A TIRE COMPRISING A TREAD

Abstract

A tire has a tread comprising a rubber composition based on at least: an elastomer matrix; a reinforcing filler; a plasticizing agent; and particles; wherein the tread comprises: a tread surface; a sequence of basic pattern(s), wherein each basic pattern has a width (Wm) over at least 80% of the width (W) of the tread, each basic pattern has a pitch (P), and each basic pattern comprises a plurality of raised elements, one or more of which are provided with sipes opening onto the tread surface, wherein each sipe has a width of less than 1 mm and a depth of at least 3 mm; wherein the tread has a sipe density (SD) defined as (I), the SD being less than 60 m/mm.sup.2; where i is the number of sipe(s) in the pattern, l.sub.i is the length of the i sipe on the tread surface.

[00001]$\begin{array}{cc}\mathrm{SD}=\frac{\underset{i}{.Math.}.Math.\mathrm{li}}{P\mathrm{Wm}}& \left(I\right)\end{array}$

Claims

1.-27. (canceled)

28. A tire having a tread comprising a rubber composition based on at least: an elastomer matrix; a reinforcing filler comprising between 80 and 200 phr of a reinforcing inorganic filler; a plasticizing agent; and between 1 and 150 phr of particles having a particle size of between 100 and 10 mesh, wherein the tread comprises: a tread surface intended to be in contact with the ground when the tire is running; and a sequence of basic patterns circumferentially arranged, wherein each basic pattern has a width Wm axially extending over at least 80% of the width W of the tread, each basic pattern has a pitch P circumferentially extending, and each basic pattern comprises a plurality of raised elements, one or more of which are provided with sipes opening onto the tread surface, wherein each sipe has a width of less than 1 mm and a depth of at least 3 mm; wherein the tread has a sipe density SD defined as $\begin{array}{cc}\mathrm{SD}=\frac{\underset{i}{.Math.}.Math.\mathrm{li}}{P\mathrm{Wm}}.& \left[\mathrm{Math}..Math.1\right]\end{array}$ the sipe density SD being less than 60 m/mm.sup.2, where i is the number of sipes in the pattern, li is the length of the i.sup.th sipe on the tread surface, P is the pitch of the basic pattern, and Wm is the width of the basic pattern.

29. The tire according to claim 28, wherein the elastomer matrix comprises at least a diene elastomer selected from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers, and mixtures thereof.

30. The tire according to claim 28, wherein the elastomer matrix comprises 20 to 100 phr of a first diene elastomer bearing at least one SiOR function, R being a hydrogen atom or a hydrocarbon radical, and optionally, 0 to 80 phr of a second diene elastomer which is different from the first diene elastomer.

31. The tire according to claim 30, wherein the first diene elastomer is a styrene-butadiene copolymer.

32. The tire according to claim 30, wherein the SiOR function is located at the chain end of the first diene elastomer.

33. The tire according to claim 30, wherein R of the SiOR function is a hydrogen atom.

34. The tire according to claim 30, wherein the first diene elastomer has a glass transition temperature of lower than 40.

35. The tire according to claim 30, wherein the second diene elastomer is selected from the group consisting of polybutadienes, synthetic polyisoprenes, natural rubber, butadiene copolymers, isoprene copolymers, and mixtures thereof.

36. The tire according to claim 28, wherein the reinforcing inorganic filler is silica.

37. The tire according to claim 28, wherein the reinforcing filler further comprises less than 40 phr of carbon black.

38. The tire according to claim 28, wherein the plasticizing agent comprises 0 to 100 phr of liquid plasticizer and 5 to 100 phr of hydrocarbon resin having a glass transition temperature above 20 C.

39. The tire according to claim 38, wherein a total content of liquid plasticizer and hydrocarbon resin is more than 50 phr.

