Rubber composition containing hydroxyl terminated liquid polymer and tire with sidewall thereof

Abstract: This invention relates to a rubber composition comprised of a combination of cis 1,4-polybutadiene and at least one liquid hydroxyl terminated polyalkylene polymer together with a halogenated copolymer of isobutylene and p-methylstyrene and a minor amount of at least one conjugated diene-based elastomer, preferably cis 1,4-polyisoprene. The rubber composition contains particulate reinforcement as carbon black or as carbon black and silica together with a coupling agent. The invention also relates to a tire having a sidewall of such rubber composition.

Description: Field This invention relates to a rubber composition comprised of a combination of cis 1,4-polybutadiene and at least one liquid hydroxyl terminated polyalkylene polymer together with a halogenated copolymer of isobutylene and p-methylstyrene and optionally a minor amount of at least one conjugated diene-based elastomer, preferably cis-1,4-polyisoprene. The rubber composition contains particulate reinforcement as carbon black or as carbon black and silica together with a coupling agent. The invention also relates to a tire having a sidewall of such rubber composition. Background Pneumatic tires have sidewalls which are conventionally desired to have good flexibility yet be also scuff resistant. Accordingly, scuff resistance is desirable for a tire sidewall. However, flexibility is also a conventionally required attribute for rubber tire sidewalls. Historically, where a portion of a tire sidewall is of a color (e.g. white) in contrast with the remainder of tire, or sidewall (e.g. black), it is normally desired that the tire sidewall rubber composition be of a non-staining rubber composition to prevent, or at least retard, a staining of a tire sidewall having a color (e.g. white) other than the adjoining black color of the tire. This desirability is well known to those having skill in such art. However, it is also well known that, in general, tire sidewall rubber compositions typically contain ingredients that are considered to be staining in nature for colored sidewalls such as, for example, amine-based antidegradants, unless a rubber composition adjoining the colored (e.g. white) rubber composition in the sidewall is especially compounded to not contain such staining ingredient (e.g. does not contain amine-based antidegradant). Where it is desired that the sidewall rubber composition be non-staining in nature, or at least have a reduced tendency to stain, amine-based antidegradants are typically replaced with phenolic antioxidants in the rubber composition as is well known by those having skill in such art. However, use of phenolic antioxidants for a rubber sidewall composition are usually not as desirable as amine-based antioxidants for tire sidewalls simply because they are not effective for protection against ozone attack and resultant degradation of various properties of sulfur-vulcanized rubber compositions of diene-based elastomers. Historically, scuff resistance of a tire's rubber sidewall is conventionally enhanced, for example, by inclusion of cis 1,4-polybutadiene rubber in its rubber composition as is well known to those having skill in such art. Historically, flexibility of a tire's rubber sidewall, while conventionally provided by an inclusion of cis 1,4-polyisoprene in blends with high cis 1,4-polybutadiene rubber in its rubber composition, particularly natural rubber, may sometimes also be enhanced by an inclusion of an aromatic rubber processing oil in its composition, as is well known by those having skill in such art. It has been observed herein that the replacement of conventional rubber processing oils with selected hydroxyl terminated liquid polyalkylene-based polymers resulted in improved resistance to flex fatigue in the absence of amine-based antioxidants for a sulfur-cured tire sidewall rubber composition which was composed of cis 1,4-polybutadiene, a brominated copolymer of isobutylene and p-methylstyrene and a minor amount of cis 1,4-polyisoprene. It has further been observed herein that a replacement of conventional rubber processing oil in a tire sidewall elastomer composition of natural rubber (cis 1,4-polyisoprene) and cis 1,4-polybutadiene with a staining antioxidant (an amine-based antidegradant) resulted in no improvement in tire sidewall rubber composition flex endurance related properties. Therefore, a means of providing a tire with a suitably flexible sidewall yet maintaining resistance to ozone attack is desired in order to provide a tire sidewall of a conjugated diene rubber composition