Hydraulic hose

The invention relates to a hydraulic hose.

Conventional hydraulic hoses, which are used for transporting hydraulic liquids or gas (eg. steam), have a limited lifetime because of hose failures due to e.g. pressure, pressure changes , temperature, aging, movement , abrasion, fluid aggressiveness etc . The hose failures mostly start with micro-sized cracks and surface defects of the elastomeric material used for the innermost layer tube, which is in contact with the hydraulic liquid or gas .

It is an object of at least one embodiment of the present invention to provide a hydraulic hose which is more resistant to initial failure and to provide a method for producing a hydraulic hose . Another object is to provide a use of a self- sealing material composition for a hydraulic hose .

The objects are achieved by means of a hydraulic hose

comprising the features of claim 1, a method for producing a hydraulic hose comprising the features of claim 13 and a use of a self-sealing material composition for an innermost layer tube of a hydraulic hose according to claim 14.

Advantageous embodiments and developments of the present invention are specified in the respective dependent claims.

A hydraulic hose is specified. Here and in the following, a hydraulic hose means that the hose is capable of transporting hydraulic liquids, especially trough at least one channel, for example oils or fuels, especially under high pressure. According to one embodiment, the hydraulic hose comprises an innermost layer tube encircling at least one channel. The innermost layer tube comprises a self-sealing material composition comprising an elastomeric material and a

polyalkyleneimine .

The material composition for the innermost layer tube has a self-sealing ability. Due to the self-sealing ability of the material composition, initial cracks inside the hose,

especially of the innermost layer tube, can be healed. This prevents early life failures of the hydraulic hose and therefore increases the lifetime and the quality of the hose. Advantageously the hydraulic hose does not have to be

replaced, or at least does not have to be immediately

replaced, due to initial cracks. At least the mean time between maintenance and replacement of the hose is reduced. Advantageously the cracks of the innermost layer tube are healed automatically, in other words the self-sealing takes place without any external force or intervention. This is due to the nucleophilic and quite reactive amine groups present in the polyalkyleneimine, which forms chemical bonds with the elastomeric material in the case of a crack as a results of tube degradation. In addition the production of the hydraulic hose is easier as small defects don't have any effect as they are healed due to the self-sealing ability of the material composition. In high temperature applications the process of healing initial cracks of the innermost layer tube is

advantageously fastened.

According to one embodiment the self-sealing material

composition comprises 0.5 to 50 % per weight of the

polyalkyleneimine in relation to the overall weight of the elastomeric material and the polyalkyleneimine.

According to one embodiment, the polyalkyleneimine is

selected from polyethyleneimine, polypropyleneimine ,

polybutyleneimine, polypentyleneimine and combinations thereof . According to one embodiment, the polyalkyleneimine is linear or branched. Preferably, the polyalkyleneimine is branched.

By using a branched polyalkyleneimine more reactive amine sites are present, so that the probability of initial cracks being healed is increased. In addition by the use of branched polyalkyleneimine the tensile strength is maintained at the repaired area of the innermost layer tube.

According to one embodiment, the polyalkyleneimine is a linear or branched polyethyleneimine .

According to one embodiment, the polyalkyleneimine is a branched polyethyleneimine of the following formula:

with n ¹ 0.

According to one embodiment the polyethyleneimine can be functionalized with an urea group.

According to one embodiment, the branched polyethyleneimine has a molar mass distribution MW between 500 g/mol and 50000 g/mol, preferably between 500 g/mol and 25000 g/mol, more preferably between 800 g/mol and 5000 g/mol. For example, the branched polyethyleneimine has a molar mass distribution MW of 800 g/mol or 2000 g/mol. The higher the molar mass distribution, the better the self-sealing ability.

According to one embodiment the elastomeric material

comprises C=0 groups Then for example the following reaction takes place between the elastomeric material and the

polyalkyleneimine, in which an amide group is formed:

According to one embodiment, the elastomeric material is a butadiene polymer or a butadiene copolymer. By using those elastomeric materials for the innermost layer tube, the flexibility of the hose can be guaranteed.

According to one embodiment, the elastomeric material is a nitrile butadiene rubber. Nitrile butadiene rubbers are unsaturated copolymers of 2-propenenitrile and butadiene monomers, especially 1,2-butadiene and/or 1,3-butadiene This type of elastomeric material is very resistant to fuel, oil and other chemicals and can withstand very high internal working pressures which can occur in hydraulic hoses. In the case of an initial crack chemical bonds, especially covalent bonds, are formed between the polyalkyleneimine and the nitrile butadiene rubber such that the initial cracks are healed .

Advantageously this bond formation takes place without any external intervention and this process is even fastened at high temperature applications of the hydraulic hose.

According to one embodiment, the elastomeric material is a acrylonitrile butadiene rubber of the following formula: with m ¹ 0 and n ¹ 0.

According to one embodiment the elastomeric material is a modified acrylonitrile butadiene rubber of one of the following formula:

with m ¹ 0, n ¹ 0, i ¹ 0, k ¹ 0.

R may be, for example, a metal ion like Zn, H or an alkyl group, like a methyl or ethyl group for example.

According to one embodiment, the elastomeric material is a is a unsaturated elastomeric material. For example the

elastomeric material according to this embodiment can be a polychloroprene or a modified polychloroprene .

