Repair patch for elastic elements with improved adhesive layer

Abstract

A repair patch for an elastomeric element, in particular for a vehicle tire, its use and a method for bonding a repair patch to an elastomeric element. The repair patch (1) comprises a top layer (10), a bonding layer (30) for covering a wall (80) of the elastomeric element (40) and at least one intermediate layer (20) arranged between the bonding layer (30) and the top layer (10), wherein the bonding layer (30) has a first natural rubber component and a second natural rubber component before vulcanization together with the elastomeric element (40), wherein the first natural rubber component has a lower molecular weight Mw than the second natural rubber component, whereby the mixture of the first natural rubber component and the second natural rubber component has a bimodal molecular weight distribution.

Description

TECHNICAL FIELD

[0001] The present invention relates to a repair patch for an elastomeric element, in particular for a vehicle tire; the use of said repair patch for repairing a damaged vehicle tire; and a method for bonding said repair patch to an elastomeric element. In particular, said repair patch comprises a bonding layer having a mixture of a first natural rubber component and a second natural rubber component, wherein said mixture has a bimodal molecular weight distribution, prior to vulcanization. BACKGROUND

[0002] Generally, in the case of a small perforation on the surface area of a vehicle tire, the repair of a damaged vehicle tire is carried out by means of a so-called combo repair body. On the other hand, in the case of a larger damage on the circumferential or sidewall area, the damaged area is repaired and the so-called funnel resulting from this procedure is filled with green rubber. Subsequently, the broken reinforcement elements in the damaged area are covered by means of a repair patch, which in turn contains corresponding reinforcement elements. Since the power flow in the vehicle tire and in the reinforcement elements of the repair patch has to be transmitted through the rubber layer between both, high demands are placed on the firm and durable bond, in particular on the bonding layer between the vehicle tire and the repair patch.

[0003] In the known methods for bonding a repair patch to a vehicle tire, two elements are required to produce a durable bond between the repair patch and the vehicle tire, namely an adhesive and the bonding layer of the repair patch mentioned above.

[0004] The adhesive is generally composed of natural rubber dissolved in a solvent, resins and accelerators required for the reaction, in particular the vulcanization reaction.

[0005] In the known repair methods for vehicle tires, the repair patch is generally cleaned and roughened before the repair patch is applied in order to produce an active surface with a high structure. The next step is to apply the adhesive to the repair area. Subsequently, the solvent of the adhesive has to be evaporated. Then, the repair patch is placed on the repair area and pressed onto the repair area. Depending on the method chosen, vulcanization is then carried out at room temperature and without pressure, or by applying pressure and temperature using suitable equipment, for example in an autoclave or in a hot press. The main disadvantage of this method is the time required for the evaporation of the solvent.

[0006] Generally, the known adhesives are based on organic solvents, which pose a risk to the environment and the health of the user. In various countries, some of these solvents can no longer be used for repairing rubber components for this reason.

[0007] Furthermore, since the adhesion of the repair patch depends to a large extent on the degree of evaporation, there are high demands on the evaporation of the solvent. If the drying time of the adhesive is too long, then sufficient adhesion cannot be achieved (overdrying). On the other hand, if the drying or evaporation time is too short, then there is still too much solvent on the repair area, so that even the adhesion of the repair patch cannot be guaranteed, since the solvent remaining in the repair area leads to the formation of bubbles, especially in the case of temperature vulcanization. When flammable solvents are used, additional measures are required to prevent ignition, for example by means of vacuum suction and ventilation.

[0008] The adhesive layer of the repair patch is usually made of plasticized natural rubber and resin and does not contain accelerators. The properties of the conventional adhesive layer are usually sufficient for standard applications. However, the development in the field of elastic elements, in particular in the field of vehicle tires, will of course also influence the requirements that will be placed on repair patches in the future. For example, during the repair, the rough structure of the casing or even of the damaged area can differ significantly depending on the manufacturer or the area of application.

[0009] It is therefore the task of the present application to provide a repair patch and a method for bonding the repair patch to an elastic element, which make it possible to variably adjust the properties of the adhesive layer, in particular the adhesion strength and the load strength, depending on the application. SUMMARY

[0010] According to the application, the repair patch for elastic elements, in particular for vehicle tires, comprises a top layer, an adhesive layer for covering the wall of the elastic element and at least one intermediate layer arranged between the adhesive layer and the top layer.

