Sustainable drive belt

Abstract

A drive belt comprising a base body made of an elastomer, wherein a plurality of tensile strands are arranged in a longitudinal direction in the base body and are enclosed by the elastomer. According to the invention, the elastomer is based on a cross-linked rubber comprising at least one component produced from a naturally renewable raw material.

Description

[0001] The invention relates to a drive belt comprising a base body made of an elastomer, wherein a plurality of tensile strands are arranged in a longitudinal direction in the base body and are enclosed by the elastomer.

[0002] Drive belts are generally well-known and have a wide range of applications, for example, in automotive or industrial applications. Drive belts, which are also known as power transmission belts and are usually endless when in use, can be designed as flat belts, V-belts, ribbed belts, toothed belts, and clutch belts. Ribbed V-belts and toothed belts are particularly important. The elasticity of a drive belt is achieved by the fact that the base body, and thus the cover layer and the substructure, are made of a polymer material with elastic properties. In this case, two material groups, elastomers and thermoplastic elastomers, are particularly important. Elastomers based on a vulcanized rubber mixture are of particular importance.

[0003] Chemical raw materials for rubber are typically produced in refineries from petroleum-based precursors. These precursors are then converted into the desired end products in sometimes complex chemical processes. Oil is a fossil raw material that is not available in infinite quantities. Further processing in refineries is energy-intensive and potentially releases large amounts of carbon dioxide, which is blamed for increasing global warming.

[0004] The object of the present invention is to increase the sustainability of drive belts, in particular toothed belts, while maintaining the mechanical properties of the resulting material.

[0005] This object is achieved by providing a drive belt according to claim 1.

[0006] The drive belt according to the invention comprises a base body made of an elastomer, wherein a plurality of tensile strands are arranged in a longitudinal direction within the base body and enclosed by the elastomer. The elastomer used is based on a cross-linked rubber, which includes at least one component made from a naturally renewable raw material. The rubber generally makes up the largest proportion in the resulting elastomer material, which in turn forms the base body of the drive belt.

[0007] The elastomer in the sense of the invention corresponds to a cross-linked rubber compound. In addition to the main component, rubber, the rubber compound includes conventional additives that ensure the suitability of the resulting elastomer as the base material of a drive belt.

[0008] Other blend ingredients usually include crosslinking agents, such as sulfur, sulfur donors, or peroxides, fillers, such as carbon black and / or silica, processing aids, plasticizers, anti-aging agents, and possibly other additives (e.g., color pigments). In this regard, reference is made to the general state of rubber blending technology.

[0009] In principle, any rubber known to a person skilled in the art can be used, as long as at least one of the rubbers comprises at least one component made from a naturally renewable raw material. Examples of rubbers are ethylene-propylene copolymer (EPM) or ethylene-propylene-diene copolymer (EPDM), nitrile rubber (NBR), (partially) hydrogenated nitrile rubber (HNBR), natural rubber (NR), or polyepichlorohydrin (ECO). These rubbers can be used alone or in a blend.

[0010] The raw material source can, for example, be one or more plant varieties. Such plant varieties can, for example, be selected from the list consisting of sugarcane and sugar beet, maple, date palm, sugar palm, sorghum, agave, corn, wheat, barley, sorghum, rice, potato, cassava (manioc), sweet potato, algae, fruits, and combinations thereof. However, the raw material source can also be derived from waste and residual oils from industrial processes, e.g., biodiesel production. In preferred embodiments, the naturally renewable raw material is a sugarcane plant.

[0011] Preferably, the rubber comprises at least one ethylene component produced from a naturally renewable raw material, in particular a sugarcane plant. Alternatively or additionally, the rubber comprises at least one propylene component produced from a naturally renewable raw material, in particular a sugarcane plant.

[0012] In particularly advantageous embodiments, the elastomer comprises at least one EPDM and / or EPM rubber. In these embodiments, the rubber comprises at least one sugarcane-based ethylene component. Alternatively or additionally, the EPDM and / or EPM rubber comprises a sugarcane-based propylene component.

