Patent Application
20060169382
This invention relates to a tire having an internal component, exclusive of a visible surface of the tire, comprised of a composite of a cord reinforced rubber composition having a relatively low, silica-rich, reinforcing filler content comprised of precipitated silica and rubber reinforcing carbon black, together with silica coupler, in combination with methylene donor compound, methylene acceptor compound, cobalt salt and metaphenylene bismaleimide. Such cord reinforced tire component may be, for example, at least one of a tire carcass ply and circumferential overlay ply and/or circumferential belt ply underlying its tread. The composite of cord reinforced rubber composition may also optionally contain one or more of particulate starch/plasticizer composite and exfoliated clay platelets.
Pneumatic rubber tires conventionally contain various internal components contained within the tire in a form of cord-reinforced rubber composites which are exclusive of visible surfaces of the tire, which are relied upon to reinforce and/or stabilize various aspects of the tire. Such internal components include, for example, a carcass ply, a circumferential belt ply which underlies the circumferential tread component of the tire and a circumferential overlay ply which also underlies the circumferential tire tread as being positioned between the tire tread and said belt ply. Such internal tire components are, in general, well known to those having skill in such art.
It is sometimes desired to provide a tire with one or more of such internal components, or plies of cord reinforced rubber composites, having a relatively low hysteresis while substantially maintaining other desirable physical properties in order to contribute to a reduction in a tire's rolling resistance and hence promoting a reduction in vehicular fuel consumption for an associated vehicle on which the tire is operationally mounted and for which it may be desired to promote improved durability for the tire.
For such purpose, a cord reinforced rubber composite is provided herein of relatively low reinforcing filler content to promote an increase in its 100° C. rebound physical property, as compared to a similar rubber composition with a relatively high reinforcing filler content, with an associated predictive reduction in its hysteresis physical property.
However, it is desired herein to also provide such rubber composition of such cord reinforced rubber composite in which the reinforcing filler content is primarily composed of precipitated silica with other physical property(ies) enhanced by inclusion of a combination of methylene donor compound, methylene acceptor compound, cobalt salt and metaphenylene bismaleimide.
The rubber composition of such cord reinforced rubber composite may also contain a starch/plasticizer composite. Rubber compositions containing a starch/plasticizer composite in combination with a methylene donor and/or methylene acceptor are referred to in U.S. Pat. No. 6,931,945.
The rubber composition of such cord reinforced rubber composite may also contain exfoliated clay platelets derived from an intercalated clay such as, for example, a montmorillonite clay. A rubber composition which contains exfoliated clay platelets is referred to, for example, in EP patent publication No. EP 1 193 083.
In the description of this invention, the term “phr” where used means “parts of material by weight per 100 parts by weight of rubber”. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The terms “rubber composition” and “compound” may be used interchangeably unless otherwise indicated.
In accordance with this invention a tire is provided having at least one internal component (exclusive of an outer surface of the tire) comprised of a cord reinforced natural rubber-rich rubber composite comprised of:
(A) a rubber composition comprised of, based upon parts by weight per 100 parts by weight rubber (phr):
(B) at least one cord, preferably a plurality of parallel cords aligned substantially parallel to each other and encapsulated by said rubber composition,
wherein said cords are individually comprised of at least one filament, alternately a plurality of cabled, or twisted, filaments,
wherein said filament(s) of said cord are individually comprised of at least one filament comprised of at least one of steel, brass coated steel, glass, natural organic fiber and synthetic organic fiber.
In practice, said natural organic fibers may be comprised of cotton; and said synthetic organic fibers may be comprised of at least one of polyester, aramid, nylon and rayon.
As previously mentioned, said tire internal component of cord reinforced/rubber composite may be, for example one or more of a carcass ply, circumferential belt ply and circumferential overlay ply which are tire components well known to those having skill in such art.
