Interliner for a pneumatic tire comprising biochar

Abstract

A rubber composition for an improved butyl elastomer tire inner liner that includes a biochar filler, wherein the tire inner liner has improved resistance to oxygen permeability while exhibiting nominal changes of elasticity when compared to a tire inner liner consisting of carbon black as a filler. The rubber composition includes butyl rubber, a vulcanizing system and in some embodiments also includes zinc oxide, fatty acid and resin.

Description

INTERLINER FOR A PNEUMATIC TIRE COMPRISING BIOCHARFIELD OF THE INVENTION

[0001] The subject matter of the present invention relates to a tire inner liner having a rubber composition comprising of an elastomeric matrix based on butyl rubber and containing biochar and tires comprising such a inner liner.BACKGROUND OF THE INVENTION

[0002] Tubeless tires have an internal surface comprised of a composition having low permeability to air to prevent deflation of the tire and to protect the oxidative sensitive internal components of the tire from oxygen and water permeation. For example, the plies of a tire are comprised of oxidation-sensitive metal cords. The protection afforded by a tire inner liner makes it possible to improve the endurance of the tire and reduce repeated inflation. Protection of the internal surface of the tires is generally performed by inner liners consisting of elastomeric compositions based on butyl rubber. In fact, the performances in terms of impermeability to air of butyl rubbers are related to a not insignificant minimum thickness (of the order of a millimeter). Reduction of this thickness by improvement of the performance of the air impermeable liner reduces the weight and hysteresis of the tire, improving the overall efficiency and environmental impact of both the tire and the vehicle.

[0003] Since savings in fuel and the need to protect the environment have become a priority, it is desirable to produce inner liners which are more impermeable to air and which exhibit a weight and a hysteresis which are as low as possible, in order to obtain an improved rolling resistance of the tire and improve overall vehicle efficiency. Additionally, environmental concerns have incentivized consumers and goods manufactures to seek products that utilize products that incorporate renewable material and reduce dependency on non-renewable material such petroleum derived products.

[0004] Other publications show improved permeability by using fillers to absorb oxygen using a high surface area activated carbon such as EP1939015A2. This publication exhibits multiple layers in order to block the permeation of air and separately absorb oxygen that does permeate as disclosed in paragraph [0009-0010], Creating additionallayers adds weight and adds to the hysteretic properties of the tire reducing its overall environmental impact.

[0005] What is needed is a tire inner liner that reduced permeability enabling reduction in thickness of the inner liner enabling improvement to the overall tire environmental impact.SUMMARY OF THE INVENTION

[0006] 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.

[0007] In one exemplary embodiment a tire inner liner for a tire comprising, per 100 parts by weight of rubber: butyl rubber; a vulcanizing system; and a biochar filler is produced having improved permeability compared to the same formulation utilizing carbon black.

[0008] In another exemplary embodiment, the tire inner liner utilizes a biochar filler having a surface area of 50-600 m2 / g.

[0009] In another exemplary embodiment, the tire inner liner utilizes a biochar filler having a surface area of 400 to 600 m2 / g.

[0010] In another exemplary embodiment, the tire inner liner utilizes a biochar filler having a surface area of greater than 500 m2 / g.

[0011] In another exemplary embodiment, the tire inner liner of any one of the above also including zinc oxide.

[0012] In another exemplary embodiment, the tire inner liner of any one of the above also further including fatty acid. In at least one embodiment, the fatty acid is a steric acid.

[0013] In another embodiment, the tire inner liner of any one of the above further comprising resin. In at least one embodiment, the pneumatic tire inner liner resin is octylphenol formaldehyde resin.

[0014] In yet another embodiment, the tire inner liner of any one of the above further wherein the vulcanizing system is comprised of a sulfur and an accelerator. In at least one embodiment, the pneumatic tire inner liner where the accelerator is chosen from the group consisting of benzothiazole disulfide, 2-mercaptobenzothiazole, and benzothiazyl-2- sulphene morpholide.

