Composite pipe and methods for its manufacture

Abstract

The invention relates to a composite pipe (1, 11, 31) for conducting and guiding a fluid, comprising a stabilizing layer (2, 12, 32) with an outer surface (3, 13, 33) and an outer layer (4, 14, 34), wherein the outer layer (4, 14, 34) contains a polyolefin, characterized in that the stabilizing layer (2, 12, 32) is silanized at its outer surface (3, 13, 33) with at least one silane compound and that the outer layer (4, 14, 34) is bonded to the outer surface (3, 13, 33) of the stabilizing layer (2, 12, 32) by means of the at least one silane compound. The invention also relates to a method for manufacturing such a composite pipe.

Description

[0001] The invention relates to a composite pipe for conducting and guiding a fluid, comprising an internally arranged stabilizing layer with an outer surface and an externally arranged outer layer, wherein the stabilizing layer is silanized with at least one silane compound on its outer surface. The invention also relates to a method for manufacturing a composite pipe and to the use of a polyolefin for manufacturing a composite pipe.

[0002] Composite pipes, and especially metal composite pipes, are widely used in plumbing and heating systems for conveying water, particularly drinking water, heating and cooling water, or process water. These composite pipes often consist of an aluminum layer sandwiched between two layers of cross-linked and / or non-cross-linked polyolefin plastic.

[0003] Composite pipes have the advantage that, unlike pure plastic pipes, they are very easy to bend and retain their shape after bending, not springing back to their original state. Due to the intermediate or stabilizing layer of aluminum, the pipes are also impermeable to oxygen, preventing oxygen ingress into the heating water and thus preventing water-side corrosion in unprotected steel components such as radiators and boilers. Furthermore, these pipes are lighter than commonly used alternatives such as steel or copper pipes. However, aluminum itself is not corrosion-resistant in the long term, for example, in plumbing or heating applications.

[0004] 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 layer.

[0005] The MAH adhesion promoter is required because polyolefins do not adhere well to materials with high surface energy, such as metals, and adhesion promoters are typically needed to bond polyolefins like polyethylene to inorganic materials like metals. Therefore, special, modified polyolefin types are usually used as adhesion promoters, in which the polyolefins have been grafted with maleic anhydride. These grafted polyolefins are marketed by various manufacturers such as Mitsui Chemicals, Yparex, LyondellBasell, Silon, and Auserpolymeri under the trade names Admer, Yparex, Plexar, Tabond, and Compoline. According to the prevailing theory, ester-like bonds form with the inorganic layer via the anhydride group of the succinic anhydride side chain created during grafting.

[0006] If such a composite pipe is sealed against the fluid transported inside only on its outer circumference using a fitting, then 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 weakens over time due to the damaging effects of the fluid, especially water, and eventually fails. This leads to collapse, in particular delamination of the inner layer, and a defect in the installation.

[0007] 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 further assumed that the hydrolysis-induced delamination is self-reinforcing. During the hydrolysis of the ester-like bonds, acid groups are formed from them. These acid groups increase the osmotic pressure in a moisture pocket that has formed around the damaged metal-adhesion bonds. This attracts more water, causing the moisture pocket to enlarge into a bubble. This, in turn, destroys further ester-like bonds of the metal-adhesion bond, leading to the formation of more acid groups. These, together with dissolved aluminum ions, increase the osmotic pressure. In this way, the metal-adhesion bond is progressively destroyed, ultimately resulting in the polyolefin layer delaminating from the metal layer.

[0009] In other metal composite pipes, the aluminum pipe is replaced by a stainless steel pipe. The self-accelerating delamination described above, caused by 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 water, or it forms the middle layer of the composite pipe. However, the adhesion promoter is also of the MAH type in these cases, which is why such stainless steel composite pipes must also be internally sealed.

[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 system because the flow resistance is increased. This results in particularly high pressure losses in large installations and necessitates larger pipe sizes.

[0011] Another approach involved using perforated stainless steel sheets or meshes instead of aluminum strip as the metal pipe, thus eliminating the need for bonding agents. The inner and outer thermoplastic layers are fused together in the perforations of the sheets or meshes, preventing the collapse of the inner plastic pipe. This solution is hydrolysis- and corrosion-resistant, making it hygienically suitable for external sealing. However, this design is technically complex, and the stabilizing layer no longer functions as a barrier against, for example, oxygen ingress.

[0012] The object of the invention is therefore to provide a composite pipe and a method that do not exhibit the aforementioned disadvantages. Furthermore, the object of the invention is to provide a composite pipe that can be sealed via its outer diameter. Further objects, features, and advantages of the present invention will become clear from the following description.

[0013] The previously identified problem is initially solved by a composite pipe for conducting and guiding a fluid, in which the composite pipe has a stabilizing layer with an outer surface and an outer layer. The outer surface is silanized with at least one silane compound. The outer layer contains a polyolefin. According to the invention, the outer layer is bonded to the outer surface of the stabilizing layer by means of the at least one silane compound.