It is considered herein that an internal tire component as a medium to heavy truck tire carcass ply is particularly useful and adaptable where the cord of said cord reinforced/rubber composite is a plurality of brass coated steel cords aligned substantially parallel to each other, which may be comprised of a plurality of brass coated steel filaments, and wherein the rubber is preferably cis 1,4-polyisoprene rubber which may be natural or synthetic, often preferably synthetic, cis 1,4-polyisoprene rubber, particularly where such truck tire may be intended to be useful for relatively heavy duty use, such as for example vehicular hauling of relatively heavy loads.
It is further considered herein that an internal tire component as a passenger or light truck tire carcass ply is particularly useful and adaptable where the cord of said cord reinforced/rubber composite is plurality of polyester cords, aligned substantially parallel to each other, comprised of a plurality of twisted polyester filaments, where such passenger or light truck tire may be intended to be useful for relatively light vehicular loads. The rubber may be comprised of cis 1,4-polyisoprene and styrene/butadiene copolymer rubber.
The methylene donor compound for the rubber composition of the cord reinforced rubber composite is comprised of hexamethoxymethylmelamine. In practice, if desired, said methylene donor compound may also consist of a minor amount (less than 50 weight percent of the hexamethoxymethylmelamine) of one or more of additional methylene donor compounds selected from for example, one or more of, hexamethylenetetramine, methoxymethyl)melamaine, N,N′N″-trimethyl N,N′N″-trimethylolmelamine, hexamethylomelanime, N,N′N″-dimethylolmelamine, N-methylolmelamine, N,N′-dimethylolmelamine, N,N′N″-tris(methoxymethyl)melamine, N,N′N″-tributyl-N,N′N″-trimethylol-melamine and hexaethoxymethylmelamine. However, preferably the methylene donor compound is hexamethoxymethylmelamine.
The amount of the methylene donor compound in the rubber composition may vary. For example, it may be contained, as a component of said resinous reaction product of methylene donor and methylene acceptor, in the rubber composition in an amount in a range of from about 0.5 to about 4 phr.
The term “methylene acceptor” is known to those having skill in such art and is used to describe the reactant, or compound with which the methylene donor compound reacts to form what is believed to be an intermediate methylol monomer. It is envisioned that a condensation of the intermediate methylol monomer by formation of a methylene bridge produces a resin material. The initial reactant for which it is envisioned contributes the moiety that later forms the methylene bridge and ultimately the resin is referred to as being the methylene donor compound and the other reactant is referred to as being the methylene acceptor compound. Representative compounds which may be used as a methylene acceptor include, for example, but are not limited to, resorcinol, resorcinolic derivitives, monohydric phenols and their derivitives, dihydric phenols and their derivitives, polyhydric phenols and their derivitives, unmodified phenol novolak resins, modified phenol novolak resin, rescorcinol novolak resins, and mixtures thereof. Examples of methylene acceptors include, for example, but are not limited to those disclosed in U.S. Pat. Nos. 6,605,670, 6,472,457, 5,945,500, 5,936,056, 5,688,871, 5,665,799, 5,504,127, 5,405,897, 5,244,725, 5,206,389, 5,194,513, 5,030,692, 4,889,481, 4,605,696, 4,436,853 and 4,092,455. Examples of modified novolak resins include, for example, but are not limited to, cashew nut oil (e.g. cashew nut shell oil) modified phenol novolak resin, tall oil modified phenol novolak resin and alkyl modified phenol novolak resin such as, for example, SP6700™. In one embodiment, the methylene acceptor compound is resorcinol.
The amount of methylene acceptor compound in the rubber composition may vary, depending somewhat upon selection and amount of methylene donor compound used as well as the selection of the methylene acceptor compound itself and a desired ratio of methylene donor compound to methylene acceptor compound. For example, the amount of methylene acceptor compound, as a component of said resinous reaction product of said methylene donor and methylene acceptor, may be in a range of from about 0.5 to about 5, alternatively from about 1 to about 3 phr.
A weight ratio of the methylene acceptor compound to methylene donor compound may range, for example, from about 5/1 to about 1/5.
