Polybutylene terephthalate
Polybutylene terephthalate, also known as PBT, belongs to the polyester series. It is a crystalline thermoplastic polyester resin made by polycondensation of 1.4-pbt butylene glycol with terephthalic acid (PTA) or terephthalate (DMT), and is made through a mixing process. It is translucent to opaque in milky white. Together with PET, they are collectively referred to as thermoplastic polyester, or saturated polyester.
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PBT: Polybutylene terephthalate
1. PBT history
2. PBT Physical and chemical properties
3. PBT combustion identification
4. PBT processing technology
5. PBT injection molding process characteristics and process parameter settings
6.1 PBT Process characteristics
7.2 Injection molding machine
8.3 Product and mold design
9.4 Raw materials preparation
10.5 Injection molding process parameters
11.6 Precautions
Development Status and Prospect of PBT in China
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PBT: Polybutylene terephthalate

PBT history
PBT was first developed by German scientist P. Schlack in 1942. Later, Celanese Corporation (now Ticona) of the United States conducted industrial development and went public under the trade name Celanex. In 1970, PBT was launched as 30% glass fiber reinforced plastic under the trade name X-917, which was later changed to CELANEX. In 1971, Eastman Company launched products with glass fiber reinforced chains and non-reinforced ones, under the trade name Tenite (PTMT); In the same year, GE also developed similar products, including three types of non-enhanced, enhanced, and self-extinguishing products. Subsequently, world-renowned manufacturers such as BASF and Bayer from Germany, GE and Ticona from the United States, Toray from Japan, Mitsubishi Chemical, Taiwan's New Light Synthetic Fiber, Changchun Artificial Resin, and South Asia Plastics have successively put into production, with a total of over 30 global manufacturers.

PBT physical and chemical properties
PBT is an opalescent translucent to opaque, crystalline thermoplastic polyester. It has high heat resistance, toughness, fatigue resistance, self-lubrication, low friction coefficient, low weather resistance, and only 0.1%. water absorption. It still maintains various physical properties (including electrical properties) in a humid and electrical insulation, but has large bulk resistance and dielectric loss. Resistant to hot water, alkalis, acids, and oils, but susceptible to halogenated hydrocarbons, poor hydrolysis resistance, rapid crystallization at low temperatures, and good formability. The disadvantages are low notch impact strength and large molding shrinkage. Therefore, most of them are reinforced with glass fibers or modified with inorganic fillers, which can increase their tensile strength and bending strength by more than twice, and greatly increase their thermal deformation temperature. It can work at 140 ℃ for a long time. After glass fiber reinforcement, the longitudinal and transverse shrinkage of the product are inconsistent, which is easy to cause warpage of the product.

PBT combustion identification
Not easy to burn, no liquid flows down during combustion, it is extinguished within 5 seconds after leaving the flame, (similar to PC)

PBT processing technology
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.
PBT has a fast crystallization rate, and the most suitable processing method is injection molding. Other methods include extrusion, blow molding, coating, and various secondary processing molding. Predrying is required before molding, and the moisture content should be reduced to 0.02%.
Injection molding process characteristics and process parameter setting of PBT
The polymerization process of PBT is mature, with low cost, and 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.
1 PBT  Process characteristics
PBT has a significant melting point of 225 to 235 ℃, and is a crystalline material with a crystallinity of up to 40%.
The viscosity of melt PBT 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
Anisotropy of PBT molded products. PBT is prone to degradation when exposed to water at high temperatures.

2 Injection molding machine
The following points should be considered when selecting a screw injection molding machine.
①The 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.
②To choose the gradual change type three stage screw, with a length to diameter ratio of 15 to 20 and a compression ratio of 2.5 to 3.0.
③To choose the Self-locking nozzle with heating and temperature control device
④When molding flame retardant PBT, the relevant components of the injection molding machine should undergo anti-corrosion treatment

3 Product and mold design
①product should not be too thick, and PBT is very sensitive to notches. Therefore, transition points such as right angles of the product should be connected by circular arcs.
②The molding shrinkage of unmodified PBT is relatively large, ranging from 1.7% to 2.3%. The mold should have a certain release angle.
③The mold needs to be equipped with exhaust holes or slots
④The diameter of the gate should be large.
⑤The mold needs to be equipped with a temperature control device. The maximum temperature of the mold cannot exceed 100 ℃.
⑥Flame retardant PBT molding, mold surface to be chrome plated to prevent corrosion.

