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3.1 μ m PET aluminum plated film · Ultra thin metallization and composite current collector scheme
In the selection of ultra-thin PET aluminum plated film, engineers are faced with a seemingly simple choice: since the goal is "thinner and lighter", why not directly choose a substrate of 2.3 μ m or even thinner?
The answer lies at the intersection of process yield and engineering reliability. The 2.3 μ m PET substrate is approaching the physical limit of an independent film - during the vacuum evaporation process, the heat capacity of the film is extremely small, and small temperature fluctuations can cause shrinkage or even melting; The winding tension window is extremely narrow, and slight tension deviation can cause wrinkles or tensile deformation. Industry data shows that the thickness of ultra-thin PET substrates that can be used for stable metallization is usually above 3 μ m. Although 2.3 μ m is feasible in the laboratory, it still faces significant challenges in terms of mass production yield and batch consistency.
Core proposition:3.1 μ m is in a "just right" position in engineering: it is significantly thinner than 4 μ m or 6 μ m, bringing considerable volume efficiency and weight reduction benefits to the composite current collector of metalized thin film capacitors and lithium batteries; At the same time, it retains sufficient mechanical strength and thermal capacity margin, enabling roll to roll vacuum deposition to operate stably within an acceptable yield range. The engineering positioning of this "mass production critical point" has made 3.1 μ m a watershed for ultra-thin PET aluminum plated film to move from "can do" to "easy to use".
In metallized film capacitors, PET film serves as the dielectric, and its thickness directly determines the volumetric efficiency of the capacitor. The capacitance of a capacitor is inversely proportional to the thickness of the dielectric - the thinner the film, the greater the capacitance within the same volume.
Industry data shows that the thickness range of PET film used for capacitors covers 1.2 μ m to 12 μ m. The thinner the film, the higher the capacity density, but the breakdown voltage decreases accordingly, requiring a balance between miniaturization and long-term reliability. 3.1 μ m is at a critical balance point between high volumetric efficiency and process feasibility.
In terms of dielectric properties, the dielectric constant of PET film is about 3.0-3.2, and its capacity density is higher than that of polypropylene capacitors. The thickness of the metalized electrode is only 50-100nm, which not only reduces contact resistance but also has a certain self-healing ability. When the dielectric partially breaks down, the extremely thin metal layer rapidly evaporates around the breakdown point, allowing the capacitor to resume normal operation. The thickness of the aluminum layer needs to be balanced with the working voltage and self-healing energy.
Capacitor film is the core performance and cost cornerstone of thin-film capacitors, accounting for 39% of the total production cost and approximately 60% of the raw material cost. The performance of thin film capacitors largely depends on the quality of the base film and the accuracy of the metallization process. The core barrier of the industry lies in the difficulty of ultra-thin manufacturing, and domestic production lines highly rely on overseas suppliers for supply and operation. The mass production capability of 3.1 μ m PET aluminum coated film is a key breakthrough in this ultra-thin barrier.
The application of 3.1 μ m PET aluminum coated film in the field of lithium battery composite current collectors is one of the most concerned technological directions in recent years.
The composite current collector adopts a sandwich structure of "metal conductive layer polymer material support layer metal conductive layer", with a PET or other polymer base film in the middle and aluminum or copper plated metal films on the outer two layers. Compared with traditional current collectors, composite current collectors have the advantages of high safety, low manufacturing cost, and strong compatibility. Batteries using composite current collectors also have significant improvements in energy density and cycle life.
According to BYD's experimental data, the negative electrode uses a composite current collector consisting of a 3 μ m base film and 1 μ m copper foil layers at the bottom, which can increase the energy density of the battery by 3.3% compared to the traditional 6 μ m copper foil current collector; If the positive electrode also uses a composite current collector, the energy density of the battery can be increased by a total of 6.1%. The density of PET substrate is only about 1/6.5 of copper. By replacing some of the metal layer with 3.1 μ m PET, the surface density of the current collector is significantly reduced, which directly translates into an increase in battery energy density.
