PBT raw material of touch switch/ toggle switch/ jack

Self-lubrication, low friction coefficient but large volume resistance and dielectric loss. The disadvantages are low notch impact strength and high shrinkage. Therefore, most of them are modified by glass fiber reinforced or inorganic filling. Their tensile strength and bending strength can be increased more than doubled, and the thermal deformation temperature can be greatly increased. It can work for a long time at 140℃. The longitudinal and transverse shrinkage of glass fiber reinforced products are inconsistent, which makes the products warp easily.

Combustion identification
It is not easy to burn. When burning, there is no liquid flowing down. It will extinguish within 5 seconds after leaving the flame. (Similar to PC).

Processing technology
PBT is thermoplastic. In order to be suitable for different processors, additives are usually added or mixed with other plastics. With the different proportion of additives, different specification products can be manufactured. PBT is widely used in electronic appliances, automotive parts, machinery and household products because of its heat resistance, weather resistance, chemical resistance, good electrical properties, low water absorption and good gloss. And PBT products with PPS, PC, POM and PA etc. are also called five general engineering plastics .

PBT has obvious melting point, the melting point is 225 - 235 C, and it is a crystalline material with a crystallinity of up to 40%.
The viscosity of PBT melt is less affected by temperature than by shear stress. Therefore, in injection molding, the influence of injection pressure on the flowability of PBT melt is obvious.

PBT products are anisotropy. PBT is easy to degrade when it's under water at high temperature.

Selection of injection molding machine
When selecting screw injection moulding machine. The following points should be considered.

①The material consumption of the product should be controlled at 30%-80% of the rated maximum injection volume of the injection moulding machine. It is not suitable to use large injection moulding machine to produce small products.

②Gradient type three-stage screw should be selected with length-diameter ratio of 15-20 and compression ratio of 2.5-3.0.

③Self-locking nozzle with heating and temperature control device should be selected.

④When forming the flame retardant PBT, the relevant parts of injection moulding machine should be treated with anticorrosion.

The shrinkage rate of the unmodified PBT is larger, ranging from 1.7% to 2.3%. The die must have a certain demoulding slope.

③Exhaust holes or vent grooves are required for the die.
④Gate diameter should be large.
⑤Temperature control device should be set in the mould. The maximum temperature of the die can not exceed 100 C.
⑥Flame-retardant PBT moulding, the surface of the die to be chrome-plated, in order to prevent corrosion.

Raw material preparation
The corresponding time does not exceed 6h, 4h, 2h. The thickness of material is less than 30 mm.

5
①Injection temperature. PBT decomposition temperature is 280 C, so the actual production is generally controlled between 240 - 260℃.

②The injection pressure is generally 50-100 MPa.

③The injection rate. Cooling speed of PBT is fast, so the injection rate should be fast.

④The screw speed and back pressure. The screw speed of forming PBT should not exceed 80 r/min, generally between 25 and 60 r/min. Back pressure is generally 10%-15% of injection pressure.

⑤The temperature of the die is generally controlled at 70-80℃, and the temperature difference of each part is not more than 10℃.

⑥The forming period is generally 15-60 s

Attention
①Use of Recycled Materials. The ratio of recycled material and new material is generally 25%-75%.

②Use of release agent. In general, the release agent is not used, and the silicone release agent can be used when necessary. 

③Shutdown treatment. The shutdown time of PBT is within 30min, and shut down when the temperature drops to 200℃. When the production is reproduced after long-term shutdown, the material in the barrel should be emptied and new material added before normal production can be carried out.

④Reprocessing of parts. Normally, no treatment is needed, and if necessary, it is treated for 1-2 hours at 120℃.

Physical characteristics

PBT is one of the toughest engineering thermoplastic materials. It is a semi-crystalline material with excellent chemical stability, mechanical strength, electrical insulation characteristics and thermal stability. These materials have good stability in a wide range of environmental conditions. The hygroscopicity of PBT is very weak. The tensile strength of non-reinforced PBT is 50 MPa, and Tension strength of glass additive PBT is 170MPa. Excessive glass additives will lead to brittle materials. PBT crystallizes rapidly, which results in bending deformation due to uneven cooling. For materials with glass additives, the shrinkage rate in the process direction can be reduced, but it is basically the same as that in the vertical direction of the process. The shrinkage of general materials ranges is from 1.5% to 2.8%. The material containing 30% glass additive shrinks between 0.3% and 1.6%. The melting point (225℃) and high temperature deformation temperature are lower than those of PET materials. Vicat softening temperature is about 170 C. The glass trasitio temperature ranges is from 22℃ to 43℃. Due to the high crystallization speed of PBT, its viscosity is very low, and the processing cycle time of plastic parts is generally low.

Applied range
Household appliances (food processing blades, vacuum cleaner components, fans, hair dryer housing, coffee utensils, etc.), electrical components (switches, motor housing, fuse box, computer keyboard keys, etc.), automotive industry (radiator panels, body panels, wheel covers, door and window components, etc.).