GB1570398A

GB1570398A - Polybutene compositions

Info

Publication number: GB1570398A
Application number: GB2468379A
Authority: GB
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1977-02-08
Filing date: 1977-02-08
Publication date: 1980-07-02

Description

(54) POLYBUTENE COMPOSITIONS (71) We, DUNLOP LIMED, A British Company of Dunlop House, St. James's, London SW1 6PX, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to compositions 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.

UK Patent No 1,359,468 describes and claims a pneumatic tyre which, when mounted on a wheel rim for which it is designed and inflated to its normal working pressure, has an aspect ratio of between 30 and 75% and a tread portion whose width is greater than the width between the bead heels, having a coating of a lubricating material disposed on at least a portion of its interior surface to facilitate a relative movement between contacting portions of the interior surface of the tyre when 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 made to provide an assembly which could cope with the problem of punctures to eliminate danger or vehicle immobilization; these earlier attempts being centred primarily around two approaches. One of these was to provide a safety member in the form of a second inflation chamber, special filling, or a rigid saddle onto which the tyre was supported when deflated, and the other was to provide a puncture sealing layer on the inside of the tyre to prevent the tyre from becoming deflated. The problem of the latter approach is that unless the sealing layer is 100% efficient in preventing air-loss there is a danger that some air will be lost before the puncture 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 puncture 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.

The concept of allowing a tyre to run deflated without extra supports enables various other possibilities to be introduced. Thus in UK Patent Specification No 1,359,467 the present applicants describe the use of a tyre and wheel rim assembly with 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 UK Patent Specification No 1,435, 915 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 UK Patent Specification Nos 1,444,347 and 1,532,216.

It is to 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 the latter have failed if they allow the tyre pressure to fall by more than a very few psi.

Our Cognate UK Specification Nos 5674/76 Serial No 1570397 and 42864/76 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 the need for the volatile liquids and liquid lubrication systems. The present invention relates to compositions suitable for providing 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 agent for the polybutene, and a particulate solid puncture sealing material, the particles of said puncture sealing material being of sizes distributed in a range extending from particles passing through a 7 mesh B S screen and retained on a 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 8% and no more than 66% of the total volume of said composition.

The polybutene is preferably a polyisobutylene, for example one having a number average molecular mass in the range 1000 to 1300. Examples of suitable polyisobuylenes are the commercial products sold under the trade marks Hyvis 10 and Hyvis 30. These products have viscosities (measured according to BS.188 - 1957 at 989 C.) of 1000 to 1200 and 2900 and 3200, respectively. They consist of polyisobutylene containing up to 107e by weight of l-butene.

Where the gelling agent is a polyolefin it is conveniently a polyethylene, preferably a mixture of low density and high density polythylene. The amount of polyethylene is conveniently in the range 6% to 10% by weight of the total weight of polybutene and polyethylene. Uhere a mixture of low density and high density polyethylene is used the weight of low density polyethylene can be, 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 be 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 produce 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 idling 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 thread. 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 15,000 N sec/M2 at a shear rate of 0.3 sec.- and a temperature of 20or.

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 UK Patent Specification No. 1,487,997.

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

If desired the gelled lubricant may also con tain a volatile liquid, such as water, 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. Chemicals 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 overleaf.

The low density polyethylenes AC 6 and AC 8 (sold by Allied Chemicals Limited) and the

Hyvis 10 Hyvis 30 Molecular Mass 1000 1300 (number averageS Viscosity at 989 C (Saybolt Universal 1000-1200 2900-3200 Seconds:BS 188 1957) high density polyethylene Rigidex 140/60 (Sold by B9. Chemicals Limited) have the following properties.

Softening Relative Point(C) Density AC6 116* 0.92 AC 8 106 * 0.93 Rigidex 140/60 129 ** 0.965 * as measured according to ASTM E-28 ** as measured according to ASTM D-1525 EXAMPLE 1 A gelled polybutene composition was prepared by mixing the following ingredients: Parts by Weight Hyvis30 90 AC6 10 30 mesh rubber crumb 30 130 The Hyvis 30 was heated to about 130"C.

and the AC 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 1000C. 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 980C. after which it began to slump and eventually, at a temperature of 103 C., to flow freely. At a temperature of about 1200C. the composition was fluid and mobile, similar to a water slurry, and continuous stirring was necessary to ensure that the crumb did not settle out. A spray test showed that provided the composition was maintained at 1200C. and the spray gun was heated to about llO"C. the composition could readily be sprayed onto the inner layer of a tyre.

