Vulcanizable rubber mixture, vulcanizate and vehicle tire

Abstract

The invention relates to a vulcanizable rubber mixture, comprising: i) one or more diene rubbers, and ii) a melamine-based methylene donor composition. The melamine-based methylene donor composition comprises two or more melamine-based methylene donors of the general formula I), wherein each of the radicals R1, R2, R3, R4, R5 and R6 is a hydrogen or a methyl group; for at least two of the melamine-based methylene donors, at least three of the radicals R1, R2, R3, R4, R5 and R6 are methyl groups such that the number of methyl group radicals of the melamine-based methylene donors n(Me) is three or more; for said at least two melamine-based methylene donors, n(Me) differ from one another; and the mass-averaged number of methyl group radicals of the melamine-based methylene donors in the melamine-based methylene donor composition <n(Me)> ranges from 3.5 to 5.2.

Description

[0001] Vulcanizable rubber compound, vulcanizate and vehicle tires

[0002] Description

[0003] The invention relates to a vulcanizable rubber mixture, a vulcanizate producible therefrom and a rubber product containing this vulcanizate, as well as a process for producing such a vulcanizable rubber mixture.

[0004] Also disclosed is the use of a melamine-based methylene donor composition as a methylene donor in the manufacture of rubber products to reduce the diffusion rate of the methylene donor through the rubber product

[0005] The automotive industry is one of the sectors that has been confronted with fundamental challenges since the beginning of the 21st century and simultaneously shaped by numerous technological innovations. Growing customer awareness of ecological aspects such as emissions profiles and resource efficiency requires new mobility concepts. At the same time, demand for improved vehicle performance and requirements regarding driving safety are increasing. Meeting these challenges is not just the responsibility of the actual vehicle manufacturers. In practice, many of these aspects are strongly influenced by tire properties, making the optimization of tire properties an important field of innovation.

[0006] Several relevant properties of pneumatic vehicle tires, such as wet grip and abrasion resistance, are closely linked to the rubber composition of the tread. However, the physicochemical properties of the other tire components, such as the materials used in the belt layers, also influence the performance characteristics of vehicle tires. Against this background, many research efforts are focused on optimizing the properties of the various rubber compositions and their additives used in a vehicle tire. Given the detailed coordination of the various rubber compositions to different requirements and the sometimes very different chemical compositions, a new aspect is increasingly coming into focus in the development work of inventors.After the green tire is built, potentially very different rubber compounds come into contact. Within the green tire and during its vulcanization at elevated temperatures, but especially during subsequent use as a vulcanized tire, individual components of the rubber compounds can diffuse into the surrounding components between the contacting tire components.

[0007] This undesirably reduces the proportion of migrating compounds in the original tire component, while the concentration in the adjacent tire components can increase. This can, in particular, lead to undesirable contamination of components into the surrounding rubber compounds, which could, for example, lead to an undesirable change in the physicochemical properties of the material.

[0008] The inventors' experiments have shown an undesirable tendency to migrate, particularly for some melamine-based compounds. Such melamine-based compounds, especially hexamethoxymethylmelamine (HMMM), are used as methylene donors in the manufacture of vehicle tires. These methylene donors are used particularly in the vulcanizable rubber compounds of reinforcement layers, for example, the belt layers, where they act together with complementary methylene acceptors, such as resorcinol, as part of so-called methylene acceptor-methylene donor pairs. In many cases, the corresponding methylene acceptor-methylene donor pairs contribute to the advantageous bonding of textile or metallic reinforcements embedded in the corresponding vulcanizable rubber compounds.Hexamethoxymethylmelamine (HMMM) is one of the most established methylene donors in the field of technology and is preferred for use in methylene acceptor-methylene donor pairs for numerous reasons. However, the inventors' investigations have shown that HMMM exhibits a relatively high tendency to migrate from the vulcanizable rubber compounds of the reinforcement layers into the surrounding tire components. However, the presence of HMMM and other melamine-based compounds is undesirable in many tire components, especially not in the tread.

[0009] The primary object of the present invention was to eliminate or at least reduce the disadvantages of the prior art.

[0010] In particular, it was an object of the present invention to provide a vulcanizable rubber mixture which, with regard to the performance of the methylene acceptor-methylene donor pairs used, is comparable to the methylene acceptor-methylene donor pairs known from the prior art, in particular to HMMM-based methylene acceptor-methylene donor pairs, but should exhibit a reduced diffusion rate of the methylene donors, so that the undesired entry of methylene donors into the surrounding tire components can be reduced.

[0011] It was an object of the present invention that the vulcanizable rubber mixture to be specified should be suitable for the rubberization of textile and metallic reinforcements and, after vulcanization, should in particular have a high adhesion to these reinforcements, which should in particular be as close as possible to the level that can be achieved with HMMM-based methylene acceptor-methylene donor pairs.

