JP3469382B2 - Large tires with excellent fuel efficiency and low heat generation - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-sized vehicle, such as a truck or a bus, which has improved fuel economy and low heat generation while maintaining wear resistance, and also reduces damage at the end of use. Regarding tires.

[0002]

2. Description of the Related Art A tire is repeatedly deformed during use, and heat is generated due to hysteresis loss accompanying the deformation. Especially the fever of the tread is large. The heat generation amount of the tread increases as the hysteresis loss when the unit stress of the rubber composition forming the tread acts, as the deformation amount increases, or as the rubber amount forming the tread increases. on the other hand. Due to the low thermal conductivity of the rubber composition, the heat generated in the inside of the tread is transferred to the surface and is less likely to be dissipated in the atmosphere, so heat is accumulated and the temperature rises until the heat generation and the heat dissipation are balanced. When the temperature rises, the strength of the rubber composition decreases, deterioration is promoted, and separation easily occurs between the tread and the belt. For large tires with a large tread thickness and high load, the surface of the tread is made of a wear resistant rubber composition in order to suppress the temperature rise of the tread and prevent the occurrence of separation, and the inside has low heat generation. A so-called cap base structure made of a flexible rubber composition is used.

Generally, in order to reduce the heat generation of the rubber composition, it is sufficient to reduce the hysteresis loss. Therefore, the compounding amount of carbon black is reduced. Use carbon black with a large particle size. A method using a rubber polymer having a small hysteresis loss has been carried out, and a base rubber not directly related to wear is made to have a low heat generation property by appropriately combining these methods.

[0004]

In order to reduce hysteresis loss, a rubber composition in which the amount of carbon black blended is reduced or carbon black having a large particle size is used is not sufficiently reinforced, so that the rubber composition is torn It has low strength, low wear resistance, and low rigidity. By the way, when a tire mounted on an automobile and running rotates and an arbitrary part of the tread lands, the inner side of the tread rubber fixed to the belt continues to rotate at a constant speed, but the front side of the tire is on the road surface. Rotation is delayed due to friction with the tread rubber, and the tread rubber is sheared and deformed by the load of the vehicle body. These deformations cause a phase difference between the front surface and the back surface of the tread rubber, and the front surface portion follows the surface of the tread rubber as if sliding on the road surface, and further rotates to be released from the ground to restore the original shape. In this case, the greater the deformation, the more accelerated the wear. Further, these deformations are superposed and repeated every landing, which causes a hysteresis loss. Since the amount of deformation increases as the shear rigidity of the base rubber decreases, even if the base is formed of a rubber composition having low hysteresis loss but low rigidity, fuel consumption and heat generation increase. Further, as compared to a tire in which a tread is formed solely of a rubber composition used for a cap, wear resistance is reduced due to a large movement of the tread rubber, wear progresses and the remaining thickness of the cap rubber becomes thin. When stones directly damage the base rubber, the base rubber has a small tear resistance, so many small tears, so-called tiers, occur and wear is promoted, which reduces fuel consumption by adopting a cap base structure. The low heat generation does not reach the expected level of improvement in durability.

In view of the above, the present invention reduces rolling resistance (fuel consumption) and heat generation and wear by forming a base rubber from a rubber composition having a low hysteresis loss property but a high rigidity and a high tear strength. It is an object to provide a large tire having a long life.

[0006]

SUMMARY OF THE INVENTION The present invention comprises a cap rubber of a wear resistant rubber composition having a tread rubber disposed on an exposed surface thereof and a base rubber of a low heat generating rubber composition located inside the cap rubber. In a large-sized tire having a layered structure, a rubber component containing natural rubber as a main component of a rubber component, carbon black and silica as a reinforcing agent, and a nitrogen adsorption specific surface area (N ₂ SA) of at least 15 m ² / g as a dispersing agent of silica.
Calcium carbonate and a silane coupling agent as a physical property improver are blended at least, a base rubber is formed of a rubber composition having a 300% modulus of 16 to 22 MPa, and the average thickness of the base rubber is 20 times the tread rubber thickness.
It is a large tire with excellent fuel economy and low heat buildup of up to 50%.

The preferable amount of carbon black and silica compounded in the rubber composition used for the base of the large-sized tire of the present invention is (1), 35 ≦ (carbon black amount) + 0.75 × with respect to 100 parts by weight of the rubber component. (Amount of silica) ≤ 50 (2), 0.2 ≤ 0.75 x (Amount of silica) / (Amount of carbon black) ≤ 1.0 In parts by weight specified by the relational expressions (1) and (2) above. is there. The preferred amount of the silane coupling agent and calcium carbonate is (3), 0.05 ≦ (calcium carbonate amount) / (silica amount)
≦ 0.40 (4), 0.05 ≦ (amount of silane coupling agent) / (amount of silica) ≦ 0.15 The number of parts by weight specified by the relational expressions (3) and (4) above.

