PI Film: The Super Material in the New Energy Sector

As the world's best-performing insulating film material, polyimide (PI) film, along with carbon fiber and aramid fiber, is considered one of the three critical high-performance polymers constraining the development of high-tech industries in China.

Thanks to its excellent physical and chemical properties, PI film is widely used in flexible printed circuit boards (FPCs), consumer electronics, high-speed rail transportation, wind power, 5G communications, flexible displays, aerospace, and more.

With the development of copolymer modification and other new technologies, continuous optimization in formulation and production processes has led to more functional derivatives of PI film, expanding its downstream applications.

Overview of the Polyimide Industry

Polyimide (PI) refers to a class of polymers containing imide groups in their molecular backbone. High-performance PIs typically feature aromatic or heterocyclic main chains.

Key characteristics:

• Highest flame resistance rating (UL-94)

• Excellent electrical insulation, mechanical properties, chemical resistance, aging resistance, and radiation resistance

• Dielectric constant of 4.0 and loss factor of 0.004–0.007 at 10³ Hz

• Functional from –269°C to 400°C

• Classified as F to H-grade insulation

Nicknamed “The Problem Solver”, PI is hailed as one of the most promising engineering plastics of the 21st century and sits atop the polymer performance hierarchy. It's often said: “Without PI, there would be no modern microelectronics.”

PI Film Production Process

Common Manufacturing Techniques:

• Casting

• Biaxial stretching (casting + stretching)

• Impregnation (aluminum foil coating)

• Spraying

• Extrusion

• Deposition

Among these, casting and biaxial stretching are the most commonly used. The impregnation method is being phased out due to inferior insulation properties. The spray, extrusion, and deposition methods—technically challenging—were mainly dominated by Japanese companies before 2016.

Imidization Methods:

1. Thermal Imidization: Simpler process, but the resulting film is inferior in performance.

2. Chemical Imidization: Used for high-grade electronic PI films. Requires stricter conditions (low temperatures and chemical catalysts), but offers superior film quality.

Before 2014, most Chinese manufacturers used thermal imidization. Since then, international leaders have transitioned to chemical imidization. In 2017, Times Huaxin established China’s first wide-format (1545 mm) chemical film production line, followed by an even larger 2100 mm line in 2019.

Development Timeline

• 1908: PI was first reported.

• 1920s–1960s: Gained attention; commercial PI film began in the 1960s for electrical insulation.

• 1970s–2000s: Expanded into electronics; later into flexible displays, thermal graphite films, etc.

• 2000–2020: Slow domestic progress; dependent on independent R&D for traditional electrical insulation films.

• 2020 onward: Accelerated domestic substitution. Opportunities arise in electronic-grade PI film with high barriers to entry and significant room for import replacement.

Application Scenarios

1. Flexible Electronics

• Used in FCCL (Flexible Copper Clad Laminates), key to FPCs.

• From 2014–2019, global FCCL market rose from $2.64B to $4.48B.

• Electronic-grade PI film demand hit 14,877 tons globally in 2019; 4,869 tons in China.

• FPC output value in China grew from ¥29.07B (2014) to ¥52.6B (2020); projected to reach ¥54.44B in 2021.

2. Aerospace and Foldable Screens

• In aerospace, PI films are used as rocket insulation due to their weather and radiation resistance.

• China’s commercial space industry surpassed ¥800B in 2019, with a CAGR of 22.1%.

• In foldable phones, flexible CPI films are the mainstream cover solution. By 2024, global foldable phone shipments may reach 45.3M units (13.2M in China).

3. Consumer Electronics

• Thermal PI films are processed into graphite thermal sheets for LED substrates and electronics cooling.

• Domestic thermal interface material market expanded from ¥660M (2014) to ¥1.27B (2020), with a CAGR of 9.9%.

• 5G technology boosts demand for thermally conductive PI films.

4. Wind Power and High-Speed Rail

• Electrical-grade PI films are used in high-end insulation systems for motors and generators.

• China is the global leader in wind energy, with 282 GW of installed capacity by the end of 2020 (34.3% YoY growth).

• In high-speed rail, China holds more than 60% of global operating mileage.