[0014] In a further embodiment of the composite pipe, an inner surface of the stability layer is silanized with at least one silane compound, wherein an inner layer is provided, wherein the inner layer contains a polyolefin and wherein the inner layer is bonded to the inner surface of the stability layer by means of the at least one silane compound.

[0015] The previously identified problem is further solved by a composite pipe for conducting and guiding a fluid, in which the composite pipe has a stabilizing layer with an inner surface and an inner layer. The inner layer contains a polyolefin. According to the invention, the stabilizing layer is silanized on its inner surface with at least one silane compound, and the inner layer is bonded to the inner surface of the stabilizing layer by means of the at least one silane compound.

[0016] The outer and / or inner layers contain a polyolefin. Theoretically, the proportion can be 100 wt%. However, a lower proportion is also possible. The remaining portion can, for example, comprise or consist of other polyolefins. The outer and / or inner layers can also contain a grafted polyolefin, for example, in a proportion of 10 wt% or more. The grafted polyolefin can be a polyolefin grafted with a silane compound or an amine compound. Furthermore, glycidyl ethers or other oxiranes, isocyanates, (meth)acrylates, or silane as a coupling group are conceivable. A coating of the stabilizing layer with tetraalkoxysilanes or, for example, sodium silicate is also conceivable.

[0017] In a particularly preferred embodiment, the composite pipe is further designed such that the stabilizing layer contains, and in particular consists of, a metallic material. The metals used can be, in particular, aluminum, iron, steel, stainless steel, copper, titanium, chromium, nickel, or alloys of two or more of the aforementioned metals.

[0018] The silane compound is preferably in the form of alkylsilane orthoacid esters, in particular C 1-20 -Alkylsilane orthotic esters. According to one embodiment, the silane compound is formed as an alkenylsilane orthotic ester, in particular C 2-20 -Alkenylsilane orthotic ester, formed.

[0019] Silanizing a surface with a silane compound refers to the chemical bonding of the silane compound to the surface. This bonding can occur, in particular, through a condensation reaction between hydrolyzable groups of the silanes used and chemical groups on the surface, for example, hydroxyl groups. Preferably, the silanized surface of the stability layer exhibits the silane compound bonded to the surface via a condensation reaction. Without being bound to a scientific theory, it is assumed that the silane compound has formed Si-O metal bonds with reactive groups such as oxy or hydroxyl groups on the metal surface. These Si-O metal bonds appear to provide higher hydrolysis resistance compared to the ester-like bonds derived from maleic anhydride.

[0020] Surprisingly, it was found that an outer layer containing a polyolefin can form a strong bond via the silane compound with which the surface of the stabilizing layer is silanized. Depending on the type of silane compound and polyolefin, various possibilities exist for how this strong bond can be achieved, without adhering to a specific scientific theory. If the surface is silanized with a silane compound containing an alkyl group, it is conceivable that the alkyl group is incorporated into the polyolefin phase, for example, the polyethylene phase, of the outer or inner layer, thereby creating the strong bond.If the surface is silanized with a silane compound that has a reactive group such as an epoxide, and the polyolefin also has a reactive group such as an amine, for example by grafting, it is conceivable that the reactive groups react with each other, thereby producing the well-adhering bond.

[0021] By incorporating an alkyl group of the silane compound into the polyolefin phase of the outer layer, the adhesive bond between the stability layer and the outer layer appears to be so strong in at least some aspects that the hydrolysis resistance is largely determined by the hydrolysis stability of the Si-O metal bonds. The same applies if a reactive group of the silane compound has reacted with a reactive group on the polyolefin.

[0022] These Si-O-metal bonds appear to provide higher hydrolysis resistance compared to ester-like bonds derived from maleic anhydride. In this way, the polyolefin-containing outer layer appears to adhere well to the stabilizing layer, preferably a metal surface. The silane compound with which the stabilizing layer is silanized appears to act as an adhesion promoter between the outer layer and the stabilizing layer. In particular, the silane compound appears to act as the adhesion promoter in the typical composite pipe structure described above, replacing the maleic anhydride.

[0023] Furthermore, the hydrolysis of Si-O bonds produces only an extremely weak acid, which at most slightly lowers the pH and does not promote the hydrolysis of further bonds. Additionally, the silane compounds that have already formed Si-O-metal bonds can cross-link with each other, which can further increase hydrolysis resistance. This effectively prevents delamination of the polyolefin layer from the metal surface. The maleic anhydride-grafted adhesion promoter commonly used in the prior art can therefore be omitted.

[0024] Preferably, the surface of the silanized stability layer features alkylsilane groups, which are shown schematically below: where Met stands for metal and n is an integer from 0 to 20. In the schematic representation above, further molecular components are present at the locations marked with wavy lines, for example, alkyl groups such as methyl groups or alkoxy groups such as methoxy groups or oxygen atoms, to which in turn alkyl groups or Si or Si-O groups are linked. For example, a Si-O network can be formed, which further increases the hydrolysis stability and the adhesive strength.

[0025] In the described composite pipe, there is direct, planar, and in particular full-surface contact between the stability layer and the outer layer and / or the inner layer, without the presence of a previously common primer, in particular MAH polyolefin, as an adhesion promoter.