[0015] In another embodiment of the invention, wherein a tire comprises any one of the herein described tire inner liners.

[0016] In another exemplary embodiment a tire inner liner for a tire comprising butyl rubber; a vulcanizing system; and a biochar filler, wherein the pneumatic tire inner liner has 50% of the biochar filler particles have an average particle diameter in a range of O. lum to 2.0um.

[0017] An embodiment in accordance with the above preceding embodiment, wherein 50% of the biochar filler particles have an average particle diameter in a range of 0.2um to l.Oum.

[0018] An embodiment in accordance with the above preceding embodiment, wherein 50% of the biochar filler particles have an average particle diameter smaller than l.Oum.

[0019] In another exemplary embodiment a tire inner liner for a tire comprising butyl rubber; a vulcanizing system; and a biochar filler, wherein the pneumatic tire inner liner has 50% of the biochar filler particles have an average particle diameter smaller than 2.0um.

[0020] 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 embodiments of the invention and, together with the description, serve to explain the principles of the invention.DETAILED DESCRIPTION OF THE INVENTION

[0021] Particular embodiments of the present invention include inner liners and tires having such inner liners that have improved transfer rate and permeability characteristics. This improvement in transfer rate and permeability has been achieved by forming unique composition of rubber containing biochar as a filler. Such tires are particularly suitable for use on passenger cars and / or light trucks and while certain embodiments are limited to such uses, other embodiments are broader and may include tires useful for other vehicles including heavy trucks, aircraft and so forth.

[0022] For purposes of describing the invention, reference now will be made in detail to embodiments and examples 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 anotherembodiment 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] It has been found that by combining a butyl rubber, such as bromo butyl elastomer, with a ground biochar yields a surprisingly improved rubber having superior impermeability and transfer rate as compared to a composition containing carbon black.

[0024] In one embodiment, the inner liner forms the innermost layer of the tire.

[0025] The inner liner butyl rubber layer is comprised of a bromo butyl rubber-based rubber composition which contains a dispersion of ground biochar. In one embodiment, the inner liner contains no other reinforcing agent. In an alternative embodiment, a de minimis amount of another reinforcing carbon black may be present. In yet another embodiment, equivalent amounts of carbon black and biochar are present. In another embodiment 10 phr of biochar is present.

[0026] Any butyl rubber used for inner liner would be useful for the invention presented here, including halogenated butyl rubbers such as chlorobutyl, bromobutyl rubbers and non-halogenated butyl rubber such as regular butyl rubber, such as mixtures of isobutylene rubber and isoprene, may be used. Likewise, combinations of butyl rubbers may be used and not deviate from the invention.

[0027] Vulcanization system: The vulcanization system is preferably, for particular embodiments, one based on sulfur and on an accelerator but other vulcanization agents known to one skilled in the art may be useful as well. Vulcanization agents as used herein are those materials that cause the cross-linkage of the rubber and therefore may be added only to the productive mix so that premature curing does not occur. Such agents including, for example, elemental sulfur, sulfur donating agents, and peroxides. Use may be made of any compound capable of acting as an accelerator of the vulcanization of elastomers in the presence of sulfur, in particular those chosen from the group consisting of 2-mercaptobenzothiazyl disulfide (abbreviated to "MBTS"), N-cyclohexyl-2- benzothiazolesulphenamide (abbreviated to "CBS"), N,N-dicyclohexyl-2- benzothiazolesulphenamide (abbreviated to "DCBS"), N-tert-butyl-2- benzothiazolesulphenamide (abbreviated to "TBBS"), N-tert-butyl-2-benzothiazole- sulphenimide (abbreviated to "TBSI") and the mixtures of these compounds. Preferably, a primary accelerator of the sulfenamide type is used.

[0028] The rubber composition may also include vulcanization retarders, a vulcanization system based, for example, on sulfur or on a peroxide, vulcanization accelerators, vulcanization activators, and so forth.

