WO2022146440A1

WO2022146440A1 - Tin coupling for rubber mixes containing acetylene carbon black

Info

Publication number: WO2022146440A1
Application number: PCT/US2020/067646
Authority: WO
Inventors: Frederic Vautard
Original assignee: Compagnie Generale Des Etablissements Michelin
Priority date: 2020-12-31
Filing date: 2020-12-31
Publication date: 2022-07-07

Abstract

The subject matter of the present invention relates to rubber mix having increased thermal conductivity and increased durability comprised of tin functionalized elastomer and an acetylene black reinforcing filler. The resulting rubber has improved thermal conductivity better rigidity versus energy dissipation compromise and better fatigue resistance as compared to rubber mixes having non-functionalized and elastomer carbon black reinforcement.

Description

TIN COUPLING FOR RUBBER MIXES CONTAINING ACETYLENE CARBON BLACK

FIELD OF THE INVENTION

[0001] The subject matter of the present invention relates to a thermally conductive rubber compositions and particularly to thermally productive rubber compositions comprising tin-functionalized elastomer and an acetylene carbon black reinforcing filler.

BACKGROUND OF THE INVENTION

[0002] Rubber elastomers are used in products where resiliency and compliance is a desired trait. As the rubber deforms, the rubber generates heat due to the hysteretic properties of the rubber compositions and the composite structures the rubber is part of. Rubber is also a fairly good thermal insulator, preventing the dissipation of heat from the article in which it is used. A solicitation rate limit is reached when the article cannot dissipate the heat generated by the deformation and temperatures rise to levels that cause damage to the rubber elastomers or other components making up the article. For example, in the mining industry, large rubber tires are used to support extremely heavy equipment, commonly known as earth moving equipment, which can exceed a gross vehicle operating weight of more than 650 tons. The economic demands of the mining industry require the vehicles to travel at as high of speed that can safely be managed by the equipment. The limiting factor is often the tires’ maximum acceptable speed limit for a given vehicle load due to the inability of the tire to dissipate the heat generated by the solicitation as the tire rolls across the ground.

[0003] A need exists for a more thermally conductive elastomer that possesses good heat dissipation properties as well as good wear resistance. The use of acetylene carbon black has been found to increase the thermal conductivity of the rubber elastomer. Other properties, such as wear resistance, however, are difficult to maintain and the ability for rubber formulators to predict which combination of elastomers with reinforcements creates uncertainty as to the optimum combinations of elastomers and reinforcements.

[0004] Acetylene carbon black reinforcements have shown good promise of having high thermal conductivity with mixes at iso-rigidity to carbon black showing 40% more thermal conductivity. These mixes however have poor wear resistance making them a inferior choice for use in tread rubber where the excessive wear rates become problematic. [0005] The use of a tin-coupled functional elastomers is known in the industry for use in rubber products as well as in tire applications but lack teaching how such elastomers may be utilized with high surface are acetylene carbon blacks. Prior publications do not teach how the acetylene carbon black, with its high specific surface area and high structure, will interact with a tin coupled elastomer, as compared to furnace carbon blacks.

[0006] Cambon et al. described in US Patent No. 9593226B2, granted in 2017, the use of a star-branched tin functionalized elastomer, especially a functionalized styrene butadiene elastomer, with carbon blacks having a specific surface area measured by CT AB between 100 and 200 m2/g. The patent focuses on furnace type carbon blacks of ASTM grades, like the 100 and 200 series, N123 and N234. The 600 and 700 series are also mentioned, specifically the carbon blacks N660 and N772. But acetylene carbon blacks are not mentioned, and this publication fails to teach how any tin functionalized elastomer may interact with an acetylene carbon black.

[0007] In the patent application by Mehlem, WO 2011/123406 A1, the use of a tin coupled SBR is used to improve the rolling resistance of a tire by decreasing the energy dissipation of the corresponding rubber products as shown by tan delta of the elastomer. The filler is a furnace carbon black of 100, 300, and 600 series. Acetylene carbon blacks, however, are not mentioned. The novelty of the patent application comes in the disclosure that using a sunflower oil gives better performance than using an aromatic oil when combined to a tin coupled SBR. This patent application teaches the reduction of energy dissipation associated to tin coupling when using carbon black. It also teaches of a decrease in tear resistance with tin coupling. It fails to teach of the interaction of an acetylene carbon black with a tin functionalized elastomer.

