JPS63156840A - Pneumatic radial tire - Google Patents

Abstract

PURPOSE:To obtain the titled tire having excellent low fuel consumption and low rolling resistance, by using a rubber material prepared by blending a blend of natural rubber with a specific styrene-butadiene copolymer rubber with carbon black as an underlayer of a double tread. CONSTITUTION:A pneumatic radial tire obtained by using a rubber material, prepared by blending 100pts.wt. rubber consisting of (A) 20-80pts.wt. natural rubber and/or synthetic polyisoprene rubber with (B) 80-20pts.wt. styrene- butadiene copolymer rubber and/or polybutadiene rubber (containing >=10pts.wt. rubber having at least one atomic group expressed by the formula linked to the molecular chain) with (C) 25-75pts.wt. carbon black of 30-50g/kg I2 adsorption and having <=0.1 loss tangent of a vulcanized rubber at 60 deg.C and >=300% elongation at 100 deg.C as an underlayer of a double tread and placing the above- mentioned underlayer not to expose to the surface until a slip sign of a tire is exposed.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention has excellent braking performance on lubricated road surfaces and durability when turning repeatedly under severe conditions, as well as low fuel consumption and
Related to pneumatic radial tires with excellent low rolling resistance.

[Prior art]

In recent years, social demands for resource and energy conservation have become stronger, and improvements in automobile fuel efficiency have been strongly promoted. The fuel consumption of automobiles is influenced by the tire characteristics as well as the operating conditions such as driving speed, but among these factors, it is said that reducing transfer resistance is effective in improving automobile fuel efficiency. There is. The rolling resistance of a tire primarily depends on energy loss during deformation of the materials that make up the tire. Therefore, it is effective to use rubber, which has a low energy loss during deformation, especially in the tread portion, which has a large volume among the constituent components of the tire. However, these rubbers generally have the disadvantage of reducing the braking performance of the tire on wet road surfaces. It is not easy to overcome this contradictory relationship, that is, the relationship between low rolling resistance and braking performance on wet road surfaces by modifying the tread rubber.

Conventionally, even in steel radial tires for passenger cars (hereinafter referred to as Pcs), which are composed of a tread part, a side part, a carcass part, a bead part, and a steel belt part between the tread and the carcass, the tread part is located in the radial direction of the tire. A so-called double tread method is used in which rubber having at least two different physical properties is arranged from the center to the shoulder. Hereinafter, the tread portion closest to the road surface will be referred to as the cap layer (outer surface rubber layer), and the tread portion made of at least one type of rubber closer to the belt portion will be referred to as the underlayer (inner surface rubber layer). In Pcs, rubber mixed with a large amount of oil is sometimes used in the cap layer, and the oil migrates to the steel belt part, reducing the rigidity of the belt part, accelerating the occurrence of separation at the belt end, and shortening the life of the tire. It may cause short calyxes. Therefore, in Pcs, a thin underlayer is sometimes arranged as a film to reduce energy loss during deformation and at the same time to prevent oil from migrating to the belt portion.

In order to reduce rolling resistance without reducing braking performance on wet road surfaces, the camp layer of this double tread is made of conventional rubber that has excellent braking performance on wet road surfaces, and the under layer is designed to further reduce energy loss during deformation. It is best to place small rubber bands.

However, since the under layer of the Pcs was arranged for the purpose of preventing oil from migrating to the belt portion, the volume fraction α of the under layer defined by the following equation is usually in the range of 3 to 14%.

The present inventors have found that it is effective to make α at least 5% or more, preferably 15% or more, in order to reduce the rolling resistance of tires.

However, with Pcs that has a large α tread section that uses rubber with low energy loss during deformation in the underlayer, when an extremely severe turning test is performed, chunk-out occurs early in part of the tire shoulder. A phenomenon was observed that occurs. In these turning tests,
Since the tire is subjected to a strong centrifugal force in the range of 0.7 to 0.9 G in the lateral direction, a large stress is applied to a portion of the shoulder of the tire due to the bending of the extremely rigid steel belt. At this time, the surface temperature of a part of the tire's shoulder was measured with an infrared thermometer and was over 95 degrees Celsius, indicating that the tire was running under extremely harsh conditions.

