TBR pneumatic tire

Abstract

A TBR pneumatic tire includes a carcass, a tread, and at least one "high elongation belt" formed of a single cord with a layup angle θ between 0.03° and 0.1°, and includes an axially extending CW, wherein the ratio of the axially extending CW to the axially extending tread (TW / CW) is between 1.1 and 1.4. The tread is made of a rubber compound comprising a crosslinkable unsaturated chain polymer base containing at least 50% by weight of natural rubber (NR), and a filler mixture comprising (a) a surface area of ​​99 to 170 m². 2 (b) Carbon black with a density between 120cc / 100g and a structure greater than 120cc / 100g, and a surface area less than 100m². 2 / g of the first silicon dioxide, and (c) a surface area greater than 190m² 2 / g of second silicon dioxide.

Description

Technical Field

[0001] This invention relates to a TBR pneumatic tire. The abbreviation "TBR" is an acronym for "radial tire for trucks and buses". Background Technology

[0002] For some time now, research in the TBR pneumatic tire sector has also focused in part on improving its rolling resistance performance. More recently, this requirement has been mandated by numerous international regulations that mandate significant reductions in fuel consumption and the resulting CO2 emissions into the environment.

[0003] As is known to those skilled in the art, solutions to improve the rolling resistance of pneumatic tire treads involve increasing the amount of silica in the relevant rubber compound.

[0004] Despite improvements in rolling resistance, the increased silica content in the compound inevitably leads to a decrease in wear resistance.

[0005] As is immediately apparent, wear resistance is one of the primary requirements for the efficiency of TBR pneumatic tires. For TBR pneumatic tires, any degradation in wear resistance is unacceptable due to the improved rolling resistance.

[0006] The tire shoulder is the part of the tread where wear is most common in TBR pneumatic tires.

[0007] This type of wear arises from both the difference in rigidity between the tread center and the shoulder, and from the lateral force experienced by the pneumatic tire during rolling. In the pneumatic tire industry, this lateral force is referred to as "ply steer" and is caused by the asymmetry present within the pneumatic tire body.

[0008] Wear on the tire shoulder, in addition to causing noise problems, may lead to the replacement of the pneumatic tire, even if the center of the tread remains largely intact.

[0009] Therefore, a solution is needed to enable the production of TBR pneumatic tires that will provide improved rolling resistance without causing deterioration in tread wear.

[0010] The inventors of this invention have implemented a solution that satisfies the above requirements by intervening in the composition of the belt pack and the tread.

[0011] It has long been known that belts labeled "high elongation belts" can be used instead of traditional belts labeled "wavy belts".

[0012] The term "high elongation belt" refers to a belt characterized by a stiffness modulus that varies as a function of deformation. Specifically, the stiffness modulus is low for minimum forces and high for larger forces. This allows the cord to expand during the vulcanization process and ensures a high stiffness modulus during operation.

[0013] To be clearer, "high elongation belt" is a belt containing cords with a stiffness modulus ranging from about 3,000 MPa (low modulus, from 0 to about 2% deformation or elongation) to 125,000 MPa (high modulus, for greater than about 2% deformation).

[0014] Currently, several known types of "high elongation belts" are available.

[0015] The application of "high elongation belts" offers significant advantages compared to traditional ("corrugated belts") construction.

[0016] In this regard, it should be remembered that those strips defined as “corrugated strips” are used as strips with multiple rolled cords (preferably nine cords).

[0017] The application of such strips inevitably anticipates a significant "laying angle" or "tread belt angle," θ, which is the angle between the cord and the longitudinal plane of symmetry L. Furthermore, it is well known that the edges of this strip must be protected by overlapping with another belt strip. As those skilled in the art know, the larger the angle θ and the larger the additional protective belt strip, the greater the asymmetry of the pneumatic tire, and therefore the greater the "ply steering" experienced by the pneumatic tire.

[0018] Conversely, as long as the "high elongation belt" is applied as a single cord, it can be set at a very small angle θ, and there is no need to add a coating to protect the free edges of the strip. All of this translates into lower belt layer asymmetry, and therefore, less "cord layer turning".

[0019] Another advantage of using high-elongation belts compared to corrugated belts is their potential to extend almost axially to the tire shoulder. Conversely, if corrugated belts extend to the tire shoulder, they will be subjected to fatigue loads, which will compromise their effectiveness.