In terms of safety, the polymer substrate in the middle has flame-retardant properties, and the metal conductive layer is relatively thin. When short circuited, it will melt like a fuse and quickly melt before thermal runaway. Battery damage is limited to the puncture site, forming a "point break". The burr size generated by the composite current collector is small, and the short-circuit current can be greatly reduced in a short period of time due to the short-circuit effect caused by the heating of the polymer material layer.
Industry verification:In 2025, GAC Aion magazine battery 2.0 adopts composite current collector materials, becoming the first battery in China to announce the use of composite current collectors; The NP2.0 technology of CATL Kirin batteries also mainly relies on composite current collectors. The technological choices of these leading enterprises have validated the engineering feasibility of 3 μ m scale base membranes in composite current collectors.
The aluminum layer preparation of 3.1 μ m PET aluminum plated film adopts vacuum evaporation process - in a high vacuum environment, high-purity aluminum is heated to the evaporation temperature, and the aluminum vapor is condensed and deposited on the surface of the high-speed running PET film, forming a continuous and dense aluminum layer.
Vacuum deposition on ultra-thin substrates with a thickness of 3.1 μ m faces a series of technical challenges that are far more stringent than conventional thickness substrates:
If the winding tension is too high, the film will be "squeezed" out, wrinkled, or even stretched and deformed; If the tension is too low, it is easy to cause detachment. In industry practice, the coiling speed of vacuum aluminum plating is usually controlled within the range of 280-320 m/min, and the aluminum feeding speed is controlled within 0.4-0.7 m/min. For ultra-thin substrates, the tension parameters need to be precisely adjusted according to the thickness of the film, while coordinating with the winding speed.
The temperature resistance of PET film is about 180 ° C, while the evaporation temperature of aluminum can reach 1200-1400 ° C. If too much heat accumulates, the film will shrink, warp, or even burn through to form holes. During the vapor deposition process, it is necessary to turn on the cooling system to avoid stretching and deformation of the film due to heating.Advanced Institute of TechnologyBy precisely controlling the matching relationship between evaporation rate and substrate operating speed, the substrate temperature rise is controlled within a safe range.
On a very thin substrate of 3.1 μ m, any tiny substrate defects or dust particles can become penetrating pinholes. Advanced Institute Technology conducts plasma activation pretreatment on PET film, introducing active sites without damaging the substrate, ensuring a strong bonding interface between the aluminum layer and the PET substrate, while minimizing pinhole defects.
The lack of active functional groups and strong hydrophobicity on the surface of PET materials can lead to insufficient adhesion between the metal coating and the substrate, resulting in the detachment of the aluminum layer during subsequent processing or capacitor operation. The plasma pretreatment process of Advanced Institute Technology effectively improves the bonding strength between PET and aluminum layer, ensuring that the adhesion of the coating meets the application requirements.
Based on a 3.1 μ m PET substrate, aluminum plated film products with different aluminum layer thicknesses can be prepared by precisely controlling the evaporation process parameters. The thickness of the aluminum layer is characterized by optical density (OD), with higher OD values indicating thicker aluminum layers and lower light transmittance. Different thicknesses correspond to different performance focuses:
| Product Type | Optical Density (OD) | Aluminum Layer Thickness | Key Characteristics | Typical Applications |
|---|---|---|---|---|
| 3.1 0.1PET aluminum plated film | ~0.1 OD | Extremely thin aluminum layer (<20nm) | Extremely flexible, semi transparent, and lowest material cost | Ultra thin capacitors, precision optical films, low barrier packaging |
| 3.1 0.3PET aluminum plated film | ~0.3 OD | Thin aluminum layer (~30nm) | Good flexibility and moderate barrier properties | Metallized film capacitors, electronic shielding |
| 3.1 0.7PET aluminum plated film | ~0.7 OD | Medium aluminum layer (~70nm) | High reflectivity, strong conductivity, and high barrier properties | High reliability capacitors, electromagnetic shielding |
| 3.1 1PET aluminum plated film | ~1.0 OD | Thicker aluminum layer (~100nm) | High reflectivity, low surface resistance, high barrier properties | Lithium battery composite current collector, high-end capacitor, EMI shielding |
When selecting, engineers should weigh the requirements of capacitance density, flexibility, and barrier properties comprehensively: the lower the OD value, the better the flexibility of the film and the stronger the winding adaptability; The higher the OD value, the stronger the conductivity and barrier properties. For capacitor applications, the thickness of the aluminum layer needs to be balanced with the operating voltage and self-healing characteristics; For the application of composite current collectors, it is necessary to ensure that the surface resistance of the aluminum layer meets the conductivity requirements.
