Formation of Latex Coagulum Composite for Tire Composition
A tire comprising a rubber composition based on at least an elastomer composite formed by the method of flowing a coagulating mixture of a first elastomer latex comprising a first elastomer and a particulate filler slurry along a conduit; and introducing a second elastomer latex comprising a second elastomer into the flow of the coagulating mixture.
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This application is a continuation of application Ser. No. 13/497,034 filed Jul. 23, 2012 which claims the priority under 35 U.S.C. 371 of International application No. PCT/US2010/002518 filed Sep. 16, 2010. Priority is also claimed of U.S. Provisional Application Nos. 61/276,876 filed Sep. 17, 2009 and 61/280,453 filed Nov. 4, 2009, the entire contents of all of which are hereby incorporated by reference.
FIELD OF THE INVENTIONThis invention relates to the introduction of additional elastomer latex into a latex coagulum composite, more particularly this invention concerns tire comprising rubber composition based on such elastomer composite,
DESCRIPTION OF THE RELATED ARTIn order to obtain the optimum reinforcement properties imparted by a filler in a tire tread and thus high wear resistance, it is known that this filler should generally be present in the elastomeric matrix in a final form which is both as finely divided as possible and distributed as homogeneously as possible. Now, such conditions can only be obtained insofar as this filler has a very good ability firstly to be incorporated into the matrix during mixing with the elastomer and to be disagglomerated, and secondly to be dispersed homogeneously in this matrix.
Since fuel economies and the need to protect the environment have become priorities, it has proved necessary to produce tires having reduced rolling resistance, without adversely affecting their wear resistance. To improve the dispersion of filler into the elastomeric matrix, numerous solutions have been proposed, some of them proposing the use of masterbatches including elastomer and filler.
It is common to produce a masterbatch, that is, a premixture of filler, elastomer and various optional additives, such as extender oil. Carbon black masterbatch, for example, is prepared with different grades of commercially available carbon black which vary both in surface area per unit weight and in structure, which describes the size and complexity of aggregates of carbon black formed by the fusion of primary carbon black particles to one another.
There are a variety of methods for producing carbon black masterbatch. In one method, disclosed in U.S. Pat. No. 6,841,606 (“the '606 patent”), a carbon black slurry and an elastomer latex are combined in a vat and then coagulated by the addition of a coagulant, such as an acid. In a variation of this process, disclosed in Japanese Patent Publication No. 2005220187, natural rubber latex is diluted to 20% rubber content (from about 24% rubber) and combined with a protease to cleave amide bonds the non-rubber components of the latex. The cleavage is believed to improve the performance of the final rubber product. In another method, disclosed in U.S. Pat. No. 6,048,923, the contents of which are incorporated by reference herein, a continuous flow of a first fluid including an elastomer latex is fed to the mixing zone of a coagulum reactor. A continuous flow of a second fluid including a carbon black slurry is fed under pressure to the mixing zone to form a mixture with the elastomer latex. The mixing of the two fluids is sufficiently energetic to substantially completely coagulate the elastomer latex with the carbon black prior to a discharge end of the coagulum reactor. As disclosed in U.S. Pat. No. 6,075,084, additional elastomer may be added to the material that emerges from the discharge end of the coagulum reactor. As disclosed in U.S. Pat. No. 6,929,783, the coagulum may then be fed to a dewatering extruder.
At high loadings of carbon black, the coagulum emerges from the coagulum reactor not as a continuous flow of carbon black-elastomer composite but as a plurality of discrete carbon black-elastomer composite regions carried by a substantially coagulum-free aqueous phase. Generally, such a discontinuous material does not pass as easily through the dewatering extruder and can backflow within the dewatering extruder, causing clogging. It is therefore desirable to prepare a continuous flow of coagulum containing a high volume fraction of carbon black that can be more easily handled in an apparatus such as a dewatering extruder.
Moreover, surprisingly we discover that tire comprising rubber compositions based on elastomer composite having high volume fraction of filler and in particular of carbon black, present improved properties (notably processability, reinforcement, vulcanized kinetic) compared to already improved properties of tire comprising rubber composition based on elastomer composite having lesser volume fraction of the same filler prepared by the method described in U.S. Pat. No. 6,048,923.
SUMMARY OF THE INVENTIONOne aspect of the present invention is directed to a process for manufacturing a rubber composition for tire, comprising the steps of a) manufacturing a coagulated latex composite by the method comprising a1) flowing a coagulating mixture of a first elastomer latex comprising a first elastomer and a particulate filler slurry along a conduit, wherein the particulate filler comprises a carbon black having a dibutyl phthalate adsorption greater than 60 mL/100 g, and wherein the carbon black has a surface area and is present in the coagulated latex composite in an amount satisfying L≧−0.26*S+94, where L is the amount of the carbon black in the coagulated latex composite in parts per hundred of rubber (phr) and S is the surface area in m2/g as measured by STSA; and a2) introducing a second elastomer latex comprising a second elastomer into the flow of the coagulating mixture to obtain a coagulated latex composite in a form of coherent coagulum and the second elastomer latex is not decorated with filler particles prior to the introduction step; b) dewatering the coagulated latex composite obtained in step a) into a desired water content c) incorporating all the constituents of the composition for tire, including the dewatered coagulated latex composite obtained in step b), in a mixer by thermomechanically kneading the whole mixture at high temperature, up to a maximum temperature of between 130° C. and 200° C., then d) performing mechanical working of the resulting mixture, with incorporation of a crosslinking system, at a temperature of less than 120° C.
Another aspect of the invention relates to a tire or tire tread comprising a rubber composition based on at least one elastomer composite formed by a method, comprising flowing a coagulating mixture of a first elastomer latex comprising a first elastomer and a particulate filler slurry along a conduit; and introducing a second elastomer latex comprising a second elastomer into the flow of the coagulating mixture.
The tire or tire tread made according to this method may be formed by a further method comprising, before flowing the coagulating mixture, generating the coagulating mixture by feeding a continuous flow of the first elastomer latex to a mixing zone of a coagulum reactor defining an elongate coagulum zone extending from the mixing zone to a discharge end and comprising the conduit, and feeding a continuous flow of a fluid comprising particulate filler under pressure to the mixing zone of the coagulum reactor to form the coagulating mixture.
The tire or tire tread made according to this method may be formed by a further method comprising steps wherein the continuous flow of the fluid comprising particulate filler has a velocity from about 30 m/s to about 250 m/s, the continuous flow of the first elastomer latex has a velocity of at most about 10 m/s, and a residence time of the coagulating mixture in the coagulum reactor before introducing the second elastomer latex is from 1×10−2 s to about 6×10−2 s.
The tire or tire tread made according to this method may be formed by a further method comprising steps wherein the conduit comprises a first conduit portion having a first diameter, a second conduit portion having a second diameter greater than the first diameter, and a transition zone therebetween having a diameter that increases from the first diameter to the second diameter, wherein flowing comprises flowing the coagulating mixture into the second conduit portion from the first conduit portion, and introducing comprises introducing the second elastomer latex into the coagulating mixture in the transition region.
The tire or tire tread made according to this method may be formed by a further method comprising steps wherein flowing the coagulating mixture comprises flowing the coagulating mixture through the transition region under conditions of turbulent flow.
The tire or tire tread made according to this method may be formed by a further method comprising steps wherein the amount of the second elastomer in the composite is from about 0.5 wt % to about 50 wt %; wherein the amount of the second elastomer in the composite is from about 16 wt % to about 38 wt %; wherein the second elastomer is a synthetic elastomer or natural rubber latex, and wherein the natural rubber latex comprises field latex, latex concentrate, skim latex, or a combination of two or more of these; and, optionally, wherein a component of the natural rubber latex has been chemically or enzymatically modified.