According to one embodiment the elastomeric material, especially the nitrile butadiene rubber, the modified nitrile butadiene rubber, the polychloroprene or the modified polychloroprene is vulcanised.

According to one embodiment the innermost layer tube has a layer thickness of between 0.5 mm and 4.0 mm. According to one embodiment, the hydraulic hose further comprises at least one intermediate layer and/or an outer layer covering the innermost layer tube.

According to one embodiment, the at least one intermediate layer is a metal or textile braiding covering or spiraling covering the innermost layer tube. Preferably the metal or textile braiding or spiraling covers the innermost layer tube completely .

According to one embodiment, the outer layer comprises a self-sealing material composition comprising an elastomeric material and a polyalkyleneimine and covers the at least one intermediate layer. Preferably the outer layer covers the intermediate layer completely. According to this embodiment also in the outer layer, which is preferably the outermost layer of the hydraulic hose, initial cracks which may occur from light abrasion or any other environmental effects can be healed due to the self-sealing ability of the self-sealing material composition used.

All features concerning the self-sealing material mentioned for the innermost layer tube can also be features of the self-sealing material of the outer layer.

According to one embodiment the innermost layer tube and the outer layer, preferably the outermost layer, comprise the same self-sealing material composition.

The specified embodiments of the hydraulic hose can be produced in accordance with the method mentioned below. All features of the hydraulic hose that are mentioned under the method can also be features of the above-explained exemplary embodiments of the hydraulic hose and vice versa.

A method for producing a hydraulic hose is specified.

According to one embodiment, the hydraulic hose comprises an innermost layer tube encircling at least one channel wherein the innermost layer tube comprises a self-sealing material composition comprising an elastomeric material and a

polyalkyleneimine .

The method comprises the following steps, preferably in the given sequence:

A) mixing an elastomeric material and a polyalkyleneimine,

B) extruding the mixture of step A) ,

C) curing the extruded mixture of step B) to form an

innermost layer tube encircling at least one channel and which comprises an elastomeric material and a

polyalkyleneimine .

Advantageously the polyalkyleneimine is stable to

temperatures up to 250 °C such that it can be mixed to the elastomeric material and does not degrade in the extruding step and/or in an optional vulcanization step.

Polyalkyleneimines , especially polyalkyleneimines with different molar mass distributions, are commercially

available .

The method of producing the elastomeric material is known to a person skilled in the art. For example nitrile butadiene rubber can be produced by a co-polymerisation of 2- propenenitrile and butadiene monomers e.g. 1,2-butadiene and 1 , 3-butadiene .

Further, the use of a self-sealing material composition comprising an elastomeric material and a polyalkyleneimine for an innermost layer tube of a hydraulic hose is specified.

All features of the hydraulic hose that are mentioned above and all features mentioned above for the method of producing a hydraulic hose can also be features of the use of the self sealing material composition and vice versa.

In the following, the present invention will be demonstrated based on a working example and a comparative example. For the working example a tube made of a mixture of a standard elastomeric material is mixed with a

polyalkyleneimine , and as a comparative example a standard tube consisting of the same standard elastomeric material is used.

Comparative physical loss tests after crack generation was done with the working and the comparative example. The results are shown in the table below:

What can be seen from these tests, is that the working example shows a reversion of the tensile strength and the elongation break 24 hours after the crack generation (cut), whereas the comparative example shows an immense drop in tensile strength and elongation break. This shows the excellent self-sealing ability of the material composition for an innermost layer tube of a hydraulic hose. By using the inventive self-sealing material composition for an innermost layer tube of a hydraulic hose, early life failures of the hydraulic hose due to cracks or pin-holes in the production process can be reduced. Further advantageous embodiments and developments of the invention will be apparent from the exemplary embodiments described below in association with the figures.

Figures 1 and 2 show schematic cross-sectional views of different embodiments of hydraulic hoses.

In the figures, identical or identically acting constituent parts are provided in each case with the same reference signs. The illustrated elements and their size relationships to each other should not be regarded as true to scale.

Rather, individual elements, in particular layer thicknesses, may be illustrated with an exaggerated size in order to afford a better understanding.

The hydraulic hose 10 in accordance with Figure 1 exhibits a channel 1 in which hydraulic fluids can be transported. An innermost layer tube 2 encircles the channel 1. The innermost layer tube 2 comprises a self-sealing material composition comprising a nitrile butadiene rubber and a branched

polyethyleneimine with a molar mass distribution of, for example, 800 g/mol or 2000 g/mol. Due to the self-sealing ability of the material composition, initial cracks due to for example pressure, pressure drops, temperature, aging, movement, abrasion and fluid aggressiveness of the innermost layer tube can be healed. This prevents early life failures of the hydraulic hose and therefore increases the lifetime and the quality of the hose.

In comparison to the hydraulic hose of Figure 1, the

hydraulic hose 10 of Figure 2 further comprises an

intermediate layer 3, for example a metal braiding and an outer layer 4 comprising a self-sealing material composition which can comprise the same elastomeric material and the same polyalkyleneimine as the innermost layer tube 2. Here in the outer layer 4, which is preferably the outermost layer of the hydraulic hose 10, initial cracks which may occur from light abrasion or any other environmental effects can also be healed due to the self-sealing ability of the material composition . The invention is not restricted by the description on the basis of the exemplary embodiments. Rather, the invention encompasses any novel feature and also any combination of features, which in particular includes any combination of features in the patent claims even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.