In life, many people must have seen the phenomenon of whitening of rubber products after using for a period of time. For example, in the case of high humidity, the paint is easy to turn white.
Rubber is divided into unvulcanized rubber (hereinafter referred to as rubber material) and vulcanized rubber (hereinafter referred to as product). Bloom is the appearance of liquid or solid compounding agent moving from the inside of the rubber to the surface of the rubber [1]. It can be seen that the internal compounding agent of the rubber is separated, which constitutes a frosting. The methods of rubber spraying can be roughly divided into three types. That is, powder spraying, wax spraying, and oil spraying (also called oozing).
Powder spraying is a powdery compounding agent such as vulcanizing agent, accelerator, active agent, antioxidant, filler, etc., which is separated on the surface of the rubber to form a layer of powder.
Spray wax is a wax-like substance such as white wax and ceresin wax that is separated from the surface of the rubber to form a layer of wax film.
Oil injection is a liquid compounding agent such as softeners, tackifiers, lubricants, and plasticizers separated on the surface of the rubber to form a layer of oil. In practice, the way the rubber surface is frosted is sometimes presented in one way, and sometimes in two or three ways.
Poor recipe planning:
Plump ejection: common in sulfur, accelerators, active agents, antioxidants Relocation ejection: common in processing aids, relocation antioxidants. Antistatic agent generation and ejection: common in the sulfur vulcanization system Accelerator and reaction product reaction stay: common in the organic peroxide vulcanization system low molecular substances Excessive stress ejection: common in inorganic fillers: such as calcium carbonate.
Improper technical operation:
Uneven mixing results in poor dispersion, some parts exceed the fullness, the rubber mixing temperature is too high, the compounding agent is partly excessive, the weighing is inaccurate (overweight, underweight, missing, wrong), the vulcanization temperature is too high, the polymer Degradation to form frosting, the vulcanization temperature is too low, the formation of undersulfur frosting that occurs due to incomplete response, and the vulcanization time cannot be performed, and the release agent or mold washing water that forms the undersulfur frosting spray is improperly operated, resulting in the appearance of whitening on the surface of the rubber.
The quality of raw materials fluctuates due to different raw materials, different production methods, different technologies, and different batches. Same. Changes in purity, moisture, ash, pH, physical properties, etc.
Poor storage conditions Temperature: The solubility of compounding agents in rubber usually rises and falls with the rise and fall of temperature (pressure and humidity): The pressure of rubber storage, the humidity of the surrounding air and the time also affect the solubility of compounding agents, usually The situation has little effect. However, if the pressure is high, the compounding agent in the rubber at the pressure part will form a crystal nucleus, which will be separated from the surface of the rubber to form a frost; if the humidity of the air is too high, the compounding agent with high polarity in the rubber will affect the raw rubber ( The effect of non-polarity) is weakened, the solubility of the compounding agent is reduced, and then frosting is caused; the longer the storage time, the more obvious the frosting of the rubber surface, because the temperature and humidity of the air in the storage environment vary with the seasons, and they are not the same. Larger, it is easy to cause the solubility of the compounding agent to change, and then cause blooming.
The aging of rubber mostly causes damage to the well-balanced network structure of the vulcanizate, and then also damages the chemical or physical relationship between various compounding agents in the rubber system and the raw rubber molecules and compounding agents, reducing the compounding agent in the rubber. solubility in the system. Therefore, those compounds that are partially in an over-saturated state will be separated from the rubber to form blooming.
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2022-05-10
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