The tire or tire tread made according to this method may be formed by a further method comprising steps wherein the particulate filler comprises a carbon black having a surface area of at least 95 m2/g as measured by STSA and a dibutyl phthalate adsorption greater than 80 mL/100 g, and wherein the coagulated latex composite comprises at least 65 phr of the carbon black; or wherein the particulate filler comprises a carbon black having a surface area of at least 75 m2/g as measured by STSA and a dibutyl phthalate adsorption greater than 60 mL/100 g, and wherein the coagulated latex composite comprises at least 70 phr of the carbon black; or wherein the particulate filler comprises a carbon black having a dibutyl phthalate adsorption greater than 60 mL/100 g, wherein the carbon black has a surface area and is present in the coagulated latex composite in an amount satisfying L≧−0.26*S+94, where L is the amount of the carbon black in the coagulated latex composite in parts per hundred of rubber (phr) and S is the surface area in m2/g as measured by STSA; or wherein the elastomer composite includes at least 10 phr of the particulate filler.
Another aspect of the invention relates to a tire or tire tread comprising a rubber composition based on at least one elastomer composite formed by a method, comprising:
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- generating a flow of a coagulating mixture of a first elastomer latex comprising a first elastomer and a particulate filler slurry having a first degree of turbulence;
- causing the first degree of turbulence to change to a second degree of turbulence; and
- introducing a second elastomer latex into the coagulum at a location where the coagulum flow has the second degree of turbulence.
The tire or tire tread made according to this method may be formed by a further method comprising generating a flow comprises feeding a continuous flow of the first elastomer latex to a mixing zone of a coagulum reactor defining an elongate coagulum zone extending from the mixing zone to a discharge end, and feeding a continuous flow of the particulate filler slurry under pressure to the mixing zone of the coagulum reactor to form the coagulating mixture.
The tire or tire tread made according to this method may be formed by a further method, wherein the continuous flow of the fluid comprising particulate filler has a velocity from about 30 m/s to about 250 m/s, the continuous flow of the first elastomer latex has a velocity of at most about 10 m/s, and a residence time of the coagulating mixture in the coagulum reactor before introducing the second elastomer latex is from 1×10−2 s to about 6×10−2 s.
The tire or tire tread made according to this method may be formed by a further method comprising steps wherein the amount of the second elastomer in the composite is from about 0.5 wt % to about 50 wt %; wherein the amount of the second elastomer in the composite is from about 16 wt % to about 38 wt %; wherein the second elastomer is a synthetic elastomer or natural rubber latex, and wherein the natural rubber latex comprises field latex, latex concentrate, skim latex, or a combination of two or more of these; and, optionally, wherein a component of the natural rubber latex has been chemically or enzymatically modified.
The tire or tire tread made according to this method may be formed by a further method comprising steps wherein the particulate filler comprises a carbon black having a surface area of at least 95 m2/g as measured by STSA and a dibutyl phthalate adsorption greater than 80 mL/100 g, and wherein the coagulated latex composite comprises at least 65 phr of the carbon black; or wherein the particulate filler comprises a carbon black having a surface area of at least 75 m2/g as measured by STSA and a dibutyl phthalate adsorption greater than 60 mL/100 g, and wherein the coagulated latex composite comprises at least 70 phr of the carbon black; or wherein the particulate filler comprises a carbon black having a dibutyl phthalate adsorption greater than 60 mL/100 g, wherein the carbon black has a surface area and is present in the coagulated latex composite in an amount satisfying L≧−0.26*S+94, where L is the amount of the carbon black in the coagulated latex composite in parts per hundred of rubber (phr) and S is the surface area in m2/g as measured by STSA; or wherein the elastomer composite includes at least 10 phr of the particulate filler.
The invention is described with reference to the several drawings, in which:
While it is often desirable to produce elastomer composite with higher loadings of fillers such as carbon black in a continuous wet masterbatch process, coagulated rubbers containing higher loadings of filler are sometimes difficult to pass through downstream processing equipment. We have unexpectedly discovered that adding additional elastomer latex into a coagulating mixture having a high weight fraction of filler results in the formation of a continuous masterbatch crumb, termed a “coherent coagulum. Because the coherent coagulum is a cohesive mass, it does not crumble when handled and can be easily dewatered using standard equipment such as the dewatering extruder available from the French Oil Machinery Company (Piqua, Ohio, USA). This enables the continuous production of elastomer composites having high loadings of filler and which can be used to produce vulcanized rubbers having superior properties. In contrast, masterbatch crumb that is not cohesive can backflow in downstream equipment, causing it to clog or to become ineffective at de-watering.
In one embodiment, a tire comprises a rubber composition which is based on elastomer composite formed by a method of flowing a coagulating mixture of a first elastomer latex and a particulate filler slurry along a conduit and introducing a second elastomer latex into the flow of the coagulating mixture.
Accordingly, said rubber composition may be used for the tread portion, sidewalls, wire skim and/or carcass.
As shown in
The second elastomer latex, is introduced via injection system 22. Injection system 22 includes a holding tank 24 and a pump 26 that directs the second elastomer latex into the coagulum reactor 11 via an injection line 28. Preferably, pump 26 is operated to generate sufficient pressure to prevent back flow of the coagulating mixture into injection line 28. Other suitable apparatus, e.g., different type pumping or compression equipment, may be employed to introduce the second elastomer latex into the coagulating mixture. As shown in
Elastomer latex is an emulsion of rubber particles in water. The rubber in the particles is a highly viscous fluid of rubber molecules, surrounded by a shell of naturally occurring substances that stabilize the rubber particles against aggregation and coalescence. Destabilization of the latex causes it to coagulate, i.e, the rubber particles aggregate and coalesce with one another. In preferred embodiments, the velocity of the particulate filler slurry is significantly higher than that of the first elastomer latex. The resulting high shear destabilizes the latex. Without being bound by any particular theory, it is believed that rapid mixing of the particulate slurry with the latex results in decoration of the rubber particle surface by the particulates, which also destabilizes the latex. Filler particles colliding with each other also form agglomerates that can collide with and destabilize latex particles. The combination of these factors causes the elastomer latex to destabilize; rubber particles aggregate by forming rubber-rubber contacts or by bridging through filler particles on their surfaces to form rubber-filler composite aggregates.
Without being bound by any particular theory, it is believed that in the presence of excess particulate filler, the rubber particles or small aggregates of rubber particles become completely decorated with the filler, with little or no free rubber surface area to form rubber-rubber contacts with other rubber particles. This limits the extent to which the rubber-filler composite aggregates can further aggregate to form a continuous network. Instead, rather than forming a coherent coagulum, the masterbatch crumb takes the form of discontinuous composite domains dispersed in an aqueous phase. The second elastomer latex introduces fresh latex particles that, because they are not yet decorated with filler particles, can bind together the discrete rubber-filler composite aggregates to form a continuous rubber-particle composite in the form of a coherent coagulum.
For apparatus similar to that shown in
According to the theory above, there is a limit beyond which the introduction of additional latex will not enable the discrete rubber-filler composite aggregates to form a coherent coagulum. That is, if there is excess filler in the mixture after the rubber particles have been completely decorated, the rubber particles in the second elastomer latex stream will become decorated with the excess filler rather than binding the existing rubber-filler aggregates together. Thus, while the use of the second elastomer latex stream can increase the filler loading level obtainable while still producing coherent coagulum, the potential increase is not infinite. The concentration of the filler in the slurry, the feed rate and velocity of the filler slurry into the mixing zone, and the proportion of the rubber introduced with second elastomer latex with respect to the total rubber in the final composite may all be optimized to maximize the effectiveness of the second elastomer latex.
In certain embodiments, the secondary latex improves the achievable filler loading (e.g., elastomer composite produced with this amount of filler has the morphology of a coherent coagulum) by at least 0.5 phr with respect to elastomer composite produced in a continuous wet masterbatch process without secondary latex, for example, from 0.5 phr to about 15 phr, from about 1 phr to about 14 phr, from about 2 phr to about 13 phr, from about 3 phr to about 12 phr, from about 4 phr to about 11 phr, from about 5 phr to about 10 phr, from about 6 phr to about 9 phr, from about 7 phr to about 8 phr, from about 1 phr to about 7 phr, from about 1 phr to about 6 phr, or from about 1 phr to about 5 phr.
