Elastomer compositions

Abstract

Tires having good grip on wet road surfaces and low frictional resistance to rolling on the road surface have treads formed from vulcanisates of elastomer compositions comprising a major component consisting of one or more polymers having a glass transition temperature (Tg) of minus 50.degree. C. or lower temperature, and a minor component consisting of one or more polymers having a glass transition temperature of ambient temperature or higher temperature. The major component can consist of one or more rubbery polymers selected from natural rubbers, polybutadienes synthetic polyisoprenes and rubbery styrene-butadiene copolymers; and the minor component can consist of a resinous styrene-butadiene co-polymer.

Description

This invention relates to elastomer compositions, to vulcanised compositions obtained by vulcanising them and to tires containing said vulcanised compositions.

In designing tires for road vehicles it is normally desirable to seek maximum grip on wet road surfaces and minimum frictional resistance to rolling of the tire on the road surface. Unfortunately, the one property is, in general, improved only at the expense of the other, and in consequence the design tends to be a compromise insofar as the selection of elastomer used for the tread portion of the tire is concerned.

We have now found according to the present invention that excellent combinations of grip on wet road surfaces and rolling resistance can be obtained by using in the tread portion of the tires vulcanised elastomer compositions containing blends of polymers having low glass transition temperatures with polymers having high glass transition temperatures.

Accordingly, a first aspect of the invention provides an elastomer composition comprising a major component consisting of one or more polymers having a low glass transition temperature (as hereinafter defined), and a minor component consisting of one or more polymers having a high glass transition temperature (as hereinafter defined).

Glass transition temperature (Tg) can be measured by various known methods. In this specification it is defined as the temperature at which there is a change in the shape of a curve of volume plotted against temperature as measured by dilotometry. In the glassy state there is a lower volume coefficient of expansion than in the rubbery state, thus producing the change in shape of said curve. As used herein "low glass transition temperature" is one of minus 50.degree. C. or lower temperature, and "high glass transition temperature" is one of ambient temperature (15.degree. C.) or higher temperature.

Reference to "major" and "minor" components relate to the weight of each component as a proportion of the total weight of the major and minor components. The size of the minor component depends on the glass transition temperature of the polymer or polymers it contains, but in general it can, for example, constitute up to 45% by weight of said total weight, and especially a proportion in the range from 3 to 25%.

Polymers having high glass transition temperatures are, for example, polymers (for example styrene-butadiene or other styrene copolymers) containing a substantial proportion of styrene. Suitable styrene copolymers, for example, are copolymers whose properties in general at ambient temperatures (say 15.degree. C.) are such that the copolymer is to be regarded as being more resinous than elastomeric in character. Where the styrene copolymer is one consisting substantially of styrene and butadiene, examples of suitable proportions of styrene are in the range from 50 to 90%, for instance 80-90% styrene. Examples of suitable commercial resinous styrene-butadiene copolymers are those sold by Goodyear Company under the trade mark Pliolite 6SF and Pliolite 6SH, which have styrene contents in the range 85-90% by weight. Other suitable polymers for use in the minor component are various styrene-butadiene rubbers.

Polymers having low glass transition temperatures (as hereinbefore defined) are for example natural rubbers, polybutadienes and polyisoprenes.

The unvulcanised elastomer compositions of the first aspect of the invention can be vulcanised, for example using the procedures referred to below in the Examples, to produce vulcanised compositions which constitute a second aspect of the invention. These vulcanised compositions can, for example, be in the form of tires. Accordingly, a third aspect of the invention is tires whose tread portion comprises a vulcanised composition according to the second aspect of the invention.

The invention is illustrated by the following Examples in which the amounts of ingredients are amounts by weight unless stated otherwise.

In the Examples some of the ingredients are referred to simply by their trade names. The nature of those ingredients and their glass transition temperatures (as hereinbefore defined) where appropriate, is as follows:

______________________________________TradeName Material Tg(.degree.C.)______________________________________SMR 20 a natural rubber minus 70Intene polybutadiene of high cisNF 45 content (95% or more) minus 105LTP a styrene-butadiene rubber minus 551502Natsyn a synthetic polyisoprene of minus 702200 high cis content (98% or more)IR309 a synthetic polyisoprene of minus 70 a low cis content (less than 92%)OEP1712 an oil-extended styrene-butadiene copolymer comprising 100 parts of a styrene butadiene copolymer (comprising 23 parts styrene and 77 parts butadiene and having a Tg of minus 55.degree. C.) and 37 parts of extending oilPliolite resinous styrene-butadiene6SF and copolymers having styrenePliolite contents in the range from6SH 85% to 90% of the copolymer 90Hyvis 30 a low molecular weight poly- isobutylene having a viscosity average molecular weight of about 1,000Vistonex a high molecular weight poly-MML isobutylene having a viscosity100 average molecular weight in the range from 1,060,000 to 1,440,000CBS an acceleratorArrcon- an antioxidant comprising 75%nox GP BLE and 25% of a silicateI.P.P.D. N--isopropyl-N'--phenyl-p-phenylene diamine.______________________________________

EXAMPLES 1-4

Four natural rubber compositions were obtained by blending together the following ingredients. It will be seen that Examples 2, 3 and 4 which are examples of elastomer compositions of the invention, differ from Example 1 (which is for the purpose of comparison) in that in them part of the natural rubber is replaced by 10, 20 and 30 parts, respectively, of Pliolite 6SH.

