PNEUMATIC VEHICLE TIRE AND METHOD FOR PRODUCING A TREAD FOR A PNEUMATIC VEHICLE TIRE

Description

[0001] The invention relates to a pneumatic vehicle tire for commercial vehicles with a radial carcass, a multi-layer belt and a tread with three radially superimposed layers consisting of a tread base and a profiled tread top having circumferential grooves, wherein the profiled tread top consists of two layers of different rubber compounds arranged one above the other in the radial direction, wherein the rubber compound of the radially outermost layer of the tread top, which comes into contact with the road surface, is optimized with regard to the property of resistance to abrasion.

[0002] Such a pneumatic vehicle tire is known from EP 2 108 530 B1. The tread comprises a base section (also called the "base") and an upper section (also called the "cap") consisting of two radially arranged layers of different rubber compounds. The tread thus consists of three radially arranged layers of different rubber compounds. The two rubber compounds of the upper section of the tread exhibit different rebound resilience, while the lower section of the tread consists of a base compound commonly used in commercial vehicles. This resolves the conflicting objectives between resistance to irregular wear and rolling resistance at a higher level.

[0003] EP 2 108 525 A1 also discloses a pneumatic vehicle tire, in particular for commercial vehicles, wherein the tread of the pneumatic vehicle tire consists of three layers in the radial direction, a lower tread section and an upper tread section. The rubber compounds of the three layers of the upper tread section differ from one another with regard to the amount of butadiene rubber they contain, with the radially outermost layer having the largest proportion of butadiene rubber, and the proportion of butadiene rubber in the two radially inner layers gradually decreasing from layer to layer toward the inside of the tire. The tire is said to have good traction properties, high abrasion resistance, and low rolling resistance.

[0004] An important property for the tread of pneumatic tires for commercial vehicles is abrasion resistance. Abrasion resistance should be as high as possible to ensure the tire's long service life. Furthermore, it is desirable to use fuel-efficient tires wherever possible to reduce fuel consumption. Furthermore, it is well known that cracks can be initiated in the groove area, especially at the groove base, which can damage the tread and also reduce the tire's service life.

[0005] The invention is based on the object of providing a pneumatic vehicle tire that is fuel-efficient and also has the longest possible service life. Furthermore, the object of the invention is to provide a method for producing a tread for the aforementioned pneumatic vehicle tire.

[0006] The object is achieved according to the invention with regard to the pneumatic vehicle tire by that the rubber compound of the tread base is optimized with regard to the rolling resistance property, that the rubber compound of the radially outermost layer of the tread cap contains 60 phr to 100 phr natural rubber, 0 phr to 40 phr butadiene rubber, where the butadiene rubber is High cis-1.4 or SSBR, 35 phr to 80 phr carbon black, where the carbon black is N234 / N121 / N339, 0 phr to 20 phr silica or further filler, 0 phr to 10 phr plasticizer and 3 phr to 10 phr crosslinking agent and that the rubber compound of the radially innermost layer of the tread cap is optimized with regard to the crack prevention property in the circumferential grooves, where this rubber compound contains 70 phr to 100 phr natural rubber, 0 phr to 30 phr Butadiene rubber, wherein the butadiene rubber is high cis-1.4 or SSBR, 30 phr to 60 phr carbon black, wherein the carbon black is N234 / N121 / N339, 0 phr to 20 phr silica or other filler, 0 phr to 10 phr plasticizer and 3 phr to 10 phr crosslinking agent. .

[0007] In pneumatic vehicle tires for commercial vehicles designed according to the invention, the tread has three radially superimposed layers, each of which comprises rubber compounds optimized for different tasks. The radially outermost layer is optimized for abrasion resistance, the middle layer, which comprises the groove bases / bottoms of the tread pattern, is optimized to prevent cracks in the groove base area, and the radially innermost layer is optimized for rolling resistance. Thus, a pneumatic vehicle tire for commercial vehicles is provided that is improved in its durability and simultaneously economical in terms of fuel consumption.

[0008] It is advantageous if the tread base consists of a rubber compound containing natural rubber between 80-100 phr, butadiene rubber, high-cis-1.4 or SSBR between 0-20 phr, carbon black, N234 / N121 / N339 between 20-50 phr, silica or other filler between 0-20 phr, plasticizer between 0-10 phr, and crosslinking agent between 3-10 phr. This rubber compound is optimized for improved rolling resistance, thus reducing fuel consumption.

[0009] The term phr (parts per hundred parts of rubber by weight) used in this document is the standard quantity used in the rubber industry for compound formulations. The dosage of the parts by weight of the individual substances is always based on 100 parts by weight of the total mass of all rubbers present in the compound. The mass of all rubbers present in the compound adds up to 100.