[0026] The outer layer and / or the inner layer thus preferably have a connection with the stabilizing layer, which is more hydrolysis-resistant 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 arising from contact with the fluid, especially water.

[0027] The outer surface of the stability layer and / or the inner surface of the stability layer are preferably characterized as follows.

[0028] Firstly, the outer surface of the stability layer and / or the inner surface of the stability layer, particularly before silanization, can exhibit a static initial contact angle with water of 110° or less, preferably 100° or less, and more preferably 90° or less, after 3 minutes of equilibration. The initial contact angle is preferably determined according to DIN EN ISO 19403-2:2020-04.

[0029] On the other hand, the outer layer can adhere to the outer surface of the stability layer and / or the inner layer 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 50 mm / min peel speed.

[0030] The polyolefin contained in the outer layer and / or the polyolefin contained in the inner layer can be an ungrafted polyolefin. Furthermore, the polyolefin contained in the outer layer and / or the polyolefin contained in the inner layer can be a grafted polyolefin. For example, the polyolefin can be grafted with a silane compound, an amine compound, or an epoxy compound. An amine-grafted polyolefin can, for example, be obtained by treating a polyolefin in an NH3-containing plasma.

[0031] Furthermore, at least one additional outer layer and / or at least one additional inner layer can be provided. The additional outer layer and / or the additional inner layer can, in particular, be a polyolefin layer. According to an advantageous embodiment, the composite pipe has at least one additional outer polyolefin layer. According to a further advantageous embodiment, the composite pipe has at least one additional inner polyolefin layer. The additional inner polyolefin layer can be present instead of or in addition to the additional 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, a stabilizing layer, an inner layer containing a polyolefin, and an inner polyolefin layer.

[0032] The polyolefin contained in the outer layer can be the same or different from the polyolefin contained in the inner layer. The same or different polyolefins can be used in the subsequent outer polyolefin layer, the outer layer itself, the inner layer, and the subsequent inner polyolefin layer.

[0033] The outer layer preferably has a thickness of 0.005 to 35 mm, more preferably of 0.01 to 7.5 mm, and particularly preferably of 0.03 to 3 mm. The inner layer preferably has a thickness of 0.005 to 35 mm, more preferably of 0.01 to 7.5 mm, and particularly preferably of 0.03 to 3 mm. The further outer layer preferably has a thickness of 0.5 to 30 mm, more preferably of 1 to 10 mm, and particularly preferably of 1.5 to 3 mm. The further inner layer preferably has a thickness of 0.5 to 30 mm, more preferably of 1 to 10 mm, and particularly preferably of 1.5 to 3 mm.

[0034] The above-mentioned problem is also solved according to the invention by a method in which a stability layer with an outer surface is provided, wherein the stability layer is silanized on the outer surface with at least one silane compound, and in which an outer layer is applied to the outer surface of the stability layer, wherein the outer layer contains a polyolefin.

[0035] Preferably, the outer layer is applied to the stabilizing layer by tube extrusion. Alternatively, the outer layer can also be applied by overmolding.

[0036] Furthermore, an inner surface of the stability layer can be silanized with at least one silane compound and an inner layer can be applied to the inner surface of the stability layer, wherein the inner layer contains a polyolefin.

[0037] Likewise, the above-mentioned problem is also solved by a method for producing a composite pipe in which a stability layer with an inner surface is provided, wherein the inner surface of the stability layer is silanized with at least one silane compound, and in which an inner layer is applied to the inner surface of the stability layer, wherein the inner layer contains a polyolefin.

[0038] In the process, the inner and / or outer surface of the stability layer can be silanized with at least one silane compound in a preliminary step.

[0039] In this process, the stabilizing layer can be heated before and / or after the application of the inner and / or outer layer, particularly by induction heating. Preferably, the time after the application of the outer layer and the cooling process are kept long.

[0040] If a composite pipe is manufactured with a stability layer, an outer layer and a further outer layer, the outer layer and the further outer layer are preferably co-extruded onto the stability layer.

[0041] Various temperatures and / or pressures can be used in the application process described above. Advantageously, a temperature of 100 to 300 °C, preferably 160 to 260 °C, and particularly preferably 200 to 260 °C, is used during application. A pressure of 1 to 300 bar, more preferably 10 to 200 bar, and particularly preferably 50 to 150 bar, is preferably used during application. This improves adhesion.

[0042] Preferably, when applying the outer layer and / or the inner layer, the adhesive bond is formed by the silanized silane compound on the outer and / or inner surface of the stability layer, for example by incorporating the alkyl group into the polyolefin phase of the outer layer or by a chemical reaction of a reactive group on the silane compound with a reactive group on the polyolefin, as shown schematically below.

[0043] Scheme: a) Application with a pressure of 100 bar and / or a temperature of 250 °C.

[0044] The cross-linking of the silane groups shown in the diagram can occur before or simultaneously with application, or in a subsequent step. For example, cross-linking can occur during storage or use of the composite pipe. In particular, further cross-linking can occur in the presence of moisture in the system. Humidity is sufficient for this reaction.