[0020] In summary, using a "high elongation belt" with a layup angle θ close to zero and extending to the tire shoulder provides pneumatic tires with improved wear resistance. Summary of the Invention

[0021] The inventors of this invention have unexpectedly discovered that combining a "high elongation belt" with a specific tread composition not only ensures the expected improvement in wear resistance but also results in a significant improvement in rolling resistance.

[0022] As described below, an unexpected synergistic effect was demonstrated between the presence of the "high elongation belt" and the specific tread composition.

[0023] The object of the present invention is a TBR pneumatic tire comprising a carcass, a tread, and at least one "high elongation belt" formed of a single cord with a layup angle θ between 0.03° and 0.1°, and comprising an axially extended CW, wherein the ratio of the axially extended CW to the axially extended tread (TW / CW) is between 1.1 and 1.4; the tread is made of a rubber compound comprising a crosslinkable unsaturated chain polymer base comprising at least 50% by weight of natural rubber (NR), a filler mixture comprising silica and carbon black, and a vulcanization system; the pneumatic tire is characterized in that the filler mixture comprises (a) a surface area of ​​99 to 170 m² 2 (b) Carbon black with a structure greater than 120cc / 100g and a surface area less than 100m² 2 / g of the first silicon dioxide, and (c) a surface area greater than 190m² 2 / g of second silicon dioxide.

[0024] Here and below, the term "crosslinkable unsaturated chain polymer matrix" refers to any natural or synthetic non-crosslinked polymer that is capable of exhibiting all the chemical, physical, and mechanical properties typically exhibited by elastomers when crosslinked (vulcanized) by a crosslinking agent (such as sulfur).

[0025] Here and below, the term vulcanization system refers to a complex comprising at least one crosslinking agent (e.g., sulfur) and accelerating compounds, which are added during the final mixing step in the preparation of the compound and are intended to promote the vulcanization of the polymer base.

[0026] Preferably, the filler mixture comprises (a) 15-40 wt% of the carbon black, (b) 10-35 wt% of the first silica, and (c) 40-80 wt% of a surface area greater than 190 m². 2 / g of second silicon dioxide.

[0027] Preferably, the filler mixture comprises (a) 25-35% by weight of the carbon black, (b) 15-25% by weight of the first silica, and (c) 50-60% by weight of the second silica.

[0028] Preferably, the carbon black has a density of 120 to 150 μm. 2 (a) The first silica has a surface area between 120 and 170 cc / 100g and a structure between 120 and 170 cc / 100g, and (b) the first silica has a surface area between 70 and 100 m² / g. 2 (c) The second silica has a surface area between / g and (d) 190 to 250m². 2 Surface area between / g.

[0029] Preferably, the "high elongation belt" (5) is made of RT (conventional tensile) steel, HT (high tensile) steel, SHT (ultra-high tensile) steel, or UHT (ultra-high tensile) steel. Detailed Implementation

[0030] The following are purely illustrative and non-limiting exemplary embodiments illustrated with the aid of accompanying drawings, which show a portion of an inflatable tire according to the invention in cross-section.

[0031] Example

[0032] The pneumatic tire according to the present invention Figure 1 The entirety of the tire is represented by 1. The pneumatic tire 1 includes the tire body 2, the tire tread 3, and multiple belts 4.

[0033] The tread consists of a central portion 3a and a pair of shoulder portions 3b.

[0034] The belt 4 includes at least one belt 5 of the type described above as a "high elongation belt". For example... Figure 1 As shown, the belt 5 has an axial extension that satisfies the requirements defined in the claims.

[0035] Specifically, the pneumatic tire 1 includes four belts, the second of which, starting from the tire carcass 2, is a "high elongation belt" 5.

[0036] The three tread blends (AC) were used to manufacture test pneumatic tires, in which properties related to rolling resistance, wear resistance and uneven wear were studied.

[0037] Blend A contains a filler mixture that does not satisfy the composition of the present invention, while blends B and C contain filler mixtures that satisfy the composition of the present invention.

[0038] The process for preparing the mixtures described in the examples is given below. This process does not represent a limitation of the present invention.

