Method for introducing thin elements with improved electrical conductivity into an extrudate

Abstract

The invention relates to a method for producing a strand-shaped vulcanisable rubber product (24) comprising a modification layer (26) with an average layer thickness of 30 µm or less, using an extrusion template (10), comprising the method steps of: i) extruding a material strand of at least one vulcanisable rubber mixture with an extruder, wherein a material gap is created in the material strand by the injector element (18); ii) injecting an injection composition into the material gap for contacting the material strand with the injection composition at the walls of the material gap, to obtain a modified material strand; and iii) closing the material gap in the modified material strand by joining the walls of the material gap contacted with the injection composition in a joining region (22), the injection composition having a dynamic viscosity ƞ of 50 Pa*s or less at 20°C, and the injection composition comprising: x) one or more diene rubbers, the injection composition comprising polyisoprene in a combined mass fraction of 5 phr or more, y) one or more electrically conductive fillers in a combined mass fraction of 30 phr or more, and z) one or more paraffinic plasticiser oils in a combined mass fraction of 500 phr or more.

Description

[0001] Process for introducing thin elements with improved electrical conductivity into an extrudate

[0002] Description

[0003] The invention relates to a process for producing a strand-shaped vulcanizable rubber product, a process based thereon for producing a vulcanized rubber product, and a vulcanized rubber product produced by this process.

[0004] A key component of modern pneumatic vehicle tires, which in many cases is significantly responsible for the performance characteristics of these products, is the tread. Today, treads usually consist of several different components, particularly various rubber materials, which can be obtained by vulcanization from vulcanizable rubber compounds. Such treads are regularly produced by coextrusion of various vulcanizable rubber compounds and, in terms of their structure, can usually be conveniently described by their cross-section, which, apart from any influences from the tread pattern, is usually uniform throughout the entire tread.

[0005] In cross-sectional view, most treads, especially those used on cars and trucks, comprise one or more rubber materials intended to come into contact with the road surface during later use, and whose properties are optimized for this purpose. This layer, which essentially acts as a top layer, is made from a vulcanizable rubber compound, sometimes referred to as a "cap compound," which often contains large amounts of non-electrically conductive fillers, such as precipitated silica. A base layer (often referred to as a "base") is usually located beneath the rubber material intended for road contact.In the majority of cases, this basis serves primarily to create sufficient adhesion between the cover layer intended for road contact and the other parts of the pneumatic vehicle tyre, so that a high bond strength between the tread and the other components of the pneumatic vehicle tyre can be ensured.

[0006] Those skilled in the art are aware that, for the vast majority of applications, a tread must, for technical and / or regulatory reasons, exhibit a certain degree of electrical conductivity throughout, which can prevent unwanted static charging. In many cases, however, the rubber material of the cover layer does not possess sufficient electrical conductivity to ensure this.

[0007] Therefore, the electrical conductivity of the entire tread in the prior art is usually achieved by the base mixture of the underlying base, which has increased electrical conductivity, particularly as a result of a high carbon black content. For this purpose, for example, a material strand is guided from the base to the upper side of the tread, thereby creating an electrically conductive connection between the surface of the tread and the base. The electrically conductive base mixture is usually formed up to the surface of the tread by a pre-template in the extruder. The corresponding structure is also referred to as a "carbon center beam" (CCB). Information on the technological background is disclosed, for example, in DE 4445758 B4, DE 69717958 T2, EP 1792720 A2, NL 2006420 C2 and US 2018170123 A1.However, the formation of a CCB from the vulcanizable rubber compound of the underlying base is often considered disadvantageous from a manufacturing perspective, for example, with regard to the number of extruder units required, the often complex flow guidance in the extruder head, and the material requirements. Furthermore, the "base" compound is usually not intended for road contact, so that the resulting partial coverage of the tread surface with "base" compound is sometimes also perceived as disadvantageous in terms of driving characteristics. Furthermore, some treads do not even have a suitable "base" compound with which to create a CCB, so the electrical connection between the underside of the tread and the surface must be formed using an additional extruder.

[0008] Against this background, there is a need in the field of technology to provide tread designs that have sufficient electrical conductivity while showing as little influence of the CCB on the driving characteristics as possible.

[0009] For this purpose, devices and methods have been developed that make it possible to create a particularly thin conductive region during tread production. This conductive region extends radially through the tread in the final vehicle tire and is advantageously sufficient to reliably prevent static charging. These new concepts are based on injecting an electrically conductive rubber compound into the tread during the molding of the vulcanizable rubber compounds by applying a thin layer to the side surface of the extruded strands.To form the side surface to be coated, the extruded tread can, for example, be cut in its longitudinal direction, as disclosed in DE 102007039100 A1, or only a part of a tread is directly extruded, which, after the corresponding coating, is combined with other parts to form the tread, as disclosed, for example, in DE 102007039101 A1. Further disclosures of this approach can be found, for example, in EP 2520421 B1 and EP 3253553 B1. Depending on the requirements of the technology used in each case, electrically conductive rubber mixtures or suitable precursors of such a conductive rubber mixture can be used as injection compositions as electrically conductive materials for the coating, in particular solutions or dispersions in evaporable solvents, so that coating from an advantageously flowable solution is possible.