In certain preferred embodiments, use of secondary latex enables use of a continuous wet masterbatch process to produce elastomer composite having at least 65 phr, for example, at least 70 phr or from 65 to 75 phr, of a carbon black having a surface area of at least 95 m2/g, as measured by the statistical thickness method (STSA), expressed as square meters per gram of carbon black, according to the procedure set forth in ASTM D6556 (STSA) and a structure, measured by dibutyl phthalate (DBP) adsorption (ASTM D6854), greater than 80 mL/100 g. Alternatively or in addition, the use of secondary latex may enable use of a continuous process to produce elastomer composite having at least 70 phr, for example, at least 75 phr or from 70 phr to 80 phr, of carbon black having a surface area of at least 68 m2/g as measured by STSA, for example, at least 75 m2/g, and structure, as measured by DBP adsorption, greater than 60 mL/100 g. Alternatively or in addition, use of secondary latex enables use of a continuous wet mastermatch process to produce elastomer composite containing carbon black having a DBP adsorption greater than 60 mL/100 mg, for example, greater than 80 mL/100 mg, greater than 100 mL/100 mg or from 60 mL/100 mg to 160 mL/100 mg, and having a surface area and being present in an amount that satisfies L≧−0.26*S−0.26*S+94, for example, L≧−0.26*S−0.26*S+97, or L≧−0.26*S+100, or L≧−0.26*S+104, or −0.26*S+94≦L≦−0.26*S+110, where L is the amount of carbon black in the elastomer composite in parts per hundred of rubber (phr) and S is the surface area measured as STSA (ASTM D6556), where S is optionally greater than 65 m2/g, greater than 95 m2/g, greater than 110 m2/g, or between 65 m2/g and 400 m2/g, for example between 65 m2/g and 220 m2/g, between 95 m2/g and 200 m2/g, or between 110 m2/g and 180 m2/g.
Furthermore, according to the above theory, the effectiveness of the second elastomer latex will be maximized if it is not introduced until substantially all the filler has been adsorbed onto the rubber particles in the first elastomer latex. Otherwise, the secondary latex particles become decorated with the filler rather than binding the existing rubber-filler aggregates. The time required for the filler slurry and the elastomer latex to mix together and allow the filler particles to adsorb onto the rubber particles depends in part on how energetically the two fluids are mixed together. For apparatus similar to that depicted in
The physical configuration of the injection system 22 also may be adjusted to optimize the mixing of the second elastomer latex into the mixture. The initial flow of the coagulating mixture through the upstream portions of the diffuser is relatively turbulent. This turbulence gradually subsides as the coagulating mixture proceeds downstream, and the flow of the coagulum from the outlet 34 of the diffuser is roughly laminar. Without being bound by any particular theory, it is believed that the turbulence associated with the expansion of the flow cross-section between the first and second sections 18a and 18b at transition 20a facilitates mixing of the second elastomer latex injected at that point into the coagulating rubber-filler composite. Other factors influencing mixing and turbulence include the distance from the point of slurry injection, the injection velocity, the difference in cross-sectional area between the first and second diffuser sections, the injection velocity of the secondary latex stream, and the angle of injection of the secondary latex stream.
For example, the second section of the diffuser 18b may have a cross-sectional area from about 1.2-3.5 times the cross-sectional area of the first section of the diffuser 18a, for example, from about 1.2 to about 1.4 times, from about 1.4 to about 1.6 times, from about 1.5 to about 1.7 times, from about 1.7 to 1.9 times, from about 1.9 to about 2.1 times, from about 2.1 to about 2.3 times, from about 2.3 to about 2.5 times, from about 2.5 to about 2.7 times, from about 2.7 to about 2.9 times, from about 2.9 to about 3.1 times, from about 3.1 times to about 3.3 times, or from about 3.3 to about 3.5 times greater. In specific examples, the ratio of the cross-sectional areas of sections 18b and 18a may be about 2, about 2.5, or about 3. The lengths of the various sections of the diffuser 18a-18d and the dimensions of the downstream sections 18c and 18d may be as described in U.S. Pat. No. 6,048,923, the contents of which are incorporated herein by reference. In certain embodiments, the length of first section 18a may be from about 2 inches (5.08 cm) to about 9 inches (35.8 cm), for example, from about 2 inches (5.08 cm) to about 3 inches (7.62 cm), from about 3 inches (7.62 cm) to about 4 inches (10.2 cm), from about 4 inches (10.2 cm) to about 5 inches (12.7 cm), from about 5 inches (12.7 cm) to about 6 inches (15.2 cm), from about 6 inches (15.2 cm) to about 7 inches (17.8 cm), from about 7 inches (17.8 cm) to about 8 inches (20.3 cm), or from about 8 inches (20.3 cm) to about 9 inches (35.8 cm). The optimal length may vary and generally increases with the production rate.
An exemplary approach for introducing the second elastomer latex to the coagulating mixture is illustrated in
The second elastomer latex may have the same composition as that used to prepare the coagulating mixture, or it may differ in some way. For example, the second elastomer latex may be an elastomer latex from a different source or with a different concentration of rubber and fluid. Alternatively or in addition, it may be subjected to different chemical modifications (including no modification) than the first elastomer latex.
In certain embodiments, at least one of and preferably both the first elastomer latex (i.e., the elastomer latex in the coagulating mixture) and the second elastomer latex are prepared from a natural rubber latex. Exemplary natural rubber latices include but are not limited to field latex, latex concentrate (produced, for example, by evaporation, centrifugation or creaming), skim latex (a by-product of the centrifugation of natural rubber latex) and blends of any two or three of these in any proportion. The latex should be appropriate for the wet masterbatch process selected and the intended purpose or application of the final rubber product. The latex is provided typically in an aqueous carrier liquid. Selection of a suitable latex or blend of latices will be well within the ability of those skilled in the art given the benefit of the present disclosure and the knowledge of selection criteria generally well recognized in the industry.
The natural rubber latex may also be chemically modified in some manner. For example, it may be treated to chemically or enzymatically modify or reduce various non-rubber components, or the rubber molecules themselves may be modified with various monomers or other chemical groups such as chlorine. Exemplary methods of chemically modifying natural rubber latex are disclosed in European Patent Publications Nos. 1489102, 1816144, and 1834980, Japanese Patent Publications Nos. 2006152211, 2006152212, 2006169483, 2006183036, 2006213878, 2006213879, 2007154089, and 2007154095, U.S. Pat. Nos. 6,841,606 and 7,312,271, and U.S. Patent Publication No. 2005-0148723. Other methods known to those of skill in the art may be employed as well.
In an alternative embodiment, at least one of the first elastomer latex (i.e., the elastomer latex in the coagulating mixture) and the second elastomer latex is prepared using synthetic latex of rubber or “diene” elastomer. The term “diene” elastomer or “diene” rubber (elastomer and rubber are well known to be synonymous terms) should be understood as meaning, in a known way, an (one or more are understood) elastomer resulting at least in part (i.e., a homopolymer or a copolymer) from diene monomers (monomers carrying two carbon-carbon double bonds which may or may not be conjugated).
These diene elastomers can be classified into two categories: “essentially unsaturated” or “essentially saturated”. The term “essentially unsaturated” is understood to mean generally a diene elastomer resulting at least in part from conjugated diene monomers having a level of units of diene origin (conjugated dienes) which is greater than 15% (mol %); thus it is that diene elastomers such as butyl rubbers or copolymers of dienes and of α-olefins of EPDM type do not come within the preceding definition and can in particular be described as “essentially saturated” diene elastomers (low or very low level of units of diene origin, always less than 15%). In the category of “essentially unsaturated” diene elastomers, the term “highly unsaturated” diene elastomer is understood to mean in particular a diene elastomer having a level of units of diene origin (conjugated dienes) which is greater than 50%.