40. The tire according to claim 38, wherein the liquid plasticizer is selected from the group consisting of liquid diene polymers, polyolefinic oils, naphthenic oils, paraffinic oils, Distillate Aromatic Extracts (DAE) oils, Medium Extracted Solvates (MES) oils, Treated Distillate Aromatic Extracts (TDAE) oils, Residual Aromatic Extracts (RAE) oils, Treated Residual Aromatic Extracts (TRAE) oils, Safety Residual Aromatic Extracts (SRAE) oils, mineral oils, vegetable oils, ether plasticizers, ester plasticizers, phosphate plasticizers, sulphonate plasticizers and mixtures thereof.

41. The tire according to claim 38, wherein the hydrocarbon resin is selected from the group consisting of cyclopentadiene homopolymer or copolymer resins, dicyclopentadiene homopolymer or copolymer resins, terpene homopolymer or copolymer resins, C.sub.5 fraction homopolymer or copolymer resins, C.sub.9 fraction homopolymer or copolymer resins, alpha-methyl styrene homopolymer or copolymer resins, and mixtures thereof.

42. The tire according to claim 28, wherein the particles are made of particles selected from the group consisting of potassium tetraborate, sodium tetraborate calcium tetraborate, potassium chloride, sodium chloride, zirconia bead, alkali feldspar, kureha microsphere, silica sand, porous silica bead, cellulose powder, porous cellulose bead, walnut hull, oyster shells, chitin, polyvinyl alcohol powder, polyethylene resin, crumb rubber and mixtures thereof.

43. The tire according to claim 42, wherein the particles are crumb rubber particles.

44. The tire according to claim 43, wherein the crumb rubber particles are mechanically processed.

45. The tire according to claim 43, wherein the crumb rubber particles are generated from scrap tires.

46. The tire according to claim 28, wherein an angle .sub.i is the positive or negative angle formed on the tread surface by the i.sup.th sipe with the axle direction, where |.sub.i|45.

47. The tire according to claim 28, wherein the tire is a snow tire.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0150] Further features and advantages of the invention will become apparent from the following description, given by way of nonlimiting example, with reference to the attached drawings (in particular not to a specific scale) in which:

[0151] FIG. 1 schematically represents a partial view of a tread (2) of a tire (1) in accordance with the invention;

[0152] FIG. 2 illustrates how the axial edge of a tread (2) is determined according to a first determination method;

[0153] FIG. 3 illustrates how the axial edge of a tread (2) is determined according to a second determination method;

[0154] In the description that is to follow, elements that are identical or similar will be denoted by identical references.

[0155] FIG. 1 partially depicts the tread surface (3) of a tread (2) of the tire (1) of dimension 205/55R16.

[0156] The tread (2) comprises a sequence of n basic patterns (41, 42) arranged in the circumferential direction X, where n is a natural integer greater than or equal to 1. To make FIG. 1 easier to understand, only a first basic pattern (41) and a second basic pattern (42) have been represented.

[0157] Each basic pattern (41, 42) extends in the circumferential direction X at a determined pitch P.

[0158] The pitch of the first basic pattern (41) here is identical to the pitch of the second basic pattern (42). As an alternative, the pitches of the basic patterns can be different. The pitch of the first basic pattern may be between 15.0 and 50.0 mm, preferably 20.0 to 45.0 mm.

[0159] Each basic pattern (41, 42) extends over at least 80% of the width W of the tread (2). In the example of FIG. 1, the width Wm of the basic pattern (41, 42) here is substantially identical to about 93% of the width W of the tread (2), and wherein here in particular, Wm=190.0 mm, and W=205.0 mm.

[0160] Each basic pattern (41, 42) here comprises several raised elements (5i), and is provided with i sipes (6i) opening onto the tread surface (3), wherein i is a natural integer greater, and wherein in particular, i=11-16, and 21-26.

[0161] The i sipes (6i) are distributed across the various raised elements (5i).

[0162] For each i sipe (6i), it is possible to determine a sipe length l.sub.i corresponding to the length of the line of the sipe on the tread surface (3).

[0163] An angle i (alpha i) is also determined for each i sipe, wherein |i|45 wherein here in particular, |i|=20. The angle i corresponds to the angle formed by the i.sup.th sipe (6i) with the axel direction Y.

