Biaxially oriented tube

Abstract

The present invention relates to a biaxially oriented tube prepared from a polymer composition comprising a propylene-based polymer, wherein the propylene-based polymer comprises a random copolymer of propylene and a comonomer, wherein the comonomer is ethylene and / or an α-olefin having 4-10 carbon atoms, wherein the comonomer content of the propylene-based polymer is 0.5-3.8 wt % based on the propylene-based polymer.

Description

Technical Field

[0001] The present invention relates to a pipe produced by biaxial stretching of a polypropylene composition. Background Art

[0002] It is known that physical and mechanical properties of polymeric materials can be improved by orienting the material. In many cases, orienting the material in one direction to improve properties can result in degradation of the same property in a direction perpendicular to the orientation direction. In order to adjust the properties in two directions, biaxial orientation of the material can be applied. Biaxial orientation means that the polymeric material is oriented in two mutually perpendicular directions. The tube can be oriented in both the axial and circumferential directions (annular directions) to improve properties such as long-term hydrostatic performance and low temperature impact resistance.

[0003] Pipes prepared by biaxial stretching of polypropylene compositions are known. US5910346 describes stretched pipes prepared from isotropic polypropylene pipes (ICI grade GSE 108). Morath et al., in Biaxially oriented polypropylene pipes, Plastics, Rubber and Composites 2006 vol 35 no 10, p. 447-454, describe biaxially oriented polypropylene pipes prepared from random polypropylene copolymers having a melt flow rate of 0.3 dg / min and an ethylene content of 4%.

[0004] One of the most important properties of a pipe is its resistance to crack growth.

[0005] An object of the present invention is to provide a biaxially oriented polypropylene pipe having good long term hydrostatic properties.

[0006] Therefore, the present invention provides a biaxially oriented tube prepared from a polymer composition comprising a propylene-based polymer, wherein the propylene-based polymer comprises a random copolymer of propylene and a comonomer, wherein the comonomer is ethylene and / or an α-olefin having 4 to 10 carbon atoms, and wherein the comonomer content of the propylene-based polymer is 0.1 to 3.8 wt % based on the propylene-based polymer.

[0007] The biaxially oriented tube prepared from the polymer composition refers to a biaxially oriented tube prepared by a method comprising the following steps:

[0008] a) forming the polymer composition into a pipe, and

[0009] b) stretching the tube of step a) in axial and circumferential directions to obtain a biaxially oriented tube.

[0010] The term "comonomer content" is understood herein as the amount of comonomer derived units. In propylene based polymers, the sum of the comonomer content and the amount of propylene derived units is 100%.

[0011] The terms "tube" and "tube" are understood here as hollow elongated articles which may have a cross section of various shapes. The cross section may be, for example, annular, elliptical, square, rectangular or triangular. The term "diameter" is understood here as the largest dimension of the cross section.

[0012] It has surprisingly been found that the biaxially oriented tubes of the present invention have good long term hydrostatic properties.

[0013] Propylene polymer

[0014] The propylene-based polymer comprises a random copolymer of propylene and a comonomer selected from ethylene and / or an α-olefin having 4 to 10 carbon atoms. It should be understood that the copolymer can be prepared from propylene and one comonomer substance or multiple comonomer substances (e.g., a terpolymer). The comonomer is preferably: ethylene, 1-butene, 1-hexene and / or 1-octene, such as ethylene (in which case the random copolymer is a propylene-ethylene copolymer); ethylene and 1-butene (propylene-ethylene-1-butene terpolymer); ethylene and 1-hexene (propylene-ethylene-1-hexene terpolymer) or ethylene and 1-octene (propylene-ethylene-1-octene terpolymer). The comonomer is most preferably ethylene.

[0015] The propylene-based polymer is preferably a propylene-ethylene copolymer, ie the comonomer units in the propylene-based polymer are ethylene-derived units.

[0016] The melt flow index of the propylene-based polymer measured according to ISO 1133-1:2011 (230° C. / 2.16 kg) is preferably 0.1 to 10.0 g / 10 min, more preferably 0.1 to 4.0 g / 10 min, particularly preferably 0.1 to 1.0 g / 10 min.