[0039] The term "interlocking mixer" refers to a machine for mixing rubber as described and claimed in US5368383.

[0040] The term "non-productive mixing step" refers to a mixing step in which compound components other than the vulcanization system are added and mixed with a crosslinkable unsaturated chain polymer base; while the term "productive mixing step" refers to a mixing step in which the vulcanization system is added and mixed with the mixture in preparation.

[0041] -Preparation of the mixture-

[0042] (First non-productive mixing step)

[0043] Before mixing, load the first mixing chamber of the 5-liter "interlocking mixer" with the ingredients listed in Tables I and II, excluding sulfur, stearic acid and accelerator, at a filling factor of 60-70%.

[0044] The first mixing step is carried out while maintaining a temperature of 140°C for 60 seconds.

[0045] (Second non-productive mixing step)

[0046] The mixture from the first step is discharged into the second 5-liter chamber of the "meshing" mixer to achieve a fill factor of 35-41%.

[0047] The second mixing step is carried out while maintaining a temperature of 155°C for 210 seconds.

[0048] (Productive mixing step)

[0049] The mixture obtained from the second non-productive mixing step is discharged into a 2-liter tangential rotor mixer, where sulfur, stearic acid, and an accelerator are added to achieve a fill factor of 70%.

[0050] The mixer operates at 20-40 rpm and unloads the resulting mixture when it reaches a temperature of 100-110°C.

[0051] Table I shows the composition of the mixtures from the examples, in phr.

[0052] Table I

[0053] A B C NR 70 70 70 SBR 30 30 30 carbon black 37 15 18 Variable silica (VLSA) -- 20 10 Secondary silica (HSA) 10 23 30 sulfur 1.2 1.2 1.2 stearic acid 3.5 3.5 3.5 Accelerator 2.15 2.15 2.15

[0054] NR is a naturally derived 1,4-cis-polyisoprene rubber.

[0055] S-SBR is a polymer base obtained by solution polymerization, with an average molecular weight of 800-1500×10⁻⁶. 3 Between and 500-900×10 3 The styrene content is between 10-45%, and the vinyl content is between 20-70%.

[0056] The surface area of ​​carbon black is 138m² 2 / g.

[0057] The surface area of ​​the first type of silica (VLSA) is 80m². 2 / g.

[0058] The surface area of ​​the second silica (HSA) is 200m². 2 / g.

[0059] The vulcanization accelerator used is N-tert-butyl-2-benzothiazolyl sulfinamide (TBBS).

[0060] The formulations reported in Table I were used to construct five types of pneumatic tires (IV). In particular, pneumatic tires I-IV are comparative examples, while pneumatic tire V represents a pneumatic tire according to the invention.

[0061] Specifically, pneumatic tire I does not include a "high elongation belt" and includes a tread made using a compound, wherein its filler mixture includes carbon black and only high surface area silica (compound A); pneumatic tire II does not include a "high elongation belt" and includes a tread made using a compound, wherein its filler mixture includes carbon black according to the invention, high surface area silica, and low surface area silica in a different proportion than the proportion according to the invention (compound B); pneumatic tire III does not include a "high elongation belt" and includes a tread made using a compound, wherein its filler mixture includes carbon black according to the invention, high surface area silica, and low surface area silica in a different proportion than the proportion according to the invention (compound B); The filler mixture comprises carbon black, high surface area silica, and low surface area silica in proportions according to the invention (component C); the pneumatic tire IV comprises a "high elongation belt" with characteristics according to the invention and comprises a tread made using the compound, wherein its filler mixture comprises carbon black and only high surface area silica (component A); the pneumatic tire V comprises a "high elongation belt" with characteristics according to the invention and comprises a tread made using the compound, wherein its filler mixture comprises carbon black, high surface area silica, and low surface area silica in proportions according to the invention (component C).

[0062] For pneumatic tires IV and V, the "high elongation belt" is made when the cord is applied at a layup angle θ of 0.042.

[0063] For pneumatic tires IV and V, the TW / CW ratio is 1.25.

[0064] For pneumatic tires I-III, the TW / CW ratio (in these cases, CW is the extension of the widest bundle) is 1.5.

[0065] A series of tests were conducted on IV pneumatic tires to evaluate properties related to rolling resistance, wear resistance, and uneven wear.

