GB2083486A - Pneumatic rubber tire - Google Patents

Abstract

A pneumatic rubber tire has a sulfur cured, rubber tread composition comprising 10 to 40% cis 1,4- polybutadiene, 35 to 90% styrene/butadiene rubber, and 0 to 25% cis 1,4-polyisoprene containing 45 to 60 phr carbon black, having carbon black/processing oil ratio in the range 2.5/1 to 3/1 and a hot rebound value in the range 70 to 85. The pneumatic tire in its mounted and inflated condition under about 75 DEG of its rated load is indicated to have a decrease in its rolling resistance.

Description

SPECIFICATION Pneumatic rubber tire FIELD OF INVENTION This invention relates to pneumatic tires. The invention particularly relates to pneumatic tires having a modified tread composition.

BACKGROUND OF THE CONVENTION Pneumatic rubber passenger tires conventionally have a resilient, ground-contacting tread of a rubber, elastomeric composition. The tread rubber is conventionally compounded to provide reasonable passenger comfort, good wear and traction.

However, for passenger tire application for vehicular transportation, increasing the energy efficiency of the tire by reducing its rolling resistance has become increasingly important. Such a reduction would desirably reduce required engine fuel, thereby enhancing an energy savings, without substantially degrading the wear and traction features of the tire itself.

It should be pointed out that the vehicular drive train energy ultimately transmitted to the road has, in part, been generally dissipated both as mechanical energy in the drive train and as heat loss in the tire itself due to flexural stresses and internal rubber friction. To effect an energy savings it would be desirable to reduce mechanical energy needed to drive the vehicle and to also reduce heat energy loss.

Thus, a reduction in rolling resistance of the inflated tire is an important factor.

Therefore, it is an object of this invention to provide a pneumatic tire having a reduced rolling resistance and a tread that tends to generate less heat under vehicular driving conditions.

DISCLOSURE AND PRACTICE OF INVENTION In accordance with this invention, a pneumatic rubber tire is provided with a ground contacting, sulfur cured, rubber tread composition characterized as being comprised of about 10 to about 40 phr cis 1 ,4-polybutadiene about 0 to about 25 phr cis 1,4-polyisoprene and about 35 to about 90 phr styrene/butadiene rubber and containing about 45 to about 60 phr carbon black, with a weight ratio of carbon black to rubber processing oil in the range of about 2.5/1 to 3/1 and where said cured tread rubber composition is further characterized by having hot rebound value in the range of about 70 to about 85.

Indeed, as compared to a somewhat heretofore conventional passenger tire tread, the tread could be described as having a modification of its carbon black content and processing oil content values and ratio thereof which had been optimized for a hot rebound value of the cured rubber in the range of about 55 to about 65.Such modification, for the purpose of this invention, can be accomplished by manipulating its rubber composition in combination with decreasing its carbon black content value about 30 to about 50 percent, decreasing its said processing oil content value about 30 to about 50 percent, thereby increasing its rubber content and increasing its oil to carbon black weight ratio about 20 to about 40 percent to effect both an increase in the rubber's hot rebound about 20 to about 40 percent to a value in the range of about 70 to about 85 and to effect a decrease in the rolling resistance of about 10 to about 30 percent of the inflated, pneumatic tire when mounted on a rigid rim under about 75 percent of its rated load.

The reduction in rolling resistance of the pneumatic tire is important because it is a measure of its ability to save energy, particularly when coupled with an increase in the tread rubber's hot rebound value which is a measure of the compound's resiliency and its tendency to save energy by generating less internal heat under load and working conditions.

It has been pointed out that pneumatic rubber passenger tires conventionally have treads of a rubber optimized for a low hot rebound value in the range of about 55 to about 65. Such optimized rubber compound can typically have a total carbon black in the range of about 70 to about 90 phr with an oil to carbon black weight ratio in the range of about 1.4 to about 1.9. The carbon black content used in this invention ranged from 45 to 60 phr (parts per 100 parts by weight of rubber), with a black/oil weight ratio of 2.5/1 to 3.0/1 for the improved rolling resistance.

An important feature of this invention is that the rubber tread composition is essentially modified from a somewhat conventional tread composition by changing its carbon black and oil content as well aswtheir ratio of carbon black to oil, thereby resulting in an increase in the rubber content of the composition and increasing its hot rebound value to have a net effect of reducing the rolling resistance of the inflated tire. Thus, by this manipulation, an energy savings potential for a vehicle is provided.

The vehicle tire's rated load referred to in this specification is the load prescribed by the Tire and Rim Association, Inc. and published in their Year Book with tire type and size charted with various inflation pressures and corresponding load limits.

Representative of particularly suitable carbon blacks for the tread of this invention are typical tread blacks such as intermediate super abrasion furnace type black which is sometimes referred to as ISAF, super abrasion furnace type black which is sometimes referred to as SAF, and high abrasion furnace type black which is sometimes referred to as HAF.

For the practice of this invention, various oils which are compatible with rubber can be used and are generally referred to as rubber processing oils. Representative of such conventional rubber processing oils are paraffinic, naphthenic, aromatic, pine tar and synthetic oils.

The tread stock of compounded rubber is generally desired to utilize a synthetic rubber processing oil of the aromatic/naphthenic type with a major portion of the oil being naphthenic and a minor portion being aromatic.

