WO2010128211A1

WO2010128211A1 - Vehicle tyre and method of its manufacture

Info

Publication number: WO2010128211A1
Application number: PCT/FI2010/050368
Authority: WO
Inventors: Jaakko Ristola
Original assignee: Just Jaakon Uunisuunnittelutoimisto Oy
Priority date: 2009-05-07
Filing date: 2010-05-06
Publication date: 2010-11-11
Also published as: FI123762B; FI20095516A; FI20095516A0

Abstract

The present invention relates to a vehicle tyre and a method for manufacturing thereof. Particularly, the invention relates to improving the friction properties of tyres used in a vehicle in poor road conditions, mostly in winter, and most commonly provided with the marking M+S. The friction properties are improved by arranging mainly solid glass spheres having a diameter of 0.1-2 mm within the rubber compound forming the tread.

Description

Vehicle tyre and method of its manufacture

(0001 ) The present invention relates to a vehicle tyre and a method for manufacturing thereof. Particularly, the invention relates to improving the friction properties of tyres used in a vehicle in poor road conditions, mostly in winter, and most commonly provided with the marking M+S. The invention is particularly advantageously suitable for improving the friction properties of the so-called friction tyres, that is, studless winter tyres, when driving especially on a wet surface.

(0002) In poor driving conditions, which are chiefly considered snowy and/or icy roads here in the Nordic countries, vehicles employ tyres which are better or worse equipped for the road conditions. Heavy vehicles i.e. lorries and buses still mostly rely on the weight of the vehicle i.e. use tyres the tread pattern of which is somewhat coarser than that of the so-called summer tyres, but which do not utilise studs or equivalent anti-skid means improving the friction properties of the tyre. In very poor conditions i.e. mostly when driving on forest lorry roads and equivalent snowy surfaces, it is possible to use relatively easily removable snow chains. Very few heavy vehicles employ studded tyres which, again, are very popular in passenger cars and delivery vehicles.

(0003) A problem of the tyres of heavy vehicles is their poor grip on a wet and icy road surface resulting in that roads have to be kept unfrozen when the temperature is zero or some degrees below zero by salting the roads in all hours. This incurs both environmental problems in the form of salt applied on the road and costs due to the round-the-clock service and, naturally, due to the salt itself and the vehicles required to apply it.

(0004) In the so-called studded tyres, the tread pattern is coarser than in tyres used in summer or generally in unfrozen road conditions, because the purpose of the pattern is to take a grip of the snowy road surface. There are studs located in recesses made in the tread in the manufacturing phase of the tyre , the purpose of which is to improve the friction properties of the tyre on a hard and icy surface. The studs are most often of metal, and they advantageously include a tip of hard metal such that they also endure driving on a surfaced road without wearing unfit for use unreasonably quickly.

(0005) A primary problem of studded tyres is that they wear the road surface, which is visible in springs as road grooves and dust which is mainly fine solids cut by the studs from the surfacing. Another problem is the noise created by the studs when impacting the surfacing, which can be heard both inside and particularly outside the vehicle as unpleasant howling.

(0006) In the past two or three decades, the so-called friction tyres have entered the market the tread of which clearly differs from the one of traditional winter tyres. The most essential tread pattern in the friction tyres is, except for the coarser pattern than the one of summer tyres, the so-called lamelling which refers to dividing the tyre tread in the axial direction into lamellas of only some millimetres thick i.e. rubber strips which densely rise radially from the tyre surface, located completely onto each other. The purpose of the lamellas together with the hardness of the tread rubber slightly lower than usual is to ensure that the tyre is able to grip even to the smallest of irregularities of the surface, whether it is trodden snow, ice, wet ice or molten surface.