Synthetic diene elastomer of the first elastomer latex or of the second elastomer latex in accordance with the invention is preferably chosen from the group of the highly unsaturated diene elastomers consisting of polybutadienes (abbreviated to “BR”), synthetic polyisoprenes (IR), butadiene copolymers, isoprene copolymers and the mixtures of these elastomers. Such copolymers are more preferably chosen from the group consisting of butadiene/styrene copolymers (SBR), isoprene/butadiene copolymers (BIR), isoprene/styrene copolymers (SIR) and isoprene/butadiene/styrene copolymers (SBIR).
The elastomers can, for example, be block, random, sequential or microsequential elastomers and can be prepared in dispersion or in solution; they can be coupled and/or star-branched or also functionalized with a coupling and/or star-branching or functionalization agent. For coupling with carbon black, mention may be made, for example, of functional groups comprising a C—Sn bond or of aminated functional groups, such as benzophenone, for example; for coupling with a reinforcing inorganic filler, such as silica, mention may be made, for example, of silanol functional groups or polysiloxane functional groups having a silanol end (such as described, for example, in U.S. Pat. No. 6,013,718), of alkoxysilane groups (such as described, for example, in U.S. Pat. No. 5,977,238), of carboxyl groups (such as described, for example, in U.S. Pat. No. 6,815,473 or US 2006/0089445) or of polyether groups (such as described, for example, in U.S. Pat. No. 6,503,973). Mention may also be made, as other examples of such functionalized elastomers, of elastomers (such as SBR, BR, NR or IR) of the epoxidized type.
The following are preferably suitable: polybutadienes, in particular those having a content of 1,2-units of between 4% and 80% or those having a content of cis-1,4-units of greater than 80%, polyisoprenes, butadiene/styrene copolymers in particular those having a styrene content of between 5% and 50% by weight and more particularly between 20% and 40%, a content of 1,2-bonds of the butadiene part of between 4% and 65% and a content of trans-1,4-bonds of between 20% and 80%, butadiene/isoprene copolymers, in particular those having an isoprene content of between 5% and 90% by weight and a glass transition temperature (“Tg”—measured according to ASTM D 3418-82) of −40° C. to −80° C., or isoprene/styrene copolymers, in particular those having a styrene content of between 5% and 50% by weight and a Tg of between −25° C. and −50° C.
In the case of butadiene/styrene/isoprene copolymers, those having a styrene content of between 5% and 50% by weight and more particularly of between 10% and 40%, an isoprene content of between 15% and 60% by weight and more particularly between 20% and 50%, a butadiene content of between 5% and 50% by weight and more particularly of between 20% and 40%, a content of 1,2-units of the butadiene part of between 4% and 85%, a content of trans-1,4-units of the butadiene part of between 6% and 80%, a content of 1,2- plus 3,4-units of the isoprene part of between 5% and 70% and a content of trans-1,4-units of the isoprene part of between 10% and 50%, and more generally any butadiene/styrene/isoprene copolymer having a Tg of between −20° C. and −70° C., are suitable in particular.
In some embodiments, it may be desirable to inject a coagulant, for example, a salt or acid solution, along with the elastomer latex stream, to promote coagulation of the elastomer.
The particulate filler fluid may be a carbon black slurry or any other suitable filler in a suitable carrier fluid. Selection of the carrier fluid will depend largely upon the choice of particulate filler and upon system parameters. Both aqueous and non-aqueous liquids may be used, with water being preferred in many embodiments in view of its cost, availability and suitability of use in the production of carbon black and certain other filler slurries. Small amounts of water-miscible organic solvents may also be included in aqueous carrier fluids.
Selection of the particulate filler or mixture of particulate fillers will depend largely upon the intended use of the elastomer masterbatch product. As used here, particulate filler can include any material which is appropriate for use in the masterbatch process used to produce the masterbatch crumb. Suitable particulate fillers include, for example, conductive fillers, reinforcing fillers, fillers comprising short fibers (typically having an L/D aspect ratio less than 40), flakes, etc. In addition to carbon black and silica-type fillers, discussed in more detail below, fillers can be formed of clay, glass, polymer, such as aramid fiber, etc. It is expected that any filler suitable for use in elastomer compositions may be incorporated into elastomer composites according to various embodiments of the invention. Of course, blends of the various particulate fillers discussed herein may also be used.
When a carbon black filler is used, selection of the carbon black will depend largely upon the intended use of the elastomer masterbatch product. Optionally, the carbon black filler can include also any material which can be slurried and combined with a latex in the particular wet masterbatch process selected by the skilled artisan. Exemplary particulate fillers include but are not limited to carbon black, fumed silica, precipitated silica, coated carbon black, chemically functionalized carbon blacks, such as those having attached organic groups, and silicon-treated carbon black, either alone or in combination with each other. Exemplary carbon blacks include ASTM N100 series-N900 series carbon blacks, for example N100 series carbon blacks, N200 series carbon blacks, N300 series carbon blacks, N700 series carbon blacks, N800 series carbon blacks, or N900 series carbon blacks. Elastomer composites containing ASTM N100, N200, and/or N300 series blacks and/or carbon blacks having similiarly high or higher surface areas, e.g, a surface area measured by the statistical thickness method (STSA), expressed as square meters per gram of carbon black, according to the procedure set forth in ASTM D6556 (STSA) of 68 m2/g or greater, for example, 75 m2/g or greater, or 95 m2/g or greater, for example, from 68 m2/g to 400 m2/g may especially benefit from the teachings herein. In certain preferred embodiments, such carbon blacks have a structure, as measured by dibutyl phthalate adsorption, of at least 60 mL/100 g, for example, at least 80 mL/100 g, or from 60 mL/100 g to 160 mL/100 g. Carbon blacks sold under the Regal®, Black Pearls®, Spheron®, Sterling®, and Vulcan® trademarks available from Cabot Corporation, the Raven®, Statex®, Furnex®, and Neotex® trademarks and the CD and HV lines available from Columbian Chemicals, and the Corax®, Durax®, Ecorax®, and Purex® trademarks and the CK line available from Evonik (Degussa) Industries, and other fillers suitable for use in rubber or tire applications, may also be exploited for use with various embodiments. Suitable chemically functionalized carbon blacks include those disclosed in International Application No. PCT/US95/16194 (WO 96/18688), the disclosure of which is hereby incorporated by reference.
Both silicon-coated and silicon-treated carbon blacks may be employed in various embodiments. In silicon-treated carbon black, a silicon containing species such as an oxide or carbide of silicon is distributed through at least a portion of the carbon black aggregate as an intrinsic part of the carbon black. Conventional carbon blacks exist in the form of aggregates, with each aggregate consisting of a single phase, which is carbon. This phase may exist in the form of a graphitic crystallite and/or amorphous carbon, and is usually a mixture of the two forms. Carbon black aggregates may be modified by depositing silicon-containing species, such as silica, on at least a portion of the surface of the carbon black aggregates. The result may be described as silicon-coated carbon blacks.
The materials described herein as silicon-treated carbon blacks are not carbon black aggregates which have been coated or otherwise modified, but actually represent a different kind of aggregate having two phases. One phase is carbon, which will still be present as graphitic crystallite and/or amorphous carbon, while the second phase is silica (and possibly other silicon-containing species). Thus, the silicon-containing species phase of the silicon-treated carbon black is an intrinsic part of the aggregate; it is distributed throughout at least a portion of the aggregate. A variety of silicon-treated blacks are available from Cabot Corporation under the Ecoblack™ name. It will be appreciated that the multiphase aggregates are quite different from the silica-coated carbon blacks mentioned above, which consist of pre-formed, single phase carbon black aggregates having silicon-containing species deposited on their surface. Such carbon blacks may be surface-treated in order to place a silica functionality on the surface of the carbon black aggregate as described in, e.g., U.S. Pat. No. 6,929,783.