[0045] The methods described above achieve the same properties and advantages as those previously described with regard to the composite pipes according to the invention and their configurations.

[0046] The task outlined above is also solved by a system for creating a pipe connection using a previously described composite pipe and an externally sealing fitting.

[0047] The fitting preferably comprises a base body and an associated press sleeve. 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 open by the press sleeve and the elements contained therein until it abuts, for example, a stop formed on the base body. By radially pressing the press sleeve with a suitable pressing tool, typically with two pressing jaws, the press sleeve is uniformly deformed radially. This engages the clamping elements with the surface of the composite pipe, thus securing the composite pipe against being pulled out of the fitting. Simultaneously, the sealing element seals the outside of the composite pipe against the press sleeve and thus against the fitting.

[0048] According to the invention, this allows the described composite pipe and its preferred embodiments to be connected to a fitting that only provides an externally sealing press connection. Since the composite pipe represents a sufficiently stable composite system due to the hydrolysis-resistant bond between the polyolefin layer(s) and the stabilizing layer, no damage occurs despite the end face of the stabilizing layer being exposed to fluid within the fitting. Thus, collapse or delamination of the layers of the composite pipe, and consequently installation errors, can be avoided.

[0049] Furthermore, the above-mentioned task is also solved by using a previously described composite pipe in a water-carrying pipe arrangement, especially for drinking water or heating water.

[0050] Furthermore, the problem shown above is solved by using a silane compound as an adhesion promoter for bonding a polyolefin-containing layer with a stabilizing layer, in particular a metal layer, in a composite pipe.

[0051] As previously explained for the composite pipe according to the invention, a good adhesive bond between a stability layer and a layer containing a polyolefin can be achieved by means of the silane compound.

[0052] The statements made herein regarding the silane compound, the polyolefin and the stability layer shall apply accordingly to the silane compound, the polyolefin and the stability layer.

[0053] In the uses described above, the same properties and advantages are achieved as previously described with regard to the composite pipes according to the invention and their configurations.

[0054] The following are specific examples of the design of the material of the stability layer and the inner and outer layers.

[0055] The stabilizing layer may contain a metallic material. In particular, the stabilizing layer may contain at least 60 wt.%, preferably at least 80 wt.%, more preferably at least 90 wt.% 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 stabilizing layer, or consist thereof.

[0056] Alternatively, the stabilizing layer can also consist at least partially of a non-metallic material. In particular, the stabilizing layer can contain at least 60 wt.%, preferably at least 80 wt.%, further 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 stabilizing layer.

[0057] Preferably, the outer layer contains at least 50 wt.%, more preferably at least 70 wt.%, and particularly preferably at least 90 wt.% of the polyolefin, based on the total weight of the outer layer.

[0058] The outer layer can contain an ungrafted polyolefin. The outer layer can contain a grafted polyolefin. The outer layer can contain a mixture of an ungrafted and a grafted polyolefin. Examples of grafted polyolefins include a polyolefin grafted with a silane compound, a polyolefin grafted with an amino group, and a polyolefin grafted with an epoxy group.

[0059] The outer layer can contain varying amounts of ungrafted and grafted polyolefin. If the outer layer contains a grafted polyolefin, it is preferably present in a proportion of 1 to 100 wt.%, more preferably 5 to 15 wt.%, and more preferably 8 to 12 wt.%, based on the total weight of the outer layer.

[0060] To prepare a polyolefin grafted with a silane compound, a silane compound can conveniently be grafted to the polyolefin via a carbon-carbon double bond of the silane compound using a radical initiator. For example, vinyltrimethoxysilane can be grafted onto polyethylene using a radical initiator such as dibenzoyl peroxide. The polyethylene grafted with vinyltrimethoxysilane then contains 2-(trimethoxysilyl)ethyl groups. A polyolefin with grafted epoxide groups can be obtained, for example, from a silane compound containing both a vinyl group and an epoxide group. Polyolefin grafted with epoxide groups, particularly polyethylene, can also be obtained by radical grafting of the polyolefin with glycidyl methacrylate. A polyolefin with grafted amine groups can be obtained by treating a polyolefin in an NH3-containing plasma.A polyolefin with grafted epoxy groups can also be obtained by grafting butadiene monoxide onto the polyolefin with a radical initiator.

[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.

[0062] What has been said above regarding the outer layer applies accordingly to the inner layer. What has been said above regarding the further outer layer applies accordingly to the further inner layer.

[0063] Furthermore, the polyolefin may be 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. This applies independently to both grafted and ungrafted polyolefins. In particular, the polyolefin of the outer layer and / or the inner layer may be selected independently from the group consisting of polyethylene, cross-linked polyethylene, high-temperature polyethylene, polypropylene, polyisobutylene, polybutylene, polymethylpentene, polyalphaolefins, and mixtures thereof.

[0064] Examples of cross-linked polyethylene are PE-Xa, PE-Xb, and PE-Xc. Polyethylene with increased thermal resistance can also be referred to as PE-RT.

