WO2024120586A1

WO2024120586A1 - Method for introducing thin elements with improved electrical conductivity into an extrudate

Info

Publication number: WO2024120586A1
Application number: PCT/DE2023/200230
Authority: WO
Inventors: Christian Kunze; Sven Kastens; Peter Wichmann; Oliver Schramm
Original assignee: Continental Reifen Deutschland Gmbh
Priority date: 2022-12-05
Filing date: 2023-11-22
Publication date: 2024-06-13
Also published as: DE102022213081A1

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

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

Description

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.

A key component of modern pneumatic vehicle tires, which in many cases is largely responsible for the performance characteristics of these products, is the tread. Nowadays, treads usually consist of several different components, in particular different rubber materials, which can be obtained from vulcanizable rubber mixtures by vulcanization. Corresponding treads are regularly produced by so-called coextrusion of various vulcanizable rubber mixtures and their structure can usually be conveniently described by their cross-section, which, apart from any influences of the tread pattern, usually runs evenly through the entire tread strip.

In cross-sectional view, most treads, especially in the car and truck sector, include one or more rubber materials that are intended to come into contact with the road surface during later use and whose properties are optimized for this purpose. This layer, which acts as a kind of top layer, is made from a vulcanizable rubber mixture, sometimes referred to as a "cap mixture", which often contains large amounts of non-electrically conductive fillers, such as precipitated silicon dioxide. There is usually a base (often referred to as a "base") beneath the rubber material intended for contact with the road. In the majority of cases, this base serves primarily to create sufficient adhesion between the top layer intended for contact with the road and the other parts of the pneumatic vehicle tire, so that a high bond strength can be ensured between the tread and the other components of the pneumatic vehicle tire.

The person skilled in the art is aware that for the majority of applications, a tread must, for technical and/or regulatory reasons, have a certain electrical conductivity as a whole, which can prevent undesirable static charging. In many cases, however, the rubber material of the cover layer does not have sufficient electrical conductivity to ensure this.

Therefore, in the prior art, the electrical conductivity of the entire tread is usually achieved by the base mixture of the underlying base, which has an increased electrical conductivity, in particular as a result of a high carbon black content. For this purpose, for example, a strand of material from the base is guided to the top of the tread, which thereby creates an electrically conductive connection between the surface of the tread and the base. The electrically conductive base mixture is usually formed 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 mixture of the underlying base is often seen as disadvantageous from a manufacturing point of view, for example in terms of the number of extruder units required, the often complex flow guidance in the extruder head and the material requirements. In addition, the "base" mixture is usually not intended for contact with the road, so that the resulting partial coverage of the tread surface with "base" mixture is sometimes also seen as disadvantageous in terms of driving characteristics. In addition, some treads do not have a suitable "base" mixture with which a CCB could be realized, so that the electrical connection between the underside of the tread and the surface has to be formed with an additional extruder.

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.

For this purpose, devices and methods have been developed with which it is possible to create a particularly thin conductive area during the production of the treads, which extends radially through the tread in the subsequent vehicle tire and which is advantageously sufficient to reliably prevent static charging. These new concepts are based on the fact that during the molding of the vulcanizable rubber mixtures, an electrically conductive rubber mixture is introduced into the tread as an injection composition by applying it in 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 extruded directly, which is combined with other parts to form the tread after the corresponding coating, as is 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.

The inventors have recognized that in principle those designs 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 pm is set, for example. This not only minimizes the influence of the web on the driving properties, but also enables reliable joining of the tread parts separated before coating, which, in the opinion of the inventors, 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.

However, the reliable introduction of correspondingly thin CCBs is difficult in many cases from a manufacturing point of view, especially in the preferred process with intermediate separation of the material strand during extrusion. In the opinion of the inventors, the injection compositions known in the prior art are particularly responsible for this. In many cases, these are not sufficiently suitable for the task. In the specific process control involving 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. With many of the injection compositions known from the prior art, in particular those which comprise a highly volatile solvent, uncontrolled gas evolution can occur on contact with the warm, extruded rubber mixture, which is not only disadvantageous from the point of view of health and/or environmental pollution, but can also lead to defects and/or inclusions in the extruded strand. In the opinion of the inventors, many of the injection compositions known from the prior art which 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 an unsuitable chemical compatibility with the vulcanizable rubber mixture of the extruded material strand. In addition, in the opinion of the inventors, many of the injection compositions known from the prior art result in a functional limitation of the extrusion speed, 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 ensure sufficient bond strength between the temporarily separated parts of the material strand after they have been brought together, which results in a vulcanized rubber product after vulcanization, which, despite the CCB introduced, ensures mechanical resilience that is also suitable for This aspect is taken into account in the state-of-the-art

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

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

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 made of conductive material can be reliably introduced into the strand-shaped vulcanizable rubber product.

