Reinforcement layer for objects made of elastomeric material, preferably for vehicle pneumatic tires, and vehicle pneumatic tires

Abstract

A rubberized reinforcement layer for articles made of elastomeric material, preferably for vehicle pneumatic tires, wherein the reinforcement layer has a plurality of parallel and spaced-apart reinforcing elements, each reinforcing element consisting of at least one twisted multifilament yarn made of polyethylene terephthalate (PET), wherein the multifilament yarn has a yarn count (fineness) of 50 to 1100 dtex and a fineness-related maximum tensile strength of ≥ 70 cN / tex according to ASTM D885-16, and wherein the rubberizing layer has a thickness D, characterized in that the multifilament yarn has an elongation at break of 10 to 20 % according to ASTM D885-16, a crystallinity determined by DSC of 55 to 65 % and a birefringence Δn with 0.21 ≤ Δn ≤ 0.25.

Description

[0001] The invention relates to a rubberized reinforcement layer for objects made of elastomeric material, preferably for vehicle tires, wherein the reinforcement layer comprises a plurality of parallel and spaced-apart reinforcing elements, each reinforcing element consisting of at least one twisted multifilament yarn made of polyethylene terephthalate (PET), the multifilament yarn having a yarn count (fineness) of 50 to 1100 dtex and a fineness-related maximum tensile strength of ≥ 70 cN / tex according to ASTM D885-16, and wherein the rubber coating has a thickness D. The invention further relates to a vehicle tire containing this reinforcement layer.

[0002] Reinforcing layers for objects made of elastomeric material, such as technical rubber products and vehicle tires, are of paramount importance and are generally well-known to those skilled in the art. These reinforcing layers comprise a multitude of reinforcing, thread-like elements, known as reinforcing elements. These are completely embedded in elastomeric material. The reinforcing elements of these layers can take the form of, for example, woven fabrics or calendered, endlessly wound reinforcing strands.

[0003] The rubberized reinforcement layers of suitable size and design are joined with other components to form a technical rubber product or a vehicle tire. The rubberized reinforcement layers strengthen the product in question.

[0004] A wide variety of materials can be used as reinforcing layers in rubber products. Examples include steel or textile reinforcing layers. In the rubber industry, textile reinforcing layers such as rayon or polyester are commonly used.

[0005] For the carcass of passenger car tires, so-called HMLS polyester yarns have become established as the primary reinforcing material. These yarns are produced by spinning industrial polyester yarns under high tension and are characterized by a high modulus and low shrinkage. HMLS polyester multifilament yarns with a yarn count (fineness) of 1440 dtex are frequently used in the carcass of passenger car tires. Yarns with this count have a relatively large diameter. This has the disadvantage of increasing the calendered ply thickness within the tire. This, in turn, leads to greater heat buildup during tire operation when these plies are subjected to flexural forces. This heat buildup results in a reduction in high-speed performance and rolling resistance.

[0006] From EP 0 908 329 B1, it is known to provide rubberized reinforcement layers for the carcass of pneumatic vehicle tires with textile cords made of synthetic multifilament yarns of the polyester types PET (polyethylene terephthalate) or PEN (polyethylene naphthalate). Due to the yarn count used and their construction, the textile cords are comparatively thin, resulting in a relatively thin rubberized reinforcement layer. This has the advantage that less rubber material is required to rubberize these reinforcement layers, thus saving on material costs. Furthermore, a thin rubberized reinforcement layer in the product, for example in a vehicle tire, reduces the tire's weight. At the same time, the reduced material thickness results in lower hysteresis, which has a positive effect on the tire's rolling resistance.

[0007] Reinforcing layers according to the preamble of claim 1, as well as methods for their production, are known, for example, from CN 104494169. The multifilament yarns used therein have a tensile strength of 500 to 1000 D and a modulus of 105 to 120 mN / dtex. Further relevant prior art is disclosed in WO 2009 / 123 414 A2, EP 2 660 370 B1, and US 2015 / 0 328 928 A1.

[0008] The invention is based on the objective of providing a rubberized reinforcement layer which, while possessing sufficient strength, is further optimized with regard to its heat build-up in the resulting rubber products.

[0009] The problem is solved by the multifilament yarn having an elongation at break of 10 to 20 % according to ASTM D885-16, a crystallinity determined by DSC of 55 to 65 % and a birefringence Δn of 0.21 ≤ Δn ≤ 0.25.

[0010] The term "multifilament yarn" refers to a multifilament yarn that is twisted and thus has the construction x1 as a strength carrier and which has already undergone the process of hot drawing including impregnation.

[0011] Multifilament yarns with the aforementioned properties can be used to produce rubberized reinforcement layers that exhibit high overall strength despite their very small diameter. The interplay of birefringence and crystallinity leads to greater yarn orientation, which appears to result in increased strength. This allows for further improvement in heat dissipation in rubber products manufactured with these reinforcement layers. The even thinner multifilament yarns enable a further reduction in the amount of rubber material required. In addition to saving on material costs, this results in a thinner rubber layer, which, for example, when used as a carcass ply in pneumatic tires, leads to weight reduction and significantly lower heat build-up under flexing and centrifugal forces. The latter has a positive effect on rolling resistance and high-speed performance.

