WO1993009178A1

WO1993009178A1 - Tire and belt compositions

Info

Publication number: WO1993009178A1
Application number: PCT/EP1992/001030
Authority: WO
Inventors: Andreas Herman Hogt; Auke Gerardus Talma; Rudolf Frank De Block; Rabindra Nath Datta
Original assignee: Akzo NV
Current assignee: Akzo NV
Priority date: 1991-10-29
Filing date: 1992-05-07
Publication date: 1993-05-13
Anticipated expiration: 1994-04-29
Also published as: BR9206688A; EP0610197A1; FI941968A0; FI941968A7; FI941968L; SK49694A3; JPH07500616A; CZ104794A3; CA2122347A1

Abstract

The present invention relates to a tire wherein at least one of the tread, steel-cord skim stock, sidewall and carcass portions contains a rubber composition formed by curing a blend of a. natural rubber, polyisoprene or a mixture thereof, b. butadiene rubber, styrene-butadiene rubber or a mixture thereof, c. carbon black, d. activator, e. zinc oxide, f. sulfur or a sulfur donor, and g. curing accelerator, characterized in that said rubber composition has a heat buildup of 20-35 °C. These tires exhibit one or more improvements in a wide variety of properties. The present invention relates also to a belt which contains such a rubber composition, characterized in that said rubber composition has a heat buildup of 10-25 °C. These belts exhibit also one or more improvements in a variety of properties.

Description

Tire and Belt Compositions

The present invention relates to tires and belts which have improved properties as compared to standard tire and belt compositions. The inventors have found that tire and belt compositions having a reduced heat buildup exhibit improved properties, especially when subjected to environments which lead to ageing of the rubber compositions.

The importance of heat buildup is recognized in the article, "Carbon Black in NR/BR Blends for Truck Tires," Rubber Chemistry and Technology, Vol. 58, pp. 350-368 (1985), wherein it is stated that treadwear, heat buildup, resistance to cutting and chipping and fuel economy are important to heavy duty truck tire performance. Accordingly, there is a need in the art for tire and belt products which exhibit a low heat buildup, since such products exhibit a better performance as well as having, in many cases, a longer service life.

Many attempts have been made to produce products with a low heat buildup. For example, European Patent application 0314271 discloses the use of an improved processing aid to improve handling, durability and rolling resistance of tires, as well as reducing heat buildup.

European Patent application 0451 603 relates to the use of an anionic polymerization initiator for curing elastomers to improve their hysteresis. Improved hysteresis leads to tires having a lower rolling resistance. One aspect of hysteresis is heat buildup.

PCT patent application WO 91/05821 discloses a tire sidewall composition comprising a particular polymer which leads to sidewalls having a desirable reduced internal heat buildup and improved adhesion to adjacent rubber carcass and tread portions of the tire. Finally, the publication, "Natural Rubber Compounds for Truck Tires," NR Technology, Vol. 16, Part 1 (1985) suggests the use of additional stearic acid activator in order to reduce the heat generation, among other properties, in truck tires.

However, all of these solutions fall short of the goal of providing tires and belts with longer service life, better ageing characteristics, lower rolling resistance and better fuel economy. The present inventors have surprisingly found that tire and belt compositions having a particular heat buildup exhibit several improved properties, particularly when the tires and belts are subjected to service conditions. More specifically, the present invention relates, in one aspect to a tire wherein at least one of the tread, steel-cord skim stock, sidewall and carcass portions contains a rubber composition formed by curing a blend of at least: 50-100 weight percent of natural rubber, polyisoprene or a mixture thereof,

0-50 weight percent of butadiene rubber, styrene-butadiene rubber or a mixture thereof,

20-65 phr, based on the total rubber content, of carbon black,

0.5-4.0 phr of activator,

1.0-10.0 phr of zinc oxide,

1.0-10.0 phr of sulfur or a sulfur donor, and

0.5-5.0 phr of curing accelerator, characterized in that said rubber composition has a heat buildup of 20-35°C. These tires exhibit one or more improvements in a wide variety of properties such as abrasion resistance, rolling resistance, ageing resistance, adhesion to steel, cutting and chipping resistance and service life. In a second aspect, the present invention relates to a belt which contains a rubber composition formed by curing a blend of at least:

50-100 weight percent of natural rubber, polyisoprene or a mixture thereof,

20-65 phr, based on the total rubber content, of carbon black,

0.5-4.0 phr of activator,

1.0-10.0 phr of zinc oxide,

1.0-10.0 phr of sulfur or a sulfur donor, and

0.1-5.0 phr of curing accelerator, characterized in that said rubber composition has a heat buildup of 10-25°C. These belts exhibit one or more improvements in a variety of properties including tear strength, tensile strength, service life and ageing resistance.