[0010] In one embodiment of the invention, the layers of the tread upper have matching thicknesses.

[0011] In another embodiment of the invention, however, it can also be provided that the layers have different thicknesses, for example such that their thickness increases from the radially outermost to the radially innermost layer or vice versa.

[0012] It is advisable for the radially innermost layer of the tread cap to encompass the groove bases of the circumferential grooves. Because the groove bases are enclosed on all sides by the rubber compound, which is optimized to prevent cracks in the groove base, crack formation can be largely prevented.

[0013] A wear indicator (TWI) can be arranged in the groove base of at least one circumferential groove. This wear indicator protrudes radially outward beyond the groove base and indicates critical tire wear due to its maximum radial height, its maximum distance in the radial direction from the groove base. It is particularly expedient to design the thickness of the radially outermost layer such that the at least one wear indicator does not protrude into this radially outermost layer. This ensures that the abrasion-resistant outermost layer is completely worn away when the wear indicator is worn away to its maximum radial height, thus indicating critical tire wear.

[0014] The stated object is achieved with regard to the method for producing a tread of a pneumatic vehicle tire for commercial vehicles according to one or more of the preceding embodiments, wherein the rubber mixture of the tread base is optimized with regard to the property of rolling resistance, wherein the rubber mixture of the radially outermost layer of the tread top, which comes into contact with the road surface, is optimized with regard to the property of resistance to abrasion (wear), and wherein the rubber mixture of the radially innermost layer of the tread top is optimized with regard to the property of crack prevention in the circumferential grooves, according to the invention in that the tread is extruded by means of a triplex extruder, wherein the extrusion head of the extruder is constructed in such a way that the extruded tread has correspondingly contoured grooves in cross-section in the region of the later circumferential grooves.

[0015] In order to avoid squashing of the different rubber compounds, it is advisable to cut the grooves into the three-layer endless tread using cutting tools arranged in the die head.

[0016] Further features, advantages and details of the invention will now be described in more detail with reference to the drawings, which schematically illustrate an embodiment. Fig. 1 an embodiment of the invention based on a cross section through a pneumatic vehicle tire in the area of ​​the tread and Fig. 2 a cross-section of the tread of the Fig.1 with profiling directly after extrusion.

[0017] The Fig. 1shows a simplified cross-section through the tread area of ​​pneumatic tires for commercial vehicles. Among the usual tire components, a tread 1, a belt 2 consisting of four belt plies with rubber-embedded reinforcements, preferably made of steel cord, and a radial carcass 3, also reinforced with reinforcements, are shown. Only the radially outer end sections of the tire's sidewalls 7 are shown. Bead areas with bead cores, core profiles, and other bead components are not shown.

[0018] The tread 1 is divided in a known manner into an upper tread section 4 and a lower tread section 5. Profiling is not shown. The lower tread section 5 has a substantially constant thickness in the range of 2 mm to 5 mm and consists of a rubber compound optimized for rolling resistance. An example rubber compound is listed in Table 1 below.

[0019] The tread upper part 4 is that part of the tread 1 which is covered with a Fig. 2 shown profiling is provided with circumferential grooves, whereby the Fig. 2 shows the freshly extruded cross-section of a tread, with the circumferential grooves "pre-cut" as grooves 6. The correct profile will be pressed in later, once the green tire is covered with the tread component and vulcanized.

[0020] According to the invention, the tread cap 4 consists of two superimposed layers 4a, 4b. These two layers 4a, 4b have a thickness in the range of 14 mm to 22 mm. The rubber compound of the radially outermost layer 4a of the tread cap 4, which comes into contact with the road surface, is optimized for abrasion resistance, and the rubber compound of the radially innermost layer 4b of the tread cap 4 is optimized for crack prevention in the grooves. One rubber compound optimized for abrasion resistance and another rubber compound optimized for crack prevention in the groove bottoms are listed in Table 1 below. Table 1 Rubber mixture containing (in phr) radially outermost layer of the tread cap radially innermost layer of the tread cap Tread base Natural rubber 100 100 100 Butadiene rubber, high cis-1.4 or SSBR 0 0 0 Soot, N234 / N121 / N339 55 45 40 Silica or other filler 0 13 15 plasticizers 0 0 0 Crosslinking agents 7.5 7.5 8.5 Abrasion (%, road test) 120 105 100 Rebound (RT) 43 42 54

[0021] Tests show that the wear of the radially outermost layer of the cap tread exhibits a 15% and 20% improvement in the wear of the radially innermost layer of the cap tread and the base tread, respectively, with the wear being determined in the road test (L-EXT). It is also evident that the base tread exhibits advantages over the other two layers in terms of rebound resilience and thus rolling resistance. The rebound resilience was determined using a pendulum impact tester according to DIN 53512:2000-04 (Schob version) from Zwick, Type 5109.

