur, sublimation sulfur, deacid sulfur. Sulfur is the main vulcanizing agent, and the acid will delay the vulcanization, so the solubility of sulfur-free acid in rubber compounds varies with the rubber type. As the temperature increases, the solubility of sulfur will increase. Some improvements such as; increase in M will increase the phenomenon of sulfur injection. In order to prevent frost, generally sulfur is added at the last low temperature. The amount of sulfur is generally 2 to 2.5 parts. The use of insoluble sulfur can avoid frosting during the early curing of the rubber.
2. Sulfur-containing compounds, such as dimorpholine disulfide, morpholine tetrasulfide, thiuram accelerators, etc.
3. Peroxide curing agent, such as dicumyl peroxide DCP, is stable under normal conditions and is one of the low-toxic peroxides. For natural and synthetic polyethylene resins. Can not vulcanize butyl rubber. For white, transparent, low compression deformation, extremely heat-resistant products. As the amount of peroxide increases, the crosslinking density increases, the tensile stress increases, the compression deformation improves, the heat resistance is excellent, and the tear resistance becomes worse.
Second, the accelerator
Adding accelerators to rubber can promote the reaction between rubber and vulcanizing agent, increase the vulcanization speed, reduce the vulcanization temperature, shorten the vulcanization time, reduce the amount of vulcanizing agent, and improve the physical and mechanical properties and chemical properties of the vulcanizate.
A. Different rubbers use different vulcanization systems and different types of accelerators.
B. Accelerator scorch performance has a decisive influence. The correct accelerator selection helps the compounding, calendering, extrusion and operation safety of the rubber compound. Generally, a certain amount of scorch time is required for molding vulcanization, and no long scorch time is not required for moldless sulfur.
C. The scorch resistance of the accelerator is related to its critical temperature. Above the critical temperature, the accelerator is activated quickly. When multiple accelerators are used in combination, some accelerators will be inhibited, and some accelerators will appear larger at the critical temperature. Of activity.
D. The combination of accelerators should make the rubber material have broad vulcanization flatness.
Rubber is a poor thermal conductor, and the internal heating condition of the rubber material surface is not uniform. The broad vulcanization flatness is to ensure that the sulfur is not vulcanized and that all parts of the product are vulcanized uniformly.
E. The reasonable combination of accelerators can also improve the aging performance of vulcanizates, and has a certain plasticizing effect, which can improve the processing performance of rubber compounds. Disadvantages: Accelerators have poor dispersibility and contamination. Accelerators currently used are generally non-toxic.
Introduction of accelerator
1. Dithiocarbamates, commonly used such as PZ are suitable for butyl rubber requiring low compression deformation, nitrile rubber and EPDM rubber with excellent aging resistance. The critical temperature of vulcanization is about 100 degrees, and the activity is similar to the accelerator TMTD. It is easy to vulcanize early, and has an activating effect on thiazole and sulfenamide. Often used as a secondary accelerator.
2, Xanthanate accelerator SIP is generally used for natural, styrene butadiene latex and low temperature vulcanization. Super accelerator, high activity and higher zinc oxide.
3, thiuram type accelerator, TMTD; super accelerator for natural rubber, synthetic rubber and latex, effective sulfur content 13.3% critical activation point is about 120 degrees. Used as a vulcanizing agent in an effective vulcanization system. The amount of 2-4 parts is not dangerous. The amount of sulfur is very high, and the stronger the activation performance, it is often used as the second accelerator of thiazoles.
4. Thiazole accelerators are widely used and consumed in the rubber industry. It is a semi-super accelerator. Compared with super accelerators, it has better anti-scorch performance, lower activity, and faster vulcanization speed. Slow, the sulfur in the rubber should be appropriately increased, and the temperature should be appropriately increased. Thiazole accelerators have a low degree of vulcanization. Generally used in combination with dithioamino acids or thiurams can improve the vulcanization degree of rubber compounds, tensile strength and tensile stress, high hardness, elasticity, and excellent dynamic products.
Increasing the amount of accelerator and reducing the amount of sulfur can improve the heat resistance of vulcanizates. Commonly used accelerators are such as DM, M. Accelerator M General-purpose accelerator is widely used in various general-purpose rubbers. It has a rapid vulcanization promotion effect and has a wide vulcanization flatness. Vulcanization critical temperature is 125 ° C. It can be used as vulcanization retarder and anti-scorch agent in chloroprene rubber and sulfur-free vulcanization system. M is also a chemical peptizing agent, often used in combination with PZ in latex products. M has no coke-based scorch, and it is easy to vulcanize early with glue. It is often used as the first and second accelerator in daily production.
Accelerant DM vulcanization critical temperature is higher than 130 degrees, the activity is intensified above 140 degrees. Significant after-effects. The vulcanization speed is slow, and thiurams, aldehydes, guanidines and other accelerators should be used together to improve the activity. Its properties and uses are the same as those of M. DM has an anti-coke base, and generally does not undergo early curing.
5, guanidine accelerators, the activity of the accelerator is relatively low, the promotion is relatively slow, the rubber has good safety, which can make the rubber vulcanize for a long time, rarely used as the first accelerator, generally used as an acid accelerator For activators, its activation is particularly strong. The activation of sulfenamides is much smaller.
Adding a small amount will greatly increase the vulcanization degree of the vulcanizate. Commonly used like
1. Indirect method zinc oxide, active agent for natural and synthetic rubber and latex. Reinforcing agents, colorants, and vulcanizing agents that can also be used in neoprene rubber, can enhance the thermal conductivity of the rubber, increase the crosslinking density, and strengthen the uniformity of the rubber. Dosage is generally increased by 3-5 parts only for filling.
2. Activate zinc oxide, use 85% lower zinc oxide to prepare zinc sulfate, and then obtain zinc carbonate through refining. Product obtained by processing and roasting. The performance is basically equivalent to zinc carbonate.
3. Zinc carbonate is also a kind of active zinc oxide. Because of its high transparency, it is often used in transparent products to harden the rubber compound more than zinc oxide.
4. Diethylene glycol, used as an active agent, plasticizer, softener, and rubber can improve the processing performance of the rubber compound, so that the kneaded rubber is not too sticky. To adjust the acidity of the rubber.
The rubber needs certain unsaturated groups. Due to the activity of these groups, sulfur can be used for vulcanization. It is the existence of these unsaturated groups that makes the rubber easily react with oxygen, ozone and other active materials. The chain is broken, crosslinked, and the like. Even after vulcanization, there are still unsaturated groups affected by the above factors. The higher the temperature, the more severe the sulfur over phenomenon. Anti-aging performance
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