Testing Methods for Pharmaceutical Aluminum Foil: Pinholes, Adhesion, un barjeras īpašības

Pharmaceutical aluminum foil is a crucial packaging material in the medical industry, providing a protective barrier for tablets, kapsulas, ampoules, and other pharmaceutical products. Its performance directly affects the stability, drošību, and shelf life of drugs—any defects or inconsistencies may lead to product contamination, degradation, or failure to meet regulatory standards. Among the key quality indicators of pharmaceutical aluminum foil, pinhole density, adhesion strength, and barrier properties are the most core, which directly determine the foil’s ability to resist external contaminants, maintain product integrity, and adapt to packaging processes. This article details the standardized testing methods, key considerations, and industry requirements for these three core properties, helping manufacturers, quality control teams, and packaging professionals ensure product compliance and excellent quality.

1. Ievads: The Key Role of Pharmaceutical Aluminum Foil Testing

Pharmaceutical packaging is subject to strict global regulations, including the Current Good Manufacturing Practices (cGMP) of the U.S. Pārtikas un zāļu pārvalde (FDA), the European Pharmacopoeia (Ph. Eur.), and the Chinese Pharmacopoeia (ChP). These standards mandate that packaging materials—especially aluminum foil widely used in blister packaging, sachet packaging, and lidding materials—must undergo rigorous testing to verify their performance. Unlike ordinary aluminum foil, pharmaceutical-grade aluminum foil requires extremely high precision; even microscopic defects can compromise the sterility and stability of drugs.

Pinholes, poor adhesion (between aluminum foil layers or with other packaging materials), and insufficient barrier properties are the most common causes of pharmaceutical packaging failure. Pinholes allow moisture, skābeklis, and microorganisms to penetrate; poor adhesion leads to foil delamination or blister rupture; and inadequate barrier properties accelerate drug degradation. Tāpēc, standardized testing of these three properties is a necessary prerequisite for ensuring patient safety and regulatory compliance.

2. Pinhole Testing: Identifying Microscopic Defects

2.1 What Are Pinholes in Pharmaceutical Aluminum Foil?

Pinholes are tiny microscopic pores in aluminum foil, usually with a diameter between 5 μm and 50 μm. They are mostly caused by impurities in raw aluminum, inconsistencies during rolling, or mechanical damage during manufacturing. In pharmaceutical applications, even a single pinhole with a diameter exceeding 20 μm can have serious consequences, as it provides a direct channel for contaminants to enter the packaging.

2.2 Standardized Testing Methods for Pinholes

The most widely adopted standards for pinhole testing in pharmaceutical aluminum foil include ASTM F1864, Iso 16232-2, and Ph. Eur. 2.4.14. The choice of method depends on the foil thickness (typically 20–80 μm for pharmaceutical use) and regulatory requirements. Below are the two most common testing methods:

2.2.1 Transmitted Light Method (Visual Inspection with Magnification)

This method is suitable for thin foils (≤50 μm) and is based on the principle that pinholes allow light to pass through, making them visible under magnification. The steps are as follows:

Sample Preparation: Cut 10–15 specimens of the foil, each measuring 100mm × 100mm. Ensure the samples are free from wrinkles, scratches, or contamination that could mimic pinholes.
Testing Setup: Place each specimen on a light box with a uniform, diffused light source (500–1000 lux). Use a stereomicroscope (10–50× magnification) to inspect the entire surface of the specimen.
Evaluation Criteria: Count the number of pinholes per specimen. Record the diameter of each pinhole using a calibrated reticle. According to Ph. Eur. standards, pharmaceutical aluminum foil must have no pinholes larger than 20 μm, and the total number of pinholes per 100cm² must not exceed 3.

2.2.2 Water Immersion Method (Pressure Test)

This method is more sensitive for thicker foils (>50 μm) or when higher precision is required. It uses pressure to force water through pinholes, making them detectable. The steps are as follows:

Sample Preparation: Cut specimens of 150mm × 150mm and mount them on a waterproof test fixture, ensuring a tight seal around the edges to prevent water leakage.
Testing Setup: Fill the fixture with deionized water and apply a pressure of 0.1–0.2 MPa (1–2 bar) to the water side of the foil. Maintain the pressure for 30 seconds.
Evaluation Criteria: Inspect the dry side of the foil for water droplets. Any droplet indicates a pinhole. Measure the diameter of the pinhole and count the number per specimen. This method can detect pinholes as small as 5 μm, making it ideal for high-sensitivity applications (Piem., sterile drug packaging).

2.3 Key Considerations for Pinhole Testing

Environmental Control: Test in a cleanroom (Class 1000 vai augstāks) to avoid dust or debris interfering with results.
Sample Randomization: Collect samples from different rolls and different positions on each roll to ensure representativeness.
Calibration Requirements: Regularly calibrate the microscope, light box, and pressure gauge to ensure accuracy.

