RUBBER COMPOSITIONS

Abstract: A vulcanisable rubber precursor tube has selected properties to render it suitable for subsequent vulcanisation to produce a bore liner for an underground pipe, sewer or other conduit. The precursor tube can be formed from vulcanisable rubber compositions containing particular proportions of elastomer, filler, process oil and vulcanisation adjuvants. The precursor tube can be converted in situ in the conduit to a vulcanised self-supporting form under the influence of internal fluid pressure and vulcanising conditions.

Description: RUBBER COMPOSITIONS This invention relates to vulcanisable rubber compositions and to methods of vulcanising them to give hard rubber products. The invention also relates to vulcanisable rubber compositions in the form of precursor tubes for use in the production of tubes useful as liners for underground conduits. In a first aspect the invention provides a vulcanisable rubber precursor tube for subsequent vulcanisation to produce a bore liner to line under- ground pipes, sewers or other conduits, the precursor tube having the following features: (a) it is sufficiently pliable that it can adopt a substantially flat cross-section without cracking; (b) when inserted lengthwise in said conduit .it can be shaped by fluid pressure applied to the interior of the tube so as substantially to conform the tube to the interior shape of the conduit; and (c) it is vulcanisable in situ in the conduit after being so shaped. Preferred forms of the vulcanisable rubber precursor tube of the invention have one or more of the following features: it is capable of being fol .ded one or more times along its length without cracking or other weakening; the interior walls should not stick to each other, i.e. the material must not adhere to itself to such an extent that it damages itself when the walls are separated; it is capable of being wound onto a drum, one metre diameter at the centre; such bending as is required for this must be capable of being resisted without cracking or other weakening; capable of remaining pliable for a substantial time, for example for the minimum practicable time between being formed and being inserted in an underground conduit; non-porous to enable it to be inflated in situ. Further preferred properties of the precursor tube are one or more of the following features: The composition of the tube includes a hardening agent throughout its bulk so as to give uniform strength characteristics; the vulcanisation of the tube when positioned can be initiated by a specific action, e.g. by heating with hot air or with steam; it does not need special processing to preserve its pliability; the time period during which hardening to produce the bore liner takes place should be such as to allow the hardening process to be completed after installation. Preferred forms of the vulcanised bore liner of the invention have one or more of the following features : length - up to 205 metres; diameter - up to 1.5 metres wall thickness - from 3 to 12mm surface finish - exterior - any; interior- as smooth as possible. Strength - after the material has been inflated and cured within its final conduit location it should maintain its shape substantially indefinitely. Further preferred properties of the bore liner are one or more of the following: resistance to attack by chemicals normally found in sewer systems in particular household detergents; resistance to abrasion by solids which may be present in the liquid flow; a general ability to meet the standards laid down by gas, water and sewerage authorities. The fluid pressure used to shape the precursor tube can be applied by gaseous or liquid means, though where the conduit is of substantial cross section, for example large sewers, it is normally preferable to use gaseous means. Suitable gaseous means are, for example, compressed air or steam. Where steam is used as the gaseous means it will normally be necessary to provide a means of removing the condensed steam from the tube or, at least, permitting it to drain therefrom. With regard to the vulcanisation in situ of the precursor tube in the conduit, a convenient means is, for example, to form the precursor tube from a vulcanisable rubber composition containing vulcan¬ isation ingredients chosen so that vulcanisation can be effected by means of heat applied, for instance, using hot air or steam. Where either of these latter means is used it can be used under such