(0007) Even though these so-called friction tyres spare the road surface from wear and even though they are very quiet in use, they have their weaknesses. As their operation is based on the utilisation of existing roughness in the road surface, to operate properly, the road surface has to be roughened in some way or another. Nowadays, this is not a problem, because studded tyres roughen the road surface quite enough, but, if the use of studded tyres diminishes for some reason or another (in some countries the use of studded tyres is already prohibited), the problem is easier to see. The most important problems are, on the one hand, the most slippery winter conditions probable, i.e. a wet and icy roadway, and, on the other hand, a wet asphalt or paving. When the temperature rises in winter, ice or trodden snow on the road starts to melt, possibly further assisted by rain, whereby the roughness due to studs disappears quickly. Sometimes, subcooled water falling on a surfaced road also creates an equivalent wet and icy surface of which the so-called friction tyre cannot take a grip almost at all. Furthermore, a problem of friction tyres often is that, when aiming at maximal friction properties, a lot of the wear resistance of the tyre is lost, whereby the lifetime of friction tyres is at worst only one winter. In addition, the all-year use of these friction tyres is prevented by both their weakish wear resistance and the slipperiness of the rubber material used on a wet road surface.

(0008) The use of studdable friction tyres has also been suggested, because they seem optimal particularly from the viewpoint of friction properties. In fact, some of the recent studdable tyres are manufactured of a rubber compound softer than conventional and, at the same time, the tread pattern is altered to include more lamellas than earlier. Whatever the tread structure, design or rubber quality, a problem of those tyres still is that the studs wear the road surface and create noise although both are slightly more moderate than those of conventional studded tyres.

(0009) Thus, it seems that neither the studded M+S (Mud+Snow) tyres, friction tyres nor studded friction tyres will solve the various problems of winter traffic: wear of road surface and created dust, tyre noise, wear of tyres, and slipperiness on a wet and/or icy surfacing.

(0010) There have been attempts, some even partially successful, to solve the problems mentioned above by arranging within the tread rubber of the tyre solid particles, the materials of which are various. Tyres of this kind are described, inter alia, in patents US-A-2766800, FI-B-52684, EP-A2-0780245, US-A-2607386, and EP-A1 -2108527. These documents describe the use of various mineral, ceramic, sinter, hard rubber and metal particles, for instance, as the non-slip material. Furthermore, the use of dried corn particles or wood- based particles as the non-slip material is mentioned.

(0011 ) It can be stated on the above-listed materials that, primarily due to the sole fact that they are lighter than the studs used today, they decrease the wear of the road surface. However, each material used has its own disadvantages. The corn or wood-based particles in themselves hardly have any friction-increasing property. Particles softer than the material of the roadway create dust when crumbling, which is very much equivalent to the current dust loosened of the roadway by studs. And metal particles again, depending principally on their hardness, when wearing themselves and wearing theroadway, create dust and loosen as particulates which are harmful to the environment. The loosening of solid non-slip particles from rubber is most often due to the fact that no such gripping joint can be created between those particles and rubber which would for long endure deformations continuously occurring in the rubber as the tyre rotates, but the joints become loose and the centrifugal force throws the non-slip particle away.

(0012) Therefore, the primary object of the present invention is to eliminate or at least diminish the above-mentioned problems.

(0013) That is, the different embodiments of the present invention aim at facilitating, at its best even simultaneously, the problems related to the wear of the roadway, the creation of dust, the friction properties of the tyre, and the adhesion of friction particles.

(0014) Those problems will be solved by utilising the already known arrangement of the non-slip particles used being smaller and lighter than the traditional studs. Then naturally, their impact force on the road surface is smaller, which minimises the wear of the road surface. Also, the density of those non-slip particles in the tread is still greater, which compensates their smaller impact force and ensures a friction force large enough for the tyre. The centrifugal force enhancing the loosening of the non-slip particle is also so small that it cannot break the joint between the non-slip particle and the rubber.

(0015) Those non-slip particles are manufactured according to an advantageous embodiment of the invention of material which is harder than ice but softer than road surfacing materials (mostly aluminium silicate), whereby the wear of road surfaces decreases more and more. An advantageous embodiment of the present invention introduces ordinary glass as the non-slip material suitable of its hardness, costs and operating properties.

