Vehicle tire compositions containing rice husk ash and silica

Abstract

This invention relates to a vehicle tire composition comprising: 100 phr of a rubber component; and 50 to 160 phr of silica obtained from rice husk ash, wherein the silica has a potassium content of less than or equal to 300 ppm based on the silica and measured by inductively coupled plasma optical emission spectrometry as described in the examples, and wherein the silica has a weak coefficient of less than or equal to 20 as measured by laser scattering as described in these examples. The invention also relates to methods for preparing vehicle tire compositions; vehicle tires made from these compositions; methods for selecting rice husk ash silica to be included in tire rubber compounds; and the use of rice husk ash silica in vehicle tire compositions.

Description

Technical Field

[0001] This invention relates to vehicle tire compositions, methods for their preparation, and vehicle tires made from these compositions. These compositions contain rice husk ash silica as a reinforcing filler. The invention also relates to a method for selecting rice husk ash silica to be included in vehicle tire compositions, and the use of rice husk ash silica in vehicle tire compositions. Background Technology

[0002] For many years, reinforcing fillers have been used in tires to improve the mechanical properties of rubber compositions. Traditionally, fillers have included carbon black, chalk, talc, kaolin, bentonite, titanium dioxide, and silica. Silica has been found to be particularly advantageous in reducing rolling resistance and improving traction, especially on wetted surfaces. Traditionally, silica derived from sand has been used.

[0003] In recent years, the tire industry has strived to improve its environmental sustainability at all levels. One focus has been on using more environmentally sustainable raw materials, particularly those available from renewable sources. In this regard, silica derived from rice husk ash (referred to herein as "RHA silica") has already been used in tire compositions. However, the inclusion of this silica can adversely affect tire performance.

[0004] It has long been desirable to include RHA silica in tire compositions to improve tire sustainability, and the objective of this invention is to achieve this without adversely affecting the performance properties of the tire. Summary of the Invention

[0005] Due to the natural source of RHA silica, it may contain trace amounts of metals derived from soil or fertilizers applied during rice cultivation. The inventors have now discovered that the presence of one of these elements, potassium, above a certain level can lead to poor performance in tires containing RHA silica. This is believed to be because high potassium content can cause silica agglomeration, meaning that the RHA silica is less easily dispersed when used as a reinforcing filler in vehicle tire compositions. The dispersion of silica fillers is crucial in preparing high-performance tire compositions with the desired mechanical properties.

[0006] The inventors have discovered that when silica with a potassium content of less than or equal to 300 ppm is used in tire compositions, tire performance in key parameters such as stiffness can be maintained or even improved compared to sand silica and compared to RHA silica with a higher potassium content.

[0007] The inventors have also discovered that the weak coefficient of RHA silica is important, and that when the weak coefficient is less than or equal to 20, it indicates a good dispersibility level that will result in good performance properties when used as a reinforcing filler in tire compositions.

[0008] According to a first aspect, the present invention relates to a vehicle tire composition comprising: 100 phr of a rubber component; and 50 phr to 160 phr of silica obtained from rice husk ash, wherein the silica has a potassium content of less than or equal to 300 ppm based on the silica and measured by inductively coupled plasma optical emission spectrometry as described in the embodiments, and wherein the silica has a weak coefficient of less than or equal to 20 as measured by laser scattering as described in these embodiments.

[0009] According to a second aspect, the present invention relates to a vehicle tire comprising a vehicle tire composition according to a first aspect.

[0010] According to a third aspect, the present invention relates to a method for producing a vehicle tire composition according to a first aspect, the method comprising the steps of: introducing a silica filler into a rubber component to produce a vulcanizable rubber compound; and subjecting the vulcanizable rubber compound to vulcanization by heating to a predetermined temperature and for a predetermined time; wherein the silica filler is obtained from rice husk ash, has a potassium content of less than or equal to 300 ppm based on the silica and measured by inductively coupled plasma optical emission spectrometry as described in the embodiments, and wherein the silica filler has a weak coefficient of less than or equal to 20 as measured by laser scattering as described in these embodiments.

[0011] According to a fourth aspect, the present invention relates to a method for selecting rice husk ash silica to be included in a tire composition, the method comprising the steps of: determining the potassium content of the rice husk ash silica; selecting rice husk ash silica having a potassium content of less than or equal to 300 ppm based on the silica, as measured by inductively coupled plasma optical emission spectrometry as described in the examples; and including the selected rice husk ash silica in the tire composition at a content of 50 phr to 160 phr.

[0012] According to a fifth aspect, the present invention relates to the use of rice husk ash silica having a potassium content of less than or equal to 300 ppm based on silica, as measured by inductively coupled plasma optical emission spectrometry as described in the embodiments, in a vehicle tire composition for improving the stiffness of the vehicle tire composition compared to an equivalent vehicle tire composition containing rice husk ash silica having a potassium content of greater than 300 ppm. Detailed Implementation

[0013] This invention relates to a vehicle tire composition comprising 100 phr of rubber component. Conventionally, "phr" refers to parts per hundred parts of rubber component. "Rubber component" refers to the rubber component in the composition. As used herein, the term "rubber" is intended to include both natural and synthetic rubber. Unless otherwise specified, the terms "rubber" and "elastomer" are used interchangeably.

[0014] Any known rubber component or blend of rubber components can be used in the vehicle tire composition according to the invention, and those skilled in the art can readily select suitable rubbers or blends of rubbers taking into account the intended use of the composition. Non-limiting examples of suitable rubbers for the composition are well known to those skilled in the art and include natural rubber (NR), synthetic polyisoprene rubber, styrene-isoprene rubber, styrene-butadiene rubber, styrene-isoprene-butadiene rubber, butadiene-isoprene rubber, polybutadiene, butyl rubber, chloroprene rubber, nitrile rubber (NBR), silicone rubber, fluorinated elastomers, ethylene acrylate rubber, ethylene propylene rubber, ethylene-propylene terpolymer (EPDM), ethylene-vinyl acetate copolymer, epichlorohydrin rubber, chlorinated polyethylene propylene rubber, chlorosulfonated polyethylene rubber, hydrogenated nitrile rubber, and tetrafluoroethylene propylene rubber. The proportions of any rubber blend can be selected as needed, for example, based on the viscoelastic properties of the rubber composition. Those skilled in the art can readily determine which elastomers might be appropriate and their relative amounts to provide the desired range of viscoelastic properties.