[0010] The inventors have recognized that, in principle, those embodiments are preferred in which a very thin conductive web is formed using this method, i.e., when—depending on the viscosity of the conductive rubber mixture used—a thickness of less than 20 μm is set, for example. This not only minimizes the influence of the web on the driving characteristics, but also, in particular, enables reliable joining of the tread parts separated before coating, which, in the inventors' opinion, cannot always be sufficiently guaranteed with significantly thicker webs. At the same time, the inventors have recognized that corresponding thicknesses are sufficient to dissipate static electricity.

[0011] However, the reliable introduction of correspondingly thin CCBs is often difficult from a manufacturing perspective, especially with the preferred process involving the temporary separation of the material strand during extrusion. According to the inventors, this is primarily due to the injection compositions known in the prior art, which are often not sufficiently suitable for this task. In the specific process involving the introduction of the injection composition in the extrusion system, a material gap is temporarily formed in the extrusion template, into which the injection composition is injected.Many of the injection compositions known from the prior art, particularly those that comprise a highly volatile solvent, can lead to uncontrolled gas evolution upon contact with the warm, extruded rubber mixture. This is not only detrimental to health and / or the environment, but can also lead to defects and / or inclusions in the extruded strand. According to the inventors, many of the injection compositions known from the prior art that do not rely on a highly volatile solvent are also not satisfactorily suitable for forming particularly thin CCBs in this process because, for example, they have an unsuitable viscosity and / or unsuitable chemical compatibility with the vulcanizable rubber mixture of the extruded material strand.In addition, in the opinion of the inventors, numerous of the injection compositions known from the prior art result in a functional limitation of the extrusion rate, since the material strand must be extruded slowly enough to allow, for example, the evaporation of the solvent and / or the formation of a separate layer. In addition, in the opinion of the inventors, some of the injection compositions known from the prior art are not optimally suited to ensuring sufficient bond strength between the temporarily separated parts of the material strand after rejoining, which results in a vulcanized rubber product after vulcanization, which, despite the introduced CCB, ensures mechanical resilience that is also suitable for high-performance applications. This aspect is not taken into account in the injection compositions known from the prior art.

[0012] Injection compositions are sometimes also reinforced by the fact that the layers obtained with them after vulcanization have different mechanical properties, in particular a different stiffness, than the surrounding rubber materials, which can lead to additional stresses in the material and, as a result, additional material defects.

[0013] It was the primary object of the present invention to eliminate or at least reduce the disadvantages of the prior art.

[0014] In particular, it was an object of the present invention to provide a method for producing a strand-shaped vulcanizable rubber product, in particular a tread, with which particularly thin webs of conductive material can be reliably introduced into the strand-shaped vulcanizable rubber product.

[0015] It was a further object of the present invention that advantageous vulcanizable or vulcanized rubber products should be producible by the method to be specified, in particular treads which have a very thin CCB and consequently have excellent rolling properties.

[0016] Furthermore, it was an object of the present invention that the method to be specified should require less mechanical effort and / or have a lower material requirement compared to the prior art.

[0017] Furthermore, it was an object of the present invention that the method to be specified should be as time- and cost-efficient as possible and, in particular, should also be operable with increased extrusion speeds.

[0018] It was an additional object of the present invention that the vulcanizable or vulcanized rubber products that can be produced by the method to be specified should have an advantageous bond strength in the region of the web, wherein the occurrence of defects and solvent inclusions should desirably be avoided.

[0019] It was a supplementary object of the present invention that the method to be specified should be as advantageous as possible with regard to the resulting health and / or environmental impact.

[0020] It was a further object of the present invention to provide advantageous vulcanized rubber products which can be produced by the processes to be specified.

[0021] The inventors of the present invention have now found that the objects described above can surprisingly be achieved if a specific injection composition is used in a specific process using a specific extrusion template, as defined in the claims.

[0022] The above-mentioned objects are thus 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.

[0023] 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 one 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 vulcanized rubber products result from the features of preferred processes.

[0024] To the extent that both specific amounts or proportions of an element and preferred embodiments of the element are disclosed below for an element, for example, a mixture component of the injection composition, for example, for the diene rubber or the electrically conductive fillers, the specific amounts or proportions of the preferably configured elements are also disclosed in particular. Furthermore, it is disclosed that, with the corresponding specific total amounts or total proportions of the elements, at least some of the elements can be configured in a preferred manner and, in particular, that preferably configured elements can in turn be present in the specific amounts or proportions within the specific total amounts or total proportions.

[0025] The term phr (parts per hundred parts of rubber by weight) used in the present invention is the quantity commonly used in the rubber industry for mixture formulations, which specifies 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 molar mass is determined by means of gel permeation chromatography in accordance with DIN 55672-1: 2016-03 (GPC with tetrahydrofuran as eluent, polystyrene standard;

[0026] Size exclusion chromatography (SEC = size exclusion chromatography).

