WO2022090382A1

WO2022090382A1 - Hybrid cord for tires using basalt and cellulose fibers

Info

Publication number: WO2022090382A1
Application number: PCT/EP2021/079962
Authority: WO
Inventors: Maria Carolina SEGHINI
Original assignee: Bridgestone Europe Nv/Sa
Priority date: 2020-10-28
Filing date: 2021-10-28
Publication date: 2022-05-05

Abstract

The present invention relates to a sustainable hybrid cord characterized by the combination of mineral basalt fibers and cellulose-based fibers for use in the production of reinforcement materials for pneumatic tyres, as well as to a production method for said hybrid cord. The invention also relates to a pneumatic tyre comprising said reinforcement materials.

Description

HYBRID CORD FOR TIRES USING BASALT AND CELLULOSE FIBERS

DESCRIPTION

FIELD OF THE INVENTION

The present invention relates to a sustainable hybrid cord characterized by the combination of basalt mineral fibers and cellulose-based fibers for use in the production of reinforcement elements for pneumatic tyres, as well as to a production method of said hybrid cord.

STATE OF THE ART

The need to ensure a more sustainable mobility represents a key factor in explaining the growing importance of ecological pneumatic tyres.

In recent years, automotive firms have made a significant transition to a greater sustainability by incorporating more and more recyclable materials into vehicle production, selecting alternative or differentiated-propulsion fuels, and modifying vehicle components in order to make them more ecological. In order to minimize as much as possible the environmental impact associated with the manufacturing processes of the products thereof, "original equipment" manufacturers (OEM) are asking for "green" pneumatic tyres with lesser rolling resistance in order to reduce CO2 emissions or in order to ensure greater autonomy for electric vehicles and containing an increasing percentage of sustainable materials, whether they are recycled or recyclable materials, or those coming from natural sources. Polyester and polyamide fibers are the most used synthetic materials in the production of pneumatic tyre reinforcement materials. Based upon the performance thereof, these industrial yarns are nowadays used as the cap plies or as the body ply itself. However, with the need for a more sustainable development, the use of petrochemical-derived reinforcement materials will no longer be permitted in the years to come. In fact, these materials show a significant environmental impact that is linked both to the production process and to the life cycle thereof.

By virtue of the natural origin and good mechanical properties thereof, basalt fibers represent an ideal candidate for the replacement of the synthetic fibers that are traditionally used in pneumatic tyre technology. Basalt fibers are mineral fibers characterized by an amorphous structure (very similar to glass). Due to the excellent heat resistance thereof, mechanical properties, chemical stability, relatively low cost and a manufacturing process with a low environmental impact, basalt can be introduced into pneumatic tyre technology as a reinforcement material within the cap ply or within the body ply itself or within the sidewall reinforce or within the chafer of the pneumatic tyre. However, the use of basalt fibers within pneumatic tyres can have some disadvantages. In particular, cords made entirely from basalt fibers, due to the high modulus, can result in deformations of the pneumatic tyre during the vulcanization step. Furthermore, in applications relating to the cap ply, high stiffness can cause belt separation phenomena of the pneumatic tyre during the use thereof, which could represent serious safety problems.

In this context, the production of hybrid cords has an excellent potential in promoting greater use of basalt in pneumatic tyre technology. The production of cords with a hybrid structure by means of the combination of basalt with other fibers produced from different materials, could in fact mitigate the disadvantages linked to the use of basalt fibers alone. In recent years, the use of basalt fibers has been the subject of great interest and study in the field of pneumatic tyre technology. Several patent documents, known in the state of the art, describe materials obtained from the combination of basalt yarns with synthetic yarns, in particular polyamides (NY), in order to produce high- performance hybrid cords for pneumatic tyre applications. In the international patent application W02014102719A1 an ecological hybrid cord is described for use in the production of the cap ply of pneumatic tyres, comprising polyamide 6.6 fibers (nylon 6.6) and basalt fibers.

Patent application CN106012159A describes a method for manufacturing the cap ply of pneumatic tyres that uses a cord consisting mainly of basalt fibers, further comprising cotton fibers or nylon 6.6 fibers.

The European patent application EP3441237A1 describes a hybrid cord for use within vehicle pneumatic tyres.

Patent application EP2781371 B1 describes a reinforcement layer for vehicle pneumatic tyres wherein said reinforcement element comprises a plurality of monoyarns consisting of basalt fibers.