[0015] In one embodiment, the rubber component contains repeating units derived from butadiene. Examples of such rubbers include, but are not limited to, styrene-butadiene rubber (SBR) and butadiene rubber (BR). In one embodiment, the rubber used in this invention is SBR, which is generally intended to refer to any synthetic rubber made by polymerization of styrene and butadiene monomers, i.e., any styrene-butadiene copolymer. SBR is commonly used in the tire industry and can be prepared by well-known methods, such as copolymerization of the corresponding monomers in emulsions, suspensions, or solutions. The styrene and butadiene monomers can be selected in suitable proportions according to the intended use and properties of the rubber compound.

[0016] In one embodiment, the rubber component comprises SBR; NR; and / or BR. The rubber component may comprise 30 phr to 100 phr of SBR and 0 phr to 70 phr of NR and / or BR, preferably 40 phr, 50 phr, 60 phr, or 70 phr to 90 phr of SBR and 10 phr to 30 phr, 40 phr, 50 phr, or 60 phr of NR and / or BR, preferably BR. In one embodiment, the SBR is solution-polymerized styrene-butadiene rubber (SSBR). In one embodiment, the rubber component comprises or is composed of SBR and BR.

[0017] NR is a natural product and can therefore be advantageously included to improve the sustainability profile of tire compositions. Furthermore, when RHA silica is used instead of sand silica in rubber compounds containing a high filler content of NR, the inventors believe that the higher metal content in RHA silica compared to sand silica may interact with polar impurities in NR, resulting in higher compatibility between RHA silica and NR compared to sand silica. This improves the dispersibility of silica, thereby improving the dispersion of both uncured (via RPA) and cured (via Payne's effect) fillers compared to corresponding compounds containing sand silica. Additionally, in tire compositions, when RHA silica is used, the dispersibility of fillers evaluated by the shape of the tan δ curve (tan δ 0°C / 60°C) is better, and the RR (reduction ratio) predicted by tan δ at 60°C is also improved. Therefore, in one embodiment, the rubber component comprises 35 phr to 90 phr, preferably 50 phr to 80 phr or 60 phr to 70 phr of natural rubber.

[0018] The vehicle tire composition contains silica derived from rice husk ash, meaning silica obtained from the ash produced by burning rice husks. This is referred to herein as "rice husk ash silica" or "RHA silica".

[0019] Rice is one of the world's oldest crops, cultivated in over 100 countries and consumed as a staple food by more than half the world's population. Rice husks are the outer layer of rice grains, and a large amount of them are generated as waste during the processing of rice. Due to their hard surface, poor nutritional value, high silica content, and low bulk density, rice husks are difficult to utilize efficiently. They are also not easily decomposed, so most of the rice husks produced globally end up either dumped or burned in open spaces, damaging the land and causing environmental pollution. One of the most common disposal methods currently is incineration in thermal power plants and gasification plants used for power generation, but this has the problem of generating very large amounts of RHA (reactive silica). Therefore, using RHA silica in tires would be a desirable solution to address this serious problem.

[0020] Rice husks can be directly incinerated with or without pretreatment as explained in Maejo Int. J. Sci. Technol. 2012, 6(03), 430-448 to produce silica of varying purities. The key to converting the raw husks into clean white, gray, or light gray ash depends on the incineration temperature. Temperatures between 300°C and 450°C only convert fresh rice husks into carbonized shells, while temperatures between 500°C and 650°C produce white or gray ash, depending on the homogenization time (the duration of incineration allowed within the stated temperature range). Rice husk ash produced at temperatures between 500°C and 650°C with a homogenization time of 2.5 to 6 hours is considered ideal for producing white amorphous silica, while crystallinity begins to appear when the incineration temperature rises above 700°C.

[0021] Rice husks can be directly incinerated to produce rice husk ash using known methods, such as in the open air, in a muffle furnace, in fluidized bed combustion technology, or by direct incineration in a TORBED reactor (Indian technology). Fluidized bed processes are a practical and flexible way to produce different grades of rice husk ash (RHA) and result in lower levels of ignition and carbon loss, and therefore higher silica content, compared to other combustion conditions.

[0022] Hydrothermal methods have also been used to produce rice husk ash, whereby rice husks are decomposed under high temperature and pressure in the presence of acidic or alkaline media with strong oxidizing activity, converting trace metals into soluble ions. This method can purify silica from rice husks using only water. However, achieving complete dissolution of organic matter in rice husks is virtually impossible. Therefore, the process still requires an incineration step.

[0023] Due to differences in location, variety, climate, soil, and fertilizers used during rice cultivation, the chemical composition of rice husk ash varied among different samples. The percentage of silica (SiO2) in the ash varied and was typically greater than 80% or 90%, and at most 99%, with the remainder consisting of impurities including: K2O; P2O5; CaO; SO3; MgO; Al2O3; Fe2O3; MnO; Rb2O; ZnO; CuO; and Na2O. The composition of rice husk ash by geographical location, as reported in Table 2 of Maejo Int. J. Sci. Technol. 2012, 6(03), 430-448, is as follows:

[0024] Table 2. Composition of rice husk ash by geographical location (according to the percentage of components in square brackets and outside brackets) (Method of use)

[0025]

[0026] Method not specified; From the author's laboratory; ND = Undetermined

[0027] This shows that the natural potassium oxide content in rice husk ash can range from 1.23% to 4.76%, or 12,300 ppm to 46,700 ppm. The impurity content of both sand silica and RHA silica will depend on the production method, but RHA silica generally has a higher potassium content than sand silica.

[0028] The inventors have discovered that when silica has a typically high potassium content, silica agglomeration can occur, resulting in silica being less dispersed in the rubber component and potentially leading to unfavorable mechanical properties. Therefore, advantageously, in this invention, RHA silica is selected to have a potassium content of less than or equal to 300 ppm based on silica. In one embodiment, RHA silica has a potassium content of less than or equal to 280 ppm, 270 ppm, 260 ppm, or 240 ppm based on silica. Silica may have a potassium content of greater than or equal to 100 ppm, 150 ppm, 180 ppm, 190 ppm, 200 ppm, 210 ppm, or 220 ppm based on silica. Any reference to the potassium content of any silica herein is intended to refer to the potassium ion (K) content of silica. + The potassium content can be determined by inductively coupled plasma optical emission spectrometry as described in the examples. In this method, silica is dispersed in water, and HCl is added to generate K+ in the solution. + Ions. Detection and measurement of K + ion.

