It has excellent physical and mechanical properties in a wide temperature range, the long-term use temperature can reach 65438 0 20℃, and the electrical insulation performance is excellent. Even at high temperature and high frequency, its electrical properties are still good, but its corona resistance is poor, and its creep resistance, fatigue resistance, friction resistance and dimensional stability are good.
Basic introduction Chinese name: polyethylene terephthalate English name: polyethylene terephthalate nickname: polyester; Chemical formula of polyester etc. : COC6H4COOCH2CH2O Molecular weight: -CAS registration number: 25038-59-9 Melting point: 250-255℃ Boiling point:-Water solubility: density at -25℃: 1.38g/ml Appearance: highly crystalline polymer with milky white or yellowish color. Brief introduction, advantages, properties, uses, processing methods, molding and introduction of smooth and shiny surface English name: polyethylene PET (abbreviated as PET) alias: polyethylene terephthalate; Polyethylene terephthalate; Polyester; Polyester; Polyethylene terephthalate; Polyester and so on. Si Nuo. : 25038-59-9 Density:1.38g/mlat25 C Melting point: 250-255°C Polyethylene terephthalate is the most important variety of thermoplastic polyester, commonly known as polyester resin. It is formed by transesterification of dimethyl terephthalate and ethylene glycol or esterification of terephthalic acid and ethylene glycol to synthesize dihydroxyethyl terephthalate, and then polycondensation. Together with PBT, it is called thermoplastic polyester, or saturated polyester. 1946, the first patent for preparing PET was published in Britain, 1949, and the pilot test of ICI formula in Britain was completed. However, after purchasing the patent, DuPont Company of the United States set up a production device at 1953, which took the lead in realizing industrial production in the world. In the early days, PET was almost entirely used in synthetic fibers (commonly known as polyester and polyester in China). Since 1980s, PET has made a breakthrough as an engineering plastic, and successively developed nucleating agent and crystallization promoter. At present, PET and PBT, as thermoplastic polyester, have become one of the five major engineering plastics. PET is divided into fiber grade polyester chips and non-fiber grade polyester chips. ① Fiber-grade polyester is used to manufacture polyester staple fibers and polyester filaments, and it is the raw material for processing fibers and related products in polyester fiber enterprises. Polyester is the largest variety of chemical fiber. ② Non-fiber grade polyester is also used in bottles, films and other fields, and is widely used in packaging industry, electronic appliances, medical and health care, construction, automobiles and other fields. Packaging is the largest non-fiber application market of polyester and the fastest developing field of PET. Widely used as fiber, engineering plastic resin is divided into two categories: non-engineering plastic grade and engineering plastic grade. Non-engineering plastic grade is mainly used for bottles, films, tablets, baking-resistant food containers and so on. PET is a kind of high crystalline polymer with milky white or light yellow, and its surface is smooth and shiny. It has excellent physical and mechanical properties in a wide temperature range, the long-term use temperature can reach 65438 0 20℃, and the electrical insulation performance is excellent. Even at high temperature and high frequency, its electrical properties are still good, but its corona resistance is poor, and its creep resistance, fatigue resistance, friction resistance and dimensional stability are good. PET has ester bond, which will decompose under the action of strong acid, strong alkali and steam, and has good organic solvent resistance and weather resistance. The disadvantages are slow crystallization speed, difficult molding, high molding temperature, long production cycle and poor impact performance. Generally, the processability and physical properties of resin are improved by reinforcement, filling and * * * mixing. Glass fiber has obvious reinforcement effect, which improves the rigidity, heat resistance, drug resistance, electrical properties and weather resistance of the resin. However, it is still necessary to improve the shortcoming of slow crystallization speed, and measures such as adding nucleating agent and crystallization promoter can be taken. Adding flame retardant and anti-dripping agent can improve the flame retardancy and self-extinguishing property of PET. Advantages: 1 Good mechanical properties, impact strength 3~5 times that of other films, and good folding resistance. 2. Oil resistance, grease resistance, acid resistance, dilute alkali resistance and resistance to most solvents. 3. It can be used in the temperature range of 55-60℃ for a long time, and can withstand the high temperature of 65℃ and the low temperature of -70℃ for a short time, and the temperature has little influence on its mechanical properties. 4. The permeability of gas and water vapor is low, and it has excellent resistance to gas, water, oil and odor.