The hybrid cords currently used in the sector, however, all involve the use of materials of a petrochemical origin, considerably reducing the possibility of gains in terms of environmental sustainability that would be derived from the use of basalt fibers alone. The significant requirement therefore remains to identify and develop new reinforcement materials, such as hybrid cords, suitable for the production of ecological pneumatic tyres that can combine the excellent mechanical properties of synthetic materials with the high sustainability offered by materials of a natural origin.

SUMMARY OF THE INVENTION The object of the present invention is to reduce the environmental impact of general purpose vehicle pneumatic tyres by providing a sustainable hybrid cord that is suitable for manufacturing high performance pneumatic tyre reinforcement materials.

The authors of the present invention have designed and developed a hybrid cord that is suitable for being incorporated into the cap ply or into the body ply itself, or into the sidewall reinforce or into the chafer of the pneumatic tyre, characterized by the combination of basalt mineral fibers and cellulose-based fibers, for a highly sustainable final product. The authors of the invention have found that by combining basalt fibers with cellulose-based fibers it is possible to mitigate the unfavorable characteristics of basalt fibers, obtaining surprising advantages in terms of modulus and elongation properties, equally providing evident improvements from the point of view of the environmental impact. As evident from the experimental results illustrated in the present description, the hybrid cord, object of the invention, is characterized by intermediate properties with respect to those of the single materials that comprise it, and in particular by a reduced tension modulus value and by a better elongation percentage at break.

In a preferred embodiment, the hybrid cord, object of the present invention, can also be manufactured by combining basalt fibers with cellulose fibers produced using ionic liquids (hereinafter referred to as "IL-cellulose fibers"), for a 100% sustainable product. In general, the traditional cellulose dissolution process requires relatively drastic conditions and the use of toxic and uncommon reagents, which usually cannot be recovered at the end of the process. By virtue of the chemical and thermal stability thereof and the non-flammability and good miscibility thereof with many other solvents, ionic liquids represent an economically and environmentally sustainable option for processing cellulose. Advantageously, the low vapor pressure, low reactivity and good recyclability of ionic liquids mean that IL-technology is cleaner and more ecological than the conventional process used for the production of rayon fibers. The application of IL-cellulose fibers in the production of hybrid cords, according to the present invention, therefore makes it possible to obtain more sustainable reinforcement materials from the point of view of the production process.

Ecological pneumatic tyres that can be produced using the hybrid cord, object of the present invention, as a reinforcement material have an incredibly promising commercial potential in the field of sustainable mobility. These pneumatic tyres can in fact find application in the design of hybrid and electric vehicles.

The proposed invention therefore has the objective of reducing the environmental impact of pneumatic tyres for general use. Sustainable mobility currently represents one of the greatest environmental challenges. In order to reduce, as far as possible, the environmental impact associated with the products thereof, vehicle manufacturers are calling for "green" pneumatic tyres with lower rolling resistance and that contain an increasing percentage of sustainable materials. The use of the hybrid cord, object of the present invention, can promote a decrease in those CO2 emissions that are produced during the production of pneumatic tyres, thus contributing to a significant reduction in the environmental impact thereof. By virtue of the excellent physical properties thereof, basalt can contribute to improving several aspects of pneumatic tyre performance. The high elastic modulus of basalt, similar to that of aramidic fibers, can promote an increase in the stiffness of the carcass, consequently improving the handling characteristics of a pneumatic tyre produced using the hybrid cord, object of the present invention. In addition, by virtue of the excellent heat resistance thereof, the basalt used for the production of the present hybrid cord is capable of significantly improving the thermal stability of a pneumatic tyre, promoting better durability at high speed and under low or no pressure rolling conditions.

Forming, therefore, the object of the invention are: a pneumatic tyre hybrid cord comprising or consisting of:

- at least one yarn consisting of basalt fibers;

- at least one yarn consisting of cellulose-based fibers; a pneumatic tyre reinforcement material comprising and/or consisting of a plurality of said hybrid cords; a pneumatic tyre body ply comprising and/or consisting of said reinforcement material; a cap ply of a pneumatic tyre comprising and/or consisting of said reinforcing material; a sidewall reinforce comprising and/or consisting of said reinforcement material; a chafer comprising and/or consisting of said reinforcement material; a pneumatic tyre comprising said reinforcement material or said pneumatic tyre body ply and/or said cap ply of the pneumatic tyre and/or said sidewall reinforce and/or said chafer; the use of a hybrid cord according to any one of the embodiments for the manufacture of the cap ply and/or the body ply and/or said sidewall reinforce and/or said chafer of a pneumatic tyre; and a process for the manufacture of said pneumatic tyre hybrid cord, comprising the following steps: a. preparing at least one yarn consisting of basalt fibers; b. preparing at least one yarn consisting of cellulose-based fibers; c. braiding together the yarns obtained from steps a. and b. in such a way as to obtain said hybrid cord.

