ELECTRICAL WIRE AND CABLE

Abstract: A transmission line, for example an electrical wire or optical fibre, has a layer of insulating or jacketing material that is formed from a composition comprising: (a) a polyamide, polyester, polyphenylene oxide, silicone or alkene/vinyl acetate polymer; and (b) from 10 to 30 % by weight based on the total weight of the composition of magnesium hydroxide, the magnesium hydroxide having a specific surface area A and a weight average particle size S such that the ratio of the specific surface area to the average particle size (A/S) is at least 8 x 10<9> mkg<-1>. The choice of magnesium hydroxide has been found to give improved smoke reduction in electrical insulation or jacketing materials based on the above polymers as compared with other polymers.

Description: ELECTRICAL WIRE AND CABLE This invention relates to transmission lines, for example electrical wire and cable, optical fibres or the like. According to the present invention, there is pro¬ vided a transmission line having a layer of insulating or jacketing material that is formed from a composition comprising: (a) a polyamide, polyester, polyphenylene oxide, silicone or alkene/vinyl acetate polymer; and (b) from 10 to 30% by weight based on the total weight of the composition of magnesium hydroxide, the magnesium hydroxide having a specific surface area A and a weight average particle size S such that the ratio of the specific surface area to the average particle size (A/S) is at least 8 x 10 9 mkg~l. We have observed that in certain polymer systems , the ability of the magnesium hydroxide to suppress the evolution of smoke when the line is subjected to a fire is markedly improved as the surface area/particle size ratio is increased to values above 8 x 10 9 mkg ~ l. Preferably the surface area/particle size ratio is at least 1.0 x 10 10 . more preferably 1.1 x 10 10 , and especially at least 1.2 x 10 10 mkg -1 . The reason for this effect is not understood. The effect does not appear to depend on other characteristics of the magne¬ sium hydroxide such as the specific surface area or particle size when taken alone, the method of manufac¬ ture or the purity of the material. The magnesium hydroxide preferably has a weight average particle size in the range of from 0.1 to 20, preferably 0.3 to 6 micrometres as measured by a photo- sedimentation method. in addition or alternatively, the magnesium hydroxide has a specific surface area in the range of 1000 to 100,000, preferably 5000 to 50,000 m 2 kg"l. The transmission line according to the invention may for example comprise an electrical wire, an electrical cable in which the cable jacket is provided with the composition described herein, a jacketed coaxial cable or a waveguide for very high frequency transmission e.g. an optical waveguide. The insulation contains from 10 to 30% by weight magnesium hydroxide since quantities significantly below 10% will not have a sufficiently pronounced smoke suppression effect, while it may be difficult and unnecessary to incor¬ porate more than 30% magnesium hydroxide in the com¬ position. The composition preferably contains from 15 to 30% by weight and especially from 17 to 25% by weight magnesium hydroxide, based on the total (filled) weight of the material. As stated above, the polymer used in the resin may be a polyamide, polyester, polyphenylene oxide, sili- cone or alkene/vinyl acetate copolymer. Preferably the polymer is substantially halogen-free. Examples of such preferred polymers include copolymers of ethylene with vinyl acetate, methyl acrylate or ethyl acrylate; nylon 12, nylon 6,12, nylon 6,10, nylon 6 and nylon 11; polyphenylene oxide and especially blends of polypheny¬ lene oxide with polystyrene or a polyamide; and polyesters such as polycaprolactone and terephthalate polymers. Polytetramethylene terephthalate is par¬ ticularly preferred, as are polymers that contain