Tyre for vehicle wheels

Abstract

The present invention relates to a tyre for vehicle wheels comprising at least one external structural element comprising at least one external structural element comprising a crosslinked elastomeric material obtained by crosslinking a crosslinkable elastomeric composition comprising (i) at least one diene elastomeric polymer, and (ii) a system for protection against ozone substantially free of polymeric static protective agents which essentially consists of at least one phenolic antioxidant in an amount substantially equal to or higher than 3 phr.

Claims

1. A tyre for vehicle wheels comprising: at least one external structural element comprising a crosslinked elastomeric material, wherein the crosslinked elastomeric material comprises, before vulcanization, a crosslinkable elastomeric composition and the crosslinkable elastomeric composition comprises: at least one diene elastomeric polymer, a system for protection against ozone substantially free of polymeric static protective agents, wherein the system consists essentially of at least one phenolic antioxidant and the at least one phenolic antioxidant is present in an amount equal to or higher than 3 phr and lower than 15 phr; and wherein the system further consists essentially of at least one cyclic-acetal or enol-ether antioxidant, and the at least one cyclic-acetal or enol-ether antioxidant is present in an equal amount to or higher than 1 phr and lower than 10 phr.

2. The tyre according to claim 1, further comprising: at least one carcass structure with opposite side edges associated with respective annular reinforcing structures, a tread band in a radially out position to the carcass structure, and a pair of sidewalls laterally on opposite sides with respect to the carcass structure.

3. The tyre according to claim 1, wherein the at least one external structural element is chosen from a sidewall and a pair of sidewalls.

4. The tyre according to claim 3, further comprising one or more decorative elements on an external surface of the sidewall or the pair of sidewalls.

5. The tyre according to claim 1, wherein the system is substantially free from antiozonants and/or antioxidants different from the phenolic, cyclic-acetal or enol-ether antioxidant.

6. The tyre according to claim 1, wherein the at least one phenolic antioxidant is present in an amount lower than 12 phr.

7. The tyre according to claim 1, wherein the at least one cyclic-acetal or enol-ether antioxidant is present in an amount lower than 8 phr.

8. The tyre according to claim 1, wherein the at least one phenolic antioxidant is chosen from: pentaerythritol tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate]; 2,2-thio-diethylene bis-[(3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate)]; octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate; isoocyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate; 1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl) benzene; 4,6-bis (dodecylthiomethyl)-o-cresol; 4,6-bis (octylthiomethyl)-o-cresol; triethylene glycol-bis[(3-(3-t-butyl-5-methyl-4-hydroxyphenyl) propionate)]; 1,6-hexanediol-bis[3,5-di-t-butyl-4-hydroxyphenyl) propionate]; and 4{[4,6-bis(octylsulphanyl)-1,3,5-triazin-2-yl]amino}2,6-di-t-butylphenol.

9. The tyre according to claim 1, wherein the at least one phenolic antioxidant is chosen from 4,6-bis(octylthiomethyl)-o-cresol and 4{[4,6-bis(octylsulphanyl)-1,3,5-triazin-2-yl]amino}2,6-di-t-butylphenol.

10. The tyre for vehicle wheels according to claim 1, wherein the at least one cyclic-acetal or enol-ether antioxidant is chosen from 3,9-di-3-cyclohexen-1-yl-2,4,6,10-tetraoxaspiro-[5.5]undecane and cyclohexen-3-ylidenemethyl-benzyl ether.

Description

DRAWINGS

(1) The description will be presented herein below with reference to the attached drawings, provided solely for illustration purposes and thus non-limiting, in which:

(2) FIG. 1 depicts in cross half-section a tyre for motor vehicle wheels according to a first embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(3) In FIG. 1, “a” indicates an axial direction and “r” indicates a radial direction. For simplicity, FIG. 1 shows only a portion of the tyre, the remaining portion not shown being identical and arranged symmetrically with respect to the radial direction “r”.

(4) With reference to FIG. 1, the tyre 100 for motor vehicle tyres comprises at least one carcass structure, comprising at least one carcass layer 101 having respectively opposite ends fastened to respective annular anchoring structures 102, called bead wires, optionally combined with a bead filling 104. The region of the tyre comprising the bead wire 102 and the filling 104 forms an annular reinforcing structure 103, the so-called bead, intended for anchoring the tyre onto a corresponding mounting rim, not depicted.

(5) The carcass structure is usually of the radial type, that is the reinforcing elements, parallel to one another, of the at least one carcass layer 101 are located on planes comprising the axis of rotation of the tyre and substantially perpendicular to the equatorial plane of the tyre.

