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Causes of rubber spray frost in cold weather products


Recently, with the decrease of temperature, the phenomenon of rubber frosting has also become serious. For the rubber products that are ready to be shipped, they have encountered a lot of quality pressure.


The status of rubber spit cream, wax spit, oil spit


1. It is a powdered compounding agent such as vulcanizing agent, accelerator, active agent, anti-aging agent, filler, etc .;


2. Waxes such as paraffin and ozokerite;


3. It is a liquid compounding agent such as softener, tackifier, lubricant, etc. which is deposited on the surface of the rubber.


The solubility of the compounding agent in rubber generally rises and falls as the temperature rises and falls; the pressure on the rubber storage, the humidity of the surrounding air, and the time also have an effect on the solubility of the compounding agent, although the effect is generally not large, but If the pressure is high, the compounding agent in the rubber at the pressured part will form crystal nuclei, which will precipitate out of the rubber surface and form a frost; if the humidity of the air is too high, the compounding agent with large polarity in the rubber Sex), the solubility of the compounding agent is reduced, resulting in frost spraying; the longer the storage time, the more obvious the frost spray on the rubber surface, because the temperature and humidity of the air in the storage environment vary with the seasons, and the difference is very large. It is easy to cause the solubility of the compounding agent to change, resulting in frost.


Cause analysis of frost spraying:


1. Excessive coordination


The solubility of various additives in rubber is different. The smaller the solubility of additives in rubber, the more likely to be frosting caused by excessive compounding (that is, the content of additives in rubber exceeds its solubility in rubber). When the frost is sprayed in excess, it often drives other components to spray out together (this phenomenon is called passive frosting), although these passive frosts are far from saturated in rubber.


2. Temperature change


The solubility of additives in rubber varies with temperature. In general, the solubility is high when the temperature is high, and the solubility is reduced when the temperature is reduced. Because rubber products are usually used at room temperature, once the outside temperature is lower than room temperature, the content of some additives in the formula is close to its solubility and precipitates, resulting in frost.


3. Under-sulfur


The solubility of additives in rubber is affected by vulcanization conditions. Taking NR as an example, under normal vulcanization conditions, the cross-linking density is the largest, the free sulfur is reduced, and the probability of sulfur spraying is reduced.The chance of other additives shuttled through the three-dimensional network is also reduced, so the probability of frost spraying is reduced. Under the condition that the network crosslink density is relatively small, the chance of frost spraying increases accordingly.


4. Aging


Aging means that the part of the three-dimensional network structure of the vulcanizate is damaged due to bond breakage, thereby weakening the ability of the network structure to adsorb and lock the auxiliary agent, and the auxiliary agent migrates to the surface and causes frost. "


5. Uneven stress


When the rubber is subjected to external force, it often causes stress concentration and ruptures the surface, which accelerates the precipitation of the super-saturated compound additive particles, forms frost on the crack surface, and extends to the periphery


6. Uneven mixing


Uneven mixing results in uneven dispersion of the compounding agent in the rubber, and localized mixing aids exceeding the solubility may cause frosting. "

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