[0065] The aforementioned polyolefins, especially polyethylene, have the advantage that their grafting with silane compounds such as vinyltrimethoxysilane is known to those skilled in the art. This allows grafted polyolefins to be produced in a simple and generally known manner. The grafting can be carried out, for example, as shown schematically below:

[0066] The grafting of vinylsilanes and their crosslinking is known to those 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.

[0067] The outer layer and / or the optional additional outer layer may also contain other substances commonly used in polyolefins, such as antioxidants, pigments, fillers, reinforcing materials, or processing aids. The same applies to the inner layer and / or the optional additional inner layer.

[0068] Specific examples of the design of the at least one silane compound with which the outer surface of the stability layer is silanized are described below. The same applies to the at least one silane compound of the inner surface of the stability layer.

[0069] Advantageously, the silane compound may contain 1 to 30 carbon atoms, preferably 2 to 30 carbon atoms, and particularly preferably 3 to 25 carbon atoms. Preferably, the silane compound comprises a functional group selected from the group consisting of -C 1-20 -Alkyl, especially -C 5-20 -Alkyl, Vinyl, -NH2, -OH, -NCO, -(CHCH2O), -OCH2(CHCH2O), -OCH3 and OC2H5.

[0070] The silane compound may contain other groups, such as alkylene groups, amine groups, ether groups, thioether groups, hydroxyl groups, epoxide groups, carbamate groups, carbonyl groups, and / or alkyl groups.

[0071] Preferably, the silane compound comprises 1 to 30, more preferably 2 to 30, and particularly preferably 3 to 25, carbon atoms and at least one functional group selected from the group consisting of -C 5-20 -Alkyl, Vinyl, -NH2, -OH, -NCO and -(CHCH2O).

[0072] Conveniently, the silane compound has the general structural formula (I). Stab-O-Si(R 2 ) 3-m-o (R 3 ) o ((CH2) n R 1 ) m , (I) where m 1 or 2 is, o 0, 1 or 2 is, where m and o together result in at most 3, Each n is independently an integer from 0 to 10, Stab-O- the bond to the stability layer means, each R 1 independently of each other -C 5-20 -Alkyl, vinyl, -NH2, -OH, -NCO, -(CHCH2O) or -O-CH2(CHCH2O), means, each R 2independently of each other -O-, -OH, methoxy, ethoxy, iso-propoxy, n-propoxy, n-butoxy, sec-butoxy or iso-butoxy means, or two R 2 each by C 1-S -Alkylene groups are linked together and each R 3 independently of each other C 1-4 -Alkyl, especially methyl or ethyl, means.

[0073] In structural formula (I) an R can be used 2 , the -O- means that a bond to a neighboring silane compound is present or another bond to the stability layer.

[0074] Preferably, in the structural formula (I) n is zero only if R 1 -C 5-20 -Alkyl means.

[0075] The silane compounds with the general structural formula (I) are preferably derived from silane compounds with the structural formula (Ia) (R 3 ) o Si(R 2 ) 4-m-o ((CH2)nR 1 )m, (Ia) where m, n, o, R 1and R 3 as defined for the silane compounds with the general structural formula (I), m and o together yield at most 3 and each R 2 independently of each other means methoxy, ethoxy, iso-propoxy, n-propoxy, n-butoxy, sec-butoxy or iso-butoxy, or two or three R 2 each independently by C 1-5 -Alkylene groups are linked together.

[0076] In a further preferred manner, it may be provided that the silane compound has the structural formula (II) Stab-O-SiR 2 2(CH2) p -R 4 (II) exhibits where each R 2 independently of each other -O-, -OH, methoxy, ethoxy, iso-propoxy, n-propoxy, n-butoxy, sec-butoxy or iso-butoxy means, or two R 2 each by C 1-5 -alkylene groups are linked together R 4-CH3, vinyl, -(CHCH2O), -O-CH2(CHCH2O), -NH2, -NCO or -OH means, and rod-O- means the bond to the stability layer, p is an integer from 0 to 20.

[0077] In structural formula (II) an R can be used 2 , the -O- means that a bond to a neighboring silane compound is present or another bond to the stability layer.

[0078] According to a preferred embodiment, in structural formula (II) p is an integer from 10 to 20 and R 4 means -CH3.

[0079] According to another preferred embodiment, in structural formula (II) p is an integer from 1 to 5 and R 4 means -NH2, -OH, -NCO, -(CHCH2O) or -O-CH2(CHCH2O), in particular -NH2 or -O-CH2(CHCH2O).

[0080] The silane compounds with the general structural formula (II) are preferably derived from silane compounds with the structural formula (IIa) R 2 3Si(CH2)p -R 4 (IIa) where p and R 4 as defined for the silane compounds with the general structural formula (II), and each R 2 independently of each other means methoxy, ethoxy, iso-propoxy, n-propoxy, n-butoxy, sec-butoxy or iso-butoxy, or two or three R 2 each independently by C 1-5 -Alkylene groups are linked together.

