Vehicle tire, vulcanizate, and sulphur-crosslinkable rubber mixture with protection against ageing phenomena

Abstract

The invention relates to a rubber mixture containing at least the following components: a) 10-20 phr of polyisoprene, selected from natural and synthetic polyisoprene, and b) 80-90 phr of at least one diene rubber, selected from butadiene rubber and styrene-butadiene rubber, wherein 60-70 phr of the diene rubber are partially hydrogenated, and wherein the degree of hydrogenation, i.e. the proportion of the original double bonds of the partially hydrogenated diene rubber that have been completely hydrogenated, is 50-90%. The invention also relates to the vulcanizate of the rubber mixture, and to the use in vehicle tires.

Description

[0001] 202402861

[0002] - 1 -

[0003] Description

[0004] Vehicle tires, vulcanizate and sulfur-crosslinkable rubber compound with protection against aging phenomena

[0005] The invention relates to a vehicle tire. Furthermore, the invention relates to a vulcanizate, in particular for use in vehicle tires or components of the vehicle tire, and to a rubber composition or a sulfur-curable rubber mixture from which the vulcanizate can be formed.

[0006] The rubber composition largely determines the properties of a vehicle tire. Therefore, these rubber compounds are subject to high demands.

[0007] In particular, the aging behavior plays a crucial role. Aging here refers specifically, but not exclusively, to the changes in the rubber material due to interactions with oxygen and especially ozone in the atmosphere. Aging leads, in particular, to an increasing porosity or stiffening of the rubber material.

[0008] In the prior art, there are basically two ways to protect a rubber compound from aging: The use of anti-aging agents in the rubber compound (see, for example, K. Berghus et al.: Handbook for the Rubber Industry, 2nd edition, chapter 4) or the coating of the surface of the formed vulcanizate, e.g. with a polymer with saturated carbon chains, as known from EP 0 228 982 A2.

[0009] Both of the above-mentioned options have disadvantages. For example, the antioxidants used in current technology are inherently toxic. The necessary addition of antioxidants for antioxidant protection leads to significant environmental pollution. Therefore, legal limits regarding the use of known antioxidants such as 6PPD (N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine) or DTPD (N,N'-di-(p-tolyl)-p-phenylenediamine, N,N'-(p-phenylene)-ditoluidine) or other phenylenediamines (PD) are already under discussion. 202402861

[0010] - 2 -

[0011] Applying additional coatings, in turn, involves difficulties and increased effort and costs in the processing and manufacturing of the tires. Furthermore, the protective effect of coatings is limited once abrasion occurs.

[0012] It is therefore at least one object of the present invention to reduce the dosage of anti-aging agents, while maintaining the properties of the tires in their new and used condition, in particular their resistance to aging.

[0013] With the rubber compound, the vulcanizate and the vehicle tire according to the invention, the properties of the tire can be maintained and the proportion of toxic aging agents can be reduced.

[0014] The invention encompasses all advantageous embodiments, which are reflected, inter alia, in the claims. In particular, the invention also encompasses embodiments resulting from the combination of different features, for example, components of the rubber compound or elements of the tire, with varying degrees of preference given to these features, such that a combination of a first feature designated as "preferred" or described within the framework of an advantageous embodiment with a further feature designated, for example, as "particularly preferred," is also encompassed by the invention.

[0015] The following section describes in more detail the components of the rubber compound according to the invention and the properties of the vulcanizate and tire produced therefrom.

[0016] All information regarding the components of the rubber compound according to the invention, regardless of the grade in which these features are preferred, also applies accordingly to the vulcanizate according to the invention, the vehicle tire according to the invention, and uses according to the invention. 202402861

[0017] - 3 -

[0018] The unit phr (parts per hundred parts of rubber by weight) used in this document is the standard unit of measurement for compound formulations in the rubber industry. The dosage of the parts by weight of the individual substances is based on 100 parts by weight of the total mass of all rubbers present in the mixture with a molecular weight Mw according to GPC greater than 20,000 g / mol. The specified value ranges always include the limit values.

