Problems and Process Improvement of Coating Brittleness in Pharmaceutical Aluminum Foil

Pharmaceutical aluminum foil is a critical material in drug packaging, widely used in blister packaging for solid dosage forms and sealing of infusion containers due to its excellent barrier properties, sealing performance, และความปลอดภัย. The quality of the coating directly affects the storage stability, usage safety, and packaging compliance of pharmaceuticals. Coating brittleness, one of the most common quality defects in the production and application of pharmaceutical aluminum foil, not only compromises barrier performance, leading to moisture absorption, ออกซิเดชัน, and contamination of drugs, but may also introduce safety hazards due to the detachment of coating fragments.

1. Problem Characterization and Hazards of Coating Brittleness

1.1 Forms of Brittleness

Brittleness primarily manifests as cracks, detachment, or powdering of the coating at different stages, which can be categorized into three types:

1.1.1 Brittleness During Production

Surface cracks appear immediately after coating and curing, or brittleness occurs at the edges during slitting or winding due to tension.

1.1.2 Brittleness During Storage and Transportation

Brittleness occurs due to temperature and humidity fluctuations or external pressure, potentially accompanied by substrate damage.

1.1.3 Brittleness During Usage

The coating easily detaches, ผง, or even tears off in sheets during blister punching or patient opening.

According to General Rule 4055 of the ตำรับยาจีน2025 Edition, brittleness directly results in burst strength falling below the standard requirement (≥98 kPa). Brittle samples often exhibit burst strengths below 60 ปาสคาล, while water vapor and oxygen transmission rates are prone to exceed limits, compromising drug protection.

โต๊ะ 1: Main Characteristics and Impacts of Coating Brittleness in Pharmaceutical Aluminum Foil

1.2 Main Hazards of Brittleness

1.2.1 Drug Safety Risks

Coating fragments may contaminate drugs; reduced barrier properties can lead to moisture absorption, ออกซิเดชัน, and degradation, particularly affecting light-sensitive and hygroscopic drugs. Studies show that packaging with brittle defects can increase drug moisture content by an average of 2.3% หลังจาก 6 months of accelerated testing (40°C/75% RH), exceeding pharmacopoeial standards.

1.2.2 Compliance and Quality Risks

Coating brittleness is a severe quality defect that fails to meet standards such as the ตำรับยาจีนและ Pharmaceutical Aluminum Foil(YBB00152002-2015), potentially resulting in product registration failure, GMP audit non-conformity, การเรียกคืนผลิตภัณฑ์, and administrative penalties. Since the implementation of the associated review system, ประมาณ 18% of aluminum foil manufacturers have been eliminated due to coating quality issues.

1.2.3 Economic and Brand Risks

Increased scrap rates raise production costs; quality issues damage corporate reputation and customer relationships. Under the pressure of green procurement mechanisms, companies with poor quality face marginalization in the market.

2. Cause Analysis of Coating Brittleness

The causes of brittleness involve multiple factors, including raw materials, กระบวนการ, pretreatment, และสภาพแวดล้อม, all of which are interrelated.

โต๊ะ 2: Key Cause Analysis of Coating Brittleness in Pharmaceutical Aluminum Foil

2.1 Inadequate Raw Material Compatibility

2.1.1 Aluminum Foil Substrate Defects

Substrates (เช่น., 8011, 8021 โลหะผสม) with low purity, high impurities, ความเรียบไม่ดี, or excessive thickness tolerance (>±2 ไมโครเมตร) can lead to uneven coating and stress concentration. Surface oil stains or excessively thick oxide layers also reduce coating adhesion.

2.1.2 Improper Coating Resin Selection

Common resins (เช่น., อะคริลิค, polyurethane, อีวา) with poor flexibility, excessively high glass transition temperatures (เช่น., >50องศาเซลเซียส), or broad molecular weight distribution can result in high brittleness after curing. Melt flow index fluctuations of heat-seal resins exceeding ±15% also increase brittleness risk.