The thickness of the base rubber, which is measured and averaged at three points, the so-called quarter point at which the tread width is divided into four and the center, is set so as to account for 20 to 50% of the total thickness of the tread. The rubber composition forming the rubber composition is not particularly limited, and a conventionally used abrasion-resistant rubber composition can be continuously used.

[0009]

DETAILED DESCRIPTION OF THE INVENTION A rubber composition in which carbon black and silica are used together as a reinforcing agent and a silane coupling agent is added is known. When mixing a rubber composition containing this type of carbon black and silica, the aggregate of secondary agglomerates of silica is less likely to break into primary aggregates during the mixing, so the state of agglomerates of secondary aggregates There are many particles scattered in the matrix rubber, and once dispersed, they re-aggregate and
It tends to be a lump of secondary aggregate. Therefore, when a base rubber is formed from a rubber composition containing silica, when a stress acts on the base rubber, the secondary agglomerate, which is a lump in the rubber composition, and an interface between the surrounding rubber and The stress was concentrated and became the starting point of tearing, and the tear resistance varied greatly depending on the mixed state of the rubber composition, and the level thereof was not sufficient. Further, a tire using a rubber composition in which carbon black and silica are used in combination with a reinforcing agent as described above and a silane coupling agent is added in the tread portion is 0.2% to 10% from the outside in the tread portion during running. Subject to repeated% distortion. As a result, the secondary agglomerate structure of silica repeatedly breaks and re-aggregates. This process causes an increase in internal loss (friction) of the rubber, resulting in a large hysteresis loss, which is not preferable. This effect is called the Payne effect. In order to suppress this Payne effect, when a rubber composition is prepared, a method of extending the mixing time to improve the dispersion of silica and widening the interval between silica aggregates is performed. The molecular weight of the molecule itself is reduced, the number of free terminal chains is increased, and the hysteresis loss reduction efficiency is reduced, and as a result, it does not contribute to the reduction of hysteresis loss as expected. On the other hand, when the method according to the present invention is used, that is, when silica is mixed in the presence of ultrafine calcium carbonate, calcium carbonate promotes the destruction of the secondary agglomerates of silica and the primary agglomerates are added to the matrix rubber. Along with dispersing, it is possible to prevent the once dispersed thing from re-agglomerating to form lumps, and to disaggregate the re-aggregated lumps to maintain a good dispersion state, and to improve tear resistance. Can be higher. Therefore,
The rubber composition used in the present invention is a natural rubber having a low exothermic property and a large tear resistance and a large modulus, or, if necessary, 30% or less of the natural rubber is used for the purpose of improving cut resistance and the like. Carbon black, silica, calcium carbonate, a silane coupling agent is blended with a rubber component substituted with a system rubber, and other components essential for a rubber composition such as sulfur, a vulcanization accelerator, zinc white, and stearic acid are included. A 300% modulus of 16 to 22 MPa is obtained by compounding additives such as an antiaging agent and a softening agent, which are usually compounded in a rubber composition, if necessary. The compounding amounts of carbon black, silica, calcium carbonate and a silane coupling agent are the following (1), (2), (3), (4) with respect to 100 parts by weight of the rubber component (hereinafter simply referred to as "parts by weight"). Are adjusted so that the relational expression of is satisfied. (1), 35 ≦ (carbon black amount) + 0.75 × (silica amount) ≦ 50 (2), 0.2 ≦ 0.75 × (silica amount) / (carbon black amount) ≦ 1.0 (3) , 0.05 ≦ (calcium carbonate amount) / (silica amount)
≦ 0.40 (4), 0.05 ≦ (amount of silane coupling agent) / (amount of silica) ≦ 0.15 If any of the above formulas is not satisfied, fuel economy, low heat buildup, wear resistance Either the resistance or the tear resistance becomes worse. On the other hand, when the base rubber is made of a rubber composition having a 300% modulus after vulcanization of less than 16 MPa, the amount of deformation at the ground contact portion of the tread becomes large and wear resistance, low fuel consumption and low heat buildup deteriorate. , 22 MPa, the amount of carbon black or silica becomes larger than the amount specified above, resulting in poor fuel economy and low heat buildup.

As the carbon black (hereinafter, carbon black is abbreviated as carbon) to be blended in the rubber composition used in the present invention, any carbon black generally known for tires can be used. Among them, the classification number of ASTM is 100 to 30
Those in the 0s are preferable.

