Composite pipe and method for producing same

Abstract

The invention relates to a composite pipe (1, 11) for guiding and conducting a fluid, said composite pipe comprising a stability layer (2, 12) having an outer surface (3, 13) and having an outer layer (4, 14), the outer layer (4, 14) containing a polyolefin grafted with at least one silane compound, characterised in that the outer layer (4, 14) is adhesively bonded to the outer surface (3, 13) of the stability layer (2, 12) by means of the at least one silane compound of the grafted polyolefin. The invention also relates to a method for producing such a composite pipe.

Description

[0001] Composite pipe and process for its production

[0002] The invention relates to a composite pipe for conducting and guiding a fluid, comprising an internally arranged stability layer with an outer surface and an externally arranged outer layer, wherein the outer layer at least partially contains a polyolefin grafted with a silane compound. The invention also relates to a method for producing a composite pipe and the use of a polyolefin for producing a composite pipe.

[0003] Composite pipes, and especially metal composite pipes, are widely used in plumbing to convey water, especially drinking water, heating water, or domestic water. These composite pipes often feature an aluminum layer between two plastic layers of cross-linked or non-cross-linked polyolefin.

[0004] The composite pipes have the advantage that, unlike pure plastic pipes, they are very easy to bend and retain their shape after bending, rather than springing back to their original shape. Thanks to the intermediate or stability layer of aluminum, the pipes are impermeable to oxygen, preventing oxygen from entering the heating water, for example, and thus preventing water-side corrosion in unprotected steel parts such as radiators and boilers. Furthermore, these pipes are lighter than commonly used alternative steel or copper pipes. However, aluminum itself is not long-term corrosion-resistant, for example in plumbing or heating applications.

[0005] The typical structure of a composite pipe consists of five layers, from the inside out: (1) Polyolefin (2) Maleic anhydride (MAH) adhesion promoter (3) Aluminum (4) MAH adhesion promoter (5) Polyolefin. The maleic anhydride is grafted onto a polyolefin. The MAH adhesion promoter is required because polyolefins alone have virtually no adhesion to materials with high surface energy such as metals, and adhesion promoters are normally required to bond polyolefins such as polyethylene to inorganic materials such as metals. For this reason, special, modified polyolefin types are usually used as adhesion promoters, in which the polyolefins have been grafted with maleic anhydride. These grafted polyolefins are sold by various manufacturers such as Mitsui Chemicals, Yparex, LyondellBasell, Silon and Auserpolimeri under the trade names Admer, Yparex, Plexar, Tabond and Compoline.According to current theory, ester-like bonds to the inorganic layer are formed via the anhydride group of the succinic anhydride side chain formed by grafting.

[0006] JPH 1015679 and DE 10 2006018466 A1 each describe such a composite pipe in which an adhesion promoter is used to bond the metal layer and the plastic layer. However, such composite pipes have the disadvantages described below.

[0007] If such a composite pipe is sealed with a fitting only on the outer circumference against the fluid transported inside, the cut edge of the composite pipe inside the fitting is exposed to the medium. However, the bond between the MAH adhesion promoter (2) and (4) and the aluminum is not hydrolysis-resistant, and the aluminum is not corrosion-resistant. If the cut edge is exposed inside the fitting, the adhesion will weaken over time due to the damaging effects of the fluid, particularly water, and will eventually fail. This leads to collapse, particularly delamination of the inner layer, and an installation error. It is assumed that the ester-like bonds formed are hydrolyzed, thereby removing the bond between the metal layer and the adhesion promoter layer.

[0008] It is also assumed that hydrolysis-induced delamination is self-reinforcing. During hydrolysis, acid groups are formed from the ester-like bonds. These acid groups increase the osmotic pressure in a moisture pocket that has formed around destroyed metal-bond bonds. This attracts more water, causing the moisture pocket to expand into a bubble. This destroys further ester-like bonds in the metal-bond bond, which in turn forms more acid groups, which, together with dissolved aluminum ions, increase the osmotic pressure. In this way, the metal-bond bond is further destroyed, eventually causing the polyolefin layer to delaminate from the metal layer.

[0009] In other metal composite pipes, the aluminum pipe is replaced with a stainless steel pipe. The self-accelerating delamination described above due to adhesion promoter hydrolysis and acid-driven metal corrosion does not occur with sufficiently stable stainless steels. The stainless steel pipe is either the innermost layer in contact with the fluid, especially the water, or the stainless steel pipe represents the middle layer of the composite pipe. However, the adhesion promoter is also of the MAH type, which is why such stainless steel composite pipes must also be sealed internally.

[0010] The disadvantage of an internal seal is the support sleeve inserted into the pipe as part of the fitting, which either seals itself or has grooves for O-rings. However, such internal seals always lead to undesirable pressure losses in the pipe arrangement because they increase flow resistance. Particularly in large installations, this results in high pressure losses and the need for larger dimensions. Another approach involved using perforated stainless steel sheets or meshes instead of aluminum strip as the metal pipe, thus avoiding the use of adhesion promoters. The inner thermoplastic layer and outer thermoplastic layer are fused together in the holes of the perforated sheets or meshes, preventing the collapse of the inner plastic pipe. This solution is hydrolysis- and corrosion-resistant and therefore hygienically suitable for external sealing.However, the technical effort involved in such a design is considerable and the stability layer in this construction no longer functions as a barrier layer against, for example, the ingress of oxygen.

[0011] US 2019 / 0001625 A1 describes a coated metal surface, wherein the coating comprises a crosslinkable polymer with silane groups and a filler, in particular glass fibers. The crosslinkable silane groups of the polymer are bonded to the filler via covalent bonds. An adhesive bond to the metal surface by means of the silane compound is possible.

[0012] US 2019 / 0001625 Al does not apply because the silane groups are already consumed by cross-linking with the filler and can therefore no longer bind to the metal surface.

[0013] The object of the invention is therefore to provide a composite pipe and a method that do not have the aforementioned disadvantages. Furthermore, the object of the invention is to provide a composite pipe that can be sealed across the outer diameter. Further objects, features, and advantages of the present invention will become clear from the following description.