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

In addition, 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.

Furthermore, it was an object of the present invention that the method to be specified can be carried out as time- and cost-efficiently as possible and, in particular, should be operable at increased extrusion speeds.

It was an additional object of the present invention that the vulcanizable or vulcanized rubber products that can be produced using 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.

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.

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.

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.

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.

Such embodiments, which are referred to below as preferred, are combined in particularly preferred embodiments with features of other embodiments referred to as preferred. Combinations of two or more of the embodiments referred to below as particularly preferred. Also preferred are embodiments in which a feature of an embodiment referred to as preferred to any extent is combined with one or more further features of other embodiments referred to as preferred to any extent. Features of preferred vulcanized rubber products result from the features of preferred processes.

Insofar as both specific amounts or proportions of this 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. In addition, it is disclosed that with the corresponding specific total amounts or total proportions of the elements, at least some of the elements can be preferably configured and in particular also that preferably configured elements can in turn be present in the specific amounts or proportions within the specific total amounts or total proportions.

The phr (parts per hundred parts of rubber by weight) specification used in the context of the present invention is the quantity specification for mixture recipes commonly used in the rubber industry, by which the mass fractions of the components in the rubber mixture are specified in relation to 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;

Size exclusion chromatography (SEC).

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

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

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 plasticizer oils, in particular paraffinic mineral oils, in a combined mass fraction of 500 phr or more.

The method according to the invention is used to produce strand-shaped vulcanizable rubber products, preferably tread components. However, the method 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. An example of a method according to the invention is accordingly 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 method according to the invention is preferred, wherein the strand-shaped vulcanizable rubber product is a tread blank or a partial layer of a tread blank.

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. This predetermined maximum thickness According to the inventors' knowledge, the modification layer leads to the fact that in the case of an integrated formation of the modification layer in the extrusion system, as specified by the above process steps i) to iii), particularly high demands must be placed on the injection composition in order to achieve the tasks described above. In the inventors' opinion, with a view to the properties of the extrudates that can be produced in this way, particularly in the case of treads, particularly thin modification layers are preferred in principle, which is advantageously made possible by the injection composition used in the process according to the invention. Accordingly, a process 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, particularly preferably 5 pm or less.

The extrusion template to be used according to the invention is suitable for use in the extrusion of rubber products. Extrusion templates are well known to those skilled in the art in the rubber processing industry. Extrusion templates are often divided by those skilled in the art into so-called pre- and end templates, which express the position in the extrusion system at which they are used. Pre-templates usually initially guide the rubber strands used into closer spatial proximity, for which they usually comprise several recesses, each of which serves to guide a rubber strand. In contrast, end templates usually have only one recess through which the individual rubber strands of the pre-template are guided. For the extrusion template used according to the invention, the design as end templates is particularly expedient. According to the inventors, the extrusion templates according to the invention can be In many cases, the thin modification layers to be produced cannot be transferred sensibly from the preliminary to the final template, since when they are 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 exactly, so that the 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.

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.

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. In this respect, trapezoidal cross sections have proven to be particularly suitable for the extrusion of treads. Accordingly, a method according to the invention is preferred, wherein the template recess has a polygonal cross section in the plane perpendicular to the extrusion direction E, preferably has a square cross-section, particularly preferably a trapezoidal cross-section.

Since the stencil body will have a non-negligible thickness, a recess penetrating the stencil body is inevitably delimited by surrounding wall surfaces. A circular stencil recess would, for example, be delimited by just one surrounding wall surface, whereas a square stencil recess comprises four distinguishable individual wall surfaces as a surrounding wall. In this respect, a method according to the invention is preferred, wherein the stencil recess is delimited by four or more, preferably exactly four, wall surfaces.

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.

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 in the extrusion direction behind the injector element, which acts as a flow obstacle. The injector element now 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 be The walls exposed by the gaps are contacted with the injection composition. 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 or wherein the injection gap is arranged such that it points in the direction of the material gap.

To implement the desired injection function, it is expedient to connect the injector element to a supply of injection compositions, for example via lines. A method according to the invention is relevant for most cases, wherein the injector element is or can be connected in a fluid-conducting manner to a fluid supply device, wherein the fluid supply device preferably comprises a pump device and a reservoir for storing the injection composition.

With regard to the arrangement of the injector element, in the case of template recesses with a polygonal cross-section, it is particularly preferred that the injector element extends between opposite parts of the wall. A method according to the invention is therefore preferred, wherein the injector element extends from a wall surface of the template recess to an opposite wall surface.