[0017] Relative to the propylene-based polymer, the amount of random copolymer is preferably 50-100wt%, such as greater than 50wt%, at least 55wt%, at least 60wt%, at least 70wt%, at least 80wt%, at least 90wt%, at least 95wt%, at least 98wt%, at least 99wt% or 100wt%.

[0018] The polymer composition of the present invention comprises a propylene-based polymer. The propylene-based polymer comprises a random copolymer. The random copolymer may comprise, preferably consist of, the following substances:

[0019] A) a low-comonomer random copolymer of propylene and a comonomer, the comonomer being ethylene and / or an α-olefin having 4 to 10 carbon atoms, wherein the low-comonomer random copolymer has a comonomer content of less than 3.8 wt%, based on the low-comonomer random copolymer, and / or

[0020] B) a high comonomer random copolymer of propylene and a comonomer which is ethylene and / or an α-olefin having 4 to 10 carbon atoms, wherein the high comonomer random copolymer has a comonomer content of at least 3.8 wt% based on the high comonomer random copolymer.

[0021] The propylene-based polymer may also include C) a propylene homopolymer.

[0022] It will be appreciated that the amounts of A), B) and C) are selected so that the comonomer content of the propylene based polymer is from 0.1 to 3.8 wt% of the propylene based polymer, and therefore the propylene based polymer will not comprise only B) or only C).

[0023] The total amount of A), B) and C) is typically at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% of the propylene-based polymer.

[0024] The comonomer content of the propylene-based polymer is determined by the comonomer content in the propylene-based polymer and the weight ratio of the components, such as A), B) and C). The comonomer content of the propylene-based polymer is 0.1-3.8 wt% of the propylene-based polymer, such as at least 0.5 wt% or at least 1.0 wt% and / or at most 3.7 wt%, at most 3.6 wt%, at most 3.5 wt%, at most 3.4 wt%, at most 3.0 wt%, at most 2.5 wt% or at most 2.0 wt%, preferably 0.5-3.5 wt%, more preferably 0.5-3.4 wt%, more preferably 0.5-3.0 wt%, more preferably 1.0-2.0 wt%.

[0025] The comonomer content of the low comonomer random copolymer is preferably at least 0.1-3.8 wt% of the random copolymer, such as at least 0.5 wt% or at least 1.0 wt% and / or up to 3.7 wt%, up to 3.6 wt%, up to 3.5 wt%, up to 3.4 wt%, up to 3.0 wt%, up to 2.5 wt% or up to 2.0 wt%, preferably 0.5-3.5 wt%, more preferably 0.5-3.4 wt%, 0.5-3.0 wt% or 1.0-2.0 wt%. In the low comonomer random copolymer, the comonomer is ethylene and / or an α-olefin having 4-10 carbon atoms. The comonomer is preferably ethylene, 1-butene, 1-hexene and / or 1-octene, such as ethylene; ethylene and 1-butene; ethylene and 1-hexene or ethylene and 1-octene. The comonomer is most preferably ethylene. The low-comonomer random copolymer preferably has a melt flow index of 0.1-10.0 g / 10 min, more preferably 0.1-4.0 g / 10 min, and even more preferably 0.1-1.0 g / 10 min, as measured according to ISO 1133-1:2011 (230° C. / 2.16 kg).

[0026] The comonomer content of the high comonomer random copolymer is generally preferably 3.8-10.0wt% of the random copolymer, such as 4.0-8.0wt% or 4.2-6.0wt%. In the high comonomer random copolymer, the comonomer is ethylene and / or an α-olefin having 4-10 carbon atoms. The comonomer is preferably ethylene, 1-butene, 1-hexene and / or 1-octene. The comonomer is most preferably ethylene. The melt flow index of the high comonomer random copolymer measured by ISO1133-1:2011 (230°C / 2.16kg) is preferably 0.1-10.0g / 10min, more preferably 0.1-4.0g / 10min, more preferably 0.1-1.0g / 10min.

[0027] The melt flow index of the propylene homopolymer measured according to ISO 1133-1:2011 (230° C. / 2.16 kg) is preferably 0.1 to 10.0 g / 10 min, more preferably 0.1 to 4.0 g / 10 min, more preferably 0.1 to 1.0 g / 10 min.

[0028] The propylene-based polymer may consist of A).

