Flame-Proofing, High Melting Point Thermoplastic Polymers With Lactam-Impregnated Red Phosphorus

The invention is further illustrated by the following Examples in which parts and percentages are by weight. The K values given were determined by the method described by H. Fikentscher in Cellulosechemie, 13, 58 (1932). The term "melt blended" is used in these examples and throughout this specification to define the mixing and fine distribution or homogenization of the particulate red phosphorus in a melt of the thermoplastic polymer. During this melt blending, the lactam impregnant may change from a solid to a liquid to a gas, depending upon the processing conditions, and may be at least partly or even substantially completely removed by volatilization.

74 parts of polycaprolactam (K value 73.0) are pre-mixed in a 500 liter fluid mixer with the usual additives, 20 parts of chopped glass-fiber strands and 8 parts of caprolactam-impregnated red phosphorus (25% caprolactam) and the pre-mix is continuously fed to a twin-disc kneader. After melting, the material is passed to a mixing zone where it is intimately mixed for a short period at 220.degree. to 260.degree. C. It then passes to a devolatilizing zone where it is substantially feed from monomeric caprolactam under a vacuum of 50 mm of Hg before it is extruded through dies. The product is quenched, granulated and dried in the usual manner and part of it is hermetically packed while the other part is immediately injection molded to form shaped articles. There is thus obtained a glass-fiber-reinforced polycaprolactam of good flameretardant properties.

Following the general procedure described in Example 1, 91 parts of polyhexamethylene adipamide (K value 72.5) are premixed with the additives usually employed in nylon 6,6 injection molding compositions and with 12 parts of a mixture of 70% of red phosphorus and 30% of caprolactam, and the pre-mix is vigorously kneaded on a twin-disc kneader at 260.degree.-300.degree. C. and devolatilized without any technical problems occuring during processing of the impregnated red phosphorus. The granular product, obtained in the usual manner, posseses a K value of 73.8.

64 parts of polycaprolactam (K value 73.0) are continuously fed to the inlet of a twin-disc kneader together with the additives usually employed in polycaprolactam injection molding compositions. 30 parts of chopped strands and 8 parts of a red phosphorus/caprolactam mixture (40% lactam) are continuously fed to a second inlet disposed down-stream of the melting zone of the kneader. The heterogeneous mixture is vigorously kneaded for a short period at 220.degree.-260.degree. C. and the monomeric caprolactam is removed through a vacuum port down-stream of the mixing zone. The product is extruded as a strand or ribbon and then granulated.

62 parts of polyhexamethylene adipamide (K value 72.5) are continuously fed to the inlet of a twin-disc kneader together with additive. Through a second inlet, which is disposed downstream of the melting zone, there are continuously added 35 parts of powdered chalk and 4 parts of a mixture of 65% of red phosphorus and 35% of caprolactam, which mixture was obtained by a melting technique, and these second additives are readily incorporated in the molten polymer at 260.degree.-300.degree. C. After passing through the devolatilizing zone, in which the monomeric caprolactam is partially removed, the product is discharged through dies and is then granulated by a conventional hot granulator or an underwater granulator.

a. A red phosphorus/polyamide masterbatch is produced by continuously melting 50 parts of polycaprolactam in a twin-disc kneader and continuously addint to the melt, through a second inlet, 66,7 parts of a mixture of 80% of red phosphorus and 20% of caprolactam (prepared by a melting technique). After vigorous kneading at 220.degree.-270.degree. C., the monomeric caprolactam is removed through a vacuum port disposed downstream of the mixing zone, and the molten masterbatch is discharged and granulated in the usual manner.

b. Following the general procedure described in Example 1, 70 parts of polycaprolactam, 20 parts of chopped strands and 10 parts of the red phosphorus/polyamide masterbatch prepared as described under (a) above are continuously pre-mixed, together with the usual additives, on a drum mixer, and the resulting premix is continuously fed to a twin-disc kneader, where it is melted, thoroughly mixed at 220.degree.-260.degree. C. and discharged in the usual manner. There is thus obtained a material having very good mechanical properties and good flame-retardant properties.

There are mixed, in a high-speed mixer, 100 parts of polycaprolactam granules, 0.2 parts of calcium stearate, 0.5 part of N-(p-hydroxyphenyl)-benzamide and 0.5 parts of Cadmium Yellow, and the resulting mixture is fed to a twin-screw extruder and melted at 230.degree.-250.degree. C., while 7 parts of a homogeneous mixture of 70% of red phosphorus and 30% of caprolactam are added to the melt through a second inlet. About 65-70% of the monomeric caprolactam introduced is recovered through a vacuum port and the remaining composition is discharged through a die-head in the form of strands, which are quenched in water and granulated, the granules being dried at 110.degree. C.

Following the general procedure described in Example 3, 65 parts of a stable polyformaldehyde (K value 76, as measured in 1% solution in o-dichlorobenzene), 30 parts of chalk and 6.7 parts of a virtually homogeneous mixture of 75% of red phosphorus and 25% of caprolactam are continuously mixed in a twin-disc kneader at about 200.degree. C., the caprolactam being removed by devolatilization. The resulting flame-retardant mixture is extruded through dies.

Following the general procedure described in Example 3, 61 parts of polyethylene glycol terephthalate, 30 parts of asbestos and 12 parts of a mixture of 60% of red phosphorus and 40% of caprolactam are mixed and melt-blended in a twin-disc kneader at 230.degree.-250.degree. C. The monomeric caprolactam is sucked off after mixing has been completed in the extruder.