Heat deflection additives

Table 3.17 contains general information on heat deflection additives... 

Automated soldering operations can subject the mol ding to considerable heating, and adequate heat deflection characteristics ate an important property of the plastics that ate used. Flame retardants (qv) also ate often incorporated as additives. When service is to be in a humid environment, it is important that plastics having low moisture absorbance be used. Mol ding precision and dimensional stabiUty, which requites low linear coefficients of thermal expansion and high modulus values, ate key parameters in high density fine-pitch interconnect devices. 

The addition of 40% fiberglass increases the heat deflection temperature to 250 °C. 

POLYARYLATES. These are clear, amorphous thermoplastics that combine clarity, high heat deflection temperatures, high impact strength, good surface hardness, and good electrical properties with inherent ultraviolet stability and flame retardance. No additives or stabilizers are required to provide these properties. Polyarylates are aromatic polyesters that are manufactured from various ratios of iso- and terephthalic acids with bisphenol A.1 The resultant products are free-flowing pellets which can be processed by a variety of thermoplastic techniques in transparent and... 

An increase in heat deflection temperature of some thermoplastic polymers can be achieved by the addition of polyfunctional aromatic cyanates (BPA/DC in particular) and trimerization catalysts. A rigid network is formed as a resul t of the cyanate trimerization. The polymer material consists of a linear polymer and a crosslinked network and belongs to the class of semi-IPNs (semi-interpenetrating Polymer Networks) the corresponding classification is given in [34-37]. 

The major disadvantages of polymercaptan curing agents are their odor, skinning, and low heat deflection temperature. Progress has been made in the areas of odor and skinning through additives to the adhesive formulation. However, the low heat resistance is an artifact of the epoxy-mercaptan chemistry. 

In common with most thermoplastics, ABS polymers are not flame resistant. In principle, a flame-resistant ABS could be made by incorporating halogen- and/or phosphorus-containing structures either by (a) copolymerization of appropriate monomers or (b) addition of small molecules containing these structures as plasticizers. Recognizing that the second approach can involve a serious loss in heat deflection temperature, hardness, and occasionally impact strength (4), we have favored the copolymerization approach in the work described here. 

Plasticizers and waxy additives can give good initial color and physical property results yet cause the finished product to have poor heat deflection properties that can lead to latent part warpage. Much of this delayed defect phenomenon is associated with crystalline or semicrystalline products that must recrystallize after melting in order to reach their full property potential. Waxes and plasticizers can hinder recrystallization, and the effects can be different in thick sections that cool slower than thin sections. 

The addition of carbon black to ABS resin improves its hardness, modulus of rigidity, heat deflection temperature, and ultraviolet stability but reduces its ultimate strength, particularly its impact strength. Fine particle size and high structure carbon blacks have the greatest effects. 

Table 8.4 shows that substantial gains can be obtained by filling crystalline polymers but amoiphous polymers are not much affected by reinforcement. Also, particulate fillers are substantially less effective than fibrous fillers. Glass fiber is the most useful filler in this application. Figure 8.55 shows the effect of two grades of particulate fillers on the heat deflection temperature of polypropylene." Small changes are obseiwed at smaller additions followed by a rapid increase in HDT above a 30% filler content. The particle size has only small difference. 

Figure 8.55. Heat deflection temperature of polypropylene containing hydrated K-Mg aluminosilicate. [Adapted, by permission, from Schott N R, Rahman M, Perez M A, J. Vinyl and Additive Technol., 1, No.l, 1995,36-40.]...

III) PE blends with up to 30 wt% of a rigid polymer. The additional polymer plays the filler role Increasing both the modulus and the heat deflection temperature. At low concentration, say below 5% of rigid polymer, the coiqiatlblllzatlon Is seldom necessary, but It Is a must for blends at higher loadings. 

The low-speed mechanical properties of polymer blends have been frequently used to discriminate between different formulations or methods of preparation. These tests have been often described in the literature. Examples of the results can be found in the references listed in Table 12.9. Measurements of tensile stress-strain behavior of polymer blends is essential [Borders et al., 1946 Satake, 1970 Holden et al., 1969 Charrier and Ranchouse, 1971]. The mbber-modified polymer absorbs considerably more energy, thus higher extension to break can be achieved. By contrast, an addition of rigid resin to ductile polymer enhances the modulus and the heat deflection temperature. These effects are best determined measuring the stress-strain dependence. 

The nylon casting process is relatively more economical and is a more practical technique for the production of large and thick parts than comparable extrusion and injection molding processes. In addition, the crystallinity and molecular weight of cast nylon are higher than those of extruded or molded nylon. Consequently, cast nylon has a much higher modulus and heat deflection temperature, improved solvent resistance, and better hygroscopic characteristics and dimensional stabflity. 

Figure 3.42. Concentration of poly(acrylonitrile-styrene-acrylate) in PVC blend vs. heat deflection temperature. [Data from Zerafati, S.,J. Vinyl Additive TechnoL, 4,1, 35-38,1998.]...

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