In the hot summer, is your compound "dead glue", "cooked glue" or "scorched?


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Release time:

Aug 11,2021

rubber overvulcanization: refers to the state of the rubber compound at high temperature for a long time.

  Dead glue:Due to improper operation, the early vulcanization of the compound with vulcanizing agent in the process of processing or parking is essentially: local crosslinking of the compound. The glue produced in this way is called dead glue. This phenomenon is called scorching in professional terms, and is generally called dead glue in factories. In fact, it is the glue that scorched.

Remarks: For the compound formula in winter and summer, try to modify the dosage of accelerator, so that the scorch period of the compound can be extended appropriately, and the ML reduction can meet the production and processing process.

In the actual processing process, in order to avoid the risk of scorch and make the rubber material have better in-mold fluidity, the method of adding anti-scorch agent is often used to solve the problem.

Rubber in the process of processing or vulcanization before the occurrence of early vulcanization phenomenon, also known as self-sulfur (bin cure).

The main reasons for the scorch of the rubber compound are improper formula design, such as inappropriate accelerator varieties and excessive dosage. The temperature of mixing, pressing and pressing delay is too high; The parking temperature of the rubber material is too high and the time is too long.

In addition to improving the formulation and process for the above reasons, the scorch prevention can also be achieved by using an anti-scorch agent to extend the scorch time of the compound.

Cause:

(1) improper formulation design, vulcanization system configuration imbalance, vulcanizing agent, accelerator dosage is abnormal.

(2) For some rubber species that need to be plasticized, the plasticization does not meet the requirements, the plasticity is too low, and the colloid is too hard, resulting in a sharp rise in temperature during rubber refining. The roll temperature of the rubber mill or other roll devices (e. g. remill, calender) is too high and cooling is insufficient, which may also cause on-site scorching.

(3) When the mixed rubber is discharged, the film is too thick, the heat dissipation is poor, or it is stored hastily without cooling, and the factors such as poor ventilation and high temperature in the warehouse cause heat accumulation, which will also cause scorching.

(4) The rubber material is poorly managed during storage. After the remaining scorching time is exhausted, it is still stacked and unused, resulting in natural scorching. Processing difficulties; affect the physical properties of the product and the smoothness of the outer surface; and even lead to the disconnection of the product joint.

Solution:

(1) the design of the rubber material should be appropriate and reasonable, such as the accelerator as far as possible to take a variety of ways and use. Suppression of scorching. In order to adapt to the high temperature, high pressure, high speed rubber mixing process, in the formula can also be equipped with the right amount (0.3~0.5 parts) of the anti-scorch agent.

(2) Strengthen the cooling measures for rubber materials in rubber mixing and subsequent processes, mainly by strictly controlling the machine temperature and roller temperature and ensuring sufficient cooling water circulation, so that the operating temperature does not exceed the scorching critical point.

(3) Pay attention to the management of semi-finished rubber materials. Each batch of materials should be followed by a running water card, implement the principle of "first in, first out" storage, and stipulate the maximum storage time for each vehicle material, which shall not be exceeded. The warehouse shall have good ventilation conditions.

(4) adjust the vulcanization system, for the use of sulfonamide accelerator, greatly improve the anti scorch performance.

(5) Improve the storage and processing conditions of rubber materials, such as strengthening cooling;

(6) Use anti-scorching agent.

Influencing Factors and Solutions of Scorch

Rubber in the processing, storage, pressure in the process of the role of heat, the occurrence of early vulcanization (crosslinking) and loss of mobility and reprocessing ability, is the so-called scorch phenomenon. (I. e., the accumulation of the influence of heat and time on the compound in the process, which can also be called the thermal history of the compound. If the thermal history of the compound is longer and the temperature is higher, the scorching time of the compound can be gradually shortened.) So in the case of the compound formula to determine, the main factors causing the scorch of the compound and the solution to those?

1. The glue discharging temperature and cooling storage temperature are too high

Solution: The discharging temperature of the master rubber is generally 135 ℃, and the maximum is not more than 150 ℃; The discharging temperature of the final rubber is generally not more than 105 ℃, and the maximum is not more than 110 ℃. The storage temperature is generally below 45 ℃, and the maximum is not more than 50 ℃.

2. Parking time

Solution: If the parking time is too short, the fatigue recovery of the rubber compound cannot be fully relieved, the scorch time becomes short, and the shortest parking time is generally not less than 6 hours; If the master rubber is parked for too long, it is easy to cause difficulties in final refining production, relatively prolonged rubber mixing, more scorch loss and shorter scorch time. If the final refining and parking time is too long, frost spray or self-sulfur will easily occur, resulting in shorter scorch.

3. Poor uniformity of mixing

Solution: to avoid local concentration of some compounding agents, accelerate the vulcanization speed, and cause local scorch changes.

4, rubber mixing process, that is, the length of rubber mixing time

Solution: On the premise of ensuring the quality (uniformity) of the rubber, shorten the rubber mixing time as much as possible.

5. Equipment cooling effect

Solution: good equipment cooling, relatively reduce the temperature of the compound, extend the scorch time. Clean the equipment frequently to improve the heat exchange capacity of equipment cooling.

6. Extrusion or calendering temperature and speed

Solution: In the case of ensuring the production process and capacity, as far as possible to reduce the process temperature and speed.

The ideal anti-scorching agent should have the following properties:(scorch retarderCTP is only suitable for sulfur vulcanization system, not for peroxide and metal oxide vulcanization)

The scorch retarder mainly consists of organic acids, nitroso compounds and thioimide compounds.

 

1. It has excellent anti-coking performance, small selectivity to different accelerators and rubber species, and is not sensitive to other compounding agents;

2. There is no adverse effect on the vulcanization characteristics of the rubber compound and the properties of the vulcanized rubber;

3, storage stability and good operation performance, no agglomeration, no flying, dispersion, no spray frost, etc;

4, in line with industrial production safety and health requirements;

5. High cost performance;

6, it is best to have other beneficial functions.