[0013] Advantageous embodiments comprise a drive belt having a base body made of EPDM, wherein the EPDM is produced from naturally renewable raw materials to an extent of at least 45%, preferably at least 60% by weight, most preferably at least 70% by weight, based on the total weight of the raw rubber.

[0014] The proportion of double bonds is generally freely selectable. EPDM with an ENB content of at least 2 wt.%, preferably at least 5 wt.%, and most preferably at least 9 wt.%, based on the weight of the raw rubber, has proven particularly suitable for use in drive belts. The high diene component allows for a high degree of crosslinking. In peroxide-crosslinked elastomers, a high degree of crosslinking can be achieved even with low ENB contents. In such cases, the ENB content serves to adjust the desired mechanical properties. In preferred embodiments, the EPDM is peroxide-crosslinked.

[0015] In advantageous embodiments, the drive belt is a toothed belt.

[0016] For example, the timing belt has helical teeth. Helical teeth can reduce the sometimes very loud meshing noise, especially in high-speed drives, by providing the belt with helical teeth known from the prior art. Another advantageous design is that the angle of the helical teeth is between 4° and 8° relative to an axis transverse to the longitudinal direction of the drive belt. This advantageously achieves good acoustic properties while simultaneously maintaining tolerable lateral forces.

[0017] According to a further aspect of the present invention, the tooth pitch is more than 1.5 mm and at most 14 mm. Preferably, the tooth pitch is at most 11 mm, and in further preferred embodiments, at most 2.5 mm. A pitch in this range offers the best compromise between good acoustic properties and sufficient power transmission capacity. Simultaneous good noise behavior and high power transmission performance can be achieved if the timing belt is manufactured with a pitch between 1.5 mm and 2.5 mm and a width between 10 mm and 35 mm. The positive influence on the acoustics of the smaller pitch is greater than the negative influence of a larger belt width.

[0018] According to a further aspect of the present invention, the width of the drive belt is at least 6 times the tooth pitch. Such a ratio between the pitch and the belt width offers particularly advantageous acoustic properties and a sufficiently high power transmission capacity.

[0019] In preferred embodiments, the outer diameter of the tension cord is generally less than 2.4 mm, preferably less than 1.8 mm, more preferably less than 0.5 mm, most preferably from 0.3 mm to 0.45 mm. Compared to tension cords with a larger outer diameter, economic advantages can be generated due to the lower material usage. Furthermore, tension cords with a larger outer diameter lose their tensile strength as the bending radii decrease during operation. The tension cord according to the invention can therefore be particularly suitable for belt drives with small-diameter pulleys, since the reduction in tensile strength is less than with tension cords with a larger diameter.

[0020] In addition, the tensile strength of thinner tensile cords is lower, so a larger number of tensile cords would have to be arranged in the belt to compensate for the lower tensile strength. Therefore, compared to tensile cords with an outer diameter of less than 0.3 mm, the production of the drive belt is more economical, as the time required to wind the tensile cord around a cylindrical tool on which the belt blank is built is reduced.

[0021] In advantageous embodiments, the tensile strands are made of a single-twisted yarn. Alternatively or additionally, at least one tensile strand can be based on carbon, glass, and / or aramid.

[0022] According to DIN 60 900 Part 1, a yarn is a linear structure made from textile fibers.

[0023] To prevent the entire drive belt from twisting or unwinding, the yarns of adjacent tension cords in the drive belt can be twisted alternately or in groups in an S-lay and a Z-lay. The main advantage of this type of tension cord and belt design is that the fineness and geometry of the yarns and tension cords achieve a high tensile strength against stresses caused by high-frequency loads and alternating bending cycles, which is not possible with other tension cord designs of larger diameters.

[0024] According to a further aspect of the present invention, the weight of the tensile strand is at most 16,000 dtex, preferably at most 10,000 dtex, most preferably 2,000 dtex. Alternatively or additionally, the weight of the tensile strand may be at least 200 dtex.

[0025] According to DIN 60 900 Part 2, the tex system indicates the fineness, or length-related mass, of a yarn. In other words, the tex system represents the quotient of the yarn's mass and length. One decitex, or dtex for short, corresponds to 1 dg / km.

