Why Is Demolding Rubber So Difficult?
Demolding difficulties are a frequent challenge in the rubber processing industry, often resulting from a combination of material, process, and equipment-related factors. These challenges not only hinder production efficiency but also compromise product quality. Below is an analysis of the key contributing factors.
1. High Adhesion to Mold Surface
Cause: Rubber compounds, especially those with high tackiness (e.g., natural rubber or certain synthetic rubbers), can strongly adhere to the mold surface due to chemical affinity or surface tension.
Impact: This leads to sticking, making it difficult to release the product without damage.
2. Complex Mold Geometries
Cause: Intricate mold designs with undercuts, sharp corners, or deep cavities can trap rubber, increasing resistance during demolding.
Impact: Products may tear or deform when forcibly removed.
3. Improper Mold Release Agent Application
Cause: Inadequate or uneven application of mold release agents, or using an unsuitable agent for the rubber compound, can fail to reduce adhesion.
Impact: Results in sticking and inconsistent demolding.
4. Thermal Expansion and Shrinkage
Cause: Rubber undergoes thermal expansion during curing and shrinkage upon cooling, which can cause it to grip the mold tightly, especially in rigid molds.
Impact: Increased friction and difficulty in ejection.
5. Surface Imperfections of the Mold
Cause: Rough or worn mold surfaces can increase friction, while contaminants (e.g., rubber residue or dirt) can enhance adhesion.
Impact: Products stick to the mold, leading to defects or damage.
6. Inadequate Mold Design
Cause: Molds lacking proper draft angles or ejection mechanisms (e.g., pins or air vents) can hinder smooth release.
Impact: Increased manual effort or risk of product damage during demolding.
7. Curing Process Issues
Cause: Over-curing or under-curing can alter the rubber’s surface properties, making it either too sticky or too brittle.
Impact: Sticky surfaces adhere to the mold, while brittle surfaces may crack during demolding.
8. Material-Related Factors Affecting Rubber Demolding
1) Interaction Between Rubber and Mold Surface Materials
Rubber compounds vary widely in polarity and chemical structure, influencing how they interact with mold surfaces. For instance, nitrile rubber (NBR) contains polar cyano groups that tend to form strong physical or chemical bonds with metal molds, making release difficult. Conversely, fluororubber (FKM), known for its excellent chemical resistance and low surface energy due to the presence of fluorine atoms, can still exhibit mold adhesion issues under certain processing conditions.
2) High Viscosity Before Vulcanization
Uncured rubber typically exhibits high viscosity, which causes it to cling tightly to mold surfaces during molding. This adhesion intensifies under elevated temperatures, increasing resistance during demolding. Natural rubber, for example, is particularly viscous in the early phases of processing, and if not carefully managed, this can lead to serious demolding problems.
3) Influence of Additives in the Compound
Formulation additives are essential for rubber performance, but can inadvertently hinder demolding. Overuse of plasticizers may overly soften the compound, increasing the surface contact area and adhesion with the mold. Incorrect type or dosage of curing agents may result in incomplete crosslinking, weakening the product’s ability to release cleanly. Additionally, some additives may migrate to the mold interface during vulcanization, altering surface interactions and further complicating demolding.
Innovative and Effective Additive Solutions: Technologies for Demolding Based on Silicone Additives
Strategies to Improve Mold Release and Efficiency in Rubber Processing
Demolding challenges can significantly impact cycle times, surface quality, and overall productivity. To address these issues, SILIKE offers a comprehensive portfolio of silicone-based additives and release agents that optimize the demolding process for rubber products, e.g., SILIMER 5322.
Although SILIMER 5322 was originally developed as a specialized lubricant and processing aid for WPC (Wood-Plastic Composite) applications, market feedback has revealed unexpected benefits in rubber processing as well. Rubber compounders—particularly those working with polar rubber systems—have found that this additive significantly enhances formulation performance. It helps improve dispersion, optimize processing conditions, and upgrade overall formulation efficiency, making it a valuable solution beyond its initial design scope.
Why SILIMER 5322 Can Be Used as a High-Performance Silicone-Based Release Additive for Rubber Compounds？
The core component of SILIKE SILIMER 5322 is modified polysiloxane with polar active groups. It offers excellent compatibility with resins, wood powder, and rubber compounds. During processing, it enhances the dispersion of rubber compounds without interfering with the performance of compatibilizers in the formulation. SILIMER 5322 not only improves the processability of the base resin but also imparts a smoother surface finish to the final product, outperforming traditional additives like waxes or stearates.
Key Benefits of SILIKE SILIMER 5322 Mold Release Lubricants for Rubber Demolding Solutions
Acts as an internal lubricant and release agent
— Reduces friction and adhesion to mold surfaces from within the matrix.
Minimizes surface tack
— Without compromising mechanical properties, helping achieve clean and easy part release.
Protects molds
— Reduces wear and residue buildup, extending mold life and reducing maintenance.
As rubber processing additives
— Enhances processing efficiency, improves surface finish, speeds up demolding cycles, and lowers defect rates.
Excellent Compatibility
—Suitable for a wide range of rubber systems, including NR, EPDM, NBR, FKM, and more.
Ideal for complex molded parts, such as precision seals, gaskets, grips, functional components with intricate geometries, and more.
Boost Productivity, Reduce Waste, and Enhance Surface Quality
Whether you’re molding automotive seals, industrial parts, or consumer goods, SILIKE’s silicone-based demolding technologies for rubber help you achieve Smoother release, Higher production throughput, reduced scrap rates, and consistent surface aesthetics.
Looking to improve demolding efficiency in rubber processing?
Explore SILIKE’s silicone-based mold release solutions designed to optimize performance and reduce cycle times.
Chengdu Silike Technology Co., Ltd.
Since 2004, we have been a leading manufacturer of innovative silicone additives for high-performance polymers. Our products enhance the performance, functionality, and processing of a wide range of materials—including industrial thermoplastics, engineering plastics, modified compounds, rubber formulations, color masterbatches, paints, coatings, and more.
By improving formulation efficiency and cost-effectiveness, SILIKE helps manufacturers achieve consistent quality and greater production reliability.
If you don’t find what you need, contact us for a customized solution that fits your requirements perfectly.
Tel: +86-28-83625089 or via email: amy.wang@silike.cn.
Post time: Jul-16-2025
