GB2569321A

GB2569321A - An improved solid tyre

Info

Publication number: GB2569321A
Application number: GB1720739.0A
Authority: GB
Inventors: Scarsi Colin
Original assignee: Flat Free Tyres Ltd
Current assignee: Flat Free Tyres Ltd
Priority date: 2017-12-13
Filing date: 2017-12-13
Publication date: 2019-06-19
Anticipated expiration: 2037-12-13
Also published as: GB2569321B; GB201720739D0

Abstract

A non-pneumatic solid tyre 1 including a circumferential inner portion 2 of microcellular polyurethane and an outer layer 3 of non-microcellular polyurethane on at least a portion of the outer circumference of the tyre that will come into contact with the ground during use. There is chemical cross-linking between the inner portion and outer layer. Also claimed is a method of making such a tyre comprising providing a mould, pouring a first curable non-microcellular polyurethane into the mould, allowing the non-microcellular polyurethane to begin to set for a period of time and pouring a second curable microcellular polyurethane into the mould before the first polyurethane has reached the tack-free stage of curing. The tyre may include a shaped tread portion in the outer layer and/or one or more nylon cords positioned circumferentially within the body of the tyre. Preferably the inner includes a closed cell foamed microcellular structure with a density of 0.2 to 0.5kg/dm3. The mould may rotate when the curable mixtures are poured into it and may include3 supports for tension members.

Description

The present invention relates to an improved solid tyre. In particular it relates to a two-part tyre which exhibits improved rolling resistance and in particular improved skid resistance properties when compared to traditional solid tyres.

Pneumatic tyres have been used for many years on vehicles from bicycles to scooters. However, whilst pneumatic tyres have many benefits, all such tyres generally have an air chamber that will over time result in leakage, either as a slow release or a more significant blow out. In fact, few small tyres can last more than a few weeks without losing air to a point below their optimum operational efficiency. When they fail completely it can mean that a piece of equipment comes to a standstill and may even be the source of damage to that which the tyre was carrying, or in the case of bicycle tyres a mid journey tyre change is required.

As an alternative to pneumatic tyres, solid tyres can be used. Wheels are often used that, around the rim, are made of solid rubber and plastic compounds, obtained through moulding operations. Typically solid tyres comprise a single moulded material with an internal portion called heel, an intermediate portion called middle and an external portion called tread. The heel is the portion of the tyre that is mounted around the rim, while the tread is the portion of the structure of the tyre that is in contact with the ground on which the wheel turns. With these solid tyres the solid, typically foam, interior provides the flexibility for the shock absorption characteristics, while the outer surface provides a wear resistant riding surface. This concept maintains the flat proof characteristics by eliminating the need for compressed air. The tyres are held on the rim through the use of tension members or glue.

By way of example, solid tyres are used on many types of industrial vehicles, trucks and trailers. In some cases solid tyres are made of microcellular polyurethane foam and can be of varying hardness used for applications as diverse as agriculture, trolleys for garden centres, wheelbarrows, wheelchairs, rollers, golf carts, children's buggies and a host of other applications. As the solid tyres don’t comprise an inner air tube which can fail they are much more robust and not prone to the same failure or even regular running below optimum that pneumatic tyres suffer from.

Although composite solid tyres of the type described above provide superior longevity when compared to pneumatic tyres, they do suffer from performance limitations, particularly when being used as bicycle tyres or similar where the performance of the tyre and the resulting ride quality is important. Generally solid tyres are heavier, and have poorer rolling resistance and rebound and skid resistant qualities. In particular, the microcellular polyurethane that is typically used can be problematic on certain road surfaces, with wet surfaces causing particular braking problems. These limitations can be particularly noticeable on bicycle tyres where an increase in rolling resistance makes for a heavier ride.

Certain efforts have been made to improve slip resistance by using particular tread formations or coating the surface with anti-slip materials but these methods continue to have limitations. The tread formations do not alter the material contacting the wet surfaces and as such can assist only to a degree, whilst coatings tend to rapidly be removed from the tyre during use, either through wear or by de-lamination.