[0029] The vulcanization system may further include various known secondary accelerators or vulcanization activators, such as zinc oxide, stearic acid and guanidine derivatives (in particular diphenylguanidine).

[0030] Mixing

[0031] The rubber compositions that are embodiments of the present invention may be produced in suitable mixers in a manner known to those having ordinary skill in the art. Typically the mixing may occur using two successive preparation phases, a first phase of thermo-mechanical working at high temperature followed by a second phase of mechanical working at a lower temperature.

[0032] The rubber compositions that are embodiments of the present invention may be produced in suitable mixers in a manner known to those having ordinary skill in the art. Typically the mixing may occur using two successive preparation phases, a first phase of thermo-mechanical working at high temperature followed by a second phase of mechanical working at a lower temperature.

[0033] The first phase, sometimes referred to as a "non-productive" phase, includes thoroughly mixing, typically by kneading, the various ingredients of the composition but excluding some of the vulcanization system such as the vulcanization agents, the accelerators, and the retarders. It is carried out in a suitable kneading device, such as an internal mixer of the Banbury type, until under the action of the mechanical working and the high shearing imposed on the mixture, a maximum temperature of generally between 120°C. and 190°C. is reached, indicating that the components are well dispersed.

[0034] After cooling the mixture a second phase of mechanical working is implemented at a lower temperature. Sometimes referred to a "productive" phase, this finishing phase consists of incorporating some of the aforementioned vulcanization system that were not added in the “non-productive” phase, including the vulcanization agents, the accelerators, and the retarders into the rubber composition using a suitable device, such as an open mill. It is performed for an appropriate time (typically, for example, between 1 and 30 minutes or between 2 and 10 minutes), and at a sufficiently low temperature, i.e., lower than the vulcanization temperature of the mixture, so as to protect against premature vulcanization.

[0035] Example 1

[0036] Prospective exemplary illustrative oxygen barrier rubber compositions comprising a bromo butyl rubber which contains a dispersion of a ground biochar are presented as sample A, B, and C.

[0037] The biochar used was commercially obtained Rogue BioChar obtained from Oregon Biochar Solutions 2350 Ave G.; White City, OR 97503; USA. The Rogue BioChar had a surface area of 553 m2 / g and an ash content of less than 3%. The biochar is ground to 0.32 um mean diameter size, by SEM examination of the particle in the rubber mix. The particle “diameter” is understood to be the largest diameter of the particle. A person of ordinary skill in the art should understand that this results in a range of sizes of the particles of the biochar as would be expected with such a grinding process with 50% of the particles (by particle count) falling within a range of particle size between 0.1 and 2.0 um mean diameter size.

[0038] The grinding in the example shown as sample A, B and C here were accomplished without a solvent, otherwise referred to as “dry grinding”. Alternatively the grinding may occur under solvent. Such solvents may be comprised of as methanol, ethanol, acetone, or isopropyl alcohol. The grinding may also occur with a grinding coagent present, such as a proton acceptor such as diphenyl guanidine (“DPG”), polyethylene glycol (“PEG”), rosin amine or 2,2,4-trimethyl-l,2-dihydroquinoline, polymerized (“TMQ”). Grinding may occur by method known to a person of ordinary skill in the art such as shown in PCT Publication No. WO 2022 / 146432.

[0039] Biochar useful for the invention would have a high surface area, measured as 50-600 m2 / g as measured by a BET surface area measurement. In other embodiments the biochar would have a surface area of 400-600 m2 / g. In other embodiments the biochar would have a surface area greater than 500 m2 / g. In other embodiments the biochar would have a surface area of 500 to 600 m2 / g. The rubber composition comprising the high surface area biochar was found to have favorable permeability performance compared to a N722 carbon black with a lower surface area. Although a carbon black with a similarly high surface area to the ground biochar used would result in a rubber having a high modulus of elasticity negatively affecting the usefulness of the resulting rubber composition, the high surface area of the ground biochar resulted in a rubber composition having a modulus of elasticity similar to that of the N772 carbon black formulation used in the witness sample “W”.

