Polyethylene Terephthalate (PET) film is selected as the release liner for lidocaine patches primarily due to its exceptional chemical inertness and specific surface energy characteristics. This material acts as a critical interface that stabilizes the drug formulation during storage while ensuring mechanical reliability when the patient prepares to apply the patch.
Core Takeaway PET serves a dual function: it acts as a chemically inert barrier that prevents the active lidocaine from degrading or volatilizing on the shelf, and provides a controlled low surface energy interface that allows for smooth removal without tearing the delicate adhesive gel matrix.
Preserving Formulation Integrity During Storage
The primary function of the release liner is to protect the drug before it ever reaches the patient. PET is uniquely suited for this due to its stability.
Superior Chemical Inertness
Lidocaine is a reactive chemical compound. PET film is chosen because it is chemically inert, meaning it does not react with the active ingredients within the drug matrix.
This inertness prevents the drug from degrading over time, ensuring the patch retains its potency from the manufacturing line to the medicine cabinet.
Preventing Volatilization
Lidocaine patches rely on a precise concentration of medication. PET films provide a robust barrier that prevents the volatilization (evaporation) of active ingredients.
By sealing the matrix, the liner ensures the drug remains suspended in the adhesive layer rather than escaping into the packaging, preserving the intended dosage.
Optimizing the User Application Experience
A patch is useless if it cannot be applied correctly. The physical properties of PET are essential for the mechanical mechanics of application.
Low Surface Energy
PET film naturally possesses low surface energy. This property is critical because lidocaine patches use pressure-sensitive adhesives (PSAs) that are designed to stick aggressively to skin.
The low surface energy of the PET prevents the adhesive from forming a permanent bond with the liner itself, acting effectively as a "non-stick" surface.
Engineered Release Force
The separation of the liner from the patch must be calibrated precisely. PET allows for an engineered release force.
This ensures the liner can be peeled away smoothly. If the release force were too high, the user might stretch or tear the soft gel structure (the drug matrix) during removal, rendering the patch unusable.
Understanding the Trade-offs
While PET is the standard, it is important to understand the nuances of its application to avoid manufacturing defects.
The Necessity of Coatings
While PET has naturally low surface energy, it is not always sufficient for every adhesive formulation.
For particularly aggressive adhesives, the PET film may require an additional fluoropolymer or silicone coating. Without this, the "release" might still be too difficult, causing the adhesive to stay stuck to the liner rather than the backing.
Material Confusion
It is vital to distinguish the release liner from the backing layer. PET is often used for both components due to its strength.
However, the backing layer functions to protect the patch during wear (supporting the hydrogel), while the release liner protects it before wear. Confusing the specifications of these two PET layers can lead to product failure.
Making the Right Choice for Your Goal
When selecting a liner material for transdermal applications, align your choice with your specific stability and usability requirements.
- If your primary focus is Long-Term Stability: Prioritize a PET liner with high barrier properties to prevent the volatilization of unstable active ingredients like lidocaine.
- If your primary focus is User Experience: Ensure the PET liner has an engineered release force that is calibrated specifically to the tackiness of your adhesive matrix to prevent gel tearing.
The correct PET liner transforms a delicate drug matrix into a robust, consumer-ready medical product.
Summary Table:
| Feature | Benefit for Lidocaine Patches | Why It Matters |
|---|---|---|
| Chemical Inertness | Prevents reaction with active lidocaine | Ensures long-term drug potency |
| Barrier Properties | Inhibits volatilization of ingredients | Maintains precise dosage concentration |
| Low Surface Energy | Natural non-stick characteristics | Allows smooth removal from adhesive |
| Engineered Release | Calibrated peeling force | Prevents tearing of the delicate gel matrix |
| Mechanical Strength | Dimensional stability | Facilitates high-speed manufacturing |
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We provide a comprehensive range of transdermal drug delivery products—including Lidocaine, Menthol, Capsicum, Herbal, and Far Infrared pain relief patches, as well as Eye Protection, Detox, and Medical Cooling Gel patches (excluding microneedle technology).
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References
- Srinivas Nalamachu, Arnold R. Gammaitoni. Use of the Lidocaine Patch 5% in the Treatment of Neuropathic Pain. DOI: 10.3109/j426v02n04_02
This article is also based on technical information from Enokon Knowledge Base .
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