[0012] With regard to the reduced diffusion rate of the methylene donors, it was desirable that the diffusion rate be advantageously reduced both in the unvulcanized green vehicle tire and during vulcanization at elevated temperatures, as well as in the vulcanized vulcanizate. It was a desirable objective of the present invention that the proposed solution should rely on methylene donors whose processing and handling properties should be as close as possible to those of the established HMMM.In particular, it was desirable that the proposed solution should rely on methylene donors that would not lead to premature reaction in the vulcanizable rubber compound—or at least not to an excessive degree—even at processing temperatures of approximately 100 °C, while simultaneously ensuring efficient reaction of the methylene acceptor-methylene donor pair during crosslinking. Accordingly, one object of the present invention was to advantageously resolve the related conflict of objectives between processability at elevated temperatures and effectiveness during vulcanization.

[0013] The inventors of the present invention have now found that the objects described above can be achieved if a melamine-based methylene donor composition is used in vulcanizable rubber mixtures, which comprises a mixture of melamine-based methylene donors of a specific basic structure, provided that the mass-average number of methyl group residues of the melamine-based methylene donors in the melamine-based methylene donor composition is within a specific range.

[0014] Surprisingly, the systematic use of such mixtures not only yields vulcanizable rubber compounds highly suitable for use as rubber linings for reinforcements, but also advantageously reduces the diffusion rate of the melamine-based methylene donors through the green or vulcanized tire, resulting in lower penetration of the methylene donors into the surrounding vehicle components. This results in advantageous processing and handling properties similar to those of the use of HMMM alone. Even at 100 °C, the methylene acceptor-methylene donor pair does not react excessively prematurely, yet the methylene acceptor-methylene donor pair remains effective during vulcanization. It was found that the effectiveness of the specific mixtures during vulcanization is also advantageously increased compared to conventional HMMM products.Based on this, it was found that the planned use of the specific melamine-based methylene donor composition of the present invention allows to reduce the total amount of methylene donor used without any significant loss in effectiveness and thus to save resources.

[0015] The above-mentioned objects are accordingly achieved by the subject matter of the invention as defined in the claims. Preferred embodiments of the invention emerge from the subclaims and the following statements.

[0016] Such embodiments, which are designated as preferred below, are combined in particularly preferred embodiments with features of other embodiments designated as preferred. Combinations of two or more of the embodiments designated as particularly preferred below are thus very particularly preferred. Likewise preferred are embodiments in which a feature of an embodiment designated as preferred to any extent is combined with one or more further features of other embodiments designated as preferred to any extent. Features of preferred vulcanizates, rubber products, processes, and uses emerge from the features of preferred vulcanizable rubber mixtures.

[0017] To the extent that both specific amounts or proportions of this mixture component and preferred embodiments of the mixture component are disclosed below for a mixture component, for example for the diene rubbers or the melamine-based methylene donor composition, the specific amounts or proportions of the preferably configured mixture components are also disclosed in particular. Furthermore, it is disclosed that, with the corresponding specific total amounts or total proportions of the mixture components, at least some of the mixture components can be preferably configured, and in particular also that preferably configured mixture components can in turn be present in the specific amounts or proportions within the specific total amounts or total proportions.

[0018] The invention relates to a vulcanizable rubber mixture comprising: i) one or more diene rubbers, and ii) a melamine-based methylene donor composition, wherein the melamine-based methylene donor composition comprises two or more melamine-based methylene donors of the general formula I): wherein the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each a hydrogen or a methyl group, wherein for at least two of the melamine-based methylene donors at least three of the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6Methyl groups, so that the number of methyl group residues of the melamine-based methylene donors n <Me) drei oder mehr beträgt, wobei n<Me) für diese zumindest zwei melaminbasierten Methylendonoren voneinander verschieden ist, wobei die massengemittelte Zahl der Methylgruppen-Reste der melaminbasierten Methylendonoren in der melaminbasierten Methylendonor-Zusammensetzung <n(Me)>in the range of 3.5 to 5.2. Vulcanizable rubber compounds per se and their typical components, as well as typical production processes for obtaining corresponding vulcanizable rubber compounds, are well known to those skilled in the art of rubber processing.

[0019] Where components are referred to in the present invention as "one or more," "two or more," or in a similar manner, this refers, as is customary in the industry, to the chemical nature of the corresponding compounds and not to their amount. For example, the vulcanizable rubber mixture may comprise exclusively natural rubber as a diene rubber, which would mean that the vulcanizable rubber mixture comprises a plurality of the corresponding molecules.

[0020] Where mass fractions are specified below, these are usually stated as combined mass fractions of one or more components, as is customary in the industry, thereby expressing that the mass fraction of the correspondingly formed components taken together meets the corresponding criteria. The phr (parts per hundred parts of rubber by weight) specification used here is the quantity specification commonly used in the rubber industry for mixture formulations, which indicates the mass fractions of the components in the rubber mixture based on the mass of the high-molecular-weight rubbers (weight-average molar mass Mw according to GPC greater than 60,000 g / mol) present in the rubber mixture, whereby the combined mass fraction of the high-molecular-weight rubbers in the rubber mixture corresponds to 100 phr.The weight-average molecular weight is determined by gel permeation chromatography according to DIN 55672-1: 2016-03 (GPC with tetrahydrofuran as eluent, polystyrene standard).

[0021] Size exclusion chromatography (SEC = size exclusion chromatography).

