JPWO2018148725A5 - Guayule tire tread compound - Google Patents

Description

Background The tire industry is extremely competitive, so it is important to be able to switch raw materials as prices change. In passenger tire treads, a typical elastomer system is a mixture of styrene-butadiene rubber (SBR) and polybutadiene rubber (BR). The SBR can be a solution-based polymer or an emulsion-based polymer. BR is typically highly cis. SBR is commonly used in large amounts in tread compounds having SBR/BR elastomer systems, and the type and amount of SBR is selected based on the performance characteristics desired in the tire end use.

Tread compound performance is primarily determined by the glass transition temperature (Tg) of the elastomer system. High cis BR has a glass transition temperature of about -105°C. The Tg of the SBR can be controlled with values ranging from -75°C (or below) to over 0°C depending on the styrene and vinyl content. Thus, the tread compound has extreme flexibility to set the Tg of the tread compound by both the styrene/vinyl content in the SBR and the ratio of SBR to BR. Depending on the price, the SBR/BR ratio can also be optimized for prices within the range.

More natural rubber in passenger tire compounds , especially when there is a large price difference between natural rubber, SBR and BR, and especially non-hevea sources of natural rubber such as natural rubber derived from guayule; There is an industrial need to be able to use However, typically natural rubber is used only in limited amounts in passenger tire treads and most of the material is used in heavy truck and bust tread compounds and can be all natural rubber. Ideally, if the price of natural rubber were low relative to SBR and BR, it would be highly advantageous to have a tread compound that uses only natural rubber in elastomer systems used in passenger tires.

One of the challenges in using all natural rubber in passenger tread compounds is the low Tg (approximately -65°C) associated with natural rubber. Mixing pure natural rubber with conventional process oils will result in a low Tg tire tread compound that will not have the wet traction characteristics required for modern passenger tires.

Additives such as resins have long been used in the tire industry to improve the processability of tire compounds . These materials can act as homogenizers to promote elastomer mixing, batch-to-batch uniformity, improve filler dispersion, and improve building tack. These types of resins include hydrocarbons (e.g. C5, C9, mixed C5-C9, dicyclopentadiene, terpene resins, high styrenic resins, and mixtures), coumarone-indene resins, rosins and their salts, pure monomers. resins, and phenolic resins.

Resins have been used to adjust the Tg of synthetic tread compounds to maximize properties such as wear without compromising other properties such as wet traction. For example, Labauze U.S. Pat. No. 7,084,228 discloses that certain terpene-based resins can be incorporated into SBR/BR tread compounds in such a way that higher BR levels can be achieved to improve wear. As taught, the Tg of the tire tread compound remains the same.

A guayule natural rubber tread having additives capable of increasing the Tg of guayule natural rubber to provide increased Tg to improve wet traction without adversely affecting properties such as rolling resistance or wear. There is a continuing need for compounds . Desirably, only small amounts of such additives will be required to minimize cost.

SUMMARY According to the present disclosure, additions can increase the Tg of guayule natural rubber to provide increased Tg to improve wet traction without adversely affecting properties such as rolling resistance or wear. It has been surprisingly found that guayule natural rubber tread compounds with additives that require only small amounts of such additives to minimize cost.

In certain forms, the present disclosure includes guayule natural rubber tread compounds that include a high softening point resin that is designed to be miscible with guayule natural rubber. The miscibility of the resin in the polymer system is important in tread compounds . This is because when the resin/polymer system becomes immiscible, the resin exerts less influence on the Tg of the elastomeric system and forms a separate phase in the polymer matrix that can reduce dynamic properties. This is because it can actually be formed. Some resins are miscible with guayule natural rubber to a limited extent, but the miscibility depends on the difference in polarity between the resin and the polymer, the molecular weight of the resin, and any functional group, will depend.

This equation indicates that the higher the Tg of the high Tg component in such a blend, the less high Tg component is required to achieve any particular Tg in the blend. In a tire tread polymer system, this means that the higher the glass transition temperature of the resin, the less need to adjust the overall Tg of the compound to a higher value.