(0016) Those objects of the invention can then be implemented with a vehicle tyre according to claim 1 , which primarily consists of a tyre frame structure with its bead wires, tyre carcass and tyre belts as well as a rubber tread, in the manufacturing phase of which solid particles have been mixed within the tread material, the tyre being characterised in that, for improving the friction properties of the tyre, 5-30 % by volume of the tread material solid particles having an average diameter of 0.1-2 millimetres which, when wearing out, create particulates, which are water-soluble, have been mixed within the tread material before the vulcanising of the tyre.

(0017) On the other hand, those objects are met by manufacturing the vehicle tyre in question with a method for manufacturing a vehicle tyre according to claim 10, in which method, various rubber compounds are prepared, different tyre components are manufactured, said components are rubberised as well as the components are arranged in a proper order as green tyre, and the green tyre is vulcanised into a tyre, which method is characterised by, when preparing the rubber compound to be used for the tread, mixing within it 5-30 % by volume of the tread material in question non- slip particles having a diameter of 0.1-2 millimetres which, when wearing out, create particulates, which are water-soluble.

(0018) Additionally, the present invention relates to a manufacturing method of a retreaded tyre according to claim 11 , in which the tread of a used tyre is milled away and a new tread is vulcanised or otherwise fastened in its place, whereby the method is characterised by, when preparing the rubber compound to be used for the new tread, mixing within it for 5-30 % by volume of the tread material in question non-slip particles having a diameter of 0.1-2 millimetres which, when wearing out, create particulates, which are water-soluble.

(0019) Other characteristic features of the vehicle tyre and its manufacturing method according to the invention will become evident from the appended dependent claims.

(0020) Advantages achievable with the present invention are the following, inter alia:

• Does not wear the roadway surfacing

• Does not create dust but rather binds existing dust • Increases the friction force of the tyre exactly where the other friction properties of the tyre are at their poorest, i.e., improves the gripping capacity of the tyre o on plain ice o on wet ice o on wet asphalt o on wet paving, whereby the tyres can be used all year round safely

• Non-slip material used is cost-effective

• The use of non-slip particles does not require measures after the tyre has been vulcanised like studding does

• The adhesion of non-slip particles in the tyre is better than that of

• conventional studs

(0021 ) Next, the vehicle tyre according to the invention and its alternative manufacturing methods will be described in more detail with reference to the enclosed figure which shows a radial, partial cross section of a vehicle tyre according to an advantageous embodiment of the invention. (0022) In accordance with the figure, the vehicle tyre 2 consists of a great number of various components which are here mainly divided for simplicity into a frame structure 4 and a tread 10. The frame structure 4 includes, inter alia, a bead wire (not shown in the figure) located in the bead base of the tyre (the section setting against the rim in use), a tyre carcass 6 which extends from one wire to another, and tyre belts 8 which are located below the tread 10 between it and the carcass 6. The tread 10 is provided with grooves 12, lamellas or some other patterns of different sizes and directions depending on the intended operating conditions. According to the invention, in the tread 10 are arranged in the manufacturing phase of the tyre small-sized particles 14 the average diameter of which is in the range of 0.1-2 mm. In the figure, the particles 14 are shown as closed glass spheres, part of which are worn out on the surface of the tyre.

(0023) Even though the impact force of those small glass spheres, more broadly glass particles, on the roadway surface is very small compared to the impact force of traditional studs, the required effect increasing the friction of the tyre is ensured by the density of the glass spheres on the tread being substantially greater than that of studs (10-1 , 000-fold). When the tread of the tyre is manufactured in this manner, the effect of the tyre wearing the road surface can be minimised and, at the same time, the large enough friction force of the tyre can be ensured.

