Injection molding moldability

The low thermal stability of many poly(iminocarbonates) limits the use of melt fabrication techniques such as injection molding or extrusion. For example, among all six polymers tested, only poly-(Dat-Tyr-Hex) and poly(CTTH) had low enough softening points to be compression moldable without a significant degree of thermal decomposition. ... 

These moldable thermoplastic polyesters are marketed under the trade names Celanex, Tenite, and Valox. These highly crystalline thermoplastics may be extruded or injection molded and may also be reinforced by fiberglass. 

Figure 4.67. Processability diagrams (moldability) for injection molding of thermoplasuc materials. I - thermal degradation zone II - incomplete filling m - melting IV bum. [Adapted, by permission, from Z. Tadmor,...

Figure 4.70. Processability diagram (moldability) for the stage of mold filling in reactive injection molding dependence of material temperature (or average temperature on flow rate G). I - premature filling II - poor impregnation mixing III - flow instabilities.

In creating a process window for the combination of material, machine and heater used in this study, the first consideration was the moldability, which was dictated by the maximum injection pressure and the maximum clamp force. No changes in melt and mold temperature, injection velocity, or gate size could remedy this situation. Thus, an injection molding machine with higher injection speeds, pressures and clamp force was required to mold thin-walled syndiotactic polystyrene. 

The addition of antinucleating agents permits the injection molding of PET (Rynite). Injection moldable glycol-modified polyesters (PETG, Kodar) have been produced by partial replacement of the ethylene glycol by cyclohexanol dimethylol. 

Cell Hardware. Cell jars are constructed almost exclusively of injection-molded plastics, which are resistant to the strong alkali electrolyte. The most generally used materials are modified styrenes or copolymers of styrene and acrylonitrile (SAN). Another material that has been found to increase shock resistance of cells is ABS plastic (acrylonitrile—butadiene—styrene). All of these plastics can be injection-molded, are solvent-sealable and, in general, meet operating temperature ranges up to about 70°C. For applications that require greater resistance to temperature, some of the more recent plastics such as polysulfone and poly(phenylene oxide) (PPO) injection-moldable materials able to withstand operating temperatures up to 150°C are used. 

Poly(dihydroxymethylcyclohexyl terephthalate) was introduced by Eastman Kodak as Kodel in 1958. Here, the insertion of the cyclohexyl moiety gives a more hydrophobic material (in comparison to PET and PBT) as well as a more moldable product that can very readily be injected-molded. (See Figure 7.) The polymer s sole raw material is dimethyl terephthalate. Reduction of dimethyl terephthalate yields the dialcohol, cyclohexa-nedimethanol. Kodel, along with its blends and mixtures, is often extruded into film and sheeting for packaging. Kodel-type materials are used to pack-... 

Characterization and Moldability Analysis of Epoxy Reaction Injection Molding Resins... 

The wholly aromatic copolyester for injection molding is available in filled and unfilled grades. It can be molded into thin-wall components at high speeds. The high melt flow also enables it to be molded into heavy-wall parts. No mold release is required because of the inherent lubricity and nonstick properties. No post-curing is necessary because the material is completely thermoplastic in nature. The material is expected to have many applications because of its moldability and its resistance to high temperatures, fire, and chemicals. 

Monsanto Chemical Co. produce injection molded Nylon/ABS alloys (Triax) that are characterized by good toughness, high chemical resistance, and easy moldability. Applications of these alloys include industrial power tools, lawn and garden equipment housing and handles, gears, pump impellers, and car fascia. 

Electrically conductive compositions are fabricated by blending an injection-moldable LCP and nickel-coated graphite fibers that are impregnated with a non-liquid-crystalline thermoplastic binder resin. The blending is done below the melting point of the LCP. The mixture is processed in an injection molding machine. A balance among conductivity, process-ability, and structural properties is desirable. Materials for electrically conductive compositions are summarized in Table 16.6. 

Polyurethanes (PU or PUR) and polyureas are classified as TS resins, but their chemistry is so flexible that they can be formulated different ways. There are moldable solid and expanded TSs, with (RPUR) or without reinforcement, flexible and rigid foams, elastomers and thermoplastic molding compounds. As RPs they are important in reinforced reaction injection molding (RRIM) (Chapter 5) and are also available as reinforced thermoplastic molding compounds. A variant on the process employs a structural preform of the reinforcement that is placed in the mold cavity and is called structural reaction injection molding (SRIM). 

Could a similar phenomenon occur in the melt Were thermotropic polymers possible They were possible, and indeed the number reported to date by academic and industrial researchers is nearly beyond count. In addition, as it later turned out, aromatic thermotropic polymers were found to offer a great many more useful properties than just their now well-known tensile capabilities. These polymers are injection moldable, albeit at temperatures in the vicinity of 400° C, a temperature not compatible with common melt-spinning equipment. The rate of thermal degradation of such a polyester at 400° C makes stable fiber production particularly difficult. Moreover, most conventional injection-molding equipment requires modification to operate at the high temperatures needed to ensure reasonable processing of this polymer. 

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