It is to be understood that in the practice of this invention, in the compounding of the tread rubber,' various conventional compounding materials can be used and mixed with the rubber such as antioxidants, antiozonants. accelerators, fillers, pigments, plasticizers, peptizers, tackifying resins, and the like.

The invention can be illustrated by the accompanying drawing which is a perspective view of a vehicular pneumatic rubber tire 1, of a generally toroidal shape, with a cut-away section showing a cross-section of its tread 2, sidewalls 3 and supporting carcass plies 4.

The tire is shown in a position of being mounted on a rim 5 and inflated.

The tread 2 is of the compounded rubber of the elements described and required by this invention in order to enhance a reduction in the mounted and inflated tires rolling resistance under load, thereby effecting a potential vehicular energy savings.

The thickness of the rubber tread composition 2 on the tire 1 and over its carcass 4 can vary over a reasonably considerable range depending somewhat upon a number of factors which may primarily include the actual size of the tire and its intended vehicular use.

The pneumatic rubber tire of this invention is particularly useful because, when mounted on the Rim 5 and inflated in a position of being mounted on a vehicle and placed under load, a reduction in resistance to rolling as compared to heretofor more conventional tires which is enhanced with an increase in the tread rubber's hot rebound value. The increase in the rebound value is a measure of the tread rubber's resiliency and tendency to generate less internal heat while working under load which tends to be related to the durability of the tire.

The practice of this invention is further illustrated by reference to the following examples which are intended to be representative rather than restrictive of the scope of the invention. Unless otherwise indicated, all parts and percentages are by weight.

EXAMPLE 1 Rubber compositions were formulated to prepare an extruded tread stock according to the following general recipe shown in Table 1. In Table 1 formulation A is experimental and represents the practice of this invention. In formulation B, a control of a more conventional formulation is understood to have been optimized to provide carbon black and oil content suitable for optimizing to a hot rebound value in the cured composition in the range of about 55 to about 65.

TABLE 1 Components A (Experimental) B (Control) Polybutadiene rubber, oil extended 12.50 12.50 Butadiene/styrene rubber, oil extended 123.75 123.75 Carbon black (ISAF) 55 80 Waxes 4.00 4.00 Processing oil 1.00 12.00 Antioxidant 2.00 2.00 Accelerator 1.00 1.00 Zinc oxide 3.00 3.00 Sulfur 1.50 1.50 The compounds shown in Table 1 were mixed, extruded and applied to a radial ply rubber tire carcass and accompanying sidewalls. The tire was then molded through shaping and curing under pressure to form the resulting vehicular tire.

Samples of such compounded rubber (A) were cured and tested and found to have a hot rebound value of about 70 according to ASTM 1054-66.

The pneumatic tire was then mounted on a rim, inflated and driven by a 67.2 inch (271 cm) diameter fly wheel. The tire was tested for rolling resistance by adjusting fly wheel torque and measuring torque by transducer in the drive line or fly wheel. Compared to a control tire under such conditions with a conventional tread having carbon black content of 80 phr, a processing oil content of 47 phr and a hot rebound value of 62, the test tire had twenty five percent less rolling resistance than the control tire as indicated by showing twenty five percent less torque against the fly wheel.

In the description of this invention a relatively conventional pneumatic rubber tire has been described which has an enhanced reduction in rolling resistance and its tread rubber compound has an enhanced increase in hot rebound value, both properties enhancing the tire's ability to save energy.

Relating to the description of a general pneumatic rubber tire it should be understood that such tire includes pneumatic tires having two spaced relatively inextensible beads, a ground contacting tread portion, a pair of individual sidewalls extending radially from the axial, outer edyes of said tread portion to join the respective beads, a supporting carcass structure for said tread portion. and sidewalls generally extending from bead to bead with the required, characterized, rubber tread composition.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.

Claims (2)

1. A pneumatic rubber tire having a sulfur cured, rubber tread composition characterized as being comprised of about 10 to about 40 phr cis 1,4-polybutadiene about 0 to about 25 phr cis 1 .4- polyisoprene and about 35 to about 90 phr styrene/butadiene rubber and containing about 45 to about 60 phr carbon black and sulphur as required, e.g. about 1.5 phr, with a weight ratio of carbon black to rubber processing oil in the range of about

2.5/1 to 3/1 and where said cured tread rubber composition is further characterized by having hot rebound value according to ASTM 1054-66 in the range of about 70 to about 85.

1. A pneumatic rubber tire having a sulfur cured, rubber tread composition characterized as being comprised of about 10 to about 40 phr cis 1.4-polybutadiene about 0 to about 25 phr cis 1,4polyisoprene and about 35 to about 90 phr styrene/butadiene rubber and containing about 45 to about 60 phr carbon black, with a weight ratio of carbon black to rubber processing oil in the range of about 2.5/1 to 3/1 and where said cured tread rubber composition is further characterized by having hot rebound value in the range of about 70 to about 85.

2. The pneumatic tire of claim 1 where said carbon black is selected from at least one of ISAF, SAF and HAF type blacks, said oil is a rubber processing oil selected from at least one of paraffinic, naphthenic, aromatic, pine tar and synthetic oils and said high unsaturation rubber is selected from at least one of natural and synthetic cis 1,4-polyisoprenes, polybutadiene, and butadiene styrene copolymers.

3. A tire as claimed in claim 1, substantially as described in the foregoing Example 1 A.

New claims or amendments to claims filed on 1.12.81.

New or amended claim: