FIRE-RETARDANT COMPOSITIONS

Abstract: This invention relates to fire-retardant polymer compositions, and preferably, but not exclusively, to fire-retardant polyamide compositions. It has now been found that the combination of a zinc borate and a divalent metal stannate, particularly zinc stannate, in halogen-containing polymeric compositions provides an increased fire-retardant effect, which is greater than that expected from the use of either zinc borate or the stannate alone. The combination also suppresses smoke production. Preferably the stannate is zinc stannate.

Description: Fire-Retardant Compositions This invention relates to fire-retardant polymer compositions, and preferably, but not exclusively, to fire-retardant polyamide compositions. It will be understood by those in the art that the tern "fire-retardant" encompasses "flame-retardant" . The use of zinc borate or zmc stannate as components αf fire-retardant compositions is well known in the art. The use of zinc borate is described in U.S. Patent o. 4360blD and U.S. Patent No. 4504611. U.S. Patent No. 436061b describes a glass-reinforced flame-retardant polyamide composition having good arc tracking resistance and consisting of: a) 40-65 weight percent of a polyamide of flln-forning molecular weight, b ) 16-35 weight percent of πeiarame, neian, neiamne cyanurate or a πelaπune derivative, c) 1-7 weight percent selected from the grou consisting of a chlorinated compound obtained frcπ the condensation of two moles of perchloro-c clopentadiene and one nole of 1 , 5-cyclooctadιene, or a broninated polystyrene, d) 1-4.9 weight percent of zinc borate or zmc . and e) 5-30 weight percent of glass fibres. SUBSTITUTE SHEET U.S. Patent No. 4,504,611 similarly describes flame-retardant polyamide consisting, in percent b weight, of: a) 35-76% polyamide, b) 6-10% zinc borate, c) 10-15% melamine cyanurate, d) 0-35% fibreglass, e) 0-3% antimony trioxide, and f) 8-15% of a chlorinated compound. Although there is disclosure of the use of a z c borat with zinc oxide, there is no reference in this prior ar to the use of zmc stannate. It has now been found that the combination of a zm borate and a divalent metal stannate, particularly zm stannate, in halogen-containing polymeric composition provides an increased fire-retardant effect, which i greater than that expected from the use of either zm borate or the stannate alone. The combination a l s suppresses smoke production. Where the term "stannate" i used herein in a general sense it includes "hydrox stannate" in view of their similar fire-retardan properties. According to the present invention, there is provided a fire-retardant polymer composition comprising a polymer and a fire-retardant amount of a mixture of a zmc borate and a divalent metal stannate, wherein the composition includes a source of halogen. The source of halogen can be the polymer itself or can be a separate component, such as an organic SUBSTITUTE SHEET halogen-contaming fire-retardant, provided that the component is compatible with the polymer. Preferably the fire-retardant compositions of the present invention comprise, by weight percent: a) 40-94% polyamide, b) 5-40% halogen-containing organic fire retardant, c) 1-20% of a mixture of zinc borate and a divalent metal stannate in a weight percentage ratio of between 10:90 and 90:10, more preferaoiy of the order of 50:50. Examples of suitable stannates that can be used are zinc stannate, z c hydroxystannate, calcium hydroxystannate and magnesium hydroxystannate. Preferably the stannate is zinc stannate. The constitution of zmc borate is variable as is described in the paper entitled "Applications of zinc borate in polymer blends and alloys" by .J. Kennelly m the report of the Proceedings of the Fire Retardant Chemicals Association meeting held at Hilton Head Island, South Carolina, March 17th to 20th 1991 pages 199 to 205. Whilst any zinc borate can be used, that of the formula 2Zn0 2 . 3B 2 0 3 . 3.5H 2 0 - known as "ZB 2335" - is preferred and is the borate that is intended in this speci icaton unless indicated to the contrary. Examples of suitable polymers include polyesters, epoxy resins, ABS combinations and the like, but preferably, a polyamide is used. Halogenated polymers sucft a PVC can also be used in this invention and since thev act as a SUBSTITUTE SHEET source of halogen no separate halogen-containin component is needed. Polya ides are thermoplastic compounds, constructed o the bifunctional monomers, dicarboxylic acid and diam e the properties of which are related to the length of th hydrocarbon radicals. One general class of polyamide used in the present invention is "nylon". One example of nylon is polyhexamethylene adipamiά (Nylon 66) formed by condensing hexamethylene dianine an adipic acid. Other examples include polyhexamethylen azelaamide (Nylon 69), polyhexamethylene sebacamid (Nylon 610), polylauric lactaπ, polycaprolactan (Nylo 6), poly-11-amιnoundecanoιc acid an poly-bis-(4-aminocyclohexyl ) methane dodecanoamide . The organic halogen-containing fire-retardant used can b any of those known in the art, such as those described i U.S.