Method for producing a multi-composite tread for a road vehicle tire

Abstract

A method for manufacturing a tread band, wherein the blocks of the tread band comprise different portions with different hysteresis losses. The method comprises a step of extruding an initial tread band constituted by a first rubber compound and an injection step, wherein said initial tread band, once extruded, is subjected to the action of at least one injector, said injector being configured such as to penetrate the layers of the initial tread band and release a second rubber compound distributed in the layers constituted by said first compound, leaving exposed a surface suitable for defining a portion of the contact patch of the resulting tread band.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a multi-composite tread for a pneumatic road vehicle tire. Background Art

[0002] In the field of road vehicle pneumatic tires, it is known that low rolling resistance and good wet grip performance are properties that are difficult to reconcile in the same tread. In fact, although in order to give a pneumatic tire good rolling resistance, a tread made of a compound with low hysteresis losses is used, in order to give a pneumatic tire good wet grip performance, a compound with relatively high hysteresis losses becomes necessary.

[0003] Therefore, the best tread compound for simultaneously enhancing all dynamic responses should exhibit opposing hysteresis characteristics at least at some desired performance limit.

[0004] It is known that the properties of the above-mentioned rubber compounds not only influence the balance between wet grip performance / rolling resistance, but also influence other properties of the pneumatic tire, such as the balance between winter / wet grip performance.

[0005] As is known, the tread is composed of a plurality of blocks, which are elements delimited by a plurality of grooves formed in the tread. These grooves can have different sizes, depending on the function they must fulfill. For example, when the grooves are small in size, they are called sipes and are intended to provide greater grip on snow and ice.

[0006] In other words, a tread block is a rubber filled portion delimited by a plurality of grooves, possibly independent of the size of the grooves.

[0007] The inventors have discovered that if the blocks of the tread consist of different parts made with respective compounds having different hysteresis losses, a synergistic effect can be obtained which can give a significant improvement in the wet grip performances without thereby adversely affecting the rolling resistance.

[0008] The inventors of the present invention have implemented a method and a related apparatus to enable the manufacture in an efficient and productive manner of treads comprising blocks composed of different parts having different hysteresis losses. Summary of the invention

[0009] The object of the present invention is a method for manufacturing a tread band, wherein the blocks of the tread band comprise different portions having different hysteresis losses; said method is characterized in that it comprises a step for extruding an initial tread band constituted by a first rubber compound and an injection step, wherein the initial tread band, once extruded, is subjected to the action of at least one injector, such as is configured to penetrate into the layer of the initial tread band and release a second rubber compound, which is distributed in the layer constituted by the first compound, leaving exposed a surface suitable for defining a portion of the contact surface of the resulting tread band; said first compound and said second compound having different dynamic properties in terms of: dynamic modulus at 30°C, tan δ at 0°C, tan δ at 30°C and tan δ at 60°C; the first compound has a 30°C tan delta of 1.5 and a tan delta of 2.5 at 1.5 ... The dynamic modulus of the second compound at 30°C is between 11.0 and 17.0 MPa, the tan δ at 0°C is between 0.85 and 1.1, the tan δ at 30°C is between 0.45 and 0.65, and the tan δ at 60°C is between 0.19 and 0.30; the dynamic modulus of the second compound at 30°C is between 5.5 and 15 MPa and is at least 2 MPa less than the dynamic modulus of the first compound at 30°C, the tan δ at 0°C is between 0.40 and 0.99 and is at least 0.02 less than the tan δ of the first compound at 0°C, the tan δ at 30°C is between 0.21 and 0.63 and is at least 0.02 less than the tan δ of the first compound at 30°C, and the tan δ at 60°C is between 0.10 and 0.28 and is at least 0.02 less than the tan δ of the first compound at 60°C.

[0010] Preferably, the extrusion step is continuous and the injection step is discontinuous.