There are practical limits to this benefit. For example, the resin and polymer system must be mixed, and typical mixing temperatures for tread compounds do not exceed 165°C. This temperature is achieved in a very limited time, so the resin must first soften so that it can be fully incorporated into the polymer matrix. Thus, resins with softening points above 165°C have been found to be unsuitable for tire tread compounds of the present disclosure. It has also been found that the dump temperature during master mixing should be at least 20-30° C. above the softening point of the resin to ensure adequate incorporation in the elastomer system.

The practical lower limit for resin softening point is 110°C. This is because below this level, significantly higher levels of resin are required to achieve the desired Tg of the overall compound . Softening points and glass transition temperatures are well related for hydrocarbon resins, with softening points about 45° C. above Tg.

It should be understood that immiscible systems will not obey this Fox equation, and that Tg behavior in differential scanning calorimetry (DSC) can change substantially as a result. be. An example of this immiscibility determination is graphically represented in FIG. In highly immiscible systems, the original Tg of both components is found, but what is more typical is a shift in the Tg of each component depending on the degree of miscibility. It should be considered that the further the Tg of the mixture deviates from the value predicted by the Fox equation, the less miscible the system. Substantially complete miscibility is desired in tire tread compounds .

In another aspect, the tire tread compounds of the present disclosure relate to the use of certain resins in a 98% cis-polyisoprene polymer. This includes both natural or synthetic rubber compounding. Natural rubber can come from any source. Hevea is the most common, but guayule and Russian dandelion can also be used. In the most particular form, guayule-based natural rubber is used, due in part to the surprising and unexpected performance benefits found with guayule-based natural rubber, which are further detailed below.

FIG. 1 shows a first rubber compound (indicated by the solid line) with a sufficiently miscible resin as determined by the agreement between the Tg predicted by the Fox equation (indicated by the solid line) and the actual Tg. ) and a second rubber compound (indicated by the dotted line) deviating from the Tg predicted by the Fox equation, thus illustrating an immiscible resin, where the second The curve for rubber compound No. 2 shows a significant deviation from the curve for rubber compound No. 1. The miscibility of "immiscible" resins is so limited that once the elastomer is saturated with the resin, the resin will not have a significant effect on the Tg of the mixture. Thus there is a flattening of the curve. It should be understood that the resin can form separate phases if it is sufficiently immiscible.

FIG. 10 is a bar graph showing comparative tire test results for wet handling and wet braking with a natural rubber tread compound according to the present disclosure versus an entirely synthetic rubber tread compound .

The resin is added to the rubber compound at a level in the desired range such that the Tg of the overall compound is between about -50°C and -5°C. In particular, the amount of resin added can also be maximized to provide the desired compound Tg and associated traction performance, but not so much that it interferes with mixing under conventional mixing operations.

Through testing of the Tg of natural rubber compounds with different resin types and different resin loadings, certain types of hydrocarbon resins were found to be the most miscible with the natural rubber of the elastomeric system at the aforementioned loading levels, and therefore , has the desired effect on the overall Tg of the resulting tread compound . As non-limiting examples, resins used in tire tread compositions of the present disclosure can be selected from the group consisting of: cycloaliphatic hydrocarbon resins, aliphatic hydrocarbon resins, polymerized pinene resins (alpha or beta ), and hydrocarbon resins made by thermal polymerization of aromatic styrenic monomers and mixed dicyclopentadiene (DCPD) derived from petroleum feedstocks, and combinations thereof.

Through laboratory testing of the Tg of natural rubber compounds with different resin types and different resin loadings, it was found that the particular type of resin was the least miscible with the natural rubber of the elastomeric system at the aforementioned loading levels, and that Thus, it has been surprisingly found that it does not have the desired effect on the overall Tg of the resulting tread compound . As a non-limiting example, resins used in tire tread compositions of the present disclosure cannot be selected from the group consisting of indene-cumarone resins, phenolic resins, alpha-methylstyrene (AMS) resins, and combinations thereof. .

Compound performance:

Compound formulations for the 100% natural rubber tread compounds evaluated are shown in Table 3 below, using resin at the 20 phr level.

Compounds according to Table 3 were mixed in a 5.5 L intermesh mixer using a conventional mixing protocol.

