Tire tread compound
阅读说明：本技术 轮胎胎面胶料 (Tire tread compound ) 是由 霍华德·科尔文 蒂莫西·唐利 扎克利·沃尔特斯 于 2018-02-13 设计创作，主要内容包括：轮胎胎面组合物包含一定量的弹性体和一定量的基本均匀地遍布弹性体分布的烃树脂。所述弹性体包含天然橡胶。所述烃树脂具有在所述天然橡胶中的预定混溶性。通过与在所述轮胎胎面组合物中使用的弹性体和烃树脂相一致的弹性体-树脂混合物的实际Tg与所计算的预测Tg的偏差来测量所述预定混溶性。特别地,所述天然橡胶中的预定混溶性是在20phr填充量下实际Tg与预测Tg的小于约百分之六(6％)偏差。(The tire tread composition includes an amount of an elastomer and an amount of a hydrocarbon resin substantially uniformly distributed throughout the elastomer. The elastomer comprises natural rubber. The hydrocarbon resin has a predetermined miscibility in the natural rubber. The predetermined miscibility is measured by the deviation of the actual Tg of the elastomer-resin mixture, consistent with the elastomer and hydrocarbon resin used in the tire tread composition, from the calculated predicted Tg. In particular, the predetermined miscibility in the natural rubber is less than about six percent (6%) deviation of the actual Tg from the predicted Tg at 20phr loading.)
1. A tire tread composition comprising:
a quantity of an elastomer comprising natural rubber; and
an amount of a hydrocarbon resin substantially uniformly distributed throughout the elastomer, the hydrocarbon resin having a predetermined miscibility in the natural rubber at a predetermined concentration of 20phr of the resin in the elastomer as measured by a deviation of an actual Tg of an elastomer-resin mixture from a predicted Tg of the elastomer-resin mixture consistent with the elastomer and hydrocarbon resin used in the tire tread composition, wherein the predetermined miscibility in the elastomer-resin mixture is less than about six percent (6%) deviation of the actual Tg from the predicted Tg, and wherein the hydrocarbon resin has a softening point of 110 ℃ to 165 ℃.
2. The tire tread composition of claim 1, wherein the elastomer is comprised of natural rubber.
3. The tire tread composition of claim 1, wherein the natural rubber is guayule natural rubber.
4. The tire tread composition of claim 1, wherein the natural rubber is a TKS natural rubber.
5. The tire tread composition of claim 1, wherein the elastomer-resin mixture has an actual Tg of about-80 ℃ to about-15 ℃.
6. The tire tread composition of claim 1, wherein the tire tread composition has an actual Tg of about-50 ℃ to-5 ℃.
7. The tire tread composition of claim 1, wherein the hydrocarbon resin is selected from the group of hydrocarbon resins consisting of cycloaliphatic hydrocarbon resins, aliphatic hydrocarbon resins, polymerized pinene resins (α or β), and hydrocarbon resins produced by thermal polymerization of mixed dicyclopentadiene (DCPD) and aromatic styrenic monomers derived from petroleum feedstocks, and combinations thereof.
8. The tire tread composition of claim 1, wherein the tire tread composition is free of natural plasticizers.
9. The tire tread composition of claim 1, wherein the elastomer-resin mixture is substantially free of fillers and plasticizers.
10. The tire tread composition of claim 1, wherein the hydrocarbon resin is present in an amount of at least about 10 phr.
11. The tire tread composition of claim 10, wherein the hydrocarbon resin is present in an amount of at least about 20 phr.
12. The tire tread composition of claim 1, wherein the predetermined miscibility is calculated by a mathematical model of the elastomer-resin mixture.
13. The tire tread composition of claim 12, wherein the mathematical model is a Fox equation.
14. The tire tread composition of claim 1, wherein the elastomer-resin mixture has an additive material that is the same as an additive material found in the tire tread composition and affects the Tg.