The low heat buildup rubber compositions of the present invention can be used in tire treads for truck tires and off-the-road tires, in particular, for sidewalls, for tire carcasses and for steel-cord skim stocks. In belts, the rubber compositions of the present invention are particularly useful for conveyor belts and V-belts which are subjected to high loading and abrasion in service.

A typical truck tire tread composition in accordance with the present invention comprises the cured product of a blend containing:

50-100 weight percent of natural rubber, polyisoprene or a mixture thereof,

45-65 phr, based on the total rubber content, of carbon black,

1.0-3.0 phr of activator, 1.0-10.0 phr of zinc oxide,

1.0-5.0 phr of sulfur or a sulfur donor, and

0.5-5.0 phr of curing accelerator. Of course, these truck tire treads may contain other conventional additives such as 0-20 phr silica, 2-10 phr tackifier, 5-50 phr of processing oil, 1-5 phr waxes, 1-5 phr antioxidant and 1-5 phr antiozonants. Important properties for truck tire treads include abrasion resistance, rolling resistance, resistance to cracking, thermal and oxidative stability and durability.

A typical steel-cord skim stock composition in accordance with the present invention is the cured product of a blend comprising:

85-100 weight percent of natural rubber, polyisoprene or a mixture thereof,

0-15 weight percent of butadiene rubber, styrene-butadiene rubber or a mixture thereof,

45-65 phr, based on the total rubber content, of carbon black having an average particle size of 10-30 nm,

0.5-2.0 phr of activator,

1.0-10.0 phr of zinc oxide,

4.0-8.0 phr of sulfur or a sulfur donor, and

0.5-1.5 phr of curing accelerator.

These steel-cord skim stocks may also contain 0-20 phr silica, 0-2.0 phr of a cobalt salt and 1-3 phr of antidegradants. Adhesion to steel is an important property for this portion of the tire.

A typical carcass portion of a tire in accordance with the present invention is the cured product of a blend comprising: 50-80 weight percent of natural rubber, polyisoprene or a mixture thereof,

20-50 weight percent of butadiene rubber, styrene-butadiene rubber or a mixture thereof,

20-50 phr, based on the total rubber content, of carbon black having an average particle size of 45-70 nm,

1.0-3.0 phr of activator,

1.0-10.0 phr of zinc oxide,

2.0-5.0 phr of sulfur or a sulfur donor, and

0.5-5.0 phr of curing accelerator.

These carcass portions may also contain 1-3 phr antioxidant and 2-8 phr processing oil, if desired. Important properties for the carcass portion are the thermal resistance and the rebound resilience.

A typical sidewall portion of a tire in accordance with the present invention is the cured product of a blend comprising:

50-100 weight percent of natural rubber, polyisoprene or a mixture thereof,

40-60 phr, based on the total rubber content, of carbon black having an average particle size of 20-70 nm,

1.0-4.0 phr of activator,

2.0-6.0 phr of zinc oxide,

1.0-3.0 phr of sulfur or a sulfur donor, and

0.5-1.5 phr of curing accelerator. These sidewall portions may also contain from 5-10 phr of whitening. Important properties for the sidewall portion are fatigue resistance, ozone resistance, cutting and chipping resistance and reversion resistance. A typical off-the-road tire tread in accordance with the present invention is the cured product of a blend which comprises:

80-100 weight percent of natural rubber, polyi soprene or a mixture thereof,

0-20 weight percent of butadiene rubber, styrene-butadiene rubber or a mixture thereof,

20-50 phr, based on the total rubber content, of carbon black having an average particle size of 10-30 nm,

1.0-3.0 phr of activator,

1.0-10.0 phr of zinc oxide,

10-25 phr of silica having a surface area of 100-200 irμ/g,

1.0-2.0 phr of sulfur or a sulfur donor, and

1.0-2.0 phr of curing accelerator.

Off-the-road tire treads may also include 5-50 phr of processing oil, 0-5 phr of resin, 0-2 phr wax, 1-4 phr antiozonants and 0.5-2.0 phr antioxidants. Important properties for off-the-road tire treads are tread wear, cutting and chipping resistance and hysteresis.