(0024) As for manufacturing the glass spheres, two slightly differing techniques exist in common use for manufacturing small-sized glass spheres. In one technique, a molten material mixture is formed e.g. of waste glass resulting from the productionof a window glass factory or of actual original materials of glass, which mixture is allowed to cool. After cooling, the mixture is crushed and sieved into suitable fractions. Then, crush of desired size is fed into a hot gas flow in which the crush particles melt again. Surface tension forces shape the particles into spheres. Another way to manufacture glass spheres is to spill molten glass on top of a rotating roll, whereby the molten glass splashes as beads into a suction box in which spheres are created. The use of glass material as the non-slip material is also supported by the surface of glass being in practice the smoothest providable surface at molecular level, whereby the joint formed between that surface and rubber is very strong. In other words, even though the surface of rubber at molecular level is relatively uneven, the smooth glass surface facilitates finding suitable binders the molecules of which extend all over the glass surface from the glass surface until the rubber surface.

(0025) Another advantageous embodiment of the present invention aims at realising the object of the invention of eliminating dust as well as possible. In that further embodiment, glass particles according to the invention are manufactured of water glass or equivalent glass grade water-soluble when abraded into fine dust. Water glass, besides being well soluble in water in its particulate form, also forms a glue-like sticky material when dissolving, in which other road traffic dust adheres. In other words, glass dust produced by the vehicle tyres according to the invention as they wear dissolves in rainwater, thaw water or moisture of ground and binds other disadvantageous particles produced by traffic in itself. An advantage of using water glass is naturally also the fact that it is totally harmless to health, as it is used, inter alia, in food products and toothpastes.

(0026) Water glass is a special grade of glass. Glass can generally be defined as a network formed of silica molecules (Siθ₂) in which other atoms are joined. When those atoms are alkali metal atoms, we refer to water glass. Commercially viable alkali metals in this invention are sodium and potassium, of which sodium is somewhat more favourable than potassium. Thus, in the following the so-called sodium water glass is discussed as an example. Because Na atoms break the network, the size of the molecule is dependent on the concentration of Na. The higher the concentration of alkali in the water glass, the more easily the water glass dissolves in water. In order for water glass be suitable for friction material, it cannot be too easily soluble in water. That is, when manufacturing water glass for the non-slip purpose, its molar ratio SiO₂ / Na₂O should be adjusted for over 2.5. When water glass is melted, "metasilicates," Na₂SiO₃, Na₄SiO₄, Na₆Si₂O₇, are first formed. And when SiO₂ is dissolved in these melts, the final molecule properties are dependent on the molar ratio. Both above-described manufacturing methods of glass spheres are also suitable for manufacturing glass particles of water glass, although it is considerably simpler, because there is no need to crush water glass but the starting point is directly the melting of water glass raw materials.

(0027) Furthermore, the use of water glass in the manufacture of glass particles is also favoured by the fact that, when using the nozzle technique in manufacturing glass spheres, there probably is no need to use expensive platinum nozzles which most other glass grades require. When manufacturing glass spheres of water glass, the nozzle material can be considerably more cost-effective nickel-based lnconel or cobalt-based Stellit grades. The reason is that, when using water glass in the manufacture of glass particles, the manufacturing temperature of particles or rather the tensile temperature of the spin is below 1 ,200⁰C.

(0028) Of prior art, some specifications are known in which glass spheres are used in the manufacture of vehicle tyres. US-A1 -2004/0118496 employs at the bottom of grooves in the tread of a vehicle tyre light-reflecting particles, e.g. glass micro spheres. EP-A2-1561605 utilises in the rubber compound of the tread hollow glass spheres of the diameter of 50 - 200 μm. EP-B1 -1752491 uses glass spheres on the sides of the tyre, whereby the purpose of the spheres is to brace the so-called run-flat tyre particularly when the tyre is damaged and air within the tyre is not able to carry the load of the tyre. Not a single document suggests the use of solid glass spheres as friction material neither the use of water glass nor any other such material as friction material which, when abraded fine, would be water-soluble and would bind road dust and/or other road traffic fines. Thus, there was no need for any of the documents to consider how the glass particle can be kept fast on the tyre surface even when part of it is exposed such that stresses caused by both the roadway and the tyre deformation are applied in the exposed point in question. (0029) In other words, the invention entails that glass particles are manufactured in some above-described or some other suitable way and that the glass particles manufactured in such a manner are mixed within the rubber material used for forming the tread of vehicle tyres. It should be noticed from the above that the manufacture of glass particles employed in the invention aims at producing solid glass particles or spheres but, as far as we know, the possibility of a part of the glass particles being hollow cannot be left out. Thus, the invention also covers such tyres which include a small number of hollow glass spheres, even though their functional properties compared to solid particles/spheres are considerably weaker.