[0022] The vulcanizable rubber mixture according to the invention comprises at least one diene rubber. In accordance with the expert understanding, diene rubbers are referred to as rubbers obtained by (co)polymerization of dienes and / or cycloalkenes and thus having C=C double bonds either in the main chain or in the side groups. It can be seen as an advantage of the vulcanizable rubber mixture according to the invention that it is very flexible with regard to the diene rubbers to be used, so that in principle all rubbers customary in the industry can be used. However, in the opinion of the inventors, a vulcanizable rubber mixture according to the invention is preferred, wherein the one or more diene rubbers are selected from the group consisting of natural polyisoprene, synthetic polyisoprene, epoxidized polyisoprene, butadiene rubber, solution-polymerized styrene-butadiene rubber,emulsion-polymerized styrene-butadiene rubber, polynorbornene, ethylene-propylene-diene rubber, nitrile rubber, acrylate rubber, styrene-isoprene-butadiene terpolymer, butyl rubber, and halobutyl rubber, wherein the one or more diene rubbers are preferably selected from the group consisting of natural polyisoprene (NR), synthetic polyisoprene (IR), butadiene rubber (BR), solution-polymerized styrene-butadiene rubber (SSBR), and emulsion-polymerized styrene-butadiene rubber (ESBR), wherein the one or more diene rubbers are particularly preferably selected from the group consisting of natural polyisoprene (NR) and butadiene rubber (BR).

[0023] For obtaining vulcanizable rubber mixtures which can be converted into particularly high-performance vulcanizates by vulcanization, SBR, BR and IR or NR have proven particularly suitable as diene rubbers. Preference is therefore initially given to a vulcanizable rubber mixture according to the invention, wherein the vulcanizable rubber mixture comprises natural polyisoprene and / or synthetic polyisoprene, preferably natural polyisoprene, as diene rubber, preferably in a combined mass fraction of 50 phr or more, particularly preferably 60 phr or more, very particularly preferably 70 phr or more. This can be, for example, either cis-1,4-polyisoprene or 3,4-polyisoprene. However, the use of cis-1,4-polyisoprenes with a cis 1,4 fraction of more than 90%, based on the mass, is preferred.Such a polyisoprene can be obtained synthetically, for example, by stereospecific polymerization in solution with Ziegler-Natta catalysts or using finely divided lithium alkyls. Furthermore, natural rubber (NR) is also such a cis-1,4 polyisoprene, with the cis-1,4 content in natural rubber being greater than 99%, based on the mass of the rubber.

[0024] Additionally or alternatively, a vulcanizable rubber mixture according to the invention is also preferred, wherein the vulcanizable rubber mixture comprises butadiene rubber as the diene rubber, preferably in a combined mass fraction of 5 phr or more, particularly preferably 10 phr or more, very particularly preferably 15 phr or more. The butadiene rubber can be, for example, cis-1,4-polybutadiene. Preference is given to using cis-1,4-polybutadiene with a cis-1,4 content of more than 90%, based on the mass, which can be produced, for example, by solution polymerization in the presence of rare earth catalysts.

[0025] Additionally or alternatively, a vulcanizable rubber mixture according to the invention is also preferred, wherein the vulcanizable rubber mixture comprises styrene-butadiene rubber, preferably solution-polymerized styrene-butadiene rubber (SSBR), as the diene rubber, preferably in a combined mass fraction of 5 phr or more, particularly preferably 10 phr or more, very particularly preferably 15 phr or more. For example, these can be solution-polymerized styrene-butadiene copolymers having a styrene content, based on the mass of the polymer, in the range of approximately 1 to 45% and a vinyl content (content of 1,2-bonded butadiene, based on the total polymer) in the range of 10 to 90%, which can be produced, for example, using lithium alkyls in an organic solvent.

[0026] The diene rubbers used in the mixture, in particular the styrene-butadiene copolymers, can also be used in partially or fully functionalized form. The functionalization can be carried out with groups that can interact with the fillers used, in particular with fillers bearing OH groups. Against this background, a vulcanizable rubber mixture according to the invention is preferred, wherein at least one of the diene rubbers, preferably all of the one or more diene rubbers, is an end-group-modified and / or chain-modified diene rubber, preferably an end-group-modified diene rubber, wherein the functionalization is preferably a functionalization with hydroxyl groups and / or epoxy groups and / or siloxane groups and / or amino groups and / or phthalocyanine groups and / or carboxyl groups and / or silane sulfide groups.

[0027] With regard to the design of the diene rubbers, preference is generally given to a vulcanizable rubber mixture according to the invention, wherein the diene rubber(s) have a weight-average molecular weight Mw, measured by GPC, in the range from 200,000 to 5,000,000 g / mol, preferably in the range from 250,000 to 2,500,000.

[0028] It has proven particularly advantageous for the overall performance profile of the vulcanizable rubber mixtures according to the invention to combine two or more different diene rubbers with the melamine-based methylene donor compositions to be used according to the invention. Accordingly, a vulcanizable rubber mixture according to the invention is particularly preferred, wherein the vulcanizable rubber mixture comprises two or more, preferably three or more, different diene rubbers as the diene rubber, particularly preferably at least natural polyisoprene and butadiene rubber.