poly¬ tetramethylene terephthalate units. The preferred polymeric material comprise (1) a polyester in which at least 70 mole % of the repeating units are tetramethylene terephthalate; and (2) a. copolyester block copolymer having long-chain ester units of the general formula 0 0 II II -OGO-C-R-C- and short-chain ester units of the formula 0 0 II II -ODO-C-R-C- in which " G is χ a divalent radical remaining after the removal of terminal hydroxyl groups from a polyalkylene oxide) glycol, preferably a poly (C2 to C4 alkylene oxide) having a molecular weight of about 600 to 6000; R is a divalent radical remaining after removal of carboxyl groups from at least one dicarboxylic acid having a molecular weight of less than about 300; and D is a divalent radical remaining after removal of hydroxyl groups from at least one diol having a molecular weight less than 250. Preferred copolyesters are the polyether ester polymers derived from terephthalic acid, polytetramethylene ether glycol and 1,4-butane diol. These are random block copolymers having crystalline hard blocks with the repeating unit: -(CH ) and amorphous, elastomeric polytetramethylene ether terephthalate soft blocks of repeating unit having a molecular weight of about 600 to 3000, i .e. n = 6 to 40. The amount of polymer (2) preferably employed will depend on the balance needed, for the particular end use in view, between physical properties which are influenced by the presence of polymer (2). Polymers (1) and (2) are preferably the only orga¬ nic polymers in the composition. If other organic polymers are present, the amount thereof is preferably less than 20%, based on the combined weights of poly¬ mers (1) and (2) . Although by no means essential, it is possible, and in many cases desirable for the polymeric material to include other fillers, for example additional flame retardants. In particular it may be desirable to incorporate a halogen containing flame retardant, for example decabromodiphenyl ether or ethylene-bis- tetrabromophthalimide, as well as other aromatic and aliphatic compounds . Such halogenated flame retardants are known to generate large quantities of smoke, and the reduction in smoke obtained by using the particular magnesium hydroxide can be substantial. The amount of bromine-containing flame-retardant present will generally be at least 3%, preferably at least 5%, e.g. 5-30% or 5-25%, by weight of the composition. The bromine-containing flame retardants are frequently used in conjunction with inorganic flame retardants, for example antimony trioxide, which are known to demonstrate a synergistic effect with halogen-contain¬ ing organic flame retardants. Thus preferred com¬ positions contain 3 to 15% by weight of antimony trioxide. In other instances it may be desirable for the insulation to be substantially halogen-free in order to reduce the evolution of toxic gases during a fire, in which case other flame retardants e.g. those based on phosphorous derivatives may be used. The insulation and jacketing materials used in the present invention preferably contain at least one antioxidant. Suitable antioxidants include the hin¬ dered phenols which are well known in the art, present for example in amount from 0.25 to 5% by weight of the composition. The materials can also contain conventional addi¬ tives such as other fillers, processing aids and stabi¬ lisers. The insulation or jacketing materials may be used in their uncrosslinked form or may be crosslinked. They may be crosslinked by means of chemical cross- linking agents or by irradiation, for example by expo¬ sure to high energy radiation such as an electron beam or gamma rays. Radiation dosages in the range 2 to 80 Mrads, preferably 5 to 50 Mrads, e.g. 10 to 30 Mrads are in general appropriate. For the purpose of promoting cross-linking during irradiation preferably from 0.2 to 5 weight per cent of a prorad such as a poly-functional