[0012] The reinforcement layer according to the invention fulfills the requirements for use, particularly in vehicle tires, especially with regard to breaking strength, modulus of elasticity, fatigue resistance and elongation at break.

[0013] The multifilament yarn for the reinforcement layer according to the invention is produced in such a way that a raw yarn is spun without any twisting, which is then twisted in a twisting machine.

[0014] The multifilament yarn is converted into a fabric suitable for calendering by following steps known to the expert: - the twisting of the multifilament yarn(s) to create the desired reinforcement structure - the production of a fabric containing the desired strengthening agent - the activation of the rubber adhesion of the fabric, for example by means of an RFL dip carries out.

[0015] It is advantageous if the multifilament yarn has a yarn count (fineness) in the range of 420 dtex to 1100 dtex. In this way, particularly thin reinforcement layers can be achieved in combination with the high tensile strength. In particular, advantages are gained with regard to the fatigue properties of a vehicle tire that uses the reinforcement layer according to the invention as a carcass layer, as well as with regard to the process capability of manufacturing the reinforcement layers.

[0016] For use in articles made of elastomeric material that are regularly vulcanized, it has proven advantageous if the multifilament yarn exhibits a heat shrinkage of less than 4% at 180 °C under a prestress of 0.1 cN / dtex for a 2-minute exposure time. This ensures that the vulcanization of the products has very little impact on the multifilament yarn within the product.

[0017] According to a preferred embodiment of the invention, the multifilament yarn exhibits an elongation at break of 10 to 15% according to ASTM D885-16. A pneumatic tire with such a reinforcing layer as a carcass ply is more fatigue-resistant, even under extreme conditions such as curb impacts.

[0018] For rubber products, especially vehicle tires, it has proven advantageous if the fineness-related rubber thickness GD is calculated according to the following formula GD = Rubber thickness D * (Fineness / Breaking strength) The tensile strength of the rubberized reinforcement layer ranges between 1.0 mm*g / (m*cN) and 3.2 mm*g / (m*cN), with the breaking strength being determined according to ASTM D885-16. With such reinforcement layers, particularly good results have been achieved in vehicle tires with regard to rolling resistance and high-speed suitability.

[0019] It is also advantageous if the reinforcing element is a textile cord consisting of at least two polyethylene terephthalate multifilament yarns twisted together, which is preferably arranged in the reinforcement layer at a density of at least 130 epdm.

[0020] “epdm” means ends per decimeter and describes, in a manner customary for experts, the cord density in the reinforcement layer.

[0021] It is advantageous if the polyethylene terephthalate multifilament yarns have a twist of 395 tpm (turns per meter) to 620 tpm and if the textile cord has an end twist of 395 tpm to 620 tpm. The twist factor α should therefore be between 185 and 205. The twist factor α is defined as α = Twist [t / m] * (Fineness [tex] / 1000) 1 / 2 The multifilament yarns can be S- or Z-twisted, while the end twist is opposite to the multifilament yarn twist.

[0022] Reinforcement layers with textile cords made of polyethylene terephthalate multifilament yarn with a construction of 550 dtex x2 to 1100 dtex x2 have proven particularly suitable. These textile cords are very thin and exhibit very high fatigue resistance.

[0023] The invention is solved with respect to the vehicle pneumatic tire by providing it with a previously described rubberized reinforcement layer.

[0024] The reinforcement layer here is in particular a carcass and / or a bead reinforcement.

[0025] The invention will be explained in more detail below using exemplary embodiments, without, however, being limited to these.

[0026] In a preferred embodiment of the invention, the reinforcement layer is used as the carcass (carcass ply) for passenger car pneumatic tires. The reinforcement layer is a rubberized fabric which, as a strengthening element, comprises textile cords made of two twisted polyethylene terephthalate multifilament yarns of construction 550 x 2 with a density of 175 epdm. The multifilament yarns each have a twist of 580 tpm, and the respective textile cord has an end twist in the opposite direction of rotation of 580 tpm. The multifilament yarns have a tensile strength of 72.7 cN / tex according to ASTM D885-16, and the rubber thickness is 0.80 mm. The rubber thickness (GD) is 1.1 mm*g / (m*cN). The elongation at break is 13.5% according to ASTM D885-16. The multifilament yarn has a crystallinity of 56.6% and a birefringence of 0.210.

[0027] Crystallinity was determined by differential scanning calorimetry (DSC) using an instrument from TA Instruments. In a first heating cycle, 2 to 5 mg of the multifilament yarn were heated from room temperature to 300 °C at a rate of 10 K per minute. They were then cooled from 300 °C to room temperature at a rate of 10 K per minute and subsequently heated again from room temperature to 300 °C at a rate of 10 K per minute. Crystallinity was determined based on the latent heat of fusion of the polymer and expressed as a percentage of the latent heat of fusion of a 100% crystalline sample of the same material.