Testing Method	Testing Principle	Applicable Foil Thickness	Detection Precision (Minimum Pinhole)	Core Standards	Operation Difficulty
Transmitted Light Method	Pinholes transmit light, identified by visual inspection with magnification	≤50μm (Thin Foil)	20μm	ASTM F1864, Iso 16232-2, Ph. Eur. 2.4.14	Simple
Water Immersion Method (Pressure Test)	Pressure forces water through pinholes, identified by visual inspection of water droplets	>50μm (Thick Foil)	5μm	ASTM F1864, Iso 16232-2	Vidējs

3. Adhesion Testing: Ensuring Layer Integrity

3.1 The Importance of Adhesion for Pharmaceutical Aluminum Foil

Most pharmaceutical aluminum foils are multi-layered (Piem., alumīnija folija + polymer coating + heat-seal layer) or are laminated to other materials (Piem., PVC, Zeķēt) for blister packaging. Adhesion strength refers to the force required to separate these layers—poor adhesion can lead to delamination during packaging, transports, or use, exposing the drug to contaminants. For heat-sealable lidding foils, adhesion to the blister base (Piem., PVC/PVDC) is also critical to ensure a secure seal that is easy to peel but not prone to accidental rupture.

3.2 Standardized Testing Methods for Adhesion

The primary standards for adhesion testing include ASTM D903, Iso 11339, and GB/T 27708 (Chinese Standard). The two most common methods are the T-peel test and the cross-cut test, depending on the foil structure.

3.2.1 T-Peel Test (For Laminated Foils)

This method measures the peel force required to separate two laminated layers (Piem., aluminum foil and polymer coating) at a 180° angle. It is suitable for multi-layer foils and laminated structures. The steps are as follows:

Sample Preparation: Griezt 5 specimens of 150mm × 25mm. Separate the two layers at one end (approximately 25mm) to create a “tab” for clamping.
Testing Setup: Mount the two tabs of the specimen in the clamps of a universal testing machine (UTM), ensuring the specimen is aligned horizontally and the layers are separated at a 180° angle. Set the testing speed to 100mm/min.
Evaluation Criteria: Run the test until the layers are fully separated. Record the average peel force (in N/25mm) across the entire length of the specimen. According to industry standards, the minimum adhesion strength for pharmaceutical laminated foil is 1.5 N/25mm—values below this indicate poor layer bonding.

3.2.2 Cross-Cut Test (For Coated Foils)

This method is used to evaluate the adhesion of a coating (Piem., heat-seal coating) to the aluminum foil substrate. It involves cutting a grid pattern into the coating and measuring the resistance to peeling. The steps are as follows:

Sample Preparation: Cut a 100mm × 100mm specimen and clean the surface to remove any dirt or oil.
Grid Cutting: Use a cross-cut tool to make 11 parallel cuts (1mm apart) in one direction, then 11 parallel cuts perpendicular to the first set, creating a 10×10 grid of 1mm² squares. Ensure the cuts penetrate the coating but not the aluminum foil substrate.
Peeling Test: Apply a piece of pressure-sensitive tape (Piem., 3M 600 tape) to the grid, press firmly to ensure full contact, then peel the tape off quickly at a 180° angle.
Evaluation Criteria: Inspect the grid for coating detachment. Use the ISO 2409 rating scale (0–5), kur 0 = no detachment and 5 = complete detachment. Pharmaceutical aluminum foil requires a rating of ≤1 to ensure adequate coating adhesion.

3.3 Key Considerations for Adhesion Testing

Testing Speed: The UTM speed must be consistent (100mm/min is standard) to ensure reproducible results.
Temperature Control: Test at 23±2°C and 50±5% relative humidity, as temperature and humidity can affect adhesion strength.
Seal Conditions: For heat-sealable foils, test adhesion after simulating actual packaging conditions (Piem., heat-seal temperature, pressure, and time) to mimic real-world performance.

Testing Method	Testing Principle	Applicable Objects	Core Standards	Evaluation Indicators	Operation Difficulty
T-Peel Test	Peeling at 180° angle to measure the peel force required for separation	Multi-layer laminated aluminum foil (interlayer testing)	ASTM D903, Iso 11339, GB/T 27708	≥1.5N/25mm	Vidējs
Cross-Cut Test	Cutting grid + tape peeling to observe coating detachment	Coated aluminum foil (testing between coating and substrate)	ASTM D903, Iso 11339, GB/T 27708	≤1 (Iso 2409 rating scale)	Simple

4. Barrier Properties Testing: Protecting Against External Contaminants

4.1 The Role of Barrier Properties in Pharmaceutical Packaging

Pharmaceutical aluminum foil must act as an effective barrier against three key contaminants: skābeklis, mitrums, un gaisma. Oxygen and moisture can cause oxidation, hydrolysis, and microbial growth in medications, while light (especially UV light) can degrade photosensitive drugs (Piem., antibiotics, vitamins). The barrier performance of aluminum foil is determined by its ability to resist the transmission of these substances, and it is one of the most critical quality indicators for long-shelf-life drugs.