[0029] Several methods for reducing the purity of RHA silica and lowering the content of metallic impurities, including potassium, are known in the art and generally involve pretreating rice husks before incineration to produce rice husk ash. Various pretreatment methods have been used, including acid leaching, alkali pretreatment, and microbial pretreatment, which are typically combined with some kind of acid. For acid leaching, different kinds of acids have been used, with HCl proving effective in removing metallic impurities. H₂SO₄, HNO₃, and organic acids, including citric acid, acetic acid, or oxalic acid, can also be used. Alkalis (such as NaOH and NH₄OH) can also be used to pretreat rice husks to lower potassium content, as can microbial fermentation. These methods are outlined in Maejo Int. J. Sci. Technol. 2012, 6(03), 430-448 and Chemistry, Processing and Utilization, 2019, 207, the entire contents of which are incorporated herein by reference, and these methods can be used to produce RHA silica with a potassium content of less than 300 ppm.

[0030] When the ash from acid-soaked rice husks is ground, finer particles with a uniform size distribution, high surface area, and high microporosity are obtained. Acid soaking of the rice husks is typically performed before combustion to obtain silica powder with a high specific surface area and high quality. After combustion, if a high content of potassium ions is present, the surface area decreases due to the strong interaction between silica and potassium ions. This is why the potassium content is limited to less than or equal to 300 ppm in this invention.

[0031] Silica can also be extracted from rice husk ash by precipitation. This method is characterized by extracting silica gel with NaOH and precipitating silica with CO2. This has environmental advantages, namely, NaOH and CO2 can be regenerated using fresh calcium hydroxide, as described in Chemistry, Processing and Utilization, 2019, 207. A similar method is disclosed in EP 3 770 115, which is incorporated herein by reference, involving dissolving rice husk ash and an inorganic alkali such as NaOH in water to obtain a silicate slurry, subjecting the slurry to solid-liquid separation, and drying to provide silica.

[0032] The inventors have also discovered that the weak (WK) coefficient of silica is an important indicator of good performance in tire compositions, and specifically, in one embodiment, the RHA silica used in the present invention has a weak coefficient of less than or equal to 20, preferably less than or equal to 15 or 10.

[0033] The weakness coefficient, also known as WK, is measured by laser scattering as described in the examples and is an index of silica dispersion, which can be described as the ratio between the size of larger agglomerates and the size of smaller agglomerates. A higher WK indicates lower silica dispersion and larger agglomerates formed. The dispersion of any reinforcing fillers and filler-rubber interactions are critical properties when preparing high-performance rubber compounds with desired mechanical properties. Therefore, WK is related to performance properties.

[0034] RHA silica with a potassium content of 300 ppm or less and a weakness coefficient of less than 20 is commercially available from various sources. An example of such a product is RHA silica sold by Wilmar under the trade name K2000.

[0035] Silica agglomeration also has the effect of reducing the surface area of ​​silica. Therefore, in one embodiment, the silica has a surface area of ​​at least 175 μm. 2 / g, preferably at least 180m 2 / g, preferably at least 185m 2 / g of CTAB surface area. The CTAB surface area can be up to 220m². 2 / g, preferably up to 200m 2 / g, preferably up to 190m 2 / g. CTAB surface area was measured according to ISO 5794-1G as described in the examples.

[0036] The vehicle tire composition contains 50 phr to 160 phr of RHA silica. In one embodiment, the vehicle tire composition contains 60 phr to 130 phr of RHA silica, preferably 60 phr to 120 phr of RHA silica, such as 70 phr to 110 phr of RHA silica.

[0037] The amount of silica can be selected depending on the overall composition. Different compositions can be formulated for different environments, such as winter and summer tires, and these different compositions may be characterized by rubber components having different glass transition temperatures (Tg). In one embodiment, the rubber component has a Tg of -20°C to -40°C as described in the examples, measured by DTMA, and contains 80 phr to 160 phr, preferably 90 phr to 140 phr, or 100 phr to 110 phr of RHA silica. This is a “low Tg” composition suitable for winter tires. In another embodiment, the rubber component has a Tg of -0°C to -20°C and contains 50 phr to 100 phr, preferably 60 phr to 90 phr, or 60 phr to 80 phr of RHA silica. This is a “high Tg” composition suitable for summer tires.

[0038] In addition to RHA silica and rubber components, vehicle tire compositions may also contain other components. These additional components may include other polymers, processing aids (such as oils, waxes, resins, and plasticizers), vulcanization systems (such as vulcanizing agents, vulcanization accelerators, and vulcanization accelerator additives), degradation inhibitors (such as antioxidants or anti-ozone agents), pigments, other fillers, filler compatibilizers (such as silane coupling agents or covering agents), fibers, etc. Those skilled in the art can readily select combinations and appropriate amounts of vulcanizable rubber compounds for subsequent mixing and vulcanization based on the specific rubber product desired. These additives may be selected and used in conventional amounts depending on the intended use of the vulcanizing material.

[0039] Processing aids improve the processability of the composition and include oils, such as mineral oils, vegetable oils, synthetic oils, or any mixtures thereof. These processing aids may be used in amounts from about 5 phr to 75 phr, preferably from about 10 phr to 50 phr. Typical processing aids include oils such as aromatic oils. Examples of such oils include treated distillate aromatic hydrocarbon extracts (TDAEs), residual aromatic hydrocarbon extracts (RAEs), mild extract solvates (MESs), and bio-based oilseed derivatives. There are no particular limitations on the oil used in the rubber compositions of the present invention, and it may be any oil known to those skilled in the art. For example, the oil may be one or more selected from the group consisting of processed oils (such as aromatic oils, naphthenic oils, and paraffin oils), vegetable oils (such as coconut oil), and synthetic oils (such as alkylbenzene oils and castor oil). Preferably, the oil is a RAE oil and / or 2-ethylhexyl oleate.