(0030) In general terms, the manufacture of the actual new tyre takes place in the way described in patent specifications FI-B-112339, FI-B-116891 and Fl- A-20041214, for instance. However, it is evident that the rubber material according to the invention including glass spheres can also be used as the tread rubber material of retreaded tyres such that the worn tread layer is milled of the used tyre and in its place is vulcanised or otherwise fastened a new tread layer including particles according to the invention. Therefore, it is evident that this invention i.e. locating mostly solid glass particles within the tread rubber of a tyre can be employed in the tyres of all kinds of vehicles and that it can be used for the whole width of the tyre tread or for a part of the width of the tread.

(0031 ) Vehicle tyres are manufactured in a way known as such mainly from natural rubber, synthetic rubber, oil and carbon black as well as various cord layers functioning as reinforcements. Furthermore, different vulcanising agents and auxiliary chemical are employed in the manufacture. Different parts of the tyre require different rubber compounds and the rubber compounds also vary in tyres for different running conditions or different seasons. Each rubber compound is mixed of its own original materials and heated to the temperature of about 12O⁰C. Mixtures manufactured in this manner are used to rubberise different tyre components, such as bead wires, tyre carcass and tyre belts (textile or steel). The tyre is assembled of said components into a green tyre using assembly machines by drawing the components onto the belt drum of the assembly machine and by setting the tyre carcass on the bulkheads of the stretching machine, after which the loading wheel of the machine transfers the unit formed by the tread and the tyre belts onto the tyre carcass. Then, the tyre carcass is pressurised and stretched to fuse with the unit. This is how a green tyre is produced. Green tyres are vulcanised in curing presses. High steam pressure conveyed in the curing pad inside the curing press presses the green tyre against a tread pattern and side texts within a mould, giving the tyre its final appearance.

(0032) When applying the use of glass spheres/particles and additionally possibly other suitable particles according to the invention in the tyre manufacture briefly described above, the manufacture differs only for the part of the layer forming the tyre tread. Within the tread material i.e. rubber material forming that layer is mixed a desired amount of glass spheres/particles (and possibly other friction particles), advantageously for 5 - 30 % by volume.

(0033) An advantageous embodiment of the method according to the invention is characterised by treating the surface of the glass particles at some phase after their manufacture with an applicable material, which protects the surface of the glass particles from scratching in connection with their mechanical handling (including various packaging, storage and transport phases) before inserting the particles in question within the rubber compound. Advantageously, the protective treatment is performed immediately after the manufacture of the glass particles. As the protective material in question, inter alia, silanes may be applied the silanes being also used as a binder to bind the glass particles tightly in the rubber material of vehicle tyres when vulcanising the tyre. Silane operates in a way already briefly described above such that its long molecule chain includes one part which forms a chemical bond with the silica of the glass and another part which forms a chemical bond with the elastomers of the rubber. Silane molecules thus extend from the surface of the glass particle until the surface of the rubber. In fact, silanes are already used in the manufacture of tyres to bind other particles, e.g. micro silica particles, in rubber being vulcanised, thus the use of silane with rubber is known.

(0034) When the glass particles have, thus, been pretreated with silane or equivalent, the bond between the binder and the glass is ready as early as before vulcanising. Protecting the surfaces of glass particles with silane or equivalent material is important as the glass particles can break not only when packaging, storing and transporting them but also when the glass particles make contact with the roadway. The silane coating ensures the adhesion of the surface of the glass particle and the rubber material in connection with the vulcanising of the tyre manufacturing phase for the whole surface area of the glass particle. At the same time, the bond between the glass particle and the rubber becomes very strong and elastic. This is to ensure that the glass particle starts to abrade into dust only of its surface when contacting the road surface, the other parts of the particle being intact. Namely, if there is a notch on the surface of the glass particle on the opposite wall in relation to the impact coming from the road surface, the particle may break due to the tensile stress of the opposite wall, and not due to the compression stress at the point of impact.

