FLAME RETARDANT COMPOSITIONS

Abstract: An additive composition used to impart flame retardency to a polymer or copolymer derived from at least one ethylenically unsaturated monomer, for example polypropylene, comprises the following: (i) 15 to 50 wt % of a nitrogenous organic base such as a melamine salt, (ii) 15 to 60 wt % of red phosphorus or a phosphorus compound and (iii) 7 to 30 wt % of one or more saturated aliphatic polyols such as pentaerythritol.

Description: FLAME RETARDANT COMPOSITIONS This invention relates to additive compositions for imparting flame retardency to polymers and copolymers Numerous attempts have been made to impart flame retardency to polyolefinic materials such as poly- D propylenes and ethylene-propylene copolymers. One such approach has been the introduction of halogenated organic materials and antimony trioxide into the polymer being protected. However when such materials are involved in a fire it has been found that large volumes of smoke are 10 emitted which contain hydrogen halides and these are both corrosive and are liable to cause asphyxiation. In consequence of the above noted drawbacks a num¬ ber of attempts have been made to provide materials which do not suffer from these difficulties. Certain 15 urea-formaldehyde condensation products exhibit intu- mescent properties e.g. the condensation product of ethylene-urea with formaldehyde and this together with ammonium polyphosphate, has been used to formulate flame retardant compositions (see U.S. specification No. 20 No. 4 363 906A) . The present invention accordingly provides an additive composition capable of imparting flame retar¬ dency to a polymer or copolymer derived from at least one ethylenically unsaturated monomer and to compositions 25 containing such polymers or copolymers, characterised in that it comprises: i) 15 to 50 wt % of a nitrogenous organic base or salt thereof solid at room temperature and containing at least two nitrogen atoms per molecule; ^ u ii) ±5 to 60 wt % of one or more of red phosphorus, phosphorus pentoxide, an ammonium poly- phosphate, an ammonium orthophosphate or a phosphoramide and iii) 7 to 30 wt % of one or more saturated aliphatic polyols containing at least four carbon atoms and at least four hydroxyl groups, each hydroxyl group being attached to a different carbon atom, all said percent¬ ages being based on the total additive composition. These compositions are preferably incorporated into the olefinic polymers in the thermoplastic state. The exact proportion included depends upon the actual composition of the additive as well as upon the chemical composition of the polymer. The polymer composition in its final state comprises35-85 wt % of the polymer or copolymer and 15 to 65 wt % in total of the additives (i) to (iii), but the additives may be supplied in master batches, mixed with smaller amounts of polymer or with another compatible carrier such as a wax. Such a master batch might for example contain up to 90 wt % of the additives. The preferred maximum content of the additives in the final polymer composition is 45 wt %. The polymer in which the additive composition of the invention is used, which we also designate the base polymer, is an addition homopolymer or copolymer derived from at least one ethylenically unsaturated monomer such as an aliphatic mono- or polyene, e.g. a diene. The base polymer may be a copolymer of an ethy¬ lenically unsaturated monomer such as an aliphatic olefinic hydrocarbon with another copolymerisable monomer. Examples of base polymers include polyolefins ■ such as polyethylene, ethylene-propyiene copolymer, polypropylene, polybutene, ethylene-vinyl acetate copolymer, poly butadiene and butadiene-isoprene co¬ polymer and other polymers and copolymers such as poly¬ styrene , ABS resins and styrene/olefin block copoly¬ mers. The polymers can be cross linked. The nitrogenous organic compon'ent (i) is pre¬ ferably a melamine salt or mixture of two or more mela- mine salts. These melamine salts are preferably salts with halogen-free polybasic inorganic acids such as ortho- phosphoric acid (melamine and dimelamine phosphates), sulphuric acid and boric acid. As an example, melamine phosphate and melamine borate may be used in equal pro¬ portions by weight. Other nitrogen compounds which may be used include melamine itself and guanidine. This component is preferably included in an amount of 30 to 40 wt %. with regard to the phosphorus-containing con¬ stituents of the present compositions we have found the various salts among the listed compounds to be very convenient as they can easily be produced in finely divided form and are thus readily incorporated with the base polymer. The preferred compound is ammonium polyphosphate. The preferred content of the phosphorus component is 30 to 50 wt %. The aliphatic polyols that are used as constit- uents of the present compositions contain at least four carbon atoms and four hydroxyl groups in the molecule. Preferably these compounds have 4 to 6 carbon atoms and 4 to 6 hydroxyl groups in the molecule. The number of carbon atoms is preferably either equal to or greater than the number of hydroxyl groups. Examples of suitable polyols are erythritol, pentaerythritol, di- and