[0027] The invention relates to a process for producing a strand-shaped vulcanizable rubber product, comprising a

[0028] Modification layer with an average layer thickness of 30 pm or less, using an extrusion template, comprising: a) a template body, b) a penetrating the template body along an extrusion direction E and delimited by surrounding wall surfaces

[0029] Template recess, and c) an elongated injector element extending between the wall surfaces through the template recess, with an injection gap, comprising the method steps: i) extruding a material strand made of at least one vulcanizable rubber mixture with an extruder through the extrusion template along the extrusion direction E, wherein a material gap is created in the material strand by the injector element, ii) injecting an injection composition from the injection gap into the material gap to contact the material strand with the injection composition on the walls of the material gap, to obtain a modified material strand, and iii) closing the material gap in the modified material strand by joining the walls of the material gap contacted with the injection composition in a joining region spaced apart from the injector element along the extrusion direction E,wherein the injection composition has a dynamic viscosity q measured according to DIN 53211:1987-06 of 50 Pa*s or less at 20 °C, and wherein the injection composition comprises: x) one or more diene rubbers, wherein the injection composition comprises polyisoprene in a combined mass fraction of 5 phr or more, y) one or more electrically conductive fillers, in particular carbon black, in a combined mass fraction of 30 phr or more, and z) one or more paraffinic processing oils, in particular paraffinic mineral oils, in a combined mass fraction of 500 phr or more.

[0030] The process according to the invention serves to produce strand-shaped, vulcanizable rubber products, preferably tread components. However, the process according to the invention is not limited to treads, but is suitable for adding an electrically conductive modification layer to all thick-walled extrudates with a certain thickness, for example, more than 2 mm, through which electrostatic charge can be reliably dissipated. Accordingly, an example of a process according to the invention is one in which the strand-shaped, vulcanizable rubber product has an average thickness of 2 mm or more perpendicular to the extrusion direction E. A preferred process according to the invention is one in which the strand-shaped, vulcanizable rubber product is a tread blank or a partial layer of a tread blank.

[0031] The method according to the invention introduces a particularly thin CCB, which is referred to as a modification layer in the context of the present invention. According to the inventors' findings, this predetermined maximum thickness of the modification layer means that, in the case of an integrated formation of the modification layer in the extrusion system, as specified by the above method steps i) to iii), particularly high demands must be placed on the injection composition in order to achieve the objects described above. In the inventors' opinion, with regard to the properties of the extrudates thus producible, particularly in the case of treads, particularly thin modification layers are generally preferred, which is advantageously made possible by the injection composition used in the method according to the invention.Accordingly, a method according to the invention is preferred, wherein the modification layer has an average layer thickness of 20 pm or less, preferably 15 pm or less, particularly preferably 10 pm or less, especially preferably 5 pm or less.

[0032] The extrusion template used according to the invention is suitable for use in the extrusion of rubber products. Extrusion templates are widely known to those skilled in the rubber processing industry. Extrusion templates are often divided by those skilled in the art into so-called preliminary and final templates, which express the position in the extrusion system at which they are used. Preliminary templates usually initially guide the rubber strands into closer spatial proximity, for which purpose they usually comprise several recesses, each of which serves to guide a rubber strand. In contrast, final templates usually have only one recess through which the individual rubber strands of the preliminary template are guided. For the extrusion template used according to the invention, the design as final templates is particularly expedient.According to the inventors' assessment, the thin modification layers to be produced according to the invention cannot in many cases be effectively transferred from the preliminary to the final template, since when introduced into the preliminary template, there is a risk that the fine structure produced will be deformed in the final template and / or that the corresponding modification layers in the individual material strands of the preliminary template will not fit together precisely, so that the conductive path in the final material strand is interrupted. For essentially all embodiments, a method according to the invention is preferred, wherein the extrusion template is a final template. In other words, for essentially all embodiments, a method according to the invention is preferred, wherein the extrusion template comprises exactly one template recess.

[0033] Analogous to extrusion templates known from the prior art, the extrusion template according to the invention initially comprises a template body. This term refers to the workpiece in which the various template recesses of the extrusion template are arranged. An example of a method according to the invention is one in which the template body is made of metal, preferably steel.

[0034] The template recesses in the template body serve to guide the extruded material through the extrusion template. In the context of the present invention, the direction in which the material to be extruded is guided through the extrusion template is referred to as the extrusion direction E. The shape of the template recess correlates with the desired cross-sectional shape of the extruded material strand. For the extrusion of treads, trapezoidal cross-sections have proven particularly suitable. Accordingly, a method according to the invention is preferred, wherein the template recess has a polygonal cross-section, preferably a quadrangular cross-section, particularly preferably a trapezoidal cross-section, in the plane perpendicular to the extrusion direction E.

[0035] Since the stencil body will have a non-negligible thickness, a recess penetrating the stencil body is necessarily bounded by surrounding wall surfaces. A circular stencil recess, for example, would be bounded by only one surrounding wall surface, whereas a rectangular stencil recess would comprise four distinguishable individual wall surfaces as the surrounding wall. In this respect, a method according to the invention is preferred, wherein the stencil recess is bounded by four or more, preferably exactly four, wall surfaces.

[0036] With regard to the components a) and b) described above, the extrusion template to be used according to the invention corresponds in principle to the extrusion templates known from the prior art. However, the extrusion template to be used according to the invention now also comprises an injector element with an injection gap, which extends between the wall surfaces of the template recess, so that it runs through the template recess.