5. High transparency, blocking ultraviolet rays and good gloss. 6. Non-toxic, tasteless, good health and safety performance, and can be directly used for food packaging. High-performance PET is a kind of high crystalline polymer with milky white or yellowish color, and its surface is smooth and shiny. It has good creep resistance, fatigue resistance, wear resistance and dimensional stability, low wear and high hardness, and has the greatest toughness among thermoplastics: good electrical insulation, little influence by temperature, but poor corona resistance. Non-toxic, weatherproof, good chemical stability, low water absorption, weak acid and organic solvent resistance, but not hot water immersion and alkali resistance. PET resin has high glass transition temperature, slow crystallization speed, long molding cycle, large molding shrinkage, poor dimensional stability, brittle crystallization and low heat resistance. By improving nucleating agent, crystallizing agent and glass fiber reinforcing agent, PET has the following characteristics besides PBT. 1. The thermal deformation temperature and long-term service temperature are the highest among thermoplastic general engineering plastics. 2. Because of its high heat resistance, reinforced PET is immersed in a solder bath at 250℃ for 10S, and hardly deforms or discolors, so it is especially suitable for welding electronic and electrical parts. 3. The bending strength is 200MPa, the elastic modulus is 4000MPa, the creep resistance and fatigue resistance are also very good, the surface hardness is high, and the mechanical properties are similar to those of thermosetting plastics. 4. Because the price of ethylene glycol used to produce PET is almost half that of butanediol used to produce PBT, PET resin and reinforced PET are the lowest in engineering plastics, with high cost performance. In order to improve the properties of PET, PET can be blended with PC, elastomer, PBT, PS, ABS and PA. PET (reinforced PET) is mainly processed by injection molding, and other methods include secondary processing methods such as extrusion, blow molding, coating and welding, sealing, machining and vacuum coating. It must be fully dried before molding. Polyethylene terephthalate is synthesized by transesterification of dimethyl terephthalate and ethylene glycol or esterification of terephthalic acid and ethylene glycol, and then condensed. It is a crystalline saturated polyester with an average molecular weight of (2-3)× 104, and the ratio of weight average to number average molecular weight is 1.5- 1.8. Glass transition temperature is 80℃, Martin heat resistance is 80℃, and thermal deformation temperature is 98℃( 1. 82MPa), and the decomposition temperature is 353℃. It has excellent mechanical properties, high rigidity, high hardness, low water absorption and good dimensional stability. Good toughness, impact resistance, friction resistance and creep resistance. Good chemical resistance, soluble in cresol, concentrated sulfuric acid, nitrobenzene, trichloroacetic acid and chlorophenol, insoluble in methanol, ethanol, acetone and alkanes. Service temperature-100 ~ 120℃. Bending strength 148-3 10MPa water absorption 0. 06%-0. 129% impact strength 64. 1- 128J/m rockwell hardness M 90-95 elongation 1.8%-2.7% is widely used: mainly used in electronic appliances: electrical sockets, electronic connectors, rice cookers. Flow control valve, carburetor cover, window controller, pedal transmission and switchboard cover in automobile industry; Machinery industry gears, blades, pulleys, pump parts, in addition to wheelchair body and wheels, lampshade shell, illuminator shell, drain pipe connector, zipper, clock parts, sprayer parts. In addition, it can also be spun into polyester fiber, that is, polyester. Can be made into thin films for substrates, insulating films, product packaging, etc. Audio, video and movies. As a plastic, it can be blown into various bottles, such as coke bottles and Potter bottles. Can be used as electrical parts, bearings, gears and so on. Processing method: polyester polyester is formed by polycondensation of terephthalic acid and ethylene glycol, following the general law