[0026] The best results can be achieved within the specified weight range while maintaining cost-effective production.

[0027] According to a further advantageous aspect of the present invention, the twist of the yarn is at least 20, preferably at least 100 tpm, and at most 300 tpm (turns per meter). This ensures particularly good tensile strength and fatigue strength of the tensile cords, and thus of the entire belt.

[0028] The tensile cords can be made of glass fibers. Such tensile cords made of glass fibers have proven their worth due to their low thermal expansion, their temperature resistance, and especially their dynamic stability—that is, their tolerance to high-frequency, alternating vibration loads, such as those found in a steering gear. Even under these conditions, timing belts with glass fiber tensile cords retain their tear strength for a long time.

[0029] Alternatively or additionally, the tensile cords can comprise aramid fibers. It has also been shown to be particularly advantageous that para-aramid tensile cords exhibit greater kink resistance, or in other words, a lower degradation of tensile strength under kink stress, compared to glass cords known from the prior art.

[0030] According to a further aspect, the drive belt according to the invention is, in addition to other fields of application, particularly suitable for use in a steering gear in an electromechanical steering system of a motor vehicle due to the load situation. Examples:

[0031] The invention is illustrated by the following non-limiting examples.

[0032] Two elastomer compounds suitable for use as base materials in drive belts were compared. For the inventive compound (Compound 2), an EPDM rubber was used as the rubber base. It was composed of 48 wt.% of naturally renewable raw materials (here: the ethylene component was made from sugarcane), based on the total weight of the raw rubber. This compound was compared with a reference compound (Compound 1), which comprised a conventional, petroleum-based EPDM rubber. Some characteristics of the rubbers compared are shown in Table 1.

[0033] For this purpose, the ingredients were mixed in a standard kneader according to the quantities listed in Table 2. The mixing time was 360 seconds. The discharge temperature was 115°C. Table 1: Characteristics of the rubbers used Keltan 6950 Keltan ECO 6950 ML 1+4 (100°C), ISO 289 65 MU 65 MU Proportion of ethylene component (%) 48 48 Share of ENB (%) 9 9 Share of bio-based components (%) 0 48 Table 2: Composition of the compounds used (all in phr; parts per hundred rubber) Mixture 1 (reference) Mixture 2 Keltan 6950 100 Keltan ECO 6950 100 Zinc dimethacrylate 25 25 Soot (N550) 30 30 Diplast TM 8-10 10 10 peroxide 9 9 Other additives (anti-aging agents, 14 14 processing aids, etc.)

[0034] To determine the physical properties (Table 3), test specimens were prepared from the compounds. The test specimens were vulcanized in a laboratory press at elevated pressure. The conditions were 180°C for 20 minutes. Hardness tests were conducted according to DIN 53504. Strength, elongation, and stress values ​​were determined according to DIN 53504, DIN 53455, and DIN 53571. Table 3: Physical properties Mixture 1 (reference) Mixture 2 MDR 2000 (180°C) Fa [dNm] 1,77 1,71 Fe [dNm] 45,17 46,95 Fe - Fa [dNm] 43,40 45,24 Mooney ML 1+4 (100°C) 92 87 20 min@180°C Hardness [Shore A] 82 88 Strength [MPa] 16,1 17,9 Elongation [%] 167 179 Stress value 50% [MPa] 4,5 6,7 Stress value 100%[MPa] 9,2 11,7

[0035] The vulcanizate properties of Compound 2 are comparable to or even slightly better than those of the reference compound (hardness, modulus values ​​at 50 and 100%). This results in higher stiffness and a longer service life. The torque peak shows a slightly increased cure yield compared to the reference compound.

[0036] Conventional timing belts were also produced from compounds 1 and 2. The running times for the product (two-pulley drive (41 and 117 teeth) at 120°C) are listed in Table 4 (axle load 167 N; rotational speed 300 rpm; reversing operation; torque 13 Nm). Table 4: Running times on the product 2-disk drive Mixture 1 (reference) Mixture 2 Test temperature 120[°C] Running time [h] 227 213

[0037] The results show that the use of EPDM with 48% bio-based content reduces the ecological footprint of the belt but does not have a negative impact on the mechanical properties.