ComprehensiveAdvanced Institute of TechnologyAccording to industry public information, the key performance characteristics of 3.1 μ m PET aluminum plated film are as follows:
This is the core application area of 3.1 μ m PET aluminum plated film. In miniaturized capacitors that require high capacitance density, a 3.1 μ m ultra-thin PET substrate can achieve higher capacitance within limited packaging space. Metallized PET film capacitors are widely used in fields such as consumer electronics, automotive electronics, and industrial power supplies. Aluminum metallized polyester film with a thickness of 2 microns to 12 microns is the standard specification for manufacturing capacitors.
This is the fastest-growing application area for 3.1 μ m PET aluminum coated film. The composite aluminum foil adopts a sandwich structure of "PET based film double-sided aluminum plating", which can replace traditional aluminum foil as the positive electrode current collector of lithium batteries. The 3.1 μ m PET substrate significantly reduces the weight of the composite current collector, while the polymer material layer produces a circuit breaking effect during thermal runaway, fundamentally reducing the risk of fire caused by internal short circuits in the battery.
In electronic devices with extremely limited space, 3.1 μ m PET aluminum coated film can serve as an ultra-thin electromagnetic shielding layer. Aluminum coated PET film has excellent electromagnetic shielding performance in the electronics industry. Its extremely thin thickness allows it to adhere to narrow spaces that traditional shielding materials cannot enter.
The aluminum plating layer endows PET film with certain conductivity, and low surface resistance can effectively eliminate electrostatic effects. Advanced Institute Technology adopts advanced aluminum plating technology to ensure uniform and firm aluminum plating layer, effectively reducing the surface resistivity of PET aluminum plating film, suitable for packaging electronic components sensitive to static electricity.
When engineers choose 3.1 μ m PET aluminum plated film, the following dimensions deserve special attention:
Selection warning:3.1 μ m is not a 'second best' choice - it is the optimal balance between mass production feasibility and weight reduction benefits. Although 2.3 μ m has laboratory feasibility, it still faces significant challenges in terms of metallization yield and batch consistency; 4 μ m or 6 μ m sacrifices considerable volumetric efficiency and weight reduction space. Understanding the boundaries of this project is more valuable than simply pursuing the 'thinnest'.
The essence of 3.1 μ m PET aluminum coated film is to find an engineering balance between the physical limits of PET film and the feasibility of mass production. It is thinner than 4 μ m or 6 μ m, bringing tangible volume efficiency and weight reduction benefits to the composite current collector of metalized thin film capacitors and lithium batteries; At the same time, it retains sufficient process margin to ensure stable operation of roll to roll vacuum deposition within an acceptable yield range.
From the measured results of BYD's patent data showing a 3.3% increase in energy density with a 3 μ m composite current collector, to the complete product system and customization capability of Advanced Institute Technology covering 4.5 μ m to 188 μ m in the field of PET film aluminum plating - behind the thickness figure of 3.1 μ m is a complete process system from substrate tension control, temperature management to coating uniformity and adhesion guarantee. For engineers, understanding why it is 3.1 μ m instead of 2.3 μ m or 4 μ m - the answer to this question is precisely the technological watershed for ultra-thin PET aluminum coating to move from "can be plated" to "precision plated".
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