[0008] Halasa et al. in US Patent No. 7279531B1, tin functionalized BR and SBR are described to “provide desirable dispersion” in the case of a carbon black-based mix. Such carbon black-based rubber products can be used for tire treads, in other to achieve better wear resistance without sacrificing other performances. The tin functionalization provides the rubber with good cold flow, desirable Mooney viscosity, and provides the associated tire with good rolling resistance. The chemical bonding between the rubber matrix and the surface of the carbon black is mentioned. The concentration in carbon black is described as between 30 and 90 phr but does not disclose an acetylene black. [0009] In US Patent No. 6084022 Blok et al. discloses a blend of tin-functionalized BR with high vinyl BR and NR is used to obtain improved traction and wear resistance without impacting rolling resistance. The improved interaction between the tin-coupled rubber matrix and carbon black is mentioned. Carbon black may be at concentrations between 5 and 80 phr. Blends of carbon black and silica may be used, with a concertation in carbon black not being higher than 10 phr. The patent mentions that asymmetrically coupled BR is beneficial versus symmetrically coupled BR, especially regarding the cold flow of the rubber mix. There is no mention of the use of acetylene carbon black.

[0010] In US Patent Application No. 2015/0299437A1, Mruk et al. disclose the use of a tin coupled elastomer with graphenes and carbon nanotubes. Mruk et al. foils to explain the use of graphenes or carbon nanotubes and does not provide data supporting their use. This disclosure does not disclose the use of acetylene carbon black.

[0011] A need exists for an elastomer composition with good thermal conductivity, improved tensile properties and good wear resistance while still maintaining adequate resistance to aggression and adequate tear resistance.

SUMMARY OF THE INVENTION

[0012] Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention.

[0013] In one exemplary embodiment, a tin functionalized elastomer is combined with a high surface area acetylene carbon black to produce an elastomer having superior thermal conductivity and wear resistance.

[0014] These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate properties of embodiments of the invention and, together with the description, serve to explain the principles of tire invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: [0016] FIG. 1 shows a graph of the RPA curves of Li435 and N234-based mixes, in SBR2300 and SBR2309.

[0017] FIG. 2 shows the MSV curves of N234 and Li435 mixed with SBR2300 and

SBR2309.

[0018] FIG. 3 shows the DMA G* strain sweep at 23 °C. N234 and Li435 mixed with SBR2300 and SBR2309.

[0019] FIG. 4 shows the DMA Tan delta strain sweep at 23 °C. N234 and Li435 mixed with SBR2300 and SBR2309.

[0020] FIG. 5 provides a bar graph of the tear resistance of mixes with N234 and Li435 coupled with SBR2300 and SBR2309.

[0021] FIG. 6 shows a comparison of the fatigue resistance of mixes with N234 and

Li435 coupled with SBR2300 and SBR2309.

DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention provides a rubber composition having improved thermal conductivity, an acceptable rigidity versus energy dissipation compromise and improved wear resistance. This rubber formulation may find particular use for articles including tires and particularly for the tread rubber and the under-tread rubber of tires and tires such as for large earth moving equipment. For purposes of describing the invention, reference now will be made in detail to embodiments and/or methods of the invention. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features or steps illustrated or described as part of one embodiment, can be used with another embodiment or steps to yield a still further embodiments or methods. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0023] For purposes of describing the invention, reference now will be made in detail to embodiments and/or methods of the invention, one or more examples of which are illustrated in or with the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features or steps illustrated or described as part of one embodiment, can be used with another embodiment or steps to yield a still further embodiment or method. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

[0024] In the examples that follow, various material properties are described. These properties were obtained using tests as ordinarily used to quantify such properties and are described as follows:

[0025] “Mn” is the average molecular weight in number. This is the total weight of all polymer molecules contained in a sample divided by the total number of polymer molecules of the sample. It is an arithmetic average - all chains are equally important when calculating this parameter.