[0029] The vulcanizable rubber mixture according to the invention comprises at least two chemically structurally different methylene donors, namely at least two melamine-based methylene donors of the general formula I): where the residues R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each a hydrogen or a methyl group.

[0030] In this case, the vulcanizable rubber mixture may, at least in theory, also comprise other methylene donors which are not melamine-based methylene donors, although this is less preferred.

[0031] The term "melamine-based" serves as a clear linguistic identification and expresses that the methylene donors of general formula I) have a central structural element derived from melamine (i.e., 2,4,6-triamino-s-triazine). Such melamine-based methylene donors can be obtained by reacting melamine with formaldehyde and, if necessary, with methanol.

[0032] In the context of the present invention, for the purpose of a clearer definition, all melamine-based methylene donors of the general formula I), ie regardless of the values ​​for n <Me) oder <n(Me)>, the so-called "melamine-based methylene donor composition." This does not mean that the melamine-based methylene donors contained in the vulcanizable rubber mixture must be added together, for example, as a mixture, although this is preferred in many cases. Rather, two successively added melamine-based methylene donors, which are subsequently present in the vulcanizable rubber mixture, are assigned to the melamine-based methylene donor composition for the purposes of the above definition. In formula I) are the residues R 1 , R 2 , R 3 , R 4 , R 5 and R 6each either a hydrogen or a methyl group. The “each” expresses that the residues R 1 , R 2 , R 3 , R 4 , R 5 and R 6 regardless of the nature of the other radicals, may be either a hydrogen or a methyl group, provided that the other requirements of the above definition are met.

[0033] For example, a compound of formula I) for which R 1 , R 2 , R 3 , R 4 and R 5 each hydrogen and only R 6 a methyl group, is indeed a melamine-based methylene donor of the formula I within the meaning of the invention), but would not represent one of the required melamine-based methylene donors in which at least three of the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are methyl groups.

[0034] According to the invention, the vulcanizable rubber mixture must comprise at least two of the above-defined melamine-based methylene donors, which comprise three or more methyl groups as radicals. In this connection, it is important, in the opinion of the inventors, that these melamine-based methylene donors differ in the number of their methyl groups. <Me) unterscheiden, beispielsweise weil diese drei und vier oder vier und sechs Methylgruppen als Reste umfassen, so dass das bloße Vorliegen von Isomeren nicht ausreichend ist.

[0035] As defined above, it is important that the average number of methyl group residues, ie the residues R 1 , R 2 , R 3 , R 4 , R 5 and R 6 , which are methyl groups, is within a given range, with the average number of methyl group residues being<n(Me)> is called.

[0036] The averaging is carried out on a mass basis, ie each melamine-based methylene donor present in the melamine-based methylene donor composition has a certain number of methyl groups n <Me) gemäß dem jeweiligen Massenanteil der entsprechenden melaminbasierten Methylendonoren an der melaminbasierten Methylendonor-Zusammensetzung beiträgt.

[0037] The range defined above corresponds to the range in which, in the inventors' estimation, the conflict of objectives between the diffusion rate, the processing properties and the effectiveness of the vulcanization is resolved in an advantageous manner.

[0038] According to the inventors' assessment, particularly advantageous solutions to the conflict of objectives described above are achieved with values ​​in the medium range, whereby, particularly with regard to advantageous processing properties before vulcanization, it is preferable not to choose the lower limit too low. Therefore, a vulcanizable rubber mixture according to the invention is preferred, wherein the mass-average number of methyl group residues of the melamine-based methylene donors in the melamine-based methylene donor composition<n(Me)> 3.7 or more, preferably 3.9 or more, particularly preferably 4.1 or more, most preferably 4.3 or more, and / or wherein the mass-average number of methyl group residues of the melamine-based methylene donors in the melamine-based methylene donor composition<n(Me)> 5.0 or less, preferably 4.9 or less, more preferably 4.8 or less, more preferably 4.7 or less.

[0039] According to the inventors' assessment, melamine-based methylene donors with only three methyl groups exhibit less advantageous behavior, particularly with regard to processing properties prior to vulcanization, than compounds with more methyl groups. Accordingly, the inventors consider it advantageous to at least additionally provide two or more of these compounds, with particular preference being given to the melamine-based methylene donors with only three methyl groups being present only as minor constituents in the melamine-based methylene donor composition. Accordingly, a vulcanizable rubber mixture according to the invention is preferred, wherein for at least two of the melamine-based methylene donors, at least four of the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6 Methyl groups, so that the number of methyl groups of the melamine-based methylene donors n <Me) vier oder mehr beträgt.

[0040] With regard to the chemical nature of the melamine-based methylene donors, a vulcanizable rubber mixture is particularly preferred, wherein the melamine-based methylene donor composition comprises: ii.i) hexamethoxymethylmelamine, preferably in a mass fraction of 20% or more, preferably of 30% or more, particularly preferably of 40% or more, based on the mass of the melamine-based methylene donor composition.

[0041] With regard to the chemical nature of the melamine-based methylene donors, particularly preferred is additionally or alternatively a vulcanizable rubber mixture, wherein the melamine-based methylene donor composition comprises: ii.ii) penta(methoxymethyl)methylolmelamine, preferably in a mass fraction of 20% or more, preferably of 30% or more, particularly preferably of 40% or more, based on the mass of the melamine-based methylene donor composition.

