From Pinhole Standards to Rolling Solutions: Enhancing 6.35μm 8079 Aluminum Foil’s Pet Food Oil Barrier Performance

1. Introduction: Application Background and Core Requirements of 6.35μm 8079 Aluminum Foil in Pet Food Packaging

Pet food packaging must simultaneously meet three core requirements: “barrier property (preventing oil penetration), kakayahang umangkop (adapting to packaging forming), and safety (no migration risk)”.

Among various materials, 6.35μm thin-gauge 8079 aluminyo foil for food packaging has become the mainstream choice. Its advantages include “high barrier property (oxygen transmission rate ≤0.1cc/(m²·24h·atm)), magandang formability (elongation ≥3%), and cost adaptability”.

Notably, sa 2024, ang 8079 alloy accounted for over 65% of the global pet food aluminum foil packaging market.

Specifically, the 6.35μm gauge is growing at a rate of 18%. This growth is driven by its lightweight advantage—it is 20% lighter than the 8μm gauge (source: China Packaging Federation).

Gayunpaman, animal oils in pet food (e.g., chicken oil, fish oil) have strong permeability. Their viscosity is typically 20-30cP@25℃.

If pinholes exist in this aluminum foil, oils will migrate to the outer layer of the packaging. This causes problems such as “adhesion, deterioration, and shortened shelf life”.

According to industry statistics, packaging defects caused by pinholes in this aluminum foil account for 12% of total pet food packaging defects. This results in direct annual losses exceeding 500 million yuan.

Fundamentally, the core contradiction lies in the thickness of 6.35μm thin-gauge 8079 aluminyo foil para sa pagkain packaging. It is only 53% as thick as conventional food aluminum foil (12M).

Pinholes are easily generated due to improper process parameters during rolling.

Moreover, ang 8079 haluang metal (Al-Fe-Si series) contains Fe-Si compound phases. If not properly controlled, these phases can become “stress concentration points” for pinhole initiation.

Consequently, clarifying pinhole rate control standards and optimizing rolling processes are key to solving oil penetration in pet food packaging.

2. Pinhole Rate Control Standards for 6.35μm Thin-Gauge 8079 Aluminum Foil: Based on Pet Food Oil Barrier Requirements

Pinhole rate is a core indicator for measuring the barrier property of thin-gauge aluminum foil.

Formally, it is defined as “the number of pinholes with a diameter ≥0.05mm per unit area” (GB/T 3198 Aluminum and Aluminum Alloy Foil).

Yet, pet food has high oil permeability. This requires stricter enterprise standards for 6.35μm thin-gauge 8079 aluminyo foil para sa pagkain packaging.

(1) Graded Pinhole Rate Control Standards (Compared with Conventional Food Aluminum Foil)

Application Scenario	Aluminum Foil Specification	Pinhole Size Category	Pinhole Rate Requirement (pcs/m²)	Allowable Oil Penetration (mg/(m²·24h))	Basis Standard/Requirement
Pet Food Packaging	6.35M 8079 aluminyo foil para sa pagkain packaging	φ0.05-0.1mm	≤5	≤5	Enterprise Internal Standard (Q/XXX 001-2024)
Pet Food Packaging	6.35M 8079 aluminyo foil para sa pagkain packaging	φ＞0.1mm	0 (Not Allowed)	0	National Food Safety Standard for Pet Food (GB 31604.1)
Conventional Snack Food Packaging	12M 8011 aluminyo foil	φ0.05-0.1mm	≤15	≤15	GB/T 3198

(2) Basis for Standard Formulation: Correlation Between Oil Penetration and Pinholes

To validate this standard, a modified experiment was conducted to derive the quantitative relationship between pinhole rate and oil penetration.

Specifically, the experiment was based on GB/T 1037-2021 Determination of Water Vapor Transmission Rate of Plastic Films and Sheets – Cup Method.

Notably, water vapor was replaced with simulated pet food oil: a mixture of 50% chicken oil and 50% sunflower oil.

Dito na, the test sample was 6.35μm 8079 aluminyo foil para sa pagkain packaging.

