Overmolding Techniques: Solving Adhesion Issues between LSR and Thermoplastics.

Overmolding Techniques: Solving Adhesion Issues between LSR and Thermoplastics

Problem Statement

Overmolding liquid silicone rubber (LSR) onto thermoplastics often results in poor adhesion due to incompatible surface energies and thermal expansion coefficients. This leads to delamination, especially in high-temperature or chemically aggressive environments.

Material Science Analysis

LSR exhibits low surface energy (22-24 mN/m), making it inherently difficult to bond with high-surface-energy thermoplastics like polycarbonate (PC) or polyamide (PA). Adhesion failures occur due to insufficient chemical bonding and mechanical interlocking. Surface modification and specialized primers enhance adhesion by increasing surface energy and promoting covalent bonding.

Technical Specs

• Material: LSR (Shore A 40)
• Temperature Range: -50°C to 200°C
• Tensile Strength: 8 MPa
• Elongation at Break: 500%
• Compression Set: 10% (22 hours at 150°C)

Technical Comparison

Material	Adhesion Strength (N/mm²)	Chemical Resistance	Compression Set (%)
LSR (Primer-treated)	2.5	Excellent	10
TPE	1.2	Good	25
EPDM	0.8	Moderate	15

Standard Compliance

RubberQ adheres to IATF 16949 standards for batch-to-batch consistency. Our overmolding process complies with ASTM D2000 for material callouts and ISO 3601 for sealing performance. Surface preparation and primer application are validated using ASTM D429 adhesion testing.

For custom material compound development or IATF 16949 documentation, consult RubberQ's engineering department.