Causes of scorching of rubber compound and methods for preventing scorching of rubber compound

1. The cause and treatment of scorching of rubber compound

1. Improper cooperation

Such as vulcanizing agent, too much accelerator;

2. Improper rubber mixing operation

If the temperature of the rubber mixer is too high, the cooling device is not good, or sulfur is added prematurely, or the vulcanizing agent and accelerator are locally concentrated due to uneven dispersion, or the roll is prematurely rolled without heat, or the roll is too large. Or it is not sufficiently cooled after filming;

3. Improper parking

Including the rubber compound has been parked for too long, the temperature of the parking place is too high, or the air does not circulate, or it is stacked for a long time after hot smelting.

2. Prevent Scorch

The general dosage of scorch inhibitor should not exceed 0.4 parts. Add it before the vulcanizing agent and accelerator.

Method for preventing scorching of mixing rubber in internal mixer

The scorch of the mixing rubber of the internal mixer is more common at the beginning of the rainy season. Thanks to the Mooney viscometer and vulcanization instrument, whether it is freshly mixed rubber or regrind compound can be measured at any time, so as to prevent the compound from scorching. In an internal mixer factory that produces a large amount of compounded rubber, there is no need to conduct a comprehensive measurement. Only one method of measurement can be used for the rubber compound that requires attention.

The following describes the methods to prevent scorch:

First of all, it is necessary to reduce the amount of vulcanization accelerator, but this will cause the physical properties of rubber products to decline. It is very important to understand this. Vulcanization accelerators are rarely used alone, and most of them use two or three accelerators in combination. The way. Once there is a problem with the compounding, the scorching of the rubber compound cannot be prevented. Generally speaking, the main accelerator used for general rubber is an exposed pill or sulfophthalamide accelerator. The main accelerator DM is a universal accelerator; the accelerator M has a high scorch resistance. Although the sulfophthalamide accelerators have scorch resistance, because the vulcanization start speed is slow, it should be selected according to the requirements of the rubber compound. . Muscles, thiurams are auxiliary accelerators. In the high temperature season of midsummer, the auxiliary accelerator should be used in a reduced amount, while the main accelerator should not reduce its blending amount as much as possible.

Add 10-20 parts by mass of reclaimed rubber to general-purpose rubber, and the rubber compound made by blending can prevent scorch. In addition, for the blended compound, it is necessary to consider the design of additive formula, and make some necessary corrections based on the study of scorch and physical properties of vulcanized rubber. In the compounding of white carbon black compound, it is necessary to add diethylene glycol, polyethylene glycol, organic amine promoter SL and so on. However, excessive addition of the above compounding agent may cause scorch, so care must be taken. The standard blending amount should be (compared with white carbon black) diethylene glycol and polyethylene glycol (molecular weight 400) 60%, organic amine accelerator SL 2.5%.

Although a lot of research has been done on the blending as mentioned above, if scorch cannot be prevented, a scorch inhibitor (vulcanization retardant) may be added. Vulcanization retarders are organic synthetic compounds such as anhydrous phthalic acid and benzoic acid organic acids, nitroso compounds and phthalimide. Because nitrosodiphenylamine is polluting, it cannot be used for light-colored rubber products.

Anti-scorching agent slows down the vulcanization speed at the same time, because it will reduce the degree of cross-linking, so do not use a large amount. According to experience, the dosage should not exceed 0.4%. If it must exceed 0.4%, the amount of vulcanization accelerator should be reduced first. It is not advisable to use a combination of high accelerator and anti-scorching agent.

Precautions for preventing scorch will be introduced. For each batch of rubber compound, based on the original data, set the range of scorch time, and continuously adjust and solve within this range. For example, set to Mooney scorch time, 125 ℃

Mixed rubber can be cooled to room temperature by water cooling, air cooling, or both. Even if the rubber material is rolled and rolled, if there is a risk of scorching, it can be wind-cooled while winding, or cut according to a certain length and then air-cooled. It can also be stored in air-conditioned rooms and cold storages as needed.

For most rubber compounds that need to be re-mixed, first put the compound that needs to be re-mixed into a hot mixer and heat it. After confirming that the compound has not been scorched, add a new compound to mix it. If the procedure is reversed, it will result in scorching of all the mixer rubber.

Third, deal with scorch

On the mill, the roller is low, and the temperature of the roller is low, the glue loading capacity should be small, the roller can not be wrapped, packaged, rolled, parked for 24 hours, and then mixed into the good material, the dosage is 15-20%. If the scorch is serious, add stearic acid and oil softener during the thin pass to destroy its cross-linked structure.