A puncture sealing experiment was then carried out using a 155/65-310 radial ply failsafe tyre.

Four equally spaced punctures were burned in the centre rib of the tyre with red-hot wire and the leak rate of each puncture measured by inflating the tyre to 30 psi and noting the loss of pressure with time as shown below.

300 gms of the gelled polybutene composition of this Example was heated to 1300C.

and hot sprayed onto the inner crown and shoulder of the tyre in a uniform coating 2 mm thick. At 130"C. the composition was very fluid and sprayed without difficulty through a conventional air spray gun, but below 100 C.

it gelled to a stiff stable coating on the tyre.

The 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 coating to be built up on the tyre inner crown and shoulder.

In order to plug the punctures in the tyre and simulate puncturing objects, ordinary 1" round wire nails were inserted into the punctures. The tyre was then fitted to a rim and with the internal pressure set at 5 psi each nail was removed in turn and the punctures tested with a soap solution to see if the mere act of removing the nail would draw the puncture sealant into the hole and seal the puncture. In fact none of the four punctures sealed even at this low pressure.

The nails were re-inserted into the tyre to plug the puncture and with the internal pressure set at 30 psi the wheel was run on a drum for 15 minutes at a speed of 60 mph under a nominal load. Tests were then carried out on the punctures as follows: a) the tyre pressure was reduced to 5 psi and Pressure PSI Time Puncture A Puncture B Puncture C Puncture D 0 30 30 30 30 15 secs 281k 281/4 25 23 30 secs 27J/4 27 211/2 181k 45 secs 251S 26 181k 15 1 mien 241/4 25 15 12 2 mins 201/4 21 71/4 43/4 3 mins 17 18 3 11/4 4 mins 133/4 15 1 1 5 mins 11 123/4 6 mins 9 11 8 mins 6 714 10 mins 4 51/4 12 mins 21/4 31k 14mins 11S 2 16 mins 1 1 18 mins 1 the nail was removed from puncture A - the puncture did not seal. The wheel was then run for a further 5 minutes at a speed of 50 mph after which it was found that the puncture 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 puncture B - the puncture did not seal. The wheel was then run for a further 5 minutes at a speed of 50 mph after which it was found that the puncture had sealed with the pressure at 23 psi. The tyre pressure was increased to 35 psi and both punctures A and B remained sealed.

c) with the tyre pressure at 30 psi the nail was removed from puncture C - the puncture did not seal. The wheel was then run for a further 5 minutes at a speed of 50 mph after which it was found that the puncture 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 which 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 puncture.

EXAMPLE 2 A gelled polybutene composition was prepared by mixing the following ingredients in the order given by simple stirring at 1300C; Parts by Weight Hyvis 10 85 AC8 9 94 When the polyethylene had dissolved the following were added: Aerosil 300 (Silica) 6 20 mesh rubber crumb 35 135 The mixture was allowed to cool. Later it was re-heated to 1200C. 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.

Parts by Weight Hyvis 10 92 AC8 6 98 When the polyethylene had dissolved 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 crown 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 face of a glass beaker. On the other hand the viscosity at 1300C. was sufficiently low to enable the composition to be readily sprayed onto the inner crown or tread region of a tyre.

When tested in the tyre it was found that at low temperatures, 10"C.-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 such that it could flow into the puncture and seal it. For instance in one test a standard puncture was made in a cold tyre with the pressure set at 25 psi ("cold" here means an ambient temperature of 20 C.). The puncture did not seal when the tyre was driven at 50 mph. As the pressure dropped the tyre temperature rose and eventually the puncture sealed at a tyre pressure of 17 psi. The temperature of the tyre had by then risen to 450C. From then on three further standard punctures in the same tyre sealed with a maximum loss of pressure of 1 psi, i.e. the tyre was set at 25 psi before each puncture was made and the pressure in the tyre after it had sealed was 24, 24 and 24 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.

