Patent Description:
Studs for winter tires have been known for decades and have helped to significantly improve traction characteristics on snow and particularly ice-covered surfaces to improve the grip of the tire to icy roads and other icy pavements. However, conventional tire studs also have some drawbacks which have limited their use in winter tires. For example, conventional tire studs typically have a body which is made of a metal material, such as aluminum, and have a pin extending from the body for ensuring non-skid behavior of the tire on icy roads. Aluminum has however the disadvantage of generally high cost and fluctuating prices. Moreover, the use of a metal body may affect the structure of the rubber composition in the tires due to high temperature. Furthermore, the use of such metal body may result in relatively high level of noise generation.

Recently studs based on polymeric material have been developed which may overcome some of these disadvantages associated with conventional studs. An example of a polymer stud is given in <CIT>. In this application, the stud body is made of a polymer-based material, in particular a mixture of syndiotactic <NUM>,<NUM>-polybutadiene (SPBD) and another polymer, and the pin is made of steel or carbon tungsten.

<CIT> discloses an anti-skid stud, wherein the pin fitted within a polymeric stud body has a base width (within the body) larger than its top width (outside the body). In any case, the use of polymeric material in tire studs is not very well-established and there is still a need for improvement in stud design.

With the tire stud of the present invention, it was found that by adapting the design and/or position of the pin in the polymeric stud body of a tire stud it was possible to improve durability compared to well-known tire stud, such as those comprising aluminum stud body.

<CIT> and <CIT> describe a tire stud in accordance with the preamble of claim <NUM>. A similar tire stud is known from <CIT>. Further tire stud designs are described in <CIT> and <CIT>.

The invention relates to a tire stud in accordance with claim <NUM> and to a tire in accordance with claim <NUM>.

The tire stud comprises a stud body comprising at least one polymer, a pin comprising a first portion P<NUM> adjacent to a second portion P<NUM>, wherein the stud body comprises a hole T for receiving the pin, the second portion P<NUM> of the pin being located in T and the first portion P<NUM> of the pin extending out of the stud body, wherein the pin has a length LP being defined as the maximum radial distance between the top of P<NUM> and the bottom of P<NUM>, with LP = LP1 + LP2, LP1 being the radial length of P<NUM> and LP2 being the radial length of P<NUM>. The ratio of the radial length LP2 of said second portion P<NUM> of the pin relative to the radial distance from the radially outermost point or surface of said stud body to the radially innermost point or surface of said stud body HSB is in a range of from <NUM>:<NUM> to <NUM>:<NUM>.

The present invention further relates to a tire or pneumatic tire comprising at least one tire stud according to the present invention.

In the context of the present invention, the term "radial" or "radial direction" refers to a length or distance that is parallel to the axis from the top of the pin of the tire stud to the bottom of the stud body. Hence, the radial direction is parallel to the axis of rotation or to the symmetry axis of the tire stud, if any. "Radial" also refers to the direction when the tire stud is inserted into the tread of a tire, i.e., in accordance with its intended use. Hence, a "radial" direction of the tire stud is also a radial direction of the tire.

In the context of the present invention, the term "axial" or "axial direction" refers to a length or distance that is perpendicular to the radial direction. "Axial" also refers to the direction when the tire stud is inserted into the tread of a tire, i.e., in accordance with its intended use. Hence, an "axial" direction of the tire stud is also an axial direction of the tire, i.e., parallel to the axis of rotation of the tire.

The present invention relates to a tire stud comprising a stud body comprising at least one polymer, a pin comprising a first portion P<NUM> adjacent to a second portion P<NUM>, wherein the stud body comprises a hole T for receiving the pin, the second portion P<NUM> of the pin being located in T and the first portion P<NUM> of the pin extending out of the stud body, wherein the pin has a length LP being defined as the maximum radial distance between the outer surface of the top of P<NUM> and the outer surface of the bottom of P<NUM>, with LP = LP1 + LP2, LP1 being the radial length of P<NUM> and LP2 being the radial length of P<NUM>. The ratio of the radial length LP2 of said second portion P<NUM> of the pin relative to the radial distance from the radially outermost point or surface of said stud body to the radially innermost point or surface of said stud body HSB is in a range of from <NUM>:<NUM> to <NUM>:<NUM>.