15. A tire tread manufactured using the tire tread composition of claim 1.
16. A tire comprising a tire tread manufactured using the tire tread composition of claim 1.
17. A tire tread composition comprising:
a quantity of an elastomer, said elastomer consisting of natural rubber; and
an amount of a hydrocarbon resin substantially uniformly distributed throughout the elastomer, the hydrocarbon resin having a predetermined miscibility in the natural rubber at a predetermined concentration of the resin in the elastomer as measured by a deviation of an actual Tg of an elastomer-resin mixture from a predicted Tg of the elastomer-resin mixture consistent with the elastomer and hydrocarbon resin used in the tire tread composition, wherein the predetermined miscibility in the elastomer-resin mixture is less than about six percent (6%) deviation of the actual Tg from the predicted Tg, and the predetermined concentration of the resin in the elastomer is twenty (20) phr, and
wherein the hydrocarbon resin is selected from the group of hydrocarbon resins consisting of alicyclic hydrocarbon resins, aliphatic hydrocarbon resins, polymerized pinene resins, and hydrocarbon resins produced by thermally polymerizing dicyclopentadiene (DCPD) mixed with petroleum feedstock and aromatic styrene-based monomers derived from petroleum feedstock, and combinations thereof, and wherein the hydrocarbon resin has a softening point of 110 ℃ to 165 ℃.
18. A tire comprising a tire tread manufactured using the tire tread composition of claim 17.
19. A tire tread composition comprising:
a quantity of an elastomer comprising natural rubber; and
an amount of a hydrocarbon resin substantially uniformly distributed throughout the elastomer, the hydrocarbon resin having a predetermined miscibility in the natural rubber at a predetermined concentration of 20phr of the resin in the elastomer, as measured by a deviation of an actual Tg of the tire tread composition from a predicted Tg of the tire tread composition, wherein the predetermined miscibility in the tire tread composition is less than about six percent (6%) deviation of the actual Tg from the predicted Tg, and wherein the hydrocarbon resin has a softening point of 110 ℃ to 165 ℃.
20. A tire comprising a tire tread manufactured using the tire tread composition of claim 19.
Technical Field
The present disclosure relates to a rubber composition for a tire, and more particularly, to a natural rubber composition used as a tread of a tire.
Background
The tire industry is extremely competitive, whereby it is crucial to be able to convert raw materials as prices shift. In treads for passenger tires, a typical elastomer system is a mixture of styrene-butadiene rubber (SBR) and polybutadiene rubber (BR). SBR may be a solution-based polymer or an emulsion-based polymer. BR is typically of the high cis type. SBR is typically used in relatively large amounts in tread compounds having an SBR/BR elastomer system, and the amount and type of SBR is selected based on the performance characteristics desired for the tire end use.
The properties of the tread compounds are governed primarily by the glass transition temperature (Tg) of the elastomer system. The high cis BR has a glass transition temperature of about-105 ℃. The Tg of SBR can be controlled to a value of-75 ℃ (or lower) to above 0 ℃ depending on the styrene and vinyl content. Thus, the tread compound has great flexibility to set the Tg of the tread compound by the ratio of SBR to BR and the styrene/vinyl content in the SBR. Depending on pricing, the SBR/BR ratio can also be optimized for prices within a range.
There is an industrial need to be able to use more natural rubber for passenger tire compounds, especially when there is a large price difference between natural rubber, SBR and BR. However, typically, natural rubber is used in passenger tire treads only in limited amounts, and most materials are used in tread compounds for heavy trucks and buses, which may all be natural rubber. Ideally, if natural rubber pricing is low relative to SBR and BR, it would be highly advantageous to have a tread compound with only natural rubber in the elastomer system for passenger tires.
One challenge with the overall use of natural rubber in passenger tread compounds is the low Tg associated with natural rubber (about-65 ℃). Compounding of pure natural rubber with common processing oils produces low Tg tire tread compounds that do not have the wet skid characteristics (wet traction characteristics) necessary for contemporary passenger tires.
For many years, additives such as resins have been used in the tire industry to improve the processability of tire compounds. These materials can be used as a homogenizing agent that facilitates blending of the elastomer, batch-to-batch uniformity, improves filler dispersion, and can improve build tack. These types of resins include hydrocarbons (e.g., C5, C9, mixed C5-C9, dicyclopentadiene, terpene resins, high styrene resins, and mixtures), coumarone-indene resins, rosins and their salts, pure monomer resins, and phenol resins.