One or more additives also may be pre-mixed, if suitable, with the particulate slurry or with the elastomer latex fluid or may be combined with the mixture of these during coagulation. Additives also can be mixed into the coagulating mixture. Numerous additives are well known to those skilled in the art and include, for example, antioxidants, antiozonants, plasticizers, processing aids (e.g., liquid polymers, oils and the like), resins, flame-retardants, extender oils, lubricants, and a mixture of any of them. Exemplary additives include but are not limited to zinc oxide and stearic acid. The general use and selection of such additives is well known to those skilled in the art. It should be understood that the elastomer composites disclosed here include vulcanized compositions (VR), thermoplastic vulcanizates (TPV), thermoplastic elastomers (TPE) and thermoplastic polyolefins (TPO). TPV, TPE, and TPO materials are further classified by their ability to be extruded and molded several times without loss of performance characteristics.
The fraction of the second elastomer with respect to the total rubber in the composite (i.e., the amount of rubber contributed to the coagulum by the second elastomer latex with respect to the total amount of rubber in the coagulum) may be adjusted, e.g., by adjusting the relative flow rates of the two elastomer latices. Other variables that may be manipulated to optimize the filler loading include the absolute flow rate of the first elastomer latex and filler slurry (e.g., the production rate), the relative flow rate of the first elastomer latex and filler slurry (e.g., the filler loading), the location where the second elastomer latex is injected, and the size of injector 42. The fraction of the second elastomer with respect to total rubber may be from about 0.5 wt % to about 50 wt %, for example from about 1 wt % to about 45 wt %, from about 5 wt % to about 40 wt %, from about 10 wt % to about 15 wt %, from about 15 wt % to about 20 wt %, from about 20 wt % to about 25 wt %, from about 25 wt % to about 30 wt %, from about 30 wt % to about 35 wt %, from about 35 wt % to about 40 wt %, or from about 40 wt % to about 45 wt %. In certain embodiments, the fraction may be from about 16 wt % to about 38 wt %. The proportion of the second elastomer that may be used depends in part on the desired composition but may be physically limited depending on the amount of the first elastomer latex that should be injected into mixing portion 10 to generate the initial coagulating mixture.
The amount of filler in the elastomer composite may be any amount of filler that is used to make elastomer composites. For example, rubbers may be produced with at least about 10 phr (parts per hundred of rubber by weight), at least about 20 phr, at least about 30 phr, at least about 40 phr, at least about 50 phr, at least about 55 phr, at least about 60 phr, at least about 65 phr at least about 70 phr, at least about 75 phr, at least about 80 phr, at least about 85 phr, at least about 90 phr, at least about 95 phr, or at least about 100 phr of filler. However, the teachings herein will provide greater advantages with respect to other wet masterbatch methods at higher loadings of filler, for example, from about 40 phr to about 100 phr, from about 50 phr to about 95 phr, from about 55 phr to about 90 phr, from about 60 phr to about 85 phr, from about 60 phr to about 80 phr, from about 65 phr to about 75 phr, or from about 45 phr to about 70 phr. One of skill in the art will recognize that what constitutes a “high loading” will depend on the morphology of the filler, including, e.g., its surface area and structure.
In some embodiments, the use of secondary latex increases the maximum filler loading (e.g., the maximum loading of filler while producing a coherent coagulum), by about 3% to about 30%, for example, from about 3% to about 5%, from about 5% to about 10%, from about 10% to about 15%, from about 15% to about 20%, from about 20% to about 25%, or from about 25% to about 30%, with respect to the maximum loading of filler while producing a coherent coagulum without the use of secondary latex.
The masterbatch crumb produced from the first elastomer latex, the particulate filler slurry, and the second elastomer latex emerges from the discharge end of the coagulum reactor as a substantially constant flow of coagulum concurrently with the on-going feeding of the elastomer latices and particulate filler slurry streams into the coagulum reactor 11. Preferably, the masterbatch crumb is in the form of a “coherent coagulum,” a continuous composite in which the carbon black is dispersed within the coagulated latex, rather than a discontinuous flow of composite in which discrete globules of coagulated latex are separated by an aqueous carrier. Nonetheless, discontinuous coagulum may be processed by manual or batch dewatering methods, followed by thermal drying. Preferably, continuous coagulum is created and then formed into a desirable extrudate, for example, having about 70-85% water content. After formulation, the resulting masterbatch crumb may be passed to suitable drying and compounding apparatus.
In one embodiment, the masterbatch crumb is passed from coagulum reactor 11 to a de-watering extruder via a simple gravity drop or other suitable apparatus known to those of skill in the art. The dewatering extruder may bring the elastomer composite from, e.g., approximately 70-85% water content, to a desired water content, e.g., approximately 1% to 20% water content. The optimal water content may vary with the elastomer employed, the type of filler, and the desired downstream processing procedure. Suitable de-watering extruders are well known and commercially available from, for example, the French Oil Mill Machinery Co. (Piqua, Ohio, USA).
After de-watering, the resulting dewatered coagulum may be dried. In certain embodiments, the dewatered coagulum is simply thermally dried. Preferably, the dewatered coagulum emerging from the de-watering extruder is mechanically masticated while drying. For example, the dewatered coagulum may be mechanically worked with one or more of a continuous mixer, an internal mixer, a twin screw extruder, a single screw extruder, or a roll mill. Suitable masticating devices are well known and commercially available, including for example, a Unimix Continuous Mixer and MVX (Mixing, Venting, eXtruding) Machine from Farrel Corporation of Ansonia, Conn., a long continuous mixer from Pomini, Inc., a Pomini Continuous Mixer, twin rotor corotating intermeshing extruders, twin rotor counterrotating non-intermeshing extruders, Banbury mixers, Brabender mixers, intermeshing-type internal mixers, kneading-type internal mixers, continuous compounding extruders, the biaxial milling extruder produced by Kobe Steel, Ltd., and a Kobe Continuous Mixer. Alternative masticating apparatus suitable for use with various embodiments of the invention will be familiar to those of skill in the art. Exemplary methods for mechanically masticating dewatered composite are disclosed in U.S. Pat. Nos. 6,929,783 and 6,841,606, and PCT Application No. US09/000732, the contents of all of which are incorporated herein by reference.
In certain embodiments, additives can be combined with the dewatered coagulum in the mechanical mixer. Specifically, additives such as filler (which may be the same as, or different from, the filler used in the coagulum reactor; exemplary fillers include silica and zinc oxide, with zinc oxide also acting as a curing agent), other elastomers, other or additional masterbatch, antioxidants, antiozonants, plasticizers, processing aids (e.g., stearic acid, which can also be used as a curing agent, liquid polymers, oils, waxes, and the like), resins, flame-retardants, extender oils, lubricants, and a mixture of any of them, can be added in the mechanical mixer. In certain other embodiments, additional elastomers can be combined with the dewatered coagulum to produce elastomer blends. Exemplary elastomers include, but are not limited to, rubbers, polymers (e.g., homopolymers, copolymers and/or terpolymers) of 1,3-butadiene, styrene, isoprene, isobutylene, 2,3-dialkyl-1,3-butadiene, where alkyl may be methyl, ethyl, propyl, etc., acrylonitrile, ethylene, and propylene and the like. Methods of producing masterbatch blends are disclosed in our commonly owned U.S. Pat. Nos. 7,105,595, 6,365,663, and 6,075,084. Alternatively or in addition, traditional compounding techniques may be used to combine vulcanization agents and other additives known in the art with the dewatered coagulum or, where a masticating apparatus is used to dry the material, the resulting masticated masterbatch, depending on the desired use.
The invention also concerns the use of resulting elastomer composite blend accordingly to any of the mentioned embodiments for the fabrication of tires, in particular for the compositions of tire treads, carcass, tire sidewalls, wire-skim for tires, and cushion gum for retread tires.
The rubber compositions of the invention also comprise all or a portion of the usual additives generally used in the elastomer compositions intended for the manufacture of tires, such as, for example, protection agents, such as antiozone waxes, chemical antiozonants, antioxidants, reinforcing resins, methylene acceptors (for example phenolic novolak resin) or methylene donors (for example HMT or H3M), a crosslinking system based either on sulphur or on donors of sulphur and/or peroxide and/or bismaleimides, vulcanization accelerators, or vulcanization activators.
