The condition of rubber frost, wax, and oil spitting
1. It is a powder like compound agent such as vulcanizing agent, accelerator, activator, antioxidant, filler, etc;
2. It is a waxy substance such as paraffin and floor wax;
3. It is a liquid mixture of softeners, tackifiers, lubricants, etc. that precipitates on the surface of rubber.
The solubility of the mixture in rubber generally increases and decreases with the increase of temperature; The pressure experienced during rubber storage, the humidity of the surrounding air, and time also have an impact on the solubility of the compounding agent. Although the effect is generally not significant, if the pressure is high, the compounding agent in the rubber under pressure will form crystal nuclei and precipitate on the rubber surface, forming frost; If the humidity of the air is too high, the effect of the highly polar compounding agent in rubber on the raw rubber (non polar) is weakened, and the solubility of the compounding agent decreases, leading to frost spraying; The longer the storage time, the more obvious the frost on the rubber surface. Due to the temperature and humidity of the air in the storage environment changing with the seasons, and the significant differences, it is easy to cause changes in the solubility of the mixture, leading to frost spraying.
Analysis of the causes 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 prone it is to frost caused by excessive coordination (i.e. the content of additives in rubber exceeds its solubility in rubber).
2. Temperature changes
The solubility of additives in rubber varies with temperature. Generally, the solubility increases when the temperature is high, but decreases when the temperature decreases.
3. Undersulfur
The solubility of additives in rubber is influenced by vulcanization conditions.
4. Aging
Aging means that the local structure of the three-dimensional network of vulcanized rubber is damaged due to bond breakage, which weakens the ability of the network structure to adsorb and lock auxiliary agents, and the auxiliary agents migrate to the surface, resulting in frost spraying“
5. Uneven force distribution
When the rubber is subjected to external force, it often causes stress concentration and surface fracture, which accelerates the precipitation of the original Supersaturation auxiliary particles, forms frost on the crack surface, and extends to the periphery“
6. Uneven mixing
Uneven mixing leads to uneven dispersion of the compounding agent in the rubber, and local occurrences of the compounding agent exceeding its solubility may result in spraying.
Design principles of EPDM anti spray formula
1. The formula design should be as simple as possible, and the simpler the requirement to achieve the goal, the better.
2. Reduce or eliminate the use of various functional additives, and minimize the use of low molecular weight substances that are prone to migration.
3. Properly use some heterocyclic tackifiers such as ancient maronites.
4. The use of anti frost agents and anti spray comprehensive promoters should be noted in terms of dosage.
5. Use paraffin oil or naphthenic oil with higher viscosity.
6. Promoters should be used in a small amount and with multiple varieties. Promoters of the same type with a larger molecular weight are better than those with a smaller molecular weight, and the larger the substituent group, the safer it is.
7. Pay attention to the combination and reaction between various additives.
8. It is best to use two types of raw rubber together, learning from each other's strengths and weaknesses, and the selection of brand is very important.