[0037] The injector element has two main tasks in the method according to the invention. The injector element running through the template recess serves, on the one hand, to split the material strand extruded through the template recess by blocking part of the template recess. This creates a material gap behind the injector element, which acts as a flow obstacle, in the direction of extrusion. The injector element then serves to inject an injection composition into the material gap through an injection gap pointing in the direction of this material gap. This allows the extruded material strand to come into contact with the injection composition on the walls exposed by the splitting. The person skilled in the art will understand that this is a method according to the invention, wherein the injector element is designed to be able to inject an injection composition through the injection gap.wherein the injection gap is arranged so that it points in the direction of the material gap.

[0038] To implement the desired injection function, it is expedient to connect the injector element to a supply of injection compositions, for example, via lines. Accordingly, a method according to the invention is relevant for most cases, wherein the injector element is fluidly connected or connectable to a fluid supply device. The fluid supply device preferably comprises a pump device and a reservoir for storing the injection composition.

[0039] With regard to the arrangement of the injector element, in the case of template recesses with a polygonal cross-section, it is particularly preferred for the injector element to extend between opposing parts of the wall. Thus, a method according to the invention is preferred, wherein the injector element extends from one wall surface of the template recess to an opposite wall surface.

[0040] Those skilled in the art will understand that the template recess is divided into two parts by the injector element. In view of the properties of the strand-shaped rubber products that can be produced therewith, the inventors believe it is particularly advantageous to position the injector element as centrally as possible so that the modification layer introduced by the injector element also runs as centrally as possible in the strand-shaped rubber product. A preferred method according to the invention is one in which the injector element is positioned in the template recess such that, when viewed from above along the extrusion direction E, the template recess is divided by the injector element into two partial areas, the areas of which differ by 50% or less, preferably by 30% or less, particularly preferably by 10% or less, particularly preferably by 5% or less.

[0041] The desired splitting of the extruded material strand can, in principle, be achieved with any shape of obstacle that divides the template recess into two or more regions, so that, for example, injector elements with a round cross-section are also suitable, which then have a cylindrical shape. However, in the inventors' opinion, it is particularly advantageous if a controlled splitting of the material strand is promoted by providing a wedge shape or a similar taper, which promotes the separation along the flanks of the wedge, which in particular improves the flow behavior of the extruded material strand. Accordingly, an example of a method according to the invention is one in which the injector element is at least partially cylindrical, preferably over the entire length of the part of the injector element running in the template recess.However, a method according to the invention is preferred, wherein the injector element tapers on the side facing away from the injection gap opposite to the extrusion direction E, preferably in a drop-shaped manner.

[0042] At least in theory, it is possible to arrange the injector element obliquely in the extrusion template relative to the extrusion direction, so that the extruded material strand contacts the injector element earlier in one section and later in another section relative to the extrusion direction. Even if such a configuration is conceivable, the inventors believe that this does not provide advantages that would justify the additional design effort. Rather, the inventors believe that particularly good results can be achieved if the injector element is positioned essentially orthogonally to the extrusion direction, so that the extruded material strand is split by the injector element essentially orthogonally to the extrusion direction E.A method according to the invention is therefore preferred, wherein the longitudinal axis of the injector element encloses an angle in the range of 70° to 110°, preferably an angle in the range of 80° to 100°, particularly preferably in the range of 85° to 95°, most particularly preferably of substantially 90°, with the extrusion direction E.

[0043] Depending on the subsequent arrangement of the extrusion template and thus depending on the gravity acting during use, it is in principle not necessary to execute the injection gap over the entire length of the injector element, since depending on the volume flow of the injection composition it is possible that the injection composition emerging through a shorter injection gap fills the material gap sufficiently to contact the extruded material strand over the entire height at the walls, which is particularly preferred.In view of this preferred embodiment, however, the inventors consider it particularly advantageous if the injection gap also extends substantially over the entire length over which the coating is to be applied, since this enables a significantly more controlled and precise application of the injection composition into the material gap and onto its walls, which is particularly advantageous for the particularly thin CCBs desired by the invention. Accordingly, a method according to the invention is preferred, wherein the injection gap extends over the entire length of the part of the injector element running in the template recess.With regard to the process control, a process according to the invention is also preferred, wherein the injection of the injection composition in process step iii) is carried out in such a way that the walls of the material gap are contacted with the injection composition essentially completely, in particular over the entire height of the material gap.

[0044] Within the scope of the present invention, the mode of operation is mostly described with reference to the presence of precisely one injector element, wherein an extrusion template to be used according to the invention, which comprises precisely one injector element, is correspondingly suitable for the production of strand-shaped rubber products that comprise precisely one modification layer as a CCB. In this respect, however, the inventors propose that the extrusion templates to be used according to the invention can also be designed such that they can be used to form several thin CCBs in the extruded material. Accordingly, a method according to the invention is preferred for certain applications, wherein the extrusion template comprises two or more, preferably three or more, preferably identical, injector elements.