[0011] According to the application, the adhesive layer has a first natural rubber component and a second natural rubber component before vulcanization with the elastic element, wherein the first natural rubber component has a lower molecular weight Mw than the second natural rubber component, whereby the mixture of the first natural rubber component and the second natural rubber component has a bimodal molecular weight distribution. Thus, the adhesion strength of the adhesive layer can advantageously be adjusted by means of the first natural rubber component, while the load strength of the adhesive layer can be adjusted by the second natural rubber component.

[0012] In this context, bimodal means a distribution having two modes or two maxima. The bimodal distribution can be symmetric and asymmetric. According to the present application, the bimodal molecular weight distribution (molar mass distribution) is generated by the proportional superposition of two corresponding unimodal (one mode, one maximum) molecular weight distributions of the first and the second natural rubber component. Thus, the maximum of the unimodal molecular weight distribution of the first natural rubber component is at a lower molecular weight than the maximum of the unimodal molecular weight distribution of the second natural rubber component. In other words, according to the present application, the first natural rubber component has a maximum of the unimodal molecular weight distribution at a lower molecular weight than the maximum of the unimodal molecular weight distribution of the second natural rubber component.

[0013] The values given herein refer to the so-called mass average Mw. Thus, the bimodal molecular weight distribution is correspondingly described by the weight proportion distribution depending on the molecular weight.

[0014] According to the present application, natural rubber is used in the adhesive layer. Structurally, natural rubber is cis-1,4-polyisoprene, which is formed by polymerization of isoprene monomers:

[0015]

[0016] Natural rubber belongs to the so-called elastomer family. Elastomers are wide-meshed polymers that exhibit rubber-elastic behavior. Elastomers can be crosslinked directly during polymerization or later by vulcanization.

[0017] In one preferred embodiment, the first natural rubber component has a molecular weight of Mw = 1 x 10 6 g / mol. In another preferred embodiment, the second natural rubber component has a molecular weight of Mw = 2 x 10 6 g / mol. In both embodiments, the molecular weight can be determined by diffusion-sedimentation and / or permeation. In particular, according to the present application, commercially available products having the respective molecular weight can be used. For example, commercially available natural rubber having a constant low viscosity, which is generally formed by cutting rubber tree sap from trees to form a latex, precipitating it with acid to form rubber crumbs and pressing to form rubber bales, can be used as the first natural rubber component. For example, natural rubber having a constant higher viscosity, such as RSS type 1 or RSS type 3 rubber, can be used as the second natural rubber component.

[0018] Since natural rubber as a natural product contains an insoluble gel component, the molecular weight of natural rubber is generally difficult to determine. Alternatively or additionally, a so-called Mooney viscosity can be used for characterization. In this case, two polymers of the same type which differ significantly in Mooney viscosity can also be clearly distinguished by molecular weight. In a preferred embodiment, the Mooney viscosity of the first natural rubber component and the second natural rubber component can thus differ by a factor of at least 2. In a particularly preferred embodiment, the Mooney viscosity ML=1+4 / 100°C of the first natural rubber component can be 35-40 MU. In another preferred embodiment, the Mooney viscosity ML=1+4 / 100°C of the second natural rubber component can be 70-90 MU. The Mooney viscosity can be determined, for example, in accordance with DIN 53523.

[0019] According to the application, it is of no significance whether the first natural rubber component and / or the second natural rubber component is a single natural rubber or a mixture of natural rubbers, wherein in each case the molecular weight Mw is in the low or high range, respectively. In a preferred embodiment, however, the first natural rubber component and / or the second natural rubber component can comprise a mixture of natural rubbers. In another preferred embodiment, the first natural rubber component and / or the second natural rubber component can comprise a single natural rubber.