Resins have also been used to adjust the Tg of synthetic tread compounds to maximize properties such as abrasion resistance without compromising other properties such as wet skid resistance. For example, U.S. patent No. 7,084,228 to labauce teaches that certain terpene-based resins can be incorporated into an SBR/BR tread compound in such a way that higher BR content can be achieved to improve abrasion resistance, but the Tg of the tire tread compound remains the same.
There is an ongoing need for natural rubber tread compounds having additives that can increase the Tg of the natural rubber to provide an increase in Tg to improve wet skid resistance, while not negatively affecting properties such as rolling resistance or abrasion resistance. Desirably, only small amounts of such additives are required to minimize cost.
Disclosure of Invention
In concordance with the instant disclosure, a natural rubber tread compound having an additive that can increase the Tg of natural rubber to provide an increase in Tg to improve wet skid resistance while not negatively affecting properties such as rolling resistance or abrasion resistance, and which requires only a small amount of such additive to minimize cost, has surprisingly been discovered.
In one embodiment, a tire tread composition includes an amount of an elastomer and an amount of a hydrocarbon resin substantially uniformly distributed throughout the elastomer. The elastomer comprises, and in particular embodiments, consists entirely of, natural rubber. The hydrocarbon resin has a predetermined miscibility at a predetermined concentration in the natural rubber as measured by a deviation of an actual Tg of the elastomer-resin mixture from a predicted Tg of the elastomer-resin mixture consistent with the elastomer and hydrocarbon resin used in the tire tread composition.
As used herein, the phrase "elastomer-resin mixture consistent with the elastomer and hydrocarbon resin used in the tire tread composition" means that the unit weight ratio of resin to elastomer in the elastomer-resin mixture is substantially the same as the unit weight ratio of resin to elastomer in the tire tread composition.
In particular, when 20phr resin is used in the elastomer-resin mixture, the predetermined miscibility in the elastomer-resin mixture is less than about six percent (6%) deviation of the actual Tg from the predicted Tg. In this embodiment, the effect of fillers and oils on Tg is advantageously removed from consideration, since only the elastomers in the tire tread composition at their relative loading are considered for determining the deviation of the actual Tg from the predicted Tg.
In another embodiment, the elastomer-resin mixture used to determine the effect of the hydrocarbon elastomer on Tg may be the same or approximately the same as the tire tread composition. For example, the elastomer-resin mixture can be compounded to have the same additive materials that have an effect on Tg at the same relative concentration as the tire tread composition. In particular, the tire tread composition may include an amount of elastomer and an amount of hydrocarbon resin substantially uniformly distributed throughout the elastomer. The elastomer comprises, and in particular embodiments, consists entirely of, natural rubber. The hydrocarbon resin has a predetermined miscibility at a predetermined concentration in the natural rubber. The predetermined miscibility is measured by the deviation of the actual Tg of the tire tread composition from the predicted Tg of the tire tread composition. In particular, the predetermined miscibility in natural rubber is less than about six percent (6%) deviation of the actual Tg of the tire tread composition from the predicted Tg when 20phr of resin is used in the tire tread composition. In this embodiment, the fillers and oils in the tire tread composition will have an effect on the actual Tg that needs to be considered when determining the deviation of the actual Tg from the predicted Tg.
In particular embodiments, the present disclosure includes natural rubber tread compounds having a high softening point resin designed to be compatible with natural rubber. Compatibility of the resin with the polymer system is important in tread compounds because as the resin/polymer system becomes incompatible, the resin has less of an impact on the Tg of the elastomer system and can actually form a separate phase in the polymer matrix, which can reduce dynamic properties. Some resins are compatible with natural rubber to a limited extent, but compatibility will depend on the difference in polarity between the resin and the polymer, the molecular weight of the resin, and any functional groups that the resin or polymer may contain.