Preferably, the outer surfaces of the sidewalls of the pin in the second portion P<NUM> are in contact with a portion of the stud body and wherein the hole T of the stud body has a length LT being the radial distance between the top of the stud body to the deepest outer surface of the hole, with LT ≥ LP2.

Preferably, the stud body height HSB is in the range of from <NUM> to <NUM>, more preferably in the range of from <NUM> to <NUM>, more preferably in the range of from <NUM> to <NUM>.

Preferably, the pin length LP is in the range of from <NUM> to <NUM>, more preferably in the range of from <NUM> to <NUM>.

Preferably, LP1 of the pin is in the range of from <NUM> to <NUM>, more preferably in the range of from <NUM> to <NUM>, more preferably in the range of from <NUM> to <NUM>.

Preferably, the outer surface of the bottom of P<NUM> of the pin is in contact with a portion of the stud body, being the deepest outer surface of the hole T, with LT = LP2.

Preferably, LP2/HSB is of at least <NUM>:<NUM> and in the range of from <NUM>:<NUM> to <NUM>:<NUM>, more preferably in the range of from <NUM>:<NUM> to <NUM>:<NUM>, more preferably in the range of from <NUM>:<NUM> to <NUM>:<NUM>.

According to a preferred embodiment, there is a void space between the outer surface of the bottom of P<NUM> and the deepest outer surface of T of the stud body, with LT > LP2. Preferably, the void space has a length LVS being defined as the radial distance between the outer surface of the bottom of P<NUM> and the deepest outer surface of T of the stud body, with LVS/LT > <NUM>:<NUM>, more preferably LVS/LT > <NUM>:<NUM>, more preferably LVS/LT > <NUM>:<NUM>.

According to said alternative, preferably, LP2/HSB is in the range of from <NUM>:<NUM> to <NUM>:<NUM>, more preferably in the range of from <NUM>:<NUM> to <NUM>:<NUM>.

According to a preferred embodiment, the ratio of LP1/LP2 is of at most <NUM>:<NUM>, more preferably in the range of from <NUM>:<NUM> to <NUM>:<NUM>, more preferably in the range of from <NUM>:<NUM> to <NUM>:<NUM>, more preferably in the range of from <NUM>:<NUM> to <NUM>:<NUM>.

Preferably, the stud body comprises a top portion, an intermediate portion and a bottom portion, the top portion being adjacent to the intermediate portion being adjacent to the bottom portion, wherein the hole T extends from the top portion of the stud body through the intermediate portion of the stud body and optionally a part of the bottom portion of the stud body.

The top portion has a width W1 being determined by the maximum distance between the sidewalls of the stud body in the top portion, the intermediate portion has a width W2 being determined by the maximum distance between the sidewalls of the stud body in the intermediate portion, with W1 > W2.

Preferably, the width W1 is at least <NUM> percent, more preferably in the range of from <NUM> to <NUM> percent, larger than W2.

Preferably, the top portion has a width W1 being determined by the maximum distance between the sidewalls of the stud body in the top portion, the bottom portion has a width W3 being determined by the maximum distance between the sidewalls of the stud body in the bottom portion, with W1 < W3.

Preferably, the width W3 is at least <NUM> %, more preferably in the range of from <NUM> to <NUM> percent, more preferably in the range of from <NUM> to <NUM> percent, larger than W1.

Preferably, the pin has a varying width along its radial length LP (symmetry axis), wherein the largest width WPL is located at the top of the first portion P<NUM> and the smallest width WPS is located at the bottom of the second portion P<NUM>.

Preferably, the pin is made of metal and/or ceramic material, wherein the metal is one or more of tungsten carbide and steel, more preferably tungsten carbide. More preferably the pin is made of tungsten carbide.