which also contains sufficient saturated, or essentially saturated with only minimal unsaturation, polymers so that it can be produced without a requirement for use of staining amine antidegradants. Historically, it has sometimes been proposed to use various diene-based liquid polymers which contain carbon-to-carbon double bond unsaturation to replace at least a portion of rubber processing oil contained in various rubber compositions. One philosophy has been for the liquid polymer to initially enhance the processability of a high viscosity unvulcanized rubber composition by reducing its viscosity and to later co-vulcanize with the elastomer upon vulcanizing the rubber composition. Such use of rubber processing oil and proposed use of unsaturated, diene-based liquid polymers is well known to those having skill in such art. Indeed, while rubber processing oils have been used to improve the processability of various unvulcanized high viscosity elastomers, the inclusion of processing oils in such rubber compositions often results in a decrease in their vulcanized modulus of elasticity. Accordingly, the use of substantial amounts of processing oils in rubber compounds for a purpose of enhancing their unvulcanized processability is not necessarily a desirable option. In the description of this invention, the term "phr" as used herein, and according to conventional practice, refers to "parts of a respective material per 100 parts by weight of rubber elastomer". The terms "rubber" and "elastomer" can be used interchangeably, unless otherwise distinguished. The terms "rubber composition", "compounded rubber" and "rubber compound" can be used interchangeably to refer to "rubber which has been blended or mixed with various ingredients and materials" and the terms "cure" and "vulcanize" may also be used interchangeably herein, unless otherwise noted and such terms are well known to those having skill in the rubber mixing or rubber compounding art. Practice and Summary of the Invention This invention relates to a rubber composition comprised of, based upon 100 parts by weight per 100 parts by weight elastomers (phr) (A) 100 parts by weight of (i) 30 to 70, alternately 35 to 65, phr of cis 1,4-polybutadiene rubber and (ii) from zero to 30, alternately 5 to 25, phr of cis 1,4-polyisoprene rubber, (B) 2 to 30, alternately 5 to 25, phr of liquid hydroxyl terminated polyalkylene polymer selected from at least one of (i) mono-hydroxyl terminated polymers with primary hydroxyl groups and (ii) di-hydroxyl terminated polymers with primary hydroxyl groups; wherein the alkylene mer units of said liquid polymer contains from 2 to 5, alternately from 2 to 4, carbon atoms, (C) 30 to 70, alternately 40 to 60, phr of brominated copolymer of isobutylene and p-methylstyrene comprising 85 to 99 weight percent units derived from isobutylene, and (D) 15 to 70 phr of carbon black reinforcing filler and from zero to 20 phr of amorphous silica. It is a significant aspect of this invention that the rubber composition is suitable for a tire sidewall rubber composition where high flex endurance properties over a considerable period of time and good resistance to atmospheric ozone degradation without use of an amine-based antioxidant in the rubber composition itself is desired. This is considered herein to be advantageous for a tire sidewall rubber composition in order to improve, or substantially maintain, visible tire sidewall surface appearance after aging while maintaining good durability properties of the sidewall rubber composition itself. Such rubber composition may also contain up to 15, preferably 2 to 15, phr of at least one additional diene-based elastomer selected from at least one of organic solvent solution polymerization prepared, or emulsion polymerization prepared, styrene/butadiene copolymer rubber, isoprene/butadiene copolymer and styrene/isoprene/butadiene terpolymer. Said additional solvent polymerization prepared elastomer may also be a tin coupled elastomer. In practice, the cis 1,4-polyisoprene rubber for the rubber composition may be natural or synthetic rubber, usually preferably natural rubber. In further accordance with this invention, an article of manufacture is provided having at least one component as the rubber composition of this invention. In additional accordance with this invention, a tire is provided having at least one component as the rubber composition of this invention. In further accordance with this invention, a tire, namely a rubber tire, is provided with a sidewall comprised of the rubber composition of this invention. In practice, it is preferred that said reinforcement is