A typical conveyor belt in accordance with the present invention is the cured product of a blend comprising:

95-100 weight percent of natural rubber, polyisoprene or a mixture thereof,

0-5 weight percent of butadiene rubber, styrene-butadiene rubber or a mixture thereof,

30-50 phr, based on the total rubber content, of carbon black having an average particle size of 20-40 nm.,

0.5-4.0 phr of activator,

1.0-10.0 phr of zinc oxide,

1.0-10.0 phr of sulfur or a sulfur donor, and

0.1-5.0 phr of curing accelerator. Other additives such as 1-4 phr antiozonants, may be employed. Important properties for conveyor belts are fatigue resistance, abrasion resistance and tear strength. A typical V-belt in accordance with the present invention is the cured product of a blend comprising:

50-100 weight percent of natural rubber, polyisoprene or a mixture thereof,

30-65 phr, based on the total rubber content, of carbon black having an average particle size of 20-100 nm,

0.5-4.0 phr of activator,

1.0-10.0 phr of zinc oxide,

1.0-10.0 phr of sulfur or a sulfur donor, and

0.1-5.0 phr of curing accelerator.

Other additives such as 1-4 phr antiozonants, may be employed. Important properties for V-belts are fatigue resistance and service life.

Examples of sulfur which may be used in the present invention include various types of sulfur such as powdered sulfur, precipitated sulfur and insoluble sulfur. Also, sulfur donors may be used in place of, or in addition to sulfur in order to provide the required level of sulfur during the vulcanization process. Examples of such sulfur donors include, but are not limited to, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, dipentamethylene thiuram hexasulfide, dipentamethylene thiuram tetrasulfide, dithiodimorpholine, caprolactam disulfide and mixtures thereof. In this text, references to sulfur shall include sulfur donors and mixtures of sulfur and sulfur donors. Further, references to the quantity of sulfur employed in the vulcanization, when appl ied to sulfur donors, refer to a quantity of sulfur donor which is required to provide the equivalent amount of sulfur that is specified.

In most circumstances it is also desirable to have a vulcanization accelerator in the rubber compound. Conventional , known vulcanization accelerators may be employed. The preferred vulcanization accelerators include mercaptobenzothiazole, 2,2'-mercaptobenzothiazole disulfide, sulfenamide accelerators including

N-cyclohexyl-2-benzothi azole sulfenamide,

N-tertiary-butyl-2-benzothiazole sulfenamide,

N,N'-dicyclohexyl-2-benzothiazole sulfenamide, and

2-(morpholinothio)benzothiazole; thiophosphoric acid derivative accelerators, thiurams, dithiocarbamates, diphenyl guanidine, diorthotolyl guanidine, dithiocarbamyl sulfenamides, xanthates, triazine accelerators and mixtures thereof. Other rubber additives may also be employed in their usual amounts. For example, reinforcing agents such as carbon black, silica, clay, whiting and other mineral fillers, as wel l as mixtures of fillers, may be included in the rubber composition. Other additives such as process oils, tackifiers, waxes, anti oxidants, antiozonants, pigments, resins, plasticizers, process aids, factice, compounding agents and activators such as stearic acid and oleic acid, and zinc oxide may be included in the listed amounts. For a more complete listing of rubber additives which may be used in combination with the present invention see, W. Hofmann, "Rubber Technology Handbook", Chapter 4, Rubber Chemicals and Additives, pp. 217-353, Hanser Publishers, Munich 1989.

Further, scorch retarders such as phthalic anhydride, pyromellitic anhydride, benzene hexacarboxylic trianhydride, 4-methylphthalic anhydride, trimellitic anhydride, 4-chlorophthalic anhydride, N- cyclohexyl-thiophthalimide, salicylic acid, benzoic acid, maleic anhydride and N-nitrosodiphenylamine may also be included in the rubber composition in conventional, known amounts. Finally, in specific applications it may also be desirable to include steel-cord adhesion promoters such as cobalt salts and dithiosulfates in conventional, known quantities.

The process of curing the blends of the present invention is preferably carried out at a temperature of 110-220°C over a period of up to 24 hours. More preferably, the process is carried out at a temperature of 120-190°C over a period of up to 8 hours. All of the additives mentioned above with respect to the rubber composition may also be present during the vulcanization process. In a more preferred embodiment of the vulcanization process, the vulcanization is carried out at a temperature of 120-190°C over a period of up to 8 hours and in the presence of at least one vulcanization accelerator. The best heat buildup in accordance with the present invention is found when vulcanization is carried out at a temperature above 160°C and/or for a period exceeding t₉₀.