tri- pentaerythritol, mannitol and sorbitol as well as mixtures of any two or more of these polyols. These compounds intumesce and are important constituents of the compositions. The preferred content of this component is 15 to 25 wt %. In producing the retardant compositions of this invention the solid materials as particles or finely divided form are preferably first admixed and the resul¬ ting blend then blended with the polymer. Typic¬ ally, 70-85 % by weight of the latter may be blended with a total of 15-30 % by weight of the other three ingredients to form an intimate dispersion which constitutes a flame retardant composition. Suitable means for carrying out blending of polymer and additives is a high speed blender such as a Henschel mixer, a Pappenmeyer mixer or a Baker Perkins dridisperser. Since the base polymers are essentially thermoplastic materials the base polymer and the additives may be compounded in a Baπbury mixer or in a single or twin screw compounding extruder or a multiroll mixer. A preferred additive composition in accordance with the invention is as follows:- Ammonium polyphosphate 30-50 % by weight Melamine Phosphate 15-20 % by weight Melamine borate 15-20 % by weight Pentaerythritol 15-25 % by weight Such a composition can for example be used to prepare a polymer composition as follows: Polypropylene 65-73 % by weight Ammonium polyphosphate 11-15 % by weight Melamine phosphate 4.5-6.5% by weight Melamine borate 4.5-6.5% by weight Pentaerythritol 6.0-9.0% by weight The pentaerythritol may be replaced by a mixture of pentaerythritols e.g. a mixture of pentaerythritol and dipentaerythritol. For example, it may be replaced by a mixture consisting of 90% by weight pentaerythritol and 10% by weight dipentaerythritol. Other conventional additives may be included in the composition, for example fillers such as talc, antistatic agents, pigments and stabilizers such as hindered phenol antioxidants. An important advantage of the present compo¬ sitions is that they avoid the marked increase in weight which has been a feature of some prior composit¬ ions and have good thermal stability. Low thermal stability has been noted to lead to discolouration in the finished products. Thus two important disad¬ vantages of known prior art compositions are avoided by use of the present compositions. A surprising feature of the invention is the relatively high minimum content of the polyol component which is used. Any significant reduction below the 7% minimum content for this component in the additive component in the additive composition gives unsatis¬ factory results. This 7% figure is however considerably higher than would be expected from the known uses of compounds of this type in other fields such as textiles and coatings. The following Examples and references illustrate the invention. The percentages given are by weight. Example 1 An additive was prepared by blending: Ammonium polyphosphate 46.93% Melamine phosphate 29.48% Pentaerythritol 23.59% 28.93% of this additive was incorporated with 71.07% polypropylene homopolymer on a heated 2 roll mill. Test pieces 127 mm by 12.5 mm by 3.2 mm were produced by injection moulding of the resultant composition and tested for flame retardency by the method des¬ cribed in Underwriters Laboratories Specification UL 94 Vertical Burning Test. The material met the requirements of classification VO. Example 2 A fire-retardant polypropylene (PP) composition was prepared as in Example 1 but replacing pentaerythritol with dipentaerythritol. Tested as in Example 1, this material met the requirements of classification VO. Example 3 An additive was prepared by blending: Ammonium polyphosphate 52.38 % Melamine cyanurate 23.81% Mixture of 90% pentaerythritol with 10% dipentaerythritol " 23.81% 29.58% of this additive was incorporated with 70.42% PP. homopolymer and tested as in Example 1. The material met the requirements of UL 94 classification V2. Example 4 An additive was prepared by blending: Ammonium polyphosphate 52.91% Melamine phosphate 33.24% Pentaerythritol 13.85% 26.52% of this additive was incorporated with 73.48% PP homopolymer and tested as in Example 1. The material met the requirements of UL 94 classification VI. Example 5 (Reference) An additive was prepared by blending: Ammonium polyphosphate 51.86% Melamine phosphate 22.22% Melamine borate 22.22% Pentaerythritol 3.70% 27.00% of this additive was incorporated with 73% of PP homopolymer and tested as in Example 1. The material did not self extinguish on this test. This illustrates the non-effectiveness of the system if an inadequate level of pentaerythritol is used. Example 6 An additive was prepared by blending: Ammonium polyphosphate 42.43% Melamine phosphate 18.18% Melamine borate 18.18% Pentaerythritol 21.21% 31.13% of this additive was incorporated with 68.87% of PP homopolymer and tested as in Example 1. The material met the requirements of UL 94 classification VO. Flame-retardant polymer compositions in accord¬ ance with the invention have a wide variety of uses, for example in injection-moulded products, extruded cables, wire insulation and sheathing, extruded and calendered sheets, extruded sections and flow-moulded articles such as bottles.