[0028] The birefringence was determined using a polarizing microscope (Olympus BX50) with a Berek compensator. The sample was placed diagonally in the instrument, and the degree of rotation was measured as it was turned clockwise and counterclockwise until the sample appeared darkest. The difference in rotation was divided by 2 to obtain the tilt angle. Using a reference table, the optical path difference γ in nm was determined from the tilt angle. The birefringence was calculated using the formula Δn = (optical path difference γ / thickness d), with the sample thickness being determined using an eyepiece micrometer.

[0029] The passenger car pneumatic tire equipped with this reinforcement layer as a carcass layer is characterized by high high-speed suitability and the rolling resistance could be reduced by approximately 2% compared to a tire with a conventional PET carcass layer.

[0030] The following Table 1 provides an overview of the parameters of PET textile cords of the aforementioned construction as well as the tires produced from them with the determined rolling resistance. Table 1 Example / Parameters 1 Comparison material PET PET Cord construction 550x2 1100x2 Yarn titer [dtex] 550 1100 Rotations [tpm] 580 410 Diameter [mm] 0,38 0,54 Maximum tensile strength related to fineness [cN / tex] 72,7 62,7 Rubber coating thickness [mm] 0,80 0,95 Fineness-related rubber coating thickness [mm*g / (m*cN)] 1,1 3,3 Elongation at break [%] 13,5 14,7 Crystallinity [%] 56,6 52,2 Birefringence [-] 0,21 0,20 Tires Cord density [epdm] 175 110 Rolling resistance [%] 102 100

[0031] A rolling resistance of 100% corresponds to the reference. Rolling resistances > 100% indicate a reduced (improved) rolling resistance, while rolling resistances < 100% indicate an increased (worsened) rolling resistance.

[0032] Table 2 below shows the properties of PET textile cords with identical cord construction (1100x2). Table 2 Example / Parameters 2 Comparison material PET PET Cord construction 1100x2 1100x2 Yarn titer [dtex] 1100 1100 Rotations [tpm] 410 410 Diameter [mm] 0,54 0,54 Maximum tensile strength related to fineness [cN / tex] 72,7 62,7 Rubber coating thickness [mm] 0,95 0,95 Fineness-related rubber coating thickness [mm*g / (m*cN)] 2,8 3,3 Elongation at break [%] 14,4 14,7 Crystallinity [%] 56,0 52,2 Birefringence [-] 0,21 0,20

[0033] With the same cord construction, the maximum tensile strength per unit of fineness is higher, which is also reflected in the higher crystallinity and birefringence. This makes it possible to switch to thinner cord diameters. The thickness of the rubber coating per unit of fineness is reduced in the reinforcement layer according to the invention.

Claims

[1] Rubberized reinforcement layer for articles made of elastomeric material, preferably for vehicle pneumatic tires, wherein the reinforcement layer has a plurality of parallel and spaced-apart reinforcing elements, each reinforcing element consisting of at least one twisted multifilament yarn made of polyethylene terephthalate (PET), wherein the multifilament yarn has a yarn count (fineness) of 50 to 1100 dtex and a fineness-related maximum tensile strength of ≥ 70 cN / tex according to ASTM D885-16, and wherein the rubberizing layer has a thickness D, characterized by , that the multifilament yarn has an elongation at break of 10 to 20 % according to ASTM D885-16, a crystallinity determined by DSC of 55 to 65 % and a birefringence Δn of 0.21 ≤ Δn ≤ 0.

25. [2] Reinforcement layer according to claim 1, characterized by , that the multifilament yarn has a yarn titer (fineness) of 420 dtex to 1100 dtex. [3] Reinforcement layer according to claim 1 or 2, characterized by that the multifilament yarn exhibits a heat shrinkage of less than 4% at 180°C under a prestress of 0.1 cN / dtex for 2 min exposure time. [4] Reinforcement layer according to at least one of the preceding claims, characterized by that the multifilament yarn has an elongation at break of 10 to 15% according to ASTM D885-16. [5] Reinforcement layer according to at least one of the preceding claims, characterized by , that it has a fineness-related rubber thickness GD calculated according to the following formula GD = rubber thickness D*(fineness / breaking strength) between 1.0 mm*g / (m*cN) and 3.2 mm*g / (m*cN), where the breaking strength is determined according to ASTM D885-16. [6] Reinforcement layer according to at least one of the preceding claims, characterized bythat the reinforcing element is a textile cord consisting of at least two polyethylene terephthalate multifilament yarns twisted together and that the reinforcing elements are arranged in this reinforcement layer at a density of at least 130 epdm. [7] Reinforcement layer according to claim 6, characterized by , that the multifilament yarns have a twist of 395 tpm to 620 tpm and that the textile cord has an end twist of 395 tpm to 620 tpm. [8] Reinforcement layer according to claims 6 to 7, characterized by , that the textile cord has a construction of 550 dtex x2 to 1100 dtex x2. [9] Vehicle pneumatic tire comprising at least one reinforcement layer according to at least one of the preceding claims. [10] Vehicle pneumatic tires according to claim 9, characterized by that the reinforcement layer is a carcass and / or a bead reinforcement.