[0045] The person skilled in the art understands that in the method according to the invention, after the material strand has been separated and the walls of the material gap have subsequently been brought into contact with the injection composition, the previously separated parts of the material strand will be re-joined and joined, thereby closing the material gap, as defined in method step iii). This joining takes place in a joining region. Such a joining region can, for example, be provided by a separate, downstream template structure. For essentially all embodiments, however, it is preferred if the length of the template recess in the extrusion direction E is selected to be sufficiently large that the joining of the material gap can still take place within the extrusion template when the extruded material extends further along the walls of the template recess in the extrusion direction behind the injection element.Such a joining region of the template recess can also comprise a section that has an at least slightly reduced overall cross-section than the template recess at the level of the injector element, so that the two split parts of the material strand are pressed together by a corresponding taper. Accordingly, a method according to the invention is preferred, wherein the extrusion template comprises a joining region spaced apart from the injector element along the extrusion direction E, wherein the extrusion template is configured to close the material gap created in the material strand in the joining region by joining the walls of the material gap contacted with the vulcanizable injection composition.A method according to the invention is preferred, wherein the joining region is formed by a joining section of the template recess in which the template recess tapers along the extrusion direction E. Additionally or alternatively, a method according to the invention is preferred, wherein the joining region extends along the extrusion direction E over 50% or more, preferably over 70% or more, of the length of the template recess.

[0046] A major advantage of the process according to the invention is that it is, in principle, very flexible with regard to the vulcanizable rubber mixtures used, i.e., with regard to the material of the extruded strand. In this respect, it can be advantageously stated that the process according to the invention can be applied to essentially all typical vulcanizable rubber mixtures, in particular those used in the treads of vehicle tires, so that at this point, reference can be made in particular to the prior art known to those skilled in the art.By way of example, a process according to the invention is provided, wherein the vulcanizable rubber mixture comprises one or more diene rubbers, and / or wherein the vulcanizable rubber mixture comprises one or more non-electrically conductive fillers, preferably precipitated silicon dioxide, and / or wherein the vulcanizable rubber mixture comprises one or more additives selected from the group consisting of plasticizers, age inhibitors and coupling agents.

[0047] The joint extrusion of treads with cap / base construction, for example, is a process according to the invention, wherein the vulcanizable rubber mixtures have a different chemical composition.

[0048] Despite the broad applicability of the process according to the invention to essentially all typical vulcanizable rubber mixtures, the inventors believe that particularly advantageous processes are achieved with certain vulcanizable rubber mixtures.

[0049] Vulcanizable rubber mixtures with a low carbon black content particularly benefit from the introduction of the modification layer, which ensures electrical conductivity after vulcanization. Accordingly, a process according to the invention is preferred, wherein at least one of the vulcanizable rubber mixtures comprises less than 10 phr, preferably less than 5 phr, particularly preferably less than 3 phr, in particular less than 0.1 phr, of carbon black.

[0050] Furthermore, it is particularly advantageous to match the non-conductive components of one or more vulcanizable rubber compounds as closely as possible to the injection composition. This advantageously allows modification layers to be obtained whose physicochemical and, in particular, mechanical properties after vulcanization match those of the surrounding rubber materials as closely as possible.

[0051] Against this background, a process according to the invention is preferred, wherein at least one, preferably all, of the vulcanizable rubber mixtures comprise at least one, preferably all, diene rubbers of the injection composition, wherein the mass fraction in phr of the diene rubber(s) preferably differs between the vulcanizable rubber mixture and the injection composition by 20% or less, preferably by 10% or less, particularly preferably by 5% or less. A process according to the invention is particularly preferred, wherein at least one, preferably all, of the vulcanizable rubber mixtures comprise at least one polyisoprene, preferably in a combined mass fraction of 5 phr or more, wherein preferred mass fractions arise from the following disclosures regarding the injection composition.

[0052] Additionally or alternatively, a process according to the invention is also preferred, wherein at least one, preferably all of the vulcanizable rubber mixtures comprise one or more paraffinic plasticizer oils, preferably paraffinic mineral oils of the injection composition, as plasticizer, preferably in a combined mass fraction of 50% or less, particularly preferably of 30% or less.

[0053] In the process according to the invention, a specific injection composition is used, comprising: x) one or more diene rubbers, wherein the injection composition comprises polyisoprene in a combined mass fraction of 5 phr or more, y) one or more electrically conductive fillers, in particular carbon black, in a combined mass fraction of 30 phr or more, and z) one or more paraffinic process oils in a combined mass fraction of 500 phr or more.

[0054] In accordance with standard practice, the above-defined components of the injection composition are each used as "one or more." The term "one or more" refers, as is customary in the industry, to the chemical nature of the respective compounds, not to their quantity. For example, the vulcanizable rubber compound, as a diene rubber, may comprise exclusively polyisoprene, which would mean that the vulcanizable rubber compound comprises a plurality of the respective molecules.

[0055] The injection composition to be used according to the invention can be produced by processes known to those skilled in the art, as described, for example, in EP 3 385 090 A1. The solid constituents of the injection composition, for example carbon black and rubber, are dissolved or dispersed in the liquid constituents, ie in particular the paraffinic plasticizer oils, by stirring and / or shaking and / or vibrating, which can also be done, for example, using pre-solutions or pre-dispersions. The injection composition to be used according to the invention can be produced in a particularly simple and efficient manner in a sealable mixing container with mixing movement, which is moved, for example, in the plane with a power in the range of 300 to 1000 W per kilogram of injection composition over a period of time in the range of 1 to 15 minutes, preferably in the range of 1 to 10 minutes.

[0056] Those skilled in the art will understand that the injection composition will usually be a dispersion. Thus, in most cases, the process according to the invention involves the injection composition being a dispersion. A dispersion is a heterogeneous mixture of liquid and solid substances (disperse phase) that are finely distributed in a continuous substance (dispersion medium), in particular the paraffinic plasticizer oil.

