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1、 Overview of Polyimide Film (PI Film)
Polyimide (PI) refers to a high molecular weight polymer with an imide structure in its main chain. Polyimide is a very large family, and the main chain of high-performance PI is mostly composed of aromatic and heterocyclic rings as the main structural units. PI has the highest flame retardant rating (UL-94), good electrical insulation performance, mechanical performance, chemical stability, aging resistance, radiation resistance, a dielectric constant of 4.0 at 103 Hz, and a dielectric loss of only 0.004-0.007. It belongs to the F to H level insulation, and these properties will not undergo significant changes in a wide temperature range (-269 ℃ to 400 ℃). It is known as "one of the most promising engineering plastics of the 11th century" and is known as a "problem-solving expert". It can be said that "without polyimide, there would be no microelectronics technology today". Its performance ranks at the top of the pyramid of high molecular materials.
PI film has excellent mechanical properties, dielectric properties, chemical stability, as well as high radiation resistance, corrosion resistance, and high and low temperature resistance. It is currently one of the best performing super engineering polymer materials in the world and is known as the "golden film". Along with carbon fiber and aramid fiber, it is one of the three key polymer materials that constrain the development of high-tech industries in China.
Polyimide film (PI film)
2、 Production process of polyimide film (PI film)
Polyimide films need to be molded before imidization, and the main molding methods include casting, extrusion stretching (biaxial oriented stretching), impregnation (aluminum foil gluing), spraying, extrusion, and deposition. The molding process has a significant impact on the performance and production methods of thin films. Currently, the commonly used methods are tape casting and tape stretching. Compared to tape casting, tape stretching is commonly used to prepare high-performance polyimide films. Both the casting method and immersion method are relatively mature in China, among which the immersion method is gradually being phased out due to poor insulation performance of the products. The spraying method, extrusion method, and deposition method, which are technically difficult, were mainly mastered by advanced Japanese companies in 2016.
At present, there are two main methods for imidization, namely thermal imidization and chemical imidization. Thermal imidization heats polyamic acid to a certain temperature to dehydrate and cyclize it; The chemical imine method involves adding a certain amount of dehydrating agent and catalyst to a polyamide acid solution maintained at a temperature below -5 ℃, rapidly mixing them, and heating them to a certain temperature to dehydrate and cyclize them. The process and equipment of thermal imidization method are simpler than those of chemical imidization method, but the physical and chemical properties of the obtained film are insufficient compared to chemical imidization method, and it cannot produce PI films that meet electronic grade and above. Before 2014, the vast majority of manufacturers in China used thermal imidization, but almost all polyimide film manufacturers in developed countries have completed the technology and equipment transition from thermal imidization to chemical imidization. The 180 ton polyimide film production line newly built by Times New Materials is one of the first production lines in China to use chemical imidization method for imidization step, which can produce high-performance polyimide films that meet the needs of rail transit.
Typical manufacturing process flow of polyimide film
3、 Application scenarios of polyimide film (PI film)
1) The output value of flexible circuit boards (FPCs) has increased, promoting the continuous expansion of the electronic grade PI film market
Flexible copper-clad laminate (FCCL) is an important substrate for manufacturing flexible circuit boards (FPCs). The global FCCL market size has grown from 2.64 billion US dollars in 2014 to 4.48 billion US dollars in 2019. Electronic grade PI film, as the main raw material for FCCL, has seen a synchronous increase in demand with FCCL. In 2019, the global demand for PI film in the FCCL industry reached 14877.5 tons, with a domestic demand of 4869.0 tons. From the perspective of FPC output value, the domestic FPC output value increased from 29.07 billion yuan to 52.6 billion yuan from 2014 to 2020, with a compound growth rate of 10.4%. The development of downstream new electronic products injects new growth momentum into the FPC industry, and the FPC output value can grow to 54.44 billion yuan in 2021, promoting the continuous expansion of the electronic grade PI film market.
2) The rapid development of commercial aerospace and flexible screens is driving the continuous growth of the special grade PI film market
In the aerospace field, PI film is used as a rocket protection material due to its excellent weather resistance and radiation resistance. In 2019, the market size of the entire commercial aerospace industry chain exceeded 800 billion yuan, with a compound growth rate of 22.1%. Due to the fact that the raw material cost of a single launch vehicle can account for 35% of the total cost, the localization of raw materials is bound to significantly reduce manufacturing costs, thereby promoting the growth of special grade PI films. In the field of flexible screens, flexible CPI film is the screen cover material used by most foldable phone manufacturers. With the continuous commercialization of flexible displays, foldable phones have gradually become a new form of mobile phones. According to relevant predictions, the global shipment of foldable phones will reach 45.3 million units in 2024, and the domestic shipment will reach 13.2 million units. As the core component of foldable phones, flexible cover plates will drive the continuous growth of special grade PI films.
