The scorch of compound rubber is more common at the beginning of the rainy season.
Thanks to the Mooney viscometer and vulcanizer, it can be measured at any time, whether it is a freshly mixed compound or a remelted compound, so that the compound can be prevented from scorching. In factories that produce compound rubber in large quantities, it is not necessary to carry out a comprehensive measurement, and only a determination method can be used for the rubber material specified to be noted. The following describes how to prevent scorch.
First of all, it is necessary to reduce the amount of vulcanization accelerators, 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. Mostly, two or three accelerators are used in combination. The way. Once the problem occurs, the scorch of the rubber cannot be prevented. Generally speaking, the main accelerator for general rubber is a pill-type or sulfenylamine-type accelerator. The main accelerator DM is a universal accelerator. The accelerator M has high scorch properties. Although the sulfenyl phthalamide accelerators have scorch resistance, they have a slow starting speed for vulcanization, so they should be selected according to the requirements of rubber compounds. . Auxiliary promoter of thiuram. In the hot summer season, the auxiliary accelerator should be used in a reduced amount, while the main accelerator should not be used in a reduced amount.
10-20 parts by mass of recycled rubber is added to general rubber, and the compound made by blending has the function of preventing scorch. In addition, for blending compounds, the design of additive formulas should be considered, and some necessary corrections should be made on the basis of studying scorch properties and physical properties of vulcanizates.
In the compound of white carbon black, diethylene glycol, polyethylene glycol, organic amine co-promoter SL and the like are added. However, it is necessary to pay attention to scorch if adding the above complexing agent in excess. The standard blending amount should be (compared with white carbon black) 60% of diethylene glycol and polyethylene glycol (molecular weight of 400), and the organic amine accelerator SL is 2.5%.
In terms of compounding, although many discussions have been made as described above, if scorch cannot be prevented, a scorch retarder (vulcanization retarder) may be added. The vulcanization retarder is an organic synthetic compound such as anhydrous phthalic acid and benzoic acid-based organic acids, nitroso compounds, and phthalphthalamide. Nitrosodiphenylamine is contaminating, so it cannot be used for light-colored rubber products.
The scorch retarder slows down the vulcanization speed while delaying the vulcanization, because it will reduce the degree of crosslinking, so do not use it in large quantities. According to the author's experience, the amount 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 high accelerant and high anti-scorching agent.
The following is an introduction to the problems that should be paid attention to in preventing scorch in the operation process. For each batch of compound, based on the original data, set the range of scorch time, and continuously adjust and solve within this range. For example, set Mooney scorch time, 125 ° C, MS, 15-25min.
The compound can be cooled to room temperature by water cooling, air cooling, or both. Even if it is rolled and rolled, if there is a danger of scorching, it can be winded while being air-cooled, or cut to a certain length before being air-cooled. It can also be stored in air-conditioned rooms and refrigerators as required.
For most rubbers that need to be re-melted, first put the rubbers that need to be re-melted into a hot-melt mixer for hot-refining. After confirming that the rubber does not scorch, add a new compounded rubber for mixing. The process is reversed, resulting in scorching of the entire compound.
Analysis of the Causes of Glue Burning
Everyone knows that peroxide vulcanization is not easy to scorch, and the scorch time of peroxide is generally shorter than that of sulfur vulcanization, but why is it not easy to produce scorch? The fundamental reason is that the process of peroxide vulcanization is a half-life process, which must be above the activation or decomposition point to produce cross-linking. Of course, for example, some peroxides with carboxyl groups also vulcanize quickly because of its decomposition. The point is very low, although the decomposition activation point is generally above 110 degrees, in other words, the temperature will not be scorched under 110 degrees during operation, even if it is not easy to scorch at high temperatures for a short time Burned, as long as the operating temperature of the rubber material is not too high and the heat is released as soon as the film is released, some such as DCP, double 2, 5 are more difficult to scorch, and the external temperature during parking will not exceed 45 degrees. Right! Therefore, it is generally not affected by the length of the parking time. I think that most of our engineering technicians can recognize this.
But sulfur vulcanization is not the same thing. Sometimes the formula is designed to be scorched for a long time, but it will still be dead when it is parked for a long time. Sometimes the formula is not scorched for a long time, but it may not be dead for a long time. Winter Not easy to die, summer is the most easy to die, why?
You can check the data. The critical activation temperature of various accelerators is generally above 110 degrees. If you only look at the critical activation resolution of the accelerators, it will not scorch when parked at a temperature below 40 degrees. But in fact, it is not so much, because the rubber coke has undergone a chemical reaction during the beating process. At a higher operating temperature, the vulcanizing agent, the active agent, and the accelerator have a small amount of mutual activation. A small amount of vulcanized precursor complex was formed, which is a normal-temperature vulcanizing agent that can vulcanize even above 20 degrees. Some of the methods described by KRMQ are actually preventing or reducing the amount of complex formation. In fact, choosing the type of accelerator is to choose an accelerator with a higher critical activation temperature, and to adjust the amount of surfactant is to adjust the activation energy of the active agent. The purpose of using the water machine and ice water machine in the process is to reduce the formation of network. Operation time of the compound.
I. Scorch cause and processing method of compound rubber
1. Improper cooperation
Such as vulcanizing agent, too much accelerator;
2. Improper rubber mixing operation
If the temperature of the mixer is too high, the cooling device is not good, or sulfur is added too early, or the vulcanizing agent and accelerator caused by uneven dispersion are locally concentrated, or the roll is rolled up prematurely without heat dissipation, or the roll is too large. Or it is not sufficiently cooled after the film is placed;
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 circulating, or it has been stored for too long after being hot-finished. copyright Rubber Technology Network
The general amount of anti-scorching agent should not exceed 0.4 parts, added before the vulcanizing agent and accelerator. This article comes from Rubber Technology Network
Third, deal with scorch
It is thin on the open mill, and the roller temperature is low, and the rubber loading capacity is small. It cannot be wrapped, rolled, rolled, and parked for 24 hours, and then mixed into the good material for use. Severe scorch, stearic acid and oil softener are added during thin pass to destroy its crosslinked structure.
Spring green leaf dividing line
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