[0011] Preferably, said method comprises an interconnection step in which said initial tread band produced continuously is stopped at intervals in order to be subsequently resumed and subjected to said injection step.

[0012] Preferably, the first compound has a dynamic modulus at 30°C between 11.0 and 17.0 MPa, tanδ at 0°C between 0.85 and 1.1, tanδ at 30°C between 0.45 and 0.65, and tanδ at 60°C between 0.19 and 0.30, the second compound has a dynamic modulus at 30°C smaller than the dynamic modulus at 30°C of the first compound, with a value between 7.5 and 10.5 MPa, tanδ at 0°C smaller than the tanδ at 0°C of the first compound, with a value between 0.70 and 0.84, tanδ at 30°C smaller than the tanδ at 30°C of the first compound, with a value between 0.21 and 0.42, and tanδ at 60°C smaller than the tanδ at 60°C of the first compound, with a value between 0.10 and 0.17.

[0013] The dynamic properties are measured according to ISO 4664. As known to those skilled in the art, the tan δ value at 60°C is strictly correlated with the properties of the rolling resistance: the smaller the tan δ value at 60°C, the better the rolling resistance.

[0014] Another object of the present invention is a device for manufacturing a tread band, wherein the blocks of the tread band include different portions with different hysteresis losses; the device is characterized in that it comprises an extrusion station, in which an initial tread band is formed, an injection station, and a moving device, in which a portion of a second rubber compound is injected into the initial tread band, the moving device being suitable for moving the initial tread band from the extrusion station to the injection station; the extrusion station comprises at least one extruder and at least one supply device, the supply device being suitable for supplying a first rubber compound to the extruder; the injection station comprises a dispenser (10) of the second rubber compound and a plurality of injectors (11) connected to the dispenser (10), the injectors (11) being used to receive a determined amount of the second rubber compound to be injected into the initial tread band.

[0015] Preferably, said plant comprises interconnection stations wherein said preliminary tread band is stopped at intervals in order to be subsequently recovered and conveyed to said injection station. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The following are exemplary, non-limiting embodiments of the present invention for the purpose of illustration with the aid of the accompanying drawings, Figure 1 The apparatus and objects of the present invention are illustrated in schematic form.

[0017] In the attached Figure 1 In the figure, the apparatus and purpose of the present invention are indicated by 1 as a whole. DETAILED DESCRIPTION

[0018] The plant 1 comprises an extrusion station 2 , an interconnection station 3 , an injection station 4 and movement means 5 responsible for advancing the preliminary tread band from the interconnection station 3 to the injection station 4 .

[0019] The extrusion station 2 comprises a hopper 6 into which a first rubber compound is loaded and an extruder 7 capable of producing an initial tread band 8 using the first rubber compound.

[0020] The interconnection station 3 comprises two rollers 9 , which are arranged, for example, to rotate idly and between which a loop is realized which is variable according to the action of the moving device 5 .

[0021] The injection station 4 comprises a distributor 10 connected to a supply line 10a of the second rubber compound and a plurality of injectors 11, wherein each injector 11 extends from said distributor 10 and receives a determined amount of the second rubber compound from said distributor 10. Each injector 11 has a free dispensing end capable of penetrating into a layer of the initial tread band and releasing a certain amount of the second rubber compound inside the layer itself.

[0022] The moving means 5 comprise a plurality of rollers 12 moved by actuator means (known but not described in detail). Essentially, the rollers 12 act as conveyor belts.

[0023] The first and second compounds have different dynamic properties in terms of dynamic modulus at 30°C, tan δ at 0°C, tan δ at 30°C, and tan δ at 60°C.