Furthermore, rubbers with low energy loss during deformation generally have the disadvantage of poor physical properties at break at high temperatures. In other words, if we simply increase the volume fraction of the underlayer using rubber with low energy loss during deformation in order to improve the transfer resistance of Pcs, it will be difficult to ensure sufficient tire durability in severe turning tests. there were. This severe turning test was conducted to simulate endurance driving on roads with continuous sharp curves, such as mountain roads.

As the rubber for the underlayer, various rubbers with low energy loss during deformation have been investigated. For example, natural rubber (NR) with low energy loss and synthetic isoprene rubber (I
When a single blend of R) is used in the underlayer,
If the vulcanization temperature is high, a problem of reversion (reversion) occurs, which is a decrease in tensile strength due to overvulcanization. To avoid this drawback, it is necessary to blend polybutadiene rubber (BR) or styrene-butadiene copolymer rubber (SBR). However, BR and SBR are NR and I
Compared to R, it has a lower tensile strength at high temperatures and cannot be blended in large amounts.

Therefore, natural rubber (including IR) and synthetic rubber (e.g.
In blended rubbers consisting of BR and 5BR, reinforcing carbon black is preferably blended.

The reinforcing property of carbon black increases as its particle size decreases. However, on the contrary, a rubber using a carbon blank with a small particle size has a larger energy loss during deformation than a rubber using a carbon black with a large particle size. In other words, if the particle size of carbon black becomes smaller,
Although the reinforcing properties of the rubber increase, the energy loss during deformation increases, and it cannot be said that particles with a small particle size are suitable for the underlayer rubber. For the above reasons, in conventional rubber blended with synthetic rubber, there is a limit to the use of reinforcing carbon black, and as an underlayer rubber, it is difficult to simultaneously satisfy energy loss during deformation and elongation at high temperatures. was not sufficient.

[Purpose of the invention]

The present invention was developed in view of the above circumstances, and uses a rubber that has low energy loss during deformation as an under layer of rubber and has excellent breaking properties in a high temperature atmosphere. It significantly reduces tire rolling resistance without reducing braking performance on the road or durability when repeatedly making sharp turns, ensuring tire life and driving safety while significantly improving fuel efficiency. The purpose of the present invention is to provide a pneumatic radial tire with improved performance.

[Structure of the Invention] Therefore, the present invention provides a pneumatic tire in which the tread portion is composed of at least two layers, an outer surface rubber layer and an inner surface rubber layer, wherein the inner surface rubber layer is made of (1) natural rubber and /
or 20 to 80 parts by weight of synthetic polyisoprene rubber, 80 to 20 parts by weight of styrene-butadiene copolymer rubber and/or polybutadiene rubber, the amount of polybutadiene rubber not exceeding 50 parts by weight, and the rubber content A total of 100 parts by weight, at least 10 parts of the styrene-butadiene copolymer rubber and/or polybutadiene rubber.
Parts by weight or more are styrene-butadiene copolymer rubber and/or polybutadiene rubber in which at least one atomic group represented by the following formula % is bonded to the molecular chain with a carbon-carbon bond, and ( 2) As a reinforcing agent, carbon black with an iodine adsorption amount of 30 to 50 g/kg is added at 25 to 70 parts by weight per 100 parts by weight of raw rubber.
(3) loss tangent at 60°C is 0.1 or less, elongation at 100°C is 300% or more, and (4) is not exposed to the tire surface until at least the tire slip sign is exposed. The gist is a pneumatic radial tire characterized by being arranged in

Hereinafter, the configuration of the present invention will be explained in detail.

FIG. 1 is an explanatory diagram of a meridional half cross section of an example of the tire of the present invention. In FIG. 1, T is a tread portion, which is composed of a cap layer (outer surface rubber layer) 1 and an under layer (inner surface rubber layer) 2. 3 is a pair of left and right bead portions 4,
The belt reinforcing layer 5 is arranged so as to surround the outer periphery of the carcass 3 in the tread T. 6 is a tread groove, and 7 is a side portion.