[0019] According to the invention, the rubber mixture contains at least polyisoprene (isoprene rubber, IR / NR) and at least one diene rubber selected from one or more of a butadiene rubber (synonyms: BR, BR rubber, polybutadiene) and styrene-butadiene rubber (SBR).

[0020] According to the invention, the isoprene rubber can preferably contain natural polyisoprene (NR) or synthetic polyisoprene (IR) or both.

[0021] The proportion of polyisoprene in the rubber mixture is a maximum of 30 phr and preferably a minimum of 5 phr, more preferably between 10 and 20 phr, more preferably between 12 phr and 18 phr, and particularly preferably 15 phr.

[0022] Diene rubbers are rubbers that are formed by polymerization or copolymerization of dienes and / or cycloalkenes and thus have C=C double bonds either in the main chain or in the side groups.

[0023] According to the invention, the proportion of diene rubbers BR and / or SBR in the rubber mixture is at least 70 phr and at most 95 phr.

[0024] Preferably, the proportion of diene rubbers BR and / or SBR in the rubber mixture is at least 80 phr and at most 90 phr, more preferably between 82 phr and 88 phr, particularly preferably 85 phr.

[0025] Preferably, the rubber compound contains at least SBR. The proportion of SBR in the rubber compound is preferably over 40 phr, more preferably over 50 phr, more preferably over 60 phr, and particularly preferably at least 65 phr. 202402861

[0026] - 4 -

[0027] The styrene-butadiene rubber is preferably selected from the group consisting of styrene-butadiene rubbers with a glass transition temperature Tg, measured by DSC, in the range of -120 to -20 °C, preferably in the range of -100 to -20 °C, particularly preferably in the range of -95 to -20 °C, very preferably in the range of -95 to -45 °C, most preferably in the range of -95 to -55 °C, and especially preferably in the range of -85 to -55 °C.

[0028] The proportion of BR in the rubber mixture is preferably at least 5 phr, more preferably 10 phr, more preferably at least 15 phr and further preferably not more than 30 phr, more preferably a maximum of 25 phr.

[0029] SBR is advantageous for the variable adjustment of rubber properties such as the glass transition temperature. SBR can be functionalized and modified effectively and in various ways.

[0030] According to the invention, one or more of the diene rubbers used are partially hydrogenated, meaning that at least a proportion of the diene rubbers used are in partially hydrogenated form.

[0031] Preferably at least 5 phr, more preferably at least 10 phr, more preferably at least 15 phr, particularly preferably at least 20 phr of the diene rubbers BR and SBR used are in non-hydrogenated form.

[0032] In the context of this text, “partially hydrogenated” means that a proportion of the original double bonds in the diene rubbers have been fully hydrogenated and exist as saturated single bonds.

[0033] Preferably, 50 to 80 phr of the diene rubbers used are present in partially hydrogenated form, more preferably 60 to 70 phr, more preferably 62 to 68 phr, and particularly preferably 65 phr. 202402861

[0034] - 5 -

[0035] Preferably, the SBR used is partially hydrogenated (hy-SBR). The degree of hydrogenation, i.e., the proportion of the double bonds of the SBR that have been completely hydrogenated, is preferably 50 to 90%, more preferably 70 to 80%, and particularly preferably between 75 and 80%.

[0036] An excessively high degree of hydrogenation leads to too few double bonds, which are the target points for vulcanization chemistry during the cross-linking of rubbers. Consequently, the vulcanized rubber would be insufficiently cross-linked.

[0037] Too low a degree of hydrogenation would lead to an undesirable decrease in the aging resistance of the rubber compound, especially when reducing the proportion of toxic antioxidants such as PD.

[0038] The inventors have surprisingly discovered that when using partially hydrogenated diene rubbers, in particular SBRs, with a degree of hydrogenation according to the present invention, the properties of the vulcanizate can surprisingly be retained and at the same time the aging resistance of the vulcanizate can be increased, or the aging resistance of the vulcanizate can be maintained when reducing toxic anti-aging agents in the rubber mixture.

[0039] The proportion of anti-aging agents in the rubber mixture is preferably reduced by 40% to 80%, more preferably by 50% to 70% compared to usual mixing ratios.

