PBT was first developed by German scientist P. Schlack in 1942. Afterwards, Celanese Company (now Ticona) in the United States carried out industrial development and went public under the Celanex trade name. It was put on the market in 1970 as 30% glass fiber reinforced plastic. It was X-917 and later changed to CELANEX. In 1971, Eastman introduced glass fiber reinforced and non-reinforced products under the trade name Tenite (PTMT); in the same year, GE also developed similar products with three varieties of non-reinforced, reinforced and self-extinguishing. Then the world-renowned manufacturers BASF, Bayer, American GE, Ticona, Japan Toray, Mitsubishi Chemical, Taiwan Shinkong Synthetic Fiber, Changchun Synthetic Resin, Nanya Plastics and other companies have successively put into production, and there are more than 30 global manufacturers.
1. Overview of polybutylene terephthalate (PBT)
Polybutylene terephthalate (Polybutylene terephthalate), also known as polytetramethylene terephthalate. Referred to as PBT. It is a condensation polymer of terephthalic acid and 1,4-butanediol. PBT and PET together are called thermoplastic polyester.
2. Characteristics and applications of polybutylene terephthalate (PBT)
Application of PBT (usually referring to modified varieties);
a. Electronic appliances: connectors, switch parts, household appliances, accessory parts, small electric covers or (heat resistance, flame resistance, electrical insulation, molding processability);
1. Exterior parts: mainly include corner grid, engine vent cover, etc.;
2. Internal components: mainly include endoscope stays, wiper brackets and control system valves;
3. Automotive electrical parts: automotive ignition coil twisted tubes and various electrical connectors, etc.
(The number of PBT used in automobiles is not as good as nylon, polycarbon and polyoxymethylene, but with the emergence of low-warpage PBT, it will definitely be used in automobile parts in the future)
c. Mechanical equipment: belt drive shaft of video tape recorder, electronic computer cover, mercury lamp cover, electric iron cover, baking machine parts and a large number of gears, cams, buttons, electronic watch casings, camera parts (with heat resistance, Flame retardant requirements)
3. Bonding of PBT plastic:
According to different needs, you can choose the following adhesives:
1. TG-3200: one-component room temperature curing soft elastic shockproof adhesive, resistant to high and low temperature, but the bonding speed is slow, the glue usually takes 1 day or several days to cure.
2. TS-8602 instant adhesive can quickly bond PBT in a few seconds or tens of seconds, but the adhesive layer is hard and brittle and not resistant to water.
3. TE-9270 type, two-component glue, soft glue layer, suitable for large area bonding or compounding of PBT. But the high temperature resistance is poor.
4. TE-9249 glue: two-component glue, high temperature resistance.
5. Sili-1706: One-component room temperature vulcanizate. After curing, it is an elastomer with excellent waterproof, shockproof adhesive, high and low temperature resistance. If the thickness is 1-2mm, it will basically cure in 5-6 hours and has a certain strength. It takes at least 24 hours to fully cure. Single-component, no need to mix, just apply after extruding and let it stand without heating.
Process characteristics of PBT
Before PBT injection, it must be dried at a temperature of 110-120°C for about 3 hours, the molding processing temperature is 250-270°C, and the mold temperature should be controlled at 50-75°C. Since the material is cooled from the molten state, it will immediately solidify and crystallize, so its cooling time is shorter; if the nozzle temperature is not properly controlled (lower), the flow channel (nozzle) is easy to cool and solidify, which will cause a plugging phenomenon. If the barrel temperature exceeds 275°C or the molten material stays in the barrel for more than 30 minutes, the material will decompose and become brittle. In PBT injection molding, a larger nozzle is required to feed the glue. It is not suitable to use a hot runner system. The mold must be well exhausted. It is advisable to use "high speed, medium pressure, and medium temperature" conditions for molding. For recycling, PE or PP material should be used to clean the material pipe in time when the machine is shut down to avoid carbonization.