[0026] “Mw" is the average molecular weight in weight. This is based on tiie fact that a bigger molecule contains more of the total weight of the polymer sample than smaller molecules. This parameter is highly susceptible to chains of high molecular weight [0027] “IP” is the polydispersity of an elastomer. This measures the amplitude of the Molecular Weights Distribution curve (MWD) and represents the ratio between the average molecular weight (Mw) and the average molecular weight in number (Mn).

[0028] A true secant modulus of elongation (MPa) was measured at 10% (MA10),

100% (MA100) and 300% (MA300) at temperature of 23°C based on ASTM Standard D412 on dumb bell test pieces. The measurements were taken in the second elongation; i.e., after an accommodation cycle.

[0029] The elongation property was measured as strain at break (%) and the corresponding stress at break (MPa), which is measured at 23°C in accordance with ASTM Standard D412 on ASTM C test pieces.

[0030] The shear modulus G* at 10% strain and the maximum tan delta dynamic properties for the rubber compositions were measured at 23 °C on a Metravib Model VA400 ViscoAnalyzer Test System in accordance with ASTM D5992-96. The response of a sample of vulcanized material (double shear geometry with each of the two 10 mm diameter cylindrical samples being 2 mm thick) was recorded as it was being subjected to an alternating single sinusoidal shearing stress at a frequency of 10 Hz under a controlled temperature of 23° C. Scanning was effected at an amplitude of deformation of 0.05 to 50% (outward cycle) and then of 50% to 0.05% (return cycle). The shear modulus G* at 10% strain and the maximum value of the tangent of the loss angle tan delta were determined during the return cycle. [0031] To test fatigue of the elastomer samples, fatigue to fracture or “FTF” testing in accordance with ASTM D4482 - 11(2017) Standard Test Method for Rubber Property was carried out. The extension cycling fatigue temperature was set at 25°C.

[0032] The “Hot Dz test” is used to test tear strength of the elastomer samples, testing in accordance with ASTM D624 - 00(2012) “Standard Test Method for Tear Strength of Conventional Vulcanized Rubber and Thermoplastic Elastomers” was conducted at 100°C. The Dz index is equivalent to the rupture force times the elongation at break divided by 100.

[0033] Testing of thermal conductivity of the rubber mix was performed in accordance with the following equation:

The mix density was calculated based on its composition using the rule of mixtures applied to the densities of the individual components, the specific heat was measured by Differential Scanning Calorimetry (DSC) and the thermal diffusivity was measured with a LFA 447 NanoFlash system from Netzsch.

[0034] To determine the wear rate of rubber, an “erosion test” was conducted where a rubber specimen of known mass was loaded against a simulated road surface to a pressure of 1 bar, and moved under pressure for a distance of 4 m. The mass was measured again to determine the amount of wear.

[0035] Symmetrically tin functionalized SBR, where the tin atom is attached to the elastomer carbon chain on the middle of the carbon chain, was used with both high specific surface area acetylene carbon black Li435 (from Denka) and furnace carbon black N234. These have a specific surface area (BET, N2) of 155 m²/g and 112 m²/g respectively. The properties of the corresponding mixes were compared with mixes made with the same formulation using a non-functionalized SBR (with the same microstructure as the functionalized SBR-Table 1). [0036] Table 1: Macro and microstructure of the non-functionalized SBR (SBR2300) and the tin functionalized SBR (SBR2309)

[0037] III.l Composition of the rubber mixes

[0038] The concentration of the high specific surface area acetylene carbon black Li435 was 35 phr in order to obtain iso-rigidity versus the reference mix with N234 at 50 phr.

[0039] Conventional mixing and milling processes were used: Bandbury mixer (Haake PolyLab OS RheoDrive from ThermoFisher) and Brabender mill.