[0020] According to the application, the ratio of the first natural rubber component to the second natural rubber component in the mixture is not limited. In a preferred embodiment, the proportion of the first natural rubber component can be 25-50% by weight, based on the total mass of the first natural rubber component and the second natural rubber component, and the proportion of the second natural rubber component can be 50-75% by weight, based on the total mass of the first natural rubber component and the second natural rubber component. It is particularly preferred that the proportion of the first natural rubber component can be 35-45% by weight and the proportion of the second natural rubber component can be 55-65% by weight. It is even more preferred that the proportion of the first natural rubber component can be 44% by weight and the proportion of the second natural rubber component can be 56% by weight. Thus, it can be advantageously ensured at the same time that good adhesive strength and improved load strength.

[0021] Furthermore, in a preferred embodiment, the adhesive layer can additionally comprise a filler system comprising 5-15% precipitated silica, 20-30% silica and a colorant. Furthermore, in another preferred embodiment, the adhesive layer can comprise at least 2% sulfur. In each case, the proportions correspond to the percentage by weight based on the total mass of the adhesive layer. During vulcanization, the sulfur may, for example, crosslink the first natural rubber component and the second natural rubber component:

[0022]

[0023] In another preferred embodiment, a removable protective film can also be provided to protect the adhesive layer from contamination prior to use.

[0024] In another preferred embodiment, the intermediate layer can comprise a plurality of fibrous inserts arranged in a substantially structured manner.

[0025] According to the present application, the above-mentioned repair patch can be used to repair a damaged vehicle tire.

[0026] According to the present application, the method for bonding the above-mentioned repair patch to an elastic element comprises the steps of preparing an adhesive layer comprising a first natural rubber component and a second natural rubber component, wherein the first natural rubber component has a lower molecular weight Mw than the second natural rubber component, whereby the mixture of the first natural rubber component and the second natural rubber component has a bimodal molecular weight distribution. According to the present application, the adhesive layer is prepared by (a) homogenizing the second natural rubber component in a closed mixer; (b) stripping the second natural rubber component; and (c) mixing the first natural rubber component with the homogenized second natural rubber component. The method according to the present application further comprises the steps of providing an elastic element; applying the repair patch to the elastic element, in particular at the repair area, via the adhesive layer; and vulcanizing the repair patch to the elastic element.

[0027] In a preferred embodiment, in step c) of manufacturing the adhesive layer, the first natural rubber component and the homogenized second natural rubber component can be additionally mixed with at least 2% of sulfur and a filler system comprising 5-15% of precipitated silica, 20-30% of silica, and a colorant. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 Schematically shows a cross-sectional view of a repair patch for a vehicle tire according to one embodiment.

[0029] Figure 2 Schematically shows a bimodal molecular weight distribution resulting from the superposition of two unimodal molecular weight distributions of a first natural rubber component and a second natural rubber component.

[0030] Figure 3 Shows a block diagram of a part of a method for bonding a repair patch to an elastic element according to one embodiment.

[0031] Figure 4 Shows a bar chart of different adhesive strengths of adhesive layers with natural rubber in unimodal and bimodal molecular weight distribution.

[0032] Figure 5 Shows a bar chart related to the structural resistance of adhesive layers with natural rubber in unimodal and bimodal molecular weight distribution. DETAILED DESCRIPTION

[0033] Examples or embodiments of the present application are schematically described below with reference to the accompanying drawings. It should be noted, however, that the application is in no way limited to or by the examples of the embodiments described below and their features, but also encompasses modifications of the examples of the embodiments, in particular those covered by a modification of the features of the described examples or a combination of individual or multiple features of the described examples within the scope of protection of the claims.

[0034] Referring to Figure 1 , a repair patch 1 according to the present application for a vehicle tire is schematically shown. A top layer 10 is formed on the upper surface of the repair patch 1 and does not have a ready tack before and after repair. An intermediate layer 20 is formed adjacent to the top layer 10. In a preferred embodiment, the intermediate layer 20 can include a plurality of fiber inserts 70. These inserts 70 can be arranged in one or more layers within the thickness of the intermediate layer 20 and each individual layer can have a structural arrangement of fiber inserts 70. The orientation of the individual layers in the intermediate layer 20 can differ from one another. In particular, in the case of a severe damage in the tread or sidewall area, these inserts 70 can serve to bridge the broken reinforcement in the damaged area.