2.1.3 Improper Additive Usage

Inappropriate amounts of plasticizers, poor compatibility between additives and resins, and high solvent residues can affect coating cohesion and flexibility, leading to cracking.

2.2 Unreasonable Production Process Parameters

2.2.1 Coating Parameter Deviations

Improper control of coating speed, ความหนา, or doctor blade pressure can result in uneven coating thickness (ส่วนเบี่ยงเบน >±3%). Excessively thick coatings are prone to internal stress due to inconsistent shrinkage, while overly thin coatings fail to form a complete protective layer.

2.2.2 Poor Curing Process Control

Excessively high temperatures or prolonged times in hot air curing can over-crosslink the coating, making it brittle; insufficient temperature or time leads to incomplete curing and low strength. Improper UV intensity or exposure time can cause uneven curing or localized overheating.

2.2.3 Improper Slitting and Winding

Excessive slitting speed or tension can cause edge cracking; excessive winding tension places the coating under continuous tensile stress, making it prone to brittleness during storage.

2.3 Insufficient Substrate Pretreatment

Poor surface cleanliness and roughness significantly affect coating adhesion. Superficial cleaning without chemical degreasing or electrochemical oxidation leaves oil and dust residues, weakening coating adhesion. Insufficient surface roughness (surface energy <35 mN/m) also hinders adequate wetting and spreading of the coating.

2.4 Environmental Factors

Production temperatures below 15°C or humidity above 80% can affect coating leveling and curing efficacy. Extreme temperature and humidity fluctuations during storage and transportation create thermal stress due to mismatched coefficients of thermal expansion between the foil and coating. Physical impacts or compression can directly cause brittleness. Poor production environment cleanliness allows dust particles to create stress concentration points, accelerating brittleness.

3. Process Improvement Measures for Coating Brittleness

โต๊ะ 3: Key Control Parameters for Pharmaceutical Aluminum Foil Process Improvement

3.1 Optimizing Raw Material Selection and Control

3.1.1 Strict Substrate Selection

Use high-purity, low-impurity 8011/8021 alloys with thickness tolerance controlled within ±2 μm and surface tension ≥31 mN/m. For high-demand products, substrates with thickness ≥0.030 mm can be selected, with pinhole rates below 0.1 ต่อตารางเมตร.

3.1.2 Optimizing Resin and Additive Selection

Select resins with moderate glass transition temperatures (20–40°C) and uniform molecular weight distribution. Water-based or UV-curable resins are recommended to replace solvent-based types. Melt flow index variation of heat-seal resins should be ≤±10%. Optimize additive formulations, such as using plasticizers to improve flexibility and silane coupling agents to enhance adhesion, ensuring additive compatibility.

3.1.3 Establishing Raw Material Inspection Mechanisms

Strengthen incoming inspection, monitoring resin flexibility, molecular weight distribution, substrate cleanliness, ความหยาบ, เป็นต้น, to prevent unqualified materials from entering production.

3.2 Optimizing Production Process Parameters

3.2.1 Precise Coating Process Control

Control coating speed at 10–15 m/min, doctor blade pressure at 0.1–0.3 MPa, and coating weight at 2–5 g/m², ensuring thickness uniformity deviation ≤±3%. Regularly maintain equipment to ensure coating uniformity.

3.2.2 Optimizing Curing Process Parameters

Hot air curing should be controlled at 80–100°C for 3–5 minutes with uniform air velocity of 1–2 m/s; UV curing intensity should be 80–120 mJ/cm² for 1–2 seconds. Monitor and adjust parameters in real-time.

3.2.3 Improving Slitting and Winding Processes

Slitting speed should be 5–10 m/min, winding tension controlled at 50–100 N using constant tension winding. Allow wound coils to rest for 24–48 hours to release internal stress. Heat-sealing temperature fluctuations should be controlled within ±1°C.

