Polyimide film is made of PMDA and ODA in strong polar solvents by condensation, casting and imidization. It is yellow transparent and has a relative density of 1.39-1.45. It is especially suitable for flexible printed circuit board substrate and various high-temperature electrical insulation materials.
Characteristics of PI film
(1) excellent heat resistance
The decomposition temperature of polyimide is generally more than 500 ℃, sometimes even higher. It is one of the most thermostable organic polymers known at present, mainly because there are a lot of aromatic rings in the molecular chain.
(2) excellent mechanical properties
The tensile strength of the unreinforced matrix material is above 100MPa. The tensile strength of Kapton films prepared with homo-anhydride is 170MPa, while that of biphenyl polyimide (Upilex S) is 400 MPa. The elastic modulus of polyimide fiber can reach 500MPa, second only to carbon fiber.
(3) good chemical stability and heat resistance.
Polyimide materials are generally insoluble in organic solvents, and are resistant to corrosion and hydrolysis. Changes in molecular design can yield varieties of different structures. Some varieties can withstand 2 atmospheres, 120 degrees, and 500h.
(4) good radiation resistance.
The strength of polyimide film remained 86% after 5 *109 rad irradiation. The strength retention rate of some polyimide fibers was 90% after 1 *10 10 rad fast electron irradiation.
(5) good dielectric properties
The dielectric constant is less than 3.5. If fluorine atoms are introduced into the molecular chain, the dielectric constant can be reduced to about 2.5, the dielectric loss is 10, the dielectric strength is 100-300 kV/mm, and the volume resistance is 1015-17_ cm. Therefore, the synthesis of fluorinated polyimide materials is a popular research field.