[0035] A bonding layer 30 is formed underneath the repair patch 1 and is in contact with the wall 80 of the vehicle tire during and after repair. Furthermore, the bonding layer 30 is also in contact with the green rubber composition 50 before and after vulcanization of the vehicle tire. The bonding layer 30 and its particular properties will be described in more detail below with reference to Figure 2 Detailed Description.

[0036] As part of the repair of the damaged vehicle tire, the damaged area of the vehicle tire is roughened to remove dust and dirt and to expose the undamaged layer of the components contained within the vehicle tire, thereby forming a generally conical shape of the repair area 60 in the vehicle tire. Next, the repair area 60 is filled with the green rubber composition 50, followed by the vulcanization of the bonding layer 30.

[0037] Next, the repair patch 1 is placed on the repair area 60, the repair patch being dimensioned such that the repair area 60 is completely covered thereby. Furthermore, the repair patch 1 is also dimensioned such that the tire wall 80 is sufficiently covered by the bonding layer 30 for stable bonding. The repair patch 1 can be, for example, preheated to an appropriate joining temperature.

[0038] After the application of the repair patch 1 to the tire, the repair area 60 and the repair patch 1 are vulcanized under pressure and temperature by means of suitable devices or in an autoclave.

[0039] In a preferred embodiment, a removable protective film can also be provided to protect the bonding layer 30 from contamination before use.

[0040] The structure of a vehicle tire is shown exemplarily for the side wall region of a radial truck tire, so that the wall 80 of the vehicle tire is formed by an inner liner 90, an adjacent carcass 100 having cords 120 in the form of inserts. A side wall rubber 110 of the vehicle tire is adjacent to the carcass 100.

[0041] Referring to Figure 2 , a bimodal molecular weight distribution (solid line) resulting from the superposition of two unimodal molecular weight distributions (dashed lines) corresponding to a first natural rubber component (dashed line) and a second natural rubber component (dashed line) is shown schematically. As indicated by the position of the maximum, the first natural rubber component has a lower molecular weight Mw than the second natural rubber component, as indicated by the position of the maximum. Figure 2 Both the first natural rubber component and the second natural rubber component have a unimodal molecular weight distribution. This results from the fact that natural rubber generally always has a certain molecular weight distribution, wherein the width of the curve can indicate the purity or quality of the natural rubber.

[0042] If the first natural rubber component and the second natural rubber component are now mixed together, a bimodal molecular weight distribution results from the superposition of the two unimodal molecular weight distributions corresponding to the mixing ratio. The position of the two maxima in the bimodal molecular weight distribution is also determined by the difference of the maxima of the unimodal molecular weight distributions. If, for example, the maxima of the two unimodal molecular weight distributions are close to each other, i.e. if the first natural rubber component has a molecular weight close to that of the second natural rubber component, this is also reflected in the bimodal distribution. The same applies in the opposite case. According to the present application, the bimodal molecular weight distribution is therefore bimodal, as soon as two maxima can be distinguished. In one preferred embodiment, however, the first natural rubber component can have a molecular weight Mw = 1 x 10 6 g / mol. In another preferred embodiment, the second natural rubber component can have a molecular weight Mw = 2 x 10 6 g / mol. In both embodiments, the molecular weight can be determined by diffusion sedimentation and / or permeation.

[0043] Since natural rubber as a natural product contains an insoluble gel component, the molecular weight of natural rubber is generally difficult to determine. Alternatively or additionally, a so-called Mooney viscosity can thus be used for characterization. In one preferred embodiment, the Mooney viscosity of the first natural rubber component and the second natural rubber component can thus differ by a factor of at least 2. In one particularly preferred embodiment, the Mooney viscosity ML = 1 + 4 / 100°C of the first natural rubber component can be 35 to 40 MU. In another preferred embodiment, the Mooney viscosity ML = 1 + 4 / 100°C of the second natural rubber component can be 70 to 90 MU. The Mooney viscosity can be determined, for example, in accordance with DIN 53523.