It has been found that one way to measure compatibility is to compare the actual Tg of the system with the predicted Tg calculated for a fully miscible system. While a variety of mathematical models may be used to predict Tg, and all are contemplated to be within the scope of the present disclosure, such calculations may be performed using the fox equation (shown below), which relates the weight percent of each component to the overall glass transition temperature,
where Tg is the overall glass transition of the blend, Tg, 1 is the glass transition temperature of
The equation indicates that the higher the Tg of the high Tg component in such blends, the less high Tg component is needed to achieve any particular Tg of the blend. In the polymer system of the tire tread, this means that the higher the glass transition temperature of the resin, the less resin is needed to adjust the overall Tg of the compound to a higher value.
It is understood that a suitable mathematical model for use in the present disclosure will predict Tg at least as accurately as the well-known fox equation, thus yielding substantially the same prediction. Thus, the predetermined miscibility predicted by Focus' equation of less than six percent (6%) deviation at 20phr of resin in the elastomer-resin mixture is equally applicable to these other suitable mathematical models.
There are practical limits to this benefit. For example, the resin and polymer systems must be mixed and the typical mixing temperature of the tread compound does not exceed 165 ℃. This temperature is achieved within a very limited time, so that the resin must first soften, so that it can be completely incorporated into the polymer matrix. Thus, resins having softening points above 165 ℃ have been found to be unsuitable for the tire tread compounds of the present disclosure. It has been found that the tapping time during master mixing (master mixing) should be at least 20-30 ℃ higher than the softening point of the resin to ensure adequate combination with the elastomer system.
The practical lower limit of the softening point of the resin is 110 ℃, since below this level, much higher levels of resin are required to achieve the desired Tg of the overall compound. For hydrocarbon resins, the softening point and glass transition temperature are generally related and the softening point is about 45 ℃ above the Tg.
It is recognized that incompatible systems do not follow this fox equation, and as a result, Tg behavior in differential scanning calorimetry can vary significantly. An example of such an incompatibility assay is depicted in graphical form in fig. 1. For extremely incompatible systems, the original Tg's of the two components can be seen, but more typically the Tg's of each component are shifted, depending on the degree of compatibility. The mixture Tg deviates further from the value predicted by the fox equation and the system should be considered as more incompatible. For tire tread compounds, substantially complete compatibility is desired.
In another embodiment, the tire tread compounds of the present disclosure involve the use of specific resins in a > 98% cis polyisoprene polymer. This includes natural or synthetic rubber formulations. The natural rubber may be derived from any source. Hevea (Hevea) is the most common, but guayule and Hevea (TKS) may also be used.
Synthetic high cis polyisoprenes are well known in the industry and are commercially available from Goodyear Chemical
Drawings
The above and other advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description, particularly when considered in light of the figures described herein.
FIG. 1 is a model of a first rubber compound (shown in solid lines containing fully compatible resins as determined by the agreement between the actual Tg and the Tg predicted by the Focus equation (also shown in solid lines)) and a second rubber compound (shown in dashed lines which deviates from the Tg predicted by the Focus equation, thus indicating an incompatible resin), where the curve of the second rubber compound exhibits a significant deviation from the curve of the first rubber compound. Because the compatibility of "incompatible" resins is very limited, once the elastomer is saturated with the resin, the resin does not have a major effect on the Tg of the composite, and thus there is a flattening of the curve. It should be recognized that the resins may form separate phases if they are sufficiently incompatible.
FIGS. 2-9 show DSC test results for two different resin types at different PHR loadings in a natural rubber composition, wherein one resin is compatible as described herein and the other resin is incompatible as described herein; and
FIG. 10 is a bar graph depicting comparative tire test results of wet handling and wet braking using the natural rubber tread compounds of the present disclosure relative to a fully synthetic rubber tread compound.
Detailed Description
The following detailed description and the annexed drawings describe and illustrate various embodiments of the compositions. The description and drawings serve to enable one skilled in the art to make and use the composition, and are not intended to limit the scope of the composition in any way. For the disclosed methods, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical unless otherwise disclosed.
