Traditional silicone molding relies on release agents for demolding, but release agent residue seriously affects surface quality, bonding performance, and biological safety. Release-agent-free molding technology is an important development direction for LSR precision manufacturing.
1. Problems with Release Agents
1.1 Hazards of Residue
- Surface contamination: Affects appearance and feel
- Bonding failure: Primer/adhesive cannot effectively adhere
- Biological risk: Migration into body may cause toxicity
- Coating difficulty: Printing/spraying adhesion reduced
- Electrical impact: Insulation performance reduced
1.2 Limitations
Uneven spraying causes inconsistent demolding, frequent reapplication affects cycle time, cavity buildup affects dimensional accuracy, and VOC emissions are an environmental concern.
2. Principles of Release-Agent-Free Molding
2.1 Mold Surface Modification
- Nano-coating: DLC diamond-like carbon, friction coefficient 0.05-0.1
- PVD coating: TiN/TiCN/TiAlN, hardness HV2000-3500
- Fluorine coating: Low surface energy, silicone non-adhesive
- Micro-nano texturing: Biomimetic surface structure, reduced contact area
2.2 Self-Release Mold Steel
- Polmax (Assab): Pre-hardened corrosion-resistant steel
- STAVAX (Assab): Martensitic stainless steel
- S136 (Daido): High-polish corrosion-resistant steel
2.3 Process-Assisted Demolding
- Compressed air demolding: Air pressure assists ejection
- Mold temperature control: Rapid cooling reduces adhesion
- Draft angle: Optimized mold geometry
- Ultrasonic assistance: Reduces interfacial adhesion
3. Mold Coating Technology Details
3.1 DLC Coating
Thickness 1-3 micrometers, hardness HV 2000-5000, friction coefficient 0.05-0.15, temperature resistance below 350 degrees, service life 500K-2M cycles
3.2 PVD Coating
Thickness 2-5 micrometers, hardness HV 2000-3500, friction coefficient 0.3-0.5, color gold (TiN) / gray (TiAlN), service life 1M-3M cycles
3.3 Fluorine Coating
Thickness 0.5-2 micrometers, contact angle greater than 100 degrees, friction coefficient 0.05-0.1, temperature resistance below 260 degrees, service life 50K-200K cycles
4. Surface Quality Control
4.1 Surface Roughness Management
Optical products Ra less than 0.05 micrometers (mirror polish), appearance products Ra less than 0.1 micrometers (fine polish), functional products Ra less than 0.4 micrometers (standard polish), structural products Ra less than 0.8 micrometers (general polish)
4.2 Surface Defect Control
- Bubbles: Optimize venting, vacuum, reduce injection speed
- Flow marks: Adjust gate position and injection speed profile
- Flash: Improve clamping accuracy, reduce injection pressure
- Sink marks: Optimize holding pressure and cooling
4.3 Surface Cleanliness
No release agent residue (FTIR detection), no dust particles, no oil contamination (contact angle measurement), no chemical residue (extraction testing)
5. Application Advantages
- Medical products: No residue risk, meets biocompatibility requirements, direct packaging without cleaning
- Overmolded products: Significantly improved bond strength, no post-cleaning, yield rate improvement 5-10%
- Optical products: Flaw-free surface, unaffected transmittance, lower haze values
- Food contact products: No chemical migration risk, meets FDA/LFGB requirements
6. Common Issues and Solutions
- Demolding difficulty: Increase draft angle, optimize mold temperature profile, regular coating inspection
- Product deformation: Uniform cooling, reduce demolding speed, air-blow positioning
- Coating wear: Regular integrity check, avoid hard object scratching, timely replacement or recoating
Conclusion
Release-agent-free molding is the development trend in LSR precision manufacturing. Through the synergy of mold surface modification, process optimization, and quality control, release agent residue issues can be completely eliminated, significantly improving product quality and production efficiency.