(1) In the present invention, the following formula (
1) Styrene-putadiene copolymer rubber (hereinafter referred to as modified SBR) and/or polybutadiene copolymer rubber in which at least one atomic group represented by the formula % (1) is bonded to the molecular chain through a carbon-carbon bond. Gen rubber (hereinafter referred to as modified BR) is contained. This is for the following reasons. That is, originally, the performance required of the under tread portion of a fuel-efficient tire is: (1) low energy loss, (2) low reversion during overvulcanization, and high zero strength. Taking these into consideration, currently NR/SBR/B
R, NR/BR.

Alternatively, a mixed rubber such as NR/SBR is used in the under layer. However, it still does not fully satisfy this required performance. Therefore, it is possible to consider (b) using a polymer with lower energy loss, and (b) using carbon black with lower reinforcing properties and keeping its blending amount low. However, in method (b), the strength of the rubber decreases, and in method (b), for example, simply increasing the blending ratio of BR, which has low energy loss, reduces the strength, especially the strength at high temperatures. This is not desirable as it will be extremely low. From this point of view, as a result of intensive study, the above modified BR1 modified S
BR, iodine adsorption! The use of carbon blanks weighing 30-50 g/kg was reached. In other words, by using modified SBR and modified BR, which have lower energy loss than conventional polymers, and a carbon blank with greater reinforcing properties, we aim to improve the tire's fuel efficiency and turning durability. .

The modified SBR preferably has a bound styrene content of 5 to 30% by weight and a 1.2 vinyl bond in the butadiene moiety of 5 to 80% by weight. If the amount of bound styrene is 30% by weight or more and/or if the 1,2 vinyl bond in the butadiene moiety is 80% by weight or more, the energy loss will increase extremely, which is inappropriate, whereas if the amount of bound styrene is less than 5% by weight, it is inappropriate. This is inconvenient because it shows almost the same performance as BR.

In the present invention, the underlayer 2 is made of natural rubber and/or
or 20 to 80 parts by weight of synthetic polyisoprene rubber, 80 to 20 parts by weight of styrene-butadiene copolymer rubber and/or polybutadiene rubber, the amount of polybutadiene rubber not exceeding 50 parts by weight, and the rubber content A total of 100 parts by weight, at least 10 parts of the styrene-butadiene copolymer rubber and/or polybutadiene rubber.
The parts by weight are replaced with modified SBR and/or modified BR. A version in which the amount of natural rubber and/or synthetic polyisoprene rubber exceeds 8 parts by weight poses a problem, and if it is less than 20 parts by weight, the breaking strength at high temperatures decreases.

(2) Further, in the present invention, carbon black with an iodine adsorption amount of 30 to 50 g/kg is contained in the underlayer 2 as a reinforcing agent at a ratio of 25 to 70 parts by weight per 100 parts by weight of raw rubber. The amount of iodine adsorbed by carbon black is a measure of the particle size, and if the value is less than 30 g, the reinforcing property will be significantly reduced, which is not preferable. Also,
If the amount of carbon black is less than 25 parts by weight, reinforcing properties will be significantly reduced, and if it exceeds 70 parts by weight, energy loss will increase.

Examples of this carbon black include GPF, FE,
A soft type such as F is used.

(3) The vulcanized rubber of the underlayer 2 formed in this way has a loss tangent (tan δ) of 0.1 or less at 60°C and an elongation of 300% or more at 100°C.

When the loss tangent at 60° C. exceeds 0.1, the effect of reducing the rolling resistance of the tire is not significant, and when the elongation at 100° C. is less than 300%, the durability of the tire in severe turning tests is significantly reduced.

In the present invention, tan δ determined by a known method using a viscoelastic spectrometer (manufactured by Wakagi Seisakusho) is used to evaluate the energy loss during deformation of rubber. That is,
The test rubber was attached to the device as a strip-shaped sample with a length of 1Q mm, a width of 91) and a thickness of 21 m, and the temperature was 60°C and the frequency was 50.
Shear vibration tan δ is measured under the conditions of Hz and dynamic strain of 5%. To evaluate the fracture physical properties of rubber, JIS K 6
The elongation (%) is measured by the tensile test specified in 301.

The test machine is Autograph l5-2000C manufactured by Shimadzu Rakusakusho)
The test piece was in the shape of a No. 3 dumbbell.