[0066] Rolling resistance is measured according to the R 117 standard.

[0067] The following process was used to evaluate abrasion resistance:

[0068] Pneumatic tires are mounted on comparable tractors and trailers and subjected to the same operating conditions (e.g., type of road travel, mileage traveled, and load).

[0069] During this process, record the depth of the main grooves in the pneumatic tire tread, as well as whether there are signs of uneven wear on the tread, such as cupping, rib depression, alternating wear on the fenders, or shoulder wear.

[0070] The data on wear resistance are as follows:

[0071] WTD = OTD - RTD

[0072] KPM = (Coverage KM) / WTD

[0073] OTD = Original tread depth

[0074] RTD = Remaining tread depth

[0075] KPM is the parameter used in this specification to classify wear.

[0076] Table II presents the results related to rolling resistance and abrasion resistance in exponential form, based on the results associated with pneumatic tire I. Higher reported values ​​indicate better rolling resistance and abrasion resistance.

[0077] Uneven wear is evaluated using a rigid profile shaped according to the new tread pattern. After using a pneumatic tire, the rigid profile is placed against the tread, and the tread is evaluated to see if it still adheres to the profile. If the tread wears evenly after using a pneumatic tire, the portion of the tread associated with the shoulder will still adhere to the rigid profile. Conversely, if the tread wears irregularly, the portions associated with the shoulder will no longer adhere to the rigid profile.

[0078] In Table II, the irregular wear values ​​are given as a percentage of the missing volume of rubber adhering to the rigid profile relative to the missing volume of rubber adhering to the rigid profile in the pneumatic tire I used as a reference.

[0079] Table II

[0080] I II III IV V Rolling resistance 100 105 107 101 110 abrasion resistance 100 60 80 145 145 Uneven wear 100 60 70 50 50

[0081] As can be clearly seen from the data reported in Table II, the pneumatic tires obtained according to the present invention ensure significant improvements in rolling resistance, wear resistance, and uneven wear by combining specific filler mixtures and "high elongation belts".

[0082] In this regard, it should be noted that there is an unexpected synergistic effect in terms of rolling resistance. In fact, although the same compound (compound C) is used, the pneumatic tire of the present invention (pneumatic tire V) gives better rolling resistance results than pneumatic tire III.

[0083] In other words, the use of "high elongation belts" ensures improvements in wear resistance and uneven wear, and surprisingly produces a synergistic effect with a specific combination of tread compound fillers in terms of rolling resistance.

[0084] In this way, it will be possible to manufacture pneumatic tires with improved rolling resistance without causing any degradation in wear resistance.

Claims

1. A TBR pneumatic tire comprising a carcass, a tread, and at least one "high elongation belt" formed of a single cord with a layup angle θ of 0.03° to 0.1° and including an axially extending CW, wherein the ratio of the axially extending CW to the axially extending tread, TW / CW, is 1.1 to 1.4; the tread is made of a rubber compound comprising a crosslinkable unsaturated chain polymer base comprising at least 50% by weight of natural rubber (NR), a filler mixture comprising silica and carbon black, and a vulcanization system; the pneumatic tire is characterized in that the filler mixture comprises (a) a surface area of ​​120 to 150 m² 2 (b) Carbon black with a structure greater than 120cc / 100g and less than 170cc / 100g, and a surface area of ​​70m². 2 / g or more and less than 100m 2 / g of the first silicon dioxide, and (c) a surface area greater than 190m² 2 / g and 250m 2 The second silica below / g, The filler mixture comprises (a) 15-40% by weight of the carbon black, (b) 10-35% by weight of the first silica, and (c) 40-60% by weight of the second silica.

2. The TBR pneumatic tire according to claim 1, characterized in that, The filler mixture comprises (a) 25-35% by weight of the carbon black, (b) 15-25% by weight of the first silica, and (c) 50-60% by weight of the second silica.

3. The TBR pneumatic tire according to claim 1, characterized in that, It includes four belts (4), the second of which, starting from the carcass (2), is a "high elongation belt" (5).

4. The TBR pneumatic tire according to any one of claims 1 to 3, characterized in that, The "high elongation belt" (5) has a layup angle θ of 0.042° and an elongation that results in a TW / CW ratio of 1.25.

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