carbon black. If desired, silica, particularly amorphous silica which can include an aluminosilicate, can be present at a level of up to 20 phr (e.g. from 2 to 20 phr). As would be understood by those having skill in such art, a coupling agent would normally be used for said silica, although the silica might be used exclusive of a coupling agent. Such coupling agent normally has a moiety reactive with hydroxyl groups on the surface of the silica (e.g. silanol groups) and another moiety interactive with a said elastomer(s). Such coupling agent may be, for example, a bis-(3-triethoxysilylpropyl) polysulfide having an average of from 2 to 2.6 or from 3.5 to 4 connecting sulfur atoms in its polysulfide bridge. In practice, the polyalkylene component for said polyalkylene of said hydroxyl terminated polyalkylene is derived by hydrogenating, for example, anionically polymerized isoprene, 1,3-butadiene or combination thereof, thereby yielding a hydroxyl terminated polyalkylene comprised of at least one of ethylene, propylene and butylene units. In practice, said liquid hydroxyl terminated polyalkylene polymer preferably may have an equivalent weight range from 250 to 70,000, more preferably 500 to 7,000, so long as it is liquid at room temperature, or at 23°C, namely that it is readily pourable at such temperature. An example of suitable liquid hydroxyl terminated polyalkylene polymers are those available from Shell Chemical as Kraton L-1203 for a mono-hydroxyl terminated polymer and Kraton L-2203 for a di-hydroxyl terminated polymer. The brominated copolymer (C) comprises from 85 to 99 weight percent units derived from isobutylene and 1 to 15 weight percent units derived from para-methylstyrene. Desirably, the copolymer has a bromine content of up to 5 weight percent and, more preferably, from 0.2 to 1.5 or even up to 2.5 weight percent in the copolymer. Conjugated diene monomers having from 4 to 8 carbon atoms may optionally be present in amounts up to 5 or even to 8 weight percent and more desirably from 0.5 to 3 weight percent of the copolymer. The preferred copolymer of isobutylene and para-methylstyrene is essentially free of isoprene and other conjugated dienes (e.g. less than one percent and preferably less than 0.2 percent by weight of the copolymer. A preferred copolymer is post-brominated copolymer of isobutylene and para-methylstyrene as, for example, EXXPRO from the Exxon Chemical Company reportedly having a Mooney Viscosity ML(1-8) at 125°C of 50 +/- 10, an isobutylene content of 94 to 95 weight percent, and a para-methylstyrene content of 5 percent, with a total bromine content of 0.8 weight percent. EP-A- 0 344 021 contains a description of how to make such copolymer. Also, reference may be made to EP-A- 0 801 105. Such additional elastomers are typically derived from the polymerization of conjugated diene monomers which typically contain from 4 to 12 carbon atoms and preferably contain from 4 to 8 carbon atoms. Representative examples of such additional conjugated diene monomers include, for example, 1,3-butadiene and isoprene. The additional elastomer can also contain units derived from copolymerization of various vinyl aromatic monomers with one or more of such conjugated dienes such as, for example, styrene. An exemplary list of elastomers which can be prepared from the diene monomers and utilized in the rubber compositions of this invention include styrene/isoprene/butadiene rubber, styrene/butadiene rubber (SBR) whether solvent or emulsion polymerization prepared, isoprene/butadiene rubber and trans 1,4-polybutadiene. The rubber compositions of this invention can be prepared by simply mixing the liquid hydroxyl terminated polyalkylene polymer into the rubber elastomer. This can be done utilizing a wide variety of mixing techniques. In most cases, the mixing will be carried out utilizing a Banbury mixer or a mill mixer. It will generally be preferred to mix the liquid polymer into the elastomer during the non-productive compounding stage. However, in the alternative, the hydroxyl polyalkylene terminated polymer can be mixed throughout the elastomer in a separate mixing stage. In such case, it is advantageous to mix the hydroxyl liquid terminated liquid polymer into the elastomer before it is compounded with other materials to reap the benefits of improved processability during the preparation of the non-productive and productive compounds. It should be noted that the non-productive compounds do not contain a curative, such as sulfur, or accelerators for the curative. On the other hand, productive compounds contain a curative which will cure (vulcanize) the rubber after it is