IE44882B1 - Polybutene compositions - Google Patents

Description

This invehtion relates to ooapositions for application to the . Interior surfaoe of the tread of a pneumatio tyre to facilitate relative movement between contacting portions of the interior surfaoe of the tyre when the tyre is driven deflated.

Our Patent Specification No.3561] describes and claims a pneumatio tyre which, when mounted on a wheel rim for which it is desired and inflated to its normal working pressure, haB an aspeot ratio of between 30 and 75$ and a . tread portion whose width'is greater than the width between the bead heels, having a oeating of a lubricating material disposed on at least a portion of its interior surfaoe to facilitate a relative movement between contacting portions of the interior surface·of the tyre whan the tyre is used in a deflated condition.

The tyre thus described marked a new step forward in the field of safety tyres. Hitherto many attempts had been mad©.to provide an assembly which oould oope with the problem of punctures to eliminate danger1or vehicle immobilisations these earlier attempts being oeatred primarily around two approaches. One of these was to provide a safety member in the form of a eeoond inflation chamber, special filling, or a rigid saddle onto which the.tyre was supported when deflated, and the other was to provide a punoture sealing layer on the inside of the tyre to prevent the tyre from becoming deflated. The problem of th© latter approach is that unless the sealing layer is 100$ effioient in preventing air-loss there is a danger that some air will be lost before the punoture seals, resulting in an under-inflated tyre without the driver being aware that something was wrong. This, with a conventional tyre, can be more dangerous than a punoture since extended running at high speed on an under-inflated tyre is a prime cause of blow-outs on fast roads, and the necessary 100% efficiency is, in practice, a very elusive goal,. -.-4 4 8 8 2 3.

The concept of allowing a tyre to run deflated without .'xtru supports enables various other possibilities to bo introduced, Thu a '.n Our Latent Specification No. 35347 the present applicants describe the use of a tyre and wheel ria assembly i.xth a liquid lubricant containing a volatile component and a puncture sealing material so that a puncture can be sealed and a low pressure generated in the tyre by evaporation of the volatile liquid. The concept of puncture sealing by this means is developed further in our Latent Specification No. 38209 wherein the volatiles are enclosed and a gelled lubricant is coated on the tyre interior, solid puncture sealing materials being carried by the gel, In this instance release of the volatiles when the tyre deflates is followed by breakdown of the gel and mobilization of the puncture sealing materials to seek out and seal the puncture, Lubricant gels suitable for use in this system are described in Latent Specification Nos 38352 and 42706.

It is fo be appreciated that the purpose of the puncture sealing and vapour inflation in these instances is not to totally reinflate the tyre but simply to provide a low inflation pressure of the order of 1 to 5 psi in the tyre to reduce its deflection and thus the heat generated in running the tyre without inflation pressure. This, of course, is a quite different problem from that of the puncture sealing layers and materials of past proposals, since fhe latter have failed if they allow the tyre pressure to fall by more than a very few psi.

Our Patent Specification No. 44881 relates to a new approach to the problem of providing a low inflation pressure to reduce the deflection of a deflated, internally lubricated run-flat tyre, The tyre of the invention of that specification have a puncture sealing layer capable of retaining an inflation pressure of the order of 1 to 5 psi when a puncture occurs, which permits deflated running of the tyre without tha need for the .volatile liquids and liquid lubrication systems, Tha present invention relates to.compositions suitable for providins such puncture sealing layers.

Accordingly, the present invention provides a composition for application to the interior surface of the tread of a pneumatic tyre to facilitate relative movement between contacting portions of the interior surface of the tyre when the tyre is driven deflated, said composition comprising a polybutene, an acrylic polymer or a polyolefin / as gelling e-gent for the polybutene, and a particulate solid juncture sealing material, the particles of said puncture sealing material boing of sizes distributed in a range extending from partioles passing through a 7 mesh B S screen and retained on a 10 mesh B S screen to partioles which will pass through a 150 micron aperture sieve, the volume of particulate solid material being at least ofi and no more than 66$ of ' the total volume of said composition.

She polybutene is preferably a polyisobutylene, for example one having a number average molecular mass in the range 1000 to 1300. Examples of suitable polyisobutylenes are the commercial products sold under, the trade marks Hyvis 10 and Hyvis.30, These products have visoosities (measured according to BS.1Q0 - 1957 at 98.9eO·) of 1000 to 1200 and 29ΟΟ to 3200, respectively. They consist of polyisobutylene containingup to 10$ by weight of 1-butene.

Where the gelling agent is a polyolefin it is conveniently a polyethylene, preferably a mixture of low density and high density polyethylene. The amount of polyethylene is conveniently in the range 6% to 10$ by weight of the- total weight of polybutene and polyethylene. /Where a mixture of low density and high density polyethylene is used the weight of low density polyethylene can be, 4488S for example, greater than the weight of high density polyethylene.