Representative of cobalt salts, are, for example, cobalt salts of fatty acids such as, for example, stearic, palmitic, oleic, linoleic acids; cobalt salts of aliphatic or alicyclic carboxylic acids having from 6 to 30 carbon atoms; cobalt neodecanoate; cobalt chloride;
cobalt naphthenate; cobalt carboxylate and orano-cobalt-boran complex such as, for example Manobond D™ from the Wyrough and Loser company. Oftentimes it is desired that the cobalt salt is comprised of cobalt naphthenate.
The amount of cobalt salt in the rubber composition may vary considerably, depending somewhat upon the cobalt selected. For example, it may range, for example, from zero (where its presence may not be required by this invention) to about 5, alternately from about 0.2 to about 5 phr.
In practice, it is preferred that said rubber composite of said composite has a hot cured rebound property (100° C.) in a range of from about 65 to about 85, alternately from about 70 to about 80.
In practice, it is desired that said rubber composition of said rubber/cord composite, so long as it has said hot rebound property (100° C.) in a range of from about 65 to about 85, has a dynamic loss modulus (G′) at a low strain (10 percent) and 100° C. in a range of from about 1400 to about 2000 MPa, and a Shore A hardness (100° C.) in a range of from about 60 to about 70. It may also be desired that said rubber composition has a tan delta at low strain (10 percent) and 60° C. in a range of from about 0.03 to about 0.08. In practice, the relatively low level of carbon black reinforcement for said rubber composition of said cord reinforced composite, namely a maximum of about 25, alternately a maximum of about 15, phr, as compared to what is considered herein as being a more normal 45 to about 60 phr of rubber reinforcing carbon black, is provided in order to endeavor to achieve said aforesaid relatively high hot (100° C.) rebound value (and correspondingly relatively low hysteresis) in a range for the rubber composition.
A significance of using natural rubber for the cis 1,4-polyisoprene rubber of the rubber composition of the cord reinforced rubber composite is to obtain a relatively high tear strength and good processability in combination with its relatively low hysteresis (relatively high hot rebound property).
A significance of using a combination of methylene donor compound and methylene acceptor compound for the rubber composition of the cord reinforced rubber composite is considered herein to be beneficial to promote high low strain stiffness (G′ at 10 percent strain at 100° C.) values for the rubber composition and good adhesion of the rubber composition to the reinforcing cord.
A significance of using the cobalt salt, particularly the cobalt naphthenate, for the rubber composition of the cord reinforced rubber composite is considered herein to be beneficial to promote high low strain stiffness (G′ at 10 percent strain at 100° C.) values and good cord adhesion where brass coated steel wire is used for the cord.
A significance of using the metaphenylene bismaleimide for the rubber composition of the cord reinforced rubber composite is considered herein to be beneficial to promote good low strain stiffness (G′ at 10 percent strain at 100° C.) while maintaining a balance between other physical properties of the rubber composition and which may also promote good adhesion of the rubber composition to nylon and polyester cord fibers.
A significance of using precipitated silica reinforcement, in combination with a silica coupling agent, is considered herein to be beneficial to promote low hysteresis and good tear strength for the rubber composition of the composite.
While any single one of the aforesaid ingredients in the tire component composite of cord reinforced rubber composition are known materials for use in various rubber compositions, a significant aspect of this invention is the required use of the combination of the ingredients for the cord reinforced rubber composite as an internal component of a tire, particularly a pneumatic rubber tire.
Various conventional compounding ingredients may be used in the preparation of the rubber composition of the cord reinforced rubber composite, so long as the cured rubber composition has the aforesaid hot (100° C.) rebound property characteristic in a range of from about 65 to about 85.
