Recently, with the decrease of temperature, the phenomenon of rubber frosting has become more and more serious. For the ready to ship rubber products, we have encountered a lot of quality pressure.

 

 

 

Condition of rubber defrosting, waxing and oiling

 

 

 

1. It is a powder mixture of curing agent, accelerant, active agent, antioxidant, filler, etc;

 

 

 

2. It is a wax like substance such as paraffin and ground wax;

 

 

 

3. It is the liquid complexing agent such as softener, tackifier and lubricant that precipitates on the rubber surface.

 

 

 

However, the solubility of compounding agent in rubber generally rises and falls with the rise and fall of temperature; the pressure, humidity of surrounding air and time when rubber is stored also have influence on the solubility of compounding agent. Although the influence is not obvious in general, if the pressure is large, the compounding agent in rubber at the pressure part will form a crystal nucleus, which will be separated from the rubber surface and form a spray frost; If the air humidity is too high, the effect of the polar compound on the raw rubber (nonpolar) will be weakened, and the solubility of the compound will be decreased, which will lead to 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 large, it is easy to cause the change of the solubility of the mixture, which leads to the frost spray.

 

1. Overmatch

 

The solubility of various additives in rubber is different. The smaller the solubility of additives in rubber, the more likely to appear frost spray caused by excessive coordination (that is, the content of additives in rubber exceeds its solubility in rubber). When spraying with excessive coordination, other components are often driven to spray together (this phenomenon is called passive frost spraying), although these passive frost sprays are far from saturated in rubber.

 

2. Temperature change

 

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

 

3. Under sulfur

 

The solubility of additives in rubber is affected by curing conditions. Taking NR as an example, under the condition of positive vulcanization, the crosslinking density is the largest, the free sulfur is reduced, the probability of spraying sulfur is reduced, and the chance of other auxiliaries shuttling through the three-dimensional network is also reduced, so the probability of spraying frost is reduced; on the contrary, under the condition of under sulfur, the network crosslinking density is relatively small, and the probability of spraying frost is correspondingly increased.

 

4. Aging

 

Aging means that the local part of the three-dimensional network structure of the vulcanizate is damaged due to bond fracture, which weakens the ability of the network structure to adsorb and the ability of the solid lock coordination agent, and the migration of the agent to the surface leads to frost spraying“

 

5. Uneven stress

 

When the rubber is affected by external force, it often leads to stress concentration and surface fracture, which makes the particles of the original supersaturated auxiliary accelerate to precipitate, form frost spray on the crack surface, and extend to the periphery“

 

6. Uneven mixing

 

Uneven mixing results in uneven dispersion of the compounding agent in the rubber, and frost spray will occur in some parts due to the excessive solubility of the compounding agent“