[0040] The vulcanizing agent in this composition is not particularly limited and can be any of those vulcanizing agents commonly known in the art. For example, the vulcanizing agent can be sulfur. The amount of vulcanizing agent is not particularly limited, and those skilled in the art can readily select an amount that effectively achieves satisfactory curing of the composition. The vulcanizing agent (e.g., sulfur) can be used in amounts ranging from about 0.1 phr to about 10 phr, preferably from about 0.1 phr to about 5 phr, for example from about 1 phr to about 3 phr. For example, a rubber composition may contain 0.1 phr to 3 phr, preferably from 0.5 phr to 2 phr, for example from 1 phr to 1.5 phr of vulcanizing agent.

[0041] There are no particular limitations on the vulcanization accelerator used in this composition, and it can be any vulcanization accelerator commonly known in the art. Accelerators include thiazoles, dithiocarbamates, thiurams, guanidines, and sulfonamides. Examples of suitable accelerators include thiazole vulcanization accelerators such as 2-mercaptobenzothiazole (MBT), dibenzothiazole disulfide (MBTS), N-cyclohexyl-2-benzothiazole sulfenamide (CBS), and N-tert-butyl-2-benzothiazole sulfenamide (TBBS); guanidine vulcanization accelerators such as 1,3-diphenylguanidine (DPG); thiuram-based vulcanization accelerators such as tetramethylthiuram disulfide, tetrabutylthiuram disulfide, tetradodecylthiuram disulfide, tetraoctylthiuram disulfide, and tetrabenzylthiuram disulfide; and dithiocarbamate compounds such as zinc dimethyldithiuram; and other dialkyldithiophosphate zinc. Preferably, the vulcanization accelerator can be a combination of dibenzothiazole disulfide (MBTS), N-cyclohexyl-2-benzothiazole sulfinamide (CBS), 1,3-diphenylguanidine (DPG), and / or tetrabenzylthiuram disulfide (TBZTD). The amount of vulcanization accelerator used in the composition is not particularly limited and can range, for example, from about 0.5 phr to about 10 phr, preferably from about 1 phr to about 8 phr, and more preferably from about 2 phr to about 6 phr. Preferably, the vulcanization accelerator may be 0.3 phr to 2 phr of dibenzothiazole disulfide (MBTS), 1 phr to 3 phr of N-cyclohexyl-2-benzothiazole sulfinamide (CBS), 1 phr to 3 phr of N-cyclohexyl-2-benzothiazole sulfinamide (CBS), 1 phr to 3 phr of N-tert-butyl-2-benzothiazole sulfinamide (TTBS), or 0.1 phr to 2 phr of tetrabenzylthiuram disulfide (TBZtD).

[0042] There are no particular limitations on the vulcanization accelerator used in this composition, and it can be any vulcanization accelerator known to those skilled in the art. For example, the vulcanization accelerator can be zinc oxide (ZnO) and fatty acids. The fatty acid can be any fatty acid, whether saturated or unsaturated, straight-chain or branched. There are no particular limitations on the number of carbon atoms in the fatty acid, but it can be 1 to 30 or 15 to 30. For example, the fatty acid can be one or more fatty acids selected from: cyclohexanoic acid (cyclohexane carboxylic acid); cycloalkanoic acids with side chains, such as alkylcyclopentanes; saturated fatty acids, such as hexanoic acid, octanoic acid, decanoic acid (including branched carboxylic acids, such as neodecanoic acid), dodecanoic acid, tetradecanoic acid, hexadecanoic acid, and octadecanoic acid (stearic acid); unsaturated fatty acids, such as methacrylic acid, oleic acid, linoleic acid, and linolenic acid; and resin acids, such as rosin, tall oil, and rosin acid. Preferably, the vulcanization accelerator of the present invention is zinc oxide (ZnO) and stearic acid. The total amount of vulcanization accelerators is not particularly limited, but can be from 1 phr to 10 phr, preferably from 1.5 phr to 7 phr, for example from 2 phr to 5 phr. Preferably, zinc oxide can be used in an amount from about 1 phr to about 10 phr, preferably from about 2 phr to about 5 phr, more preferably from about 2 phr to about 3 phr. Stearic acid can be used in an amount from about 0.1 phr to about 5 phr, preferably from about 0.5 phr to about 3 phr.

[0043] The rubber composition of the present invention may also contain additional reinforcing fillers, such as carbon black, carbon nanotubes, short carbon, polyamide, polyester, natural fibers, calcium carbonate, clay, alumina, aluminosilicates, or any mixture thereof. In one embodiment, the rubber composition comprises aluminum hydroxide, preferably 10 phr to 40 phr, as an additional inorganic filler.

[0044] In the presence of carbon black, the carbon black can be furnace black, channel black, or lampblack. For example, the carbon black can be one or more selected from the group consisting of: super abrasion furnace (SAF) black, high abrasion furnace (HAF) black, rapid extrusion furnace (FEF) black, fine furnace (FF) black, medium super abrasion furnace (ISAF) black, semi-reinforced furnace (SRF) black, medium-process channel black, difficult-to-process channel black, and conductive channel black. Other carbon blacks that can be used include acetylene black. The carbon black can be in granular form or non-granular flocculent form. A specific example of carbon black used in the rubber compositions of the present invention is CORAX supplied by Orion Engineered Carbons. ® N234. There is no particular limitation on the amount of carbon black that may be present, but it can be from 0.1 phr to 10 phr, for example 0.5 phr to 5 phr, or from 1 phr to 4 phr, for example 2 phr to 3 phr.

[0045] Advantageously, the only silica-based filler present in the vehicle tire composition of the present invention is RHA silica as described herein, i.e., no additional silica is present. Therefore, RHA silica can constitute all silica filler materials in the composition. In some embodiments, the RHA silica can constitute all reinforcing fillers in the rubber composition. However, the presence of additional silica-based fillers or additional non-silica-based fillers is not necessarily excluded. In the presence of any additional silica, the additional silica can be selected from any silica known in the art, including but not limited to precipitated amorphous silica, wet silica (hydrated silica), dry silica (anhydrous silica), pyrolytic silica, calcium silicate, aluminum silicate, magnesium silicate (e.g., Mg₂SiO₄, MgSiO₃), calcium magnesium silicate (CaMgSiO₄), and calcium aluminum silicate (e.g., Al₂O₃·CaO₂SiO₂).

