How to control solvent residues within the standard for food-coated aluminum foil?

Food Coated Aluminum Foil, due to its advantages in barrier properties, heat sealability, និងសុវត្ថិភាព, ត្រូវបានគេប្រើយ៉ាងទូលំទូលាយក្នុងការវេចខ្ចប់អាហារ. Its solvent residues mainly originate from organic solvents (such as ethyl acetate, methyl ethyl ketone, alcohols, ស៊េរី benzene, ល។) used in coating, ការបោះពុម្ព, និងដំណើរការ lamination. Exceeding limits can contaminate food, affect sensory quality, and even harm health. Controlling solvent residues requires closed-loop management across the entire chain—from source formula, process control, and environmental management to testing verification—ensuring compliance with standards like ជីវ៉ាបី 31604.60-2024 (Total residual ≤5.0 mg/m², benzene series undetectable).

ខ្ញុំ. Sources and Hazards of Solvent Residues

1. Primary Sources
   • Coating/Printing Process:​ Diluent solvents (អេទីលអាសេតាត, ethanol, methyl ethyl ketone, តូលូអ៊ីន, ល។) from solvent-based coatings and inks, incompletely volatilized, remain in the coating/ink layer.
   • ដំណើរការស្រទាប់:​ Solvents from dry bond adhesives, and solvents secondarily introduced during lamination.
   • Materials and Environment:​ Impurities inherent in raw/auxiliary materials, solvent contamination in workshop air, and solvent entrapment due to insufficient drying.
2. Core Hazards
   • Food Safety Risks:​ Benzene series (benzene, តូលូអ៊ីន, xylene) are carcinogenic and neurotoxic; residual esters/ketones may migrate into food, causing off-odors and spoilage.
   • Regulatory Compliance Risks:​ Non-compliance with standards like ជីវ៉ាបី 31604.60-2024, ជីវ៉ាបី 9685-2016, leading to product recalls and penalties.
   • Production and Quality Risks:​ Excessive residue can cause poor coating adhesion, weak heat seals, and product odor, affecting market competitiveness.

II. ការគ្រប់គ្រងប្រភព: Eliminating Residue Risks from Formula and Materials

1. Solvent Selection: Low Residue, High Volatility, ភាពបរិសុទ្ធខ្ពស់។
   • Prioritize low-boiling-point, high-volatility solvents:​ Prefer អេទីលអាសេតាត (b.p. 77°C), ethanol (78°C), isopropyl alcohol (82°C)​ over high-boiling-point (ឧ។, cyclohexanone, តូលូអ៊ីន) and high-affinity solvents to reduce residue risk.
   • Strictly control solvent purity:​ Use electronic grade/food grade solvents. Ethyl acetate purity ≥99.9%, water content <0.05%, alcohol impurities <1000 ppm. Prohibit benzene series and high-boiling-point impurities.
   • Ban/Restrict high-risk solvents:​ Strictly prohibit benzene, តូលូអ៊ីន, xylene, ល។. Restrict high-boiling-point, difficult-to-volatilize solvents like methyl ethyl ketone, cyclohexanone. If necessary, optimize drying processes.
2. Coating/Ink/Adhesive Selection: Low Solvent, High Release
   • Select high-solid, low-solvent formulas:​ Coatings/adhesives with solid content ≥40% reduce solvent use. Prioritize water-based, solvent-free, UV-curing​ systems to eliminate solvent residues at source.
   • Select materials with high solvent release:​ Prefer polyester-based adhesives (better solvent release than polyolefin-based). Choose alcohol-soluble, water-based, benzene-free ink systems to avoid strong hydrogen bonding with solvents.
   • Strictly control raw/auxiliary material residues:​ Incoming inspection of សន្លឹកអាលុយមីញ៉ូម ស្រទាប់ខាងក្រោម, ថ្នាំកូត, ទឹកថ្នាំ, adhesives for solvent residues. Reject unqualified materials.
3. Formula Optimization: Reduce Solvent Dependence
   • Reduce working concentration:​ Control coating/adhesive working concentration at 30%-35%​ to reduce solvent use while ensuring coating uniformity.
   • Add volatilization aids:​ Add appropriate amounts of high-volatility, low-residue co-solvents (ឧ។, អាសេតូន, isopropyl acetate) to lower the boiling point via azeotropic effect and accelerate volatilization.
   • Optimize coating/ink layer thickness:​ Control coating weight (dry basis: 3-5 ក្រាម / មការ៉េ) and printing ink thickness to reduce solvent entrapment and improve drying efficiency.