(6) Alternatively, tyres (not depicted) equipped with cross ply carcass structures are made.

(7) In such tyres the carcass structure can comprise at least a first and a second carcass ply, radially superimposed, each made of elastomeric material and comprises a plurality of reinforcing elements arranged parallel to one another.

(8) The carcass plies are radially superimposed in a manner such that the reinforcing elements of one ply are tilted with respect to the reinforcing elements of the radially superimposed carcass ply and to the equatorial plane.

(9) Said reinforcing elements can be composed of metallic and/or textile cords, such as for example steel in the case of metallic cords or rayon, nylon or polyester (for example polyethylene naphthalate (PEN)) in the case of textile cords. Each annular reinforcing structure is associated with the carcass structure by back-folding of the opposite lateral edges of the at least one carcass layer 101 around the annular anchoring structure 102 so as to form the so-called carcass backfolds 101a as depicted in FIG. 1.

(10) In one embodiment, the coupling between carcass structure and annular reinforcing structure can be provided by a second carcass layer (not shown in FIG. 1) applied in an axially outer position relative to the first carcass layer.

(11) An anti-abrasive strip 105 is positioned in an outer position to each annular reinforcing structure 103. Preferably, each anti-abrasive strip 105 is positioned at least in an axially outer position to the annular reinforcing structure 103 extending at least between the sidewall 108 and the radially lower portion to the annular reinforcing structure 103.

(12) Preferably, the anti-abrasive strip 105 is positioned so as to wrap the annular reinforcing structure 103 along the axially inner and outer and radially lower portion of the annular reinforcing structure 103 in such a manner as to interpose itself between the latter and the rim of the wheel when the tyre 100 is mounted on the rim.

(13) Attached to the carcass structure is a belt structure 106 comprising one or more belt layers 106a, 106b arranged in radial superposition one relative to the other and relative to the carcass layer, having typically metallic reinforcing cords. Such reinforcing cords can have a crossed orientation with respect to a circumferential development direction of the tyre 100. “Circumferential” direction is understood to mean a direction generally turning in accordance with the direction of rotation of the tyre.

(14) In the radially outermost position to the belt layers 106a, 106b there can be applied at least one zero degrees reinforcing layer 106c, commonly known as “0° belt”, which generally incorporates a plurality of reinforcing cords, typically textile cords, oriented in a substantially circumferential direction, thus forming an angle of a few degrees (for example, an angle between about 0° and 6°) relative to the equatorial plane of the tyre, and coated with an elastomer material.

(15) A tread band 109 in elastomeric compound is applied in a position radially external to the belt structure 106.

(16) In some embodiments (for example tyres for motorcycle or scooter wheels) the belt structure can be absent.

(17) Furthermore, on the lateral surfaces of the carcass structure, each extending from one of the lateral edges of the tread band 109 up to the respective annular reinforcing structure 103, respective sidewalls 108 of elastomeric compound made according to the present invention are applied in an axially outer position.

(18) In a radially outer position, the tread band 109 has a rolling surface 109a intended to come into contact with the ground. Circumferential grooves, which are linked by transverse incisions (not shown in FIG. 1) in such a manner as to define a plurality of wedges of various shapes and dimensions distributed on the rolling surface 109a, are generally made in this surface 109a, which for simplicity in FIG. 1 is shown as smooth.

(19) A sublayer 111 is positioned between the belt structure 106 and the tread band 109.

(20) A strip constituted of elastomeric material 110, commonly known as “mini-sidewall”, can possibly be present in the connecting region between the sidewalls 108 and the tread band 109, this mini-sidewall generally being obtained by co-extrusion with the tread band 109 and allowing an improvement in the mechanical interaction between the tread band 109 and the sidewalls 108. Preferably, the end portion of the sidewall 108 directly covers the lateral edge of the tread band 109.

(21) In the case of tyres with no inner tube, a layer of rubber 112, generally known as “liner”, which provides the necessary impermeability to the inflating air of the tyre, can also be provided in a radially inner position with respect to the carcass layer 101.

(22) On the external surface of the sidewalls 108, decorative elements 120 such as coloured strips or writings, preferably in bright colours, can be applied for example by gluing or co-vulcanization.

(23) The decorative elements 120 can be made of polymeric material of the elastomeric, plastic or elasto-plastic type filled with colourant metal oxides or with organic dyes.

(24) Preferably, the decorative elements 120 are made with a composition comprising EPDM rubber, halobutyl, preferably chlorobutyl, rubber and natural rubber. Particularly preferred is a composition comprising 1-10% by weight of EPDM rubber, 10-30% by weight of halobutyl, preferably chlorobutyl, rubber and 15-35% by weight of natural rubber with respect to the total weight of the composition, the remaining percentage comprising pigments and other additives, and vulcanizing and coadjuvant chemical products.

