Causes and treatment of scorch of rubber compound
1. Improper cooperation

Such as vulcanizing agent, the amount of accelerator is too much;

2. Improper rubber mixing operation

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

3. Improper Parking

Including the rubber has been parked for too long, the temperature of the parking place is too high, or the air is not ventilated, or it has been stacked for a long time after hot-melting.


2. Prevent scorch


The general amount of anti-scorch agent should not exceed 0.4 parts, and it should be added before vulcanizing agent and accelerator.

Methods to prevent the scorch of the rubber compound in the mixer

The scorch of the rubber compound of the internal mixer is more common at the beginning of the rainy season. Thanks to the Mooney viscometer and vulcanometer, it can be measured at any time whether it is freshly mixed or re-mixed, which can prevent the scorching of the compound. In an internal mixer plant where high-volume compounds are produced, it is not necessary to carry out a comprehensive measurement, and only one measurement method can be used for the compounds that require attention.


Here's how to prevent scorch

First of all, it is necessary to reduce the compounding amount of the vulcanization accelerator, but this will lead to the decline of the physical properties of the rubber products. It is very important to understand this. The vulcanization accelerator is rarely used alone, and most of the two or three accelerators are used in combination. The way. Once there is a problem with the combination, the scorch of the rubber compound cannot be prevented. Generally speaking, the main accelerator for general rubber is exposed pill type or sulfenamide type accelerator. The main accelerator DM is a universal accelerator; the accelerator M has high scorch property, and the sulfenamide accelerator has scorch resistance, but due to the slow starting speed of vulcanization, it should be selected according to the requirements of the rubber compound. . Muscle and thiuram are auxiliary accelerators. In the summer and high temperature season, the auxiliary accelerator should be used in a reduced amount, while the main accelerator should not reduce its compounding amount as much as possible.


Add 10-20 parts by mass of reclaimed rubber into general-purpose rubber, and the rubber compound made after blending has the effect of preventing scorch. In addition, for the blended compound, it is necessary to consider the design of the additive formula, and make some necessary corrections on the basis of studying the scorch property and the physical properties of the vulcanizate. Diethylene glycol, polyethylene glycol, organic amine co-accelerator SL, etc. should be added to the silica compound. However, if the above compounding agent is added in excess, it will also cause scorch, so care must be taken. The standard compounding amount should be (compared to silica) diethylene glycol and polyethylene glycol (molecular weight 400) 60%, and the organic amine accelerator SL is 2.5%.


In terms of blending, although many discussions have been made as described above, if scorch cannot be prevented, a scorch retarder (vulcanization retarder) can be added. Vulcanization retarders are organic synthetic compounds such as anhydrous phthalic acid and benzoic acid-based organic acids, nitroso compounds, and phthalamide. Because nitrosodiphenylamine is polluting, it cannot be used for light-colored rubber products.


While retarding vulcanization, the scorch retarder also slows down the vulcanization speed, because it will reduce the degree of cross-linking, so do not use it in large quantities. As a rule of thumb, 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 suitable to use the combination method of high accelerator and high anti-scorch agent.


Introduce the problems that should be paid attention to to prevent scorch. For each batch of compounded rubber, on the basis of 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°C


For the mixed rubber, the film can be cooled to room temperature by water cooling, air cooling or both. Even for calendered and coiled rubber, if there is a danger of scorching, it can be coiled while air-cooled, or cut to a certain length and then air-cooled. It can also be stored in air-conditioned rooms and refrigerators as needed.


For most of the rubber materials that need to be re-melted, first put the rubber material to be re-melted into the hot mixer, and after confirming that the rubber material is not scorched, add a new rubber compound for mixing. The reverse of the procedure will result in scorching of the entire compound in the mixer.


Treatment of scorch

On the open mill, it is thin and smooth, and the roll temperature is low, and the glue loading capacity is small. It cannot be wrapped, packaged, rolled, parked for 24 hours, and then mixed with good materials for use, and the mixing amount is 15-20%. When the scorch is serious, add stearic acid and oil softener to destroy its cross-linked structure.