Where the gel is formed using an acrylic polymer as gelling agent the following procedure can he followed, for example. An acidic emulsion of an acrylic copolymer containing carboxyl groups is added to the lubricant to form a mobile mixture into which puncture sealing solids can be blended» This mixture is neutralised, e.g. with ammonia or sodium hydroxide solution, to destroy the emulsion so that the acrylic copolymer goes into solution to produoe a viscous gel.

Preferably the coating includes an elastomer soluble in polybutene such as butyl rubber, ethylene-propylene rubber or natural rubber.

Use of compositions of the present invention provides a puncture sealing capability which is sufficient to seal or partially seal a puncture in the tread of a tyre against a low pressure, thus providing a low inflation pressure in the tyre during deflated running which will reduce the deflection of the tyre in this condition and thus reduce heat build-up in the tyre.

The compositions are particularly useful in tyres Of radial ply construction comprising a radial ply carcass and a circumferential tread reinforcement. The tread preferably has a substantially flat profile both externally and internally, the latter being preferred since in a tyre with a deeply dished interior profile, the very high centrifugal forces generated in fast running will tend to fling the composition to the centre of the tread, and a very thick coating of the lubricant material is then required to fill the dish and prevent migration of the coating away from the interior surface of the tyre adjacent the edges of the tyre tread. For sufficient stability not to flow around the tyre under running conditions and under gravity the gelled lubricant preferably has a viscosity in the range from 2,000 to 15>00Q sec/M at a shear rate of 0,3 sec and. at a 44883 •temperature of 20°C.

Preferably the sidewalls of the tyre are thickened, to reduce their radius of curvature during the deflections suffered in deflated running of the assembly e.g. as described in our Patent Specification No, 40710.

The particulate solid puncture sealing material preferably has a density in the range 0.8 to 1.5 gm/oo, a particularly suitable material being rubber crumb, wood-flour (sawdust) or a mixture of the two.

If desired the gelled lubricant may also contain a volatile liquids 10 such as waters which will generate a vapour pressure in the tyre after puncture sealing during deflated running.

There is now described, by way of example, several gelled polybutene compositions which constitute preferred embodiments of the invention.

In the Examples some of the ingredients are referred to by their trade names. The nature of those ingredients Is as follows.

The Hyvis compounds are synthetic hydrocarbon polymers sold by B.P.

Ghemioals Limited and manufactured by polymerisation of isobutene, They consist of polyisobutylenes containing up to 10/ by weight of 1-butene, Hyvis 10 and Hyvis 30 have the properties indicated in the table: Hyvis 10 Hyvis 30 Molecular Mass (number average 1000 Viscosity at 9θ»9°Ο (Saybolt Universal Seconds:BS 188 - 1957) 1000-1200 1300 2900-3200 The low density polyethylenes AC 6 and AC 8 (sold, by Allied Chemicals Limited) and the high density polyethylene HIgidex 140/60 (sold by B.P, Chemicals Limited) have the following properties.: *4893 Softening Point (°C) Relative Density AO 6 116 * 0.92 ac a 106 * 0.93 Rigidex 140/60 129 ** 0.965 * as measured according to ASTM E-28 ** as measured aooording to ASM B-1525 MMIPLE 1 A gelled polybutene composition was prepared by mixing the following ingredients »Hyvis 30 90 AC 6 10 mesh rubber crumb 30 130 The Hyvis 30 was heated to about 130°C. and the AO 6 added and stirred until the liquid was clear and mobile. The rubber crumb was then stirred in and stirring continued until the temperature had fallen to below 100°C. to ensure that the crumb did not settle out. The composition thus made was tested and found to be stable on a vertical aluminium surface at temperatures up to 90¾. after which it began to slump and eventually, af a temperature of 103°C., to flow freely. At a temperature of about 120°C, the oompoeition was fluid and mobile, similar to a water slurry, and oontinuoue stirring was neoessary fo ensure that the crumb did not settle out, A spray test showed that provided the composition was maintained at 120°C, and the spray gun was heated to about 110°C, the composition could readily be sprayed onto the inner layer of a tyre.

A punoture sealing experiment was then carried out using a 155/65-310 Λ A® 8 3 radial ply failsafe tyre.