These compositions can also comprise coupling activators when a coupling agent is used, agents for covering the inorganic filler or more generally processing aids capable, in a known way, by virtue of an improvement in the dispersion of the filler in the rubber matrix and of a lowering of the viscosity of the compositions, of improving their property of processing in the raw state; these agents are, for example, hydrolysable silanes, such as alkylalkoxysilanes, polyols, polyethers, amines, or hydroxylated or hydrolysable polyorganosiloxanes.
The rubber compositions of the invention are manufactured in appropriate mixers using two successive preparation phases according to a general procedure well known to a person skilled in the art: a first phase of thermomechanical working or kneading (sometimes described as “non-productive” phase) at high temperature, up to a maximum temperature of between 130° C. and 200° C., preferably between 145° C. and 185° C., followed by a second phase of mechanical working (sometimes described as “productive” phase) at a lower temperature, typically of less than 120° C., for example between 60° C. and 100° C., finishing phase during which the crosslinking or vulcanization system is incorporated.
The crosslinking system proper is preferably based on sulphur and on a primary vulcanization accelerator, in particular on an accelerator of sulphenamide type. Added to this vulcanization system are various known secondary accelerators or vulcanization activators, such as zinc oxide, stearic acid, guanidine derivatives (in particular diphenylguanidine), and the like, incorporated during the first non-productive phase and/or during the productive phase. The level of sulphur is preferably between 0.5 and 12 phr, preferably between 1 and 10 phr, and that of the primary accelerator is preferably between 0.5 and 5.0 phr.
Use may be made, as accelerator (primary or secondary) of any compound capable of acting as accelerator of the vulcanization of diene elastomers in the presence of sulphur, in particular accelerators of the thiazoles type and their derivatives, accelerators of thiurams types, or zinc dithiocarbamates. These accelerators are more preferably chosen from the group consisting of 2-mercaptobenzothiazyl disulphide (abbreviated to “MBTS”), N-cyclohexyl-2-benzothiazolesulphenamide (abbreviated to “CBS”), N,N-dicyclohexyl-2-benzothiazolesulphenamide (“DCBS”), N-tert-butyl-2-benzothiazolesulphenamide (“TBBS”), N-tert-butyl-2-benzothiazolesulphenimide (“TBSI”), zinc dibenzyldithiocarbamate (“ZBEC”) and the mixtures of these compounds.
The final composition thus obtained is subsequently calendered, for example in the form of a sheet or of a plaque, in particular for laboratory characterization, or else extruded in the form of a rubber profiled element which can be used directly like for example tire tread.
The vulcanization (or curing) is carried out in a known way at a temperature generally of between 130° C. and 200° C. for a sufficient time which can vary, for example, between 5 and 90 min depending in particular on the curing temperature, the vulcanization system adopted and the vulcanization kinetics of the composition under consideration.
The invention relates to the rubber compositions and to the treads described above, both in the raw state (i.e., before curing) and in the cured state (i.e., after crosslinking or vulcanization).
The present invention will be further clarified by the following examples which are intended to be only exemplary in nature
EXAMPLES Example 1 Carbon Black Slurry PreparationDry carbon black (grade indicated in Table 1, below, obtained from Cabot Corporation) was mixed with water and ground to form a slurry having a concentration of about 10-15 wt %. The slurry was fed to a homogenizer at an operating pressure of around 3000 psig to produce a finely dispersed carbon black slurry, and the slurry was introduced as a jet into the mixing zone. The carbon black flow rate was adjusted to about 690-960 kg/hr (wet basis) to modify final carbon black loading levels in composites produced with field latex and to about 1145 kg/hr (wet basis) when latex concentrate was employed.
Natural rubber materials described in Table 2 (field latex unless indicated otherwise in Table 2) were pumped to the mixing zone of the coagulum reactor. The latex flow rate was adjusted between about 320-790 kg/h (wet basis) in order to modify final carbon black loading levels.
Carbon Black and Latex MixingThe carbon black slurry and latex were mixed by entraining the latex into the carbon black slurry in a mixing portion (e.g., mixing portion 10) of a coagulum reactor similar to that shown in
Natural rubber latex materials described in Table 2 were pumped into various locations downstream of the mixing portion of the coagulum reactor at a pressure of 3-8 bar starting at a rate of about 80 kg/hour (wet basis). The latex was injected at a right angle to the wall of the coagulum reactor to which the injection line (e.g., element 28) is affixed. The pumping rate was gradually increased to at most 300 kg/hr (wet basis) until the coagulum emerging from the diffuser exhibited the desired morphology. Downstream of the mixing portion, a diffuser portion had a series of sections, each one having progressively higher diameter than the previous section, with a beveled transition portion in between sections. The first section of the diffuser (e.g., 18a in
For successful examples incorporating secondary latex according to an embodiment of the invention, a masterbatch crumb exited the coagulum reactor as a continuous flow of coherent coagulum. Unsuccessful examples employing secondary latex may be contrasted with successful samples having similar operating conditions; in general, rubber recovered from such examples contained higher loadings of carbon black. Such samples emerged from the coagulum reactor as a discontinuous, sandy coagulum that caused the dewatering extruder to back up. Table 3, below, shows the maximum loading, i.e., the maximum filler content in the elastomer composite, in parts per hundred of rubber (phr), for which coherent coagulum was produced (that is, attempts to produce masterbatch crumb with higher filler content did not result in a coherent coagulum).
The results show that operating variables such as the flow rate of the primary and secondary latex streams, the production rate, the proportion of secondary rubber, and the carbon black loading may be optimized with respect to one another to improve processability and increase filler loading.
The masterbatch crumb discharged from the coagulum reactor was dewatered to 10-20% moisture with a dewatering extruder (The French Oil Machinery Company). In the extruder, the masterbatch crumb was compressed, and water squeezed from the crumb was ejected through a slotted barrel of the extruder.
Drying and CoolingThe dewatered coagulum was dropped into a continuous compounder (Farrel Continuous Mixer (FCM), Farrel Corporation) where it was masticated and mixed with 1 phr of antioxidant (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD, Flexsys, St. Louis, Mo.). The moisture content of the masticated masterbatch exiting the FCM was around 1-2%. The masticated masterbatch was further masticated and cooled on an open mill to form a dried elastomer composite. The actual carbon black loading levels were determined by nitrogen pyrolysis (values listed on Tables 2A-2E) or TGA (values listed on Table 2F) on dried product. The dried elastomer composite was vulcanized; the mechanical properties of the vulcanized elastomer composite (e.g., tan delta, ratio of stresses at 300% and 100% strain) exhibited a variation with loading similar to that of vulcanized elastomer composites having lower filler loadings and prepared using the same techniques but without secondary latex. The use of secondary latex injection enables the manufacture of more highly loaded elastomer composites without sacrificing performance of the final rubber compounds.
Example 2 Filler Slurry PreparationSilicon-treated carbon black (CRX™ 2000 ECOBLACK® silicon-treated carbon black, available from Cabot Corporation) is mixed with water and ground to form a slurry having a concentration of about 10-15 wt %. The slurry is fed to a homogenizer at an operating pressure of around 3000 psig to produce a finely dispersed carbon black slurry, and the slurry is introduced as a jet into the mixing zone. The slurry flow rate is adjusted to about 690-960 kg/hr (wet basis) to modify final filler loading levels in composites produced with field latex and to about 1145 kg/hr (wet basis) when latex concentrate is employed.
Primary Latex DeliveryEither field latex having a dry rubber content of about 27-31% or natural rubber latex concentrate is pumped to the mixing zone of the coagulum reactor. The latex flow rate is adjusted between about 320-790 kg/h (wet basis) in order to modify final filler loading levels.
Filler and Latex MixingThe filler slurry and latex are mixed by entraining the latex into the filler slurry in a mixing portion (e.g., mixing portion 10) of a coagulum reactor similar to that shown in
Field latex is pumped into the coagulating mixture of filler slurry and latex at the transition between the first and second sections (e.g., 20a in
The masterbatch crumb discharged from the coagulum reactor is dewatered to 10-20% moisture with a dewatering extruder (The French Oil Machinery Company). In the extruder, the masterbatch crumb is compressed, and water squeezed from the crumb is ejected through a slotted barrel of the extruder.