For example, the sulfur cured rubber of the cord reinforced rubber composite may contain conventional additives including fillers which may include calcium carbonate, peptizing agents, pigments, stearic acid, accelerators, sulfur vulcanizing agents, antiozonants, antioxidants, processing oils, activators, initiators, plasticizers, waxes, pre-vulcanization inhibitors, extender oils and the like. Representative of conventional accelerators may be, for example, amines, guanidines, thioureas, thiols, thiurams, sulfenamides, dithiocarbamates and xanthates which are typically added in amounts of from about 0.2 to about 3 phr. Representative of sulfur vulcanizing agents include element sulfur (free sulfur) or sulfur donating vulcanizing agents, for example, an amine disulfide, polymeric polysulfide or sulfur olefin adducts. The amount of sulfur vulcanizing agent will vary depending on the type of rubber and particular type of sulfur vulcanizing agent but generally range from about 0.1 phr to about 3 phr with a range of from about 0.5 phr to about 2 phr being preferred. Representative of the antidegradants which may be in the rubber composition include monophenols, bisphenols, thiobisphenols, polyphenols, hydroquinone derivatives, phosphites, phosphate blends, thioesters, naphthylamines, diphenol amines as well as other diaryl amine derivatives, para-phenylene diamines, quinolines and blended amines. Antidegradants are generally used in an amount ranging from about 0.1 phr to about 10 phr with a range of from about 2 to 6 phr being preferred. Amine based antidegradants, however, are not preferred in the practice of this invention. Representative of a peptizing agent that may be used is pentachlorophenol which may be used in an amount ranging from about 0.1 phr to 0.4 phr with a range of from about 0.2 to 0.3 phr being preferred. Representative of processing oils which may be used in the rubber composition of the present invention include, for example aliphatic, naphthenic and aromatic oils. The processing oils may be used in a conventional amount ranging from about 0 to about 30 phr with a range of from about 5 to about 15 phr being more usually preferred. Initiators are generally used in a conventional amount ranging from about 1 to 4 phr with a range of from about 2 to 3 phr being preferred.
Accelerators may be used in a conventional amount. In cases where only a primary accelerator is used, the amounts range from about 0.5 to about 2 phr. In cases where combinations of two or more accelerators are used, the primary accelerator is generally used in amounts ranging from 0.5 to 1.5 phr and a secondary accelerator is used in amounts ranging from about 0.1 to 0.5 phr. Various types of conventional accelerators include, for example, amines, disulfides, guanidines, thioureas, thiazoles, thiurams, sulfenamides, dithiocarbamates and xanthates. Preferably, the primary accelerator is a sulfenamide. If a secondary accelerator is used, it is preferably a guanidine, dithiocarbamate or thiuram compound such as for example diphenyl guanidine.
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.
Rubber samples were prepared to evaluate a suitable level, or content, and ratio of reinforcing silica and rubber reinforcing carbon black for a rubber composition of a cord reinforced rubber composite for an internal component of a tire, particularly a pneumatic tire in order to obtain a suitable hot (100° C.) rebound property while substantially maintaining other desirable physical properties
The rubber samples are referred to herein as Samples A through H.
The rubber compositions were prepared by blending the ingredients in an internal rubber mixer in a series of sequential mixing steps while sheeting out the rubber mixtures and cooling to a temperature below 40° C. between mixing steps. The sequential mixing steps were comprised of a first non-productive mixing step followed by a second non-productive mixing step and thence by a productive mixing step (in which sulfur and accelerators were added).
Such sequential non-productive and productive rubber mixing steps are well known to those having skill in such art.
The basic recipe for the rubber Samples A through H is presented in the following Table 1 in terms of parts by weight.
1Carbon black as freely added rubber reinforcing carbon black N330, an ASTM reference, plus a minor amount of carbon black (also understood to be N330, or similar, carbon black) contained in the silica coupler composite.
2Precipitated silica as HiSil 210 ™ from PPG Industries
3Silica coupler as a bis(3-triethoxysilylpropyl) polysulfide, understood to have an average of connecting sulfur atoms in its polysulfidic bridge in a range of from about 2.2 to about 2.5, provided as Si266 ™ from Degussa as a composite of the silica coupler and carbon black (believed to be N330 or similar carbon black) in a 50/50 weight ratio, reported in Table 1 in terms of the silica coupler and not the complete composite of coupler and carbon black.