[0046] The rubber composition may contain additional fillers known to those skilled in the art. For example, the rubber composition may contain one or more additional fillers selected from the following: aluminum hydroxide, talc, alumina (Al2O3), alumina monohydrate (Al2O3·H2O), aluminum hydroxide (Al(OH)3), aluminum carbonate (Al2(CO3)2), magnesium aluminum oxide (MgOAl2O3), pyrophyllite (Al2O3·4SiO2·H2O), bentonite (Al2O3·4SiO2·2H2O), mica, kaolin, glass beads, glass spheres, calcium oxide (CaO), calcium hydroxide (Ca(OH)2), calcium carbonate (CaCO3), magnesium carbonate, magnesium hydroxide (Mg(OH)2), magnesium oxide (MgO), magnesium carbonate (MgCO3), potassium titanate, barium sulfate, zirconium oxide (ZrO2), zirconium hydroxide (Zr(OH)2·nH2O), zirconium carbonate (Zr(CO3)2), crystalline aluminosilicate, and reinforcing grade zinc oxide (i.e., reinforcing zinc oxide). The amount of additional filler can be from 5 phr to 200 phr, for example, 10 phr to 150 phr or 25 phr to 100 phr.

[0047] The anti-degradation agent used in the rubber composition of the present invention is not particularly limited and can be any anti-degradation agent known to those skilled in the art. The anti-degradation agent can be an antioxidant and / or an anti-ozone agent. For example, the anti-degradation agent can be one or more selected from the following: N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMQ), and N'-(1,3-dimethylbutylene)-3-hydroxy-naphthoylhydrazine (BMH). Preferably, the anti-degradation agent is a combination of N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD) and 2,2,4-trimethyl-1,2-dihydroquinoline polymer (TMQ). The amount of each anti-degradation agent can be from 0.1 phr to 3 phr, preferably from 0.2 phr to 2 phr. The total amount of anti-degradation agent can be from 0.1 phr to 5 phr, preferably from 1 phr to 3 phr.

[0048] Covering agents can be used to reduce the formation of silica agglomerates during compounding. If present, these covering agents can be used in amounts of up to 20 phr, preferably about 1 to about 15 phr. In one embodiment, no additional covering agent is used. There are no particular limitations on the covering agent, and it can be any of those covering agents known in the art. Suitable silica-based covering agents include silanes, such as alkylalkoxysilanes, for example, hexadecyltrimethoxysilane, octyltriethoxysilane, and hexyltrimethoxysilane. In one embodiment, the covering agent can be pre-grafted onto the polymer. It can also be used in a free state (i.e., without pre-grafting) or grafted onto the surface of silica.

[0049] Coupling agents may be present, which bind to the silanol groups of silica to inhibit its aggregation, and also serve to covalently link the silica filler to the rubber component matrix. The appropriate amount of any coupling agent can be determined by those skilled in the art taking into account factors such as its molecular weight, the number of functional groups it contains, and its reactivity. Most coupling agents can be used in equimolar amounts based on the amount of silica. There are no particular limitations on the coupling agent used in the vehicle tire compositions of the present invention, and it can be any of those coupling agents known to those skilled in the art. In one embodiment, the coupling agent may be pre-grafted onto the polymer. It may also be used in a free state (i.e., without pre-grafting) or grafted onto the surface of silica.

[0050] Typically, the coupling agent will be a silane coupling agent, such as a bifunctional silane. For example, the silane coupling agent may be selected from one or more of the following: tetrasulfide bis(3-triethoxysilylpropyl) ester, trisulfide bis(3-triethoxysilylpropyl) ester, disulfide bis(3-triethoxysilylpropyl) ester, tetrasulfide bis(2-triethoxysilylethyl) ester, tetrasulfide bis(3-trimethoxysilylpropyl) ester, tetrasulfide bis(2-trimethoxysilylethyl) ester, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 2-mercaptoethyltrimethoxysilane, 2-mercaptoethyltriethoxysilane, 3-trimethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, 3-triethoxysilylpropyl-N,N-dimethylthiocarbamoyltetrasulfide, etc. Alkylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, 2-triethoxysilylethyl-N,N-dimethylthiocarbamoyl tetrasulfide, 3-trimethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropylbenzothiazole tetrasulfide, 3-triethoxysilylpropyl methacrylate monosulfide, 3-trimethoxysilylpropyl methacrylate monosulfide, tetrasulfide bis(3-diethoxymethylsilylpropyl) ester, 3-mercaptopropyldimethoxymethylsilane, dimethoxymethylsilylpropyl-N,N-dimethylthiocarbamoyl tetrasulfide, dimethoxymethylsilylpropylbenzothiazole tetrasulfide. Preferably, the silane coupling agent is bis(3-triethoxysilylpropyl) tetrasulfide. A specific example of the silane coupling agent used in this invention is Si 363 from Evonik Industries AG. ® The amount of silane coupling agent is not particularly limited, but can be from 2 phr to 20 phr, preferably from 5 phr to 18 phr, more preferably from 7 phr to 16 phr, for example from 10 phr to 16 phr.

[0051] The vehicle tire composition according to the invention can be prepared by methods known in the art and involves the step of introducing RHA silica filler into the rubber component to produce a vulcanizable rubber compound; in other words, mixing (also referred to as compounding) the rubber component with RHA silica and any other components described herein to produce a vulcanizable rubber compound. In preparing the rubber composition of the invention, the method for combining each of these components is not limited, and any method known in the art can be used. For example, all components can be blended and kneaded at once, or they can be blended and kneaded in multiple stages. For blending and kneading, a kneading machine (such as a roll kneader), an internal mixer, or a Banbury mixer can be used. To mold the rubber composition into any desired shape, such as sheet or strip, any known molding machine, such as an extrusion molding machine or a compression molding machine, can be used.