[0042] With regard to the chemical nature of the melamine-based methylene donors, particularly preferred is additionally or alternatively a vulcanizable rubber mixture, wherein the melamine-based methylene donor composition comprises: ii.iii) tetra(methoxymethyl)dimethylolmelamine, preferably in a mass fraction of 10% or more, preferably of 15% or more, particularly preferably of 20% or more, based on the mass of the melamine-based methylene donor composition.

[0043] Particularly preferred is also, additionally or alternatively, a vulcanizable rubber mixture, wherein the combined mass fraction of all melamine-based methylene donors with n <Me) von 4 oder mehr, 70 % oder mehr, bevorzugt 80 % oder mehr, besonders bevorzugt 90 % oder mehr, beträgt, bezogen auf die Masse der melaminbasierte Methylendonor-Zusammensetzung.

[0044] In the eyes of the inventors, the mixture of corresponding melamine-based methylene donors proves to be particularly advantageous for solving the problem, so that it is considered particularly preferable to provide not just two, but three or more of the preferably methyl group-rich melamine-based methylene donors. Accordingly, a vulcanizable rubber mixture is preferred, wherein the melamine-based methylene donor composition comprises three or more melamine-based methylene donors of the general formula I), preferably three or more melamine-based methylene donors for the at least three, preferably at least four, of the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6 Methyl groups, where n(Me) is different for these at least three melamine-based methylene donors.

[0045] The inventors have succeeded in identifying particularly favorable ranges for the dosage of the melamine-based methylene donor composition. A vulcanizable rubber mixture is preferred, wherein the vulcanizable rubber mixture comprises the melamine-based methylene donor composition in a mass fraction of 0.2 phr or more, preferably 0.5 phr or more, particularly preferably 0.7 phr or more. Additionally or alternatively, a vulcanizable rubber mixture is preferred, wherein the vulcanizable rubber mixture comprises the melamine-based methylene donor composition in a mass fraction in the range from 0.7 phr to 6 phr, preferably in the range from 0.7 phr to 5 phr, particularly preferably in the range from 0.7 phr to 4.5 phr.

[0046] In the vast majority of cases, in addition to the advantageous melamine-based methylene donor compositions, a methylene acceptor will also be provided, with which a methylene acceptor-methylene donor pair is formed. Accordingly, a vulcanizable rubber mixture according to the invention is relevant for most applications, wherein the vulcanizable rubber mixture additionally comprises: iii) one or more methylene acceptors, wherein the one or more methylene acceptors are selected from the group consisting of resorcinol, novolak resins, and precondensates of novolak resins, wherein the one or more methylene acceptors are preferably present in a combined mass fraction in the range from 0.2 to 10 phr, preferably in the range from 0.5 to 7.5 phr, particularly preferably in the range from 1 to 5 phr.

[0047] Fillers can be included in the vulcanizable rubber mixtures in a conventional manner to optimize the mechanical properties of the vulcanizates produced. In this case, it is a vulcanizable rubber mixture according to the invention, wherein the vulcanizable rubber mixture additionally comprises: iv) one or more fillers.

[0048] Particularly preferred in this respect is a vulcanizable rubber mixture according to the invention, wherein the one or more fillers are selected from the group consisting of amorphous silicon dioxide, in particular precipitated amorphous silicon dioxide and pyrogenic amorphous silicon dioxide, and carbon black, particularly preferably selected from the group consisting of precipitated amorphous silicon dioxide and carbon black. Additionally or alternatively, particularly preferred is a vulcanizable rubber mixture according to the invention, wherein the vulcanizable rubber mixture comprises the one or more fillers in a combined mass fraction of 50 phr or more, preferably 55 phr or more, particularly preferably 60 phr or more.

[0049] With regard to the selection of fillers, a vulcanizable rubber mixture according to the invention is preferred, wherein at least one, preferably all, of the fillers are selected from the group consisting of carbon blacks with a CTAB surface area according to ASTM D 3765-03 of 30 m 2 / g or more, preferably 40 m 2 / g or more. In this respect, additionally or alternatively, a vulcanizable rubber mixture according to the invention is also preferred, wherein at least one, preferably all of the fillers are selected from the group consisting of amorphous silicon dioxide, in particular precipitated amorphous silicon dioxide, with a CTAB surface area according to ASTM D 3765-03 in the range of 30 to 350 m 2 / g, preferably in the range of 110 to 250 m 2 / G.

