Aluminum semi rigid container foil is a specially processed aluminum alloy foil. It is different from the common household aluminum foil used to wrap food. It has higher strength and certain rigidity, can be independently formed into containers and maintain its shape, while maintaining many excellent properties of aluminum foil.
Specific grades of aluminum alloys are usually used in semi rigid container foil, and the common ones are 8000 series alloys (such as 8011), 3003 (corrosion resistance) and 5052 (high strength). Among them, the tensile strength of 5052-H14 state (semi-cold hardening) can reach 240-290MPa, which is suitable for containers that require a certain degree of rigidity. The 8000 series alloys contain elements such as iron and silicon, and can provide good strength, formability and anti-sagging (the ability to resist deformation when heated) after processing. For example, the mousse cake aluminum foil cup uses 0.015-0.02mm 8011 aluminum foil, which takes into account both formability and structural stability. The alloy composition and processing technology (especially the degree of cold rolling hardening) together determine the hardness (rigidity) and strength of the final container.
Thickness of semi rigid container foil:
Much thicker than ordinary household aluminum foil (usually around 10-20 microns).
The thickness of aluminum foil for semi-rigid containers usually ranges from 40 microns to 150 microns (0.04mm – 0.15mm), which belongs to the category of single zero foil or thick foil. Common lunch boxes, pie plates, etc. may be around 50-100 microns thick.
Thickness is one of the key factors that determine the rigidity and strength of the container. The thicker, the stiffer the container and the greater its load-bearing capacity.
Processing technology (hardening):
– The core process is cold rolling hardening:
During the rolling process of aluminum foil, by controlling the rolling reduction rate (degree of deformation) of the last few passes, the internal grain structure of the aluminum material changes (dislocation density increases), thereby significantly improving the strength and hardness of the material.
– Temper:
Aluminum foil for containers is usually in the H state (such as H22, H24, H26). The larger the number behind it, the higher the degree of cold work hardening and the harder the material.
– Annealing control:
Fully annealed (O state) aluminum foil is very soft. In order to obtain semi-hard characteristics, partial annealing (sometimes called “tempering annealing”) or control of the deformation of the final cold rolling will be carried out to achieve the desired balance of hardness and formability.
Surface treatment (coating):
A thin layer of food-grade coating is applied to the inner surface of most semi-rigid aluminum foil containers. Its main functions are:
– Corrosion protection: Prevent acidic or salty foods from reacting with aluminum to cause corrosion perforation or produce odors (such as “metallic taste”).
– Anti-stick: Makes food easy to demould.
Provide additional barrier (optional): Some coatings can further enhance the barrier to specific substances (such as acidic ingredients).
– Easy to print (outer surface): Brand and instructions can be printed on the outer surface.
There are many types of coatings, and common ones are water-based or solvent-based coatings such as acrylic resins, polyester resins, and epoxy resins. It is necessary to ensure that they meet food safety standards.
Key performance requirements:
– Strength and rigidity:
Able to bear the weight of the contents and not easily deformed or crushed during stacking, transportation and use.
– Formability:
Able to be processed into complex container shapes (such as lunch boxes with flanges and deep baking trays) through processes such as stamping and deep drawing without breaking.
– Anti-sagging:
In an oven or steam heating environment, it can resist the bottom sagging or side wall bulging caused by its own gravity when containing food. This is closely related to alloy selection, thickness and hardening state.
– Barrier:
Provides excellent barrier to water vapor, gas (oxygen), light and microorganisms, protecting food flavor, freshness and extending shelf life.
– Temperature resistance:
Able to withstand temperature changes such as refrigeration, freezing, oven baking (usually in the range of -40°C to +250°C, depending on the alloy and coating), steam heating (steaming). The melting point of pure aluminum is about 660°C, but the actual temperature resistance of the container is affected by the alloy, coating and structural design.
– Food safety:
Must comply with relevant regulations on food contact materials (such as FDA, EU 10/2011) to ensure that no harmful substances migrate.
– Thermal conductivity:
The excellent thermal conductivity of aluminum allows food to heat evenly and quickly, which also means faster cooling.
– Lightweight:
Aluminum itself has a low density, and the container made is light.
– Recyclability:
Aluminum has a very high recycling value and recycling rate, making it an environmentally friendly choice.
Applications of semi rigid container foil:
Ready-to-eat meal boxes (takeaway, airline meals, supermarket refrigerated/frozen meals)
Baking molds (pie pans, cake pans, tart pans)
Grilling trays
Food trays (e.g. frozen meat trays)
Takeaway soup/noodle bowls
Pet food containers
Processing and transport containers in the food industry
The aluminum semi rigid container foil is a thicker (40-150 microns), specific alloy (e.g. 8011), cold-rolled work-hardened (to states such as H22-H26) aluminum alloy foil. It is given sufficient strength and rigidity by increasing the thickness and internal hardening treatment to enable it to be formed into a container with a stable shape, while retaining the excellent barrier properties, thermal conductivity, temperature resistance, lightness and recyclability of the aluminum foil. A food-grade coating is usually applied to prevent corrosion and adhesion. This material is one of the ideal choices in the field of food packaging, especially in applications that require heating, shape stability and good barrier properties.