[0052] The mixing of components typically takes place in stages where components can be added. Multi-step mixing methods are generally preferred for optimizing the dispersion of silica filler systems and may include the use of more than one internal mixer, such as different internal mixers arranged in series. For example, in the case of mixing tire tread compounds, the mixing process may include an initial mixing stage in which a masterbatch is produced, followed by one or more additional non-productive mixing stages, and finally a productive mixing stage in which a curing agent (i.e., sulfur or sulfur donor and accelerator) is added. Internal mixers that can be used are well known in the art and include, for example, open mills or Banbury type internal mixers with tangential or intermeshing rotors.

[0053] Typically, rubber and RHA silica are mixed with any optional processing aids, zinc oxide, stearic acid, degradation inhibitors (e.g., antioxidants, anti-ozone agents), pigments, additional fillers, compatibilizers, and coupling agents (if present) to produce an initial masterbatch. This initial masterbatch may be followed by another masterbatch in which additional fillers and additives are added, or by a non-productive mixing stage in which no additional components are added. Any non-productive mixing stage may be used to further disperse components (e.g., fillers) within the rubber, or to reduce the viscosity of the mixed rubber compound.

[0054] During mixing, the temperature is maintained below a predetermined level to avoid premature crosslinking of the composition. Typically, the temperature can be kept below 150°C, preferably below 140°C. When producing the initial masterbatch, mixing can be carried out, for example, at a temperature of about 80°C to about 110°C, such as about 100°C. During non-productive mixing phases, the temperature can be increased, for example, up to about 150°C, such as about 130°C. If any additional compatibilizers are added during mixing, it may be necessary to mix at higher temperatures to ensure that these compatibilizers react with the silica surface. Mixing time can vary, but can be readily determined by those skilled in the art based on the composition of the mixture and the type of internal mixer used. Typically, a mixing time of at least 1 minute, preferably 2 to 30 minutes, should be sufficient to obtain the desired homogeneous composition.

[0055] The final mixing stage involves adding curing agents, including accelerators and anti-degradation agents. The temperature used for this mixing stage will typically be low, in the range of approximately 40°C to approximately 60°C, for example, approximately 50°C. This final mixing may be followed by a further non-productive mixing stage in which no additional components are added.

[0056] The most suitable mixing type can be easily selected to obtain a vulcanizable rubber compound. The mixing speed can be easily determined, but can be, for example, in the range of about 20 rpm to about 100 rpm, for example, about 30 rpm to about 80 rpm, preferably about 50 rpm.

[0057] Vulcanizable rubber compounds can be provided as uncured (so-called "green") tire components for the final vulcanization of the composition. Curing that crosslinks the rubber components can be carried out by known methods. Therefore, a subsequent step in the process is to subject the vulcanizable rubber compound to vulcanization by heating to a predetermined temperature and for a predetermined time. For example, in the tire industry, uncured rubber (so-called "green") is produced and then cured in a mold that simultaneously crosslinks the rubber components and molds them into the final tire. Vulcanization cures the rubber through crosslinking, primarily via sulfur crosslinking. Vulcanization methods and conditions for curing the rubber composition are well known to those skilled in the art. Suitable vulcanization conditions typically involve heating to a predetermined temperature in the range of 120°C to 200°C, for example, 140°C to 180°C, for a predetermined duration of 5 minutes to 180 minutes, for example, 5 minutes to 120 minutes.

[0058] The vehicle tire compositions described herein are specifically designed for the manufacture of vehicle tires, and particularly for the manufacture of tire components such as tire treads. Tire treads can be used for tires of any vehicle, but they are specifically designed for the manufacture of tire treads for motor vehicles.

[0059] As described above, it is important in this invention to select specific RHA silica, i.e., RHA silica with a potassium content of less than or equal to 300 ppm based on silica. Therefore, in one aspect, the present invention relates to a method for selecting rice husk ash silica to be included in tire compound, the method comprising the steps of: determining the potassium content of the rice husk ash silica; selecting rice husk ash silica with a potassium content of less than or equal to 300 ppm based on silica; and including the selected rice husk ash silica in the tire compound at a content of 50 phr to 130 phr.

[0060] The potassium content of the silicon dioxide in rice husk ash can be determined by inductively coupled plasma optical emission spectrometry (ICP-OES) as described in the examples. Preferably, the method further includes determining the weak coefficient of the silicon dioxide in the rice husk ash and selecting rice husk ash silicon dioxide having a weak coefficient less than or equal to 20. The weak coefficient is measured by laser scattering as described in the examples.

[0061] One aspect of the invention is the intended use of RHA silica with a potassium content of less than or equal to 300 ppm in a vehicle tire composition to improve performance, specifically to improve the stiffness of the vehicle tire composition compared to an equivalent vehicle tire composition containing rice husk ash silica with a potassium content of greater than 300 ppm.

[0062] The invention is further illustrated by the following non-limiting embodiments and accompanying drawings, in which:

[0063] Figure 1 - The stiffness of the rubber compound with "low Tg Cpd" and "high Tg Cpd" at E' at 30°C. The results are shown as a % increase / decrease relative to the comparative example composition based on silica 1.

[0064] Figure 2 - Tan δ of the rubber compound with “low Tg Cpd” at 0°C and 60°C. The results are shown as a % increase / decrease relative to the comparative composition based on silica 1.

[0065] Figure 3 - Tan δ of the rubber compound with "high Tg Cpd" at 0°C and 60°C. The results are shown as a % increase / decrease relative to the comparative composition based on silica 1.

[0066] Example

[0067] Measurement methods

[0068] Potassium content

[0069] The metal content (including potassium) in RHA silica was measured by inductively coupled plasma-optical emission spectrometry (ICP-OES) according to ISO 19050:2021 (en). In short, silica elements are dissolved in hydrochloric acid. The solution is digested on a hot plate to dissolve the elements of interest, and then analyzed in the instrument.

[0070] Weak (WK) coefficient

[0071] The weak coefficient of RHA silica was measured by laser scattering based on the principle of laser diffraction, as described in US 6,180,076, the contents of which are incorporated herein by reference. Measurements were performed using a CILAS particle size analyzer 1064 L. For determination, 1.3 g of precipitated silica was transferred to 25 ml of water and sonicated at 100 W (90% pulse) for 4.5 min. The solution was then transferred to a measurement cell and sonicated again for 1 min. During sonication, detection was performed using two laser diodes at different angles to the sample. The laser beam was diffracted according to the principle of photodiffraction. The resulting diffraction pattern was evaluated using a computer. This method enables the determination of particle size distribution over a wide measurement range (approximately 40 nm to 500 μm).