The present invention aims to obviate or mitigate at least some of the drawbacks associated with the prior art.

According to the present invention there is provided a non-pneumatic tyre for mounting on a wheel rim, said tyre being substantially circular and comprising; a circumferential inner portion comprising a microcellular polyurethane; and an outer layer comprising a non-microcellular polyurethane on at least a portion of the outer circumference of the tyre that will come into contact with the ground surface during use;

wherein chemical cross linking has occurred at the junction between the microcellular polyurethane inner portion and the non-microcellular outer layer.

Advantageously, by utilising an outer layer or overcoat of non-microcellular polyurethane that has formed a chemically cross-linked bond with the microcellular polyurethane inner portion the rolling resistance, rebound and skid resistance is significantly improved. Further, as the inner portion and outer layers are cross-linked they remain permanently bonded together and there are no problems with delamination, i.e. the two materials separating, during use.

Preferably the non-microcellular polyurethane is a pourable polyurethane (i.e. it can be poured prior to curing).

Preferably the outer layer is provided on the entire outer circumference of the tyre.

Optionally, the tyre comprises a shaped tread portion.

Preferably the tread portion is formed in the outer layer.

Optionally the tread portion extends into the inner portion.

Preferably the tyre comprises one or more cords positioned circumferentially within the body of the tyre.

Optionally the cords have 18% stretch. Optionally the cords are nylon cords.

Advantageously the cords reduce the amount of stretch in the tyre.

Preferably the outer layer has a depth greater than 5mm.

Optionally, the outer layer has a depth of between 5mm and 10mm. Preferably the outer layer has a depth of between 5mm and 8mm.

Preferably there is no integral skin formed between the outer layer and the inner portion.

The inner portion of a solid tyre is typically a foamed or cellular core with an integral skin that forms during the tyre casting/manufacturing process - in tyres of the present invention there is no integral skin between the inner portion and out layer as the two are chemically bonded, via chemical cross-linkage, together. The may however still be an integral skin on the exposed or outer parts of the inner portion that do not form a boundary with the outer layer.

Preferably, a flexible polyurethane elastomer with a closed cell foamed microcellular structure, with a final density of the structure ranging from 0.2 to 0.5 kg/dm³.

According to a second aspect of the present invention there is provided a method of making the solid tyre of the first aspect, comprising;

providing a mould shaped to form a tyre or a portion thereof; pouring a first curable non-microcellular polyurethane into said mould; allowing the non-microcellular polyurethane to begin to set for a period of time; pouring a second curable microcellular polyurethane into the mould before the first curable non-microcellular polyurethane has reached the tack-free stage of curing.

Preferably the first curable non-microcellular polyurethane is poured in a manner that ensures the material is positioned on the outer circumferential surface of the solid tyre.

Optionally the mould is rotatable symmetrically on an axis of rotation and the mould rotates when the first curable non-microcellular polyurethane and/or second curable microcellular polyurethane are poured in.

Preferably a mould release composition is applied to the mould prior to polyurethane being poured in.

Optionally the mould comprises supports that can receive one or more tension members.

Preferably, the method comprises positioning tensioning members on the supports prior to pouring the first or second polyurethane into the mould.

In order to provide a better understanding of the present invention, an embodiment will now be described by way of example only and with reference to the following figures in which;

Figure 1 is a diagram showing a cross section of a tyre according to the present invention;

Figure 2 is a chart comparing the rolling resistance of various tyres;

Figure 3 is a chart comparing skid resistance of various tyres;

Figure 4 is a chart comparing fitting of various tyres;

Figure 5 is a chart comparing weight of various tyres; and

Figure 6 is a chart comparing wear of various tyres.

A cross section portion of an exemplary tyre 1 in accordance with an embodiment of the present invention is shown in figure 1. The tyre 1 consists of a substantially solid inner microcellular foamed portion 2 with an outer layer 3 of nonmicrocellular, skid-resistant polyurethane provided on the surface of the tyre that will make contact with the ground in use. The boundary 4 between the inner portion 2 and the outer layer 3 comprises cross-linked bonds between the two different polyurethane materials. In this preferred embodiment the substantially solid inner microcellular foamed portion 2 has an external skin 5.