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

The desired splitting of the extruded material strand can in principle be achieved with any form of obstacle that divides the template recess into two or more areas, so that, for example, injector elements with a round cross-section are also suitable, which then have a cylindrical shape. In the opinion of the inventors, however, 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. An example of a method according to the invention is accordingly one in which the injector element is at least partially cylindrical, preferably over the entire length of the part of the injector element that runs 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 against the extrusion direction E, preferably tapers in a drop shape.

At least in theory, it is possible to arrange the injector element at an angle in the extrusion template with respect to the direction of extrusion, so that the extruded strand of material contacts the injector element earlier in one section and later in another section with respect to the direction of extrusion. Even if such a design is conceivable, the inventors believe that this is not associated with any advantages. which would justify the additional design effort. Rather, in the opinion of the inventors, particularly good results can be achieved when 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 with the extrusion direction E 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°, very particularly preferably of essentially 90°.

Depending on the later arrangement of the extrusion template and thus depending on the gravity acting during use, it is in principle not necessary to make the injection gap over the entire length of the injector element, since depending on the volume flow of the injection composition, it is possible for the injection composition emerging through a shorter injection gap to fill the material gap sufficiently to contact the extruded material strand over the entire height on 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 essentially over the entire length on which the coating is to take place, 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 sought according to 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 Method according to the invention, wherein the injection of the injection composition in method step iii) is carried out such that the walls of the material gap are contacted substantially completely, in particular over the entire height of the material gap, with the injection composition.

In the context of the present invention, the mode of operation is mostly described in relation to the presence of exactly one injector element, whereby an extrusion template to be used according to the invention, which comprises exactly one injector element, is correspondingly suitable for producing strand-shaped rubber products which comprise exactly 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 in such a way that they can be used to form several thin CCBs in the extruded material. For certain applications, a method according to the invention is preferred, whereby the extrusion template comprises two or more, preferably three or more, preferably identical, injector elements.

The person skilled in the art will understand 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 brought together again and joined together, thereby closing the material gap, as defined in method step iii). This joining takes place in a joining area. Such a joining area can be provided, for example, 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 chosen to be so large that the joining of the material gap is still within the extrusion template if the extruded material extends further along the walls of the template recess behind the injection element in the extrusion direction. Such a joining region of the template recess can also comprise a section which 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 designed 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.

It can be seen as a great advantage of the method according to the invention that it is in principle very flexible with regard to the vulcanizable rubber mixtures used, ie with regard to the material of the extruded strand. In this respect, it can be advantageously stated that the method according to the invention can be used for essentially all typical vulcanizable rubber mixtures, in particular those which are used in the treads of vehicle tires, so that In this regard, reference can be made in particular to the prior art known to the person skilled in the art. An example in this regard is a process according to the invention, 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, anti-aging agents and coupling agents.

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.

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.

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 method 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.

In addition, it is particularly advantageous to match the one or more vulcanizable rubber mixtures as closely as possible to the injection composition with regard to the non-conductive components. This advantageously enables Modification layers are obtained whose physical-chemical and, in particular, mechanical properties after vulcanization match those of the surrounding rubber materials as closely as possible.

Against this background, a method 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 method 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.

Additionally or alternatively, a process according to the invention is also preferred, wherein at least one, preferably all of the vulcanizable rubber mixtures, comprises 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.

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 processing oils in a combined mass fraction of 500 phr or more.

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

The injection composition to be used according to the invention can be produced by methods known to those skilled in the art, as described, for example, in EP 3 385 090 A1. The solid components of the injection composition, for example carbon black and rubber, are dissolved or dispersed in the liquid components, i.e. in particular the paraffinic plasticizer oils, by stirring and/or shaking and/or rattling, 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.

The person skilled in the art will understand that the injection composition will usually be a dispersion. It is therefore in the In most cases, it is a process according to the invention, wherein the injection composition is a dispersion. A dispersion is a heterogeneous mixture of liquid and solid substances (disperse phase) which are finely distributed in a continuous substance (dispersion medium), in particular the paraffinic plasticizer oil.

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 to be too high, with particularly good results being achieved with low viscosities. A method according to the invention is preferred, wherein 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 plasticizer oils.

Many of the injection compositions known from the prior art rely on the use of a volatile solvent as a carrier liquid. This allows the components of the rubber composition contained in the injection composition, which are 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 it is advisable to avoid the use of volatile solvents as much as possible, both for process engineering and health reasons, as well as with a view to the quality of the thin modification layers obtained. Instead, the inventors have recognized that the carrier liquid of the injection composition can be replaced by a high-boiling component, namely at least one paraffinic Plasticizer oil, and in particular a paraffinic mineral oil, must be formed. Paraffinic plasticizer oils have a mass fraction of paraffinic, ie saturated and correspondingly aliphatic, hydrocarbons of more than 60%, preferably more than 80%, particularly preferably more than 90%. Paraffinic plasticizer oils are considered harmless to health in most cases.