heated to a curing temperature. The rubber compositions of this invention will frequently contain a variety of additional compounding ingredients and/or additives. Typical amounts of processing aids and rubber compounding ingredients comprise 1 to 50 phr. Such processing aids can include, for example, aromatic, naphthenic, and/or paraffinic processing oils. Stearic acid is typically referred to as a "rubber compounding ingredient". As purchased, it typically contains primarily stearic acid with small amounts of at least one of oleic acid, linolenic acid and/or palmitic acid. The mixture may also contain small amounts (less than six weight percent) of myristic acid, arachidic acid and/or arachidonic acid. Such material, or mixture, is conventionally referred to in the rubber compounding art as "stearic acid". The vulcanization is conducted in the presence of a sulfur-vulcanizing agent. Examples of suitable sulfur-vulcanizing agents include elemental sulfur (free sulfur) or sulfur donating vulcanizing agents, for example, an amine disulfide, polymeric polysulfide, alkyl phenol polysulfides or sulfur olefin adducts. As known to those skilled in the art, sulfur-vulcanizing agents are used in an amount ranging from 0.5 to 4 phr, or even, in some circumstances, up to 8 phr, with a range of from 1.5 to 2.5, sometimes from 2 to 2.5, being preferred. It is to be appreciated, however, that the cure system, including desired cure package ingredients as well as the following discussion concerning cure accelerators, may vary depending upon the rubber compound ingredients, including the chosen polymers and elastomers. Accelerators are used to control the time and/or temperature required for vulcanization and to improve the properties of the vulcanizate. In one embodiment, a single accelerator system may be used, i.e., primary accelerator. Conventionally and preferably, a primary accelerator(s) is used in total amounts ranging from 0.5 to 4, preferably 0.8 to 2.8, phr. In another embodiment, combinations of a primary and a secondary accelerator might be used with the secondary accelerator being used in smaller amounts (of 0.05 to 3 phr) in order to activate and to improve the properties of the vulcanizate. Combinations of these accelerators might be expected to produce a synergistic effect on the final properties and are somewhat better than those produced by use of either accelerator alone. In addition, delayed action accelerators may be used which are not affected by normal processing temperatures but produce a satisfactory cure at ordinary vulcanization temperatures. Vulcanization retarders might also be used. Suitable types of accelerators that may be used in the present invention are amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates and xanthates. Some representative examples of primary accelerators which can be utilized include thiazole accelerators, such as benzothiazyldisulfide and 2-mercaptobenzothiazole; sulfenamide accelerators, such as N-oxydiethylene benzothiazole-2-sulfenamide, N-t-butyl-2-benzothiazolesulfenamide and N-cyclohexyl-2-benzothiazolesulfenamide; dithiocarbamate accelerators, such as bismuth dimethyldithiocarbamate, cadmium diethyldithiocarbamate, copper dimethyldithiocarbamate, lead dimethyldithiocarbamate, selenium diethyldithiocarbamate, tellurium diethyldithiocarbamate and zinc dimethyldithiocarbamate; thiuram accelerators such as dipentamethylene thiuram hexasulfide, tetramethylthiuram monosulfide and tetraethylthiuram monosulfide; and thiourea accelerators, such as trimethyl thiourea and dimethylethyl thiourea. If a second accelerator is used, the secondary accelerator is preferably a guanidine, dithiocarbamate or thiuram compound. As hereinbefore discussed in an alternative embodiment of this invention, the formulation can additionally contain silica, usually with a silica coupling agent; wherein the amount of particulate silica, namely an amorphous silica, ranges from zero to 20, optionally 2 to 10 or 15 phr and, wherein the silica coupling agent, if used, is used in an amount wherein the weight ratio of silica coupler to silica may be from 0.1/1 to 0.2/1. The commonly employed siliceous pigments used in rubber compounding applications can be used as the silica in this invention, including pyrogenic and precipitated siliceous pigments (silica), although precipitated silicas are preferred. The siliceous pigments preferably employed in this invention are precipitated silicas such as, for example, those obtained by the acidification of a soluble silicate, e.g., sodium silicate. The following examples are used to illustrate the invention. The parts and percentages