Further advantages and features of the present invention will become apparent from the following detailed description.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1. Schematic representation of cellulose production using Ionic Liquids. Figure 2. Comparison between the stress-strain curves obtained for basalt cords and IL-cellulose cords.

Figure 3. Image depicting the effects of the basalt/IL-cellulose hybridization and the influence of the twist level on the tensile properties of the hybrid cords.

DETAILED DESCRIPTION OF THE INVENTION

GLOSSARY

Within the context of the present invention, a "yarn" is a linear structure consisting of numerous individual filaments, i.e. continuous fibers. The filaments that make up the yarn are preferably woven together.

Within the context of the present invention, the term "cord" refers to a linear structure consisting of two or more yarns woven together.

Within the context of the present invention, the term "twist coefficient" refers respectively to the twist imparted to a yarn before it is incorporated into the cord, or to the twist imparted to two or more yarns when these are twisted together in order to form said hybrid cord.

Consistently with the established industry terminology, within the present context the term "cap ply" indicates the layer of reinforcement fabric positioned above the carcass of a pneumatic tyre, while the term "body ply" refers to the carcass ply of the pneumatic tyre, the term "sidewall reinforce" refers to the layer of reinforcement fabric positioned on the side of the pneumatic tyre while the term "chafer" refers to the layer of fabric positioned as lateral protection for the bead core.

Where specified, the unit of measurement "decitex", abbreviated "dtex", represents the unit of measurement for the linear density that is used in order to determine the count (or titration) of a yarn, corresponding to 1 gram in 10 kilometers. The unit of measurement tpm , used in the present invention for the twist coefficient, or twist, corresponds to the number of twists per meter.

Where specified, the term braiding indicates the intertwining of two or more yarns together, with the aim of obtaining the construction of the final cord.

The term elastic modulus refers to the ratio between the stress applied to a filament/cord and the resulting deformation thereof. The modulus of elasticity is a measure of the resistance of a yarn/cord to elastic deformation.

The term elongation at break refers to the deformation percentage value reached by the filament/cord at the break thereof. Where specified, the Elongation At Specific Load (EASL) represents the deformation percentage value of the filament (or cord) when subjected to a specific force value.

Where specified, the toughness or tensile strength represents the breaking strength of the yarn in relation to the linear density thereof (unit count, tex).

The term "Shrinkage" refers to the dimensional shrinkage to which a filament/string is subjected if subjected to a specific temperature value. Where specified, "Hot Air Shrinkage" represents the shrinkage value of the filament/cord when subjected to a specific force and temperature value.

The term "ionic liquids", within the present description, refers to a wide class of ionic compounds that remain liquid at relatively low temperatures (<100°C): these compounds are characterized by good thermal and chemical stability, nonflammability, miscibility with water and/or organic solvents, together with an extremely low vapor pressure.

The "cellulose" referred to in the present description is a homopolymer that exists in nature in the form of long chains with a high molecular weight, consisting of the repetition of D-glucopyranose rings (glucose molecules) that are linked together by means of a p-(1 - >4) glycosidic (C-O-C) bond. Occasionally, cellobiose is considered to be the constituent unit of the polymer, namely two glucopyranose rings. The dimensions of the polymer chain depend upon the degree of polymerization (DP). The presence of -OH hydroxyl groups lends hydrophilic characteristics to the polymer and is also responsible for the formation of a complex network of intra and inter-molecular hydrogen bonds that are capable of stabilizing the single chain, as well as the crystalline systems that are characteristic of cellulose fibers.

The term "cellulose-based fibers", within the present description, refers to fibers containing an amount of cellulose of at least 60%, preferably between 70-100%; for example cellulose-based fibers that are suitable for use within the present invention contain at least 70, 80, 90, 100% cellulose.

The object of the present invention is to provide a sustainable hybrid cord, suitable for the manufacture of reinforcement materials for pneumatic tyres, that is capable of ensuring good mechanical performance and at the same time ensuring a low environmental impact.

A first aspect of the present invention therefore refers to a pneumatic tyre hybrid cord, comprising or consisting of:

- at least one yarn consisting of basalt fibers;

- at least one yarn consisting of cellulose-based fibers.