conditions that it acts as the means of shaping the precursor tube so as to conform to the interior shape of the conduit and then effect vulcanisation of the tube so shaped. Where this procedure is adopted it is necessary, in general, for the rubber composition and in particular the vulcanisation ingredients con¬ tained therein to be so chosen as to avoid a degree of hardening of the tube which would impede the shaping of the precursor tube before it has conformed to the interior of the conduit. Thus, preferably, at least the latter part of the vulcanisation process takes place after the tube has conformed to the conduit. The invention is illustrated by the following Examples in which, unless stated to the contrary, all "parts" are parts by weight and all pressure (psiJ are lb./inch gauge. Abbreviations used in the Examples have the following meanings: DPG - diphenylguanidine BA - butyraldelhyde-aniline condensation product EFA - ethyl chloride formaldehyde ammonia EXAMPLES 1 to 3 The vulcanisable rubber compositions of Examples 1 to 3 were obtained by blending together in an internal mixing machine the ingredients shown in Table 1 below before being sheeted off on a mill to a thickness of about 2mm. The sheets were evaluated for 'tack' (the ability to stick to themselves) and pliability. Table 1 Example No. Ingredients (Parts by Weight) 1 2 .3 Natural rubber 100 100 100 China clay 100 100 100 Magnesium oxide 5 5 5 Process oil 5 5 5 Sulphur 45 45 45 Accelerator DPG Accelerator BA Accelerator EFA The sheets thus obtained performed well in terms of having good tack and remaining pliable. EXAMPLES 4 to 6 The sheets obtained as described above from Example 1 were divided into three batches which were then subjected, respectively, to the following three sets of vulcanisation conditions (Examples 4 to 6) under steam pressure. Example No . 4 5 6 Temperature (°C) 130 140 150 Time (hours) 8 4 2 Pressure (psig) 25 38 55 The product thus obtained in Examples 4, 5 and 6 was in the form of hard rigid sheets which can be regarded as a form of ebonite, EXAMPLES 7 to 12 Examples 4, 5 and 6 were repeated but using respectively, in Examples 7 to 9, the vulcanisable compositions of Example 2 and, in Examples 10 to 12, the vulcanisable compositions of Example 3. The vulcanised products thus obtained were comparable with those obtained in Examples 4 to 6. EXAMPLE 13 This Example describes the production of a tube suitable for use as an underground bore liner. The tube was formed from two calendered layers, each 2mm thick, of the unvulcanised composition of Example 1, between which was sandwiched a fabric reinforcement material. The fabric used was a 1007 o high tenacity PA66 nylon of Leno weave and having a resorcinol- formaldehyde latex nitrile dipped finish. The fabric was one supplied by John Heathcoat Limited of Tiverton, Devon. A rig was set up to simulate a drain pipe and consisted of a 4" diameter metal cylinder 6 feet long and adapted so that steam could be fed into it under pressure and resulting water condensate could be drained away through a steam trap. The bore liner was made up from a laminate of the two 2mm calendered layers of unvulcanised composition with a single layer of the fabric sandwiched between them. The tack of the composition was sufficient to hold the two layers, penetrating between the spaces in the fabric weave. A longitudinal overlap joint was made so as to convert the laminate into a closed sleeve or flat tube. This was achieved by using a solvent wash along the length of the overlap before sticking the two overlap portions together. The resulting unvulcanised precursor tube was fed into the metal cylinder of the rig until it was housed completely therein, and the cylinder was then closed. Steam under pressure was fed into the cylinder so as to cause the rubber tube to be urged radially outwardly against the inner wall of the cylinder and to be held co-axially with respect to the cylinder during vulcanisation the conditions which were as follows: Temperature 140°C Time 4 hours Pressure 40 psig The pressure was maintained continuously for the whole of the 4 hours period and then until the rig had cooled to room temperature The bore liner thus obtained was a rigid tube having excellent resistance to abrasion and to acid and alkali. The present invention can be used in conjunction with the method and/or apparatus of International Application PCT/GB 88/00435 (Publication NO. WO88/09897).