[0164] A twenty sixth aspect of the invention is the tire (1) according to any one of the first to the twenty fifth aspects, wherein an angle i (alpha i) is the positive or negative angle formed on the tread surface (3) by the i.sup.th sipe (6) with the axel direction, wherein |i|45 (degrees), preferably |i|35 (degrees), more preferably |i|25 (degrees).

[0165] The angle .sub.i (alpha i) is also determined for each i sipe, |i|=20 in FIG. 1. The angle .sub.i corresponds to the angle formed by the ith sipe (6i) with the axel direction Y.

[0166] The way in which the angles of the sipes are defined is explained later on in the description.

[0167] The sipe angle is said to be positive with respect to the axel direction Y if the rotation that brings said axel direction Y onto the line of the sipe on the tread surface (3) is in the counterclockwise direction.

[0168] Conversely, the sipe angle is said to be negative with respect to the axel direction Y if the rotation that brings said axel direction Y onto the line of the sipe on the tread surface (3) is in the clockwise direction.

[0169] For i=11, 13, 15, 21, 23, and 25, the elements (5i) have sipes (6i) that form a negative angle with the axel direction Y.

[0170] For i=12, 14, 16, 22, 24, and 26, the elements (5i) have sipes (6i) that form a positive angle with the axel direction Y.

[0171] The sipes belonging to one and the same raised element are oriented here with the same angle.

[0172] As a variant, it is possible to have sipes of different orientation in one and the same raised element.

[0173] A sipe density (SD) is also defined for the basic pattern (41).

[0174] The sipe density (SD) corresponds to the equation.

[00004]$\begin{array}{cc}\mathrm{SD}=\frac{\underset{i}{.Math.}.Math.\mathrm{li}}{P\mathrm{Wm}}.& \left[\mathrm{Math}..Math.1\right]\end{array}$

[0175] In this equation it is reminded that i is the number of sipes (6i) in the basic pattern (41), l.sub.i is the length of the ith sipe (6i) on the tread surface (3), P is the pitch of the basic pattern and Wm is the width of the basic patterns, and wherein here in particular, wherein in particular, i=1116, each of l.sub.i=26.6 mm, P=30.0 mm, Wm=190.0 mm, and SD=28 m/mm.sup.2.

[0176] In the FIG. 1, the raised elements (51i, 52i) are delimited by grooves (7i, 8i), and the sipes (61i, 62i) are both side open sipes which are distributed across the raised element elements (51i, 52i), wherein in particular, i=1-6, the circumferential length of raised elements (51i, 52i): 27.0 mm, the axial raised elements (51i, 52i): 25.0 mm, the width of grooves (7i) in the axial direction of the tire: 8.0 mm, the width of groove (8i) in the circumferential direction of the tire: 3.0 mm, the depth of grooves (7i, 8i) in the radial direction of the tire: 9.0 mm, the width of sipes (61i, 62i): 0.6 mm, that is, the width of sipes (61i, 62i) in the circumferential direction of the tire: 0.6 mm/cos(|i|=20), the depth of sipes (61i, 62i) in the radial direction of the tire: 9.0 mm.

[0177] The width W of the tread (2) corresponds to the distance between a first axial edge (91) and a second axial edge (92) of the tread (2).

[0178] The way in which the width W of a tread (2) is determined is illustrated in FIGS. 2 and 3, each of which show the partial profile of a tread (2) and the part of a sidewall (101) adjacent to it. In certain designs of tire, the transition from the tread (2) to the sidewalls is very clear cut, as in the case represented in FIG. 2, and the first axial edge (91) and the second axial edge (not represented) can be determined intuitively.

[0179] However, there are tire designs in which the transition between the tread (2) and the sidewalls is continuous. An example is represented in FIG. 3.

[0180] In this FIG. 3, the first axial edge (91) and the second axial edge of the tread (2) are determined as follows. On a radial section through the tire (1), the tangent to the tread surface (3) at every point on said tread surface (3) in the region of transition toward the sidewall is plotted. The first axial edge (91) is the point at which the angle (beta) between said tangent and an axial direction is equal to 30. When there are a number of points for which the angle between said tangent and an axial direction is equal to 30, the point adopted is the radially outermost one. The same procedure is followed in order to determine the second axial edge of the tread (2).

