How to Select Glassine for Medical Label Applications
Created on 09.01
Selecting the right glassine for medical label applications is a critical process that balances material performance, regulatory compliance, and manufacturing efficiency. Here is a comprehensive guide on how to make the right selection.
Executive Summary: Why Glassine is Chosen
Glassine is a smooth, glossy, and air-resistant super-calendered paper. Its primary advantages for medical labels are:
- High Purity & Inertness: Chemically neutral, it doesn't interact with medications or medical devices.
- Excellent Die-Cutting: Cuts cleanly without dusting, crucial for complex label shapes.
- Moisture & Grease Resistance: Naturally resistant to oils and fats, protecting the adhesive.
- Deadfold & Stability: Holds its crease and lies flat, important for application onto syringes, vials, and equipment.
- Printability: Provides an excellent surface for high-quality printing and variable information.
Step-by-Step Selection Criteria
1. Regulatory and Compliance Requirements (The First Priority)
This is non-negotiable. The material must meet stringent standards.
- FDA 21 CFR Part 175.105 / 175.125: This certifies that the adhesives and face stock are safe for indirect food contact, a common benchmark for pharmaceutical packaging. Ensure your supplier provides a Letter of Guarantee (LOG) or a Statement of Compliance for these regulations.
- USP <661> / USP <661.1> (US Pharmacopeia): These chapters specify testing protocols for plastic packaging systems and their materials of construction. While traditionally for plastics, the extractables and leachables principles are increasingly applied to paper-based materials like glassine. Confirm with your supplier that their product is tested and compliant with the spirit of these requirements.
- REACH / RoHS: Ensure the materials are free from substances of very high concern (SVHC) and restricted hazardous materials, especially important for the EU market.
- Supplier Documentation: Your supplier must provide full traceability and Certificates of Analysis (CoA) for each batch to ensure consistency and compliance.
2. Functional Performance Properties
Evaluate the glassine based on the specific needs of the application.
- Basis Weight/Thickness:
Measured in grams per square meter (gsm) or pounds per ream (lbs).
Standard: 60-90 gsm is common.
Thinner (e.g., 60 gsm): Offers high flexibility, conforms well to small diameters (e.g., syringe barrels), and is cost-effective.
Thicker (e.g., 90 gsm): Provides more rigidity, better "pop-up" in automated applicators, and a premium feel. Better for large device labels.
- Caliper (Thickness): Measured in mils or microns. A consistent caliper is crucial for smooth dispensing and die-cutting.
- Moisture Vapor Transmission Rate (MVTR):
While glassine is a good barrier, some high-potency drugs or sensitive devices may require an extra level of protection.
Ask your supplier for MVTR data. If a better barrier is needed, consider clay-coated glassine or a film-based liner (e.g., PET polyester).
- Lay Flat & Curl: The liner must lie perfectly flat on the roll to prevent jamming in high-speed printing and dispensing equipment. Humidity can affect this, so discuss environmental conditions with your supplier.
- Release Level: This is the force required to peel the label from the glassine liner. It is controlled by the silicone coating.
Standard Release: The most common choice.
Low Release (Easy Release): Used for very aggressive permanent adhesives or very fragile labels to prevent tearing or "flagging."
High Release ( Tight Release): Used for less aggressive adhesives to ensure the labels don't fall off the liner during conversion and shipping.
Your label converter will help specify the correct release level.
3. Conversion and Printing Considerations
How will the material behave during the label manufacturing process?
- Die-Cutting Performance: This is a key strength of glassine. It must die-cut cleanly (to allow for easy matrix stripping) without fracturing or "nickering," which creates paper dust that can contaminate sterile environments.
- Printability:
Surface Energy: Should be >38 dynes/cm to ensure good ink adhesion. Most quality glassine liners are treated to meet this.
Porosity: Affects ink absorption and drying time. Discuss with your printer to match the ink system (e.g., UV flexo, water-based).
- Matrix Removal: The "waste" material around the labels must strip away cleanly and reliably at high speeds without breaking.
4. End-Use Application Environment
Where will the final label be applied and stored?
- Temperature Extremes: Will the labeled product be autoclaved, frozen (e.g., -80°C storage), or exposed to high heat? Ensure the adhesive is matched to this, and confirm the glassine's performance won't degrade (e.g., become brittle when frozen).
- Chemical Exposure: Will the label be exposed to alcohol swabs, solvents, or sterilants (e.g., VHP, ETO, gamma radiation)? While the label face stock and adhesive are the primary barriers, the liner must not degrade or become difficult to remove during application.
- Application Method:
- Manual Application: Less critical for liner performance.
- High-Speed Automated Application: The liner must have consistent caliper and roll geometry to run smoothly on automatic label applicators (ALAs). It must also release the label predictably and cleanly.
Common Types of Glassine for Medical Use
Type | Description | Best For |
Standard Glassine | The most common type, natural white, super-calendered. | General-purpose pharmaceutical labels, vial labels, device labels. |
Clay-Coated Glassine | Has a thin coating of clay on the surface, creating an even smoother, more impermeable barrier. | Higher barrier requirements, superior print quality and ink holdout. |
PEGylated (Polycoated) Glassine | Coated with a polyethylene (PEG) layer. Provides a significantly higher moisture and chemical barrier. | Applications requiring the best possible barrier in a paper-based liner, often used for freezer-grade labels. |
Thermal Glassine | A specific grade designed to withstand the heat of thermal transfer printers without releasing gases that can clog print heads. | Labels that require variable information (barcodes, serialization) printed via thermal transfer. |
Decision-Making Flowchart
1. Define Compliance Need: Must meet FDA CFR 21 & USP. → Get supplier LOG/CoA.
2. Assess Barrier Requirement:
Standard moisture/grease resistance? → Standard Glassine.
Enhanced barrier for sensitive drugs? → Clay-Coated or PEGylated Glassine.
Extreme barrier or chemical exposure? → Consider a Film Liner (PET).
3. Determine Application Method:
High-speed automated application? → Prioritize consistent caliper and lay-flat
Manual application? → Focus on cost and ease of use.
4. Consider Printing:
Printing variable data with thermal transfer? → Specify Thermal Glassine.
High-quality graphics? → Clay-Coated Glassine offers superior printability.
5. Prototype and Test: This is the most crucial step. Work with your label converter to run trials. Test:
Die-cutting on your specific label shape.
Dispensing on your automatic applicators.
Label application and adhesion under real-world conditions (sterilization, freezing, etc.).
Partner with Experts
Ultimately, the best way to select the right glassine is to partner closely with two entities:
1. Your Label Converter: They have the technical expertise to recommend materials based on your printing, die-cutting, and application equipment.
2. The Paper Manufacturer (e.g., Xianhe, Heming, Mondi, Sappi, Expera, Nordic Paper): They can provide technical data sheets, compliance documentation, and recommendations based on the end-use environment.
By systematically evaluating these factors—starting with compliance and moving through functionality, conversion, and application—you can reliably select the optimal glassine liner for your medical label application.
Ray
Ferrill
Evelyn