[0081] In a further preferred manner, it may be provided that the silane compound with which the outer and / or the inner surface of the stability layer is or has been silanized is selected from the group consisting of decyltrimethoxysilane, decyltriethoxysilane, dodecyltrimethoxysilane, dodecyltriethoxysilane, tetradecyltrimethoxysilane, tetradecyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, octadecyltrimethoxysilane, octadecyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, (3-isocyanatopropyl)trimethoxysilane, (3-isocyanatoproyl)triethoxysilane, 3-hydroxypropyltrimethoxysilane, 3-hydroxypropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane and 3-glycidoxypropyltriethoxysilane.

[0082] If the polyolefin is grafted with a silane compound, it can preferably be provided that the silane compound has the structural formula (III) R 5 rR 6 sSi(CH2)pR 7 (III) exhibits where r is 0 or 1, s is an integer from 0 to 3, r and s together result in at most 3, p is an integer from 0 to 20, R 5 -(CHCH2O), -O-CH2(CHCH2O), -NH2, -NCO or -OH means each R 6 independently of each other -OH, methoxy, ethoxy, iso-propoxy, n-propoxy, n-butoxy, sec-butoxy or iso-butoxy means, or two R 6 each by C 1-5 -alkylene groups are linked together R 7 Vinyl, -OC(=0)-C(=CH2)H (acryloyloxy) or -OC(=0)-C(=CH2)CH3 (methacryloyloxy). EXAMPLE

[0083] An ethanol / water mixture (95 / 5 w / w) was adjusted to a pH between 4.5 and 5.5 with acetic acid. 2 wt% vinyltrimethoxysilane (Silquest A-171, supplied by Momentive), based on the weight of the ethanol / water mixture, was slowly added to the mixture with continuous stirring. This solution was sprayed at room temperature onto stainless steel 1.4435 (Arinox, Italy) and rinsed with ethanol after 5 minutes. The silane layer was formed by storage at 120°C for 30 minutes. A silanized steel sheet was thus obtained.

[0084] Conventional PE (Sclair 74B, sourced from Nova Chemicals) was pressed onto a silanized steel sheet prepared according to the above instructions using a plate press at a temperature of 250°C and a pressure of 120 bar for a duration of 5 minutes. The peel strength 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.

[0085] For comparison, this test was otherwise carried out identically with non-silanized steel sheet. 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.

[0086] Test specimens prepared according to the previously described procedure were immersed in water at 105°C. In parallel, samples coated with a conventional, high-performance PE-gMAH-based adhesion promoter (Admer NE072 from Mitsui) were immersed. The peel strength was then determined over the immersion period for comparison. While the PE-gMAH-based samples exhibited a peel strength 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 polyethylene-coated, silanized steel sheets, prepared according to the above-described procedure, showed a peel strength >30 N / cm according to DIN EN ISO 11339:2022-05 at 25°C and a peel speed of 50 mm / min. No delamination was observed in the silanized steel sheet samples.

[0087] The differences in pull-off force retention between PE-gMAH-based adhesion promoter systems and silanized steel sheets are directly transferable to composite pipe samples produced by extrusion.

[0088] The invention will now be explained using exemplary embodiments with reference to the drawing. The drawing shows... Fig. 1 a first embodiment of a composite pipe, Fig. 2 a second embodiment of a composite pipe, Fig. 3 a third embodiment of a composite pipe, Fig. 4 a fourth embodiment of a composite pipe and Fig. 5 an unpressed fitting for connecting a composite pipe to Fig. 2 and Fig. 6. Connect the fitting to the composite pipe. Fig. 5 in the compressed state.

[0089] In the following description of the various embodiments according to the invention, components and elements with the same function and mode of operation are provided with the same reference numerals, even if the components and elements may differ in their dimensions or shape in the various embodiments.

[0090] Fig. Figure 1 shows a composite pipe 1 for conducting and guiding a fluid, preferably water in the form of drinking water or heating water. The composite pipe 1 has a stabilizing layer 2 with an outer surface 3 and an outer layer 4.

[0091] The outer surface 3 of the stability layer is silanized with at least one silane compound. The outer layer 4 contains a polyolefin.

[0092] According to the invention, the outer layer 4 is bonded to the outer surface 3 of the stability layer 2 by means of the at least one silane compound with which the surface 3 is silanized. Thus, the stability layer 2 and the outer layer 4 form a firmly bonded and more hydrostable connection than with MAH adhesion promoters, without the layers being attacked by moisture penetration and the composite pipe being damaged. The outer surface 3 was silanized with an alkyltrimethoxysilane, in particular dodecyltrimethoxysilane. For the presumed mechanism, reference is made to the general description.

[0093] Fig. Figure 2 shows another composite tube 11 with a stabilizing layer 12 having an outer surface 13 and an inner surface 15, as well as an outer layer 14. An inner layer 16 is also provided. The outer surface 13 and the inner surface 15 are silanized with at least one silane compound. The same silane compound can be used for both surfaces, or different silane compounds can be used. Preferably, the outer surface 13 and the inner surface 15 are silanized with an alkyltrimethoxysilane, in particular dodecyltrimethoxysilane, or vinyltrimethoxysilane. The outer layer 14 contains a polyolefin and is bonded to the outer surface 13 of the stabilizing layer 12 by means of the at least one silane compound with which the surface 13 is silanized.The inner layer 16 contains a polyolefin and the inner layer 16 is bonded to the inner surface 15 of the stability layer 12 by means of the at least one silane compound with which the inner surface 15 is silanized.