(25) The side of the decorative elements 120 intended for cohesion on the sidewall of the tyre can be coated with a heat-sensitive adhesive which can co-crosslink or can physically interact with the sidewall compound fixing the decorative element to the sidewall itself.

(26) The surface of the decorative element exposed to atmospheric agents can advantageously be coated with a clear resin protective film in order to maintain for a longer time the aesthetic qualities of the decorative element during the use of the tyre.

(27) The manufacture of the tyres 100 as described above, can be performed by assembly of respective semi-finished products on a moulding drum, not depicted, by means of at least one assembly device.

(28) At least a part of the components intended to form the carcass structure of the tyre can be constructed and/or assembled on the moulding drum. More particularly, the moulding drum is suitable for receiving firstly the possible liner, then the carcass structure and the anti-abrasive strip. Next, devices not shown engage coaxially around each of the terminal rims one of the annular anchoring structures, position an external sleeve comprising the belt structure and the tread band in a position coaxially centred around the cylindrical carcass sleeve and adapt the carcass sleeve according to a toroidal configuration by means of radial expansion of the carcass structure, so as to bring about its application against a radially internal surface of the external sleeve.

(29) Following the manufacture of the raw tyre, a moulding and vulcanization treatment is performed for the purpose of effecting the structural stabilization of the tyre by crosslinking the elastomeric compounds and of printing on the tread band a desired tread pattern and printing onto the sidewalls optional distinctive graphic symbols.

(30) The decorative elements 120 can be affixed directly on the moulding drum before assembling the sidewalls, or can be positioned on the raw tyre before moulding and vulcanization, or can be applied to the sidewalls of the finished tyre downstream of the moulding and vulcanization treatment.

(31) The present invention will be further illustrated hereinafter by means of a number of preparative examples, which are provided purely for illustrative purposes and without any limitation of this invention.

Example 1

(32) The elastomeric compositions R (reference) and from 1 to 11 which comprise various quantities of 6PPD or of other antioxidants, in presence or absence of static protective agents (wax, PEG1500 or Melflux™ PP100) as shown in Table 1, were prepared as follows (the quantities of the various components are given in phr).

(33) All the components, except for sulphur, retardant and accelerant (CBS), were mixed together in an internal mixer (model Pomini PL 1.6) for about 5 minutes (first phase). As soon as the temperature reached 145±5° C., the elastomer composition was discharged. The sulphur, the retardant and the accelerant (CBS) were then added and the mixing was performed in an open roll mixer (second phase).

(34) TABLE-US-00001 TABLE 1 Sample R 1 (c) 2 (c) 3 (c) 4 (c) 5 (c) 6 (c) 7 (c) 8 (c) 9 (i) 10 (i) 11 (i) First phase Natural rubber 40 40 40 40 40 40 40 40 40 40 40 40 Butadiene rubber 60 60 60 60 60 60 60 60 60 60 60 60 Carbon black 660 50 50 50 50 50 50 50 50 50 50 50 50 Adhesive resin 2 2 2 2 2 2 2 2 2 2 2 2 Stearic acid 2 2 2 2 2 2 2 2 2 2 2 2 Zinc oxide 2.85 2.85 2.85 2.85 2.85 2.85 2.85 2.85 2.85 2.85 2.85 2.85 Wax 2 2 2 2 2 2 2 / / / / / PEG 1500 / / / / / / / 2 / / / / Melflux ™PP100 / / / / / / / / 2 / / / 6PPD 3 / / / / / / / / / / / Vulkazon AFS / 4 2 2 2 2 / / / 2 2 / Durazone 37 / / 2 / / / / / / / / / Genox EP / / / 2 / / / / / / / / Irganox 1520 / / / / 2 4 8 8 8 4 6 8 Second phase Retardant 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 CBS 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 Sulphur 2 2 2 2 2 2 2 2 2 2 2 2 Adhesive resin: Quintone A100, Zeon Corporation 6PPD: N-(1,3-dimethylbutyl)-N′-phenyl-phenylenediamine Vulkazon AFS: 3,9-di-3-cyclohexen-1-yl-2,4,6,10-tetraoxaspiro[5.5]undecane Durazone 37: 2,4,6-tris-(N-1,4-dimethylpentyl-p-phenylenediamino)-1,3,5- triazine Genox EP: amines, bis(hydrogenated rape-oil alkyl)methyl, N-oxides Irganox 1520: 4,6-bis [(octylthio)methyl]-o-cresol Retardant: N-cyclohexylthiophthalimide CBS: N-cyclohexyl-2-benzothiazyl sulphonamide Melflux ™PP100: Copolymer of (meth)acrylic acid with ethylenically unsaturated monomers containing polyoxyethylene side chains (Degussa)

Example 2

(35) Using the compounds of Table 1, rubber samples of dimensions 15×5×0.5 cm, vulcanized at 170° C. for 10 minutes, were made. Decorative labels of yellow colour (supplier Transfergomma) were applied onto the resulting samples by hot-transfer method in a manual press by applying a pressure of 10 kg/cm.sup.2 for 10 seconds at 120° C.