Preferably, the at least one polymer comprised in the stud body is selected from the group consisting of polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyphenyl ether (PPE), polypropylene (PP), polyethylene (PE), polycarbonate (PC), polysulfone (PSU), polyetherimide (PEI), polyphenylene sulfone (PPSU), polyarylamide (PARA), polyamine (PA), syndiotactic <NUM>,<NUM>-polybutadiene (SPBD), phenolic resin, melamine resin, epoxy resin, benzoxazine-based polymer, cyanate ester resin, polyurethane (PU), polyacrylic ester, a polyimide and a mixture of two or more thereof.

SPBD offers the advantage of becoming securely bound to the rubber of the tire tread. It is believed that the syndiotactic <NUM>,<NUM>-polybutadiene (SPBD) co-cures with the rubber of the tire tread during the curing of the tire, resulting in a strong adhesion between the SPBD and the tire tread. SPBD can be prepared in an inert organic solvent utilizing the technique described in <CIT> or in an aqueous medium utilizing the process described in <CIT>.

The latter more specifically reveals a process for producing polybutadiene composed essentially of SPBD comprising the steps of:.

Preferably, the SPBD utilized for preparing the stud body comprised in the tire stud of the present invention has a melting point of <NUM> or less, more preferably in the range of from <NUM> to <NUM>, more preferably in the range of from <NUM> to <NUM>, more preferably in the range of from <NUM> to <NUM>. The melting points referred to herein are the minimum endotherm values determined from DSC (differential scanning calorimetry) curves.

It is conceivable that the stud body comprises a blend of polymers, including SPDB (from <NUM> to <NUM> weight - percent based on the weight of the blend) and at least one rubber (from <NUM> to <NUM> weight percent based on the weight of the blend) which is curable with the SPBD. The rubber component used in such blends can be virtually any type of elastomer which contains unsaturation that allows for sulfur curing. Typically, the elastomer will be one or more polydiene rubbers. Some representative examples of suitable polydiene rubbers include cis-<NUM>,<NUM>-polybutadiene, natural rubber, synthetic polyisoprene, styrene butadiene rubber, EPDM (ethylenepropylene- diene monomer) rubbers, isoprene-butadiene rubbers, and styreneisoprene-butadiene rubbers. In many cases it will be desirable to utilize a combination of diene rubbers in the blend. For instance, the rubber portion of the blend can be a combination of chlorobutyl rubber, natural rubber, and EPDM rubber. Preferably, the rubber component comprises from <NUM> to <NUM> weight - percent, more preferably from <NUM> to <NUM> weight - percent, chlorobutyl rubber, from <NUM> to <NUM> weight percent, more preferably from <NUM> to <NUM> weight - percent, natural rubber, and from <NUM> to <NUM> weight - percent, more preferably from <NUM> to <NUM> weight - percent, EPDM, the weight percent being based on the weight of the rubber component.

In the context of the present invention, it is believed that the inclusion of high content of SPBD in the stud body results in better adhesion, abrasion, and tear resistance for the cured material. High contents of SPBD also result in increased green strength and stiffness. Additionally, it is believed that the use of high levels of SPBD reduces green tack which makes handling. However, the incorporation of large amounts of SPBD into the blend also results in reduced flexibility and modulus. Accordingly, for the best balance of overall properties, the blend utilized preferably contains from <NUM> to <NUM> weight - percent SPBD and from <NUM> to <NUM> weight - percent co-curable rubbers. More preferably, the blend in the stud body contains from <NUM> to <NUM> weight - percent SPBD and from <NUM> to <NUM> weight - percent of the elastomeric component.

The SPBD used for preparing the blend can be in powder or pellet form. The SPBD powder or pellets can be mixed into the rubber component utilizing standard mixing techniques. However, the mixing is normally carried out at a temperature which is at least as high as the melting point of the SPBD being utilized. During the mixing procedure, the SPBD powder pellets are fluxed into the rubber with additional desired compounding ingredients. Such mixing is typically carried out in a Banbury mixer, a mill mixer or in some other suitable type of mixing device.

Such blends of SPBD and rubber component may further contain other standard rubber chemicals. For instance, such blends may contain sulfur and at least one desired colorant or pigment, e.g., titanium dioxide can be of interest as it can be used as pigment and filler. They will also typically contain other rubber chemicals, such as antioxidants, accelerators, oils, and waxes in conventional amounts. The typical content of sulfur and first and secondary accelerators are disclosed in <CIT>.