First, when the pinhole rate is 5 pcs/m² (φ0.05-0.1mm), the oil penetration rate is 4.2mg/(m²·24h). This meets the 12-month shelf life requirement of pet food (oil migration ≤50mg/package).

Second, when the pinhole rate increases to 10 pcs/m², the oil penetration rate surges to 18.5mg/(m²·24h). This leads to oil adhesion on the outer packaging within 6 months.

Third, if there is one pinhole with φ0.15mm, the oil penetration of a single pinhole reaches 25mg/(m²·24h). This far exceeds the safety limit.

Based on these findings, pinholes with φ＞0.1mm must be prohibited.

3. Analysis of Pinhole Causes in 6.35μm Thin-Gauge 8079 Aluminum Foil: Full-Process Tracing from Raw Materials to Rolling

Pinhole formation in 6.35μm thin-gauge 8079 aluminyo foil para sa pagkain packaging is the result of two combined factors: “raw material defects and mismatched process parameters”.

Notably, among these, the rolling process is the key link for pinhole expansion and new pinhole generation.

(1) Raw Material Defects: Inherent Characteristics and Inadequate Control of 8079 haluang metal

Specifically, ang 8079 alloy of 8079 aluminyo foil para sa pagkain packaging belongs to the Al-Fe-Si series.

To elaborate, its composition is: Fe 0.7-1.3%, Si Si 0.1-0.3%, Al≥98.5%.

Primarily, the source defects of pinholes fall into three categories:

First, Metal Inclusions: If Fe-Si compound particles (e.g., Al₃Fe, Al₆Fe) exist in the raw ingot, pinholes may form. This happens when particle size exceeds 3μm, leading to “hard particle crushing” during rolling.

Notably, experiments show that for every 1μm increase in inclusion particle size, the pinhole rate of this aluminum foil increases by 3 pcs/m².

Second, Residual Bubbles: Degassing is critical during ingot melting. If degassing is insufficient (hydrogen content ＞0.15mL/100g Al), bubbles will remain.

Over time, as this aluminum foil thins during cold rolling, the bubbles burst. This forms “circular pinholes” with a diameter typically ranging from 0.08-0.2mm.

Third, Grain Boundary Defects: Grain size uniformity matters after ingot hot rolling. If grain size is uneven (＞50μm), local differences in deformation resistance occur.

This leads to “tear-type pinholes” at grain boundaries during subsequent cold rolling.

(2) Mismatched Rolling Processes: Key Risk Points for Thin-Gauge Aluminum Foil

Beyond raw material defects, the rolling process itself introduces significant pinhole risks. For the rolling process, the 6.35μm 8079 aluminyo foil para sa pagkain packaging requires 4-5 passes of cold rolling.

Specifically, the process chain is: “hot rolling (to 4mm) → rough rolling (to 0.5mm) → intermediate rolling (to 0.1mm) → finish rolling (to 6.35μm)”.

Notably, finish rolling and intermediate rolling are high-risk processes for pinhole generation. The main issues are:

First, Imbalance Between Rolling Force and Reduction Rate: The reduction rate of the finish rolling pass is critical. If it exceeds 25%, problems arise.

To illustrate, rolling from 8μm to 6.35μm requires a safe reduction rate of 20.6%. Exceeding this causes local stress to surpass the 8079 alloy’s yield strength (140MPa). This leads to “local rupture” of this aluminum foil, forming pinholes.

Second, Improper Tension Control: Tension difference between front and back rolls must be controlled. If it exceeds 5kN, issues occur.

Typically, tension during finish rolling is 20-25kN. A larger tension difference causes this aluminum foil to “deviate and stretch”. This generates “long-strip pinholes” with a length of up to 0.5-1mm.

Third, Deteriorated Roll Condition: Roll surface quality directly affects the foil. If there are scratches (depth ＞0.5μm) or foreign matter adhesion, problems occur.

Consequently, during rolling, “indentation-type pinholes” are pressed on the surface of this aluminum foil. As rolling passes increase, these pinholes gradually penetrate the foil.

Fourth, Lubrication Failure: Rolling oil viscosity is a key factor. If it is lower than 2.5cSt (40℃), lubrication fails.