The corresponding injection composition is (at least not primarily) converted into a coating by evaporating the solvent, but the paraffinic plasticizer oil can be absorbed in large parts 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, is obtained as a surface layer which in particular has an increased carbon black content and consequently has advantageous electrical conductivity. This specific choice of carrier liquid, which is geared towards a particularly high chemical compatibility of the injection composition with the rubber mixture, advantageously makes it possible to obtain particularly thin modification layers of high quality, whereby the use of paraffinic plasticizer oils as a carrier liquid also promotes the joining of the divided parts of the extruded material strand due to the locally or superficially increased plasticizer concentration. In addition, the infiltration of the paraffinic plasticizer oil results in 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 area of the vulcanized modification layer. A method according to the invention is preferred, wherein the Injection composition comprising one or more paraffinic plasticizer oils in a combined mass fraction of 550 phr or more, preferably 650 phr or more. Particularly preferred is a process according to the invention, wherein the injection composition comprises one or more paraffinic plasticizer oils in a combined mass fraction in the range of 500 to 800 phr, preferably in the range of 550 to 750 phr.

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 160 °C or more.

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.

The viscosity can advantageously also be adjusted by the additional use of liquid diene compounds, which can be linked during vulcanization and thereby contribute to an advantageous crosslinking of the modification layer. Accordingly, a method 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 method 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 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. Mass fraction in the range from 1 to 25 phr, preferably in the range from 10 to 20 phr. Additionally or alternatively, a process according to the invention is particularly preferred, wherein the injection composition comprises at least one liquid polyisoprene as liquid diene polymer.

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% by weight 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% by weight. 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 weight 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.

The electrically conductive fillers can in principle be metallic or carbon-based materials, which can also be used in a mixture. The preferred carbon-based materials include, for example, carbon blacks, graphenes, carbon nanofibers or carbon nanotubes. A method according to the invention is preferred in which one or more electrically conductive fillers are selected from the group consisting of carbon blacks, for example those of the N339 type. A method according to the invention is preferred, wherein 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 wherein 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.

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.

For essentially all applications that provide for subsequent vulcanization of the strand-shaped vulcanizable rubber product, it is expedient to design the injection composition in such a way that it is itself vulcanizable - at least after part of the paraffinic plasticizer oil has been absorbed. In other words, it is a process according to the invention, wherein the injection composition is a vulcanizable injection composition. A process according to the invention is preferred for this, 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 of sulfur or sulfur donor, vulcanization accelerator and zinc oxide and optionally vulcanization retarder, these components being 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.

The invention further relates to a method for producing a vulcanized rubber product, comprising the method steps of the method 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.

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.

Finally, the invention also relates to a vulcanized rubber product, produced or producible using the method 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.

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

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

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

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

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

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.

In the example shown in Fig. 2, the extrusion template 10 is designed as a pre-template and has a template body 12 made of steel in which there is 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 arranged exactly centrally in the example shown.

At the end of the injector element 18 lying outside the extrusion template 10, a hole 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 essentially orthogonal to the wall surfaces 14, with the injection gap 20 extending essentially over the entire height of the template recess 16.

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.

Fig. 3 shows a schematic cross-sectional view of 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 so large 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 hole in the lower part of the template body 12.

Fig. 4 now shows a highly simplified schematic cross-sectional representation of a strand-shaped vulcanizable rubber product 24, which can be obtained in 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 about 8 pm. Such a strand-shaped vulcanizable rubber product 24 can be vulcanized into a vulcanized rubber product 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.

The strand-shaped vulcanizable rubber product 24 of Fig. 1 can be produced, for example, with 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 the material strand, the injector element 18 creates a material gap 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 the entire height. The material gap thus formed is closed in the extrusion direction behind the injector element 18 in the joining area 22 in order to obtain the strand-shaped vulcanizable rubber product 24 at the exit of the final template.

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.

Table 1 - Composition of the injection composition, all data in phr.

a ⁾ cis-polyisoprene, Mw = 300000 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) List of reference symbols

10 Extrusion template

12 template bodies

14 Wall surfaces 16 Template recess

18 Injector element

20 Injection gap

22 Joining area

24 Vulcanizable rubber product 26 Modification layer

E Extrusion direction

Claims

Expectations

1. A method for producing a strand-shaped vulcanizable rubber product (24) comprising a modification layer (26) with an average layer thickness of 30 pm 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 surrounding wall surfaces (14), and c) an elongated injector element (18) extending between the wall surfaces (14) through the template recess (16), with an injection gap (20), comprising the method steps: i) extruding a material strand made 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 made of the injection gap (20) in the material gap for contacting 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 at 20 °C of 50 Pa*s or less, 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. Method according to one of claims 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. Vulcanized rubber product produced or producible by the process of claim 9.