Claims: CLAIMS 1. A vulcanisable rubber precursor tube for subsequent vulcanisation to produce a bore liner for an underground pipe, sewer or other conduit, the precursor tube having the following features: .(a) it is sufficiently pliable that it cart adopt a substantially flat cross-section without cracking; (b) when inserted lengthways in said conduit it can be shaped by fluid pressure applied to the interior of the tube so as substantially to conform the tube to the interior shape of the conduit; and (c) it is vulcanisable in situ in the conduit after being so shaped. 2. A vulcanisable rubber precursor tube according to Claim 1, which in an uninflated state has the following features: it is capable of being folded one or more times along its length without cracking or other weakening; the internal surface of the tube wall does not self-adhere to such an extent that it damages itself when the tube is inflated; it is capable of remaining pliable for a substantial time; and it is sufficiently non-porous to enable it to be inflated in said conduit. 3. A vulcanised rubber tube in the form of a bore liner of an underground pipe, sewer or other conduit, obtained by subjecting to vulcanisation conditions a vulcanisable rubber precursor tube as claimed in Claim 1. 4. A vulcanisable rubber tube according to Claim 3, where the vulcanisation conditions include a vulcanisation temperature in the range 120°C to 160°C and a vulcanisation time in the range 10 hours to 1 hour. 5. A vulcanised rubber tube according to Claim 3, where the vulcanisation conditions include a vulcanisation temperature in the range 130° to 150°C and a vulcanisation time in the range 8 hours to 2 hours. 6. A vulcanisable rubber composition suitable for the production of a vulcanisable precursor tube as claimed in Claim 1, said composition comprising a blend of one or more of each of the following: elastomer 100 parts filler in the range 50 to 150 parts inorganic vulcanisation accelerator in the range 2 to 10 parts organic vulcanisation accelerator in the range 0.5 to 4 parts sulphur 15 or more parts process oil in the range 2 to 10 parts all parts being parts by weight. 7. A vulcanisable rubber composition according to Claim 6, in which the elastomer is a natural rubber. 8. A vulcanisable rubber composition according to Claim 6 or 7, in which the filler is China clay in an amount in the range 80 to 120 parts by weight. 9. A vulcanisable rubber composition according to Claim 8, in which the China clay is in an amount in the range 95 to 105 parts by weight. 10. A vulcanisable rubber composition according to any of Claims 6 to 9 , in which the inorganic accelerator is magnesium oxide. 11. A vulcanisable rubber composition according to any of Claims 6 to 10, in which the inorganic accelerator is magnesium oxide in an amount in the range 4 to 6 parts by weight. 12. A vulcanisable rubber composition according to any of Claims 6 to 11, in which the sulphur is in an amount in the range 30 to 60 parts by weight. 13. A vulcanisable rubber composition according to Claim 12 in which the sulphur is in an amount in the range 40 to 50 parts by weight. 14. A vulcanisable rubber composition according to Claim 6, in which said composition comprises a blend in substantially the following proportions: natural rubber 100 parts China clay 100 parts magnesium oxide 5 parts process oil 5 parts sulphur 45 parts organic accelerator in the range 1 to 2 parts, all parts being by weight. 15. A method of lining a conduit, which comprises: locating inside the conduit a vulcanisable rubber precursor tube as claimed in Claim 1, the tube being in uninflated condition; passing a fluid into the tube thereby to inflate the tube so that it lines the conduit; and subjecting the inflated tube to vulcanisation conditions thereby to convert the tube into a self-supporting liner for the conduit. 16. A method according to Claim 15, in which said fluid serves also to provide the vulcanisation conditions. 17. A method according to Claim 16, in which said fluid is steam. 18. A method according to Claim 15, 16 or 17, in which the self-supporting liner comprises an ebonite.

Inventors: HINDMARCH RONALD SANGSTER, HUTTON FRANK ARTHUR, JONES DAVID BRYN, HINDMARCH, RONALD, SANGSTER, HUTTON, FRANK, ARTHUR, JONES, DAVID, BRYN
Applicants: PIPE & SEWER RENOVATIONS LIMIT, PIPE & SEWER RENOVATIONS LIMITED
Application year: 1990
Main classification: C08L7
IPC codes: C08K3, F16L55