In one embodiment, in order to manufacture the tyre 1, a tyre mould is provided. The mould is adapted to spin about a fixed axis such that material that enters the mould is acted on by centrifugal forces that result in the material being pushed outwards. In some embodiments one or more tension members are suspended inside the mould on circumferentially spaced supports that may be in the form of pins, which span the mould. The tension members can be in the form of cords with approximately 18% stretch or may be material such as nylon. The tension members assist in providing additional structural integrity to the finished tyre product. If required a mould release composition can be applied, for example by spraying, into the inner surface of the mould.

A first pourable polyurethane material is poured into the mould, sufficient to provide an outer layer of 5-8mm thickness, and is allowed to settle and begin to cure or set. Prior to the first pourable material reaching the tack free stage the second pourable microcellular polyurethane, formed by combining a urethane pre-polymer and an appropriate catalyst, such as water, is poured or charged into the mould and allowed to cure. The first material is less than 7/8^th set when the second material is poured into the mould. In one embodiment the second material is poured in after 1 minute or less. In an alternative embodiment the second material is poured in after 7.5 minutes. It is essential that the second material is poured into the mould prior to the first material reaching the tack free stage to ensure that chemical cross linking occurs between the first and second materials.

In the preferred embodiment the second pourable microcellular polyurethane when catalysed and cured results in an open celled structure with an external skin.

Microcellular polyurethanes can be formed in many ways known to those skilled in the art. A common procedure for forming a microcellular polyurethane involves mixing a polyisocyanate with a polyol and suitable catalyst. Addition of a blowing agent causes the polyurethane to foam, resulting in a microcellular polyurethane material. Water, if present, can function as a blowing agent during polyurethane formation because the carbon dioxide generated by the reaction of water and isocyanate becomes trapped within the polyurethane matrix and produces a foam structure. Water can also be used in combination with an auxiliary blowing agent such as fluorochlorohydrocarbons.

For example, according to CA1092296 microcellular polyurethane tyres can be obtained by forming a mixture of 4,4'-diphenylmethane diisocyanate (MDI) with at least three polyols, said polyols being a monomeric polyol of 2 to 3 hydroxyls having a molecular weight of less than 250, a polyester polyol of about 2 to 3 hydroxyls having a molecular weight of about 800 to 3000 and a polyether polyol of about 2 to 3 hydroxyls having a molecular weight of 4000 to 7000 and reacting said mixture in the presence of a blowing agent such as water to give a microcellular polyurethane. Other representative polyurethanes useful in this invention are the reaction product of 8.4 to 22.7 mols of organic polyisocyanate, preferably solid MDI or liquid MDI, 1.2 to 3.2 mols of a polyester polyol of 800 to 3000 molecular weight, 1 mol of a polvether polyol, preferably polypropylene ether glycol per se or one ethylene oxide capped, 5.2 to 17.8 mols of a curative of the monomeric polyol type.

The tyres of the present invention were investigated further to determine how their properties compared to pneumatic tyres, tyres which use a solid inner tube with a separate rubber outer casing, and a traditional 'Greentyre’ solid tyre.

Figures 2 to 6 show the results of the tests. As can be seen in Figure 2, rolling resistance of the new tyre has closed the gap on traditional pneumatic tyres by nearly 30%. Further, as shown in Figure 3, skid resistance is 98% of a pneumatic, a significant improvement on existing traditional solid tyres (shown as ‘Greentyres’). The weight of the new⁷ tyres, as shown in figure 5, is also slightly less than that of pneumatic tyres and significantly less than tyres that use a solid inner tube with a separate rubber outer casing. Figure 4 shows that, the new⁷ tyres are as easy to fit as pneumatic or traditional ‘Greentyre’ solid tyres whilst Figure 6 shows the wear characteristics of the new tyres are significantly better than pneumatic tyres. Overall, this gives a new⁷ tyre that shows improved use characteristics compared to traditional solid tyres, but has significantly improved wear characteristics.