[0057] The inventors have recognized that for the efficient formation of the desired thin modification layers, the viscosity of the injection composition must not be chosen too high, with particularly good results being achieved with low viscosities. A preferred method according to the invention is one in which the injection composition has a dynamic viscosity q of 30 Pa*s or less, preferably 20 Pa*s or less, particularly preferably 15 Pa*s or less, at 20°C. The viscosity is influenced in particular by the content of paraffinic process oils.

[0058] Many of the injection compositions known from the prior art rely on the use of a volatile solvent as a carrier fluid. This allows the components of the rubber composition contained in the injection composition, dispersed in the solvent, to be applied to the walls of the material gap, where they remain as a coating after the solvent has evaporated. However, the inventors of the present invention have found that, for both process-related and health reasons, as well as with a view to the quality of the resulting thin modification layers, it is expedient to avoid the use of volatile solvents wherever possible. Instead, the inventors have recognized that the carrier fluid of the injection composition must be formed by a high-boiling component, namely at least one paraffinic plasticizer oil, and in particular a paraffinic mineral oil.Paraffinic process oils have a mass fraction of paraffinic, i.e., saturated and correspondingly aliphatic, hydrocarbons of more than 60%, preferably more than 80%, particularly preferably more than 90%. Paraffinic process oils are generally considered harmless to health.

[0059] The corresponding injection composition is (at least not primarily) converted into a coating by evaporation of the solvent, but the paraffinic plasticizer oil can be absorbed to a large extent into the underlying vulcanizable rubber mixture, so that a coating, i.e. the modification layer, remains, which, as a result of contact with the injection composition, receives a superficial layer which, in particular, has an increased carbon black content and, as a result, has advantageous electrical conductivity. Through this specific choice of carrier fluid, which is geared to a particularly high chemical compatibility of the injection composition with the rubber mixture, particularly thin, high-quality modification layers can be obtained, whereby the use of paraffinic plasticizer oils as a carrier fluid is made possible by the local orA superficially increased plasticizer concentration also promotes the joining of the divided parts of the extruded material strand. In addition, the infiltration of the paraffinic plasticizer oil creates a surface gradient of the plasticizer concentration in the vulcanized rubber mixture, which contributes to a particularly uniform progression of the mechanical properties of the vulcanizate in the region of the vulcanized modification layer. Preference is given to a process according to the invention wherein the injection composition comprises the one or more paraffinic plasticizer oils in a combined mass fraction of 550 phr or more, preferably 650 phr or more. A process according to the invention is particularly preferred wherein the injection composition comprises the one or more paraffinic plasticizer oils in a combined mass fraction in the range from 500 to 800 phr, preferably in the range from 550 to 750 phr.

[0060] Additionally or alternatively, a process according to the invention is also preferred, wherein the one or more paraffinic plasticizer oils are selected from the group consisting of plasticizer oils having a boiling point of 150 °C or more, preferably of 160 °C or more.

[0061] Very preferred is a process according to the invention, wherein the one or more paraffinic plasticizer oils are selected from the group consisting of paraffinic mineral oils, in particular paraffinic plasticizer oils.

[0062] The viscosity can advantageously also be adjusted through the additional use of liquid diene compounds, which can be linked during vulcanization and thereby contribute to advantageous crosslinking of the modification layer. Accordingly, a process according to the invention is preferred, wherein the injection composition comprises at least one liquid diene polymer, preferably in a combined mass fraction in the range from 40 to 90 phr, preferably in the range from 55 to 80 phr, wherein the liquid diene polymer preferably has a weight-average molar mass Mw, measured by GPC, in the range from 15,000 to 50,000 g / mol. A process according to the invention is particularly preferred, wherein the injection composition comprises at least one liquid polybutadiene as liquid diene polymer, preferably in a combined mass fraction in the range from 1 to 25 phr, preferably in the range from 10 to 20 phr.Additionally or alternatively, a method according to the invention is also particularly preferred, wherein the injection composition comprises at least one liquid polyisoprene as liquid diene polymer.

[0063] According to the invention, the injection composition comprises polyisoprene as one of the diene rubbers. The polyisoprene can be natural and / or synthetic polyisoprene, with both cis-1,4-polyisoprene and 3,4-polyisoprene being possible. However, the use of cis-1,4-polyisoprenes with a cis-1,4 content of > 90 wt. % is preferred. On the one hand, such a polyisoprene can be obtained by stereospecific polymerization in solution with Ziegler-Natta catalysts or using finely divided lithium alkyls. On the other hand, natural rubber (NR) is such a cis-1,4 polyisoprene; the cis-1,4 content in natural rubber is greater than 99 wt. %.Preference is given to a process according to the invention, wherein the injection composition comprises polyisoprene in a combined mass fraction in the range from 5 to 50 phr, particularly preferably in the range from 10 to 25 phr, wherein the polyisoprene preferably has a weight-average molecular mass Mw, measured by GPC, in the range from 200,000 to 1,000,000 g / mol, particularly preferably in the range from 300,000 to 600,000 g / mol.

