Flameproof polymer moulding material

Salt mixtures made from aluminum phosphinates, aluminum hydroxide and/or aluminum phosphonates and/or aluminum phosphates are thermally stable and are suitable as flame retardants for polymeric molding compositions, in particular for polyesters and polyamides. The use of these salt mixtures is more effective and more cost-effective than the use of aluminum phosphinates alone.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The invention relates to flame-retardant polyester molding compositions and
 flame-retardant polyamide molding compositions which contain aluminum
 phosphinates, aluminum hydroxides and/or aluminum phosphonates and/or
 aluminum phosphates.
 2. Description of the Prior Art
 Polymers are frequently rendered flame-retardant by adding to them
 phosphorus-containing or halogen-containing compounds or mixtures of
 these. Some polymers are processed at high temperatures, e.g. at
 250.degree. C. or at higher temperatures. For this reason, many of the
 known flame retardants are not suitable for applications of this type,
 because they are too volatile or have insufficient thermal stability.
 Aluminum salts of phosphinic acids are thermally stable and have already
 been proposed as flame-retardant additives for polyesters and polyamides
 (EP-A-0 699 708). However, the phosphinic acids needed for their
 preparation are relatively expensive. For cost reasons, therefore, there
 is a need for polymeric molding compositions with phosphinates as flame
 retardants which can be produced at lower cost.
 SUMMARY OF THE INVENTION
 The invention relates to a polymeric molding composition which contains a
 phosphinate of the formula (I) and/or a diphosphinate of the formula (II)
 and/or polymers of these,
 ##STR1##
 where R.sup.1 and/or R.sup.2 is C.sub.1 -C.sub.6 -alkyl, preferably C.sub.1
 -C.sub.3 -alkyl, which may be linear or branched, e.g. methyl, ethyl,
 n-propyl, isopropyl, n-butyl or tert-butyl, where R.sup.1 and R.sup.2 may
 also be linked to a ring, and R.sup.3 is C.sub.1 -C.sub.10 -alkylene,
 which may be linear or branched, e.g. methylene, ethylene, n-propylene,
 isopropylene, n-butylene, tert-butylene, n-pentylene, n-octylene,
 n-dodecylene or phenylene,
 and also aluminum hydroxide and/or aluminum phosphate and/or aluminum
 phosphonate of the formula (III),
 ##STR2##
 where R.sup.4 is C.sub.1 -C.sub.6 -alkyl, preferably C.sub.1 -C.sub.3
 -alkyl, which may be linear or branched, e.g. methyl, ethyl, n-propyl or
 isopropyl, R.sup.5 is C.sub.1 -C.sub.3 -alkyl. preferably methyl, n is 0
 or 1, and X is 1 if n is 1, and X is 2 if n is 0.
 DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Polymeric compositions which may be mentioned are polyester molding
 compositions and polyamide molding compositions, in particular
 polyethylene terephthalate and polybutylene terephthalate. Examples of
 aluminum salts of phosphinic acids (aluminum phosphinates) are: aluminum
 salts from dimethylphosphinic acid, ethylmethylphosphinic acid,
 isopropylmethylphosphinic acid, methane-1,2-di(methylphosphinic acid) and
 benzene-1,4-(dimethylphosphinic acid), of
 1-hydroxy-3-methyl-2,5-dihydro-1H-phosphole-1-oxide and of
 1-hydroxy-2,5-dihydro-1H-phosphole-1-oxide. Examples of aluminum salts of
 phosphonic acids (aluminum phosphonates) are: an aluminum salt of
 monomethyl methanephosphonate, of monomethyl propanephosphonate, of
 methanephosphonic acid, of ethanephosphonic acid and of propanephosphonic
 acid.
 The aluminum phosphinates and aluminum phosphonates may be prepared by
 known methods, by reacting the corresponding acids in aqueous solution
 with aluminum hydroxide.
 The preparation of the salt mixtures according to the invention is likewise
 simple, and takes place by intensive mixing or grinding. However, in
 individual cases it may be advantageous to use specific methods of
 preparation. For example, a mixture of an aluminum salt of
 ethylmethylphosphinic acid and aluminum hydroxide in a weight ratio of
 about 70:30 is prepared by reacting ethylmethylphosphinic acid with
 aluminum hydroxide in a molar ratio of 1:1. It is possible moreover to
 prepare mixtures of the aluminum phosphinates with phosphonates and
 phosphoric acid by mixing the corresponding acids in the desired molar
 ratio and reacting with aluminum hydroxide in the appropriate molar ratio.
 For example, ethylmethylphosphinic acid and monomethyl methanephosphonate
 may be reacted in a weight ratio of 80:20 with appropriate stoichiometric
 amounts of aluminum hydroxide in glacial acetic acid as solvent, in
 accordance with German Patent Application 196 45 125.6.
 The amounts of the salt mixtures to be added to the polymers may vary
 within wide limits. The amount used is generally from 5 to 35% by weight,
 based on the polymer, preferably from 10 to 25% by weight and in
 particular from 10 to 20% by weight. The ideal amount of the salt mixture
 depends on the nature of the polymer and on the type of salt mixture used,
 and may readily be determined by trials.
 The ratio of the aluminum phosphinates to the other components of the salt
 mixture may likewise vary within wide limits. The amount of aluminum
 phosphinate used is generally about 50% by weight, preferably from 70 to
 80% by weight, based on the salt mixture.
 The salt mixtures are thermally stable do not decompose the polymers during
 processing and do not affect the process of preparing the polymeric
 molding composition. The salt mixtures are nonvolatile under the
 conditions of preparation and processing of polymers.
 The salt mixtures according to the invention may be used in various
 physical forms, depending on the type of polymer used and the properties
 desired. For example, to achieve better dispersion in the polymer the salt
 mixtures may be ground to give fine particles.
 The salt mixtures may be incorporated into the polymer by mixing both
 together and then melting the polymer in a compounding system (e.g. in a
 twin-screw extruder) and homogenizing the salt mixture in the polymer
 melt. The melt may be drawn off as extrudate, cooled and granulated. It is
 also possible to meter the salt mixture directly into the compounding
 system.
 It is likewise possible to mix the flame-retardant additives into finished
 granules and to injection-mold directly, or to granulate after melting in
 an extruder and to process after drying.
 The salt mixtures may also be added during the process of preparing the
 polymer.
 Besides the salt mixtures, fillers and reinforcing materials such as glass
 fibers, or minerals such as chalk, may be added to the polymer. The
 products may contain other additives besides these, such as stabilizers,
 lubricants, colorants, fillers, nucleating agents and antistats.