[0029] The propylene-based polymer may consist of A) and B), and the weight ratio of A) to B) is preferably 1:10 to 10:1.

[0030] The propylene-based polymer may consist of A) and C), and the weight ratio of A) to C) is preferably 1:10 to 10:1.

[0031] The propylene-based polymer may consist of B) and C), and the weight ratio of B) to C) is preferably 1:10 to 10:1.

[0032] The propylene-based polymer may consist of A), B), and C), the weight ratio of A) to B) is preferably 1:10 to 10:1, and the weight ratio of A) to C) is preferably 1:10 to 10:1.

[0033] In some embodiments, A) consists of a type of oligomer random copolymers.

[0034] In some embodiments, A) consists of at least two types of low comonomer random copolymers, wherein the comonomer content and / or melt flow index measured according to ISO 1133-1:2011 (230° C. / 2.16 kg) of the at least two types of low comonomer random copolymers are different from each other. It should be understood that the comonomer content and melt flow index of A) are determined by the weight ratio of the components in A).

[0035] In some embodiments, B) consists of a type of high comonomer random copolymer.

[0036] In some embodiments, B) consists of at least two types of high comonomer random copolymers, wherein the at least two types of high comonomer random copolymers differ from each other in comonomer content and / or melt flow index measured according to ISO 1133-1:2011 (230° C. / 2.16 kg).

[0037] In some embodiments, C) consists of a type of propylene homopolymer.

[0038] In some embodiments, C) consists of at least two types of propylene homopolymers, wherein the at least two types of propylene homopolymers are different from each other in melt flow index measured according to ISO 1133-1:2011 (230° C. / 2.16 kg).

[0039] In some preferred embodiments, the propylene-based polymer consists of A), wherein

[0040] A) is composed of a type of low comonomer random copolymer,

[0041] wherein the comonomer in the low comonomer random copolymer is ethylene, and

[0042] The propylene-based polymer has a melt flow index of 0.1-1.0 g / 10 min, measured according to ISO 1133-1:2011 (230° C. / 2.16 kg).

[0043] In some preferred embodiments, the propylene-based polymer consists of A), wherein A) consists of at least two types of low-comonomer random copolymers, wherein the comonomer of each of the at least two types of low-comonomer random copolymers is ethylene, and

[0044] The propylene-based polymer has a melt flow index of 0.1-1.0 g / 10 min, measured according to ISO 1133-1:2011 (230° C. / 2.16 kg).

[0045] In some preferred embodiments, the propylene-based polymer consists of A) and B), wherein

[0046] A) is composed of a type of low comonomer random copolymer,

[0047] B) is composed of a class of high comonomer random copolymers,

[0048] The comonomers in the low comonomer random copolymer and the high comonomer random copolymer are both ethylene.

[0049] The melt flow index of the low comonomer random copolymer measured according to ISO1133-1:2011 (230°C / 2.16kg) is 0.1-1.0g / 10min.

[0050] The high comonomer random copolymer has a melt flow index of 1.1-10.0 g / 10 min measured according to ISO1133-1:2011 (230°C / 2.16 kg).

[0051] The weight ratio of A) to B) is 1:10-10:1,

[0052] The propylene-based polymer has a melt flow index of 0.1-1.0 g / 10 min, measured according to ISO 1133-1:2011 (230° C. / 2.16 kg).

[0053] In some preferred embodiments, the propylene-based polymer consists of A) and C), wherein

[0054] A) is composed of a type of low comonomer random copolymer,

[0055] C) consists of a type of propylene homopolymer,

[0056] The comonomer in the low comonomer random copolymer is ethylene,

[0057] The melt flow index of the low comonomer random copolymer measured according to ISO1133-1:2011 (230°C / 2.16kg) is 0.1-1.0g / 10min.

[0058] The melt flow index of propylene homopolymer measured according to ISO1133-1:2011 (230°C / 2.16kg) is 0.1-10.0g / 10min.

[0059] The weight ratio of A) to C) is 1:10-10:1,

[0060] The propylene-based polymer has a melt flow index of 0.1-1.0 g / 10 min, measured according to ISO 1133-1:2011 (230° C. / 2.16 kg).