[0040] The rubber compound preferably contains no more than 4.5 phr of antioxidants. More preferably, the rubber compound contains a reduced proportion of 0.5 to 3.5 phr of antioxidants, in particular 6PPD or DTPD, more preferably 1.0 to 3.0 phr (see also E2 in Table 1).

[0041] The diene rubber styrene-butadiene rubber (SBR) can preferably be solution-polymerized styrene-butadiene rubber (SSBR) or emulsion-polymerized styrene-butadiene rubber (ESBR).

[0042] Preferably, one or more of the diene rubbers BR and SBR used are functionalized for the binding of carbon black or silica as fillers. 202402861

[0043] - 6 -

[0044] It can be BR rubber with a high cis content (high-cis) or low cis content (low-cis) or with a high or low trans content (high-trans, low-trans).

[0045] Preferably, the rubber mixture consists of BR / SBR and NR / IR. That is, the proportions of BR and / or SBR and NR and / or IR in phr preferably add up to 100 phr.

[0046] Other possible diene rubbers that may be present in smaller quantities in the mixture according to the invention are butadiene-isoprene rubber, styrene-isoprene rubber, halobutyl rubber, polynorbornene, isoprene-isobutylene copolymer, ethylene-propylene diene rubber, nitrile rubber, chloroprene rubber, acrylate rubber, fluorocarbon rubber, silicone rubber, polysulfide rubber, epichlorohydrin rubber, styrene-isoprene-butadiene terpolymer, hydrogenated acrylonitrile butadiene rubber and hydrogenated styrene-butadiene rubber.

[0047] The diene rubber(s) used preferably have a weight-average molar mass Mw, measured by GPC, in the range of 200000 to 5000000 g / mol, preferably in the range of 250000 to 2500000.

[0048] In this process, plasticizers, vulcanization systems and additives known to experts for these rubbers are used preferentially.

[0049] The invention's components of butadiene rubber (BR) and / or SBR and NR or IR particularly well solve the problem underlying the invention.

[0050] The sum of the contained rubbers, by definition, equals 100 phr.

[0051] The diene monomer rubber used is preferably end-group modified and / or functionalized along the polymer chains with modifications and functionalizations corresponding to the fillers used. The diene monomer rubber can be modified simply or with any number of modifications. The modifications can include hydroxy groups and / or ethoxy groups and / or epoxy groups and / or 202402861

[0052] - 7 -

[0053] Siloxane groups and / or Amino groups and / or Aminosiloxane and / or Carboxy groups and / or Phthalocyanine groups and / or Silane sulfide groups.

[0054] However, other modifications, also known as functionalizations and known to experts, are also possible. Metal atoms can be part of such functionalizations.

[0055] These functionalizations or modifications are specifically selected for the filler used, in particular according to the invention specifically for silica fillers or carbon fillers or carbon blacks. The terms "silica", "silica" and "silicon dioxide" are used synonymously within the scope of the present invention.

[0056] All rubber materials used can be based on recycled, renewable and / or bio-based raw materials or on recycled material, e.g. recycled rubber, in particular recycled natural rubber or IR / BR / SBR recycled rubber.

[0057] The rubber compound according to the invention preferably contains at least 75 phr of fillers. More preferably at least 100 phr, more preferably at least 110 phr, and particularly preferably at least 120 phr.

[0058] The fillers are preferably reinforcing fillers, which are selected in particular from silicic acid (= silica / silika, = silicon dioxide) and carbon black.

[0059] The carbon black can be selected from industrial carbon black (also known as "carbon black") and pyrolysis carbon black. Carbon blacks familiar to experts for use in rubber compounds can be employed.

[0060] The filler used (e.g., silica, carbon black, or other fillers) may consist partially or entirely of recycled, renewable, and / or bio-based material, e.g., recovered or recycled filler or filler based on sustainable or renewable raw materials, e.g., silica based on rice hulls or carbon black based on vegetable oil, such as palm oil, rapeseed oil, etc. 202402861

[0061] - 8 -

[0062] Other optional non-reinforcing fillers within the scope of the present invention include, for example, aluminosilicates, kaolin, chalk, starch, magnesium oxide, titanium dioxide or rubber gels as well as fibers (such as aramid fibers, glass fibers, carbon fibers, cellulose fibers).