are by weight unless otherwise indicated. EXAMPLE I (Comparative Example) A series of comparative samples were prepared to evaluate the use of liquid hydroxyl terminated polyalkylene polymers in diene-based rubber compositions which were reinforced with carbon black and referred to herein as Samples A-D. The diene-based elastomers are cis 1,4-polybutadiene rubber and cis 1,4-polyisoprene natural rubber. Control Sample A contained an aromatic rubber processing oil. It is to be appreciated that aromatic rubber processing are usually considered as being staining oils insofar as rubber compositions are concerned. Samples B and C rubber compositions were similar to Control Sample A except that they contained liquid hydroxyl terminated polyalkylene polymers and did not contain the aromatic rubber processing oil of Control Sample A. Sample D rubber composition was similar to Control Sample A except that they contained octadecanol and did not contain the aromatic rubber processing oil of Control Sample A. The Sample A-D rubber compositions are prepared of ingredients shown in the following Table 4 which represents a formulation in which 3.5 phr of aromatic rubber processing oil is shown as being "variable". Actual amounts of aromatic rubber processing oil are shown in the following Table 2. The Samples are prepared in a two stage, sequential, mixing process in an internal rubber mixer, namely, a non-productive mixing stage in an internal rubber mixer followed by a productive mixing stage in an internal rubber mixer. The elastomers, indicated compounding ingredients and processing oils are added in the first, non-productive mixing stage. The mixing is conducted in the first stage for four minutes to a temperature of 160°C, dumped from the internal mixer, open roll milled and cooled to below 30°C. The sulfur curative and accelerator(s) are added in a subsequent, productive, mixing stage for two and a half minutes to a temperature of 110°C. Parts First Non-Productive Mix Stage Natural rubber 40 Polybutadiene rubber 60 Carbon black 50 Resin oil as a tackifier 11 Zinc oxide 3.5 Fatty acid 1 Antdegradant 5.3 Wax 1 Processing oil variable Mono-hydroxyl terminated polyalkylene polymer variable Di-hydroxyl terminated polyalkylene polymer variable Octadecanol variable Productive Mix Stage Sulfur 1.6 Accelerators 0.7 The aforesaid series of Samples A-D, with Sample A being a Control, were prepared as described in this Example using the referenced "variable" amounts of processing oil and the Kraton liquid hydroxyl terminated polymers and octadecanol as shown in the following Table 2. The rubber compositions were vulcanized in a suitable mold by heating for 36 minutes to a temperature of 150°C. Various physical properties of the vulcanized rubber Samples A-D are also shown in the following Table 2. The stress-strain, hardness, and rebound physical properties were determined with a ring tensile specimen on an automated basis via an Automated Testing System (ATS) instrument. Ingredients Sample A Control Sample B Sample C Sample D Processing oil, aromatic 3.5 0 0 0 Mono-hydroxyl terminated polyalkylene polymer 0 3.5 0 0 Di-hydroxyl terminated polyalkylene polymer 0 0 3.5 octadecanol 3.5 Properties Rheometer (150°C) Max. torque, dNm 26.7 25.7 25.7 26.7 Min. torque, dNm 6.5 6 6 6.3 Delta torque 20.2 19.7 19.6 20.4 T 90 , minutes 19 20 21 19 Stress-Strain Tensile, MPa 13.8 13.4 13.4 13.4 Elongation, % 713 714 709 696 Modulus, 100%,MPa 1.4 1.3 1.3 1.4 Modulus, 300%, MPa 5.0 4.7 4.7 5.0 Rebound, 100°C, % 60.1 58 58.1 63.2 Hardness, Shore A, 100°C 46.2 44.6 44.7 46.1 Tear strength, N,95°C 136 114 121 121 Ozone, visual evaluation Static 1 , 25% 0 0 0 0 Kinetic , 25% 3 Edges Edges Edges Edges Cyclic , 20 days Edges Edges Edges Edges Rooftop, Kinetic 181 156 181 146 It is readily seen from Table 2 that the replacement of an aromatic processing oil with the liquid hydroxyl terminated polyalkylene polymers or octadecanol resulted in no improvement in physical properties of the cured Samples insofar as the aforesaid Static, Kinetic, Cyclic and Rooftop ozone exposure tests were concerned. EXAMPLE II A further series of Samples was prepared to evaluate the use of liquid hydroxyl terminated polyalkylene polymers in rubber compositions which contain cis 1,4-polybutadiene rubber, cis 1,4-polyisoprene rubber and a brominated copolymer of isobutylene and p-methylstyrene which may also contain a minor amount of isoprene. The Samples are referred to herein as Samples E-H with Sample E being a Control Sample and of the same composition of Sample A of Example I. It was mixed in this study for comparative purposes. Samples F-H