[0061] In some preferred embodiments, the propylene-based polymer consists of B) and C), wherein

[0062] B) is composed of a class of high comonomer random copolymers,

[0063] C) consists of a type of propylene homopolymer,

[0064] The comonomer in the high comonomer random copolymer is ethylene.

[0065] The high comonomer random copolymer has a melt flow index of 0.1-1.0 g / 10 min measured according to ISO1133-1:2011 (230°C / 2.16 kg).

[0066] The melt flow index of propylene homopolymer measured according to ISO1133-1:2011 (230°C / 2.16kg) is 0.1-10.0g / 10min.

[0067] The weight ratio of B) to C) is 1:10-10:1,

[0068] The propylene-based polymer has a melt flow index of 0.1-1.0 g / 10 min, measured according to ISO 1133-1:2011 (230° C. / 2.16 kg).

[0069] The polymer composition containing propylene-based polymers preferably contains substantially no other polymers except propylene-based polymers. The amount of propylene-based polymers may be at least 95 wt%, at least 98 wt%, at least 99 wt% or 100 wt% relative to the total amount of polymers in the polymer composition.

[0070] The polymer composition may contain components other than the propylene-based polymer, such as additives and fillers.

[0071] Examples of additives include: nucleating agents, stabilizers such as heat stabilizers; antioxidants; UV stabilizers; colorants such as pigments and dyes; clarifying agents; surface tension modifiers; lubricants; flame retardants; mold release agents; flow improvers; plasticizers; antistatic agents; external elastic impact modifiers; foaming agents; and / or components that enhance the interface connection between the polymer and the filler, such as maleated polyethylene. The amount of additives is generally 0-5wt%, such as 1-3wt%, relative to the total amount of the composition.

[0072] Examples of fillers include glass fiber, talc, mica, nanoclay. The amount of filler is generally 0-40 wt%, such as 5-30 wt% or 10-25 wt%, relative to the total amount of the composition.

[0073] Therefore, in some embodiments, the polymer composition further comprises 0-5 wt% of additives and 0-40 wt% of fillers.

[0074] The polymer composition may be obtained by melt mixing the propylene-based polymer and any other optional components.

[0075] Preferably, the total amount of the propylene-based polymer and the optional additives and the optional filler is 100 wt% relative to the total amount of the composition.

[0076] Method steps

[0077] A biaxially oriented tube is prepared by a process comprising the steps of:

[0078] a) forming the polymer composition into a pipe, and

[0079] b) stretching the tube of step a) in axial and circumferential directions to obtain a biaxially oriented tube.

[0080] The process for producing the pipe can be carried out as a continuous process or as a batch process. A continuous process is understood here to be a process in which the polymer composition is fed continuously for the pipe production step a) while the stretching step b) is carried out continuously.

[0081] The polymer composition may be formed into a tube by any known method such as extrusion or injection molding (step a). Biaxial stretching (step b) may be performed by any known method.

[0082] A method of forming a polymer composition into a tube and biaxially stretching the tube is described in US6325959:

[0083] Conventional devices for extruding plastic pipes include an extruder, a nozzle, a calibrator, a cooling device, a pulling device, and a device for cutting or winding the pipe. The molten material of the polymer passes from the extruder through the nozzle and reaches the calibrator, and the cooling and finished pipe is subjected to shearing and stretching along the axial direction of the pipe, and a pipe with a substantially uniaxial orientation along its axial direction will be obtained. Another reason that contributes to the orientation of the polymer material along the direction of material flow is that the pipe can withstand the tension associated with the preparation.

[0084] In order to achieve biaxial orientation, the device can be supplemented downstream of the traction device with equipment for controlling the temperature of the tube to a temperature suitable for biaxial orientation of the tube, orientation equipment, calibration equipment, cooling equipment and traction equipment for providing the biaxially oriented tube to a cutting device or a winder.

[0085] It is also possible to carry out the biaxial orientation after extrusion directly in connection with a first calibration device, in which case the above-mentioned supplementary device follows the first calibration device.

[0086] Biaxial orientation of the tube can be accomplished in a variety of ways, such as mechanically by an internal mandrel or by an internal pressurized fluid such as air or water or the like. Other methods are orienting the tube by rollers, such as by placing the tube on a mandrel and rotating the mandrel and tube relative to one or more pressure rollers engaged with the tube, or by internally disposed pressure rollers rotating relative to the tube against an externally disposed die or calibration device.