Alternatively or in addition to SPBD, other polymers such as those disclosed in the foregoing can be used for the stud body.

Optionally, the stud body is reinforced with one or more fibers. Preferably, the one or more fibers are glass fibers, woven fibers or staple fibers.

Further, the stud body may further comprise one or more of a pigment and a dye.

Preferably, the stud body is produced by injection molding or the like. Methods for its production are known in the art.

Preferably, in the context of the present invention, the axis of rotation of the tire stud is also the symmetry axis of the tire stud.

The present invention further relates to a pneumatic tire comprising at least one tire stud according to the present invention.

Preferably, the pneumatic tire further comprises a tread, wherein the tread comprises the at least one tire stud, more preferably a plurality of tire studs according to the present invention, which are embedded therein. The pin of the tire stud extends out of the tread.

Preferably, the pneumatic tire further comprises a polymeric layer coated onto the stud body of the at least one tire stud and being in contact with the tread.

Preferably, the pneumatic tire is a winter, snow and/or ice pneumatic tire.

The present invention is further illustrated by the following set of embodiments and combinations of embodiments resulting from the dependencies and back-references as indicated. In particular, it is noted that in each instance where a range of embodiments is mentioned, for example in the context of a term such as "The tire stud of any one of embodiments <NUM> to <NUM>", every embodiment in this range is meant to be explicitly disclosed for the skilled person, i.e. the wording of this term is to be understood by the skilled person as being synonymous to "The tire stud of any one of embodiments <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>". Further, it is explicitly noted that the following set of embodiments represents a suitably structured part of the general description directed to preferred aspects of the present invention, and thus, suitably supports, but does not represent the claims of the present invention.

According to embodiment <NUM> of the present invention relating to a tire stud, the tire stud comprises a stud body comprising at least one polymer, a pin comprising a first portion P<NUM> adjacent to a second portion P<NUM>, wherein the stud body comprises a hole T for receiving the pin, the second portion P<NUM> of the pin being located in T and the first portion P<NUM> of the pin extending out of the stud body, wherein the pin has a length LP being defined as the maximum radial distance between the outer surface of the top of P<NUM> and the outer surface of the bottom of P<NUM>, with LP = LP1 + LP2, LP1 being the radial length of P<NUM> and LP2 being the radial length of P<NUM>, wherein the ratio of LP2 relative to HSB is of at least <NUM>:<NUM>, HSB being the stud body height.

The tire stud of embodiment <NUM>, wherein the outer surfaces of the sidewalls of the pin in the second portion P<NUM> are in contact with a portion of the stud body and wherein the hole T of the stud body has a length LT being the radial distance between the top of the stud body to the deepest outer surface of the hole T, with LT ≥ LP2.

The tire stud of embodiment <NUM>, wherein the outer surface of the bottom of P<NUM> of the pin is in contact with a portion of the stud body, being the deepest outer surface of the hole T, with LT = LP2.

The tire stud of embodiment <NUM>, wherein LP2/ HSB is of at least <NUM>:<NUM> and in the range of from <NUM>:<NUM> to <NUM>:<NUM>, more preferably in the range of from <NUM>:<NUM> to <NUM>:<NUM>, more preferably in the range of from <NUM>:<NUM> to <NUM>:<NUM>.

The tire stud of embodiment <NUM>, wherein there is a void space between the outer surface of the bottom of P<NUM> and the deepest outer surface of T of the stud body, with LT > LP2.

The tire stud of embodiment <NUM>, wherein the void space has a length LVS being defined as the radial distance between the outer surface of the bottom of P<NUM> and the deepest outer surface of T of the stud body, with LVS/LT > <NUM>:<NUM>, preferably LVS/LT > <NUM>:<NUM>, more preferably LVS/LT > <NUM>:<NUM>.

The tire stud of embodiment <NUM> or <NUM>, wherein LP2/ HSB is in the range of from <NUM>:<NUM> to <NUM>:<NUM>, preferably in the range of from <NUM>:<NUM> to <NUM>:<NUM>.

