Polybutylene terephthalate (PBT) is a general-purpose engineering plastic. The polymerization process of PBT is mature, with low cost, easy molding and processing. The performance of unmodified PBT is poor. In practical applications, it is necessary to modify PBT, with glass fiber reinforced modification grades accounting for more than 70% of PBT. Process characteristics of PBT has a significant melting point of 225~235 ℃. It is a crystalline material with a crystallinity of up to 40%. The viscosity of PBT melt is not affected as much by temperature as by shear stress. Therefore, in injection molding, the impact of injection pressure on the fluidity of PBT melt is significant. PBT has good fluidity and low viscosity in the molten state, second only to nylon, and is prone to "tape casting" during molding.
Polybutylene terephthalate (PBT) is a general-purpose engineering plastic. The polymerization process of PBT is mature, with low cost, and easy molding and processing. The properties of unmodified PBT are not anisotropic for PBT molded products. PBT is prone to degradation when exposed to water at high temperatures. When the screw type injection molding machine is selected as the injection molding machine. The following points should be considered. ① The material consumption of the product should be controlled within 30% to 80% of the rated maximum injection volume of the injection molding machine. It is not suitable to use large injection molding machines to produce small products The gradual change type three-stage screw should be selected, with a length-diameter ratio of 15 to 20 and a compression ratio of 2.5 to 3.0 The self-locking nozzle should be selected and equipped with a heating and temperature control device. ④ When molding flame retardant PBT, the relevant components of the injection molding machine should undergo anti-corrosion treatment.
3.Product and mold design ① The thickness of the product should not be too thick, and PBT is very sensitive to gaps. Therefore, transition points such as right angles of the product should be connected by circular arcs. ② The molding shrinkage of PBT is relatively large, ranging from 1.7% to 2.3%. The mold should have a certain release angle The mold needs to be equipped with exhaust holes or slots. ④ The diameter of the gate should be large The mold needs to be equipped with a temperature control device. The maximum temperature of the mold cannot exceed 100 ℃. ⑥ Flame retardant PBT molding, mold surface to be chrome plated to prevent corrosion.
4.The raw materials should be dried before injection molding, and the moisture content should be controlled below 0.02%. When using hot air circulation drying, when the temperature is 105 ℃, 120 ℃, or 140 ℃, the corresponding time does not exceed 8h, 5h, or 3h. The material layer thickness is less than 30mm.
5.Injection molding process parameters ① The injection temperature PBT decomposition temperature is 280 ℃, so in actual production, it is generally controlled between 245~260 ℃. ② Injection pressure The injection pressure is generally 50~100MPa. ③ Injection rate PBT has a fast cooling rate, so a faster injection rate should be used. ④ The screw speed and the screw speed of back pressure molding PBT should not exceed 80 r/min, generally between 25 and 60 r/min. The back pressure is generally 10% to 15% of the injection pressure. ⑤ The mold temperature is generally controlled at 70~80 ℃, and the temperature difference between various parts does not exceed 10 ℃. ⑥ The molding cycle is typically 15 to 60 seconds. 6 Precautions: ① The ratio of recycled materials to new materials is generally between 25% and 75%. ② The use of release agent generally does not use release agent, and if necessary, silicone release agent can be used The shutdown time for processing PBT is within 30min, and it can be stopped when the temperature drops to 200 ℃. When reproducing after a long-term shutdown, it is necessary to empty the material in the barrel and add new material before normal production can proceed Generally, the post-treatment of products does not require treatment, and if necessary, it should be treated at 120 ℃ for 1-2 hours.

Polybutylene terephthalate is a crystalline thermoplastic engineering plastic that is polymerized from dimethyl terephthalate (DMT) and 1,4-butanediol. Due to the growth of the - CH2 - chain of PBT resin, the molecular chain is prone to flexion, so the glass transfer temperature is lower than PET, and the crystallization rate increases rapidly. The chemical structure formula of PBT is as follows: PBT was successfully studied by Celanese Company of the United States in the early 1970s, and was listed under the Celanex trade name. Subsequently, world-renowned manufacturers such as BASF, Bayer, GE, Ticona of the United States, Toray of Japan, Mitsubishi Chemical, Taiwan's New Light Synthetic Fiber, Changchun Artificial Resin South Asia Plastics and other companies have successively put into production, with a total of over 30 global manufacturers. PBT, also known as thermoplastic polyester plastic, is suitable for use by different processors. Generally, additives are added or mixed with other plastics. Depending on the proportion of additives, different specifications of products can be manufactured. Due to its heat resistance, weather resistance, drug resistance, excellent electrical properties, low water absorption, and good gloss, PBT is widely used in electronic appliances, automotive parts, machinery, household products, and so on. PBT products, together with PPE, PC, POM, PA, are known as the five major general-purpose engineering plastics.

The downstream applications of PBT are related to industries including automotive, electronic/electrical, and mechanical industries. (1) Connectors are bridges between signals and are indispensable components for transmitting electronic signals and power connections. The balanced physical properties and prices of PBT meet the needs of connectors. PBT is usually mixed with 30% glass fiber as a connector. PBT is widely used due to its mechanical properties, solvent resistance, excellent formability, and low price. Due to the poor heat resistance of soldered tin, PBT cannot be used on SMT type connectors. (2) The second major use of a heat dissipation fan PBT is to use it as a heat dissipation fan. The heat dissipation fan is placed in the machine for a long time to help dissipate heat. The physical properties of the plastic require heat resistance, flame retardancy, insulation, and mechanical strength. PBT is usually used in the form of 30% fiber addition as the outer frame and fan blade (3) bobbin of the heat dissipation fan. The third use of PBT is to serve as a winding shaft in transformers and relays, and is generally formed by injecting 30% fiber into the PBT. The physical properties required for the winding shaft include insulation, heat resistance, solder resistance, fluidity, strength, etc. Suitable materials include phenolic resin, PBT, PA6, and PET. Phenolic resin has good properties, but its formability is not as good as PBT. Therefore, products with small sizes and complex shapes are all made of PBT resin. Although PBT solder has poor heat resistance, countries such as Europe, America, and Japan with high environmental awareness have a trend to increase the use of recyclable PBT. (4) The automotive industry consumes approximately 2200 metric tons of PBT in the automotive industry, half of which is formed from PBT/PC alloys with PCs, which can be used as automotive bumpers. In addition, PBT can also be used for window motor housings, locomotive motor parts, automotive transmission gear boxes, and so on. Other uses of PBT include adding 15% glass fiber as the inner seat and outer shell of the base of the energy-saving lamp bulb, using PBT/PC adhesive as the sole of skates, and other applications such as relay housings, sockets, switches, and tuner housings.