4Flexon 641 ™ from ExxonMobil
5Primarily stearic acid as a blend of stearic, palmitic and oleic acids
6Cobalt naphthenate, 10.5 percent by weight cobalt
7Cashew nut shell oil modified phenol novolac resin as SP6700 ™ from Schenectady
8Wingstay 100 ™ from The Goodyear Tire & Rubber Company
9Insoluble sulfur, 80 percent active
10Hexamethoxymethylmelamine
The following Table 2 illustrates cure behavior and various physical properties of rubber Samples A through H based upon the basic recipe of Table 1.
1Data obtained according to Moving Die Rheometer instrument, model MDR-2000 by Alpha Technologies, used for determining cure characteristics of elastomeric materials, such as for example Torque, T90, etc.
2Data obtained according to Automated Testing System instrument by the Instron Corporation which incorporates six tests in one system. Such instrument may determine ultimate tensile, ultimate elongation, modulii, etc. Data reported in the Table is generated by running the ring tensile test station which is an Instron 4201 load frame.
3Data obtained according to a peel strength adhesion test to determine interfacial adhesion between two samples of a rubber composition. In particular, such interfacial adhesion is determined by pulling one rubber composition away from the other at a right angle to the untorn test specimen with the two ends of the rubber compositions being pulled apart at a 180° angle to each other using an Instron instrument. The area of contact at the interface
4,5Standard wire and textile cord adhesion tests (SWAT) were conducted by embedding a respective cord in a respective rubber composition. The rubber/cord samples were then cured at the indicated temperatures. The respective cords in the rubber samples were subjected to a pull-out test according to ASTM D2229-73. The results of the pull-out tests are expressed in Newtons.
6Data obtained according to Rubber Process Analyzer as RPA 2000 ™ instrument by Alpha Technologies, formerly the Flexsys Company and formerly the Monsanto Company. References to an RPA-2000 instrument may be found in the following publications: H. A. Palowski, et al, Rubber World, June 1992 and January 1997, as well as Rubber & Plastics News, April 26 and May 10, 1993.
It can be seen from Table 2 that the Tear Strengths of Samples E and G are significantly lower than the Tear Strengths of Samples F and H.
It can be seen from Table 2 that the Wire Cord Adhesion (aged in water) values for Samples G and H are significantly lower than the corresponding aged in water wire cord adhesion for Samples E and G.
It can be seen from Table 2 that the Storage Modulus (G′) at low strain for Sample G is significantly higher than the corresponding Storage Modulus (G′) at low strain for Samples E, F and H
This is considered herein to be significant in that a Storage Modulus (G′) at low strain is indication of a higher hysteresis for the rubber composition of Sample G and therefore an indication, as compared to Samples E, F and H that the silica/carbon black ratio of 4.12/1 for Sample G is too low.
It can be seen from Table 2 that the tan delta at low strain for Sample G, which contained is significantly higher than the corresponding tan delta at low strain for Samples E, F and H
This is considered herein to be significant in that a higher tan delta value at low strain is indication of a higher hysteresis for the rubber composition of Sample G and therefore an indication, as compared to Samples E, F and H that the silica/carbon black ratio of 4.12/1 for Sample G is too low.
Accordingly, it is concluded herein that, for the rubber composition for the cord reinforced rubber composite of this invention, the weight ratio of the precipitated silica to rubber reinforcing carbon black should be in a range greater than 2/1 and more preferably greater than 3/1.
Rubber samples were prepared to evaluate the significance of the inclusion of the methylene acceptor, methylene donor, metaphenylene bismaleimide, coupling agent and cobalt salt in the rubber composition for the cord reinforced rubber composite.
The rubber samples are reported herein as rubber Sample I and comparative Samples J through N.
In particular, the methylene acceptor was omitted from Sample J; the methylene donor was omitted from Sample K; the methaphenylene bismaldimide was omitted from Sample L; the coupling agent was omitted from Sample M and the cobalt sale was omitted from Sample N.