4 Raw material preparation
Before injection molding, it is necessary to dry and control the moisture content below 0.02%. When using hot air circulation drying, with the temperature 105 ℃, 120 ℃, or 140 ℃, the corresponding time does not exceed 6h, 4h, or 2h. The material layer thickness is less than 30mm.

5 Injection molding process parameters
①The decomposition temperature of the injection temperature PBT is 280 ℃, so in actual production, it is generally controlled between 240-260 ℃.
②The injection pressure is generally 50 to 100 MPa.
③Injection rate PBT has a fast cooling rate, so a faster injection rate should be used
④The 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.
⑤The mold temperature is generally controlled at 70 to 80 ℃, and the temperature difference between various parts does not exceed 10 ℃.
⑥The molding cycle is generally 15 to 60 seconds.

6 Attention:
①The ratio of recycled materials to new materials is generally between 25% and 75%.
②Use of release agent : Usually, no release agent is used, silicone release agent can be used when necessary,
③The shutdown process: PBT shutdown time process is within 30min, 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.
④Product post-treatment: Generally, it is not required, if necessary, it is treated at 120 ℃ for 1-2 hours.

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Development Status and Prospect of PBT in China
PBT resin, known as polybutylene terephthalate, is one of the five major general-purpose engineering plastics, mainly used in the fields of PBT modification, PBT filament drawing, film pulling, and optical fiber sheath. After enhanced modification, it can be widely used in the fields of automotive manufacturing, electronics, instrumentation, lighting appliances, household appliances, textiles, machinery, and communications. In recent years, due to the development of domestic related industries, the demand for PBT resin has increased year by year. Japanese and Taiwan PBT manufacturers have significantly increased their production capacity since 2002, and their exports to China have increased significantly in the past three years, accounting for about 90% of the total imports of Chinese Mainland, which has impacted domestic PBT manufacturers. Due to the impact of the international financial crisis and the appreciation of the RMB, from January to June 2009, China imported 50368 tons of polybutylene terephthalate (PBT), a decrease of 35.7% compared to the same period in 2008; The import value was US $117.81 million, a decrease of 40.4% compared to the same period in 2008.
With the rapid development of China's national economy, especially the rapid development of the downstream electronics and automotive industries, the demand for PBT market has increased rapidly. In the context of the country's anti-dumping measures against imported products, with the booming car market, which is completely different from the depression caused by the financial crisis, various favorable policies of the government to encourage car consumption and activities such as moving cars to the countryside have played a catalytic role. With the rapid demand for plastics in the automotive industry in recent years, the plastic industry and the automotive industry in China have formed a trend of "prosperity and loss for all". Plastics industry insiders have shifted their goal to modifying PBT plastics and using lighter, stronger, and better automotive accessories to alleviate the high oil price situation.
Modified PBT plastics refer to the addition of small molecular inorganic or organic substances to polymers (resins) to impart or improve certain properties through physical or chemical actions. Such as toughening, reinforcing, plasticizing, flame retarding, etc., and through modification technologies, plastics have become fresh and distinctive, especially in the fields of automobiles and household appliances, modified PBT plastics has the greatest application and potential development of
Modified PBT plastic is the most important lightweight material for automobiles. It not only reduces the weight of components by about 40%, but also reduces procurement costs by about 40%. Therefore, the use of PBT plastic in automobiles has increased rapidly in recent years. Currently, automotive interiors have basically realized plasticization, and the development of "replacing steel with plastics" in automobiles is driving the continuous development and innovation of modified PBT plastics in automobile applications towards a broader field.
In the field of automotive manufacturing, PBT is widely used in the production of bumpers, carburetor components, fenders, spoilers, spark plug terminal boards, fuel supply system components, instrument panels, automotive igniters, accelerators, clutch pedals, and other components. The competition between PBT and enhanced PA, PC, and POM in the automotive manufacturing industry is fierce. PA is easy to absorb water, and the thermal resistance of PC is less than that of PBT; In terms of automotive use nozzles, PBT will gradually replace PA due to its superior water resistance to PA. In situations where the relative humidity is high and very humid, modified PBTs can often be used because humidity can easily lead to reduced plasticity and corrosion at electrical nodes. PBT can still be used normally at 80 ℃ and 90% relative humidity, and the effect is very good.
Among them, PBT/PC alloy is the most widely used in high-end cars; It has good heat resistance, stress cracking resistance, excellent wear resistance, chemical corrosion resistance, high low-temperature impact strength, easy processing and good finishing performance, it is mainly used in high-end car bumpers, car floor panels, panels, and motorcycle guards.