[0044] Also asFigure 2 As shown in the middle, the adhesion strength of the adhesive layer can be adjusted by the proportion of the first natural rubber component, while the load strength can be adjusted by the second natural rubber component. According to the present application, the proportion of the first natural rubber component to the second natural rubber component in the mixture is not limited. However, in a preferred embodiment, the proportion of the first natural rubber component can be 25 to 50% by weight, based on the total mass of the first natural rubber component and the second natural rubber component, and the proportion of the second natural rubber component can be 50 to 75% by weight, based on the total mass of the first natural rubber component and the second natural rubber component. It is particularly preferred that the proportion of the first natural rubber component can be 35 to 45% by weight, and the proportion of the second natural rubber component can be 55 to 65% by weight. Even more particularly preferred is that the proportion of the first natural rubber component can be 44% by weight, and the proportion of the second natural rubber component can be 56% by weight. However, it is advantageous to place more emphasis on the adhesion strength, and therefore, the proportion of the first natural rubber component should be selected so that the adhesion strength is high even in the case of improved load strength.

[0045] According to the present application, it does not matter whether the first natural rubber component and / or the second natural rubber component is a single natural rubber or a mixture of natural rubbers. As mentioned above, a natural rubber that is considered a single component always has a certain molecular weight distribution. However, the same applies to the case of a mixture of two or more individual natural rubbers, which can be prepared to have a corresponding unimodal molecular weight distribution. Therefore, in a preferred embodiment, the first natural rubber component and / or the second natural rubber component can include a mixture of natural rubbers. In another preferred embodiment, the first natural rubber component and / or the second natural rubber component can include a single natural rubber.

[0046] Furthermore, in a preferred embodiment, the adhesive layer 30 can additionally include a filler system containing 5 to 15% of precipitated silica, 20 to 30% of silica, and a colorant, in addition to the first natural rubber component and the second natural rubber component.

[0047] Furthermore, in another preferred embodiment, the adhesive layer can contain at least 2% of sulfur. During vulcanization, the first natural rubber component and the second natural rubber component can thereby be crosslinked by sulfur bridges.

[0048] Referring to Figure 3 , the following describes a part of a method for bonding a repair patch to an elastic element according to an embodiment. As Figure 3As shown, in order to manufacture a bonding layer comprising a first natural rubber component and a second natural rubber component, wherein the first natural rubber component has a lower molecular weight Mw than the second natural rubber component, whereby the mixture of the first natural rubber component and the second natural rubber component has a bimodal molecular weight distribution, in step S101 the second natural rubber component is first homogenized in a closed mixer. After homogenization, in step S102 the second natural rubber component is removed from the closed mixer. Subsequently, the now homogenized second natural rubber component is mixed with the first natural rubber component. According to Figure 3 As shown in the embodiment described in the paragraph, in step S103 the homogenized second natural rubber component can be mixed with the first natural rubber component, the filler system described above and at least 2% of sulfur.

[0049] Reference is made to Figure 3 The steps described are part of a method according to the present application, which further comprises the steps of providing an elastic element; applying the repair patch to the elastic element via the bonding layer, in particular at the repair region; and vulcanizing the repair patch to the elastic element.

[0050] The advantages of the present application will now be explained with reference to Figure 4 and 5 The repair patch and method described herein allow for tailoring the properties of the bonding layer based on the bimodal molecular weight distribution of the two natural rubber components, according to the compatibility of the repair patch with different rough structures of different casings or damaged regions. From Figure 4 and 5 It can be seen that the mixture of the first natural rubber component and the second natural rubber component having a bimodal molecular weight distribution not only exhibits an improved adhesion strength compared to the corresponding unimodal distribution of the natural rubber components, but also at the same time an improved structural resistance. In other words, the bonding layer having a bimodal molecular weight distribution by mixing the first natural rubber component and the second natural rubber component shows an improved ability to bond to rough surfaces due to the proportion of low molecular weight natural rubber, while an increase in the structural resistance of the bonding layer can be achieved due to the proportion of high molecular weight natural rubber, thereby resulting in an improvement in durability.