Results of DSC analysis of elastomer-resin mixtures and a selection of formulation data for compounds containing those mixtures are presented in Table 4 below and FIGS. 2-9.

In addition to the detailed laboratory test results described above, actual test tires were manufactured with natural rubber tread compounds according to the present disclosure. It is specified in Table 3. Control tires used an entirely synthetic rubber tread compound .

As shown in Table 5 and FIG. 10, natural rubber tread compounds according to the present disclosure resulted in directional improvements in both wet braking and wet handling in actual tire testing.

Comparing wet traction results from compounds using the deviation or percentage difference from the expected glass transition temperature and the rubber/resin ratio used in the rubber/resin DSC test, the upper limit of miscibility with natural rubber is about 6%. , where any resins and polymer mixtures that differ from the expected glass transition temperature by more than 6% are outside the scope of this disclosure. It should be understood that in certain forms, polymer and resin mixtures that differ from the expected glass transition temperature by no more than about 5% are preferred.

Compound performance:

Compound formulations for the 100% natural rubber tread compounds evaluated are shown in Table 6 below, using resin at the 20 phr level.

For comparison purposes, two different compounds were prepared according to the formulations in Table 6. The first compound contained a hevea-based natural rubber and the second compound contained a guayule-based natural rubber.

Compounds according to Table 6 were factory mixed using a conventional mixing protocol.

The first compound and the second compound were then subjected to conventional laboratory testing. The normalized results of this laboratory test are shown in Table 7 below.

Laboratory testing of the first compound and the second compound showed significant improvements in each of the winter performance, wet performance, and rolling resistance indicators associated with the guayule-based tire tread compound compared to the Hevea-based tire tread compound . The improvement was shown surprisingly and unexpectedly. Without being bound by any particular theory, these differences in physical properties are due to the presence of different naturally occurring materials in guayule-based natural rubber compared to conventional hevea-based natural rubber. It is possible.

Claims (8)

an elastomer comprising an amount of guayule natural rubber;
an amount of hydrocarbon resin distributed throughout the elastomer and present in an amount of at least 20 phr;
A tire tread composition comprising:
Moreover, the amount of resin in the elastomer, as measured by the deviation between the actual Tg of the elastomer-resin mixture consistent with the elastomer and hydrocarbon resin used in the tire tread composition, and the expected Tg of the elastomer-resin mixture. A hydrocarbon resin has a given miscibility in guayule natural rubber at a given concentration of 20 phr, where the expected Tg is the Fox equation:

where Tg _,1 is the glass transition temperature of the elastomer, Tg _,2 is the glass transition temperature of the hydrocarbon resin, and χ _is the weight fraction of the elastomer.
and the predetermined miscibility in the elastomer-resin mixture is less than six percent (6%) deviation between the actual Tg and the expected Tg;
Moreover, the hydrocarbon resin has a softening point of 110° C. to 165° C.,
Moreover, the hydrocarbon resins are prepared by thermal polymerization of mixed dicyclopentadiene (DCPD) with aromatic styrenic monomers derived from petroleum feedstocks, and polymerized alpha-pinene resins, and polymerized beta-pinene resins. is selected from the group of hydrocarbon resins consisting of: , aliphatic hydrocarbon resins, cycloaliphatic hydrocarbon resins, and combinations thereof;
Moreover, the hydrocarbon resin does not include coumarone-indene resins, phenolic resins, and alpha-methylstyrene resins.
The composition described above. 2. The tire tread composition of claim 1, wherein the elastomer comprises guayule natural rubber. The tire tread composition of Claim 1, wherein the actual Tg of the elastomer-resin mixture is from -80°C to -15°C. The tire tread composition of claim 1, wherein the actual Tg of the tire tread composition is between -50°C and -5°C. 2. The tire tread composition of claim 1, wherein the tire tread composition does not contain natural plasticizers. 2. The tire tread composition of claim 1, wherein the elastomer-resin mixture is free of fillers and plasticizers. A tire tread made from the tire tread composition of claim 1 . A tire comprising a tire tread made from the tire tread composition of claim 1.

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