contain the liquid hydroxyl terminated polyalkylene polymers, isobutylene/p-methylstyrene copolymer as well as cis 1,4-polyisoprene and cis 1,4-polybutadiene elastomers. One significant difference in the Samples E-H is the selection of oils for the individual formulations. In particular, an elastomer composition is prepared from ingredients shown in Table 3 which represents a formulation in which the amount of liquid hydroxyl terminated polyalkylene polymer are used in Samples F and G and octadecanol is used in Sample H. Actual amounts of each processing oil and liquid hydroxyl terminated polyalkylene polymers, or octadecanol, are shown in Table 4 and the Samples thereof identified therein as Samples EH together with various associated physical properties. The Samples F-H are prepared in a three stage, sequential, mixing process in an internal rubber mixer, namely a first and second non-productive mixing stage followed by a productive mixing stage. The elastomers, indicated compounding ingredients and liquid hydroxyl terminated polyalkylene polymer are added in the first, non-productive mixing stage. The second non-productive mixing stage is a re-mixing of the ingredients added in the aforesaid first mixing stage. The mixing is conducted in the first stage for four minutes to a temperature of 160°C, dumped from the internal mixer, open roll milled for 30 seconds and cooled to below 30°C. The rubber composition is then re-mixed in the second mixing stage for two minutes to a temperature of 150°C. The mixture was dumped from the mixer, open roll milled for 30 seconds and allowed to cool to below 30°C. The sulfur curative and accelerator(s) are added in a subsequent productive mixing stage for two minutes to a temperature of 110°C. The various ingredients are shown in the following Table 3. A second non-productive mixing in an internal rubber mixer is used between the first non-productive mix stage and productive mix stage, as hereinbefore described, and without additional ingredients. Parts First Non-Productive Mix Stage Natural rubber 10 Polybutadiene rubber 50 Exxpro 40 Carbon black 40 Tackifier/fatty acid 11 Naphthenic/paraffinic rubber processing oil 7 Liquid polymer zero or 5 Liquid polymer zero or 5 Octadecanol zero or 5 Productive Mix Stage Zinc oxide 0.75 Stearic acid 0.5 Sulfur 0.4 Accelerators 1.9 The Samples were prepared from the formulation represented in Table 3 using the referenced "variable" amounts of processing oil as shown in the following Table 4. The rubber compositions were vulcanized in a suitable mold by heating for 36 minutes to a temperature of 150°C. Various physical properties of the vulcanized rubber Samples E-H are also shown in the following Table 4. The stress-strain, hardness, and rebound physical properties were determined with a ring tensile specimen on an automated basis via an Automated Testing System (ATS) instrument. Ingredients Sample E Control Sample F Sample G Sample H (Comparative) Processing oil, aromatic 0 7 7 7 Mono-hydroxyl terminated polyalkylene polymer 0 5 0 0 Di-hydroxyl terminated polyalkylene polymer 0 0 5 0 Octadecanol 0 0 0 5 Properties Rheometer (150°C) Max Torque, dNm 27.0 23.7 23.0 23.9 Min Torque, dNm 5.4 4.3 4.5 4 Delta torque 21.6 19.4 18.5 19.9 T 90 , minutes 19 19 18.5 19.9 Stress-Strain Tensile, MPa 13.4 10.5 10.4 10.8 Elongation, % 677 605 596 657 Modulus, 100%,MPa 1.3 1.4 1.3 1.4 Modulus, 300%, MPa 5.2 5.3 5.0 4.8 Rebound, 100°C, % 57.8 64.9 67.6 69.1 Hardness, Shore A, 100°C 45.7 42.2 41.0 41.5 Tear strength, N, 95°C 132 39 38 38 Ozone Testing 1 Static test 0 0 0 0 Kinetic 2 , 25°C Edges 0 0 0 Cyclic 3 , 18 days Edges 0 0 0 Rooftop 4 , Kinetic, 25%, Kinetic days to failure (434 day test) 185 193 434 193 Pierced groove flex, cm/min. (240 min.) 0 0.0018 0 0.0069 The Static Ozone test visual results show that no cracking of the Samples was observed. The Kinetic test visual results show that Samples F, G and H are better than the natural rubber/polybutadiene composed Control Sample E. The Cyclic test visual results show the same superiority of Samples F, G and H over Control Sample E. The Rooftop test visual results show that Samples F, G and H are equal to or better than the Control Sample E for flex life. The Pierced Groove Flex test results show that the hydroxyl and di-hydroxyl polymer-containing rubber compositions, namely Samples F and G, illustrated the best cut growth resistance as compared to the octadecanol-containing Sample H. It is readily seen from Table 4 that fatigue resistance properties, of cured Samples F and G are similar to or better than those of the Control Sample E and ozone resistance for cured Samples F, G