______________________________________ Example Number 1 2 3 4______________________________________SMR 20 100.00 90.00 80.00 70.00Pliolite 6SH -- 10.00 20.00 30.00Zinc Oxide 4.00Stearic Acid 2.00Sulphur 1.50MBS 1.00Arrconnox DP 1.00I.P.P.D. 1.00Paraffin Wax 1.00N326 Black 53.00______________________________________

EXAMPLES 5-8

Four polyisoprene compositions were obtained by blending together the following ingredients. It will be seen that Examples 6, 7 and 8, which are further examples of elastomer compositions of the invention, differ from Example 5 (which is for the purpose of comparison) in that in them part of the polyisoprene is replaced by 10, 20 and 30 parts, respectively, of Pliolite 6SH.

______________________________________ Example Number 5 6 7 8______________________________________Natsyn 2200 100.00 90.00 80.00 70.00Pliolite 6SH -- 10.00 20.00 30.00Zinc Oxide 4.00Stearic Acid 2.00Sulphur 1.50MBS 1.00Arrconnox GP 1.00I.P.P.D. 1.00Paraffin Wax 1.00N326 Black 53.00______________________________________ The four polyisoprene compositions were vulcanised,and the mechanical properties and power loss figures forthe vulcanisate of Example 6 were as follows:Tensile strength MPa 21.6Stress @ 300% MPa 11.0Elongation @ break % 505Hardness IRHD 84.9Resilience @ 50.degree. C. % --______________________________________Power loss 50.degree. C. 80.degree. C. 100.degree. C.______________________________________Elastic modulus (E') MPa 9.35 6.29 5.60Loss modulus (E") MPa 1.71 0.92 0.69Loss factor (E"/E') 0.183 0.146 0.123E"/E*).sup.2 MPa.sup.-1 0.0189 0.0227 0.0216______________________________________

EXAMPLE 9

A further natural rubber composition was obtained by blending together the ingredients shown below which are followed by mechanical properties and power loss figures for the resulting vulcanisate.

______________________________________SMR 20 90.00Pliolite 6SH 10.00Renacit VII 0.15Zinc oxide 4.00Stearic acid 2.00Sulphur 1.35MBS 0.90IPPD 1.00Arrconnox GP 1.00Paraffin Wax 1.00N110 black 30.00N326 black 15.00Tensile strength MPa 27.0Stress @ 300% MPa 14.0Elongation @ break % 480Hardness IRHD 71.5Resilience @ 50.degree. C. % 64.4______________________________________Power loss 50.degree. C. 80.degree. C. 100.degree. C.______________________________________Elastic modulus (E') MPa 5.96 4.63 4.26Loss Modulus (E") MPa 0.81 0.51 0.37Loss factor (E"/E') 0.137 0.109 0.087E"/E*).sup.2 MPa.sup.-1 0.0225 0.0235 0.0205______________________________________

EXAMPLE 10

A styrene-butadiene rubber composition was obtained by blending together the ingredients shown below which are followed by the mechanical properties and power loss figures for the resulting vulcanisate.

______________________________________OPE 1712 67.50LTP 1502 22.50Pliolite 6SH 10.00N339 black 55.00Enerflex 94 15.00Arrconnox GP 1.33IPPD 0.75Zinc oxide 2.50Stearic acid 1.00MBS 0.80Sulphur 1.6040 mesh rubber crumb 8.00PVI-50 0.20Tensile strength MPa 16.2Stress @ 300% MPa 9.2Elongation @ break % 480Hardness IRHD 71.3Resilience @ 50.degree. C. % 37.5______________________________________Power loss 50.degree. C. 80.degree. C. 100.degree. C.______________________________________Elastic modulus (E') MPa 6.19 3.96 3.69Loss modulus (E") MPa 1.53 0.64 0.52Loss factor (E"/E') 0.248 0.163 0.141E"/E*).sup.2 MPa.sup.-1 0.0377 0.0400 0.0374______________________________________

EXAMPLE 11

A composition comprising a low temperature styrene-butadiene and a low molecular weight polyisobutylene was obtained by blending together the following ingredients.