A gelled polybutene composition consisting of the following ingredients: Parts by Weight Hyvis 10 94 Rigidex 140/60 2 AC8 4 Polysar 301 (butyl 2 rubber) 20 mesh rubber crumb 50 152 1J' was prepared by dissolving the Rigidex 140/60, AC 8 and butyl rubber as a 33% solution in polybutene by stirring at 180-1900C. The rubber crumb was then added to the hot solution and stired while maintaining the temperature above 140 C.

350 g. of this mixture was hot sprayed at 140-150 C. onto the inner liner of a 155/65310 tyre to cover the tread area to a depth of 2-3 mm and when tested was found to ade quately 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 which shows in section, 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 Cognate UK Specification 5674/76 Serial No 1570397 and 42864/76.

WHAT WE CLAIM IS: 1. 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 agent for the polybutene, and a particulate solid puncture sealing material, the particles of said puncture sealing material being of sizes distributed in a range extending from particles passing through a 7 mesh B.S. screen and retained on a 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 8% and no more than 66% of the total volume of said composition.

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

3. A composition according to Claim 2, in which the amount of polyethylene is in the range from 6% to 10% by weight of the total weight of polybutene and polyethylene.

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

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

6. A composition according to Claim 4 or 5, in which the high density polyethylene has a density of substantially 0.96 g./cc and the low density polyethylene has a density in the range from 0.92 to 0.93 g./cc.

7. A composition according to any of the preceding claims in which the polybutene is a polyisobutylene.

8. A composition according to Claim 7, in which the polyisobutylene has a 1 - butene content of up to 10%.

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 which the amount of said elastomer is approximately 2% by weight of the polybutene.

12. A composition according to any of the preceding claims, which 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 cc.

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 the preceding claims, in which the amount of the said puncture sealing material is in the range from 33% to 53% by weight of the polybutene.

17. A composition according to any of the preceding claims, in which the composition has a viscosity in the range from 2000 to 15000 N sec/M2 at a shear rate of 0.3 sec-1 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 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, substantially as descirbed in Example 1,2,3 or 4.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

350 g. of this mixture was hot sprayed at 140-150 C. onto the inner liner of a 155/65310 tyre to cover the tread area to a depth of 2-3 mm and when tested was found to ade quately 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 which shows in section, 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 Cognate UK Specification 5674/76 Serial No 1570397 and 42864/76.

WHAT WE CLAIM IS: 1. 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 agent for the polybutene, and a particulate solid puncture sealing material, the particles of said puncture sealing material being of sizes distributed in a range extending from particles passing through a 7 mesh B.S. screen and retained on a 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 8% and no more than 66% of the total volume of said composition.
2. A composition according to Claim 1, in which the gelling agent is a polyethylene.
3. A composition according to Claim 2, in which the amount of polyethylene is in the range from 6% to 10% by weight of the total weight of polybutene and polyethylene.
4. A composition according to Claim 2 or 3, in which the polyethylene is a mixture of high density and low density polyethylene.
5. A composition according to Claim 4, in which the weight of low density polyethylene is greater than the weight of high density polyethylene.
6. A composition according to Claim 4 or 5, in which the high density polyethylene has a density of substantially 0.96 g./cc and the low density polyethylene has a density in the range from 0.92 to 0.93 g./cc.
7. A composition according to any of the preceding claims in which the polybutene is a polyisobutylene.
8. A composition according to Claim 7, in which the polyisobutylene has a 1 - butene content of up to 10%.
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 which the amount of said elastomer is approximately 2% by weight of the polybutene.
12. A composition according to any of the preceding claims, which 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 cc.
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 the preceding claims, in which the amount of the said puncture sealing material is in the range from 33% to 53% by weight of the polybutene.
17. A composition according to any of the preceding claims, in which the composition has a viscosity in the range from 2000 to 15000 N sec/M2 at a shear rate of 0.3 sec-1 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 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, substantially as descirbed in Example 1,2,3 or 4.