of linear polycondensation. In order to produce polyester, two synthetic technologies, transesterification and direct esterification, have been developed. (1) transesterification or indirect esterification This is a traditional production method, which consists of three steps: methyl esterification, transesterification and final polycondensation. The purpose of methyl esterification is to promote the purification of dimethyl terephthalate. ① Methylated terephthalic acid reacts with a little excess methanol and then esterifies to dimethyl terephthalate. Low-boiling substances such as water, excess methanol and methyl benzoate are distilled, and then purified dimethyl terephthalate is obtained by rectification. (2) Ester exchange reaction Under the temperature of 190~200℃, dimethyl terephthalate and ethylene glycol (molar ratio of about 1:2.4) were subjected to ester exchange reaction with cadmium acetate and antimony trioxide as catalysts to produce polyester oligomer. Distilling methanol to make transesterification complete. (3) Final polycondensation: at a temperature higher than the melting point of polyester, such as 283℃, using antimony trioxide as a catalyst, ethylene glycol terephthalate is self-polycondensed or transesterified, and by means of decompression and high temperature, ethylene glycol is continuously distilled out, and the degree of polymerization is gradually improved. In the stages of methyl esterification and transesterification, the proportion of isoenzymes is not considered. In the final polycondensation stage, according to the distillation amount of ethylene glycol, the proportion of the two groups is naturally adjusted to gradually approach the amount of other substances, so that ethylene glycol is slightly excessive and the two ends of the molecule are closed, reaching the predetermined degree of polymerization. (2) After the direct esterification purification technology of terephthalic acid is solved, this is the preferred economic method. Terephthalic acid and excess ethylene glycol are esterified at 200℃ to form polyethylene terephthalate with low polymerization degree (such as X= 1~4), and finally condensed at 280℃ to form the final polyester product with high polymerization degree (n= 100~200). This step is the same as indirect esterification. With the increase of polycondensation reaction degree, the viscosity of the system increases. In engineering, it is more advantageous to carry out polycondensation in two reactors in stages. Pre-polycondensation: 270℃, 2000~3300Pa. Late final polycondensation: 280~285℃, 60~ 130Pa. Molding processing The molding processing of PET can be injection molding, extrusion, blow molding, coating, bonding, machining, electroplating, vacuum metallization and printing. The following mainly introduces two kinds. 1. Injection stage ① Temperature setting: nozzle: 280~295℃, front stage 270~275℃, middle forging 265~275℃, rear stage 250 ~ 270℃; Screw speed 50~ 100rpm, mold temperature 30~85℃, amorphous mold temperature below 70℃, back pressure 5 ~ 15kg. (2) Try a dehumidifying dryer, with feed pipe temperature of 240~280℃, injection pressure of 500~ 1400℃, injection molding temperature of 260~280℃, drying temperature of 120~ 140℃ for 2~5 hours. 2. In the film-forming stage, the PET resin chips are pre-dried to prevent hydrolysis, and then the amorphous thick chips are extruded through a T-shaped die at 280℃ in an extruder, and then quenched by a cooling drum or a cooling liquid to keep the amorphous state for tensile orientation. The thick sheet was stretched in two directions by a tenter to form a PET film. Longitudinal stretching is to preheat the thick plate to 86~87℃, and stretch it about 3 times along the plane extension direction of the thick plate at this temperature, so that its orientation can improve the crystallinity and reach a higher temperature: the preheating temperature of transverse stretching is 98~ 100℃, the stretching temperature is120℃, and the stretching multiple is 2.5. The film after vertical and horizontal stretching needs heat setting to eliminate the deformation of the film caused by stretching and make it a film with good thermal stability.