(4) Furthermore, in order to arrange this underlayer 2, the volume fraction α is set to be 5% or more, preferably 15% or more. When α is less than 5%, the reduction in tire rolling resistance is not significant. On the other hand, if the underlayer 2 is placed beyond the position of the slip sign on the tread, the underlayer will come into contact with the road surface after the cap layer wears out, so it will remain in contact with the tire surface at least until the tire's slip sign is exposed. Place it so that it is not exposed.

In the pneumatic radial tire of the present invention, other than the tread portion, vulcanized rubber having suitable physical properties depending on the purpose may be used.

In addition, various compounding agents commonly used in the rubber industry can be appropriately selected and used in all parts including the tread part.

EXAMPLES The effects of the present invention will be specifically explained below with reference to Examples and Comparative Examples.

Examples, Comparative Examples (al) Table 1 below shows polymers used here (modified SB
R, modified BR) microstructure is shown. Further, Table 2 below shows the physical properties of a rubber obtained by vulcanizing a rubber compound obtained by blending only these polymers at 160° C. for 15 minutes.

(Margins below this page) As is clear from Table 2, modified 5BR-2 and -3 maintain the level of elongation while maintaining the ta
It can be seen that nδ is significantly reduced.

(b) A tire (165SR13 size, PCS tire) was produced using the above rubber compound for the underlayer and cap layer, and the tire performance was measured. The results are shown in Table 3 below. The rolling resistance index, turning durability, and underlayer failure pattern of each tire were measured and evaluated as follows. The air pressure at the time of measurement was 1.7 kg.
/ca.

Rolling resistance index: The rolling resistance of a tire is measured on a steel drum with a diameter of 1707 nm at a speed of 60 km/hr, and is expressed as an index using the following formula based on the value of tire resistance 1.

Durability at 80.1G) evaluate. Turn with a diameter of 15m A PC attached to the front wheel of a vehicle If either the left or right wheel of 8 is inside Part of the steel belt is exposed. Measure the number of turns it takes. Ta The following formula is based on the value of ear 1. It is displayed as an index.

Fracture form: In the above rotation test, observe whether there is any fracture inside the underlayer around the exposed part of the belt. When there is destruction in the under layer, it is said that the destruction form is bad.

(Margins below this page) Comparing tire sizes 1 to 5, it can be seen that the use of modified 5BR-2 and 5BR-3 reduces the rolling resistance of the tires.

This result shows that tires using a special polymer in the underlayer can reduce rolling resistance without reducing turning durability.

〔Effect of the invention〕

As explained above, according to the present invention, a pneumatic radial tire with excellent transfer resistance can be provided.

[Brief explanation of the drawing]

FIG. 1 is a meridional half-sectional view of an example of the tire of the present invention. T... Tread portion, 1... Cap layer, 2... Underlayer, 3... Carcass, 4... Bead portion, 5...
・Belt reinforcement layer.

Claims (1)

[Scope of Claims] A pneumatic tire in which the tread portion is composed of at least two layers, an outer surface rubber layer and an inner surface rubber layer, wherein the inner surface rubber layer is made of (1) natural rubber and/or synthetic polyisoprene rubber 20 ~80 parts by weight, styrene-butadiene copolymer rubber and/or 80 to 20 parts by weight of polybutadiene rubber, the amount of polybutadiene rubber not exceeding 50 parts by weight, and a total rubber content of 100 parts by weight, and the styrene・At least 10 parts by weight of the butadiene copolymer rubber and/or polybutadiene rubber has at least one atomic group represented by the following formula ▲Mathematical formula, chemical formula, table, etc.▼ attached to the molecular chain with a carbon-carbon bond. A bonded styrene-butadiene copolymer rubber and/or polybutadiene rubber, and (2) as a reinforcing agent, carbon black with an iodine adsorption amount of 30 to 50 g/kg is added at 25 to 70 parts by weight per 100 parts by weight of the raw material rubber.
(3) loss tangent at 60°C is 0.1 or less, elongation at 100°C is 300% or more, and (4) is not exposed to the tire surface until at least the tire slip sign is exposed. A pneumatic radial tire characterized by being arranged in.