Industry analysis of polyimide film

Overview of Polyimide Film (PI Film)

Polyimide (PI) is a polymer containing an imide structure in its molecular backbone. It belongs to a large family of high-performance polymers, with most high-performance PI materials having aromatic and heterocyclic structures as their main backbone components. PI has the highest flame retardancy rating (UL-94) and exhibits excellent electrical insulation, mechanical properties, chemical stability, aging resistance, and radiation resistance. It has a dielectric constant of 4.0 at 103 Hz and a dielectric loss as low as 0.004–0.007, making it a Class F to H insulation material. These properties remain stable over a wide temperature range (-269°C to 400°C), earning PI the reputation of being "one of the most promising engineering plastics of the 21st century" and "the problem solver." It is often said that "without polyimide, modern microelectronics would not exist," as PI materials sit at the pinnacle of the polymer materials hierarchy.

Polyimide Film (PI Film)

PI film offers exceptional mechanical properties, dielectric properties, chemical stability, and outstanding resistance to radiation, corrosion, and extreme temperatures. It is considered one of the best-performing advanced engineering polymer materials worldwide and is often referred to as the "golden film." Alongside carbon fiber and aramid fiber, PI film is one of the three key polymer materials that significantly impact the development of high-tech industries in China.

 

Manufacturing Process of Polyimide Film (PI Film)

Before undergoing imidization, PI film must first be formed into a membrane using various methods, including casting, casting-stretching (biaxial stretching), impregnation (aluminum foil coating), spraying, extrusion, and deposition. The choice of processing method greatly affects the film's properties and production efficiency. Among these methods, casting and casting-stretching are the most commonly used. The latter is preferred for producing high-performance PI films. In China, both casting and impregnation methods are well developed, though the impregnation method is gradually being phased out due to its inferior insulation properties. More advanced techniques such as spraying, extrusion, and deposition remained predominantly under Japanese control as of 2016.

Currently, two primary imidization methods exist: thermal imidization and chemical imidization.

 

Thermal imidization involves heating polyamic acid to a specific temperature, inducing dehydration and cyclization.

 

Chemical imidization involves adding a dehydrating agent and catalyst to polyamic acid at temperatures below -5°C, rapidly mixing, and then heating to promote dehydration and cyclization.

 

Compared to chemical imidization, the thermal method is simpler in terms of process and equipment but produces films with inferior physical and chemical properties, making it unsuitable for electronic-grade PI films. Before 2014, most Chinese manufacturers relied on thermal imidization, whereas almost all major PI film manufacturers in developed countries had transitioned to chemical imidization. The newly built 180-ton PI film production line by Times New Materials was among the first in China to adopt the chemical imidization process, enabling the production of high-performance PI films for railway transportation applications.

 

Applications of Polyimide Film (PI Film)

1) Expanding Market for Electronic-Grade PI Film Driven by Flexible Printed Circuit Boards (FPCs)

Flexible Copper-Clad Laminate (FCCL) is a critical base material for manufacturing flexible printed circuit boards (FPCs). The global FCCL market grew from $2.64 billion in 2014 to $4.48 billion in 2019. As the primary raw material for FCCL, electronic-grade PI film demand has increased accordingly, reaching 14,877.5 tons worldwide in 2019, with 4,869 tons consumed in China.

From 2014 to 2020, China's FPC market grew from CNY 29.07 billion to CNY 52.6 billion, with a compound annual growth rate (CAGR) of 10.4%. Emerging electronic products continue to drive FPC demand, with the market projected to reach CNY 54.44 billion in 2021, further expanding the demand for electronic-grade PI film.

 

2) Growing Market for Specialty-Grade PI Film in Aerospace and Flexible Displays

In the aerospace sector, PI film is used as a protective material for rockets due to its excellent weather and radiation resistance. The global commercial aerospace market surpassed CNY 800 billion in 2019, with a CAGR of 22.1%. Since raw material costs account for about 35% of the total cost of a single rocket launch, domestic material production will significantly reduce manufacturing expenses, driving the growth of specialty-grade PI film.

 

In the flexible display sector, colorless PI (CPI) film is the preferred cover material for foldable smartphone screens. As flexible displays become more commercialized, foldable smartphones are emerging as a new form factor. By 2024, global foldable smartphone shipments are expected to reach 45.3 million units, with China accounting for 13.2 million units. As a core component of foldable screens, CPI film will continue to drive demand for specialty-grade PI film.

 

3) Rising Demand for Thermal Management PI Film in Consumer Electronics

Thermal graphite film, a derivative of thermal PI film, is widely used in LED substrates, electronic components, and other heat dissipation applications. The domestic market for thermal interface materials has grown from CNY 660 million in 2014 to CNY 1.27 billion in 2020, with a CAGR of 9.9%. The development of 5G technology is expected to further increase demand for thermal-grade PI film.

 

4) Expanding Market for Electrical-Grade PI Film in Wind Power and High-Speed Rail

Electrical PI film is mainly used in high-grade insulation systems for variable frequency motors and generators, which are essential in wind power and high-speed rail applications.

 

Wind Power: As of the end of 2020, China's wind power installed capacity reached 282 GW, growing by 34.3% year-over-year, accounting for 36% of the global total. With the push for renewable energy, domestic production of wind power materials, including electrical PI film, will continue to expand.

High-Speed Rail: China has the world's largest high-speed rail network, accounting for over 60% of the global total.

 

Polyimide Film (PI Film) Industry Chain Analysis

1) Upstream

Raw materials include dianhydride PMDA, diamine ODA, and other essential compounds. Some specialty PI monomers have been localized in China. PI film raw materials consist of PI monomers and PI resin solutions. Key PI monomers include dianhydride and diamine monomers.

2) Midstream

PI film is a highly versatile material with applications across numerous industries. The primary PI product forms include films, foams, fibers, photosensitive PI, and PI-based composites, with PI film accounting for over 70% of the total market. PI film production involves resin polymerization, casting, stretching, imidization, and post-processing.

Common PI film types and applications:

Thermal control PI film: Precursor for high thermal conductivity graphite film.

Electronic PI film: Used for electronic substrates and printed electronics.

Electrical PI film: Used in corona-resistant applications and Class C insulation.

Aerospace PI film: Used in polyimide composite aluminum foil (MAM).

 

3) Downstream

Common substrates for FCCL include PI film, polyester (PET), polyethylene naphthalate (PEN), and liquid crystal polymer (LCP).

FPCs, also known as flexible PCBs, use PI or PET films as base materials. Compared to rigid PCBs, FPCs offer higher production efficiency, higher wiring density, lighter weight, thinner profiles, and flexibility for three-dimensional wiring, making them ideal for aerospace, military, mobile communications, laptops, computers, digital cameras, and other electronics.

 

Industry Barriers for Polyimide Film (PI Film)

High Equipment Customization & Long Lead Times: Key equipment is mainly sourced from overseas, with procurement cycles of 18–24 months.

Complex Manufacturing Process & High Customization: PI film production, especially imidization, is technically demanding.