vinyl or allyl com¬ pound, for example, triallyl cyanurate, triallyl iso- cyanurate or pentaerythritol tetramethacrylate are incorporated into the composition prior to irradiation. The degree of cross-linking of the compositions may be expressed in terms of the gel content (ANSI/ASTM D2765-68) of the cross-linked polymeric composition, i.e. excluding non-polymeric additives that may be pre¬ sent. Preferably the gel content of the cross-linked composition is at least 10% more preferably at least 20%, e.g. at least 30%, more preferably at least 40%. The materials are preferably used according to the invention as wire insulation, and especially as primary insulation for equipment wire although it is possible for other materials to be used as well, e.g. in dual- wall insulation, in which case the material may be used as a primary insulation or a primary jacket or both. Thus, for example, equipment wire may be provided with a primary insulation based on a polyolefin such as polyethylene or an olefin copolymer, an ionomer, an ethylene-vinyl acetate copolymer or blends thereof, and a primary jacket formed from a composition according to the present invention. In the case of electrical wiring, the wire size is generally from 4 AWG to 38 AWG, preferably 10 to 30 AWG, and the coating has a thickness of 0.05 to 0.76 mm (0.002 to 0.030 inch) preferably 0.1 to 0.38 mm (0.004 to 0.0150 inch) . The invention is illustrated in the following Examples in which parts and percentages are by weight unless otherwise specified. Examples 1 to 6 Electrical wires were formed by extruding a 200 micrometre thick primary insulation onto a 20 AWG tinned copper conductor. The primary insulation was formed from the following composition. Parts by weight polybutylene terephthalate 36 Block copolymer comprising 15 87% by mole polytetra¬ methylene terephthalate (hard blocks) and 13% by mole poly(polytetramethy¬ lene ether) terephthalate (soft blocks) having a flex modulus of about 208 MPa (30,000 p.s.i.) ethylene bis-tetrabro- mophthalimide 13 magnesium hydroxide 20 antimony trioxide 4 phosphite antioxidant 2 phenolic antioxidant 2 hydrolysis stabilizer 3 triallyl isocyanurate cross- linking promotor (optional) Samples of wire were formed using different grades of magnesium hydroxide. The properties of the magne¬ sium hydroxide are given in Table I. Ta le l Bar L≥ l(cπrpariscn) 2(αuιμ___iscn) 6( Er_paris n) ιr_=an particle siae 3.0 2.5 2.0 0.60 0.7 0.8 irax particle size 40 40 4 pacif c surface 22000 U800 35000 8500 8000 4300 area (χ^kg~i) surtVp area fnean particle size πk '-^xlO 10 0.73 0.472 1.75 1.42 1.14 0.54 The wires were tested for smoke generation according to specification UTE C20 452-1 and the values for maximum smoke density (Dmax) and cumulative smoke density after 4 minutes (VoF4) were recorded. The results are shown in Table II . Table II Example Dmax VoF4 1(comparison) 141 338 2(comparison) 225 439 3 111 211 4 98 180 5 119 185 6(comparison) 215 522 Examples 7 to 15 A number of wires were formed by extruding a 200 micrometre thick primary insulation onto a 20 AWG tinned copper conductor. The wires had the composition given in Table III. For each Example one composition (having the suffix A) employed magnesium hydroxide as in Example 4 having a mean particle size of 0.6 micro¬ metres and a specific surface area of 8500 m-^ g-- ! (A/S ratio = 1.42 x 10-^0 mkg~l), while the other composition (having the suffix B) employed magnesium hydroxide as in Example 6 having a mean particle size of 0.8 micro¬ metres and a specific surface area of 4300 m-^kg-l (A/S ratio 0.54 mkg"!) m The samples were tested to UTE C20 452-1 as in Example 1 and the results are given in Table IV from which it can be seen that while no impro¬ vement is seen using a high A/S ratio magnesium hydroxide in a polyethylene based insulation, a signi¬ ficant reduction in V0F4 can be achieved with a high A/S ratio magnesium hydroxide in a polyphenylene oxide based insulation (Examples 13 A & B) and a large reduc¬ tion in both V0F4 and Dmax can be seen with a high A/S ratio magnesium hydroxide in a polyester based insula¬ tion (Examples 15 A & B) . TOTR TTT Qup ai Bsrple 7 8 9 10 11 12 13 14 15 low dsnsit_y poLy- et±ylee 73.9 53.9 773 573 373 -__Ly_x4yl=_ne t=re- jhάalae 513 37.8 l=ciLv ___yl___πe efcbs: l-βsf tiaate block cqpolyra. C£s Barples 1-6) 23.7 17.6 R__Lyf.