It will be appreciated that features from one embodiment may be appropriately incorporated into another embodiment unless technically unfeasible to do so.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims are generally intended as “open terms {e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as “having at least,” the term “includes should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases at least one and one or more to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles a or an limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases one or more or at least one and indefinite articles such as a or an {e.g., “a” and/or “an” should be interpreted to mean “at least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number {e.g., the bare recitation of two recitations, without other modifiers, means at least two recitations, or two or more recitations).

It will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope and spirit being indicated by the

Claims

1. A non-pneumatic tyre for mounting on a wheel rim, said tyre being substantially circular and comprising; a circumferential inner portion comprising a microcellular polyurethane; and an outer layer comprising a non-microcellular polyurethane on at least a portion of the outer circumference of the tyre that will come into contact with the ground surface during use;

2. A non-pneumatic tyre according to Claim 1 wherein the non-microcellular polyurethane is a pourable polyurethane (i.e. it can be poured prior to curing).

3. A non-pneumatic tyre according to Claims 1 or 2 wherein the outer layer is provided on the entire outer circumference of the tyre.

4. A non-pneumatic tyre according to any of the previous Claims wherein the tyre comprises a shaped tread portion.

5. A non-pneumatic tyre according to Claim 4 wherein the tread portion is formed in the outer layer.

6. A non-pneumatic tyre according to Claim 4 or 5 wherein the tread portion extends into the inner portion.

7. A non-pneumatic tyre according to any of the previous Claims wherein the tyre comprises one or more cords positioned circumferentially within the body of the tyre.

8. A non-pneumatic tyre according to Claim 7 the cords have 18% stretch.

9. A non-pneumatic tyre according to any of Claims 7 or 8 wherein the cords are nylon cords.

10. A non-pneumatic tyre according to any of the previous Claims wherein the outer layer has a depth greater than 5mm.

11. A non-pneumatic tyre according to any of the previous Claims wherein the outer layer has a depth of between 5mm and 10mm.

12. A non-pneumatic tyre according to any of the previous Claims wherein the outer layer has a depth of between 5mm and 8mm.

13. A non-pneumatic tyre according to any of the previous Claims wherein there is no integral skin formed between the outer layer and the inner portion.

14. A non-pneumatic tyre according to any of the previous Claims wherein the non-microcellular polyurethane is a flexible polyurethane elastomer with a closed cell foamed microcellular structure, with a final density of the structure ranging from 0.2 to 0.5 kg/dm3.

15. A method of making a solid tyre comprising;

providing a mould shaped to form a tyre or a portion thereof; pouring a first curable non-microcellular polyurethane into said mould; allowing the non-microcellular polyurethane to begin to set for a period of time;

pouring a second curable microcellular polyurethane into the mould before the first curable non-microcellular polyurethane has reached the tack-free stage of curing.

16. A method of making a solid tyre as in Claim 15 wherein the tyre is that of Claims 1 to 14.

17. A method of making a solid tyre as in Claim 15 or 16 wherein the first curable non-microcellular polyurethane is poured in a manner that ensures the material is positioned on the outer circumferential surface of the solid tyre.

18. A method of making a solid tyre as in any of Claims 15 to 17 wherein the mould is rotatable symmetrically on an axis of rotation and the mould rotates when the first curable non-microcellular polyurethane and/or second curable microcellular polyurethane are poured in.

19. A method of making a solid tyre as in any of Claims 15 to 18 wherein a mould release composition is applied to the mould prior to polyurethane being poured in.

20. A method of making a solid tyre as in any of Claims 15 to 19 wherein the mould comprises supports that can receive one or more tension members.

21. A method of making a solid tyre as in Claims 20 wherein, the method comprises positioning tensioning members on the supports prior to pouring the first or second polyurethane into the mould.