The tire stud of any one of embodiments <NUM> to <NUM>, wherein the ratio of LP1/LP2 is of at most <NUM>:<NUM>, preferably in the range of from <NUM>:<NUM> to <NUM>:<NUM>, more preferably in the range of from <NUM>:<NUM> to <NUM>:<NUM>, more preferably in the range of from <NUM>:<NUM> to <NUM>:<NUM>.

The tire stud of any one of embodiments <NUM> to <NUM>, wherein the stud body comprises a top portion, an intermediate portion and a bottom portion, the top portion being adjacent to the intermediate portion being adjacent to the bottom portion, wherein the hole T extends from the top portion of the stud body through the intermediate portion of the stud body and optionally a part of the bottom portion of the stud body.

The tire stud of embodiment <NUM>, wherein the top portion has a width W1 being determined by the maximum distance between the sidewalls of the stud body in the top portion, the intermediate portion has a width W2 being determined by the maximum distance between the sidewalls of the stud body in the intermediate portion, with W1 > W2; wherein preferably the width W1 is at least <NUM> percent, more preferably in the range of from <NUM> to <NUM> percent, larger than W2.

The tire stud of embodiment <NUM> or <NUM>, wherein the top portion has a width W1 being determined by the maximum distance between the sidewalls of the stud body in the top portion, the bottom portion has a width W3 being determined by the maximum distance between the sidewalls of the stud body in the bottom portion, with W1 < W3; wherein preferably the width W3 is at least <NUM> percent, more preferably in the range of from <NUM> to <NUM> percent, more preferably in the range of from <NUM> to <NUM> percent, larger than W1.

The tire stud of any one of embodiments <NUM> to <NUM>, wherein the pin has a varying width along its radial length LP, wherein the largest width WPL is located at the top of the first portion P<NUM> and the smallest width WPS is located at the bottom of the second portion P<NUM>.

The tire stud of any one of embodiments <NUM> to <NUM>, wherein the pin is made of metal and/or ceramic material, wherein the metal is one or more of tungsten carbide and steel, more preferably tungsten carbide, more preferably the pin is made of tungsten carbide.

The tire stud of any one of embodiments <NUM> to <NUM>, wherein the at least one polymer comprised in the stud body is selected from the group consisting of polyetheretherketone (PEEK), polyphenylene sulfide (PPS), polyphenyl ether (PPE), polypropylene (PP), polyethylene (PE), polycarbonate (PC), polysulfone (PSU), polyetherimide (PEI), polyphenylene sulfone (PPSU), polyarylamide (PARA), polyamine (PA), syndiotactic <NUM>,<NUM>-polybutadiene (SPBD), phenolic resin, melamine resin, epoxy resin, benzoxazine-based polymer, cyanate ester resin, polyurethane (PU), polyacrylic ester, a polyimide and a mixture of two or more thereof.

A pneumatic tire comprising at least one tire stud according to any one of embodiments <NUM> to <NUM>.

The pneumatic tire of embodiment <NUM>, further comprising a tread, wherein the tread comprises the at least one tire stud, more preferably a plurality of tire studs according to any one of embodiments <NUM> to <NUM>, which are embedded therein and wherein the pin of the tire stud extends out of the tread.

The pneumatic tire of embodiment <NUM> or <NUM>, further comprising a polymeric layer coated onto the stud body of the at least one tire stud and being in contact with the tread.

The pneumatic tire of any one of embodiments <NUM> to <NUM>, being a winter, snow and/or ice pneumatic tire.

Stud durability tests during tread wear test have been performed on a control tire stud which is a commercially available aluminum stud and two tire studs according to the present invention illustrated in <FIG> and <FIG>. In particular, the tests have been performed with passenger vehicle on road under various meteorological conditions with a maximum temperature of <NUM>, on dry and wet roads. The number of broken and lost studs have been determined at different times (Period <NUM> to Period <NUM>) depending on the mileage in km and NSK (the thickness of the tread wherein the tire studs are embedded) in mm.

As shown in Table <NUM>, the tire studs according to the present invention have an improved durability compared to the control stud. Indeed, for both studs, the number of broken and lost studs is reduced starting from Period <NUM> up to Period <NUM>.