Drying and CoolingThe dewatered coagulum is dropped into a continuous compounder (Farrel Continuous Mixer (FCM), Farrel Corporation) where it is masticated and mixed with 1 phr of antioxidant (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD, Flex sys, St. Louis, Mo.) and 1.5 phr of a coupling agent (bis-(triethoxysilylpropyl)tetrasulfide (TESPT, Si-69, available from Evonik Industries, Essen, Germany)). The moisture content of the masticated masterbatch exiting the FCM is around 1-2%. The product is further masticated and cooled on an open mill.
Example 3 Filler Slurry PreparationA mixture of carbon black and silica (N234 carbon black, available from Cabot Corporation, and HiSil® 233 silica, available from PPG Industries, Pittsburgh, Pa.) is mixed with water and ground to form a slurry having a concentration of about 10-15 wt %, in which the ratio of carbon black to silica ranges from 60:40 to 80:20 by mass. The slurry is fed to a homogenizer at an operating pressure of around 3000 psig to produce a finely dispersed carbon black slurry, and the slurry is introduced as a jet into the mixing zone. The slurry flow rate is adjusted to about 690-960 kg/hr (wet basis) to modify final filler loading levels in composites produced with field latex and to about 1145 kg/hr (wet basis) when latex concentrate is employed.
Primary Latex DeliveryEither field latex having a dry rubber content of about 27-31% or natural rubber latex concentrate is pumped to the mixing zone of the coagulum reactor. The latex flow rate is adjusted between about 320-790 kg/h in order to modify final filler loading levels.
Filler and Latex MixingThe filler slurry and latex are mixed by entraining the latex into the filler slurry in a mixing portion (e.g., mixing portion 10) of a coagulum reactor similar to that shown in
Field latex is pumped into the coagulating mixture of filler slurry and latex at the transition between the first and second sections (e.g., 20a in
The masterbatch crumb discharged from the coagulum reactor is dewatered to 10-20% moisture with a dewatering extruder (The French Oil Machinery Company). In the extruder, the masterbatch crumb is compressed, and water squeezed from the crumb is ejected through a slotted barrel of the extruder.
Drying and CoolingThe dewatered coagulum is dropped into a continuous compounder (Farrel Continuous Mixer (FCM), Farrel Corporation) where it is masticated and mixed with 1 phr of antioxidant (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD, Flexsys, St. Louis, Mo.) and 1.5 phr of a coupling agent (bis-(triethoxysilylpropyl)tetrasulfide (TESPT, Si-69, available from Evonik Industries, Essen, Germany)). The moisture content of the masticated masterbatch exiting the FCM is around 1-2%. The product is further masticated and cooled on an open mill to form a dried elastomer composite.
Example 4Dry carbon black (N234, obtained from Cabot Corporation) was mixed with water and ground to form a slurry having a concentration of about 10-15 wt %. The slurry was fed to a homogenizer at an operating pressure of around 3000 psig to produce a finely dispersed carbon black slurry, and the slurry was introduced as a jet into the mixing zone. The carbon black flow rate (dry basis) is specified in Table 4, below.
Primary Latex DeliveryField latex having a dry rubber content of about 27-31% was pumped to the mixing zone of the coagulum reactor. The delivery rate of primary rubber (dry rubber basis) into the mixing zone is listed in Table 4, below.
Carbon Black and Latex MixingThe carbon black slurry and latex were mixed by entraining the latex into the carbon black slurry in a mixing portion (e.g., mixing portion 10) of a coagulum reactor similar to that shown in
Field latex was pumped into the downstream, diffuser portion of the coagulum reactor at the transition between the first and second sections of the diffuser (e.g., 20a on
Results from Examples 4-1 through 4-4 are shown in
The masterbatch crumb discharged from the coagulum reactor was dewatered to 10-20% moisture with a dewatering extruder (The French Oil Machinery Company). In the extruder, the masterbatch crumb was compressed, and water squeezed from the crumb was ejected through a slotted barrel of the extruder.
Drying and CoolingThe dewatered coagulum was dropped into a continuous compounder (Farrel Continuous Mixer (FCM), Farrel Corporation) where it was masticated and mixed with 1 phr of antioxidant (N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD, Flexsys, St. Louis, Mo.). The moisture content of the masticated masterbatch exiting the FCM was around 1-2%. The product was further masticated and cooled on an open mill to form a dried elastomer composite. The actual carbon black loading levels were determined by TGA on the dried elastomer composite and are listed in Table 4. The dried elastomer composite was vulcanized; the mechanical properties of the vulcanized elastomer composite (e.g., tan delta, ratio of stresses at 300% and 100% strain) exhibited a variation with loading similar to that of vulcanized elastomer composites having lower filler loadings and prepared using the same techniques but without secondary latex. The use of secondary latex injection enables the manufacturing of more highly loaded elastomer composites without sacrificing performance of the final rubber compounds.
Example 5This example shows the improvements of rubber composition properties including elastomer composite with high volume fraction of carbon black prepared according to the invention, compared to the already improved properties of tire comprising rubber composition based on elastomer composite having lesser volume fraction of carbon black prepared by the wet mix method used in Example 4 to prepare control samples and to vulcanized rubber compositions prepared by dry mixing.
Preparation of MasterbachesMasterbaches A were prepared according to Example 1, as follows:
-
- Masterbatch A1 corresponds to N234, measured CB loading of 66.1 phr, of table 2D,
- Masterbatch A2 corresponds to Experimental Black 1, measured CB loading of 59 phr, of table 2F,
- Masterbatch A3 corresponds to N134, measured CB loading of 64.4 phr, of table 2F
Masterbatches B were prepared with the same carbon black and the same field latex according to the wet mix method used in Example 4 to prepare control samples, as follows:
-
- Masterbatch B1 includes 50 phr of N234,
- Masterbatch B2 includes 49 phr of Experimental Black 1,
- Masterbatch B3 includes 50 phr of N134,
The tests which follow are carried out in the following way: the diene elastomer and the reinforcing filler or the masterbatches including diene elastomers and reinforcing fillers were introduced into an internal mixer, 70% filled and having an initial vessel temperature of approximately 50° C., followed, after kneading for one minute, by the various other ingredients, with the exception of the sulphur and sulphenamide primary accelerator. Thermomechanical working (non-productive phase) was then carried out in one or two stages (total duration of the kneading equal to approximately 5 min), until a maximum “dropping” temperature of approximately 165° C. is reached.
The mixture thus obtained was recovered and cooled and then sulphur and sulphenamide accelerator were added on an external mixer (homofinisher) at 30° C., the combined mixture was mixed (productive phase) for 3 to 4 minutes.
The compositions were subsequently either calendered in the form of plaques (thickness of 2 to 3 mm), for the measurement of their physical or mechanical properties.
Rubber CompositionsRubber compositions CA1 to CA3 and CB1 to CB3 were produced with masterbatches A1 to A3 and B1 to B3, respectively. Comparative rubber compositions CD1 to CD3 and CE1 to CE3 were fabricated using a dry mixing process from the same carbon blacks in dry form and solid natural rubber.
Thus all the compositions included 100 phr of natural rubber (whether introduced in the form of a masterbatch, or in a solid form) and different grades of carbon black as shown in the following Table 5.
All these compositions also included the additional ingredients shown in Table 6.
The diene rubber compositions were characterized, before and after curing, as indicated below.
1. Mooney PlasticityUse was made of an oscillating consistometer as described in French Standard NF T 43-005 (1991). The Mooney plasticity measurement was carried out according to the following principle: the composition in the raw state (i.e., before curing) was moulded in a cylindrical chamber heated to 100° C. After preheating for one minute, the rotor rotated within the test specimen at 2 revolutions/minute and the working torque for maintaining this movement was measured after rotating for 4 minutes. The Mooney plasticity (ML 1+4) is expressed in “Mooney unit” (MU, with 1 MU=0.83 newton·metre).