[0050] If the rubber compound contains precipitated amorphous silica or other polar fillers, silane coupling agents can be added to the compound to improve processability and bond the polar filler to the rubber. The silane coupling agents react with the surface silanol groups of the silica or other polar groups during mixing of the rubber or rubber compound (in situ) or even before the filler is added to the rubber as a pretreatment (premodification). Silane coupling agents can be any silane coupling agents known to those skilled in the art for use in rubber compounds.Such coupling agents known from the prior art are, for example, bifunctional organosilanes which have at least one alkoxy, cycloalkoxy or phenoxy group as a leaving group on the silicon atom and which have as another functionality a group which, if appropriate after cleavage, can enter into a chemical reaction with the double bonds of the polymer. The latter group can, for example, be the following chemical groups: -SCN, -SH, -NH2 or -Sx- (where x = 2-8). Thus, as silane coupling agents, for example, 3-mercaptopropyltriethoxysilane, 3-thiocyanatopropyltrimethoxysilane or 3,3'-bis(triethoxysilylpropyl)polysulfides with 2 to 8 sulfur atoms, such as e.g. B. 3,3'-bis(triethoxysilylpropyl)tetrasulfide (TESPT), the corresponding disulfide or mixtures of the sulfides with 1 to 8 sulfur atoms with different contents of the various sulfides can be used.In this case, it is a vulcanizable rubber mixture according to the invention, wherein the vulcanizable rubber mixture comprises amorphous silicon dioxide as a filler, and additionally: v) one or more silane coupling agents, preferably in a combined mass fraction of 2 phr or more, preferably 4 phr or more, particularly preferably 6 phr or more. Particularly preferred is a vulcanizable rubber mixture according to the invention, wherein the one or more silane coupling agents are selected from the group consisting of blocked mercaptosilanes.

[0051] In addition, the vulcanizable rubber compound may contain plasticizers, particularly to adjust the processing properties. The term "plasticizer" is clear to those skilled in the art and functionally refers to substances added to vulcanizable rubber compounds to make them and the resulting vulcanizates softer. Plasticizers are commercially available under these names from numerous manufacturers.Thus, for many applications, a vulcanizable rubber mixture according to the invention is preferred, wherein the vulcanizable rubber mixture additionally comprises: vi) one or more plasticizers, wherein the plasticizers are preferably selected from the group consisting of mineral oils, synthetic plasticizers, fatty acids, fatty acid derivatives, factices, glycerides, terpenes, biomass-to-liquid oils (BTL oils) and rubber-to-liquid oils (RTL oils), wherein the vulcanizable rubber mixture preferably comprises the plasticizers in a combined mass fraction in the range from 0.2 to 40 phr, preferably in the range from 0.5 to 30 phr, particularly preferably in the range from 1 to 20 phr. The use of resins, for example as plasticizer resins or in the form of reinforcing resins, is also advantageous for many applications.A person skilled in the art of rubber processing is readily able to distinguish resins from diene rubbers and any liquid polymer components, which in practice is done in particular via the average molecular weight or the glass transition temperature. In this case, it is a vulcanizable rubber mixture according to the invention, wherein the vulcanizable rubber mixture additionally comprises: vii) one or more resins, wherein the resins are preferably selected from the group consisting of hydrocarbon resins and rosin, wherein the vulcanizable rubber mixture preferably comprises the resins in a combined mass fraction in the range from 0.2 to 15 phr, more preferably in the range from 0.5 to 10 phr, most preferably in the range from 1 to 10 phr.In this respect, a vulcanizable rubber mixture according to the invention is particularly preferred, wherein the one or more resins have a weight-average molecular mass Mw, measured by GPC, in the range from 200 to 50,000 g / mol, preferably in the range from 400 to 40,000 g / mol, particularly preferably in the range from 600 to 30,000 g / mol, very particularly preferably in the range from 800 to 20,000 g / mol.

[0052] In accordance with the understanding of those skilled in the art, the vulcanizable rubber mixture comprises a vulcanization system that generally relies on the use of sulfur or sulfur sources. In other words, it is a vulcanizable rubber mixture according to the invention, wherein the vulcanizable rubber mixture additionally comprises: vii) a vulcanization system.

[0053] An example in this respect is a vulcanizable rubber mixture according to the invention, wherein the vulcanization system comprises sulfur or a sulfur donor, preferably sulfur, preferably in a combined mass fraction in the range from 0.5 to 10.0 phr, preferably in the range from 1 to 8 phr, particularly preferably in the range from 2 to 6 phr, based on the mass of the vulcanizable rubber mixture.

[0054] For some applications, a vulcanizable rubber mixture according to the invention is preferred, wherein the vulcanization system comprises one or more further vulcanization components, wherein the further vulcanization components are selected from the group consisting of crosslinkers, vulcanization retarders and vulcanization accelerators, for example thiazole accelerators, mercapto accelerators, sulfenamide accelerators, thiocarbamate accelerators, thiuram accelerators, thiophosphate accelerators, thiourea accelerators, xanthate accelerators or guanidine accelerators, preferably in a combined mass fraction in the range from 0.1 to 10.0 phr, preferably in the range from 0.2 to 5 phr, particularly preferably in the range from 0.5 to 2.5 phr, based on the mass of the vulcanizable rubber mixture.

