Precise Definition and Multi-Dimensional Classification Analysis of Aluminum Foil Pinholes

HW-A. Definition of Aluminum Foil Pinholes: From General Standards to Industry-Specific Requirements

The definition of अॅल्युमिनियम फॉइल pinholes is not a single standard; it must be comprehensively defined based on basic material standards, international specifications, and industry-specific needs. The core lies in the size, morphology, and risk correlation of “penetrating holes”. The specific differences are as follows:

(ए) Definitions in General Material Standards (Basic Common Requirements)

Standard Code	Issuing Authority	Core Definition of Pinholes	Dimensional Control Threshold	Testing Method Requirements
GB/T 3198-2020	Standardization Administration of China (SAC)	Tiny holes penetrating the entire thickness of aluminum foil, requiring distinction between “acceptable defects” आणि “unacceptable defects”	Holes with diameter ≥20μm are controlled defects; holes with diameter ≥50μm are not allowed	Offline metallographic microscope method (500x magnification), online laser scanning method
ASTM B479-22	American Society for Testing and Materials (ASTM)	Penetrating open defects on the aluminum foil surface, requiring recording of “number of holes per unit area” आणि “maximum hole size”	Holes with diameter ≥25μm need to be counted; holes with diameter ≥60μm are deemed unqualified	Visual inspection (aided by 10-50x magnifying glass), image analysis method
मध्ये 546-2:2021	European Committee for Standardization (CEN)	Continuous holes penetrating the thickness of aluminum foil, excluding “non-penetrating defects such as indentations and scratches”	Holes with diameter ≥20μm need to be counted; holes with diameter ≥40μm require position marking	Backlight detection method (light intensity 500-800lux), laser diameter measurement method
JIS H4160:2020	Japanese Industrial Standards Committee (JISC)	Tiny holes penetrating both sides of aluminum foil, requiring verification of penetrability through “light transmittance” (not surface depressions)	Holes with diameter ≥15μm need to be counted; holes with diameter ≥45μm are unqualified	Light transmittance method (resolution 10μm), electron microscope method

Key Differences:

Dimensional Threshold: China/Europe have the strictest requirements (control starts at 20μm), while the US is slightly more lenient (control starts at 25μm);

Judgment Logic: GB/T 3198-2020 clearly defines “diameter 50μm as an absolute forbidden zone” for the first time, while ASTM B479-22 allows a small number of pinholes below 60μm (≤3 holes/m²).

(B) Industry-Specific Definitions (Risk-Adapted)

Different application fields further refine the definition of aluminum foil pinholes based on “safety and functional requirements”, with the core being “size + risk correlation”:

Pharmaceutical Packaging Industry (Most Stringent)

- According to YBB 00152002-2015 Aluminum Foil for Pharmaceutical Packaging (China Pharmaceutical Packaging Material Standard):

Aluminum foil pinholes are defined as “penetrating holes that may cause microbial intrusion or content leakage”. Even “micro-pinholes” with a diameter of 10-20μm must meet the requirement of “density ≤3 holes/m²” (compared to ≤10 holes/m² for ordinary aluminum foil);
Special Requirement: For aluminum foil used in sterile pharmaceutical packaging (उदा., PTP aluminum-plastic blisters), एक “integrity test” (उदा., dye penetration method) is required. Any detectable pinhole (even with diameter <10μm) is deemed unqualified.

Food Packaging Industry (Category-Based Control)

- High Oxygen-Sensitive Foods (chilled fresh meat, शिजवलेले अन्न): Referring to the Examination Rules for Production Licensing of Plastic Packaging, Containers, Tools and Other Products for Food Contact, aluminum foil pinholes are defined as “penetrating defects that cause oxygen transmission rate (ओटीआर) to exceed 1.0cc/(m²·24h·atm)”. Corresponding pinholes with diameter ≥30μm must be strictly prohibited;

- Ordinary Foods (खाद्यपदार्थ, dried foods): Pinholes with diameter ≤40μm are allowed, but the density must be ≤8 holes/m² (to avoid food oxidation and discoloration caused by light transmission).