[0072] The curves show a first maximum value in the particle size distribution range of 1.0 μm to 100 μm and another maximum value in the range <1.0 μm. The peak in the 1.0 μm to 100 μm range indicates the proportion of undiluted silica particles after ultrasonic treatment. These relatively coarse particles have poor dispersibility in rubber mixtures. The second peak, with significantly smaller particle sizes (<1.0 μm), indicates the portion of silica particles that were pulverized during ultrasonic treatment. These very small particles have excellent dispersibility in rubber mixtures.

[0073] Therefore, the WK coefficient is the ratio of the peak height of non-degradable particles (B) (whose maximum value is in the range of 1.0 μm to 100 μm) to the peak height of degradable particles (A) (whose maximum value is in the range of <1.0 mm).

[0074] WK coefficient = B / A

[0075] in:

[0076] B = Peak height of non-degradable particles (maximum value in the range of 1 μm to 100 μm); and

[0077] A = Peak height of the degradation particles (maximum value in the range of <1μm).

[0078] Therefore, the WK coefficient is a measure of the "degradability" (=dispersibility) of silica. A smaller WK coefficient indicates more particles degrade during rubber incorporation.

[0079] Precipitated silica is more easily dispersed. The key point here is that the energy input via ultrasound is a simulation of the energy input via mechanical force in a kneader used in the tire industry. It has been shown that the WK coefficient is a measure of the dispersibility of precipitated silica.

[0080] Adsorption method for hexadecyltrimethylammonium bromide (CTAB)

[0081] CTAB specific surface area refers to the outer surface area. The surface area of ​​RHA silica is measured according to ISO 5794-1G using the CTAB method.

[0082] Bruno-Emet-Teller (BET) specific surface area

[0083] The average specific surface area of ​​RHA silica was measured by N2 adsorption according to the BET method as described in the Journal of the American Chemical Society, Vol. 60, p. 309, February 1938, and corresponding to standard NF ISO 5794-1, Appendix D (June 2010).

[0084] Loss factor (tan δ)

[0085] Rolling resistance and wet traction are evaluated using loss factors (tangent δ or tan δ) at different temperatures. Tan δ at a lower temperature (0°C) is an indicator of wet traction. An increase in tan δ at lower temperatures compared to a control compound is associated with improved wet traction in the tread compound. When developing rubber compositions for tire treads to improve rolling resistance, the loss tangent (tan δ) near 60°C is typically used as an indicator. Using rubber compositions with low tan δ near 60°C in the tread rubber suppresses heat generation in the tire, reducing rolling resistance and thus improving fuel efficiency. Therefore, tan δ at 60°C is an indicator of rolling resistance (RR). A lower result compared to a control compound indicates reduced rolling resistance. Polymer miscibility is indicated by the ratio of tan δ at 0°C to tan δ at 60°C. Tan δ is determined by dynamic physical testing according to ISO 4664.

[0086] Elastic modulus (E')

[0087] The modulus of elasticity (E') is used to evaluate grip performance. Dynamic physical testing is performed according to ISO 4664 to determine E' at 30°C. E' at 30°C is used as an indicator of dry balance / handling.

[0088] Tensile strength at break and elongation at break

[0089] Tensile strength at break and elongation at break (TB and EB) were measured according to ISO 37 standard (2017 version).

[0090] Curing time (t90)

[0091] T90, or the time to reach 90% curing level, is measured according to ISO 6502.

[0092] Tg of elastomer / rubber components

[0093] Tg is measured using DTMA according to ISO 4664.

[0094] General methods

[0095] The following components are compounded in a Banbury mixer in the amounts specified in Table 1 to prepare a low Tg compound (“CPD Low Tg” - for winter applications) and in the amounts specified in Table 2 to prepare a high Tg compound (CPD High Tg - for summer applications).

[0096] Components

[0097] Elastomers:

[0098] CPD low Tg

[0099] Functionalized solution styrene-butadiene rubber (ENEOS HPR540) (SSBR)

[0100] CPD high Tg

[0101] Functionalized solution styrene-butadiene rubber (ENEOS HPR520) (SSBR1)

[0102] Solution-modified styrene-butadiene rubber ARLANXEO Buna 3038-2HM (SSBR2). Filled with 27.3% TDAE oil.

[0103] High cis-ratio BR ARLANXEO Buna ND22EZ (BR)

[0104] Silica: Sandy silica 1 (HSA-SiO2) (Ultrasil 9001 GR, Evonik)

[0105] Sandy silica 2 (HSA-SiO2) (Zeosil 200MP, Solvay)

[0106] Rice husk silica 1 (HSA-SiO2) (K2000, Wilmar)

[0107] Rice husk silica 2 (HSA-SiO2) (HR200MP, Oryzasil)

[0108] Hydrocarbon resin:

[0109] CPD low Tg

[0110] Hydrogenated HC resin (Synthomer Imperia E1780)

[0111] CPD high Tg

[0112] C9 resin (Rain Carbon, Novales TD 100)

[0113] Oil: CPD low Tg

[0114] 2-Ethylhexyl oleate (Tranquisa Permavis T)

[0115] RAE oil (Repsol Extensoil 14)

[0116] Other additives:

[0117] Carbon black (Corax) ® N234)

[0118] Silane (Evonik Industries Si363)

[0119] Aluminum hydroxide (Al(OH)3)

[0120] Zinc stearate

[0121] sulfur

[0122] 1,3-Diphenylguanidine (DPG)

[0123] Zinc oxide (ZnO)

[0124] stearic acid

[0125] Wax-microcrystalline wax blend (Cera SER AO 768, SER)

[0126] MBTS - Dibenzothiazole disulfide

[0127] CBS-N-cyclohexyl-2-benzothiazolyl sulfinamide

[0128] TBBS-N-tert-butyl-2-benzothiazole sulfinamide

[0129] TBZtD-Tetrabenzylthiuram Disulfide

[0130] TMQ-2,2,4-trimethyl-1,2-dihydroquinoline polymer

[0131] 6PPD-N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine

[0132] PVI - Pre-vulcanization inhibitor.