[0094] Thus, the inner layer 16 is bonded to the stability layer 12 via the inner surface 15 in a more hydrolysis-stable manner than with a MAH adhesion promoter. For an explanation of this bond, please refer to the general section of the description.

[0095] Fig. Figure 3 shows a further embodiment of a composite pipe 21 for conducting and guiding a fluid. In this embodiment, a stabilizing layer 22 and an inner layer 26 are provided. An outer layer, as in the embodiments according to the Fig. 1 and Fig. The number 2 is not present here.

[0096] The inner surface 25 of the stability layer 22 is silanized with at least one silane compound. The inner surface 25 is preferably silanized with an alkyltrimethoxysilane, in particular dodecyltrimethoxysilane, or vinyltrimethoxysilane. The inner layer 26 contains a polyolefin. Furthermore, the inner layer 26 is bonded to the inner surface 25 of the stability layer 22 by means of the at least one silane compound with which the inner surface 25 is silanized.

[0097] Thus, the inner layer 26 is bonded to the stability layer 22 via the inner surface 25 in a more hydrolysis-stable manner than with a MAH adhesion promoter. For an explanation of this bond, please refer to the general section of the description.

[0098] Fig. Figure 4 shows another composite tube 31 with a stabilizing layer 32 having an outer surface 33 and an outer layer 34. The outer surface 33 is silanized with at least one silane compound. The outer surface 33 is preferably silanized with an alkyltrimethoxysilane, in particular dodecyltrimethoxysilane, or vinyltrimethoxysilane. The outer layer 34 contains a polyolefin. Furthermore, the composite tube 31 has another outer polyolefin layer 37, which is connected to the outer layer 34 via the outer surface 38 of the outer layer 34.

[0099] According to the invention, the outer layer 34 is bonded to the outer surface 33 of the stabilizing layer 32 by means of the at least one silane compound with which the outer surface 33 is silanized. Thus, the stabilizing layer 32 and the outer layer 34 form a firmly bonded and more hydrostable connection than with MAH adhesion promoters, without the layers being attacked by moisture penetration and the composite pipe being damaged. For the presumed mechanism, reference is made to the general description. The further outer polyolefin layer 37 adheres to the outer layer 34 via mechanisms known to those skilled in the art.

[0100] In the Fig. In the embodiments shown in Figures 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.

[0101] The outer layer 4, 14, 34 and / or the inner layer 16, 26 comprise a polyolefin, preferably more than 80 wt.%, based on the weight of the outer layer or the inner layer, respectively. The outer layer 4, 14, 34 and / or the inner layer 16, 26 may additionally comprise a polyolefin grafted with a silane compound, for example, a proportion of PEX-b.

[0102] 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.

[0103] The Fig. 5 and Fig. Figure 6 shows a system for creating a pipe connection, using a composite pipe 11, as described in Fig. 4 is shown, and an externally sealing fitting 40.

[0104] The fitting 40 has a base body 44 and a stop element 45 formed circumferentially in the base body 44 and projecting inwards. Furthermore, a press sleeve 41 is provided, connected to the base body 44 and forming an outer contour 42, which has a chamber 43 directed inwards towards the pipe 11 to be received. A clamping ring 46, consisting of a plastic material with a plurality of clamping elements 47 oriented against the direction of extension of the pipe 31 to be inserted, is arranged in the chamber 43. In addition, a sealing element 48 is arranged in the chamber 43 adjacent to the stop element 45.

[0105] The press sleeve 41 is integrally connected with 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.

[0106] The pipe 31 is secured against pull-out and / or excessive internal pressure by the clamping ring 46, which is designed as a plastic clamping ring and incorporates metallic cutting edges as clamping elements 47. The plastic clamping ring 46 also has circumferential slots, which make the clamping ring 46 flexible overall and thus facilitate its installation in the fitting 40 within the press sleeve 41.

[0107] The clamping elements 47 are designed as cutting edges in the form of wire elements that are inserted into designated recesses. The clamping elements 47 are thus positively locked into the plastic of the clamping ring 46. The clamping elements 47 can be manufactured in various ways, for example as castings or stampings. In this case, there are six clamping elements 47, but this number can be adjusted depending on the requirements and / or dimensions of the clamping ring 47.

[0108] The clamping elements 47 are further arranged in the distal area of ​​the chamber 43 opposite the stop elements 45 and absorb the pull-out force by deforming the tube 31 at specific points, see Fig. 6, and thereby bear against the wall in a distal outer corner area 41a of the press sleeve 41. Thus, a direct force transmission from the pipe 31 via the press sleeve 41 into the fitting 40 is ensured. After pressing, the clamping ring 46 only has a supporting function and contributes only minimally or not at all to the pull-out protection.