[0055] In addition to the diene rubbers and the other components disclosed above, further typical components can advantageously be used in the vulcanizable rubber mixtures according to the invention, which serve, for example, to influence the physico-chemical properties, for example the processing and handling properties, of the vulcanizable rubber mixtures or the mechanical properties of the vulcanizates that can be produced therefrom.In this case, it is a vulcanizable rubber mixture according to the invention, wherein the vulcanizable rubber mixture comprises one or more further additives, wherein the further additives are preferably selected from the group consisting of, ageing inhibitors, for example N-phenyl-N'-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), N,N'-diphenyl-p-phenylenediamine (DPPD), N,N'-ditolyl-p-phenylenediamine (DTPD), N-isopropyl-N'-phenyl-p-phenylenediamine (IPPD), 2,2,4-trimethyl-1,2-dihydroquinoline (TMQ), activators, for example zinc oxide and fatty acids, waxes, mastication aids, for example 2,2'-dibenzamidodiphenyl disulfide (DBD) and processing aids, wherein the vulcanizable rubber mixture preferably comprises the further additives in a combined mass fraction in the range of 0.1 to 20 phr, preferably in the range of 0.5 to 15 phr, particularly preferably in the range of 1 to 10 phr.

[0056] Vulcanizates or rubber products can be produced in the usual way from the vulcanizable rubber mixtures according to the invention. The corresponding process for producing a vulcanizate or a rubber product comprises, in addition to producing the vulcanizable rubber mixture according to the invention, for example, the additional step of vulcanizing the vulcanizable rubber mixture according to the invention, preferably as part of a rubber blank, particularly preferably an unvulcanized vehicle tire blank, to obtain a vulcanizate, preferably as part of a rubber product, preferably a pneumatic vehicle tire.

[0057] The vulcanizable rubber mixture according to the invention is vulcanized, for example, by the process customary in the tire industry, for example by sulfur-based crosslinking.

[0058] The invention accordingly also relates to a vulcanizate that can be produced or is produced by vulcanizing a vulcanizable rubber mixture according to the invention. Preferred in this respect is a vulcanizate according to the invention that can be produced by vulcanization at a temperature in the range of 130 to 200°C, particularly preferably in the range of 140 to 190°C.

[0059] The invention therefore also relates to a rubber product comprising a vulcanizate according to the invention. An example of a rubber product according to the invention is one in which the rubber product is selected from the group consisting of shoe soles, belts, hoses, and straps. However, for essentially all cases, a rubber product according to the invention is preferred, wherein the rubber product is a vehicle tire, preferably a pneumatic vehicle tire.

[0060] Through the use of the specific methylene donors, the vulcanizable rubber mixtures according to the invention are particularly suitable for use as rubber coatings for reinforcements, such as those used, for example, in belts or wound bandages of vehicle tires. Accordingly, a rubber product according to the invention is preferred, wherein the rubber product comprises one or more reinforcements embedded in the vulcanizate, preferably as reinforcement layers of a vehicle tire, wherein the reinforcements are selected from the group consisting of textile reinforcements, in particular textile reinforcements made of polyester and / or polyamides and / or viscose fiber, and metallic reinforcements, in particular metallic reinforcements made of steel, preferably textile reinforcements.Additionally or alternatively, a rubber product according to the invention is preferred, wherein the rubber product comprises the vulcanizate in a reinforcement layer, preferably a belt layer and / or a wound bandage. In turn, additionally or alternatively, a rubber product according to the invention is preferred, wherein the rubber product comprises the vulcanizate in an internal component, so that the vulcanizate is not present on the surface of the rubber product.

[0061] In light of the above, the use of a melamine-based methylene donor composition as a methylene donor in the production of rubber products for reducing the diffusion rate of the methylene donor through the rubber product is also disclosed here, wherein the melamine-based methylene donor composition comprises two or more melamine-based methylene donors of the general formula I): wherein the radicals R 1 , R 2 , R 3 , R4 , R 5 and R 6 are each a hydrogen or a methyl group, wherein for at least two of the melamine-based methylene donors at least three of the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6 Methyl groups, so that the number of methyl group residues of the melamine-based methylene donors n <Me) drei oder mehr beträgt, wobei n(Me) für diese zumindest zwei melaminbasierten Methylendonoren voneinander verschieden ist, wobei die gewichtsgemittelte Zahl der Methylgruppen-Reste der melaminbasierten Methylendonoren in der melaminbasierten Methylendonor-Zusammensetzung <n(Me)>in the range of 3.5 to 5.2.

[0062] Finally, the invention also relates to a process for producing a vulcanizable rubber mixture according to the invention, comprising the process steps: a) producing or providing a melamine-based methylene donor composition, wherein the melamine-based methylene donor composition comprises two or more melamine-based methylene donors of the general formula I): wherein the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each a hydrogen or a methyl group, wherein for at least two of the melamine-based methylene donors at least three of the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6, methyl groups, so that the number of methyl groups of the melamine-based methylene donors n <Me) drei oder mehr beträgt, wobei n(Me) für diese zumindest zwei melaminbasierten Methylendonoren voneinander verschieden ist, wobei die gewichtsgemittelte Zahl der Methylgruppen der melaminbasierten Methylendonoren in der melaminbasierten Methylendonor-Zusammensetzung <n(Me)>is in the range of 3.5 to 5.2, and b) mixing the melamine-based methylene donor composition with one or more diene rubbers and other components of the vulcanizable rubber mixture.