The tire and belt products of the present invention have reduced heat buildup. With respect to the tire products, they exhibit a heat buildup of 20-35°C whereas the belt products exhibit a heat buildup of from 10-35°C.

Heat buildup, for the purposes of the present specification, was measured using ASTM 623 A at a starting temperature of 100°C. The actual heat buildup is the temperature rise from 100°C to the temperature at which equilibrium was reached. Equilibrium temperature is when the temperature stabilizes and does not rise any further. Note that for some prior art products, the temperature never stabilizes. One way to produce products in accordance with the present invention is to carry out the curing of the blend in the presence of 0.1-5.0 parts by weight of a coagent represented by the general formula A:

Ql-D-(Q₂)n (A); wherein D, optionally containing one or more heteroatoms or groups selected from nitrogen, oxygen, silicon, phosphorus, boron, sulphone and sulphoxy, is a monomeric or oligomeric divalent, trivalent or tetravalent group, n is an integer selected from 1, 2 or 3, Q₁ and Q₂ are independently selected from the formulas I and II:

and;

wherein R₁ , R₂ and R₃ are i ndependently selected from hydrogen, C₁-C₁₈ al kyl groups, C₃-C₁₈ cycloal kyl groups, C₆-C₁₈ aryl groups, C₇-C₃₀ aral kyl groups and C₇-C₃₀ al karyl groups and R₂ and R₃ may combine to form a ring when R₁ is hydrogen; B and B₁ are independently selected from the fol lowing hetero atoms: oxygen and sulfur. These imides are, in general, known compounds and may be prepared by the methods disclosed in, "The synthesis of Biscitraconimides and Polybiscitraconimides," Galanti, A.V. and Scola, D.A., Journ. of Poly. Sci.: Polymer Chemistry Edition, Vol. 19, pp. 451-475, (1981); and "The Synthesis of Bisitaconamic Acids, Isomeric Bisimide Monomers," Galanti, A.V. et al., Journ. Poly. Sci.: Polymer Chemistry Edition, Vol. 20, pp. 233-239 (1982) and Hartford, S.L., Subramanian, S. and Parker, J.A., Journ. Poly. Sci.: Polymer Chemistry Edition, Vol. 16, p. 137, 1982, the disclosures of which are hereby incorporated by reference. Particularly useful imide compounds are disclosed in PCT patent application PCT/EP 91/02048.

The invention is further illustrated by the following examples which are not to be construed as limiting the invention in any way. The scope of the invention is to be determined from the claims appended hereto.

EXPERIMENTAL METHODS USED IN THE EXAMPLES

Compounding, Vulcanization and Characterization of Compounds

In the following examples, rubber compounding, vulcanization and testing was carried out according to standard methods except as otherwise stated:

Base compounds were mixed in a Farrel Bridge BR 1.6 liter Banbury type internal mixer (preheating at 50°C, rotor speed 77 rpm, mixing time 6 min with full cooling).

Vulcanization ingredients and coagents were addded to the compounds on a Schwabenthan Polymix 150L two-roll mill (friction 1:1.22, temperature 70°C, 3 min). Optimum cure time (t₉₀) is the time to 90% of delta torque above minimum, reversion time (t_r2) is the time to 2% of delta torque below maximum torque. Final torque (Tf) is the torque measured after the overcure time.

Sheets and test specimens were vulcanized by compression molding in a Fontyne TP-400 press.

Tensile measurements were carried out using a Zwick 1445 tensile tester (ISO-2 dumbbells, tensile properties according to ASTM D 412-87, tear strength according to ASTM D 624-86).

Hardness was determined according to DIN 53505, and ISO 48 (IRHD). Rebound resilience was measured at room temperature (RT) according to ASTM D 1054-87.

Compression set was determined after 24 h at 70°C or 72 h at 23°C according to ASTM D 395-89.

Heat build-up temperature rise and compression set after dynamic loading were determined using a Goodrich Flexometer (load 1 MPa, stroke 0.445 cm, frequency 30 Hz, start temperature 100°C, running time 30 min; ASTM D 623-78). Blow out time was determined according to ASTM D 623-78 (load 2 MPa, stroke 0.645 cm, frequency 30 Hz, start temperature 100°C).

Abrasion was determined using a Zwick abrasion tester as volume loss per 40 m path travelled (DIN 53516).

Ageing of test specimens was carried out in a ventilated air oven at 70°C or 100°C for periods up to 14 days (ISO 188) Examples 1-3 and Comparative Example A

Examples 1-3 and Comparative Example A are formulations for truck tire treads. The components of each formulation are given in Table 1 and the physical and mechanical properties for different curing conditions are given in Tables 2a-2d. The heat buildup and permanent set are given for different curing conditions in Tables 3a-3b.