Basalt fibers are fibers of a natural origin originating from the fusion and subsequent spinning of basaltic rock, a volcanic rock rich in minerals, in particular: plagioclases, pyroxenes and olivines.

Basalt fibers that are suitable for making a hybrid cord according to the present invention, can be obtained according to any of the procedures known to a person skilled in the art. By way of example only, such basalt fibers can be obtained by means of a process which anticipates (i) a first step for the pre-processing of the basaltic rock; (ii) a step for melting the rock in a furnace in order to obtain continuous fibers; (m) a continuous spinning processing step; and optionally (iv) a weaving processing step or other specific forms of processing in case it is necessary to obtain other required forms.

Typically, the energy expenditure associated with the production of basalt fibers is very low, and this aspect contributes to reducing the environmental impact associated with the use of this material as a reinforcement component in pneumatic tyre technology.

Basalt fibers are characterized by a wide range of working temperatures (from -250 to + 600°C), low hygroscopicity, excellent chemical resistance, such as acid resistance or alkali resistance, good abrasion resistance, high tensile resistance, high electrical insulation properties, acoustic insulation properties and flexibility.

The exact chemical composition of basalt fibers depends upon the manufacturer and the percentages wherein different basalt rocks can be dissolved during a single melting step. Basalt fibers that are suitable for being used in the production of a hybrid cord according to the present invention, include, but are not limited to, basalt fibers characterized by an SiC>2 content typically of between 42-55%, an AI2O3 content typically of between 14-18%, 11-13% Fe2Os iron oxide, while the CaO calcium oxide and MgO magnesium oxide occupy similar percentages, generally of around 4-12%. Other oxides (i.e. , Na2O, TiO2, K2O) have percentages that do not go beyond 5%.

Basalt fibers that are suitable for being used in the production of a hybrid cord according to the present invention, include, but are not limited to, basalt fibers characterized by a density of 2.6 g/cm³, a Poisson's ratio of 0.24 and a melting point of 1560 C. Regarding the mechanical performance, basalt fibers that are suitable for being used in the production of a hybrid cord have a tensile tenacity of between 66- 80 cN/tex, a deformation at break equal to 2.1 % and a Young's modulus of between

90-100 GPa. Basalt fibers that are suitable for the preparation of a hybrid cord according to the present invention also have a diameter of between 10 and 30 microns. The linear density values of the basalt yarns used in the hybrid cord, object of the invention, can be comprised within a range of between 600 and 4000 dtex, preferably between 1100 and 3300 dtex.

In a preferred embodiment of the hybrid cord, object of the invention, the basalt fibers are characterized by a linear density value that is at least equal to 2000 dtex.

According to an aspect of the present invention, cellulose-based fibers that can be used for the production of a hybrid cord comprise fibers of purified and/or regenerated cellulose, or fibers obtained by dissolving cellulose pulp in such a way as to obtain a spinnable fluid that can be subjected to a spinning process, and/or modified cellulose fibers, wherein the -OH groups of the cellulose are reacted, all or in part, in order to obtain fibers with chemical characteristics that are different when compared to the original cellulose.

In an embodiment of the present invention, said cellulose-based fibers are in particular purified and/or regenerated cellulose fibers. Examples of purified and/or regenerated cellulose fibers include cellulose fibers produced from the dissolution of cellulose pulp by any of the conventional methods known in the art, for example rayon and/or viscose fibers, or fibers obtained by means of the Lyocell method, or also combinations of these fibers.

Preferably, cellulose-based fibers that are used for making the hybrid cord, object of the invention, are purified cellulose fibers produced using ionic liquids (IL-cellulose fibers). The advantage of this configuration lies in the use of cellulosic materials that are obtained by means of a highly sustainable process when compared to conventional methods for the production of cellulose-based fibers. As already mentioned, by virtue of the chemical-physical properties and the good recyclability of ionic liquids, the technology that is based upon the use of these compounds offers several advantages from an environmental point of view when compared to those conventional processes that are used for the production of cellulose-based fibers, particularly reduced toxicity. Advantageously, the spinning process for the cellulose fibers by means of ionic liquids, can be performed in the absence of antioxidants or surfactants. Furthermore, ionic liquids do not possess explosive properties and therefore ensure greater safety during the cellulose fibers production step.