[0014] The above-described problem is initially solved by a composite pipe for conducting and guiding a fluid, in which the composite pipe has a stability layer with an outer surface and an outer layer. The outer layer contains a polyolefin grafted with at least one silane compound. According to the invention, the outer layer is adhesively bonded to the outer surface of the stability layer by means of the at least one silane compound of the grafted polyolefin.

[0015] In a further embodiment of the composite pipe, an inner layer is provided, wherein the inner layer contains a polyolefin grafted with at least one silane compound and wherein the inner layer is adhesively bonded to an inner surface of the stability layer by means of the at least one silane compound of the grafted polyolefin.

[0016] The above-described object is further achieved by a composite pipe for conducting and guiding a fluid, in which the composite pipe has a stability layer and an inner layer. The inner layer contains a polyolefin grafted with a silane compound. According to the invention, the inner layer is adhesively bonded to an inner surface of the stability layer by means of the at least one silane compound of the grafted polyolefin.

[0017] The outer layer and / or the inner layer comprise a proportion of a polyolefin grafted with a silane compound. Theoretically, this proportion can be 100 wt.%. However, a lower proportion of 10 wt.% is preferred. The remaining proportion can, for example, comprise or consist of one or more ungrafted polyolefins.

[0018] Particularly preferably, the composite pipe is further configured such that the stability layer contains, in particular consists of, a metallic material. Metals that can be used include, in particular, aluminum, iron, steel, stainless steel, copper, titanium, chromium, nickel, or alloys of the aforementioned metals.

[0019] To produce the polyolefin grafted with a silane compound, the silane compound can be advantageously grafted to the polyolefin via a carbon-carbon double bond and / or triple bond of the silane compound using a radical initiator. For example, vinyltrimethoxysilane can be grafted to polyethylene using a radical initiator such as dibenzoyl peroxide. The vinyltrimethoxysilane-grafted polyethylene then contains corresponding 2-(trimethoxysilyl)ethyl groups.

[0020] The silane compound on the grafted polyolefin can react, for example, with hydroxyl groups, to form a bond via the silicon atom or the oxygen atom bonded to the silicon atom. The reaction can be accelerated with a crosslinking-promoting catalyst, in particular dibutyltin dilaurate, tin fluoroacetate, tin fluorooctate, dibutyltin dioctoate, dioctyltin bis(isooctylthioglycolate), and / or bismuth fluorooctane neodecanoate. Preferably, however, no crosslinking-promoting catalyst is used to create the adhesion to the stability layer. Advantageously, the outer layer is adhesively bonded to the outer surface of the stability layer by means of the at least one silane compound of the grafted polyolefin without the use of crosslinking-promoting catalysts.The inner layer is advantageously adhesively bonded to an inner surface of the stability layer by means of the at least one silane compound of the grafted polyolefin without the use of crosslinking-promoting catalysts.

[0021] The silane compound on the grafted polyolefin preferably has not reacted with the silicon atom prior to application to the stability layer. The silane compound is preferably in the form of an alkylsilane ortho acid ester, in particular a C2-11 alkylsilane ortho acid ester. Before grafting, the silane compound is preferably in the form of an alkenylsilane ortho acid ester, in particular a C2-11 alkenylsilanoic acid ortho ester. For example, the polyolefin can be grafted with vinyltrimethoxysilane, so that the 2-(trimethoxysilyl)ethyl groups can react to form new bonds via the silicon atom.

[0022] According to a further embodiment, the silane compound on the grafted polyolefin is preferably formed as an alkenylsilane ortho acid ester, in particular C2-11 alkenylsilane ortho acid ester. According to this embodiment, the silane compound prior to grafting is preferably formed as an alkynylsilane ortho acid ester, in particular C2-n-alkynylsilane ortho ester.

[0023] According to a further embodiment, the silane compound is preferably formed as a precondensate prior to grafting. In a precondensate, a portion of the alkoxide groups of the silane compound is hydrolyzed and condensed, so that a portion of the silane compound is present as dimers, trimers, tetramers, and / or further oligomers. Precondensates can be composed of various silane compounds, in particular of various alkenylsilane orthoesters. For example, precondensates can be composed of a mixture of vinyl trialkoxy orthoesters, propyl trialkoxy orthoesters, and butyl trialkoxy orthoesters. The alkoxy groups are preferably methoxy and / or ethoxy groups. Furthermore, precondensates can be composed of tetraalkoxysilanes, for example tetramethoxysilane and tetraethoxysilane, as a further component.Corresponding precondensates can be composed of a mixture of tetramethoxysilane, tetraethoxysilane, vinyltrialkoxyorthoesters, propyltrialkoxyorthoesters and butyltrialkoxyorthoesters, wherein the alkoxy groups are preferably methoxy and / or ethoxy groups.

[0024] When the polyolefin grafted with a silane compound is applied to the stability layer, an adhesive bond between the grafted polyolefin and the stability layer is achieved by means of the silane compound grafted to the polyolefin. Surprisingly, it has also been found that a significantly better adhesive bond is achieved when the application is carried out without the use of crosslinking-promoting catalysts. Therefore, the stability layer is preferably bonded to the outer layer containing the polyolefin grafted with a silane compound without the use of crosslinking-promoting catalysts.

[0025] Without wishing to be bound by any scientific theory, it is suspected that the silane compound on the grafted polyolefin reacts with reactive groups such as hydroxyl groups on the metal surface to form Si-O-metal bonds. These Si-O-metal bonds appear to result in greater hydrolysis resistance than the ester-like bonds derived from maleic anhydride. Thus, the polyolefin grafted with a silane compound appears to adhere well to the metal surface. The polyolefin grafted with a silane compound appears to act as an adhesion promoter between the outer layer and the stability layer. In particular, the grafted silane compound appears to act as an adhesion promoter instead of the MAH in the typical composite tube structure described above.

[0026] Furthermore, the hydrolysis of Si-O bonds only produces an extremely weak acid, which at most lowers the pH slightly and does not promote the hydrolysis of further bonds. Furthermore, the silane compounds that have already formed Si-O-metal bonds can crosslink with each other, which can further increase hydrolysis resistance. This effectively counteracts delamination of the polyolefin layer from the metal surface. The maleic anhydride-grafted adhesion promoter commonly used in the prior art can be dispensed with.

