Delamination in Injection Molded Parts: Buyer Review Before Approval

Delamination is a severe molding defect that points directly to material contamination or preparation failures rather than simple process drift. When a part sheds thin layers, flakes near a gate, or peels under impact, the surface skin has failed to bond with the underlying material. Because it fundamentally compromises part strength, delamination is rarely a cosmetic issue you can waive. It requires root-cause verification before you approve the lot.

Identifying Delamination

Delamination presents as a flaky, layered surface that can be lifted with a fingernail or peeled back when the part flexes. It often looks like fish scales, particularly near the gate or at sharp geometric transitions. Sometimes, the layers only separate cleanly at an impact point or fracture line rather than showing a solid cross-section.

Critically, delamination can remain hidden until the part experiences mechanical stress. A sample that passes visual inspection on the bench may delaminate during assembly or field use. Unlike splay (silver streaks), which is purely a surface defect, delamination represents a physical separation within the wall thickness.

Why Delamination Blocks Approval

An unbonded wall cannot carry load. Even if the part looks acceptable, it will likely fail drop, snap-fit, or fatigue testing because the internal layers shear apart. Delamination must be treated as a structural failure. Require the supplier to identify the specific mechanism—such as cross-contamination, excess moisture, incompatible regrind, or release agent—and prove that the corrected parts are fully bonded through the cross-section.

Root Causes to Verify

Incompatible Material Contamination: Mixing resins that do not chemically bond—such as introducing Polypropylene (PP) into Polycarbonate (PC)—creates distinct layers that refuse to fuse. This is the most common cause and frequently traces back to inadequate purging, a shared hopper or dryer, or contaminated regrind.

Excess Moisture: Hygroscopic resins must be dried properly. If wet material enters the barrel, the moisture flashes to steam at the melt front, creating a separated skin layer. While this mechanism shares similarities with moisture-driven splay, it results in physical layer separation rather than just surface streaking.

Release Agent or Oil Migrations: Excessive mold release or leaking hydraulic oil migrating onto the cavity surface creates a physical boundary that prevents the advancing melt layer from bonding to the cooling skin.

Foreign Particles or Film: A flake of degraded polymer, carbon, or unmelted material trapped at the gate can seed a delamination layer. If dark inclusions accompany the flaking, review the black specks diagnostic page.

High Shear or Local Overheating: Extremely aggressive gate geometry, or injecting the melt too fast at too high a temperature, can physically degrade the polymer skin at the gate, destroying the local bond.

Technical Questions for the Supplier

• Where exactly does the delamination occur, and is it isolated to specific cavities or specific shots?
• What precise grade is running? Was any regrind, masterbatch, or purge compound introduced into the barrel?
• Was the resin dried to the manufacturer’s specifications? Can you provide the dryer log showing the dew point and residence time?
• Was the machine, hopper, or dryer used for a different material family immediately prior to this run?
• What mold release is being used, how heavily is it applied, and was the tool thoroughly cleaned before these samples were pulled?

Required Verification Evidence

Do not accept a generic “process adjusted” resolution. Demand verifiable records:

• High-resolution, marked-up photos detailing where the layers separate. If available, request cross-section or fracture-surface photos.
• The material lot record, specifying the exact regrind percentage and masterbatch let-down ratio.
• The drying log (temperature, time, dew point) for moisture-sensitive resins.
• The purge and changeover log for all shared material handling equipment.
• A formal corrective action plan that identifies the precise mechanism (e.g., contamination vs. shear) and details how the fix was validated.

When to Hold Tool or Production Approval

Halt approval immediately if:

• Delamination appears anywhere on a load-bearing or structural feature.
• The supplier cannot definitively rule out cross-contamination from shared dryers, hoppers, or regrind streams.
• The supplier attempts to classify delamination at a break or impact point as a cosmetic issue.
• The proposed fix is purely a process adjustment, but the supplier cannot explain why the layers failed to bond initially.

Securing Material Integrity in the RFQ

Prevent contamination issues early by explicitly stating your material purity requirements in the RFQ. Define whether regrind is allowed and set a strict maximum percentage. Ask suppliers to detail their changeover and purge validation procedures between different resin families. Finally, for structural components, specify a mechanical acceptance test—such as a drop, flex, or impact test—rather than relying solely on visual inspection, because delamination often hides beneath the surface.

Disclaimer

PlasticsTechnologyAlliance.com is an independent buyer resource. It does not manufacture parts, inspect tooling, or certify suppliers. Delamination causes are material- and process-specific; always verify root causes through the supplier’s material records and require structural evidence that the correction was successful.