[0040] Table 2: Composition of the four mixes used in this study (concentrations in phr)

[0041] The rubber formulations were prepared by mixing the components given in Table 3, except for the sulphur and the accelerator (CBS), in a HAAKE Banbury mixer. With the mix chamber at 110°C operating at 90 RPM the rubber is added and mixed for 1 minute. The rotation speed is decreased to 30 RPM and the filler is added and mixed for an additional 1 minute. The rotation speed is increased to 90 rpm and mixed for an additional 1 minute. Finally the ZnO, 6PPD and SAD are added and mixed for an additional minute.

The mixer piston is dropped and mixed for an additional minute. The mix is dropped allowed to cool and placed in a mill for a second phase of mixing with the mix at 50°C.

The accelerator and sulfur were added at this point and were milled for a total of 12 passes after full incorporation of the accelerator and sulfur.

[0042] Rheometry showed that the overall shape of the RPA curve did not change when switching from non-functional SBR to the functional SBR, for both fillers as seen in

FIG. 1. The scorch time was increased, for both fillers. The shear modulus decreased both in green and cured states, and for both fillers. The decrease was sharper in the case of

N234. This may indicate that the state of dispersion is slightly worse in the functional SBR in compassion to the non-functional SBR, for both Li435 and N234. But using the functional SBR is perfectly compatible with industrial practices.

[0043] The influence of tin coupling on the tensile properties strongly depended on the type of filler. No significant evolution of the properties was noticed with N234 shown in

FIG 2 and Table 3. On the contrary, with Li435, the use of tin coupling resulted in a clear increase of the MSV MA 300 and of the ratio MA 300 / MA 100, with the same tensile strength at break. This clearly highlights an improvement of interfacial adhesion. Tin coupling did generate covalent bonding at the interface SBR2309/Li435.

[0044] Table 3: Tensile properties indicators associated with FIG. 2.

[0045] Dynamic properties showed that all the mixes had the same rigidity and that the energy dissipation was lower for the mix made with Li435 shown in FIG. 3 and FIG. 4 and

Table 4. Tin coupling really reduced the energy dissipation with N234, but did not have any significant impact with Li435. [0046] Table 4: Dynamic properties indicators corresponding to FIG. 3 and FIG. 4.

[0047] Tin coupling resulted in an increase of the wear resistance for both fillers. But the amplitude of the improvement was higher with Li435 (+20%) than with N234 (+4%). This surprising result may be explained by the difference in the level of improvement of interfacial adhesion and an unexpected synergistic effect of the high surface are acetylene carbon black with the tin functionalized elastomer.

[0048] This is very important for tread rubber and under-tread rubber formulation where wear is an important consideration in the choice of elastomer and filler. Since Li435 may be considered for tread rubber and under-tread rubber formulation in the case of tires generating a lot of self-heating, such as found with large tires such as earth mover mining tires, decreasing the risk associated to insufficient wear resistance is essential. This is an excellent way to fully take advantage of the high thermal conductivity generated by high specific surface area acetylene carbon blacks like Li435.

[0049] Table 5: Influence of tin coupling on the resistance to wear, as measured by the erosion test.

[0050] With tin coupling, the tear resistance, as measured by the Hot Dz test, decreased sharply when using N234 (-75%), as compared to Li435 (-40%). It can be interpreted as a lack of degree of freedom for the elastomer when it is covalently bonded to the surface of the filler. It is thought that the elastomer cannot relax as efficiently and dissipate energy during the crack propagation. This could affect the aggression resistance of a tire having a tread rubber based on tin functionalized elastomer, as compared to the non-functionalized version.

[0051] With tin coupling, the fatigue resistance, as measured by the FTP test, decreased also for both fillers. This was a trend that was not statistically significant though. The decrease was -30% with N234 and -20% with Li345.

[0052] The use of tin coupling with a high specific surface area acetylene carbon black will be advantageous for tread rubber or under-tread rubber formulation showing an increase of wear resistance and decrease of energy dissipation at iso-rigidity. An acceptable aggression resistance as shown by the moderate decrease of Hot Dz index was observed. This supports the use of the high surface area acetylene black, Li435, as a good filler for tin functionalized elastomer products particular for those submitted to self-heating and low fatigue susceptibility such as found in tire tread.