Claims: CLAIMS 1. An additive composition capable of imparting flame retardency to a polymer or copolymer derived from at least one ethylenically unsaturated monomer and to compositions containing such polymers or copolymers, characterised in that it comprises: i) 15 to 50 wt % of a nitrogenous organic base or salt thereof solid at room temperature and containing at least two mitrogen atoms per molecule; ii) 15 to 60 wt% of one or more of red phosphorus, phosphorus pentoxide, an ammonium polyphosphate, an ammonium orthophosphate or a phosphoramide and iii) 7 to 30 wt % of one or more saturated aliphatic polyols containing at least four carbon atoms and at least four hydroxyl groups, each hydroxyl group being attached to a different carbon atom, all said percent¬ ages being based on the total additive composition. 2. An additive composition according to claim 1 characterised in that component (i) is selected from melamine and melamine salts with acids. 3. An additive composition according to claim 2 characterised in that component (i) comprises melamine phosphate and/or melamine borate. 4. An additive composition according to any preceding claim characterised in that the or each saturated aliphatic polyol(iϋ) has 4 to 6 carbon atoms and 4 to 6 hydroxyl groups in the molecule. 5. An additive composition according to claim 4 characterised in that the saturated aliphatic polyol (iii) is selected from erythritol, pentaerythritol, dipentaerythritol, tripentaerythritol, mannitol, sorbitol and mixtures thereof. 6. An additive composition according to any preceding claim characterised in that it includes from 15 to 25 wt % of the polyol or polyols (iii). 7. An additive composition according to claim 6 characterised in that it comprises 30 to 40 wt % of the nitrogen compound (i) and 30 to 50 wt % of the phosphorus or phosphorus compound (ii). 8. A flame-retardant polymer composition comprising at least one addition polymer or copolymer. derived from at least one ethylenically unsaturated monomer, characterised in that it includes an additive composition as defined in any preceding claim, in an amount sufficient to impart flame-retardency. 9, A polymer composition according to claim 8 charac¬ terised in that it comprises 35 to 85 wt % of the polymer or copolymer and 15 to 65 wt % of the additive composition. 10. A polymer composition according to claim 9 charac¬ terised in that it comprises 55 to 85 wt % of the polymer or copolymer and 15 to 45 wt % of the additive composition. 11. A polymer composition according to any one of claims 8 to 10 characterised in that at least one said polymer or copolymer is selected from aliphatic olefinic or polyolefinic hydrocarbon homopolymers and copolymers, polystyrene, ABS polymers and styrene/olefin block copolymers. 12. An additive composition according to any one of claims 1 to 7 combined in master batch with a carrier which is, or is compatible with, a polymer and/or co- polymer as defined in claim 1. 13. A method of making an additive composition capable of imparting flame retardency to a polymer or copolymer derived from at least one ethylenically unsaturated monomer and to compositions containing D such polymers or copolymers, characterised in that it comprises mixing the following components in the following proportions by weight based on the total additive composition: i) 15 to 50 % of a nitrogenous organic base or 10 salt thereof solid at room temperature and containing at least two nitrogen atoms per molecule, ii) 15 to 60 % of one or more of red phosphorus, phosphorus pentoxide, an ammonium polyphosphate, an ammonium orthoplhsphate or a phosphoramide and 15 iii) 7 to 30 % of a saturated aliphatic polyol or polyols containing at least four carbon atoms and at least four hydroxyl groups, each hydroxyl group being attached to a different carbon atom. 14. A method of imparting flame-retardant properties 20 to a polymer or copolymer derived from at least one ethylenically unsaturated monomer, characterised by adding to said polymer or copolymer the following addi¬ tives, in the following proportions by weight based on the total additives, in amounts sufficient to give a 5 flame-retardant composition comprising 35 to 85 wt % of said polymer or copolymer and a total 15 to 65 wt % of said additives: i) 15 to 50 . of a nitrogenous organic base or salt thereof solid at room temperature and containing 0 at least two nitrogen atoms per molecule, ii) 15 to 60 % of one or more of red phosphorus, phosphorus pentoxide, an ammonium polyphosphate, an ammonium orthophosphate or a phosphoramide and iii) 7 to 30% of a satured aliphatic polyol or polyols containing at least four carbon atoms and at least four hydroxyl groups, each hydroxyl group being attached to a different carbon atom. 15. A shaped article made from a flame-retardant composition according to any one of claims 8 to 11.

Inventors: CHALLENGER PETER, CHALLENGER, PETER
Applicants: PLASCOAT UK LTD, PLASCOAT U.K. LIMITED
Application year: 1985
Main classification: C08K13
IPC codes: C08K3, C08K5, C08K13