III. ការគ្រប់គ្រងដំណើរការ: Precise Management of Drying and Lamination

1. Coating/Printing Drying: Gradient Heating + High Airflow + Slight Negative Pressure (ដំណើរការស្នូល)(1) Drying Temperature Profile: Gradient heating to avoid “skin formation”

   ប្រើ three-stage gradient drying​ to balance solvent removal and coating quality:

   • ដំណាក់កាល 1 (Leveling Zone):​ 50-60°C, high air speed. Low temperature, high airflow removes >60% ការដោះស្រាយផ្នែកខ្លះ, preventing surface skinning and internal solvent entrapment.
   • ដំណាក់កាល 2 (Constant-Rate Drying Zone):​ 70-85°C, gradual temperature increase. Maintains open internal diffusion channels for efficient, continuous volatilization.
   • ដំណាក់កាល 3 (Intensive Drying Zone):​ 85-100°C (near resin softening point), high temperature and airflow. Breaks solvent molecular bonds for complete removal.(2) Air Speed and Pressure: High Airflow + Slight Negative Pressure for Enhanced Mass Transfer
   • Air Speed Control:​ Air nozzle speed ≥15 m/s. Prioritize increasing airflow over just raising temperature (airflow has a more significant effect on ethyl acetate evaporation efficiency).
   • Air Pressure Control:​ Maintain slight negative pressure​ in oven (exhaust volume > intake volume). Install exhaust fans to promptly remove volatilized solvents, avoiding re-condensation and re-absorption.
   • Nozzle Optimization:​ Nozzles close to foil surface (5-10 mm gap). Use impingement-type nozzles to enhance heat exchange and solvent volatilization.(3) Line Speed Matching: Dynamic Adaptation to Drying Capacity
   • Adjust line speed based on coating thickness, solvent type, oven temperature/airflow​ to ensure drying time ≥3-5 minutes for sufficient solvent removal.
   • Avoid blindly increasing speed, which leads to incomplete drying and residue exceedance.
2. ដំណើរការស្រទាប់: Secondary Drying + Curing Control
   • Secondary drying before lamination:​ Add a 80-90°C​ secondary oven before lamination to remove residues from coating/printing, reducing carry-over into lamination.
   • Lamination roll temperature:​ Control at 55-70°C to promote adhesive activation/bonding and assist solvent volatilization.
   • Curing Process:​ Curing temperature 45-55°C, ពេលវេលា 24-48 ម៉ោង. Promotes adhesive cross-linking and releases residual solvents. Ensure good curing room ventilation to prevent solvent accumulation.
3. Equipment Maintenance: Prevent Cross-Contamination and Residue Buildup
   • Oven Cleaning:​ Regularly clean ovens, nozzles, exhaust ducts of tar and debris to prevent airflow blockage, and avoid old solvent contamination of new coatings.
   • Roll Cleaning:​ Regularly clean coating rolls, lamination rolls, guide rolls to prevent solvent/coating residue contamination on the foil.
   • Solvent Delivery System:​ Use dedicated pipelines and sealed storage tanks to prevent solvent volatilization, leakage, and cross-contamination.