According to an aspect of the present invention, said IL-cellulose fibers are produced by means of a process that provides for a first step of dissolving the cellulose pulp in a solution consisting of one or more ionic liquids and a polar solvent, such as water or alcohol, followed by a spinning step. An example of a process for the production of cellulose fibers using ionic liquids is schematically shown in Figure 1.

Ionic liquids that are suitable for being used for the dissolution of cellulose pulp and therefore for the preparation of cellulose-based fibers that can be used in the present invention, are ionic liquids having the lowest possible toxicity. They are easy to prepare, recyclable in large quantities (>99.5%), characterized by an almost zero vapor pressure at room temperature, a low melting point, a low propensity to degradation and secondary reactions, as well as a high dissolving capacity, also for sources of pulp that are different therebetween.

Ionic liquids that are suitable for being used for the preparation of said IL-cellulose fibers comprise a cationic part and an anionic part, wherein the cationic part can be selected, for example, from amongst imidazolium ion, pyridinium ion, ammonium ion or phosphonium ion. Said ionic liquids can be used alone or in mixture.

Non-limiting examples of said ionic liquids include: 1-butyl-3-methylimidazolium chloride ([BMIM][CI]), 1-ethyl-3-methylimidazolium acetate ([EMIM][OAc]), 1-allyl-3- methylimidazolium chloride ([AMIM][CI]), 1 ,5-diazabicyclo[4.3.0]non-5-ene acetate ([DBNH][OAc]), 1 ,3-dimethylimidazolium methyl-H-phosphonate [MMIM] [MMP]’, 1- butyl-3-methylimidazolium chloride [C4MIM] [Cl], 1-ethyl-3-methylimidazolium methylphosphonate ([EM IM] [CH3PO3]), 1-ethyl-3-methylimidazolium propionate ([C2MIM]⁺[OPr]'), 1-butyl-3-methylimidazolium acetate (C4AMIMAc), 1-ethyl-3- methylimidazolium acetate (C2AMIMAc), and 1-ethyl-3-methylimidazolium diethyl phosphate (C2MIMDEP).

According to a preferred embodiment of the invention, the ionic liquids to be used for the preparation of said IL-cellulose fibers are 1-butyl-3-methylimidazolium chloride ([BMIM][CI]), 1-allyl-3-methylimidazolium chloride ([AMIM][CI]), 1-ethyl-3- methylimidazolium acetate ([EMIM][OAc]) and 1-butyl-3-methylimidazolium acetate (C4AMIMAC).

The IL-cellulose fibers spinning step can be performed by applying any of the spinning techniques known in the sector, for example by applying a process chosen from wet spinning or else a process deriving from the combination of wet spinning and dry spinning, known as "dry jet-wet spinning".

Preferably, in one embodiment of the present invention, said cellulose-based fibers are IL-cellulose fibers obtained by means of a "wet-spinning" spinning process.

The use of ionic liquids for the production of cellulose fibers also offers the possibility of chemically modifying said fibers in-situ, directly during the spinning process. Therefore, IL-cellulose fibers that are suitable for being used for the production of a hybrid cord according to the present invention, also include fibers comprising chemically functionalized IL-cellulose derivatives. Examples of IL-cellulose derivatives include acetate derivatives, carboxymethylates, benzoylates, carbamates, methacrylates, carbonates, sulfates, sulfonates, phthalates, furoates, maleic esters or esterified resins. According to an aspect of the invention the IL-cellulose fibers used for the production of said hybrid cord, have a density of between 1.5 and 1.52 g/cm3 and a thermal degradation starting in air at temperatures below 300 °C.

According to an aspect ot the invention the IL-cellulose fibers used for the production of said hybrid cord have a tensile tenacity strength of between 30 and 60 cN/tex, a deformation at break of between 5 and 10 % and a tensile modulus of between 160 and 220 cN/dtex.

According to an aspect of the invention, the cellulose-based fibers used for the production of said hybrid cord have a linear density of between 800 and 4000 dtex, preferably of between 1100 and 3000 dtex. According to a preferred embodiment of the invention, the cellulose-based fibers used for making said hybrid cord have a linear density value that is at least equal to 1800 dtex.

The total linear density of the hybrid cord according to any one of the embodiments described herein can therefore range between 1500 and 8000 dtex, preferably it will be at least equal to 3800 dtex.

