Why does blooming occur during the production of rubber shoe soles?

Summary Description:

Rubber soles are characterized by their softness, excellent elasticity, and shock-absorbing properties. Rubber product manufacturers typically use natural rubber, synthetic rubber, or a combination of both with reclaimed rubber to produce rubber soles.

 
Rubber soles are characterized by their softness, excellent elasticity, and shock-absorbing properties. Rubber product manufacturers typically produce rubber soles using natural rubber, synthetic rubber, or a combination of both with reclaimed rubber. During production, various issues can arise; one common problem is blooming, which not only detracts from the aesthetic appearance of the sole but also compromises its performance and service life. So, how can blooming be prevented in the manufacture of rubber soles? Next, Linghui Plastics will explain the underlying causes and offer effective solutions.

 

I. Causes of Blooming
1. Improper process operations. Uneven mixing during processing leads to poor dispersion and localized saturation, resulting in material extrusion. Excessive rubber‑mixing temperatures can cause localized over‑addition of compounding agents. Inadequate application of release agents or mold‑cleaning water may cause whitening on the rubber surface.
2. Rubber soles may develop blooming due to external temperature fluctuations. The solubility of additives in rubber varies with temperature: generally, higher temperatures increase solubility, while lower temperatures decrease it.
3. Excessive use of compounding agents can lead to their saturation and subsequent exudation. Since each rubber additive has a different solubility in rubber, overuse may cause the additive to migrate to the surface.
4. Improper control of process parameters. Both excessively high or low vulcanization temperatures and insufficient vulcanization time can lead to blooming.

II. Methods for Preventing Frosting
1. In practical operations, process parameters must be strictly controlled. Vulcanization temperature and time should be tightly regulated to prevent under‑vulcanization and polymer degradation that can lead to blooming.
2. During mixing, ensure thorough blending to achieve uniform dispersion of the rubber compound. Prior to extrusion, allow the compound to stand for at least 8 hours to enable complete distribution of all compounding agents. Maintain appropriate mixing temperatures to prevent localized over‑dispersion and subsequent bleeding of additives. When cleaning rubber sole molds, follow the prescribed procedures, and apply release agents in accordance with the operating instructions for demolding and use.
3. Synthetic rubber and reclaimed rubber exhibit higher solvent compatibility with additives than natural rubber. In practical production, appropriately blending these materials can help prevent blooming while also improving processing performance and reducing manufacturing costs.
4. The dosage of additives should be carefully controlled; multiple additives can be used in combination to reduce the overall amount required. A single additive, when used in too small a quantity, may fail to deliver the desired performance, while excessive use can lead to blooming. By combining several additives, both efficacy can be achieved without causing blooming.
5. When formulating rubber soles, it is essential to account for seasonal temperature fluctuations and carefully select appropriate compounding agents and their dosages. During storage, attention should be paid to changes in ambient temperature. Frosting on rubber soles is sometimes caused by multiple factors; therefore, rubber product manufacturers should consider various aspects during production to minimize the occurrence of this phenomenon.