(0035) Silane above refers to a group of silanes applicable as a binder, which are e.g. organo mercapto silane (e.g. alkoxy organo mercapto silane) and particularly alkoxy organo mercapto silane the mercapto function of which is capped. Other usable silanes are organo alkoxy mercapto silanes, e.g. triethoxy mercaptopropyl silane, trimethoxy mercaptopropyl silane, methyl dimethoxy mercaptopropyl silane, methyl diethoxy mercaptopropyl silane, dimethyl methoxy mercaptopropyl silane, triethoxy mercaptoethyl silane, tripropoxy mercaptopropyl silane, ethoxy dimethoxy mercaptopropyl silane, ethoxy diisopropoxy mercaptopropyl silane, ethoxy didodecyloxy mercaptopropyl silane, and ethoxy dihexadecyloxy mercaptopropyl silane. (0036) Other applicable binders may be e.g. bis(3-trialkoxysilylalkyl) polysulphide which includes on average 2-4 sulphur atoms in its polysulphide bridge. An equivalent binder is also bis(3-triethoxysilylpropyl) polysulphide, e.g. bis(3-triethoxysilylpropyl) tetrasulphide which includes a polysulphide bridge comprising on average 3.2-3.8 sulphur atoms forming the bond or bis(3- triethoxysilylpropyl) disulphide which includes a polysulphide bridge comprising on average 2.1-2.6 sulphur atoms forming the bond.

(0037) A tyre including the tread rubber compound according to the invention wears in use, whereby particles on the tread are slowly worn out producing a somewhat uneven fracture plane which bites firmly on a softer material, such as e.g. ice. The wearing out occurs such that, while the tyre rubber contacts the roadway, the rubber deforms and the glass particle extending until the rubber surface slides for an instant against the roadway surface. Then, the roadway scratches the glass particle and loosens fine dust from it. At the same time, small scratches are created on the glass surface which bite well into ice. In an equivalent way, the non-slip particle operates e.g. in relation to wet asphalt when the rubber compound of the tyre for some reason (traditional friction tyre in summer conditions) cannot develop an adequate friction force. When the particles are evenly divided through the whole thickness of the tread, the friction properties of the tyre do not change at all in practice for the whole lifetime of the tyre. For instance when using studded tyres, even hard-metal studs wear and break, whereby the friction properties of the tyre weaken all the time from the first kilometres.

(0038) As seen from the above, a novel type of a vehicle tyre and a novel type of a method for manufacturing that tyre have been developed. It should be noticed of the above description of the invention that it represents only some of the most advantageous embodiments of the invention without any purpose to limit the scope of the invention of what is presented in the enclosed claims.

Claims

1. A vehicle tyre, which mainly consists of a frame structure (4) of the tyre (2) with its bead wire, tyre carcass (6) and tyre belts (8) as well as a rubber tread (10), in the manufacturing phase of which solid particles (14) have been mixed within the tread material, characterised in that, for improving the friction properties of the tyre, 5-30 % by volume of the tread material solid particles having an average diameter of 0.1-2 millimetres which, when wearing out, create particulates, which are water-soluble, have been mixed within the tread material before the vulcanising of the tyre.

2. A vehicle tyre according to claim 1 , characterised in that said particles are mainly solid glass spheres manufactured of water glass.

3. A vehicle tyre according to claim 2, characterised in that the molar ratio Siθ₂ / Na₂θ in the water glass is more than 2.5.

4. A vehicle tyre according to claim 1 , 2 or 3, characterised in that said solid glass spheres are coated with silane or some other applicable coating material before being added within the tread material.

