Chloroprene rubber (CR) is a synthetic rubber obtained by polymerization of chloroprene. It is widely used because of its excellent aging resistance, oil resistance, corrosion resistance and other properties. Polychloroprene Rubber CR2442 vulcanized rubber has good physical properties and can be used in many occasions (Such as chloroprene rubber adhesive). However, since the process of CR2442 in internal mixing, open mixing and vulcanization is not easy to master, the physical properties of the prepared vulcanized rubber are sometimes poor, which affects its production and application.
1. The influence of process parameters on the preparation of mixed rubber and vulcanized rubber
1.1 Internal mixer mixing process
CR2442 has high requirements for the mixing process. When preparing CR2442 mixed rubber, the initial temperature, mixing time and rotor speed of the internal mixer have a great influence on the discharge temperature. The discharge temperature is an important parameter for measuring the mixing process. The optimal discharge temperature of CR2442 is 110℃. The order of adding various materials during the mixing process is also important. The correct way to add materials to CR2442 during the mixing process is: add CR2442 and small materials at the same time → add carbon black → add white carbon black and operating oil in sequence.
1.2 Mixing process of open mill
After the mixed rubber prepared by the internal mixer is cooled, the vulcanization system is added on the open mill. The vulcanization system includes vulcanizing agent and accelerator. The correct way to add is to add accelerator first and then vulcanizing agent. When adding the vulcanization system to the mixed rubber on the open mill, it is generally required that there is accumulated rubber on the roller. With the shearing and extrusion of the open mill, the roller temperature will increase significantly. When the temperature of the rubber is too high, the rubber should be cut, pulled out and cooled, and then the rubber should be mixed after it is completely cooled.
1.3 Vulcanization process
After adding the vulcanization system on the open mill, the rubber is cooled and placed for 16~24h before vulcanization. Since the CR2442 mixed rubber is easy to crystallize at low temperatures, it is generally necessary to perform indirect heating treatment in an oven. The vulcanization time of CR2442 was set to 30, 40, 50, 60, 70 and 80 minutes respectively. After many tests, it was found that the tensile strength and elongation at break of the vulcanized rubber were the largest when the vulcanization time was 60 minutes. Therefore, the optimal vulcanization time of CR2442 was determined to be 60 minutes.
1.4 Bonding operation
In the process of bonding the mixed rubber and brass, the rubber is first cut into sheets with the same length and width as the mold. After the mold is preheated, the cut film is placed in the mold cavity. Since the mold is heated, placing it too slowly will cause early vulcanization of the rubber, reduce the fluidity of the rubber, make the bonding insufficient, and then reduce the bonding force. Therefore, the scorch time should be controlled to be much longer than the placement time of the film.
2. Influence of vulcanization system, reinforcement system and bonding system
Vulcanization system: When CR2442 uses only zinc oxide and magnesium oxide for vulcanization, the resulting rubber's physical properties are worse compared to when zinc oxide, magnesium oxide, sulfur, and accelerator DM are used as a system.
Reinforcement system: The reinforcement system of CR2442 is often based on carbon black and supplemented by white carbon black.
Bonding system: Rubber as a single material can no longer meet the needs of society, and it is often necessary to bond rubber to metal to expand its scope of use. CR2442 is usually bonded to metal using a resorcinol-methylene-white carbon black-cobalt salt bonding system.
3. Conclusion
When mixing, it's important to think about temperature, how long you mix, and how fast the rotor spins. Also, when you add the vulcanization system using the open mill, pay attention to the order you add things. The heat from the rollers can really change things.For vulcanization and bonding, if you make sure the scorch time is longer than it takes to place the sample, you can get better quality vulcanized rubber and better bonding with other types of materials. The CR2442 discharge temperature matters too. It's a good idea to add white carbon black as a reinforcement in CR2442. This helps control how fast vulcanization and bonding happen.
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