[0181] A twenty seventh aspect of the invention is the tire (1) according to any one of the first to the twenty sixth aspects, wherein the tire (1) is a snow tire.

[0182] The invention is further illustrated by the following non-limiting examples.

Examples

[0183] In the test, two rubber compositions (C-1 and C-2) are compared. The two rubber compositions are based on a diene elastomer (SBR bearing a SiOR function) reinforced with a blend of silica (as inorganic filler) and carbon black, and a plasticizing agent with/without crumb rubber particles (as particles). The formulations of the three rubber compositions are given at Table 1 with the content of the various products expressed in phr. [0184] C-1: without the particles; [0185] C-2: with the particles.

[0186] Each rubber composition was produced as follows: The reinforcing filler, its associated coupling agent, the plasticizing agent, the particles, the elastomer matrix and the various other ingredients, with the exception of the vulcanization system, were successively introduced into an internal mixer having an initial vessel temperature of approximately 60 C.; the mixer was thus approximately 70% full (% by volume). Thermomechanical working (non-productive phase) was then carried out in one stage, which lasts in total approximately 3 to 4 minutes, until a maximum dropping temperature of 165 C. was reached. The mixture thus obtained was recovered and cooled and then sulphur and an accelerator of sulphenamide type were incorporated on an external mixer (homofinisher) at 20 to 30 C., everything being mixed (productive phase) for an appropriate time (for example, between 5 and 12 min).

[0187] The rubber compositions thus obtained were subsequently calendered, either in the form of sheets (thickness of 2 to 3 mm) or of fine sheets of rubber, for the measurement of their physical or mechanical properties, or in the form of profiled elements which could be used directly, after cutting and/or assembling to the desired dimensions, for example as tire semi-finished products, in particular as tire treads.

[0188] In order to confirm the effect of the present invention, six tires (denoted T-1 and T-2 references), T-3 (a comparative example), T-4, T-5 (examples according to the invention), and T-6 (another comparative example) having treads comprising the above rubber compositions (C-1 and C-2). T-1 and T-4 have a tread shown in FIG. 1, each of raised elements in the tread has one sipe, and the sipe density is 28 m/mm.sup.2. Each of raised elements in the others (T-2, T-3, T-5 and T-6) has one or two more sipe(s) than that in T-1 and T-4, and the sipe density is 56 or 84 m/mm.sup.2; [0189] T-1: Rubber composition C-1, Sipe density: 28 m/mm.sup.2 (a reference); [0190] T-2: Rubber composition C-1, Sipe density: 56 m/mm.sup.2 (another reference); [0191] T-3: Rubber composition C-1, Sipe density: 84 m/mm.sup.2 (a comparative example); [0192] T-4: Rubber composition C-2, Sipe density: 28 m/mm.sup.2 (an example according to the invention); [0193] T-5: Rubber composition C-2, Sipe density: 56 m/mm.sup.2 (an example according to the invention); [0194] T-6: Rubber composition C-2, Sipe density: 84 m/mm.sup.2 (another comparative example).

[0195] The additional sipe(s) are arranged at equal interval on each of raised elements of the tire tread (T-2, T-3, T-5 and T-6), and the angle formed by the additional sipe(s) with the axel direction Y is 20 or 20.

[0196] These tires, for radial carcass passenger vehicle winter tires, having a size of 205/55R16, were conventionally manufactured and in all respects identical apart from the rubber compositions of treads.

[0197] All the tires were fitted to the front and rear a motor vehicle, under nominal tire inflation pressure, and were first of all subjected to rolling on a circuit [of about 100 km], on a dry ground surface for running in and the beginning of wear.

[0198] A 1,400 cc passenger car provided on all the four wheels with the same kind of test tires under 220 kPa of tire inflation pressure mounted onto 6.5J16 rim was run on a snow covered road at a temperature of 10 C., the deceleration from 50 to 5 km/h during sudden longitudinal braking while anti-lock braking system (ABS) activated was measured. The above snow tests were conducted on a hard pack snow with a CTI penetrometer reading of about 90 in accordance with Standard ASTM F1805.