4.2 Standardized Testing Methods for Barrier Properties

The main standards for barrier testing include ASTM D3985 (Skābekļa pārraides ātrums), ASTM E96 (Moisture Vapor Transmission Rate), and ISO 15105-1 (Light Transmission Rate). Below are the testing methods for the three key barrier properties:

4.2.1 Skābekļa pārraides ātrums (OTR) Testing

OTR measures the amount of oxygen that passes through a unit area of foil per unit time, expressed in cm³/(m²·day·atm). For pharmaceutical foil, a low OTR (≤0.01 cm³/(m²·day·atm)) is required to prevent drug oxidation. The method uses a Gas Transmission Analyzer (GTA) and follows ASTM D3985:

Sample Preparation: Cut a 100mm × 100mm specimen and mount it in the GTA’s test cell, ensuring a tight seal to prevent gas leakage.
Testing Setup: Fill one side of the test cell with pure oxygen (O₂) and the other side with nitrogen (N₂) carrier gas. The O₂ that passes through the foil is carried by the N₂ to a detector (Piem., coulometric detector).
Evaluation Criteria: Run the test until the OTR reading stabilizes (typically 24–48 hours). Record the average OTR value. Pharmaceutical aluminum foil must have an OTR of ≤0.01 cm³/(m²·day·atm) to meet regulatory requirements.

4.2.2 Moisture Vapor Transmission Rate (MVTR) Testing

MVTR measures the amount of moisture vapor that passes through the foil, expressed in g/(m²·day). A low MVTR (≤0.1 g/(m²·day)) is critical to prevent drug hydrolysis. The method follows ASTM E96 (Gravimetric Method) or ASTM F1249 (Electrolytic Detection Method):

Sample Preparation: Cut a specimen and mount it on a cup containing a desiccant (Piem., calcium chloride) or water, depending on the test method.
Testing Setup: For the gravimetric method, place the cup in a controlled environment (23±2°C, 50±5% relative humidity) and weigh it daily to measure the change in mass (due to moisture absorption or loss).
Evaluation Criteria: Calculate the MVTR based on the mass change, specimen area, and test duration. Pharmaceutical aluminum foil must have an MVTR of ≤0.1 g/(m²·day) to ensure adequate moisture protection.

4.2.3 Light Transmission Rate Testing

This test measures the amount of light (especially UV light, 200–400 nm) that passes through the foil. Pharmaceutical aluminum foil is typically opaque, with a light transmission rate of ≤0.1% to protect photosensitive drugs. The method uses a spectrophotometer and follows ISO 15105-1:

Sample Preparation: Cut a 50mm × 50mm specimen and place it in the spectrophotometer’s sample holder.
Testing Setup: Measure the light transmission across the visible (400–760 nm) and UV (200–400 nm) ranges.
Evaluation Criteria: Record the maximum light transmission rate. Pharmaceutical aluminum foil must have a UV transmission rate of ≤0.1% to meet the requirements for photosensitive drug packaging.

4.3 Key Considerations for Barrier Properties Testing

Environmental Stability: Test at standard conditions (23±2°C, 50±5% RH) to ensure consistency with industry standards.
Sample Thickness: Biezāka folija (≥50 μm) typically has better barrier properties, but testing must still be performed to verify compliance.
Lamination Impact: Multi-layer foils (Piem., alumīnija + PVDC) have superior barrier properties, but adhesion between layers can affect OTR/MVTR—ensure adhesion testing is paired with barrier testing.

Testing Item	Core Testing Standards	Key Indicator Requirements	Applicable Scenarios
Pinhole Testing	ASTM F1864, Iso 16232-2, Ph. Eur. 2.4.14	1. Pinhole diameter ≤20μm; 2. Total pinholes ≤3 per 100cm²; 3. ≤5μm for high-sensitivity scenarios	Plāna folija (≤50μm), thick foil (>50μm), sterile drug packaging
Adhesion Testing	ASTM D903, Iso 11339, GB/T 27708	1. T-Peel Test ≥1.5N/25mm; 2. Cross-Cut Test ≤1 (Iso 2409)	Laminated aluminum foil (interlayer testing), pārklāta alumīnija folija (coating-substrate testing), heat-sealable lidding materials
Barrier Properties Testing	ASTM D3985 (Skābekļa pārraides ātrums)	OTR ≤0.01cm³/(m²·day·atm)	All types of pharmaceutical aluminum foil packaging requiring oxidation resistance
	ASTM E96, ASTM F1249 (Moisture Vapor Transmission Rate)	MVTR ≤0.1g/(m²·day)	All types of pharmaceutical aluminum foil packaging requiring moisture resistance and hydrolysis prevention
	Iso 15105-1 (Light Transmission Rate)	UV transmission rate ≤0.1%	Packaging for photosensitive drugs (antibiotics, vitamins, utt.)