[0027] Preferably, bonds of the Si-O-Met type are present between the outer layer and the stability layer, where Met stands for metal. The metal is selected in particular from the aforementioned metals. This is shown schematically below: where n is an integer from 0 to 10, preferably 1. In the schematic representation shown above, additional molecular moieties are present at the points marked with wavy lines, for example, alkyl radicals such as methyl groups or alkoxy groups such as methoxy groups or oxygen atoms, which in turn are linked to alkyl radicals or Si or Si-O groups. For example, an Si-O network can form, which further increases hydrolytic stability.

[0028] In the described composite pipe, there is direct, particularly full-surface contact between the stability layer and the outer layer and / or the inner layer, without the need for a conventional primer, such as MAH polyolefin, as an adhesion promoter. The strong bond is preferably achieved without the use of catalysts, particularly without catalysts such as dibutyltin dilaurate, tin fluoroacetate, tin fluoroacetate, dibutyltin dioctoate, dioctyltin bis(isooctylthioglycolate), and / or bismuth(III) neodecanoate.

[0029] The outer layer and / or the inner layer thus preferably have a bond with the stability layer that is more hydrolysis-stable than with MAH polyolefin. This property has the advantage that the composite pipe can be permanently and reliably connected to an externally sealing fitting without the known and previously described problems due to contact with the fluid, especially water.

[0030] The outer surface of the stability layer and / or the inner surface of the stability layer are preferably characterized as follows.

[0031] Firstly, the outer surface of the stability layer and / or the inner surface of the stability layer can have a static initial contact angle of water after 3 minutes of equilibration of 110° or less, preferably 100° or less, more preferably 90° or less. The initial contact angle is preferably determined according to DIN EN ISO 19403-2:2020-04. Secondly, the outer layer can adhere to the outer surface of the stability layer and / or the inner layer can adhere to the inner surface of the stability layer with a peel force of at least 15 N / cm, preferably at least 30 N / cm, more preferably at least 50 N / cm, determined according to DIN EN ISO 11339:2022-05 at 25°C and a peel speed of 50 mm / min.

[0032] Furthermore, at least one further outer layer and / or at least one further inner layer can be provided. The further outer layer and / or the further inner layer can in particular be a polyolefin layer. According to a further advantageous embodiment, the composite pipe has at least one further outer polyolefin layer. According to a further advantageous embodiment, the composite pipe has at least one further inner polyolefin layer. The further inner polyolefin layer can be present instead of or in addition to the further outer polyolefin layer. In particular, a five-layer composite pipe can thus be formed, comprising an outer polyolefin layer, an outer layer containing a polyolefin grafted with at least one silane compound, a stability layer, an inner layer comprising a polyolefin grafted with at least one silane compound, and an inner polyolefin layer.

[0033] The polyolefin grafted with at least one silane compound contained in the outer layer may be the same as or different from the polyolefin grafted with at least one silane compound contained in the inner layer.

[0034] The outer layer preferably has a layer thickness of 0.005 to 35 mm, more preferably from 0.01 to 7.5 mm, particularly preferably from 0.03 to 3 mm. The inner layer preferably has a layer thickness of 0.005 to 35 mm, more preferably from 0.01 to 7.5 mm, particularly preferably from 0.03 to 3 mm. The further outer layer preferably has a layer thickness of 0.5 to 30 mm, more preferably from 1 to 10 mm, particularly preferably from 1.5 to 3 mm. The further inner layer preferably has a layer thickness of 0.5 to 30 mm, more preferably from 1 to 10 mm, particularly preferably from 1.5 to 3 mm. The outer layer and / or the further outer layer preferably serve to increase the processability of the composite pipe. The outer layer and / or the further outer layer preferably do not serve as a protective layer, in particular not as a mechanical protective layer.Therefore, the outer layer and / or the further outer layer can be thin, especially a few millimeters thick. The same applies to the inner layer and / or the further inner layer.

[0035] The object indicated above is also achieved according to the invention by a method in which a stability layer having an outer surface is provided and in which an outer layer is applied to the outer surface of the stability layer, wherein the outer layer contains a polyolefin grafted with at least one silane compound.

[0036] The outer layer is preferably applied to the stability layer by tube extrusion. Alternatively, the outer layer can also be applied by overmolding.

[0037] Furthermore, an inner layer can be applied to the inner surface of the stability layer, wherein the inner layer contains a polyolefin grafted with at least one silane compound.

[0038] Likewise, the above-mentioned object is also achieved by a method for producing a composite pipe, in which a stability layer with an inner surface is provided and in which an inner layer is applied to the inner surface of the stability layer, wherein the inner layer contains a polyolefin grafted with at least one silane compound.

[0039] In the process, the stability layer can be heated before and / or after the application of the inner and / or outer layer, in particular by induction heating. Preferably, the time after the application of the outer layer and a cooling process is kept long.

[0040] Preferably, the inner and / or outer layer are applied without the use of crosslinking-promoting catalysts.

[0041] If a composite pipe is manufactured with a stability layer, an outer layer and another outer layer, the outer layer and the other outer layer are preferably co-extruded onto the stability layer.

[0042] When carrying out the processes described above, various temperatures and / or pressures can be set. Advantageously, a temperature of 100 to 300°C, preferably 160 to 260°C, particularly preferably 200 to 260°C, is set during application. During application, a pressure of 1 to 300 bar, more preferably 10 to 200 bar, particularly preferably 50 to 150 bar, is preferably set. This can improve adhesion.

[0043] Preferably, when applying the outer layer and / or the inner layer, covalent bonds are formed by the polyolefin grafted with a silane compound, as schematically illustrated below by way of example.

[0044] Scheme: a] Application at a pressure of 100 bar and / or a temperature of 250 °C. b] Exposure to water. The optional further crosslinking in step b] shown in the scheme can occur simultaneously during application or - as shown in the scheme - in a subsequent step. For example, crosslinking can occur during a storage phase or during use of the composite pipe. In particular, the optional further crosslinking can occur in the presence of moisture in the system.