[0064] The electrically conductive fillers can in principle be metallic or carbon-based materials, which can also be used in a mixture. Preferred carbon-based materials include, for example, carbon blacks, graphenes, carbon nanofibers, or carbon nanotubes. Preference is given to a process according to the invention in which the one or more electrically conductive fillers are selected from the group consisting of carbon blacks, for example those of type N339. Preference is given to a process according to the invention in which the injection composition comprises the one or more electrically conductive fillers in a combined mass fraction in the range of 60 to 90 phr, and / or in which the injection composition comprises the one or more electrically conductive fillers in a combined mass fraction of 40 phr or more, preferably 50 phr or more.

[0065] Particularly preferred is a process according to the invention, wherein the injection composition comprises at least two carbon blacks, wherein the first carbon black has a BET surface area in the range of 800 to 1200 m 2 / g and a DBP number in the range of 350 to 450 cm 3 / 100 g and the second carbon black has a BET surface area in the range of 70 to 90 m 2 / g and a DBP number in the range of 90 to 130 cm 3 / 100 g.

[0066] For essentially all applications that envisage downstream vulcanization of the strand-like vulcanizable rubber product, it is expedient to design the injection composition in such a way that it is itself vulcanizable, at least after incorporating a portion of the paraffinic plasticizer oil. In other words, this is a process according to the invention, wherein the injection composition is a vulcanizable injection composition. Preference is given to a process according to the invention, wherein the injection composition comprises a sulfur-based vulcanization system, preferably comprising at least one vulcanization accelerator, particularly preferably in a combined mass fraction of 2.5 phr or more, preferably 5 phr or more. Such a sulfur-based vulcanization system is, for example, a system comprising sulfur or sulfur donor, vulcanization accelerator and zinc oxide and optionallyVulcanization retarders, whereby these components are known to the person skilled in the art on the basis of his specialist knowledge, so that reference can be made to the state of the art at this point.

[0067] The invention further relates to a process for producing a vulcanized rubber product, comprising the process steps of the process according to the invention for producing a strand-shaped vulcanizable rubber product, as well as the step: iv) vulcanizing the strand-shaped vulcanizable rubber product or a rubber blank comprising the strand-shaped vulcanizable rubber product with vulcanization of the vulcanizable rubber mixtures to obtain a vulcanized rubber product.

[0068] Here, the strand-shaped vulcanizable rubber product is vulcanized, for example, according to the process customary in the tire industry, for example by sulfur-based crosslinking, for example at a temperature in the range of 130 to 200 °C, preferably in the range of 150 to 180 °C.

[0069] Finally, the invention also relates to a vulcanized rubber product produced or producible by the process according to the invention for producing a vulcanized rubber product. A vulcanized rubber product according to the invention is particularly preferred, wherein the vulcanized rubber product is a vehicle tire, preferably a pneumatic vehicle tire.

[0070] The invention and preferred embodiments of the invention are explained and described in more detail below with reference to the accompanying figures. Figure 1 shows a schematic representation of an extrusion template suitable for the method according to the invention in a first preferred embodiment;

[0071] Fig. 2 is an enlarged view of the area around the injector element of the extrusion template according to Fig. 1;

[0072] Fig. 3 is a schematic cross-sectional view through an extrusion template suitable for the method according to the invention in a second preferred embodiment; and

[0073] Fig. 4 is a schematic cross-sectional view of a vulcanizable rubber product that can be produced by the process according to the invention.

[0074] Fig. 1 shows an extrusion template 10 suitable for the method according to the invention, in a preferred embodiment. The extrusion direction E is indicated in Fig. 1.

[0075] The extrusion template 10 comprises a template body 12 and, in this template body 12, a template recess 16 enclosed by wall surfaces 14. Between the wall surfaces 14, an injector element 18 extends through the template recess 16 and comprises an injection gap 20.

[0076] In the example shown in Fig. 2, the extrusion template 10 is designed as a pre-template and has a steel template body 12 containing a template recess 16 with a trapezoidal cross-section. The injector element 18 extends through the template recess 16 between the wall surfaces 14 and is positioned precisely centrally in the example shown.

[0077] At the end of the injector element 18 located outside the extrusion template 10, a bore is indicated, through which the injector element 18 can be connected to a reservoir for the injection composition via fluid lines (not shown). The cylindrical injector element 18 is positioned substantially orthogonally on the wall surfaces 14, with the injection gap 20 extending substantially over the entire height of the template recess 16.

[0078] Fig. 2 shows an enlarged section of the extrusion template 10 according to Fig. 1 , wherein in particular the details in the area of ​​the injector element 18 are shown enlarged.

[0079] Fig. 3 shows a schematic cross-sectional view through an alternative extrusion template 10 suitable for the method according to the invention. In the embodiment shown in Fig. 3, it can be seen that the length of the template recess 16 in the extrusion direction E was chosen to be large enough that the material gap behind the injector element can be joined within the extrusion template (10) when the extruded material extends further along the walls 14 of the template recess 16 in the extrusion direction E behind the injection element 18. In addition, Fig. 3 shows the fluid line inside the injection element 18, which can be supplied with injection composition via a supply bore in the lower part of the template body 12.