Electronic Packaging Industry (Moisture-Proof Oriented)

- According to IPC/JEDEC J-STD-033B (Moisture-Proof Packaging Standard for Electronic Components):

Aluminum foil pinholes are defined as “holes that cause water vapor transmission rate (डब्ल्यूव्हीटीआर) to exceed 0.1g/(m²·24h)”. The pinhole size is inferred through WVTR testing—pinholes with diameter ≥20μm will cause WVTR to exceed the standard. त्यामुळे, pinholes with diameter ≥20μm must be controlled, with a density ≤5 holes/m².

HW-B. Classification of Aluminum Foil Pinholes: Based on Formation Mechanisms and Influencing Factors

The core of classifying aluminum foil pinholes is to “trace the source”. Different types of pinholes vary significantly in morphology, distribution, and risk level, and can be divided into production-stage pinholes (प्रती लेखा 90%) आणि application-stage pinholes (accounting for less than 10%), as detailed below:

(ए) Production-Stage Pinholes: Formed During Aluminum Foil Manufacturing (Core Control Category)

1. Raw Material-Based Pinholes (Accounting for 35% of Production-Stage Pinholes)

Definition: Penetrating holes formed after rolling due to impurities and defects in aluminum ingots and pre-rolling billets, classified as “innate defects”.
Detailed Causes and Quantitative Impact:

Defect Type	Specific Source	Morphological Characteristics of Pinholes	Incidence Correlation (Impurity Content vs. Pinhole Density)	Typical Case
Metal Impurity-Type	Unremoved impurities (फे, आणि, कु, इ.) in aluminum ingots	Irregular hole edges, often accompanied by residual metal particles	When Fe content increases from 0.3% करण्यासाठी 0.5%, pinhole density increases from 5 holes/m² to 18 holes/m² (data from Light Alloy Processing Technology, 2023)	An aluminum foil factory used 1235 aluminum ingots with Fe content of 0.45% to roll 0.006mm aluminum foil, resulting in a pinhole density of 22 holes/m²
Non-Metal Impurity-Type	Oxides, carbides mixed in during aluminum ingot melting	Holes are “irregular polygons” with rough inner walls	When oxide content >0.05%, the incidence of pinholes increases by 40%	Insufficient purity of protective gas (nitrogen) (<99.99%) during melting caused aluminum liquid oxidation, resulting in a large number of pinholes after rolling
Billet Defect-Type	Air bubbles, cracks in cast-rolled billets	Holes are “long strips” distributed along the rolling direction	When the diameter of air bubbles in the billet >50μm, 100% of them form pinholes after rolling	Excessively fast cast-rolling speed (>1.5मी/मिनिट) led to 80μm-diameter air bubbles in the billet, which formed corresponding pinholes after rolling into 0.006mm aluminum foil

Key Control Points: During raw material inspection, test the impurity content of aluminum ingots (Fe ≤0.35%, Si ≤0.25%) and conduct billet flaw detection (no air bubbles/cracks >30μm).

2. Process-Based Pinholes (Accounting for 50% of Production-Stage Pinholes)

Definition: Pinholes formed during aluminum foil rolling due to “acquired operational factors” such as improper rolling process parameters and contaminated rolling oil, which are “defects avoidable through process optimization”.
Detailed Process Links and Impact Mechanisms:
(1) Rolling Speed Fluctuation-Type

Definition: Sudden increases or decreases in rolling speed during the process (उदा., time from 500m/min to 600m/min <10s) cause uneven local stress on the aluminum foil, तयार करणे “tensile pinholes”;

Morphological Characteristics: Pinholes are “elliptical” with the major axis along the rolling direction, and the diameter is usually 30-60μm;

Quantitative Data: When the speed fluctuation amplitude >10%/मि, the incidence of pinholes increases by 60% (report from SMS Group, जर्मनी, on rolling technology).