[0038] The invention will now be explained using exemplary embodiments with reference to schematic drawings.

[0039] Fig. 1 shows the schematic structure of a timing belt.

[0040] Fig.1 shows a drive belt 1 in the form of a toothed belt with a cover layer 2 as the belt back, with several tension strands 3 embedded in the belt longitudinal direction and running parallel, and with a substructure 4. The substructure is provided with a tooth-shaped profile, comprising teeth 5 and toothed webs 6, and comprises the power transmission zone 7.

[0041] The cover layer 2 and the substructure 5 form the base body as a whole unit made of a polymeric material with elastic properties (vulcanized rubber mixture) containing at least one rubber component and mixture ingredients.

[0042] The tensile cords 3 are embedded in the base body without any intermediate layer. Each tensile cord in the cord construction is made of a filament material, for example, glass filaments.

[0043] In particular, the substructure 4 of the drive belt 1 can also contain evenly distributed fibers, in particular textile fibers. The fibers consist of cotton, cellulose, aramid, in particular p-aramid, polyamide, in particular PA6 or PA.6.6, polyvinyl acetal (PVA), or polyethylene terephthalate (PET). The fibers can be in the form of a pulp (fiber slurry) or as short fibers. For short fibers, the length is 8 mm, in particular 6 mm.

[0044] The power transmission zone 7 of the exemplary drive belt 1 is particularly susceptible to wear due to abrasion, heat, and the influence of oils. For this reason, the power transmission zone can advantageously be provided with a coating in the form of a textile overlay 8, for example in the form of a woven, knitted, or warp-knitted fabric. According to the teachings of document WO 2005 / 080821 A1, this textile overlay can, for example, be additionally impregnated with a fluorine-containing plastic, which is in particular polytetrafluoroethylene (PTFE), with a high filler content of this plastic, simultaneously forming a polymer coating (seal) as an additional oil-resistant protective layer 9. The two partial layers 8 and 9, with different functions, act here as a common protective layer.

[0045] The cover layer 2 of the drive belt 1 can also be provided with a coating, for example in the manner described above. List of reference symbols 1 drive belt 2 cover layer as belt back 3 Tension cord 4 Substructure 5 tooth 6 Tooth bar 7 Power transmission zone 8 Coating in the form of a textile overlay (tooth overlay) 9 Protective layer QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] WO 2005 / 080821 A1

[0044]

Claims

[1] Drive belt comprising a base body made of an elastomer, wherein a plurality of tensile strands are arranged in the base body in a longitudinal direction and are enclosed by the elastomer, characterized by that the elastomer is based on a cross-linked rubber which comprises at least one component made from a naturally renewable raw material. [2] Drive belt according to claim 1, characterized by that the rubber comprises at least one ethylene component which is produced from a naturally renewable raw material. [3] Drive belt according to claim 2, characterized by that the rubber is EPDM and / or EPM. [4] Drive belt according to claim 3, characterized by that the EPDM and / or EPM is made from naturally renewable raw materials to an extent of at least 45% by weight based on the total weight of the raw rubber. [5] Drive belt according to one of claims 1 to 4, characterized bythat the rubber is peroxide crosslinked. [6] Drive belt according to one of claims 1 to 5, characterized by that the naturally renewable raw material is a sugar cane plant. [7] Drive belt according to one of the preceding claims, characterized by that the drive belt is a toothed belt. [8] Drive belt according to one of claims 7, characterized by that the tooth pitch is at least 1.5 and at most 14 mm. [9] Drive belt according to claim 7 or 8, characterized by that the drive belt is a helical toothed drive belt, the angle of the helical toothing being between 4° and 8° relative to an axis transverse to the longitudinal direction of the drive belt. [10] Drive belt according to one of claims 1 to 9, characterized by that the tensile strands are constructed from a single twisted yarn made of glass and / or aramid, wherein the twist of the yarn is preferably between 100 and 300 tpm. [11] Drive belt according to one of claims 1 to 10, characterized by that the outer diameter of the tensile strand is less than 2.4 mm.

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