[0087] In addition, Morath et al., Biaxially oriented polypropylene pipes, Plastics, Rubber and Composites 2006 vol 35 no 10, p. 447-454, describe a method for preparing biaxially oriented tubes from random propylene copolymers.

[0088] Conditions of step b)

[0089] Those skilled in the art can select suitable conditions such as temperature of step b) to obtain a biaxially oriented tube. Step b) is carried out at a stretching temperature that orients the propylene-based polymer in the polymer composition.

[0090] The stretching temperature is selected according to the melting point of the propylene-based polymer in the polymer composition.

[0091] The stretching temperature is defined here as the temperature at the surface of the tube in step a) just before step b). Before step b), the mandrel and the tube in step a) are heated so that they have the desired stretching temperature. This can also be achieved by soaking the mandrel and the tube in step a) in the stretching temperature for a sufficient time (e.g. 30 minutes) to reach thermal equilibrium (the temperature is preferably controlled within ±1°C).

[0092] Melting points are measured by differential scanning calorimetry according to ASTM D3418. DSC measurements are performed using a DSC TA Q20 and a mechanical refrigerator capable of reaching -90°C. To avoid degradation, the measurements can be performed under a nitrogen flow. The method followed is:

[0093] First heating: -40℃ to 230℃@10℃ / min (maintain at the end temperature for 3min)

[0094] Cooling: 230℃ to -40℃@10℃ / min

[0095] Second heating: -40℃ to 230℃@10℃ / min

[0096] The sample used is 3-5 mg

[0097] The melting point was recorded from the second heating cycle.

[0098] The stretching temperature may be selected to be below the melting point of the propylene-based polymer in the polymer composition.

[0099] The stretching temperature may be 1-30°C lower than the melting point of the propylene-based polymer in the polymer composition, for example 2-20°C or 3-10°C lower.

[0100] When the propylene-based polymer comprises different propylene-based polymers having different melting points, the stretching temperature may be determined so as to orient most of the propylene-based polymers. Those skilled in the art may appropriately determine a suitable stretching temperature according to the type and amount of the propylene-based polymer present in the polymer composition.

[0101] Generally, it is possible to select the stretching temperature within a suitable temperature range based on the melting point of each propylene-based polymer present in the polymer composition.

[0102] When the melting points of the propylene-based polymers present in the polymer composition vary greatly, the stretching temperature can be selected based on the propylene-based polymers present in large amounts. For example, the stretching temperature can be selected based on the melting point of the propylene-based polymer present in the largest amount in the polymer composition. When determining the stretching temperature, it is possible to ignore the propylene-based polymers present in small amounts (e.g., less than 5 wt % of the polymer composition).

[0103] In some embodiments, step b) is carried out at a stretching temperature of 140-160°C, preferably 145-155°C.

[0104] Stretch ratio

[0105] Typically, step b) is carried out with an axial stretch ratio of 1.1 to 5.0 and an average hoop stretch ratio of 1.1 to 3.0.

[0106] The average hoop stretch ratio is preferably 1.1-2.0.

[0107] The axial stretch ratio is preferably 1.1-4.0, such as 1.1-3.6 or 1.1-3.2. For obtaining a biaxially oriented tube with a larger outer diameter, the axial stretch ratio is usually larger.

[0108] The axial stretch ratio of the stretched tube is defined as the ratio of the cross-sectional area of ​​the starting isotropic tube to the cross-sectional area of ​​the biaxially oriented tube (i.e., the product), i.e.:

[0109]

[0110] OD stands for outside diameter and ID stands for inside diameter.

[0111] In the case of expanded tube stretching, the hoop stretch ratio of the product varies from the inner wall to the outer wall. These stretch ratios are defined as:

[0112]

[0113]

[0114] The average hoop stretch ratio can be defined as:

[0115]

[0116] in:

[0117] Biaxially oriented tube

[0118] The biaxially oriented tube of the present invention can be a pressure tube or a non-pressure tube. The preferred tube is a pressure tube.

