Patent Application
20070169458
The invention relates to a cord that consists of a core and sheath.
Such a cord is described, for instance, in EP 1 411 159; in this cord, the core is made of glass fibres and the sheath is made of aramid yarns. This cord serves to reinforce elastomeric materials such as tires or belts.
The need still exists to develop such cords that have properties that are at least comparable with or better than the known cords. In particular, such cords should ensure as long a lifespan as possible of the reinforced composites. In addition, when using such cords in belts, they must also be oil-resistant and/or hydrolytically stable.
The object of the present invention is to provide other suitable cords for reinforcing elastomeric materials. In particular, exemplary embodiments of such cords should ensure a long lifespan of the elastomeric material reinforced with such cords. Further, cords having a good hydrolytic stability should be provided in exemplary embodiments. In addition, exemplary embodiments should provide a cord that can be manufactured cost-effectively.
The object of the invention is achieved, in exemplary embodiments, by a cord that consists of a core and a sheath, whereby the core contains high-modulus fibres embedded in a matrix and is at least predominantly ensheathed with fibres that form the sheath.
The core of exemplary embodiments serves as a strength carrier that in particular is distinguished by its high dimensional stability.
Such a cord can be manufactured, for example, in such a way that the high-modulus fibres are impregnated with the matrix material. After that, the core is spun over, for instance with staple fibres, whereupon the staple fibres form the sheath.
In embodiments, at least one multifilament yarn, which is wrapped around the core, is used as the fibres that form the sheath. The wrapping is carried out, in embodiments, in such a way that after the wrapping, the core is covered as much as possible, i.e. is virtually not visible. If multiple multifilament yarns are used for manufacturing the sheath of embodiments, these yarns can be wrapped around the core in the same and/or opposite direction. Also, multiple multifilament yarns can be braided to form a sheath, in embodiments.
It has been found to be particularly advantageous if the core matrix of the cord according to embodiments of the invention is a thermoplastic.
Besides the usual impregnating processes for introducing the matrix into the high-modulus fibres, thermoplastic fibres can be mixed with the high-modulus fibres in exemplary embodiments, whereby in a later step this mixture is heated in such a way that the thermoplastic fibres melt to form the matrix in which the high-modulus fibres are embedded. In such embodiments, the high-modulus fibres can be present as continuous fibres, for instance as multifilament yarn, and the thermoplastic fibres can be well mixed with the high-modulus fibres, for example by an intermingling process using air, which is known per se. However, finite-length fibres such as staple fibres or fibres that were manufactured through the process of stretch-breaking can be used as the high-modulus fibres of embodiments as well. In such embodiments, it is recommended to use thermoplastic fibres that are also staple fibres or stretch-broken fibres. In stretch-breaking of fibres, the stretch-broken fibres show varying lengths, whereby the average length and length distribution of the fibres can be influenced to a certain extent. The high-modulus fibres in the core of the cord according to embodiments of the invention have an average length of 70 to 170 mm, such as of 110 to 130 mm or approximately 120 mm, and a length distribution of 40 to 230 cm. Such fibres can then, in a manner known per se, be mixed and employed, either untwisted or in the form of a yarn, as the core, around which the multifilament yarn that forms the sheath is wrapped. In the process of exemplary embodiments, the mixed yarn, consisting of high modulus and thermoplastic fibres, can be heated already before the sheathing with multifilament yarn in such a way that the thermoplastic fibres melt and as the matrix embed the high-modulus fibres.
In particular embodiments, the mixture made of high-modulus and thermoplastic fibres are first wrapped with at least one multifilament yarn. Because an adhesion agent, such as an RLF (resorcinol formaldehyde latex), which is cross-linked under the influence of temperature, may be applied to the cords before embedding them in the elastomeric material, the temperature treatment required for cross-linking of the adhesion agent can also be used to melt the thermoplastic fibres and transform them into matrix material in embodiments.
In exemplary embodiments, it may be favorable for the core matrix material of the cord to be a thermoplastic with a melting point or a melting point range between 150 and 420° C., such as between 180 and 260° C. In some embodiments, a melting point or a melting point range between 200 and 230° C. for the thermoplastic may be particularly useful. Virtually all materials spinnable to fibres by means of melt spinning are suitable for use as the thermoplastic material for the core matrix, including for example, thermoplastic polyurethanes (TPU), polyesters (PET), polyphenylene sulfides (PPS), polyethylenes (PE) or polyamides (PA). In particular embodiments, the polyamide may be PA 4, PA 4.6, PA 6, PA 6.6, PA 6.10, PA 10 or PA 12.