[0109] The pressing process is described by a comparison of the Fig. 5 and Fig. Figure 6 clearly shows that the press jaw halves (not shown) move radially inwards and come into contact with the press sleeve 41, causing the press sleeve 41 to deform radially inwards. This deforms the clamping ring 46 so that the clamping elements 47 press inwards into the material of the pipe 31, thus securing the pipe 31 to the fitting 40. Simultaneously, the seal 48 is also deformed radially inwards during the deformation of the press sleeve 41, creating a seal between the pipe 31 and the press sleeve 41.

[0110] As explained above, an important advantage of the designs of the composite pipe 31 - as well as the other described composite pipes 1, 11 and 21 - is that the outer layer 34 is bonded to the stability layer 32 by means of the at least one silane compound with which the outer surface 33 of the stability layer 32 is silanized, resulting in a more hydrolysis-resistant bond between the stability layer 32 and the outer layer 34 than with an MAH bonding agent.

[0111] This allows, as in Fig.Figure 6 shows that, due to the externally pressed connection between the composite pipe 31 and the fitting 40, the end face 39 of the composite pipe 131 comes into unprotected contact with the medium, such as water, contained in the pipe 31 and the fitting 40, without hydrolysis-related damage to the layers 32, 34, and 37 occurring. Therefore, the described design of the composite pipe 31 eliminates the need for internal pressing with a conventional support body.

[0112] The advantage lies particularly in the fact that the cross-section of the connection between the composite pipe 31 and the fitting 40 with a support body is avoided. This results in lower pressure losses in a pipe assembly. QUOTES INCLUDED IN THE DESCRIPTION

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

[0000] DIN EN ISO 19403-2:2020-04

[0028] Polyethylene Cross-linking by Two-step Silane Method: A Review", Iranian Polymer Journal, 18 (2), 2009, 103-128

[0066] DIN EN ISO 11339:2022-05 [0084, 0085]

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, characterized by , - that the stability layer (2, 12, 32) is silanized on the outer surface (3, 13, 33) with at least one silane compound and - 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. [2] Composite pipe (11) according to claim 1, characterized by , - that the stability layer (12) is silanized on an inner surface (15) with at least one silane compound, - that an inner layer (16) is provided, wherein the inner layer contains a polyolefin and - that the inner layer (16) is adhesively bonded to the inner surface (15) of the stability layer (12) by means of the at least one silane compound. [3] Composite pipe (21) for conducting and guiding a fluid, - with a stability layer (22) with an inner surface (25) and - with an inner layer (26), - wherein the inner layer (26) contains a polyolefin, characterized by , - that the stability layer (22) is silanized on the inner surface (25) with at least one silane compound and - that the inner layer (26) is adhesively bonded to the inner surface (25) of the stability layer (22) by means of the at least one silane compound. [4] Composite pipe (1, 11, 21, 31) according to one of claims 1 to 3, characterized by that the stability layer (2, 12, 22, 32) contains a metallic material, in particular consists thereof. [5] Composite pipe (1, 11, 21, 31) according to one of claims 1 to 4, characterized by that the stability layer (2, 12, 22, 32) consists at least partially of a non-metallic material. [6] Composite pipe (1, 11, 21, 31) according to one of claims 1 to 5, characterized by 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. [7] Composite pipe (1, 11, 21, 31) according to one of claims 1 to 6, characterized by that the polyolefin contained in the outer layer (4, 14, 34) and / or the polyolefin contained in the inner layer (16, 26) is a grafted polyolefin. [8] Composite pipe (1, 11, 21, 31) according to one of claims 1 to 7, characterized by 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. [9] Method for producing a composite pipe (1, 11, 31) according to one of the preceding claims, - in which a stability layer (2, 12, 32) having an outer surface (3, 13, 33) is provided, wherein the stability layer is silanized on the outer surface (3, 13, 33) with at least one silane compound, 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. [10] Method according to claim 9, wherein the outer layer (4, 14, 34) is applied to the stability layer (2, 12, 32) by means of tube extrusion. [11] Method according to claim 9 or 10, - in which an inner surface (15) of the stability layer (12) is silanized with at least one silane compound and - 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. [12] Method for producing a composite pipe (21) according to one of claims 3 to 8, - in which a stability layer (22) having an inner surface (25) is provided, wherein the inner surface (25) of the stability layer (22) is silanized with at least one silane compound, and - in which an inner layer (26) is applied to the inner surface (25) of the stability layer (22), - wherein the inner layer (26) contains a polyolefin. [13] Method according to one of claims 9 to 12, wherein the stability layer (2, 12, 22, 32) is heated before and / or after the application of the inner (16, 26) and / or the outer layer (4, 14, 34), in particular by induction heating. [14] System for creating a line connection, - with a composite pipe (1, 11, 21, 31) according to one of the preceding claims and - with an externally sealing fitting (40). [15] 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. [16] Use of a silane compound as an adhesion promoter for a connection of a polyolefin-containing layer with a stability layer, in particular a metal layer, in a composite pipe.

Images