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Polyimide Characteristics And Application

Nov 02, 2015

 I. Overview
Polyimide as a special engineering materials, it has been widely applied in the fields of aviation, aerospace, microelectronics, nano, LCD, separation membranes, laser. Recently, countries are polyimide research, development and utilization of the inclusion of engineering plastics in the 21st century one of the most promising. Polyimide, its outstanding performance characteristics and synthesis, whether as a structural material or as a functional material, its potential application has been fully recognized, known as a "problem solver" ( protion solver), and that "there would be no polyimide microelectronic technology today."
Second, the performance of polyimide
1, wholly aromatic polyimide by thermal gravimetric analysis, it begins the decomposition temperature is generally about 500 ℃. Biphenyl dianhydride and p-phenylenediamine synthetic polyimide, the thermal decomposition temperature of 600 ℃, is one of the highest in the thermal stability of the polymer species so far.
2, polyimide can withstand very low temperatures, such as liquid helium will not rattle in the -269 ℃.
3, the polyimide having excellent mechanical properties, tensile strength unfilled plastics are 100Mpa or more, pyromellitic polyimide film (Kapton) is 170Mpa or more, and biphenyl type polyimide ( Upilex S) reaches 400Mpa. As a plastic, elastic modulus generally 3-4Gpa, fibers can be achieved 200Gpa, according to theoretical calculations, pyromellitic dianhydride and p-phenylenediamine synthetic fibers up to 500Gpa, after the carbon fiber.
4, a number of varieties of polyimide is insoluble in organic solvents, acid stable, generally little hydrolysis varieties, this seemingly shortcoming performance while filling the polyimide is different from a lot of other high-performance polymers characteristics, i.e., the raw material can be recovered by alkaline hydrolysis dianhydride and a diamine, for example, Kapton film having a recovery of up to 80% -90%. Changing the structure can be obtained quite hydrolysis resistant varieties, such as withstand 120 ℃, 500 小时 boiled.
5, the thermal expansion coefficient of the polyimide in 2 × 10-5-3 × 10-5 ℃, wide as the thermoplastic polyimide 3 × 10-5 ℃, biphenyl up 10-6 ℃, individual species can up 10-7 ℃.
6, polyimide has a high resistance to radiation performance, the film after 5 × 109rad fast electron irradiation strength retention rate of 90%.
7, the polyimide having good dielectric properties, dielectric constant of about 3.4, the introduction of fluorine, or dispersed in a nano-sized air polyimide, the dielectric constant can be reduced to about 2.5. Dielectric loss 10-3, a dielectric strength of 100-300KV / mm, wide as the thermoplastic polyimide 300KV / mm, volume resistivity of 1017Ω / cm. These properties over a wide temperature range and frequency range can maintain at a high level.
8, polyimide polymer is self-extinguishing, fuming rate.
9, polyimide in a high vacuum gas rarely decentralized.
10, polyimide non-toxic, used to make cutlery and medical equipment, and can withstand thousands of sterilization. Some polyimide also has good biocompatibility, for example, in blood compatibility test non-hemolytic, non-toxic in vitro cytotoxicity experiments.
Third, on the synthesis of a variety of ways:
Polyimide variety, in various forms, in the synthesis of a variety of ways, it can be selected according to various application purposes, variable continuity of this synthesis is also on other polymers are difficult to possess.
1, the polyimide is mainly of a dibasic acid anhydride and diamine synthesis, the two monomers with numerous other heterocyclic polymers, such as polybenzimidazole, polybenzoxazole dumb yl, polybenzothiazoles, polyquinoline dumb Compare morpholino and poly quinoline monomer, wide source of raw materials, synthesis is also easier. Dianhydride, diamine wide variety of different combinations of different properties can be obtained a polyimide.
2, may be formed of a polyimide dianhydride and a diamine in a polar solvent, such as DMF, DMAC, NMP, or THE / methanol mixed solvent of low temperature polycondensation to obtain a polyamic acid soluble, film-forming or spinning It was heated to about 300 ℃ dehydration ring-converted to a polyimide; may also be added acetic anhydride and the tertiary amine catalyst to the polyamic acid, the chemical dehydration cyclization to obtain a polyimide solution and a powder. Diamines and dianhydrides can also be in a high boiling solvent, such as phenolic solvent was heated polycondensation step to obtain a polyimide. In addition, it can by a four yuan acid dibasic esters and diamine reaction to obtain a polyimide; polyamide acid can also be made into a poly isoimide first, and then converted to a polyimide. These methods are easy to process brings, the former is called PMR method, you can obtain a low viscosity, high solid content solution, a low melt viscosity during processing window has a has, especially for the manufacture of composite materials in; the latter increase solubility, in the process of transformation does not release low molecular weight compounds.