[0119] The wall thickness of the biaxially oriented tube can generally be 0.3mm to 10cm. The outer diameter of the biaxially oriented tube can generally be 10-2000mm. In some embodiments, the outer diameter of the biaxially oriented tube is 10mm to 10cm, and the thickness is 0.3-3mm or 1-3mm. In some instances, the outer diameter of the biaxially oriented tube is 10-50cm, and the thickness is 1mm to 1cm. In some instances, the outer diameter of the biaxially oriented tube is 50cm to 2m, and the thickness is 5mm to 10cm.

[0120] The biaxially oriented tube of the present invention preferably has a time to failure measured according to ISO 1167-1 at a stress level of 20 MPa and a temperature of 20° C. of at least 100 hours, preferably at least 400 hours, more preferably at least 1000 hours.

[0121] It should be noted that the present invention relates to all possible combinations of features described herein, particularly preferably those combinations of features appearing in the claims. It should therefore be understood that all combinations of features relating to the compositions of the present invention, all combinations of features relating to the methods of the present invention, and all combinations of features relating to the compositions of the present invention and to the methods of the present invention are described herein.

[0122] It should also be noted that the term 'comprising' does not exclude the presence of other elements. However, it should be understood that the description of a product / composition comprising a certain component also discloses a product / composition consisting of these components. A product / composition consisting of these components may be advantageous because it provides a simpler and more economical method for preparing the product / composition. Similarly, it should also be understood that the description of a method comprising certain steps also discloses a method consisting of these steps. A method consisting of these steps may be advantageous because it provides a simpler and more economical method.

[0123] When lower and upper numerical limits for parameters are mentioned, it is also understood that the range resulting from the combination of the lower and upper values ​​is disclosed.

[0124] The present invention will now be described by way of the following examples, but the present invention is not limited thereto.

[0125] Material:

[0126] rPP1: propylene-ethylene copolymer with a comonomer content of 4 wt% and MFR 230°C / 2.16kg of 0.3 g / 10 min, Tm = 142.1°C

[0127] rPP2: propylene-ethylene copolymer with a comonomer content of 1.5 wt% and MFR 230°C / 2.16kg of 0.3 g / 10 min, Tm = 156°C

[0128] rPP3: propylene-ethylene copolymer with a comonomer content of 4 wt% and MFR 230°C / 2.16kg of 1.7 g / 10min, Tm = 142°C

[0129] Production of Biaxially Oriented Tubes:

[0130] The propylene-ethylene copolymer was pelletized using a twin-screw extruder. The processing temperature and screw profile were standard for polypropylene compounding. Standard additives for propylene-based pipes were added during pelletization.

[0131] Thick tubular structures having dimensions of about 32 mm outer diameter and about 16 mm inner diameter were produced using these compounded pellets. These thick tubes were stretched over an expanding tapered mandrel having an outlet diameter of 32 mm and a half angle of 15 degrees at the temperatures shown in Table 1. The tubes stretched very uniformly through the thickness and could be stretched to relatively low axial stretch ratios.

[0132] These thick tubes were stretched at a stretching speed of 100 mm / min over an expanded tapered mandrel with an outlet diameter of 61-65 mm and a half angle of 15 degrees at the temperature shown in Table 1. The axial stretch ratio was 3 and the average annular stretch ratio was 1.3.

[0133] The internal pressure resistance of the pipes was measured according to ISO 1167-1 at stress levels of 16 and 20 MPa at 20° C. The failure times of the pipes are given in Table 1 below.

[0134] Table 1

[0135]

[0136] It is understandable that the time to failure of biaxially oriented tubes made from propylene-ethylene copolymers having lower comonomer content is much longer.

Claims

1. A biaxially oriented tube prepared from a polymer composition comprising a propylene-based polymer, wherein the propylene-based polymer comprises a random copolymer of propylene and a comonomer, wherein the comonomer is ethylene and / or an α-olefin having 4 to 10 carbon atoms, wherein the comonomer content of the propylene-based polymer is 0.5 to 3.0 wt % based on the propylene-based polymer.