The present disclosure includes rubber formulations having an amount of elastomer and an amount of hydrocarbon resin. The hydrocarbon resin is distributed substantially uniformly throughout the elastomer, for example, by way of non-limiting example, by a mixing operation prior to an extrusion or forming operation. It is to be understood that a substantially uniform distribution of resin throughout the elastomer can be facilitated by thorough mixing operations, and that one of ordinary skill in the art would be able to perform such mixing operations.
Rubber formulations can be compounded by methods known in the rubber compounding art, for example, mixing a variety of sulfur-vulcanizable ingredient polymers with a variety of commonly used additive materials, such as curatives (curatives) such as sulfur, activators, retarders, and accelerators, processing additives such as oils, e.g., tackifying resins, silicas, plasticizers, fillers, pigments, fatty acids, zinc oxide, waxes, antioxidants and antiozonants, debonders, and reinforcing materials such as carbon black, and the like. Other suitable additives for rubber formulations may also be used as desired. Depending on the intended use of the rubber formulation, the usual additives are selected and used in conventional amounts.
In a particular embodiment, the elastomer system comprises natural rubber. In the most particular embodiment, the elastomer system consists entirely of natural rubber.
Although the type and loading of the resin is primarily constrained by compatibility (as defined by the agreement of the actual Tg at a particular resin loading level with the predicted value of Tg), the molecular weight (Mn) of the selected hydrocarbon resin is typically 500-3000g/mol, and typically does not exceed more than 4000g/mol, in order to provide sufficient compatibility with the natural rubber.
Although Focus' equation is identified herein as a particularly suitable way of calculating the predicted value of Tg at a particular resin fill level, one of ordinary skill in the art will appreciate that other equations and models (e.g., artificial intelligence models, etc.) may be used within the scope of the present disclosure to predict Tg at a particular resin fill level, as desired. Thus, the present disclosure is not limited to the application of Focus' equation to the problem of resin miscibility in polymers.
The resin is added to the rubber formulation to a level where the total compound Tg is in the desired range (e.g., about-50 ℃ to-5 ℃). In particular, the resin loading can also be maximized to provide the desired compound Tg and associated traction properties, but not so high as to prevent mixing under conventional mixing operations. In particular, the amount of resin added may be from about 5phr to about 40 phr. For example, the resin may be added to a content of at least about 10phr, in some examples at least about 15phr, and in even further examples at least about 20 phr. One of ordinary skill in the art can select an appropriate resin content within this range as desired depending on the final application of the tire tread and the type of resin selected.
As a non-limiting example, the resins used in the tire tread compositions of the present disclosure may be selected from the group consisting of cycloaliphatic hydrocarbon resins, aliphatic hydrocarbon resins, polymerized pinene resins (α or β), and hydrocarbon resins produced by thermal polymerization of mixed dicyclopentadiene (DCPD) and aromatic styrenic monomers derived from petroleum feedstocks, and combinations thereof.
An example of a suitable resin is known as ESCOREZTM5340 a cycloaliphatic hydrocarbon resin which is one of the 5300 series resins commercially available from ExxonMobil Chemical Company. ESCOREZTM5340 the resin is a water white cycloaliphatic hydrocarbon resin originally designed to tackify a variety of adhesive polymers including Ethylene Vinyl Acetate (EVA), styrenic block copolymers (e.g., SIS, SBS, and SEBS block copolymers), metallocene polyolefins, amorphous polyolefins (e.g., APP and APAO). ESCOREZTM5340 the resin is typically provided in pellet form and has a typical softening point of about 283.1 ° F (139.5 ℃) based on the ETM 22-24 test protocol. The ETM test protocol is a published ExxonMobil test method for the american region, and was developed according to ASTM test methods and obtained on request from ExxonMobil, and is hereby incorporated by reference. Based on ETM 22-14, ESCOREZTM5340 the resin has a melt viscosity (356 ° F (180 ℃)) of 3600cP (3600 mPas). ESCOREZTM5340 the resin has a number average molecular weight (Mn) of about 400g/mol and a weight average molecular weight (Mw) of about 730g/mol, both based on ETM 300-83. Based on ETM 300-90, ESCOREZTM5340 the glass transition temperature of the resin is about 187 ° F (86 ℃).