3) The momentum of consumer electronics is rapid, and there is a greater demand for thermal grade PI films
Thermal conductive graphite film is a downstream product of thermal conductive PI film, mainly used in LED substrates, electronic component heat dissipation and other fields. It is currently the mainstream heat dissipation material used in the consumer electronics industry. In recent years, the domestic market for thermal interface materials has gradually expanded, growing from 660 million yuan in 2014 to 1.27 billion yuan in 2020, with a compound growth rate of 9.9%. The driving force of 5G technology will bring greater demand space for thermal grade PI films.
4) The wind power and high-speed rail industry markets are steadily rising, and the scale of the electrical grade PI film industry continues to expand
Electrical PI film is mainly used in high-grade insulation systems such as variable frequency motors and generators, and ultimately applied in fields such as wind power generation and high-speed rail transit. In the wind power industry, China is the world's largest market for wind power development. As of the end of 2020, the cumulative installed capacity of domestic wind power reached 282GW, a year-on-year increase of 34.3%, accounting for 36% of the global cumulative installed capacity. Against the backdrop of advocating for new energy, with the localization of the wind power industry chain, electrical PI films will have broader market prospects. In the high-speed rail transit industry, China has the world's largest operating mileage of high-speed rail, accounting for over 60%.
4、 Analysis of the polyimide film (PI film) industry chain
1) Upstream
Binary anhydride PMDA, binary amine ODA, and other raw materials. The upstream special PI monomers have been localized, and the raw materials for PI film are PI monomers and PI slurry. PI monomers include dianhydride monomers and diamine monomers.
2) Midstream
PI film has superior performance and a wide range of downstream applications. The product forms of polyimide include film, foam, fiber, photosensitive polyimide and polyimide based composites, among which PI film accounts for more than 70%, which is the most important product form of polyimide industry. The manufacturing of PI film requires production processes such as resin polymerization, salivation casting, directional stretching imidization, and post-treatment.
Application of various types of PI films: thermal control PI film (high thermal conductivity graphite film precursor PI film), electronic PI film (PI film for electronic substrates, PI film for electronic printing), electrical PI film (corona resistant PI film, C-grade electrical PI film), aviation PI film (polyimide composite aluminum foil MAM).
3) Downstream
Common types of FCCL sheet films include polyimide film (PI), polyester (PET), polyethylene naphthalate (PEN), liquid crystal display polymer (LCP), and other polymer plastic films.
FPC, also known as flexible PCB, is mainly made of eight types of raw materials including flexible copper-clad laminate (FCCL), cover film, electronic components, shielding film, adhesive paper, steel sheet, electroplating additives, dry film, etc. Among them, FCCL is the most important substrate for producing FPC, accounting for 40%. All processing steps of FPC are completed on FCCL. The global FCCL production capacity is mainly concentrated in Japan, Chinese Mainland, South Korea and Taiwan, China, of which Chinese Mainland accounts for 21%, ranking third. FPC is a flexible PCB made of polyimide (PI) or polyester (PET) film as the substrate. Compared with traditional PCB hard boards, it has significant advantages such as high production efficiency, high wiring density, light weight, thin thickness, foldable bending, and three-dimensional wiring. It is more in line with the downstream electronic industry's trend of intelligence, portability, and lightweight. It can be widely used in fields or products such as aerospace, military, mobile communication, laptops, computers, digital cameras, etc. It is the fastest-growing category among various sub products in the PCB industry in recent years.
5、 Barrier to the polyimide film (PI film) industry
The technical barriers to production capacity are relatively high, and the main technical barriers to high-end PI membranes lie in equipment processes and talent
1) The equipment customization cycle is relatively long. The procurement of core equipment mainly comes from overseas, with a procurement cycle of about 18-24 months, which provides sufficient predictive ability for manufacturers' technology and market, otherwise they dare not place orders for procurement rashly.
2) The process is difficult and the degree of customization is high. The preparation of PI film itself is difficult, especially whether the imidization process can break through chemical methods is a common challenge. And the relevant parameters and processes of PI film vary for different industries and customers, requiring repeated debugging and technical breakthroughs to achieve stable mass production. The downstream high-end markets of PI film, such as electronics, communication, and rail transit, are extremely demanding on product quality. If stable mass production cannot be guaranteed, it will be difficult to gain customer recognition.
3) Technical talents are scarce. R&D and workshop operators with PI film production capabilities require a high level of theoretical knowledge and long-term R&D practice, which is difficult to achieve quickly. Therefore, for any PI film manufacturer, the core R&D team is highly valued.