EXAMPLE 1
 7 parts of aluminum ethylmethylphosphinate and 3 carts of aluminum
 hydroxide were mixed well. Surprisingly, the mixture is stable when
 exposed to temperatures up to 285.degree. C., above which noticeable
 elimination of water commences: in contrast, aluminum hydroxide begins to
 eliminate water from 200.degree. C.
 Compounds reinforced with 30% of glass fibers were prepared from the salt
 mixture and polybutylene terephthalate (PBT) without other additives, and
 test specimens of thickness 0.8 mm were injection-molded and tested with
 the following result:
 ##STR3##
 For comparison, aluminum ethylmethylphosphinate was used alone instead of
 the salt mixture. This comparison took place under the same conditions,
 but with a concentration of 14%. This corresponds to the same content of
 aluminum ethylmethylphosphinate as in a formulation containing 20% of the
 salt mixture mentioned above.
 In the comparative experiment, the UL 94 flammability classification V-2
 was not achieved.
 EXAMPLE 2
 7 parts of aluminum ethylmethylphosphinate and 3 parts of aluminum
 phosphate were mixed well. The mixture is stable when exposed to
 temperatures up to 360.degree. C.
 Compounds reinforced with 30% of glass fibers were prepared from this salt
 mixture and PBT without other additives, and test specimens of thickness
 0.8 mm were injection-molded and tested with the following result:

UL 94 Breaking Elongation Modulus
 Concentration flammability stress at break of elasticity
 % classification N/mm.sup.2 % N/mm.sup.2
 20 V-1 87.5 1.2 10741
 For comparison, aluminum ethylmethylphosphinate was used alone. The
 comparison again took place under the same conditions and at a
 concentration of 14%.

UL 94 Breaking Elongation Modulus
 Concentration flammability stress at break of elasticity
 % classification N/mm.sup.2 % N/mm.sup.2
 14 -- 116.3 1.8 11240
 EXAMPLE 3
 7 parts of aluminum ethylmethylphosphinate and 3 parts of aluminum
 monomethyl methanephosphonate were mixed well. Compounds reinforced with
 30% of glass fibers were prepared from this salt mixture and PBT without
 further additives, and test specimens of thickness 0.8 mm were
 injection-molded and tested with the following result:

UL 94 Breaking Elongation Modulus
 Concentration flammability stress at break of elasticity
 % classification N/mm.sup.2 % N/mm.sup.2
 20 V-0 96.1 1.2 11635
 Experiment for comparison with Example 3
 Aluminum monomethyl methanephosphonate was used to prepare, with PBT,
 compounds reinforced with 30% of glass fibers without other additives.
 Test specimens of thickness 0.8 mm were Injection-molded and tested with
 the following result: