Abstract:
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.

Description:
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° 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,                           
     where R 1  and/or R 2  is C 1 -C 6 -alkyl, preferably C 1 -C 3 -alkyl, which may be linear or branched, e.g. methyl, ethyl, n-propyl, isopropyl, n-butyl or tert-butyl, where R 1  and R 2  may also be linked to a ring, and R 3  is C 1 -C 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),                           
     where R 4  is C 1 -C 6 -alkyl, preferably C 1 -C 3 -alkyl, which may be linear or branched, e.g. methyl, ethyl, n-propyl or isopropyl, R 5  is C 1 -C 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° C., above which noticeable elimination of water commences: in contrast, aluminum hydroxide begins to eliminate water from 200° 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:                           
     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° 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 2   
                 % 
                 N/mm 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 2   
                 % 
                 N/mm 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 2   
                 % 
                 N/mm 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: 
     
       
         
               
               
               
               
               
             
           
               
                   
               
               
                   
                 UL 94 
                 Breaking 
                 Elongation 
                 Modulus 
               
               
                 Concentration 
                 flammability 
                 stress 
                 at break 
                 of elasticity 
               
               
                 % 
                 classification 
                 N/mm 2   
                 % 
                 N/mm 2   
               
               
                   
               
             
             
               
                 20 
                 — 
                 53.7 
                 0.6 
                 10911