and H is better than Control Sample E. Sample H is observed to have improved ozone resistance compared to that of Control Sample E but not as good cut growth and flex resistance as cured Samples F and G. This is considered herein to be particularly advantageous for a tire sidewall rubber composition because the Samples F-G exhibit cut growth flex life (resistance to flex fatigue) and excellent ozone resistance without the presence of the staining amine-based antidegradant used in Control Sample E. EXAMPLE III A series of additional Samples were prepared to evaluate the use of liquid hydroxyl terminated polyalkylene polymers in diene-based rubber compositions, which contained cis 1,4-polyisoprene, cis 1,4-polybutadiene elastomers as well as a brominated isobutylene/p-methylstyrene copolymer, and which were reinforced with carbon black and referred to herein as Samples I-K, with Sample I being a Control Sample. Control Sample I is the same composition as Control Samples A and E in Examples I and II. It was mixed for this Example. Sample J contained 12 phr of processing oil and the composition and mixing conditions are the same as shown in Table 3 for Samples F, G and H. Samples K-N rubber compositions are similar to Sample J except that they contained liquid hydroxyl terminated polyalkylene polymers at 5 phr or 12 phr as replacements for the rubber processing oil of Sample J. Control Sample I was prepared as described in Example I for Control Sample A. Samples K-N were prepared according to the sample preparation in Example II shown in Table 3. Actual amounts of rubber processing oil and liquid hydroxyl terminated polyalkylene polymers are shown in the following Table 5. The Samples (J-N) were prepared in a three stage, sequential, mixing process in an internal rubber mixer, namely, a first non-productive mixing stage in an internal rubber mixer in which the indicated ingredients were added, followed by a second non-productive mixing stage in an internal rubber mixer where no additional ingredients were added, followed by a productive mixing stage in an internal rubber mixer in which the sulfur curatives were added. The rubber compositions were vulcanized in a suitable mold by heating for about 36 minutes to a temperature of about 150°C. Various physical properties of the vulcanized rubber Samples I-N are also shown in the following Tables 5 and 5A. Ingredients Sample I Control Sample J (Comparative Sample K Processing oil, naphthenic/paraffinic 0 12 7 Mono-hydroxyl terminated polyalkylene polymer 0 0 5 Properties Rheometer (150°C) Max Torque, dNm 26.9 24 23.1 Min Torque, dNm 6.2 4.6 5.1 Delta torque 20.7 19.4 18 T90, minutes 19.3 21.5 21.4 Stress-Strain Tensile, MPa 13.8 9.3 9.3 Elongation, % 705 595 642 Modulus, 100%. MPa 1.3 1.3 1.3 Modulus, 300%, MPa 4.9 4.5 4.2 Rebound, 100°C, % 58.6 65.2 63.8 Hardness, Shore A, 100°C 46 41 41 Tear strength, N, 95°C 138 35 40 Static 1 , 25% 0 0 0 Kinetic 2 , 25% Edges 0 0 Cyclic 3 , 20 days Edges 0 0 Rooftop, Kinetic4, 372 days maximum 83 24 373 Ingredients Sample L Sample M Sample N Processing oil, naphthenic/paraffinic 0 7 0 Mono-hydroxyl terminated polyalkylene polymer 12 5 12 Properties Rheometer (150°C) Max Torque, dNm 21.9 23.7 22.5 Min Torque, dNm 5.1 5.5 5.4 Delta torque 16.8 18.2 17.1 T 90 , minutes 19.9 21.4 21.2 Stress-Strain Tensile, MPa 11.2 9.1 11 Elongation, % 715 638 698 Modulus, 100%. MPa 1.3 1.3 1.3 Modulus, 300%, MPa 4.4 4.1 4.3 Rebound, 100°C, % 62.5 65.1 61.1 Hardness, Shore A, 100°C 40 41-40 41 Tear strength, N, 95°C 42 30 45 Static , 25% 0 0 0 Kinetic , 25% 3 0 0 0 Cyclic , 20 days 0 0 0 Rooftop, Kinetic , 372 days maximum 372 372 372 It is readily seen from Table 5 that the replacement of a naphthenic/paraffinic processing oil with the liquid hydroxyl terminated polyalkylene polymers resulted in an improvement in Kinetic, Cyclic and Rooftop ozone test results. This is considered herein to be significant because an improved sidewall appearance obtained without ozone cracking of the rubber compound normally requires the use of non-staining antidegradants. Also, as hereinbefore discussed, the use of non-staining antidegradants often provides poor flex behavior of the rubber compound. However, it is shown in this Example that the combination of good ozone resistance and flex resistance is obtainable without the use of amine type (non-staining) antidegradants. It is also readily observed from Table 5 that Samples K-N are superior to Control Sample I of the natural rubber/cis 1,4-polybutadiene rubber composition as well as Control J which used the same rubber composition without the liquid hydroxyl terminated polyalkylene polymers.