[0040] It was found that the biochar used had a density of 1.5-1.7 g / cm3and a total surface energy of 40-42 (pol.; disp. 29.2-29.3) mJ / m2 and a polar surface energy of 11-13 mJ / m2 and a dispersive surface energy of 29.2 to 29.3 mJ7m2 which are otherwise similar to the carbon black witness N772 used in the composition “W” as shown in TABLE 1 below.

[0041] TABLE 1. Properties of the biochar and carbon black N772.

[0042] In one embodiment, the biochar was wet ground under ethanol. In an alternative embodiment the biochar was dry ground.

[0043] A witness, W, is comprised of a bromo butyl rubber containing a dispersion of N772 Carbon black.

[0044] The rubber was comprised as shown below in TABLE 2. All exemplary compositions are comprised of 100 phr of bromo butyl rubber; 1.5 phr of zinc oxide; 1.5 phr of a fatty acid, here steric acid; 2.5 phr of resin, here octylphenol formaldehyde resin;1.5 phr of sulfur: 1.2 phr of an accelerator; and 50 phr of a filler. The accelerator was chosen from the group consisting of benzothiazole disulfide (MBTS), 2- mercaptobenzothiazole (MBT), and benzothiazyl-2-sulphene morpholide (MBS).

[0045] TABLE 2. Rubber samples composition.

[0046] For the witness W, the accelerator used was MBTS and the filler was N772 carbon black.

[0047] For the comparative samples A, B, and C each used the same reinforcement, a ground biochar, while each had a different accelerator was used. For comparative A the accelerator was MBTS, for comparative B the accelerator was MBT and for comparative C the accelerator was MBS.

[0048] The rubber compositions that are embodiments of the present invention may be produced in suitable mixers in a manner known to those having ordinary skill in the art. The rubber samples were prepared by mixing the elastomers together with reinforcing fillers and other rubber compounding ingredients in a non-productive mixing stage in an internal rubber mixer for a period of, for example, about 4 minutes to a temperature of, for example, less than 110°C. The rubber composition and curatives would then be milled and cooled between the non-productive mixing and the productive mixing steps.

[0049] The samples were prepared having a thickness (T) of 1.1 mm to 1.4 mm. The permeability values are measured using a Mocon Oxtran 2 / 60 permeability “tester” at 40°C. Cured samples in the form of discs with a predetermined thickness (approximately 1.1 to 1.4 mm) are fitted to the device and rendered leaktight with vacuum grease. One of the faces of the disc is kept under 10 psi of nitrogen while the other face is kept under 10 psi of oxygen. The increase in the concentration of oxygen is monitored using an oxygen detector on the face kept under nitrogen. The concentration of oxygen on the face kept under nitrogen which makes it possible to achieve a constant value, used to determine the permeability to oxygen, is recorded.

[0050] The results are shown as a Transmission Rate in cc / m2per day reporting the volume of gas measured in cubic centimeters divided by the surface area of rubber measured in square meters and a Permeability Rate in cc-mm(m2-day) reporting the volume of gas measured in cubic centimeters times the thickness of the rubber measured inmillimeters divided by surface area of rubber which is measured in square meters, to account for the thickness variation of each sample. The results of testing is shown in TABLE 3 below.

[0051] TABLE 3. Permeability of rubber samples.

[0052] The results show significant improvement of permeability of all samples containing biochar as the filler.

[0053] Example 2

[0054] Sixteen test samples where created, each sample comprising the mix used in sample A of Example 1 above. Two samples were each tested for increasing durations demonstrating that absorption alone was not responsible for the increased reduction of permeability of oxygen through the samples.