5. Regulatory Compliance and Quality Control Best Practices

For pharmaceutical aluminum foil, testing is not just a quality control measure—it is a regulatory requirement. Below are best practices to ensure compliance and consistent performance:

Establish a Comprehensive Testing Program: Test pinholes, adhesion, and barrier properties for every production batch. Use random sampling to ensure representativeness.
Adopt International Standards: Align testing methods with ASTM, Iso, and Pharmacopoeia standards to ensure global compliance (critical for exporters).
Invest in Calibrated Equipment: Regularly calibrate microscopes, UTMs, GTAs, and spectrophotometers to ensure accurate results. Maintain calibration records for regulatory audits.
Train Quality Control Teams: Ensure staff are trained in standardized testing methods, sample preparation, and result interpretation to avoid human error.
Document Everything: Maintain detailed records of test results, sample information, equipment calibration, and corrective actions (if defects are found). Documentation is critical for regulatory audits.

6. Secinājums

Pharmaceutical aluminum foil testing—focused on pinholes, adhesion, and barrier properties—is essential to ensuring the safety, stability, and efficacy of pharmaceutical products. By following standardized testing methods, adhering to regulatory requirements, and implementing robust quality control practices, manufacturers can minimize packaging failures, protect patient safety, and maintain compliance with global standards.

As the pharmaceutical industry evolves, the demand for high-performance aluminum foil will continue to grow—along with the need for precise, reliable testing. By prioritizing these three core properties, packaging professionals can ensure that pharmaceutical aluminum foil meets the rigorous demands of modern healthcare.

7. Bieži uzdotie jautājumi (FAQ)

Q1: Must both the Transmitted Light Method and Water Immersion Method be used for pinhole testing of pharmaceutical aluminum foil?

No need to use both; select based on foil thickness: Transmitted Light Method for thin foil (≤50μm), Water Immersion Method for thick foil (>50μm) or high-sensitivity scenarios. For mass production, use the Transmitted Light Method for routine screening first, and recheck unqualified batches with the Water Immersion Method.

Q2: Is the 1.5N/25mm standard for the T-Peel Test applicable to all pharmaceutical laminated aluminum foils?

This is the minimum requirement, which needs to be adjusted according to the application: adhesion for blister lidding materials is controlled at 1.5-3.0N/25mm (balancing seal and easy peeling), and can be increased to above 3.0N/25mm for sachet packaging, ultimately complying with GB/T 27708 and customer requirements.

Q3: Do ambient temperature and humidity have a significant impact on the results of barrier properties testing?

The impact is significant; oxygen and moisture vapor transmission rates increase with rising temperature and humidity. Testing must be strictly conducted under standard conditions (23±2°C, 50±5% RH) with parameters noted; additional comparison testing at 40°C and 75% RH can be performed for high-temperature and high-humidity areas.

Q4: What are the common corrective measures for unqualified pharmaceutical aluminum foil testing?

Targeted corrections: ① Unqualified pinholes: Check raw aluminum purity, rolling process and equipment, and strengthen sampling testing; ② Unqualified adhesion: Optimize coating formula and adjust lamination/heat-sealing parameters; ③ Unqualified barrier properties: Check foil thickness and laminated layers, and replace with high-quality substrates.

Q5: What are the core differences between international standards (ASTM, Iso) and Chinese Pharmacopoeia (ChP) testing requirements?

Core requirements are consistent, with differences in details: ASTM and ISO focus on test operability and precision, while ChP and GB/T 27708 are combined with domestic industry practices. Export products must comply with international standards of the target market, and domestic products must meet both ChP and GB standards.

Par mums

We are a leading supplier of high-quality pharmaceutical aluminum foil, committed to delivering products that meet the strictest regulatory standards and quality requirements. Our foil is manufactured using premium raw materials, advanced rolling and lamination technologies, and undergoes rigorous testing for pinholes, adhesion, Barjeru īpašības, and other critical indicators. With a focus on quality, piemērotība, and customer satisfaction, we provide tailored packaging solutions for pharmaceutical manufacturers worldwide. Contact us today to learn more about our pharmaceutical aluminum foil products and quality assurance processes.

Testing Methods for Pharmaceutical Aluminum Foil: Pinholes, Adhesion, un barjeras īpašības