__3yl_3_ add?/ polystyrene ϋsrl 773 573 aπt±ray triadcfe 3.8 3.8 3.8 3.8 3.8 3.7 3.7 πagesiun l^αdds 20 40 20 40 20 . 20 EtecriLc aπtiαddaπt 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.7 1.7 E-Xsgfaite ant-ictri aπt 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 0.9 c_rnsliτ n rcπ±cr 3.4 3.4 3.4 3.4 3.4 3.4 3.4 3.3 3.3 TABLE IV Example Polymer Bromine Mg(OH) V0F4 Dmax Flame Content (%) Retardant 7A polyethyle No 20 20 14.5 7B II No 20 14.5 14.5 8A n No 40 21 20.5 8B No 40 18 15.5 9 Yes 0 177 132 10A Yes 20 212 143 10B Yes 20 183 138 11A Yes 40 143 208 11B π Yes 40 119 190 12 PPO/nylon Yes 0 310 205 13A II Yes 20 233 247 13B II . Yes 20 320 251 14 polyester Yes 0 674 273 15A II Yes 20 127 74 15B 11 Yes 20 291 218

Claims: CLAIMS : 1. A transmission line having a layer of insulating or jacketing material that is formed from a composition comprising: (a) a polyamide, polyester, polyphenylene oxide, silicone or alkene/vinyl acetate polymer; and (b) from 10 to 30% by weight based on the total weight of the composition of magnesium hydroxide, the magnesium hydroxide having a specific surface area A and a weight average particle size S such that the ratio of the specific surface area to the average particle size (A/S) is at least 8 x 10 9 mkg -1 . 2. A line as claimed in claim 1, wherein the ratio of the specific surface area to the mean particle size of the magnesium hydroxide is at least 1.1 x 10-^0 mkg -1 . 3. A line as claimed in claim 2 , wherein the ratio of the specific surface area to the mean particle size of the magnesium hydroxide is at least 1.2 x lO 1 ^ mkg" *1 . 4. A line as claimed in any one of claims 1 to 3, wherein the magnesium hydroxide has weight average par¬ ticle size in the range of from 0.1 to 20 micrometres. 5. A line as claimed in claim 4, wherein the magne¬ sium hydroxide has a weight average particle size in the range of from 0.3 to 6 micrometres . 6. A line as claimed in any one of claims 1 to 5, wherein the magnesium hydroxide has a specific surface area in the range of from 1000 to 100,000 m 2 kg -1 . 7. A line as claimed in claim 6, wherein the magne¬ sium hydroxide has a specific surface area in the range of from 5000 to 50000 m kg" 1 . 8. A line as claimed in any one of claims 1 to 7, wherein the insulating or jacketing material comprises a polyester. 9. A line .as claimed in claim 8, wherein the insu¬ lating or jacketing material comprises a polyester that includes tetramethylene terephthalate units. 10. A line as claimed in claim 8 or claim 9, wherein the insulating or jacketing material comprises a block copolymer in which one of the blocks is composed of repeating units which have the formula -0-(CH 2 ) -O-C-Ar-C- in which p is an integer of at least 2 and Ar represents an unsubstituted or substituted aryl group, and the other of the blocks comprises a polyalkylene ether. 11. A line as claimed in any one of claims 1 to 10, in which the polymeric insulating material comprises a plurality of layers . 12. A line as claimed in any one of claims 1 to 11, wherein the composition contains a halogenated flame retardant. 13. A line as claimed in any one of claims 1 to 11, which is an electrical wire. * * * * * *

Inventors: COLLETT DARREN JOHN, GENTILCORE GIOVANNI, SMITH TIMOTHY STEPHEN, COLLETT, DARREN, JOHN, GENTILCORE, GIOVANNI, SMITH, TIMOTHY, STEPHEN
Applicants: RAYCHEM LTD, RAYCHEM LIMITED
Application year: 1988
Main classification: H01B7
IPC codes: C08K3, H01B3, H01B7