Four equally spaced punctures were burned in the oentre rib of the tyre with red-hot wire and the leak rate of each puncture measured by inflating the tyre tojQ psi and noting the loss of pressure with time as fellows «- Time Pressure PSI Puncture A Puncture B Puncture C Puncture B 0 30 30 30 - 30 15 secs 28|_ 28¾ 25¾ 23 10 30 secs 27? 2? 21¾ 18¾ 45-sacs 25έ ' 26 iei 15 1 min 24¾ 25 15¾ 12 2 mins 20¾ 21 7¾ 43 3 mins 17 18 3 1¾ 15 4 mins 135- 15 1 1 5 mins ni - 12¾ 6 mins 9 11 8 mins 6 7i 10 mins .4 5¾ .20 12 mins -2¾ 3¾ 14 mins 1¾ :- 2¾ 16 mins 1 1| 18 mins 1 300 gas pf the gelled polybutene composition of this Esample was -heated tp 130°C» and hot sprayed onto the inner crown and shoulder of the tyre in a uniform coating 2 mm thick. At 130θ0, the composition was very fluid and sprayed without difficulty through a conventional air spray gun, but below 1O0°O, it gelled to a stiff stable coating on the tyre. The 44883 composition had probably cooled and gelled immediately after being atomised by the spray gun but this was not important because the thick nature of the gelled composition enabled a coherent ooating to be built up on the tyre inner crown and shoulder. 3h order to plug the punotures in the tyre and simulate puhoturing objects, ordinary 1j round wire nails were inserted into the punotures, She tyre was then fitted to a rim and with the internal pressure set at 5 psi eaoh nail was removed in turn and the punctures tested with a soap solution to see if the mere aot of removing the nail would draw the puncture sealant into the hole and seal the puncture, Di fact none of the four punotures sealed even at this low pressure, Ihe nails were re-inserted into the tyre to plug the puncture and with the internal pressure set at 30 pal the wheel waa run on a drum for 15 minutes at a speed of 60 mph under nominal load, Tests were then oarried out on the punotures as follows ia) the tyre pressure was reduced to 5 psi end the nail was removed from punoture λ - the punoture did not seal, Ihe wheel was then run for a further 5 minutes at a speed of 50 mph after which it was found that the punoture had sealed with the pressure at 3 psi. The tyre was re-inflated to 26 psi and the puncture remained sealed, b) with the tyre pressure at 26 psi the nail was removed from punoture B - the punoture did not seal, The wheel wae then run for a further 5 minutes at a speed of 50 mph after which it was found that the punoture had sealed with the pressure at 23 pel. The tyre pressure was increased to 35 psi and both punctures A and B remained sealed, o) with the tyre pressure at 30 psi the nail was removed from punoture 0 - the puncture did not seal. The wheel was then run for a further 5 minutes at a speed of 50 mph after whioh it was found that the punoture ,$8®’ .10 .had sealed with the pressure at 4 psi. The tyre was re-inflated to 28 psi and the puncture remained sealed for approximately one minute when the seal broke. Puncture C was re-plugged with a nail, d) with the tyre pressure at 26 psi the nail was removed from puncture D - the puncture did not seal. The wheel was then run for a further 5 minutes at a speed of 50 mph after whioh it was found that the puncture had sealed at 8 psi, The test was. concluded at this point, Five hours later the tyre pressure remained at 8 psi, It will be appreciated from this test that rotation of the wheel was necessary to move the sealant composition into the ponoture, EXAMPLE 2 A gelled polybutene composition was prepared by mixing the following ingredients in the order given by simple stirring at 130°C,f Parts by_Weij&jt Hyvis 10 85 AC 8 _2.

When the polyethylene had dissolved the following were added :Aerosil 300..(Silica) 6 mesh rubber crumb 35 135 The mixture was allowed to bool, later it v.’as reheated to 120°C„ and 350 gms of it were uniformly sprayed into the inner crown of a 155/65=310 radial ply failsafe tyre, EXAMPLE 3 A gelled polybutene composition was prepared.by mixing the following ingredients in the order given by simple stirring at 130°C,. ^’issa Barts by Weight Hyvis 10 92 AC θ J> When the polyethylene had diasoved 4 parts by weight Aerosil 300 (Silica) and 35 parts by weight 20 mesh wood flour were added, 300 gms of the resulting gel were hot sprayed onto the inner orown of a 155/65-310 radial ply failsafe tyre, The addition of the fine particle silica (Aerosil 300) increased the viscosity of the composition so that even at a temperature of 130°C, it did not slump on the vertical faoe of a glass beaker. On the other hand the visoosity at 130°C, was sufficiently low to enable the composition to be readily sprayed onto the inner orown or tread region cf a tyre, When tested in the tyre it was found that at low temperatures, °0, - 20°C,, the viscosity of the composition was too great for it to flow into the puncture at 50 mph vehicle speed, but as the tyre pressure dropped the tyre rapidly warmed up and reduced the viscosity of the composition to a level suoh that it could flow into the punoture and seal it. For instanoe in one test a standard punoture. was made in a cold tyre with the pressure set at 25 psi (cold here means an ambient temperature of 20°C,), The punoture did not seal when the tyre was driven at 50 mph. As the pressure dropped the tyre temperature rose and eventually the punoture sealed at a tyre pressure of 174 psi. The temperature of the tyre had by then risen to 45°θ. From then on three further standard punctures in the same tyre sealed with a maximum lose of pressure of 1 psi, i.e, the tyre was set at 25 psi before eaoh punoture was made and the pressure in the tyre after it had sealed was 24, 244 and 24i respectively.