[0063] Other potentially reinforcing fillers include, for example, carbon nanotubes (CNTs) including discrete CNTs, so-called hollow carbon fibers (HCF) and modified CNTs containing one or more functional groups, such as hydroxy, carboxy and carbonyl groups), graphite and graphene and so-called "carbon-silica dual-phase filier".

[0064] The rubber compound preferably contains a reduced proportion of antioxidants, such as diamines, like N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), N,N'-diphenyl-p-phenylenediamine (DPPD), N,N'-ditolyl-p-phenylenediamine (DTPD), N-(1,4-dimethylpentyl)-N'-phenyl-p-phenylenediamine (7PPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), and / or dihydroquinolines, such as 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), and / or substituted bisphenols, such as 2,2'-methylenebis(4-methyl-6-tert-butylphenol) (BPH), and / or substituted phenols, such as butylhydroxytoluene (BHT).

[0065] The total amount of the aforementioned anti-aging agents is preferably not more than 3 phr, more preferably not more than 2.5 phr, and most preferably not more than 2.2 phr.

[0066] It is also possible, in particular, that the rubber compound contains less than 1.5 phr, less than 1 phr, less than 0.5 phr, less than 0.1 phr, or no antioxidants.

[0067] Reducing the amount of antioxidants does not lead to a deterioration in aging or ozone protection compared to reference compounds, as the aging protection of the rubber compound or vulcanizate is advantageously improved by the partial hydrogenation of the diene rubbers used. 202402861

[0068] - 9 -

[0069] Furthermore, the rubber compound may contain common additives in usual proportions by weight, which are preferably added during its manufacture in at least one basic mixing stage. These additives include:

[0070] 1) Activators, such as zinc oxide and fatty acids (e.g., stearic acid) and / or other activators, such as zinc complexes like zinc ethylhexanoate,

[0071] 2) further activators and / or agents for the binding of fillers, in particular carbon black, such as S-(3-Aminopropyl)-thiosulfuric acid and / or its metal salts,

[0072] 3) Hydrocarbon resins, in particular phenolic resins, especially as adhesive resins,

[0073] 4) Mastication aids, such as 2,2'-dibenzamidodiphenyldisulfide (DBD) and

[0074] 5) Process aids, in particular fatty acid esters and metal soaps, such as zinc soaps and / or calcium soaps,

[0075] 6) Plasticizers, in particular aromatic, naphthenic or paraffinic mineral oil plasticizers, such as MES (Mild Extraction Solvate) or RAE (Residual Aromatic Extract) or TDAE (Treated Distillate Aromatic Extract), or rubber-to-liquid (RTL) or biomass-to-liquid (BTL) oils, preferably with a polycyclic aromatic content of less than 3 wt% according to method IP 346, or triglycerides, such as rapeseed oil, or Faktisse or hydrocarbon resins or liquid polymers, whose mean molecular weight (determined by GPC = gel permeation chromatography, in accordance with BS ISO 11344:2004) is between 500 and 20000 g / mol.

[0076] When using mineral oil, it is preferably selected from the group consisting of DAE (Distilled Aromatic Extracts), RAE (Residual Aromatic Extract), TDAE (Treated Distilled Aromatic Extracts), MES (Mild Extracted Solvents), and naphthenic oils. 202402861

[0077] - 10 -

[0078] The proportion of other additives in the total quantity is preferably between 30 and 100 phr, particularly preferably 50 to 100 phr, and most preferably 60 to 100 phr. Preferably, at least 50 phr of these additives are plasticizers. Preferably, the rubber compound contains no other components.

[0079] The rubber compound according to the invention is preferably used in vulcanized form. The invention also includes the vulcanizate of the rubber compound.

[0080] The terms “vulcanized” and “crosslinked” are used synonymously within the scope of the present invention.