-A-4,360,616 and U.S .-A-4 , 504 , 611 , particularly tha sold under the trade mark Dechlorane. Other example include poly-dibromo-phenylene oxide, decar-romo-dipheny oxide and octabromo-diphenyl oxide. A z c borate and a divalent netal stannate adde together, preferably in a weight ratio of 50:50, to th composition results in an unexpected synergisti fire-retardant effect, i.e. increase in th fire-retardant properties of the compositions beyond tha expected. The inclusion of both a zmc borate and a divalent metal stannate in the fire-retardant composition also has th SUBSTITUTESHEET -o- result that antimony compounds are not required. This is extremely useful as these compounds are expensive, relatively hazardous and promote smoke when burning. One or more conventional fire-retardants such as zmc oxide and tin oxide can be used in addition to the combination of a zinc borate and a divalent metal stannate, if desired. The composition may also include other known additives such as glass fibre, calcium carbonate, talc or clay. The present invention will now be described by way of the following Examples. Example 1 In order to test the fire-retardant characteristics of the present invention, the following tests were performed on sample test strips. A UL94 test developed by the U.S. Underwriters Laboratory involves the use of a test strip 12 mm wide. The thickness of the strip can vary but is stated m each test. The strip is held vertically and the flame of a Bunsen burner applied for 10 seconds before being removed. After the strip is extinguished the Bunsen flame is applied for a further 10 seconds and then removed. The total burning time after the two applications is measured. SUBSTITUTESHEET - ". - The whole procedure is then repeated for verification. Results from the various tests are then eva-iuateα and classified as either V-ϋ (the best) , V-i, v-2 or fail. For thermoplastics a V-0 pass for a 1.5 nπ strip thickness is considered to be a good pass. The second test used in evaluating the fire-retardant properties of the compositions is the COI test. This involves limiting the oxygen concentration an oxygen nitrogen mixture to that which will -ust sustain combustion. The test strip is here again ne d vertically and the flame applied to the top of the strip. A number of test strips were prepared according to normal practice form Nylon 66 using three different loadings of fire-retardant. The chlorine-containing fire-retardant Declorane was also present. The composituns cf the three formulations are set out Table 1 inc are expressed as weight percentages of tne total composition. Three thicknesses of test strip ..ere used, namely 3, L.5 and 0.75 mm, and the fire-retardant used was also varied so that zinc borate alone, zinc stannate aione and the comcination of both z c ooratc --no zmc stannate were tested. The results of the UL94 and COI tests on the test strips are set out in Tables 2, 3 and 4. From the Tables it can be seen that wnen zmc norate and zinc stannate are used together -; weiαnt ratio of 50:50 the ire-retardant properties are synerg stical v increased. SUBSTITUTESHEET For Formulation 1 with a fire retardant loadinc of 10% ϋy weight, z c Dorate alone gave a value of V-0 m the UL94 test for the 3 mm and 1.5 nm thicxness specimens. The thinnest specimen, nowever, gave a vaiue of '. ' -1. Zinc stannate aione on the other nanα gave a value jf 7-0 for all three thicknesses. The combination of zmc borate and zmc stannate also gave a value of V-0 for a l l three thicKnesses . The results for Formulation 2 - a 7.5 cy weignt ire-retardant load α - aαair. snow a trenα :c an unexpected increase in fire-retardant properties using the comoination of the two zinc compounds. Formulation 3 with a 5- : s by weight fire retardant oad g again snowed an increased effect with the combination of zinc borate and zmc stannate. Z c stannate alone gave a value of V-i for all three test thicxnesseε ana in comoination with zinc oorate aiso gave a vaiue ? 7-*'" for all three samples. Example 2 → series of six samples Daseα on polyviny cr.icnαe were prepared having the basic composition as set out m Table Ξ and including a total of 10 pnr of zmc fire-retardant out m wnicn the relative amounts of zinc Dorate and z c stannate were varied between 0 and 100%. Eac sample was flame tested and the COI amounts ι-f smoxe and raroon monoxide CO) measured. The smoxe test followed ΞS '-401:1983 using wire nesn-supporteα 0.3 nm specimens, wniist the CO concentration was measured SUBSTITUTE SHEET after 2 minutes after insertion of the sample into th flame test. The results are presented m Table o and snow that oette fire-retardant properties were obtained from tne samples containing both zinc borate and zinc stannate than woul have been expected for the relative proportion used. As well as resulting in a synergistic ire-retardant effect the present invention aiso ailows for the use of a decreased amount of zmc oorate anc zinc stannate relative to the amount used wnen either component is used It should also be noted that antimony tπoxide is not required