______________________________________ LTP 1502 90.00 Pliolite 6SH 10.00 Hyvis 30 50.00 Zinc oxide 2.50 Stearic acid 1.00 MBS 0.80 Sulphur 1.60 PVI-50 0.20 Arrconnox GP 1.33 IPPD 0.75 N234 black 60.00______________________________________

The composition was vulcanised at 140.degree. C. for 40 minutes. The mechanical properties and power loss figures for the resulting vulcanisate are as follows:

______________________________________Tensile strength MPa 8.6Stress @ 300% MPa 6.7Elongation at break % 350Hardness IRHD 60.9Resilience @ 50.degree. C. % 33.9______________________________________Power loss 50.degree. C. 80.degree. C. 100.degree. C.______________________________________Elastic modulus (E') MPa 3.85 2.02 1.61Loss modulus (E") MPa 1.04 0.55 0.46Loss factor (E"/E') 0.270 0.273 0.285E"/(E*).sup.2 MPa.sup.-1 0.0654 0.1255 0.1639______________________________________

EXAMPLE 12

A further composition of the invention was obtained by blending together the following ingredients. The composition was vulcanised at 140.degree. C. for 40 minutes and the mechanical properties and power loss figures for the resulting vulcanisate are given below:

______________________________________SMR 20 50.00Vistonex MML 100 50.00Pliolite 6SH 5.00Zinc oxide 5.00Stearic acid 1.00Sulphur 2.50CBS 0.50Arrconnox GP 1.00IPPD 1.00Paraffin wax 1.00Mineral oil 5.00N110 black 25.00N660 black 25.00Tensile strength MPa 11.9Stress @ 300% MPa 9.0Elongation @ break % 380Hardness IRHD 64.6Resilience @ 50.degree. C. % 61.4______________________________________Power loss 50.degree. C. 80.degree. C. 100.degree. C.______________________________________Elastic modulus (E') MPa 6.21 5.16 4.91Loss modulus (E") MPa 0.86 0.57 0.48Loss factor (E"/E") 0.138 0.111 0.097E"/(E*).sup.2 MPa.sup.-1 0.0218 0.0212 0.0195______________________________________

For the purposes of further comparison two rubber compositions of conventional formulation were obtained by blending together the following ingredients:

______________________________________ Parts by weight______________________________________Comparative composition TSMR-20 natural rubber 80.00IR309 20.00(low cis-polyisoprene)N375 black 52.50Santocure M.O.R. 0.70P.V.I.-50 0.40Stearic acid 2.00Zinc oxide 4.00Dutrex R.T. oil 6.00Arrconnox GP 2.00I.P.P.D. 0.50Paraffin wax 1.0040 mesh rubber crumb 5.00Sulphur 2.50 176.60Comparative composition COEP 1712 77.50SBR 1502 22.50N339 black 60.00Dutrex R.T. oil 5.00Process Oil 5.00Arrconnox GP 1.33I.P.P.D. 0.75Zinc oxide (indirect) 2.50Stearic acid 1.00Sulphur 1.75MBS 1.00Vulcatard A (vulcanisation 0.40retarder)40 mesh rubber crumb 5.00 183.73______________________________________

The compositions of Examples 6, 9, 10, 11 and 12 have been tested to assess their wet grip and rolling resistance properties on a road surface. Each of those compositions was used as the tread compound of model cross ply tires of size 2.25-8 (dimensions in inches). These model tires were subjected to two tests as follows.

Grip on a wet Delugrip road surface (Delugrip is a Trade Mark) was measured using the variable speed internal drum machine (VSIDM) described in a paper by G. Lees and A. R. Williams in Journal of the Institute of the Rubber Industry, Vol. 8, No. 3, June 1974. Measurements of the wet grip were made for both peak and locked wheel friction at speeds of 16, 32, 48, 64, 80 and 96 Km/hour) (10, 20, 30, 40, 50 and 60 mph) respectively. Rolling resistance was measured using the dynamics machine described in U.K. Pat. No. 1,392,033. Measurements were made at speeds of 20, 40, 60 and 80 km/hour respectively.

The results obtained from these tests are shown graphically in FIGS. 1 and 2 (relating to Example 6), FIGS. 3 and 4 (relating to Example 9), FIGS. 5 and 6 (relating to Example 10, FIGS. 9 and 10 (relating to Example 11) and FIGS. 11 and 12 (relating to Example 12) of the accompanying drawings.

The composition of Example 10 was further tested in the form of a tread compound of 155 SR 13 Dunlop SP4 tires, the rolling resistance being assessed by use of the dynamics machine referred to above and the wet grip by measurements of the deceleration of a Chrysler Avenger car adapted for front wheel braking only fitted with the tires. The results of these further tests are shown in FIGS. 7 and 8 of the accompanying drawings.

In the drawings the thick lines relate to the results obtained with the tires whose treads comprise vulcanised elastomer compositions of the stated Examples of the invention. The thin lines marked "C" or "T" relates respectively to the results obtained with tires whose treads comprise vulcanised comparative elastomer compositions (C or T) referred to above.

Claims

1. A tire having the combined properties of good grip on a wet road surface and low frictional resistance to rolling on the road, the tread of said tire comprising a material obtained by vulcanizing an elastomer blend comprising:

(a) as a major component a polymer selected from the group consisting of natural rubber, synthetic polyisoprene, rubbery styrene-butadiene copolymer and mixtures thereof having a glass transition temperature at most equal to -50.degree. C.; and

(b) as a minor component at least one resinous styrene-butadiene copolymer having a glass transition temperature above 15.degree. C.; said blend being substantially free of polybutadiene and said minor component being present in an amount up to 45% of the total weight of the major and minor components, which amount is effective to product said combined properties, and wherein said resinous styrene-butadiene copolymer has a styrene content in the range from 80-90% by weight.