[0051] List of reference signs

[0052] 1 repair patch

[0053] 10 top layer

[0054] 20 intermediate layer

[0055] 30 bonding layer

[0056] 40 elastic element

[0057] 50 raw rubber composition

[0058] 60 repair region

[0059] 70 fiber insert

[0060] 80 wall

[0061] 90 inner liner

[0062] 100 carcass

[0063] 110 sidewall rubber of a vehicle tire

[0064] 120 cord

Claims

1. A repair patch (1) for an elastic element (40), said elastic element being a vehicle tire, said repair patch comprising: a top layer (10), a bonding layer (30) for covering a wall (80) of said elastic element (40), and at least one intermediate layer (20) arranged between said bonding layer (30) and said top layer (10), wherein said bonding layer (30) has a first natural rubber component and a second natural rubber component before being vulcanized together with said elastic element (40), wherein said first natural rubber component has a lower molecular weight Mw than said second natural rubber component, whereby a mixture of said first natural rubber component and said second natural rubber component has a bimodal molecular weight distribution, wherein the adhesion strength of said bonding layer (30) is adjusted by means of said first natural rubber component, the load strength of said bonding layer (30) is adjusted by means of said second natural rubber component.

2. The repair patch (1) according to claim 1, wherein the Mooney viscosity of said first natural rubber component and said second natural rubber component differs by at least a factor of 2.

3. The repair patch (1) according to claim 2, wherein the Mooney viscosity ML=1+4 / 100°C of said first natural rubber component is 35 to 40 MU.

4. The repair patch (1) according to claim 2 or 3, wherein the Mooney viscosity ML=1+4 / 100°C of said second natural rubber component is 70 to 90 MU.

5. The repair patch (1) according to any one of claims 1 to 3, wherein said first natural rubber component and / or said second natural rubber component consists of a mixture of natural rubbers.

6. The repair patch (1) according to any one of claims 1 to 3, wherein said first natural rubber component and / or said second natural rubber component consists of a single natural rubber.

7. The repair patch (1) according to any one of claims 1 to 3, wherein said first natural rubber component has a molecular weight of Mw = 1 x 10 6 g / mol, and wherein the molecular weight is determined by diffusion- sedimentation and / or permeation.

8. The repair patch (1) according to any one of claims 1 to 3, wherein The second natural rubber component has a molecular weight of Mw = 2 x 10 6 g / mol, and wherein the molecular weight is determined by diffusion- sedimentation and / or permeation.

9. The repair patch (1) according to any one of claims 1 to 3, wherein the proportion of said first natural rubber component is 25 to 50 weight-% based on the total mass of said first natural rubber component and said second natural rubber component, and the proportion of said second natural rubber component is 50 to 75 weight-% based on the total mass of said first natural rubber component and said second natural rubber component.

10. The repair patch (1) according to any one of claims 1 to 3, wherein said bonding layer (30) additionally comprises a filler system containing 5 to 15% precipitated silica, 20 to 30% silica and a colorant.

11. The repair patch (1) according to any one of claims 1 to 3, wherein said bonding layer (30) comprises at least 2% sulfur.

12. The repair patch (1) according to any one of claims 1 to 3, wherein a removable protective film is provided which protects said bonding layer (30) from contamination before use.

13. The repair patch (1) according to any one of claims 1 to 3, wherein the intermediate layer (20) comprises a plurality of fibrous inserts (70) arranged in a substantially structured manner.

14. Use of a repair patch (1) according to any one of claims 1 to 13 for repairing a damaged vehicle tire.

15. A method for bonding a repair patch (1) according to any one of claims 1 to 13 to an elastic element (40), the method comprising the steps of: preparing a bonding layer (30) comprising a first natural rubber component and a second natural rubber component, wherein the first natural rubber component has a lower molecular weight Mw than the second natural rubber component, whereby a mixture of the first natural rubber component and the second natural rubber component has a bimodal molecular weight distribution: (a) homogenizing the second natural rubber component in a closed mixer (S101); (b) stripping the second natural rubber component (S102); and (c) mixing the first natural rubber component with the homogenized second natural rubber component (S103); providing the elastic element (40); applying the repair patch (1) to the elastic element (40), in particular at a repair region (60), via the bonding layer (30); and vulcanizing the repair patch (1) to the elastic element (40).

16. The method according to claim 15, wherein in step c) of preparing the bonding layer, the first natural rubber component and the homogenized second natural rubber component are additionally mixed with at least 2% of sulfur and a filler system comprising 5 to 15% of precipitated silica, 20 to 30% of silica and a colorant.

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