[0063] The process according to the invention is based on the finding that particularly advantageous vulcanizable rubber mixtures can be obtained if the melamine-based methylene donor composition is prepared in a separate step prior to addition, rather than, for example, adding its components successively one after the other. Without wishing to be bound by this theory, the inventors believe that this makes it easier to avoid the occurrence of adverse concentration gradients of the different melamine-based methylene donors in the vulcanizable rubber mixture, and that the advantages of using mixed melamine-based methylene donor compositions are particularly effective and reliable.

[0064] The invention and preferred embodiments of the invention are further explained and described below with reference to exemplary compositions.

[0065] The preparation of the exemplary vulcanizable

[0066] Rubber compounds can be produced using processes commonly used in the rubber industry under standard conditions, for example, in three stages in a laboratory mixer (300 mL, Brabender Mixer, CW Brabender GmbH & Co., South Hackensack, NJ, US). In a first mixing stage (basic mixing stage, rotor speed: 70 rpm, starting temperature: approx. 130 °C, final temperature: approx. 149 °C), all components except the vulcanization system (sulfur and vulcanization-influencing substances) are mixed. The vulcanizable rubber compound can be produced by adding the vulcanization system in the second stage (final mixing stage; rotor speed: 55 rpm, temperature: approx. 80 °C). Vulcanized vulcanizates can be produced from corresponding vulcanizable rubber compounds by vulcanization (example vulcanization conditions: t: 20 min, T: 160 °C).

[0067] The compositions of the exemplary vulcanizable rubber compounds are summarized in Table 1. Commercially available products can be used for the substances listed alongside the melamine-based methylene donor compositions. B1 is an example of a vulcanizable rubber compound particularly suitable for rubberizing textile reinforcements, whereas examples B2 to B7 are specifically designed for rubberizing metallic reinforcements.

[0068] Table 1 - Examples of vulcanizable rubber compounds (all values ​​in phr)

[0069] 1) Silane coupling agent on carbon black in a weight ratio of 1:1.

[0070] Exemplary methylene donor compositions that can be used in the exemplary vulcanizable rubber compounds of Table 1 are summarized in Table 2. Table 2 - Exemplary methylene donor compositions for use in exemplary vulcanizable rubber compounds B1 to B7

Claims

Claims 1. A vulcanizable rubber mixture comprising: i) one or more diene rubbers, and ii) a melamine-based methylene donor composition, wherein the melamine-based methylene donor composition comprises two or more melamine-based methylene donors of the general formula I): wherein the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each a hydrogen or a methyl group, wherein for at least two of the melamine-based methylene donors at least three of the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6Methyl groups, so that the number of methyl group residues of the melamine-based methylene donors n <Me) drei oder mehr beträgt, wobei n(Me) für diese zumindest zwei melaminbasierten Methylendonoren voneinander verschieden ist, wobei die massengemittelte Zahl der Methylgruppen-Reste der melaminbasierten Methylendonoren in der melaminbasierten Methylendonor-Zusammensetzung <n(Me)>in the range of 3.5 to 5.

2.

2. Vulcanizable rubber mixture according to claim 1, wherein the vulcanizable rubber mixture comprises two or more different diene rubbers as diene rubber.

3. Vulcanizable rubber mixture according to one of claims 1 or 2, wherein the mass-average number of methyl group residues of the melamine-based methylene donors in the melamine-based methylene donor composition<n(Me)> 3.7 or more.

4. Vulcanizable rubber mixture according to one of claims 1 to 3, wherein the mass-average number of methyl group residues of the melamine-based methylene donors in the melamine-based methylene donor composition<n(Me)> 5.0 or less.

5. Vulcanizable rubber mixture according to one of claims 1 to 4, wherein for at least two of the melamine-based methylene donors at least four of the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6 Methyl groups, so that the number of methyl groups of the melamine-based methylene donors n <Me) vier oder mehr beträgt.

6. Vulcanizable rubber mixture according to one of claims 1 to 5, wherein the melamine-based methylene donor composition comprises three or more melamine-based methylene donors of the general formula I).

7. Vulcanizable rubber mixture according to one of claims 1 to 6, wherein the vulcanizable rubber mixture comprises the melamine-based methylene donor composition in a mass fraction in the range of 0.7 phr to 6 phr.

8. A process for producing a vulcanizable rubber mixture according to claim 1, comprising the process steps: a) producing or providing a melamine-based methylene donor Composition, wherein the melamine-based methylene donor Composition of two or more melamine-based methylene donors of the general formula I): wherein the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each a hydrogen or a methyl group, wherein for at least two of the melamine-based methylene donors at least three of the radicals R 1 , R 2 , R 3 , R 4 , R 5 and R 6, methyl groups, so that the number of methyl group residues of the melamine-based methylene donors n <Me) drei oder mehr beträgt, wobei n(Me) für diese zumindest zwei melaminbasierten Methylendonoren voneinander verschieden ist, where the mass-average number of methyl group residues of the melamine-based methylene donors in the melamine-based methylene donor composition<n(Me)> is in the range of 3.5 to 5.2, and b) mixing the melamine-based methylene donor composition with one or more diene rubbers and other components of the vulcanizable rubber mixture.

9. Vulcanizate, producible or produced by vulcanization of a vulcanizable rubber mixture according to one of claims 1 to 7.

10. A rubber product comprising a vulcanizate according to claim 9.

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