2. The biaxially oriented tube of claim 1, wherein the comonomer content of the propylene-based polymer is 1.0-2.0 wt%.

3. The biaxially oriented tube of claim 1 or 2, wherein the propylene-based polymer is a propylene-ethylene copolymer.

4. The biaxially oriented tube of claim 1 or 2, wherein the propylene-based polymer has a melt flow index of 0.1 to 10.0 g / 10 min as measured at 230°C / 2.16 kg according to ISO 1133-1:2011.

5. The biaxially oriented tube of claim 1 or 2, wherein the amount of propylene-based polymer is at least 95 wt% relative to the total amount of polymers in the polymer composition.

6. The biaxially oriented tube of claim 1 or 2, wherein the amount of propylene-based polymer is at least 98 wt% relative to the total amount of polymers in the polymer composition.

7. The biaxially oriented tube of claim 1 or 2, wherein the amount of propylene-based polymer is at least 99 wt % relative to the total amount of polymers in the polymer composition.

8. The biaxially oriented tube of claim 1 or 2, wherein the amount of the propylene-based polymer is 100 wt% relative to the total amount of polymers in the polymer composition.

9. The biaxially oriented tube of claim 1 or 2, wherein the polymer composition further comprises 0-5 wt% of an additive and 0-40 wt% of a filler.

10. The biaxially oriented tube of claim 1 or 2, wherein the biaxially oriented tube is prepared by a method comprising the following steps: a) forming the polymer composition into a pipe, and b) stretching the tube of step a) in the axial and circumferential directions to obtain a biaxially oriented tube, The step b) is carried out at a stretching temperature of 140-160° C., an axial stretching ratio of 1.1-5.0 and an average hoop stretching ratio of 1.1-3.

0.

11. The biaxially oriented tube of claim 1 or 2, wherein the biaxially oriented tube has a time to failure of at least 100 hours measured according to ISO 1167-1 at a stress level of 20 MPa and a temperature of 20°C.

12. The biaxially oriented tube of claim 11, wherein the biaxially oriented tube has a time to failure of at least 1000 hours measured according to ISO 1167-1 at a stress level of 20 MPa and a temperature of 20°C.

13. The biaxially oriented tube of claim 1 or 2, wherein the random copolymer comprises: A) a low-comonomer random copolymer of propylene and a comonomer, wherein the comonomer is ethylene and / or an α-olefin having 4 to 10 carbon atoms, wherein the low-comonomer random copolymer has a comonomer content of less than 3.8 wt%, based on the low-comonomer random copolymer, and / or B) a high comonomer random copolymer of propylene and a comonomer, wherein the comonomer is ethylene and / or an α-olefin having 4 to 10 carbon atoms, wherein the high comonomer random copolymer has a comonomer content of at least 3.8 wt% based on the high comonomer random copolymer, and The propylene-based polymer optionally comprises: C) Propylene homopolymer.

14. The biaxially oriented tube of claim 13, wherein the total amount of A), B) and C) is at least 95 wt% of the propylene based polymer.

15. The biaxially oriented tube of claim 13, wherein the total amount of A), B) and C) is at least 98 wt% of the propylene based polymer.

16. The biaxially oriented tube of claim 13, wherein the total amount of A), B) and C) is at least 99 wt% of the propylene based polymer.

17. The biaxially oriented tube of claim 13, wherein the total amount of A), B) and C) is 100 wt% of the propylene-based polymer.

18. The biaxially oriented tube of claim 13, wherein the low comonomer random copolymer has a comonomer content of 0.1 to 3.8 wt% of the random polymer.

19. The biaxially oriented tube of claim 13, wherein the high comonomer random copolymer has a comonomer content of 3.8-10.0 wt% of the random polymer.

20. The biaxially oriented tube of claim 13, wherein the propylene based polymer consists of A).

21. The biaxially oriented tube of claim 13, wherein the propylene-based polymer consists of A) and B), wherein the weight ratio of A) to B) is 1:10 to 10:1, or The propylene-based polymer consists of A) and C), wherein the weight ratio of A) to C) is 1:10-10:1, or The propylene-based polymer consists of A), B) and C), wherein the weight ratio of A) to B) is 1:10-10:1, and the weight ratio of B) to C) is 1:10-10:

1.

22. The biaxially oriented tube of claim 13, wherein the propylene-based polymer consists of B) and C), wherein the weight ratio of B) to C) is from 1:10 to 10:1.

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