[0053] Selected combinations of aspects of the disclosed technology correspond to a plurality of different embodiments of the present invention. It should be noted that each of the exemplary embodiments presented and discussed herein should not insinuate limitations of the present subject matter. Features or steps illustrated or described as part of one embodiment may be used in combination with aspects of another embodiment to yield yet further embodiments. Additionally, certain features may be interchanged with similar devices or features not expressly mentioned which perform the same or similar function. [0054] The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm." Also, the dimensions and values disclosed herein are not limited to a specified unit of measurement. For example, dimensions expressed in English units are understood to include equivalent dimensions in metric and other units (e.g., a dimension disclosed as “1 inch” is intended to mean an equivalent dimension of “2.5 cm”).

[0055] As used herein, the term “method” or “process” refers to one or more steps that may be performed in other ordering than shown without departing from the scope of the presently disclosed invention. As used herein, the term "method” or "process" may include one or more steps performed at least by one electronic or computer-based apparatus. Any sequence of steps is exemplary and is not intended to limit methods described herein to any particular sequence, nor is it intended to preclude adding steps, omitting steps, repeating steps, or performing steps simultaneously. As used herein, the term "method" or "process" may include one or more steps performed at least by one electronic or computer-based apparatus having a processor for executing instructions that carry out the steps.

[0056] As used herein, "phr" is “parts per hundred parts of rubber by weight” and is a common measurement in the art wherein components of a rubber composition are measured relative to the total weight of rubber in the composition, i.e., parts by weight of the component per 100 parts by weight of the total rubbers) in the composition.

[0057] As used herein, elastomer and rubber are synonymous terms.

[0058] As used herein, “based upon” is a term recognizing that embodiments of the present invention are made of vulcanized or cured rubber compositions that were, at the time of their assembly, uncured. The cured rubber composition is therefore “based upon” the uncured rubber composition. In other words, the cross-linked rubber composition is based upon or comprises the constituents of the cross-linkable rubber composition.

[0059] The terms "a," "an," and the singular forms of words shall be taken to include the plural form of the same words, such that the terms mean that one or more of something is provided. The terms "at least one" and "one or more" are used interchangeably. Ranges that are described as being "between a and b" are inclusive of the values for "a" and "b." [0060] The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

Claims

WHAT IS CLAIMED IS:

1. A rubber composition comprising: a tin functionalized elastomer; an acetylene carbon black; and a crosslinking system.

2. The rubber composition of claim 1 wherein the tin functionalized elastomer is a diene elastomer.

3. The rubber composition of claim 2 wherein the tin functionalized elastomer is a symmetrically functionalized diene elastomer.

4. The rubber composition of any one of the above claims wherein the acetylene carbon black is a high surface area acetylene carbon black.

5. The rubber composition of claim 4 wherein the acetylene carbon black has a specific surface area between 120 m^2/g and 190 m^2/g

6. The rubber composition of claim 5 wherein the acetylene carbon black has a specific surface area of at least 150 m^2/g.

7. The rubber composition of claim 6 wherein the acetylene carbon black has a specific surface area no greater than of 160 m^2/g.

8. The rubber composition of claim 7 wherein the acetylene carbon black has a specific surface area of 155 m^2/g.

9. The rubber composition of any one of the above claims wherein the elastomer is selected from the group of diene elastomers consisting of polybutadienes, synthetic polyisoprenes, natural rubber, isoprene copolymers, butadiene copolymers including styrene-butadiene and mixtures of these elastomers.

The rubber composition of any of the above claims wherein the crosslinking system is an insoluble sulfur.

10. The rubber composition of any of the above claims further comprising of an anti- degradant.

11. The rubber composition of claim 10 wherein the anti-degradant is comprised of

6PPD and zinc oxide

12. The rubber composition of any of the above claims, wherein the elastomer is a styrene butadiene rubber.

13. The rubber composition of claim 12 wherein the styrene butadiene rubber is obtained by solvent polymerization.

14. The rubber composition of any one of the above claims, wherein the acetylene carbon black has a high structure.

15. A tire comprised of the rubber composition of any one of the above claims.