According to an aspect of the invention, on the basis of the total weight of the hybrid cord, the basalt fibers present within said hybrid cord represent between 40 and 80% by weight, preferably about at least 60% by weight, while the cellulose-based fibers represent between 20 and 60% by weight, preferably about at least 40% by weight. The hybrid cord, object of the invention according to any one of the embodiments thereof, as well as the fibers of each yarn of said hybrid cord, are characterized by a twist direction in the Z or S directions. As known to those skilled in the art, the direction of the twist refers in particular to the direction of the turns of a yarn or a cord to the right (Z) or to the left (S), when they are held in a vertical position. Preferably, the basalt fibers and the cellulose-based fibers that make up each yarn of the hybrid cord have the same twist direction, while the final hybrid cord, obtained by joining the aforementioned yarns, is characterized by an opposite twist direction.

In a preferred embodiment of the present invention, the twist direction of the basalt fibers and the cellulose-based fibers is S, while the twist direction of the final hybrid cord is Z.

An aspect of the invention relates to a hybrid cord wherein each yarn is characterized by a twist coefficient of between 100 and 500 tpm, and in particular it is equal to 100S tpm.

According to a preferred aspect of the invention, said hybrid cord is characterized by a twist coefficient of between 100 and 500 tpm, and preferably equal to 350Z tpm.

One embodiment of the invention relates to a hybrid cord characterized by a total linear density equal to 3800 dtex, consisting of a first yarn composed of basalt fibers having a linear density equal to 2000 dtex, and of a second yarn composed of fibers of IL-cellulose having a linear density equal to 1800 dtex, with a twist coefficient value for each yarn equal to 100S tpm, and a twist coefficient value for the final hybrid cord equal to 250Z tpm.

A further embodiment of the hybrid cord object of the invention refers to a hybrid cord characterized by a linear density equal to 3800 dtex, consisting of a first yarn composed of basalt fibers having a linear density equal to 2000 dtex, and a second yarn composed of IL-cellulose fibers having a linear density equal to 1800 dtex, wherein the twist coefficient of each yarn is equal to 100S tpm, while the twist coefficient of the final hybrid cord is equal to 300Z tpm.

A preferred embodiment of the hybrid cord object of the invention refers in particular to a hybrid cord characterized by a linear density equal to 3800 dtex, consisting of a first yarn composed of basalt fibers having a linear density equal to 2000 dtex, and a second yarn composed of IL-cellulose fibers having a linear density equal to 1800 dtex, wherein the twist coefficient of each yarn is equal to 100S tpm, while the twist coefficient of the final hybrid cord is equal to 350Z tpm.

In a further aspect of the invention, the hybrid cords may further comprise one or more PET filaments, in particular BIO-PET or R-PET, according to any of the embodiments described in the Italian patent application No. 102020000023578, integrally incorporated herein by reference.

According to an aspect of the invention, the hybrid cord, according to any one of the embodiments described therein, is characterized by a modulus value of between 7 and 18 cN/tex.

Such a hybrid cord may also exhibit a tensile force of between 150 and 200 N, and in particular of about O N. The hybrid cord object of the invention will be characterized by a break elongation percentage of between 5 and 7%.

According to a further aspect of the invention, said hybrid cord may exhibit a tensile strength of between 30 and 50 cN/tex.

As known to a person skilled in the art, the mechanical properties mentioned above can be determined by subjecting said hybrid cord to a tensile test according to the ASTM D885 standard method, "Standard Test Methods for Tire Cords, Tire Cord Fabrics, and Industrial Filament Yarns Made from Manufactured Organic-Base Fibers".

As already mentioned, the good mechanical performances of the hybrid cord, object of the invention, allow it to be used as a reinforcement component within pneumatic tyres for road vehicles. According to an aspect of the invention, the hybrid cord according to any one of the embodiments described herein can be used for the manufacture of the cap ply and/or the body ply and/or said sidewall reinforce and/or said chafer of a pneumatic tyre. An aspect of the present invention therefore refers to the use of a hybrid cord according to any one of the previously described embodiments for the manufacture of the cap ply and/or the body ply and/or said sidewall reinforce and/or said chafer of a pneumatic tyre.

The object of the invention is also a reinforcement material for a pneumatic tyre comprising a plurality of hybrid cords according to any of the previously described embodiments. Said reinforcement material can be used in particular for the production of specific reinforcement components for pneumatic tyres.

The object of the invention also comprises a cap ply of a pneumatic tyre and a pneumatic tyre body ply and a sidewall reinforce and a chafer of a pneumatic tyre constituted or comprising a reinforcement material as mentioned above.