[0045] According to one embodiment, the outer layer and / or inner layer can be applied to the stability layer by applying the polyolefin and the silane compound as a physical mixture, optionally with the addition of a radical initiator, to the stability layer without prior grafting. This can be achieved by dissolving the silane in the polyolefin in a compounding process and subsequently pelletizing the compound. This compound is then fed to the raw material production. Alternatively, in a one-step process, silane and polyolefin can be fed separately to the extruder for pipe production. In the second case, the compound is produced in situ during pipe layer extrusion.

[0046] The methods explained above achieve the same properties and advantages as those previously described with regard to the composite tubes according to the invention and their configurations.

[0047] The above-mentioned task is also solved by a system for creating a pipe connection with a previously described composite pipe and with an externally sealing fitting.

[0048] For this purpose, the fitting preferably has a base body and a press sleeve connected to it. The press sleeve is further preferably provided with a chamber in which a clamping ring for holding and fixing clamping elements and a sealing element are arranged. The composite pipe is inserted into the space left free by the press sleeve with the elements contained therein until it rests, for example, against a stop formed on the base body. By radially pressing the press sleeve with a suitable pressing tool, usually with two pressing jaws, the press sleeve is evenly radially deformed. On the one hand, this brings the clamping elements into engagement with the surface of the composite pipe and the composite pipe is thus secured against withdrawal of the composite pipe from the fitting. On the other hand, the sealing element seals the outside of the composite pipe against the press sleeve and thus against the fitting.

[0049] The invention thus achieves that the described composite pipe and its preferred embodiments can be connected to a fitting that only implements an externally sealing press connection. Since the composite pipe represents a sufficiently stable composite system due to the more hydrolysis-resistant bond between the polyolefin layer(s) and the stability layer, no damage occurs within the fitting despite the fluid impinging on the stability layer at the front. This prevents collapse or delamination of the composite pipe layers and thus installation errors.

[0050] Furthermore, the above-mentioned object is also achieved by using a previously described composite pipe in a water-carrying pipe arrangement, in particular for drinking water or heating water.

[0051] Likewise, the above-mentioned object is achieved by using layers containing a polyolefin grafted with a silane compound in a composite pipe for hydrolysis-resistant connection of the layers, in particular the polyolefin-containing layers, with a stability layer, in particular a metal-containing stability layer.

[0052] The above-described object is further achieved by using a polyolefin grafted with a silane compound as an adhesion promoter for bonding a polyolefin-containing layer to a stability layer, in particular a metal layer. As previously explained for the composite pipe according to the invention, the silane compound of the grafted polyolefin can achieve a well-adhering bond to a stability layer.

[0053] The statements made herein regarding the polyolefin grafted with a silane compound, the polyolefin and the stability layer apply accordingly to the polyolefin grafted with a silane compound, the polyolefin and the stability layer.

[0054] In the above-described uses, the same properties and advantages are achieved as have been previously described with regard to the composite tubes according to the invention and their designs.

[0055] Specific examples of the design of the material of the stability layer and the inner and outer layers are given below.

[0056] The stability layer may contain a metallic material. The stability layer may in particular contain or consist of at least 60 wt.%, preferably at least 80 wt.%, more preferably at least 90 wt.%, of aluminum, iron, steel, stainless steel, copper, manganese, titanium, chromium, nickel, or alloys of two or more of the aforementioned metals, based on the total weight of the stability layer.

[0057] Alternatively, the stability layer can also be at least partially made of a non-metallic material. In particular, the stability layer can contain or consist of at least 60 wt.%, preferably at least 80 wt.%, more preferably at least 90 wt.%, ceramic, ethylene-vinyl alcohol, polyvinyl alcohol, polar thermoplastics and thermosets, in particular polyamides and melamine resins, wood, cellulose, glass, or mixtures thereof, preferably ethylene-vinyl alcohol, polyvinyl alcohol, polar thermoplastics and thermosets, in particular polyamides and melamine resins, or mixtures thereof, based on the total weight of the stability layer.

[0058] Preferably, the outer layer contains at least 1 wt.%, at least 10 wt.%, at least 20 wt.%, at least 30 wt.%, at least 40 wt.%, at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, at least 80 wt.%, or at least 90 wt.%, preferably at least 10 wt.%, of the polyolefin grafted with a silane compound, based on the total weight of the outer layer. In particular, the outer layer can contain 1 to 30 wt.%, preferably 3 to 20 wt.%, more preferably 5 to 15 wt.%, particularly preferably 8 to 12 wt.% of the polyolefin grafted with a silane compound, based on the total weight of the outer layer.

[0059] In addition to the polyolefin grafted with a silane compound, the outer layer may contain an ungrafted polyolefin. The outer layer may contain the ungrafted polyolefin in varying amounts.

[0060] The outer layer preferably contains at least 5% by weight, at least 10% by weight, at least 20% by weight, at least 30% by weight, at least 40% by weight, at least 50% by weight, at least 60% by weight, at least 70% by weight, at least 80% by weight, at least 90% by weight, or at least 99% by weight, preferably at least 80% by weight, more preferably at least 90% by weight, of the ungrafted polyolefin, based on the total weight of the outer layer. In particular, the outer layer can contain 70 to 99% by weight, preferably 80 to 97% by weight, more preferably 85 to 95% by weight, particularly preferably 88 to 92% by weight of the ungrafted polyolefin, based on the total weight of the outer layer.

[0061] The further outer layer can contain at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, at least 80 wt.%, at least 90 wt.% or at least 99 wt.%, preferably at least 80 wt.%, more preferably at least 90 wt.%, of an ungrafted polyolefin, based on the total weight of the further outer layer. It is preferably provided that the inner layer contains at least 1 wt.%, at least 10 wt.%, at least 20 wt.%, at least 30 wt.%, at least 40 wt.%, at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, at least 80 wt.% or at least 90 wt.%, preferably at least 10 wt.%, of the polyolefin grafted with a silane compound, based on the total weight of the inner layer. In particular, the inner layer can contain 1 to 30 wt.%, preferably 3 to 20 wt.%, more preferably 5 to 15 wt.%, particularly preferably 8 to 12 wt.-% of the polyolefin grafted with a silane compound, based on the total weight of the inner layer.

[0062] In addition to the polyolefin grafted with a silane compound, the inner layer may contain an ungrafted polyolefin. The inner layer may contain the ungrafted polyolefin in varying amounts.