[0024] In particular, the first compound has a dynamic modulus at 30°C between 11.0 and 17.0 MPa, a tanδ at 0°C between 0.85 and 1.1, a tanδ at 30°C between 0.45 and 0.65, and a tanδ at 60°C between 0.19 and 0.30, while the second compound has a dynamic modulus at 30°C that is smaller than the dynamic modulus at 30°C of the first compound, with a value between 7.5 and 10.5 MPa, a tanδ at 0°C that is smaller than the tanδ at 0°C of the first compound, with a value between 0.70 and 0.84, a tanδ at 30°C that is smaller than the tanδ at 30°C of the first compound, with a value between 0.21 and 0.42, and a tanδ at 60°C that is smaller than the tanδ at 60°C of the first compound, with a value between 0.10 and 0.17.

[0025] As is evident from the above description, the method and the apparatus of the present invention ensure an efficient preparation and a high productivity of a tread band whose blocks consist of portions having different hysteresis losses.

[0026] In this way, it is possible to produce a tread band whose technical characteristics are such as to ensure a significant improvement in wet grip performance while maintaining the advantages obtained in rolling resistance. In particular, the tread band manufactured by the method and the apparatus of the invention relates to a "multi-pintread" for winter / all-season applications. In fact, those elements manufactured using the second rubber compound (harder compound) are incorporated into the initial tread band manufactured using the first rubber compound (softer compound) and act as studs when on icy and snowy roads.

Claims

1. A method for manufacturing a tread band, wherein the blocks of said tread band comprise different portions having different hysteresis losses; said method being characterized in that it comprises a step for extruding an initial tread band consisting of a first rubber compound and an injection step, wherein said initial tread band is planar, said initial tread band once extruded being subjected to the action of at least one injector, said injector being configured to penetrate into a layer of said initial tread band and to release a second rubber compound, said second rubber compound being distributed in the layer consisting of said first rubber compound, leaving exposed a surface suitable for defining a portion of the contact surface of the resulting tread band, said step for extruding an initial tread band consisting of a first rubber compound being continuous, while said injection step being discontinuous, said method comprising an interconnection step, wherein said initial tread band produced continuously is stopped at intervals in order to be subsequently resumed and subjected to said injection step; said first rubber compound and said second rubber compound having different dynamic characteristics in terms of: dynamic modulus, tan δ at 0°C, tan δ at 30°C and tan δ at 60°C of the first rubber compound; the dynamic modulus at 30°C of the first rubber compound is between 11.0 and 17.0 MPa, the tan δ at 0°C is between 0.85 and 1.1, the tan δ at 30°C is between 0.45 and 0.65 and the tan δ at 60°C is between 0.19 and 0.30; the dynamic modulus of the second rubber compound at 30°C is between 5.5 and 15 MPa and is greater than that of the first rubber compound. The dynamic modulus of the rubber compound at 30°C is at least 2 MPa less, the tan δ at 0°C is between 0.40 and 0.99 and is at least 0.02 less than the tan δ of the first rubber compound at 0°C, the tan δ at 30°C is between 0.21 and 0.63 and is at least 0.02 less than the tan δ of the first rubber compound at 30°C, and the tan δ at 60°C is between 0.10 and 0.28 and is at least 0.02 less than the tan δ of the first rubber compound at 60°C.

2. A device (1) for manufacturing a tread band suitable for implementing the method according to claim 1, wherein the pattern blocks of the tread band include different portions with different hysteresis losses; the device is characterized in that it comprises an extrusion station (2) in which an initial tread band (8) is formed, the initial tread band (8) being in planar form, an injection station (4) in which portions of a second rubber compound are injected into the initial tread band, and a moving device (5) suitable for moving the initial tread band (8) from the extrusion station (2) to the injection station (4). ); the extrusion station (2) comprises at least one extruder (7) and a supply device for supplying a first rubber compound to the extruder (7); the injection station (4) comprises a dispenser (10) for the second rubber compound and a plurality of injectors (11) connected to the dispenser (10), the injectors (11) being used to receive a determined amount of the second rubber compound to be injected into the initial tread band, the device comprising an interconnection station in which the initial tread band (8) is stopped at intervals in order to be subsequently resumed and conveyed to the injection station (4).

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