The appearance of white powdery precipitates on the surface of silicone rubber products—commonly known as "blooming" or "exudation"—is a relatively common issue in production. Depending on the stage at which it occurs, the causes and solutions differ.

Blooming During Manufacturing

When silicone molds are manufactured in low-temperature environments, blooming and slow curing can occur. This type of blooming is related to weather humidity and temperature. The solution is to operate in a non-low-temperature environment, or to wait until the silicone is fully cured before proceeding with subsequent processing.

Blooming After Product Use

When silicone products develop blooming after a period of use, the main causes include the following:

First, the amount of compounding agents exceeds the saturation solubility. When compounding agents such as stearic acid, paraffin wax, rubber oil, and anti-aging agents exceed their saturation solubility under changing external conditions (prolonged low temperature, humidity, or UV exposure), blooming occurs.

Second, excessive mold release agent addition. Adding too much mold release agent during open-mill mixing with the vulcanizing agent may result in precipitation after vulcanization. Secondary vulcanization can slightly improve this, but may leave marks.

Third, problems with the raw material itself. Components such as zinc stearate in some silicone raw gums may still precipitate after prolonged use, and even high-temperature baking treatment cannot completely eliminate this. For source-level prevention, silicone raw materials can be tested in high-temperature, high-humidity environments—for example, holding at 80°C and 80% humidity for 48 hours—to verify whether the material is prone to blooming.

Treatment Methods

For silicone products that have already developed blooming, fully immersing the product or applying a blooming treatment agent to the surface, followed by air drying or oven drying, will suffice. After treatment, the product surface can be restored to a clean condition while also gaining a certain degree of blooming resistance.

Prevention Recommendations

Controlling the amount of silicone oil added, avoiding the use of composite silicone oils containing white mineral oil, reasonably controlling mold release agent dosage, and selecting raw materials that are not prone to blooming from the source are the key measures for preventing blooming issues.

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