[0080] Fig. 4 now shows a highly simplified schematic cross-sectional representation of a strand-shaped vulcanizable rubber product 24, which can be obtained using the process according to the invention and in which the central modification layer 26 is indicated, which in the example shown has a substantially constant width of approximately 8 μm. Such a strand-shaped vulcanizable rubber product 24 can be converted into a vulcanized rubber product by vulcanization, in which the then vulcanized modification layer 26 ensures sufficient electrical conductivity. The schematically illustrated vulcanizable rubber product 24 is a tread blank with a so-called "cap" and "base" construction.

[0081] The strand-shaped vulcanizable rubber product 24 of Fig. 1 can be produced, for example, using the extrusion template 10 of Fig. 1, wherein a material strand made of the vulcanizable rubber mixtures of the "cap" and the "base" is extruded through the extrusion template 10 with an extruder. In this process, a material gap is created in the material strand by the injector element 18, into which an injection composition is injected through the injection gap 20 in order to contact the walls of the material gap with the injection composition over their entire height. The material gap thus formed is closed in the joining region 22 behind the injector element 18 in the extrusion direction in order to obtain the strand-shaped vulcanizable rubber product 24 at the exit of the final template.

[0082] For example, a particularly preferred dispersion according to Table 1 can be used as the injection composition, the viscosity of which at 20 °C is 10 Pa*s.

[0083] Table 1 - Composition of the injection composition, all data in phr. a ) cis-polyisoprene, Mw = 300,000 g / mol b ) liquid polyisoprene, Mw = 28000 g / mol c ) liquid polybutadiene, trade name PBT 030, Zeon d ) paraffinic processing oil, trade name Catenex T 121 , Shell e> carbon black N339, BET surface area according to ASTM D 6556: 88 m 2 / g, DBP number according to ASTM D 2414: 99 ml / 100 g, electrical conductivity: medium electrically conductive carbon black, trade name Printex XE2-B, Orion Engineered Carbons, BET surface area according to ASTM D 6556: 1000 m 2 / g, DBP number according to ASTM D 2414: 420 ml / 100 g, electrical conductivity: high g ) Tetrabenzylthiuram disulfide (TBzTD) h ) N-Cyclohexyl-2-benzothiazolesufenamide (CBS) Reference Symbol List

[0084] 10 Extrusion template

[0085] 12 stencil bodies

[0086] 14 Wall surfaces 16 Template recess

[0087] 18 Injector element

[0088] 20 Injection gap

[0089] 22 Joining area

[0090] 24 Vulcanizable rubber product 26 Modification layer

[0091] E Extrusion direction

Claims

Claims 1. A method for producing a strand-shaped vulcanizable rubber product (24) comprising a modification layer (26) with an average layer thickness of 30 μm or less, using an extrusion template (10) comprising: a) a template body (12), b) a template recess (16) penetrating the template body (12) along an extrusion direction E and delimited by circumferential wall surfaces (14), and c) an elongate injector element (18) extending between the wall surfaces (14) through the template recess (16), having an injection gap (20), comprising the method steps: i) extruding a material strand of at least one vulcanizable rubber mixture with an extruder through the extrusion template (10) along the extrusion direction E, wherein a material gap is created in the material strand by the injector element (18),ii) injecting an injection composition from the injection gap (20) into the material gap to contact the material strand with the injection composition on the walls of the material gap to obtain a modified material strand, and iii) closing the material gap in the modified material strand by joining the walls of the material gap contacted with the injection composition in a joining region (22) spaced apart from the injector element along the extrusion direction E, wherein the injection composition has a dynamic viscosity q measured according to DIN 53211:1987-06 of 50 Pa*s or less at 20 °C, and wherein the injection composition comprises: x) one or more diene rubbers, wherein the injection composition comprises polyisoprene in a combined mass fraction of 5 phr or more, y) one or more electrically conductive fillers in a combined mass fraction of 30 phr or more, and z) one or more paraffinic process oils in a combined mass fraction of 500 phr or more.

2. The method according to claim 1, wherein the modification layer has an average layer thickness of 20 pm or less.

3. The method according to claim 1 or 2, wherein the injection of the injection composition in method step iii) is carried out such that the walls of the material gap are substantially completely contacted with the injection composition.

4. A process according to any one of claims 1 to 3, wherein the injection composition has a dynamic viscosity q of 30 Pa*s or less at 20°C.

5. A method according to any one of claims 1 to 4, wherein the injection composition comprises polyisoprene in a combined mass fraction in the range of 5 to 50 phr.

6. The method according to any one of claims 1 to 5, wherein the injection composition comprises at least one liquid diene polymer, wherein the liquid diene polymer has a weight-average molecular weight Mw, measured by GPC, in the range of 15,000 to 50,000 g / mol.

7. The method according to any one of claims 1 to 6, wherein the one or more paraffinic processing oils are selected from the group consisting of paraffinic mineral oils.

8. Method according to one of claims 1 to 7, wherein the extrusion template (10) is a final template.

9. A method for producing a vulcanized rubber product, comprising the method steps of the method for producing a strand-shaped vulcanizable rubber product (24) according to one of claims 1 to 8, and the step: vi) vulcanizing the strand-shaped vulcanizable rubber product (24) or a rubber blank comprising the strand-shaped vulcanizable rubber product (24) with vulcanization of the vulcanizable rubber mixtures to obtain a vulcanized rubber product.

10. A vulcanized rubber product produced or producible by the process according to claim 9.

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