[0199] Moreover, the above passenger car with the above test tires under the above tire inflation pressure mounted onto the above rim was run on a dry road at an air temperature of 25 C., and the braking distance from 100 to 0 km/h during sudden longitudinal braking while anti-lock braking system (ABS) activated was measured.

[0200] The results of the running tests on snow and dry roads are reported in Table 2, in relative units, the base 100 being selected for the reference tire T-1 (it should be remembered that a value of greater than 100 indicates an improved performance).

[0201] It is noted in Table 2 that the snow braking performance of the tire according to the invention (T-4) is significantly better than that of the reference tire (T-1) with same sipe density (28 m/mm.sup.2), while T-4 equivalently performs on the dry braking as T-1.

[0202] Similarly, Table 2 indicates that the other tire according to the invention (T-5) improves the grip performance on snow in comparison to that of the other reference tire (T-2) with same sipe density (56 m/mm.sup.2), while the T-5 maintains equivalent dry braking performance as T-2.

[0203] Moreover, as shown in this Table 2, the mean of these grip performances of the tires according to the invention (T-4, T-5) is better than that of the others (T-1, T-2, T-3 and T-6).

[0204] In conclusion, the treads of the tires in accordance with the invention allow an improvement braking performance on snow without deterioration of a grip performance on dry ground.

TABLE-US-00001 TABLE 1 C-1 C-2 BR (1) 40 40 SBR (2) 60 60 Carbon black (3) 4 4 Silica (4) 115 115 Coupling agent (5) 9.2 9.2 Liquid plasticizer (6) 40 40 Hydrocarbon resin (7) 30 30 Particles (8) 26 ZnO 1.4 1.4 Stearic acid 3 3 Antiozone wax 1.9 1.9 Antioxidant (9) 2.7 2.7 DPG (10) 2.1 2.1 Sulphur 1.4 1.4 Accelerator (11) 1.6 1.6

[0205] (1) BR: BR with 0.3% of 1,2 vinyl; 2.7% of trans; 97% of cis-1,4 (Tg.sub.DSC=105 C.);

[0206] (2) SBR1: SBR with 27% of styrene unit and 24% of unit 1,2 of the butadiene part (Tg.sub.DSC=48 C.) bearing a SiOR function, R being hydrogen, the SiOR being dimethylsilanol function at the end of the elastomer chain, the SBR prepared according to a process described in a patent EP 0 778 311 B1;

[0207] (3) Carbon black: Carbon black (ASTM grade N234 from Cabot);

[0208] (4) Silica: Silica (Zeosil 1165MP from Rhodia (CTAB, BET: about 160 m.sup.2/g));

[0209] (5) Coupling agent TESPT (Si69 from Evonik);

[0210] (6) Oleic sunflower oil (Agripure 80 from Cargill, Weight percent oleic acid: 100%);

[0211] (7) Hydrocarbon resin C.sub.5/C.sub.9 type (Escorez ECR-373 from Exxon, Tg.sub.DSC=44 C.);

[0212] (8) Crumb rubber particles: Cut ground rubber chip, Particle size: between 35 mesh and 18 mesh from Global Corporation;

[0213] (9)N-(1,3-dimethylbutyl)-N-phenyl-para-phenylenediamine (Santoflex 6-PPD from Flexsys);

[0214] (10) Diphenylguanidine (Perkacit DPG from Flexsys);

[0215] (11)N-dicyclohexyl-2-benzothiazolesulphenamide (Santocure CBS from Flexsys).

TABLE-US-00002 TABLE 2 T-1 T-2 T-3 T-4 T-5 T-6 Rubber composition C-l C-1 C-1 C-2 C-2 C-2 Sipe ratio (m/mm.sup.2) 28 56 84 28 56 84 Snow braking 100 119 128 124 125 126 Dry braking 100 95 90 100 95 90 Mean 100 107 109 112 110 108