2 DispersionIn a known way, filler dispersion in rubber matrix can be represented by Z value, which was measured, after reticulation, according to the method described by S. Otto and A1 in Kautschuk Gummi Kunststoffe, 58 Jahrgang, NR 7-8/2005, article titled “New Reference value for the description of Filler Dispersion with the Dispergrader 1000NT” according to standard ISO 11345.
The calculation of Z value is based on the percentage of undispersed area, as measured by the apparatus “disperGRADER+” provided with its procedure and its operating software “disperDATA” by the Dynisco company according to the equation:
Z=100−(percentage of undispersed area)/0.35
The percentage of undispersed area was measured using a camera with a light source at an angle of 30° with respect to the observation surface. Light dots are associated with filler and agglomerates, while the dark background is associated the rubber matrix; numerical treatment transforms the image into a black and white image, and allows the determination of the percentage of undispersed area, as described by S. Otto in the above mentioned document.
The higher the value Z, the better the dispersion of the filler in the rubber matrix (a Z value of 100 corresponding to perfect mix and a Z value of 0 to poorer mix)
3 RheometryThe measurements were carried out at 150° C. with an oscillating disc rheometer, according to Standard DIN 53529-part 3 (June 1983). The change in the rheometric torque as a function of time describes the change in the stiffening of the composition as a result of the vulcanization reaction. The measurements are processed according to Standard DIN 53529-part 2 (March 1983): “ti” is the induction period, that is to say the time necessary for the start of the vulcanization reaction; tα (for example t90) is the time necessary to achieve a conversion of α %, that is to say α % (for example 90%) of the difference between the minimum and maximum torques. The conversion rate constant, denoted K (expressed in min−1), which is first order, calculated between 30% and 80% conversion, which makes it possible to assess the vulcanization kinetics, was also measured.
4. Tensile TestsThese tensile tests make it possible to determine the elasticity stresses and the properties at break. Unless otherwise indicated, they were carried out in accordance with French Standard NF T 46-002 of September 1988. The nominal secant moduli (or apparent stresses, in MPa) were measured in second elongation (i.e., after a cycle of accommodation to the degree of extension expected for the measurement itself) at 10% elongation (denoted M10), 100% elongation (denoted M100) and 300% elongation (denoted M300).
The properties measured before and after curing at 150° C. for 40 minutes are given in the Tables 7, 8 and 9 (each table corresponding to one specific carbon black grade).
It can be seen that all compositions prepared by a wet mix method (CA1 to CA3 and CB1 to CB3), when compared with a composition having the same ingredients but prepared by dry mix method (CD1 to CD3 and CE1 to CE3), exhibited an improvement of all the properties mentioned above: dispersion (shown by Z value), processability (Mooney), rheometry (T99 and K) and reinforcement (M300 and M300/M100). Thus, higher loading of carbon black enabled by the processes of the invention preserves the improvements obtained by a wet mix, mechanical coagulation method of the type described in U.S. Pat. No. 6,048,923.
Moreover, when comparing compounds prepared by a wet mix method to those prepared by a dry mix method, the percent of improvement obtained at high loadings of carbon black is, for all the properties discussed above, higher that what was obtained at lower loadings of carbon black.
The foregoing description of preferred embodiments of the present invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings, or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto, and their equivalents.
Claims
1. A process for manufacturing a rubber composition for tire, comprising the steps of:
- a) manufacturing a coagulated latex composite by the method comprising a1) flowing a coagulating mixture of a first elastomer latex comprising a first elastomer and a particulate filler slurry along a conduit, wherein the particulate filler comprises a carbon black having a dibutyl phthalate adsorption greater than 60 mL/100 g, and wherein the carbon black has a surface area and is present in the coagulated latex composite in an amount satisfying L≧−0.26*S+94, where L is the amount of the carbon black in the coagulated latex composite in parts per hundred of rubber (phr) and S is the surface area in m2/g as measured by STSA; and a2) introducing a second elastomer latex comprising a second elastomer into the flow of the coagulating mixture to obtain a coagulated latex composite in a form of coherent coagulum and the second elastomer latex is not decorated with filler particles prior to the introduction step;
- b) dewatering the coagulated latex composite obtained in step a) into a desired water content;
- c) incorporating all the constituents of the composition for tire, including the dewatered coagulated latex composite obtained in step b), in a mixer by thermomechanically kneading the whole mixture at high temperature, up to a maximum temperature of between 130° C. and 200° C., then
- d) performing mechanical working of the resulting mixture, with incorporation of a crosslinking system, at a temperature of less than 120° C.
2. The process according to claim 1, comprising, before flowing the coagulating mixture, generating the coagulating mixture by feeding a continuous flow of the first elastomer latex to a mixing zone of a coagulum reactor defining an elongate coagulum zone extending from the mixing zone to a discharge end and comprising the conduit, and feeding a continuous flow of a fluid comprising a particulate filler under pressure to the mixing zone of the coagulum reactor to form the coagulating mixture.
3. The process according to claim 2, wherein the continuous flow of the fluid comprising particulate filler has a velocity from about 30 m/s to about 250 m/s, the continuous flow of the first elastomer latex has a velocity of at most about 10 m/s, and a residence time of the coagulating mixture in the coagulum reactor before introducing the second elastomer latex is from 1×10−2 s to about 6×10−2 s.
4. The process according to claim 1, wherein the conduit comprises a first conduit portion having a first diameter, a second conduit portion having a second diameter greater than the first diameter, and a transition zone therebetween having a diameter that increases from the first diameter to the second diameter, wherein flowing comprises flowing the coagulating mixture into the second conduit portion from the first conduit portion, and wherein introducing comprises introducing the second elastomer latex into the coagulating mixture in the transition region.
5. The process according to claim 4, wherein flowing the coagulating mixture comprises flowing the coagulating mixture through the transition region under conditions of turbulent flow.
6. The process according to claim 1, wherein in step b) the coagulated latex composite is dewatered into a desired water content of 1% to 20%.
7. The process according to claim 1, comprising, before step c), a further step of drying the dewatered coagulated latex composite.
8. The process according to claim 1, wherein in step c) the constituents are thermomechanically kneaded at a temperature between 145° C. and 185° C.
9. The process according to claim 1, wherein in step d) the constituents are worked at a temperature between 60° C. and 100° C.
10. The process according to claim 1, comprising the step of calendering or extruding the rubber composition obtained after step d).
11. The process according to claim 1, wherein the amount of the second elastomer in the composite is from about 16 wt % to about 38 wt %.
12. The process according to claim 1, wherein the second elastomer is a synthetic elastomer.
13. The process according to claim 1, wherein the second elastomer latex is natural rubber latex.
14. The process according to claim 13, wherein the natural rubber latex comprises field latex, latex concentrate, skim latex, or a combination of two or more of these.
15. The process according to claim 13, wherein a component of the natural rubber latex has been chemically or enzymatically modified.
16. The process according to claim 1, wherein the elastomer composite includes at least 10 phr of the particulate filler.
17. The process according to claim 1, wherein the ingredients of step c) comprise an additive selected from the group consisting of filler, other elastomers, other or additional masterbatch, antioxidants, antiozonants, plasticizers, processing aids, resins, flame-retardants, extender oils, lubricants, methylene acceptors or methylene donors, coupling activators, and a mixture of any of them.
18. The process according to claim 1, wherein the rubber composition is a tire tread.
Type: Application
Filed: Dec 17, 2014
Publication Date: Apr 16, 2015
Applicants: , ,
Inventors: Ting Wang (Lexington, MA), Meng-Jiao WANG (Shanghai), Bernard MARIADASS (Port Dickson), Thirunavuc Karasu GOVINDAN (Port Dickson), Anthony das THIRUHELVANATHAN (Port Dickson), Boon Kwang LEE (Port Dickson), Xuan ZHANG (Acton, MA)
Application Number: 14/574,174
International Classification: C08J 3/20 (20060101); C08J 3/00 (20060101);
