Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Patent
1997-09-29
1999-08-24
Hampton-Hightower, P.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
525420, 524100, 524122, 524123, 524494, 524600, 524606, C08L 7700, C08G 6948, C08K 534
Patent
active
059425849
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a process for producing flame-retardant polyamides.
Synthetic polyamides (PA) are used in a variety of applications in many areas of the industry and for everyday consumption. This is due mainly to the good processing properties and the possibility of tailoring these polymers to the application. At present, just under 90% of polyamide consumption consists of the standard types polyamide 6 (poly-.epsilon.-caprolactam) and polyamide 66 (polyhexamethyleneadipamide); polyamide 11 (polyundecaneamide), polyamide 12 (poly-.epsilon.-laurinlactam), polyamide 610 (polyhexamethylenesebacamide) and polyamide 612 (polyhexamethylenedodecaneamide) and copolyamides account for the remaining 10%. More than 80% of worldwide polyamide production is processed to fibers and fabrics; just under 20% is used in industrial applications, in particular in automotive engineering, the electronics industry, the packaging sector and construction of machinery and equipment. The good mechanical properties often required industrially are achieved with fiber reinforcement or mineral fillers. In the field of electrical engineering, the use of polyamides has been successful because of their high insulation resistance, good tracking resistance and solvent resistance as well as good thermo-mechanical properties, in particular for insulation and switch parts, solenoid valves, busbars, cable mounts, coil bodies, plug connectors, and casings.
Although polyamides are self-extinguishing according to some test methods, they lose this property after the addition of fillers such as glass fibers or pigments. For numerous applications in electrical engineering and in automotive engineering, however, reinforced, flameproof polyamide is needed. The flameproofing should offer enough time to rescue people and valuables in the event of a fire.
At the present time, mainly organic halogen compounds and red phosphorus are used as flameproofing agents. The halogen compounds are mainly chlorinated or brominated hydrocarbons, which are often combined with zinc compounds or antimony trioxide, the latter of which has a synergistic effect but has been found to be carcinogenic in animal experiments. Halogen compounds have the disadvantage that they release highly corrosive and highly toxic degradation products such as hydrogen chloride and hydrogen bromide in a fire and they cause heavy production of smoke; they also reduce the toughness and tracking resistance of polyamides. Red phosphorus is usually used in encapsulated form. Despite the encapsulation, however, there is the danger of phosphorus fires at high processing temperatures. This can lead to increased wear on the processing machines and even explosions as a result of disproportionation to phosphine and phosphates. Another disadvantage is the poor electrical corrosion property of polyamide materials finished with red phosphorus to be flame-retardant, besides their dark color.
To avoid the disadvantages associated with halogen compounds and red phosphorus, there have been attempts for several years to develop flameproofed polyamides without such flameproofing agents. For example, the use of nitrogen compounds such as dicyanodiamide (German Offenlegungsschrift No. 3,909,145), melamine and melamine salts (German Offenlegungsschrifts Nos. 3,609,341 and 4,141,861) and melamine adducts (German Offenlegungsschrift No. 3,722,118) has been proposed. To achieve adequate flame retardancy, in particular with glass fiber-reinforced materials, however, very high filler levels are required, which have a negative effect on the mechanical properties. Magnesium hydroxide, which has also been proposed (Kunststoffe, vol. 80 (1990) pages 1107-1112), also causes a weakening of the mechanical strength, when used in the required high concentrations; the release of water, which begins at the processing temperature, also causes bubbles to form. For partially aromatic polyamides, the use of high concentrations of polyphosphonates has also been proposed (German Offenlegungsschrift No. 3
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Hampton-Hightower P.
Siemens Aktiengesellschaft
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