[0063] The inner layer preferably contains at least 5% by weight, at least 10% by weight, at least 20% by weight, at least 30% by weight, at least 40% by weight, at least 50% by weight, at least 60% by weight, at least 70% by weight, at least 80% by weight, at least 90% by weight, or at least 99% by weight, preferably at least 80% by weight, more preferably at least 90% by weight, of the ungrafted polyolefin, based on the total weight of the inner layer. In particular, the inner layer can contain 70 to 99% by weight, preferably 80 to 97% by weight, more preferably 85 to 95% by weight, particularly preferably 88 to 92% by weight of the ungrafted polyolefin, based on the total weight of the inner layer.

[0064] The further inner layer can contain at least 50 wt.%, at least 60 wt.%, at least 70 wt.%, at least 80 wt.%, at least 90 wt.%, or at least 99 wt.%, preferably at least 80 wt.%, more preferably at least 90 wt.%, of an ungrafted polyolefin, based on the total weight of the further inner layer. Furthermore, it can be provided that the silane-grafted polyolefin and the ungrafted polyolefin are each independently composed of monomers selected from the group consisting of ethene, propene, isobutene, 1-butene, 2-butene, 4-methyl-1-pentene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, butadiene, isoprene, and mixtures thereof.In particular, the silane-grafted polyolefin and the ungrafted polyolefin may each be independently selected from the group consisting of polyethylene, cross-linked polyethylene, polyethylene with increased thermal resistance, polypropylene, polyisobutylene, polybutylene, polymethylpentene, polyalphaolefins and mixtures thereof.

[0065] Examples of cross-linked polyethylene are PE-Xa, PE-Xb, and PE-Xc. Polyethylene with enhanced thermal resistance can also be referred to as PERT.

[0066] If polyethylene is used as a polyolefin, medium-density polyethylene is preferred. Medium-density polyethylene can be referred to as MDPE. Medium-density polyethylene advantageously has an average density of 0.92 g / cm 3 up to 0.94 g / cm 3 , more preferably 0.93 g / cm 3 up to 0.94 g / cm 3,. Medium density polyethylene expediently has a melting point of 125°C to 128°C. Medium density polyethylene can be used for both grafted and ungrafted polyethylene. If a grafted or ungrafted polyethylene is used in the outer and / or inner layer, medium density polyethylene or grafted medium density polyethylene is preferably used. If a grafted or ungrafted polyethylene is used in the further outer layer and / or the further inner layer, medium density polyethylene or grafted medium density polyethylene is preferably used. Medium density polyethylene has the advantage that it supports the processability, in particular the bendability and connectability, of composite pipes and thus the laying of corresponding composite pipes.The aforementioned polyolefins, especially polyethylene, have the advantage that their grafting with silane compounds such as vinyltrimethoxysilane is familiar to those skilled in the art. This allows the grafted polyolefins to be produced in a simple and generally known manner. Grafting can, for example, be carried out as shown schematically below:

[0067] Polyolefin

[0068] Scheme: a) Radical initiators such as di-tert-butyl peroxide.

[0069] The grafting of vinylsilanes and its crosslinking is known to the person skilled in the art and is described, for example, in “Polyethylene Cross-linking by Two-step Silane Method: A Review”, Iranian Polymer Journal, 18 (2), 2009, 103-128.

[0070] The outer layer and / or the optional additional outer layer may also contain other substances commonly used in polyolefins, such as antioxidants, pigments, fillers, reinforcement materials, or processing aids. The same applies to the inner layer and / or the optional additional inner layer.

[0071] Examples of fillers are glass fibers, glass beads, calcium carbonate, talc, carbon fibers, natural fibers, polymer beads and / or carbon black.

[0072] According to one embodiment, the outer layer comprises less than 5 wt. %, preferably 3 wt. % or less, more preferably 2 wt. % or less, of fillers, based on the total weight of the outer layer. According to a further embodiment, the inner layer comprises less than 5 wt. %, preferably 3 wt. % or less, more preferably 2 wt. % or less, of fillers, based on the total weight of the inner layer. According to a preferred embodiment, the outer layer and / or the inner layer are substantially free of fillers. If the composite pipe has an outer and an inner layer, the outer layer and the inner layer are particularly preferably substantially free of fillers. The same applies to the optional further inner and / or outer layer.

[0073] Advantageously, the silane compound can contain 1 to 30 carbon atoms, preferably 2 to 20 carbon atoms, particularly preferably 2 to 10 carbon atoms. The silane compound expediently has a carbon-carbon double bond and / or triple bond, preferably a carbon-carbon double bond. The carbon-carbon double bond and / or triple bond can be used, as described above, to graft the silane compound to the polyolefin.

[0074] The silane compound may contain further groups, for example alkylene groups, amine groups, ether groups, thioether groups, hydroxyl groups, epoxy groups, carbamate groups, carbonyl groups, and / or alkyl groups.

[0075] Preferably, the silane compound has 1 to 30, more preferably 2 to 20, particularly preferably 2 to 10, carbon atoms and at least one functional group selected from the group consisting of propargyl, vinyl, acrylic, methacrylic, -OCHs and -OCH2CH3, more preferably from the group consisting of vinyl, acrylic, methacrylic, -OCH3 and -OCH2CH3.

[0076] Conveniently, the silane compound has the general structural formula (1)

[0077] [R 2 )4-m-oSi[R 3 )o[[CH2)nR 1 )m, [1] where m is 1 or 2, o is 0, 1 or 2, each n is independently an integer from 0 to 10, each R 1 independently of one another propargyl, vinyl, -OC(=O)-C(=CH2)H (acryloyloxy), -OC(=O)-C(=CH2)CH3 (methacryloyloxy), in particular vinyl, -OC(=O)-C(=CH2)H (acryloyloxy), -OC(=O)-C(=CH2)CH3 (methacryloyloxy), each R 2independently of one another are methoxy, ethoxy, iso-propoxy, n-propoxy, n-butoxy, sec-butoxy or iso-butoxy, or two or three R 2 are each independently linked to each other by Ci-s-alkylene groups and each R 3 independently of one another, are Ci-4-alkyl, in particular methyl or ethyl.