The silica compounded in the rubber composition used in the present invention has a nitrogen adsorption specific surface area (hereinafter, nitrogen adsorption specific surface area is referred to as N ₂ SA) of 140 to 280 m ² / g as long as the requirement is satisfied. Any of those prepared for use can be used, and in accordance with a conventional method for compounding silica, mercaptopropyltrimethoxysilane, γ-glyoxidoxypropyltrimethoxysilane, γ-amidinopropylethoxy for the purpose of suppressing heat generation. A silane coupling agent such as silane is added in an amount of 0.05 to 0.15 times the amount of silica. When silica having an N ₂ SA of less than 140 m ² / g is blended, the rigidity is low, and when N ₂ SA is more than 280 m ² / g, workability in the tire manufacturing process is poor, which is not preferable. When the relationship between the amount of (carbon black amount) + 0.75 × (silica amount) of carbon black and silica expressed in parts by weight relative to 100 parts by weight of the rubber component is more than 50, fuel consumption and heat buildup deteriorate, and less than 35. Results in poor wear resistance and tear resistance.

The calcium carbonate compounded in the rubber composition used in the present invention is an ultrafine calcium carbonate having N ₂ SA of 15 m ² / g or more. Among them, N ₂ SA whose surface is treated with higher fatty acid, resin acid, surfactant or the like is 15
Activated calcium carbonate of m ² / g or more is preferable because it has a large rubber reinforcing property. N ₂ SA of less than 15 m ² / g is not preferable because it lowers the abrasion resistance of the rubber composition. The blending amount is preferably 0.05 to 0.40 times the amount of silica, and when it is less than 0.05 times, the effect of improving the dispersibility of silica is small, and when it is more than 0.40 times, the wear resistance decreases. Sometimes.

The thickness of the base rubber is such that the ratio of the ratio of the base rubber to the total tread thickness is measured at 1/4 of the tread width and at three points in the center, and the average value is 20 to 50%. Is set. When the thickness of the base rubber is less than 20%, the effect of forming the cap base structure is small and the fuel economy and the low heat buildup are not improved, and when it is more than 50%, the wear life is shortened.

[0014]

EXAMPLE Natural rubber and carbon, silica, silane coupling and calcium carbonate shown in Table 1 were mixed in a ratio of parts by weight shown in Table 1, and in addition to these, 3 parts by weight of zinc white (hereinafter, parts by weight are abbreviated as parts). ), 1 part stearic acid, 5 oils
Parts, and 1 part of an antioxidant (trade name: Nocrac 6C, manufactured by Ouchi Shinko Chemical Industry Co., Ltd.) were added and mixed to prepare non-pro rubber of each of the examples and comparative examples.
And 1 part of vulcanization accelerator CBS were mixed to obtain a rubber composition for base rubber. A part of the obtained rubber composition was sampled to measure the Mooney viscosity, and then vulcanization molded into a test piece having a predetermined shape to measure the 300% modulus. The results are shown in Table 1.

On the other hand, 100 parts of natural rubber, 55 parts of N220 carbon black, 3 parts of zinc white, 1 part of stearic acid,
5 parts of oil, 1 part of antioxidant, 1 part of wax, 2 parts of sulfur and 1 part of vulcanization accelerator CBS were mixed to obtain a rubber composition for cap rubber. A rubber composition for a cap rubber and the above rubber composition for a base rubber were integrally extruded to form a tread rubber having a cap base structure, and a tire of size 10.00R20 was manufactured using this tread rubber.
The trial tires of Examples and Comparative Examples were tested for rolling resistance, wear resistance, heat generation and tear resistance according to the test conditions described below, and the results are shown in Table 1.

Rolling resistance: American Society of Automotive Engineers standard SA
It was carried out according to E J1270, and the value calculated by the formula of (rolling resistance of each trial tire) × 100 / (rolling resistance of Comparative Example 1) was shown. The smaller the value, the smaller the rolling resistance, which is preferable. Abrasion resistance: After being mounted on the rear wheel of a truck and running for 100,000 km, the groove depth was measured, and the wear amount was calculated from the difference with the groove depth before running, (wear amount of Comparative Example 1) × The value calculated by the formula of 100 / (wear amount of each trial tire) was shown. The larger the value, the better the abrasion resistance. Heat generation: Immediately after running on the drum under the high speed endurance test conditions specified in the FMVSS119 automobile safety standard, insert a thermistor at the belt end position where the tread thickness becomes maximum on the belt, and measure the temperature (each trial tire temperature). The value calculated by the formula of × 100 / (temperature of Comparative Example 1) was shown. The smaller the value, the better the exothermicity. Tear resistance: Attached to the rear wheel of a truck, run until the groove is worn and the depth is about 1.6 mm, peel off the tread rubber from the belt, and remove the scratches on the back surface of the peeled tread rubber. The individual lengths were measured and totaled, and the value calculated by the formula (Scratch length of Comparative Example 1) × 100 / (Scratch length of each prototype tire) was shown. The higher the value, the better the tear resistance.