3, as long as two anhydride (or four acid) and diamine purity qualified Regardless of the condensation method, are easy to obtain a sufficiently high molecular weight, added anhydride unit or units can be easily amine molecular weight regulation.
4, with the dianhydride (or tetracarboxylic acid) and a diamine polycondensation, as long as to reach an equimolar ratio, in a vacuum heat treatment, the solid low molecular weight prepolymer greatly increased molecular weight, and thus to the processing into powder with to facilitate.
5, it is easy to introducing a reactive group at the chain end or chain to form an active oligomers to obtain a thermosetting polyimide.
6, the use of polyimide carboxy, esterified or salified, or introducing a photosensitive group to give a long-chain alkyl amphiphilic polymer, photoresist or can be used for the preparation of LB films.
7, the general synthetic process does not produce polyimide inorganic salts, for the preparation of an insulating material is particularly advantageous.
8, as the dianhydride and diamine monomer is easily sublimated under high vacuum, it is easy to polyimide film vapor deposition method is formed on the workpiece, in particular the use of the uneven surface of the device.
Fourth, the polyimide applications:
Because of the characteristics of the polyimide in performance and synthetic chemistry, in many polymers, such as polyimide so hard to find with such a wide range of applications, but also in every aspect of the show a very outstanding performance .
1 film: polyimide is one of the first commodity, for motor slot insulation and cable wrapping material. The main products are DuPont Kapton, Ube of Upilex series and Kaneka Apical. Transparent polyimide film solar cells can be used as a soft bottom plate.
2. Paint: as an insulating paint for magnet wire, or as a high-temperature coatings.
3. Advanced Composites: for the aerospace, aircraft and rocket parts. It is one of the most high-temperature structural materials. E.g., U.S. supersonic aircraft speed plan is designed 2.4M, flight surface temperature of 177 ℃, requires the service life of 60000h, is reported to have been determined as 50% of the structural material to a thermoplastic polyimide matrix resin Carbon fiber reinforced composite material, the amount of each aircraft is about 30t.
4. Fiber: elastic modulus after the carbon fiber as the medium and high-temperature filter material and radioactive substances bulletproof, fireproof fabric.
5. Foam: as high temperature insulation material.
6. Engineering Plastics: thermosetting also thermoplastic, thermoplastic molding can also be used for injection molding or transfer molding. The main lubrication, sealing, insulation and construction materials for the self. Wide polyimide materials have begun to use the rotary vane compressor, piston rings and special pump seals and other mechanical parts.
7. Adhesive: as high temperature structural adhesive. Wide polyimide adhesives as electronic components insulation potting material has high production.
8. membranes: for a variety of gases, such as the separation of hydrogen / nitrogen, nitrogen / oxygen, carbon dioxide / nitrogen or methane, etc., to remove moisture from the air the hydrocarbon feed gas and alcohols. But also as a pervaporation membrane ultrafiltration. Since the polyimide heat resistance and organic solvent properties, has a special significance in the separation of organic gases and liquids.
9. photoresist: negative and positive rubber glue, with sub-micron resolution. And pigments or dyes can be used with a color filter film, which can greatly simplify processing operations.
10. In the microelectronic device applications: used as an interlayer dielectric layer insulation, as a buffer layer can reduce stress and improve yield. As the protective layer can reduce the impact of the environment on the device, it can also a- particles from the shielding effect, reducing or eliminating soft error (soft error) devices.
-oriented Agent 11. The LCD used: polyimide in TN-LCD, SHN-LCD, TFT-CD aligning agent material and future aspects of ferroelectric liquid crystal display occupies a very important position.
12. - The light material: material used for passive or active waveguide optical switch materials, fluorine-containing polyimide in the communication wavelength range of transparent polyimide as a chromophore base material can be improved stability.
In summary, it is easy to see many of the aromatic heterocyclic polyimide polymer can reason from the 1960s, 1970s stand out, eventually become reasons for an important class of polymer materials.