Analysis of the causes of heat sealing failure in medical blister tray

In medical blister tray packaging, packaging serves not only as the "outer garment" of products but more importantly as a Sterile Barrier System (SBS) ensuring patient safety. This system maintains the sterility of medical devices and drug-device combination products throughout their lifecycle—from production to use—preventing contamination and secondary injuries, thereby serving as the first line of defense in medical safety.

Current Medical Packaging Formats

The mainstream medical blister tray formats include:

• Medical dialysis bags

• Medical blister trays + lid materials

• Automatic blister packaging

Among these, medical blister tray + lid material combinations are widely used for high-end medical devices (e.g., implants, surgical instruments) and Class III medical devices (e.g., cardiovascular stents, orthopedic instruments) due to their superior protective properties and convenience.

Heat Sealing: The Core of Sterile Barrier Systems

The sterile barrier system is formed when lid materials are heat-sealed to blister trays, followed by sterilization. Ideal heat sealing must meet four critical requirements:

• Seal strength compliance: Per EN 868-5:2018, adhesive-coated paper must achieve ≥1.5N/15mm without fiber tear

• Continuous adhesive transfer: Visual inspection shows no breaks in adhesive application

• Absence of micro-channels: Validated through dye penetration tests

• Clean peelability: Ensures medical staff can open packaging without contamination risk

However, production environments present multiple challenges to heat sealing reliability. Below are five common heat sealing failure modes with corresponding solutions to optimize packaging processes.

1. Incomplete Adhesive Transfer

Problem: Non-uniform adhesive transfer to medical blister tray, resulting in incomplete seals

Potential causes:

• Contaminated sealing surface (mold release agents, glove residues)

• Uneven sealer tooling surface (causing localized pressure variations)

• Suboptimal sealing parameters (temperature/pressure/duration)

Solutions:

• Surface cleaning: Wipe sealing surface with alcohol-soaked lint-free wipes

• Tooling calibration: Verify and adjust sealer tooling flatness (laser-based flatness testing recommended)

• Parameter optimization: Implement step-sealing (e.g., low-temperature pre-press followed by optimal sealing temperature)

2. Delamination During Opening

Problem: Lid material delamination leaves paper residue on medical blister tray, compromising sterility

Potential causes:

• Excessive sealing parameters (over-temperature/pressure/duration)

• Poor lid design (e.g., full-perimeter sealing causing stress concentration)

• Material incompatibility (e.g., insufficient fiber strength)

Solutions:

• Parameter adjustment: Reduce temperature/pressure to balance strength and openability

• Lid design optimization: Create unsealed margins (≥2mm edge buffer) and stepped structures (tray height differentials to reduce tear risk)

• Material upgrade: Switch to high-strength adhesive-coated Tyvek® or medical composite films

3. Edge Warping Post-Sealing

Problem: Medical blister tray edge warping affects package integrity and sterilization compatibility

Potential causes:

• Excessive sealing parameters causing thermal deformation

• Structural/material inconsistencies (wall thickness variations, additive effects)

Solutions:

• Reduce sealing parameters

• Optimize medical blister tray design

4. Condensation in Transport

Problem: Internal condensation appears in intact packages after transportation

Potential causes:

• Extreme temperature/humidity fluctuations

• Insufficient lid material breathability

Solutions:

• Use high-breathability lid materials

• Conduct simulated transport testing

5. Seal Failure Post-EO Sterilization

Problem: Medical blister tray edges separate after ethylene oxide (EO) sterilization, breaching barrier integrity

Potential causes:

• Gas shock during aeration (over-stacking or insufficient ventilation)

• Surface contamination reducing bond strength

Solutions:

• Optimize sterilization cycle parameters

• Clean sealing surfaces: Remove contaminants with alcohol wipes

• Enhance lid material breathability