[0078] Preferably, in the structural formula (1), n ​​is only zero if R 1 Vinyl means.

[0079] In a further preferred manner, it can be provided that the silane compound has the structural formula (11)

[0080] R 4 -(CH2)p-Si(OR 5 )3(11), where

[0081] R 4 HC=C-, H2C=CH-, H2C=CH-C(O)-O- (acryloyloxy) or H2C=C(CH3)-C(O)-O- (methacryloyloxy), in particular H2C=CH-, H2C=CH-C(O)-O- (acryloyloxy) or H2C=C(CH3)-C(O)-O-(methacryloyloxy), means that each R 5independently of one another -CH3, -C2H5, -C3H7, -C4H9 or -C5H11 or two or three R 5 are each independently linked to one another by Ci-s-alkylene groups, and p is an integer from 0 to 10.

[0082] Particularly preferably, R 4 H2C=CH-, each R 5 independently means -CH3 or -CH2CH3 and p is 0. If R 4 HC=C-, p is preferably an integer from 1 to 10.

[0083] In a further preferred manner, it can be provided that the silane compound is selected from the group consisting of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltrialkoxysilane, in which different alcohols were used for the esterification, propargyltrimethoxysilane, propargyltriethoxysilane, propargyltrialkoxysilane, in which different alcohols were used for the esterification, 4-pentenyltrimethoxysilane, 4-pentenyltriethoxysilane, 10-undecenyltrimethoxysilane, 10-undecenyltriethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltriethoxysilane, 2-acryloyloxyethyltrimethoxysilane, 2-acryloyloxyethyltriethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropyltriethoxysilane, 2- Methacryloyloxyethyltrimethoxysilane, 2-methacryloyloxyethyltriethoxysilane and mixtures thereof, preferably from the group consisting of vinyltrimethoxysilane, vinyltriethoxysilane, vinyltrialkoxysilane, in which different alcohols were used for esterification,4-Pentenyltrimethoxysilane, 4-pentenyltriethoxysilane, 10-undecenyltrimethoxysilane, 10-undecenyltriethoxysilane, 3-acryloyloxypropyltrimethoxysilane, 3-acryloyloxypropyltriethoxysilane, 2-acryloyloxyethyltrimethoxysilane, 2-acryloyloxyethyltriethoxysilane, 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropyltriethoxysilane, 2-methacryloyloxyethyltrimethoxysilane, 2-methacryloyloxyethyltriethoxysilane, and mixtures thereof. The silane compound is particularly preferably vinyltrimethoxysilane, vinyltriethoxysilane, or a mixture thereof.

[0084] EXAMPLE

[0085] Conventional PE (Sclair 74B supplied by Nova Chemicals) was reactively grafted in a twin-screw extruder with 2m% vinyltrimethoxysilane (Silquest A-171 supplied by Momentive) and 0.05m% 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane (supplied by VWR) over a temperature profile of 150°C to 220°C. The product was cooled and pelletized after exiting the die.

[0086] Vinyltrimethoxysilane-grafted polyethylene (hereinafter "PE-gSil") produced according to the above instructions was pressed onto a steel sheet using a platen press at a temperature of 250°C and a pressure of 100 bar for a period of 2 minutes. The peel force of the polyethylene from the steel sheet was determined to be >50 N / cm according to DIN EN ISO 11339:2022-05 at 25°C and a peel speed of 50 mm / min.

[0087] For comparison, an ungrafted polyethylene (Sclair 74B) was pressed onto a steel sheet at a temperature of 250°C and a pressure of 100 bar for a period of 2 minutes. The peel force of the polyethylene from the steel sheet was determined to be 0 N / cm according to DIN EN ISO 11339:2022-05 at 25°C and a peel speed of 50 mm / min.

[0088] Test specimens produced according to the previously described procedure were aged in water at 105°C. In parallel, samples were aged with a conventional PE-gMAH-based adhesion promoter from the upper performance segment (Admer NE072 from Mitsui). For comparison, the peel force was determined over the exposure time. While the PE-gMAH-based samples only exhibited a peel force of <2.5 N / cm according to DIN EN ISO 11339:2022-05 at 25°C and a peel speed of 50 mm / min after 3,000 hours, the PE-gSil samples produced according to the procedure described above showed a peel force of >40 N / cm according to DIN EN ISO 11339:2022-05 at 25°C and a peel speed of 50 mm / min. No delamination was detected in the PE-gSil-based samples.

[0089] The differences in peel force retention between PE-gMAH-based and PE-gSil-based adhesion promoter systems are directly transferable to composite pipe samples produced by extrusion.

[0090] In the following, the invention is explained using exemplary embodiments with reference to the drawing. In the drawing,

[0091] Fig. 1 shows a first embodiment of a composite pipe,

[0092] Fig. 2 shows a second embodiment of a composite pipe, Fig. 3 shows a third embodiment of a composite pipe,

[0093] Fig. 4 shows a fourth embodiment of a composite pipe and

[0094] Fig. 5 an unpressed fitting for connecting a composite pipe according to Fig. 2 and

[0095] Fig. 6 the fitting with the composite pipe according to Fig. 5 in the pressed state.

[0096] In the following description of the various embodiments according to the invention, components and elements with the same function and the same mode of operation are provided with the same reference numerals, even if the components and elements in the various embodiments may have differences in their dimensions or shape.

[0097] Fig. 1 shows a composite pipe 1 for conducting and transporting a fluid, preferably water in the form of drinking water or heating water. The composite pipe 1 has a stability layer 2 with an outer surface 3 and an outer layer 4.

[0098] The outer layer contains a polyolefin grafted with at least one silane compound.

[0099] According to the invention, the outer layer 4 is adhesively bonded to the outer surface 3 of the stability layer 2 by means of the at least one silane compound of the grafted polyolefin. Thus, the stability layer 2 and the outer layer 4 form a firmly adhesive and more hydrostable bond than with MAH adhesion promoter, without the layers being attacked by moisture penetration and the composite pipe being damaged. Reference is made to the general description for the presumed mechanism. Fig. 2 shows another composite pipe 11 with a stability layer 12 with an outer surface 13 and with an outer layer 14. Furthermore, an inner layer 16 is provided. The inner layer 16 contains a polyolefin grafted with at least one silane compound, and the inner layer 16 is adhesively bonded to an inner surface 15 of the stability layer 12 by means of the at least one silane compound of the grafted polyolefin.When bonding the inner layer 16 and the stability layer 12, no crosslinking-promoting catalysts were used.