ចវិវចេញព្រោះផ្លើនៅ. Environment and Process Management: Minimize External Interference

1. Workshop Environment Control
   • សីតុណ្ហភាព & Humidity:​ Temperature 20-25°C, Humidity 40-60%. High humidity reduces solvent volatilization efficiency; low humidity causes static and affects coating.
   • ការធេវីអាេយមានខ្យល់:​ Enforced workshop ventilation, air changes ≥10 times/hour. Install solvent recovery/purification systems to lower ambient solvent concentration and prevent re-adsorption.
   • Zoning Management:​ Isolate coating, ការបោះពុម្ព, lamination, and curing areas to prevent cross-contamination between processes.
2. Process Monitoring and Documentation
   • ការត្រួតពិនិត្យតាមអ៊ីនធឺណិត:​ Install online monitors for oven temperature, air speed, សម្ពាធ, solvent concentration. Real-time monitoring with automatic alarms for abnormalities.
   • Batch Records:​ Document each batch’s solvent type, ភាពបរិសុទ្ធ, working concentration, ទម្ងន់ថ្នាំកូត, drying parameters (temp/speed/time), line speed, curing parameters. Achieve full traceability.
   • Personnel Management:​ Operators receive professional training. Strictly follow process parameters. Unauthorized adjustments to temperature, air speed, line speed are prohibited.

ផាន់ខ. Testing Verification: Accurate Determination, Closed-Loop Improvement

1. Testing Standards and Limits
   • Core Standards: ជីវ៉ាបី 31604.60-2024​ (Headspace Gas Chromatography, detects 25 សារធាតុរំលាយ), GB / T 10004-2008.
   • Limit Requirements:​ Total solvent residue ≤ 5.0 mg / m²; Benzene, តូលូអ៊ីន, xylene, ល។. (ស៊េរី benzene) undetectable​ (detection limit <0.01 mg / m²); Single solvent (ឧ។, អេទីលអាសេតាត) ≤30 mg/m².
2. វិធីសាស្រ្តសាកល្បង (Headspace Gas Chromatography HS-GC)
   1. ការរៀបចំគំរូ:​ Cut 50 cm² sample into 5 mm x 5 mm pieces, place in headspace vial, ត្រា.
   2. Headspace Equilibration:​ Equilibrate at 80°C ±1°C for 30 minutes to volatilize residual solvents into gas phase.
   3. Chromatographic Analysis:​ DB-624 capillary column, FID detector, quantification by external/internal standard method.
   4. Result Judgment:​ Pass if total and benzene series residues meet limits. Fail entire batch if any limit is exceeded.
3. Testing Frequency and Control
   • ការត្រួតពិនិត្យចូល:​ Test solvent residue for each batch of raw/auxiliary materials. Use only if qualified.
   • In-process Sampling:​ Sample online product every 2 hours to monitor drying effectiveness and adjust process promptly.
   • ការត្រួតពិនិត្យចុងក្រោយ (100%):​ Test every finished product batch. Ship only if qualified. Isolate, rework, or scrap non-conforming products.
   • Third-Party Verification:​ Periodically send samples to third-party labs (ឧ។, Customs Technology Center, professional testing institutes) to ensure accurate, compliant results.

VI. Common Issues and Solutions

VII. Key Process Parameter Control Table

VIII. Summary and Long-Term Control

Achieving compliant solvent residue levels in food coated aluminum foil is a systematic project. Adhere to the principles of “strict source control, precise process control, rigorous testing judgment, and continuous improvement”:

1. Prioritize low-residue raw/auxiliary materials like water-based/solvent-free/UV systems to reduce solvent use at source.
2. Optimize the three-stage gradient drying process, achieving efficient solvent volatilization through “high airflow + slight negative pressure + precise temperature control”.
3. Establish a full-process testing system, strictly enforce national standard limits, ensuring every batch is compliant.
4. Continuously optimize processes, ឧបករណ៍, and management to establish a long-term mechanism for solvent residue control, ensuring food packaging safety and enhancing product market competitiveness.