[0133] Table 1 - CPD Low Tg

[0134]

[0135] Table 2 - CPD with High Tg

[0136]

[0137] Properties of silicon dioxide

[0138] Table 3 - Properties of Silicon Dioxide

[0139]

[0140] The results in Table 3 show that the higher the potassium concentration in RHA silica, the larger the agglomerates (WK coefficient) and the lower the surface area of ​​CTAB.

[0141] Based on the measurement techniques described above, a series of tests were performed on the obtained rubber compound. The results are presented in Tables 4 and 5. Figures 1 to 3 In the report, the properties of the rubber compound are reported as a percentage index (based on silica 1).

[0142] Table 4 - Properties of CPD Low Tg Compound

[0143]

[0144] Table 5 - Properties of CPD High Tg Compound

[0145]

[0146] From Tables 4 and 5, and Figures 1 to 3 The results showed that the high potassium content in RHA silica significantly affected the properties of the compound, consistent with the reduced surface area and higher WK coefficient of CTAB. Due to the smaller surface area and larger agglomerates of RHA silica, the stiffness of both low-Tg and high-Tg compounds decreased. In both low-Tg and high-Tg compounds, tan δ at 0°C and tan δ at 60°C increased and decreased with increasing potassium content in silica, respectively. This is related to the fact that the lower the surface area of ​​CTAB, the better the silica particle dispersion, and the steeper the tan δ curve.

[0147] By selecting a threshold limit of 300 ppm for potassium content in RHA silica, sustainable silica can be used without adversely affecting tire performance.

Claims

1. A vehicle tire composition comprising: 100 phr of a rubber component; and 50 phr to 160 phr of silica obtained from rice husk ash, wherein the silica has a potassium content of less than or equal to 300 ppm based on the silica and measured by inductively coupled plasma optical emission spectrometry as described in the embodiments, and wherein the silica has a weak coefficient of less than or equal to 20 as measured by laser scattering as described in the embodiments.

2. The vehicle tire composition according to claim 1, wherein the silica has a weak coefficient of less than or equal to 15, preferably less than or equal to 10.

3. The vehicle tire composition according to claim 1 or 2, wherein the vehicle tire composition comprises 60 phr to 130 phr of the silica, preferably 70 phr to 110 phr of the silica.

4. The vehicle tire composition according to any of the preceding claims, wherein the rubber component comprises styrene-butadiene rubber (SBR); natural rubber, and / or butadiene rubber (BR); preferably wherein the rubber component comprises 30 phr to 90 phr of styrene-butadiene rubber (SBR), and 10 phr to 70 phr of natural rubber, and / or butadiene rubber (BR); preferably wherein the styrene-butadiene rubber (SBR) is solution-polymerized styrene-butadiene rubber (SSBR).

5. The vehicle tire composition according to any of the preceding claims, wherein the rubber component has a Tg of -20°C to -40°C as described in the embodiments by DTMA, and the rubber component comprises 80 phr to 160 phr of the silica, preferably 90 phr to 140 phr or 100 phr to 110 phr of the silica.

6. The vehicle tire composition according to any of the preceding claims, wherein the rubber component has a Tg of 0°C to -20°C as described in the embodiments by DTMA, and the rubber component comprises 50 phr to 100 phr of the silica, preferably 60 phr to 90 phr or 60 phr to 80 phr of the silica.

7. The vehicle tire composition according to any of the preceding claims, wherein the silica has a silica content of at least 175 μm. 2 / g, preferably at least 180m 2 / g, preferably at least 185m 2 / g CTAB surface area, and / or said silica has at most 220m² 2 / g, preferably up to 200m 2 / g, preferably up to 190m 2 / g of CTAB surface area.

8. The vehicle tire composition according to any of the preceding claims, wherein the vehicle tire composition further comprises aluminum hydroxide, preferably wherein the composition comprises 10 phr to 40 phr of aluminum hydroxide.

9. The vehicle tire composition according to any of the preceding claims, wherein the rubber component comprises 35 phr to 90 phr, preferably 50 phr to 80 phr or 60 phr to 70 phr of natural rubber.

10. The vehicle tire composition according to any of the preceding claims, wherein the silica has a potassium content of less than or equal to 270 ppm, preferably less than 250 ppm or 240 ppm based on the silica, and / or wherein the silica has a potassium content of greater than or equal to 100 ppm, preferably greater than or equal to 200 ppm or 220 ppm based on the silica.

11. A vehicle tire comprising the vehicle tire composition according to any one of claims 1 to 10.

12. A method for producing a vehicle tire composition according to any one of claims 1 to 10, the method comprising the following steps: A silica filler is introduced into the rubber component to produce a vulcanizable rubber compound; and the vulcanizable rubber compound is subjected to vulcanization by heating to a predetermined temperature and for a predetermined time; wherein the silica filler is obtained from rice husk ash, has a potassium content of less than or equal to 300 ppm based on the silica and measured by inductively coupled plasma optical emission spectrometry as described in the embodiments, and wherein the silica filler has a weak coefficient of less than or equal to 20 as measured by laser scattering as described in the embodiments.

13. A method for selecting rice husk ash silica to be included in tire rubber compounds, the method comprising the following steps: The potassium content of silica in the rice husk ash was determined; Select rice husk ash silica with a potassium content of less than or equal to 300 ppm based on the silica, as measured by inductively coupled plasma optical emission spectrometry as described in the embodiments; and The selected rice husk ash silica is included in the tire compound at a content of 50 phr to 160 phr.

14. The method for selecting silicon dioxide from rice husk ash according to claim 13, wherein the method further comprises the following steps: The weak coefficient of silica in the rice husk ash was determined; Select rice husk ash silica with a weak coefficient of less than or equal to 20, as measured by laser scattering, as described in the embodiments described above; and The selected rice husk ash silica is included in the tire compound at a content of 50 phr to 160 phr.

15. The use of rice husk ash silica having a potassium content of less than or equal to 300 ppm based on silica, as measured by inductively coupled plasma optical emission spectrometry as described in the embodiments, in a vehicle tire composition for improving the stiffness of the vehicle tire composition compared to an equivalent vehicle tire composition containing rice husk ash silica having a potassium content of greater than 300 ppm.

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