[0081] The vulcanization of the rubber compound according to the invention is preferably carried out in the presence of sulfur and / or sulfur donors using vulcanization accelerators, wherein some vulcanization accelerators can also act as sulfur donors. The accelerator is selected from the group consisting of thiazole accelerators, mercapto accelerators, sulfenamide accelerators, thiocarbamate accelerators, thiuram accelerators, thiophosphate accelerators, thiourea accelerators, xanthate accelerators, and guanidine accelerators. Preferably, at least one sulfenamide accelerator is selected from the group consisting of N-cyclohexyl-2-benzothiazole sulfenamide (CBS), N,N-dicyclohexylbenzothiazole-2-sulfenamide (DCBS), benzothiazole-2-sulfene morpholide (MBS), N-tert-butyl-2-benzothiazole sulfenamide (TBBS), N-tert-butyl-2-benzothiazole sulfenimide (TBSI), and / or at least one guanidine accelerator, such as diphenylguanidine (DPG).

[0082] In particular, two or more accelerators can also be used.

[0083] Any sulfur-donating substance known to experts can be used as the sulfur-donating substance.

[0084] Furthermore, one or more reversion protectants, such as 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane, hexamethylene-1,6- 202402861, may be included in the rubber compound.

[0085] - 11 - bis(thiosulfate) disodium salt dihydrate, and / or tetrabenzylthiuram disulfide (TBzTD), are used.

[0086] Furthermore, vulcanization retarders may be present in the rubber compound.

[0087] The rubber compound is otherwise produced according to the standard procedure in the rubber industry, in which a base mixture containing all components except the vulcanization system (e.g., sulfur and vulcanization-influencing substances) is first produced in one or more mixing stages. The finished mixture is then produced by adding the vulcanization system in the mixing stages, preferably in the final stage.

[0088] The finished compound is further processed, for example by extrusion or calendering, and formed into the appropriate shape. The rubber compound according to the invention is particularly suitable for use in vehicle tires, especially pneumatic tires.

[0089] For use as a component in vehicle tires, the mixture is formed into the appropriate shape as a ready-made mixture before vulcanization and applied and vulcanized as usual during the production of the vehicle tire blank.

[0090] As already explained at the outset, the subject of the present invention is in particular a vehicle tire which comprises in at least one component a vulcanizate made from the vulcanized rubber compound according to the invention.

[0091] Within the scope of the present invention, vehicle tires are understood to include pneumatic and solid rubber tires as well as non-pneumatic tires such as spoked tires, including tires for industrial and construction vehicles, truck, car and two-wheeler tires.

[0092] The invention will now be explained in more detail using comparative and exemplary embodiments. 202402861

[0093] - 12 -

[0094] The examples according to the invention are marked with E1 and E2, the comparative example with V1.

[0095] In E1 and E2, a partially hydrogenated SSBR was used. The degree of hydrogenation of the SSBR in the application example is 78%. This means that 78% of the double bonds of the SSBR have been hydrogenated. Specifically, in the application examples, a partially hydrogenated SSBR with a 78% degree of hydrogenation was sourced from the company Asahi Kasei. In E1, the same proportion of antioxidants was used as in V1. In E2, the proportion of antioxidants was reduced by 50%.

[0096] The mass fractions in phr are given in Table 1.

[0097] 15 tabs 202402861

[0098] - 13 -

[0099] The mixture was produced according to the procedure commonly used in the rubber industry.

[0100] Test specimens were produced from the mixtures V1, E1 and E2 by vulcanization according to a procedure common in the rubber industry and material properties were determined using the test procedures specified below.

[0101] • Shore A hardness at room temperature (RT) according to ISO 868,

[0102] • Rebound elasticity at room temperature (RT) according to ISO 4662,

[0103] • Stress value at 300% elongation (M 300) at RT, tensile strength and elongation at break at room temperature (RT), according to DIN 53 504.

[0104] Table 2:

[0105] Reducing the antioxidant content results in similar properties (E1 vs. E2).

[0106] Ozone tests were also carried out to characterize the aging behavior.

[0107] For this purpose, tests were carried out in accordance with the VW test specification VW 2.8.1.