[0100] Thus, the inner layer 16 is bonded to the stability layer 12 via the inner surface 15 with greater hydrolysis stability than with an MAH bonding agent. For an explanation of this bond, please refer to the general part of the description.

[0101] Fig. 3 shows another embodiment of a composite pipe 21 for conducting and guiding a fluid. This embodiment includes a stability layer 22 and an inner layer 26. An outer layer, as in the embodiments according to Figs. 1 and 2, is not present.

[0102] The inner layer 26 contains a polyolefin grafted with at least one silane compound. Furthermore, the inner layer 26 is adhesively bonded to an inner surface 25 of the stability layer 22 by means of the at least one silane compound of the grafted polyolefin. No crosslinking-promoting catalysts were used in bonding the inner layer 26 and the stability layer 22.

[0103] Thus, the inner layer 26 is bonded to the stability layer 22 via the inner surface 25 with greater hydrolysis stability than with an MAH bonding agent. For an explanation of this bond, please refer to the general part of the description.

[0104] Fig. 4 shows another composite pipe 31 with a stability layer 32 having an outer surface 33 and an outer layer 34. The outer layer contains a polyolefin grafted with at least one silane compound. Furthermore, the composite pipe 31 has another outer polyolefin layer 37, which is bonded to the outer layer 34 via the outer surface 38 of the outer layer 34.

[0105] According to the invention, the outer layer 34 is adhesively bonded to the outer surface 33 of the stability layer 32 by means of the at least one silane compound of the grafted polyolefin. Thus, the stability layer 32 and the outer layer 34 form a firmly adhesive and more hydrostable bond than with MAH adhesion promoter, without the layers being attacked by moisture penetration and the composite pipe being damaged. Reference is made to the general description for the presumed mechanism. The further outer polyolefin layer 37 adheres to the outer layer 34 by mechanisms known to those skilled in the art.

[0106] In the embodiments shown in Figs. 1 to 4, the stability layer 2, 12, 22, 32 contains a metallic material; in particular, the stability layer consists of a metallic material. The use of copper and aluminum is preferred.

[0107] The outer layer 4, 14, 34 and / or the inner layer 16, 26 comprise a proportion of polyolefin grafted with a silane compound, preferably polyethylene grafted with vinyltrimethoxysilane. Theoretically, this proportion can be 100 wt.%. However, a lower proportion of 10 wt.% is preferred. The remaining proportion can then be an ungrafted polyolefin, preferably polyethylene.

[0108] To characterize the outer surface 3, 13, 33 of the stability layer 2, 12, 32 and / or the inner surface 15, 25 of the stability layer 2, 12, 22, 32, these have a static initial contact angle of water after 3 minutes of equilibration of 110° or less, determined according to DIN EN ISO 19403-2:2020-04. Furthermore, the outer layer 4, 14, 34 adheres to the outer surface 3, 13, 33 of the stability layer 2, 12, 32 and / or the inner layer 16, 26 adheres to the inner surface 15, 25 of the stability layer 12, 22 with a peel force of at least 15 N / cm, determined according to DIN EN ISO 11339:2022-05 at 25°C and 50 mm / min peel speed.

[0109] Figs. 5 and 6 show a system for creating a pipe connection, with a composite pipe 11, as shown in Fig. 4, and an externally sealing fitting 40.

[0110] The fitting 40 comprises a base body 44 and an inwardly projecting stop element 45 formed circumferentially in the base body 44. Furthermore, a compression sleeve 41 is provided, which is connected to the base body 44 and forms an outer contour 42 and has a chamber 43 directed inwards towards the pipe 11 to be received. In the chamber 43, a clamping ring 46 consisting of a plastic with a plurality of clamping elements 47 aligned opposite to the extension direction of the pipe 31 to be inserted is arranged. In addition, a

[0111] 45 arranged sealing element 48 is arranged.

[0112] The press sleeve 41 is integrally connected to the base body 44, so that the press section in the form of the press sleeve 41 and the base body 44 can advantageously be manufactured in one piece.

[0113] The securing of the pipe 31 against pulling out and / or against excessive internal pressure is effected by the clamping ring 46, which is designed as a plastic clamping ring and in which metallic cutting edges are arranged as clamping elements 47. The plastic clamping ring 46 further has circumferential slots which secure the clamping ring

[0114] 46 overall flexible and thus facilitates assembly in the fitting 40 within the compression sleeve 41. The clamping elements 47 are designed as cutting edges in the form of wire elements that are inserted into recesses provided for this purpose. The clamping elements 47 are thus fixed in the plastic of the clamping ring 46 in a form-fitting manner. The clamping elements 47 can be manufactured in various ways, for example, as cast parts or as stamped parts. The number of clamping elements 47 is six in this case, but can be determined depending on the requirements or dimensions of the clamping ring 47.

[0115] The clamping elements 47 are also arranged in the distal region of the chamber 43, opposite the stop elements 45, and absorb the pull-out force by selectively deforming the pipe 31 (see Fig. 6), while supporting themselves against the wall in a distal outer corner region 41a of the compression sleeve 41. This ensures a direct flow of force from the pipe 31 via the compression sleeve 41 into the fitting 40. After pressing, the clamping ring 46 merely has a supporting function and contributes only slightly or not at all to the pull-out protection.

[0116] The pressing process becomes clear by comparing Fig. 5 and 6. By a radially inward movement of the pressing jaw halves (not shown) and by the contact of the pressing jaw halves with the pressing sleeve 41, the pressing sleeve 41 is deformed radially inward. This deforms the clamping ring 46 so that the clamping elements 47 press inward into the material of the pipe 31, thus securing the pipe 31 to the fitting 40. On the other hand, when the pressing sleeve 41 is deformed, the seal 48 is also deformed radially inward, and the seal 48 seals off the pipe 31 and the pressing sleeve 41.