The object of the invention is furthermore a pneumatic tyre comprising said reinforcement material or a plurality of reinforcement materials as defined above. Said pneumatic tyre may comprise all of the other elements that are commonly used in the configuration of these products such as, for example, a rim whereupon the following are anchored: the body ply, a tread belt comprising at least two plies, two bead cores, an innerliner and any other layers of additional material located between the innerliner and the inner cavity of the pneumatic tyre.

An object of the present invention is also a process for the production of a pneumatic tyre hybrid cord as described herein, comprising the following steps: a. preparing at least one yarn consisting of basalt fibers; b. preparing at least one yarn consisting of cellulose-based fibers; c. braiding together the yarns obtained from steps a and b, in such a way as to obtain said hybrid cord. According to an aspect of the invention, a twist coefficient of between 100 and 390 tpm, in particular equal to 100S tpm, can be applied in steps (a) and/or (b) of the process.

According to a further aspect of the invention, a twist coefficient of between 100 and 390 tpm, in particular equal to 350Z tpm, can be applied in said step (c) of the process described herein.

According to an aspect of the invention, cellulose-based fibers produced by means of ionic liquids (IL-cellulose fibers) will be used in any one of the previously described embodiments.

In an embodiment of the present invention, the process described above may comprise, before step b., a further step (i) of dissolving cellulose pulp in a solution comprising one or more ionic liquids, followed by a step (ii) for the preparation of said cellulose-based fibers by means of spinning. In particular, in step (ii), just described, a spinning process of the "wet spinning" type will be used.

The procedure may include a further step wherein each yarn of the hybrid cord and/or the final hybrid cord is treated with a "spin finish" type product chosen from amongst lubricants, emulsifiers or antistatic agents, preferably biodegradable, in order to protect the yarns from rubbing against each other and/or against the equipment used, ensuring excellent cohesion results for the fibers and improving the workability thereof.

The invention also relates to a process for the production of a pneumatic tyre, wherein the manufacturing step of the cap ply and/or of the body ply and/or of the sidewall reinforce and/or of the chafer of a pneumatic tyre a reinforcement material comprising a plurality of hybrid cords according to any one of the embodiments described herein is used. EXAMPLES

Non-limiting examples of embodiments of the hybrid cord, object of the present invention, are given below.

EXAMPLE 1

Hybrid cord: 3800 dtex (2000 dtex basalt - 1800 dtex IL-cellulose), with a twist level equal to 100S tpm for each yarn and equal to 250Z tpm for the final cord.

EXAMPLE 2

Hybrid cord: 3800 dtex (2000 dtex basalt - 1800 dtex IL-cellulose), with a twist level equal to 100S tpm for each yarn and equal to 300Z tpm for the final cord.

EXAMPLE 3

Hybrid cord: 3800 dtex (2000 dtex basalt - 1800 dtex IL-cellulose), with a twist level equal to 100S tpm for each yarn and equal to 350Z tpm for the final cord.

Experimental tests

Tensile tests on basalt and IL-cellulose cords

A first experimental investigation was performed with the aim of understanding the potential of different constructions of basalt-based or IL-cellulose-based cords. Tensile tests were performed on:

- basalt-based cord characterized by a linear density of 2000/2 dtex and a twist coefficient of 260S - 260Z;

- IL-cellulose based cord characterized by a linear density of 1800/2 dtex and a twist coefficient of 470S - 470Z. Figure 2 shows a comparison between the tensile curves obtained for the basalt cord and for the IL-cellulose cord, respectively. The results show that basalt cords are characterized by higher tensile resistance and tensile strength compared to those of cellulose cords. Basalt shows lower deformation values than cellulose. These results reflect a basalt fatigue strength that is unsuitable for pneumatic tyre applications. In addition, due to the high elastic modulus thereof, basalt is expected to distort the geometry of the pneumatic tyre during the vulcanization step and to favor pneumatic tyre belt separation processes.

Characterization of the mechanical properties of basalt and IL-cellulose based hybrid cords

A mechanical characterization of the hybrid cords specified in Examples 1-3 was carried out in performing tensile tests. Figure 3 shows the stress-strain curves obtained for the different types of construction of hybrid cords, in comparison with the curves obtained for cords consisting of 100% basalt and for IL-cellulose cords, respectively.

The results obtained show that the combination of basalt yarns with IL-cellulose yarns determines an increase in the deformation properties of the basalt and a reduction in the tensile modulus of the basalt cord. An in-depth analysis of the influence of the twist level on the mechanical performance of hybrid cords was also conducted. In Figure 3 it can be seen that an increase in the twist coefficient favors an increase in the elongation properties of hybrid cords.