3.3 Strengthening Substrate Pretreatment Processes

Implement a full-process pretreatment of “chemical degreasing – water rinsing – electrochemical oxidation – water rinsing – drying.” การล้างไขมัน (50–60°C, 1–2 minutes) removes oils; electrochemical oxidation (10–15 V, 30–60 seconds) improves surface roughness and activity; use deionized water for rinsing; drying (80–90°C, 2–3 minutes) ensures surface dryness. Post-treatment substrate surface tension should be ≥35 mN/m.

3.4 Enhancing Environmental Control

3.4.1 Controlling the Production Environment

Maintain workshop temperature at 20–25°C, relative humidity at 50%–60%, and cleanliness at Grade D standards to reduce dust contamination.

3.4.2 Optimizing Storage and Transportation Conditions

Store finished products in a cool (15–25°C), แห้ง (ความชื้น ≤60%), and ventilated warehouse, avoiding direct sunlight and excessive stacking. Use shockproof and moisture-proof packaging during transportation, avoiding extreme temperature/humidity fluctuations and mechanical impacts.

3.5 Improving Quality Inspection Systems

3.5.1 Establishing Full-Process Inspection Mechanisms

Perform online monitoring of coating thickness and uniformity; test finished products for flexibility, การยึดเกาะ, burst strength (≥98 kPa), อัตราการส่งผ่านไอน้ำ (≤0.5 g/(ตรม.·24ชม)), เป็นต้น.

3.5.2 Utilizing Professional Testing Equipment

Equip with pharmacopoeia-compliant burst testers (เช่น., NPD-01บี), use headspace gas chromatography for solvent residue testing, and employ microscopes to observe coating microstructure.

3.5.3 Establishing Quality Traceability and Stability Testing Systems

Create batch quality records for full traceability. Conduct regular stability tests to evaluate coating performance under different environmental conditions.

4. Verification of Improvement Effectiveness and Industry Trends

4.1 Example of Improvement Effectiveness

After implementing the above improvements, a company achieved a 30% increase in coating flexibility, ก 25% improvement in adhesion, coating thickness uniformity deviation ≤±2%, curing completion rate >99%, and substrate pretreatment qualification rate of 100%. The scrap rate due to brittleness decreased from 8.5% ไปด้านล่าง 0.3%, and product qualification rate reached 99.7%, with burst strengths meeting pharmacopoeial requirements. By switching to water-based coatings, VOC emissions were reduced by over 80%, successfully entering the supply chain of leading pharmaceutical companies.

โต๊ะ 4: Comparison of Key Indicators Before and After Process Improvement in a Company

4.2 Industry Development Trends

4.2.1 Greening of Coating Technologies

Water-based, UV-curable, and electron beam-curable coatings with low or zero VOCs will gradually replace solvent-based products.

4.2.2 Functional Development Towards Precision and Intelligence

Coatings are evolving towards intelligent anti-counterfeiting, one-item-one-code traceability, dynamic light protection, and smart sensing to meet the protective needs of highly active drugs.

4.2.3 Deepening Industry Regulations

เดอะ ตำรับยาจีนstandards continue to advance, with testing extending towards microstructure, chemical characterization, and biocompatibility, driving process and quality control upgrades in enterprises.

5. บทสรุป

Coating brittleness in pharmaceutical aluminum foil is a quality defect caused by multiple factors, including raw materials, กระบวนการ, pretreatment, และสภาพแวดล้อม, posing threats to drug safety, corporate compliance, and economic interests. By systematically optimizing raw materials, precisely controlling process parameters, strengthening substrate pretreatment, strictly controlling environmental conditions, and improving quality inspection systems, the risk of brittleness can be effectively eliminated, enhancing product reliability.

ในอนาคต, enterprises should follow industry trends towards greening, ความแม่นยำ, and functionalization, increase R&D investment, continuously advance process upgrades, strictly adhere to pharmacopoeia and related standards, and improve quality management systems to ensure drug safety with high-quality products and elevate the overall industry level.