Another example of a compatible resin is known as ESCOREZTM1102 resin, which is one of a 1000 series resin commercially available from ExxonMobil Chemical Company. ESCOREZTMThe 1102 resin was originally designed as an adhesive for a variety of applications, including use in thermoplastic pavement marking formulations. ESCOREZTMThe 1102 resin is a yellow aliphatic hydrocarbon resin, typically provided in pellet form. It should be recognized that ESCOREZ is based on the ETM 22-24 test protocolTMThe 1102 resin has a softening point of about 212.0 ° F (100 ℃), however, this resin falls outside the optimum range of softening points for material utilization and is therefore considered unsuitable for this application. Based on ETM 22-31, ESCOREZTMThe 1102 resin has a cP of 1650 (1650 mPas)Melt viscosity (320 ℃ F. (160 ℃ C.)). Based on ETM 300-83, ESCOREZTMThe number average molecular weight (Mn) of the 1102 resin was about 1300 g/mol. The weight average molecular weight (Mw) was about 2900g/mol based on ETM 300-83. Based on ETM 300-90, ESCOREZTMThe glass transition temperature of the 1102 resin was about 126F (52 c).
Yet another example of a suitable resin is known as DERCOLYTE ATM115 polymerization of resins α pinene resin, a type of polyterpene resin commercially available from headquarters in southwestern France as DRT (D riv s R si niques et Terp niques.) DERCOLYTE ATM115 resin is typically provided in sheet form. Production of DERCOLYTE ATM115 resins were used for the polymerization of α pinene and were originally developed as tackifying resins to improve the adhesive properties (i.e., tack and adhesion) of hot melt formulations or solvent-based adhesivesTMThe 115 resin had a softening point of about 239 ° F (115 ℃) (ring-and-ball process). The weight average molecular weight (Mw) was about 900 g/mol. DERCOLYTE ATMThe glass transition temperature of the 115 resin was about 158 ° F (70 ℃).
Yet another example of a suitable resin is
As a non-limiting example, the resins employed in the tire tread compositions of the present disclosure may not be selected from the group consisting of indene-coumarone resins, phenol resins, α -methyl styrene (AMS) resins, and combinations thereof.
An example of an unsuitable resin is NovaresTMC160 resin, commercially available from Duisburg, Germany
Another example of an unsuitable resin is
Yet another example of an unsuitable resin is KRATONTMAT8602 resin, which is one of the α -methyl styrene (AMS) resin series commercially available from Kraton corporation, and was developed as an aromatic tackifier having low odor and water-white color KRATONTMThe AT8602 resin had a softening point (ring-and-ball) of about 239 ° F (115 ℃). KRATONTMThe measured Tg of the AT8602 resin was about 160 ℃ F. (71 ℃).
It should be recognized that the rubber formulations of the present disclosure do not contain natural plasticizers, such as sunflower oil, canola oil, and the like. Not only are such natural plasticizers more expensive, they are also known to undesirably affect wet skid resistance. Thus, the use of natural plasticizers is believed to be contrary to the objectives of the present disclosure, which are to enhance wet skid resistance by using the appropriate resin type and specific resin loading in a rubber formulation containing natural rubber.
The present disclosure also includes articles containing rubber formulations having a natural rubber and a hydrocarbon resin having a predetermined miscibility at a predetermined concentration. It is to be appreciated that the rubber formulation can be extruded, molded or otherwise formed into a desired shape and cured by application of at least one of heat and pressure. As a particular example, the rubber formulation may be used in a tire as a tread. For this purpose, the actual Tg of the elastomer-resin mixture present in the rubber formulation may be from about-80 ℃ to about-15 ℃ and the elastomer-resin mixture is comprised of natural rubber, typically from-65 ℃ to about-15 ℃.
The following examples are presented for illustrative purposes and do not limit the invention. All parts are parts by weight unless specifically identified otherwise.