Why Compression Molded Silicone Products Blooming?

Why Compression Molded Silicone Products Blooming?

Silicone “Blooming” refers to the milky discoloration or white powder caused by the migration of compounds to the surface of the rubber. Sometimes, we see white stuff on surface of Silicone Handle, Silicone Grips, or Molded Silicone Rubber Products etc. Actually, it is one kind of migrations of solid or liquid materials/substances used in rubber compounding. Silicone blooming does not affect the quality of a silicone rubber product. But if the white “dust” is undesired for appearance reasons, it can be washed off in light mineral oil/solvent. The incidence of bloom may be reduced under good storage including shielding parts from fluorescent light. The presence of by-products or excess compounds can cause blooming, affecting both the functionality and aesthetics of the silicone rubber. Depending on the application, utmost purity and cleanliness of materials are essential.

Reasons of Compression Molded Silicone Products Blooming:

• Improper Formula:

Full blooming: it is mainly caused by sulfur, accelerant, active agent, antiaging agent relocation blooming; processing AIDS, relocation antiaging agent; Antistatic agent generation blooming; sulfur vulcanization system accelerant and reaction products reaction stay; organic peroxide vulcanization system low molecular material excessive stress blooming; inorganic filler: such as calcium carbonate.

• Technical Errors in Operation:

Mixing uneven badly, some parts beyond fullness;

Mixing temperature is too high, so that part of the compound excessive;

Weighing is not accurate (more, less, missing, wrong);

Vulcanization temperature is too high, polymer degradation formed spray frost;

The vulcanization temperature is too low, which constitutes an incomplete reaction and the onset of sulfur spray curing time is not good, which constitutes the improper release agent or washing water operation of the sulfur spray spraying, and constitutes the appearance of white frost.

• The quality of raw materials fluctuates due to different raw materials of origin, different production methods, different technologies and different batches. The

composition technology of raw rubber is different: polymerization temperature, catalyst, monomer and so on, resulting in different solubility. Purity, moisture, ash, pH value, physical properties, etc

• Storage Conditions of Temperature

the solubility of the agent in rubber is usually followed by the rise and fall of the temperature (pressure and humidity) : rubber

storage by the pressure, the humidity of the surrounding air and the time of the solubility of the agent also has an impact, usually not much.

However, if the pressure is large, the pressure part of the rubber with the agent will constitute a crystal nucleus, points out of the rubber surface, constitute a spray frost; If the humidity of the air is too large, the rubber with large polarity of the effect of raw rubber (non-polar) is weakened, the solubility of the agent is reduced, and then the frost spray; The longer the storage time, the more significant the rubber surface frost spraying, because the temperature and humidity of the air in the storage environment with the change of the season is not the same, but not the same, it is easy to form a change in the solubility of the agent, and then lead to frost spraying.

• Rubber Aging

Rubber aging mostly lead to the damage of the balanced network structure of vulcanized rubber, and then also damaged the chemical or physical connection between the rubber system and the raw rubber molecules and the coordination agent, reducing the solubility of the coordination agent in the rubber system. As a result, those parts in the full condition of the compound will be separated from the rubber, forming a spray frost.