The distinguishing property of the cord according to embodiments of the invention lies in the fact that the core contains 15 to 50 vol. %, such as 25 to 40 vol. %, of the matrix; this is with respect to the core without the sheath. It is not essential that the high-modulus fibres be completely embedded in the matrix material, but it may be advantageous, in embodiments, if the core shows as little excessive matrix material as possible, which would embed a considerable portion of the filaments of the multifilament yarn that forms the sheath in the heat, which is applied during the embedding of the cored in the elastomeric material. Similarly, it may be favorable, in certain embodiments, if the matrix material is distributed as consistently as possible in the core.
Further, the core of exemplary embodiments may be distinguished in that the high-modulus fibres in the core have a modulus of 200 to 550 GPa, such as 200 to 350 GPa or 200 to 250 GPa. In such embodiments, carbon fibres may be particularly suitable.
In embodiments, it was also found to be advantageous if the multifilament yarn or the multifilament yarns have a lower modulus than the high-modulus fibres of the core. For such embodiments in particular, multifilament yarns with a modulus of 70 to 150 GPa, such as 70 to 120 GPa, have proven particularly suitable. A multifilament yarn made from aramid has proved to be particularly suitable as multifilament yarn for wrapping the core of the cord according to embodiments of the invention.
The cord according to embodiments of the invention is optimally suitable for the manufacturing of fibre-reinforced elastomeric materials.
In this respect, the object of embodiments of the present invention is a V-belt, and also a toothed belt, that contains a cord according to exemplary embodiments of the invention.
The invention will be explained in more detail on the basis of the following example.
For manufacturing a cord according to embodiments of the invention, the following yarns were used:
Yarn 1: Carbon fibres available from Toho Tenax Europe GmbH with the designation Tenax STS 5411, whose single filaments have a linear density of 0.67 dtex and a fibre density of 1.76 g/cm3.
Yarn 2: Thermoplastic fibres of polyamide 6 (PA 6) multifilament yarn available from Rhodia, whose single filaments have a linear density of 6.9 dtex and a fibre density of 1.14 g/cm3. This multifilament yarn has a melting point range of 215 to 220° C.
Yarn 3: Twaron 1,100 dtex f 1000 available from Teijin Twaron BV.
First, 12,000 filaments from yarn 1 and 300 filaments from yarn 2 were stretch-broken, and subsequently mixed intensively, in such a way that a hank of 10,100 dtex was formed that had filaments with an average length of 120 mm, whereby the length of the filaments varied between 40 and 230 mm. Out of this hank, the core component with a linear density of 10,100 dtex was manufactured using a worsted spinning method. This core component thus contained 80% by weight of carbon fibres (yarn 1) and 20% by weight of polyamide 6 fibres (yarn 2). This core component was wrapped twice with yarn 3 in opposite directions, each time with 250 twists per meter (one yarn with 250 twists per meter in the Z-direction and one yarn with 250 twists per meter in the S-direction), whereby an untreated cord was obtained that contained filaments of yarns 1 and 2 in the core component. This cord was treated with an RFL dip in two steps as follows. In the first step, the cord surface (substantially the filaments of yarn 3) was epoxidised in a surface treatment. In the second step, the cord was dipped in an aqueous RFL solution and cured at 235° C., whereby the filaments of yarn 2 melted and became the matrix for the filaments of yarn 1.
The following properties were determined:
The dipped cord obtained was embedded in hydrogenated butadiene acrylonitrile rubber. Further, two commercially available cords, glass A and glass B, that contained glass filaments in the core were dipped and embedded in the same way in hydrogenated butadiene acrylonitrile rubber.
Cord A is offered and sold by NGF Europe Ltd. under the designation “Type EC9, 34, 3/11 80S, black-dipped,” whereas cord B is offered and sold by Sovoutri as reinforcing cord.
On all three cords, the properties that are relevant for the adhesive strength between cord and rubber were measured. The results are summarized in the following table.
Here, the strap peel adhesion force means the force that is necessary to pull the cord out of the composite, a 2 cm wide strip. This force is determined according to ASTM D 4393-00.
These values show clearly that the cord according to the exemplary embodiment, with regard to the breaking strength and the force, shows considerably higher values for the measured elongations than the current conventional cords having glass fibres in the core. Besides, the cord according to the exemplary embodiment is distinguished by a lower elongation at break. Regarding the adhesion to rubber, the cord according to the exemplary embodiment shows properties that are comparable with the cords available today. In this respect, the cord according to the exemplary embodiment can be regarded as a clear improvement.
| Number | Date | Country | Kind |
|---|---|---|---|
| 05015392.3 | Jul 2005 | EP | regional |