In particular, better results were obtained in terms of elongation at break for the hybrid cord having a twist coefficient equal to 350Z tpm, characterized by a basalt-based yarn (100S tpm twist) and an IL-cellulose based yarn (100S tpm twist).

Claims

1. Pneumatic tyre hybrid cord, comprising or consisting of: at least one yarn consisting of basalt fibers; at least one yarn consisting of cellulose-based fibers, wherein said cellulose-based fibers are cellulose fibers produced using ionic liquids (IL-cellulose fibers).

2. Hybrid cord according to claim 1, wherein said cellulose-based fibers are purified and/or regenerated cellulose fibers.

3. Hybrid cord according to claim 1 or 2, wherein said cellulose-based fibers are cellulose fibers produced using ionic liquids (IL-cellulose fibers).

4. Hybrid cord according to any one of the claims from 1 to 3, wherein said basalt fibers have a linear density of between 600 and 4000 dtex.

5. Hybrid cord according to claim 4 wherein said basalt fibers have a linear density value that is at least equal to 2000 dtex.

6. Hybrid cord according to any one of the claims from 1 to 5, wherein said cellulose-based fibers have a linear density of between 800 and 4000 dtex.

7. Hybrid cord according to claim 6, wherein said cellulose-based fibers have a linear density that is at least equal to 1800 dtex.

8. Hybrid cord according to any one of the claims from 1 to 7, wherein the total linear density of said hybrid cord ranges between 1500 and 8000 dtex, in particular it is equal to 3800 dtex.

9. Hybrid cord according to any one of the claims from 1 to 8, wherein each yarn is characterized by a twist coefficient ranging between 100 and 500 tpm, in particular equal to 100S tpm.

10. Hybrid cord according to any one of the claims from 1 to 9, wherein said hybrid cord is characterized by a twist coefficient ranging between 100 and 500 tpm.

11. Hybrid cord according to claim 10, wherein said hybrid cord is characterized by a twist coefficient equal to 350Z tpm.

12. Hybrid cord according to any one of the claims from 1 to 11 , wherein said hybrid cord is a hybrid cord characterized by at least one yarn consisting of basalt fibers having a linear density value equal to 2000 dtex and at least one yarn consisting of IL-cellulose fibers having a linear density value equal to 1800 dtex, wherein each yarn is characterized by a twist coefficient equal to 100S tpm, and wherein said hybrid cord is characterized by a twist coefficient equal to 350Z tpm.

13. Hybrid cord according to any one of the claims from 1 to 12, wherein said basalt fibers represent between 40 and 80% by weight and said cellulose- based fibers represent between 20 and 60% by weight with respect to the total weight of said hybrid cord.

14. Pneumatic tyre reinforcement material comprising and/or consisting of a plurality of hybrid cords according to any one of the claims from 1 to 13.

15. Pneumatic tyre body ply comprising and/or consisting of a reinforcement material according to claim 14.

16. Cap ply of a pneumatic tyre comprising and/or consisting of a reinforcement material according to claim 14.

17. Pneumatic tyre sidewall reinforce comprising and/or consisting of a reinforcement material according to claim 14.

18. Pneumatic tyre chafer comprising and/or consisting of a reinforcement material according to claim 14.

19. Pneumatic tyre comprising a reinforcement material according to claim 14.

20. Use of a hybrid cord according to any one of the claims from 1 to 14 for the manufacture of the cap ply and/or the body ply and/or the sidewall reinforce and/or the chafer of a pneumatic tyre.

21. Process for the manufacture of a pneumatic tyre hybrid cord according to any one of the claims from 1 to 14, comprising the following steps: a. preparing at least one yarn consisting of basalt fibers; b. preparing at least one yarn consisting of cellulose-based fibers; c. braiding together the yarns obtained from steps a and b, in such a way as to obtain said hybrid cord.

22. Process according to claim 21 , wherein, during said steps (a) and/or (b), a twist coefficient of between 100 and 390 tpm, in particular equal to 100S tpm, is applied.

23. Process according to claims 20 or 22, wherein, during said step (c), a twist coefficient of between 100 and 390 tpm, in particular equal to 350Z tpm, is applied.

24. Process according to any one of the claims from 20 to 23 wherein said cellulose-based fibers are cellulose fibers produced using ionic liquids (IL- cellulose fibers).