(36) The test samples thus obtained were exposed to a UV irradiation cycle (48 hours at 50° C.) using a Xenon chamber (supplier Q-Sun) according to the ASTM D1148 methodology, modified for use of the UV exposure only, with no washing cycles.

(37) At the end of the test the test samples were visually inspected to assess their colouring alteration (browning) with respect to a reference sample not subjected to the treatment. A subjective mean qualitative score was given to the appearance of the surface of each test sample, as summarized below.

(38) TABLE-US-00002 Score Appearance A no stains B slightly stained C stained

(39) The results of the subjective assessment are shown in the following Table 2.

(40) TABLE-US-00003 TABLE 2 Sample R 1 (c) 2 (c) 3 (c) 4 (c) 5 (c) 6 (c) 7 (c) 8 (c) 9 (i) 10 (i) 11 (i) Visual test C B B B B B B B B A A A results

(41) The results obtained demonstrated that the replacement of the conventional paraphenylenediamine antiozonant (6PPD) with various types of antioxidants allowed a certain, but not entirely satisfactory, improvement even with large quantities.

(42) The complete absence of stains was surprisingly observed in the samples containing the system for protection against ozone of the present invention, samples 9(i), 10(i) and 11(i), containing variable amounts of Irganox, alone or in combination with Vulcazon AFS, and free of polymeric static protective agents.

Example 3

(43) The samples were then subjected to the dynamic ozone test, performed as follows, in accordance with the standard ISO 1431-1, to verify the compliance with the necessary requirements in spite of the elimination of the wax or other polymeric static protective agents.

(44) The samples of the crosslinked elastomeric compositions described above (vulcanized at 170° C. for 10 minutes) having dimensions 50 mm×10 mm×2 mm were positioned inside a glass bell into which ozonized air was channelled [ozone concentration equal to 50+/−5 pphm (parts per hundred million)] and were subjected dynamically and continuously to traction from 0% to 20% deformation. The test was performed at 50+/−2° C.

(45) Starting from the first hour, and then after every 2 hours (for a total time of 17 hours) under the aforesaid conditions, the samples were examined under the optical microscope (40×) to determine the presence of cracks.

(46) The results of this test, summarized in the following Table 3, were expressed by means of an assessment scale which goes from 1 to 5, in which 1 indicates no cracks visible with the optical microscope (40×) and 5 indicates cracks visible with the optical microscope (40×) and to the naked eye.

(47) TABLE-US-00004 TABLE 3 Sample 1 (c) 2 (c) 3 (c) 4 (c) 5 (c) 6 (c) 7 (c) 8 (c) 9 (i) 10 (i) 11 (i) Dynamic 4 4 4 4 3 5 5 5 2 2 1 ozone test results

(48) The results obtained showed that antiozonant systems containing 2 phr of wax and 4 phr of an antioxidant compound selected from Vulkazon AFS, Durazone, Genox EP, Irganox 1520, or 1:1 mixtures thereof, did not offer sufficient protection against the damaging action of ozone (samples 1-4 (c)).

(49) The use of wax and of 6 phr of a 1:2 mixture of Vulkazon AFS and Irganox 1520 (sample 5(c)) provided a protection greater than that obtainable using the other antioxidants tested, but nonetheless not acceptable. Further, the antiozonant system containing 2 phr of various static protective agents and 8 phr of Irganox (samples 6-8 (c)) resulted in a lower resistance to ozone.

(50) Surprisingly, the use of Vulkazon AFS/Irganox 1520 mixtures in the absence of static protective agents, made it possible to obtain antiozonant systems with an increasing protective action, proportional to the increase in the amount of Irganox 1520 used, until attainment of the optimal performances obtained using 8 phr of Irganox 1520 alone (sample 11(i)).

(51) Even though the results obtained with the samples 1-8 (c) would have discouraged further experimentation, the Applicant decided to continue, arriving at the optimal and unexpected result in terms of resistance to atmospheric ozone and colour alteration, obtained with the use of 8 phr of Irganox 1520 alone (sample 11(i)).