In the field of metalized thin films and flexible electronics, substrate thickness is a physical quantity that is continuously compressed. The thickness of PET film has gradually decreased from 50 μ m and 25 μ m in the early days to 12 μ m and 6 μ m, and now it has been advanced to 4 μ m or even 3.1 μ m. 6 μ m is at the core of this ultra-thin range - maintaining sufficient mechanical strength to support mass production and processing, while achieving significant benefits in thinning and thinning.

What is the concept of 6 μ m? The diameter of a standard adult hair is approximately 60-80 μ m. The thickness of 6 μ m PET film is only about one tenth of the diameter of a hair.Advanced Institute of TechnologyThe thickness of PET film can be accurately controlled within the range of 4-100 μ m, with 6 μ m being in the extremely thin range of this range. The thickness range of PET aluminum plated film is between 5 μ m and 125 μ m, with 6 μ m located at the extremely thin end of this range. At this scale, PET film faces significant process challenges in coating, rewinding, and winding processes, but has mature mass production capabilities.

2、 The logic of "volume efficiency" of capacitors: how to improve the capacitance density of 6 μ m

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.

The capacitor with PET as the dielectric is called Mylar capacitor. The dielectric constant of PET film is about 3.0-3.8 at a frequency of 1MHz, with a dielectric loss of less than 0.008. The working temperature range covers -40 ° C to 125 ° C. The thickness of the metallized electrode is only 50 to 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.

3、 The "weight reduction logic" of composite current collectors: how 6 μ m base film can improve battery energy density

The application of 6 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 layers on the outer two layers. PET composite aluminum foil is made of 6 μ m PET as the substrate, and then coated with 1 μ m aluminum layers on both sides, with a total thickness of 8 μ m, compared to 10 μ m rolled aluminum foil. Compared with traditional current collectors, composite current collectors have advantages such as high safety, low manufacturing cost, and strong compatibility.

4、 Vacuum evaporation: a core technological challenge on 6 μ m substrates

The aluminum layer of 6 μ m PET aluminum coated film was prepared using vacuum evaporation technology. In a vacuum environment, high-purity aluminum is heated to the evaporation temperature, causing aluminum vapor to condense and deposit on the surface of high-speed PET film, forming a continuous and dense aluminum layer. Vacuum evaporation is the process of placing a roll of film in a vacuum chamber. When the vacuum degree reaches 5.0 × 10 ² Pa or higher, the evaporation boat is heated to 1300 ℃ to 1400 ℃, and then aluminum wire with a purity of 99.9% is continuously sent to the evaporation boat for evaporation. The aluminum vapor condenses and deposits on the surface of the PET film to form a coating.

Vacuum deposition on ultra-thin substrates with a thickness of 6 μ m faces a series of technical challenges that are far more stringent than conventional thickness substrates:

5、 Aluminum layer thickness: performance span from OD 0.12 to OD 1.0

Based on a 6 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 usually characterized by optical density (OD). Optical density is the logarithm of the ratio of incident light to transmitted light, calculated as OD=log ₁₀ (1/transmittance).

Industry research data shows that the optical density value of aluminum film is about 0.5 to 2.5, corresponding to a physical thickness of about 6 to 40nm. The correspondence between OD value and aluminum layer thickness can refer to the following data: OD 1.6 corresponds to an aluminum layer thickness of about 320 Å, OD 2.0 corresponds to about 400 Å, OD 2.4 corresponds to about 480 Å, and OD 2.8 corresponds to about 560 Å.

Different aluminum layer thicknesses correspond to different performance focuses:

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.

6、 Key performance: Technical boundary of 6 μ m specification

ComprehensiveAdvanced Institute of TechnologyAccording to industry public information, the key performance characteristics of 6 μ m PET aluminum plated film are as follows:

• Dielectric properties.The dielectric constant of PET film is approximately 3.0 at a frequency of 1MHz, with a dielectric loss factor of 0.002 and a dielectric strength of 17 kV/mm. PET has a high dielectric constant and breakdown strength, can operate stably within a temperature range of 125 ° C, and has excellent self-healing properties.
• Barrier performance.The presence of aluminum layer significantly reduces the permeability of PET film to oxygen and water vapor. PET aluminum plated film can effectively block moisture, oxygen, and other gases, extending the shelf life of products.
• Reflectance.The reflectivity of the aluminum surface can reach over 95%, and the aluminum layer endows the PET film with metallic luster and high reflectivity.
• Temperature resistance.The upper limit of the working temperature for PET film is 125 ° C. After aluminum plating, the temperature resistance remains basically unchanged.
• Mechanical performance.The tensile strength of PET aluminum plated film (biaxially oriented film) can reach 190-260MPa, with good mechanical strength and toughness.

7、 Core application scenarios: from capacitors to composite current collectors

8、 Selection considerations: from OD value to processing adaptation

When engineers choose 6 μ m PET aluminum plated film, the following dimensions deserve special attention:

• Selection of aluminum layer thickness (OD value).The higher the OD value, the stronger the barrier and conductivity, but the flexibility decreases. The application of capacitors requires the selection of appropriate OD values based on voltage levels and capacity requirements; The application of composite current collectors requires ensuring that the surface resistance meets the conductivity requirements.
• Pinhole density.For ultra-thin substrates with a thickness of 6 μ m, pinhole control is the core indicator of product quality. High end capacitors and composite current collector applications have strict requirements for pinhole density.
• Winding adaptability.The 6 μ m film requires high process control during the winding process. When selecting, it is necessary to evaluate the compatibility of the material with the existing winding equipment, and the tension parameters and winding speed need to be accurately matched according to the thickness.
• Working temperature.The long-term use temperature of PET substrate is 125 ° C. Applications beyond this temperature range require consideration of higher temperature resistant substrates such as PEN or PI.
• Processing accuracy.Advanced Institute Technology supports flexible adjustment of aluminum layer thickness and PET substrate functionalization, and can customize specifications such as square resistance, thickness, and width according to customer needs. PET aluminum plated film supports subsequent processing such as slitting, lamination, printing, and die-cutting. The thickness of the aluminum layer and product size can be customized according to needs.

9、 Conclusion

The essence of 6 μ m PET aluminum coated film is to find an engineering balance between the thinning and mass production feasibility of PET film. It is significantly thinner than 12 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 data of 36.7% weight reduction of composite aluminum foil made by double-sided aluminum plating on 6 μ m PET base film, to the complete product system and customization capability covering 5 μ m to 125 μ m in the field of PET film aluminum plating by Advanced Institute Technology - behind the thickness of 6 μ m is a complete process system from substrate tension control, temperature management to coating uniformity and interface bonding guarantee. For engineers, understanding the process constraints and performance opportunities behind the thickness of 6 μ m - how OD values affect capacitance density and barrier performance, and how to choose aluminum layer thickness - is more valuable than simply remembering a specification.