5. A vehicle tyre according to claim 4, characterised in that said coating material is an organo mercapto silane or organo alkoxy mercapto silane.

6. A vehicle tyre according to claim 4 or 5, characterised in that said coating material is triethoxy mercaptopropyl silane, trimethoxy mercaptopropyl silane, methyl dimethoxy mercaptopropyl silane, methyl diethoxy mercaptopropyl silane, dimethyl methoxy mercaptopropyl silane, triethoxy mercaptoethyl silane, tripropoxy mercaptopropyl silane, ethoxy dimethoxy mercaptopropyl silane, ethoxy diisopropoxy mercaptopropyl silane, ethoxy didodecyloxy mercaptopropyl silane, and ethoxy dihexadecyloxy mercaptopropyl silane.

7. A vehicle tyre according to claim 4, characterised in that said coating material is bis(3-trialkoxysilylalkyl) polysulphide, bis(3-triethoxysilylpropyl) polysulphide, e.g. bis(3-triethoxysilylpropyl) tetrasulphide, or bis(3- triethoxysilylpropyl) disulphide.

8. A vehicle tyre according to any one of preceding claims 1 - 7, characterised in that the glass spheres in question are manufactured by the nozzle method.

9. A vehicle tyre according to any one of preceding claims 1-8, characterised in that the glass spheres in question have a hardness of greater than that of ice but less than the hardness of road surfacings.

10. A method for manufacturing a vehicle tyre, in which method, various rubber compounds are prepared, different tyre components are manufactured, said components are rubberised as well as the components are arranged in a proper order to form green tyres, and the green tyre is vulcanised into a tyre, characterised by, when preparing the rubber compound to be used for the tread, mixing within it 5-30 % by volume of the tread material in question non- slip particles having a diameter of 0.1-2 millimetres which, when wearing out, create particulates which are water-soluble.

11. A method for manufacturing a vehicle tyre, in which method, the tread of a used tyre is milled away and a new tread is vulcanised or otherwise fastened in its place, characterised by, when preparing the rubber compound to be used for the new tread, mixing within it for 5-30 % by volume of the tread material in question non-slip particles having a diameter of 0.1-2 millimetres which, when wearing out, create particulates which are water-soluble.

12. A method according to any one of preceding claims 10 or 11 , characterised by manufacturing the glass spheres of water glass into a mainly solid form.

13. A method according to claim 12, characterised by that, in the manufacture of water glass, adjusting its molar ratio SiO₂ / Na₂O to more than 2.5.

14. A method according to any one of preceding claims 10-13, characterised by manufacturing the glass spheres with the nozzle method into mainly solid form.

15. A method according to any one of preceding claims 10-14, characterised by coating said mainly solid glass spheres before mixing them within the rubber compound with silane or some other equivalent binder.

16. A method according to any one of preceding claims 10-15, characterised by coating the glass spheres with the binder immediately after their manufacture.

17. A method according to any one of preceding claims 15-16, characterised by coating the glass spheres either with organo mercapto silane or organo alkoxy mercapto silane.

18. A method according to any one of preceding claims 15-17, characterised by coating the glass spheres with at least one of the following: triethoxy mercaptopropyl silane, trimethoxy mercaptopropyl silane, methyl dimethoxy mercaptopropyl silane, methyl diethoxy mercaptopropyl silane, dimethyl methoxy mercaptopropyl silane, triethoxy mercaptoethyl silane, tripropoxy mercaptopropyl silane, ethoxy dimethoxy mercaptopropyl silane, ethoxy diisopropoxy mercaptopropyl silane, ethoxy didodecyloxy mercaptopropyl silane, and ethoxy dihexadecyloxy mercaptopropyl silane.

19. A method according to any one of preceding claims 15-18, characterised by coating the glass spheres with at least one of the following: bis(3-trialkoxysilylalkyl) polysulphide, bis(3-triethoxysilylpropyl) polysulphide, e.g. bis(3-triethoxysilylpropyl) tetrasulphide, and bis(3-triethoxysilylpropyl) disulphide.