Example 4 and Comparative Example B

Example 4 and Comparative Example B are also formulations for truck tire treads. The components of each formulation are given in Table 4 and the physical and mechanical properties for different curing conditions are given in Tables 5a-5b. The heat buildup and permanent set are given for different curing conditions in Tables 6a-6b.

Examples 5-7 and Comparative Examples C-D

Examples 5-7 and Comparative Examples C-D are formulations for off- the-road tire treads. The components of each formulation are given in Table 7 and the physical and mechanical properties for different curing conditions are given in Tables 8a-8d. The heat buildup and permanent set are given for different curing conditions in Tables 9-10.

Example 8 and Comparative Examples E-F

Example 8 and Comparative Examples E-F are formulations for conveyor belts. The components of each formulation are given in Table 11 and the physical and mechanical properties for different curing conditions are given in Tables 12a-12b. The heat buildup and permanent set are given for different curing conditions in Table 13.

Claims

Claims:

1. A tire wherein at least one of the tread, steel-cord skim stock, sidewall and carcass portions contains a rubber composition formed by curing a blend of at least:

50-100 weight percent of natural rubber, polyisoprene or a mixture thereof,

20-65 phr, based on the total rubber content, of carbon black,

0.5-4.0 phr of activator,

1.0-10.0 phr of zinc oxide,

1.0-10.0 phr of sulfur or a sulfur donor, and

0.5-5.0 phr of curing accelerator, characterized in that said rubber composition has a heat buildup of 20-35°C.

2. A tire wherein said tread portion contains a blend in accordance with claim 1 which contains 45-65 phr of carbon black.

3. A tire as claimed in any one of claims 1-2 wherein said steel -cord skim stock portion contains a blend in accordance with claim 1 containing 85-100 weight percent of natural rubber, polyisoprene or a mixture thereof and 0-15 weight percent of butadiene rubber, styrene-butadiene rubber or a mixture thereof, and wherein said carbon black has an average particle size 10-30 nm.

4. A tire as claimed in any one of claims 1-3, wherein said carcass portion contains a blend in accordance with claim 1 containing 50-80 weight percent of natural rubber, polyisoprene, or a mixture thereof, 20-50 weight percent of butadiene rubber, styrene butadiene rubber or a mixture thereof, and 20-50 phr of carbon black having an average particle size of 45-70 nm.

5. A tire as claimed in any one of claims 1-4, wherein said sidewall portion contains a blend in accordance with claim 1 containing

40-60 phr of carbon black having an average particle size of 20-70 nm.

6. A tire as claimed in any one of claims 1 and 3-5 wherein said tread portion contains a blend in accordance with claim 1 containing 80-100 weight percent of natural rubber, polyisoprene or a mixture thereof, 0-20 weight percent of butadiene rubber, styrene-butadiene rubber or a mixture thereof, 20-50 phr carbon black having an average particle size of 10-30 nm., and 10-25 phr of silica having a surface area of 100-200 m²/g.

7. A tire as claimed in any one of claims 1-6 wherein said blend is cured at a temperature above 160°C to form said rubber composition.

8. A tire as claims in any one of claims 1-7 wherein said blend is cured for a time period of greater than t₉₀.

9. A tire as claimed in any one of claims 7-8 wherein the heat buildup of said rubber composition is 20-30°C.

10. A belt which contains a rubber composition formed by curing a blend of at least: 50-100 weight percent of natural rubber, polyisoprene or a mixture thereof,

20-65 phr, based on the total rubber content, of carbon black,

0.5-4.0 phr of activator,

1.0-10.0 phr of zinc oxide,

1.0-10.0 phr of sulfur or a sul fur donor, and

0.1-5.0 phr of curing accelerator, characterized in that said rubber composition has a heat buildup of 10-25°C.

11. A conveyor belt as claimed in claim 10 wherein said blend comprises 95-100 weight percent of natural rubber, polyisoprene or a mixture thereof, 0-5 weight percent of butadiene rubber, styrene-butadiene rubber or a mixture thereof and 30-50 phr of carbon black having an average particle size of 20-40 nm.

12. A V-belt as claimed in claim 10 wherein said blend comprises 50-100 weight percent of natural rubber, polyisoprene or a mixture thereof, 0-50 weight percent of butadiene rubber, styrenebutadiene rubber or a mixture thereof and 30-65 phr of carbon black having an average particle size of 20-100 nm.