EXAMPLE 4 The incorporation of granular rubber crumb into the gelled polybutene composition of this Example was found to provide a very satisfactory puncture sealant without inhibiting the sprayability of the heated composition, 5 A gelled polybutene composition consisting of the following ingredients: Farts by Weight Hyvis 10 94 Rigidex 14Ο/6Ο ' 2 AC 8 · 4 Polysar 301 (butyl rubber) 2 mesh rubber crumb _^0 1%. was prepared by dissolving ths Rigidex 140/60, AC 8 and butyl rubber as a-33$ solution in polybutene.by stirring at 180 - 19O°C, The rubber crumb was then added to the hot solution and stirred while maintaining the temperature above 140°C. 350 g. of this mixture was hot sprayed at 140 - 15θοθ» onto the inner liner of a 155/65—310 tyre to cover the tread area to a depth of 2 - 3 mm and when tested was found to adequately seal standard test punctures, A tyre to which there has been applied to the interior surface of the tread a gelled polybutene composition of the invention is shown in the accompanying drawing whioh shows in seotion, a failsafe tyre mounted on a wheel rim.

The drawing shows a radial ply tyre 1 having a tread portion 4 braced by a breaker assembly 2, The interior of the tread portion 4 has a coating 5 of the gelled polybutene composition of the invention} and the tyre is mounted on a two-piece wheel rim 6..

Tyres having on the interior surface of the tread a coating of a composition of this invention form the subject of our Patent Specification No. 44881.

Claims (19)

1. 'CLAIMS ί, A composition for application to ths interior surface of the tread of a pneumatic tyre to facilitate relative movement between contacting portions of the interior surface of the tyre when the tyre is driven deflated, eaid composition comprising a polybutene, an aorylio polymer or a polyolefin as gelling agent for the polybutene, and a particulate solid punoture sealing material, the particles of said punoture sealing material being of sizes distributed in a r$2ge extending from particles passing through a 7 mesh B.S. screen and retained on s, 10 mesh B.S. screen to particles which will pass through a 150 micron aperture sieve, the volume of particulate solid material being at least 80 and no more than 660 of the total volume of said composition.

2. A composition according to Claim 1, in which the galling agent is a polyethylene.

3. « A composition aooording to Claim 2, in which the amount of polyethylene is in the range from 60 to 100 by weight of the total weight of polybutene and polyethylene.

4. A composition aooording to Claim 2 or 3, in which the polyethylene is a mixture of high density and low density polyethylene.

5. A composition aooording to Claim 4, in whioh the weight of low density polyethylene is greater than the weight of high density polyethylene,

6. A composition aooording to Claim 4 or 5, in whioh the high density polyethylene has a density of substantially O,96g./co and the low density polyethylene has a density in the range from 0,92 to O,93g./oo.

7. A composition according to any oi the preceding claims in whioh the polybutene is a polyisobutylene.

8. A composition according to Claim 7s in which the polyisobutylene has a 1 - butene oontent of up to 100.

9. A composition according to any of the preceding claims, which includes an elastomer soluble in the polybutene.

10. A composition according to Claim 9, in which the elastomer is butyl rubber, ethylene-propylene rubber or natural rubber,

11. A composition according to Claim 10, in whioh the amount of said elastomer is approximately 20 by weight of the polybutene.

12. A composition according to any of the preceding claims, whioh contains silica as a further gelling agent,

13. A composition according to any of the preceding claims, in which said puncture sealing material has a density in the range from 0.8 to 1.5 g. per oo,

14. A composition according to Claim 13, in which said puncture sealing material comprises rubber crumb,

15. A composition according to any of the preceding claims, in which said puncture sealing material comprises wood flour.

16. A composition according to any of ths preceding claims, in whioh the amount of the said puncture sealing material is in the range from 330 to 530 by weight of the polybutene.

17. A composition according to any of the preceding claims, in whioh the composition bas a viscosity in the range from 2000 to 15000 λ 2 —d 0 Ii seo/M at a shear sate of 0.3 seo ” and a temperature of 20°C,

18. A composition according to Claim 1, substantially as described herein.

19. » A gelled polybutene composition for application to the interior