in the present invention, thus ruminating potential toxic waste posed by the use of this compound. SUBSTITUTESHEET .'ABLE .veiαnt Formulation Formulation Fornu ation --u Total 100 .00 :oc 'ABLE 2 ZINC FIRE RETARDANT ■ Formula ion . INC EORATΞ ZINC STANNATE ZINC BORATE ZINC ΞTANNA: 50 50 7-0 7-0 7-0 7- ■ HEET TABLE 3 ZINC FIRE RETARDANT (Formulation 2) ZINC BORATE ZINC STANNATE ZINC BORATE/ TEST ZINC STANNATE 50- 50 V-0 7-0 V-0 7-0 V-0 7-1 31 30 TABLE 4 ZINC FIRE RETARDANT (Formulation 2! ZINC BORATE ZINC STANNATE ZINC BORATE/ TEST ZINC STANNATE 50 50 V-l V-l V-l 29 SUBSTITUTESHEET TABLE 5 TABLE 6 SUBSTITUTE SHEET Example 3 Eight samples of Nylon 66 were prepared ano tested for their fi»-e-retardant properties and their strength. The composition of these samples and the results are given in Table 7. It can be seen that a substantial proportion of the expensive zinc stannate can be replaced by tne cheaper zmc borate with no loss of fire-retardant performance, even though zmc borate on its own exhibited a very poor fire-retardant effect. Example 4 It is known that Nylon 6 is more difficult to render fire-retardant than Nylon 66, partially due to its ower meitmg point of 220°C, as compared with 260°C for Nylon 66. A number of samples of Nylon 6 were prepared, all of which included 15% by weight of the halogen-containing fire-retardant Decnlorane. Various levels of zmc stannate were tested for strength and accordance with UL-94, along with combinations with zmc borate. The results are given in Table 8, together with those for formulations containing tin and zinc oxides for comparison. All of the samples were conditioned at 23°C and a relative humidity of 50% for seven days before testing. It can be seen that relatively hign levels of additives are required to reach UL-94 V-0 at 0.8 mm or .ess, but that the combination of zmc stannate and zinc borate demonstrates an improved result. SUBSTITUTESHEET Example 5 A number of different stannates were tested with rigid PVC using samples having the composition: - 100 phr PVC Hydro Polymers VY110.51 2 phr Calcium stearate 2 phr TI7M, Tin stabilizer, Ciba Geigy 5 phr Flame Retardant (as specified) . 300 g batches of the samples were made up oy compounding at 150 β C in a two roll mill, and their COI ' s were measured using samples compression moulded to 2 mm and cut into 1 cm thick strips. The results are as follows:- Fire Retardant COI Zmc hydroxystannate 67.5 Calcium hydroxystannate 57.2 Magnesium hydroxystannate 60.5 Zinc borate ZB2335 55.2 Zmc borate ZB223 67.0 Zmc Hydroxystannate/ZB2335 66.b 5.0) Calcium hydroxystannate/ZB2335 64.6 ( 8.2) Magnesium hydroxystannate/ ZB2335 66. -, (8.4) Zmc hydroxystannate/ZB2335 66.6 .5.0) Zinc hydroxystannate.- ZB223 72.4 ' 5.2; ZB223 is a borate of the formula 2Zn0 2 .2 B 2 0 3 . 3H 2 0. SUBSTITUTESHEET All of the blends are 50-50 by weight, and the figures i brackets are the amounts by which the blends' COI 's are greater than would be predicted by simple averaging of th two components. The results show that the two zinc borates are effectiv fire retardants and give the same synergistic effect wit z c stannate, and that calcium and magnesiu hydroxystannates also give a synergistic effect that is i anything larger than that of the zinc compound. Magnesium hydroxystannate performed better in the tests a a smoke suppressant for rigid PVC than the other stannate tested. SUBSTITUTESHEET TABLE 7 FORMULATION - WEIGHT % Nylon 66 100 77.5 80 80 82 82 82 82 Dechlorane 15 15 15 12 12 12 12 Zinc Stannate 7.5 5 3 6 4 ZB2235 UL-94 V-2 V-0 V-0 V-0 V-0 V-0 V-0 V-0 V-2 V-0 V-0 V-0 V-0 V-0 V-0 Fail V-2 V-0 V-0 V-0 V-l V-l 7-0 Fail 135 69 88 83 84 91 83 70 66 74 73 71 73 BIP Occidental Chemical Corp. SUBSTITUTESHEET TABLE 8

Claims: CLAIMS: 1. A fire-retardant polymer composition comprising a polymer and a fire-retardant amount of a mixture of a zxnc borate and a divalent metal stannate, wherein the composition includes a source of halogen. 2. A composition as claimed in claim 1 wherein the stannate s zinc stannate. 3. A composition as claimed in claim 1 or claim 2 wherein the source of halogen is the polymer itself. 4. A composition as claimed in claim 3 wherein the polymer is polyvinylchloride. 5. A composition as claimed in claim 1 or claim 2 wherein the source of halogen is an organic halogen-containing fire-retardant which is compatible with the polymer. 6. A composition as claimed in claim 5 wherein the polymer is a polyamide. 7. A composition as claimed in claim 6 containing from 40 to 94% by weight of polyamide, from 5 to 40% by weight of a halogen-containing organic fire-retardant which is compatible with the polyamide, and from 1 to 20% by weight of a mixture of zmc borate and zinc stannate. 8. A composition as claimed in any one of the preceding claims wherein the zinc borate and the stannate are present in the composition in approximately the same amounts by weight. E HEET

Inventors: CHAPLIN DOMINIC, CHAPLIN, DOMINIC
Applicants: ALCAN INT LTD, ALCAN INTERNATIONAL LIMITED
Application year: 1991
Main classification: C08K3
IPC codes: C08K3, C08L27, C08L77, C08L101, C09K21