[0017]

[Table 1]

[0018]

[Table 2]

Footnote * 1 in Table 1: N ₂ SA = 240 m ² / g, oil absorption = 240 cm ³ / 100g * 2: N ₂ SA = 140 m ² / g, oil absorption = 170 cm ³ / 100g * _{3: N 2 SA = 120 m} 2 / g, oil absorption ^{= 160 cm 3 / 100g * 4} : mercaptopropyltrimethoxysilane _{* 5: N 2 SA = 16m} 2 / g fatty acid surface treatment activated calcium carbonate * 6: N ₂ SA = 5 m ² / g Slightly light calcium carbonate * 7: (carbon black amount) + 0.75 x (silica amount) * 8: 0.75 x (silica amount) / (carbon black amount) * 9: (carbonic acid Calcium amount) / (silica amount) * 10: (silane coupling agent amount) / (silica amount)

Compared to the control comparative example 1 in which silica and calcium carbonate were not blended, the example tire had less rolling resistance, less heat generation, and had higher tear resistance and abrasion resistance. It is shown that low rolling resistance, low heat buildup, tear resistance, and abrasion resistance are simultaneously improved by using and calcium carbonate together. Comparative Example 3 in which silica is blended but calcium carbonate is not blended is excellent in low rolling resistance, but inferior in wear resistance, and Comparative Example 4 is 0.75 × (silica amount) /
When the value of (carbon black amount) is larger than 1.0, the tear resistance is poor. Calcium carbonate having N ₂ SA of less than 15 m ² / g has a large particle size and acts rather as a foreign substance, so that Comparative Example 9 using this is inferior in wear resistance and tear resistance. Comparative Example 11 using silica having N ₂ SA of less than 140 m ² / g is inferior in abrasion resistance.

[0021]

The rubber composition of the tread base rubber of a large tire has a rubber component containing natural rubber as a main rubber component and carbon black as a reinforcing agent as well as N ₂ SA.
40 to 280 m ² / g of silica is blended, and the amount of N ₂ SA of 0.05 to 0.4 times the blending amount of silica is 15 m ^2.
/ G or more of calcium carbonate and 0.05 to 0.1
By adding 5 times the amount of the silane coupling agent, the dispersibility of silica is improved as compared with the case where calcium carbonate is not added, and the rolling resistance, abrasion resistance, heat generation and tear resistance are improved. The property is improved.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ identification code FI C08K 5/541 C08L 7/00 C08L 7/00 C08K 5/54 (56) Reference JP-A-7-118443 (JP, A) JP-A-61-287802 (JP, A) JP-A-3-7602 (JP, A) JP-A-63-180505 (JP, A) JP-A-60-60002 (JP, A) JP-A-1-115943 (JP, A) JP-A-9-77915 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) B60C 1 / 00,11 / 00 C08K 3 / 04,3 / 26,3 / 36,5 / 541 C08L 7/00

Claims (3)

(57) [Claims] 1. A large tire having a two-layer structure of a cap rubber of a wear-resistant rubber composition having a tread rubber disposed on an exposed surface and a base rubber of a low heat-generating rubber composition located inside the cap rubber, A rubber component containing natural rubber as a main component, carbon black and silica as a reinforcing agent, and a nitrogen adsorption specific surface area (N ₂ S as a dispersing agent of silica).
A) contains at least 15 m ² / g of calcium carbonate and a silane coupling agent as a physical property improving agent, and a base rubber is formed from a rubber composition having a 300% modulus of 16 to 22 MPa. Is 20 to 50% of the tread rubber thickness, and is a large tire with excellent fuel economy and low heat buildup. 2. The blending amount of carbon black and silica blended in the rubber composition forming the base rubber is (1), 35 ≦ (carbon black amount) + 0.75 × (with respect to 100 parts by weight of the rubber component. Silica amount) ≤ 50 (2), 0.2 ≤ 0.75 x (silica amount) / (carbon black amount) ≤ 1.0 Amount satisfying the relational expressions (1) and (2) above (parts by weight). ) Is a large tire having excellent fuel economy and low heat buildup. 3. The respective amounts of calcium carbonate and silane coupling agent compounded in the rubber composition forming the base rubber are (3), 0.05 ≦ (calcium carbonate amount) relative to the silica compounding amount. / (Silica amount) ≤
0.40 (4), 0.05 ≦ (silane coupling agent amount) / (silica amount) ≦ 0.15 The amount (parts by weight) satisfying the relational expressions (3) and (4) above. A large tire excellent in low fuel consumption and low heat generation according to Item 1.