<FIG> is a schematic cross-sectional view of a tire stud according to a preferred embodiment of the present invention. The tire stud <NUM> comprises a pin <NUM>, preferably a metal pin, and a stud body <NUM> comprising at least one polymer. The stud body <NUM> comprises a hole wherein the pin <NUM> is fitted. In particular, the second portion P<NUM> is located in the hole of the stud body <NUM>, said portion having a radial length LP2. The first portion P<NUM> of the pin extends out of the stud body <NUM>, said portion having a radial length LP1. The stud body <NUM> has a top portion <NUM> adjacent to an intermediate portion <NUM> adjacent to a bottom portion <NUM>, wherein the width W3 > width W1 > width W2. According to the preferred embodiment, the radial length of P<NUM> is equal to the radial length LT of the hole T (hole not shown in <FIG> has filled with the pin <NUM>). The hole T was extending through the top portion <NUM> and the intermediate portion <NUM>. The hole could extend through a part of the portion <NUM> (not shown here). The ratio of LP2/HSB is of <NUM>:<NUM> such that said FIG. can be representative of inventive stud <NUM> mentioned above.

<FIG> is a schematic cross-sectional view of a tire stud according to another preferred embodiment of the present invention. The tire stud <NUM> comprises a pin <NUM> and a stud body <NUM>. The stud body <NUM> is similar to the stud body <NUM> in <FIG> except that the pin <NUM> is fitted in the hole of the stud body <NUM> such that there is a void space <NUM> which is formed between the outer surface of the bottom of P<NUM> and the deepest outer surface of the hole of the stud body <NUM>. The hole extends through the top portion <NUM>, the intermediate portion <NUM> and a part of the bottom portion <NUM>. The relationship between the width of the portions <NUM>, <NUM> and <NUM> is similar to <FIG>. However, the ratio of LP2/HSB is of <NUM>:<NUM> such that said figure can be representative of inventive stud <NUM> mentioned above.

Claim 1:
A tire stud comprising a stud body (<NUM>) comprising or consisting of at least one polymer and a pin (<NUM>) comprising a first portion (P<NUM>) radially adjacent to a second portion (P<NUM>,), and wherein the stud body (<NUM>) further comprises a hole for receiving the pin (<NUM>), the second portion (P<NUM>) of the pin (<NUM>) being located in said hole and the first portion (P<NUM>) of the pin (<NUM>) extending radially out of the stud body (<NUM>), wherein the pin (<NUM>) has a length (LP) being defined as the maximum radial distance between the radially outermost surface of said first portion (P<NUM>) and the radially innermost surface of the bottom of said second portion (P<NUM>), and wherein said pin length (LP) is the sum of the radial length (LP1) of said first portion (P<NUM>) of the pin (<NUM>) and the radial length (LP2) of said second portion (P<NUM>) of the pin (<NUM>), characterized in that
the ratio of the radial length (LP2) of said second portion (P<NUM>) of the pin (<NUM>) relative to the radial distance from the radially outermost point or surface of said stud body (<NUM>) to the radially innermost point or surface of said stud body (HSB) is in a range of from <NUM>:<NUM> to <NUM>:<NUM>; and
the stud body (<NUM>) comprises a top portion (<NUM>), an intermediate portion (<NUM>) and a bottom portion (<NUM>), the top portion (<NUM>) being radially adjacent to the intermediate portion (<NUM>) and the intermediate portion (<NUM>) being radially adjacent to the bottom portion (<NUM>), wherein the hole extends from the top portion (<NUM>) of the stud body (<NUM>) through the intermediate portion (<NUM>) of the stud body (<NUM>), wherein the top portion (<NUM>) has an axial width (W1) being determined by the maximum axial distance between the sidewalls of the stud body (<NUM>) in the top portion (<NUM>), wherein the intermediate portion (<NUM>) has an axial width (W2) being determined by the maximum axial distance between the sidewalls of the stud body (<NUM>) in the intermediate portion (<NUM>), and wherein said top portion axial width (W1) is larger than said intermediate portion axial width (W2).