[0117] As stated above, an important advantage of the embodiments of the composite pipe 31 - as well as the other described composite pipes 1, 11 and 21 - is that the outer layer 34 is adhesively bonded to the outer surface 33 of the stability layer 32 by means of the at least one silane compound of the grafted polyolefin, whereby a more hydrolysis-resistant bond than with an MAH coupling agent is achieved between the stability layer 32 and the

[0118] Outer layer 34 is present. Preferably, no crosslinking-promoting catalysts are used when bonding the stability layer and the outer layer.

[0119] As a result, as shown in Fig. 6, the connection between the composite pipe 31 and the fitting 40, which is only pressed from the outside, allows the end surface 39 of the composite pipe 131 to come into unprotected contact with the medium, such as water, carried in the pipe 31 and the fitting 40, without hydrolysis-induced damage to the layers 32, 34, and 37 occurring. The described design of the composite pipe 31 therefore eliminates the need for internal pressing using a conventional support body. The advantage then lies in the fact that the cross section of the connection between the composite pipe 31 and the fitting 40 is avoided by a support body. Lower pressure losses in a pipe arrangement are thus achieved.

Claims

Patent claims 1. Composite pipe (1, 11, 31) for conducting and guiding a fluid, with a stability layer (2, 12, 32) with an outer surface (3, 13, 33) and with an outer layer (4, 14, 34), wherein the outer layer (4, 14, 34) contains a polyolefin grafted with at least one silane compound, characterized in that the outer layer (4, 14, 34) is adhesively bonded to the outer surface (3, 13, 33) of the stability layer (2, 12, 32) by means of the at least one silane compound of the grafted polyolefin.

2. Composite pipe (11) according to claim 1, characterized in that an inner layer (16) is provided and that the inner layer (16) contains a polyolefin grafted with at least one silane compound and that the inner layer (16) is adhesively connected to an inner surface (15) of the stability layer (12) by means of the at least one silane compound of the grafted polyolefin.

3. Composite pipe (21) for conducting and guiding a fluid, with a stability layer (22) and with an inner layer (26), wherein the inner layer (26) contains a polyolefin grafted with at least one silane compound, characterized in that that the inner layer (26) is adhesively bonded to an inner surface (25) of the stability layer (22) by means of the at least one silane compound of the grafted polyolefin.

4. Composite pipe (1, 11, 21, 31) according to one of claims 1 to 3, characterized in that the outer layer (4, 14, 34) is adhesively bonded to the outer surface (3, 13, 33) of the stability layer (12, 22, 32) by means of the at least one silane compound of the grafted polyolefin without the use of crosslinking-promoting catalysts and / or that the inner layer (16, 26) is adhesively bonded to an inner surface (15, 25) of the stability layer (12, 22) by means of the at least one silane compound of the grafted polyolefin without the use of crosslinking-promoting catalysts.

5. Composite pipe (1, 11, 21, 31) according to one of claims 1 to 4, characterized in that the stability layer (2, 12, 22, 32) contains a metallic material, in particular consists thereof.

6. Composite pipe (1, 11, 21, 31) according to one of claims 1 to 5, characterized in that the stability layer (2, 12, 22, 32) consists at least partially of a non-metallic material.

7. Composite pipe (1, 11, 21, 31) according to one of claims 1 to 6, characterized in that the outer surface (3, 13, 33) of the stability layer (2, 12, 32) and / or the inner surface (15, 25) of the stability layer (12, 22) has a static initial contact angle of water after 3 minutes of equilibration of 110° or less, preferably 100° or less, more preferably 90° or less, in particular determined according to DIN EN ISO 19403-2:2020-04.

8. Composite pipe (1, 11, 21, 31) according to one of claims 1 to 7, characterized in that the outer layer (4, 14, 34) adheres to the outer surface (3, 13, 33) of the stability layer (2, 12, 32) and / or the inner layer (16, 26) adheres to the inner surface (15, 25) of the stability layer (12, 22) with a peel force of at least 15 N / cm, preferably at least 30 N / cm, more preferably at least 50 N / cm, determined according to DIN EN ISO 11339:2022-05 at 25°C and 50 mm / min peel speed.

9. Composite pipe (1, 11, 21, 31) according to one of claims 1 to 8, characterized in that at least one further outer layer, in particular at least one further outer polyolefin layer (37), and / or at least one further inner layer, in particular at least one further inner polyolefin layer, is provided.

10. A method for producing a composite pipe (1, 11, 31) according to one of the preceding claims, in which a stability layer (2, 12, 32) with an outer surface (3, 13, 33) is provided and in which an outer layer (4, 14, 34) is applied to the outer surface (3, 13, 33) of the stability layer (2, 12, 32), wherein the outer layer (4, 14, 34) contains a polyolefin grafted with at least one silane compound.

11. The method according to claim 10, wherein the outer layer (4, 14, 34) is applied to the stability layer (2, 12, 32) by means of tube extrusion.

12. Method according to claim 10 or 11, in which an inner layer (16) is applied to the inner surface (15) of the stability layer (12), wherein the inner layer (16) contains a polyolefin grafted with at least one silane compound.

13. A method for producing a composite pipe (21) according to any one of claims 3 to 9, wherein a stability layer (22) having an inner surface (25) is provided and wherein an inner layer (26) is applied to the inner surface (25) of the stability layer (22), wherein the inner layer (26) contains a polyolefin grafted with at least one silane compound.

14. Method according to one of claims 10 to 13, in which the stability layer (2, 12, 22, 32) is heated before and / or after the application of the inner layer (16, 26) and / or the outer layer (4, 14, 34), in particular by induction heating and / or in which the inner layer (16, 26) and / or the outer layer (4, 14, 34) is applied without the use of crosslinking-promoting catalysts.

15. System for creating a pipe connection, with a composite pipe (1, 11, 21, 31) according to one of the preceding claims and with an externally sealing fitting (40).

16. Use of a composite pipe (1, 11, 21, 31) according to one of the preceding claims in a water-conducting pipe arrangement, in particular for drinking water or heating water.

7. Use of a polyolefin grafted with a silane compound as an adhesion promoter for a bond between a polyolefin-containing layer and a stability layer, in particular a metal layer.

Images