(2) Rolling Oil Contamination-Type

Definition: Metal chips, धूळ, and other impurities (particle size >5μm) mixed in rolling oil are pressed into the aluminum foil during rolling, तयार करणे “extrusion pinholes”;

Morphological Characteristics: Impurity particles often remain in the center of pinholes, and the holes are “circular or quasi-circular”. The diameter is positively correlated with the impurity particle size (5μm impurity diameter → 15-20μm pinhole diameter; 10μm impurity diameter → 30-40μm pinhole diameter);

Control Standard: Rolling oil must meet ISO 4406 cleanliness class 16/13 (≤130 particles >15μm and ≤20 particles >25μm per 100mL of oil), otherwise the pinhole density will exceed 10 holes/m².

(3) Roll Defect-Type

Definition: स्क्रॅच, wear, and nodules on the roll surface cause “pressed-out” penetrating holes on the aluminum foil surface during rolling;

Detailed Types:

① Roll Scratches: Foreign objects (उदा., metal chips) scratch the roll surface, forming grooves with depth >3μm. Corresponding “long strip pinholes” (length 50-100μm, width 10-20μm) form on the aluminum foil at the corresponding positions after rolling;
② Roll Wear: After rolling more than 1000 tons of aluminum foil, the roll surface roughness Ra increases from 0.15μm to 0.3μm, causing uneven local rolling pressure on the aluminum foil and forming “dispersed pinholes” (density 8-12 holes/m²);
③ Roll Nodules: Aluminum powder in rolling oil accumulates on the roll surface (nodule height >5μm) and is pressed into the aluminum foil during rolling, तयार करणे “irregular pinholes” (diameter 20-50μm).

3. Equipment-Based Pinholes (Accounting for 15% of Production-Stage Pinholes)

Definition: Pinholes formed due to unbalanced stress on the aluminum foil during transmission and rolling caused by insufficient precision of equipment such as rolling mills and guide rolls, classified as “equipment precision-related defects”.
Key Equipment and Impact Mechanisms:

Equipment Name	Precision Defect Type	Morphology and Distribution of Pinholes	Quantitative Risk (Precision vs. Pinhole Density)	उपाय
Rolling Mill Housing	Excessive housing clearance (>0.1मिमी)	Pinholes are evenly distributed along the width direction of the aluminum foil, with diameter 20-40μm	When clearance increases from 0.05mm to 0.15mm, pinhole density increases from 3 holes/m² to 15 holes/m²	Regularly measure housing clearance and adjust to ≤0.08mm using gaskets
Guide Roll	Excessive guide roll runout (>0.05मिमी)	Pinholes show “periodic distribution” (spacing consistent with guide roll circumference), with diameter 15-30μm	When runout increases from 0.03mm to 0.07mm, the incidence of pinholes increases by 80%	Detect guide roll runout with a dial indicator and replace bearings if exceeding the standard
Tension Control System	Tension fluctuation exceeding ±5% (उदा., unstable uncoiling tension)	Pinholes concentrate in the edge area (within 50mm) of the aluminum foil, showing “long strips”	When tension fluctuation is ±8%, the edge pinhole density reaches 20 holes/m²	Adopt closed-loop tension control to limit fluctuation within ±3%

(B) Application-Stage Pinholes: Formed During Aluminum Foil Lamination, Transportation, and Storage

1. Lamination Process-Based Pinholes (Accounting for 60% of Application-Stage Pinholes)

Definition: New penetrating holes formed in aluminum foil due to improper processes when laminating aluminum foil with other substrates (पीईटी, CPP, इ.).
Main Causes:

Excessive lamination pressure (>0.5एमपीए): 0.006mm aluminum foil is thin and has poor ductility. Excessive pressure causes local rupture of the aluminum foil, तयार करणे “crushing pinholes” (diameter 20-30μm), which are common at both ends of the laminator pressure roll (uneven pressure distribution);

Substrate Impurity Press-In: Dust and adhesive particles (diameter >10μm) remaining on the substrate surface before lamination are pressed into the aluminum foil during lamination, तयार करणे “impurity pinholes”. Impurities (उदा., adhesive particles) can be detected in the center of the holes;

Excessively High Oven Temperature (>100℃): Uneven thermal contraction of the aluminum foil causes local tensile stress, तयार करणे “thermal stress pinholes” (diameter 15-25μm), which are common in the third oven of the laminator (area with the highest temperature).