[0055] The samples were prepared having a thickness (T) of 1.1 mm. The permeability values are measured using a Mocon Oxtran 2 / 60 permeability “tester” at 40°C. Cured samples in the form of discs with a predetermined thickness (approximately 1.1) are fitted to the device and rendered leaktight with vacuum grease. One of the faces of the disc is kept under 10 psi of nitrogen while the other face is kept under 10 psi of oxygen. The increase in the concentration of oxygen is monitored using an oxygen detector on the face kept under nitrogen. The concentration of oxygen on the face kept under nitrogen which makes it possible to achieve a constant value, used to determine the permeability to oxygen, is recorded.

[0056] The results are shown as a Transmission Rate in cc / m2per day reporting the volume of gas measured in cubic centimeters divided by the surface area of rubber measured in square meters and a Permeability Rate in cc-mm(m2-day) reporting the volume of gas measured in cubic centimeters times the thickness of the rubber measured in millimeters divided by surface area of rubber which is measured in square meters, to account for the thickness variation of each sample. The results of testing is shown in TABLE 4 below.

[0057] Table 4. Sample test over eight days of testng.

[0058] The stabilization of the permeability of the samples over time indicates a factor of something other than adsorption causing improved permeability.

[0059] 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 aremeasured 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 rubber(s) in the composition.

[0060] As used herein, elastomer and rubber are synonymous terms.

[0061] 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.

[0062] 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."

[0063] 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 pneumatic tire inner liner comprising, per 100 parts by weight of rubber: butyl rubber; a vulcanizing system; and a biochar filler.

2. The pneumatic tire inner liner of claim 1 wherein the biochar filler has a surface area of 50-600 m2 / g.

3. The pneumatic tire inner liner of claim 2 wherein the biochar filler has a surface area of 400 to 600 m2 / g.

4. The pneumatic tire inner liner of claim 3 wherein the biochar filler has a surface area of 500 to 600 m2 / g.

5. The pneumatic tire inner liner of claim 1 wherein the biochar filler has a surface area greater than 500 m2 / g.

6. The pneumatic tire inner liner of any one of the above claims further comprising zinc oxide.

7. The pneumatic tire inner liner of any one of the above claims further comprising fatty acid.

8. The pneumatic tire inner liner of any one of the above claims further comprising resin.

9. The pneumatic tire inner liner of claim 7 wherein the fatty acid is stearic acid.

10. The pneumatic tire inner liner of any one of the above claims wherein the vulcanizing system is comprised of: sulfur and an accelerator.

11. The pneumatic tire inner liner of claim 7 wherein the accelerator is chosen from the group consisting of benzothiazole disulfide, 2-mercaptobenzothiazole, and benzothiazyl-2- sulphene morpholide.

12. A pneumatic tire inner liner comprising: butyl rubber; sulfur; an accelerator; a zinc oxide; a resin; anda biochar filler having a surface area of 500 to 600 m2 / g.

13. The pneumatic tire inner liner of claim 9 wherein the accelerator is chosen from the group consisting of benzothiazole disulfide, 2-mercaptobenzothiazole, and benzothiazyl-2- sulphene morpholide.

14. The pneumatic tire inner liner of claim 12 or claim 13 further comprising fatty acid.

15. The pneumatic tire inner liner of claim 14 wherein the fatty acid is stearic acid.

16. The pneumatic tire inner liner of any one of claims 12-15 wherein the resin is octylphenol formaldehyde.

17. A tire comprising an inner liner as claimed in any one of the above claims.

18. The pneumatic tire inner liner of any one of the above claims wherein 50% of the biochar filler particles have an average particle diameter in a range of 0. lum to 2.0um.

19. The pneumatic tire inner liner of any one of the above claims wherein 50% of the biochar filler particles have an average particle diameter in a range of 0.2um to l.Oum.

20. The pneumatic tire inner liner of any one of the above claims wherein 50% of the biochar filler particles have an average particle diameter smaller than l.Oum.

21. The pneumatic tire inner liner of any one of the above claims wherein 50% of the biochar filler particles have an average particle diameter smaller than 2.0um.

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