Claims: A rubber composition characterized by being comprised of, based upon 100 parts by weight per 100 parts by weight elastomers (phr) (A) 100 parts by weight of (i) from 30 to 70 phr of cis 1,4-polybutadiene rubber and (ii) from zero to 40 phr of cis 1,4-polyisoprene rubber, (B) 2 to 30 phr of liquid hydroxyl terminated polyalkylene polymer selected from at least one of (i) mono-hydroxyl terminated polymers with primary hydroxyl groups and (ii) di-hydroxyl terminated polymers with primary hydroxyl groups; wherein the alkylene mer units of said liquid polymer contains from 2 to 5 carbon atoms, (C) 30 to 70 phr of brominated copolymer of isobutylene and p-methylstyrene comprised of 85 to 99 weight percent units derived from isobutylene, and (D) reinforcing filler comprised of 15 to 70 phr of carbon black reinforcing filler and from zero to 20 phr of amorphous silica. The rubber composition of claim 1 characterized in that said elastomers are comprised of (i) from 35 to 65 phr of cis 1,4-polybutadiene and (ii) from 5 to 25 phr of cis 1,4-polyisoprene. The rubber composition of any of the preceding claims characterized in that said rubber composition also contains 2 to 15 phr of at least one additional elastomer selected from at least one of (A) organic solvent polymerization prepared, (B) emulsion polymerization prepared and (C) tin coupled solvent polymerization prepared styrene/butadiene copolymer, isoprene/butadiene copolymer rubber and styrene/isoprene/butadiene terpolymer. The rubber composition of any of the preceding claims characterized in that said brominated copolymer also contains from 0.5 to three weight percent units derived from isoprene. The rubber composition of any of the preceding claims characterized in that said hydroxyl terminated polyalkylene is an hydrogenated elastomer of anionically polymerized isoprene, 1,3-butadiene or combination thereof. The rubber composition of any of the preceding claims 1 through 4 characterized in that said polyalkylene portion of said hydroxyl terminated polyalkylene comprised of at least one of ethylene, propylene and butylene units, has an equivalent weight range from 250 to 70,000, provided that it is characterized by being a liquid at 23°C and wherein said liquid hydroxyl terminated polyalkylene polymer is selected from at least one of mono-hydroxyl terminated polymer(s) and di-hydroxyl terminated polymer(s). The rubber composition of any of the preceding claims characterized in that said reinforcement is (A) carbon black or (B) carbon black and amorphous silica; wherein said silica is present in an amount of from 2 to 15 phr and contains a silica coupling agent having a moiety reactive with hydroxyl groups on the surface of said silica and another moiety interactive with said elastomer(s). The rubber composition of claim 7 characterized in that said coupling agent is a bis (3-triethoxysilylpropyl) polysulfide having an average of from 2 to 2.6 or from 3.5 to 4 connecting sulfur atoms in its polysulfidic bridge. A tire characterized by having at least one component comprised of the rubber composition of any of the preceding claims 1 through 8. A tire characterized by having a sidewall comprised of the rubber composition of any of the preceding claims 1 through 8.

Inventors: SANDSTROM PAUL HARRY, SANDSTROM, PAUL HARRY
Applicants: GOODYEAR TIRE & RUBBER, THE GOODYEAR TIRE & RUBBER COMPANY
Application year: 2000
Main classification: C08L21
IPC codes: C08L23, C08K3, C08L9, B60C1, C08L21, C08L101