[0022] The Fig. 2 shows a cross section through the extruded tread, which will later be used as a tire component for pneumatic tires for commercial vehicles of the Fig. 1The rubber compound, optimized to prevent cracking in the groove base 8, surrounds the groove bases. The radially innermost layer 4b has a thickness corresponding to 10% - 30% of the thickness of the entire tread upper part 4. List of reference numbers

[0023] 1Tread 2Belt 3Radial carcass 4Cover tread 4aLayer 4bLayer 5Bottom tread 6Groove 7Sidewall 8Groove base rRRadial direction aRAxial direction

Claims

1. Pneumatic vehicle tyre for commercial vehicles comprising a radial carcass, a multilayered belt (2) and a tread (1) having three layers (4a, 4b, 5) radially arranged one atop the other and composed of a tread lower portion (5) and a profiled tread upper portion (4) comprising circumferential grooves, wherein the profiled tread upper portion (4) is composed of two layers (4a, 4b) of different rubber mixtures arranged one atop the other in the radial direction, wherein the rubber mixture of the radially outermost layer (4a) of the tread upper portion (4) which comes into contact with the roadway surface is optimized with respect to the characteristic of resistance to abrasion, characterized in that the rubber mixture of the tread lower portion (5) is optimized with respect to the characteristic of rolling resistance, in that the rubber mixture of the radially outermost layer (4a) of the tread upper proportion (4) contains 60 phr to 100 phr of natural rubber, 0 phr to 40 phr of butadiene rubber, wherein the butadiene rubber is high cis-1,4 or SSBR, 35 phr to 80 phr of carbon black, wherein the carbon black is N234 / N121 / N339, 0 phr to 20 phr of silica or further filler, 0 phr to 10 phr of plasticizer and 3 phr to 10 phr of crosslinking agent and in that the rubber mixture of the radially innermost layer (4b) of the tread upper portion (4) is optimized with respect to the characteristic of tear prevention in the circumferential grooves, wherein this rubber mixture contains 70 phr to 100 phr of natural rubber, 0 phr to 30 phr of butadiene rubber, wherein the butadiene rubber is high cis-1,4 or SSBR, 30 phr to 60 phr of carbon black, wherein the carbon black is N234 / N121 / N339, 0 phr to 20 phr of silica or further filler, 0 phr to 10 phr of plasticizer and 3 phr to 10 phr of crosslinking agent.

2. Pneumatic vehicle tyre according to Claim 1, characterized in that the tread lower portion (5) is composed of a rubber mixture containing 80-100 phr of natural rubber, 0-20 phr of butadiene rubber, high cis-1,4 or SSBR, 20-50 phr of N234 / N121 / N339 carbon black, 0-20 phr of silica or further filler, 0-10 phr of plasticizer and 3-10 phr of crosslinking agent.

3. Pneumatic vehicle tyre according to Claim 1 or 2, characterized in that the layers (4a, 4b) of the tread upper portion (4) have matching thicknesses.

4. Pneumatic vehicle tyre according to any of Claims 1 to 3, characterized in that the radially innermost layer (4b) of the tread upper portion (4) comprises the groove bottoms (8) of the circumferential grooves.

5. Pneumatic vehicle tyre according to any of Claims 1 to 4, characterized in that in at least one circumferential groove in the groove bottom a wear indicator which protrudes radially outwards beyond the groove bottom and due to its maximum radial height indicates critical tyre wear is arranged, wherein the thickness of the radially outermost layer (4a) is configured such that the wear indicator does not protrude into the radially outermost layer (4a) with its maximum radial height.

6. Process for producing a tread of a pneumatic vehicle tyre for commercial vehicles according to one or more of the preceding Claims 1 to 5, wherein the rubber mixture of the tread lower portion (5) is optimized with respect to the characteristic of rolling resistance, wherein the rubber mixture of the radially outermost layer (4a) of the tread upper portion (4) which comes into contact with the roadway surface is optimized with respect to the characteristic of resistance to abrasion and wherein the rubber mixture of the radially innermost layer (4b) of the tread upper portion (4) is optimized with respect to the characteristic of tear prevention in the circumferential grooves, characterized in that the tread is extruded by means of a triplex extruder, wherein the injection head of the extruder is constructed in such a way that in cross section the tread (1) being extruded has correspondingly contoured grooves (6) in the region of the later circumferential grooves.

7. Process for producing a tread (1) of a pneumatic vehicle tyre for commercial vehicles according to Claim 6, characterized in that the grooves (6) are cut into the tread (1) by cutting edges arranged in the extrusion head.