Polybutylene terephthalate injection molding

Polyesters, which are a class of engineering thermoplastics, are found in a wide variety of applications including carbonated drink bottles, fibers for synthetic fabrics, thin films for photographic films and food packaging, injection molded automotive parts, and housings for small appliances. In this chapter, we svill explore the synthesis of this class of polymers. We will also look at the typical properties and end uses for the most common of these resins, polyethylene terephthalate and polybutylene terephthalate, which are commonly known as PET and PBT, respectively. 

Polyethylene terephthalate is most often extruded into films or fibers, or blow molded into bottles. Polybutylene terephthalate is primarily found in injection molded parts. Such parts are highly crystalline, which makes them opaque. Polybutylene terephthalate is often modified with glass fibers or impact modifiers. Table 24.1 contains applications by processing method and resin. 

Injection molding grades of polyethylene terephthalate and polybutylene terephthalate have low melt viscosities. Because of this, they can be used to manufacture intricate parts within... 

Typically, polyester resins are used for high-end applications that require excellent electrical and thermal resistance. When dimensional stability under load is more critical, glass fibers are incorporated to increase the heat distortion temperature and the stiffness of the part. Examples of glass fiber reinforced parts include electrical housings, electrical adapters, computer components, telephone housings, and light bulb sockets. When impact modified, polybutylene terephthalate can be injection molded to make car bumpers. 

Polyesters exhibit excellent high temperature strength and electrical properties making them a good choice for many demanding applications. They also are physiologically inert allowing them to be used in food contact applications. The two common polyesters, polyethylene terephthalate and polybutylene terephthalate, are both used in injection molded products. Polyethylene terephthalate is often used in both extrusion and blow molded processes also. 

What properties of polybutylene terephthalate make it amenable to injection molding processing ... 

Heating polybutylene terephthalate with 3 mol% of a tin catalyst in o-dichlorobenzene converted it to cyclic oligomers, which might be of value in reaction injection molding.204... 

Laminated tubes are made from multilayer materials that usually contain paper as well as plastic, and often also include aluminum foil as a barrier layer. The preprinted tube bodies are sealed into a cylinder, with the edges of the sleeve overlapped and compressed, squeezing some of the plastic out around the raw edges of the foil and paper to make a good seal. Next the tube is cut to length, and finally the head is molded and assembled to the body. To improve the barrier in the head, a premolded insert of polybutylene terephthalate or urea can be incorporated in the injection mold when the head is formed. 

Thermoplastic alloy of styrene maleic anhydride copolymer and polybutylene terephthalate. Has improved dimensional stability and tensile strength. Processed by injection molding. Also called SMA PBT Alloy. 

S. J. Liu, M. J. Lin and Y. C. Wu, An experimental study of the water-assisted injection molding of glass fiber filled polybutylene terephthalate (PBT) composites, Composites Science and Technology, 67,1415-1424 (2007). 

Polybutylene Terepbtbalate Thermoplastic polymer of dimethyl terephthalate and butanediol. Has good tensile strength, dielectric properties, and chemical and water resistance, but poor impact strength and heat resistance. Processed by injection and blow-molding, extrusion, and thermo forming. Used in auto body parts, electrical devices, appliances, and housings. Also called PBT. 

---