Industry knowledge about polyimide films

Polyimide (PI) refers to a class of high-performance polymers with molecular structures containing imide groups. PI is a broad family, with most high-performance variants featuring aromatic and heterocyclic structures in their backbone.

Known for its top-tier flame resistance (UL-94 rating), excellent electrical insulation, mechanical strength, chemical stability, aging resistance, and radiation tolerance, PI stands out as a versatile material. It boasts a dielectric constant of 4.0 and a dielectric loss as low as 0.004 to 0.007 at 10³ Hz. Rated as F to H class insulation, these properties remain stable across an extreme temperature range of -269°C to 400°C.

Often called "the problem-solver" in materials science, PI has been hailed as one of the most promising engineering plastics of the 21st century. It's no exaggeration to say, "without polyimide, modern microelectronics wouldn't exist." With its unmatched performance, PI sits at the top of the polymer materials hierarchy.

Polyimide (PI) Film: Properties and Production Process

Outstanding Properties of PI Film

PI film is renowned for its exceptional mechanical strength, dielectric properties, chemical stability, and resistance to radiation, corrosion, and extreme temperatures. As one of the world's best-performing super-engineering polymer materials, it's often referred to as the "golden film." Alongside carbon fiber and aramid fiber, it is considered one of the three critical polymer materials impacting the development of high-tech industries in China.

PI Film Production Process

Before imidization, PI film must first go through a film-forming process. The primary forming methods include:

Casting

Cast stretching (biaxial orientation)

Impregnation (adhesive coating on aluminum foil)

Spray coating

Extrusion

Deposition

Among these, casting and cast stretching are the most commonly used methods. Compared to casting, cast stretching is typically employed to produce high-performance PI films. In China, the casting and impregnation methods are well-developed; however, the impregnation method is being phased out due to inferior insulation properties. Advanced techniques such as spray coating, extrusion, and deposition-requiring higher technological expertise-were predominantly controlled by Japanese companies as of 2016.

Imidization Techniques

The imidization process, critical to producing PI films, is performed using one of two main methods:

Thermal Imidization:

Involves heating polyamic acid to a specific temperature to induce dehydration and cyclization.

While simpler in process and equipment, films produced by this method generally lack the physical and chemical properties required for electronic-grade PI films or higher.

Chemical Imidization:

This method involves adding a dehydrating agent and catalyst to a polyamic acid solution at a temperature below -5°C. The mixture is then rapidly heated to promote dehydration and cyclization.

Although more complex, this method yields superior film performance and is essential for producing high-performance PI films.

Applications of Polyimide (PI) Film

1) Growth in Flexible Printed Circuit Boards (FPC) Drives Expansion of the Electronic-Grade PI Film Market

Flexible Copper-Clad Laminate (FCCL) is a critical material for manufacturing Flexible Printed Circuit Boards (FPC). The global FCCL market grew from $2.64 billion in 2014 to $4.48 billion in 2019. As the main raw material for FCCL, demand for electronic-grade PI film has grown in tandem. In 2019, global demand for PI film in the FCCL industry reached 14,877.5 tons, with 4,869.0 tons consumed in China.

From 2014 to 2020, the domestic FPC market grew from RMB 29.07 billion to RMB 52.6 billion, representing a compound annual growth rate (CAGR) of 10.4%. With the development of new electronic products, the FPC industry gained fresh momentum, driving FPC production value to RMB 54.44 billion in 2021. This growth continues to expand the electronic-grade PI film market.

2) Rapid Development of Commercial Space and Flexible Screens Fuels Growth in Specialty-Grade PI Film

In aerospace, PI film is used as a protective material for rockets due to its outstanding weather resistance and radiation tolerance. In 2019, the commercial space industry's global market value exceeded RMB 800 billion, with a CAGR of 22.1%. Since raw materials can account for 35% of a rocket's total cost, increasing material localization is expected to significantly reduce manufacturing costs, driving demand for specialty-grade PI films.

In flexible screens, PI-based CPI film is widely used as cover materials for foldable smartphone displays. As flexible display technology becomes more commercialized, foldable phones are emerging as a key trend. Global shipments of foldable phones are projected to reach 45.3 million units by 2024, with 13.2 million units in China alone. As a core component of foldable phones, flexible covers will continue to boost demand for specialty-grade PI film.

Applications of Polyimide (PI) Film

1) Growth in Flexible Printed Circuit Boards (FPC) Drives Expansion of the Electronic-Grade PI Film Market

Flexible Copper-Clad Laminate (FCCL) is a critical material for manufacturing Flexible Printed Circuit Boards (FPC). The global FCCL market grew from $2.64 billion in 2014 to $4.48 billion in 2019. As the main raw material for FCCL, demand for electronic-grade PI film has grown in tandem. In 2019, global demand for PI film in the FCCL industry reached 14,877.5 tons, with 4,869.0 tons consumed in China.

From 2014 to 2020, the domestic FPC market grew from RMB 29.07 billion to RMB 52.6 billion, representing a compound annual growth rate (CAGR) of 10.4%. With the development of new electronic products, the FPC industry gained fresh momentum, driving FPC production value to RMB 54.44 billion in 2021. This growth continues to expand the electronic-grade PI film market.

 

2) Rapid Development of Commercial Space and Flexible Screens Fuels Growth in Specialty-Grade PI Film

In aerospace, PI film is used as a protective material for rockets due to its outstanding weather resistance and radiation tolerance. In 2019, the commercial space industry's global market value exceeded RMB 800 billion, with a CAGR of 22.1%. Since raw materials can account for 35% of a rocket's total cost, increasing material localization is expected to significantly reduce manufacturing costs, driving demand for specialty-grade PI films.

In flexible screens, PI-based CPI film is widely used as cover materials for foldable smartphone displays. As flexible display technology becomes more commercialized, foldable phones are emerging as a key trend. Global shipments of foldable phones are projected to reach 45.3 million units by 2024, with 13.2 million units in China alone. As a core component of foldable phones, flexible covers will continue to boost demand for specialty-grade PI film.

 

3) Surging Consumer Electronics Market Increases Demand for Thermal-Grade PI Film

Thermal-grade PI film is primarily used to produce thermal graphite sheets, which are essential for LED substrates and electronic component cooling. These are the mainstream thermal management materials in the consumer electronics industry.

In recent years, China's thermal interface materials market has expanded steadily, growing from RMB 660 million in 2014 to RMB 1.27 billion in 2020, with a CAGR of 9.9%. The rise of 5G technology is expected to further amplify demand for thermal-grade PI film in the coming years.