[0108] In particular, a dynamic test with movement of the test specimen and static tests with stationary test specimens were carried out, and the results are listed in Table 3. The test specimens are extruded bodies of revolution made from the vulcanizate according to the invention, the radius of which was varied. A smaller radius means higher mechanical stresses in the test specimen, which 202402861

[0109] - 14 - leads to faster aging. The aging behavior in the ozone atmosphere was measured and rated on a scale from 0 to 3, where a lower number indicates less aging. A rating of 0 means that no significant aging was detected.

[0110] Table 3:

[0111] In the case of a small test specimen radius of 20 mm, significant aging (3) was observed for each rubber compound in the tests. In the case of a large test specimen radius of 60 mm, no significant aging (0) was observed for each rubber compound in the tests.

[0112] In the case of a test specimen radius of 40 mm, significant aging (3) was observed for the comparison example (V1). However, when the non-hydrated SSBR was replaced by partially hydrated SSBR according to the invention (E1), no significant aging (0) was observed. When the amount of added oxidizing agents was additionally reduced by 50% (E2), the aging was comparable to that in comparison example V1 (3).

[0113] The dynamic ozone test also showed a decrease in the aging effect for E1 (1.25) compared to V1 (1.5) when the non-hydrated SSBR was replaced by partially hydrated SSBR according to the invention. When the amount of antioxidants was reduced by 50% (E2), the observed aging effect was again comparable to that in the comparison example V1 (1.5). 202402861

[0114] - 15 -

[0115] By using the partially hydrogenated diene monomer rubber (SSBR) instead of non-hydrogenated diene monomer rubbers, aging behavior can be improved and / or aging protection increased. This allows the use of conventional additives for aging protection, which often have toxic properties, to be advantageously reduced or avoided altogether.

[0116] The other properties of the vulcanizate remain surprisingly advantageously comparable to the properties of conventional vulcanizates such as the reference vulcanizate.

Claims

202402861 - 16 - Patent claims 1. Rubber mixture comprising at least the following components: a) 10 to 20 phr of polyisoprene selected from natural and synthetic polyisoprene, b) 80 to 90 phr of at least one diene rubber selected from butadiene rubber and styrene-butadiene rubber, preferably solution-polymerized SBR, wherein 60 to 70 phr of the diene rubber is partially hydrogenated, wherein the degree of hydrogenation, i.e. the proportion of the original double bonds of the partially hydrogenated diene rubber that have been fully hydrogenated, is 50 to 90%.

2. Rubber compound according to claim 1, wherein the proportion of the diene rubbers butadiene rubber and styrene-butadiene rubber in the rubber compound is preferably 85 phr.

3. Rubber compound according to one of claims 1 or 2, wherein the proportion of SBR in the rubber compound is above 60 phr, preferably 65 phr.

4. Rubber compound according to any one of claims 1 to 3, wherein the rubber compound contains SBR, wherein the SBR contained is partially hydrogenated.

5. Rubber compound according to claim 4, wherein only the diene rubber SBR is partially hydrogenated.

6. Rubber compound according to any one of claims 1 to 5, wherein the degree of hydrogenation is 70% to 80%, preferably between 75% and 80%.

7. Rubber compound according to any one of claims 1 to 6, wherein the rubber compound comprises at least 100 phr, preferably at least 110 phr, more preferably at least 120 phr fillers.

8. Rubber compound according to any one of claims 1 to 7, wherein the rubber compound comprises a maximum of 3 phr, preferably not more than 2.5 phr, particularly preferably not more than 2.2 phr of anti-aging agents. 202402861 - 17 - 9. Rubber compound according to any one of claims 1 to 8, wherein the rubber compound further comprises at least plasticizers, sulfur, vulcanizing chemicals and optionally further additives.

10. Vulcanizate obtained by sulfur vulcanization of a rubber mixture according to any one of claims 1 to 9.

11. Use of the vulcanizate according to claim 10 in a vehicle tire.

12. Vehicle tire, which is a new tire, a hot retreaded tire or a cold retreaded tire, which is a pneumatic tire, a solid rubber tire or a non-pneumatic tire with a spoke construction, wherein the tire contains in at least one component the vulcanizate according to claim 10.

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