Ultimately, “insufficient boundary lubrication” occurs between the roll and this aluminum foil. This causes local frictional overheating, leading to abnormal grain growth. Cracks easily form during subsequent rolling, generating pinholes.

4. Rolling Process Optimization for Resisting Pet Food Oil Penetration: Multi-Dimensional Parameter Coordinated Regulation

Given the above pinhole causes, to address the pinhole causes of 6.35μm thin-gauge 8079 aluminyo foil para sa pagkain packaging, optimization must cover four aspects.

Specifically, these aspects are: “raw material pretreatment, rolling parameters, roll management, and lubrication system”.

With the core objective of reducing pinhole generation through process coordination, the core goal is to minimize pinhole formation at every stage.

(1) Raw Material Pretreatment Optimization: Reducing Pinhole Risks from the Source

First, raw material pretreatment optimization focuses on reducing pinhole risks at the source. This includes two key steps:

1. Ingot Purification Process:

• • Specifically, a “dual system of online degassing + filtration” is adopted. For degassing, a rotating nozzle is used with an argon flow rate of 15-20L/min. This controls the hydrogen content at ≤0.10mL/100g Al.

• • Additionally, for filtration, a 3-layer ceramic filter plate is used. The precision gradient is 20μm→10μm→5μm. This removes Fe-Si inclusion particles, ensuring inclusions ＞3μm are ≤0.5 pcs/kg.

• • Furthermore, ingot homogenization annealing is performed: hold at 580℃ for 4h. This controls grain size at 20-30μm, reducing grain boundary defects. It provides high-quality blanks for subsequent rolling.

2. Hot Rolling Process Adjustment:

• • Notably, the final hot rolling temperature is controlled at 380-400℃. The recrystallization temperature of 8079 alloy is 350℃, so this ensures sufficient dynamic recrystallization.

• • Moreover, a hot rolling pass reduction rate gradient is applied. It gradually reduces from 50% (rough rolling) sa 30% (finish rolling). This avoids local stress concentration.

(2) Core Cold Rolling Parameter Optimization (Taking 6.35μm Finish Rolling as an Example)

For the core cold rolling process—taking 6.35μm finish rolling as an example—key parameters are optimized as follows:

Process Link	Key Parameter	Traditional Process Value	Optimized Process Value	Optimization Goal	Pinhole Rate Improvement (pcs/m²)
Finish Rolling	Pass Reduction Rate	28%	18-22%	Avoid local stress exceeding limits	From 12 sa 6
Finish Rolling	Front-Back Tension Difference	8kN	≤3kN	Prevent deviation and stretching	From 6 sa 4
Finish Rolling	Rolling Speed	800m/min	600-700m/min	Reduce frictional overheating between rolls and foil	From 4 sa 3
Intermediate Rolling	Intermediate Annealing Temp./Time	320℃×1h	340℃×1.5h	Eliminate work hardening and uniformize structure	From 3 sa 2
Finish Rolling	Roll Roughness Ra	0.4M	0.2-0.3M	Improve rolling oil adhesion and reduce friction	From 2 sa 1

Notably, each optimized parameter targets a specific pinhole cause. Halimbawa na lang, lower rolling speed reduces frictional overheating, while smaller tension difference prevents stretching-induced pinholes.

5. Verification of Process Optimization Effects: Dual Compliance of Pinhole Rate and Oil Penetration Performance

To confirm the effectiveness of the optimized processes, industrial verification was conducted by an aluminum foil enterprise.

Notably, its annual output of thin-gauge aluminum foil is 20,000 tons.

Specifically, the verification focused on 6.35μm 8079 aluminyo foil para sa pagkain packaging after the above process optimization.

Importantly, results showed significant improvements in both pinhole rate and oil barrier performance.

(1) Pinhole Rate Test Results (According to GB/T 3198, Using Fluorescent Detection Method)

First, pinhole rate test results (conducted in accordance with GB/T 3198 using the fluorescent detection method) demonstrated significant improvements:

Test Item	Before Optimization (pcs/m²)	After Optimization (pcs/m²)	Industry Standard (pcs/m²)	Pet Food Packaging Requirement (pcs/m²)
Pinholes (φ0.05-0.1mm)	15	3	≤15	≤5
Pinholes (φ＞0.1mm)	2	0	≤3	0
Total Pinhole Rate	17	3	≤18	≤5

Notably, the optimized pinhole rate fully meets pet food packaging requirements. Specifically, pinholes larger than 0.1mm were completely eliminated.