2. Transportation and Storage-Based Pinholes (Accounting for 30% of Application-Stage Pinholes)

Definition: Pinholes formed in aluminum foil rolls due to external impact and environmental factors during transportation and storage.

Impact and Extrusion: Excessively high stacking of aluminum foil rolls (>5 स्तर) during transportation causes the bottom rolls to bear pressure >500किलो, leading to local deformation and rupture of the aluminum foil, तयार करणे “extrusion pinholes” (diameter 30-80μm) concentrated in the inner 1/3 area of the aluminum foil roll;

Excessive Environmental Humidity (RH >80%): Surface oxidation of aluminum foil (especially non-passivated aluminum foil) causes the oxide layer to peel off during subsequent processing, तयार करणे “oxidation pinholes” (diameter 10-20μm) सह “gray-white” edges (oxidation traces).

3. Secondary Processing-Based Pinholes (Accounting for 10% of Application-Stage Pinholes)

Definition: Pinholes formed in aluminum foil laminated products during secondary processing such as bag making and cutting.

Wear of Cutting Tools: Notches on the tool edge (खोली >5μm) tear the aluminum foil during cutting, तयार करणे “tearing pinholes” (diameter 20-40μm) distributed along the cutting edge;

Uneven Heat-Sealing Pressure in Bag Making: Local pressure of the heat-sealing knife >0.4MPa causes rupture of the aluminum foil in the heat-sealing area, तयार करणे “heat-sealing pinholes” (diameter 15-25μm) concentrated near the heat-sealing line.

HW-C. Identification Methods and Risk Priority of Different Types of Pinholes

(ए) Identification of Pinhole Types: Morphology + Distribution + Testing Methods

Pinhole Type	Morphological Characteristics	Distribution Pattern	Core Identification Method
Raw Material-Based	Irregular edges, often containing impurities	Random distribution, no obvious pattern	Observation with metallographic microscope (500x magnification) to detect impurities in holes
Process-Based (रोलिंग)	Elliptical (along rolling direction)	Evenly distributed along rolling direction	Online laser scanning to analyze the angle between the pinhole major axis and rolling direction (>60° indicates rolling speed fluctuation)
Equipment-Based (Guide Roll)	Periodic distribution (fixed spacing)	Spacing consistent with guide roll circumference	Measure pinhole spacing and compare with guide roll circumference (if spacing = guide roll circumference, it is a guide roll issue)
Lamination Process-Based	Containing adhesive particles/dust in the center	Concentrated at both ends of the laminator pressure roll	Scanning Electron Microscope (SEM) detection to check for impurities (उदा., adhesive particles) in the hole center

(B) Risk Priority Ranking (From High to Low)

Pinholes in sterile aluminum foil for pharmaceutical packaging (any size leads to product scrapping, risk level: ★★★★★);

Pinholes in aluminum foil for high oxygen-sensitive food packaging (diameter ≥30μm, risk level: ★★★★☆);

Pinholes in moisture-proof aluminum foil for electronic packaging (diameter ≥20μm, risk level: ★★★★☆);

Pinholes in aluminum foil for ordinary food packaging (diameter 30-40μm, risk level: ★★★☆☆);

Pinholes in aluminum foil for industrial packaging (diameter ≤40μm, risk level: ★★☆☆☆).

Precise Definition and Multi-Dimensional Classification Analysis of Aluminum Foil Pinholes