The optimized precipitated silica and rubber reinforcing carbon black content of 40 phr and weight ratio of 3/1 of Example I was used for Samples I through L and N. The amount of 37 phr and ratio of 4.29/1 was used for Sample M to reflect the absence of the carbon black which would have been contained in the omitted coupling agent composite for Sample M.
The rubber compositions were prepared a manner similar to Example I by blending the ingredients in an internal rubber mixer in a series of sequential mixing steps while sheeting out the rubber mixtures and cooling to a temperature below 40° C. between mixing steps. The sequential mixing steps were comprised of a first non-productive mixing step followed by a second non-productive mixing step and thence by a productive mixing step (in which sulfur and accelerators were added).
The basic recipe for the rubber Sample I and comparative Samples J through N is presented in the following Table 3 presented in parts by weight.
The above numerically referenced ingredients are the same as the corresponding numerically referenced ingredients of Table 1.
The following Table 4 illustrates cure behavior and various physical properties of rubber compositions based upon the basic recipe of Table 3 and reported herein for rubber Sample I and comparative Samples J through N.
The above numerically referenced tests are the same as the corresponding numerically referenced tests of Table 2.
It can be seen from Table 4 that the Shore A hardness values for Comparative Samples K through N, in which the methylene donor, metaphenylene bismaleimide, coupling agent and cobalt salt were individually respectively omitted, were significantly lower than the Shore A hardness value for Samples I and Comparative Sample J.
This is considered herein to be significant in the sense of illustrating the significance of the inclusion of the combination of the methylene donor, methphenylene bismaldimide, coupling agent and cobalt salt in the rubber composition for the cord reinforced rubber composite for the Shore A hardness property.
It can be seen from Table 4 that the Tear Strength property for Comparative Sample J, in which the methylene acceptor was omitted, was significantly lower than the Tear Strength properties for Sample I and Comparative Samples K through N.
This is considered herein to be significant in the sense of illustrating the significance of the inclusion of the methylene acceptor in the rubber composition for the cord reinforced rubber composite for the Tear Strength property.
It can be seen from Table 4 that the Wire Cord Adhesion (water aged) property for Comparative Sample J, in which the methylene acceptor was omitted, was significantly lower than the Wire Cord Adhesion (water aged) properties for Sample I and Comparative Samples K through N.
This is considered herein to be significant in the sense of illustrating the significance of the inclusion of the methylene acceptor in the rubber composition for the cord reinforced rubber composite for the Wire Cord Adhesion property.
It can be seen from Table 4 that the Nylon cord Adhesion properties for Comparative Samples J and M, in which the methylene acceptor (Comparative Sample J) and the coupling agent (Comparative Sample M) were individually respectively omitted, were significantly lower than the Nylon Cord Adhesion properties for Sample I and Comparative Samples K, L and N.
This is considered herein to be significant in the sense of illustrating the significance of the inclusion of the methylene acceptor and coupling agent in the rubber composition for the cord reinforced rubber composite for the Nylon Cord Adhesion property.
It can be seen from Table 4 that the Storage Modulus (G′) at low strain properties for Comparative Samples K through N, in which each of the methylene donor, methaphenylene bismaleimide, coupling and cobalt salt were individually selectively omitted from the respective Comparative Samples, were significantly lower than the Storage Modulus (G′) at low strain properties for Sample I and Comparative Sample J.
This is considered herein to be significant in the sense of illustrating the significance of the inclusion of the methylene donor, methaphenylene bismaleimide, coupling and cobalt salt in the rubber composition for the cord reinforced rubber composite for the Storage Modulus (G′) at low strain property.
Accordingly, it is concluded herein that, for the rubber composition for the cord reinforced rubber composite of this invention, an inclusion of a combination of the methylene acceptor, methylene donor, methaphenylene bismaleimide, coupling and cobalt salt in the rubber composition for the cord reinforced rubber composite is significantly beneficial for the rubber composition for the cord reinforced rubber composite insofar as the indicated physical properties are concerned.
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.