(2) Oil Penetration Performance Test (Simulated Pet Food Oil, Temperature 25℃, Relative Humidity 60%)

Second, oil penetration performance tests—using simulated pet food oil at 25℃ and 60% relative humidity—further validated the optimization:

Test Indicator	Before Optimization	After Optimization	Safety Limit
Oil Penetration Rate (mg/(m²·24h))	22.5	3.8	≤5
Oil Migration in 12-Month Shelf Life (mg/package)	68.2	11.5	≤50
Packaging Adhesion Rate (%)	15	0.5	≤2

Strikingly, the oil penetration rate dropped by 83% after optimization. This ensures no oil adhesion during the 12-month shelf life.

6. Industry Application Case: Packaging Upgrade Practice of a Pet Food Enterprise

For a practical industry application case, a leading pet food enterprise faced packaging issues in 2023.

With an annual output of 50,000 tons of dry food, the enterprise relied heavily on high-quality packaging to maintain product quality.

Initially, the enterprise faced a critical issue: “oil adhesion on fish oil-flavored food packaging”.

Upon investigation, the root cause was identified as pinhole issues in 6.35μm 8079 aluminyo foil para sa pagkain packaging.

Consequently, the complaint rate reached 8%, causing significant losses in both reputation and revenue.

To address this challenge, the enterprise cooperated with an aluminum foil enterprise.

Together, they implemented the aforementioned optimized processes.

Following implementation, after optimization:

1. First, the pinhole rate of this aluminyo foil decreased from 18 pcs/m² to 4 pcs/m². Pinholes with φ＞0.1mm were completely eliminated.

2. Second, the oil penetration rate decreased from 25mg/(m²·24h) to 4.2mg/(m²·24h). No packaging adhesion occurred during the shelf life.

3. Third, the packaging defect rate decreased from 12% sa 1.5%. This reduced annual losses by over 8 million yuan.

Furthermore, subsequently, this process was promoted to the full range of pet food packaging.

Notably, although the purchase cost of this aluminum foil increased by only 3% (due to process optimization), the comprehensive benefit increased by 15%.

Ultimately, this confirmed the economic value and practicality of the optimized process.

7. Conclusions and Outlook

First, core conclusions can be drawn as follows:

Notably, when 6.35μm thin-gauge 8079 aluminyo foil para sa pagkain packaging is used in pet food packaging, strict pinhole rate control is mandatory.

Specifically, the required standard is: “≤5 pcs/m² for φ0.05-0.1mm and 0 for φ＞0.1mm”. Which is the sole means to effectively prevent oil penetration.

Second, the core implementation path to achieve this standard is clear:

Fundamentally, the key to achieving this standard is “raw material purification + coordinated optimization of rolling processes”.

• On one hand, source defects are reduced through ingot degassing, filtration, and homogenization annealing.

• On the other hand, the pinhole rate of this aluminum foil is stably controlled below 5 pcs/m² via precise parameter regulation.

Specifically, key regulated parameters include: finish rolling reduction rate (18-22%), tension difference (≤3kN), roll roughness (Ra 0.2-0.3μm), and rolling oil viscosity (3.0-3.5cSt).

Collectively, this also ensures the oil penetration rate stays below 5mg/(m²·24h).

Third, future development directions for thin-gauge 8079 aluminum foil for food packaging will focus on two key areas:

Looking ahead, in the future, the process development of thin-gauge 8079 aluminyo foil para sa pagkain packaging will focus on two directions:

2. First, Intelligent Rolling: Specifically, AI algorithms will be used to adjust rolling force-tension-speed matching in real time. Which predicts pinhole generation risks, further improving process stability.
3. Second, Alloy Composition Improvement: For instance, adding 0.1% Ti to the 8079 alloy will refine grains to 15-20μm. Ultimately, this enhances pinhole resistance while maintaining formability.